A Diagnostic Expert System for the Coloration of Textile ...

ABSTRACT

ZUBAIR, MUHAMMAD. A Diagnostic Expert System for the Coloration of Textile Fiber Blends.

(Under the direction of Dr. Renzo Shamey).

Materials based on fiber blends are among the most common textile products and they are

projected to continue to expand. The coloration of textile fiber blends, however, is challenging

when compared to single fiber materials. This is due to differences in the dyeing behavior of the

fiber components of the blend. The colorant class and application conditions required for one fiber

may damage or not be suitable for the other component in the blend. Th colorants may cross-stain

the fiber they are not designed for, and moreover there is a possibility of physical and chemical

interaction between different colorant classes and chemicals used during the process. These issues

increase the complexity of the coloration of fiber blends. With an increasing demand for the right-

first-time dyeing approach to reduce costs and remain competitive, the need to producing dyed

materials that are free of faults and possess suitable levels of quality, at an affordable cost, is more

apparent.

Troubleshooting problems in the coloration of blends is a difficult task considering the

large numbers of factors involved. The determination of the exact cause of the problem can be

very difficult. Dyehouses usually utilize human experts to troubleshoot problems. Such experts are

often able to considerably reduce the number of probable causes involved. In some cases, however,

the determination of the actual cause of the problem requires a detailed analysis. Over the years

the availability of human expertise in the domain of textile coloration has declined considerably

and experts have become rather scarce.

An Expert System is a computer program that can be used to mimic the knowledge and

experience of human experts in troubleshooting problems in various domains. The goal of the

present study is to develop a functional knowledge-based expert system for troubleshooting

problems in the coloration of fiber blends (DEXPERT-B). The system was developed in three

phases; Phase I involved the identification of common blends and knowledge acquisition. Phase

II covered the design and development of the system and in Phase III testing and evaluation of the

system were performed.

Polyester/cellulosic (PES/CELL) blends are among the most common and widely used

fiber blends in textiles. This blend type was identified and selected based on trade statistics and

published literature. The most common problems in the coloration of these blends in different

material forms (e.g. yarn, knitted and woven fabrics) with various colorants classes (pigment,

disperse, reactive, direct, vat and sulfur dyes), utilizing different coloration process (batch, semi-

continuous and continuous), methods (one bath, two bath) and corresponding coloration machines

was reviewed in detail. This was achieved through a survey of technical literature and interviews

with practical dyers. Based on the knowledge base gathered, an electronic survey comprising

common coloration faults and their potential causes in the PES/CELL blends was developed. The

survey was employed to acquire specialized knowledge from coloration experts. The experts’

responses were analyzed and used to complement the knowledge base. The expert system shell

was developed using wxCLIPS which is the modified version of the C Language Integrated

Production System (CLIPS) to provide a custom GUI functionality.

The system was verified, validated and evaluated using human experts. Several faulty dyed

samples were obtained from production mill and used for the assessment of the comparative

performance of human experts and expert system in identification of the type and root causes of

faults. The test results showed good performance of the expert system when compared to human

experts. This system is developed for use in actual production settings for the diagnosis of common

coloration problems in the PES/CELL blends. With the aid of the expert system the number of

probable causes for a particular problem can be isolated and reduced considerably. The developed

system has a potential utility for use as an educational and training tool for novice and practical

dyers. DEXPERT-B can help practical dyers in a quick resolution of problems by identifying

causes and recommending solutions to problems which can help improve the efficiency of the

coloration of PES/CELL blends.

A Diagnostic Expert System for the Coloration of Textile Fiber Blends

by

Muhammad Zubair

A dissertation submitted to the Graduate Faculty of

North Carolina State University

in partial fulfillment of the

requirements for the degree of

Doctor of Philosophy

Fiber and Polymer Science

Raleigh, North Carolina

2020

APPROVED BY:

_______________________________ _______________________________

Dr. Renzo Shamey Dr. Jeffrey Joines

Chair of Advisory Committee

_______________________________ _______________________________

Dr. George Hodge Dr. Peter Bloomfield

ii

DEDICATION

To my lovely wife and our son playing in heaven.

iii

BIOGRAPHY

Muhammad Zubair was born in Karachi, Pakistan, the largest metropolitan city and

financial hub of the country. He completed his Bachelor and Masters in Textile Engineering from

NED University of Engineering & Technology (NEDUET), Karachi in 2007 and 2009

respectively. He worked for one year in a dyehouse where he was involved in troubleshooting and

R&D. Later, he joined NEDUET as Lecturer where he was responsible for both advising and

teaching undergraduate students. In 2011, he was selected for Fulbright scholarship for Ph.D. at

North Carolina State University, Wilson College of Textiles.

His main research interests include sustainable processes in textile coloration, color

evaluation, and color management.

iv

ACKNOWLEDGMENTS

I express my sincere gratitude to Dr. Renzo Shamey for the invaluable guidance,

mentorship, encouragement, support and regular technical feedback he has given me throughout

this work and introducing me to the fascinating world of color; and Dr. Jeff Joines for his guidance

and great support in developing my programming skills.

I would also like to thank Dr. George Hodge and Dr. Peter Bloomfield for their valuable

suggestions.

I am extremely grateful to the US Department of State and Institute of International

Education (IIE) for awarding me Fulbright scholarship. I would also like to extend my gratitude

to Graduate School, Department of Textile Engineering Chemistry and Science (TECS) and Dr.

Renzo Shamey for their financial support.

I am very thankful to Mr. Jeff Krauss for his help and insightful discussions during dyeing

experiments and Mr. Brian Davis for help in producing knitting samples. I am also grateful to Mr.

Atiq-ur-Rehman and Mr. Idrees Shaikh for providing faulty dyed samples, Ms. Cheryl Smyre

(Parkdale Mills), Mr. Bryan Dill (Archroma), Mr. Mike Cheek (Huntsman), and Mr. Julian

Metcalfe (Dystar) for providing required materials for dyeing experiment. In addition, I would also

like to thank all dyeing experts who took part in the survey and assessment of faulty dyed samples.

Special thanks to my friends in Raleigh and Karachi: Zohaib, Ali, Owais, Raza and

Maqbool bhai for making my time memorable and helping me in difficult times.

Finally, I would like to thank my wife and parents for their patience, understanding,

motivation, and encouragement.

v

TABLE OF CONTENTS

LIST OF TABLES ......................................................................................................................... ix

LIST OF FIGURES .......................................................................................................................xv

CHAPTER 1 INTRODUCTION ..................................................................................................1

1.1 Background ......................................................................................................................... 1

1.2 Statement of the problem and goals .................................................................................... 2

1.3 Research methodology ........................................................................................................ 6

CHAPTER 2 TEXTILE FIBER BLENDS ...................................................................................8

2.1 Introduction ......................................................................................................................... 8

2.2 History of blends ................................................................................................................. 8

2.2.1 Blends of natural fibers ............................................................................................. 9

2.2.2 Blends of manufactured fibers .................................................................................. 9

2.3 Global fiber market and blends ......................................................................................... 12

2.4 Purpose of blending .......................................................................................................... 19

2.5 Types of fiber blends ........................................................................................................ 20

2.6 Properties of blended yarns and fabrics ............................................................................ 23

2.6.1 Compatibility of fibers in the blend ........................................................................ 24

2.6.2 Effect of blend ratio ................................................................................................ 26

2.6.3 Blending and resultant properties ........................................................................... 28

2.7 Polyester/cellulosic blends ................................................................................................ 31

2.8 Other common blends ....................................................................................................... 35

2.8.1 Polyester/wool blends ............................................................................................. 35

2.8.2 Polyamide/cellulosic blends.................................................................................... 35

2.8.3 Elastane blends........................................................................................................ 36

2.8.4 Microfiber blends .................................................................................................... 36

2.9 Application classes of fiber blends ................................................................................... 37

2.9.1 Intimate yarn blends ................................................................................................ 37

2.9.2 Bulked yarns ........................................................................................................... 37

2.9.3 Composite yarns...................................................................................................... 37

2.9.4 Structurally blended yarns ...................................................................................... 37

2.9.5 Structurally designed hawsers ................................................................................. 38

2.9.6 Structurally blended fabrics .................................................................................... 38

2.9.7 Filling material blends ............................................................................................ 38

2.9.8 Biomaterial blends .................................................................................................. 39

2.9.9 Static controlling blends ......................................................................................... 39

2.9.10 Apparel blends ........................................................................................................ 39

2.10 Manufacturing/production of blended textiles .................................................................. 39

2.10.1 Fiber distribution in blended yarns ......................................................................... 41

CHAPTER 3 COLORATION OF TEXTILE FIBER BLENDS ...............................................43

3.1 Introduction ....................................................................................................................... 43

3.2 Classification of blends according to their dyeing behavior ............................................. 43

3.3 Color effects produced on blends ..................................................................................... 45

3.4 Factors affecting the dyeing of fiber blends ..................................................................... 48

vi

3.5 Challenges in the coloration of fiber blends ..................................................................... 48

3.5.1 Cross-staining of the fiber by the dye intended for the other fiber type ................. 49

3.5.2 Fastness problems ................................................................................................... 50

3.5.3 Interaction between dye classes and dyebath auxiliaries ........................................ 51

3.5.4 Dye stability at high temperature and pH conditions .............................................. 52

3.5.5 Effect of additional processing required to fix the dye class .................................. 53

3.5.6 Effective liquor ratio and blend ratio ...................................................................... 53

3.5.7 Distribution of single dye and fiber saturation differences ..................................... 54

3.5.8 Obtaining solid shade in the blend by matching shade of an individual fiber type 55

3.5.9 Fiber damage and/or yellowing .............................................................................. 56

3.6 Coloration of polyester/cellulosic blends .......................................................................... 56

3.7 Pigment coloration ............................................................................................................ 59

3.7.1 Pigment preparations .............................................................................................. 62

3.7.2 Binders .................................................................................................................... 66

3.7.3 Auxiliaries ............................................................................................................... 71

3.7.4 Combined pigment coloration and finishing ........................................................... 75

3.7.5 Application method ................................................................................................. 75

3.7.6 Equipment ............................................................................................................... 79

3.8 Dyeing of polyester/cellulosic blends using a two-dye system ........................................ 79

3.8.1 Dye classes used for polyester/cellulosic blends .................................................... 79

3.8.2 Batch dyeing of polyester/cellulosic blends ........................................................... 93

3.8.3 Continuous dyeing of polyester/cellulosic blends .................................................. 99

CHAPTER 4 PRACTICAL PROBLEMS IN THE COLORATION OF TEXTILE FIBER

BLENDS ............................................................................................................................106

4.1 Introduction ..................................................................................................................... 106

4.2 Troubleshooting faults in coloration ............................................................................... 109

4.3 Dyeing problems arising from the fiber .......................................................................... 115

4.4 Problems arising from yarn formation ............................................................................ 137

4.4.1 Faults caused by spun yarns .................................................................................. 139

4.4.2 Faults due to filament yarns .................................................................................. 153

4.4.3 Problems due to the winding process.................................................................... 160

4.4.4 Problems due to conditioning ............................................................................... 172

4.5 Problems arising from fabric formation .......................................................................... 173

4.5.1 Yarn preparation for fabric formation ................................................................... 173

4.5.2 Weaving faults ...................................................................................................... 179

4.5.3 Knitting faults ....................................................................................................... 191

4.6 Problems caused by water ............................................................................................... 206

4.7 Problems caused due to pretreatment ............................................................................. 219

4.7.1 Problems caused during singeing.......................................................................... 223

4.7.2 Problems caused during desizing .......................................................................... 230

4.7.3 Problems caused during scouring ......................................................................... 239

4.7.4 Problems caused during bleaching ........................................................................ 244

4.7.5 Problems caused during weight reduction ............................................................ 256

4.7.6 Problems caused during mercerization and causticization ................................... 256

4.7.7 Problems caused during heat setting ..................................................................... 265

4.8 Problems in coloration .................................................................................................... 270

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4.8.1 Reproducibility in the dyeing of fiber blends ....................................................... 271

4.8.2 Problems caused in batch dyeing machines .......................................................... 274

4.8.3 Problems caused in continuous dyeing machines ................................................. 301

4.9 Problems in pigment coloration ...................................................................................... 326

4.9.1 Fastness of pigment colored fabrics ...................................................................... 330

4.10 Problems in the dyeing of polyester/cellulosic blends .................................................... 345

4.10.1 Disperse/reactive system ....................................................................................... 347

4.10.2 Disperse/direct system .......................................................................................... 374

4.10.3 Disperse/vat system .............................................................................................. 378

4.10.4 Disperse/sulfur system .......................................................................................... 388

CHAPTER 5 EFFECT OF BLEND RATIO ON DYEING PROPERTIES OF

POLYESTER-COTTON BLENDED FABRICS ........................................................................392

5.1 Introduction ..................................................................................................................... 392

5.2 Experimental ................................................................................................................... 395

5.2.1 Materials ............................................................................................................... 395

5.2.2 Methods................................................................................................................. 398

5.2.3 Evaluation methods ............................................................................................... 403

5.3 Results and discussion .................................................................................................... 404

5.3.1 Amount of dye required to match a target color ................................................... 404

5.3.2 Light fastness ........................................................................................................ 410

5.3.3 Crocking fastness .................................................................................................. 412

5.3.4 Washing fastness ................................................................................................... 415

5.3.5 Water fastness ....................................................................................................... 421

5.4 Conclusions ..................................................................................................................... 426

CHAPTER 6 DESIGN AND DEVELOPMENT OF AN EXPERT SYSTEM .......................428

6.1 Experts and expert systems ............................................................................................. 428

6.2 Benefits of expert systems .............................................................................................. 430

6.3 Domains of expert system ............................................................................................... 430

6.4 Application of expert systems in the textile industry ...................................................... 431

6.5 Components of an expert system .................................................................................... 435

6.6 Knowledge base .............................................................................................................. 436

6.6.1 Selection of most common coloration faults ........................................................ 438

6.6.2 Identification of common causes of coloration problems in PES/CELL blends .. 449

6.6.3 Knowledge acquisition.......................................................................................... 469

6.6.4 Analysis of expert responses ................................................................................. 472

6.7 Construction of a diagnostic expert system for dyeing of fiber blends (DEXPERT-B) . 479

6.7.1 Expert system building tool .................................................................................. 481

6.7.2 Knowledge representation .................................................................................... 482

6.8 Inference engine .............................................................................................................. 484

6.8.1 Effect of blend ratio .............................................................................................. 491

6.9 User interface .................................................................................................................. 494

6.9.1 Material function ................................................................................................... 495

6.9.2 Coloration function ............................................................................................... 496

6.9.3 Symptom function ................................................................................................. 497

6.9.4 Explanation function ............................................................................................. 501

6.10 Using the designed expert system ................................................................................... 502

viii

CHAPTER 7 TESTING AND EVALUATION OF AN EXPERT SYSTEM .........................504

7.1 Testing of the expert system ........................................................................................... 504

7.1.1 Verification ........................................................................................................... 505

7.1.2 Validation .............................................................................................................. 506

7.2 Evaluation of the expert system ...................................................................................... 514

CHAPTER 8 CONCLUSIONS AND FUTURE WORK ........................................................520

8.1 Conclusions ..................................................................................................................... 520

8.2 Recommendations for future work ................................................................................. 522

REFERENCES ............................................................................................................................525

APPENDICES ............................................................................................................................546

Mean expert responses for symptoms and their causes. ................................ 547

Questions related to various causes for diagnosis of symptom(s). ................ 563

DEXPERT-B installation guide..................................................................... 575

Analysis of the expert responses of the faulty colored samples. ................... 576

ix

LIST OF TABLES

Table 2.1: Global fiber use for the year 2013. ............................................................................13

Table 2.2: Summary of common textile fiber blends and their potential applications. ..............22

Table 2.3: Primary and secondary properties of textile fibers. ...................................................24

Table 3.1: Classification of binary blends according to their dyeing properties [9]. .................44

Table 3.2: Color effects in binary blends [9]. .............................................................................46

Table 3.3: Methods for dyeing of fiber blends. ..........................................................................47

Table 3.4: Effect of blend ratio on effective liquor ratios in the dyeing of blends. ....................54

Table 3.5: Characteristics of colorants for polyester/cellulosic blends. .....................................57

Table 3.6: Comparison of one bath and two bath methods used for dyeing of PES/CELL

blends. ........................................................................................................................59

Table 3.7: Advantages and limitations of pigment coloration. ...................................................60

Table 3.8: Comonomer types and polymer properties. ...............................................................70

Table 3.9: Factors affecting staining of cellulose by disperse dyes. ..........................................87

Table 3.10: Dyeing properties of reactive and disperse dyes [136]. ..........................................104

Table 4.1: Typical finished fabric quality levels [139]. ............................................................106

Table 4.2: Dyeing costs associated with not meeting the specifications. .................................107

Table 4.3: Classification of faults. ............................................................................................109

Table 4.4: Relationship between fiber properties and spun yarn characteristics. .....................116

Table 4.5: Factors affecting the dyeing behavior of cotton. .....................................................119

Table 4.6: Dyeing problems attributed to fiber. .......................................................................128

Table 4.7: Yarn classification. ..................................................................................................137

Table 4.8: Effect of different spinning operations on yarn properties. .....................................140

Table 4.9: Influence of yarn parameters on fabric properties ...................................................151

Table 4.10: Common problems related to spun yarns. ...............................................................152

x

Table 4.11: Effect of texturizing process parameters on yarn properties. ..................................155

Table 4.12: Problems due to filament yarn faults. ......................................................................159

Table 4.13: Types of winding systems. ......................................................................................165

Table 4.14: Problems caused by the winding process. ...............................................................169

Table 4.15: Objectives of the yarn preparation processes and associated fabric defects. ..........176

Table 4.16: Problems in woven fabrics their causes and countermeasures. ...............................181

Table 4.17: Causes and remedies of frequent problems in knitted fabrics. ................................194

Table 4.18: Sources of water and their constituents. ..................................................................206

Table 4.19: Requirements of water for textile processing units. ................................................207

Table 4.20: Problems in wet processing associated with water impurities. ...............................212

Table 4.21: Requirements to be fulfilled by pretreatment. .........................................................220

Table 4.22: Possible steps in the preparation of blended materials. ...........................................222

Table 4.23: Problems caused during singeing, its causes and remedial measures. ....................224

Table 4.24: Sizing agents and their removal processes. .............................................................231

Table 4.25: Problems caused during desizing, its causes and remedial measures. ....................233

Table 4.26: Problems caused during scouring, its causes and remedial measures. ....................241

Table 4.27: Bleaching agents and their suitability for different fibers. ......................................244

Table 4.28: Problems caused during bleaching, its causes and remedial measures. ..................247

Table 4.29: Problems in mercerization and causticization and possible solutions. ....................259

Table 4.30: Problems caused during heat setting, its causes and remedial measures. ...............267

Table 4.31: Main objectives of the dyeing process. ...................................................................270

Table 4.32: Important factors affecting reproducibility in the batch dyeing of fiber blends. .....272

Table 4.33: Dyehouse factors and associated tolerances. ...........................................................272

Table 4.34: Factors affecting continuous dyeing of PES/CELL blends by the continuous

method. ....................................................................................................................273

Table 4.35: Important characteristics of different batch dyeing machines. .................................275

xi

Table 4.36: Dyeing faults due to package dyeing machine. .......................................................278

Table 4.37: Dyeing problems related to batch dyeing machines and their countermeasures. ....287

Table 4.38: Different sequences used in the dyeing of blends by semi-continuous and

continuous process. ..................................................................................................302

Table 4.39: Migration in intermediate drying and associated faults. .........................................306

Table 4.40: Suitability of thermofixation conditions for different synthetic fibers. ...................309

Table 4.41: Dyeing problems in continuous dyeing machines and their countermeasures. .......311

Table 4.42: Pigment dyeing components and their corresponding effect on dyed fabric. .........328

Table 4.43: Problems in pigment coloration and possible solutions. .........................................334

Table 4.44: Problems and their possible solutions in the dyeing of polyester/cellulose

blends using a disperse/reactive system. .................................................................348


blends with disperse and direct dyes. ......................................................................375


blends using disperse/vat system. ............................................................................379

Table 4.47: Dyeing problems associated with disperse/sulfur system. ......................................388

Table 5.1: Properties of yarns and fabric codes. .......................................................................395

Table 5.2: List of chemicals and auxiliaries. ............................................................................396

Table 5.3: Properties of disperse dyes used in the study. .........................................................396

Table 5.4: Characteristics of reactive dyes used in the study. ..................................................397

Table 5.5: CIE whiteness and tint indices of fabrics after pretreatment. ..................................398

Table 5.6: Dye combinations used to match target colors using different dyeing methods. ....399

Table 5.7: Total amounts of dye required to match the target colors in fabrics of different

blend ratio using different dyeing methods. ............................................................405

Table 5.8: The effective liquor ratio for each fiber in the blend at a bath liquor ratio of

20. ............................................................................................................................406

Table 5.9: Light fastness results of polyester, cotton and their blends dyed in different

shade depths. ............................................................................................................411

xii

Table 5.10: Dry crocking fastness of fabrics of different colors and blend ratio dyed by

different dyeing methods. ........................................................................................413

Table 5.11: Wet crocking fastness results of polyester, cotton and their blends. .......................414

Table 5.12: Wash fastness properties of dyed polyester, cotton and polyester/cotton

fabrics. .....................................................................................................................416

Table 5.13: Water fastness of dyed polyester/cotton fabrics with different blend contents. ......422

Table 6.1: Characteristics of experts. .......................................................................................428

Table 6.2: Human expert versus the expert system. .................................................................429

Table 6.3: Categories of expert systems. ..................................................................................431

Table 6.4: Summary of the expert systems developed for textiles. ..........................................433

Table 6.5: Categorized list of possible causes associated with symptoms in the coloration

of polyester/cellulosic materials. .............................................................................462

Table 6.6: Sorting of causes into different categories based on their origin, ...........................469

Table 6.7: An example of different analytical methods that can be applied to aggregate

expert responses in two different scenarios (E=Expert). .........................................474

Table 6.8: List of causes associated with the reproducibility symptom after being

prioritized based on the weighted CFs obtained from experts (E represents

expert). .....................................................................................................................475

Table 6.9: Analysis of causes according to category and commonness. ..................................479

Table 6.10: Possible causes for S15 and weighted average CF. .................................................488

Table 6.11: Possible causes for S16 and weighted average CF. .................................................488

Table 6.12: Causes for S17 and weighted average CF. ..............................................................489

Table 6.13: The new salience values of the all the cause asserted for S15-S17. .........................490

Table 6.14: Mostly likey causes for S1 reproducibility with existing and new salience

values as the blend ratio is increased. ......................................................................493

Table 7.1: Expert responses and expert system’s knowledge base for presence of holes

and tears (S15). ........................................................................................................507

Table 7.2: Responses from human experts and the expert system for poor color yield

(S4). .........................................................................................................................509

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Table 7.3: Responses from human experts and the expert system for widthwise shade

variation in pigment coloration (S10). .....................................................................512

Table 7.4: Evaluation results of the expert system. ..................................................................515

Table 7.5: Comparison of diagnosis of faulty colored samples, human vs expert system. ......517

Table 7.6: Diagnosis results of human experts and DEXPERT-B. ..........................................518

Table A.1: Mean responses of experts for symptoms and their causes related to dyes. ............547

Table A.2: Mean response of experts for symptoms and their causes related to pigments .......558

Table B. 1: Questions to user related to various causes for diagnosis. ......................................563

Table D.1: Expert responses and expert system’s knowledge base for reproducibility (S1). ...576

Table D.2: Expert responses and expert system’s knowledge base for unlevelness (S2). ........582

Table D.3: Expert responses and expert system’s knowledge base for streaks (S3). ................588

Table D.4: Expert responses and expert system’s knowledge base for shade change (S5). .....591

Table D.5: Expert responses and expert system’s knowledge base for inadequate washing

fastness (S6). ............................................................................................................595

Table D.6: Expert responses and expert system’s knowledge base for dark stains or spots

(S7). .........................................................................................................................598

Table D.7: Expert responses and expert system’s knowledge base for light stains or sports

(S8). .........................................................................................................................601

Table D.8: Expert responses and expert system’s knowledge base for lengthwise shade

variation (S9). ..........................................................................................................603

Table D.9: Expert responses and expert system’s knowledge base for shade variation

within layers (S11). .................................................................................................606

Table D.10: Expert responses and expert system’s knowledge base for two sidedness

(S12). .......................................................................................................................610

Table D.11: Expert responses and expert system’s knowledge base for reduced strength

(S13). .......................................................................................................................611

Table D.12: Expert responses and expert system’s knowledge base for irregular surface

appearance (S14). ....................................................................................................612

Table D.13: Expert responses and expert system’s knowledge base for poor hand (S16). .........614

xiv

Table D.14: Expert responses and expert system’s knowledge base for poor dimensional

stability (S17). .........................................................................................................615

xv

LIST OF FIGURES

Figure 2.1: World fiber production for the year 2013. .................................................................14

Figure 2.2: Global consumption of textile fibers by end-use. ......................................................15

Figure 2.3: Cotton content in the cotton yarn-world average. .....................................................16

Figure 2.4: Material distribution of yarn blends in the short-staple spinning system. .................17

Figure 2.5: Share of major fiber blends in dyeing processes. ......................................................18

Figure 2.6: Stress-stain curves of Pima cotton, regular and high tenacity polyester fibers

used in blended yarns [49]. ........................................................................................26

Figure 2.7: Effect of polyester levels in PES/CO blends on abrasion resistance and

wrinkle recovery properties of fabric [51]. ................................................................27

Figure 2.8: Properties of different fibers in the blend [54]. .........................................................29

Figure 2.9: Property spectrum of different fiber blends with optimum blend proportions

[54]. ...........................................................................................................................31

Figure 2.10: Variation in yarn strength of PES/CO as a function of polyester content [8]. ..........32

Figure 2.11: Variation in moisture regain properties of PES/CO fabrics with polyester

content [60]. ...............................................................................................................33

Figure 2.12: Fiber distribution in the blended yarns produced by sliver and flock blending

methods [74]. .............................................................................................................42

Figure 3.1: Staining of different fibers by disperse dyes during the dyeing process [80]. ..........50

Figure 3.2: Continuous pigment coloration process. ...................................................................61

Figure 3.3: Binder film formation and fixation mechanism. .......................................................67

Figure 3.4: Relationship between curing temperature and time. .................................................78

Figure 3.5: Batch dyeing system for polyester/cellulosics blends. ..............................................94

Figure 4.1: Fault investigation process in a dyehouse. ..............................................................111

Figure 4.2: Cause and effect model for investigating faults in the dyed fabric. ........................115

Figure 4.3: Factors influencing the spinning process of polyacrylonitrile fibers. .....................124

Figure 4.4: Steps involved in woven and knitted fabric production. .........................................175

xvi

Figure 4.5: Aspects of fabric quality. .........................................................................................180

Figure 4.6: Fabric quality assurance. .........................................................................................180

Figure 4.7: Continuous dyeing range for PES/CELL blends. ....................................................302

Figure 4.8: Schematic representation of migration types during intermediate drying (G

represents the direction of fabric movement). .........................................................305

Figure 4.9: Binder to pigment ratio and fastness properties. .....................................................331

Figure 4.10: Pigment coloration fixation conditions. ..................................................................333

Figure 5.1: Clearing mechanism of disperse dye stain [383]. ....................................................394

Figure 5.2: Simulations of Pantone colors used as target colors. ..............................................399

Figure 5.3: Dyeing profiles of different dyeing methods used. .................................................402

Figure 5.4: The effect of liquor ratio on the relative strength of cotton dyed with reactive

dyes (Liquor ratio of 20 is taken as the reference). .................................................409

Figure 5.5: The effect of liquor ratio on the relative strength of polyester dyed with

disperse dyes (Liquor ratio of 20 is taken as reference). .........................................410

Figure 5.6: Color change ratings for the navy blue color dyed fabrics after the washing

test. ...........................................................................................................................420

Figure 5.7: Nylon staining results for the navy blue color dyed fabrics. ...................................420

Figure 5.8: Cotton staining results of the navy blue color dyed fabrics. ...................................421

Figure 5.9: Grey scale rating for staining of nylon for the brown color after water fastness

test. ...........................................................................................................................425

Figure 5.10: Grey scale rating for staining of cotton for the brown color after water fastness

test. ...........................................................................................................................426

Figure 6.1: Components of an expert system [16]. ....................................................................436

Figure 6.2: Schematic of developing knowledgebase by a knowledge engineer. ......................437

Figure 6.3: A list of common faults in the coloration of polyester/cellulosic blends. ...............438

Figure 6.4: An example of reproducibility issues where the reproduced color from a new

dyed batch in not consistent with the original shade. ..............................................439

Figure 6.5: An example of unlevelness. .....................................................................................440

xvii

Figure 6.6: An example of bands in fabric. ................................................................................440

Figure 6.7: An example of low color yield (on the right) compared to the standard (left). .......441

Figure 6.8: An example of shade change. ....................................................................................441

Figure 6.9: An example of a dyed sample and a stained multifiber strip after the washing

test. ...........................................................................................................................442

Figure 6.10: An example of dark stains. ......................................................................................442

Figure 6.11: An example of light stains. ......................................................................................443

Figure 6.12: An example of lengthwise shade variation. .............................................................444

Figure 6.13: An example of widthwise shade variation (note the fabric is folded on itself). ......444

Figure 6.14: An example of shade variation within layers in a yarn package. ............................445

Figure 6.15: An example of two sidedness. .................................................................................445

Figure 6.16: An example of fabric with reduced strength. ..........................................................446

Figure 6.17: An example of crease marks. ..................................................................................447

Figure 6.18: An example of holes (left) and tears (right). ...........................................................447

Figure 6.19: an example of fabric with a poor hand. ...................................................................448

Figure 6.20: A symbolic representation of poor dimensional stability of the fabric. ..................448

Figure 6.21: A symbolic representation of the coating of rollers during pigment coloration. ....449

Figure 6.22: Cause and effect diagram for faults in the dyeing of fiber blends. ..........................451

Figure 6.23: Possible causes originating from the measurement. ................................................453

Figure 6.24: Possible causes originating from the machinery. ....................................................454

Figure 6.25: Possible causes originating from the materials. ......................................................457

Figure 6.26: Possible causes originating from method. ...............................................................458

Figure 6.27: Possible causes originating from the environment. .................................................459

Figure 6.28: Possible causes originating from human-related factors. ........................................461

Figure 6.29: A screenshot of the electronic survey distributed to experts in spreadsheet

format ......................................................................................................................471

xviii

Figure 6.30: System architecture of DEXPET-B. ........................................................................481

Figure 6.31: Knowledge representation in DEXPERT-B in the form of rules. ...........................484

Figure 6.32: The main screen for the DEXPERT-B system. .......................................................495

Figure 6.33: Interface for the selection of material related information. .....................................496

Figure 6.34: Interface for the selection of the coloration process in DEXPET-B. ......................497

Figure 6.35: The user interface containing images of the faulty dyed PES/CELL yarns. ...........498

Figure 6.36: The user interface containing images of the faulty dyed PES/CELL knitted

fabric. .......................................................................................................................499

Figure 6.37: The user interface containing images of the faulty dyed polyester/cotton

woven fabric. ...........................................................................................................499

Figure 6.38: Diagnosis interface for woven fabric dyed by batch process using one bath

process in a jet dyeing machine. ..............................................................................500

Figure 6.39: An example of the diagnosis function with a question prompt based on the

selected symptom. ...................................................................................................501

Figure 6.40: Example of explanation function for DEXPET-B. ..................................................502

Figure 6.41: An example of the use of DEPXET-B system for diagnosis. .................................503

1

CHAPTER 1 INTRODUCTION

1.1 Background

Textiles and clothing constitute one of the basic necessities of human beings and are among the

most important trade commodities. They are often colored to increase their aesthetic appeal, as

color is one of the primary factors that directly influences the sale of the product. The world of

fashion may not be conceivable in the absence of color. Another reason to impart color to textiles

is for a functional purpose such as for camouflage. The process of imparting color to textiles is

very old [1, 2]. Approximately 75-80% of textile products comprise colored materials [3]. The

coloration is therefore considered as one of the most important processes in the textile industry.

The process of imparting color to the substrate using either dyes or pigments is known as

coloration. This can be achieved through a process of dyeing or printing. Dyeing involves a

uniform application of color while printing deals with localized color application. During the

dyeing process, the uniform adsorption and distribution of dyes inside the fiber takes place. This

excludes pigments, which are generally attached to the fiber surface with the help of binders or via

a process known as spun dyeing. The main objective of the dyeing process is to obtain a correct

shade that matches a target color, with a uniform distribution of the colorant, and whenever

possible, in the first attempt. However, dyeing is a complex process that involves many variables

such as fibers, water, dyes, chemicals, operators, machinery and process parameters. Any

variations in raw materials and in conditions during the dyeing process may lead to a faulty dyeing.

From the viewpoint of a consumer, the product should be free of faults and must be adequately

resistant to various conditions during use. The consumer requirements are often described in the

form of specifications. These requirements are met by the dyers through proper selection and

application of dyes, understanding of fiber properties and process control during each

manufacturing step involved in the production of textiles [1-5].

The importance of product quality is continuously increasing in the textile industry.

Consumer demands have increased while expectations for no increases in cost remain. Therefore,

for textile producers and retailers it is essential to determine and understand the factors that

influence the product quality and ultimately the value of the end product. With global sourcing,

retailers are establishing quality management systems in order to reduce the costs associated with

poor quality products. The cost of production comprises of direct and indirect costs. Direct costs

2

include raw material, machines, labor, storage, loans, customs duty, etc. Although direct costs can

be controlled up to some extent, since they depend upon external factors, it is the indirect cost that,

if controlled properly, gives an edge to the manufacturer or retailers over its competitors in today's

highly competitive market. Indirect costs are influenced by the reliability, right-first-time

production, just in time delivery, and goodwill, etc. It is therefore essential to understand the

concept of quality in terms of producing goods that meet the customer specifications at minimal

cost whenever possible. When a textile material is processed through different processing stages,

its value is increased; it is, therefore, essential to remove the causes of potential defects in the

material as early as possible. Sub-standard finished products incur high losses to retailers and

manufacturers. Therefore, in order to obtain high-quality products that meet the demands of the

end-user, the correct process parameters and specifications of raw material, yarn, fabric, and

finished fabric, must be selected and integrated into the retailer's supply chain operations and

strategy. This level of control leads to the desired product without the low-quality claims at the

end of the textile supply chain [6].

Today's textile market incorporates a significant amount of fiber blends. Blends are textile

materials which are the mixture of physically or chemically different fibrous polymers. Textile

materials can be fibers, filaments, yarns or fabrics such as bicomponent fibers, filament mixtures,

core-spun yarns, uniformly blended staple yarns and fabrics made from them. They also include

union fabrics which are produced by using different types of yarns in the fabric. Fibers are blended

for various reasons which include enhancement of performance properties, reduction of the price

of raw material and to obtain novel color effects. Blended textiles are widely used in apparel, home

textiles and carpets [7-9]. Although there are no reported figures about the use of fiber blends, it

is estimated that textile fiber blends account for 30-40% of textile products worldwide.

1.2 Statement of the problem and goals

According to Murphy's Law, anything that has a tendency to go wrong will go wrong. This also

holds true for the dyeing process where problems do occur, even if the process is properly

controlled, and the plant is efficiently managed. In addition, problems occur not only in new

processes but also in well-established processes. They may be in the form of processing faults or

consumer complaints. There are many causes of such problems. Some are due to faulty raw

materials, machine malfunctions, human errors and inappropriate use of textile goods against their

3

intended use [10, 11]. For troubleshooting purposes, it may be beneficial to have a sample of the

original substrate either in the dyed or undyed form so that the required investigation is carried

out. These samples are generally available from the quality control department. Troubleshooting

the processing defects involves some detective work to obtain information about processing details

and quality control records pertaining to the defective batch. With respect to consumer complaints,

the information obtained from the consumer must also be checked. The production site should also

be visited to determine potential problem spots. This is usually followed by appropriate laboratory

tests to investigate the causes of problems and eliminate them in a systematic manner. The sample

size, time limit, and economic considerations limit the number of tests that can be carried out.

Proper laboratory investigations require specific instruments and methods to determine the root

cause of the symptom. This necessitates a specialized laboratory setup [10].

Troubleshooting often requires much experience to investigate the causes of the defects.

This is usually performed by senior personnel or an expert who has spent years in handling such

types of problems, has a working knowledge about the process, machines, substrate, and dyestuff

characteristics, and specializes in such type of work. An expert based on experience recognizes

the causes of a problem and may suggest specific tests. The economic implications of the specific

problem determine the amount of time and expense spent on troubleshooting. It can be concluded

that effective troubleshooting requires experience and skill, and the technique is time-consuming

and may need specialized laboratory methods and equipment [10, 11].

In a dyehouse, the expert has to deal with questions arising from different sectors, which

may include measures to improve processes, causes of defects, facts, and data. Additional

information may thus be required to supplement their expertise. An expert, therefore, must possess

three qualities: factual knowledge, awareness of cause and effect relationships and systems, and

the ability to analytically answer questions which arise in day to day situations. Factual knowledge

refers to a comprehensive understanding of textile processes, products, and machinery. An expert

must also be able to deduce important causes based on the current situations and be able to suggest

measures for success. This is known as know-how relationships. Lastly, systematic thinking refers

to the analysis of the complex system as a whole. This makes problem-solving easier and more

effective [12].

4

The main problems and challenges with human experts and troubleshooting are [13]:

▪ A dyeing plant normally works seven days a week without any stoppages, a dyeing

expert, on the other hand, is only available on a working day. The problems may arise

during night and holidays and these are generally not resolved until the expert becomes

available. This results in delays and sometimes the production of faulty materials.

▪ The expert's knowledge is limited to themselves; if they quit, retire or die that expertise

is lost.

▪ The performance of a human expert is not the same at all times, as it depends on many

factors such as fatigue or stress. Also, experts do not always provide explanations for

resolving the problem as they may be too tired, unwilling or unable to do this. This also

limits the learning/training of new people joining the dyehouse.

▪ The current availability of dyeing experts is limited, as many experts have retired over

the recent decades, and cost constraints due to economic and competitive reasons limit

their availability. Dyeing plants have senior personnel who are responsible for

troubleshooting problems, but they may have limited experience and may not be

considered as experts.

▪ Dyeing plants often lack a proper system for documenting problems and their causes,

which limits the retrieval of information when required.

▪ Some of the troubleshooting involves routine practices. In these cases, a human expert

has to dedicate expertise to overcome routine matters. This leads to a loss of expert

time which could be spent on more important or difficult problems; and

▪ Human experts sometimes do make mistakes due to fatigue or stress, and there is

generally no second opinion available.

An expert system may resolve all the above-mentioned problems and challenges. An expert

system is a computer program, which can be installed on a computer. This makes expertise

available at all times without disrupting the work of individuals involved in dyeing and is not

confined to a person. Problems can be resolved as soon as they occur, and this results in time and

cost savings. Some routine tasks which require human expertise can also be easily performed by

the expert system. The performance of an expert system remains consistent at all times and it can

provide necessary explanations to overcome the dyeing problems. It can also be used as a training

5

tool. The expert system combines the knowledge from multiple experts, technical literature and

books, i.e. it combines theoretical knowledge, practices, and specialized knowledge. The combined

expertise usually exceeds that of a single human expert. It also increases the reliability of a human

expert by providing a second opinion and in cases where there are conflicts among multiple

experts. Depending on the design, the problems and their causes can be saved and retrieved when

required. This can help the dyehouse in identifying the recurrence of the problems when

monitoring the performance of personnel and machinery. This results in improving the efficiency

of the dyehouse. An expert system also provides a systematic troubleshooting approach which

avoids duplication of efforts for resolving problems and may provide cost and time savings [13].

Textile materials comprising of textile fiber blends are widely produced. It can be estimated

that at least 1/3 of all textile material dyed today consists of blends [14]. This signifies the

importance of blends. Almost all the troubleshooting expert systems that have been developed so

far are based on single fiber types. The development of an expert system for troubleshooting

problems in the dyeing of fiber blends would thus be beneficial for dyehouse managers, dyers,

management and training purposes as it would cover this important area.

The final properties of the blend are not the sum of individual properties of fibers making

up the blend and neither to its proportion to the concentration of constituent fibers in the blend

[15]. There are certain challenges and problems in coloration which are specific to fiber blends.

These include differences in the dyeing behavior of individual fibers, the requirement of different

dyeing conditions, cross-staining, interaction effects between different colorant classes and

coloration chemicals. All these behaviors make the coloration of blends different than the

individual fibers in the blends.

The primary aim of this research is to design and develop an expert system for

troubleshooting problems in the coloration of commercially important fiber blends. The diagnostic

expert system provides the dyer with the most likely cause(s) of common problems that occur

during the coloration of fiber blends in yarn, knitted or woven materials. The identification of the

cause(s) will help the dyer in resolving the problem in a timely manner and would likely

recommend a method to prevent the recurrence of the problem. The specific goals of this research

are:

▪ Development of a database of the most common faults and their causes in the coloration

of commercially important fiber blends (specifically polyester/cellulose);

6

▪ Design and development of a functional diagnostic expert system for dyeing of fiber

blends; and

▪ Validation and verification of the expert system.

A diagnostic expert system for coloration of textile fiber blends, DEXPERT-B was built

using wxCLIPS, a modified version of the CLIPS with functionality to provide a customized

graphical user interface (GUI). CLIPS is an acronym for C Language Integrated Production

System. CLIPS is an expert system programming language and available as an open source. It is a

rule-based language that is specifically used for developing an expert system [13, 16].

The rule-based expert system was developed in a Windows environment. The expert

system consists of two components: the knowledge base and the inference engine. The knowledge

base and the inference engine were coded in CLIPS. The GUI serves as the user interface for the

expert system. Two types of information are obtained from the user. The first deals with problem-

based knowledge, which contains background information about the fiber type, blend ratios,

material form, colorants used and the coloration process. The second set of information deals with

the problem-specific components, which involve facts about the problem through a series of

questions. The information is passed on to the expert system first to trigger the specific module.

The problem-specific component is then used to provide answers to the user queries. The inference

engine uses the knowledge base and the user-provided information to draw conclusions.

1.3 Research methodology

The DEXPERT-B system was developed in three phases. Phase I resulted in the identification of

the most common fiber blends and their practical coloration problems along with the possible

causes. The commercially significant fiber blends were identified through published reports, fiber,

dyes and machinery manufacturers and experts. A detailed survey of technical literature (reference

books, dissertation, and theses, technical reports and journals) was carried out to collect, organize

and analyze the potential faults and their possible causes in the coloration of fiber blends. Several

dyers were also interviewed to determine the nature of practical coloration problems in the dyeing

of these blends. A technical survey comprising of practical dyeing problems along with potential

causes was sent to dyeing experts to obtain their responses. Phase II resulted in the development

of a diagnostic expert system for the coloration of textile fiber blends (DEXPERT-B). The

7

responses obtained from experts were analyzed and coded in the form of rules in the expert system

language (CLIPS). The questions used for inference purposes were created based on the causes.

Phase III concluded the study by validation and verification of the developed expert system in

Phase II. This was achieved by testing the expert system against the known causes to check its

validity, evaluation of the expert system against the unknown causes and comparing its

performance against human experts. The final testing and debugging completed Phase III.

The findings of this study provide an important contribution to troubleshooting problems

in the coloration of polyester/cellulosic blends. It can not only help the dyer in finding the probable

causes for particular problems but will also help to find the root causes of the problem and correct

them at the source.

The dissertation is divided into eight chapters, which depending upon the requirement of

the subject matter are made up of sections. Chapter 2 deals with an in-depth review of textile fiber

blends. Reasons for blending fibers and their manufacturing are covered. Furthermore, the

optimum properties of fiber blends and common blend ratios are also included. The global fiber

market in the context of fiber blends is also discussed. Chapter 3 presents in a readily

comprehensible manner the dyeing processes for common blends. The coloration process is

discussed in the context of both pigment and dyes commonly applied for the coloration of blends.

The color effects that can be produced on different blend types are covered. Chapter 4 is concerned

with the commonly encountered problems in the coloration of blends discussed in chapters 2 and

3. The problems that occur in yarns, knitted and woven fabrics that are made up of fiber blends are

reviewed. The basic philosophy behind the troubleshooting of faults is also covered. The problems

are divided according to their origin. The common problems along with their causes and probable

solutions are summarized. Chapter 5 presents the effect of blend ratio on the coloration of

polyester/cotton blends. The dyeing method and the effect of different blend ratios are discussed.

The fastness results obtained are presented in detail. Chapter 6 deals with the development of

DEXPERT-B. The factors that lead to a problem in the dyeing of blends are presented in the form

of a cause and effect diagram. The most common faults along with their definitions are presented.

The strategy used to create the expert system, combining expert responses and inference engines

is covered. Chapter 7 is concerned with the validation and verification strategies used for the

testing of the DEXPERT-B. Chapter 8 is devoted to the conclusion and future work. The summary

of the results of this study is presented along with the recommendations for future work.

8

CHAPTER 2 TEXTILE FIBER BLENDS

2.1 Introduction

Today's textile market is predominantly based on blends. Fiber blends are materials produced by

mixing two or more fiber types. Their high popularity is due to unique properties and performance

characteristics that can be achieved in the case of blends. Each textile fiber, weather natural or

synthetic, has specific properties. Materials based on single fibers may not satisfy the specific

requirements of a given end-use. In such cases, two or more fibers are combined in such a way

that optimum properties are obtained according to the required end-use by enhancing a particular

product characteristic [17, 18]. The fiber blends comprise any textile materials either in the form

of fibers or filaments, yarns, and fabrics that contain a premeditated combination of chemically or

physically different fibrous polymers. This covers bicomponent fibers, filament mixtures, core-

spun yarns, the intimate blending of fibers during spinning, combination yarns, and union fabrics,

to name a few. The number of possible blends and blend levels are very large but noticeably a

small number of blends are commercially used. The most common and traditional type of blends

consist of two physically or chemically different fibrous polymers such as polyester/cotton and

polyester/wool. The use of blends consisting of three or four fibers is also popular especially in

apparel due to the unique nature of properties that can be obtained by such combinations, a good

example is polyester/cotton/elastane [7].

2.2 History of blends

Fiber blends have been in use for a long time and their use continues to grow [19]. Many

explanations can be found for the use of textiles made of more than one fiber type. The main reason

was likely the shortage of good quality fibers in large quantities. Silk, for example, is expensive

and its application was mainly reserved for dignitaries. To overcome this problem, silk was often

blended with different fibers. Another reason for the use of fiber blends in fabrics was the

possibility of creating specific designs by using two different fibers. This, however, was not widely

done until the twentieth century mainly due to technical difficulties [20].

Historically fiber blends were used for different purposes. The early blends consisted of

natural fibers as they were the only available fiber type at that time. With the development of

9

manufactured fibers at the beginning of the 19th century, blends of natural and manufactured fibers,

as well as blends of manufactured fibers themselves, appeared in the market.

2.2.1 Blends of natural fibers

Historically, natural fiber blends were used as separate warp and weft yarns and in some cases,

mixtures of fibers were used to make yarn. Paracas textiles showed the use of llama and other hair

fibers of different colors [19, 20]. In Ptolemaic textiles, Coptic textiles, and in textiles of early

New England, wool and linen blends have been found with generally wool being used as warp and

linen as weft yarns [19, 20]. These fabrics were known as linsey-woolsey and were made of

handspun linen and wool. These finely woven fabrics were moth-resistant and were used for

apparel and household purposes. Silk and wool blends have also been found in Regensburg fabrics

and silk and cotton in Hyderabad textiles. Other examples of historic blends include oriental yarns

consisting of silk and gold or silver and central Asian fabrics with linen or hemp warps and wool

weft. Blends of silk and wool are still common in Persian handwoven carpets. Soft fabrics

comprised of silk mixed with cotton or linen were woven by Phoenicians. Watertight tent fabrics

made of wool mixed with camel hair or goat hairs were found in Tunisian and Peruvian textiles.

Mixtures of cotton and bast fibers were used in the fabrics found in Nigeria. Decorative fabrics of

cotton and silk were woven in India. In England, for some time after 1720, the printing of pure

cotton fabrics was forbidden to protect the wool industry. Linen-cotton blends known as fustian

was used to evade the ban. In France, men's apparel consisting of wool-linen blends, women's

clothing containing silk warp and cotton weft and silk-wool blends for upholstery have also been

found [20-24].

2.2.2 Blends of manufactured fibers

Manufactured fiber blends emerged in the market soon after the appearance of manufactured

fibers. Rayon fiber, also known as artificial silk, was introduced in the market in 1892 [21]. Dress

materials made of rayon warp and cotton weft emerged shortly thereafter. One of the advantages

of these blends is the possibility of producing various cross-dyed effects. Other common blends

of rayon fibers included those with casein fibers, flax, nylon, and wool. Blends of rayon staple

fiber were also popular. The appearance of acetate fibers in the 1920s created a possibility of

producing three-component blends consisting of natural fibers, rayon, and acetate. Blends of

10

acetate and rayon can be used to generate a cross-dyeing effect, while the acetate fiber component

in the blend is used to improve the crease resistance property of the fabric. Another common blend

involved acetate and wool blends. These blends were used for the production of tropical suiting,

flannels and blouse fabrics. The acetate component in the blend reduced the fabric shrinkage,

improved the pleating and permanent fabric creases and created a possibility of cross-dyeing.

During World War I, rayon was blended with wool in order to develop new compositions. This

was partly due to the limited availability of wool and the long-distance shipment from a limited

number of wool growing regions. German army defeat in the USSR has been linked with the

inadequacy of rayon/woolen blends [19]. Some examples of rayon blends during this period are as

follows. Staple viscose fibers of coarser denier were blended with low crossbred wool, mohair,

and goat hairs. Fabrics made of 50/50 blends of rayon staple and casein fibers were produced that

exhibited the wooly handle. Casein fibers were blended with wool and rayon in felts. A modified

rayon fiber, Rayolanda-X, with an affinity for acid dyes was also used to give two-tone effects in

dyed blends. Three-component blends were also produced. In the early 1950s, due to the rising

prices of wool different blends of wool were experimentally produced to retain wool in the yarn

while reducing the amount of wool used [21, 22]. Examples of wool blends during this period

include wool and nylon, for excellent wearing qualities and wool-like hand, production of rayon

or acetate with wool for piece dyeing to obtain heather look and wool and Rayolanda-X for the

tone on tone effect [25]. Common blends used in hosiery were wool-rayon, wool-nylon and wool-

acetate-nylon [21, 22].

Nylon was commercially produced in 1939 and its high strength and good abrasion

resistance properties made it a prime blend component with weaker fibers to improve the yarn

properties. Nylon was successfully blended with wool. For example in the case of military textiles,

product life and light exposure were increased, while the weight of the product was reduced for

the same performance. Nylon/cotton blends, however, exhibited serious property problems. Blends

containing less than 50% nylon showed lower strength than cotton alone due to the lower modulus

of the nylon fibers. To counter this problem a new nylon, Dupont 420, was engineered that had the

same stress-strain curve as that of cotton up to the breaking point [21]. The US army has researched

the fiber blends as part of its wool conservation program. After the World War II, the quantity of

wool in the US was insufficient to meet domestic demand and this led to an aggressive wool

11

conservation program by the US army. The US Army adopted the first synthetic fiber nylon in

1951 as a blending fiber with wool [19].

Acrylic staple fibers became available in 1952. They were blended with other fibers or the

modified acrylic fiber. Hi-bulk acrylic fiber, a modified acrylic fiber, which shrinks on heating

was blended with acrylic fibers to make a lofty yarn. Acrylic fibers were also blended with nylon

or polyester in socks and with polyester in woven fabrics to improve the wrinkle recovery

properties. Blending of acrylic fibers with wool, angora, and silk was also done to improve physical

performance and to reduce cost. Modacrylic staple fibers were introduced in 1950. Blending with

modacrylic fibers was done due to its flame resistance properties. Polyester was blended with

modacrylic fibers to improve its abrasion resistance properties [21].

Polyester fibers were commercially available in the fifties and due to the excellent

properties of this fiber type, it was immediately used for blending with other fibers. One of the

earliest blends produced was polyester-wool. These blends have excellent wrinkle-resistance and

crease retention properties. The visual and tactile aesthetics of wool fabrics were also retained.

These blends continued to develop through the 1960s and their production became routine. The

most successful blend is probably polyester-cotton blends. One of the reasons for developing these

blends was the good wrinkle resistant properties of the polyester component in the blend. In the

late fifties and during sixties blends were developed that exhibited wash and wear properties. This

was achieved due to the development of durable press finishes [26]. Polyester has an advantage

compared to nylon in these blends as the properties of the polyester match better with the cotton

fiber. Due to excellent properties that can be achieved, these blends have become the most

commonly used blend types over the years [21].

Spandex fiber has high elongation properties and can be used in blends. After their

introduction in the market in the 1960s, they were blended with cotton, polyester, nylon, and

viscose to impart elastic properties to the fabric [21, 22]. Before the production of spandex, natural

rubber was used as an elastomeric fiber in apparel fabrics. Rubber yarn had many problems such

as it needed to cover with the outer layer of textile for protection during processing, low retractive

force, poor abrasion resistance, low heat settability, poor resistance against aging, low yarn

modulus and tenacity. Many of these problems were overcome by spandex fiber and thus it soon

replaced the rubber yarn and provided new ways for its use in apparel fabrics [27].

12

Many different combinations and blend proportions have been tried but only a few fibers

in a small number of combinations are commonly used nowadays [21].

2.3 Global fiber market and blends

Textiles and clothing comprise one of the most important trade commodities. In 2013, they were

the fifth largest merchandise exported in the world and showed the second-highest growth of 8%

in merchandise trade, four times higher than the average world export growth rate which amounted

to US$766 billion [28, 29]. One of the important indicators of textile and clothing industry trade

as a whole is the world fiber demand. Approximately 196.3 billion pounds (90 million tons) of

fibers were produced in 2013 which was increased by 4% compared to 2012. These figures can

also be considered as reasonable estimations of usage in recent years since the data collection and

reporting often lags by several years. Manufactured fibers accounted for the largest share (72%)

in global fiber production. The share of natural fibers was 28%. For the manufactured fibers

consisting of synthetic and regenerated cellulose fibers, the share was approximately 66% and 5%

respectively. Polyester fibers dominate overall fibers production worldwide with a share of about

52% while cotton was the second highest with a share of 27% [30-33]. The consumption of

manufactured fibers continues to expand (was 30% in 1980) while the share of the cotton is on a

decline. The second time ever the market share of cotton reached below 30% was in 2013.

Polyester fibers, on the other hand, showed an upward trend in their consumption and the share

lost by cotton was occupied mainly by polyester [34]. The main reasons for the substitution of the

natural fibers with manufactured fibers are due to the following [35]:

▪ Almost unlimited availability (not dependent on cultivation area and other factors);

▪ Not dependent on weather/climate;

▪ Cheap and cost-efficient;

▪ Large range of end-use; and

▪ Can be recycled (environmentally friendly).

Table 2.1 shows the global fiber production and share for the year 2013 [30]. The world

fiber use is differentiated according to the material (individual fibers) and fiber type (filament &

staple). Filaments account for approximately 2/3rd while staple fibers share is about 1/3rd of

manufactured fiber production respectively [35]. Figure 2.1a shows the consumption of textile

13

fibers according to their use in different industry segments along with the recycled fibers. Short

staple fibers comprising of cotton, cellulose and synthetic staple fiber have the highest share

followed by the filaments. The share of wool fibers (long-staple fibers) was approximately 2%.

Mill consumption of textile fibers which mainly utilize short-staple fibers is shown in Figure 2.1b.

Cotton fiber has the highest consumption of 47% followed by polyester with 27%. Nylon fibers

have the lowest share of 0.2% [36]. Figure 2.1c shows the production of manufactured fibers by

fiber type in the form of staple fibers and filaments [30].

Table 2.1: Global fiber use for the year 2013.

Fiber type Filament yarns Staple & Tow Total % Share

Natural fibers 55,710 28.4%

Cotton 52,395 26.7%

Wool 2,471 1.3%

Linen 540 0.3%

Silk 304 0.2%

Man-made fibers 90,261.9 50,328.7 14,0591 71.6%

Cellulosics 878.1 9,705.8 10,583.8 5.4%

Synthetics 8,9383.8 40,622.9 13,0007 66.2%

Polyester 69,032.4 33,844.3 102,916.7 52.4%

Nylon 9,200.7 369.3 9,569.9 4.9%

Olefin 9,587 1,451 11,039 5.6%

Acrylic 4,311.8 4,311.8 2.2%

Others 1,563.7 606.5 2,1702.2 1.1%

Total 196,301 100%

14

(a) World fiber type distribution [36].

(b) World textile fiber mill consumption by material distribution [36].

(c) World textile fiber mill consumption by fiber type [36].

Figure 2.1: World fiber production for the year 2013.

Cotton: 23,534; 47 %

Polyester: 13,553; 27 %

Recyling fiber: 6,309; 13 %

Polypropylene: 1,024; 2 %

Cellulosic: 4,178; 9 %

Acrylic: 934; 2%

Polyamide: 132; 0.3%

Manufactured Cellulosics Synthetic Polyester Nylon Acrylic0

20

40

60

80

100

% S

har

e

Filaments

Staple & Tow

15

World textile fiber consumption for the year 2013, according to the application is shown

in Figure 2.2. According to the end-use, textile products can be divided into four main segments

viz.: apparel, home textiles, carpets and rugs, and industrial and other products. The apparel sector

had the highest market share of 45% (42 million tons) followed by industrial and other products

with 34.7 million tons used with a share of 38%. Home textiles accounted for 9% of the fiber used

with 8.5 million tons while carpet and rugs accounted for 8% of world fiber use with 7 million

tons [37].

Figure 2.2: Global consumption of textile fibers by end-use.

World yarn production of all fibers was 100.4 million tons in 2012. The share of cotton

yarn was 46.3 million tons while the share of manufactured fiber production was 54.2 million tons.

The production of yarn classified as cotton (with 50% or more cotton) compared with cotton mill

use indicates that the increase in cotton yarn production was due to the increased use of other fibers

in blends. Before 2011, the amount of cotton spun into the yarn exceeded the amount of yarn

classified as cotton yarn. This is due to the use of cotton in blends with other fibers with less than

50% content. The average cotton content in cotton yarn was declined from 99% in 2002 to 51% in

2012 as shown in Figure 2.3 [34]. This indicates that a small portion of yarn types use cotton in

their blends and most cotton yarns include blends of cotton and other fibers with at least 50%

cotton portion [34].

Apparel: 45%

Industrial and others: 38%

Home textiles: 9%

Carpets and rugs: 8%

16

Figure 2.3: Cotton content in the cotton yarn-world average.

Spinning plants have increased the proportion of synthetic fibers, especially in blends due

to the high cotton prices in recent years. The ratio of the blends will continue to remain at such a

high-level [36]. Approximately 58% of all short-staple spun yarns produced nowadays is a blended

yarn. Figure 2.4 shows the distribution of blended yarn produced worldwide on short-staple

spinning systems. The distribution is given in the form of the main portion of the blend e.g.

CO/PES refers to a cotton-polyester blended yarn with CO as the main portion inside the blend.

The same is the case for the other blend types shown. Cellulosic fibers (CEL) include viscose,

Modal, and Tencel. The blended yarn produced can be divided into three broad categories based

on the main component as CO blend, CEL blend, and PES blend. CO blend has the highest share

of the market with approximately about 60%, CEL blend accounts for 21% and PES blend for 19%

of the short-staple blended yarn produced worldwide. No information about the exact blend ratio

and blended yarn produced on the long-staple spinning system is available. Based on the

information available it can be inferred that PES/CO blends comprise the largest produced blends

and PES/CEL are the second-largest blends available.

99%

51%

0%

20%

40%

60%

80%

100%

2001 2006 2011

17

Figure 2.4: Material distribution of yarn blends in the short-staple spinning system.

PES/CO blend is the major blend used currently and will remain the significant type due

to the unique characteristics of individual fibers used in the blend. Polyester consumption will

continue to increase by 3.6%, while the predicted growth rate of cotton is 2% per annum for the

next ten years [38, 39]. The cotton production is limited due to allocated growing regions, loss of

soil fertility, pollution, water availability, product yield and increasing food demand. With the

increase in fiber demand, cotton will not be able to cover the required demands, and this will cause

the so-called cotton gap. It was predicted that some part of this gap would be covered by increased

consumption of polyester fibers and partly by cellulosic fibers [40]. The best substitute for filling

this gap is cellulosic fibers due to having similar properties to those of cotton. One-third of textile

fibers based on the end-use are required to have specific properties such as absorbency and

moisture management which only cellulose-based fibers can provide [40-42]. With the increase in

the production and demand for polyester fibers and the limited production of cotton fibers, the use

of PES/CEL blends will continue to increase and this blend will maintain its popularity.

Unfortunately, information concerning the consumption of other fibers in the blend is not readily

available. It is estimated that approximately 55-60% of the polyester fibers are used in blends with

cotton and wool, out of which 40-45% is used for blends with cotton [3, 43]. Approximately 40%

of polyamide fibers are used in blends. About 50% of polyacrylonitrile fibers are also used in

blends with wool [3].

Fabric blends can be produced by two methods: yarns of different materials are combined

within the fabric structure, or intimately blended yarns are processed into fabric [36]. Similar to

cotton yarn designation, cotton fabrics are specified in the same manner i.e. fabrics with a cotton

CO/PES: 46%

PES/CO: 14%

PES/CELL: 5%

CELL/PES: 9%

CO/CELL: 14%

CELL/CO: 12%

18

component of at least 50% are termed as cotton fabric in the trade. According to the world textile

demand, an increased blending of cotton yarn is done in fabric production. This is evident from

the increased proportion of cotton yarn used in the production of synthetic fabrics. This implies

that cotton yarns are blended with other yarn types to produce blended fabrics [34].

Up to date information about the use of blended fabrics in dyeing is sadly not available.

However, it is estimated that 30-40% of the material dyed today comprise fiber blends and PES/CO

and PES/CEL blend are the largest blended fabric type in the dyeing process. Figure 2.5 shows the

estimates of the use of blended fabrics in the batch and continuous dyeing processes. The most

common blend types used are PES/CEL, PA/CEL, and PAN/CEL [44].

(a) Exhaust (including Cold Pad Batch)

(b) Continuous process

Figure 2.5: Share of major fiber blends in dyeing processes.

PES/CEL: 72%

Others: 3%

PAN/CEL: 4%

PA/CEL: 21%

2006

PES/CEL: 70%

Others: 3%

PAN/CEL: 5%

PA/CEL: 23%

2010

PES/CEL: 90%

Others: 4%PAN/CEL:6%

2006

PES/CEL: 89%

Others: 3%PAN/CEL:8%

2010

19

2.4 Purpose of blending

There are many reasons which are responsible for producing fiber blends.

▪ Economy

Expensive fibers are blended with cheaper ones to reduce cost. Expensive wool was

blended with viscose for cost reasons in the past. With the rising cost of cotton, the

polyester proportion in the polyester/cotton blend is increased due to economic reasons.

The cheaper fiber, however, should not have too much adverse effect on the properties

of the expensive fiber in the blend [8, 9, 18]. A similar approach was also used to blend

economical fibers with a luxury fiber such as silk and linen to produce

polyester/viscose/silk or polyester/viscose/silk blends for women’s apparel [7].

▪ Durability

A weaker fiber with a soft hand can be blended with a strong and durable fiber to

improve the useful life of the weaker fiber [8, 9]. This increases the resiliency and

durability of the resultant blend [45]

▪ Physical properties

One of the most important reasons for producing blends is the wide range of combined

physical properties that can only be achievable in blends. Two fibers with different

properties such as moisture regain, tenacity, elongation and initial modulus can be

combined to produce a blend that has the combined properties of both fibers. This may

be required to obtain uniquely desirable performance properties. The weaknesses of

one fiber, for instance, can be balanced with the strength of another. The most obvious

and common example is polyester/cotton. Polyester fibers have high tenacity, abrasion

resistance, and dimensional stability but low moisture regain. They can be blended with

cotton which has high absorbency, reduced pilling and comfort but low tenacity [7-9,

45, 46]. The properties that can be enhanced include abrasion resistance, strength,

absorbency (comfort), bulk and warmth, hand, dimensional stability, and wrinkle

resistance [18]. Most blends that are utilized today optimize the physical properties of

their component fibers and are usually a combination of natural fibers with a synthetic

fiber [45].

▪ Color

20

Different aesthetic color effects can be created using fiber blends. This leads to the

development of novel garments, color designs [8, 9] and multi-colored fabrics [18].

Different color effects such as tone in tone and cross-dyeing can be obtained by

combining regular dyeable fibers with differential dyeable fibers of the same material

type or by combining two different fiber types [7].

▪ Appearance

Yarns of different luster, crimp or denier can be combined to produce an attractive

appearance, visual effect, and tactile qualities. Although both yarns are dyed uniformly

with the same color, they still differ in appearance [8, 9, 18, 45]. For example, a small

amount of viscose provides luster to the cotton [46].

▪ Improved processing and uniformity

Fiber blends improve the productivity of yarn manufacturing, fabric manufacturing and

wet processing operations or increase the uniformity of the product. This type of

blending is called self-blending which is done in natural fibers that have variations in

diameter and length [18, 46, 47].

2.5 Types of fiber blends

The fiber combinations which provide optimum end-use properties and improve processability in

the blend are as follows [17, 48]:

▪ Manufactured fibers with natural fibers

Examples: Polyester with nylon, wool, cotton, viscose, modal, lyocell or linen; nylon

with wool or cotton; acrylic with wool or cotton; viscose, modal or lyocell with wool

or cotton

▪ Manufactured fibers with one another

Examples: Nylon 6 with viscose, nylon 66 or polyester; polyester with acrylic, elastane

or viscose

▪ Natural fibers with one another

Examples: cotton with wool or linen, wool with ramie; mohair with silk

21

With the technical advancements and for fashion reasons new fiber blends are constantly

being developed. The prevailing blends may vanish from the market and sometimes find their way

back to the market later [17].

The fiber blends made up of staple fibers or filaments may consist of similar or different

fibrous polymers with distinct chemical and physical properties. These include, but are not limited

to [17]:

▪ Fiber combinations having different morphology such as fineness, cross-section, and

crimp;

▪ Fibers having different physical properties involving shrinkage (normal/high

shrinkage), elastic modulus, flat/textured, luster (bright/matte); and

▪ Differences in the dye sites or the presence of different dye groups to obtain differential

dyeing effects.

When discussing blends, it is important to distinguish between the intimate blends, union

and combination yarns. When two or more fiber types are mixed intimately to produce a yarn, the

resulting mixture is known as an intimate blend. In intimate blends, different fibers are arranged

next to each other. Combinations yarns are produced by twisting of single yarns of different fibers.

Each ply in the yarn has different fibers as compared to the other ply, though their use is relatively

limited. The mixture or union fabrics are produced when yarns made from one fiber type are

combined with yarns produced from another fiber type. The usual arrangement consists of

lengthwise yarn of one fiber type and widthwise yarn of another fiber type. Other arrangements

are also possible in which yarns of different fiber types are used side by side or intimately blended

yarns of two fibers are used in on direction and yarns made of third fiber type are used in the other

fabric direction. Historically blended fabrics were produced in the union form as discussed in

section 2.2. Currently, union fabrics are produced to achieve various color effects that are difficult

and costly to produce by yarn dyeing of single fiber type. Another example of these fabrics is the

stretch denim in which textured polyester yarn is used in the widthwise direction with cotton yarn

in the lengthwise direction [46, 49].

Table 2.2 gives a summary of the most commonly used blend types, along with typical

blend ratios and end uses [17, 48].

22

Table 2.2: Summary of common textile fiber blends and their potential applications.

Blend components Blend proportions End use

Polyester/cotton 50/50, 65/35, (67/33) Underclothing, shirts, blouses,

nightwear, clothing, poplin coats

Polyester/viscose 70/30, 50/50 Work- and sportswear

Polyester/linen 65/35, 80/20 Leisurewear, clothing

Polyester/silk 70/30, 75/25, 80/20, 85/15 Leisurewear, clothing

Polyester/wool 55/45, 70/30 Suits, trousers, costumes, dresses,

coats, jerseys, pullovers, uniforms

Polyester/acrylic 50/50, 60/40, 65/35, 70/30 Leisurewear, clothing, women's

slack, pullovers, jerseys, tableware

Polyamide/cotton 10-50/90-50 Dress wear leisure shirts

Acrylic/wool 55/45, 70/30, 60/40 Jerseys, clothing, pullover, socks,

blanket, floor covering

Acrylic/viscose

Acrylic/cotton 55/45, 70/30 Jerseys, clothing

Acrylic/linen 55/45, 80/20 Leisurewear, knitted goods

Wool/polyamide 75/25, 80/20, 85/15 Uniforms, socks, hand knitting

yarns, woven carpets

Wool/viscose

Wool/cotton 50/50, 70/30 Suits, jackets, sports coats

Polyester/acrylic/wool 55/15/30, 30/40/30 Jerseys, clothing, pullovers.

Polyester/acrylic/cellulose Household textiles

Nylon/cotton/elastane Elastane 10-20% Knitted underwear

Staple combinations of

high shrinkage acrylic or

high shrinkage polyester

30-40% of high shrinkage

component

Jerseys, clothing, pullovers, hand

knitting yarns, trousers, clothing,

jackets

23

2.6 Properties of blended yarns and fabrics

For any textile fiber to be commercially successful, it must possess both primary and secondary

properties. Primary properties include certain essential fiber properties which enable them to be

converted to acceptable textiles. Secondary properties refer to those properties that improve

consumer satisfaction with the end-product made from the fiber. The fibers that exhibit high values

in all these properties do not exist in practice due to tradeoffs employed to achieve higher

performance in certain properties. The primary and secondary properties of different commercially

successful fibers are shown in the form of ratings. It can be seen that fibers can have lower values

in certain fiber properties. Consider the example of wool and acrylic fibers. The wool fibers have

good electrical conductivity and wicking properties but poor crease recovery and laundering

properties. The acrylic fiber on the other hand has good crease recovery and laundering properties

but poor electrical conductivity and wicking properties [46, 50].

Blending is an effective method of enhancing the positive and reducing the negative

properties of each fiber. This is commonly practiced in the case of natural fibers where the fibers

belonging to the same fiber category are blended before spinning to produce uniform properties in

the spun yarn. In the case of fiber blends, this is achieved by mixing different fibers such as

polyester and cotton where the positive properties of each fiber mask the negative properties of

other fiber and the resultant blend has excellent properties. However, it is important to know that

blending cannot enhance the properties of the blended material above the maximum levels

observed in the similarly constructed material produced from only of the fiber types found in the

blend [49]. For example, the strength of polyester/cotton blended yarn cannot be greater than the

strength of the yarn made from 100% polyester. However, polyester/cotton yarn is stronger than

100% cotton yarn. Similarly, if blending is not done properly, the blended fabric may even have

lower strength than a fabric produced entirely from the lower strength fibers. As shown in Table

2.3 synthetic fibers such as polyester and nylon having higher strength, abrasion resistance,

durability, and lower shrinkage are blended with natural fibers that have good moisture absorption,

comfort and exhibit no static generation. However, two properties of the resultant blends are

greatly affected which are pilling and flame retardancy. Pilling is not observed in the case of all

cotton fabrics but can be seen in blends made of polyester/cotton [47]. The burning time of the

polyester/cotton blend is lower than all cotton fabrics. The all-cotton fabrics were found to be less

flammable as compared to polyester/cotton fabrics of similar fabric types [65].

24

Table 2.3: Primary and secondary properties of textile fibers.

2.6.1 Compatibility of fibers in the blend

The fiber type used in a blend must be selected or produced according to the other fiber in the

blend. Special fiber variants have been developed by the manufacturers to obtain the required

properties in the blend. Specially developed viscose and polyester fibers are available in the market

for blending with cotton [50]. Each fiber in in the blend should be compatible otherwise the

properties of the blended yarn will be inferior when compared to the individual fibers in the blend.

Each fiber type in the blend must behave similarly under stress for the successful production of

yarn and to ensure adequate yarn strength during use [49]. The blended yarn is a composite

structure. The gauge length used during strength measurement has a strong influence on the yarn

strength and depends on the closeness and strength of the surrounding fibers [49]. It has been found

that predicted strength of a blend is often lower than experimental value. The fibers in the blend

must also have similar initial modulus and elongation at break [49]. When the strain level in the

25

yarn reaches the level of rupture of the less extensible component in the blend, that component

fails and this may lead to the rupture of the whole yarn [19].

Consider the example of producing polyester/cotton yarns by blending Pima cotton with

either the modified regular tenacity or high tenacity polyester fibers. The stress strains of these

fibers are given in Figure 2.6 [49]. The Pima cotton has an initial modulus and considerable force

is required to break the fibers. The cotton fibers break at 3.5 g/denier at 10% elongation. In the

case of modified regular tenacity polyester, fiber breaks at 4.8 g/denier at elongation of 45-55%.

Although regular tenacity polyester fibers are stronger than cotton but their contribution to the

strength of the blended yarn is minimal as they are in the elongation phase when the cotton fibers

start breaking at around 10% elongation. However, the high tenacity polyester contributes more to

the strength of the blended yarn because it has similar elongation properties thus increasing the

strength of the blended yarn [49].

It has been found that certain fiber types are not suitable for blends. In the case of 50/50

nylon/cotton blends the strength of the blend is less than the strength of 100% cotton yarn due to

significant differences in the extension properties of the two fibers. As nylon has considerably

higher extensibility than cotton, the cotton fibers in the blend break when the nylon fibers are still

within this extension region [50]. In the case of polyester/cotton or nylon/cotton yarn, the earlier

rupture takes place in the 7-10% extension range. The failure of one fiber in the blend does not

cause yarn extension to drop severely. In some cases, the blended yarn continues to extend even

up to the breaking extension of the most extensible component. The lateral pressure in the yarn

tends to grip the broken fiber segments of the less extensible fiber and thus aid in their reduced

level contribution to yarn strength. This phenomenon is affected by twist levels, blend ratio and

arrangement of components in the blended yarns. In polyester/cotton yarn, if the polyester

percentage is lower the extension percentage is found to be close to the cotton level, the failure

propagation tends to concentrate, and yarns would break at the lower extension levels. The effect

is more noticeable in highly twisted yarns, cotton-rich yarns, and yarns with cotton clustering [19].

26

Figure 2.6: Stress-stain curves of Pima cotton, regular and high tenacity polyester fibers used in

blended yarns [49].

2.6.2 Effect of blend ratio

Blends can be produced in many ratios, but certain blend levels are more dominant than others.

The required end use properties can be achieved by adjusting the ratios of each fiber in the blend.

Much research has been done by the fiber manufacturers to determine the necessary proportion of

each fiber to achieve desired properties. Only a specific blend ratio can produce the required

enhancement of properties. It is difficult to generalize the blend ratios, however, as they vary with

the fiber type, fabric construction and the desired end use [47]. Certain properties of the blend will

result in insignificant changes if the proportion of the fiber responsible for the effect (based on the

key fiber) is not significant [46, 49]. In general, it can be said that if the proportion of the key fiber

is less than 10%, the blend will not show any noticeable changes in its properties. The actual effect

of increasing the level above 10% depends on the properties of the key fiber and the component

fiber in the blend. For example, 15% nylon in nylon/wool blends improves the strength of the

blend but in the case of nylon/rayon blends, 60% nylon is required to show a significant change in

strength. In the case of wool/acrylic blends, 50% acrylic fiber is blended for use in a woven fabric

and 75% for knitted fabric production to improve the stability. If the blend proportion of the key

27

fiber is increased above 20%, the blend begins to show some noticeable differences in hand,

appearance and other properties. At around 50% level, the properties of the key fiber show a

significant effect on the properties of the resultant blend and this effect will continue with

increasing the proportion of the fiber [47]. The abrasion resistance of the PES/CO blend show

improvement if the polyester content is at least 20% in the blend. To obtain a significant

improvement the polyester content should be around 50%. Similarly wrinkle recovery properties

of the blend are increased gradually with increasing the polyester content of the blend with

prominent changes occurring at 50% polyester level. In order to obtain wrinkle free fabric without

resin treatment the PES/CO blend ratio should be 67/33. The effect of changing polyester levels

in PES/CO blends on abrasion resistance and crease recovery angle is shown in Figure 2.7 [49-

51].

Figure 2.7: Effect of polyester levels in PES/CO blends on abrasion resistance and wrinkle

recovery properties of fabric [51].

At around 90% the properties of the key fiber overtake the influence of the other component

in the blend [50]. Extensive research has been performed by fiber manufacturers to determine

what blend ratio is suitable for different applications. This is one of the primary reasons for

availability of certain blend ratios in practice. For example, PES/CO in 50/50 ratio is mostly

recommend for light to medium weight fabrics while 65/35 PES/CO is recommend for suit weight

materials [46]. The resultant properties of the blends do not necessarily correspond to the

28

percentage of each fiber in the blends as many properties of the fibers are not additive in nature

[46].

2.6.3 Blending and resultant properties

Several studies have been conducted to evaluate the benefit of fiber blends and their effect on

fabric appearance, tailorability, drapeability and handling, shape retention, shrinkage, and comfort

[19]. Dupont carried out extensive studies on the implications of combining hydrophobic synthetic

fibers with hydrophilic natural fibers. The blends of polyester, nylon and acrylic with wool and

viscose have been studied and impressive results were obtained. Their results can be summarized

as follows [15, 52]:

▪ Fabric strength and abrasion resistance are increased as the proportion of the synthetic

fiber component are increased.

▪ Dimensional stability with respect to humidity effects increases.

▪ Moisture content is reduced in wool synthetic blends as synthetic proportion is

increased.

▪ Crease recovery of polyester containing blended fabrics is increased as polyester

content is increased.

▪ Swelling induced shrinkage of polyester containing blends is reduced.

The polyester fibers when blended with other fibers enhance the crease recovery, press

retention, laundering stability, strength, abrasion resistance and wash and wear performance. The

main problems associated with polyester are static generation and pilling. The acrylic fibers in the

blend enhances the bulk, dimensional stability, press retention and melt resistance properties.

Acrylic has good crease recovery properties though this is lower than that of polyester and wool

fibers. The static generation and pilling properties of acrylic are lower compared to polyester

fibers. Nylon fibers have good dimensional stability, strength, and abrasion resistance. A smaller

proportion of the nylon in a blend increases the abrasion resistance but a significant proportion of

nylon is required to improve the strength. The improvement is strength is usually achieved if the

stress-strain characteristics of the component fibers in the blend are similar to nylon. If the stress-

strain properties are different the blend may have lower strength. The properties of different fibers

in the blends are schematically represented in Figure 2.8 [15, 52-54].

29

Figure 2.8: Properties of different fibers in the blend [54].

If properly blended, polyester/wool blends represent an excellent balance of properties that

cannot be achieved otherwise. The blend ratio that provides the best results is 65% polyester and

35% wool. This blend has outstanding aesthetic properties, wrinkle resistance, press retention,

dimensional stability, strength and abrasion resistance characteristics. The static generation is also

found to be lower. The 65/35 blend ratio also provides practically minimum wash and wear

properties for the worsted type suiting [54].

Viscose blended with polyester reduces the static generation and pilling. The blend ratio

that provides optimum properties is 70% polyester and 30 % viscose. The blend has good wash

and wear properties [53, 54].

Polyester/acrylic blends at 50/50 blend level provide superior properties. The polyester in

the blend enhances the strength and abrasion resistance of the blended fabric. The polyester and

acrylic fibers in the blend provide press retention and laundering stability. The acrylic fiber

improves the hand and add bulk to the blend. The pilling tendency is also reduced. However, this

blend is prone to static buildup due to hydrophobic nature of both fibers [53, 54].

The presence of viscose fiber in acrylic/viscose blends reduces static generation. The blend

containing as low as 15% viscose provides lower levels of static generation. The blends containing

approximately 25% rayon provides comparable results as compared to 100% viscose in terms of

static propensity. The blend level that provides optimum properties is 75% acrylic and 25% viscose

[53, 54].

In nylon/acrylic blends, nylon improves the abrasion resistance thus enhancing the

durability. The blend containing 25% nylon increases the abrasion resistance significantly higher

than that for the 100% worsted wool fabrics. To achieve significant increases in the strength of the

Aesthetics Texture

Liveliness

Bulk

Wear-care

properties

Crease recovery – 65% R.H.


Crease retention – 65% R.H.

Crease retention – Wet

Stability – Laundering

Durability

Strength – Tear

Abrasion resistance

Garment

performance

Static resistance

Melt resistance

Polyester Acrylic Nylon Viscose Wool

Key

Outstanding

Excellent

Moderate

Poor

30

blend, approximately 40% nylon is required. The blend ratio that provides the best combination of

properties is 75% acrylic and 25% nylon [53, 54].

For nylon and viscose blends, the optimum properties are obtained when blend contains

40% rayon and 60% viscose. The resultant blend has superior strength, abrasion resistance, static

resistance and melt resistance properties. However, wash and wear properties, wrinkle recovery

and press retention properties are inferior to polyester/rayon blends. For worsted type suiting

polyester/viscose blend with 70/30 blend ratio provides superior properties than nylon/viscose

blend [53, 54].

The combined property spectrum of different blends with optimum blend ratio is shown in

Figure 2.9 . The vertical rectangle represents the blend compositions with optimum wash and wear

properties [54]. A simple rule of mixtures, according to which the resultant properties of the blend

is the weighted average of the individual fiber properties according to their proportion in the blend

may not accurately predict the properties of the blend. This may be attributed to following reasons

[55]:

▪ The properties of the two fibers may be incompatible with each other under certain

conditions.

▪ There is an interaction effect between two fiber components in the blend where the

behavior of one fiber component is affected by the other component.

▪ The blend is not exactly uniform in terms of fiber distribution and contains regions

exhibiting properties different than the average properties of the blend.

31

Polyester-wool Polyester-viscose

Aesthetics

Texture

Liveliness

Bulk

Wear-care

properties






Durability

Strength – Tear

Abrasion resistance

Garment

performance

Static resistance

Melt resistance

% polyester % polyester

Polyester-acrylic Wool-acrylic

Aesthetics

Texture

Liveliness

Bulk

Wear-care

properties






Durability

Strength – Tear

Abrasion resistance

Garment

performance

Static resistance

Melt resistance

% polyester % acrylic

Nylon-acrylic Viscose-nylon

Aesthetics

Texture

Liveliness

Bulk

Wear-care

properties






Durability

Strength – Tear

Abrasion resistance

Garment

performance

Static resistance

Melt resistance

% acrylic % nylon

Figure 2.9: Property spectrum of different fiber blends with optimum blend proportions [54].

2.7 Polyester/cellulosic blends

Polyester/cellulosic (PES/CELL) blends occupy an important place in textile materials and are the

most commonly produced blend in the market. The primary reason for their success is their

excellent performance properties and low cost. Cotton and other cellulosic fibers have been used

in textiles for centuries and with the introduction of polyester they were blended in different

proportions. These blends became extremely popular since their introduction in the early 1960s

[56, 57]. The polyester fiber is more commonly blended with cotton and viscose compared to wool.

This may be attributed to the ease of processing, effective removal of disperse dye stains (clearing),

32

and a multitude of applications in the case of cotton. A wide range of dyed and finished effects

thus can be produced [9].

PES/CELL are available in different blend ratios such as 80/20, 67/33, 50/50, 55/45, and

20/80. Some blend ratios are more popular than others such as 50/50 and 67/33 (65/35). The

polyester provides easy care properties while the cotton contributes comfort properties in the blend

[58]. A small percentage of polyester fiber in the blend improves abrasion resistance but does not

provide a significant benefit in strength as shown in Figure 2.10 [8, 59]. With higher percentage

of polyester fibers in the blend the strength is improved and is better than the 100% cotton yarn.

Polyester contributes to the high crease recovery and durable press while cotton improves the

moisture absorbency properties of PES/CELL blends. Since cotton has a higher moisture regain

than polyester it absorbs moisture and provides comfort in garments made of PES/CELL blends

[59]. The moisture regain properties of PES/CO blend decreases with increase in the polyester

content of the blend as shown in Figure 2.11 [60].

Figure 2.10: Variation in yarn strength of PES/CO as a function of polyester content [8].

33

Figure 2.11: Variation in moisture regain properties of PES/CO fabrics with polyester content

[60].

While polyester was available in the market in the very early 1950s, commercial blends of

polyester/cotton did not become available until the late 1950s. Initially polyester was blended with

wool [61]. Over the years polyester fibers were blended with almost every fiber available in the

market due to economic reasons or to achieve other attractive properties and effects. However,

only a few blends have survived in the market [56, 57].

The most common PES/CELL blend is polyester/cotton, but polyester/viscose is also used

depending upon the application. They are blended in different ratios depending on the end-use

[57]. Other cellulosic fibers such as Modal, Lyocell and linen are also blended with polyester.

These blends offer a perfect break-even of contrasting physical properties of natural and synthetic

fibers. They are used in a multitude of applications in the form of yarn, wovens, and knits with

different colored and finished effects [9].

In yarns, they are used in sewing threads and slub yarns for apparel. The application of

woven PES/CELL blends includes shirting, sheeting, outerwear, and workwear. The most common

blends are the staple PES/CO blend with the 65/35 blend ratio and the PES/CO of 50/50 ratio.

These blends are made in different constructions and are mostly dyed by continuous methods. The

common knitted constructions of PES/CELL blends are fleece knits, interlocks, and jerseys which

are used in sportswear, T-shirts, and dress wear. The presence of polyester in the blend improves

34

the elastic recovery of knit goods [62]. These fabrics are generally dyed by a batch process on jet

dyeing machines due to their lower dimensional stability. Jets offer shorter dyeing cycles, lower

liquor ratio, high turbulence, and strong washing conditions. If the fabric is not prone to creasing

during dyeing in jets, presetting can often be avoided [9].

Polyester/cotton is the most important blend. The fabric ranges from lightweight poplin

shirting to heavy drill workwear. The most important shortcoming of the woven blended fabrics

in the late 1950s was their inability to retain creases in garment form. This was overcome with the

development of durable press finish with deferred curing option i.e., where the reaction of the

finish with the cotton component of the blend in the constructed garment takes place once the

creases have set in. This finish, when applied to cotton alone in the early 1960s, resulted in the

loss of strength and abrasion resistance. In the case of blends, polyester provides durability and

crease resistance and thus this problem was overcome. This finish type is further optimized by

improvements in finish formulations, fiber blending, and garment curing methods [9]. Woven

polyester/cotton blends are used in a broad spectrum of apparel due to their performance and

aesthetics reasons. They are produced in large quantities and often their price is determined by

commercial factors instead of their characteristics. [63]

Polyester/viscose has become a vital blend for apparel substituting polyester to a larger

extent in the late 1980s and early 1990s. The main reasons for their popularity include the superior

comfort and the physical and chemical finishes that can make these fabrics unrecognizable from

the starting material. This makes them suitable for a diverse range of applications [64]. Regular or

crimped viscose types can be used with polyester in blends. Crimped viscose, a specialized type

of viscose, can be made by chemical crimping during the regeneration process. This produces

filaments with asymmetric cross-sections that leads to helical curves in the filaments, thus forming

crimped fibers. The crimped fiber is blended with polyester in 65/35 ratio which has become a

popular blend for production of apparels [65]. Other important regenerated cellulosic fibers that

are often blended with polyester are Modal and Lyocell. Their applications include lightweight

tropical suiting, fashionwear, raincoats, leisure clothing, and sportswear. Due to their higher luster

and softness, they are more suitable than cotton for blends used in knitwear [9]. Modal in the blend

improves the dimensional stability and shape retention of the knitted goods [62]. Polyester rich

blends with modal are of interest for rainwear, and for lightweight constructions as summer

clothing [9].

35

Polyester/linen can be used as an alternative to polyester/cotton in luxury applications due

to the characteristic nature of the linen texture. It is used in high-quality fashion articles, tableware,

and bed linen [9].

Conventional polyester is generally used in blends. The fiber type used is generally fine

and round with no profiles. The length and diameter of polyester fibers should be adapted based

on cotton spinning system used. For the cotton system, the length and diameter should be similar

to cotton fibers. Initially, the polyester fibers known as the first-generation had a cut length

between 38-40 mm and fineness of 1.7 dtex. The fiber finishes and crimps levels were optimized

to match the cotton spinning systems. Polyester fibers of 0.7-1.3 dtex are currently used [66]. For

yarns up to 30 Ne, 1.7 dtex is suitable and for yarns of Ne 20, 2.6 dtex are generally used.

Commonly produced blended fabrics contain polyester/cotton warp and weft yarns at 65:35 or

50:50 blend ratio. Texturized or flat polyester may also be used in the weft to produce a blended

fabric with either blended or cotton warp yarns [57].

2.8 Other common blends

2.8.1 Polyester/wool blends

Wool fiber is often blended with polyester in various ratios mainly due to cost but also to provide

good properties. These blends are mainly used in apparel applications such as dresses, suits, skirts,

blouses, etc. Polyester/wool is the most popular blend due to its lightweight, good strength,

drapability, easy washability, and lower cost compared to 100% wool materials. The wool

contributes warmth, resiliency while polyester provides strength, abrasion resistance, and lower

cost. Typical blend ratios are 55/45, 65/35, and 50/50 [67, 68]. The polyester fibers are

technologically modified to make them suitable for blending with wool. They are completely

preshrunk before blending and have stronger crimp and lower strength. They have a lower degree

of stretching and higher affinity for disperse dyes than other polyester types [68].

2.8.2 Polyamide/cellulosic blends

Nylon is often blended with cellulosic fibers to improve durability. The blending of nylon with

cellulose improves the strength and abrasion resistance while maintaining comfort properties of

cellulosic fibers in the resultant blends [46]. These blends find their use in the sportswear market.

Cotton or viscose fibers can be blended with nylon [69]. The blended material comprise of either

36

intimately blended yarns or different warp and weft yarns to form union mixtures. The blend ratio

varies greatly and the nylon content in the blend may be in the range of 10-50%. These are typically

used for shirting and blouse material, ladies’ garments and work clothing. The union blends of

polyamide/cellulose consist of texturized polyamide yarn in warp and cotton or viscose yarn in

weft [70].

2.8.3 Elastane blends

Textile materials containing elastane yarns are widely used for production of clothing material for

lingerie, swimwear, sportswear, outerwear and hosiery products. Elastane yarns have very high

elastic stretch (550-600%) properties. They are blended with both natural (cotton, regenerated

cellulosic fibers) and synthetic fibers (polyester, polyamides) in a wide range of proportions (5-

35%). Elastane yarns are processed into woven, warp and weft knitted fabrics in different forms.

These include bare route, covered, twisted, core-spun and air-intermingled. The presence of

elastane in the material provides extensibility, elasticity, comfort and ability to retain shape after

extension. The selection of material containing elastane yarns depends on whether the material is

used in stretched form or in the loose state [71, 72].

2.8.4 Microfiber blends

These blended fabrics, made from standard diameter fibers and microfibers or filaments, were first

introduced in the late 1980s and early 1990s. The main reason for the development of microfiber

containing fabrics was to obtain finer and richer look without a characteristic synthetic shine and

good drapability as compared to blends made from standard diameter fibers. Microfibers are

classified as having a diameter of 1 denier or less, but the microfibers used in the production of

blended fabrics are slightly coarser. Polyester microfibers are blended with wool for tailored

clothing. The polyester microfiber component varies from 5-65% by weight. The standard

polyester used for worsted blends has a denier of 3.5. The microfibers currently employed have a

diameter in the range of 1.5-1.9 denier. The polyester fibers may be finer than the wool fiber

depending on the wool type [8, 49]. Polyester microfibers are also blended with viscose having

50/50 ratio to produce a casual shirt. Nylon microfibers are successfully blended with cotton, wool

and elastane for a variety of garment types [8]. Polyester/nylon microfiber blends are also produced

37

by conjugate spinning. They are used in imitation suede, silk-like fabrics, active sportswear, ultra-

high-density fabrics and high-tech cleaning cloths [73].

2.9 Application classes of fiber blends

Fiber blends found their use in a variety of applications. They are used in apparel workwear

clothing, military textiles and clothing, industrial fabrics, cords, ropes, geotextiles, medical

textiles, and home textiles [19].

2.9.1 Intimate yarn blends

These can be classified as parameter or structural blends. Parameter blends are mixtures of fibers

that vary in mechanical or chemical properties, in diameter, length or cross-section. Structural

blends contain fibers or yarns of different properties placed at particular locations in yarn or fabric

to target distinct product property [19].

2.9.2 Bulked yarns

These yarns have greater voluminosity because of mechanical or chemical treatments. In the case

of staple fibers, different shrinkage levels are blended to increase bulk since high shrink fibers in

subsequent wet and heat treatments contract. Fibers are converted to top and then blended in the

pin drafting process, thus any blend ratio can be achieved. A high shrink level of 40-60% is

generally used. This is very common in acrylic fibers. Bulky yarns containing 50% high shrink

polyester, 20% normal polyester and 20% natural fibers are also available for knitwear. Bulky

yarns containing 50% high shrink polyester and 50% normal polyester are also used [19].

2.9.3 Composite yarns

These yarns consist of both staple fibers and filaments of the same or different types. Core spun

yarns, with filament core and staple sheath and wrap spun yarn with staple core and filament wrap

are the examples of composite yarns [19].

2.9.4 Structurally blended yarns

These types of yarns are produced under conditions that facilitate preferential migration of fiber

or filaments in the yarn. One of the components is migrated to the core while the other fiber moves

38

to the surface of the yarn. The process control requires proper selection of fiber types based on

their stress-strain properties, differences in fiber diameter or staple length. The proper allocation

of fibers to the core and the surface is complete after a rope making process where fiber migration

is suppressed [19].

2.9.5 Structurally designed hawsers

The hawser structure contains filaments of different physical and chemical properties restricted to

specific locations. This is possible due to the special rope making equipment. A

polyester/polypropylene rope is used extensively in the utility and marine industry. For ocean

tugs, polyester hawsers made of different types of polyester yarns are used to compensate for the

cyclic loading incurred during use. They are made of high tenacity polyester in the core with a

different elongation to rupture as compared to the sheath braid. These two fiber arrangements

according to individual stress-strain characteristics compensate for the local strain [19].

2.9.6 Structurally blended fabrics

They are mostly used in technical fabrics such as paper maker felts. Such fabrics are made by

covering the base structure of filament yarns with the staple batting. This is done by needle

punching to reduce porosity and provide a smooth surface for contact with the processed paper.

Woven fabrics containing different warp and weft yarns are typical examples of the structural

blend. Warp yarns differ in fiber content and processing history from weft yarns. An example of

such structure is the geotextile lining materials used in oil containment booms. They are made of

two different yarns as this structure requires higher strength in one direction and higher elongation

in the other [19].

2.9.7 Filling material blends

Polyester fibers are widely used as filling materials in pillows, sleeping bags, quilted covers, and

furniture padding. The fiber can be a hollow type which provides more insulation per unit weight

or blended product. These blended products may contain fibers or filaments of the bicomponent

type that can be bonded together at the contact points to provide structural support or microfibers

to provide thermal conductivity like down and feathers [19].

39

2.9.8 Biomaterial blends

These are the type of structural blends found in prosthetic devices in which polyester is blended

with bioabsorbable polyglycolides. The polyester maintains the integrity of the implant [19].

2.9.9 Static controlling blends

The main problem associated with hydrophobic fibers is static charge generation. This may cause

many problems such as fabric clinging, and discharge of unpleasant sparks when walking on

carpets. To resolve this problem in carpets steel fiber was cut to staple fiber length and blended

with nylon or polyester pile yarn. Fibers containing conductive carbon are also used to overcome

this problem. One approach to incorporate carbon is the use of a bicomponent fiber. These

conductive yarns are woven into fabric in special locations to dissipate the charge. These materials

are also an example of structural blends where incorporating specific fiber provides specific

functions in the material [19].

2.9.10 Apparel blends

The garment itself may be a blend of different materials to provide different properties and

functions. Different fibers and fabric structures are used for outerwear clothes, linings, and

trimmings. The layered design of functional clothing, used by the army and in sports for protection

against cold, contains blended materials. Each layer has a different function to perform, the base

layer is responsible for moisture management, the insulating layer traps and stores warm air, and

the outer layers protect against wind, water, tear and abrasion and allowing water vapors to pass

through [19].

2.10 Manufacturing/production of blended textiles

Blending is a complex and expensive process but the resultant combination of properties of the

blend are permanent [47]. There are different ways the blending of fibers can occur depending

upon the fiber components. Obtaining a perfect blend ratio distribution is impossible to achieve as

local blend varies across and along the yarn. Blend constancy is important for uniformity of color

although heather effects can also be produced by blending different stock dyed fibers [19]. The

following methods can be used to produce blends [17, 18]:

▪ Staple fibers can be combined in flock or sliver form;

40

▪ Staple and/or filament yarns can be combined utilizing twisting, plying or entangling;

and

▪ Yarns made of individual fibers are combined during the fabric manufacturing.

The first method is usually performed during opening, carding, drawing; combing, sliver,

ring and rotor spinning. The second method involves plying yarns and core-spun yarns. In the third

method filament yarns and staple yarns may be employed to produce the blend [18].

Intimate blending involves the mixing of fibers in stock form. This blending method

provides a uniform distribution of fibers across the yarn cross-section and along its length. It can

occur in the early stages of processing such as during the opening stage. Several bales of fiber are

laid near the bale picker and each bale is fed alternatively. In another method, sandwich blending

is carried out, where the precise amount of each fiber is spread over the preceding layer to form

the sandwich. Vertical sections are then removed from the sandwich and fed to the picker. The

fibers can be mixed before being fed to the carding machine. This requires separate cleaning stages

as natural fibers may require more cleaning stages [19, 47]. This is carried out by blending hoppers.

Each fiber after the cleaning stage is fed into the hopper. The individual hoppers precisely feed

each fiber into the mixing belt. Precise blend ratios can be obtained by this method [47].

Blending can also be done later at the blending draw frame. This provides the advantage

of proper cleaning at the carding stage as settings can be optimized for a particular fiber type. It is

also more suitable for fibers that have different physical properties. The fibers can be processed

separately until the carding or combing stage depending upon the yarn type. In the case of

polyester/cotton blends, the carded or combed cotton slivers and carded polyester slivers are used.

In the case of wool and synthetic fiber blends spun on the worsted system, the blending can be

done in different ways. They can be blended before recombing or before drawing stages. The

synthetic fibers are used in the form of tops produced from tow to top conversion processes [19].

The blending process can also be done on the roving and spinning stage. The fiber strands

are combined to reduce linear density and increase the amount of twist to achieve the required yarn

linear density and twist level. This is mostly used for blending colors to produce novel color

effects [47].

41

In another method of blending at the spinning stage, core spun yarns are produced. A core

yarn consists of staple fiber covered with filament or staple fiber core, generally of a different

material [19].

2.10.1 Fiber distribution in blended yarns

In blended yarns, if the fibers are randomly distributed there is an equal chance of fiber to settle at

a given radius in the yarn’s cross-section. This does not imply that fibers will remain in a set radial

ring all the time. The control of the fiber placement in the blended yarn is an important control

parameter. In ring spun yarns, fibers are arranged in the form of helices. The helices are nearly

concentric yet migrate from the yarn surface to the core and back to the surface. It has been found

that in the yarns made of two fiber types fibers show preferential distribution. One fiber component

tends to prefer the core or central region while the other tends to reside in the outer radial rings

[19]. The short, coarser fibers in the blend tend to migrate to the outside edge of the yarn while the

shorter, fine fibers migrate to the center of the yarn [47]. This type of distribution has both

favorable and unfavorable implications. If the fiber present in the outer layers has a higher dye

affinity than the other component, then this distribution is favorable in piece dyeing. During the

spinning of polyester/cellulosic blends, the cellulose fibers tend to migrate to the surface of the

yarn creating a blended yarn with more cellulosic fibers on the surface than the whole yarn.

Viscose fibers show more migration than cotton and this effect is more prominent at higher

humidity levels in spinning. However, if the shade correction is required then the fiber present in

the outer layer will pick up more dye than the one present in the core [19]. This migration may

result in a more prominent effect if shading is done in a cellulosic component to match the target

[57]. For high fabric durability, it is desirable to have the fiber with higher abrasion resistance on

the surface of the yarn. The concentration of hydrophilic fibers on the surface improves the hand

and comfort of the fabric [19].

The earlier the fibers are blended during spinning, the better is the arrangement of the fiber

in the blends. The longitudinal and radial distribution of the fibers in the blended yarns is shown

in Figure 2.12. The fibers blended in flock form are more uniformly distributed than the ones

blended in sliver form [47, 74].

42

Figure 2.12: Fiber distribution in the blended yarns produced by sliver and flock blending

methods [74].

43

CHAPTER 3 COLORATION OF TEXTILE FIBER BLENDS

3.1 Introduction

The dyeing of textile materials is an old art. As blends of two or more fibers entered into the market

the dyer has to go through new learning experiences to deal with new problems and challenges

that are created. There has been an increasing pressure on the dyer to reduce dyeing cost by right

first time dyeing methods along with low water and energy consumption, reduced effluent costs

keeping higher fastness properties [75]. With the increasing popularity of the blends, special

attention is required in the dyeing due to differences in the dyeing characteristics of each fiber

component in the blend. Each fiber component in the blend can be dyed either separately or

simultaneously. The main criteria that decide the dyeing method is the cost and the required

fastness properties. Both dyes and pigments can be used in the dyeing of blends [9, 76].

3.2 Classification of blends according to their dyeing behavior

Blends are usually classified in terms of the fiber type in a blend. This classification is not useful

for dyeing purposes as it is based on a particular fiber type in the blend. The useful classification

may take into consideration the dyeing behavior of the fiber component in the blend. The blends

can be classified into four substantive groups based on the classes of dyes used to obtain dyeings

in full depth. This is known as the ABCD classification. This classification of fibers based on their

ability to obtain full depths in dyeing is useful as many challenges in the dyeing of blends become

more prominent under these conditions. Fibers can be dyed with acid dyes in full depth. These

include wool, silk, elastane, and acid-dyeable fiber variants. B for fiber dyed with basic dyes in

full depths such as acrylic and modacrylic fibers and basic dyeable polyester and nylon fibers. C

fibers can be dyed with cellulosic dyes in full depths. This comprises of cotton, viscose, modal,

lyocell and linen fibers. D for fibers dyed with disperse dyes in full depth such as cellulose acetate,

triacetate, and polyester fibers [7, 9, 77]. The classification of binary blends according to this

method is given in Table 3.1.

44

Table 3.1: Classification of binary blends according to their dyeing properties [9].

AA blends

Wool/silk

Nylon/wool

Nylon/silk

Wool/polyurethane

Nylon/polyurethane

AB blends

Wool/acrylic

Silk/acrylic

Nylon/acrylic

Elastane/acrylic

Wool/modacrylic

Nylon/modacrylic

AC blends

Wool/cotton

Nylon/cotton

Elastane/cotton

Wool/viscose

Silk/viscose

Nylon/linen

CB blends

Cotton/acrylic

Viscose/acrylic

Cotton/modacrylic

Viscose/modacrylic

CC blends

Cotton/viscose

Cotton/modal fiber

Cotton/linen

Linen/viscose

DA blends

Polyester/wool

Polyester/silk

Polyester/nylon

DB blends

Polyester/acrylic

Polyester/modacrylic

Normal/basic-dyeable polyester

DC blends

Polyester/cotton

Polyester/viscose

Polyester/modal

Polyester/linen

DD blends

Cellulose triacetate/polyester

Normal/deep-dye polyester

45

3.3 Color effects produced on blends

The various color effect can be produced during the dyeing of blends [7, 9]. These are as

follows:

▪ Solid or union

All components of the blend are dyed as close as possible to the same, hue, depth and

brightness. Binary blend, a blend of two or more fibers, are often dyed to achieve this

effect. The underlying reason is due to their design criteria. These blends are produced

to achieve economics, durability and desired physical properties and not for achieving

multicolored designs. Fiber components in the blend determine the extent to which

solid dyeing can be achieved. The solid effect is difficult to achieve in blends of

polyester with cellulose acetate in which both components can be dyed with disperse

dyes. For polyester/nylon or polyester/acrylic, this effect can be achieved by shading

with acid or basic dyes. In blends of nylon with wool, elastane or cellulosic fibers,

reserving or blocking agents can be used to achieve this effect.

▪ Reserve or resist

One of the fiber components in the blend remains undyed. Cross-staining is the major

problem in this type of dyeing effect. This problem is more common in fiber blends

with different dyeing properties such as disperse dyeable synthetic fiber blended with

natural fibers. It is also difficult to achieve reserve effect in acid dyeable fibers blended

with wool. The problem leads to poor fastness properties. Proper section of dye and

dye conditions or use of resist agent or reduction clearing treatment may help in

minimizing the degree of cross-staining.

▪ Shadow or cross stain or two-tone or tone-in-tone

All the fiber components in the blend have the same hue but different depths. This color

effect is in between solid and reserve effects. This effect is best achieved when paler

depth is between one-third and one-half of the deep-dyed fiber component. This effect

can easily be achieved in blends with all components of the fiber can be dyed with the

same dye class as compared to the blend requiring different dye classes.

▪ Contrast or cross dye

In this type of dyeing effect, fiber components in the blend are dyed with the same

depths but contrasting hues. This color effect cannot be achieved on blends where fiber

46

components have similar dyeing properties such as blends of cellulosic fibers with one

another, polyester fibers with one another and blends of nylon, wool or elastane blends

with themselves. Blended fabrics comprising of acid-dyeable with basic-dyeable

synthetic yarns showed the best contrast effect. For blends that are more prone to cross-

staining only partial contrast effect are possible.

The different color effects that can be achievable in binary blends are shown in Table 3.2.

Table 3.2: Color effects in binary blends [9].

Blend type

(example)

Color effect

Solid Reserve Shadow Contrast

AA (nylon/wool) Use of

auxiliaries

Neither

component

Easily

controlled

Not

possible

AB (nylon/acrylic) Easily

controlled Acrylic reserve

Seldom

required

Wide range

available

AC (nylon/cellulosic) Easily

controlled

Cellulosic

reserve

Seldom

required

Wide range

available

CB (cellulosic/acrylic) Easily

controlled

Either

component

Seldom

required

Wide range

available

CC (cotton/viscose) Dyeing

conditions

Neither

component

Viscose

deeper Not possible

DA (polyester/wool) Dyeing

conditions

Polyester

reserve

Seldom

required

Limited range

DB (polyester/acrylic) Easily

controlled

Polyester

reserve Acrylic deeper

Limited

range

DC

(polyester/cellulosic)

Easily

controlled

Either

component

Seldom

required

Wide range

available

DD

(triacetate/polyester)

Dyeing

conditions

Polyester

reserve

Easily

controlled

Not

possible

47

Due to economic reasons, it is desirable to have a dyeing time of blend less than the sum

of dyeing time required to dye individual components in the blends keeping high-quality levels

and operational flexibility. The process of dye blend can be classified into conservative or rapid,

depending on how the fiber blend materials are dyed. During the conservative process, the

individual fiber components in the blend are dyed separately. On the other hand, the rapid process

involves the elimination of some process steps involved in a conservative process thereby

achieving short process timings [7].

Dyeing methods can also be classified based on the number of dye classes and dyebaths

used to dye fiber blends. A fiber blend can be dyed with a single dye class in which one dye is

distributed between two fiber components in the blend. This is only possible if both fibers have

the same dyeing properties. Solid and shadow effects can be obtained with this method, but reserve

and contrast effects are not possible. Fiber blend materials can also be dyed with two separate dye

classes using appropriate dyeing conditions according to fiber and dye class. Because of the

separate dyeing process, the cross-staining can be eliminated. This method can achieve solid,

reserve shadow and contrast color effects. Due to economic reasons and flexibility, different

dyeing methods have been developed. These are one-bath and two-stage methods. In one bath

method, separate dye classes are used for each component in which both components are dyed at

the same time. The two-stage method involves the dyeing of individual fiber components using

separate dye classes in succession. Table 3.3 shows the classification of dyeing methods [9].

Table 3.3: Methods for dyeing of fiber blends.

Methods Dyebaths Dye classes Stages

Single-class One One One

One-bath One Two simultaneously One

Two-stage One Two in sequence Two

Two-bath Two Two Two

48

3.4 Factors affecting the dyeing of fiber blends

Important points that need to be considered in the dyeing of blends are [18, 78]:

▪ Effect of pretreatment on the individual fibers in the blend.

This can include desizing, scouring, bleaching, etc. The effect of any of the chemicals

used on all of the fibers in the blend must be established before processing

▪ Fastness properties required

Wet fastness is the most common challenge dyeing of blends

▪ Dyestuff cross-staining properties

Many dyes that are used to dye one fiber may stain the other fiber(s) in the blend. In

some cases, a selection of non-staining dyes will be available.

▪ Dyes and auxiliaries' compatibility and their chemical/physical effect

There might be chemical and/or physical interaction between dyes and chemicals used

for dyeing of each fiber. The compatibility problems such as perception or blocking

should be considered.

▪ Dyeing method

Dye procedure is determined by dye selection. The limitation of the dyeing procedure

is determined by the properties of the specific fibers in the blend.

▪ Effect of finishing processes on the dyed material.

This includes the effect of chemical and or mechanical finishing on the dyed materials.

3.5 Challenges in the coloration of fiber blends

The main challenges associated with the coloration of fiber blends are [7, 9, 77, 79]:

▪ Cross-staining of the fiber by the dye intended for the other fiber type;

▪ Fastness problems;

▪ Interaction between dye classes or between a dye and dyebath auxiliaries;

▪ Dye stability at high temperature and in different pH conditions;

▪ Effect of additional processing required to fix each dye class on a respective fiber

component on the other fiber component in the blend;

▪ Effect of second fiber component in the blend on increasing the liquor ratio

significantly;

49

▪ Problems in obtaining solid shade in the same fiber type due to differences in saturation

limits of the component fibers;

▪ Obtaining solid shade in the blend by matching shade of an individual fiber type; and

▪ Fiber damage and/or yellowing.

3.5.1 Cross-staining of the fiber by the dye intended for the other fiber type

Cross-staining is a serious problem in the dyeing of fiber blends especially containing fiber

components having different dyeing properties. This is generally observed in the blends of natural

fibers with synthetic fibers. The synthetic fibers which are only dyed with disperse dyes are more

prone to this problem [9]. The staining tendency of different fibers with disperse dyes are shown

in Figure 3.1. Elastane and wool fibers are much strongly stained by disperse dyes due to the

hydrophobic nature of these fibers as compared to cotton and viscose fibers [80]. The wool cuticle

is hydrophobic that allows disperse dyes to heavily stain the wool component. The mechanism of

wool staining consists of hydrogen bonding, dipolar and van der Waals interaction between

disperse dye molecules and sorption of the aggregated particles of the disperse dyes on the cuticle

of the wool fiber [9].

Cross-staining also important if a reserve effect is required. It is very difficult to achieve

reserve effect on acid dyeable fiber blends such blends of wool, nylon or elastane blends. The

nylon fibers give poor reserve effect with polyester, cellulosic and acetate fibers. Acrylic fibers

are difficult to reserve with disperse dyeable polyester fibers. In the case of blends containing deep

dyeable and normal dyeable variants, it is impossible to reserve a deep dyeable component. The

reserve effect is usually easy to achieve in blends of acrylic or polyester fibers with cellulosic

fibers and in synthetic fiber blends containing acid dyeable and basic dyeable fiber types [9].

The following approaches can be used to minimize cross-staining [9]:

▪ Selection of dyes with high affinity for the fiber to be dyed with that dye class and

lower affinity for other fiber components in the blend.

▪ Using dyebath conditions that allow maximum exhaustion of the dyes to the intended

fiber to be dyed with that dye class.

▪ To achieve reserve effect on one fiber, special colorless dyebath additives may be

added that preferentially absorbed to the fiber to be reserved and resist the sorption of

dyes.

50

▪ Depending upon the dye class a clearing treatment may be performed to remove the

dye stain that may involve desorption of dye by washing with detergent or dye

destruction either by reduction or oxidation treatments.

Figure 3.1: Staining of different fibers by disperse dyes during the dyeing process [80].

3.5.2 Fastness problems

The fastness properties of the fiber blends are generally inferior as compared to single fiber

materials. They may be attributed to the cross-staining of the fiber by dye class used for the dyeing

of the other fiber component. The stain has poor fastness properties [9]. Since some fibers such as

wool, acrylic, and elastance can be damaged at higher dyeing temperature used for disperse dyeing

of polyester component, the dyeing temperature is reduced to minimize this problem. This

aggravated the staining problem in two ways. Firstly, the staining of disperse dyes is excessive at

lower dyeing temperature. Secondly, the dye selection may be limited to lower energy disperse

dyes that may give lower fastness properties [9, 77, 81, 82].

Fiber blended with polyester

Low

High

Cotton

Viscose

Acrylic

Polyamide

Wool

Elastane

Deg

ree

of

dis

per

se

dye

stai

n

51

The disperse dyes have a tendency to desorb from the polyester and stain the cellulose

component of the blends during subsequent dyeing of the cellulosic fiber. This results in additional

staining of cellulose. However, this problem is limited to low energy disperse dyes in comparison

to several medium and high energy they didn’t exhibit this behavior [83]. The polyester/cellulosic

blends are often resin finish to improve the crease recovery and pilling properties. At high resin

finishing temperature (> 150 oC) disperse dye may migrate from the interior of the fiber to the

fiber surface at high temperature. This phenomenon is known as thermomigration. This

deteriorates the fastness properties of the blends and causes more staining of adjacent nylon during

the fastness tests [9, 79, 83].

3.5.3 Interaction between dye classes and dyebath auxiliaries

Polyester/cellulosic blends can be dyed either by one or two bath process using disperse and

reactive dyes. During one bath process, both dyes are fixed simultaneously. Dye selection is

important especially for one bath process due to the risk of interaction between the two dye classes.

These interactions lead to a loss in color yield or dye precipitation. The two dye classes may react

with each other to form a covalent bond. Other types of interactions may be between reactive dyes

and dispersing agent or instability of the dispersion system under the alkaline conditions [9].

It has been found that during the one bath thermosol process, disperse containing phenol

and amino groups may react with reactive dyes containing highly reactive monochlorotriazine

groups to form a covalent bond. The bond form found to be unstable and easily decomposed by

alkaline hydrolysis [84]. This problem can be avoided by selecting reactive dyes of low reactivity

or disperse dyes that do not have amino or phenolic acid groups. Using reactive dyes of low

reactivity allows a wider range of disperse dyes can be selected. Another approach is to control

the pH of the pad liquor to minimize problems of a chemical reaction by using the two-stage, pad-

dry-thermosol-chemical-pad steam process. The two-stage process allows a broader range of dye

selection. During this process, both disperse ad reactive dyes are padded first under neutral pH

conditions. The pad bath usually contains an anti-migrating agent along with a mild oxidizing

agent (sodium meta-nitrobenzenesulphonate) to avoid reductive decomposition of certain azo

reactive dyes. The disperse dyes are fixed by the thermosol process. The fabric is then padded with

alkali and salt followed by steaming to fix the reactive dyes. The rinsing and washing complete

the process [9].

52

The disperse dye dispersions are not stable under high quantities of salt used in dyeing with

reactive and disperse dyes to promote dye exhaustion. This may cause dye aggregation and

prevents the leveling and migration of disperse dyes. Since powder and grain type disperse

contains more dispersing agent than liquid dyes, they exhibit more stability as compared to liquid

dyes [79].

In polyester/acrylic blends the presence of anionic dispersing agents may interact with

basic dyes or cationic retarding agents used for the dyeing of acrylic fibers. Different approaches

may be used to minimize this problem. The use of nonionic emulsifier and anionic retarder may

help in reducing the interaction. The anionic dispersing agent must be avoided if possible.

However, the alternate products maybe not as effective in their performance as compared to actual

products. The anionic dispersing agents already present in the disperse dye formulation cannot be

excluded [9, 77].

The anionic dispersing agent present in the vat dyes is incompatible with the basic dyes

and cationic retarding agents during one bath dyeing of cellulose/acrylic blends. The basic dyes

are also chemically unstable under strongly alkaline conditions required for the vat dyes. This

limits the application of the vat/basic dye system to be applied by two bath process [9].

3.5.4 Dye stability at high temperature and pH conditions

The dyes selected in the dyeing of blends must be stable under the dye bath conditions (pH and

temperature) employed for other fiber components of the blend. During one-bath, dyeing of

polyester/cellulosic blends using disperse and vat dyes, the stability of vat dye dispersion is

important under disperse dye conditions. The vat dyes in the oxidized form are chemically stable

under high temperature conditions employed in the dyeing of a polyester component with disperse

dyes, However, dyeing carried out for a longer duration at high temperature may cause instability

of the vat dye dispersion. It is recommended during batchwise dyeing to add vat dyes at a lower

temperature after high temperature dyeing of polyester component The direct dyes applied along

with disperse dyes in one bath process should be soluble and stable under slightly acidic and high

temperature conditions employed for disperse dyeing. Not all direct dyes are stable under these

conditions. This is also applicable to th one bath and reverse two bath dyeing with reactive dyes.

Some reactive dyes may not be stable at high temperature and slightly acidic pH conditions

employed for disperse dyeing. The high temperature and slightly acidic conditions cause acidic

53

hydrolysis of reactive dyes leading to a depth of shade. This effect is more prominent in highly

reactive dyes compared to dyes of medium reactivity. Some disperse dyes are very sensitive to

alkaline pH conditions employed during reactive dyeing. The color yield of disperse dyes tend to

be lower under alkaline conditions [56, 79].

3.5.5 Effect of additional processing required to fix the dye class

In the dyeing of polyester/cellulosic blends, the disperse dyes once diffused into the interior of

polyester fibers are usually resistant to subsequent chemical and physical treatments. This is due

to the hydrophobic nature of the polyester fibers which prevents the penetration of many

chemicals. The disperse dyes, however, are susceptible to physical and chemical interactions when

they are present in the dyebath. The direct and reactive dyes applied to cellulosic fibers are

susceptible to damage whether they are present in the dyebath or on the fiber. The reduction

clearing process performed to remove the disperse dye stain and surface disperse dye will also

destroy the reactive and direct dyes. The alkaline conditions required to fix the reactive only

destroy the surface disperse dyes. The disperse dyes present in the fiber interior are not affected

[79].

3.5.6 Effective liquor ratio and blend ratio

Liquor ratio directly influences the reproducibility and economics of the batch dyeing process. The

effective liquor available for the dyeing each fiber component in the blend depends on the blend

ratio. The effect of the blend ratio on the effective liquor ratio is shown in Table 3.4 [79].

At a liquor ratio of 10:1, the effective liquor ratio available for a blend ratio of 50/50 is

20:1 for each fiber component. When the blend ratio is increased to 80/20 the effective liquor is

changed to 12:1 for fiber 1 and 50:1 for fiber 2. This causes a significant change in the effective

liquor ratio for fiber 2. It is well known that at higher liquor ratio the exhaustion and fixation of

the dyes are lower compared to lower liquor ratio. This requires more quantity of dye to match a

given shade at a high liquor ratio compared to a lower liquor ratio. Therefore, to achieve good

color yield and fixation values, the dyes having high substantivity should be selected. This ensures

an efficient, inexpensive and reproducible dyeing process [79].

54

Table 3.4: Effect of blend ratio on effective liquor ratios in the dyeing of blends.

Effective liquor ratio

Blend ratio 50/50 65/35 80/20

Liquor ratio Fiber 1 Fiber 2 Fiber 1 Fiber 2 Fiber 1 Fiber 2

5:1 10:1 10:1 8:1 14:1 6:1 25:1

10:1 20:1 20:1 15:1 29:1 12:1 50:1

15:1 30:1 30:1 23:1 43:1 20:1 75:1

20:1 40:1 40:1 31:1 57:1 25:1 100:1

3.5.7 Distribution of single dye and fiber saturation differences

During the dyeing of blends, a single dye may be distributed between the fiber component. This

distribution is determined by differences in the dyeing properties of the fiber components in the

blends, dyeing conditions, depth of shade, blend ratio and the dye structure. The dye distribution

that may be unequal in an early stage of dyeing is leveled out by the transfer of the dye from the

fiber component that initially absorbs a high quantity of the dye to the fiber that has a high affinity

for the dye. In the long run, more dye is absorbed by the fiber component that dye has more affinity

as compared to the fiber component that has lower affinity although it absorbs more dye at the

early stage of the dyeing process [9].

Nylon/wool blends are dyed by a single class of anionic dyes. These include acid and metal-

complex dyes. To achieve solidity of shades in these blends the dye selection is important. The

dye selected should have similar dye rates and exhaustion properties. Both fibers are dyed under

acidic conditions where both fibers acquire a positive charge. The dye rates of nylon and wool are

different from each other. The nylon shows a higher rate of dyeing in lower shade depths at 60-80

oC. The nylon fiber is more hydrophobic as compared to wool, so it attracts dyes containing a

lower number of sulfonated groups. The wool fibers exhibit more attraction for dyes which are

hydrophilic in nature. The saturation concentration in the wool is much higher than nylon. This

effect is more prominent in dark shades where wool absorbs more dye as compared to nylon.

Depending upon the dyeing conditions and at some intermediate depth, both fibers are dyed to the

same depth although nylon has higher dye uptake. This critical depth depends on the dye type.

55

Above the critical depth, the dye distribution greatly favors the wool as compared to nylon in

nylon/wool blends [9].

The cellulosic blends such as cotton/viscose or cotton/modal require proper control of

dyeing temperature and salt concentration. The viscose and modal fibers are dye darker with direct

dyes as compared to cotton. In general, it is difficult to obtain solidity of shade with direct or

reactive dyes as compared to vat or sulfur dyes. The lower temperature may also be used to ensure

solidity [9].

3.5.8 Obtaining solid shade in the blend by matching shade of an individual fiber type

One of the main challenges that a dyer has to deal with in case of blends is the solidity of shade.

The shade required to be balanced in depth and tone in each fiber component. The required degree

of solidity varies with a product, for example, dyed woven blend fabrics require excellent solidity

while carpet yarns lower solidity levels are acceptable to provide characteristic broken appearance

or difficulty in achieving solid shade due to surface features [9].

The distribution of the fiber in the blend influence the overall solidity of shade. The

blending process must be controlled. If the fiber clumps are not properly opened up and mixed,

they may give an unlevel or hazy appearance [9]. The blend ratios should be controlled to avoid

difficulties in producing uniform appearance [77]. Since the scattering properties of different fiber

types in the blends are different due to differences in fiber denier, shape, and luster, the depth of

shade in one fiber may be kept higher than the other to achieve shade solidity. In

polyester/cellulosic blends, the cellulosic component of the blend is usually dyed darker than

polyester component to achieve a uniform appearance.

Another factor that may affect the solidity of shade is staining. In polyester/wool blends,

wool is heavily stained by disperse dyes. This becomes more critical due to lower temperature

employed in the dyeing of these blends as wool may be damaged at higher dyeing temperature.

The carriers employed to obtain good penetration on the polyester component at lower

temperatures minimize this problem. The addition of a wool protecting agent also minimizes the

wool staining during prolonged dyeing [9, 85]. Some vat dyes employed in the dyeing of

polyester/cellulosic blends stained the polyester component under thermofixation conditions

employed for disperse dyes during the one-bath process [7, 9, 79].

56

3.5.9 Fiber damage and/or yellowing

The cotton component of the polyester/cellulose blend may degrade at the higher temperature

required for the fixation of disperse dyes by a thermosol process. The actual effect depends on

different factors such as treatment temperature and time, pH and additives present in the dye liquor.

The degradation increases rapidly above 150 oC. The degradation and yellowing effect are more

severe under alkaline conditions at a higher temperature. The presence of a dispersing agent

usually causes browning of cellulose at higher thermofixation temperature [56, 79].

The wool, acrylic and elastane fibers blended with polyester are damaged at higher dyeing

temperature employed for the dyeing of a polyester component with disperse dyes. To avoid

yellowing or strength the dyeing is, therefore, is carried out at 100-105 oC to minimize this damage.

During dyeing of polyester/wool blends wool protective agents may be used to minimize the

damage. This also allows dyeing to be carried out higher temperature (120 oC) [9, 77, 81, 82].

3.6 Coloration of polyester/cellulosic blends

Polyester/cellulosic blends are the most important and commonly dyed fiber blends. They are

available in different blend ratios, but 50/50 and 65/35 combinations are most common. The

polyester and cellulosic fibers exhibit different dyeability characteristics and therefore dyed with

different dye class and require different dyeing conditions [58]. The polyester is dyed only by

disperse dyes while cellulose portion can be colored by various dye classes such as direct, reactive,

vat and sulfur dyes. The selection of dyes and dyeing methods depends upon hue, depth of shade

and required fastness properties [9, 18, 57, 86, 87]. Table 3.5 shows the features and challenges

associated with colorants used for these blends [56, 83, 87]. The commonly used dye systems are

disperse/direct, disperse/reactive and disperse/vat. The disperse/reactive dye system is the most

popular due to brilliant hues, the possibility of achieving dark shades along with excellent fastness

properties [57].

57

Table 3.5: Characteristics of colorants for polyester/cellulosic blends.

Dye

systems Colorants Advantages Challenges

Two-

dye

process

Disperse/

direct

▪ Economy

▪ Shortest process time.

▪ Excellent reproducibility

through proper dye

selection

▪ Lower water, chemicals

and energy

consumption. Shades are

easy to correct

▪ High exhaustion levels.

▪ Lower quantities of salt

required

▪ Moderate wet fastness

in pale/medium shades

▪ Staining on cellulose

portion by disperse

dyes

▪ Limited selection of

direct dyes for one bath

process

Color

matching

is

dependent

on a blend

ratio

Disperse/

vat

▪ Excellent light and wet

fastness

▪ Shorter one-bath dyeing

process

▪ Heavy depth of shade

▪ Dull shade

▪ Proper control is

required in jet dyeing

Disperse/

reactive

▪ Brilliant shades

▪ Good reproducibility,

Colorfastness

▪ Lower fixation

temperature of reactive

dyes

▪ Staining on cellulose

portion by disperse

dyes

▪ Large quantity of salt

required

▪ High wastewater load

▪ Decomposition of

disperse dyes due to

alkaline conditions in

one bath process which

reduce color yield.

58

Table 3.5 (continued).

Dye

systems Colorants Advantages Challenges

Dye

systems

▪ Decomposition of

disperse dyes due to

alkaline conditions in

one bath process which

reduces color yield.

▪ Re-staining by wash

water

▪ Lower color yield for

one bath process (about

60%).

Pigment Pigment-

binder

system

▪ Economy

▪ Workability

▪ Poor rubbing fastness in heavy

shades

▪ Poor hand

These blends are dyed by both batch and continuous processes using either a one-bath or a

two-bath method depending on the lot size, availability of equipment, blend type and suitability

and process economics [18, 56, 57, 85]. Table 3.6 shows the comparison of one and two bath

dyeing methods used for dyeing [87]. Polyester/cellulosic yarns and knit fabrics are generally dyed

by a batch process. Package dyeing is more commonly used for yarns while the jet is common for

knitted and woven fabrics. Some fabrics are also dyed on beam dyeing. The majority of the woven

fabric is dyed by a continuous method using pad-thermosol, pad-steam and pad-batch ranges [9,

57].

The selection of suitable dyeing process and a particular dye class depends on [68]:

▪ Economy;

▪ Availability of equipment;

▪ Batch size;

▪ Shade and brilliancy required;

▪ Depth of shade;

59

▪ Required color effect;

▪ Type of polyester and cellulosic fiber; and

▪ Blend ratio.

Table 3.6: Comparison of one bath and two bath methods used for dyeing of PES/CELL blends.

One bath Two bath

▪ Shorter process

▪ Lower consumption of energy and water

▪ Selection of disperse dye is important as

reduction clearing is not possible

▪ Longer process

▪ Flexibility in machinery use

▪ Reduction clearing can be performed

depending upon the fastness requirement

The standard two-bath dyeing process of these blends has a long cycle time and higher

cost. Furthermore, the standard process employs a reduction clearing that uses hydrosulfite. This

creates environmental challenges. With increasing brand focus towards environment and

sustainability, the production process aims to minimize water and energy consumption along with

minimum environmental impact [88]. This is usually achieved by the one-bath method.

Although the dyeing of polyester-cellulosic blends is more challenging, requires a longer

process, more utilities, and energy they are sold at lower price owing to lower cost of polyester.

This creates a challenge for the dyer to have a balance between profit and performance. The

selection of dyes for both fibers is a prerequisite to achieving good fastness properties and shorter

dyeing process [88]. The selection of dye combinations largely determined by the end-use

requirements.

3.7 Pigment coloration

Pigment coloration involves the application of dyeing liquor by usual dyeing methods such that

the dyeing liquor consists of pigments as a coloring component and binder. Unlike dyes which are

fiber substantive, pigments are anchored to the substrate with the help of binders, which attach

itself to the fiber and traps the pigment particles. Other than pigments and binder, auxiliaries

depending on the requirements are also used. These include processing aids and fastness and hand

60

feel improver e.g. wetting agents, defoamer, anti-migrating agents, softeners, etc. [89, 90].

Pigments can be applied by both batch and continuous methods. The batch method is usually used

for garments to create wash-down effects. Fabrics made of single fiber or blends are largely colored

by the continuous method. Continuous pigment coloration is a well-established field and accounts

for 10% of the total pigment used in textile applications. The main application areas include home

textiles, bed linen, upholstery fabrics, and leisurewear. Polyester/cotton blend is the most

commonly dyed fiber blends by this method. In home textiles, they provide fastness properties

equivalent to that of vat dyes with wash fastness and adequate handle to meet the quality

requirements. Therefore, they have almost entirely replaced vat dyes resulting in time and cost-

saving [90, 91]. Generally, coloration with pigments is limited to the pale shades. The advantages

and limitations of pigment coloration are given in Table 3.7 [89, 91-95].

Table 3.7: Advantages and limitations of pigment coloration.

Advantages Limitations

Coloristic

▪ Reproducible and safe process.

▪ Faults can be easily detected.

▪ Good to excellent fastness and fabric

quality meeting market demands, excellent

lightfastness.

▪ Application is not fiber specific

Ecology

▪ Low amount of wastewater, as washing is

not required

Economy

▪ Simple application process and fixation

conditions.

▪ Can be combined with finishing, saving

time, cost, and energy

Limited shade depth

▪ Limited buildup of shade (e.g. due to high

penetration into the fabric)

▪ Large amount of binder is required for

deeper shades results in poor fabric hand

feel

▪ Special binders are required for achieving a

high depth of shade

Wet fastness profile

▪ Limited washing fastness in heavy shades.

▪ Limited results in brush wash testing, due

to the cracking of binder film

▪ Poor rubbing fastness in heavy shades

Running properties

▪ Can buildup on rollers

61

Table 3.7 (continued).

Advantages Limitations

▪ Low capital investment, no requirement of

complicated machinery

▪ Economical process and short delivery

times

▪ Low requirement of time, energy and

personnel resources

Economy

▪ For heavy shades, special binder & a large

amount of pigment are needed, increasing

the cost of the process.

Hand

▪ Dyed materials can have poor hand if

binder and softener are not properly

selected. This effect is more prominent in

thin or very heavy substrates

The fabric, appropriately prepared, is padded with a pigment coloration liquor and then

dried. To reduce the tendency of migration, the fabric is generally passed through pre-dryer before

the drying and curing process. The dyed fabric is usually fixed in a separate operation at a high

temperature. The fixation time and temperature depend on the type of binder used and the nature

of the substrate. After fixation, the dyed fabric does not need any wet after treatment e.g. washing

[89]. The standard pigment coloration process is shown in Figure 3.2 [96].

Figure 3.2: Continuous pigment coloration process.

Pad

Dry

Cure

▪ at room temperature (25-30ºC)

▪ Pick-up 60-70%

▪ at 100-120ºC

▪ In a hot-flue or in a pin stenter frame

(preferably infra red-dryer)

▪ at 140-150ºC – 5 min or 170ºC – 2 min or

185-200ºC – 1 min

62

The pigment coloration liquor normally consists of [92, 94, 97]:

▪ Pigment preparations;

▪ Binder; and

▪ Auxiliaries.

- Additives; and

- Surfactants.

Pigment preparations are the coloring agents and can be either inorganic or organic. The

pigments are restrained to the substrate with the help of binders which are film-forming substances

and tie themselves with the fiber and trap the pigments inside the film formed during the fixation

process. To improve the application properties and hand feel of a fabric, auxiliaries are also a part

of pigment coloration formulation. These include additives and surfactants. Additives are required

to improve the handle and compensate for the loss of softness due to the binder. These include

softening and smoothing agents. Surfactants are used as emulsifiers, wetting agents, stabilizers and

foam suppressants. These are added to ensure the rapid wetting of fabric during padding, improve

the stability of liquor and to avoid roller deposits. Generally, a specially formulated surfactant

auxiliary capable of performing all these functions is used. For foaming problems, anti-foaming

agents are also used [89, 97].

Product selection for pigment coloration must take into consideration the following aspects

[92]:

▪ Compatibility of products;

▪ Stability of liquor under high shear forces of padding; and

▪ Presence of dispersing agents in pigment formulation that promote wetting.

3.7.1 Pigment preparations

Pigments are class of colorants, can be chromatic or achromatic and are insoluble in the medium

in which are applied. This does not imply the pigments are insoluble in all solvent types, it refers

to the fact that they are insoluble in water or lipophilic media. There are certain solvents in which

some pigments are partially or completely soluble e.g. a chlorinated hydrocarbon such as

perchloroethylene which is used in dry-cleaning. They belong to almost all classes of dyes, based

on their chemical constitution. Pigments, unlike dyes, do not contain water-soluble or fiber reactive

63

chemical groups. Therefore, they have no affinity and can be applied irrespective of fiber type.

They need a binder to attach them to the fiber surface with good fastness properties [89, 91-94].

To acheive right first time coloration, and to meet fastness and ecological requirements,

there are certain physical and chemical properties of the pigments that have to meet during

synthesis and formulation, i.e. influenced by the manufacturer, these are [91]:

▪ Particle size and particle size distribution;

▪ Crystal shape;

▪ Conductivity;

▪ pH;

▪ Viscosity;

▪ Storage stability of pigments;

▪ Re-dispersibility;

▪ Shade (purity) and color strength;

▪ Suitability and stability of pigments under different application conditions;

▪ Formaldehyde free; and

▪ Ecological and toxicological compliance.

These physical and chemical properties, if adjusted optimally, resulted in, high brilliance,

high color yield, flexibility in usage, high reproducibility, ecological safely and user-friendly

handling in color kitchens and production. Quality assurance of pigment preparations start from

the synthesis of the pigments and include the dispersion and milling steps to maintain batch to

batch reproducibility [91]. The auxiliaries used in milling and dispersing pigments to produce

pigment preparations includes [91]:

▪ Dispersing agent;

▪ Wetting agent;

▪ Preservatives;

▪ Anti-frost agents;

▪ Water retention agents; and

▪ pH regulators.

64

3.7.1.1 Application properties

Modern pigment preparations used in pigment coloration have to meet the following application

properties [98]:

▪ Coloration properties

Pigments are available as fine dispersions and they give more color value as they

remain on the fabric surface. In order to show uniform buildup across the whole

spectrum in light to dark shades and good color value by pigments, the particle size and

its distribution are the key factors. An ideal particle size would in between 0.1 and 0.5

µm and a maximum size of < 1 µm. The particular size of around 0.5 µm is considered

good [94, 98, 99]. Pigment preparations should remain stable for a long time and

without agglomerates formation. Additionally, if the product is stabilized sufficiently,

this will result in excellent brilliancy and optimum build-up. This, in turn, provides that

a lower amount of pigments is required to achieve the required shade. Therefore, the

binder amount will be less and ultimately cost is reduced and a soft handle is achieved.

Fewer coarse particles in the pigment system will result in good fastness properties due

to the fact that larger particles are difficult to fix to the fabric and reduce fastness [94,

98].

▪ Handling properties

For ease of use in the color kitchen, pigment preparations should have low viscosity,

which should be between 50 and max. 500 mPas. For some inorganic pigments, to

ensure product stability, high viscosity is up to 1000 mPas is required. Too low

viscosity may result in increased sedimentation and/or agglomeration, which can result

in shade fluctuations if the pigment system inside the drum is not properly mixed. Too

high viscosity may cause dosing or filtration problems. During normal use, slight

skinning of pigments preparations might form. This should be readily and completely

redispersable to prevent the risk of specking and pin-holing. Another important factor

related to the handling of pigment preparations is the presence of toxic substances or

irritants [94, 98].

▪ Reproducibility/application reliability

For pigment coloration, these properties are dependent on storage stability, tendency to

sediment out and viscosity of pigment system. This affects the dosage and re-

65

dispersibility and may cause pin-holing and specking. For an optimum application of

pigments, there should be good compatibility between pigment formulations and

additives and commercial products used to prepare dye liquors [98].

3.7.1.2 Performance and processing properties

Performance properties

Colorfastness of pigment dyed fabric may be affected by the following factors: the substrate, pre-

treatment, application process, pigments, binder, other auxiliaries (softener, etc.), drying and

fixation conditions. Pigment-specific properties are highly variable and vary between different

chemical classes of pigments or even the same class if the constituents of pigment preparations are

different. Fastness properties also depend on substrate properties (fiber type, yarn type,

construction, etc.), pretreatment, padding, drying and curing conditions.

Pigments are selected according to fastness requirements such as fastness to light,

weathering, the light at elevated temperature, solvents, dry cleaning, PVA, dry heat fixation [93,

98].

Processing properties

These include stability to heat and specific conditions or chemicals used during the process. If the

fixation of pigments is carried out above the recommended temperature of 150 oC for technical or

economic reasons or because of current production practice, heat stability is an important property

that needs to be considered. For fixation of pigment dyed substrate on stenter generally, fixation

temperatures are raised to reduce the reaction/drying time for getting production speeds. The

pigments which are not heat stable at high temperatures show a marked change in shade. This is

more common in commercially available yellow, orange and red shades. The structure of the

pigment is the principal factor. At higher temperatures and a lower concentration of pigments, the

change in shade is more prominent. Therefore, pigments for this case need to be selected with care.

For improving reproducibility and process reliability, heat stability can be the first property that

can be considered. Generally, pigment for a particular substrate, fastness properties, and

application conditions are selected with the help of a manufacturer's pattern card [98].

66

3.7.2 Binders

The binders are film-forming high molecular weight polymers. They are present in homogeneous

form as dissolved or finely dispersed state. On heating, evaporation of a solvent or dispersing

medium takes place and polymer chains connect together to form a thin and coherent film that is

attached to the fiber. Pigment particles are enclosed by this several microns thick film. Since the

only connection between the pigments and the fiber is a binder so it greatly influences the fastness

properties. The fastness properties, such as rubbing, washing, and dry-cleaning, depend largely on

binder [89].

In order to meet the properties required from a binder, careful selection and combination

of the different monomers and control polymerization methods are of greater importance. Reactive

groups can be incorporated into the binder molecules which on heating form crosslinks with binder

chains and improve the resistance against the actions of physical and chemical agents [89].

The binders used in pigment coloration nowadays are made up of synthetic polymers.

Common types used are derivatives of acrylic acid, mostly their esters, butadiene, and vinyl

acetate. Commercially used binders are available both in the form of solutions and aqueous

dispersion, later being commonly used. In aqueous dispersion, water-insoluble high molecular

weight macromolecules in the form of 0.1-0.5 µm droplets are dispersed in the encompassing

aqueous medium. The dispersion has a low viscosity although having high solids content. The

polymer chains in the dispersion need only a small number of solubilizing groups, an advantage

as compared to a true solution. Accordingly, it is not required to make them inoperative either by

blocking them through chemical means after binder application or through inactivation by

crosslinking. The use of solution-based binders is limited [89].

The binder film formation is a two-step process. In the first step, water is removed from

the binder and the dye solution through vaporization and capillary action of fiber and dispersion is

removed. The binder and pigment coagulate to form an unstable gel-like layer. In the next step,

the gel layer merges under simultaneous deformation to form a film which has no elasticity and is

attached loosely to the substrate. During the curing process, cross-linking of binder film took place

making a film elastic and strongly attached to the substrate. The cross-linking reaction is a

condensation process which takes place in acidic conditions (pH < 4) to create a networked

structure. Hot air is the best fixation medium. The curing process is generally carried out at 150

oC for 5 min or at 175 oC for 45-60 sec. Wet steam and superheated (HT) steam is not suitable as

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a fixation medium in which low fixation yield is achieved due to hydrolysis [100]. Figure 3.3

shows the film formation and fixation process in a pigment coloration process [101].

Figure 3.3: Binder film formation and fixation mechanism.

3.7.2.1 Binder selection

Binder is the main component of the pigment coloration system and a significant number of

problems associated with pigment coloration are related to binders. The binder has to fulfill many

properties, both during application as well after it is anchored to the substrate. The list of required

properties is very long and often balancing them is not possible. The quality of dyed fabric in terms

of its handle and fastness properties is determined by the quality of the binder. A binder for

successful pigment coloration system should have to fulfill the following requirements [93-95, 99,

100]:

▪ High pigment binding ability;

▪ Resistance against acids and alkalies;

▪ Wash resistance;

▪ Abrasion resistance;

▪ Dry cleaning fastness;

▪ Resistance against swelling;

▪ Lightfastness;

After drying (still polymers)

Incomplete fixation (too short time, low temperature, or incompatible additives)

Completed fixation

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▪ Resistance to aging, weather, and heat;

▪ Should not be thermoplastic, as it affects the heat related fastness properties;

▪ Dry and wet rubbing fastness;

▪ Chlorine resistance;

▪ Soft handle (no or little effect on fabric handle);

▪ Compatibility with auxiliaries;

▪ Inhibit the migration of pigment particles during the drying and curing process;

▪ Smooth running properties (no buildup on padders, guide rollers and drying cylinders

and easy removal from machine components); and

▪ Film formation.

The most important characteristic is the film formation. The binder film must be [89, 94,

95, 99, 100]:

▪ Colorless and clear;

▪ Of uniform thickness and smooth;

▪ Neither too soft nor too harsh;

▪ Flexible;

▪ Have good substrate adhesion without being tacky;

▪ Resistant to physical and chemical agents after fixation;

▪ Coat and effectively bond to the pigment;

▪ Good adherence to the fiber;

▪ Not pre-polymerize during normal heating condition; and

▪ Transparent so that color and brilliance of pigments are not masked.

To produce a binder with required properties, several different monomers need to be

combined to produce a copolymer as homopolymers would not produce usable binders [89, 102].

Each monomer depending on its chemical structure give specific characteristics to the binder film

[102]. A copolymer is produced from these monomers represent the best possible compromise of

their properties [100]. For example, a copolymer can be formulated that gives necessary, uniform

film hardness from two comonomer types, one whose homopolymer yields hard and brittle films,

69

e.g. styrene, methyl methyacrylate and other types whose homopolymer produce very soft but

tacky films e.g. butadiene, butyl acrylate [89].

Comonomers are selected based on the following properties of the binder film [100, 102]:

▪ Flexibility (softness and elasticity).

▪ Strength and toughness;

▪ Durability (cohesion and adhesion);

▪ Surface tack;

▪ Adhesion;

▪ Water resistance;

▪ Solvent resistance;

▪ Resistance to hydrolysis;

▪ Thermoplasticity;

▪ Ease of fixation;

▪ Stability to light; and

▪ Resistance to aging.

The chemical composition of comonomers and their properties are given in Table 3.8 [100,

102-104]. The softness of the film is directly related to glass transition temperature (Tg), lower the

Tg, greater the softness of the film [100]. The main criteria for monomer selection are the soft

handle and good wet fastness properties. Additionally, the binder is the decisive cost factor in

pigment coloration so monomers are also selected according to the cost [103, 104].

The polymers apart from basic components usually contain cross-linking agents--

monomers that provide reactive groups [104]. On curing, polycondensation of linear groups into

the three-dimensional network takes place, thereby improving the fastness, temperature stability

and permanency of binder effects. The cross-linking monomers can be subdivided into two

categories based on their reaction mechanism. The first type, known as foreign crosslinking type

consists of monomers that have groups that can be reacted with bifunctional compounds e.g.

acrylamide and methyl acrylamide have free amide groups that can be cross-linked with

condensation products of urea or melamine. This type of cross-linking is essential for if the

functional group of binders cannot react themselves. The second type, known as self cross-linking

type consists of monomers such as methylol acrylamide and methylolmethacrylamide or their

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ethers. The reactive groups present are capable of reacting themselves. The cross-linking reaction

takes place at high temperature and under acidic conditions. For binder application under alkaline

conditions monomers containing epoxy or chlorohydrin groups are used [89, 100, 104]. Cross-

linking of binder molecules influence the viscoelastic and swelling properties of the binder film.

The later one affects the washing and solvent fastness. As the degree of cross-linking is increased

the elasticity of the film is reduced i.e. film hardness increases but swelling resistance is increased.

The balance needs to be maintained between the greatest possible swelling resistance and lowest

possible cross-linking [100].

Table 3.8: Comonomer types and polymer properties.

Basic components

Film characteristics

Tg (oC) Tacky Harshness Swells in

Water Solvent

CH2=CH-CO-OCH3

methyl acrylate 5 - medium no somewhat

CH2=CH-CO-OC2H5

ethyl acrylate -27 + soft no somewhat

CH2=CH-CO-OC4H9

N-butyl acrylate -57 ++ very soft no yes

H2C CH

styrene

95 -- very harsh no yes

CH2=CH-C≡N

acrylonitrile 105 -- very harsh no no

CH2=CH-CH-CH2

butadiene -86 ++ very soft no yes

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The most commonly used binders types are [89, 100]:

▪ The first class is the most commonly used type. They are formed from acrylate esters

and styrene but also from vinyl ester copolymer and have good fastness to aging and

running properties. They show good stability to an electrolyte and but inferior fastness

to dry-cleaning. The film is non-tacky and produces soft handle in combination with

silicone softeners.

▪ The second class consists of acrylonitrile along with acrylic esters. They have good

fastness to aging and dry-cleaning but not stable to electrolytes. In general, they

produce unsatisfactory handle.

▪ The third type is based on butadiene. They have an extremely soft handle but have poor

dry-cleaning fastness and resistance against the light. This is due to the presence of

double bonds which under the action of light or/and heat makes binder film brittle and

decolorized. Dry-cleaning fastness can be improved by the incorporation of

acrylonitrile. They have marginal stability against electrolyte but show excellent

running properties.

3.7.3 Auxiliaries

Auxiliaries are generally used to correct or control the problems that might occur during the

pigment coloration process. They generally have a specific function to perform but can affect

different properties at the same time. The role of auxiliaries is also dependent on the coloration

system. It is very important to understand the properties of the auxiliaries as well as the coloration

system so that appropriate auxiliaries can be selected [102].

3.7.3.1 Anti-migrating agent/migration inhibitors

In continuous coloration, pigments tend to migrate during the drying step. This is due to the

migration of dye liquor towards the hotter regions of the fabric. The migration process is

uncontrolled and random in nature and will cause uneven coloration that leads to shade variation.

The effect can be in the form of either patchiness or an undesirable two-sided effect. To prevent

this problem, migration inhibitors are used. Chemically they are either anionic which includes

polyacrylates and polyacrylamides or nonionic which consists of polyethoxylates. Polyethoxylates

consist of block copolymers consisting of poly (oxyethylene) and poly(oxypropylene) segments.

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Their mechanism of action is based on coagulation. At the start of the drying process, it physically

absorbs the pigment and attaches it strongly with the substrate thereby inhibiting migration. By

doing this, it also maintains the soft handle of the substrate. It also improves the hydrophilic

properties of the fabric which favors the uniform application of coloration liquor by padding.

Magnesium chloride or diammonium phosphate promotes the effect of migration inhibitors [95,

100, 105]. Migration inhibitor used should not make the fabric handle stiff, because the fabric is

not washed after the coloration or combined coloration and finishing process. Conventional

migration inhibitors e.g. alginates are not suitable [92].

3.7.3.2 Dispersing agent/emulsifier

The main function of the dispersing agent is to maintain the stable dispersion in the pigment

coloration system, prevent roller deposits and wet the fabric [97]. The pigment coloration system

usually contains the dispersing agents from pigment preparations and binders. Pigments

preparations contain up to 25% commonly of anionic or nonionic types. Binders also contain the

same type and the amount is 2-5% depending upon the solid content of the binder [89]. Emulsifiers

are also added directly to the pigment coloration system to prevent roller deposits [106]. When

pigment coloration components are mixed together there is a local exchange of surfactants until a

dynamic equilibrium is achieved. Therefore, compatibility is of prime importance. Also, they must

function properly in the mixture as they work individually. In practice, this aspect is not usually

given much attention. Unstable pigment coloration liquor or poor running properties can result

from mixing incompatible products or poor selection of emulsifier type as they are not able to meet

the requirement because of the structure. It also needs to be considered that emulsifier because of

its proportion in the system influence the film formation which ultimately affects the brilliance

and fastness properties. For each g of binder around 0.5 g of a dispersing agent is present in the

coloration liquor and both components are non-volatile. The emulsion breakage point, film

formation and nature of the film formed are affected by the type of dispersing agent and changes

in the concentration during and curing process. Therefore, manufacturers make sure that the

compatibility of the pigments, binders, and auxiliaries used in their ranges [89].

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3.7.3.3 Catalyst

The catalyst is generally added to accelerate the crosslinking reaction and maybe acid or basic

depends upon the system. They provide the catalytic effect by lowering or raising the pH when the

temperature is increased during the fixation process. The appropriate pH and high temperature

conditions are necessary for a high degree of polymerization of the binder. They are generally

ammonium salts such as ammonium sulfate, phosphate, and nitrate which generate mineral acid

during curing conditions. Metal salts such as magnesium chloride may also be used. The amount

of catalyst should be properly used, otherwise, it may cause tendering of the fabric due to the

excess generation of acid. For lower fixation temperatures (< 120 oC) free acids such as phosphoric

or tartaric acid may be used however if crosslinkers are present in the system problems related to

stability might occur due to rapid reaction [89, 99].

3.7.3.4 Crosslinkers/fixing agents

A pigment coloration system may contain a fixing agent depending on the fastness requirement

[106]. The term crosslinker is also used for these products. They improve the crosslinking of binder

film which enhances the rubbing, washing and dry-cleaning fastness. The disadvantage of this

improvement in crosslinking is the firmer handle. Crosslinkers are substances that have at least

two reactive groups per molecule. The most commonly used are low molecular weight nitrogen

based formaldehyde products e.g. dimethylolurea or dimethylolethyleneurea, hexamethoxymethyl

melamine or their ethers, hydroxymethyl urethane compounds and urea-formaldehyde products.

The addition of crosslinker is dependent on the type of crosslinking component present in the

binder. They are needed if the binder has no self-crosslinking groups present. But they can also be

used with the binder having self-crosslinking groups and markedly improve the fastness properties.

The crosslinking reaction is a condensation reaction and requires elevated temperature and a

catalyst to increase the rate of reaction between the binder and the crosslinkers. The selection of

crosslinker is dependent on the existent curing temperature, time and pH conditions. If a very

reactive crosslinker is used it may cause premature crosslinking and hinder the binder film

formation process [89, 103].

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3.7.3.5 Hand modifiers

The main drawback associated with pigment coloration is the stiffening effect of binder film on

the hand feel. One of the prime reasons for this effect is the restricted relative mobility of the fibers

due to their mutual adhesion by the binder. The stiffening can be restricted up to a certain extent

by ensuring the correct amount of binder required. The hardness of binder film can be controlled

by the proper selection of monomer types and crosslinking agents and the degree of crosslinking.

The relative movement of molecules in the binder film determines its hardening effect. Strongly

polar groups or hydrogen bond forming groups can restrict the mobility of binder chain. To

increase the interchain mobility, low molecular weight compounds known as plasticizers are added

in binder formulation. These compounds increase the distance between the binder chains through

swelling. This imparts softness due to greater interchain mobility. Mostly these compounds are a

long chain with aliphatic groups and their amount in binder formulation depends upon the level of

effect required, usually up to around 30% based on solid content. The addition of a plasticizer is

accompanied by the drawback that swollen film is prone to attack by the mechanical agents. To

counteract this effect balance in the fastness properties and softness of binder film is obtained by

selecting the appropriate type and quantity of plasticizer fit for the particular binder. The handle

of binder film can also be improved by a formulation of soft binder types i.e. selecting of monomer

types that give soft hand such as butadiene and acrylates. In the case of soft binders, the steric

hindrance of binder chains is small at room temperature and therefore have a low glass transition

temperature. However, binder film of this type is tacky and in certain substrates give a sticky or

soapy handle [89]. This problem can be overcome by incorporating silicone base softeners which

improves the dry handle. There is no swelling of binder film as silicone softeners have no

interaction with the binder, therefore no negative influence on the fastness properties. These

softeners compensate for the film brittleness and therefore increase the dry rubbing fastness [89,

103].

3.7.3.6 Defoaming agent

To counteract the foam formation due to the entrapment of air which can result in coloration defect,

defoamers are used in pigment coloration. They act by increasing the surface tension of the

coloration liquor so that foam formation is suppressed. The main requirement of the defoamer is

its suitability in the pigment coloration system [89]. They are generally based on an emulsion of

75

silicone oils [102, 106]. Alkoxylate based defoaming agents are also used for combined pigment

coloration and finishing [97].

3.7.4 Combined pigment coloration and finishing

Coloration with pigments have an advantage, as compared to conventional coloration methods,

that coloration and finishing can be done in the same bath. This is contrary to a normal processing

method in which coloration is followed by finishing. This one bath procedure is now an established

process and has several advantages like savings in cost, in equipment, and also in time, labor and

water [92]. The depth is generally limited to light to medium shades (5 g/L to 10 g/L). Two types

of finishing are most common: soft finishing or resin finishing. In the case of soft finishing, silicone

or polyethylene based softeners are used alone or in combination. Compatibility with the pigment

coloration system should be considered in selecting softeners. The use of cationic softeners with

pigment preparations containing anionic emulsifiers may cause finishing spots [93]. In the case

of resin finishing, cross-linking agent and catalyst are used. In general selection of a cross-linking

agent is based on the same requirements as those for resin finishing without pigment coloration.

The effect of resin finishing on the lightfastness of dyed fabric needs no longer to be considered.

Modified DMDHEU is used as a crosslinker and magnesium chloride is commonly used as a

catalyst. In order to compensate for the harsh handle and loss in strength due to resin finishing

softening agents and additives are used [92, 97]. Product compatibility and bath stability is an

important factor in the selection of products. Special auxiliaries based on ethoxylation product on

curing of cross-linking agent may degrade certain pigments and result in loss of depth of shade

[92].

3.7.5 Application method

Pigment coloration and combined pigment coloration and finishing involve the following

operations [92]:

▪ Padding;

▪ Drying; and

▪ Curing

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3.7.5.1 Padding

The aim of the padding process is the even and uniform distribution of the pigments over the fabric.

It must be ensured that coloration padders and guide rollers are clean, because droplets may cause

stains on the fabrics resulting in a faulty fabric. In order to ensure the uniform application of

pigments, the surface of padders must be even and smooth and pad rollers must apply pressure

evenly i.e. wet pickup of the fabric should be constant along the length and width. High pressures

should be used so that fabric pick-up is kept as low as possible to minimize the effect of migration

[92, 100]. The dye bath must be agitated continuously to avoid settling of pigments. Depending

upon availability, air exposure should be given to fabric after the padding process. This improves

the penetration of pigment. The penetration of dye liquor is also influenced by the good

pretreatment of the fabric [95, 100]. The wetting agent may be added in the dye bath to increase

the penetration of liquor into the fabric [93].

3.7.5.2 Drying

After the dye liquor has been applied to the fabric, drying is generally carried out in infra-red pre-

dryer. They are arranged in parallel such that fabric passed through them and get dried from both

sides. One of the important aspects need to be considered is migration. Migration should be

avoided as much as possible to ensure level/uniform coloration. Level coloration depends on

penetration and migration. The migration process begins with the drying step. As the fabric surface

is dried, the liquor from the inside of the fabric moves to the dried surface causing the pigment to

move to the surface and accumulate. This results in poor penetration. Migration continues until the

interruption of the liquid phase due to the non-availability of migration-active surface water. The

threshold values are dependent upon fiber type and are about 25% for cotton fibers and 5-10% for

synthetic fibers [92, 100]. Water in the liquid phase is only responsible for the migration problem,

so the following steps may be taken to overcome or reduce the severity of the problem [92, 95,

100]:

▪ Keep the wet pick-up low as possible (e.g. by high squeeze off, or installation of

vacuum suction slot after padder).

▪ Short liquor trough with a short dip to reduce the wet pick-up.

77

▪ Long-air passage of 30-60 seconds. The migration active surface is converted to

migration-neutral swelling water during this time. When water evaporates during

drying, no migration occurs.

▪ Gentle drying, reduction of fan speed and keep the maximum temperature to 120 oC in

the first two drying zones.

▪ In stenter, run the first chamber with air circulation. This primarily results in heating

up of fabric instead of drying. Also, the migration inhibitor effect will be developed

before the drying starts. IR dryer used for drying serves the same purpose.

▪ Use an anti-migrating agent. On heating, it precipitates in its solution causing viscosity

increase or coagulate depending on the type. This effect controls the pigments from

migration.

The migration of pigments is also influenced by the type of heat supply. A hot flue is most

suitable for uniform and mild drying and curing conditions. The air circulation should be uniform

and tension on the fabric should be kept minimum as possible. This includes the even distribution

of airflow of the top and bottom to minimize the face-back problem. Temperature variation should

be controlled along the sides to prevent width-wise shade variation. Guide rollers in the starting

section should be Teflon coated to avoid binder deposits [92, 93].

Stenters can also be used for both drying and curing process. Pins found to more suitable

as compared to clips as its possible with proper adjustment of overfeed, shrinkage can be

minimized. Selvage dark pin marks can be avoided by proper temperature control [92].

3.7.5.3 Curing

Optimum fastness is achieved when pigment dyed fabric is fixed in the hot air. The temperature

should not exceed 170 oC. The fixation process can be carried out on hot flue machines or stenters.

In hot flue machines, the time and temperature required are dependent on the binder or

reactivity of the cross-linking agent. Optimum fixation is achieved by curing for 4-5 min at 150

oC. Fixation time can be reduced at higher temperatures. A general rule of thumb is, with 10 oC

increase in temperature, fixation time is reduced by 1 min [92, 107]. The relationship between

curing time and temperature is shown in Figure 3.4. The temperature and time correspond to the

binder condensation reaction [101].

78

Dry and fixation can be carried out simultaneously on stenter. This process is known as

flash curing and is carried out at an elevated temperature, e.g. 160-200 oC. This method is less

reliable as compared to performing drying and curing separately. Fixation is carried out when a

fabric is dried, so the exact moment at which fabric is dried is difficult to determine. This results

in uncontrollable fixation time and therefore affects the fastness properties. This method is only

recommended for dryers having large fabric capacity [107]. The machine speed is dependent on

the type of binder, type of fiber, fabric weave and in case of combined coloration and finishing

cross-linking agent and catalyst used need to be considered. It must be taken into consideration

that an increase in the curing rate may have a processing risk such as temperature fluctuations

within stenter, non-uniformity in liquor pickup, machine stoppages and varying heating up times

of the textile materials [92].

Figure 3.4: Relationship between curing temperature and time.

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3.7.6 Equipment

Pigment coloration can be carried out on a variety of equipment [93]:

▪ Padder - stenter

It minimizes the equipment cost. But it has some disadvantages such as limited

migration control, limited shade range, clip buildup. These problems can be controlled

by the proper selection of binders and anti-migrating agent.

▪ Padder - drying cylinder - stenter

This machine configuration can be found in old finishing departments. It offers a full

range of color and migration control. Deposits on the drying cylinder are very excessive

in this case.

▪ Padder - pre-dryer - drying cylinder - stenter

It offers better migration control and minimizes the roller build-up.

▪ Padder - vacuum slot - pre-dryer - stenter

Vacuum slot allows the low pick up which minimize the migration problem. The

unbound moisture on the fabric surface is removed. It also minimizes the roller buildup

and improves the appearance of the dyed fabric.

3.8 Dyeing of polyester/cellulosic blends using a two-dye system

3.8.1 Dye classes used for polyester/cellulosic blends

3.8.1.1 Disperse dyes

Disperse dyes are used to dye polyester filament and staple fibers. Disperse dyes on polyester

generally give adequate light and wet fastness properties. As polyester is extremely crystalline and

has hydrophobic nature, dyes are generally protected from the chemical attack. Some disperse dyes

are sensitive to heavy metals ions (iron and copper), reducing agents and alkaline conditions. They

are applied under acidic conditions (pH 4-5) and sequestering and mild oxidizing agents may be

used depending on the sensitivity of certain dyes [9]. Different chemistries of disperse dyes are

available such as aminoazobenzene, anthraquinone, nitrodiphenylamine, styryl (methine),

quinophthalone, aminoketone, and benzodifuranone derivatives [75]. Almost all chemical classes

of disperse dyes can be used for the dyeing of polyester/cellulosic blends [9]. The dyeing

requirements for dyeing polyester in polyester/cellulosic blends are often different than that of

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100% polyester. They are generally required to higher thermomigration properties as

polyester/cellulosic blends are often resin finished [79].

Disperse dyes are partially soluble in water and usually dispersed as a fine, uniform and

stable suspension. For good dispersion smaller particle size is essential. Disperse dye already

contains dispersing agent and sometimes additional dispersing agents may be added during the

dyeing process. The dispersing agent is added to improve dye dispersion, improve dye solubility

and prevent it from breakage due to a variety of factors such as higher dyeing temperature, water

impurities, and dyebath chemicals. The agglomeration of dye is also prevented. Optimum

quantities must be added as an extra dispersing agent may create problems in dye exhaustion. Both

nonionic and anionic type dispersing agents are available but anionic are preferred due to their

high-temperature stability [108]. They must be compatible with the dyes being used. The disperse

dye usually contains dispersing agent one-third of its weight, therefore, the additional dispersing

agent must be added during dyeing when essentially needed especially in light to medium shades

[109].

The polyester portion in the blend can be dyed by different methods [85, 110]. These are

as follows:

▪ Carrier or atmospheric dyeing;

▪ High temperature (HT) dyeing (also known as high pressure dyeing); and

▪ Thermosol dyeing.

The carrier and HT dyeing methods are batch processes while Thermosol is a continuous

process. In the batch dyeing process, commercially available disperse dyes along with auxiliaries

are dispersed in a dyeing machine containing water and polyester. The temperature of the dyeing

system is raised to 100 oC (for carrier dyeing) or 130 oC for (high-temperature dyeing) and is held

for required dyeing duration. The dyeing system is then cooled and the substrate is removed from

the machine [109]. The carrier dyeing as the name implies uses carriers for the dyeing of polyester.

The carriers are swelling agents which permit the dyeing of polyester to be carried out at 100 oC

(atmospheric pressure). Several problems such as lower dye built up on fiber, environmental issues

related to the carriers and odor development during dyeing have significantly declined the use of

carrier dyeing method for polyester/cellulosic blends [85, 110]. The blends containing the sensitive

fiber that can be damaged at higher temperature such as wool and acrylic employs carrier dyeing

81

up to a certain extent. Polyester/cellulosic blended fabrics are usually performed by high-

temperature jet or overflow dyeing machines under pressure 2 to 2.5 times higher than atmospheric

pressure) at 130-135 oC [75, 85, 110]. The beam dyeing machines may also be used. The use of

winch and jig is limited due to the economy and steam consumption. A good selection of disperse

dye is required to ensure uniform dyeing [67]. The selection of disperse dyes depends on [111]:

▪ Stable dispersion under dyeing temperature in the presence of dyebath chemicals;

▪ Good leveling behavior;

▪ Higher exhaustion values;

▪ No buildup or shade change after 20 minutes at 120 oC; and

▪ Compatibility of dyes in combination shades.

Batch dyeing of polyester fibers from the dye liquor occurs in three distinct stages termed

as exhaustion, diffusion, and migration. In the initial stages of dyeing at a lower temperature (<

60 oC) dye is present in a dispersed state. With the increase in temperature, some disperse dye

dissolves in the aqueous medium and absorbed onto the fiber surface. This drives more dye to

become soluble [111]. The rate of exhaustion depends on the substrate, concentration, and

solubility of the dye. The rate of dye exhaustion should be controlled to ensure uniform dye

distribution throughout the substrate. The temperature ramp rate during the dyeing process is the

key factor that determines the dyeing rate. This rate needs to be carefully controlled during the

initial dyeing phase, especially after the glass transition temperature (greater than 75 oC). For

polyester dyeing with disperse dyes, there is a temperature range where there is maximum

exhaustion rate (between 80 oC and 120 oC) depending on the dye type. This temperature range is

termed as the critical dyeing temperature, ∆Tcrit. Slow diffusing dyes have higher ∆Tcrit while

rapidly diffusing dyes have lower ∆Tcrit. The actual value depends on temperature ramp rate, dye

amount, liquor flow rate, liquor ratio, substrate type. The temperature is increased slowly in the

∆Tcrit region to control the exhaustion rate that allows level dyeing. The temperature is then

increased from just above the ∆Tcrit to the maximum dyeing temperature at a higher rate possible

[9, 112]. The rate of dyeing depends on following factors [108]:

▪ Fiber crystallinity and degree of orientation;

▪ Molecular weight of the dye;

▪ Dye particle size and its distribution;

82

▪ Dye solubility; and

▪ Dye concentration in the bath.

The dyeing of polyester fibers is carried out at temperatures (dyeing temperature: T) which

is above the glass transition temperature (Tg). Generally, dyeing of polyester can be carried out at

130-135 oC known as high-temperature dyeing or can be done at 100 oC using carriers that act as

plasticizers and lowers the Tg. As the temperature is increased to dyeing temperature and more dye

is diffused into the fiber interior. Dyeing is continued at this temperature for a certain duration to

permit complete diffusion. Dye diffusion into the fibers is determined by Williams, Landell, and

Ferry equation. During this phase, migration also takes place which enhances uniformity and

penetration in tight structures. At the end of the dyeing process, the dye is uniformly distributed

throughout the fiber. The rate of diffusion depends on the substrate, the molecular weight of the

dye and temperature. The migration rate is based on dye properties and temperature [75, 111].

In all dye systems used for coloration of polyester/cellulosic blends, the leveling agents are

seldom required as compared to the dyeing of polyester alone. During the starting phase of batch

and continuous processes, the cellulosic portion of the blend owing to its high hydrophilicity

absorbs a majority of the disperse dye. With an increase in temperature to the final dyeing or fixing

temperature the dye gradually and subsequently migrates towards the polyester. Thus it can be said

that the cellulose is acting as a leveling/retarding agent for disperse dyes [86]. For certain disperse

dyes and lighter shades leveling agents are still used [9]. The leveling agents should have the

following characteristics [111]:

▪ Satisfactory leveling properties.

▪ Easy to remove from the substrate.

▪ Little or no foaming.

▪ Little or no effect on dye yield.

▪ Easy to handle.

The continuous dyeing of the polyester portion of the blend is carried out by a thermosol

process. This process comprises padding of dye liquor, Infrared pre-drying, drying and

thermofixation (thermosol process) [9, 113, 114]. The fabric is padded with a disperse dye,

dispersing agent, non-ionic wetting agent and a migration inhibitor. The disperse dye is in the form

83

of fine dispersion and the pH of the bath is maintained at 5-6 generally with acetic acid. The

migration inhibitor used is anionic polyelectrolyte. This includes sodium alginate, polyacrylamide,

polyacrylates, polyvinyl alcohol, and carboxymethylcellulose [9, 115]. They agglomerate the dye

particles that lead to the enlargement of particle size. Thus the movement of larger dye particles to

the surface is restricted during the drying phase [9, 116-118]. On the other hand, they should allow

the dye transfer to take place during the thermofixation process. The polyacrylamides are preferred

over alginates because of this property. Both liquid and powder types of the dyes can be used. The

liquid brands make the preparation of dye liquor easier, give less migration during drying, are less

prone to staining of the cellulosic component of the blend and produce high color yields. However,

they may settle down during storage which requires agitation before use, also during storage of

used container water may evaporate or solids may deposit at the surface leading to strength

variations [9, 115].

Before thermofixation step disperse dye is present in an aggregated state along with wetting

and dispersing in the matrix of antimigrating agent. The dye is converted from aggregated to the

monomolecular form during the thermofixation and migrates to the fiber surface. The dye is then

diffused to the interior of the fibers. The suitability of disperse dye for the thermofixation method

should be checked by plotting its time-temperature curve. Not all disperse dyes have the same

fixation profile. For trichromatic shades, the dye selected should have a similar fixation profile

[113, 115]. Suitable disperse dye can be grouped into two categories, the first requires fixation at

200-210 oC and the second produces reproducible results at 210-200 oC. Selecting the dyes should

be based on the fastness properties that can be obtained using the chosen dyeing route on the blend

as a whole and the cost [115].

The behavior of disperse dyes in the thermofixation process depends on [115]:

▪ Pad liquor pH;

▪ Concentration of the dye;

▪ Dispersion behavior of the dye;

▪ Fixation temperature; and

▪ Fixation time.

During impregnation, most of the dye liquor is absorbed the hydrophilic portion of the

blend as compared to hydrophobic polyester fibers. More dye is present on the cellulose portion

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than where it is required [114]. The staining of cellulose may take place by disperse dyes during

drying and the theormofixation stages. This depends on the drying unit, fabric construction, and

pad liquor composition. A good dispersion system allows the transfer of disperse dye from

cellulosic fibers to the polyester during the drying and the thermofixation stage [9, 114]. This is

carried out through the vapor phase where dye sublimes off of the cotton to the polyester. Many

factors affect this transfer such as the surface area of dye particles, the morphology of dye particles,

morphology and surface area of cellulose, and substantivity of dye towards the cellulose. Dye that

cannot sublime shows poor transfer to the polyester [114]

Disperse dyes can be classified into three classes depending upon the molecular weight and

sublimation properties. These are low energy, medium energy, and high energy. These classes

determine the dyeing temperature and thermomigration properties of disperse dyes. Low energy

disperse dyes have a molecular weight less than 300 and they are applied in lighter shades due to

their good leveling properties [9]. Medium energy dyes have a molecular weight between 300-

400. High energy disperse dyes have a molecular weight in the range of 550-650. These dyes

require high energy for dye diffusion into polyester fibers and therefore can be raised at a higher

temperature gradient. They also have a higher critical temperature zone than for most disperse

dyes [75]. These dyes are designed to have extra solubilizing groups to improve their dyeing

properties and slightly better solubility as compared to medium energy dyes. If the fabric is not

subjected to high temperature 160-170 oC, good thermomigration properties are seldom required.

The fastness to cold water or perspiration is inferior as compared to medium energy dyes because

of color migration in aqueous medium [109].

Over the years many developments have been done in polyester dyeing and disperse dyes

[75]:

▪ Dye selection having a similar compatible strike rate for rapid dyeing;

▪ Application methods to ensure proper dye penetration and avoid ring dyeing;

▪ Use of granular, pearl and liquid disperse dyes;

▪ Alkali-clearable dyes that do not require reducing agents;

▪ Development of novel chromophores that gives excellent thermomigration and wet

colorfastness;

▪ Alkali-stable disperse dyes that are stable up to pH 8.5-9.5; and

▪ Development of high brilliance disperse dyes.

85

There are some fastness issues associated with the dyeing of weight-reduced and

microfibers. It is difficult to achieve level dyeing and desirable fastness properties in the dyeing

of polyester/cellulosic blends containing polyester microfiber variant. These problems are due to

[9]:

▪ Polyester microfilament yarns of 0.6 denier or less cannot be dyed on package or beam

because of inadequate liquor circulation due to the high density of the wet substrate.

▪ Microfiber requires much more disperse dye than conventional polyester to achieve the

same visual depth. Due to the smaller proportion of microcrystalline material in

microfilament structure, absorb dye forms larger aggregates in the amorphous regions.

This leads to reduced tinctorial power.

▪ The rate of dyeing is much faster in microfibers as compared to conventional polyester

fibers. Starting dyeing at very high temperature, using a higher ramp rate above 90 oC,

differences in the rate of dyes used and insufficient fabric agitation at slow speeds leads

to uneven dyeing.

▪ Inferior lightfastness, washing and rubbing fastness as compared to standard polyester.

High-temperature treatment after dyeing often magnifies these issues. Scouring of

unfixed dye is more difficult and reduction clearing is always recommended.

By modifying dyeing procedures and proper dye selection these challenges can be dealt

with. It is suggested to select dyes with similar dyeing rates, higher fastness properties, star the

dyeing process at low temperature and use slower ramp rates. Jet or overflow dyeing machines are

recommended with small fabric lengths to promote agitation. Over the years new disperse dyes

have also been developed to overcome these problems. Azo dyes containing diester groups and

some azothiophene based dyes that become soluble under mild alkaline conditions give good

results in the dyeing of polyester microfiber/cellulose blends. They offer numerous advantages

such as minimal or no cross-staining of cellulose, ability to combine clearing step in reactive

dyeing, no need for reducing agent to remove disperse dye stain and desirable fastness properties

after post dyeing heat treatment [9].

Alkaline dyeing of polyester offers numerous advantages such as less oligomer problem,

less requirement for reduction clearing and soft and smooth hand of the substrate. This also

provides an option to combine high-temperature scouring/bleaching of cotton with a disperse

86

dyeing of polyester saving time and energy costs [75]. Oligomers are low molecular weight

substances and polyester fiber contains between 1.3 and 1.7% by weight mainly composed of the

cyclic trimer. During high-temperature dyeing, they move from the fiber into the dye bath. They

remain in solution until the dyebath temperature is lowered below 110-115 oC. They crystallize

and form deposits on fabric and in various zones of the machine. The latter may cause problems

in liquor flow in the machine. Nonionic residues in the fabric and dye remaining in the bath at high

temperature may combine with oligomers. Oligomer controlling products may be added to increase

oligomer solubility and prevent redeposition [109].

One of the important criteria that determine the selection of disperse dyes, for both exhaust

and continuous dyeing of polyester/cellulosic blends, is their affinity for cellulose. The cellulosic

component of the blend is stained by disperse dyes. Staining leads to reduced light and wet

fastnesses. For continuous dyeing rapid clearing and sensitivity of staining to the thermofixation

conditions are essential factors to consider [9, 111]. Different factors that may influence staining

are summarized in Table 3.9 [9, 111]. The migration of disperse dye from cellulose to the polyester

is promoted by prolonged boiling. Also, cellulose damage is minimum at boiling temperature. At

the end of the dyeing cycle, some disperse dye remains in the dye bath. As the dye bath is cooled

this dye will redeposit onto the fabric surface. Therefore, it is recommended to drain the dyebath

at higher temperatures [9]. Lignin present in linen fibers has more tendency to get stained by

disperse dyes [9].

The removal of unfixed disperse dyes on polyester and stain on the cellulose component is

essential to ensure the highest fastness properties. Different methods can be used to remove the

disperse dye stain depending on the chemistry of disperse dye. These methods include soaping

with detergent or reduction clearing or in some cases oxidative bleaching. Reduction clearing is

the most common and effective method to remove any surface and residual dyes on the polyester

and the staining on the component fiber in the blend. It cannot be used when the cellulose portion

of the blend is already dyed with direct or reactive dyes. In vat and sulfur dyes the reduction stage

can be combined with reduction clearing. Standard reduction clearing procedure is carried out

usually for 20 minutes at 70 oC using sodium hydrosulfite, caustic soda and non-ionic detergent

depending upon the depth of shade [9, 79].

87

Table 3.9: Factors affecting staining of cellulose by disperse dyes.

Favors staining Reduce staining

▪ Lower dyebath pH

▪ High affinity of disperse dyes for cellulose.

▪ Poor dispersion stability

▪ Slow cooling of disperse dyebath

▪ Non-ionic chemicals

▪ Carriers

▪ Lignin (linen)

▪ Disperse dye having less substantivity

for cellulose

▪ Draining of dyebath at a higher

temperature

▪ Use of leveling agents

The disperse dyes may migrate to the surface of polyester fiber during soaping treatment

at a boil. This treatment is necessary for the dyeing of the cellulosic component with reactive, vat,

or sulfur dyes. Some disperse dye may remain on the surface even reduction clearing treatment is

given after soaping. This leads to inadequate wash fastness properties. Selecting disperse dyes

which have a minimum or no tendency to migrate to fiber surface at boil during soaping mitigate

this problem [9]. Some dye movement may take place during post-heat treatment after dyeing

carried out a temperature higher than the dyeing temperature. This leads to deterioration in fastness

[109]. High energy disperse dyes are preferred where the fabric has to undergo subsequent high-

temperature treatment such as durable press finishing [9, 109]. The additional reduction clearing

process performed after disperse dyeing is not beneficial for lower energy disperse dyes as these

dyes tend to move from the interior of the fiber to the outer surface during post-heat treatment.

Reduction clearing though improves the fastness but in subsequent heat treatment deteriorates the

fastness [109].

3.8.1.2 Reactive dyes

These dyes form a covalent bond with the fibers containing hydroxyl, amino or mercapto groups.

Cellulosic, proteins and polyamide fibers can be dyed with reactive dyes. They have excellent

fastness properties and produce brighter shades [7, 64]. Reactive dyes are characterized by having

a reactive group attached directly or through a bridge to the chromophore. The reactive group is

responsible for forming a bond between the fiber and the dye. Over the years several reactive

88

groups have been introduced having different reactivities and can be classified into two broad

categories based on their mechanism of reaction with the fibers [119]. These include addition and

substitution type reactive dyes. The reactive dyes based on their reactivity can be classified into

three groups [79]:

▪ Group 1: High reactivity dyes

Examples: Dichlorotriazine, dichloroquinoxaline, fluorodichloropyrimidine and

fluorotriazine.

▪ Group 2: Medium reactivity dyes

Examples: Vinyl sulphone

▪ Group 3: Low reactivity dyes

Examples: Monochlorotriazine and tricholorpyrimidine.

The dyeing temperature in the batch process depends on the reactivity. High reactivity dyes

require lower temperature (40 oC) while low reactivity dyes require higher dyeing temperature (80

oC). The medium energy dyes require moderate dyeing temperature (60 oC) for fixation. In the

case of continuous dyeing, this is controlled by changing the alkalinity where strong alkali is used

for low reactive dyes while weak alkali is used for high reactivity dyes while keeping the fixation

conditions the same. It is important to note the reactive dye may contain more than one reactive

group to improve the dye fixation and application temperature. In some cases, a dye may contain

3 reactive groups. The dye molecular design is matched with the nature of the reactive group. High

reactivity dyes generally have smaller dye molecules while low reactive dyes have large

molecules. The mismatch dye molecular design gives leveling and wash-off problems. The dyes

having lower substantivity are easier to wash-off compared to one having higher substantivity.

This factor is more important in continuous dyeing. Furthermore, highly substantive dyes give

tailing problem. Therefore, low to medium energy dyes should be used in a continuous process

whole high substantivity dyes should be used for a batch process [79].

Reactive dyes can be applied to polyester/cellulose blends by a variety of routes. These

include batch, semi-continuous and continuous process. The suitability of a reactive group for a

particular route and fastness properties requires determines their selection. The reactive dye

selection is important to ensure good fastness properties and level dyeing [56].

89

The batch dyeing of reactive dyes involves three steps that include exhaustion, fixation,

and soaping. Exhaustion stages require a large quantity of salt to promote dye exhaustion. This

phase is dependent on the substantivity of the dye. Different reactive systems have different levels

of substantivity but substantivity levels tend to be of the same order within a given type of reactive

system. The dye is exhausted into the substrate under neutral dyebath conditions. When alkali is

added to the dyebath, secondary exhaustion takes place along with the fixation of the dye with the

cellulose. For good level dyeing in highly reactive dyes, the difference between the initial

exhaustion and alkali exhaustion should be smaller. The soaping process is done to remove the

hydrolyzed dye. This makes the batch dyeing process quite lengthy [7, 79].

Pad-batch is an economical route used mainly for dark shades. The fabric is padded with

reactive dyes and alkali and the batched for 3-24 hours while rotating slowly. The fixation time

depends on the depth of shade, padding temperature, alkali system and batching temperature [113].

The reactive dyes can be applied by a continuous process through variety of routes which

are [113]:

▪ Pad-dry-thermofix;

▪ Pad-dry (Econtrol);

▪ Pad-steam (pad- chemical pad steam);

▪ Pad-dry-steam; and

▪ Pad-dry-chemical pad steam

The pad-dry-chemical pad steam and pad-dry-thermofix are most commonly routes used

for polyester/cellulosic blends. In a continuous dyeing process, the reactive dyes must fulfill the

following requirements [120]:

▪ Similar affinity factors of dyes used in combination shade including shading elements

(low tailing, high reproducibility);

▪ Good dye bath stability (low tendency for hydrolysis);

▪ High reactivity (especially for pad batch so that fixation is not affected by variations in

batching temperatures);

▪ Higher lightfastness; and

▪ Good wash-off behavior.

90

In the dyeing of polyester/cellulosic blends with reactive dyes following points need to be

considered:

▪ The reactive dyes do not exhibit any cross-staining effects on the polyester fibers. The

only exception is phthalocyanine-based dyes (turquoise blues and greens) that may

show a very small amount of staining [79].

▪ The reactive dye system may undergo interaction between disperse dye system during

dyeing. Highly reactive dyes may form a covalent bond with disperse dyes. This

problem is more likely to be seen when the disperse and reactive dyes are present in

the same bath. The use of two bath process is recommended [79].

▪ Reactive dyes require a large quantity of salt for dye exhaustion. This salt can interfere

with the disperse dye dispersion system. The use of two bath process or lower quantity

of salt is recommended [79].

▪ The reactive dyes require alkaline conditions for their fixation. Many disperse dyes are

not stable under these conditions. The use of one-bath two stage or two bath process is

recommended. The alkaline bath can serve as a wash-off bath for disperse dyes

depending on the chemical groups present [79].

▪ The reactive dyes are sensitive to change in liquor ratio. The effective liquor for the

cellulose component is higher than the bath liquor. The reactive dyes with lower

substantivity give lower color yield than high substantivity dyes in higher liquor ratios

[79].

The real challenge in dyeing with reactive dyes is the removal of unfixed hydrolyzed

reactive dye. The washing off process is critical and requires a large quantity of water and higher

washing temperature for effective dye removal. The washing off process involves rinsing followed

by soaping at high temperature. Initial rinse reduces the salt and alkali concentration. Lowering

the salt reduces the dye substantivity and makes the removal of unfixed dye easier. The favorable

conditions are a high number of bath changes, higher liquor ratio, and strong mechanical action.

Reactive dyes containing vinyl sulphone groups may hydrolyze at higher pH and temperature

conditions. The soaping process is carried out near the boil (95 oC). It removes the unfixed

hydrolyzed dye form the fiber interior. The favorable conditions are high bath temperature, low

amount of unfixed dyes, lower electrolyte concentration, higher liquor ratio, a high number of bath

91

changes and lower substantivity of the dye. The cold reactive dyes having lower substantivity may

cause less problem during washing. [61, 87, 113].

3.8.1.3 Direct dyes

These dyes are still used to dye of cellulose portion of the blend because of their shorter dyeing

cycle, lower cost, good dye compatibility, and acceptable fastness properties in lower depth.

However, they have limited fastness properties and produce dull shades. The strengths and

weaknesses are given in Table 3.5. Their application process is simple. They require salt for their

exhaustion. Direct dyes are normally applied to polyester/cellulosic blends by a batch process only

[61].

In the early 1980s, Sandoz presently Archorma launched a reactant fixable series of direct

dyes called Indosols. These are specialized direct dyes that can be fixed with specialized cationic

fixing agents giving good washing fastness properties. Most of them are pre-metalized copper

complex dyes. A new series of reactive fixable direct dyes called Optisols were introduced in the

1990s that do not contain metal [9, 64, 121]. These ranges are later combined and now called

Indosols [122]. The high-temperature stability of these dyes makes them suitable for one-bath one

stage dyeing of polyester/cellulosic blends. For the production of black, alkaline pH is required to

maintain solubility, one bath two-stage is therefore required [64, 122].

Disperse/direct system is usually restricted to the cheaper product segment that requires

relatively low fastness properties. This also provided leverage for disperse dye selection based on

their staining tendency for the cellulosic component. This system is commonly used for dyeing of

polyester blends containing viscose and other regenerated cellulosic fibers. These blends are used

as a suiting material where high wet fastness is not required. The aftertreatment with cationic fixing

agents along with resin finishing give direct dyeing adequate wet fastness properties [9, 56, 57, 64,

83, 87]. Shade change after this treatment, however, may be observed [83].

The solid color effect is usually achieved on blended staple yarns. Direct dyes give a good

reserve on a polyester component. This enables one bath bleaching and direct dyeing to be

performed. The polyester/cotton blended fabric can be scoured and bleached followed by dyeing

with selected disperse and direct dyes in the same bath [123].

Reactant fixable direct dyes can be used for dyeing of cotton portion in wool/cotton,

cellulosic/polyamide and cellulosic/acrylic blends by one bath one stage method with good

92

fastness properties. The acidic conditions required for dyeing of wool, nylon and acrylic fibers

complement the use of these dyes [9, 122].

3.8.1.4 Vat dyes

Cellulose fibers can be dyed with vat dyes by both batch and continuous processes. Batch dyeing

usually involves package, jet or overflow dyeing machines. The factors that may affect the dyeing

of cellulose portion with vat dyes are given below.

The presence of oxygen inside the machine can create problems during vat dyes assuming

that the machine is airtight, and no air can enter the machine once the process is started. There is

a higher contact between the dye liquor and the entrapped air because of the turbulence effect in

jet dyeing machines. This entrapped air can cause decomposition of hydrosulfite and therefore

cause problems in the reduction of vat dyes. Also, the decomposition products are acidic in nature,

so an extra amount of caustic is required for their neutralization. As a rule of thumb, 1 cm3 of air

requires 2 liters of caustic soda (36 oBé) and 1.7 kilograms of sodium hydrosulfite. Sufficient

quantities of caustic and hydrosulfite must, therefore, be used at the start of the dyeing process.

Additions during the dyeing process may cause problems. The actual quantity required depends

upon the machine and remains fixed for that machine under a particular set of conditions [57].

The important points to consider in deciding whether the jet or overflow dyeing machine

is suitable is given below [57]:

▪ The presence of large enough expansion tank so that complete dyeing liquor can be

prepared in it before it enters the machine.

▪ The rinsing system in the machine. The material should be rinsed, and liquor should be

drained while it is moving inside the machine and should not be stationary.

▪ The entrance of rinsing water in the machine. Water should either be entered through a

jet or through the inner walls of the machine and should not be fed from one side of the

machine.

The presence of alkaline earth metals in the material to be dyed should be avoided. The

dyeing process used can either be one bath two stage or two bath process. Dye selection is critical

to obtain good results. Certain vat dyes are sensitive to over reduction so either glucose or sodium

93

nitrate must be used [57]. The final rising and oxidation are critical for vat dyeing. Initial rinsing

helps in the removal of unexhausted leuco dye and chemicals [57].

Selection of vat dyes for jet dyeing depends on the following factors [57]:

▪ Less desorption tendency;

▪ Better leveling characteristics;

▪ Easily oxidized; and

▪ Higher exhaustion rate.

Sodium dithionite (hydro) is very sensitive to atmospheric oxygen in air and temperature.

Due to the exothermic nature of decomposition, it accelerates with a rise in temperature. The stock

solution is kept at a lower temperature and covered to prevent air. The stock solution with higher

hydro to caustic ratio is prepared separately and diluted with a caustic solution to bring it to a 1:1

ratio before it is fed into the trough. The volume of a trough is important as it affects the

decomposition of hydro [61]. Oxidation can be done either with hydrogen peroxide and sodium

metanitrobenzene sulphonate. Sometimes two oxidation steps are required for dye which has slow

oxidation rates or difficult to oxidize [57].

The reduction clearing step can be combined with the reduction step of vat and dyes used

to dye the cellulose component of the blend. For the two-bath dyeing process using

disperse/reactive system, the reduction clearing process is done as a separate step after disperse

dyeing to achieve excellent fastness properties [9]. In the case of vat dyes, oxidation and washing

of dyed materials are performed. For other dye classes such as reactive, direct and disperse,

washing off of unfixed dyes are carried out [61].

3.8.2 Batch dyeing of polyester/cellulosic blends

Figure 3.5 shows the commonly used dye system for batch dyeing of polyester/cellulosic blends

along with their color fastness properties and dyeing times [87]. The disperse/reactive although it

provides good fastness properties required much longer dyeing time than the disperse/direct and

disperse/vat system. The disperse/vat system is usually restricted to high end products that require

excellent fastness properties which are not usually achievable with disperse/reactive system. The

high cost of the vat dyes restricts their application to specialized products only [87].

94

Figure 3.5: Batch dyeing system for polyester/cellulosics blends.

3.8.2.1 Disperse/reactive system

PES/CELL blends can be dyed by batch process using a variety of methods. These methods are

described as follows.

Two bath method:

This is the traditional and standard method of dyeing PES/CELL blends. It allows optimum

fixation conditions for reactive and disperse dyes that provide good color yield and excellent

fastness properties. The polyester and cellulosic portions of the blends are dyed in two separate

baths. The Polyester is dyed first at 130-135 oC for 30-60 minutes followed by reduction clearing.

The cellulose portion of the blend may be stained by disperse dye thus affecting the reproducibility,

washing, and crock fastness. Reduction clearing is employed to remove the stain using sodium

hydrosulfite and alkali. The dyeing is then rinsed, and the cellulose portion is dyed with reactive

dyes for 45-60 minutes at 60 or 80 oC depending upon the reactive dye. This is followed by soaping

and washing to remove the hydrolyzed dye. This method gives excellent fastness properties.

However, the process is very time-consuming and consumes higher water and energy. The total

dyeing time required is around 9-10 hours [7, 87, 111]. No special disperse and reactive dye

selection is required for this method as all the dyes that are used for batch dyeing process are

suitable [87].

disperse/reactive

highColour Fastness

Dyei

ng

pro

cess

tim

e(h

ou

rs)

2

disperse/

4 direct

6

8

10

12

disperse/

vat

moderate

95

The two-bath method can be modified to reduce the dyeing time to 7-8 hours. This is

achieved by omitting the reduction clearing process. The polyester is dyed first with disperse dyes

and the dyebath is dropped. The dyeing with reactive dyes is then carried out in a separate bath

followed by rinsing and soaping. The reactive bath also serves as an alkaline clearing bath for

disperse dyes. This method is preferred for package dyeing and in cases where the stock tank is

not available [87].

Reverse two-bath method:

In this method, cellulose is dyed first with reactive dyes followed by dyeing of polyester with

disperse dyes. The higher temperature of disperse dyeing (130 oC) will serve to remove the unfixed

reactive dye. The separate washing and soaping are thus eliminated. However, not all reactive dyes

are suitable due to the saponification of dye fiber linkage under high temperature (130 oC) and

acidic conditions (pH 4.5-5). The reactive dyes which are most suspectable to this form ester bonds

(substitution type) with a hydroxyl group of the cellulose. Suitable buffer such as monosodium

phosphate can be used to prevent this problem [111]. Since reactive dyes are destroyed by

reduction clearing so this process cannot be performed. The disperse dyes must be selected that

show minimum staining of the cellulosic component. This process is shorter than two bath process

and saves water and time thus allowing more productivity. The total dyeing time is reduced to

about 7 hours [7, 87].

Type of alkali used for reactive dyeing should be such that it would not create effervesce

when pH is reduced for disperse dyeing so bicarbonates cannot be used. This necessitates the use

of either caustic soda, trisodium phosphate or sodium silicate. Scarlet and red colors can be easily

dyed with this method. For tertiary shades that require shading are dyed by conventional methods

as the cellulose portion is the one in which shade is adjusted according to target color [57].

One bath two stage method:

This method is very popular due to the shorter process. The Glauber's salt is added first at 60 oC

followed by the addition of dyebath auxiliaries. The dyebath pH is adjusted to pH 4.5-5.5 with

acetic acid. Disperse and reactive dyes are then added, and the temperature is raised to 130-135

oC. The dyeing is carried out at 15-30 minutes. The temperature is then dropped to 80 oC and pH

is adjusted with alkali to dye the cellulosic component with reactive dyes for 45-60 min. This is

96

followed by rinsing and soaping [64, 87]. The disperse dye selection is important as disperse dye

dispersion may not be stable under a large quantity of salt. The reactive dyes selected must be

stable under acidic conditions at a higher temperature. Since no reduction clearing is possible the

disperse dye should not stain the cellulose component and must be easy to wash-off. This requires

specialized disperse dyes which can be saponified at 80 oC with soda ash [7, 64].

In the modified one bath two stage process, the disperse dye is added first to dye the

polyester component under acidic conditions at 130-135 oC for 15-60 minutes. The dye bath

temperature is then dropped to 90 oC and salt is added. The temperature is then further reduced to

the dyeing temperature and reactive dyes are added. The dyeing process is carried at 80 oC or 60

oC depending on the reactive dye for 30-45 min. This is followed by rinsing and soaping. This

process allows common or Glauber’s slat to be used [87]

One bath method:

Reactive and disperse dyes can be applied to polyester/cellulosic blend by one bath method. The

bath pH is adjusted to 9-9.5 and the dyeing temperature is raised to 130-135 oC with simultaneous

fixation of both reactive and disperse dyes. The process is simple and less time consuming as

compared to the conventional two-bath process. Not all reactive and disperse dyes are suitable for

this method. Therefore, proper dye selection of reactive and disperse dyes are required as dye yield

is effected at compromised pH [7, 64].

3.8.2.2 Disperse/direct system

This is the simplest of two dye system used for the dyeing of polyester/cellulosic blends. The

dyeing is the shortest of all the dye systems currently applied and but the fastness properties are

moderate especially in dark shades as shown in Figure 3.5 [85, 87]. As compared to

disperse/reactive system many advantages can be obtained with this system. These are

significantly reduced dyeing times, less quantity of salt is required, less labor-intensive due to one

bath one stage process and uniform dyeing. The main disadvantage associated is the restricted

range of brighter shades as compared to reactive dyes [69, 122].

The disperse and direct dyes can be applied to polyester/cellulosic blends by one bath or

two bath process [57]. One bath provides a cheaper and simpler process [9]. Considerable savings

in water, steam, electricity, and labor along with increased productivity is obtained [124].

97

One bath method:

Dyeing by one bath is performed by either one or two-stage methods. In one bath one step process

all dyebath chemicals and dyes are added and bath temperature is increased to 130 oC. The dyebath

pH is maintained at 5-5.5 with acetic acid. The bath is then cooled to 80 oC for the exhaustion of

direct dyes and dyeing is continued until target depth is achieved. For some black direct dyes (C.I.

Direct Black 22) the pH needs to be adjusted to 9-9.5. Direct dyebath serves as a soaping bath for

clearing of disperse dyes. This is followed by cold rinsing and after treatment. The dyeing time

required varies from 3 to 4.5 hours [7, 9, 87, 125].


During this method high temperature stable direct dyes are added along with the disperse dyes.

The polyester is dyed first at high temperature (130 oC). The temperature is then reduced to 80 oC

and electrolyte is added. The dyeing process is then carried out for direct dyeing. The traditional

reduction clearing process is not suitable due to the instability of direct dyes [86]. The cycle time

is slightly longer requiring 3.5-5 hours. The process is suitable for package dyeing in dyeing

difficult shades and processes requiring a large quantity of salt (longer liquor ratios). The dye

selection is important as all direct dyes are not suitable for one bath process [7, 9, 125]. The dyes

used are mainly self-leveling or salt controllable disazo multisulphonated dyes [9]. Staining of

cellulose by disperse dyes is not problematic for lighter to medium shade depths. However, for

darker shades, special approaches may be used to destroy the disperse dye stain. In the first

approach, silicone-based chemicals are used in resin finishing that liberates hydrogen. In the other

approach, the mild reducing agent is used and treatment is performed 70 oC under alkaline

conditions after cationic after-treatment [69].

Two bath method:

In the traditional two-bath method, the polyester and cellulosic portion are dyed separately with

intermediate reduction clearing. The polyester is dyed at 130 oC followed by reduction clearing to

remove the disperse dye stain. This is followed by neutralization. Direct dyeing of cellulosic

component is then carried out at 90 oC. For pale shades, the reduction clearing process can be

omitted. The two-bath process provides better fastness due to the intermediate reduction clearing

98

step. A large selection of direct dyes is available and moderate to good fastness can be achieved.

This method, however, requires longer cycle time [7, 9, 85].

The cellulosic component dyed with selected direct dyes can be post-treated to obtain

adequate fastness properties. Cationic fixing agents or resin finishing can be employed [125]. The

fastness of disperse dye may be affected by resin finishing and must be checked [86]. Leveling

and dispersing agents are seldom used. It is recommended that they should be electrolyte stable

especially for one bath process [75].

3.8.2.3 Disperse/vat system

The batch dyeing with disperse/vat system is usually carried out for package dyeing of yarns. They

can be applied by both one bath and two bath methods. The main advantage of this system is that

the reduction bath requires for vat dyeing also perform reduction clearing of disperse dyes [85].

In one bath method, both disperse and vat dyes are simultaneously applied from the same

bath. The disperse dyes are fixed in the first stage in the acidic medium followed by reduction and

oxidation of vat dyes in the second stage. The vat dyes should be in a fine state of dispersion to be

suitable. The IK type vat dyes are not preferred as they required a lower temperature of 30 oC after

vatting for fixation. The vat and disperse dyes are applied along with the dispersing and wetting

agent. The dye bath pH is maintained at 4-5. The temperature of the dyebath is increased to 130

oC. The heating rate needs to be carefully controlled and should be in the range of 1.5-2 oC/min to

avoid unlevelness. The dyeing is performed for 60-90 mins depending on the depth of shade

required on the polyester component. This also causes pre-pigmentation of the cellulose

component with the vat dyes. The temperature is then reduced to 80 oC and sodium hydrosulfite

and caustic soda are added for the reduction of vat dyes. The reduction of vat dyes and reduction

clearing of disperse dyes occur simultaneously. The dyeing is continued for 30-45 minutes. To

prevent the over-reduction of some vat dyes, sodium nitrite is added. The fabric is then rinsed

followed by oxidation and soaping. The oxidation is carried out using hydrogen peroxide at 50 oC

for 10-15 minutes. The soaping is usually performed at a boil for 10-15 min using detergent [7,

81, 85].

The two-bath dyeing method is used for dark shades. Disperse dyes are applied first, the

dyeing temperature is then reduced, and vat dyes are added. The reduction bath for vat dyes served

99

as a reduction clearing bath for disperse dyes. The method provides better vat dye stability and

fastness properties than one-bath method [7, 87].

3.8.2.4 Disperse/sulfur system

The use of this system is limited for the dyeing of certain dark shades such as dark browns, navy

blue, and blacks [7, 85]. The main drawbacks associated with this system are [85]:

▪ Damage of polyester component due to large quantities of reducing agent at high

temperature;

▪ Long dyeing process;

▪ Damage of cotton component due to residual sulfur; and

▪ Environmental problems due to a reducing agent.

They can be dyed by both one bath dyeing and two bath dyeing methods similar to vat dyes [7].

3.8.3 Continuous dyeing of polyester/cellulosic blends

The continuous dyeing is the most common method of dyeing woven polyester/cellulosic blends.

Due to differences in the dyeing properties of each fiber in the blend two dye system is usually

used. The disperse/reactive and disperse/vat combinations are the most common dye system

applied to these blends by continuous process [9].

3.8.3.1 Disperse/vat system

Earlier dye system used for the coloration of polyester/cellulosic blends was based on disperse and

vat dyes. The continuous chemical pad-steam dye range was developed in 1944 for dyeing with

vat dyes preliminary to fulfill the demand to dye large quantities of uniforms to uniform shade [61,

126]. To ensure trouble-free pad-steam process it was recommended to consider the following

factors [126]:

▪ The temperature of the pad liquor, as high temperature may lead to instability of dyes

and chemicals.

▪ The distance between the padder exit and steamer inlet. The reducing agent may

prematurely decompose due to exposure to air.

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▪ The presence of air in the steamer. This may cause the decomposition of the reducing

agent.

▪ Steamer roof and inlet heating to prevent condensation drops.

The thermosol process which was introduced for polyester dyeing with disperse dyes in

the 1950s was subsequently applied to polyester/cotton blend [61, 127, 128]. It was suggested to

consider the following points in the dyeing of polyester/cotton blends [127]:

▪ It is better to dye the polyester portion first with disperse dye as shade control is easier.

▪ In the dyeing of disperse/vat system, the economical process at that time, some vat dyes

tend to fix into the polyester during the thermosol process. Thus, creating problems in

shade matching.

▪ Due to shrinkage problems of fabric during disperse dyeing, it was suggested to heat

set on the stenter before the thermosol process.

▪ Disperse dye gave less color yield during thermofixation due to alkali in the dye pad.

In initial studies carried out for dyeing of polyester/cotton blends, it was recommended to

use vat dyes by the pad-steam process for pale shades, disperse dyes by a thermosol process for

medium shades and vat-disperse combination for dark shades. The fabric was dyed first with

disperse dyes by pad-dry-thermosol process and then vat dyes are applied by the pad-dry-chemical-

pad-steam process [129, 130]. A more economical approach was later used to apply both disperse

and vat dyes from the same bath. The selected vat and disperse dyes were padded together along

with the anti-migrating agent followed by infrared drying. The thermofixation process is carried

out at 200-210 oC for 60-90 seconds. The fabric is then chemically pad with hydro and caustic

followed by steaming at 105 oC for 25-40 seconds. The fabric is then oxidized, soaped and dried

[130-132]. This approach had problems as some of the vat dyes were fixed to the polyester portion

of blend this creating a shade matching problem [127]. To counteract this problem, it was

suggested to keep the thermosling temperature around 190 oC. At this temperature, the diffusion

of vat dyes in the polyester was found to be lower. Although the fixation of disperse dye was also

lower at that temperature but shade matching problems were avoided. At higher temperatures

during thermofixation, some vat dyes may aggregate and cause dulling of shade and specky

dyeing. To rectify this problem, it was recommended to carry out the chemical pad-steam process

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at 107 oC. Furthermore, to avoid migration, approximately half of the applied pad liquor (30-40%)

needed to remove by infrared drying [133]. As the disperse dyes require reduction clearing to

achieve good fastness properties, the reducing pad-steam method used to convert vat dyes into

their leuco form was also utilized for the clearing of the disperse dyes on the polyester surface

[128]. The advantage of this process was good fastness properties, dark shades can be dyed easily,

availability of a wide selection of dyes and the possibility of producing a cross-dyeing effect. The

limitations were dull shades and crock fastness problems in dark shades [130-133].

In the early 1960s, selected vat dyes from the Indanthrene range were selected and marked

as Polyestren. They can give the same depth of shade on polyester/cotton but there was a limit on

the color depth that can be achieved. For dark colors, a mixture of vat and disperse dyes were

required [134]. In the 1960s the largest and well-established dye system used for continuous dyeing

of polyester/cotton blend was based on disperse/vat combination. Although reactive dyes were

available but at a higher cost of dyeing dark shades with disperse/reactive system, disperse/vat

system was recommended. Different configurations of padder were used. Pre-drying was carried

out using either can driers or infrared chambers. For thermofixation, gas-fired ovens with top and

bottom rollers were used [131].

Disperse/vat dyes are currently applied to polyester/cellulosic blends by a pad-dry-

thermosol-chemical pad-steam process. Light to dark shades with excellent fastness level is

obtained by this process. Both disperse dyes and vat dyes are applied from the same pad liquor

under acidic conditions (pH 5.5 with acetic acid) along with wetting agent and anti-migrating

agent. In the first stage, disperse dyes are fixed by thermofixation at 200-220 oC. In the second

stage, pad-steam development of vat dyes is performed where vat dyes are first reduced and then

oxidized to complete the fixation process. The fabric is padded with hydro and alkali and is then

steamed for 60 seconds at 102-105 oC using saturated steam. The alkali and hydro in the steamer

destroy the unfixed disperse dye. The water seal and first two washing units kept at 40 oC remove

the caustic to lower the fabric pH before the oxidation process. Oxidation is then performed in

subsequent washing units at 60 oC by feeding peroxide and occasionally acetic acid. The pH is

kept at or below 9 to avoid the problem of greener and duller shade of indanthrone blue dyes due

to higher pH in the oxidation process. The removal of caustic is more problematic in heavier

fabrics and it is found that in a typical vertical washing unit caustic removal is more at the sides as

compared to the fabric center. This may cause width wise shade variation. Proper feeding of

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chemicals across the width can help to solve this issue. The remaining units are for soaping and

washing off at 95 oC. After washing fabric is dried on drying cylinders [61, 113].

3.8.3.2 Disperse/reactive system

In the late 1950s and earlier 1960s, the continuous dyeing of polyester/cotton blend was mostly

carried out by disperse/vat system. With the introduction of reactive dyes, disperse/reactive dyes

have become common [61, 130]. The continuous dyeing with disperse/direct dyes can be carried

out by both one and two bath methods. During the two-bath process, the disperse dyes are fixed

on a polyester component by thermofixation. This is followed by an intermediate reduction

clearing process. The reactive dye fixation is then achieved on the cellulose component by pad-

dry chemical pad-steam process.

For one bath process, either one bath two stage or one bath one stage methods can be used:

▪ In one bath two stage method, the fabric is padded with disperse and reactive dyes. The

disperse dyes are fixed by thermofixation. The fabric then padded with alkali followed

by steaming to fix the reactive dye [85, 113].

▪ During one bath one stage method, the fabric is padded with disperse and reactive dyes

along with alkali followed by simultaneous fixation of both dyes [85, 113].

Two bath method:

During the two bath the disperse and reactive dyes are applied in two separate stages. The reduction

clearing process is optional and can be performed depending upon the fastness requirement and

depth of shade. This method is very time consuming is restricted to dark shades where excellent

fastness properties are required. The first stage involves the dyeing of the polyester component

with disperse dyes by the pad-thermosol process. The process involves padding, drying, and

thermosol treatment. During the second stage, the cellulose component of the blend is dyed. The

dyeing of cellulose component can be carried out by a various method that includes pad-thermofix,

pad-steam, pad-dry-chemical pad-steam or pad-moist (Econtrol) process. The dye material is then

rinsed and soaped at boil [135].

During the pad-thermofix process, the fabric is padded with reactive dyes along with urea,

alkali and anti-migrating agent. The fabric is then dried and thermofixed at for 1 minute at 150 C.

The exact duration and temperature of fixation depend on the type of reactive dye used. The main

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disadvantage associated with this process is the excessive urea fumes. These fumes cause white

resist marks on fabric requiring frequent cleaning of the machine. Not all reactive dyes are suitable

for this method [135].

Pad-moist or Econtrol is a specialized process that requires specialized thermosol unit to

carry out fixation of reactive dyes at 120-130 oC in 25-30% relative humidity. The thermosol unit

is supplied with a steam injection unit to maintain the required relative humidity inside the

thermosol unit. This process is environmentally friendly and requires fewer chemicals and no urea.

This method provides good color yield and fastness properties [135].

Pad-dry-chemical pad-steam is a classical continuous method with reactive dyes. The

process gives excellent fastness properties and bright shades. This process is not suitable for

shorter runs and requires large quantities of salt [135].


The application of disperse/reactive dyes is carried out by pad-thermosol-chemical pad-steam

process. This is an economical and energy saving process as compared to two bath process. This

process is mainly used for medium to dark shades. The process gives good dye yields and good

appearance of the fabric [113].

During this process, the fabric is padded with disperse and reactive dyes along with anti-

migrating agent, wetting agent, mild oxidizing agent and dispersing agent under slightly acidic

conditions (pH 5.5 with acetic acid). The fabric is then pre-dried using an infrared dryer followed

by drying at 110-130 oC. The thermofixation of disperse dyes is carried out at 200-220 oC for 60-

90 seconds. In the second stage, the fabric is padded with salt, sodium hydroxide and sodium

bicarbonate followed by steaming at 102-105 oC for 60 seconds using saturated steam. The

steaming process under alkaline conditions also serves to clear the disperse dye. The fabric is then

rinsed, soaped and neutralized followed by drying [113].

One bath one stage method:

This is an economical and environmental method for dyeing PES/CELL blends. Several attempts

have been carried by dye manufacturers to develop a suitable one-bath method. As reactive dyes

can be fixed with pad-thermofix process, the one-bath process was attempted to use thermosol

phase for fixation of both disperse and reactive dyes to PES/CELL blends. The main challenge

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associated with a suitable one-bath method is differences in dyeing conditions required for disperse

and reactive dyes as shown in Table 3.10 [136].

The one step theromosol process is recommended for the dyeing of mercerized PES/CO

woven and PES/CV blends with at least 50% polyester. Good pad liquor stability and

reproducibility acan be obtained in this process. The fastness properties are inferior as compared

to one bath two stage. This method is restricted to pale to medium depths. This process is shorter

and economical. However, the dye selection is limited due to compromised fixation conditions

[85, 113].

Table 3.10: Dyeing properties of reactive and disperse dyes [136].

Reactive dyes Disperse dyes

Applied to cellulose Applied to disperse

Alkali required to fix the dye Sensitive to alkali (reduction in color yield)

pH 10.8-13.5 pH 4-6

Sensitive to reduction Reductive clearing is necessary to achieve

excellent fastness properties

Fixation of damp goods (moist conditions) Fixation of dry goods

Cotton yellows at elevated temperature Fixation at elevated temperature (200-200 oC)

The fabric is padded with disperse and reactive dyes followed by simultaneous

thermofixation of both dyes under milder alkaline conditions [85, 113]. The dye liquor consists of

wetting agent, ant-migrating agent, urea, dicyandiamide, and sodium bicarbonate. The reactive and

disperse may interact with each other and dyebath auxiliaries such as urea and dispersing agent.

The dicyandiamide is added in especially in dark shades. The use of dicyandiamide creates a

challenge because of its availability and lower solubility. Since cotton may yellow at high

temperature and under alkaline conditions borax may be added in the dye bath. The liquor

temperature is kept at 20-30 oC. The pickup is usually set at 60-65% followed by infrared drying

to 50% residual moisture before the final drying is carried out at 110-130 oC. Thermofixation is

carried out at 210-220 oC for 60 seconds. The fabric is then washed by a special wash-off process

to optimum fastness properties. During washing the fabric is soaped at boil under alkaline

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conditions first followed by soaping without alkaline. The fabric is then rinsed, neutralized and

dried [113, 136].

Recently Dystar in collaboration with Monforts developed a new one-bath process known

as Econtrol T-CA. This process is based on the already established Econtrol process used for

reactive dyes [136]. The main advantages associated with this process are [136]:

▪ Good degree of fixation of reactive dyes as compared to the standard process;

▪ Good color yield of diperse dyes;

▪ No yellowing of cellulosic fibers;

▪ Good fastness properties that meet the customer requirements without reduction

clearing;

▪ Wide range of shades; and

▪ All necessary dyebath chemicals and dyes can be applied from one-bath.

Only specialized reactive dyes with medium to high reactivity and disperse dyes are

suitable by this process. These dyes provide excellent color yields under the Econtrol T-CA

fixation conditions. The shades up to 30 g/l can be produced with good fastness properties. The

fabric is padded with reactive and disperse dyes along with wetting agent and anti-migrating agent.

Sodium carbonate along with the buffer is used to maintain alkaline conditions. The fabric after

infra-red pre-drying is dried at 110-130 oC under 25-30% humidity. This is followed by thermosol

treatment at 190-215 oC for 60-100 seconds. The fabric is then rinsed and soaped at the boil to

achieve good fastness properties [136].

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CHAPTER 4 PRACTICAL PROBLEMS IN THE COLORATION

OF TEXTILE FIBER BLENDS

4.1 Introduction

Fiber blends have been dyed for a long time and despite many developments in the process,

including dyes, chemicals, and machinery there are still challenges and problems in their dyeing

process [57]. In addition, although the dyeing process is properly controlled and required

procedures are properly implemented and the plant is efficiently managed issues still arise [10, 11,

137]. The occurrence of faults in the dyeing process is an ongoing concern for all those who run a

dyehouse. The nature of faults may vary from one dyehouse to another. It is the attitude and

approach towards process control and eradicating defects that differentiates one dyehouse from

another [138].

The estimates of fabric quality levels produced in typical dyehouse are given in Table 4.1

[139]. The finished fabric produced by a dyehouse can be grouped as whites, dyed and printed

material. These are just estimates and vary with the material type being processed. A fabric with

minor faults may still be marketable at reduced cost depending upon the severity of the fault. Major

faults, on the other hand, are often sold at a lower tier quality [140]. Due to the increased demand

to maintain product quality standards, the importance of recognizing faults and a means to resolve

such issues is increased. The product quality level that may have been considered salable a few

years ago may not be acceptable by consumers today [141].

Table 4.1: Typical finished fabric quality levels [139].

Finished fabric Fresh % Minor fault % Major fault%

White 95-98 2-3 up to 3

Dyed 92-94 4-5 up to 5

Printed 85-90 5-8 up to 10

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In the current global competitive environment, there is added pressure on the dyehouse to

make the dyeing processes more competitive [142]. To meet the customer's requirements and make

a profit, low fault levels and high-quality productions are required [141]. The profitability of

dyeing blends, like any other dyeing process, is based on three parameters: quantity, quality, and

cost [64]. This necessitates a review of the process as well as cost reductions wherever possible

[142]. To make any dyehouse profitable the reprocessing and amount of faulty materials must be

minimized. The use of appropriate processing techniques can avoid the generation of faulty

materials. This can result in savings due to reduced reprocessing and increased production of new

materials [143].

Over the years, the textile industry had achieved drastically higher productivity gains

mainly by reducing processing times. However, the lots that are processed under increased time

constraints can lead to complaints either due to not meeting the requirements or having insufficient

quality. Generally, companies maintain a record of costs associated with customer complaints and

waste at the final inspection stage. However, the costs that may incur due to reprocessing and

laboratory trials associated with fault identification and rectification are often not recorded. These

costs influence the final turnover (profit) of the company. Table 4.2 shows the dyeing process costs

associated with not meeting the target [144]. Faulty articles cost the same to produce as the right

quality articles but have a lower market value. To repair such faulty products requires certain

procedures that incur cost and may also have a lesser chance to meet the required target [138]. To

achieve optimum profits, the production and reprocessing costs should be minimized [145]. The

key steps in this direction are the process reproducibility and the reduction of dyeing times [142].

Table 4.2: Dyeing costs associated with not meeting the specifications.

Process Cost Productivity Profit

Blind dyeing 100 100 100

Small addition 110 80 48

Large addition 135 64 -45

Strip and redye 206 48 -375

108

To make the operation of dyehouse profitable, it is important to set certain targets. The key

performance indicators of dyehouse are given below [143]:

▪ Dyeings match the target shade within a given tolerance range and are uniform.

▪ High levels of right-first-time dyeing without any additions (> 95%).

▪ Minimum percentage of rejects attributed to different processing operations (< 2.5%).

▪ Shortest possible processing time (< 4 hours)

▪ Proper monitoring of the water and energy consumption and nature and quantity of

effluent production (efforts to reduce water and energy consumption and effluent

production).

▪ Meeting production targets (total quantity and ratio of products).

▪ A proper definition of responsibilities and management structure.

Since a dyehouse involves highly technical operations having a good laboratory is

necessary to provide technical services and training facilities for production personnel. Good plant

layout and production planning are essential to obtain good workflow and avoid bottlenecks.

Future changes in demands and product diversification must be considered when the plant is being

set up. With the increasing pressure due to cost and environmental reasons older machines may be

replaced with new machines whenever possible. Regular audits of the plant are also necessary to

monitor water and energy consumption. This provides the possibility of reducing processing costs.

The standard procedures that are documented in manuals must be made available to all production

personnel [143].

The first prerequisite to eradicate faults is management commitment which then trickles

down to the entire team. Some signs that show a lack of management commitment include lack of

resources, unrealistic product requirements, and poor communication between marketing and

manufacturing [138]. In any dyehouse not meeting the targets may be attributed to [138, 143]:

▪ Shortage of resources;

▪ Lack of knowledge;

▪ Scarcity of skills;

▪ Improper attitudes; and

▪ Lack of management commitment.

109

4.2 Troubleshooting faults in coloration

In order to troubleshoot faults it is important to first define faults so that the concerned personnel

have the same understanding of what constitutes a fault. A fault is an imperfection that may negate

or reduce the value or serviceability of the product. It may be something undesirable or an

imperfection or a deficiency [100, 141, 146].

Several approaches that can be used to classify faults are given in Table 4.3. In terms of

diagnosis, the most useful approach is to classify faults based on their origin. Thus, the processing

stage/or stages responsible for generating faults can be identified accordingly [100, 114].

Table 4.3: Classification of faults.

Types Description

Major and minor [100]

Minor faults have a slight effect on meeting the intended

requirements and can be corrected.

Major faults make the product unfit for the intended end-use.

Visible and hidden

[100, 146]

Visible faults are immediately recognizable while the hidden fault

can only be detected during use or through testing.

Aesthetic and

functional [146]

Aesthetic faults are deviations from the target specification in

terms of appearance, hand, and other visible differences.

Functional faults are related to not meeting the required end-use

properties.

Origin based [17, 100,

114]

The faults are identified based on the process stage responsible for

the fault, e.g., weaving faults, spinning faults.

Many faults in fabrics are only visible after the dyeing process. The slight variations in

intensity or hue can easily be detected and can adversely affect the aesthetics of the dyed materials

[114, 138]. In order to produce a satisfactory high-quality product at a competitive price, faults

must be eliminated. There is always a cost associated with a fault when the product does not meet

the intended requirement [100, 138]. The faults also include quality concerns raised during the

preceding processes and provide an improvement opportunity in the coloration process. Faults,

110

depending on their severity, either can be reworked or result in selling the product as seconds. The

reworking process will increase the cost of the product [141].

The troubleshooting process can be considered analogous to the criminal investigation

process [147-150]. An expert acting as a detective is responsible for determining the root cause of

the fault. The level of expertise associated with troubleshooting faults varies among experts. A

dyehouse expert, however, must possess the necessary skills to troubleshoot and eradicate the

defect. This requires proper understanding and knowledge of the process and raw materials

involved. Proper troubleshooting requires a proper approach to solving the problem more

effectively and efficiently [141, 149, 150]. A successful troubleshooter possesses three attributes

that include high curiosity, diversified experienced background, and good communication skills.

Having high curiosity inclines a troubleshooter to explore causes of faults. Having a broad

background allows effective determination of the cause and effect relationship and possessing

good communication skills leads to the organization of thoughts, asking questions and hearing

answers objectively [137]. It is important to note that two faults that may have a similar appearance

can be caused by different sources and in different ways. Thus, each fault should be investigated

based on its own characteristics and specific circumstances. A fault that is produced in one mill

may not necessarily be exactly reproduced in a different mill [138, 151]. However, fundamental

knowledge and techniques can be applied to mill specific faults [138].

The systematic investigation process requires at least four steps. Firstly, the data is gathered

through visual evaluation and a series of questions and answers specifically related to the fault.

This includes specific details about the current and preceding processing stages, chemicals and

process parameters used, time and shift when this fault occurs and fault trend. Secondly, a

hypothesis is developed using a list of probable causes related to the fault. Thirdly, experiments

may be performed to test the hypothesis. This requires laboratory analyses of the fault and attempts

are made to synthesize the fault based on the probable causes. This serves as a verification of the

causes. Lastly, the results obtained after analyses are interpreted to determine the exact cause of

the fault [137, 146-148, 152].

Figure 4.1 shows a typical troubleshooting process for a dyeing fault. The main goal of a

troubleshooting process is to investigate the causes of faults, determine their solutions and steps

taken to avoid them in the future. The nature and cause of the faults must be properly investigated

[143].

111

Figure 4.1: Fault investigation process in a dyehouse.

The visual assessment of faulty fabric is done to determine the relationship between fabric

appearance and causes of the defect [152, 153]. Assessment is carried out to ascertain [153]:

▪ Nature of the fault’s appearance - periodic or sudden, size, directionality, start and

endpoint location;

▪ The actual appearance of the fabric - color change, differences or changes in fabric,

yarn differences as compared to the non-faulty area.

Common faults can easily be traced by a careful investigation. The source of coloration

faults can be traced to preceding processing stages or even to raw material [147]. Other

investigations to narrow down the origin of defects may only be possible after visual assessments

[153]. Although the probable cause of faults can be large in number, the likely sources can be

shortlisted through the process of elimination. To prevent fault from happening again, it is

important to determine the exact cause of the issue [147, 152]. If the appearance of the fault is not

direction biased, it may be attributed to the pretreatment or dyeing processes. If further

investigation is required, the fabric may be stripped and redyed. If the fault reappears it may be

attributed to yarn or fabric related issues [153]. The faults confronted in a dyehouse can be

analyzed from three dimensions [140]:

Detective work

Processing details

Quality control records pertaining to the defective batch

Visit of production site

Expert or senior personnel

Experience

Working knowledge

Specialization

Specialized laboratory

Specific instruments and methods

Time

Cost

fastness

RFT Practical dyeing know-how

compatibility

shade constancy

DYEHOUSE EXPERT

112

▪ Faults produced in the dyehouse;

▪ Faults identified in the dyehouse due to causes from preceding steps; and

▪ Faults from preceding stages but can be covered-up in the dyehouse.

Troubleshooting faults is multifaceted for many reasons. Firstly, current industrial

coloration processes include many processing elements, such as preparing dye recipes, dyeing

process, and washing off, which can introduce faults. Process inputs such as fabric or yarn, water,

dyes, and chemicals can also introduce faults. Another problem with faults is that often they are

only observed after several succeeding operations and many do not appear in the same process

step where they were created [141].

Generally, the dyed fabric is inspected for any faults in folding or cut for sewing. This

implies faults in the fabric may not be observed until the final stages of processing. This strategy

lacks the target of preventing defects from occurring in the first place. A yarn fault, for example,

may not be observed when the yarn is dyed but may be detected when the yarns are converted into

fabric. Additionally, faults can occur within the product development cycle that starts with

laboratory dyeing and goes through bulk dyeing in a plant. Each stage may introduce faults and

their removal at the initial stages does not guarantee fault free processing at the later stages[138,

141].

Moreover, a fault may occur randomly from time to time. Also, the same type of fault may

have many causes and their occurrence may be different from the others. As mentioned earlier,

faults can occur due to a variety of reasons and may be classified according to their origin [143].

Faults may originate from fiber, yarn, fabric, water, preparation, dyes, dyeing methods, or

machines. Faults can be machine-related and may be attributed to the inherent design limitations

and capability of devices [141]. For instance, the following examples illustrate different origins of

unlevelness [143]:

▪ If only observed on one type of fabric, the cause may be associated with the particular

fabric or it’s pretreatment.

▪ If seen only on one machine the likelihood may be a machine related fault.

▪ With a particular processing method or dye, the fault is likely caused by an inadequate

processing method or wrong dye selection.

113

▪ If only noted among material from a given shift, the case may be associated with the

personnel involved.

All these factors make the troubleshooting process quite complex in nature. A formally

structured troubleshooting system protocol will give a more accurate, rapid and cost-effective

solution to a problem as compared to a random unstructured or empirical approach that is more

resource and time-intensive. Determining a true cause may require testing a number of possible

causes. It is quite possible that if the dyehouse expert is analyzing the other causes to solve the

problem, the actual conditions which have caused the problem might have changed accidentally

or by chance. Thus, the effort required to solve the problem may be duplicated. The problem may

not be completely resolved and may reoccur in the future. Formal problem-solving methods are

cost-effective and efficient as compared to random hit and trial methods [141].

A troubleshooting protocol is a reactive program that is used when faults occur in the

process and need to be eliminated. In order to prevent a fault from occurring in the future, a

proactive program is required in which information obtained from the troubleshooting system can

be used. So, the latter system complements the former method [141]. The most effective

troubleshooting strategy is one that will not let faults to happen in the first place [11].

Troubleshooting protocols may consist of the following elements [141]:

▪ Standard operating procedure for problem-solving;

▪ Identification of faults in the process and key process elements;

▪ Practical knowledge and fundamental understanding of the process. Identification of

key process parameters. Consideration of actual workplace conditions is equally

important. This is the key element for the determination of cause and ultimately fault

elimination;

▪ Use of statistical techniques for identification of key factors, design of experiment and

data analysis; and

▪ An accessible computer database for data storage and workplace-specific problems and

experiences.

Controls in every stage of processing are required to prevent the occurrence of faults and

stopping them from going further until the issues are resolved. Thus, in order to reduce faulty

114

products, the responsible causes must be removed [138]. A proper diagnosis is the key to prevent

the reoccurrence of faults [140]. In that regard, there are four key areas to consider [138]:

▪ Recognition of specific faults and their causes;

▪ Preventing defects that occur in a dye house;

▪ Detecting defects from earlier stages; and

▪ Regulating variations in raw materials.

As indicated variations in a dyed product may be due to process or raw material variations

including the substrate. In order to control any process, it is important to ensure all the raw

materials remain constant in terms of their properties. This must be controlled first as processing

factors can be optimized. Hence, in order to optimize and control any process to produce defect-

free products the raw materials must be controlled first. Raw materials include substrate and

chemicals used in processing. For a substrate, it is important to know the defect levels from prior

processes and any residues that the substrate may contain from previous processes. It is important

to know the test methods to identify these residues and how to remove them. Residues may include

sizing reagents, knitting oils, alkali, surfactants, metal impurities, spinning oils, etc. The impurities

present in the chemicals and quality variations must also be determined. Dyes and other special

chemicals should be selected according to some prescreening criteria. Every lot of chemicals and

dyes received by the dyehouse should be tested [138].

The equipment selected for processing should be based on end-use requirements of the

product and fabric properties. Not all substrates can be processed on all equipment types and their

compatibility must be checked. The equipment should be properly maintained, and its limitations

should be known. Controlling the process requires a thorough understanding of the process. The

critical factors related to a process must be identified. Products requiring special care and controls

should be identified and required precautions must be properly implemented [138].

The relationship between the dyeing faults and the potential sources can be very complex.

This requires a deep understanding of each process involved in the manufacturing of the product.

The dyeing of blended materials can be done either in yarn, fabric or garment form. The raw

materials and preceding manufacturing stages standout as possible sources of faults as shown in

Figure 4.2 [17, 100, 114].

115

Figure 4.2: Cause and effect model for investigating faults in the dyed fabric.

4.3 Dyeing problems arising from the fiber

The fiber is a basic component of any textile product and plays a significant role in the making

and properties of a product as shown in in Table 4.4 [6, 154, 155]. The fiber characteristics are

selected based on the fabric requirements and differences between them can be a major source of

faults in a product [6]. Fibers can be natural or manufactured and are used to make a variety of

products, each with different properties. The dyeing properties of a substrate is influenced by the

chemical structure and molecular arrangement of the polymer molecules making up the fiber,

treatment conditions during growth or manufacturing, subsequent processing stages, yarn and

fabric formation, as well as preparation [114, 156]. Fibers can be natural or manufactured and are

used to make a variety of products, each with different properties. The dyeing properties of a

substrate is influenced by the chemical structure and molecular arrangement of the polymer

molecules making up the fiber, treatment conditions during growth or manufacturing, subsequent

processing stages, yarn and fabric formation, as well as preparation [157].

Raw material

Spinning

Winding

Warping and sizing

TEXTILEFABRIC

Make-upcutting

Finished goods

Weaving

Knitting Preparation

Coloration

Finishing

Direct effect

Indirect effect

116

Table 4.4: Relationship between fiber properties and spun yarn characteristics.

Fiber Properties

Yarn quality characteristics

Even

nes

s

Th

ick

pla

ces

Th

in p

lace

s

Nep

s

Hair

ines

s

Str

ength

Elo

ngati

on

Ap

pea

ran

ce

Dyea

bil

ity

Micronaire/fineness/diameter/ diameter

variability D D D D D D D D D

Maturity D D D D N D D D D

Length/length variability D D D D D D D D N

Short fiber content D D D D D D D D N

Strength N N N N N D D N N

Elongation N N N N N D D N N

Nep content I N N D N N N D D

Dust, trash content, vegetable matter I D I D N D D I N

Contamination/dark and medullated fibers N N N N N N N D D

Color/color deviation within lot N N N N N N N D D

UV value/UV deviation within lot N N N N N N N I N

D: direct relationship, I: indirect relationship, N: no relationship

The differences in dyeing properties of a substrate may be due to the variations in fiber

structure either due to the inherent properties of particular fiber, or changes occurring during

processing or the dyeing process. The chemical composition and structure of the fiber is often the

deciding factor determining the suitability of a dye for dyeing that fiber. The physical forces of

attraction and chemical reactions between fiber and dye determine the dye retention in the fiber.

However, due to the geometrical structure of fiber, the movement of the dye molecules to the

interior of the fiber can be restricted despite the attraction between the dye and the polymer. The

following factors affect the dyeing properties of textile materials [114]:

▪ The differences in the chemical structure of the fibers;

▪ The physical structure of fiber;

117

▪ Effect of pre-dyeing processes on fiber structure; and

▪ Fiber properties affected during the dyeing process.

The penetration of the dye inside the fiber is greatly influenced by the interaction between

the fiber and dyebath medium. Hydrophilic fibers that swell in water are best dyed with ionic dyes

while nonionic dyes are best suited for hydrophobic fibers. Some fibers that fall in between these

two categories can be dyed by both non-ionic and ionic dyes. The fiber swelling during dyeing

directly depends upon the molecular orientation or crystallinity [114].

The internal structure of fibers can be categorized into two broad areas. The area where the

polymeric molecules are arranged in a systematic order is termed as the crystalline region and the

area where there is no order is called the amorphous region. Textile fibers contain both amorphous

and crystalline regions. The ratio of these two regions affects the dyeability of the fiber [156]. The

relative proportion of these regions influences dyeing properties. Amorphous regions are more

accessible to dyes and liquids compared to crystalline regions [114, 156]. The degree of

crystallinity is affected by a variety of factors depending upon whether it is a natural or

manufactured fiber. For natural fibers, it depends on conditions during growth and in the case of

manufactured fibers, extrusion, and subsequent drawing and heat setting affect the crystallinity of

the material. Dyeing processes also affect the fiber structure, as the dyed or stripped fabric dye to

different extents compared to the undyed fabric. The fiber dyeability and the result of dyeing are

affected by the internal structure of the fiber since it controls the penetration and distribution of

dye molecules inside the fiber [156]. The fiber swelling during dyeing directly depends upon the

molecular orientation or crystallinity. This either changes the availability of functional groups or

their interaction with the dye. The physical properties of the fiber are also affected by the degree

of crystallinity [114].

The dyeing properties of natural fibers such as the nature of functional groups and the

permeability of dyes are difficult to control as they are often determined during fiber growth [114].

The dyeability of cotton fibers depends on a multitude of factors such as the area of growth, color,

natural fluorescence level, weathering history, maturity, and heating history. Table 4.5 shows the

factors along with their effect on dyeing behavior [158]. Cotton fiber contains different types of

impurities which can be classified as physical and natural contaminants. The amount of non-

cellulosic substances in cotton varies considerably from 3-12% depending on various factors such

118

as variety, growth area, environmental factors, maturity level, and agronomic factors. These

impurities include proteins, waxes, and minerals which may impart color and interfere in the

dyeing process. It is important to note that natural constituents such as neps and seed coat

fragments may also be considered as contaminants considering their effect on the quality of end

products. Every effort should be made to reduce the external impurities present in the fabric. The

metal constituents in cotton fiber can cause a serious problem in preparation, dyeing, and finishing

if present in large quantities. Metals may be introduced from different sources such as soil

conditions, and harvesting aids [158, 159].

Fiber maturity is one of the most important quality parameters. It has a strong effect on

processing behavior and dyeing properties. Matured fibers have fully developed cell walls in

contrast to immature fibers which have thinner cell walls. This may be caused by insects, plant

disease, drought, bad weather, and premature harvesting. The dye uptake of immature fibers is

lower than that on mature fibers. After dyeing, these fibers may appear as white or light-colored

specks on cotton or cotton blend fabrics. Areas of fabric may have a lighter color which can cause

shade variation if the distribution of immature fiber is not uniform. These fibers can cause several

other problems such as nep formation, fiber breakage, poor fabric appearance, low yarn strength

and increased yarn breakage [6, 160-163]. Several preventive actions need to be taken at the

spinning stage to minimize or avoid these problems. These include selecting bales with low

immature fibers, measurement of the immature fiber content of every bale, proper blending at bale

laydown and controlled waste recycling [6]. If these controls are not employed, immature fibers

may appear in the fabric. The dyer may be able to deal with this problem, to some extent, by a

proper selection of dyes and through mercerization. It is important to note, however, that the

performance of dyes varies from class to class and based on the dyeing process employed [161-

163].

119

Table 4.5: Factors affecting the dyeing behavior of cotton.

Factors Implications

Area of growth Rain gown cotton fibers, compared to irrigated cotton, are dyed to more

fuller and more solid colors in appearance due to differences in fibers

reflectance characteristics. Thus, the ratio of these types must be controlled

carefully in cotton mixes. Some dyeing differences may be minimized by

mercerization.

Color

(yellowness and

grayness)

Varies depending on the variety, growth area, weathering, maturity, and

non-cellulose content and this may affect the final dye shade. It is difficult

to minimize significant color differences in raw cotton after scouring and

bleaching.

Fluorescence Variation in fluorescence affects dyeing characteristics and may result in

weft band formation in critical fabrics such as weft-faced fabrics.

Weathering Long weathering of cotton leads to yellower or grayer color and an increase

in carboxyl groups which can repel certain dyes such as direct dyes.

Mercerization may even out certain differences.

Heating history Excessively overheated cotton will dye lighter. This is attributed to an

increase in hydrogen bonding and carboxyl group formation (see above).

The former affects penetration while the latter repels certain dyes. Using

higher heat in ginning, over drying or uneven drying during preparation

affects the dyeing.

Maturity Immature cotton leads to lighter shades, undyed clumps of fibers, uneven

appearance, and inferior wash fastness. Mixing cotton of varying maturity

levels may cause weft bands. Maturity also affects nep formation and leads

to poor yarn appearance and uneven dyeing. The neps in combination with

trash particles appear as light or dark specks in dyed fabrics. The dyeing

behavior of ring-spun yarn is more affected by maturity variations than

rotor spun yarn.

120

Wool fibers are obtained from different sheep breeds and are available in different fiber

lengths and diameters. The raw wool consists of 25-70% impurities such as wool grease, suint,

dirt, and vegetable matter. Various processes are performed to remove these impurities. Wool

contains different types of amino acid side chains which vary in size and chemical nature. These

side chains contain acidic and basic groups and have a strong influence on the dyeing properties

of wool [164]. There are 170 different types of proteins found in wool which are not uniformly

distributed throughout the fiber [165]. Wool contains different types of cells knowns as cuticle,

cortex, and medulla. Cuticle cells are on the outside layer while the cortex is found in the inner

layer. The cortical cells are separated from each other by the cell membrane. Prolonged dyeing at

low pH damages this cell membrane and leads to lower abrasion resistance [164].

Wool fibers may exhibit unlevel dyeing due to the damage of the tip of the fiber during

growth (on sheep's back) because of exposure to sunlight and weather. The tip of the wool is dyed

differently than the rest of the fiber due to the differences in its affinity for dyes. The outer layer

(cuticle) of the wool fiber is hydrophobic and resists the penetration of hydrophilic dyes.

Photodegradation makes the outer layer hydrophilic due to partial removal of the epicuticle and

oxidation of cystine. The tips of the fibers undergo these changes to a larger extent which results

in a preferential adsorption of acid dyes known as tippy dyeing. The epicuticle may also be

damaged due to mechanical processing. It is difficult to differentiate tippy dyeing from fiber

damage during growth or from mechanical processing of the fiber. In either case if a single dye is

used, this may show up as a difference in the depth of shade of the tip as compared to the rest of

the fiber. In the case of dye mixtures, this fault may show up as dichroism [82, 149, 166].

Wool and silk fibers have small quantities of chromophores which is linked to their growth.

These chromophores give a creamy off white color to wool and silk fibers. The bleaching process

can be carried out to improve the whiteness of the wool fiber [167]. However, it is not possible to

generate a brilliant white look on these fibers by the commercial bleaching process. Careful

selection of wool fibers with finer diameters can improve the color of raw wool. The yellowing of

wool may occur due to some problems associated with growth such as bacterial damage, oxidation

of protein and increase in pH of suint during growth. These problems are more common in

crossbred types of wool as compared to Merino wool. Different grades of wool exhibit different

dyeability and dye penetration. Coarser or low-grade wools are more yellowish and more difficult

to dye in lighter or brighter shades as compared to high-grade wool types. Improper mixing of

121

different grades of wool will cause difficulties in obtaining a balanced shade in wool blended

materials [67].

The structure of manufactured fibers is affected by various stages involved in fiber

manufacturing and processing from extrusion to drawing or texturing, and all the way to the fabric

finishing stage. Therefore, variations in parameters during these processes lead to changes in fiber

properties. The dyeing behavior and the resulting shade of the fabric are greatly affected by these

processing conditions. The extrusion, drawing and texturing conditions are important to dyeing

and dimensional stability properties of fibers and issues can be seen after the fabric has been dyed

and finished [168, 169]. The iodine sorption test can be carried out to ascertain the differences in

the structure after different treatments [170].

The chemical structure of synthetic fibers is mainly determined during the polymerization

process. The dyeability of synthetic fibers is influenced by various factors during polymerization.

These are given below:

▪ Quality of monomers used - recycled vs virgin monomers

Recycled monomers influence the color, end group concentration and may form

polymer gels. These gels cause problems during fiber spinning and drawing and may

lead to faults in dyeing [168].

▪ The concentration of end groups in the polymer

This directly affects the dyeing behavior such as the rate of dye uptake and fiber

saturation values. These groups may vary from one manufacturer to another and from

source to source. The end group concentration varies by the changes in monomers’

concentration, temperature and polymerization times. Nylon and acrylic fibers’

dyeability is determined by the concentration of these groups [114]. For acrylic fibers,

the number of dye sites are inversely related to polymer’s molecular weight and the

extent of the low molecular weight composition of the fiber. For finer fibers more dye

sites are required to achieve the target shade, the molecular weight of the polymer may

thus be reduced to achieve this. Neutral copolymers are also added to increase the rate

of dyeing by increasing amorphous regions in the fiber [171]. The mixing of fibers with

differences in concentration of the end group leads to faulty dyeings. Different dye

variant fibers are also available which either have different dyeability (cationic dyeable

122

polyester and nylon) or differences in dyeability (ultradeep, deep, low dyeing types)

[114].

▪ Presence of byproducts of side reactions

Diethylene glycol formed during the polymerization of polyester influences the dyeing

properties of the fiber. Cyclic oligomers of polyester are problematic in dyeing [168].

▪ The use of polymers that are recycled during the spinning

This produces fibers with generally lower strength, color, and uneven dyeability.

Mixing such fibers with fibers produced from virgin polymer produces products with

uneven properties [168].

▪ Chemical changes in the polymer during spinning and processing

Nylon may oxidize and form cross-links. This leads to gel formation in fiber and causes

variability during dyeing. Solutions of polyacrylonitrile have a tendency to yellow. This

depends on temperature, residence time, and availability of oxygen or inert gases in the

surrounding atmosphere, solvent stability, comonomers, and impurities present in the

spinning solution [172].

Oligomers are lower molecular weight species formed during the polymerization process.

The commercially available polyester fiber contains cyclic oligomers that contain two or more

repeating units without an end group. The major proportion of oligomers consists of a trimer (1.5%

by mass) which is important in fiber processing as it tends to move to the fiber surface during

thermal treatment such as heat-setting and dyeing. Oligomers form a deposit on the fiber surface

and affect the fiber properties. Trimers are soluble in high-temperature dyebaths but recrystallize

on fiber surface or on machine components on cooling as white deposits [173-175]. Their presence

reduces the brilliance of dyeing and shade depth in dark shades [158]. The main problems

associated with oligomers include adverse spinning properties of yarns, reduced liquor flow during

package and beam dyeing, and agglomeration of dyes. Several approaches are suggested to deal

with oligomers during dyeing. The dyebath can be dropped at high temperatures without cooling.

The oligomers are released from the fiber at temperatures around 120 oC and at shorter dyeing

times. Non-ionic leveling agents may be added to prevent their redeposition. The reduction

clearing process can also remove oligomer deposits from the fiber surface [174]. The dyeing of

123

polyester can be carried out in an alkaline medium using alkali-stable disperse dyes and this

process can dissolve the majority of oligomers though saponification [176].

Manufactured fibers are produced by either dry, wet or melt spinning. The viscous liquid

(melt/dope) of fiber-forming polymer is extruded through a spinneret which is then solidified by

blowing air on filaments or passing them through a coagulation bath. This is followed by a spin

finish application [114, 168]. The spin finish should be easy to remove during fiber preparation to

prevent dyeing problems. Otherwise, unlevel dyeing of nylon and acrylic fibers with acid and

cationic dyes respectively, can occur due to emulsion formation. This also affects the thermal

migration of dyes [177].

The spun filaments should have a uniform diameter and are affected by various factors

such as variation in diameter of spinneret hole, poor quality of the viscous liquid, variations during

solidification, differences in liquid throughput, presence of gels, cross-linked polymers and mixing

of incompatible polymers. The partial blocking of spinneret holes would produce a fiber with a

small diameter and high orientation. The turbulence during the fiber solidification phase would

lead to short term unevenness in the fiber. Many of these faults are further enhanced during the

drawing process. The variations in the fiber diameter cannot be changed in later processing stages

and affects dyeing behavior. The final appearance of the final product is thus affected [114, 168].

Different stages and corresponding factors involved in the wet spinning of acrylic fibers

are shown in Figure 4.3 [178]. The wet spinning process is very complicated and involves a lot of

variables. During polymerization along with acrylic comonomers, one to two monomers are added

to modify the acrylic fiber properties such as its’ dyeability and flame retardancy. The control of

molecular weight and molecular weight distribution is essential not only to obtain the desired fiber

properties but to avoid problems during dope formation. The partially soluble gels of high

molecular weight may influence the preparation of homogenous dope required for spinning. The

molecular weight also influences the dope viscosity. The lower molecular weights are preferred

due to ease in the dope formation and enhanced dyeability keeping the required levels of fiber

strength [171]. To prepare the dope for spinning the polymer is dissolved in a solvent. The polymer

content in the dope is based on polymer solubility in a solvent and the spinning pressure. The

temperature control is essential to avoid gel formation in dope. In general, the wet spinning

spinnerets have a large number of capillaries and thin plate designs to operate at lower speeds thus

limiting the polymer molecular weight and polymer content of the dope. In coagulation, it is

124

essential to control the polymer content, flow rate, temperature, coagulant type and concentration

as they determine the fiber structure. The difference in fiber structure obtained from wet and dry

spinning is due to the differences in the initial fiber formation step. The interaction between the

solvent, coagulant and polymer composition generates a characteristic fiber structure in the

coagulation bath. All these factors need to be controlled properly as they influence the structure

and dyeing behavior of acrylic fibers [179]. The rate of dyeing of acrylic fibers is dependent on

the physical structure of the fiber. The dyeing rates of wet and dry spun fibers are different [180].

The wet spun fiber has a more open structure (voids) and a circular cross-sectional shape. This

results in lowering the glass transition temperature (Tg), a higher dyeing rate and a larger surface

area than the dry spun fiber counterpart which has a bean-shaped cross-section and relatively

closed structure [112]. The differences in voids in wet spun fibers lead to appearance and dyeing

problems [114, 168].

Figure 4.3: Factors influencing the spinning process of polyacrylonitrile fibers.

COAGULATION

POLYMER

DOPE

SPINNERET

Type and amount of comonomers

Molecular weight

Molecular weight distribution

Type of solvent

Polymer content

Temperature

Rheological behavior

Type of material

Hole geometry

Injection speed

Solvent concentration

Nature and quantity of the precpitant

Temperature

Coagulation

Spinline

Cross-sectional shape

Gel filament structure

Nozzle speed

Stretchability

SPIN BEHAVIOR

125

The drawing process improves the orientation of molecular chains which leads to an

increase in crystallinity. The relative increase in orientation and crystallinity is fiber dependent.

Polyester has a considerable degree of crystallinity compared to nylon 6,6 due to the orientation

of chains in the undrawn state. However, there are no significant structural differences between

the two fibers after the drawn state. Generally increasing the draw ratio leads to a decrease in the

rate of dye diffusion [114]. Variations in the draw ratio and differences in relaxation temperature

during or after stretching produce changes in the physical structure. Weft bars and streaky dyeing

may have their origin in the faulty drawing process. The combined effect of faulty spinning and

drawing will produce faulty filaments and large variations in properties. Slight overstretching or

under stretching of filaments causes different shrinkage and dyeing properties. This is due to

differences in the orientation of chains and crystallinity of the fiber. Improper drawing of the

filaments may occur due to slippage of filaments on the drawing gadgets, inappropriate spin finish

composition failing to keep the filaments together, inadequate lubrication, and unsuitable

temperature of drawing godets. The filaments which are not drawn fully may have a larger

diameter than normal fibers and dye darker than the rest [114, 168].

The diffusion of disperse dyes by polyester is dependent on both draw ratio and heat setting

temperature. The heat treatment affects the physical fiber structure as it affects the size and volume

of the voids. The heat setting and drawing process are correlated. The usual heat setting

temperature range is 170-200 oC. The fiber shows reduced dye uptake in this temperature region

compared to temperatures before and after this range where they exhibit higher dye uptake. The

change in fiber structure is not confined to very high temperatures. The treatment of acetate and

nylon 6,6 in a boiling solution, for example, also affects the diffusion behavior of the dyes [114].

Variations in yarn tension and temperature during heat setting may also lead to dyeing

problems. Differences in tension within and between yarns can cause permanent deformation of

polymer. The yarns on the outer layer of the package dye differently than those in the inner layer

due to their differential shrinkage. Tension variations may also cause differences in the heat setting

process [114].

Synthetic fibers are cut in length to match the length of the fiber(s) that they will be blended

with. In the case of blended yarn, the length of the fibers and their fineness determine the

irregularities in yarns and affect variations in yarn strength [181].

126

Fibers with similar chemical compositions may exhibit different dyeing behaviors due to

having different structures. For instance, cellulosic fibers have a similar chemical structure, but

they have differences in proportions of amorphous and crystalline regions, pore size of the fibers

and accessibility of their internal adsorption regions [114]. The dyeability of cellulosic fibers is

influenced by the following factors [182]:

▪ Fiber structure (skin/core);

▪ Orientation;

▪ Crystallinity;

▪ Fiber pore structure; and

▪ Inner fiber pore volume.

Regenerated cellulosic fibers are obtained from wood pulp. These include viscose, modal,

and lyocell fibers. Although they are chemically similar to cotton, they have different

morphological structures and hence differences in dyeing behaviors. They are made up of cellulose

II and have different degrees of crystallinity. Viscose fibers have the lowest crystallinity of all with

41% followed by modal 49% and lyocell 80% [183]. The differences in their morphological

structure may be due to different factors involved in their manufacture which are [184]:

▪ The ripeness of alkali cellulose;

▪ The ripeness of the viscose (degree of xanthation);

▪ Compositions of precipitation baths; and

▪ Draw ratio.

Important fiber properties that may affect the wet processing of regenerated cellulose fibers

include [182]:

▪ Wet tenacity and elongation;

▪ Wet modulus;

▪ Water retention capacity;

▪ Fiber swelling;

▪ Fibrillation; and

▪ Dyeing behavior.

127

Viscose rayon has a skin and core structure where the skin is highly ordered when

compared to the core. The skin and the core exhibit different degrees of dyeability [158]. An

adequate supply of dyes with suitable kinetic energy is required for adequate dye penetration [185].

Treatments involving fiber swelling may be performed to improve penetration [114]. The pore

volume of viscose is larger than that of cotton. Therefore, the dye uptake is more for viscose as

compared to cotton [186]. Viscose fibers exhibit the lowest wet tenacity and highest wet elongation

among cellulosic fibers. This necessitates extreme care in processing [182]. Due to the reductive

nature of viscose certain dyes may reduce during dyeing. This is due to either aldehyde content or

high sulfur content (as CS2Na2S) remaining from fiber manufacturing. The aldehyde may easily

reduce azo dyes under certain conditions. High sulfide levels in fully flooded machines may

destroy some dyes and affect the shade under acidic conditions. Sulfide contents as low as 10 mg/L

can be problematic for dyeing operations [64].

Modal fibers are modified forms of viscose fibers by making changes during the

coagulation process. They have near-circular cross-sections and more highly oriented crystalline

regions than viscose rayon [114]. Lyocell has a higher degree of crystallinity due to stretching

during manufacturing and also has a near-circular cross-section. They have a tendency to undergo

longitudinal splitting known as fibrillation under wet state due to weaker cohesion between

crystalline regions. This produces microfibers of 1-4 µm in diameter and imparts a peach-skin

characteristic to the fabric. This may cause pilling problems and a frosty appearance in medium to

heavy shades [158, 187]. Modal and viscose show good wet tenacity and lower wet elongation.

Compared to viscose they show better stability during wet processing [182, 188]. The color yield

of various regenerated cellulosic fibers obtained after dyeing with direct, vat and sulfur dyes,

compared to cotton follows the following decreasing order: viscose, lyocell and cotton [189].

When dyed with direct dyes, the modal fibers dye lighter than viscose, lyocell and cotton due to

having a lower affinity. With reactive dyes modal dyes darker than cotton but lighter than viscose

and lyocell. In order to produce a solid color effect (similar color tone and equal depth) in cellulosic

blends, the dye affinity for each of the fibers should be similar e.g. cotton/modal or lyocell/viscose

[182, 188].

Synthetic fibers such as polyester and acrylic show an increase in the rate of dye diffusion

around a particular temperature due to the increase in segmental mobility of polymer chains. This

temperature is known as the glass transition temperature (Tg). As dyeing temperature is increased,

128

the diffusion of dye into the fiber (rate of dyeing) increases exponentially. This requires a close

control of dyeing conditions to avoid unlevel dyeings [114]. In acrylic fibers, there is a high degree

of affinity between the dye molecules and the ionizable active groups in the fiber. This is in

combination with the fact that a higher rate of dyeing above Tg demands a proper control of dyeing

conditions to obtain a level dyeing. For instance, retarders are used in acrylic dyeing to control the

rate of dyeing. Cationic or anionic retarders may be used. The former works by competing with

the dye for the available dye sites in the fiber. The latter temporarily associates itself with the dye

limiting the amount of dye available for dyeing at any particular time [114]. Acrylic fibers that are

spun by dry or wet spinning methods differ in their dyeability [156]. The commonly used nylon

fibers are nylon 6 and nylon 6,6. Although they are similar, their structure, dyeability, dyeing rate,

and colorfastness are different. Nylon 6 has a more open structure, higher affinity for dyes, faster

dyeing rates and lower colorfastness. On the contrary, nylon 6,6 has a lower affinity for dyes,

slower dye strike rates, higher colorfastness, and more oriented fiber structure. It is also

recommended to heatset nylon 6 at a lower temperature than nylon 6,6 due to its’ lower heat

stability [190].

Common problems affecting the dyeing of fiber blends, their causes, and remedial

measures are summarized in Table 4.6.

Table 4.6: Dyeing problems attributed to fiber.

Problems Probable causes Remedial measures Ref.

Dark areas,

stains, or spots

▪ Oil and grease

contamination from

harvesters, gin presses, truck

or warehouse floors

Ensure the sorting of contaminated

fibers and proper handling of

material.

[159,

160,

162,

191,

192] ▪ Presence of vegetable matter

such as seed husks, leaf and

stem remnants due to:

- Improper scouring

conditions

The recipe and process parameters

(time and temperature) should be

followed.

129

Table 4.6 (Continued)


- No scouring is given to

blends containing smaller

cotton components

Design process routes keeping into

consideration the actual

contamination level where a

scouring process may be required.

- Not enough removal in

opening and carding

stages due to choosing

inappropriate machine

settings (wide gaps) to

accommodate polyester in

an intimate blending

process

Use proper machine settings to

effectively remove trash without

damaging the fiber.

- Use of unbleached

backing fabric in

processes with a different

face and back

Use a backing fabric with a good

appearance.

▪ Presence of high quantities of

calcium and magnesium in

cotton may lower dye

solubility and lead to

precipitation

1. Use sequestering agents during

pretreatment and dyeing

processes.

2. The demineralization process

may be required depending upon

the severity of the problem.

▪ Undrawn filament due to

filament slippage during

drawing, inappropriate spin

finish and unsuitable

temperature of drawing

godets

1. Use a suitable spin finish

combination.

2. Check the drawing process for

slippage and required

temperature.

[114,

168]

130



▪ Due to the presence of dark

wool fibers

Proper identification and sorting

system should be implemented in

the early stage of fiber processing

to remove dark wool fibers.

▪ Due to splinters generated

during polyester fiber

spinning, containing

irregularly drawn fibers

Check the spinning process for

faults.

[193]

▪ Fusion of fibers due to

damage caused by the

crimper

1. Check the settings of the

crimper.

2. Ensure proper feed of the tow.

▪ Agglomeration of disperse

dyes due to the presence of

oligomers

1. Drop the dyebath at a high

temperature.

2. Use a non-ionic reducing agent

during dyeing.

3. Dye polyester in an alkaline

medium depending on the

feasibility of the operation.

[174,

194]

Resist/colored

areas

▪ Presence of foreign matter

such as polypropylene or

polyethylene or jute

impurities in the fibers

▪ Melting of polypropylene

fibers during singeing and

drying and subsequent rolling

out to form a thin film

1. Avoid the use of plastic and jute

bags for storing and

transportation.

2. Inspection and removal of

foreign material during

spinning. Installation of foreign

fiber detector during fiber

opening and winding stages.

[100,

149,

159,

161,

162]

131



▪ Insecticides and pesticides

used during cotton growth

Ensure proper washing of

substrate before the dyeing

process.

Pale spots/areas ▪ Presence of immature cotton

fibers in the material

Ensure proper blending and

measurement of immature fiber

content at bale laydown.

[6,

149,

159,

162,

163,

191,

192]

▪ Due to the presence of

medullated wool fibers.

These fibers have different

light reflecting properties and

take up less dye due to less

protein available to take up

the dye compared to the rest

of the wool fibers.

Ensure proper detection and

segregation of fibers at the early

stage of processing.

▪ Excessive overheating causes

cotton to dye lighter

The temperatures in ginning and

drying processes should be within

specified limits.

[159]

Shade change ▪ Using different cotton fibers

with differences in

weathering and maturity can

lead to color differences

Avoid mixing cotton from

different sources.

[159]

▪ The presence of sulfur

residues in viscose from

manufacturing

A peroxide bleach might be

recommended to remove sulfur.

Use a mild oxidizing agent during

dyeing.

[64,

185]

▪ The presence of aldehyde in

viscose from manufacturing


dyeing that should be stable under

dyebath conditions.

[64]

132



▪ Deposit of polyester

oligomers on fiber reduces

brilliance and shade depth

1. Drop the dyebath at high

temperature.

2. Use a non-ionic wetting agent

during dyeing.

3. If possible, dye polyester in an

alkaline medium.

[174]

Unlevelness ▪ Damaged wool fiber tips

during growth because of

sunlight and weather

1. Use a leveling agent during

wool dyeing.

2. Select acid dyes with good

leveling properties.

[149,

166,

192]

▪ Variations in the degree of

polymerization, end group

content

Check the degree of

polymerization and end group

content before extrusion.

[82]

▪ Mixing fibers with different

end group concentrations.

Check the end group content of

polymers before extrusion and

avoid mixing polymers from

different sources.

[114]

▪ Use of recycled monomers

causes gel formation that

leads to problems in spinning

and drawing.

Avoid using recycled monomers

during polymerization or their

concentration should be kept as

low as possible.

[168]

▪ Mixing of virgin and recycled

polymers during extrusion

produces fibers with uneven

properties

Avoid mixing different polymer

types.

[168]

▪ Differences due to improper

extrusion, drawing and heat

setting

Check proper controls are

implemented during fiber spinning

and processing stages.

[82]

133



▪ Variation in temperature

during extrusion, drawing or

heat setting process

Ensure uniformity of temperature

during extrusion, drawing and heat

setting.

[177,

195]

▪ Differences in voids in

acrylic fibers

Ensure uniformity of parameters in

the extrusion process.

[114,

168]

▪ Formation of emulsion due to

spin finish in the dyeing of

nylon and acrylic fibers.

1. Improper selection of spin finish

with poor removal properties.

2. Residual spin finish due to

inadequate pretreatment process.

▪ Instability of spin finish at

higher heat setting

temperature required for

nylon/elastane blends.

Use special spin formulations that

are stable and protect the nylon

from damage at a higher

temperature.

▪ Agglomeration of disperse


oligomers

▪ Reduced liquor flow in

package dyeing due to

oligomer deposits

1. Drop the dyebath at a high (e.g.

120 oC) temperature.

2. Use a non-ionic wetting agent

during dyeing.

3. Dyeing of polyester in an

alkaline medium depending

upon the possibility.

[174,

194]

▪ Differences in yarn tension

and temperature during heat

setting cause differential

shrinkage in a package

leading to unlevelness

Ensure uniformity of yarn tension


setting.

[114]

Stripes/bars ▪ Higher proportion of short

fiber content increases the

yarn hairiness, neps, and

Check and control short fiber

content for each bale lay down.

[100,

160,

162,

134



irregularity which may

appear in the form of stripes

163,

196,

197] ▪ Variation in micronaire,

fluorescence, and maturity of

cotton fibers cause horizontal

stripes in knitted fabrics

Control the micronaire, maturity,

and fluorescence of the fiber

within a mix and among mixes.

The variation in fluorescence

(measured in terms of UV) should

be < 10, micronaire should be <

0.2 within a mix.

▪ Variation in draw ratio and

temperature

Ensure uniformity of draw ratio

and temperature.

[114,

168]

▪ Differences in yarn tension


setting

Ensure uniformity of yarn tension


setting.

[114]

Inferior

colorfastness,

thermomigration

▪ Presence of spin finish

facilitates the movement of

disperse dyes to the fiber

surface

Ensure complete removal of spin

finish during pretreatment process.

[177]

Holes ▪ Presence of iron causes

catalytic damage of cellulose

due to rapid decomposition of

bleaching bath


pretreatment.

2. A demineralization process may

be required depending on the

severity of the issue.

[162,

198]

▪ Melting of polypropylene

fibers present in cotton

1. Avoid plastic and jute bags for

storing and transportation.

2. Inspect and remove foreign

material during spinning. Install

135



a foreign fiber detector in fiber

opening and winding stages.

Reduced

strength

▪ Wrong selection of cotton

variety. The fiber strength

depends on the source,

variety, fineness and growth

conditions

The selection should be based on

end-use requirements.

[159,

160,

162]

▪ Overheating of fiber during

ginning

The ginning should be carried out

at a lowest possible temperature (<

170 oC).

▪ Higher proportion of

immature and short fibers

Check each bale laydown for

immature and short fiber contents.

▪ Damage due to weathering The fiber strength should be

checked before purchasing cotton.

▪ Presence of metal impurities

(iron) in fiber cause catalytic

decomposition of hydrogen

peroxide and leads to fiber

damage


pretreatment.




▪ Damage of wool fiber during

growth due to environmental

factors leads to fiber strength

loss or a decrease in fiber

diameter

Ensure proper blending of fibers.

The fibers should be checked for

strength and diameter before

processing.

[192]

▪ Damage due to chemical

treatments, excessive heating

and storage under hot and

humid conditions

1. Avoid storage in hot and humid

environments.

136



2. Avoid high temperature, low pH

conditions and long treatment

times during processing.

▪ Presence of very low

micronaire cotton leads to

weight loss during scouring

and bleaching

Check each bale laydown for

micronaire.

[159]

Poor appearance ▪ Frosty appearance and pilling

due to fibrillation of lyocell

fibers under wet conditions

Use lower alkalinity during

dyeing, reduce dyebath

temperature, and tension during

processing.

[158,

187]

▪ Excessive hairiness due to the

higher content of short fibers

Check each bale laydown for short

fiber content.

Whiteness

variation/lower

degree of

whiteness

▪ Insufficient bleaching action

due to the presence of metal

impurities such as iron in

cotton fibers


pretreatment.




[159,

162]

▪ Creamy off-white color of

wool fibers due to damage

during growth, oxidation and

pH change which makes it

difficult to obtain brilliant

white

1. Use a bleaching process to

increase whiteness.

2. Consider the use of optical

blighters.

[167]

Creases or rope

marks

▪ High lateral swelling of

lyocell fibers causes

stiffening of fabric

1. Use high liquor temperature (>

50 oC).

2. Use lubricating agents in rope

processing.

[187,

199]

137

4.4 Problems arising from yarn formation

Yarn is a basic building block in a fabric which is composed of linear, ordered twisted or parallel

fiber strands. There are many types of yarn produced in the market depending on the required

physical properties and performance characteristics. Yarns can mainly be classified as continuous

filament or spun yarns. In the first type, multiple filaments are arranged side by side in parallel.

This type of yarn is made by extruding a polymer liquid through a spinneret which is then solidified

to form a continuous filament. Filament yarns can be further classified as monofilament, when the

yarn contains a single filament, or multifilament when the yarn consists of a group of filaments.

Multifilament yarns can be converted into bulky or stretched forms by a process known as

texturizing. The second type of yarn is known as spun yarns which are made from staple fibers of

natural or synthetic origin using a number of spinning stages such as opening, cleaning, blending,

drawing, combing and spinning. Spun yarns can be further classified based on the method of

spinning into ring-spun, rotor-spun or air-jet spun yarn and by the method of preparation into

carded, combed, woolen or worsted yarn. Structurally yarns can be single, plied, cable and

composite yarns [200]. The different yarn types are shown in Table 4.7 [181, 200].

Table 4.7: Yarn classification.

Division Group Subgroup Class

According to fiber

length

Continuous

filament

Continuous monofilament

yarn

Continuous

multifilament yarn

▪ Flat yarns

▪ Textured yarns

Spun yarns Short-staple spun yarn ▪ Carded yarn

▪ Combed yarn

Long-staple spun yarn ▪ Woolen yarn

▪ Semi-worsted yarn

▪ Worsted yarn

Conventional yarn ▪ Ring-spun yarn

▪ Compact yarn

138


Division Group Subgroup Class

▪ Rotor spun yarn

Unconventional yarn

▪ Air-jet spun yarn

▪ Friction spun yarn

Fancy/effect yarn

▪ Slub yarn

▪ Fancy twisted yarn

According to fiber

content

Blended yarn

▪ Intimate blended yarn

▪ Drawframe blended

yarn

Composite yarn Core spun yarn

According to yarn

structure

▪ Single yarn

▪ Folded yarn

▪ Cabled yarn

In theory, yarns can be produced without any fault, but in practical mass production

conditions, faults do occur. A fault in the yarn is determined based on its end-use requirements

and performance. It does not include the normal variations present in the yarn. Yarn faults can be

attributed to one or more of the following reasons [157, 201, 202]:

▪ Raw material

Faulty raw material and an incorrect selection of raw material are major sources of

faults. There are many fiber properties that influence formation of faults in yarns such

as fiber length, length uniformity, short fiber content, fineness, maturity, strength,

elongation, trash, contamination, crimp, and finish. A determination of individual

values, as well as variation in these properties, is important as these values directly

influence the appearance, hand and performance characteristics of the yarn. Raw

material factors are covered in more detail in section 4.3. For blended yarns, this factor

is more critical because of the differences in the fiber properties of blend components.

139

▪ Machines

Incorrect machine settings, improper speeds, incompatible or damaged machine

elements affect the fiber processing and can lead to forming faulty yarns.

▪ People/practices

This includes operator negligence, unskilled or poor operator training, incorrect

material handling, poor machine maintenance, lack of machine and environmental

cleanliness and improper or no housekeeping practices.

▪ Ambient conditions

Temperature and humidity control is essential for proper fiber processing. The correct

conditions depend on the fiber type and process stage. Static generation, roller lapping,

and strength related problems may occur if conditions are not properly controlled.

Yarn faults can lead to problems during further processing in the following ways [157]:

1. End breakage rate in warp preparation (warping, sizing), weaving and knitting.

2. Fabric quality problems due to yarn faults.

3. Fabric faults due to yarn breakage in yarn preparation or fabric formation processes.

As yarns can be produced by different methods, their structure and properties vary from

each other. Therefore, the selection of yarn is important for a particular end-use. A wrong selection

of yarn leads to problems in subsequent processing and not meeting the target product

characteristics [203]. For example, yarn produced for weaving and knitting have different

properties due to the nature of these fabric formation processes.

4.4.1 Faults caused by spun yarns

Spun yarns are made by the process known as spinning in which a large quantity of individual

unordered fibers of relatively short length is converted into a very long ordered and linear product

known as yarn [204]. The spun yarn can be produced by two common spinning systems: short

staple or cotton system and long staple or wool system. The important characteristics of both

systems are the fiber length and diameter. The fiber type that needs to be processed in either of

these two systems must adhere to these requirements. Therefore, for the production of blended

yarn, the length and fineness of fibers are important. Synthetic fibers are cut in length to match the

140

spinning system and the length of the fiber they are blended with. For instance, waste material

from the production and processing of raw silk can be used to produce spun silk yarns. Depending

upon the fiber length, spun silk yarns can be produced either on cotton or worsted spinning

systems. Wool and silk fibers need to be scoured before the spinning process to remove their

natural impurities (e.g. waxes in wool, and sericin in silk) to make their processing easier [205].

Table 4.8: Effect of different spinning operations on yarn properties.

Fiber Properties


Even

nes

s

Th

ick

pla

ces

Th

in p

lace

s

Nep

s

Hair

ines

s

Cou

nt

Str

ength

Elo

ngati

on

Ble

nd

reg

ula

rity

Bale lay-down D D D D D N D D N

Blowroom D D D D N N D D D

Card D D D D D D I I N

Drawframe I I I I N D I I D

Comber D D D D D N D D N

Roving frame I I I N I I I I N

Spinning machine I I I I I I I I D

Winding machine I I I D D N I D N

D: direct relationship, I: indirect relationship, N: no relationship

In yarn production, staple fibers go through a series of operations depending on the fiber

and yarn requirements. These include opening, cleaning, blending, aligning, uniting, equalizing,

attenuating, twisting and winding [204]. Yarn quality is dependent on each of these different

processing stages in spinning. Proper process control is essential in order to achieve the required

yarn quality levels. The influence of different spinning processes on quality characteristics of spun

yarn is shown in Table 4.8 [6]. It can be seen that the presence of neps in yarns, which influences

the dyeing of fabrics, is directly affected by bale lay-down, blowroom, card, comber, and the

141

winding machine. Similarly, blend regularity, which is denoted by the distribution of different

fiber types in the yarn and affects the color of the blend, is dependent on the blending process done

in blowroom, drawframe or spinning process. Thus, different stages of the spinning process

directly influence the properties of fabric formed from yarns [6].

Roller drafting is one of the most common sources of errors in yarn formation. Defective

or damaged machine parts such as rollers, aprons, guides, etc. lead to defects in the yarn. Fly fibers

from the atmosphere can spin into the yarn creating defects. Therefore, proper cleaning of the

spinning environment is essential for fault free yarn production. In the case of yarn blends, fiber

finish can accumulate on the balloon control rings, rings and travelers causing problems during

spinning [157].

Many yarn faults originate from inadequate fiber preparation for spinning such as carding.

For intimate blending, which is performed in the blowroom, compromised card settings need to be

used to adjust the fiber type in the blends. This may lead to various problems such as inadequate

removal of neps, improper cleaning, etc. Another factor is the increased production speed. If the

material that is fed to the spinning machine is already faulty, yarn production will be faulty [181].

The common faults found in spun yarns are: seldom occurring faults, incorrect yarn count, yarn

count variations, unevenness, periodicities, high levels of imperfections, excessive hairiness and

hairiness variation, yarn contamination including trash and dust, low tensile strength and

elongation, improper fiber blending, and melt spots or local fusion of yarn [6].

Seldom occurring faults

Random variations in a yarn cannot be controlled as it is difficult to achieve the same number of

fibers in the yarn’s cross-section at every moment, but it should be within close limits. These

variations are among frequent yarn faults and are not removed from the yarn. Seldom yarn faults

include large mass or diameter or length causing thick and thin places which are removed during

the yarn clearing process. These faults are classified as short thick places (0.2 cm to 1 cm) or N,

medium-thick places (1 cm to 8 cm) or S, and long thin places (> 8 cm) or L [6]. The possible

causes and countermeasures for their formation are:

▪ Improper functioning of drawframe auto-leveling system;

▪ High short fiber content in sliver or roving after combing operation. Optimization of

comber noil is required;

142

▪ Fly waste is spun into roving or yarn;

▪ Draft distribution is not proper in drawframe, roving frame, and spinning machine;

▪ Twist level is incorrect in roving;

▪ Tension problem in a roving frame;

▪ High unevenness in roving;

▪ Large fly fiber contamination on the spinning machine;

▪ Air-conditioning system is not working properly;

▪ Higher amount of yarn breaks which result in excessive fly generation and outlier

bobbins;

▪ Eccentric rollers in roving and spinning machines;

▪ Damaged or worn out aprons, worn out rings and travelers. Improper settings of aprons;

▪ Wrong selection of traveler;

▪ Static generation;

▪ False draft in spinning machine creel or draft distribution is not proper; and

▪ Too high winding speed and tension during the winding process.

Incorrect yarn count

Mixing of different yarn counts in the yarn lot can result in a poor fabric appearance, which will

depend on either mixed yarns being used in the length or widthwise direction of the fabric. The

use of different colors of bobbin tubes can prevent or minimize yarn count mix-up [6].

Yarn count variations

Variation in the yarn count exceeding the limits is also known as long-term mass variation. It may

result in uneven fabric appearance [6]. Possible reasons are:

▪ Missing fiber component or missing sliver at the draw frame for a short period of time;

▪ Use auto leveler or finisher drawframe;

▪ Unevenness or weight variations in rovings result in count variation within a bobbin;

▪ Incorrect trumpet hole diameter and cleanliness;

▪ Incorrect roller weights;

▪ Improper alignment of the spinning creel, dragging bobbin holder, blocked spinning

trumpet;

143

▪ False draft in spinning machine creel; and

▪ Mixing up of bobbins of different count. Use different colors for bobbin tubes to avoid

yarn count mix-up.

Uneven yarn

Random mass variations in yarns exceeding the limits will produce an irregular or uneven yarn

and result in a cloudy fabric appearance [6, 206]. Uneven yarns are caused by the following:

▪ Improper card maintenance;

▪ Improper functioning of the auto-leveling system in the finisher drawframe and

inadequate maintenance of the drafting system;

▪ Wrong setting for the roving traverse;

▪ Incorrect break drafts and roller settings. Improper roller weights;

▪ Wrong selection of the size of the apron. Inadequate quality or replacement schedule

of the aprons. Excessively worn out aprons. Improper apron spacing;

▪ Inadequate hardness, grinding schedule and minimum diameter of top rollers. Incorrect

position of top front rollers;

▪ Improper roller chatter and dimensions of spacers;

▪ Cutting of top roller due to improper operator training;

▪ Yarn diameter differences;

▪ High balloon tension and centering of a pigtail;

▪ Worn rings;

▪ Periodic mass variation from card, drawframe or roving;

▪ Thermal fiber damage due to excessive spinning speed;

▪ Dust accumulation in rotors;

▪ Damaged rotor groove surface or rotor cover; and

▪ Damaged wire or lapping on the opening roller.

Periodicities

These faults are repeated at the same interval and are extremely disturbing. They can be related to

yarn mass and can cause a pattern in the fabric [6]. The important factors associated with this type

of fault are [6, 155]:

144

▪ Incorrect settings of the comber piecing process;

▪ Eccentricity or fault of front rollers or opening roller of the spinning machine;

▪ Contaminated front roller (honeydew etc.);

▪ Symmetrical yarn tension variation with reversal movement of the spinning package;

▪ Asymmetrical yarn tension variations with reversal movement of spinning package;

▪ Dust or dirt in the rotor groove of the rotor spinning machine;

▪ Opening roller damage, or asymmetrically supported rollers in the rotor spinning

machine; and

▪ Defective joint in the apron of the ring spinning machine.

High levels of imperfections

This refers to yarns consisting of too many thick and thin places, neps and may result in a poor

quality fabric. These faults are caused either due to raw material or processing during the spinning

process. Thick places, thin places, and neps are classified as imperfections exceeding -30% or

+35% or +140% of the mean yarn cross-sectional size. Table 4.4 shows the raw material factors,

which include length uniformity, short fiber content (SFC), high micronaire variations and high

level of neps [6].

The main reasons for thick and thin places in yarn due to processing are [6, 207]:

▪ High SFC after the combing process;

▪ Accumulation of lint or fly on roving;

▪ Accumulation of lint on drafting roller, blow in lint and bad operation of overhead

cleaner in ring spinning frame;

▪ Wrong roving traverse, apron and cot conditions, apron spacing, out of position top

roller, roller spacing, incorrect hardness and bad surface of top cots, eccentric or

damaged front rollers, incorrect break draft and main draft settings of the drafting

system of ring spinning frame;

▪ High balloon tensions and loaded travelers in ring spinning;

▪ Use of too coarse fibers;

▪ Improper air conditions, wrong settings or improper working of the air conditioning

system; and

145

▪ Incorrect oiling or oil concentration during long-staple spinning or spin finish for

synthetic fibers.

Neps in a yarn are caused by [6]:

▪ High nep levels in roving;

▪ Deteriorated apron, the opening of a tensor pin;

▪ Damaged or worn out ring and traveler, improper setting of traveler clearers and

deteriorated balloon control ring.

Excessive hairiness and hairiness variation

A yarn with a large number of protruding fibers may cause pilling and reduce abrasion resistance

of fabric. However, high hairiness may be desirable when requiring a softer yarn hand. The high

hairiness of yarns is strongly correlated to the pilling of fabrics, which is the formation of small

entanglements of fibers on the fabric surface due to wear. Knitted fabrics are more prone to pilling

due to high hairiness of the knitting yarns which are produced with less twist compared to yarns

manufactured for the woven fabrics. Hairiness may also cause problems during the fabric

formation process. If hairiness variation is high it may affect the fabric appearance. Hairiness is

dependent on both fiber and process-related factors [6]. Fiber properties that have an influence on

yarn hairiness are fiber length, length uniformity and high short fiber content as shown in Table

4.4.

The main causes of hairiness due to processing are [208]:

▪ Low roving twist;

▪ Wrong selection and worn out or bad conditions of rings and ring travelers;

▪ Improper spinning tension during ring spinning;

▪ Low yarn twist;

▪ Spindle belt slippage;

▪ Damaged or improper centering of pigtail guides;

▪ Spindle and rings are not centered;

▪ Improper traveler changes or wrong traveler weights;

▪ Separator slap;

▪ Incorrect positioning or missing balloon control rings;

146

▪ Improper spindle speed and curve;

▪ Damaged rubber coverings;

▪ Variation in spinning atmospheric conditions; and

▪ High winding speed.

Yarn contamination

Any foreign matter, such as plastic, jute, or polypropylene, spun into the yarn is considered as

contamination. Contamination in natural fibers such as cotton is a major problem in the spinning

mill and has increased in recent years [6]. The major type of contamination found in cotton

includes organic matter such as leaves, feathers, paper, leather, etc., strings made of woven plastics

and cotton, fabrics made of cotton and strings made of jute/hessian [209]. They are embedded in

cotton during harvesting, ginning or the spinning process. They can be of different origin,

composition, color, and structure than the fibers in the yarn. They exist in the form or single fibers

as well as fiber bundles of variable length, but are generally limited to 10 cm in length [210]. ].

Early detection and removal of these contaminations is essential as later processing steps (e.g.

carding) open up and spread these foreign matters and may result in the production of many

contaminated yarn packages. Contaminations may cause several problems in processing such as

end breaks in warping, weaving, and knitting, non-uniform dyeing and a poor fabric appearance

[6]. Their appearance in fabrics depends on their length and thickness, as well as fabric type and

wet processing employed. Bleaching is the most critical step in wet processing for the removal of

contaminations [210]. Generally, contaminations are seen after finishing processes due to their

difference in dyeing affinity, fiber size or color and cause quality problems [157]. The approaches

used to eliminate the foreign matter in order to keep the defect levels within acceptable limits

include selection of fibers containing low contamination levels, use of manual labor to pick foreign

matter before the opening process, use of foreign material detector devices before the card and

foreign fiber clearer in winding [210]. Foreign matters may also be originally present in cotton

bales but may also be embedded into the fibers due to improper stripping down of bale during the

bay lay down process [157].

Some of the possible reasons and preventive actions in the spinning process to counteract

contamination issues are [6, 210]:

▪ Cotton with high contamination levels;

147

▪ Use of plastic bags for fiber waste collection and transportation;

▪ Use of manual labor and foreign fiber detector in the blowroom;

▪ Controlled recycling of the waste in the blowroom;

▪ Efficient carding, combing and blending at all drawframes;

▪ Optimization of comber setting for effect foreign fiber reduction; and

▪ Use of foreign fiber clearer in the winding.

Trash and dust

High content of trash and dust may lead to problems in spinning, weaving and knitting processes.

They may lead to weak places in rotor spun yarns and wear and tear and abrasion of metal parts

e.g. needle wear on a knitting machine, wear of yarn guide elements and accelerated wear of

production parts in the spinning process [6]. One of the main objectives of the spinning process is

the removal of impurities present in the fiber. Trash and dust content are significantly reduced after

the spinning process. The blowroom, carding, and combing are important spinning stages for the

removal of trash and dust from fibers. Improper functioning of these processes can lead to the

presence of a small amount of trash and dust in the yarn [157].

Low tensile strength and elongation

Yarn strength and elongation influence the selection of yarn for a particular end-use and therefore

are of prime importance [155]. If the yarn strength is low, it leads to low tensile, tear and bursting

strength in the fabric, which may be contrary to the requirements in the final product. It also causes

yarn breakages during warping and weaving and produces holes in knitted fabrics thereby reducing

process efficiency and increases costs [6, 155]. Dimensional properties of the fabric are directly

influenced by the elongation of the yarn [6]. Both yarn properties are influenced by raw material

selection and the spinning process as shown in Table 4.4 and Table 4.8 respectively. Raw material

causes are low fiber strength and elongation, high short fiber content and the use of coarse fibers

[202]. For blended yarns, length and fineness of the individual fibers determines the yarn

irregularity which influences the yarn strength variation. The mean strength of the blended yarn is

always less than the yarns of the same count made from individual fiber types. This is due to the

difference in the extensibility of the fibers used in the blends [181]. The relative humidity must be

taken into consideration as it affects the yarn strength properties especially for cellulosic fibers

148

and their blends. Low strength and elongation in yarns may be due to the following causes Low

strength and elongation in yarn having the following causes [202, 211]:

▪ Low yarn twist levels;

▪ Improper fiber blending (blend regularity and blend levels);

▪ Damaged roller drive system (periodic faults);

▪ High spinning tensions; and

▪ Thermal fiber damage due to very high spinning speed for processing synthetic fibers

or their blends.

One of the problems found only in air-jet spun yarns is known as weak yarn. This slightly

weaker yarn has less twist. This leads to a higher volume and hairiness. Such a yarn survives the

downstream processing but will create barré in the dyed fabric. The possible causes of weak yarn

formation are [212]:

▪ Partially blocked suction system at a spinning position; and

▪ Spin finish or oligomer or fiber wax deposits on ceramic spin tips.

Improper fiber blending

Blended yarns should have good longitudinal and lateral blending. Longitudinal blending refers to

the arrangement of blend components along the length of yarn whereas lateral blending indicates

the arrangement of the fiber components along the cross-section. It is impossible to maintain

constant values of longitudinal and lateral blending, but higher variations must be avoided. Fiber

properties such as fineness and length have an influence on the arrangement of fibers on the blends,

e.g. finer and longer fibers tend to concentrate in the center of the ring-spun yarns. Blending faults

may be due to systematic (with specific values in different measurements) and accidental errors

(different values in every measurement). Systematic errors in longitudinal blending lead to a

difference between fabric batches produced from these yarns [213]. Optimum blending is essential

for the production of a uniform appearance of the fabric after dyeing and in achieving a particular

color effect. This also holds true for the production of mélange yarns in which dyed fibers are

mixed to produce the yarn [6, 181]. Low blending irregularity is also required for uniform physical

properties of the yarn [181].

149

Problems in fiber blending may be caused by:

▪ Use of drawframe blending for critical blend ratios;

▪ Mixing of fiber waste collected from card and drawframe; and

▪ Missing or broken sliver at drawframe feed.

In the case of core-spun yarns, the core should be properly centered and covered by the

outer fiber sheath as the most important properties of this yarn type are stretch and recovery [6].

Two types of fault can be found in core-spun yarns: core voids and sheath voids [214].

Core voids can be further classified as short core voids in which short sections of yarn have

nowhere to stretch due to broken core after spinning and long core voids which are characterized

by long portions of yarn without a core. The possible reasons for short core voids are [214]:

▪ Poor alignment of core yarn with roving, especially for finer yarns;

▪ Over drafting of core yarn;

▪ Improper lubrication or worn out rings;

▪ Use of heavy travelers; and

▪ Excessive traveler speed.

Long core voids are caused due to [214]:

▪ Over drafting of core yarn;

▪ Guide with a rough surface or sharp edges;

▪ Insufficient feed roller contact; and

▪ Missing yarn tubes.

In sheath void, a certain length of core yarn is without or contains partial covering. This is

caused due to [214]:

▪ Roving breakage during drafting;

▪ Worn aprons and roller coverings;

▪ Uneven roving or high spinning drafts and speeds; and

▪ Improper alignment of core yarn and roving at the front roller.

150

Melt spots or local fusion of yarn

This type of defect occurs for yarns made-from man-made fibers such as PES and PA or their

blends due to their thermoplastic nature. The friction between the fibers and part of the machinery

can result in the generation of excessive local heat, which causes melt spots or local fusion [193,

211]. Such changes in fiber may lead to a reduction of yarn strength and elongation, generation of

fiber particles, increase in yarn breakage and dust generation during winding, yarn unevenness and

dyeability variation [206].

The main causes are [193, 211]:

▪ Excessive speeds at the balloon control ring, traveler and ring;

▪ Incorrect hardness of roller coverings; and

▪ Running of carding and drawframe at excessive speed.

The yarn produced after a spinning process has a direct effect on fabric properties. Table

4.9 shows the correlation between yarn and fabric characteristics [6, 154, 202]. Yarn failure during

the weaving or knitting process may result in production of off quality fabrics. The cost of repairing

yarn faults is far less if repairs occur before the fabric formation. Most of the quality related

problems during the fabric formation process are related to errors occurring during the spinning or

yarn preparation processes. Maintaining high yarn quality along with the package quality are very

important to producing fault free fabrics [215].

151

Table 4.9: Influence of yarn parameters on fabric properties

Fabric Properties


Even

nes

s

Th

ick

pla

ces

Th

in p

lace

s

Nep

s

Hair

ines

s

Hair

ines

s vari

ati

on

Dia

met

er

Dia

met

er v

ari

ati

on

Sh

ap

e

Den

sity

Tra

sh a

nd

du

st

Fore

ign

mate

ria

l

Str

ength

Elo

ngati

on

Tw

ist

Ble

nd

reg

ula

rity

Appearance D D D D D D D D D D D D D D

Dimensional stability D D D

Thickness D D D D D

Hand/Drape D D D D D D D D

Pilling D D D

Warp and weft

breakage rate D D D D D D D D D

Holes, knitting D D D D D D D

Spirability D

Dyeability/color

intensity, fastness D D D D D D D D D D D D

Wash and wear

properties D D D D

Strength D D D D D D

Elongation D D D D

D: direct relationship

Table 4.10 gives the common type of problems found in dyed and finished fabrics

attributed to yarn defects. These defects are caused due to raw material, machinery or improper

procedures. Some of the problems cause issues in the fabric formation process.

152

Table 4.10: Common problems related to spun yarns.

Problems Probable causes Ref.

Uneven/poor/

cloudy fabric

appearance

▪ Seldom occurring thin and thick places. [6]

▪ Imperfections (thick and thin places, neps). [6, 216]

▪ Excessive yarn hairiness, hairiness variation. [6, 216]

▪ Yarn contamination. [6]

▪ Yarn mixing (uneven yarn, mass variation, combed and

carded, imperfections).

[6]

▪ Improper lateral blending and short-term longitudinal

blending.

[149, 213]

▪ Melt spots/thermal damage in yarn. [206]

Horizontal

line/stripes/barré

▪ Seldom occurring thin places. [6]

▪ Long term mass variation. [6]

▪ Excessive yarn hairiness and hairiness variation. [6]

▪ Short term longitudinal blending problems (accidental

errors).

[6, 213,

216]

▪ Yarn mixing (different counts, twist direction, periodic

mass variation).

[6]

▪ Periodic mass variation (e.g. Moiré). [6]

▪ Twist variation. [6, 212]

▪ Surface damage of yarn caused during spinning causing

fusing of fibers.

[193]

Vertical streaks ▪ Long term mass variation. [216]

▪ Yarn mixing (different counts, periodic mass variation). [6]

▪ Periodic mass variation. [6]

▪ Long term longitudinal blending problems (accidental

errors).

[213]

Holes, yarn

breakage

▪ Seldom occurring thin places. [6]

▪ Neps in yarn. [181]

▪ Low yarn strength. [216]

153



▪ Yarn contamination. [6]

Pilling/abrasion ▪ Excessive yarn hairiness, hairiness variation. [6]

Poor dye uptake ▪ Yarn contamination. [6]

▪ Neps in yarn. [181]

Variation in

dyeability

▪ Melt spots/thermal damage in yarn. [193,

206]

Dimensional

stability

▪ Low elongation. [6]

▪ Low tensile strength. [6]

Fluff ▪ Excessive yarn hairiness. [216]

Abrasion of

machine parts

▪ Trash and dust. [6]

4.4.2 Faults due to filament yarns

Filament yarns are used to produce union fabrics, in which two or more yarns of different fiber

types are combined to produce a fabric. Filament yarns depending upon the type may consist of

one or more filaments. Filaments can either be natural, such as silk, or manufactured such as

polyester, nylon, viscose, etc.

4.4.2.1 Faults in manufactured filament yarn

Manufactured filaments are produced either by melt, wet or dry spinning depending upon the fiber

type. The extruded filaments are then partially drawn during the spinning process. These partially

drawn filaments are further stretched to their desired draw ratio to produce filament yarns in a

continuous or separate processing step. Filament yarns for textile applications are used as either

flat yarns or textured yarns. Flat yarns are generally produced by drawing the partially drawn

filaments directly after the spinning process. Textured yarns are produced through a process known

as texturizing in which flat filaments are converted into stretchy or bulky yarns. Texturizing is a

modification process to create bulk, stretch or texture in filament yarns [200, 217]. This gives them

the desired warmth, hand, natural texture, extensibility and appearance to use them in textile

154

applications. The process of modification is carried out by thermal, mechanical or chemical

transformation of the individual filaments and their spatial arrangement in the yarn bundle keeping

the continuity of original filaments [218]. Different types of texturizing processes used depend on

the desired yarn characteristics such as false-twist, stuffer-box, knife-edge crimping, knit-de-knit,

air-jet, intermingling, etc. The most common type is the false twist texturing [218, 219]. The

important factors affecting the quality of textured yarns are yarn tension (before spindle (T1), after

spindle (T2) and winding (T3)), draw ratio, primary heater temperature, twist insertion (D/Y ratio),

second heater temperature, overfeed and package build [219]. These process variables must be

controlled properly according to yarn and fiber type to ensure a problem-free yarn production. The

most common faults that occur in manufactured filament yarns include variation in polymer

morphology, tight spots, broken filaments, bulk variation, intermingling faults, surging, package

build and density problems, and mass variations. The relationship between different texturizing

process parameters and various yarn properties during the texturizing process is given in Table

4.11 [219].

155

Table 4.11: Effect of texturizing process parameters on yarn properties.

156

Variation in polymer morphology

Polymer morphology differences during texturizing lead to differences in dye uptake, tenacity,

elongation, and dimensional stability. Hence, thermal and mechanical stress histories of the

filaments during texturizing are of prime importance. Differences in dye uptake in the textured

yarn are generally observed as both within or among packages. Dyeability variation within a

package is generally due to the variation in the raw material. The difference in dyeability between

packages is commonly due to the texturizing process. Correct machine settings should be used

especially during a material change over. The tension and temperature should be uniform during

processing within and in between machines. The storage of raw materials for texturizing also

influences the dyeing behavior and crimp of filaments and varies with the age of raw material.

Therefore, long storage of raw material should be avoided. The raw materials should be

acclimatized to atmospheric conditions for 1-2 days before being used. The yarn strength and

dyeing behavior are often used as indicators of variation in polymer morphology since low and

high strength yarns show differences in their dyeing behavior. During the twisting and untwisting

process filament migration takes place. If core filaments are drawn and heated differently than the

outer filaments the filament migration due to twisting may result in dyeability variation.

Depending upon the variation in polymer morphology, the dyeing defect may appear as random

defects in the form of dark flashes and streaks and periodic defects such as moiré and barré [157,

218-222]. The main reasons for structural variations are [218-221]:

▪ Damaged yarn transportation devices;

▪ Dirty primary heaters;

▪ Faulty yarn feeding;

▪ Wearing off of twisting disk;

▪ Improper contact of the cooling plate;

▪ Variation in yarn cooling;

▪ Melting of filaments due to contact with the secondary heater walls;

▪ Application of coning oil to the package intended for yarn dyeing;

▪ Variation in draw ratio;

▪ Differences in the primary heater temperature; and

▪ Improper atmospheric conditions.

157

Tight spots

These are regions of highly twisted yarn compared to the rest of the yarn and hence do not have

the same bulk. The length and frequency of this fault are highly variable. Non-steady state

functioning of the texturing machine and differences in yarn structure along the thread line should

be avoided. The underlying reason for tight spots is the use of too high torque or too low yarn

tension. Tight spots of more than one per 20 m of yarn are considered unacceptable. This type of

fault appears as dark bands in fabrics [218, 220, 223]. They can be detected by inspecting the yarn

or by using a knitted sleeve or via on-line monitoring [219].

Broken filaments

This problem is due to many causes, such as variation in properties of raw material, mechanical

damage in the yarn path and incorrect settings of the texturizing machine. Yarns containing fine

filaments exhibits this problem more often compared to coarse filament yarns [219].

Bulk variation

These variations occur either along the yarn length or from one package to another. These are

caused due to high throughput speeds, low draw ratio, and incorrect rate of twist insertion [219].

Intermingling faults

These faults comprise two broad groups. The first group includes intermingling properties such as

intermingling knot frequency and strength, and the second group comprises of irregularity. Thus,

a proper selection of intermingling jet and its operating parameters should be made. The jets should

be clean and replaced after a certain period. The irregularity is seen as the presence of long and

short gaps without interlace [219].

Surging

This is the thread line instability during the texturing process and observed as the untextured

appearance of the yarn. This problem occurs as the texturing speed increases. Surging is caused

by the raw material properties and parameters of the texturizing machine. This problem can be

overcome by increasing the draw ratio, reducing throughput speed and increasing the D/Y ratio

(ratio of speeds between friction discs and throughput speed of yarn) [219].

158

Package build and density problems

Package density is important in order to obtain level dyeings. Incorrect package density, either too

soft or too hard, and variation within and in between packages are common causes of dyeing

problems [219]. This problem is discussed in more detail in section 4.4.3.

Package structure faults are caused due to improper winding parameters such as winding

angle, traverse length, take-up tension, and package density. Poor housekeeping and incorrect

handling procedures may also cause package faults. The most common faults are bulging,

webbing, overthrown ends, ridges, saddling, shouldering, no-tail package and dirty or damaged

packages [219].

Mass variations

Short to medium mass variations (length: 0.01 to 50 m) are caused during texturizing. These

variations can be periodic or non-periodic depending upon their occurrence. The main reasons for

such variations are differences in drawing, twisting and defective traversing mechanisms during

winding [224]. Some coloration problems due to mass variations include barré in knits, warp

streaks or weft bands in woven fabrics [225].

4.4.2.2 Faults in natural filament yarn

Natural raw silk yarn is a continuous filament yarn made up of a number of individual silk

filaments. It is obtained by the process of reeling in which filaments from several silk cocoons

(approx. 7-8) are combined to produce a raw silk yarn (approx. size 20/22 den). They are then re-

reeled and twisted, depending upon the requirements, to produce 2 or 3-ply yarns [205]. Common

faults found in raw silk yarns include uneven yarns, cleanness, and neatness.

Uneven yarn

The silk filament produced by the silkworm is not uniform. Moreover, the number of filaments in

the cross-section of the yarns vary, which reduces the evenness of the yarn. Evenness values of

raw silk are considerably higher than the synthetic filament yarns of the same count. It depends on

the number of fibrils removed from the cocoons and finished cocoon replacement during the

reeling process. Periodic unevenness in the yarn is attributed to a new cocoon added during the

reeling process [205].

159

Cleanness/defects

These are the randomly occurring thick and thin places in yarn and are defined per 100m. Thick

place refers to mean mass > +35% of the mean mass of silk yarn while for the thin place the

threshold is -40% of the mean value. They are mainly caused by operator performance and skills

and also by cocoon unwinding process. These defects may lead to yarn breakage, stoppages and

poor fabric appearance [205].

Neatness/impurities

These include frequently occurring thick places of shorter length (< 4 mm) having mean mass >

140% of the mean mass of silk yarn. These impurities are caused by the reeling process. Damaged

yarn guides also cause this type of impurities. They may cause poor fabric appearance and dark

spots due to more adsorption [205].

A summary of the problems caused by filament yarns due to yarn faults in downstream

processing is given in Table 4.12.

Table 4.12: Problems due to filament yarn faults.


Manufactured filament yarn

Dark flashes/dark dye

defects

▪ Variations in polymer morphology [222]

Streaks/bars in woven

fabric or barré in knits

▪ Variations in polymer morphology [218-220]

▪ Mass variations [222, 225,

226]

▪ Yarn mixing (different deniers, number

of filaments, twists)

[226]

▪ Intermingling faults [226]

▪ Bulk variation [149]

Uneven/poor fabric

appearance

▪ Mass variations [226]

▪ Tight spots

160



▪ Broken filaments

▪ Bulk variations

▪ Intermingling faults

▪ Surging

Dimensional stability ▪ Variations in polymer morphology [226]

Crease formation in fabric ▪ Yarn mixing (number of filaments) [226]

▪ Intermingling faults [226]

Natural silk filament yarn

Poor fabric appearance ▪ Uneven yarn [205]

▪ Defects [205]

▪ Impurities [205]

Dark spots ▪ Impurities [205]

4.4.3 Problems due to the winding process

Winding is usually the last process stage in the yarn formation and the starting point for the

subsequent processing stages (weaving, knitting, and dyeing). The yarn winding process is used

in various stages of processing depending on product type [157, 181, 208, 227, 228]. The main

aim of the winding process is to collect a large quantity of yarn on the package suitable for use in

downstream processing [157, 181]. The winding step is dependent on spinning methods. In most

of the spinning systems, except ring spinning, such as open-end (rotor), air-jet spinning and

filament production, the winding step is integrated with the spinning process. The yarn is taken

directly from spinning for use in the knitting process or as weft in weaving or in the warping

process. The ring-spun yarn needs to go through a separate winding process due to package size

limitations which are normally carried out in a spinning mill [157, 181, 215, 227, 228].

The winding process must meet the following requirements:

▪ Creation of suitable package type meeting the requirements of downstream processing.

Yarn packages are created in various forms which depends on the intended application.

The main considerations for packages are shape and size, density, stability and

161

unwinding performance. Yarn packages for warping, weft, knitting, twisting, and

dyeing require different package shape, density and geometry. The common package

shapes are cheese (cylindrical) and cones. For cones, there are different types of cone

tapers depending on the end-use. The taper may be constant and known as a straight

ended package or accelerated taper with a concave end at the top and convex end at the

bottom called dished ends. For transport and storage, high package density is desirable

but for dye packages low and uniform package density is required for good and even

dye penetration. Yarn tension is the most important parameter for homogeneous

package structure and depends on the yarn and package parameters. The yarn tension

during the entire package buildup should be constant. The package should be free from

critical pattern zones to avoid sloughing-off during unwinding and unlevel dyeing. The

package should also be stable so that it can bear the stresses and retain the structure

during subsequent handling and processing. Also, the package must have a regular

structure for error-free unwinding at high speeds. Lastly, the package should be free

from any defects [157, 181, 227, 229].

▪ Removal of yarn faults with a low number of yarn joints as possible.

Spun or filament yarns contain different types of faults which must be removed in the

winding process. This process is known as clearing. In this process the yarn fault is

detected, and depending on the clearing limit, it is cut and yarn ends are then joined by

the splice. The main objectives of the clearing process are the detection and elimination

of seldom occurring yarn faults such as thick places, thin places, and foreign fibers.

Additionally, any quality problems throughout the whole yarn bobbins should be

detected and the off-quality should be separated and the operator should be alerted if

the process is out of control. Special attention is required for count change in the

machine. Yarn tension is an important fault detection, so it must be uniform. There

should be a proper fluff removal installed on the machine to remove the fly fibers [208,

230]. The selection of splicer type is important which depends on the type of yarn to

be processed. Important points related to splicing are retention of specific yarn

structure, quality, yarn appearance, elastic property and strength of the spliced joints

[229].

162

▪ Uniform application of lubricant (wax) depending upon the requirement such as

knitting.

Knitted yarns are waxed in order to reduce their coefficient of friction for better knitting

performance. The amount of wax applied should be sufficient and constant throughout

the whole yarn length and from package to package. This is essential to avoid yarn

breakage, fly generation and needle breakage during knitting [216, 227]. The quality

of waxing is dependent on the yarn to wax, roller contact pressure, rotation of wax

roller against the yarn, proper dimensions and quality of the wax (softness and melting

point) [227]. The amount of wax deposited is generally 0.5-1 g/kg of yarn. The

selection of wax grade for good running performance depends on fiber type, yarn

structure, count, moisture content, temperature and humidity during the winding area,

conditioning, storage and shipment [181].

The preparation of a suitable yarn package is an essential requirement for successful

package dyeing [231-233]. Many problems in yarn dyeing are due to inadequate winding of

packages. There can be two approaches for producing a correct package for yarn dyeing. In the

first type, a spun yarn package is produced on perforated cones which are produced directly by the

spinner. This eliminates the winding process but may cause problems during dyeing. Also, yarn

density is not controlled by the dyer. Texturized yarn packages are generally prepared on the

texturizing machine thereby reducing the need for an extra winding step. In the second approach,

which is the most common, yarn cones from spinning are rewound on perforated dye tubes [232].

Package rewinding has two main functions [234]:

▪ Package buildup according to end-use requirement. This includes package rewinding

for dyeing, after dyeing and sample packages.

▪ Adjustment of yarn quality.

The most important requirements to be fulfilled by a winding process for package dyeing

are [235]:

▪ Production of yarn packages on current dye tubes;

▪ Uniform package density, diameter, and format with as little variations as possible;

▪ Reproducibility of package qualities to ensure reproducible dyeings;

163

▪ Good package stability for resistance against mechanical stresses during the dyeing

process; and

▪ Flexibility in lot size.

Yarn package has an influence on the levelness, quality, and reproducibility of the dyeing

process [236]. There are many factors that affect the properties of yarn packages which are package

shape and size, dye tubes, type of winding system, winding angle, traverse ratio, yarn shrinkage,

yarn conditioning and length, and package density [231, 236, 237].

Package shape

Two package shapes are commonly used in yarn dyeing which include conical and cylindrical

packages. The cylindrical package is a preferred package shape used for dyeing. This package

shape gives a uniform liquor flow along the package axis, as well as optimum packing and sealing

between the packages in the dyeing machine. This leads to good dyeing levelness, maximized

machine loading and dye house cost savings [228, 232, 233, 238, 239]. Cones have a difference in

liquor penetration along the package axis, especially along the edges due to their shape.

Furthermore, they need expensive spacing devices which are difficult to obtain complete column

sealings and result in unsatisfactory pressing leading to dyeing problems. Also, the slippage of

cones may lead to channeling and unlevel dyeings. Residual dyestuff may also be deposited around

spacers [232, 233, 240].

Package size

Package diameter influences the uniform flow of dye liquor across the entire package [228].

Depending upon the machine and spindle, different package sizes are used [238]. Larger diameter

packages are preferred as they give more carrier capacity, with a lower tendency of leakage and

more uniform liquor flow. Therefore, they require less liquor flow rate [241]. Large diameter

packages give long flow channels in which the flow resistance is largely affected by the fiber

swelling, shrinkage or deposits as compared to short flow channels such as in small package

diameters. If this parameter is not properly controlled it may lead to package deformation, unlevel

dyeing and damage to spindle locks. Liquor flow must be controlled properly depending on the

package resistance characteristics. The diameter of a package must correspond to machine vessel

164

diameter as there is not a single package diameter which gives optimum machine capacity and

dyeing performance [242].

Dye tubes

There are different types of dye tubes with a broad range of designs and materials. Some common

types are inflexible, flexible, tapered, cylindrical, plastic, spring, steel, one-way or reusable [233,

235]. Tubes are made up of different materials such as plastics, aluminum alloys and stainless steel

[228]. The dye tubes must have a perfectly cylindrical body, axial stability, good temperature and

pressure stability and must be resistant to dye staining [228, 231]. Dyeing tubes are selected based

on cost, durability and staining behavior [233]. Depending on the winding process and dye tubes,

the packages are axially pressed. However, density variation might occur due to reverse flow and

errors in pressing. Also, it increases yarn hairiness due to the sliding of yarn and problems in

unwinding after winding [228].

Type of winding method

The winding process should produce a suitable package in terms of weight, diameter, traverse, and

density with good unwinding properties with a minimum waste generation [239]. There are three

common types of winding systems: random, precision and step precision winding. Table 4.13

shows the comparison between the different winding types [181, 231, 237, 243]. In random

winding, which is mainly used for spun yarns, the yarn is laid randomly which can result in forming

pattern zones if the anti-patterning device is not used. The package density, however, is uniform

due to a constant angle of winding over all diameters. Due to the random arrangement of yarn, a

yarn package having varying structure of cavities is produced. Precision winding is mainly used

for filament yarns in which the distance between adjacent yarns is controlled. The winding angle

decreases as package diameter increases keeping the winding ratio constant. This is accompanied

by a uniform increase in package density outwards. Higher package density can be achieved as

compared to random winding. The degree of package density increase can be controlled with the

help of parameters such as yarn distance, starting angle of winding or yarn tension according to

the end-use. There are more chances of producing a package with hard flanks. Lastly, step

precision winding combines constant winding angle of random winding and a constant winding

ratio of precision winding. Package structure can be controlled by the selection of any winding

165

parameter resulting in a wide range of end-use applications [181, 237, 238, 243]. For dye packages,

step precision is the most suitable type as it is free from pattern zones and the almost constant

winding angle produces a homogeneous package density [228]. Package density is affected by a

number of winding parameters that depend on the type of winding system used [238]. During the

winding process, some margin must be considered to take shrinkage or swelling into consideration

[244].

Table 4.13: Types of winding systems.

Characteristics Random winding Precision winding Step precision

winding

Arrangement of yarn

layers

Random Precise Precise

Winding angle Constant Decreasing Slightly reduced

Winding ratio Reducing Constant Reducing

Winding density High Low High

Package density Uniform Varies from inside

to outside

Uniform

Package stability Stable Fragile Stable

Critical pattern zone

(Ribboning)

Possible

(Anti-patterning

device required)

No No

Unwinding performance Poor (pattern zones) Good Good

Liquor flow

characteristics

Not optimum Good Good

Capital cost Low High Moderate

During yarn dyeing, yarn packages are pressed to increase the column density. When

packages are pressed, the package geometry must be such that pressing would not cause local

changes in the density. For some cylindrical packages where the package face is not flat and

rectangular, as in random and precision wound packages, higher pressing force is required to avoid

166

leakages due to uneven faces which may cause non-uniform flow due to high local densities in a

package. The maximum package density is around the package center and cavities may form

around the dye tube. Water and deposits may accumulate in these cavities and lead to unlevel

dyeing and problems in washing, soaping, cleaning, and drying. In contrast, packages produced by

step precision winding have flat faces and soft edges. They also don't require high pressing

pressure and uniformity in package density is maintained [236].

Winding angle

Many package characteristics such as package density, unwinding performance, sloughing-off,

hard package flanks are affected by the winding angle. For dyeing, a higher winding angle is used

to create an open structure and low winding density [228].

Traverse ratio and length

Traverse influences the package structure and thus it must be chosen in a way to result in an open

package structure and low density as required for dyeing. Hard flanks may be formed at the yarn

reversal points during winding and must be avoided in order to obtain a uniform dyeing. It also

results in the abrasion of package flanks with winding drums. To solve this problem either edges

are pressed after winding or rounded side flanks are created. Traverse stroke is gradually reduced

to produce rounded side flanks of the desired rounding radius [228].

Package density

Package density influences the liquor flow. A dye package should have a uniform package

structure and density, from the inner to the outer layers of the package and in-between packages

[231, 238, 243, 245]. The package should have an open construction to allow optimum liquor flow

and should be stable against the mechanical, hydrostatic and hydraulic forces during package

dyeing [238]. Package density determines the porosity of the package. Therefore, it affects the

liquor flow and dyeing behavior [246]. All packages in the same lot must have the same density

and diameter. The density variation should not be more than ± 2.5%. This is required for uniform

and similar liquor flow through entire packages inside the machine and for reducing within lot

variation. Uniform package geometry and density are essential to avoid channeling within and in

between yarn packages. This problem occurs due to the high liquor flow through areas of least

167

resistance compared to high-density areas. This leads to unlevel dyeing within and in-between

packages [231]. Soft wound packages may distort during dyeing and cause channeling. The

package distortion also causes problems in handling and rewinding [232, 233, 240]. Synthetic

fibers shrink during dyeing. Therefore, the package structure should allow yarn shrinkage without

yarn deformation and affecting the package flow [244].

The yarn package must also have uniform and symmetrical package flanks with the same

density as the remaining portions of the package and must be firm and stable as these affect the

package durability [157, 231]. Poor dye penetration (dead zones) may occur due to package flanks

despite a low density being used. To solve this problem package edges are broken by mechanical

deformation. This process leads to a damaged package build and affects the yarn winding due to

the movement of yarn layers. Package rounding during winding of dye packages may solve this

problem and there is no need for edging and rewinding processes [157, 181, 238, 243].

Yarn packages for dyeing are created with a constant diameter (volume). Package density

is affected by a number of winding parameters which depends on the type of winding system used.

The important parameters are winding speed, winding tension, angle of winding and cradle

pressure. Package density may be adjusted during the winding process by changing the traverse

and winding ratio. Cradle pressure controls the winding tension. The winding tension should be

kept below a certain limit to avoid damage to the yarn. The package should be free from critical

pattern zones (ribboning) and an uneven package density. Dye penetration is different in pattern

zones compared to the rest of the package and this results in unlevel dyeing [157, 181, 233, 238,

243, 247]. Despite proper control during winding, variations in packaging density occur.

Variations in yarn properties (count, twist, etc.) within the tolerance range during yarn

manufacturing may also lead to fluctuations in yarn compactness during winding. In practice, a

deviation in package density of ± 5-8% is considered normal while those around ± 3% are very

rare [247].

The flow resistance of the dye liquor through the yarn packages inside the dyeing machine

is indicated by the differential pressure which may determine the liquor throughput. The

differential pressure increases with an increase in package density. Yarn packages with higher

package densities in close proximity to dyeing tubes may lead to non-uniform dyeing. The radial

package density is altered due to a reduction in the coefficient of friction of yarn in the dye liquor

and chemicals in the dye liquor. The shearing force exerted by the dye liquor may cause yarn

168

slippage and change the liquor flow direction. The changes in the winding density in areas adjacent

to the dye tube lead to an increase in the differential pressure which is beyond the control of the

dyer [248]. Liquor throughput affects the movement of dyestuff to the fiber surface of yarn

assembly and ultimately influences the uniformity of dyeing. The aim of the dyer is to produce

level dyeings despite having some variations in package densities. For practical purposes, the dyer

has to take into consideration ± 10% variation in package density within and between packages.

It has been found that for yarn packages with varying winding densities within and in between

packages, the difference in dimensions of the package will not affect the dyeing results if liquor

throughput is controlled with a preselected differential pressure. Radial variations in package

density especially in the areas adjacent to the yarn tube may cause a high amount of dye liquor

flow. This is due to the high differential pressure and shearing forces operating in these zones. The

outside regions of the package, therefore, have a low amount of dye supply. This may lead to

lighter edges if the dye movements are slower than the diffusion rate of the fiber. Generally, this

is not the case as dyer considers the yarn type and dyestuff behavior. For synthetic yarns, this

problem can be overcome by controlling the heating rate. In the case of vat dyeing, where the

movement of dye is faster during the initial stage, the variations in density are compensated in the

end by the leveling stage. Therefore, the local variations in the liquor throughput have a minor

influence on the variation in dyeing results as compared to the radial difference in package density

which has a significant impact [247].

After yarn dyeing has been carried out, two procedures may be performed on the winding

machine which are known as 1:1 rewinding and peeling. In 1:1 rewinding, one feed package is

rewound to form a finished package to avoid color differences in the finished package due to the

deviations in several feed packages. Another operation performed in reference to the rewinding of

dye packages is termed as peeling. This is done to even out color differences within a dyed

package. Quality improvement of dye package exhibiting a difference in dye penetration from the

core to surface is achieved by unwinding the defined length of yarn from the start and or the end

of the package [234, 235].

Table 4.14 presents the problems caused in subsequent processing due to the winding

process and their solutions.

169

Table 4.14: Problems caused by the winding process.


Problems in weaving and knitting

Yarn breakages during

the warping process

▪ Faulty yarn package The yarn packages should be

fault-free.

[249]

▪ Improper splicing The spliced joined strength

should be as close to yarn

strength as possible.

Drop stitches, holes or

cloth fall-out

▪ Insufficient waxing of

yarn

Ensure proper contact of waxing

roller and the yarn. The preferred

wax deposition ranges between

0.5-1 g/kg of yarn.

[181,

216]

▪ Faulty yarn package Check the yarn package after

winding. It should be free from

defects.

[249]

▪ Improper splicing The spliced joint should have at

least an average strength of 80%

of the yarn strength with low

strength CV%.

[181,

216]

Barré or horizontal

stripes in knitted

fabrics/weft stripes or

bars in woven fabrics

▪ Fluctuation in package

density leads to uneven

yarn tension during

unwinding.

The package should have uniform

density and yarn tension during

winding should be constant.

[216,

250-

252]

Problems in yarn dyeing

Channeling ▪ Uneven winding density The package density should be

uniform within the package.

[231,

253]

▪ Very low winding

density (soft package)

Use optimum package density

according to yarn count and fiber

type.

[231]

170



Leakage in package

column

▪ Poor stability of dye

tubes against

temperature and pressure

Select dye tubes which should be

stable against temperature,

mechanical, hydrostatic and

hydraulic forces.

[231]

Unlevelness

(Uneven dyeing)

▪ High package density Use optimum package density.

The yarn shrinkage factor should

be considered.

[231,

253]

▪ Uneven waxing of yarn Ensure proper contact of waxing

roller and the yarn.

[149]

Shade variation within

package layers

▪ Uneven package density The density should be uniform

within layers inside the package.

[231]

Pressure or luster

marks on inner yarn

layers

▪ Very high package

density

1. Use proper package densities

according to fiber type and

yarn count.

2. Cover the tube or cone with a

paper or PP woven sleeve.

[231]

Package deformation

and yarn abrasion

▪ Varying package

density, within and in

between packages

1. The package density should be

homogeneous.

2. Control the winding

parameters to produce yarn

packages with uniform and

reproducible densities.

[231]

▪ Non uniform winding of

packages

Ensure uniform package density

throughout. Use step precision

winding if possible.

▪ Improper coverage of

tube perforations

The winding process should

properly cover the tube

perforations with the yarn.

171



▪ Use of damaged tubes Use defect free dye tubes.

▪ Poor temperature

stability of the dye tubes

leads to shrinkage and

deformation of dye tubes

Select dye tubes according to

their temperature stability.

▪ Edging process for

rounding of package

flanks

Use rounding during winding. [243]

Poor liquor

penetration in edges of

the package (dead

zones)

▪ Yarn reversal points

during package winding

Gradually reduce the traverse

length.

[228]

▪ Improper edging or

rounding of package

flanks

Perform proper edging or use

rounding during winding.

[243]

Swelled package

shoulders with a puffy

appearance

▪ Too soft package

winding

Use optimum package density. [254]

White or light streaks

of yarn on package

▪ Too soft package

winding

Use proper package density. [254]

Package yellowing ▪ Too high winding

density can lead to

partial over drying of

packages

Use the optimum winding

density.

[231]

Variation in moisture

content

▪ Differences in winding

density

Check the winding density. [231]

172

4.4.4 Problems due to conditioning

The spinning and winding process may generate stresses in the yarn. These stresses may cause

instability in the yarn which may have a tendency to untwist or form snarls and loops [100]. The

conditioning process is performed to stabilize the yarn. Different types of processes can be

performed which include relaxing, twist-setting, pre-shrinking, fixation and stabilization

depending upon the yarn and fiber type [255]. The main aim of the conditioning process is to

increase yarn strength and elongation, reduce snarling tendency and improve the performance of

yarn during downstream processing. The process is carried out in a closed pressure vessel with

vacuum and steam. Indirect or direct steam conditions may be used [100, 227]. The conditioning

temperature depends on the type of process and fiber type. For example, a minimum temperature

of 90 oC is required for wool while for synthetic fibers the temperatures of 110-140 oC are needed

[100]. For stabilization of blended yarn, the temperature must be selected according to fiber with

the least temperature stability without affecting the color and properties of the fiber [100]. Twist

setting is generally carried out below 100 oC (70 oC, max. 80 oC for polyester and their blends),

while pre-shrinking is carried out at temperatures above 100 oC (max. 115 oC for polyester and

their blends) [206].

Cotton yarns are conditioned after the spinning process to increase their moisture content

and enable the moisture to evenly distribute throughout the yarn package. The moisture content in

the yarn influences the physical properties of the fiber and yarn [227]. Very high and uneven

moisture distribution should be avoided as it may cause variations in yarn elongation when tension

is applied. The stretched areas in the yarn are fixed during drying. When yarn undergoes a wet

process the overstretched areas can contract and form tight regions. This type of fault is more

common in wool [149].

Waxed yarns should be not be steamed or conditioned at high-temperature conditions.

These conditions can cause the wax on the yarn to melt which may also penetrate into the yarn,

which would increase the coefficient of friction. Waxed yarns that needs to be processed by this

method should have high wax content in order to counteract this problem. Alternatively, waxes

with high-temperature stability should be utilized [181].

The important factors for conditioning include the penetration of vapor inside the package,

temperature, treatment time and steam type. In the production of large and high-density packages,

an even and uniform penetration of steam should be ensured. This is usually obtained by increasing

173

the treatment time. The steam penetrates from the surface of the package inwards at a variable rate.

It can also penetrate from the side of the yarn carrier if the carrier is perforated or deformed. Even

penetration can be obtained by using the intermediate vacuum during the first third of the treatment

time. Using very short or long treatment times, or variability in package density can result in

variation in fiber properties which leads to problems in further processing of yarn. The formation

of condensate inside the machine should also be avoided [100, 206, 255]. Storage time before

conditioning and package size should be similar for all packages in the lot [221]. The treatment

program (time and temperature) from one yarn lot to another should be constant to ensure obtaining

the same yarn properties.

The major problems caused by improper yarn conditioning comprise increased unwinding

tension, knitting needle breakages, variation in yarn frictional values, static generation, fly

generation, yarn breakages, improper yarn strength, reduced size pick-up, yarn snarling, tight

threads, shade variation, and streaks during dyeing [149, 157, 206, 256].

4.5 Problems arising from fabric formation

The textile fabric is a combination of fiber or yarn or both and can be produced by different

methods: weaving, knitting, braiding, tufting and non-woven manufacturing [215, 257]. The

selection of fabric for a particular application depends on the required performance and/or aesthetic

characteristics, keeping into consideration cost and price. The main application areas for fabric are

apparel, home furnishings and industrial [215]. Weaving and knitting constitute the major

applications typically used for apparel and home furnishings while non-wovens are mainly used

for industrial applications. Braiding and tufting use is limited to specific purposes [257]. The

majority of the fabric produced nowadays is by weaving and knitting, although non-wovens are

gaining importance.

4.5.1 Yarn preparation for fabric formation

Yarn is a basic building block of woven and knitted fabrics [215]. In order to produce quality

fabrics, the yarn must be presented in a form which is appropriate for the fabric formation process.

Yarn obtained after the spinning process in most cases cannot be used directly to produce a fabric.

The yarn preparation involves a series of processes that improve the properties of yarn to meet the

174

requirements of knitting or weaving processes [215, 258]. The preparation requirements for yarns

according to different fabric forming processes are [258]:

▪ Weaving yarns

a. Warp:

- Good yarn alignment (on weaver's beam);

- Good yarn strength (weaving tensions);

- Low hairiness;

- Good yarn smoothness; and

- Good elongation and flexibility.

b. Weft:

- Good yarn package for proper unwinding.

▪ Knitting yarns.

a. Warp knitting:

- Low yarn friction;

- Low fiber shedding; and

- Good yarn smoothness.

b. Weft knitting:

- Low yarn friction;

- Low fiber shedding;

- Good yarn smoothness; and

- Proper alignment of yarns with respect to needles.

175

Figure 4.4: Steps involved in woven and knitted fabric production.

The weft and warp yarns in the weaving process and yarns for the knitting process are

subject to different conditions, requirements and therefore preparations. The processes used are

also dependent on the yarn type [215, 216]. The steps involved in fabric manufacturing using

knitting and weaving processes are given in Figure 4.4 [215, 258]. As already discussed, the

winding process is normally carried out in a spinning mill. Section 4.4.3 covers the potential faults

that can arise from the winding process. Table 4.15 shows the common yarn preparation processes

and their objectives [215, 230, 258-260].

Yarn production

Weaving Knitting

Weft Warp Weft knit Warp knit

Winding

Quilling (Shuttle loom)

Winding

Warping

Sizing

Winding and Waxing

Warping

Drawing-in orTying-in

Winding and Waxing

Knit fabric

Knit fabric

Woven fabric

176

Table 4.15: Objectives of the yarn preparation processes and associated fabric defects.

Processes Objectives Fabric defects caused

Quilling ▪ Package formation (for

shuttle loom).

Knots, sloughing-off, coarser or finer weft,

foreign body.

Warping ▪ Preparation of even and

uniform sheet of yarn.

Knots, double ends, missing or broken ends,

mixed count, loose or slack ends, streaks.

Sizing ▪ Improvement in strength,

smoothness, elasticity,

lubrication and abrasion

resistance of yarn.

▪ Reduction of yarn

hairiness.

Missing ends, wrong pattern, bad selvages,

sticky ends, loose or slack ends, double ends,

missing or broken ends, lint balls, floats,

abraded ends, stiff warp, incomplete

desizing, wax deposits, hard size, streaks,

harsh hand.

Drawing-in or

tying in

▪ Setting up of yarn ends in

the weaving machine.

Wrong pattern, reed marks, streaks in the

warp direction.

The defects that are present in the woven or knitted fabric can be due to numerous reasons.

Some faults are attributed to the yarn preparation processes. The underlying reasons for such

defects are due to:

▪ Yarn related problems: yarn quality and mixing

The quality of the yarn used is a very important aspect of producing good quality

fabrics. Many defects during the knitting or weaving process are due to yarn alone. It

is important to check the incoming yarn for different yarn quality parameters, which

should be within the tolerance limits. These parameters and their values depend on

whether the yarn is intended for the knitting or weaving process and the yarn type (spun

or filament). Variation in parameters is equally important along with individual values.

Section 4.4 covers the quality of yarn and associated faults in more detail. Another

aspect of equal importance is the mixing of different yarn types (different fibers, blend

compositions, count, etc.) during the yarn preparation processes. A proper yarn

segregation system should be designed, and workers should be trained. If the yarn

mixing takes place it would be very difficult to identify them in the subsequent

177

processes until the fabric is dyed or printed. The chance of yarn mixing is very high in

the winding process, especially in the case of ring spinning process. The incoming yarn

bobbin should be checked for the presence of marks or tints. This is very important in

the case of blends when the mill is producing yarns with different blend ratios or fiber

components. If the bobbins are faulty or stained they must be separated otherwise faulty

fabrics may be created. For filament yarns, attention should be given to different yarn

manufacturers, lot numbers, yarn denier and number of filaments as dye uptake varies

from lot to lot and may result in the formation of weft bars in dyed fabrics [230].

▪ Wrong machine settings and parameters

Machinery related parameters constitute important factors in the production of quality

fabrics include machine settings and selection of process parameters. Proper machine

settings are essential for efficient machine operation. The fiber component in the yarn

has an influence on the processing behavior of the yarn and therefore needs proper

attention. The polyester component in the blend may generate static charges. The

polyester/cotton blended yarns are thus hairier and bulkier than the equivalent count

cotton yarns. These differences in properties must be considered for machine settings

as well as process parameters when blended yarns are processed in winding, warping

and sizing machines [230]. Filament yarns may be frayed or ruptured during high-speed

processes due to static charges and may thus cause defects during the weaving process

[252]. The following points are important in relation to yarn preparation machines for

fault-free fabric production in weaving and knitting:

- Warping:

Stoppages of yarn amounting to 0.1-0.2 per million meters are considered good for

the warping process. It has been found that yarn, package and machine settings

faults are equally responsible (33% each) for yarn breaks during the warping

process. The distance between a yarn package and the yarn guide element must be

optimized to obtain a uniform take up-speed [249]. Proper working of stop motion

is essential to avoid broken ends which may lead to lappers and migratory ends.

Machine speeds should be set according to material being processed. For blended

yarns which can generate static electricity the use of a static eliminator device is

recommended. The yarn tension should be uniform, otherwise, warp-way streaks

178

may occur. The average yarn running tension should be as low as possible, and

must not exceed 1/15th of the single yarn strength and should be uniform. Yarn

should be free from any fluff (lint accumulation) and the mixing of wrong ends

must be avoided [215, 230]. The yarn guide should not have sharp edges [261].

- Sizing:

The end goal of the sizing process is to eliminate or reduce warp breaks during the

weaving process. The size application should be uniform along the length and width

of the yarn. The yarn tension, stretch and size add-on need to be controlled properly

by correct machine settings and conditions to avoid abrasion, stretching, and

improper sizing of warp. The yarn spacing must be proper on the slasher box and

on the drying cylinders. Crossing and missing ends due to migration of ends must

be avoided. Size recipe is selected according to fiber type, blend ratio, yarn type,

fabric weave and construction and loom type. The anti-static agent is also used for

synthetic fibers. Blended yarn is more hairy, bulky and hydrophobic than cotton

yarns [215, 230, 262].

- Pirn winding:

The yarn tension should be uniform and slough-off of yarns must be avoided. The

mixing of yarn (wrong yarn) must also be avoided [215, 230].

▪ Operator related faults

The personnel involved in fabric formation processes such as machine operators,

supervisors, etc. are of equal importance for producing fault free fabrics. They should

be trained and made aware of the quality aspects, the importance of reducing defects

and machine downtimes [230]. Many defects such as wrong and broken ends are due

to the carelessness of the machine operators. The mixing of yarn packages during

clearing due to operator negligence is one of the common sources of warp streaks. Their

role is crucial in achieving the right-first-time production.

▪ Faults due to improper practices

Good housekeeping practices are important for improving quality. Blended yarn

accumulates dust and fluff due to static charge, so it need special attention. Yarn

packages and beams must be properly covered to avoid settling of dust and dirt. The

179

package movements in between processes should be done properly to avoid damaged

yarn packages or beams, rust marks and stains [230].

4.5.2 Weaving faults

The weaving process produces fabric by the interlacing of two sets of yarns that are perpendicular

to each other. The structure and appearance of the fabric are largely dependent on the weaving

pattern [215]. In todays’ weaving plants there are increasing requirements for performance,

productivity, and quality improvement. Some of the underlying reasons include market

competition, cost pressure, quick response, and market demand. The quality of the fabric is

measured in terms of two factors: fabric properties and the fabric defects as shown in Figure 4.5

[263, 264]. These aspects of fabric are dependent on a multitude of parameters extending from raw

material to the finished fabric and have complex interdependence between them. There are some

physical aspects of fabric that can be predetermined by the raw material, yarn type, density and

weave collectively known as style. But there is a large number of quality demands which are only

fulfilled by optimizing spinning, weaving and finishing process dependent factors. Figure 4.6

shows the flow chart of various factors that has an influence on fabric quality in fulfilling customer

requirements [263]. The interdependence of two areas of fabric quality on various factors is not

similar. The creation of fabric defect is more dependent on the weaving process as compared to

the fabric properties [263]. The properties of woven fabric are dependent on material

characteristics, properties, and structure of fiber and yarn and the structure and geometry of fabric

[215]. The weaving parameters need to be set properly and according to yarn type, blend

component, and fabric design in order to obtain the required fabric properties.

Today's most important quality criteria in the weaving mill is a cost-effective production

of acceptable fabrics free of defects [263]. A defective fabric sells at a lower price and therefore

results in lower profits [215, 230]. Fabric defects can be attributed to many reasons and can be

classified as yarn defects and process defects. Process defects arise from the processes involved in

the fabric formation process: winding, warping, sizing, drawing-in, weaving process, operator

related and due to improper material handling. The fabric defects are a combination of all such

defects [230]. The defects mending process is generally very costly and acceptable defects levels

are steadily declining [264]. The permissible number of stoppages that are considered acceptable

are 2 stoppages per 100,000 picks [249] or 1-2 non-repairable defects per 100 m length of fabric

180

[263, 264]. Along with the fabric quality, machine stoppages due to yarn breakages, fabric faults

and seconds must be avoided [215]. Ten weft breaks or 4 warp breaks correspond to 1% loss in

weaving machine efficiency in an 8 h shift [249]. It has been found that 20% of machine stoppages

are due to the weft and 80% are associated with warp yarns. The stoppages due to deficiencies in

warp can be subdivided into 20-30% due to yarn faults; 30-40% related to the weaving preparation

process and 30-40% associated with the weaving process [264]. A proper quality control system

is essential for controlling the production of defective fabrics which need to be kept at minimum

levels [215, 230].

Figure 4.5: Aspects of fabric quality.

Figure 4.6: Fabric quality assurance.

Fabric quality

Fabric defectsFabric properties

Textile physics(Styles)

AestheticsWeaving

technology (Processes)

Type of yarn Finishing

Fashion

Function

Fabric

Weave

Density

Yarn

Fabricconstruction

Pro-perties

Preparation

Finishing

Weaving

Process

Defects

FulfillmentConsumers'requirements

Secondaryrequirements

181

Fabric quality can be improved by minimizing yarn stress on warp and weft downtime

reduction and good housekeeping practices [215]. The primary and secondary weaving motions

should be properly timed. Defects will occur if the motions are not properly configured. These

include picking, shedding, beating, let-off, take-off, warp, and weft stop motion. In a shedding

process, healds with good surface properties must be selected to reduce friction. There should be

a proper cleaning system to avoid fluff and fly accumulation [230]. Segregation should be made if

colored yarns or different fiber types are processed under the same shed. The temperature and

relative humidity of the air has an influence on the weaving performance, so they must be

controlled properly. The temperature varies between 21 to 25 oC and the relative humidity levels

are dependent on the fiber type being processed which is between 50% for some synthetic fibers

to 80% for low grades of cotton. Humidity also reduces the generation of static, lint, dust and fly

[215].

The common woven fabric defects are given in Table 4.16. It can be seen than defects can

be attributed to yarn, yarn preparation and weaving processes. The fabric fault is described along

with their appearance in the fabric, following which causes and countermeasures are discussed.

Table 4.16: Problems in woven fabrics their causes and countermeasures.

Problems Description and probable causes Remedial measures Ref.

Faults in weft direction

Stripe/

streak/ bar/

thick place

Excessive weft density due to

compaction of yarns creates a

difference in shade or brightness.

Usually, extended along the full

fabric width.

[6,

215,

250-

252,

261]

▪ Irregular weft density Check weft density and ensure it

is uniform.

▪ Excessive yarn tension during the

preparatory process changes the

yarn reflectance properties

Ensure the yarn is not subjected

to excessive tension in the yarn

preparatory process.

182



▪ Due to the starting mark,

standing place, set mark or

uneven let-off or uneven take-up

1. The loom startup should be

proper.

2. Delay start, slight tensioning or

loosening of the warp

depending on the length of the

stoppage

3. Check the setting of the let-off,

take-up, shedding mechanisms.

▪ Uneven yarn tension during yarn

unwinding of packages

The yarn tension during

unwinding should be uniform.

Thin place Normally visible as a translucent

fault but in extreme cases only a

few weft yarns per cm. It usually

extends across the full width of the

fabric.

[6,

250,

251,

261]

▪ Insufficient weft yarn density. Check the setting of the let-off,

shedding, and take-up

mechanisms.

▪ Improper yarn tension. The warp tension needs to be

controlled.

▪ Faulty weft insertion system. Check the weft insertion system.

▪ It may also be caused by faults

such as standing place, starting

mark, pulling back place, and

repping.

Lashed-in/

pulled-in/

dragged-in/

Some part of weft yarn is

accidentally pulled into the shed

from the following pick. It varies

[6,

215,

250,

183



jerked-in

weft

widely depending upon the length,

thickness, and the number of yarns

drawn into the shed.

251,

261]

▪ Due to damaged pickers,

improper working of trimmers,

tuckers, and holders.

Ensure proper working of the

picking system and weft selvage

devices.

▪ Incorrect timing of picking. Adjust correct pick timings.

Extraneous

yarn/

sloughed-off

weft/ double

pick

Appears as a thick place of varying

thickness depending on the form

the yarn is incorporated and in

some cases as projecting loops.

[6,

250,

261]

▪ Individual unrelated lengths of

yarn in a single or doubled form

in the same shed are woven into

the fabric due to improper

setting or functioning of the weft

insertion system.

Check the settings the functioning

of weft insertion system.

Fly/ slub/

foreign body/

lump/ gout

Generally visible in the fabric as

contrasting color in the form of

lumpy thick place.

[6,

250,

261]

▪ Foreign substances such as

fibrous fly, dust or contaminants

are woven into the fabric

1. There should be a proper loom

cleaning system and

segregation of loom where

colored yarns are present.

2. Check the humidity system.

Broken

pick/missing

Missing weft yarn for whole or

part of the fabric. It appears as a

[6,

250,

184



pick/dropped

pick/ chapped

weft

bar with no weft present for whole

or part of the fabric width.

251,

261]

▪ Due to breakage, running out, or

premature release of the weft

1. Ensure correct settings and

proper working of yarn feeder

and picking system.

2. Yarn tension during pick

insertion should be kept at

minimum levels.

Short pick Weft yarn missing at the edge zone

of the fabric and the end of the

inserted pick is pulled back into

the shed. It appears as a broken

pick in the fabric edge zone and as

a slack pick in the remaining zone,

especially where the weft is

inserted.

[6,

250]

▪ Improper working of weft

insertion system

Ensure the weft inserting is

working properly and weft is

correctly inserted till the end.

Faults in the warp direction

Reed mark/

stripe/ crack

It appears as a narrow transparent

stripe running in the warp

direction.

. [6,

250,

261]

▪ Irregular lateral spacing of the

warp ends with intact weave

interlacing

1. Check the reed plan.

2. Warp yarns are stressed more

than intended, check the shed

and warp tension settings.

185



▪ Due to non-uniform reed dent

spacing, defective or damaged

reed

1. Check the reed surface

(damaged reed).

2. Use finer reed if possible

Temple

mark/ pin

mark

A slight disturbance in the edge

zone of the fabric in warp direction

occurring periodically or full

length.

It appears either in the form locally

distorted warp threads or small thin

stripes or holes are created near the

selvage.

[6,

250,

251,

261,

265]

▪ Improper selection of temples 1. Correct selection of temples.

2. Use temples with cylinders

having a differential

arrangement of the rings in

spiral form.

▪ Damaged or worn out temples Replace worn out or damaged

temples.

Drawing-in

fault/ double

end/

misdraw/

wrong draft

Appearance depends on the type of

weave. It is in the form of two

parallel warp ends with equal

interlacing sequence in plain

weave and narrow warp-way stripe

differing in construction in other

weaves. In some cases, extra warp

ends are drawn in resulting in

incorrect warp density.

[6,

250]

186



▪ Incorrect sequence of drawing-in

through heald eye resulting in a

recurring incorrect interlacing

warp ends

Incorrect drawing-in or wrong

drawing-in-draft or reed plan.

Warp break/

missing end/

end out

▪ Warp end is missing over a

certain length of fabric. It is

present as a narrow transparent

stripe with incorrect construction

running along the warp direction

and insufficient warp density of

varying lengths.

[6,

250,

251,

261]

▪ Lower yarn strength 1. Check the yarn quality. The

yarn should have enough

strength and extensibility to

bear the weaving tensions.

2. Check the sizing process.

▪ Yarn abrasion from the guide

element

Yarn guide elements, reed

surface, and heald eye should

have a smooth surface.

▪ Faulty warp stop motion Check the warp stop motion

which should be free from any

lint or broken wires.

▪ Carelessness of the operator in

the tying of broken ends

Proper attention should be given

by the operator to repair broken

ends.

Direction independent faults

Poor

appearance

Fabric variations in large areas in

appearance, structure or

187



characteristics. The severity of the

fault varies depending on the form

and may be in fabric or along the

selvages.

[250,

259,

266]

▪ Abrasion caused by an emery

roller

Check the surface of the emery

roller or surfaces coming in

contact with the fabric.

▪ Incorrect tension in the left off

and take-up system

The let-off and take-up motion

should be fault-free.

▪ Incorrect working of the

shedding process

Check the shedding process.

▪ Faulty yarn The yarn should be uniform and

defect-free.

Stain/soiling/

oil/ rust

stain/fog

mark

Local discoloration in the fabric,

which may be periodic if the fabric

layers are pressed to each other.

[250,

251,

259,

261] ▪ Oil spots caused by the weaving

loom.

1. The machine should be

properly clean and the

lubrication system should be

working properly. Avoid

spilling and dripping.

2. Use stain remover.

▪ Discoloration caused by rust and

soiling during transport and

storage.

▪ Streaks due to rubbing.

The fabric should be transported

properly, and contacts rusty or

dirty areas should be avoided.

▪ Carelessness of the operators. Ensure proper yarn handling and

storage.

188



Yarn defect Usually, appear as an indistinct

changes in yarn thickness or shade

difference.

For mixed yarns, it can be seen as

wide stripes. It can occur both in

warp and weft directions.

[6,

250,

251]

▪ Fault in the yarn

(thick/thin/slub/knot/

unevenness/foreign fiber/

soiling/gassing mark)

Check the yarn quality. The yarn

should be free from defects.

▪ Mixing of incorrect yarn (wrong

yarn).

Good housekeeping is essential to

avoid yarn and lot mixing.

▪ Differences in blend

composition or using yarn from

different lots.

Blend ratio variation should be

within the tolerance limit (< 7%

for 67/33 PES/CO).

▪ Manufactured fiber coming from

different lots show variation in

dye pick-up if used side by side.

Use yarns from the same lot type

in case of manufactured yarns.

Snag/pick-

out mark/

pulling-back

place/ hang

pick

Appears as lumpy fault with

locally displaced lines of weft and

the faulty warp is either broken or

highly tensioned.

[250,

267]

▪ Rough or knotted warp end

causes one or more pick to snag

on and get jammed or displaced.

1. Use flat knot for broken warp

yarns.

2. Check the surface of the emery

roller

Interlacing

fault/

Usually appears as a compact and

distinct fault

[250,

261]

189



disturbed

place/ broken

pattern

▪ Faulty interlacing of several

adjacent warp and weft yarns

▪ Wrong drawing of yarns,

incorrect pick insertion in a shed

and faulty shedding

Check the settings of the picking

and shedding mechanism.

Snarl/looped

yarn

Appears as a short thick place with

projecting loops.

It may also occur at irregular

intervals in the center of the fabric.

[6,

250,

251,

259,

261] ▪ Yarn twisted around itself in

short lengths thereby resulting in

loops that are woven in.

1. Use optimum twist levels in

yarn.

2. Setting of yarn improves the

twist setting for high twist

yarns.

3. Use appropriate humidity in the

shed.

▪ Loosely woven yarns Ensure proper setting of weft

feeders and picking mechanism to

control yarn tension.

▪ Due to defective weft-fork Set the correct shedding timing

Hole/tear/cut Several adjacent weft and warp

yarns are broken or cut and vary

widely in size and form.

Check the surface of emery roller,

cloth roll and front rest.

[250,

259,

261]

▪ Wrong selection of temple Select the temple according to the

fabric type.

▪ Due to sharp edges on loom

parts

1. Ensure the machine surface is

smooth and free of sharp

objects.

190



2. Proper attention should be

given during fabric transport.

Slack yarn/

pick/ end/

cockled yarn

▪ Yarn with insufficient tension

during warping and sizing

(warp) or winding (weft)

process.

Check the warp or weft tension

during warping, sizing or winding

process.

[6,

250,

259]

▪ Longer length of yarn is woven

in and yarn appears bulky. This

results in a change in fabric

structure.

1. Ensure the correct working of

the let-off, picking, and take-up

system.

2. The warp tension should be

uniform over the entire warp

width.

Tight yarn/

fiddle string

▪ Yarn with excessive tension or

having less crimp.

Check the yarn tension. The

tension of warp ends in the beam

should be proper.

[6,

250]

▪ Shorter length is woven into the

fabric resulting in slightly

disturbed structure. It is often

difficult to detect but occurs

commonly.

Check the picking, let-off and

take-up system.

Float/

stitching/

undershot

▪ Yarn with defective interlacing

at one or more successive points

resulting in a portion of yarn

remaining free on the fabric

surface.

Ensure warp stop motion is

working properly and the broken

pick should be repaired.

[250-

252,

259,

261]

▪ Due to entanglement of warp

ends due to breakage, knots with

long tails, fluff or foreign matter,

1. Keep the leasing rod near the

heald shaft.

191



improper working of warp stop

motion.

2. Special attention should be

given during the preparation of

yarn for weaving.

▪ Due to frayed filaments,

improper sizing, and improper

shedding.

1. For PES-CO yarn, wax the ends

after sizing.

2. Proper yarn tension and

checking of guide elements’

roughness is required.

▪ Sticking of ends due to static

charge.

Check the humidity level in the

weaving shed.

Warp end-

repair/ shuttle

trap mark/

smash

Broken and tied warp yarns with

ends projecting or woven in as a

narrow thick place in the weft

direction.

[250,

251,

261]

▪ Improper knotting of broken

yarn. The broke yarn is missing.

The broken yarn end should be

correctly knotted.

▪ Slack ends in a certain portion

obstruct the movement of the

picking system.

In shuttle loom, check the timing

of shedding, shuttle in boxes,

shuttle balance, picking system,

pirn transfer and proper startup of

loom after a stoppage.

4.5.3 Knitting faults

Knitting is a fabric construction technique in which one or a set of straight yarns are formed into

columns of vertically intermeshed loops. The fabric is made up of a cohesive structure of

intermeshed loops. The loop structure provides stretch, comfort recovery and dimensional

flexibility which is normally associated with the knitted fabrics. The knitting process can be

divided into two categories based on the yarn presentation and processing known as weft knitting

192

and warp knitting. In weft knitting, yarn is fed horizontally to the knitting zone and the same yarn

feeds all knitting needles of one knitting course. In warp knitting the set of yarns, aligned

longitudinally, are interloped with another. Several yarns are presented to all the needles and

collective needle movement produces a loop row simultaneously [216, 257, 268, 269].

Knitters and finishers usually specify knitted fabrics in terms of stitch density, which is the

total number of loops in a measured area of fabric, which in turn is related to loop length. They

are usually measured as courses per inch (or cm) or wales per inch (or cm) respectively [216, 257,

268-270]. A difference in loop length within fabric produces appearance related defects such as

horizontal stripes [270]. As loop length increases, the wale density and fabric width stability

decreases. Another term commonly used for knitted fabrics is run-in, in weft knitting, which is the

amount of yarn required to produce one complete course of fabric, that determine the aesthetics

and performance of the knitted fabric [268].

The acceptability of the knitted fabric by a customer is dependent on its quality, which

includes fabric properties and defects. In order to meet the customer's required specifications and

reduce faults, an effective process and quality control is essential. This includes systematic and

continuous monitoring and control of the yarn supply, knitting process and the end product [203,

270]. Important quality aspects are loop length, GSM (g/m2), stitch density, fabric width, yarn

count, fabric construction and defects [270].

The faults in the knitted fabric may be due to various reasons, some common causes are

given below [203, 216, 270].

▪ Yarn faults and package defects

Any fault in the yarn could result in producing a faulty fabric. The important points that

need to be considered are the appropriate selection of yarn type, count, storage and

quality aspects. The yarn count selection is generally based on machine gauge [216,

270]. Yarn related problems are covered in more detail in section 4.4, 4.4.3 and 4.5.1.

Proper yarn storage is essential for good knitting behavior. Yarns should have

sufficient moisture for easy processing. The storage conditions should be as close to

knitting conditions as possible. Storage under extreme conditions and large temperature

fluctuations must be avoided. Elastic yarn storage is critical in order to obtain the

required fabric properties such as stretch recovery and modulus repeatably. If the

193

temperature is high, wax migration might occur. Under cold conditions, condensation

may occur [216, 271].

▪ Yarn feeding and yarn feed regulator

Monitoring and regulation of yarn feeding is an important aspect in knitted fabric

production. Improper feeding of yarn leads to tension variation which may cause yarn

breakage [216, 270].

▪ Machine settings and pattern faults

Control of machine settings is important for producing quality fabrics in which several

factors must be balanced in order to achieve optimal settings. Optimum settings are

calculated each time for a given yarn type and structure. A balanced relationship must

be set between yarn tension before and after the feeder, yarn drawing-in at the cylinder

and dial, the height of dial and fabric take-up tension. Important settings that need to

be considered include the minimum yarn tension during a feed, low fabric take-up

tension, the right setting of dial and cylinder needles, and the optimum spacing between

dial and cylinder [216, 270]. The correct machine settings mainly depend on yarn and

article to be made.

▪ Machine state and maintenance

Maintenance includes proper lubrication, repair of machine defects, and replacement

of broken and defective parts. For example, a bent needle can cause improper needle

movement which leads to an increase in yarn tension. This may cause a variation in

loop length or even needle or yarn breakage [270].

The important points in relation to machine’s state are: horizontal and vibration-

free installation, proper yarn transport and tension system from bobbin to the knitting

zone, defect-free surface of yarn guide paths, proper selection and routine replacement

of knitting elements, appropriate drive system between needle dial and cylinder,

centering of needle beds, right fabric take-off, and the wind-on tension system. For

example, the improver setting of the yarn feeder can cause dropped stitches [216].

▪ Plant climatic conditions

The knitting plant should be air-conditioned in order to produce good quality knitted

fabrics [216, 270]. Appropriate conditions can avoid yarn drying during processing,

reduce the number of yarn breaks (which leads to holes) and improve the surface

194

structure of the knitted fabric. The optimum conditions are a relative humidity of

55±10% at a temperature of 25 ± 3 oC [216].

▪ Machine cleanliness and fluff

A proper fluff removal system is essential in the knitting plant as it may produce defects

in the knitted fabric such as colored fly fibers. There must be a proper separation in the

plant where different colored yarns or fiber types are processed, otherwise, there is a

chance of fly accumulation on the knitted fabric which leads to defects in later

processing. The fly agglomerates from the cams and residual wax from yarn guide

elements should also be removed [216].

Table 4.17 gives a description of frequent faults in knitted fabrics, their causes and how to

eliminate them. After the determination of the cause, the remedy of the faults can be provided. The

faults given in the table mainly occur during the knitting process and are observed in gray fabrics.

Table 4.17: Causes and remedies of frequent problems in knitted fabrics.


Cracks or

holes

▪ Incorrect relation between dial

loop and cylinder

Use optimal settings according to

yarn type and pattern.

[203,

216,

272-

275]

▪ Bad setting of the yarn feeder or

stitch cams

Use optimal settings according to


▪ Weak places in yarn lead to

breakages during loop

formation

1. Check the quality of the yarn.

2. Use yarn with optimal

properties for the knitting

process. ▪ Thick and thin places, too low

yarn strength and high trash

content cause the yarn to break

▪ Knots or splice in yarn cause the

yarn to sit tightly in the last

stitch and lead to breakage

Use flat knots. Check the quality

of the yarn.

195



▪ Uneven yarn removal from a

package or a faulty package

Avoid using a faulty package.

▪ Improper machine elements or

position of the cones

Placement of the yarn package

should be as required.

▪ Too high yarn running tension Check the yarn feeding system

and reduce the tension settings.

▪ Too dry yarn due to insufficient

waxing or oiling

1. The knitting plant should

have optimum humidity to

ensure problem-free running

of yarn.

2. The yarn should be properly

waxed or oiled during the

spinning process.

▪ Defective guide elements, the

surface is edgy or not uniform

1. Replace the guide elements.

2. Use elements with good

surface properties.

▪ Fabric movement is improper

and it is pulled strongly or

intermittently

Check the fabric take-up

system.

▪ Incorrect yarn size for machine

gauge

Use proper yarn size according

to machine gauge or needle

hook.

▪ Excessive yarn hairiness

resulting in increased yarn

tension and lint shedding

Check the quality of the yarn.

▪ Improper setting of stitch cams Use the right settings for

stitching cams. ▪ Cams set too low

196



▪ Wrong sinking ratio between rib

and cylinder cam

Use the right sinking ratio.

▪ Too high machine speed Run the machine at the speed

recommended by the

manufacturer and according to


▪ Damaged needles 1. Replace the damaged needles.

2. Implement and follow a

routine checking system for

needles.

Dropped

stitches

▪ Bad setting of the yarn feeder,

yarn is being fed at improver

angle

Check the yarn feeding system. [216,

272,

273,

275] ▪ Wrong threading-in of yarn

feeder

The yarn should be properly

threaded through the dial bore

and cylinder needles.

▪ Dial and cylinder loop lengths

are not properly related. The

loop jumps out of the needle

hook.

Use correct dial and loop

cylinder lengths.

▪ Bad take-up, the already formed

loop comes out before the next

course.

Check the take-up system.

▪ Too dry or stiff yarn which

jumps out of the needle hook

when laid-in.

1. Re-adjust the yarn feeder or

increase yarn tension.

2. Check humidity levels of the

plant and waxing/oiling of

yarn.

197



▪ Yarn tension is insufficient.

Yarn is not easily caught by the

needle hook.

Tension compensation should

be as close as possible to the

knitting zone.

▪ Defective needle (bent latch,

hook)

Replace defective needles.

▪ Knitting pattern not properly

designed. Same take-off tension

on all loops and all yarn types

cannot be maintained.

Ensure optimal design of

knitting patterns according to

machine type.

▪ Thick and thin places in yarn Check the quality of the yarn.

▪ Yarn with excessive hairiness Use yarn with low hairiness.

▪ Too high yarn twist level

causing the yarn to kink, which

changes the yarn tension and

diameter.

Use optimal twist levels in yarn.

Cloth fall-out

or runners

Yarn is not stitched by several

adjacent needles. Occurs after a

dropped stitch. The yarn from the

hooks of the subsequent needles is

removed due to the impact of an

empty needle with a closed latch

with yarn feeder. Yarn breakage

without any immediate

connection.

[216,

272,

274,

275]

▪ Too stiff or brittle yarn Check the humidification

system. Ensure proper

lubrication of yarn

(waxing/oiling).

198



▪ Excessive tendency of yarn to

curl

Too high twist levels in yarn.

The twist level in the yarn

should be optimum.

▪ Thick places or knots in the

yarn

Use flat knots. Check the quality

of the yarn.

▪ Too high incoming yarn tension Check the yarn path.

▪ Too low yarn tension during

running.

Check the yarn tension is set

correctly.

▪ Wrong yarn feed and

adjustment

Ensure the right setting for yarn

feeding and adjustment.

▪ Improper setting of the cam

sinking ratio

Use the right setting of the cam

sinking ratio.

▪ Incorrect setting distance

between dial and cylinder

Set the right distance between

the dial and cylinder.

▪ Improper take-off Ensure the fabric take-off

system is working properly.

▪ Defective needle or sinker

elements

Replace the defective needle or

sinker elements.

▪ Improper adjustment or worn

cleaning brushes

Select the right adjustment or

replace the brushes if required.

▪ Machine vibration The machine must be installed

properly and without any

vibrations.

Snagging or

Snags

▪ Specific sensitivity of the

filament yarns

Use yarns with a coarser dpf,

less crimp elasticity, and higher

twist.

[216,

274]

▪ Mechanical strain during the

knitting process due to damage

Avoid rough surfaces on the

knitting machine and ensure the

199



to fabric take-off or spreader,

damage to lap rod.

take-off system is in a proper

working condition.

Tuck or double

stitches or

bunch-ups

▪ Insufficient sliding ability of the

yarn due to a high coefficient of

friction. The spinning oils or

waxes are not applied properly.

Ensure proper application of

spinning oils and waxes. Check

the humidity levels of the plant.

[216,

274]

▪ Thick places in yarn Check yarn quality.

▪ Too high dial setting. Dial

needle is not able to support the

fabric and thus pulled up.

Use an optimal dial setting.

▪ Too small needle clearance. The

old loops are not brought safely

behind the latch and remain on

the spoon.

Use optimal needle clearance.

▪ Incorrect setting of course

density. Too tight loops. These

loops are not removed from the

needles.

Check the settings, use correct

settings.

▪ Too weak fabric take-up. It has

a one sided drag or is not

continuous

Must be readjusted to ensure

uniform and continuous fabric

drag.

▪ Damaged needles Replace the damaged needles.

The needles must be replaced

regularly.

Vertical lines

or longitudinal

streaks

▪ Wrong selection of yarn count

according to gauge. Yarn is too

fine for machine gauge.

Select the yarn count according

to machine gauge. For coarse

density check the machine

settings.

[203,

216,

272,

200



▪ Incorrect course density/stitch

size

Check the machine settings. 274-

276]

▪ Broken or bent or dirty needles

and needle elements.

Replace the damaged needles.

Implement a proper needle

replacement plan.

▪ Heavily running needles Ensure needle movements is

uniform and smooth. The

needles should be of the same

type.

▪ Dial and cylinder needle

misalignment lead to rubbing of

needles.

Check the alignment of dial and

cylinder needles. Ensure the

correct setting of needles.

▪ Improper setting of yarn guides Check the yarn guides settings

and must be adjusted correctly.

▪ Machine vibration Check machine placement,

installation should be horizontal

and vibration-free.

▪ Spreader abrasion/creasing Check the settings and surface

of the spreader.

▪ Improperly set spacers on take-

up

Spacers must be adjusted

correctly.

▪ Too narrow spreading at take-up

causing folds

Use optimum spreading.

▪ Wrong or mixed needles Select needles according to yarn

count and type. Use same needle

type for same yarn count.

201



Barré or

horizontal

stripes

▪ Yarn irregularities or

differences in cross-section.

Fabric’s irregular stripes or

fuzzy appearance is mainly due

to yarn.

Check the yarn quality. The

defects must be within tolerance

limits.

[196,

203,

216,

272,

274-

276] ▪ Yarn running-in tension is not

constant.

Check the settings of the yarn

feeding system, there should be

no hindrance in yarn delivery.

▪ Wrong yarn-size, color, blend

level, twist direction

The yarn package should be

properly numbered and

segregated. Check the quality of

the yarn. Spinning related fault.

▪ Mixing of yarns (a) of different

spinning, raw material or

production batches (b) with

different fiber properties, (c)

from different production types.

Yarn packages should be

properly segregated.

▪ Oiling or waxing of yarn is not

even.

Check the incoming yarn

quality.

▪ Differences in yarn bulkiness,

crimp, and strength

The yarn quality should be

checked regularly.

▪ Fluctuations in bobbin hardness Inspect the yarn packages before

installation.

▪ Deflector in dial cam brought

into a tuck position. The

deflector not completely

switched off. The needle can

The knitting machine must be in

a properly working condition.

202



still grip the yarn and form a

tuck loop.

▪ Improper setting of yarn feeder Ensure the correct setting of

stitch size and that yarn

consumption on feeders is

uniform.

▪ Couliering not constant at all

feeders

The yarn drawing-in ratio

between dial and cylinder must

be constant.

▪ Jerks in fabric take-up Ensure that fabric take-up is

uniform and working properly.

▪ Different stitch settings (stitch

lengths)

Check the stitch settings and

ensure they are correct.

▪ Dirt, lint or yarn fragments in

needle elements or faulty needle

selection

The knitting elements must be

cleaned on regular intervals and

needle selection should be

according to yarn type.

▪ Rib dial or needle cylinder

skewness

Check the machine settings.

▪ Differences in sinking depths The sinking depth should be set

correctly.

▪ Machine vibration The machine installation should

be vibration-free.

Soil stripes ▪ Stripes in the direction of wales

are due to the knitting machine.

Mostly, they are called needle

stripes. They are due to the

individual replacement of

The needles should be replaced

at regular intervals and machine

lubrication should be working

properly without leaks or

drippings.

[216,

275]

203



needles or defective working of

oiling or greasing device.

▪ Stripes in course direction can

be caused by:

- Soiled places in the yarn

The yarn should be clean and

must be stored in a proper place.

- Standing course due to

machine stoppage

Keep equipment clean all the

time.

- Oil lines Ensure the machine lubrication

system is working properly and

there should be no leaks or

drippings. Oiling quantity

readjustment.

Color fly ▪ Natural remnants present in the

fiber. In the case of wool, hairs

with natural dark colors,

vegetable and food residue,

bast, etc.

It is impossible to completely

avoid these residues and a

certain amount must be

tolerated.

[216]

▪ During different stages from the

spinning process, a color fly can

be embedded in the yarn.

Individual colors during yarn

production must be carefully

separated.

▪ Knitting plant processing a large

number of colors or producing

color jacquards along with

single-colored fabrics with close

machine spacing.

There should be a proper fluff

removal system and colored

articles should be knitted

separately.

Distorted

stitches or

▪ Due to the bad setting of a

knitting machine, mainly

Check the machine settings. The

sinking depth must be adjusted

204



skittery

appearance

unequal sinking depths between

dial and cylinder needles. The

heads of stitches in wales are

not round but tilted to either

side. They result in disordered

fabric appearance and most

disturbing in single colored

goods. The fabric appearance is

skittery.

correctly according to article

type.

[203,

216,

274]

▪ Faulty yarn (short term

variations in yarn count, crimp,

thick and thin places)

Check the incoming yarn

quality. The defects should be

within tolerance limits.

Foreign yarn ▪ Worker carelessness Train workers to recognize

different yarn types.

[275]

▪ Presence of the same yarn type

having the same color on the

same creel

Rigorous yarn sorting and

storage system.

Elastomeric

yarn

misplacement

▪ Defective elastic yarn feeder Check the yarn feeding system

and knitting elements.

[275]

▪ Improper setting of elastic roll-

guide

Resetting of elastic roll-guide.

Side crease ▪ High pressure applied by take-

down rolls on the tubular fabric

causing permanent fiber

deformation (e.g. elastane).

Use of take-down rolls with

movable side rubber rings.

[275]

▪ The tubular grey fabric is stored

for a long time

Keep the storage of grey fabric

as short as possible.

205



▪ Take-down devices not properly

selected

Use of open width take-down

devices.

Spirality Wales follow a spiral bath around

the tube axis, caused due to yarn

or weft knitting machine.

[6,

203]

▪ High number of feeders in the

knitting machine. Due to more

course inclination, increasing

spirality

1. Use a lower number of

feeders if possible.

2. Do tight knitting when

possible.

▪ Uneven working of take-down

equipment leading to uneven

tensioning, spreading and

winding of fabric.

Ensure proper working of fabric

take down equipment.

▪ The yarn used has only one

direction of the twist.

1. The direction of twist is

dependent on the machine

rotation direction. Increase

knitting tightness.

2. The use of ply yarn instead of

single yarn reduces the

spirality.

3. The s- and z-twist yarn must

be alternately fed to feeders.

▪ Very high twist level in yarns The yarn used should have

lower twist values (twist factor).

▪ Unbalanced twist ratio in a plied

yarn

Ensure the twist ratio is

balanced.

206

4.6 Problems caused by water

Water is one of the most important and widely used ingredients of a dyehouse and performs

different functions such as wetting, removal of dirt, fiber swelling and solubility of dyes and

chemicals. It is used in the plant either in boilers (steam supply) or in different wet processing

operations such as desizing, scouring, bleaching, mercerizing and dyeing, etc. There is no common

standard of water required for different applications and it depends on its intended use [277-281].

Many problems in wet processing are caused by the inadequate quality of water. The physical

properties and chemical composition of water need to be monitored on a regular basis. The

important water quality parameters are temperature, pH, suspended solids, and dissolved

substances [100, 278, 281]. Table 4.18 gives the different types of water sources and substances

present in them [277, 278, 281]. It is important to note that the quality of water varies depending

on the source, location, and season [280, 281].

Table 4.18: Sources of water and their constituents.

Sources Color and constituents

Well water Clear; with Ca, Mg, Fe salts and may contain CO2

Swamp water Clear or colored, acidic pH, tannins or other organic residues

Surface water Turbid, with Ca, Mg and other metal salts depending on the

area characteristics and rainfall, variable compositions

Municipal water Generally constant in content. Clear, may contain Ca, Mg and

Fe salts. It also contains treatment chemicals such as chlorine,

alum, copper sulfate, acids, and alkalis.

Water supply for the textile wet processing unit should have a minimum set of requirements

to be considered fit for use in different wet processing operations such as pretreatment, dyeing,

printing, and finishing. The important parameters and the corresponding limits are given in Table

4.19 [231, 282, 283]. In order to meet these standards, water might be treated before it is supplied

to wet processing operations [231].

207

Table 4.19: Requirements of water for textile processing units.

Parameters Tolerances

- Water hardness Total max: 5 dH (17.85 mg/l)

- Suspended solids < 1 mg/l

- Organic load (KMnO4 absorption) < 20 mg/l

- Filterable solids < 50 mg/l

- Solid residues from evaporation < 500 mg/l

- Iron (Fe) < 0.1 mg/l

- Manganese (Mn) < 0.02 mg/l

- Copper (Cu) < 0.005 mg/l

- Nitrate (NO2-) < 50 mg/l

- Nitrite (NO3-) < 5 mg/l

- Chlorine < 1 mg/l

- pH 7-8

- Odor Odorless.

- Color Colorless.

- Free CO2 As close to 0 as possible.

- NaHCO3 Daily monitoring for dyebath pH adjustment.

Different sources of water often have considerable variations in temperature. Ground and

surface water are more prone to this variation compared to a municipal water supply. The pH also

varies depending upon the source. The soft water may be acidic with a pH of ~5 and hard water

may be alkaline in nature approximately around pH 8. The acidic conditions are attributed to the

organic and inorganic acids (in air-free water), sulfuric acid (swamp water) and silicic acid. This

may damage machinery components and cause various problems during processing [100]. Water

may contain a variety of dissolved substances. These substances change the equilibrium of H and

OH ions present in water thereby affecting the pH of water. The pH shift may affect the solubility

of different soluble substances. Water containing a high content of oxygen may interfere with the

processes involving reduction. This also affects pipes and boilers. Deaeration of boiler feed and

208

addition of oxygen scavengers can help in controlling the problems. The carbonic acid in different

states may also be present such as CaCO3, Ca(HCO3)2 and CO2. On heating, bicarbonates are

converted into gas while carbonates are partially precipitated. The free carbonic acid content, in

the form of CO2, increases with an increase in temperature [100].

The water for wet processing should be colorless, clear and free of suspended matters.

Water turbidity is due to suspended particles that can be organic and inorganic. These particles

consist of finely divided vegetable matter, microorganisms, clays, silica, calcium carbonate [282,

284]. The suspended matters may deposit on the cross points of the fabric surface. In yarn or beam

dyeing, the package or beam may act as a filter for water used in the process. Any residue present

in the water will concentrate on the package and result in staining [284]. The suspended matter

may have an acidic character or might be reductive in nature. They may cause dark-colored

precipitation in dyeing from soaps, auxiliaries and dyes, stains like deposits and dully cloudy

dyeings. Also, precipitation in boilers may also be caused. The condensate water may be

contaminated with lubricants that contain oils and grease. This leads to spot-like stains, faulty

dyeing, and many problems in boiler operation [100]. To remove these suspended matters

mechanical or chemical (coagulants) purification may be used. This procedure is followed by

filtration [282, 284].

Another substance found in the municipal water supply is chlorine. Chlorine is highly

reactive and oxidizing in nature. Low levels of chlorine in a dyebath even at low temperatures may

cause dye degradation thus affecting the shade and reproducibility. The chlorine levels in water

may vary depending upon the season. Proper monitoring of dyehouse water is thus essential. The

water supply coming to the laboratory should also be monitored for chlorine and other impurities.

One approach to solve this problem is to select dyes that are stable to chlorine, but this is not

always possible due to shade, fastness requirements and cost. During dyeing, reducing agents may

be added such as sodium thiosulfate or sodium bisulfite where the former is better as its excess

amount does not typically affect dyes. The sequence of adding dyebath chemicals is critical and

reducing agents should be added before dyes [281, 285, 286].

Depending on the source water may also contain different matters in a soluble or insoluble

form such as alkaline and alkaline earth, and heavy metal salts. The common heavy metals found

are iron (Fe), copper (Cu), manganese (Mn), nickel (Ni), Zinc (Zn) or cobalt (Co) with small traces

of aluminum (Al). Alkaline earth salts commonly found are calcium (Ca), and magnesium (Mg).

209

These salts exist in the form of chlorides, sulfates, and carbonates. These metals may interfere with

various processes [277, 281, 283, 286, 287]. In some cases, the presence of alkaline and alkaline

earth salts is favorable. The degradation of starch size by enzymes is favored by calcium salts due

to their activating and stabilizing effect on the enzyme [286, 287]. The presence of magnesium

ions in the bleach liquor has a stabilizing effect along with organic stabilizers [286, 287].

The presence of transition metal ions may cause the following problems:

▪ The presence of Cu and Zn ions deactivates the enzyme and makes sizes insoluble [280,

286, 288].

▪ The presence of Fe, Cu and Mn strongly affect the stability of the bleaching bath. The

catalytic damage leads to pinhole damage and strength loss. The substrate may have a

lower degree of whiteness and yellowing due to oxycellulose formation [277, 280, 283,

286, 289].

▪ Stains on the substrate may be formed due to Fe and Cu deposits [280].

▪ Reduced absorbency, luster and process efficiency may be observed due to the

formation of metal oxides during mercerization [280, 289].

▪ Some anionic dyes may chelate metal ions and cause the shade to become duller [290].

▪ Insoluble complexes or precipitate dyes, especially reds, may be formed that cause

shade change, unlevelness, dull shades, and reduce dye diffusion and result in poor

fastness [280, 290-292].

▪ Bronzing of shades may occur in the case of sulfur dyes [290].

The alkaline and alkaline earth salts lead to many problems which are given below:

▪ The solubility characteristics of different sizes in water containing alkaline and alkaline

earth salts are not the same and vary depending on their chemical structure. The

removal of anionic sizing agents is strongly affected. The sizing agents that may be

affected are polyacrylates, polyester, polyvinyl alcohol, and polyvinyl acetate. The

desizing of polyvinyl alcohol is strongly affected by the presence of sodium chloride

in washing liquor [287].

▪ During alkaline scouring, Ca and Mg ions depend on the alkali form calcium hydroxide,

magnesium hydroxide, calcium carbonate, and magnesium carbonate. These salts have

poor water solubility and may deposit on the scoured yarns or fabric. These deposits

210

affect fabric hand, sewability, knittability, water absorbency, and dirt removal [283,

289].

▪ The products formed by saponification of natural waxes, fats, and oils may be

precipitated in hard water and form sticky deposits on the fabric that lead to spots,

uneven absorbency, and uneven dyeing. It also reduces the efficiency of scouring,

bleaching, mercerizing, and soaping [280, 283, 286, 288].

▪ Poor stability of the stabilizer in peroxide bleaching should be considered. Some

stabilizers are strongly affected as compared to others thus affecting the whiteness and

strength of the material. Stabilizers based on polyhydroxy carboxylic acid show poor

stabilizing effects as compared to those based on soda glass, magnesium sulfate system

[293].

▪ The solubility of surfactants due to the formation of complexes with alkaline and

alkaline earth salts may be reduced. This may cause improper removal of surfactants

during pretreatment. Anionic surfactants may form deposits on fiber surface during

washing [288, 294].

▪ Sodium bicarbonate may be introduced from the ion-exchange method where zeolite

resin absorbs alkaline earth metals ions and replaces it with Na ions. The heating

process during dyeing converts sodium bicarbonate to sodium carbonate. This provides

alkali in the dyeing process before alkali is added in the process. The change in the bath

pH causes premature hydrolysis and early fixation before the migration of reactive

dyes. This leads to unlevel dyeing, lower dye yield, and poor reproducibility [283, 295,

296]. Sodium bicarbonate also has a buffering effect and affects dyebath exhaustion.

The required dyebath pH value may not be reached [297].

▪ The Ca and Mg ions reduce the solubility of dyes and lead to aggregation which may

precipitate on the fiber. The dye in this form cannot migrate or diffuse into the substrate.

This causes low color yields, uneven dyeing, stains, shade change, and machine

deposits. Turquoise and blue dyes are more sensitive to this problem. The crock

(rubbing) fastness is also reduced [280, 290, 292, 296].

▪ Due to the above-mentioned problem, the substantivity of the dyes is increased. Mg

ions have stronger influence as compared to Ca ions due to their higher aqueous

211

solubility. The sensitivity of dye to be affected by hard water depends on its

substantivity. Highly substantive dyes are more affected [283, 298].

▪ The leuco form of the vat and sulfur dyes are very sensitive to Ca and Mg ions and

form insoluble salts. This leads to poor color yield, unlevelness, and poor rub fastness

[290, 292].

▪ Disperse dyes may agglomerate due to the formation of Ca salt with an anionic

dispersing agent present in the disperse dyes [292].

▪ Dull shades and harsh hand may be observed due to the deposits of insoluble Ca and

Mg carbonates on the substrate [277, 283].

▪ Ca ions can result in poor removal of the dye during the rinsing and soaping thus

affecting wet fastness. Nonionic detergents should be used for washing. The

electrolytic effect of anionic detergent affects wash off behavior of reactive dyes

thereby affecting wet fastness properties [277, 283, 296, 298].

▪ Spots on substrate and loss in color yield depend upon the concentration of magnesium

or calcium where the former has a more detrimental effect. Alkali precipitates the

calcium and Mg salts dissolved in water. These precipitates absorb dye and lead to

incomplete utilization of dyebath. Redyeing may be required to achieve the target depth

[298, 299].

The problems mentioned earlier can be minimized using two approaches. The first

approach involves monitoring water supply on a regular basis and the treatment of water to make

it fit for the required process. Sever water treatment methods such as filtration and ion exchange

method can be employed to achieve this objective. In the second approach special chemical known

as a sequestering agent is added during preparation and dyeing processes. Their function is to

suppress the functionality or reaction of polyvalent cations without removing them from the

solution. They achieve this function by forming a complex with a metal ion. There are different

classes of sequestering agents used in different wet processing stages. These are polyphosphonic

acids, amino polycarboxylic acids, polyphosphates, hydro carboxylic acids, polymeric carboxylic

acids. It is important to know that not one type of sequestering agent is suitable for all applications

as they differ in their functionality and properties. The sequestrants differ in terms of their

sequestering power, specific metal sequestering, the effect of temperature and pH on sequestering

212

power and specific metal sequestering, sequestering capacities, stability to oxidation or hydrolysis

and their effect on dyes [278, 290, 292, 300].

It can be concluded that successful wet processing greatly depends on the quality of the

water. It strongly influences the solubility of chemicals and dyes, stability of the system, removal

of impurities, and wash off of unfixed dyes. Several problems in preparation, dyeing, and finishing

that may be caused due to inadequate quality of water along with their possible solutions are shown

in Table 4.20.

Table 4.20: Problems in wet processing associated with water impurities.


Incomplete

desizing

▪ Deactivation of the enzyme by Cu

and Zn ions

1. Regularly monitor water

and ensure appropriate

treatment before use.

2. Use sequestering agents

during desizing.

[277,

286,

287] ▪ Insolubility of the sizing materials

due to Ca and Mg ions

Incomplete

removal of

impurities

during

preparation

▪ Reduced activity of the detergent

(cleaning efficiency) due to Ca and

Mg





during preparation.

[277,

286]

▪ Reduction of water sorption due to

Ca and Mg deposits

Decreased

absorbency

▪ Deposits of insoluble Ca/Mg

carbonates/ hydroxides on fabric

formed during scouring due to Ca

and Mg ions





during preparation and

dyeing.

[277,

280,

283,

301]

▪ Formation of insoluble metal oxides

due to the presence of Fe and Cu

Low luster ▪ Formation of insoluble metal oxides

due to the presence of Fe

Use sequestering agents

during mercerization.

[277]

▪ Fe in water due to the bad condition

of water tanks/pipes

Check water tanks and pipes

for rust and clean them.

[301]

213



Low degree of

whiteness

▪ Catalytic decomposition of bleach

baths due to Fe and Cu

1. Use magnetic filters in

water lines.


during preparation.

3. The demineralization

process may be carried

out depending upon the

severity of the problem.

[277,

279,

280,

282,

283,

286,

301]

▪ Low stability of the bleaching process

due to interaction with Ca ions

▪ Formation of oxycellulose due to Fe

and Cu

▪ Fe in water due to the bad condition of

water tanks/pipes

Check water tanks and

pipes for rust and clean

them.

[301]

Variation in

whiteness

▪ Presence of alkaline earth metals in

fabrics that over stabilizes peroxide

Perform demineralization

of fabric before bleaching.

[301]

Fabric

damage/loss in

strength/

pinhole

formation

▪ Catalytic damage during bleaching due

to Fe and Cu


water lines.


during preparation.





[277,

282,

283,

286,

301]


water tanks/pipes



them.

[301]

Deposits on

fabric

▪ Deposits of suspended matter onto the

cross points of the fabric surface or on

package surface




[280,

282,

294]

214



▪ Incomplete removal of anionic and

nonionic surfactants due to the

formation of complexes with Ca and

Mg ions



dyeing.

▪ Deposits on the substrate due to the

formation of insoluble Ca and Mg

salts.

Poor

reproducibility

▪ Presence of bicarbonate that converts

into carbonate on heating and

increases dyebath pH

Use acetic acid to partially

eliminate the bicarbonate.

Adjust the pH to 5.5-6.5.

[283,

288,

295-

297] ▪ Buffering effect of sodium bicarbonate

that causes poor dye exhaustion






dyeing.





▪ Formation of dye-metal complex or

dye precipitation due to Fe and Cu

▪ Reduced solubility of dye due to the

presence of Ca and Mg ions

▪ Dye aggregation caused by Ca and Mg

ions

▪ White precipitates of Ca and Mg on

the substrate

▪ Degradation of dyes due to chlorine 1. Select dyes that are

stable to chlorine.

2. Use reducing agents

such as sodium

thiosulfate or sodium

bisulfite in the dyebath.

[285,

286]

215



Shade change ▪ Chelation of Cu, Fe, and Mn by

anionic dyes resulting in dull or

change in shade





during preparation.

[277,

280,

282,

286,

290-

292,

296]

▪ Formation of insoluble complexes or

precipitation of dyes due to Fe, Cu,

and Mn




formation of insoluble Ca and Mg salts


water tanks/pipes



them.

[301]

▪ Buffering effect of sodium bicarbonate





[297]


stable to chlorine.


such as sodium



[285,

286]

Poor color

yield

▪ Low dye diffusion due to the

formation of insoluble complexes or


and Mn






dyeing.

[277,

283,

285,

286,

295,

297]



216





▪ Formation of dye metal-complex

resulting in a change of shade



increases dyebath pH causing dye

hydrolysis




▪ Buffering effect of sodium bicarbonate



stable to chlorine.


such as sodium



Unlevelness ▪ Formation of insoluble complexes or


and Mn





during preparation.

[100,

277,

280,

282-

284,

286,

295,

296]

▪ Low diffusion or migration of dye due

to dye precipitation caused by Ca and

Mg ions

▪ Increased substantivity of the dye due

to the presence of Mg and Ca ions

▪ Precipitation of scouring products and

soap by Ca and Mg ions which form

sticky deposits on to the substrate

217





package surface

▪ Increased rate of dyeing due to large

quantities of sulfates





increases dyebath pH causing

premature fixation




[297]

▪ Poor reduction of vat and sulfur dyes

due to the higher content of dissolved

oxygen in the water

Use higher quantities of

reducing agent.

[100]


water tanks/pipes



them.

[301]

Spots or stains ▪ Formation of insoluble complexes or


and Mn





during dyeing.

[277,

280,

282-

284,

286,

292,

296,

298]

▪ Reduction in dye solubility leads to

dye precipitation caused by Ca and Mg

ions

▪ Increased substantivity of the dye due

to the presence of Mg and Ca ions

▪ Agglomeration of disperse dyes due to

the formation of Ca salt with an

anionic dispersing agent

218





sticky deposits on the substrate



package surface

▪ Deposits of metal salts on the substrate

▪ Emulsion breakage due to the presence

of Ca and Mg ions



[149]

Inadequate

fastness

▪ Poor removal of unfixed dye due to the






during preparation.

[277,

283,

286,

296,

298,

299]

▪ Lower solubility or precipitation of

dye caused by Fe, Cu, Ca and Mg ions

Poor hand ▪ Deposits on the substrate due to the






during preparation.

[282,

283]



sticky deposits on the substrate

Poor

dimensional

stability

▪ Presence of metals ions may cause a

loss in the activity of resins, additives,

catalysts and wetting agents




2. Use sequestering agents.

[277,

286]

219

4.7 Problems caused due to pretreatment

Preparation is one of the important stages in textile processing as good and thorough prepared

fabric largely determines the efficiency and reproducibility of the coloration and finishing

processes. It is recommended that the quality of prepared fabrics should not be compromised by

the cost savings approach, a challenge constantly faced by a dyehouse along with increased

productivity [61, 302, 303]. Approximately 70% of the dyeing faults can be traced back to

inadequate preparation [304]. Many problems of inadequate pretreatment are only visible after the

coloration and finishing process [67, 305]. To achieve trouble-free preparation following specific

areas need to be monitored and assessed on a regular basis, these are [305]:

▪ Greige substrate (yarn/fabric).

▪ Chemicals and auxiliaries.

▪ Water.

▪ Preparation process and control variables.

▪ Pretreated fabric.

The blended yarns and fabrics contain different types of impurities that may hinder the

coloration process [9, 61]. These include size, fats, waxes, proteins, ash, metal salts, vegetable

matter, proteins, spin finishes, weaving and knitting oils, dirt, and colored substances. The main

goal of the preparation step is to remove impurities and contaminations for the successful

application of dyes and pigments. In addition, chemical and physical modification of the fibers

may also be performed [303, 306, 307]. To meet these goals, it is important to know the different

substances present in the substrate such as types (mineral oils, silicone oils, etc.) and amount of

oils, type and amount of inorganic impurities. By having this knowledge correct pretreatment steps

can be selected, and correct chemical products may be chosen to deal with these substances [308].

The quality of chemicals and auxiliaries should not be taken for granted. This is not true

always and can cause problems during pretreatment. The strength and activity of the product may

vary from lot to lot due to small variations in the manufacturing process, improper dilution or

decomposition of the product. The concentration of chemicals used in pretreatment is set based on

their strength and activity. If the product has lower strength and activity it may lead to inadequate

pretreatment. It is important to analyze each lot of chemicals and auxiliaries before use. This is

usually performed in a laboratory. The chemicals and auxiliaries should also be tested for

220

functionality under actual conditions encountered in a process they will be used. The standards

methods are available that can be used for analysis [305]. The chemicals should also be analyzed

for impurities that may create problems during preparation e.g. iron content in caustic [138].

Table 4.21: Requirements to be fulfilled by pretreatment.

Chemical Physical (mechanical)

▪ Thoroughness and consistency of effects,

levelness.

▪ High absorbency.

▪ Higher degree of whiteness.

▪ Complete removal of size.

▪ Absolute absence of husks/vegetable

matter.

▪ Reduction of impurities and contaminants

to very low levels.

▪ Minimum or no damage to the material.

▪ Neutral pH.

▪ High dye-absorbing power (high color

yield).

▪ Complete removal of processing

chemicals (surfactants, bleaching agents

and caustic).

▪ Good dimensional stability.

▪ Absence of wrinkles and creases.

▪ Constant residual moisture content.

Uniformity is the key to preparation. Inconsistent pretreatment is more problematic than

insufficient absorbency, whiteness or mote removal. Many problems in dyeing and finishing

originates from preparation, these include unlevelness, spots, shade variations, holes and lower

strength [9, 64, 94, 308]. Table 4.21 enlists the requirements that need to be met by the preparation

step to avoid problems in subsequent processing [63, 302, 303, 309]. These are the requirements

for a substrate based on cotton and cotton blends and may vary whether the prepared substrate

needs to be dyed, printed or finished white. For example, a fabric that is to be dyed in the dark

221

shade does not require a very high degree of whiteness. Similarly, the needs of dyer using pigment

coloration on polyester/cotton blend can be different from that of dyer who is dyeing

polyester/cotton blend with disperse and reactive dyes [310]. The fabric pH is also critical as it

may directly influence the dyeing process [93, 94]. For blends, hydrophobic fibers tend to absorb

less liquor hence associated fibers in the blend such as cellulosic fibers should have high

absorbency [133]. Additionally, all acid, alkali, chlorine and peroxide residues should be

completely removed.

The pretreatment stage is constantly faced with a challenge of varying substrate qualities

but must have to meet the quality requirements in time and without reprocessing. The blends add

to this problem as impurities level and sensitivity of the individual fibers in the blend to different

pretreatment steps need to be considered [68].

The pretreatment involves several steps, depending on the material composition, one or

several pretreatments may be necessary. The pretreatment of synthetic materials is simple and

involves washing and setting [68]. The bleaching process is optional and may be employed where

higher whiteness is desired. Table 4.22 shows the possible steps involved in the preparation of

fiber blends. As shown due to differences in the nature of the material involved not all steps are

required [311, 312]. Each fiber in the blend has different properties that must be taken into

consideration during their processing by selecting the appropriate process sequence [67]. These

steps can be carried out by either batch or continuous process depending upon the availability of

machines and material suitability [9]. Woven materials are generally processed by the continuous

method while knitted fabrics are more suitable by batch methods [63]. The different processes

carried out in the preparation of woven polyester/cotton blend fabrics include singeing, enzymatic

desizing, alkaline scouring and bleaching, mercerizing and heat setting. Different fabric types are

prepared by this route and include home textiles, shirting, light suiting, rainwear, workwear, and

uniforms. Most of these treatments only remove surface impurities from the polyester component

in the blend as little penetration is achieved by the alkaline solution [9, 63]. However, the surface

saponification and reduction in denier may take place under highly alkaline and higher temperature

conditions that may be employed during scouring and mercerization of cotton based materials. The

concentration of alkali and process conditions must be adjusted accordingly [68]. The regenerated

cellulosic fibers differ in their wet stability and alkali resistance. Although they can be pretreated

222

similarly, special care must be given to viscose which has a lower wet strength and alkali stability

than lyocell and modal [311, 312].

Table 4.22: Possible steps in the preparation of blended materials.

Pretreatment process Fiber blends

PES/Co PES/CV PES/Wo Co/PA EL blend

Singeing x x x x

Desizing x x x x

Demineralization x x

Acid treatment x x

Washing x

Scouring x x x x

Combined scouring and

bleaching x

x

Crabbing x

Bleaching x x x x

Mercerizing x

Causticizing x x

Heat setting x x x x

PES=Polyester, Co=Cotton, CV=Viscose, Wo=Wool, PA=Polyamide, EL=Elastane

x: represents pretreatment process performed for the particular blend

223

4.7.1 Problems caused during singeing

The fabrics made of staple blends are singed to remove protruding fibers to produce a smooth and

clean surface and reduce the possibility of skittery appearance and pilling tendency. Singeing can

be performed on yarn, knitted and woven fabrics [9, 63, 64, 149, 168, 313].

Gas singeing is the commonly used singeing technique used nowadays that uses a flame to

burn the protruding fibers without damaging the firmly bounded fibers in the fabric. Before

singeing, the fabric is passed through a brushing and cleaning system for removal of dust and

loosening of surface fibers [68, 314]. The fibers due to their inherent nature show two distinct

behaviors when exposed to gas flames exothermic and endothermic. The former continues to burn

once ignited and the later requires continuous supply to burn. Cotton, wool, and viscose exhibit

exothermic nature while polyester and nylon show endothermic behavior respectively. The

polyester fiber melts at 250-260 oC and ignites at 480-500 oC. To burn the polyester and prevent

melting which cayuse bead formation, energy must be supplied in shock form. This creates a real

challenge in the singeing blends composed of fibers having different burning behaviors. The most

sensitive fiber in the blend determines the singeing process. The balance needs to obtained between

the thoroughness of singeing and over singeing [313-317].

The factors affecting singeing are [63, 168, 313, 314]:

▪ Flame intensity;

▪ Angle of contact between flame and fabric (singeing position);

▪ Fabric or singeing speed; and

▪ Distance between burner and fabric.

In modern singeing machines to prevent fiber damage fabric temperature is continuously

monitored. If the fabric temperature is increased beyond the threshold value the flame intensity is

reduced. The blends of polyester with wool and cotton can be heated up to 150 oC without any

damage [313, 318]. The singeing machine usually has an impregnation unit following singeing

operation on economic grounds that may be used for the application of desizing or bleaching liquor

depending upon the process [67, 314].

It is recommended to singe fabric after dyeing if the fabric is to be dyed by a batch process.

This is due to the formation of beads of molten fibers due to the insufficient supply of energy that

causes the synthetic fiber to melt instead of burning. The fiber beads absorb more dye as compared

224

to the rest of the fiber. This may cause dark spots and unlevelness depending on the severity [133,

253, 313, 316, 317]. This problem is generally not observed in thermosol dyeing. These fabrics

can, therefore, be singed before dyeing. For fabrics singed after dyeing, the dye selection is critical

to avoid unlevel dyeing [67].

Table 4.23: Problems caused during singeing, its causes and remedial measures.


Uneven

singeing

▪ Incorrect singeing position Use correct singeing position

according to fiber blend and fabric

construction.

[313]

▪ Inadequate flame intensity Use correct flame intensity according

to fiber blend and fabric construction.

[313]

▪ Variation in flame height 1. Ensure the flame height is constant.

2. Clean the burner regularly.

3. Check burner for clogged areas.

[149]

▪ Incorrect or variation in

fabric speed

Correct fabric speed to provide

adequate flame contact time.

[149]

▪ Too high moisture content

in the fabric

Ensure the residual moisture content of

the fabric according to fiber type and

blend ratio (moisture regain).

[67,

149]

▪ Presence of raise and

depressed areas in fabric

1. Ensure the fabric is smooth and

properly open before it enters the

singeing zone.

2. Check the proper working of the

expander and edge guiders.

[149]

▪ Presence of creases in the

fabric

The entry should have an expander

roller to ensure crease-free entry.

[67,

149]

225



Uneven

singeing

across the

fabric width

▪ Uneven flame height or

intensity across the fabric

width

1. Ensure the flame height and

intensity is the same across the

fabric width.

2. Clean the burner regularly.

3. Check burner for clogged areas.

[313,

315,

319]

▪ Fluctuation in the moisture

content of the fabric along

the width

1. Ensure the residual moisture

content of the fabric is uniform.

2. The fabric should be stored and

transported properly.

▪ Inadequate setting of the

guide rollers

Ensure guide rollers are properly

aligned.

▪ Uneven smoke evacuation

over the burners

Check the exhaust system is working

properly.

Uneven

singeing

across the

fabric length

▪ Differences in the fuel

mixture supply to the burner

Ensure a uniform supply of the fuel

mixture to the burner.

[313]

▪ Fluctuation in the flame

outlet of the burner

Ensure the flame intensity remains

the same throughout the process.

▪ Variations in the fabric

speed

Use constant fabric speed according

to fiber type and fabric construction.

▪ Fluctuation in the moisture

content of the fabric along

the length

1. Ensure the residual moisture

content of the fabric is uniform.

2. The fabric should be stored and

transported properly.

Horizontal

stripes or

bands

▪ Eccentric or improper

alignment of the rollers

Ensure guide rollers are properly

aligned and centric according to

burner position.

[313]

▪ Sudden increase in fabric

tension

Ensure the compensators and guide

rollers are working properly

226



▪ Redeposition of beads on the

fabrics collected on the

guide roller

Clean the guide rollers regularly. [315]

Vertical

stripes or

bands

▪ Partial blockage of burner

outlet

Clean the clogged burner outlet. [313,

320,

321]

▪ Fluctuation in flame outlet

of the burner

Ensure the flame intensity remains

the same throughout the process.

[321]


fabric

The entry should have an expander

roller to ensure crease-free entry.

▪ Incorrect stitching of fabric

ends leading to the

formation of creases.

Check the fabric ends are properly

stitched without any creases

[322]

▪ Selvage curling Ensure the proper adjustment and

functioning of the edge guiders.

Poor hand ▪ Long contact time between

flame and fabric

Check the fabric speed and flame

intensity. It should be selected

according to the fabric weight and

blend ratio.

[168,

313,

318]

▪ Using higher flame intensity Use correct flame intensity according

to fiber blend and fabric

construction.

▪ Long contact time between

flame and fabric due to

slower fabric speed

Increase fabric speed to provide

appropriate contact time between the

flame and fabric.

▪ Deep penetration of the

flame into the fabric

Adjust the distance between the

fabric and the burner. It should be 6-

8 mm.

[149]

227



▪ Inappropriate singeing

position

Use an appropriate singeing position.

▪ Deformation of synthetic

fibers under tension

immediately after singeing

Ensure cooling of the fiber

immediately after singeing.

[149]

▪ Cooling system of the guide

rollers in the singeing zone

is not working properly.

Ensure the water circulation system

for cooling of the guide roller is

working properly.

▪ Thermal damage of the size

(PVA) causes it to become

hardened and difficult to

remove during desizing.

1. Check the fabric speed and flame

intensity. The contact time should

be as low as possible.

2. Perform singeing after desizing for

heat-sensitive size, if possible.

[67,

149]

Reduction in

strength

▪ Long contact time between

flame and fabric due to

slower fabric speed

Increase fabric speed to provide

appropriate contact time between the

flame and fabric.

[168,

313]

▪ High flame intensity Use correct flame intensity according


construction.

[149]

▪ Deep penetration of the

flame into the fabric

Adjust the distance between the

fabric and the burner. It should be 6-

8 mm

[149]

▪ Inappropriate singeing

position

Use correct singeing position


construction.

[149]

Dark spots ▪ Formation of beads due to

insufficient supply of energy

that dye darker.

1. Use high-energy non-luminous

flame.

[68,

133,

253,

228



2. Use correct flame intensity,

singeing position and fabric speed


construction.

3. Avoid grey singeing. Singe fabric

after dyeing for fabrics to be dyed

by a batch process.

313,

316-

318]

▪ Redeposition of the burned-

out fiber on the fabric

surface

1. Ensure proper brushing of the

fabric before and after the

singeing process.

2. Exhaust blower system should in

proper working order.

[323]

Dark areas ▪ Damage/melting of synthetic

fibers during singeing that

dye darker


flame.




construction.

3. Correct fabric speed to provide

adequate flame contact time.

[149]

Unleveleness ▪ Insufficient supply of energy

that causes beads formation


flame.




construction.

[318]

229



3. Avoid grey singeing. Singe fabric

after dyeing for fabrics to be dyed

by a batch process.

▪ Morphological changes in

synthetic fibers due to high

temperature in singeing that

dye differently than

unchanged areas.

Check the fabric speed and flame

intensity. It should be selected

according to the fabric construction

and blend ratio.

[68,

318]

▪ Dark dyeing of protruding

fibers compared to the base

fibers due to unenven

singeing

1. Ensure the singeing is uniform by

proper selection of flame intensity,

singeing machine and fabric speed.

2. Ensure the fabric is dry and have

uniform residual moisture.

Poor color

yield

▪ Presence of protruding fibers

due to improper singeing

gives a lighter perception

1. Ensure the singeing is uniform by

proper selection of flame intensity,

singeing machine and fabric speed.

2. Ensure the fabric is dry and have

uniform residual moisture.

[319]

Streaks/ bar ▪ Damage of a large number

of polyester fibers during

singeing that dye lighter by

continuous dyeing


flame.




construction.

[149]

▪ Damage of synthetic fibers

during singeing that dye

darker by batch dyeing

Two

sidedness

▪ Uneven singeing of the face

and back of fabric due to

Ensure the same settings for both of

the singeing burners.

[317]

230



differences in settings of the

two singeing burners

Light areas ▪ Thermal damage of the size

(PVA) causes it to become

hardened and difficult to

remove during desizing.

1. Check the singeing speed and

flame intensity. The contact should

be as low as possible.

2. Perform singeing after desizing for

heat-sensitive size, if possible.

[67,

149]

Pilling ▪ Improper singeing of fabric.

The protruding fibers may

lead to pill formation

Use correct flame intensity, singeing

position and fabric speed according


construction.

[317,

320]

Poor

appearance

▪ Due to uneven singeing and

may be random or

directional depending on the

severity

Use correct flame intensity, singeing

position and fabric speed according


construction.

[67,

149]

4.7.2 Problems caused during desizing

Desizing process is carried out to remove sizing chemicals from woven fabrics. For cellulosic

fibers, it also aims to perform some precleaning with initial swelling. This is required for uniform

bleaching, even dyeing, and soft hand [100, 324]. A typical size mixture may contain film-forming

compounds (size), softeners, plasticizers, and antiseptics. For effective size removal, it is important

to know the type of size used on warp yarns. This is essential to avoid problems in subsequent

processes as weavers regularly change sizing formulation to optimize the weaving process without

notification to the dyer [64, 325, 326]. Often the size used is a mixture of different size, the desizing

recipe should be adjusted based on the most difficult size to remove [306, 326].

231

Table 4.24: Sizing agents and their removal processes.

Size Removal

mechanism Chemicals Process Precautions

Native starch Enzymatic α-amylase CPB, Pad

steam,

Immersion

Aged or

crystalizes starch

difficult to

dissolve Alkaline

Oxidative

Persulphate,

peroxide

CPB

Acidic Oxalic, sulfuric or

hydrochloric acid

CPB

Tapioca starch Alkaline

Oxidative

Persulphate,

peroxide

CPB Oxidative and

acidic

decomposition

only

Acidic Oxalic, sulfuric or

hydrochloric acid

CPB

CMC Swelling Detergents Wash off (all

process)

Rapid increase in

viscosity after

dissolving

PAC Swelling

(alkaline)

Detergents Wash off (all

process)

Sensitive to acid

PVA Swelling

(neutral)

Detergents Wash off (all

process)

Sensitive to alkali

and heat

PES Dispersion Detergents Wash off (all

process)

Sensitive to

electrolytes and

alkali

Fatty substances

& additives

Emulsification Detergents Wash off (all

process)

Table 4.24 shows the different types of size and their corresponding removal methods.

Batch, semi-continuous (CPB) and the continuous process can be employed. The starch and starch-

based size can easily be removed by enzymatic or oxidative methods usually by pad-batch process

232

immediately following singeing. Most of the synthetic size is soluble in water but they are difficult

to remove due to film formation. Singeing and heat setting of the sized fabric (especially containing

PVA) can make their removal more challenging if the size is exposed to very high temperature or

for long duration [303, 306, 307, 324-329]. They are generally removed by hot water though they

are more sensitive to pH as compared to natural size and may coagulate creating problems in their

removal [64, 306, 325, 329]. The factors affecting size removal are [327, 328]:

▪ Viscosity of the size in solution;

▪ Ease of dissolution of the size film on the fiber;

▪ Concentration of applied size;

▪ Drying and storage conditions;

▪ Nature and amount of size auxiliaries (paraffin, tallow, waxes, fungicides);

▪ Fabric construction;

▪ Selection of desizing chemicals;

▪ Method and nature of washing-off; and

▪ Washing temperature and pH.

The residual size can cause different problems in subsequent processes. These include

resist areas, poor wettability, reduction in dye yield, precipitation in dyebath, the formation of

creases and poor hand. The origin of these problems can be classified into two groups as sizing

and process problems. The first problem has origin in sizing process. Larger quantities of waxes

and lubricants that are difficult to emulsify, higher size content, over drying of sized yarns, and

variations in drying temperature are some of the challenges. Process problems include poor wetting

and lower pickup, less swelling of size, variation in dwell time, deactivation of enzyme, drying of

edges during dwelling and ineffective washing [100, 317, 326, 329]. The problems in subsequent

processes attributed to desizing along with their causes and remedial measures are given in Table

4.25.

233

Table 4.25: Problems caused during desizing, its causes and remedial measures.


Incomplete

removal of

size

▪ Variation in bath pH or

incorrect bath pH

1. Check the bath pH before the

start of the process.

2. Monitor the water pH regularly.

3. Ensure the post-cleaning after

singeing is working properly.

Singeing dust may fluctuate the

bath pH.

[67,

149,

305-

307,

324,

328,

329]

▪ Variation in

bath/impregnation

temperature

Ensure the bath temperature is

followed according to the process

guidelines and must be constant

throughout the process.

▪ Lower liquor pickup 1. Reduce the padder pressure.

2. Use wetting and aerating agent.

▪ Variation in dwell/treatment

time and temperature

The batching and treatment should

be constant according to the

process guidelines.

▪ Use of live steam for heating

of bath leads to the

deactivation of an enzyme

Avoid direct heating of the bath.

Use indirect steam heating if

possible.

▪ Poor quality of the wetting

agent

Check the stability of the wetting

under desizing conditions

(temperature and pH).

▪ Poor compatibility of wetting

agents with other chemicals

in the desize bath

Check the computability of

wetting agents with the desize bath

chemicals in the lab before bulk

processing.

234



▪ Poor quality of water 1. Monitor the quality of water

regularly.

2. Use a sequestering agent.

▪ Presence of contaminants in

the bath (peroxide etc)

Ensure proper cleaning of the

machine after the change in the

process.

▪ Wrong washing pH Use the correct washing bath pH

according to the type of sizing

agents. The synthetic sizing agents

are sensitive to pH variation and

may coagulate.

▪ Wrong washing temperature Use correct washing bath

temperature according to the type

of sizing agents. High washing is

temperature is preferred for

washing of the size and degraded

size fragments.

▪ Hardening of size from

previous heat treatment

(singeing and/or heat setting).

1. Check the fabric speed and

flame intensity. The contact time

should be as low as possible.

2. Perform singeing after desizing

for heat-sensitive size, if

possible.

3. Avoid heat setting of fabric

containing PVA size.

Incomplete

removal of

▪ Variation in liquor pickup

along the fabric width

Check the padder pressure across

the fabric width.

[128,

305]

235



size across the

width

Incomplete

removal of

size along the

length


along the length

Ensure the padder pressure remains

consistent throughout the padding

process.

[128,

305]

Uneven

removal of

size

▪ Poor quality of the wetting

agent




[305]

▪ Incorrect selection of wetting

agent having a lower cloud

point than the process

temperature




▪ Uneven pickup of the

desizing chemicals due to

lower bath levels

Ensure the level sensor is working

properly.

▪ Variation in treatment/dwell

temperature

Follow the treatment/dwell time

procedures according to the

manufacturer’s recommendation.

▪ Variation in the washing

process (pH, temperature and

time)

Follow the wash process according

to the manufacturer’s

recommendation.

▪ Presence of water or

condensation drops in the

fabric

Ensure the fabric should be dry and

free of any moisture drops.

Unlevelness ▪ Incomplete removal of size Check desizing conditions. Ensure

required time, temperature and pH

[100]

236



according to size type must be

followed.

▪ Wrong selection of detergent Select detergent with good wetting

and emulsifying properties.

[309]

Resist areas ▪ Incomplete removal of size Check desizing conditions. Ensure



followed.

[100,

317]

▪ Coagulated PVA or PES size Ensure the required pH is

maintained during desizing to

avoid coagulation.

[100,

329]

▪ Inadequate removal of oils,

grease, and waxes due to

wrong selection of detergent

Select detergent with good wetting


[309]

Light

stains/areas

▪ Incomplete removal of oil

stains from the fabric

Use special surfactant intended for

oil stain removal. The fabric

should not be allowed to dry before

washing off.

[67,

100]

▪ Inadequate removal of size. Check desizing conditions. Ensure



followed.

[100]

Dark stains ▪ Incomplete removal of grease

stains from the weaving

process containing graphite

residues

Use a surfactant with good oil

emulsifying properties.

[100]

237



▪ Incomplete removal of rust

stains from transport and

storage

Select the complexing agent

according to its ability to remove

rust. Perform demineralization if

required.

[100,

149]

Size stains ▪ Coagulated PVA or PES size Ensure the required pH is

maintained during desizing to

avoid coagulation.

[100,

329]

▪ More pickup of the dye by

the residual size

Check desizing conditions. Ensure



followed.

[325]

Lower color

yield

▪ Reduction in dye pickup due

to lower absorbency caused

by residual size




followed.

[67,

100,

326,

329]

▪ Reaction of reactive dyes

with the residual size




followed.

▪ Presence of hydrolyzed starch

that may act as a reducing

agent


dyeing.

Insufficient/

reduced

absorbency

▪ Presence of residual size. Check desizing conditions. Ensure



followed.

[100,

309,

326]

▪ Wrong selection of surfactant Select surfactant with good wetting


238



▪ Setting of tint due to salt used

in enzymatic desizing

Check the tint used in fabrics.

Avoid using salt in the fabric

containing tint.

[150]

Creases ▪ Inadequate size removal Check desizing conditions. Ensure



followed.

[100]


ends leading to the formation

of creases

Ensure proper stitching of the

fabric ends with the correct thread

type.

[322]

Streaks ▪ Incomplete removal of the

size from the warp yarns




followed.

[149,

150]

Poor hand ▪ Inadequate size removal Check desizing conditions. Ensure



followed.

[100,

326]

Luster

differences.

▪ Presence of residual size Check desizing conditions. Ensure



followed.

[150]

Inadequate

fastness

▪ Holding up of dye on the

fiber surface due to the

presence of residual size




followed.

[326]

239



▪ Thermomigration of the

disperse dyes to the residual

size.




followed.

[67]

Insufficient

removal of

metal ions

▪ Incorrect selection of a

sequestering agent

Select the sequestering agent based

on its chelation power for metal

ions under desizing conditions.

[309]

4.7.3 Problems caused during scouring

Natural fibers contain many natural impurities such as fats, waxes, protein, pectin, seed husks,

alkaline earth, and heavy metals. Manufactured fibers and yarns during processing are treated with

spin finishes and lubricating agents to enhance their running behavior in spinning, knitting or

weaving processes. These substances inhibit rapid wetting, absorbency, and absorption of dyes

and chemicals. The scouring process is carried out to remove impurities found in textile materials.

In cotton containing fabrics, softening and swelling of seed husks also take place. This is essential

for a good appearance. Several mechanisms that may take place during scouring are saponification,

emulsification, solubilization, hydrolysis, and dissolution. Along with caustic or sodas ash, several

other auxiliaries like surfactants and sequestering agents are required [149, 277, 278, 297, 303,

305, 317, 327].

Incomplete removal of oils, waxes, size leads to resist areas in the dyed fabric. The

redeposition of impurities during the preparation process may also cause this problem. These are

only visible after the dyeing process and therefore difficult to resolve [305, 317]. It is

recommended the check the residual oils, waxes, and spin finish levels in the fabric containing a

higher proportion of synthetic fibers. Many spin finishes used are a combination of products of

varying melting points. The different combinations of anionic and nonionic scouring agents may

be required for their proper removal. The spin finish in some cases may contain nonionic surfactant

that can cause foaming with scouring surfactants. Severe foaming can lead to pump cavitation,

rope tangling, and stoppages. The best solution is to drain the bath immediately and does not

240

immediately add defoamer as it makes the situation worse instead of making it better due to the

formation of hard scum that is difficult to remove [297]. The cloud point of these surfactants is

lower than the temperature typically encountered in disperse dyeing. If they are not removed

properly during scouring, they may precipitate cause instability of dye dispersion which leads to

poor colorfastness [109]. If the foaming is less it may be advisable to add defoamer [297].

A typical scouring recipe for cotton blends consists of caustic soda or soda ash, surfactant

and sequestering agent [301]. The amount of chemicals is reduced as compared to 100% cotton

based on the proportion of manufactured fibers in the blend [312]. The surfactant should be stable

under alkaline conditions. Not all surfactant types are stable hence penetration of alkali for

saponification inside the fiber is hindered. The emulsification of wax is also affected due to poor

detergency and dispersing properties [301]. Both exhaust and continuous methods are available

for scouring. The batch process can be done on winches or jets using anionic detergents and soda

ash at 70-80 oC [9, 305]. The continuous process is usually performed wet on wet on continuous

pad-steam range. J-box type system is not suitable for polyester/cotton blends due to the formation

of the crease by the thermoplastic polyester component [317]. The parameters affecting the

scouring process are given as follows [63, 303, 305]:

▪ Chemical concentrations (caustic soda, soda ash);

▪ Type and concentration of auxiliaries;

▪ Stability and computability of surfactants;

▪ Wet pickup;

▪ Liquor levels;

▪ Liquor feed rates;

▪ Reaction time;

▪ Treatment temperature;

▪ Exclusion of air;

▪ Water flow rates;

▪ Washing temperature;

▪ Final pH;

▪ Degree of drying;

▪ Moisture content of incoming fabric; and

▪ Residual size level of incoming fabric.

241

The scouring process in addition to the removal of impurities also helps in the relaxation

of fabric. The fabric shrinks due to residual stresses from previous processes. Uneven shrinkage

due to differences in heat history, variation in yarn twist and count may cause puckering. In rope

processing on jets, attention should be given on the possibility of crease formation [81].

After the scouring process, the fabric should be tested for wetting out the behavior of fabric

to ascertain the thoroughness of scouring. A water drop test can be used as a measure. The

polyester/cotton usually have less absorbency than cotton fabrics. This test is more applicable if

the polyester portion in the blend is less than 50%. The fabric should be tested systematically at

different points along the width (side – center – side) and length [305]. The main problems

associated with the scouring process along with probable causes and suggested corrections are

given in Table 4.26.

Table 4.26: Problems caused during scouring, its causes and remedial measures.


Inadequate

scouring or

absorbency or

removal of

impurities.

▪ Inadequate impregnation

temperature.

Ensure proper heating of

impregnation liquor.

[305,

323]

▪ Lower liquor pickup. Use a wetting agent.

▪ Higher levels of residual

moisture in the fabric

causing dilution of

chemicals.

Ensure the residual moisture of the

fabric as low as possible in the wet-

on-wet application.

▪ Inadequate

steaming/treatment time.

Main proper steaming/treatment time

depending upon blend ratio and

fabric type.

▪ Inadequate washing

temperature

Check the temperature settings for

the washing chamber.

▪ Inadequate concentration

of chemicals

Use the proper concentration of

scouring chemicals (alkali and

detergent).

242



▪ Poor quality of surfactant Check the stability of the wetting

under scouring conditions.

▪ Incorrect selection of

surfactant having a lower

cloud point than the

process temperature

Select anionic surfactant or use

non-ionic surfactant with a higher

cloud point.

Uneven scouring

or absorbency or

removal of

impurities across

the width.



Check the padder pressure is

uniform across the width.

[305]

Uneven scouring

or absorbency or

removal of

impurities across

the length.

▪ Variation in chemical feed

rates to the impregnation

trough

Ensure the dosing system is

working properly. Ensure the

concentration bath by titration.

[305]

▪ Variations in the moisture

content of the incoming

fabric

Check the squeeze pressure of the

washing unit. The pressure should

be constant to maintain similar wet

pickup levels.

Nonuniform

scouring or

absorbency or

removal of

impurities


detergent having a lower

cloud point than the

process temperature

Select anionic detergent or use

non-ionic surfactants with a higher

cloud point.

[305]

▪ Poor quality of surfactant Select surfactant with good

wetting and emulsifying

properties.


sequestering agents for

Select sequestering with good Ca

and Mg complexing properties.

243



sequestering Ca and Mg

ions

▪ Uneven distribution of the

chemicals in the

impregnation trough

Check the liquor distribution


▪ Presence of water or

condensation drops in the

fabric

Ensure the fabric should either be

dry or should have a uniform

moisture level.

▪ Variation in the washing

process (temperature and

time)

Ensure the required dwell time and

the temperature is maintained

during the washing process.

▪ Nonuniform removal of

size

Check the desizing conditions.

Spots ▪ Incomplete removal of fats,

waxes and knitting and

weaving oils

Ensure optimum scouring

conditions for the effective

removal of fats, waxes, and oils.

[67]

Reduced strength ▪ Damage of wool

component due to strong

alkali used in scouring.

Use mild alkali such as soda ash

for scouring of blended fabrics

containing wool.

[67]

▪ Damage of cellulose due to

atmospheric oxygen and

alkali

Ensure the steam level is properly

maintained inside the steamer.

Maintain slight overpressure.

[70]

▪ Too high concentration of

scouring chemicals or too

long treatment/steaming

time causing higher weight

loss

Use a proper concentration of

chemicals as per the blend ratio.

Maintain required

treatment/steaming time.

[323]

244

4.7.4 Problems caused during bleaching

Bleaching is carried out to destroy the natural and acquired coloring matter in the fiber and bring

it to a white state. Natural fibers contain natural colored pigments that are destroyed by the

bleaching process. This is accompanied by the removal of residual size, fats and waxes and in the

case of cotton seed husks are also removed. In comparison to natural fibers, manufactured fibers

contain no natural coloring matter and impurities (pectin, seed husks). For most cases scouring

process is enough but in some cases where higher whiteness is required bleaching may be required

[277, 278, 305, 317, 327].

There are two types of bleaching system, oxidative and reductive. Oxidative bleaching

includes peroxide, hypochlorite, chlorite and peracetic acid. In a reductive system either

hydrosulfite, sulphoxylates may be used. It is important to note that one type of bleaching agent

that is suitable for one fiber may not be appropriate for other fibers as shown in Table 4.27. The

polyester fibers cannot be bleached with hydrogen peroxide hence the degree of whiteness and

final shade of white after preparation depends on inherent whiteness and luster of the polyester

fiber. Alternatively, sodium chlorite can be used for polyester bleaching but due to environmental

reasons, this process cannot be used [63]. The bleaching process is necessary for blended fabrics

containing cellulose fibers. Nylon containing fabrics may also need bleaching if fabric turns yellow

during the setting process [133].

Table 4.27: Bleaching agents and their suitability for different fibers.

Bleaching agent Fibers

Co PES PA PAN EL

Hydrogen peroxide I N P N I

Sodium dithionite N N I N I

Sulfoxylate formaldehyde N N I N I

Sodium hypochlorite I N D D D

Sodium chlorite I I N I D

Peracetic acid N D N D D

I=Important, N=Not important, D=no effect, damaging, P=only with fiber protection

245

Hydrogen peroxide is the most commonly used bleaching agent for 100% cotton and cotton

blends. A hydrogen peroxide bleach bath consists of caustic soda, stabilizer, surfactant, and

sequestering agent. The concentration of chemicals is adjusted according to the proportion of the

cotton component in the blend. Hydrogen peroxide is a strong oxidizing agent that is activated by

alkali that increases pH that generates bleaching species. To control the process stabilizers are

added that can either be organic and inorganic. They create an equilibrium between activation and

stabilization of the bleaching system. However, this equilibrium is shifted by the presence of

catalysts (heavy metals) that increases the rate of activation leading to overoxidation of cellulose.

Heavy metals such as iron, copper, nickel and magnesium ions along with their oxides and salts

are responsible for catalytic damage during bleaching. The most common among all these is iron.

There are different sources of iron during the bleaching process. It may be present in water or

fabric from abraded metal and grease stains. The rust particle and iron chips may be spun in yarns

or embedded during fabric manufacturing. The caustic may also contain iron contaminants. The

raw cotton may also have iron and manganese. The presence of iron may cause spontaneous

decomposition of hydrogen peroxide producing free radicals that cause a breakdown of fiber

chains. This lowers the degree of polymerization and fiber strength and may lead to tears and holes

depending upon the severity. The presence of air in the machine or steamer may cause the

formation of oxycellulose under alkaline conditions. The oxidized portion of the cellulose is dyed

lighter as compared to undamaged areas producing uneven dyeing. The amount of peroxide

available for bleaching is also reduced due to reaction with catalysts. This lowers the degree of

whiteness. To prevent this problem two approaches may be used. In the first approach, the fabric

is treated with oxalic or hydrochloric acid before bleaching. This process is known as

demineralization. In the second approach sequestering agents are added in the bleaching bath [149,

303, 305].

The process can be done by the batch, semi-continuous and continuous method [9, 63,

149]. The batch process can be performed on winches or jets [9]. Cold pad-batch bleaching can be

used as an economical alternative process to increase production rate and quality of

polyester/cotton knit goods [330]. The continuous process is generally a wet-on-wet process. The

fabric containing desizing chemicals is first washed to remove the degraded size followed by

impregnation with caustic soda and detergent. The fabric is then fed to steamer where the action

of steam and caustic break down the impurities and cotton seeds. The steaming is an important

246

process. The temperature should not vary within the steamer. Widthwise variation may occur due

to temperature differences in the steamer [100]. The fabric is then washed to remove the degraded

impurities. The scoured fabric is then immediately impregnated with bleaching liquor containing

hydrogen peroxide, caustic soda, stabilizer, sequestering agent and surfactant. The fabric is then

steamed to break down colored and residual impurities. Washing and drying complete the process.

In the last washing, chamber fabric is neutralized [63, 317]. The factors affecting the process are

chemical concentrations, wet pickup, liquor levels, chemical flow rates, dwell times and

temperature, final pH, water flow rates and degree of drying [63].

The crease marks are developed when the tightly woven heavyweight fabric is creased in

a swollen state and stored for some time. They may be developed inside steamer when the fabric

is pleated during the continuous scouring and bleaching process. After the continuous dyeing, they

may show up as irregular dark dyed line-shaped marks. They may depend on the size and intensity

referred to as crow’s feet. These marks appear due to the crushing of the swelled fibers when they

are folded and compressed in the crease areas. When the fibers are deswelled and stretched in the

wash box the cracks are developed. The severity of the problem can be reduced by using a special

chemical that improves the elasticity and flexibility of the fibers [149]. After the scouring and

bleaching process, the fabric should be tested for residual size, pH, wetting out, and residual

peroxide. Residual hydrogen peroxide interferes with the dyeing process [297].

The final drying of fabric before dyeing is of critical importance. Both over-drying and

under-drying should be prevented. The fabrics with different moisture regain exhibit variations in

dye uptake especially in continuous dyeing. Over-dried fabric batches, other than increasing the

cost of drying, also lead to uneven conditioning of top layers and edges as compared to the center

and inside. This may cause dyeing problems and affects reproducibility. To prevent this problem

the drying stage should be equipped with an automatic residual moisture control system [317].

The scouring and bleaching can be combined in one stage called the Solo-Matic process

depending on blend ratio and fabric type. The fabric containing higher proportions of cotton,

higher weight (gsm) and requires higher whiteness usually requires separate scouring and

bleaching stages.

After bleaching the substrate should be checked for whiteness and fiber damage. The

whiteness is measured using the whiteness index (WI) along the fabric length and across the fabric

width and should be uniform. The fiber damage should be kept minimum. There is a maximum

247

whiteness that can be obtained keeping the fiber damage to a minimum [305]. Table 4.28

summarize the problems that occur during the bleaching process and their associated causes and

corrective actions.

Table 4.28: Problems caused during bleaching, its causes and remedial measures.


Lower

whiteness

▪ Lower concentration of

bleaching chemicals

Adjust the recipe according to the

blend ratio of the material. Ensure

required bath concentration by

titration or proper flow rates.

[305]

▪ Inadequate setting of pH

during the bleaching process

Check/monitor the pH of the bath

regularly.

▪ Lower liquor pickup Use a wetting agent or lower padder

pressure.

▪ Inadequate

treatment/steaming time and

temperature

Ensure proper steaming time

according to fabric type and blend

ratio. The fabric with high thread

count requires more time for

treatment than fabric having lower

thread counts.

▪ Incomplete removal of tint 1. Check the tint for its sensitivity

to pH.

2. Follow tint manufacturer

recommendation for effective tint

removal.

3. Check the bleaching recipe.

[150]

▪ Poor stabilization of

peroxide

1. Select a suitable stabilizer.

2. Use the optimum quantity of

stabilizer based on the bleaching

agent concentration.

[301,

305]

248



▪ 3. The residual peroxide after the

bleaching process should be at

least 15%.

▪ Higher content of Fe and Ca

in fabric interfering with

peroxide.

Perform a demineralization

process.

[301]

▪ Presence of residual alkali in

a fabric that causes

yellowing during drying.

1. Wash at a higher temperature

to remove residual alkali.

2. Finish the fabric in slightly

acidic pH 5.5-6.

3. Keep fabric away from nitrous

oxide.

4. Provide enough dwell time to

fabric for proper

neutralization.

[301,

309]

▪ Loss in whiteness/yellowing

of fabric after storage due to

poor working practice and

storage conditions.

1. Finish the fabric in slightly

acidic pH 5.5-6.


oxide.

3. Use wrapping sheet without of

butylated hydroxy toluene

(BHT).

4. Do not store goods in

excessive light.

[301]

▪ Poor storage conditions. Avoid storing the fabric in a hot

and humid environment.

249



▪ Local drying marks due to

delay in hydro extraction

and drying.

Dry the hydro extracted fabric as

early as possible.

[301]

▪ Inadequate selection of

bleaching method

(especially for elastane

containing fabrics)

Perform reductive pre-scour with

hydrosulfite at 75-80 oC to

improve the whiteness of elastane

followed by peroxide bleaching.

[301]

Variation in

whiteness

▪ Variations in liquor pickup


Check the padder/doctor blade

settings.

[305]

▪ Variations in chemical

concentration of the

impregnation uni

Periodically check the

concentration of chemicals.

[323]

▪ Variations in the

treatment/steaming

temperature

Ensure proper steaming time

according to fabric type and blend

ratio. The fabric with high thread

count requires more time for

treatment than fabric having lower

thread counts.

Unlevelness ▪ Instability of the dye

dispersion system due to

incomplete removal of

spinning lubricants

Ensure proper removal of spinning

lubricants by using detergents

with good emulsifying properties.

[109]

▪ Inadequate or uneven dye

penetration due to

incomplete removal of spin

finishes, oils, fats, and waxes

[100,

150,

253]

250



▪ Production of oxycellulose

due to catalytic damage that

dye lighter than undamaged

areas

1. Check the incoming water

quality and iron deposits in

fabric.

2. Perform a demineralization

process before bleaching for

fabric with high iron content.

3. Use a sequestering agent with

good iron binding capacity.

[149]

▪ Alkali residues in the fabric Neutralize the fabric. The fabric

pH should be neutral.

[253]

Oil stains ▪ Oxidation of knitting oils on

prolonged storage depending

on the quality of knitting oil

1. Use a special scouring agent to

remove oxidized oil marks.

2. Perform lab trials do determine

optimum recipe and process

conditions.

[301]

▪ Incomplete removal of oil

stains from the fabric

Use special surfactant intended for

oil stain removal. The fabric

should not be allowed to dry

before washing off.

▪ Improper handling and

housekeeping of fabric rolls

during processing

Ensure proper housekeeping.

Ensure clean machines and clean

working methods.

[301]

Inadequate

wash fastness

▪ Incomplete removal of

spinning lubricants causing

instability of dye dispersion

system

Ensure proper removal of spinning

lubricants by using detergents

with good emulsifying properties.

[109]

251



Poor

reproducibility

▪ Residual peroxide from the

bleaching process destroys

the dyes

Ensure the residual peroxide

levels after bleaching. Ensure

proper washing of fabric after

bleaching.

▪ Lower whiteness due to

decomposition of peroxide

caused by Ca and Fe

Use a sequestering agent. [100]



[253]

Poor color

yield

▪ Residual peroxide from the

bleaching process destroys

the dyes

1. Check washing parameters

(water flow, temperature).

2. Check peroxide level in the

fabric after bleaching before

rinsing through titration.

3. Use catalase enzyme in washing

for removing peroxide.

[301]

▪ Uneven dye penetration due

to incomplete removal of

spin finishes, oils, fats, and

waxes

Ensure the required concentration

of scouring chemicals, treatment

time and temperature.

[100,

150]

▪ Residual alkali due to

improper neutralization

Neutralize the fabric. The fabric


[194]

Widthwise

shade variation

▪ Temperature differences in a

steamer

Check the steam pressure.

Maintain a slight overpressure

inside the steamer.

[100]


during chemical application

Check the padder pressure/doctor

blade settings.

[128]

252





[253]

▪ Variation in residual

moisture of the fabric across

the width

Prevent over drying of the fabric.

Install the residual moisture

control system.

[317]

Lengthwise

shade variation

▪ Variation in residual

moisture of the fabric across

the length.

Prevent over drying of the fabric


control system.

[317]

Dark stains,

patches

▪ Direct contact of

concentrated alkali with

fabric in the saturator

causing localized swelling of

unmercerized cotton

1. Ensure proper dilution of alkali

before feeding into the

saturator.

2. Ensure the careful addition of

alkali.

[323]

▪ Inadequate removal of motes

(seed husks)

1. Check the pH of the bleaching

bath. It should be between 10.2-

10.7.

2. Ensure the optimum

stabilization of the peroxide.

3. Check the scouring process. The

seed husks should be softened

in scouring.

[149,

305]



[253]

▪ Foaming caused by residual

surfactants in the fabric

1. Ensure the substrate is properly

washed.

2. Use defoamer during dyeing.

[253]

Lower strength ▪ Catalytic damage due to the

presence of iron

1. Perform demineralization

process.

[100,

149]

253





▪ Formation of oxycellulose

due to the presence of air

Ensure slight overpressure in the

steamer.

[323]

▪ Wool fiber damage due to

higher alkali content and

temperature

Adjust the concentration of the

bath according to the blend ratio

and the sensitivity of the fiber in

the blend.

[150]

Light areas or

patches

▪ Problems in dye penetration

as fats, waxes, spin finishes,

and mineral oil are not

properly removed

1. Use a scouring agent with good

emulsification and detergency.

2. Use a suitable wetting agent

which good stability under

alkaline conditions.

3. Avoid heat setting in a gray

stage.

[100,

149,

253,

317]

▪ Production of oxycellulose

due to catalytic damage or

presence of air that dye

lighter than undamaged

areas


process.



[149,

305]

Crease marks ▪ Due to crease formation

inside the steamer during the

scouring and bleaching

process

Use a lubricating agent. [149]

▪ Distortion of weft due to the

application of too much

vacuum in the wash box

Check the vacuum settings

according to the fabric type.

[317]

254



leading to the formation of

creases


ends leading to the

formation of creases

Ensure fabric ends are properly

aligned when stitched.

[322]

Holes ▪ Catalytic damage due to the

presence of Fe in bleaching

bath

▪ Presence of heavy metals

(Fe, Cu) in the fabric, water,

and caustic soda


water/steam lines.


preparation.

3. Perform a demineralization

process.

[100,

149]

Streaks

(longitudinal

stripes)

▪ Incomplete removal of spin

finishes

Use detergent with good

emulsifying properties.

[149]

Poor hand ▪ Over drying of the fabric Prevent over drying of the fabric.


control system.

[317]

▪ Catalytic damage due to Fe 1. Use a sequestering agent with

good iron binding power in

bleaching.


process.

[301]

Loss of elastic

properties

▪ Use of strongly acidic or

alkaline conditions during

processing

Avoid processing of elastane

blends in strongly acidic (pH < 4)

and strongly alkaline (pH > 10.5).

[301]

Poor

dimensional

▪ Insufficient relaxation of the

substrate

Ensure the tension in the substrate

is minimum during the washing

process.

[253]

255



stability

(shrinkage)

Entanglement

of fabrics.

▪ Ballooning of fabric as air is

entrapped due to densely

sewn seam and tightly knit

fabric structure

1. Cut a vertical slit of 10-15cm

near the joint to allow air to

escape.

2. Use a larger diameter nozzle.

3. Use a deaerating and

penetration agents.

4. Use a chain stitch or butt stitch

to join the rope pieces.

[297,

301]

▪ Due to foaming caused by

lubricants used in knitting or

surfactants used in scouring

and bleaching

1. Use non-silicone based

antifoaming agent.

2. Check the filter and clean it

before the start of the process.

[301]

Poor

appearance

▪ Pilling due to the rubbing of

fabric surface with each

other or machine parts

1. Singe the fabric to remove the

protruding fibers.

2. Run the machine at optimum

speed.

3. Check the machine lining is

smooth.

4. Use a lubricating agent.

[301]

▪ Fluff formation on the fabric

surface due to poor running

of fabric, the action of alkali

and low quality wetting

agent

Use a lubricating agent. [301]

▪ Longer duration of running

due to reprocessing

Use a lubricating agent.

[301]

256



Insufficient

absorbency

▪ Poor quality of surfactant

that has low stability under

alkaline conditions

Use a good quality surfactant

having good stability under

alkaline conditions.

[301]

▪ Redeposition of oil and

waxes

Use a higher rinsing temperature

(> 80 oC).

[301]

Alkaline pH ▪ Buffering action of sodium

acetate formed by acetic acid

that prevents penetration of

acid inside the fiber core

Use specialized products for

neutralization.

[301]

4.7.5 Problems caused during weight reduction

The fabrics containing polyester filaments are treated with hot caustic solutions to hydrolyze the

fiber surface causing weight loss. The weight loss is controlled by the concentration of caustic and

treatment temperature. The alkali cleaves the ester linkages in polyester fibers to water soluble

terephthalate salts and ethylene glycol. The weight loss occurring at the fiber surface leads to the

reduction of the fiber denier. The surface of the polyester fibers is removed layer by layer. This

process improves slight hydrophilicity and imparts silk-like hand to the material and the stiffness

is greatly reduced. The propensity of the fabric to develop crack marks is also reduced. The factors

affecting the process are treatment temperature, the concentration of sodium hydroxide, treatment

time and type of accelerator. Insufficient weight reduction due to inadequate concentration of

caustic, treatment time and temperature leads to crack marks during dyeing. On the other hand,

too much weight reduction leads to a reduction in the strength of the material. The process needs

to be controlled to achieve the required degree of weight loss [331, 332].

4.7.6 Problems caused during mercerization and causticization

Mercerization is an optional process and generally performed for all cotton-based fabrics to

enhance dye uptake, luster, tear strength, dimensional stability. It also improves appearance by

coverage of immature cotton fibers due to the leveling of structural differences. The fiber swelling

257

takes place and the internal structure of the cellulose is modified. The percentage of micropores

responsible for dye adsorption is also increased. The wetting agent may be required to improve the

penetration of caustic soda into the substrate. The treatment can be carried out under cold or hot

conditions. [9, 63, 133, 168, 333].

A typical mercerization process consists of an impregnation zone, dwelling zone,

stabilization, and a washing zone. It can be performed by both dry-on-wet and wet-on-wet process.

In the impregnation zone, the caustic soda solution (28-30 oBé) is applied to the fabric followed

by the dwelling zone where some reaction time is provided. For good results, the good circulation

of the caustic soda solution is essential. During impregnation, if the space between the rollers is

not completely filled with caustic, it may cause stripes in a fabric that may be seen after the dyeing

process. The caustic should not be sprayed directly on to the fabric. This may also cause stripes in

the fabric. In a stabilization zone, the concentration of caustic is reduced to 6-8 oBé. This is

important to provide dimensional stability to the fabric and prevent shrinkage in the washing zone.

After caustic treatment, the fabric is washed to remove the caustic soda from the substrate. The

fabric is then neutralized followed by drying. Fabric pH control is critical to obtain reproducible

dyeing results. It should be uniform both along the length and width of the fabric [317]. During

continuous processing, the neutralization process is carried out in the first half of the last wash box

divided into two zones. The fabric, based on the fabric content of the washer, approximately has

10 sec of reaction time for neutralization. This time may be suitable for light to medium weight

fabrics but for heavier fabrics, this time is insufficient to achieve complete neutralization. It is

recommended to use to complete washing box for neutralization to achieve the required results

[309].

The factors controlling the mercerization effect are [63, 305, 317, 334]:

▪ Origin and degree of maturity of cotton;

▪ Cellulose content;

▪ Concentration of caustic soda in the impregnation section (min. 28 oBé) and on the

fabric (220-240 g 100% NaOH per kg substrate);

▪ Wet pickup;

▪ Temperature (hot: 60-65 oC, cold: 18-20 oC);

▪ Reaction time (hot: 25-30 sec, cold: 45-60 sec);

▪ Tension (rollers or stenter); and

258

▪ Removal of caustic (caustic in wash water, water flow rates, temperature, final pH).

Polyester/cotton blends having a high proportion of cotton can be mercerized to improve

the properties of cotton. This process has little or no effect on polyester. The absorbency of

polyester/cotton blend is low as compared to cotton. This is because the blended fabrics have not

been given the usual thorough scouring and bleaching treatment of all cotton fabrics. The wetting

agents are therefore required to improve the penetration of caustic in the blended fabric. The

operating conditions required for cotton can be followed for the mercerization of polyester/cotton

blends. The mercerization of the cotton/regenerated cellulosic blend is only beneficial provided

that the blend proportion of the regenerated cellulosic fibers does not exceed 50%. The regenerated

cellulosic fibers are swelled by the action of caustic. Special precautions must be followed as

different regenerated cellulosic fibers different in their wet strength and alkali stability. The lyocell

and modal fibers have higher wet strength and alkali resistance compared to viscose. Improper

conditions for the mercerization of cotton/regenerated cellulosic blends leads to the stiff, brittle

and weaker fabric. The use of a wetting agent is essential due to the higher absorbency of

regenerated cellulose fibers as compared to cotton. The cotton/modal and cotton/lyocell blend can

be mercerized using a caustic solution of 28 oBé at 30 oC to obtain maximum swelling. The reaction

time should be kept minimum (30-60 sec) but kept as long as possible to achieve the uniform and

even penetration of caustic. The overstretching of fabric should be avoided. During stabilization,

the concentration of caustic should be reduced to 6 oBé as fast as possible at a higher temperature.

This is followed by washing and neutralization [100, 312, 334-336].

Blends containing viscose are not generally mercerized due to lower wet tenacity and

greater sensitivity to alkali. Fabric containing regenerated cellulose fibers are treated with caustic

soda solution without tension to achieve high color yields. This process is known as causticization.

The improvement in dyeability may be attributed to the easy dye diffusion and a higher degree of

dye fixation. The caustic soda modifies the internal structure of regenerated cellulose fibers. The

concentration of caustic soda is more important than treatment time in the causticization process.

The fabric is treated with a 6-8 oBé caustic soda solution for 30-60 sec at room temperature without

tension followed by a rinsing process [9, 184, 333, 337, 338].

Barium activity number is the test used to ascertain the degree of mercerization. For

complete mercerization, the number should be greater than 125. The test should be performed

259

along several places in the fabric to check for non-uniformity [305]. Uneven mercerization effects

are caused by many reasons such as uneven distribution and or wetting of caustic, uneven moisture

levels in fabric, uneven squeezing or rinse off caustic and creases in the fabric. Table 4.29 enlists

the problems in the mercerization and causticization process and possible solutions to resolve these

problems.

Table 4.29: Problems in mercerization and causticization and possible solutions.


Lower degree

of

mercerization

(Barium

activity

number) or

lower color

yield


caustic on fabric

1. Check the concentration of caustic

on fabric by titration. It should be

220g 100% NaOH per kg substrate.

2. Lower machine speed to provide

adequate time to achieve required

caustic concentration on fabric.

[305,

334]

▪ Inadequate reaction time Reduce the fabric speed. The reaction

time should be 25-30 sec for hot or

45-60 sec for cold mercerization.

▪ Low concentration of

process caustic lye

Check the concentration of caustic

lye in the impregnation zone, it

should be 28 oBé.

▪ Improper selection of a

wetting agent

Select a wetting agent that is stable

under higher alkaline conditions.

▪ Inadequate application of

caustic during impregnation

1. Use a good quality of wetting

agent.

2. Provide enough time by adjusting

machine speed for the proper

application of caustic.

260



Variation in

the degree of

mercerization

along the

length

▪ Dilution in the

concentration of caustic due

to increase in water content

of the fabric

1. Check the water content of the

infeed fabric, it should remain the

same.

2. Use a higher concentration of

caustic lye (35-40 oBé).

[305]

▪ Increase in temperature of

the process due to the

reaction between water and

caustic

Check the water content of the infeed

fabric, it should remain the same.

Uneven

mercerization

▪ Uneven distribution of

caustic in the impregnation

zone

Ensure the caustic distribution is

working properly and the same levels

are maintained in the impregnation

zone.

[305]

▪ Improper penetration of

caustic in the fabric due to

poor wetting agent

Select a wetting agent with good

stability under alkaline conditions.

▪ Uneven squeezing of

caustic after impregnation

Check the padder uniform. It should

be uniform.


fabric

Ensure fabric should be free of

creases when it enters the

mercerizing range.

Insufficient

dimensional

stability

(shrinkage)


caustic on fabric

Check the concentration of caustic on

fabric by titration. It should be 220g

100% NaOH per kg substrate.

[253,

305,

334]


process caustic lye



should be 28 oBé.

261



▪ Too low temperature of

caustic soda solution

Use higher caustic temperature. The

best dimensional stability is obtained

at 60 oC.

▪ Not enough washing water

in stabilization

Use an adequate amount of water, it

should be at least 4 L/kg of substrate.

▪ Too low washing

temperature in stabilization

The temperature during stabilization

should be 90-95 oC.

▪ Non-functional stenter

spray system

Check the operation of the spray

system.

Selvage center

differences or

widthwise

shade variation

▪ Very high stretching on

stenter

Use optimum stretch settings on

stenter. Best results are obtained

when stretched width is equal to the

final width.

[323,

334]

▪ Inadequate removal of

caustic from selvage areas

Check the working of the selvage

extraction device.

Lower luster ▪ Lower concentration of

caustic on fabric

Check the concentration of caustic on

fabric by titration. It should be 220g

100% NaOH per kg substrate.

[323,

334]

▪ Inadequate reaction time.

Lower dwell time

Reduce machine speed. The reaction

time should be 25-30 sec for hot or

45-60 sec for cold mercerization.


process caustic lye



should be 28 oBé.

▪ Inadequate stretching of a

substrate during

mercerization


stenter. The stretched width should be

equal to the final width.

262



▪ Higher concentration of

residual alkali after

stabilization

1. Use an adequate amount of water,

it should be at least 4 L/kg of

substrate.

2. The temperature during

stabilization should be 90-95 oC.

3. Check the operation of the spray

system.

Creases ▪ Distortion of weft due to

excessive pressure during

chain mercerization leading

to the formation of creases


stenter. Best results are obtained

when stretched width is equal to the

final width.

[317]


ends leading to the




[322]

Lower

whiteness

▪ Presence of residual alkali

in a fabric that causes

yellowing during drying

1. Wash at a higher temperature to

remove residual alkali.

2. Finish the fabric in slightly acidic

pH 5.5-6.


oxide fumes.

4. Provide enough dwell time to

fabric for proper neutralization.

[301,

309]

Two sidedness ▪ Differential mercerization

due to superimposed layers

of fabric

Restrict the mercerization of

superimposed layers of fabric to

thinner fabrics.

[194]

Alkaline or

variation in

fabric pH

▪ Insufficient or variation in

water flow rate in the wash

boxes

Control and monitor the washer water

flow rates according to the fabric

[317,

334]

263



weight, speed, and concentration of

caustic soda.

▪ Incorrect setting of liquor

counterflow in the wash

boxes

Use correct settings of counterflow.

▪ Use of too low or variation

in washing temperature

The washing temperature should be

90-95 oC.

▪ Wrong pH adjustment

during neutralization

process

Control and monitor the dosage of

acid in the neutralization chamber.

Set pH at approximately 5.5

depending on fabric weight.

▪ Inadequate time is given for

the neutralization process

Ensure enough time is given to

achieve the core neutralization of

fabric. Use the second last washing

chamber for neutralization.

[309]


caustic along the selvages

during stabilization

Check working of selvage extraction

device.

▪ Inadequate neutralization of

fabric due to the formation

of sodium acetate buffer in

the fiber

Use a specialized mixture of organic

acid for neutralization.

[305,

309]

▪ Use of a very higher

concentration of caustic

during impregnation

Check the concentration of caustic lye

in the impregnation zone, it should be

28 oBé.

Light or dark

streaks/bars

▪ Uneven mercerization 1. Check the concentration of caustic

on fabric by titration. It should be

220g 100% NaOH per kg substrate.

[323]

264



2. The reaction time should be 25-30

sec for hot or 45-60 sec for cold

mercerization.

▪ Incomplete filling of space

between rollers during

impregnation zones

The space between rollers should be

completely filled with caustic.

[149]

▪ Direct spraying of caustic

on to the fabric

The caustic should not be sprayed

directly on to the fabric.


caustic after mercerization

Ensure proper washing of the fabric

during mercerization.

▪ Machine stoppage Avoid frequent machine stoppages. [323]

Shade change ▪ Presence of higher

concentration of iron in

fabric carried over from the

residual caustic

1. Check the iron content of the

caustic. Install filters in the caustic

infeed.

2. Ensure proper washing of the

fabric.

3. Use sequestering agent during

dying having good iron binding

capacity at a higher temperature.

[301]

Dark patches ▪ Drying of improperly

neutralized/residual alkali

1. Ensure proper washing and

neutralization.

2. Remercerize using a higher

concentration of caustic.

[194,

301]

Poor color

yield

▪ Residual alkali due to

improper neutralization

Neutralize the fabric. The fabric pH

should be neutral.

[194]

Torn selvages

or clip cuts or

clip miss

▪ Over stretching of the

fabric

1. Avoid overstretching of fabric.

2. Select grey width in accordance

with the finished width.

[194]

265



3. Increase the reed spacing and use

coarser reed during weaving.

▪ Too tight grip or improper

grip due to inadequate

maintenance

Ensure proper maintenance of the

stenter clips on regular basis.

[194]

▪ Bursting of fabric selvages

due to alkali sensitivity of

regenerated cellulosic fibers

1. Check the caustic concentration.

Use lower caustic concentration.

2. Ensure proper tension control.

Avoid too high tension.

[194]

Reduced

strength

▪ Improper control during

caustiziation

1. Avoid using a higher concentration

of caustic. Viscose fibers are

sensitive to higher alkali

concentrations.

2. Ensure proper washing of fabric for

effective alkali removal.

[323]

4.7.7 Problems caused during heat setting

Heat setting is carried out to remove the tendency of the substrates containing synthetic fibers to

shrink and form creases during heat treatment. This is obtained by stabilization of structure by

removing stresses in fibers and fabric. The blends containing 65% or more polyester must be heat

set to obtain uniform dyeing results. Heat setting also improves crease recovery, dimensional

stability, and pilling resistance [9, 63, 64, 68, 168, 339]. The fabric becomes a little stiffer after the

heat setting process so higher temperatures should be avoided. At higher temperature, the damage

and yellowing of fiber may take place. The preferred approach is to use the minimum best possible

temperature that provides required dimensional stability [168, 339]. As a general rule of thumb,

the heat setting temperature should be 10 oC higher than the temperature at which maximum

stability is required [339, 340]. The fabrics containing texturized polyester yarns should not be

266

heat set above 160-170 oC. Above this temperature range (180-200 oC) the fabric loses its extension

and recovery and aesthetic qualities [81, 109].

The heat setting process may be carried out at different stages during wet processing. It is

usually performed after the scouring and bleaching process [83, 168]. Heat setting before dyeing

prevents creasing and fabric shrinkage during the dyeing process. Although, some shrinkage

margin must be also be given. The medium to heavy weight fabrics should be heat set before

dyeing [339]. If done after dyeing it removes the creases that might be introduced during dyeing

and stabilize the fabric at its finished width. All the blended fabrics to be dyed by thermosol process

need to be heat set before dyeing [9, 168, 339].

Heat setting under hot air is the most commonly used method for the setting of polyester

blends. This process is carried out, on stenter for open width fabrics and special heat setting

machine for tubular fabrics, at temperatures greater than usually encountered in dyeing [9, 63, 64,

340]. The temperature is set based on the ratio of polyester component, substrate weight and

structure, energy classification of disperse dyes and whether carried out before and after dyeing

[317]. The polyester/cellulosic blended fabrics are usually heat set at 195-205 oC for 30 seconds

[83, 168]. The polyester/wool blends should be heat set at 185 oC for 30 seconds [67]. Heat setting

on stenter provides dimensional control of fabric in a longitudinal and horizontal direction [168].

For elastane containing fabrics, the fabric should be relaxed before heat setting to reduce

residual stresses. The heat setting temperature and dwell time should be set keeping into

consideration the percentage and kind of elastic yarn in the fabric. The shrinkage behavior,

stretchability, recovery capacity, and residual elasticity must be considered.

A consistent moisture level in the fabric is essential for uniform drying and heat setting.

Uniformity of treatment is critical to avoid dyeability variations. A small variation in temperature

can induce variations in fiber morphology and drastically affect the dyeing rate. The temperature

across the fabric width, lengthwise in heat setting bays, upper and lower part of the heat setting

bay should be kept uniform [317]. Thermopaper can be used to check temperature along with

routine calibration checks of temperature sensors [339]. Residual size and oil stains if present may

get fixed into the fabric during heat setting and therefore difficult to remove [9, 64, 168]. Table

4.30 shows the heat setting problems along with their causes and corresponding corrective

measures.

267

Table 4.30: Problems caused during heat setting, its causes and remedial measures.


Poor

dimensional

stability

(Shrinkage)

▪ Inadequate heat setting

conditions (temperature and

time)

1. Use optimum settings (time and

temperature) according to the fabric

blend ratio and setting process.

2. For cases where fabric is wet before

heat setting attention should be paid to

the drying time as it influences the

heat setting duration.

3. Ensure proper cooling of fabric after

steneter to stabilize the set structure.

[67,

194,

253,

320,

323]

▪ Inadequate overfeed Provide a desired overfeed depending

upon the blend ratio and fabric width.

[194,

323]

Differential

shrinkage

▪ Differences in setting

conditions

Ensure the same heat settings ae

maintained within a lot and between

lots.

[320]

▪ Omitting setting step from

one part of the batch

Ensure the lots are properly tagged and

following the processing route as

planned.

Poor hand ▪ Too high heat setting

temperature

The fabric should heat set according to

the most sensitive fiber in the blend and

required dimensional properties.

[168]

▪ Longer heat setting time For cases where fabric is wet before


the drying time as it influences the heat

setting duration.

Unlevelness ▪ Variations in heat setting

conditions (temperature and

time)

Ensure uniformity of heat setting

conditions along the length and width.

[168,

323]

268



▪ Burnt-in or diffused

residual oils and grease

Avoid grey heat setting

Ensure the stenter sieves are cleaned

regularly.

[149]

▪ Irregular heat setting due to

variations in the moisture

content of the incoming

fabric

For cases where fabric is wet before



setting duration.

[67]

Dark stains ▪ Burnt-in or diffused

residual oils and grease

1. Avoid grey heat setting

2. Ensure the stenter sieves are cleaned

regularly.

[149]

▪ Localized variations in the

moisture content of the

fabric before heat setting

Ensure the padder pressure is uniform

before the heat setting process.

[149]

Streaks ▪ Overstretching of fabric

across the width


2. Select grey width in accordance to the

finished width.



[341]

Widthwise

variation/

listing

▪ Fluctuations in temperature/

airflow rate across the

width of the fabric

Ensure the air velocity is uniform across

the stenter. Check the temperatures

using thermal paper.

[128,

168,

253]

Edge marks ▪ Unlevel dyeing of materials

along the selvages due to

clip/pin marks

Ensure the clips/pins are cooled when

they grab the new incoming fabric.

[194,

320]

Weft streaks ▪ Local overheating of fabric

during the machine

stoppage

Check the proper working of nozzle shut

off system on stenter.

[149]

269



Poor

appearance/

yellowing

▪ Too high heat setting

temperature

The fabric should heat set according to

the most sensitive fiber in the blend and

required dimensional properties.

[149,

320]

▪ Longer heat setting time For cases where fabric is wet before



setting duration.

▪ Setting of tint Avoid the heat setting of fabric during

the gray stage.

[150]

Luster

marks

▪ Excessive heat setting. Use optimum settings according to the

fabric.

[253]

Creases/

rope marks

▪ Improper heat setting Ensure proper heat setting. [253,

320]

Stich

distortion

▪ Inadequate heat setting

conditions (time and

temperature)

Use optimum settings according to the

fabric.

[253]

▪ Too high air circulation 1. Control air circulation according to

fabric type.

2. Use a perforated belt for material

transport if possible.

[68]

Pilling ▪ Improper heat setting Ensure proper heat setting. [253,

320]

Loss of

elastic

properties

▪ Higher tension and

temperature during

processing

The temperature should not more than

150 oC and tension should be kept lower

during the process.

[301]

Lengthwise

shade

variation

▪ Stoppage or slowing of

stenter

Avoid stopping or reducing machine

speed. Use j-scray for fabric change to

avoid fabric damage.

[326]

270



Torn

selvages or

clip cuts or

clip miss

▪ Over stretching of the

fabric


2. Select the grey width according to the

required finished width.



[194]

▪ Too tight grip or improper

grip due to inadequate

maintenance

Ensure proper maintenance of the

stenter clips regularly.

[194]

Poor color

yield

▪ Use of too high heat setting

temperature or longer dwell

time leading to reduced

fiber swelling capacity

Use appropriate heat setting conditions

according to fiber type in the blend.

[342]

4.8 Problems in coloration

The objective of the coloration process is the uniform application of color to achieve shade and

colorfastness as enlisted in Table 4.31. The coloration process depends on the colorants (dyes or

pigments), material form and fiber blend. The coloration process produces the most visible results

in all the wet processing operations. Any variations in the previous processing stages may not be

evident under the material is dyed [1].

Table 4.31: Main objectives of the dyeing process.

▪ Dyeing fibers to desired shade.

▪ Obtain a uniform and level dyeing.

▪ Maintain required fastness properties according to the intended end-use.

▪ Prevent damage to the material (fiber, yarn, fabric).

▪ Maintain cost levels.

271

4.8.1 Reproducibility in the dyeing of fiber blends

High shade reproducibility or right first time (RFT) is the prerequisite to increase productivity and

reduce the cost of any dyehouse in today’s competitive market. This requires skill, attention to

detail and will to succeed. A dyeing process said to be reproducible if the required shade is matched

within specified limits at the end of the first process without any additions or reprocessing [61,

142]. These include but not limited to dye or chemical addition, extra run time, stripping and re-

dyeing, and shading.

In batch dyeing, RFT dyeing technique can also be termed as blind dyeing or no-addition

dyeing. The term blind dyeing refers to the dyeing process in which dyed substrate is only

examined for shade and levelness and found acceptable after it is out of the dyeing machine and

the next dyeing cycle is started. In contrast, in no addition dyeing, the substrate is examined in the

usual way for shade while in the machine, but it is found to be matched. Blind dyeing not only

reduces the dyeing time, as the assessment process is done after the substrate is offloaded from the

machine but also energy savings [142].

To achieve blind dyeing, excellent reproducibility is required. This can only be obtained

by identifying and controlling the variables involved in the dyeing process [142]. Table 4.32 lists

important factors that may affect the reproducibility in batch dyeing of fiber blends [77, 142].

It is important to note that no two dyehouse is the same and must determine their tolerances

for each of the variables. Some variables such as moisture content and weighting errors of both

substrate and the dye can be simulated in the laboratory by measuring the effect of these on the

color difference. These tolerances are critical in obtaining reproducible results. Table 4.33 lists

some of the factors along with their allowable variability as a guide for the dyehouse. These

tolerances indicate that reproducible results within a ΔEcmc < 1 would be obtained if the tolerances

are kept within the mentioned limits [142].

272

Table 4.32: Important factors affecting reproducibility in the batch dyeing of fiber blends.

▪ Water quality

▪ Blend ratio of material

▪ Dyeing characteristics of the substrate

▪ Substrate pretreatment

▪ Weight and moisture content of the

substrate

▪ Weighing of dyes and chemicals

▪ Dye and chemicals dispensing

▪ Dye selection for each fiber type

▪ Dye combinations for each fiber

▪ Compatibility between dye classes

▪ Cross-staining of each fiber type

▪ Water impurities

▪ Dye standardization

▪ Dye moisture content

▪ Dyeing weighing

▪ Dye dispensing

▪ Compatibility of auxiliaries

▪ Chemical weighing and dispensing

▪ Dyebath auxiliaries

▪ Liquor ratio with respect to each fiber type

▪ Machine flow and reversal or material

circulation rate

▪ Time/temperature profile

▪ Dye bath pH

▪ Shade assessment procedure

Table 4.33: Dyehouse factors and associated tolerances.

Factors Variability (%)

Moisture content of the dye ± 3.5

Moisture content of the substrate ± 0.5

Substrate weight ± 0.5

Weighing of dyes and chemicals < 0.5

Dyebath pH 0.35 units

Dyes standardization ± 2.5

To obtain high lab to bulk reproducibility in continuous dyeing, the tailing and reverse

tailing behavior of dyes must be considered. During bulk dyeing, the equilibrium shade on the

fabric is reached after several minutes. It is important to consider the relationship between the

laboratory padder, stock tank and pad liquor formulations. The dye produced in lab scale is

equivalent to the first few meters dyed in bulk and may give off-shade dyeing in bulk once

273

equilibrium is reached. The allowance factors can be calculated to quantify these differences so

that required adjustments in lab scale formulations and stock feed can be performed. This ensures

the matching of target shade once the pad liquor reaches equilibrium. The process variables that

may influence the continuous dyeing of polyester/cotton blends by pad-dry-chemical pad steam

process are listed in Table 4.34. They need to be controlled according to the dye type to ensure

excellent reproducibility, levelness, and fastness properties.

Table 4.34: Factors affecting continuous dyeing of PES/CELL blends by the continuous method.

Process stage Variables

Dye application ▪ Impurities level, absorbency, residual moisture

and temperature of fabric (material quality)

▪ Dye type and concentration (recipe quality)

▪ Chemicals concentration

▪ Liquor pick-up

▪ Liquor temperature

▪ Trough volume

Infrared pre-drying ▪ Intensity

▪ Levelness

▪ Residual moisture

Hotflue drying and

thermofixation

▪ Temperature

▪ Time

▪ Humidity

▪ Ventilation

Chemical application ▪ Chemicals concentration

▪ Salt quality

▪ Liquor pick-up

▪ Material temperature

▪ Liquor temperature

▪ Trough volume

Steaming ▪ Temperature

274


Process stage Variables

▪ Time

▪ Steam quantity

▪ Steam quality

▪ Water lock

Wash-off ▪ Temperature

▪ Water quantity

▪ Dwell time (fabric speed)

▪ pH

▪ Water quality (impurities)

4.8.2 Problems caused in batch dyeing machines

Batch dyeing machines are commonly used for dyeing of various blended materials such as yarns

and fabrics. Yarns are dyed either in cones, cheeses or on beams [9]. For tabular or open width

knitted fabric, jet or overflow dyeing machines are most commonly used. The problem of creasing

at the edges of tubular fabrics favors the batch dyeing process [9, 57].

The batch dyeing machines can be classified into three types of machines based on the

movement of dye liquor and substrate. In the first type known as circulating liquor machine, the

substrate is stationary while the dye liquor is circulated. These machines include yarn package

dyeing and fabric beam dyeing machines. The second type is known as circulating goods machines

in which the substrate is moving. The winch and jig dyeing machines are the circulating good

machines. In the last type called circulating liquor and good machines, both substrate and dye

liquor is moving. Jet and overflow dyeing machines are of this type. Table 4.35 lists the

characteristics of different batch dyeing machines [233].

275

Table 4.35: Important characteristics of different batch dyeing machines.

Fabric dyeing Yarn dyeing

Winch or beck

▪ Versatile and less expensive

▪ High fabric tension

▪ Long cycle time

▪ Variations in temperature

▪ Large energy and water consumption.

▪ Requires carrier for polyester dyeing

Jet and soft flow

▪ Minimum tension of the fabric

▪ Short cycle

▪ Good leveling and barre coverage

▪ Can be used for fabrics containing

texturized yarns

▪ High temperature dyeing possible (130-

135 oC)

▪ Expensive

▪ Fabric weight limitations

▪ Foam formation

Jig

▪ Open width.

▪ High tension on the fabric

▪ Economical than jet dyeing

▪ Large quantity of fabric can be dyed

▪ Lower liquor ratios possible

▪ Mainly suitable for woven fabric

▪ Knitted fabrics, stretch woven fabric and

very light weight fabrics cannot be dyed

▪ Listing and ending problems

Beam*

▪ Open width processing of the fabric

▪ Rapid dyeing process

▪ Economical

▪ Large fabric quantity can be dyed.

▪ Minimum tension on the fabric.

▪ Requires light weight flat, plain fabrics

having open constructions.

▪ Uniform batching is critical for levelness.

Package

▪ Yarn wound on cheese or cones.

▪ High temperature dyeing possible (130-

135 oC)

▪ Lower liquor ratios possible.

▪ Special winding process to produce a

package for dyeing

▪ Uniformity in packing essential for

levelness

Hank dyeing

▪ Good bulk in yarn, yarns allow to shrink

▪ Expensive process

▪ High water and energy consumption

▪ Difficulty in achieving uniformity

▪ Special winding and reeling requirements

*Can also be used for yarn dyeing.

276

In circulating liquor machines, the uniform and strong circulation of liquor throughout the

material is required to obtain uniformity in dyeing. The turbulence during liquor flow should be

avoided. There must be no liquor flow through spaces between packages in yarn dyeing. The

perforations in the beam dyeing must also be completely covered with the textile material [68]. To

produce level dyeing, the initial dye uptake must be similar throughout the material. If the liquor

circulation rate is lower and higher dyeing rate is used they may lead to nonuniform dyeings. The

exhaustion rate should be restricted to a maximum of 2% per cycle to ensure uniform dyeing. The

machines should have an option to drain exhausted liquor under pressure [9]. During the dyeing

process, large changes in pressure must be avoided to prevent material damage and non-uniform

dyeing. This is often linked to shrinkage of the material during the dyeing process. The materials

must, therefore, be heat set before dyeing to have lower residual shrinkage [68].

4.8.2.1 Yarn dyeing

The blended yarns are usually dyed in package form. For yarns where high bulk is required skein

method can be used. To obtain level dyeing, the dye exhaustion needs to be controlled. The

difference in exhaustion at various points in the material leads to unlevelness. The exhaustion

depends on the concentration of dye on the fiber surface and in the bath. As the liquor pass through

the substrate, there is a change in the dye concentration which decreases as in the direction of

liquor flow. Therefore, the ratio of the rate of exhaustion to the rate of flow determines levelness.

During package dyeing of yarn if the liquor flow is not uniform across the whole package it may

cause unlevelness [343].

Numerous mechanical factors may affect the dyeing of yarn in package form[100, 231,

244]. These are as follows:

▪ Yarn package

These include package shape, size, dye tubes, winding method, winding angle, traverse

ratio and length, and package density [231]. These are covered in section 4.4.3.

▪ Number of dye packages per spindle

It is decided based on the uniform flow of liquor through each of the dye package. The

balance must be reached between the number of dye package and liquor supply. This

depends on the machine capacity, the liquor flow rate and flow properties of the

package [231]. The spindle loading is decided by:

277

- Carrier type (top and bottom plate or bottom plate only);

- Carrier inlet, tube diameter and type of spindle;

- Speed and pressure of liquor at the spindle inlet;

- Liquor flow rate;

- Number of material to liquor interchanges;

- Type of dye package (diameter, shape and inter package sealing); and

- Winding and pressed density of the yarn.

▪ Liquor flow rate

The optimum liquor flow rate is essential for level dyeing. The right liquor flow

conditions should be followed for each blend. The liquor throughput affects the

movement of dyestuff to the fiber surface of yarn assembly and ultimately uniformity

of dyeing. Using very high liquor flow may cause package deformation and yarn

damage. The actual flow rate depends on package winding density, fiber specific

gravity, liquor exchange factor, and liquor loss in the package column [231, 248]. The

yarn packages can be classified into three types based on the maximum flow rate it can

handle before deformation or channeling or other defects can occur. These are low flow

rate dyeable, medium flow rate dyeable and high flow rate dyeable packages. These

flow rate limits depend on the properties of yarn and the winding process [344].

▪ Liquor ratio and number of contact cycles

The liquor should be enough to ensure uniform wetting of dye packages. The use of a

very low liquor ratio may lead to dye unlevelness. Any additions made during the

dyeing process must be considered in the calculation of liquor ratio. The number of

times liquor passes through a material in a given time is known as contact time and it

is calculated based on liquor flow rate and liquor ratio [231].

▪ Differential pressure

The flow resistance of the dye liquor through the yarn packages inside the dyeing

machine is indicated by the differential pressure which may determine the liquor

throughput. This pressure can give an estimate of the liquor flow rate. The differential

pressure increases with an increase in winding density [248].

The faults related to the yarn dyeing machine are shown in Table 4.36.

278

Table 4.36: Dyeing faults due to package dyeing machine.


Reproducibility ▪ Variation in the liquor ratio Ensure the liquor ratio is the same in

every batch.

[231]

▪ Variation in liquor flow

rates

Maintain the same liquor flow rates.

▪ Stoppages in between

process due to delays in

addition of dyes and

chemicals

Avoid any standing times. The dyes

and chemicals should be ready for

addition at the right time.

▪ Presence of air in the

machine

The air in the machine should be

neutralized by the addition of hydro

or displacement with nitrogen. 1.7

kg hydro and 1.7 L caustic 38 oBé is

required or each 1 m3 of air in the

system.

Unlevelness ▪ The temperature ramp rate is

higher in the critical dyeing

region

Use the correct dyeing program to

control the temperature ramp rate. It

should be kept between 1-1.5 oC/

min to ensure level dyeing.

[9,

253]

▪ Slower liquor circulation

rate leading to higher

exhaustion of the dye

Use the optimum circulation rate.

The maximum exhaustion should be

restricted to 2% per cycle.

[79]

▪ Improper liquor flow rate

due to package and carrier

leakage.

Check the carrier spacers. [231]

▪ Improper penetration of the

dye liquor due to the

oligomer deposits

Check the machine for oligomer

deposits and clean it regularly.

[67]

279



▪ Too low liquor flow rate due

to higher package density

1. Increase the liquor flow rate.

2. Reduce the package density.

3. Use low temperature ramp rate.

[231]


to leakage in package

column

Check column sealing and for

leakage.


to high residual shrinkage

Check fibers for residual shrinkage

(maximum 5%).

▪ Differences in liquor flow

rates in coupled machines

1. Ensure the proper operation the

control valves and cross coupling

device.

2. Check both pumps are set for the

same flow rate.

▪ Differences in liquor levels

in coupled machines

1. Check the liquor level is same in

both kiers.

2. Load each carrier with same size

carrier and batch.

▪ Trapped air bubbles (air

pockets) in the material

causing problems in liquor

penetration

Ensure proper wetting and

deaerating of the package

[110,

149,

253]

▪ Incorrect addition of

chemicals (salt, hydro,

alkali) in the bath leading to

rapid exhaustion

Use metered dosing system for

optimum exhaustion of dyes.

Shade change ▪ Presence of air in the

machine




[231,

345]

280





system.

Dark stains or

spots

▪ Improper cleaning of the

machine and preparation

tanks

Clean the machines, dye preparation

tanks and supply lines regularly.

[231]

Light spots ▪ Trapped air bubbles (air


leading to reserve areas

1. Ensure proper wetting and

deaerating of the package.

2. The temperature ramp rate should

be kept between 1-1.5 oC/ min.

[110,

149,

253]

Leakage in

package

column

▪ Use of inappropriate sealing

cap

The package column must be fitted

with a suitable and proper sealing

cap.

[231]

▪ Using too low pressing

density

The compression between 10-35%

should be used. The recommended

pressed densities are 420-460 g/l for

PES/Co and 420-500 g/l for

PES/Wo.

▪ Long height of the package

column

1. Reduce the height of the package

column.

2. Use of double carrier is better than

single carrier.

Shade variation

within package

layers

▪ Variation in pressed density Check the homogeneity of the

pressed density.

[231]

▪ Inappropriate liquor flow

times (in-out and out-in)

Change the liquor flow times.

▪ Use of incorrect flow rate Select the correct flow rate.

281



Pressure or

luster marks on

inner yarn

layers

▪ Using too high pressed

density

Reduce the package density. [231]

▪ Too high yarn shrinkage The residual yarn shrinkage should

be less than 5%.

Package

deformation

and yarn

abrasion

▪ Incorrect setting of spacers

leading to leakage

Correct fit the right type of

intermediate spacers.

[231]

▪ Use of too high flow rates Reduce the flow rate.

▪ Inappropriate circulation

times

Use correct liquor circulation times

as per material type.

▪ Incorrect wetting out of the

material due to the presence

of air

1. Ensure proper wetting out of

material and remove any air

from the package.

2. Set the flow converter in a

neutral position when filling for

liquor blow in both directions.

▪ Abrupt increase in the

differential pressure.

Slowly increase the differential

pressure.

Sloughing of

outer yarn

layers

▪ Abrupt increase in the

differential pressure

Slowly increase the differential

pressure.

[231]

▪ Inadequate wetting out of

the yarn package.

1. Add a wetting agent.

2. Set the flow converter in a

neutral position when filling for

liquor blow in both directions.

Swelled

package

shoulders with

a puffy

appearance

▪ Foaming caused by wetting

agent

Use a non-foaming wetting agent. [254]

▪ Foaming due to leakage in

the pump. The air can enter

the pumping chamber and

Ensure the pump is properly sealed.

282



produce foam with

circulating dye liquor

Poor color

yield

▪ Oligomer deposits leading to

reduced liquor flow

Check the machine for oligomer

deposits and clean it regularly.

[85]


machine






system.

[231,

345]

Poor hand ▪ Oligomer deposit on the

yarn surface


temperature.


during dyeing.

3. Dyeing of polyester in alkaline

medium depending upon the

possibility.

[85]

4.8.2.2 Fabric dyeing

Various machines can be used to dye blended fabrics in rope and open width form. These include

jet, beam, jig, and winch.

In winch dyeing, the fabric is processed in the form of endless rope through a stationary

liquor with the help of winch reel. The dye liquor exchange in a bath with the liquid in the fabric

is low. This can be enhanced by increase winch speed, but it is accompanied by high stress in the

fabric. The use of a winch is limited [346].

During beam dyeing, the fabric is wound on a perforated metal cylinder and liquor is

circulated through the beam with the help of a pump. The uniform circulation through the whole

batch and across the complete width is required for uniform dyeing [68]. The variation in batching

283

density, too tight winding and improper location of selvages on the beam leads to problems. This

method of dyeing is only suitable for fabrics having enough permeability, uniform fabric

constructions and knit goods that can uniformly wind with appropriate tension on to a beam. As

the fabric has little or no chance of relaxation and shrinkage the fabric has a firmer and flatter hand

and high luster. This is suitable for certain polyester/cotton and polyester/linen fabrics [9, 110].

Jig dyeing is a circulating goods type dyeing machine where the fabric in open width form

is passed back and forth from one roll to another through an open dyebath. The lengthways fabric

tension should be kept minimum to avoid the extension of fabric under hot and wet conditions.

The jigs can be open where the fabric roll is exposed to the atmosphere or can be enclosed by

covers. The open type jigs may cause temperature variation of the roll especially the selvage areas.

This affects the rate of the dyeing and leads to a listing problem. The cooling of the roll reduces

the rate of dyeing thus creating problems in achieving dark shades. Since in jig dyeing the fabric

is passed back and forth from one roll to another, the dwell time in roll for fabric at each end of

the batch is much smaller than the center of the batch. This provides inadequate time for the

complete absorption of liquor to fiber interior before it meets the liquor again. This may cause the

fabric end to be dyed paler or of a different shade than the rest of the batch. This problem is known

as ending. To reduce the listing and ending problems, the temperature of the fabric batch and

dyeing bath temperature should be as close as possible. This is achieved by using hoods that reduce

heat loss and by heating the air space within the dyeing chamber to dyeing temperature [347].

During jig and beam dyeing of fabric, the following factors need to be controlled to avoid

unlevel dyeing due to batch related problems [68, 85]:

▪ Correct tension during batching;

▪ Adequate size of the batch; and

▪ Right amount of overlap.

The jet dyeing technology is well-established and most popular method of batch dyeing

blended fabrics in rope form. The jet of dyeing liquor created through venturi action is used to

move the fabric in the machine. A modified form of jet dyeing machine known as soft flow is very

common which consists of a winch reel along with the jet to transport the fabric. The fabric can be

dyed at higher temperature conditions and very liquor ratios can be used. For error free dyeing the

important factors to consider are rope speed, rate of rise of temperature, dwell time and rate of

284

cooling. Due to the high speed of fabric movement foaming may take place. This can be overcome

by using a suitable antifoaming agent. It is sometimes necessary to add a lubricant to minimized

friction and reduce the tendency for crease marks. The machine cleaning is essential to remove

dye deposits, if any, especially after dyeing of darks shades and to remove oligomer deposits. The

jet dyeing machine offers much more lengthwise relaxation of fabric than winch dyeing. The

problems associated with winches are fabric extension, crease marks and hydro-setting synthetic

fabrics in high temperature machines that cannot be rectified by post heat-setting [346].

Sensitive fabrics such as velvet and corduroy are not suitable for dyeing on jet dyeing

because of the possibility of crushing and creasing. The cooling rate of the dyebath up to around

80 oC should be kept lower to avoid creasing of the dyed fabric. For lightweight fabrics, there may

be a problem of the larger lengths to ensure economical machine loading. The jet or overflow

dyeing machine provides relaxed and tensionless conditions to fabrics. The dyed fabrics have

softer, bulkier and some luster. This is preferred for fabrics such as polyester/viscose knit goods

[9].

Most of the knitted fabrics are dyed by soft flow dyeing machines. The following machine

factors influence the batch dyeing process [297]:

▪ Chamber loading

The machine should not be overloaded otherwise the fabric will not float causing the

fabric to jam in front of the machine and create problems for a winch to lift the fabric.

The machine loading depends on construction, width, blend ratio, weight per unit meter

of the fabric.

▪ Rope cycle time

The rope circulation speed and rope length influence the rope cycle time. It should be

1-1.5 min for disperse, 1-2 min for vat, 2-3 min for reactive dyeing.

▪ Nozzle (jet) pressure and size

The size is based on fabric weight and must be ½ to ¾ occupied by fabric. Lower jet

pressure cause fabric to jam in front of the machine. Too high pressure cause

entanglement of the fabric at the winch and accumulate fabric at the back of the

machine.

285

▪ Liquor ratio

It is calculated from actual bath volume and fabric weight. The additions carried out

during the dyeing cycle with increase the liquor ratio. The heavier fabric requires more

liquor than light fabrics.

Of all the cellulosic fibers, the regenerated cellulosic fibers are more sensitive and therefore

requires more attention in dyeing as compared to cotton or linen. The dyeing properties of

regenerated cellulosic fibers depends on the dye class, dyeing process and fiber type and the origin

of the fiber. It is important to understand that not two regenerated cellulosic fibers are the same

[312]. The dyeing in rope form needs to consider the creasing tendency of these fibers. The heating

and cooling rate should be kept lower to avoid crease formation. It is recommended to add a

lubricating agent in all processing baths. The thicker and denser woven fabrics can form creases

during rope dyeing. The fabric speed should be set according to fabric construction and dye class.

For fabrics having open structure and knitted fabrics should use lower fabric speed to avoid

hairiness problems and longitudinal stretching of fabric [188].

The elastic recovery of cotton is lower compared to synthetic fibers. A lubricating agent is

required to avoid the formation of creases during rope processing in a batch dyeing machine. It is

important to note that not all lubricant agents are suitable for all fiber types due to differences in

fiber properties. The selection must be done keeping into consideration the fiber type being

processed [301]. During processing of fabrics containing flat polyester filaments if the fabric is

not moving at even speed at the required fabric speed it may be essential to increase the nozzle

pressure or use a smaller nozzle size. The cotton rich fabrics if the fabric is running smoothly the

nozzle pressure can be reduced.

In the dyeing of polyester containing blends by batch process, the dyer has to deal with the

problem of oligomers. Oligomers are low molecular weight polymers (trimers) formed as a

byproduct during polymerization of polyester fibers. Although they are present in small quantities,

they may cause serious problems in dyeing [67]. The degree of timer release to the fiber surface

depends on the various processing stages the fiber has gone through such as drawing, texturizing

and heat setting [85]. The oligomers during dyeing may lead to frosting, poor running of material

in subsequent processing and soiling of the machine. To avoid these problems, it is recommended

to follow multiple approaches such as discharging the liquor at high temperature, use of short

286

dyeing cycle, avoid carriers and reduction clearing [253]. Special auxiliaries are available that

helps in dispersing or dissolving of oligomers. The machine should be cleaned regularly to avoid

redeposition on the fabric [67, 233].

The machine malfunction may occur due to a variety of mechanical and electrical related

reasons. The common problems caused by these malfunctions are summarized below [297]:

▪ Water filling problem;

▪ Faulty pressure release system;

▪ Unsatisfactory heating and cooling rate;

▪ Boiling of liquor above 100 oC;

▪ Problems in adjusting differential pressure;

▪ Inadequate nozzle pressure;

▪ Problems in dyeing related to one chamber in a multi-chamber machine;

▪ Differences in liquor level between chambers;

▪ Faulty chemical tank pressure pump; and

▪ Liquor circulation pump not working.

It is recommended to check the residual oils present in the fabric before dyeing. Any oil

present in the fabric is removed from the fabric during dyeing and the actual fabric weight available

for dyeing is affected. Since the weight of the fabric is measured in the dry state before the start of

the dyeing process and determines the amount of the dyes, this reduction in fabric weight leads to

more dye in the dyebath than actually required. This cause matching problem and poor

reproducibility. The bath appearance after 5 minutes of fabric loading into the machines may help

in determining the residual oils present in the fabric. If the bath has a very pale or white milky

appearance and contains no or low foam it is safer to start the dyeing process. The bath needs to

be dropped if it has a white or pale creamy appearance and some foam. Lastly, if the appearance

of the bath is thick creamy and contains heavy foam and pump is cavitating it is recommended to

drain the machine and refill [297].

The main dyeing problems associated with batch dyeing machines are summarized in Table

4.37.

287

Table 4.37: Dyeing problems related to batch dyeing machines and their countermeasures.


Reproducibility ▪ Variations in rope lengths in

batches

Use the same rope lengths to give

the same rope cycle time to each

batch.

[297]

▪ Variation in fabric length in

batches

Strictly follow the procedure to

measure the batch size.

Correlate the variation in length

and shade deviation from the target.

▪ Damaged or worn out Teflon

rollers of winches causing

different reel speeds.

1. Replace worn out Teflon rollers.

2. Avoid using low cost lubricating

agents based on acrylamide. Use

fatty acid based lubricant and

wetting agent.

[301]

▪ Use of different dyeing

programs

Use consistent dyeing conditions. [297,

301]

▪ Use of different liquor ratios. Use consistent dyeing conditions. [301]

▪ Fabric with variation in gsm

leading to differences in a

rope length

Ensure gsm of the fabric are the

same in different ropes and batches.

[301]

▪ Difference in the tightness

factors of the ropes

Ensure the fabric tightness factor is

similar for all ropes.

[301]

▪ Differences in liquor ratio Maintain the same liquor ratio.

Adjust the bath volume based on

fabric weight.

[297]

▪ Variation in liquor ratio due

to direct heating system

1. Use an indirect heating system

if possible.

2. Take into consideration change

in liquor level due to

condensation of steam.

288



▪ Differences in nozzle settings

from one chamber to another

Ensure the same nozzle settings. [297]

▪ Differences in winch speed

from one chamber to another

Check winch speeds, especially

after maintenance work.

[297]

▪ Blockage of nozzle gaps Check the filter. It should be

working properly.

▪ Differences in the timings of

the addition of chemicals

Ensure the operators add the

chemicals at the same time and

temperature.

[297]

▪ Differences in the number of

passages of fabric

Ensure in each batch the fabric

passes through nozzle the same

number of times.

[297]


machine




kg hydro and 1.7 L caustic 38 oBé

is required or each 1 m3 of air in the

system.

[231]

Unlevelness ▪ Poor circulation of the fabric

due to interruptions, knots,

and overloading

Setup the machine carefully. The

fabric ends should be properly

joined.

[253]

▪ The temperature ramp rate is

higher in the critical dyeing

region


control the temperature ramp rate.

It should be kept between 1-1.5 oC/

min to ensure level dyeing.

[9,

253]

▪ Too slow or too fast rope

speed

Check rope speed. The rope cycle

time should be the same.

[297,

301]

289



Check the correct rope speed is

programmed for this rope length.

Recheck the correct

synchronization of motor speed.

▪ Variation in pressure head in

the tubes leading to a

reduction in speed of the rope

Increase the pump rate to increase

the pressure. The pressure should

be even in all tubes.

▪ Stoppage of the rope due to

damaged stitches during

running

Ensure the rope ends are stitched

properly with strong threads.

▪ Stoppage of certain portions

of fabric in the dyebath due

to entanglement and twisting

Avoid accumulation of the fabric in

the dyebath.

[301]

▪ Use of a low tension during

jig dyeing leading to the

formation of folds

Use optimum tension settings

according to fabric.

[67]

▪ Insufficient agitation of the

liquor in the dyebath

Use high fabric speed.

▪ Insufficient flow of liquor

through the fabric layers

during beam dyeing

Use high liquor flow rate.

Check winding of the fabric on the

beam.

[347]

▪ Variation in the flow of

liquor across the fabric due to

channeling caused by too

tight or too loose fabric

winding

Ensure the winding of the fabric is

uniform on the beam.

[347]

290



▪ Slower liquor circulation rate

leading to higher exhaustion

of the dye

Use the optimum circulation rate.

The maximum exhaustion should

be restricted to 2% per cycle.

[79]

▪ Variation in dyebath

temperature due to heat loss

1. Ensure the dyeing machine is

covered with lid.

2. Ensure the heating system is

working properly.

▪ Trapped air bubbles (air


causing problems in liquor

penetration

After beam loading, fill the

autoclave with water and circulate

the water alone without any

chemicals.

[110,

149,

253]

▪ Use of direct steam heating

causing the disperse dye

dispersion to break down

Avoid exposing disperse dye

solution to live steam heating. Use

indirect heating.

[348]

Poor color

yield

▪ Lower dyebath exhaustion

due to high residual moisture

in fabric before the dyeing

process

Check the last drying step in

pretreatment. The residual moisture

should be uniform and according to

the fiber type and blend ratio

(moisture regain).

[342]

▪ Reduction in fabric

temperature due to heat loss

in open jigs

Use closed jigs whenever possible.

▪ Cooling of selvages due to

heat loss in jig causing

differences in rate of dye

uptake

1. Use closed jigs with hoods to

avoid heat loss.

2. Ensure proper heating of the air

space inside the jig.

[347]

Shade change ▪ Use of different liquor ratios Use consistent dyeing conditions. [301]

291




machine




kg hydro and 1.7 L caustic 38 oBé

is required or each 1 m3 of air in the

system.

[231]

Abrasion or

chafe mark,

Pilling of

fabrics

▪ Rubbing of fabric surface

caused by uneven or

damaged machine lining and

fabric guiding elements

The machine lining, fabric guiding

elements should be even.

[150,

346,

349]

▪ Mechanical friction due to

machine overloading

Avoid using very large batches.

Use a lubricant agent.

[67,

253]

▪ Stationary material in the

running machine (knots)

Ensure the fabric ends are properly

stitched before dyeing.

[253]

▪ Using very high machine

speed

Use optimum machine speed

according to the rope cycle time.

[253]

▪ Incorrect nozzle size and gap Use correct nozzle size and gap to

ensure proper opening of rope. The

cotton/lycra fabric requires a higher

flow.

[297]

Poor

appearance

▪ Longer duration of running

due to reprocessing.


[301]

▪ Variation in fabric tension in

a jig during dyeing leading to

structure distortion

Ensure the tension is properly

adjusted according to the fabric.

[67]

Moire (wavy

appearance)

▪ Too tight batching on the

beam

1. Avoid tight winding of the

fabric on the beam.

[110,

194,

350]

292



poor

appearance

2. Avoid using too high

differential pressure.

3. Ensure the fabric has high

absorbency.

▪ Incorrect flow of liquor in

beam dyeing

1. Ensure the dye liquor circulation

as per the following sequence:

Inside-out: 5 minutes

Outside-in: 3 minutes

until temperature reaches 110 oC.

After that maintain inside-out.

2. Perform caustisizing or treat with

3-5 g/L carrier at 130 oC for 30

minutes.

[194]

Dimpling or

cockling of

fabric surface

▪ Using too low rope speed

during cooling

1. Use increased liquor ratio.

2. Run the machine at optimum

speed.

3. Use a large diameter nozzle.

[301]

▪ Too slow fabric speed during

the cooling phase

Use optimum machine speed


[346]

▪ Dropping the bath at too high

temperature leading to shock

cooling of fabric (especially

viscose blends)

Avoid draining the bath at a very

high temperature.

[297]

Crush marks ▪ Running fabric at a very high

speed

1. Increase the liquor ratio.

2. Use a slower rate of cooling.

[297]

▪ Improper selection of nozzle

diameter

Use a suitable diameter nozzle

depending on the fabric.

[323]

293



Creases/ rope

marks

▪ Poor suitability of the dyeing

machine.

Select a dyeing machine based on

the fabric.

[253]

▪ Too heavy fabric batch.

machine overload

1. Avoid using very large batches.

2. Use a lubricant agent.

[253,

297]

▪ Using too low liquor ratio Use a sufficient quantity of the

liquor in the machine.

[297,

321]

▪ Too slow fabric speed 1. Use optimum machine speed


2. Use a lubricant agent.

[75,

253,

321]

▪ Twisting of the rope

accompanied by weight or

pressure

Use a lubricating agent. [67,

301]

▪ Incorrect nozzle size and gap Use correct nozzle size and gap to

ensure proper opening of rope.

[110]

▪ Improper loading of the

fabric into the machine

1. Ensure proper loading of the

machine.

2. In the case of rope dyeing, the

length of each rope and the

number of ropes need to be

determined in advance.

3. Check the batch for creases. It

must be straightened to remove

creases and folds.

[67,

150,

253,

301]

▪ Too rapid rates of

temperature rise or cooling

Use optimum heating and cooling

rates.

[347]

▪ Dropping the bath at too high

temperature leading to shock

cooling of fabric

Avoid draining the bath at a very

high temperature.

[297]

294



▪ Improper opening of fabric in

jig during dyeing

Ensure the fabric is properly

opened and crease free during

running.

[194]


ends leading to the formation

of creases

The fabrics should be stitched with

ends properly aligned and using

correct stitching thread.

[322]

End-marks ▪ Storage of fabric rolls on

their ends

Store and transport the fabric

horizontally in suitable bags.

[301]

▪ Improper dyeing process

(heating, cooling)

Adjust the temperature program.


[253]

Seam marks ▪ Incorrect flow direction of

liquor in beam dyeing.

Avoid liquor flow in both

directions (in-out and out-in) in the

early stages of dyeing. In the early

stages, in-out flow is preferred.

[85]

Light spots ▪ Trapped air bubbles in the

material leading to reserve

areas

Ensure proper wetting and

deaerating of the package.

The temperature ramp rate should

be kept between 1-1.5 oC/min.

[110,

149]

Pale areas ▪ Use of wrong dyeing

machine settings (heating,

pressure, speed)



It should be kept between 1-1.5

oC/min to ensure level dyeing.

[253]

Streaks/stripes/

bar/bands

▪ Chafe or rub marks caused by

uneven or damaged machine

lining and fabric guiding

elements appear as dark

streaks (if occur before

1. Inspect the machine surface

regularly.


[149,

150,

321]

295



dyeing) and light streaks (if

occur after dyeing)

▪ Crush fiber surface that dyes

darker than undamaged areas

Avoid rope tangling and crushing

during dyeing.

[149]

▪ Uneven distribution of dye

liquor at the bottom of the

batch due to prolong machine

stoppage

1. Avoid stopping the machine for

longer period.

2. Avoid using very big batch sizes.

[67,

194,

321]

▪ Too high tension on fabric

during jigger dyeing

Ensure the fabric tension is

optimum by proper adjustment of

guide rollers and tensioning device.

[321,

323,

350]

▪ Improper nozzle selection in

jet dyeing

Select nozzle based on fabric

construction and type.

[321]

▪ Improper rinsing of dyed

fabric

Ensure washing conditions are

adequate (speed, temperature, water

quantity).

[321]

▪ Localized uneven squeeze by

tension bar on a jig

Ensure the surface of the tension

bar is uniform and is properly

aligned.

[321]

Lustrous

stripes

▪ Pressing carried out at a too

high temperature and

pressure

Check the machine's settings

(nozzle pressure, reel speed) to

avoid tangling of a fabric rope.

[320]

Holes ▪ Projecting sharp objects in

the dyeing machine causes

punctured holes or tears.

Check the presence of sharp objects

in the machine.

[150,

301]

Dark spots ▪ Dye deposits in the machine Ensure the machine is cleaned

properly before the dyeing process.

[253]

296



▪ Foaming caused by high

turbulence in the dyebath

Use a defoamer [317,

351]

▪ Foaming caused due to air

leak in the circulation system

Check the liquor circulation system

for any leaks

[317]

▪ Use of direct steam heating

causing the disperse dye

dispersion to break down

Avoid exposing disperse dye steam

to live steam heating. Use indirect

heating

[348]

Dark patches ▪ Dark dyeing of damaged

fiber portions due to higher

nozzle pressure (especially

viscose)

1. Load the fabric with a lubricating

agent.

2. Ensure proper piling and smooth

running of fabric.

[301]

Widthwise

shade

variation/

listing

▪ Inadequate circulation of

liquor within fabric rope

1. Avoid too tight ropes.

2. Use correct size of nozze

[346]

▪ Too rapid cooling of selvages

due to heat loss in jig causing

differences in rate of dye

uptake

1. Use enclosed dyeing machine if

possible, to avoid heat loss from

the sides.



3. Select dyes with which are less

sensitive to temperature

variations.

[150,

347]

▪ Uenven heating along the

width in jigger leading to

temperature variations

1. Ensure uniform heating the

dyeing liquor.

2. Circulate the liquor in the dyeing

trough.

[68,

323]

▪ Poor winding of fabric on the

beam or roller causing

1. Ensure proper winding of fabric

on the beam.

[110,

253]

297



uneven package density

across the width

2. Check the shrinkage of fibers in

the blend.

▪ Poor batching of the fabric

leading to a difference in

liquor pickup and cooling of

the selvages

Ensure the winding of the fabric is

edge to edge and tension should be

uniform.

[67]

Center selvage

variation

▪ Uneven overlapping of the

beam perforations

Ensure the fabric is properly rolled

on to the beam edge to edge with

no overlapping of selvages.

[67,

85]

▪ Tight batching on the beam Check the shrinkage of fibers in the

blend.

[110]

▪ Using too big batch size on a

jig

Avoid using too big batch size. [323]

Perforation

marks

▪ Incorrect rolling of the fabric

on the beam

The beam should be lapped with 5-

10 layers of loosely woven PP

material.

[67]

▪ One direction (in-out) flow of

liquor in beam dyeing

1. Ensure the dye liquor is flowing

in both directions (in-out and

out-in).

2. The beam should be lapped

with 5-10 layers of loosely

woven PP material.

[85]

Inadequate

fastness

▪ Improper rinsing of the

substrate due to lower water

pressure

The water supply pressure should

be 2-3 bar.

[297]

Rubbing

fastness

▪ Inadequate dye fixation

conditions (lower

Use appropriate dyeing fixation

conditions (time and temperature).

Perform reduction clearing.

[253]

298



temperature or shorter dyeing

time)

Two sidedness ▪ Slight difference in depth

between face and back of

fabric due to very high

tension or differences in

tension during batching

Ensure correct batching of fabric

with uniform tension.

[67,

323]

Tailing ▪ Insufficient flow of liquor

through the fabric layers

during beam dyeing

1. Check the fabric is not tightly

wound or use of oversized batch.

2. Use a pump with a larger liquor

flow rate.

3. Ensure the reverse circulation


[67,

110]

▪ Variation in tension during

winding of the fabric on the

beam due to an increase in

the diameter of the batch

1. Ensure the fabric tension remains

the same in the batch during

winding.

2. Avoid using an oversized batch.

[110]

▪ Incorrect additions of the

dyes and chemicals

Ensure the dyes and chemicals are

added in a proper manner.

[323]

▪ End portions of the batch are

dyed differently than the

middle portions of the blend

on jig due to differences in

the speed of the fabric

Ensure the fabric speed remains the

same irrespective of batch size and

during loading and normal run.

[67]

▪ Denser winding of the pre-

runner cloth on the beam

affecting liquor flow

Use an adequate number of

windings of the pre-runner fabric.

The fabric should have open

structure.

[110]

299



▪ One direction (in-out) flow of

liquor in beam dyeing

Ensure the dye liquor circulation as

per the following sequence:

Inside-out: 5 minutes

Out-in 3 minutes

till the temperature reaches 110 oC.

After that maintain in-out.

[85,

194,

323,

350]

▪ Inadequate dwell time for

complete adsorption of dyes

during batch reversal in jig

Inherent jig problem. It cannot be

corrected.

[347]

▪ Variation in dye rate of fiber

due to variation in the

temperature

1. Use closed jigs with hoods to

avoid heat loss.



3. Use rubber rollers or metal

rollers with long leader cloth to

prevent heat loss.

[68,

346,

347]

▪ Use of wrong dye program

having a higher temperature

ramp rate in the critical

dyeing region



It should be kept between 1-1.5 oC/

min to ensure level dyeing

[9,

253]

Poor

dimensional

stability

(shrinkage)

▪ Lengthwise distortion caused

by the machine

Adjust machine settings according

to the substrate being processed.

[253]

Fabric/stitch

distortion

▪ Improper or too high tension

on the fabric

Adjust machine settings according

to the substrate being processed.

[253,

346]

▪ Incorrect seams Use straight seams. [253]

300



▪ Using too high fabric speed. Reduce the nozzle pressure and

winch speed.

[297]

Luster marks ▪ Physical change in fiber

caused by local pressure and

higher temperature

Avoid prolonged contact of

stationary material with the hot

machine.

[253]

Poor hand ▪ Wrong dyeing program

(temperature/time)

Select a suitable dyeing program. [253]

▪ Oligomer deposit on the

fabric surface


temperature.


during dyeing.



possibility.

[85]

Entanglement

of fabrics

▪ Lower jet pressure Adjust the jet pressure based on

fabric.

[297,

301]

▪ Overloading of the machine Avoid overloading the machine.

Calculate fabric weight based on

fabric gsm, rope length, tube

diameter.

[297,

301,

346]

▪ Too high jet pressure 1. Adjust the jet pressure based on

fabric.

2. Load the fabric at a warm

temperature.

[301]

▪ Ballooning of fabric as air is

entrapped due to densely

sewn seam and tightly knit

fabric structure.

1. Cut a vertical slit of 10-15 cm

near the joint to allow air to

escape.

2. Use a larger diameter nozzle.

[297,

301]

301



3. Use a deaerating and penetration

agents.

4. Use a chain stitch or butt stitch to

join the rope pieces.

4.8.3 Problems caused in continuous dyeing machines

The continuous dyeing is the most commonly used method of dyeing woven polyester/cotton

blends. Continuous dyeing usually involves long runs (> 5000 m) and gives high color yields,

reproducible results at lower costs as compared to batch methods. With increasing trends of shorter

trends put pressure on continuous dyeing to produce results at lower costs [9]. Different methods

can be used for the continuous dyeing of blends. The common procedure is to impregnate the

fabric using a padder with the dye solution or dispersion (depending upon the dye class). The fabric

containing dye liquor is then subjected to various treatments to fix the dyes. It can be obtained

either by chemical treatment or application of energy or a combination of both. The heat in the

form of steam or dry heat is usually used as a source of energy that creates required chemical

and/or physical changes. The fixation of the applied dye is thus achieved [352]. During semi-

continuous dyeing, the fabric is continuously impregnated with the dye liquor followed by a slower

fixation treatment. The dye liquor in the fabric gradually diffuses into the fiber interior and fixation

of dye is gradually achieved. The unfixed dye is then removed by rinsing and soaping. This is

followed by drying. Table 4.38 shows the common sequences used in semi-continuous and

continuous dyeing of blended fabrics [128].

302

Table 4.38: Different sequences used in the dyeing of blends by semi-continuous and continuous

process.

Process Type Dye class Blend

Pad-batch-beam Semi-continuous Disperse/reactive Polyester/cellulosic

Pad-batch-jet Semi-continuous Disperse/reactive Polyester/cellulosic

Pad-dry-thermofix-jig develop Semi-continuous Disperse/vat Polyester/cellulosic

Pad-dry-thermofix Continuous Disperse/reactive Polyester/cellulosic

Cellulosic/elastane

Disperse Polyester/elastane

Pad-dry-chemical pad-steam Continuous Reactive Cotton/viscose

Cotton/modal

Pad-dry-thermofix- chemical

pad-steam

Continuous Disperse/reactive Polyester/cellulosic

Disperse/vat Polyester/cellulosic

Disperse/sulfur Polyester/cellulosic

A typical continuous dye range for polyester/cellulosic blends depending upon the dyeing

method, as shown in Figure 4.7, consists of scray, a compensating device, padder, infrared dryer,

hot flue, cooling cylinders, scray, chemical padder, steamer, washing range, can dryers and finally

scray [61]. This range is designed for dyeing both the polyester and cellulosic components in the

blend in one pass through the range. The polyester is dyed by a pad-dry-thermosol process in the

first stage of the range. Latter stages of the range are used to dye cellulosic fibers using a pad-

steam process [353]. Typically in dyehouse, this range exists in two units: Pad-dry-thermosol and

pad-steam-wash-dry [61].

Figure 4.7: Continuous dyeing range for PES/CELL blends.

pad

hot flue dry wash-off I.R.

pre-dry chemical

pad steam

303

The padder is the critical unit in continuous dyeing and gets great attention from dyehouse

technicians [61, 353]. After creases, width-wise shade differences are the largest cause of customer

rejects [61]. The hardness of rubber covering depends on fiber and fabric construction and should

be the same for both padders [133]. The nip-width or contact zone of the padder needs to be the

same across the full working width of the padding rollers. This can be checked by a carbon paper

sandwich test or powder spray test. The width of impressions or rectangular band between different

points is recorded. When pressure is applied to the sides of the central mandrel, the pad rollers

may deflect causing more pickup at the center than at the edges. Different approaches used to

overcome this problem involves medication of the camber of the rubber bowl or using alternative

padder design (e.g., Kuesters swimming roller) [61, 353]. As fabric pick-up is affected by various

factors other than uniformity of the nip such as fabric running speed, variations in the fabric due

to preparation or weaving, continuous monitoring during production is important. This is usually

done by measuring the moisture of the fabric at the center as well as the sides. These sensors are

part of a closed-loop system. Any variation in the pickup detected by the sensors is sent to the

padder for automatic pressure adjustment. It is recommended to install such a system before and

after padder as variation in incoming moisture may cause shade differences [354, 355].

The correct stitching of fabric ends is essential to avoid stich marks in dyed fabric. If cotton

thread is used for dyeing it absorb more solution as compared to synthetic fibers and may cause

stich impression on fabric layers. It is recommended to stich polyester containing blends with

100% polyester thread to avoid this problem [67, 322].

For level dyeing, fabric running speed and the immersion length should be constant during

the padding process. The immersion length refers to the distance between the point of entry to the

pad liquor to the point where the fabric exits the liquor. The level control can be used as a measure

to control immersion length but may not be very accurate for small trough sizes. Small troughs are

preferred due to less wastage. Different trough designs are available depending on fabric

characteristics [61].

The important factors affecting the padding process are as follows [100].

▪ Fabric related:

- Uniform fabric width;

- Free of creases;

- Free of curled selvages;

304

- Consistent absorbency; and

- Uniform temperature.

- Homogeneous moisture content.

▪ Padder related:

- Defect-free roller covering;

- Uniform roller pressure across the width;

- Homogenous liquor temperature;

- Uniform liquor feed; and

- Consistent liquor level in the pad trough.

A common problem that may be encountered in the continuous dyeing attributed to padding

is tailing and listing. Tailing is the gradual decrease in dye concentration in the pad liquor leading

to variations in hue or depth along the fabric length of a dye lot. Tailing stops once the equilibrium

is reached between the dye moving towards the fabric and dye fed into the pad trough. Another

similar problem seen in the pad-dry-thermofix-chemical pad-steam process for polyester/cellulosic

blends is known as reverse tailing or chemical pad bleeding. The unfixed dye present on the dried

substrate desorbs into the chemical pad. This also causes shade variation along the fabric length.

This movement stops as the equilibrium is reached after several minutes. A large quantity of

electrolyte is added in the pad liquor to avoid this problem. Another approach is to add a small

quantity of the pad liquor into the chemical pad [128].

The padding liquor temperature is an important parameter as it affects the stability of the

dyes. An increase in temperature may cause instability and leads to tailing. It has been found that

an increase in temperature of pad liquor from 20 oC to 25 or 30 oC results in higher color depth

due to higher wet pickup. These temperature variations are due to the temperature differences

within the fabric rolls especially when big batching is done, or fabric may be over dried. It is

recommended to have a cooling roller before padding to avoid this problem also final drying

temperature should be controlled [353, 356]. It is recommended to pass the fabric through a skying

unit before drying. The skying units consist of a series of top and bottom roller that provides

adequate time for dye penetration [357].

The drying section aims to remove the moisture and leave the dye uniformly deposited on

the fabric. Drying is performed in two stages; firstly using infrared units for preliminary drying

305

and secondly utilizing hot flue to complete the drying [133]. During the drying process as the water

is evaporated the dye present in the fabric moves to the surface and this movement is known as

migration [118]. After impregnation and squeezing, the distribution of the dye liquor on the fabric

is nearly homogenous and is held in capillary pores. During drying, the water starts evaporating

from the fabric surface is substituted with water moved by capillary forces from the fabric interior.

The dye dissolved in water also carries to the fabric surface during this movement. The water

movement also occurs due to the concentration difference between the fabric surface and the

interior provided the capillaries contain water. The movement stops when the dye size becomes

large so that its movement is hindered (agglomeration due to anti migrating agent) or the coherence

of the water channel is broken (migration threshold). The migration stops on reaching the

migration threshold and varies considerably for different materials. Hydrophobic fibers contain

more water on the fabric surface as compared to hydrophilic fibers that have more swelling water.

A typical cotton fabric having a wet pickup of 75% has a migration threshold of 25% (2/3rd of the

water is evaporated). For other fibers the corresponding values are: viscose or lyocell 40%, wool

36%, polyester/cotton 20%, nylon 10%, polyester 5% [100, 118]. Fabrics with the smaller specific

surface area have lower migration threshold values [118].

Figure 4.8: Schematic representation of migration types during intermediate drying (G represents

the direction of fabric movement).

Depending upon the movement of the dyes in the fabric during drying, the migration can

be categorized as four types as shown in Figure 4.8. These are horizontal migration (A), selective

horizontal migration (B), vertical migration (C), and selective vertical migration (D) [358]. In

horizontal migration, the dye particles migrate over the fabric surface while vertical migration

involves the movement of the dye particles from the interior to the fabric surface. The selective

G

A B

C D

306

horizontal and vertical migration are the special case of horizontal and vertical migration that

involves movement of the dye particles of different class at different rates on the fabric surface

and from interior to the surface respectively. These are important specially in blends where

different classes of dyes are present in the substrate at the same time. Numerous faults may occur

in continuous dyeing due to migration, that is difficult to rectify, are described in Table 4.39 [9,

100, 118, 358].

Table 4.39: Migration in intermediate drying and associated faults.

Migration related faults Description

Unlevelness Faded or washout appearance of the portions of the dyed

fabric.

Tailing Variation in the shade or hue along the fabric length due to

variation in drying rate.

Listing Variation in the shade or hue along the width of the fabric.

Stripes or streaks Differences in rates of drying over the fabric surface,

uneven drying.

Frosting Dye migration from inside to the surface of the fabric.

Two-sidedness Shade difference between two sides of the fabric due to

differences in drying rate of two sides of the fabric, one side

being hotter than the other. Hotter side dye darker than

another side.

Dark selvages Selvage area dyes deeper as this region has a higher

temperature than the center of the fabric.

Light selvages Selvage area dye lighter as the fabric center has a higher

temperature than the side of the fabric.

Poor penetration Undyed zones in the fabric at the yarn crossover point and

interior of the fabric.

Infrared pre-drying prevents the migration of the dye by rapidly reducing the moisture

content of the fabric moisture to the migration threshold that is considered optimal to avoid dye

307

migration [353]. In radiation drying, the temperature difference between fabric interior and surface

is minimal as compared to convection and conduction radiation [128]. The infrared drying units

are either gas or electric fired. The radiant heat source has a temperature of around 800 oC and the

radiation peak is 3 µm. The infrared radiators are placed in superimposed rows on each side and

fabric is passed vertically. The unit is usually located just after the padder. For some fabrics, the

skying unit is required as mentioned earlier [9, 133, 354, 355].

The dyes used for both fibers in the blend must show low migration and have similar

migration behavior. Disperse dyes having the same color index numbers may contain different

dispersing agents and thus exhibit different migration behavior. The liquid dye shows fewer

problems as compared to powder to grain type [118]. Dyes having smaller particle size show

greater migration tendency. Similarly, coarse yarns and more dense fabrics exhibit more migration

problems. Polyester/cotton blends have more tendency to show migration as compared to cotton

fabrics [100]. It has been reported that migration increases with the increase in polyester content

of the blend [359].

The following points are important to control migration [9, 100, 118]:

▪ Lower pick-up (less surface or free water molecules);

▪ Skying between padding and drying (better swelling, penetration);

▪ Addition of electrolyte to increase dye affinity (but a risk of tailing);

▪ Infra-red pre-drying (residual moisture after pre-drying);

▪ Well balanced airflow in the dryer (rate of drying);

▪ Use of an anti-migrating agent (especially for disperse and vat dyes);

▪ Better dye selection (dyes with similar affinity/diffusion properties, physical form of

the dye, dye class and constitution); and

▪ Good pretreatment of the fabric (levelness).

It is possible to measure the fabric moisture exiting from the infrared unit which can be

used to regulate the infrared unit. The moisture detectors are installed just before the drying unit

and measure fabric residual moisture [360]. Modern infrared units, to conserve energy and prevent

fabric charring or fusion, are equipped with an option to shut the sides off based on fabric width

and rotation option which moves the infrared panels away from the fabric or heat shields which

move in front of radiation panels in the event of machine stoppage [361].

308

The hot flue is the most common unit employed for drying and thermofixation of dyed

fabrics. Drying is carried out at 100-120 oC. A typical dye range consists of two or three of these

units depending on the dyeing process, first one serving as a drying unit and remaining as a dye

fixation unit. It consists of a series of driven top rollers and free bottom rollers. Drying is achieved

through circulating hot air which is directed to the fabric through nozzles. The drying and fixation

rate is managed by the temperature of circulating air, airflow volume, and nozzle pressure. For

optimum results drying should be uniform over width and length of the fabric [9, 133, 361].

Stenters can be used for thermofixation of dyes but their use is limited due to lower production

rates. The main drawback associated with it is the machine speed as some time is required for the

fabric to heat up and reach the dye fixation temperature. Their main advantage is the ability to

control fabric shrinkage along the width. Shade variations may occur at selvages if the dyed fabric

comes in contact with the base of the pin plates [61, 128, 133].

During the thermofixation process, the fabric is heated in hot air to a higher temperature

to carry out the fixation of dyes for 30 to 60 seconds depending on the dye class [114]. It is

important to control the temperature across the width of the fabric and should not exceed ± 3 oC

[128]. Higher the fixation temperature shorter will be the thermofixation time. It is recommended

to use the highest possible fixation temperature possible. To avoid ring dyeing and fastness

problems, the temperature or dwell time or both should not be too low [115]. Excess temperature

and dwell must be avoided to prevent fiber damage during dyeing. It is essential to consider the

stability of fibers under thermofixation conditions. The stability depends on the exposed

temperature and treatment time. Table 4.40 shows the suitability of different fibers in different

thermofixation conditions. The diacetate fibers damage starts damaging at 80 oC at so it is not

suitable [133].

The steaming is an important process for the fixation of vat, sulfur or reactive dyes on

cellulosic fibers. The tight-strand roller steamers are used to provide required steaming conditions

(102 to 105 oC, 20 to 120 seconds, depending upon the dye class). The uniformly distributed dye

present on the fiber surface diffused into the fiber interior during treatment with saturated steam

[128]. For vat or sulfur dyes, the steamer should be free from air. This gives full development of

shade. This is achieved by a slight overpressure in the steamer [128, 362]. The temperature should

not vary within the steamer. Widthwise variation may occur due to temperature differences in the

steamer [100, 363]. For steamer, inlet and outlet zones are important. [362]. To prevent steam

309

condensation and dropping the entry and roof the steamer is heated. There is a water seal at the

exit to prevent air from entering into the steamer and is fed with a slight overflow [61].

Table 4.40: Suitability of thermofixation conditions for different synthetic fibers.

Fiber

Maximum allowable temperature

(oC) with a treatment time of

20 sec 60 sec

Diacetate Not suitable Not suitable

Triacetate 220 210

Polyamide 210 200

Polyester 220 220

Acrylic 170-180 160-170

The washing stage performs different tasks depending upon the dye class used. It can be

classified as dilution wash, fastness wash and reaction process. The dilution wash removes caustic,

salts and chemicals from the fabric. During rinsing wash also called diffusion wash the unfixed

dye is removed. In the reaction process, oxidation of vat and sulfur dyes and neutralization are

performed. A typical washing section consists of six to eight boxes. In each washbox the fabric is

passed through a series of top and bottom rollers. The bottom rollers are filled with the washing

liquor. The movement of the rollers creates turbulence inside the washing chamber. The agitation

and excessive turbulence during washing at high temperature (100 oC) lead to a creasing problem.

The nip between the roller surface and the fabric create a force that squeezes washing liquor from

the fabric. The multiple dip and nip in each washbox facilitate the removal of impurities. The

washing efficiency is enhanced by use of counterflow within each wash box. The bottom roller in

the wash box is separated by dividing the plate that facilities counterflow. The wash boxes are

interconnected with each other such that overflow from one washbox is feed to the other to save

the water consumption. In between washboxes intermediate squeezers are present to reduce the

carryover liquor from the previous washbox. This helps in reduction of contamination from one

washbox to another [61, 128, 353].

The washing process is affected by the following factors [128, 364]:

310

▪ Amount of unfixed dye;

▪ The time allowed for washing (fabric speed and wash box capacity);

▪ The temperature of the washing liquor;

▪ Quantity of water;

▪ Quality of the water (impurities);

▪ Agitation (mechanical action);

▪ The attraction of the unfixed dye for the fiber; and

▪ The chemicals used to facilitate washing.

The washing process can be considered as a two-phase process. During the first phase

unfixed dyes and chemicals removed from the fabric surface that facilitates the removal of the

unfixed dye from the fabric interior in the subsequent step. This phased in favored by a high

number of bath changes, larger water quantity, and high mechanical action. In the second phase,

soaping and hot rinsing is performed to remove the unfixed dye and chemical from the fabric

interior. This phase is facilitated by higher washing temperature, lower water hardness, larger

water quantity, a high number of bath changes, lower quantity of unfixed dye to be removed, lower

substantivity of the dye with high diffusion.

With short runs, high-quality standards and short delivery times require the dyeing process

to be controlled precisely. To increase machine utilization grouping of shades is a must along with

automatic controls for a padder, drying units, drying cylinders and water usage. The control

equipment is widely available to make the dyeing process more efficient. Proper maintenance is

essential for avoiding machine faults along with quick fault rectification is mandatory for

maximizing machine efficiency [365]. That being said, the quality of the workforce cannot be

overlooked. Sometimes it is seen that the sophisticated equipment is available in the dyehouse but

not been used as its goal was not properly known to the workforce or middle management. Also,

it might have developed problems over time which were not corrected. It is the responsibility of

the senior management to make proper use of talent and equipment available. Producing the right

quality product for the right cost is always a challenge for all management [61].

Table 4.41 summarize the dyeing problems caused in different sections of the continuous

dyeing machine along with their causes and remedial measures.

311

Table 4.41: Dyeing problems in continuous dyeing machines and their countermeasures.


Reproducibility ▪ Dye hydrolysis Check the pad trough cooling


[120]

▪ Differences in drying conditions Ensure uniformity of the drying

conditions by controlling the IR

intensity, airflow rates, and

temperature.

[120]

▪ Differences in fixation

temperatures during batching

(CPB dyeing)

1. Consider the actual

atmospheric condition during

batch fixation.

2. Ensure the same temperature

during fixation if possible or

adjust batching time

accordingly.

[120]

▪ Variation in fabric immersion

time

Ensure the fabric speed is

uniform to have the same

immersion time.

[120]

▪ Variation in dwell time during

fixation

Maintain the contestant machine

speed.

[128]

▪ Variation in dwell time during

aftertreatment

Maintain the contestant machine

speed.

[128]

▪ Presence of air in the steamer

that retards reduction

Maintain a slight overpressure in

the steamer.

[366,

367]

Unleveleness ▪ Dye migration during drying 1. Set low pickup as possible.

2. Select dyes with a low

tendency to migration.

3. Use a suitable anti migrating

agent.

[67,

367]

312



▪ Variation in nozzle pressure in

hot flue dryer

Check nozzle cleanliness and

air supply over.

▪ Uneven padder pressure due to

the accumulation of fluff on the

padder surface

1. Ensure proper singeing of the

fabric.

2. Give the fabric extra wash to

remove excess fluff.

3. Clean the padder surface

regularly.

[67]

▪ Incomplete removal of moisture

after drying

Check the IR intensity and

drying conditions (dwell time,

temperature).

[79]

Pale spots or

areas

▪ Light areas where yarns cross

due to poor penetration

1. Use a wetting agent.

2. Increase impregnation time.

3. Change the pressure of the

rollers.

[118,

253]

▪ Light areas in the fabric due to

heavy migration

1. Use dyes with low migration

behavior.


the anti-migrating agent.

3. For cotton wovens, use a wet

steaming method.

[118,

253]

▪ Condensation droplets from

steamer roof, exhaust canopies,

and stationary steamer rollers

1. Regularly check dryer and

pad-steam units.

2. The roof of the dryer and the

steamer should be heated.

3. Increase the steam flow.

4. Carefully skip the roller in

the steamers. The top rollers

[128,

253,

317,

366]

313



must be in contact with the

fabric.

▪ Differences in residual moisture

of the fabric


pretreatment. The residual

moisture should be uniform and

according to the fiber type and


[342]

▪ Accumulation of lint on the

padder or guide rollers

Clean the padder and guide

rollers regularly.

[317]

Widthwise

shade

differences/

listing

Variation in padder pressure across

the width

1. Check the fabric pick-up

regularly.

2. Check the padder pressure

settings.

3. Ensure constant air pressure

at the padder controls.

[61,

149,

253,

367-

369]

▪ Differences in fabric moisture

entering the padder

Ensure the fabric moisture

levels are uniform. Check the

drying settings of the preceding

stage.

[355]

▪ Differences in fabric weight

across the width

1. Adjust the padder pressure to

compensate for fabric

differences.

2. Check the incoming fabric

quality for uniformity in

fabric weight.

[355]

▪ Variation in intensity of the

infrared predryer

Ensure the IR intensity is

uniform across the width and

both sides of the fabric.

[348,

363]

314



▪ Variation in the moisture content

of fabric during drying




[128]

▪ Variation in air velocities across

the width in hot flue dryer

Check nozzle cleanliness and

air supply over the entire width.

[67,

317,

361,

363]

▪ Dye migration during drying 1. Set low pickup as possible.



3. Use a suitable anti-migrating

agent.

[85,

118,

253,

369]

▪ Variation in temperature during

fixation (thermosoling)

1. Check temperature over the

entire width using

thermopaper or temperature

sensors.

2. Select dyes with lower

sensitivity to temperature

differences.

[118,

253,

348,

370]

▪ Variation in steaming

temperature

Ensure the sufficient supply of

steam in the steamer.

[100,

363]

▪ One sided inflow of dyeing

liquor into the trough

1. Check the injection pipe.

2. Ensure the liquor feeding is

uniform across the dyeing

trough.

[253,

368]

▪ Zone formation in the trough Keep the liquor circulated in

pad trough.

[369]

315



▪ Uneven dye bath temperature 1. Check the cooling system for

variations.

2. Check the temperature

variations in the fabric.

[368]

▪ Uneven hardness of the padder Check the hardness and renew

rubber covering.

▪ Wear of the roller covering Inspect the padder on regular

basis and grind the rubber

covering if required.

[317,

348,

370]

▪ Differences in dye fixation due to

neutralization of alkali in fabric

edges during batching in CPB

process

Wrap the batch in plastic to

avoid contact with CO2 in the

air.

[7]

Variation in fabric tension across

the width

Ensure the compensator is

working properly and guide

rollers are properly aligned.

▪ Differences in vertical tension of

the fabric into the infrared drying

zone

Check alignment of the guide

rollers.

Shade change ▪ Migration in drying due to high

residual moisture

30-40% liquor should be

removed during infrared pre-

drying.

[133]

▪ Inadequate dye penetration 1. Use the skying unit before

infrared drying for adequate

dye penetration.

2. Check the incoming fabric

temperature.

[120,

357]

316



▪ Variation in pickup during

chemical pad leading differential

reduction of vat/sulfur dyes

Ensure the wet pick-up should

be uniform during the chemical

pad.

[366]



Maintain the slight

overpressure in the steamer.

[366]

▪ Inadequate steam condition 1. Check the steam supply,

valves, and gauges regularly.

2. The steamer conditions

should be maintained

according to dye type:

Reactive: 102 oC, saturated

steam, 60-90 sec.

Vat: 102-105 oC, dry

saturated steam.

[128,

370]

▪ Long distance between the water

seal and washing unit leading to

over-oxidation of dyes

1. After steamer/water seal

fabric should have sufficient

quantities of hydro.

2. Ensure proper water flow in

the water seal for removal of

alkali.

[371]

Lengthwise

shade

variation/

Tailing

▪ Variations of moisture in the

fabric batch entering the padder

Ensure the fabric moisture

levels are uniform. Check the

drying settings of the preceding

stage.

[317,

369]

▪ Differences in temperature of

fabric throughout a batch

1. Check the fabric cooling

device is working properly.

2. Check the drying settings of

the preceding stage.

[317]

317



▪ Variation in fabric running speed Ensure the same fabric running

speed. Use j-scray for batch

change.

[61]

▪ Differences in fabric immersion

length

Ensure the same fabric running

speed and settings of the spacer

in the trough.

[61]

▪ Variation in dye trough level Monitor the trough level.

Ensure the level sensor is

working properly.

[194,

323]

▪ Settling of dye in the dyebath

(due to anti-migrating agent)

Keep the liquor circulated in

the stock tank and the pad

trough.

[118,

368]

▪ Variations in the air pressure

controlling the padder

1. Check the air supply for any

variations in pressure or

leaks.

2. Ensure same pressure

settings.

[317]

▪ Change in dyeing trough

temperature. High padding liquor

temperature causes instability of

disperse/reactive mixture

1. Check the cooling system for

variations.



[61,

120,

368]

▪ Longer immersion times Use smaller trough for smaller

immersion times.

[120,

323]

▪ Slower liquor turnover in the

trough

Use a smaller trough for faster

liquor turn over.

[120,

350]

▪ Dye migration during drying 1. Set low pickup as possible.



[85,

118,

318



3. Use a suitable anti migrating

agent.

253,

369]

▪ Variation in infrared intensity

during pre-drying




▪ Variation in drying temperature Monitor the drying

temperature. It should be same

thought the process and across

the machine.

▪ Variations in fixation

temperature during streaming

and thermofixation

1. Monitor the thermofixation

temperature. It should be the

same thought the process and

across the machine.

2. Check the steam pressure.

[317]

▪ Marginal dwell times in the

fixation

Ensure optimum dwell times. [128,

317]

▪ Variations in the washing process

(water flow, time, temperature)

Ensure similar water flow

levels, dwell time and

temperature within a lot.

[128,

317]

▪ Differences in dye fixation due to

drying of outer fabric layers

during batching in CPB process.


avoid drying.

[7]

▪ Improper rotation of batch during

CPB dyeing causing collection of

dye liquor at the lower portion of

the batch

Ensure the fabric batch is

rotating without any

interruption.

319



Two sidedness ▪ Uneven migration due to

variations in air flow or heating

on both sides of the fabric (faulty

drying equipment and process

control)

1. Check nozzle cleanliness,

temperature, and air supply.

2. Set low pickup possible.


the anti-migrating agent%

4. Dye selection based on their

migration behavior.

5. Examine migration

parameters of disperse dyes.

[67,

118,

370]

▪ One sided contact of the guide

rollers

1. Check the entry of fabric.

Replace the guide roller, if

necessary.

2. Change the fabric direction.

[67,

368]

▪ Blocked guide rollers Fix the guide roller. [368]

▪ Contact of the material with the

edge of the dyebath

Install guide rollers. [368]

▪ One side feeding of dyeing liquor

at the fabric exit

Check the liquor feeding

system for uniformity.

[368]

▪ Differences in the hardness of

padders

Check hardness of the padders

is the same.

[133,

194]

▪ Differences in rates of drying of

two sides of the fabric

Check temperature and air

current in drying chambers.

[128,

133]

▪ The fabric is not guided

vertically to the padder

Replace the guide roller. [368]

Dark and light

edges

▪ Due to uneven drying across the

fabric width

Check nozzles and exhaust

settings.

[118]

▪ Improper distribution of dye

liquor across the dyeing trough

Check the liquor feeding

system for uniformity.

[253,

368]

320



▪ Poor liquor circulation in the

dyeing trough

Check the liquor circulation


[368]

▪ Using a wider width padder for

the padding of narrower width

material

Use a suitable machine with a

smaller width padder.

[253,

368]

▪ Overstressed rollers due to

construction or hydraulics

problem

1. Check the pressure effect.

2. Replace rollers.

3. Check the hydraulic system.

[253,

368]

▪ Worn out padders or bent

padders due to higher loading.

1. Check the pressure effect.

Grind the padder rubber

covering.

2. Lower the padder pressure.

[253,

368]

▪ Curling of selvages during

padding

Ensure the proper adjustment

and functioning of the edge

guiders.

[323,

350]

Streaks/

stripes/ bar/

bands

▪ Light and dark bands caused by

uneven nozzle pressure

Check nozzle for evenness in

pressure.

[118]




elements appear as dark streaks

(if occur before dyeing) and light

streaks (if occur after dyeing)

Inspect the machine parts

coming in contact with the

fabric frequently.

[149,

150]

▪ Variation in tension in the dryer

and fixation unit

Check proper settings of

tensioning device and working

of guide rollers.

[253,

323]

▪ Jammed or slowly rotating guide

rollers inside the steamer

Check the steamer rollers for

proper working.

321



▪ Machine stoppage for a longer

period

Use j-scray for fabric change

when possible.

[194]

▪ Inadequate stitching Use proper stitching for fabric

ends. The stitches should be

parallel to weft yarns.

[321]

▪ Use of wrong stitching thread

that causes stitch marks during

batching of wet padded fabric

Use proper stitching thread as

per blend being processed.

[67,

322]

Holes ▪ Projecting objects in the dyeing

machine cause punctured holes

or tears

Inspect the machine parts

coming in contact with the

fabric regularly.

[150]

Creases ▪ Improper entry of the fabric in

the padder

The entry should have an

expander roller to ensure

crease-free entry.

[150,

253,

363]

▪ Improper batching of the fabric Ensure proper batching of the

fabric in the last preparatory

process.

[301]

▪ Excessive, insufficient or

variable tension during fabric run

Perform machine inspection

and maintenance regularly.

[128,

370]

▪ Improper alignment of the guide

rollers leading to variation in

tension on the fabric

1. Check the proper alignment

of guide rollers regularly.

2. Perform machine

maintenance regularly.

[128,

253,

317,

370]

▪ Incorrect setting of bow rollers Perform machine maintenance

on regular basis.

[317,

370]

▪ Differences in tension at the

padder or variation in pressure

across the padder

1. Ensure proper tension control

at the padder.

[370]

322



2. Check the padder pressure

for variation across the

width.

▪ Hard deposits of lint and loose

thread on rollers

Ensure routine machine

cleaning.

[128,

317,

370]

▪ Shrinkage of fabric during drying

and fixation units.

1. Heat set the fabric before

dyeing to finished width.

2. Check guide rollers.

[127,

253]

▪ Turbulence due to boiling in a

wash box

Check the steam settings in the

washbox. Avoid using live

steam.

[317]

▪ Distortion of weft due to the

application of too much vacuum

in the wash box leading to the


Use optimum settings

according to fabric construction

and weight.

[317]

▪ Selvage curling during padding

and thermofixation process

Ensure the proper adjustment

and functioning of the edge

guiders.

[194]

▪ Improper drying cylinder

temperature

Control the drying temperature

according to fabric type.

[370]

▪ Incorrect stitching of fabric ends

leading to formation of creases



[322]

Dark stains,

spots or specks

▪ Dents in the roller containing dye

deposits

Grind the rollers to produce a

smooth surface.

[368]

▪ Foaming spots due to excessive

foaming in the pad liquor

1. Avoid high turbulence in the

dyeing trough.

[253,

317]

323



2. Use chemicals with lower

foaming tendency.

3. Add defoamer.

▪ Foaming caused by an air leak in

the circulation system

Check the liquor circulation

system for any leaks.

[317]

▪ Incorrect preparation of the pad

liquor

1. Follow the standard

operating procedure of

preparing pad liquor.

2. Filter pad liquor before

feeding into the trough.

[367]

▪ Settling of dye in the dye trough Keep the liquor circulated in

the stock tank and the padding

trough.

[253]

▪ Transfer of dye deposit to the

fabric from the guide rollers

1. Clean the guide roller

regularly.

2. Avoid too dry conditions

during steaming.

[366]

Poor color

yield

▪ Inadequate dye penetration

during impregnation due to fabric

construction

1. Use the skying unit before

infrared drying for adequate

dye penetration.

2. Use wetting agent.

[120,

357,

366]


during impregnation due to high

fabric temperature

Check the incoming fabric

temperature. The fabric should

be cold before it enters the dye

bath.


during impregnation due to high


pretreatment. The residual

moisture should be uniform and

324



residual moisture content of the

fabric

according to the fiber type and


▪ Hydrolysis of dye due to increase

in dyebath temperature

1. Check the cooling system

for variations.



[120,

368]

▪ Ring dyeing of fiber caused by

poor penetration due to use of too

low thermofixation temperature

or short dwell time

Use appropriate thermofixation

conditions depending upon the

dye class and depth of shade.

[67]

▪ Incomplete fixation of the dyes

due to variation in temperature

and/or dwell time during

steaming/thermofixation

1. Use appropriate

thermofixation conditions

depending upon the dye

class and depth of shade.

2. The steamer conditions

should be maintained

according to dye type:

Reactive: 102 oC, saturated

steam, 60-90 sec.

Vat: 102-105 oC, dry

saturated steam

[79,

85]



Maintain a slight overpressure

in the steamer.

[128,

366]

▪ Long distance between the

reducing bath nip to the steamer

entry slot leading to oxidation of

dithionate in the absorbed dye

liquor

Keep the passage time within 2

seconds.

[128]

325



▪ Incomplete removal of moisture

after drying

Check the IR intensity and

drying conditions (dwell time,

temperature).

[79]

▪ Lower dye fixation due to

neutralization of alkali in the

fabric during batching in CPB

process


avoid contact with CO2 in the

air.

[7]

▪ Using too high thermofixation

temperature or dwell time

Use appropriate thermofixation

conditions depending upon the

dye class and depth of shade.

[79,

85]

Inadequate

fastness

Inadequate

wash and

rubbing

fastness

▪ Inadequate theromofixation

conditions (lower temperature or

shorter dyeing time)

1. Use appropriate

thermofixation conditions

(time and temperature)

depending upon the dye class

and depth of shade.

2. Perform reduction clearing.

[79,

253]

Abrasion or

chafe mark




elements appear as dark streaks

(if occur before dyeing) and light

streaks (if occur after dyeing)

Inspect the fabric guide

elements regularly. Perform

routine maintenance of the

machine.

[149,

150]

Poor

dimensional

stability

(shrinkage)

▪ Lengthwise distortion caused by

the machine.

Adjust machine settings

according to the substrate being

processed.

[253]

326

4.9 Problems in pigment coloration

Coloration with pigments is a well-established process due to its simplicity, economics, and

environmental reasons. Pigments have no affinity for the fiber so they can be applied to all fibers

and fiber blends. The coloration procedure consists of padding, drying and curing steps similar to

the classical resin finishing process. Pigments are fixed to the fabric with the help of binders, by

film formation that physically traps the pigments [89, 91-95, 102].

There are three main elements of the pigment coloration process, which are [102]:

▪ Substrate: Fiber type and blend ratio, fabric structure, pretreatment;

▪ Coloration process: Padding, drying and curing process and equipment; and

▪ Dye liquor: Pigments, binder, auxiliaries (migration inhibitor, dispersing agents,

catalyst, fixer, softeners, defoamers, etc.).

Uniform and even pretreatment is key to good pigment coloration. The fabric must be free

of residual chemicals and should have neutral pH and be defect free. Many of the faults that occur

during pigment coloration are related to fiber, yarn, fabric or pretreatment [89, 92-94, 102].

The uniform application of the coloration liquor, even and gentle drying and curing along

with appropriate speed and temperature are key to successful pigment coloration. In addition, all

devices must be in proper working order [89, 92-94, 102, 372].

The coloration liquor should be properly formulated. The binder to pigment ratio and the

amount of auxiliaries should be optimally set. One of the important aspects that affect running and

fastness properties is product compatibility [89, 91-94, 102].

In order to produce a pigmented fabric that meets customer requirements proper process

control for fabric pretreatment, padding, drying and fixation process and dye bath formulation is

required. This also helps in the early identification and correction of problems [102].

Pigments are supplied as paste-like preparations in the form of fine dispersions by means

of surfactants. The particles are variably shaped and partially dependent on their chemical

constitution. The surfactants stabilize the particle form and size during the grinding process.

Pigment agglomeration in coloration liquor is also prevented by surfactants. The requirements

include the highest possible pigment amount, good flow properties and protection against crust

formation. High pigment concentrations result in minimum transport and warehouse cost while the

327

flow properties ensure ease during the dosing process. The last factor ensures the homogeneity and

therefore prevents speck formation [89].

The pigments are anchored to the substrate with the help of a binder. The binders are

synthetic polymers with a low degree of polymerization in their unfixed form. At higher

temperatures and in the presence of acidic conditions that are generated with the help of a catalyst,

the polymerization of binder chains takes place, making the binder linked to the substrate

simultaneously attaching the pigments [99]. The fastness properties are therefore mainly

dependent on the properties of the binder used [92]. They influence the hand and almost all fastness

properties of the pigmented fabric such as fastness to washing, wet scrubbing, rubbing (dry and

wet), abrasion, etc. The type and amount of binder and other auxiliaries used to affect the

achievable results. This aspect needs to be considered in the selection of binders and auxiliaries

[91, 94]. Commercially available binders are a mixture of co-polymers, softeners, thickeners, and

emulsifiers. The binders are formulated in such a way that they give optimum running, good

fastness properties and soft hand to the pigmented fabric [94]. The fastness properties of pigmented

fabrics are dependent on the adhesion of the binder to the substrate. The adhesion of the binder to

the fiber can be viewed from three aspects [100]:

▪ Physical bonding forces: which depend on the binder type and the quantity of the cross-

linker. The concentration of cross-linker has no influence on the fastness level of the

given binder type.

▪ Chemical bonding forces: they are only present if both the binder and the fiber possess

reactive functional groups. In the case of cellulosic fibers, the binder may react with

the hydroxyl groups on fiber thereby creating chemical bonding between the binder

and the fiber.

▪ Mechanical adhesion of the binder due to surface characteristics. Cotton fiber has high

mechanical adhesion with the binder due to the rough surface of the fiber.

The colorant and auxiliaries used in pigment coloration must be compatible with each

other. It is necessary to check for the compatibility before and during the coloration process.

Incompatible products lead to problems in the process. There are many factors that may affect the

compatibility of the products in the mixture; these include ionic characteristics, solubility,

emulsion stability, pH conditions, and temperature. Binder, pigments, softeners and the

328

formulation contain emulsifiers for product stabilization. The emulsion should be stable when

products are mixed during the coloration process and must be stable under the action of forces

involved during solution preparation and coloration process. Products should be selected in such

a way that their ionic characteristics are similar. When there is a change in the amount of the

products or old products is replaced with a new product due to non-availability, cost or ecological

reasons, compatibility should be checked in the laboratory before the changes are made in the bulk

process [373].

One of the common problems found in coloration with pigments is the agglomeration of

the binder on the pad rollers. These agglomerates can easily transfer during the application process

from the roller and deposit on the fabric in the form of dark areas. There are many factors that can

affect this problem such as shear forces due to pressure, hardness, width and diameter of the rollers,

roller speed, swelling and absorption properties of the substrate, dispersing agents, wetting agents

and chemical composition of the binder. Suitable products with good emulsifying properties such

as a mixture of alkoxylates may be used to avoid this problem [92, 97, 374].

During the coloration process, there are certain requirements that have to be met in order

to produce a successful product. These requirements are function-related based on end-use e.g.

fastness properties, and hand or application related e.g. foam inhibition, drying, and curing. The

colorant and auxiliaries used have the largest impact on both functional and application

requirements. Table 4.42 shows the components of the pigment coloration system and their

influence on different outcomes of the process. The properties of the individual component are

related to the particular effect for which they are responsible.

Table 4.42: Pigment dyeing components and their corresponding effect on dyed fabric.

Component Properties Effect

Pigment ▪ Particle size Agglomeration (dye spots), rubbing,

dry-cleaning fastness, color yield

▪ Particle shape Rubbing, wash fastness

▪ Heat resistance Shade variation, shade change

▪ Solubility Dry-cleaning

▪ Quantity Fastness, buildup

329


Component Properties Effect

Binder ▪ Tg of the comonomers Softness

▪ Chemical resistance of

comonomer

Fastness properties

▪ Heat and light resistance of

comonomer

Lightfastness, shade change

▪ Adhesion and cohesion Rubbing, wash fastness

▪ Crosslinker Wash, rubbing fastness

▪ Amount of crosslinker Fastness, softness

▪ Quantity Fastness, softness, buildup

▪ Film formation Appearance, softness, color yield

Migration inhibitor ▪ Type and quantity Migration, appearance, shade

variation

Emulsifier ▪ Type and quantity Stable dispersion, prevent dye

spots and roller deposits

Softener ▪ Type and quantity Dry rubbing fastness, fabric

handle

Defoamer ▪ Type and quantity Prevention of dye spots

Padding ▪ Pressure Liquor pickup, migration

▪ Uniform application Side-to-side variation

▪ Liquor circulation Shade change

▪ Liquor feed Shade change

Drying ▪ Temperature and uniform

airflow

Migration, appearance

Fixation ▪ Time and temperature,

uniformity in airflow

Fastness properties, color yield,

handle, shade change

330

4.9.1 Fastness of pigment colored fabrics

The following factors affect the fastness properties of pigmented fabrics [372]:

▪ Binder quality;

▪ Amount of binder;

▪ Pigment quality;

▪ Fabric quality;

▪ Fixation method; and

▪ Fixation conditions.

4.9.1.1 Binder quality

Binder quality refers to the components making up the binder which include comonomers,

crosslinkers, plasticizers, and emulsifiers. This is an important factor which is mainly responsible

for achieving the required fastness. The hand of the pigmented fabric is largely dependent on the

binder used. Important factors affecting the hand are the comonomers, crosslinkers and the level

of crosslinking. Other factors affecting the hand feel is the type and amount of softener used. The

binder also influences the wash fastness. Resistance against wash fastness depends on the swelling

behavior of the binder film which is controlled by the amount and level of crosslinkers used in the

binder formulation. Rubbing fastness is partially influenced by the binder. The crosslinker present

in the binder is responsible for the wet rubbing fastness, and the softener is added in the formulation

to improve the dry rubbing fastness. The fastness to light and dry cleaning is least dependent on

the binder used and is largely based on the resistance of the comonomer against aging and solvent

respectively.

4.9.1.2 Amount of binder

To achieve the best fixation of pigments on the substrate, the optimum quantity of binder is

required in relation to the amount of pigment being used. A low amount of binder will result in

inferior fastness properties while a higher than the optimum amount will affect the hand of the

fabric and increase the cost of the coloration process [94]. The thickness of the pigment layer is

approximately 0.5 µm, depending on the particle size of pigments. The amount of binder should

be adequate to cover this layer of pigments. For a binder with a 40% solid content, for excellent

fastness properties, the binder to pigment ratio should be around 4:1. The minimum binder level

331

should be around 6%. The relationship between binder to pigment ratio and fastness properties are

shown in Figure 4.9 [375].

The binder to pigment ratio depends on the following [94]:

▪ Quality of the fabric;

▪ Binder efficiency;

▪ Pigment quality;

▪ Required fastness properties; and

▪ Hand of the fabric.

Figure 4.9: Binder to pigment ratio and fastness properties.

4.9.1.3 Pigment quality

Pigments are supplied in the form of a dispersion in water. They are insoluble in water, therefore

wash fastness is primarily dependent on the binder used. Rubbing fastness also depends on the

binder used but is also influenced by the particle form, size, and hardness of the pigment.

Lightfastness, on the other hand, is primarily dependent on the pigment used. Since pigments are

0

50

100

150

200

250

300

0 10 20 40 50 6030

High fastness Level

Good fastness Level

Low fastness Level

3:1

2.5 :1

0:1 2:1 3:1 4:1Fabric

Pigment 0.3-0.5 µBinder

Binder : Pigment Ratio

4:1

g/k

g o

f 40

% A

ctiv

e B

inder

Pigment Concentration (g/kg)

Binder : Pigment Ratio

0.5 µ

332

in the form of molecular aggregates, they have superior fastness compared to individual molecules.

The solubility of pigments in a solvent determines their fastness to dry-cleaning [89].

4.9.1.4 Fabric quality

This includes residual impurities such as sizing agent present, fabric pH, residual moisture, surface

appearance, and yarn type. Pretreatment should be uniform, and fabric should be free from defects.

Fiber type and blend ratio affect the fastness properties. Cotton fiber has a rough surface which

results in more adhesion of the binder as compared to polyester which has a smooth surface [100].

Therefore, rubbing fastness of the pigmented layer is superior to cotton rich blends as compared

to polyester rich blends.

4.9.1.5 Fixation method

Pigmented fabrics are generally fixed by the curing process. The curing process can be done on a

hot flue or a stenter. The curing time and temperature should be properly monitored to ensure

proper and even fixation. Hot air is the preferred method of fixation. High-temperature steamers

do not usually give the desired fixation levels and therefore result in inferior fastness properties.

4.9.1.6 Fixation conditions

Binder polymer chains are linked together through cross-links during the fixation process which

is carried out at elevated temperatures. Cross-linking helps in attaching the trapped pigments to

the substrate. Acidic conditions during curing are essential for the effective fixation of a binder.

The pH of the system should be alkaline before the curing process to avoid premature fixation of

binders. As the curing process commences the pH is gradually changed from alkaline to acidic

conditions resulting in the fixation of binder [94]. Figure 4.10 shows the factors responsible for

the fixation during pigment coloration of the fabric which affects the fastness properties of the

pigmented fabric. These include temperature, time and pH. Insufficient fixation time for a

particular temperature would result in poor fastness properties attained. The time and temperature

required for the fixation are inversely related. However, adjustments are also limited by the

machine, fiber and pigment’s thermal properties. The temperature cannot be increased over a

certain limit due to the chance of fiber damage or due to yellowing or sublimation of pigments.

Similarly, the time that can be given for curing is limited by production requirements and the

333

machine configuration [372]. The pH is also an important factor affecting the fixation process.

Generally, the fixation is performed at 150 oC for 4-5 min. The pH should be < 5 [101, 375].

Figure 4.10: Pigment coloration fixation conditions.

A summary of the faults that can occur during the pigment coloration process and the

possible solutions are given in Table 4.43.

To achieve successful pigment coloration, the following preventive measures must be

taken [94, 96]:

▪ The binder drums should be stored in a cool place to avoid the formation of a skin. The

binder must be filtered through a fine fabric before preparing the padding liquor. The

binder left off on the fabric should not be pressed or squeezed. This might cause some

polymer particles to escape and form a nucleus for further agglomeration in the liquor.

▪ Padding mangle should not be exposed to hot conditions. The location should not be

very close to other machines.

▪ The substrate should be uniformly dried and should not be hot before the padding

process.

▪ The fabric should have uniform absorbency and be free from the residual size and other

impurities.

▪ Filtering of padding liquor should be done before feeding it into the dyeing trough.

▪ When two or more pigments are used according to shade requirements, it may be

possible that one pigment may settle at a faster rate, hence the padding liquor should

be properly stirred before starting the process and there should be a proper liquor

circulation system.

▪ Padders should have the same uniform hardness and diameter.

Temperature

Fixation binder

Fixation pigment

Time pH

334

▪ The liquor pickup should be around ~ 60% (pick up depends on the fiber type

processed.). Lower pick up values are preferred as the tendency of pigment migration

is reduced.

▪ If there is a film formation on rollers, it should be cleaned immediately.

▪ Loosely, woven and open structures have a low tendency for migration as compared to

tightly woven and compact structures.

▪ Fabrics containing synthetic fiber should be heat-set before coloration. High

temperatures during fixation may cause yellowing.

▪ Fluorescent whitening agents are not recommended for use on substrates that are to be

to be pigmented, as FWAs tend to turn yellow during the curing process which will

impact the final shade of the goods.

▪ Shade matching should be done after the curing process, as there may be a tone change

for some pale shades during the curing process.

▪ All the guide rollers should be moving, as stationary rollers may cause accumulation

of the liquor on them and would drip resulting in dark patches or spots on the fabric.

Table 4.43: Problems in pigment coloration and possible solutions.


Dark stains or

spots or areas

▪ Pigment preparations not

properly diluted

Dilute the pigments with a small

amount of cold water while stirring.

[92,

93,

100] ▪ Pigments not strained

properly

The diluted solution should be added

to the preparation tank through a filter

cloth or a fine sieve. A finer filter

must be employed if speckiness still

occurs.

▪ Crust formation in pigment

during storage

1. Select good quality pigments.

2. Ensure proper storage conditions.

3. Inverse the hold can often.

▪ Mix incompatibility 1. Colorants and auxiliaries should be

compatible with each other.

335



▪ Excessive foaming of the

padding liquor, pigments

may accumulate in the

foam and on drying cause

stains on the goods

Use defoamers to inhibit foam

formation.

▪ Poor pigment dispersion 1. Select good quality pigments.

2. Increase the amount of emulsifier.

▪ Pigments with very small

particle size may result in

agglomeration

Coating of the primary particles with

dispersing agents during

manufacturing.

▪ Transfer of film, formed on

the pad rollers, to the cloth

during the padding

Increase the amount of emulsifier to

prevent roller deposits.

Pale spots ▪ Moist parts in the fabric

before padding may cause

less liquor pick-up

Ensure that the fabric is uniformly

dried.

[92]

▪ Contact of condensate

water drops with unfixed

colorants

Avoid the formation of condensate in

all parts of the machine through

which the fabric passes before the

fixation

▪ Deposits of hardened resin

that resist pigment

penetration

Ensure the compatibility of chemicals

used in one step coloration and

finishing.

[149]

Unlevelness Instability of liquor due to: [92,

93,

96,

▪ Incompatibility of products Ensure the products used are


336



▪ High amounts of polyether-

based softening agents

used (more than 15 g/L)

Use the recommended concentration

of softening agents. Follow the

manufacturer’s recommendation.

100,

376]

▪ High temperature of bath

liquor caused by the heated

substrate entering the bath

may result in some

auxiliaries such as

ethoxylate based

antimigrating agents to

precipitate

1. The temperature of the bath liquor

must not increase over 40 oC.

2. Allow the liquor or the substrate to

cool, before processing.

3. Use cold water to prepare the

liquor.

4. Do not immediately use the fabric

for coloring after the stentering or

drying processes.

▪ Presence of Ca and Mg

ions in fabric affects

pigment dispersion

Fabric should be free from impurities

after pretreatment.

▪ Poor pigment penetration 1. Ensure uniform and proper

pretreatment of fabric.

2. Use a wetting agent to increase

pigment penetration.

3. Give airing time between padding

and drying.

▪ Pigment migration during

drying

1. Reduce the uptake of liquor by

increasing the padder pressure.

2. Provide adequate swelling time for

fabric.

3. Reduce the fan speed and keep the

maximum temperature to 120 oC.

337



4. Select appropriate anti-migrating

agents or increase the amount of

anti-migrating agent.

▪ Improper drying Airflow and temperature should be

uniform along the length and width of

the dryer.

▪ Cracking of the binder film Add a softener.

▪ Fabric imperfections like

knots, slubs, lint, etc

Ensure the fabric is properly

inspected and free from defects

before pretreatment.

Pin marks ▪ Due to colorant migration,

stenter pins may cause

marks along the selvages

1. Increase the amount of anti-

migrating agent.

2. Use low temperature for drying.

[92]

Coating of

rollers

▪ Due to agglomeration of

binder on the padder

because of shear forces

1. Increase the amount of emulsifier.

2. Select the appropriate emulsifier.

3. Coating of rollers is generally less

for hard rollers as compared to soft

rollers.

[92]

Streaks or

stripes

▪ Pale stripes along the

length of fabric may be due

to the rubbing of the

unfixed substrate against

the guide roller or a

machine part

Ensure all the machine parts which

come in contact with the fabric before

fixation are Teflon coated and

moving.

[92]

▪ Uneven drying may result

in dark longitudinal stripes

due to improper

Ensure the dryer air jets are properly

cleaned and the airflow is uniform.

338



functioning of the jets of

the dryer

▪ Fabric fault Ensure the fabric is properly

inspected and free from defects

before pretreatment.

Shade change ▪ Improper color selection.

Due to melting,

sublimation or destruction

of pigment under

application temperature

Use shade card to select appropriate

pigment type according to

requirements.

[92,

93,

96,

100]

▪ Polyester containing

fabrics are sometimes

darker in shade due to the

dissolution of pigments

like disperse dyes in the

polyester fiber during the

curing process

This fault is observed after the curing

process. Shade matching should be

done after the curing process.

▪ Pigment migration 1. Reduced the uptake of the liquor by

increasing the padder pressure.

2. Provide adequate swelling time for

fabric.

3. Reduce fan speed and keep the

maximum temperature to 120 oC in

the first two chambers of the

stenter.

4. Select appropriate anti-migrating

agents or increase their amount.

339



▪ Pale shade due to anti-

migrating agent. The

migration of pigment is

prevented so that the fabric

surface is lighter in shade

as compared to when

migration takes place and

pigment accumulates on

the surface.

Use the optimum amount of anti-

migrating agent.

▪ Sensitivity of some

pigments (reds and blues)

to reduction results in the

paler or changed shade

Avoid using chemicals having

reductive nature.

▪ pH variation or too high

pH

▪ Alkaline pH on fabric can

neutralize the padding

liquor so anti-migrating

agents can be blocked and

binder fixation slows

down.

The pH of the fabric should be neutral

or slightly acidic.

▪ Settlement of pigment due

to the improper stirring of

the liquor

Continuous agitation of the bath by a

circulation system.

▪ Improper bath preparation

procedure

Follow the mixing procedure as per

the manufacturer’s recommendation.

▪ Poor pretreatment of fabric. Ensure adequate and uniform

pretreatment of fabric.

340



▪ Comonomers making up

the binder. The resistance

of comonomer against heat.

Select a binder with good aging

resistance.

▪ Higher curing temperature

or time. Yellowing of fiber

may take place at high

temperatures or long curing

times.

Select the treatment time and

temperature according to the most

sensitive fiber in the blend.

Inadequate

fastness

1. Rubbing

fastness

▪ Poor fastness properties of

binder

Select a binder with good fastness

properties.

[90,

93,

100,

376]

▪ Insufficient curing or

improper curing conditions

Ensure proper curing time,

temperature and pH according to

manufacturer recommendations are

employed.

▪ Particle shape of the

pigmen

Pigments must be properly ground

during manufacturing. Sharped edge

crystals can easily scratch the binder

film under rubbing loads as compared

to round off shapes.

▪ Particle size of the

pigment. Difficulty for the

binder to cover large

pigment particles

Select good quality pigments. The

particle size should be between 0.1

and 0.5 µm.

▪ Fabric structure and

surface

Very smooth fiber surface e.g.

polyester has low adhesion to a

341



binder, compared to cotton which has

a rough surface.

There is a limit of maximum fastness

level achievable for a particular fiber.

Uneven fabric surface will deteriorate

the fastness. Use fabric which is free

from defects and protruding fibers.

(a) Dry

rubbing

fastness

▪ Due to the brittleness of the

binder film

Use a softener to reduce the

brittleness.

▪ Insufficient amount of

binder

Increase the amount of binder.

(b) Wet

rubbing

fastness

▪ Improper selection of

binder. Crosslinking agents

are incorporated in the

binder to enhance the

crosslinking of binder film.

Select binder that can meet the

fastness requirement.

2. Wash

fastness

▪ Binder selection. Select a binder that can meet the

fastness requirements.

[93]

▪ Inadequate curing The fabric should be properly cured

as per the recommended curing

conditions.

▪ Shade too heavy Do not use pigment for dark/deep

shades.

▪ Poor pretreatment.

Impurities present in the

fabric hinder the proper

fixation of the binder.

Ensure pretreatment is uniform and

even.

342



▪ Particle size of the

pigment. Difficulty for a

binder to cover large

pigment particles

Select good quality pigment. The


and 0.5 µm.

3. Dry-

cleaning

fastness

▪ Pigment, due to their

solubility in the dry

cleaning solvents

Select recommended pigments. [93,

102]

▪ Binder selection. Due to

increased swelling of the

binder film under the

action of solvents

Select a binder with good fastness

against dry-cleaning solvents.

▪ Pigments with very small

particle size diffuse

through binder film

Select good quality pigments. The


and 0.5 µm.

▪ Improper curing conditions Follow the recommended curing

conditions.

4.

Lightfastness

▪ Pigment selection

(selection of primaries for

making mixes)

Select recommended pigments. [93,

100,

102]

▪ Binder. Select binders with good fastness to

light.

▪ Calibration of lightfastness

tester.

Ensure the light fastness tester is in

proper working order.

Listing/ side-

to-side shade

variation/

▪ Uneven padder pressure

along the width.

Check the padder pressure along the

width.

[93]

▪ Temperature variation. 1. Check the temperature of the fabric

along the width.

343



width wise

shade variation

2. Ensure the filters and nozzles in

dryer and hotflue are cleaned and

airflow is uniform.

▪ Uneven fabric preparation. Ensure the uniform pretreatment of

the fabric.

▪ Formulation liquor feed is

not uniform.

The liquor should be fed uniformly

along the width of the dye trough.

▪ Thread-up. The machine should be properly

thread-up before the process.

Poor color

yield or build-

up

▪ Low quantity of the binder. Use binder amounts corresponding to

the amount of pigment.

[93,

100]

▪ Particle size of pigment

influences the yield and

brilliance. Large particles

have lower total surface

areas as compared to small

particles of the same mass.

Select good quality pigments. Particle

size should be between 0.1 and 0.5

µm.

▪ Excessive binder/pigment.

Higher concentrations of

pigments give poor build-

up due to the overlapping

of pigments on the

individual fiber.

Use pigments for medium to light

shades.

▪ Dry cans (no predryer). Use correct settings for a dry cans.

The temperature should be gradually

increased.

▪ Excessive pick-up Increase the pad pressure setting.

344



▪ Incompatible mix Ensure all the auxiliaries are


Tailing/

ending/

lengthwise

shade variation

▪ Inadequate agitation in the

mix tank

Ensure the bath is properly agitated

by a circulation system.

[93]

▪ Change in bath stability

over time either due to a

change in pH or

temperature

Monitor the bath pH and temperature

over time. This fault is also related to

fabric pretreatment.

▪ Variation in fabric

pretreatment

Ensure pretreatment is uniform and

fabric is cool when entering the bath.

▪ Mixing procedures Make sure a proper mixing procedure

is in place.

Poor hand ▪ Poor binder binder

selection. The composition

of the binder determines

the softness attained. The

softness of the binder film

is related to the Tg of the

comonomers and the level

of crosslinking

Select binder with good softness

properties.

[100]

▪ Improper softener selection Select a suitable softener.

▪ Too high curing

temperature. The substrate

depending on the fiber type

may be damaged at high

temperatures.

Select a curing temperature taking

into consideration the fiber type and

blend ratio.

345



▪ Longer curing time Select a curing time in relation to

temperature. Follow manufacturer

recommendations.

▪ Fabric structure and yarn

count

Select a fabric according to hand

requirements. There is a limit to the

level of softness achievable on a

particular fabric type.

4.10 Problems in the dyeing of polyester/cellulosic blends

The polyester/cellulosic are the most common blend. The dyeing of these blends creates a

challenge as each fiber type is dyed with a different class of dyes that requires different process

conditions. These blends can be dyed by both exhaust, semi-continuous and continuous processes

using following colorant systems [9, 18, 56-58]:

▪ The two-dye system using dyes for polyester (disperse dyes) together with dyes for

cellulose (direct, reactive, vat or sulfur); and

▪ Pigment coloration using the pigment-binder system.

The typical dye combinations are disperse/reactive, disperse/direct and disperse/vat or

sulfur. The use of pigments is also becoming common for light shades due to excellent light

fastness, shorter and economical coloration process. Although pigments have excellent light

fastness and the coloration process is shorter and economical this system is restricted to light to

medium shades due to fastness and hand limitations. The important aspects and problems in

pigment coloration are covered in section 4.9.

The choice of dye classes for the dyeing of polyester/cellulosic blends depends on the

following factors [79, 377] :

▪ The attainable fastness standards in relation to different shade depths;

▪ The color space available in a particular dye class; and

346

▪ The total cost of the dyeing process.

The disperse dye is the only class available for the dyeing of polyester components. They

vary in their fastness properties depending on the dye chemistry and energy levels. The later

property determines their thermomigration behavior. This property is required to be higher in

PES/CELL blends as compared to 100% polyester materials. This restricts the choice of dyes to

medium and higher energy levels. Another problem associated with their application is the staining

of the cellulose component which affects the fastness properties. The stain needs to be removed to

achieve good fastness properties. This often requires a separate reduction clearing process,

especially in dark shades. This limits the attainable fastness levels and the choice of the dyeing

methods [79].

For the cellulose portion of the blend, a wide range of dye classes are available that include

vat, reactive, direct and sulfur dyes. The vat dyes have limited color space but can provide excellent

fastness properties. The dyes are usually expensive and limited to a special application that requires

excellent fastness properties. The reactive dyes can be applied by various methods and have a wide

range of color gamut available. The direct dyes and sulfur dyes are limited to applications that

require lower fastness levels. They are cheaper than reactive and vat dyes. The use of sulfur dyes

is usually restricted to dark shades.

The dye classes can be applied by various methods which include one-bath and two-bath

methods. In one-bath methods both dye classes used to dye each of the two fiber are applied to the

substrate at the same time but are fixed in two stages because of their differences in the

requirements for fixation. The fastness achieved is usually inferior as compared to the one-bath

process. In the two-bath process, each fiber is dyed separately. This also provides the possibility

of reduction clearing to remove the disperse dye stain. The machine occupation time varies

significantly from one dye method, it is important to select the process that provides the required

fastness levels with good reproducibility and shortest possible time [377].

The occurrence of faults in a dyehouse is inevitable due to a large number of variables

affecting the dyeing process. These vary from growth or manufacturing conditions of fiber to the

dyeing process [67, 108]. In comparison to dyeing single fiber, the dyeing of blends creates a

challenge because of the following [79]:

▪ Cross-staining of the fiber by the dye intended for the other fiber type;

347

▪ Interferences between dye classes or between a dye and dyebath auxiliaries;

▪ Effect of additional processing required to fix both dyes for cellulose and the dye for

polyester; and

▪ Effect of second fiber component in the blend on increasing the liquor ratio

significantly.

These effects vary based on the different dye classes uses. The disperse dye is more affected

by the chemical and physical interaction in the dye bath and before it is diffused. The disperse

once absorbed and diffused into the fiber is not affected much by the chemical and physical effects.

For the cellulosic component, the reactive and disperse dyes can be destroyed by reduction clearing

whether they have been absorbed by the cellulose. Some disperse dyes, on the other hand, are only

affected in the dyebath but are protected once present in the polyester fiber [79].

4.10.1 Disperse/reactive system

This is the most common dye system used for the dyeing of polyester/cellulosic materials. The

selection of disperse dyes and reactive dyes is critical depending upon the methods used for dyeing.

Following points need to be considered for proper dye selection [56]:

▪ Staining

The disperse dyes tend to stain the cellulosic fibers in the blend. This takes place during

dyeing, washing or fastness tests [56, 88]. This may cause poor wash fastness and dull

shade, especially in one bath process. It is important to select dyes that give low staining

and can easily wash off either in alkaline or higher temperature conditions and do not

require a reduction clearing step. The staining tendency adjacent fibers, especially

nylon, in wet fastness tests is critical for disperse dyes [9].

▪ Thermomigration

Thermomigration involves the movement of dye during post heat treatment operations

(finishing). Disperse dyes should have a minimum tendency to thermomigration at a

temperature above 140 oC. High energy dyes are suitable in such cases where high

temperatures are involved in a finishing stage (e.g. resin finishing).

348

▪ Reduction sensitivity

This causes a reduction in dye yield and poor reproducibility. Certain shades such as

bluish-red, blue and navy are more sensitive to reduction. In fully flooded machines

with an absence of air, the risk is even higher. The reductive chemicals come from

fibers such as wool, viscose, cotton. The dispersants based on sulfonated lignin also

have a reductive effect [88].

▪ Material suitability

The dyes that are suitable for single fiber type may not give satisfactory results in a

blend. It has been seen the some disperse dyes that show good fastness results on 100%

polyester would not give similar results in the polyester cellulosic blends. It is

important to consider this factor in dye selection [88].

▪ Stability under alkaline conditions

Generally, disperse dyes give optimum fixation under acidic conditions (pH < 5). The

disperse dyes may decompose under alkaline conditions and lose color yield. There are

some disperse dyes available that are stable up to pH of 8-9. This is important in the

case of one bath dyeing process.

Table 4.44 shows the most common problems that are faced in the dyeing of

polyester/cotton blends using disperse and reactive dyes along with their possible reasons and

corrections.

Table 4.44: Problems and their possible solutions in the dyeing of polyester/cellulose blends

using a disperse/reactive system.


Reproducibility ▪ Sensitivity of dye to

hydrolysis, reduction, and

electrolyte

1. Careful selection of dyes

according to the dyeing method.

2. Proper control of dyebath pH.

3. Use dyes that are stable under

high electrolyte concentration.

[253,

301]

349



▪ Sensitivity of dye to metal

ions

Use a sequestering agent.

▪ Incompatibility of same

class dyes of the different

chemical constitutions

Select dyes having good

compatibility with each other.

▪ Improper dye buildup due to

dyebath chemicals such as a

retarding agent

Carry out lab trials to determine the

dye buildup with special chemicals

used in the dyebath.

▪ Too short dyeing time Ensure the dyeing time is sufficient

such that dye in the fiber is

uniformly distributed.

[57]

▪ Poor dye selection in

combination shade

Select dyes with a similar dyeing rate

(strike rates).

[75]

▪ Staining of cellulose portion

with disperse dyes

1. Select disperse dyes with lower

staining tendency on cellulose.


[111]

▪ Hydrolysis of dye 1. Maintain the temperature of the

bath as cold as possible.

2. Use a dosing pump.

3. Use dyes with prolonged dyebath

stability.

[120]

▪ Inappropriate dye

combination

Select dyes have similar dyeing

behavior.

[253,

301]

▪ Variations in dye strengths 1. Check dye strength for each lot.

2. Establish correlation between

laboratory report and experience in

bulk.

[253,

301]

350



▪ Differences in the quality of

the chemicals

1. Test the strength of each lot.

2. Establish correlation between

laboratory report and experience in

bulk.

▪ Settling of liquid dyes Stir the dye container before use. [253]

▪ Effect of other blend

components on dye

exhaustion

Select dyes and processes based on

fiber type in the blend.

[253]

▪ Error is the weighing of

dyes and chemicals

1. Check the accuracy of the

weighing instruments.

2. Train the workers about the

importance of accuracy.

[317]

▪ Dye reduction due to

reductive chemicals in the

dyebath

Add mild oxidizing agent for dyes

sensitive to reduction.

[251]

Unlevelness ▪ Rapid addition of dyes and

chemicals (mainly alkali)

1. Follow the linear dosing of dyes

and chemicals.

2. Check the dyes and chemicals are

dissolved properly before addition.

3. Use a dosing system.

[297,

301]

▪ Rapid shift in pH Gradually change the dyebath pH. [345]

▪ Use of incorrect pH leading

to instability of disperse

dyeing system

Set the pH of the dyeing bath

according to disperse dye class. Not

all dyes gave optimum results in the

same pH range.

[67]

▪ Non-compatible dye

combination in combination

shade

1. Check the compatibility of dyes

used for combination shade.

[231,

348]

351



2. Use dyes form the same supplier

for combination shade.

▪ Poor dispersion stability of

the dye

Use dispersing agents for beam and

package dyeing.

[75]

▪ Dyeing leveling in light

shades and microfibers

Use a leveling agent for light shades

and finer fibers.

[75]

▪ Addition of dyes in the

dyebath at a very high

temperature

Avoid the addition of the dyes at a

very high temperature.

[347]

▪ Insufficient dyeing time to

allow migration of dye onto

the substrate

Ensure optimum dyeing time as per

dye manufacturer recommendations.

[347]

▪ Too much foam in the

dyebath

Use an antifoaming agent. [67,

253]

▪ Dye precipitation during the

dyeing process

Ensure proper dyeing conditions

(time, temperature, chemicals) as per

dye class.

[85,

149,

150,

253,

345]

▪ Inadequate mixing and

dissolution of dye with an

insufficient amount of water

or at incorrect temperature

or operator negligence

1. Use an adequate amount of water

to dissolve the dye.

2. Use filters to avoid undissolved

particles to enter the dyeing

chamber.

3. Use recommend temperature for

mixing the dyes.

[297,

301,

317]

352



4. Ensure the standard operating

procedure for mixing and

dissolving of the dye is followed.

▪ Non-compatibility of

different chemicals and

auxiliaries used

Auxiliaries should be compatible

with each other and different dyes

present in the system.

[86,

253]

▪ Unstable chemicals and

auxiliaries

Select chemicals and auxiliaries that

are stable under dyeing conditions.

[253]

▪ Migration of dye during pre-

drying due to substantivity

differences. The migration

of water soluble dyes is

inversely proportional to

substantivity

Use anti-migrating agents and

electrolyte in pad liquor.

[128]

▪ Using dyes of very high

reactivity leading to partial

fixation of dye during pre-

drying and competes with

migration

Check the reactivity of dyes

according to the application method

and dyeing conditions.

[128]


reactive dyes without

considering the exhaustion,

migration, and reactivity of

dyestuffs

1. Select dyes based on the dyeing

method. Not all dyes are suitable

for all dyeing process.

2. Modify the dye exhaustion curve.

[231,

345]


disperse dyes with poor

diffusion and migration

behavior

1. Select dyes with good diffusion

and muigration properties.

2. Modify the dye exhaustion curve.

[68,

231]

353



▪ Residual alkali in the fabric Add acetic acid in pad liquor to

maintain pH 5-6.

[253]

▪ Improper absorption of dyes

by very light or heavy gsm

fabrics

Use dyes with good leveling

properties.

[301]

▪ Lower diffusion or

migration of dye due to dye

aggregation caused by Ca

and Mg ions present in the

salt

Use a sequestering agent with good [301]

▪ Presence of dye residues

due to inadequate removal

of hydrolyzed dye

Treat the fabric with a good soaping

agent to remove dye residues.

[301]

▪ Using large quantities of salt

leading to dye aggregation

Use the salt quantity based on the

dye manufacturer’s recommendation.

[345]

▪ Using too high rate of

dyeing followed by poor

migration

Use a lower heating rate to avoid the

rapid exhaustion of dye into the fiber

surface.

[346]

▪ Using of very low liquor

ratio

Use optimum liquor low. Ensure

sufficient liquor is available for

proper movement of fabric inside the

machine.

▪ Use of salt of varying

quality and high levels of

impurities

1. Use Glauber’s salt, if possible.

2. Check the salt quality regularly.

[297]

▪ Using an excessive amount

of anti-migrating agent

Use the optimum amount of anti-

migrating agent.

[348]

354



causing a reversal of the

migration

▪ Break down of dye

dispersion due to excessive

amount of electrolyte (salt)

1. Check the disperse dye stability.

2. Avoid using an excess amount of

salt.

[7]

Dark stains or

spots

▪ Dye precipitation during the

dyeing process

Ensure proper dyeing conditions

(time, temperature, chemicals) as per

dye class.

[149,

150,

253,

317]

▪ Inadequate mixing and

dissolution of dye with an

insufficient amount of water

or at incorrect temperature

or operator negligence

1. Use an adequate amount of water

to dissolve the dye.

2. Use filters to avoid undissolved


chamber.

3. Use recommend temperature for

mixing the dyes.

4. Ensure the standard operating

procedure for mixing and

dissolving of the dye is followed.

[297,

301,

317]

▪ Improper storage of the dye

leading to the formation of a

dried film on top

Use filters to avoid undissolved


chamber.

Store the dye in a proper place and

mix it properly before use.

[348]

▪ Using too high temperature

during dye preparation

leading to breakage of the

dispersion

1. Avoid using hot water (> 50 oC) in

preparing disperse dye mixture.

2. Mixture should run slowly at all

times.

[348]

355



▪ Addition of dyes in the

dyebath at a very high

temperature

Add dyes at a lower temperature as

per the manufacturer’s

recommendations.

[347]

▪ Insufficient dyeing time to

allow migration of dye onto

the substrate

Provide enough dying time

depending the depth of shade and

dye class as per manufacturer’s

recommendations.

[347]

▪ Poor dispersion system

leading to filtration effect

during beam and package

dyeing

1. Follow manufacturer instructions

for dispersing dye in the bath. Use

a good dispersing agent that is

stable under application

conditions.


for combination shade to assure

that the dispersion system is the

same.

[253,

348]

▪ Dyes with poor dispersion

stability

1. Select dyes with good dispersion

stability.


for combination shade to assure

that dispersion system is the same.

[253,

348]



amount of dispersing agent

Use the optimum quantity of the

dispersing agent.

[67]




1. Check disperse dye stability

against an excessive amount of

electrolyte.

2. Add salt after disperse dyeing.

[7, 68]

356



3. Use the two-bath process.

▪ Crystallization of dye due to

temperature variation in the

dyebath

Ensure proper liquor circulation. [253]

▪ Incompatibility of dyes used

in combination shades

Select dyes based on their dyeing

behavior in combination shade.

Follow manufacturer

recommendation for combination

shade.

[323]

▪ Incompatibility between

different classes of dyes

Check the dyes for computability

before using in the one-bath dyeing

process. Follow manufacturer

recommendation.

[128]

▪ Non-compatibility of

different chemicals and

auxiliaries used

Auxiliaries and chemicals should be

compatible with each other and

different dyes present in the system.

[85,

86,

253]

▪ Fluctuation in dye bath pH 1. Ensure the bath pH is kept uniform

during the whole dyeing process.

2. Check the incoming water for

bicarbonate.

[128]

▪ Unstable chemicals and

auxiliaries

Select chemicals and auxiliaries that

are stable under dyeing conditions.

[253]

▪ Using a too high

concentration of dyes

Check the solubility limit of the dyes

before preparing the dye liquor.

[323]

▪ Foaming caused by

dispersants in the dye

Use a silicone free defoamer.

357



▪ Foaming caused by excess

quantities of anti-migrating

agent

Use optimum quantities of anti-

migrating agent depending upon the

depth of shade.

[128]

▪ Foaming caused by excess

quantities of wetting agent

Use optimum quantities of wetting

agent.

[317]

▪ Use of silicone based

defoamers that breaks under

high turbulence and

temperature

Use a silicone free defoamer. [253,

351]

▪ Presence of oligomers in the

dyebath

1. Drop dye bath at a higher

temperature (> 120 oC).

2. Avoid longer dyeing times.

3. Use special auxiliaries.

[253]

▪ Contamination of substrate

by dyestuff dust

1. Avoid storing material near the

dye storage area.

2. Use low dusting/granular dyes.

[253]

▪ Contamination of substrate

by rust, oil, dust, etc

Ensure proper housekeeping.

Ensure clean machines and clean

working methods.

[253]

▪ Drying out of liquid dyes

due to inappropriate storage

Avoid drying out of dyes. [253]


maintain pH 5-6.

[253]

▪ Foaming caused by residual

surfactants in the fabric

Use defoamer. [253]

▪ Improper addition of the

caustic

Do not add caustic directly into the

dyeing chamber. Dilute before

addition.

[301]

358



▪ Incorrect addition of the

dyes

Carefully add dye into the dyeing

chamber. Avoid direct contact of

dyes with the fabric without dilution.

▪ Very fast dye strike rate due

to dyes of high reactivity

Control the dye strike rate by

optimum process control.

[345]

▪ Use of short liquor ratio The quantity of water should be

enough to feed the pump and

movement of the fabric.

[345]

▪ Inadequate washing of

unfixed/hydrolyzed dyes

Use a good quality soaping agent to

remove the hydrolyzed dye and

prevent redeposition.

[345]

▪ Using large quantities of salt

leading to dye aggregation

Use the salt quantity based on the

dye manufacturer’s recommendation.

[345]

▪ Redeposition of disperse

vapors on the fabric due to

very high fixation

temperature

1. Follow the thermofixation

temperature as per the dye

manufacturer recommendation.

2. Avoid using too high

thermofixation temperature.

[317]

▪ Improper handling of dyes

in the vicinity of fabric or

machinery

The dyes should be handled carefully

and should not be stored near a

fabric storage area or dyeing

machine.

[128]

▪ Condensation of volatile

carriers on the roof that falls

back on the fabric

1. Select suitable carriers (non-steam

volatile carriers).

2. Use overhead heating in the

machine to prevent condensation.

[67,

253]

359



▪ Presence of the carrier stains

that dye deeper than the rest

of the fabric

Ensure proper measures for leveling

and removal of carrier stains.

[85]

▪ Crystallization of carrier on

the fabric on cooling of the

dye bath

1. Test the carrier for its

crystallization behavior. Select

carriers with a lower melting

point.

2. Drop the dye bath at a high

temperature.

[85]

▪ Transfer of film to the fabric

from the guide roller due to

an excessive amount of anti-

migrating agent

1. Use the optimum amount of anti-

migrating agent

2. Clean the guide roller regularly.

[348]

Light stains ▪ White deposits on the fabric

due to oligomer deposits.


temperature.


during dyeing.



possibility.

[67,

149]

Light

spots/areas

▪ Effect of strong vapors from

the surroundings (acids etc.)

1. Use of proper ventilation system.

2. Avoid contact with substances that

may damage the substrate.

[253]

▪ Poor stability of silicone

defoamer

Use a silicone-free dofoamer. [253]

▪ Fiber tips not dyed (e.g.

viscose)

Use a wet fixation method

(steaming)/

[253]

360



▪ Incorrect addition of acid Avoid direct contact of acid with the

substrate. Using a mixing tank.

[320]

▪ Precipitation of anti-

migrating agent

Check the stability of the anti-

migrating agent under pad liquor pH.

▪ Condensation of volatile

carriers on the roof that falls

back on the fabric

1. Select suitable carriers (non-steam

volatile carriers).

2. Use overhead heating in the

machine to prevent condensation.

[67,

253]

Shade change ▪ Incomplete dye diffusion

due to short dyeing time

Use appropriate dyeing conditions

according to material and depth of

shade.

[57,

253]

▪ Inadequate sublimation

fastness

Select dyes with good sublimation

fastness.

[253]

▪ Variation in exhaustion

rates of dyes

Select dyes with similar exhaustion

rates in a combination shade.

[150]

▪ Sensitivity of dyes to metal

ions

Use a sequestering agent. [253]

▪ Presence of alkali residues

in the substrate

Neutralize the substrate properly. [253]

▪ Higher pH during soaping

may hydrolyze the dye-fiber

bond of vinyl sulphone

based reactive dyes

Perform soaping under neutral

conditions.

[61,

301]

▪ Acidic hydrolysis of

reactive dye-cellulose fiber

bonds during acidic pH in

disperse dyeing

1. Adjust the pH of dyebath 6-6.5.

2. Select reactive dyes having stable

dye-fiber bond under acidic

conditions required for disperse

dyeing.

[7]

361



▪ Use of higher quantities of

dye fixative

Use optimum quantities of fixing

agent based on dye type and

concentration.

[301]

▪ Wrong selection of dye

fixative

Carry out laboratory trials before

dyeing in bulk.

[301]

▪ Browning of the cellulose

component at thermosoling

temperature under alkaline

condition

Avoid using too high temperature

during one-bath dyeing.

[79,

85]



temperature caused by

dispersing agent

Use optimum quantities of a

dispersing agent.

[79]

▪ Gas fading of dyes due to

exposure to hot air during

thermofixation.

Select dyes with good stability

against gas fading.

[359]

▪ Destruction of reactive dyes

under higher temperature

Select dyes with good stability under

high temperature conditions.

[79]


with disperse dyes due to

dye properties

1. Select dyes with lower staining

tendency.

2. Select an appropriate blend dyeing

method.

3. Select disperse dyes with good

wash properties in an alkaline

medium.

4. Perform reduction clearing if

possible.

[79,

253]

362



Poor color

yield

▪ Hydrolysis of dye during

dyeing

1. Maintain the temperature of the

bath as cold as possible.

2. Use a dosing pump.

3. Use dyes with prolonged dyebath

stability.

[120]

▪ Higher pH during soaping

may hydrolyze the dye-fiber

bond of vinyl sulphone

based reactive dyes

Perform soaping under neutral

conditions.

[61,

301]

▪ Formation of sodium acetate

with acetic acid in the

presence of highly alkaline

fabrics

1. Ensure the fabric should be neutral

before dyeing.

2. Using a specialized product for pH

adjustment.

3. The pH of the dye bath should be

~5.5.

[348]

▪ Differences in a buildup of

dyes on different materials

Perform preliminary dyeing tests

before bulk dyeing.

[253]

▪ Reduction of dyes due to the

presence of reductive

substances in fabric or water


dyeing.

[301]

▪ Using dyes of low

substantivity

Select dyes with low-medium

substantivity.

[345]

▪ Using a low concentration

of electrolyte

Use the optimum quantity of

electrolyte.

[345]

▪ Low dyebath pH 1. Use the required quantity of

alkali/acid to achieve desired

dyebath pH (based on the reactive

group).

[85,

345]

363



2. Select reactive dyes that require

lower pH for fixation in one bath

process.

▪ Poor stability of reactive

dyes under higher dyeing

temperature required for

disperse dyeing

Select reactive dyes with good

stability under high temperature

conditions.

[79,

81]

▪ Physical or chemical

interaction of disperse and

reactive dyes in the dye bath

Check the compatibility of dyes in

the lab before using it in bulk. Select

dyes with minimum or no

interaction.

[79]

▪ Use of compromised pH

during one bath dyeing

Select dyes with good color yield in

compromised pH

▪ Improper weighing/

dispensing of dyes leading

to loss of dyes

Careful weighing/dispensing of the

dyes.

[345,

348]

▪ Dye reduction due to

reductive chemicals in the

dyebath

Add mild oxidizing agent for dyes

sensitive to reduction.

[251]

▪ Improper dye selection

having different fixation

profiles

Select dye combinations with a

similar fixation profile.

[370]

▪ Poor stability of disperse

dye under alkaline

conditions

1. Select disperse with good stability

under alkaline conditions.

2. Modify the dyeing method. Either

use one bath two stage or two bath

process.

[79,

81,

85]

364



▪ Acidic hydrolysis of

reactive dye-cellulose fiber

bonds during acidic pH in

disperse dyeing

1. Adjust the pH of dyebath 6-6.5.

2. Select reactive dyes having stable

dye-fiber bond under acidic

conditions required for disperse

dyeing.

[7, 85]



thermofixation


against gas fading.

[359]

Streaks/bars ▪ Deposition of dye in the

crease areas of fabric due to

poor dispersion

1. Select good dispersing agent.

2. Select dyes with good migration

properties.

3. The temperature should be raised

at a slower rate.

[67]

▪ Staining of the warp or weft

yarns of different fiber types

due to improper washing

1. Select dyes with minimum

staining tendency.

2. Use a good quality soaping agent

to remove the unfixed dye and


Inadequate

fastness

1. Rubbing

fastness

▪ Redeposition of dye on to

the fabric on bath cooling.

Drop the dyebath under pressure

without cooling.

[79,

85]



dye properties


tendency.


method.

[88,

111,

253]

365





medium.


possible.

▪ Incomplete diffusion of dye Ensure dye is properly diffused by

the selection of optimum dyeing

conditions (time, temperature,

auxiliaries).

[345]

▪ Inadequate removal of

unfixed/ hydrolyzed dye

1. Use good quality soaping agent to



2. Check washing parameters (water

flow, washing temperature and

time).

3. Use an adequate number of wash

cycles/baths.

[68,

301,

345]






electrolyte.


3. Use the two bath process.

[7, 68]

▪ Leveling agent not

completely removed from

the substrate after dyeing. A

small quantity of dye is

retained by the leveling

agent on the fiber surface.

1. Ensure proper washing of fabric

after dyeing.

2. Select a leveling agent with good

wash-off properties.

[111]

366



▪ Presence of oligomers on

the fiber surface


temperature.


during dyeing.



possibility.

[351]

▪ Nonionic softener

containing mineral oils used

in finishing

Use cationic polyethylene or

silicone-based softeners.

[83]


by disperse dyes due to the

presence of urea


method.


wash properties in alkaline

medium.


4. Lower the concentration or replace

urea.

[79]

▪ Lower fixation of disperse


urea


method.


urea.

[79]

2. Wash and

water fastness



dye properties


tendency.


method.

[79,

111,

253]

367





medium.


possible.


the fabric on bath cooling.


without cooling.

[79,

85]

▪ Improper fixation of

dyestuff due to short dyeing

time or low dyeing

temperature or inappropriate

pH.

Check the fixation conditions (pH,

dyeing temperature and time).

[301]

▪ Inadequate washing of

unfixed/hydrolyzed dyes

1. Use good quality soaping agent to



2. Check washing parameters (water

flow, washing temperature and

time).

3. Use an adequate number of wash

cycles/baths.

[301,

345,

370]

▪ Poor washing of surface

disperse dyes due to poor

washing behavior

1. Select disperse dyes with a good

wash off behavior in one bath

process.

2. Performed reduction clearing.

3. Check reduction clearing

conditions.

[85]

368



▪ Poor washing of surface

disperse dye due to

inadequate reduction

clearing

1. Maintain the required

concentration of caustic and hydro.

2. Keep the temperature at 80-90 oC

during the process.

▪ Using reactive dyes of too

high substantivity which are

difficult to wash-off

Select dyes with good wash-off

properties (low substantivity).

[345]


leveling agent after dyeing.

A small quantity of dye is

retained by the leveling

agent on the fiber surface.

1. Ensure proper washing of fabric

after dyeing.

2. Select leveling agent with good

wash-off properties.

[111]

▪ Inherent properties of the

dyes

1. Select dyes with good wash-off

properties.

2. Treat with a fixing agent after

reactive dyeing.

[75,

345]

▪ Low and certain medium

energy dyes exhibit lower

fastness properties

Use high energy disperse dyes. [83]

▪ Thermomigration of

disperse dyes at higher

temperature, > 170 oC (e.g.

resin finishing)

1. Use medium to high energy

disperse dyes.

2. Use the lowest drying/possible

curing time and temperature.

3. Perform reduction clearing of

material after dyeing.

[83,

88,

253]

▪ Nonionic softener

containing mineral oils used

in finishing

Use cationic polyethylene or

silicone-based softeners.

[83]

369



▪ Presence of spinning

lubricants in the substrate

Ensure scouring is done properly and

spinning lubricants should be

completely removed.

[109]

▪ Use of poor quality of salt

that contains Ca and Mg

ions leading to problems in

dye removal

1. Check the salt quality.

2. Use sequestering agent during

dyeing.

[301]

▪ Use of low energy disperse

dyes having poor

sublimation fastness during

thermosol process

Select disperse dye of medium to

high energy level for thermosol

process.

[348]

▪ Improper removal of

unfixed disperse dye due to

poor removal of surfactant.

The surfactant carries

unfixed dye to the final

drying

Select surfactants that are easy to

remove in the rinsing process.

[348]



presence of urea


method.



medium.



urea.

[79]



urea


method.

[79]

370




urea.

3.

Lightfastness

Inadequate removal of unfixed

dye from the fabric

Perform proper soaping of fabric.

Check the washing temperature.

[370]

Presence of carrier residues Perform reduction clearing. [253,

350]

Staining of cellulose portion

with disperse dyes due to dye

properties


tendency.


method.



medium.


possible.

[253]


the fabric on bath cooling


without cooling.

[79,

85]

▪ Catalytic fading due to

inappropriate dye

combination

Carry out laboratory trials before

dyeing in bulk.

[253]

▪ Improper selection of dyes Select dyes based on shade and

dyeing method.

[301]

▪ Use of low energy disperse

dyes having poor

lightfastness fastness during

thermosol process

Select disperse dye of medium to

high energy level for thermosol

process.

[348]

371



▪ Use of cationic fixing agent Select after treatment agents with

minimum effect on lightfastness.

[301]



temperature under alkaline

conditions having lower

fastness

Avoid using too high temperature

during one-bath dyeing.

[79,

85]



temperature caused by the

dispersing agent

Use optimum quantities of a

dispersing agent.

[79]



presence of urea


method.



medium.



urea.

[79]



urea


method.


urea.

[79]

Widthwise

shade

▪ Using disperse dyes which

are sensitive to temperature

variations

Select dyes with which are less

sensitive to temperature variations.

[347]

372



differences/

listing

▪ Inadequate concentration of

anti-migrating agent causing

migration

Use the optimum concentration of

the anti-migrating agent depending

on the depth of shade.

[118]

▪ Using dyes with poor

migration properties


migration behavior.

2. Examine migration parameters of

disperse dyes.

Two sidedness ▪ Poor migration properties of

disperse dyes

1. Use the optimum quantity of the

anti-migrating agent.


migration behavior.

3. Examine migration parameters of

disperse dyes.

[118]

▪ Differences in the

substantivity of the dyes in

the combination shade

Select dyes with similar

substantivity.

[128]

Lengthwise

shade variation

/tailing/ ending

▪ Higher substantivity of dyes 1. Select dyes having lower

substantivity.

2. Use small trough volume.

3. Rapid circulation of liquor from

pad trough to stock feed tank.

[128,

253]

▪ Sedimentation of dye 1. Keep the liquor in circulation.

2. Keep the trough temperature

below 35 oC.

[253]

▪ Dye hydrolysis. 1. Select dyes with good dye bath

stability.

[369]

373



2. Keep the trough temperature

below 35 oC.

▪ Unstable dye dispersion 1. Use dyes with good dispersion

stability.

2. Use dispersing agent during

dyeing.

[253]

▪ Different adsorption

behavior of the dye due to

inappropriate dye

combination

Select dyes have similar dyeing

behavior.

[253,

369]

▪ Poor migration of the dyes Select dyes with good migration

properties.

[301]

▪ Differences in the affinity of

the dyes for the fiber

1. Use dyes with similar affinities.

The affinity factor of the dye

should be as low as possible.

2. Use short liquor trough.

[120,

368]

▪ Bleeding of the dye form

padded and dried fabric in

the chemical padding trough

1. Use a high concentration of

electrolyte.

2. Use some quantity of dyeing

liquor in the chemical pad.

[128,

317]

▪ Differences in dye

concentrations from one dye

preparation tank to another

Ensure the concentration of the dye

preparation remains consistent.

Dark and light

edges


maintain pH 5-6.

[253]

Pilling of

fabrics

▪ Increase in specific gravity

of bath by addition of salt


[301]

374



and alkali leading to higher

fabric-to-fabric friction

▪ High fabric to fabric friction

especially fabrics with a

very sensitive surface


2. Turn the fabric inside out.

[297]

Lower strength ▪ Fiber damage during drying

due to residual alkali after

dyeing (especially viscose

Ensure proper neutralization of the

fabric after dyeing.

[301]

Poor

appearance

▪ Improper color matching of

the shade on fibers in the

blend having differences in

depth and tone

1. Check the shade obtained on

polyester fiber by dissolving the

cotton component.

2. Keep the shade 10-20% deeper

after polyester dyeing.

[351]

4.10.2 Disperse/direct system

PES/CELL blends dyed with disperse and direct dyes often show unsatisfactory fastness. This is

usually attributed to the lower fastness properties of direct dyes as the washing fastness tests

performed on cotton dyed with direct dyes showed staining of cotton in the multifiber strip.

However, this statement is partially correct for PES/CELL blends. Poor selection of disperse dyes

are also responsible for lower fastness properties. The washing tests performed on the polyester

materials dyed with disperse dyes showed staining of nylon and acetate fibers in the multifiber

strip and for some dyes staining of cotton was also observed. As disperse dye tend to stain the

cellulose during dyeing, this led to unsatisfactory fastness properties. During the washing fastness

test, the dye present on the cellulose can easily stain the multifiber. The stain on the cellulose may

wash off during the washing fastness test and but stain the nylon fiber in the multifiber. For fabrics

subjected to resin finishing, the problem is further aggravated. The curing process during resin

finishing may cause the migration of dyes, known as thermomigration, from the inside to the

surface of the fiber. Thermomigration depends on time and temperature of curing, resin type,

375

softener type, depth of shade, and energy level of disperse dyes. Disperse dyes of low energy and

certain medium energy dyes have low fastness properties as compared to high energy dyes as they

show more migration as compared to high energy disperse dyes. The cationic softeners usually

exhibit the least problems as compared to nonionic softeners [83].

The important points needed to be considered during dyeing with disperse/direct dyes are

[9, 57]:

▪ Effect of salt on dyeing with disperse dyes; and

▪ Stability of direct dyes to the higher temperature and acidic pH used in dyeing with

disperse dyes.

As compared to reactive dyes, direct dyes required less quantity of salt around 10-15 g/l

depending upon the depth of shade. This may have less effect on the dispersion stability of disperse

dyes although the problem may observe in short liquor dyeing machines such as a beam or package

[86]. The salt may interfere with the exhaustion of the disperse dyes and may cause rubbing

fastness problems [57]. The leveling and dispersing agents used for disperse dyes generally do not

affect the direct dyeing process [86, 125]. Many direct dyes, however, are affected by the acidic

pH (4.5-5.5) and the high temperature (120-130 oC) and sequestering agents used for disperse

dyeing. Under these conditions, dyes must be adequately soluble and chemically stable [9, 69, 125,

378]. Some direct dyes may stain the polyester component and may cause fastness problems.

However, carriers and leveling agents minimize the direct dye staining [125].

The summary of the main problems associated with disperse/direct system is given in Table

4.45. Many problems listed in the disperse/reactive system are also applicable to disperse and

direct dyes.

Table 4.45: Problems and their possible solutions in the dyeing of polyester/cellulose blends with

disperse and direct dyes.


Reproducibility ▪ Variation in soda ash content

of direct dyes.

Check bath pH when dye when the

alkali is added and should be

adjusted if required.

[64]

376



▪ Partial destruction of

disperse dye due to the

interaction between free

copper in metal complex

direct dyes in one bath

process

Removal of copper from the

dyeing system by using

specialized complexing agents.

[69]

Unlevelness ▪ Variation in soda ash content

of direct dyes. For certain

direct that require alkaline

pH for their solubility,

higher than normal soda ash

content leads to a very high

pH. Also, lower than normal

soda ash may cause a lower

pH. The desired pH at the

later stage may not be

achieved when alkali is

added.




[64]

▪ Decrease in the solubility of

direct dyes under acidic

conditions and high

temperature used for

polyester dyeing

Select dyes that are stable in one

bath dyeing. Follow

manufacturers' recommendations.

[79]

Shade change ▪ Partial destruction of

disperse dye due to the

interaction between free

copper in metal complex

direct dyes in one bath

1. Use of copper-free direct dyes if

possible.

2. Use of metal complex dyes

having no free copper.

[69]

377



process. Especially taken

place in fully flooded

machines

3. Removal of copper from the

dyeing system by using

specialized complexing agents.

▪ Variation in exhaustion rates

of dyes

Select dyes with similar

exhaustion rates in the

combination shade.

[150]

▪ Destruction of direct dyes

under high dyeing


polyester dyeing

1. Select direct dyes with good

stability at a higher temperature.

2. Use a mild oxidizing agent.


[68]

▪ Destruction of direct dyes

under acidic conditions used

for polyester dyeing

Check the stability of direct dyes.

Select dyes which are stable under

acidic and high temperature

conditions used in disperse dyeing.

[79]

Poor color yield ▪ Destruction of direct dyes

under high dyeing


polyester dyeing

1. Select direct dyes with good

stability at a higher temperature.

2. Use a mild oxidizing agent.


[68]

▪ Physical interaction of

disperse and direct dyes in

the dye bath

1. Check the interaction between

the dyes in the lab before

dyeing.

2. Select dyes that show no or

minimum interaction effect.

3. Use the two-bath process if

possible.

[79]

Stains ▪ Variation in soda ash content

of direct dyes makes dye

insoluble in the dyebath




[64]

378



Dark stains ▪ Precipitated or undissolved

dye

Ensure proper dye solution

procedure as per dye manufacturer

recommendation.

[149,

150]

▪ Decrease in the solubility of

direct dyes under acidic

conditions and high


polyester dyeing

Select dyes that are stable in one

bath dyeing. Follow the

manufacturers' recommendations.

[79]

Inadequate

fastness

1. Rubbing

fastness






elecltrolyte.



[7, 68]

2. Wash fastness ▪ Inherent dye property, due to

weak attachment with the

fiber through Vander wall

forces

1. Treat with a fixing agent after

direct dyeing.

2. Use reactant fixable direct dyes.

[69,

75]

4.10.3 Disperse/vat system

This system is mainly used in package dyeing of yarns, semi-continuous and continuous dyeing of

fabrics [85]. This system is used where excellent fastness properties are required. They can be

applied by a relatively simple one bath two-stage process. The reduction bath required for the

reduction of vat dyes may also serve as a reduction clearing bath for disperse dyes. The vat dye

tends to strongly stain the polyester component of the blend at thermofixation temperature during

the one bath continuous processes [85, 359]. However, this cross-staining does not affect the

fastness properties achieved in PES/CELL blends. The vat dyes have limited stability under the

379

higher temperature dyeing conditions required for polyester in the batch dyeing process. The vat

dye dispersion for longer duration at high temperature is not stable. It is therefore recommended

to add vat dyes in the cooling bath after dyeing of polyester [79].

Many problems that occur during disperse/reactive system are also applicable to

disperse/vat dyes. Table 4.46 shows the specific problems and their causes and preventive

measures

Table 4.46: Problems and their possible solutions in the dyeing of polyester/cellulose blends

using disperse/vat system.


Unlevelness ▪ Rapid exhaustion of dye due

to a higher rate of rise

1. Gradually increase the

temperature to control the

exhaustion.

2. Use a leveling agent.

▪ Inadequate reduction of the

dye caused by variation in

alkalinity due to higher

quantities of hydro

Use the correct amount

caustic/hydro as per manufacturer

recommendations.

[67]

▪ Inadequate reduction of the

dye to lower concentration of

hydro/caustic



recommendations.

[194,

345]

▪ Using vat dyes of high

substantivity leading to higher

exhaustion of dyes to the

substrate

1. Select dyes with lower

substantivity, if possible.

2. Use leveling agent.

[254]

▪ Use of lower dyeing

temperature

Using higher dyeing temperature as

possible to promote leveling.

[7]

▪ Poor dispersion of the vat

pigments in the bath

Use dispersing agents. [70,

150]

380



▪ Poor selection of dyes for

combination shade using dyes

of extremely different groups

Dyes used in combination shade

should belong to the same group.

[67,

70]

▪ Incomplete oxidation of the

dye due to inadequate

concentration oxidizing

chemicals and residual alkali

in the fabric

1. Check the concentration of the

oxidizing agent, pH, temperature

and proper replenishment.

2. Ensure proper rinsing of fabric

before oxidation.

▪ Poor dispersion stability of vat

dyes under high dyeing

temperature and longer dyeing

time

Add vat dyes to the cold bath after

the high temperature dyeing of

polyester.

[79]

Dull shade ▪ Partial diffusion of dye during

steaming due to inadequate

reduction.

Using optimum quantities of

hydro/caustic

▪ Too high dye fixation

temperature during disperse

dyeing.

The fixation temperature should be

lower than 190 oC.

[133]

▪ Over-reduction of vat dyes

due to excess quantities of

hydro or excess

steaming/dyeing times or high

temperatrure

1. Add sodium nitrite during the

dyeing process.

2. Following manufacturer

recommendation for

hydro/caustic concentration and

temperature.

3. Use adequate dyeing/steaming

time depending on the depth of

shade.

[7,

67]

381



▪ The shade becomes duller of

indanthrone blue dyes due to

higher pH values in oxidation

The pH in the oxidation process

should be or below 9.

[61]

▪ Over-oxidation of dyes due to

strong oxidizing agent

Use a mild oxidizing agent (sodium

metanitrobenzenesulfonate) for

oxidation.

[7]

Shade change ▪ Improper reduction due to

inadequate concentrations of

the hydro and caustic

Check the concentration of

hydro/caustic. It should be

according to the dye concentration.

[359,

366]

▪ Greener shade of indanthrone

blue dyes due to higher pH

values in oxidation

Oxidation of vat dyes should be

carried out at or below pH 9.

[61,

67]

▪ Over-reduction of vat dyes

due to excess quantities of

hydro or excess

steaming/dyeing times or high

temperature

1. Add sodium nitrite during the

dyeing process.

2. Following manufacturer

recommendation for

hydro/caustic concentration and

temperature.

3. Use adequate dyeing/steaming

time depending on the depth of

shade.

[7]

▪ Variation in exhaustion rates

of dyes

Use dyes with similar exhaustion

rates in combination shade.

[150]





in the fabric





before oxidation.

[68,

345,

370]

382



▪ Combination shade produced

by mixing dyes of extremely

different groups

Select dyes with same groups or

nearby groups. Do not use dyes of

extremely different groups.

[67]

▪ Oxidation of detergents used

for soaping at high

temperature for longer

duration cause oxidation of

vat dyes

1. Select detergents which are

stable at high temperature.

2. Avoid using too long dwell

times.

[67]

▪ Bleeding of dye due to high

rinsing temperature

The temperature of the rinsing bath

should not exceed 40 oC.

▪ Staining of polyester by vat

dyes at high thermofixation

temperature

1. Perform the two bath process, if

possible.

2. Select vat dyes with lower

staining properties for

polyester.

[79,

85]



thermofixation


against gas fading.

[359]

▪ Over-oxidation of dyes due to

strong oxidizing agent

Use a mild oxidizing agent (sodium

metanitrobenzenesulfonate) for

oxidation

[7]

Widthwise

shade

variation/

listing

▪ Differences in caustic removal

from sides and the center of

fabric during washing lead to

differences in oxidation

Ensure the caustic is properly

removed from the fabric before

oxidation.

[61]

▪ Variation in oxidation of the

selvages as compared to the

center

Avoid the exposure of selvages due

to air.

[67,

194]

383



▪ Nonuniform reduction of the

dye across the width of the

fabric

Ensure the distribution of the

reducing agent and caustic is

uniform across the fabric width.

Lengthwise

shade

variation/

tailing/ending

▪ Bleeding of the dye form

padded and dried fabric in the

chemical padding trough

Use a high concentration of

electrolyte.

Use some quantity of dyeing liquor.

[317,

379]

▪ Bleeding of dye due to high

rinsing temperature

The temperature of the rinsing bath

should not exceed 40 oC.



Use dispersing agents. [379]

▪ Settling of the dye in the

preparation tank and the

dyeing trough

1. Ensure proper agitation in

preparation tank and the dyeing

trough.

2. Use dispersing agent with good

dispersion properties.

[379]

Dark stains ▪ Precipitated or undissolved

dye

1. Use optimum temperature for dye

solution preparation.

2. Use dispersing agents.

[149,

150]



Use dispersing agents. [150]

▪ Settling of the dye in the

preparation tank and the

dyeing trough

1. Ensure proper agitation in the

preparation tank and the dyeing

trough.

2. Use a dispersing agent with good

dispersion properties.

[379]

▪ Agglomeration and

sedimentation of vat dyes due

to anti-migrating agent

1. Use optimum quantities of anti-

migrating agent.

[371]

384



2. Control the dye bath pH. The pH

of 4 reduces or cancels the

agglomeration effect.

▪ Poor compatibility of the dyes

and the auxiliaries

Check the dyes and auxiliaries for

computability in the laboratory

before dyeing in the bulk.

[379]

▪ Variation in the alkalinity of

the bath due to higher

quantities of hydro leading to

precipitation of vat dyes



recommendations.

[67]

▪ Reoxidation of leuco

compounds desorbed from the

fabric surface in particulate

form due to foaming caused

by excessive wetting agent or

turbulence of the dye liquor

Use a defoamer. [128]

▪ Premature or improper

localized oxidation of the dye

1. Maintain proper oxidation

conditions (chemical

concentration, pH and

temperature).

2. Rinse the fabric with sodium

bicarbonate before oxidation for

easy removal of caustic.

3. After steamer/water seal fabric

should have sufficient quantities

of hydro.

[323]

385



▪ Formation of insoluble leuco

acid form in rinsing due to

inadequate pH

The pH must remain between 9-

10.5 during rinsing.

▪ Variation in the particle size

of the vat dyes. The large dye

particles may cause crystal

growth or form deposits on the

yarn surface or difficult to

reduce

1. Perform dye filtration test for

new lot.

2. Add dispersing agent to avoid

crystal growth.

3. Wound a woven PP fabric on the

dye tube.

[254,

379]

Poor color

yield

▪ Inadequate reduction of dye

due to the presence of air in

the water/dyeing machine

1. Remove air from the machine at

the start of the dyeing cycle.

2. Minimize the contact of reduced

fabric with air.

3. Use closed chamber machines.

[345]

▪ Inadequate reduction of dye

due to insufficient quantities

of hydro/caustic

Check that sufficient reduction

potential is maintained by

controlling the concentration of

hydro/caustic.

[345,

370]

▪ Premature oxidation of the

dye due to the presence of air

in the water/dyeing machine




fabric with air.


[345]





in the fabric





before oxidation.

[68,

345,

370]

386





thermofixation


against gas fading.

[359]

Inadequate

fastness

1. Rubbing

fastness

▪ Partial diffusion of dye during

steaming due to inadequate

reduction

Using optimum quantities of

hydro/caustic

▪ Inadequate removal of unfixed

dye from the fabric

1. Perform thorough soaping of the

fabric.

2. Check the washing temperature.

[370]

▪ Insufficient quantities of

caustic in the dyebath

Add an adequate quantity of caustic

depending on the concentration and

class of vat dye used.

[254]

▪ Inadequate rinsing of the

fabric before oxidation

Ensure proper rinsing of the fabric

with an adequate amount of water

supply.

[345]



in the water/dyeing machine




fabric with air.


[345]

▪ Inadequate oxidation of the

dye by using peroxide/

perborate and acetic acid

leading to the formation of vat

acid pigment

Replace acetic acid with sodium

bicarbonate for oxidation.

[194]

387







in the fabric.


oxidizing chemicals and proper

replenishment.


before oxidation.

[345,

370]

2. Wash

fastness


dye from the fabric.


fabric.

2. Check the washing temperature.

[370]

▪ Inadequate rinsing of the

fabric before oxidation.

Ensure proper rinsing of the fabric

with adequate amount of water

supply.

[345]



in the water/dyeing machine.




fabric with air.

[345]

▪ Use of non-ionic soaping

agent having lower cloud

point temperature.

Use an anionic soaping agent. [254]





in the fabric.


oxidizing chemicals and proper

replenishment.


before oxidation.

[345,

370]

▪ Inadequate soaping

temperature or dwell time.

Use adequate soaping temperature

and dwell time.

[7]


dye from the fabric.


fabric.

2. Check washing temperature.

[370]

388



3.

Lightfastness

▪ Catalytic fading of vat dyes. Select dyes with good light fastness

in combination shades.

[7]

▪ Poor dye selection. Select dyes with good light fastness

in combination shades.

Poor

appearance

(haziness)

▪ Random concentration of a vat

dye on the fabric surface.

Strip and re-dye the fabric. [67]

Reduced

strength

▪ Photo tendering of cellulose

by some vat dyes.

Carefully select the dyes with a

lower tendency to phototendering.

[7]

4.10.4 Disperse/sulfur system

This combination is usually restricted to dull and dark shades such as black, navy, brown, olive

and green. They are generally used in low cost articles due to limited fastness properties. They can

be applied to PES/CELL blends by both bath and continuous dyeing methods. The sodium sulfide

used for the reduction of sulfur dyes has an adverse effect on the polyester, sodium hydrosulfide

is therefore preferred to minimize this problem [79, 380]. The use of disperse/sulfur system for the

dyeing of PES/CELL blends is very limited. The main problems related to disperse/sulfur system

and possible solutions are given in Table 4.47.

Table 4.47: Dyeing problems associated with disperse/sulfur system.


Unlevelness ▪ Addition of the dyes in the bath

at a very high temperature.

Add dyes at a lower temperature.

Start the dyeing process at a lower

temperature.

[380]

▪ Higher temperature ramp rate. 1. Use slower ramp rate.

2. Increase liquor circulation rates

with higher ramp rates.

389



▪ Too quick addition of

electrolyte

Add electrolyte gradually during the

dyeing process.

▪ Inadequate rinsing before

oxidation leading to

precipitation of unfixed dye on

the fiber surface during the

acidic oxidation stage

Ensure proper rinsing conditions

(time, temperature and adequate

water supply)

Bronziness ▪ Premature oxidation of dye 1. Use the excess quantity of hydro.

2. Remove air from inside the

machine.

3. Strip to remove some of the

surface dye.

[345]

▪ Using too much concentration

of the dye

1. Use dyes with high tinctorial

strength.

2. Avoid using too high dye

amounts.

3. Strip to remove some of the

surface dye.

▪ Excess quantity of salt used

during dyeing.

Use the optimum quantity of the salt

based on the shade.

[150]

[345]

▪ Using poor quality or lower

quantity of sodium sulfide

leading to incomplete reduction

of the dye

1. Check the reduction potential of

the sodium sulfide.


sodium sulfite based on the shade.

[345]

▪ Presence of free sulfur in the

dye bath

Use sodium sulfite along with

sodium sulfide for dissolving free

sulfur in the dye bath.

[323]

390



Tailing or

ending

▪ Addition of all dyes and

auxiliaries at the start of the

process

Add dyes and auxiliaries gradually

during the dyeing process.

[380]

▪ Beginning of the dyeing at a

very high temperature

Add dyes at a lower temperature.

Start the dyeing process at a lower

temperature

▪ Addition of electrolyte at the

start of the dyeing process

1. Don’t add electrolyte along with

the dye. Allow the dye to run with

the substrate for some time before

electrolyte is introduced.

2. Add electrolyte gradually in steps.

Acid

tendering

▪ Storage of fabric in warmer

and humid conditions leading

to the release of acid by some

sulfur dyes

1. Store the fabric at low

temperature and humidity.

2. Finish the fabric to slightly

alkaline pH after dyeing.

[345]

▪ Incomplete removal of sulfur

residues from the fabric

1. Ensure proper rinsing before

oxidation.

2. Thorough soaping of the dyed

fabric after oxidation.

3. Finish the fabric to slightly

alkaline pH after dyeing.

[345]

Dark stains ▪ Precipitated or undissolved dye Use a dispersing agent. [149,

150]

▪ Re-oxidation of leuco

compounds desorbed from the

fabric surface in particulate

form due to foaming caused by

Avoid using an excessive amount of

wetting agent and high turbulence.

[128]

391



excessive wetting agent or

turbulence of dye liquor

Lower

strength

▪ Adverse effect of sodium

sulfide on polyester

Use hydro as a reducing agent. [79]

392

CHAPTER 5 EFFECT OF BLEND RATIO ON DYEING

PROPERTIES OF POLYESTER-COTTON BLENDED FABRICS

5.1 Introduction

Polyester/cotton blends are the most important and commonly dyed fiber blends. Their profound

success is due to their excellent properties. Both single colorant and two colorants system can be

used to dye these blends. The single colorant system uses pigments which are attached to the

substrate (fiber) with the help of a binder. Although pigment coloration is economical but it is

mostly limited to light to medium shades due to inadequate fastness of the colored substrate and

harsh fabric hand at higher concentrations. The two colorant system involving separate dye classes

for each component of the blend is applicable at different depths of shade and for a wide range of

fastness properties depending upon the end use. Disperse dyes are used to dye the polyester

component only, but reactive, vat, direct and sulfur dyes can be applied to cotton. Although the

cotton portion of the blend can be dyed with different dyes reactive dyes exhibit a high level of

fastness properties and a wide shade range. The disperse/reactive system is, therefore, the most

common dye system used for the dyeing of polyester/cotton blends in most applications.

Different methods can be used to dye polyester/cotton blends using disperse and reactive

dyes. These include conventional two-bath, reverse two-bath and one-bath methods. The

conventional two bath method is recommended for medium to dark shades with good fastness

properties. A reduction clearing can be performed to provide good to excellent fastness properties.

The reverse two bath is the modified process in which cotton is dyed first followed by polyester.

The reduction clearing process is not suitable in this case as it may destroy the reactive dyes. Some

reactive dyes may not be stable under high temperature conditions and acidic pH employed in

disperse dyeing. The one bath process significantly reduces the dyeing times as both dye classes

are added together at the start of the dyeing process. Fixation is usually achieved in two stages. In

the first stage disperse dyes are fixed and the bath temperature is then reduced to fix the reactive

dyes. Good dye selection is important to achieve good fastness results and color yield [7, 9, 381].

393

Factors affecting the selection of the disperse dyes for polyester/cellulosic blends include

the required hue, depth of shade, level dyeing behavior, cross-staining, and fastness properties.

The dyes that may be suitable for dyeing of 100% polyester fibers may not give satisfactory

performance in the dyeing of blends. The migration properties of disperse dyes are generally

inferior on polyester/cellulosic blends compared to those on 100% polyester. Due to the

hydrophilic nature of the cellulosic fibers, the dyeing liquor movement is preferred in cellulosic

regions compared to the polyester which is more hydrophobic. This inhibits the migration of

disperse dyes to the polyester [86, 381].

The overall appearance of the dyed polyester/cotton blends need to be controlled to achieve

good union effects due to differences in the distribution of polyester and cotton fibers in the yarn

body and the reflectance properties of the polyester and cotton fibers. In the case of polyester rich

fiber blends such as polyester/cellulose with 67/33 blend ratio, it seems logical that the color

obtained on the polyester portion mainly determines the overall dyeing effect. However, due to the

migration of cellulosic fibers to the surface of the yarn during spinning, their color can have the

main contributing effect on the appearance of the yarn. It has been found that in the case of medium

to deep shades the color of the cellulosic component predominates while in case of light shades

the reverse is true. This makes shade corrections difficult for the polyester component of the blend.

The amount of dyes required to match a shade may also vary due to the differences in the

distribution of fibers [381].

During the dyeing of blends with disperse dyes, the dye is distributed between the two fiber

components while some also remains in the dyebath. Some disperse dyes may superficially attach

to cotton, forming stains, which can be heavy and result in poor washing fastness properties.

Therefore, often for the same type of dyes employed the polyester/cotton blends exhibit lower

washing fastness as compared to 100% cotton [87]. The superficially attached disperse dyes need

to be removed to obtain good fastness properties. Two approaches can be used to deal with this

problem. The first approach involves the use of disperse dyes with a minimum tendency to stain

the cotton which have good wash-off properties. This can be achieved by using alkali clearable

disperse dyes that have a lower tendency to stain cotton or dyes that do not require a conventional

reduction clearing process. They can be removed in the alkaline medium used for reactive dyeing.

The second approach employs the reduction clearing process for the removal of surface dye from

cotton and polyester fibers. This requires a two bath process where polyester is dyed first followed

394

by reduction clearing. The cotton is dyed in the second stage. The mechanism for the removal of

disperse dye is shown in Figure 5.1 [7, 9, 87, 381, 382].

Figure 5.1: Clearing mechanism of disperse dye stain [383].

One of the objectives of this study was to investigate the effect of different proportions of

polyester and cotton fibers in the blend on the dyeing behavior of polyester/cotton blend fabrics.

The following hypotheses, pertaining to batch dyeing by standard dyeing methods, were tested to

determine the effect of blend ratio on the dyeing properties of the polyester/cotton blends.

▪ The amount of dye required for dyeing of each fiber in the blend varies with the blend

proportion of each fiber in the blend. For example, by using approximately 50% of the

original amount of disperse and reactive dyes respectively on 50/50 PES/CO blend a

similar shade to that obtained on 100% polyester and 100% cotton can be produced.

▪ The two-bath method will yield better fastness properties as compared to reverse two

bath and one bath methods.

▪ The fastness properties of the polyester/cotton blends vary with the blend ratio.

Increasing the polyester component in the blend results in deteriorated wet fastness

properties in general especially for staining nylon in a multi-fiber strip during wash

fastness tests. In addition, as the cotton portion of the blend increases there will be a

decrease in the wet rubbing fastness.

TS S&W BD PES June 2008

Polyester/cellulose

blend

Dye

polyester

fibre

dye on fibre

surface

reduction/

alkali clear

Page 3/23Main menu

Dye inside the fiber and on

the surface

395

5.2 Experimental

5.2.1 Materials

Six knitted fabrics were used in this study. Single jersey knitted fabric samples were produced

from each of the yarns kindly supplied by Parkdale Mills. The count and the composition of the

yarns are given in Table 5.1.

Table 5.1: Properties of yarns and fabric codes.

Yarn count Fiber Composition Fabric codes

Ne 18/1 100% Cotton CT

Ne 20/1 100% Polyester PET

Ne 16/1 65% High tenacity polyester, 35% Cotton PC1

Ne 18/1 50% Cotton, 50% Polyester PC2



All the yarns used were knitting yarn that were waxed during spinning except the 65%

polyester/35% cotton yarn which was a weaving yarn and was waxed before knitting. The blended

yarns were produced by intimate blending and spun by rotor spinning. For all yarns, the cotton

fiber used was Memphis Eastern with an average length of 1.12 inches. Two types of polyester

fiber were used. For all yarn types except 65% polyester/35% cotton yarn, the polyester used had

a linear density of 1.2 deniers, with a cut length of 32mm, optically brightened, having a tenacity

of 6.2 grams/denier. For 65/35 blend ratio the high tenacity polyester was used having a linear

density of 1.2 deniers, 38 mm staple length and tenacity 6.9 grams/denier.

Table 5.2 shows the list of general chemicals and auxiliaries used. In order to dye the

polyester/cotton blends disperse and reactive dyes were obtained from Archroma (Foron,

Drimaren), Huntsman (Terasil, Novacron), and Dystar (Dianix, Procion, Remazol). The disperse

dyes used are presented in Table 5.3 while the reactive dyes are listed in Table 5.4.

396

Table 5.2: List of chemicals and auxiliaries.

Name Application Supplier

Sodium hydroxide (NaOH, 50%) Alkali for scouring and

bleaching

Brenntag

Hydrogen peroxide (H2O2, 35%) Bleaching agent Brenntag

Acetic acid (glacial) Acid for disperse dyeing and

neutralization

Brenntag

Clarite Max Stabilizer Huntsman

Invadine PBN Wetting agent Huntsman

Sodium sulfate (Glauber's salt) Electrolyte Brenntag

Sodium carbonate (Soda ash) Alkali for dyeing Trontox

Novadye NT9 Dispersing agent (A) Boehme Filatex

Sera Sperse M-IS Dispersing agent (B) Dystar

Sera Gal P-SDL Leveling agent Dystar

ApolloScour SRDS Surfactant Apollo Chemicals

Table 5.3: Properties of disperse dyes used in the study.

Dye name Color Index number Chemical Class Energy level

Foron Brilliant Yellow S-6GL Disperse Yellow 231 Azo High

Foron Rubine S-WF Not assigned Azo High

Foron Blue S-BGL Disperse Blue 73 Anthraquinone High

Foron Navy S-2GRL Disperse Blue 79:1 Azo High

Dianix Flavine XF Disperse Yellow 126 Pyrolidone High

Dianix Blue XF Disperse Blue 284 Azo thiophene Medium

Dianix Crimson SF Mix Benzodifuranone High

Dianix Yellow CC Disperse Yellow 241 Pyrolidone Medium

Dianix Rubine CC Mix Azo Medium

Dianix Blue CC Mix Azo Medium

397


Dye name Color Index number Chemical Class Energy level

Dianix Red CC Disperse Red 343 Azo Medium

Terasil Yellow 4G Disperse Yellow 211 Pyridone Medium

Tersail Rubine 2GFL Disperse Red 167.1 Azo High

Terasil Blue 3RL-02 Disperse Blue 56 Anthraquinone Low

Terasil Brown 2RFL Disperse Orange 30 Azo High

Terasil Navy GRL-C Disperse Blue 79.1 Azo High

Table 5.4: Characteristics of reactive dyes used in the study.

Dye name Color Index number Reactive group

Drimaren Yellow CL-2R Reactive Yellow 145 MCT, VS

Drimaren Red HF-6BL Not assigned TFP, VS

Drimaren Blue HF-RL Not assigned TFP, VS

Procion Yellow H-EXL Not assigned 2 x MCT

Procion Dark Blue H-EXL Not assigned 2 x MCT

Procion Red H-E3B Reactive Red 120 2 x MCT

Remazol Yellow RR Mixture VS

Remazol Red RR Mixture VS, MCT

Remazol Blue RR Mixture VS

Remazol Black B Reactive Black 5 2 x VS

Novacron Yellow FN-2R Reactive Yellow 206 2 x FT

Novacron Ruby S-3B Mixture 2 x MCT, VS

Novacron Blue FN-R Reactive Blue 235 FT, VS

Novacron Orange W-3R Reactive Orange 131 2 x VS

Novacron Navy S-G Mixture 2 x VS + 2 x VS,

MCT

MCT:Monochlortriazine, VS: Vinyl suplhone, MFT: Monoflorotriazine, TFP:

Trifloropyrimidine, FT: Florotriazine

398

5.2.2 Methods

5.2.2.1 Knitting

The fabric samples were produced on a Shima Seiki flat knitting machine with a 14 gauge. The

fabric codes for different blend compositions are given in Table 5.1.

5.2.2.2 Pretreatment

The solomatic bleaching (combined scouring and bleaching) of the greige knitted fabrics was

carried out in a laboratory-scale Thies Jet Machine using a 15:1 liquor to goods ratio. The fabrics

were scoured and bleached using 2 g/L of NaOH, 4 g/L of H2O2, 2 g/L of stabilizer and 1 g/L of a

wetting agent at the boil for 1 hour. The fabrics were then rinsed twice and neutralized using 0.5

g/L acetic acid to adjust the fabric pH to 6-7. The fabrics were then centrifuged and dried. The

fabrics containing polyester, whole or in a blend, were heatset on a Mathis laboratory-scale stenter

at 200 oC for a dwell time of 2 minutes. The fabric absorbency was tested by a drop test after

pretreatment and was found to be less than 3 seconds for all fabrics. The CIE whiteness and tint

values of the fabrics after pretreatment are given in Table 5.5.

Table 5.5: CIE whiteness and tint indices of fabrics after pretreatment.

Fabric Whiteness Index Tint Index

CT 73.50 -0.95

PET 127.99 2.35

PC1 112.63 0.65

PC2 121.46 1.56

PC3 115.44 1.08

PC4 108.83 0.64

5.2.2.3 Dyeing

Disperse and reactive dyes were used to dye polyester and cotton components respectively. Three

colored chips, two dark and one light were selected from the Pantone book of color as target colors.

The selected chips were Pantone 462U (brown), Pantone 2768U (navy) and Pantone 468U (beige)

and are simulated in Figure 5.2. These target colors were matched on four polyester/cotton blended

399

fabrics, as well as on 100% cotton, and 100% polyester fabrics. The dyes were provided by

Archroma, Dystar, and Huntsman. The dyes were selected from the manufacturer's

recommendations based on the target color and their suitability for the batch dyeing method. The

dye combinations used to produce the target colors in different dyeing methods are given in Table

5.6. In the first step, the primaries were produced from each dye on CT and PET fabrics according

to the recommended dyeing method. The various dye concentrations used are 0.05, 0.1, 0.25, 0.5

and 1% owf. The Datacolor Match Textile software was used to generate recipes to match a target

color. The blended, as well as cotton and polyester fabrics, were then dyed based on generated

recipes according to different dyeing methods. The dyeings were corrected until a match with

DEcmc < 1.5 was obtained. Approximately 4-5 corrections were needed to match the color of the

dyed substrate for the target shades. The dyeings were then replicated on a larger sample. All

dyeings were carried out in a laboratory-scale Ahiba IR Pro dyeing machine. A liquor to goods

ratio of 20:1 was employed. A total of 90 samples (6 fabrics, 3 colors, 3 dyeing methods: two-bath

with 3 different dye combinations, reverse two-bath and one bath) were produced.

(a) Pantone 462U (b) Pantone 2768U (c) Pantone 468U

Figure 5.2: Simulations of Pantone colors used as target colors.

Table 5.6: Dye combinations used to match target colors using different dyeing methods.

Shade Supplier Dyeing

method Dye combinations

Brown Dystar C2B

PES: Yellow CC, Blue CC, Red CC

CO: Yellow RR, Red RR, Black B

Archroma C2B PES: Brilliant Yellow S-6G, Rubine S-WF Navy S-2GRL 200

CO: Yellow CL-2R, Red HF-6BL, Blue HF-RL

400



method Dye combinations

Huntsman C2B PES: Yellow 4G, Rubine 2GFL, Navy GRL-C

CO: Navy S-G, Ruby S-3B, Yellow FN-2R

Huntsman R2B PES: Yellow 4G, Rubine 2GFL, Blue 3RL-02


Dystar 1B PES: Flavine XF, Blue XF, Crimson SF

CO: Red HE3B, Dark Blue HEXL, Yellow HEXL

Navy

Dystar C2B


CO: Yellow RR, Red RR, Black B

Archroma C2B

PES: Brilliant Yellow S-6G, Rubine S-WF, Navy S-2GRL

200


Huntsman C2B PES: Brown 2RFL, Rubine 2GFL, Navy GRL-C

CO: Navy S-G, Ruby S-3B, Orange W-3R

Huntsman R2B PES: Brown 2RFL, Rubine 2GFL, Blue 3RL-02

CO: Navy S-G, Ruby S-3B, Orange W-3R



Beige

Dystar C2B


CO: Yellow RR, Blue RR

Archroma C2B PES: Brilliant Yellow S-6G, Rubine S-WF


Huntsman C2B PES: Yellow 4G, Rubine 2GFL, Blue 3RL-02

CO: Blue FN-R, Ruby S-3B, Yellow FN-2R

Huntsman R2B PES: Yellow 4G, Rubine 2GFL, Blue 3RL-02




PES: Polyester, CO: Cotton

401

The different dyeing methods used for the dyeing of polyester/cotton blended fabrics were

conventional two-bath (C2B), reverse two-bath (R2B) and one bath two-stage (1B). During the

C2B method, as shown in Figure 5.3a, the polyester portion is dyed first with disperse dyes at 130

oC for 45 minutes for navy and brown colors and 30 minutes for beige color using 0.5 g/L

dispersing agent. The heating rate of the dye bath was kept at 2 oC/min. The pH of the dye bath

was maintained at 5.5 with acetic acid. The reduction clearing process was then performed with 2

g/L hydro and 2 g/L caustic at 80 oC for 10 min. This was followed by rinsing and neutralization.

In the second bath, the cotton portion was dyed with reactive dyes using Glauber’s salt and soda

ash. The pH of the dye bath was 10.8. The amount of Glauber’s salt used depended on the depth

of shade. The dyeing was carried out at 60 oC for 60 minutes for the navy and brown colors and

45 minutes for the beige color. The dyed fabric was then soaped at 95 oC for 10 min using 1 g/L

surfactant to remove the unfixed reactive dye. The rinsing and neutralization completed the

process.

In the R2B method shown in Figure 5.3b, the cotton portion was dyed first followed by

polyester dyeing using the same chemicals and conditions used as in the C2B method except the

reduction clearing process was replaced with the rinsing and neutralization process as reactive

dyes are not stable under reduction clearing conditions. The polyester was then dyed with disperse

dyes. The soaping process was then used to remove the unfixed and hydrolyzed dyes.

The dyeing in the 1B method was carried out in two stages as shown in Figure 5.3c. Both

disperse and reactive disperse dyes were added together with a dispersing agent, leveling agent

and Glauber’s salt. The pH of the bath was maintained at ~ 4 with the help of acetic acid. The

temperature of the bath was then increased to 135 oC to dye the polyester portion. The temperature

gradient was kept at 1 oC/min in the critical dyeing region (65-135 oC). The disperse dyes used

were sensitive to dyeing conditions so different dispersing agent and leveling agent were used

according to manufacturer recommendations. The pH of the dyebath was also adjusted to be more

acidic as compared to the two-bath methods. The dyeing was continued for 45 minutes for the

navy and blue colors and 30 minutes for the beige color. The temperature was then dropped to 80

oC and soda ash was added to maintain a pH of ~ 11. The dyeing was then carried out for 60

minutes for the navy and brown and 45 minutes for the beige colors. The dyed fabrics were soaped

similarly as in the two-bath methods.

402

(a) Conventional two-bath dyeing method.

(b) Reverse two-bath dyeing method.

(c) One-bath two-stage dyeing method.

Figure 5.3: Dyeing profiles of different dyeing methods used.

The PET and CT fabrics were dyed according to the methods used for the dyeing of the

respective portion of the blend. The PET fabrics were reduction cleared while the CT fabrics were

2 oC/min

2 oC/min

130 oC, 30-45 min

80 oC, 10 min

60 oC, 45-60 min

95 oC, 10 min

0.5 g/L Dispersing agent (A)

Acetic acid, pH ~ 5.5Glauber's salt

Soda ash, pH ~ 11

1 g/L surfactant

Tem

per

atu

re,

oC

Time, min

Polyester Dyeing Reduction

clearingCotton dyeing SoapingRinsing &

Neutralizationn

Rinsing &

Neutralization

2 oC/min

2 oC/min

130 oC, 30-45 min

60 oC, 45-60 min

95 oC, 10 min

0.5 g/L Dispersing agent (A)

Acetic acid, pH ~ 5.5

Glauber's salt

Soda ash, pH ~ 11

1 g/L surfactant

Tem

per

atu

re,

oC

Time, min

Polyester DyeingCotton dyeing SoapingRinsing &

Neutralizationn

Rinsing &

Neutralization

95 oC, 10 min

1 g/L surfactant

Tem

per

ature

, oC

Time, min

Polyester Dyeing Cotton dyeing SoapingRinsing &

Neutralization

80 oC, 45-60 min

2 oC/min

1 oC/min

135 oC, 30-45 min

2 g/L Dispersing agent (B)

1 g/L Leveling agent

Acetic acid, pH ~ 4

Glauber's salt

Soda ash, pH ~ 1165

oC

403

soaped according to the different methods employed. In the 1B and R2B methods no reduction

clearing was performed. In such cases the PET fabric was soaped to match the same treatment.

5.2.3 Evaluation methods

5.2.3.1 Color strength

The colorimetric attributes of the fabrics were measured using a calibrated Datacolor 850

reflectance spectrophotometer with Tools® software. The color match predictions were computed

using Datacolor Match Textile software. The settings used for measurement were illuminant D65,

CIE 10o standard observer with specular and UV included. Three readings were taken at random

points of the samples and then averaged.

The color strength of the dyed samples was calculated using the Kubelka-Munk equation

given below:

𝐾

𝑆=

(1 − 𝑅)2

2𝑅 (5.1)

Where R is the reflectance of the samples at a wavelength of maximum absorbance. The relative

color strength of the samples is calculated by dividing the K/S value of the sample by the K/S

value of the reference. The relative strength value is reported in percentage.

5.2.3.2 Color fastness

Different fastness properties, e.g. light fastness, crocking fastness, washing fastness and water

fastness were evaluated for the dyed fabrics. These were selected based on the most commonly

used fastness tests for dyed polyester/cotton blended fabrics in the industry.

Color fastness to light was measured according to the AATCC TM 16.3, Option 3. The

strip of fabric, part of which was covered was placed in a light fastness tester and exposed to 40

hours of accelerated fading units (AFU). After the exposure, the color of the exposed and protected

portion of the samples were compared. The color change was then quantified using grey scale for

color change [384].

Crockfastness was determined using the AATCC TM 8. Both dry and wet rubbing fastness

assessments were carried out by using a digital crockmeter. The ratings were assigned to the

amount of color transferred to the white fabric [385].

404

The color fastness to washing was assessed using a Launder-o-meter according to the

AATCC TM 61. The settings used were according to option 2A (49 oC). A multifiber strip was

attached to each sample to evaluate staining. After the test, the color change of the test specimen

and the magnitude of staining of the multifiber strip were determined using the grey scale ratings

[386].

Color fastness to the water of the dyed samples was determined using a perspirometer

according to the AATCC TM 107 and the staining of the multifiber was recorded [387].

The greyscale ratings, from 1 to 5, were determined instrumentally using the AATCC

Evaluation Procedure 7 for change in color [388] and the AATACC Evaluation Procedure 12 for

staining [389]. The scale grades were then converted to step values. The grade of 5 implies no

color change or staining [390, 391].

5.3 Results and discussion

5.3.1 Amount of dye required to match a target color

The actual amounts of dyes used to generate a match are given in Table 5.7. The amount of dyes

required to match a given shade varied with the depth of shade and blend ratio of the fabric as

expected. The navy color required the largest dye amounts followed by brown and beige colors.

The results for dye concentrations showed that the dye amounts vary with the blend ratio of the

fiber in the blend. It is interesting to note that the dye amounts required to match the shade on a

blend were significantly higher compared to the blend ratio for all three colors. In some cases, the

disperse and reactive dye amounts required to match the respective portion of the blend were found

to be similar to those used to produce a match on 100% cotton and polyester fabrics.

405

Table 5.7: Total amounts of dye required to match the target colors in fabrics of different blend

ratio using different dyeing methods.

Color Fabric C2B-Dystar C2B-Archroma C2B-Huntsman R2B-Huntsman

D R D R D R D R

Brown

PET 0.212 0.228 0.262 0.304

PC1 0.321 0.584 0.351 0.790 0.409 0.501 0.463 0.519

PC2 0.257 0.820 0.305 1.215 0.324 0.732 0.416 0.779

PC3 0.194 0.948 0.229 1.414 0.255 0.873 0.325 0.896

PC4 0.091 1.141 0.124 1.559 0.134 0.887 0.173 0.914

CT 0.839 1.138 0.654 0.645

Navy

PET 0.254 0.329 0.349 0.465

PC1 0.386 0.550 0.565 0.783 0.539 0.649 0.719 0.641

PC2 0.321 0.820 0.581 1.316 0.453 0.946 0.623 0.949

PC3 0.214 0.975 0.511 1.821 0.332 1.075 0.457 1.195

PC4 0.104 1.109 0.239 2.061 0.150 1.108 0.231 1.113

CT 0.733 1.669 0.787 0.798

Beige

PET 0.014 0.015 0.015 0.015

PC1 0.021 0.045 0.020 0.039 0.023 0.027 0.025 0.046

PC2 0.019 0.082 0.021 0.055 0.021 0.044 0.023 0.058

PC3 0.013 0.103 0.017 0.072 0.017 0.053 0.018 0.062

PC4 0.007 0.105 0.009 0.080 0.008 0.053 0.009 0.057

CT 0.071 0.060 0.040 0.038

D: Disperse, R: Reactive

In blends, the amount of dyes required to produce the same color as on a single fiber is

usually adjusted according to the blend ratio of the fabric. For example as shown in Table 5.7, if

0.212 % owf disperse dye and 0.839 % owf reactive dyes were required to produce the same shade

on 100% polyester and 100% cotton fabrics respectively, the same shade can be matched on

polytester/cellulosic blends by adjusting the dye amount according to blend ratio. For 65/35

polyesyer/cotton blend (PC1) the adjusted disperse and reactive dye amount is expected to be

406

around 0.138% owf (65% of 0.212% owf total disperse dye) and 0.294% owf (35% of 0.8393%

owf of total reactive dye) respectively. This assumes that the fiber type used is the same and both

single fibers and fiber blend are processed under the same dyeing conditions. This behavior is not

exhibited by the dyes and dyeing methods used in this study. The amount of dyes required to match

the same shade on polyester/cotton blends were found to be approximately two times the

theoretical amounts based on the match obtained on all polyester and all cotton fabrics irrespective

of the color to be matched. The only exception is the one bath method that shows 3-5 times more

dye amounts than calculated based on the blend ratio. The use of higher dye amounts than expected

may be attributed to a loss in color yield of the reactive and disperse dyes with a change in the

blend ratio. Although in the case of continuous dyeing the amount of dyes required to match the

given shade may vary slightly as compared to the blend ratio, the results obtained by batch dyeing

in this study show higher amounts than in practical continuous dyeings [139].

Table 5.8: The effective liquor ratio for each fiber in the blend at a bath liquor ratio of 20.

Fabric Blend ratio Effective liquor ratio

PES CO PES CO

CT 100 20

PET 100 20

PC1 65 35 31 57

PC2 50 50 40 40

PC3 40 60 50 33

PC4 25 75 80 27

As the required pH was maintained according to dye type and the dyeing auxiliaries were

used based on g/L, the drop-in dye yield may be due to the change in the effective liquor available

for each fiber type in the blend as shown in Table 5.8. At a liquor ratio of 20, the effective liquor

ratio available for PES/CO 50/50 is 40 for cotton and for a polyester portion of the blend. For

PES/CO with a 25/75 ratio, this will increase to 80 for polyester and 27 for cotton. The increase in

liquor ratio may be attributed to the drop in the color yield thus requiring more dye to produce the

same color. Liquor ratio is one of the important aspects of the batch dyeing process. It can vary in

407

the dyeing process due to changes in the dye bath water level or variation in the fabric load. The

effect of variation in the liquor ratio is well known as it affects the reproducibility and economics

of the dyeing process [79].

It is well known that the exhaustion of dyes is reduced when the liquor ratio is increased.

To compensate for this more dye is required to match the given shade [392]. The relation between

equilibrium exhaustion (𝐸∞) of dye and liquor ratio (L) is given by Equation 5.3 [392]:

𝐾𝑒𝑓𝑓 =[𝐷]𝑓

[𝐷]𝑠 (5.2)

𝐸∞ =𝐾𝑒𝑓𝑓

[𝐾𝑒𝑓𝑓 + 𝐿] (5.3)

Where K is constant and depends on the dye isotherm. [𝐷]𝑓 and [𝐷]𝑠 are the concentration

of dye on the fiber and in dyebath at equilibrium. The effect of liquor ratio is commonly observed

in laboratory and production dyeing where the laboratory recipe (normally higher) needs to be

adjusted according to the liquor ratio used in the production (generally lower) [392]. In the case of

reactive dyes, the fixation efficiency (F) of the reactive dyes is the ratio of the rate of fixation and

the rate of hydrolysis. The higher the hydrolysis the lower will be the fixation. The F can be

described by the equation 5.4 [393] which is a modified version of the equation (5.3):

𝐹 =

Rate of exhaustion

Rate of hydrolysis=

𝑆[𝐷]𝐹√𝐷𝑘𝐹′

𝐿[𝐷]𝑆𝑘𝐻′ (5.4)

Where S is the surface area of the substrate, D is the diffusion coefficient of the dye in the

substrate and 𝑘𝐹′ and 𝑘𝐻

′ are the reaction constants for the dye fixation and hydrolysis respectively.

This implies if all the other factors remain constant, an increase in the liquor ratio will lower the

fixation efficiency of reactive dyes. The amount of dye required to achieve the given depth of

shade must thus be increased [393]. The reactive dyes with low substantivity are more sensitive to

variations in liquor ratio in comparison to dyes with high substantivity which are more robust

[144].

408

Several studies have been carried out to ascertain the effect of liquor ratio on the color

strength of dyeings using reactive and disperse dyes. It has been found that for reactive dyes that

an increase in liquor ratio lowers the exhaustion values of the dyes and the resultant depth of shade.

One study examined the effect of different liquor ratios from 15 to 50 on dyeings [394]. In another

study, it was reported that the color strength of the reactive dyes applied to mercerized fabrics was

significantly different when the liquor ratio was changed from 2 to 15 for deep shades. It was also

observed that at a lower liquor ratio the uptake was greater than at a higher liquor ratio [395]. It

has been claimed that reactive dyes containing bifunctional groups are less sensitive to liquor

variations [396]. In the case of package dyeing of polyester with disperse dyes, it was noted that

the increase in liquor ratio from 10 to 50 reduced the dyebath exhaustion. As a result, the resultant

shade depth was lower at higher liquor ratios. They also observed that combination shades, exhibit

different exhaustion rates. Therefore, the tone of the shade was also found to be different [397]. In

another study on polyester fabric a liquor ratio ranging from 6 to 12 was used. The color strength

and exhaustion rates were found to be different at different liquor ratios [398]. The influence of

liquor ratio on dyeing of cotton with reactive dyes and polyester with disperse dyes were studied

at various liquor ratios that are typically encountered in the dyeing of these materials. It has been

observed that a large change in liquor ratio leads to a significant change in the dye shade and this

behavior depends on the dye type, with some dyes exhibiting more change than the others [399].

To study the effect of liquor ratio, the same dye amounts that produced the match by the

C2B method, using dyes from Archroma as shown in Table 5.6, were applied on cotton and

polyester reference fabrics at different liquor ratios analogous to effective liquor ratios that may

be encountered in blends. The different liquor ratios used were 20, 25, 30, 40, 50, 60, 80 and 100.

The relative color yield obtained for three colors considering a liquor ratio of 20 was taken as the

reference, as shown in Figure 5.4 for reactive dyes and Figure 5.5 for disperse dyes. As can be

seen for reactive dyes the relative color yield is reduced to as low as 60% at a liquor ratio of 100

as compared to the reference liquor ratio of 20. The biggest drop is observed in the navy (63%),

followed by beige (74%) and brown (80%). Disperse dyes exhibited higher drops in yield in

comparison to reactive dyes. The beige color showed a drop in the relative color yield by 31%,

brown by 41%, and navy by 54%. This may explain why the actual dye amounts required to match

the same shade on blends are significantly greater than theoretically required. The DE*ab of the

samples corresponding to the effective liquor ratios of 30, 40, 50, 80 for polyester and 25, 30, 40,

409

60 for cotton were also measured using a liquor ratio of 20 as a reference. Polyester showed a large

color difference as compared to cotton and following the same trend as the relative color yield

discussed above. For polyester, DE*ab values were 3.4, 5.9, 8.9 and 10.9 for respective liquor to

goods ratios for the brown, 3.3, 5, 7.2, 11.1 for navy and 2.6, 3.7, 4, 6.6 for beige. In the case of

cotton, the brown showed color difference values of 0.6, 0.7, 2.1, 2.5, navy: 1.1, 1.3, 2.1, 4.3 and

beige: 1.3, 1.4, 1.4, 2.7. While the actual relative color yields may vary with different dye types,

they are likely to follow a similar trend.

Figure 5.4: The effect of liquor ratio on the relative strength of cotton dyed with reactive dyes

(Liquor ratio of 20 is taken as the reference).

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

20 25 30 40 50 60 80 100

Rel

ativ

e st

reng

th

Liquor ratio

Brown Navy Beige

410

Figure 5.5: The effect of liquor ratio on the relative strength of polyester dyed with disperse dyes

(Liquor ratio of 20 is taken as reference).

5.3.2 Light fastness

Dyed materials often fade when exposed to light for prolonged periods. The lightfastness of dyed

materials depends on many factors such as the type of dyes used, depth of shade, fabric surface,

and finishing treatment, among others. The lightfastness is mainly the property of colorant

molecule and therefore it is influenced by the selection of colorants [400]. If disperse dyes and

reactive dyes of good lightfastness are selected, good light fastness results are obtained. The dyes

selected in this study were based on the manufacturer’s recommendations to obtain good fastness

results under different dyeing methods. The disperse dyes Dianix XF/SF recommended by Dystar

for the 1B method are marketed as dyes with superior fastness properties. These dyes are based

on special chemistries indicated in Table 5.3 that enable them to provide good fastness properties

[382].

The light fastness results in the form of grey scale ratings of different dyed fabrics after

exposure to 40 AFUs are shown in Table 5.9. The CT fabric dyed with reactive dyes, in general,

showed more fading compared to PET fabric dyed with disperse dyes. With increasing the

polyester content in the blend, fading was reduced. The highest fading was observed for beige,

whereas navy and brown exhibited quite similar fading results. The fading for lighter colors was

found to be higher compared to dark colors due to the fact that smaller dye amounts are present

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

20 25 30 40 50 60 80 100

Rel

ativ

e st

reng

th

Liquor ratio

Brown Navy Beige

411

and exposed to light in the former substrate compared to darker colors where more dye molecules

are present. For the brown shade on average, the 2B method showed lower fading compared to

the R2B and 1B methods. The Archroma’s 2B method exhibited more fading as compared to other

dyeing methods used for the navy color. The light fastness results for navy color in ascending order

are Huntsman-R2B, Dystar-1B, Huntsman 2B, Dystar-2B and Archroma-2B. For the beige, a

slight change in the lightfastness ratings is observed in the case of blends depending upon the light

fastness obtained in CT and PET fabrics.

Table 5.9: Light fastness results of polyester, cotton and their blends dyed in different shade

depths.


method

Fabrics

PET PC1 PC2 PC3 PC4 CT

Brown Dystar C2B 4.5 4.5 4 3.5 3.5 3.5

Archroma C2B 4 3.5 4 4 4 4

Huntsman C2B 4.5 4 4 3.5 3.5 3.5

Huntsman R2B 4.5 4 3.5 3 3 3

Dystar 1B 4 3.5 3.5 3.5 3.5 3.5

Navy Dystar C2B 4 3.5 3.5 3.5 3 3

Archroma C2B 3.5 3.5 3.5 3.5 4 4.5

Huntsman C2B 4.5 4 4 3.5 3.5 3.5

Huntsman R2B 4 4 3.5 3.5 3 3

Dystar 1B 4 4 3.5 3.5 3.5 4

Beige Dystar C2B 3.5 3.5 3.5 3 2.5 2.5

Archroma C2B 3.5 3.5 3.5 3.5 3 3

Huntsman C2B 3.5 3.5 3 3 3 2.5

Huntsman R2B 3.5 3.5 3.5 3.5 3 3

Dystar 1B 3.5 3.5 3.5 3.5 3 3

It can be seen that fading characteristics of the dyed fabric varies with the blend, but this

change was not found to be directly related with the change in blend ratio. In some cases, the

412

lightfastness was not changed much until the blend ratio was significantly changed. The dye

selection is critical to obtain good light fastness results on blends as the resultant fading of the

dyed material is influenced by both reactive and disperse dyes used.

5.3.3 Crocking fastness

Crocking fastness involves the transfer to colorant from the dyed material to another fabric surface

by rubbing. The crock fastness depends on many factors which include the dyed substrate, rubbing

cloth, the surface of the dyed substrate and rubbing cloth, dye class, depth of shade, dyeing method,

aftertreatment process and amount of moisture present when rubbing is performed. The dry

crocking fastness results after dyeing are shown in Table 5.10. In all fabrics, the dry rubbing

fastness ratings of 5 was obtained. The wet crocking results are presented in Table 5.11. The wet

rubbing fastness of all cotton fabric was found to be inferior for all polyester fabrics in brown and

navy colors. The fastness improves with the increase in the portion of the polyester component in

the blend. In the case of beige color, no color transfer to crocking cloth was observed i.e. rating of

5 was obtained. It can be concluded that for light shades good dry and wet crocking fastness was

obtained, independent of the dyeing method and blend ratio employed.

For the brown and navy colors, good wet crock fastness results were obtained for the C2B

method as compared to the R2B and 1B methods. This is due to the fact that in the 2B method a

separate reduction clearing treatment was given as compared to the R2B and 1B methods where

no reduction clearing was performed. The results obtained in the R2B method are generally lower

than the 2B methods due to mode of treatment of disperse dyes. The reactive dyes were washed-

off at the high temperature used for the dyeing of the polyester portion of the blend. Since reduction

clearing was not performed some disperse dye may have transferred during the wet crocking test.

For the 1B however, only one soaping process was given which may increase the chances of

residual dye remaining on the surface of the fiber thus resulting in some dye transfer to the crocking

cloth.

413

Table 5.10: Dry crocking fastness of fabrics of different colors and blend ratio dyed by different

dyeing methods.


method PET PC1 PC2 PC3 PC4 CT

Brown

Dystar C2B 5 5 5 5 5 5

Archroma C2B 5 5 5 5 5 5

Huntsman C2B 5 5 5 5 5 5

Huntsman R2B 5 5 5 5 5 5

Dystar 1B 5 5 5 5 5 5

Navy

Dystar C2B 5 5 5 5 5 5




Dystar 1B 5 5 5 5 5 5

Beige

Dystar C2B 5 5 5 5 5 5




Dystar 1B 5 5 5 5 5 5

The problem of reduced wet rubbing fastness for darker colors in cotton fabrics is well

known. During the wet crocking test due to the abrasive action of crocking cloth on the dyed

substrate, small fiber particles from the dyed material are rubbed off from the fiber surface which

stain the crock cloth. As wet crocking test involves the use of a wet fabric the dye may bleed out

of the damaged fiber material and rub off on fiber particles. By selecting dyes with good fastness

properties, some improvements can be obtained. However, there is a limit to which this

improvement in crock fastness can be obtained. Since the amount of colorant rubbing off is

determined by the substrate, there is a limit to improving the wet crock fastness [401, 402]. If a

suitable dye selection is performed and good washing of dyed fabric is performed, poor crock

fastness results may be attributed to fiber damage. It has been observed that mercerized fabric

414

exhibits better wet crocking fastness than unmercerized fabric [402]. In the case of polyester fibers,

crock fastness depends on good dye selection and wash-off process. Dyes of high energy levels

exhibit high sublimation fastness and therefore they do not migrate to the surface of the fiber during

the finishing process at high temperatures. If a proper reduction clearing treatment is given to the

dyed fabric or dyes with good wash off properties that can be washed-off in alkaline conditions

without a reduction clearing are selected, good crock fastness can be obtained. It can be concluded

that lower wet crock fastness in polyester/cotton fabrics in dark shades is due to the cotton portion

of the blend. As the cotton portion of the blend decreases, an improvement in wet crocking fastness

is attained.

Table 5.11: Wet crocking fastness results of polyester, cotton and their blends.


method PET PC1 PC2 PC3 PC4 CT

Brown

Dystar C2B 5 5 4.5 4.5 4.5 4

Archroma C2B 5 5 5 5 4.5 4

Huntsman C2B 5 5 5 4.5 4.5 4

Huntsman R2B 5 4.5 4.5 4.5 4.5 4

Dystar 1B 5 5 4.5 4.5 4.5 4

Navy

Dystar C2B 5 5 5 4.5 4.5 4

Archroma C2B 5 5 5 4.5 4.5 4

Huntsman C2B 5 4.5 4.5 4.5 4.5 4

Huntsman R2B 4.5 4.5 4.5 4.5 4.5 4

Dystar 1B 5 5 4.5 4.5 4.5 4

Beige

Dystar C2B 5 5 5 5 5 5




Dystar 1B 5 5 5 5 5 5

415

5.3.4 Washing fastness

Color fastness to washing is one of the important quality parameters in polyester/cotton dyed

materials. The test determines the change in color of the dyed substrate and staining of the

multifiber fabric in the washing process. Improper dye fixation or presence of unfixed dye on the

fiber surface at the end of the dyeing process reduces the wash fastness [383]. Table 5.12 and

Figure 5.6 show the color change and staining results after the washing test. Very good wash

fastness results were obtained for the beige color which is found to be independent of the blend

ratio and the dyeing method used. This may be attributed to the lower concentration of dyes present

on the substrate in this case, the use of dyes with good fastness properties and the reduction clearing

performed in the C2B methods. Good to moderate color change and staining ratings were obtained

for the brown and navy colors. The polyester and polyester rich fabrics in general exhibited better

results compared to the cotton and cotton rich fabrics in the 2B methods. This may be attributed

to the reduction clearing performed in the 2B methods as shown in Figure 5.1. Similar results were

obtained in the 1B method except the color change ratings were slightly worse for the PC2 fabric

for the brown and for the PC2 and PC3 fabrics for the navy shade when compared to the 2B

methods. The good results of the 1B method are due to the use of disperse dyes with good wash-

off properties which do not require a reduction clearing process. These dyes contain alkali soluble

groups which make them easy to wash off during the reactive dyeing of cotton [87, 382]. On the

other hand, interesting results were obtained in the R2B method. Cotton fabrics exhibited better

fastness properties compared to polyester and polyester/cotton blended fabrics. Since the cotton

portion was dyed first followed by polyester dyeing and since no reduction clearing was

performed, these results could be expected. The hydrolyzed and unfixed reactive dyes are removed

due to the high temperature conditions involved in the disperse dyeing section of the process. Since

no reduction clearing is possible in this method, the fastness properties are compromised due to

disperse dye stains present on cotton and dye residues on the polyester surface.

The nylon staining results for the navy color dyed by different dyeing methods are shown

in Figure 5.7. The staining of nylon and acetate fibers with disperse dyes in the wet fastness test is

well known. Good dye selection and the use of two bath method with a reduction clearing can

minimize the staining tendency [9, 383]. Increased staining of nylon was observed in blends due

to the disperse dyes present on cotton. The reverse 2B method showed more staining than other

methods. Figure 5.8 shows the cotton staining results of the navy dyed fabrics. Reactive dyes tend

416

to stain wool and cotton fabric during wet fastness tests. Unfixed and hydrolyzed reactive dyes

may also stain the cotton portion of the multifiber strip. The use of dyes with a high fixation yield

and good fastness properties along with adequate washing of unfixed dyes is essential to attain

good fastness results.

Table 5.12: Wash fastness properties of dyed polyester, cotton and polyester/cotton fabrics.

Color Supplier Dyeing

method Fabric

Shade

change

Staining

Wo PAN PES PA Co Ac

Brown

Dystar

C2B

PET 4.5 4.5 4.5 4.5 4 4.5 4.5

PC1 4.5 4.5 4.5 4.5 3.5 4.5 4

PC2 4.5 4.5 4.5 4.5 3.5 4.5 4.5

PC3 4.5 4.5 4.5 4.5 4 4 4.5

PC4 4 4 4.5 4.5 4.5 4 4.5

CT 4 4 4.5 4.5 4.5 4 4.5

Archroma

C2B

PET 4.5 4.5 4.5 4.5 4 4.5 4

PC1 4.5 4.5 4.5 4.5 3.5 4.5 4

PC2 4.5 4.5 4.5 4.5 4 4.5 4.5

PC3 4 4.5 4.5 4.5 4.5 4 4.5

PC4 4 4.5 4.5 4.5 4.5 4 4.5

CT 4 4 4.5 4.5 4.5 4 4.5

Huntsman

C2B

PET 4.5 4.5 4.5 4.5 4 4.5 4

PC1 4.5 4.5 4.5 4.5 3.5 4.5 4.5

PC2 4.5 4.5 4.5 4.5 4 4.5 4.5

PC3 4 4.5 4.5 4.5 4.5 4 4.5

PC4 4 4 4.5 4.5 4.5 4 4.5

CT 4 4.5 4.5 5 4.5 4 4.5

Huntsman

R2B

PET 4 4.5 4.5 4.5 4 4.5 4

PC1 4 4.5 4.5 4.5 4 4.5 4

PC2 4 4.5 4.5 4.5 3 4.5 4.5

417



method Fabric

Shade

change

Staining

Wo PAN PES PA Co Ac

PC3 4.5 4.5 4.5 4.5 3.5 4.5 4.5

PC4 4.5 4.5 4.5 4.5 4 4.5 4.5

CT 4.5 4.5 4.5 4.5 4.5 4 4

Dystar

1B

PET 4.5 4.5 4.5 4 4 4.5 4

PC1 4.5 4.5 4.5 4.5 4 4.5 4.5

PC2 4 4.5 4.5 4.5 4.5 4 4.5

PC3 4 4.5 4.5 4.5 4.5 4 4.5

PC4 4 4.5 4.5 4.5 4.5 4 4.5

CT 4 4 4.5 4.5 4.5 4 4.5

Navy

Dystar

C2B

PET 4.5 4.5 4.5 4 4 4.5 4

PC1 4.5 4.5 4.5 4 4 4.5 4

PC2 4.5 4.5 4.5 4.5 3.5 4.5 4

PC3 4.5 4 4.5 4.5 4 4.5 4.5

PC4 4.5 4 4.5 4.5 4.5 4 4.5

CT 4 4 4.5 4.5 4.5 4 4.5

Archroma

C2B

PET 4.5 4.5 4.5 4.5 4 4.5 4

PC1 4.5 4.5 4.5 4.5 3.5 4.5 4

PC2 4.5 4.5 4.5 4.5 4 4.5 4.5

PC3 4.5 4.5 4.5 4.5 4.5 4 4.5

PC4 4 4.5 4.5 4.5 4.5 4 4.5

CT 4 4 4.5 4.5 4.5 4 4.5

Huntsman

C2B

PET 4.5 4.5 4.5 4.5 4 4.5 4

PC1 4.5 4.5 4.5 4.5 4 4.5 4.5

PC2 4.5 4.5 4.5 4.5 3.5 4.5 4.5

PC3 4.5 4.5 4.5 4.5 4 4 4.5

PC4 4.5 4 4.5 4.5 4.5 4 4.5

CT 4 4.5 5 5 4.5 4 4.5

418



method Fabric

Shade

change

Staining

Wo PAN PES PA Co Ac

Huntsman

R2B

PET 4 4 4.5 4.5 4 4.5 4.5

PC1 4 4 4.5 4 3 4.5 3

PC2 4 3.5 4.5 4.5 3.5 4.5 4

PC3 4.5 4 4.5 4.5 3.5 4.5 3.5

PC4 4.5 4 4.5 4.5 4 4.5 4.5

CT 4.5 4 4.5 4.5 4.5 4.5 4.5

Dystar

1B

PET 4.5 4.5 4.5 4.5 4 4.5 4

PC1 4.5 4.5 4.5 4.5 4 4.5 4

PC2 4 4.5 4.5 4.5 3.5 4.5 4

PC3 4 4.5 4.5 4.5 3.5 4.5 4.5

PC4 4 4.5 4.5 4.5 4.5 4.5 4.5

CT 4 4 4.5 4.5 4.5 4 4.5

Beige

Dystar

C2B

PET 5 4.5 4.5 4.5 4.5 4.5 4.5

PC1 5 4.5 4.5 4.5 4.5 4.5 4.5

PC2 5 4.5 4.5 4.5 4.5 4.5 4.5

PC3 5 4.5 4.5 4.5 4.5 4.5 4.5

PC4 5 4.5 4.5 4.5 4.5 4.5 4.5

CT 5 4.5 4.5 4.5 4.5 4.5 4.5

Archroma

C2B

PET 5 4.5 4.5 4.5 4.5 4.5 4.5

PC1 5 4.5 4.5 4.5 4.5 4.5 4.5

PC2 5 4.5 4.5 4.5 4.5 4.5 4.5

PC3 5 4.5 4.5 4.5 4.5 4.5 4.5

PC4 5 4.5 4.5 4.5 4.5 4.5 4.5

CT 5 4.5 4.5 4.5 4.5 4.5 4.5

Huntsman

C2B

PET 5 4.5 4.5 4.5 4.5 4.5 4.5

PC1 5 4.5 4.5 4.5 4.5 4.5 4.5

PC2 5 4.5 4.5 4.5 4.5 4.5 4.5

419



method Fabric

Shade

change

Staining

Wo PAN PES PA Co Ac

PC3 5 4.5 4.5 4.5 4.5 4.5 4.5

PC4 5 4.5 4.5 4.5 4.5 4.5 4.5

CT 5 4.5 4.5 4.5 4.5 4.5 4.5

Huntsman

R2B

PET 5 4.5 4.5 4.5 4.5 4.5 4.5

PC1 5 4.5 4.5 4.5 4.5 4.5 4.5

PC2 5 4.5 4.5 4.5 4.5 4.5 4.5

PC3 5 4.5 4.5 4.5 4.5 4.5 4.5

PC4 5 4.5 4.5 4.5 4.5 4.5 4.5

CT 5 4.5 4.5 4.5 4.5 4.5 4.5

Dystar

1B

PET 5 4.5 4.5 4.5 4.5 4.5 4.5

PC1 5 4.5 4.5 4.5 4.5 4.5 4.5

PC2 5 4.5 4.5 4.5 4.5 4.5 4.5

PC3 5 4.5 4.5 4.5 4.5 4.5 4.5

PC4 5 4.5 4.5 4.5 4.5 4.5 4.5

CT 5 4.5 4.5 4.5 4.5 4.5 4.5

420

Figure 5.6: Color change ratings for the navy blue color dyed fabrics after the washing test.

Figure 5.7: Nylon staining results for the navy blue color dyed fabrics.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

PES PC6535 PC5050 PC4060 PC2575 CO

Gre

y s

cale

rat

ing

Fiber proportion

Dystar-C2B

Archroma-C2B

Huntsman-C2B

Huntsman-R2B

Dystar-1B

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

PES PC6535 PC5050 PC4060 PC2575 CO

Gre

y s

cale

rat

ing

Fiber proportion

Dystar-C2B

Archroma-C2B

Huntsman-C2B

Hunstman-R2B

Dystar-1B

421

Figure 5.8: Cotton staining results of the navy blue color dyed fabrics.

5.3.5 Water fastness

Water fastness measures the transfer of color from a dyed fabric to the adjacent fiber when dipped

in water or under moist conditions. The two materials are in immediate contact with each other.

This test is a useful measure to assess the presence of loose color in the material. The staining

results of the multifiber fabric after the water fastness ratings of the dyed materials are given in

Table 5.13. Very good water fastness results were observed for the beige color with slight or no

staining of the multifiber fabric. All fibers in the multifiber fabric showed a rating of 4.5 for all

fabrics and dyeing methods used. The brown and navy colors showed moderate to good water

fastness ratings. As expected, the polyester and polyester rich fabrics showed staining of nylon in

the multifiber strip and in some cases, staining of polyester and acetate fibers was also observed

[9]. The staining of the nylon fiber component was found to be heavier in blends compared to

100% polyester fabric. The cotton and wool staining were observed in all fabrics which was

reduced as the polyester component of the blend was increased. Good results were obtained in the

C2B method as compared to the R2B method. Since no reduction was performed and thus disperse

dye stains were not properly removed in the R2B method, the nylon staining was found to be

heavier in the blend fabrics during the wash fastness test. The extra reduction clearing process

performed in the C2B method is designed to remove the loose surface disperse dyes thus improving

the fastness property of the dyed substrate. Good fastness results were obtained in the 1B method,

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

PES PC6535 PC5050 PC4060 PC2575 CO

Gre

y s

cale

rat

ing

Fiber proportion

Dystar-C2B

Archroma-C2B

Huntsman-C2B

Huntsman-R2B

Dystar-1B

422

which may be attributed to the use of dyes with very good fastness properties. These dyes do not

require reduction clearing and can be easily removed in the alkaline conditions employed for a

cotton dyeing portion of the blend [87, 382].

Table 5.13: Water fastness of dyed polyester/cotton fabrics with different blend contents.


method Fabric

Staining

Wo PAN PES PA Co Ac

Brown

Dystar

C2B

PET 4.5 4.5 4 4 4.5 4

PC1 4.5 4.5 4.5 3.5 4.5 4.5

PC2 4.5 4.5 4.5 3.5 4.5 4.5

PC3 4.5 4.5 4.5 4 4 4.5

PC4 4.5 4.5 4.5 4 4 4.5

CT 4 4.5 4.5 4.5 3.5 4.5

Archroma

C2B

PET 4.5 4.5 4.5 4 4.5 4

PC1 4.5 4.5 4.5 3.5 4.5 4.5

PC2 4.5 4.5 4.5 4 4.5 4.5

PC3 4.5 4.5 4.5 4 4 4.5

PC4 4.5 4.5 4.5 4.5 4 4.5

CT 4 4.5 4.5 4.5 3.5 4.5

Huntsman

C2B

PET 4.5 4.5 4.5 4 4.5 4

PC1 4.5 4.5 4.5 3.5 4.5 4

PC2 4.5 4.5 4.5 4 4.5 4.5

PC3 4.5 4.5 4.5 4 4 4.5

PC4 4.5 4.5 4.5 4.5 4 4.5

CT 4 4.5 4.5 4.5 3.5 4.5

Huntsman

R2B

PET 4.5 4.5 4.5 3.5 4.5 3.5

PC1 4.5 4.5 4.5 3 4.5 4

PC2 4.5 4.5 4.5 3 4.5 4

PC3 4.5 4.5 4.5 3.5 4 4.5

PC4 4.5 4.5 4.5 4 4 4.5

423



method Fabric

Staining

Wo PAN PES PA Co Ac

CT 4 4.5 4.5 4.5 3.5 4.5

Dystar

1B

PET 4.5 4.5 4.5 4 4.5 4.5

PC1 4.5 4.5 4.5 4 4.5 4.5

PC2 4.5 4.5 4.5 3.5 4.5 4.5

PC3 4.5 4.5 4.5 3.5 4 4.5

PC4 4 4.5 4.5 4 3.5 4.5

CT 4 5 4.5 4.5 3 4.5

Navy

Dystar

C2B

PET 4.5 4.5 4.5 4 4.5 4

PC1 4.5 4.5 4.5 3.5 4.5 4

PC2 4.5 4.5 4.5 3.5 4.5 4.5

PC3 4.5 4.5 4.5 4 4.5 4.5

PC4 4.5 4.5 4.5 4.5 4 4.5

CT 4 4.5 4.5 4.5 3.5 4.5

Archroma

C2B

PET 4.5 4.5 4.5 3.5 4.5 4

PC1 4.5 4.5 4.5 3.5 4.5 4.5

PC2 4.5 4.5 4.5 4 4.5 4.5

PC3 4.5 4.5 4.5 4.5 4.5 4.5

PC4 4.5 4.5 4.5 4.5 4 4.5

CT 4 4.5 4.5 4.5 3 4.5

Huntsman

C2B

PET 4.5 4.5 4.5 3.5 4.5 4

PC1 4.5 4.5 4.5 3.5 4.5 4

PC2 4.5 4.5 4.5 4 4.5 4.5

PC3 4.5 4.5 4.5 4 4.5 4.5

PC4 4.5 4.5 4.5 4.5 4 4.5

CT 4.5 4.5 4.5 4.5 4 4.5

Huntsman

R2B

PET 4.5 4.5 4.5 3.5 4.5 3.5

PC1 4.5 4.5 4.5 3 4.5 4

424



method Fabric

Staining

Wo PAN PES PA Co Ac

PC2 4.5 4.5 4.5 3 4.5 4

PC3 4.5 4.5 4.5 3.5 4.5 4.5

PC4 4.5 4.5 4.5 4 4 4.5

CT 4.5 4.5 4.5 4 4 4.5

Dystar

1B

PET 4.5 4.5 4.5 4 4.5 4.5

PC1 4.5 4.5 4.5 4 4.5 4.5

PC2 4.5 4.5 4.5 3.5 4.5 4.5

PC3 4.5 4.5 4.5 3.5 4.5 4.5

PC4 4.5 4.5 4.5 4 4.5 4.5

CT 4.5 4.5 4.5 4.5 4.5 4.5

Beige

Dystar

C2B

PET 4.5 4.5 4.5 4.5 4.5 4.5

PC1 4.5 4.5 4.5 4.5 4.5 4.5

PC2 4.5 4.5 4.5 4.5 4.5 4.5

PC3 4.5 4.5 4.5 4.5 4.5 4.5

PC4 4.5 4.5 4.5 4.5 4.5 4.5

CT 4.5 4.5 4.5 4.5 4.5 4.5

Archroma

C2B

PET 4.5 4.5 4.5 4.5 4.5 4.5

PC1 4.5 4.5 4.5 4.5 4.5 4.5

PC2 4.5 4.5 4.5 4.5 4.5 4.5

PC3 4.5 4.5 4.5 4.5 4.5 4.5

PC4 4.5 4.5 4.5 4.5 4.5 4.5

CT 4.5 4.5 4.5 4.5 4.5 4.5

Huntsman

C2B

PET 4.5 4.5 4.5 4.5 4.5 4.5

PC1 4.5 4.5 4.5 4.5 4.5 4.5

PC2 4.5 4.5 4.5 4.5 4.5 4.5

PC3 4.5 4.5 4.5 4.5 4.5 4.5

PC4 4.5 4.5 4.5 4.5 4.5 4.5

425



method Fabric

Staining

Wo PAN PES PA Co Ac

CT 4.5 4.5 4.5 4.5 4.5 4.5

Huntsman

R2B

PET 4.5 4.5 4.5 4.5 4.5 4.5

PC1 4.5 4.5 4.5 4.5 4.5 4.5

PC2 4.5 4.5 4.5 4.5 4.5 4.5

PC3 4.5 4.5 4.5 4.5 4.5 4.5

PC4 4.5 4.5 4.5 4.5 4.5 4.5

CT 4.5 4.5 4.5 4.5 4.5 4.5

Dystar

1B

PET 4.5 4.5 4.5 4.5 4.5 4.5

PC1 4.5 4.5 4.5 4.5 4.5 4.5

PC2 4.5 4.5 4.5 4.5 4.5 4.5

PC3 4.5 4.5 4.5 4.5 4.5 4.5

PC4 4.5 4.5 4.5 4.5 4.5 4.5

CT 4.5 4.5 4.5 4.5 4.5 4.5

Figure 5.9: Grey scale rating for staining of nylon for the brown color after water fastness test.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

PES PC6535 PC5050 PC4060 PC2575 CO

Gre

y s

cale

rat

ing

Fiber proportion

Dystar-C2B

Archroma-C2B

Huntsman-C2B

Huntsman-R2B

Dystar-1B

426

Figure 5.10: Grey scale rating for staining of cotton for the brown color after water fastness test.

5.4 Conclusions

The dyeing properties of polyester/cotton fabrics at different blend ratios along with cotton as well

as polyester only fabrics, used as a reference, were examined. Three target colors, namely navy,

brown and beige were matched as typical examples of different shades encountered in practice. It

was found that the color yield of disperse and reactive dyes are reduced in blends compared to

when they are applied to polyester and cotton only fabrics respectively. This is attributed to a

change in the effective liquor to goods ratio available for each fiber in the blend which can vary

significantly.

It was found that the fastness properties of dyed material vary for different blend ratios and

in some cases nylon staining was found to be inferior for the reference polyester fabrics used in

this study. The actual variation in the light fastness of dyed substrates with a change in the blend

ratio was found to be dependent on the dye class used. When the light fastness of the dyed sample

was better for the cotton only reference fabric compared to the polyester only fabric, increasing

the proportion of the polyester component would lead to a reduction of the light fastness of the

blend. The light fastness did not vary much with a change in the dyeing method. Among the three

target shades examined, the lightfastness was found to be inferior for the beige as compared to

brown and navy colors due to a smaller amount of colorant present on that fabric which was

expected.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

PES PC6535 PC5050 PC4060 PC2575 CO

Gre

y s

cale

rat

ing

Fiber proportion

Dystar-C2B

Archroma-C2B

Huntsman-C2B

Huntsman-R2B

Dystar-1B

427

All the fabrics in this study exhibited very good dry crocking fastness properties. The wet

crocking was found to be inferior for cotton and cotton rich blends. The two-bath process exhibited

better crocking results than the reverse two-bath process due to employing a separate reduction

clearing step. The wet crock fastness of the substrates from the one bath process was also found to

be good due to the use of disperse dyes with good fastness properties.

Good water and washing fastness results were obtained for the beige color which showed

almost no dye transfer to the multifiber test strip. The staining of nylon was found to be worse for

blends compared to 100% polyester fabric. However, higher levels of cotton and wool staining

were observed as the cotton content of the blend was increased in fabrics. The reverse two-bath

process showed lower fastness properties compared to the two-bath process.

The color fastness requirements for polyester/cellulosic blends can vary greatly depending

upon their intended end-use. It is difficult to generalize trends obtained from the fastness results

obtained in this study. The fastness properties of the polyester depend on a large number of factors

which include the depth of shade, dye selection, dyeing methods used, blend ratio and post

treatments employed. Good dye selection and proper washing-off are essential to ensure good

fastness results. The fastness results obtained under one set of conditions and a dyeing method

may not be applicable to another dyeing method or for a change in the depth of shade. It can be

said, however, that the blending ratio has an influence on the fastness properties of the blends. The

results obtained from this study on 100% cotton and 100% polyester fabrics may not necessarily

be applicable to polyester/cotton blends.

428

CHAPTER 6 DESIGN AND DEVELOPMENT OF AN EXPERT

SYSTEM

6.1 Experts and expert systems

An expert is a person who is recognized as a reliable source of knowledge, technique or skill in a

specific domain and whose judgment is considered to be the authority by the public or people in a

particular area. Human experts acquire knowledge and skills based on research, experience,

occupation or education in a specialized area. Expertise consists of characteristics, skills, and

knowledge that distinguishes an expert from the others in the same domain and reason for their

superior performance [403, 404]. The characteristics of an expert are summarized in Table 6.1

[405]. These characteristics describe the ways in which experts are different from novices [405].

Table 6.1: Characteristics of experts.

Strengths Shortcomings

▪ Generating the best response fast and

accurately.

▪ Accurate detection and recognition ability.

▪ Ability to do qualitative analyses.

▪ More accurate self-monitoring skills to

detect errors and status of their

understanding.

▪ Ability to choose specific strategies.

▪ Opportunistic in using resources to solve

problems.

▪ Ability to retrieve domain knowledge in

minimal cognitive effort.

▪ Expertise is domain limited.

▪ Overly confident.

▪ Glossing over.

▪ Context-dependence within a domain.

▪ Inflexible.

▪ Inaccurate prediction, judgment, and advice

under uncertainty.

▪ Bias and functional fixedness.

429

Expert systems fall under the category of artificial intelligence, which is a branch of

computer science that deals with the design and development of programs that simulate the

reasoning of humans. The expert system mimics an expert’s cognitive activities to reduce the time

and money associated with complex problem-solving. A comparison of the expert system with the

human expert is given in Table 6.2 [16, 406, 407].

Table 6.2: Human expert versus the expert system.

Factors Human Expert Expert System

Availability Workday Always

Geographic constraints Local Anywhere

Security Irreplaceable Replaceable

Perishable/consumable Yes No

Performance Variable Consistent

Speed Variable Consistent

Cost High Reasonable

Ability to explain Depends Yes

Flexibility No Yes

Meta-knowledge Yes No

An expert system is a computer program that uses knowledge and inference procedures to

solve complex problems or give advice in a specific domain at a high level of expertise. The

purpose of developing an expert system is to make a computer system that can act similar to a

human expert in relevant respects. An expert system may be used as a direct replacement of a

human expert or can be used as an assistant to help in the decision-making process where it can be

directly used by an expert to increase their productivity. Alternatively, expert systems can help a

person to generate responses at a level of performance similar to that of an expert. Expert systems

are designed to solve the problem in a specific domain called problem domain like human experts.

The expertise of the expert system is derived from the knowledge it possesses, known as the

knowledge domain. In order to come up with a solution to the problem, expert systems make

inferences. The inference is based on information about the problem (facts) and a series of rules

430

which are either satisfied or not (knowledge base) [13, 16]. Expert systems are built by knowledge

engineers.

6.2 Benefits of expert systems

An expert system can provide several benefits which are given below [16]:

▪ Availability: The expert system is a computer program that is stored on a computer. It

is available at any time irrespective of geographic location.

▪ Reasonable cost: The cost of expertise per user is usually less for expert systems. Once

an expert system is developed it can be mass-produced.

▪ Permanent: The expertise provided by the expert system is not “typically” perishable

and can last for a long time.

▪ Multiple expertise: The expert system is usually developed by combining expertise

from multiple experts. Its’ performance may be better than a single expert.

▪ Reliability: Expert systems provide the second opinion and increase the confidence of

the decision. An expert can make a mistake due to fatigue or stress, whereas the same

level of reliable expertise can be provided by the expert system.

▪ Explanation: The expert system can have an explanation facility to provide reasons and

explanation for reaching a specific conclusion.

▪ Quick response: Since the expert system is available at all times, the response times

may be faster especially in emergency situations.

▪ Consistency: The expert system provides consistent responses at all times irrespective

of the time of the day or situation.

▪ Learning tool: The expert system can be used as a learning tool by novice users.

▪ Intelligent database: The expert system can be used to retrieve information from the

database in an intelligent manner. It can also store information related to a specific

problem and can be recalled when required.

6.3 Domains of expert system

Over the years various expert systems dealing with different problems have been developed. They

have been widely used in many areas to perform different tasks. They are used as a research tool

431

or to perform various business and industrial functions. The typical tasks performed by expert

systems range from inferring information to predicting, repairing, and monitoring system

behaviors. Table 6.3 shows the broad classes of expert systems based on their functionality [13,

16, 408].

Table 6.3: Categories of expert systems.

Type Areas

Interpretation Ascertain information about the situation from the given data.

Prediction Inferring likely outcome from given situations.

Diagnosis Determining the causes of the specific problem from observations.

Design Devising objects satisfying specific requirements.

Planning Design actions for a certain course.

Monitoring Comparing system behavior to predict flaws in the planned outcomes.

Debugging Providing probable solutions for a specific problem.

Repair Executing the plan to monitor the prescribed solution.

Instruction Determining causes and providing solutions to student behaviors.

Control Governing overall behavior of the system by interpretation,

formulation, and monitoring.

6.4 Application of expert systems in the textile industry

The use of expert systems in the textile industry is not new and many expert systems have been

developed in the past that cover an entire field of textiles such as fibers, spinning, weaving, knitting

and dyeing. The initial expert system applications were introduced in 1987 at ITMA held in Paris.

Examples of different expert systems developed for specific textile domains and their brief

descriptions are given in Table 6.4. The broad category in which these expert systems fall and the

year of their development are also given. Almost all of these systems have been developed keeping

into consideration a single fiber type.

The problems and issues mentioned about the human expert and the troubleshooting

process have motivated our group to develop a comprehensive expert system for the diagnosis of

432

faults in the coloration industry. Several expert systems have been developed by our group in the

past. These include an expert system for the diagnosis of problems in the coloration of cotton

(DEXPERT) [409], polyester (DEXPERT-P) [410], ink-jet printing (INKJETEXPERT) [411] and

protein fibers (Dexpert-PT) [412] for various types of textiles, including yarns, woven and knitted

constructions. All of these systems were developed by a rule-based approach using wxCLIPS, a

modified version of clips with GUI functionality.

DEXPERT was developed for troubleshooting problems in the dyeing of cotton yarn and

fabrics with direct, reactive, vat, sulfur and azoic dyes. The system is capable of diagnosing a total

of 132 faults comprising pretreatment and dyeing faults along with explanations and suggestions

for corrective and preventive actions [409].

An expert system for diagnosing problems in the coloration of polyester material was

developed in 2009. DEXPERT-P can troubleshoot issues in the dyeing of the polyester material in

yarn, knitted or woven fabrics with disperse dyes for different dyeing methods. A total of total 14

faults and 116 associated causes originating from fiber, yarn, fabric, pretreatment, dyestuff, water,

dyeing bath, auxiliary, machinery and post dyeing operations are identified and coded to build this

expert system [410].

In order to troubleshoot problems associated with ink-jet printing of cotton fabric an expert

system, INKJETEXPERT, was developed. This system examines 13 faults and 61 causes to

diagnose a wide range of problems in ink-jet printing process [411].

More recently, an expert system for troubleshooting problems in the dyeing of protein

fibers, Dexpert-PT, for fibers, yarns, fabrics or garments was developed. Twelve protein fibers

were covered in the system which include alpaca, camel, cashmere, guanaco, llama, mohair,

muskox, rabbit, silk, vicuna, wool, and yak. A list of 16 faults and their causes originated from

raw materials, yarn and fabric formation, pretreatment and water was created and incorporated into

the program [412].

433

Table 6.4: Summary of the expert systems developed for textiles.

Area Expert

system class Description Year Ref.

Fiber Classification Color grading of cotton. 1999 [413]

Spinning Monitoring

and planning

Evaluation of spinning technique, costing, and

prediction of yarn characteristics.

1990 [414]

Drafting Planning and

prognosis

Determination of optimum pin settings for gill

drafting.

1991 [415,

416]

Spinning Planning and

prognosis

Prediction of the characteristics of the yarn

based on fiber properties or vice versa.

1996 [417]

Filament

spinning

Diagnosis and

monitoring

On-line diagnosis of faults during the spinning

of filament yarns.

1996 [418]

Rotor

spinning

Planning and

prognosis

Selection of optimum machine settings and

rotor spinning machine parts according to end-

use (COROSULT), Schlafhorst.

1991 [419]

Weaving Diagnosis Identification of causes responsible for

excessive warp stops and end breaks in

weaving (WEBAS).

1985 [420]

Dyeing of

wool

Planning and

prognosis

Determination of fastness requirements,

processing rate, dye selection, and recipe in

the dyeing of wool (WOOLY), Sandoz.

1991 [421-

423]

Finishing Planning Optimization of textile finishing recipes and

their performance (TEXPERTO), Sandoz.

1992 [424]

Finishing Planning and

diagnosis

Process optimization and troubleshooting in

the dyeing of various fiber materials

(OPTIMIST), BASF.

1988 [423,

425]

Pretreatment Planning Recipe selection in the pretreatment of cotton

fabric (PREMATIC), Ciba-Geigy.

1988 [423,

426]

434


Area Expert

system class

Description Year Ref.

Dyeing Planning Determination of dye recipe and behavior of dyes

according to fiber and dyebath variables (IGCS

Expert system).

1989 [427,

428]

Dye recipe Planning Generation of the dye recipe for continuous

dyeing of cotton and cotton/polyester by pad

steam method (BAFAREX), BASF.

1992 [429]

Exhaust

dyeing

Planning and

prognosis

Prediction of dyeing behavior of disperse dyes

and compatibility index for polyester.

Recommendation of process parameters.

2001 [430]

Exhaust

dyeing

Planning and

prognosis

Determination of optimized dyeing profile and

compatibility index for dyeing of polyamide with

acid dyes.

2002 [431]

Color

matching

Planning and

prognosis

Expert system for the generation of color

formulation for dyeing (SmartMatch), Datacolor.

1995 [432,

433]

Color

matching

Planning and

prognosis

Expert system for color matching in dyeing and

printing. Correct dye combinations based on

compatibility, fastness, environmental

considerations, and cost, (COLPOCA), Ciba.

2000 [434,

435]

Fluorescen

t whiteners

Planning and

prognosis

Selection of suitable fluorescent whitening agent

based on whiteness requirement, shade and

application method.

1991 [436]

Wet

processing

Diagnosis Expert system for the diagnosis of defects in

woven fabrics. Faults were divided into five main

fault categories, the system suggests tests and

investigations determine the precise cause of a

defect, (TESS), EMPA.

1992-

1998

[437-

439]

435


Area Expert

system class

Description Year Ref.

Dyeing Planning and

prognosis

Expert system for optimizing dyeing process,

process recommendations, recipe calculations and

problem-solving, different modules for PES, PA,

PAN, WO, and CO fibers, (Optidye), Dystar.

1999 [440]

6.5 Components of an expert system

An expert system consists of different elements which are shown in Figure 6.1. They are briefly

described as follows [16]:

▪ Knowledge base: It contains the domain knowledge represented in the form of rules. In

a rule-based system knowledge base is also known as production memory.

▪ Inference engine: It draws conclusions from the knowledge base. It takes existing

information in the knowledge base and information provided by the end-user to reach

a conclusion. It determines which rules are satisfied, orders the satisfied rules and

executes the rules based on their priority. The prioritized list of rules created by the

inference engine is known as an agenda. The global database of facts is stored in the

working memory.

▪ User interface: It provides communication between the end-user and the expert system.

The end-user provides process and problem-specific information to the expert system

to get advice on how to solve the particular problem.

▪ Explanation facility: It provides justification and reasoning for the conclusion(s)

provided by the expert system.

▪ Knowledge acquisition: It allows the knowledge engineer to interact with the system

and make some changes or add new information into the system.

A rule-based expert system can use two different methods for inference which are as

follows [16]:

436

▪ Backward chaining system: This system assumes the likely hypothesis and then works

backward to collect the information and evidence (facts) required to support the

conclusion. Expert systems developed for planning often use a backward chaining

system.

▪ Forward chaining system: It gathers evidence and information (facts) to reach the

conclusion. Expert systems used for diagnosis are often based on a forward chaining

system.

Figure 6.1: Components of an expert system [16].

The main goal of the current project is to develop an expert system for troubleshooting

problems in the coloration of PES/CELL blends (DEXPERT-B). DEXPERT-B can help practical

and novice dyers obtain a quick resolution to common problems by identifying causes and

recommending associated solutions.

6.6 Knowledge base

Knowledge base (KB) is the major part of an expert system which contains a comprehensive

collection of domain knowledge. It contains data (facts) and rules that use those facts as the basis

of decision making. The knowledge base of an expert system is a combination of expertise and

KNOWLEDGE BASE

Rules

INFERENCE ENGINE

Agenda

WORKING MEMORY

facts

EXPLANATION SUBSYSTEM

USER INTERFACE

KNOWLEDGE ACQUISITION

PROCESS AND PROBLEM RELATED

INFORMATION

437

knowledge obtained from books, technical reports, journals, etc. The expertise contains the

symbolic representation of the expert’s factual and heuristic knowledge. It represents what the

expert has learned in schools and through many years of experience in their specialized field. The

person responsible for the development of KB is called knowledge engineer and the process is

called knowledge engineering. Knowledge engineering is a process of acquiring knowledge from

experts or other sources and coding it in the expert system. The process of knowledge engineering

continues until the system’s performance is found to be satisfactory in comparison to the expert’s

knowledge [16]. Figure 6.2 shows a schematic of building a knowledgebase.

Figure 6.2: Schematic of developing knowledgebase by a knowledge engineer.

The knowledge base for DEXPET-B was developed in three stages. The first stage led to

the development of a list of most common problems in the coloration of PES/CO. In the second

stage, the most common causes responsible for these faults were identified. A cause and effect

diagram was produced for the systematic arrangement of causes. In the third stage, an electronic

survey was created and distributed to experts to determine the relationship between the causes and

the problems in the form of certainty values. The certainty factors ranged from 0-10 where 0

represents no relationship between the cause and symptom and 10 represents the cause is the main

source of the problem. The responses collected from expert were analyzed to develop the

knowledge base.

438

6.6.1 Selection of most common coloration faults

The first task in the development of a knowledge base for DEXPERT-B was to determine and

categorize the frequent faults in the coloration of polyester/cellulosic blends. A list of potential

faults was generated through literature review and discussions with the dyeing personnel in

different companies. The list was modified based on the feedback from several dyeing experts and

dye manufacturers. The final list comprising 18 faults in coloration of PES/CELL blends is given

in Figure 6.3.

S1 Reproducibility

S2 Unlevelness

S3 Streaks, stripes or bands

S4 Poor color yield

S5 Change of shade

S6 Inadequate fastness

a. Inadequate rubbing fastness

b. Inadequate water fastness

c. Inadequate washing fastness

d. Inadequate light fastness

e. Inadequate dry-cleaning fastness

S7 Dark stains or spots

S8 Light stains or spots

S9 Lengthwise shade variation

S10 Widthwise shade variation

S11 Shade variation within layers

S12 Two sidedness

S13 Reduced strength

S14 Irregular surface appearance

S15 Holes or tears

S16 Poor hand

S17 Poor dimensional stability

S18 Coating of rollers

Figure 6.3: A list of common faults in the coloration of polyester/cellulosic blends.

439

The faults are briefly described in the following section.

6.6.1.1 Reproducibility

Reproducibility or “right-first-time” in a dyeing process refers to the production of dyed material

within the tolerance limits at the end of the first process without any additions or reprocessing [61,

142]. In simple terms, it is the consistency of the dyeing process to produce the target color in the

first attempt as depicted in Figure 6.4. This includes accuracy and reproducibility within a

laboratory (laboratory reproducibility), accurate transfer from laboratory and scale-up in bulk

production (laboratory to bulk reproducibility) and repeatability between bulk dyed batches dyed

to the same color (bulk to bulk reproducibility). There are many factors that may affect

reproducibility of dyeing which include substrate properties, dyeing liquor characteristics,

machine parameters and the properties of dyes.

Figure 6.4: An example of reproducibility issues where the reproduced color from a new dyed

batch in not consistent with the original shade.

6.6.1.2 Unlevelness

In the coloration of the textile materials uniform appearance of the colored material is the primary

requirement. Differences in shade depth over the entire dyed area, as shown in Figure 6.5, are

termed as unlevel dyeing. In yarn or fabric dyeing small differences in shade from different parts

of the material can exhibit unlevelness [82].

440

Figure 6.5: An example of unlevelness.

6.6.1.3 Streaks, stripes or bands

Streaks are lines that appear to be different in color and/or texture from the surround. Streaks

usually follow straight lines either parallel or perpendicular to the fabric length direction. Streaks

can occur as single or multiple lines. Multiple adjacent lines which are different from the

surrounding material are referred to as bands, as shown in Figure 6.6. Streaks are usually shorter

in length than bands.

Figure 6.6: An example of bands in fabric.

6.6.1.4 Poor color yield

Color yield refers to the depth of color obtained when the standard weight of colorant is applied to

a substrate under standard coloration conditions. It is related to the amount of colorant fixed on

441

the substrate based on the application amount. A poor color yield is obtained when the color of the

dyed material is lighter than the target based on the quantity of colorants used due to a number of

factors including low fixation. An example of poor color yield is shown in Figure 6.7. The image

on the left shows the color obtained under standard dyeing conditions. The image on the right

shows the poor color yield due to low dye fixation.

Figure 6.7: An example of low color yield (on the right) compared to the standard (left).

6.6.1.5 Shade change

This is also known as inconsistent shade or off shade. It refers to the color of the substrate not

exactly matching the target color, as shown in Figure 6.8.

Figure 6.8: An example of shade change.

442

6.6.1.6 Inadequate fastness

Color fastness refers to the resistance of the colored material to a change in its color or a transfer

of color to an adjacent material (staining) due to the action of various chemicals or because of

mechanical influences. Different types of color fastness are defined based on the end use

requirements. The important fastness types are rubbing fastness, water fastness, washing fastness,

light fastness, and dry-cleaning fastness. An example of a stained multifiber strip after the washing

fastness test is shown in Figure 6.99.

Figure 6.9: An example of a dyed sample and a stained multifiber strip after the washing test.

6.6.1.7 Dark stains or spots

These are small regions with a darker color than the adjacent material as shown in Figure 6.10.

They can be in the form of small dots or dark areas in the substrate.

Figure 6.10: An example of dark stains.

443

6.6.1.8 Light stains or spots

These are small regions with a lighter color than the adjacent material. Like dark stains, they can

be in the form of small light dots or light areas in the substrate (see for example Figure 6.111).

Figure 6.11: An example of light stains.

6.6.1.9 Lengthwise shade variation

Lengthwise shade variation refers to a difference in shade between the starting layers of the

substrate and the point where the final shade is achieved. This is also known as tailing and ending.

The term ending is more commonly used in batch dyeing. Ending refers to change in color from

one end of the fabric to the other end. An example of lengthwise shade variation is shown in Figure

6.122. The color appearance of the top fabric taken at the start of the roll is different than the

bottom fabric taken at the end of the roll. Both fabrics are from the same lot dyed with the same

colorants and coloration process.

444

Figure 6.12: An example of lengthwise shade variation.

6.6.1.10 Widthwise shade variation

This refers to a variation in shade across the substrate or gradation of shade from the selvage to

the center of the dyed substrate. This is also known as listing or side to side shade variation. Figure

6.133 shows an example of listing where the shade of the left side of the fabric is different than

the right side.

Figure 6.13: An example of widthwise shade variation (note the fabric is folded on itself).

445

6.6.1.11 Shade variation within layers

This refers to a variation in depth of shade between the inner, middle and outer layers of a yarn

package or a beam dyed fabric. Figure 6.14 shows an example of shade variation within the layers

of a yarn package.

Figure 6.14: An example of shade variation within layers in a yarn package.

6.6.1.12 Two sidedness

This is also known as the face and back problem in which the front side of the fabric has a different

color appearance than the backside of the fabric. Figure 6.15 shows an example of two sidedness.

The left side shows the front and the right side shows the back of the fabric.

Figure 6.15: An example of two sidedness.

446

6.6.1.13 Reduced strength

The strength of material demonstrates its ability to resist the action of external forces. It is related

to the durability of the material. The fabrics with reduced strength can easily be torn and would

not meet the common end-use use requirements of the material. An example of a fabric with

reduced strength is shown in Figure 6.16. It can be seen that due to a reduction in strength, the

fabric can easily be torn.

Figure 6.16: An example of fabric with reduced strength.

6.6.1.14 Irregular surface appearance

These are faults in which the surface of the substrate is distorted due to the action of mechanical

forces or friction. These include abrasion marks, creases (as shown in Figure 6.17), rope marks,

crush marks, fabric distortion, wavy fabric appearance, and perforation marks. These usually have

a different appearance compared to the substrate body.

In yarn packages, these may be evident in the form of package deformation, yarn

deformation or luster marks in yarn layers.

447

Figure 6.17: An example of crease marks.

6.6.1.15 Holes or tears

Holes are small punctures in the fabric where a portion of yarn may be broken or missing. A tear

is a large cut or puncture in the fabric. Examples of holes and tears are given in Figure 6.18. Pin

marks due to stentering fabrics also constitute an example of holes.

Figure 6.18: An example of holes (left) and tears (right).

6.6.1.16 Poor hand

This refers to a material which is harsh or rough to touch. An example of a poor hand is given in

Figure 6.19.

448

Figure 6.19: an example of fabric with a poor hand.

6.6.1.17 Poor dimensional stability

This is also known as shrinkage. It is the ability of the substrate to retain its dimensions when

exposed to certain conditions such as water, steam, washing, drying or other processes. A symbolic

representation of this problem is given in Figure 6.20.

Figure 6.20: A symbolic representation of poor dimensional stability of the fabric.

6.6.1.18 Coating of rollers

This problem is machine-oriented which is generally seen in pigment coloration. It refers to the

accumulation of binder film on the dye padder and guide rollers. A symbolic representation of this

problem is given in Figure 6.21.

449

Figure 6.21: A symbolic representation of the coating of rollers during pigment coloration.

6.6.2 Identification of common causes of coloration problems in PES/CELL blends

The coloration process is quite complex and affected by a very large number of factors. Proper

attention and control are required for the coloration process to be successful. Each variable in the

coloration process has a direct or indirect influence on the processing of material and may cause

problems if not properly controlled. Since the dyeing of fiber blends has more variables than single

fiber dyeing, there are more chances of producing faulty dyed materials [140].

The problems in the coloration of blends can be attributed to a number of causes ranging

from fiber harvesting or manufacturing, yarn, and fabric manufacturing to the preparation,

coloration process and conditions, machinery, water, and chemicals used. It can be seen that

coloration issues may originate from a large number of factors that are sometimes not in the control

of the dyer. It is also not feasible to control or standardize all the factors due to economical

limitations. Thus, it will be better to focus on important or key causes that are responsible for

deviation from achieving the required target. These key factors or causes can be determined using

the Pareto principle [441]. It is essential to have an in-depth knowledge of the properties of

materials, machines, processes, and dyestuffs to prevent or solve coloration problems [11]. Actual

conditions in the dyehouse should also be considered. Once the key factors or causes are identified

they can be standardized in order to achieve process control [441].

The cause-and-effect (CED) or fish-bone diagram is one of the important tools used for

quality control and process improvement along with other statistical tools. CED shows the

relationship between the problem and factors or causes that are considered to influence the

problem. These factors can be considered as bones of a fish or branches of a tree. A typical CED

consists of different parts which include the head, spine, and bones. The head represents the

450

problem under consideration and is positioned on the far-right side of the diagram. The spine of

the CED is represented with the horizontal arrow pointing towards the head. The direction of the

arrow and all the items that join the arrow represent the causes that may be responsible for the

problem described in the head. Several large bones feed into the spine using smaller arrows. They

represent the broad categories of probable causes. Broad categories are added using smaller arrows

from the left side and according to the order of the process. The categories are based on the

principle of 6Ms, though other categories can also be used. The 6Ms comprise machinery,

methodology, materials, man power, measurements, and Mother Nature (environment). Multiple

levels of smaller bones show sub-categories of the causes of the problem. The connection between

the smaller bones and larger bones show their relationship. The number of small bones keeps on

adding until the cause that can be acted on is reached. Once all causes have been accounted for,

they are ranked according to their influence on the outcome of the process based on their technical

significance. In order to avoid biases when creating the CED, the relevant people, including those

from other departments, should be consulted. Important points that need to be considered are

management-related causes, sampling and measurement errors, and the interaction effect between

these causes [441, 442].

A CED diagram was created to identify and organize possible causes of problems in the

coloration of PES/CELL blends in a structured format. Figure 6.22 shows the CED for the faults

or problems that occur in the dyeing of fiber blends. This diagram was created according to the

process described above. Several brainstorming sessions were conducted and technical

information was obtained from the literature survey to ascertain the causes that may affect the

coloration problems for the PES/CELL blends. A special symbol (*) was used to show the

interaction effect between the broad categories. The developed CED diagram is composed of six

major categories or large bones that are responsible for problems in the coloration of PES/CELL

blends: measurement, machine, materials, method, environment, and people. Each of these broad

categories is discussed as follows.

451

Figure 6.22: Cause and effect diagram for faults in the dyeing of fiber blends.

Dyes/

Pigments

Quality control

Material handling

Inspection

Color kitchen

Controls

Production

Ventilation

Problems in the Coloration of Fiber Blends

Water

Utilities

Auxiliaries/

Chemicals

Chemicalproperties

Work forcePersonnel

Contaminants

Laboratory

Storage

Substrate

Standard

Dyeing

Bath preparation

Inspection

Sampling

Maintenance

Process planning

Physiologicalissues

Attitude

Training

Culture

Experience

Attention

Qualification

Accuracy &repeatability

Dyeing

Control unit

MeasurementMaterialsEnvironment

MachineMethodPeople

People*

Method*

Machine*

Standard operating procedure (SOP)

Color assessment

Communication

Cleanliness

452

6.6.2.1 Measurement

Measurement covers the monitoring of the ‘coloration’ process. The success of the coloration

process is incomplete without a proper measurement system in place. The broad categories include

quality control and color assessment as shown in Figure 6.23. The quality controls cover various

parameters that are essential to control the proper running of the coloration equipment. Any

variations in these parameters may lead to coloration problems. Color evaluation includes various

factors such as instrumental and visual assessment of colored samples to ensure the conformance

of the colored material to the target shade. There are many factors that may affect the color

assessment of dyed materials such as the illumination conditions, viewing angle, sample size, the

distance between the sample and the observer, orientation of samples, instrument settings used and

type of assessment. Thus, these factors must be controlled for accuracy and reproducibility of the

results.

6.6.2.2 Machine

The PES/CO blends can be dyed by various processes such as batch, semi-continuous and

continuous. The type of process used depends on material form (yarn, knit, woven), fiber type,

size of dye lots and quality requirements of the dyed fabric. Based on the dyeing process, different

dyeing machines are used. The selection of different dyeing machines depends upon the dyeing

process, material suitability, dyeing conditions (atmospheric or high temperature), and open or

rope processing of the material.

In order to ensure proper running of the machines certain factors need to be controlled. For

example, in continuous dyeing uniformity of liquor pickup is a prerequisite for successful dyeing.

The liquor pickup is controlled with the help of padder roll pressure and speed. Any variations in

padder pressure may lead to widthwise shade variation. The temperature of the trough should be

controlled to avoid instability of the dye liquor that causes tailing and poor color yield. Similarly,

the temperature of the hot flue dryer and steamer should be controlled properly for efficient dye

fixation. For batch dyeing machines, such as the jet a proper control of heating rates and the

sequence of chemical additions including dyes are important to attain a level dyeing. Proper control

of the liquor ratio is required for reproducible dyeing results.

453

Other machines that may affect the outcome of the dyeing process include inspection related

machines such as light booths, inspection tables, and spectrophotometers. The role of a color

kitchen cannot be ignored as accuracy of weights and dye liquor preparation related problems are

originated from here. The machines should be properly maintained and routinely calibrated to

avoid problems. Various machine-related causes are shown in Figure 6.24.

Figure 6.23: Possible causes originating from the measurement.

.

Quality control

pH Pick-up

No. of measurements

Orientation

Type of assessment

Distance

ConductivityRedox

potentialFlow rate

ConcentrationOxygencontent

Temperature

Substrate

Liquor

Water

Entry

Exit

Moisture

Residual

Application

Exhaust

Accuracy &repeatability

Measurement

People*

Method*

Machine*

SpecularIncluded/Excluded

Aperture size

Std. Observer

Illumination*

Color assessment

InstrumentalVisual

Type

Pass/Fail

Whiteness

Matching

Fastness

Viewing angle

Sample size

Illumination*

Sample type

454

Figure 6.24: Possible causes originating from the machinery.

Liquor

Material handling

Inspection

Weighing Balance

Color kitchen

Automation

Spectrophotometer

System drift

Availability

Light cabinet

Illumination

Dispensing system

Laboratory

Cleanliness

Maintenance

Calibration

Accuracy

Calibration Accuracy

Preparationtanks

Machineconnections

Steam pipe

Availability

Watersupply

Linear

Progressive

Controls

Liquor ratio

Amountof water

Substrateweight

Fill level

Dye addition

Chemicals addition

Time

Amount

Rate

Rate

Amount

Time

Temperature

Heating rate

Cooling rate

Dyeing

Washing

Preparation

Dyes

Chemicals

Time

Drying Dyeing

Cleanliness

Vacuum

Fill

Filters

Drain

Substrate

Speed

Substratetension

Drying

Curing

Moisture

Steamcontent

Entry

Exit

Liquorpick-up

ExhaustHumidity

Residual

Washing

Curing

Dyeing

Degree of controls

Maintenance

Sensors

Automation level

Displays

Breakdowns

Delays in supply

Malfunctions

Availability

Infra-red Intensity

Liquor circulation

rate

Pressure

Padder

Nozzle

Substrate

Reel

Materialcirculation

rate

Vessel

Troughvolume

Liquor turnover rate

Continuous

Exhaust

SteamerThermosol

Water-lockRoof

Uniformity

Control unit

Software

Signals

Availability

Hardware

ControllersMaintenance

Calibration

Computers

Monitors

Alarms

Air flow

People*

Machine

Geometry

DirectionalSphere

Equipement

Illumination

Source

UV content

BenchtopHandheld

Type

Surround

CalibrationMaintenance

UV content

Yarn

Space

Fabric

Type

Package

Hank

Jet

Jigger WinchBeam

Air-flow

Over-flow

Soft-flowVertical

Horizontal

Tube

Continuous

Pad-Batch

Pad-SteamPad-Theromosol

Accuracy

455

6.6.2.3 Materials

Any variation in the coloration process may be attributed to two fundamental causes which are

variation in raw materials and processing. Various causes attributed to materials are shown in

Figure 6.25.

Raw materials include the substrate, water, dyes, and chemicals. Many problems in the

dyed substrate are due to defects present in the fabrics, yarn or fiber [443]. For example, the

presence of immature fibers may lead to the appearance of white spots in the fabric after dyeing.

The variation in fiber crystallinity and orientation due to variations in extrusion, heat setting, and

drawing conditions may cause unlevelness or streaks in the dyed fabric. The variation in blend

ratio causes reproducibility issues and off shades. Yarn mixing during weaving may appear as bars

in the dyed fabric. The presence of hard sizing agent may cause problems during desizing as it is

difficult to remove and leads to streaks or spots in the dyed fabric.

The pretreatment of fabric or yarn is critical for successful coloration. Many problems in

coloration originate from, or are due to, improper pretreatments. The pretreatment of PES/CELL

blends includes various operations such as singeing, desizing, scouring, bleaching, heat setting,

and mercerization. Any variations in process parameters of chemical concentrations can cause an

improper pretreatment. After pretreatment fabrics should have good absorbency, neutral pH, good

dimensional stability, minimum levels of residual impurities, and no deposits of residual peroxide.

The pretreatment conditions should be selected such that fibers are not damaged. This is critical

especially in PES/CELL blends due to differences in their sensitivities and impurity levels. The

process parameters and chemical concentrations are often adjusted according to the blend to

achieve optimum results.

The chemicals and auxiliaries are added to provide different functions such as controlling

dye strike and minimizing unlevelness, improving dye exhaustion, providing required chemicals

for dye fixation and increasing the color fastness of dyed materials. Auxiliaries include

electrolytes, wetting agents, alkalis, acids, oxidizing agents, reducing agents, leveling agents,

dispersing agents and others. They should be checked on a regular basis for their purity, chemical

and performance properties. Several problems in the coloration process may be attributed to the

wrong selection, high impurity levels and inadequate /low performance properties of the chemicals

and auxiliaries [443].

456

The PES/CELL blends can be dyed using dyes or pigments and with one or two colorants

systems. The one colorant system uses pigments that can be attached to both fibers in the blend

with the help of a binder. In the two colorant system separate dyes for each fiber in the blend are

used. The polyester portion of the blend is dyed with the disperse dyes while cellulose can be dyed

with direct, reactive, vat and sulfur dyes. Many factors should be considered in dye selection for

each fiber in the blend as the conditions required for dye class for each fiber are different. The dye

class use for each fiber should be compatible with each other under dyeing conditions. Some

reactive dyes may react with disperse dyes and cause instability issues. Some reactive and direct

dyes are not stable under high temperatures and acidic conditions used in disperse dyeing. Disperse

dye tends to stain the cellulose component of the blend which may cause fastness related problems.

In order to remove the disperse dye stain from the cellulose component of the blend a reduction

clearing is required. Direct and reactive dyes are not stable under these treatment conditions. This

forces the dyer to use either a longer two-bath process or skip the reduction clearing process to

shorten the dyeing time. Some requirements related to specific dye classes can be used as an

advantage such as reduction clearing step required for disperse dye stain removal can be combined

with the reduction step required for vat and sulfur dyes. The dyes should be checked for color

strength on a regular basis to adjust the dyeing formula if a change in the color strength of dyes in

a new lot is observed.

457

Figure 6.25: Possible causes originating from the materials.

Dyes/

Pigments

Amount

Blendregularity

Yarn mixing

Moisture content

Thermal damage/melt spots

Priodicities

Broken fllaments

Improper steam conditioning (twist setting, stabilization, pre-shrinking, heat-setting)

Splicing

Storage stablity

Particle size and its distribution

Dispersion

Heat stability

Reduction sensitivity

Metameric

Phototrophic StructureYarn denisty

Fixation behavior

Shape SizeDensityDye tube

StrucutrePattern zones

Hard flanks

Package

SpiralityDrop

stiches

Cloth fall-out

Bunch-ups

Pretreatment Fabric

AbsorbencyResidual alkalinity

Whiteness

Degree of mercerization

ImpuritiesDimensional

stability

OilsWaxesSeed

fragments

Spinfinishes

Sizing agent

Fiber degradation

Defect

Surfaceproperties

Residual H2O2

Hard sizeSize selection

Wax deposits

Stripe

Sizing

Thin place

Lashed-in weft

Extraneous thread Fly

Broken pick

Short pick

Appearance fault Stain Snag

Interlacing fault

Snarl Hole Slack thread

Tight thread

Float Warp end repair

Reed mark

Temple marking

Drawing-in fault

Warp end break

Crease

Tights spots

Bulk

Intermingling

Auxiliaries/

Chemicals

PurityPerformance

propertiesAmount

Chemicalproperties

pHIonic character

Viscosity

Color

CompatibilityI.D.

Supply

Effect of Moisture

Substrate

Fiber properties

Maturity

Ioniccharacter

TemperaturestabilityCrystallinity

pH stability

Fiber saturation value

Fineness

Orientation

Degree ofpolymerization

Glass transitiontemperature

Chemical stability

Degree of fibrillation

Winding

Weight

Standard

Hank

Ageing

Twist Lot size

Batch size

Numberof strands

Length

Blend components

Blendingmethod

Blend ratio

Chemicalproperties

Compatibility

Affinity

Fastness

Color

Reactivity

pH sensitivity

Sensitivity to metal ions

Hard water sensitivity

Ionic character

Staining

DiffusionSalt sensitivity

MigrationMolecular weight

DyesChemicals

PurityI.D.Moisturecontent

Dye Substitutes

Supply

Form

Solubility

Color

Materials

Variation inproperties

Dust & trash

Length

Neps

Short fibercontentStrength

Elongation

Oligomer

Winding System

Yarn tension

Construction

Width

Count variation

Irregularity

Seldom occuring faults

Imperfections

Density

Hairiness

Trash & Dust

Diameter

Strength

Elongation

Shape

Wax

Yarn

Number of end groups

Selection Amount

Contamination

Lot characteristics

Faulty package

458

6.6.2.4 Method

The method includes procedures to ensure consistent coloration results. The procedure covers the

dyeing process, bath preparation, inspection, sampling, process planning, and maintenance, as

depicted in Figure 6.26. These procedures are usually implemented in the form of the standard

operating procedure (SOP). An SOP is a standardized document that contains step by step

instructions to carry out a routine or a repetitive operation. SOP helps in performing the operation

more effectively and efficiently and allows the consistent implementation of a process and

procedure within an organization [444]. The SOPs can be developed using technical data sheets of

dyes and chemicals, machine manuals, and standardized testing methods.

Figure 6.26: Possible causes originating from method.

Addition sequence

People*

Dyeing

Bath preparation

Inspection

Sampling

Procedures

Machine*

Process

Color effect

Dyeing method

Dye selection

Sampling

Sample preparation

Maintenance

Preventive

Breakdown

Schedules

SOP

Procedures

Process

SOP

Weighing

Machine*

Lab recipe

Adjustments

AdditionsDyes &

Chemicals

Dilution

Filtration

Process planning

People*

Delays

Schedules

JobsequenceParameters

Measurement*

Process planning

Bottlenecks

Availability

Method

Standard operating procedure (SOP)

Specifications

People*

People*Measurements*

People*

SOP

Machine*

SOP

Conditioning

Test methods

Standards

Sample selection Identification

Handling

SOP

Sampling

AATCC

ISO

ASTM

Buyer

Others

Internal

Machine manual

Operation

Maintenance

Calibration

Dyes & chemicals technical data sheet

Storage

Handling

Reprocessing

Tolerances

Inspection

459

6.6.2.5 Environment

The environment includes several factors, shown in Figure 6.27, which are not usually under the

control of the dyer. These include working and storage conditions, utilities and water. The water

quality needs to be monitored on a regular basis to avoid problems in coloration. The water may

contain several impurities that may interfere with the coloration process. The impurities in water

other than the source may come from broken or rusted pipes, and improperly cleaned storage tanks.

A dyehouse is generally equipped with a water treatment plant such that water is made available

for coloration operation. For a good lab to bulk reproducibility, it is important to use the water of

the same quality in both cases.

Figure 6.27: Possible causes originating from the environment.

Production

Ventilation

Water

pH

Dissolved CO2

HardnessDissolvedsolids

Heavy metals

ChlorineSuspended

matterNitrate &

Nitrite

Iron

Copper

Manganese

Organicsubstances

ColorOdor

NaHCO3

Utilities

Impurities

Pressure

Electricity

Availability

Flow rate

AirSteam

Water

Air

Steam

Voltage fluctuation

AirSteam

Water

Electricity

Contaminants

Humidity

Laboratory

Temperature

Temperature

Humidity

Storage

Temperature

Humidity

Environment

Cleanliness

460

6.6.2.6 People

People are the most important resource of a dyehouse. They can serve in different functions that

include but are not limited to establishing and controlling processes and production, selection and

controlling of raw material supplies, defining and controlling product quality, plant maintenance,

operations supervision and carrying out the process efficiently and safely [445]. The most

recurring source of a problem in a dyehouse is a human error. The dyehouse personnel should be

well informed and have strong knowledge about the process so that human-related faults can be

avoided [11]. The human-related causes can be sub-divided into physiological issues, experience,

training, attention, qualification, attitude, communication and different types of workforce

personnel involved in the dyeing factory as shown in Figure 6.28. The physiological factors

include fatigue, health-related problems, age, and color vision deficiency. The personnel involved

in a dyehouse include production, inspection, color kitchen, maintenance, and management crew.

Several errors in the coloration process may be caused due to tiredness, distraction or loss of

concentration of people involved. Dyehouse personnel should have adequate training, knowledge

or experience to carry out their tasks effectively and efficiently. The mental and physical or

abnormal surrounding conditions, however, may still lead to stress or loss of concentration or

sensitivity thus causing human errors.

A lot of coloration problems can be prevented if proper attention is given to people

management. The selection of employees is a factor that influences the day to day running of the

dyehouse. A cooperative attitude is important for the successful operation of the dyehouse and can

be cultivated over time. The personnel involved in a production floor should be healthy to deal

with the physical and mental demands of the production environment. A structured payment

system is important for people's well-being and a good working environment. The attitude of the

people is important for the efficient working of the plant. Several factors that influence the attitude

include appreciation, job security, promotions, good wages, management loyalty, resolution of

problems in a timely manner and good working conditions. A proper training program is essential

to improve quality and productivity, promote a healthy and safe working environment, reduce the

learning time for new employees, reduce labor turnover and improve the quality of new and

existing employees [445].

461

Figure 6.28: Possible causes originating from human-related factors.

As shown there are several factors that may be responsible for the problems observed in

the coloration of PES/CELL blends. A detailed list of the potential causes of various problems in

the coloration of PES/CELL blends is given in Table 6.5. The list was developed to illustrate

important factors that may be considered by dyers on a daily basis and can be useful to ascertain

the root cause of problems. The causes of coloration problems may vary when the process and

machinery are different and this was considered in the development of the list. Potential causes

were segregated into 11 different categories based on their origin as shown in Table 6.6.

Work force

Inspection

Maintenance

Color KitchenManagment Production

Quality control

Laboratory

Personnel

Physiologicalissues

Gender

Color defeciency

Age

Acquired Inherited

Attitude

Training

Culture

Experience

Attention

Qualification

Health

People

Communication

462

Table 6.5: Categorized list of possible causes associated with symptoms in the coloration of

polyester/cellulosic materials.

Cause Category Description

C001 Bath

preparation

Errors in the weighing of colorants and chemicals

C002 Improper bath preparation procedure

C003 Too fast/quick addition of chemicals in the bath

C004 Too fast/quick addition of dyes in the bath

C005 Colorants Too high colorant concentration

C006 Wrong selection of dyeing method (1 bath, 2 bath)

C007 Poor dye selection for polyester component

C008 Poor dye selection for cellulose component

C009 Poor dye combinations for each fiber type

C010 Variation in colorant strength

C011 Incompatibility between dye classes

C012 Cross-staining of fiber

C013 Bleeding of unfixed dye into the bath/trough during development

C014 Poor pigment selection

C015 Crust formation in pigments during storage

C016 Poor pigment dispersion system

C017 Differences in pigment particle size and particle size distribution

C018 Poor disperse dye dispersion system

C019 Poor disperse dye dispersion stability

C020 Poor disperse dye diffusion properties

C021 Poor disperse dye leveling and migration properties

C022 Poor thermomigration property of disperse dye

C023 Too high substantivity of reactive/direct dyes

C024 Poor solubility of reactive/direct dyes

C025 Poor diffusion properties of reactive/direct dyes

C026 Poor migration properties of reactive/direct dyes

463



C027 Poor stability of reactive/direct dyes under polyester dyeing

conditions

C028 High dye reactivity

C029 Too high substantivity of vat/sulfur dye in the leuco form

C030 Too low substantivity of vat/sulfur dye in the leuco form

C031 Poor diffusion properties of vat/sulfur dyes

C032 Poor leveling properties of vat/sulfur dyes

C033 Poor vat/sulfur dyes dispersion system

C034 Poor color matching of each fiber in the blend

C035 Auxiliaries Variations in strength and purity of dyebath chemicals

C036 Chemical or physical interaction between colorants and chemicals

C037 Poor selection of dyebath chemicals

C038 Formation of binder film on padder or rollers

C039 Agglomeration of binder

C040 Binder with poor fastness properties

C041 Brittleness (poor softness) of the binder film

C042 Insufficient amount of binder

C043 High amount of binder

C044 Poor resistance of binder against aging

C045 Binder with poor swelling resistance

C046 High amount of softener

C047 Improper softener selection

C048 Inappropriate electrolyte (salt) concentration

C049 Inappropriate concentration of dispersing agent

C050 Too low amount of lubricating agent

C051 Too high concentration of carriers

C052 Lower quantity of anti-migrating agent

C053 Precipitation of anti-migrating agent

464



C054 Too high concentration of dye fixative

C055 Use of silicone based defoamer

C056 Pre and post

dyeing

operations

Too low concentration of reducing agent and/or alkali

C057 Presence of air in the machine

C058 Inappropriate rinsing temperature

C059 Inadequate water flow rates/liquor ratio during rinsing

C060 Inadequate number of rinse cycles/rinse baths

C061 Inappropriate pH during oxidation

C062 Insufficient concentration of oxidizing agent

C063 Inappropriate temperature during oxidation

C064 Inadequate reduction clearing temperature

C065 Inadequate reduction clearing time

C066 Inadequate concentration of hydro and caustic during reduction

clearing

C067 Inadequate soaping temperature

C068 Inadequate pH during soaping

C069 Inadequate soaping time

C070 Improper selection of detergent for soaping

C071 Inadequate water flow rates/liquor ratio during soaping

C072 Improper neutralization of substrate after dyeing

C073 Too high drying temperature

C074 Dyeing

machine

Improper storage and handling of substrate

C075 Machine stoppage for a longer duration

C076 Presence of dye deposits in the dye preparation tank and machine

C077 Presence of reductive chemicals in substrate, water or steam

C078 Excessive foaming in the dye bath/trough

C079 Non-uniform or damaged machine parts

C080 Excessive, insufficient or variable tension during fabric run

465



C081 Longer duration of substrate run due to reprocessing

C082 Variations in dyeing program

C083 Rubbing of unfixed substrate against the guide roller/machine part

C084 Batch dyeing Too fast increase in the differential pressure

C085 Too low liquor flow rate

C086 Too high liquor flow rate

C087 Inappropriate liquor flow times (in-out and out-in)

C088 Too high pressing density

C089 Too low pressing density

C090 Leakage in package column

C091 Defective locking caps

C092 Too large batch size (machine overloading)

C093 Presence of oligomer and other deposits in the machine

C094 Presence of oligomer deposits on the substrate surface

C095 Trapped air pockets in the material during dyeing

C096 High temperature rise rate

C097 Inappropriate dyebath pH

C098 Use of too low liquor ratio

C099 Use of too high liquor ratio

C100 Too low dyeing temperature

C101 Too high dyeing temperature

C102 Too slow fabric/rope speed

C103 Too fast fabric/rope speed

C104 Too short dyeing time

C105 Too long dyeing time

C106 Shock cooling of fabric after completion of dyeing cycle

C107 Too low liquor flow rate

C108 Too high liquor flow rate

466



C109 Incorrect liquor flow direction

C110 Incorrect overlap of fabric covering the beam perforations

C111 Uneven winding of fabric on the beam

C112 Variation in pressure head in the tubes

C113 Poor circulation or stoppage of fabric

C114 Incorrect nozzle size (diameter)

C115 Twisting or pressing of the rope at high temperature

C116 Inappropriate nozzle pressure

C117 Cooling of outer/inner fabric layers

C118 Cooling of selvages

C119 Variation in dyebath temperature

C120 Too tight or too loose fabric edges

C121 Continuous

dyeing

Deposits of fluff/lint on the padder surface and guide rollers

C122 Damaged, worn out or uneven padder surface

C123 Too high pad trough temperature

C124 Difference in the hardness of dye padders

C125 Too high wet pickup

C126 Too low wet pickup

C127 Improper distribution and circulation of dye liquor

C128 Uneven wet pickup

C129 Inadequate airing time between padding and drying

C130 Selvage curling during padding and thermofixation process

C131 Improper rotation of the fabric batch during batching

C132 Poor covering of fabric batch during batching

C133 Differences in fixation temperature or time during batching

C134 Variation in the intensity of the IR pre-dryer

C135 Non-uniform air velocity or flow

C136 Too high drying temperature

467



C137 Too low thermofixation temperature

C138 Too high thermofixation temperature

C139 Too long thermofixation time

C140 Too short thermofixation time

C141 Temperature variation in the hotflue

C142 Contact of condensation drops with unfixed colorant

C143 Inadequate steaming temperature

C144 Inadequate steaming time

C145 Variation in temperature inside the steamer

C146 Too high water seal temperature

C147 High turbulence in the washbox

C148 Pretreatment Difference in the singeing of fabric’s face and back

C149 Fiber damage during singeing

C150 Incomplete singeing

C151 Incomplete removal of sizing agents and sizing wax

C152 Incomplete removal of oil, rust and grease stains

C153 Fiber damage during scouring and bleaching

C154 Too high weight loss during scouring

C155 Insufficient relaxation of the substrate during washing

C156 Localized swelling of fiber

C157 Incomplete removal of fats, waxes, spin finishes, and knitting oils

C158 Inadequate weight reduction of polyester

C159 Catalytic damage during bleaching

C160 Presence of residual peroxide in substrate

C161 Incomplete removal of motes (seed husks)

C162 Inadequate whiteness of substrate

C163 Improper heat setting of substrate

C164 Fiber damage during heat setting

468



C165 Physical damage of substrate (pin marks, cuts)

C166 Excessive overstretching of substrate on stenter

C167 Incomplete mercerization

C168 Differential mercerization due to superimposed layers of substrate

C169 Alkaline pH of substrate before dyeing

C170 Improper stitching of substrate ends

C171 Presence of insect residues in substrate

C172 Water Presence of Ca and Mg ions (hardness) in water

C173 Presence of heavy metals (Cu, Fe, Mn, Zn) in water

C174 Presence of suspended matter in water

C175 Presence of bicarbonate in water

C176 Presence of chlorine in water

C177 Fabric

manufacturing

Presence of holes, tears or cuts in greige substrate

C178 Presence of bands or stripes in greige substrate

C179 Fabric rolls from different knitting or weaving machines or batch or

factory

C180 Yarn mixing

C181 Variation in yarn tension during warping/sizing

C182 Winding Too high package density

C183 Too low package density

C184 Uneven package density

C185 Edging process for rounding of package flanks

C186 Improper rounding of package flanks

C187 Improper coverage of dye tube perforations

C188 Use of damaged dye tubes

C189 Poor temperature stability of dye tubes

C190 Yarn

manufacturing

Too many yarn imperfections

C191 Lower yarn strength and elongation

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C192 Variation in blend ratio

C193 Foreign fiber contamination

C194 Fiber and

filament

Variations in crystallinity and orientation of fiber

C195 Variations in the degree of polymerization of fiber

C196 Presence of immature fibers

Table 6.6: Sorting of causes into different categories based on their origin,

No. Category Causes

A Bath preparation C1-C4

B Colorants C3-C34

C Auxiliaries C35-C55

D Pre and post dyeing operations C56-C73

E Dyeing machines C74-C83

F Batch dyeing C84-C120

G Continuous dyeing C121-C147

H Pretreatment C148-C171

I Water C172-C176

J Fabric manufacturing C177-C181

K Winding C182-C189

L Yarn manufacturing C190-C193

M Fiber and filament C194-C196

6.6.3 Knowledge acquisition

Knowledge acquisition involves the transfer and transformation of problem-solving expertise from

some knowledge source to a program. The sources of knowledge comprised human experts,

textbooks, scientific data, technical reports and other resources [446]. In order to develop a

relationship between the symptoms and various causes in the coloration of PES/CELL blends, an

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electronic survey was constructed. Electronic surveys are commonly used nowadays as a method

to collect information. The main advantages of using an electronic survey include [447]:

▪ Fast turnover time;

▪ Lower cost as no printing or postage is required;

▪ Wider reach to a large number of respondents which can lead to higher response rates;

▪ Variety of formats: email, web survey, and others;

▪ Many types of response formats such as dropdowns, radio buttons, input boxes;

▪ Instant and convenient data analysis since manual entry of data is not required;

▪ Easy to respond to by participants; and

▪ Flexibility in design.

The survey was designed in the form of a Microsoft Excel spreadsheet. A screenshot of the

survey is shown in Figure 6.29. The survey consisted of one excel spreadsheet containing 18

symptoms and 196 causes. The symptoms are represented in columns while the causes are

provided in the form of rows. Each cell in the excel sheet represented the interrelationship between

the causes and symptoms. A certainty factor (CF) was provided for each response from 0-10. The

CF of 10 indicates a very strong correlation between the cause and the symptom, while a CF of 0

denotes no correlation exists between the cause and the symptom. If the experts were not sure

about the relationship between the cause and the symptom they could select X. A cell that was left

blank was considered to indicate no relationship existed between the cause and the symptom.

As the coloration of PES/CELL blends can be achieved by both pigments and dyes, the

survey was distributed to experts with experience and expertise covering both coloration systems.

A total of 10 dyeing experts from the USA, South Korea, Italy, Germany, India, and Pakistan

participated in the study. Five experts were from pigment coloration domain and five had expertise

in the conventional dyeing domain. Experts’ responses were analyzed and coded into rules to

develop the knowledge base. The analysis of expert responses is covered in the next section.

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Figure 6.29: A screenshot of the electronic survey distributed to experts in spreadsheet format

472

A common challenge that was encountered when seeking responses from experts was

finding willing experts who could complete the work in a timely fashion. Although, some experts

provided a quick response many experts found it difficult to complete the survey due to their busy

schedules and could not respond in time. In addition, the task was found to be very time-consuming

according to some experts. It should be noted that the survey was carefully designed and broken

down into sections for easy completion. The experts who participated in this study were from

different sectors of the industry including dye manufacturing, as well as practical dyers and dyeing

consultants with a wide range of experience from 10-40 years. The weighted average responses

from experts are given in Appendix A.

6.6.4 Analysis of expert responses

It has been found that, usually, a single expert may not be enough to get suitable responses to

resolve a particular problem. It is important to recognize that experts other than having shared

expertise of the domain usually specialize in a sub-section of a domain [448]. For example, a

dyeing expert may have working experience and deep knowledge of different dyeing processes,

but they may have more expertise in the area of continuous dyeing. Experts may also differ in their

expertise level, with some having more expertise than others because of training, experience, and

intelligence. Using responses from different experts increases the reliability and confidence in the

knowledge base as compared to responses obtained from a single expert [449]. Therefore, the use

of multiple experts in the development of an expert system is recommended. This is useful in the

development of a high-quality practical expert system in a particular domain.

When dealing with multiple experts, three strategies can be used to develop a knowledge

base by a knowledge engineer. This can be achieved either by using experts individually, or

designating primary and secondary experts or by combining multiple responses [450]. The main

advantages associated with combining multiple experts’ responses are summarized as follows

[450]:

▪ The understanding of the knowledge domain is improved;

▪ The developed knowledge base will be more comprehensive and accurate;

▪ Broader domains can be combined; and

▪ Complex problems can be dealt with.

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Several strategies can be used to integrate responses depending on the nature of responses

obtained from multiple experts. The analytical approach is useful when dealing with numerical

values such as probabilities, weights, etc. The treatment of expert responses in such cases is

mathematical in nature [450, 451].

For the construction of this knowledge base the expert responses were obtained in the form

of certainty factors (CF). The certainty factors, ranging from 0-10, were used to interrelate the

symptoms with the causes. Certainty factors are useful because it is often very difficult to have

complete information to arrive at a solution to a problem with complete certainty. Often one

symptom may be due to multiple causes, in such cases, the cause with a higher CF has a higher

likelihood of being the correct cause as compared to the cause with a lower CF. To develop the

knowledge base for this study, CFs ranging from 0-10 were segregated and categorized into three

groups based on their values. Causes with high CF values (7-10) were listed as the most likely,

medium CF values (4-6) were considered likely and low CF (0-3) were categorized as the least

likely. In troubleshooting coloration problems, it seems logical to consider those causes first which

are more likely responsible for the problem under consideration to reduce the time and effort

required to reach a solution.

The combination of expert responses or aggregation into a single value can be challenging.

Since the data involved in this case were numerical in nature (CF), a variety of techniques could

be used to perform the mathematical aggregation. Different statistical techniques can be used to

calculate a single value based on the data. The most commonly used estimators for central tendency

are mean, median, mode and geometric mean. The mean gives equal weight to each expert

response. In this case the extreme value in the expert responses greatly influences the mean value.

This value may not be suitable especially in cases where extreme values are reported or where

values seem unreasonable. The median is the 50th percentile value. It is not influenced by extreme

values but by central values. The geometric mean is the average based on a logarithmic scale. It

can be useful for expert judgments in applications where small values are suitable to fit in a log

scale compared to the linear scale used by the mean. The mode uses the more frequent value in the

data set. The main problem associated with the mode is that a set can have multiple modes. Another

approach involves the use of weighted mean in which expert’s answer is assigned its own weight.

The main challenge is to determine a suitable weight for each expert which requires information

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about how experts reach a particular answer. However, this information is often difficult to obtain.

A simple approach involves assigning equal weights to the expert responses [452].

Table 6.7: An example of different analytical methods that can be applied to aggregate expert

responses in two different scenarios (E=Expert).

Scenario Cause Expert responses Analytical

method Result

E1 E2 E3 E4 E5

A C144: Inadequate

steaming time 8 6 5 8 8

Weighted mean 7

Median 8

Mode 8

B

C053: Precipitation

of anti-migrating

agent

10 8 0 0 0

Weighted mean 4

Median 0

Mode 0

The weighted average with equal weights was found to be a suitable method for

aggregating expert responses in a previous study involving the development of a diagnostic expert

system for the dyeing of protein fibers (Dexpert-PT) [412]. The same approach is used in this

study. Although the weighted mean may be affected by outlier responses experts CF responses are

likely affected by their expertise pertaining to a particular problem and can vary among experts.

The experts who participated in this study were from different sectors with many years of

experience and had different types of professional experience and education. The use of median

and mode which rely on the central value and the most frequently occurring value may result in

ignoring the highest rating provided by an expert and may change the rank of the cause. The use

of the weighted average is more reliable in this case as it gives equal weight to each expert’s

response. The example shown in Table 6.7 illustrates different analytical methods that can be used

to aggregate expert responses. The two scenarios with different expert responses are assessing the

causes of reproducibility (symptom 1) issues in the dyeing of PES/CELL blends by the continuous

method. It can be seen if the response varies widely from one expert to another the median and

475

mode may not provide a good aggregation response. The weighted mean on the hand appears to

provide a better approach as it covers the whole range of responses given by different experts.

All causes associated with reproducibility (symptom 1) in the case of pigment coloration

are shown in Table 6.8. The CF was calculated from 1-10 with fractions rounded off to the nearest

number using a weighted average method. The causes are prioritized based on high (CF 7-10),

medium (CF 4-6) and low (CF 0-3) values using the ranking approach. The cause with the largest

CF is assigned the highest priority among all causes and the associated rule is fired first during

diagnosis. All responses obtained from the experts were analyzed by the same method and

aggregated responses were used in the development of the expert system in this study.

Table 6.8: List of causes associated with the reproducibility symptom after being prioritized

based on the weighted CFs obtained from experts (E represents expert).

Cause Description E1 E2 E3 E4 E5 Weight High

CF

Medium

CF

Low

CF

C001

Errors in the weighing

of colorants and

chemicals

10 10 8 10 8 46 9

C135 Non-uniform air

velocity or flow 10 10 7 10 8 45 9

C137

Too low

thermofixation

temperature

9 7 9 10 8 43 9

C136 Too high drying

temperature 10 5 8 8 8 39 8

C005 Too high colorant

concentration 9 9 8 5 8 39 8

C002 Improper bath

preparation procedure 9 7 5 8 29 7

C140 Too short

thermofixation time 5 7 10 6 28 7

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CF

Medium

CF

Low

CF

C075 Machine stoppage for

a long duration 5 6 8 5 7 31 6

C128 Uneven wet pickup 5 10 8 0 8 31 6

C052 Low quantity of anti-

migrating agent 5 5 7 17 6

C127

Improper distribution

and circulation of dye

liquor

5 6 5 6 22 6

C078 Excessive foaming in

the dye bath/trough 5 5 6 16 5

C125 Too high wet pickup 5 6 5 16 5

C015

Crust formation in

pigments during

storage

5 5 5 6 21 5

C016 Poor pigment

dispersion system 5 5 5 15 5

C053 Precipitation of anti-

migrating agent 5 5 10 5

C134

Variation in the

intensity of the IR

pre-dryer

5 5 10 5

C141 Temperature variation

in the hotflue 0 10 5 5 20 5

C179

Fabric rolls from

different knitting or

weaving machines or

batch or factory

5 5 5 15 5

477



CF

Medium

CF

Low

CF

C162 Inadequate whiteness

of the substrate 2 7 5 14 5

C036

Chemical or physical

interaction between

colorants and

auxiliaries

5 0 7 12 4

C049

Inappropriate

concentration of

dispersing agent

5 0 7 12 4

C163 Improper heat setting

of substrate 5 2 5 5 2 19 4

C157

Incomplete removal

of fats, waxes, spin

finishes, and knitting

oils

2 5 4 0 5 16 3

C126 Too low wet pickup 3 4 2 9 3

C173

Presence of heavy

metals (Cu, Fe, Mn,

Zn) in water

2 3 5 3

C174 Presence of suspended

matter in water 2 3 5 3

C175 Presence of

bicarbonate in water 2 3 5 3

C176 Presence of chlorine

in water 2 3 5 3

C164 Fiber damage during

heat setting 2 2 1 2 5 12 2

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CF

Medium

CF

Low

CF

C59 Catalytic damage

during bleaching 2 3 2 7 2

C157

Incomplete removal

of sizing agents and

sizing wax

2 2 0 5 9 2

C149 Fiber damage during

singeing 2 1 2 0 5 10 2

C172

Presence of Ca and

Mg ions (hardness) in

water

2 3 0 3 8 2

C014 Poor pigment

selection 0 0 5 5 2

C169

Alkaline pH of

substrate before

dyeing

2 2 0 2 6 2

C180 Yarn mixing 3 0 1 4 1

C166

Fiber damage during

scouring and

bleaching

2 0 2 1

There are many causes that may be responsible for a specific coloration problem. Similarly,

a single cause can lead to multiple problems. Therefore the commonness of causes among

symptoms along with their origin category was analyzed. The example given in Table 6.9 shows

the most likely causes selected by experts for unleveleness (S2) in continuous dyeing with

pigments. It can be seen that the cause C128: uneven wet pickup is also the most likely cause of

reproducibility (S1), streaks or stripes (S3), poor color yield (S4) and lengthwise shade variation

(S9).

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Table 6.9: Analysis of causes according to category and commonness.

Cause Description High

CF Category Commonness

C128 Uneven wet pickup 10 G S1, S3, S4, S9

C002 Improper bath preparation procedure 9 A S1, S5, S7, S9, S10,

S18

C039 Agglomeration of binder 8 C S4, S7-S8, S18

C125 Too high wet pickup 8 G S5, S10, S18

C005 Too high colorant concentration 7 B S1, S4, S6a, S7, S9,

S10, S18

C036 Chemical or physical interaction

between colorants and auxiliaries 7 C S7, S18

C135 Non-uniform air velocity or flow 7 G S1, S3, S10

C052 Low quantity of anti-migrating agent 7 C S4

C157 Incomplete removal of fats, waxes, spin

finishes and knitting oils 7 H S4

C134 Variation in the intensity of the IR pre-

dryer 7 G S5, S10

C151 Incomplete removal of sizing agents

and sizing wax 7 H S4

6.7 Construction of a diagnostic expert system for dyeing of fiber blends

(DEXPERT-B)

The functional knowledge-based expert system, DEXPEPRT-B has been developed to diagnose

problems in the coloration of fiber blends (DEXPERT-B). The system is designed to determine

the root cause(s) of the most common faults specifically in the coloration of PES/CELL blends

using pigments and dyes.

DEXPET-B has been organized with three components to perform its diagnosis. The

system architecture of DEXPERT-B is shown in Figure 6.30: System architecture of DEXPET-B.

480

. The direction of arrows indicates the path of flow of information.

▪ Component A- Interface: The system consists of four interfaces. The first interface is

designed to seek material related information from the end-user which includes fiber

types, blend ratio, and material form. The fiber types can be selected from the two

groups provided. Each group contains six fibers, polyester and five cellulosic fibers

namely cotton, viscose, modal, lyocell, and linen. Different combinations of polyester

with cellulosic fiber types can be selected in any order. Three material forms: yarn,

knitted fabric, and woven fabrics are provided. After the material selection is performed

the information about the coloration process is required from the end-user in the second

interface. The user selects the corresponding colorants according to fiber type, dyeing

process, method, and machines. The third interface enables the user to select the

corresponding coloration faults based on the selections made in the first two interfaces.

The material and coloration selections lead to the initial sorting of the symptoms. The

fourth and final interface shows the selected material, coloration process, and selected

symptoms by the end-user. This interface also interacts with the end-user to perform

diagnosis through a series of questions. The interface is shown in grey color.

▪ Component B- Inference: During this process, the facts inserted by the user in the first

component are evaluated and compared based on the rules coded in the knowledge

base. The material, coloration, and symptoms selected by the user (facts) are analyzed

and compared with the knowledge base containing rules for causes related to

symptoms. The rules satisfied by the analysis are prioritized and fired to initiate the

queries for diagnosis.

▪ Component C- Diagnose: This component asks appropriate questions from the user

through a dialog box based on the prioritized rules which are fired in Component B.

The system starts with the most likely causes for troubleshooting to facilitate a quick

resolution of the problem. The end-user is provided with an option to display all

possible suggested causes for the symptom. The system is also provided with an

explanation facility based on the causes selected by the user through an Explanation

button.

481

Figure 6.30: System architecture of DEXPET-B.

6.7.1 Expert system building tool

These include the programming language and the support package used to build the expert system.

Experts systems are often built from scratch using specialized expert system languages.

Specialized software products are available that provide the methodology and system tool that can

be used to build an expert system. The structure for coding the knowledge base and inference

engine is provided in such systems. These software products provide two basic functions. First,

they provide the development environment for building an expert system and second they support

a delivery system that allows the end-user to actually use the system [453].

482

The coloration expert system for fiber blends (DEPXERT-B) was developed using wxCLIPS

(version 1.64), a modified version of expert system tool CLIPS (version 6.0), developed to allow

portability and graphical user interface that can run under windows environment.

CLIPS is an acronym for C Language Integrated Production System. CLIPS is an expert

system programming language which is available as an open-source software. Its source code is

well documented. It was developed at NASA in the mid-1980s and was originally written in C.

CLIPS is a rule-based language that is specifically used for developing an expert system. A CLIPS

program consists of facts, knowledge-base, and an inference engine. Facts are data or information

and represent the current state of the problem. The knowledge base contains all the rules which

are fired based on facts. The inference engine works by matching facts against the rules, choosing

which rule to fire and executing the actions. It takes a decision based on rule matching and rule

priorities [13, 16].

In wxCLIPs, the structure of CLIPS is modified to include GUI functions. Essentially

wxCLIPS is a combination of CLIPS and wxWindows. The wxWindows enables GUI

functionality in the CLIPS. wxCLIPS is also available as an open-source software and was

developed by Julian Smart at the Artificial Intelligence Applications Institute, University of

Edinburgh, UK in the 1990s [454].

6.7.2 Knowledge representation

The knowledge representation step deals with steps involved in setting up methodology for storing

facts and rules in the knowledge base. It represents how knowledge is structured in a knowledge

base [453, 455]. The knowledge can be represented using standard sets of techniques. The

technique helps in making a program more efficient, easy to understand and easy to modify.

Different techniques can be used such as rules, semantic nets, frames, etc. The knowledge

representation based on rules uses IF condition THEN action statements. When the current

situation matches the IF part of a rule the action specified by THEN part of the rule is carried out.

These rules can be of different nature such as obtaining responses from the end-user, may cause a

particular set of rules to be tested and fired based on the end-user input or may instruct the system

to reach a conclusion based on the rules satisfied [453].

In rule-based expert systems also known as production systems, the knowledge domain is

represented in the form of rules. The rules are statements that define the relationships between the

483

facts. The information related to the current problem or situation (facts) is checked against the

rules. The rules whose IF portion are satisfied by the facts fire the action in the THEN portion of

the rule. The IF portion of rules in the system is compared with facts by a rule interpreter. Matching

of facts with the IF portion of the rule leads to the execution of that rule [453]. The IF statement

of the rule may consist of several conditions. These conditions are joined by connecting words

AND and OR, depending on the condition. The rule is then executed IF all conditions (AND) or

any of the (OR) conditions of the rule is satisfied [455].

A knowledge engineer must select a way for the reasoning to reach a conclusion in the

expert system based on the rules and facts stored in the knowledge base. To search for the solution

of a problem, a statement for a problem is required. An expert system should be designed in such

a way to take this problem and break it down into small sub-problems [455].

In CLIPS the rules are represented as follows:

(defrule <rule-name>

pattern-1 ... pattern-n ; Rule Properties; Left-Hand Side (LHS)

=>

action-1 ... action-m) ; Right-Hand Side (RHS)

The header of the rule consists of three parts. The rule must start with a defrule keyword

followed by the name of the rule. Then there are (zero or more) conditional elements which are

called patterns. Each pattern has one or more constraints intended to match the fields. CLIPS

attempts to match the pattern against the facts list. If the pattern of the rule matches all facts, the

rule is activated and placed on the agenda which is a collection of activated rules. CLIPS

automatically determines which rule to fire based on the priority called Salience [16].

The example given in Figure 6.31 illustrates how rules are coded in CLIPS for the

development of DEXPERT-B. In this example the user selected the lengthwise shade variation as

the symptom, woven fabric as the material type, pigment as colorant, and pad-thermosol process

as the dyeing method. When all the conditions of rules are matched, the rule is activated and the

system will insert “uneven pickup” as the mostly likely cause. Since the coloration problems are

usually due to multiple causes, as shown, the system needs to assess various possible causes and

identify them in the initial stage to diagnose the possible causes of the problem. In this case

continuous dyeing, bath preparation and colorant are the categories. The continuous dyeing

category is further divided into sub-categories padder, pre-drying and hotflue. The descriptions

484

under these sub-categories represent the most likely causes for the symptom which in this example

are uneven wet pickup, variation in the intensity of the IR pre-dryer and non-uniform air velocity

or flow respectively.

Figure 6.31: Knowledge representation in DEXPERT-B in the form of rules.

6.8 Inference engine

The collection of problem-solving processes is called the inference engine. The inference engine

can be a part of the coded language, or separately designed and implemented. The use of the latter

approach provides an option to organize the inference strategy [453]. Although the knowledge

base and inference engine complement each other they are separate and distinct parts of the expert

system. The knowledge base can be replaced with new rules and facts and the inference engine

can then be used for the new knowledge base [455].

An inference engine is a complex program. It consists of two main components: an

inference mechanism and control mechanism [455]. The inference mechanism contains the

reasoning approach used by the expert system to develop new facts based on existing or established

facts. It decides how to apply rules based on facts to infer a new knowledge. The control

mechanism decides the order for rule execution. It is a technique for controlling its reasoning

process. The two most common control strategies are backward chaining and forward chaining

[453, 455].

(defrule PC-pigment

(Lengthwise shade variation)

(Woven fabric)

(Pad-Thermosol)

=>

(assert (uneven wet pickup))

)

Lengthwise shade variation

Continuous dyeing

Padder

Uneven wet

pickup

Pre-drying

Variation in the

intensity of the IR pre-

dryer

Non-uniform air

velocity or flow

Hotflue

Bath preparation Colorant

485

The study of making valid inferences is called logic. An inference can be valid depending

on the conclusion it reaches based on the facts that are either true or false [16]. The knowledge can

be represented symbolically in the form of proposition logic. The proposition refers to statements

that can either be true or false. In propositional logic, it is checked whether a statement is true or

false by comparing it to known facts and rules that are available for manipulating these facts. The

conclusion can be reached by combining several propositions together. The propositions can be

combined using logical operators such as AND, OR, NOT, etc. The relationship between two or

more statements can be defined with the help of predicate logic [455].

In CLIPS the inference engine controls the overall execution of the rules. The working

memory may contain one or many facts at the same time. The facts in the working memory have

no interaction with each other. The inference engine compares each rule in the knowledge base

with the facts in the working memory. If the IF part of the rule is satisfied by the facts, then the

THEN action part of the rule is accomplished, and the rule is placed on the agenda. The rule may

contain multiple patterns and these patterns must be simultaneously matched to execute the rule.

A rule is said to be activated whose patterns are satisfied. An agenda may contain multiple

activated rules at the same time. The inference engine then decides which rule to fire. Rule based

expert systems are designed to prevent trivial loops. When the rules fire the list of actions is

executed in the THEN part of the rule. The inference works in a way that is known as recognize-

act cycles. The inference will repetitively perform the groups of tasks until certain termination

criteria is reached which causes execution to stop. This criterion is known as conflict resolution.

The inferences accomplish tasks based on the priority. The task with a high priority will be

executed first followed by a task with the second-highest priority until no activation is left in the

agenda. When the rule is satisfied it is put on the agenda. When the rule fires a new fact may be

obtained which is added to the working memory. The inference chains are obtained by firing rules

which determine how expert systems reach a conclusion. Conflicts may occur on the agenda while

activating different rules that have the same priority. In CLIPS the rules have the same default

priority unless assigned by the knowledge engineer [16].

Different strategies can be used to deal with conflict resolution in CLIPS using certainty

factors and salience. In real-world scenarios, human experts are often not completely sure of their

information. Sometimes they try to reach a conclusion based on the limited information available.

The expert system must be able to deal with uncertainty. One way for the expert system to deal

486

with uncertainty is by using certainty factors. The certainty factors (CF) represent uncertainty

numerically using some type of scale. The scales can be from 0 to 5, 0 to 100 or -1 to +1, etc. The

higher value of the scale represents the higher confidence in the answer while the lower value

shows lower confidence. In CLIPS the CF ranges from 0 to 1 [16, 455].

Another approach that can be used to deal with uncertainty is salience. Salience allows the

priority of the rules to be defined using a numerical value. The higher the salience value of

activated rule the higher will be its order on the agenda regardless of when it is activated. This

allows more important rules to stay on top of the agenda and be fired first. The salience can range

from -10,000 to 10,000. The rules with no explicitly defined salience are assigned a neutral salience

value of 0. This does not imply the rule has no salience value since 0 denotes the middle value of

the salience range. The salience allows the rules to be fired in a sequential order [16]. The salience

approach was used in developing DEXPERT-B.

CLIPS has seven conflict resolution strategies built in the system to determine the

execution order of the rules that have the same salience. These include depth, breadth, simplicity,

complexity, lex, mea, and random. The default strategy used by CLIPS is depth in which a newly

activated rule is placed above all the rules of the same salience [454].

The interface of the expert system in this study was designed to enable the end-user to

select more than one symptom, if desired. This is to address the practical possibility of having a

faulty dyed fabric that may exhibit more than one symptom. In an extreme case, a user may select

all displayed symptoms. This was made possible in the system by using a dynamic salience

approach. The other reason to adopt a dynamic salience was to rapidly fire the rules for the most

likely causes of all symptoms based on the selection by the end-user. The dynamic salience

approach was applied by separating the rules in the knowledge base with codes. The rules are

coded in a separate file and can be called when required. The dynamic salience applied in the

development of the system is based on the summation of weighted average values obtained from

the expert responses.

In the user interface designed for DEXPERT-B, the observer was provided with the option

to select the symptom from a list of symptoms based on the material and coloration process

selections. The survey consists of 18 symptoms and 196 possible causes. The causes in the

knowledge base were defined as single rules with salience values defined as global variables at the

487

beginning of the ‘diagnose’ module. The default values were set to zero. The rules are saved in a

separate file. The structure of the rules is given below:

(defrule cause001

(declare (salience ?*salience001*))

(c001)

=>

(ask-question-update causes “question related to cause 1” YES “answer related to cause 1”)

)

……

(defrule cause196


(c196)

=>

(ask-question-update causes “question related to cause 196” YES “answer related to cause 196”)

)

The following example illustrates the actual rule built into the expert system:

(defrule cause001)


(c001)

(ask-question-update-causes "Were the colorants and chemicals weighed accurately?" NO "Errors

in the weighing of colorants and chemicals")

)

Consider a scenario where a user selects symptoms S15 (holes and tears), S16 (poor hand)

and S17 (poor dimensional stability) for a dyed PES/CELL woven fabric. The possible causes and

their weighted average expert responses are given in Table 6.10-

Table 6.12. The causes in bold represent common causes, C166 and C173, among

symptoms S15, S16, and S17.

488

Table 6.10: Possible causes for S15 and weighted average CF.

Cause Description CF

C159 Catalytic damage during bleaching 8

C079 Non uniform or damaged machine parts 7

C165 Physical damage of substrate (pin marks, cuts) 7

C177 Presence of holes, tears or cuts in greige substrate 7

C153 Fiber damage during scouring and bleaching 5

C166 Excessive overstretching of substrate on stenter 4

C081 Longer duration of substrate run due to reprocessing 4

C193 Foreign fiber contamination 4

Table 6.11: Possible causes for S16 and weighted average CF.


C164 Fiber damage during heat setting 8



C151 Incomplete removal of sizing agents and sizing wax 6

C094 Presence of oligomer deposits on the substrate surface 5

C158 Inadequate weight reduction of polyester 5




C073 Too high drying temperature 4

C138 Too high thermofixation temperature 4

C139 Too long thermofixation time 4

C154 Too high weight loss during scouring 4

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Table 6.12: Causes for S17 and weighted average CF.


C163 Improper heat setting of substrate 8


C080 Excessive, insufficient or variable tension during fabric run 6



C155 Insufficient relaxation of the substrate during washing 6

C180 Yarn mixing 5

C191 Lower yarn strength & elongation 5



Based on the selections, the system will run the following code to assert the causes. It can

be noted that default salience values of all causes are zero and when new causes are asserted their

specific salience value are added into the existing salience value. Symptom S15 is presented here

as an example.

(if (neq ?*factsymptom15* 0) then

(bind ?*salience159* (+ ?*salience159* 8))






;;;asserting likely and most likely causes

(bind ?*salience159* (assert (c159)))





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Similarly causes related to S16 and S17 will be inserted into the system. As mentioned

earlier the system calls the related saliences and adds up their values. For example, the resultant

salience value for C153 would be 5+7+6=18. The resultant salience of a total of 22 causes is given

in Table 6.13. The number of questions that needs to be answered is increased to 22 questions in

this case and can be increased considerably if more causes are selected.

Table 6.13: The new salience values of the all the cause asserted for S15-S17.







C163 Improper heat setting of substrate 8

C079 Non uniform or damaged machine parts 7

C165 Physical damage of substrate (pin marks, cuts) 7

C177 Presence of holes, tears or cuts in greige substrate 7

C080 Excessive, insufficient or variable tension during fabric run 6

C151 Incomplete removal of sizing agents and sizing wax 6

C155 Insufficient relaxation of the substrate during washing 6

C094 Presence of oligomer deposits on the substrate surface 5

C158 Inadequate weight reduction of polyester 5

C180 Yarn mixing 5

C191 Lower yarn strength & elongation 5

C073 Too high drying temperature 4

C138 Too high thermofixation temperature 4

C139 Too long thermofixation time 4


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C193 Foreign fiber contamination 4

In scenarios like these where a user can select more than one symptom, the questions that

need to be answered by the end-user are increased considerably. To deal with such scenarios the

threshold salience values were defined at the beginning of each rule. Since salience values are

dynamic the threshold values should also be dynamic. With a constant value it is possible to disable

the rules that are required to be fired. The approach used to deal with such cases is based on the

principle of checking the maximum salience value of the selection and dividing it by 2. The system

considers this value as a threshold and compares the actual value of the salience with the threshold.

The rule is only fired if the actual value is greater than the threshold. This allows the end-user to

access the most likely causes and find the root cause of the symptom as quickly as possible. The

use of half of the maximum salience value as threshold allows the upper half of the most likely

rules to be fired. In cases where only one symptom is selected by the end-user the threshold values

allow all of the most likely rules to be fired. The new version of the rule is given below:

(defrule cause001


(c001)

(test (> ?*salience001* (/ (max ?*salience001* ?*salience002* ….. ?*salience196*) 2)))

=>

(ask-question-update-causes " question related to cause 1" YES "answer related to cause ")

)

6.8.1 Effect of blend ratio

This study aims at troubleshooting coloration problems for PES/CELL blends. One important

factor that may determine the dyeing properties of the material is the blend ratio. These properties

may change when the blend ratio is changed. In general, the PES/CELL blends with different blend

ratios are processed in similar machinery and using the same processes. The process parameters

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and conditions are also usually kept the same for ease in processing. Specific changes required

based on the blend ratio are usually small and the process parameters and conditions are usually

optimized to cover a wide range of conditions. This is due to the fact that a change often requires

a long adjustment time and may not be practical or feasible due to production conditions. Thus, in

practical terms, there is almost no difference in process parameters and conditions for a 50/50

PES/CELL blend when compared to 65/35 or 35/65 blends. However, when the share of one fiber

is increased such it gets very close to the 100% fiber, the dyeing properties may change drastically.

For example, in PES/CELL blends with very high polyester content more precautions are required

for processing the polyester component as compared to the cotton component of the blend as PES

determines the main properties. Similar results may also be obtained for a PES/CELL blend with

a higher cotton component.

Thus, the effect of the blend ratio was incorporated in the system rules. For this, the fiber

groups were divided into three categories, namely polyester rich or PC1, polyester/cotton or PC2

and cotton rich or PC3. As the name implies this division is based on the blend ratio of the

respective portion of each fiber component in the material. The PES/CELL blends with a blend

ratio of 75/25 or above are placed in the PC1 group while the PES/CELL with a blend ratio of

25/75 or less is placed in the PC3 group. Blend ratios within the two are placed in the PC2 group.

This is in relation to the results reported in CHAPTER 5 where it was shown that blends with very

high ratio of one fiber exhibited properties similar to the 100% fiber. Table 6.14 shows the

aggregated responses of the most likely cause of causes of symptom 1 (reproducibility) of a fabric

dyed using disperse/reactive dyes by a batch process. The PC2 represents the aggregated responses

of experts obtained from a survey for a polyester/cellulosic blends. The causes that may affect

dyeing properties of the respective fiber in the blend are selected based on the importance of these

causes when 100% fiber is dyed. These are represented as P and C. The P and C represent causes

that are more important when processing 100% polyester and 100% cotton respectively. As the

portion of a fiber in the blend is increased, the causes become more important for the dyeing of

that specific fiber. As the rules in the expert system are fired based on their priority, the causes that

have a larger effect on the symptom should have a higher priority. To incorporate this strategy into

the design of rules in the expert system, the salience values of the causes that directly affect the

symptoms based on the given blend ratio are increased. As the causes in the most likely (CF 7-10)

category have a salience range of 4, the salience values of all causes that may affect the symptom

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based on the blend ratio of material are increased by 4. For example, if a cause C008 has a salience

of 8 in PC2, its new salience value in PC3 (higher cotton content) will be 12. This results in a

change in the firing sequence of causes as shown in columns PC1 and PC3 in Table 6.14 The

causes C007 and C008 have the same priority in PC2 but as the blend ratio is increased C007 has

a higher priority in PC1 and C008 will be fired first in PC3. This strategy was incorporated for all

symptoms during the development of rules in this expert system.

Table 6.14: Mostly likey causes for S1 reproducibility with existing and new salience values as

the blend ratio is increased.

Cause Description P C PC2 PC1 PC3

C001 Errors in the weighing of colorants and chemicals 9 13 13

C003 Too fast/quick addition of chemicals in the bath 8 12 12

C007 Poor dye selection for polyester component P 8 12 8

C008 Poor dye selection for cellulose component C 8 8 12

C082 Variations in dyeing program 8 12 12

C096 High temperature rise rate 8 12 12

C135 Non-uniform air velocity or flow 8 12 12

C087 Inappropriate liquor flow times (in-out and out-in) 7 11 11

C140 Too short thermofixation time 7 11 11

C097 Inappropriate dyebath pH 7 11 11

C179 Fabric rolls from different machines or batch or factory 7 11 11

C002 Improper bath preparation procedure 7 11 11

C004 Too fast/quick addition of dyes in the bath 7 11 11

C010 Variation in colorant strength 7 11 11

C011 Incompatibility between dye classes 7 11 11

C019 Poor disperse dye dispersion stability P 7 11 7

C027 Poor stability of reactive/direct dyes under polyester

dyeing conditions C 7 7 11

C034 Poor color matching of each fiber in the blend 7 11 11

C092 Too large batch size (machine overloading) 7 11 11

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Cause Description P C PC2 PC1 PC3

C100 Too low dyeing temperature 7 11 11

C128 Uneven wet pickup 7 11 11

C133 Differences in fixation temperature or time during

batching C 7 11 11

C137 Too low thermofixation temperature 7 11 11

C143 Inadequate steaming temperature 7 11 11

C144 Inadequate steaming time 7 11 11

C145 Variation in steam pressure inside the steamer 7 11 11

C167 Incomplete mercerization C 7 7 11

C009 Poor dye combinations for each fiber type 7 11 11

C104 Too short dyeing time 7 11 11

C136 Too high drying temperature 7 11 11

C099 Use of too high liquor ratio 7 11 11

C109 Incorrect liquor flow direction 7 11 11

C184 Uneven package density 7 11 11

P: Causes having more effect on the symptom in polyester rich blends

C: Causes having more effect on the symptom in cotton rich blends

6.9 User interface

The user interface is one of the important components of an expert system and a prerequisite for

the success of the expert system. It allows communication between the expert system and the end-

user. The end-user is a person who consults the expert system to solve problems. The interaction

can be in the form of dialog boxes, command prompts, forms or other input methods. In the

development of the user interface, it is important to consider the needs of the user and the tasks

the system is expected to support [456]. The user interface serves two main aspects of the expert

system. The first aspect is a process and problem-specific information. This allows the user to

input the details about the problem and process in the expert system which are used to form the

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basis for the diagnosis. The second aspect is the explanation facility in which the expert system

provides a solution to the problem based on user input along with an explanation [16].

In the development of DEXPERT-B system, the knowledge acquisition from the end-user

includes the material information, and details about the coloration process and symptoms. The

output includes the possible causes of the selected symptoms and explanation pertaining to the

diagnosis. The user interaction starts with the first window of the system as shown in Figure 6.32.

It is a window that provides the end-user with some information about how to run the program

through the help menu and start the program.

Figure 6.32: The main screen for the DEXPERT-B system.

6.9.1 Material function

After the end-user starts the program, a new window appears which deals with the material

function. The material function window is shown in Figure 6.33, where the user is prompted to

provide information pertaining to the material. Three options are provided to the user for selection.

The first option is to select the fiber type from the list of fibers provided. Two dropdown menus

(Fiber 1 and Fiber 2) are provided and the user can select the fiber type in any order. The second

option needs information about the blend ratio of the material (Fiber 1 ratio and Fiber 2 ratio). For

this, a slider is provided and the blend ratio can be selected by moving the slider. The sliders are

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interlinked and changing the blend ratio for one fiber will automatically change the blend ratio of

the other fiber. The third option in the material window is the selection of the substrate type, where

the user can select either yarn, or knitted fabric or woven fabric. After making all selections the

user needs to click the Next button to move to the coloration interface window. If any of the

required information is missing a warning dialogue box appears which asks the user to provide the

missing information.

Figure 6.33: Interface for the selection of material related information.

6.9.2 Coloration function

The coloration function window is shown in Figure 6.34. The window is designed to attain

pertinent information from the user about the coloration process. The available options are mapped

based on the information provided in the material window. In this window, four options are

provided, namely, colorants for each fiber type, dyeing process, dyeing method used and the

machinery. All the options are interlinked, and the end-user is prompted to select the options in

order. Under the colorant option, the various colorants that are applicable to the fiber type are

provided. The colorant options are interlinked based on the knowledge about the coloration

process. For example, if the user selects pigment as the colorant for fiber 1 the system

automatically selects pigment as the colorant for fiber 2 also. The second option deals with the

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dyeing process. The user is prompted to select either a batch, semi-continuous or continuous

process. As some colorants are not applied or cannot be applied through certain dyeing processes

the user is prompted if a wrong selection is made. The third option prompts the user to select the

desired dyeing method, either 1-bath or 2-bath, for the application of colorants and for the dyeing

process selected. In the fourth section, the list box of appropriate coloration machines is

automatically populated based on the information provided by the user in the first three selections.

When multiple choices are available the user is prompted to select the desired machine. Once all

selections are made, the user can proceed to select symptom(s) by clicking the Continue button.

Figure 6.34: Interface for the selection of the coloration process in DEXPET-B.

6.9.3 Symptom function

In order for the expert system to generate accurate results, the end-user must be capable of mapping

the observed symptoms. To facilitate the end-user’s task in selection of the symptoms and to

improve the likelihood of correctly answering the diagnosis questions images showing various

dyeing problems were incorporated in the expert system’s interface. DEXPERT-B contains a total

of 18 faulty dyed sample images. These images are from real faults and were added to improve the

end-user's ability to better categorize and select the symptoms. This also serves as a basis for better

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and more accurate diagnosis of the problem by applying the reasoning process to the selected

symptom(s). Various interfaces for symptoms based on the material and coloration selection are

shown in Figure 6.35 to Figure 6.37.

An end-user can select a minimum of 1 symptom to a maximum of 18 symptoms

simultaneously. A user can only proceed to diagnosis if at least 1 symptom is selected. Changes in

the selection of symptoms images can be made by clicking the same image again to deselect the

image or by using the reset button provided in the symptom window which removes all selections.

Figure 6.35: The user interface containing images of the faulty dyed PES/CELL yarns.

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Figure 6.36: The user interface containing images of the faulty dyed PES/CELL knitted fabric.

Figure 6.37: The user interface containing images of the faulty dyed polyester/cotton woven

fabric.

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The interface window for the diagnosis provides two functionalities as shown in Figure

6.38. On the left side of the window, the information pertaining to the material, colorants used,

dyeing process, machine used, and selected symptoms is provided. In the example provided, the

user selects the polyester/cotton woven fabric dyed using disperse and reactive dyes by the one-

bath process in a jet dyeing machine. The right side of the window provides the diagnosis and the

most probable causes(s) of the symptoms. On pressing the diagnosis button a series of questions

are promoted pertaining to the causes that may be responsible for the symptom(s) under

consideration, as shown in Figure 6.39. Based on the end-user response to these questions the

probable causes responsible for the symptom will be shown under suggested (causes). The detailed

questions related to diagnoses are given in Appendix B. The end-user is also provided with an

option to view all possible causes responsible for the specific symptom(s).

Figure 6.38: Diagnosis interface for woven fabric dyed by batch process using one bath process

in a jet dyeing machine.

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Figure 6.39: An example of the diagnosis function with a question prompt based on the selected

symptom.

6.9.4 Explanation function

The expert system reaches the conclusion for the selected problem(s) by inference. An explanation

function provides reasoning for a particular cause(s) associated with the selected symptom(s).

Many expert systems provide this functionality so that the end-user understands the reasoning

process. In DEPXPERT-B this is implemented by using the “Explain” option after diagnosing the

symptom. Explanation option can be selected from the suggested causes(s) to obtain additional

details. The explanation provides the reason for how this cause is responsible for a particular

symptom(s) and thus providing a better understanding of the process and how to prevent them

from occurring in the future. An example of the explanation interface is given in Figure 6.40.

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Figure 6.40: Example of explanation function for DEXPET-B.

6.10 Using the designed expert system

DEXPERT-B can be run on any windows environment after installing the wxclips application.

The procedure for installation and running the software is given in Appendix C. Different options

are provided to facilitate the use of the program. The user is provided with the option to go back

and change their selections using the “Back” button. The user selections from the preceding

interface windows are shown and the end-user can make the required changes. A “Reset” button

is provided to reset all selections on a particular interface. A “home” button provides the

functionality if the end-user wishes to run the program again from the start. The help option is also

provided to guide the end-user on how to use the interface and select the provided options.

An example of polyester/cotton woven fabric, pigment colored using pad-thermosol

machine is given in Figure 6.41. The end-user selected dark stain or spots (S06) as a symptom. By

clicking the diagnose button the system initiates a series of questions related to specific selections.

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Figure 6.41: An example of the use of DEPXET-B system for diagnosis.

Step 1 Step 2

Step 3 Step 4

Step 5

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CHAPTER 7 TESTING AND EVALUATION OF AN EXPERT

SYSTEM

7.1 Testing of the expert system

Expert systems are computer programs designed to mimic human expert cognitive problem-

solving capabilities. Human experts acquire those capabilities that are garnered through training,

experience, and intelligence. During the development of an expert system, the focus is usually to

extract the knowledge and skills from the domain experts and compile them in the form of a

knowledge base. Expert systems tend to evolve over time. Once the expert system is developed, it

needs to be reviewed, analyzed and tested to ensure a quality system is produced. This whole

process is known as verification, validation, and testing. Verification involves checking the system

against a set of requirements. It is mainly concerned with the structure and form of the system. It

is a process of checking if the expert system is made correctly. The validation is a process of

checking for the correctness of the expert system. It determines if the right product is being made.

Validation is concerned with the behavior of the expert system. Testing involves the examination

of the expert system program by execution on a small dataset. The testing phase determines the

correctness of the expert system [457]. The quality of the expert can also be checked through

evaluation, which involves a testing system for its usability and usefulness [458].

Verification is a process of checking the expert system for its consistency, completeness,

accuracy, and correctness. It involves checking the knowledge base and inference engine. The

main aim is to remove errors in the system. The types of errors that occur in the expert system are

related to the knowledge representation scheme and methods of dealing with conflict resolution

during inference. Verification therefore involves checking the rules and codes for any errors and

making sure, they are correct [458]. This is mostly concerned with the structure or form of the

expert system. The verification process can be considered to be analogous to the paper activity

[16, 457].

Validation is a process to determine if the chain of correct inferences is responsible for

getting the right answer. It is concerned with the model of the expert system. It aims to determine

the quality of the decisions made by the expert system. It is independent of technology or software

used to implement the system. It involves checking the final product and determining if the output

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is meeting the required target. It is an activity that involves testing. Test cases are used to compare

the conclusions obtained from the experts and the expert system [16, 457, 458].

Evaluation deals with value of the expert system. The value of the system depends on its

acceptance by the end-user and its performance during use. During the evaluation phase the system

is assessed against different criteria such as user-friendliness and usefulness by a potential user.

An expert system that is already verified and validated may fail during evaluation if it is found to

have no value to the end-user or it is difficult to use or if it solves something that is rarely required

in practice [459].

7.1.1 Verification

The construction of an expert system is a programming task that involves coding of rules in the

knowledge base and the inference engine. During the verification process, the rules and their

structure are verified for anomalies. The verification checks the technical aspects of the expert

system that can be performed by the developer or knowledge engineer [458].

DEXPERT-B was verified during the development phase and after the complete

development of the final program. Verification of the system was performed using the following

approaches:

▪ Reviewing and proofreading the knowledge base and inference rules for syntax and

correct logic and making revisions if and when required. This involved checking the

system for consistency, completeness, and correctness [458].

▪ Checking the results obtained from the expert system using sample cases and

comparing it with the knowledge obtained from various sources during the knowledge

acquisition step. This is known as a domain dependent verification [458].

▪ Checking the system for anomalies which involves the unusual representation of

knowledge scheme. This is known as domain independent verification. Anomalies can

be of different types that include duplication, inconsistency, looping and

incompleteness [458, 460].

▪ Examining system for incorrect or incomplete input from the end-user. This involves

checking the working of the rules if incorrect input or combination is selected by the

end-user or required information is missing.

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7.1.2 Validation

The validation of DEXPERT-B was performed using actual faulty colored samples acquired from

Lucky Textile Mills in Pakistan and ACS Textile Mills in Bangladesh. The faulty dyed samples

were taken randomly from the dyed fabric rolls during the inspection process. The dyed fabric roll

was examined for faults during the inspection process and the faulty portion of the fabric was cut.

These faulty samples were then segregated based on the nature of the faults. They comprised

seventeen faulty PES/CELL samples that were colored either using pigments or dyes by batch and

continuous processes. These samples were examined by a number of coloration experts to obtain

their opinion pertaining to the root cause of faults in these samples. The samples presented to

experts for examination were ironed to remove creases. Five experts with a broad range of

experience in coloration and research took part in this validation phase. These responses were then

used to validate the knowledge base of DEXPERT-B.

Experts were provided with the categorized list of possible causes along with faulty colored

samples to suggest most likely causes responsible for the occurrence of each fault. The experts

were also provided the colorants and process related information. The responses obtained were

then analyzed to perform the validation process. During validation, the possible causes suggested

by the experts were compared to the knowledge base developed using expert responses and the

literature obtained during the knowledge acquisition phase of DEXPERT-B development.

Expert responses for the diagnosis for one of the symptoms “holes and tears” (S15) are

given in Table 7.1. The left side of the table shows the expert system knowledge base along with

the weighted average response. The right side of the table shows the responses from the individual

experts who participated in the validation stage. Expert responses were mostly consistent among

experts and most selected response was referred to catalytic damage during bleaching (C159) as

the most likely cause of the problem. This was also the most likely cause according to the expert

system knowledge base. The majority of the experts also selected a longer duration of substrate

run due to reprocessing (C081) as one the causes that may be responsible for the occurrence of

holes in the observed sample. No experts selected foreign fiber contamination (C193) as one of

the cause that may be responsible for the holes.

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Table 7.1: Expert responses and expert system’s knowledge base for presence of holes and tears (S15).

Expert system’s knowledge base

Literature Experts


Commonness H M A B C D E

C159 Catalytic damage during bleaching 8 S13, S16 [100, 149, 303, 305,

323] x x x x x

C079 Non uniform or damaged machine parts 7 S3, S14 [149, 150] x x x

C165 Physical damage of substrate (pin marks, cuts) 7 [67, 194, 341] x x

C177 Presence of holes, tears or cuts in greige substrate 7 [203, 216, 250, 259,

261, 272-275] x

C153 Fiber damage during scouring and bleaching 5 S2, S13, S14,

S16, S17 [70] x x

C166 Excessive overstretching of substrate on stenter 4 S14, S15, S17 [194, 341] x x

C081 Longer duration of substrate run due to

reprocessing 4

S13, S14,

S16, S17 [301] x x x x

C193 Foreign fiber contamination 4 S7 [6, 157, 209, 210]

CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections

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Expert responses for the occurrence of poor color yield, symptom (S4), are shown in Table

7.2. According to the expert system knowledge base, poor color yield in the colored fabric may

occur due to multiple causes. In fact, a total of 30 causes with high and medium certainty factors

may be attributed to this symptom. According to the results obtained from human experts, most

agreed that the “presence of residual alkali/hydro after dyeing cycle” (C072) and “incomplete

mercerization (C167)” were the most probable causes of this symptom. According to the expert

system’s knowledge base, the most likely causes responsible for this symptom included too low

dyeing temperature (C100) which was also chosen by two experts (Expert B and E).

Experts’ responses together with the expert system knowledge base for the symptom S10

“widthwise share variation in pigment colored fabric” are given in Table 7.3. The experts were

very consistent in their response when selecting “uneven pickup” (C128) as the cause which is

also the second most likely cause according to the expert system’s database. Three experts

diagnosed additional possible causes whereas Experts C and D chose only two causes for the

symptom. The expert system, on the other hand, provided 11 likely causes for the symptom.

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Table 7.2: Responses from human experts and the expert system for poor color yield (S4).


Literature Experts



C100 Too low dyeing temperature 9 S1, S2, S6a-c, S11 [297, 301] x x

C048 Inappropriate electrolyte (salt)

concentration 7 S1, S2, S9, S11 [128, 317, 345] x x x

C027 Poor stability of reactive/direct dyes under

polyester dyeing conditions 7 S1, S2, S7

[64, 68, 79, 122,

253] x x x

C072 Presence of residual alkali/hydro after

dyeing cycle 7 S1, S2, S5, S8 [251, 253, 348] x x x

C011 Incompatibility between dye classes 7 S1-3, S5-7, S9,

S10, S11

[7, 9, 79, 92, 93, 100,

128, 253, 301] x x

C019 Poor disperse dye dispersion stability 7 S1, S2, S7, S9,

S10, S11

[7, 67, 68, 75, 79,

81, 85, 253] x x

C167 Incomplete mercerization 7 S1, S2, S3, S9,

S10

[9, 184, 253, 305,

333, 334, 337, 338]. x x x x

C097 Inappropriate dyebath pH 7 S1, S2, S5, S6a-c,

S9, S10, S13 [301] x x x

C018 Poor disperse dye dispersion system 6 S1, S2, S5, S7, S9,

S10, S11 [75, 253, 348] x x

510



Literature Experts



C077 Presence of reductive chemicals in

substrate, water or steam 6 S1, S2, S5 [64, 251, 301] x x

C160 Presence of residual peroxide in substrate 6 S1, S2, S5, S8 [100, 150, 253,

301] x x x

C163 Improper heat setting of substrate 6 S1, S2, S3, S5, S9,

S10, S14, S17

[67, 83, 168, 194,

253, 320, 323] x x

C099 Use of too high liquor ratio 5 S1, S4, S5 [297] x x x

C001 Errors in the weighing of colorants and

chemicals 5 S1, S2, S5, S9

[77, 142, 317, 345,

348] x

C010 Variation in colorant strength 5 S1, S2, S5 [253, 301] x x

C024 Poor solubility of reactive/direct dyes 5 S1, S2, S5, S6b,

S6c, S7, S9-11

[9, 68, 75, 100, 111,

118, 231] x x

C035 Variations in strength and purity of

dyebath chemicals 5

S1, S2, S5, S6a-d,

S7 [79, 89, 103] x

C036 Chemical or physical interaction between

colorants and auxiliaries 5

S1-3, S5, S6a-d,

S7-11

[18, 78, 79, 86, 89,

103, 253] x x

C049 Inappropriate concentration of dispersing

agent 5

S1, S2, S5, S9,

S10,S11

[67, 89, 97, 106,

109] x x

511



Literature Experts



C068 Inadequate pH during soaping 5 S6a-c [61, 85, 301, 345,

370] x

C082 Variations in dyeing program 5 S1, S2, S5 [9, 253, 297, 301] x

C151 Incomplete removal of sizing agents and

sizing wax 5

S1-3, S5, S7-10,

S16

[67, 149, 303, 305-

307, 324-329] x x


finishes, and knitting oils 5 S1-3, S5, S8-10

[149, 277, 278, 297,

303, 305, 317, 327] x x

C028 High dye reactivity 5 S1, S2, S7-10 [9, 68, 100, 118,

128, 231] x x

C175 Presence of bicarbonate in water 5 S1, S2, S5 [283, 295-297] x x

C176 Presence of chlorine in water 4 S1, S2, S5, S11 [281, 285, 286] x x

C162 Inadequate whiteness of substrate 4 S1, S2, S5 [150, 301, 305,

309] x x

C172 Presence of Ca and Mg ions (hardness) in

water 4

S1, S2, S5, S6a-c,

S7, S11

[277, 280, 283, 290,

292, 296, 298, 299] x

C169 Alkaline pH of substrate before dyeing 4 S2, S9, S10 [301, 305, 309, 317,

334] x x

512



Literature Experts



C173 Presence of heavy metals (Cu, Fe, Mn,

Zn) in water 4

S1, S2, S5, S7,

S13

[277, 280, 283, 286,

288-292] x x


Table 7.3: Responses from human experts and the expert system for widthwise shade variation in pigment coloration (S10).


Literature Experts



C134 Variation in the intensity of the IR

pre-dryer 9 S1-3, S5, S9, S12 [348, 363] x x x x

C128 Uneven wet pickup 9 S1-3, S9 [61, 100, 128, 133,

353] x x x x x

C135 Non-uniform air velocity or flow 8 S1-3, S5, S6a, S9, S12 [67, 317, 361, 363] x x x

C136 Too high drying temperature 7 S1-3, S5, S6a, S6e,

S9, S12 [85, 118, 253, 369] x x x

C052 Lower quantity of anti-migrating

agent 6 S1, S2, S3

[92, 95, 100, 105,

118, 130-132] x x x

513



Literature Experts




between colorants and chemicals 5

S1-5, S6a, S6d, S6e,

S7-9, S16, S18

[18, 78, 79, 89, 103]

[86, 253] x x x

C053 Precipitation of anti-migrating agent 5 S1-5, S8, S9 [92, 95, 100, 105, 118,

130-132]

C141 Temperature variation in the hotflue 5 S1, S5, S6e, S9 [118, 253, 348, 370] x x x

C002 Improper bath preparation procedure 4 S1, S2, S5, S7, S9,

S18 [297, 301, 317] x

C005 Too high colorant concentration 4 S1-5, S6a, S7, S9,

S16, S18 [93, 100] x

C127 Improper distribution and circulation

of dye liquor 4 S1, S2, S5, S9, S12

[61, 100, 128, 133,

353] x x


514

A detailed comparison of the remaining symptoms is given in Appendix D. The experts’

opinion pertaining to the most likely cause(s) of the symptoms tend to contain few causes when

compared to the expert system’s knowledge base. This may be due to the fact that the expert

system’s knowledge based was developed by aggregating responses from multiple sources based

on a wide range of scientific and technical knowledge and expertise.

The performance of individual experts was found to be below par as compared to

DEXPERT-B. In some cases the individual responses were found to be inconsistent with each

other. There may be many reasons that are responsible for these results. Individual experts often

have different expertise based on their training, experience, and intelligence and they usually

consider only a few most common causes based on their experience or observations. This is not

the case for expert systems where the knowledge base is developed by combining responses from

multiple experts and using causes reported in the technical and scientific literature. This provides

the expert system with the ability to generate a more comprehensive list of causes responsible for

a specific fault. While a list comprising multiple potential causes can be useful from an educational

perspective, it may also hinder the rapid identification of the root cause of a problem. Nonetheless,

expert systems can be useful tools since they often perform better than individual experts. They

can also be effective when in dealing with contradictions or differences in opinions among human

experts dealing with a particular problem.

In conclusion the performance of DEXPERT-B in troubleshooting a range of symptoms in

the dyeing of PES/CT blends was found to be better than that of individual experts tested in this

study. Therefore, it can be said that this system provides comprehensive and useful information

when attempting to determine the actual root causes of dyeing faults.

7.2 Evaluation of the expert system

The evaluation of an expert system is an important step. The process of evaluation includes the

determination of the appropriateness of the system against its requirements, to establish its

usefulness by the end-user and performance in the field [459, 461]. The main challenge associated

with the evaluation of the expert systems is to establish common evaluation criteria for its

usefulness and functionality as different domains may have different requirements and applications

of the expert system [461]. In general, for the evaluation of expert systems one may consider the

following points [459, 461]:

515

▪ User-friendliness and acceptance by the end-user;

▪ Correctness of the results and reasons provided by the system;

▪ Improvements in the practices of the domain where the system is designed to be used;

▪ Easiness in the learning of the system by the end-user;

▪ Training potential of the system;

▪ Manageability of the system by the organization where it is deployed;

▪ Practical use of the system in the actual work environment;

▪ Ability of a system to replace human experts in the decision-making process; and

▪ Financial impact.

The evaluation of DEXPERT-B was performed based on the criteria adopted in previous

studies used to develop a diagnostic expert system for the coloration of polyester [410] and protein

fibers [412]. The criteria chosen were usefulness, user-friendliness, response time, educational/

training value and overall performance. Five experts with a wide range of experience in the

coloration industry took part in the evaluation of the software using a Likert scale with five ratings

comprising, very poor, poor, fair, good and excellent. The results obtained from the expert

evaluations are given in Table 7.4.

Table 7.4: Evaluation results of the expert system.

Criteria Very poor Poor Fair Good Excellent

Usefulness 3/5 2/5

User-friendliness 2/5 3/5

Response time 2/5 3/5

Educational/ training value 1/5 1/5 3/5

Overall performance 4/5 1/5

The results showed overall positive results for the system. All experts found the system to

be useful and user-friendly with 40% giving it a rating of ‘Good’ and the remaining 60%

‘Excellent’. The response time was also found to be good to excellent. One out of five experts

chose a rating of ‘Fair’ for its educational/training value and suggested the development of a

516

mobile application as a preferable platform. In terms of the overall performance criterion, the

evaluators found the system to be good (80%) to excellent (20%). Many evaluators showed quite

an interest in the developed system and asked that the full version be made available for

deployment in their industry. The evaluators provided the following suggestions regarding the

system:

▪ Availability of the system in an easy to deploy platform, such as Windows applications.

▪ Availability of the system in a mobile application format.

▪ Availability of the system for other blends like elastane blends.

▪ Ability to store and taking printouts of the diagnosis results.

▪ Ability of the system to take pictures of the actual fault and storage of results in a

database.

The expert system was also evaluated for its diagnosis accuracy using the seventeen faulty

colored samples. The exact causes of all the faults were known in advance. Each faulty sample

was examined by five human coloration experts. To compare the responses from human experts

against those from the expert system and to avoid bias DEXPERT-B was run by a potential user

who was not aware of the actual causes of the symptoms. The results obtained are shown in Table

7.5. The average accuracy of experts was found to be 58% with the highest rate achieved by Expert

A (76%). The accuracy of DEXPERT-B was found to be 100%. The difference in the performance

of human experts and expert system is because the experts tend to consider only the more common

causes of symptoms based on their experience. The knowledge base of DEXPERT-B was more

comprehensive since it was developed by combining the expertise of multiple experts and

knowledge reported in the literature. Therefore, it is highly unlikely for the expert system to miss

the cause of the given symptom.

Table 7.6 shows the details of the faulty colored samples that were observed by human

experts along with their responses in comparison with DEXPERT-B. It can be seen that the

expert’s accuracy for diagnosis varied for each symptom. The highest fault diagnosis accuracy of

100% was obtained for three symptoms ‘widthwise shade variation’ (S11), ‘holes and tears’ (S12)

and ‘poor dimensional stability’ (S17). The lowest accuracy of 20% was obtained for ‘darks stains’

(S7) and ‘lengthwise shade variation’ (S9).

517

Table 7.5: Comparison of diagnosis of faulty colored samples, human vs expert system.

Details Expert A Expert B Expert C Expert D Expert E DEXPERT-B

Experience 20 15 20 35 30 -

Correct

diagnosis 12 8 11 10 7 17

Accuracy % 76% 48% 65% 59% 42% 100%

Table 7.6 shows the details of the faulty colored samples that were observed by human

experts along with their responses in comparison with DEXPERT-B. It can be seen that the

expert’s accuracy for diagnosis varied for each symptom. The highest fault diagnosis accuracy of

100% was obtained for three symptoms ‘widthwise shade variation’ (S11), ‘holes and tears’ (S12)

and ‘poor dimensional stability’ (S17). The lowest accuracy of 20% was obtained for ‘darks stains’

(S7) and ‘lengthwise shade variation’ (S9).

It can be seen that the expert’s ability to correctly diagnose the problem varies among

experts. Experts A, C, and D are directly involved in the production of dyed material whereas

experts C and D while having previously had industrial experience are no longer involved in a

production setting and conduct research-related activities. The experts who are involved in the

coloration process on a day to day basis are often better in diagnosing faults as compared to ones

who have coloration experience but are not currently involved in the production of colored

material. The experts who are currently working in the industry are more aware of the actual causes

of the problems because of dealing with these types of faults on a daily basis. The difference,

however, may also be due to differences in the educational background and the nature of the

experience of experts in production settings. The performance of DEXPERT-B, on the other hand,

was found to be significantly better than the human experts in the diagnosis of faulty colored

samples. Since the expert system has an explanation facility along with the diagnosis it is

considered to be more useful and helpful in determining the root causes of faults and providing

solutions to avoid or minimize their repeated occurrence.

518

Table 7.6: Diagnosis results of human experts and DEXPERT-B.

Symptom

Actual cause

Exp

ert

A

Exp

ert

B

Exp

ert

C

Exp

ert

D

Exp

ert

E

% c

orr

ect

DE

XP

ER

T-B

S1 Reproducibility C099 Use of too high liquor ratio x x 40% x

S2 Unlevelness C096 Higher temperature rise rate x x x 60% x

S3 Streaks, stripes or bands C135 Non-uniform air velocity or flow x x 40% x

S4 Poor color yield C072 Presence of residual alkali/hydro after

dyeing cycle x x x 60% x

S5 Shade change C192 Variation in blend ratio x x 40% x

S6 Inadequate washing

fastness C066

Inadequate concentration of hydro & caustic

during reduction clearing x x x x 80% x

S7 Dark stains or spots C156 Localized swelling of fiber x 20% x

S8 Light stains or spots C053 Precipitation of anti-migrating agent x x 40% x

S9 Lengthwise shade

variation C145

Variation in steam pressure inside the

steamer x 20% x

S10 Widthwise shade

variation C128 Uneven wet pickup x x x x x 100% x

S11 Shade variation within

layers

C107 Too low liquor flow rate x x x 60% x

S12 Two sidedness C134 Variation in the intensity of the IR pre-dryer x x x 60% x

519


Symptom

Actual cause

Exp

ert

A

Exp

ert

B

Exp

ert

C

Exp

ert

D

Exp

ert

E

% c

orr

ect

DE

XP

ER

T-B

S13 Reduced strength C149 Fiber damage during singeing x x 40% x

S14 Irregular surface

appearance C122

Damaged, worn out or uneven padder

surface x x 40% x

S15 Holes or tears C159 Catalytic damage during bleaching x x x x x 100% x

S16 Poor hand C164 Fiber damage during heat setting x x x x 80% x

S17 Poor dimensional stability C166 Excessive overstretching of substrate on

stenter x x x x x 100% x

520

CHAPTER 8 CONCLUSIONS AND FUTURE WORK

8.1 Conclusions

The research work has provided a functional expert system that contains and utilizes expert

problem-solving knowledge to identify the specific causes of different problems in the coloration

of PES/CELL blends using dyes and pigments. The problem of troubleshooting is covered

holistically using knowledge from the experts and published literature. The system was developed

in three phases. In phase I common blends were identified and knowledge acquisition was carried

out. In phase II, the design and development of the system were performed. In phase III, the system

was tested and evaluated for its functionality and usefulness.

The first phase was divided into sub-phases (A and B). In sub-phase A, common blend

types were identified. This is necessary as there are many blend combinations available in the

market and a coverage of every blend type is not realistic nor practical. Through consultations with

fiber and yarn producers, and a study of the reported trade data, it was found that PES/CELL blends

represent the majority of the blends currently produced. Once the blend type was identified sub-

phase B was carried out which led to the development of a comprehensive knowledge base.

Selected manuscripts from scientific journals, textbooks, published reports and technical

information from dye manufacturers were used to develop a comprehensive list of common

coloration problems and their potential causes. A comprehensive cause and effect diagram was

created to systematically analyze problems in the coloration of PES/CELL blends. The list of

common coloration problems and their causes was finalized in consultation with the practical dyers

and machinery manufacturers. A final list of eighteen problems in the coloration of PES/CELL

was thus obtained. An electronic survey, based on the list of common dyeing problems and

potential causes, in the form of an excel spreadsheet was developed to determine the

interrelationship between the problems and causes. Several coloration experts from different

regions with a broad range of experience from 10-40 years participated in the electronic survey.

They were from different sectors of the industry including practical dyers, dye manufacturers, and

dyeing consultants. The experts were asked to provide the relationships between the causes and

coloration problems using certainty factors ranging from 0 (no correlation) and 10 (excellent

correlation). Additionally, they were also provided with an option to use X if they felt unsure about

the existence of a relationship. The responses obtained from different experts were analyzed and

521

evaluated. These were then incorporated in the knowledge base according to three categories: most

likely, likely and least likely causes of each symptom. Responses were aggregated using the

weighted average method.

During phase II, the comprehensive knowledge obtained in the previous phase was coded

in the form of rules using the CLIPS expert system tool. The system was designed in the form of

two modules covering both dyes and pigments that are used in the coloration of PES/CELL blends.

A modified version of CLIPS with GUI functionality, wxCLIPS, was used to code the knowledge

base. The inference engine was also developed to determine rule priority. Several practical

functionalities were also incorporated in the design and development phase. These included the

use of dynamic rules to calculate new values based on selected problems, the ability of the system

to deal with multiple problems at the same time and the incorporation of the effect of blend ratio

on the nature of coloration problems. The system was also provided with an explanation facility

based on the causes that are found to be responsible for a particular problem and which may change

based on the fiber type and blend ratio. Some other functionalities, related to the use of the

program, included the option for the user to return to their previous selections and replace them if

required, or to reset their selections in the current interface if errors are made, or to restart the

program for a new diagnosis. In the diagnosis screen, the end-user is provided with the material

and coloration related problem along with problems selected for diagnosis. The user is also

provided with the help option for guidance on how to use the program and definitions of some

terms used in the software to make the system user-friendly and easy to use.

In phase III, the system was tested and evaluated using a validation and verification

approach. During the verification phase, the system was checked for any errors or anomalies. In

the validation phase, the knowledge base of the system was authenticated by testing the

performance of the system against human experts using actual faulty dyed samples taken from

production facilities. The system was then evaluated for its usefulness using multiple criteria that

included usefulness, user-friendliness, response-time, educational/training value, and overall

performance.

To compare the performance of DEXPERT-B against human experts in diagnosing

problems, several faulty samples were obtained from production facilities that covered both

pigment and dye based coloration processes. The exact causes of the faults were known to

determine the accuracy of the designed system and compare its diagnosis ability against human

522

experts. The samples were then diagnosed and evaluated by five human experts as well as the

expert system. It was found that the expert system was able to correctly diagnose all faults whereas

in the case of human experts comparatively lower accuracy was obtained.

Since the system was developed by combining the expertise of several experts as well as

the reported literature, it outperformed individual experts. In fact the average accuracy for human

experts was found to be 58%. Troubleshooting is a complex process and may take considerable

time. It depends to a large extent on the level and type of expertise of the human expert which can

vary widely among individuals based on their experience and training. The expert system, on the

other hand, can provide a comprehensive knowledge base to determine the root causes of faults in

the coloration of material, in this case PES/CELL blends, in a relatively shorter period. Since the

system covers all major sectors that are involved in the production of material and may thus be

responsible for the development of a specific problem, the results obtained from an expert system

are likely more comprehensive and can be helpful in practical settings for different users.

8.2 Recommendations for future work

PES/CELL blends occupy a very important position in the textile industry due to their compatible

and enhanced properties. However, their coloration can be challenging due to the large number of

variables involved. The coloration of blends requires different dye classes due to differences in the

dyeing behavior of the two materials. Dyeing challenges include cross-staining of the fiber by the

dye intended for the other fiber type, interferences between dye classes and dye bath chemicals, as

well as the additional time required to fix both dyes for each component, in this case cellulose and

polyester. However, PES/CELL blends are sold at cheaper prices than 100% cotton. With

increasing labor and production costs and due to the exerted pressure to enhance profits, the need

to rapidly resolve coloration problems for blends is becoming increasingly evident.

The diagnostic expert system developed for the coloration of PES/CELL blends in this

study was designed to assist practical dyers and the personnel involved in the coloration of these

materials to quickly identify the root causes of problems and provide rapid solutions. This is

expected to help the industry by improving the shade reproducibility of blended products and by

reducing their coloration cost thus making their processing more competitive, environmentally

friendly and profitable.

Nonetheless, it is recommended to consider further work in the following areas:

523

▪ Expert systems are useful in diagnosing a problem in the complex coloration domain.

However, they have certain shortcomings which can result in making errors. The

systems should have the ability to adapt and adjust their response based on

consideration of the mistakes made.

▪ A feedback mechanism should be incorporated into the design and development of the

expert system.

▪ Neural networks or other inference techniques could be incorporated in the system to

improve the performance of the inference engine and make them more useful and

practical. In a rule-based system, the expert system may be unable to diagnose the fault

if the knowledge base does not have essential information about a particular fault i.e.

no specific rules are present in the knowledge base for an unknown fault. However,

this limitation can be overcome by using models of the process structure and functions

using an artificial neural network (ANN). ANN has an inherent property of learning

that maps a functional relationship between causes and symptoms. In case of an

unknown fault, the ANN can provide the closest possible cause(s) that may be

responsible for the particular fault.

▪ The system could include a built-in option to store all the diagnostic data for retrieval

and ease of access for future use.

▪ Furthermore, other modules for coloration of elastane containing fiber blends may also

be incorporated. Elastane is extensively used in blends and approximately 35-40% of

all apparel contains elastane due to its unique functional and fashion related properties.

▪ The newly developed expert system in this study can be combined with the existing

expert systems to create a comprehensive expert system for troubleshooting faults in

the coloration of textiles.

▪ Several additional modules such as denim finishing, conventional printing, and

finishing can be developed to increase the expertise domains in textile wet processing.

▪ The system was developed using wxCLIPS that has limited functionality in the

development of a user friendly GUI. JAVA, VB.net, or other suitable environments can

be incorporated to develop more user-friendly and easier to deploy systems. The main

challenge associated with using these environments is to allow information to be easily

exchanged by calling CLIPS functions from these environments. This requires writing

524

of interface functions. Clearly, knowledge engineer would also need good

programming skills along with coloration knowledge to allow complete language

mixing.

▪ A new expert system can be developed that uses a real-time image capturing facility to

diagnose root causes of problems for actual faulty dyed materials.

▪ Several faults’ accurate diagnosis requires laboratory analysis to reach the root cause

of the problem. The ability to add laboratory analysis during the troubleshooting

process can be helpful in making a more accurate diagnosis of the problem.

▪ The system should be developed as a web-based or mobile application to facilitate its

use and provide real-time functionality.

525

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546

APPENDICES

547

Mean expert responses for symptoms and their causes.

Table A.1: Mean responses of experts for symptoms and their causes related to dyes. C

au

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C001 9 4 0 5 4 0 0 0 0 2 0 5 0 0 0 0 0 0 0 0

C002 7 5 0 2 4 0 0 0 0 6 2 4 0 0 0 0 0 0 0 0

C003 8 9 3 0 0 0 0 0 0 3 0 6 2 7 0 3 0 0 0 0

C004 7 9 0 0 0 0 0 0 0 0 0 6 2 6 0 0 0 0 0 0

C005 2 2 2 0 0 5 5 5 0 4 0 2 0 0 0 0 0 0 0 0

C006 0 3 0 0 0 9 9 9 0 0 0 0 0 0 0 0 0 0 0 0

C007 8 3 0 0 0 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0

C008 8 3 0 0 0 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0

C009 7 8 0 0 6 0 0 0 5 0 0 5 5 4 3 0 0 0 0 0

C010 7 4 0 5 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C011 7 7 4 7 7 5 5 5 5 6 0 5 5 6 0 0 0 0 0 0

C012 3 2 0 0 3 9 9 9 4 0 0 0 0 0 3 0 0 0 0 0

C013 2 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0

C018 6 7 1 6 7 0 0 0 0 8 0 7 5 7 3 0 0 0 0 0

C019 7 7 0 7 0 0 0 0 0 8 0 4 4 5 0 0 0 0 0 0

C020 5 6 2 3 3 0 0 0 0 0 0 0 0 7 0 0 0 0 0 0

548

Table A.1 (Continued) C

au

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C021 6 6 2 0 5 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0

C022 0 0 0 0 0 9 9 9 0 0 0 0 0 0 0 0 0 0 0 0

C023 6 6 0 0 0 5 5 5 0 0 0 8 4 5 0 0 0 0 0 0

C024 6 7 0 5 7 3 4 4 0 8 0 5 5 7 0 0 0 0 0 0

C025 5 5 0 0 0 2 3 3 0 0 0 0 0 7 0 0 0 0 0 0

C026 6 6 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0

C027 7 4 0 7 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0

C028 5 6 0 5 0 0 0 0 0 5 0 7 4 0 0 0 0 0 0 0

C029 6 7 0 0 0 0 0 0 0 0 0 8 4 5 0 0 0 0 0 0

C030 4 4 0 0 0 0 0 0 0 0 0 2 3 5 0 0 0 0 0 0

C031 5 5 0 0 0 0 0 0 0 0 0 0 3 7 0 0 0 0 0 0

C032 6 6 0 0 5 0 0 0 0 0 0 0 3 6 0 0 0 0 0 0

C033 6 7 1 6 7 0 0 0 0 7 0 7 5 7 3 0 0 0 0 0

C034 7 0 0 0 8 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0

C035 5 5 0 5 4 4 4 4 4 5 0 2 0 0 3 0 0 0 0 0

C036 5 5 5 5 5 4 4 4 4 5 4 4 4 6 0 0 0 0 0 0

C037 5 5 4 0 4 4 4 4 4 5 4 5 5 4 3 0 4 0 0 0

549

Table A.1 (Continued)

Cau

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C048 5 4 2 7 0 3 3 3 0 0 0 4 3 7 3 0 0 0 0 0

C049 5 5 1 5 5 0 0 0 0 0 0 4 5 5 0 0 0 0 0 0

C050 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0

C051 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0

C052 5 6 7 0 4 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0

C053 5 5 5 0 5 0 0 0 0 0 6 4 4 0 0 0 0 0 0 0

C054 3 0 0 0 6 0 0 0 7 0 0 0 0 0 0 0 0 0 3 0

C055 0 0 0 0 0 1 1 1 0 7 0 0 0 0 0 0 0 0 0 0

C056 5 5 0 6 5 5 5 5 0 0 0 0 0 5 3 0 0 0 0 0

C057 5 5 0 5 4 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0

C058 5 0 0 0 3 4 4 4 0 0 0 2 3 0 0 0 0 0 0 0

C059 5 0 0 0 2 4 4 4 0 0 0 3 0 4 0 0 0 0 0 0

C060 5 3 2 0 3 6 6 6 0 0 0 3 3 0 0 0 0 0 0 0

C061 5 5 2 0 5 6 6 6 0 0 0 2 5 4 0 0 0 0 0 0

C062 5 5 0 6 5 5 5 5 0 0 0 5 5 4 0 0 0 0 0 0

C063 5 0 2 0 4 5 5 5 0 0 0 2 3 0 0 0 0 0 0 0

C064 3 3 2 2 2 8 8 8 0 0 0 2 0 0 0 0 0 0 0 0

C065 3 3 2 1 2 8 8 8 0 0 0 2 0 0 0 0 0 0 0 0

550


Cau

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C066 3 3 2 0 2 8 8 8 0 0 0 2 0 0 0 0 0 0 0 0

C067 3 3 2 0 4 8 8 8 0 0 0 5 5 4 0 0 3 0 0 0

C068 3 2 1 5 2 7 7 7 0 0 0 2 2 0 0 0 0 0 0 0

C069 3 3 3 2 5 8 8 8 0 0 0 0 3 0 0 0 0 0 0 0

C070 3 3 1 0 1 8 8 8 0 0 0 2 2 0 0 0 1 0 0 0

C071 3 3 2 1 4 7 7 7 0 0 0 5 5 4 2 0 2 0 0 0

C072 5 5 0 7 5 0 0 0 0 3 5 0 0 0 0 3 0 0 0 0

C073 0 0 0 2 3 1 1 0 1 0 1 0 0 0 0 2 0 4 3

C074 1 0 3 1 0 0 0 0 0 1 0 1 0 0 0 2 3 2 3 1

C075 2 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0

C076 0 2 1 0 0 0 0 0 0 6 0 0 0 0 0 0 2 0 0 0

C077 6 5 0 6 5 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0

C078 2 5 2 0 0 0 0 0 0 7 5 0 0 0 0 0 2 0 0 0

C079 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 6 7 0 0

C080 0 0 0 0 0 0 0 0 0 0 0 3 3 0 0 0 6 0 0 6

C081 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 6 4 7 6

C082 8 8 0 5 6 2 2 2 0 0 0 3 3 0 3 0 1 0 0 0

C083 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0

551


Cau

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C084 4 2 5 0 0 0 0 0 0 0 0 0 0 5 0 0 6 0 0 0

C085 5 6 0 4 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 0

C086 3 1 7 0 0 0 0 0 0 0 0 0 0 4 0 0 8 0 0 0

C087 7 8 5 4 5 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0

C088 4 7 6 4 2 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0

C089 2 2 3 2 2 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0

C090 6 7 3 3 4 0 0 0 0 0 0 0 0 7 0 0 2 0 0 0

C091 3 3 3 3 3 0 0 0 0 0 0 0 0 3 0 0 6 0 0 0

C092 7 7 5 0 2 0 0 0 0 0 0 2 3 7 2 0 7 0 3 1

C093 5 5 2 2 1 0 0 0 0 5 5 1 0 7 0 0 0 0 0 0

C094 3 2 1 1 1 0 0 0 0 5 5 1 0 0 0 0 1 0 5 0

C095 2 4 0 2 2 0 0 0 0 0 5 0 0 6 0 0 0 0 0 0

C096 8 9 5 0 3 0 0 0 0 0 0 5 0 8 0 0 8 0 0 0

C097 7 7 3 7 5 6 6 6 0 2 0 5 5 0 0 5 1 0 0 0

C098 2 6 4 0 2 0 0 0 0 4 0 3 0 6 2 0 4 1 3 3

C099 7 0 1 5 5 0 0 0 0 1 0 2 0 2 0 0 2 0 0 0

C100 7 6 2 9 0 6 6 6 0 0 0 3 3 8 3 0 3 0 0 0

C101 3 0 2 0 0 0 0 0 0 0 0 2 0 3 0 3 2 0 1 0

552


Cau

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C102 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0

C103 2 5 0 1 1 0 0 0 0 0 0 1 0 0 0 0 5 0 3 0

C104 7 6 3 2 4 6 6 6 0 3 0 2 3 8 3 0 2 0 1 0

C105 2 1 2 0 1 0 0 0 0 0 0 2 0 3 0 0 5 0 3 0

C106 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 2 0

C107 5 6 2 4 0 0 0 0 0 2 0 0 4 8 0 0 1 0 0 0

C108 2 5 2 1 0 0 0 0 0 0 0 0 0 4 0 0 8 0 0 0

C109 7 7 0 4 0 0 0 0 0 0 0 0 0 9 0 0 8 0 0 0

C110 3 0 0 0 0 0 0 0 0 0 0 0 7 6 0 0 7 0 0 0

C111 5 7 0 0 0 0 0 0 0 0 0 0 7 7 0 0 5 0 0 0

C112 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0

C113 6 5 0 0 0 0 0 0 0 0 0 4 0 0 0 0 9 0 0 0

C114 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0

C115 0 4 5 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 0 0

C116 3 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0

C117 5 5 0 6 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0

C118 2 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0

C119 6 0 2 0 0 0 0 0 0 0 0 5 5 0 0 0 0 0 0 0

553


Cau

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C120 1 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0

C121 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0

C122 1 3 2 0 0 0 0 0 0 2 0 0 2 0 0 0 6 3 0 0

C123 5 6 0 7 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0

C124 0 0 0 0 0 0 0 0 0 0 0 0 5 0 7 0 2 0 0 0

C125 5 7 0 0 0 0 0 0 0 0 0 5 5 0 0 0 0 0 0 0

C126 2 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C127 4 4 0 0 4 0 0 0 0 0 0 0 6 0 5 0 0 0 0 0

C128 7 7 7 0 0 0 0 0 0 0 0 7 9 0 0 0 1 0 0 0

C129 1 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C130 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0

C131 6 8 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0

C132 6 8 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0

C133 7 3 0 8 0 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0

C134 5 7 5 0 7 0 0 0 0 0 0 6 8 0 9 0 0 0 0 0

C135 8 7 7 0 6 0 0 0 0 0 0 5 8 0 9 0 0 0 0 0

C136 7 6 2 0 6 0 0 0 0 0 0 5 7 0 6 0 3 0 3 2

C137 7 0 0 9 5 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0

554


Cau

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C138 2 3 3 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 4 3

C139 1 0 2 3 2 0 0 0 0 0 0 0 0 0 0 0 1 0 4 3

C140 7 0 1 8 5 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0

C141 5 7 0 0 6 0 0 0 0 0 0 6 6 0 0 0 0 0 0 0

C142 0 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0

C143 7 5 0 7 0 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0

C144 7 0 0 7 0 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0

C145 7 5 0 0 0 2 2 2 0 0 0 6 0 0 0 0 0 0 0 0

C146 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C147 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0

C148 1 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 1 0

C149 1 7 0 0 0 0 0 0 0 5 0 0 0 0 0 7 0 2 3 2

C150 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C151 5 6 7 5 5 2 2 2 0 4 5 4 4 0 0 0 2 0 6 0

C152 0 3 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0

C153 1 4 2 0 2 0 0 0 0 0 0 1 0 2 0 7 4 5 7 6

C154 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 4 4

C155 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 6

555


Cau

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C156 0 3 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0

C157 5 6 6 5 5 0 0 0 0 0 5 4 4 3 0 0 0 0 0 0

C158 2 0 6 0 0 0 0 0 0 0 0 0 0 0 0 4 5 0 5 3

C159 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 3 8 5 3

C160 4 5 2 6 5 0 0 0 0 2 4 2 0 3 0 0 3 0 3 0

C161 0 0 0 0 0 0 0 0 0 7 0 0 0 0 0 0 0 0 0 0

C162 5 4 3 4 4 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0

C163 3 7 6 6 6 3 3 3 0 0 0 5 5 0 0 0 9 0 0 8

C164 2 0 0 0 2 0 0 0 0 0 0 0 0 0 0 8 0 2 8 4

C165 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 0 3

C166 0 1 2 2 1 0 0 0 0 1 0 2 0 2 0 3 4 4 3 7

C167 7 5 6 7 0 2 2 2 0 0 0 5 5 0 0 0 0 0 0 0

C168 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0

C169 2 4 0 4 0 0 0 0 0 0 0 4 4 0 0 0 0 0 0 0

C170 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C171 2 0 0 0 0 0 0 0 0 0 5 2 0 0 0 0 0 0 0 0

C172 6 5 3 4 5 4 4 4 0 5 0 2 0 4 0 0 0 0 2 0

C173 5 5 1 4 5 0 0 0 0 5 0 2 0 3 0 4 0 0 2 0

556


Cau

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C174 5 5 0 2 2 0 0 0 0 4 0 1 0 4 0 0 0 0 0 0

C175 5 7 0 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C176 5 5 2 4 5 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0

C177 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 7 0 0

C178 2 0 9 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0

C179 7 2 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0

C180 6 2 8 0 4 2 2 2 0 0 0 0 0 0 0 3 4 0 3 5

C181 0 0 7 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0

C182 5 8 7 1 4 0 0 0 0 2 0 0 0 8 0 0 1 0 0 0

C183 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 0 0

C184 7 6 5 2 5 0 0 0 0 3 0 0 0 7 0 0 5 0 0 0

C185 2 3 1 1 2 0 0 0 0 1 0 0 0 0 0 0 6 0 0 0

C186 1 6 1 0 1 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0

C187 1 4 1 2 3 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0

C188 1 4 1 2 2 0 0 0 0 1 0 0 0 0 0 0 5 0 0 0

C189 2 2 1 2 2 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0

C190 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 3 4 0 0 0

C191 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 3 0 5

557


Cau

se

S01

S02

S03

S04

S05

S06a

S06b

S06c

S06d

S07

S08

S09

S10

S11

S12

S13

S14

S15

S16

S17

C192 6 0 5 0 7 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0

C193 1 2 2 2 2 0 0 0 0 4 0 0 0 0 0 3 0 4 0 0

C194 5 4 6 2 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0

C195 4 4 1 2 2 0 0 0 0 1 0 0 0 0 0 3 0 0 0 0

C196 1 4 0 2 2 0 0 0 0 0 4 0 0 0 0 3 0 0 0 0

558

Table A.2: Mean response of experts for symptoms and their causes related to pigments

Cau

se

S01

S02

S03

S04

S05

S06a

S06d

S06e

S07

S08

S09

S10

S12

S13

S14

S15

S16

S17

S18

C001 9 4 0 4 4 0 0 0 0 0 5 0 0 0 0 0 0 0 0

C002 7 9 0 2 7 0 0 0 8 3 4 4 0 0 0 0 2 0 5

C005 8 7 6 7 6 9 0 3 7 0 4 4 3 0 0 0 5 0 7

C014 2 3 3 5 4 6 9 9 0 0 2 0 0 0 0 0 0 0 0

C015 5 6 0 5 0 3 0 0 8 0 0 0 0 0 0 0 0 0 5

C016 5 6 0 5 0 3 0 0 7 0 0 0 0 0 0 0 0 0 5

C017 0 5 0 0 4 5 0 0 3 0 0 0 0 0 0 0 5 0 0

C036 4 7 5 5 6 6 5 5 8 5 6 5 0 0 0 0 5 0 7

C038 0 5 7 6 0 0 0 0 6 5 0 3 0 0 0 0 2 0 9

C039 0 8 5 7 0 5 0 0 9 6 0 3 0 0 0 0 3 0 9

C040 0 0 0 0 0 9 8 9 0 0 0 0 0 0 0 0 0 0 0

C041 0 3 0 0 0 4 0 0 3 3 0 0 0 0 0 0 9 0 6

C042 0 0 0 6 0 9 7 8 2 2 0 0 0 0 0 0 0 0 0

C043 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 9 0 6

C044 0 0 0 0 0 5 9 2 0 0 0 0 0 0 0 0 0 0 3

C045 0 0 0 0 0 5 0 1 0 0 0 0 0 0 0 0 0 0 3

C046 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 3

C047 0 2 3 1 0 9 0 0 0 2 0 3 0 0 0 0 6 0 3

559


Cau

se

S01

S02

S03

S04

S05

S06a

S06d

S06e

S07

S08

S09

S10

S12

S13

S14

S15

S16

S17

S18

C049 4 6 0 0 5 5 0 0 4 0 0 0 0 0 0 0 0 0 9

C052 6 7 5 0 2 0 0 0 2 2 2 6 0 0 0 0 2 0 0

C053 5 4 5 5 5 1 0 0 0 7 5 5 0 0 0 0 2 0 7

C055 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0

C075 6 0 5 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 0

C076 7 0 0 0 0 0 0 0 6 0 0 0 0 0 2 0 0 0 0

C077 0 5 0 0 2 5 5 0 0 3 0 0 0 0 0 0 0 0 0

C078 5 5 2 0 0 3 0 0 7 6 0 0 0 0 2 0 0 0 0

C079 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 7 0 0 0

C080 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 6 0

C081 0 0 0 0 0 0 0 0 0 0 0 0 0 6 6 4 0 6 0

C083 0 0 5 0 2 0 0 0 0 0 0 0 0 0 0 0 3 0 0

C121 0 2 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0

C122 0 0 0 0 0 0 0 0 4 0 0 0 0 0 6 3 0 0 0

C124 0 1 0 0 0 0 0 0 0 0 0 7 0 0 0 0 0 0

C125 5 8 5 0 8 4 0 3 0 3 5 2 0 0 0 0 3 0 6

C126 2 3 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0

C127 6 4 0 0 4 0 0 0 0 0 4 4 5 0 0 0 0 0 0

C128 6 10 8 0 3 3 0 3 0 2 8 9 0 0 1 0 0 0 1

560


Cau

se

S01

S02

S03

S04

S05

S06a

S06d

S06e

S07

S08

S09

S10

S12

S13

S14

S15

S16

S17

S18

C129 0 3 0 0 2 3 0 0 0 0 0 0 0 0 0 0 0 0 0

C130 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0

C134 5 7 4 1 7 3 0 0 0 3 6 9 9 0 0 0 0 0 0

C135 9 7 7 2 6 5 0 0 0 0 5 8 9 0 0 0 1 0 1

C136 8 6 5 2 6 5 0 4 0 0 5 7 6 0 3 0 2 2 0

C137 9 0 0 0 6 9 0 7 0 0 0 0 0 0 0 0 0 0 0

C138 0 0 0 0 5 0 0 3 0 0 0 0 0 0 0 0 6 2 0

C139 0 0 0 0 2 0 0 3 0 0 0 0 0 0 1 0 2 2 0

C140 7 0 0 0 4 9 0 7 0 0 0 0 0 0 0 0 0 0 5

C141 5 3 0 3 6 1 0 5 0 0 6 5 0 0 0 0 2 0 1

C142 0 2 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0

C148 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0

C149 2 0 0 0 0 0 0 0 0 0 0 0 0 6 0 2 3 2 0

C150 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C151 2 7 5 5 6 5 3 5 3 2 2 2 0 0 2 0 5 0 0

C152 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0

C153 1 0 0 0 0 0 0 0 0 0 0 0 0 7 7 5 2 6 0

C154 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 4 0

C155 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 6 0

561


Cau

se

S01

S02

S03

S04

S05

S06a

S06d

S06e

S07

S08

S09

S10

S12

S13

S14

S15

S16

S17

S18

C157 3 7 3 4 5 3 3 3 2 2 2 2 0 0 0 0 0 0 0

C159 2 0 0 0 0 0 0 0 0 0 0 0 0 7 3 8 0 1 0

C161 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0

C162 5 4 3 2 3 0 3 1 0 0 2 2 0 0 0 0 0 0 0

C163 3 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 8 0

C164 2 0 0 0 0 0 0 0 0 0 0 0 0 8 0 2 7 4 0

C165 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 0 3 0

C166 0 0 0 0 0 0 0 0 0 0 0 0 0 3 4 4 0 7 0

C169 2 3 3 3 3 5 3 4 2 1 2 2 0 0 0 0 0 0 1

C172 2 3 0 0 2 4 1 1 0 0 0 0 0 0 0 0 0 0 1

C173 3 2 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0

C174 3 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C175 3 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C176 3 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C177 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 7 0 0 0

C178 0 0 4 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0

C179 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

C180 1 0 7 0 0 0 0 0 0 0 0 0 0 3 5 0 0 5 0

C181 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0

562


Cau

se

S01

S02

S03

S04

S05

S06a

S06d

S06e

S07

S08

S09

S10

S12

S13

S14

S15

S16

S17

S18

C190 0 3 0 0 0 2 0 0 0 0 0 0 0 3 4 0 0 0 0

C191 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 3 0 5 0

C192 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0

C193 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0

C195 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0

563

Questions related to various causes for diagnosis of symptom(s).

Table B. 1: Questions to user related to various causes for diagnosis.

Cause Description Question to the user


chemicals Were the colorants and chemicals weighed accurately?

C002 Improper bath preparation procedure Was the bath prepared as per the colorant manufacturer’s recommended

procedure?

C003 Too fast/quick addition of chemicals in the

bath Were the chemicals added too quickly during the dyeing process?

C004 Too fast/quick addition of dyes in the bath Were the dyes added too quickly during the dyeing process?

C005 Too high colorant concentration Was the depth of shade too high?

C006 Wrong selection of dyeing method (1 bath, 2

bath)

Was the dyeing method selected according to the depth of shade and

fastness properties?

C007 Poor dye selection for polyester component Were the dyes selected correctly according to depth of shade, fastness

properties for polyester fiber in the blend?

C008 Poor dye selection for cellulose component Were the dyes selected correctly according to depth of shade, and

fastness properties for the cellulose fiber?

C009 Poor dye combinations for each fiber type Were the dyes selected in combination shade have similar dyeing

properties?

C010 Variation in colorant strength Were the colorants checked for their strength prior to their application?

C011 Incompatibility between dye classes Were the dye classes selected compatible to each other?

C012 Cross-staining of fiber Were the disperse dyes selected have lower staining tendency of the

cellulose component and good wash-off behavior?

C013 Bleeding of unfixed dye into the bath/trough

during development

Was there any change in the bath appearance before and after chemical

development?

C014 Poor pigment selection Were the pigments selected according to depth of shade, fastness and

application properties?

C015 Crust formation in pigments during storage Were the pigment cans stored properly and stirred prior to the coloration

process?

564

Table B.1 (Continued)


C016 Poor pigment dispersion system Were the pigments evaluated for their dispersion properties?

C017 Differences in pigment particle size and

particle size distribution Were the particle size of pigments and their distribution uniform?

C018 Poor disperse dye dispersion system Were the disperse dyes tested for their dispersion properties?

C019 Poor disperse dye dispersion stability Were disperse dyes selected according to their stability under electrolyte

and alkaline pH?

C020 Poor disperse dye diffusion properties Were the disperse dye used have good diffusion properties?

C021 Poor disperse dye leveling and migration

properties Were the disperse dye used have good leveling and migration properties?

C022 Poor thermomigration property of disperse

dye

Were the disperse dyes of low or medium energy levels used in the

dyeing process?

C023 Too high substantivity of reactive/direct dyes Was the substantivity of dye too high?

C024 Poor solubility of reactive/direct dyes Was the solubility of dye good under the dyeing conditions?

C025 Poor diffusion properties of reactive/direct

dyes

Were the dyes with poor diffusion properties used for the dyeing of

cellulose component?

C026 Poor migration properties of reactive/direct

dyes

Were the dyes with poor migration properties used for the dyeing of



polyester dyeing conditions

Were the dyes for cellulose component selected based on their stability

under acidic and high-temperature dyeing conditions used in polyester

dyeing?

C028 High dye reactivity Were the reactive dyes of high reactivity used in the dyeing process?

C029 Too high substantivity of vat/sulfur dye in the

leuco form Was the dye substantivity too high in the lueco form?

C030 Too low substantivity of vat/sulfur dye in the

leuco form Was the dye substantivity too low in the lueco form?

C031 Poor diffusion properties of vat/sulfur dyes Were the dyes with poor diffusion properties used for the dyeing of


565



C032 Poor leveling properties of vat/sulfur dyes Was the dye with poor leveling properties used for the dyeing of


C033 Poor vat/sulfur dyes dispersion system Were the dyes used for cellulose component tested for their dispersion

properties?

C034 Poor color matching of each fiber in the

blend Is the appearance of the both fiber components look similar?

C035 Variations in strength and purity of dyebath

chemicals

Were the dyebath chemicals tested for their chemical properties prior to

their application?


colorants and auxiliaries

Were the colorants and auxiliaries used have good compatibility with

each other?

C037 Poor selection of dyebath chemicals Were the dyebath chemicals selected based on their application and

performance properties for the coloration of blends?

C038 Formation of binder film on padder or rollers Was the binder evaluated for its agglomeration properties?

C039 Agglomeration of binder Was the binder stored and stirred properly before use?

C040 Binder with poor fastness properties Was the binder tested for its dispersion properties?

C041 Brittleness (poor softness) of the binder film Was the binder film evaluated for its softness?

C042 Insufficient amount of binder Was the amount of binder too low according to the depth of shade?

C043 High amount of binder Was the amount of binder too high according to the depth of shade?

C044 Poor resistance of binder against aging Was the heat stability of binder not good?

C045 Binder with poor swelling resistance Was the swelling resistance of binder not good?

C046 High amount of softener Was the amount of softener used too high?

C047 Improper softener selection Was the softener selected according to fabric hand and its effect on

coloration properties?

C048 Inappropriate electrolyte (salt) concentration Was the electrolyte concentration too low according to the depth of

shade?


agent

Was the dispersing agent concentration too low according to the depth of

the shade?

C050 Too low amount of lubricating agent Was the concentration of lubricating agent too low for a given substrate?

566



C051 Too high concentration of carrier Was the carrier concentration too high as compared to the depth of

shade?

C052 Low quantity of anti-migrating agent Was the concentration anti-migrating agent too low according to the

depth of shade?

C053 Precipitation of anti-migrating agent Was the anti-migrating agent tested for its stability under the coloration

process conditions?

C054 Too high concentration of dye fixative Was the concentration of dye fixative used according to the depth of

shade?

C055 Use of silicone based defoamer Was the defoamer used based on silicone?

C056 Too low concentration of reducing agent

and/or alkali

Was the concentration of reducing agent and alkali too low according to

the dye recommendations?

C057 Presence of air in the machine Was there any air present in the machine before or during the dyeing

process?

C058 Inappropriate rinsing temperature Was the rinsing water temperature too high?

C059 Inadequate water flow rates/liquor ratio

during rinsing

Was the appropriate quantity of water/liquor used for the rinsing process

according to the depth of shade?

C060 Inadequate number of rinse cycles/rinse baths Was the required number of rinse cycles given to the dyed substrate


C061 Inappropriate pH during oxidation Was the pH acidic during the oxidizing process?

C062 Insufficient concentration of oxidizing agent Was the concentration of oxidizing agent too low?

C063 Inappropriate temperature during oxidation Was the temperature too high during oxidation?

C064 Inadequate reduction clearing temperature Was the temperature too low during reduction clearing (<70 C)?

C065 Inadequate reduction clearing time Was appropriate time given for reduction clearing according to the depth

of shade?

C066 Inadequate concentration of hydro and

caustic during reduction clearing

Was the concentration of hydro and caustic used for reduction clearing


C067 Inadequate soaping temperature Was the temperature during soaping too low?

C068 Inadequate pH during soaping Was the pH during soaping maintained based on dye stability?

567



C069 Inadequate soaping time Was appropriate time given for soaping according to the depth of shade?

C070 Improper selection of detergent for soaping Was the detergent used evaluated for its dye wash-off properties?


during soaping

Was the appropriate quantity of water/liquor used for the soaping process


C072 Presence of residual alkali/hydro after dyeing

cycle

Were there any residues of alkali/hydro present in the substrate after

reduction clearing process?

C073 Too high drying temperature after the dyeing

process Was the substrate dried at very high temperature after dyeing?

C074 Improper storage and handling of substrate Was the substrate stored under controlled conditions and transported

carefully?

C075 Machine stoppage for a long duration Was the machine stopped for a longer duration during the dyeing

process?

C076 Presence of dye deposits in the dye

preparation tank and machine

Were the dyeing machine and preparation tanks properly cleaned after

the dyeing process?

C077 Presence of reductive chemicals in substrate,

water or steam Were the dyes used sensitive to reduction?

C078 Excessive foaming in the dye bath/trough Was there a foam formation during the dyeing process?

C079 Non-uniform or damaged machine parts Was the surface of the dyeing machine and fabric guide elements non-

uniform or damaged?

C080 Excessive, insufficient or variable tension

during fabric run Was there a change in fabric tension during the dyeing process?


reprocessing Was the substrate reprocessed (pretreatment or dyeing)?

C082 Variations in dyeing program Were there any changes made in the dyeing program (time, heating and

cooling rates)?

C083 Rubbing of unfixed substrate against the

guide roller/machine part

Was the substrate rubbed with the guide roller or machine part before dye

fixation?

C084 Too fast increase in the differential pressure Was the differential pressure increased too quickly?

568



C085 Too low liquor flow rate Was the liquor flow rate too low according to package density?

C086 Too high liquor flow rate Was the liquor flow rate too high according to package density?

C087 Inappropriate liquor flow times (in-out and

out-in)

Were there any differences in the duration of the liquor flow between in-

out and out-in?

C088 Too high pressing density Was the pressing density too high?

C089 Too low pressing density Was the pressing density too low?

C090 Leakage in dye package Was there any leakage in the dye package and package column?

C091 Defective locking caps Were the defective locking caps used during the dyeing process?

C092 Too large batch size (machine overloading) Was the batch size too large according to the machine capacity?

C093 Presence of oligomer and other deposits in

the machine Were there any oligomer deposits in the machine?

C094 Presence of oligomer deposits on the

substrate surface Is there any oligomer deposits present on the substrate?

C095 Trapped air pockets in the material during

dyeing

Were the air pockets removed from the material at the start of the dyeing

cycle?

C096 High temperature rise rate Was the dyebath temperature increased too rapidly?

C097 Inappropriate dyebath pH Was the pH maintained according to the dye class and fiber type?

C098 Use of too low liquor ratio Was the liquor ratio too low according to the substrate type and machine?

C099 Use of too high liquor ratio Was the liquor ratio too high?

C100 Too low dyeing temperature Was the dyeing temperature too low as compared to the recommended

dyeing temperature?

C101 Too high dyeing temperature Was the dyeing temperature too high as compared to the recommended

dyeing temperature?

C102 Too slow fabric/rope speed Was the fabric speed too slow during the dyeing process?

C103 Too fast fabric/rope speed Was the fabric speed too fast during the dyeing process?

C104 Too short dyeing time Was the dyeing duration too short based on the depth of shade and

substrate type?

569



C105 Too long dyeing time Was the dyeing duration too long based on the depth of shade and

substrate type?

C106 Shock cooling of fabric after completion of

dyeing cycle Was the substrate cooled too rapidly after the dyeing process?

C107 Too low liquor flow rate Was the liquor flow rate too low?

C108 Too high liquor flow rate Was there any increase in the liquor ratio during the dyeing process?

C109 Incorrect liquor flow direction Were there any differences in the duration of the liquor flow between in-

out and out-in?

C110 Incorrect overlap of fabric covering the beam

perforations Were the beam perforations correctly overlapped with the fabric?

C111 Uneven winding of fabric on the beam Was the fabric wound uniformly on to the beam?

C112 Variation in pressure head in the tubes Were there any differences in pressure heads among the dyeing tubes?

C113 Poor circulation or stoppage of fabric Were there any interruptions in the fabric circulation during the dyeing

process?

C114 Incorrect nozzle size (diameter) Was the correct nozzle size used according to fabric weight per running

meter?

C115 Twisting or pressing of the rope at high

temperature Was there any twisting or pressing of the rope during the dyeing process?

C116 Inappropriate nozzle pressure Was the nozzle pressure set according to the required rope dwell time?

C117 Cooling of outer/inner fabric layers Were the top layers and inner layers of the fabric batch cooler due to heat

loss?

C118 Cooling of selvages Was there any variation in temperature across the fabric width due to heat

loss?

C119 Variation in dyebath temperature Was there any variation in the dyebath temperature during the process?

C120 Too tight or too loose fabric edges Was the fabric correctly wound without tension differences?

C121 Deposits of fluff/lint on the padder surface

and guide rollers Was there any lint or fluff deposits on the padder or guide rollers?

C122 Damaged, worn out or uneven padder surface Was the padder surface uniform and free of defects?

570



C123 Too high pad trough temperature Was there an increase in the pad trough temperature during the dyeing

process?

C124 Difference in the hardness of dye padders Were there any differences in hardness of the dyeing padders?

C125 Too high wet pickup Was the fabric wet pickup too high?

C126 Too low wet pickup Was the fabric wet pickup too low?

C127 Improper distribution and circulation of dye

liquor Was the dye liquor circulation and distribution system working properly?

C128 Uneven wet pickup Were there any differences in wet pickup across the fabric?

C129 Inadequate airing time between padding and

drying Was the fabric not given adequate airing time after the padding process?

C130 Selvage curling during padding and

thermofixation process Were the edge guiders and fabric guiding elements not working properly?

C131 Improper rotation of the fabric batch during

batching

Were there any differences in the rotation of fabric batches during the

dyeing process?

C132 Poor covering of fabric batch during batching Was the fabric batch not covered properly with the plastic bag after dye

padding?

C133 Differences in fixation temperature or time

during batching

Was there any fluctuation in the temperature of the surroundings during

the batching process?

C134 Variation in the intensity of the IR pre-dryer Were there any variations in the intensity of IR pre-dryer?

C135 Non-uniform air velocity or flow Were there any variations in airflow in the hotflue dryer?

C136 Too high drying temperature Was the drying temperature too high as compared to the recommended

temperature?

C137 Too low thermofixation temperature Was the thermofixation temperature too low as compared to dye

recommendation?

C138 Too high thermofixation temperature Was the thermofixation temperature too high as compared to dye

recommendation?

C139 Too long thermofixation time Was the thermofixation time too long?

C140 Too short thermofixation time Was the thermofixation time too short for a given depth of shade?

571



C141 Temperature variation in the hotflue Were there any differences in temperature in different regions of the

hotflue?

C142 Contact of condensation drops with unfixed

colorant Were the steamer roof and exhaust canopies properly heated?

C143 Inadequate steaming temperature Was the required steaming temperature maintained according to the dye

class used?

C144 Inadequate steaming time Was the steaming time sufficient according to the dye class and depth of

shade?

C145 Variation in steam pressure inside the

steamer Were there any variations in steam pressure inside the steamer?

C146 Too high steamer water seal temperature Was the temperature of the steamer water seal too high?

C147 High turbulence in the washbox Was there a high turbulence in the wash box due to steam?

C148 Difference in the singeing of fabric’s face

and back

Were there any differences in the appearance of the fabric's face and back

after singeing?

C149 Fiber damage during singeing Were the singeing conditions not selected according to the fiber type,

blend ratio, and fabric construction?

C150 Incomplete singeing Was the singeing position and flame intensity selected correctly?


sizing wax Was the degree of desizing of fabric too low?

C152 Incomplete removal of oil, rust and grease

stains

Are there any oil or grease stains present on the substrate that glows

under UV light?

C153 Fiber damage during scouring and bleaching Were the concentration of scouring and bleaching chemicals used

according to the fiber type and blend ratio?

C154 Too high weight loss during scouring Was the weight loss of substrate too high after the scouring process?

C155 Insufficient relaxation of the substrate during

washing

Was enough dwell time provided to substrate for relaxation during the

washing process?

C156 Localized swelling of fiber Was there any direct contact for concentrated alkali with the substrate?

572




finishes, and knitting oils Was the absorbency of fabric too low after scouring process?

C158 Inadequate weight reduction of polyester Was the fabric weight loss after the weight reduction process too low?

C159 Catalytic damage during bleaching Were there any pinholes present in the fabric after bleaching due to

chemical damage?

C160 Presence of residual peroxide in substrate Were there any residues of peroxide on the substrate left from the

bleaching process?

C161 Incomplete removal of motes (seed husks) Are there any broken seed particles present in the substrate?

C162 Inadequate whiteness of substrate Was there any variation in the whiteness across the fabric?

C163 Improper heat setting of substrate Were the heat setting conditions set properly according fiber type and

blend ratio?

C164 Fiber damage during heat setting Was the substrate exposed to too high temperature during heat setting?

C165 Physical damage of substrate (pin marks,

cuts)

Was the fabric physically damaged in the form of cuts and pin marks

during heat setting?

C166 Excessive overstretching of substrate on

stenter Was the fabric stretched too much on the stenter?

C167 Incomplete mercerization Was the degree of mercerization of substrate too low (<125) and varied

across the substrate?

C168 Differential mercerization due to

superimposed layers of substrate Was the fabric mercerized in the form of superimposed layers?

C169 Alkaline pH of substrate before dyeing Was the pH of the fabric alkaline after the preparation stage?

C170 Improper stitching of substrate ends Was the fabric ends properly stitched using correct thread?

C171 Presence of insect residues in substrate Were there any insect residues in the fabric?


water Was the hardness of the dyeing water too high?

C173 Presence of heavy metals (Cu, Fe, Mn, Zn) in

water Were there high levels of heavy metals in the dyeing water?

C174 Presence of suspended matter in water Was the appearance of water used for dyeing water turbid?

573



C175 Presence of bicarbonate in water Was the dyeing water monitored for bicarbonates level?

C176 Presence of chlorine in water Was there any presence of chlorine in the dyeing water?

C177 Presence of holes, tears or cuts in greige

substrate Were there any holes or cuts present in the greige substrate?

C178 Presence of bands or stripes in greige

substrate Were there any bands or stripes present in the greige substrate?

C179 Fabric rolls from different machines or batch

or factory Were the rolls used in the same lot obtained from different sources?

C180 Yarn mixing Do the fabric contains yarns which are different in appearance than

neighboring yarns?

C181 Variation in yarn tension during

warping/sizing

Do the fabric contains yarn which are loose or too tight as compared to

the neighboring yarns?

C182 Too high package density Was the yarn package density too high?

C183 Too low package density Was the yarn package density too low?

C184 Uneven package density Was there any variation in density within a package?

C185 Edging process for rounding of package

flanks Was the edging process used for the rounding of package flanks?

C186 Improper rounding of package flanks Were the package flanks rounded properly during the winding process?

C187 Improper coverage of dye tube perforations Were the dye tubes perforations not covered properly by the yarn?

C188 Use of damaged dye tubes Were the damaged tubes used during the dyeing process?

C189 Poor temperature stability of dye tubes Were the dye tubes used have poor temperature stability?

C190 Too many yarn imperfections Was the level of imperfections in the yarn too high?

C191 Lower yarn strength and elongation Were the yarns present in the griege fabric had lower strength and

elongation?

C192 Variation in blend ratio Are there any differences in the blend ratio of the substrate compared to

actual?

C193 Foreign fiber contamination Are there any foreign fibers present in the substrate?

574



C194 Variations in crystallinity and orientation of

fiber

Are the fibers used in the substrate came from the different batch and had

differences in crystallinity and draw ratio?

C195 Variations in the degree of polymerization of

fiber

Are the fibers used in the substrate came from the different batch and had

differences in degree of polymerization?

C196 Presence of immature fibers Are there any immature fibers or neps present in the substrate?

575

DEXPERT-B installation guide

1. Open the DEXPERT-B folder.

2. Open the “wxclips” folder and double-click “wxclips.exe” file to run the application on your

computer.

Method 1

a. Once the wxclips application is open, the wxclips screen will appear on your computer.

b. Find the file named “0start” in the folder and drag it to wxclips icon.

c. The DEXPERT-B-Blends will run automatically.

Method 2

a. Once the installation is done, locate the wxClips program among the installed program on your

computer and double click the file to open the application.

b. Once the wxClips window is open, click on “File” tab and click on the dropdown menu functions

“load definitions”.

c. Locate the file “0Start” in the DEXPERT-B folder and open it

d. Once the file loads in the wxClips window, click on “Applications” tab, and then click on the

dropdown menu functions “start application”.

e. The DEXPERT-Blends will run promptly.

If you have any questions, please feel email: [email protected] for troubleshooting installation

and problems regarding the program.

576

Analysis of the expert responses of the faulty colored samples.

Table D.1: Expert responses and expert system’s knowledge base for reproducibility (S1).


Literature Experts





[77, 142, 317, 345,

348] x x x

C003 Too fast/quick addition of chemicals in the

bath 8 S2, S9, S11 [297, 301, 345] x x x x

C007 Poor dye selection for polyester component 8 S6a-d

[9, 56, 57, 64, 67,

77, 83, 87, 125, 142,

161-163]

x x x

C008 Poor dye selection for cellulose component 8 S6a-d

[9, 56, 57, 64, 67,

77, 83, 87, 125, 142,

161-163]

x x x x

C082 Variations in dyeing program 8 S2, S4, S5 [9, 253, 297, 301] x x x x

C096 Higher temperature rise rate 8 S2, S3, S9, S11,

S14

[9, 112, 231, 253,

380] x x x x

C097 Inappropriate dyebath pH 7 S2, S4, S5, S6a-

c, S9, S10, S13 [301] x x x x

C002 Improper bath preparation procedure 7 S2, S5, S7, S9 [297, 301, 317] x x x x

577

Table D.1 (Continued)


Literature Experts



C179 Fabric rolls from different machines or batch or

factory 7 S9 [139] x x x x

C004 Too fast/quick addition of dyes in the bath 7 S2, S9, S11 [297, 301, 347] x x

C010 Variation in colorant strength 7 S2, S4, S5 [253, 301] x

C011 Incompatibility between dye classes 7 S2-S5, S6a-d,

S7, S9-11

[7, 9, 79, 92, 93, 100,

128, 253, 301] x x x x

C019 Poor disperse dye dispersion stability 7 S2, S4, S7, S9-

11

[7, 67, 68, 75, 79,

81, 85, 253] x x x


polyester dyeing conditions 7 S2, S4, S7

[64, 68, 79, 122,

253] x x x x

C034 Poor color matching of each fiber in the blend 7 S5 [139] x x

C092 Too large batch size (machine overloading) 7 S2, S3, S11,

S14 [67, 231, 253] x x x x

C100 Too low dyeing temperature 7 S2, S4, S6a-c,

S11 [297, 301] x x x x

C104 Too short dyeing time 7 S2, S5, S6a-c,

S11 [297, 301] x x x x

578



Literature Experts




S10

[9, 184, 253, 305,

333, 334, 337, 338] x x x x

C009 Poor dye combinations for each fiber type 7 S2, S5, S6d, S9-

11 [231, 345, 348] x x x x

C099 Use of too high liquor ratio 7 S4, S5 [297] x x

C109 Incorrect liquor flow direction 7 S2, S4, S11,

S14 [9, 68, 85, 110, 194] x x x

C180 Yarn mixing 6 S3, S5, S14,

S17 [215, 230, 258-260] x x


properties 6 S2 ,S5, S11

[9, 68, 75, 100, 111,

118, 231] x x

C023 Too high substantivity of reactive/direct dyes 6 S2, S6a-c, S9-

11 [128, 253, 345] x x

C024 Poor solubility of reactive/direct dyes 6 S2-5, S6b, S6c,

S7, S9-11

[9, 68, 75, 100, 111,

118, 231] x x

C026 Poor migration properties of reactive/direct

dyes 6 S2, S11

[9, 68, 100, 111,

118, 231, 345] x x x

C112 Variation in pressure head in the tubes 6 [297, 301] x x x

579



Literature Experts




water 6

S2, S4, S5, S6a-

c, S7, S11

[277, 280, 283, 290,

292, 296, 298, 299] x x x

C192 Variation in blend ratio 6 S3, S5 [6, 181, 213]

C119 Variation in dyebath temperature 6 S9, S10 [68, 323] x x x

C018 Poor disperse dye dispersion system 6 S2, S4, S5, S7,

S9-11 [75, 253, 348] x x x


water or steam 6 S16 [64, 251, 301]

C113 Poor circulation or stoppage of fabric 6 S2, S9, S14 [253] x

C102 Too slow fabric/rope speed 5 S2, S14 [301, 346] x x x

C151 Incomplete removal of sizing agents and sizing

wax 5

S2-5, S7-10,

S16

[67, 149, 303, 305-

307, 324-329] x x x

C157 Incomplete removal of of fats, waxes, spin

finishes and knitting oils 5 S2-5, S8-10

[149, 277, 278, 297,

303, 305, 317, 327] x x x x

C093 Presence of oligomer and other substance

deposits in the machine 5 S2, S7, S8, S11

[67, 85, 173-175,

233, 253] x



S2-5, S6a-d,

S7-11

[18, 78, 79, 86, 89,

103, 253] x x x

580



Literature Experts



C020 Poor disperse dye diffusion properties 5 S2, S11 [9, 68, 75, 100, 111,

118, 231] x x

C025 Poor diffusion properties of reactive/direct

dyes 5 S2, S11

[9, 68, 75, 100, 111,

118, 231] x x

C028 High dye reactivity 5 S2, S4, S7, S9,

S10

[9, 68, 100, 118,

128, 231] x x x


chemicals 5

S2, S4, S5, S6a-

d, S7 [79, 89, 103] x x

C037 Poor selection of dyebath chemicals 5

S2, S3, S5, S6a-

d, S7, S8-11,

S14

[443] x x

C048 Inappropriate electrolyte (salt) concentration 5 S2, S4, S9, S11 [128, 317, 345] x x x

C049 Inappropriate concentration of dispersing agent 5 S2, S4, S5, S9,

S10, S11

[67, 89, 97, 106,

109]

C056 Too low concentration of reducing agent

and/or alkali 5

S2, S4, S5, S6a-

c, S11 [67, 194, 345, 370] x x

C072 Presence of residual alkali/hydro after dyeing

cycle 5 S2, S4, S5, S8 [251, 253, 348] x x x x x

581



Literature Experts



C085 Too low liquor flow rate 5 S2, S4, S11 [9, 68, 85, 110]

C163 Improper heat setting of substrate 5 S2-5, S9, S10,

S14, S17

[67, 83, 168, 194,

253, 320, 323] x x x


water 5

S2, S4, S5, S7,

S13

[277, 280, 283, 286,

288-292] x x

C174 Presence of suspended matter in water 5 S2, S7, S11 [100, 282, 284] x x x


C176 Presence of chlorine in water 5 S2, S4, S5, S11 [281, 285, 286] x

C194 Variations in crystallinity & orientation of fiber 5 S2, S3 [114, 157, 168, 218-

222]

C107 Too low liquor flow rate 5 S2, S4, S10,

S11 [9, 68, 85, 110] x x

C162 Inadequate whiteness of substrate 5 S2, S4, S5 [150, 301, 305, 309] x x

C160 Presence of residual peroxide in substrate 4 S2, S4, S5, S8 [100, 150, 253, 301] x x x x x

C195 Variations in degree of polymerization of fiber 4 S2 [82, 114, 171]


582

Table D.2: Expert responses and expert system’s knowledge base for unlevelness (S2).


Literature Experts



C003 Too fast/quick addition of chemicals in

the bath 9 S1, S9, S11 [297, 301, 345] x x x x

C004 Too fast/quick addition of dyes in the

bath 9 S1, S9, S11 [297, 301, 347] x x x x

C096 Higher temperature rise rate 9 S1, S3, S9, S11, S14 [9, 112, 231, 253,

380] x x x

C082 Variations in dyeing program 8 S1, S4, S5 [9, 253, 297, 301] x x x

C009 Poor dye combinations for each fiber

type 8 S1, S5, S6d, S9-11 [231, 345, 348] x x x

C018 Poor disperse dye dispersion system 7 S1, S4, S5, S7, S9-11 [75, 253, 348] x x x

C019 Poor disperse dye dispersion stability 7 S1, S4, S7, S9-11 [7, 67, 68, 75, 79, 81,

85, 253] x x x

C024 Poor solubility of reactive/direct dyes 7 S1, S4, S5, S6b, S6,

cS7-11

[9, 68, 75, 100, 111,

118, 231] x x x x

C011 Incompatibility between dye classes 7 S1, S3-5, S6a-d, S7, S9-

11

[7, 9, 79, 92, 93, 100,

128, 253, 301] x x x x x

C097 Inappropriate dyebath pH 7 S1, S4, S5, S6a-c, S9,

S10, S13 [301] x x

583



Literature Experts



C149 Fiber damage during singeing 7 S7, S13 [67, 149, 168, 313,

318] x x

C163 Improper heat setting of substrate 7 S1, S3, S4, S5, S9,

S10, S14, S17

[67, 83, 168, 194,

253, 320, 323] x x x


C092 Too large batch size (machine

overloading) 7 S1, S3, S11, S14 [67, 231, 253] x x


finishes and knitting oils 6 S1, S3-5, S8-10

[149, 277, 278,

297, 303, 305, 317,

327]

x x x


sizing wax 6 S1, S3-5, S7-10, S16

[67, 149, 303, 305-

307, 324-329] x x x

C026 Poor migration properties of

reactive/direct dyes 6 S1, S11

[9, 68, 100, 111,

118, 231, 345] x x

C020 Poor disperse dye diffusion properties 6 S1, S11 [9, 68, 75, 100,

111, 118, 231] x x x


properties 6 S1, S5, S11

[9, 68, 75, 100,

111, 118, 231] x x

584



Literature Experts



C023 Too high substantivity of reactive/direct

dyes 6 S1, S6a-c, S9-11 [128, 253, 345] x x x

C098 Use of too low liquor ratio 6 S3, S7, S11, S14 [297, 301] x

C100 Too low dyeing temperature 6 S1, S4, S6a-c, S11 [297, 301]

C104 Too short dyeing time 6 S1, S2, S5, S6a-c, S11 [297, 301]

C028 High dye reactivity 6 S1, S4, S7, S9, S10 [9, 68, 100, 118,

128, 231] x


agent 5 S1, S4, S5, S9-11

[67, 89, 97, 106,

109] x x x

C078 Excessive foaming in the dye

bath/trough 5 S7, S8

[89, 97, 253, 254,

317, 346, 351] x x x x x

C172 Presence of Ca and Mg ions (hardness)

in water 5

S1, S4, S5, S6a-c, S7,

S11

[277, 280, 283,

290, 292, 296, 298,

299]

x x

C176 Presence of chlorine in water 5 S1, S4, S5, S11 [281, 285, 286] x x x

C002 Improper bath preparation procedure 5 S1, S5, S7, S9 [297, 301, 317] x x x

C025 Poor diffusion properties of


[9, 68, 75, 100,

111, 118, 231] x x x

585



Literature Experts




dyebath chemicals 5 S1, S4, S5S, 6a-d, S7 [79, 89, 103] x x


between colorants and chemicals 5

S1, S3-5, S6aS6a-d,

S7-11

[18, 78, 79, 86, 89,

103, 253] x x x x x

C037 Poor selection of dyebath chemicals 5 S1, S3, S5, S6aS6a-d,

S7-11, S14 [443] x x x

C072 Improper neutralization of substrate after

dyeing 5 S1, S4, S5, S8 [251, 253, 348]

C077 Presence of reductive chemicals in

substrate, water or steam 5 S1, S4, S5 [64, 251, 301] x x x x

C113 Poor circulation or stoppage of fabric 5 S1, S2, S9, S14 [253] x x x

C167 Incomplete mercerization 5 S1, S3, S4, S9, S10 [9, 184, 253, 305,

333, 334, 337, 338] x x x


Zn) in water 5 S1, S4, S5, S7, S13

[277, 280, 283,

286, 288-292] x x x

C174 Presence of suspended matter in water 5 S1, S7, S11 [100, 282, 284] x x

C160 Presence of residual peroxide in

substrate 5 S1, S4, S5, S8

[100, 150, 253,

301] x x x x

586



Literature Experts



C102 Too slow fabric/rope speed 5 S1, S14 [301, 346] x x x

C103 Too fast fabric/rope speed 5 S14 [253]


concentration 4 S1, S4, S9, S11 [128, 317, 345] x x x x x

C095 Trapped air pockets in the material

during dyeing 4 S8, S11 [110, 149, 253]

C169 Alkaline pH of substrate before dyeing 4 S4, S9, S10 [301, 305, 309,

317, 334] x x

C194 Variations in crystallinity and orientation

of fiber 4 S1, S3

[114, 157, 168,

218-222] x x x x

C196 Presence of immature fibers 4 S8 [6, 160-163] x x x x

C027 Poor stability of reactive/direct dyes

under polyester dyeing conditions 4 S1, S4, S7

[64, 68, 79, 122,

253] x

C115 Twisting or pressing of the rope at high

temperature 4 S3, S14

[149, 297, 301,

323]

C195 Variations in the degree of

polymerization of fiber 4 S1 [82, 114, 171] x

587



Literature Experts



C153 Fiber damage during scouring and

bleaching 4 S13-17 [70] x x

C162 Inadequate whiteness of substrate 4 S1, S4, S5 [150, 301, 305,

309] x



[77, 142, 317, 345,

348]


588

Table D.3: Expert responses and expert system’s knowledge base for streaks (S3).


Literature Experts



C178 Presence of bands or stripes in greige

substrate 9 S10

[6, 203, 215, 216, 250-

252, 261, 272, 274-276] x x x x x

C180 Yarn mixing 8 S1, S5, S14, S17 [215, 230, 258-260]

C128 Uneven wet pickup 7 S1, S2, S9, S10 [61, 100, 128, 133, 353] x x x x

C052 Lower quantity of anti-migrating agent 7 S1, S2, S5, S10 s x

C135 Non-uniform air velocity or flow 7 S1, S2, S5, S9,

S10, S12 [67, 317, 361, 363] x x


sizing wax 7

S1, S2, S4, S5,

S7-10, S16

[67, 149, 303, 305-307,

324-329] x x


warping/sizing 7 S14 [215, 230, 258-260] x x

C163 Improper heat setting of substrate 6 S1, S2-5, S9,

S10, S14, S17

[67, 83, 168, 194, 253,

320, 323] x x x

C158 Inadequate weight reduction of polyester 6 S13, S14, S16 [331, 332] x

C194 Variations in crystallinity & orientation

of fiber 6 S1, S2

[114, 157, 168, 218-

222] x

C075 Machine stoppage for a longer duration 6 S14 x x

589



Literature

Experts


Commonness

H M A B C D E


finishes and knitting oils 6

S1, S2, S4, S5,

S8-10

[149, 277, 278, 297,

303, 305, 317, 327] x


S10

[9, 184, 253, 305, 333,

334, 337, 338] x x



S1, S2, S4, S5,

S6a-d, S7-11

[18, 78, 79, 86, 89, 103,

253] x x

C053 Precipitation of anti-migrating agent 5 S1, S2, S5, S8-10 [92, 95, 100, 105, 118,

130-132] x x

C079 Non uniform or damaged machine parts 5 S14, S15 [149, 150] x x x


dryer 5

S1, S2, S5, S9,

S10, S12 [348, 363] x x

C170 Improper stitching of substrate ends 5 [67, 322]

C192 Variation in blend ratio 5 S1, S5 [6, 181, 213] x

C011 Incompatibility between dye classes 4 S1, S2, S4, S5,

S6a-d, S7, S9-11

[7, 9, 79, 92, 93, 100, 128,

253, 301] x


guide roller/machine part 4 S14 [92, 149, 150]

C190 Too many yarn imperfections 4 S14 [6, 207, 216] x

590



Literature

Experts


Commonness

H M A B C D E

C037 Poor selection of dyebath chemicals 4 S1, S2, S5. S6a-

d, S711, S14 [443] x x


591

Table D.4: Expert responses and expert system’s knowledge base for shade change (S5).


Literature Experts



C034 Poor color matching of each fiber in the blend 8 S1 [139] x x x x x

C018 Poor disperse dye dispersion system 7 S1, S2, S4, S7, S9-

11 [75, 253, 348] x x x

C010 Variation in colorant strength 7 S1, S2, S4 [253, 301] x x x

C011 Incompatibility between dye classes 7 S1-4, S6a-d, S7,

S9-11

[7, 9, 79, 92, 93,

100, 128, 253, 301] x x x

C024 Poor solubility of reactive/direct dyes 7 S1, S2, S4, S6b,

S6c, S7, S9-11

[9, 68, 75, 100, 111,

118, 231] x x x

C192 Variation in blend ratio 7 S1S3 [6, 181, 213] x x

C163 Improper heat setting of substrate 6 S1-4, S9, S10, S14,

S17

[67, 83, 168, 194,

253, 320, 323] x x x

C009 Poor dye combinations for each fiber type 6 S1, S2, S6d, S9-11 [231, 345, 348] x x x x

C141 Temperature variation in the hotflue 6 S1, S2, S9, S10 [118, 253, 348, 370] x x x

C054 Too high concentration of dye fixative 6 S6d [301] x x x x


water or steam 5 S1, S2, S4 [64, 251, 301] x x x

C160 Presence of residual peroxide in substrate 5 S1, S2, S4, S8 [100, 150, 253, 301] x x x x

C176 Presence of chlorine in water 5 S1, S2, S4, S11 [281, 285, 286] x

592



Literature Experts





[9, 68, 75, 100, 111,

118, 231] x x



S1-4, S6a-d,

S7-11

[18, 78, 79, 86, 89,

103, 253] x x x


agent 5

S1, S2, S4, S9-

11

[67, 89, 97, 106,

109] x x x

C053 Precipitation of anti-migrating agent 5 S1, S2, S3, S8-

10

[92, 95, 100, 105,

118, 130-132] x

C069 Inadequate soaping time 5 S6a-c [85, 301, 345, 370] x

C072 Presence of residual alkali/hydro after

dyeing cycle 5 S1, S2, S4, S8 [251, 253, 348] x x

C097 Inappropriate dyebath pH 5

S1, S2, S4,

S6a-c, S9,

S10, S13

[301] x x x

C140 Too short thermofixation time 5 S1, S4, S6a-c [114, 115, 128, 133] x x x


sizing wax 5

S1-4, S7-10,

S16

[67, 149, 303, 305-

307, 324-329]

593



Literature Experts




finishes and knitting oils 5 S1-4, S8-10

[149, 277, 278, 297,

303, 305, 317, 327] x x x

C173 Presence of heavy metals (Cu, Fe, Mn, Zn)

in water 5

S1, S2, S4, S7,

S13

[277, 280, 283, 286,

288-292] x x x

C175 Presence of bicarbonate in water 5 S1, S2, S4 [283, 295-297] x


water 5

S1, S2, S4,

S6a-c, S7, S11

[277, 280, 283, 290,

292, 296, 298, 299] x x x

C180 Yarn mixing 4 S1, S3, S14,

S17 [215, 230, 258-260]

C067 Inadequate soaping temperature 4 S6a-c, S9-11 [85, 301, 345, 370] x

C002 Improper bath preparation procedure 4 S1, S2, S7, S9 [297, 301, 317]


chemicals 4

S1, S2, S4,

S6a-d, S7 [79, 89, 103] x x


S1, S2, S3,

S6a-d, S7-11,

S14

[443] x

C052 Lower quantity of anti-migrating agent 4 S1, S2, S3,

S10

[92, 95, 100, 105,

118, 130-132] x x

594



Literature Experts



C138 Too high thermofixation temperature 4 S16 [114, 115, 128, 133] x x

C162 Inadequate whiteness of substrate 4 S1, S2, S4 [150, 301, 305, 309] x



[77, 142, 317, 345,

348] x x


during soaping 4 S6a-c, S9-11 [85, 301, 345, 370] x x


595

Table D.5: Expert responses and expert system’s knowledge base for inadequate washing fastness (S6).


Literature Experts



C007 Poor dye selection for polyester component 9 S1, S6b-d [9, 56, 57, 64, 67, 77, 83,

87, 125, 142, 161-163] x x x x x

C008 Poor dye selection for cellulose component 9 S1, S6-d [9, 56, 57, 64, 67, 77, 83,

87, 125, 142, 161-163] x x x x x

C012 Cross-staining of fiber 9 S6b-d [7, 9, 18, 77-79, 142] x x x x x

C022 Poor thermomigration property of disperse

dye 9 S6b, S6c

[9, 56, 79, 83, 88, 177,

253] x x x x x

C006 Wrong selection of dyeing method (1 bath,

2 bath) 9 S6b, S6c

[9, 56, 57, 64, 67, 83, 87,

125, 161-163] x x x x x

C069 Inadequate soaping time 8 S5, S6b, S6c [85, 301, 345, 370] x

C067 Inadequate soaping temperature 8 S5, S6b, S6c,

S9-S11 [85, 301, 345, 370] x x x x x

C070 Improper selection of detergent for soaping 8 S6b, S6c [85, 301, 345, 370] x x

C064 Inadequate reduction clearing temperature 8 S6b, S6c [9, 85, 109, 301, 345,

370] x x x x

C065 Inadequate reduction clearing time 8 S6b, S6c [9, 85, 109, 301, 345,

370] x x x

596



Literature Experts



C066 Inadequate concentration of hydro and

caustic during reduction clearing 8 S6b, S6c

[9, 85, 109, 301, 345,

370] x x x x

C068 Inadequate pH during soaping 7 S4. S6b, S6c [61, 85, 301, 345, 370] x x


during soaping 7

S5, S6b, S6c,

S9-S11 [85, 301, 345, 370] x

C060 Inadequate number of rinse cycles/rinse

baths 6 S1, S6b, S6c [57, 61, 81] x x

C100 Too low dyeing temperature 6 S1, S2, S4,

S6b, S6c, S11 [297, 301] x x x

C097 Inappropriate dyebath pH 6

S1, S2, S4, S5,

S6b, S6c, S9,

S10, S13

[301] x

C104 Too short dyeing time 6 S1, S2, S5,

S6b, S6c, S11 [297, 301] x x

C011 Incompatibility between dye classes 5 S1-5, S6b-d,

S7, S9-11

[7, 9, 79, 92, 93, 100,

128, 253, 301] x x

C023 Too high substantivity of reactive/direct

dyes 5

S1, S2, S6b,

S6c, S9-11 [128, 253, 345] x

597



Literature Experts



C005 Too high colorant concentration 5 S6, bS6c, S7 [93, 100] x


colorants and chemicals 4

S1-5, S6, S6b-

d, S7-11

[18, 78, 79, 86, 89, 103,

253] x


S1, S2, S3, S5,

S6b-d, S7-11,

S14

[443] x x x

C058 Inappropriate rinsing temperature 4 S1, S6, bS6c [61, 81] x x x x


chemicals 4

S1, S2, S4, S5,

S6b-d, S7 [79, 89, 103] x x x


during rinsing 4

S1, S6b, S6c,

S11 [61, 81] x x x


598

Table D.6: Expert responses and expert system’s knowledge base for dark stains or spots (S7).


Literature

Experts


Commonness

H M A B C D E

C018 Poor disperse dye dispersion system 8 S1, S2, S4, S5, S9-

S11 [75, 253, 348] x x x

C019 Poor disperse dye dispersion stability 8 S1, S2, S4, S9-11 [7, 67, 68, 75, 79, 81, 85,

253] x x

C024 Poor solubility of reactive/direct dyes 8 S1, S2, S4, S5, S6b,

S6c, S9-11

[9, 68, 75, 100, 111, 118,

231] x x x

C078 Excessive foaming in the dye

bath/trough 7 S2, S8

[89, 97, 253, 254, 317,

346, 351] x x x

C055 Use of silicone based defoamer 7 [253, 351] x x x x

C161 Incomplete removal of motes (seed

husks) 7 [149, 305] x x

C011 Incompatibility between dye classes 6 S1-5, S6a-d, S9-11 [7, 9, 79, 92, 93, 100, 128,

253, 301] x x x

C156 Localized swelling of fiber 6 [323] x

C076 Presence of dye deposits in the dye

preparation tank and machine 6 [231] x x x

C002 Improper bath preparation procedure 6 S1, S2, S5, S9 [297, 301, 317] x

599



Literature Experts




dyebath chemicals 5

S1, S2, S4, S5,

S6a-d [79, 89, 103] x x

C149 Fiber damage during singeing 5 S2, S13 [67, 149, 168, 313,

318] x x

C027 Poor stability of reactive/direct dyes

under polyester dyeing conditions 5 S1, S2, S4 [64, 68, 79, 122, 253] x x

C028 High dye reactivity 5 S1, S2. S4, S9,

S10

[9, 68, 100, 118, 128,

231] x x x


between colorants and auxiliaries 5

S1-5, S6a-d, S8-

11

[18, 78, 79, 86, 89,

103, 253] x x x

C037 Poor selection of dyebath chemicals 5 S1-3, S5, S6a-d,

S8-11, S14 [443] x x

C172 Presence of Ca and Mg ions

(hardness) in water 5

S1, S2, S4, S5,

S6a-c, S11

[277, 280, 283, 290,

292, 296, 298, 299] x x x


Zn) in water 5

S1, S2, S4, S5,

S13

[277, 280, 283, 286,

288-292] x x x

C193 Foreign fiber contamination 4 S15 [6, 157, 209, 210] x x

600



Literature Experts



C151 Incomplete removal of sizing agents

and sizing wax 4 S1-5, S8-10, S16

[67, 149, 303, 305-

307, 324-329] x x x

C005 Too high colorant concentration 4 S6a-c [93, 100] x x x

C174 Presence of suspended matter in water 4 S1, S2, S11 [100, 282, 284] x x


601

Table D.7: Expert responses and expert system’s knowledge base for light stains or sports (S8).


Literature Experts



C142 Contact of condensation drops with unfixed

colorant 8

[100, 128, 362,

363] x x x

C152 Incomplete removal of oil, and grease stains 6 [67, 100, 301] x x

C053 Precipitation of anti-migrating agent 6 S1-3, S5, S9,

S10 x x

C121 Deposits of fluff/lint on the padder surface and

guide rollers 6 [67, 317] x x

C078 Excessive foaming in the dye bath/trough 5 S2, S7 x x x


wax 5

S1-5, S7, S9,

S10, S16

[67, 149, 303, 305-

307, 324-329] x x x x x


finishes, and knitting oils 5 S1-5, S9, S10

[149, 277, 278, 297,

303, 305, 317, 327] x x x

C171 Presence of insect residues in substrate 5 [139] x x x

C160 Presence of residual peroxide in substrate 4 S1, S2, S4, S5 [100, 150, 253,

301] x x x x



S1-5, S6a-d, S7,

S9-11

[18, 78, 79, 86, 89,

103, 253] x x x

C196 Presence of immature fibers 4 S2 [6, 160-163] x x x

602



Literature Experts




S7, S9-11, S14 [443] x x


603

Table D.8: Expert responses and expert system’s knowledge base for lengthwise shade variation (S9).


Literature Experts



C023 Too high substantivity of reactive dye 8 S1, S2, S6a-c, S10,

S11 [128, 253, 345] x x x x x

C028 High dye reactivity 7 S1, S2, S4, S7,

S10

[9, 68, 100, 118, 128,

231] x x x

C128 Uneven wet pickup 7 S1, S2, S3, S10 [61, 100, 128, 133, 353] x x x


S10, S11

[7, 67, 68, 75, 79, 81,

85, 253] x x x

C141 Temperature variation in the hotflue 6 S1, S2, S5, S10 [118, 253, 348, 370] x x x


dryer 6

S1, S2, S3, S5,

S10, S12 [348, 363] x x x

C145 Variation in steam pressure inside the

steamer 6 S1, S2 [100, 363] x

C179 Fabric rolls from different machines or

batch or factory 6 S1 [139] x x x

C013 Bleeding of unfixed dye into the

bath/trough during development 6 [128, 139] x x x x


S10, S11

[7, 9, 79, 92, 93, 100,

128, 253, 301] x x x x

604



Literature Experts



C135 Non-uniform air velocity or flow 5 S1, S2, S3, S5, S10,

S12 [67, 317, 361, 363] x

C125 Too high wet pickup 5 S1, S2, S10 [61, 100, 128, 133,

353] x x x



[77, 142, 317, 345,

348] x x

C009 Poor dye combinations for each fiber type 5 S1, S2, S5, S6d,

S10, S11 [231, 345, 348] x x x

C024 Poor solubility of reactive/direct dyes 5 S1, S2, S4, S5, S6-

c, S7, S10, S11 [231, 345, 348] x

C067 Inadequate soaping temperature 5 S5, S6a-c, S10, S11 [85, 301, 345, 370] x x x


during soaping 5 S5, S6a-c, S10, S11 [85, 301, 345, 370] x x x

C163 Improper heat setting of substrate 5 S1-4, S5, S10, S14,

S17

[67, 83, 168, 194,

253, 320, 323] x x x

C037 Poor selection of dyebath chemicals 5 S1-3, S5, S6a-d, S7,

S8, S10, S11, S14 [443] x x x

605



Literature Experts



C136 Too high drying temperature 5 S1, S2, S5, S10,

S12 [85, 118, 253, 369] x x x

C019 Poor disperse dye dispersion stability 4 S1, S2, S4, S7, S10,

S11

[7, 67, 68, 75, 79,

81, 85, 253] x x


agent 4

S1, S2, S4, S5, S10,

S11

[67, 89, 97, 106,

109] x x x

C053 Precipitation of anti-migrating agent 4 S1, S2, S3, S5, S8,

S10

[92, 95, 100, 105,

118, 130-132] x


finishes, and knitting oils 4 S1-4, S5, S8, S10

[149, 277, 278, 297,

303, 305, 317, 327] x x x

C169 Alkaline pH of substrate before dyeing 4 S2, S4, S10 [301, 305, 309, 317,

334] x x



S1-5, S6a-d, S7, S8,

S10, S11

[18, 78, 79, 86, 89,

103, 253] x x

C002 Improper bath preparation procedure 4 S1, S2, S5, S7 [297, 301, 317] x x


606

Table D.9: Expert responses and expert system’s knowledge base for shade variation within layers (S11).


Literature Experts



C109 Incorrect liquor flow direction 9 S1, S2, S4, S14 [9, 68, 85, 110,

194] x x x x x

C096 Higher temperature rise rate 8 S1-3, S9, S14 [9, 112, 231, 253,

380] x x x x

C104 Too short dyeing time 8 S1, S2, S5, S6a-c [297, 301] x x x

C107 Too low liquor flow rate 8 S1, S2, S4, S10 [9, 68, 85, 110] x x x

C100 Too low dyeing temperature 8 S1, S2, S4, S6a-c [297, 301] x x x


S9, S10 [75, 253, 348] x x x

C020 Poor disperse dye diffusion properties 7 S1, S2 [9, 68, 75, 100,

111, 118, 231] x x x

C024 Poor solubility of reactive/direct dyes 7 S1, S2, S4, S5, S6b,

S6c, S7, S9, S10

[9, 68, 75, 100,

111, 118, 231] x x x

C025 Poor diffusion properties of reactive dyes 7 S1, S2 [9, 68, 75, 100,

111, 118, 231] x x x


concentration 7 S1, S2, S4, S9 [128, 317, 345] x x x

607



Literature Experts



C092 Too large batch size (machine

overloading) 7 S1-3, S14 [67, 231, 253] x x x x x

C093 Presence of oligomer and other deposits

in the machine 7 S1, S2, S7, S8

[67, 85, 173-

175, 233, 253] x x x x

C111 Uneven winding of fabric on the beam 7 S1, S2, S10, S14 [9, 68, 85, 110] x x x x

C003 Too fast/quick addition of chemicals in

the bath 7 S1, S2, S9 [297, 301, 345] x x x x

C095 Trapped air pockets in the material

during dyeing 6 S2, S8 [110, 149, 253] x x

C098 Use of too low liquor ratio 6 S2, S3, S7, S14 [297, 301] x x x

C004 Too fast/quick addition of dyes in the

bath 6 S1, S2, S9 [297, 301, 347] x x


S9, S10

[7, 9, 79, 92, 93,

100, 128, 253,

301]

x x



[9, 68, 75, 100,

111, 118, 231] x x

608



Literature Experts



C026 Poor migration properties of


[9, 68, 100, 111,

118, 231, 345] x x x


between colorants and auxiliaries 6

S1-5, S6a-d, S7-

10

[18, 78, 79, 86,

89, 103, 253] x x x

C110 Incorrect overlap of fabric covering the

beam perforations 6 S10, S14 [9, 68, 85, 110] x x

C019 Poor disperse dye dispersion stability 5 S1, S2, S4, S7,

S9, S10

[7, 67, 68, 75,

79, 81, 85, 253] x x x

C023 Too high substantivity of reactive dyes 5 S1, S2, S6a, S6b,

S6c, S9, S10 [128, 253, 345] x x x


agent 5

S1, S2, S4, S5,

S9, S10

[67, 89, 97, 106,

109] x x

C176 Presence of chlorine in water 4 S1, S2, S4, S5 [281, 285, 286] x x x

C009 Poor dye combinations for each fiber

type 4

S1, S2, S5, S6d,

S9, S10 [231, 345, 348] x x


S7-10, S14 [443] x x

609



Literature Experts



C067 Inadequate soaping temperature 4 S5, S6a-c, S9,

S10

[85, 301, 345,

370] x x

C172 Presence of Ca and Mg ions (hardness)

in water 4

S1, S2, S4, S5,

S6a-c, S7

[277, 280, 283,

290, 292, 296,

298, 299]

x x


during soaping 4

S5, S6a-c, S9,

S10

[85, 301, 345,

370] x x

C108 Too high liquor flow rate 4 S2, S14 [9, 68, 85, 110] x x

C174 Presence of suspended matter in water 4 S1, S2, S7 [100, 282, 284] x


610

Table D.10: Expert responses and expert system’s knowledge base for two sidedness (S12).


Literature Experts



C134 Variation in the intensity of the IR pre-dryer 9 S1, S2, S3, S5,

S9, S10 [348, 363] x x x

C135 Non-uniform air velocity or flow 9 S1, S2, S3, S5,

S9, S10

[67, 317, 361,

363] x x x x

C124 Difference in the hardness of dye padders 7 S10 [133, 194] x x

C148 Difference in the singeing of fabric’s face and

back 6

[67, 149, 168,

313, 318] x

C136 Too high pre-drying temperature 6 S1, S2, S5, S9,

S10

[85, 118, 253,

369] x x x

C127 Improper distribution and circulation of dye

liquor 5 S1, S2, S5, S10

[61, 100, 128,

133, 353] x x

C168 Differential mercerization due to superimposed

layers of substrate 4 [194] x


611

Table D.11: Expert responses and expert system’s knowledge base for reduced strength (S13).


Literature Experts



C164 Fiber damage during heat setting 8 S16, S17 [67, 168, 323] x x x

C149 Fiber damage during singeing 7 S2, S7 [67, 149, 168,

313, 318] x x

C153 Fiber damage during scouring and bleaching 7 S2, S14-17 [70] x x x

C159 Catalytic damage during bleaching 7 S15, S16 [100, 149, 303,

305, 323] x x

C154 Too high weight loss during scouring 6 S16, S17 [323] x x x


reprocessing 6 S14-17 [301] x x x

C097 Inappropriate dyebath pH 5 S1, S2, S4, S5,

S6-c, S9, S10 [301] x x x


water 4

S1, S2, S4, S5,

S7

[277, 280, 283,

286, 288-292] x x x

C191 Lower yarn strength and elongation 4 S17 [6, 155, 181, 202,

211] x

C158 Inadequate weight reduction of polyester 4 S3. S14, S16 [331, 332]


612

Table D.12: Expert responses and expert system’s knowledge base for irregular surface appearance (S14).


Literature Experts

Cause Literature CF



S17

[67, 83, 168, 194, 253,

320, 323] x x x x

C122 Damaged, worn out or uneven padder

surface 6 [317, 348, 370] x x

C079 Non-uniform or damaged machine parts 6 S3, 15 [149, 150]


reprocessing 6 S13, S15-17 [301] x x x x x


during fabric run 6 S17

[67, 110, 128, 323,

370]

C158 Inadequate weight reduction of polyester 5 S3, S13, S16 [331, 332] x x

C075 Machine stoppage for a longer duration 5 S3 [67, 149, 194, 321,

323] x x x


guide roller/machine part 4 S3 [9, 68, 85, 110, 231]

C130 Selvage curling during padding and

thermofixation process 4 [194]

C153 Fiber damage during scouring and bleaching 4 S2, S13, S15-17 [70] x x


613



Literature

Experts


Commonness

H M A B C D E


warping/sizing 4 S3 [215, 230, 258-260] x x

C190 Too many yarn imperfections 4 S3 [6, 207, 216]


stenter 4 S15, S17 [194, 341] x x


614

Table D.13: Expert responses and expert system’s knowledge base for poor hand (S16).


Literature Experts



C164 Fiber damage during heat setting 8 S13, S17 [67, 168, 323] x x x x


reprocessing 7 S13-17 [301] x x

C153 Fiber damage during scouring and bleaching 7 S2, S13-15,

S17 [70] x x x x


wax 6 S1-5, S7-10

[67, 149, 303, 305-

307, 324-329] x x x

C094 Presence of oligomer deposits on the substrate

surface 5 S7, S8

[67, 85, 173-175, 233,

253] x x x x

C158 Inadequate weight reduction of polyester 5 S3, S13, S14 [331, 332] x

C159 Catalytic damage during bleaching 5 S13, S15 [100, 149, 303, 305,

323] x x

C073 Too high drying temperature 4 [301] x

C138 Too high thermofixation temperature 4 S5 [114, 115, 128, 133] x x

C139 Too long thermofixation time 4 [114, 115, 128, 133] x x

C154 Too high weight loss during scouring 4 S13, S17 [323] x x


615

Table D.14: Expert responses and expert system’s knowledge base for poor dimensional stability (S17).


Literature Experts




S14

[67, 83, 168, 194,

253, 320, 323] x x


stenter 7 S14, S15

[9, 184, 253, 305,

333, 334, 337, 338] x x x x


during fabric run 6 S14

[67, 110, 128, 323,

370] x x x x x


reprocessing 6 S13-16 [301] x x

C153 Fiber damage during scouring and bleaching 6 S2, S13-16 [70] x x x x x

C155 Insufficient relaxation of the substrate during

washing 6 [253] x x x


C191 Lower yarn strength & elongation 5 S13 [6, 155, 181, 202,

211] x x x x x

C154 Too high weight loss during scouring 4 S13, S16 [323] x

C164 Fiber damage during heat setting 4 S13, S16 [67, 168, 323] x


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