Investigation of Alternative Colouration Processing Medium ...

Investigation of Alternative Colouration Processing

Medium for Textiles and Novel Filtration Media for

Recycling of Textile Effluent

A dissertation submitted to the University of

Manchester for the degree of Doctor of Philosophy in

the Faculty of Engineering and Physical Sciences

2014

Mohammad Abbas Uddin

School of Materials

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TABLE OF CONTENTS

TABLE OF CONTENTS .................................................................................................. 2

LIST OF TABLES ............................................................................................................ 8

LIST OF FIGURES ........................................................................................................ 12

LIST OF SCHEMES ...................................................................................................... 18

LIST OF EQUATIONS .................................................................................................. 19

LIST OF NOTATIONS .................................................................................................. 21

ABBREVIATIONS ......................................................................................................... 23

ABSTRACT ..................................................................................................................... 25

DECLARATION AND COPYRIGHT ......................................................................... 28

THE AUTHOR ................................................................................................................ 29

ACKNOWLEDGEMENT .............................................................................................. 32

THESIS OVERVIEW ..................................................................................................... 34

1. Literature Review.................................................................................................... 36

1.1 Introduction to the Water Resource ................................................................................................ 36

1.1.1 Water Reserves on Earth ....................................................................................................... 36 1.1.2 Water Reserves for Bangladesh ............................................................................................. 39 1.1.3 Water Consumption in Textiles ............................................................................................. 39 1.1.4 Sources of Water ................................................................................................................... 41 1.1.5 Effect of seawater on industrial processing ........................................................................... 43 1.1.6 Water Quality for Textile Processing .................................................................................... 45

1.2 Textile Wastewater ........................................................................................................................ 46

1.2.1 Textile Wastewater in Bangladesh ........................................................................................ 48 1.2.2 Effluent Treatment Methods.................................................................................................. 50

1.2.2.1 Coagulation, Flocculation and Precipitation ................................................................ 51 1.2.2.2 Oxidation Methods ...................................................................................................... 52 1.2.2.3 Adsorption Methods .................................................................................................... 52 1.2.2.4 Biological Treatments .................................................................................................. 52 1.2.2.5 Membrane Processing .................................................................................................. 53

1.3 Textile Fibres .................................................................................................................................. 53 1.4 Textile Dyes .................................................................................................................................... 55

1.4.1 Characteristics of Dyes .......................................................................................................... 55 1.4.2 Classification of Dyes ........................................................................................................... 56

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1.4.2.1 Based on Chemical Constitution .................................................................................. 57 1.4.2.2 Based on Application Method ..................................................................................... 57

1.5 Textile Dyeing ................................................................................................................................ 59

1.5.1 Theory of Dyeing .................................................................................................................. 59 1.5.2 Absorbance ............................................................................................................................ 61 1.5.3 Colour Fastness ..................................................................................................................... 61 1.5.4 Degree of Dye Fixation and Dye Loss .................................................................................. 62

1.6 Introduction to Filtration ................................................................................................................. 64

1.6.1 Filtration Process ................................................................................................................... 64 1.6.2 Process Fundamentals ........................................................................................................... 65

1.6.2.1 Filter Permeability ....................................................................................................... 65 1.6.2.2 Flux .............................................................................................................................. 66 1.6.2.3 Pressure Drop ............................................................................................................... 66

1.6.3 Filtration Mechanism ............................................................................................................ 66

1.6.3.1 Conventional Filtration ............................................................................................... 68 1.6.3.2 Cross-flow Filtration .................................................................................................... 71

1.7 Filter Media..................................................................................................................................... 72

1.7.1 Woven fabric ......................................................................................................................... 74 1.7.2 Nonwoven ............................................................................................................................. 75

1.7.2.1 Composite Structures ................................................................................................... 76

1.7.3 Woven Wire and Screen ........................................................................................................ 76

1.8 Membranes...................................................................................................................................... 77

1.8.1 Membrane separation types ................................................................................................... 79

1.8.1.1 Microfiltration (MF) ................................................................................................... 79 1.8.1.2 Ultrafiltration (UF) ..................................................................................................... 79 1.8.1.3 Nanofiltration (NF) ..................................................................................................... 79 1.8.1.4 Reverse osmosis (RO) ................................................................................................ 80 1.8.1.5 Electrodialysis (ED) ..................................................................................................... 80

1.8.2 Membrane Fouling ................................................................................................................ 80

1.8.2.1 Membrane Fouling due to Dyes ................................................................................... 82

1.8.3 Cost of Membrane System for Wastewater Treatment .......................................................... 82

1.9 Surface Modification of Filter Media ............................................................................................. 83

1.9.1 Fluorination ........................................................................................................................... 84

1.9.1.1 Barrier Properties. ........................................................................................................ 85 1.9.1.2 Membrane Technology ................................................................................................ 85 1.9.1.3 Chemical Resistance .................................................................................................... 85 1.9.1.4 Adhesion and Printability Properties ........................................................................... 85 1.9.1.5 Frictional Coefficient ................................................................................................... 86 1.9.1.6 Anti-reflecting Coating and Reduction of UV radiation .............................................. 86

1.9.2 Fluorocarbon (FC) Finishes ................................................................................................... 86 1.9.3 Plasma Technology ............................................................................................................... 87

1.10 Coagulation/Flocculation ................................................................................................................ 88

1.10.1 Types of coagulants/flocculants ....................................................................................... 90

1.10.1.1 Metal Coagulants ......................................................................................................... 90 1.10.1.2 Organic Polymers as Coagulants/Flocculants .............................................................. 91 1.10.1.3 Synthetic Cationic Polyelectrolyte Polymers ............................................................... 92

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1.10.2 Mechanism of Coagulation/Flocculation .......................................................................... 93

1.10.2.1 Coagulation by Charge Neutralization ......................................................................... 93 1.10.2.2 Coagulation by Double Layer Compression ................................................................ 93 1.10.2.3 Flocculation via Polymer Bridging .............................................................................. 95

1.10.3 Dual Component System .................................................................................................. 97

1.11 References ....................................................................................................................................... 99

2. Experimental ......................................................................................................... 116

2.1 Simulated Seawater (SSW) ........................................................................................................... 116 2.2 Textile Fibres and Dyes used in this Research .............................................................................. 117 2.3 Filter Media................................................................................................................................... 118 2.4 Slurry ............................................................................................................................................ 118 2.5 Coagulants and Flocculants .......................................................................................................... 119 2.6 Filtration ....................................................................................................................................... 120 2.7 Experimental Methods .................................................................................................................. 121

2.7.1 Dye Exhaustion ................................................................................................................... 121 2.7.2 Dye Fixation ........................................................................................................................ 122 2.7.3 Colour Measurement ........................................................................................................... 123 2.7.4 Dye Removal ....................................................................................................................... 124 2.7.5 Fastness ............................................................................................................................... 124 2.7.6 Wettability Test ................................................................................................................... 125 2.7.7 Oil and Water Repellency ................................................................................................... 125 2.7.8 Tensile Strength ................................................................................................................... 125 2.7.9 Abrasion Resistance ............................................................................................................ 126 2.7.10 Turbidity Test ................................................................................................................. 126 2.7.11 Flow Rate and Solution Recovery % .............................................................................. 126 2.7.12 Filtrate Properties ........................................................................................................... 127 2.7.13 Properties of Filter cake .................................................................................................. 127 2.7.14 Kawabata Evaluation System (KES) .............................................................................. 128

2.8 Microscopic and Spectroscopic Analysis...................................................................................... 130

2.8.1 X-ray Photoelectron Spectroscopy (XPS) ........................................................................... 130 2.8.2 Attenuated Total Reflectance Fourier Transform Infrared (ATR FTIR) ............................. 130 2.8.3 Surface Morphology Analysis by Scanning Electron Microscopy ...................................... 131 2.8.4 Contact Angle Measurements.............................................................................................. 131

2.9 References ..................................................................................................................................... 133

3. Dyeing of Wool with Acid dyes ............................................................................ 138

3.1 Introduction ................................................................................................................................... 138 3.2 Experimental ................................................................................................................................. 139

3.2.1 Materials .............................................................................................................................. 139 3.2.2 Dyeing ................................................................................................................................. 142 3.2.3 Wash-off .............................................................................................................................. 143

3.3 Results and Discussion ................................................................................................................. 143

3.3.1 Effect of Simulated Seawater on Dye λmax Absorption and Dye Concentration Linearity .. 143 3.3.2 Effect of Wash-off on Fibre Topography ............................................................................ 146 3.3.3 Effect of Saline Environment on Wool ............................................................................... 147 3.3.4 Effects of Salts on Wool/Acid Dye System ......................................................................... 148 3.3.5 Colour Characteristics ......................................................................................................... 152 3.3.6 Fastness Properties .............................................................................................................. 155 3.3.7 Kawabata Evaluation System (KES) Analysis .................................................................... 158

3.4 Conclusions ................................................................................................................................... 160 3.5 References ..................................................................................................................................... 162

4. Dyeing of wool with Reactive dyes ....................................................................... 165

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4.2.1 Materials .............................................................................................................................. 166 4.2.2 Dyeing ................................................................................................................................. 167 4.2.3 After-treatment and Wash-off ............................................................................................. 168 4.2.4 Dye Exhaustion and Fixation .............................................................................................. 168


4.3.1 Effect of SSW on Dye Solution........................................................................................... 168 4.3.2 Exhaustion and Fixation of Dye .......................................................................................... 175 4.3.3 Colour Characteristics ......................................................................................................... 176 4.3.4 Colour Fastness Performance .............................................................................................. 179 4.3.5 Tensile Strength ................................................................................................................... 180 4.3.6 Abrasion Resistance ............................................................................................................ 182


5. Dyeing of Polyester with Disperse Dyes .............................................................. 190


5.2.1 Materials .............................................................................................................................. 191 5.2.2 Dyeing ................................................................................................................................. 193 5.2.3 Alkaline Reduction Clearing ............................................................................................... 193


5.3.1 Effect of Simulated Seawater on Dye Dispersion ............................................................... 194 5.3.2 Colour Characteristics ......................................................................................................... 194 5.3.3 Fastness Properties .............................................................................................................. 197 5.3.4 Surface Morphology ............................................................................................................ 203


6. Dyeing of Nylon with Acid dyes ........................................................................... 209


6.2.1 Materials .............................................................................................................................. 209 6.2.2 Dyeing ................................................................................................................................. 209


6.3.1 Initial studies: Effect of Simulated Seawater on Dye λmax Absorption and Dye Concentration

linearity 210 6.3.2 Effect of Salts on Nylon/Acid Dye System ......................................................................... 211 6.3.3 Exhaustion of Dye ............................................................................................................... 211 6.3.4 Colour Characteristics ......................................................................................................... 212 6.3.5 Colour Fastness Properties .................................................................................................. 214


7. Dyeing of Acrylic with Cationic Dyes .................................................................. 219


7.2.1 Materials .............................................................................................................................. 219 7.2.2 Dyeing ................................................................................................................................. 220

7.3 Results and Discussions ................................................................................................................ 221

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7.3.1 Effect of Simulated Seawater on dye λmax Absorption and Dye Concentration Linearity ... 221 7.3.2 Effect of Salts on Exhaustion of Dye .................................................................................. 222 7.3.3 Fastness Properties .............................................................................................................. 225


8. Surface Characterisation of Filter Media ........................................................... 230


8.2.1 Materials .............................................................................................................................. 231 8.2.2 Fluorination ......................................................................................................................... 232 8.2.3 Fluorocarbon (FC) Finish Application ................................................................................ 233 8.2.4 Plasma Treatment ................................................................................................................ 234


8.3.1 SEM Analysis ...................................................................................................................... 235 8.3.2 ATR FTIR Analysis of Filter Media ................................................................................... 237 8.3.3 XPS ..................................................................................................................................... 240 8.3.4 Wettability ........................................................................................................................... 247


9. Performance of coagulation/ flocculation with selected filter media ................ 255

9.1 Introduction ................................................................................................................................... 255 9.2 Filter Media Benchmarking Study ................................................................................................ 255

9.2.1 Experimental ....................................................................................................................... 255 9.2.2 Results and Discussion ........................................................................................................ 256

9.2.2.1 Average Flow Rate and Filtrate Properties ................................................................ 256 9.2.2.2 Cake Properties .......................................................................................................... 258

9.3 Filtration Performance Comparison Test ...................................................................................... 258

9.3.1 Results and Discussion ........................................................................................................ 258

9.3.1.1 Average Flow Rate and Filtrate Properties ................................................................ 258 9.3.1.2 Cake properties .......................................................................................................... 260

9.3.2 Conclusions ......................................................................................................................... 261

9.4 Coagulation/flocculation ............................................................................................................... 262

9.4.1 Experimental ....................................................................................................................... 262

9.4.1.1 Materials .................................................................................................................... 262 9.4.1.2 Model Dye Effluents .................................................................................................. 263 9.4.1.3 Coagulation/Flocculation and Filtration .................................................................... 263

9.4.2 Results and Discussion ........................................................................................................ 264

9.4.2.1 Optimisation of Flocculation Parameters ................................................................... 264 9.4.2.2 Effect of pH ............................................................................................................... 264 9.4.2.3 Effect of Pluspac 2000 and HPSS Concentration ...................................................... 265

9.4.3 Discussion ........................................................................................................................... 269

9.4.3.1 Effect of Dye Structure in Coagulation/flocculation Process .................................... 269 9.4.3.2 Effect of SSW in Coagulation/flocculation Process .................................................. 271 9.4.3.3 Effect of Dual Component System in Coagulation/flocculation Process ................... 272

9.4.4 Conclusions ......................................................................................................................... 273

9.5 References ..................................................................................................................................... 275

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10. Recycling of Textile Wastewater and Re-use of Exhausted Dyebaths ......... 280


10.2.1 Materials ......................................................................................................................... 280 10.2.2 Coagulation/Flocculation and Filtration ......................................................................... 281 10.2.3 Acid Dyeing of Wool ..................................................................................................... 281 10.2.4 Dyebath Reuse and Recycling Procedure ....................................................................... 281


10.3.1 Dyebath Exhaustion ........................................................................................................ 283 10.3.2 Colour Characteristics .................................................................................................... 284 10.3.3 Fastness........................................................................................................................... 291 10.3.4 Abrasion Resistance ....................................................................................................... 294 10.3.5 Tensile Strength .............................................................................................................. 295


11. Conclusions and Future Work ......................................................................... 299

11.1 Overall conclusions ....................................................................................................................... 299

11.1.1 Simulated Seawater Dyeing ............................................................................................ 299 11.1.2 Filtration and Reuse of Dyebath ..................................................................................... 301

11.2 Further Research ........................................................................................................................... 304

Word count: 78793

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LIST OF TABLES

Table 1.1 Typical water usage, Lkg-1

of product, in woven fabric wet processing ................ 40

Table 1.2 Water consumption in typical textile wet processing and machines ...................... 41

Table 1.3 Comparison of surface water and groundwater characteristics .............................. 42

Table 1.4 Survey of water sources used by selected European dyers and finishers in 2000 .. 42

Table 1.5 Common impurities found in freshwater and seawater .......................................... 44

Table 1.6 Dyehouse water standard ........................................................................................ 46

Table 1.7 Colour indicators in wastewater effluent ................................................................ 47

Table 1.8 Characteristics of dyeing effluents .......................................................................... 48

Table 1.9 Characteristics of textile wastewater and standard in Bangladesh ......................... 49

Table 1.10 Suggested quality requirements to achieve colourless water from recycled

textile effluent ......................................................................................................................... 50

Table 1.11 Wastewater treatment levels and processes .......................................................... 51

Table 1.12 Chromophores typically present in colorants ....................................................... 56

Table 1.13 Chemical classes of dyes ....................................................................................... 57

Table 1.14 Dye characteristics, associated fibres and method of application ......................... 58

Table 1.15 Percentage of unfixed dye that may be discharged in the effluent along with

benchmark fixation................................................................................................................... 63

Table 1.16 Particle size range for various filtration technologies ............................................ 65

Table 1.17 Effect of Weave pattern on fabric performance .................................................... 74

Table 1.18 Membrane separation process and influencing factors ......................................... 78

Table 1.19 Comparison of effluent treatment in the UK ........................................................ 83

Table 1.20 Classification of polymeric flocculants by molecular weight and size ................. 92

Table 2.1 Composition of 3.50% salinity simulated seawater .............................................. 116

Table 2.2 Composition of SSW used in this research ........................................................... 117

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Table 2.3 Slurry used in the filtration tests ........................................................................... 119

Table 2.4 Cake rating scale used in this research................................................................... 127

Table 2.5 KES parameters for woven fabrics ........................................................................ 129

Table 3.1 Sandolan E acid dyes used in this study and their characteristics ......................... 139

Table 3.2 Lanasan CF acid dyes used in this study and their characteristics......................... 140

Table 3.3 Sandolan MF acid dyes used in this study and their characteristics ...................... 140

Table 3.4 Lanasyn S acid dyes used in this study and their characteristics ........................... 141

Table 3.5 Lanaset acid dyes used in this study and their characteristics ............................... 141

Table 3.6 Other Acid Black dyes used and their characteristics ............................................ 141

Table 3.7 Washing conditions for dyed fabrics ..................................................................... 143

Table 3.8 λmax for wool dyes in distilled and simulated saltwater solutions .......................... 144

Table 3.9 Exhaustion levels of Acid Red dyes at 0.05, 1.0 and 3.0% o.m.f. on wool ........... 150

Table 3.10 Exhaustion levels of Acid Blue dyes at 0.05, 1.0 and 3.0% o.m.f. on wool ........ 150

Table 3.11 Exhaustion levels of Acid Yellow dyes at 0.05, 1.0 and 3.0% o.m.f. on wool .... 150

Table 3.12 Exhaustion levels of Acid Black dyes at 1.0, 2.0 and 4.0% o.m.f. on wool ........ 151

Table 3.13 K/Sλmax, of Acid Red dyes at 0.05, 1.0 and 3.0% o.m.f. on wool fabric ............... 152

Table 3.14 K/Sλmax, of Acid Blue dyes at 0.05, 1.0 and 3.0% o.m.f. wool fabric .................. 153

Table 3.15 K/Sλmax, of Acid Yellow dyes at 0.05, 1.0 and 3.0% o.m.f. on wool fabric ......... 153

Table 3.16 K/Sλmax, of Acid Black dyes at 1.0, 2.0 and 4.0% o.m.f. on wool fabric ............. 153

Table 3.17 Colour difference, ΔE*94, between Acid Red, Yellow and Blue dyed wool

fabrics dyed in SSW aqueous media with DSW is being the standard. ................................. 154

Table 3.18 Colour difference, ΔE*94, between Black dyed wool fabrics dyed in SSW

aqueous media with DSW is being the standard. ................................................................... 154

Table 3.19 Fastness performance of Lanasan, Lanaset and Lanasyn dyed wool fabrics. ..... 156

Table 3.20 Fastness performance of Sandolan E and Sandolan MF dyed wool fabrics ....... 157

Table 3.21 Fastness performance of Acid Black dyed wool fabrics. ..................................... 158

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Table 3.22 Mechanical and surface properties of wool fabrics dyed in DSW and SSW ....... 159

Table 3.23 Primary Hand Values of fabrics dyed in DSW and SSW .................................... 159

Table 4.1 Absorbance of 1.0% dye solution: before and after (without fabric) .................... 171

Table 4.2 Exhaustion (%E), Fixation quotient (%F) and Total Fixation (%T) of Lanasol

dyes at 0.05, 1.0, 3.0% and 5.0% o.m.f. on wool fabric ........................................................ 175

Table 4.3 Colour difference of comparable Lanasol dyed wool fabrics in DSW and SSW

at three stages: after dyeing; after ammonia treatment; and after wash-off. .......................... 178

Table 4.4 Comparison of fastness properties of Lanasol dyed wool fabrics ......................... 179

Table 5.1 Disperse dyes used in this research and their characteristics ................................. 192

Table 5.2 Colour strength, K/Sλmax, of Red, Yellow and Blue dyed polyester fabric at 0.05,

1.0 and 2.0% o.m.f. application levels ................................................................................... 195

Table 5.3 Colour strength, K/Sλmax, of Black dyed polyester fabric at 0.05, 1.0 and 2.0%

o.m.f. application levels ......................................................................................................... 195

Table 5.4 Colour difference, ΔECMC(2:1), between Red, Yellow and Blue dyed polyester

fabrics dyed in DSW and SSW aqueous media. .................................................................... 196

Table 5.5 Colour difference, ΔECMC(2:1), between Black dyed polyester fabrics dyed in

DSW and SSW aqueous media. ............................................................................................. 197

Table 5.6 Wash fastness and staining, dry rub fastness performance of Disperse Red and

Yellow dyes at 0.05, 1.0 and 2.0% o.m.f. depth on polyester ................................................ 199

Table 5.7 Wash fastness and staining, dry rub fastness performance of Disperse Blue and

Black dyes at 0.05, 1.0 and 2.0% o.m.f. depth on polyester .................................................. 200

Table 5.8 Alkaline perspiration fastness and staining, sublimation fastness and staining,

and light fastness performance of Disperse Red and Yellow dyes at 0.05, 1.0 and 2.0%

o.m.f. on polyester fabrics ...................................................................................................... 201


and light fastness performance of Disperse Blue and Black dyes at 0.05, 1.0 and 2.0%

o.m.f. depths on polyester fabrics .......................................................................................... 202

Table 6.1 Colour strength, K/Sλmax and colour difference of dyed nylon fabrics at 0.05, 1.0

and 2.0% o.m.f. of applied metal complex dyes .................................................................... 213

Table 6.2 Fastness performance of Lanasan, and Acidol dyed nylon 6,6 fabrics .................. 215

Table 7.1 K/Sλmax and ΔE*94 of cationic dyes at 0.05, 1.0 and 3.0% o.m.f. ............................ 225

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Table 7.2 Comparison of fastness properties of cationic dyes ............................................... 225

Table 8.1 Modification of Azurtex media and its modification details ................................. 232

Table 8.2 Average wet pick-up % of original and fluorinated Azurtex media ...................... 234

Table 8.3 XPS surface analysis of fluorinated and plasma treated Azurtex media ............... 243

Table 8.4 Oil/Water repellency and wetting times for treated Azurtex media. 4800s has

been the upper measurable limit ............................................................................................ 249

Table 9.1 Properties of the filter media used in the benchmarking study .............................. 256

Table 9.2 Properties of permeate for benchmarking testing .................................................. 257

Table 9.3 Performance properties of cake for benchmarking test ........................................ 258

Table 9.4 Properties of permeate after filtration process, a value of 1000 NTU was the

upper measurable limit ........................................................................................................... 260

Table 9.5 Properties of cake after filtration ........................................................................... 261

Table 10.1 Colour strength, K/Sλmax, of Lanaset Blue 2R, λmax at 610nm, and Sandolan

Red MF-GRLN, λmax at 510nm, dyed wool fabric. ................................................................ 285

Table 10.2 Fastness properties of Lanaset Blue 2R dyed wool at different stages of dyeing

(Bold indicates dyeing stage after filtration) .......................................................................... 291

Table 10.3 Fastness properties of Sandolan Red MF-GRLN dyed wool at different stages

of dyeing................................................................................................................................. 292

Table 10.4 Turbidity at different stages of filtration for Sandolan Red MF-GRLN dye,

Tap water 0.59 NTU, DSW 0.21 NTU, SSW 1.63 NTU, a value of 1000 NTU was the

upper measurable limit. .......................................................................................................... 293

Table 10.5 Average abrasion resistance of wool dyed fabric in reused dyebath ................... 294

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LIST OF FIGURES

Figure 1.1 Distribution of freshwater in the world in 2007 .................................................... 37

Figure 1.2 Available freshwater for use on earth .................................................................... 38

Figure 1.3 Water withdrawal a) by source and b) sector in Bangladesh.................................. 39

Figure 1.4 Consumption of water in a) textile industry; b) wet processing industry ............. 40

Figure 1.5 Regions of corrosion with metals and alloys in seawater ....................................... 43

Figure 1.6 Potential chemical releases in textile dyeing and finishing, redrawn from ........... 47

Figure 1.7 Discharge of textile wastewater in Bangladesh a) direct discharge to water

flow b) stream of wastewater towards the river ...................................................................... 49

Figure 1.8 Evolution of world apparel fibre consumption, in million tons ............................ 54

Figure 1.9 Global share of textile fibre in 2009 ...................................................................... 54

Figure 1.10 Chemical structures of some chromophores ......................................................... 56

Figure 1.11 Example of chemical structure of dyes ................................................................. 57

Figure 1.12 Particle collection mechanisms ............................................................................ 67

Figure 1.13 Conventional cake filtration, a) typical process; b) flow over time ..................... 68

Figure 1.14 Cross-flow filtration, a) typical process; b) flow over time ................................. 72

Figure 1.15 Classification based on the structure of filters ..................................................... 73

Figure 1.16 Mechanisms of membrane fouling, a) concentration polarisation; b)

adsorption; c) gel layer formation d) complete blocking; e) standard blocking; f)

intermediate blocking .............................................................................................................. 81

Figure 1.17 FC repellent finish on fibre surface. ..................................................................... 87

Figure 1.18 Structures of the cationic polyelectrolytes: PDADMAC, polymers from

epichlorohydrin and dimethylamine (ECH/DMA), CPAM, chitosan and Anionic PAM. ...... 92

Figure 1.19 Visualisation of the double layer .......................................................................... 94

Figure 1.20 Net interaction curve according to the DVLO theory . ........................................ 95

Figure 1.21 The bridging flocculation model ......................................................................... 96

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Figure 1.22 The charge patch agglomeration model ............................................................... 97

Figure 2.1 SEM micrograph of a cross-section of Primapor Blue filter, showing the upper

layer of microporous polyurethane coating combined with the polypropylene woven

support (x 400 magnification) ................................................................................................ 118

Figure 2.2 Structures of PDADMAC (polydiallyldimethylammonium chloride) and

cationic aluminium polymer - the active components of Pluspac 2000................................. 119

Figure 2.3 Hydrosolanum PSS-copolymer of hydrolysed vegetable protein and

polystyrene sulphonate ........................................................................................................... 120

Figure 2.4 Schematic diagram of a filtration apparatus used in this study ............................ 121

Figure 2.5 Associated image for cake disposal rating used in this research. Since rating 5

is an unbroken flat cake it is not included here. ..................................................................... 128

Figure 2.6 Water droplet on a surface .................................................................................... 131

Figure 3.1 Classification of wool dyestuffs in relation to migration and fastness ................ 138

Figure 3.2 Structure of acid dyes used in this study a) Everacid Black LD CI Acid Black

172; b) Sandolan Yellow E-2GL CI Acid Yellow 17; c) Lanaset Blue 2R- CI Acid Blue

225; d) Lanaset Yellow 2R CI Acid Yellow 220. .................................................................. 142

Figure 3.3 Graph of Sandolan Rubylon E-3GSL dye absorbance versus concentration in

water, λmax 512nm . ................................................................................................................. 145

Figure 3.4 Graph of Lanaset Black B dye absorbance versus concentration in water with

dyebath auxiliaries, λmax 583nm ........................................................................................... 145

Figure 3.5 SEM micrographs of dyed wool fabric washed in a) 2 gL-1

detergent at room

temperature for 10 minutes in SSW, magnification x 1.0 K; b) 2 gL-1

detergent at 70°C

for 10 min in SSW, magnification x4.0 K. ............................................................................ 146

Figure 3.6 SEM X-ray microanalysis of dyed wool that had been washed in 2 gL-1

detergent at room temperature for 10 minutes in DSW. ........................................................ 147

Figure 3.7 Wool Fabrics Dyed with Lanasyn Black S dye: left dyeing in DSW and right

dyeing in SSW a) 1.0% o.m.f.; b) 4.0% o.m.f. ...................................................................... 151

Figure 4.1 Chemical structure of (a) C.I. Reactive Red 84; (b) C.I. Reactive Blue 69; (c)

C.I. Reactive Yellow 39 . ....................................................................................................... 166

Figure 4.2 Chemical structure of Albegal B ......................................................................... 167

Figure 4.3 Reactive dyeing profile for wool and post-washing process ................................ 167

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Figure 4.4 Graph of Lanasol Red 6G dye absorbance versus concentration in distilled

water, λmax 499nm and in simulated seawater λmax 496nm ..................................................... 169

Figure 4.5 Graph of Lanasol Red 6G dye absorbance versus concentration ......................... 170

Figure 4.6 Blank dyeing of wool (with no dyes), (a) DSW, before dyeing; (b) SSW,

before dyeing; (c) DSW, after dyeing, λmax, 300nm, A, 0.4; (d) SSW, after dyeing, λmax,

300nm, A, 0.3. ........................................................................................................................ 171

Figure 4.7 Dye solutions of DSW and SSW at 3.0% o.m.f., before dyeing and exhausted

dyebath after full dyeing cycle, a) DSW before dyeing; b) DSW after dyeing; c) SSW

before dyeing; and d) SSW before dyeing. ............................................................................ 172



before dyeing; and d) SSW before dyeing. ............................................................................ 173

Figure 4.9 Dye solutions of SSW after full dyeing cycle without fabric, a) at 3.0% o.m.f.;

b) 5.0% o.m.f. ......................................................................................................................... 173

Figure 4.10 Effect of DSW and SSW on the mass of the dyed fabric at 0.05%, 1.0%,

3.0% and 5.0% o.m.f. depth compared to undyed fabric of 295.0 gm-2

................................ 174

Figure 4.11 K/Sλmax values of wool dyed with Lanasol Blue 3G dye in DSW and SSW ....... 177

Figure 4.12 K/S values of wool dyed in Lanasol Red 6G dye in DSW and SSW. ................ 177

Figure 4.13 K/Sλmax values of wool dyed in Lanasol Yellow 4G dye in DSW and SSW ...... 178

Figure 4.14 Tensile strength in warp direction of wool dyed fabric in DSW and SSW at

0.05%, 1.0%, 3.0% and 5.0% o.m.f. application levels compared to blank dyed fabric ....... 180

Figure 4.15 Tensile strength in weft direction of wool dyed fabric in DSW and SSW at

0.05%, 1.0%, 3.0% and 5.0% o.m.f. application levels compared to blank dyed fabric ....... 181

Figure 4.16 Abrasion resistance of wool fabric dyed in DSW and SSW at 0.05%, 1.0%,

3.0% and 5.0% o.m.f. application levels compared to undyed fabric .................................... 183

Figure 5.1 Chemical structure of PET fibre ........................................................................... 190

Figure 5.2 Structure of Dianix Yellow 4GSL-FS 400 dye (C.I. Disperse Yellow 227) ........ 192

Figure 5.3 Dyeing profile for Dianix, Dispersol and Terasil Dyes ....................................... 193

Figure 5.4 SEM micrograph of polyester fibres, a) after reduction clearing and cold rinse

in DSW; b) reduction cleared in SSW and rinsed in DSW .................................................... 203

15

Figure 5.5 SEM X-ray microanalysis of dyed wool that had been reduction cleared, acid

washed and then, washed in 2 gL-1

detergent at room temperature for 10 minutes in DSW

. ............................................................................................................................................... 204

Figure 6.1 Graph of Lanasan Red CF-WN dye absorbance versus concentration in

distilled water, λmax 498nm ..................................................................................................... 210

Figure 6.2 Exhaustion levels of Lanasan CF dyes at 0.05, 1.0 and 2.0% o.m.f. on nylon..... 212

Figure 6.3 Exhaustion levels of Acidol KM dyes at 0.05, 1.0 and 2.0% o.m.f. on nylon ..... 212

Figure 7.1 Molecular structure of (a) C. I. Basic Blue 41; (b) C. I. Basic Red 46; and (c)

C. I. Basic Yellow 45 . ........................................................................................................... 220

Figure 7.2 Dyeing profile for acrylic fabrics ......................................................................... 221

Figure 7.3 Graph of C. I. Basic Blue 41 absorbance versus concentration in DSW, λmax

608nm. .................................................................................................................................... 221

Figure 7.4 Graph of C. I. Basic Red 46 absorbance versus concentration in DSW, λmax

531nm. .................................................................................................................................... 222

Figure 7.5 Graph of C. I. Basic Yellow 45 absorbance versus concentration in DSW, λmax

440nm. .................................................................................................................................... 222

Figure 7.6 The effect of salt on the equilibrium sorption of cationic dyes on acrylic

fibres.. ..................................................................................................................................... 223

Figure 7.7 %E of Cationic dyes at different depths ............................................................... 224

Figure 8.1 Images of Fluorinated Azurtex filter membrane: a) untreated; b) Az 2%F2, 10';

c) Az 10%F2 batch 1; and d) Az 10%F2 batch 2. ................................................................... 233

Figure 8.2 SEM micrographs of fluorinated untreated PP fabric and Azurtex media at

different fluorination levels: a) Untreated PP, base fabric, magnification x 1.0K; b)

Untreated Azurtex, magnification x 1.0K; c) Az 2% F2, 10′, magnification x 2.0K; and d)

Az 10% F2, magnification x 1.0K. ......................................................................................... 236

Figure 8.3 SEM micrographs of modified Azurtex media at 2.0K magnification: a) Az

Ito; b) Az 2%F2, 10' Ito; c) Az 10%F2, Ito; and d) Az P2i std. .............................................. 237

Figure 8.4 ATR FTIR spectra of untreated Azurtex media ................................................... 238

Figure 8.5 ATR FTIR spectra of Fluorinated FC treated Azurtex medias............................. 239

Figure 8.6 ATR FTIR spectra of Fluorinated and FC treated Azurtex media ....................... 239

Figure 8.7 ATR FTIR spectra of Plasma treated Azurtex media ........................................... 240

16

Figure 8.8 Widescan XP spectra of Fluorinated Azurtex filter media ................................... 241

Figure 8.9 Widescan XP spectra of Itoguard FC treated fluorinated Azurtex filter media ... 241

Figure 8.10 Widescan XP spectra of plasma treated Azurtex filter media ............................ 242

Figure 8.11 C(1s) XP spectra of untreated Azurtex filter media ........................................... 244

Figure 8.12 C(1s) XP spectra of fluorinated Azurtex filter media: a) Az 2%F2, 2'; b) Az

2%F2, 10'; c) Az 5%F2, 2'; d) Az 5%F2, 10'; and e) Az 10%F2 . ............................................ 245

Figure 8.13 C(1s) XP spectra of Itoguard treated fluorinated Azurtex filter media: a) Az

Ito; b) Az 2%F2, 2', Ito; c) Az 2%F2, 10', Ito; d) Az 5%F2, 2', Ito; e) Az 5%F2, 10', Ito;

and f) Az 10%F2, Ito. .............................................................................................................. 246

Figure 8.14 C(1s) XP spectra of plasma treated Azurtex filter media: a) P2i std; b) P2i 1°;

and c) P2i 2°. .......................................................................................................................... 247

Figure 8.15 Relationship between contact angles and (CF2+CF3)/C(1s) in modified

selected filter media ............................................................................................................... 250

Figure 9.1 Average flow rate of Azurtex and proprietary filter media. ................................. 257

Figure 9.2 Average flow rate of modified Azurtex filter media ............................................ 259

Figure 9.3 Effect of pH on dye removal on SSW dyebath. Coagulation/flocculation with

12 gL-1

Pluspac 2000 and 8 gL-1

HPSS .................................................................................. 265

Figure 9.4 Removal of Lanaset Blue 2R dye with different concentration of PP2000 and

HPSS at different pH .............................................................................................................. 266

Figure 9.5 Colour removal and turbidity as a function pH for Lanaset Blue 2R dye with

15 gL-1


HPSS (turbidity of original dye solution was 46.2

NTU). ..................................................................................................................................... 266

Figure 9.6 Removal of Sandolan Red MF-GRLN dye with different concentration of

PP2000 and HPSS in gL-1

at different pHs.. .......................................................................... 267

Figure 9.7 pH effect on turbidity after coagulation/flocculation for Sandolan Red MF-

GRLN dye at different ratio of Pluspac 2000 and HPSS in gL-1

. .......................................... 268

Figure 9.8 Colour removal and Turbidity in a function of pH for Sandolan Red MF dye

with 15 gL-1


HPSS. ...................................................................... 269

Figure 10.1 Exhaustion, %E, of Lanaset Blue 2R dye at different stage of dyeing, λmax at

588nm, in SSW. ..................................................................................................................... 283

Figure 10.2 Exhaustion, %E, of Sandolan Red MF-GRLN dye at different stage of

dyeing, λmax at 494nm, in SSW .............................................................................................. 284

17

Figure 10.3 ∆ECMC (2:1) plots for fabrics dyed with Lanaset Blue 2R dye with no filtration

of the dyebath ......................................................................................................................... 286

Figure 10.4 ∆ECMC(2:1) plots for fabrics dyed with Lanaset Blue 2R dye with filtration

after the 3rd

reused dyebath .................................................................................................... 286

Figure 10.5 ∆ECMC (2:1) plots for fabrics dyed with Lanaset Blue 2R dye with filtration

after 4th

reused dyebath .......................................................................................................... 287


after the 5th

reused dyebath .................................................................................................... 287

Figure 10.7 ∆ECMC (2:1) plots for fabrics dyed with Sandolan Red MF-GRLN dye with no

filtration .................................................................................................................................. 288

Figure 10.8 ∆ECMC (2:1) plots for fabrics dyed with Sandolan Red MF-GRLN after

filtration of the 3rd

, 6th

, and 9th

reused dyebath ..................................................................... 288


filtration of the 4th

, and 8th

reused dyebath ............................................................................ 289

Figure 10.10 ∆ECMC(2:1) plots for fabrics dyed with Sandolan Red MF-GRLN after


and 10th

reused dyebath ........................................................................... 289

Figure 10.11 Turbidity results of reused dyebath with no filtration. ..................................... 293

Figure 10.12 Tensile strength of weft of wool dyed fabric in SSW at 3.0% (o.m.f.) depth

compared to blank dyed fabric ............................................................................................... 295

18

LIST OF SCHEMES

Scheme 1.1 Fluorination Process .......................................................................................... ..84

Scheme 1.2 Mechanism of coagulation with aluminium-based coagulants ........................... 90

Scheme 3.1 Mechanism of wool and acid dye ....................................................................... 138

Scheme 3.2 Effects of anions on water absorbency ............................................................... 148

Scheme 3.3 Effects of cations of chlorides on water absorbency .......................................... 148

Scheme 4.1 Possible formation of groups after nucleophilic and addition reactions with

Lanasol reactive dye and wool .............................................................................................. 165

Scheme 4.2 Possible further reactions of wool and Lanasol reactive dyes ........................... 181

Scheme 4.3 Formation of thi-irane ring due to thiol-disulphide interchange reaction .......... 182

Scheme 10.1 Sequence of recycling stages in acid dyeing reuse process .............................. 282

19

LIST OF EQUATIONS

Equation 1.1

60

Equation 1.2 60

Equation 1.3

60

Equation 1.4

61

Equation 1.5

61

Equation 1.6 61

Equation 1.7

69

Equation 1.8

69

Equation 1.9 ( ) 69

Equation 1.10

( )

69

Equation 1.11

( ) 69

Equation 1.12

( )

70

Equation 1.13

( )

70

Equation 1.14

70

Equation 1.15 ( )

( ) 70

Equation 1.16

70

Equation 1.17

( )

70

20

Equation 1.18

( )

71

Equation 1.19

71

Equation 1.20

71

Equation 1.21

71

Equation 2.1 ( )

121

Equation 2.2 ( )

122

Equation 2.3 ( ) ( )

122

Equation 2.4 [(

)

(

)

(

)

]

123

Equation 2.5 ( )

124

Equation 2.6 ( )

124

Equation 2.7

127

Equation 2.8 ( )

127

Equation 2.9

132

Equation 4.1 ( ⁄

)

( ⁄

) 168

Equation 4.2

168

21

LIST OF NOTATIONS

A/A after ammonia treatment

A/D after dyeing

A0 absorbance of solution before filtration or before dyeing

Af absorbance of solution after filtration

A/W after wash-off

c mass of solid per unit volume of suspending liquid (kg)

C0 concentration of dye initially in solution (gL-1

)

Cs concentration of dye in solution after dyeing (gL-1

)

D1, D2… consecutive dyeing 1, 2….

dp dynamic (hydraulic) pressure difference across thickness

dx thickness of porous filter medium (m)

dw unit mass of solid deposited

%E percentage exhaustion

%F degree of fixation or fixation quotient

k cake permeability (m2)

K absorption coefficient

K0 Kozeny constant

K/S colour strength

( ⁄

) colour strengths of the dyed samples before washing

( ⁄

) colour strengths of the dyed samples after washing

L cake thickness (m)

m wet to dry cake mass ratio

p liquid (filtrate) pressure (Pa)

po operating pressure (Pa)

q superficial liquid velocity (ms−1

)

R proportional reflectance of the dyed fabric

Rm medium resistance m−2

Rc resistance of cake m-2

s particle mass fraction of suspension

S scattering coefficient

22

S0 specific surface area of the particles

t time (s)

%T percentage of total dye fixed or fixation ratio

V cumulative filtrate volume per unit medium surface area (m)

w cake mass per unit medium (or bowl) surface area (kgm−2

)

x distance away from medium (m)

Greek letters

α specific cake resistance (mkg−1

)

αav average specific cake resistance (mkg−1

)

molar absorbtivity with units (Lmol-1

cm-1)

λmax maximum wavelength (nm)

ΔC* difference in chroma

ΔE colour difference

ΔH* difference in hue

ΔL* difference in lightness/darkness value

Δp pressure gradient

Δpc pressure drop across cake (Pa)

ΔPm pressure drop across medium (Pa)

µ fluid viscosity (Pas)

ρ filtrate density (kgm−3

)

ρs filtrate density (kgm−3

)

23

ABBREVIATIONS

AATCC American Association of Textile Chemists and Colorists

ADMI American Dye Manufacturers Institute

AOX Adsorbable Organic Halogens

ASTM American Society for Testing and Materials (ASTM)

ATV Abwasser Technishe Vereinigung (Waste Water Technical

Association), Germany

BOD Biological Oxygen Demand

CD Charge density

CIE Commission Internationale de l’Eclairage

CMC Colour Measurement Committee

COD Chemical Oxygen Demand

CSIRO Commonwealth Scientific and Industrial Research Organisation

DLVO Theory Derjaguin, Landau, Verwery and Overbeek Theory

DSW Distilled water

ED Electrodialysis

EPA US Environmental Protection Agency

FC Fluorocarbon

HPSS Hydrosolanum polystyrene sulphonate

INDA Associations for Nonwoven Fabric Industry

KES-F Kawabata Evaluation System for Fabrics

MF Microfiltration

NF Nanofiltration

NTU Nephelometric Turbidity Units

OECD Organisation for Economic Co-operation and Development

o.m.f. On the mass of fabric

PAC Polyaluminium chloride

PAM Polyacrylamide

PDADMAC Polydiallyldimethylammonium chloride

PET Polyethylene Terephthalate

PHV Primary Hand Value

PP Polypropylene

24

RO Reverse osmosis

SAE Society for Automotive Engineers

SDC Society of Dyers and Colourists

SEM Scanning Electron Microscope

SSW Simulated Seawater

THV Total Hand Value

UF Ultrafiltration

VOC Volatile Organic Compound

XPS X-ray Photoelectron Spectroscopy

25

ABSTRACT

The aim of this research was to find a suitable alternative medium for scarce freshwater

for textile dyeing, and to recycle and reuse the dyebath using a combined

coagulation/flocculation and microfiltration technique. Simulated seawater (SSW) was

tested as the alternative dyeing medium with a salt concentration of 3.5% where NaCl

was the major component.

Fibre/dye systems of wool/acid and metal complex, wool/reactive, polyester/disperse,

nylon/acid and metal complex, and acrylic/cationic dyes were tested in simulated

seawater and the performances of dyed fabric were compared to conventional dyeing

system of distilled water (DSW). The study found that commercial dyeing processes were

robust and can be practically transferable into the seawater medium. The dye exhaustions,

build-up, colour characteristics, and fastness to wash, cross-staining, rub and light were

satisfactory within the dye ranges studied, which covers commercially available

monochromatic Red, Yellow and Blue at light, medium and deep shades. Although SEM

micrographs didn’t show any presence of salt, a typical wash-off process of 1gL-1

with a

non-ionic detergent at 70°C was sufficient to remove any salt that could be present on the

surface or sub-surface of the dyed fabric.

At room temperature, some acid and metal complex dyes were only partially soluble in

SSW but this improved with gentle heating and addition of levelling agents. At dyeing

temperatures near the boil, these dyes were completely soluble. A saturation limit was

found to be existed for acrylic dyeing of cationic dyes over 1.0% o.m.f. depth. Although

ionic interaction was the dominant mechanism for dyeing of wool, nylon and acrylic fibre

with acid, metal complex and cationic dyes, the adsorption in highly saline dyebath most

likely depended on the combined effects of ionic and physical/hydrophobic interactions.

The resultant effect was higher dye exhaustion and consequently higher colour difference

in SSW for some dyes. Reactive dyes are known to be sensitive to the hardness of water

but this study confirmed the viability for deep dyeing for wool fibre in SSW. Reactive

dyeing of wool followed a similar mechanism of gradual phase transfer as was observed

for disperse dyeing of hydrophobic fibres over 3.0% o.m.f. depth. In contrast disperse

dyeing of polyester produced consistent results for all dyes but some black dyeings

26

produced superior colour strength in SSW. The build-up of colour in SSW compared to

DSW can be different depending on the application level.

To improve permeate flux by reducing membrane fouling, a number of surface

modification were carried out to introduce fluorine based functional groups. Gaseous

fluorination, fluorocarbon finish (FC) and plasma polymerisation were performed to

introduce hydrophilic and oleophobic properties on supplied Azurtex media. The

fluorinated Azurtex media exhibited increased wettability although it was not directly

proportional to an increase in the fluorination level and treatment time. The water and oil

repellency of FC and plasma treated filter media provided a reasonable level of

repellency while the contact angle remained in the range of 130 to 145°. Pre-fluorination

of filter media before FC treatment didn’t change the water and oil repellency.

Surface characterisation of Azurtex media was performed with ATR-FTIR, XPS and

SEM. An increased level of fluorination at 10% F2 and prolonged gaseous exposure

showed a degradation of the surface along with colour change. The fluorinated, FC

treated and plasma polymerised membrane showed a typical C-F stretching vibration in

the region of 1100-1350 cm-1

and weakly at 400-800 cm-1

. The XPS study showed a

gradual increase in the -CF2 and -CF3 functionality signal intensities that resulted in

imparting hydrophobicity The benchmarking of these modified Azurtex filter media

against newly developed materials proved that plasma treatment improved the flow,

reduced turbidity and provided an easy cake removal compared to fluorinated and FC

finished filter media.

Recycling of exhausted dyebath using a dual component coagulant/flocculant system of

Pluspac 2000 and polyanionic Hydrosolanum protein derivative (HPSS) and

microfiltration with Azurtex filter media was investigated. The process parameters such

as pH and dosage of coagulants/flocculants were very critical during

coagulation/flocculation for overall colour removal. The trial with model dye solution in

SSW showed that the system worked in the saline environment with a relatively high

concentration ratio of coagulant/flocculants but highly depends on the class and structure

of dyes. Maximum colour removal was achieved for Lanaset Blue 2R and Sandolan Red

MF-GRLN dye and was 89% and 61%, respectively, based on a ratio of 15:10 and 15:15

for PP2000: HPSS at pH 4.0 and 5.0, respectively.

27

The reuse of the dyebath with combined physicochemical and microfiltration treatment

was demonstrated to be feasible with wool/acid dye system. The colour profile of Lanaset

Blue 2R and Sandolan Red MF-GRLN dyed fabrics up to 12th

dyeing, with dyebath

filtration undertaken after the 3rd

/4th

/5th

reuse of the dyebath, remained comparable to

dyeing in fresh baths. The colour strength, K/S, of dyed fabric decreased after every

filtration and the colour differences, ΔE* increased, but reversed in subsequent dyeing in

reused dyebath. The wash and dry rub fastness of the dyed fabrics remained comparable

and significant improvements in the abrasion resistance were observed.

28

DECLARATION AND COPYRIGHT

The experiments in this project constitute work carried out by the candidate and no

portion of the work referred to in this thesis has been submitted in support of an

application for another degree or qualification at this or any other university or institute

of learning.

The author of this thesis (including any appendices and/or schedules to this thesis) owns

any copyright in it (the “Copyright”) and he has given the University of Manchester the

right to use such Copyright for any administrative, promotional, educational and/or

teaching purposes.

Copies of this thesis, either in full or in extracts, may be made only in accordance with

the regulations of the John Rylands University Library of Manchester. Details of these

regulations may be obtained from the Librarian. This page must form part of any such

copies made.

The ownership of any patents, design, trademarks and any and all other intellectual

property rights except for the Copyright (the “Intellectual Property Rights”) and any

reproductions of copyright works, for example graphs and tables (“Reproductions”),

which may be described in this thesis, may not be owned by the author and may be

owned by third parties. Such Intellectual Property Rights and Reproductions cannot and

must not be made available for use without the prior written permission of the owner(s)

of the relevant Intellectual Rights and/or Reproductions.

Further information on the conditions under which disclosure, publication and

exploitation of this dissertation, the Copyright and any Intellectual Property Rights and/or

Reproductions described in it may take place is available from the Head of School of

Materials.

29

THE AUTHOR

Mohammad Abbas Uddin graduated as a Textile Technologist from Bangladesh

University of Textiles, previously College of Textile Technology under The University of

Dhaka, in 2002. From then onward, he has been working in various capacities in the

textile and apparel supply chain.

After graduation, he joined the Textile and Apparel Division of Bangladesh Export

Import Company Limited, (previously known as Beximco Textiles Ltd.) one of the

largest South Asian vertically integrated textile and garment companies. After two

months intensive industrial training in yarn dyeing, woven and knit fabric dyeing and

finishing, and weaving/knit fabric production, he joined as a Quality Assurance officer in

the woven fabric processing segment. He was promoted later to the Design and Product

Development, which showcased the range of fabrics and garments at international fairs

and to respective buyers. As part of the job he produced fabric CADs, and successfully

developed those designs from initial stages to the final finishing stages. He carried out

chemical and mechanical tests of fabrics, solved online technical problems, and often

suggested creative solutions for intended products for retailers like M&S, Zara, PVH. He

actively helped Beximco laboratory to gain Oeko-Tex certificates and M&S

accreditation. Subsequently he joined to Interfab (BD) Ltd., an M&S approved garment

production site, and a sister concern of Viyellatex group, where he was responsible for

the creation of the product development department and diversified the product ranges

from school shirts to fashion products. He executed orders and followed up until

shipment.

In 2005 he was selected for prestigious Australian Development Scholarship (ADS) for

his Masters of Design course in Curtin University of Technology. He conducted his

dissertation titled, ‘Readymade Garment Industry of Bangladesh: How the industry is

affected in post MFA period?’ under Prof. Dr. Suzette Worden, which involved

questionnaires and interviews of factories in Bangladesh. He achieved a ‘High

Distinction’ grade and graduated within the top 2% of his class.

He returned to Bangladesh and joined in Primeasia University as a faculty member. He

taught undergraduate theory and laboratory classes in Dyeing and Finishing, textile raw

30

materials, textile testing and quality control, introduction to ready-made garment industry

of Bangladesh. He directed and supervised various projects during his time on

improvement of dyeing, how to achieve right first time dyeing (RFT), filtration with

natural materials and dyeing with natural colours to name a few.

In 2009 he was awarded a prestigious Commonwealth Scholarship from the British

government for conducting his PhD at the University of Manchester under the

supervision of Prof. Chris Carr and Dr. Muriel Rigout. He won Best Poster in

Postgraduate Conference 2011 and presented as plenary speaker in 2012. Apart from his

research as daily activities, he also worked as a Teaching Assistant in various textiles

labs, Facilitator for problem based learning for cases of sustainable development, Skills

for Sustainability and Social Responsibility (SSSR) and Interdisciplinary Sustainable

Development (ISD), for Manchester Business School and Electronics and Electrical

Engineering department. He also holds a position as Associate Editor of Bangladesh

Textile Today, the first Bangladeshi Textile publication.

Professional Affiliations:

Member, The Textile Institute, Manchester, UK

Member, Institute of Engineers of Bangladesh (IEB)

Member, Institute of Textile Engineers and technologists (ITET), Bangladesh

List of publications/Conferences:

Uddin, M. A., C. Carr, and M. Rigout. The use of seawater as dyeing medium for

commercial textile processing. Accepted for conference presentation to 2nd

Annual

International Conference on Water, 2014, 14-17 July 2014, Athens, Greece.

Uddin, M. A., C. Carr, and M. Rigout. Investigation of acrylic/cationic dye system in

simulated seawater. Accepted for conference presentation to 6th

International Istanbul

Conference on Future Technical Textile, FTT 2014, 15-17 Oct; Istanbul, Turkey.

Uddin, M. A., C. Carr, and M. Rigout. Reuse of dyebath in simulated seawater medium

for wool/acid dye system. Accepted for poster presentation to Ozwater'14 conference,

Australia's International Water Conference & Exhibition, 2014, 29 Apr-1 May; Brisbane,

Australia.

31

Uddin, M. A., C. Carr, and M. Rigout. Bulk trial of nylon dyeing in simulated seawater

Dyeing. Plenary speaker at Postgraduate research conference in School of Materials, The

University of Manchester, 2012, 17-18 May; Manchester, UK.

Uddin, M. A., C. Carr, and M. Rigout. Seawater Dyeing of Textiles: A possible solution.

Poster Session presented at Postgraduate Conference in School of Materials, The

University of Manchester, 2011, 18-20 May; Manchester, UK.

Uddin, M. A., C. Carr, and M. Rigout. Investigation of the use of novel filtration media

for colouration processing and recycling of textile effluent. Paper presented at

Postgraduate research conference in School of Materials, The University of Manchester,

2010, 20-21 May; Manchester, UK.

32

ACKNOWLEDGEMENT

It is a great pleasure for me to thank my supervisor Prof Chris Carr. It has been a good

experience to work under his supervision for the last three years. I have always been

benefited from his excellent scientific knowledge, constructive comments and solutions

to problems that I faced during laboratory work. His support, guidance and incessant

encouragement were invaluable all through the first year of work. I would also like to

thank my co-supervisor Dr. Muriel Rigout for her helpful suggestions and guidance in the

thesis work and ideas for the future.

I would also like to express my sincere gratitude to Dr. Huw Owens for the technical

discussion on colour physics and assistance on interpreting data.

I am very thankful to the following technical staffs in the Textile Department for their

training and assistance: Mr. Phil Cohen, Ms. Alison Harvey, Mr. Adrian Handley and Ms.

Xiangli Zhong.

I am grateful to Dr. Richard Lydon, VP Technology and Business Development at Clear

Edge Filtration, for supplying the filter media, filter bomb and for his suggestions and

arrangement for the trainings. I would also like to thank Mr. Joe Johnson, laboratory

technician for his technical support.

I wish to express my gratitude to all my colleagues for creating an excellent research

environment and to all my friends for their friendship and support.

I would like to thank Commonwealth Scholarship Commission for their financial support

through commonwealth scholarship.

In addition, I wish to thank my family, especially my mother Hosney Ara Begum, for

their support and love to my cause. I indebted to my wife, Farida Yasmin, who has taken

the most pains during my final year. My late father, Md. Abdul Manan would have been

proud to see this work.

33

Dedication

To my late father Md. Abdul Manan

and

mother Hosney Ara Begum

34

THESIS OVERVIEW

The main purpose of this thesis was to find a suitable alternative medium of dyeing for

textiles and to recycle/reuse the exhausted dyebath with a filter media. The alternative

medium was simulated seawater, a far more bountiful resource compared to the

freshwater. The thesis was conducted mainly in two phases. In the first phase

commercially successful dye ranges were evaluated under typical textile dyeing

conditions using distilled water and simulated seawater, and the performances of the dyed

fabrics assessed. Since dyeing in seawater would probably need a filtration process prior

to use in dyeing, a commercial Azurtex filter media from Clear Edge Ltd. was assessed as

a possible pre- and post-filter media.

The main body of the thesis starts with the introduction of the water resources and their

availability in the world. This is followed by an overview of the consumption of water in

textiles, and generated wastewater and their treatment methods. Textile fibres and dyes

and dyeing processes are discussed in terms of exhaustion and dye fixation. Literature

reviews on filtration, membrane process and surface modification of the filter media are

extensively discussed in Chapter 1. The composition of simulated seawater, materials and

the experimental approaches used are discussed in Chapter 2. The methods of

modification of the filter media and performances of modified filter media are also

discussed in this chapter.

The main experimental works of five fibre/dye systems using a simulated seawater

environment and their results are evaluated in Chapter 3 to 7. These fibre/dye systems

are: wool/acid and metal complex, wool/reactive, polyester/disperse, nylon/acid and

metal complex, and acrylic/cationic. A bulk trial of nylon fabric was also performed. In

addition to the results, the objectives, materials and experimental designs are also

included at the beginning of each chapter.

The modification and performance of Azurtex are assessed in Chapter 8 to 10. The

modified microfilter media are evaluated with a view to reducing membrane fouling and

increase permeate flow. The characterisation of the modified filters and their performance

is benchmarked against the new Azurtex media, Chapter 8 and 9. Before the

microfiltration, a dual component coagulation/flocculation was carried out with Pluspac

35

2000 and HPSS in order to determine the optimum concentration and pH. Based on these

results, laboratory saline wastewater was filtered after a coagulation/flocculation process

with commercial agents followed by microfiltration, Chapter 10. The filtered wastewater

was reused in dyeing and its properties/performance is compared to reused aqueous baths

with no filtration.

Finally, overall conclusions are drawn, and future work is suggested at the end of this

thesis in Chapter 11.

Literature Review

36

1. Literature Review

The need for freshwater for human consumption is a comparable environmental

challenge to that of climate change and is high on the international development agenda.

An abundant supply of clean water is necessary for many industrial activities and the

textiles industry has traditionally been one of them. The textile industry is also a

chemically intensive industry as water is the carrier medium for the wet processing [1].

The consumption of freshwater for textile processing is significant and provides the

need for the ongoing search for alternative processing media and optimization of the

existing processes [2]. Therefore, two approaches were set for this study: firstly, to

establish the potential use of the more abundant seawater as dyeing medium instead of

freshwater; secondly, to examine the performance of filter media for treatment of textile

dyeing effluent by surface modification. As a result, this study addresses two inter-

related issues, one the scarcity of freshwater for textile processing and secondly the

recycling and reuse of textile wastewater. Consequently a proper understanding of

freshwater, sources of water, impurities and their removal, and a knowledge of textile

wastewater is essential for this study and in general.

1.1 Introduction to the Water Resource

1.1.1 Water Reserves on Earth

Freshwater is a vital natural resource for plant irrigation, wildlife survival, and human

consumption. The 2010 report by World Health Organization/United Nations Children's

Fund Joint Monitoring Programme on water supply and sanitation stated that 884

million people, mostly from the developing regions do not receive their drinking water

from acceptable sources and that 3.3 million people die from the water related health

problems [3]. According to a UN report on Water, it was estimated that, by 2025, two

thirds of the population would suffer from a lack of water resources in agriculture,

energy, domestic purposes, and the environment, with a threshold limit, defined as 1700

m3/person/year [4]. Figure 1.1 shows the distribution of freshwater in the world, where

the scarcity of water is severe particularly for developing countries or regions, with an

availability of 500m3/person/year in a group of 1.8 billion people. In the Middle East,

water is already in short supply [5].

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Figure 1.1 Distribution of freshwater in the world in 2007 [5]

The quantity of freshwater on the earth's surface is constant. Seawater consists of 97.4%

of total water while freshwater contributes only of 2.6%, Figure 1.2 indicates that for

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every litre of water on the earth's surface just 26 mL is freshwater. However, this

amount of freshwater is not available for use, rather only 0.6% is economically

accessible for humans through ground, rivers, or rainwater [6].

Figure 1.2 Available freshwater for use on earth [6]

Consumption of freshwater increased six fold between 1900 and 1995, more than

double the expected considering population growth. In the EC, approximately half the

countries representing 70% of the population are facing a water shortage and the

situation requires a comprehensive management of water supply and demand. In India, a

large number of villages are facing inland salinity with a recurring water shortage

problem. China is classified as one of the 13 poorest water shortage countries in the

world [7].

In developing countries, 85% of freshwater is extracted from grounds or rivers and is

used in agriculture [8]. In China, the overdraft rate of groundwater for irrigation exceeds

25%, and in parts of northwest India it is over 56% [9]. In the UK, the cost of mains

water supply in 2000/01 was around £0.70/m3 while private supply from reservoirs is

around £0.10/ m3. Water softening can add a further £0.10 per m

3 [10]. Water UK [11]

has estimated that the average cost of the water supply has increased more than three

fold in last 15 years from 1984-85 to 1999-2000.

The factors related to the water shortage in developing countries are extremely complex

and often interrelated. High growth of the population, lack of investment in

infrastructure and scarcity of natural water resources all play their part simultaneously

in the water shortage [12].

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1.1.2 Water Reserves for Bangladesh

Bangladesh has been called the ‘land of rivers’. Three principal rivers have surrounded

the major plains of Bangladesh: the Ganges, Brahmaputra and Meghna, with their

tributaries the Tista, Dharla, Surma and Kushiyara and the Karnafully [13]. These river

systems drain into the Bay of Bengal through the mainland of Bangladesh, with the

main port being Chittagong [14].

The rivers are a significant source of water, but they are in many cases unusable due to

the pollution. In 2008, approximately 79% of the total water supply came from

underground sources, Figure 1.3a, with agriculture being the biggest sector user of

freshwater, around 88%, Figure 1.3b. Even though, the ratio of water usage has not

changed in last two decades for industry (2% in 2008 and 1990) [15], the overall

consumption rate has been increased from 14.6 km3 in 1990 to 35.87 km

3 in 2008. As a

result, the extraction of water has dramatically increased but without any significant

replenishment of the water reserves.

Figure 1.3 Water withdrawal a) by source and b) sector in Bangladesh. Total water

withdrawal was 35.87 km3 in 2008

1.1.3 Water Consumption in Textiles

Textile processing, particularly dyeing and finishing is a water intensive process.

Almost all dyes, specialty chemicals, and finishing chemicals are applied to textile

substrates from water baths. Rinsing and washing consumes further large amounts of

water together with steam still being the main heat transfer media for dyeing &

finishing.

21%

79%

Surface water

Goundwater

a)

88%

10%

2%

Irrigation and

livestock

Municipalties

Industry

b)

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Table 1.1 Typical water usage, Lkg-1

of product, in woven fabric wet processing [16]

Subcategory Minimum Median Maximum

Simple processing 12.5 78.4 275.2

Complex processing 10.8 86.7 276.9

Complex processing plus desizing 5.0 113.4 807.9

Table 1.1 showed that the textile operations vary considerably in water consumption

depending on the complexity of processing and the steps required to fulfil the end use,

the equipment used, and the prevailing management philosophy concerning water use.

In general the ratio of water consumption in a factory depends on the everyday use to

processing needs, Figure 1.4. Wool and felted fabric processes are more water intensive

than other processing sub-categories such as wovens, knits, stock, and carpet [17].

Water use can also vary widely between similar operations. For example, a knit-dyeing

factory uses an average of 120 L of water for 1 kg of cotton dyeing with reactive dye,

yet usage of water ranges from a low of 70 L to a high of 200 L [18]. Orhon, Kabdasli

and others [19] reported that Turkish factories require 20–230 L of water to produce 1

kg of textile fabric.

Figure 1.4 Consumption of water in a) textile industry; b) wet processing industry [20]

72%

8%

8% 6% 5% 1%

Wet processing

Sanitary

Water treatment for specific purpose

Cooling water

Steam production

Fire fighting

a)

1% 2% 5%

4% 13%

3% 2%

70%

Desizing Scouring

Bleaching Mercerising

Dyeing Printing

Finishing Several Intermediate

b)

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Water consumption varies considerably among unit processes, Figure 1.4b, and

intermediate washing stages after the each unit processes are the more intensive steps.

Within the dyeing category, certain unit processes are particularly low in water

consumption such as pad/batching. Different types of processing machinery use

different amounts of water, Table 1.2, particularly in relation to the liquor ratio in

dyeing processes.

Wet processing, therefore, is considered a critical component in textile manufacturing

because of its frequent use and strong economic impact. Manufacturers increasingly

focus their attention on reducing water consumption, which leads to subsequent energy

and hot water savings and consequently a reduction in wastewater.

Table 1.2 Water consumption in typical textile wet processing and machines [21]

Dyeing machine/process Water consumption (Lkg-1

)

Beam 167

Beck 234

Jet 200

Jig 100

Paddle 292

Skein 250

Stock 167

Pad-batch 17

Package 184

Continuous 167

Indigo range 8 to 50

1.1.4 Sources of Water

Dyehouses are usually located in areas where the natural water supply is sufficiently

fresh and plentiful. Water mainly comes from surface or underground from a depth of at

least 50 ft below the surface depending on the availability of the reserve. Rain, rivers

and melting snow are a few of the sources that recharge the supply of underground

water. Due to the many sources of recharge, groundwater may contain any or all of the

contaminants found in surface water as well as the dissolved minerals it collects during

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its long stay underground. A comparison of characteristics of surface and ground water

is given in Table 1.3. The physical and chemical characteristics of surface water may

vary frequently e.g. drought and flood or over extended period of time. In comparison,

ground water is very stable and depends on the strata. A high iron content in

groundwater may contain surface reducing bacteria, which is a source of fouling and

corrosion in industrial water systems [22].

Table 1.3 Comparison of surface water and groundwater characteristics [22]

Characteristic Surface Water Groundwater

Turbidity high low

Dissolved minerals low-moderate high

Biological content high low

Temporary variability very high low

Table 1.4 shows the survey results carried out in 2000 by CRIET (the European Textile

Finishers’ Organisation) which found that in Europe and the UK the patterns of water

extraction are the same, reflecting geographical proximity as necessary for the selection

of water sources [18].

Table 1.4 Survey of water sources used by selected European dyers and finishers in

2000 [23]

Water source %

Country Main supply River Ground

Austria 12 88 0

Belgium 6 17 77

Germany 10 0 90

Denmark 58 7 35

France (1999) (1) (99) (0)

UK 10 0 99

Italy 6 5 89

The Netherlands 19 29 52

Turkey (1999) (50) (0) (50)

Weighted average* 16 9 75

*values obtained in 2000 only

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In general, source water for usage in dyehouses comes from either surface or ground

water. Surface waters mainly require treatments which reduce turbidity, colouration and

the concentration of organic substances, while groundwater requires treatments aimed at

eliminating alkaline earth metals, iron and manganese.

1.1.5 Effect of seawater on industrial processing

Water is ‘the universal solvent’ as it can dissolve every natural substance to some

degree. The nature of this solvency poses major threats such as corrosion [22]. The

impact of corrosion on the economy and environment is huge which includes

infrastructure, oil and gas rigs, bridges, highways, chemical processing, and water and

wastewater systems [24]. Corrosion reduces the lifetime of assets, requires high

maintenance and causes severe damage and increases the risk of public safety. The

annual cost of corrosion is US$2.2 trillion, equivalent to the 3% of the world’s GDP

[25].

Figure 1.5 Regions of corrosion with metals and alloys in seawater

The presence of large amounts of inorganic salts e.g. chlorides and associated high

conductivity results in seawater being highly corrosive [26]. The oxygen present in

marine environments, in the surface region and sometimes at greater depths exacerbates

the corrosion. Corrosion by seawater is an electro-chemical process, where under acid

or alkaline pH seawater generates an electrical potential (or corrosion potential) with

metals and alloys [22, 27]. Figure 1.5 shows the regions of free metal corrosion; the

region of passive corrosion where stable oxide or other films cause quiet corrosion; the

Pote

nti

al (

Volt

s)

Pitting

Corrosion

Passivity

Immune

0 7 14

pH

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region of pitting where corrosion potential of metal overcomes that of its oxides; and

the region of immunity where the metal is usually resistant to corrosion [27]. Seawater

desalination plants are particularly prone to corrosion problems, as in addition to the

aggressive marine environment, movement of liquids containing particulates or deposit

forming liquids could be involved. The localised corrosion such as pitting and crevice

corrosion are quite common [28]. The common impurities that are found in freshwater

and seawater along with their associated difficulties are given in Table 1.5.

Table 1.5 Common impurities found in freshwater and seawater [27]

Constituent Difficulties Caused

Hardness: Ca2+

,

Mg2+

salts

Main source of scale in boiler, pipe lines, heat exchange

equipment etc.; interferes with dyeing and other processing

Alkalinity: HCO3-,

CO32-

, and OH-

Creates foam, carries solids with steam; embrittlement of boiler

steel; causes corrosion in condensate as produces CO2 in steam

CO2 corrosion in steam and condensate lines

Cl - Increases solids content and corrosiveness of water

O2 Corrosion of water lines, heat exchange equipment, boilers, pipes

Fe2+

, Fe3+

Discolours water on precipitation; source of deposits in boilers,

water lines etc.; interferes with dyeing, tanning, papermaking, etc.

SO42-

Forms calcium sulphate scale

NO3- Adds to solids content, useful for control of boiler metal

embrittlement

Na+ Adds to solids content of water: when combined with OH-, causes

corrosion in boilers under certain conditions

SiO2 Scale in boilers and cooling water systems

Mn2+

Same as iron

AI3+

Deposits in cooling systems, contribute to complex boiler scales

H2S Corrosion, cause of "rotten egg" odour

NH3 Corrosion of Cu/Zn alloys by formation of complex soluble ion

Free mineral acid Corrosion

Dissolved Solids Process interference at high concentrations and cause of foaming

in boilers

Suspended Solids Deposits in boilers, heat exchange equipment, water lines, etc.

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Corrosion in seawater can be controlled by painting or coating, using corrosion

inhibitors, changing the pH of the local environment, using more corrosion resistant

material or composites [27]. The corrosion behaviour of stainless steel, carbon steel, α-

aluminium bronze, titanium, copper-nickel alloys, copper alloys and composites in

natural seawater has extensively studied [28, 29, 30, 31, 32, 33, 34]. Modern day

industrial equipment which used in marine applications are copper-nickel alloys with

different ratios because these materials provides corrosion resistance, good electrical

and thermal conductivities and ease of fabrication of the equipment [35]. The 90/10

copper-nickel alloy is particularly suitable for desalination plant where seawater is used

as a coolant for condensers and heat exchangers [36, 37]. These alloys are resistant to

corrosion cracking by ammonia and sulphide ions [38] and to pitting and crevice

corrosion [39]. A guideline of using copper-alloys in seawater has also been established

[40].

1.1.6 Water Quality for Textile Processing

The raw material that is used in the greatest quantity in virtually every stage of textile

wet processing is water. There are several key categories to be considered for

processing, utilities, potable and laboratory use of water. Each requires different water-

quality parameters. Process water (for preparation, dyeing, and finishing) is mainly used

for making concentrated bulk chemical stock solutions, substrate treatment solutions,

and washing. Potable water is for drinking and food preparation. Utility use includes

non-contact applications uses such as boiler use, equipment cleaning etc. [41].

Consistent water quality plays a significant role in the success of textile wet processing

operations. Water from almost all supply sources contains impurities to some extent.

The type and amount of impurities in water depend upon the type of water source.

Generally, process water should have little or no chlorine, low metals content (i.e. iron

and copper) and low salts concentrations (i.e. chloride and sulphate) and acceptable

water hardness. The established requirements of the water used in textile processing are

given in Table 1.6.

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Table 1.6 Dyehouse water standard [42]

Characteristic Permissible Limit

Colour Colourless

Smell Odourless

pH value Neutral pH 7–8

Water hardness < 5 dH (6.25eH; 8.95fH; 5.2USA)

Dissolved solids < 1 mgL-1

Solid deposits < 50 mgL-1

Organic substances < 20 mgL-1

(KMnO4 consumption)

Inorganic salts < 500 mgL-1

Iron (Fe) < 0.1 mgL-1

Manganese (Mn) < 0.02 mgL-1

Copper (Cu) < 0.005 mgL-1

Nitrate ( NO3-) < 50 mgL

-1

Nitrite ( NO2- ) < 5 mgL

-1

Contaminants from the water source are not the only materials found in textile water

supplies. There may be substantial internal contamination from such sources as the grey

substrate, machinery, plumbing and valves and prior treatment of water [43].

1.2 Textile Wastewater [44, 45, 46, 47]

The amount of wastewater generated by the textile industry is significant with the

colour of the water channels providing a crude indicator of the quality of the water,

Table 1.7. Industrial waste is one of the main reasons for changing of the original water

colour, and the textile industry was notorious for producing such change [44]. Textile

mills produce huge amounts of effluent; particularly the textile wet processing industry.

In 2003, industrial wastewater generated in China was about 21.2 billion m3/year, of

which textile industry wastewater amounted to 1.6 billion m3/year [45].

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Table 1.7 Colour indicators in wastewater effluent [18]

Colour Problem Indicated

Grey None

Red Blood or other industrial wastes

Green, yellow Industrial wastes (e.g., paints) not pre-treated

Red or other soil colour Surface runoff into influent; industrial flows

Black Septic conditions or industrial flows

As previously discussed, among the wet processes, dyeing and finishing are responsible

for 80% of the total wastewater generated [46]. Figure 1.6 summarizes the potential

chemicals that can be released during textile wet processing except heat-setting which

doesn’t involve any chemicals during the processing, Figure 1.1.

Little or no wastewater generated

VOCs, BOD from water-soluble packaging waste; sizes e.g. PVA, starch, lint; yarn waste; cleaning lubricants; biocides; etc.

VOCs, scouring solvents, NaOH; detergents, fats; oils; pectin; wax; knitting lubricants; spin finishes; spent solvents

H2O2, sodium silicate or organic stabilizer; AOX or chlorine by product, high pH

High pH; NaOH

VOCs, metals; salt; surfactants; toxics; organic processing assistants; cationic materials; colour; BOD; COD; sulphide; acidity/ alkalinity; spent solvents

VOCs, BOD; COD; suspended solids; toxics; spent solvents

Cotton or cotton blends

Singeing

Desizing (only for woven)

Scouring

Bleaching

Mercerizing (optional)

Dyeing and/or printing

Mechanical and/or Chemical Finish

Finished fabric

100% Synthetic

Scouring

Heat setting

Potential release in wastewaterWater* use

(Lkg-1)

--

3-9

26-43

3-124

232-308

16-22

10-15

Figure 1.6 Potential chemical releases in textile dyeing and finishing, redrawn from [48]

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The types of chemical release depend on the number of processing steps and the

corresponding application process; hence pollution loads can be related to specific

dyeing applications, Table 1.8. A common feature is that modern dyes are highly stable

to external agents such as chemical compounds or light. Therefore, removal of colour

can be difficult, and low concentrations of dyes are visible [47].

Table 1.8 Characteristics of dyeing effluents [47]

Dye Fibre Colour

(ADMI)

BOD

(mgL-1

)

TOC

(mgL-1

)

TSS

(mgL-1

)

TDS

(mgL-1

) pH

Acid Nylon 4000 240 315 14 2028 5.1

Cationic Acrylic 5600 210 255 13 1469 4.5

Direct (copper

treated)

Cotton 525 87 135 41 2763 5.0

Reactive (Batch) Cotton 3890 0 150 32 12500 11.2

Reactive

(Continuous)

Cotton 1390 102 230 9 691 9.1

Sulphur

(Continuous)

Cotton 450 990 400 34 2000 3.7

Vat Cotton 1910 294 265 41 3945 11.8

Disperse (high

temp)

Polyester 1245 198 360 76 1700 4.2

ADMI: American Dye Manufacturers Institute, BOD: Biological Oxygen Demand; COD:

Chemical Oxygen Demand; TOC: Total Oxygen Content; TSS: Total Suspended solid; and

TDS: Total Dissolved Solid

1.2.1 Textile Wastewater in Bangladesh

In Bangladesh, most of the textile effluents go directly to the public sewerage, river,

lands or other surface channels, Figure 1.6. The effect of wastewater is enormous as

freshwater is getting even scarcer, crop production is decreasing, and fish and livestock

are now endangered species.

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Figure 1.7 Discharge of textile wastewater in Bangladesh a) direct discharge to water

flow b) stream of wastewater towards the river [49]

Accordingly the Ministry of Environment and Forestry of Bangladesh has now

produced water standards for the ever growing textile dyeing and finishing industry,

Table 1.9, however, maintaining that standard is far reaching.

Table 1.9 Characteristics of textile wastewater and standard in Bangladesh [50]

Parameters Typical values found Standard

Appearance Colloidal -

pH 8-10 6-9

Colour Intensively coloured -

Suspended solids (ppm) 200 – 300 150*

Heavy Metals (ppm) 10 – 15 Varies depending on

type

Total Dissolved Solids TDS (ppm) 5000 – 6000 2100

Chemical Oxygen Demand COD (ppm) 1500 – 1750 200

Biochemical Oxygen Demand BOD5

20°C (ppm) 500 – 600 50

Oil & Grease (ppm) 40 – 60 10

Sulphide as S (ppm) 50 – 60 1

Wastewater Flow of fabric processing 120-200 Lkg-1

100 Lkg-1

*BOD limit of 150 mgL-1

will be applicable only for physicochemical processing

method

a) b)

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1.2.2 Effluent Treatment Methods [51, 52, 53, 54, 55, 56, 57, 58, 59]

Textile wastewater pollution can be reduced in three ways: (1) by using new and less

polluting technologies; (2) by treating effluent effectively to conform to specified

discharge requirements; and (3) recycling effluent through different processes several

times before discharge [51], and this latter approach is considered the most practical

solution [52, 53]. The quality requirement for recycled water depends on the end use.

Reusing for washing and rinsing would require less-pure freshwater while for dyeing a

fresh quality of water is regarded as essential. Hoehn [54] has further suggested a

chemical specification of recycled water, Table 1.10.

Table 1.10 Suggested quality requirements to achieve colourless water from recycled

textile effluent [54]

Parameter Level

pH Neutral

COD < 20–50 mgL-1

Total hardness < 90 ppm (as CaCO3)

Iron < 0.1 ppm

Chromium < 0.1 ppm

Copper < 0.005 ppm

Aluminium < 0.2 ppm

Inorganic salts < 500 mgL-1

Effluent can be treated in various ways depending on the pollution load and the levels of

treatment required. These levels are known as preliminary, primary, secondary and

tertiary. The mechanism of treatment can be divided into three broad categories:

physical, chemical and biological, under which there are a number of different

processes, Table 1.11. A single treatment plant consists of different level of treatment,

combining two or more as required.

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Table 1.11 Wastewater treatment levels and processes [55, 56]

Treatment

level

Description

Process

Preliminary Removal of large solid, equalisation,

neutralisation

Physical

Primary Removal of floating materials, undissolved

chemicals and particulate matters

Physical and chemical

Secondary Removal of biodegradable organic matter Chemical and

Biological

Tertiary Removal of dissolved solids, ions, suspended

solids

Biological and/or

Membrane

Treatment and source is preferred rather than end of pipe treatment [57] and can reduce

the overall flow and complexity of the effluent [58, 59]. The estimated dye

concentration for end-pipe treatment is 10-800 gL-1

while after dyeing the effluent is

highly concentrated. The most important methods that are widely used for effluent

treatments are listed below and discussed in more details in subsequent sections:

Coagulation, flocculation and precipitation methods;

Oxidation methods;

Adsorption methods;

Biological methods;

Membrane methods.

1.2.2.1 Coagulation, Flocculation and Precipitation [45, 60, 61]

Coagulation and flocculation are widely used in diverse applications, which includes

biochemistry, rubber and cheese manufacturing, and in water and wastewater treatment

[60]. This is the first step, in most cases, in an effluent treatment plant. In the process,

adjustment of pH or treatment with some inorganic or organic chemical causes

precipitation of impurities to form microflocs. Flocculation then aggregates these

microflocs into larger particles. As a result, a large amount of sludge is produced, which

is then removed by flotation, settling or other physical techniques. The subsequent

disposal of the sludge, which may also contain hazardous chemicals, may have some

restrictions on its disposal.

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The common coagulants used are alum, iron salts, lime, and other organic polymers

[61] and typically has almost no effect on the elimination of soluble dye. However,

recent developments in organic polymer and polyelectrolytes have improved colour

removal significantly [45]. The process will be discussed in details in Section 1.10.

1.2.2.2 Oxidation Methods [45, 62, 63, 64]

Oxidation techniques are widely used for treatment of wastewater, particularly for

discolouration, sterilization and for biological treatments [45]. A variety of oxidation

techniques can be used for decolouration of wastewater. The process could be in single

or in combinations such as ozone and UV irradiation or ozone and hydrogen peroxide,

which is widely used for industrial treatment [62]. Other oxidising agents available are

sodium hypochlorite, nitric acid and Fenton’s reagent (a solution of hydrogen peroxide

and an iron catalyst) [63].

Production of less complex and lower amounts of sludge has put oxidation treatments in

favour over other treatments. However the typical levels used can still only produce

partial discolouration of the dye loaded wastewater, does not reduce the Chemical

Oxygen Demand (COD) significantly [64] and the cost of installation is very high [63].

1.2.2.3 Adsorption Methods [65, 66, 67]

The use of adsorbents in water treatment is one of the oldest methods available. Initially

activated carbon was used as an all-purpose adsorbent [65] and used specifically to

absorb dye from solution. Since then, various other adsorbents based on inorganic,

synthetic and bio-adsorbents were introduced [66]. The adsorbents have high surface

areas and depending on the type, can absorb the high levels of dye. Nevertheless,

adsorbents are commonly used in combination with pre-treatments as suspended solids

rapidly clog the filter [67].

1.2.2.4 Biological Treatments [68, 69]

Biological processing uses the natural bacterial metabolism for degrading waste

material. There are two types of bacterial degradation, aerobic (in presence of free

oxygen) and anaerobic (without oxygen, reduction process) [68]. In the aerobic process,

liquid waste is fed into the microorganism system, and air is passed through for multiple

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growth cycles. The anaerobic process is advantageous as the end product are gases like

methane and carbon dioxide, with very little amount of solid waste. Nevertheless, the

process is more difficult to control as the bacteria are distinctly different to the aerobic

types and highly sensitive to oxygen. In addition, the initial investment is very high and

generation of greenhouse gases is potentially problematical. The two most common

biological processes are through activated sludge and biological filtration. Since dyes

are manufactured to achieve better fastness, most of them have low biodegradability,

and as a result, in many cases the activated sludge process is less effective [69].

1.2.2.5 Membrane Processing [70]

Membranes are the most popular method individually and in combination can be used

for "in-process" treatment rather than so called "end-of-pipe" treatment. The choice of

membrane process depends on the quality of the final products and is discussed further

in Section 1.8 . In this study only coagulation/flocculation and membrane separation are

of interest.

1.3 Textile Fibres

The demand for textile products has continued to grow with the per capita consumption

in the world increasing from 3.7 kg to 11.1 kg in 1950 to 2007, Figure 1.8 [71]. The rate

of consumption of textiles increased by 35% between 2000 and 2007 but declined 4.3%

in 2008 which was equivalent to 2.9 million tons. In 2010 demand rose again to a record

of 69.7 million tons, a 7.4% increase. Despite reaching these record levels in 2010, the

per capita consumption was still lower than 2007; a steady decline to 10.5 kg, 10.4 kg in

2008 and 2009, respectively which partially recovered in to 11.0 kg in 2010. The

consumption levels also varied between developed and developing countries: 13% and

20% between 2007 and 2010, respectively [72].

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Figure 1.8 Evolution of world apparel fibre consumption, in million tons [72]

The total volume of natural and manmade fibres that are used in textiles and nonwovens

was over 70 million tonnes in 2009 and the share of natural to man-made fibres was

around 44:56, Figure 1.9. The relative proportion of polyester fibre continues to grow

[73] while natural fibre production is gradually approaching its plateau limit of around

32-35 million tonnes per year [74]. The annual production of cotton and wool is around

25 and 1 million tonnes, respectively, with a share of 36% and 2%, respectively, of the

total production of textile fibres [75, 76]. However it is accepted that the two major

fibre types are cellulosics and polyester and provide a focus for textile recycling.

Figure 1.9 Global share of textile fibre in 2009 [73]

36%

2%

0.4%

45%

5%

3% 4%

5%

0%

Cotton

Wool

Silk

Polyester

Polyamide

Acrylics

Polypropylene

Cellulosics

Others

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1.4 Textile Dyes [45, 77, 78, 79, 80, 81, 82]

Colouration of textiles is perhaps as old as human civilization itself and the colorant is

the key component for imparting colour to textiles and other products. There are two

types of colorants, i.e. dyes and pigments, which differ in their methods of application,

nature, performance and processing [77]. Natural dyes dominated the colouration

industry until the mid-19th

century, when in 1856 Perkin first discovered the process of

chemically synthesizing dye. Subsequently and within 50 years synthetic dyes

accounted for more than 90% of dyes used [45]. In contrast pigments are water

insoluble and mostly used for plastics, paints, printing inks. Pigments are commonly

used in textile printing in combination with a polymer binder or in mass colouration by

melt spinning [45].

The 38,000 new dye products that has been named, but only 8000 of them have a

different structure and of those only 4000 have commercial and technical importance

[78]. The rapid growth of dyestuffs was possible due to the development of new

precursor materials, adding functionality or through improved synthetic manufacturing

routes [79]. The estimated global annual production of dyestuff is 700,000 tonnes [80]

and two thirds of the market is accounted for by the textile industry [81]. Traditionally

synthetic dyes were manufactured from coal tar, but these days are derived from the

petrochemical industries. The raw materials, such as benzene, toluene, xylene,

naphthalene etc., are converted into dye intermediates through chemical reactions such

as oxidation, reduction, halogenation, nitration, sulphonation etc. followed by various

chemical reactions in multi-stage batch processes [82]. Essentially the dye provides the

colour in the visible region, can be applied to a substrate/medium and have some kind

of bonding with the textile substrate.

1.4.1 Characteristics of Dyes [45, 78, 83]

Otto Witt in 1876 first formulated his theory which established the relationship between

colour and the structure of the dye molecule and proposed that the dye chromogen

consisted of a chromophore and auxochrome. Chromophores are the colour bearing

group containing an unsaturated conjugated system, whose presence gives colour to the

molecule. Some of the most widely used chromophores are given in Figure 1.10 and

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Table 1.12 and identify the hues associated with the chromophore.

Nitroso Azo P- quinoide O-quinoide

Figure 1.10 Chemical structures of some chromophores

Table 1.12 Chromophores typically present in colorants [83]

Hue Typical Chromophore

Brilliant yellow Methine; Coumarins, Pyridone

Yellow Nitrodiphenylamine, Heterocyclic, Azo with pyridone couplers

Orange Azo

Red Azo, Anthraquinone, Benzodifuranone

Pink Anthraquinone

Violet Azo, Anthraquinone

Blue Azo, Anthraquinone, Thiophene

Black Azo

Auxochromes are used to intensify colours even though they alone cannot produce

colour. They could be salt producing groups and hence could be acidic (-OH, -COOH, -

SO3H) or alkaline (-NHR, -NH2, -NR2) in nature. Some of these auxochrome groups

such as –SO3H may also help to solubilise dye.

1.4.2 Classification of Dyes [45, 78, 84]

Dyes and pigments were first catalogued by the Society of Dyers and Colourists, (SDC)

and the Colour Index was first published in 1924. The recent edition is jointly published

by the SDC and AATCC. The main classification is done by the chemical structure of

dyes and its application method.

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1.4.2.1 Based on Chemical Constitution [45, 78]

Classification based on chemical structure is particularly of interest to the chemists and

virtually unlimited as new structures are continuously added to the ranges. Some of the

chemical classes are illustrated in Table 1.13 and Figure 1.11

Table 1.13 Chemical classes of dyes [45, 78]

Azo dyes Polymethine dyes Thiazole

Anthraquinone dyes Stilbene dyes Diphenylmethane

Heterocyclic dyes Sulphur dyes Azine

Indigoid dyes Triphenylmethane dyes Vinylsulphone

Nitro dyes Polymethine dyes Chlorotriazinyl

Phthalocyanine dyes Hydroxyketone

Azo Anthraquinoid Azine

Triphenylmethane Stilbene Phthalocyanine

Figure 1.11 Example of chemical structure of dyes

1.4.2.2 Based on Application Method [45, 78]

The dye application methods are quite varied, but in all cases the dye has to be soluble

in water at some point in the dyeing cycle. Water is the universal medium of dyeing and

some of the dyes are readily soluble while some are solubilised through chemical

Ar N N Ar'

O

O

N

N

+H

H

N

N

N

N

N

N

N

NH

H

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modification. The classification based on the method of application is appropriate for

the dyers:

Water Soluble: Acid, Cationic, Reactive, Direct, Solubilised Vats, Optical

brighteners;

Water Insoluble: Vat, Sulphur, Disperse, Mordant;

Ingrain dyes: Azoic dye, Oxidation and Mineral Colours.

The basic characteristics of different dyes and their relations with the substrate are

presented in Table 1.14.

Table 1.14 Dye characteristics, associated fibres and method of application [85]

Class Characteristics Substrates Method of application

Acid Anionic, water

soluble

Nylon, wool, silk Usually from neutral to acidic

dyebaths

Cationic Cationic, water

soluble

PAN, modified

nylon, polyester

Applied from acidic dyebaths

Direct Anionic, water

soluble

Cotton, rayon,

leather, nylon

Applied from neutral or slightly

alkaline baths containing

additional electrolytes

Disperse Low water

solubility

Polyester,

polyamide,

acetate, plastic,

acrylic

Fine aqueous dispersions often

applied by high temperature

pressure or lower temperature

carrier methods

Reactive Anionic, water

soluble

Cotton, wool,

silk, nylon

Reactive site on dye reacts with

functional groups on fibre to bind

dye covalently under the influence

of heat and pH (alkaline)

Sulphur Colloidal,

insoluble

Cotton, rayon Aromatic substrate vatted with

sodium sulphide and re-oxidized

to insoluble sulphur containing

products on fibre

Vat Colloidal,

insoluble

Cotton, rayon Water-insoluble dyes solubilised

by reduction with sodium

hydrosulphite, then exhausted on

fibre and re-oxidized

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1.5 Textile Dyeing [45, 77, 86]

Dyeing is the application and fixing of dye to a substrate, normally with the intention of

obtaining an even distribution throughout the substrate. Dyeing is mostly a

physicochemical process and in some cases a chemical process as well and involves

essentially a transport phenomenon, in which dye molecules leave one medium such as

water, emulsion or solvent and enters the fibre structure. For dyeing, generally four

forms of energy are normally employed: Chemical (through bonding with the fibre),

thermal (high temperature), mechanical (fabric transport in a stationary dyeing bath),

the fluid (for example circulation of dye liquor through a stationary textile material in

package form) [77].

1.5.1 Theory of Dyeing [45, 86]

The dyeing process is essentially a distribution process: the dye is distributed over at

least two phases or phase systems: dyebath or dye solution and the substrate i.e. textile

material. The theory of dyeing is used to explain phenomena such as [86]:

The state of dyes in solution or dispersion in the dyebath and the substrate

during and after dyeing;

Effects occurring at the dye–substrate interface;

Kinetics of diffusion of dye molecules into the substrate matrix;

Thermodynamics of the dye–substrate equilibrium; and

Interactions between dye molecules and fibrous polymer segments.

The entire dyeing process can be divided into a number of stages as shown [45]:

Transfer of dye molecule from dyebath to the fibre surface;

Adsorption of dye molecule on the surface of the fibre;

Diffusion of the dye from the surface to the interior of the fibre;

Interaction of dye molecule with the fibre by ionic, covalent or hydrogen bonds,

or other forces of physical nature.

These successive stages of dyeing are described below:

Transport of dye to the fibre surface: the first step of dyeing is for the dye to come

into contact with the textile substrate. Therefore, dye should be in a soluble molecular

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state in the dyebath. To assist in the process efficiently, the dyebath or material, or both,

are circulated or agitated. In most cases dyeing starts around 400C and dye is dosed into

the machine within a set duration of time. The part of the material that comes contact

with dye first is dyed first and therefore there is always possibility of unlevellness.

Dye adsorption at the fibre surface: fundamentally dyeing starts at the interface of

substrate and aqueous dyebath. Dye in solution reduces surface tension thus trying to

accumulate on the surface of fibre i.e. deposition on the solid surface rather than in the

fibre bulk. This is known as adsorption and is usually studied by plotting dye

concentration in the dyebath, Ds, and corresponding dye concentration in the fibre, Df, at

equilibrium, and is known as an adsorption isotherm. Three different isotherms are

recognised:

The Langmuir isotherm, which is most appropriate for hydrophilic fibres where the dye

interacts strongly with the fibre and can be represented as:

Equation 1.1

The Freundlich isotherm is used for fibres which interact weakly with the dye by

hydrogen bonding or van der Waals’ force and may be written as:

Equation 1.2

The Nernst isotherm is linear and is obtained with disperses dyes on hydrophobic fibres.

This is the simplest equation and can be expressed as . In all cases K is

constant and N is a fraction, usually 0.5.

Diffusion of Dye: Once the dye adsorbed on the fibre surface, dye starts diffusing and

penetrating into the fibre. The diffusion in the fibre is usually slowest step in the entire

dyeing process and depends on the morphological structure of the fibre. Natural fibres

have pores and synthetic fibres that create free space during dyeing show different rates

and paths of diffusion. The rate of diffusion can be expressed by Ficks law, Equation

1.3.

Equation 1.3

Where F is flux, i.e. rate of transfer per unit area of cross section;

is the concentration

gradient in section X; and D is the diffusion coefficient.

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Fixation of Dyes: Fixation of the dye to the fibre is important for end-use fastness

requirements. Dye could be fixed with either physically or chemically with the fibre by

covalent, hydrogen, van der Waals’ force, ionic/salt linkage or through insolubilisation

inside the fibre.

1.5.2 Absorbance [45, 87]

Many compounds absorb visible or ultra-violet light. Therefore absorbance, A can be

defined in terms of light transmittance, T. Transmittance is expressed in Equation 1.4

with a monochromatic beam of power I0 that was directed to the sample with I radiant

power leaving behind.

Equation 1.4

Thus absorbance A can be expressed as Equation 1.5

Equation 1.5

The Beer-Lambert Law, Equation 1.6 states that there is a linear relationship between

absorbance of dye and concentration for very dilute solutions. Typically a calibration

curve of absorbance versus concentration allows the determination of the concentration

of the dye in an unknown solution, provided that the curve is linear irrespective of

composition and temperature of the solution. The calibration study requires preparation

of dye solution of known concentration and measurement of absorption at specified

wavelength.

Equation 1.6

Where is the molar absorptivity with units of Lmol-1

cm-1,

l is the path length of the

sample (cell length), and c is the concentration of the compound in solution, expressed

in molL-1

.

1.5.3 Colour Fastness

For dyers, fastness is probably the second most important parameter after the required

colour. A good dye must withstand the subsequent treatment (e.g. laundering, dry

cleaning, etc.) or environmental wearing (e.g. rubbing, light exposure, etc.). The degree

to which a dyed material can withstand such treatment is called the colour fastness,

which is the most practical importance for the consumer. In many cases, fastness is

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tailor-made during the synthesis of dye. Fastness depends on the complex number of

variables such as [78]:

Molecular structure of the dye;

Manner in which the dye is bound to the fibre, or the physical form present;

Amount of dye present in the fibre;

Chemical nature of the fibre;

Presence of other chemicals in the material;

Actual conditions prevailing during exposure of any agencies.

1.5.4 Degree of Dye Fixation and Dye Loss

The degree of fixation of any individual dye varies according to type of fibre, depth, and

dyeing parameters. It has been estimated that about 450 kilotonnes of synthetic dyes are

manufactured annually worldwide, with around 9 kilotonnes (2%) and 41 kilotonnes

(41%) are wasted during manufacturing and application, respectively [88]. The extent of

dyeloss in exhausted dyebaths and wash liquors are continuously assessed with on

average, losses for deep shades typically 10%, while for medium and pastel dyeing, the

loss is about 2% for all classes of dyes [89]. Table 1.15 shows the losses of dyes in

textile wastewater assessed by different environmental agencies corresponding with the

benchmark fixation with each dye classes.

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Table 1.15 Percentage of unfixed dye that may be discharged in the effluent along with

benchmark fixation

Dyestuffs EPA OECD ATV Bayer (1)

Euratex Spain Benchmark

Fixation %

Acid dyes

- for wool

- for polyamide

10

20

7 - 20

7 - 20

-

5 - 15

5 - 15

90

-

Cationic dyes 1 2 - 3 2 - 3 2 - 0 - 2 97

Direct dyes 30 5 - 20 5 - 30 10 5 - 35 5 - 20 85

Disperse dyes

- for acetate

- for polyester 1 bar

- for polyester HT

25

15

5

8 - 20

8 - 20

5

1 - 15

0 - 10

-

95

-

-

Reactive dyes (2)

- for cotton

- for wool

50 -

60

20 –

50

5 - 50

5 - 50

20 – 45

3 – 10

10 –35

70

Metal complex 10 2 - 5 2 - 5 5 2 - 15 5 - 15 94

Chrome dyes - - 1 - 2 - - 5 - 10 -

Vat dyes 25 5 - 20 5 - 20 - 5 - 30 5 - 30 90

Sulphur dyes 25 30 - 40 30 - 40 - 10 - 40 15 - 40 75

Azoic dyes 25 5 - 10 5 - 10 - 10 - 25 10 - 25 -

Source: US-EPA [16], Euratex [90], Spain [91],

EPA: US Environmental Protection Agency

OECD: Organisation for Economic Co-operation and Development

ATV: Abwasser Technishe Vereinigung (Wastewater Technical Association of

Germany)

Notes: (1)

Now Dystar (including BASF) (2)

High Fixation reactive dye is available

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1.6 Introduction to Filtration [66, 70, 92, 93, 94]

Public and government concerns over the environment are creating pressure for a

reduction in energy consumption and increased fresh water provision, and filtration has

a vital role to play in delivering sustainable technologies [92]. Filters are traditionally

used in the automotive, construction, agriculture, industrial, pharmaceuticals, food,

medical, and water and beverage industries and are now impacting in biotechnology and

medicine [70].

Filtration is considered to be the separation of distinct or mixed phases [66, 70, 92, 93,

94]. The phases include solid from solid, solid from liquid, liquid from liquid, and

liquid from gas or gas from liquid. In addition some advanced membrane processes

work with molecular diffusion instead of separation of phases but still is popularly

considered as filtration. Filtration and separation achieve two crucial purposes, firstly,

to remove impurities from the mixtures as pre-determined by legal limits, and, secondly,

to recover valuable materials that can be reused or recycled, which is an important

theme for waste management.

Solid/liquid filtration is the most common due to the industrial pollution of water,

however, solid/gas filtration is also increasing due to the rapid pollution of air through

machines, automobiles or boilers exhaust gases [70]. The types of contaminant and their

concentrations in the filtration environment decide the success and failure of filtration.

1.6.1 Filtration Process [70, 92, 93]

Filtration can occur through four mechanisms, depending on the size of the solid

particle and how the solid particle is trapped in the filter media [70, 92, 93]. These are

surface straining, depth screening, depth filtration and cake filtration [70]. However,

any filtration process can occur by a combination of two or more mechanisms

depending on the circumstances present.

Filtration entirely depends on the particle size and to some extent the shape of the

particles. However, mean particle size and particle size distribution play major influence

on the filtration efficiency. Size of the particles that are filtered by the media is used to

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describe various terms in the filtration process. Coarse filtration is used for separating

particles over 2 mm while fine filtration covers from 15 to 75µm, Table 1.14.

Table 1.16 Particle size range for various filtration technologies

Type Approximate size range (µm, microns)

Screening or sieving >2000

Coarse filtration 75-2000

Fine filtration 15-75

Microfiltration 0.1-15

Ultrafiltration (UF) 0.005-0.1

Nanofiltration (NF) 0.001-0.005

Reverse Osmosis (RO) 0.0001-0.0010

In any filtration process, the filter is placed along the liquid flow, which works as a

barrier to this flow. However, NF and RO operate on a different principle, with no

physical holes to trap the particulates instead one or more molecular species diffuse

through the membrane itself under high pressure. It should be noted that in this case the

solution should have no or very little suspended matter.

1.6.2 Process Fundamentals

1.6.2.1 Filter Permeability [70, 94]

Permeability refers to flow of a fluid and is reciprocal to the resistance of flow through

the filter media. High permeability means a low resistance by the filter media and vice

versa. Permeability of any medium in filtration depends on filter size, fluid temperature,

and filtration time. The higher the size i.e. the filter area and temperature, the higher

permeability of a fluid but a prolonged filtration time would reduce the permeability.

Again, it also depends on the thickness of the media, as the thicker the media, the higher

the pressure drop and in the case of asymmetric membranes, the pressure drop will vary

across the density of the media [70].

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1.6.2.2 Flux

Flux is defined as the flow of fluid passing through a unit area of membrane per unit

time and is expressed in m3 per day or m/sec or Lm

-2h

-1. The flux of permeate depends

on the following factors [70]:

The membrane resistance;

Driving force per unit membrane area;

Hydrodynamic conditions at the membrane-liquid interface;

Fouling and subsequent cleaning of the membrane surface.

The general flux for membrane operation is between 10 to 1000 Lm-2

h-1

and directly

relates to the driving force and total resistance offered by the membrane.

1.6.2.3 Pressure Drop [70]

This is the measure of differential pressure between the upstream and downstream side

of the filter media and the pressure drop is inversely proportional to the filter area.

1.6.3 Filtration Mechanism

Since filtration operates by capturing particles of all sizes, there are a number of

theories to explain its action through four mechanisms: inertial impaction, interception,

diffusion or electrostatic attractions [70, 92, 95]. In many cases, multiple mechanisms

work in a single filtration process, Figure 1.12. These four mechanisms are discussed as

follows:

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Figure 1.12 Particle collection mechanisms [93]

Inertial Impaction: Fluids or gases always follow the direction that is easily

accessible, however some particles, specifically larger ones or particles moving fast

have a high inertia to follow the path. Hence the particles are breaking away from the

streamlines, collide with the filter fibres and are trapped;

Direct Interception: when the streamlines bend to get around the filter fibre,

some particles with a distance less than half of its diameter from the fibre surface

become trapped on the fibre. This mechanism known as direct interception, and by

definition, it should occur on the side of the fibre and not trapped directly in front of it;

Diffusion behaviour is known as Brownian motion, where the particles,

especially the finer ones (> 0.5µm) become directly trapped across the media while

following the streamlines;

Electrostatic Attraction: when the particle and/or fibre are charged electrically

or electrostatically, and this charge is used to force the particle from streamline to the

fibre.

The dominant mechanism depends on the size of the particles. Very small particles

follow Brownian motion while large particles with more momentum are captured

through inertia. There are two distinctive mechanisms in filtration, i.e. conventional and

cross-flow filtration.

Particles

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1.6.3.1 Conventional Filtration [70]

In conventional filtration fluid flows vertically through the filter media, so that all the

liquid passes through the medium and the solids are either held on the surface or trapped

inside the medium, Figure 1.13a, to form a cake. This is also called through-flow or

dead-end filtration, and in this process a heavy pressure is created over the filter

medium and separates most or all of the suspended solids. The build-up of particles

increased the thickness of the cake as the filtration proceeds [96].

Figure 1.13 Conventional cake filtration, a) typical process [96] b) flow over time

In this research cake filtration is relevant due to the use of filter media. Filtration starts

at the surface of the medium and particles deposit on the surface. After subsequent

layers of deposition, it forms a cake which itself then acts as filter medium. Particles

larger than the pore size are trapped in the surface as with surface straining until those

particles form a cake. In case of smaller particles, they can also be trapped by bridging

together at the entrance of the pore, which acts as a base to build cake particularly if the

solid concentration is higher (>2% by weight in a liquid).

The primary operating variable for cake filtration is the pressure applied. The filtration

process could be carried out under constant pressure, variable pressure i.e. P0, the

applied pressure, is a specified function of time or under constant rate [96]. The most

important factor in cake filtration is the permeate flow or the resistance of the filter cake

[97].

b) a)

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a. Theory of cake filtration through porous media [96, 97, 98, 99]

The model of cake formation has been derived from Darcy’s Law (1856) which was

originally developed to describe flow of water through porous sand beds. It was found

that the flow rate is proportional to the pressure gradient and therefore Equation 1.7 was

developed to show the relationship for steady laminar flow through homogeneous

porous media:

Equation 1.7

Where is the is the dynamic (hydraulic) pressure difference across thickness dx of

porous medium of permeability k (m2), q is the superficial velocity of liquid (volume

flow rate per unit cross-sectional area of the medium, m3 m

-2 s

-1) and µ is the liquid

viscosity which was not included in Darcy's original equation.

In filtration, the law is used in modified form, where permeability, k, was replaced by

local specific flow resistance α, and the pressure gradient,

, was replaced by pressure

loss per unit mass of solid deposited,

, on the medium:

Equation 1.8

Where w is the mass of dry cake per unit filter area deposited within the distance x from

the filter medium. The mass dw and dx are related by:

( ) Equation 1.9

Where ε is cake porosity. From Equation 1.8 and 1.9, we get:

( )

Equation 1.10

The relationship between k and α is:

( ) Equation 1.11

The cake porosity and permeability are the two key factors in cake filtration. The cake

porosity, ε, is the fraction of a porous medium available for fluid flow while the cake

permeability, k, is a measure of the ease of flow of fluid through the voids. The extent

of the permeability is thus determined by the perceived openness of the filter medium.

The complex geometry of the pores present in the internal structure of the filter media is

almost impossible to describe mathematically, therefore a simplistic model of Kozeny

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(1927) and Carman (1938) has been used. Equation 1.12 is known as the Kozeny-

Carman equation.

( )

Equation 1.12

Where is the Kozeny constant, is the specific surface of the particles is the

pressure gradient and L is the length of straight circular capillary. Since -

is the same

as

from Darcy’s law so it can be written as:

( )

Equation 1.13

In cake filtration processes, the two conditions prevail during liquid flow. Initially the

applied pressure, , is available across the filter medium. The permeation across the

medium can be expressed as:

Equation 1.14

Where is the flow resistance of the medium and pressure drop across filter

medium. As the time goes, cake deposited on the medium and decreases pressure drop

which builds resistance towards the flow. In this case, Equation 1.14 can be written as

( )

( ) Equation 1.15

Where is the flow resistance of the cake and pressure drop across cake. Equation

1.15 is the most commonly used model for cake filtration for incompressible cakes. It

states that filtration rate is directly proportional to the applied pressure and inversely

proportional to the flow of the resistance due to cake and medium.

The performance of cake filtration can be expressed with volume of filtrations collected,

and the solid particles recovered per unit medium surface area, V, over time, t. The

filtrate rate thus simply is

Equation 1.16

Combining Equation 1.15 and 1.16, the new model is

( )

Equation 1.17

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The Equation 1.17can be re-written in the form of Equation 1.18 since, may assumed

to be directly proportional to the amount of cake deposited over time, therefore average

cake resistance was more significant

( )

Equation 1.18

Here V is the filtrate volume and c is the mass of solids, which can be expressed through

Equation 1.19

Equation 1.19

Where is the filtrate density, m is the moisture or liquor content defined by Equation

1.20 and s is the mass fractions of solid in the feed slurry as given in Equation 1.21.

Equation 1.20

Equation 1.21

1.6.3.2 Cross-flow Filtration

In this mode, fluid flows parallel to medium, and some of the fluid passes through the

medium due to the pressure difference between the two sides of the media, Figure 1.11b

[100]. Cross-flow filtration can be used for both sub-millimetre and sub-micron ranges

and for the former during filtration a filter cake will develop [101]. The maximum

amount of contaminants flows on and out of the filter, thus a minimum amount is

retained by the medium, which increases its service life. This filtration usually employs

surface filtration, as passing contaminants across the medium would be damaging and

would reduce the service life. To keep the filter medium free of deposits, a high velocity

can be applied across the medium, or alternatively some sort of rotation or movement of

the media would be employed. A great number of parameters influence cross-flow

filtration such as membrane pressure, layer resistance, cross-flow velocity, particle size,

form, distribution and agglomeration behaviour, surface effects of the particles etc.

[102].

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Figure 1.14 Cross-flow filtration, a) typical process [96]; b) flow over time

The cross-flow filtration in some ways solves fouling, the critical problem of any filter

media [103] and thus maintains almost similar permeability throughout its lifetime.

This mechanism is now increasingly used in food, water purification, beverage, and

biotechnology industry [104].

1.7 Filter Media [92, 93, 105, 106, 107]

A filter is a device that is used to separate one substance from another and is placed in

the path of the fluid/gas flow to block/trap/isolate the target material or contaminants.

The Filtration Dictionary and Glossary defines a filter medium as:

“Any permeable material used in filtration and upon which, or within which,

the solids are deposited.”

However this definition is old and assumes the solid as the main contaminant. This

definition does not cover the array of filtration and separations that occurs currently.

Therefore a new definition has been developed:

“A filter medium is any material that, under the operating conditions of the

filter, is permeable to one or more components of a mixture, solution or

suspension, and is impermeable to the remaining components” [92].

The components that are retained are known as the concentrate/retentate and may be

solid particles, liquid droplets, colloidal material or ionic species in solution and

components that pass through are known as the permeate or filtrate, and often are fluid

or gas. The filter medium is the critical component of the filtration process from

economic and performance standpoint [105]. A variety of filter media are used for

a) b)

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different application, and a range of technologies and materials are employed to meet

the ever growing demand. Figure 1.15 summarizes the classification of filter media

based on structure of filters.

Figure 1.15 Classification based on the structure of filters [106]

The mechanistic action of the filter media could be as an absorbent (i.e. sponge like

absorption of fluid e.g. paper), adsorbent (i.e. attraction at molecular level e.g.

powdered carbon) or coalescing (i.e. two immiscible liquid i.e. oil mists in water) [92].

The type of materials that can be used for filters is wide, ranging from organic (natural

and synthetic) to inorganic such as minerals, carbon, glass, metals and ceramics. These

materials can be used in all different types of format, ranging from loose, bonded or

needled felts to woven/knitted fabric to nonwovens. Woven or nonwoven textiles are

extensively used for filtration application and can be from natural sources such as

cotton or wool or from synthetic polymers such as polyester, polypropylene, PTFE or

other fine fibres such as carbon, glass, metals and ceramics [93].

The characteristics of filter medium made of textile material, therefore, inherently

depend on the type of fibre material and its associated properties. The most notable

factor is the size of the fibre/filament. Filter media made of finer fibres would retain

finer particles, but would also be the weakest. Therefore fibre choice would influence

some properties such as degree of filtration required (cut-off point and the efficiency),

pressure drop (energy consumption in the process) and mechanical strength [70]. In

addition the primary factors that influence the selection or design of the filter media

depend on [107]:

Thermal and chemical conditions;

nonwoven filter media

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Filtration requirements;

Equipment considerations;

Cost.

Since both woven and nonwovens play an important role in filter media, they are

discussed further.

1.7.1 Woven fabric [70, 92, 93]

Most filter media are made of woven fabrics components. They are characterized as

being relatively less stiff compared to paper and may need some support to be used as a

filter medium. Properties of woven fabric would depend on the fibre and the nature of

yarn: spun or continuous filament. The woven fabrics may be made of monofilament or

multifilament yarn or twisted staple yarn. Fabrics made of natural fibres are usually

thicker than corresponding media based on synthetic materials. With monofilament

media, filtration occurs in spaces between the yarns while in the case of multifilament

and staple yarns filtration also occurs in the spaces within the yarn. The physical and

chemical properties of yarn can be tailored to suit specific filtration application.

In addition to the material and types of yarn, the almost unlimited variety of woven

fabric can be used for woven fabric. In basic terms these are three types of weave: plain,

twill and satin, with associated derivatives. Of the three, plain weaves produce the

tightest fabrics, have the highest filtration efficiency and rigidity [107] while satins are

very flexible with lowest efficiency of filtration. Twill fabrics fall in between these two

extremes and are easier to fit into a filter, Table 1.3.

Table 1.17 Effect of Weave pattern on fabric performancea [94]

Maximum

filtrate

clarity

Minimum

resistance to

flow

Minimum

moisture in

cake

Easiest cake

discharge

Maximum

fabric life

Least

tendency to

blind

Plain Satin Satin Satin Twill Satin

Twill Twill Twill Twill Plain Twill

Satin Plain Plain Plain Plain Plain

ain decreasing order performance

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1.7.2 Nonwoven [70, 92, 93]

Nonwoven media dominate the filtration sector, and with the filtration industry

continuously looking for finer filtration, of both liquid and gases, nonwoven fabrics

made of fine spun or filament material are capable of meeting those requirements.

The definition of a nonwoven is contentious and in most cases is due to their distinction

from paper. ISO and Nonwoven Fabrics Handbook (INDA) define nonwoven as:

‘A sheet, web or batt of natural and/or manmade fibres or filaments, excluding

papers, that have not been converted into yarns, and that are bonded to each

other by any of several means.’

This definition also includes more than 50% by mass of fibres with a length to diameter

ratio greater than 300 (ISO) or more than 30% by mass of fibres with a length to

diameter ratio more than 600 (INDA) to distinguish nonwoven from paper. A nonwoven

fabric, therefore, is essentially made of an agglomeration of fibres and filaments with

bonding. The chemical property of the material along with the bonding chemicals (if

applied) directly influences the properties of the filter media.

However there is still confusion in defining nonwoven materials which can be used for

filtration. Therefore Hutten [93] combines all of them with the following definition:

‘A nonwoven filter medium is a porous fabric composed of a random array of

fibres or filaments and whose specific function is to filter and/or separate phases

and components of a fluid being transported through the medium or to support

the medium that does the separation.’

The media may contain additional components which are used for during formation

such as ‘particulate fillers (clays, calcium, adsorptive powders, etc.), sizing agents, wet

strength agents, antimicrobial additives, plasticizers, dyes and pigments, softening

agents, and wetting agents etc.

Nonwovens are classified by the process of formation: dry formed and wet laid. The

same material would show different types of properties because the different types of

formation. The dry formed processes uses air as a medium whereas the wet laid process

uses water similar to paper manufacturing for formation of web. There are five major

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dry formed processes: air laid, dry laid (carding operations), spunbonded, melt-blown

and electrospun.

1.7.2.1 Composite Structures

A composite structure is a layered medium, in which every layer has its specific

characteristics or purpose. The layers could be a fibrous nonwoven, or a woven material

or plastic or metal mesh material for structural support. The nonwoven layers could be

needle punched, needle felt or electrospun. Some of the functions of composite

structures are:

One or more layer provides mechanical support to the whole media;

Different layers have different gradient density, usually from lighter to denser to

assist in depth filtration;

One layer may act as pre-filter media; while following layers provide higher

filtration efficiency as they remove smaller and finer particles;

Different separation technology can be employed in different layers, for

example, one layer could be sand or activated carbon combined with one or

more nonwoven layer;

The outer layer protects the medium from outside intervention of dust or

movement of layers in between.

The composite structures can be bonded in numerous ways: laminating, needle

punching or hydroentanglement, wet laying or using different techniques such as

spunbond/melt-blown/spunbond or during collection for forming the other layers.

1.7.3 Woven Wire and Screen

The greatest amount of filter media is made from metal in the form either woven

wire/mesh or perforated sheets. These filter media are stronger, have high resistance to

corrosion and abrasion like the original metal and can be made exactly as per

specification required for filter media.

These types of filters have two major applications: separating the solid particles and

pre-screening of gas or liquid before the finer filtration. Woven wire is made of nickel

chrome stainless steel, copper, and aluminium alloys etc, whereas screen or mesh is

made of different types of weaves, most commonly, Dutch or Hollander weaves.

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1.8 Membranes [70, 108, 109, 110, 111, 112, 113]

Membranes are now used an alternative to conventional separation methods and the

fastest growing market for filter media [108, 109]. As a filtration media, the membrane

is based on thin, porous or nonporous, flexible or rigid, semi-permeable sheets of

different polymers that separate two phases and/or act as passive or active barrier at the

molecular and ionic level (0.1 µm or below). Membranes were first used for purification

of salt from water by reverse osmosis (which is not truly a filtration process) and now

extended to microfiltration, ultrafiltration and nanofiltration [70]. They can be used for

separating liquids from liquids, solids from liquids, gases from liquids and gases from

gases [70, 110]. The specific capability of separating micro-level particles makes

membrane technology very popular in the filtration sector. Membranes can be called

porous if the separation of particles is in the region of 0.005-1 µm. When pores are on

the size of 0.001-0.005 µm, then the membrane is microporous while any separation of

particles below 0.005 µm or in the nanometre range is not a true pore but rather the

spaces in between the molecules of the membrane material that are “open” during

operation. The latter, is a diffusion process and, hence, such a membrane is deemed

non-porous or semi-permeable.

The basic criteria of membranes for use in filtration and separation application are [70]:

Chemically resistant to feed and cleaning fluids;

Mechanically and thermally stable;

High throughput/permeability;

Better cake release;

High selectivity to desired permeate constituent;

Low energy requirement;

Stable in operation for prolonged periods;

Strong enough to be resistant to the trans-membrane pressure;

Low cost per unit membrane area.

Membranes can be distinguished based on their: i) geometry; ii) separation regime; iii)

bulk structure; iv) production method; v) and application [111]. Membranes can be

constructed either symmetrically or asymmetrically. Symmetric membranes have the

same physical and chemical structure throughout their thickness in the direction of

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filtration while asymmetric or anisotropic membranes have different density gradients

along the thickness. This density gradient can be different in some materials, or in many

cases, due to the use of different material, which are highly selective and can be used for

structural support.

Membranes hold great promise [112] for recycling water, but membranes can also be

used to recover chemicals that can be reused in the process. Membrane technology

operates at ambient temperature, and in general requires less energy to operate

compared to other processes. Table 1.18 shows briefly the factors that influence the

membrane separation process. The choice of membrane process depends on the quality

of the final products.

Table 1.18 Membrane separation process and influencing factors [113]

Process Usual purpose

Influencing Factors

Size Diffusivity Ionic

charge

Solubility

Microfiltration

(MF)

Removal of suspended

solids, including

microorganisms

+ +

+

- - -

Ultrafiltration

(UF)

Removal of both large,

dissolved solute molecules

and suspended colloidal

particles

+ +

+

- + -

Nanofiltration

(NF)

Selective removal of

multivalent ions and certain

charged or polar molecules

+ +

+

+ + -

Reverse

osmosis (RO)

Removal of inorganic/

monovalent ions

+ + + + + + + +

Electrodialysis

(ED)

Selective extraction from

water and/or concentration

+ + + + + -

‘+’ represents positive influence, more the ‘+’ sign, greater the influence

‘-’ represents negative influence

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1.8.1 Membrane separation types

Five different types of membrane process are available for liquid application,

microfiltration, ultrafiltration, nanofiltration, reverse osmosis and electrodialysis [113].

They are usually classified according to the pore size or size of the particles that they

can retain. They are suitable for specific applications but have recognised limitations.

1.8.1.1 Microfiltration (MF) [45]

Microfiltration can filter particles in the range of 0.1µm and above and let the liquid

flow through relatively quickly. It is suitable for treating pigment dyebaths [114] and

suspensions containing detergents and dispersing agents [45]. The auxiliary chemicals

are retained in the permeate [115]. As a final single end treatment, it is not satisfactory,

so it is used as a pre-treatment for other membrane process like nanofiltration or reverse

osmosis [116].

1.8.1.2 Ultrafiltration (UF) [45, 70]

Ultrafiltration (UF) is effective for elimination of macromolecules and particles, but

removal of dye is incomplete, between 31% and 76% [117]. As a single step treatment

for secondary wastewater, the recycled water can be reused in secondary processes like

washing and rinsing [118] in which salinity is not a problem [56]. This is a pressure

driven process and can remove particle size of over 0.01µm. They are used to filter

colloids and polymers with molecular weights ranging from 1,000 to 5,000,000. This is

useful for multi-stage treatment processes, such as a pre-treatment for reverse osmosis

[119] or in combination with a membrane bioreactor [120, 121, 122]. The UF

membranes are typically composed of polyvinylidene chloride, polyethersulphone,

polysulphone, polyacrylonitrile, cellulose acetate and regenerated cellulose or inorganic

materials such as alumina, zirconia and titania [123].

1.8.1.3 Nanofiltration (NF) [70, 124]

Nanofiltration can retain smaller sizes of molecule than UF and MF and separates low

molecular weight organic compounds, divalent salts of Ca2+

, Mg2+

, large monovalent

ions, hydrolyzed reactive dyes and auxiliaries with an appropriate softening effect. Most

studies suggest that NF treatment of dyehouse effluents should not have more than 20

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gL-1

mineral salts and 1.5 gL-1

of dyestuffs [125]. Chakraborty, Purkait et al. [126]

have reported in their study that NF can retain over 90% of dye effluent and the pressure

and driving forces are much lower compared to RO. However, Van der Bruggen,

Cornelis et al. [127] found that the NF treatment process is negatively influenced by

membrane fouling assumed to be due to adsorption of organic compound. A

combination of the methods are suggested for treatment of effluent, and it was found

that for a combination UF/NF system, colour, TDS, bivalent ions can be retained at

95%, 80%, 95%, respectively [128]. In another study, after coagulation/flocculation

treatment, NF showed better flux then RO [129].

1.8.1.4 Reverse osmosis (RO) [45, 70]

Reverse osmosis system is based on molecular diffusion, where effluent is forced under

pressure to cross a semi-permeable membrane to produce a pure permeate and

concentrate. RO has a retention rate of over 90% for most ionic compounds [116] and

monovalent salts, such as NaCl, can be recovered to an efficiency of 30-98% [45] and

larger species from dyebath effluents. A single step RO can decolorize and remove

chemical auxiliaries in textile effluent. However, the high concentration of salt in

effluent increases the osmotic pressure, hence higher processing pressures are required

to separate mixtures [52].

1.8.1.5 Electrodialysis (ED) [45]

A charged membrane that operates as an electrochemical separation technique and as a

result can separate ionic species from water and other uncharged species.

1.8.2 Membrane Fouling [124, 127, 130, 131]

Membranes work by creating barriers for particles based on porosity. Accordingly there

is a tendency for blockage of pores by fine particles. The blockage mainly occurs at the

surface, but with increased thickness, depth filtration may cause blockage of pore inside

the material, which is known as membrane fouling. Fouling lowers the flux of permeate,

reduces the serviceability of membrane and increases maintenance or chemical costs

[124]. Membrane fouling is classified as reversible or irreversible and could be

responsible for up to 18% and 26-46% reduction of permeate flux, respectively [127].

The mechanism of reversible fouling is based on gel layer formation, concentration

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polarisation and osmotic pressure [124], Figure 1.16. While the expected causes for

irreversible fouling are adsorption, cake layer formation and pore blocking [130]. The

blocking of pores can further be characterized by standard, intermediate and complete

pore blocking, [131], Figure 1.16.

Figure 1.16 Mechanisms of membrane fouling, a) concentration polarisation; b)

adsorption; c) gel layer formation d) complete blocking; e) standard blocking; f)

intermediate blocking [132]

The main fouling categories are inorganic, organic, biological and particulate fouling

[124]. The fouling in itself is an extremely complex process. Adsorption takes place

with dissolved organic compounds while the dominant mechanism for dissolved

inorganics is precipitation. Colloidal fouling takes place through cake layer formation or

blocking of pores while biological fouling is due to the growth and attachment of

biolayers on the membrane surface [133]. The membrane fouling depends on three main

factors [134]:

Properties of the membrane;

Properties of the suspension;

Properties of the process (hydrodynamics).

Fouling layers need to be cleared periodically by cleaning, however, that also reduces

the efficiency of media and encourages approaches to cleaning and avoiding the

formation of a fouling layer.

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1.8.2.1 Membrane Fouling due to Dyes

Dye molecules can be found in colloidal solutions of disperse, sulphur and vat dyes or

in dissolved forms of acid, cationic, direct, and reactive dyes [60]. The chromophore

and auxochrome in the dye molecule are recognised as the main sources of the foulants

[135]. These chemical groups interact with the functional groups, such as amino, amide,

carboxyl in the membrane. The interaction could be strong as dyes are designed to be

fast to fibres and similarly fouled membrane could be difficult to clean [127].

Depending on the types of dye, dye/membrane interactions could be based on ionic,

covalent bond, hydrophobic, hydrogen bond and/or van der Waals forces. Adsorption of

dyes on membrane will cause irreversible fouling depending on the size of the dye

molecule (or aggregates) or the size of the membrane pore [124]:

With dye molecules < pore size of 0.5-2nm, pore penetration and/or blocking is

possible, and adsorption of dye molecules takes place on the surface, in the

pores, and the back of the membrane;

With dye molecules > pore size of 0.5-2nm pore blocking is possible and

adsorption of dye molecules occurs on the surface only.

1.8.3 Cost of Membrane System for Wastewater Treatment

The economic feasibility of the implementation of membrane technology has been

evaluated extensively. Ciardelli, Corsi et al. [119] carried out a study in Italy, where it

was found that about £0.85/m3 would be a reasonable cost to implement membrane

technique for treating dyehouse wastewater, leading to reuse of the water. In addition

Ranganathan, Karunagaran et al. [136] reported that the total cost of water treatment

and recovery of effluent in Tamilnadu, India, including commissioning and

maintenance of a RO/NF system, was about £1.12/m3. Similarly in a study in Istanbul,

Turkey, it was reported that in the current market conditions, the membrane recovery

system for treatment of textile effluent would cost around £0.35/m3 [137]. In a similar

study in the UAE it was shown that desalting of wastewater would cost around £0.29/m3

whereas it costs around £0.65/m3

for 35% recovery of desalination of seawater [138].

Lockerbie and Skelly [23] compared the effluent treatment cost in the UK, Table 1.19 ,

and membrane processes produced acceptable quality of water but was found to be

expensive compared to others.

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Table 1.19 Comparison of effluent treatment in the UK [23]

Reuse of dyebaths has been a key research target for more than sixty years and many

pilot studies and laboratory experiment have been carried out. Volooj [44] and others

[139] extensively studied recycling of textile effluent with Primapor filter media and

concluded that bleach and dyebath could be reused following dyeing. The area will be

discussed more in Chapter 10. In another study, it was found that recycling of water

substantially saved on chemical costs [140]. Numerous studies also concluded that a

membrane system alone was not sufficient to recycle water in a cost effective way and

therefore, various combinations have been studied [85].

1.9 Surface Modification of Filter Media [44, 141, 142, 143,

144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154]

The filtration of filter media depends on the specific capability of separating micro-level

particles, high throughput, efficient cake release, chemically resistant to feed and

cleaning liquids, mechanical and thermal stability and low energy requirements [70].

The performance of filter media for filtration can be improved by employing two

distinct strategies. Firstly, by chemical modification of the polymer [142] and a phase

inversion method to prepare polymeric membranes [143]. The improvements can be

Parameter Membrane Adsorption

Chemical

oxidation/

electrochemical

Biological Coagulation/

flocculation

Water quality Excellent Moderate/

good Moderate/ good Poor/moderate Poor/

moderate

Footprint Small Small Small Moderate/large Small/large

Characteristics Fouling,

cake

release

More space AOX Less sludge Large sludge

Capital costs High Moderate/

high Moderate Moderate Moderate

Operating

costs High Moderate/

high High Low Moderate

Civil costs Low Low Low High Low/high

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achieved by modifying the polymer through halogenation [144, 145, 146, 147, 148],

carboxylation [149], sulphonation [150, 151] etc. The other approach is a post-media

process where finished media is modified, especially on the surface to improve the

overall performances by imparting certain properties [152]. These properties include

increasing flux and selectivity and chemical resistance (e.g. solvent resistance, swelling

etc.). Selective chemical modification of the membrane surface by halogen gas or

plasma treatment can improve the blinding/fouling resistance of media and membranes

along with change in flux [153]. Chemical stability, oil repellency or selectivity of

membranes for reverse osmosis, electrodialysis, evaporation and gas separation

applications can be improved by cross-linking of polymers [154].

1.9.1 Fluorination [155, 156, 157, 158, 159, 160, 161, 162, 163]

Direct gaseous fluorination is a popular method for surface modification of polymers

[155, 156, 157, 158]. This is a dry gaseous technology that is applied for thin surface

modification, with treatment thickness ranges of 0.01-10µm in the media. Direct

fluorination is a heterogeneous reaction where the highly electronegative fluorine

molecule modifies the polymer surface [159], Scheme 1.1. Usually fluorine is diluted

by nitrogen, helium, or argon in order to prevent excessive uncontrolled damage on the

polymer surface [160, 161]. Surface fluorination involves absorption and diffusion

of the F2 into the polymer, R, and subsequent chemical reactions [152].

RH+ F2 R· +HF +F

·

R· + F2 RF + F

·

Scheme 1.1 Fluorination Process [163]

The main advantage of gaseous fluorine is that it can modify any material shape due to

its gaseous nature and high diffusion characteristics. During fluorination most of the H

atoms are substituted by F atoms and double and saturated bonds are fluorinated with

the formation of C-F bonds, followed by CF2, CF3 bond formation in a strong

exothermic process [159]. Destruction of C-C and C-Si bonds with cross-linking

(formation of C-C bonds) may occur [162, 163]. The degree of modification depends on

concentration of fluorine, duration and temperature of treatment.

Surface fluorination differs from other surface modification techniques in that this dry

modification is long lived and has no reported lifetime limits [159]. The change is stable

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due to high penetration depth during the reaction and incorporation of fluorine in the

polymer backbone. The rotational motions of chain segment are prevented below the

softening temperature, which would otherwise invert the chain and thus adversely

affecting the repellency effect [161].

Direct fluorination is used, in many cases, to increase the application properties of

polymeric materials. Fluorinated polymers have shown a set of unique properties, such

as good barrier properties, improved chemical stability, thermostability etc. [161].

1.9.1.1 Barrier Properties [157, 161, 164, 165, 166, 167, 168, 169].

This is the most commercially significant application at present. Direct fluorination

creates a barrier for permeation of hydrocarbons especially in automotive polymer fuel

tanks and vessels for volatile liquids and storage of toxic materials [157, 161, 164, 165,

166, 167, 168, 169].

1.9.1.2 Membrane Technology [160, 161, 165, 167, 168, 170]

Polymeric membranes are very effective material for filtration of gas mixtures such as

He/CH4, H2/ CH4, H2/CO2, CO2/ CH4, H2/ N2, O2/ N2, CO2/ H2S, CH4/CO2/ H2/He, etc.

[167]. However, highly permeable membranes often have low separation factors, and

vice versa. Direct fluorination can be used to increase separation factor without

reducing permeability significantly [161, 165, 167, 168]. In the same way, fluorine as a

highly electronegative material, imparts hydrophilicity to a surface, therefore, increases

the permeability considerably [160, 170].

1.9.1.3 Chemical Resistance [166, 168]

Direct fluorination improves physical and chemical properties of polymeric materials.

Crosslinking during the treatment process increases resistance to chemical such as

aggressive reagents and physico-mechanical resistance such as swelling to materials

[166, 168].

1.9.1.4 Adhesion and Printability Properties [159, 164, 166, 167]

One of the main disadvantages of polyolefins and some other polymers is that they have

low adhesion properties due to their lower surface energy and low polarity of the

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surface. Direct fluorination can modify those characteristics such as wettability,

hydrophobicity by imparting polar component on the surface [165, 166, 168].

Kharitonov and others [159, 164, 166, 167] also listed the possible commercial

application of gaseous fluorination, namely, the increased of adhesion of polymer fibres

and fabric to rubber, enhancement of dyeability of polymer goods, reinforcement of

polymer composites increased resistance to delamination in coated flexible films [164].

1.9.1.5 Frictional Coefficient [161, 166, 168, 171]

Direct fluorination can improve the wear life of polypropylene (PP) and elastomeric

materials made of co-polymer by reducing the static and dynamic friction coefficient

[168]. The modification takes place without degradation of the bulk tensile strength of

materials [166, 168, 171]. The fluorinated surface may act as a protective coating and

become more stable to aggressive liquids and gases [161].

1.9.1.6 Anti-reflecting Coating and Reduction of UV radiation [159, 165]

A layer of anti-reflecting properties can be imparted on the surface by direct

fluorination [165]. In the same way, a protective coating can be imparted which

decreases the transparency of UV light through polymer materials [159].

1.9.2 Fluorocarbon (FC) Finishes [172, 173, 174, 175, 176, 177]

Textile surfaces can be modified both physical/mechanical and chemical textile finishes.

The chemical finishing includes different functional finishes to the fibres such as oil-

and water-repellent, softening, antimicrobial, antistatic, flame-retardant, easy-care and

soil-release agents [172, 173, 174, 175, 176]. The modification of the surface is due to

change of the surface free energy, and therefore, depends on the chemical structure of

agent used [177].

Paraffin or silicone-based water repellent finishing agents do not offer sufficient liquid

repellency protection of textiles therefore, fluorocarbon polymers, commonly known as

fluorocarbons (FC) are used. FCs are an integral part of oil, water, and soil-repellent

finishing and provides the lowest surface energies of all the repellent finishes in use

[176]. Conventional FC based finishes contain a combination of resins, catalysts, homo-

and co-polymers, pH adjusters, cross-linking agents, and solvents [178]. They are

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synthesized by incorporating perfluoroalkyl groups into acrylic or urethane monomers

and then polymerised to form fabric finishes. The final polymer, after application to the

fibre, forms a structure with dense CF3 at the outer surface for maximum repellency. A

typical structure of the final polymer is given in Figure 1.17 [176].

A

A

Where, m = 8-10. X and Y are co-monomers, mainly stearylacrylates. R = H or CH3

(polyacrylic or polymethacrylic acid esters). A is the fibre surface.

Figure 1.17 FC repellent finish on fibre surface.

The application method for most FC products is a simple pad-dry-cure process. At low

active add-ons (<1.0% on the mass of fabric) drying and heat curing will provide a

durable repellent finish to the textile. Heat treatment at the elevated temperature causes

the orientation of the perfluoro side chains to the air interface and creates crystalline

structures [176].

1.9.3 Plasma Technology [179, 180, 181, 182, 183, 184, 185, 186, 187,

188, 189, 190, 191, 192, 193, 194]

Plasma polymerisation is another popular dry surface modification techniques as

treatment time is short with a consistent and reproducible chemical modifications and

gaseous byproducts can be easily removed under vacuum [179]. The process is also

versatile as many different types of gases such as Air, Ar, H2, He, O2, CO2, N2, NH3, F2

and SO2 can be used to introduce required properties [180, 181]. Thus obtaining a C-F

film through plasma could provide several favourable advantages such as controlled

thickness, high deposition rate, and less production cost [182]. The depth of film is

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usually limited to 10 nm or less, which means plasma only influences the outermost thin

layer of the substrate [183]. The chemical structure of the polymer invariably affects

the properties of a plasma polymer film, which is dependent on input plasma

characteristics [182]. Fluorocarbon thin films deposited by plasma polymerisation can

provide a variety of desirable properties, such as low dielectric constant, chemical

inertness [184], hydrophobicity [182], hydrophobic non-stick coatings [186], low-

friction coatings [188]. Therefore plasma polymerisation of fluorocarbon thin films has

been previously studied [185, 186] but offers the potential for improved filter media.

In all of the cases, fluorine content and its distribution along the polymeric chain

determine the properties of the materials. In general, higher fluorine content provides

better liquid repellency, weatherability, chemical and thermal stability, solvent

resistance [189]. The properties of the fluorinated surface depend on both the coverage

and degree of order of fluorocarbon on the surface [187].

The main disadvantage of any plasma treated polymers is that the surface modifications

are not stable over extended periods of time, for example, the wettability decreases on

storage after treatment [190, 191, 192, 193]. The stability also varies depending on the

type of plasma treatment. For instance, on storage of samples in air for few days,

contact angle marked increased for ammonia plasma-treated samples but remained

constant for water plasma-treated samples over many weeks [194]. The long term

stability of fluorocarbon polymer surfaces of water plasma-treated samples was

reasoned to be deeper modification of the surfaces. Wang et al.[195] plasma-

polymerised fluorocarbon on PET surfaces with monomers CF4, C2F6, C3F6, C4F8, and

mixtures thereof with CH4 to create a water barrier layers and found that the barrier was

relatively stable particularly the mixture of C3F6 and CH4 .

1.10 Coagulation/Flocculation [44, 45, 59, 60, 61, 196]

Coagulation and flocculation, if used, is considered to be the most critical stage for

overall colour removal [60] Therefore the need for understanding

coagulation/flocculation processes is important, which usually works by colloidal

suspension. Colloidal material includes mineral substances, silt, bacteria, plankton,

viruses, biopolymers, macromolecules and small aggregates of precipitated and

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flocculated matter. The particle size of colloids is between 1-10 nm [60]. The key to

effective coagulation and flocculation depends how individual colloids interact with

each other. In water, the behaviour of colloids is strongly influenced by their

electrokinetic charge. Each colloidal particle carries a similar charge, which repels each

other and effectively prevents agglomeration and flocculation. The reduction of charges

brings them together to agglomerate and flocculate, which will ultimately produce

visible, larger flocs.

Coagulation works by destabilising the stable colloidal dispersion, which is generally

carries a positively charged species in an appropriate amount to neutralize the charge in

dispersion. Flocculation then aggregates these microflocs into larger sizes [61]. As a

result, sludge is produced which is then removed by flotation, settling or other physical

techniques. The disposal of this sludge, which commonly contains hazardous chemicals,

has some restrictions.

In water/wastewater treatment hydrolysed metal salts such as aluminium or iron salts or

synthetic organic polymers are widely used [196]. However these metal salts have

almost no effect on elimination of soluble dye, especially acid and reactive dyes, which

are designed to withstand microbial, chemical and photodegradation [59]. However,

recent developments in organic polymer and polyelectrolytes have improved colour

removal significantly [45]. Volooj [44] worked extensively on wool keratin dyeing in

order to remove dyebath colour after the dyeing process with a hybrid

coagulant/flocculant and demonstrated beneficial effects.

Generally, the coagulant is added under conditions of intense and rapid mixing followed

by the flocculant, with slower agitation, in order to promote larger floc formation. A

rapid mixing allows coagulant to be distributed evenly throughout the suspension,

which is crucial as poor mixing can lead to destabilisation or local overdosing of some

particles [196]. The efficiency of coagulation/flocculation process in water treatment

depends on many variables, such as [60]:

Type of coagulant used and dosages;

Coagulant feed concentration;

Final pH;

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Type of dosage of chemical additives other than primary coagulant (e.g.

polyelectrolytes);

Sequence of chemical addition and time lag between dosing points;

Intensity, duration and type of rapid mixing;

Velocity gradients applied during flocculation stage;

Flocculator retention time and its geometry;

Types of stirring device used.

1.10.1 Types of coagulants/flocculants

Coagulants and flocculants used for treatment of wastewater can be classified into two

groups: Inorganic compounds (metal coagulants) and organic polymers [197].

1.10.1.1 Metal Coagulants [132, 197, 198, 199, 200]

Metal salts are widely used as coagulant due to their low cost and relatively high

effectiveness. The commercial range is focused on aluminium sulphate, ferric chloride,

aluminium chloride, ferrous sulphate [132]. Aluminium based coagulants are

considered particularly effective as coagulants and flocculants, but polyaluminium

chloride (PAC), a polymer derived from Al3+

, has several advantages over other

metallic salts, which includes, improved floc formation, lower volume of sludge, and

effectiveness over a wide range of pH [198]. It has been reported that PAC improved

turbidity compared to other metallic coagulants such as aluminium sulphate and ferric

chloride [197]. Aluminium-based coagulants generally work by two major mechanisms

when removal of dye is involved: namely precipitation and adsorption. At pH lower

than 6.5 the precipitation mechanism dominates while at higher pH the dominant

mechanism is adsorption or sweep coagulation, Scheme 1.2[199, 200].

Scheme 1.2 Mechanism of coagulation with aluminium-based coagulants [199, 200]

Precipitation: At pH 4-5 Dye + monomeric Al [dye – monomeric Al] (s)

At pH 5-6 Dye + polymeric Al [dye – polymeric Al] (s)

Adsorption: Dye + Al(OH)3 (s) [particle]

[Dye + polymeric Al] (s) + Al(OH)3 (s) [particle]

These flocs polymerise as: n Al(OH)3 Aln(OH)3n

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Although aluminium-based coagulants are very effective in removal of dye the residual

aluminium in the permeate is a major concern due to its association with Alzheimer’s

disease [60]. As a result an alternative approach is necessary either focused on reducing

the dosage, or a blend or alternative coagulant [132].

1.10.1.2 Organic Polymers as Coagulants/Flocculants [61, 201, 202, 203,

204, 205]

In many industrial applications such as mineral processing, water treatment,

biotechnology, papermaking, polymers have been widely used for flocculants for

suspensions [201, 202] and in water and wastewater treatments for decades [61, 203].

All flocculants that are used in water or related application are water soluble and mainly

synthetic in nature [203]. Natural polymers have low toxicity but are less effective.

Flocculants can be broadly classified according to the nature of the charge, molecular

weight (MW) and charge density (CD), Table 1.20. The nature of the charge could be

anionic, cationic, zwitterionic or non-ionic. Usually polymer structures are linear, but

there are some branched or cross-linked polymers effective for certain applications

[204]. Some examples of polymeric flocculants are [205]:

Non-ionic: Polyethylene oxide (PEO); polyacrylamide (PAM); polyvinyl

alcohol (PVA); polyvinyl pyrrolidone (PVP);

Anionic: Hydrolyzed polyacrylamide; polyacrylic acid (PAA); polyvinyl

sulphate;

Cationic: Poly(diallyldimethylammonium chloride) (PDADMAC),

diallyldimethylammonium chloride (DADMAC); cationic polyacrylamide

(CPAM); polyethyleneimine (PEI); polyvinyl pyridine (PVP).

The charge density can be expressed as mole percent of charged groups or as milli-

equivalents per gram (meqg-1

). For highly-charged polyelectrolytes, such as

PDADMAC, CD values are extremely high, up to around 7 meqg-1

[205], however,

exact information for commercial products is not always available.

Literature Review

92

Table 1.20 Classification of polymeric flocculants by molecular weight and size [61]

Amount MW (Dalton) CD (mol %)

High ca. 107 50-100

Medium 105-10

6 ca. 25

Low 104-10

6 ca. 10

In comparison with the more common coagulant alum, the use of polymers provides

some benefits such as lower dosing, smaller volumes of sludge, smaller increases in

ionic load and reduced level of aluminium in treated water [206]. It is commonly found

that polymeric flocculants provide stronger, and larger flocs compared to the flocs

produced by hydrolysing metal coagulants [196].

1.10.1.3 Synthetic Cationic Polyelectrolyte Polymers [61, 203]

The different types of organic polyelectrolytes are reviewed in detail and generally

cationic polymers are most effective followed by anionic and non-ionic [61, 203]. The

most common cationic structures are given in Figure 1.18, and usually contain

quaternary ammonium groups with a positive charge irrespective of the pH. Some

natural products, chitosan or its derivatives are also available for water treatment [61].

Figure 1.18 Structures of the cationic polyelectrolytes: PDADMAC, polymers from

epichlorohydrin and dimethylamine (ECH/DMA), CPAM, chitosan and Anionic PAM.

Literature Review

93

1.10.2 Mechanism of Coagulation/Flocculation

The mode of actions of inorganic salts or synthetic organic polymers is well understood

and described below [196, 205].

1.10.2.1 Coagulation by Charge Neutralization [61, 199]

Alum, iron salts, lime, and organic polymers as hydrolysable salts are a widely

accepted technology, and have been thoroughly investigated [199]. Charge

neutralization takes place when the cations are brought into the solution with anions,

which produces microflocs and the amount depends on the operating pH [61]. In the

case of aluminium, different mono-hydroxo species are formed instantaneously, such as

Al(OH)2+

, Al(OH)2+ and Al(OH)4

-. Also other species such as the dimer Al2(OH)2

4+ or

polymeric forms Al13(OH)345+

can be formed. The Al(OH)3 can be formed

instantaneously and continues during the period of treatment [199].

For coagulation of humic substances by aluminium ions, several mechanisms have been

proposed. At pH 4-5, there is a stoichiometric reaction to produce aluminium humate

when the organic acids are present at least 50% levels.

2RCOO- + AlOH

2+ (RCOO)2AlOH

At pH 5-6 and above, the same reactions proceed, but by adsorption of the organics on

aluminium hydroxide through ligand exchange reaction:

RCOO- + OH-Al< RCOO-Al< + OH

-

1.10.2.2 Coagulation by Double Layer Compression [44, 207]

Double layer compression involves the addition of large quantities of electrolytes such

as NaCl. Any colloidal suspension in an ionic environment can be visualised by a

double layer model, Figure 1.19, and explains how repulsive forces operate between the

particles. The negative colloid initially attracts some positive ions, which forms a firmly

attached layer, known as the Stern layer of counter ions. Additional positive ions are

still attracted but repelled by the Stern layers and other approaching positive ions to the

colloids. This dynamic formation causes a diffuse layer of counter ions. The charge

density is highest near the colloid and gradually diminishes to zero as the positive and

negative ions concentration merges together. Together the Stern layer and diffuse layer

are known as the double layer. The thickness of the layer depends on the concentration

Literature Review

94

and types of ions in solution, and can be several hundred nanometres. The mobility of

the particles, known as the zeta potential, is the work done to move charges around.

Figure 1.19 Visualisation of the double layer [207]. The right side of the diagram shows

the distribution of positive and negative ions while the left view shows the change in

charge density around the cloud.

The stability of any suspension depends on the repulsive and attractive forces operating

among the particles. The balance of repulsion and attraction in a colloidal suspension

can be explained by the DLVO theory (named after Derjaguin, Landau, Verwey and

Overbeek), Figure 1.20, which combines two opposing forces: electrostatic repulsion

and van der Waals attraction. The theory proposes that an energy barrier exists due to

the repulsive forces between approaching and adhering colloids. However, if the

particles collide with sufficient energy to overcome the barrier, then the net attractive

force would pull them together strongly to agglomerate, but this process will be

irreversible.

The energy barrier in a colloidal suspension can be increased or decreased depending on

the requirements. The effective aggregation of particles requires a reduction or removal

Literature Review

95

of this energy barrier so that the net interactive force is effective. Addition of inorganic

salts would compress the double layer or addition of coagulants would reduce the

surface charge, which will eventually encourage particles to aggregate.

Figure 1.20 Net interaction curve according to the DVLO theory [208].

1.10.2.3 Flocculation via Polymer Bridging [61, 203, 205, 209, 210, 211, 212,

213]

The small flocs that are created during the coagulation steps are agglomerated when a

flocculant polymer is added, producing accelerated rates of sedimentation. When the

polymers have a low level of charge density then polymer bridging occurs as

polyelectrolytes attach, loop and bind with nearby particles. After coagulation, the net

charge is normally close to zero although the nature of the surface charges on the flocs

depends on the dose of metal salt used or the environment that prevails. In this situation,

an anionic polymer can increase the size of the flocs by interacting with the positive

sites of the flocs [209]. The bridging takes place in the adsorbed chain with other flocs

as shown in Figure 1.21.

Literature Review

96

Figure 1.21 The bridging flocculation model [210]

When the polyelectrolytes have high density charges, polymers will adsorb where there

is an excess of positive charges, which is known as the electrostatic patch model [211].

The adsorption onto the particles is likely to be in flat patches of the polymer surface

domain with associated excess charges. As a result, direct electrostatic attraction occurs,

which aggregate the flocs [61], Figure 1.22. Further it was also suggested that the

possible random coil configuration is somewhat expanded due to the repulsion between

segments but in a solution with high ionic strength, the repulsion is lessened due to the

screening of ions [203, 205]. It was also reported that the formation of a higher

adsorption layer on the polymeric surface occurred [212]. The removal of metal ions in

solution is possible either by precipitation or formation of a soluble polymer-metal

complex which can be removed via membrane technology [61].

Literature Review

97

Figure 1.22 The charge patch agglomeration model [210]

The balance between the two mechanisms depends on the charge neutralisation with

high charge density polymers and polymer bridging with low ionic content polymers

[213]. Therefore,the practical implication on the process, such as reaction rates, size and

strength of the flocs, are dependent on the degree of charge, molecular size and the ionic

strength [61].

1.10.3 Dual Component System

Coagulation and flocculation play a significant role in the treatment of wastewater and

for alleviating the fouling of membrane. When the process is used as a pre-treatment for

microfiltration (or other membranes), it is mainly aimed to improve permeability and

throughput of the filtration process [214]. Polymers can be used alone, or in addition to

flocculant aids, such as inorganic salts, a second polymer or surfactants [215]. More

often, metal components can be used as the primary coagulant to a flocculant polymer

[132]. It was reported that a dual component system, consisting of two oppositely

charged polymers, could improve the performance of the flocculation process [205, 216,

217]. Two or more components, if used in sequence as a flocculant system, can produce

synergistic effects under suitable conditions [218, 219, 220, 221]. It has been shown that

in an optimised polymer/polymer system of highly charged polycations and a high

Literature Review

98

molecular weight polyanion, this system could be beneficial to the paper industry for

applications such as dewatering, superior retention, and shear resistant flocs [218, 219,

222]. In this case the mechanism that operates involves charge patch formation and

polymer bridging [216, 217]. The first polymer adsorbs on the particles to create

primary flocs, which serve as anchors for the adsorption of the second polymer as

shown with alumina particles [216]. The effectiveness of cationic polymers, such as

polyacrylamide (PAM) and polydiallyldimethylammonium chloride (PDADMAC) has

been widely investigated in synthetic colloidal systems and water treatment [201].

In the study of PDADMAC and different polycations, Petzold et al. [217, 222] found

that the flocculation behaviour essentially depends on the concentration of polycation

(as related to anionic character of suspension) and the molar ratio of anionic and

cationic charges. The amount of polycation necessary for flocculation could be high if

complexation between polyanion and polycation is the mechanism for flocculation. A

molar ratio of anionic charges to cationic charges of n-/n

+ of 0.6 should be obtained for

effective flocculation. In addition to complexation, with relatively high molecular

weight (>1,000,000) polyanion patchwise adsorption and bridging occurs.

Literature Review

99

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Experimental

116

2. Experimental

This chapter will discuss the materials used in this research, experimental approaches

and their materials performances.

2.1 Simulated Seawater (SSW)

Many investigations have been carried out in order to find out the major constituents of

seawater. Marcet in 1819 examined samples collected from the Arctic and Atlantic

Oceans, the Mediterranean, Black, Baltic, China and White Seas [1] and concluded that

seawater constitutes the same ingredients with nearly same proportion but differs in the

total amount of salt contents [1, 2]. In later studies, it was found that the major

constituents of seawater consist of eleven ions: chloride, sodium, sulphate, magnesium,

calcium, potassium, bicarbonate, bromide, strontium, borate and fluoride [1]. Seawater

is a saline solution, a solution of predominantly sodium chloride, NaCl. Na and Cl

account for more than 86% of salt content in water by mass. The other cations present

are Mg2+

> Ca2+

> K+> Sr

2+, in order of concentration. The anion Cl

- is approximately

equal to the sum of the other anions, SO42-

, HCO3-, Br

-, F

- [3].

Table 2.1 Composition of 3.50% salinity simulated seawater [4]

Gravimetric salt

Salt Mol. Wt. gL-1

Sodium chloride (NaCl) 58.44 23.926

Potassium chloride (KCl) 74.56 0.677

Sodium sulphate (Na2SO4) 142.04 4.008

Potassium bromide (KBr) 119.01 0.098

Boric acid (H3BO3) 61.83 0.026

Sodium bicarbonate (NaHCO3) 84.00 0.196

Sodium fluoride (NaF) 41.99 0.003

Volumetric salt

Salt Molecular wt. moleskg-1

of solution

Magnesium chloride (MgCl2.6H2O) 203.33 0.05327

Calcium chloride (CaCl2.2H2O) 147.03 0.01033

Strontium chloride (SrCl2.H2O) 266.64 0.00009

Experimental

117

The most used standard formulation for producing simulated seawater was proposed by

Lyman and Fleming, in 1940, who considered the seawater salinity at 3.50% [5, 6].

Kester, Duedall et al. [4] revised the formula of simulated seawater to bring down the

difference of composition to 1 mgkg-1

from natural seawater, Table 2.1. The recipe

consists of two types of mineral salt; one anhydrous the other based on hydrous salts

and is added into seawater as a solution.

In this research, SSW was prepared according to recipe given in Table 2.1, however, for

simplicity a formula from Marine Biological Laboratory was followed, Table 2.2. SrCl2,

H3BO3, NaF and KBr were omitted as they can be regarded as insignificant

components. NaHCO3 was not added when the dyeing condition was acidic. Laboratory

grade salts were used in all cases, and distilled water was used to make the test

simulated seawater solution. The pH of SSW was 7.80 at 19.6°C.

Table 2.2 Composition of SSW used in this research [7]

Salt gL-1

molar

NaCl 24.72 0.425

KCl 0.67 0.009

CaCl2 1.03 0.0093

MgSO4. 7H2O 6.29 0.0255

MgCl2. 6H2O 4.66 0.023

NaHCO3 0.18 0.002

2.2 Textile Fibres and Dyes used in this Research

The four major fibre types, wool, polyester, nylon and acrylic were examined under

dyeing conditions in simulated seawater environment. These fabrics were supplied by

Whaleys, Bradford and Phoenix Calico, Manchester. The dyeing systems evaluated

were wool/acid, wool/reactive, polyester/disperse, nylon/acid, acrylic/cationic dye/fibre

combinations. These are discussed in Chapters 3, 4, 5, 6 and 7.

Experimental

118

2.3 Filter Media

Azurtex filter media was supplied by Clear Edge Filtration, Germany (formerly

Madison Filtration Limited), which is an advanced development of Primapor, Figure

2.1. The filter media is a microporous multi-filament polypropylene plain weave fabric

with a polyurethane (PU) coating. The media is used across a range of processing

conditions [8]. The average pore size is 6µm with a corresponding liquid permeability

of 110 Lm-2

min-1

[9]. Azurtex provides an excellent liquid throughput and cake release,

and good particle retention, combined with good abrasion resistance [8]. The maximum

width available is 1.65m, with a nominal weight is around 620 gm2-

[9, 10] and can be

used for fine filtration of liquid slurries TiO2, china clay and dyestuffs.

Figure 2.1 SEM micrograph of a cross-section of Primapor Blue filter, showing the

upper layer of microporous polyurethane coating combined with the polypropylene

woven support (x 400 magnification)

2.4 Slurry

The titanium dioxide, TiO2 slurry used in this research was supplied by Huntsman,

Germany, and its composition and properties are given in Table 2.3. This is common

slurry that is used in the filtration industry and was studied as a model filtration

material. The slurry was thoroughly stirred prior to each filtration to ensure reproducible

results.

Experimental

119

Table 2.3 Slurry used in the filtration tests [9, 11, 12]

Parameters Composition and Properties

Titanium Dioxide 80-90%

Aluminium hydroxide 0-9%

Amorphous silica 0-10%

Solubility insoluble in water

Specific gravity 1.8-2.4

pH of slurry 6.7

2.5 Coagulants and Flocculants

Volooj [9] used a dual system of highly cationic polyaluminium salts and an anionic

flocculant to treat Acid dyebath solutions, based on freshwater, and achieved dye

removal up to 99.2%, although the result varied with dye structure and dye class.

Therefore, similar chemicals were investigated for the SSW dyebath recycling. Pluspac

2000 (Feralco, UK) is a coagulant based on low charge density PAC blended with an

organic polymer, polydiallyldimethylammonium chloride, Figure 2.2, which is a blend

of cationic inorganic coagulant and organic polyelectrolyte flocculant. The active

component is [Al13O4(OH)24(H2O)12]7+

, a highly cationic aluminium polymer in low

concentrations [13].

Figure 2.2 Structures of PDADMAC (polydiallyldimethylammonium chloride) and

cationic aluminium polymer - the active components of Pluspac 2000

HPSS (Croda Chemicals, UK) is a copolymer of anionic hydrolysed vegetable protein

and sodium polystyrene sulphonate with high charge density, Figure 2.3 [14].

Experimental

120

Figure 2.3 Hydrosolanum PSS-copolymer of hydrolysed vegetable protein and

polystyrene sulphonate

Generally, the coagulant was added to the solution with intense and rapid mixing

(approximately 250 rpm) followed by the flocculant with slower mixing (20 rpm) in

order to promote larger flocs. A rapid mixing allows coagulant to be distributed among

the suspension, which is essential as proper mixing can lead destabilisation or local

overdosing of some particles [14].

2.6 Filtration

Pressure filtration tests, typically duplicates or triplicates, were carried out in a low

pressure filter bomb vessel, supplied by Clear Edge Filtration. The system consisted of a

filter bomb vessel and a pressure unit, Figure 2.4. The filter media was positioned at the

bottom end of the vessel and tightly sealed in order to prevent leakage of the solution

through the joint under pressure. The slurry of known weight, 100±0.8% gm, was

transferred into the vessel and then the lid was closed with connection to pressure pipe.

A variable pressure of 2.5 to 5.5 bar was applied to the system with an effective

filtration area of 38.48 cm2.

Experimental

121

Air compressor

Figure 2.4 Schematic diagram of a filtration apparatus used in this study

2.7 Experimental Methods

2.7.1 Dye Exhaustion

The rate and extent of the exhaust dyeing process can be defined as the degree of

dyebath exhaustion in relation to time [15]. For a single dye, the exhaustion is defined

as the amount of the dye taken up by the material divided by the total initial amount of

dye in the solution, in a bath of constant volume, Equation 2.1:

( )

Equation 2.1

Where

C0 = Concentration of dye initially in solution;

CS = Concentration of dye in solution after dyeing.

The exhaustion of dyeing of a textile is aided by auxiliaries or controlled by a gradual

increase of temperature. While there is always equilibrium at the end of a dyeing

process, in reality, commercial practical dyeing attaining equilibrium may not be

economically feasible as it would require an infinite amount of time. In addition

prolonged exposure to the dye liquor could have a detrimental effect on the substrate

material being dyed. The levelness is of critical importance in exhaust dyeing as the

initial strike of dye to the material maybe uneven and will need correction.

Filter bomb

Experimental

122

The uptake of dye by the fabric was determined spectrophotometrically by measuring

the amount of dye remaining in the dyebath. In this study initially calibration curves

were calculated for each sample dye in SSW and DSW by appropriate dilution of the

solution. λmax was determined for each of the dyes using a Perkin Elmer Lambda 18 UV-

Vis Spectrophotometer (10 mm cell). Based on the variation between linearity of the

calibration curve, either DSW or both were chosen for subsequent calculation of

exhaustion.

To calculate exhaustion, the absorbance was measured at λmax for the exhausted dyebath

at room temperature and the concentration of the dye solution was determined from the

corresponding calibration curve. The percentage of dye exhaustion was calculated using

Equation 2.2.

( )

Equation 2.2

Where %E is the percentage exhaustion after dyeing, and are the concentrations

(gL-1

), measured at λmax, of the dyebath before and after dyeing, respectively.

2.7.2 Dye Fixation [15]

One of the main environmental concerns within the textile colouration industry is the

release of dyes from the process or material itself. In all cases, it depends on the level

and strength of fixation of dye with the fibre. Fixation is the amount of dye fixed with

the fibre after all the washes. The formula for fixation is given in Equation 2.3:

( )

( )

Equation 2.3

Where C0 = Initial concentration of dye;

Cs= Concentration of dye after dyeing;

CW1, CW2 are concentrations of the dye in each wash.

The fixation value of exhaust dyeing depends to a large extent on dyeing conditions.

The higher the affinity of the dye for the fibre or the lower the liquor ratio and dye

concentration, the higher is the fixation value for fibre and dye.

Experimental

123

2.7.3 Colour Measurement [16, 17, 18, 19]

An objective colour difference formula to accurately represent visual perceptual

assessments of colour to control the quality of the materials is desirable and critical to

communicate the data [20].The Commission Internationale de l’Eclairage (CIE)

committee on Industrial Colour Difference Evaluation proposed a generic colour

difference equation, which is based on CIE LAB given in Equation 2.4[16]. In this

equation differences in lightness, ∆L*, Chroma, ∆C* and hue, ∆H* are always

computed from the CIE L*a*b* and is an improved version of 1976 original to include

perceptual uniformity (weighting functions W) and the parametric factors (K). For

visual assessment of colour under the reference conditions, it was suggested that KL, KC,

and KH, should set to 1 [19]. The colour difference ellipse predicted by CIE94 or CMC

(Colour Matching Committee) are radially oriented in the plane of a* and b*. The CMC

equation allows varying the size of the ellipsoid to match the visual acceptability. As the

eye will generally accept larger differences in lightness (l) than in chroma (c), therefore

a default ratio of l:c=2:1 was considered as better match to visual assessment [17, 18].

Therefore the CMC(l:c) colour difference formula is among the most widely used and is

incorporated to the International Standards Organization (ISO) , the American Society

for Testing and Materials (ASTM) [21], the Society for Automotive Engineers (SAE)

[22], and the American Association of Textile Chemists and Colorists (AATCC) [23]

standard . With an optimised weighting factor (KL or l) the performance CMC(l:c) or

CIE94 would not be significantly different with other standard colour difference models

such as CIE DE2000 and BFD(l:c) at the 95% confidence level [24, 25].

[(

)

(

)

(

)

]

Equation 2.4

The reflectance value of the blank and dry dyed samples were measured using a

Datacolor SpectraFlash 600 spectrophotometer with the illuminant D65, 10° standard

observer with specular component excluded and UV component included. The colour

difference, ΔE*94 or ΔECMC (2:1) between the fabrics dyed in DSW and SSW were

measured for acceptability of colour. Levelness of the dyed fabric was measured at

different locations on the surface of the fabric.

Experimental

124

Measurement of colour strength, K/S was based on the reflectance values of dyed fabric

and was measured at λmax using the Kubelka-Munk, Equation 2.5 [26];

( )

Equation 2.5

Where K is the absorption coefficient, S is the scattering coefficient, and R is the

proportional reflectance of the dyed fabric at λmax.

2.7.4 Dye Removal

Following the exhaustion method, the dye removal after the coagulation/flocculation

and filtration process was determined by measuring absorbance with a Perkin Elmer

Lambda 18 UV-Vis Spectrophotometer (10 mm cell) using the Equation 2.6:

( )

Equation 2.6

Where is the absorbance before filtration (i.e. after dyeing) and is the absorbance

after the filtration process

2.7.5 Fastness

Wash fastness to domestic laundering was carried out according to the ISO 105-CO6

C2S and B2S test standard using a Roaches Washtec P (Roaches International, UK) and

a Gyrowash (James H. Heal, Halifax, UK). The tests were performed at 60°C with or

without steel balls (for wool) and SDC adjacent multi-fibre strips incorporated into

wash liquor solution [27]. The dry rubbing and sublimation fastness were assessed

according to the ISO 105-X12:2001 and ISO 105-PO1:1990 (210 ±2°C, 30 sec) test

standards, respectively. Alkaline perspiration fastness was determined according to the

ISO 105:EO4:1990 method while light fastness was measured using blue wool standard

ISO B02/02 in Weatherometer with a xenon arc lamp.

After testing, fabrics were visually assessed in a colour matching cabinet relative to the

standard grey scale according to ISO 105:A02 and ISO 105:A03 test methods in order

to determine the degree of colour change and cross-staining. In the nine-step grey scale,

rating 5 represents no colour difference between samples, which increases geometrically

when moving from 5 to 1. The choice of psychophysical method is a primary concern

during the assessment of colour change [28]. Before doing any visual assessment, the

Experimental

125

researcher was tested for normal colour vision. The researcher evaluated at least 5

samples within a viewing booth visually which were matched instrumentally to confirm

the visual rating. The same viewing cabinet and sample presentation conditions were

used in each case. It was reported that an ‘expert’ with experience in commercial shade

matching industry, on average, produced 43% higher visual difference ratings than a

‘novice’ who had no prior experience of commercial pass/fail colour difference

assessments at 95% confidence level [20]. Since the researcher has over 3 years of

experience of commercial shade matching, therefore visual assessment of colour change

and cross-staining was carried out for each dyed fabric.

2.7.6 Wettability Test

Wetting time was determined by the standard drop test (AATCC-39-1980), where a

drop of water was placed onto the fabric surface and spreading time was measured in

seconds until totally disappeared. If the drop of water had not completely disappeared

after 4800 seconds, the measurement was stopped, and the result value set to 4800

seconds. The time was selected because some filter media tested didn’t change their

wettability behaviour even after this time period.

2.7.7 Oil and Water Repellency

The oil and water repellency were performed using the 3M oil and water repellency

tests (AATCC 118-1972). A range of eight different water/isopropyl alcohol mixtures

and hydrocarbon liquids with different surface tensions were used [29]. At least three

drops of each test liquid were dropped onto the surface of the filter media, and evaluated

within the specified 60 seconds. The wetting rating was based on test liquids over a

scale of 1 to 8, with 8 being the highest water or oil repellency.

2.7.8 Tensile Strength

The tensile strength of wool dyed fabrics was measured using an Instron 3345 tensile

tester according to the BS EN ISO 13934-1:1999 method. 50 mm wide fabric samples

with a grip distance of 150 mm were used under standard conditions (20 ±1°C and 65

±2% RH) in laboratory for testing. Five separate samples were tested, and the mean

value calculated. A 5 kN load was applied with an extension speed of 100 mm/min.

Experimental

126

2.7.9 Abrasion Resistance

The abrasion resistance of the fabrics were determined according to the BS EN ISO

12947-2: 1999 method using a Martindale abrasion tester. Four circular fabric samples

of 38 mm from different area of same fabric were abraded against a standard worsted

wool abradant fabric at a constant pressure of 9 kPa. The standard abradant cloth was

replaced after 50,000 cycles. Abrasion resistance was measured by subjecting the test

sample to a geometric rubbing motion, known as Lissojous motion which was initially a

straight line and gradually becomes gradually a widening ellipse until it forms another

straight line in the opposite direction. The advantage of the Martindale abrasion test is

that the fabric sample gets abraded in all directions [30]. The number of cycles required

under 10 kPa to produce two yarn breaks for woven fabric or a hole in knit fabric was

considered as the end point of the testing for the particular sample [31]. After first 2000

cycles, the pills were cut from the fabric surface.

2.7.10 Turbidity Test

Industrially the quality of filtrate water is routinely monitored in water treatment plants

by turbidity measurements [32] and measurement of the degree of particulate

contamination in the water [33]. The higher the level of turbidity, the cloudier the water

is and vice versa. Turbidity is defined as an “expression of the optical property that

causes light to be scattered and absorbed rather than transmitted in straight lines through

the sample [9].” Turbidity is typically measured in Nephelometric Turbidity Units

(NTU) or in Jackson Turbidity units (JTU) but these measurements do not indicate the

size of the suspended particles in water, but rather the amount of particles. The turbidity

of the filtrate was measured using a Hach 2100Q portable turbidimeter, with an upper

limit of 1000 NTU, and five measurements were done for each filtrate and the average

NTU calculated.

2.7.11 Flow Rate and Solution Recovery %

The flow rate was determined by plotting the weight of the filtrate (100 g) against time

(seconds), and the average of two cycles was taken without changing the filter media.

Experimental

127

2.7.12 Filtrate Properties

The filtrate weight was measured after the filtration. The solution recovery was

calculated adding weight of filtrate and wet cake. Solid contents of the filtrate were

calculated from Equation 2.7 after drying in an oven for 24 hours at 80±3°C.

Equation 2.7

2.7.13 Properties of Filter cake

The moisture contents of the filter cake, as a weight percentage, were calculated

following the evaporation of water in an oven for at least 24 hours at 80°±3°C, Equation

2.8.

( )

Equation 2.8

The slurry thickness was measured with slide callipers at four different locations over

the filter cake and the average values were determined. The cake disposal rating was

assessed arbitrarily using a scale of 1 to 5, where 1 is very poor, and 5 is very good. A

description of this scale was given in Equation 2.4. The associated rating images for this

this research is given in Figure 2.5.

Table 2.4 Cake rating scale used in this research

Rating Interpretation Description

1 Very poor Cake is attached heavily with the bomb and the media, broke

down into pieces and needs extra effort while taking the cake out

2 Poor Cake is attached moderately to media and bomb, broke into mini

pieces while coming out from the bomb.

3 Moderate The number of chunks are regular in size and mild effort is

needed to remove from the bomb and media

4 Good Few chunks of cake, easy to remove from the filter bomb and

media

5 Very Good Cake fell down in one chunk from the filter bomb and the media

with no attachment

Experimental

128

Cake disposal rating: 1 Cake disposal rating: 2

Cake disposal rating: 3 Cake disposal rating: 4

Figure 2.5 Associated image for cake disposal rating used in this research. Since rating

5 is an unbroken flat cake it is not included here.

2.7.14 Kawabata Evaluation System (KES)

The KES system measured the tensile, shear, bending, surface and compression

properties of fabrics using similar forces to those applied by a human hand during the

subjective assessment of fabric handle [34]. Sixteen mechanical parameters were

determined using 20×20 cm fabric samples that had been conditioned at 201ºC and

652% relative humidity in a laboratory for 24 hours prior to analysis in an air-

Experimental

129

conditioned laboratory. The list of measured parameters for the test is given in Table

2.5. These parameters uniquely define the characteristics of fabric, known as a ‘handle

fingerprint,’ which then can be used for quality control and process characterisation.

Table 2.5 KES parameters for woven fabrics

Property Symbol Description Unit

Tensile

LT Linearity of extension curve -

WT Tensile energy gf.cm/cm2

RT Tensile Resilience %

EMT Extension at 500 gf.cm-1

load %

Shear

G Shear Stiffness gf.cm-1

.degree

2HG Shear Hysteresis (0.5º) gf.cm-1

2HG5 Shear Hysteresis (5.0º) gf.cm-1

Bending B Bending Stiffness gf.cm

2/cm

2HB Bending Hysteresis gf.cm/cm

Surface

MIU Coefficient of Friction -

MMD Mean Deviation of MIU -

SMD Geometrical Roughness µm

Compression

LC Linearity of Compression Curve -

WC Compression Energy gf.cm/cm2

RC Compression Resilience %

To Thickness at 0.5 gf.cm-2

Pressure mm

Tm Thickness at 50 gf.cm-2 Pressure mm

Weight W Weight Per Unit Area mg.cm-2

Primary Hand

Value

Koshi Stiffness -

Numeri Smoothness -

Fukurami Soft and Fullness -

Total Hand Value THV - -

Experimental

130

2.8 Microscopic and Spectroscopic Analysis

2.8.1 X-ray Photoelectron Spectroscopy (XPS)

XPS, which is also known as Electron Spectroscopy for Chemical Analysis (ESCA), is

an important and widely used analytical technique for surface analysis and is capable of

providing quantitative and qualitative information about fibre surfaces [35, 36, 37, 38].

The popularity of XPS techniques can be attributed to the breadth of information

obtained and flexibility in examining a wide variety of samples [39, 40]. While surface

and interface analysis is the main application of the technique, new promising areas of

measurement include magnetic properties, surface and bulk electronic structure, and

time-resolved processes including chemical kinetics [41]. XPS is particularly suited to

examining the fluorinated layers of filter media as it will specifically analyse the surface

active regions [42]. A Kratos Axis XPS spectrometer, equipped with an Al Kα (1486.69

eV) X-ray source and power of 150W was used to analyse the samples. Samples were

mounted onto the sample plate with double sided adhesive tape. The exposed surface

area was approximately 10 mm2. Binding energy values were calculated relative to the

C(1s) photoelectron peak at 285.0 eV. Wide scan spectra were taken at a pass energy of

80 eV for determining the surface composition of N, O, C and F while high resolution

spectra were obtained at pass energy of 40 eV in order to characterise the elemental

chemical states of C(1s), N(1s), O(1s) and F(1s). The analysis depth at the materials

surface was in the range of 1-5 nm. The data was analysed using the CASA XPS

software [43].

2.8.2 Attenuated Total Reflectance Fourier Transform Infrared (ATR

FTIR)

ATR-FTIR spectra of the modified media were collected using a Nicolet 5700

spectrophotometer equipped with a diamond crystal for a penetration depth analyses of

5-20μm. A total of 32 scans were recorded with a resolution of 4 cm-1

. The OMNIC

spectroscopy software was used to collect process and present the data.

Experimental

131

2.8.3 Surface Morphology Analysis by Scanning Electron Microscopy

The surface morphology of fibres and coatings were observed using a Hitachi S-4000

Scanning Electron Microscope (SEM), operating at an accelerating voltage of 5 kV. The

samples were coated with gold, under vacuum, prior to analysis in order to dissipate

charge. In addition, the elemental composition of acid-dyed wool fabric was determined

using an EDX (INCA PentafetX3) system operating at 10 to 15 kV. In this case samples

were coated with either carbon or gold.

2.8.4 Contact Angle Measurements

The hydrophobicity/hydrophilicity of a surface can be expressed in terms of liquid

wettability and can be quantified by contact angle measurements. The contact angle, θ,

is defined geometrically as the angle formed by a liquid at the three-phase boundary

where a liquid, gas and solid interact, as shown in Figure 2.6. A high value of θ

indicates the liquid is poorly wetting and vice-versa. If the angle θ is less than 90°, then

that liquid wets the solid. Alternatively if θ is greater than 90° it is said to be non-

wetting. A zero contact angle represents complete wetting. The primary focus of the

contact angles studies was in assessing the wetting characteristics of solid/liquid

interactions. Contact angle is commonly used as the most direct measure of wetting [9].

However, contact angle depends on many factors such as surface roughness, surface

heterogeneity, surface preparation and contamination, surface electrical charge,

surrounding environment, pressure, temperature, drop size and heat transfer [44].

Figure 2.6 Water droplet on a surface

The contact angle of each sample was measured using the T 458 om-84 method using

the drop shape analysis system based on the AB Lorentzen and Wettre (L & W) tester

Experimental

132

contact angle meter. The video contact angle system used distilled water with a drop

size of 0.004 µl ±10% as the test liquid. A Panasonic WV-CL700 camera, connected to

a video monitor, captured the image of the drop, with a background light for

illumination. After 60s of contact, the height (h) and width (a) of the drop were

measured from the base and then used to calculate the contact angle, α, from Equation

2.9. Four measurements were obtained at different locations over the media surface and

the mean presented. A measurement error of ±3° was typical.

Equation 2.9

Experimental

133

2.9 References

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Experimental

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137

Part A: Dyeing of Textiles in Distilled

Water and Simulated Seawater

Wool/Acid dyes

138

3. Dyeing of Wool with Acid dyes

3.1 Introduction

Wool is the most extensively used natural fibre after cotton and is a heterogeneous fibre

both chemically and physically. There are about 25-70% impurities in raw wool, which

includes suint, grease, dirt and vegetable matter [1]. Clean wool is a protein

biopolymer, of which about 82% is keratin. In wool, the amount of amino and

carboxylic acid groups are almost equal (820 and 770 mmolg-1

, respectively) [2]. Acid,

metal-complex, chrome, and reactive dyes may be used for wool dyeing [1]. The dye is

anionic in aqueous solution and is therefore attracted to the cationic ammonium ion in

the protein fibre, Scheme 3.1.

Wool –NH2 + H+

+ HSO4- Wool-NH3

+HSO4

-

Wool-NH3+HSO4

- + Dye-SO3

- Wool-NH3

+Dye-SO3

- + HSO4

-

Scheme 3.1 Mechanism of wool and acid dye

Acid dyes have molecular weights in the range 300–1000 gmol-1

. The commercially

available acid dye ranges varies enormously in respect to molecular size and the polarity

of the molecule. Most dyestuffs are monosodium sulphonates or carboxylates [3]. In

general, higher molecular mass and low polarity dyes would show the highest wet

fastness with low migration properties and vice versa, Figure 3.1.

Figure 3.1 Classification of wool dyestuffs in relation to migration and fastness [3]

Fast

acid

1:1 Metal

Complex

Sandolan

MF

Level

Dyeing

acid

Super

milling /

1:2 metal

complex

Milling

Chrome

Reactive

Fastness

Lev

elli

ng/m

igra

tion

Wool/Acid dyes

139

In this chapter, wool fibre was tested in simulated seawater environment with

commercially available acid and metal complex dyes and the performances of the fabric

were evaluated against that in freshwater.

3.2 Experimental

3.2.1 Materials

A woven 100% wool botany serge (2/2 twill, scoured and set) fabric (295 gm-2

) was

supplied by Whaley’s (Bradford) Ltd. In order to encompass the whole spectrum of

available acid and metal complex dyes, five different commercial ranges were selected

These are the acid milling, levelling, metal complex and mixture of these dyes, Table

3.1 to 3.6, and were kindly donated by Clariant, Everlight and Huntsman and assessed

over a range of colour depths, given in Section 3.2.2. The structures of the some

available dyes were given in Figure 3.2.

Table 3.1 Sandolan E acid dyes used in this study and their characteristics

Manufacturer Dye Structure/CI

number Dye Class Properties of dye

Clariant

Sandolan Rubylon

E-3GSL

Monoazo Levelling Exhibits high migration

power with good

penetration and high

light fastness. They are

particularly used for

piece dyeing and the

hat industry.

Sandolan Blue E-

FBLL

Anthraquinone Levelling

Sandolan Yellow

E-2GL

CI Acid Yellow

17

Levelling

Wool/Acid dyes

140

Table 3.2 Lanasan CF acid dyes used in this study and their characteristics



Clariant

Lanasan Red

CF-WN

Blend of acid

milling and 1:2

metal complex

Metal Produces ‘Frostless

wool’ through good

levelness and optimized

root-tip distribution.

Have a wide colour

spectrum, economical

cost with high fastness.

The dyeing process is

in the isoelectric region

in order to minimise

strength loss [4].

Lanasan Brilliant CF-

BA combination

contains brightening

element.

Lanasan

Brilliant Blue

CF-BA

1:2 Metal

Complex, Acid

Blue 256

Milling

Lanasan

Brilliant

Yellow CF-

BA

Blend of acid

milling and 1:2

metal complex

Milling

Table 3.3 Sandolan MF acid dyes used in this study and their characteristics



Clariant

Sandolan Red

MF-GRLN

Mixture of

monosulphonated

half milling and

disulphonated

milling

Levelling,

Fast Acid

Eco-friendly and is

gentle dyeing to piece

goods and yarn [4].

Sandolan MF dyes are

claimed to be the

fastest acid dyes with

good migration

properties relative to its

molecular size range

[3]. Sandolan MF

offers trichromatic

dyeing in the isoelectric

region at low

temperature.

Sandolan

Blue MF-GL

Mixture of

monosulphonated

half milling and

disulphonated

millling

Levelling,

Fast Acid

Sandolan

Golden

Yellow MF-

RLN

Mixture of

monosulphonated

half milling and

disulphonated

millling

Levelling,

Fast Acid

Wool/Acid dyes

141

Table 3.4 Lanasyn S acid dyes used in this study and their characteristics



Sandoz/

Clariant

Lanasyn Red

S-G

Monosulphonated,

CI Acid Red 315

1:2 Metal

Complex

Very good light and

wet fastness properties

with simple and

reliable dyeing process

[3]. Especially suitable

for the low temperature

dyeing of loose stock or

tops and knitted goods

[5].

Lanasyn Blue

S-GB

Monosulphonated 1:2 Metal

Complex

Lanasyn

Yellow S-GB


Complex

Lanasyn

Black S-G


Complex

Table 3.5 Lanaset acid dyes used in this study and their characteristics



Huntsman/

Ciba

Lanaset Red

G

Monoazo 1:2 Metal

Complex

Shows good

combination with other

dyes and covers root-

tip differences. These

are considered ideal for

polyester/wool blends

with good build-up

during dyeing and good

fastness [6].

Lanaset Blue

2R

Anthraquinone, CI

Acid Blue 225

1:2 Metal

Complex

Lanaset

Yellow 2R

Azo, CI Acid

Yellow 220

1:2 Metal

Complex

Lanaset

Black B

Monoazo, CI Acid

Black 172 and a

non-CI Acid Black

1:2 Metal

Complex

Table 3.6 Other Acid Black dyes used and their characteristics



Clariant Sandolan

Black NR

Disulphonated Milling N/A

Everlight

Chemical

Everacid

Black LD

CI Acid Black 172 Metal

complex

Provides deep colour

and high light and wet

fastness [7]

Wool/Acid dyes

142

Figure 3.2 Structure of acid dyes used in this study a) Everacid Black LD CI Acid Black

172; b) Sandolan Yellow E-2GL CI Acid Yellow 17; c) Lanaset Blue 2R- CI Acid Blue

225; d) Lanaset Yellow 2R CI Acid Yellow 220.

3.2.2 Dyeing

All dyeings were performed using a Mathis IR laboratory dyeing machine using both

DSW and SSW, at a liquor to goods ratio of 10:1 and a pH of 4.5-5.5 (pH adjusted with

acetic acid/acetate buffer) or pH 3.0-3.5 for the Sandolan E range (pH adjusted with

sulphuric acid). The dye application levels were 0.05, 1.0 and 3.0% on mass of fibre

(o.m.f.) for the red, blue and yellow dyes and 1.0, 2.0, and 4.0% o.m.f. for the black

dyes. The recommended commercial dyeing conditions commenced at 40-50ºC, raised

to 98ºC at 2ºC per minute and the dyebath maintained at 98ºC for 45 minutes, or for 60

minutes with the black dyes. In addition to dye, the aqueous bath contained a non-ionic

wetting agent (Matexil WA-KBN, ICI) and the levelling agents recommended by the

dye manufacturers i.e. Lyogen MF and Albegal Set [4] at 1-2 gL-1

. The recommended

10% (o.m.f.) sodium sulphate was not added to simulated seawater baths for Sandolan

E, Sandolan MF and Sandolan N-R dyeings. The dyeings were performed in duplicate

to confirm reproducibility.

(a)

(b)

(c)

(d)

Wool/Acid dyes

143

3.2.3 Wash-off

The standard wash-off procedures for the acid and metal complex dyeings were

followed, based on a cold rinse, a wash with detergent and finally a cold rinse, Table

2.3. However, since salt could be present on the surface of wool fabric dyed with SSW

it was necessary to determine the optimum wash off process, and a range of wash off

trials were carried out with the Lanaset Blue dye at 3.0% o.m.f. Initially the SSW dyed

fabric was cold rinsed for 5 minutes with tap water and then washed with non-ionic

detergent (Eriopon R, Ciba Specialty Chemicals) in conditions as described in Table

3.7.

Table 3.7 Washing conditions for dyed fabrics

Water type Conc. of Detergent, gL-1

Temp., °C Time, mins.

Trial 1 DSW 2 Room 10

Trial 2 SSW 2 Room 10

Trial 3 SSW 2 40 10

Trial 4 DSW 1 70 10

Trial 5 SSW 1 70 10

Trial 6 SSW 2 70 10

After the washing, the fabric was cold rinsed and line dried at ambient conditions.

3.3 Results and Discussion

3.3.1 Effect of Simulated Seawater on Dye λmax Absorption and Dye

Concentration Linearity

In a preliminary study, the solubility, λmax and light absorption behaviour of six dyes

from each range of dyes was evaluated at 1.0% o.m.f. depth. It was found that Sandolan

Rubylon E-3GSL and Lanaset Red G were completely soluble in pure SSW at room

temperature, Table 3.8. In contrast Lanasan Red CF-WN, Sandolan Red MF-GRLN,

Lanasyn Red S and Lanaset Black B dyes had reduced solubility in the SSW at ambient

temperature, but gentle warming of the dyebath increased dye solubility. In addition it

was found that incorporating levelling agent into the dyebath with gentle warming

further significantly improved the dye solubility and dye solubility in seawater was not

Wool/Acid dyes

144

envisaged to be a processing problem. A slight shift of λmax was observed when dyeing

auxiliaries were present, however, comparable results were observed with both DSW

and SSW.

Table 3.8 λmax for wool dyes in distilled and simulated saltwater solutions

λmax, nm

DSW SSW DSW + chemicals SSW + chemicals

Lanasan Red CF-WN 498 -* 504 503

Sandolan Rubylon E-3GSL 512 510 512 512

Sandolan Red MF-GRLN 494 -* 501 501

Lanasyn Red S-G 501 -* 503 -*

Lanaset Red G 494 494 502 501

Lanaset Black B 572 -* 583 581

* Insoluble dyes were found after heating and cooling, therefore the measurement was

not performed.

Previously Valko [8] found that higher amounts of salt causes higher dye aggregation,

but increasing the temperature of dyebath reduced aggregation either by complete

dispersion or dissolution. Further studies of acid dyes at 55, 75 and 95°C showed that

dyes were highly aggregated, particularly when the non-polar nature of the dyes

increased [9].

The addition of levelling agents was reported to reduce dye aggregation [10] and was

particularly effective in covering tippy dyeing, even with dyes which are more likely to

produce these faults [11] and allow reproducibility with high exhaustion [3]. The

amphoteric levelling agents that are used in this study, Lyogen MF and Albegal SET,

are dye-substantive in acidic media [12]. Lyogen MF is based on an ethoxylated tertiary

aliphatic amine [13] and Albegal SET is based on a modified nitrogen-containing fatty

alcohol ethoxylates [14]. Both are able to form dye/complexes and capable of tolerating

high salinity, especially in the presence of divalent magnesium and calcium cations

[15].

The dye absorbance studies indicated that for all six dyes in SSW the

absorbance/concentration graphs were linear and comparable to the DSW based

dyebaths, Figure 3.3 and 3.4, thus obeying Beer-Lambert Law.

Wool/Acid dyes

145

Figure 3.3 Graph of Sandolan Rubylon E-3GSL dye absorbance versus concentration in

water, λmax 512nm, ▲ - distilled water dyeing; and ■ - simulated seawater dyeing.

Figure 3.4 Graph of Lanaset Black B dye absorbance versus concentration in water

with dyebath auxiliaries, λmax 583nm, ▲ - distilled water dyeing; and ■ - simulated

seawater dyeing.

RDSW² = 0.999

RSSW² = 0.988

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Ab

sorb

an

ce, A

Concentration, gL-1

RDSW+ Auxiliaries² = 0.989

RSSW+ Auxiliaries² = 0.997

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Ab

sorb

an

ce, A

Concentration, gL-1

Wool/Acid dyes

146

3.3.2 Effect of Wash-off on Fibre Topography

SEM analysis of dyed fabrics followed by different wash-off conditions, Table 3.7,

showed that the fibre surfaces were relatively smooth and uniform for the DSW dyed

fabrics. Similarly, no cracking or etching on the surface of wool was visible for SSW

dyed fabric at a magnification of 1.0K, Figure 3.5a. However, examination of the fibre

surfaces at higher magnification indicated some particulates were present on the fibre

surface, Figure 3.5b. Fabric dyed in DSW also exhibited similar surface properties,

albeit in a lower quantity. Examination of the surface particulates using X-ray

microanalysis indicated the absence of sodium, magnesium, calcium or chloride or other

inorganics and suggested that the material was organic in nature, Figure 3.6.

Figure 3.5 SEM micrographs of dyed wool fabric washed in a) 2 gL-1

detergent at room

temperature for 10 minutes in SSW, magnification x 1.0 K; b) 2 gL-1

detergent at 70°C

for 10 min in SSW, magnification x4.0 K.

a) b)

Wool/Acid dyes

147

Figure 3.6 SEM X-ray microanalysis of dyed wool that had been washed in 2 gL-1

detergent at room temperature for 10 minutes in DSW.

Although SEM/EDX analysis showed none of the wash-off processes left any sodium

chloride deposits on the fibre surface, a 2gL-1

at 70°C for 10 minutes standard wash-off

process was selected for further studies.

3.3.3 Effect of Saline Environment on Wool

The wettability of fibre in dyeing medium is very crucial factor, as it can influence the

uptake of dyes from the solution. The outer layers of the fibre surface plays an

important role in wettability and dye penetration and the permeability of water is

influenced by cell membrane lipids [16]. The interaction between wool and liquid water

is complex and depends on the binding strength, with water being bound to wool with

Wool/Acid dyes

148

varying strength [17]. Both adsorption to the surface and swelling are reported to

contribute to fibre wettability [18, 19]. Chemical degradation of wool results in

cleavage of the surface long chain fatty acids linked by ester and thioester bonds to the

surface protein [20].

In a study of water absorbency in untreated wool in the presence of 1M salt solution at

29°C, Nostro [16] showed that behaviour of wool in highly saline water depends on the

specific ion-ion pairing, which follows ‘Hofmeister effects’ and is dominated by

dispersion forces. Anions and cations have different effects on the water absorption

where anions induce stronger variations in the amount of absorbed water. When

compared to water with no salts, anions can reduce water absorbency significantly, with

the following order sequence, Scheme 3.2:

F- ≈ HCOO

- > WO4

2- > SO3

2- ≈ SO4

2- > VO3

- > Cl

- > SiF6

2- > H2PO4

- ≈ IO3

- ≈ CO3

2- >

NO3- > SeO4

2- > ClO3

- > Br

- > NO2

- > CH3COO

- > BrO3

- > I

- > ClO4

- ≈ SCN

- > N3

- >

PO43-

> CrO42-

Scheme 3.2 Effects of anions on water absorbency

Similarly when cations are considered, trivalent ions have lower solubility compared to

divalent or monovalent species. Thus for chlorides the absorbency order is, Scheme 3.3.

Al3+

> Cr3+

> Mg2+

> Ca2+

> K+ ≈ NH4

+ > Rb

+ ≈ Na

+ ≈ Sr

2+ > Cs

+ > Ba

2+ ≈ Li

+

Scheme 3.3 Effects of cations of chlorides on water absorbency

This peculiar behaviour of chlorides with different cations can be attributed to the

interplay of the positive and the negative ions, and essentially depends on the specific

ion pair.

3.3.4 Effects of Salts on Wool/Acid Dye System

Wool contains both cationic and anionic functionalities, and under acidic dyeing

conditions ionic interactions prevail as main bonding mechanism with fibre. However, it

was reported that salt affects both ionic and hydrophobic interactions between the fibre

and dye [21], and this phenomenon has been reported for both acid and cationic dyes

[22, 23], where salt affects the dyeing properties by reducing ionic interactions between

fibre and dye. Thus for acid and cationic dyes, salt reduces dye sorption due to reduced

Wool/Acid dyes

149

ionic attraction between dye and fibre, whereas for direct and reactive dye, salt

increased dye sorption due to reduced ionic repulsion between dye and fibre [24]. It has

been reported that in saline dyebath the dye sorption is a function of combined effects of

ionic and physical interactions [23, 25, 26, 27]. At low salt concentration (e.g. <

0.05M), electrolytes provide stronger ionic interactions than physical interactions,

which resulted in decreased dye sorption. In contrast when salt concentration increased

(e.g. > 0.50M), for some anions such as sulphates and phosphates, the effect of physical

interactions exceeded the ionic interactions resulting an increased dye sorption [24].

The exhaustion levels of the 15 dyes onto wool in DSW and SSW was in the range of

78% to 98%, Table 3.9, 3.10 and 3.11. The swelling of wool can be affected by salts,

acids and other chemicals [28] and exhaustion values depend on the structure of fibre

and dyeing conditions. However, it appears SSW does not have any major impact on the

uptake of dyes into wool fibre. It has been reported that that sorption of dyes also

depends on type of electrolytes. NaCl and NaNO3 reportedly decreased the dye

adsorption due to the reduction of ionic attraction, but for Na2SO4 and NaH2PO4 the

adsorption behaviour is less clear [24, 29]. Therefore the slightly increased value of

exhaustion observed in some cases in the SSW dyeing can be explained by the

increased physical interactions between the dye and fibre. This result agreed with other

studies where at very high concentrations of salt dye sorption increased for acid dyes on

wool [25, 26]. This phenomenon is explained by increased hydrophobic/ physical

interactions between the dye and fibre, although a salt-out effect has also been widely

considered. The salt-out effect results in a strong interaction between water and salt

ions, and as the relative concentration of dye increases the dye sorption increases [26].

The addition of Na2SO4 as reported by Duffield [3] increased exhaustion for the

levelling and fast acid dyes, such as Sandolan E and Sandolan MF, respectively. In the

absence of Na2SO4, SSW dyed fabric produced similar exhaustion values indicating the

salts present in SSW fulfilled the function of the Glauber’s salt.

Wool/Acid dyes

150

Table 3.9 Exhaustion levels of Acid Red dyes at 0.05, 1.0 and 3.0% o.m.f. on wool

Dye Applied

Dye Exhaustion, % at Specified Application Level

0.05%

o.m.f.+

0.05%

o.m.f. *

1.0%

o.m.f.+

1.0%

o.m.f.*

3.0%

o.m.f.+

3.0%

o.m.f.*

Lanasan Red CF-WN 95.1 96.0 91.0 90.8 90.8 90.4

Sandolan Rubylon E-3GSL 95.2 94.3 92.2 90.8 90.4 91.6

Sandolan Red MF-GRLN 98.0 98.1 89.2 90.6 81.0 79.3

Lanasyn Red S-G 97.9 97.4 94.3 93.4 92.9 92.4

Lanaset Red G 98.0 96.7 85.9 89.7 84.8 87.6

+ Dyed in distilled water

* Dyed in simulated seawater

Table 3.10 Exhaustion levels of Acid Blue dyes at 0.05, 1.0 and 3.0% o.m.f. on wool

Dye Applied


0.05%

o.m.f.+

0.05%

o.m.f. *

1.0%

o.m.f.+

1.0%

o.m.f.*

3.0%

o.m.f.+

3.0%

o.m.f.*

Lanasan Brilliant Blue CF-BA 97.2 96.5 89.9 90.2 80.3 82.2

Sandolan Blue E-FBLL 98.0 96.9 97.4 95.8 96.9 95.9

Sandolan Blue MF-GL 92.9 93.3 91.1 91.8 88.4 90.8

Lanasyn Blue S-GB 93.7 91.7 88.2 87.6 83.2 85.0

Lanaset Blue 2R 93.0 97.8 93.5 94.5 92.3 92.5



Table 3.11 Exhaustion levels of Acid Yellow dyes at 0.05, 1.0 and 3.0% o.m.f. on wool

Dye Applied


0.05%

o.m.f.+

0.05%

o.m.f. *

1.0%

o.m.f.+

1.0%

o.m.f.*

3.0%

o.m.f.+

3.0%

o.m.f.*

Lanasan Brilliant Yellow CF-BA 96.2 95.6 86.6 85.7 88.8 87.3

Sandolan Yellow E-2GL 97.8 96.7 96.0 96.3 95.9 96.2

Sandolan Golden Yellow MF-RLN 84.5 89.4 83.5 85.1 80.4 77.4

Lanasyn Yellow S-2GL 93.8 92.1 90.1 88.4 89.2 87.2

Lanaset Yellow 2R 94.1 94.1 84.6 81.0 82.2 80.8



Wool/Acid dyes

151

Exhaustion levels of the black dyes range onto the wool was similar for DSW and SSW

dyeings, Table 3.12. The results for Lanasyn Black S dye has not been presented since

it was not entirely soluble in SSW and was very sensitive to the presence of Ca2+

and

Mg2+

ions, even in the presence of levelling agents. As a result unlevel dyeing with dark

and light colour patches were observed on the fabrics particularly for higher depths of

shade, Figure 3.7. This observation supports the study reported by Speakman and Clegg

[30], where higher aggregation dyes in solution will be salted out more easily and will

produce unlevel dyeing. Since the structure of Lanasyn black dye is unknown, the

interaction of the dye with the salt solution cannot be easily established, but it is likely

that the aggregation behaviour depends on dye structure [10] and the relatively higher

salinity in this study increased aggregation.

Table 3.12 Exhaustion levels of Acid Black dyes at 1.0, 2.0 and 4.0% o.m.f. on wool

Dye Applied


1.0%

o.m.f. +

1.0%

o.m.f. *

2.0%

o.m.f. +

2.0%

o.m.f. *

4.0%

o.m.f. +

4.0%

o.m.f. *

Lanaset Black B 80.8 83.6 82.9 81.2 83.5 86.5

Sandolan Black NR 88.1 86.8 88.5 86.3 85.8 91.5

Everacid Black LD 79.9 78.8 79.7 78.9 77.0 79.7



Figure 3.7 Wool Fabrics Dyed with Lanasyn Black S dye: left dyeing in DSW and right

dyeing in SSW a) 1.0% o.m.f.; b) 4.0% o.m.f.

b) a)

Wool/Acid dyes

152

3.3.5 Colour Characteristics

In this research three application levels of dye were used to determine the build-up of

colour on wool in DSW and SSW dyebath and λmax to measure colour strength, K/Sλmax,

was within acceptable 5 nm ranges to each other.

Table 3.13, 3.14, 3.15, and 3.16 indicated that increasing the dye application level

similarly increased K/Sλmax of the fabrics dyed in DSW and SSW, irrespective of the

saline solution of SSW. In general, the K/Sλmax values of the fabrics dyed in SSW, for all

the dye ranges, were comparable to the DSW dyeings, as expected from the exhaustion

values in 3.3.4. For Lanasyn Red and Blue dyes and Yellow dyes, at the 3% o.m.f.

level, higher K/Sλmax values were observed, possibly due to the increased hydrophobic

interactions. The on-tone dye build up with increasing dye application indicated that

successful dyeing could be achieved in SSW with the milling to metal dye complex

ranges.

Table 3.13 K/Sλmax, of Acid Red dyes at 0.05, 1.0 and 3.0% o.m.f. on wool fabric

Dye Applied

K/Sλmax

0.05%

o.m.f.+

0.05%

o.m.f.*

1.0%

o.m.f.+

1.0%

o.m.f.*

3.0%

o.m.f.+

3.0%

o.m.f.*

Lanasan Red CF-WN 0.5 0.5 7.5 6.8 23.3 22.4

Sandolan Rubylon E-3GSL 0.7 0.7 8.2 7.9 20.2 19.1

Sandolan Red MF-GRLN 0.8 0.8 10.0 10.0 26.1 25.6

Lanasyn Red S-G 0.8 0.9 15.2 15.3 29.8 33.9

Lanaset Red G 0.9 0.9 11.0 10.8 27.0 27.9



Wool/Acid dyes

153

Table 3.14 K/Sλmax, of Acid Blue dyes at 0.05, 1.0 and 3.0% o.m.f. wool fabric

Dye Applied

K/Sλmax

0.05%

o.m.f.+

0.05%

o.m.f.*

1.0%

o.m.f.+

1.0%

o.m.f.*

3.0%

o.m.f.+

3.0%

o.m.f.*

Lanasan Brilliant Blue CF-BA 0.7 0.6 9.2 8.9 24.4 25.1

Sandolan Blue E-FBLL 0.6 0.6 3.1 3.2 12.6 10.1

Sandolan Blue MF-GL 0.8 0.8 9.9 10.4 27.9 27.5

Lanasyn Blue S-GB 0.5 0.4 7.4 6.5 21.7 22.2

Lanaset Blue 2R 0.6 0.6 8.5 8.4 24.5 24.5



Table 3.15 K/Sλmax, of Acid Yellow dyes at 0.05, 1.0 and 3.0% o.m.f. on wool fabric

Dye Applied

K/Sλmax

0.05%

o.m.f.+

0.05%

o.m.f.*

1.0%

o.m.f.+

1.0%

o.m.f.*

3.0%

o.m.f.+

3.0%

o.m.f.*

Lanasan Brilliant Yellow CF-BA 1.0 0.9 6.7 6.5 18.2 19.7

Sandolan Yellow E-2GL 1.3 1.2 8.0 10.4 23.1 23.2

Sandolan Golden Yellow MF-RLN 1.3 1.4 12.7 12.7 26.8 27.1

Lanasyn Yellow S-2GL 0.8 0.8 9.3 8.6 24.4 27.6

Lanaset Yellow 2R 0.9 0.8 6.4 6.9 20.4 20.5



Table 3.16 K/Sλmax, of Acid Black dyes at 1.0, 2.0 and 4.0% o.m.f. on wool fabric

Dye Applied

K/Sλmax

0.05%

o.m.f.+

0.05%

o.m.f.*

1.0%

o.m.f.+

1.0%

o.m.f.*

3.0%

o.m.f.+

3.0%

o.m.f.*

Lanaset Black B 7.1 6.3 15.3 13.2 25.4 25.2

Sandolan Black NR 17.2 18.4 29.9 29.8 34.4 33.7

Everacid Black LD 13.9 11.2 22.8 19.5 26.7 29.6



A progressive build-up of colour depth was observed in dyeing of wool with the range

of black dyes with very little batch to batch variation, Table 3.16. Sandolan Black NR

displayed the highest K/Sλmax values over the application levels studied and again the

Wool/Acid dyes

154

Lanasyn Black S data was omitted due to its poor solubility and associated unlevellness.

The resulting colour difference, ΔE*94, between fabrics dyed in DSW and SSW, Table

3.17, and 3.18 was between 1-3 CIE L*a*b* units [31, 32]. Typically differences of

greater than 2 are considered commercially unacceptable [31, 33, 34, 35], while ΔE*94

below 1-2 is commercially acceptable.

Table 3.17 Colour difference, ΔE*94, between Acid Red, Yellow and Blue dyed wool

fabrics dyed in SSW aqueous media with DSW is being the standard.

ΔE*94, at Specified Application Level

Dye Applied 0.05% o.m.f. 1.0% o.m.f. 3.0% o.m.f.

Lanasan Red CF-WN 2.3 3.2 1.0

Sandolan Rubylon E-3GSL 1.8 1.1 1.1

Sandolan Red MF-GRLN 0.9 0.5 0.4

Lanasyn Red S-G 0.9 0.6 1.6

Lanaset Red G 0.4 0.4 0.5

Lanasan Brill Blue CF-BA 1.7 0.7 1.2

Sandolan Blue E-FBLL 2.0 0.8 1.9

Sandolan Blue MF-GL 1.5 0.5 0.6

Lanasyn Blue S-GB 0.6 1.6 1.0

Lanaset Blue 2R 1.5 0.6 0.7

Lanasan Brilliant Yellow CF-BA 1.6 2.3 3.7

Sandolan Yellow E-2GL 1.8 2.9 0.9

Sandolan Golden Yellow MF-RLN 3.0 1.2 2.0

Lanasyn Yellow S-GB 1.5 1.6 2.5

Lanaset Yellow 2R 1.4 1.6 0.7

Table 3.18 Colour difference, ΔE*94, between Black dyed wool fabrics dyed in SSW

aqueous media with DSW is being the standard.

ΔE*94, at Specified Application Level

Dye Applied 1.0% o.m.f. 2.0% o.m.f. 4.0% o.m.f.

Lanaset Black B 0.3 2.1 2.6

Sandolan Black NR 2.4 0.1 0.3+

Everacid Black LD 2.4 0.4 0.6

Wool/Acid dyes

155

The most notable colour difference between DSW and SSW dyeings was found for

lighter depths, particularly for yellow, blue and black dyes, which indicated that SSW

may not be suitable for pastel shades. However, when the depth of shade increased the

colour difference diminished. The Lanasan CF and Sandolan E dye ranges showed the

highest variation, which may be due to the increased dye sorption due to enhanced

hydrophobic interactions leading to increased K/Sλmax values. Among them, the variation

in yellow dyes in particular resulted increased differences, which may be due to the

effect of salts on the dye structure as the type of dye varied from metal complex to

milling dyes. Since there was on tone build-up colour, the effect of salts on the

chromogen and auxochrome is important and it might be possible to get lower ΔE*94 by

decreasing the concentration of dyes when the K/Sλmax value is higher in SSW and vice

versa [36]. In contrast the black dyes, Table 3.18, showed almost no difference as the

colour depth increased.

3.3.6 Fastness Properties

Examination of the colour fastness of wool fabrics dyed with the acid dye ranges

indicated that the fastness properties of wool fabrics dyed in DSW and SSW were

comparable, Table 3.19 and 3.20. The wash fastness ratings for the dyed fabrics were in

general commercially acceptable, except for the Sandolan E range, where ratings of 2-3

were observed. Nevertheless these ratings were comparable in DSW and SSW,

reflecting the inherent nature of lower fastness of the levelling dye class [37]. The level

of cross-staining for the dyed fabrics was in general fair to excellent for light and deep

shades with the wool and nylon consistently the most discoloured components in the

multi-fibre strip due to the higher substantivity of acid dyes towards those fibres.

The dry rubbing fastness rating of both the DSW and SSW dyed fabrics was very good

to excellent, Table 3.19 and 3.20. Similarly, the light fastness of both the DSW and

SSW dyed fabrics were in the grey scale 3-5 range.

Wool/Acid dyes

156

Table 3.19 Fastness performance of Lanasan, Lanaset and Lanasyn dyed wool fabrics.

Dye %

o.m.f.

Wash

Fastness

Wool

Staining

Nylon

Staining

Dry Rub

Fastness

Light

Fastness

DSW SSW DSW SSW DSW SSW DSW SSW DSW SSW

Lanasan Red

CF-WN

0.05 5 5 4/5 4/5 4/5 4/5 5 5 2/3 2/3

1.0 4/5 4/5 4/5 4/5 4 4 4/5 4/5 2/3 2/3

3.0 4/5 4/5 5 5 3/4 3/4 4 4 3/4 3/4

Lanasan

Brilliant Blue

CF-BA

0.05 5 5 5 5 4/5 4/5 5 5 3/4 3/4

1.0 4/5 4/5 5 5 4 4 4/5 4/5 4 4

3.0 3/4 4 5 5 4 3/4 4/5 4/5 4/5 4/5

Lanasan

Brilliant

Yellow

CF-BA

0.05 5 5 5 5 4/5 4/5 5 5 3 3

1.0 4/5 4/5 4/5 4/5 4 4/5 5 5 4/5 4

3.0 4 4 4/5 4/5 4/5 4/5 4/5 4/5 5 5

Lanaset Red

G

0.05 4/5 4/5 4 4/5 5 5 5 5 4 4

1.0 4/5 5 4 4 5 5 4/5 4/5 4 4

3.0 4/5 4/5 4 4 4/5 4 4/5 4 5 5

Lanaset

Yellow 2R

0.05 5 4/5 4/5 4 4/5 4/5 5 5 5 5

1.0 4/5 4/5 4/5 4/5 4/5 4/5 5 5 5 5

3.0 5 4/5 4 4 4/5 4 4/5 4/5 5 5

Lanaset Blue

2R

0.05 4/5 4/5 4 4 5 5 5 5 4 4

1.0 4 3/4 4 4 4 4/5 4/5 4/5 4 4

3.0 3/4 4 4 4 4 4 4 4 4 4

Lanasyn Red

S-G

0.05 4/5 4/5 4 4 5 5 5 5 3 3

1.0 4/5 4 4 4 4 4 4/5 4/5 3/4 3/4

3.0 4/5 4/5 4 3/4 3/4 3 4 4 4/5 4/5

Lanasyn Blue

S-GB

0.05 4/5 4/5 4/5 4/5 4/5 4 5 5 4 4

1.0 4/5 4 4 4 4 3/4 4/5 4/5 3/4 3/4

3.0 5 5 4 4 4 2/3 4 4 3/4 3/4

Lanasyn

Yellow

S-GB

0.05 5 5 4 4 5 5 5 5 4/5 4/5

1.0 4/5 4/5 4 4 4/5 4 5 5 5 4/5

3.0 4/5 4/5 4 4 4 3/4 4/5 4/5 4/5 4/5

Wool/Acid dyes

157

Table 3.20 Fastness performance of Sandolan E and Sandolan MF dyed wool fabrics

Dye %

o.m.f.

Wash

Fastness

Wool

Staining

Nylon

Staining

Dry Rub

Fastness

Light

Fastness


Sandolan

Rubylon

E-3GSL

0.05 3/4 3/4 4/5 4/5 4/5 4/5 5 5 4/5 4/5

1.0 3 2/3 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

3.0 2/3 2/3 4 4 4/5 4/5 4 4 4/5 4/5

Sandolan

Blue

E-FBLL

0.05 3 2 3/4 4/5 4/5 4/5 5 5 4 4

1.0 2/3 2 4/5 4 4/5 4/5 4/5 4/5 4 4

3.0 2/3 2 4 2/3 3 3 4/5 4/5 4/5 4/5

Sandolan

Yellow

E-2GL

0.05 3 2/3 4 4 4/5 4/5 5 5 4/5 4/5

1.0 3 2/3 4 4 3/4 4 5 5 4/5 4

3.0 2/3 2/3 4 4 3 2/3 4/5 4/5 5 5

Sandolan

Red

MF-

GRLN

0.05 4 4 4/5 4/5 4/5 4/5 5 5 4/5 4/5

1.0 4 4 4 3/4 3 2/3 4/5 4/5 4 4

3.0 4 4 3/4 3/4 2 2 4 4 4/5 4/5

Sandolan

Blue

MF-GL

0.05 4/5 4 4/5 4/5 4/5 4/5 5 5 4/5 4/5

1.0 4 3/4 3 3 2/3 2/3 4/5 4/5 4 4

3.0 3/4 4 3 3 2/3 2/3 4 4 4/5 4/5

Sandolan

Golden

Yellow

MF-RLN

0.05 4/5 4/5 4/5 4/5 4/5 4/5 5 5 4/5 4/5

1.0 3/4 3/4 3/4 3/4 3 3 4/5 4/5 4/5 4/5

3.0 3/4 3/4 3 3 2/3 2/3 4 4 4/5 4/5

The level of cross-staining, Table 3.21, for the black dyes was overall comparable.

Wash fastness and cross-staining was lowered in Sandolan Black and Everacid black

dyes as the depth increased. The cross-staining of the nylon components for Lanaset

Black dyes at 4.0% depth showed a maximum difference of 1.0 grey scale units.

Wool/Acid dyes

158

Table 3.21 Fastness performance of Acid Black dyed wool fabrics.

Dye %

o.m.f.

Wash Wool Staining

Nylon

Staining

Dry Rub Light

Fastness Fastness Fastness


Lanaset

Black B

1 3/4 4 4 4 4/5 4/5 4/5 4/5 4/5 4/5

2 4 4 4 4 4 4 4/5 4 5 5

4 4 4 4 4 4/5 3/4 4/5 4 5 5

Sandolan

Black

NR

1 4 4 4/5 4/5 4 4 4/5 4/5 4/5 4/5

2 3/4 3/4 3/4 3/4 3/4 4 4/5 4/5 4 4

4 3 3/4 3/4 3/4 3 2/3 4 4 4/5 4/5

Everacid

Black

LD

1 4 4 4 4 4 4 4/5 4/5 3/4 3/4

2 3/4 3/4 3/4 4 3/4 4 4 4 4 4

4 3/4 3/4 3 3 3/4 3/4 4 4 4/5 4/5

3.3.7 Kawabata Evaluation System (KES) Analysis [38]

Table 3.22 illustrates the major difference in handle properties exhibited by the fabric

dyed with 4 dyes in DSW and SSW at 3.0% o.m.f. depth. The mixed tensile resilience

(RT), elongation (EM), compressive resilience (RC) and shear rigidity (G) indicated

that the effect of dyeing in SSW was negligible on the fabric’s mechanical properties.

Inter-yarn friction, 2HG5, is a sensitive indicator of fabric softness [39] and with both

dyeing systems little difference in the dyed fabric’s softness was observed.

The primary hand values for softness, stiffness and smoothness presented in Table 3.23

truly reflected the mechanical and surface properties of the fabrics. The values for the

primary hand qualities are in the range of 0-10 and the higher the value within the

range, the stronger the intensity of this particular hand (tactile) feeling [40]. The results

indicated that the primary hand values were similar for both dyeing systems.

Wool/Acid dyes

159

Table 3.22 Mechanical and surface properties of wool fabrics dyed in DSW and SSW

Parameter

Lanasan Brilliant

Blue CF-BA

Sandolan Yellow

E-2GL

Sandolan Red

MF-GRLN

Lanasyn

Black S

DSW SSW DSW SSW DSW SSW DSW SSW

EMT 13.2 14.4 12.6 12.0 14.7 13.0 13.5 13.7

LT 0.6 0.6 0.6 0.6 0.6 0.7 0.6 0.6

WT 18.2 23.1 18.8 17.6 20.7 21.7 18.5 18.8

RT 57.8 61.8 59.8 62.5 61.5 58.1 64.3 63.7

B 0.1 0.1 0.1 0.2 0.1 0.1 0.1 0.1

2HB 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

G 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4

2HG 0.6 0.6 0.5 0.7 0.5 0.6 0.6 0.6

2HG5 0.8 0.8 0.7 0.8 0.7 0.8 0.8 0.8

MIU 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3

MMD 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

SMD 4.9 5.2 4.9 4.9 5.1 4.9 4.7 4.5

LC 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4

WC 0.7 0.7 0.7 0.7 0.8 0.7 0.7 0.7

RC 50.7 50.2 52.6 52.2 52.1 50.2 50.4 50.6

T 1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.6

W 25.6 26.4 24.3 25.4 25.3 26.5 25.5 25.7

Table 3.23 Primary Hand Values of fabrics dyed in DSW and SSW

PHV Parameter

Lanasan

Brilliant Blue

CF-BA

DSW SSW

Sandolan

Yellow E-

2GL

DSW SSW

Sandolan

Red

MF-GRLN

DSW SSW

Lanasyn

Black S

DSW SSW

Stiffness (Koshi) 2.3 2.3 2.3 3.0 2.7 2.6 2.7 2.7

Smoothness (Numeri) 6.7 6.4 6.5 6.0 6.7 6.4 6.1 6.2

Fullness and Softness

(Fukurami) 8.8 8.6 8.6 8.3 8.1 8.4 8.5 8.4

Wool/Acid dyes

160

3.4 Conclusions

The study found that commercial dyeing processes were robust and can be practically

transferred into the simulated seawater medium. Based on the experimental results, it

can be stated that:

The absorbance/concentration curve at λmax was linear and comparable for all six

dyes in SSW;

Although SEM micrographs didn’t show any presence of salt, a typical wash-off

process of 1gL-1

with a non-ionic detergent at 70°C would be sufficient to remove any

salt that could be present on the surface or sub-surface of the dyed fabric;

At room temperature, some acid and metal complex dyes were only partially

soluble in SSW but this improved with gentle heating and addition of levelling agents.

At dyeing temperatures near the boil, with the exception of Lanasyn S dye, the dyes

were fully soluble during dyeing;

Although ionic interaction was the dominant mechanism for dyeing wool/acid

and metal complex dyes, the adsorption in the saline dyebath most likely depended on

the combined effects of ionic and physical/hydrophobic interactions;

With the exception of Lanasyn Black S, there was relatively little difference in

the colouration of the final dyed fabric. The uptake of dyes was high in a range of 78 to

98% for both DSW and SSW dyes and consistent. In some cases, for example black

dyes at 4.0% o.m.f. depth, the slightly higher exhaustion in SSW can be explained by

the increased hydrophobic interactions between the dye and fibre due to high salt

conditions;

Although with the colour difference, ΔE*94 of Lanasan CF and Sandolan E was

in the range of 0.8 to 3.0, particularly for pastel shades hence not commercially

acceptable, it would be possible to reduce the colour difference by optimising the

dyeing conditions. Indeed some dyes such as Lanasyn S and Lanasan CF displayed

higher colour difference mainly due to the increased sorption in SSW;

The Lanasyn Black S did not dye acceptably in SSW, and low colour strength

and poor uniformity was observed. This was probably related to the dye structure and

the associated lower dye solubility and higher aggregation in seawater. In contrast, all

other black dye performed well in SSW and exhibited good colouration performance

and comparability with the distilled water dyeing;

Wool/Acid dyes

161

Overall the fastness of the SSW dyed fabrics was comparable to the DSW dyed

fabrics with wash, cross-staining, rub and light fastness rated commercially acceptable

ranges of 4 to 5 except for Sandolan MF range, which is a moderate fast dye ;

KE-SF analyses of the dyed fabrics indicated the softness sensitive 2HG5 value

was unaffected by the SSW dyebath and the overall fabric handle was comparable to the

DSW dyed wool.

Wool/Acid dyes

162

3.5 References

1. Rippon, J. A., The Structure of wool, in Wool dyeing, D. M. Lewis, Editor, 1992,

Society of Dyers and Colourists, Bradford.



3. Duffield, P. A., Dyeing wool with acid and chrome dyes, in Wool dyeing, D. M.

Lewis, Editor, 1992, Society of Dyers and Colourists, Bradford.

4. Stakelbeck, H. P. (1999) Economy, ecocompatibility, process optimization, PL

Acid / Metal Complex 2010, Clariant (Schweiz) AG

5. Sandoz, Dyes and chemicals for wool dyeing and finishing, in Business Sector

Textiles, 1994, Sandoz Chemicals Ltd Muttenz.

6. Huntsman, Lanaset dyes: Dyeing system for wool and wool blends, in Textile

Effects, 2007, Huntsman Ltd.

7. Everlight, Everacid, in Acid dyes, 2009, Everligh Chemical industries

Corporation, Taipei.

8. Valkó, E., Particle size in wool dyeing, Journal of the Society of Dyers and

Colourists, 1939, 55 (4), p.173-182.

9. Datyner, A. and M. T. Pailthorpe, A study of dyestuff aggregation. part II. The

influence of temperature on the aggregation of some anionic dyestuffs, Journal

of Colloid and Interface Science, 1980, 76 (2), p.557-562.

10. Datyner, A. and M. T. Pailthorpe, A study of dyestuff aggregation: Part III—The

effect of levelling agents on the aggregation of some anionic dyes, Dyes and

Pigments, 1987, 8 (4), p.253-263.

11. Welham, A. C., ed. The role of auxiliaries in wool dyeing. Wool Dyeing, ed. D.

M. Lewis. 1992, Society of Dyers and Colourists, Bradford, West Yorkshire,

p.88-110.


Enfield, N.H.

13. Clariant, Chemicals wool, in Exhaust dyeing of wool & silk : with Reactive, Acid

& Metal-complex dyes, 2004, Clariant, TLP Division/ BU Textile Cheimcals/ PL

Dyeing and Printing.

14. TPI, Nomenclature of Textile Auxiliaries, in Textilhilfsmittel-Katalog 1991,

TEGEWA, Editor, 1991, Textil Praxis International, Konradin Verlag Robert

Kohlhammer GmbH, Leinfelden-Echterdingen.

Wool/Acid dyes

163

15. Salager, J. L., ed. Surfactants, types and uses. FIRP Booklet no. 300A. 2002,

University of Los Andes, Merido, Venezuela.

16. Nostro, P., L. Fratoni, B. W. Ninham and P. Baglioni, Water absorbency by

wool fibers: Hofmeister effect, Biomacromolecules, 2002, 3 (6), p.1217-1224.

17. Gregorski, K. S., An x-ray diffraction study of thermally-induced structural

changes in alpha-keratin, Adv Exp Med Biol, 1977, 86A, p.329-344.

18. Jones, L. N., D. E. Rivett and D. J. Tucker, Wool and related mammalian fiber

in Handbook of Fiber Chemistry, M. Lewin and E. M. Pearce, Editors, 1998,

Marcel Dekker, Inc., New York.

19. Slade, P. E., Antistats, 2nd ed. Handbook of Fiber Chemistry, 1998, Marcel

Dekker, Inc., New York.

20. Bradley, R. H., I. Mathieson and K. M. Byrne, Spectroscopic studies of modified

wool fibre surfaces, Journal of Materials Chemistry, 1997, 7 (12), p.2477-2482.

21. Yang, Y. Effect of Electrolytes on Hydrophobic Interaction in Dyeing. Proc. in

AATCC International Conference and Exhibition. 1992, Research Triangle Park,

NC, American Association of Textile Chemists and Colorists, p.266-269.

22. Yiqi Yanh, I. and C. M. Ladisch, Hydrophobic Interaction and Its Effect on

Cationic Dyeing of Acrylic Fabric, Textile Research Journal, 1993, 63 (5),

p.283-289.

23. Yang, Y., S. Li and T. Lan, Ion sorption by polyamide with consideration of

ionic interaction and other physical interactions, Journal of Applied Polymer

Science, 1994, 51 (1), p.81-87.

24. Yiqi, Y., Effect of salts on physical interactions in wool dyeing with acid dyes,

Textile Research Journal, 1998, 68 (8), p.615-620.

25. Bell, J. P., Effect of fiber and dyebath variables on the rate of acid dyeing of

nylon 6, 6, Textile Research Journal, 1968, 38 (10), p.984-989.

26. Vickerstaff, T., The Physical Chemistry of Dyeing, 1954, Imperial Chemical

Industries, London, U.K.

27. Alberghina, G., S. Fisichella and S. Occhipinti, Donnan approach to equilibrium

sorption: influence of electrolytes on dyeing of Dralon X-100 with CI Basic Blue

3, Textile Research Journal, 1990, 60 (9), p.501-507.

28. Bird, C. L., The theory and practice of wool dyeing, 4th ed, 1972, Society of

Dyers and Colourists, Bradford.

29. Bell, J. P., W. C. Carter and D. C. Felty, Dye concentration profiles within

single nylon filaments, Textile Research Journal, 1967, 37 (6), p.512-516.

Wool/Acid dyes

164

30. Speakman, J. B. and H. Clegg, Some Relationships between the Chemical

Constitution and Levelling Properties of Acid Dyes as applied to Wool, Journal

of the Society of Dyers and Colourists, 1934, 11 (50), p.348-365.

31. Tzanov, T., S. Costa, G. M. Guebitz and A. Cavaco-Paulo, Effect of temperature

and bath composition on the dyeing of cotton with catalase-treated bleaching

effluent, Coloration Technology, 2001, 117 (3), p.166-170.

32. Chen, C.-C., R. H. Wardman and K. J. Smith, The mapping of a surface of

constant visual depth in CIELAB colour space, Coloration Technology, 2002,

118 (6), p.281-294.

33. Harold, R. W., Textiles: appearance, analysis and shade sorting, Textile

Chemists and Colorist, 1987, 19 (12), p.23-31.

34. Li, Y. S. W., C. W. M. Yuen, K. W. Yeung and K. M. Sin, Regression analysis

to determine the optimum colour tolerance level for instrumental shade sorting,

Coloration Technology, 1999, 115 (3), p.95-99.

35. Bauman, W., R. Brossman, B. T. Grobel, N. Kleinemeier, M. Krayer, A. T.

Leaver and H. P. Oesch, Determination of relative color strength and residual

color difference by means of reflectance measurements. Part II. Determination

of residual color difference, Textile Chemists and Colorist, 1987, 19, p.21-22.

36. Tzanov, T., S. Costa, G. M. Guebitz and A. Cavaco-Paulo, Dyeing in catalase-

treated bleaching baths, Coloration Technology, 2001, 117 (1), p.1-5.

37. Lewis, D. M., Dyeing wool with reactive dyes, in Wool dyeing, D. M. Lewis,

Editor, 1992, Society of Dyers and Colourists, Bradford.

38. Bishop, D. P., Fabrics: Sensory and mechanical properties, Textile Progress,

1996, 26 (3), p.1-62.

39. Sule, A. D. and M. K. Bardhan, Objective evaluation of feel and handle,

appearance and tailorability of fabrics. Part-II: The KES-FB system of

Kawabata, Colourage, 1999, 46, p.23-28.

40. Radhakrishnaiah, P., S. Tejatanalert and A. P. S. Sawhney, Handle and comfort

properties of woven fabrics made from random blend and cotton-covered

cotton/polyester Yarns, Textile Research Journal, 1993, 63 (10), p.573-579.

Wool/Reactive dyes

165

4. Dyeing of wool with Reactive dyes

4.1 Introduction

Reactive dyes have been developed for wool in order to achieve better wash fastness

through the covalent bonding between the dye and fibre [1, 2]. Therefore, the reactive

dye is unique among dyes, where the dye and fibre substrate share electrons to form a

bond and the energy required to split this bond is similar to a carbon-carbon bond in the

substrate itself [3]. Although commercial usage is still relatively new the awareness of

the potential for reactive dyes was recognised much earlier in 1932 [4, 5]. At present,

reactive dyeing of wool is increasingly preferred over metal-complex dyes, despite their

good fastness properties, particularly for deep shades of black and navy blue [5], and to

increasing environmental pressure . In contrast to acid dyeing of wool, levelness is a

significant problem in reactive dyeing of wool, due to the difficulties with diffusion and

migration processes, especially once the dye is fixed [5].

The most commercially successful reactive dyes for wool have been the Lanasols and

were introduced in 1966 by Ciba-Geigy. These dyes are based on the α-

bromoacrylamide (-NHCO-C(Br)=CH2) functionality although is usually referred to as

α,β-dibromopropionylamide, believed to be the precursor of α-bromoacrylamide dyes

[3]. Lanasol dyes, along with a proprietary levelling agent, Albegal B, have eliminated

the initial levelling problems associated with reactive dyes [6]. Lanasol dyes for wool

dyeing react either by nucleophilic substitution or by a Michael addition reaction [3],

with the possible formation of aziridine derivatives [7], Scheme 4.1.

D-NH-C-C=CH2

Br

peptide NH2

substitution

reaction

addition

reaction

wool fragment

aziridine derivatives

aziridine ring

D-NH-C-C=CH2

D-NH-C-CH-CH2

NH-peptide

NH-peptideD-NH-C-CH-CH2

Br

NH-peptide

Scheme 4.1 Possible formation of groups after nucleophilic and addition reactions with

Lanasol reactive dye and wool [7]

Wool/Reactive dyes

166

After the research of wool/acid and metal complex dyes in Chapter 3, this study of

reactive dyeing on wool in simulated seawater (SSW) environment provides another

processing opportunity but very much with the background that reactive dyes are

considered to be sensitive to water hardness and ions such as Ca2+

and Mg2+

[8, 9]

which are often present in SSW in significant amounts [10]. In contrast, the exhaustion

of reactive dye on cotton increases greatly in the presence of electrolytes such as sodium

chloride [8, 9].

4.2 Experimental

4.2.1 Materials

Scoured woven wool fabric (2/2 twill, 295 gm-2

) was supplied by Whaley’s Bradford.

The compatible trichromatic system of α-bromoacrylamide Lanasol reactive dyes were

evaluated in the study without further purification. These dyes were Lanasol Red 6G

(C.I. Reactive Red 84), Lanasol Blue 3G (C.I. Reactive Blue 69) and Lanasol Yellow

4G (C.I. Reactive Yellow 39), Figure 4.1. All of the dyes are disulphonated and contain

one reactive group. The reactive red and yellow dyes are azo based whereas the

reactive blue dye is anthraquinone-based [11],

Figure 4.1 Chemical structure of (a) C.I. Reactive Red 84 [12]; (b) C.I. Reactive Blue

69; (c) C.I. Reactive Yellow 39 [13].

(a)

(b)

(c)

Wool/Reactive dyes

167

The levelling agent, Albegal B is a derivative of an ethoxylated fatty acid amine [14]

with a general chemical structure of Figure 4.2 [3] . It was described as a representative

of the modern dyebath additives used for reactive dyeing of wool fibre [15]. The

Albegal B was used with wetting agent Matexil WA-KBN (ICI). Glauber’s salt

(Na2SO4) was used only for DSW dyeing.

Figure 4.2 Chemical structure of Albegal B [3]

4.2.2 Dyeing

All dyeings were performed in either DSW or SSW at a liquor to goods ratio of 1:10, at

dyeing depths of 0.05, 1.0, 3.0 and 5.0% o.m.f., Figure 4.3. Albegal B was used in all

experiments at the recommended level of 1.0 % o.m.f. [3]. For dyeings at 5.0% o.m.f.,

the amount of Albegal B and Na2SO4 was increased to 2% and 10%, respectively.

Repeat samples were performed; the first series being based on 5 g of fabric, while the

second batch was performed using 30 g fabric.

Figure 4.3 Reactive dyeing profile for wool and post-washing process

a)

1-2 % Albegal B2g/L Wetting agent pH 4.5~5.5 acetic acid

5-10% Na2SO4 (Dst only)

Dyes

5'

100°C

70°C

Room Temperature

4°C/min

3°C/min

60 '

20 '

4°C/min

20'

80°C

1 g/L ammonia pH 8.5~9.5

1. Cold rinse, 5'2. 2g/L washing agent at 70C, 10'

3. Cold rinse, 5'

5°C/min

b)

Wool/Reactive dyes

168

4.2.3 After-treatment and Wash-off

An alkaline after-treatment, using 1 gL-1

ammonia, was performed, Figure 4.4 b, for

fabric dyed in DSW and SSW in a second corresponding “fresh” DSW or SSW bath in

order to improve wet fastness properties, especially in deeper shades of more than 1.0%

o.m.f. [3, 9].

After-treated samples were rinsed with cold water (DSW or SSW) for 5 minutes and

neutralised in 1 gL-1

acetic acid. Afterwards, samples were washed at 70°C for 10

minutes with 2 gL-1

Eriopon R, a non-ionic surfactant, to remove any salt on the fabric

surface, as discussed in Section 3.2.3. Previous studies have indicated the non-ionic

surfactant has no effect on the alkali damage of wool [16]. The fabric was then finally

cold rinsed in DSW and dried under ambient conditions.

4.2.4 Dye Exhaustion and Fixation

In reactive dyeing, hydrolysis during the dyeing process is a significant factor therefore,

in addition to determining the exhaustion, as described in Section 2.7.1, two more

performance criteria were determined. Fixation can been expressed as, %T, the

percentage of total dye fixed or fixation ratio, and, %F, degree of fixation or fixation

quotient, and are, described in Equation 4.1 and 4.2 respectively [3, 17]. T refers to the

dye chemically bound to the sample relative to the dye applied to the sample.

( ⁄

)

( ⁄

) Equation 4.1

Equation 4.2

Where ( ⁄

) and ( ⁄

) are the colour strengths of the dyed samples

before and after washing.


4.3.1 Effect of SSW on Dye Solution

Reactive dyeing in “hard” water has been recognised as a difficult problem in cotton

dyeing where inconsistencies in shades and/or the production of blotches are most

Wool/Reactive dyes

169

common faults. As a result, water softening below 5°dH is recommended [8, 18].

However since there is no reported literature on dyeing wool with reactive dyes in

seawater, therefore, an initial series of experiments with Lanasol Red 6G were

performed in order to determine the absorption behaviour and dyeability of wool with

reactive dyes in SSW. Four depths at 0.05, 1.0, 3.0 and 5.0% o.m.f. were used and

fabrics dyed in both DSW and SSW without any after-treatment. In addition, blank

dyeing (without dye) and dyeing without fabric at 1.0% depth for the entire dyeing

cycle was carried out with or without dyebath chemicals and the dye absorbances were

measured.

The dye absorbance studies indicated that the relationship between dye absorbance and

dye concentration in SSW was linear according to the Beer-Lambert Law for very dilute

solutions [9], Figure 4.4 and 4.5. In addition this linearity was also apparent with DSW,

with little effect on corresponding exhaustion values observed. A slight change of λmax

was observed with or without the presence of chemicals in dyebath however this was

not perceived as a potential problem.

Figure 4.4 Graph of Lanasol Red 6G dye absorbance versus concentration in distilled

water, λmax 499nm and in simulated seawater λmax 496nm, ■ - distilled water dyeing; and

▲ - simulated seawater dyeing.

RDSW² = 0.999

RSSW² = 0.999

0.00

0.50

1.00

1.50

2.00

2.50

0.01 0.03 0.05 0.07 0.09 0.11 0.13 0.15

Ab

sorb

an

ce, A

Concentration, gL-1

Wool/Reactive dyes

170

Figure 4.5 Graph of Lanasol Red 6G dye absorbance versus concentration, ■ - distilled

water dyeing with chemicals, λmax 500nm; ▲ - simulated seawater dyeing with

chemicals, λmax 502nm.

Both blank dyebaths before dyeing were visually clear, Figure 4.6a and 4.6b, however,

after dyeing both DSW dyebaths turned more yellowish than that of SSW, Figure 4.6c

and 4.6d. This may be an indication of wool degradation during boiling in the presence

of auxiliaries and acidic pH. Since dyeing wool in SSW released less colour, a series of

dye solutions at 1.0% o.m.f., without fabric, were performed, and a full dyeing cycle

carried out on each to determine the change in absorbance before and after dyeing,

Table 4.1. There is only a small change in absorbance before and after dyeing,

increasing for dyeing in DSW while decreasing for dyeing in SSW. This observation is

supported by results found by Cegarra, Riva and Aizpurua [1], who concluded that the

presence of electrolytes lowers the absorbance of the dye solution.

RDSW + Chemicals² = 0.998

RSSW + Chemicals² = 0.996

0.00

0.50

1.00

1.50

2.00

2.50

0.01 0.03 0.05 0.07 0.09 0.11 0.13 0.15

Ab

sorb

an

ce, A

Concentration, gL-1

Wool/Reactive dyes

171

Figure 4.6 Blank dyeing of wool (with no dyes), (a) DSW, before dyeing; (b) SSW,

before dyeing; (c) DSW, after dyeing, λmax, 300nm, A, 0.4; (d) SSW, after dyeing, λmax,

300nm, A, 0.3.

Table 4.1 Absorbance of 1.0% dye solution: before and after (without fabric)

Dye solution without fabric Absorbance, A

Before dyeing After dyeing

DSW 14.5 14.8

DSW + chemicals 14.5 15.0

SSW 12.7 12.0

SSW + Chemicals 12.8 12.2

At depths of 0.05 and 1.0% o.m.f. of dye, the dye was readily soluble in SSW at room

temperature; however, at greater than 3.0% o.m.f. the dye was only partially soluble,

Figure 4.7c and 4.8c. During dyeing, dye was exhausted gradually into the fabric

leaving a soluble lighter exhausted dyebath, Figure 4.7d and 4.8d. A similar mechanism

was observed during the disperse dyeing of hydrophobic fibres, known as aqueous

phase transfer, where dye particles are exhausted by the fabric during dyeing, from the

saturated aqueous bulk dispersion [19, 20, 21, 22, 23, 24, 25]. As Albegal B is strongly

recommended for reactive dyeing of wool, the effect of Albegal B on Lanasol dyeing

has been well documented [1, 3, 13, 15, 26, 27, 28]. This levelling agent produces a

more uniform colour [3, 26], as well as considerably enhancing the rate and the extent

of dye uptake leading to high colour yield [13], particularly at lower temperatures [15],

(a) (b) (c) (d)

Wool/Reactive dyes

172

but only works for halogen based reactive dyes [11, 29]. It has been suggested that

Albegal B has disaggregating effects on Lanasol dye solutions [15, 27], potentially

caused by formation of dye complexes, or fibre or surface mechanisms [28, 30]:

The Dye complex mechanism results in the formation of a relatively

hydrophobic complex between the auxiliary and dye which leads to an increased

affinity for the more hydrophobic root of the wool fibre [4];

The Fibre mechanism relates to a greater mobility of dyes inside the fibre due to

the auxiliary and therefore a faster reduction of tip/root differences [28];

The Surface mechanism considers different extents of accumulation of auxiliary

at the tips and roots, resulting in an improved distribution and levelling of dyes

between the two parts of the fibre [28].

This could be an explanation for the level dyeing observed for dyeing in SSW at and

over 3.0% o.m.f. depth.



before dyeing; and d) SSW before dyeing.

a) c) b) d)

Precipitation

before dyeing

SSW shows lighter solution

compared to DSW before dyeing No precipitation

after dyeing

Wool/Reactive dyes

173



before dyeing; and d) SSW before dyeing.

Figure 4.9 Dye solutions of SSW after full dyeing cycle without fabric, a) at 3.0%

o.m.f.; b) 5.0% o.m.f.

In the absence of wool fabric, the partial insolubility of dyes at 3.0 and 5.0% o.m.f.

depth in SSW remained even after the entire dyeing cycle, Figure 4.9, which means the

dye is highly stable to the hydrolysis at the boil under weakly acid conditions and the

dyeing auxiliaries were not able to solubilise reactive dyes. This result is supported by

Precipitation

before dyeing SSW shows lighter solution

compared to DSW before dyeing

No precipitation

after dyeing

a) c) b) d)

a) b)

Precipitation still present after dyeing without fabric

Wool/Reactive dyes

174

other study [7], which showed that even after prolonged boiling of Lanasol dyes for 15

hours with no wool, no bromide ion was liberated.

In view of the results obtained in this initial research, it was found that the existing

dyeing process was feasible to dye wool fabric over 3.0% o.m.f. in SSW and provided

level dyeing. Calculated exhaustion from absorbance values remained comparable,

therefore all subsequent calculations of exhaustion were made based on the calibration

curve for DSW.

Wool fibres swell when immersed in water, and the swelling is further promoted by the

ammonia after-treatment [3]. The presence of electrolytes in SSW could enhance the

swelling, so changes in mass were determined. Fabric was cut into 4 squares, each 5 x

5 cm, and conditioned in a standard atmosphere (20±1°C and 65±2% RH) for 24 hours

and then weighed. Mean values were calculated and % change in mass compared to the

undyed fabric was determined. Figure 4.10 showed the progressive increase in mass

with increasing depth. At a given depth, the change in mass was slightly higher in the

case of SSW, the exception of 0.05% depth. Since the maximum change in fabric mass

between DSW and SSW was just over 1%, analysis for the other dyes was not carried

out.

Figure 4.10 Effect of DSW and SSW on the mass of the dyed fabric at 0.05%, 1.0%,

3.0% and 5.0% o.m.f. depth compared to undyed fabric of 295.0 gm-2

. - distilled

water dyeing; and - simulated seawater dyeing

-1

0

1

2

3

4

5

6

7

0.05% 1.0% 3.0% 5.0%

mass

loss

gain

rati

o, %

Depth of dyeing , o.m.f.

Wool/Reactive dyes

175

4.3.2 Exhaustion and Fixation of Dye

Examination of the data, Table 4.2, indicates the three reactive dyes have higher

exhaustion values in SSW compared to DSW, which can be attributed to the increased

electrolytes present in SSW. Each of the dyed fabrics showed level dyeing, again

highlighting the importance of Albegal B in processing. The results also suggested that

an aqueous dye transfer mechanism for reactive dyeing in SSW works well with the

Albegal B, even in the presence of hard water ions, and achieved the similar level of

exhaustion for untreated wool as demonstrated by Graham [15].

Table 4.2 Exhaustion (%E), Fixation quotient (%F) and Total Fixation (%T) of Lanasol

dyes at 0.05, 1.0, 3.0% and 5.0% o.m.f. on wool fabric

Dye

applied

%E, at Specified Dye application level

0.05% o.m.f. 1.0% o.m.f. 3.0% o.m.f. 5.0% o.m.f.


Lanasol

Blue 3G

%E 93.7 99.5 95.7 98.2 94.6 97.5 91.6 96.3

%F 100 98.9 98.9 94.5 99.9 99.9 98.2 99.2

%T 93.7 98.4 94.7 92.8 94.5 97.4 90.0 95.6

Lanasol

Red 6G

%E 87.4 93.4 96.4 97.6 93.2 98.4 91.8 95.9

%F 99.3 98.6 99.7 100.0 92.7 98.1 95.4 98.7

%T 86.8 92 96.1 97.5 86.4 96.5 87.6 94.7

Lanasol

Yellow

4G

%E 70.6 89.8 91.6 95 86.9 91.9 89.6 87.8

%F 96.2 98.8 96.4 99.9 97.1 99.9 95.7 95.1

%T 67.9 88.7 88.3 94.9 84.4 91.8 85.7 83.6

In reactive dyeing, there is always a possibility of hydrolysed and unfixed dye being

present on the fabric. In order to improve wet fastness, an after-treatment with ammonia

was carried out. In both cases dye substantivity increased significantly at higher depths,

particularly for dyeing in DSW, as evident by %F, Table 4.2.

At the isoelectric region (pH 4 to 5) less damage to wool fibres occurs during dyeing

because of the increased salt linkage cohesion and stabilisation of the fibre. This

stability is disrupted when the aqueous pH is changed to either strongly acidic or

alkaline conditions and this effect is significantly enhanced in the presence of

Wool/Reactive dyes

176

electrolytes. Internal and external pH in wool are also important in dyeing and the

presence of neutral salt reduces the difference in the pH [31]. Peryman [32]

comprehensively studied the effect of solution pH, in the range of 1.5 to 9.0, when

treating wool in boiling liquors for three hours and concluded that there was marked

increase in wool damage in the presence of sodium sulphate in alkaline liquor. Another

study found that amine pre-treatment of wool increased the rate of dyeing, a result of

alkaline modification to the wool surface, particularly prominent in presence of salt

[33]. The slight increase in exhaustion in acidic solution compared to the marked

increase in fixation in alkaline solution concur with the study of Lewis and Seltzer [34].

It was shown that ammonia after-treatment was essential to achieve the maximum

fixation values, and was due to the active fixation of partially hydrolysed reactive dyes

to the wool fibre, which was inactive in cellulose fibres. In acid conditions of the wool

pad-batch dyeing process, the dye residue was in the reactive ketone form and reacted

with highly nucleophilic thiol and amino residues in wool keratin. Overall, %T was in a

range of 83 to 98% for SSW and 85 to 96% for DSW, Table 4.2, and in agreement with

fixation results reported by others in DSW [15, 35].


Figure 4.11, 4.12, 4.13 and Table 4.3 demonstrated a consistent build-up of dye on the

wool fabric, both in DSW and SSW, for three different stages: after dyeing, after

ammonia treatment and after wash-off. It was evident that for deeper shades, dyeing in

SSW produced higher K/Sλmax values in comparison to DSW dyeings, a contrast of the

previous findings where it was reported that electrolytes caused no marked effect on the

colour for hetero bi-functional reactive dyes[11]. Also with the SSW blank dyed fabric,

the changes of K/Sλmax after ammonia treatment in SSW from 0.62 to 0.77, imparted a

more intense shade of yellow. In contrast, little change in the K/Sλmax value was observed

for the fabric in blank dyed in DSW. This again confirmed the observation identified in

Section 4.3.1 where exhausted solutions were clearer in SSW than in DSW solution,

and consequently resulted in a yellowish fabric when blank dyed in SSW.

The effect of ammonia and other aliphatic amines on wool under alkaline conditions has

been previously studied by Asquith, Garcia-Dominguez and other co-workers [36, 37,

38]. Hydrolysis of wool breaks the disulphide cross-links, producing cysteine, which

Wool/Reactive dyes

177

may then be converted to a β-amino acrylic acid residue. This residue could undergo a

variety of reactions in the presence of ammonia producing lanthionine [39] and

ultimately leading to alkali stable cross-links and an associated characteristic yellow

colour. The modification of wool in ammonia was possibly enhanced in the presence of

salt, allowing further dye to react and hence, increasing the K/Sλmax value. The small

change in K/Sλmax before and after ammonia treatment did not correlate with the deeper

shade observed for SSW upon visual inspection, and could be due to the slight change

of texture due to fibre swelling and therefore, a limitation of colour measurement of

spectrophotometer due to surface effect [40, 41].

Figure 4.11 K/Sλmax values of wool dyed with Lanasol Blue 3G dye in DSW and SSW.

- 0.05% DSW; - 0.05% SSW; - 1.0% DSW; - 1.0% SSW; - 3.0% DSW; -

3.0% SSW; - 5.0% DSW; and - 5.0% SSW.

Figure 4.12 K/S values of wool dyed in Lanasol Red 6G dye in DSW and SSW.


3.0% SSW; - 5.0% DSW; and - 5.0% SSW.

0

5

10

15

20

25

30

35

After Dyeing After Ammonia

treatment

After Wash-off

K/S

0

5

10

15

20

25

30

35


treatment

After Wash-off

K/S

Wool/Reactive dyes

178

Figure 4.13 K/Sλmax values of wool dyed in Lanasol Yellow 4G dye in DSW and SSW.


3.0% SSW; - 5.0% DSW; and - 5.0% SSW.

The colour difference, ΔE*94 is commercially acceptable when the range is within 1 to

1.5 units for blue and red dyes after dyeing, whereas a high difference was found for

yellow dyes over 3.0% o.m.f. depth. ΔE*94 was increased, for the majority of

comparable fabrics, from the after dyeing stage to the final after wash-off stage, Table

4.3, indicating that after the ammonia treatment some partial hydrolysed dye was further

bonded to the fibres leading to increased dye exhaustion and fixation, as previously

mentioned. The slight decrease in ΔE*94 between the ammonia treatment stage and

washing is due to the removal of unfixed dye.

Table 4.3 Colour difference of comparable Lanasol dyed wool fabrics in DSW and

SSW at three stages: after dyeing; after ammonia treatment; and after wash-off.

Dye applied

ΔE*94

0.05% o.m.f. 1.0% o.m.f. 3.0% o.m.f. 5.0% o.m.f.

A/D+ A/A* A/W

^ A/D

+ A/A* A/W

^ A/D

+ A/A* A/W

^ A/D

+ A/A* A/W

^

Lanasol Blue 3G 0.7 2.7 2.1 1.1 1.0 3.4 1.1 1.5 0.7 0.8 1.4 1.4

Lanasol Red 6G 1.2 0.6 2.1 0.7 1.1 0.3 0.6 0.7 1.0 1.7 2.1 1.0

Lanasol Yellow 4G 0.7 1.3 1.4 1.4 3.0 3.0 2.1 4.1 3.8 2.2 3.7 3.7

+A/D: After Dyeing, *A/A: After Ammonia treatment, ^A/W: After Wash-off

0

5

10

15

20

25

30

35


treatment

After Wash-off

K/S

Wool/Reactive dyes

179

4.3.4 Colour Fastness Performance

The colour fastness properties of the Lanasol dyed fabrics are shown in Table 4.4,

where excellent colour fastness to light, rubbing and wash fastness were observed.

Generally fastness ratings in a range of 4 to 5, following the ammonia after-treatment

were obtained, which removed hydrolysed/original dye and soluble coloured peptide

material [3]. The improvement in wash fastness by alkaline after-treatment is solely due

to the increased covalent bonding, leading to a high fixation ratio [42].

Table 4.4 Comparison of fastness properties of Lanasol dyed wool fabrics

Dye

applied

%

o.m.f.

Wash

fastness

Staining to adjacent fabric Dry Rub

Fastness

Light

Fastness Wool Nylon Cotton

DSW SSW DSW SSW DSW SSW DSW SSW DSW SSW DSW SSW

Lanasol

Blue 3G

0.05 4/5 4/5 4/5 4/5 4/5 4/5 5 5 5 4/5 4/5 4/5

1.0 4/5 4/5 4/5 4/5 4/5 4/5 5 5 4/5 4/5 4/5 4/5

3.0 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4 4/5 4/5 4/5 4/5

5.0 4 4 4 4 4 3/4 4/5 5 4 4 4/5 4/5

Lanasol

Red 6G

0.05 5 5 4/5 4/5 4/5 4/5 5 4/5 5 5 4 4

1.0 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

3.0 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 5 5

5.0 3 3 4/5 4/5 4/5 4/5 4/5 4/5 4 4 5 5

Lanasol

Yellow 4G

0.05 4/5 4/5 4/5 4/5 4/5 4/5 5 5 5 5 4 4

1.0 4 4 4/5 4/5 4/5 4/5 5 5 5 5 4/5 4/5

3.0 4 4 4/5 4/5 3/4 3 4/5 4 5 4/5 5 4/5

5.0 3/4 4 4/5 4/5 4 4 4/5 4/5 5 4/5 4/5 4/5

Wool/Reactive dyes

180


All types of reactive dyes exert a fibre-protective effect to some extent irrespective of

the functionality [43, 44, 45]. Lanasol reactive dyes as have been shown by Lewis [46],

using a wet burst strength measurements, significantly prevent damage to the wool

fibres at moderate to heavy depths, over 3.0% o.m.f . These dyes are suggested to form

cross-links within the fibre thus enhancing the fibre protective effect, especially at

higher dyeing temperatures. Werkes [47] also demonstrated that at concentrations up to

10.0% o.m.f. the cross-linking dyes imparted a protective effect from alkali degradation.

Figure 4.14 and 4.15 indicate the tensile strength test results clearly supports the work

reported by Lewis and Werkes. Generally, at lower depths, the strength decreased but as

the dye application increased the strength consistently increased. It can also be seen that

this increase in strength was different for the red, blue and yellow dyes, which can be

attributed to dye structure. The increase in strength is more prominent for the yellow

dye with increased strength being as high as 5% and 7% for the warp and weft,

respectively.

Figure 4.14 Tensile strength in warp direction of wool dyed fabric in DSW and SSW at

0.05%, 1.0%, 3.0% and 5.0% o.m.f. application levels compared to blank dyed fabric,

- distilled water dyeing; - simulated seawater dyeing; and Blank dyed fabric.

8.00

8.20

8.40

8.60

8.80

9.00

9.20

9.40

0.05% 1.0% 3.0% 5.0% 0.05% 1.0% 3.0% 5.0% 0.05% 1.0% 3.0% 5.0%

Lanasol Blue 3G Lanasol Red 6G Lanasol Yellow 4G

Ten

sile

str

en

gth

, k

Nm

-1

Wool/Reactive dyes

181

Figure 4.15 Tensile strength in weft direction of wool dyed fabric in DSW and SSW at

0.05%, 1.0%, 3.0% and 5.0% o.m.f. application levels compared to blank dyed fabric,

- distilled water dyeing; - simulated seawater dyeing; and Blank dyed fabric.

The increase in strength can be explained on the basis that α-bromoacrylamide reactive

dyes as well as reacting mono-functionally can potentially react bi-functionally, Scheme

4.2 and so cross-link the protein and reduce protein loss and maintain fibre strength.

Scheme 4.2 Possible further reactions of wool and Lanasol reactive dyes [3]

The nature of fibre-protective effect of reactive dyeing was explained by Lewis and

Smith [48] and involved two mechanisms. Firstly, a sufficient amount of reactive dyes

5.50

5.70

5.90

6.10

6.30

6.50

6.70

6.90

7.10

0.05% 1.0% 3.0% 5.0% 0.05% 1.0% 3.0% 5.0% 0.05% 1.0% 3.0% 5.0%


Ten

sile

str

eng

th, k

Nm

-1

Wool/Reactive dyes

182

present in boiling dyebaths restrict wool fibre setting by interfering the thiol-disulphide

interchange reaction, which blocks cysteine thiol groups and attack hydrogen sulphide.

Lee-Son and Hester [49] obtained a thi-irane ring at 695 cm-1

for C.I. Reactive Red 84,

Scheme 4.3, which supported this mechanism. Secondly, the covalent boding of reactive

dyes may take place at different morphological regions of the wool fibres, preferably

with the non-keratinous regions of cell membrane complex and the endocuticles [5],

where proteins are easily accessible.

Scheme 4.3 Formation of thi-irane ring due to thiol-disulphide interchange reaction


Abrasion is one of the most important factors which can make many textile materials

unserviceable. Abrasion is resulted from the physical destruction of fibres, yarns, and

fabrics due to the rubbing of textile surface over another surface [50]. Abrasion occurs

during washing, wearing, cleaning or any other methods of end use. Certain parts of

apparels such as collar, cuffs and pockets are subjected to heavy wear in use [51]. The

resultant effect is loss of performance characteristics such as strength and appearance of

fabric [52]. Similarly abrasion is a critical problem for carpets and upholstery fabrics,

technical textiles and socks.

Abrasive wear in textiles is caused by friction which could occur due to [53]:

Friction with the same textile material such as rubbing of jacket or coat lining of

a shirt, pockets against pants fabric;

Friction with external objects such as yarn to needles or rubbing of trousers to

the seat;

Friction with the fibres and dust/grit such as swimwear with unremoved sand;

Friction with the fabric components during flexing, stretching or bending of the

fibres.

Abrasion resistance of the textile materials is very complex and can be affected my

many factors such as fibre, yarn, fabric properties and finishing process. Some of these

Wool/Reactive dyes

183

factors affect the surface of the fabric while others have an influence on the internal

structure of the fabric [54]. In the case of woven fabric, weave type, fabric construction,

weight, thickness, thread density and interlacement per unit area are the fabric

properties that can affect abrasion resistance. Similarly in knit fabric, structure plays an

important role as the average abrasion resistance for interlock knitted fabric is higher

than that of rib and single jersey fabrics [55].

Abrasion kinetics can be explained by the surface and structural degradation of the

fabric. During the first stages of abrasion, a surface degradation occurs, which increased

the structural damage as the test progressed. The effect of dyeing on wool fabric was to

reduce the flat abrasion, Figure 4.16 with the strength loss being due to damage to the

cell membrane complex [56, 57]. ‘Wool gelatins’ are known to be produced during

boiling and can be released into solution and can impart a 25% wet strength loss when

gelatin is extracted up to 2% o.m.f. [58]. Previous studies have identified this region as

the weak fracture point in the fibre and that multi-functional reactive dyes can cross-link

the low sulphur protein and maintain fibre strength [59, 60, 61]. Examination of Figure

4.16 indicates the effect of the reactive dyes on abrasion resistance was entirely clear

but the cross-linking effect of the Lanasol dyes may cross-link the cell membrane

complex (CMC), improve CMC cohesion and maintain fibre strength. The SSW

dyeings may be marginally better than the comparable DSW dyeings.

Figure 4.16 Abrasion resistance of wool fabric dyed in DSW and SSW at 0.05%, 1.0%,

3.0% and 5.0% o.m.f. application levels compared to undyed fabric, - distilled water

dyeing; - simulated seawater dyeing; and Blank dyed fabric

0

2

4

6

8

10

12

14

16

18

20

1.0% 3.0% 5.0% 1.0% 3.0% 5.0% 1.0% 3.0% 5.0%


Av

era

ge

no

. o

f cy

cles

Th

ou

san

ds

Wool/Reactive dyes

184

4.4 Conclusions

Reactive dyes were known to be sensitive to hardness of water but this study confirmed

that reactive dyes could be used as an alternative for deep dyeing for wool fibre in SSW.

Based on the experimental study it can be concluded that:

Reactive dye solutions in SSW produce a linear and similar

absorbance/concentration curves to DSW as measured in λmax;

Blank dyeing of wool with no dye, produced a yellower exhausted solution in

DSW than SSW at boiling, indicating possibly a higher wool damage. Similarly after

dyeing solution of blank dyebath without fabric showed a lower absorbance values than

before dyeing solution confirming the previous results that presence of electrolytes

lowers the absorbance of the dye solution;

Lanasol dye is readily soluble in SSW at lower concentrations at room

temperature but at higher application levels, >3.0% o.m.f., the dye was only partially

soluble, even using dyeing temperatures near boiling in the presence of chemicals and

auxiliaries;

Reactive dyeing of wool followed a similar mechanism of gradual phase transfer

as was observed for disperse dyeing of hydrophobic fibres over 3.0% o.m.f. depth.

After-treatment with ammonia increased dye fixation possibly due to more

reactive groups being available in alkaline conditions due to modification of wool,

which could be enhanced in presence of electrolytes. A total fixation of 83 to 98% in

SSW was observed compared to 85 to 96% in DSW;

Coloration properties of the SSW dyed fabric of wool were comparable to DSW

dyed wool except when it produced higher colour strength after dyeing, ammonia

treatment and wash-off. A lower colour difference after wash-off proved that some dyes

were bonded when dye substantivity was increased after ammonia treatment;

Wash, light and rubbing fastness properties of DSW and SSW dyed fabric were

high following ammonia treatment, a characteristic of Lanasol dyes and comparable

performance with DSW and SSW;

The use of monofunctional Lanasol reactive dyes on wool appeared to increase

the tensile strength and abrasion resistance of wool, particularly at greater than 1.0%

o.m.f. application levels, and is probably due to the crosslinking of the protein polymer

and reduced loss of protein gelatin.

Wool/Reactive dyes

185

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5. Lewis, D. M., ed. The coloration of wool. Advances in Wool technology, ed. N.

A. G. Johnson and I. Russell. 2009, Woodhead Publishing Limited in

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6. Burkinshaw, S. M. and K. Gandhi, The dyeing of conventional decitex and

microfibre nylon 6,6 with reactive dyes- I. Chlorodifluoropyrimidinyl dyes, Dyes

and Pigments, 1996, 32 (2), p.101-127.

7. Mäusezahl, D., Die Reaktion von Lanasol-Farbstoffen mit Wolle und

Wollmodellen, Textiiveredlung, 1970, 5.

8. Shamey, R. and T. Hussein, Critical Solutions in the dyeing of cotton textile

materials, Textile Progress, 2005, 37 (1-2), p.1-84.


Enfield, N.H.

10. Culkin, F. and R. A. Cox, Sodium, potassium, magnesium, calcium and

strontium in sea water, Deep Sea Research and Oceanographic Abstracts, 1976,

13 (5), p.789-804.

11. Cho, H. J. and D. M. Lewis, Reactive dyeing systems for wool fibres based on

hetero-bifunctional reactive dyes. Part 1: Application of commercial reactive

dyes, Coloration Technology, 2002, 118 (4), p.198-204.

12. Naebe, M., P. G. Cookson, J. Rippon, R. P. Brady, W. Xungai, N. Brack and G.

van Riessen, Effects of plasma treatment of wool on the uptake of sulfonated

dyes with different hydrophobic properties, Textile Research Journal, 2010, 80

(4), p.312-324.

13. Naebe, M., P. G. Cookson, J. A. Rippon and X. G. Wang, Effects of leveling

agent on the uptake of reactive dyes by untreated and plasma-treated wool,


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14. Clariant, Chemicals wool, in Exhaust dyeing of wool & silk : with Reactive, Acid

& Metal-complex dyes, 2004, Clariant, TLP Division/ BU Textile Cheimcals/ PL

Dyeing and Printing.

15. Graham, J. F., R. R. D. Holt and D. M. Lewis. New possibilities for the low

temperature dyeing of wool. Proc. in 1st International Wool Research

Conference. 1975, Aachen, Germany, p.200-210.

16. Meichelbeck, H. and H. Knittel, Der Einfluß von Anion- und kationtensiden auf

die chemische reaktionsfähigkeit von Wolle, Fette, Seifen, Anstrichmittel, 1971,

73 (1), p.25-29.

17. Zollinger, H., Grundlagen und Problematik des Reaktivf & aumlrbens von

Text, Textilveredlung, 1971, 6, p.57-61.

18. Heetjans, J. H. and R. Tindall, A handbook for the yarn dyer, 1995, Thies GmbH

& Co.

19. Bird, C. L., The dyeing of acetate rayon with disperse dyes. I -Aqueous solubility

and the influence of dispersing agents II -The relation between aqueous

solubility and dyeing properties, Journal of the Society of Dyers and Colourists,

1954, 70 (2), p.68-77.

20. Bird, C. L., Disperse dyes on hydrophobic fibres, Journal of the Society of

Dyers and Colourists, 1956, 72 (7), p.343-351.

21. Bird, C. L., M. P. Harris and F. Manchester, The dyeing of acetate rayon with

disperse dyes III-The influence of dispersing agents on the rate of dyeing,

Journal of the Society of Dyers and Colourists, 1955, 71 (3), p.139-142.

22. Bird, C. L. and F. Manchester, The dyeing of acetate rayon with disperse dyes IV

- The adsorption isotherms, Journal of the Society of Dyers and Colourists,

1955, 71 (10), p.604-609.

23. Bird, C. L., H. K. Partovi and G. Tabbron, The dyeing of cellulose acetate with

disperse dyes VIII– determination of fibre saturation values, Journal of the

Society of Dyers and Colourists, 1959, 75 (12), p.600-604.

24. Clavel, R., Rev. Gen. Matiere Col., 1923, 28, p.145-147, 167-169.

25. Clavel, R. and T. Stanisz, Rev. Gen. Matiere Col., 1924, 29, p.94-96, 158-160,

222-224.

26. Burkinshaw, S. M. and K. Gandhi, The dyeing of conventional and microfibre

nylon 6,6 with reactive dyes. Part 2. α-bromoacrylamido dyes, Dyes and

Pigments, 1997, 33 (4), p.259-280.

Wool/Reactive dyes

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Pigments, 1987, 8 (4), p.253-263.

28. Hannemann, K., Mechanistic investigations on the action of levelling agents in

reactive wool dyeing, Journal of the Society of Dyers and Colourists, 1992, 108

(4), p.200-202.

29. Cho, H. J. and D. M. Lewis, Reactive dyeing systems for wool fibres based on

hetero-bifunctional reactive dyes. Part 2: Investigation of dyeing properties

during the dyeing cycle, Coloration Technology, 2002, 118 (5), p.220-225.

30. Rippon, J. A., The Structure of wool, in Wool dyeing, D. M. Lewis, Editor, 1992,

Society of Dyers and Colourists, Bradford.

31. Baumann, H. and L. Mochel, Textil Praxis, 1974, 29, p.507.

32. Peryman, E. V., The effect on wool of boiling in aqueous solutions i-solutions at

ph 1.5–9 with and without sodium sulphate, Journal of the Society of Dyers and

Colourists, 1954, 70 (2), p.83-92.

33. AlHariri, D. K., I. D. Rattee and I. Seltzer, Improvements in the dyeing of wool

at low temperatures by the use of amine or ammonia pretreatments, Journal of

the Society of Dyers and Colourists, 1978, 94 (4), p.149-155.

34. Lewis, D. M. and I. Seltzer, Pad-Batch dyeing of wool with reactive dyes,


35. Church, J. S., A. S. Davie, P. J. Scammells and D. J. Tucker, Chemical

interactions of α–bromoacrylamide reactive dyes with wool, Review of Progress

in Coloration and Related Topics, 1999, 29 (1), p.85-93.

36. Asquith, R. S. and J. J. Garcia-Dominguez, New amino acids in alkali-treated

wool, Journal of the Society of Dyers and Colourists, 1968, 84 (3), p.155-158.

37. Asquith, R. S. and J. J. Garcia-Dominguez, Crosslinking reactions occurring in

keratin under alkaline conditions, Journal of the Society of Dyers and

Colourists, 1968, 84 (4), p.211-216.

38. Asquith, R. S. and J. D. Skinner, Textilveredlung, 1970, 5.

39. Miro, P. and J. Garcia-Dominguez, Action of ammonium and sodium hydroxides

on keratin fibres in relation to their morphological structure, Journal of the


40. Xin, J. H., H.-L. Shen and C. C. Lam, Investigation of texture effect on visual

colour difference evaluation, Color Research & Application, 2005, 30 (5),

p.341-347.

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41. Williams, S., Practical colour management, Optics & Laser Technology, 2006,

38 (4–6), p.399-404.

42. Carlini, F., U. Meyer and H. Zollinger, Melliand Textilber., 1979, 60, p.587.

43. Flensberg, H. and W. Mosimann. Proc. in 7th International Wool Textile

Research Conference. 1985, Tokyo, Society of Fiber Science and Technology,

5, p.39.

44. Baumann, H. and M. Schepp. Proc. in 7th International Wool Textile Research

Conference. 1985, Tokyo, Society of Fiber Science and Technology, 4, p.372.

45. Ball, P., U. Meyer and H. Zollinger. Proc. in 7th International Wool Textile

Research Conference. 1985, Tokyo, Society of Fiber Science and Technology,

5, p.33.

46. Lewis, D. M., The effect of reactive dyes on damage in wool dyeing, Journal of

the Society of Dyers and Colourists, 1990, 106 (9), p.270-274.

47. Werkes, N., The effect of reactive dyeing on the urea bisulphite solubility of

wool, Melliand Textilber, 1989, 70, p.52-63.

48. Lewis, D. M. and S. M. Smith. Proc. in 8th International Wool Textile Research

Conference. 1990, Christchurch, Wool Research Organisation of New Zealand,

4, p.50.

49. Lee-Son, G. and R. E. Hester, Laser raman studies of bromoacrylamide reactive

dyes on wool Journal of Society of Dyers and Colourists, 1990, 106 (2), p.59-63.

50. Morton, W. E., The designing of fabrics to meet consumers' requirements,

Journal of the Textile Institute Proceedings, 1948, 39 (6), p.187-P192.

51. Hu, J., Fabric testing, 1st ed., 2008, Woodhead Publishing, ISBN

9781845692971.

52. Collier, B. J. and H. H. Epps, Textile Testing and Analysis, 1999, Prentice Hall,

New Jersey.

53. Mehta, P. V., An introduction to quality control for the apparel industry, 1985,

J.S.N. International.

54. Manich, A. M., M. D. de Castellar, R. M. Saurí, R. A. L. Miguel and A. Barella,

Abrasion kinetics of wool and blended fabrics, Textile Research Journal, 2001,

71 (6), p.469-474.

55. Özguney, A., G. Özcelik and K. Özkaya, A study on specifying the effect of laser

fading process on the colour and mechanical properties of the denim fabrics,

Tekstil ve Konfeksiyon, 2009, 19 (2), p.133–138.

Wool/Reactive dyes

189

56. Hine, R. J. and M. J. R. Minimizing damage in dyeing and chemical treatment of

wool. Proc. in 3rd International Wool Textile Research Conerence. 1965, Paris,

3, p.261.

57. Feldtman, H. D. and J. R. McPhee, The spreading and adhesion of polymers on

wool, Textile Research Journal, 1964, 34 (7), p.634-642.

58. Baumann, H., Fibrous proteins-scientific, industrial and medical aspects, D. A.

D. Parry and L. K. Creamer, Editors, 1979, Academic Press, London.

59. Holmes-Brown, R. L., E. J. Wood and G. A. Carnaby, Damage to wool during

stock-dyeing, Journal of the Society of Dyers and Colourists, 1982, 98 (7-8),

p.243-247.

60. Kilpatrick, D. J. and I. D. Rattee. The low temperature dyeing of wool. Proc. in

5th International Wool Textile Conference. 1975, Aachen, II, p.189-193.

61. Zollinger, H. Wool dyes and wool dyeing. Proc. in 5th International Wool

Textile Conference. 1975, Aachen, I, p.167-169.

Polyester/Disperse dyes

190

5. Dyeing of Polyester with Disperse Dyes

5.1 Introduction

Polyester is the most important synthetic textile apparel fibre [1]. The ongoing growth

in the usage of polyester fibre is high [2] due to the fibre’s high strength, dimensional

stability, light stability and suitability for blending with natural fibres [1, 3]. Although

there are many variants of polyester, Polyethylene Terephthalate (PET), Figure 5.1,

remains the predominant fibre type, enjoying worldwide production and commercial

success [4]. Chemically PET fibre is highly resistant to oxidising agents, reducing

agents, many solvents and is hydrophobic in nature. Therefore, hydrophobic disperse

dyes are invariably used for dyeing of polyester fibre [1, 4] and fulfil all types of

commercial needs and applications [1]. Due to their nature, disperse dyes are sparingly

soluble in water at room temperature and contain some polar groups in order to form a

stable dispersion in aqueous dyebaths [5]. The dye essentially should be in

monomolecular form to be absorbed during the high temperature dyeing process and

progressively migrates towards the interior of the fibre allowing more dye to dissolve.

A dispersing agent is used to aid aqueous solubility and to maintain the dye as a stable

dispersion especially at high temperature [4, 6]. High temperature (HT) dyeing at 125-

135°C is now the accepted norm for commercial dyeing of polyester fibres resulting in

shorter dyeing times, better dye migration, high colour yield, excellent coverage of

barré, and superior fastness properties in some cases [4].

Figure 5.1 Chemical structure of PET fibre

Most disperse dyes consists of azo, anthraquinone, pyridone or methine chromophores

and their chemistry has been extensively discussed [4, 7, 8, 9]. It is known that dyeing

processes can be differentially affected by the presence of alkaline-earth metal or heavy

metals such as iron and copper due to the aggregation of dyestuffs [10]. It is reported

that dulling of the colour shade of anthraquinone disperse dyes can occur, although it

varies from dye to dye [11]. The presence of calcium and magnesium cations are

reported to affect anionic dispersing agents, anionic wetting agents and levelling agents


191

[12]. Therefore a sequestering agent is usually used to chelate metal ions and maintain

the dispersion stability, however, their presence in the dyebath can adversely affects azo

dyes, particularly over pH 5-7 [13].

The main aim of this experiment was to study the suitability of commercially

established exhaust dyeing of PET polyester with disperse dyes in a simulated seawater

(SSW) environment as an alternative to freshwater.

5.2 Experimental

5.2.1 Materials

100% polyester double jersey knitted fabric (120 gm-2

, Phoenix Calico, UK) was used

throughout this work. Four disperse dye ranges were used in order to encompass a

realistic commercial application range, In particular the Foron, Dianix, Dispersol and

Terasil ranges and their performance properties are described in Table 5.1. The dye

structures are unknown with the exception of Dianix Yellow 4gSL-FS 400 (C.I.

Disperse Yellow 227), Figure 5.2. Matexil DA-N (a condensate of naphthalene

sulphonic acid and formaldehyde from ICI) was used as the dispersing agent during

dyeing.


192

Table 5.1 Disperse dyes used in this research and their characteristics

Manufacturer Name of Dyestuffs Characteristics

Dystar Dianix Red AC-E Designed for rapid and reliability in dyeing,

and production of high-quality dyeing for

pale shades [14]

Dianix Blue AC-E

Dianix Yellow 6GSL-FS

Dianix Black AD-R

Huntsman/

Ciba

Terasil Red R Suitable for rapid exhaust dyeing with good

levelling properties. The range provides

trichromaticity with acceptable wash fastness

[15].

Terasil Blue R

Terasil Yellow 4G

Terasil Black LBSN

Zeneca Dispersol Rubine XFN Thiophene based azo dyes, developed to

meet most critical wash fastness

requirements for polyester and its blend with

cellulosics. They show high fastness with

almost no staining of adjacent nylon, yellow

and ester fibres in washing tests at 60°C with

detergent [16].

Dispersol Yellow XF

Dispersol Blue XF

Dispersol Black XF

Clariant

Foron Red RD-GL 200% Distinguished by rapid exhaustion, high

diffusion power and are insensitive to

temperature or time deviations and hence

have short fixation times at 130°C. They are

also stable to hydrolysis, hence can be used

over a wide pH range, from pH 4 to 9. These

dyestuffs have low sublimation fastness [17].

Foron Yellow RD -4GRL

Foron Blue RD-GLF

Foron Black RD-3G 300%

Figure 5.2 Structure of Dianix Yellow 4GSL-FS 400 dye (C.I. Disperse Yellow 227)


193

5.2.2 Dyeing

Dianix, Terasil and Dispersol dyeings were performed according to the procedure

illustrated in Figure 5.3 using a Werner Mathis Labomat IR laboratory dyeing machine.

For the Foron RD dyes the dyeing process varied slightly from this procedure. The

temperature was raised to 130°C in two stages, initially at 2°C/minutes up to 100°C and

then at 4°C/minutes. A 5g piece of fabric was dyed with liquor to goods ratio of 10:1 at

pH 4.5 to 5.5, adjusted by acetic acid. Each of the dyes was applied at 0.05%, 1.0% and

2.0% o.m.f. depth of shade. Dispersing agent, Matexil DA-N was added at 1, 2, 2 gL-1

,

respectively. For all Black dyes, the depth was set at 1.0%, 2.0%, and 4.0% o.m.f.

Duplicate dyeing was carried out with 10g of fabric while other parameters remained

constant.

Figure 5.3 Dyeing profile for Dianix, Dispersol and Terasil Dyes [14, 15]

5.2.3 Alkaline Reduction Clearing

The dyed fabric was cold rinsed before alkaline reduction clearing was carried out

according to manufacturer’s instructions in order to remove unfixed surface dye and

oligomer. The process is illustrated in Figure 5.3 using a non-ionic detergent (Eriopon

R) at a liquor ratio of 10:1. After reduction clearing and/or neutralising, the fabric was

cold rinsed and line dried at ambient conditions.

1. Dispersing agent 2. Dyes 3. Alkaline reduction clear 4. Acetic acid

pH 4.5~5.5 acetic acid 1% caustic soda 20°Bé to neutralise

2 gL-1

Hydrosulphite

60°C

4°C/min

3°C/min

2°C/min

30’

80°C

5’

130°C

1 2 20’

3

40°C

4


194


5.3.1 Effect of Simulated Seawater on Dye Dispersion

It was confirmed that, even though dye dispersions do not obey the Beer–Lambert law,

like fully soluble dye solutions, the relationship between dye concentration and the

total light absorbed and scattered was approximately linear [18]. In this context, the λmax

and light absorption behaviour of sixteen dyes were evaluated. During the experimental

work, it was noted that some of the dye dispersions in SSW took a little longer to

produce stable dispersions. However, calibration curves of absorbance versus

concentration were found to be linear for each of the dyes both in DSW and SSW, with

similar gradients, confirming the salt had no effect on dispersion properties. The

inclusion of dispersing agent is important for disperse dyeing providing a higher

apparent solubility for the dye, although it also depends on the nature of the agent.

Addition of dispersing agent during the dyeing process makes the dispersion stable. It

was also reported that in presence of alkali metal salts, such as calcium ions, the

dispersibility of ligninosulphate-based dispersing agent was improved [19]. Subsequent

study confirms that Mn2+

, Mg2+

and Zn2+

can also inhibit azo dye reduction [20] and

perhaps explains the improved stability of the dye dispersion in SSW.


Most of the literature suggests that dyeing of polyester with disperse dyes occurs with

the dye in the monomolecular form, in a mechanism known as “aqueous phase transfer”

[1, 4, 21]. Dye is continuously adsorbed on the surface and then subsequently migrates

into the interior of the fibre. The temperature of the dyebath controls the rate of

exhaustion in disperse dyeing [12]. As the temperature increases, the dissolution of dyes

in the dispersion increases, with the net effect being an enhancement of dye uptake and

a progressive build-up of colour, as evidenced through higher K/Sλmax values. Any

possible decrease in K/Sλmax values in SSW can be due to the increased aggregation of

disperse dyes or due to the release of trimer, which minimizes the penetration of dyes in

the compact structure of polyester fibre [22]. The results showed that the K/Sλmax values

of fabrics dyed in DSW or SSW were similar, Table 5.2 and 5.3 except for Foron Blue

RD-GLF which produced slightly higher K/Sλmax values at the 2.0% o.m.f. depth for the

SSW dyeing. The uniformity of the dyeing in SSW confirms the effectiveness of

anionic dispersing agents in maintaining dispersion stability during dyeing at room and


195

elevated temperature. The study also confirms that anionic dispersing agent can prevent

dye aggregation/agglomeration and crystal growth [23].

Table 5.2 Colour strength, K/Sλmax, of Red, Yellow and Blue dyed polyester fabric at

0.05, 1.0 and 2.0% o.m.f. application levels

K/Sλmax, at Specified Application Level

Dye Applied 1.0%

o.m.f.+

1.0%

o.m.f.*

2.0%

o.m.f.+

2.0%

o.m.f.*

4.0%

o.m.f.+

4.0%

o.m.f.*

Dianix Red AC-E 0.4 0.4 5.1 5.0 13.1 12.3

Dianix Yellow 6GSL-FS 1.0 1.0 14.7 14.7 24.5 24.9

Dianix Blue AC-E 0.6 0.5 8.0 8.3 17.4 17.3

Terasil Red R 1.0 1.0 17.9 16.3 26.7 27.3

Terasil Yellow 4G 1.4 1.6 21.7 22.8 27.3 27.1

Terasil Blue R 0.5 0.6 8.0 7.8 15.0 15.0

Dispersol Red XFN 1.0 1.2 14.0 14.7 24.8 24.3

Dispersol Yellow XF 1.7 1.8 20.7 19.0 22.9 22.7

Dispersol Blue XF 0.7 0.7 10.9 10.4 21.9 23.0

Foron Red RD-GL 200% 1.5 1.6 22.3 22.4 27.9 28.5

Foron Yellow RD -4GRL 1.1 1.3 19.2 19.3 26.2 28.1

Foron Blue RD-GLF 1.2 1.2 16.4 17.4 25.6 27.9



Table 5.3 Colour strength, K/Sλmax, of Black dyed polyester fabric at 0.05, 1.0 and 2.0%

o.m.f. application levels

K/Sλmax, at Specified Application Level

Dye Applied 1.0%

o.m.f.+

1.0%

o.m.f.*

2.0%

o.m.f.+

2.0%

o.m.f.*

4.0%

o.m.f.+

4.0%

o.m.f.*

Dianix Black AD-R 9.5 9.4 18.4 19.1 27.3 26.4

Terasil Black LBSN 11.6 11.3 20.3 20.3 28.9 28.9

Dispersol Black XF 6.9 7.2 14.7 14.5 24.4 23.6

Foron Black RD-3G 300% 14.1 14.9 23.9 24.0 31.1^ 31.6

^




196

Table 5.4 illustrates the colour difference, ΔECMC(2:1), between fabrics dyed in red,

yellow and blue in DSW and SSW. Overall the result was satisfactory since in most

cases, ΔECMC(2:1) was below the commercial acceptance level of 1.0 units [24]. There

were also some odd results observed, for example with Dianix Red and Foron Blue

RD-GLF, where the ΔECMC(2:1) was relatively low at 1.0% and 2.0% o.m.f. depth, yet

produced a relatively high ΔECMC(2:1) at 0.05% o.m.f. depth with a slight difference in

K/Sλmax values, whereas Terasil Yellow, Dispersol Red, Foron Yellow at 0.05% o.m.f.

produced a higher colour difference possibly due to the limitation of colour

measurement in lighter depth [25].

Table 5.4 Colour difference, ΔECMC(2:1), between Red, Yellow and Blue dyed polyester

fabrics dyed in DSW and SSW aqueous media.

ΔECMC(2:1)

Dye 0.05% o.m.f. 1.0% o.m.f. 2.0% o.m.f.

Dianix Red AC-E 2.5 0.3 0.3

Dianix Yellow 6GSL-FS 0.4 3.1 0.4

Dianix Blue AC-E 1.3 0.8 1.1

Terasil Red R 0.9 3.9 0.2

Terasil Yellow 4G 1.8 0.7 0.5

Terasil Blue R 1.6 0.5 0.8

Dispersol Red XFN 1.7 0.4 0.5

Dispersol Yellow XF 2.7 2.4 3.8

Dispersol Blue XF 0.2 1.2 1.2

Foron Red RD-GL 200% 1.0 0.2 0.4

Foron Yellow RD -4GRL 1.8 0.7 0.5

Foron Blue RD-GLF 2.0 1.0 0.6

The most notable colour differences were consistently produced in fabrics dyed with

Dispersol Yellow XF at all depths. Visual inspection of the fabric also confirmed the

dyed fabric in SSW looked greener compared to that of DSW. Although the exact

structure of Dispersol Yellow XF is unknown, it is a thiophene-based azo dye and it was

reported that bulky azo chromophores are sensitive to alkaline reduction. A high pH can

cleave the azo groups which is responsible for producing a characteristic lighter and

greener appearance [12]. In contrast, Dianix Yellow 6GSL-FS at 0.05% o.m.f. depth


197

produces a greener tone in DSW and SSW, but as the depth increases, the tone gets

yellower and redder at 1.0% in SSW. The difference in dyeing properties of disperse

dyes in SSW may be due to a number of factors such as molecular weight, chemical

structure, extent of solubility, migration power, compatibility with other ingredients, or

diffusion characteristics [4, 6, 22, 26, 27, 28]. Alternatively in minimising colour

differences, other reduction clearing treatments such as blowing ozone directly on the

fabric surface during the finishing stage could be advantageous as reported [29].

Each of the black dyes produced acceptable dyed fabrics, with ΔECMC(2:1) as low as 0.2

units, Table 5.5, yet when the difference was higher as in the cases of Dianix Black at

2.0% o.m.f. depth, it was because the K/Sλmax value was higher in the dyed fabric in

SSW.

Table 5.5 Colour difference, ΔECMC(2:1), between Black dyed polyester fabrics dyed in

DSW and SSW aqueous media.

ΔECMC(2:1)

Dye 1.0% o.m.f. 2.0% o.m.f. 4.0% o.m.f.

Dianix Black AD-R 0.8 1.9 1.0

Terasil Black LBSN 0.2 0.4 0.3

Dispersol Black XF 0.2 0.7 0.7

Foron Black RD-3G 300% 0.3 0.2 0.4


Wash fastness of any disperse dyed polyester fabric depends on reduction clearing of

the fibre surfaces, the temperature and duration of any heat treatment and chemical

finishing. All the dyed fabrics used in our study have been alkaline reduction cleared in

order to remove any loose dye or oligomers from the surface.


198

Table 5.6 and 5.6 show the wash fastness of fabrics dyed in DSW and SSW were very

good with the dry rub fastness in the range of 4 to 5. Diacetate and nylon were

consistently the most stained components of the multi-fibre strip, presumably since the

dye has substantivity for these fibres and are dyeable at the test temperatures. Diffusion

of dyes into polyester and acrylic was less pronounced than nylon and acetate due to the

relatively higher Tg of these polymeric fibres. The cross-staining results indicated that

although the reduction clearing process was acceptable for most dyes but it may need to

be adjusted with certain dyes, as it is reported that ease of removal varies with

chromophore to chromophore and dye to dye [12]. The effect of salts on staining was

apparent in other ways, for example with Terasil Red R both fabrics had a similar rating

of 2 on nylon but were differently stained as the depth increased. Initially the nylon

component remained bluer for both cases at 0.05% o.m.f. depth, and became redder as

the depth increased in SSW.

It is also known that subsequent chemical finishing such as softening, antistatic

finishing of dyed polyester fabric could increase the thermal migration of dyes,

presumably as the finishing agent can act as a carrier for the dyes, which might decrease

the overall fastness of the fabric [12, 30]. The effect of SSW on chemical finishes also

needs to be investigated, although the degree of thermal migration may not necessarily

reflect the results of fastness tests [31].


199

Table 5.6 Wash fastness and staining, dry rub fastness performance of Disperse Red and

Yellow dyes at 0.05, 1.0 and 2.0% o.m.f. depth on polyester

Name of

Dyestuffs

%

o.m.f.

Wash

fastness

Polyester

staining

Nylon

staining

Acetate

staining Dry Rub


Dianix

Red AC-E

0.05 5 5 5 5 4/5 4/5 5 5 5 5

1.0 4/5 4/5 4/5 4/5 5 5 5 5 5 5

2.0 4/5 5 5 5 5 5 3/4 3 5 5

Terasil

Red R

0.05 5 5 4/5 4/5 2/3 2 5 5 5 5

1.0 4/5 4/5 4/5 4 2 2 3/4 2/3 4/5 4/5

2.0 4 4 4/5 4 2 2 4 3 4/5 4

Dispersol

Red XFN

0.05 5 5 5 5 4/5 4/5 4/5 4/5 5 5

1.0 4/5 4/5 5 5 4/5 4/5 4/5 4/5 5 5

2.0 4/5 4/5 4/5 4 4/5 4 4 4 5 4/5

Foron Red

RD-GL

0.05 4/5 4/5 5 4/5 4/5 4/5 5 5 5 5

1.0 4/5 4/5 4/5 4/5 3/4 3 3 2/3 4/5 4/5

2.0 4/5 4/5 4 4 2/3 2 2 1/2 4/5 4/5

Dianix

Yellow

6GSL-FS

0.05 4/5 5 5 4/5 4 4 4/5 4/5 5 5

1.0 4/5 4/5 4/5 4/5 4 4 4/5 4/5 5 5

2.0 4/5 4/5 4/5 4/5 2/3 3 4/5 3 4/5 4/5

Terasil

Yellow

4G

0.05 4/5 4/5 4/5 4/5 2/3 3 4/5 4/5 5 5

1.0 4/5 4/5 4/5 4/5 2 3 4/5 4/5 5 5

2.0 4/5 4/5 4/5 4/5 2/3 2/3 4/5 4/5 5 5

Dispersol

Yellow

XF

0.05 5 4/5 5 5 4/5 4/5 4/5 4/5 5 5

1.0 4/5 4/5 5 5 4/5 4/5 4/5 4/5 4/5 4/5

2.0 4/5 4/5 5 4/5 4/5 3 4/5 3/4 5 4

Foron

Yellow

RD -

4GRL

0.05 5 5 5 5 5 5 5 5 5 5

1.0 5 5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

2.0 4/5 4 4/5 4/5 4/5 4/5 4 4 4/5 4


200

Table 5.7 Wash fastness and staining, dry rub fastness performance of Disperse Blue

and Black dyes at 0.05, 1.0 and 2.0% o.m.f. depth on polyester

Name of

Dyestuffs

%

o.m.f.

Wash

fastness

Polyester

staining

Nylon

staining

Acetate

staining Dry Rub


Dianix

Blue AC-E

0.05 4/5 4/5 5 5 4/5 4/5 4/5 4/5 5 5

1.0 4/5 4/5 5 5 4/5 4 4/5 4/5 5 5

2.0 4 4 4/5 4/5 3 2/3 3/4 3/4 5 5

Terasil

Blue R

0.05 4/5 4/5 4/5 5 4 4/5 5 5 5 5

1.0 4/5 4/5 4/5 4/5 4 4 4/5 4/5 5 5

2.0 4 4/5 4/5 4/5 3/4 3 4 4 5 4/5

Dispersol

Blue XF

0.05 5 5 4/5 4/5 4/5 4/5 5 5 5 5

1.0 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 5 5

2.0 4 4 4/5 4/5 4/5 4/5 4/5 5 5 5

Foron Blue

RD-GLF

0.05 4/5 5 5 5 5 5 5 5 5 5

1.0 4/5 4/5 4/5 4/5 4 3/4 4 4 5 4/5

2.0 5 4/5 4 3/4 3/4 3 3/4 3 4/5 4

Dianix

Black

AD-R

1.0 4/5 4/5 4/5 4/5 4/5 4/5 5 5 5 5

2.0 4 4/5 4/5 4 4 3/4 5 5 5 4/5

4.0 4 4 4 3/4 3/4 2/3 4/5 3 4/5 5

Terasil

Black

LBSN

1.0 4/5 4/5 5 5 4/5 4/5 5 5 5 5

2.0 4/5 4/5 5 5 4/5 4/5 5 5 5 5

4.0 4/5 4/5 5 5 4/5 4/5 5 5 5 5

Dispersol

Black XF

1.0 5 4/5 5 4/5 4/5 4/5 4/5 4/5 5 5

2.0 4/5 4/5 4/5 5 4/5 4/5 4 4/5 5 5

4.0 4/5 4/5 4/5 4/5 4/5 4/5 4 4/5 5 5

Foron

Black

RD-3G

1.0 4 4/5 4/5 4 4 3/4 4 3 5 4/5

2.0 4/5 4/5 4 4 4 3/4 4 3 4/5 4/5

4.0 4/5 4/5 3/4 3 3 2/3 2/3 1/2 5 4

Table 5.8 and 5.7 indicated that the light, alkaline perspiration, sublimation fastness and

staining on multi-fibre strip fabrics were comparable for both SSW and DSW dyeing.

Each black dye at 2.0% and 4.0% o.m.f. showed cross-staining values as low as 2.


201


and light fastness performance of Disperse Red and Yellow dyes at 0.05, 1.0 and 2.0%

o.m.f. on polyester fabrics

Name of

Dyestuffs

%

o.m.f.

Alkaline

perspiration

fastness

Nylon

staining

Sublimation

Fastness

Polyester

staining

Light

Fastness


Dianix

Red AC-E

0.05 5 5 5 5 4/5 4/5 4 4 5 5

1.0 5 5 5 5 3/4 4 3 3 5 5

2.0 4/5 4/5 4/5 4/5 3 4 2 2 5 5

Terasil

Red R

0.05 5 5 5 5 5 5 4/5 4/5 5 5

1.0 5 5 5 5 4 4 3/4 3/4 5 5

2.0 5 4/5 4/5 4/5 4/5 4/5 2/3 3 4/5 4/5

Dispersol

Red XFN

0.05 5 5 5 5 5 5 5 5 4/5 4/5

1.0 5 5 5 5 4/5 4/5 3 3 4 3/4

2.0 4/5 4/5 4/5 4/5 4/5 4/5 2/3 2/3 4/5 4

Foron Red

RD-GL

0.05 5 5 5 5 4/5 4/5 4/5 4/5 5 5

1.0 5 5 4/5 4/5 4/5 4/5 3/4 3/4 5 5

2.0 5 4/5 4/5 4 4 4/5 2 2 5 5

Dianix

Yellow

6GSL-FS

0.05 5 5 5 5 4/5 4/5 4/5 4/5 5 5

1.0 4/5 4/5 5 5 4/5 4 3/4 3/4 4/5 4/5

2.0 4/5 4/5 5 5 4/5 4 3/4 3/4 4/5 4/5

Terasil

Yellow

4G

0.05 5 5 5 5 4/5 4/5 4/5 4/5 5 5

1.0 4/5 4/5 5 5 4/5 4/5 4 4 5 5

2.0 4 4/5 4/5 4/5 4/5 4 3 3 5 5

Dispersol

Yellow

XF

0.05 5 5 5 5 4/5 4/5 4/5 4/5 5 5

1.0 4/5 4/5 5 5 3 4 3/4 3/4 5 5

2.0 4/5 4/5 4/5 4/5 2/3 3/4 2/3 2/3 5 5

Foron

Yellow

RD-4GRL

0.05 5 5 5 5 4/5 4/5 4/5 4/5 4/5 4/5

1.0 4/5 4/5 5 5 3/4 3/4 3/4 3/4 4/5 4/5

2.0 4/5 5 4/5 5 4 4 2/3 2/3 5 4/5


202


and light fastness performance of Disperse Blue and Black dyes at 0.05, 1.0 and 2.0%

o.m.f. depths on polyester fabrics

Name of

Dyestuffs

%

o.m.f.

Alkaline

perspiration

fastness

Nylon

staining

Sublimation

Fastness

Polyester

staining

Light

Fastness


Dianix

Blue

AC-E

0.05 5 5 5 5 4/5 4/5 3/4 3/4 5 5

1.0 4/5 4/5 5 5 4 4 2/3 2/3 4/5 4/5

2.0 4/5 4/5 5 5 4 4 2 2 4/5 4/5

Terasil

Blue R

0.05 5 5 5 5 4/5 4/5 4/5 4/5 4/5 4/5

1.0 5 5 5 5 4/5 4/5 4 4 4 4/5

2.0 5 4/5 4/5 4/5 4/5 4/5 3/4 3/4 4 4

Dispersol

Blue XF

0.05 5 5 5 5 5 5 4/5 4/5 4/5 4/5

1.0 5 5 5 5 4/5 4/5 4 4 4 4

2.0 4/5 4/5 4/5 4/5 4/5 4/5 3/4 3/4 4/5 4/5

Foron

Blue

RD-GLF

0.05 5 5 5 5 5 5 4/5 4/5 4/5 4/5

1.0 5 5 5 5 4/5 4/5 3/4 3/4 4 4

2.0 5 5 5 5 4 4 2/3 2/3 4 4/5

Dianix

Black

AD-R

1.0 5 5 5 5 4/5 4/5 4 4 3 3

2.0 4/5 4/5 4/5 4/5 4/5 4/5 2/3 2/3 4 4

4.0 4/5 4/5 4 4/5 4 3/4 2/3 2/3 4/5 5

Terasil

Black

LBSN

1.0 5 5 5 5 4/5 4/5 4/5 4/5 2 2

2.0 4/5 4/5 4/5 4/5 4/5 4/5 3/4 3/4 1/2 1/2

4.0 5 5 4/5 4 4/5 4/5 3 3 3 3

Dispersol

Black XF

1.0 5 5 5 5 4/5 4/5 4 4 4 4

2.0 5 5 5 5 4/5 4/5 2/3 2/3 4/5 4/5

4.0 5 4/5 5 5 4 4/5 2 2 4/5 4/5

Foron

Black

RD-3G

1.0 5 5 5 5 4/5 4/5 4 4 3/4 3/4

2.0 5 5 5 5 4/5 4/5 2/3 2/3 4/5 4/5

4.0 5 5 4/5 4/5 4 4 2 2 4/5 4/5


203

5.3.4 Surface Morphology

The SEM micrographs of polyester fibres after dyeing in DSW and SSW showed

particulates at the surface of the fibre, Figure 5.4a and 5.4b. These particulates were

both visible in DSW and SSW, and did appear to be salt crystals. In addition further

EDX analysis showed that these particulates were not sodium chloride and arose from

oligomer migration, Figure 5.5. A 70°C wash with 2 gL-1

non-ionic detergent for 10

minutes removed most "particulates” from the surface like wool fabric dyed in SSW

with acid dye in Chapter 3.

Figure 5.4 SEM micrograph of polyester fibres, a) after reduction clearing and cold

rinse in DSW; b) reduction cleared in SSW and rinsed in DSW

a)

b)


204

Figure 5.5 SEM X-ray microanalysis of dyed wool that had been reduction cleared, acid

washed and then, washed in 2 gL-1

detergent at room temperature for 10 minutes in

DSW (Peak at 2.3units is gold from coating)


205

5.4 Conclusions

The results of the dyeing study on polyester fabric indicated:

The relationship between absorption and scattering of light with disperse dye

concentration is approximately linear in SSW;

Although for some dye dispersions in SSW took longer to stabilise in SSW, the

robustness and effectiveness of the commercial dispersing agents was evident;

Disperse dyeing of polyester produced consistent results for all dyes but some

black dyeings higher colour strength values in SSW;

An alkaline reduction process in the presence of salt may adversely affect yellow

azo chromophores resulting in lighter and greener hues. Alternative reduction clearing

processes may need to be identified;

Wash, dry rub, light and sublimation fastness were very good to excellent for

SSW dyeings, with cross-staining of nylon and diacetate being the greatest;

The effect of chemical finishing needs to be investigated as it could cause

increased thermal migration of dyes similar to that observed with residual carriers;

The presence of salt on the surface if any of the polyester fibres can be easily

removed by established procedure of detergent wash at 700C.

The results indicated that disperse dyeing in SSW is feasible without any major changes

to the processing conditions.


206

5.5 References

1. Mock, G., Dyeing of polyester fibres, in Synthetic Fibre Dyeing, C. J.

Hawkyard, Editor, 2004, Society of Dyers and Colourists, Bradford.

2. Aizenshtein, E., Polyester fibres continue to dominate on the world textile raw

materials balance sheet, Fibre Chemistry, 2009, 41 (1), p.1-8.

3. Ward, J. S., Aspects of Man-made fibre development 1934–1984, Review of

Progress in Coloration and Related Topics, 1984, 14 (1), p.98-113.

4. Burkinshaw, S. M., Chemical principles of synthetic fibre dyeing, 1995, Blackie

Academic & Professional, Chapman & Hall, Glasgow.

5. Murray, A. and K. Mortimer, Dye auxiliaries in the application of disperse dyes

to man-made fibres, Journal of the Society of Dyers and Colourists, 1971, 87

(6), p.173-181.

6. Bird, C. L., The dyeing of acetate rayon with disperse dyes. I -Aqueous solubility

and the influence of dispersing agents II -The relation between aqueous

solubility and dyeing properties, Journal of the Society of Dyers and Colourists,

1954, 70 (2), p.68-77.

7. Gregory, P., ed. Classification of dyes by chemical structure. The Chemistry and

application of dyes, ed. D. R. Waring and G. Hallas. 1990, Plenum Press, New

York.

8. Shuttleworth, L. and M. A. Weaver, eds. Dyes for polyester fibers. The

Chemistry and application of dyes, ed. D. R. Waring and G. Hallas. 1990,

Plenum Press, New York.

9. Stead, C. V., ed. The Chemistry of Synthetic Dyes, ed. K.Venkataraman. Vol.

III. 1970, Academic Press, New York, p.385-462.

10. Balland, J., Dyeing process using a sequestering agent, U. S. Patent, Editor,

1980, Manufacturer de Produits Chimiques Protex Societe Anonyme, France.

11. Leuck, J. F., Squestrants in dyeing and finishing, American Dyestuff Reporter,

1979, 68 (11), p.49.

12. Aspland, J. R., A Series on Dyeing, Chapter 8: Disperse Dyes and Their

Application to Polyester, Textile Chemists and Colourists, 1992, 24 (12), p.18-

23.

13. Clark, G. T., M. A. Weaver and H. W. Somers, Textile Chemists and

Coloursists, 1981, 13, p.238.

14. Dystar, Dianix dye, 2005, DyStar Textilfarben GmbH.

15. Huntsman, Terasil dyes, in Textile Effects, 2007, Huntsman Ltd.


207

16. Park, J. and J. Shore, Fibre Types and Dyeing Processes, in Practical Dyeing,

2004, Society of Dyers and Colourists, Bradford.

17. Clariant, Technical paper: Ecoswat, in Textile Chemicals, M. Maïsseu, Editor,

January 2003, T. L . P Division, Clariant, Basel. p.53.

18. Schindler, W., B. Trunk, T. Dorfler and V. Reith, Can thermosol dyeing be

improved by photometric measurements of the pad liquor?, Melliand

International 1991, 9, p.744-748.

19. Blaisdell, L. A., Dyestuffs and alkali metal salths of wood sugar acids and lignin

sulfonate, U. S. P. Office, Editor, 1964, American Can Company, New York , a

corporation of New Jersey, US.

20. Dilling, P., Effect of cation type on lignosulfonate dispersant performance in

disperses dye systems, Textile Chemist and Colourists, 1988, 20 (5), p.17-22.



22. Imafuku, H., An alkaline dyeing system for polyester, Journal of the Society of

Dyers and Colourists, 1993, 109 (11), p.350-352.

23. Kenneth, J. and S. Kelly, Dyeing of texturised polyester yarn, Journal of the


24. Hassan, M. M. and C. J. Hawkyard, Reuse of spent dyebath following

decolorisation with ozone, Coloration Technology, 2002, 118 (3), p.104-111.


Enfield, N.H.

26. Nakamura, T., S. Ohwaki and T. Shibusawa, Dyeing properties of polyester

microfibers, Textile Research Journal, 1995, 65 (2), p.113-118.

27. Odvárka, J. and H. Schejbalová, The effect of dispersing agents on the dyeing of

polyester with a disperse dye, Journal of the Society of Dyers and Colourists,

1994, 110 (1), p.30-34.

28. Teli, M. D. and N. M. Prasad, Influence of thermal modification of carrier-free

dyeable polyester on dyeability with disperse dyes, American Dyestuff Reporter,

1991, 80 (6), p.18-22.

29. Eren, H. A., D. Ozturk and S. Eren, Afterclearing of disperse dyed polyester

with gaseous ozone, Coloration Technology, 2012, 128 (2), p.75-81.

30. Avinc, O., M. Wilding, J. Bone, D. Phillips and D. Farrington, Evaluation of

colour fastness and thermal migration in softened polylactic acid fabrics dyed

with disperse dyes of differing hydrophobicity, Coloration Technology, 2010,

126 (6), p.353-364.


208

31. Baldwinson, T. M., Post-stentered wash fastness of disperse dyes on Polyester-

The significance of various test conditions, Journal of the Society of Dyers and

Colourists, 1989, 105 (7-8), p.269-276.

Nylon/Acid dyes

209

6. Dyeing of Nylon with Acid dyes

6.1 Introduction

The global total market share of nylon fibre was 5% in 2009 [1] and it has a large share

in the synthetic fibres sector. Nylon fibres are hydrophobic in nature and have low

reactivity to chemical agents [2]. The chemical behaviour of nylon fibre depends on its

functional end groups (-NH2 and –COOH) and chain amide groups (-CONH) [3]. The

presence of terminal amino groups determines the dyeing properties of nylon fibre [4]

and dye substantivity can be enhanced by increasing the concentration of terminal

amino groups [5].

Following wool/acid dye in Chapter 3, nylon fibre was tested in simulated seawater

with acid and metal complex dyes and their performances were evaluated against that in

freshwater.

6.2 Experimental

6.2.1 Materials

Knitted nylon 6, 6 fabric (sharkskin construction, 140 gm-2

, interlock) was supplied by

Phoenix Calico, UK and was used with no further treatment. The six commercial acid

dyes that were assessed were Lanasan Red CF-WN, Lanasan Brilliant Yellow CF-BA,

Lanasan Brilliant Blue CF-BA from Clariant and Acidol Red KM-S, Acidol Yellow

KM-F, Acidol Blue KM-R from BASF. Lanasan CF brand is a mixture of 1:2 metal

complex and milling dyes although the structures of these component dyes and the

structures of the individual dyes are unknown. Lyogen P (Clariant) was used as

levelling agent as recommended and Nylofixan PSA (Clariant) was applied as a fixation

agent, which is reported to improve wet fastness, with excellent tolerance to acid pH

[6].

6.2.2 Dyeing

Dyeing experiments with acid dyes were performed in DSW and SSW using the

following experimental parameters: liquor ratio, 1:10, 0.05, 1.0, and 2.0% o.m.f. dye

application levels; 2% o.m.f. levelling agents, and pH 4.5 to 5.5 adjusted with a buffer

Nylon/Acid dyes

210

system of acetic acid and sodium acetate [4]. 5g fabric samples were dyed in a Mathis

IR laboratory dyeing machine following the standard dyeing procedure provided by

Clariant [7]. Initially the fabric was in the dyebath for 10 minutes at 40°C and then the

temperature was increased at a rate of 2°C/minute until 98°C was reached. After 45

minutes at 98°C the dyebath was cooled and the fabric removed. The samples were then

cold rinsed in DSW for 5 minutes, and then after-treated with 2% Nylofixan PSA 70°C

for 20 minutes in corresponding DSW or SSW medium and then cold rinsed and air

dried. In all cases, duplicate runs were performed.


6.3.1 Initial studies: Effect of Simulated Seawater on Dye λmax

Absorption and Dye Concentration linearity

It has been shown in Chapter 3 that acid and metal complex dyes were suitable for

dyeing wool in a simulated seawater environment. It has also been shown that most

metal complex dyes were readily soluble at room temperature, and if not, like Lanasan

Red CF-WN, gentle warming of the dyebath dissolved the dyes completely. Dye

absorbance studies indicated that absorbance/concentration in SSW graph was linear

and comparable to the DSW-based dyebath, Figure 6.1, for all six dyes, and therefore

obeyed the Beer-Lambert Law [8]. The shift of λmax was minimal in SSW and as a result

the subsequent exhaustion value was calculated based on the DSW calibration curves.

Figure 6.1 Graph of Lanasan Red CF-WN dye absorbance versus concentration in

distilled water, λmax 498nm. ▲ - distilled water dyeing; and ■ - simulated seawater

dyeing.

RDSW² = 0.998

RSSW² = 0.995

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Ab

sorb

an

ce, A

Concentration, gL-1

Nylon/Acid dyes

211

6.3.2 Effect of Salts on Nylon/Acid Dye System

In Chapter 3 it had been noted that the presence of high levels of salt caused dye

aggregation of acid dyes but higher temperatures and the incorporation of levelling

agents reduced aggregation in the wool dyebath [9, 10, 11]. Therefore while dyeing of

nylon 6,6 with metal complex dyes appears similar to that of dyeing wool there are

some significant differences, in particular nylon is more hydrophobic and the ratio of

amino groups in wool relative to nylon is in the ratio of approximately 23:1 [12].

Although, the major dye/fibre interaction for nylon/metal complex dyes is ionic, it is

also believed that hydrophobic interactions (or physical interactions) are as important as

the ionic interactions [13, 14] and are greatly influenced by the presence of electrolytes

due to their different effects on water structure [15, 16]. Unlike the salt-out effect of

ionic interaction, the ionic distribution coefficient in any nylon/dye system depends on

the magnitude of the activities and properties of electrolytes ions in the solution [17,

18]. Some of these ions are water-structure makers (kosmotropes) and others are water-

structure breakers (chaotropes) [18]. The change in ionic distribution in nylon/dye

systems is considered to be negligible in presence of simple electrolytes such as NaCl

and Na2SO4 due to their small ionic size [18]. However, NaCl at higher concentrations

produces decreased dye sorption because it neutralised the charges on both the nylon 6,6

and dye, although this behaviour does offer improved levelling [17, 18]. It has also

been reported that in highly saline dyebaths, the dye sorption depends on combined

effects of ionic and physical interactions [18, 19]. Ionic interaction prevails at low salt

concentration (e.g. < 0.05M) over physical interactions, which results in decreased dye

sorption. However, at concentration over 0.50M, for some anions such as sulphates and

phosphates, the combined effect of the ionic interactions and increased physical

interactions result an increased dye sorption [18, 19, 20, 21].

6.3.3 Exhaustion of Dye

The exhaustion levels onto nylon are presented in Figures 6.2 and 6.3 indicate the

uptake of dye depends on dye structure and the environment of dyeing. Dyeing nylon

with Lanasan CF dyes resulted in exhaustion levels of over 90% in both DSW and SSW

dyebaths. The slightly increased exhaustion values, with consistent build-up, of Lanasan

CF dyes in SSW appeared similar to the behaviour observed with comparable wool

dyeings, suggesting this particular range of dyes is suitable for dyeing in SSW. In

contrast the Acidol ranges showed a lower dye exhaustion values and this may be

Nylon/Acid dyes

212

related to the nature and size of the dye molecule, in particular the degree of

sulphonation and larger planar structure [22]. It can be also seen that adsorption of

Acidol Red and Yellow dye at over 1.0% o.m.f. was higher in SSW compared to that of

DSW possibly due to greater physical interactions that existed in the saline dyebath. As

discussed earlier, the concentration of salt over 0.5M concentration increased dye

adsorption in the presence of sodium sulphate and phosphate salts. The results in this

study also prove that a mixture of salts, of similar molar concentrations, could provide

enough physical interactions to increase dye sorption, particularly in presence of

chloride salts with a mixture of larger ionic sizes such as magnesium and calcium.

Figure 6.2 Exhaustion levels of Lanasan CF dyes at 0.05, 1.0 and 2.0% o.m.f. on nylon,

- distilled water dyeing; and - simulated seawater dyeing.

Figure 6.3 Exhaustion levels of Acidol KM dyes at 0.05, 1.0 and 2.0% o.m.f. on nylon,

- distilled water dyeing; and - simulated seawater dyeing.


Like the exhaustion values, an excellent build-up of colour was observed in both DSW

and SSW and is a typical characteristics of metal complex dyes [12], Table 6.1. The

50

60

70

80

90

100

0.05% 1.0% 2.0% 0.05% 1.0% 2.0% 0.05% 1.0% 2.0%

Lanasan Red CF-WN Lanasan Brilliant yellow CF-

BA

Lanasan Brilliant Blue

CF-BA

%E

50

60

70

80

90

100

0.05% 1.0% 2.0% 0.05% 1.0% 2.0% 0.05% 1.0% 2.0%

Acidol Red KM-S Acidol Yellow KM-F Acidol Blue KM-R

%E

Nylon/Acid dyes

213

rate of dyeing did not depend on the concentration of dyes in the dyebath or the

molecular size of the acid in the formic acid-hexanoic acid series [17]. Thus it can be

assumed that the established dyeing process for nylon 6, 6-acid dye was easily

reproducible in saline environment. The colour strength, K/Sλmax, was quite similar in

0.05% and 1.0% o.m.f. depth for both dyeings, but the difference increased when the

depth increased to 2.0% o.m.f. This difference in K/Sλmax was particularly obvious for

each Acidol dyes, consistent with the corresponding exhaustion data, confirming that

the physical interactions in presence of salts greatly contributed to the dye fibre

substantivity. As a result the colour difference, ∆ECMC (2:1), also increased to a level that

was more than the commercial acceptable range of 1.0.

Table 6.1 Colour strength, K/Sλmax and colour difference of dyed nylon fabrics at 0.05,

1.0 and 2.0% o.m.f. of applied metal complex dyes

Dye Applied

K/Sλmax ΔECMC(2:1)

0.05%

o.m.f.+

0.05%

o.m.f.*

1.0%

o.m.f.+

1.0%

o.m.f.*

2.0%

o.m.f.+

2.0%

o.m.f.*

0.05%

o.m.f.

1.0%

o.m.f.

2.0%

o.m.f.

Lanasan Red CF-

WN

0.4 0.4 7.0 7.1 14.2 14.6 0.8 0.3 0.4

Lanasan Brilliant

yellow CF-BA

0.6 0.6 6.3 6.4 12.3 12.9 0.8 0.6 0.6

Lanasan Brilliant

Blue CF-BA

0.5 0.6 8.1 8.5 16.6 18.2 0.2 0.5 0.5

Acidol Red KM-S 0.7 0.6 11.9 12.0 18.4 23.5 1.2 1.2 0.7

Acidol Yellow

KM-F

0.9 0.9 10.2 10.2 16.0 17.9 0.6 0.5 0.9

Acidol Blue KM-R 0.5 0.6 10.1 10.6 17.6 20.8 1.3 0.9 0.5



The uniformity of dyeing is an important characteristic of the finished coloured textile

fabrics and in nylon, the ionic interactions between the metal complex dyes with the

protonated terminal amino groups influences the exhaustion and levellness. The ionic

attraction is relatively strong, which hinders the movement of dyes after the initial

strike. Levelling occurs when dye anions at the surface move to the unoccupied dye

anions at the interior of the fibre. The nature of chemical and physical irregularities

present in nylon 6, 6 fabric, and the sensitiveness of anionic dyes towards this

Nylon/Acid dyes

214

variability resulted in this area of study receiving much attention [4]. Metal complex

dyes have different abilities to cover variations in the fibre and dyeing auxiliaries are

used to control these variations [12, 23]. Lyogen P, is anionic in nature and thus has

fibre affinity and hence competes with the dyes for levelling both internally and on the

surface [24]. However, their effect is temporary and replaces the dye anions as the

dyeing progresses and temperature rises [12].

The observed colour of dyed fabric was uniform in SSW and DSW. However, a

characteristics barré effect of nylon-acid dyeing was observed in each Acidol dyes but it

was severe for Acidol Blue along with Lanasan Blue to some extent. Although

previously known the effect can result from chemical variations in production of

polymer but nowadays physical variations during the fibre processing is considered the

main reason for variation [12]. Dyed fabric in Lanasan Red and Yellow dyes displayed

almost no barré effect, which validated the claim that Lyogen P can prevent barré

dyeing of nylon 6, 6 with acid dyes [6]. However, it also generated the question of

relationship of dye structure and levelling agent with the quality of substrate. Levelling

agents vary in their ability to promote level dyeing and a careful match of dye affinity

and levelling agents may require achieving optimum results [25, 26]. A suitable

alternative levelling agent or higher temperature (110-115°C) can be employed to

overcome barré effect [23, 26].

In the light of the laboratory results a bulk trial with 2000 g of nylon 6, 6 fabric was

carried out in Roaches (UK) Rotohouse rotary dyeing machine (120L capacity). Fabric

was dyed with Lanasan Blue dye in DSW and SSW at 2.0% o.m.f. depth in a liquor

ratio of 1:10. K/Sλmax was slightly higher than obtained in the laboratory trials but have

similar values in DSW and SSW. The colour difference, ΔEcmc(2:1) was 0.68, which was

within the commercially acceptable range. The change in mass due to shrinkage in

water in highly agitated dyebath produced similar changes in both DSW and SSW.

6.3.5 Colour Fastness Properties

In general, the light and wash fastness of nylon coloured with the Acidol and Lanasan

metal complex dyes was very good, Table 6.2. The good wash fastness was probably

due the ionic interactions in terminal amino groups of the nylon 6,6 fibre [12] and the

use of the fixing agent Nylofixan PSA. The excellent light fastness performance was a

Nylon/Acid dyes

215

reflection of dye energy transfer to the chelated metal and subsequent deactivation of

excited energy states through the empty d orbitals and heat dissipation.

The grey scale rating for staining of dry rub fastness was 5 for each of the dyes, and was

not included in the data. In the wash fastness testing, the six dyes displayed similar

behaviour over the three depths examined. The cross-staining of wool was in the

acceptable range of 4 to 5. Light fastness was lower for the Lanasan Red dye; otherwise

they displayed similar ratings on dyed fabric in DSW and SSW. The wash fastness and

cross-staining of a larger scale bulk trial produced similar results to the laboratory trials

and accordingly were encouraging.

Table 6.2 Fastness performance of Lanasan, and Acidol dyed nylon 6,6 fabrics

Dye applied %

o.m.f.

Wash fastness Wool Staining Nylon Staining Light fastness


Lanasan Red

CF-WN

0.05 5 5 4/5 4/5 4/5 4/5 2 2

1.0 4/5 4/5 4/5 4/5 4/5 4/5 3 3

2.0 4/5 4/5 4/5 4/5 4/5 4/5 3/4 3/4

Lanasan

Brilliant Yellow

CF-BA

0.05 5 5 4/5 4/5 4/5 4/5 4 4

1.0 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

2.0 4/5 4/5 4/5 4/5 4 4 4/5 4/5

Lanasan

Brilliant Blue

CF-BA

0.05 5 5 4/5 4/5 4/5 4/5 4/5 4/5

1.0 4/5 4/5 4/5 4/5 4/5 4/5 4 4

2.0 4 4/5 4/5 4/5 4 4 4 4/5

Acidol Red

KM-S

0.05 5 5 4/5 4/5 5 5 5 5

1.0 4/5 4/5 4 4 4/5 4/5 4 4

2.0 4/5 4/5 4 4 4/5 4/5 4/5 4/5

Acidol Yellow

KM-F

0.05 5 5 5 5 5 5 5 5

1.0 4/5 4/5 4/5 4/5 5 5 4/5 4/5

2.0 4/5 4/5 4 4 5 5 4/5 5

Acidol Blue

KM-R

0.05 5 5 5 5 5 5 5 5

1.0 4 4/5 4/5 4/5 5 5 4/5 4/5

2.0 3/4 4 4/5 4/5 5 5 4/5 4/5

Nylon/Acid dyes

216

6.4 Conclusions

It was found in Chapter 3 that acid and metal complex dyeing of wool in SSW was

possible for bulk scale of production. Similarly the colouration study of metal complex

dyes on nylon concluded that:

The absorbance/concentration curve in SSW obeys Beer-Lambert law and any

shift of λmax was minimal;

The dye exhaustion levels onto the nylon fabric using metal dye complexes were

similar for both DSW and SSW dyeings. Excellent build-up of colour was observed

throughout with acceptable small colour differences between SSW and DSW dyed

fabrics;

The relationship of dye structure and levelling agent to cover barré effect of

nylon fibre needs to be investigated as Lyogen P could cover some dyes but failed to

perform adequately with Lanasan Blue and Acidol Blue dyes;

The wash, dry rub and light fastness of the SSW and DSW dyed fabrics was

comparable and excellent while cross-staining on wool and nylon 6, 6 produced similar

results. The colorimetric data and fastness of bulk trials confirmed the laboratory

results.

Nylon/Acid dyes

217

6.5 References

1. Oerlikon, The Fiber Year 2009/10 A World Survey on Textile and Nonwovens

Industry, 2010, Oerlikon Corporation AG, Pfäffikon. p.100.

2. Lewin, M. and E. M. Pearce, Chapter 2, in Handbook of Fiber Chemistry, M.

Dekker, Editor, 1998, New York, p.72-73.

3. Mark, H. F., S. M. Atlas and E. Cernia, Man-made fibers: science and

technology, 1967, Interscience Publishers.

4. Burkinshaw, S. M., Chemical principles of synthetic fibre dyeing, 1995, Blackie

Academic & Professional, Chapman & Hall, Glasgow.

5. De Winter, W. and A. Decorte, Polyamide 6,6 for deep dyeing, Textile Research

Journal, 1971, 41 (9), p.726-732.

6. Clariant, Textile chemicals for pretreatment, optical brightening, dyeing &

printing and finishing, in Directory for Textile Chemicals Department, 2003,

Clariant Corporation, Textile Business Unit, Charlotte, NC.

7. Park, J. and J. Shore, Fibre Types and Dyeing Processes Practical Dyeing, Vol.

2, 2004, Society of Dyers and Colourists, Bradford.


Enfield, N.H.

9. Valkó, E., Particle size in wool dyeing, Journal of the Society of Dyers and

Colourists, 1939, 55 (4), p.173-182.

10. Datyner, A. and M. T. Pailthorpe, A study of dyestuff aggregation. part II. The

influence of temperature on the aggregation of some anionic dyestuffs, Journal

of Colloid and Interface Science, 1980, 76 (2), p.557-562.



Pigments, 1987, 8 (4), p.253-263.

12. Lewis, D. M. and D. J. Marfell, Chapter 3: Nylon dyeing, in Synthetic fibre

dyeing, C. Hawkyard, Editor, 2004, Sociey of Dyers and Colourists, Bradford.

13. Giles, C. H., in The Theory of Coloration of Textiles, C. L. Bird and W. S.

Boston, Editors, 1975, Dyers Company Publication Trust, Bradford, England.

14. Yang, Y. Effect of Electrolytes on Hydrophobic Interaction in Dyeing. Proc. in

AATCC International Conference and Exhibition. 1992, Research Triangle Park,

NC, American Association of Textile Chemists and Colorists, p.266-269.

Nylon/Acid dyes

218



p.283-289.

16. Yiqi, Y., Effect of salts on physical interactions in wool dyeing with acid dyes,


17. Bell, J. P., W. C. Carter and D. C. Felty, Dye concentration profiles within

single nylon filaments, Textile Research Journal, 1967, 37 (6), p.512-516.

18. Yang, Y., S. Li and T. Lan, Ion sorption by polyamide with consideration of

ionic interaction and other physical interactions, Journal of Applied Polymer

Science, 1994, 51 (1), p.81-87.

19. Bell, J. P., Effect of fiber and dyebath variables on the rate of acid dyeing of

nylon 6, 6, Textile Research Journal, 1968, 38 (10), p.984-989.

20. Vickerstaff, T., The Physical Chemistry of Dyeing, 1954, Imperial Chemical

Industries, London, U.K.




22. Atherton, E., D. A. Downey and R. H. Peters, Studies of thedyeing of nylon with

acid dyes: part I: Measurement of affinity and the mechanism of dyeing, Textile

Research Journal, 1955, 25 (12), p.977-993.

23. Ginns, P. and K. Silkstone, The dyeing of synthetic polymer and acetate fibres,

D. M. Nunn, Editor, 1979, The Society of Dyers and Colourists, Bradford.

24. Cockett, K. R. F., Industrial Application of Surfactants, 1988, Royal Society of

Chemistry, London.

25. Holfeld, W. T. and R. H. Pike, Role of fiber surface in dye rate uniformity,

Textile Chemist and Colorist, 1985, 17 (12), p.19.

26. Bittles, J. A., J. Brooks, J. J. Iannarone and H. P. Landerl, The dyeing of filament

Nylon with acid dyes, American Dyestuff Reporter, 1958, 47 (194), p.183-186.

Acrylic/Cationic dyes

219

7. Dyeing of Acrylic with Cationic Dyes

7.1 Introduction

Acrylic fibre is the third most used synthetic textile material in the world [1] and is an

alternative to wool products [2]. Currently, acrylic has extensive application in the

apparel and industrial sectors due to its chemical and physical properties, for example,

high strength, microbial resistance and good abrasion properties [3]. Acrylic fibres

contain long chain polymers composed of at least 85% acrylonitrile and are commonly

referred to as PAN fibres. The remaining 1-15% are co-monomers, such as methacrylic

acid, vinyl acetate or similar vinyl compounds, and in some cases acidic groups, are

incorporated to improve dyeability and other mechanical properties [1, 4]. Acrylic fibre

is the major consumer of cationic or basic dyes even though their level dyeing is

difficult [5]. Acrylic fibres are resistant to chemical attack due to their hydrophobic

nature and show excellent fastness properties when dyed with cationic dyes [6]. A

retarding agent is usually used in the dyeing process to overcome the difficulties of

levelling and added electrolytes also improve the levelness and migration in dyeing [7].

Based on the successful performance of the wool, polyester, nylon fibres in Chapter 3 to

6, acrylic fibre was dyed with cationic dyes in simulated seawater. The performance of

the dyed fabric was compared and evaluated against the fabric dyed in freshwater.

7.2 Experimental

7.2.1 Materials

Plain knitted acrylic fabric (scoured and set, 395 gm-2

, Phoenix Calico, UK) was used

with no further pre-treatment. Three representative commercial cationic dyes from

Huntsman Textile Effects were used to assess dyeability performance: Maxilon Red

GRL 150% (C. I. Basic Red 46), Maxilon Blue GRL 300%, (C. I. Basic Blue 41) and

Maxilon Yellow GL 200% (C. I. Basic Yellow 45) and used as supplied. The structures

of the dyes are given in Figure 7.1.


220

Figure 7.1 Molecular structure of (a) C. I. Basic Blue 41[8]; (b) C. I. Basic Red 46 [9];

and (c) C. I. Basic Yellow 45 [9].

A cationic retarder, Tinegal MR (Ciba Specialty Chemicals) was used to improve

levelling and its structure was based on a colourless quaternary ammonium compound,

n-tetra-alkyl ammonium halide [11].

7.2.2 Dyeing

5 g samples of fabric were dyed in a 200 mL of either DSW or SSW at depths of 0.05,

1.0, and 3.0 % o.m.f., respectively, using a Mathis IR lab dyeing machine. The liquor

ratio was 1:10 and the solution was adjusted to pH 3.5-4 with the addition acetic acid

and sodium acetate. 1 gL-1

sodium sulphate was added to the DSW dye bath. The

standard dyeing procedure provided by Ciba was followed, Figure 7.2, and incorporated

1-2% o.m.f. of Tinegal MR [6]. A typical wash-off process as shown in Figure 7.2 was

performed in DSW. In all cases, duplicate samples were performed.

(a)

(c) (b)


221

Figure 7.2 Dyeing profile for acrylic fabrics

7.3 Results and Discussions

7.3.1 Effect of Simulated Seawater on dye λmax Absorption and Dye

Concentration Linearity

Initially, the linearity of the calibration curve and the corresponding shift in λmax were

determined keeping DSW and SSW as the reference solutions for the corresponding

measurements. λmax for each of the dyes was identical (RedDSW, 531nm; RedSSW,

531nm; BlueDSW, 609nm, BlueSSW, 608nm; YellowDSW, 440nm; YellowSSW, 440nm).

The calibration curve was also found to be linear, Figure 7.3 and 7.4, however, with a

different gradient was observed for the yellow dye, Figure 7.5. Therefore, subsequent

calculations of %E for each dye were measured using respective DSW and SSW

calibration curves.

Figure 7.3 Graph of C. I. Basic Blue 41 absorbance versus concentration in DSW, λmax

608nm. ▲ - distilled water dyeing; and ■ - simulated seawater dyeing.

RDSW² = 0.990

RSSW² = 0.977

0.00

0.50

1.00

1.50

2.00

2.50

0 0.01 0.02 0.03 0.04 0.05

Ab

sorb

an

ce

Concentration, gL-1

Room Temperature

1-2 % Tinegal MR pH 3.5~4 1gL

-1 sodium acetate

Cold rinse Washing with 1 gL

-1

detergent at 70°C for 10 min Cold rinse and dry

105°C

75°C

4°C/min

1°C/min

Dyes 5'

45' 20' 0.5°C/min


222

Figure 7.4 Graph of C. I. Basic Red 46 absorbance versus concentration in DSW, λmax

531nm. ▲ - distilled water dyeing; and ■ - simulated seawater dyeing.

Figure 7.5 Graph of C. I. Basic Yellow 45 absorbance versus concentration in DSW,

λmax 440nm. ▲ - distilled water dyeing; and ■ - simulated seawater dyeing.

7.3.2 Effect of Salts on Exhaustion of Dye

The chemical and physical interactions between dyes and fibres in the colouration

process are fundamental to understanding the substantivity between the materials. Like

other dye classes and fibres cationic dyes also have a saturation limit for the dye

adsorption on the acrylic fibres [10, 11]. The effect of different electrolytes on the

acrylic fibre/cationic dye system has been previously studied [12, 13] with an emphasis

on the dyeing rate and the dye saturation values of the fibre. In general, electrolytes in a

cationic dye bath for acrylics tend to retard dyeing, Figure 7.6 (Curve II) and the effect

can be attributed to the cations [13], but is of smaller magnitude, ~20-30%, to the total

retarding effect observed with cationic levelling agents. The retarding effect depends on

RDSW² = 0.988

RSSW² = 0.999

0.00

0.50

1.00

1.50

2.00

2.50

0 0.01 0.02 0.03

Ab

sorb

an

ce

Concentration, gL-1

RDSW² = 0.999

RSSW² = 0.999

0.00

0.50

1.00

1.50

2.00

2.50

0 0.01 0.02 0.03 0.04 0.05

Ab

sorb

an

ce

Concentration, gL-1


223

the nature of cations, for example, K+ ion has more retarding effect than that of Na

+ ion

due to the higher electropositivity and smaller ionic volume [14]. Furthermore, the

retarding effect increases as the concentration of salt increases.

The effect levels at a certain concentration for monovalent ions is illustrated in Figure

7.6, Curve II [14] and the effect of retarding agent was attributed to ionic interaction,

the reduction of zeta potential and mechanical obstruction [15]. In addition for some

electrolytes at higher concentration increased dye sorption for acrylic fibres was

observed [15, 16].

Although previously some researchers found that the effect of anions had little influence

on dye sorption [13, 17], the increase of dye sorption in Figure 7.6, Curve I), was

attributed to the anions present in dyebath such as sulphates and phosphates [15]. The

increase in sorption due to salt effects was explained by the increase in surface tension

(except MgCl2) for proteins [18], the increase in the free energy of the solutes [19, 20]

or hydrophobic interactions [14, 17]. The increase in sorption in acrylic due to anions

follows the lyotropic series of Hofmeister as shown in Section 3.3.3 for wool, and in the

sequence of sulphates > acetates > chlorides > iodides [21]. Others reported that Cl- was

more effective than other anions [10].

Figure 7.6 The effect of salt on the equilibrium sorption of cationic dyes on acrylic

fibres. Curve I represents sulphates and phosphates; Curve II represents chlorides,

nitrates, and bromides [16], redrawn from the experimental results of reference [15].

Thus the exhaustion values presented in Figure 7.7 exhibited two distinct phenomena

for cationic dyeing of acrylic fibres. Firstly, up to 1.0% o.m.f., the exhaustion was over

Salt concentration in dyebath

Dye

sorp

tion o

n f

ibre


224

95%, which means the saturation values of fibre was yet to be reached. A slight

reduction in exhaustion at 1.0% o.m.f. depth in SSW can be explained by the

competition between dye cations and salts for the sorption sites which the reduced ionic

interactions between dye and fibre. Secondly, at 3.0% o.m.f. depth, a much lower

exhaustion value was observed compared to below 1.0% o.m.f. depth, which means a

saturation limit was established in the dyeing system. A slightly higher exhaustion value

was observed in SSW and may be explained by the increased hydrophobic interactions

due to presence of salt at higher concentration in SSW. It can be concluded that a

combined total concentration of around 0.5M chloride ions of K, Na, Mg, Ca and

MgSO4 can increase dye sorption, as was observed with a high concentration of Na2SO4

(i.e. 0.922 M) [15]. Further the Na2SO4 (0.028 M) used in this study for DSW dyeing

was functioning as a retarding agent for improved levelling as evidence in the

exhaustion values.

Figure 7.7 %E of Cationic dyes at different depths. - distilled water dyeing; and -

simulated seawater dyeing

Coupled to the dye exhaustion studies it was observed that a consistent build-up of

colour was achieved for all dyes, Table 7.1. The colour yield increase from 1.0% to

3.0% o.m.f. depth, for both DSW and SSW, was relatively small. The increment in

conjunction with the exhaustion values indicates that the saturation point of dyeing for

acrylic fibre has been achieved. Colorimetric data for trial 1 and 2, also supported this

result, providing almost comparable L*a*b* values. Colour difference values, ΔE*94,

under 1.0 is within an acceptable range. At 0.05% and 1.0% o.m.f. depth, the ΔE*94 was

due to the higher K/Sλmax values in DSW whereas at 3.0% depth, the increased K/Sλmax

values resulted in increased colour difference.

0

10

20

30

40

50

60

70

80

90

100

0.05% 1.0% 3.0% 0.05% 1.0% 3.0% 0.05% 1.0% 3.0%

CI Basic Red 46 CI Basic Blue 41 CI Basic Yellow 45

%E


225

Table 7.1 K/Sλmax and ΔE*94 of cationic dyes at 0.05, 1.0 and 3.0% o.m.f.

Dye Applied

K/Sλmax ΔE*94

0.05%

o.m.f.+

0.05%

o.m.f.*

1.0%

o.m.f.+

1.0%

o.m.f.*

3.0%

o.m.f.+

3.0%

o.m.f.*

0.05%

o.m.f.

1.0%

o.m.f.

3.0%

o.m.f.

Basic Red 46 2.1 2.2 32.9 32.4 42.1 45.2 0.9 0.8 2.0

Basic Blue 41 2.4 2.3 36.8 32.4 42.2 43.0 0.9 1.2 0.8

Basic Yellow 45 1.3 1.3 21.4 20.6 32.0 33.8 4.3 2.2 3.7




Cationic dyes on acrylic fibre show good fastness to washing and rubbing because the

washing temperature is well below the Tg of the fibre polymer [5]. It also shows

outstanding resistance to weather, micro-organisms and sunlight due to its hydrophobic

nature [6]. Similar wash and rub fastness result were found in this study for DSW and

SSW dyeings, Table 7.2 with a range from 4 to 5. The cross-staining was also in the

range from 4 to 5, with little or no difference between SSW and DSW. Staining of the

blue dye at 3.0% o.m.f. depth, on the nylon strip, was as low as 2/3 for both fabrics.

Table 7.2 Comparison of fastness properties of cationic dyes

Dye %

o.m.f.

Wash fastness Wool

Staining

Nylon

Staining

Acetate

Staining

Dry Rub

fastness


C. I. Basic

Red 46

0.05 5 5 5 5 5 5 5 5 5 5

1.0 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 5 5

3.0 4 4 4/5 4 4 4 3/4 3 5 5

C. I. Basic

Blue 41

0.05 4/5 4/5 4/5 4/5 4/5 4/5 5 5 5 5

1.0 4 4 4/5 4/5 4 4 4/5 4/5 5 5

3.0 4 4 4/5 4/5 2/3 2/3 4/5 4/5 5 5

C. I. Basic

Yellow 45

0.05 5 5 5 5 5 5 5 5 5 5

1.0 4/5 5 4/5 4/5 4/5 4/5 4/5 4/5 5 5

3.0 4/5 4/5 4/5 4/5 4/5 4 4/5 4/5 5 5


226

7.4 Conclusions

Based on the experimental results on acrylic dyeing with cationic dyes it can be

concluded that:

A linear absorbance/concentration curves were found for each of the dyes

although yellow dyes exhibited a slightly different gradient in SSW;

A saturation limit was observed as at 1.0% o.m.f. application the exhaustion

value was over 90% while at 3.0% o.m.f. depth it only reached over 77%;

The saturation level of dye sorption in acrylic fibre through ionic interactions

can be increased by addition of electrolytes or their anions due to increased physical

interactions as showed at 3.0% o.m.f. depth in SSW. At low concentrations, electrolytes

retard dyeing thus acting as levelling agents;

Colorimetric data reflected the exhaustion data where K/Sλmax increased with as

the application level increased to 3.0% o.m.f. The colour differences again mirrored the

colour strength profiles and at lower depths colour differences were acceptable but at

the same time build-up can be at different depending on the application level;

Cationic dyes on acrylic fibre in general show good fastness properties, and this

was observed over wash and rubbing fastness and cross-staining for the both DSW and

SSW dyebath.


227

7.5 References


Enfield, N.H.

2. Gupta, V. B. and V. K. Kothari, eds. Manufactured Fibre Technology. 1997

Chapman & Hall, New York.

3. El-Shishtawy, R. M. and N. S. E. Ahmed, Anionic coloration of acrylic fibre.

Part 1: Efficient pretreatment and dyeing with acid dyes, Coloration

Technology, 2005, 121 (3), p.139-146.

4. Cox, R., Acrylic and modacrylic fibers, 1st ed. Synthetic fibre dyeing, ed. C.

Hawkyard, 2004, Society of Dyers and Colourists, Bradford, p 122-163.



6. Park, J. and J. Shore, Fibre Types and Dyeing Processes Practical Dyeing, Vol.

2, 2004, Society of Dyers and Colourists.

7. Trotman, E. R., Dyeing and Chemical Technology of Textile Fibres, 4th ed.,

1970, Griffin, London.

8. Vončina, B., V. Vivod and D. Jaušovec, β-Cyclodextrin as retarding reagent in

polyacrylonitrile dyeing, Dyes and Pigments, 2007, 74 (3), p.642-646.

9. Huntsman, Technical Information Data, 2007, Huntsman International LLC.

10. Balmforth, D., C. A. Bowers and T. H. Guion, Acrylic polymer composition and

its relation to basic-dye substantivity, Journal of Society of Dyers and

Colourists, 1964, 80, p.577-583.

11. Laucius, J. F., R. A. Clarke and J. A. Brooks, Dyeing "Orlon" acrylic fiber and

blends with other fibers, American Dyestuff Reporter, 1955, 44 (11), p.362-366.

12. Arcoria, A., M. L. Longo and M. Torre, Dyeing rate of cationic dyes, effects of

pH, dyebath concentration, temperature and electrolytes, Chim. Ind., 1981, 63,

p.330-332.

13. Longo, M. L., D. Sciotto and M. Torre, The role of electrolytes in the cationic

dye-acrylic fiber system, Textile Research Journal, 1982, 52 (4), p.233-237.

14. Beckmann, W., Dyeing polyacrylonitrile fibres with cationic dyes, Journal of the






228



p.283-289.

17. Cegarra, J., Physical chemistry of the dyeing of acrylic fibres with basic dyes,


18. Melander, W. and C. Horváth, Salt effects on hydrophobic interactions in

precipitation and chromatography of proteins: An interpretation of the lyotropic

series, Archives of Biochemistry and Biophysics, 1977, 183 (1), p.200-215.

19. Arakawa, T., Thermodynamic analysis of the effect of concentrated salts on

protein interaction with hydrophobic and polysaccharide columns, Archives of

Biochemistry and Biophysics, 1986, 248 (1), p.101-105.

20. Arakawa, T. and S. N. Timasheff, Mechanism of protein salting in and salting

out by divalent cation salts: balance between hydration and salt binding,

Biochemistry, 1984, 23 (25), p.5912-5923.

21. Hofmeister, F., On the understanding of the effect of salts, second report, on the

regularities in the precipitating effect of salts and their relationship to their

physiological behavior, Arch. Exp. Pathol. Pharmakol., 1888, 24, p.247-263.

229

Part B: Development of Novel Filter

Media for Textile Effluent Treatment

Surface Characterisation of Filter Media

230

8. Surface Characterisation of Filter Media

8.1 Introduction

Filtration of liquids can be achieved either through microfiltration, nanofiltration,

ultrafiltration or reverse osmosis [1]. The simplest filtration approach is through a

microfilter media which typically consists of a coated woven fabric with a well-defined

pore size. A number of factors can affect the filtration performance of dye solutions and

removal of colour from waste effluent.

As discussed in Section 1.6.8 the major problem for all filtration processes is the

reduction of flow as the filtration continues due to the accumulation of

particles/molecules on media surface, known as membrane fouling or media blinding

[2]. Therefore, several approaches and various combinations have been proposed to

recycle and then reuse textile wastewater in a cost effective way [3, 4, 5]. The methods

that were investigated to control the propensity to fouling/blinding include [6]:

By reducing the concentration of foulant, e.g. through coagulation/flocculation;

By promoting mass transfer from media surface to bulk, e.g. through turbulence;

By reducing the foulant capacity to attach to media surface, e.g. media fibre or

surface modification.

Microfilters are the dominant sector in separation technology and are relatively cheap.

The attractive performance profile also includes a higher filtration rate per unit area

with much less media surface and cost effective for many applications [7, 8]. It has been

reported that inorganic microfilters such as titania-coated stainless steel and ceramic

filters can remove soluble anionic dyes such as C. I. Direct Red 2 and C. I. Acid Red 1

and ions from aqueous solution [9, 10]. In addition, a polypropylene microfilter with a

pore size 0.2 micron removed a maximum 50% of dye [8]. Soluble ionic dye can be

removed with filters with nominal pore diameters below that of the ionic dye

dimensions. Nevertheless a performance limitation would be always apparent if removal

levels of over 95% are required and a smaller pore size ultrafiltration or nanofiltration

would be necessary [8]. The assumption that molecular salt ions can easily pass through

the microfilter media was in contrast to results reporting that trace contaminants, time of

operation, construction of material and number of cleaning can influence the passage of

ions [7, 8].


231

Therefore in this study in order to develop robust separation systems a standard Azurtex

media has been surface modified and the influence of surface character of the media's

hydrophobicity/hydrophilicity on filtration rate, cake formation, cake release and

turbidity was investigated. The effect of surface modification was evaluated by direct

gaseous fluorination, fluorocarbon (FC) finishing or plasma polymerisation technology.

In all these modification techniques the fluorine content and fluorine species were

determined and the properties of the materials assessed. In general, it has been reported

that a higher fluorine content provides better weatherability, chemical and thermal

stability, solvent resistance to materials [11]. The properties of the fluorinated surface

depends on both the coverage and degree of order of fluorocarbon on the surface [12].

The aim of the treatments on the media was to introduce the surface functional groups

that can increase filtration efficiency and improve anti-fouling properties. In this

chapter, these surface modifications were characterised.

8.2 Experimental

8.2.1 Materials

With the success of Primapor filter media by Volooj [13], the newly advanced Azurtex

filter media (polyurethane coated polypropylene woven, 620gm-2

) was used for this

research and kindly supplied by Clear Edge Filtration, Haslingden, UK. Some of the

recent developments of Azurtex family have been given in 9.2.1. The Azurtex filter

media was surface modified by gaseous fluorination, plasma polymerisation and

gaseous fluorination followed by a fluoropolymer application, Table 8.1 the

fluorocarbon Itoguard LJC6MUL, supplied by LJ Specialities, UK, and is classified as a

cationic multi-purpose C6 fluorocarbon finish, 30% solids, typically applied at 10-80

gL-1

, dried at 100ºC for 1 minute and cured at 160ºC for 3 minutes.


232

Table 8.1 Modification of Azurtex media and its modification details

Reference Details

Untreated Azurtex filter media

Az Ito Azurtex treated with 50 gL-1 Itoguard LJC6MUL

Az 2%F2, 2' Fluorinated at 2% F2 for 2 minutes

Az 2%F2, 2', Ito Fluorinated at 2% F2 for 2 minutes and then treated with 50

gL-1 Itoguard LJCC6MUL

Az 2%F2, 10' Fluorinated at 10% F2 for 2 minutes

Az 2%F2, 10', Ito Fluorinated at 2% F2 for 10 minutes and then treated with

50 gL-1 Itoguard LJCC6MUL

Az 5%F2, 2' Fluorinated at 5% F2 level for 2 minutes

Az 5%F2, 2', Ito Fluorinated at 5% F2 level for 2 minutes and then treated

with 50 gL-1 Itoguard LJCC6MUL

Az 5%F2, 10' Fluorinated at 5% F2 level for 10 minutes

Az 5%F2, 10', Ito Fluorinated at 5% F2 level for 10 minutes and treated with


Az 10%F2 Fluorinated at 10% F2 level for 2 minutes

Az 10%F2, Ito Fluorinated at 10% F2 level for 2 minutes and treated with


P2i std Standard plasma treatment for textile surface

P2i 1° Plasma treatment for 40 minutes

P2i 2° Scale up plasma treatment

8.2.2 Fluorination

Following the work of Volooj [13] Azurtex media was gaseous fluorinated by Fluor

Technik GMBH, Germany (http://www.fts-de.com/) in an autoclave-type chamber. The

media were exposed to 2%, 5% and 10% of fluorine diluted with gaseous nitrogen, N2,

for specified time periods. A further batch was fluorinated in a 10%/90% F2/N2 gas

mixture, however the filter media could not withstand the intensive fluorination and

heat degradation was observed. It was observed that as the fluorination intensified, the

fluorinated sample changed its colour, Figure 8.1, from light blue to yellow green,

suggesting that extensive surface fluorination had progressed into the bulk [14] and sub-

surface as suggested by Mohr and Paul [15] and had modified the blue pigment.

http://www.fts-de.com/


233

Figure 8.1 Images of Fluorinated Azurtex filter media: a) untreated; b) Az 2%F2, 10'; c)

Az 10%F2 batch 1; and d) Az 10%F2 batch 2.

8.2.3 Fluorocarbon (FC) Finish Application

The Azurtex media were treated with the Itoguard LJC6MUL finish by a conventional

pad/dry/cure (PDC) method. Since the wet pick-up percentage was low, around 15%

o.m.f., a number of application variations were explored, such as varying the

concentration of the FC, the use of iso-propanol as wetting agent, increase the dipping

time and number of dips, and lowering the padding pressure. All of these measures

provided a maximum of 26% o.m.f. wet pick-up. The final processing conditions

selected were 50 gL-1

Itoguard, 30 seconds dipping time, 1 bar pad pressure and

1m/minute padding speed, respectively. The wet pick-up percentage was in the range of

19 to 23.5%, Table 8.2. Three 1/3 size of A4 media sheets were first dipped into the FC

solution, padded through a horizontal two-roll laboratory padder (Mathis Switzerland),

then dried at 90°C for 5 minutes and cured at 150°C for 2 minutes in a Mathis

baker/steamer. A lower curing temperature than the conventional temperature (180°C)

was chosen because polypropylene has lower melting points.

a) b) c) d)

10.0 mm


234

Table 8.2 Average wet pick-up percentge of original and fluorinated Azurtex media

Sample Average pick up % Standard error

Untreated 23.0 0.3

Az 2% F2, 2', Ito 23.3 0.2

Az 2% F2, 10', Ito 23.1 1.1

Az 5%F2, 2', Ito 21.9 0.4

Az 5% F2, 10', Ito 22.6 1.2

Az 10% F2, Ito 19.2 0.7

8.2.4 Plasma Treatment

The surface characteristics of polypropylene (PP) based materials, such as wettability

and adhesion, can be significantly altered by applying the appropriate plasma treatments

(e.g. argon, oxygen or fluorine) [16]. P2i (www.p2i.com) has developed nano-coating

technology to impart liquid repellent properties to the surface of materials. Its patented

“cold” non-equilibrium plasma technology, known as glow plasma, for materials

coating is claimed to produce thin layers, only molecules thick over the entire product

surface and does not adversely affect the bulk properties [6]. Depending on the initial

chemical composition of the plasma polymerisation feedstock variable composition

coatings can be grafted onto the surface and can impart a wide range of properties such

as increased liquid protection [17]. Therefore the resultant material has increased oil

and water repellency without affecting the material’s bulk properties or porosity and air

flow. Accordingly in this study we explored the potential for improved cake release in

filtration processing which offers performance improvements over a number of

application sectors. Overall the technology is claimed to be cost effective, quick,

substrate-independent, reliable, environment friendly and can produce high efficiency

oil/water repellent media [18] without using catalysts, cross-linking agents or

surfactants that require in traditional fluorocarbon application.

P2i have previously discussed their patented experimental process in several reported

studies [19, 20, 21]. In a typical plasma treatment for fluorocarbon application, the

experiments were carried out in an inductively coupled cylindrical glow discharge

reactor (5 cm diameter, 470 cm3 volume, base pressure of 6 × 10

-3 mbar, and a leak

rate of better than 6 × 10-9 mols-1

). The reactor was initially scrubbed with detergent

and rinsed with isopropyl alcohol and oven dried. The system was re-assembled and

http://www.p2i.com/


235

further cleaned with a 50W air plasma for 30 minutes. Then chamber was vented to air

and an A4 size Azurtex filter media was placed in the centre of the reactor. Next the

chamber was evacuated down to base pressure. Subsequently, the fluorochemical

feedstock vapour was introduced into the chamber at a constant pressure of ~0.2 mbar

and continued to purge for 5 minutes, followed by ignition of the glow discharge. After

5 minutes the deposition process was terminated, and the monomer vapour was passed

over the substrate for another 5 minutes. At the end of the cycle the plasma chamber

pressure was evacuated and then vented to atmosphere. The samples was treated under

three different conditions, the standard commercial process and two more aggressive

scaled-up processes, P2i std, P2i 1° and P2i 2°, respectively to see the fluorination

effect.


8.3.1 SEM Analysis

SEM was used initially to investigate the effect of surface treatments on the physical

topography of the media surface. Examination of the untreated polypropylene base

fabric showed the polypropylene filaments had relatively rough surfaces with some

roughening and surface particulates, Figure 8.2a. In contrast the untreated Azurtex has a

smooth surface due to polyurethane coating but there was variable coverage and

adhesion of the coating to the PP surface, Figure 8.2b. When the untreated Azurtex was

fluorinated, the roughening and etching increased with the increasing level of

fluorination, Figure 8.2c. More obvious fracturing/fusing occurred at the surface treated

with 10% F2 due to the exothermic nature of the gaseous treatment, Figure 8.2 d. It was

found that this roughness depends on the level of fluorination but that prolonged

exposure was not advantageous and led to degradation of the treated surface. In other

studies, extended fluorination was reported to cause increased surface roughness and

damage to the polymer structure [22].


236

Figure 8.2 SEM micrographs of fluorinated untreated PP fabric and Azurtex media at

different fluorination levels: a) Untreated PP, base fabric, magnification x 1.0K; b)

Untreated Azurtex, magnification x 1.0K; c) Az 2% F2, 10′, magnification x 2.0K; and

d) Az 10% F2, magnification x 1.0K.

SEM micrographs of the modified Azurtex media with the Itoguard fluorochemical

showed that, whether fluorinated or non-fluorinated, a physical layer was formed on top

of the PU coating or exposed fibres, hence smoothing out the rough surface, Figure

8.3a, b, and c. In contrast, the plasma polymerised treated samples showed surface

cracking and particles to varying degrees on the surface of the media, Figure 8.3d,

which also varied depending on the treatment time.

a a)

d)

b)

c)


237

Figure 8.3 SEM micrographs of modified Azurtex media at 2.0K magnification: a) Az

Ito; b) Az 2%F2, 10' Ito; c) Az 10%F2, Ito; and d) Az P2i std.

8.3.2 ATR FTIR Analysis of Filter Media

The ATR-FTIR technique provides chemical information up to several microns into the

fibre surface and offers potentially complementary information to the more surface

specific XPS technique [23].

The FTIR spectra of the untreated media, Figure 8.4, exhibited the typical vibrational

bands for a polyurethane: - NHstr (free and bonded) at 3300-3400 cm-1

, CH2str at 2850-

2950 cm-1

, C=Ostr in bonded urethane groups at 1620-1680 cm-1

(referred to as amide I),

NHstr stretch (amide II) and NH bending at 1533, 1540, 1313 and 1224 cm-1

[24, 25],

respectively, and -C-O-C-str in urethane groups at around 1000-1200 cm-1

[26, 27, 28].

Several kinds hydrogen bonds can be formed due to the presence of donor N-H group

and a C=O group in the urethane linkage [25]. C-C stretching vibrations, between 1373

to1600 cm-1

, originate from the aromatic ring from PU or aliphatic chain of PP.

a)

c) d)

b)


238

Figure 8.4 ATR FTIR spectra of untreated Azurtex media

Typically the C-F stretching vibration is observed in the 1100-1350 cm-1

region, Figure

8.5 and 8.6 and can also be observed weakly at 400-800cm-1

[26]. The band observed at

about 550cm-1

can be assigned to the asymmetric deformation mode of CF3 groups. The

presence of the C-Ostr in the urethane at a similar wavelength made it difficult to detect

the changes that occur due to fluorination and FC finishing. Due to high electronegative

inductive effect of fluorine atom, ester C=O group can shift up to 5.7 x 10-4

cm-1

[29],

which was observed in these specimens. After fluorination polymers can be oxidised by

the gaseous fluorine and in the spectra of the treated media there is an increase in signal

intensity between 1690 to 1780 cm-1

due to the formation of carbonyl species, Figure

8.5. With the gaseous fluorination of polypropylene polymer, acid fluoride species can

be formed and it’s C=Ostr absorption would occur at about 1820 cm-1

, however no

spectral intensity was found with the polyurethane coating. A broad peak appeared in the

region of 1103 cm−1 can be attributed to the C-F stretch [30]. The appearance of the 1145

cm−1 band for only FC finished media, Figure 8.6, was due to the C-F stretching.


239

Figure 8.5 ATR FTIR spectra of Fluorinated Azurtex media

Figure 8.6 ATR FTIR spectra of Fluorinated and FC treated Azurtex media

In the same way plasma treated medias produced similar bands in the C-F region,

Figure 8.7, with different intensities compared to each other and to the corresponding


240

FC finished media, suggesting different compositions and thicknesses of the fluorine-

based molecular species attached in order to impart water repellency.

Figure 8.7 ATR FTIR spectra of Plasma treated Azurtex media

8.3.3 XPS

The XPS wide scan spectra Figure 8.8, 8.9 and 8.10 indicate that fluorine has been

introduced into the filter media surface either by gaseous fluorination, aqueous

fluorocarbon application or plasma polymerisation. In this study, the C(1s) and F(1s)

regions were of particular interest in that they allowed good characterisation of the outer

1-10 nm. The surface nitrogen concentration, N(1s), attributed to the polyurethane

polymer, was below 1% and appears to be relatively low due to probable surface

coating of fluorine. As the degree of fluorination increased, a well-defined F(1s) peak at

a binding energy of 686.0 eV was evident demonstrating the surface enrichment of

fluorine at the media interface. The increasing abundance of surface oxygen, O(1s), as

the gaseous fluorination treatment severity increased, reflected the oxidative nature of

the treatment on exposure to subsequent atmospheric oxygen. Subsequent FC treatment

on both non-fluorinated and fluorinated surfaces produced an obvious increase in

fluorine concentration. Similar behaviour was also shown by the plasma treated

samples, Figure 8.10.


241

Figure 8.8 Widescan XP spectra of Fluorinated Azurtex filter media

Figure 8.9 Widescan XP spectra of Itoguard FC treated fluorinated Azurtex filter media

1100 1000 900 800 700 600 500 400 300 200 100

F1s

N1s O1s 10%F2

5%F2, 10'

5%F2, 2'

2%F2, 10'

2%F2, 2'

CP

S (

Arb

itra

ry u

nit

s)

Binding Energy, eV

Untreated

C1

s

1100 1000 900 800 700 600 500 400 300 200 100

CP

S (

Arb

itra

ry u

nit

s)

Binding Energy, eV

F1s

N1s O1s 10%F2, Ito

5%F2, 10', Ito

5%F2, 2', Ito

2%F2, 10', Ito

2%F2, 2', Ito

Az Ito

C1s


242

Figure 8.10 Widescan XP spectra of plasma treated Azurtex filter media

It was suggested that thickness of the gaseous fluorinated layer depends on the

fluorination time [15], composition of fluorination mixture and polymer nature [31].

This study shows that level of fluorine at the outer surface reached a maximum within

the first 2 minutes of gaseous fluorination. The result supported the findings of others

[13, 22, 32], which showed fluorination on the surface was a rapid process. Thus the

fluorine surface saturation remained almost the same for both 2 and 10 minutes of

gaseous treatment time. In contrast, the 10% fluorination treatment on the media

showed high levels of fluorine, with a fourfold increase relative to the initial 2% level,

and caused a colour change of the original media, due to severe oxidative degradation to

the polyurethane coating and the incorporated pigment. Table 8.3 also showed a

significant enrichment of fluorine on the surface after the FC finish, in the range of over

60% atomic fluorine. Az 10% F2 and Itoguard post-treatment showed a lower value of

surface fluorination than Az 5% F2, Ito, possibly for two reasons. Firstly, due to be

potential development CF3 group at fluorination stage, which reduced pick up of FC

chemical or alternatively available groups for cross-linking with PU were minimized.

Similarly plasma treated media produced a highly fluorine enriched surface, as high as

over 87%, for the standard treatment.

1100 1000 900 800 700 600 500 400 300 200 100 C

PS

(A

rbit

rary

un

its)

Binding Energy, eV

F1s

O1s P2i 2°

P2i 1°

P2i std

C1s


243

Table 8.3 XPS surface analysis of fluorinated and plasma treated Azurtex media

Sample Elemental composition, % Atomic ratio

C O F N Si F factor* F/O C/Si

Untreated 77.5 17.6 1.2 0.4 3.3 - - 23.9

Az Ito 64.1 24.7 9.2 0.5 1.6 9.2 0.4 40.3

Az 2%F2, 2' 64.4 24.6 9.4 0.6 1.1 9.4 0.4 59.0

Az 2%F2, 2', Ito 63.0 23.8 12.2 0.6 0.5 12.4 0.5 136.9

Az 2%F2, 10' 63.9 22.6 12.5 0.7 0.3 12.6 0.6 220.3

Az 2%F2, 10', Ito 50.2 20.1 28.7 0.9 0.1 36.6 1.4 502.1

Az 5%F2, 2' 46.8 8.5 43.8 - 0.8 60.0 5.1 58.5

Az 5%F2, 2', Ito 45.6 9.0 44.4 - 1.0 62.4 4.9 45.6

Az 5%F2, 10' 46.7 7.7 45.1 - 0.6 61.9 5.8 83.3

Az 5%F2, 10', Ito 43.8 8.1 47.7 - 0.5 69.8 5.9 93.1

Az 10%F2 45.2 7.7 46.8 - 0.4 66.5 6.1 118.8

Az 10%F2, Ito 45.8 7.7 46.1 - 0.4 64.4 6.0 109.1

P2i std 39.5 6.4 54.1 - - 87.8 8.4 -

P2i 1° 44.9 7.1 48.0 - - 68.5 6.7 -

P2i 2° 40.8 6.9 52.3 - - 82.2 7.6 -

*F factor is surface enrichment factor and defined as ratio between surface F/C and

stoichiometric F/C level [33].

The C(1s) XP spectrum of the untreated media was curve fitted using a Gaussian

Lorentzian procedure and showed two peaks from PU coating: C-H at 285.0 eV; C-O

and C-N at 286.6 eV, Figure 8.11. The characteristic peak of urethane (NH–CO2) at

289.5 eV was too small to allow accurate peak resolution. Similarly, the C(1s) XP

spectra of gaseous fluorinated, FC treated and plasma polymerised filter media were

curve fitted and quantified into six different components: C-H at 285.0 eV; C-O/CC-F

species at 286.6 eV; O-C=O/CHF at 289.0 eV, CF2 at 290.9 – 291.4 eV; and CF3 at

291.7-293.7 eV [13, 20]. The CHx functional groups decreased with fluorination and

other higher binding energy species were formed, in particular, oxygen related

functional groups formed such as C-OH, C=O, O-C-O and O-CO-O due to oxidation

and the electronegative fluorinated species. As shown in Figure 8.12, following

fluorination, the higher binding energy carbon species increase and additional oxidised

species start to appear. However as the CFx components increased, the CF3 component


244

only appeared when the media was extensively fluorinated at 10% level. The intensities

of CF2 and CF3 peaks relative to original fluorinated media also increased when the FC

chemical was applied, Figure 8.13. The peak intensities were also increased when same

amount of FC chemical was applied on the fluorinated media. In contrast the plasma

treated samples showed immediate peak intensities at CF2 and CF3, the highest levels

were for the P2i std sample, Figure 8.14.

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

Binding energy, eV

CHX

C-O

C-N

Figure 8.11 C(1s) XP spectra of untreated Azurtex filter media


245

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity, C

PS

a)

Binding energy, eV298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298296294292290288286284282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

Binding energy, eV

b)

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000c)

Binding energy, eV

Inte

nsity, C

PS

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000d)

Binding energy, eV

Inte

nsity, C

PS

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

C-O

C-CF

Binding energy, eV

e)

CF3

CF2

O-C=O

C-F

CHX

Figure 8.12 C(1s) XP spectra of fluorinated Azurtex filter media: a) Az 2%F2, 2'; b) Az

2%F2, 10'; c) Az 5%F2, 2'; d) Az 5%F2, 10'; and e) Az 10%F2 .


246

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298296294292290288286284282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

Binding energy, eV

a)

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

b)

Inte

nsity,

CP

S

Binding energy, eV

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298296294292290288286284282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

Binding energy, eV

c)

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

Binding energy, eV

d)

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

Binding energy, eV

e)

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

CHX

Binding energy, eV

f)

CF3

CF2

O-C=O

C-F C-O

C-CF

Figure 8.13 C(1s) XP spectra of Itoguard treated fluorinated Azurtex filter media: a) Az

Ito; b) Az 2%F2, 2', Ito; c) Az 2%F2, 10', Ito; d) Az 5%F2, 2', Ito; e) Az 5%F2, 10', Ito;

and f) Az 10%F2, Ito.


247

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

Binding energy, eV

a)

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

Binding energy, eV

b)

298 296 294 292 290 288 286 284 282

0

2000

4000

6000

8000

Inte

nsity,

CP

S

CHX

Binding energy, eV

c)

CF3

CF2

O-C=O

C-F

C-O

C-CF

Figure 8.14 C(1s) XP spectra of plasma treated Azurtex filter media: a) P2i std; b) P2i

1°; and c) P2i 2°.

8.3.4 Wettability

In this study, the surface wetting properties of the treated filters are of interest since in

general, it is known that the hydrophobic surfaces are prone to fouling/blinding due to

the hydrophobic interactions between the surface of filter materials, solutes, and

microbial cells [34]. The adsorption of organic species and the precipitation of inorganic

salts could be other factors [34]. Previously it was shown that the anti-fouling property

of microporous polypropylene media can be improved by surface modification through

grafting hydrophilic polymer [35, 36, 37] or plasma technology [34, 38]. Thus

hydrophilicity/hydrophobicity of the surface can be an influential indicator to organic

fouling. Lower surface contact angle, a measure of hydrophilic surface, has been

correlated with improved fouling/blinding resistance [39, 40]. Consequently, imparting

hydrophilicity could make blinding less critical and improve filtration performance [41].

However it is also known that surface characterization of media may not reflect their

bulk properties [40].

Polypropylene-based media are widely used for microfiltration but their hydrophobicity

is high which may cause the adsorption of hydrophobic and amphoteric solutes [42].


248

The contact angles, wetting time and 3M oil/water repellency of the media can indicate

the hydrophilicity or hydrophobicity of the media. The water/oil repellency and wetting

time of the filter media are shown in Table 8.4 and it can be seen that the fluorinated

Azurtex media exhibited increased wettability. Although the result was unexpected as

fluorine is a highly electronegative oxidative molecule nevertheless the water repellency

rating remained zero as measured after 60 seconds. Similar trends were reported for the

surface fluorination of PP in other studies [43, 44, 45], and Volooj [13] reported that

fluorination of the Primapor media increased wettability but that it was not directly

proportional to an increase in the fluorination treatment time.

The Azurtex media has a PU coating with hard segment fraction which similarly reacts

with the PP material during fluorination. The shorter fluorination times was resulted an

increase in the polar component of the surface energy, but decreased with increasing

fluorination. Although the change in wetting time was significant as the degree of

fluorination or treatment time increased, with the wettability decreased dramatically for

Az 10%F2, where it is likely the higher amounts of CF3 and CF2 on the surface, as

evident by XPS analysis , reduced wetting. The surface hydrophobicity of the gaseous

treated media was significantly increased with the further addition of FC chemicals. It

was evident that the FC chemical finish was responsible for maximum wetting time of

4800 seconds considered in this study, whether the surface was fluorinated or non-

fluorinated. Plasma treated filter media also showed an increasing wetting time

particularly for plasma std and 2° treatments. It is also known that the location of

plasma-polymerised fluorocarbon films is essentially a surface phenomenon [46].


249

Table 8.4 Oil/Water repellency and wetting times for treated Azurtex filter media. 4800s

has been the upper measurable limit

Sample Water Repellency

Rating

Oil Repellency

Rating

Wetting time

(s)

Untreated 0 0 8

Az 2%F2, 2′ 0 0 15

Az 2%F2, 10′ 0 0 21

Az 5%F2, 2′ 0 0 22

Az 5%F2, 10′ 0 0 26

Az 10%F2 0 0 386

Az Ito 4 3 4800

Az 2%F2, 2′, Ito 4 4 4800

Az 2%F2, 10′, Ito 4 3 4800

Az 5%F2, 2′, Ito 4 3 4800

Az 5%F2, 10′, Ito 4 3 4800

Az 10%F2, Ito 4 4 4800

P2i std 4 3 4800

P2i 1° 4 3 2000

P2i 2° 4 3 4800

Although hydrophilic surfaces were reported to be favourable for anti-fouling

applications, nevertheless a decrease of flux was also observed due to the deposition of

cake layer. Thus an improvement of flux and ease of cake removal was considered

important and achievable by imparting a hydrophobic FC treatment after fluorination of

the Azurtex filter fabric. The results of the 3M oil/water repellency in Table 8.4 showed

that the 60 seconds threshold for the test was enough to get similar

hydrophilic/oleophilic properties for both the original and fluorine treated filters. The

FC and plasma treated filter media were found to have water and oil repellency ratings

of 4 and 3, respectively, which means they can repel 40% water/60% isopropyl alcohol

mixtures and hexadecane, offering a reasonable level of liquid repellency. In contrast,

Pre-fluorination of filter media before FC treatment didn’t change the water and oil

repellency, except at the 10% level. This effect can be explained by the FC coating

cross-linking the porous structure of the filter fabric thus making the fabric more

“impenetrable” to any effect that can be caused by the fluorination.


250

The contact angle remained in the range of 130 to 145°, but it did not correlate with Az

2%F2, 2′, Ito and P2i 1° due to the presence of CF2 and CF3 groups compared to the

overall alkyl C(1s) species, Figure 8.15. It has been established that surface tension

decreases in the order of CH2 (36 mN/m) > CH3 (30 mN/m) > CF2 (23 mN/m) > CF3

(15 mN/m) [47]. CF3 is more effective than CF2 at lowering the surface tension due to

the bulky F atom lowering the density of attractive centres per unit area at the surface

[48], which could be attributed to the lower contact angles for Az 2%F2, 2′ Ito and P2i

1° samples. Additionally, the wetting properties of fluorinated surfaces depend on both

the coverage of surfaces and degree of order in the surface [12]. A uniformly organized

or closely packed CF3 groups can create the lowest possible surface tension [47].

Figure 8.15 Relationship between contact angles and (CF2+CF3)/C(1s) in modified

selected filter media. ■ – contact angle (°); and ▲- (CF2+CF3)/C(1s).

8.4 Conclusions

The results illustrate that a combination of XPS and ATR FTIR analysis provides

information about the chemical structure of the surface of the filter media. Fluorination

can improve and impart stable hydrophilic properties, which could reduce media

fouling/blinding. The XPS study showed a gradual increase in the -CF2 and -CF3

functionality signal intensities that resulted in imparting hydrophobicity. These

modifications on untreated filter media provides water repellency and oil repellency

could alter the cake discharge performance. The presence of electronegative group,

fluorine, could potentially improve the flux, hence promote improvements in efficiency.

0%

10%

20%

30%

40%

50%

60%

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

Untr

eate

d

Az

10%

F₂

Az

Ito

Az

2%

F₂,

2',

Ito

Az

2%

F₂,

10',

Ito

Az

5%

F₂,

2',

Ito

Az

5%

F₂,

10',

Ito

Az

10

%F₂,

Ito

P2i

std

P2i

1°

P2i

2°

Ato

mic

% (

CF₂+

CF₃)

/C(1

s)

Conta

ct a

ngle

, d

egre

e


251

8.5 References

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ISBN 9781856174640.

2. Akbari, A., J. C. Remigy and P. Aptel, Treatment of textile dye effluent using a

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3. Lau, W.-J. and A. F. Ismail, Polymeric nanofiltration membranes for textile dye

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348.






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6. Yang, J., Prospects for flux enhancement in anaerobic membrane bioreactors

treating saline wastewater, in Civil Engineering and Geosciences, 2013, Delft

University of Technology. p.141.

7. Porter, J. J., P. J. Brown and J. Malphrus, Influence of pH on the rejection of

salts and ionic dyes by microfilters, Desalination, 2005, 184 (1–3), p.23-35.

8. Porter, J. J. and A. C. Gomes, The rejection of anionic dyes and salt from water

solutions using a polypropylene microfilter, Desalination, 2000, 128 (1), p.81-

90.

9. Porter, J. J. and S. Zhuang, Microfiltration of sodium nitrate and Direct Red 2

dye using asymmetric titanium dioxide membranes on porous ceramic tubes,

Journal of Membrane Science, 1996, 110 (1), p.119-132.

10. Porter, J. J. and R. S. Porter, Filtration studies of selected anionic dyes using

asymmetric titanium dioxide membranes on porous stainless-steel tubes, Journal

of Membrane Science, 1995, 101 (1–2), p.67-81.

11. Grampel, R. D. V. D., Surfaces of fluorinated polymer systems, 2002,

Technische Universiteit Eindhoven, Eindhoven. p.151.

12. Genzer, J., E. Sivaniah, E. J. Kramer, J. Wang, H. Körner, M. Xiang, K. Char,

C. K. Ober, B. M. DeKoven, R. A. Bubeck, M. K. Chaudhury, S. Sambasivan

and D. A. Fischer, The orientation of semifluorinated alkanes attached to

polymers at the surface of polymer films, Macromolecules, 2000, 33 (5), p.1882-

1887.


252




14. Rehwinkel, C., Fluorination of filter media, 2010, Fluor technik, Lauterbach.




16. Borcia, G., C. A. Anderson and N. M. D. Brown, The surface oxidation of

selected polymers using an atmospheric pressure air dielectric barrier

discharge. Part I, Applied Surface Science, 2004, 221 (1–4), p.203-214.

17. Coulson, S. and D. Cowieson, Plasma: efficient filter enhancement, Filtration &

Separation, 2005, 42 (9), p.38-40.

18. Coulson, S., Plasma processing: Nano-coating enhances filtration media,

Filtration & Separation, 2010, 47 (4), p.34-36.

19. Coulson, S. R., I. S. Woodward, J. P. S. Badyal, S. A. Brewer and C. Willis,

Plasmachemical functionalization of solid Surfaces with low surface energy

perfluorocarbon chains, Langmuir, 2000, 16 (15), p.6287-6293.

20. Coulson, S. R., I. S. Woodward, J. P. S. Badyal, S. A. Brewer and C. Willis,

Ultralow surface energy plasma polymer films, Chemistry of Materials, 2000, 12

(7), p.2031-2038.

21. Coulson, S. R., I. Woodward, J. P. S. Badyal, S. A. Brewer and C. Willis, Super-

repellent composite fluoropolymer surfaces, The Journal of Physical Chemistry

B, 2000, 104 (37), p.8836-8840.

22. Le Roux, J. D., D. R. Paul, M. F. Arendt, Y. Yuan and I. Cabasso, Surface

fluorination of poly (phenylene oxide) composite membranes: Part II.

Characterization of the fluorinated layer, Journal of Membrane Science, 1994,

90 (1-2), p.37-53.

23. Simon, F., G. Hermel, D. Lunkwitz, C. Werner, K. Eichhorn and H. J.

Jacobasch, Surface modification of expanded poly(tetrafluoroethylene) by means

of microwave plasma treatment for improvement of adhesion and growth of

human endothelial cells, Macromolecular Symposia, 1996, 103 (1), p.243-257.

24. Nakayama, K., T. Ino and I. Matsubara, Infrared spectra and structure of

polyurethane elastomers from polytetrahydrofuran, diphenylmethane-4, 4′-

diisocyanate, and ethylenediamine, Journal of Macromolecular Science: Part A -

Chemistry, 1969, 3 (5), p.1005-1020.

25. Oprea, S. and V. Oprea, Influence of crosslinkers on properties of new

polyurethane elastomers, Materiale Plastice, 2010, 47 (1), p.54-58.


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26. Stuart, B., Infrared spectroscopy: Fundamentals and applications Analytical

Techniques in the Science, ed. D. J. Ando, 2004, John Wiley and Sons, Ltd,

West Sussex.

27. Kuptsov, A. H. and G. N. Zhizhin, Handbook of Fourier Transform Raman and

Infrared spectra of polymers Physical Sciences data, Vol. 45, 1998, Elsevier,

Netherlands.

28. Schoonover, J. R., D. M. Dattelbaum, J. C. Osborn, J. S. Bridgewater and J. W.

Kenney, Pressure-dependent Fourier Transform Infrared spectroscopy of a poly

(ester urethane), Spectrochimica Acta Part A: Molecular and Biomolecular

Spectroscopy, 2003, 59 (2), p.309-319.

29. Rappaport, G., M. Hauptschein, J. F. O'Brien and R. Filler, Fluorinated Esters.

IV. The Effect of Neighboring Fluorine Atoms on the Ester Carbonyl Frequency,

Journal of the American Chemical Society, 1953, 75 (11), p.2695–2697.

30. Peng, H., P. Reverdy, V. N. Khabashesku and J. L. Margrave, Sidewall

functionalization of single-walled carbon nanotubes with organic peroxides,

Chemical Communications, 2003 (3), p.362-363.

31. Kharitonov, A. P., Direct fluorination of polymers-from fundamental research to

industrial applications, Progress in Organic Coatings, 2008, 61 (2-4), p.192-204.

32. Le Roux, J. D., D. R. Paul, J. Kampa and R. J. Lagow, Surface fluorination of

poly (phenylene oxide) composite membranes Part I. Transport properties,

Journal of Membrane Science, 1994, 90 (1–2), p.21-35.

33. Ming, W., L. van Ravenstein, R. van de Grampel, W. van Gennip, M. Krupers,

H. Niemantsverdriet and R. van der Linde, Low surface energy polymeric films

from partially fluorinated photocurable solventless liquid oligoesters, Polymer

Bulletin, 2001, 47 (3-4), p.321-328.

34. Yu, H.-Y., Y.-J. Xie, M.-X. Hu, J.-L. Wang, S.-Y. Wang and Z.-K. Xu, Surface

modification of polypropylene microporous membrane to improve its antifouling

property in MBR: CO2 plasma treatment, Journal of Membrane Science, 2005,

254 (1–2), p.219-227.

35. Liu, Z. M., Z. K. Xu, J. Q. Wang, J. Wu and J. J. Fu, Surface modification of

polypropylene microfiltration membranes by graft polymerization of N-vinyl-2-

pyrrolidone, European Polymer Journal, 2004, 40 (9), p.2077-2087.

36. Ulbricht, M. and G. Belfort, Surface modification of ultrafiltration membranes

by low temperature plasma II. Graft polymerization onto polyacrylonitrile and

polysulfone, Journal of Membrane Science, 1996, 111 (2), p.193-215.

37. Xu, Z., J. Wang, L. Shen, D. Men and Y. Xu, Microporous polypropylene

hollow fiber membrane. Part I. Surface modification by the graft polymerization

of acrylic acid, Journal of Membrane Science, 2002, 196 (2), p.221-229.


254

38. Liu, Z.-M., Z.-K. Xu, L.-S. Wan, J. Wu and M. Ulbricht, Surface modification of

polypropylene microfiltration membranes by the immobilization of poly(N-vinyl-

2-pyrrolidone): a facile plasma approach, Journal of Membrane Science, 2005,

249 (1–2), p.21-31.

39. Nabe, A., E. Staude and G. Belfort, Surface modification of polysulfone

ultrafiltration membranes and fouling by BSA solutions, Journal of Membrane

Science, 1997, 133 (1), p.57-72.

40. Gilron, J., S. Belfer, P. Väisänen and M. Nyström, Effects of surface

modification on antifouling and performance properties of reverse osmosis

membranes, Desalination, 2001, 140 (2), p.167-179.

41. Chang, I. S., S. O. Bag and C. H. Lee, Effects of membrane fouling on solute

rejection during membrane filtration of activated sludge, Process Biochemistry,

2001, 36 (8-9), p.855-860.

42. Shim, J. K., H. S. Na, Y. M. Lee, H. Huh and Y. C. Nho, Surface modification of

polypropylene membranes by γ-ray induced graft copolymerization and their

solute permeation characteristics, Journal of Membrane Science, 2001, 190 (2),

p.215-226.

43. du Toit, F. J., R. D. Sanderson, W. J. Engelbrecht and J. B. Wagener, The effect

of surface fluorination on the wettability of high density polyethylene, Journal of

Fluorine Chemistry, 1995, 74 (1), p.43-48.


Characterisation of surface properties, Journal of Fluorine Chemistry, 1999, 98

(2), p.107-114.


Adhesion properties, Journal of Fluorine Chemistry, 1999, 98 (2), p.115-119.

46. Gnanappa, A. K., C. O'Murchu, O. Slattery, F. Peters, B. Aszalós-Kiss and S. A.

M. Tofail, Effect of annealing on hydrophobic stability of plasma deposited

fluoropolymer coatings, Polymer Degradation and Stability, 2008, 93 (12),

p.2119-2126.

47. Zisman, W. A., Relation of the equilibrium contact angle to liquid and solid

constitution, in Contact Angle, Wettability, and Adhesion, Advances in

Chemistry Series, F. M. Fowkes, Editor, 1964, American Chemical Society,

Washington DC.

48. Johnson, R. E., Jr. and R. H. Dettre, eds. Chapter 1. Wettability, ed. J. C. Berg.

1993, Marcel Dekker, New York.

Performance of Filter Media

255

9. Performance of coagulation/ flocculation with

selected filter media

9.1 Introduction

Colour removal by pressure-driven media processing is industrially preferred over

conventional chemical treatments, e.g. ozonation, electro-chemical etc., as it provides

high removal efficiency and allows reuse of water and ingredients in the residual

dyebath [1, 2, 3]. However, a single filter stage may not be adequate for full removal of

colour, and even though there is continuous improvement in filter media treatment

processing, new materials for media are still being developed and sought. Ultrafiltration

has been successfully used for high molecular weight and insoluble dyes such as indigo,

and chemicals like PVA [4]. Nanofiltration and reverse osmosis can efficiently remove

low molecular soluble dyes like acid and direct dye, and are considered essential for

using reuse of dyeing wastewater [4, 5, 6].

In this chapter, the modified Azurtex filter media, as discussed in Chapter 8, was

selected as an appropriate separation system, but prior to testing surface modified filters

were benchmarked against newly developed filter materials in order to compare their

performance.

9.2 Filter Media Benchmarking Study

9.2.1 Experimental

A series of modified Azurtex filter media were supplied by Clear Edge Filtration, UK

were assessed as part of the benchmarking investigation. The proprietary filters were

identified as 28730A, 28730C, 28730K, 97400A, 97400C and 97400T, and their details

are given in Table 9.1. A standard TiO2 slurry was tested for measuring the performance

of media. The details of the slurry are given in Section 2.4. Ease of cake removal was

arbitrarily rated in a scale of 1 to 5, where 5 is the very good and commercially

attractive.


256

Table 9.1 Properties of the filter media used in the benchmarking study

Ref Fibre Weight Liquid Permeability

(l/m²/min@20kPa)

Warp x

Weft

Thickness

(Micron)

28730A Microporous

Polymer

Coating on PP

620 >110 31 x 14 950

28730C Microporous

Polymer

Coating on PP

620 <80 31 x 14 900

28760K PP 590 2 max. 31 x 14 900

97400A Polyester 620 >110 24 x 9.5 1000

97400C Polyester 610 <50 24 x 9.5 750

97400T Polyester 620 >80 24 x 9.5 850

9.2.2 Results and Discussion

9.2.2.1 Average Flow Rate and Filtrate Properties

The average flow rate of the filter media supplied by Clear Edge showed little

difference in the filtrate flows, Figure 9.1. Typically it took 80 to 90 seconds to filter a

50 mL slurry, except for filter media 28760K which took 100 seconds. In this

assessment, due to the limitation of air pressure system, the pressure was low and

variable, in a range of 2.5 to 5.5 bar, and therefore, a clear explanation was not possible.


257

Figure 9.1 Average flow rate of Azurtex and proprietary filter media, 28730A;

28730C; 28760K, 97400A; 97400C; and 97400T.

Table 9.2 shows the properties of the filtrate after filtration process. The recovery of

solution was over 96% for all the samples, which means a little slurry was lost in the

process. The average filtrate recovery was similar for all the media tested. The

differences in turbidity and solid contents percentage were much more obvious and

indicated that 97400C filter media was able to filter the slurry to an acceptable level,

with a much clearer filtrate compared to the other filters.

Table 9.2 Properties of permeate for benchmarking testing

Sample Solution recovery% Filtrate (g) Solid content% Turbidity (NTU)

28730A 97.1 43.9 0.38 >1000

28730C 98.0 44.9 0.28 291

28760K 97.2 44.9 0.68 >1000

97400A 97.1 43.9 0.34 299

97400C 97.5 44.4 0.05 33

97400T 96.9 43.1 0.24 232

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

filt

ra

te, g

ms

time (seconds)


258

9.2.2.2 Cake Properties

The properties of cake in terms of moisture content, thickness, and disposal rating is

given in Table 9.3. There was no difference in terms of moisture content and thickness

of the cake but the ease of cake removal was much better with filter 97400C. In general,

the 97400 series performed better for cake disposal with less filter fouling.

Table 9.3 Performance properties of cake for benchmarking test

Sample Moisture content% thickness (mm)

Cake disposal rating (arbitrary) wet dry

28730A 41.2 8.0 7.6 3

28730C 41.2 8.2 7.8 3

28760K 41.5 8.1 7.9 4

97400A 40.9 8.0 7.7 4

97400C 41.0 8.1 8.0 4

97400T 41.3 8.3 7.9 3

9.3 Filtration Performance Comparison Test

Modified Azurtex media as shown in Section 8.2.1, were tested and compared with the

9700C from the benchmarking test. The filtration of the plasma treated media was

carried out over six months of the plasma treatment.


9.3.1.1 Average Flow Rate and Filtrate Properties

The average flow rate of selected modified media is given in Figure 9.2. Fluorinated and

FC finished media imparted water repellency and hence it was difficult for slurry to

pass through the media. The 10% gaseous fluorinated and their corresponding FC

finished media violently shaked the filter bomb at the end of the filtration process due to

their inherent hydrophobicity. This study expected a higher flow rate with fluorinated

sample, which was achieved as it took lesser time to filter the slurry suspension.

Fluorination at the 2% or 5% F2 levels for 10 minutes increased the flow rate compared

to fluorination for 2 minutes. Extended fluorination imparted hydrophobicity and


259

reduced the process flux. Plasma treated filters displayed similar results to the

fluorinated filters. In contrast, FC finishing of non-fluorinated filter media surprisingly

improved the flow rate. The repeating filtration in each media produces a reduced flow

and cleaner permeates due to efficient cake formation and filtration.

Figure 9.2 Average flow rate of modified Azurtex filter media: Untreated; Az

Ito; Az 2%F2, 2′; Az 2%F2, 10′; Az 5%F2, 10′; P2i 1°; and

97400C.

Typically all the filter solution recoveries were over 95%, table 9.4, however

differences in turbidity were observed. Each gaseous fluorinated filter media produced

solutions with turbidity values below 600 NTU, while the comparable FC treated filters

displayed the highest turbidity values. In contrast the plasma polymerised

fluoropolymer treatments produced filtrates with much lower turbidity. The improved

flux of the Itoguard treated Azurtex filter media, compared to 97400C, was due to the

lower ability to filter TiO2 particles, as evidenced by the higher turbidity.

0

5

10

15

20

25

30

35

40

45

0 5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

Fil

trat

e m

ass,

g

time, s


260

Table 9.4 Properties of permeate after filtration process, a value of 1000 NTU was the

upper measurable limit

Sample Solution recovery,

%

Filtrate,

g

Solid content,

% Turbidity (NTU)

Untreated 97.8 41.4 0.06 491

Az Ito 97.3 40.1 0.09 >1000

Az 2%F2 2′ 97.8 40.1 0.05 406

Az 2%F2 2′ Ito 97.3 43.2 0.12 >1000

Az 2%F2 10′ 96.6 43.4 0.10 419

Az 2%F2 10′ Ito 97.7 43.3 0.11 >1000

Az 5%F2 2′ 98.0 44.5 0.07 663

Az 5%F2 2′ Ito 96.2 41.8 0.18 >1000

Az 5%F2 10′ 95.3 40.4 0.08 583

Az 5%F2 10′ Ito 97.2 40.8 0.13 >1000

Az 10%F2 96.5 40.1 0.05 479

Az 10%F2 Ito 93.1 42.3 0.20 >1000

P2i std 96.1 43.1 0.06 354

P2i 1° 96.7 41.2 0.06 357

P2i 2° 95.5 42.7 0.06 299

9.3.1.2 Cake properties

The moisture content, thickness and ease of cake removal of modified samples are given

in Table 9.5. The moisture content of the cake and weight of the dry cake remained

constant for each of the sample. The ease of cake removal is very important due to the

necessity for ease of cleaning and durability of media. Plasma treated filters provided

bigger size cake pieces and better cake removal compared to the other samples. Similar

results were obtained for Az 10%F2 and Az 5%F2, 10′ treated filters, perhaps due to the

increased CF2 and CF3 groups that were generated during the gaseous fluorination

imparting water repellency or due to the greater adhesion to the surface. In contrast, the

expected ease of cake removal of fluorinated and FC finished fabric was not achieved,

perhaps due to the "needle-like" orientation of the CF3 groups on the surface. The cake

often hardly attached to the filter bomb or the media and broke into pieces.


261

Table 9.5 Properties of cake after filtration

Sample Moisture

content%

thickness

(mm) Cake disposal rating

(arbitrary) wet dry

Untreated 40.9 8.3 7.9 3

Az ito 40.6 8.7 8.2 3

Az 2%F2 2′ 40.8 8.1 7.8 3

Az 2%F2 2′ Ito 41.1 8.5 8.0 2

Az 2%F2 10′ 40.6 8.3 8.0 2

Az 2%F2 10′ Ito 40.8 8.6 8.2 2

Az 5%F2 2′ 39.8 8.8 8.4 2

Az 5%F2 2′ Ito 39.9 8.5 8.1 3

Az 5%F2 10′ 39.8 8.6 8.3 4

Az 5%F2 10′ Ito 41.2 8.7 8.0 3

Az 10%F2 39.8 8.6 8.1 4

Az 10%F2 Ito 40.0 8.8 8.4 3

P2i std 40.6 9.0 8.3 4

P2i 1° 40.4 8.7 8.4 4

P2i 2° 40.9 8.7 8.4 3

9.3.2 Conclusions

Based on the research findings it can be concluded that:

Fluorination can improve the flux but the performance depends on the extent

and time of fluorination. However extended fluorination reduced the flux of the

process and destabilises the system. In contrast plasma polymerised

fluoropolymer surface coatings can improve the flow;

Fluorinated and FC finished filters offered little benefit in terms of improved

flow rate or lowering the turbidity of permeate. The ease of cake removal was

also low perhaps due to the orientation of CF3 groups on the surface;

Plasma treatment improved the flow, reduced turbidity and ease of cake removal

compared to the other modification;

Overall the 97400C filter performed better than any of the modified filters with

reference to lowering filtrate turbidity and ease of cake removal. Therefore this

media was used for recycling and re-used studies of exhausted dyebaths.


262

9.4 Coagulation/flocculation

Coagulation, flocculation and precipitation are often considered as the first steps in any

effluent treatment plant and are used to eliminate organic substances. The process itself

is not effective for removal of soluble dyes and can generate a large amount of sludge

[4, 7, 8]. However, it can enhance the retention of dyes in the subsequent media

filtration [9] with an associated reduction of fouling/blinding. Therefore,

coagulation/flocculation followed by membrane treatments is considered the most

successful combination for water reuse in textile processing [10, 11, 12, 13].

Generally, studies have focused on the complete removal of colour and reuse of the

effluents for standard dyeing processes. In addition, other studies have focused on the

reuse of wastewater and subsequent dyeing through electrochemical processing [14],

filtering, pH regulation or ion-exchange [15]. The combination of

coagulation/flocculation pre-treatment and microfiltration has been aimed at improving

the permeability and flux of the filtration processes [16, 17] by removing organic load.

Previously a 50% removal of organic load and 70% increment of flux have been

achieved with a coagulation-flocculation pre-treatment and the subsequent

microfiltration removed a further 30-70% organic load [16].

In this section, the efficiency of coagulation/ flocculation was evaluated with model dye

effluents. The coagulant/flocculant concentrations and pH were optimised and water

quality was determined, after microfiltration, in terms of colour removal and turbidity

reduction. Since microfiltration is only suitable for large molecular weight dyes, such as

pigment dyes [18], filtration was focused on removing organic loads and colloidal

particles in wastewater that would be generated from the reused wool dyeing baths.

9.4.1 Experimental

9.4.1.1 Materials

Woven wool (100%) Botany Serge fabric (2/2 twill, scoured and set, 295 gm-2

) was

supplied by Whaley’s, Bradford. Lanaset Blue 2R (λmax at 588 nm) and Sandolan Red

MF-GRLN (λmax at 494 nm) acid dyes were kindly supplied by Huntsman (formerly

Ciba) and Clariant, UK, respectively, and were applied to the wool at 3.0% o.m.f.,

without further purification. These dyes were selected as they performed well in


263

saltwater, as shown in Chapter 3 and are widely used in the textile industry. The

dyebath contained a wetting agent, Alpocol CPB (Ciba Specialty Chemicals), a pH

regulator (CH3COOH and NaOH) and a levelling agent, Lyogen MF (for the Sandolan

Red MF-GRLN dye), and Albegal Set (for the Lanaset Blue 2R dye), as recommended

[19].

9.4.1.2 Model Dye Effluents

Lanaset Blue 2R and Sandolan Red MF-GRLN acid dyes were used in this study and in

a typical acid dyeing process of wool, the average residual dye concentration is 0.15%

o.m.f. [20], or lower than 400 mgL-1

[21], and would include, apart from solid wool

particles, dyeing auxiliaries and substantial quantities of acids. Therefore a model dye

solution was prepared with 0.15% o.m.f. dye, 1.0 gL-1

levelling agent and 1.0 gL-1

wetting agent in simulated seawater. The aqueous pH for Lanaset Blue 2R and Sandolan

Red MF dyebaths was 5.80, respectively. Concentrated acetic acid or dilute caustic was

added to adjust the pH for filtration treatments. Filter bomb was used to carry out the

filtration through Azurtex filter media.

9.4.1.3 Coagulation/Flocculation and Filtration

The basic principle of Jar testing has been used in assessing the dual coagulation and

flocculation system with a vertical stirrer. 50 mL of model wastewater was placed in a

jar and the required amount of Pluspac 2000 was added and mixed rapidly at high speed

for 10 minutes at room temperature. The flocculant was then gradually introduced and

stirred into solution at slow speed for 5 minutes. The jar was then left unstirred and the

solution was settled for 24 hours. The test parameters evaluated were pH and the

concentrations of coagulant and flocculant. Since 12 gL-1


HPSS (Hydrosolanum PSS) was reported to be effective as a dual coagulation and

flocculation system for Lanaset Blue 2R dye solution with distilled water [20], initially

the solution pH was investigated in the range of 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 and 9.0 at

fixed coagulation and flocculation concentrations. Subsequently after selecting a

suitable pH, the amount of Pluspac 2000 and HPSS was varied to 12:8 gL-1

, 12:12 gL-1

,

15:10 gL-1

, 18:12 gL-1

, and 20:10 gL-1

in a ratio of 1:1, 2:1 and 3:2 to achieve maximum

removal of colour. The pH of the samples was adjusted by HCl or CH3COOH and

NaOH. In the filtration step of the reuse of dyebaths, the optimum pH and concentration

was used.


264

The coagulated/flocculated dye solution was strained in a 500µm steel sieve and

experiments with filter media performed in a pressure vessel, which has an active

filtration area of 38.48cm2. The operating conditions were using a variable pressure of

2.5 to 5 bar at room temperature. Removal of dye from the model dye effluents was

determined using a Perkin Elmer UV-Vis spectrophotometer at the wavelength of

maximum absorption.


9.4.2.1 Optimisation of Flocculation Parameters

Optimisation of parameters for coagulation/flocculation process is vital for filtration of

recycling dyebath effluents. Inefficient coagulation/flocculation can cause acceleration

of fouling [22]. The process strongly depends on the environment of the solution such

as pH, salt concentration, dye concentration, auxiliaries and the properties of

coagulant/flocculant itself [23, 24].

The addition of cationic Pluspac 2000 in the model dye effluent or exhausted dye bath,

did not produce any flocs possibly due to the use of smaller dye molecules and ions

rather than colloidal particles [24] or presence of salts, and no visible colour removal

was obtained. However when the anionic HPSS added to the effluent stable microflocs

or gels was formed.

9.4.2.2 Effect of pH

Volooj [24] used a concentration ratio of 12 gL-1

PP2000 and 8 gL-1

HPSS at pH 4.0 for

Lanaset Blue 2R dye to achieve a dye removal over 96% after filtration in DSW.

Similarly in this research the same ratio was initially used and the effect of pH in the

range of 3.0 to 9.0 was assessed, Figure 9.3. Using the Equation 2.6 the dye removal

was calculated and the results indicated that only 89% dye removal for Lanaset Blue 2R

dye was achieved. Nevertheless the optimum dye removal was obtained at pH 4.0, as

like Volooj [24], when flocs started to appear after flocculation [24, 25]. This can be

attributed to the overlapping of complex formation and sweep coagulation of the species

[25]. At pH 6 to 9, the colour of model dye effluent changed, and as the pH increased

the change of colour was rapid and fewer and fewer beads formed. In presence of

aluminium salts, the flocs were physically attached at the surface as the hydrous metal

oxide.


265

In contrast the treated Sandolan Red MF-GRLN dyebath did not show any significant

dye removal, with just below 30% removed across the tested pH range. The result

proved that there is a strong correlation between pH and dye removal for acid dye and

varies depending on the types of dyes in the stated pH range as reported earlier [26].

Figure 9.3 Effect of pH on dye removal on SSW dyebath. Coagulation/flocculation

with 12 gL-1


HPSS. ▲ – Lanaset Blue 2R; and ■ – Sandolan

Red MF-GRLN

9.4.2.3 Effect of Pluspac 2000 and HPSS Concentration

It is known that the optimal dosage of coagulant differs from one structure to another

[27]. For Pluspac coagulants dosing could be an important method to control media

binding/fouling [28]. When the suitable pH range was found, in order to address the

effect of the saline water environment, a further optimal concentration for PP2000 and

HPSS was determined. Lanaset Blue 2R dyebath set at pH 3.0 and 4.0 was more

effective with 15 gL-1

PP2000 and 10 gL-1

HPSS compared to the other concentrations

ratio, Figure 9.4. A similar level of dye removal was found with a concentration ratio of

18:12 gL-1

however, the former conditions would take lesser amounts of chemicals. A

further test was performed at a concentration of 15:10 gL-1

at pH 3.5, Figure 9.5.

Contrary to the other results in distil water [20] at pH 3.0, 3.5 and 4.0 the dye removal

percentage was not that variable in SSW and pH 4.0 was chosen as it was closer to the

dyeing pH. In all cases turbidity removal was very high, often achieving the same

10

20

30

40

50

60

70

80

90

100

3 4 5 6 7 8 9

Co

lou

r re

mo

val

, %

pH of the model dye effluent


266

clarity as tap water. It is reported that removal of turbidity at pHs below 5 depends on

charge neutralisation [29] but that the presence of dissolved organic matter makes the

system re-stabilised due to the displacement of the equilibrium of the positively charged

species [25].

Figure 9.4 Removal of Lanaset Blue 2R dye with different concentration of PP2000 and

HPSS at different pH. ■ – pH 3.0; ▲ – pH 4.0; and ●– pH 5.0

Figure 9.5 Colour removal and turbidity as a function pH for Lanaset Blue 2R dye with

15 gL-1


HPSS (turbidity of original dye solution was 46.2

NTU). ▲ – colour removal; and ■ – turbidity.

20

30

40

50

60

70

80

90

100

12:8 15:10 18:12 12:12 20:10

Co

lou

r re

mo

val

, %

PP2000:HPSS, gL-1

0

0.5

1

1.5

2

2.5

0

10

20

30

40

50

60

70

80

90

100

3.0 3.5 4.0 5.0

Tu

rbid

ity, N

TU

Co

lou

r R

emoval

%

pH of the model dye effluent


267

Since processing of the Sandolan Red MF-GRLN dyebath offered only minimal dye

removal, therefore various concentration ratios at pH range from 3.0 to 7.0 were

examined. Figure 9.6 showed that the optimum PP2000 and HPSS coagulant/flocculant

ratio improved the performance that was seen in Figure 9.3, and 61% dye removal was

possible at pH 5.0, at a concentration of 15:15 gL-1

. It can be seen the influence of pH

and concentration of flocculant was critical, and at pH 3 to 5 the increase of flocculant

concentration improved dye removal. However a sharp drop in performance was

observed when the flocculant concentration was reduced. This can be attributed to the

fact that flocculant concentration was not high enough to neutralise the positive charge

of the flocs. This effect can also be observed with the bath turbidity after

coagulation/flocculation, Figure 9.7. The initial increase in turbidity means there were

more particles available in the suspension and an incremental level of removal

efficiency was obtained. In contrast, the removal of dye at pH 6 and 7 remained level

over the concentration ratio range studied. In general, such low removal of Sandolan

Red MF-GRLN dye from solution was related to the dye structure. This acid milling

dye has a smaller molecular size compared to the Lanaset Blue 2R metal complex dye

and it is known that the greater the interaction between the coagulant and the dye, the

greater would be the dye removal [30].

Figure 9.6 Removal of Sandolan Red MF-GRLN dye with different concentration of

PP2000 and HPSS in gL-1

at different pHs. ■ - 3.0; ▲ - 4.0; ● - 5.0; ▬ - 6.0; and ♦- 7.0.

0

10

20

30

40

50

60

70

12:8 15:10 18:12 12:12 15:15 16:8

Colo

ur

rem

oval

, %

PP2000:HPSS, gL-1


268

Figure 9.7 pH effect on turbidity after coagulation/flocculation for Sandolan Red MF-

GRLN dye at different ratio of Pluspac 2000 and HPSS in gL-1

. - 3.0; - 4.0; - 5.0;

- 6.0; and - 7.0. A value of 1000 NTU was the upper measurable limit.

It is reported that the adsorption forces are the poorest for red dyes, where the

aluminium coagulant, Al2(SO4)3 has no effect on dye removal [31]. As a result

Sandolan Red MF-GRLN dye produced fewer beads and gels after flocculation

compared to Lanaset Blue 2R dye. In addition, the blinding due to

coagulation/flocculation of Sandolan Red MF-GRLN dye, in particular at pH 3 and 4,

was difficult to remove, and as reported was to be more or less reversible as a function

of molecular weight and class of dyes [6] and also a function of pH. The decrease of

flux was also observed particularly at pH 3 and 4 and the filtration process was not

stabilized even after 6 hours of operation. After stirring, the flow improved a little

although it was known that back-flushing would be more effective than stirring [32].

The effectiveness of the flocculation process can be measured by the reduction of

turbidity [25]. The concentration conditions of 15:15 gL-1

Pluspac 2000: HPSS at pH

5.0, where maximum removal of dye achieved, increased the turbidity over the upper

measurable limit of 1000 NTU after coagulation and flocculation but after filtration was

reduced to an acceptable value, Figure 9.8. In contrast, at pH 3.0 and 4.0, although the

turbidity was again low over 6 hours the flux was also very low due to the increased

physical attachment of gel and flocs to the media surface.

0

100

200

300

400

500

600

700

800

900

1000

Original 12:8 15:10 18:12 12:12 15:15 16:8

Tu

rbid

ity, N

TU

PP2000:HPSS, gL-1


269

Figure 9.8 Colour removal and Turbidity in a function of pH for Sandolan Red MF dye

with 15 gL-1


HPSS. ▲ – colour removal; and ■ – turbidity.

9.4.3 Discussion

To analyse the overall results in addition to the effect of the individual dyes, three

scenarios have to be considered. Firstly, the environment is simulated seawater, with a

total concentration of salt of over 35 gL-1

. Secondly, the effect of coagulant as a mixture

of metallic aluminium salts and organic polyelectrolyte in combination with a highly

anionic HPSS working in a dual component system. Thirdly there is microfiltration of

the flocculated effluent with modified Azurtex filter media.

9.4.3.1 Effect of Dye Structure in Coagulation/flocculation Process

The influence of chromophore and auxochrome groups is very important during

coagulation/flocculation, with dye retention reportedly varying according to the

molecular size and concentration of the dyes [21]. The lower anionic charge, smaller

chain lengths and non-linear structure of dye molecules decreased the effectiveness of

coagulation [26]. Due to the variety of dye molecules, the removal of dye is therefore

complex. Any removal of dye depends on the physicochemical coagulation and/or

chelation/complexation [33, 34]. It was found that acid dyes with positively and

negatively charged auxochrome groups do not coagulate well [35]. Therefore, selecting

an appropriate standard coagulant was difficult due to the high solubility of dyes and the

continuing development of new dye variants and associated chemical structures [30].

Even with nominally water soluble dyes, the solubility varies due to the different

0

50

100

150

200

250

300

350

400

450

0

10

20

30

40

50

60

70

3.0 4.0 5.0 6.0 7.0

Tu

rbid

ity, N

TU

Co

lou

r R

emo

val

%

pH of the model dye solution


270

chemical structures [4] and the dye formulation containing additives and impurities like

sodium chloride, sulphite cellulose [23].

The coagulation efficiency is also influenced by the type of chromophore presents in the

dye molecule. Using modified polyacrylamide as a coagulant it was observed that

decolourisation increased in following order: azo> xanthene (for acid dyes),

phthalocyanine> anthraquinone (for reactive dyes) [36]. In other study, using 12 acid

dyes with various chromophores, such as, azo, xanthenes, anthraquinone,

triarylmethane, and metal complex, Han et al. [35] concluded that levelling acid dyes

were more difficult to coagulate.

Yu et el [30] studied 27 Direct, Acid and Reactive dyes with an organic flocculant,

PAN-DCD, which is a mixture of polyacrylonitrile (PAN) and dicyandiamide (DCD),

and found that the dye removal under acidic conditions depended on the sulphonic acid

and carboxyl groups. The higher the number of acid groups, greater was the interaction

with flocculant and higher the dye removal. In contrast Han et al. [35] reported that

triarylmethane acid dyes with two sulphonic groups were easier to coagulate than dyes

with four sulphonic acid groups. Similarly, the greater the number and size of

hydrophobic groups the greater was the interaction with flocculant and resultant higher

dye removal. In the case of anthraquinone dyes, binding of flocculant depends on both

number of sulphonic acids and hydrophobic groups in the structure. Amino and

hydroxyl groups in dyes can also contribute to dye removal with the formation of

hydrogen bonds with the flocculants [30].

Aggregation of dyes also plays a role in membrane fouling and media blinding where

dye retention on the surface may lead to blocking of media pores. The permeate flow

could be low unless they form a porous cake of large particles [37]. It was reported that

molecular aggregation of dyes depends on pH and that high levels of aggregation of C.

I. Direct Red 1 at pH 4 occurred due to ionisation of the sulphonate group. Over pH 4,

the carboxyl group was dissociated which increased the solubility and hence

aggregation was reduced [38]. Dye aggregates were stated to be more dominant and

better adsorbed onto the fibre rather than the individual dye molecules [39]. This may

explain the behaviour of Sandolan Red MF-GRLN dye at pH 3 and 4, where irreversible

fouling occurred and flux was decreased drastically.


271

9.4.3.2 Effect of SSW in Coagulation/flocculation Process

The presence of inorganic salts in the SSW environment may change the interactions

between the cationic coagulants and anionic flocculants. Dye aggregation in the

presence of electrolyte is very distinctive and reported to cause similar aggregation

irrespective of dye concentration due to the screening effect of salt ions [40]. Higher

charge or higher concentration would increase the aggregates of C. I. Reactive Red 2 in

both acid and alkaline conditions. The aggregation is greater in presence of calcium and

magnesium ions than in the presence of sodium ions. In acidic conditions, the dye

aggregation due to the influence of metal ions is associated with a reduction in dye

hydrophobicity. In contrast, under alkaline conditions the dye hydrophobicity increased

[38]. The DLVO theory predicts that a colloidal suspension with low to moderate

charge should be coagulated when the concentration of salts exceeded the critical

coagulation concentration. In contrast, polyelectrolyte adsorption, in presence of salts,

increases due to non-DLVO surface interactions such as steric repulsion, depletion

forces [41, 42] and consequently dye retention could be higher [21].

The presence of NaCl influences negatively on the performance of biological

wastewater treatment and the extent of influence depends on the degree of salinity. In an

attempt to use the NaCl present in saline wastewater as a coagulant to control membrane

fouling/blinding it was found that this approach was ineffective, and concluded that an

external coagulant was necessary for long term control of fouling [28]. It was also

previously reported [43] that NaCl up to 80 gL-1

rapidly decreased flux during

nanofiltration for C. I. Reactive Black 5 but at a concentration up to 50 gL-1

the dye

rejection greater than 98.5% was achieved. Similar results were found for C. I. Acid

Red 7 and C. I. Acid Orange G, over a concentration range of 2 to 2000 mgL-1

[21]

where dye retention increased with a decline of flux as the concentration of NaCl

increased [44]. It was concluded that at low salt concentration cake layer formation was

the main cause of the decline in flux, but at higher ionic strength adsorption was the

dominant mechanism [43]. In a study of a wool effluent bath containing acid/metal

complex dyes it was shown that there was a flux decline of up to 73%, which is partly

reversible [45]. The decline of flux was largely dependent on the concentration of

organic loads, with a higher concentration causing a lower water flux [45].


272

MgCl2, one of the components of SSW, alone or in combination has been used as a

coagulant in wastewater treatment at concentrations of over 4 gL-1

, similar to in this

study [46]. MgCl2 can achieve up to 90% dye removal and was seen to perform better

than alum or polyaluminium chloride (PAC) [46], while the related MgCl2/Ca(OH)2

system was superior to MgCl2/NaOH, Al2(SO4)3, PAC and FeSO4/Ca(OH)2 in terms of

dye removal when tested with disperse and reactive dye waste [47]. In another study,

using CaCl2 as coagulant with a concentration up to 50 mgL-1

at pH 6.5 reduced the

COD and turbidity to 12 mgL-1

and 3 NTU, respectively [48]. It was also reported that

CaCl2 and MgCl2, followed by a PDADMAC cationic polymer could “clean up” some

dyehouse effluent, with CaCl2 being the more effective [49]. Similar results were found

when anionic polyelectrolytes were used as flocculant aids with calcium and

magnesium as the cation, with a concentration of moderate hardness [50] .

In other studies increasing the solution salinity from 10,000 to 25,000 ppm NaCl in

combination with PDADMAC resulted in increased removal of humic substances. A

subsequent increase of salinity up to 35,000 ppm did not produce any further increase in

dye removal as a further compression of double layer was negligible. Addition of heavy

metals with PDADMAC in the coagulation bath resulted in increased removal of humic

substances in a saline environment [51] which supports the previous study of the hybrid

Pluspac 2000 coagulant system. Monovalent electrolytes such as NaCl deteriorate the

performance properties of flocs derived from reactive dyes [24] while the direct

addition of divalent cations such as Ca2+

and Mg2+

improved biofloc strength in a pilot

study using industrial activated sludge [52].

9.4.3.3 Effect of Dual Component System in Coagulation/flocculation

Process

It was mentioned in Section 1.6.4.5 that in a dual component system the flocculation

behaviour essentially depends on the concentration of polycation and the molar ratio of

the anionic and cationic charges [53, 54]. A step by step introduction of cationic

coagulants caused “patchwise” adsorption and subsequent addition of high molecular

weight anionic flocculants, >1,000,000 caused bridging on the surface of the media [55]

. When the anionic flocculant is of low molecular weight then a complex mechanism

occurs. In this case, a molar ratio of anionic charges to cationic charges, n-/n

+ of 0.6

should be reached for effective flocculation [53, 54]. The influence of polyanions was


273

found to be critical compared to polycations for clay suspension [56]. This is evident

when the amount of polyanion flocculant was increased in Sandolan Red MF-GRLN

dye, which led to larger floc formation and higher dye removal and was also observed

in other studies [53, 57]. The size and strength of flocs depends on the molecular size,

degree of charge and ionic strength of solution [58].

In most dyebaths, there are anionic chemicals and auxiliaries and Zemaitaitiene et al.

[59] have shown that cationic polymers such as PDADMAC react with these anions,

and form intermolecular complexes of different stoichiometry. Under controlled

conditions these complexes can incorporate dye ions or molecules and precipitate

together. Flocculation is the result of this triple complex formation and can be

controlled by pH and ionic strength of solutions. Depending on the mixing ratio of

polycations/polyanions, n-/n

+, these complexes could eliminate commercial dyes, such

as C. I. Acid Blue 74 or C. I. Acid Yellow 3 due to their hydrophobicity and structure

[55].

At high salt concentrations the interaction between charges is “screened” and thicker

adsorbed layers formed, which depends on the ionic strength rather than the valency of

the counterions [60]. With increasing ionic strength, after initial screening of charges, it

is possible to have reduced adsorption affinity as salt ions compete with polymer and

surface charges [61, 62]. Overall the charge mechanism with “patchwise” adsorption

takes place when the added hybrid aluminium-organic polycation coagulant provides

adsorption sites. Subsequently, the high molecular weight polyanion causes polymer

bridging to produce larger flocs with some degree of complexation also observed.

9.4.4 Conclusions

Based on the experimental results and discussions the following conclusions can be

made:

Flocculation of dye solutions with the combined cationic hybrid Pluspac2000

and polyanionic Hydrosolanum protein derivative system was achieved;

Suitable pH and dosage of coagulants/flocculants were vital for the interaction

of dye and flocculants and, therefore floc formation and subsequent dye

removal. Each dye showed a distinctive relationship with pH and concentration

ratios in the formation of molecular aggregates;


274

The coagulant/flocculant system worked effectively in the saline environment

but was highly dependent on the class of dyes, their structure, molecular size,

concentration and structural linearity as evident through a metal complex and

levelling dye;

In the saline environment a relatively high concentration ratio of

coagulant/flocculants (PP2000:HPSS=15:10 gL-1

) was required for Lanaset Blue

2R dye compared to previous study in distilled water (PP2000:HPSS =12:8 gL-1

)

[24]. In addition only a maximum dye removal of 61% was achieved for

Sandolan Red MF-GRLN dye at these relatively high concentration ratios;

The mechanism of flocculation with polycation could be through “patchwise”

adsorption, which provides adsorption sites for polyanions and can form bridges

with polyanions. Possible complexation can occur due to the presence of salt,

the hybrid coagulant and anions. In this situation, the molar ratio of cationic

charges to anionic charges, n-/n

+ is crucial and this specificity was demonstrated

through the ratio of Pluspac 2000 and HPSS;

The model effluent used in this study had no visible turbidity and therefore

perhaps the required concentration of coagulant/flocculant compared to

industrial scenario maybe higher. Real dye effluent would be expected to contain

dissolved organic solids, which would enhance the flocculation process through

polymer adsorption;

The influence of the dye chromophore and auxochrome in the saline

environment led to a compact fouling layer as evident at pH 3 and 4 for the

Sandolan Red MF-GRLN dye. The behaviour could be explained either by the

formation of dye aggregates [39] or of the presence of di-cations, like Ca2+

and

Mg2+

, and lead to compact fouling and compression of the adsorbed double

layer [63]. The compression of the double layer by NaCl has its limitations and

above a certain ionic strength, the compression is negligible [51];

It was observed that inorganic salt such as NaCl deteriorated the floc properties,

but divalent salts improved them [52].

The decline of flux was due to the higher organic load. At higher ionic strength,

this decline was due to the dominant adsorption mechanism and cake layer

formation. The operating conditions similarly influence on the flux permeates.


275

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Recycling and Reuse of Textile Effluent

280

10. Recycling of Textile Wastewater and Re-use of

Exhausted Dyebaths

10.1 Introduction

Industrial textile wastewater contains dyes and chemicals such as salts, heavy metals,

dispersing agents, surfactants etc. and requires treatment prior to discharge [1]. A

Danish Research group in 1992 in their programme for water reclamation and reuse in

the textile industry strategized on a stepwise procedure for process optimization,

modernization of dyeing equipments, chemical savings or substitutions and water

reclamation and reuse of water and chemicals [2]. Reuse of residual dyebath has been

always considered as an alternative to prevent pollution and to reduce the consumption

of water, energy, chemicals along with the treatment of effluents [3, 4]. The majority of

work undertaken to date has focused on using cotton/Reactive, cotton/Direct, nylon

carpet/Acid, polyester/Disperse, nylon/Disperse, acrylic/Disperse, nylon

microfibre/Metal complex dye and nylon/Acid dye in package and batch dyeing in both

lab or industrial pilot scale studies [5, 6, 7, 8, 9, 10, 11, 12, 13]. The performance of

dyeing with exhausted dyebaths showed limitations compared to the “fresh” bath dyeing

as the dyeing behaviour in residual dyebath could only be applicable if processing

parameters such as pH, temperature remain compatible for subsequent dyeing [14]. The

major challenges are to reuse dyebaths with the least amount of treatments or if

possible, with no treatment at all.

The main aim of this work was to reuse “dyebath wastewater” in a simulated seawater

environment and combine a coagulation/flocculation treatment with microfiltration.

Then after identifying the optimum operating conditions, the filtration could be applied

at different stages of the dyebath sequence.

10.2 Experimental

10.2.1 Materials

For complete description of materials used in these experiments see Section 9.4.1.1.


281

10.2.2 Coagulation/Flocculation and Filtration

From Chapter 9, the optimum concentration ratios of Pluspac 2000 and HPSS were

found to be 15 gL-1

and 10 gL-1

, respectively, at pH 4 for the removal of Lanaset Blue

2R dye from dyebath. The maximum colour removal for Sandolan Red MF-GRLN was

at the ratio of 15 gL-1

Pluspac 2000 to 15 gL-1

HPSS at pH 5. The

coagulation/flocculation process followed by filtration with a filter bomb was carried

out according to Section 9.4.1.3. The 97400C material was used as the preferred filter

media as suggested in Section 9.3.2.

The concentrations of remaining dye in exhausted dyebath were determined by a Perkin

Elmer UV-Vis spectrophotometer at the wavelength of maximum absorption using

Equation 2.1. After the first filtration at any stages in the reuse dyebath, the filter media

were used for corresponding subsequent filtration at every 3rd

/4th

/5th

stages of dyeing.

10.2.3 Acid Dyeing of Wool

15 g wool fabrics were dyed at 3.0% o.m.f. depth by the procedure discussed in Chapter

3. The dyed fabric was then washed in cold water and then washed at 70°C for 10

minutes at room temperature with a 2 gL-1

non-ionic detergent (Eripon R, Ciba

Specialty Chemicals) and cold rinsed for 5 minutes with tap water and finally dried at

ambient temperature.

10.2.4 Dyebath Reuse and Recycling Procedure

The dyebath-reuse and/or dyebath-reuse-recycle-reuse sequence was repeated 11 times

(12 dyeings in total) and the sequence of the acid dyebath recycling and reuse procedure

is shown in Scheme 10.1. The standard procedure involved: 1) Dyeing of wool fabric in

three/four/five consecutive baths; 2) Coagulate/Flocculate the exhausted dyebaths; 3)

Filter the dye solution and reuse again. The optimum filtration sequence was

investigated and related to the dyeing performance. To assess the reuse test after

filtration, a reference dyeing without filtration was carried out to determine the

performance of recycled dyebath. The additional liquor contains 2 gL-1

levelling agent

and 2 gL-1

wetting agents to reconstitute the original dyebath.


282

Scheme 10.1 Sequence of recycling stages in acid dyeing reuse process

After each dyeing, the residual dyebath was analysed by the measuring absorbance at

the λmax for each dye allowing the dyebath exhaustion to be calculated and then

necessary amounts of dyes added to reconstitute the original dyebath at 3.0% o.m.f.

However, no attempts were made to determine the amount of levelling agents as there

was no evenness problem observed. Similarly no wetting agent was added, although in

some research, the original amount was added each reused dyebath without detailed

analysis of exhaustion [6, 15]. During the reuse tests, the permeate was directly used

and mixed with additional liquor required to reconstitute the dyebath to compensate for

evaporation and fabric “drag-out” losses. The percentage of additional liquor was in a

range of 6.5% to a maximum 20% of original liquor. The liquor contained 2 gL-1

of

levelling and wetting agents and the pH was readjusted after each dyeing.

It was assumed that chemicals and auxiliaries would be exhausted after consecutive

3rd

/4th

/5th

dyeing process after filtration [16]. Therefore, after each filtration process, the

dyebath was replenished with extra levelling and wetting agents to the original amounts

of 2 gL-1

. The amount of liquor to replenish the dyebath varied between 33% to

maximum 44% to make up the original amount. No attempts were made to determined

out the losses of salts from the SSW environment, as microfiltration is usually unable to

remove any significant amount of salts from the dyebath. However, the loss could be as

large as 13% if used as pre-treatment as previously shown in another study [17].


In any dyeing of textiles in addition to the exhaustion of the dye, three quality indicators

have to be maintained to validate the dyeing performance levelness, colour difference

and colour fastness of dyed fabric [14].

D1 D12 [No filtration]

D1-D3 D4-6 D7-9 D10-12 [After every 3rd

dyeing]

D1-D4 D5-8 D9-12 [After every 4th

dyeing]

D1-D5 D6-10 D11- 12 [After every 5th

dyeing]


283

10.3.1 Dyebath Exhaustion

With average exhaustion values of 88% and 78% for Lanaset Blue 2R and Sandolan

Red MF-GRLN dye, respectively, after the first dyeing, the dyeing performance is

comparable to the levels observed in the literature for acid dyes at high depths. Results

showed that despite reusing the same dyebath up to the 12th

time, the exhaustion level of

Lanaset Blue 2R dye has gradually increased, up to 4%, Figure 10.1. This result is

consistent with similar reuse experiments of up to 20 times of Acid Blue Marine Irgasol

dye [14], which concluded that dyeing from residual dyebaths has no negative effect on

the exhaustion of dyes. It was also reported that the presence of sodium chloride did not

cause any adverse effects on dye exhaustion of polyester/disperse dye [13]. In contrast

the exhaustion of the Sandolan Red MF-GRLN dye is interesting in that the exhaustion

level increased to around 90% in SSW, Figure 10.2, a 20% increase.

Figure 10.1 Exhaustion, %E, of Lanaset Blue 2R dye at different stage of dyeing, λmax at

588nm, in SSW: - no filtration; - filtration after every 3rd

dyeing; - filtration after

every 4th

dyeing; and - filtration after every 5th

dyeing.

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th

%E

Reused dyebath


284

Figure 10.2 Exhaustion, %E, of Sandolan Red MF-GRLN dye at different stage of

dyeing, λmax at 494nm, in SSW: - no filtration; - filtration after every 3rd

dyeing; -

filtration after every 4th

dyeing; and - filtration after every 5th

dyeing.

This level of increase of exhaustion is somewhat counterbalanced whenever

coagulation/flocculation and filtration of other exhausted dyebaths was performed and

the exhaustion decreased to as low as 53% and 57% for Lanaset Blue and Sandolan Red

dyes, respectively, and gradually increased in subsequent dyeing in the reused dyebaths.

It usually took three dyeings in the residual dyebath to reach the exhaustion values of

original dyeing before any further filtration takes place.

The overall filtration time for the exhausted dyebaths was up to 12 hours to filter 150

mLs of exhausted dyebath, but this would be improved with commercial filtration

systems.


Table 10.1 shows the colour strength, K/Sλmax, of dyed fabric with and without filtration

and it was evident that the K/Sλmax value remained similar in the reused dyebaths when no

filtration took place. In addition, after every filtration step, the K/Sλmax values initially

decreased, which then increased to the original values after successive dyeing. A

possible explanation could be that the unused coagulant/flocculant, limits the dye

molecules penetration into the fibre. The trend remained the same even when another

filtration was performed in the same dyebath cycle.

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th

%E

Reused dyebath


285

Table 10.1 Colour strength, K/Sλmax, of Lanaset Blue 2R, λmax at 610nm, and Sandolan

Red MF-GRLN, λmax at 510nm, dyed wool fabric. Dyeing performed in reused dyebath

with and without filtration.

Reuse

Dyebath

K/Sλmax of Dyed Wool Fabrics

Lanaset Blue 2R

λmax, 630 nm

Sandolan Red MF-GRLN,

λmax, 510 nm

No

filtration

Filtration after every No

filtration

Filtration after every

3rd 4th 5th 3rd 4th

5th

1st 25.5 24.4 23.2 25.4 24.1 25.0 24.4 25.0

2nd 22.4 22.7 22.8 22.9 23.1 23.7 23.9 23.3

3rd 22.7 22.7 23.0 22.8 23.4 24.0 25.1 24.7

4th 22.7 17.7 23.1 23.1 25.5 20.1 25.1 25.0

5th 22.9 22.8 17.2 22.2 25.2 21.4 21.9 24.3

6th 22.4 22.3 19.2 18.1 25.4 24.1 23.1 21.5

7th 22.5 16.3 19.4 21.8 27.0 21.7 23.8 23.8

8th 23.2 22.2 21.9 23.1 26.7 22.2 24.8 22.5

9th 24.0

25.3 23.3 21.1 24.5

10th 22.6

26.0 21.3 23.1 23.4

11th 22.3

26.7 22.4 22.9 20.6

12th 23.2

24.0 22.2 23.9 21.2

The distribution of dyed samples inside the acceptance ellipsoids CMC(2:1) of standard

colour difference (ΔE=1.0) for both dyes was illustrated in Figure 10.3, and 10.7. In

general, a total colour difference, ΔE CMC (2:1) value of less than 1.0 is considered

acceptable in the textile industry [13]. Figure 10.3 indicated that the ΔE CMC (2:1) values

for fabrics dyed from the reused dyebaths stayed outside the acceptable ellipse for

Lanaset Blue 2R but the values were in predictable close cluster and could allow colour

compensation and prediction.

In contrast, the Sandolan Red MF-GRLN dyed fabrics showed a close cluster near the

value of the fabric from the original dyebath, Figure 10.7, with a ΔE CMC (2:1) range of

0.33 to 0.72 units, which means no large colour difference between the 1st baths to 12

th

bath, which is acceptable in textile industry. This result was interesting in the sense that

with a remarkable increase of over 11% exhaustion, the colour difference between 1st

and 12th

bath was quite low, although a visual assessment showed a significantly deeper

colour in fabric dyed in 12th

reused bath.


286

Figure 10.3 ∆ECMC (2:1) plots for fabrics dyed with Lanaset Blue 2R dye with no

filtration of the dyebath


after the 3rd

reused dyebath

Dyebath 7

Dyebath 4

Dyebath 8

Standard

Standard


287

Figure 10.5 ∆ECMC (2:1) plots for fabrics dyed with Lanaset Blue 2R dye with filtration

after 4th

reused dyebath


after the 5th

reused dyebath

Dyebath 6

Dyebath 7

Dyebath 5

Dyebath 7, 8

Dyebath 6

Standard

Standard


288

Figure 10.7 ∆ECMC (2:1) plots for fabrics dyed with Sandolan Red MF-GRLN dye with

no filtration


filtration of the 3rd

, 6th

, and 9th

reused dyebath

Dyebath 4 Dyebath 7

Dyebath 10

Standard

Standard


289



, and 8th

reused dyebath

Figure 10.10 ∆ECMC(2:1) plots for fabrics dyed with Sandolan Red MF-GRLN after


and 10th

reused dyebath

Dyebath 5

Dyebath 12

Dyebath 9

Dyebath 6

Dyebath 12

Dyebath 8

Dyebath 11

Standard

Standard


290

Filtration of any the reused dyebaths increased the ∆ECMC (2:1) between the first dyebath

for both dyes, Figure 10.4, 10.5, 10.6, 10.8, 10.9, and 10.10, which subsequently

decreased as the reuse experiment continued without filtration. The dyed fabric after

filtration typically looked visually lighter and brighter. Thus, reuse of the residual

dyebath without filtration was sufficient to perform subsequent dyeing as it was obvious

that the filtrate has a limited influence on colour. Similar results were also found in

other studies using 4 to 20 reused dyebaths based on freshwater [2, 9, 14, 18]. This

proved the possibility of continuous use of residual dyebath over 12 cycles even in the

seawater environment without sacrificing colour conformity of the dyed sample. The

main difference in our study was gradual increment of exhaustion as the reuse of

dyebath continued.

The levelness of the dyeing is another factor that has been considered for successful

dyeing in reused dyebaths. The colour was measured at four different locations on the

surface of the fabric, and the DE values calculated between these locations. On average,

the difference between these positions remained below 0.20, with standard deviations

between 0.05 to 0.16 units. This indicated that levelness achieved over successive

reuses was excellent, irrespective of the filtration steps at any stages of reuse. It must be

noted that, this good levelness on fabrics dyed from reused dyebath with no filtration

was obtained without any further addition of auxiliaries.

In addition, levelness depends on the initial absorption and subsequent migration of

dyes in any particular dyeing cycles, and therefore, SSW provided similar levelness to

freshwater. De Vreese and Bruggen [18] also concluded that concentrations of iron and

manganese and degree of hardness do not cause any problems for reuse in

disperse/polyester and reactive/cotton systems. A contrasting result has been shown

when ammonium sulphate was used as the pH controlling agent and attributed to the

aggregating effect due to build-up of electrolytes [15].


291

10.3.3 Fastness

The results of fastness to colour change and staining for Lanaset blue 2R and Sandolan

Red MF-GRLN dye is given in Tables 10.2 and 10.3, respectively. The wash fastness

and dry rubbing fastness performance of Lanaset Blue 2R dyed fabric was in the range

4/5 to 5. Similarly for Sandolan Red MF-GRLN dyed fabric the fastness to colour

change and dry rub fastness was 4 to 4/5 in all reused dyebaths when no filtration takes

place. Staining to nylon and wool was quite low, but consistent throughout the reuse

experiments, agreeing with similar reuse experiments [9, 15]. Indeed, colour fastness

characteristics have not changed in residual dyebaths from those of initial dyebaths,

unless a filtration was performed where a decrease in wash fastness by 0.5 to 1.0 grey

scale units was observed. A possible explanation could be presence of

coagulant/flocculant in the filtered dyebath which limited the interactions of dye-fibre

and produced more surface dye on the coloured fibrous materials.

Table 10.2 Fastness properties of Lanaset Blue 2R dyed wool at different stages of

dyeing (Bold indicates dyeing stage after filtration)

Reused

Dyebath

Fastness to colour change Staining to Wool Staining to Nylon

No

filtration

Filtration after

every No

filtration

Filtration after

every No

filtration

Filtration after

every

3rd 4th 5th 3rd 4th 5th 3rd 4th 5th

1st 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

2nd 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

3rd 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

4th 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

5th 4/5 4/5 4 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

6th 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

7th 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

8th 4/5 4/5 4 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5 4/5

9th 4/5

4/5 4/5

4/5

10th 5

4 5

4/5

11th 4/5

4/5

4/5

12th 4 4 4/5


292

Table 10.3 Fastness properties of Sandolan Red MF-GRLN dyed wool at different

stages of dyeing (Bold indicates dyeing stage after filtration)

Reused

Dyebath

Fastness to colour change Staining to Wool Staining to Nylon

No

filtration

Filtration after

every No

filtration

Filtration after

every No

filtration

Filtration after

every

3rd 4th 5th 3rd 4th 5th 3rd 4th 5th

1st 4-5 4-5 4-5 4-5 3-4 3-4 3-4 3-4 2 2 2 2

2nd 4-5 4-5 4-5 4-5 3-4 3-4 3-4 3-4 2 2 2 2

3rd 4-5 4-5 4-5 4-5 3-4 3-4 3-4 4 2 2 2 2

4th 4-5 3-4 4-5 4-5 4 3-4 3-4 3-4 2-3 2-3 2 2

5th 4-5 4 4 4-5 3-4 3-4 3-4 3-4 2 2 2 2

6th 4-5 4 4 3-4 3-4 3-4 3-4 3-4 2 2 2 2

7th 4 3-4 4-5 4 3-4 3-4 3-4 3-4 2 2 2 2

8th 4-5 4 4 4-5 3-4 3-4 3-4 3-4 2 2 2 2

9th 4-5 4 3 4-5 3-4 3-4 4 3-4 2 2 2-3 2

10th 4 3-4 3-4 4 3-4 4 3-4 3-4 2 2 2 2

11th 4 4 4-5 4 3-4 3-4 3-4 3-4 2 2 2 2

12th 4 3-4 4-5 4 3-4 3-4 3-4 3-4 2 2 2-3 2

Turbidity measurements, Figure 10.11, show that except for the 3rd

and 4th

reused bath

for the Sandolan Red MF-GRLN F dyeings, the dyebath turbidity and associated

suspended particulates remained constant throughout the dyeing and reuse. The

turbidity differences between the dyes may be due to the structure of the dye or

associated components in the dyebath formulation.


293

Figure 10.11 Turbidity results of reused dyebath with no filtration. Turbidity of original

dye solution for Lanaset Blue 2R and Sandolan Red MF-GRLN dye is 46.2 and 149

NTU, respectively. ▲- Lanaset Blue 2R; and ■ – Sandolan Red MF-GRLN.

As it can be seen from Table 10.4 that combined coagulation/flocculation and filtration

has a significant effect on turbidity removal for Sandolan Red MF-GRLN dyes. The

turbidity was significantly increased after coagulation/flocculation and but reduced back

to near the value of freshwater after microfiltration.

Table 10.4 Turbidity at different stages of filtration for Sandolan Red MF-GRLN dye,

Tap water 0.59 NTU, DSW 0.21 NTU, SSW 1.63 NTU, a value of 1000 NTU was the

upper measurable limit.

Dyebath

Turbidity after Specified Filtration stage

Dyeing cycle, after Dyeing cycle, after Dyeing cycle, after

3rd

dyeing

6th

dyeing

9th

dyeing

4th

dyeing

8th

dyeing

5th

dyeing

10th

dyeing

Exhausted 299 293 303 363 217 178 273

Coagulated/flocculated 970 >1000 >1000 >1000 >1000 >1000 >1000

Filtered 16 5.4 8.58 3.49 2.21 3.77 3.68

0

50

100

150

200

250

300

350

400


Tu

rbid

ity, N

TU

Reuse dyebath


294


The effect of filtration on wool dyed fabric is clear, Table 10.5, and has produced a

twofold improvement over the comparable blank dyed fabric. Overall, the average

resistance improved albeit differently for the dyes tested. The fabric after first dyeing in

Lanaset Blue R and Sandolan Red MF-GRLN dye showed abrasion resistance levels to

10,000 and 19,000 cycles, respectively, which improved after first filtration at any

stages of reuse sequence. When no filtration takes place in reused dyebath the abrasion

resistance remained within the range of 8,000 to 13,000 cycles for Lanaset Blue R dyed

fabric. The abrasion resistance were much varied for Sandolan Red MF-GRLN dye in a

range of 9,000 to 19,000 cycles without any filtration. The latter dye produced an

abrasion resistance as high as 26,000 cycles after filtration at 5th

reused dyebath

sequence. Although no definite trend of abrasion resistance was found as a function of

the number of reused dyebath in SSW, however, it can be concluded that abrasion

resistance was at least similar if not better than the blank dyed fabric. It has been shown

in Section 4.3.6, that reactive dye induced inter and intra cross-linking with reactive

groups which improved wet burst strength and reduced loss of protein [19, 20, 21].

Table 10.5 Average abrasion resistance of wool dyed fabric in reused dyebath (Blank

dyed fabric has an abrasion level of 7500 cycles to two yarns broken)

Reused

Dyebath

Lanaset Blue 2R Sandolan Red MF-GRLN

No

filtration

Filtration after every No

filtration

Filtration after every

3rd 4th 5th 3rd 4th 5th

1st 10,000 - - - 19,000 - - -

2nd 13,000 - - - 21,000 - - -

3rd - - - - 17,000 - - -

4th - 13,000 - - 9,000 24,000 - -

5th 8,000 - 19,000 - 13,000 - 23,000 -

6th - - - 14,000 10,000 - - 26,000

7th - 19,000 - - 15,000 21,000 - -

8th 12,000 - - - 12,000 - - -

9th - - - - 11,000 - 19,000 -

10th 10,000 17,000 - - 9,500 22,000 - -

11th - - - - 19,000 - - 22,000

12th 8,000 - - - 11,000 - - -


295


Tensile strength of the wool dyed fabric in weft direction is shown in Figure 10.12.

Volooj [16] showed that bleaching of wool and cashmere fibre in recycled, and filtered

bath improved the tensile strength and attributed to the protective nature of protein

materials. However, in this study, dyeing in recycled dyebath did not produce any

significant changes. This study also found that strength remained consistent throughout

the reused dyebath and the variation lies within the standard deviation of the fabric.

Figure 10.12 Tensile strength of weft of wool dyed fabric in SSW at 3.0% (o.m.f.) depth

compared to blank dyed fabric: - Lanaset Blue 2R; - Sandolan Red MF-

GRLN; and ____

blank dyed fabric

10.4 Conclusions

The combined physico-chemical and microfiltration treatment applied to textile

wastewater achieved contrasting results on the colour removal efficiency. For the

Lanaset Blue 2R dye over 89% was removed while for Sandolan Red MF-GRLN only

approximately 61% was removed indicating the dye structure is a key factor. While the

optimum pH and concentration is important, in the SSW environment these factors are

not as critical as in fresh water, due to the presence of salt ions and their interaction with

the dual cationic/anionic coagulation/flocculation systems.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00


Ten

sile

str

ength

, K

Nm

-1

Reuse Dyebath


296

Reuse of the dyebath with filtration was demonstrated to be feasible through

coagulation/flocculation followed by microfiltration with Azurtex media. The colour

profile of Lanaset Blue 2R and Sandolan Red MF-GRLN dyed fabrics up to 12th dyeing,

with dyebath filtration undertaken after the 3rd/4th/5th reuse of the dyebath, remained

comparable to dyeing in fresh SSW baths. The colour strength, K/Sλmax, decreased after

every filtration in any reused sequence and the colour differences, ∆ECMC (2:1) increased,

but reversed in subsequent dyeing in reused dyebath. The wash and dry rub fastness of

the dyed fabrics was in the commercially acceptable range of over4 and remained

comparable after each filtration steps. Significant improvements in the abrasion

resistance were observed for Sandolan Red MF-GRLN after each filtration cycle.

This study also demonstrated that the reuse of dyebaths with no filtration for acid

dyeing of wool fabric in SSW was a feasible route for reducing water and chemicals

consumption in SSW along with freshwater. The dye exhaustion values gradually

increased as the dyebath reuse progresses, albeit differently for two dyes. An increase of

around 4% and over 12% was observed for Lanaset Blue 2R and Sandolan Red MF-

GRLN dyes, respectively over the 12 reuse sequence. The colour characteristics of dyed

fabric remained excellent throughout the dyebath reuse up to 12th

cycle. The colour

difference, ∆ECMC (2:1) was low (below 1.0) for the fabric produced in the Sandolan Red

MF-GRLN dyebath compared to the first dyebath. Even though the ∆ECMC (2:1)

difference was relatively high for the comparable Lanaset Blue 2R dyeings, the dyebath

reuse results remained in a close cluster and may allow predictive corrections to be

applied. The colour of fabrics produced from the reused dyebaths was uniform even

without replenishing the initial levelling agents and wetting agents, but it is anticipated

these additions would be beneficial for industrial scale processing.

In conclusion the degree of hardness and presence of salts did not adversely affect the

colour performances of the dyed fabric and thus the reuse of residual SSW dyebaths

offers two-fold solutions to the scarcity of freshwater.


297

10.5 References




2. Wenzel, H., H. H. Knudsen, G. H. Kristensen and J. Hansen, Reclamation and

reuse of process water from reactive dyeing of cotton, Desalination, 1996, 106

(1–3), p.195-203.

3. Park, J. and J. Shore, Water for the dyehouse: Supply, consumption, recovery

and disposal, Journal of the Society of Dyers and Colourists, 1984, 100 (12),

p.383-399.




5. Smith, B., Pollutant source reduction: Part IV- Audit procedures American

Dyestuff Reporter, 1989, 79 (6), p.31.

6. Carr, W. W. and F. L. Cook, Savings in dyebath reuse depend on variations in

impurity concentrations, Textile Chemist and Colorist, 1980, 12 (5), p.106-110.

7. Tincher, W. C., Energy conservation in carpet dyeing by dyebath recycling,

American Dyestuff Reporter, 1977, 55 (5), p.36-72.

8. Cook, F. L. and W. C. Tincher, Dye bath reuse in batch dyeing, Textile Chemist

and Colourist, 1978, 10 (1), p.21-25.

9. Koh, J., Y. Kim and J. Kim, Dyebath reuse in dyeing of nylon microfiber non-

woven fabric with 1:2 metal complex dyes, Fibers and Polymers, 2001, 2 (1),

p.35-40.

10. Agudelo, C., M. Lis, J. Valldeperas and T. Sato, Fabric color changes in

polyester micro-fibers caused by the multiple reuse of dispersed-dyes dye baths:

Part 1, Textile Research Journal, 2008, 78 (12), p.1041-1047.

11. Shams-Nateri, A., Reusing wastewater of madder natural dye for wool dyeing,

Journal of Cleaner Production, 2011, 19 (6–7), p.775-781.

12. Sundrarajan, M., G. Vishnu and K. Joseph, Ozonation of light-shaded exhausted

reactive dye bath for reuse, Dyes and Pigments, 2007, 75 (2), p.273-278.

13. Hassan, M. M. and C. J. Hawkyard, Reuse of spent dyebath following

decolorisation with ozone, Coloration Technology, 2002, 118 (3), p.104-111.

14. Moussa, A., A. El Ghali, S. Ellouzi and F. Sakli, Color and fastness study of

wool dyeing in multiple reuse dye baths using acid and reactive dyestuffs in

laboratory scale, Journal of the Textile Institute, 2013, 104 (3), p.260-269.


298

15. Koh, J., S. Park, G. Shim, D. Cho and J. Kim, pH control for dyebath reuse in

dyeing of polyamide with binary mixtures of acid dyes, Fibers and Polymers,

2004, 5 (2), p.110-116.

16. Volooj, S., Investigation into the wet processing of keratin fibre and filter

media, in Department of Textiles, 2003, University of Manchester Institute of

Science and Technology, PhD Thesis, Manchester.

17. Tahri, N., G. Masmoudi, E. Ellouze, A. Jrad, P. Drogui and R. Ben Amar,

Coupling microfiltration and nanofiltration processes for the treatment at

source of dyeing-containing effluent, Journal of Cleaner Production, 2012, 33

(0), p.226-235.

18. De Vreese, I. and B. Van der Bruggen, Cotton and polyester dyeing using

nanofiltered wastewater, Dyes and Pigments, 2007, 74 (2), p.313-319.

19. Holmes-Brown, R. L., E. J. Wood and G. A. Carnaby, Damage to wool during

stock-dyeing, Journal of the Society of Dyers and Colourists, 1982, 98 (7-8),

p.243-247.

20. Kilpatrick, D. J. and I. D. Rattee. The low temperature dyeing of wool. Proc. in

5th International Wool Textile Conference. 1975, Aachen, II, p.189-193.

21. Zollinger, H. Wool dyes and wool dyeing. Proc. in 5th International Wool

Textile Conference. 1975, Aachen, I, p.167-169.

Conclusions and Future work

299

11. Conclusions and Future Work

11.1 Overall conclusions

11.1.1 Simulated Seawater Dyeing

Simulated seawater dyeing of wool, polyester, nylon, acrylic fibres with acid, reactive,

disperse, cationic dyes indicated that the commercially established dyeing process is

robust and can be practically transferable with the seawater as dyeing medium. The dye

exhaustions and build-up was satisfactory within the dye ranges studied, which covers

red, yellow and blue at light, medium and deep shades.

The absorbance/concentration curve at λmax was linear and comparable for all dyes used

in this study in SSW, in most cases there were no differences with the linearity of

comparable DSW dye solutions. No salt crystals were found after dyeing in SSW and a

wash-off at 70°C with 1 gL-1

non-ionic detergent was found to be sufficient to remove

any surface salt crystal that may present SEM analysis showed that no or very little

surface damage occurred on fibre due to dyeing in SSW.

Some acid and metal complex dyes were only partially soluble in SSW at room

temperature but the solubility improved with gentle heating and addition of levelling

agents. The dyes were completely soluble at dyeing temperatures near the boil, with the

exception of Lanasyn Black S dye, which was partially precipitated. Acid dyeing of

wool and nylon fabric showed that there was relatively little difference in the final

colour of the dyed fabric. The uptake of dyes was high and consistent. Although ionic

interactions between acid dye and fibre is the dominant mechanism of fibre-dye bonding

the adsorption of acid dyes in highly saline dyebath most likely depended on the

combined effects of ionic and physical/hydrophobic interaction. At low concentrations

of salt, "screened out" ionic interactions caused low dye sorption but with the increasing

salt concentrations, increased physical interactions resulted in increased dye sorption.

As a result, in some cases, dye exhaustion was higher in SSW, and consequently colour

difference was higher between DSW and SSW dyed fabric. In other cases, where colour

difference was over 1.0 unit, optimising the dyeing conditions could result an

acceptable colour differences. The Lanasyn Black S showed colour patches and unlevel

dyeing due to low solubility at higher temperature, a specific examples of how high salt


300

solution could influence dye structure and dye aggregation. The Kawabata Evaluation

analysis indicated that the overall fabric handle was comparable to DSW dyed fabric.

The reactive dye in salt water is very sensitive to hardness of water such as Ca2+

and

Mg2+

for cotton dyeing, although NaCl, often in large amounts was added to increase

dye exhaustion. However the three α-bromoacrylamide-based Lanasol reactive dyes

used for dyeing of wool showed that unlike cotton dyeing, reactive dye could be a real

option for wool fibre in SSW particularly for achieving deep colours. Lanasol reactive

dyes were readily soluble at lower concentration at room temperature, however over

3.0% o.m.f. depths, the dye was partially soluble even after full dyeing cycle. However

during dyeing, dye was gradually exhausted into the fabric leaving a soluble lighter

dyebath. The mechanism is similar to the aqueous phase transfer process of disperse

dyeing of hydrophobic fibres.

In addition to provide level dyeing, Albegal B worked like a dispersing agent used in

hydrophobic fibre dyeing. A total fixation of 83 to 98% in SSW was observed compared

to 85 to 96% in DSW. After-treatment with ammonia, used for dye fixation, increased

dye substantivity and colour strength value. A characteristic yellow colour was also

observed which may be due to the formation of lanthionine, a product of hydrolysis of

wool. A lower colour difference after wash-off proved that some dyes were bonded

when dye substantivity was increased after ammonia treatment. The Lanasol reactive

dyes have been known to prevent damage to wool fibres at moderate to heavy depths of

over 3.0% o.m.f. Inter and intra-crosslinking within the chain was responsible for this

added strength and can protect from alkali degradation. Although the Lanasol type

reactive dye is mono-functional dye yet increase of tensile strength and abrasion

resistance was observed for dyed fabric in SSW. It can also be confirmed that the

increase in strength depends on the dye structure, as yellow dyes showed an increase of

5% and 7% for the warp and weft, respectively. For nylon dyeing, the colorimetric data

and fastness of bulk trials conforms the laboratory results.

Analysis of the disperse dyes used for dyeing of polyester in SSW showed that the

Beer-Lambert law of dye absorbance/concentration in dilute solutions was also

applicable for dispersions as the relationship between absorption and scattering of light

with dye concentration was approximately linear in SSW. Some dyes took longer to

disperse in SSW yet no unlevelness was observed. A satisfactory colour difference was


301

achieved although with a different dye build-up along the depth studied. Each of the

black dyed fabrics showed a close match or higher colour strength in SSW. Following

the alkaline reduction process, typical for disperse dyeing, yellow dyed polyester had

lighter and greener hues. The results indicated that disperse dyeing in SSW is feasible

without any major changes to the processing conditions.

The acrylic dyeing with basic dyes proved that there was a saturation limit exists for

ionic interactions in the system, as up to 1.0% o.m.f. depth the exhaustion value was

over 90% while at 3.0% o.m.f. depth it never reached over 77%. Similar to acid dyeing

of wool and nylon, addition of electrolytes or anions can increase hydrophobic

interactions at 3.0% o.m.f. depth in SSW. Thus the saturation limit of dye adsorption

can slightly overcome in highly saline solution as evident by the colorimetric data and

colour strength profiles. At low concentrations, electrolytes act as levelling agents by

retarding the dyeing process. Similar to disperse dyeing, the build-up can be different

depending on the application level.

Overall the fastness of the SSW dyed fabrics for each dyes used for wool, polyester,

nylon and acrylic was comparable to the DSW dyed fabrics with wash, cross-staining,

rub and light fastness rated commercially acceptable.

11.1.2 Filtration and Reuse of Dyebath

Colour removal by filter media is industrially preferred due to its’ high removal

efficiency, which also allows reuse of water and ingredients in the residual dyebath.

Nevertheless, microfilter media itself is not enough commercially for full removal of

colour. The major problem for all filtration processes is the reduction of permeates flux

due to membrane fouling or media blinding. Introducing surface functional groups such

as fluorine can increase filtration efficiency and improve anti-fouling properties.

Therefore gaseous fluorination, fluorocarbon finish and plasma polymerisation were

performed to introduce hydrophilic and oleophobic properties on the supplied Azurtex

media.

Surface characterisation of Azurtex media was performed with ATR-FTIR, XPS and

SEM. Increased fluorination caused etching and roughening of the media increased and

due to the exothermic nature of the gaseous treatment more fracturing/fusing occurred at

the surface treated with 10% F2. Therefore increased levels of fluorination and


302

prolonged exposure could lead to the degradation of surface. A physical layer was

formed on top of the PU when fluorinated/non-fluorinated media was treated with

Itoguard, which smoothened the rough surface. In contrast, plasma polymerised treated

wool samples showed cracking and particles in SEM micrographs, but again it

depended on the treatment conditions. The roughness of filter media can improve the

cake discharge performance but over time can wear out, which would reduce the

serviceability of the treated media. The FTIR spectra of the untreated media, PU coated

polypropylene fabric, exhibited the typical bands for the polyurethane coated fabrics.

Typically the C-F stretching vibration was observed in the 1100-1350 cm-1

region and

weakly at 400-800 cm-1

. The XPS study showed that introduction of gaseous fluorine

impart stable hydrophilic properties but progressive fluorination produced -CF2 and -

CF3 groups to impart hydrophobicity. The surface tension decreases in the order of CH2

(36 mN/m) > CH3 (30 mN/m) > CF2 (23 mN/m) > CF3 (15 mN/m) but also depends on

the coverage of surfaces and degree of order in the surface.

The fluorination of Azurtex media increased wettability but that it was not directly

proportional to an increase in the fluorination level and treatment time. The water and

oil repellency of FC and plasma treated filter media were 4 and 3, respectively, offering

a reasonable level of liquid repellency. Pre-fluorination before FC treatment didn’t

change the repellency, which is due to the cross-linking of FC coating with porous

structure which makes the fabric more ‘impenetrable’ to the effect of fluorination. The

contact angle remained in the range of 130 to 145°.

The performance of modified Azurtex filter media was benchmarked against newly

developed materials. It was found that, although fluorination can improve the flux

extended fluorination reduced the flux of the process and destabilised the system.

Fluorinated and FC finished filters offered little benefits in terms of flux, turbidity and

cake removal. In contrast, plasma treatment improved the flow, reduced turbidity and

provided an easy cake removal compared to the other modification. Overall, the

supplied 97400C filter performed better than any of the modified filters with reference

to lowering filtrate turbidity and ease of cake removal.

The selection of coagulation/flocculation process parameter such as pH and dosage of

coagulants/flocculants was very critical for subsequent filtration for overall colour

removal. The trial with a dual component system, a cationic hybrid Pluspac2000 and a


303

polyanionic Hydrosolanum protein derivative (HPSS) with model dye solution showed

that the system worked in the saline environment but was highly dependent on the class

of dyes, their structure, molecular size, concentration and structural linearity. Each dye

has a distinctive relationship with pH and concentration ratios in the formation of

molecular aggregates and a relatively high concentration ratio of coagulant/flocculants

may require in saline water. Maximum colour removal was achieved for Lanaset Blue

2R and Sandolan Red MF-GRLN dye and was 89% and 61%, respectively, based on a

ratio of 15:10 and 15:15 for PP2000: HPSS at pH 4.0 and 5.0, respectively.

A compact gel layer was produced at pH 3 and 4 for Sandolan Red MF-GRLN dye, due

to the formation of dye aggregates or the presence of di-cations like Ca2+

and Mg2+

which compressed the adsorbed double layer. The mechanism of flocculation with

polycation could be through “patchwise” adsorption, bridging or complexation due to

the presence of salt, the hybrid coagulant and anions. The molar ratio of cationic

charges to anionic charges, n-/n

+ was crucial to determine which mechanism would

dominate. The model dye effluent showed no visible turbidity but after

coagulation/flocculation but a decline of flux was observed due to the higher organic

load. It was also observed that monovalent salts such as NaCl deteriorated the floc

properties, but divalent salts improved them.

A combined physico-chemical and micro-filtration treatment was applied to textile

wastewater for the purpose of reusing the liquor into subsequent dyeing processes.

Reuse of the dyebath with the combined treatment was demonstrated to be feasible. The

dyeing behaviour remained the same for Lanaset Blue 2R and Sandolan Red MF-GRLN

dyes up to 12th

dyeing after the filtration that was undertaken after the 3rd

/4th

/5th

reuse of

the dyebath. When filtration took place, initially, in every case, the colour strength,

K/Sλmax, of the fabric decreased and the colour differences, ∆ECMC (2:1) increased.

Subsequent dyeing in reused dyebath showed an increased K/Sλmax values and decreased

∆ECMC (2:1) decreased until another filtration stage was introduced. The wash and dry rub

fastness of the series of dyed fabrics in the reused/filtered process were not affected and

were overall comparable and very good. Significant improvements in the abrasion

resistance were observed and were sometimes tripled in the number of cycles to failure.

In contrast, media blinding increased such an extent that sometimes filtration of 150mL

exhausted dyebath sometimes required up to 15 hours. However it must be noted that


304

the pressure used in this study was relatively low compared to other standard filtration

processes and is probably not a commercial problem.

The reuse of consecutive dyebaths without filtration could be a feasible route for acid

dyeing of wool fabric, which would eventually reduce water and chemicals

consumption. The dye uptake gradually increased with each reuse sequence for both

dyes in different rate. An overall increase of around 4% and over 12% after 12th

dyeing

was found for Lanaset Blue 2R and Sandolan Red MF-GRLN dyes, respectively. The

colour strength and levelness of dyed fabric remained excellent throughout the reuse

cycle. Dyed fabric with Sandolan Red MF-GRLN showed a commercially acceptable

colour difference (∆ECMC (2:1) =1.0) in comparison to the initial dyebath. In contrast,

Lanaset Blue 2R dyeings showed a higher ∆ECMC (2:1) compared to the first bath in the

reuse sequence yet the colour difference remained in a close cluster and may allow

predictive corrections to be applied. The degree of hardness and presence of other salts

didn’t hinder the colour performances and thus the reuse of residual SSW dyebaths

could offer two-fold solutions to the scarcity of freshwater.

11.2 Further Research

In assessing the results obtained in this study the following further work can be

proposed:

Investigate the dyeing of cotton fibre with reactive and direct dye in SSW

dyebath. Cotton is the most used natural fibre and the performance of cotton reactive

dye is known to be the lowered in the presence of increased water hardness;

Assess the behaviour of binary and trichromatic dye mixtures of wastewater

recycle and the effect of dyeing with binary/trichromatic recipes in SSW and recycled

baths;

Evaluation of other classes of acid dyestuffs as well as other class of dyes and

textile substrates used in commercial dyeing due to the potential increase bath

particulates which may adversely affect the colour reproducibility;

Investigate the relationship of dye structure and levelling agent to cover barré

effect of nylon fibre needs as Lyogen P could cover some dyes while failed to perform

adequately with Lanasan Blue and Acidol Blue dyes;

Identify suitable reduction processes for each disperse dyes for polyester dyeing;


305

Investigate the effect of chemical finishing on dyed polyester for thermal

migration of dyes;

Extend the use of SSW in textile pre-treatments (e.g. desizing, bleaching,

mercerising etc.) and chemical finishing of textiles;

Undertake pilot scale trials with pre-filtered seawater for use in the dyeing

machine and evaluate the effect of corrosion of dyeing equipment with saline solutions;

Determine the number of dyebath reuse cycles and the quality of dyebath filtrate

that is suitable for reuse for the each class of dye/fibre system;

Undertake pilot and industrial scale trials in order to validate the laboratory

work;

Evaluate the effect of Pluspac1000 as a coagulant as it carries a higher charge

density that Pluspac 2000 in SSW;

Investigate the effect of molecular weight of cationic and anionic flocculants on

the colour removal efficiency in the seawater environment;

Evaluate the performance of modified Azurtex filter media with exhausted

dyebath, both conventional and cross-sectional filtration. A suitable cartridge for cross-

sectional filtration also needs to be determined for the optimum performance of Azurtex

media.

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