Indian Journal of Fibre & Texti le Research Vol. 3 1 , September 2006, pp. 450-459

Studies on pigment dyeing of cotton by exhaust method

A K Patra", S Bhaumik & Harmandeep Kaur

The Technological I nstitute of Texti le & Sciences, Bh iwani 1 27 02 1 , India

Received / Jalll/my 2005; Revised received alld accepted 2 JUlie 2005

Exhaust dyeing with pigments was studied by varying different parameters, using different auxil iaries and carrying out studies on the physical chemistry of the coloration process. These pigments from Clariant, namely Printofix Yellow H EGR, Printofix Red H PBG and Printofix Turquoise B lue HRN, were used and various cationizing agents, leveling agents and lubricants were tried to get good and level dyeing. The cationization process, dyeing step, binder application and curing conditions were optimized for the three pigment colours. The results were mainly i nterpreted in terms of colour strength (KIS), visual assessment of evenness and fastness ratings. It was possible to get good colour depth and reasonable levelness by the exhaust dyeing. The wash fastness was quite good as expected whi le the crocking was not very encouraging. Spectral analysis along with kinetic and thermodynamic studies endorsed some of the trends observed during process optimization .

Keywords: Cationization, Cotton, Exhaust dyeing, Pigment dyeing

IPC Code: Int. Cl .8 D06P 1 100

1 Introduction Pigment colours used in textiles are molecular

aggregates i nsoluble in all the media they come in contact with during wet processing. I Pigment printing i s a very widely practiced process while dyeing with p igments i s done in only a few sites. Moreover, pig­ment dyeing by padding technique is not uncommon while exhaust dyeing with p igments is a rarity and is confined to garment appl ications for fancy effects by a few processors . However, pigments both by theory and practice can be applied by exhaust method adop­ting a suitable process.

The unpopUlarity of pigment dyeing i n exhaust technique is mainly due to the nagging unevenness problem. Moreover, many of the pigment manufac­turers are yet to standardize the process for exhaust dyeing while other application techniques are firmly established and streaml ined. Besides awaiting stan­dardization, exhaust dyeing with pigments is also not free from the problem of fastness to rubbing. One of the first companies to apply p igments by exhaust technique was an American company called Centi­grade. However, i n Europe the technique caught no attention til l 1 987. An Ital ian company introduced the system with a view to get ' ready worn ' , 'washed down' effect similar to that of stone wash effect on

aTo whom all the correspondence should be addressed. E-mail: arunkpatra@rediffmai l .com

denims? Since pigment has no substantivi ty for cotton, i t won' t exhaust on to cotton as such. Hence, cationic charge is in troduced in cotton by treating it wi th a cationizing agent. On the other hand, the pigments contain an anionic dispers ing agent, thus giving cotton and pigment substantivity for each other due to ionic attraction. The cationized substrate is then exhaust dyed with a p igment. However, the problem of u nevenness continues to be a matter of concern and thus a process development is called for. I n fact, cationization of cotton i tself has been a major area of research and a lot of work has been published on this .3-9

I n the present work, an attempt has been made to optimize the exhaustion dyeing process by using various leveling agents, cationizing agents and lubricants in order to control unleveled dyeing. The process parameters were varied for cationizing, dyeing, binder application and curing to arrive at stable and optimized process . Kinetic and thermo­dynamic studies were also carried out to observe the trends of p igment exhaustion on cotton.

2 Materials and Methods

2.1 Materials Scoured and bleached cotton fabrics of both woven

and kn itted qualities wi th fol lowing specifications were used:

PATRA et al. : PIGMENT DYEING OF COTTON BY EXHAUST METHOD 45 1

Woven - Weave, I x l plain weave; yarn count 40sx 40s ; reeds/inch, 1 14; and picks/inch, 84.

Kni tted - Knit, I x I i nterlock; yarn count, 34sx34s; courses/inch, 38 ; and wales/inch, 34.

The three pigments, namely Printofix Yellow HEGR, Pri ntofix Red HPBG, and Printofix Turquoise Blue HRN, from Clariant (India) Ltd were used without purification.

Two cationizing agents, namely Sandene 2000 of Clariant India Ltd and Solidogen NRL of Colour Chem, were used for cationization of cotton. Leveling agents, namely Lyogen SMKI , Sandogen NHI and Lyogen UL from Clariant, were used in dyeing. Other chemicals sourced from Clariant for the trials were Solidegal GL (dispers ing agent), Imacol CI Liquid ( lubricating agent), Retargal ANI (cationic retarder) and Printofix Binder 4000 l iquid (binder for pigment).

2.2 Methods

An attempt was first made to el iminate the problem of unevenness in exhaust dyeing of pigments. A serious problem of patchiness was observed in init ial rounds of dyeing for all the three pigments. Hence, various chemicals were tried in different steps of the process to arrive at a reasonably acceptable stage of even dyeing. As regards the process sequence, the bleached fabrics were first cationized and then exhaust dyed. Finally, the binder application was done. All cationization and dyeing trials were done at MLR of I :20. The various alternatives tried in the course of process stabil ization are given below.

2.2.1 Cationizatioll

The two cationizing agents (Sandene 2000 and Solidogen NRL) were applied separately, using the level i ng agents as mentioned above. In all the trials hot water bath was used. All the cationization processes were carried out at 70°C for 20 min. The concentration of cationizing agents used was 6% owf while leveli ng agents taken were I gil and 2 gil for both the fabric qualities.

The effect of above process on colour depth and levelness was gauged by subsequent dyeing with pigments. Based on the assessment of dyeing results, the best process of cationization was chosen.

2.2.2 Dyeing

Fabrics after being cationized by the chosen process were dyed with the three different pigments, using 2% dispersing agent in one set, I g/L lubricating

agent i n another set and all the leveling agents (2 gil) separately in the thi rd option . In the fourth option, I macol CI Liquid ( I gil) and Solidegal GL (2%) were taken i n the dye bath. The dyeing results on both the fabrics were judged on the basis of colour depth and levelness, without subsequent binder application.

2.2.3 Process Optimizatioll and Effect Study

This basically i nvolves making samples, varyIng the condition at cationization, dyeing and fixation step.

2.2.3. 1 Cat ionization Variables

The three parameters varied during the cationi­zation step are the concentration of Sol idogen NRL, cationizing temperature and cationization time. The various concentrations used were 0.5 , 2, 4, 6, 8, I 0 and 1 2% and the temperatures tried were 60, 70, 80 and 90°C while cationization time was fixed for 1 0, 20, and 30 min . To check out the effect of above cationizing variables on dyeing, both the woven and knitted fabrics were dyed at 1 % and 3% shades with all the pigments, using the following conditions.

Pigment Sol idegal GL I macol CI Liquid

Temperature Time

2.2.3.2 Dyeing Variables

1 % and 3% 2% owf I gil

80°C 20 min

To evaluate the process sensitiv i ty of pigments, the following two dyeing parameters were varied. The dyeing temperatures taken for study were 50, 60, 70, 80, 90, and 1 00°C whi le the dyeing t ime was fixed at 1 0, 20, 30, and 40 min . The above variations were done for both 1 % and 3% shades on the woven as well as knitted fabric.

2.2.3.3 Fixation Variables

Samples were first dyed i n 1 % and 3% shades by opting the best condition during the cationization and dyeing step. The fixation was done by treatment i n a b inder bath at 1 :20 MLR fol lowed by squeezing and curing. The fol lowing four parameters were varied during the fi xation step for evaluating the fastness properties of the pigments. The concentrations of B i nder 4000 used for the study were 3, 5, 7 and 1 0%. Application time or the treatment t ime with binder was kept at 1 0, 20 and 30 min . Curing at 1 30, 1 50 and 1 70°C for 3, 5, and 7 min was done.

452 INDIAN 1. FIBRE TEXT. RES., SEPTEMBER 2006

2.2.4 Killetic alld ThermodYllamic Studies

The kinetic studies were can-ied out for all the three pigments on the bleached kni tted fabrics. The fabric was cationized by 6% Sandene 2000 at pH of 6 and temperature of 60°C for 30 min. After cationization, the fabric was s l ightly rinsed in water and then dyed in I % shade in a bath containing Solidegal GL 2% owf and Imacol CI Liquid I g/L. The dye uptake was measured at different t ime intervals ranging from I min to 45 min at 60°C and 80°C by evaluating the extinction value of the residual bath on Perkin-Elmer Lambda Spectrometer.

Corresponding thermodynamic studies were done for the p igments on the kni tted fabric. Same cation i­zation recipe as that in kinetic study was used while dyeing was done with same recipe at 60°C and 80°C for 30 min. The standard affinity, heat of dyeing and entropy of dyeing were calculated using the fol lowing equations:

-L'lJ.! = RT In ([DJtJ[Dls) . . . ( I )

where [D], i s the concentration of colorant on the fibre (g/kg); and [DJs, the concentration of colorant in the solution (giL).

. . . (2)

where L'lJ.! ' is the standard affin ity at temperature T, ; and L'lJ.!2, the standard affin ity at temperature T2

L'lJ.! = L'lH -T L'lS (3)

where L'lJ.! i s the standard affinity ; L'lH, the standard heat of dyeing; L'lS, the standard entropy; and T, the absolute temperature.

2.2.5 Test Methods

Colour strength of the samples expressed as KIS was evaluated using the following Kubelka-Munk equation:

KIS=( I -R)2/2R

where R is the reflectance; and K and S, the Kubelka­Munk absorption and scattering coefficients respec­tively. All the measurements were performed in the Macbeth 2020+ computer colour matching system. The wash fastness of the samples was tested by standard ISO-3 method. Crock fastness, both dry and wet, was measured by the AA TCC prescribed method.

For kinetic studies, the absorbance (optical density) was recorded using Perkin-Elmer Lambda 2 U VIVIS

Spectrophotometer. Concentration of residual bath was determined by measuring the relative absorption of light with respect to a known concentration of the bath containing pigment. The absorbance (00) i s given by the following equation of Beer-Lamberts law:

A = log (fo/!) = ECL

where 10 is the intensity of incident l ight; I, the intensity of emergent light; C, the concentration; L, the path length; E, the molar extinction coefficient; and A, the absorbance.

3 Results and Discussion 3.1 Process Selection for Level Dyeing

Among the various options in cationization, the treatment simply with Sol idogen NRL gives good colour depth and more i mportantly the levelness (Table 1 ) . Hence, in all further studies Solidogen NRL was used for cationization process. As regards dyeing ass istants, the pigment bath containing 1 giL Imacol CI Liquid and 2% owf Solidegal GL shows good colour depth and levelness. Hence, these two auxil iaries were used in dyeing for further studies. The KIS values are g iven in Table 2 .

3.2 Effect of Process Parameters 3.2.1 Catiollizatioll Variables

I n both woven and knitted fabrics dyed with 1 % shade using all the three pigments, there is increase in KIS value with the i ncrease in concentration of cationizing agent (Figs 1 a & c). This may be attributed to the formation of more number of sites on fibre by stronger cationization bath. Although KIS i ncreases with the concentration, 6% cationizing agent is taken as optimum. Beyond 6% concentration, the dyeing results turn out to be inconsi stent with a nagging problem of unevenness. Besides this, the chemical cost is also considered, keeping in view that the shade is only 1 %. As shown in Figs I b & d, the fabric dyed in 3% shade also exhibits increasing trend in KIS with the concentration of cationizing agent. But in this case, 8% cationizing agent concentration is taken as optimum value due to the same reasons as that in 1 % shade, i .e . better levelness of dyeing and less chemical cost. The i ncrease in cationization temperature above 60°C does not cause much i mprovement in colour depth for both the % shades (Figs 2a & d). The colour yield, however, shows mostly an increas ing trend on increasing the treatment time from 1 0 min to 30 min (Figs 3a & d). So, a

PATRA et al. : PIGMENT DYEING OF COTTON B Y EXHAUST METHOD 4S3

Table I -KIS value and levelness of the dyed fabrics (I % shade) by using different chemicals i n cationization

Process Chemical Fabric type

Sandene 2000 Knitted Woven

Solidogen NRL Knitted Woven

2 Sandene 2000 +Lyogen SMKI Knitted Woven

Sol idogen NRL+ Lyogen SMKI Knitted Woven

3 Sandene 2000 + Retargal ANI Knitted Woven

Sol idogen NRL+ Retagal ANI Knitted Woven

'No significant change in comparison with process I .

Table 2 - KIS value and levelness of the dyed fabrics ( I % shade) by using different chemicals at the dyeing stage

Process Chemical Fabric type

Pigment Knitted alone Woven

2 Pigment + Knitted Sol idegal Woven GL

3 Pigment + Knitted Imacol Woven C.I .Liq.

4 Pigment + Knitted Lyogen UL Woven

Pigment + Knitted Sandogen Woven NHI Pigment + Knitted Lyogen Woven SMKI Pigment + Knitted Retargal Woven A N I

5 Pigment + Imacol C. I .Liq. + Solidegal GL Imacol CI Knitted" Liq. , I gpI Woven" ImacoI CI Knitted Liq., 2gpl Woven

"Best levelness observed.

Colour strength (KIS ) Printof�x Printofix Printofix Yel low Red Turq. B lue HEGR HPBG HRN

2.26 3.52 3 . 1 6

1 .70 1 .90 2.24

2.40 3.56 3.28

1 .72 1 .94 2.26

1 .85 3.20 2.98

1 .54 1 .62 1 .96

2 . 1 8 3.52 3 . 1 8 1 .62 1 .88 2.26 2.26 3.48 3 . 1 2

1 .68 1 .88 2.24

2.24 3 .44 3. 1 4 1 .65 1 .92 2.20

2.20 3.42 3 . 1 2 1 .72 1 .90 2.24

2.32 . 3.52 3 .26 1 .72 . 1 .90 2.24 1 .92 3 .35 3 . 1 2 1 .6 1 1 .73 2. 1 0

Printofix Yellow H EGR

2. 1 4 1 .52 2.26 1 .70 2 . 1 2 1 . 54 2.24 1 .68 2 . 1 4 1 .56 2.20 1 .68

Colour strength (KIS) Printofix Prin tofix Turq.

Red HPBG Blue H RN

3.26 2.98 1 .78 2.02 3.52 3 . 1 6 1 .90 2.24 3.30 2.88 1 .79 1 .98 3.45 3.28 1 .92 2.26 3.20 2.92 1 .82 2. 1 0 3.54 3. 1 4 1 .92 2.20

Levelness

Good Good Better Better

No change" No change" No change" No change" No change" No change" No change" No change"

cationization temperature of 600e and 30 mm treat­ment t ime are found to be optimum.

3.2.2 Dyeillg COllditions

Dyeing temperature has a major role m dyeing cotton fabrics with pigments. In the case of yellow and blue p igments taken for both 1 % and 3% shades, the KIS values are found to be the best at 600e dyeing temperature (Figs 4a & d). The i mprovement in depth when temperature is increased from sooe to 600e could be attributed to the better de-aggregation of pigments, resulting in higher exhaustion. However, the decline in shade depth at 700e and 800e of dyeing temperature could be due to the loss of affinity for substrate with the i ncrease in temperature. Interes­tingly, i n case of red pigment, a dyeing temperature of 800e gives the best results. The results below and above this temperature at both the % shades may be explained on the same bas is as that for temperature other than 600e i n case of yellow and blue. Also, the effect of auxil iaries, i .e. Imacol eI Liquid and Solidegal GL at different temperatures with the pigments of varying structure cannot be ruled out.

The enhancement in colour strength is l ikely to be direct consequence of the avai labi l i ty and accessi­.9i l i ty of pigment particles in the vicini ty of cellulose substrate. The influence of dyeing time is shown in Figs Sa & d. The KIS values increase with the increase in dyeing t ime, but after 30 min there is no significant change in KIS. With the increase in dyeing time, the de-aggregation of pigment particles is l ikely to improve, causing i ncrease in KIS value. After a t ime

454 I DIAN J. FIBRE TEXT. RES., SEPTEMBER 2006

4.5 4 3.5 3 2.5 1 .5 1 '" 0.5 .=

;" 0 <FJ 3.5 --_. _. - _ ." - '" � C

......

,

7

( . . . . . .

I 2.5

/ _'::

0.5 �.;, .: . II

IIH. �. � :-. � :

Yellow Red Blue Yellow Red Blue

0 0.5 1!l 2 0 4 0 6 lil a 0 10 E1 1 2 Fig. 1 - Effect of cation izing agent concentration (%) on KIS values [a - knitted I % shade, b - knitted 3% shade, c - woven I % shade, and d - woven 3% shade]

4 5 8 '0-'"

1 .:.1"--___ ••.. _----:.----.-.... 7 --'h'----__ _

3.5�-

-

--. '---0 6 ------.... - ..,. ' 1----...... -.. --. / ,,: .---1 , I- Iw : " '7

: i : IlItl,.' :. - .,;:; I .· ,: .'�I-·= ..... ·"'""-,jl,_!·LIF � , �� = III!� ' =� 1� ': 0. 5 :. - iill' .;: ::. - 1 Ii i ! l .... i ii:I ; ;: , - i ill ;: . -·

o L ...L..-""""-'--'--..L...l"'"-'-L.J.--'-""H.u.:...J: �. J..... 0 _ , 1: : . • 1 ' . III: · : .. . :, i ' ,; :2 3.5 C ; 6 1 " ;1 .. . . . 3 1---.--..

.

... ... '-'- '--'-" 'i 5 �.----.. "", . . l--� � �:;'l-! 2 ,5 f---------.,.....,.- :! -I

0.5 o '

Yellow

10 60

TII ! 'd� , 1-._-, -I r r Ii �; :. �:, � �:; '," r- !i ! 1 : '.: � =. Wi ;; ... 0 Jill ;. - II!; ' Blue Yellow I�ed

lIT! 70 o ao 8 90 Blue

Fig. 2-Effect of cationization temperature (OC) on KIS values [a - knitted 1 % shade, b - knitted 3% shade, c - woven 1 % shade, and d - woven 3% shade]

period of 30 min at an optimized temperature, perhaps there is no major i mprovement in de-aggregation and hence in the KIS values. So, the 30 min dyeing time i s considered as the optimum for all the three pigments on both the fabric qualit ies.

of fixation conditions on them. Although all the samples have been tested for fastness, the results of only a set of representative samples are g iven, as the trends are s imi lar in different fabrics and % shades. Table 3 shows that the wash fastness of pigments is excel lent and does not appear to depend much on the amount of binder, fixation time and curing conditions. Only i n a few cases, the sl ight colour change is observed on varying the conditions . The rub fastness

3.3 Fastness Properties

The wash and rub fastness values of the dyed samples were studied mainly in 'terms of the influence

PATRA el al. : PIGMENT DYEING OF COTTON BY EXHAUST METHOD 455

1 .5 h-111%1h-tIIM� 1

0.5 O �lliW���WU�llW4LlliW��

m 20 1:] 30

Fig. 3- Effect of calionization l ime (min) on KIS at 60°C and 90°C [a- knitted I % shade, b- knitted 3% shade, c- woven I % shade, and d-woven 3% shade]

5 a 4 +----·--.-I',I---n-rr---

3 2

!i ---" ' II �' I i '· _ II i .C r- . i .

I ; � I ;:: 0 w....J.w....�'-'--'-'.llL.J"-""L.L-LJ.i.ll....l"-""L.l...; Vl 6 s .......

� 5 -�.------'-------� (\ II ; 6 +-��-----�

4 .... ----------11 I :) ! 4 3 �-�-------1

Yellow Red Blue Yellow Red Blue

1 0 50 [) 60 0 70 El so &1 90 0100

Fig. 4- Effect of dyeing temperature (0C) on KIS values [a-knitted I % shade, b- knitted 3% shade, c- woven I % shade, and d- woven 3% shadel

of the dyed samples is however not quite good, i rrespective of the colour, % shade and process conditions (Table 4). The maximum dry rub fastness i s 3, while wet crocking does not exceed a rating of 2-3. When the binder concentration is increased from 3% to 5%, there is a sl ight improvement in rating ranging from half a step to one. However, beyond a binder concentration of 5%, no noticeable improve­ment in crocking is registered. As regards the binder application time, the increase in treatment t ime appears to have no influence on fastness to rubbing

and hence 10 min (minimum among the three) may be considered as the optimum value. As regards influence of curing temperature and t ime, it i s minimal. As shown in Table 4, a slight improvement in rub fastness is achieved by raising the curing temperature from 1 30°C to I SO°c. However, beyond 1 50°C, no improvement is observed and in a few cases the change in tone is observed visual ly after curing. With the increase in curing time from 3 min to 5 min at 1 50°C, rub fastness improves a l i ttle i n some samples while 7 min curing t ime does not have any

456 INDIAN 1 . FIBRE TEXT. RES., SEPTEMBER 2006

Yellow Red Blue Yellow Red Blue

UlJ 20 t:i 30

Fig 5- Effect of dyeing time (min) on KIS values [a- knitted I % shade, b- knitted 3% shade, c-wovcn I % shade, and d- woven 3% shade]

Table 3 - Wash fastness of kni tted samples dyed ',vith I % shade

Pigment

Printofix Yellow HEGR

Printofix Red HPBG

Type Amount of binder . % 3 S 7 1 0

C C 4-5 5

SC 4 4-5

CC 4-S 4-5

4-5 4-5

4-5 4-5

4-5 4-S

SC 4 4-5 4-5 4-5

Printofix CC 4-S 4-5 4-5 4-5

Turq. Blue H RN SC 4-5 4-S 5 4-5

B inder application

10

5

4-S

4-S

4-5

4-S

4-S

time. min 20 30

4-S 4-5

4-5 4-5

4-5 4-5

4-5 4-5

4-5 5

4-S 5

Curing Type _______ --=C.::u:..:.ri"'ng"'l"'i l::..:n.::.;e.c..:n""li::..:n ______ _

temp. °C Y

1 30 CC 4-S

SC 4-5

I SO CC 5

3 S

R B Y R B

4-5 4-5

4-S 4-5

4-S 4-5

4-S 4-5 4-5

4-5 4 4-5

S 4-S 4-5

SC 4-5 4-5 4-5 4-S 4-5 4-5

7 Y R I3

4-5 4-5 4

4-5 4-5 4-5

5 4-5 4·5

5 4-5 4-S

1 70 CC 4-5 4-5 4-5 4-5 4-S 4-S 4-5 4-S 4-5

SC 4-5 4-5 4-5 4-5 4-5 4-S 4-5 4-5 4-S

Y-Printofix Yellow H EGR. R-Printofix Red HPBG. B-Printofix Turq. Blue HRN. CC-Colour change, SC-Stai ning on cotton.

Table 4 - Rub fastness of knitted samples dyed with I % shade

Pigment Type Amount of binder . % 3 5 7 1 0

B inder application t ime, min

1 0 20 30

Printofix Yellow HEGR

Dry 2 2 1 3 2 1 3 2 1 3 2 1 3 2 1 3 2 1 3

Wet 2 2 1 3 2 1 3 2 / 3 2 1 3 2 / 3 2 1 3

Printofix Dry 2 2 / 3 2 / 3 2 / 3 2 / 3 2 / 3 2 / 3 Red HPBG

Wet 2 2

Printofix Dry 2 / 3 3 Turq. Blue HRN Wet 2 2 / 3

2

3

2 / 3

2 2 2 2 / 3

3 3 3 3

2 / 3 2 / 3 2 / 3 2 / 3

Curing Type ___ --::-___ -=-C-'-ur-'.i n"'g ... t_i m::-

e.:..:.-'.n_li_n ___ ---,::--__

temp. 3 S 7

°c Y R B Y R B Y R Il

1 30 Dry

Wet

1 50 Dry

Wet

170 Dry

Wet

2 2

2 2

2 2

2 2

3 2

2 2

2 / 3 2 / 3 2 2 / 3 2 / 3 2 3

2 2 / 3 2 2 / 3 2 2 2 / 3

2 / 3 2 / 3 2 / 3 3

2

2 / 3

2

2 / 3 2 2 / 3

2 / 3 2 / 3

2 2

3

2 / 3

2 / 3 2 / 3 3

2 2 2 / 3

2 / 3 2 / 3 3

2 / 3 2 2 / 3

Y-Printofix Yellow HEGR. R-Printofix Red HPIlG, B-Pri ntofix Turq. Blue HRN.

PATRA et al. : PIGMENT DYEING OF COTTON BY EXHAUST M ETHOD 457

positive effect and rather causes tone change. So, curing at 1 50°c for 5 min may be considered the right condition for fixation.

3.4 Spectral Analysis

The visible spectra of the pigments measured i n UV spectrophotometer are shown in Figs 6 a & c . The wavelengths of maximum absorbance (Amax) for the yellow, red and turquoise blue colours in dist i l led water are found to be 484 nm, 569 nm and 633.5 nm respectively. The peak wavelengths along with the extinction values are clear from the graphs. As securing level dyeing i s one of the primary objectives of the work, the rate of dyeing has been studied objectively. For this, first the optical densi ty (absorbance) at Amax of respective pigments was measured at different colour strengths. A graph was plotted between the absorbance values and concentration of pigment. The straight l i ne graph, so obtained, passing through the origin was taken as the calibration curve. Then, from the pigment dyeing bath, the residual bath solution at different time intervals was taken and the absorbance at respective Amax was measured in the spectrophotometer. On the basis of the absorbance value, the concentration of bath was determined from the cal ibration curve. The pigments used alone for dyeing show higher in i tial rate of dyeing than in presence of Imacol CI Liquid. The absorbance values determined at various time intervals clearly indicate this (Table 5) . S lower in i tial rate of dyeing i n the presence of auxi l iary i s also exhibited in terms of KIS values shown in Table 6 for all the three pigments.

Moreover, the unevenness in dyeing also caused due to fabric folding and creasing in the dye bath is

(U u C �

.c I-0 '"

.c �

+2.50 2.084

+0.00 400 484 o

+2 .00 \ .947

1 .504

+0.00 400 527 569 60

+2.50 2 . 1 89 2 . 1 26

+0.00

633.5 7 1 2

400 600 Wavelength, nm

a

800

b

800

c

800

Fig. 6 - Visible spectra of pigment colours (reference - distil led water) [a - Printotix Yellow H EGR, b - Printofix Red HPBG, and c - Printofix Turq. B lue HRN]

Table 5 - Exhaustion with respect to t ime of dyeing

Time Printofix Yellow HEGR Printofix Red H PBG Printofix Turg.B luc HRN

min With Imacol CI Lig. Without Imacol CI Lig. With Imacol CI Lig. Without Imacol CI Lig With I macol CI Lig. Without lmacol Cl Lig.

00 %E 00 %E OD %E OD %E 00 %E OD %E

I 1 .378 33.87 1 .334 35.98 1 .350 30.66 1 .246 36.00 1 .475 32.62 1 .282 4 1 .43 2 1 .363 34.59 1 .292 38.00 1 .340 3 1 .76 1 .207 38.00 1 .320 39.69 1 .268 42.07 4 1 .332 36.08 1 .27 1 39.0 1 1 .3 1 1 32.66 1 . 1 39 4 1 .49 1 .3 1 8 39.78 1 .2 1 6 44.44 6 1 .33 1 36. 1 3 1 . 209 4 1 .98 1 .209 37.90 1 .07 1 44.99 1 .298 40.70 1 . 1 84 45.9 1 8 1 .3 1 2 37.04 1 . 146 45 . 0 1 1 .002 48.53 0.934 52.02 1 .240 43.35 1 . 1 50 47.46 1 2 1 .225 4 1 .2 2 1 .084 47.98 0.83 1 57.32 0.828 57.47 1 .223 44. 1 3 1 .061 5 1 .53 20 1 . 1 1 6 46.45 1 .009 5 1 .58 0.609 68.72 0.596 69.38 1 . 1 53 47.32 0.932 57.42 30 1 .05 1 49.56 0.938 54.99 0.593 69.54 0.572 70.62 1 .087 50.34 0.866 60.43 45 1 .045 49.85 0.9 1 7 55.99 0.586 69.90 0.545 72.00 1 .084 50.48 0.820 62.54

OD-Optical density, and %E-Exhaustion

458 INDIAN 1 . FIBRE TEXT. RES . . SEPTEMBER 2006

Time Printoflx Yellow I I EGR

Table 6 - KIS value with respect to t ime of dye ing

Printolix Red HPBG Printorix Tu rq. B l ue H R N

mill With Imacol CI Liq. Without Imacol CI Liq . W i th I macol C I Liq. Without Imacol CI Liq. With I macol C I Liq. Without I macol CI Liq .

4

6

8

1 2

20

30

45

0.5 1

0.53

0.7 1

O.K2

0.99

1 .37

1 .4 1

1 .47

1 .50

0.87 0.97

0.96 1 .00

1 .07 1 . 1 8

1 . 1 6 1 .22

1 .28 1 .47

1 .36 2.22

1 .39 3.53

1 .4 1 3.74

1 .42 3.76

0.92 0.84 1 .05

1 . 1 6 1 .07 1 . 1 9

1 .44 1 .20 1 .54

1 .55 1 .30 1 .64

1 .64 1 .76 1 .87

2 . 1 2 2 . 1 7 1 .96

2 .52 2.26 2.00

2.75 2.32 2.0S

2.S 1 2.46 2.25

Table 7-Dye uptake with respect to t ime of dye ing

Time Printofix Yellow HEGR ------��������---- Printofix Red HPBG Printofix Turg. B lue HRN

min 60°C SO°C 60°C

Df Ds Dr Ds Dr Ds g/kg giL g/kg giL g/kg giL

I

2

4

6

8

1 2

20 30 45

0.608

0.622

0.654

0.656

0.674

0.762

0.S74

0.938

0.946

0.0663 0.408

0.0655 0.452

0.0640 0.542

0.0639 0.582

0.0630 0.608

0.0586 0.752

0.0530 0.S52

0.0498 0.898 0.0494 0.9 1 6

0.0763 0.66 1 0.0636

0.0740 0.7 1 3 0.06 J () 0.0696 0.7 1 6 0.0608

0.0676 0.737 0.0598

0.0663 0.794 0.0569

0.059 1 0.980 0.0476

0.054 1 0.99 1 0.047 1

0.05 1 8 1 . 1 1 4 0.0409

0.0509 1 . 1 55 0.0389

Dr -Dye on fi bre and Ds-Dye in solution.

Table 8 - Calculated values of thermodynamic studies

Parameter Prilllofix Yel low Printofix Red Printorix Turq. HEGR H PJ3G B l ue HRN

60°C 80°C 60°C 80°C 600e SO°C

-�I1. kllmol 8. 1 24 8.368 9 . 1 44 9.775 14.050 1 4. 1 68

�H. kJ/mol -4.06 1 1 .362 - 1 2.052

�S, J/mol 1 2 .20 1 12.20 1 3 1 .549 3 1 .549 6.000 5.994

taken care of by the lubricati ng action of the Tmacol CI Liquid.

3.5 Interpretation of Kinetics and Thermodynamic Studies

The resu lts of dye uptake by cotton at 60°C and 80°C for different time intervals are reported in Table 7 . In case of yel low and blue pigments, the exhaustion in terms of Dr (dye on fibre) values at 60°C is more than that at 80°C while for the red pigment, it is just the opposite. Thi s reconfirms the earl ier optimization results for dyeing temperature in terms of colour strength (KI5).

SO°C 60°C SO°C

Df Ds Df Ds Df Ds g/kg giL g/kg giL g/kg giL

0.778 0.0577 1 . 1 56 0.0388 1 .064 0.0435

0.789 0.057 1 1 .226 0.0354 1 .082 0.0426

0.82 1 0.0556 1 .230 0.0352 1 . 1 30 0.0402

0.848 0.0543 1 .276 0.0329 1 . 1 72 0.Q3S 1

0.854 0.0539 1 .352 0.029 1 1 . 1 82 0.0376

0.988 0.0472 1 .5S3 0.0 1 75 1 .2 1 4 0.0360

1 .00 1 0.0466 1 .598 0.0 1 68 1 .238 0.0348

1 . 1 23 0.040 1 1 .764 0.0 1 1 0 1 .440 0.0 1 1. ')

1 . 167 0.0383 1 .788 0.0098 1 .460 0.0 1 05

Under the thermodynamic studies the calculated standard affinity values at 60°C are found to be more than that at 80°C for al l the three pigments on cotton (Table 8). Again the heat of dyeing (/I,H) calculated for dyeing of cotton with Printofix Red HPBG is found to be posit i ve, thereby indicating the endo­thermic dyeing process. Hence, in case of red pigment, more pigment wi l l be absorbed at equi l i ­bri um with i ncreasing temperature. i .e . affin ity is increased. Perhaps, that is the reason why Red HPBG pigment dyes deeper at 80°C than at 60°C. On the contrary, for dyeing cotton with the blue and yellow pigments, heat of dyeing i s negative, i .e. dyeing process is exothermic. Hence, l ess pigment wi l l be absorbed at equ i l ibrium with increasi ng temperature, i .e. affin i ty is decreased. 10 Finally , the entropy (/1,5) at 60°C and 80°C as g iven in the table indicates that for al l the three colours, restraint on pigments when absorbed by substrate is not influenced much by the change in dyeing temperature.

PATRA et of. : PIGMENT DYEING OF COTION I3Y EXHAUST METHOD 459

4 Conclusions Exhaust dyeing by pigments on cotton can be done

with reasonably good levelness provided the cationization and dyeing steps are properly control led with suitable use of auxi l iaries. The optimum concen­tration of cationizing agent varies with % shade while the ideal dyeing temperature appears to be pigment specific. The binder used in the experiment gives good results at 5% concentration when appl ied at I 50aC for 5 min. Although the wash fastness of the pigment dyed samples is not a problem at all, the rub fastness however is a matter of concern and more so the wet crocking. Spectral studies indicate the improvement i n control of dyeing when Imacol CI Liquid is present in the dye bath. The kinetic studies justify the earl ier findings on pig­ment dyeing temperature while the values of heat of

dyeing found In thermodynamic studies further confirm i t.

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( 1 0) ( 1984) 304. 5 Chottopadhyay D P, fndian J Fibre Text Res. 26 (200 1 ) 108. 6 Guo G Y & Chen Y L, Alii Dyest Rep. 83 (9) ( 1 994) 58. 7 Lewis D M & Lei X P, J Soc Dyers Colollr, 107 (3) ( 1 99 1 )

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1 83 (2) ( 1998) 1 6. 9 Youssef Y A. J Soc Dyers C% llr, 1 16 ( 1 0) (2000) 3 1 6. I 0 Trotman E R, Dyeing of Chemical Technology of Textile

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