Dyeing of silk with Procion HE dyes

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Dyeing of silk with Procion HE dyes

M L Gulrajani, Ashish Jain &Deepali Agarwal

Department of Textile Technology, Indian Institute of Technology, New Delhi 110 016, India Received 11 July 1994; revised received and accepted 21 September 1994

The effect of various dyeing parameters on exhaustion and fixation of bifunctional monochlorotriazine dyes (Procion HE dyes) on silk has been studied. Factorial design has been used to obtain the optimum conditions of dyeing. Maximum exhaustion has been obtained with 110 g/L sodium chloride and 3 g/L sodium carbonate. Temperature in the range 60-"80°Chas no influence on exhaustion. Improvement in mechanical properties of dyed silk suggests the formation of crosslinks in the fibre by these dyes.

Keywords: Bifunctional reactive dyes, Dyeing, Monochlorotriazine dyes, Procion HE dyes, Reactive dyes, Silk

1 Introduction

Dyeing of silk with reactive dyes has been recently reviewed'. It has been reported that among the reactive dyes suggested for silk, dyes having a-bromoacrylamido group or difluoro-chloropyri- midine group show good fixation as well as good wet fastness properties. Both these types of dye have two reactive centres which may be responsi- ble for their superior properties. However, the two reactive centres in these dyes are located very close to each other.

Recently, a lot of interest has been generated in the manufacture and application of bifunctional dyes having two reactive groups located at a dis- tance from each other. One of the reasons behind this is very high realization which results in significant cost savings and reduces the effluent prob- lem.

In the late 1960s and early 1970s, ICI utilized the advantage of having two reactive groups and produced a range of Procion HE dyes. These are bifunctional dyes containing two monochlorotriazine groups. The monochlorotriazine (MeT) reactive group is characterized by its high stability to hydrolysis at elevated temperatures when it is present in neutral electrolyte. The twinned MCT structure exhibits high migration and diffusion during the neutral electrolyte phase and also gives high fixation levels on addition of alkali, since the presence of two reactive groups per dye molecule increases the probability of dye-fibre interaction.

However, these dyes have only been studied on cellulosics. In the present study, an attempt has

been made to investigate the behaviour of these dyes during application on silk, and to standar- dize the optimum conditions of dyeing. The effect of these dyes on the mechanical properties of silk has also been studied.

2 Materials and Methods

2.1 Materials

Plain woven mulberry silk fabric of 40 g/m?

weight was used. Prior to dyeing, the fabric was scoured in a solution containing 2 g!L non-ionic detergent at 100°C for 1 h. The material-to-liquor ratio was kept at 1:30.

Mulberry silk yarn of 21.6 denier was used.

The yarn was degummed using 25% (owf) Mar- seilles soap at 100°C for 90 min, keeping the material-to-liquor ratio at 1:30.

Sodium chloride, sodium carbonate, sodium dihydrogen phosphate, orthophosphoric acid and disodium hydrogen phosphate of laboratory grade were used without any further purification. Pro- cion HE dyes manufactured by Atic Industries Ltd were used.

2.2 Methods 2.2.1 Dyeing

Silk fabric was dyed in a laboratory model jig- ger whereas the silk yarn was dyed in a Pretema multicolor dyeing machine. The material-to-liquor ratio was kept at 1:100. Dyeing was carried out according to the dyeing cycle shown in Fig. 1.

Experimental Design: To study the effect of number of input variables on responses such as

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GULRAJANI et al.:DYEING OF SILK 151 exhaustion, fixation, etc., the experiments were

carried out according to the Box and Behnken response surface design. This experimental design is used for experiments with three independent variables and three levels of each variable. Table 1 gives the three independent variables and their levels used in the present study. Thus, a set of 15 experiments was performed as listed in Table 2. A quadratic polynomial was used to analyze the design with three independent variables (Eq. 1).

3 3 3

Y=Po+ LPiXi+ LPuX:+ LPijXiXj ...

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i-I i-I i-I

III SAL 1 I ALKALI U ALl< ALl

...•

... ..

IX:;:)

~ I

e ...

20 I

s

^I.

•..

₁₀ r

I

00 60 70 80 90

TIME, mill Fig. I-Dyeing cycle

where

Y

is the measured response; {3o, {3;, {3iiand {3.._{I} ,} the coefficients of the regression; and iand j, the integers with i

<

j. To test the estimated re-·

gression equation for the goodness of fit, the Fisher test was employed. The estimated coefficients of the regression equation were tested for significance using the Student t-test, The insignifi- cant coefficients were deleted from the equation and the remaining ones were recalculated and goodness of fit reassessed.

Box and Wilson central composite rotatable design was used for experiments with two variables at five levels each (Table 3).

1.1.1 Tests

The exhaustion ^(%) of the dyes was calculated from the optical densities of the dyebath before and after dyeing using the following equation:

Exhaustion (%)=ODlmuoi - ODF•naI X 100 ODln•l•oI

Table l=-Actual and coded values of independent variables

Variable Level

-1 0 +1

NaCI (XI)' gIL 0 20 40

Na2C03 (X2), glL 5 10 15

Temperature (X3), ·C 60 70 80

Table 2- Treatment conditions and observed responses [Dye=-Procion Brilliant Red HE 3B]

Exp. NaCi Na2C03 Temp. Exhaustion Fixation, %. Realization, %

No. glL glL ·C %

(XI) (X2) (X3) (Yd Method Method Method Method

1 2 1 2

1 0 5 70 10.30 84.29 92.21 8.68 9.50

2 40 5 70 28.20 72.36 81.96 20.41 23.11

3 20 5 80 17.50 71.48 84.63 12.51 14.81

4 20 5 t)0 21.75 60.23 86.12 13.10 18.73

5 40 10 8Q 27.70 81.85 76.33 22.67 21.15

6 0 10 80 12.30 86.40 90.96 10.63 11.19

7 40 10 60 30:60 66.67 79.53 20.40 24.34

8 0 10 60 12.23 85.62 78.43 10.47 9.60

9 20 15 60 16.58 71.95 75.66 11.93 12'.55

10 20 15 80 10.75 62.94 78.65 6.77 8.47

11 40 15 70 29.41 63.79 77.65 18.76 22.84

12 0 15 60 3.38 57.64 79.40 1.95 2.69

13 20 10 70 19.05 83.06 80.12 15.82 15.26

14 20 10 70 16.25 75.88 87.99 12.33 14.30

15 20 10 70 22.19 78.33 76.57 17.68 16.50

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Table 3-Actual and coded values of independent variables

Variable Level

NaCI(XI)' g/L

Na2C03 (X2), g/L

- 1.414 51.72

1.586

o

80 3

1 1.414

100 108.28

4 4.414

-1 60 2

where

OD^luitinl =Optical density of dyebath before dyeing

OD^Fillal ⁼Optical density of dyebath after dyeing

Optical density was measured on Perkin-Elmer Lambda 38 UV/VIS spectrophotometer.

The unfixed dye on the fabric was extracted by a treatment with 50°/',urea solution (wt/vol). The pH of this solution was maintained at 7 by a buf- fer of sodium dihydrogen phosphate (0.5M) and disodium hydrogen phosphate (0.1M). The treatment in urea solution was carried out for 5 min at boil.

Dye fixation (%) was determined using the following two methods:

(i) K/S values of the dyed samples were measured before and after the extraction of the unfixed dye using ACS Spectrosensor II Spectropho- tometer interfaced with an IBM Pc. Dye fixation (%) wasthen calculated as:

KIS value of dyed sample after extraction

Fixation (%)= x 100

KIS value of dyed sample before extraction

(ii) Fixation (%) was also calculated from the optical density measurements. 25 mg of dyed samples, before and after the extraction of unfixed dye, were dissolved in 25 rnl of orthophosphoric acid and the optical density was measured on Perkin-Elmer Lambda 3B UV/VlS spectrophotometer. Dye fixation (%) was then calculated as follows:

.. I" 00 of dyed sample after extraction 100

Fixation (%,= . x

OD of dyed sample before extraction

Realization ^(%), which gives the percentage of the total dye in the dyebath which has reacted with the fibre, was calculated as follows:

( 1.) % Fixation x % Exhaustion

Realization ⁰⁰ 100

Breaking load and extension at break were measured on Instron universal tensile testing machine (Model 4202). The gauge length was 50 rnrn and the cross-head speed was 10 mrri/min.

Table 4-Regression equations for per cent exhaustion for Procion Brilliant Red HE 3B

Regression equation R2 SEof F-ratio

estimate YI=20.O-l6+9.713X, - 2.203X1 0.912 2.394 30.015

-1.6l3X,- 2.81IX~

+2.033XIX2

Y,⁼35.826 +6.708X, - 2.795X, 0.961 1.328 75.831 +1.180X,+3.959X1

)S )0 z 25

o

0- III:::J

~ IS

><

UJ

-.! ¹⁰

Fig. 2-Effecl of temperature, salt and alkali on exhaustion of Procion Brilliant Red HE 3B dye on silk

Twenty readings were taken for each sample and average of these is reported.

3 Results andDiscussion

The effect of various influencing parameters, viz. concentration of salt, concentration of alkali and temperature, on per cent exhaustion, per cent fixation and per cent realization of Procion Brilli- ant Red HE3B on silk was studied and the results for the set of 15 experiments conducted are given in Table 2. The best fitted regression equation and the coefficient of correlation for per cent exhaustion are given in Table 4. Spatial diagram plotted to see the effect of independent variables on per cent exhaustion is presented in Fig. 2.'It may be seen from Fig. 2 that the exhaustion of Procion Brilliant Red HE3B dye on silk is very poor, the maximum being 30.6% at 60°C using 40 g!L sodium chloride and 10 g!L sodium carbonate. The concentration of salt has marked influence on per cent exhaustion. As the concentra-

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GULRAJANI etai.:DYEINGOF SILK 153 tion of salt in the dyebath increases, the per cent

exhaustion also increases considerably. On the other hand, an increase in the concentration of alkali results in the lowering of per cent exhaustion.

Temperature in the range of 60-80°C has no significant effect on the dye uptake.

After analyzing the results of these experiments, it was decided to further investigate the effect of concentration of salt and alkali, keeping the temperature constant at 60°C. Centrally rotatable composite design was used with 2 variables at five levels (Table 3). The values of per cent exhaustion, per cent fixation and per cent realization for the set of 13 experiments conducted are given in Table 5. In this case, per cent fixation and per cent realization were obtained by two methods. In method I, per cent fixation was determined from the KIS values of the dyed fabric before and after extraction of unreacted dye. In method II, the per cent fixation was determined from the optical density values obtained by dissolving dyed samples in orthophosphoric acid.

The regression analysis was carried out and the best fitted regression equation and the coefficient of correlation obtained for per cent exhaustion are given in Table 4. The spatial diagram showing the effect of concentration of salt and alkali on per cent exhaustion is presented in Fig. 3. It is observed that the concentration of salt has a significant effect on dye uptake. Maximum exhaustion is obtained at the salt concentration of 108.28 g/L. Per cent exhaustion, however, decreases with the increase in the concentration of alkali. Con-

side ring the realization value (Table 5), 3 g/L of alkali has been found to be optimum in combina- tion of 108.28 g/L salt.

Since the concentration of salt was found to be the most important factor affecting exhaustion and realization, it was decided to study the effect of still higher concentrations of salt, keeping the concentration of alkali and temperature costant.

Results of the experiments conducted using four different concentrations of sodium chlo ride at 60°C and 3 g/L sodium carbonate are given in Table 6. It is observed that though further increase in salt concentration improves the dye up-

68

so

z

g

^~o

11\

:)

;. ]0

)(

•••

;:: 20

Fig. 3-Effect of salt and alkali on exhaustion of Procion Brilliant Red HE 3B dye on silk at 60°C

Table 5- Treatment conditions and observed responses [Temp., 60°C; Dye- Procion Brilliant Red HE 3Bj

Exp. NaCI NazC03 Exhaustion Fixation, % Realization, %

No. g/L g/L %

(XI) (Xz) (Yz) Method Method Method Method

1 2 1 2

1 60 2 37.83 68.91 69.90 26.07 26.44

2 100 2 49.50 54.11 50.71 26.78 25.10

3 60 4 31.15 68.09 74.87 21.21 23.32

4 100 4 43.45 69.92 69.24 30.38 30.09

5 51.72 3 28.17 70.81 70.73 19.95 19.93

6 108.28 3 49.16 68.51 76.61 33.68 37.66

7 80 1.58 47.63 55.98 54.19 26.23 25.77

8 80 4.41 40.82 78.03 72.67 31.85 29.66

9 80 3 34.65 67.18 70.36 23.28 24.38

10 80 3 37.63 67.34. 69.89 25.34 26.30

11 80 3 36.79 74.38 69.35 27.36 25.52

12 80 3 34.98 79.63 72.92 27.65 25.51

13 80 3 35.08 75.11 78.00 26.55 27.37

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Table 6- Treatment conditions and observed responses [Temp., 60·C; Na2C03 cone., 3 glL; Dye.Procion Brilliant Red HE3Bj Exp. NaCI Exhaustion Fixation. % Realization, %

No. glL %

(XI)

1 2

100 150 200 250

48.00 58.80 59.79 60.97 3

4

Method 1 60.46 52.29

Method 2 56.96 52.15

Method 1 29.02 30.75

Method 2 27.34 30.66 52.48

45.78

52.15 41.27

31.38 27.91

31.18 25.16

Table 7 -Observed responses with different dyes at optimized conditions [Temp., 60·C; NaCI conc., 110 glL; and Na~CO, conc,3 g/L]

Dye Exhaustion Fixation, % Realization, %

0/0

Method Method Method Method

1 2 1 2

Procion Brill Yellow HE6G 30.65 92.67 73.57 28.4 22.55

Procion Yellow HE4R 10.07 69.45 98.83 6.99 9.95

Procion Navy Blue HER 52.47 63.59 75.00 33.35 39.34

Procion Brill. Red HE7B 42.91 116.62 114.04 37.17 36.06

Procion Brill.Orange HER 6.39 76.61 93.24 4.89 5.96

Procion Black HEL 55.66 57.33 49.87 29.51 25.57

Procion Turq. HEG 51.47 57.33 41).87 29.51 25.57

take to 60%, per cent fixation decreases with the increase in salt concentration. As a result, there is not much improvement in the per cent realization of the dye. Therefore, the salt concentration of 108.28 g/L (or 110 g/L. approximately) is consi- dered as the optimum value.

Thus, the conditions recommended for dyeing of silk using Procion HE dyes are as follows:

Sodium chloride 110 glL Sodium carbonate 3 glL

Temperature 60·C

Using these conditions, different dyes of the same class were also applied on silk in order to get a general information regarding the dyeing behaviour of these dyes on silk. The per cent exhaustion, fixation and realization values of the dyes used are given in Table 7. In general, the exhaustion of these dyes on silk has been found to be poor, maximum being 55.66% in case of Pro- cion Black HEL.

The reason for the low exhaustion of these dyes could be the hydrolysis of dye-fibre bonds during dyeing. It has been reported by Bakker and John- son? that under alkaline conditions, a determining factor in fixation of monochlorotriazine dyes is the competition between bond-forming and bond-

breaking reactions. During dyeing, an equilibrium is established between the dye in fibre and the dye in solution. This equilibrium is disturbed when dye reacts with the fibre, leading to further sorption of the dye. This process goes on till all the sites in the fibre or all the dye gets exhausted.

However, if the dye-fibre bond breaks during dyeing, the equilibrium sorption is lowered, re- sultmg in poor exhaustion of the dye on the fibre.

3.1 Mechanical Properties of Silk Yarn Dyed with Procion HE Dyes

Procion HE dyes, being bifunctional in nature, can react at two sites from the adjacent side chains in the fibre leading to crosslinks. Introduc- tion of cross links decreases chain mobility and plastic deformation. Physical properties are modi- fied; thus, there is. a decrease in extensibility and increase in tensile strength. The load-extension test is, thus, an important analytical tool which provides indirect information about the formation of crosslinks. For this purpose, mechanical properties of silk yam dyed with Procion Brilliant Red HE 3B, Procion Navy Blue HER and Pro- cion Turquoise HEG were tested. With these dyes, yams were dyed at three concentrations, viz.

1%, 3% and 5% owf. The stress and strain values

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GUlRAJANI et al.:DYEING OF SILK 155

Table 8- Tenacity values of dyed and blank dyed silk yarns

Yam Tenacity Strain Increase in strength

gIden % over that of blank dyed yam

% Blank dyed

Dyed with

Procion Brill. Red HE3B, l%owf Procion Brill. Red HE3B, 3% owf Procion Brill. Red HE3B, 5% owf.

Procion Navy Blue, 1% owf Procion Navy Blue, 3% owf Procion Navy Blue, 5% owf Procion Turquoise HEG, 1% owf Procion Turquoise HEG, 3% owf Procion Turquoise HEG, 5% owf

2.44 12.4

2.58 10.7 5.4

2.59 .2.1 6.0

2.69 11.0 10.1

2.43 12.2

2.66 12.5 8.9

2.65 13.1 8.5

2.48 12.2 \.4

2.48 13.2 \.7

2.51 12.7 2.7

are given in Table 8. It may be seen that there is a gradual increase in strength as the depth of shade increases in case of all the three dyes. With 5%

shade of Procion Brill. Red HE3B, as much as 10.069% increase in strength over that of blank dyed yarn could be observed. This increase in strength indicates the possibility of the formation of crosslii1ks in the fibre by Procion HE dyes.

4 Conclusion

Exhaustion of Procion HE brand of reactive dyes on silk is greatly enhanced by the presence of sodium chloride in the dyebajh. An increase in

the dyeing temperature from 60° to 80°C has no significant effect on the exhaustion of these dyes on silk. In general, the exhaustion of Procion HE dyes on silk has been found to be poor. The in- creased tensile strength of dyed silk indicates the possibility of the presence of crosslinks formed by Procion HE dyes in the fibre.

References

1 Gulrajani M L,Rev Prog Coloration, 23(1993) 51.

2 Bakker P G H & Johnson A, JSoc Dyers Color, 89 (1973) 203.