Jndian Journal of Fibre & Textile ResearchVol. 20, September 1995, pp. 150-155

Dyeing of silk with Procion HE dyes

M L Gulrajani, Ashish Jain & Deepali AgarwalDepartment 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 monochloro-triazine dyes (Procion HE dyes) on silk has been studied. Factorial design has been used to obtainthe optimum conditions of dyeing. Maximum exhaustion has been obtained with 110 g/L sodiumchloride and 3 g/L sodium carbonate. Temperature in the range 60-"80°Chas no influence on ex-haustion. Improvement in mechanical properties of dyed silk suggests the formation of crosslinks inthe fibre by these dyes.

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

1 IntroductionDyeing of silk with reactive dyes has been re-

cently reviewed'. It has been reported that amongthe reactive dyes suggested for silk, dyes havinga-bromoacrylamido group or difluoro-chloropyri-midine group show good fixation as well as goodwet fastness properties. Both these types of dyehave two reactive centres which may be responsi-ble for their superior properties. However, thetwo reactive centres in these dyes are located veryclose to each other.

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

In the late 1960s and early 1970s, ICI utilizedthe advantage of having two reactive groups andproduced a range of Procion HE dyes. These arebifunctional dyes containing two monochlorotria-zine groups. The monochlorotriazine (MeT) reac-tive group is characterized by its high stability tohydrolysis at elevated temperatures when it ispresent in neutral electrolyte. The twinned MCTstructure exhibits high migration and diffusionduring the neutral electrolyte phase and also giveshigh fixation levels on addition of alkali, since thepresence of two reactive groups per dye moleculeincreases the probability of dye-fibre interaction.

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

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

2 Materials and Methods2.1 Materials

Plain woven mulberry silk fabric of 40 g/m?weight was used. Prior to dyeing, the fabric wasscoured in a solution containing 2 g!L non-ionicdetergent at 100°C for 1 h. The material-to-liquorratio 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 ma-terial-to-liquor ratio at 1:30.

Sodium chloride, sodium carbonate, sodium di-hydrogen phosphate, orthophosphoric acid anddisodium hydrogen phosphate of laboratory gradewere used without any further purification. Pro-cion HE dyes manufactured by Atic IndustriesLtd were used.

2.2 Methods2.2.1 Dyeing

Silk fabric was dyed in a laboratory model jig-ger whereas the silk yarn was dyed in a Pretemamulticolor dyeing machine. The material-to-liquorratio was kept at 1:100. Dyeing was carried outaccording to the dyeing cycle shown in Fig. 1.

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

GULRAJANI et al.: DYEING OF SILK 151

exhaustion, fixation, etc., the experiments werecarried out according to the Box and Behnken re-sponse surface design. This experimental design isused for experiments with three independent vari-ables and three levels of each variable. Table 1gives the three independent variables and their le-vels used in the present study. Thus, a set of 15experiments was performed as listed in Table 2. Aquadratic polynomial was used to analyze the de-sign with three independent variables (Eq. 1).

3 3 3

Y=Po+ LPiXi+ LPuX:+ LPijXiXj ..... (1)i-I i-I i-I

III SAL 1 I ALKALI U ALl< ALl

...•.....

IX:;:)~ Ie 20 I...s I.•..

r10II

00 60 70 80 90

TIME, mill

Fig. I-Dyeing cycle

where Y is the measured response; {3o, {3;, {3ii and{3.. the coefficients of the regression; and i and j,

I} ,

the integers with i <j. To test the estimated re-·gression equation for the goodness of fit, theFisher test was employed. The estimated coeffi-cients of the regression equation were tested forsignificance using the Student t-test, The insignifi-cant coefficients were deleted from the equationand the remaining ones were recalculated andgoodness of fit reassessed.

Box and Wilson central composite rotatable de-sign was used for experiments with two variablesat five levels each (Table 3).

1.1.1 TestsThe exhaustion (%) of the dyes was calculated

from the optical densities of the dyebath beforeand after dyeing using the following equation:

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

Table l=-Actual and coded values of independent variables

Variable Level

-1 0 + 1

NaCI (XI)' gIL 0 20 40Na2C03 (X2), glL 5 10 15Temperature (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 Method1 2 1 2

1 0 5 70 10.30 84.29 92.21 8.68 9.502 40 5 70 28.20 72.36 81.96 20.41 23.113 20 5 80 17.50 71.48 84.63 12.51 14.814 20 5 t)0 21.75 60.23 86.12 13.10 18.735 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 11.197 40 10 60 30:60 66.67 79.53 20.40 24.348 0 10 60 12.23 85.62 78.43 10.47 9.609 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 22.8412 0 15 60 3.38 57.64 79.40 1.95 2.6913 20 10 70 19.05 83.06 80.12 15.82 15.2614 20 10 70 16.25 75.88 87.99 12.33 14.3015 20 10 70 22.19 78.33 76.57 17.68 16.50

152 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 1995

Table 3-Actual and coded values of independent variables

Variable Level

NaCI (XI)' g/LNa2C03 (X2), g/L

- 1.414

51.721.586

o80

3

1 1.414

100 108.284 4.414

-1

602

whereOD luitinl = Optical density of dyebath before dyeingODFillal =Optical density of dyebath after dyeing

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

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

Dye fixation (%) was determined using the fol-lowing two methods:

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

KIS value of dyed sample afterextraction

Fixation (%)= x 100KIS value of dyed sample before

extraction

(ii) Fixation (%) was also calculated from theoptical density measurements. 25 mg of dyedsamples, before and after the extraction of un-fixed dye, were dissolved in 25 rnl of orthophos-phoric acid and the optical density was measuredon Perkin-Elmer Lambda 3B UV/VlS spectro-photometer. Dye fixation (%) was then calculatedas follows:

.. I" 00 of dyed sample after extraction 100Fixation (%, = . xOD of dyed sample before extraction

Realization (%), which gives the percentage ofthe total dye in the dyebath which has reactedwith the fibre, was calculated as follows:

( 1.) % Fixation x % ExhaustionRealization 00 100

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

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

Regression equation R2 SEof F-ratioestimate

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 25o0-III:::J~ IS><UJ

-.! 10

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

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

3 Results and DiscussionThe effect of various influencing parameters,

viz. concentration of salt, concentration of alkaliand temperature, on per cent exhaustion, per centfixation and per cent realization of Procion Brilli-ant Red HE3B on silk was studied and the resultsfor the set of 15 experiments conducted are givenin Table 2. The best fitted regression equationand the coefficient of correlation for per cent ex-haustion are given in Table 4. Spatial diagramplotted to see the effect of independent variableson per cent exhaustion is presented in Fig. 2.' Itmay be seen from Fig. 2 that the exhaustion ofProcion Brilliant Red HE3B dye on silk is verypoor, the maximum being 30.6% at 60°C using40 g!L sodium chloride and 10 g!L sodium car-bonate. The concentration of salt has marked in-fluence on per cent exhaustion. As the concentra-

GULRAJANI etai.:DYEINGOF SILK 153

tion of salt in the dyebath increases, the per centexhaustion also increases considerably. On theother hand, an increase in the concentration of al-kali results in the lowering of per cent exhaustion.Temperature in the range of 60-80°C has no sign-ificant effect on the dye uptake.

After analyzing the results of these experiments,it was decided to further investigate the effect ofconcentration of salt and alkali, keeping the tem-perature constant at 60°C. Centrally rotatablecomposite design was used with 2 variables at fivelevels (Table 3). The values of per cent exhaus-tion, per cent fixation and per cent realization forthe set of 13 experiments conducted are given inTable 5. In this case, per cent fixation and percent realization were obtained by two methods. Inmethod I, per cent fixation was determined fromthe KIS values of the dyed fabric before and afterextraction of unreacted dye. In method II, the percent fixation was determined from the opticaldensity values obtained by dissolving dyed sam-ples in orthophosphoric acid.

The regression analysis was carried out and thebest fitted regression equation and the coefficientof correlation obtained for per cent exhaustionare given in Table 4. The spatial diagram showingthe effect of concentration of salt and alkali onper cent exhaustion is presented in Fig. 3. It isobserved that the concentration of salt has a sign-ificant effect on dye uptake. Maximum exhaustionis obtained at the salt concentration of 108.28g/L. Per cent exhaustion, however, decreases withthe increase in the concentration of alkali. Con-

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

Since the concentration of salt was found to bethe most important factor affecting exhaustionand realization, it was decided to study the effectof still higher concentrations of salt, keeping theconcentration of alkali and temperature costant.Results of the experiments conducted using fourdifferent concentrations of sodium chloride at60°C and 3 g/L sodium carbonate are given inTable 6. It is observed that though further in-crease in salt concentration improves the dye up-

68

sozg ~o11\:)

;. ]0)(

•••;:: 20

Fig. 3-Effect of salt and alkali on exhaustion of ProcionBrilliant 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 Method1 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 25.103 60 4 31.15 68.09 74.87 21.21 23.324 100 4 43.45 69.92 69.24 30.38 30.095 51.72 3 28.17 70.81 70.73 19.95 19.936 108.28 3 49.16 68.51 76.61 33.68 37.667 80 1.58 47.63 55.98 54.19 26.23 25.778 80 4.41 40.82 78.03 72.67 31.85 29.669 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 25.5212 80 3 34.98 79.63 72.92 27.65 25.5113 80 3 35.08 75.11 78.00 26.55 27.37

154 INDIAN J. FmRE TEXT. RES., SEPTEMBER 1995

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)

12

100150

200250

48.0058.80

59.7960.97

34

Method1

60.4652.29

Method2

56.9652.15

Method1

29.0230.75

Method2

27.3430.66

52.4845.78

52.1541.27

31.3827.91

31.1825.16

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 Method1 2 1 2

Procion Brill Yellow HE6G 30.65 92.67 73.57 28.4 22.55Procion Yellow HE4R 10.07 69.45 98.83 6.99 9.95Procion Navy Blue HER 52.47 63.59 75.00 33.35 39.34Procion Brill. Red HE7B 42.91 116.62 114.04 37.17 36.06Procion Brill. Orange HER 6.39 76.61 93.24 4.89 5.96Procion Black HEL 55.66 57.33 49.87 29.51 25.57Procion Turq. HEG 51.47 57.33 41).87 29.51 25.57

take to 60%, per cent fixation decreases with theincrease in salt concentration. As a result, there isnot much improvement in the per cent realizationof the dye. Therefore, the salt concentration of108.28 g/L (or 110 g/L. approximately) is consi-dered as the optimum value.

Thus, the conditions recommended for dyeingof silk using Procion HE dyes are as follows:Sodium chloride 110 glLSodium carbonate 3 glLTemperature 60·C

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

The reason for the low exhaustion of these dyescould be the hydrolysis of dye-fibre bonds duringdyeing. It has been reported by Bakker and John-son? that under alkaline conditions, a determiningfactor in fixation of monochlorotriazine dyes isthe competition between bond-forming and bond-

breaking reactions. During dyeing, an equilibriumis established between the dye in fibre and thedye in solution. This equilibrium is disturbedwhen dye reacts with the fibre, leading to furthersorption of the dye. This process goes on till allthe sites in the fibre or all the dye gets exhausted.However, if the dye-fibre bond breaks duringdyeing, 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 ProcionHE Dyes

Procion HE dyes, being bifunctional in nature,can react at two sites from the adjacent sidechains in the fibre leading to crosslinks. Introduc-tion of cross links decreases chain mobility andplastic deformation. Physical properties are modi-fied; thus, there is. a decrease in extensibility andincrease in tensile strength. The load-extensiontest is, thus, an important analytical tool whichprovides indirect information about the formationof crosslinks. For this purpose, mechanical pro-perties of silk yam dyed with Procion BrilliantRed HE 3B, Procion Navy Blue HER and Pro-cion Turquoise HEG were tested. With thesedyes, yams were dyed at three concentrations, viz.1%, 3% and 5% owf. The stress and strain values

GUlRAJANI et al.: DYEING OF SILK 155

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

Yam Tenacity Strain Increase in strengthgIden % over that of blank

dyed yam%

Blank dyed

Dyed with

Procion Brill. Red HE3B, l%owfProcion Brill. Red HE3B, 3% owfProcion Brill. Red HE3B, 5% owf.Procion Navy Blue, 1% owfProcion Navy Blue, 3% owfProcion Navy Blue, 5% owfProcion Turquoise HEG, 1% owfProcion Turquoise HEG, 3% owfProcion Turquoise HEG, 5% owf

2.44 12.4

2.58 10.7 5.4

2.59 .2.1 6.02.69 11.0 10.12.43 12.22.66 12.5 8.92.65 13.1 8.52.48 12.2 \.42.48 13.2 \.7

2.51 12.7 2.7

are given in Table 8. It may be seen that there is agradual increase in strength as the depth of shadeincreases in case of all the three dyes. With 5%shade of Procion Brill. Red HE3B, as much as10.069% increase in strength over that of blankdyed yarn could be observed. This increase instrength indicates the possibility of the formation ofcrosslii1ks in the fibre by Procion HE dyes.

4 ConclusionExhaustion of Procion HE brand of reactive

dyes on silk is greatly enhanced by the presenceof sodium chloride in the dyebajh. An increase in

the dyeing temperature from 60° to 80°C has nosignificant effect on the exhaustion of these dyeson silk. In general, the exhaustion of Procion HEdyes on silk has been found to be poor. The in-creased tensile strength of dyed silk indicates thepossibility of the presence of crosslinks formed byProcion HE dyes in the fibre.

References1 Gulrajani M L, Rev Prog Coloration, 23 (1993) 51.2 Bakker P G H & Johnson A, J Soc Dyers Color, 89 (1973)

203.