Indian Journal of Textile ResearchVol. 7, December 1982, pp.101-I06

Dyeing of Cellulosic Fibres with a Reactive Dye from Acetone-Water Mixture

R B CHAVAN & A SUBRAMANIAN

Department of Textile Technology, Indian Institute of Technology, New Delhi 110016

Received II June 1982; accepted 12 September 1982

The dyeability of three alkali swollen cellulosic fibres, viz., mercerized cotton, viscose rayon and hollow viscose, with areactive dye (C.!. Reactive Red 31) from acetone-water mixture has been investigated. Viscose rayon showed the least dyebathexhaustion and dye fixation. This has been attributed to the presence of skin-core structure. Pretreatment of viscose rayon withsodium zincate (15% vol/vol) has been found effective in suitably modifying the viscose rayon structure, leading to dye uptakeand fixation comparable to those on cotton and hollow viscose. The X-ray and SEM studies indicate the deorientation ofviscose rayon on treatment with sodium zincate solution.

Various attempts have been made to apply acid, directand reactive dyes to cellulosic fibres from non-aqueousmedia and emulsion systems containing smallproportions of water! -10. Chavan and cowor-kers 7 -10 studied systematically the application of acidand reactive dyes on water swollen solvent exchanged(WSSE) and alkali swollen cotton respectively fromvarious solvent mixtures. It was reported that reactivedyes based on monochloro- and dichlorotriazinereactive system can be successfully applied on cottonwith almost 100%dyebath exhaustion and 80-85% dyefixation when the dyeings are carried out fromdimethylformamide (DMF)-trichloroethylene (TCE)solvent mixture or acetone-trichloroethylene withsmall proportions of water or DMF.

The high dyebath exhaustion and dye fixation onalkali swollen cotton from these solvent mixtures wereattributed respectively to the low dye solubility in thesolvent mixture and the presence of a small quantity ofwater in the dyeing medium, leading to minimum dyehydrolysis. The criteria for the selection of suitablemixtures of polar and non-polar solvents for gettinghigh dyebath exhaustion and fixation of reactive dyeson alkali swollen cotton have been reportedelsewhere II .

In the present communication, the dyeing behaviourof three alkali swollen cellulosic fibres, viz., mercerizedcotton, viscose rayon and hollow viscose, with areactive dye (C.!. Reactive Red 31)from acetone-watermixture is reported. The difference in the dyeingbehaviour of viscose rayon is explained on the basis ofdifference in fibre structure. A pretreatment withsodium zincate solution (15% vol/vol) has beensuggested to suitably modify the viscose rayonstructure to get dyeings as good as on cotton andhollow viscose.

Materials and MethodsCotton yarn of 2/40s count was used after scouring,

slack mercerizing with 25% sodium hydroxide andhydrogen peroxide bleaching I 2 .

Viscose rayon and hollow viscose staple fibres of 1.4and 1.5denier respectively were used after boiling withdetergent solution.

Commercial Procion Brilliant Red HsB (C.I.Reactive Red 31) and standard laboratory gradeacetone and chemicals were used.

Preparation of sodium zincate solutionl3-NaOH(180 g)was dissolved in 200 ml of distilled water and 80g of ZnO (A.R.) was added to the hot solution slowlywith stirring. The hot solution was boiled till it becameclear and then it was filtered and made up to 500 mlwith distilled water. This solution was diluted todifferent concentrations (5-25% vol/vol),

Dyeing- The three cellulosic fibres (0.2 g each) werepreswollen with aqNaOH and were centrifuged beforedyeing. Dyeing was carried out using 2% shade onweight of material (owm) in 25 ml measuring glasscylinder fitted with a condenser (liquor ratio, 100:1) ina laboratory dyeing machine (Colour master, suppliedby John Jeffries Ltd, Lancashire) with polyethyleneglycol-200 bath as the heating medium. Dyebathexhaustion was carried out at 25°C for 1 hr and thefixation was carried out at 60°C for 1 hr. At the end ofdyeing, the samples were withdrawn, air dried andwashed with distilled water several times at boil. All thewashings were collected in a standard volumetric flaskand the optical density of the washed liquor wasmeasured. From this, the amount of dye fixed oncotton was determined.

Estimation of carboxyl content-Carboxyl groupcontent of cellulosic fibres was estimated iodimetri-cally using a standard procedure 14.

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INDIAN 1 TEXT RES, VOL. 7, DECEMBER 1982

Treatment of viscose rayon with sodium zincatesolution-Pretreatment of viscose rayon was carriedout with sodium zincate solution of differentconcentrations (vol/vol) at room temperature for 15min. Viscose rayon was then washed till neutral andthen air dried.

Rate of dyeing-The cellulosic fibres (cotton, viscoserayon, hollow viscose and sodium zincate treatedviscose rayon) were water swollen at room temperaturefor I hr and centrifuged. The samples wereimmediately used for measuring the rate of dyeing. Thedyeing was carried out at 25°C with 2% owm dye inwater-acetone (1:9) solvent mixture. The samples werewithdrawn at different intervals and the amount of dyeleft in the dyebaths was estimated, from which the dyeon the fibre was calculated.

Dyeing with different initial dye concentrations - Thecellulosic samples were alkali swollen (5 gjIitre NaOH)at room temperature for 4 hr, centrifuged and used fordyeing immediately. The dyebath was prepared withdye concentration varying from 2 to 10% owm. Toavoid dye precipitation in water-acetone solventmixture when the dye concentration was more than 2%owm, the initial dyeing was carried out in water-acetone (1:4) solvent mixture. The acetone content inthe dyebath was increased in two instalments at 15minintervals till the water-acetone ratio was 1:9.After this,the dyebath exhaustion was carried out at 25°C for 1hr, followed by dye fixation for 2 hr at 60°C. Theamount of dye fixed was calculated as describedearlier.

X-ray study - Wide angle X-ray diffractionphotographs were taken on X-ray diffraction unit

.Norelco-type 120-101-85 Philips electronic instru-ments employing nickel filtered Cu.K, radiation.

SEM study-The longitudinal sections of viscoserayon were scanned using S4-10 Cambridgestereoscan.

Results and Discussion

From the systematic work carried out earlier 8-II , itis well established that a polar-non-polar mixed solventsystem can be used successfully for the dyeing of alkalipreswollen cotton with a reactive dye.

Initial dyeing experiments have shown that contraryto the expectations, viscose rayon shows much less dyeuptake and dye fixation when the dyeings are carriedout on alkali swollen viscose rayon from acetone-water(9:I) solvent system.

The effect of alkali concentration used during thepreswelling of cellulosic fibres (mercerized cotton,viscose rayon and hollow viscose) on the dyebathexhaustion and dye fixation is shown in Figs 1 and 2,

102

where the difference in the dyeing behaviour of threecellulosic fibres is clearly seen. At suitable alkaliconcentration used during preswelling, it was possibleto get 100% dyebath exhaustion and 83% dye fixationon cotton, 98% dyebath exhaustion and 80% dyefixation on hollow viscose, and 76% exhaustion and52% dye fixation on viscose rayon. To explain thedyeing behaviour, it was initially thought that thepresence of carboxyl groups is probably responsiblefor the low dyebath exhaustion, leading to low dyefixation. This assumption was based on theobservations of the earlier workers who attributed thesigmoidal shape of adsorption isotherms of direct dyeson viscose rayon to the presence of carboxyl groupswhich repel dye anions at the initial stages ofdyeing+" -18 . A similar repulsion effect was observedon oxidized cotton when the dyeing was carried outwith acid dyes from DMF-TCE solvent systems!":

The carboxyl content of the cellulosic fibres wasestimated and was found to be as follows: Cotton, 1.52meq/IOO g; viscose rayon, 6.0 meq/IOO g; and hollowviscose, 7.0 meq/l Ong.

Although to some extent the high carboxyl contentmay be responsible for the low dyebath exhaustion anddye fixation, on this basis alone the difference in thedyeing behaviour of viscose rayon and hollow viscosecannot be explained. Therefore, some other factormust be responsible for the lower dye uptake onviscose rayon.

;f

/OO~~6~row 61>0 4 8 12 16 20

SODIUM HYDROXIDE CONC.,g/litr.

Fig. I-Effect of alkali concentration on dyebath exhaustion[(0-0] cotton; (0-0) viscose· rayon; and (e-e) hollow

viscose]

100,----------------;

-:zo~xu,

w>o

4 8 12 16 20SODIUM HYDROXIDE CONC., gflitre

Fig. 2-Effect of alkali concentration on dye fixation [(e-e)cotton; (a-a) viscose rayon; and (0-0) hollow viscose]

CHAVAN & SUBRAMANIAN: DYEING OF CELLULOSIC FIBRES WITH A REACTIVE DYE

The different dyeing behaviour of viscose rayoncompared to that of cotton from aqueous system hasbeen interpreted by many workers on the basis ofdifference in their fibre structure 19 -21. The presenceof skin structure in viscose rayon was firstdemonstrated by Preston+ and subsequentlyconfirmed by many other workers " -28. Based onexperimental evidence, the general view has been thatunlike the core, the skin has a highly orientedstructure 29 , as a consequence of which it acts as aretarding, membrane. Therefore, the rate of dyeingdecreases. This was confirmed by Boulton et al. 30 whofound that in aqueous dyeing, the initial rate of dyeingof viscose is slower than that of cotton orcuprammonium rayon.

The different dyeability behaviours of cotton,hollow viscose and viscose rayon observed in thepresent study may be attributed to the presence of skinstructure in viscose rayon which offers resistance todye penetration. Hence, the dye exhausted in the caseof viscose rayon was present on the surface and onlypart of it got fixed, whereas in the case of othercellulosic fibres, since there was no retarding effect, thedye penetration was better, resulting in increased dyefixation.

To modify the skin structure of viscose rayon, threepretreatment methods, viz., treatment with NaOH (50g/litre), partial acetylation from non-aqueous mediumand subsequent hydrolysis, and treatment with sodiumzincate solution of different concentrations, were tried.Among these, the use of sodium zincate was found togive encouraging results. The effect of sodium zincateconcentration on dye uptake on viscose rayon fromacetone-water mixture is shown in Table 1. At asuitable sodium zincate concentration (15% vol/vol)used for pretreatment, the dyebath exhaustion and dyefixation were equal to those in the case of cotton (Table2).This could be attributed to deorientation of the skinstructure, so that dye could penetrate inside the fibre.

The above view was supported by the rate of dyeing,the extent of dye fixation on varying the initial dyeconcentration in the dyebath, X-ray and SEM studies.

The rate of dyeing curves for four different cellulosicfibres are shown in Fig. 3. It is observed that untreatedviscose rayon has the lowest rate of dyeing, confirmingthe retarding effect of the skin structure. When thedyeings were carried out from dyebaths of varying dyeconcentration (2-10% owm), the dye fixation increasedconsistently on all the cellulosic fibres, except viscoserayon (Table 3).

These two experiments indicate that the treatment ofviscose rayon with sodium zincate helps in thedeorientation of the skin structure of viscose rayon.This has been further confirmed by the results of X-rayand SEM studies.

Table I-Effect of Sodium Zincate Pretreatment on theDyeing Behaviour of Viscose Rayon*

Sodium zincate Dyebath Dyecone. exhaustion fixation

YO<voljvoI) % %Control 76 52

5 76 5210 85 6015 100 8420 100 8425 100 84

*3 g/litre NaOH swollen samples

Table 2-Effect of Alkali Concentration on DyebathExhaustion and Dye Fixation on Sodium Zincate (15%

vol/vol) Pretreated Viscose Rayon

NaOH cone. Dyebath Dyeused for exhaustion fixation

preswelling % %g/litre

I 100 512 100 813 100 845 100 8410 98 7915 96 6220 96 57

100r----------------------,

ao

za 60ti~:z:)(...

!40>-o

20

OL------~------~-----~PERIOD, hr

Fig. 3-Dyeing rate of different cellulosic fibres [(0-0) cotton;(0-0) hollow viscose; (e-e) viscose rayon; and (.-.) sodium

zincate treated viscose rayon]

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INDIAN J TEXT RES, VOL. 7, DECEMBER 1982

The X-ray diffraction photographs of untreated andsodium zincate treated viscose rayon (Fig. 4) indicate aprogressive decrease in the orientation of the fibre asthe sodium zincate concentration used for pretreat-ment increases from S to 2S% (vol/vol),

The X-ray photographs were scanned azimuthallyusing a microdensitometer and the orientation index

. (reciprocal of-half width) was calculated. The resultsgiven in Table 4 indicate that progressive deorientationhas taken place due to sodium zincate treatment.

The longitudinal sections of untreated and sodium

Table 3-Effect of Dye Concentration on Dye Uptake ofCellulosic Fibres

zincate treated viscose rayon fibres were examined byscanning electron microscopy. The SEM micrographsof untreated and sodium zincate treated viscose rayonare shown in Fig. S. It is observed that untreatedviscose rayon (Fig. Sa) shows the hardened nature offibre surface, whereas viscose rayon treated withdifferent concentrations of sodium zincate solution(Fig. Sb, c,d) shows that the fibre surface got modifiedand became smooth and porous as the sodium zincateconcentration increased fromS to 20%. Thus, sodiumzincate treatment was found to be effective in suitably

Table 4-Effect of Sodium Zincate Concentration onOrientation Index of Viscose Rayon

Initial Dye fixation on fibres, gjlOO g fibredye cone, Sodium Orientation%owm Cotton Viscose Hollow Treated zincate cone. index

rayon viscose viscose % (vol/vol)rayon Control 2.6

2 1.64 1.04 1.60 1.70 5 2.54 3.28 1.07 3.22 3.35 10 2.36 4.98 1.12 3.77 4.98 15 2.08 6.40 1.14 4.98 6.40 20 1.8

10 7.80 1.14 6.20 7.80 25 1.4

Fig. 4 -X-ray diffraction photographs of viscose rayon [(a) untreated, (b) treated with 5% Sodium zincate, (c) treated w:~r 15% sodiumzincate, and (d) treated with 25% sodium zincate], , •

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CHAVAN & SUBRAMANIAN: DYEING OF CELLULOSIC FIBRES WITH A REACTIVE DYE

Fig. 5-Scanning electron micrographs of viscose rayon [(a) untreated, x 4500; (b) treated with 5% sodium zincate, x 6300; (c) treated with15% sodium zincate, x 6300; and (d) treated with 25% sodium zincate, x 6300]

modifying the viscose rayon structure to get dyeings solvent mixture. This dyeing behaviour of viscosecomparable to those on cotton and hollow viscose. rayon has been attributed to the presence of skin-core

structure. Treatment of viscose rayon with sodiumzincate (15% vol/vol) favourably modifies the viscoserayon structure, leading to dye uptake and fixationcomparable to those on cotton and hollow viscose. x-ray and SEM studies indicate de orientation of viscoserayon on treatment with sodium zincate solution.

\/'

Conclusion

Among the three alkali swollen cellulosic fibres,viscose rayon shows the least dye bath exhaustion anddye fixation with a reactive dye from acetone-water

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