Indian Journal of Fibre & Textile ResearchVol. 23, December 1998, pp. 261-266

Improved dyeability of acrylic fibre with cationic and disperse dyes

A K Mukherjee & S D Bhattacharya'

Department of Textile Technology, Indian Institute of Technology, New Delhi 110 016, India

and

R Varadarajan

Department of Chemistry, Indian Institute of Technology, New Delhi 1\0 016, India

Received 6 June 1997; revised received 9 March 1998; accepted 23 March 1998

Acrylic fibres were hydrolysed with sodium hydroxide of different concentrations at 50°C fordifferent durations and then dyed separately with cationic dyes (C!. Basic Red 18 and C!. Basic Blue 3)and disperse dyes (C!. Disperse Orange 3 and C.I. Disperse Red 17) in different per cent of shades. Thedyeing performance of these hydrolysed acrylic fibres was studied taking into account the structuraltransformation occurred due to hydrolysis process. It has been observed that the hydrolysed fibresalways exhibit higher dye uptake than the untreated ones. Hydrolysed fibres also have higher diffusioncoefficients than the untreated fibres. Cationic dyes show better dyeing performance than the dispersedyes. The wash fastness of dyed samples is quite satisfactory at all levels of dyeing.

Keywords: Acrylic fibre, Cationic dyes, Diffusion coefficient, Disperse dyes, Dyeing, Dye uptake

1 IntroductionAcrylic fibres have poor dyeability because of

the compactness of their structure. Therefore, thecommercial acrylic fibres always contain one ormore comonomers which enhance their dyeabilityby providing more dye receptive sites. A numberof studiesv" pertaining to the manufacture ofacrylic fibres with higher water sorption and gooddye uptake have been reported. Khamrakulovet al .. I3 reported the development of acrylic fibresfrom a blend of polyacrylonitrile (PAN) andhydrolysed PAN waste which showed betterdyeing performance as compared to theunmodified acrylic fibres. Zbigneva" preparedacrylic fibres from acrylonitrile with hydrolysedwaste ~hich showed a significant increase insorption and fixation of cationic dyes. However, nodetailed work has been reported on commercialacrylic fibres modified by hydrolysis and theirdyeing behaviour with different dyestuffs. Thecommercial acrylic fibres exhibit unlevel dyeing

'Present address: Department of Textile Chemistry, Faculty ofTechnology and Engineering, M.S. University of Baroda,Vadodara 390 001, India.To whom all the correspondence should be addressed.

with some restriction to shades. Therefore, in thepresent work, a commercial acrylic fibre was firsthydrolysed to different degrees and then thehydrolysed fibres were dyed with cationic anddisperse dyes under identical conditions and theirdyeing behaviour studied. The diffusion of dyeinto the hydrolysed fibre structure and theequilibrium dye uptake of both the dyes onhydrolysed acrylic fibres have also been

. investigated.

2 Materials and Methods

2.1 Materials

A commercial acrylic fibre (acrylonitrile, 92%;methyl acrylate, 7% and sodium methyllylsulphonate, 1%) was hydrolysed with sodiumhydroxide solution of different concentrations (5%,10% and 15%) at 50°C for different time periods.Different hydrolysed acrylic fibres were selectedon the basis of their complex structure developeddue to the hydrolysis process. For a particularsodium hydroxide concentration, three hydrolysedfibres having highest, medium and lowest nitrogencontent at 50°C were chosen. Hydrolysed fibres atthis temperature exhibit minimum strength loss

262 INDIAN 1. FIBRE TEXT. RES., DECEMBER 1998

and contribute to all possible structural changes inthe fibre at a reasonably good level.

Two cationic dyes, namely C.I. Basic Red18(BI) and C. 1 Basic Blue 3(BII) , and twodisperse dyes, namely c.I. Disperse Orange 3(DI)and c.I. Disperse Red 17(DII) were used. Thesedyestuffs were selected on the basis of thedifference in their molecular weights. Cationicdyes were purified by recrystallizing in methanoland drying in an oven at 30°C for 2h. Dispersedyes were first refluxed using soxhlet apparatus for72h in acetone, recrystallized and then dried at30°C for 2h.

2.2 Methods

2.2.1 DyeingA mixture of 0.1 % acetic acid (pH 3.5) and

0.1 % cationic retarder (Acifix TD) was added tothe 1.0% dye solution/dispersion. About 0.2-0.3 gof fibres were then put into it, maintaining thematerial-to-liquor ratio at I :50. Dispersing agent(Lyocol 01) was used in case of dyeing withdisperse dyes. Dyeing was carried out in a closedsystem (Beaker Dyeing Machine) with tlifferentdepth of shades, viz 0.5%, 1.0%, 2.0%, 3.0% and5.0%. The dyeing temperature was raised from70°C to 100°C at the rate of 10°C/min. Afterdyeing for a required period of time, the sample

was taken out, cooled slowly, washed with distilledwater, soaped at boil for 20 min, dried andconditioned at 65% RH and 20°C. Dye uptake wasmeasured on a UV -visible spectrophotometer(Perkin-Elmer, Lamda 3B).

2.2.2 Calculation of Diffusion CoefficientThe apparent diffusion coefficient (Da) was

calculated using the method of Hiil15 by measuringthe dye uptake of fibre with the time intervals of tfrom an infinite dyebath.

2.2.3 Wasb Fastness TestWash fastness of different dyed samples was

assessed by ISO test method No.3.

3 Results and Discussion

3.1 Effect of Hydrolysis on Dyeing Performance of AcrylicFibres

Tables I and 2 indicate that the hydrolysedacrylic fibre can successfully be dyed with bothcationic and disperse dyes. The dye uptake of allthe hydrolysed acrylic fibres increases withincrease in dyebath concentration (i.e. shadepercentage) and decreases- with the decrease innitrogen content in fibres, irrespective of theconcentration of sodium hydroxide. At all thelevels of dyeing, the dye uptake of hydrolysed

Table I-Dyeing performance of hydrolysed acrylic fibres[Hydrolysis temp., 50°C)

NaOH cone, Nitrogen Dye uptake, rng/g of fibre

<lnd content in B I (C I Basic Red 18) B II (C I Basic Blue 3)treatment hydrolysed Shade%~O.5 1.0 2.0 3.0 5.0 0.5 1.0 2.0 3.0 5.0time fibre, %

Contr.ol 23.7 3.85 7.2 15.3 25.60 35.5 3.61 7.05 14.8 24.7 33.5(U ntreated)5% NaOH

0.5 h 21.3 4.62 9.01 18.2 29.4 38.1 4.5 8.4 17.3 26.7 36.82h 17.0 4.41 8.8 17.40 28.8 37.1 4.28 7.9 16.9 26.2 36.324 h 14.5 4.12 7.4 16.70 27.3 35.9 3.6 7.1 16.4 25.7 35.1

10% NaOH0.5 h 19.4 4.72 9.82 18.60 29.20 44.2 4.64 8.41 18.2 28.3 40.102h 15.3 4.51 8.71 18.3 28.6 43.6 4.3 8.2 17.6 27.4 39.7024 h 12.2 4.21 8.30 17.60 27.1 42.1 3.76 7.5 16.9 26.4 38.6

15% NaOH0.5 h 18.4 4.74 9.70 18.9 29.4 46.21 4.7 9.1 18.4 28.8 42.14h 12.4 4.56 8.80 17.30 28.6 45.7 4.4 8.3 17.7 27.9 41.624 h 7.8 4.3 8.40 17.90 27.8 44.6 3.81 7.9 16.8 26.7 40.3

MUKHERJEE et al.: IMPROVED DYEABILITY OF ACRYLIC FIBRE 263

Table 2-Dyeing performance of hydrolysed acrylic fibres[Hydrolysis temp., 50°C]

NaOH cone. Nitrogen Dye uptake, mg/g of fibre

and content in 01 (C I Disperse Orange 3) n II (C I Disperse Red 11)treatment hydrolysed Shade% ~ 0.5 1.0 2.0 3.0 5.0 0.5 1.0 2.0 3.0 5.0

time fibre, %

Control 23.7 3.21 6.20 12.40 19.60 30.60 3.\0 5.9 11.60 18.70 29.30(U ntreated)5% NaOH

0.5 h 21.3 4.18 7.4 14.4 21.81 32.2 4.11 6.1 12.30 20.05 30.72h 17.0 3.80 6.92 13.6 21.52 31.9 3.62 5.62 11.75 19.70 30.224 h 14.5 3.41 6.61 13.15 20.9 30.6 3.12 5.21 11.41 19.46 29.6

10% NaOH0.5 h 19.4 4.51 8.13 15.10 22.30 33.4 4.38 7.64 12.71 21.30 31.62h 15.3 3.96 7.23 14.62 21.72 32.2 3.66 6.38 12.20 20.45 30.2524 h 12.2 3.80 6.80 13.40 21.20 31.4 3.31 6.05 11.60 20.16 29.60

15% NaOH0.5 h 18.4 4.60 8.21 15.25 22.90 34.7 4.38 7.64 14.30 21.55 31.714h 12.4 4.12 7.23 15.21 22.60 33.1 3.91 6.81 13.6 20.61 31.2514 h 7.8 4.05 7.\0 14.1 22.05 32.3 3.61 6.10 12.30 20.40 30.40

fibres is higher than that of the untreated fibre. Asthe concentration of sodium hydroxide increases,the dye uptake in the hydrolysed fibre increases,depending on the degree of hydrolysis. The degreeof hydrolysis, as indicated by the nitrogen contentvalues, does not reveal any relationship with dyeuptake. For example, the fibres hydrolysed with10% NaOH for 30 min and having 19.4% nitrogencontent show the dye uptake of 44.2 mg/g and40.1 mg/g of fibre with dyes BI .and BIIrespectively, and 33.4 mg/g and 31.6 mg/g of fibrewith dyes DI and DII respectively at 5% shade.Again, fhe fibre hydrolysed with 15% NaOH for30 min and having 18.4% nitrogen content showsthe dye uptake of 46.2 mg/g and 42.1 mg/g of fibrewith dyes BI and BII respectively, and 34.7 mg/gand 31.7 mg/g of fibres with dyes DI and DIIrespectively. This reveals that the hydrolysedfibres may have almost the same nitrogen contentvalues but they may not exhibit the same dyeuptake. This is possibly due to the fact thatdifferent reaction conditions (hydrolysis) developdifferent structural transformations in· themacromolecular polymeric chains. The samplewhich is hydrolysed to the maximum extent (N2content, 7.8%) also shows higher dye uptakecompared to untreated fibre but the improvementis less as compared to that for other hydrolysed

samples. This may be due to the structural changesthat occur due to the hydrolysis process. Thesechanges can be envisaged from the X-ray analysis.

Dye molecules penetrate the amorphous anddisoriented region of the fibres". The extent ofhydrolysis, which changes the morphology of thepolymeric chains, together with the dyeingtemperature (above the TJ help the dye moleculesto migrate into the fibre matrix to a greater extentfor level dyeing. Among the two cationic dyes, thedyeing performance of dye BI is better than that ofdye BII. This may be due to the difference in theirmolecular weights.

The dye uptake values for the disperse dyes arecomparatively lower than those for the cationicdyes at all levels of dyeing. For example, foruntreated acrylic fibres, the dye uptake withcationic dye BI is 7.2 mg/g of fibre and that withdisperse dye DI is 6.2 mg/g of fibre at 1% .shade.The same behaviour is observed for the fibreshydrolysed to the same extent and dyed withdisperse and cationic dyes. This may be due to thefact that basic or cationic dyes are attracted by theelectronegative groups present in the fibres" apartfrom the dispersion forces, common to bothdisperse and cationic dyes, that hold the dyemolecules in the fibre.

264 INDIAN J. FIBRE TEXT. RES., DECEMBER 1998

3.2 Equilibrium Dyeiug of Hydrolysed Acrylic Fibres

The equilibrium dye uptake of cationic anddisperse dyes on the fibres hydrolysed withdifferent concentrations of sodium hydroxide at50°C for different time periods is reported in Table3. It is observed that the equilibrium dye uptake ofcationic dyes is always higher than that of dispersedyes at all levels of dyeing. Similarly, thehydrolysed fibres always show higher equilibriumdye uptake than the untreated acrylic fibres in caseof both cationic and disperse dyes. This may bedue to the presence of more electronegative groupsin the hydrolysed fibres, apart from the dispersionforces, common to both disperse and cationic dyes,that hold the dye molecules in the fibre

The higher dye uptake on the hydrolysed acrylicfibres compared to untreated fibres may beexplained on the basis of following facts:- Hydrolysis loosens the compact structure ofacrylic fibres, thereby leading to higher penetrationof dye molecules into the fibre structure. Theeffect is more pronounced at a higher degree ofhydrolysis.- The presence of more voids/amorphous regionsin the hydrolysed fibres and less orientation mayalso give more dye uptake to the hydrolysed fibre.This effect will be more pronounced with higherextent of hydrolysis (i.e. with less N2 content).- Due to hydrolysis, the polymeric chainsbecome shortened, as indicated by the lower

viscosity data. This offers comparatively morenumber of dye sites in the fibres, therebyincreasing the dye uptake.- The structural development due to hydrolysismay also offer more dye receptive groups,facilitating higher dye uptake.

3.3 Dye Diffusion on Hydrolysed Acrylic FibresFigs I and 2 show the dye uptake and the ratio

of dye absorbed at time t to that after infinite time(C/Ca) respectively for untreated and hydrolysedacrylic fibres. It is observed that the untreatedacrylic fibres attain the maximum dye uptake in100 min, whereas the hydrolysed fibres withnitrogen contents 18.4% and 12.4% take 90 minand that with 7.8% nitrogen content takes 80 min.As the structure of acrylic fibre is compact andrigid, it requires longer time for the dye moleculesto diffuse and migrate into the fibre". Thediffusion of dyes into the acrylic fibres iscontrolled by the segmental mobility of thepolymer chain", void structure and, to aconsiderable extent, molecular size of the dyemolecules", The apparent diffusion coefficients(Da) (Table 4) are also higher for the hydrolysedacrylic fibres compared to the untreated acrylicfibres. For a particular dye, the Da values ofdifferent hydrolysed fibres gradually decrease withthe increase in degree of hydrolysis. The diffusionof dye into the fibre is influenced by the polymercomposition, porous structure and molecular size

Table 3-Equilibrium dye uptake of cationic and disperse dyes on hydrolysed acrylic fibres[Hydrolysis temp., 50°C]

NaOH cone. and Nitrogen content in Equilibrium dye uptake, mg/g of fibretreatment time hydrolysed fibre, % BI BII 01 011

Nil 23.7 36.10 34.6 31.5 29.4(untreated)

5% NaOH0.5h 21.3 39.3 37.2 32.6 31.22h 17.0 37.7 36.9 32.1 30.524 h 14.5 36.2 35.6 31.1 30.0

10% NaOH0.5 h 19.4 45.1 40.9 34.2 32.32h 15.3 44.2 40.1 33.3 31.124 h 12.2 42.9 39.1 32.2 30.3

15% NaOH0.5 h 18.4 46.3 42.3 34.9 31.94h 12.4 45.7 41.7 33.3 31.424 h 7.8 45.0 40.3 32.4 30.6

MUKHERJEE et al.: IMPROVED DYEABILITY OF ACRYLIC FIBRE

50'r---------------------~40

30

Q 10go

goE O~U_~ __ L_~~ __ L_~_L~

! 50.--------------------------.eQ.

~ 40••>-o

C.I. Bosic R~ 18(81)

30

20

10

265

c.i aes« 81u~3 (B II)

C.I Disp~rn R~d 17( D II)

1401601800 20 ItO 60 801001201401601&0Tim., min

Fig. I--Dye uptake vs dyeing time for cationic and disperse dyes at 100°C [untreated acrylic fibre (-e-), and hydrolysed acrylicfibres with 18.4% (-0-), 12.4% (-d-) and 7.8 % (-x-) nitrogen content]

1·0 of the dye molecules":". In the cationic dyes, dyeBII has higher Da value (2.47xlO·9 ern's") than thedye BI (1.82xlO·9 em's"), whereas in dispersedyes, dye 01 has higher Da value (2.0x 10.9 ern's")than dye 011 (1.93xlo·9 em's"). This may beattributed to the molecular size of the dyemolecule. As the molecular size of the dyeincreases, the diffusion coefficient decreases underidentical conditions of dyeing.

0"

0·6

0,'

C.I.Basic R.d 18(81)'d 0u

v1·0

0'8

0·6

0·4

0·2

or:

Fig. 2-qCa vs Ji for cationic and disperse dyes [untreatedacrylic fibre (-e-), and hydrolysed acrylic fibres with 18.4%(-0-), 12.4% (-d-) and 7.8% (-x-) nitrogen content]

30 80 90

3.4 Wash Fastness of Dyed Fibres

It has been observed that the untreated acrylicfibres dyed with cationic and disperse dyes showbetter wash fastness property at all levels ofdyeing. Among the dyes studied, the cationic dyesshow comparatively better wash fastness than thedisperse dyes. In various hydrolysed acrylic fibres,the wash fastness is very good (5 for cationic dyesand 4-5 for disperse dyes) up to 2% of shade. Forhigher per cent of shade, the wash fastness ratingvaries from 4-5 to 4 with cationic dyes and from 4to 3-4 with disperse dyes. In cationic dyes, the dyeBI shows better wash fastness. The compactstructure of untreated acrylic fibres needs higheractivation energy, compared to the hydrolysedacrylic fibres, for the dye molecules to migrate.This makes the dye molecules difficult to remove

266 INDIAN J. FIBRE TEXT. RES., DECEMBER 1998

Table 4-Diffusion coefficients of hydrolysed acrylic fibres dyed with cationic and disperse dyes[Hydrolysis condition: 15% NaOH at 50"C for different time periods]

Dye Mol. wt. of Diffusion coefficientx I09, ern's"dye Untreated fibre Hydrolysed fibre

(23.7% N2) 18.4% Nz 12.4% N2 7.8% N2

BI 390.0 1.82 2.85 2.52 2.38BII 358.5 2.47 4.84 2.67 2.50

DI 242.0 2.00 3.33 3.05 2.17DII 344.0 1.93 2.67 2.42 2.18

from the acrylic fibres and hence the high washfastness. Disperse dyed fibres (both untreated andhydrolysed) exhibit lower wash fastness than thecationic dyed fibres. This may be due to theabsence of strong dye-fibre interaction between thedisperse dyes and the fibre. The physical andchemical changes in the structure of the fibresmight also affect the wet fastness properties.

4 ConclusionsThe hydrolysed acrylic fibres show higher dye

uptake, depending on the extent of hydrolysis, atall levels of dyeing than the untreated acrylic fibre.Hydrolysed acrylic fibres also exhibit higher dyeuptake at equilibrium of dyeing and have higherdiffusion coefficients (Da) than the untreatedacrylic fibres. The higher Da values for hydrolysedacrylic fibres depend on the molecular size of thedye used. With the increase in dye concentration,dye uptake increases and it depends on the degreeof hydrolysis. The wash fastness of the dyed fibresis quite satisfactory. The dyeing performance ofthe hydrolysed acrylic fibres (in terms of dyeuptake, Da and wash fastness) is always better withcationic dyes than disperse dyes.

ReferencesI Sadaham A, J Soc Dyers Colour, 107 (1991) 449.2 Mishra S P & Elangovan S P, Text Dyer Printer, 24(25)

(\ 99\) 21.

3 Mishra S P &Elangovan S P, Text Dyer Printer, 25(1)(1992) 29.

4 Shukla S R, Hundekar R V & Saligram A N, J Soc DyersColour. 107 (1991) 463.

5 Kamat S Y, Alat D V & Murthy P K, Colourage, 38(3)(1991) 21.

6 Thorburn B D, McGuigan A A & Fresenius J, AnalChem, 34(6) (1991) 377.

7 Khamraev A L, Abdukarimova M Z, Ibragimova G I &Zaved I V, Tekhnol Tekst Promst, 5 (1991) 65.

8 Yang Y & Ladisch C M, Text Res J, 62(9) (1992) 531.9 Rizovska V, Todorova I, Karkinska M & Lashovski S,

G/as Hem Techno/ Maked, 10(1) (1991) 57.10 Giorgi De, Rita M, Risano C A & Ruggero C, Melliand

Textilber, 70(7) (1989) 526.II Cegarra K, Pucute P & Castro B, Tinctoria, 85(9) (1988)

67.12 Milyavskaya I Kh, Zakirov I Z & Ergashev K E, Khim

Volokna, I (1987) 10.13 Khamrakulov G, Milyavskaya IE, Zakirov I Z, Ergashev

I Z & Mironova T S, Uzb Khim Zh, 5( 1990) 80.14 Zbigneva Zh A, Khim Khim Tekhnol, 36(5)(1993) 129.15 Harwood R J, McGregor R & Peters R H, J Soc Dyers

Colour, 88(1972) 216.16 Flath H J, Moritz R & Badawich J, Textiltech, 28 (\978)

103.17 Herbulot G, J Soc Dyers Colour, 82 (1966) 217.18 Beevers R B, Macromol Rev, 3 (1968) 113.19 Rosenbaum S,J Polym Sci, Part A, 3 (1965) 1949.20 Flath H J, Moritz R, Kasten K & Mietz ~,

Textilveredlung, 13 (1978) 309.21 Flath H J & Moritz R, Textilveredlung, 15 (1980) 56.22 Voltz J J, Text Chem Color, 9 (1977) 113.