Indian Journal of Textile ResearchVol. 14, September 1989, Pp. 125-129

Dyeing of acrylic fibres with monoazo disperse dyes in presence of benzylalcohol: Part I

R C 0 Kaushik & S 0 DeshpandeThe Technological Institute of Textiles, Bhiwani 125 021, India

andR B Chavan

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

Received 20 February 1989; revised and accepted 24 Apri11989

The adsorption isotherms and the rate of dyeing of three monoazo disperse dyes, with and withoutbenzyl alcohol in the dye-bath, were determined and the effect of benzyl alcohol on these parameters wasstudied in the light of dye structure and solubility parameters of dyes, fibre and solvent. The basic natureof the dye and the presence of an optimum quantity of benzyl alcohol in the bath have favourable effecton the rate of dyeing and adsorption of disperse dyes on acrylic fibres.

Keywords: Acrylic fibre, Adsorption isotherms, Disperse dyes, Dyeing, Solubility parameter

1 IntroductionAcrylic fibres are dyed to a large extent with basic

dyes. The use of disperse dyes in dyeing acrylic fi-bres is limited because of the low sorption capacityof these fibres and so under normal dyeing condi-tions, disperse dyes are suitable for pale to mediumshades only. Better exhaustion can be obtained athigher temperature. However, because of the exces-sive shrinkage at higher temperature, 110°C shouldbe regarded as the temperature limit for dyeing 1.2.

Disperse dyes possess low affinity for acrylic fibresand, therefore, dye very level on these fibres. Dis-perse dyes, in general, also have excellent wet fast-ness, good light fastness, and are free from gas fad-ing on acrylics". Individual disperse dyes show widevariations in dye uptakes and some of the dyes givemuch deeper and brilliant shades, particularlythrough the transfer printing techniques". More-over, there is a possibility of increasing the dye up-take of disperse dyes by using solvent-assisted dye-ing methods:'. While studying the effect of plasticiz-ing compounds on acrylic fibres, Gur-Ariech et al?concluded that the dyeing in presence of plasticizingcompounds was controlled by plasticization ratherthan swelling. Phenol and benzyl alcohol werefound to be more effective plasticizers amongst theseveral amino and hydroxy compounds studied.These could reduce the glass transition temperatureof Acrylon filament to 41.3°e and 30Se respec-tively. The semiempirical equation proposed by

Williams Landel and Ferri (commonly termed asWLF equation) for describing the variation withtemperature of those polymer properties dependentupon the frequency of the segmental jumps in thepolymer, was used by Ingamells et al': to correlatethe plasticizing action of a solvent and the diffusionof disperse dyes in acrylic fibres. With the help ofWLF equation he confirmed that dyeing process iscontrolled by the segmental mobility of polymers.Amongst the various solvents capable of accelerat-ing dyeing rate, benzyl alcohol has an advantage ofbeing comparatively safer and nontoxic in natureand, therefore, was used in the first commercial Ir-ga-solvent process for dyeing wool and silk withneutral dyeing metal complex and selected aciddyes?". In the present work, the adsorption behavi-our of three monoazo disperse dyes in the presenceof benzyl alcohol and the effect of benzyl alcoholand dye structure on the adsorption isotherm andrate of dyeing have been studied. The correlationsof solubility parameters of dyes, fibre and solventwith the dyeing behaviour of the three monoazodyes have also been investigated.

2 Materials and Methods

2.1 Materials

2.1.1 FibreAcrylic fibre (Indacrylon 100%; IPCL, Baroda)

with staple length 64 mm and count 2/32s was used

125

INDIAN J. TEXT. RES., SEPlEMBER 1989

in the form of yarn after treating with 1 g/l non-ionicdetergent at 60°C for 20 min.

2.1.2 DyestuffsThe following three monoazo disperse dyes were

used.

02N-@-N=N-@- NH2

I

02N-@-N=N-@-OHII

NH2

H3CO-@-N=N--@-NH2

III

Dye I, a commercial dye (Disperse Orange 3) wasused after purification. Dyes II and IIJ were synthe-sized by diazotization and coupling with appropri-ate intermediates. The constitution of synthesizeddyes was checked by elemental analysis.2.1.3 Chemicals

Analytical grade benzyl alcohol, monosodium di-hydrogen phosphate and disodium hydrogenphosphate were used.

2.2 Methods

2.2.1 Dyeing

A dye-bath was set with the required amount ofdye, benzyl alcohol, sodium dihydrogen phosphateand disodium hydrogen phosphate as buffer (pH6.0). The material-to-liquor ratio was maintained at1:80 and the temperature at 100°C. For adsorptionisotherms, dyeing was continued up to equilibriumwhich took 24 to 48 h. The rate of dyeing was deter-mined for different time intervals. In each case, dye-ing was carried out in a closed container revolvingwith a constant speed in a thermostated bath.

2.2.2 Measurement of Dye Sorption

Dye uptake of each dye was measured colorimet-rically using Kissa's method". Dye concentration inthe solution in the case of equilibrium dyeing wasobtained by the difference of initial dye concentra-tion and the dye adsorbed by the fibre.

2.2.3 Determination of Density of Dyes

The densities of the three purified monoazo dyeswere determined hy specific gravity method usingn-hexane 10.

126

3 Results and Discussion

3.1 InOuence of Dye Structure on Affinity of DyesThe adsorption isotherms of three monoazo dyes

on acrylic fibres are shown in Fig. 1. The affinity va-lues were calculated using the following equation.

Affinity ( - ~~o) = R T In ((DlFD)s

where (D)F and (D)s are the equilibrium dye con-centrations in the fibre and dye-bath respectively.Other terms have their usual meanings. The - ~~o

values for the three dyes were calculated with (D)Fin moleslkg and (D)s in moles/l (Table 1). To bestrictly accurate, it is desirable to express theconcentrations in the same units. For this purpose, avolume term V, which is the fraction of total fibrevolume where the dye is contained in the fibre, mustbe introduced in the affinity equation. The affinityequation then becomes:

... (1)

... (2)

For a particular fibre, V remains the same for all thedyes and its inclusion changes the affinity value by aconstant amount. So, for the comparison of dyes, Vmay be ignored without any disadvantage 11.

Table 1 shows that dye III having two aminogroups and one electron releasing group (OCH))shows the maximum affinity among the three dyes.Dye I having one amino group and one electronwithdrawing group (N02) shows affinity less thanthat of dye III whereas dye II (a hydroxy azobenzene

80,----------------,

-0--0-0- 0 y~ 1-'-A-'- Dye II-U-IIJ-I!l-Jye 111

(----.) Set..•.alton Limit

60

~;;;.oE 40~ .>./ ----

20

//

~/

10 15 20[O]s xIO·i., molt's Il

25 )0

Fig. 1- Adsorption isotherms of three monoazo disperse dyes

KAUSHIK et al.: DYEING OF ACRYLIC FIBRES: PART I

Table I-Standard affinity values of three monoazo disperse dyes at 100°C

Dye I Dye II Dye III

(D)F (D)s -~I!0 (D)F (D)s -~I!0 (D)F (D)s _ ~I!0

moles/kg moles!1 kcallmole moles!kg moles/I kcallmole moles/kg moles!1 kcallmolex 10-3 x 10-4 X 10-3 X 10-4 X 10-3 X 10-4

2.9 2.1 1.9.58 3.0 2.2 1.947 4.1 2.1 2.2537.1 4.3 2.091 6.1 4.4 1.958 8.7 4.0 2.300

11.9 8.8 r.941 11.4 8.9 1.902 11.5 7.6 2.49419.1 13.1 1.995 23.2 17.7 1.919 45.0 16.3 2.476

42.1 27.8 2.025 40.1 30.9 1.908 75.7 26.7 2.497

2.005' 1.927' 2.404''Average value.

dye) shows the least affinity. This shows that thepresence of more number of amino groups or thepresence of electron releasing groups, which en-hance the electron donating character of a dyemolecule and, therefore, its basicity, favours higheraffinity. A strong influence of a substituent group onthe basicity of aromatic compounds can be seenfrom the basicity constants of aniline, jranisidineand jrnitroaniline, which are 4.2 x 10- 10,

20 x 10 - 10 and .001 x 10 - 10 ·respectively. Dye II,being a hydroxyazo dye, is the least basic among thethree dyes. The basicity of the three dyes is found todecrease as follows: dye III> dye I> dye II. The af-finity values of the three dyes (Table 1) show thesame trend, indicating an important role of basicityof disperse dyes in the dyeing of acrylic fibres.

80-A-I.-/;,,- 100 °C-c!)-El-i>- 70°C

60

OL---~----~-----L----~~0·2 0·30·1

Benzyl alcohol conc., motes rt

Fig. 2-Effect of benzyl alcohol concentration on dyeexhaustion of dye III

3.2' Effect of Benzyl Alcohol on Rate of Dyeing andAdsorption Isotherm

Preliminary experiments on the rate of dyeing ofthe three monoazo disperse dyes showed that ben-zyl alcohol has an accelerating effect on the dyeing.Dye uptake was found to increase with increase inbenzyl alcohol concentration up to 0.3 moleslI forall the three dyes and thereafter it decreased. Theeffect of benzyl alcohol concentration on the ex-haustion of dye III is shown in Fig. 2. This behaviouris analogous to the one reported b)Y'Balrnforth eta/.12 for the dyeing of cellulose acetate and can be at-tributed to the limited solubility of benzyl alcoholboth in water and fibre and the formation of a thirdphase in which the dye is more soluble. The rate ofdyeing curves for the three dyes obtained using opti-mum benzyl alcohol concentration are given in Figs3-5. The curves show that in all thecases dye uptakeincreases in presence of benzyl alcohol, but the ef-fect is more pronounced in the case of dye III. Tofind out the accelerating effect of benzyl alcohol

-0-0-tl- (With benzyl alcohol)

O·6 -A-A-A- (without benzyl alcohol)UJa:CDu,zoUJ>-ou, O· 4o>-•..<IizUJo..J..~ 02•..D..

o

30 60TIME. mm

Fig. 3-Rate of dyeing curvesfor dye [

0.4

90

127

wa::rniLz0w>- 040

"-0>->-<Iizw0...J

« 02~>-Q.0

INDIAN J. TEXT. RES., SEPTEMBER 1989

- •...• _a_ (with benzyl alcohol)

-A-A-!-(witnout b~nlyl alcohol0.6

wa:CD

\L

Z0

W>- 0.40

\L0>->-ii>zw0

.J 0·2<lu;::Q.0

o 30 60TIME, min

90

Fig. 4-Rate of dyeing curves for dye II

-.-.-.- (with bl!n~yl alcohol)

- •..• -.- (wilhaul benz yt alcohol)0-6

o 30 60TIME, min

90

Fig. 5-Rate of dyeing curves for dye III

quantitatively for each dye, the acceleration factorwas calculated as follows:

Dye exhausted with optimum benzylalcohol cone,

Acceleration factor = --------------Dye exhausted without benzyl alcohol

The acceleration factors for the three dyes werefound to be 1.21, 1.14 and 3.1 respectively, whichsuggest that dyes I and II are influenced by benzylalcohol nearly to the same extent whereas the effecton dye III is almost three-fold. To find how the ben-zyl alcohol affects equilibrium adsorption, the ad-

128

90r--------------------,...•...•..• - (with b.nzyl alcohol)

~.- (withOut b.nzyl alcohO« )(----) Saturation limit

70

";I-~ 50E

~s;!""~oW 30

10 20[0 J.- 10-4, mol •• II

30

Fig. 6-Effect of optimum benzyl alcohol concentration onadsorption isotherm of dye III

sorption isotherms of dye ill, with and without ben-zyl alcohol, were determined at 100°C and usingoptimum benzyl alcohol concentration. The results(Fig. 6) show that even in the presence of benzyl al-cohol the linearity of curve is maintained. The parti-tion coefficient is, however, found to increase inpresence of benzyl alcohol. Due to the linearity ofisotherms in both the cases, it should be possible toexplain the dyeing behaviour in terms of solubilityparameter values .

3.3 Solubility Parameters and Dyeing

The dyeings of all the three monoazo dyes gavelinear isotherms up to fibre saturation and accord-ing to Nerst-Henry law!', the dyeings can be consid-ered as solubilization process. It is, therefore, possi-ble to apply solubility parameter concept to under-stand more about the dyeing behaviour of thesedyes on acrylic fibres. Solubility parameter is de-fined as the square root of cohesive energy densityand its value for each dye can be found out from thedye structure using the following equation.

I.FixpSolubility parameter (b t) = ---'-

Vm

where r.Fi is the sum of molar attraction coefficientof each group; Vm, the molar volume of the dye; andp, the density of the dye which can be determinedexperimentally. The solubility parameter values ofacrylic fibre and benzyl alcohol taken from the liter-

KAUSHIK et al.: DYEING OF ACRYUC FffiRES: PART I

Table 2-Solubility parameters and dyeing characteristics ofthree monoazo disperse dyes

Solubility Dyeing characteristicsparameter _

(Ot) Equilibrium dye uptakeCa(ll2cm - 312 _

Dye

With Withoutbenzyl benzylalcohol alcohol

I ll.4P 3.50 2.89II 10.70· 3.17 2.79III 10.89' 15.34 4.70

Accele-rationfactor

1.211.14

3.26

·Calculated using Small's method (refs 15-17).Dt of acrylicfibre ,12.75 (ref. 5)Dt of benzyl alcohol, 10.90 (ref. 14)

ature.-!" and the calculated values of bt for the threedyes are given in Table 2. When a comparison bet-ween the solubility parameter values of dyes, fibreand benzyl alcohol was made with dye exhaustionand acceleration factor, no definite correlationcould be established. This observation is in agree-ment with that of Ibe13, according to whom the ap-plication of solubility parameter concept to aqueousdyeing of synthetic fibre is complicated due to thepresence of water of swelling in the polymer. Hesuggested that the correlation could be improved ifindividual components, viz. polar (ba) and nonpolar(bd), of total solubility parameter are considered.

4 ConclusionDisperse dyes having basic character show higher

affinity for acrylic fibres. Benzyl alcohol enhances

dye uptake up to a certain limit and then decreasesit. The linearity of adsorption isotherm is not affect-ed by the presence of benzyl alcohol in the bath.However, the partition coefficient is altered due tothe presence of benzyl alcohol.

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