Indian Journal of Textile ResearchVol. 14, September 1989,pp.119-124

Dyeing of polyacrylonitrile fibres with monoazo dispersedyes-adsorption studies

R BChava~Department of Textile Technology, Indian Institute of Technology, New Delhi 110 Ol6,lndia

andReD Kaushik & S D Deshpande

The Technological Institute of Textiles, Bhiwani 125 022, India

Received 20 February 1989; revised and accepted 24 April 1989

Saturation dye uptakes and affinities of six monoazo disperse dyes on. polyacrylonitrile fibres weredetermined by studying their equilibrium adsorption isotherms. The saturation values and affinities ofthe dyes were correlated with dye structure and solubility parameters of dyes and fibre. Presence of morenumber of NH2 groups and electron releasing substituent groups enhancing the basic character of thedye have a marked positive effect on its saturation values on acrylic fibre. Similarly, polar contributionand the ratio of dispersion and polar contributions to the solubility parameters of dyes and fibre arefound to be correlated with saturation dye uptakes of disperse dyes on acrylic fibre.

Keywords: Disperse dyes, Dyeing, Polyacrylonitrile fibre, Solubility parameters

1 IntroductionDisperse dyes are not commonly used for dyeing

acrylic fibres due to rather their low sorption capa-city on acrylic fibres under normal dyeing condition.Exhaustion can be better if dyed at higher tempera-ture. Dyeing at 110°C should, however, be regardedas limit because there is excessive shrinkage abovethis temperature. May be because of the limited uti-lity of these dyes on acrylic fibre, we find very fewreports in the literature regarding the adsorption be-haviour of disperse dyes on acrylic fibres I - 4. Dis-perse dyes, due to low affinity, possess excellent le-velling properties on acrylic fibres. They show widevariations in dye uptakes on these fibres and someof them give sufficiently deeper shades. Recently,while studying the transfer printability of a numberof disperse dyes on acrylic fibre, we observed thatsome disperse dyes give much deeper and brilliantprints on acrylics". In the present work, the sorptionbehaviour of six monoazo disperse dyes has beenstudied. Saturation values of the dyes were deter-mined from their adsorption isotherms and thesevalues and dye affinities were correlated with dyestructure and solubility parameters (SP) of the dyeand acrylic fibre. For this purpose, the total solubil-ity parameter (bt), dispersion solubility parameter(~d) and the association solubility parameter (ba)were theoretically calculated for each dye. All the

'three solubility parameter values for acrylic fibrewere taken from the literature".

2 Materials and MethodsIndacrylon acrylic fibre (denier, 2; and staple

length, 60 mm) supplied by IPCL (India) was used inthe form of yam with count 2/3&. Before dyeing,the material was treated with 1 g/l non-ionic deter-gent at 60°C for 30 min and dried at room tempera-ture.

2.1 Synthesis of DyesFive monoazo dyes, viz. Aniline ....•Aniline (Dye

A), Aniline ....•Phenol (Dye B), p-Nitroaniline ....•Phenol (Dye D), p-Anisidine ....•I, 3-Phenylcnedi-amine (Dye E), and m-Nitroaniline ....•,,-Toluidine(Dye F), were prepared hy the standard methods ofdiazotization and coupling?". Dye C was a com-mercial dye. The structures of dyes are given inTable I. All the six dyes wen: purified hy solventextraction and rccrystallisation methods. The per-centages of carbon, hydrogen and nitrogen of syn-thesized dyes were estimated and found to agreewell with the theoretical values.

2.2 Determination of Density of DyesThe densities of synthesized and purified dyes

were determined by specific gravity method using n-hexane".

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INDIAN J. TEXT. RES., SEPTEMBER 1989

Table l=-Chemical structure, saturation values and affinities ofsix monoazo dyes

Dye structure Mol.DyeNo.

Saturationvalue

(S)FX 10-3moles/kg

Affinity(kcal!mole)

wt

A @-N:N-@NH1 197 143.0 2.98

B @-N.N%H1 198 95.1 2.50

C O,N-@-N:N--@NH1 242 42.1 1.98

D 01N-@- N_N-@-O H 243 40.1 1.93

N"1E CH)O-@-N=N-@-NH1 242 75.7 2.48

ON CH)

F 1@-N=N-@-NH1 256 44.4 2.03

2.3 Measurement of Dye SorptionThe equ~brium dye uptake (D)F of each disperse

dye on acrylic fibres was measured in the usual man-ner ~:m Beckman Spectrophotometer by opticaldensity measurement of dyed sample at Am of thedye. The equilibrium concentration of the d;~ in thebath was then calculated as the difference betweenthe initial dye bath concentration and the dye ab-sorbed by the fibre at equilibrium. .2.4 Dyeing

For dyeing, 0.5 g of acrylic fibres was taken in a~Iosed beaker along with 1.5 g/I non-ionic dispers-mg agent, 0.5 g/l disodium hydrogen phosphate and1 g/l monosodium dihydrogen phosphate, maintain-ing a constant pH of 6.0 throughout the dyeing peri-od. The initial dye concentration in the bath wasvaried from 0.5% to 10% (owf). The liquor-to-material ratio in the bath was kept at 80:1. The dyecontainer was constantly revolving in a thermosta-ted bath at/100°C Dyeing was continued up to theequilibrium.

2.5 Determination of Solubility Parameters of Dyes

2.5.1 Total Solubility Parameter (ot)The total solubility parameter of each dye was de-

termin~d by the method of Small!" by using molarattractJ<:>nconstants (Fi) for appropriate groups. Fiof certam groups such as - NH2 (arom.), - N02 (ar-om.) and '7 N = N - (arom.) were not given inSmall's table. Fi values of these groups were deter-mined using the model compounds of known 6t va-lues II. The total solubility parameter of a dye wascalculated using the following equation:

Total solubility parameter (6t) = L F~X P ... (1)

120

where p is the density of dye; and M, the molecularweight of dye. The details of calculation for each dyeare given in Table 2.

2.5.2 Dispersion Solubility Parameter (od)Dispersion solubility parameter and refractive in-

dex (no) of dyes are correlated by the followingequation 12.

6d = 9.55 no - 5.55 ... (2)

Refractive index of dyes can be theoretically de-termined using the molar refraction of appropriategroups':', adding them to obtain total Rll. The re-fractive index of the dye can be determined from thetotal RLL using Lorenz and Lorentz equation":

2no-I MR =--x- (3)LL 2+2 ...no p

where p is the density and M, the molecular weightof dye. The details of calculations are given in Table3.

2.5.3 Association Solubility Para~eter (oa)The association solubility parameter of each dye

was calculated using the following relation betweentotal solubility parameter, dispersion solubility par-ameter and association solubility parameter (Table4).

... (4)

3 Results and Discussion

3.1 Chemical Structure of Dyes and Dyeing BehaviourThe adsorption isotherms are constructed from

equilibrium sorption of dye on fibre in relation ofequilibrium concentration in solution. Dependingon the nature of a dye-fibre-solvent system, theseequilibriums are either linear or nonlinear. Whendye is not adsorbed on specific sites but is present infree volume in the fibre, the nonlinear isotherm isFreundlich type. On the other hand, when the dye isadsorbed on specific sites in the fibre, the nonlinearadsorption isotherm obtained under such conditionis Langmuir type.When the dye is taken up by the fi-bre by the solid solution mechanism and the parti-tion between two immiscible solvents, the isothermsare linear. The standard affinity under solid solutionconditions is given by

_ ~f..I.0 = RTln (D)F= kTln (oS}(D)s (S)5

... (5)

where (S)F is the saturation dye concentration in thefibre; and (S)s, the concentration of dye in the bath

CHAVAN et al: DYEING OF POLYACRYLONITRIlE FmRES

Table 2-Det.:rmination of total solubility parameter according to the method of SmaUIO

Group F~ Molar attraction constants (at 25°C), [Cal cml)l/mole

Dye A DyeB DyeC DyeD DyeE DyeFPhenyl 735 735

(1). (1)Phenyl-Il 635

(1)Phenylene 658 658 1316 1316 658 658

(1) (1) (2) (2) (1 )

Phenylene-H 558 558(1 ) (1 )

- NH2(arom.f 342 342 684 342

(I) (1) (2) (1 )

-OH(arom.) 170 170(I) (1 )

- NO,(arom.f 287 287 287(1) (1 ) (1 )

-O(ether) 70(1)

-CHl 214 214

- N = N -(arom.) - 11.4 -11.4 -11.4 -11.4 -11.4 -11.4

(1) (II (I) (1 ) (1) ( 1)

-------....----_.-----------------------------------------------Conjugation 30 30 30 30 30 30

IFi 1753.6 1581.6 1936.6 1791.6 2202.6 2054.6

Mol.wt 197 198 242 243 242 256

Density' 1.180 1.460 1.407 1.452 1.199 1.410

Ot(Eq. II 10.50 11.66 11.41 10.70 10.89 10.01

------------------------------------------------------------------------------'Calculated using the reference compounds". "Experimentally determined,Figures in parentheses indicate the number vi groups.

Tgbk 3- Determination of dispersion solubility parameter (lid Iby using group contribution molar refraction (Rl.1.) of dyes IJ

Group Group contribution to molar refraction (Rl.1.) of dye().••••-589)

Dye A Dy~ B DyeC DyeD DyeE DyeF

l.Phenyl 25.51 25.41

I.Phenvl-H ~4.92

l.Phenvlcne 25.03 ~5.()3 50.06 50.06 25.03

l.Phenvlene-HHlarom.)=il.59 24.44 ~4.44

I-NH:(arom.l 4.89 4.89 9.]8 4.!!9

I-OH~'.Irol1l.J 2.27 2.27I-NO:iarom.l 6.662 6.662l-Oiether i 1.77

I-CH, 5.644

I-CH .tarorn.. 5.47

I-N=N' 2.64 2.64 2.64 ~.{)4 2.64 2.64--------------------------------------------------------_.-------------._----------------_.RlI or Live 58.07 55.45 64.25 01.63 69.302 69.02Refractive Index

1, "pi of dyes fromEq.:)1Dispersion solu-bility parameter(lid 1calculatedusing Eq. (~)

1.{)12 1.753 1.669 1.657 1.601 1.560

9.S..1 11.24 HUH 10.27 9.74 9.34

-Cakulared using model compound azobenzene.

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INDIAN J. TEXT. RES., SEPTEMBER 1989

Table 4-Solubility parameters (Ot, od and oa) of dyes and fibre and saturation values of dyes

Group Dye Mol.wt Solubility parameters -(Odf Saturationy- -Oa value (S)F

Ot Od Oa moles/kg

A 197 10.50 9.84 3.66 7.228 143.0B 198 11.66 11.24 3.098 13.163 92.1

II E 242 10.89 9.74 4.87 4.000 75.7C 242 11.41 10.38 4.76 4.755 42.1D 243 10.70 10.27 2.99 12.806 40.1

III F 256 10.01 9.34 3.58 6.806 44.4----------------------------------------------------------------------------------------------------Acrylic fibre 12.75 9.47 8.32 1.295

when fibre is completely saturated with the dye.Other terms have their usual meanings.

Eq. (5) shows that under solid solution condition,a linear isotherm is obtained right up to fibre satura-tion. In the present work, adsorption isotherms weredetermined for six monoazo disperse dyes on acry-lic fibres (Table 1). All the six dyes gave linearcurves up to fibre saturation (Figs 1 and 2), confirm-ing solid solution mechanism involved in their dye-ing on acrylic fibres. The standard affinities of thedyes calculated using Eq. (5) are given in Table 1along with the saturation dye uptake; values of thedyes.

There are several properties of the dye moleculewhich determine the maximum adsorption or affi-nity of the dye on textile fibres. These are molecularsize, nature of substituent groups, steric effects,etc.". Table 1 shows that Dyes A.and B show com-paratively higher affinity values, 2.98 and 2.50 kcal/mole respectively, on acrylic fibres. Higher adsorp-tion of Dyes A and B can be attributed to the smallmolecular size of these dyes, giving them more ac-cessibility into the fibre structure. Similar observa-tion was reported by Giles!" in the case of adsorp-tion of p-aminoazobenzene (Dye A) on cellulose tri-acetate. Dyes C, D and E are almost of equal mole-cular size. These dyes show a definite trend in rela-tion to the nature of substituent groups and affinityvalues. Dye E, because of the presence of two aminogroups and one electron releasing group (OCH3),

possesses maximum basicity and Dye C, being a hy-droxyazo dye, shows the least basicity whereas DyeD possesses intermediate basicity. It is clear fromTable 1 that their affinity values show a similartrend, i.e. affinity values decrease in order of theirbasicity. This shows an important role of basicity ofdyes in the adsorption on acrylic fibre. Fechmeyerand Wurz15 attributed higher affinity of certain an-thraquinone disperse dyes on acrylic fibres to the di-pole-dipole interactions between polar groups of

122

160,------------------------------,--0- ""Cr~. Dye- A

--Jr ~ -b- - 0Y' 8140 --0--0- -&-- Dye C

(-----) Saturation limit

120

~~ 100•."0e",-

I~ 80.u,

7]•....•60

40

10 15 20 25[0]. x 1O-~moiH It

Fig. I-Adsorption isotherms of monoazo disperse dyes on •polyacrylonitrile fibres

30 35

80.-----------------------------,(- •.•..- -) Saturation limit

-~~-&-D~E70 - •...•..•. - D~F

-1&)- •.•••. -.- Oy.O

60

50

10 1 25]0

[O]S X 10-4,molH/'

Fig. 2- Adsorption isotherms of monoazo disperse dyes onpoJyacrylonitrile fibres

CHAVAN et al.:·DYEING OF POLYACRYLONITRILE FIBRES

dyes and cyanide group of acrylic fibre havingstrong dipole moment (4.0 Debye). There is alsopossibility of such interactions between monoazodisperse dyes and acrylic fibre.

3.2 Solubility Parameters and Dyeing Behaviour

Dyeing of synthetic fibres can take place onlywhen space in the fibre structure (free volume) iseither already available or created by the separationof polymer chains. This has been found true for sol-vent, aqueous or solvent-assisted dyeing of syntheticpolymers". The rate of dyeing, therefore, dependson how easily such spaces in the fibre structure areavailable and, therefore, the knowledge of cohesiveenergy ~ensity is desirable to understand dyeing.Theoretically, for a solvent or a non-ionic dye to beable to penetrate into polymer structure and separ-ate. th~ polymer chains, its solubility parameter,which IS the square root of cohesive energy density,must match that of the fibre. Solubility parameterconcept has been proved very useful in understand-ing the mechanism of carrier or solvent action dur-ing dyeing of synthetic fibres-" - 18. The possibilityof using this concept in aqueous dyeing of non-ionicdyes on hydrophobic fibres exist essentially becausedyeing may be treated as a solubilization processand fundamentally there is a little difference be-tween the action of solvent and the action of non-ionic dyes on synthetic fibres. Ibe '? applied this con-cept to dyeing and found that only the solubility par-ameter consideration could not give successful re-sults. Meaningful results could be obtained when thecontribution of dispersion and association forces tosolubility parameter were also taken into considera-tion. Recently, Gerber" studied 60 azo dispersedyes and found good correlation between the solu-bility parameter of dyes, solubility parameter of pol-yester fibre and many useful dyeing properties. Tofind out the correlation between the solubility par-ameter of acrylic fibre, solubility parameter of dis-perse dyes and their dyeing behaviour, it is neces-sary to know first the adsorption characteristics ofdyes. Linearity of isotherms (Figs I and 2) show thatthe adsorption follows the Nerst-Henry law and,therefore, the saturation values of dyes representthe solubility of dyes in acrylic fibre. According tothe solubility parameter concept, these values musthave some correlation with solubility parameters ofdyes and fibre. According to Ingamells and Tho-mas!", since the dispersion and association forces ina molecule do not exist independently, it is morerealistic to assume that both have an influence ont~e dyeing behaviour. He found that the affinity ofdisperse dyes for polyester is higher when the polar

and non-polar cohesive forces associated with dyemolecules balance those of the polyester.

To study the influence of solubility parameters ofdyes and fibres, the total solubility parameter (bt)and dispersion solubility parameter (bd) were calcu-lated following the procedure given in Tables 2 and3. The association solubility parameter was calculat-ed using Eq. (4). The calculated values of solubilityparameter of dyes are given in Table 4. Table 4 alsocontains Y,the ratio bd2/ba2, for each dye and thesolubility parameter values of acrylic fibres whichhave been taken from the literature", The data havebeen arranged into three groups according to themolecular size of the dyes. Group III contains only as~ngle dye which shows independent dyeing beha-VIOUr.Table 4 shows that the saturation values ofdyes belonging to groups I and II show, within theirrespective groups, good correlations with ba and Yvalues of dyes and fibre. This has been illustratedfor the dyes of group II in Fig. 3. A comparison of btand bd of dyes, fibre and saturation values (Figs 3aa~d 3b) shows no correlation between these par-ameters, whereas ba and Yvalues of dyes and fibreshow good correlation with saturation dye uptake ofthe three dyes (Figs 3c and 3d). These results are inagreement with the observations of Ingamells andThomas!", who suggested that the relative contribu-tion of dispersion and association forces to the solu-bility parameters of dyes and fibre are important inthe adsorption of disperse dyes on synthetic fibres.

( b)

(d)

Fig. J-Correlation of solubility parameters and r values ,>1'dyes and polyacrylonitrile fihres with saturation values of dyes

12.1

INDIAN J. TEXT. RES., SEPTEMBER 1989

4 ConclusionThe monoazo disperse dyes studied gave linear

isotherms, confirming solid solution mechanism in-volved in their dyeing on acrylic fibre. The presenceof more number of NH2 groups and electron releas-ing substituent groups in a dye molecule has amarked positive effect 'on the affinity of dispersedyes. Polar cohesive forces as well as relative con-tribution of polar and dispersion forces to total solu-bility parameters of dyes and fibre showed goodcorrelation with the saturation values of dyes on ac-rylic fibre.

References1 Hadfield H R & Sokal W M, J Sac Dyers Colour, 74 (1958)

629.2 Walls I M, J Sac Dyers Colour, 72 (1956) 262.3 Hutai M & Okada S, Sen'i-Gakkaishi, 23 (1967) 321.4 Takaoka A, Katayama A, Kuioki A N & Kouishi K, Sed i

Gakkaishi; 21 (1965) 158.5 Chavan R B & Mavalkar V, Colourage, 30 Oct 1986, 31.6 Gur Arich Z, Ingamells W & Peters R H, J Appl Polym Sci,

20(1976)41.

124

7 Vankatraman K, The chemistry of synthetic dyes, Vol I(Academic Press. New York) 1952.

8 Fierz-David H E & Blangey L, Fundamental processes ofdye chemistry (Inter-Science Publishers, New York) 1949.

9 Giles C H, Yale A & Shah C D, Text Res J, 38 (1968) 467.10 Small P A, J Appl Chem, 3 (1973) 71.11 Siddiqui S A, Am Dyest Rep, 72 (1983) 36.

12 Koenhen D M & Smolders C A, J Appl Polym Sci, 19 (1975)1163.

13 Van Kravelen D W & Hoftyzer P J, Properties of polymercorrelation with chemical structure (Elsevier Publishing Co.,Amsterdam) 1972,201-202.

14 Giles C H, Text Res J, 31 (1961) 141.15 Fechmeyer F & Wurz A, J Sac Dyers Colour, 77 (1961) 626.

16 Ingamells W C, The response offibres to dyeing process, the-ory of coloration of textiles, edited by C L Bird and W S Bos-ton (Dyers Company Publication Trust, U.K.) 1975.

17 Ingamells W & Thomas M N, Text Chem Color, 16 (1984)55.

18 Guido Alberji, Ado Gerniani & Rita De Giorgi, Text Res J,55(1985)635.

19 IbeJ,JAppIPolymSci, 14(1976)837.20 Gerber H, J Sac Dyers Colour, 94 (1978) 298.