Indian Journal of Fibre & Textile ResearchVol. 20, December 1995, pp. 206-210

Dyeing of polypropylene with some azo disperse dyes of basic charactervia chlorination route

A K Samanta-Textile Chemistry Section. Institute of Jute Technology, 35 8allygunge Circular Road. Calcutta 700 019. India

andD N Sharma

The Technological Institute of Textile & Sciences. Bhiwani 125021. India

Received 5 August 1994; revised received 4 January 1995; accepted 15 February 1995

Polypropylene fabric, after chlorination by sodium hypochlorite under an optimized condition, was dyedseparately with twelve azo disperse dyes of basic character in both alkaline and acidic medium. The higheraffinity of these dyes to chlorinated polypropylene than to unmodified polypropylene has been observed inboth acidic and alkaline medium with a few exceptions. The possible mechanism of higher affinity of such dyesto chlorinated polypropylene is shown and explained. The influence of dye structure ana substituent groupson dye uptake and fastness properties is discussed on the basis of inductive effect, electrostatic interactions,steric cause, etc. It is observed that these dyes with electron donating groups as substituents when applied inacid medium give higher dye uptake and improved fastness properties with a few exceptions for otherstructural interactions including steric cause.

Keywords: Azo disperse dyes, Dyeing, Polypropylene

1 IntroductionBesides mass coloration to limiting shades, colora-

tion of polypropylene even after modification has re-mained a problem for decades. Disperse dyes onlygive tints to unmodified polypropylene fibre.'. Appli-cation of disperse dyes of different structures and pro-perties on unmodified polypropylene fibre has beenreported! - 8. However, in most of the cases, it wasfound that the saturation values were very low onunmodified polypropylene. Many approaches of dy-eing polypropylene by modification have also beenreported? - 13. Agster!" reported the chlorination ofpolypropylene for affinity of basic and few dispersedyes in 1975. Such modification was also reported in aJapanese patent IS. In our earlier work 16.17, we havestandardized the process of chlorination of polypro-pylene and studied the effect of application of fewbasic dyes of different structures on chlorinated poly-propylene. The effect of substituents on the fadingbeha viour of disperse dyes on polypropylene was stu-died by Ahmed and Mallet 18. The fading behaviourof different dyes on modified polypropylene was alsostudied by Shah and Jain 19.20. In the present work,the possibility of dyeing polypropylene, after chlorin-ation, with few azo disperse dyes of basic characterhas been explored and the effect of the dye structure

"To whom all correspondence should he addressed.

and substituent groups on dye uptake and fastnessproperties has been investigated. The results of dyeuptake and fastness properties are explained on thebasis of inductive effect, electrostatic interaction, ste-ric effect. etc of these dyes.

2 Materials and Methods

2.1 Fabric100% polypropylene fabric (3/1 twill; 1.l g/cm-:

1.15 mm thick; warp 2/14s; weft 7s; 28 picks/in.and 40ends/in) supplied by M/s Neomer Ltd, India, wasused after thorough scouring by boiling with aq. solu-tion of 1 g/L nonionic detergent (Lissapol-Nx) for 30min. followed by washing and drying.

2.2 Chemicals and Dyes20 g/L stock solutions of LR grade NaOCI and HCl

were used. All the azo disperse dyes enlisted below,except dye no. 2, were prepared in the laboratory inpure form (by solvent extraction) and ground (milled)to fine particle in crucible for use: (1) 4-aminoazoben-zene, (2) 4-(dimethylamino)azobenzene, (3) 4-meth-yl-4'-(dimethylamino)azobenzene, (4) 4-amino-4'-methylazobenzene, (5) 4-amino-4' -nitroazo-benzene, (6) 8-hydroxy-5-( 4-methylphenyl)-quinoline, (7) 8-hydroxy-5-(4-nitrophenyl)-'quinoline, (8) 4-amino-3' -chloroazobenzene, (9)

SAMANT A & SHARMA: DYEING OF POLYPROPYLENE 207

4-amino-2' -methoxy-5' -nitroazobenzene, (10)8-hydroxy-5-phenylazoquinolihe, (11) 4, 4' -bis(4-aminophenylazo)biphenyl, and (12) 4'-amino-3"-chloro-I, 4-bis(phenylazo )benzene.

1.3 ChlorinationChlorination of polypropylene fabric was carried

out under the optimized conditions'v-!? on a labora-tory scale by dipping the fabric piece in dilutedNaOCI solution (available chlorine, 10g/L), keepingthe material-to-liquor ratio at 1:40 for 45 min at pH4.5 (adjusted by HCl). The treated fabric was thenwashed thoroughly and dried at ambient temperatu-re.

The extent of chlorination of polypropylene wasmeasured by stepnows method?".

1.4 Disperse DyeingDisperse dyeing of both unmodified polypropyl-

ene and chlorinated polypropylene fabrics was car-ried out in acid medium at l00·C and 11O·C followingthe usual procedures- - 25 in a laboratory modelHT -HP beaker dyeing machine. The ,same dyeingswere also carried out in alkaline medium followingthe procedure used for application of basic dyes tochlorinated polypropylene16,17.19,20 to see whetherchlorinated polypropylene can react with dispersedyes of basic character like basic dyes. The dyeingconditions in acid and alkaline medium are given be-low:

Aqueous acid both(HT-HP beaker dyeing

machine)

Dye, 4% (owf)Setamol ws, 1 g/L(Dispersing agent)Acetic acid, 1-0.5%(to adjust pH, 4-4.5)Material-to-liquorratio ,1:40Time, 1.5 hTemperature, 100·C

and 110·C

Aqueous alkali bath(Open bath beaker dyeing

machine)

Dye, 4% (owf)Setamol ws, 1 g/L(Dispersing agent)Na2C03, After 45 min(to adjust pH, 10-11)Material-to-liquorratio,l:40Time, 1.5 hTemperature at boil,100·C

After dyeing, the dyed fabric samples were washed,soaped (Lux soap powder) for 15 min.at 65-70·C,rinsed, washed and dried.

2.5 Measurement of Depth of ShadeDepth of shade, i.e. dye uptake was measured on

the dyed sample bydetennining the KjSvalue by Ku-belka-Munk-? equation measuring reflectance atwavelength of maximum absorbance using BeckmanDK-2A reflectance spectrophotometer.

2.6 Fl6tness TestsLight fastness tests were done using SDL micros.cal

light fastness tester+' with MBTF standard fadingbulb. Wash fastness tests were done in AtlasLaunder-o-meter as per ISO-IV recommenda-tion-". Dry-rubbing fastness tests were done as perIS: 766-1956 using Shirley electronic crockmeter-".

3 Results and Discussion

3.1 Disperse Dyeing of Unmodified and Chlorinated Poly-propylene Fabric in Acid Medium

The K/Svalues of unmodified and chlorinated pol-ypropylene fabrics disperse dyed in acid and alkalinemedium are given in Table 1. It is observed that theK/ S values of unmodified and chlorinated p~lypr?-pylene disperse dyed with dyes 5-9 and 11 ~n acidmedium at l00·C have almost insignificant difference.Therefore, we may assume almost no dependenceof the uptake of above dyes on chlorination of polypr-opylene. While in case of dye 1-4, 10 and 12, the K/Svalue increases significantly on chlorination of poly-propylene. Looking at the dye structure, it may benoted that dyes 5 and 7-9 have an electron withdraw-ing group (positive inductive effect of - N02, - CIand - OCH1groups) while the dyes 1-4 have an elect-ron donating group (negative inductive effect of

CH- CH3, - NH2 and- N( CH!groups). Dye 6 proba-

bly causes steric hindrance in diffusing to isotacticpolypropylene fibre. Also, the higher basicity due toboth - CH3 group and hydroxy quinoline structuremay cause more solubility, restricting the dye to beabsorbed to polypropylene. But dye 10, differingfrom dye 6 by an - CH3 group only, shows increase inK/ S value when the PP fabric is dyed after chlorinati-on. It may be inferred from this that the inductiveeffects and basicity are much predominant here overthe stericcauses.

Interestingly, dye 12 having two groups of oppos-ing inductive effect, shows good increase in K] S value,when PP fabric is dyed after chlorination.

Also, increase in dyeing temperature from 100°C to110°C shows some improvement in dye uptake onchlorinated PP except in case of dye 7, Disperse dye-ing of polypropylene at more than II O·Cwas not stu-died as the softening temperature of polypropylene is12S-130·C.

3.2 Disperse Dyeing of Unmodtned and Chlorinated Poly-propylene Fabric in Alkaline Medium and Comparisonwith that in Acid Medium

It is reported in earlier work that basic dyes formcovalent bonds with chlorinated polypropylenewhen dyed in alkaline medium, like reactivedyes14.1S.17.19.Therefore, the disperse dyes of basic

208 INDIAN J. FIBRE TEXT. RES., DECEMBER 1995

Table I-K/S values of disperse dyed unmodified and chlorinated PP fabric dyed in different baths

Dye No. Dye structure K/S value

Unmodified (control) PP fabric Chlorinated PP fabric

Acid bath Alkali bath Alkaline bath Acid bath at Acid bathElOO"C) (IOO"q .at boi I t rorci boil (IOO"C) (lIO"q

0-N.~NHZ 7.82 6.18 11.52 11.04 11.84

2 & 0- CH)o aN, 0 H' 12.21 11.52 15.58 15.1 17.53\CHJ

3 HlC0-N-H0NtHl 3.12 3.33 5.92 4.24 5.88CHJ

4 HlC0-N_~NH! 11.88 11.52 14.64 14.30 15.68

5 OZ~N-N-0-NHZ 2.14 2.92 2.30 2.01 3.8·1

6 .,'-&-~o 0 3.19 4.20 3.23 2.92H 4.92H

7 OZ~_N~ 3.94 3.29 5.29 4.02 4.05o 0N

OH

8 ~H=N-0-HHZ 2.89 3.23 2.91 2.71 4.05Cl

Oz~.r.-0-"HZ 2.84 3.00 2.91 2.82 3.60

HJ

0-NaG;0 7.89 4.79 7.36 9.10 11.52o 010 HOH

\I ¥0-N'H-00-~NHz 2.96 1.49 3.12 3.05 3.81

12 ~N=~N=~HHZ 3.17 3.81 2.77 4.51 6.72Cl

character with different substituents were applied onunmodified and chlorinated polypropylene fabric inalkaline medium also and the results in terms of K/Svalue are given in Table I. In alkaline dyeing, dyes 5-9and 12 give lower K/S values for chlorinated polypro-pylene than for unmodified polypropylene. Whiledyes 1-4, 7and 10 show considerable increase inK/Svalue for chlorinated polypropylene. Among thesesix dyes, both dye 1 and dye 10 have unsubstitutedbenzene ring (lower molecular weight, small size andless or no substitution) and the dye 1has basic charac-ter due to - NH2 group and dye 10has basic characterwith quinoline structure and in addition it has also an- OH group. Between dye 7 and dye 10, the formerhas an additional - N02 group (electron withdraw-ing) which reduces quinolinic basic character in dye7.

In dyes 2-4 there is methyl substitution either atnitrogen or in the benzene ring and this methyl substi-tution increases the basic character of the electronlone pair on nitrogen by the electron donating induct-iveeffect (positive) of methyl group. So, as the basicityof nitrogeneous lone pair increases, the more attract-ion of these dyes towards chlorinated polypropyleneis expected.

Ofthe bis-azo dyes 11and 12, dye 11 is linear unsu-bstituted whereas dye 12 is chlorine substituted andalso has one benzene ring and one - NH2 group less incomparison with dye 11, i.e. dye 12 has less molecularweight. The dye 12shows no improvement in depth ofshade after chlorination while higher molecular we-ight but linear bis-azo dye 11 gives slight improvem-ent but not appreciable depth of shade. IR spectra foronly chlorinated polypropylene and dyed chlorina-

SAMANTA & SHARMA: DYEING OF POLYPROPYLENE 209

ted polypropylene in alkaline medium (dyed with dis-perse dyes of basic character, C. I. Solvent Yellow-2)did not show any evidence of bond formation unlikein case of application of basic dyes to chlorinatedpolypropylene. However, Table I shows that most ofthe basic character disperse dyes, specially those hav-ing electron donating group (negative inductive eff-ect) and no other effects like steric hindrance, higheraqueous solubility due to higher basicity, etc. showmore dye uptake both in acid and alkaline bath whendyed after chlorination. Dyes 7 and 12, however,show reverse result for dyeings in acid and alkalinemedium. This may be due to some unknown effectrelated with pH and/or structural peculiarities in alk-aline medium.

The possible mechanism of interaction betweenchlorinated polypropylene and one basic characterdisperse dye (C.I. Solvent Yellow-2) through electro-static attraction and negative inductive effect, gener-ating higher affinity for chlorinated polypropylene, isshown in Fig. 1.3.3 Fastness Properties

Table 2 shows that dyes 1, 3,6 and 10 have overallgood fastness properties. However, for dye 6, the dyeuptake is not acceptable. Dyes 1,3,4 and 6 show goodlight fastness (6-7). Dyes 7 and 10 give increaseddepth of shade on chlorinated polypropylene buthave moderate light fastness (4-5). Dye 4,has poorfastness to drycleaning and dry-rubbing and dye 7has poor rubbing fastness. Relating these findingswith the structural constitution of the dyes needs furt-her indepth study. Ahmed and Mallet!", however,found that the fading of some azo dyes and pigments

on polypropylene occurs usually by photoreductionrather than photooxidation in polypropylene by amechanism entailing abstraction of tertiary hydro-gen of the polypropylene molecule. As per their findi-ngs, the relative fading rate increases with increase inHammet constant of the substituent (measure of dec-rease in electron density at azo link).

Light fastness results of these dyes on chlorinatedpolypropylene show that the electron withdrawinggroups like - N02, - CI and - OCH3 with positiveinductive effect and higher Hammet constant valuecause more quick light fading. Light fastness ofbis -azo dyes (Dyes 11 and 12) has been found'to be poor inthis case. Wash fastness of all the dyes is moderate togood andacceptable. Fastness to drycleaning is alsomoderate to good for these dyes on chlorinated poly-

CHCH. H CH.H _-_. n-+ •,( 1+ 1 -r .... 01__ c-c!AV-.-c______ +~ N~N=N-'@11~1 't~CIHCIH 1lI'Eb~ clis

Chlorinated PP . t-.i.l> Di.,.r •• df! with basic character~'~'fl ~~_~. IC.LSolventVeUow-2

_lor ""'"'..;::., , (DyeNo. 2 I.CH, H eH, H· ilttlwhHdIK/.,."...1 l.!il I' /oJ_ -.-pp

--NN--C -C Po - C---.NN- .u~ c~ iM 'JIIN

I I/f I =··~~7~~-CI H, CI H _ •• ~~ ._p:if r~~ I'" $---

I

4Dyed Chlor~ PP

Fig. I-Mechanism of interaction between chlorinated PP and, - . disperse dyes .

Table 2-Fastness of disperse dyes onchlorinated polypropylene

Fastness to

Wash Drycleaning Dry rubbing

Loss of Stain on Loss of Stain Stain Stain ondepth PP depth on PP on PP cotton

3-4 3-4 2-3 4 3 33 3 2-3 3 4 4

3-4 3-4 3-4 3-4 4 3-43 2 2-3 2-3 2-3 2.33 4 5 4-5 4 43 4 3 4 4 43 4 5 4 2-3 2-33 3 4 4 5 44 5 5 5 5 4

3-4 3-4 4 4 3 33-4 3 5 5 5 53-4 4 5 4 5 5

Dye No.

Light

I 6Z 33 64 75 4-56 67 4-58 39 2-3

10 4-5

11 212 2-3

210 INDIAN J. FIBRE TEXT ..RES., DECEMBER 1995

propylene. The rubbing fastness of all the dyes, exceptdyes 4 and 7, on chlorinated polypropylene is alsogood.

4 CoDclusio~4., Some of the azo disperse dyes with bask charactershow increased depth of shade, and good fastness onchlorinated PP but no covalent bond formation occ-urs unlike in fixing of basic dyes to chlorinated polyp-ropylene by covalent bond formation as reported inearlier work14•17,19.20.

4.2 The disperse dyes studied exhibit more affinityto chlorinated polypropylene than to unmodified po-lypropylene and the extent of increase in dye affinitydepends on the nature of substituents in the dyes andalso on the medium of application (acid or alkaline).Electron withdrawing groups like - N02, - OCH3and - CI (positive inductive effect) do not favourhigher dye uptake and also show lower light fastness,while the disperse dyes of basic character with elect-ron donating groups as substituents (with negativeinductive effect) applied in acid medium give goodresults showing increased dye uptake and improvedfastness performances with a few exceptions for otherstructural interactions, steric causes, etc. Further im-proved results are obtained in acid medium at slightlyhigher temperature (l100C) for application of thesedyes to chlorinated polypropylene.

43 Dye 1 (4-aminoazobenzene), dye 3 [4-methyl-4 -(dimethylamino)azobenzene] and dye 10 (8-hydr-oxy-5-phenylazoquinoline) show acceptable depthof shade with overall good fastness on chlorinatedpolypropylene.

AcknowledgementThe authors are grateful to Prof. R C D Kaushik,

Director, TITS, Bhiwani, and Prof. S D Deshpande,Ex-Head, Textile Chemistry Department, TITS,

Bhiwani, for their keen interest during the study.They are also thankful to Dr D K Jain and Prof. R BChavan ofIIT, 'Delhi, and Dr P C Dasgupta, Ex-Prin-cipal, Institute of Jute Technology, Calcutta, for helpand valuable consultation.

References1 Bauman H P, Am Dyest Rep, 52 (1963) 527.2 Bird C L & Patel A M, J Soc Dyers Colour, 84 (1968) 11.3 TerarnuraK&HiraseS,J Soc Text Cellu Ind.Japan, 18(1962)

436.4 US Pat 3,069,220 (to Allied Chemical Corporation), 1965.5 Br Pat 880,858 (to ACNA), 1960.6 Br Pat 953,753 (to ICI), 1963.7 US Pat 2,989,358 (to VerGlanzstoffe), 1961.8 Ketajama A & Kuroki N, J Soc Text Cellu Ind, Japan, 19(1963)

828.9 Terarnura K, Hirase S & Tancka R,Sen-i-Gakaishi. 19(1963)

304.10 Leube H, Melliand Textilber, 46 (1956) 743.11 Akiesi N & Josikawa S, Kogyo Kagaku Zasshi, 65 (1962)

1390.12 Eddington E M, Am Dyest Rep, 52 (1967) 47.13 Samanta A K, Indian Text J, (1988) 208.14 Agster A, Melliand Textilber, 56 (1975) 470.15 Jap Pat 11,171 (to Toyo-Rayon), 1965.16 Samanta A K. & Sharma D N, Colourage, 37 (March 1990)

15.17 SamantaAK&SharmaDN, Text Trends.Ys (May 1990)35.18 Ahmed M & Mallet Y, J Soc Dyers Colour, 84 (1968) 313.19 Shah C D & Jain D K, Text Res J, 53 (1983) 275.20 Shah C D & Jain D K, Text Res J, 54 (1984) 742.21 Urbanski J, Czerwinki W, Jamica K. Majewska F & Zowell H,

Handbook of analysis of synthetic polymers and plastics (JohnWiley & Sons Inc, New York), 1977,42.

22 Trotman E R, Dyeing and chemical technology of textile fibres(Charles Griffin, London), 1970, 597 & 643.

23 Giles C H & Shah C D,J Soc Dyers Colour, 85 (1969) 419.24 Talwar RK. SamantaA K&SharrnaD N, Am Dyest Rep, 84

(1995) 37.25 Samanta A K,Sur D, Chattopadhyay D P, Ghosh S K & Mon-

da! S N, Indian J Fibre Text Res, 20 (1995) 23.26 ISI (BIS) Handbook of textile testing (Bureau ofIndian Stan-

dards, New Delhi), 1986,221.