Investigation of synergism during radiation graft copolymerization of binary mixtures of vinyl monomers onto different textile fabrics by a dyeing method

Polymer International 44 (1997) 181È190

Investigation of Synergism DuringRadiation Graft Copolymerization of

Binary Mixtures of Vinyl Monomers ontoDifferent Textile Fabrics by a Dyeing

Method

K. El Salmawi, A. M. El Naggar* & S. E. Attia

Department of Radiation Chemistry, National Center for Radiation Research and Technology, P.O. Box 29, Nasr City, Cairo,Egypt

(Received 3 February 1997 ; revised version received 16 May 1997 ; accepted 25 May 1997)

Abstract : Radiation-induced graft copolymerization of binary mixtures of acrylicacid (AAc) and styrene (S) onto cotton, cotton/polyesterÏ and viscose rayon hasbeen investigated. The di†erent factors that may a†ect the total graft yield (thesum of polyacrylic acid (PAAc) fraction and polystyrene (PS) fraction, such assolvent composition, comonomer mixture, and irradiation dose were studied. Itwas found that there is always a certain solvent composition of (MeOH and

and comonomer mixture at which a maximum value of total graft yieldH2O)(TGY) was obtained. Moreover, the TGY was greatly inÑuenced by other factorssuch as radiation dosage. An attempt was made to investigate synergism duringgraft copolymerization, i.e. the e†ect of each monomer on the other and theirparticipation in the resulting graft copolymer. In this respect, the PAAc and PSgraft fractions in the resulting graft copolymers of the di†erent textile fabricsunder investigation were determined approximately by dyeing with basic dye(Sandocryl Blue) and disperse dye (Samaron Blue FBL). By this method, it waspossible to determine each fraction in the graft copolymer. It was also observedthat the graft copolymerization increased the dye affinity for such dyestu†s to agreat extent. The accuracy and validity of the dyeing method applied was sup-ported by the estimation of the carboxyl group content by analytical techniquebased on acidÈbase volumetric titration.

Polym. Int. 44, 181È190 (1997)No. of Figures : 6. No. of Tables : 5. No. of References : 8

Key words : textile fabrics, radiation graft copolymerization, acrylic acid/styrenemixture, dyeing, carboxyl content

INTRODUCTION

Graft copolymerization of binary mixtures of vinylmonomers onto di†erent polymeric materials has beenreported in the literature.1h5 These investigations wereconcerned with studying the conditions and the di†er-ent factors that a†ect the grafting reaction and the

* To whom all correspondence should be addressed.

improved properties, which in general resulted fromgraft copolymerization. This is because grafting of mix-tures of vinyl monomers onto polymers introduces dif-ferent types of polymer chains with dual properties. TheidentiÐcation and estimation of the di†erent graft frac-tions from each monomer and the synergism duringgraft copolymerization is of special importance.Knowing the di†erent graft fractions corresponding tocertain compositions of the binary mixture allows a

1811997 SCI. Polymer International 0959-8103/97/$17.50 Printed in Great Britain(

182 K. El Salmawi, A. M. El Naggar, S. E. Attia

graft copolymer with desired properties for speciÐcapplications to be obtained. It is also possible to controlthe grafting conditions, such as comonomer composi-tion, solvent composition and irradiation dose, toproduce a graft polymer containing di†erent functionalgroups.

In previous work, the graft copolymerization ofbinary mixtures of acrylic acid and styrene monomersonto polypropylene Ðlms by a direct radiation methodwas investigated.2 An attempt was made to identify andestimate the poly(acrylic acid) and poly(styrene) graftfractions in the resulting graft copolymer by calculatingthe reactivity ratios and comparing these with elementalanalyses and IR spectroscopy. In the present work, thedi†erent factors that may a†ect the copolymerization bythe direct method of radiation grafting, of binary mix-tures of acrylic acid and styrene onto di†erent textilefabrics, are investigated. A dyeing method is proposedto estimate the di†erent fractions of poly(acrylic acid)and poly(styrene) in the resulting graft copolymer.

EXPERIMENTAL

Materials

T extile fabrics. The cotton fabric used was desized,scoured, bleached, and mercerized, but was not sub-jected to any Ðnishing processes. The cotton/polyesterfabric was a blend of cotton and polyester Ðbres at aratio of 35% to 65%, and was passed through the sametreatment processes as the cotton fabric. The viscoserayon fabric, which was considered as regenerated cellu-lose material, was received in the form of raw fabric.Before being used, it was washed sequentially withdiethyl ether, ethyl alcohol and distilled water. All thefabrics used were plain weave and supplied by Misr/Helwan Spinning & Weaving Co., Egypt.

Dyestu†s and monomers. Two dyestu†s belonging to dif-ferent classes were used during this work. These wereSandocryl Blue (basic dye) from Sandoz, Switzerland,and Samaron Blue from Hoechst. Acrylic acid andstyrene monomers were of purity 99% (Merck,Germany) and were used as received. The other chemi-cals were of pure grade and were used without furtherpuriÐcation.

Methods

Graft copolymerization. The direct radiation graftingmethod was used in which the di†erent textile sub-strates in contact with the grafting solution wereexposed to gamma irradiation in one step. The glasstubes containing the textile substrates and thecomonomer/solvent mixtures used were deaerated bybubbling nitrogen through for 5 min before being irra-

diated. Gamma irradiation was carried out at a doserate of 0É50È0É55 Mrad/h in the cobalt-60 gammasource (made in India), of the National Center for Radi-ation Research and Technology, Cairo, Egypt. Thegrafted substrates were removed and thoroughlywashed with hot water and extracted in benzene to con-stant weight. The total graft yield (TGY) was deter-mined by the percentage increase in weight as follows :

TGY[%]\ [(Wg [ W0/W0)]] 100

where and represent the weights of the initial andW0 Wggrafted substrate, respectively.

Dyeing procedure. Aqueous dye baths containing 1%dye concentration (based on fabric weight) were pre-pared from the di†erent dyestu†s under investigation.The preparation and dyeing procedures have alreadybeen described.

Testing and analysis

Colour strength measurements. A micro-colour unitequipped with a data station made by Dr. Lange(Germany) was used for colour measurements. The L*,a* and b* system used in this method is based on theCommission International de (CIF) colour tri-EŠ clairangle. The L* value represents the lightÈdark axis, thea* value represents the redÈgreen axis and the b* valuerepresents the blueÈyellow axis. In the present investiga-tion, the L* value was used as a measure for colourstrength, while the colour di†erence *L* was deter-mined based on the colour strength of the undyed andungrafted fabric samples.

Determination of carboxyl group content

The carboxyl content of the grafted fabrics was deter-mined by acidÈbase volumetric analysis. The sampleswere acidiÐed by soaking in 0É1 N HCl for 2 h. Accu-rately weighted samples (0É2È0É4 g) were placed in a250 ml stoppered Ñask, and 50 ml of 0É1 N of NaOH wasadded. The stoppered Ñask was allowed to stand over-night. The residual NaOH was back-titrated with0É1 N HCl to a phenolphthalein indicator end-point. Fil-tration, washing with distilled water and completion ofthe titration using methyl red indicator was then carriedout. The NaOH solution used was standardized with0É1 N HCl and taken as a reference. Carboxyl contentexpressed as the number of milli-equivalents was deter-mined as follows :

COOH (meq)\ VHCl ] NHClwhere V is the volume of HCl in ml and N is the nor-mality of HCl. Then :

COOH (g)\ COOH (meq)]0É045

1 meq COOH

POLYMER INTERNATIONAL VOL. 44, NO. 2, 1997

Copolymerization of vinyl monomer binary mixtures on textiles 183

The carboxyl content in grams was then converted tograft yield of poly(acrylic acid) as follows :

Graft yield of PAAc [%]\ COOH (g)Wg

]7245

] 100

where is the dry weight of the grafted sample and 72Wgrefers to the molecular weight of the repeating unit ofpoly(acrylic acid). The above equation may be writtenin a simple form as :

Graft yield of PAAc [%]\ VHCl] NHCl] 0É072Wg

] 100

RESULTS AND DISCUSSION

In radiation-induced grafting of individual vinyl mono-mers onto polymeric materials, it is easy to control anddetermine the graft yield of such monomers because weare dealing with a single system grafting medium.However, in graft copolymerization with a mixture ofvinyl monomers, there are other factors besides solvent,monomer concentration and irradiation dose a†ectingthe graft yield. The most important factor, which a†ectsthe grafting reaction is the synergism e†ect during graftcopolymerization. It determines the interaction betweenmonomers during the grafting reaction, together withtheir capability of reacting with the free radical formedon the backbone of the polymer chain. The net result isthat it a†ects the fractions from each monomer in theresulting graft copolymer. In the present investigation,the e†ect of di†erent factors that may inÑuence the graftcopolymerization of binary mixtures of acrylic acid andstyrene onto cotton, cotton/polyester and viscose rayonfabrics was investigated.

Effect of solvent compositions

Figures 1 and 2 show the e†ect of di†erent composi-tions of water/methanol and methanol/benzene on theTGY of a constant comonomer mixture of AAc and Sin equal ratios onto di†erent textile fabrics. It is to benoted that the total comonomer mixture concentrationwas kept constant at 20 vol% (based on the total graft-ing solution) and the radiation dose at 2 Mrad. Asshown in Fig. 1, when using di†erent compositions ofMeOH and water, the variation in solvent compositionplays an important role in determining the TGY. Thereexists a critical solvent composition at which the TGYis a maximum and it di†ers from one substrate toanother. Although the maximum TGYs onto cottonand cotton/polyester blends are the same, they areobserved at di†erent solvent compositions. However,the maximum TGYs onto cotton/polyester and viscoserayon are found at the same solvent composition

60%MeOH), although the TGY onto(40%H2Ocotton/polyester blend is higher than that obtained in

Fig. 1. E†ect of di†erent solvent compositions of water andmethanol on the total graft yield of a constant comonomermixture of AAc and S at equal ratios onto di†erent textilefabrics. Grafting conditions : total comonomer mixture con-

centration, 10%; irradiation dose, 2 Mrad.

the case of viscose rayon. In general, and regardless ofthe substrate used, solvent compositions containing lowratios of (20È40%) a†ord higher TGYs, whereas inH2Opure methanol the lowest TGY values were obtained.

The increase in TGY observed with solvent composi-tions containing low ratios of can be explained onH2Othe basis of the respective solubility of both monomersin and MeOH. AAc is completely soluble in bothH2O

and MeOH, whereas S is soluble in MeOH andH2Oinsoluble in It is believed that maximum solubilityH2O.of the comonomer mixture used was attained at solventcompositions which facilitate accessibility to the activesites on the di†erent textile fabrics. Although AAc and Smonomers are both soluble in pure methanol, lowerTGYs were observed. This may be attributed towastage reactions involving chain transfer with MeOH.The decrease in TGY associated with increasing H2Ocontent in the solvent is because of the complete solu-bility of AAc and the partial or non-solubility of S.Therefore, some sort of separation in the comonomersolution occurs leading to the di†usion of AAcmonomer only inside the Ðbres, while S monomerremains on the surface.

When was replaced with benzene (Bz) in theH2Osolvent compositions di†erent trends were observed, as



Fig. 2. E†ect of di†erent solvent compositions of methanoland benzene on the total graft yield of a constant comonomermixture of AAc and S at equal ratios onto di†erent textile

fabrics. Grafting conditions are the same as in Fig. 1.

seen in Fig. 2. Irrespective of the textile substrate used,the TGY decreases with increasing Bz ratios in thesolvent composition to a certain value, and thenincreases to reach its maximum value in the presence of100% Bz. The lower TGYs obtained in MeOH/Bzsolvent compositions compared to those in H2OMeOH may be explained on the basis of the di†erencein swelling behaviour of the di†erent textile substratesin these solvent compositions.

Effect of comonomer mixtures

The e†ect of di†erent comonomer mixtures of AAc andS on the TGY onto the di†erent textile fabrics with con-stant solvent composition 80%MeOH) is(20%H2Oshown in Fig. 3. The TGY is greatly increased withincreasing S content from 0% to 60% in the co-monomer mixtures, and then tends to decrease sharply at100% S. This was observed for grafting of cotton andthe cotton/polyester blend. In the case of viscose rayonfabric, the TGY increases slightly with increasing Sfrom 0% up to approximately 50%, and then decreasesgradually up to 100% S. The TGYs on viscose fabricare less than those obtained in the case of cotton and itsblend with polyester fabrics. Generally it can be con-cluded that a comonomer mixture of equal ratios of thetwo monomers produces the maximum TGYs onto the

Fig. 3. E†ect of di†erent comonomer mixtures of AAc and Son the total graft yield onto di†erent textile fabrics. Graftingconditions : solvent composition, 80%MeOH;20%H2O

otherwise grafting conditions are the same as in Fig. 1.

di†erent textile fabrics. This clearly shows the syn-ergistic e†ect when di†erent proportions of S and AAcmonomer are used.

Effect of radiation dose

Figure 4 shows the e†ect of irradiation dose on the totalgraft yield of a constant comonomer mixture of AAcand S at equal ratios onto di†erent textile fabrics. Thegrafting reaction was carried out in 20%H2O80%MeOH, while the total comonomer mixture con-centration was kept constant at 10% based on thevolume of the total grafting solution. It is evident thatincreasing the irradiation dose from 0É5 to 1É5 Mradcauses a signiÐcant increase in the TGYs onto the dif-ferent textile fabrics. Increasing the irradiation dose to2É5 Mrad is accompanied by further increments in theTGYs, but to a much lesser extent.

The increase in TGY observed with increasing irradi-ation dose is because of the increased number of freeradicals on both monomers and the substrates, whichincreases the chance of interaction and the formation ofgraft chains. The decreased extent of grafting observedat relatively higher irradiation doses is because of theformation of homopolymer instead of graft chains.



Fig. 4. E†ect of irradiation dose on the total graft yield for aconstant comonomer mixture of AAc and S at equal ratioonto di†erent textile fabrics. Grafting conditions are the same

as in Fig. 3.

Investigation of synergism during graftcopolymerization by a dyeing method

Cotton cellulose Ðbres are hydrophilic and have a directaffinity for direct and reactive dyestu†s because of thepresence of hydroxyl groups attached to every repeatingglucoside unit. However, they have no affinity for basic

and acidic dyes, because they do not contain negativelyor positively charged groups capable of forming saltlinkages with the dye molecule. However, syntheticÐbres such as polyester or viscose rayon are hydro-phobic in nature, lacking hydrophilic or reactivegroups. The only class of dyestu†s suitable for thesekinds of Ðbers is the disperse dyes, for which elevatedtemperature and pressure are necessary to facilitate thedi†usion and absorption of the dye inside the Ðbre toform physical bonds. The dyeability of a textile Ðbre canbe conferred or increased by introducing suitable func-tional groups along the Ðbre Ðne structure which arecapable of reacting with the appropriate dye molecules,whether they have affinity or not. This can be achievedvia graft copolymerization in which new functionalgroups can be introduced. The opening up of the Ðbremacrostructure during graft copolymerization can alsofacilitate the di†usion of the dye molecules and createadditional accessibility for dyeing.

In the present investigation, the change in dye affinityof the di†erent grafted textile fabrics with the binarycomonomer mixture of AAc and S for di†erent classesof dyestu†s was used to explain the synergism duringgraft copolymerization. Moreover, it may be possible todetermine quantitatively the graft yield fractions of bothPAAc and PS corresponding to the comonomermixture used in the grafting feed solution.

Affinity for basic dye

Table 1 shows the affinity for the basic dye (SandocrylBlue) of di†erent graft copolymers on di†erent textilefabrics obtained by grafting various comonomer mix-tures of AAc and S having constant TGYs of about30%.

It is clear that none of the ungrafted textile fabricsunder investigation has a direct affinity for the basic

TABLE 1. Effect of grafting different comonomer mixtures of AAc and S onto dif-

ferent textile fabrics on the affinity for basic dye

Comonomer

mixture

(AAc S)

Colour strength and difference

Cotton Cotton/polyester Viscose rayon

L* DL* L* DL* L* DL*

Ungrafted 88·3 6·1 80·8 9·5 84·1 7·6

20%/80% 64·4 30·0 57·9 32 66·7 25·0

50%/50% 65·9 28·5 60·9 29·0 67·8 23·9

80%/20% 63·6 30·8 56·9 33·0 65·7 26·0

100%/0% 63·4 31·0 56·5 33·4 65·1 26·6

Total comonomer mixture volume, 20% ; solvent volume, 80% ; solvent composition, 30%MeOH 70% basic dye (2% based on fabric weight), Sandocryl Blue.H

2O;

The colour strengths (L*) of the undyed and ungrafted cotton, cotton/polyester and viscose

rayon are 94·4, 89·9 and 91·7, respectively.



dye, because the colour strength L* is very high and thecolour di†erence *L* is very small. This is expectedbecause none of the textile fabrics contain negativelycharged groups capable of reacting with the cationicgroups of the basic dye. However, the relatively higherdye affinity expressed as colour di†erence for thecotton/polyester fabric compared with the other fabricsmay be because of the presence of a few terminal car-boxyl groups along the polyester chains.

Taking the graft copolymerization of cotton fabric asan example and applying the dyeing by the basic dyemethod to determine PAAc and PS fractions in the dif-ferent total graft copolymers, the following may be sug-gested :

(1) The net colour di†erence of cotton fabric graftedwith 100% AAc and dyed with the basic dyeshould equal the di†erence between the mea-sured colour di†erence and that of the ungraftedcotton sample, i.e. 31É0 [ 6É1 \ 24É9.

(2) For cotton fabric grafted with a 20%AAc 80%Scomonomer mixture, the net colour di†erencealso equals 23É9, but the net colour di†erencecalculated in (1), should be corrected on avolume basis because the total comonomer con-centration is kept constant for all the co-monomer mixtures used and becomes 24É9/5 or4É98. Therefore, the net colour di†erence becauseof the presence of 80%S in this comonomermixture will become 18É92 (by subtracting 4É98from 23É9). It follows that the PS and PAAc frac-tions in the graft copolymer can be calculatedbased on the total graft yield of 30% as follows :

PS graft fraction [%]\ 18É9223É9

] 30 \ 23É7

PAAc graft fraction [%]\ 30 [ 23É7 \ 6É3

(3) For cotton fabric grafted with a 50%AAc 50%Scomonomer mixture, the net colour di†erence in(1) should, in this case, be corrected according tothe volume of AAc in the comonomer mixture,i.e. 50%, to become 12É45. Also, the net colourdi†erence of cotton fabric grafted with the50%AAc 50%S comonomer mixture equals22É4. Thus, the net colour di†erence because ofthe presence of 50%S will become 9É95. Accord-ingly, the PS and PAAc fractions in the graftcopolymer can be calculated as follows :

PS graft fraction [%]\ 9É9522É4

] 30 \ 13É3

PAAc graft fraction [%]\ 30 [ 13É3 \ 16É7

(4) By following the same procedure for cottonfabric grafted with the comonomer mixture con-taining 80%S, it was found that the calculated

PS and PAAc graft fractions were 5É8% and24É2%, respectively.

Based on these Ðndings it may be concluded that anincrease of AAc in the comonomer mixture is accompa-nied by a decrease in the PS graft fraction in theresulting graft copolymer. Also, by using this method ofdyeing, it was possible to determine approximately thefractions of PAAc and PS in the graft copolymer.

The same procedure was then applied to the cases ofcotton/polyester and viscose rayon fabrics grafted withthe same comonomer mixtures of AAc and S. The cal-culated PS and PAAc fractions corresponding to eachcomonomer mixture are summarized in Table 2.

Affinity for disperse dye

The importance of water-insoluble disperse dyes hasincreased to a great extent recently because of thedemand for synthetic Ðbres with hydrophobic characterwhich are very resistant to conventional water solubledyes. The disperse pigments are essentially derivativesof either azo compounds or anthraquinone. It wasbelieved that the mechanism of take-up of disperse dyesby acetate Ðbres, for example, resembled the partition ofa solute between two immiscible solvents.7 Thepigment, in other words, formed a solid solution in theÐbre. Moreover, there is reason to believe that hydrogenbonding takes place between the primary amino groupsand the acetyl groups, and that Van der WaalsÏ forcesalso contribute to the retention of the dye. It is possiblethat dipole interaction may also play a part. Dyeingwith disperse dyes was also used to determine the PAAcand PS graft fractions in the graft copolymers on thedi†erent textile fabrics.

TABLE 2. Calculated PS and PAAc fractions in dif-

ferent graft copolymers corresponding to various

comonomer mixtures of AAc and S by dyeing with

basic dye

Fabric substrate Comonomer

mixture

(AAc S)

Graft copolymer

PS PAAc

Cotton 20%/80% 23·7 6·3

50%/50% 13·3 16·7

80%/20% 5·8 24·2

Viscose rayon 20%/80% 23·4 6·6

50%/50% 12·5 17·5

80%/20% 5·2 24·8

Cotton/polyester 20%/80% 23·6 6·4

50%/50% 11·6 18·4

80%/20% 5·6 24·4

Constant TGY ¼30%.



TABLE 3. Effect of grafting various comonomer mixtures of AAc and S onto dif-

ferent textile fabrics on the dye affinity for disperse dye

Comonomer

mixture

(AAc S)

Colour strength and difference

Cotton Cotton/polyester Viscose rayon

L* DL* L* DL* L* DL*

Ungrafted 90·4 4 67·8 22·1 84·7 7

0%/100% 47·6 42·8 30·2 59·7 44·2 47·5

20%/80% 51·4 43·0 31·0 58·9 45·0 46·7

50%/50% 48·3 46·1 24·2 65·7 36·5 55·2

80%/20% 53·0 41·4 33·3 56·6 39·1 52·6

The grafting conditions are the same as in Table 1; disperse dye, Samaron Blue.

The colour strengths of the undyed and ungrafted textile fabrics are the same as in Table 1.

Table 3 shows the change in dye affinity for dispersedye of the di†erent textile fabrics graft copolymerizedwith di†erent binary comonomer mixtures of AAc andS, but having constant TGYs of about 30%. It can beseen that the dye affinity of the ungrafted textile fabricsfor the disperse dye used follows the order :

Cotton/polyester ? Viscose rayon [ Cotton

This trend is expected because cotton fabric is hydro-philic and has no direct affinity for this class of water-insoluble dyes. The relatively high dye affinity of viscoserayon, compared with cotton fabric may be attributedto the processes which occur during manufacture of thiskind of Ðbres from cellulosic materials by dissolutionand spinning. These processes will eventually changethe molecular structure of bulk cellulose, which in turnfacilitates the dispersion of the dye inside the voids ofthe Ðbres.

Dyeing with disperse dye was also used to investigatesynergism during graft copolymerization of AAc and Scomonomer mixtures onto the di†erent textile fabricsunder investigation. Following the procedure describedbefore to determine the di†erent fractions of PAAc andPS corresponding to each comonomer mixture usedgave the results shown in Table 4.

Reproducibility and the validity of the dyeing method

In the above discussion, the dyeability with basic anddisperse dyes was used to investigate the synergismduring radiation graft copolymerization of binary co-monomer mixtures of AAc and S onto di†erent textilefabrics. The determination of PAAc and PS graft frac-tions in the resulting graft copolymer by the dyeabilitymethod was through calculations based on the com-position of the comonomer mixture solution beforegrafting. This depended upon the following di†erentparameters :

(1) The composition of the comonomer mixturesolution outside the material to be grafted beingapproximately the same as its composition insidethe material during grafting. This is becausegrafting is a di†usion process and depends onthe swelling and absorption of the grafting solu-tion by the substrate.

(2) The solubility of both monomers in the solventcomposition employed.

(3) The grafting system used in the dyeing methodbeing carried out in the presence of the optimumsolvent composition at which the highest TGY isobtained.

(4) The composition of the resulting graft copolymerbeing eventually proportional to the composi-tion of the comonomer mixture before graftingdepending on the mutual e†ect (synergism)

TABLE 4. Calculated PS and PAAc fractions in dif-

ferent graft copolymers corresponding to various

comonomer mixtures of AAc and S and dyeing with

disperse dye

Fabric substrate Comonomer

mixtures

(AAc S)

Graft copolymer

PS PAAc

Cotton 20%/80% 23·9 6·1

50%/50% 13·9 16·1

80%/20% 6·2 23·8

Viscose-rayon 20%/80% 24·5 5·5

50%/50% 12·6 14·4

80%/20% 5·3 24·7


50%/50% 12·8 17·2

80%/20% 6·4 23·6



between the two monomers during graft poly-merization (the main concern of this work).

(5) The volume of the total grafting solution of thecomonomer mixtures utilized, even the individ-ual monomers, being kept constant at 20%, withthe only variable being the ratio of the twomonomers.

In order to check the accuracy of the dye assaymethod, the carboxyl content of the same grafted fabricswith the di†erent comonomer mixtures used above wasestimated by acidÈbase volumetric titration and theresults are shown in Table 5. Fortunately, this methodof analysis is applicable in the present system because itcontains PAAc chains accessible to reaction with thebase used. In other comonomer mixtures containingacrylamide or acrylonitrile with acrylic acid, the graftedfractions were determined by nitrogen estimation.8However, in the case of grafting comonomer mixturescontaining other pairs of monomers, which cannot beeasily analysed by either method, other techniques suchas dyeability and IR spectroscopy may be the onlychoice. From Table 5, it can be concluded that the per-centage yield of graft fractions of PAAc by the analysisare very close to those determined by the applied dyeingmethod.

Figure 5 shows a standard curve relating the colourdi†erence (*L ) of cotton fabrics with di†erent graft

TABLE 5. Carboxyl contents of grafted fabrics

with different comonomer mixtures of AAc and S

monomers

Fabric substrate Comonomer Carboxyl PAAc graft

mixtures content yield (%)

(AAc S) (meq)

Cotton 20%/80% 0·252 5·5

50%/50% 0·725 15·8

80%/20% 1·050 22·9

Viscose-rayon 20%/80% 0·261 5·7

50%/50% 0·729 15·9

80%/20% 1·096 23·9


50%/50% 0·802 17·5

80%/20% 1·100 24·0

Constant TGY ¼30%.

yields of PAAc (obtained from AAc monomer) and dyedwith the basic dye under investigation. It is clear thatthe colour di†erence increases with increasing graftyield, which is solely because of the presence of PAAcgraft chains capable of reacting with the cationic dye.This standard curve can be used to give a satisfactory

Fig. 5. Relation between colour di†erence (*L ) and PAAc graft yield of cotton fabric dyed with the basic dye Sandocryl Blue.



independent proof of the validity of the dyeabilitymethod in the case of basic dyes and of calculating thetrue amount of PAAc graft yield fractions in the copoly-mer. The contribution of the PAAc graft yield fractionin the di†erent graft copolymers can be determineddirectly from the standard curve by reading the yieldcorresponding to the net colour di†erence calculatedfrom the dyeability method. The accuracy and validityof the dyeing method used was veriÐed by plotting thevalues of PAAc graft fractions determined by the dye-ability method and those obtained from the standardcurve at each comonomer mixture as shown in Fig. 6 :there is good agreement between both methods.8Accordingly, it can be concluded that the proposed dye-ability method for calculating the di†erent PAAc andPS graft fractions is applicable and satisfactory.

In previous work, the radiation induced grafting ofbinary comonomer mixtures of AAc and S onto poly-propylene Ðlms was investigated.2 The resulting graftcopolymers were characterized by di†erent methodsincluding elemental analysis, IR spectroscopy and deter-mination of the reactivity ratios of each monomer in thecomonomer mixture. Elemental analysis showed thatthe PAAc fraction in the graft copolymer decreasedwith increasing AAc ratio in the comonomer feed solu-tion. Also, the characterization of the fractions by IRspectroscopy showed similar trends. These results are incontradiction to the present work, in which it wasobserved that the PAAc fraction in the graft copolymer

increased with increasing AAc ratio in the comonomerfeed solution. This contradiction is understandable andcan be attributed to the di†erence in reactivity andsensitivity of polypropylene, cotton, cotton/polyesterand viscose rayon substrates towards gamma radiation.

CONCLUSIONS

The method used was based on the dyeability of thedi†erent textile fabrics containing di†erent types ofgrafts. These grafts become the centres of adsorption, orreaction, with the appropriate class of dyestu†s. Thedyeability of textile fabrics with cationic dye can beenhanced by introducing PAAc grafts, while the dyeaffinity for disperse dyes can be greatly increased byintroducing a combination of PS and PAAc grafts. Thechanges in the macrostructure of the Ðbres during graftcopolymerization are of importance in that some dyemolecules can easily di†use inside the Ðne structure andbecome adsorbed ; thus dyeing is possible. Based on theresults obtained the following can be concluded :

(1) Graft copolymerization with either AAcmonomer, or its binary comonomer mixtureswith S, enhances the dye affinity of the di†erenttypes of Ðbres used (natural, natural/syntheticblend and regenerated cellulose) and basic ordisperse dyes.

Fig. 6. Comparison of the PAAc graft yield fractions onto cotton fabric determined by the dyeability method and those(L)obtained from the standard curve shown in Fig. 5 (…).



(2) The dyeing method used to estimate approx-imately the PAAc and PS fractions in the graftcopolymer indicates the presence of positive syn-ergism during graft copolymerization of thebinary mixture of AAc and S onto the di†erenttextile fabrics. Moreover, the dyeing methodused, with either basic or disperse dyes, givesvery similar values of PAAc and PS fractions inspite of the di†erence in dyeing mechanism.These Ðndings may conÐrm the reproducibilityof the proposed procedure for dyeing and its usein estimating other graft fractions in di†erentbinary mixtures of vinyl monomers.

(3) The similar values of PAAc and PS graft frac-tions in the di†erent grafted fabrics may beattributed to the presence of a cellulose com-ponent in the three substrates under investiga-tion. In this respect, cellulose is present in the

cotton/polyester blend, while viscose rayon is aregenerated pure cellulose.

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