f•Indian Journal of Textile ReseaeehVol. 4, December 1979, pp. 121-132

Radiation Induced Graft Copolymerization of Methyl Methacrylate on Naturaland Modified Wool: Part IV-Mechanical Properties

D SoVARMA & R K SADHIR*Fibre Science Laboratories, Indian Institute of Technology, New Delhi 110029

Received 6 January 1979; accepted 7 May 1979

The mechanical properties of the graft copolymers of natural and chemically modified wool and methyl methacrylate in airand water were investigated. The average diameter of the wool fibres showed a gradual increase with increase in the degree ofgrafting. The general shape of the load-elongation curves in air and water remained intact after chemical modification andgrafting, with the exception of reduced wool. With the grafting of a rigid polymer (PMMA), the breaking load increased,breaking elongation decreased and slopes in Hookean, yield and post-yield regions increased. In reduced and grafted woolfibres, the post-yield regions disappeared due to thiol-disulphide interchange reaction. In general, the strength of natural,chemically modified and grafted fibres in water was lower than the corresponding dry strength, whereas the breakingelongation in water was higher than that in dry state. Medullated fibres were stronger than the pure fibres, Hookean slope wasmore steep and yield slope was also more. Bulk resilience and elastic recovery values were reduced after grafting.

e

Early studies on graft copolymerization were aimed atmodifying the fibre surface properties, improvingthereby the milling shrinkage of wool. Later, moreemphasis was given on the study of changes in theintrinsic properties of the grafted wool fibres, such asstress-strain behaviour, elasticity, permanent set,supercontraction, etc. Such studies are of vitalimportance because of their direct relevance to the enduse of the grafted material.

The mechanical properties of reduced and alkylatedwool fibres have been reported in literature+T '.Boardman and coworkers" investigated the effect ofdeposition of a series of vinyl polymers on the elastic,frictional and shrinkage properties of wool. Similarinvestigations ha ve been reported by several otherworkers" - 17. The mechanical properties of the graftcopolymers of wool with styrene, methyl methacrylate(MMA) and acrylonitrile prepared by y-irradiationhave been investigated I 5. At low graft-on, both thetensile strength and the initial modulus in the dry andwet states increased and the high elongation of woolwas retained, while at high percentage graft-on, theelongation decreased and the fibre became more brittleand harsh.

The present paper concerns the. mechanicalproperties in air and water of chemically modifiedwools and their graft copolymers with MMA preparedby y-irradiation technique. Preliminary experimentsrevealed that there was a large variation in thebreaking load within a sample, due to the presence of

*Present address: Central Sheep and Wool Research Institute,Avikanagar, via Jaipur 304501, Rajasthan

medullated fibres. Therefore, the load-elongationcharacteristics of the pure and medullated fibres weredetermined separately.

Experimental ProcedurePreparation of grafted samples-Malpura wool

fibres were chemically modified (i.e. oxidized, reduced,methylated and crosslinked) using hydrogen peroxide,sodium bisulphite, dimethyl sulphate and for-maldehyde. The graft copolymerziation of natural andchemically modified wool with MMA was carried outby the mutual irradiation technique using 60Co as thesource of y-radiation. The details of chemicalmodification and grafting have been reported earlier 1 8.

Average diameter and medullation percentage-Theaverage diameter and medullation percentage weredetermined according to the ISI specification makinguse of projection microscope.

Load-elongation characteristics- The load-elongation characteristics of natural, chemicallymodified and graft copolymerized wool fibres werestudied using Instron. Pure and medullated fibres fromeach sample were tested separately. The separation ofpure and medullated fibres was done with the help of 0-

dichlorobenzene 19. For studying the load-elongationbehaviour in water, the samples were kept immersed atroom temperature overnight. The lower clamp of theInstron was modified for this test. One end of the fibrewas fixed to a dead weight which rested on the bottomof a jar full of distilled water. The jar was placed on thecross-head of Instron. The whole assembly acted as thelower clamp. The other end of the fibre was fixed to theclamp of Instron. The conditions employed were:

121

INDIAN J. TEXT. RES., VOL. 4, DECEMBER 1979

Gauge length, 2.0 em; cross-head speed, 2 em/min.chart speed, 10 cm/min; and full scale load calibration,50g.

Bulk resilience- The sample (1 g) was weighedaccurately on a balance and then it was placed looselyin a sample holder. A 2.5 em height of the test samplewas kept constant for all specimens. This sample wasthen placed on the compression cell of the Instron andwith the help of a cylindrical plunger attached to thecross-head, it was compressed to 80% of maximumthickness at a constant speed. After attaining thespecified compression, the fibre mass was recoveredimmediately. The rates of compression and recoverywere identical. The conditions for the tests were:Original thickness, 2.5 em; chart speed, 3 cm/min;cross-head speed, 0.5 cm/min; and full scale loadcalibration, 1 kg.

Elastic recovery-The method used to determine theelastic recovery after 5% extension was similar to thatused by Guthrie and Norman!". The Instronspecifications used were: Gauge length, 2 em; cross-head speed, 0.5 cm/min; chart speed, 30 cm/min; andfull scale load calibration, 20 g.

Results and DiscussionA verage diameter and medullation percentage- The

values of average diameter and percentages of pure andmedullated fibres are given in Table 1. There was anincrease in diameter with chemical modification priorto graft copolymerization. A gradual increase in the

1

PUrl' Fibres

14

12

10

I••Table I-Average Diameter and Percentage Medullation of

Fibres After Chemical Modification and GraftCopolymerization

Sample Graft-on%

Average diameter

Jl CV %

Naturalwool

o17.641.163.3

41586271

Oxidizedwool

o35.853.487.1

44456072

Reducedwool

o47.558.191.3

48506371

Methylatedwool

o74.394.7

129.7

48556573

Crosslinkedwool

o21.942.853.1

48505964

(59)(61)(60)(53)

(44)(56)(61)(54)

(60)(61)(53)(52)

(64)(51)(50)(49)

(54)(58)(44)(60)

Purefibres

%

Medul-'latedfibres

%27293520

73716580

33344725

67665375

17441526

83568574

30503835

70506265

14242430

86767670

Medlllated Fibres

20

16

12

8

o 10. EXTF.NSfON, '/.

FIg. l-Load-exlension curves for natural and MMA fedfibres in air gra t wool

122

VARMA & SADHIR: RADIATION INDUCED GRAFT COPOLYMERIZATION OF METHYL METHACRYLATE ON WOOL

diameter of the wool fibres was observed with increasein the degree of grafting. The value of percentagemedullation did not show any relationship withpercentage graft-on. The increase in diameter may bedue to increase in the swelling of the fibres.

Load-elongation behaviour-The load-elongationcurves for pure and medullated natural, chemically

modified and grafted wool samples in the dry state at65% RH and 20°C temperature are shown in Figs. 1-5.The general shape of the curves did not changesignificantly after chemical modification and graftcopolymerization, except in reduced wool. From theload-elongation curves various parameters werecalculated and these are summarized in Tables 2 and 3.

Purt' Fibres

1 2EXTENSION, 0/0

Fig. 2-Load-extension curves for oxidized and MMA grafted woolfibres in air

14

12

10

C' 8•..c«9

6

4

2

00

o

2 Medullated Fibres

Pure Fibres

o 10EXTENSION, "10

Fig. 3-Load-extension curves for reduced and MMA grafted woolfibres in air

14

12

1001•..c 8«0-I

6

4

2

00

o

16

12

8

4

Medullated Fibrt's28

24

20

16

12

8

4

123

INDIAN J. TEXT. RES., VOL. 4, DECEMBER 1979

Pure Fibres

18r------------------------.----------------~~------_,

16

14129..7

94.7

o

2

12

8

4

01k---~~--~--~~--~--~0~--·10~--~--~~--~------~EXTENSION, ·1.

Fig. 4-Load-extension curves for methylated and MMA graftedwool fibres in air

Pure FibIt'S 32

o 2

o 10EXTENSION, Of.

Fig. 5-Load-extension curves for crosslinked and MMA graftedwool fibres in air

16

14

12

100-•..0<0 8-J

6

4

2

00

124

2

MedulkltedFibres

2'

24

8

4

VARMA & SADHIR: RADIATION INDUCED GRAFT COPOLYMERIZATION OF METHYL METHACRYLATE ON WOOL

Table 2-Analysis of Load-Elongation Curves for Grafted Pure Wool Fibres in Air under Standard Conditions

Sample Graft- Average Average Average Slope in Yield Initial Work ofon breaking tenacity breaking Hookean slope modulus rupture

% load gjtex elongation region g gjtex gg % g

0 7.0 7.2 35.2 148.2 9.7 143 1.8Natural 17.6 10.2 8.1 32.0 173.7 17.0 160 2.2

wool 41.1 12.5 8.2 32.2 285.6 13.0 200 3.663.3 13.4 8.1 34.3 286.3 14.7 173 3.7

0 7.1 7.0 31.9 133.0 7.7 137 1.8Oxidized 35.8 10.4 7.1 32.6 222.1 10.1 174 2.6

wool 53.4 10.7 6.6 37.8 266.9 10.7 174 2.887.1 11.5 6.6 31.5 307.4 12.3 133 2.9

0 6.2 6.8 26.7 133.2 3.5 190 1.4Reduced 47.5 8.5 6.4 22.3 222.1 4.0 190 1.5

wool 58.1 9.4 6.5 14.3 308.0 5.0 133 1.191.3 9.8 5.9 13.0 308.2 9.0 160 1.2

0 6.9 7.7 31.9 80.0 4.0 100 1.3Methylated 74.3 9.2 7.7 33.6 200.1 6.0 174 2.8

wool 94.7 13.2 7.9 34.6 235.4 10.7 160 3.3129.7 13.0 7.3 34.4 286.1 13.7 111 3.5

0 6.0 7.1 32.8 100.6 9.3 125 1.4Crosslinked 21.9 7.5 7.4 28.5 128.8 5.2 133 1.8

wool 42.8 10.8 7.3 28.5 167.1 10.7 154 2.353.1 12.6 8.0 28.3 210.9 11.3 167 3.0

Table 3-Analysis of Load-Elongation Curves for Grafted Medullated Wool Fibres in Air under Standard Conditions

Sample Graft- Average Average Average Slope in Yield Post- Initial Work ofon breaking tenacity breaking Hookean slope yield modulus rupture% load g/tex elongation region g slope g/tex g

g % g g

0 21.9 9.5 39.5 421.5 10.0 59.0 109 5.9Natural 17.6 22.7 8.3 34.0 533.2 10.7 35.5 167 6.2

wool 41.1 28.5 8.9 34.2 570.9 11.7 66.0 154 7.663.3 30.3 9.0 32.1 615.4 21.3 84.8 143 7.2

0 22.4 8.1 36.3 444.0 24.0 54.2 114 5.7Oxidized 35.8 23.2 6.4 33.0 615.9 14.0 56.0 191 6.0

wool 53.4 25.9 6.1 34.1 533.2 33.0 125 6.087.1 29.9 5.9 33.0 769.0 10.0 46.5 138 6.5

0 20.9 7.3 28.2 600.2 11.0 250 5.0Reduced 47.5 25.2 6.3 15.0 667.5 14.5 190 2.9

wool 58.1 24.7 5.7 14.2 666.7 44.0 160 2.691.3 23.0 4.6 15.6 706.5 10.0 142 3.1

0 27.2 9.8 38.4 571.4 Hi.3 55.5 222 7.5Methylated 74.3 32.4 7.3 32.3 667.2 28.7 104.0 111 7.8

wool 94.7 30.5 6.6 30.6 667.0 27.7 60.1 129 6.2129.7 35.7 7.0 31.8 750.3 19.3 49.3 143 9.4

0 26.7 9.5 34.8 278.8 13.7 69.5 105 6.5Crosslinked 21.9 26.0 8.8 31.0 461.7 10.3 37.9 148 6.3

wool 42.8 32.6 8.5 31.5 522.4 19.3 77.3 148 7.853.1 33.7 8.3 30.3 588.2 20.0 84.4 105 7.2

125

INDIAN J. TEXT. RES., VOL. 4, DECEMBER 1979

The tenacity of the chemically modified and graftedwool fibres remained similar to that of natural wool,except in reduced wool fibres, where slight decreasewas observed. There was a decrease in the averagebreaking elongation as a result of chemicalmodification in all cases. The grafting appeared todecrease further the value of average breakingelongation which was more pronounced in reducedwool fibres.

The load-extension curves of chemically modifiedand grafted fibres showed three regions-Hookean,yield and post-yield. The last region was not observedin pure fibres. The region of up to 2% extension isknown as the Hookean region; here the fibre has a highmodulus. This region is thought to arise fromreversible straining of bonds of e-helices whichcomprise the crystalline microfibrils. The region of 2-30% extension is the yield region; here the fibre has alow modulus. This constant stress region is thought tobe associated with the (X-Ptransformation. Beyond 30%extension, the stress in the fibre begins to rise sharplywith increase in extension. This region is called thepost-yield region. The slope in the Hookean and theyield regions increased with increase in percentagegraft-on in both pure and medullated fibres. The post-yield slope increased with the degree of grafting innatural and crosslinked grafted medullated fibres,whereas it decreased in oxidized and methylated graftcopolymerized fibres. Medullated reduced wool on

grafting did not show the post-yield region.Medullated fibres were slightly stronger, Hookeanslope was more steep and yield slope was also higher. Ithas been observed that all the three regions remainintact after graft copolymerization. The graftedpolymer could be considered as an additional materialwhich interacts with the microfibrils and the matrix.The value of the work of rupture showed an ascendingtrend after grafting, except in reduced wool, where agradual decrease was observed with increase inpercentage graft-on.

The load-elongation curves for natural, chemicallymodified and grafted pure and medullated fibres inwater are shown in Figs. 6-10. The three typicallydistinct regions remained intact after chemicalmodification and grafting. Similar load-elongationcurves in water have been reported by Arai et al. 14 forwool-g-MMA and wool-g-EA. The observations fromthe load-elongation curves are summarized in Tables 4and 5. The wet strength of natural and grafted woolwas found to be lower than the corresponding drystrength. The average breaking load increased withgrafting, except in reduced wool, where it decreasedconsiderably at higher graft-on. There was a decreasingtrend in the average tenacity of the methylmethacrylate grafted natural and chemically modifiedwool with increase in percentage graft-on. Thebreaking elongation values in water were higher thanthe corresponding dry elongation values in all cases.

63.39.0~------------------.-------~~----------------------------~Medullated FibresPure Fibres

8·0

1.0

32

41.1

28

Fig. 6-Load-extension curves for natural and MMA grafted woolfibres in water

126

VARMA & SADHIR: RADIATION INDUCED GRAFT COPOLYMERIZATION OF METHYL METHACRYLATE ON WOOL

The average breaking extensions of the grafted fibreswere generally less than those for the correspondingnatural and chemically modified wool.

The slopes in the Hookean, yield and post-yieldregions and work of rupture have also been calculatedfrom the load-elongation curves in water and are givenin Tables 4 and 5. The Hookean slope was more in thegrafted fibres than in natural and chemically modifiedwool. The medullated fibres were more rigid than the

pure wool fibres, as is obvious from the Hookean slopedata. Increase in yield slope was observed with increasein graft-on. The post-yield slope did not change muchafter grafting in oxidized and reduced wool, but agradual increase was observed in grafted natural,methylated and crosslinked wool. With the exceptionof reduced wool, the work of rupture was enhancedwith the degree of grafting in all the chemicallymodified wools. However, a ·gradual decrease in work

8.0r-----------------------------r-------------------------~

Pure Fibres Medutlated Fibres7. 28

6.0 240 0

5.0 20 47.5

C7>si 4.0 169

3.0 12

2.0 8

1.0 4

o.~EXTENSION I 0/0

Fig. 8-Load-extension curves for reduced and MMA grafted woolfibres in water

~~ 4.o...J

PUrl! Fibres7.0

6.0

5.0

1.0

35.8 2

Medullated Fibres

~%~--ir--~.-~~--~---~n-----IO~--~10,---f,,--~~-,~--~---J~EXTENSION, ·1.

Fig. 7-Load-extension curves for oxidized and MMA grafted woolfibres in water

20

16

12

8

4

127

INDIAN J. TEXT. RES., VOL. 4, DECEMBER 1979

Fig. 9-Load-extension curves for methylated and MMA graftedwool fibres in water

60

1.0

o..~--~~--~--~~--~--~~--~--~~--~--~~--~--~~~ o 10EXTENSKlN,o/.

Mec1JUated Fib rft

32

8

4

Fig. 10-Load-extension curves for crosslinked and MMA graftedwool fibres in water

128

VARMA & SADHIR: RADIATION INDUCED GRAFT COPOLYMERIZATION OF METHYL METHACRYLATE ON WOOL

Table 4-Analysis of Load-Elongation Curves for Grafted Pure Wool Fibres in Water

Sample Graft- Average Average Average Slope in Yield Post- Initial Work ofon breaking tenacity breaking Hookean slope yield modulus rupture01 load g/tex elongation region g slope g/tex g'0

g 0; g g/0

0 6.1 6.2 49.4 66.7 4.0 17.0 68 1.6Natural 17.6 6.4 5.1 44.9 83.3 2.3 21.6 66 1.5

wool 41.1 7.5 4.9 49.7 83.3 4.3 26.3 55 1.6

53.3 9.1 5.5 41.4 166.7 6.5 27.5 101 2.3

0 5.5 5.5 50.3 43.5 1.6 14.3 125 1.5

Oxidized 35.8 5.9 4.0 51.4 47.6 1.9 14.2 59 1.3

wool 53.4 6.: 3.9 45.9 76.9 2.9 22.8 77 1.587.1 5.5 3.2 41.8 100.1 4.9 16.8 91 1.7

0 5.4 5.9 45.6 35.7 3.0 18.4 67 1.2Reduced 47.5 5.4 4.1 39.3 71.4 1.9 21.6 83 1.4

wool 91.3 3.4 2.1 38.6 23.8 4.5 18.3 53 0.7

0 5.8 6.5 49.8 38.5 3.9 11.1 154 1.3Methylated 74.3 6.2 5.2 43.3 76.9 4.7 22.2 125 1.4

wool 94.7 7.9 4.8 42.6 90.9 5.5 26.5 91 1.6

129.7 8.1 4.5 38.4 166.7 8.0 25.0 63 1.9

0 5.8 6.9 40.1 58.8 5.0 27.0 83 1.1

Crosslinked 21.9 6.5 6.4 36.5 90.9 6.8 30.0 100 1.2wool 42.8 8.9 5.9 37.5 90.9 7.0 31.0 153 1.3

53.1 9.2 5.7 35.5 111.1 9.1 36.3 74 1.7

Table 5-Analysis of Load-Elongation Curves for Grafted Medullated Wool Fibres in Water

Sample Graft- Average Average Average Slope of Yield Post- Initial Work ofon breaking tenacity breaking Hookean slope yield modulus rupture% load gftex elongation region g slope g/tex g

g % g g

0 19.8 8.6 48.9 173.9 8.0 66.0 83 1.0

Natural 17.6 21.1 7.7 46.2 230.2 16.0 76.6 117 1.2

wool 41.1 23.2 7.2 42.9 300.4 16.8 56.5 143 1.663.3 20.9 6.2 42.0 299.7 20.0 60.7 91 1.4

0 21.7 7.8 62.3 240.0 6.8 43.3 83 1.6

Oxidized 35.8 22.2 6.1 49.8 273.4 10.8 61.5 83 1.5

wool 52.4 20.1 4.7 47.9 400.1 11.6 56.3 133 1.4

87.1 27.8 5.5 48.8 500.3 18.4 58.3 143 2.2

0 21.7 7.6 46.0 285.8 7.2 42.8 167 1.6

Reduced 47.5 20.6 5.1 41.2 286.2 7.2 67.3 95 1.6wool 58.1 13.6 3.1 38.3 230.7 7.3 66 1.0

91.3 10.1 2.4 30.5 136.3 11.0 53 0.6

0 24.0 8.6 57.7 140.0 6.6 66.7 77 1.6Methylated 74.3 29.9 6.8 47.0 261.2 16.0 68.0 87 2.1

wool 94.7 35.7 7.7 45.4 352.9 20.4 100.1 118 2.2129.7 38.5 7.5 39.0 545.0 30.0 112.0 222 2.3

0 24.9 8.8 38.1 333.2 22.4 88.5 111 1.3Crosslinked 21.9 22.8 7.8 36.2 600.0 14.6 99.3 166 1.4

wool 42.8 30.4 7.9 34.7 600.3 22.0 59.0 286 1.953.1 29.8 7.3 36.6 998.0 23.6 134.0 200 1.6

~~-,.----

129

INDIAN J. TEXT. RES., VOL. 4, DECEMBER 1979

of rupture was observed in reduced wool whenpercentage graft-on increased.

The following order was observed in the tensilestrength of medullated fibres in water: Crosslinkedwool> methylated wool> natural wool> oxidizedwool> reduced wool. Increase in the value ofelongation was observed in oxidized and methylatedwool. The tenacity and breaking elongation in wetstate were more in medullated fibres subjected tovarious chemical treatments and grafting than in thecorresponding pure wool fibres.

The shape of the load-elongation curves both inwater and in dry state did not change much afterchemical modification or grafting, indicating no majorchange in the structure of the fibre as a result ofgrafting, with the exception of the reduced wool. Thea verage breaking elongation and the tensile strengthwere reduced to a large extent after reducing the wooland subsequent grafting. The post-yield regiondisappeared completely. A similar behaviour wasreported by Crewther ' and Harris and Brown:".

The dry strength of the crosslinked fibres changedmarginally 1Il comparison to natural wool. However,the wet strength of crosslinked wool was higher thanthat of natural wool. The crosslinking reaction withformaldehyde occurred primarily in the amorphousregions of the Iibre+'. Since the crystalline regions wereunaffected by crosslinking, one can easily explain thedry strength of crosslinked fibres. The wet strengthdepends largely on the chain length, and perhaps oninterchain hydrogen bonding and not on covalentcrosslinks. The introduction of new crosslinks+',therefore, enhances the wet strength and does notappreciably increase the tensile strength of the dryfibres. Methylation of wool increased both the dry andwet strength. There was a slight drop in tensile strengthafter oxidation.

Grafting causes increase in breaking load anddecrease in the breaking elongation. Increase in theslopes of the Hookean, yield and post-yield regions isdue to the deposition of rigid polymer. The presence ofhydrophobic groups in poly(methyl methacrylate)tends to decrease water absorption. This results inlesser swelling and consequently increase in themodulus. It is quite likely that the grafted polymer islocated around the microfibril and the aggregatedmatrix. Less amount of deposited polymer does notinterfere with the general architecture of the fibre,because it is located mainly in the interfibrillar spaces.Therefore, cohesion between the polypeptide chains isnot affected at low percentage graft-on. The depositedpolymer does not act as a barrier, but contributes to thestrength of the fibre by increasing the viscosity of thesystem. The internal viscosity of the grafted systemmay increase due to a net excess of the rigid polymer-

130

polymer, polymer-microfibril and polymer-matrixinteraction over the reduction in microfibril-matrixinteraction. Collins and Chaikirr'" have reported thatthe slope of the yield region in wool is related to thevariation of fibre cumulative cross-sectional area andto the structural non-uniformity. Our results indicatethat graft polymerization does not give rise to anyvariation in the distribution of fibre cross-sectionalarea. The grafted fibre may not tend to show additionalstructural non-uniformity along the fibre axisdirection. This may be one of the reasons for theincrease in the value of the slope in the Hookean andyield regions.

In general, the strengths of natural, chemicallymodified and grafted fibre in water were lower than thecorresponding dry strengths, whereas the breakingelongation in water was higher than that in dry state. Inwet state, the fibre stretches easily due to thebreakdown of hydrogen bonds and the probableformation of new linkages by water. Hydrogen bondsremain intact in the dry state, thus increasing theunfolding of the chains. Moreover, when the fibre isstretched, new hydrogen bonds are formed whichgreatly hinder the recovery to the original length whenthe strain on the fibre is removed. Water thus acts as aplasticizer and facilitates the mobility of the chains.

Grafted fibres show larger values of the slope in thepost-yield region than the natural and chemically

Table 6-Bulk Resiliencyand Elastic Recovery of GraftedFibres

Graft- Bulk Elasticon resiliency recovery

% %Sample Permanent

set%

Workrecovery

%

Naturalwool

0 3917.6 3841.1 3463.3 27

0 4135.8 3553.4 3387.1 31

0 4547.5 3658.1 3091.3 28

0 4674.3 3994.7 35

129.7 33

0 4321.9 3442.8 3153.1 29

82 18 2976 24 2572 28 2467 33 ~2

81 19 3076 24 2775 25 2874 26 27

Oxidizedwool

84 16 3278 22 2977 23 2776 24 27

79 21 3175 25 2872 28 2770 30 26

76 24 2877 23 23Reduced

wool

Methylatedwool

Crosslinkedwool

VARMA & SADHIR: RADIATION INDUCED GRAFT COPOLYMERIZATION OF METHYL METHACRYLATE ON WOOL

• NaturoI wool

o Oxidised wool

C Re<1Jced wooltl. Methylated wool• Cross-linked wool

Elastic RecoYf!ry

Bulk Resilience

-;.~...,

uz...,:::;Vi...,a: 30~...J~

oFig. II-Effect of graft copolymerization on bulk resilience and

elastic recovery

modified wool. Lot of controversy exists among theworkers about the structural and molecularinterpretation of the post-yield region2s-27. Thebehaviour in the post-yield region may be related to thedeformation of the matrix between sheets which arecomposed of a linear arrangement of microfibrils in theorthocortex region. The deposition of the polymerwithin the microfibril matrix extends the matrix in thelateral direction, causing stress in the cystinecrosslinked network. This stress might increase theslope of the post-yield region.

For the extension of a fibre, it requires work toovercome the internal molecular restraints and toincrease orientation. Extension in a fibre causesextensive molecular rearrangement by breakingintermolecular crosslinks, so that it becomesimpossible for the original entropy of the system to beregained. The extent to which the entropy is regained ismeasured by the work recovered. The work of rupturevalues in dry and wet states show an increasing trendwith increase in graft-on, indicating greater recovery ofthe entropy of the system in grafted fibres.

Bulk resilience and elastic recol'ery~ The effect ofchemical modification and percentage graft-on on thebulk resilience and elastic recovery is evident from theresults presented in Fig. 11and Table 6. Bulk resilienceincreased after chemical modification of the fibres.However, grafting reduced the bulk resilience in all thesamples. The following order in bulk resilience wasobserved in MMA grafted wool fibres havingapproximately the same percentage graft-on (~ 50%):

methylated wool> reduced wool> oxidized wool>natural wool> crosslinked wool. There was a decreasein the percentage elastic recovery after chemicalmodification, reduced wool being affected to themaximum extent. Grafting reduced the values of elasticrecovery. There was a gradual decrease in values withincrease in percentage graft-on. Permanent set andwork recovery were also calculated from the elasticrecovery curves. There was considerable decrease inthe work recovery in the case of reduced wool. Theprofound effect of grafting on elastic properties couldresult only from polymer deposition within the fibrestructure. This is supported by the swelling whichoccurs when large amounts of polymer are present inthe fibre.

AcknowledgementFinancial assistance from the Council of Scientific

and Industrial Research IS gratefully acknowledged.

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353.4 Boardman N K & Lipson M.) Sac Dyers Colour, 69 (1953) 335.5 Lipson M & Speakman J B. J Soc Dyers Colour, 6S (1949) 390.6 Valentine L,) TO.1 lnst, 49 (1958) T265.7 Lohani B K, Valentme L & Whewell C S, J TeXT Inst, 49 (1958)

T265.8 Wolfram L J & Menkart J. Am Dyestuff Repu . 56 (1967) 1l0.9 Watt I C,) macromolec Sel, A-4 (1970) 107'1

10 Nagano M & Kuroda Y. Chem Abstr, 66 (1967) 116577k

131

INDIAN J. TEXT. RES., VOL. 4, DECEMBER 1979

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