Indian Journal of Textile ResearchVol. 4, September 1979, pp. 85-90

Texturing of Viscose Rayon

P BAJAJ, A K SENGUPTA, T K DHAR & J S CHAKRABORTYTextile Technology Department, Indian Institute of Technology, New Delhi 110029

Received 7 December 1978; accepted 17 March 1979

Texturing of viscose rayon has been accomplished by back twisting through crosslinking, The effects of collapsed and wetcrosslinking with dimethyloldihydroxyethylene urea and epichlorohydrin respectively on crimp rigidity and tensile propertieshave been investigated. Tension during curing appears to have a marked influence on tensile properties. While there is adeterioration in strength on crosslinking for samples cured without tension, the samples cured under a tension of 4%demonstrate a marked improvement in both dry and wet tenacities.

The production of textured yarn from thermoplasticpolymers has reached a high level of development.Though textured thermoplastic yarns have stable highbulk and good elastic stretch, they suffer from poorhygroscopicity and high level of proneness to staticcharges. To overcome this problem, cellulosics andtheir blends have been textured by variousmethods 1 - 5. The use of viscose is of particular interest,as the fibre has no static problem; it does not pill, it dyeseasily, it is compatible with other fibres, it has goodwearing properties and it is the cheapest man-madefibre. The first cellulosic bulking yarn was patented byHaberlein & Co. under the trade name Ersatz. ToyoRaycon Co.6 also produced viscose stretch yarns underthe trade name Lanayon. They developed the processof setting of rayon filament 7 under high pressuresteam (1.3-2 kg/ern") for 2 hr at 120°C. A variety ofmethods have been investigated for producing cottonstretch yarns" - 12. Modification of viscose rayon withvarious crosslinking agents! 3 - 20 through con-ventional pad-dry cure, moist curing and vapour phasemethods has also been studied extensively. However,the use of crosslinking for texturing of viscose has notbeen reported so far. An attempt has been made to usecrosslinking agents like dimethyloldihydroxyethyleneurea and epichlorohydrin for the production oftextured viscose yarn. The results obtained arepresented in this communication.

Materials and MethodsMaterials-Two single yarns of 4(}' count with

24 tpi of'Z' twist were doubled with a ply twist of 34 tpiZ. Dimethyloldihydroxyethylene urea (DMDHEU)was obtained as a solution with 40% solids contentfrom Ahura Chemicals (India). Epichlorohydrin(DDH) and other solvents were used after distillation.

Treatment with DMDHEU-Twisted viscose yarnwas treated with aqueous DMDHEU solution of

different concentrations (7-21%). The resin bath alsocontained 12% catalyst (magnesium chloride and citricacid in the ratio 3: 2) on the weight of the resin and 0.2%Lissapol N wetting agent. The samples were then driedat 60°C for 8 min and cured at different temperatures(70-120°C) for 2 min. The curing was carried out at 0and 4% tension. The samples were soaped with 0.2%soap-soda solution for 30 min at 80°C. The amount ofresin fixed was calculated from the nitrogen contentdetermined by the kjeldahl method.

Treatment with epichlorohydrin-It was a two-bathprocess. The samples were first impregnated with 16%sodium metasilicate and 0.2% wetting agent for about5 min under tension and then squeezed for 100% wetpick up. The samples were then treated with 20% (vol./vol.) epichlorohydrin in CCI4, as reported earlier+'.

Backtwisting- The crosslinked yarns were ba-cktwisted through zero ply twist to produce a yarn withfinal tpi of about 10 in the'S' direction. Afterdetwisting, the yarns were relaxed in water at 80°C for15 min and dried.

Evaluation of mechanical properties-The mechani-cal properties of the yarns were evaluated on anInstron tensile tester at 25°C and 65% RH. The sampleswere pretensioned to 0.002 g/d load and then clamped.The gauge length,jaw speed and the chart speeds were5 em, 5 cm/min and 20 cm/min respectively. Twenty-five readings were taken for each sample and from theload-elongation curves, the stress-strain curves werecomputed.

Crimp rigidity-Set was assessed by determining thecrimp rigidity of the textured yarns following theHATRA procedure+'. The test was carried out in bothair and water.

Cyclic test for stretch and recovery properties-Thistest measures growth after repeated stretching to thesame extension. The test was performed on an Instronwith the instrument settings as mentioned for load-

85

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

elongation curves. The work of loading and work ofrecovery of the samples were measured between 0.002g/d and 0.10 g/d over 5 cycles.

X -ray orientation-To find orientation by X-ray, thetreated fibres were combed to ensure parallelism andmounted on an aluminium holder having a slit at thecentre. The specimen to film distance was 5 ern and theexposure period was 3 hr. The azimuthal scan of thephotograph was taken by microdensitometer in 002plane through 180°. After normalizing the azimuthalintensity tracings in height, the reciprocal of theazimuthal breadth at half maximum intensity wastaken as a measure of X-ray orientation factor.

Results and DiscussionSetting of viscose through collapsed crosslinking with

DMDHEU- The effects of resin concentration, curingtemperature and tension during curing on the weightadd-on and mechanical properties of the textured yarnwere investigated. It is seen from Fig. 1 that the weightadd-on increases with increase in the resin bathconcentration. The extent of crosslinking is initiallyhigh, but tends to level off above 15% bathconcentration.

The efficiency of the catalyst under different curingtemperatures was also studied. It is evident from thedata presented in Table 2 that up to 90°C curingtemperature only 2.8% resin is fixed at 11% resin bathconcentration; thereafter, the add-on increasessignificantly when the curing temperature is increased.

A comparison of weight add-on of two samplestreated with 11% DMDHEU under 4% tension andwithout tension (Tables 1 and 2) shows a higher weightadd-on for the sample cured without tension,indicating a greater number of accessible sites forcrosslinking in this case.7r-------------~==~====~

il-6"'zaIoo<l

4

6 8 , 10 12 14 16 18 20 22SOLID RESIN APPLlED,%

Fig. I-Effect of DMDHEU bath concentration on weight add-on

Table I-Effect of DMDHEU Bath Concentration on the Mechanical Properties of Viscose"

Pad bath Weight Tenacity Crimp rigidity Initial modulus Breaking extension Loss in recoverycone, add-on gld % % % after 5th cycle

% % %Condi- Wet Air Water Dry Wet Dry Wettioned

7 4.12 1.75 0.89 8.1 8.5 11.5 7.1 16.2 19.2 7.79 4.98 1.78 0.88 9.1 10.0 16.3 7.3 15.7 18.7 7.7

11 6.11 1.82 1.01 10.2 10.8 19.7 7.6 15.4 16.1 5.113 6.81 1.72 0.88 10.8 11.2 21.4 7.9 14.9 16.0 3.915 7.03 1.69 0.86 11.4 11.5 22.4 9.0 14.8 15.8 3.718 7.10 1.65 0.86 11.2 11.5 21.0 8.5 14.6 15.4 3.5

Parent 1.56 0.72 25.0 7.1 18.3 20.3sample

·Cured at 120°C under 4% tension.

Table 2-Effect of Curing Temperature on Crosslin king of Viscose" with DMDHEU

Curingtemp.°C

Weightadd-on

%

Tenacitygld

Crimp rigidity%

Condi-tioned

Wet Air

Initial modulusg/d

Breaking extension%

Loss in recoveryafter 5th cycle

%

70 2.0 1.24 0.71 2.8690 2.8 1.25 0.70 4.32

100 4.79 1.13 0.69 7.74110 6.0 1.05 0.69 9.2120 6.36 1.02 0.65 10.8

Parent 1.56 0.72sample

-Bath cone. 11% DMDHEU cured without tension.

Water Dry Wet Dry Wet

3.1 12.6 6.14 18.52 20.11 10.65:0 15.8 7.76 18.31 19.7 8.98.1 18.95 7.55 18.0 18.7 6.19.7 20.8 7.52 18.0 17.9 5.4

11.0 21.5 7.63 16.7 17.0 5.425.0 7.10 18.3 20.3

86

BAJAJ et aJ.: TEXTURING OF VISCOSE RAYON

Mechanical PropertiesCrimp rigidity-The effect of crosslink density on the

crimp rigidity of tension cured sample is shown inFig. 2. The crimp rigidity increases linearly withincrease in weight add-on. At all levels of crosslinkdensity the crimp rigidity values- are slightly higher inwater than in air. The penetration of water in theamorphous region releases a part of the temporary setinduced during crosslinking under tension and henceallows the covalent crosslinks to participate moreeasily in the retraction of textured yarn. This beha viouris analogous to the retraction of polyester yarn aboveT 9' where the removal of temporary set above second

'der transition increases the crimp rigidity of PETn.rengthproperties-When yarns are cured without'on, strength decreases with increase in thelink density. However, a marked increase in bothinditioned and wet strengths has been observed indes cured under 4% tension. At 6.1% add-on, the

imp.ovement in strength of conditioned and wetsamples is 15.7 and 35.8% respectively (Fig. 3).

Rebenfeld and Weigmann/? reported increase in thestrength of crosslinked viscose yarn but loss in strengthin crosslinked cotton. This differential behaviour oftwo cellulosic fibres has been explained on the basis oftotal crosslink density, considering the crystallinity asa measure of crosslink density. If the crystallinity or thedegree of crosslinking is too high, molecular mobilitywill be restricted when an external load is applied,resulting in a rigid brittle system. Such a material willnot have efficient stress bearing positions. With thisanalogy, it was suggested that cotton being highlycrystalline or alternatively having high crosslinkdensity demonstrates poor tensile response withfurther reinforcement of chemical crosslinks,

Viscose, on the other hand, has an intrinsically weak,less ordered structure corresponding to lower effectivecrosslink density. The introduction of covalentcrosslinks in such a system would increase thecohesiveness and hence the strength.

On the basis of Rebenfeld's model, the loss instrength in textured viscose when cured without

. tension cannot be accounted for. It is, therefore, feltthat only increase in the crosslink density is not likelyto increase the strength of viscose; it has to beaccompanied by a high degree of orientation, asindicated by the data presented in Table 3.

Breaking extension- The breaking extensions ofcrosslinked samples are lower than that of the parentsamples cured with and without tension. This is true forboth conditioned and wet samples. Increase incrosslink density reduces the extensibility further.While in. the case of tension cured samples a betteralignment of molecular chains alongwith reinforce-

tJ..-----------.....,

7~ ~~--------~4 • •

ADD-ON,·'.

Fig. 2-EITect ofDMDHEU weight add-on on crimp rigidity [(1) Inair, and (2) in water]

+30

+20

wn

N ~x'+10 Z

~ • ~YII::Iii!: 0ILl r-"--;;----__~~ WETU

DRY

-~z~------~.~----~.~----~.ADO-ON, r.

Fig. 3-Effect ofDMDHEU crosslink density on strength propertiesof textured viscose [(1) & (2) Cured under 4% tension, and (3) &

(4) cured without tension]

Table 3-EfTect of Curing with/without Tension on theProperties of Viscose Yarns

Sl Sample Weight Tenacity OrientationNo. add-on g/d factor

%11% DMDHEU 6.3 1.01 0.115treated (curedwithout tension)

2 13% DMDHEU 6.1 1.82 0.136treated (cured undertension)

3 Parent 1.56 0.125

87

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

ment of the matrix through crosslinks may beresponsible for the lower ultimate strain value, in thecase of samples cured without tension, a relativelymore disordered amorphous region made rigidthrough crosslinking is likely to result in a moreasymmetric distribution of stress, causing de-terioration in both strength and extension values. Thelowering of wet extensibility with crossJinking is due tomatrix reinforcement by crosslinks.

Initial modulus-The initial modulus of theconditioned samples at all levels of weight add-on islower than that of the parent sample (Tables 1 and 2),being lowest at minimum add-on. Increase in crosslinkdensity increases the initial modulus almost linearly. Atlower add-on, the decrease in amorphous orientationcaused due to swelling and subsequent collapsing inthe pad-dry-cure operations has a marked influence onthe initial modulus. With increase in crosslink density,however, the buttressing effect of the crosslinksimproves the modulus (Fig. 4).

Recovery properties-The stability of the crimp inthe textured yarn is measured from the extent ofrecovery from mechanical deformation. The resultsshow that the higher the set, the better is the recovery.In other words, the work of recovery increases withincrease in the crosslink density and the percentageloss in recovery decreases (Table 1).

Cro-Hwki •• with Epidliorollyuu.Effect of reaction temperature on weight add-on-It

is seen from Tables 4, 5 and 6 that the add-on increaseswith reaction period. However, the reaction perioddecreases considerably when the reaction is carried outat 80°C instead of at 25°C. For an equivalent add-on,i.e. 2.57-2.58%, the time required at 80°C is only60 min, while it is 10 hr at 25°C.

The effect of tension on the extent of crosslinking issimilar to that observed in collapsed crosslinking withDMDHEU. The quantity of resin fixed is higher in amaterial crosslinked without tension.

Mechanical properties-Crimp rigidity increases

with increase in weight add-on due to crosslinking. Atlower add-ons, the effect of tension is quite significant,i.e. the crimp rigidity value is higher when thecrosslinking is done without tension. It is alsointeresting to note that the same level of crimprigidity can be obtained at comparatively lower add-ons with epichlorohydrin than with dimethyloldihyd-roxyethylene urea. The wet crimp rigidity valuesobserved in viscose are considerably higher than the

10

8

• 2•••••••••

",'"-*" •. --...----

•

6~--------7----- ~468ADD-ON,·'.

Fig. 4-Effect of DMDHEU crosslinking on initial modulus[(I) Dry, and (2) wet]

Table 4-ElTect of Epichlorohydrin Crosslinking on the Mechanical Properties of Viscose.

Crimp rigidity Initial modulus Breaking extension Loss in recovery% g/d % after 5th cycle

%Air Water Dry Wet Dry Wet

4.8 6.9 8.7 5.6 18.0 18.9 12.45.6 8.0 9.5 6.2 17.1 . 18.1 10.86.8 9.2 9.9 6.4 16.9 17.7 10.57.5 9.8 11.3 7.0 13.6 14.0 9.8

25.0 7.1 18.3 19.5

Reactionperiod

hr

Weightadd-on

%

Tenacityg/d

Condi- Wettioned

4 2.07 1.1 0.656 2.15 1.1 0.648 2.63 1.0 0.62

10 3.7 0.95 0.60Parent 1.56 0.72sample

·Crosslinking at 25°C without tension.

88

BAJAJ et aI.: TEXTURING OF VISCOSE RAYON

Table 5-EtTect of Wet Crosslinking with Epichlorohydrin on the Mechanical Properties of Yiscose"

Reaction Weight Tenacity Crimp rigidity Initial modulus Breaking extension Loss in recoveryperiod add-on gld % gld % after 5th cycle

min % %Condi- Wet Air Water Dry Wet Dry Wettioned

20 1.42 1.30 0.69 6.8 7.9 8.9 6.6 18.0 19.5 12.240 1.83 1.25 0.67 7.3 8.2 9.3 7.5 17.8 17.9 10.460 2.80 1.17 0.65 7.6 8.3 9.5 8.3 17.6 17.6 10.080 3.90 1.10 0.60 7.8 9.6 9.8 8.9 16.3 16.9 9.7

100 4.72 0.98 0.60 8.2 10.4 10.8 7.8 15.8 16.1 8.2Parent 1.56 0.72 25.0 7.1 18.3 20.3sample·Crosslinking at 80°C without tension.

Table 6-EtTect of Wet Crosslinking with Epichlorohydrin" on the Mechanical Properties of Viscose

Reactionperiod

min

Weightadd-on

%

Tenacitygld

Condi- Wettioned

20 1.30 1.58 0.8240 1.76 1.61 0.8360 2.58 1.65 0.8580 3.7 1.63 0.78

100 4.5 1.46 0.77Parent 1.56 0.72sample

·Crosslinked at 80°C under 4% tension

Crimp rigidity Initial modulus Breaking extension Loss in recovery% gld % after 5th cycle

%Air Water Dry Wet Dry Wet

6.1 7.9 27.1 8.1 18.0 19.0 12.76..4 8.5 29.5 7.9 17.8 18.9 9.17.0 9.6 29.8 7.8 17.4 16.7 8.97.5 9.9 29.4 8.7 16.2 15.5 8.68.6 11.2 29.5 8.9 15.5 13.0 8.5

25.0 7.1 18.3 20.0

12r-----------------------,~IO..~t:o(!) 80::I

Q.

~0::U 6

o 3ADO-ON., '"

5

strength. On the other hand, both dry and wetstrengths increase in samples crosslinked undertension, except with the sample of the highest add-on.Improvement in strength properties of viscosecrosslinked under tension with epichlorohydrin(Table 6) is generally lower than in the case of viscosecrosslinked with DMDHEU. It is interesting toobserve (Tables 1 and 6) that in the samples tensioncured with both DMDHEU and epichlorohydrin, thetenacity improves when the crosslink density reachesan optimum value and then starts falling as thecrosslink density is increased further. Thus, aspostulated by Rebenfeld+, there appears to be alimiting crosslink density on either side of which thestrength is likely to be less.

The initial modulus increases in samples crosslinkedunder tension, while the samples treated in slackcondition show considerable-lowering in conditionedinitial modulus. The breaking extension decreasesslightly in all the samples, whether they are crosslinkedunder tension or without tension. As in collapsedcrosslinking, the loss in recovery falls with increase inweight add-on in samples crosslinked with epi-chlorohydrin.

Fig. 5-Effect of epichlorohydrin cross linking on crimp rigidity[Reaction at 80°C without tension; (1) In air, and (2) in water]

dry crimp rigidity values. This is expected, as thesetting of the deformed structure is done in a wet stateby crosslinking.

Tenacity decreases with increase in the crosslinkdensity in samples treated in slack state. However, lossin conditioned strength is more than the loss in wet

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INDIAN J. TEXT. aES .. VOL. C. SEPTEMBEit 1919

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