.Indian l~urnal of Textile ResearchVol. 8, ljme 1983,42-47

Effect of Wet Processing Parameters and Type of Weave onthe Shrinkage of Polyester/Viscose Blend Fabrics

I C SHARMA, VIJA Y PANDEY, SARVESH THAKUR & S P OJHA

The Technological Institute of Textiles, Bhiwani 125022

Rece;"ed 29 May 1982; accepted 23 January 1983

The dependence of fibre shrinkage on wet processing parameters, viz. dry setting temperature, pH of the bath. conditions of

h~t water treatment and repeated wetting-drying treatments, has been studied in the case of three common polyester/viscose

blend (15/85. 30/70 and 48/52) compositions adopting different weaves--plain. twill. hopsack and satin. Blends with higher

vikcose contents showed greater combined swelling and relaxation shrinkages on treatment with distilled water and alkaline

sq!utiol1s. On the other hand. blends with higher polyester contents exhibited greater combined relaxation and swellingshrinkages on being subjected to dry heat. Weaves with longer floats and fewer interlacements showed grea'u:r shrinkage

cOJnparcd to other weaves.

Fabric~ show dimensional changes at various stages ofproces~ing and tailoring. In wet processing, thestability offabrics is one of the main factors with whichthe manufacturers are concerned. Different fabrics

undergp shrinkage to different extents. A residualshrink"ge of 1-2 % for a finished fabric is permissible,and is !tolerable; any shrinkage beyond this level isliable ~o cause problems, the type of the problemdepenciling on the end use of the fabric. Thedimensional changes resulting in a fabric should bepredictfible, and if possible they should be controllableby any lof the methods available to the satisfaction ofthe consumer. Shrinkage is the linear contraction offabric expressed as percentage of the originaldimensions. Relaxation shrinkage results from therelease of latent strains and swelling shrinkage iscaused by fibre swelling for which complex fabricinteractions are responsible. Therl11al shrinkage issynonyjrnous with relaxation shrinkage.

The 'objective of this study was to ascertain themannet in which dimensional changes occur in a wide

range qf fabrics, including slack weaves like satin andtwill abd the more compact ones like hopsack andplain. The shrinkage occurring in the fabrics after wettreatments was noted. Various blends of polyester and

viscose? viz. 15/85, 30;70 and 48/52, in the above­mentiored fOClrweaves were taken and their shrinkagebehavi0ur was studied under different conditions in

respectlof pH, temperature, dry heat and duration andnumber of treatments. The fabric samples were notsubjected to agitation during treatment. This madetheir evaluation easier.

Materillis and Methods

Prepr:maion of the samples-Polyester fibre (15 kg)

42

of 1.5 denier, length 51 mm and tenacity 4.5 g/denier,and viscose (22 kg) of the same denier, but of length 54mm and tenacity 2.5 g/denier were taken. Threemixings with different percentages of polyester andviscose, viz. 48/52,30;70 and 15/85, were made. From

these mixings, yarn was prepared through thesequential stages of scutching, carding, draw frame(two passages) simplex and ring spinning. For preparingsuitings, theyarn was doubled through cone winding,parallel cheese winding, twisting on the doubler andthen cone winding again. This yarn, with the help of asectional warping machine, was converted into threebeams of warp, woven in three stages, for the threeblends on a plain loom, with negative let-off.

Fabric samples were prepared from the differentpolyester/viscose blends in different weaves-plain,twill, hopsack and satin. The other parameters whichotherwise normally affect shrinkage were keptconstant as in a simple control experiment.

(i) All the three fabric samples were prepared on thesame sequence of machines to eliminate the machine tomachine variation.

(ii) All the yarns produced had the same number ofturns per inch.

(iii) The nominal count for all the three yarns waskept the same (single 48-Z doubled 48/2-s).

(iv) Reed-pick in all the fabric samples and alsowithin a sample was the same throughout (72 x 72nominal).

It is well established that weaves with longer floatsand fewer interlacements are not much disturbed byfibre and yarn swelling. To have an idea of themagnitude of this effect of weaves upon fabric

shrinkage, the following four weaves were adopted:

SHARMA et af.: SHRINKAGE OF POLYESTER!VISCOSE BLEND FABRICS

plain, twill-2/2, 4-thread satin and 2 x 2 hopsack. Thefabrics were subjected to the following tests:

(1) The samples were dipped in distilled water fordifferent time intervals (5, 10, 30 or 45 min).

(2) The samples were immersed in water at different

temperatures (40, 60, 80 or 95°C) for a fixed period of 40mm.

(3) The samples were subjected to dry heat at 100,200 or no°c in a conditioning oven for 4 sec toproduce thermal shrinkage in the loose condition.

(4) The samples were dipped in alkaline and acidicsolutions of pH 4, 6, 8 or 9 for 20 min. Alkalinesolutions were made with caustic soda, while acidicsolutions were made with acetic acid.

(5) The samples were given repeated wettingtreatments in ,distilled water, the duration of each

treatment being 5 min; the progressive shrinkage wasmeasured. The conditions chosen match the ones in

commercial practice.The specimens were produced as per the standards

laid down in the B S Handbook. The fabric was woven

in 91 cm width, leaving 10 cm from each selvedge.Samples of 25 x 25 cm size were cut and then markedwith the help of a template of 20 x 20 cm. Care wastaken to mark along the threads, warp and weft way,with a microtip pen using unwashable ink. Prior tomarking, the samples were allowed to attainequilibrium in standard atmosphere (R H 65~;' andtemperature 270 ± 2°C) for 24 hr. All measurementswere made under atmospheric conditions.

Results and Discussion

Efject of dry heat-It is seen from Fig. 1 (A-D) thatblends with a higher proportion of polyester undergogreater shrinkage. This is possibly related to thethermoplastic nature of the polyester fibre. According

to Hearle1, at elevated temperature, the bonds betweenthe molecular chains get weakened and the originallystrained molecules on processing settle down to theposition of least strain; this results in shrinkage. Thisdoes not happen with viscose, which is notthermoplastic. Consequently, blends containing moreof polyester show higher resultant shrinkage. Increasein temperature from 200° to no°c causes an unusualincrease in the extent of shrinkage. The softeningtemperature of polyester is 2l0°C and. the. softeningoccurring when this temperature is crossed adds to themagnitude of shrinkage 'caused. Among the variousweaves, hopsack undergoes maximum shrinkage andplain weave, the minimum.. Satin and twill weaves lie inbetween these two, satin exhioiting slightly highershrinkage. Thus, weaves with longer floats and fewerinterlacements suffer higher shrinkage.

Efject of pH-Cellulosic fibres, viscose for example,swell more in alkaline media. Harwood2 investigated

this behaviour in detail. At higher alkalinity, theswelling is more and hence the shrinkage is more in thecase of blends containing more of viscose. Alkalinityhas negligible effect on the shrinkage behaviour ofpolyester. Acidic pH has little effect on any of theblends. In the alkaline range, the magnitude ofshrinkage increases continuously with increase inalkalinity. The 48/52 blend shows minimum shrinkageand the 15/85 blend, the maximum shrinkage (Fig. 2).As for the weaves, here too, hopsack shows themaximum shrinkage, and plain weave the least, withsatin and twill lying in between. In other words, weaveswith longer floats and fewer interlacements undergogreater shrinkage.

Ejfect of temperature of washing-During wetprocessing, the fabric is repeatedly dipped in hotsolutions and this causes shrinkage. The testsconducted in the present study simulate this treatment.It is seen from Fig. 3 that the 48/52 blend exhibitsminimum shrinkage initially at temperatures of 40°and 60cC, but there is a marked increase.in the extent of

shrinkage at higher temperatures (800 and 95°C). Thecurves for the 30/70 blend lie haphazardly in betweenthe curves for the 48/52 and 15/85 blends. The 15/85blend undergoes the maximum shrinkage. This isobviously due to the swelling shrinkage of viscosepresent in high proportion in this blend. At highertemperatures, the polyester as well as the strains in the

viscose get relaxed, ..yhereby the extent of relaxationshrinkage is the same. The two add up in a complexmanner to increase the net shrinkage. The relaxationand swelling shrinkages exhibited by the 48/52 blendare by no means greater than those exhibited by the 15/85 blend. Among the different weaves tried, those withlonger floats are more free to get compact due to theirloose structure, and hence they shrink more. Thistallies with the observation of Collins3. On the other

hand, weaves with more interlacements like plainweave are already compact and tend to undergo lessershrinkage. The combined effect of these twobehaviours results in greater shrinkage in hopsack andlesser shrinkage in satin and twill weaves, while theleast shrinkage is exhibited by fabrics in plain weave.

Effect of soaking in distilled water at roomtemperature-It is seen from Fig. 4 that with increase inthe duration of soaking, there is negligible increase inshrinkage in the case of the 48/52 blend. On the otherhand, the 15/85 blend shows steep rise in shrinkage.This can be attributed to the high viscose content of the15/85 blend, which is responsible for its extensiveswelling through moisture regain. Polyester witn very

low moisture regain undergoes very little shrinkage.This is in conformity with the explanation given bySnowden and Wagh4. Relaxation shrinkage in all the

43

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INDIAN J TEXT RES, VOL. 8, JUNE 1983

three blends is of approximately the same magnitude

and hence the 15/85 blend which undergoes largeswelling shows the maximum shrinkage and 48/52, theminimum shrinkage; the 30/70 blend lies in betweenthe twq.

As for the weaves the same trend as in the earlier

experiments is observed here too.Effect of repeated treatments-Fabrics are often

subjected to repeated washing during manufacture andend use. In the first washing-drying treatment, there is

considerable swelling followed by shrinkage and localstrains get locked in the structure. These disappear inthe subsequent drying-washing cycles. These strainsare proiminent at places in the yarn where sticking hasoccurred. When the yarn dries, free spaces develop,allowing for accommodation between fibres; a lessstrained and more shrunk structure results when the

cloth is wetted again. Agitation again helps overcomethese :local strains, promoting shrinkage. This

explanation is due to Collins3, later confirmed byCryer5.

It is seen from Fig.5 that the shrinkage is minimumin the case of the 48/52 blend and maximum inthe case of the 15/85 blend. The reason for this is the

greater swelling undergone by viscose. It is alsoobserved that shrinkage is more in the first four cycles;thereafter, the rate of increase in shrinkage due torepeated treatments seems to become constant orstarts decreasing. The different weaves show the same

tTend as in the preceding tests.Conclusions

(1) In acidic and alkaline baths, blends with a highercontent of viscose undergo greater shrinkagecompared to the ones with higher polyester content.

(2) Heat treatment causes greater shrinkage inblends with higher polyester content.

(3) Weaves with longer floats and fewer interlace­

ments ex.hibit greater shrinkage for a given fabric.

71. BLEND 48/52 (A)2 BL EN D 30170

6~ 3. BLEND 15/85

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Fig. 5-Area shrinkage on repeated treatment5 in distilled water [(A) Plain weave, (B)Hopsack weave, (e) Twill weave, and (D) Satin]

46

SHARMA et at.: SHRINKAGE OF POLYESTER/VISCOSE BLEND FABRICS

(4) Most of the shrinkage occurs in the first fourdippings; there is negligible or no shrinkage beyond thesixth dipping.

(5) With increase in the temperature of the dippingbath, the extent of shrinkage increases for all theblends; the increase is more prominent in blends withhigher viscose content.

(6) On soaking the fabrics in distilled water, bulk ofthe shrinkage occurs in the first 45 min,

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

Director, T.I.T., Bhiwani, for permission to publish thispaper. Their thanks are also due to Sarvashri O.P.Jaiswani, K.C. Vaid and Pankaj Sharma for preparingthe samples.

References

I Hearle J W S & Morton W E, Physical properties of textile jibres.(Textile Institute-Butterworths, Manchester & London) 2ndEdn, 1975,220.

2 Harwood F C,J Text lnst, 27 (1936) 333.

3 Collins G E,J Text lnst, 30 (1939) 46.

4 Snowden D C & Wagh A S, Text Mj;', 94 (1968) 422.5 Cryer N, J Text lnst, 26 (1935) 331.

47