In<lian Journal of Textile Research

Vol. 7, June 1982, pp. 31-35

Mercerization of Cotton-Man-made Cellulosic Fibre Blends and Its Influenceon Yarn Quality

K P R PILLA Y & N RAMANI

South India Textile Research Association, Coimbatore 641014

Received 18 May 1982; accepteiJ 29 June 1982

The response to mercerization of 2/60s and 2/80s yarn spun from cotton and regenerated cellulosic fibre blends of viscose,Grasilene, Vincel and Koplan has been inevestigated. It is shown that cotton-cellulosic fibre blends can be mercerized andstretched satisfactorily without significant deterioration in their tensile properties, ifhot 8% solution of sodium chloride is usedas the rinsing medium to remove the alkali. Slack mercerization reduces tenacity and increases breaking elongation; however,stretching after mercerization increases the tenacity and lowers the breaking elongation of cotton-man-made fibre blends. Purecotton yarns withstand higher degrees of stretch and exhibit higher tenacities than man-made fibres, even though they havelower tenacities in untreated condition. Studies on folding abrasion showed that slack mercerization improves abrasionresistance and stretching reduces it.

It would appear on first thought that there is noadvantage in mercerizing rayon, for it alreadypossesses a high lustre and greater affinity for dyestuffsthan even mercerized cotton. However, there are manyte~tile materials which are mixtures of cotton andrayon, either in stripes or in common cotton warp andrayon weft. Many textile mills find it advantageous toblend 10-15% staple fibres in their fine count mixingsto improve their spinning performance and to reducecost. Such goods are frequently mercerized to bring thelustre of cotton nearer to that of rayon and also toreduce as far as possible the disparity in the affinity ofdyestuffs.

Regenerated cellulose fibres are much less resistantthan cotton to the action of caustic soda and the

normal mercerizing process is likely to bring about lossin weight due to dissolution of the material and thegreater swelling which take place when these fibres arewashed 1• Often the extent of damage depends on thetyPe and amount of man-made fibres in the yarn andthe yarn count. To a large extent, the strength of

mercerized yarns is governed by the extent ofshrinkage and stretching the fibres undergo during theprocess and the method of washing away the alkali.Meagre quantitative information on these aspects isavailable in literature.

The objectives of this study were: (i) to determine theoptimum conditions under which cotton-man-madecellulosic blends can be mercerized, and (ii) to study theinfluence of mercerization and degree of stretch on thetensile and abrasion resistance of blended yarns.

Materials and Methods

Materia/-Four man-made fibres, viz. (1) Viscose,(2) Vincel (high wet modulus fibres), (3) Grasilene (highperformance fibre)•.and (4) Kaplan (polynosic fibre)were used. These fibres were blended at the drawframestage with combed slivers of two cottons (MeV 5 andVaralakshmi) to spin 60s and 80s yarn respectively.The fibre characteristics of these fibres are given inTable 1.

Table I-Fibre Characteristics of Cottons and Man-Made Fibres

Fibre type LengthFineness StrengthBreakingMicronaireMaturitymm

denierat3mmelongationvaluecoefficient

g/tex%

Viscose (nominal length)

38.01.517.312.34.2Vincel (nominal length)

38.01.528.413.84.2Grasilene (nominal length)

38.01.225.612.93.4Koplan (nominal length)

38.01.232.18.93.4MCU-5 (effective length)

33.820.56.53.50.75Varalakshmi (effective length)

36.820.78.03.30.86

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INDIAN J TEXT RES, VOL 7, JUNE 1982

All the man-made fibres, except viscose, are strongerthan the cottons. Koplan had the highest tenacity (32.1g/tex) and the lowest breaking elongation (8.9%)among the man-made fibres.

Four blend proportions (12.5, 25, 37.5 and 50%)were used. The yarns were doubled with normaldoubling twist and tested in the untreated andmercerized states for tensile and abrasion resistancecharacteristics.

Methods-Mercerization was carried out at room

temperature (27°C) using caustic soda solution of56°Tw concentration. Well parallelized yarn bundleswere treated in the alkali for 6 min. Swelling andstretching of the samples to different degrees was doneon a special frame fabricated for the purpose. Theframe with the yarn was immersed vertically in atrough containing alkali for swelling and stretching tothe desired extent. All the yarn samples weremercerized under four different conditions, viz.(1) slack state, (2) slack mercerized and stretched to97% of the normal length, (3) slack mercerized andstretched to normal length, and (4) slack mercerizedand stretched to 3% over the normal length.

To reduce tendering of yarn due to the high swellingof man-made fibre components in the alkali and arriveat optimum rinsing conditions, the following rinsingbaths were tried for preliminary studies.

(1) Cold water (27°C)(2) Hot water (70°-80°C)(3) 8% sodium chloride solution at 70°-80°C(4) 20% sodium chloride solution at 70°-80°C(5) 10% sodium carbona,te solution at 70°-80°C

The mercerised samples after thorough washingwere scoured in 1% sulphuric acid solution for 5 min,washed in tap water and then finally in distilled watertill the wash liquor was neutral to litmus. They were

then squeezed and dried gently in warm air at 50°C andconditioned for testing.

Tensile tests-The Uster single yarn strength testerwas used to study the mean breaking strength,elongation and CV% of breaking strength of the rawand mercerized yarn samples.

Folding abrasion test-Folding surface abrasion testwas carried out with the help of a customs typeuniversal abrasion tester. Parallel strands of yarn of 2in width and 8 in length and having 48 threads per inchwere prepared with the help of a blackboard windingmachine. The folding abrasion was given to the testspecimen with the edge of the flexing bar. The numberof abrasions required to wear out the specimen wasnoted in each case. Six specimens were tested from eachsample.

Results and Discussion

Effect of rinsing conditions-Data pertaining to theeffect of different rinsing operations after merceri­zation on the tensile characteristics of cotton­

Grasilene and cotton-viscose blended yarns are givenin Table 2. It is seen that the reduction in strengths ofslack mercerized yarns are minimum when hotsolution of sodium chloride (8%) is used as the rinsingmedium; probably the hot solution of salt minimizedthe swelling of the man-made fibre component.

Breaking strength-The tensile characteristics ofpure and blended yarns in the untreated condition aregiven in Table 3. It is seen that 100% viscose yarn isabout 35% weaker than 100%cotton yarn in both thecounts. Pure Vincel, Koplan and Grasilene yarns havealmost similar or slightly higher tenacities than cottonyarns. Thus, the differences in tensile characteristics offibres are to some extent reflected in yarncharacteristics. The tensile strength of cotton-viscoseblends decreases progressively as the proportion of

Table 2-EfTect of Rinsing Conditions after Mercerization on Yarn Strength

Mercerizing conditions Rinsing bathMCU-5/GrasileneMCU-5jViscose75:25-2/60s

75:25-2/60s

Tenacity

ElongationTenacityElongationg/tex

%g/tex%

Control untreated

15.85.414.235.0

Cold water

12.830.412.024.6Hot water

13.024.413.621.6Slack mercerized

Hot 8% sodium chloride soIn15.323.613.819.6

Hot 20% sodium chloride soln

15.423.013.819.1

Hot 10% soda ash soln

15.323.113.520.0

Cold water

18.86.217.06.1Hot water

19.16.317.26.0

Mercerized and stretched to normal lengthHot 8% sodium chloride soln19.96.017.55.9

Hot 20% sodium chloride soln

19.96.117.45.9

Hot 10% soda ash soln

19.85.317.36.3

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PILLAY & RAMAN!: MERCERIZATION OF COTTON-MAN-MADE CELLULOSIC FIBRE BLENDS

Table 3- TensileCharacteristicsof Untreated Samples

Viscose

Breakingelongation

%

Koplan

Tenacityg/tex

Breakingelongation

%

Vincel

Tenacityg/tex

Breakingelongation

%

Grasilene

Tenacityg/tex

Breakingelongation

%

Tenacityg/tex

Cotton-staplefibre blend

composition

2/60s Count

0:100 12.010.317.19.018.59.818.26.050:50

12.39.815.66.214.96.317.75.2

62.5:37.5

13.25.015.85.715.36.517.45.475:25

14.25.015.85.415.76.518.25.587.5: 12.5

15.54.517.85.516.75.9llU5.9100:0

18.35.018.35.018.35.018.35.0

2/80s Count0:100

11.29.317.28.517.76.318.55.750:50

13.76.716.47.317.27.818.25.562.5:37.5

13.96.016.66.617.07.317.25.9

75:25

15.77.018.17.016.57.317.46.6

87.5:12.516.76.418.57.018.87.218.16.8

100:0

17.19.217.19.217.19.217.19.2

viscose increases; it is minimum for 100%viscose yarnin both the counts. On the other hand, in the case ofGrasilene, Vincel and Koplan blends, the strength firstdecreases and then shows a tendency to increaselinearly to the strength of the more extensible man­made fibres. The minimum strength occurs when theproportion of man-made fibre is about 50%.

When the component fibres in a yarn have differentbreaking extensions, fibre slippage plays an importantrole in determining yarn strength. This may explain thelower breaking strength of cotton-viscose blendedyarns. Cotton-Koplan blend shows very littledeterioration in strength with increase in theproportion of Koplan. Since the breaking elongationand strength of Koplan are comparable to those ofcotton, the blends of these fibres do not show much.variation in strength with increasing percentage ofKoplan.

The influence of mercerization on the tensilecharacteristics of different man-made fibres and their

blends are given in Table 4. When yarns are slackmercerized, in general, their tenacities are reduced, but100%viscose yarn showed a small increase in tenacityof about 18.5% in 2/60s and a decrease of 30.3% in 2/80s count. The percentage drop in tenacity forGrasilene, Vincel and Koplan yarns was 26.9,33.5 and25.7'loin 2/60s yarn. The corresponding decrease for 2/80s yarn was 34.3,10.2 and 26.5% respectively. MCU­5 and Varalakshmi cotton yarns when slackmercerized showed a reduction in tenacity of 3.8 and32.7% for 2/60s and 2/80s count respectively.

The blended yarns also show a reduction in tenacityon slack mercerization, the percentage reduction

varying between 0.5 and 10:9% for 2/60s and between10.9 and 17.6% for 2/80s count. In general, viscose­cotton blends show the minimum reduction and

Koplan-cotton blends exhibit the maximum reduction;the other fibres have intermediate values. The tenacityof slack mercerized blends in general decreases as thepercentage of man-made fibre component in theblends increases, but the percentage drop in tenacityon slack mercerization does not show any specifictrend with increase in the proportion of man-madefibre components.

The fall in strength as a result of mercerization hasbeen attributed to decrystallization and theconsequential increase in disorder in the structure offibres. In the case of cottons, in addition todecrystallization, there is a small improvement inorientation due to the deconvolusion of fibres as aresult of swelling. Viscose being not a highly orientedfibre, the extent of disorder produced as a result ofswelling may be expected to be less than that producedin Vince!, Koplan and Grasilene fibres which are betteroriented. This may account for the greater reduction instrength in Grasilene, Vincel and Koplan than inviscose. Moreover, the greater swelling that may beexpected in viscose on mercerization may be impartinggreater lateral pressure on fibres, thus influencing theirresistance to slippage with consequential improvementin yarn strength.

Stretching after mercerization improves the strengthof both pure and blended yarns having differentproportions of man-made fibres. In the case of 2/60syarn, for 100%cotton and viscose fibres, the tenacity at3% stretch was greater than the tenacity of untreated

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INDIAN J TEXT RES, VOL 7, JUNE 1982

Table 4-Tensile Characteristics of Mercerized Samples

Composition of

Slack mercerizedStretched to nominalSlack mercerizedStretched to nominalcotton-man- madefibre blend

TenacityBreakingTenacityBreakingTenacityBreakingTenacityBreakingg/tex

elongationg/texelongationg/texelongationg/texelongation%

%%%

2/60s Count Cotton/ViscoseCotton/Grasilene

0:10014.213.816.86.012.513.416.69.5

50:50I \.014.312.65.214.819.115.66.0

62.5:37.512.115.514.94.815.419.817.96.2

75:2514.714.817.55.113.318.319.96.3

87.5:12.516.414.719.95.017.516.720.86.1

100:017.518.721.75.017.618.721.75.1

Cotton/KoplanCotton/Vincel

0:10013.611.216.26.812.320.716.911.1

50:5014.815.017.85.612.818.115.05.5

62.5:37.516.113.018.85.214.618.517.36.2

75:2516.515.820.15.415.419.318.76.3

87.5:12.516.317.02\.85.716.317.019.27.3

100:017.618.721.75.017.618.721.75.7

2/80s Count Cotton/ViscoseCotton/Grasi1ene

0:1007.814.39.410.311.317.015.87.1

50:5011.215.013.15:315.116.918.98.1

62.5:37.512.315.715.04.913.818.016.96.2

75:2514.118.215.35.615.019.516.36.7

87.5:12.516.116.018.55.015.019.219.05.7

100:0I \.518.218.010.011.518.215.710.0

Cotton/Koplan

Cotton/Vincel0:100

13.611.516.56.315.916.219.07.850:50

15.414.317.26.614.016.816.26.262.5:37.5

13.9I\.917.95.814.117.616.56.475:25

14.910.718.46.013.119.116.86.587.5:12.5

14.216.619.56.218.017.019.06.4100:0

1\.518.215.710.0I \.518.215.710.0

yarn by 21.9 and 46.1 % respectively. But in other man­made fibres, the yarn tenacity at 3% stretch was 2-11 %lower than the tenacity of untreated yarn. Mercerizedand stretched blended yarns showed 9.3-27.6%increase in tenacity compared to untreated yarn. Thepercentage improvement in strength as a result ofmercerization and stretch was maximum for viscose

yarn. Vincel yarn showed the maximum reduction(11.4%) in tenacity as a result of mercerization andstretching. The blended yarns showed increase intenacity ranging from 9.3 to 27.6% over the untreatedyarns on mercerization and stretching. The maximumimprovement (27.6%) was for viscose and theminimum (9.3%) for Koplan.

The influence of mercerization and stretchrng to

some extent depends on the count of yarn. In 2/80s,although the general trend in the changes in tenacities

34

was similar, stretching of mercerized yarns to 3%brought about a reduction in tenacity compared to theuntreated yarn. The percentage increases in tenacity inblends were also on an average lower in 60s. In general,man-made fibres could not be stretched to the same

extent as cotton and in actual practice it was founddifficult to stretch mercerized blends beyond 3%.

Yam e/ongation- Values of breaking elongation of2/60s and 2/80s pure and blended yarns in theuntreated condition are given in Table 3. The breakingelongation of untreated yarns from man-made fibresvaries from 6% for Koplan to 10.3% for viscose in the2/60s count. The corresponding values for 2/80s yarnare 5.7 and 9.3%. Thus, Koplan shows the lowestbreaking elongation and viscose the highest. Foruntreated cotton yarns, the breaking elongations are5% for MCU-5 and 9.2% for Varalakshmi in the 2/60s

PILLAY & RAMANI: MERCERIZATION OF COTTON-MAN-MADE CELLULOSIC FIBRE BLENDS

and 2A80scount respectively. In general, in the blendedyarns" the breaking elongation increases as theproportion of man-made fibres in the blend increases.In Koplan/cotton yarns, this tendency is not very clear,since the breaking elongations of cotton and Koplanfibres are more or less similar.

Slack mercerization increases the breakingelongation compared to that in the untreated state(Table 4), the increase being 34% for viscose and111.2% for Vincel in 2/60s count; the correspondingvalues for 2/80s count are 53.8 and 157.1%. Cottonyarns show an increase of 274% for 2/60s and 297.8%for 2/80s count. The increase in elongation is minimumfor viscose and maximum for Vincel yarns in both thecounts. In blended yarns, the increases in breakingelongation are much higher than those in pure man­made fibre yarns. In general, 2/80s blended yarns showlower increase in elongation (116.9-114.3%) than 2/60s(166.7-224.5%).

Stretching after mercerization reduces the breakingelongation, the percentage reduction varying with thecount, blend proprotion and type offibres in the blend.Generally, when yarns are stretched to normal lengthafter mercerization, the breaking elongation is verynearly equal to the untreated yarn elongation, butwhen they are stretched to 3% over the normal length,there is a further reduction in the breaking elongation.In general, the elongation on stretching reduces by26.6152.7%of the slack mercerized yarn elongation in2/60s and by 27-70.4% in 2/80s. In blended yarns, thereduction ranges from 62 to 69% in 2/60s and from 51to 68% in 2/80s. In general, the different man-madefibre yarns and their blends do not show any specifictrend in their response to stretching.

Folding abrasion resistance-In the untreatedcondition, pure 2/60s viscose yarn showed the lowest(48) and Vincel, the highest (77) abrasion resistance.Grasilene and Koplan yarns showed intermediatevalues of 60 and 65 respectively. The abrasionresistance of MCU-5 cotton yarn (49) was very nearlythe same as that of viscose Slack mercerizationimproved the abrasion resistance by 20-40% in mostcases, probably due to the considerable increase inbreaking elongation of yarns on mercerization. Butmercerization followed by stretching reduced theabrasion resistance and in general the 3% stretchedyarns showed the minimum value, which was about30% lower than that for the slack mercerized yarn. Thereduction in folding abrasion resistance on stretchingmay be attributed to the reduction in breakingelongation and the consequential increase in thestiffness of yarns.

The folding abrasion resistance of blends showed lotof variation, but, in general, the abrasion resistance of

blends increased with increase in the proportion ofcotton in the blend. The behaviour of mercerized andmercerized and stretched blends was similar to that ofpure fibres. Here again, slack merct:rization improvedthe abrasion resistance and stretching aftermercerization reduced it significantly. Increase in yarncount from 2/60s to 2/80s reduced the folding abrasionby about 35%. The general trend in the changes inabrasion resistance with mercerization was the same inboth the counts. In addition to tensile characteristics,changes in the elastic characteristics of yarns as a resultof mercerization, blend variation, etc. might haveinfluenced the abrasion resistance to some extent.

Further studies are required to explain completely theresponse of untreated and mercerized blends to thistest.

Summary and Conclusions(1) Man-made cellulosic fibres and their blends with

cotton can be mercerized successfully withoutdeterioration in their tensile characteristics, if hotsodium chloride solution (8%) is used as the rinsingmedium.

(2) The tenacity values of blends of cellulosic man­made fibres with cotton after mercerization and stretch

are significantly higher than those in the untreatedstate.

(3) In general, the tenacity of blended yarnsincreases and breaking elongation decreases as theproportion of cotton in the blend increases.

(4) Stretching after mercerization, in general,increases the tenacity and lowers the breakingelongation.

(5) Yarns from viscose fibres have the lowest andVincel fibres, the highest folding abrasion resistance.

(6) Folding abrasion of blends increases as theproportion of cotton in the blend increases.

(7) Slack mercerization improves the abrasionresistance significantly and stretching after merceri­zation reduces it.

AcknowledgementThe authors wish to acknowledge the valuable

guidance given by Shri K. Sreenivasan, Director,SITRA, during the progress of this work. They are alsoindebted to Shri K.S. Shankaranarayana for spinningand supplying the yarn samples used in this study. Theassistance of Shri R. Rajendran in the experimentalwork is also gratefully acknowledged.

References

1 Marsh J T, Mercerizing (Chapman and Hall Ltd, London) 1951,179-99.

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