Indian Journal of Textile Research

Vo\.9, Maroh 1984, pp.8-12

A Co~parative Study of the Response to Mercerization of Open-end and RingSpun Yarns

K P R PILLA Y- & B S NAGARAJA t

South India Textile Research Association, Coimbatore 641014

Received 18 October 1982; accepted 5 December 19~3

1jhe effect of mercerization on the tensile properties, lustre, shrinkage and folding abrasion resistance of open-end and ringspun yarns has been investigated. It is observed that the reduction in the strength of OE spun yarn is reduced appreciably bymercerization. Open-end spun yarns show lower lustre and shrinkage on mercerization compared .to ring spun yarns. Ingeneral, yarn twist increases the folding abrasion resistance of open-end and ring spun yarns, while mercerization andstretching reduce it.

Mercerization is employed commonly for improvingcertain physical properties of cotton fibres and yarnslike dyeability, lustre, tensile strength, etc. Theefficiency'of this treatment and the uniformity of theI .products manufactured are, however, mfluencedlargely by the geometry and structure of the yarnsused.

Open-epd (OE) spun yarn has a structure that issignificantly different from that of ring spun yarns.Consequently, the influence of mercerization andstretching on the physical properties of these two yarnsmay be dpected to be different.

Although considerable work 1 -3 has been carriedout on the influence of mercerization on the physicalproperties of cotton fibres and yarns, reports on thecomparative response of open-end and ring spun yarnsto mercerization and stretching are rare in thej

literature. Recently, Hunter and Andrews4 studied the.response Iof open-end and ring spun yarns tomercerization by the caustic soda and ammoniatreatments. The mercerization treatments were carriedout in commercial machines and it was observed thatammonia treatment causes greater increase in tenacityand more reduction in breaking elongation thancaustic soda treatment. Strictly speaking, the results ofthese treatments are not comparable, as the conditionsof stretch in the two treatments were not the same.Also, the extent of stretch given during the caustic sodatreatmentl has not been indicated. Apart from tensilestrength and elongation, no other physical characteris­tics of the yarns were determined by Hunter andAndrews.

-Present address: Consultant, R&D Department, Lakshmi MachineWorks Ltd, Coimbatore 641020tManager, Govt Spun Silk Mills, Chennapatna, Karnataka.

8

The aim of the present investigation was to study theinfluence of (i) mercerization and stretching on thephysical properties, such as tensile strength,elongation, stress-strain relationship, lustre, flexabrasion and shrinkage, of open-end and ring spunyarns, and (ii) structural differences in yarns on theirresponse to mercerization.

Materials and MethodsSeven cottons, varying widely in fibre properties,

were chosen and spun into OE and ring spun yarns of14s count at twist for maximum strength. Someselected cottons were also spun to different counts andtwist multipliers to study the effect of twist and counton the yarn properties. Yarns from two cottons werealso doubled using a doubling TPI of about 0.7 of thesingles twist for lustre measurements. The fibreproperties of the cottons used and the counts spunfrom them are given in Table 1.

Table I-Fibre Properties of Cottons Used and CountsSpun.

Cotton 50% spanFinenessTenacityMaturity Countlength

at 1/8 incoeffi-mm

gaugecient

g/texCalifornia

15.43.5530.40.7914s9030 G

13.54.2818.20.8914sMenoufi

14.73.0529.10.8214sGiza 45

13.73.1535.90.8414sLakshmi

10.23.5515.30.7214sArwanza

12.43.9017.60.7814sCJ 73

10.75.1020.60.9314sC04

11.93.9516.40.8314s,36s

PILLAY & NAGARAJA: RESPONSE TO MERCERIZATION OF OPEN-END & RING SPUN YARNS

Mercerization and stretching-Mercerization wascarried out at room temperature (27°C) using causticsoda solution of 56°Tw concentration with 1% wettingagent. Well parallelized leas were treated with thealkali solution for 6min. Swelling and stretching of theyarns to different degrees were done on a special framefabricated for the purpose. The frame with the yarnmounted on it was immersed vertically in a troughcontaining alkali for swelling and stretching to thedesired extent. All the yarn samples wer~ mercerizedunder five different conditions, viz. (1) slack state, (2)slack mercerized and stretched to 97% of the normallength, (3) slack mercerized and stretched to normallength, (4) slack mercerized and stretched to 3% overthe normal length, and (5) slack mercerized andstretched to 5% over the normal length.

The mercerized samples were washed thoroughlyfirst with hot water and then with tap water anddistilled water till the wash liquor was neutral toIitmus. They were then dried in warm air (50-60°C)andconditioned under standard atmospheric conditionsfor testing.

Determination of stress-strain properties-Thestress-strain properties of 14sOE and ring spun yarnswere determined on the Instron tensile tester. A gaugelength of 20 cm was used. The specimen was extendedat 20 cm/min and a chart speed of 100 cm/min wasused. From the individual tensile properties, theaverage stress-strain curve was computed.

Determination of single yarn strength andelongation-The Uster single yarn strength tester wasused to determine the breaking strength, elongationand eV% of breaking strength.

Measurement of lustre-The lustre, defined as thereflectance at 45° with illumination at 45° divided byreflectance at 45° with illumination at right angles tothe yarn surface, was measured on a lustre meter. Thiscontrast ratio was used as a physical index of lustre.Pads of yarn wound on cardboards of 2 x 2 in sizewithappropriate wraps/in (cover factor, 40) were used forlustre measurements.

Folding abrasion test-The flex abrasion resistanceof the yarn samples was determined using a customstype Universal abrasion tester. Parallel strands ofyarns (2 in wide and 8 in long) having 48 threads/inwere prepared with the help of a blackboard windingmachine. Folding abrasion was given to the testspecimen with the edge of the flexing bar. The numberof rubs required to wear out the specimen was noted ineach case. Six specimens were tested from each sample.

Shrinkage of yarn samples-- The shrinkage of OEand ring spun yarns in 56°Tw caustic soda solution atnoe was determined after swelling the samples for 6min. The yarn samples were first wound on a longblackboard with the help of an appearance board

winding machine. Two lines were drawn 25 cm aparton the yarns with marking ink. Parallel bundles of yarnhaving 2 in width were then prepared by fixingadhesive tapes at both ends of the board. The bundlesthus prepared were slack mercerized in a troughcontaining alkali. They were then washed thoroughly,dried and conditioned under standard laboratoryconditions. The percentage change in length as a resultof mercerization was taken as a measure of shrinkage.

A . f 156 d d' . d' dtenSIOn 0 -- g was use urIOg wlO 109 ancount

measurement of the final length.

Results and Discussion

Single yarn tenacity and elongation-The values ofbreaking tenacity, elongation and eV% of breakingstrength for the untreated and mercerized OE and ringspun yarns from five cottons are given in Table 2. Inthe untreated state, the tenacities of the ring spun yarnsare higher than those of the OE spun yarns, thepercentage increase ranging from 30.8 for Arwanzacotton to 54.6 for 9030 G cotton, the average being39.8%.

When OE and ring spun yarns are slack mercerized,the tenacity of both the yarns decreases, but thepercentage reduction is much higher for ring spunyarns (32 - 39%)as compared to that for OE spun yarns(10 - 20%). The difference between tenacities of ringand OE spun yarns, which is minimum (4.9%) in theslack mercerized state, increases slowly on stretching,but even at the maximum degree of stretch, thereduction (30.9%) is lower than that in the untreatedcondition (39.8%). Stretching after mercerizationincreases the tenacity of both the yarns progressively,but the increase is, in general, higher for OE spun yarns(2.6 - 25.9%) as compared to that for ring spun yarns(4.6 - 11.8%). T~e maximum increase in tenacity isobserved at 5% stretch for both OE and ring spunyarns.

The results in Table 2 indicate that mercerization ismore beneficial for OE spun yarns than for ring spunyarns. The disparities between OE and ring spun yarnsare reduced significantly on mercerization andstretching. These effects may be explained on the basisof the structure of the two types of yarn.

Due to the lower twisting tension and poor fibreorientation, OE spun yarns are more bulky than thecorresponding ring spun yarns. When these yarns areslack mercerized, there is greater penetration of alkaliand better swelling of fibres, leading to higher inter­fibre friction. Radhakrishnan 5 observed that longerfibres of cotton predominate as belts or wrapped fibresin OE spun yarns. These belt fibres shrink onmercerization and restrict the slippage of fibres during

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IINDIAN J. TEXT. RES., VOL. 9, MARCH 1984

Table 2-Single Yarn Tenacity and Elongation of OE and Ring Spun Yarns

OE spun yarn

Ring spun yarn-,0..-

Stretched to

Stretched totParameter

Untr-Slack Untr-Slack

eated

merce-Normal3% over5% overeatedmerce-Normal3% over5% overrized

lengthnormalnormal rizedlength

normalnormal

length

length lengthlength

Cotton, California; Count, 14sTenacity, g/tex

11.610.113.414.414.616.210.516.317.017.5

Breaking elongation,%

8.528.610.18.87.68.024.88.67.66.8

CV of break/ing strength6.78.68.17.47.210.612.610.612.710.8

Cotton, 9030G; Count, 14sTenacity, g/rex

9.98.711.311.311.415.510.215.416.216.2 ~-Breaking elongation,%8.933.08.57.47.56.929.910.57.77.2

CV of breaking strength

9.08.57.17.2r 7.911.315.69.48.611.4

Cotton, Menoufi; Count,14sTenacity, g/tex

13.912.115.616.016.118.611.917.319.020.8

Breaking elongation,%

8.331.211.08.78.37.126.18.47.76.2

CV of breaking strength

6.412.96.86.57.914.613.311.2II.l14.1

Cotton, Giza 45; Count, 14sTenacity, g/tex

12.911.614.414.815.318.111.016.719.119.9

Breaking elongation,%

9.128.89.88.47.87.628.28.58.06.3

CV of breaking strength

6.68.96.77.56.819.519.211.016.020.5

Cotton, Arwanza; Count, 14sTenacity, g/tex

II.79.411.5II.712.015.310.416.115.816.0

Breaking elo~gation,%

9.232.711.810.67.88.429.311.310.79.8

CV of breaking strength

6.07.45.87.25.68.913.18.08.513.7 ..l....

Mean tenacity, g/tex

12.010.413.213.614.016.710.816.417.418.1

Mean elongation,%

8.830.910.28.87.87.527.79.58.47.3

Mean CV or'breaking strength6.99.36.97.27.113.015.010.011.414.1

tensile tests and thus contribute largely to theenhancement of strength (Fig. I).

Open-en.d spun yarns show 0.5-2.0% higherbreaking elongation compared to ring spun yarns. Onslack mercerization, the breaking elongation of both

types of yarn increases, the percentage increase overuntreated yarn elongations being in the range 216 - 276

Fig. I-Belt fibres on open-end yarns

10

for OE spun yarns and 210 - 333 for ring spun yarns.Stretching after mercerization reduces the elongationin both types of yarn, but at all stages, the breakingelongation ofOE spun yarns is, in general, higher thanthut of ring spun yarns. As may be expected, the valuesof CV% of breaking strength for OE spun yarns arealways considerably lower than those for ring spunyarns. It does not show any consistent tendency toincrease or decrease with mercerization and stretching.But, in general, the values of CV% for slack mercerizedyarns are higher than those for mercerized andstretche\l yarns in both the cases.

Stress-strain properties of OE and ring spun yarns­The stress-strain curves for the untreated and

mercerized OE and ring spun yarns are shown in Fig. 2.It is observed that the breakages of OE and ring spunyarns are catastrophic in nature, i.e. the yarns showsudden drop in load to oractically zero at the breakingpoint. Due to the bulky nature of OE yarns, there ishigher extension when the yarns are stressed, but asthey get progressively compact, higher inter-fibrepressures are developed and the stress-strain curves tilttowards the stress axis. In the case of ring spun yarns,

PILLA Y & NAGARAJA: RESPONSE TO MERCERIZA nON OF OPEN-END & RING SPUN YARNS

Fig. 2-Stress-strain curves for open-end and ring spun yarns

this tendency IS not very well marked and the curvesare more linear.

, The two types of yarn present different pictures onslack mercerization. The initial modulus of OE spunyarn is higher than that of ring spun yarn, but the trendis reversed in the final stage where rupture occurs. Thevalues of the initial and final modulus for the untreatedand mercerized OE and ring spun yarns are given inTable 3. It is observed that in the untreated andmercerized and stretched conditions, ring spun yarnhas higher modulus and stretch than OE spun yarn.The modifications in structure as a result of stretchingafter mercerization are clearly brought out in thestress-strain curves of untreated and 5% stretchedsamples. The curves follow distinctly separate paths.Stretching results in increase in tenacity, initialmodulus and final modulus and decrease in breakingelongation. At 5% stretch, the differences in the pathsof the stress-strain curves are extremely small.

The results further indicate that when the cottonproperties are kept constant, the main tensileproperties of yarns are greatly influenced by thespinning processes and structure of the yarn.

Lustre of OE and ring spun yarns-The values oflustre for OE spun yarns are lower than those for ringspun yarns. Values of lustre index or contrast ratio of2/14s and 2/36s OE and ring spun yarns spun from CJ73 and CO 4 cottons in untreated and mercerizedconditions are given in Table 4.

Untreated OE yarns have on an average 3-4% lowerlustre compared to ring spun yarns. Slackmercerization reduces the lustre of both OE and ringspun yarns by 3-12%. Stretching after mercerizationimproves the lustre of both types of yarn. At 5%stretch, the lustre is maximum and is higher than thatfor untreated yarn. Even at this maximum degree ofstretch, OE yarns have lower lustre compared to ringspun yarns. There is a sudden drop in lustre in the caseof slack mercerized samples, probably due to theshrinkage of y~rn and the consequent irregularities(crimp) produced on the surface of fibres. This

3.04

2.63

2.86

3.34

1.33

1.28

1.471.34

Stretchedto 5% over

normal

length

2.15

3.24

1.401.19

Stretchedto normal

length

1.80

2.24

1.051.00

merce­rized

Slack

0.61

0.72

Cotton, CJ 73; Count 2/14s

1.17 1.13 1.241.13 1.08 1.23

1.11

1.191.14

2.12

Unt- Slackreated merce­

rized

Untreated

Stretched Stretched Stretchedto normal to 3% over to 5% over

length normal normallength length

14s OE spun yarn (California cotton)0.81 0.30 1.41 1.53

Parameter

Table 4-Lustre Index of OE and Ring Spun Yarns

Table 3-lnitial and Final Modulus of OE and Ring SpunYarns

waviness disappears on stretching and ~hefibre surfacebecomes smoother with better alignment of fibres tothe yarn axis. The lower lustre ofOE yarns may be dueto the arrangement of fibres on the yarn surface. Thehooked and criss-crossed nature of fibres and thepresence of belt fibres lower the lustre of OE yarns.

Shrinkage of 0 E and ring spun yarns-Data on theshrinkage of ring and OE spun yarns on slackmercerization at different twist multipliers are given inTable 5. It is observed that in both types of yarn, theshrinkage increases with increase in twist multiplier inthe beginning, but at the highest twist multiplier, theshrinkage shows a tendency to come down. Theprobable reason for this behaviour is that at high twist

Initialmodulus, g/tex

Final

modulus, g/tex

14s Ring spun yarn (California cotton)2.01 0.19 1.55 2.62

Table 5-Percentage Shrinkage ofOE and Ring Spun Yarnson Slack Mercerization at Different Twist Multipliers

Cotton CountRing spun yarnOE spun yarntwist multiplier

twist multiplier

3.5

4.45.15.54.34.85.35.8

Arwanza

14s16.917.219.016.713.614.915.013.39030 G

14s13.814.616.216.512.213.714.912.6Menoufi

14s13.013.415.813.711.912.914.112.9

Mean14.615.117.015.612.613.814.712.9

II

Initialmodulus, g/tex

Final

modulus, g/tex

Yarn

Ring spunOE spun

Ring spunOE spun

16 20 25 30Elongation,o/.

Untreated

R. S. 106 ~ Stretched

O. E. 105' Yo Stretched

20=.•.­.tl"

1,0~•c:

11..•

INDIAN J. TEXT. RES., VOL. 9, MARCH 1984

Table 6~F1ex Abrasion Resistance of Untreated andMercerized OE and Ring Spun Yarns at Different Twist

Multipliers

4.34.85.35.83.54.14.55.0

Cotton, ArwanzaUntreated yarn7373756859737578

Slack6665646356647065

mercerized Mercerized and5458595454565860

stretched to normal length Cotton, 9030 GUntreated yarn

7776777667656873

Slack I6494778360626563

mercerized Stretched to6082687156-585860

normal length Cotton, MenoufiUntreated yarn8365696371707879

Slack I 6255565563646871

mercerized Stretched to5651535356586063

normal length

multiplier, there is insufficient penetration of alkali,

resulting in decrease in the swelling of core fibres in theyarn samples. However, the shrinkage is more in OEyarns compared to that in ring spun yarns even whenthe twist multipliers are the same in both the cases.

This behaviour ofOE yarns may be explained on thebasis of the structure of these yarns. The shrinkage thattakes p\ace in cotton yarns on swelling arises from twosources! (iJ true swelling on extension of fibres intospace, and (ii) changes in length arising from the releaseof mechanica' strains in the fibres. Since OE yarns areIspun with low tensions, there is considerable stress

relief during the spinning operations. Thus, duringswelling in alkali, OE yarns do not shrink to the same

extent as ring spun yarns. Further, due to swelling of

the peripheral fibres, there is insufficient penetrationof the swelling agent to the core and consequentlythere is less swelling of the core fibres. As a result, thelongitudinal shrinkage is reduced.

Treatment

12

OE spun yarnstwist multiplier

Ring spun yarntwist multiplier

Flex abrasion-Data on the flex abrasion resistance

of untreated and mercerized OE and ring spun yarnshaving different levels of twist are presented in Table 6.At higher level of twist, ring spun yarns show atendency for higher abrasion resistance, whereas OEyarns show no such tendency. Mercerization and

stretching reduce the flex abrasion resistance of bothring and OE spun yarns. It appears that both strengthand elongation of yarns together with their structureexert an influence on flex abrasion resistance.

Conclusions

(1) The differences between the strengths of OE andring spun yarns are reduced significantly onmercerization.

(2) The stress-strain properties of OE and ring spun

yarns in untreated and mercerized conditions clearlyreflect the structural differences between the yarns andthe changes in structure resulting from mercerizationand stretching.

(3) Mercerization and stretching improve the lustreof both OE and ring spun yarns, but spun yarns havelower lustre compared to ring spun yarns.

(4) OE spun yarns show more shrinkage onmercerization compared to ring spun yarns.

(5) The folding abrasion resistance of ring and OEspun yarns decreases on mercerization and stretching,but yarn twist increases it.

AcknowledgementThe authors are thankful to Shri T.V. Ratnam,

Director, SITRA, for his keen interest in this work.

They are also thankful to Shri R. Rajendran and ShriR. Govindarajulu for assistance in experimental workand to Shri Oka of CTRL, Bombay, for making lustremeasurements.

References

I Hunter L, Aldrich Dev & Andrews G, SA WTRI Techn Rep, 328,1976.

2 Nelson M L, Hassenbochler C B (Jr), Andrews F R & MarkezichA R, Texl Res J, 46 (1976) 872.

3 Hanckom E C & Barkhuizen F A, SA WTRI Tech Rep, 277,1975.4 Hunter L & Andrews G, SA WTRI Tech Rep, 367, 1977.5 Radhakrishnan P, Studies on rOlor spun blended yarns, Ph D thesis,

Indian Institute of Technology, New Delhi, 1980.

')

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