Indian Journal of Fibre & Textile ResearchVol. 16, September 1991, pp. 200-205

Effects of strand spacing, filament disposition, break draft and core material onthe physical properties of nylon/cotton core-spun yarns

N Tarafder & S M ChatterjeeCollege of Textile Technology, Serarnpore, Hooghly, 712201, India

Received 28 November 1990; accepted 12 February 1991

The effects of strand spacing, filament disposition, break draft and core material on the physical propert-ies of nylon/cotton core-spun yarns produced under controlled pretension of monofilament are reported. Itis recommended that for the production of yarns of20s Ne, a break draft of 1.42 may be employed when thedouble rove feeding (siro) technique along with the filament disposition at the middle of the strand isadopted.

Keywords: Break draft, Core-spun yarn, Core-sheath ratio, Filament disposition, Nylon/cotton yarn,Strand spacing, Yarn brittleness

1 IntroductionA core-spun yarn is a composite structure, spun

from two different materials at the spinning frame.The central part is covered by staple materials. Thetechnique for the preparation of core-spun yarn isvery simple and the selection of core and covermaterials can be made from a variety of fibres withpredetermined end use. Nylon and polyestercontinuous filaments are the common core materials.Balasubramanian and Bhatnagar ' recommendedthat pretensioning is necessary to obtain suitableyarn properties. Riding- presented a simplifiedmethod for the production of a true core yarn on anordinary doubler by making the length change ontwisting to obtain the required effect. Khara andJain ', in a comparative study of core yarns preparedat ring and doubler, observed that moving away fromthe intimacy of component fibres and positioning oneof the components at a certain preferential directionand position do not result in much deterioration inperformance. Harper and Ruppenicker+ described.the advantages of their technique used to producecotton/polyester filament core-spun yarns. Sawhneyet al? described the physical properties of somespecific cotton-rich high tenacity nylon-core yarnsand greige fabrics developed for military protectiveclothing.

A new technique to produce a cotton/polyesterblended yarn with improved strength has heenreported by Sawhney et al.". The siro spinningtechnique and the possibility of extension of thistechnology to cotton system have also been discussed

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and studied":". Abrasion resistance of ring-spunyarns was studied and measured 9 - I I . We have earlierdescribed+ the necessary modifications in the ringframe for the production of core-spun yarns. Wehave also reported 13-15 the important physical andmechanical properties of nylon/cotton core-spunyarns.

In the present paper, we report the effect of strandspacing, filament disposition, break draft and corematerial on the physical properties of nylon/cottoncore-spun yarns. This study will enable to have abetter understanding of core-spun yarns as apotential substitute for 100% cotton ring-spunsewing threads.

2 Materials and Methods2.1 Production of yams

A nylon monofilament (Nirlon made) of 15 den(1.67 tex) with 87.7 g breaking load and 41.0%breaking elo.ic.nion (at 10 em in Simeadzu) as coreand J -.)4 COLton(gmcut, 28 mm; 4.2 Me; 22.0 g/tex) assheath were used for spinning a 20s Ne (nominal)core-spun yarn using 4.42 TM under controlledpretension 04.377 g-wt) of the filament. Therequired pretension of the nominal yarn was obtainedaccording to the procedure described 14 and themethod suggested".

Twc I roving'. (0.96 Hk, 2.80 CV%. 0.85 tpi) of 100%1.")[[011, processed through the same set and sequenceof machines under similar conditions, were passed

TARAFDER & CHATTERJEE: NYLON/COTTON CORE-SPUN YARNS

over suitable guides and through the double rovefeeding arrangement entered the drafting zone of theUni-spinner ring frame. The nylon monofilamentfrom the supply package, placed at the feed end, wasdrawn first through suitable guides and then throughthe disc type tensioning device under controlledpretension. Finally, over a porcelain guide, it wasaccurately positioned at the centre of the draftedribbon of fibrous strand and introduced at the nip ofthe front rollers.

The nominal yam (Sample 3) was spun at a speed of9000 rpm, with 2/0-elliptical traveller, using 1.35break draft, centrally fed monofilament and 5 mmrove setting distance. Other yarns (Samples 1,2,4-9)were spun by varying the processing parameters likerove setting distance, filament feeding, break draftand core material.

2.2 Testing of SamplesThe sample bobbins were conditioned for 48 h in

the standard atmosphere of 65 ± 2% RH and20 ± 2°C. The samples were then tested and eval uatedfor the important physical properties like count,twist, core-shealth ratio, diameter, breaking loadand elongation %, peeled and un peeled strength,loop and knot strength, unevenness andimperfections, abrasion resistance, shrinkage andhairiness according to ASTM standards and, in somecases, by visual observations.

The count of yarns and core-sheath ratio weredetermined by an electronic balance (Auto-sorter).A tension twist tester (untwist and retwist) and anordinary scale were used for measuring the twist andfilament/yarn length ratio respectively. Yarndiameter and hairiness were measured with the helpof a projection microscope (Projectina). Theprocedure for the estimation of packing coefficientand measurement of hairs/unit length have alreadybeen described.

The load-elongation curves obtained from IP-2were converted to stress-strain curves for singlestrands. The toughness index and stiffness valueswere calculated from the stress-strain curvesaccording to the proced ure reported 15. Yarnbrittleness through breaking strength andelongation-at-break under loop and knot conditionwere measured using the Simeadzu (0-2 kg) singlethread tester. Strength contribution of sheathcomponent to the total strength of a yarn wasinvestigated from the strength behaviour of the yarn(10 em test length) at peeled and un peeled states in theSimeadzu (0-2 kg) instrument according to themethod described 1.1.

The unevenness (CV%) and imperfections (thinplaces, thick places and neps) of the yarns wereobserved in the Uster evenness tester. Theappearance grading of the yarns was analyzed byblack board method. The Walker abrasion tester wasused for determining the abrasion resistance of theyarns in terms of number of strokes required to breakthe yarn. The shrinkage of the yarns was measured atthe boiling temperature of water. The quality indicesof different yarns were calculated according to theformula suggested by Barella et al. 16 and comparedfor the assessment ~f yarn performance underoptimum conditions.

3 Results and Discussion

3.1 Effect of Rove Setting Distance

To improve the understanding of the effect ofspinning conditions on the geometric arrangementand yarn physical properties, the disposition of therovings was varied (Samples 1,2 and 3). The rovingswere kept apart (siro feed) and the monofilament wasfed at the centre between them. The distance betweenthe roves were 15, 10 and 5 mm for samples 1,2 and 3respectively.

The effects of rove setting distance on the physicalproperties of yarns are shown in Table 1. Themaximum tenacity and minimumelongation-at-break (%) are observed in the case ofsample 3. The loop breaking strength, % elongation,and % loss in strength in terms of knot strength and %elongation are also highest for the same yarn. Theunevenness (CV %) is lower but the imperfections,except thin places, are slightly higher for sample 3.The appearance grading is the same (rather neppy) inall the three samples. The abrasion resistance andhairiness (protruding ends plus loops) are maximumand minimum respectively for sample 3 in the group.The shrinkage at boiling water does not show anyremarkable difference amongst the yarns. The YQI ishighest for sample 2.

In a siro feed system, the twisting zone geometry iscritically dependent on the location of convergencepoint, which, in turn, depends not only on thedistance of rove separation but also on the yarntension. The optimum rove spacing, therefore, alsodepends on the traveller weight and spindle speed,which greatly affect the yarn tension. It has beenreported? that the optimum strand spacing is reachedwhen the strand length reaches about 40% of the fibrelength and that there is a sharp deterioration in theyam quality as the strand length approaches the meanfibre length. So, the optimum spacing is expected to be

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Property

Table I-Effect of rove setting distance and filament feed variation on yarn propertiesYarn sample No.

I 2 3 4 5Distance between roves, mm 15.0 10.0 5.0 5.0 5.0

Filament feed position middle middle middle right left

Actual count, tex 29.20 29.18 30.00 30.34 29.42

Actual count, Ne 20.22 20.24 19.68 19.46 20.07Twist multiplier 4.39 4.44 4.40 4.47 4.37Core content, % 10.70 8.10 11.90 8.80 8.70Sheath content, % 89.30 91.90 88.10 91.20 91.30

Filament/yarn length ratio 1.02 1.09 0.96 1.06 1.04

Actual diameter, mm 0.251 0.247 0.235 0.257 0.259Packing coefficient 0.39 0.40 0.46 0.38 0.37Strength contribution by sheath, % 79.86 80.05 80.82 83.13 82.60Single-strand strength, g 415.00 427.80 448.00 399.20 454.67Tenacity, g/tex 14.21 14.66 14.93 13.16 15.45Single-strand elongation, % 5.36 5.36 4.70 6.14 6.08Loop breaking strength, g 814.67 802.33 823.33 807.00 830.38Loop breaking elongation, % 5.63 5.68 6.00 5.53 5.92Knot breaking strength, g 416.00 427.67 412.33 436.33 430.17Knot breaking elongation, % 5.38 5.47 5.85 5.55 5.46Loss in strength, % 4.00 3.68 5.75 7.72 11.79Unevenness, CV% 15.20 15.00 14.48 16.00 15.10Thin places (- 50%) per km 490 485 480 495 485Thick places ( + 50%) per km 1660 1610 1680 1712 1600Neps (+ 200 %) per krn 300 310 352 300 350Appearance grade, subjective rather neppy rather neppy rather neppy rather neppy rather neppyAbrasion resistance, no. of strokes 107 126 155 150 219Toughness index 1.11 1.15 1.05 1.23 1.52Stiffness 0.08 0.08 0.09 0.06 0.07Shrinkage, % 4.54 4.72 4.66 4.74 4.18Hairiness, total hairs 1709 1800 1188 1172 1410Yarn quality index (YQI) 5.01 5.24 4.85 5.05 6.22

higher for longer staples. As per the fibre length(28 nun) employed, the strand length is around 11mmfor the optimum strand spacing.

In the present investigation, only the siro feed hasbeen employed to get better cover of the yarns. As it isnot the complete siro technique for yarnmanufacturing, the total benefit of this system is notexpected in the ultimate yarn. Hence, the benefit ofoptimum strand length has not been reflectedthrough the physical properties of the yarns.However, a combined effect of rove setting andfilament disposition, which might be playing the keyrole in this respect, may be discussed in thesubsequent part.

3.2 Effect of Filament Feeding

The three different filament dispositions, viz. at the

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middle, from the right and from the left of the fibrousstrand were selected for the yarn samples 3, 4 and 5respectively. The effects of filament disposition on thephysical properties of core-spun yarns are shown inTable I. It is observed that the tenacity is maximumfor the sample 5 spun from the filament disposition onthe left of the strand and the % elongation ismaximum for the sample 4 spun from the filamentdisposition at right. The loop breaking strength andelongation arc maximum for the samples 5 and 3respectively. The knot breaking strength andelongation also show the same trend. The yarn spunfrom the filament disposition at the middle (sample 3)shows the lowest % loss in the yarn strength underknot test and the lowest yarn unevenness (CV %).The thin places, thick places and neps are lowest forsamples 3, 5 and 4 respectively. The yarn appearancegrade is same (rather neppy) for all the samples. The

TARAFDER & CHATTERJEE: NYLON/COTTON CORE-SPUN YARNS

abrasion resistance is maximum for the sample 5. Thesample 4 shows maximum shrinkage % at boilingtemperature of water.

It is evident that the combination of relativedisposition of filament and the rovings at the front niphas a critical influence on the physical properties ofthe core-spun yarns. Feeding the filament at the sidesinstead of at the middle results in a pronouncedmigration of the filament from the core to the surface,which contributes in a different way to the yarnstrength. It has a direct bearing on the loop and knotstrength (Table 1). The preferential migration of corein the yarns spun from the filament disposition at thesides might have played the key role in reducing thehairs and shrinkage % of yams. The results in Table 1and the above discussion indicate that thecombination of siro feed and the filament disposition

at the middle offers better physical properties to thecore-spun yarns than any other combination. Hence,it is concluded that the filament disposition alongwith the rove spacing influences the physicalproperties of the core-spun yams.

3.3 Effect of Break Draft

To investigate the effect of break draft on thephysical properties of core-spun yarns, three yams(samples 6, 3 and 7) were spun with break draft 1.42,1.35 and 1.29 respectively. From the results given inTable 2, it is observedthat the sample 6 (with breakdraft 1.42) shows the maximum tenacity (15.99 g/tex)and % elongation-at-break (6.00). The maximumstrength (433.17 g) and % elongation (5.90) underknot tests are shown by samples 7 and 6 respectively.In terms of% loss in strength in knot tests, sample 3

Table 2-Effect of break draft and core material on yarn propertiesProperty Yarn sample No.

6 7 3 8 9Break draft 1.42 1.29 1.35 1.35 1.35

Core material, denier & make 15 15 15 15 12Nirlon Nirlon Nirlon Garware Modipon

Actual count, tex 29.77 29.97 30.00 30.25 30.53Actual count, Ne 19.83 19.70 19.68 19.52 19.34Twist multiplier 4.42 4.40 4.40 4.39 4.48Core content, % 10.00 11.00 11.90 9.80 7.90Sheath content, % 90.00 89.00 88.10 90.20 92.10Filament/yarn length ratio 0.90 1.10 0.96 1.02 1.10

Actual diameter, mm 0.252 0.247 0.235 0.258 0.258Packing coefficient 0.39 0.42 0.46 0.38 0.40Strength contribution by sheath, % 83.21 82.84 80.82 82.91 86.69Single-strand strength, g 476.00 454.80 448.00 463.00 447.00Tenacity, g/tex 15.99 15.17 14.93 15.30 14.65Single-strand elongation, % 5.80 4.62 4.70 5.40 6.48Loop breaking strength, g 805.30 772.70 823.30 837.00 836.70Loop breaking elongation, % 5.15 4.88 6.00 5.52 5.64Knot breaking strength, g 415.17 433.17 412.33 426.33 429~00Knot breaking elongation, % 5.90 5.57 5.85 5.43 5.44Loss in strength, % 13.29 6.71 5.75 6.06 7.18Unevenness, CV% 15.20 14.90 14.48 16.00 14.90Thin places (- 50%) per km 405 400 480 405 390Thick places ( + 50%) per km 1604 1640 1680 1650 1610Neps (+ 200 %) per km 300 300 352 340 305Appearance grade, subjective rather neppy rather neppy rather neppy rather neppy rather neppyAbrasion resistance, no. of strokes 163 151 155 120 149Toughness index 1.38 1.05 1.05 \.25 1.45

Stiffness 1.10 0.08 0.09 0.08 0.07Shrinkage, % 3.67 3.76 4.66 3.91 3.69Hairiness, total hairs 1298 1420 1188 1377 1490Yarn quality index (YQl) 6.10 4.70 4.85 5.16 6.37

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shows the lowest value (5.75 %). The unevenness (CV'%) of the sample 3 is comparatively low in the groupbut its imperfections are much higher. Theappearance grade of the yarns are same (ratherneppy). The sample 6 shows the maximum abrasionresistance (163 strokes) and its shrinkage % at boilingwater is lowest (3.67%) in the group. The hairiness(total hairs) is lowest in the sample 3. The YQI forsample 6 is maximum in the group.

There exists a certain amount of cohesion betweenthe fibres in a rove due to its low twist. Unless thiscohesion is removed and fibres are made free to move,the fibres will not slide past each other smoothly in themain draft zone. There is always some differencebetween real break draft and calculated break draft.Generally, the effective break drafts are high for shortstaple cotton, hard twisted roves, narrow settings andhigh total draft. Excessive break drafts areundesirable from evenness and quality point of view.Excessive break drafts on ring frames tend to spreadout the fibres as they pass through the succeeding zoneand may lead to excessive fly release at the front rollernip, a hairy yarn and more yarn breakages.

Break drafts higher than 1.35can be used if the totaldraft required for a particular application of thedrafting system exceeds the optimum range of theapron zone. The most satisfactory break draftdepends on the creel material used as well as its twistand hank. In double rove feeding, the total draftrequirement is very high to make the fibres free andopen for the main drafting process. It is evident fromthe results in Table 2 that the sample 6 (with breakdraft 1.42) shows improved physical properties in themajority of the parameters compared to other yarnsamples and thus justifies the selection of high breakdraft. Hence, it is concluded that the break draft of1.42 may be used for the production of core-spunyarns (20s Ne) with nylon monofilament core andcotton sheath, provided double roves are fed.

3.4 Effect of Core MaterialTable 2 shows the effects of core material on the

core-spun yarn properties. Monofilaments of 15den(Nirlon), 15 den (Garware) and 12 den (Modipon)were used for the production of yarn samples 3, 8 and9 respectively. A change in filament denier changesthe core-sheath ratio. The use of a comparativelyfiner denier monofilament marginally increases thesheath content, resulting in an increase in the sheathfibres contribution towards the total yarn strength,irrespective of the slight variation in the count of yarnspun. Lower tenacity and higher elongation-at-break are obtained from finer filament (12 den) thanthe coarse one (15 den). The yarn brittleness in terms

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ofloop and knot breaking strength and % elongationdoes not show any remarkable difference with thechange in core material. However, a finer filamentyarn shows a marginally high % loss in knot strengththan the coarser filament yarns.

The number of imperfections in the finer filamentyarn are less than that in the coarser filament yarns,whereas the unevenness CV % shows a differentpattern. The unevenness CV % of sample 9 is higherthan that of sample 3 but lower than that of sample 8.The appearance grade is rather neppy in all the threeyarns. The abrasion resistance of sample 9 is lowerthan that of sample 3 but is higher than that of sample8. The shrinkage of the finer filament yarn is lowerthan that of the coarser filament yarns. The yarnhairiness (total hairs) of the finer filament yarn iscomparatively higher than that of the coarserfilament yarns. The sample 9 shows the highest YQIvalue among the group.

A close resemblence is observed between thephysical properties of the core yarns spun from 15denmonofilaments obtained from different manu-facturers. It is, therefore, concluded that a change incore material in the production of core-spun yarncertainly affects the physical properties of the yarns.

4 Conclusions4.1 The spinning conditions like the filamentdisposition at the middle of the back nip of the frontrollers along with the roves fed keeping apart (10 mm)influences the physical properties of the 20s Nenylon/cotton core-spun yarns.

4.2 A break draft of 1.42 is recommended for theproduction of these yarns when the double rovefeeding (siro) technique along with the filamentdisposition at the middle of the strand is adopted.

4.3 The quality of yarn in terms ofYQI is influencedby the strand spacing, filament feed position, amountof break draft and type of core material employed.

AcknowledgementThe authors express their sincere thanks to Shri

L.K. Mukherjee of the Spinning Department, ShriM. Pal of the Textile Testing Laboratory and Shri B.Ghosh of the Textile Chemistry Laboratory of theCollege of Textile Technology, Serampore, for theirconstant help in the preparation and testing of yarnsamples.

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TARAFDER & CHATTERJEE: NYLON/COTTON CORE-SPUN YARNS

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