Indian Journal of Fibre & Textile ResearchVol. 15, September 1990. Pp. 113-119

Physical and mechanical properties of cotton covered nylon core yarnsN Tarafder & S M Chatterjee

College of Textile Technology, Serampore, Hooghly 712 20 I, India

Received 26 December 1989; revised received 16 April 1990; accepted 22 May 1990

The physical and mechanical properties of simple core-spun yarns, produced from cotton sheathand monofilament nylon core on a modified ring spinning frame under three different pretensioningconditions of the core, are described and compared with those of the equivalent 100% cotton ring-spun yarns. The yarns having about 8% nylon content as core show unique characteristic change inyarn strength and higher extensibility compared to equivalent 100% cotton ring-spun yarns. Markedimprovement is observed in the packing coefficient with better core coverage, yarn toughness andabrasion resistance.

Keywords: Abrasion resistance, Core coverage, Core-spun yarn, Cotton-nylon yarn, Ring-spun yarn,Yarn toughness

1 IntroductionNovel spinning systems have been developed to

produce the single-end yarns more economically.The most prominent feature of these system is ahigh linear production speed. But all yarns result-ing from staple-fibre spinning do not have theproperties that satisfy all the requirements fortheir use in various applications. A subsequentprocess of post twist or folding is therefore some-times applied to modify these yarns. Core-spunyarns may have potential as a substitute forfolded ring-spun yarns, but no trials have been re-ported.

The core-spun yarns generally have hydrophob-ic multifilament yarns and staple fibres (natural orman-made) as core and sheath components re-spectively. Differential twist retraction and preten-sioning are the common means by which the re-duced delivery rate for the core element is ob-tained. According to Balasubramanian and Bhat-nagar', pretensioning of the filament core whilespinning the simple core-spun yarns on a modifi-ed ring frame is necessary to restore the filamentat the centre. To produce a yarn with improveduse characteristics, an idea was conceived by Lok-anatha and Srinivasalu for the rational utilizationof the properties of both the continuous filamentyarn and the staple-fibre yarrr'. Tripathi andGandhi:', while investigating the physical propert-ies of polyester-viscose core-spun yarns, con-cluded that tenacity decreases with increase intwist factor whereas the % elongation-at-breakdoes not show and trend. The effects of preten-sion, core-sheath ratio, staple length and twist

have been studied by Aswani and De4 and Singhet al.'.

Harper and Ruppenicker" found that at equiva-lent concentration in a blend, a polyester filamentmakes a greater contribution to yarn strength thanthe polyester staple in a comparable intimateblend. According to TyagF,· nylon-viscose core-spun yarns with finer denier sheath fibres aremore regular but an increase in twist makes themuneven. Sawhney et al.8 described a newly deve-loped, relatively simple but effective technique ofproducing a novel pseudo-composite cotton-richstaple yarn with improved tensile properties. Theabrasion resistance of ring- and rotor-spun yarnsin relation to their coefficient of friction has beenstudied by Subramaniam et al". Sawhney et al."studied the cross-section of nylon-core yarns(having 70% cotton and 30% filament) producedefficiently on a slightly modified ring spinningframe to show the degree of core coverage and fi-nally used these yarns to produce greige fabrics.Modifications in the existing ring frame for core-spun yarn production have been reported earli-er".

The present study was aimed at evaluating theapplication of core-spun yarns as sewing threadsand to compare the properties of these yarns withthose of 100% cotton ring-spun yarns.

2 Materials and Methods2.1 Production of Yarns

A nylon monofilament of 15 den (1.67 tex) ascore and J-34 cotton (gincut, 28 mm, 4.2 Me,22.n gltex) as sheath were used for spinning 30

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INDIAN 1. FIBRE TEXT. RES., SEPTEMBER 1990

tex (20 Ne) yams. The sheath fibres were pro-cessed on the traditional carded cotton system us-ing standard mill procedures and practices into'0.61 g/m (0.96 hank). A pilot plant model of ringspinner (Uni-spinner) with SKF drafting system,modified with a disc type tensioner, mounted onthe top of the drafting unit, was used for the pro-duction of core yams. Processing conditions, likedouble rove feeding (Sirofeed), position of fila-ment feeding, spindle speed, traveller size andback draft were kept unaltered to produce a seri-es of experimental yams with a nominal count of30 tex for three different conditions, viz. without,constant and controlled pretension of the filamentcore at eight different twist factors for each type.

The roving from the rove bobbins was drawnover suitable guides and through a special ar-rangement made at the cradles for double rovefeeding. The filament was drawn over a porcelainguide roller through the disc of the tensioner andfinally through the eye of another porcelain guidejust above the drafted ribbon of fibres. It was po-sitioned just behind the nip of the front rollers toensure that the filament placement remains unal-tered throughout during the production of core-spun yams. During the production of core-spunyarn" without pretension, no dead weight waskept on the disc of the tensioner. For the con-stant pretension, the fixed dead weight of 14.2 gwas kept on the disc. The required tension for aparticular TM in the case of controlled pretensionwas adjusted in the following manner. For anyparticular TM, a certain length of yarn spun ac-cording to the above-mentioned procedure wastaken and a sample of 50 em length was cut fromit. The length of the filament from the yam wasmeasured after peeling off the sheath cotton. Theideal condition was reached when the filamentlength exceeded the yarn length by just 1%, assuggested by Balasubramanian and Bhatnagar '. Atthis condition, the production of the yam continu-ed till the bobbin was full. If the condition wasotherwise, pretension was adjusted by addingsmall weights (washers, each of 0.5 g) to arrive atthe required level. The tensions (g.wt) 12.8275,13.6280, 13.9840, 14.5000, 14.7130, 14.9550,14.9870 and 15.3135 were adjusted for low tohigh TM for eight yam samples respectively. Usingthe same rovings and keeping all other processingconditions unchanged, by the corresponding ma-nipulation of spinning draft and twist, equivalent100% cotton ring-spun yarns were produced.

2.2 TestingThe core yarns were tested and evaluated for

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appearance, evenness, imperfections, abrasion re-sistance, hairiness, breaking tenacity, breakingelongation, toughness index and stiffness accord-ing to the ASTM standards and, in some cases, byvisual observations. The samples were conditionedfor 48 h in the standard atmosphere of 65 ± 2%RH and 20 ± 2°C.

An electronic balance (Auto-sorter) was usedfor determining the yarn count and core-sheathratio. A tension twist (untwist and retwist) testerand an ordinary scale were used for measuringthe twist and filament/yam length ratio respect-ively. Yam diameter and hairiness were measuredwith the help of a projection microscope (Projecti-na). The packing coefficient of the yams was cal-culated from the measured diameter as follows:

. . . Fibre volumePacking coefficient (¢ )= -----

Yam volume

(X/weighted average of fibre density)

(~!~x 103)

where X is the weight of 10 m of yarn (g), and d,the yam diameter (ern).

The weighted average of fibre density was cal-culated assuming the densities of cotton and nyl-on to be 1.52 and 1.40 g/cc respectively and fromthe actual core-sheath ratio in the yarn.

Single strand breaking strength and elongation-at-break were measured on an Instron (model1026). The toughness index was calculated as fol-lows:Toughness Index = + x breaking strength (kg)

x elongation (%)

The shrinkage of yams was measured at theboiling temperature of water. Uster evenness tes-ter and black board technique were used for mea-suring the uneveness and appearance grading ofthe yarns respectively. The Walker abrasion testerwas used for determining the abrasion resistanceof yams.

3 Results and DiscussionThe physical and mechanical properties of the

experimental yams are given in Tables 1-4. It isobserved from these tables that the overall countsin tex (Ne): of the four categories of yarns are29.85 (19.78), 29.87 (19.77), 29.39 (20.09) and29.44 (20.06) with their respective range of countin tex (Ne) as 2.64 (1.76), 1.58 (1.05), 2.88 (1.99)and 0.80 (0.54). The variations of count in termsof range are slightly on higher side and are ex-

TARAFDER & CHATTERJEE: COTTON COVERED NYLON CORE YARNS

pected to be dominated by the variation of rove Qf the core-spun yams increa.ses with increase inhank (CV= 2.31.% and 3.30%). The important twist multiplier up to the optunum TM level andproperties of these yams are discussed below. then decreases (Tables 1. -3). A similar trend is ob-

served for equivalent 100% ring-spun yams3.1 Core-Sheath Ratio and Filament-Yam Length Ratio (Table 4). The core yams spun with controlled

The core-sheath ratio of the core yams spun pretensions have comparatively higher strengthunder different pretensioning conditions of the fila- and tenacity than the yam of other two categoriesment core are given in the Tables 1-3. The,overall (at corresponding TM levels) and equivalent ring-core-sheath ratios of the three categones are spun yams. The CV % of single-strand breaking8.37/91.63, 7.99/92.01 and 8.32/91.68 respect- strength decreases with the increase in TM levelively. A common trend is seen in Tables 1 and 2 for all the four categories of yams. The equivalentfor core-spun yarns spun without and constant ring-spun yams show higher CV % in breakingpretension i.e. the core % reduces with increase strength than the core-spun yarns alinost at all thein twist density. No such trend is observed for TM levels. The % elongation of core-spun yamscore-spun yams spun under controlled ~retension spun without pretension and 100% cotton equiva-(Table 3). The filament-yam length ratios of the lent ring-spun yams increases with increase infirst two categories are variable in nature whereas twist multiplier. Amongst the four categories ofthat of the third category is more or less constant yams, the controlled pretension core-spun yams(about 1%) for all the twist density levels. In the have highest elongation % almost at all the TMcase of yam spun without pretension, with the in- levels. The toughness index of all the yarns in-crease in TM the length of core increases over the creases with higher twist multiplier. A similaryam length and affects the core-sheath ratio. For trend is observed for stiffness. However, markedconstant pretension yams, similar effects are ex- differences in toughness index and stiffness valuespe~ted from the yams spun below and above the are observed for core-spun yams of controlledrequired tension for a particular sample. To get pretension type.the ideal condition (1 % ratio), the tension for The nature of raw material, method of roveeach sample was adjusted according to the ~ feeding, filament disposition, spindle speed, tra-employed and consequently the chances of wIde veller size and back draft were kept unchangedvariation in the length ratio wa~ avoi?ed. How- during the production of a series of experimentalever, this effect is not very promInent m the case yams under different conditions of pretensioningof controlled pretension core-spun yams, because the filament core with change in twist density,of the incorporation of monofilament instead of The main aim of pretensioning the core elementmultifilament as a core material. was to constrain to lie close to the central part of

the yam. It is assumed that the geometrical dispo-3.2 Packing Coefficient ., 'h h '

fThe diameter of yarns of all the categories fol- sItIon of the filament mto, t e yam as certam ,e -

I w the usual trend i.e. it reduces with higher fects on the yam propertI~s. Double rove feedmg0 , s , .

f was adopted to get supenor cover of the yams.twIst factor. Amongst ~e four categones? yams, The ex erimental results show that double rove

the core-spun yams WIth constant pretensIon have p. .th hi gh kin d 'ty Between the con- feeding and controlled pretensIon have unprovede est p~c g enSI ., the yam strength the gain being more at lower

trolled pretensIon core-spun yams and the equIv- TM I I Th ' t. I g"; n at hi'gher. h th high eve s. e compara Ive ess ...alent nng-spun yams, the former ave e er b d ' d bl .'

ty d non..

th TM I I Th TM ma y e ue to mcrease 0 IqUI an -packmg coefficIent at most of e eve s. e,diameter of the yams appears to be less sensitive simul~aneity in the occurN rence, of l brea;ks m th b e..

I h constituent components. on-sImu tanelty can e

to core-sheath ratio whereas pretensIon pays t e . b d h high .fib h . hi h.."f th attn ute to t e mter- re co esIon, w c

key rol Te hm co~trolling t the t pa.Cking~~:I~ y O cone does not allow equalization of strain along the

yams. e resIstance 0 orslon 0 e - I th f th . t d fib.. 1 '& eng 0 e ffilgra e res.trolled pretensIon yams IS more or ess ullilorm, d . d ..

bb &., , f fibres in the am The rove stran s are Issue man on lorm

causmg u.lliformThPacdking 0f e coverage Y un' -from the nip of the rollers and the filantent core

cross-sections. e egree 0 cor ..& th .ddlroves with higher twists in these yarns and con- un~er cont~olled pret~nslon IS led at e ffil e.p .kin hi h .t de- This helps m embeddmg the strands close to the

tnbutes ~o compact. sac I g, w ~d'a~et~r;' filament. The cohesion between the filament andcreases e yam specI c vo ume an I .the roves is improved and the support to the

3.3 Strength and Elongation sheath component is increased. Th~ ul~mate gainThe average single-strand strength and tenacity is the improvement in strength which IS depend-

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INDIAN J.FIBRE TBXT. RES., SEPTEMBER 1990

Table 1 -Properties of cotton-nylon cor.e yams spun without pretensioning the filament core

Parameter Yam Sample No.

1 2 3 4 5 6 7 8

Nominal count, tex 30 3~ 30 30 30 30 30 30Actual count, tex 28.48 29.59 29.30 29.44 30.04 30.34 30.96 31.12Actual count, Ne 20.73 19.96 20.15 20.06 19.66 19.46 19.07 18.97Twist multiplier 2.70 3.04 3.30 3.54 3.72 3.91 4.68 5.08Core-sheath ratIo, % 8.6/91.4 8.9/91.1 :8.5/91.5 8.3/91.7 8.0/92.0 8.1/91.9 8.1/91.9 8.4/91.6Filament-yam length ratio, % 1.24 1.54 2.68 3.48 3.20 4.20 5.68 7.06Yam diameter, mm 0.255 0.241 0.235 0.229 0.203 0.196 0.181 0.188Packing coefficient 0.37 0.43 0.45 0.47 0.61 0.66 0.80 0.74Single-strand strength, g 160.34 203.81 224.44 328.26 334.64 381.37 423.53 399.89Tenacity,g/tex 5.63 6.89 7.66 11.05 11.14 12.57 13.68 12.85Breaking strength, CV'/o 17.49 18.59 14.59 6.59 8.09 9.90 9.06 12.22Single-strand elongation, % 5.25 5.52 5.95 6.62 6.72 7.75 8.13 8.53Shrinkage, % 4.13 3.99 3.24 4.00 3.70 3.68 4.20 4.13Unevenness,CV % 13.76 12.56 12.80 12.88 13.52 13.20 13.20 15.92Thin places (- 50%) per kin 460 70 110 160 330 270 250 690Thick places (+ 50%) per kin 1350 1220 1060 1240 1480 1490 1380 1420Neps ( + 200%) per kin 330 280 260 260 310 290 350 490

Appearance grade, subjective Rather Slightly Slightly Slightly Slightly Slightly Slightly Slightlyneppy neppy neppy neppy neppy neppy neppy neppy

Hairiness, above 1 mm 160 170 105 126 65 86 71 78Abrasion resistance, No. of strokes 38 48 60 72 78 96 1120 133Toughness index 0.42 0.56 0.67 1.09 1.12 1.48 1.73 1.70Stiffness 0.030 0.037 0.038 0.049 0.050 0.049 0.052 0.469

Tabi.e 2 -Properties of cotton-nylon core yams spun with constant pretensioning the filament core

Parameter Yam Sample No.

12 3 4 5 6 7 8

Nominal count, tex 30 30 30 30 30 30 30 30Actual count, tex 30.64 30.62 29.06 29.38 30.06 30.34 29.90 29.06Actual count, Ne 19.27 19.28 20.32 20.10 19.64 19.46 19.75 20.32Twist multiplier 2.27 2.95 3.19 3.50 I 3.79 4.11 4.44 4.85Core-sheath ratio, % 8.8/91.2 7.6/92.4 7.5/92.5 7.7/92.3 7.6/92.4 7.5/92.5 8.6/91.4 8.6/91.4Filament-yam length ratio, % 0.73 0.85 0.90 0.78 2.15 3.82 7.05 4.93Yam diameter, mm 0.206 0.198 0.195 0.183 0.176 0.179 0.165 0.166Packing coefficient 0.61 0.66 0.64 0.74 0.82 0.80 0.92 0.89Single-strand strength, g 244.51 286.30 323.15 334.64 375.15 375.00 387.50 397.83Tenacity,g/tex 7.98 9.35 11.12 11.39 12.48 12.36 12.96 13.69Breaking strength, CV% 13.22 9.83 9.36 9.22 7.25 7.25 9.90 11.72Single-strand elongation, % 8.15 8.27 7.73 8.25 8.07 8.37 8.45 8.22Shrinkage, % 7.29 5.55 6.02 5.67 3.77 3.71 3.76 4.24Unevenness,CV% 12.80 12.88 13.52 13.41 14.24 14.48 14.24 14.00Thin places (- 50%) per kin 290 260 300 390 540 550 480 420Thick places (+ 50%) per kin 1330 1120 1340 1420 1600 1760 1480 1490Neps (+ 200%) per kin 320 220 340 310 350 350 360 480Appearance grade, subjective Slightly Rather Rather Rather Rather Slightly Rather Slightly

neppy neppy neppy neppy neppy neppy neppy neppyHairiness, above }, mm 52 88 156 194 94 58 48 44Abrasion resistance, No. of strokes 45 57 68 80 89 100 130 146Touglinessindex 1.00 1.18 1.25 1.38 1.51 1.57 1.64 1.63Stiffness 0.030 0.035 0.042 0.040 0.046 0.045 0.046 0.048

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TARAFDER & CHAlTERJEE: COTTON COVERED NYLON CORE YARNS

Table 3 -Properties of cotton-nylon core yarns spun with control prtensioning the filament core

Parameter Yam Sample No.

1 2 3 4 5 6 7.,8

Nominal count, tex 30 30 30 30 30 30 30 30Actual count, tex 28.86 28.92 28.54 27.80 30.00 30.12 30.68 30.44Actual count,Ne 20.46 20.42 20.69 21.24 19.68 19.60 19.25 19.40Twist multiplier 2.76 2.94 3.13 3.39 3.76 4.06 4.52 4.98Core-sheath ratio, % 7.9/92.1 7.3/92.7 8.8/91.2 9.2/90.8 8.0/92.0 8.2/91.8 8.7/91.3 8.6/91.4Filament-yam length ratio, % 0.94 0.98 1.01 1.00 0.98 1.08 1.02 1.08Yam diameter, mm 0.213 0.186 0.203 0.207 0.198 0.197 0.187 0.199Packing coefficient 0.53 0.70 0.58 0.54 0.64 0.65 0.74 0.65Single-strand strength, g 246.17 310.02 326.78 334.89 380.40 402.10 455.60 436.51Tenacity,gitex 8.53 10.72 11.45 12.05 12.68 13.35 14.85 14.34Breaking strength, CV% 10.19 6.71 8.89 8.61 8.80 8.31 8.51 7.17Single-strand elongation, % 8.35 8.37 8.15 9.10 8.87 8.22 9.43 9.95Shrinkage, % 4.30 4.11 3.80 5.73 5.84 5.44 4.45 4.76Unevenness,CV % 12.48 12.50 12.88 13.25 13.60 13.68 14.24 13.52Thin places (- 50%) per km 320 200 250 350 390 470 350 260Thick places ( + 50%) per km 850 950 1140 1200 1350 1420 1320 1300Neps ( + 200%) per km '310 320 370 270 290 300 400 350Appearance grade, subjective Rather Rather Rather Rather Rather Rather Rather Rather

neppy neppy neppy neppy neppy neppy neppy neppyHairiness, above 1 mm 48 71 36 314 177 144 179 110Abrasion resistance, No_of strokes 60 51 50 54 81 110 136 150Toughness index 1.03 1.30 1.33 1.52 1.69 1.65 2.15 2.17Stiffness 0.029 0.037 0.040 0.037 0.043 0.049 0.048 0.044

Table 4 -Properties of equivalent 100% cotton ring-spun yams

Parameter Yam Sample No.

-1 2 3 4 5 67 8

Nominal count, tex 30 30 30 30 30 30 30 30Actual count, tex 29.12 29.04 29.25 29.84 29.36 29.68 29.64 29.62Actual count, Ne 20.28 20.33 20.19 19.79 20.11 19.90 19.92 19.93Twist multiplier 2.83 2.93 3.22 3.53 3.76 4.10 4.68 4.92Yam diameter, mm 0.205 0.201 0.204 0.199 0:204 0.209 0.211 0.224Packing coefficient 0.58 0.60 0.59 0.63 0.59 0.57 0.56 0.49Single-strand strength, g 241.40 264.84 300.98 310.93 369.64 378.42 423.26 363.44Tenacity,gitex 8.29 9.12 10.29 10.42 12.59 12.75 14.28 12.27Breaking strength, CV % 20.26 13.14 10.44 9.79 8.51 9.10 7.70 13.25Single-strand elongation, % 6.20 6.40 6.28 6.57 7.25 7.12 7.27 7.52Shrinkage, % 2.48 2.73 2.71 2.97 2.55 2.80 3.22 3.06Unevenness,CV % 15.00 14.48 12.00 12:48 12.56 12.96 12.80 14.08Thin places ( -50%) per km 950 820 160 250 160 120 140 480Thick places (+ 50%) per km 1460 1380 740 870 1060 1160 1100 1400Neps ( + 200%) per km 520 450 140 280 270 380 360 430

Appearance grade, subjective Slightly Slightly Rather Rather Rather Slightly Slightly Ratherneppy neppy neppy neppy neppy neppy neppy neppy

Hairiness, above 1 mm 233 198 223 230 88 212 60 55Abrasion resistance, No. of strokes 16 26 27 41 89 87 119 140Toughness index 0.75 0.85 0.94 1.02 1.34 1.35 1.54 1.37Stiffness 0.039 0.044 0.048 0.047 0.050 0.Q53 0.058 0.048

---

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INDIAN J. FIBRE TEXT. RES., SEPTEMBER 1990

ent on the amount of twists in the yarn. It is ob-served from Table 3 that the core-spun yarns ofcontrolled pretension type show improvement instrength at low twists and a reduction in the opti-mum twist factor when compared with the equiva-lent 100% cotton ring-spun yarns.

The strength of staple-fibre yarn is governedmainly by the inter-fibre frictional forces, obli-quity in lie of fibres and non-simultaneity in theoccurrence of breaks. The relative importance ofthese factors are dictated by the twists in the yam.At low twists, the frictional forces' play the keyrole whereas at higher twists, the obliquity andnon-simultaneity dominate. In core-spun yams,the presence of a continuous filament as core re-duces ~he slippage of the sheath fibres and gain instrength is achieved at low twists. But, as the twistis increased, the effect gradually disappears due tothe diminishing influence of friction and increas-ing effect of non-simultaneity. It is also expectedthat nylon and cotton, being much different inbreaking extension, do not break simultaneously,and this serigraphic effect contributes to the lossin strength at higher TM.

The fibres on the yam surface are assumed tobe under strain during twisting and then subse-quently contract under strained length with theresultant buckling of the core, causing an addi-tional extension of the core before these are ex-tended to break in the case of controlled preten-sion yams. In the without and constant preten-sion yams, there is no or insufficient buckling tocause further extension of the core due to thewide variation in the core length over yarn. Thenon-uniform core-sheath ratio in relation to twistmultiplier employed has little or no effect on theextension-at-break.

The importance of toughness index and stiff-ness is discussed in relation to the abrasion resist-ance of the yarns.

3.4 Shrinkage of YamsTables 1-4 show that the variation in shrinkage

% is maximum for the constant pretension yamsand minimum for the equivalent 100% cottonring-spun yarns. The equivalent ring-spun yarnsshow lower shrinkage than the core-spun yarns ofany category at their corresponding TM levels.However, no particular trend is observed for anycategory of yarns between TM and shrinkage %.

The shrinkage of core-spun yarns may be re-garded as a combined effect of core and sheathcomponents and total geometry of yarn matrix.The geometry of yarn matrix in the controlledpretension yarns may be explained by the filament

118

disposition in the yarn helix. The low shrinkage ofthe equivalent 100% cotton ring-spun yarns isprobably due to the structural configuration of theyarn helix compared to controlled pretensioncore-spun yarns. The effect of core and sheathcomponent is enhanced by the controlling of pret-ension which ultimately plays the dominating rolein regulating the shrinkage of core-spun yarns.

3.5 Evenness and ImperfectionsThe core-spun yarns have less unevenness

CY % than the equivalent 100% cotton ring-spunyarns at lower twist factors and more unevennessCY % at higher twist factors (Tables 1-4). The de-terioration in yarn evenness at higher twist factorsis due to the higher crimp in the yam, which givesa wavy effect owing to mechanical hindrance.This results in a higher uster, CV %. The effect ismore prominent between TM levels in the case ofcore-spun yarns spun without and constant pret-ension. Because there is uneven length distribu-tion of the filament over yarn length in theseyarns it causes variable crimp in the yarns.

Without pretension core-spun yarns have com-paratively less thin places than constant and con-trolled pretension core-spun yarns. Thick placesin the controlled pretension yarns are lower thanthose in without and constant pretension yarns.Neps in all the three categories of core-spunyarns are more or less within the same range.However, neps, thick and thin places in the equiv-alent ring-spun yarns are higher at lower TM andlower at higher TM than those for controlledpretension yarns at corresponding TM levels.Double rove feeding and controlled pretensionare considered to be the key factors, which re-duce the imperfections of equivalent 100% ring-spun and controlled pretension core-spun yarns athigher and lower twist multipliers respectively.

3.6 Appearance and GradeA close comparison of the four categories of

yarns reveal that there is not much variation inappearance and grading according to the standardsfollowed. On the basis of ncps/yard, the appearancegrading ranges between slightly neppy to rather nep-py. The controlled pretension core-spun yarns be-long to only rather neppy grade.

The quality of yarns in terms of their appear-ance does not give any clear indication about thecomparative yam character. So far as the appear-ance is concerned, factors like colour, feel, com-parative freedom from neps, slubs, evenness of di-ameter, etc. are also to be considered. The pres-ence of neps in the yarns may be regarded as an

, TARAFDER & CHAlTERJEE: COlTON COVERED NYLON CORE YARNS

important element to classify yarn grading. A vis- stiffness is comparatively less important, becauseual examination revealed that appearance and the combination of strength and elongation is notgrading of core-spun yams are at par with equiva- reflected through it, being the ratio of the pro-lent 100% cotton ring-spun yarns. perties, In the case of core-spun yams, the pres-

ence of a continuous filament contributes to high-3.7 Hairiness er strength and extension, which finally improves

The core-spun yarns are less hairy (protruding the toughness index of the yarns and in turn theends + loops) than equivalent 100% cotton ring- abrasion resistance is improved,spun yams at all the 1M levels except at one 1M. .Amongst the three cate.gories of core-spun yams, 4 Conclusions ,controlled pretension yarns have less hairs at low- 4.1 Controlled pretension ,nylon-cott~n core-er 1M levels and higher hairs at higher 1M. The sp~n yarns h~ve better ~d uruform p~ckmg coef-number of protruding ends dominates over the ficlent an~ higher ten:cIty and ex~enslon-at-breakloops at all the 1M levels in all the categories, In than equIvalent. 100 '/0 cotto~ rmg-spun yams.the controlled pretension yarns, the reduction in T~ey show an I~p~ovement, m stre~gth at lowthe number of loops with increase in 1M is grea- tWIst and a red~ction m the optImum twist factor,ter than that in other categories. The reduction in ~.2 PretensIon on the filament re~l~tes thethe number of protruding ends is appreciable for shrinkage of core-spun yarns at the bollmg tem-

" perature of water.WIthOUt pretensIon yarns, ..

.,4.3 The core-spun yams WIth low tWISt are,In ~e core-spun yarns, there I~ a preferential more even but an increase in twist makes them

mIgration amongst the fibres m the surface uneven. These yams are at par with the equiva-(sheath) layers ~~ when the ~ompac~ess of t?e lent 100% cotton ring-spun yarns in appearancecore:sp.un yam IS mcreas~d by mcreasm.g the tWISt grading.multiphe~, the fibres which ",;ere p:eVlou~ly em- 4.4 High toughness index for core-spun yamsbedded m the surfa~e are raised, mcrea,smg the shows better abrasion resistance.number of protrudmg ends. In the rmg-spun C ' .th b ' d. f fib b ,. al f 4.5 ore-spun yams are less haIry than nng-yams, e m mg 0 res y twISt IS ways su -spun yarns, '

ficient to limit the protrusion of fibre ends and asa result protruding ends decrease considerably Acknowledgementfrom lower to higher 1M levels. Loops are The authors are thankful to Mis India Jute Co.formed on the yarn surface due to the fibre tails Ltd, Serampore, for providing materials for thethat project when laid at the points where they experiments, They are also thankful to Mis Jay-leave the last pair of rollers. In the core-spun ashree Textiles, Rishra, and UIRA, Calcutta, foryams, the continuous filament at the central part providing testing facilities at their laboratories.of the yam under controlled pretension offersbetter binding of the fibre tails with the sheath fi- References.bres At hig her 1M levels the bindin g is better I Balasubramarnan N & Bhatnagar V K, J Text Inst, 61

.., (1970) 534.which decreases the number of loops. 2 Lokanatha K L, Srinivasalu B G & Basavaraj B, Indian J

Text Res, 4 (1979) 133,3.8 Abrasion Resistance 3 Tripathi R R & Gandhi A C, Indian Text J, 81 (1981) 89.

Th b f k ( b ) ' 4 Aswani K T & De A K, in Blended textiles, edited by Me num er 0 stro es ru s requIred to rup- L G I .. [Th T t ' l A .. (I d ' ) B b]., .u raJarn e ex 1 e ssoclatlon n la, om ay

ture the smgle yams are given m Tables 1-4. For 1981 123

all the categories of yarns the number of strokes 5 Singh R K, Kaushik R C D & Sengupta K, in Polyesterrequired increases from lower to higher 1M le- textiles, edited by M L Gulrajani [The Textile Associationvels. The core-spun yams show better resistance (India), Bombay] 1980, 109.to abrasion than equivalent 100% cotton ring- 6 Harper R J & Ruppenicker G F, Text Res J, 57 (1987)

Th gh . hi k 147.spun yarns. e to~ ness mdex, w ch ta es into 7 Tyagi G K, Man-Made Text India, 30 (1987) 435.account both the strength and extensibility of the 8 Sawhney A P S, Ruppenicker G F, Kimmel L B, Salaunyams, has maximum influence on abrasion resist- H L & Robert K Q, Text Res J, 58 (1988) 601, .ance, because both the factors in combination 9 Subramaniam V, Nalankilli G, Mathivanan V & Jagana-

I ' , than K, Text Res J, 57 (1987) 369,P ay a part when the yarn IS bemg abraded. As 10 S h A P S R ' k G F & R bert K Q or t' '. aw ney ,uppernc er 0 , lexthe strength domInates, the elongation alone IS ResJ,59(1989) 185,comparatively less influential. On the other hand, II Tarafder N & Chatterje S M, Text Trend, 31 (1988) 35.

119