SomeApplications oftheCore-Spinning Techniquenopr.niscair.res.in/bitstream/123456789/33370/1/IJFTR 1(2) 43-48.pdf · SomeApplications oftheCore-Spinning Technique K. P. R. PILLA Y

Indian Journal of Textile ResearchVol. 1, June 1976, pp. 43-48

Some Applications of the Core-Spinning TechniqueK. P. R. PILLA Y & K. S. SHANKARANARA YANA

South India Textile Research Association, Coimbatore 641014

Received 1 May 1976; accepted 20 May 1976

The use of cotton/nylon filament core-spinning as a means of upgrading cottons to spin fine and superfine countshas been investigated. It is shown that core-spun yarns have improved breaking strength, elongation and elastic recoverybesides lower variation of strength compared to the corresponding all-cotton yarns. As a result, medium and long staplecottons can be upgraded to spin 15-40 counts finer by adopting the core-spinning technique. Fabrics woven from suchyarns, by virtue of their cotton surface, can be dyed without the use of special techniques and are comparable in respectof the major fabric characteristics to those made from imported long staple cottons. Some of the precautions necessaryfor spinning and weaving of core-spun yarns are described in detail.

THE term core-spun yarn may be applied to acomposite yarn in which one componentresides preferentially below the yarn surface

to achieve specified end uses. Core-spun yarns finda variety of applications. By adopting the core-spinn-ing technique, the end breaks in spinning and processesrelated to cloth manufacture are minimized to a largeextent. The special characteristics of these yarnscommend their usage for particular applications,such as light weight apparel fabrics, industrial cloth-ings, tarpaulins, tentage and sewing threads.

The methods of preparing core-spun yarns andthe physical characteristics of the yarns have beeninvestigated by several workers!". The presentstudy is concerned mainly with the use of the core-spinning technique for upgrading medium and longstaple cottons to spin fine and superfine counts.The problem has become important in recent yearsin view of the high cost of imported extra long staplecottons. The possibility of adopting this techniqueusing spun yarns in the core instead of filaments hasalso been investigated.

Materials and Methods

Four Indian cottons belonging to the medium andlong staple varieties (Table 1) and two deniers ofnylon monofilaments (12 and 20 denier) were used.

One of these cottons (MCU 5 with 15 % noil ex-tracted) was core-spun to 100s and 108s counts insufficient quantities for a small scale weaving test.For comparative purposes, the same counts of yarnspun from imported long staple cottons were pro-cured from member mills and used for weaving fabricsof identical construction.

Core-spinning - The core-spinning technique usedis illustrated in Fig. 1. A continuous filament ofnylon was drawn from a bobbin and led towards thefront drafting rollers of a standard ring spinningframe through a tensioning device. The filamentpassed between the rollers and emerged in the frontzone with the strand of fibres from the cottonroving being fed. By adjusting the tension of thefilament, it was made to sink into the core of thestrand, resulting in a filament core.

TABLE 1 - CHARACTERISTICS OF COTTONS AND COUNTS SPUN

Cotton

(Twist multiplier : 3.6)

2.5% span Micronaire Strength at Maturity Counts Nylon in the core, %length value 1/8 in coeff. spunmm gltex 12 20

denier denier

80s 18.1 30.232.5 3.62 29.5 0.890 90s 20.3 33.8

100s 22.6 37.711Os 24.8 41.3

32.0 3.45 19.3 0.840 80s 18.1 30.2l00s 22.6 37.7

26.0 4.46 19.1 0.840 50s 11.2 18.760s 13.5 22.580s 18.1 30.2

27.2 4.25 17.2 0.920 60s 13.5 22.570s 15.7 26.280s 18.1 30.2

43

Sujatha

MCU5

PRS72

C04

INDIAN J. TEXT. RES., VOL. 1, JUNE 1976

Guidr Filament

Rollers

Yorn

Fig. 1 - Core-spinning technique: Side view

Yarn characteristics -- The spun yarn samples weretested for single yarn strength, breaking elongation,coefficient of variation (CV) of breaking strength,uniformity and surface imperfections by the standardmethods. The yarn samples were also SUbjected to acyclic loading and unloading test on the Instron ten-sile tester.

Weaving of fabrics -- Two types of fabrics, a pop-lin shirting and a saree, having the following construc-tions, were woven from the core-spun yarns and all-cotton yarns from imported cottons:

2/108s x 2/108sPoplin : 84 x 84

100s x 100sSarees : 80 x 70For shirting, the warping was done on the Shirley

miniplus and weaving on an automatic loom in thelaboratory. The sarees were woven with the help ofa handloom co-operative society in the traditionalhandloom way.

Since core-yarns have a snarling tendency, thespinning bobbins were heat set in a conditioningoven in an atmosphere of steam at 1l0°C for about45 min. The fabrics after finishing were also heatset at 160°C for 40 see to impart dimensionalstability.

The fabrics in the unfinished state were tested forwarp and weft way strength, breaking elongation,abrasion resistance, bursting strength and washingshrinkage.

Results and Discussion

Yarn CharacteristicsSingle yarn strength -- The single yarn strengths

of 12 denier core-spun yarns and the correspondingall-cotton yarns of different counts from three varie-ties of cotton, are given in Fig. 2.

It is evident from Table 4 that the single yarnstrength of core-spun yarns is 7-30 % greater than

44

l~O~--------------------~------------~Bore YarnCore YarnSujothoMCU-5PR5-72

140

\\\

\\,

x X• •o 0

10;,,,,,

.', "'"J:...l? 120w0::•..Vl Q,

-,,,,,,,,

" ,,,,''0

-, ', ," ',,"" "',',, ,, ', ..,,,

~,,,

,,

: not= 100Vl I

90~

eJ::--_---.1.,--__ I'---_--I..,__ -'-,__ -'-_---I50 60 70 eo 90

YARN COUNT

Fig. 2 - Yam count vs single yam strength

100 110

the strength of the corresponding all-cotton yarns.For a particular cotton, the percentage increase instrength is generally greater for finer counts than forcoarser ones, probably due to the higher contribu-tion to yarn strength from the nylon component atthese counts. The fall in strength with increase incount is also lower for core-spun yarns than for thecorresponding all-cotton yarns. Thus, for MCU 5cotton, the fall in strength from 80s to lOOs countis 34.2 g, whereas for the core-spun yarns fromthe same cotton, the corresponding fall in strengthis only 17.8 g. It follows that core-spun yarns canbe safely spun to much finer counts than all-cottonyarns. Thus, there are definite advantages in adoptingthe core-spinning technique for fine and superfinecounts.

Yarn elongation -- The breaking elongations of thetwo types of yarns are plotted in Fig. 3. Core-spunyarns have 20-50 % greater breaking elongationthan the corresponding all-cotton yarns. In all-cotton yarns, there is a tendency for breaking elonga-tion to decrease with increase in count, probably dueto the higher draft and the consequential straigh-tening of the fibres at higher drafts, but in core yarns,the general tendency is in the reverse direction. Thisis evident from the increase observed in elongationfrom 7.2 to 8.2 % for an increase in count from 80sto 100s in core-spun yarns from MCU 5 cotton.This may be due to the fact that in core-spun yarns,when the count becomes finer, the percentage ofcotton in the yarn falls and the contribution from thehighly extensible nylon increases. It is an additionaladvantage of core-spun yarns that breaking elonga-tion is higher at finer counts.

CV of breaking strength - The CV of breakingstrength of core-spun yarns is 25-40 % lower(Fig. 4) than the corresponding values for all-cottonyarns. Whereas in cotton yarns the CV of strength

11

PILLAY & SHANKARANARA YANA : SOME APPLICATIONS OF THE CORE-SPINNING TECHNIQUE

22r-----------------------------------,

'0- - _

--- Bare YarnCore Yarn

o 0 PRS-72X X Sujatha• • MCU - 5

,,,,,,,,,10

---{)

z 9QI-«ozg 8w

,,,t,

.....• /,,

_-..f-'o

z,.,7«w

~6~

.-X''

~~0----~6~0----~7~0----~8~0----~9~0-----100~--~,10

VARN COUNT

Fig. 3 - Yarn count vs breaking elongation

generally increases with increase in count, the changein the case of core-spun yarns is much less or in theopposite direction. This again shows that whencounts are fine, the greater uniformity in strengthof the nylon monofilament improves the strengthirregularity and imparts superior characteristics tothe core-spun yarn.

Yarn irregularity -- The changes in yarn irregula-rity for different counts of core-spun and all-cottonyarns are shown in Fig. 5. Unlike strength and elon-gation, yarn irregularity of core-spun yarns is notgenerally lower than that in the case of the corres-ponding all-cotton yarns, although in both types ofyarns, irregularity increases with count. This may bedue to the fact that in core-spun yarns, especiallywhen counts are fine, the cotton component has tobe given a much higher draft than in the correspond-ing all-cotton yarn to make the composite yarncount the same. This added irregularity in cotton com-ponent obviously lowers the uniformity of the core-spun yarn to some extent in spite of the higher regu-larity of the core filament.

Elastic characteristics of core-spun yarns -- Thehigh elastic recovery of the nylon filament core maybe expected to make the core-spun yarn more elasticthan the corresponding all-cotton yarn. This is con-firmed by the hysteresis curve obtained by cyclicloading of all-cotton yarn, core-spun yarn and fila-ment yarn (Fig. 6). The yarn samples were mountedon the Instron tensile tester and stretched to 3 %elongation. They were then allowed to relax for2 min and afterwards brought back to the initialposition. The loading and unloading curves wererecorded on the chart paper. It is seen that in the caseof nylon, the loading and unloading curves almostcoincide and the stress decay at the maximum loadpoint is practically nil. In cotton, there is consi-derable hysteresis, showing a stress decay due tothe viscoelastic nature of cotton fibres. The core-spun yarn is much nearer to nylon filament than tocotton. The area under hysteresis is very small and

20

W...J

oZVl

,/

/

Bare '(arnCore Yorn

o 0 PRS-72X X Sujatho•• MCu-5

Io 18zwa::...Vl

z 16a::«>-

-:))f-I-----------,X

--- --- --"" ,,~ ,,

\ I, 1

\1'.1

ILo

p-,/

//

/

x-->u

1-

I8LI -L -L -LI ~ L_ ~

50 60 70 80 so 100 110YARN COUNT

Fig. 4 - Yarn count vs CV of single yarn strength

20r------------------~~----------__.

19

--- Bore Yarn- - - - - core Yarn

o 0 PRS-72X X SuJatho•• MCU-l

,(1I

II

II

II

II,

I,

~ 18 x- - - - - - - x- __>-1-

a::«-'(5 17wa::a::

~ 16«>-

15

14L- -L L- ~ _L ~50 60 70 80 90 100

YARN COUNT

Fig. 5 - Yarn count vs yarn irregularity

the stress decay is also very little for core-spun yarns.It is, therefore, clear that core-spun yarns have greaterelastic recovery and as such the fabrics made fromthem may be expected to exhibit superior creaserecovery characteristics than all-cotton fabrics.

Extent of possible upgrading by core-spinning -- Toascertain the extent of upgrading possible by thecore-spinning technique, the following procedure wasadopted. The curve for yarn strength vs count ofstandard good yarn (obtained from yarn quality

45

INDIAN J. TEXT. RES., VOL. 1, JUNE 1976

survey) was plotted. The strength vs count diagramsof core-spun yarns were made to intersect this lineand the point of intersection was noticed. Similarly,

C04+Nylon

3 2 0.

0>

Nylon:I:

0I-

o 3 2 °zUJ0:I-

V1

50

25

3 2 oELONGATION, "I.

Fig. 6 - Cyclic loading and unloading curves

the count limits for average and poor quality yamswere determined. Data on the extent of upgradingpossible for different counts are presented in Table 2.It is seen that cotton yarns can be upgraded 15-40counts finer by adopting the core-spinning techniquewithout loss in yarn quality. In general, in longercottons, the extent of upgrading possible is also con-siderable. Thus, in Sujatha and MeU 5 cottons, thecounts can be increased by 20-40, keeping the yarnquality good, but in PRS-n, the possible increasefor good quality is only 12 counts.

Fabric CharacteristicsDue to the limited nature of this investigation,

it was not possible to collect data for yarn breakageduring weaving, but core-spun yarns did not poseany difficulty in weaving when suitable precautionswere taken.

The important characteristics of the two types offabrics woven from core-spun yarns are given inTable 3. For comparison, the characteristics ofcontrol fabrics woven from imported long staplecottons are also given. The warp strength of bothtypes of fabrics is almost the same, while the weftstrength of core-spun fabrics is slightly lower thanthose of the corresponding all-cotton fabrics. Thebreaking elongation of core-spun yarn fabrics isalmost double that of all-cotton fabrics; consequen-tly, the work of rupture of the former is far greaterthan that of the latter. This shows that the core-spunyarn fabrics are able to withstand greater stressesduring actual use.

The abrasion resistance and the bursting strengthof core-spun yarn fabrics are equal or slightly lower

TABLE 2 - EXTENT OF UPGRADING POSSIBLE IN DIFFERENT COTTONS

Core yarn spinning (12 denier filament nylon)

Poor

All-cotton yarn spinningCotton

Good Average Poor

Sujatha , carded 70s 80s 90sMCU 1,20 % combed 60s 70s 80sPRS 72, carded 40s 50s 555C04,carded 40s 50s 55s

Good Average

88s 97s100s

52s 57s55s 57s

112s

62s60s

TABLE 3 - CHARACTERISTICS OF ALL-COTTON CORE-SPUN YARN FABRICS (BEFORE HEAT SETTING AND FINISHING)

Core-spunsaree fabric(handloorn)

13.311.823.424.5

287.8254.8

0.25574.4

(0.55)-5.3

(0.95)-9.4

(1.5)-39.4

Fabric characteristics All-cotton Core-spun All-cottonpoplin yarn poplin saree fabricshirting shirting (handloom)

Tensile strength (warp), kg 34.2 33.9 13.8Tensile strength (weft), kg 32.1 30.0 12.2Elongation (warp), % 8.6 17.4 15.6Elongation (weft), % 8.6 17.4 14.1Work of rupture (warp), kg x % 294.1 589.9 215.3Work of rupture (weft), kg x % 351.6 490.7 170.2Bursting strength, kg/em' 3.5 2.6 0.30Abrasion resistance (flat), strokes 29 25 57Washing shrinkage (warp), % 5.4 9.6 1.5

Washing shrinkage (weft), % 8.0 10.0 1.5

Shrinkage, area 12.0 L8.6 3.0

Fabric, wt/sq m (g) 81.4 76.2 40.4

·Values for heat set fabric.

46

PILLAY & SHANKARANARAYANA : SOME APPLICATIONS OF THE CORE-SPINNING TECHNIQUE

TABLE 4 - EFFECT OF INCREASING THE DEl'HER OF CORE FILAMENT ON YARN CHARACTERISTICS

Single yarn strength, gCV of single yarn

strength, % Elongation, % Uniformity CU, %)Count

70s 90s 1008 70s 90s ioo, 70s 90s 1005 70s 90s 100s

SujathaAlI-cotton 136.6 101.8 14.2 14.2 5.9 5.3 14.5 17.312 d core U5.0 J03.3 10.7 13.2 7.5 7.6 J8.0 18.020 dcore 144.5 143.7 12.7 12.9 24.1 27.3 16.0 16.0

PRS-72 50s 60s 80s 50s 60s 80s 50s 60s 80s 50s 60s 80sAlI-cotton 140.0 108.9 12.7 21.1 6.0 6.0 15.8 16.212 d core 149.0 114.0 90.6 100 12.5 10.4 10.3 9.5 9.1 17.0 19.0 20.020 d core 159.3 133.8 138.8 9.8 8.4 11.3 8.7 9.6 21.0 16.3 16.6 18.8

than those of the corresponding all-cotton fabrics.It is interesting that inspite of the higher breakingelongation of core-spun yarn fabrics, their abrasionresistance and bursting strengths are slightly lower.The probable reason may be that the cotton compo-nent which forms about 80 % of the yarn is inferiorin length, strength, etc. to that used in the all-cottonyarn.

To find out whether the core-yarn fabric showedany higher pilling tendency than the all-cotton fabric,the abraded surfaces of both fabrics were examinedand compared visually. There was practically nodifference between the appearance of the two typesof fabrics.

Effect of Increasing the Denier of Core FilamentTo study the effect of increasing the denier of corefilament on yarn properties, all the four cottons werespun with 20 denier monofilaments in the core. Theresults presented in Table 4 show that all yarnproperties are improved on increasing the denier ofthe core filament from 12 to 20. For example, thestrength of 100s core-spun yarn from Sujatha cottonand 20 denier filament is 143.7 g as against 103.3 g,when 12 denier filament is in the core. This is ob-viously due to the higher contribution to strengthfrom the synthetic core. However, it must be bornein mind that on increasing the denier of the corefilament, the proportion of the synthetic componentincreases and the raw material cost also increases.Moreover, when higher denier is used as core in finecounts, the cotton covering becomes thin and in-effective and the yarn loses its essential cotton cha-racteristics. This is evident from the value of breakingelongation (30-35 % for 100s and 11Os) of the 20denier core yarn, which nearly approaches the break-ing elongation of the nylon filament itself. In addition,there is the danger of cotton surface peeling off.

Since the yarn properties improve on increasingthe denier of the core filament, it follows that theextent of upgrading can also be increased. However,this is subject to serious limitations. As the corefilament denier increases, the cotton component hasto be given an excessively high draft to get the re-quired count for the composite yarn. This may bevery difficult under certain circumstances. It, there-fore, appears safe to use a 12 denier filament for up-grading long staple cottons to spin fine and superfinecounts (80s and above) and to use a slightly coarser

denier (20 denier) for medium staple cottons tospin fine counts (50s and 60s). The percentage ofnylon may be restricted to 20-25 % in all cases.

Studies Using Spun Yarns in the Core

The possibility of using the core-spinning techniqueto get preferential arrangement of costly or importedfibres on the surface of yarn and cheap fibres in thecore was investigated in two blends. The first attemptwas to see whether the proportion of polyester inblends could be reduced without affecting the creaserecovery properties of the fabric by arranging polyes-ter fibres on the surface of yarn. The second attemptinvolved reduction in the proportion of costly impor-ted wool in cotton/wool fabrics by putting wool fibreson the yarn surface and giving a good woollen handleto the fabric. In both these attempts, cotton yarnswere used in the core.

Since the elongation and elastic recovery of cottonyarns were much lower than those of nylon filaments,it was not possible to get a good core yarn by thismethod, but preferential arrangement of polyesteror wool could be obtained on the yarn surface. Thetwist factors of core and cover components hadalso to be adjusted to get a satisfactory yarn quality.

The yarns spun were SUbjected to weaving tests.In the case of cotton/polyester core-spun yarn fabric,not much saving in polyester could be achievedby this method and the fabric production costs werealso high. In cotton/wool fabric, although the fabrichad a woollen handle, the wool component was pre-ferentially removed from the fabric surface when thefabric was subjected to abrasion tests.

In view of the above facts, commercially successfulfabrics could not be made in the above trials. How-ever, this technique can be adopted when noveltyeffects on yarns and fabrics are attempted by changingthe arrangement of fibres on yarn structure.

Precautions Necessary for Core Yarn Processing

Since the spinning tests for this project were con-ducted with a limited number of spindles, it was notpossible to assess all the problems associated withcore-spinning.

Although core-spun yarns have several advantages,some precautions are necessary during spinning andprocessing of these yarns. The following are theimportant among them:

47

INDIAN J. TEXT. RES., VOL. 1, JUNE 1976

(1) Since the monofilaments are very fine, thefilament bobbins have to be handled with care, andit is preferable to use extra illumination near thering frame to see the filament clearly. Alternatively,tinted filaments can be used.

(2) Defects like 'sheath voids' are sometimes pro-duced during spinning due to the breakage of rav-ings or when hard fibre bunches break through thedrafting and disappear into the pneumofil. In suchcases, lengths of yarn in which sheath fibres are miss-ing are formed. Careful supervision is, therefore,necessary during spinning.

(3) Ring frames with knee brakes and arrangementfor holding filament bobbins on the creel are essen-tial in core-spinning. The piecing technique adoptedis also different from the usual method and someinitial training for operatives is necessary.

(4) Since core-spun yarns are lively, it is essentialto condition the ring yarn bobbins or cones beforefurther processing. The optimum conditions are:temperature, 212-240°C; and processing period,30 min.

(5) During winding, care should be taken that theyarn does not rub against very rough surfaces.

(6) During sizing, it is essential to use a good filmforming adhesive like PVA in the size mix. This willavoid the peeling of the sheath during brushing or dueto abrasion at heald eyes.

(7) Core-spun yarn fabrics containing syntheticsmust be heat set to get dimensional stability andremove waviness in the fabric.

Conclusions(1) Medium and long staple cottons can be up-

48

graded to spin fine and superfine counts by adoptingthe core-spinning technique.

(2) The extent of upgrading varies from 15to 30%,when 12 denier filament is used in the core.

(3) All important yarn characteristics are improvedby core-spinning, the extent of improvment dependingupon the denier of the filament and the characteris-tics of the cotton.

(4) Fabric characteristics of core-spun yarn fabricsare comparable to those of the corresponding all-cotton fabrics made from imported long staple cottons.

(5) Core-spun yarns and fabrics require heat sett-ing to avoid snarling and to ensure dimensionalstability.

(6) Core-spinning can be used at times to effectcost reduction. It can also be used for the produc-tion of yarns and fabrics for special end uses.

AcknowledgementThe authors wish to express their sincere thanks

to Shri K. Sreenivasan, Director, SITRA for hisguidance during the progress of this work. Theirthanks are also due to Shri S. Govindarajan, Head,Engineering Department for fabricating the tensioningdevice used in this experiment. The help rendered byShri V. Sriramulu of the Mechanical ProcessingDivision and other colleagues in the Physics Divisionin the spinning and testing work is also acknowledged.

References1. SLANDRlNG, P. T. & WESTROP, K. J., J. Text. Inst .• 49

(1958),453.2. MILLER, G. G., J. Text. Inst .• 56 (1965), T 73.