Indian Journal of Fibre & Textile Research Vol . 28, June 2003, pp. 1 70- 1 76

Sheath-slippage resistance and other properties of polyester-viscose MJS core-spun yarns

G K Tyagi" & A Goyal

The Technological Institute of Textile & Sciences , Bhiwani 1 27 02 1 , India

and

K R Salhotra

Department of Textile Technology, Indian Insti tute of Technology, New Delhi 1 10 0 1 6, India

Received 8 February 2002: revised received and accepted 5 June 2002

The impact of some process variables on sheath-slippage resistance and other properties of viscose-covered polyester filament MJS core-spun yarns has been studied. It is observed that the air-jet spinning can be used for producing core yarns after optimizing process parameters. A relatively higher first nozzle pressure is advantageous for improving sheath-slippage resistance. The use of higher spinning speed and wider condenser markedly improves the tenacity, breaking extension, initial modulus and sheath-slippage resistance but adversely affects the yarn hairiness, mass irregularity and flexural rigidity. Such decline in the properties at higher spinning speed is, however, more marked in the fine yarns than in coarse yarns. On the whole, MJS core yarns have hairiness and irregularity characteristics similar to those of 1 00% viscose yarns, but the mechanical properties of these yarns are better than those of pure viscose yarns, obviously due to the presence of a strong core material .

Keywords: Core-spun yarn, Murata-jet spinner, Nozzle pressure, Polyester, Sheath-slippage resistance, Viscose, Wrapper fibres

1 Introduction Core yarns with a central filament surrounded by a

sheath of staple fibres enjoy increasing demand. Core yarns are used for utilizing the favourable properties of the constituent components. The filament in the core offers significant advantages in respect of production speed, strength, machine efficiency and its running behaviour, while the staple-fibre sheath provides desirable surface properties .The articles, such as tarpulines, sewing threads, tufted carpets, car safety belts, net twines, stretch fabrics, swim suits and other form-persuasive garments, can be made from core yarns .Core yarns can be successfully spun on ring, rotor, fric�ion, air-jet and tandem spinning systems. The production and properties of core yarns produced by these spinning systems have been documented in various publications I - I I . However, such information on air-jet core yarns is scanty. This paper reports the findings of a detailed investigation on the effects of some process variables on the properties of

a To whom all the correspondence should be addressed. Phone : 24256 1 : Fax : 009 1 -0 1 664-243728 E-mail : titsintr@nde.vsnl.net.in

viscose- covered polyester filament core-spun yams produced on a Murata air-jet spinner.

2 Materials and Methods 2.1 Preparation of Yarn Samples

Three sets of core yarns of 1 1 .S and I S.4 tex were spun from 1 00% polyester core ( 50 denier/36 filaments ) and 1 00%viscose fibre sheath (S l mm, 1 . 1 dtex and 2 1 .06 cN/tex) on ring and air- jet spinning machines .The air-jet machine was modified to produce air-jet core yarns. The laps of viscose rayon fibre were made on a Lakshmi Rieters ' blowroom line and carded on a MMC card. The carded slivers were given three drawing passages on a Lakshmi Rieters' draw frame ( DOI2S ) to produce a finisher sliver of I .S7ktex which was than spun into yarns on Murata air-jet spinner (S02MJS), operating under normal mill conditions. The pre-tensioned polyester filament from the supply package placed at the creel-modified to accommodate the package of filament yam--was drawn through a guide. I t was accurately positioned at the center of the drafted ribbon of fibres and fed into the nip of the front drafting roller of the Murata air-jet spinner. The twisting action produced by two nozzles

TYAGI et at. : POLYESTER-VISCOSE MJS CORE-SPUN YARNS 1 7 1

causes the viscose fibres to wrap around the polyester filament core. Table 1 shows the important process parameters used for spinning these yarns. Various 1 l . 8 tex 1 00% viscose yarns were also spun from the same drawing stock with first nozzle pressures of 2 .5 , 3 .0 and 3.S kg/cm2 for comparison.

For ring spinning , the finished drawn sliver was converted into a suitable rove using an OKK roving frame . Equivalent core yarn ( 1 l . 8 tex ) was spun from the polyester filament and viscose materials on Lakshmi Rieters' ring frame G S/l using 1 3 ,SOO rpm spindle speed and 3.0 twist mUltiplier.

2.2 Methods 2.2.1 Tensile Properties

Instron tensile tester ( model 1 1 22 ) was used for tensile tests of yarns using SOOmm test specimen and 200mrnlmin extension rate. An average of SO observations was taken for each yarn sample.

2.2.2 Sheath-Slippage Resistance

CSI abrasion tester was used to measure sheath­slippage resistance. Thirty observations were made and the average number of cycles required to push the sheet aside was taken as a measure of sheath -slippage resistance.

2.2.3 Mass Irregularity and Hairiness

Uster-2 evenness tester with 200rnlmin yarn speed and normal setting of imperfections was used for the measurement of unevenness and imperfections.

Yarn hairiness was measured on Zweigle hairiness meter ( model GS6S ) using a test length of 200m. Twenty observations were made for each yarn sample.

3 Results and Discussion The influence of four experimental variables, viz.

yarn tex, ribbon width, first nozzle pressure and spinning speed, on the yarn properties was analysed using analysis of variance (A NOV A) (Table 2). Only first order interactions were considered.

3.1 Tensile Properties

Figs 1 -3 depict the results of tensile tests. The data show that the air-jet core yarns are about 6.4- 17 .0% weaker than the ring-spun core yarn, depending upon the process parameters used . The lower tenacity of jet core yarn can be attributed to its unique structure . Amongst air- jet yarns , the viscose-covered polyester filament core yarn has a tenacity of 1 l .37- 1 7 .88 cN/tex which is significantly greater than that of 1 00% viscose MJS yarn ( l 0.SO- 1 1 .42cN/tex) . The higher tenacity of core yarn is an expected consequence of the higher tenacity and breaking extension of polyester filament. This is consistent with the objective of deriving benefit from the constituent core filament, without the yarns being aesthetically distinguishable from pure viscose yarns. Fig. l shows that the tenacity of core yarn increases significantly with the increase in first nozzle pressure, and in all the cases the tenacity is greater than that of

Table I - Spinning parameters for polyester-viscose air-jet core-spun yams [NP2, 4.5 kg/cm

2; Feed ratio, 0.98; and Distance between first nozzle and

nip of front roller, 39 mm]

Yarn Yarn Yarn Fibre Ribbon Spinning NPI ref. type l inear composition width speed kglcm

2

no. density (polyester : viscose) mm mlmin tex

S , Polyester-viscose core yam 1 8.4 30 : 70 3 1 80 2.5/313.5

S2 Polyester-viscose core yarn 1 8 . .4 30 : 70 3 200 2.5/3/3.5

S3 Polyester-viscose core yarn 1 8.4 30 : 70 5 1 80 2.5/3/3.5

S4 Polyester-viscose core yarn 1 8.4 30 : 70 5 200 2.5/3/3.5

S5 Polyester-viscose core yarn 1 1 .8 47 : 53 3 1 80 2.5/3/3 .5

S6 Polyester-viscose core yam 1 1 .8 47 : 53 3 200 2.51313 .5

S7 Polyester-viscose core yarn 1 1 .8 47 : 53 5 1 80 2.513/3 .5

Sx Polyester-viscose core yam 1 1 .8 47 : 53 5 200 2.5/3/3.5

S,) Viscose yarn 1 1 .8 0 : 1 00 3 1 80 2.5/3/3.5

S I I) Ring-spun core yarn 1 1 .8 47 : 53

NPI - First nozzle pressure; N P2 - Second nozzle pressure

1 72 INDIAN J. FIBRE TEXT. RES. , JUNE 2003

Table 2 -Analysis of variance results for yarn properties

Process Yarn properties

variables Tenacity Breaking I n itial Sheath Hairi ness Regularity extension modulus sl ippage (U%)

resistance

A s s s

B s s s

C s s

D s s

A*B ns s s

A*C ns s s s s ns

A*D ns s

B*C ns ns ns s ns ns

B*D ns ns ns s ns ns

C*D ns ns ns ns ns ns

A*B*C ns ns ns ns ns ns

B*C*D ns ns ns ns ns s

A*B*D ns ns ns ns ns ns

A*C*D ns ns ns ns ns ns

s-Sign i ficant at 99% confidence level; and ns-Non-signi ficant at 99% confidence levcl. A-Yarn tex; B- Ribbon width; C- Spinning speed; and D-First nozzle pressure.

26�--------------------------------------------�

i 20

u � 16 u ! • ... 10

40

"I( c 0 30 .. c � • CII c :ac 20 � ID

10

A -18.4 "'jot cono r-n. 3 nwn. 1 80 IIVrnIn C - 1 1 .8 '" jot cono ywn. 3 nwn. 200 IIVrnIn E - 1 1 .8 '" viIcoee r-n. 3 nwn. 180 IIVrnIn

2.6 3

B-l1 .8 ... jot cono r-n. 3 nwn. 18011Vrn1n 0 - 1 1 .8 ... jot cono r-n. 5 nwn. 180 mlmIn F - 1 1 .8 ... ring - 8IU1 core ywn

3.6 First nozzle pre •• Unt, kg/em2

Fig. I -Variation of tenacity wi th first nozzle pressure

A - 18.4 '" jot core ywn. 3 nwn. 180 mI,,*, C - 1 1 .8 '" jot core r-n. 3 nwn. 200 mImin E . 1 1 .8 '" viIcoee ywn. 3 nwn. 1 80 _

2.6 3

B - 1 1 .8 '" jot core ywn, 3 mm. 1 80 mlmln 0 - 1 1 .8 '" jot cono ywn. 5 nwn. 180 mI,,*, F - 1 1 .8 '" ring - 8IU1 core ywn

c

First nozzle p,. .. u,., kg/em2

Fig.2-Variation of breaki ng extension with first nozzle pressure

TYAGI el at. : POLYESTER-VISCOSE MIS CORE-SPUN YARNS 1 73

1200

'" � 1000

A - 18.". jot ccn ywn. 3 mm. 180 m'II*I C - 1 1 .8 . jot ccn ywn. 3 mm. 200 m'II*I E - 1 1 .8 . >McoM ywn. 3 mm. 180 m'II*I

B - 1 1 .8 . jot ccn ywn. 3 mm. 180 m'II*I 0 - 1 1 .8 . jot ccn ywn. 5 rnm. 180 m/"*, F - 1 1 .8 ring - epun ccn ywn

u .; � "3 800 "8 E j 800 .E

400 2.5 3 3.5

First nozzle p ...... u ..... kg/cm2 Fig.3-Variation of i n itial modulus with first nozzle pressure

100% viscose yarn. Such an increase in tenacity arises due to the increase in the incidence and extent of wrapper fibres. In air-jet spinning, the yarn linear density is a highly significant factor for core yarn tenacity as is observed using the statistical analysis ANOV A . Fig. l shows that the highest tenacity is 1 8.43 cN/tex for 1 1 . 8 tex yarn at 3.5 kg/cm2 first nozzle pressure and 200 m1min spinning speed. The lowest tenacity of 1 1 .37 cN/tex belongs to 1 8 .4 tex yarn produced at 2.5 kg/cm2 first nozzle pressure and 1 80 m1min spinning speed .The effect of spinning speed is along the expected lines; a higher spinning speed results in a higher yarn tenacity. Core yarn tenacity also increases with the increase in ribbon width. With a wider condenser, the same number of fibres are spread over a greater width at the nip of the front roller which perhaps results in lower inter-fibre cohesion and thus greater number of edge fibres which lead to more and longer wrappings ' 2 .

The values of breaking extension for ring- and jet -spun core yarns ( Fig.2) show that , in general , the jet core yarns are more extensible than both pure viscose and ring- spun core yarns . While the breaking extension (%) of 1 1 . 8 tex ring core yarn is about 1 2.47, in jet-spun core and pure viscose yarns it varies between 1 2.04 and 26.09 and between 1 3 . 1 7 and 1 5 .78 respectively. Fig.2 shows that the first nozzle pressure plays a key role in influencing the breaking extension of core yarns. Within the pressure range of 2.S-3.Skg/cm2,the breaking extension increases significantly with the increase in pressure l 3 . The influence of spinning speed on breaking extension is similar to that on yarn tenacity. Moreover, the values of breaking extension are markedly lower for coarse core yarns than for fine core yarns; the values increase further significantly as the ribbon width is increased

from 3mm to Smm. This could again be attributed to the above- mentioned facts.

Fig.3 shows that the initial modulus of ring-spun core yarn is higher by about 1 3 .9-48% than that of jet-spun core yarns. A comparison of jet-spun yarns demonstrates that the core yarns have a nominal 1 1 . 1 -4 1 .9% higher initial modulus than the 1 00% viscose yarns. Fig.3 also shows that the core yarns spun with higher proportion of polyester filaments have higher initial modulus at all levels of spinning speeds. Further, the values of initial modulus of core yarns are substantially higher for wider condenser, as expected. The influence of first nozzle pressure on initial modulus is quite significant. All the yarns register a sizeable increase in initial modulus with the increase in first nozzle pressure ; this is generally true for both core and pure viscose yarns. As the first nozzle pressure increases , the vibrations of the secondary balloon formed between the nip of the front drafting roller and the first nozzle increase. This causes more edge fibres to be detached from the drafted strand , which then become wrapper fibres . Hence, as the vibrations of the secondary balloon increase, the number of wrapper fibres also increases lO which ultimately increases the transverse forces.

3.2 Sheath·Slippage Resistance

Relationship between the processing factors and the number of abrasion cycles to expose the core fi laments of ring- and jet - spun core yarns is shown in Fig. 4. As expected , the jet-spun core yarn exhibits significantly lower sheath-slippage resistance than the ring-spun core yarn. In air-jet yarn , the binding wrappers are really not large enough to protect the core consisting of twistless parallel bundle of fibres during the abrasion . The core, therefore, gets immediately exposed once the binding wrappers are

1 74 INDIAN J. FIBRE TEXT. RES., JUNE 2003

• 200 � u >- A - 1 8.4 lex j.t ccn YIIII. 3 mm. 180 m/mIn B - 1 1 .8 lex j.t ccn y.n, 3 mm. 180 mlmIn u C - " .e lex j.t ccny.n, 3 mm, 200 mImIn D - " .8 lex j.t ccn y.n, 5 mm, 180 mlmln

,,; 1 60 u E - 1 1 .8 leX ring - IfIUI1 ccn YIIII

c: I 'il f 1 20 • CIt !. .e- 80 .. i:. j (I) .0

2.5 3 3.5 First nozzle pre .. ure. kglcm2

Fig.4-Variation of sheath-slippage resistance with first nozzle pressure

120 T-------------------------------------------------�

1 00

20

o

A - 1 8.4 lex jot core ywn, 3 mm. 180 mlm C·- 1 1 .8 lex jot core y.m. 3 mm. 200 mI"*' E - 1 1 .8 lex vIocooe ywn. 3 mm. 180 mI"*'

2.5 3

B -1 1.8 lex jot core ywn. 3 mm. 180 mlm 0 - 1 1 .8 \81( jot core ywn. 5 mm, 180 mI"*' F - 1 1 .8 \81( ring - opun cor. y.m

F

3.5 First nozzle pre .. ure. kglcm2

Fig.5-Variation or hairiness with first nozzle pressure

broken and the yarn disintegrates immediately. According to ANOY A results (Table 2), both ribbon width and the core-sheath fibre ratio are highly significant factors affecting sheath- sl ippage resistance . It may be seen from Fig.4 that the abrasion cycles required to expose the core filaments are considerably higher for 1 8 .4 tex yarns and increase with the increase in ribbon width . Because the filament was the same for both the sets of yarns , the thicker sheath of 1 8 .4 tex yarn reduces the intensity of abrading action , leading to late exposure of filament core . With wider condenser , on the other hand , the inter-fibre cohesion is reduced , which , in turn , results in longer wrappings . Invariably, the sheath-slippage resistance in all the yarns tends to remarkably improve when both first nozzle pressure and spinning speed are increased. This seems to be due to the higher incidence of wrapper fibres. The wrapper fibres, which effectively bind and shield the core filaments, increase with the increase in first nozzle pressure and spinning speed, resulting in high sheath-slippage resistance.

3.3 Hairiness

The values of hairiness of ring- and jet-spun core yarns corresponding to different process parameters are shown in Fig.5 . It i s observed that , in general , the jet-spun core yarns are less hairy than the ring-spun core yarns. For jet core yarns, the i ncrease in spinning speed general ly increases the yarn hairiness. The increase in number of hairs occurs due to the increase i n front roller speed, leading to better separation of edge fibres '4, and the fai lure of the forming yarn to catch some of them. The ribbon width is another factor influencing core yarn hairiness. As may be observed from Fig.S, the use of wider condenser produces more hairy yarns on account of the increased number of floating fibres. Both yarn linear density and first nozzle pressure also have a marked effect on core yarn hairiness . Hairiness i ncreases li nearly when both first nozzle pressure and yarn linear density increase ' s . It is noteworthy that the 1 00% viscose yarn shows fewer protruding ends than the jet core yarn because more fibres i n the strand and the consequent greater surface contact between them

TYAGI et aL. : POLYESTER-VISCOSE MJS CORE-SPUN YARNS 1 75

Table 3�lnf1uence of process parameters on mass irregularity and imperfections of polyester-viscose MJS core-spun yarns

Yarn U%

ref.no 2.5 " 3.0" 3.5a 2.5a

Thick Thin Neps places places +200% +50% -50%

SI 9.3 9.6 9.8 7 2 2 1

S2 9.6 9.8 1 0. 1 9 2 22

S} 9.7 9.8 10.2 10 0 23

S4 9.9 1 0.3 1 0.6 1 2 0 26

Ss 1 0.3 1 0.6 1 1 .3 1 6 7 38

S6 1 0.5 10.8 1 1 .2 23 6 43

S7 1 0.7 1 0.9 1 1 .4 23 5 46

Sg 1 0.9 1 1 .3 1 1 .7 27 3 5 1

S� 10. 1 10 .3 1 1 .0 14 3 3 1

S IO 1 2.5 1 2.5 12.5 72 17 1 35

a First nozzle pressure, kg/em 2

make it difficult for the edge fibres to detach from the main strand at the front roller, resulting in fewer protruding ends.

3.4 Mass Irregularity and Imperfections

Table 3 shows that the jet-spun core yarn is more regular and has fewer imperfections than ring - spun core yarn . Generally the jet-spun core yarn has a mass irregularity value about 6.4- 1 7 .6% lower than that of ring- spun core yarn, depending upon the process parameters used . However, the yarn l inear density , ribbon width ,spinning speed and first nozzle pressure may play a significant role in determining the yarn unevenness . The fact that the fine yarns are less regular compared to coarse yarns also holds true for jet-spun core yarns. Table 3 shows that the mass irregularity ( U% ) of 1 1 . 8 tex and 1 8 .4 tex core yarns varies from 1 0.3 to 1 l .7 and from 9.3 to 10.6 respectively. With increased ribbon width, the evenness of all the yarns significantly deteriorates due to the increase in wrapper fibres. Incidentally, the influence of first nozzle pressure on yarn evenness appears to be of marked importance. As may be observed from Table 3, the yarn evenness significantly deteriorates when the first nozzle pressure is increased from 2 .5kg/cm2 to 3 .5kg/cm2 . At higher first nozzle pressures, the yarn evenness deteriorates due to the concentration of mass in very short lengths owing to the greater incidence of wrapper fibres 16. Spinning speed also significantly affects the yarn unevenness; the unevenness increases

Imperfections / 1 25 m

3.0a 3.5"

Thick Thin Neps Thick Thin Neps places places +200% places places +200% +50% -50% +50% -50%

1 0 I 23 1 2 I 24

I 3 I 25 14 0 26

1 1 I 26 1 4 I 29

1 5 0 32 1 7 0 33

20 1 0 42 22 1 4 46

25 8 48 26 1 3 5 1

26 7 50 28 12 53

30 4 54 34 10 57

17 8 37 20 9 39

72 1 7 1 35 72 17 1 35

with the increase in spinning speed. This increase is caused by the greater disturbance in spinning balloon due to the increased air flow at front roller nip at higher spinning speed.

Table 3 also shows that there is a general increase in the incidence of imperfections with the increase in first nozzle pressure. The use of wider condenser increases the imperfections. The increase in imperfections occurs due to the greater fibre disturbance by the air current in the less cohesive ribbon. Spinning speed also appears to significantly affect the number of imperfections, which increase with the increase in spinning speed.

It is interesting that the unevenness and imperfections of the jet-spun core yarn are well within the acceptable quality l imits, although they are at slightly higher levels than those of the 100% viscose yarn . The core spinning process is probably responsible for the yarns with relatively higher values of unevenness and imperfections .

4 Conclusions 4.1 Ring-spun core yarn is stronger, less extensible, more hairy and less regular, and has more imperfections and higher sheath-slippage resistance than jet-spun core yarn. The higher spinning speed offers considerable advantage in air-jet spinning in respect of tensile properties of core yarn . First nozzle pressure has the greatest influence on core yarn tenacity, breaking extension and initial modulus. All these properties improve to different degrees,

1 76 INDIAN J. FIBRE TEXT. RES. , JUNE 2003

depending upon the yarn l inear density and ribbon width.

4.2 The ribbon width as well as the spinning speed markedly influence the sheath- slippage resistance, which tends to increase with the increase in spinning speed and ribbon width. Sheath- slippage resistance also increases significantly when first nozzle pressure increases and , at the same time, when yarn linear density decreases.

4.3 Core-spun yarns can be spun on Murata air-jet spinning system. However, the sheath-slippage resistance of these yarns is significantly lower than that of other core-spun yarns produced by ring, rotor, friction and tandem spinning technologies. Mass irregularity and imperfections of the continuous­filament core yarn and the 1 00% viscose yarn are nearly within the same range. However, the yarns produced with a higher first nozzle pressure, a wider condenser and a higher spinning speed are more hairy, less even and have more imperfections.

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