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Short Communications

Characteristics of rotor-spun composite yarns

Haixia Zhang" & Shan yuan Wang

College of Textiles, Donghua University, Shanghai 20005 1 , P R China

and Yuan Xue

College of Clothing and Art Design, Jiaxing University, Jiaxing 3 1400 1 , P R China

Received 17 Jalluwy 2005; revised received 1 July 2005;

accepted 1 A ugust 2005

Various rotor-spun composite yarns have been produced by combining staple fibres with filament yarns under varying filament overfeed ratio on a modified open-end rotor spinning frame. The effects of filament overfeed ratio on the structure and properties of composite yarns have been studied. It is observed that the filament overfeed ratio has great influence on the filament geometric position and helix trajectory in composite yarns. As the filament tension increases with decreasing filament overfeed ratio, the filament moves from the surface into the center of the composite yarn. The tensile properties of composite yarns depend on the filament overfeed ratio, and the filament overfeed ratio alone does not explain the CVO/O and hairiness of composite yarns.

Compared with the normal rotor-spun yarn, the appearance and properties of rotor-spun composite yarns arc improved.

Keywords: Cotton, Composite yarn, Filamem overfeed ratio, Rotor-spun yarn

IPC Code: Int. CI.8 D02G3/00

Rotor spinning has been adopted worldwide at present. I ts main advantages over ring spinning are high yarn output rates, reduced production costs, increased bulkiness and i mproved evenness of the yarns. However, the relatively low breaking strength and wrapper fibres of yarn surface are sti l l matters of concern. I -3 These disadvantages may be improved by combi ning staple fibres with a continuous fi lament yarn in rotor spinning process. Some researchers have studied the spinning conditions and characteristics of rotor-spun composite yarns. Nield and Ali4 described a mechanism for producing open-end core-spun yarns.

"To whom all the correspondence should be addressed.

Present address: Department of Texti les, Henan Textile Col lege, Zhengzhou 450007, P R China

E-mail: hxzhang@mail.dhu.edu.cn

Cheng and Murray5 reported a method of making core-spun yarns on an open-end rotor spinning frame.

Pouresfandiari et al. 6 and M atsumoto et al. 7 reported their progress in producing different kinds of novel hybrid yarns on an experimental open-end spinning frame.

In the present work, different kinds of composite yarns have been produced under varying filament overfeed ratio on a modified open-end rotor spinning frame, and the effects of filament overfeed ratio on the structure and properties of rotor-spun composite yarns analyzed.

A cotton sliver (25.4mm mean fibre length, 1 .5dtex fibre linear aensity, 3.43 fibre micronaire value and 4.32g/m sliver size) was used as the staple fibre, and a polyester filament (3.33tex, 30d/ 1 5f) was used as the filament yarn fed i nto the rotor.

Figure I shows the schematic diagram of modified open-end rotor spinning process. The fi lament yarn was fed from a supply bobbin by the suitable guides to the filament feed rollers, passed straight through the filament guide tube and then drawn into the rotor freely by suction, where the fi lament yarn was combi ned with the staple fibre strand to form the composite yarn. The composite yarn was then drawn through the doffi ng tube and fi nal ly on to the take-up roller. The filament guide tube was positioned along the axis of rotation of the hollow rotor shaft, which rotated freely about it. The filament feed rollers w ere able to feed the filament yarn positively with a wide range of constant feeding speeds. During the spinning process, the tensions of both the filament and the composite yarns were measured by Rothschild R046 Tension M eter. The fi lament tension was measured between the fi lament feed rollers and the fi lament guide tube (A in Fig. 1 ), and the composite yarn

Fig. I -Schematic diagram of rotor-spun composite yarns spinning process

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SHORT COMMUNICATION 46 1

tension was measured between the doffing tube and the take-up roller (B i n Fig. I ).

Spinning parameters for composite yarns were: 58 tex normal linear density, 6 1 7 tpm designed twist, 7000 rpm opening roller speed, 45000 rpm rotor speed (50 mm rotor diameter), 72.9 m/mi n take-up speed, and 80.8 draft ratio. The fi lament overfeed ratio (OFR) was 0.9 1 , 0.94, 0.97, 1 , 1 .03, 1 .06, 1 .09 and 1 . 1 2 respectively. It was calculated by the following relationship:

OFR= Filament feed speed/Composite yarn take-up speed.

For the comparison, a normal rotor-spun yarn was produced under the same spinning conditions and parameters.

A tracer fibre technique was used to observe the yarn structure and the geometric position of the filament in the composite yarn.8-9 A black-dyed polyester filament (3.33tex, 30d1l 5f) was used as the tracer fibre. The longitudinal view of composite yarns and the spatial trajectory of the filament yarn can be observed and recorded by Questar Hi-scope Video Microscope System. The filament radial position R/

and half pitch were measured. The filament relative radial position r could be obtained from the following equation:

R was composite yarn radius

B reaking strength and extension were determined from the mean of 60 tests with a test length of SOOmm, extension rate of 500mm/min and pretension of 29cN, and the load-extension curves were obtained at the same time. Irregularity was measured with the yarn speed of 400 m/min and the testing time of 1 min. Hairiness was tested with the testing speed of 30m/min and test length of 1 00 m, and the hairs above 2mm per meter were measured. All the tests were performed under a standard atmosphere of 20±2°C and 6S±2% RH.

Figure 2 shows the relationship between the filament overfeed ratio and the yarn tension. The tensions of both the filament and the composite yarns increase with decreasing filament overfeed ratio, and the composite yarn tension is found to be higher than the filament tension. The filament overfeed ratio decreases, i.e. the filament feed speed decreases gradually under the constant take-up speed, so the filament tension increases. As the spinning tension of the composite yarn i s composed of the filament tension, staple fibre strand tension and other factors,

1 60

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0 .90 0.95 1 00 1 .0 5 ·1 .1 0

Filament Over-Feed Ratm

Fig. 2-Effect of filament overfeed ratio on yarn tension

Normal rotor-spun yarn

Composite yam, OFR= 1 . 1 2

Composite yam, OFR=O.91

Fig. 3-Yarn appearance (OFR-Filament overfeed ratio) the composite yarn tension increases with the i ncrease i n filament tension. When the filament overfeed ratio is beyond 0.9 1 , a h igh frequency of end breakage for the staple fibre strand may occur.

Figure 3 shows the typical appearance of the composite yarns and normal rotor-spun yarn. The appearance of the composite yarn is clearer than that of the normal rotor-spun yarn. Rotor-spun yarn is

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known to have a skin-core structure, consisting of a central core that resembles ring-spun yarn, and an outer sheath containing a random disarray of fibres and wrappers. 10.1 3 The morphology of wrapper fibres lying near the surface of the rotor-spun yarn is relatively loose. During the spinning process of composite yarns, the morphology of wrapper fibres on the cotton strand surface becomes tighter and clearer than that of the normal rotor-spun yarn because of the insertion and wrapping of the filament.

The filament overfeed ratio has great influence on the appearance of composite yarns as shown in Fig. 3.

When the fi lament overfeed ratio decreases, the filament moves from the surface into the center of the composite yarn gradually. If fi lament overfeed ratio decrease to 0.9 1 , the polyester fi lament is located near the center of the composite yarn and is almost completely covered by the cotton fibres. The yarn morphology is similar to a normal rotor-spun yarn, but there is less hairiness than that of the normal rotor-spun yarn. The polyester filament in the composite yarn is twisted with the cotton strand and follows a helical path. According to idealized helical yarn geometr

/

4, when a composite yarn is made from two components, i t is necessary to have different component lengths i n the yarn. If one component is a fi lament yarn, the length can be easily controlled by the tension. When the filament tension increases with the decrease of filament overfeed ratio, the filament yarn tends to lie along the axis of the composi te yarn near the center as a core and can be covered by the staple fibre strand.

Figure 4 shows three kinds of typical structures of composite yarns produced at different filament over­

feed ratids. When OFR is 1 . 1 2, the filamerit tension is relatively low and hence the filament yarn wraps over the staple fibre strand 'a nd follows a helical path.

When OFR is 1 , i.e. the filament feed .speed is equivalent to the take-up speed, the filament yarn also follows a helical path and tends to lie in the i nner layer of composite yarns. When OFR is 0.9 1 , the filament tension becomes relatively high and hence the filament yarn lies along the axis of the composite yarn near the center.

Figure S shows the relationship between the filament overfeed ratio and the filament relative radial position r and half pitch. As the filament tension increases with decreasing filament overfeed ratio, the filament yarn tends to lie near the axis of the composite yarn. Accordingly, the filament relative

OFR=I . 12

OFR=1

OFR 0.91

Fig. 4-Typical structures of composite yarns

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Filament Olrer-Feed Ratio

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0.72

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Fig. 5-Structural parameters of composite yarns radial position r decreases and the pitch of the filament helix trajectory i ncreases gradually.

Figure 6 shows the typical load-extension curves of the composite yarn, normal rotor-spun yarn and filament yarn. The breaking strength of the filament yarn (30d/ l Sf) is lower and extension is higher than other yarns. The composi te yarn shows a marked increase in breaking strength, i nitial modulus and extension as compared to the normal rotor-spun yarn.

The morphology of wrapper fibres on the surface of the rotor-spun yarn i s relatively loose and they have

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SHORT COMMUNICATION 463

little contribution to the yarn strength. During the formation of composite yarns, owing to the i nsertion and wrapping of the filament, the morphology of wrapper fibres becomes much tighter and the transverse pressure as well as cohesive forces among fibres increase and the breaking strength of the composite yarn i ncreases.

Figure 7 shows the effects of filament overfeed ratio on the tensile properties of composite yarns. I n the case o f OFR?: 1 , while the filament overfeed ratio decreases, the breaking strength of composi te yarns has a tendency to increase and the breaking extension has no significant change. As the filament tension increases with decreasing filament overfeed ratio, the wrapping of the filament yarn is greater and the yarn structure becomes tight and uniform and hence the inter-fibre cohesive forces and the breaking strength of composite yarns increase. In the case of OFR< 1 , the filament i s stretched effectively and the tensile characteristics of the filament i tself is changed, so the breaking strength of composite yarns decreases. When

UXX) o mpoSl e un

(Low OFR) ,

BOO ./Y Comp osite Yarn

£' . ..: J.' (High O FR )

600 .' / ,-

IJ '

/

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0; I': 0 400

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200 . ,.

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0 ,, � .

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ExtensKm(% ) Fig. 6-Typical load-extension curves

.-.. 850 Z ..::..

0; 8 800 ....:l

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Load

"

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Extension

'-0

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0. 92 0. 96 1 . 00 1 . 04 1 . 08 1. 12 Filament Ov er-Feed R atio

20

Fig. 7-Effect of filament overfeed ratio on tensile properties of composite yarns

the composite yarn is withdrawn from the take-up bobbin, the filament yarn recovers from its spring stretch, which makes the staple fibre strand component in the yarn slack and the breaking extension of the composite yarn increases accordingly.

Figures 8 and 9 show the effects of filament overfeed ratio on the yarn irregularity and hairiness respectively. It can be observed that the filament overfeed ratio alone does not explain the CV% and hairiness of composite yarns. Both the CV% and hairiness of composite yarns are less than that of the normal rotor-spun yarn. The evenness of the composite yarn is better and its surface is clearer, i .e.

consistent with the results drawn from the yarn longitudinal photographs (Fig. 3). The improvement in hairiness on the surface of the composite yarn is high. This phenomenon can be explained by the wrappmg of the filament yarn on the cotton fibre strand.

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9

Norm al O E Y arn

. �

.�-.---.�

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O. 92 0. 96 1. 00 1. 04 1. 08 1. 12 Filament Ov er-Feed Ratio

Fig.8-Effect of filament overfeed ratio on yarn irregularity

16 .---�

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o

No rmal O E Y arn

C o mp osite Y arn

.--.--- .--- .---.�.--.

0. 92 0 . 96 1 . 00 1. 04 1 . 08 1 . 12 F ilament {hr er-Feed Ratio

Fig. 9-Effects of filament overfeed ratio on yarn hairiness

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The results show that the changes In filament overfeed ratio can lead to the changes In filament tension and have great influence on the appearance, structure and properties of composite yarns. The polyester filament in the composite yarn is twisted with cotton strand and follows a helical path. As the filament tension i ncreases with decreasing fi lament overfeed ratio, the filament moves from the surface into the center of the composite yarn gradually. At the same time, the breaking strength of composite yarns has a tendency to increase, and the breaking extension, CV% and hairiness have no significant changes. With the filament overfeed ratio less than 1 , the breaking strength of composite yarns decreases and the breaking extension increases. In comparison with the normal rotor-spun yarn, the morphology of wrapper fibres near the composite yarn surface is tighter and clearer. The composite yarn shows a marked increase in breaking strength, initial modulus and extension. The CV% of composite yarns i s low and the i mprovement in hairiness i s high.

References

I Basu A, J Text illst, 9 1 (2000) 1 79.

2 Tyagi G K, Illdiall J Fibre Text Res, 29 (2004) 35.

3 Huh Y, Kim Y R & Oxenham W, Text Res J, 72 (2002) 1 56.

4 Nield R & Ali A R A, J Text IlIst, 68 ( 1 977) 223.

5 Cheng K B & Murray R, Text Res J, 70 (2000) 690.

6 Pouresfandiari F, Fushimi S, Sakaguchi A, Saito H, Toriumi K, Nishimatsu T, Shimizu Y, Shirai H, Matsumoto Y &

Gong H, Text Res J, 72 (2002) 6 1 .

7 Matsumoto Y, Fushimi S, Saito H, Sakaguchi A, Toriumi K, Nishimatsu T, Shimizu Y, Shirai H, Morooka H & Gong H, Text Res J , 72 (2002) 735.

8 Morton W E & Yen K C, J Text IlIst, 43 ( 1 952) 60.

9 Zhang H W, Chen 0 S & Wan Y B, Text Res J, 73 (2003) 945.

1 0 Lord P R & Grady P L , Text Res J, 46 ( 1 976) 1 23.

I I Hearle J W S, Lord P R & Senturk N, J Text IIISf. 63 ( 1 972) 605.

12 Lord P R, Text Res J, 4 1 ( / 97 1 ) 778.

1 3 Salhotra K R , Oulla B & Scott S K, Texl Res J, 5 1 ( 1 98 1 ) 360.

1 4 Hearle J W S, Gupta B S & Merchant V B, Text Res J , 35 ( 1 965) 329.

References

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