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  Properties of silk/Modal blended knitted fabrics

Silk/modal blended knitted fabrics have the highest air permeability and abrasion resistance besides least air resistance with very good thermal conductivity – all these properties making this blended fabric an excellent choice as garment material, infer A Thirugnanasambantham and M Senthilkumar.

Apparel industry is always driven by trendy fashion concepts. Fashion is a resultant of the culmination of creativeness compounded with or without simple or exotic concepts, designs, shapes, silhouettes with ornamentations and splash of colours. Fashion and trend changes can occur at any point of time.

Pure silk knitted fabrics have very good scope because it is a synonym for elegance, and silk garment are prized for their vanity, versatility, wearability and comfort. Silk is the strongest of natural fibres. Silk absorbs moisture, which makes it cool in summer and warm in winter. Because of its high absorbency, it is easily dyed in varieties of pale and deep colours. Silk retains its shape, drapes well, and sparkles with a dazzling lustre.

Similarly, knitted fabric has tremendous technological advantage over woven with regard to speed of production therefore it finds increasing acceptance in the market owing to its great adaptability to changing fashion trends. Demand for an easy care, comfortable clothing is on the rise and hence, there is a need to diversify the composition and structure of silk clothes. But, silk fabric production through knitting machines is not commercially viable even though the concept exists.

So, in the current work a novel attempt has been made to produce silk/modal blended knitted fabric and to compare their mechanical and comfort properties with 100% cotton and modal fabrics. 100% silk knitted fabrics are not included in the comparison because of the commercial production constrains.

Objective of the study
In the current work, knitted fabrics were produced from 50:50 silk/modal blend. It is compared with the mechanical and comfort properties of cotton and modal garment of equal construction. From these three fabrics casual wears were developed and they were also subjectively analysed for their comfort properties.

Materials and Methods
Yarn specifications

The selected yarn specifications are given in Table 1.

The selected modal yarn has less unevenness and less mass variation, more uniformity and low imperfections (-50% thin, +50% thick and +200% neps) than that of silk/modal blend and 100% cotton. U%, CV% and imperfections are least for modal and less for cotton and followed by silk/modal blend.

Hairiness value of silk/modal yarn is better than cotton and closer to modal itself. Single yarn strength and lea strength, elongation and CSP are higher for silk/modal yarn.

Knitting machine specifications
The selected yarns were converted into fabrics by using the following machine specifications (Table 2)

Dyeing and compacting specifications
The produced knitted fabrics were dyed and compacted. The process details are provided in Table 3.

The above three colours -- Blue FNG, Turquoise blue CLB and Yellow F4G, were mixed and treated with fabrics for 20 minutes. Then, common salt was added and the treatment was continued for another 20 minutes. After that the fabrics were treated with soda ash (10 g/l ) for one hour. Then the fabrics were taken out and washed twice. Again the fabrics were treated with acetic acid (1% concentrated) for 30 minutes. And washed for 20 minutes. Then, the fabrics were given soaping treatment for 30 minutes at 95°C. Finally, washing was carried out for 20 minutes and the fabrics were treated with 0.5% concentrated acetic acid.

Testing methodology
The mechanical and comfort properties of the selected knitted fabrics were tested as per the standards given in Table 4.

Results and discussion

Fabric geometrical properties
The fabric geometrical properties are tabulated in Table 5.
Hundred percentage Modal fabric has higher stitch density followed by Cotton and silk/modal fabric. Cotton fabric has higher dimensional stability than other two fabric due to control of inter yarn movement within the fabric because of the fibre hairiness and bulkiness. Modal fabric has higher loop length than the selected fabrics, even though they were produced in the same knitting machines. This may be due to change in fibre flexural rigidity.

Cotton fabric has higher thickness value due to higher hairiness and bulginess. There is no significant difference between the tightness factor among all three fabrics.

Silk/modal blend has higher shrinkage followed by modal fabric and cotton fabric in wale wise direction. In the case of the fabric growth, the same trend has been found in course wise direction. Modal/silk blended fabric has higher area shrinkage than other two fabrics.

Mechanical and comfort properties
The fabric mechanical and comfort properties are tabulated in Table 6.
Mechanical properties
Silk/modal fabric has lower bursting strength than 100% cotton and 100% modal fabric. Variation in bursting strength is higher in case of modal/silk blend fabric. The reason is mainly due to higher unevenness and higher mass variation of the yarn. Cotton bursting strength CV is lower than other two fabrics. Hundred per cent modal has lower bursting strength compared with cotton even though it has very good uniformity and less mass variation. Reason is due to lower lea strength.

Abrasion resistance of silk/modal blend and modal fabrics are better than cotton fabric. Because, they are man-made fibres and their surface is smooth and that smoother surface always has less friction leading to least abrasion, whereas in case of cotton, protruding fibres in the sheath obviously will come out during abrasion. That is the reason for the higher weight loss.

Silk/modal blend and modal have higher drapapility than cotton fabric. Because, silk fibre has inherent drapability, which is reflected in the modal/silk blended fabric.

Comfort properties
Wetting; Sinking method is an indirect measure of transverse wicking of the textile materials. Measurement of transverse wicking is more important than the measurement of wicking in the longitudinal direction because the fabric is clinging to the body in transverse direction only. Hundred per cent modal and silk/modal blend have quicker sinking time than that of cotton fabric. Because, uniform and smoother surface characteristics of these fibres make the absorption quicker.

Silk/modal blend has higher longitudinal wicking length followed by modal for the test time of 5 minutes than that of cotton fabric. Because the man-made fibres are uniform in nature, which enhances the capillary rise of the material.

Cotton fabric has higher air resistance and lower air permeability than the other two selected fabrics due to its thickness and hairiness. Silk/modal fabric has lowest air resistance and highest air permeability than that of other two fabrics, due to higher stitch density. In general, air resistance is inversely proportional to air permeability.

One hundred per cent modal fabric has rapid water absorbency followed by silk/modal than the cotton fabric significantly. Cotton has poor water absorbency because of its thickness and hairiness. In the case of water vapour transmission, there is no specific trend found in the selected knitted fabrics. But, silk/modal fabric has higher water vapour transmission characteristics than that of other two selected fabrics. Perspiration transmission characteristics decide the garment’s suitability for summer, winter or as sportswear.

Silk/modal fabric has higher thermal conductivity than other two fabrics. It is due to its inherent characteristics of the silk fibre.

Overview

The overall inferences gathered from the analysis are silk/modal has excellent longitudinal and transverse wicking property. It also has highest air permeability and least air resistance with very good thermal conductivity. It shows highest abrasion resistance along with very good drapability. These properties make this blended fabric an excellent choice as garment material. Its low water absorbency and low vapour transmission characteristics make it suitable for winter garment.

Subjective analysis
Grading: 5 – Excellent, 4 – Very good, 3 – Good, 2 – Fair, 1 – Poor

The subjective opinion gathered from a select group of population indicates Silk/Modal garment as having excellent look, feel and comfort, but has less absorbency character and is not preferred for summer wear but for its acceptability as winter wear.

Conclusion
The aim of the work was to study the mechanical and comfort properties of silk/modal blended knitted fabric and to compare their properties with 100% cotton and Modal fabrics. Silk/modal has excellent longitudinal and transverse wicking property. It also has highest air permeability and least air resistance with very good thermal conductivity. It shows highest abrasion resistance and with very good drapability. These properties make this blended fabric an excellent choice as garment material. Its low water absorbency and low vapour transmission characteristics make it suitable for winter garment.

Acknowledgement
The authors thank the Management, Principal and the Head of the Department of Textile and Apparel Technology of PSG Polytechnic College for their valuable support and guidance throughout this work. and the students – I Divya, S Janani, R Ramya, A Gowri, and R Uma Devi for their contribution to the work of the authors.

References
1.Senthilkumar M: Physical and Comfort Properties of Spun Silk Knitted Fabrics, The Indian Textile Journal, April 2008.
2.Senthilkumar M: Studies in Knitting of Filament Silk Yarn, Journal of the Institution of Engineers (India), Volume 89, August 2008.
3.Knapton J J F: The Dimensional Properties of Knitted Wool Fabrics - Part 1 - 5, TRJ, 1963, pp 158.
4.Ajgaonkar D B: Performance of Open-end, Twistless and Ring Yarns in Weft Knitted Fabric, TRJ, June 1974, pp 405.
5.Sharma I C: Dimensional and Physical Characteristics of Single Jersey Fabrics, TRJ, March 1985, pp 149.
6.Starfish - Prediction of Finished Dimensions of Cotton Knits, TRJ April 1985, pp 211.
7.Munden D L: The Geometry and Dimensional Properties of Plain Knit Fabrics, JTI, 1959, pp 448.
8.Knapton J J F: The Geometry and Dimensional Properties and Stabilisation of the Cotton Plain Jersey Structures, JTI 1975, No: 12.
10. Behera B K: Comfort Properties of Fabrics Woven From Ring, Rotor and Friction Spun Yarns, JTI 1997, Part 1, No: 3.
11. Hiroshi Kato and Tamako Hata: Development of Silk Yarns for Knitted Fabrics, Published at Department of Insect Processing Engineering, National Institute of Sericultural and Entomological Science, Japan.
12. Special Report, Silk Pick Up, Textile Asia, October 2000, pp 13.
13. Rajiv Kumar, et al: Feasibility of Spinning Silk/Silk Blends on Cotton System, Textile Asia, February 2001, Part I, pp 27.
14. Shiva Kumar V R: A Comparative Study of the Knitting Performance and the Properties of Fabrics Knitted from Ring and Rotor Spun Yarns, 22nd Technological Conference, pp 50.
15. Shankara Narayanan K S: Effect of Yarn Quality on the Properties of the Knitted Fabrics and Performance in Knitting, 22nd Technological Conference, pp 159.
16. Parate D M: Evaluation of Yarn Properties for Knitting (Part 1 and Part 2), Man-Made Textiles in India, October 1995.
17. Raj Kumar R: Silk Knitted Fabrics for Outer Garment, The Indian Textile Journal, July 2001, pp 127.
18. Siva Kumar M: Role of Silk in Knitted Fabrics Production, Textile Magazine, August 2000, pp 45.
Note: For detailed version of this article please refer the print version of The Indian Textile Journal January 2010 issue.

A Thirugnanasambantham
Department of Apparel Technology
PSG Polytechnic College, Coimbatore 641 004.

M Senthilkumar
PSG Polytechnic College, Coimbatore 641 004.

published January , 2010
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