Establishing the effect of machine parameters on polyester-Lycra air covered knitted fabric

by C. Prakash, Lecturer, Dept. Fashion Technology,
Sona  College of Technology, Tamil Nadu, India

Abstract

Demand for woven and knitted textiles with elastic properties for shape retention and comfort has been constantly rising for the last few years. This is mainly due to the shift in consumer preference for durability to comfort.


The main objectives of knitted garment are to provide required stretch and comfort properties to the human body. To improve these properties, Lycra, the more elastomeric filament is used along with cotton or man-made as core spun.
In this paper, Single jersey fabric is produced from Polyester / Lycra air-covered yarn with different loop lengths. The study covers about the testing of dimensional properties of the single jersey knitted fabric. After the fabric production, the fabric was dry relaxed. Wales per inch, Courses per inch, Fabric width, Loop length and Fabric thickness are all measured. Then the fabric was wet relaxed and tested for the above parameters. Then the samples were heat set at various stretch levels at 180o C.
From the study, it was found that the dimension of fabric shows considerable change during wet relaxation. The fabric shows very good appearance when heat set at all stretch levels at 180o C in course direction. The fabric with a loop length of 2.5 mm was found to have better appearance when compared to the fabrics of other loop lengths.  In particular 10% stretch level shows a better appearance for 2.5 mm loop length.

Introduction

Today fashion designers are much conscious than ever and have up-to-date information about the latest fashion trends. The present day consumer demands fashionable garments, which offer comfort and style, stretch and flexibility, freedom and figure enhancement, as he takes it as the tool of expressing his personality. As far as comfort is concerned, polyester / cotton blends are more popular than pure polyester. All cotton garments may be comfortable but have wrinkle problems. It is here Lycra comes to our help in offering wrinkle resistance and garment integrity while offering extra comfort. The wearer of Lycra containing garment feels less fatigued and muscle strain than the one wearing garments without Lycra. This value of Lycra is well recognized by the fabric and apparel manufacturers as well as the consumers.
The ongoing influence of casual clothing of life style is boosting the popularity of Lycra containing garment. As casual work attire becomes more popular, Lycra allows these types of garments more comfort. Additionally, Lycra provides a greater degree of wearability, wrinkle recovery and crease retention, making it the perfect compliment to most garments.
Researchers have found that natural fibres like cotton, silk, wool offers comfort and aesthetic properties while synthetic fibres like Nylon, Polyester, Polyurethane are more known for strength and elasticity, in other words, neither natural nor synthetic fibres can fulfil these needs when used singly in the yarn. Blending of these natural and synthetic fibres homogeneously thus becomes essential to take the advantage of better properties, blending these fibres with spandex / Lycra fulfils majority of the requirements of the consumer and it is found that Lycra is readily compatible with most other fibres, including Nylon, Polyester, Acetate, Polypropylene, acrylic, cotton, wool, and rayon. However, the proportion of Lycra in the blends with these fibres varies significantly depending upon the end uses and application of the materials.
In this paper, studies have been done on the dimensional properties of knitted fabrics produced from air-covered elastomeric yarn. Here, Lycra polyester air-covered yarn is knitted into single jersey fabric and their properties have been tested on this knitted structure.

Methodology

For the study of dimensional properties of Polyester / Lycra stretch yarn knitted fabric, Single jersey plain knitted fabric samples at various loop lengths was produced. The fabric was Dry-Relaxed by keeping on flat surface for two days.
On each sample the following test parameters are measured.
1.Wales per inch
2.Course per inch
3.Width of the fabric
4.Loop length
5.Thickness of the fabric
Then the fabric was subjected to Wet-Relaxation and again the above parameters were measured.

Results & discussions

The test results for Dry-Relaxed state are given in Table 1 and for Wet-Relaxed state in Table 2.
From the table 1, it is been found that the values of CPI, WPI, Kc, Kw, N, Ks and Kc/Kw varies with respect to loop length and also it is been found that there is a decrease in the CPI, WPI, Kc, N, Ks and Kc/Kw values and an increase in Kw value during dry relaxation process. Results are shown in figure 1a & figure 1b.
From the table 2, it is been found that the values of CPI, WPI, Kc, Kw, N, Ks and Kc/Kw varies with respect to loop length and also it is been found that there is an increase in the CPI, Kc, Ks and Kc/Kw values, a decrease in WPI & N value and a subsequent decrease and increase in Kw value during wet relaxation process. Results are shown in figure 2a & figure 2b.
From the tables 3 to table 5, it is been found that CPI and WPI  value varies with respect to stretch level at constant loop length and also it is been found that there is a decrease in the Wales per inch and increase in courses per inch.
From the above table, it is been found that Courses per inch values varies with respect to loop length and also it is been found that there is a considerable increase in the Course per inch after hot washing.
From the above table, it is been found that Wales per inch values varies with respect to loop length and also it is been found that there is a decrease in the Wales per inch after hot washing.
From the above table, it is been found that Loop length values varies before and after wet relaxation and also it is been found that there is a minimal change in the loop length after hot washing.
From the previous table-9, it is been found that width of fabric values varies with respect to loop length and also it is been found that there is a decrease in the width of fabric after hot washing.
From the  table 10, it is been found that thickness of fabric values varies with respect to loop length and also it is been found that there is an increase in the thickness of fabric after hot washing.

Conclusions

• Courses per inch increase with an increase in loop length.
• Wales per inch decrease with an increase in loop length.
• Loop length increases after wet relaxation process when compared to that of the value set in the machine.
• Thickness of fabric increases with an increase in loop length.
• From the study, it was found that the dimension of fabric shows considerable change during wet relaxation.
• The CPI increases from 17.65% to 70.49% and an average percentage change in CPI is 47.56% after Wet- Relaxation.
• The WPI decreases from 59.57% to 31.75% and an average percentage change in WPI is 44.2% after Wet- Relaxation.
• The fabric shows very good appearance when heat set at all stretch levels at 180oC in course direction.
• A fabric with a loop length of 2.5 mm was found to be better appearance when compared to the fabrics of other loop lengths which have cloudy appearance.  In particular 10% stretch level shows a better appearance for 2.5 mm loop length.

References

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