Knitters of cotton circular knitted fabrics are faced with increasing global competition and ever increasing demands for better quality and reliability. One of the key demands is for fabrics and garments with consistently low levels of potential shrinkage.
Excellent comfort properties of weft knits have seen them increasingly used in formal wear for men and women. But with technological advancement in fabric manufacturing and increasing customer awareness of quality, expectations have risen.
However, knit goods are known to be prone to deformation during manufacturing and when worn. Knitting technology has advanced considerably during the past two decades with the introduction of various knitted structures, use of new and modified yarns and the versatility of modern knitting equipment.
Dimensional stability of weft-knitted fabrics is a serious problem in view of fabric quality control. Generally the stitch density of plain knitted fabrics in the dry relaxed state is dependent only on the loop length and independent of other yarn and knitting variables. This study attempted to demonstrate the influence of loop length on the shrinkage properties of knitted fabrics.
Traditionally, cotton circular knitted products have been developed and optimised largely by trial and error methods but these methods will not be good enough for the future because they are too costly and uncertain. A modern quality assurance system requires firstly that product performance can be designed in advance by exact calculations and secondly that processing machinery can be regulated by reference to predetermined target levels of key product properties which can be measured continuously, on-line and used in feed-back loops to control some aspect of machinery settings. Figure 1 shows the stitch length (loop length) of a knitted fabric.
For cotton circular knitted fabrics, there are three major requirements for achieving ‘low shrinkage by design’.
• The fabric has to be correctly engineered for the required performance (appropriate choice of yarn and knitting conditions);
• Appropriate values have to be specified for the key fabric properties which will be used for process control (finishing targets);
• The finishing machinery has to be provided with appropriate sensors and regulators.
For a study of the dimensional properties, single jersey plain knitted fabric samples with four different loop lengths: 2.6mm, 2.65mm, 2.77mm and 2.95mm were produced. The fabrics were tested for GSM (g/sq m) and shrinkage lengthways and widthways in grey and after finishing.
The knitted fabrics produced with four different loop lengths were tested for two fabric quality parameters: fabric GSM and shrinkage, shown in Table 1.
Fabric GSM is found to be higher after the finishing treatment for all four different loop lengths due to absorption of dye in to the knitted fabric during processing.
The knitted fabric samples were tested for lengthways fabric shrinkage and results are shown in Table 2.
From statistical analysis of the data in Table 2, the ‘P’ value for fabric shrinkage in the lengthwise direction is 8.31E-09 and is less than 0.05, showing that there is a significant difference between the shrinkage values for different loop lengths. It is also found that the amount of shrinkage increases as the loop length of knitted fabric increases due to a reduction in the fabric’s stitch density.
Figure 3 shows that as the stitch length increases fabric shrinkage is also found to increase lengthwise. Fabric samples were also tested for widthwise shrinkage and the results are shown in Table 3.
The statistical analysis of data in Table 3 shows that the ‘P’ value for fabric shrinkage in the widthwise direction is 0.528193 and is greater than 0.05, showing that there is no significant difference between the shrinkage values for different loop lengths.
Figure 4 confirms that there is no such effect of variation in stitch length on the fabric shrinkage in the widthwise direction.
As stitch length in the knitted fabric reduces, GSM increases with increasing stitch density and the fabric becomes more compact. When the knitted fabric is dyed and finished, fabric GSM is increased by absorption of the dye.
This study confirms that, after the finishing of knitted fabrics of different stitch lengths, there is more shrinkage of the fabric in the lengthwise direction than in the widthwise direction. Fabric shrinkage in the lengthwise direction is found to increase with increase in stitch length which reflects the diminishing fabric dimensional stability for higher stitch length knitted fabrics. There is no significant effect of variation in the stitch length on the knitted fabric shrinkage in the widthwise direction.
Prof R N Narkhedkar is based at the Center for Textile Functions, NMIMS University, Shirpur, India
References
Bayazit Marmarali A (2003) Dimensional and physical properties of cotton/spandex single jersey fabrics, Text. Res. J. 73 (1), 11-14.
Choi MS and Ashdown SP (2000) Effect of changes in knit structure and density on the mechanical and hand properties of weft-knitted fabrics for outwear, Text. Res. J. 70 (12), 1033–1045.
Doyle PJ and Hurd JCH (1953) Fundamental aspects of the design of knitted fabrics. J. Text. Inst. 44 (8), 561-578.
Keshkari KR (2002) Effect of yarn feed length on cotton weft knitted fabrics, The Indian Tex. J., 112(6), 131-136.
Knapton JJF (1979) The wet-relaxed dimensions of plain-knitted fabrics. J. Text. Inst. 70 (9), 410. Mikučionienė (2004) The dimensional change of used pure and compound cotton knitwear. Material Sci. 10 (1), 93–96.