Analyzing the thermal shrinkage behavior of polyester / elastomeric weft knitted fabrics

Abstract

Thermoplastic polymer fabrics are normally heat set to make them dimensionally stable. These fabrics in garment panel form may again be exposed to heat during the processes such as rubber print curing and cause to change their dimensions. The key issue addressed in this study; the thermal shrinkage of heat-set polyester/elastomeric knitted fabrics during postheat treatment processes which is a practical and a current problem in the garment industry. The thermal shrinkage behavior of heat-set polyester knitted fabrics, under a wide range of conditions, mainly to simulate the post-heat treatment processes, using geometric and thermodynamic parameters were investigated. The findings present a statistically sound analysis of different thermal behavior patterns, while examining their causes based on both material properties and dimensions of the plain knitted fabrics. The key findings reveal that heat-setting and heat-curing temperatures have a significant effect on thermal shrinkage behavior. Thermal shrinkage in course direction is highly related to the width-wise extension applied during heat-setting and the wale direction is highly correlated to the shrinkage behavior of the yarns in hank form. Noticeable changes in polyester thermal behavior occur at 160°C and thermal shrinkage is heavily influenced by thermal history of materials. Taut-end and slack-end conditions maintained while heatsetting and heat-curing significantly affected thermal shrinkage. The higher percentage of overfeed during heat-setting leads to lower thermal shrinkages in subsequent thermal activities. Thermal shrinkage was evidence of a change in the structural parameters of knitted material. Structural changes are mainly due to the change of shape of the loop and/or thermal shrinkage of the stitch length. The introduction of elastomeric yarn to the polyester knitted structure led to make more thermally stable fabrics. In order to reduce thermal shrinkage during subsequent heat treatment, a high temperature heat-setting and a moderate percentage over feed should be retained during thermal setting. The post heat treatment results revealed that the low temperatures during heat treatments though have no trend but causes comparatively low thermal shrinkage or expansion, it is safe and advisable to use low post heat setting temperatures where possible.