Effect of Dry Relaxation on Lengthwise Measurement Deviation of Polyester/Spandex Plated Knitted Tubes after Dyeing

Weft knitted fabrics produced in a circular knitting machine undergo dry relaxation as soon as fabric is removed from the constraints of the machine. A significant deviation of lengthwise (wale direction) measurements was observed among the tubular articles knitted first and last within the same batch. Different elongations at heat-setting determined the final lengthwise measurement after dyeing. The deviation in lengthwise measurement due to dry relaxation at heat-setting resulted in a significant measurement variation after dyeing. Due to this reason, during the bulk production, a considerable portion of garments are not within the tolerance and ultimately increase a higher percentage of rework and rejections. This paper investigates on how dry relaxation is correlated with the lengthwise measurements of polyester/spandex blend plated knit tubes during heat-setting and dyeing. The relationship between thermoelastic behaviour and dry relaxation of the specimens was also studied. The increase in temperature from 220C to 320C accelerated the dry relaxation, and garments reached to an equilibrium condition in 10 hours with a significant improvement in relaxation time than that of 115 hours at 220C. The increase in temperature brought a higher proportion of garment within the fluctuation of 1.5cm after dyeing. This research also addresses the importance of considering dry relaxation curve while giving measurement adjustments in the pilot run.