Effect of nozzle diameter on mechanical properties of poly(ethylene terephthalate) Fibers prepared in melt spinning process

Abstract

Melt spinning of poly(cthylenc terephthalatc) with intrinsic viscosity of 1.0 dig v\as carried out to investigate the effect of the spinning nozzle diameter on characteristics of as-spun fibers. In general, tensile strength increased and elongation at break decreased with an increase in the take-up velocity. With the decrease of the nozzle diameter, such correlation in the elongation versus strength plot shifted to the upper-right direction. This result indicated the improvement of toughness. Network draw ratio of as-spun fibers prepared at different take-up velocities was analyzed through the matching of the true-stress versus true-strain curves by shifting the curves along the true-strain axis to create a master curve. The starting point of the strain hardening in the master curve shifted to lower strain with the decrease of nozzle diameter. From the linear relation between the obtained network draw ratio and thermal shrinkage stress, entanglement density was estimated based on the rubber-elasticity theory. The entanglement density was found to increase significantly with a decrease in the nozzle diameter. Numerical simulation of the melt spinning process suggested the decreases of the maximum tensile strain rate and the Deborah number in the spinning line with the decrease of nozzle diameter. There is a significant decrease of the draw-down ratio as well. It was speculated that these factors play a dominant role for the variation of the state of entanglement and network draw ratio in the as-spun fibers. Continuous two-step drawing of the as-spun fibers revealed that the improvement of toughness in the as-spun fibers prepared using a small-diameter nozzle can be maintained in the drawn fibers.