Crystallinity, density and mechanical property changes were evaluated during the course of extrusion and hot stretching processes of Poly (ethylene terephthalate) monofilament fibers in this study.
Poly (ethylene terephthalate) chips from Sun Kyung Synthetic Fiber Co. were extruded at 260-275℃ through a monofilament die and the extruded monofilaments were quenched at different temperatures (0-40℃). These quenched monofilaments were then stretched at a hot water bath (temp. 70-90℃, stretch ratio from 1:1 to 1:6). The stretched monofilaments were then thermally treated at 195℃ for 30 minutes to measure shrinkage.
The degree of crystallinity was determined from the density and X-ray diffraction data. The effect of quenching temperature was shown to be negligible (in the range of temperatures evaluated). The effect of the temperature of the hot stretching bath was that the degree of crystallinity and orientation decreased with increasing temperature. The stretch ratio had the most pronounced effect on the crystallinity and mechanical properties. The general trends were that density, % crystallinity, Yield stress, ultimate tensile stress and modulus showed decrease in the range of stretch ratios from 1:1 to 1:2 while they all showed linear increase from stretch ratios of about 1:2 to 1:6.
A maximum shrinkage was noted at the stretch ratios between 1:2 to 1:3 (max. 45%) at 80℃ stretching condition. This could be attributed to the combined effect of increased orientation and increased degree of crystallinity at high stretch ratios.