응력수준과 온도가 PVA 섬유의 시간 의존적인 형태학적 및 물리적 특성에 미치는 영향

Effects of Stress Level and Temperature on the Time Dependent Morphological and Physical Properties of PVA Fibers

The effects of the stress level and heat treatment temperature on the morphological and physical properties of poly(vinyl alcohol) (PVA) fibers were investigated with regard to treatment time. The PVA fibers were heat treated at three different temperatures (210, 220, and $230^{\circ}C$) and stress levels (0.05, 0.15, and 0.25 g/d). Increase in shrinkage was observed with an increase in the heat treatment time when treated at 220 and $230^{\circ}C$ beyond 15 min, while a little extension was observed at $210^{\circ}C$. The shrinkage in the PVA fibers heat treated at $230^{\circ}C$ increased with a decrease in stress levels, exhibiting a different dependence of the shrinkage on the heat treatment time. The WAXS patterns of the PVA fibers heat treated at $230^{\circ}C$ at 0.15 g/d showed that the crystalline peaks became sharp with time up to 15 min beyond which they became dull. The degree of crystallinity, determined from the density measurement, was maximum when heat treated for 5 min regardless of the temperature and the stress level. However, the degree of crystallinity when further treated at 220 and $230^{\circ}C$ decreased, while that showed little change when treated at $210^{\circ}C$. In addition, the variation of the degree of crystallinity with heat treatment time was in good agreement with that of the degree of amorphous orientation. In the DSC thermograms, a greater dependence of the melting temperature and the heat of fusion on the heat treatment time was observed at higher heat treatment temperatures and lower stress levels.