Effects of Swelling Conditions on the Superstructure of PVA Films during the Wet Drawing Process

The effects of swelling conditions on the superstructure of polyvinyl alcohol (PVA) films containing 10 wt% glycerol were investigated. The water content of PVA films increased as the swelling temperature and swelling time increased. An abrupt increase in water content was observed between 40 and 50∘C in the vicinity of Tg of PVA. The water content leveled off after approximately 100 s at all swelling temperatures except 50∘C , where it decreased after approximately 200 s. In the differential scanning calorimeter (DSC) measurement, the peak temperature for water evaporation was shifted to a value higher than 100∘C and became sharper with increasing swelling temperature. Wide angle X-ray diffraction (WAXD) profiles of PVA films revealed that the degree of crystallization had decreased with increasing water content; however, the average crystal size remained largely unchanged. For PVA films drawn at 50∘C in water, the diffraction peak for the (101) plane became sharper and increased with draw ratio. The degree of crystallization of swollen PVA films in water significantly increased with increasing draw ratio, whereas there was no noticeable change in the crystal size.