Self-nucleation and crystallization of polyvinyl alcohol

Polyvinyl alcohol (PVA) is a hydrophilic, biodegradable, semicrystalline polymer with a wide array of commercial uses ranging from textiles and packaging to medicine. Film samples of PVA were investigated to assess crystallization and melting behavior during self-nucleation experiments and thermal degradation, using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis, respectively. TG results show that degradation occurred at temperatures in excess of 200 A degrees C which is close to the observed peak melting temperature of 223 A degrees C. PVA was heated to various self-nucleation temperatures, T (s), within its melting range, and then cooled and reheated. Three distinct crystallization regimes were observed upon cooling, depending upon the self-nucleation temperature (T (s)) selected. At low values of T (s), T (s) < 227 A degrees C, PVA only partially melts, and upon cooling the residual crystals anneal and become more stable. At intermediate values of T (s), 228 A degrees C < T (s) < 234 A degrees C, PVA was found to crystallize exclusively from self-nucleation. For T (s) > 235 A degrees C, the PVA melts completely and absence of self-nucleation sites causes crystallization to occur at lower temperatures.