THERMAL-PROPERTIES OF SOLUTION FLOW-INDUCED PVA CRYSTALS

Poly(vinyl alcohol) was crystallized from its aqueous solution under a steady-state flow with different conditions. Using a differential sca nning calorimeter (DSC), the thermal properties of PVA precipitates ob tained by the flow-induced crystallization were measured, showing a si ngle melting peak in the DSC curve. The melting temperature of PVA cry stallized depended on the rate of stirring, crystallization temperatur e, concentration of WA, yield of precipitates, and morphology of the c rystals. Particularly, there was a closer relationship between the mel ting temperature and the yield of precipitates, i.e., it was through t he effect on the yield of precipitates that crystallization conditions influenced the melting temperature. Generally, with certain condition s, the higher the yield of precipitates, the lower the melting tempera ture. Moreover, using electron microscopy, it was observed that there were some structural differences between the inner and outer sides of a PVA crystal mat round stirrer and between film-shaped and block-shap ed crystals, leading to different melting temperatures. (C) 1997 John Wiley & Sons, Inc.