Equilibrium Melting Feature of Poly(Vinylidene Fluoride) Studied by Nonequilibrium Crystallization in a Polymer–Diluent System

Nonisothermal crystallization of poly(vinylidene fluoride) (PVDF) was investigated in pure and mixed states with a diluent. Various cooling rates (CRs) were applied to conduct the crystallization from the melt. Melting behavior of the PVDF crystals formed in polymer–diluent mixtures was studied in a dry state to reveal the diluent interference in PVDF crystallization. When PVDF was cooled slowly from the melt, the diluent could improve both crystallinity and crystalline quality, as confirmed by enhanced melting temperature and enthalpy. While the CR did not change the contents of the crystalline α and β phases significantly, diluent presence favored the α phase dominance within the crystallized PVDF. Melting behavior of the polymer was also evaluated in a wet state, to estimate the equilibrium enthalpy of fusion of PVDF based on the melting point depression approach. The approach requirements were clarified, and techniques to satisfy them were discussed. By a careful analysis of the melting data for other PVDF–diluent mixtures in the literature, we could suggest a corrected enthalpy of fusion for the PVDF perfect crystal.