Thermal behaviour and annealing of poly(vinylidene fluoride)

In this study, we report the melting behavior of poly(vinylidene fluoride) (PVF₂) annealed in a differential scanning calorimeter. PVF₂ annealed under isothermal conditions often shows double or triple melting endotherms depending on the annealing temperature (T_a) and the heating rate. The lower melting peak temperature increases as T_a increases. When the annealing time is varied, there is a systematic increase in the size of the lower endotherms. This suggests that a portion of the main endothermic response is due to reorganization during the scan. Annealing PVF₂ not only increases the degree of crystallinity, but also improves the crystal perfection. The ability of an annealing sample to reorganize decreases as the annealing time increases. However, an additional third melting peak appears when PVF₂ is annealed at 140°C for a sufficiently long time. The existence of this peak suggests that more than one kind of distribution of crystal perfection may occur when PVF₂ is quenched from the melt into liquid nitrogen and subsequently annealed.