The crystallization and transition behavior of poly(vinylidene fluoride)/copoly(chlorotriofluorethylene‐vinylidene fluoride) blends

Abstract

AbstractThermal analysis of solution precipitated blends of two crystallizable polymers, poly(vinylidene fluoride) (PVDF) and copoly(chlorotrifluorethylene‐vinylidene fluoride) (copoly(CTFE‐VDF)), has been carried out to study the transition temperatures, crystallinity, and crystallization rates. PVDF crystallizes over the whole blend composition either during precipitation from solution or upon cooling from the melt. The high degree of crystallinity attained, higher than in PVDF by itself, suggests the occurrence of partial PVDF‐copolymer cocrystallization. The melt crystallization temperature, decreasing with cooling rate, is lower in PVDF‐rich blends than for lean blends. However, the heat of crystallization increases with cooling rate, suggesting that the crystal composition depends on crystallization rate. No significant melting temperature depression due to blending was observed. However, the blends glass transition (Tg) changes linearly with composition, but less than expected by any mixing rule applicable to compatible systems. Annealing of the blends above Tg results in an additional crystalline phase consisting mainly of the copolymer. The amount of these crystals increases with PVDF content, due to partial cocrystallization and kinetic effects. The addition of the copolymer to PVDF results in a volume‐filling spherulitic structure consisting of spherulites which decrease in size with increasing copolymer content.