Crystallization kinetics and beta-phase suppression at high cooling for poly(vinylidene fluoride) and amorphous copolymer blends

摘要

We present a study of crystallization of poly(vinylidene fluoride), PVDF, and its blends with a random fluorinated copolymer (FCP) of poly(methyl methacrylate) and 1H,1H,2H,2H-perfluorodecyl methacrylate (PMMA-r-PFDMA). These blends are of interest as candidates for use as oil-water separation membranes. Non-isothermal crystallization behavior was studied by fast scanning calorimetry using heating and cooling rates from 20 to 4000 K/s. PVDF, which exhibits crystal polymorphism, crystallizes into P-phase when cooled from the melt at rates faster than 3000 K/s. Cooling rates between 2000 and 3000 K/s resulted in mixed a- and p-phase, while only a-phase occurred at rates slower than 2000 K/s. α-phase PVDF exhibited rigid amorphous fractions (RAF) of 0.21 - 0.28 whereas β-phase PVDF resulted in RAF of 0.42 - 0.46. A series of isothermal melt crystallization experiments was carried out at temperatures in the range 80 - 120 °C for holding times of 0.1-100 s. It was found that β-phase crystal formation can be completely suppressed for all blends studied, even at high cooling rates by generating a sufficient amount of a-phase crystals isothermally. The variation of these isothermal times and temperatures were also studied for the blends to study the effect of FCP in suppressing β-phase.