Crystallization Behavior and Kinetics of Blends of PVDF with a Fluorinated Copolymer

We present a study on crystallization of poly(vinylidene fluoride), PVDF, blended with a random fluorinated copolymer (FCP) of poly(methyl methacrylate) and 1H,1H,2H,2H-perfluorodecyl methacrylate. These blends are of interest as candidates for use as oil-water separation membranes. The glass transition and crystallization behavior were studied by fast scanning calorimetry using heating and cooling rates from 20 K/s to 4000 K/s. Crystal fraction and crystal formation rate decreased as the fraction of FCP increased in the blends. PVDF, which exhibits crystal polymorphism, crystallizes into β-phase when cooled from the melt at rates faster than 3000 K/s. Cooling rates between 2000 and 3000 K/s resulted in mixed α- and β-phase, while only α-phase occurred at rates slower than 2000 K/s. 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 even at high cooling rates by generating a sufficient amount of α-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.