Crystallization kinetics, polymorphism fine tuning, and rigid amorphous fraction of poly(vinylidene fluoride) blends

Fast scanning calorimetry (FSC) is used to study 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). By varying the residence time at isothermal melt crystallization temperatures T-MC = 80-120 degrees C, the amount of alpha- and beta-phase can be controlled, yielding partial or complete suppression of beta-phase for all blends studied. Nonisothermal crystallization kinetics are also studied by FSC and analyzed using the Mo model. Crystallization rates increase when FCP is present. PVDF crystallizes into beta-phase when cooled from the melt at rates faster than 3000 K/s giving PVDF crystal fractions of about 0.05-0.16. Only alpha-phase occurs at cooling rates slower than 2000 K/s yielding larger PVDF crystal fractions of about 0.30-0.43. Cooling rates between those limits result in mixed alpha- and beta-phase. The rigid amorphous fraction (RAF) of PVDF varies with alpha and beta crystal fraction in PVDF/FCP blends. RAF of alpha-phase PVDF ranges from 0.21 to 0.28 whereas RAF of beta-phase PVDF spans a wider range, reaching values from 0.42 to 0.46.