Non-isothermal crystallization of PVDF/PMMA blends processed in low and high shear mixers

Abstract

The morphological, thermal and non-isothermal crystallization behavior of poly(vinylidene fluoride) (PVDF) and its blends with poly(methyl methacrylate) (PMMA) processed in low (LSM) and high (HSM) shear mixers were studied by differential scanning calorimetry (DSC). The processing effect on the PVDF melt and crystallization kinetics was described and the effect of PMMA on the PVDF crystallization was also investigated. The addition of PMMA into PVDF increases of relative B phase content independent of the processing conditions. The validity of the modified Avrami and Kolmogorov–Johnson–Mehl–Avrami (KJMA) models for the non-isothermal crystallization of PVDF/PMMA blends are discussed. The KJMA method described accurately the non-isothermal crystallization behavior. The results showed a shift in the PVDF crystallization/fusion peak to lower temperatures. The activation energies for crystallization of PVDF and its blends evaluated through the isoconversional method using Friedman's approximation were higher for samples processed in the LSM. Differences in the activation energies were related to the ability of the molecular segments to crystallize when reaching the growing crystallization front, confirming that the mixing process has some effect on the interaction between the polymers. On the other hand, the isoconversional methods in combination with the KJMA equation provide better understanding of the kinetics of the crystallization process demonstrated by a strongly dependence of activation energy (Ea), relative crystalline fraction (XT), and global and local Avrami exponents (n and n (XT)).