Influence of Polymer Blending on Crystalline Structure of Polyvinylidene Fluoride

The changes in the crystalline structure of polyvinylidene fluoride (PVDF) were investigated via preparation of its blends with polymethyl methacrylate (PMMA), polyethylene terephthalate (PET) and polyvinyl chloride (PVC) in molten states in an internal mixer at 10% to 40 wt% of the last two polymers. In all the blends, an increase in β-crystal content of PVDF was observed at different degrees and different morphologies. Polyvinylidene fluoride blends with PMMA showed a homogeneous morphology, whereas those with PET and PVC showed two-phase morphologies. These were accounted for the solubility parameter differences of the polymers. In the case of PVC the mismatch of processing conditions was found to be the main reason for the observed morphology. The technique of FTIR spectroscopy revealed that the relative β-crystal content of PMMA blend reached 70% at 30 wt% PMMA, whereas PET and PVC achieved 80% β-crystals by only 10 wt% modification. This was attributed to the interactions of the blended polymers with PVDF molecules in amorphous regionsor at their interphases. The effects of PVC and PET on the beta-crystal content of PVDF are similar although the blends in the case of PET produce finer morphology as compared with those of PVC. It is desirable to find and maximize the content of PVDF in final piezoelectric article. The technique of WXRD shows limited changes in shape and position of PVDF/PMMA and PVDF/PVC blends spectra and considerable changes in shape of PVDF/PET blends spectra. This is found to be related to the amorphous and semi-crystalline structures of PVC and PET, respectively. Due to the sphericalsymmetry of the PVDF spherulites the piezoelectric coefficient of the blends are found to be zero.