Preparation and Properties of Poly(vinylidene fluoride)Casting Films
Poly(vinylidene fluoride)(PVDF)containing β crystals has strong polarity and is an important piezoelectric and ferroelectric material,which has received extensive attentions.In this work,three β-crystal nucleating agents were selected.Fourier transform infrared spectroscopy(FTIR)was used to compare the effects of three nucleating agents on the contents of β crystals in PVDF casting films.The results show that tetraphenylphosphonium bromide(TPPB)is the most efficient nucleating agent.The PVDF casting films with high β-crystal content were fabricated by adjusting the extrusion and stretching procedures.The crystal structures of the PVDF casting films and their post-stretching processes were studied by wide-angle X-ray scattering(WAXS)and small-angle X-ray scattering(SAXS).The mechanical properties and elastic recovery properties of the casting films were also studied.The results indicate that,with the increase of draw ratios,the β-crystal content and crystal orientation degree increase in the PVDF/TPPB casting films;the yield stress,Young's modulus,and elastic recovery also increase.During the post-stretching processes,cavities occur in the PVDF casting films with the increase of tensile strain.With the decrease of stretching temperature,the critical strain for the formation of cavities decreases,which benefits for the fabrication of PVDF-based microporous membranes containing β crystals.
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