The Structure Regulation And Energy Storage Properties Of PVDF

With the rapid development of electric industry,dielectric capacitors receive great attention because of their advantages in fast charge–discharge capability and high power density.Poly(vinylidene fluoride)(PVDF)has a greater electrical displacement than biaxially oriented polypropylene(BOPP)which is a dielectric material for commercial energy storage capacitors,resulting in a significant increase in energy storage density.So it has great research value in the field of dielectric energy storage.The performance of PVDF is closely related to its structure,such as crystal form.So the study of crystal transformation is very necessary.In this thesis,the PVDF blends were prepared by melt blending and casting.The effects of crystal form,temperature and orientation on the energy storage behavior of the blends were investigated.(1)The rheological behavior,mechanical properties and the crystal transformation of PVDF in PVDF / PA6 blends have been investigated.Due to very fine droplet morphology and specific interactions,melt elasticity and viscosity of the blends are significantly enhanced by adding PA6.Moreover,nearly solid-like melt is exhibited by the blends with high PA6 content at low frequencies.On the other hand,the presence of PA6 droplets reduces flow stress because of stress concentrating effect,thus responsible for the suppressed ??? phase transformation upon mechanical stretching.(2)The crystal transformation of PVDF in PVDF/PMMA blends and effects of temperature on energy storage behavior of blends have been investigated.The melting point,temperature of crystallization and crystallinity of the blends are decreased with the increase of PMMA content in the blends.The addition of PMMA benefits the transformation of ??? phase in the blends.when the PMMA content reaches 30wt%,the ? phase occupied the dominant position in the blends.With the increasing of the PMMA content in the blends,the relative ?-form content was increased,but the dielectric constant and the energy storage density of blends were reduced.With the temperature increasing,the dielectric constant and energy storage density of the blends were increased,but the energy efficiency was decreased.(3)The effects of orientation on phase transformation and energy storage behavior of PVDF/PMMA blends have been investigated.The orientation has a certain increase for the crystallinity of the blends and it contributes to the formation of PVDF ? phase.When the PMMA content reaches 30wt%,the ? phase relative content reaches 90% or more.Although the orientation has little effects on the dielectric constant,but the breakdown strength of blends were increased from 150 MV/m to 200 MV/m,which led to an increase in polarization strength and energy storage density.