Fabrication of PVDF/graphene composites with enhanced β phase conventional melt processing assisted by solid state shear milling technology.

The β-phase crystal, which decides the final electric properties of poly(vinylidene fluoride) (PVDF), is extremely difficult to obtain conventional melt processing due to its thermal instability. In this work, with the assistance of our independently developed solid state shear milling (SM) technology, which could provide multiple stresses and form a micro-stretching field on PVDF to promote the transformation of more α phase to β phase, PVDF/graphene (PVDF/GP) composite with relatively higher β phase (42.2%), higher than that directly prepared by melt blending without SM (33.0%), and dielectric properties was achieved through conventional melt extrusion and injection. When the GP content was 1.0 wt%, the dielectric constant of the composite was 465 at 1000 Hz, about 42 times that of pure PVDF. The special squeezing and shearing forces of SM also realized the exfoliation of GP as well as the solid grafting of GP layers on PVDF molecules, improving the dispersion of GP layers in PVDF and making them effectively exert their heterogeneous nucleation as well as enhancement effects on PVDF, thus increasing the crystallinity, thermal stability and mechanical properties of the composites.