Improved Dielectric Properties in Polypropylene/Poly(vinylidene fluoride) Binary Blends Containing Boron Nitride Nanosheets: Toward High-Voltage Current Application

Binary blends of polypropylene (PP) and poly(vinylidene fluoride) (PVDF) are often hard to process by extrusion because of the poor compatibility between the two semicrystalline polymers. Considering the fast crystallization during the stretching at room temperature, PVDF products with low molecular weight were selected in this study and consequently they presented improved compatibility with PP, which favored extruding and stretching the binary blending film (50-50 weight ratio) into micrometric thickness. The obtained binary blending film had a reasonable dielectric constant of over 3.6, a low dielectric loss of 0.54%, and a high breakdown strength of 439 MV/m. Furthermore, boron nitride nanosheets (BNNS) obtained by liquid exfoliation were introduced into PP/PVDF binary blends, and the composite film displayed further reduced dielectric loss of 0.41% and increased breakdown strength of 478 MV/m. In addition, the composite film with BNNS also had high Young's modulus and tensile strength. The enhanced dielectric and mechanical properties made PP/PVDF (50-50)/BNNS 5% display potential values in the application of film capacitors for high-voltage direct current systems.