Effect of silicon dioxide and organized montmorillonite on the crystalline morphology and dielectric properties of polypropylene-based composites

Polypropylene (PP), a thermoplastic material that can be recycled by melting, is viewed as a potential alternative to cross-linked polyethylene for insulation. In this work, PP-based composites were fabricated with surface-modified silicon dioxide (SiO2), organized montmorillonite (OMMT), and polyolefin elastomer (POE) as fillers via a two-step melt blending method. The dispersion states of SiO2 nanoparticles, OMMT, and POE in PP and their effects on PP crystallization were investigated. Moreover, the elongation at break, yield stress, energy storage modulus, damping loss factor, broadband dielectric spectrum, bulk resistivity, and alternating current (AC) breakdown strength of the specimens were tested. POE significantly increased the composite toughness, whereas the AC breakdown field strength and volume resistivity of POE/PP were lower. The homogeneously dispersed SiO2 and OMMT in the matrix acted as heterogeneous nucleation sites and reduced the grain size. To varying degrees, they effectively improved the dielectric properties, volume resistivity, and breakdown field strength of the composites. Hence, the composites simultaneously had excellent mechanical and dielectric properties. The volume resistivity of SiO2-OMMT-POE/PP with higher crystallinity was 15.4 times higher than that of POE/PP, and the breakdown field strength increased by 16.4%.