Dielectric Properties Improvement of Grafting-Modified Polypropylene by Silane for HVDC Cable Insulation

Polypropylene (PP)-based grafting modification is a promising and more applicable method to enhance dielectric properties instead of nanocomposites. In this paper, vinyltriethoxysilane (VTES)-grafted PP with different grafting monomer contents are prepared. The micro-morphology, thermal properties and dielectric properties of VTES-grafted PP are characterized and analyzed. The results show that the melting temperature and crystallinity slightly decrease after grafting VTES. Sphere-shaped dispersed phases are observed in micro-morphology characterization, which may be related to the self-polymerization of grafting monomer. The homo-charge injection near cathode is suppressed in grafting-modified PP, presenting low electric field distortion. The DC breakdown strength and DC volume resistivity of grafting-modified PP are significantly raised, exhibiting the improvement of 18.8% and an order of magnitude, respectively. Thermally stimulated current (TSC) results show a large number of deep traps introduced after grafting modification. Numerous deep traps might be beneficial to these improved dielectric properties of VTES-grafted PP as above. PP-based grafting modification shows enhanced dielectric properties and simplified modification process. This work would provide a strategy and reference for the research and development of grafting modified PP-based insulation material for HVDC cable.