Preparation and Electrical Properties of 4-allyloxy-2-hydroxybenzophenone Grafted Polypropylene for HVDC Cables

Polypropylene (PP) is considered a promising material for eco-friendly high-voltage direct current (HVDC) cable insulation. However, PP is prone to space charge accumulation under direct current (DC) electric stress, which limits its applications. In this study, 4-allyloxy-2-hydroxybenzophenone (AHB) with polar functional groups and a conjugated structure was grafted onto PP via melt grafting to improve its electrical properties. The effects of several reaction variables, specifically initiator and monomer content, reaction temperature, rotor speed, and grafting yield time were studied, and the optimal grafting conditions were determined. Evidence of grafting was examined by Fourier transform infrared (FTIR) spectroscopy. Moreover, the space charge characteristics, volume resistivity, and DC breakdown strength of the grafted PP were also studied. The FTIR results demonstrated that the AHB monomer was successfully grafted onto PP, and the maximum grafting yield obtained under the optimal grafting conditions was 0.94%. Furthermore, when the grafting yield was 0.73%, the grafted PP effectively inhibited space charge accumulation and exhibited the highest volume resistivity and DC breakdown strength. Thus, this work provides useful ideas for the design and development of environmentally friendly polymer insulating materials for HVDC applications.