Electrical Properties of Polypropylene Copolymer/Polyolefin Elastomer/SiO2 Nanocomposites

With a melting temperature of up to ~433K, high breakdown strength, and environmental friendliness, polypro-pylene (PP) has the potential to replace crosslinked polyethylene (XLPE) as a novel generation of high voltage direct current (HVDC) cable insulation material. According to the differences in polymer structure, PP can be divided into homo- polypropylene (PPH), polypropylene block copolymer (PPB) and polypropylene random copolymer (PPR). However, the virgin PP cannot be directly used as a cable material due to its high rigidity and brittleness at low temperatures. Blending with polyolefin elastomers (POE) is an effective method to improve the mechanical properties of polymers. Space charge behavior is the main concern in the development and application of HVDC cable insulation materials. Doping with nanoparticles can reduce the space charge accumulation and improve the electrical performance of HVDC cable insulation to a certain extent. Previous studies have mainly focused on the properties of the virgin PPs or the modification of PPH, while the properties of the modified PPB or PPR, especially the electrical properties, have not received enough attention. In this paper, PPB/POE/Si02 and PPR/POE/Si02 nanocomposites were prepared by the melt blending. Space charge behavior, breakdown strength and conduction current of PP nanocomposites above were investigated. It was found that the charge injected from electrode into PP copoly-mer/POE/Si02 nanocomposites is little, and the space charge ac-cumulation is not evident. They have excellent space charge char-acteristics. Their average breakdown field strength is slightly lower than that of PPH/POE/Si02 nanocomposites, but the breakdown strength distribution is more concentrated. With elec-trical aging threshold of higher than 15 kV /mm, they meet the requirements of HVDC cables. When the field strength is greater than 25 kV/mm, PPR nanocomposite, with the lowest conduction current, is suitable for operating under higher electric field. PPR nanocomposite is more suitable for recyclable cable insulation application than PPB nanocomposites.