Recyclable polypropylene-based insulation materials for HVDC cables: Progress and perspective

Polypropylene (PP)-based recyclable materials have attracted tremendous interest for HVDC cable insulation application due to their superior electrical properties, e.g., high thermal stability and superior recyclability. Compared with crosslinked polyethylene (XLPE), PP-based materials exhibit the advantages of not only higher working temperature but also facile and efficient cable manufacturing with reduced cost, which are highly desired in HVDC cable manufacturing. Considering their promising advantages, PP-based materials have received significant attention from both academia and industry in the field of HVDC cable insulation. In order to adopt PP as cable insulation material, the mechanical flexibility of PP should be improved. However, the regulation of the mechanical properties inevitably influences the electrical properties of PP. So extensive researches have been conducted on the regulations of the mechanical and electrical properties of PP. This review summarizes the research progress in recyclable polypropylene-based materials for HVDC cable insulation application. Particular attention is placed on the electrical property regulations and material structure-property relationship. The challenges that remain to be addressed and the opportunities for future studies in PP-based recyclable HVDC cable insulation materials are also presented.