Material progress toward recyclable insulation of power cables part 2: Polypropylene-based thermoplastic materials

Progress in the development of polyethylene (PE) based thermoplastic materials for power cable insulation has been reviewed in the first article on this subject [1]. New catalysis technique, copolymerization, blending, nanotechnology and additives have been used to tailor the electrical property of PE in the past few decades. However, these methods have brought about limited improvement in the thermomechanical property of PE. For instance, crosslinking reactions can improve the thermomechanical property of PE so that the cable operation temperature can be increased from 70°C to 90°C of low density polyethylene (LDPE) cables (Table 1); however, as discussed in the first article, crosslinking brings in undesirable effects. Apart from the ultra-low recyclability, the crosslinking and degassing also lead to potential safety concerns during cable installation and operation, in addition to long duration and high energy consumption needed for cable production. Since the beginning of the 21st century, polypropylene (PP) based thermoplastic insulation has attracted tremendous interests because of its high temperature stability and excellent recyclability. Compared with XLPE, PP possesses advantages of not only increased operating temperature higher than 110°C but also facile manufacturing processing with reduced cost, increased production efficiency and unlimited cable length, which are highly desirable in the power cable industry. As a promising future solution, PP based thermoplastic cable insulation starts to receive significant interest and attention from academia and industry [2]. However, conventional PP cannot be used directly as power cable insulation because of its high hardness, high crystallinity and low flexibility. In recent years, PP has been modified as thermoplastic cable insulation. This second article discusses the structure-property relationship of PP and reviews the progress on the development of PP based thermoplastic materials for power cable insulation.