Enhancement of Low-temperature Brittleness of Isotactic Polypropylene Filled with Thermoplastic Elastomer for HVDC Cables

Because of its excellent heat resistance and insulation property, thermoplastic iPP is expected to replace XLPE material as the next generation of high-performance insulating materials for HVDC cables. However, iPP has the disadvantages of insufficient flexibility at room temperature and poor toughness at low temperature. Herein, 25 wt.% EPDM, POE, and SEBS elastomer were added into iPP matrices to improve its mechanical toughness, respectively. Low-temperature brittleness testing system and pulsed electroacoustic measurement system were used to analyze the mechanical properties and space charge characteristics of iPP composites. The results show that the low-temperature brittleness property of iPP/elastomer composites has been significantly improved, and the brittle fracture temperature has dropped from
$-8^{\mathrm{o}}\mathrm{C}$
of pure iPP to −66°C, −32°C, and −22°C respectively. Space charge accumulation of iPP/elastomer composites are higher than those of pure iPP under −30 kV/ mm. The improvement of tensile property and low-temperature brittleness of iPP/EPDM are the highest, and iPP/POE composites have the best room temperature flexibility and the least space charge accumulation. On the whole, iPP/POE composites achieves a good balance in mechanical and space charge properties.