Mechanical properties and space charge behavior of thermally aged polypropylene/elastomer blends

Abstract

Polypropylene has excellent potential as a thermoplastic insulation material for HVDC cable, while its mechanical property and aging problem limit its engineering application. In this work, isotactic polypropylene (iPP) was blended with the polyolefin elastomer (POE), and the blends were thermally aged at 130 °C for various periods (up to 200 h). Taking pure iPP for a reference, the elongation at break of iPP/POE increased by 54.8%, the elastic modulus decreased by 42.5%, and the low-temperature brittleness decreased from −5 °C to −32 °C. During the 60 min polarization process of −100 kV/mm, the electric field distortion of pure iPP changed from 2.5% to 11.3% after thermal aging for 200 h, while that of iPP/POE just changed from 2.2% to 6.2%. The carrier mobility of both iPP and iPP/POE increased after thermal aging, and the carrier mobility of the latter increased by about two orders of magnitude. Combined with the results of thermally stimulated discharge current, iPP/POE was found to bring in more trapping center due to the newly generated interface between POE and iPP, which contributes to a smaller conduction current. This work provides insight into the thermal aging effects of polypropylene composite insulation for HVDC power cables.