Effect of Isotacticity on Thermal-Oxidative Aging Performance of Polypropylene Films for HVDC Capacitors

Polypropylene (PP) materials for capacitors will inevitably undergo aging during long-term operation, leading to damage to their insulation properties. The aging process is determined by the microstructure characteristics. In this article, the effect of isotacticity on the thermal-oxidative aging performance of PP was investigated. The results show that the breakdown strength and maximum discharge energy density of high-isotacticity PP are always higher than those of low-isotacticity PP during aging. Simultaneously, the aging rate is reduced by 38%, and the aging time required for the breakdown strength to drop sharply is prolonged by 112%, with the isotacticity increasing from 94.7% to 99.6%. The high isotacticity leads to higher crystallinity and a smaller spherulite size, which hinders the diffusion of oxygen, thus improving the thermal-oxidative aging performance. Furthermore, the improvement of isotacticity could inhibit the recrystallization, thereby reducing the generation of defects during the aging process. The research findings provide a reference for PP film dependability enhancement.