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 paper, 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 aging process. The research findings provide a reference for PP film dependability enhancement.