Effect of Stretching Temperature on the Breakdown Performance of Long-chain Branched Polypropylene Films for HVDC Capacitors

The purpose of this article is to study the effect of stretching temperature on the microstructure as well as dielectric breakdown property of long chain branched polypropylene (LCBPP) film and facilitate the industrial application of polypropylene-based dielectric materials. With the increase of stretching temperature, the stress-induced crystallization effect is strengthened, which increases the crystallinity of the stretched sample and helps to limit the movement of carriers. However, as the stretching temperature rises, the trap density and energy level decreases. During biaxial stretching, the appropriate stretching temperature is pivotal to achieve the best breakdown property of LCBPP film. The results show that under the test temperature of 115 °C, the breakdown strength and conductivity of LCBPP film stretched at 165 °C are significantly higher than those of pure polypropylene (PP), which increases by 27.5% and 87.6% respectively.