Effect of Microstructure and Stretching Ratio on Dielectric Properties of Polypropylene Films for HVDC Capacitors

In this paper, polypropylene (PP) pellets with different isotacticity were prepared, and PP films were obtained by different stretching ratios. The crystallization characteristics of different films were studied and the dielectric properties at various temperatures were analyzed. Further, the influence of microstructure parameter and stretching ratio on the dielectric performance of PP films was explored. The result shows that the PP film with isotacticity of 99.6% and stretching ratio of 4 × 4 has the highest breakdown strength and the lowest conductivity. The improvement of isotacticity can enhance the crystallinity and improve the loose structure of the molecular chain in the amorphous region, thus inhibiting the migration of charge carriers. In addition, a reasonable stretching ratio can elevate the orientation degree of molecular chain to form an orderly crystalline morphology, thereby improving the crystallinity. This research provides experimental and theoretical support for the enhancement of electrical performance of PP films.