Impacts of impregnation on the structure and electrical properties of biaxially oriented polypropylene film

Abstract The present study proposed a systematic impregnation test, to study the impact of the interaction of the film and the impregnating agent on the microstructure, as well as the electrical properties of biaxially oriented polypropylene (BOPP) films. BOPP films were impregnated in benzyl toluene at 80°C for 1, 3, 7, 14, and 42 days respectively. The microstructure and electrical properties of the films impregnated for different durations were investigated. The results showed that the crystallinity of films first decreased and then increased with the impregnating time. The impregnating agent came into BOPP films during the impregnating process, which suppressed the orientation of dipoles and reduced the orientation polarization, leading to a slight decrease in the dielectric constant and loss factor of films. Meanwhile, the impregnating agent would destroy the structure of the films to reduce the crystallinity, and thus the breakdown strength decreased. As the impregnating time increased, the molecules of the impregnating agent would occupy the voids in the amorphous and crystalline regions of films to repair the defects. As a result, enhanced structural uniformity with the breakdown performance improved slightly. The variation trend of the breakdown strength was consistent with that of the crystallinity.