Dielectric and Energy Storage Properties of Polypropylene by Deashing Method for DC Polymer Film Capacitors

In this paper, a novel deashing method is proposed to prepare polypropylene (PP) materials with different ash contents (60–500 ppm). Effects of the ash on dielectric and energy storage characteristics of PP in polymer film capacitors are studied. The experimental results reveal that a low content of ash will help to improve the dielectric properties. Compared to the sample with 500 ppm of ash content, the PP film with 60 ppm ash possesses a higher breakdown strength (587.1 kV/mm), a lower DC conductivity (1.12 ×10−14S/m) and dielectric loss factor (3 ×10−4). In addition, the energy storage property also shows a remarkabe improvement, the discharge energy density can be up to 3.22 J/cm3and the discharge efficiency remains at a high level. After the purification, the decline of the ash content in PP prevents the local electric field distortion and enhances the breakdown strength, which is beneficial for the improvement of the discharge energy density. Meanwhile, the reduction in the number of carriers ionized by the ash weakens the transport behavior and reduces the conductivity. It is concluded that the PP with high purity shows a great potential in polymer film capacitors.