Insulation Performance of Polypropylene Capacitor Films with Different Biaxial Orientation Ratios

In this paper, a modification method of polypropylene (PP) films is proposed for capacitors by biaxial stretching. The results show that the grain size of the stretched films decrease with the increase of the number of $\alpha$ spherulites compared with the unstretched films. Meanwhile, the stretched films show a stable advantage in breakdown performance. That is because the breakdown strength of modified films was 509.6kV/mm when the stretching ratio is 6 times, an increase of 24.2% compared with that of unstretched films. Apart from this, the crystallinity increases and the electrical conductivity decrease significantly compared with unstretched films. Therefore, biaxial stretching is an effective strategy to improve the properties of PP films, which can provide a reference for the performance improvement of PP films for MFCs.