Breakdown Performance of Polypropylene and Its Long-Chain Branched Blending for Metalized Film Capacitors

A modification method of polypropylene (PP) films is proposed in this article for capacitors, based on the physical blending of the linear PP and long-chain branched PP (LCBPP). In order to evaluate the comprehensive properties of the samples with different mixing ratios, the micro morphologies, thermal, and electrical characteristics are studied. LCBPP is proven to possess the ability of heterogeneous nucleation. On the one hand, the addition of long-chain branched structures strengthens the intermolecular interaction and promotes the overlap of microcrystalline, which helps to reduce the amorphous region and improve the dimensional stability of the film. On the other hand, impurities and interfaces are introduced, resulting in the increased polarization. Therefore, the conductivity of the PP/LCBPP film reduces, the loss decreases, and the permittivity is basically unchanged. At 20 °C, a low proportion of the LCBPP is beneficial to the increase of the breakdown strength. While at 70 °C or 120 °C, the dense microstructures, promoted by a high proportion of the LCBPP, play a decisive role in suppressing the local field distortion and improving the breakdown properties. This method provides a feasible idea to improve the high-temperature resistance of the film from the perspective of molecular and aggregate structure design.