Effect of Photoinitiator on Dielectric Properties of Polypropylene Films Modified by UV Irradiation

This article proposes a method to enhance the dielectric properties of polypropylene (PP) films for capacitors by ultraviolet (UV) irradiation modification. The effect of different photoinitiator contents on the crosslinking reaction is analyzed, and the intrinsic correlation between the crosslinking structure and the insulation properties is investigated. The results show that a moderate amount of benzophenone (BP) addition (1.0 wt%) can improve the degree of dielectric crosslinking, with a gel content of 22.3% for PP10. However, excessive amounts of BP lead to the degradation of molecular chains, increasing small molecular groups within the matrix and causing damage to the polymer insulation. Experiments on direct current (dc) conductivity and breakdown at different temperatures show that the chemically crosslinked network enhances the extent of molecular chain entanglement in the amorphous region, improving the film’s thermal stability at high temperatures. At 115 °C, the breakdown strength of PP10 was 590.5 kV/mm, an increase of 20.5% compared to pure PP. This study provides a viable idea for the reliable application of PP films under electrothermal coupling fields.