Polypropylene Films for HVDC Capacitors With Enhanced Dielectric Performance by Irradiation Crosslinking Modification

In this article, a method for enhancing the dielectric properties of polypropylene (PP) films based on crosslinking modification by gamma irradiation is presented. The effect of crosslinked structure on the dielectric properties of PP films is investigated by varying the gamma irradiation dose and the content of the sensitizer pentaerythritol triacrylate (PETA). Crosslinking forms a 3-D network structure in the amorphous region, and its strong intermolecular forces improve the thermal stability of PP. The slip and relaxation of molecular chains at high temperatures are restricted after crosslinking, thus limiting carrier transport in PP and contributing to low electrical conductivity and high breakdown strength. The results indicate that the maximum crosslinking degree of the modified samples reached 25.6% at the irradiation dose of 5 kGy and the sensitizer content of 1 wt%. The permittivity of the crosslinked films increases, and the conductivity decreases significantly at high temperatures. The breakdown strength of the crosslinked film is 595.4 kV/mm at 115 °C, which is 20.9% higher compared to PP. The maximum theoretical energy storage density after the modification reaches 3.48 J/cm3 (115 °C), which is 47.5% higher than PP. This article provides feasible ideas for enhancing the dielectric properties of PP films at high temperatures.