Effect of Gamma Radiation on the High-temperature Breakdown Strength of Polypropylene Films for Capacitors

Polypropylene (PP), a typical insulating medium for metalized film capacitors, undergoes significant reduction in electric breakdown strength at high temperatures, which affects engineering applications. In this paper, the effect of gamma radiation on crosslinking modification of the material, and the enhancement of the high-temperature breakdown strength of PP were investigated. A 0.4 wt% sensitizer trimethylolpropane triacrylate (TMPTA) was added, and radiation exposure was conducted at $25^{\circ}\mathrm{C}$ with total radiation doses of 0, 2, 5, and 10 kGy, respectively. FTIR spectra and crosslinking degrees were measured to obtain quantitative and qualitative characterization of sample crosslinking. The breakdown strength and conductivity were measured at 25 and $115^{\circ}\mathrm{C}$. The crosslinking degree and breakdown strength were found to increase and then decrease with increasing radiation dosage, reaching a maximum at 2 kGy. The breakdown strength of this sample was 566.9 kV/mm at $115^{\circ}\mathrm{C}$, which was 13.8% higher than that of pure PP. The conductivity was also minimal at $1.47 \times \mathrm{e}^{-13}$ S/m. It is considered that gamma radiation can cross-link polypropylene and enhance the high temperature breakdown properties and conductivity.