DC and High Frequency Dielectric Breakdown Characteristics of PP/Al₂O₃ Nanocomposites

Nanofillers have significant effect on dielectric properties for polymeric materials. Pure PP and its nanocomposites films with different filler contents were fabricated to conduct dc and high frequency breakdown experiment. The result shows that, the dc breakdown strength reaches the maximum value at 1wt.%, while which occurs at filler content of 7wt.% for high frequency breakdown strength Erms. Combined with conductivity, trap, dielectric loss and thermal conductivity characteristics, it is concluded that the dc breakdown is closely related to the deep trap energy. The equivalent electric field changed by deep traps is helpful for blocking charge injection, and the enhanced trapping effect can restrict the carriers' migration and multiplication process. Under the effect of the high frequency electrical stress, heating value per unit volume is higher than that under dc voltage. The combined electrical-thermal breakdown mechanism is considered under high frequency voltage. Nanofillers change both the electrical and thermal properties. The increase of thermal conductivity weakens the local temperature rise, causing the shift of the optimal nano-doping content.