Effects of Hindered Phenolic Antioxidants on Space Charge and Breakdown Properties of Polypropylene

This paper focuses on the effects of hindered phenolic antioxidants AO300 and AO736 with similar molecular structure on the electrical properties of isotactic polypropylene (iPP). Experiments of conductivity, space charge distribution, and DC breakdown strength after the hetero-polarity DC prestress are performed. The experimental results show that these two antioxidants can increase the conductivity-temperature coefficient, reduce the accumulation of space charge and improve the DC breakdown strength after the hetero-polarity DC prestress of iPP. By calculating the molecular orbitals of these two antioxidants, it is found that the antioxidants introduce local states in the forbidden band of iPP matrix to capture high-energy charges. Besides, the bond dissociation energy (BDE) of the hydrogen-oxygen bond in AO736 is lower than that in AO300, representing a stronger ability of proton transfer, which scavenges the radicals, inhibits the growth of microvoids and prevents the process of breakdown. It is concluded that the improvement of space charge and breakdown properties is attributed to the coupling effects of deep trap sites and radicals scavenging introduced by antioxidant. This research shows that AO736 has potential applications in PP insulation.