Grafted UV absorber as voltage stabilizer against electrical degradation and breakdown in cross-linked polyethylene for high voltage cable insulation

Abstract Voltage stabilizers are widely used to improve the resistance to electrical treeing degradation and breakdown of cross-linked polyethylene (XLPE) insulating materials. However, the effects of voltage stabilizers under high temperatures are not fully investigated by now, and the long-term effect of voltage stabilizers is still a concern due to its poor compatibility with polymer. In this work, the UV absorber 4-allyloxy-2-hydroxybenzophenone (AOHBP) which contains an unsaturated graftable vinyl group was demonstrated as a high-efficiency voltage stabilizer and compared with an ungraftable UV absorber as reference. Characterization by Fourier transform infrared (FTIR) spectra and differential scanning calorimetry (DSC) indicated that the AOHBP could be grafted onto the macromolecules of XLPE through radical addition reaction on the vinyl during peroxide cross-linking process. The test results of electrical tree initiation, electrical tree propagation and breakdown strength indicated that the grafted voltage stabilizer AOHBP exhibited higher efficiency than the ungrafted UV absorber and could comprehensively improve the electrical tree initiation voltage, inhibit the electrical tree propagation and improve the breakdown strength of XLPE at different temperatures. Through the electrical aging test with the longest aging time of up to 6000h, the AOHBP was confirmed to still maintain the initial effect on improving the breakdown strength after aging, which indicated that the migration and precipitation of AOHBP was restrained by the grafting reaction. The mechanism of AOHBP improving the electrical properties by scavenging high-energy electrons was analyzed by theoretical calculation based on density functional theory (DFT). It was proposed that the graftable AOHBP is a promising voltage stabilizer.