Effects of Thermo-Oxidative Aging on the Microstructure and DC Breakdown Performance of Crosslinked Polyethylene Copolymer Insulation Material

Polyolefin insulation materials are a critical component of high voltage direct current (HVDC) cables. Currently, the most widely used cable insulation is crosslinked polyethylene (XLPE). In recent years, a click-chemistry-based approach to XLPE preparation has emerged, yet few studies have reported on the performance of this novel material under thermo-oxidative aging. In this work, The novel insulation material was prepared via click-chemistry crosslinking using two vinyl copolymers. Accelerated thermal aging tests (135° C, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0-168 \mathrm{h}$</tex>) were then carried out to elucidate the effects of thermooxidative aging on the material's microstructure and DC electrical properties. Fourier-transform infrared spectroscopy (FTIR) was employed to monitor functional-group changes, and differential scanning calorimetry (DSC) was used to analyze variations in melting behavior and crystallinity during aging. Additionally, DC breakdown test characterized changes in electrical performance under thermo-oxidative stress. The experimental results demonstrate that, with increasing aging time, the absorption peaks associated with ester and carboxylic acid carbonyl groups intensify; crystallinity initially increases slightly but then declines rapidly. Moreover, after 72 h of aging, molecular-chain scission induced by oxidation produces abundant carbonyl-containing small molecules, leading to the formation of cracks and micropores, which in turn cause a precipitous drop in DC breakdown strength. This study provides a reference for the long-term service performance of novel cable insulation materials and offers guidance for cable design.