The Effect of Antioxidant Types on the Mechanical Properties of XLPE Insulation Material After Thermal-Oxidative Aging

Long-distance offshore power transmission requires longer cables, and cross-linked polyethylene (XLPE) has become the primary insulation material for high voltage direct current (HVDC) cables due to its excellent electrical insulation properties. However, antioxidants may degrade during thermal-oxidative aging, thereby affecting the mechanical properties of XLPE. Consequently, optimizing the antioxidant system to enhance resistance to thermal-oxidative aging of XLPE has become a key research focus in the industry. This study investigates the effects of different antioxidants on the mechanical properties of XLPE under thermal-oxidative aging conditions, providing theoretical and experimental support for developing insulation materials for long-distance cables. Four antioxidants (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{3 0 0} \boldsymbol{,} \mathbf{1 0 1 0} \boldsymbol{,} \mathbf{1 0 3 5} \boldsymbol{,} \mathbf{1 0 7 6}$</tex>) were used to prepare XLPE sheets via low-density polyethylene (LDPE) melt blending, dicumyl peroxide (DCP) impregnation, and hotpress cross-linking. Subsequently, yellowness index(YI) of samples was measured before and after thermal-oxidative aging, revealing varying degrees of yellowing in XLPE with different antioxidant formulations. The effects of different antioxidants and DCP content on the mechanical tensile properties of XLPE before and after thermal-oxidative aging were then analyzed. Finally, the gel content of the insulation materials was measured to explore the mechanism by which antioxidants influence thermal-oxidative aging resistance of XLPE. The results indicate that: (1) After thermal-oxidative aging, XLPE with different antioxidant formulations exhibited varying YI, with antioxidant 1076 showing the least discoloration. This indicates that fewer hydroxyl groups in antioxidant 1076 were oxidized to form chromophores (such as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{C}=\mathrm{O}$</tex>), demonstrating superior thermal-oxidative aging resistance. (2) Thermal-oxidative aging reduced the crosslinking degree in all XLPE samples, primarily due to oxidative degradation causing cross-link breakage and main-chain scission. (3) Both elongation at break and tensile strength of XLPE increased after thermal-oxidative aging, while the relative performance trends among different antioxidants remained consistent.This study provides experimental evidence for optimizing the thermal-oxidative aging resistance of XLPE insulation materials and offers guidance for material design and application in HVDC cable.