Enhanced Thermo-Oxidative Aging Resistance of Polypropylene Cable Insulation by Grafting Dual-Functional Monomer

This paper investigates the enhancement of thermo-oxidative aging resistance in PP cable insulation by grafting dual-functional monomer. Accelerated aging experiments are conducted at 135°C, and the electrical and physicochemical properties of the grafted-PP blended elastomer sample (PP-GB) and PP blended elastomer sample (PP-B) are tested at various aging times. The results show that grafting with Irganox 3052 effectively enhances the thermo-oxidative aging resistance of PP. After 1440 h of aging, PP-GB maintains excellent oxidative induction time (OIT) and elongation at break, with a significantly lower carbonyl index (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CI</i>) and less degradation of PP molecular chains than PP-B. Moreover, Irganox 3052 introduces multiple localized state energy levels, which effectively mitigate the degradation of the dielectric properties of PP cable insulation during aging. Even after 1440 h of aging, PP-GB retains excellent insulating properties, exhibiting an approximately two orders of magnitude improvement in DC volume resistivity and a 33.23% improvement in DC breakdown strength at 90 °C compared to PP-B. Additionally, dual-function grafting inhibits the generation of polar molecular groups, phase separation of PP and POE phases, and destruction of the crystalline region during aging, reducing the β relaxation strength (Δε<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">β</sub>) and increasing the activation energy of δ relaxation (E<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">δ</sub>) and α relaxation (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</sub>). These findings can be effectively applied to improve the long-term operational reliability of PP cable insulation.