Performance Evolution Analysis of Polypropylene Cable Insulation Materials under Thermal Treatment

This study investigates the effects of vacuum thermal aging on the performance of polypropylene/elastomer (POE) blended cable insulation materials. Thermal treatments were conducted under controlled conditions in a vacuum environment at 120°C for different durations (7, 14, and 21 days), and the material properties were characterized using AC breakdown strength tests, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The experimental results show that after 7 days of thermal treatment, the AC breakdown field strength increased by approximately <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1. 5 \%}$</tex>, the decomposition temperature rose from 377.6°C to 380.17°C, and the melting temperature increased from 159.7°C to 162.5°C, indicating improvements in both dielectric performance and thermal stability. However, with extended treatment durations of 14 and 21 days, material degradation was observed. Specifically, after 14 days, the breakdown strength, decomposition temperature, and melting temperature declined at rates of approximately 0.48 % per day, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.82{ }^{\circ} \mathrm{C}$</tex> per day, and 0.23°C per day, respectively. By day 21, the dielectric strength had decreased cumulatively by 6.8 %, the thermal stability dropped by 9.5°C, and the melting temperature decreased by 3.2°C. These findings suggest that moderate thermal treatment can enhance material performance, while excessive treatment duration adversely affects the insulation and thermal properties of the material.