Thermal aging characteristics of blended modified polypropylene cable insulation materials

Abstract

Cross-linked polyethylene is widely used as the main insulation material in conventional cables, which is difficult to degrade and recycle, making it contrary to the concept of green and sustainable development. In recent years, polypropylene (PP)-based blended and modified insulation systems have attracted widespread attention due to their excellent performance and recyclability. However, long-term operation will trigger the aging of the insulating material, resulting in performance degradation and shortened life. Therefore, in order to study the aging behaviour of blended modified polypropylene cable insulation materials, this paper analyses the evolution of electrical and physicochemical properties at different aging stages through accelerated thermal aging tests at different temperatures, focusing on the changes of key parameters such as melting temperature, relative dielectric constant and elongation at break with aging time. The results show that the material shows yellowing phenomenon after aging. Thermal decomposition temperature tends to stabilise after a slight rise in the early stage of aging, and decreases significantly after the occurrence of yellowing phenomenon, From an initial temperature above 400°C, it rapidly dropped to around 340°C; the overall change of melting temperature is small, but it decreases after yellowing; AC breakdown strength shows a staged trend of slow decline with the aging time, and the higher the aging temperature, the faster the rate of strength decline; The elongation at break increased by 4.89% during the initial aging phase, then entered a stable stage. When yellowing occurred, the elongation at break dropped sharply until it reached zero; The dielectric constant was 2.31 at the onset of aging, increased initially, then stabilized, and increased significantly after yellowing. The above study shows that the aging state of the blend-modified polypropylene cable insulation materials can be effectively evaluated by analysing the changes of key parameters such as thermal decomposition temperature, melt temperature, breakdown strength, elongation at break and relative dielectric constant.