Different Oxygen Diffusion Patterns in XLPE Under Thermal Oxidative Aging

The thermal oxidative aging of cross-linked polyethylene (XLPE) significantly impacts the long-term stability of high-voltage cables. However, understanding the oxygen diffusion behavior in XLPE under various aging conditions remains unclear. This study aims to explore the distribution of oxygen along the thickness direction of aged XLPE sheet samples. Experimental results show that after aging, the fracture elongation and tensile strength of severely aged samples drop to less than half of their initial values, indicating chemical changes in XLPE nearing the end of its lifespan. FTIR tests reveal a linear increase in the carbonyl index of aged samples over time. Microscopic infrared testing of fractured surfaces reveals significant differences in oxygen diffusion between XLPE aged in a high elastic state and in a molten state. In the molten state, the carbonyl index exhibits high values at the surface and low values in the middle throughout the aging stage. Initially, XLPE in the high elastic state shows a similar pattern, but in the late stage of aging, an abnormal distribution emerges, with high carbonyl index values in the middle and low values on the surface. This study highlights significant differences in oxygen diffusion patterns of XLPE with certain thicknesses during aging under different phase states. These findings provide an experimental basis for improving cable life assessment models in the industry.