High-Temperature Polypropylene Nanocomposite with Different Surface-Modified Nanoparticles for HVDC Cables

As a promising insulation material for HVDC cable, polypropylene (PP)-based nanocomposite shows excellent electrical properties under high operating temperature. The coupling agent plays an important role in the nanocomposite and may affect the high-temperature performance. In this paper, octyltrimethoxysilane and octadecyltrimethoxysilane were used to surface-modify MgO nanoparticles respectively. The PP/MgO nanocomposites were prepared and the surface-modification effect on electrical properties under 30 °C and 90 °C were investigated. The results show that deep traps were introduced in the nanocomposites by surface-modified MgO, whose density is proportional to the alkyl length of silane. Both PP/MgO nanocomposites show better electrical properties than pure PP. The nanocomposite with octadecyl-modified MgO shows the highest DC breakdown strength and lowest DC leakage current under 30 °C. Whereas octyl-modified PP/MgO nanocomposite performs better on these electrical properties under 90 °C. The reason of them may be correlated with the chemical stability of silane under high electric field and temperature. The work can be useful for selecting coupling agents in PP-based nanocomposite cable insulation considering high operating temperature.