Influence of nanoparticle surface coating on electrical conductivity of LDPE/Al2O3 nanocomposites for HVDC cable insulations

LDPE/metal oxide nanocomposites are promising materials for future high-voltage DC cable insulation. The surface coating of the nanoparticles is a key step to achieve well-balanced properties. This paper presents data on the influence of the structure of the nanoparticle coating on the electrical conductivity of LDPE/Al2O3 nanocomposites. Al2O3 nanoparticles, 50 nm in size, were coated with a series of silanes with terminal alkyl groups of different lengths (methyl, octyl and octadecyl groups). The density of the coatings in vacuum was between 200 and 515 kg m-3, indicating a porous nature on the nanoparticle surface. The dispersion of the nanoparticles in the LDPE matrix was assessed based on statistics for the nearest-neighbour particle distance. The electrical conductivity of the nanocomposites was determined at 40 and 60 \ub0C. The results show that an appropriate surface coating on the nanoparticles maintained uniform particle dispersion up to a filler loading of 10 wt.%, with a maximum reduction in the electrical conductivity by a factor of 35. Large particle agglomerates were found to increase the electrical conductivity of the nanocomposites. The composites based on the highly porous octyl-coated nanoparticles showed the greatest reduction in electrical conductivity and the lowest temperature coefficient of electrical conductivity of the composites studied