Effect of graphene nanoplatelets on space charge and breakdown strength of PP/ULDPE blends for HVDC cable insulation

In this paper, polypropylene (PP) is blended with ultra low density polyethylene (ULDPE) content to 5, 15, 25 wt% by melt blending to modify its stiffness and brittleness. The mechanical tests show that both the flexibility and tensile strength of PP are enhanced by the addition of ULDPE with a content of 15 wt%, but the other contents show a weaken elongation at break and tensile strength. Graphene nanoplatelets of 0, 0.005, 0.01 and 0.05 wt% are introduced into the PP/ULDPE (15 wt%) blend to improve its dielectric properties. The DC conductivity, space charge behavior, distribution of trap levels, and breakdown strength of PP/ULDPE/graphene nanocomposites were investigated. The results show that PP/ULDPE/graphene nanocomposites with the nanofiller content of 0.01 wt%, have lower DC conductivity, reduced space charge, and higher breakdown strength. The improved dielectric properties are largely attributable to the deep traps in the interfacial zones between the graphene nanoplatelets and PP/ULDPE blends which restricts the carrier injection and transportation in polymer. It is shown that the PP/ULDPE/graphene nanocomposites with 15 wt% ULDPE and 0.01 wt% graphene nanoplatelets show good dielectric properties for application in HVDC cable insulation.