Improvement of Space Charge Behaviors of PP/ULDPE Blends by Nano Graphene for HVDC Cable

Abstract

Polypropylene (PP) with excellent dielectric properties will make a further progress for its application in HVDC cables, if its poor toughness can be improved. Besides, the space charge accumulation is still an important issue for HVDC cable polymer insulation, which can cause a distortion of electric field, accelerate the ageing of insulation. In this paper, PP is blended with the elastomer of ultralow density polyethylene (ULDPE) content of 15wt% by melt blending method to modify its stiffness and brittleness. The graphene nanoplatelets with different content of 0, 0.005, 0.01wt% are introduced into the PP/ULDPE (15 wt%) blends to improve its dielectric properties. The dc conductivity, space charge behaviors and breakdown strength of PP/ULDPE/graphene nanocomposites are then investigated. Experimental results show that PP/ULDPE/graphene nanocomposites with the nanofiller content of 0.01 wt%, have lower dc conductivity, less space charge amount and higher breakdown strength. The improved dielectric properties can be attributed to the interfacial zones between graphene nanoplatelets and PP/ULDPE blends, which can restrict the carrier injection and transportation in polymer.