Preparation And Properties Of New Semiconductive Shielding Composites

Semiconductive polymer shielding layers are important structures ofpower cable which can incorporated to eliminate stress enhancementsdeformation and to provide a more uniform electirc field within theinsulation material. They are important for safety operation of powercable. Semiconductive shielding layers require stable volume resistivityto protect the insulation when carbon black (CB)/polymer compositeundergoes thermal cycles. For the CB-filled polymer composites, CBwould often re-aggregate when temperature is close to the melting pointof polymer matrix, so that the conductive network would be destroyed.Re-distribution of CB and re-formation of conductive CB network underthermal cycles might be the main reason for the instability of volumeresistivity.In this work, we use ethylene-vinyl acetate copolymer (EVA) asmatrix, carbon black (CB) as main conductive filler. A basic formulation of semiconductive shielding material was set up. The re-aggregation ofCB and rebuilding of conductive network in the EVA/CB composites wasdisclosed. Besides, a small amount of multi-walled carbon nanotubes(MWNTs) and graphene nano-sheets(GNS) were employed as cofillerswith CB to improve the stability of volume resistivity of the polymercomposites under thermal cycles. The total weight fraction of conductivefillers (CB or CB cofilled with MWNTs or GNS) was set as35wt%.Compared with the polymer composites loaded with CB solely, thevolume resistivity of the composites filled with CB-MWNTs was muchmore stable with changing temperature. This can be attributed to theenhancement of conductive networks when the MWNTs are employed assecond conductive filler. When loading amount was1wt%, stabilityenhancement of volume resistivity by GNS was better then MWNTs. Butmore GNS loading would have negtive effect on stability of volumeresistivity. GNS is unsuitable to be used as conductive filler ofsemiductive shielding material.