Preparation And Properties Of Conductive Polymer Composites Using For High-Voltage Cable Sheath Electrode

Based on the analysis of the existing outer sheath electrode, two new materials for sheath electrode application have be prepared including with a conductive coating and thermoplastic polymer based conductive composite.It can be found that conductive coating can’t meet the requirements of industrial production of high voltage cable due to its long time to dry. Therefore, conductive polymer composite is selected for producing new electrode.At first, conductive coating is prepared by blending epoxy, low molecular weight polyamide,T-31,flake graphite, acetone, coupling agent. The surface resistivity and substrate adhesion of conductivity coating electrode are tested by multimeter and adhesion tester instrument. The results show both the surface resistivity and substrate adhesion of conductivity coating electrode decrease with the increase of graphite.Secondly, HDPE,EVA are used as matrixes and carbon black (CB) is the conductive filler for the preparation of conductive polymer composites of outer sheath electrode.The effects of CB filler contents, ratio of HDPE/EVA and process on micro-structure, crystallization and electrical conductivity of the material are investigated through DSC,SEM and TEM.Small quantities pilot test have been done and the results provide experimental support for industrial applications.It is found that the percolation threshold and volume resistivity of HDPE/CB-EVA composite are both lower than that of HDPE/CB and EVA/CB.The volume resistivity of HDPE/EVA/CB composite is lower than100Ωcm,which meets the requirements of outer sheath electrode, when the content of carbon black is higher than16wt%.Moreover, the influence of distribution of carbon black, crystallization of HDPE and morphology variation of the matrix on electrical conductivity are studied. The results reveal that carbon black distribute in HDPE phase selectively,carbon black and EVA change the crystallization of HDPE very little,and the content of carbon black in HDPE phase dominates the electrical properties of composites.The effects of different feeding sequence and different blending time on electrical conductivity are also studied through analyzing the phase structure of matrix and the distribution and dispersion of carbon black in two immiscible phases.The results suggest that different feeding order alters the distribution of carbon black in two immiscible phases and affects the electrical conductivity of composites.Concerning the blending time,at the prophase of blending, it is mainly distribution of carbon black in two immiscible affects the electrical conductivity and at the anaphase of blending, it is mainly dispersion of carbon black in HDPE affects the electrical conductivity.