Study On The Conductive Property And Response To External Field Of Polyethylene Based Composites Filled With Graphite

In attempt to investigate the structural morphology and response to external field of electrically conductive composites, with high density polyethylene(HDPE) served as the matrix, maleic anhydride grafted polyethylene(gPE) served as intercalant and expanded graphite(EG) served as conductive filler, prepared HDPE/gPE/EG electrically conductive composites via solution intercalation(SI), direct melt mixing(DMM), masterbatch melt mixing(DMM) and extrusion-compressing moulding(EC) methods. The processing conditions of composites prepared via MMM method were optimized, which was named optimized KC. The relationship between processing, structure and properties was studied by means of electrical conductivity( o ) and tensile strength(o ) measurements and SEM, OM observations. Temperature, pressure and electrical field dependence of electrical property and electrically conductive mechanism of composites prepared via SI and DMM methods were studied. The main outcomes are obtained as follows:(1) The percolation threshold value(Cwc) of composites prepared by optimized KC, EC and non-optimized KC were 6.15%, 7.63% and 10.42%, respectively. The electrical property of composites prepared via optimized KC was superior, prepared via EC took the second place an prepared via non-optimized KC was senior. The sequence of tensile strength was contrary to that of electrical property. The result of SEM and OM observations showed that the weaker the shear action exerted to the blends during melt kneading or extrusion, the larger the size and aspect ratio of EGparticles and the regularity of EG-polymer composite structure within the particles.(2) The difference morphology of composites prepared via SI and DMM methods result in the different positive temperature coefficient(PTC) behavior. The PTC intensity of composites dropped with the EG content increased. The PTC intensity of composites with 15% EG content prepared via SI and DMM methods were 1.10 and 3.22, respectively, and the nagnitude of latter was almost as three times as that of former. The PTC intensity of composites was relative not to the EG content but the electrical conductivity() at room temperature of composites. The PTC intensity of composites prepared via DMM method was higher than that of composites prepared via SI method.(3) The axial and lateral piezoresistance characteristic of composites prepared via SI and DMM methods both behaved negative pressure coefficient of resistance(NPCR) effect on low EG content and positive pressure coefficient of resistance( PPCR) effect on high EG content. , which was obtained by minimum divided at room temperature of composites prepared via SI method, of composites with 9%, 12% and 15% EG content were 3.13, 3.5 and 4.14, respectively. The lower the EG content was of composites, the more obvious the NPCR effect was, and the lateral piezoresistance characteristic of composites showed the same tendency.(4) Within the range of low electrical field, composites prepared via SI and DMM both possess linear J-E characteristic. Within the range of experimental electrical field, the J-E figure of composites could be devided into linear and nonlinear parts, and composites possess typical intrinsic nonlinear J-E characteristic. The degree of nonlinear J-E characteristic was relative to the EG content of composites, of which the higher the EG content was, the more obvious the nonlinear J-E characteristic was. The nonlinear J-E characteristic of composites prepared via DMM method was more obvious than that of composite prepared via SI method, and with the EG content increasing, the degree of the nonlinear J-E characteristic lowered down. The nonlinear index of composites attained in this research was 1.07, indicating the nonlinear J-E characteristic was the result of response to externalelectrical field of DRRN and NLRRN electrical conductive network.