Study On The Electrical Properties Of Conductive PE Foam Composites

As one of the five most universal plastic, PE has been widely used; it is easily obtained and low-cost and has rather mature manufacturing technique. The PE development and research have become more and more prominent in practical applications and become one of the standards to evaluate the country's industry level. The theories of PE modification are abundant due to the widely studies, At present, PE conductive materials are becoming important products in our common life. The research of the PE functionality is paid attention to and the application domain of PE is further widen. Previously,The PE/CB solid PTC materials have been widely studied for use of self-controlled heaters, sensors and overcurrent protectors etc. in petrochemical industry, aviation industry, electricity generation and paper-making industry.For conductive polymer foams, physics property, high thermal expansion, cushioning ability, and conductivity are mainly utilized. They are mostly used in static testing and static elimination, some products and equipments have acquired patent rights. Otherwise, conductive polymer foams can also be used for anti-static packing of products and anti-static foams are developing to permanent conductive polyolefin from traditional impermanent ones. The electrical properties of polymer foams are mainly resistivity-temperature characteristic (PTC effect and NTC effect) and switching characteristic. The preparations and the studies of conductive foams with PE matrix have been more and more paid attention.PE/CB serious of conductive foams were made by opening milling-molding foaming method with PE, EVA and EPR as matrix, HG-1P CB and ACET CB as conductive filler, AC as foamer and DCP as crosslinker. The bubble structure and resistivity-temperature characteristic was observed. Influences of CB content, multicomponent matrix, crosslinker, foamer on conductive properties of PE/CB foaming conductive composites were investigated.It was observed that it is difficult to foam for high content CB filled PE/EVA (EPR)/CB composite. The constituent and foaming technique is rigorous during the foaming process. High content CB filled PE materials have rigidity, so it is necessary to adjust its toughness and plastics by the incorporation of rubber matrix. Otherwise, to obtain conductive foam with good obturator foramen sturcture, the foamer and crosslinker should be selected properly.In this paper the resistivity-temperature characteristic was studied for different type of CB filled PE/EVA foam system. It shows that HDPE/EVA(EPR)/CB has rather good switching characteristic: ACET CB filled HDPE conductive foam performs PTC phenomenon but HG-1P CB filled HDPE conductive foam performs NTC phenomenon. The PTC intensity of HDPE/EPR/LDPE/ACET composite was lower than that of HDPE/EVA/LDPE/ACET composite, but the NTC effect was more obvious; LDPE/EVA/ACET conductive foam and LDPE/EVA/HG-1P conductive foam all exhibit excellent switching characteristic i.e. PTC effect; For EVA/PE/CB conductive foam,the conductivity of HG-1P CB is better than that of ACET for EVA/LDPE composite and the good NTC effect is performed.The conductivity of CB filled PE/EVA foam system was related to the type of CB and PE and the PE/EVA proportion. The particle of ACET CB is big, the dispersion in the polymer is not good as the HG-1P CB, much biggish aggregated structure formed. So ACET is better fit for PTC materials. Compared to ACET CB, HG-1P CB has large specific surface area, high structuredness, better conductivity and fit for NTC materials.The molecular chains of the HDPE are mainly built up with straight-chain, the crystallinity is high. During the heating process, the molecule thermal expansion is obvious, so the conductive path was affected that the PTC intensity was higher with the increase of HDPE content. Hence HDPE is fit for PTC materials. The melting point of LDPE and EVA is close, the molecular chain structure is similar containing a large numbers of branched chains and the crystallinity is lower than HDPE. When CB is filled, CB particles mostly exist in EVA, secondly in interface of EVA and LDPE and minority in LDPE. When heating, the thermal expansion of LDPE is obsorbed equably by EVA, so the influence of thermal expansion is not remarkable and the PTC intensity is low.There are a large numbers of polar ester radicals in EVA molecules, as CB particles are added in, they are absorbed by ester radicals. With the increase of the temperature, the intermolecalar force weakens. As a result, the thermal motion and the rearrangement of CB particles take place, the resistivity decrease, the composite performs the NTC effect. In another word, high content EVA conductive foam is much fit for NTC materials.The influences of rosslinker, foamer on conductive properties of PE/CB foaming conductive composites were also investigated: for high content PE filled HDPE/EVA/CB system and LDPE/EVA/CB system, the best adding content of AC is 4phr, foaming auxiliary agent Zn-St is 1phr, DCP is 0.5phr; for high content EVA filled EVA/PE/CB system, the proper adding content of AC is 4phr, Zn-St is 1phr and DCP is 0.5phr. The obtained conductive foam composite have not only good foam performance but also excellent electrical conductivity.