Study On The Intrinsic Electric Conductivity Of Carbon Black And The Conductive Behavior Of CB/Polyethylene Composites

As a traditional carbon material, carbon black havea wide spread applications in the fields of thermal, electrochemical, mechanical and so on because of its unique structure and good thermal and conductivity properties. Carbon blacks have good electrical conductivity so that they can be added into the polymer to improve the mechanical and electrical conductivity properties of the composites significantly.However, the variationof conductive mechanism of the carbon black with temperature is not very clear. In order to increasing the properties of the composites,we could improve the processing technology of composites, or modify the carbon blacks.In our work, we choose N330, acetylene black and Ketjin black as a model.Firstly, we studied the structure and morphology of the primary particles of carbon blacks changed through high temperature treatment and the changes in the physical and chemical properties of carbon blacks. Secondly, we explored the different preparationtechnology and the carbon black modified by heat treatment impact on conductivity and mechanical properties of composites. We drawthe following conclusions:1. N330, acetyleneblack and Ketjin black were heat treated at different temperature. After 2800?, the specific surface area, structure degree, and the aggregate size of the carbon blackswere decreased. The carbon black nanoparticles were transformed from spherical structure to polyhedral structure.The crystallinity increases gradually with the rising of treated temperature after 1500?. The increasing degree is relate to the particle sizeof the carbon blacks,the bigger particle size of carbon black has the greater extent at 2800?.2. We studied the intrinsic conductivityof N330, acetylene black and Ketijin black. We found that the resistivityof the carbon blacks were decreased firstly and then increased with the rising of heat treated temperature.The minimum value was obtained at 1500?.We proposed a new model to explain this special conductive phenomenon. Although the carrier migration rate of the carbon blacksis improvedafter graphitization, the carrier concentration decreased, which lead to the increase of the resistivity sharply.3. Using the High-density Polyethylene as the polymer matrix andN330, acetylene black as conductive filler,melt blending method and solution blending method were used to prepare the conductive composites. The electrical and mechanical properties of the composites were studied. The results showed that,compared with the polyethylene, the tensile strength and modulus increased, but the elongation decreased greatly after the addition of the carbon blacks. For the graphitized carbon blacks, the percolation threshold and the volume resistance of the materials were increased, the tensile strength and modulus of the composites were decreased,the elongation were increased. Compared with the melting method,the percolation threshold and volume resistivityof the composites prepared by solution methodwere decreased, but the mechanical properties were also decreased. The reason is that the carbon black could dispersed better in the polymer, but the residual solvent led to the defects in the materials. For the graphitized carbon blacks modified by coupling agent, the dispersion in the matrix and the compatibility with polymer became better, so that the volume resistivity and percolation threshold of material was decreased, andthe mechanical properties were improved.