ELECTRICAL CONDUCTIVITY SINGULARITY IN CB/THERMOPLASTIC VULCANIZATES COMPOSITE

The electrical properties of carbon black (CB )/ thermoplastic vulcanizates (TPV) (EPDM/PP type) were investigated in details and their singularity was found. The crosslinked rubber particles in TPV can cause both exclusive effect for carbon black particles which is positive to current conduct and barrier effect which is negtive to current conduct. At the low content of rubber phase, with the increase of rubber phase the resistance of electricity of composite decreases, while at the high content of rubber phase, the higher the content of rubber phase, the higher the resistance of electricity of composite, the percolation behavior of composites with loading of carbon black is weakened apparently by rubber particles. When annealing the composites in the melt state, the resistance-time dependence of composites is strongly affected by the pressure of mold-annealing. At a certain time of annealing, the higher the pressure is, the higher the resistance is. When the pressure reaches a certain value, the resistance of composites basically has nothing to do with the annealing time. This is assumed that the restoration of deformation of compressed rubber particles in TPV would destroy the network of carbon black to some extent, which counters the positive effect of carbon black agglomerating during annealing. CB/TPV composite exhibits the NTC behavior even though the temperature is in the melting region of composite, which is attributed to the exclusive effect brought by the thermal expansion of rubber particles. The stability of resistance of composite in the melt state is ascribed to the competition between carbon black agglomerating (which is helpful to conduct) and rubber particles aggregating (which is harmful to conduct).