Morphologies And PTC Behaviors Of HDPE/PC/CB Composites

The study on Conductive Polymer Composites possessing PTC behavior (Positive Temperature Coefficient) becomes an increasingly popular topic in the world. PTC means the resistivity of Conductive Polymer Composites increases with the temperature increasing.Two different ways were used to prepare HDPE/PC/CB composites in which carbon black (CB) as conductive filler filled in immiscible polymer blends of high-density polyethylene(HDPE)and polycarbonate(PC):direct melt-mixing and using CB master batch. And we also prepared single polymer composites(HDPE/CB,PC/CB) as counterpart. Resistivity,PTC behavior,the dispersion state of CB,and the relationship of morphology,rheology were investigated in this paper.The properties of PTC materials are not only related to the properties of polymers,CB and the interaction between the polymer and CB,but also to the distribution CB filled in polymers.In comparison with single polymer composites (HDPE/CB,PC/CB),the percolation threshold of CB filled in HDPE/PC/CB is about 12%,which is obviously lower than that in HDPE/CB (20%)and PC/CB(22%).The measurement of resistivity~temperature indicated that PTC intensity and PTC reproducibility of composites prepared using CB master batch was better than composites prepared via direct mixing of CB and polymers. The composites prepared using CB master batch had a bi-percolation structure and exhibited a better PTC reproducibility especially for the composite with HDPE/PC ratio 40/60. This depends on the structure of double percolation as mentioned above.SEM showed that HDPE phase and PC phase were bi-continuous in composite prepared using CB master batch; CB mainly distributed in HDPE phase and the interface between HDPE/PC in which the conductive network were easily formed. But CB preferably distributed in PC phase in composites prepared by direct melt-mixing.The dynamic viscoelasticity of CB filled in HDPE/PC/CB composites were investigated. The results indicated that the viscoelasticity of the composites were dominantly influenced by the PC/HDPE morphologies on the case of low CB loading while CB exhibited its effect on the case of high loading.