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Abstract
The effect of molding temperature and time on the electrical conductivity of Vapor Grown Carbon Fiber (VGCF) filled High Density Polyethylene (HDPE)/Poly(methylmethacrylate) (PMMA) blends has been investigated. The dispersion state of short carbon fibers in polymeric matrix is affected not only by the volume fraction of filler, but also by the preparation conditions, such as pressing temperature and time. At a given VGCF content, the electrical conductivity of the composites, which were molded at a temperature higher than the melting temperature of HDPE, was measured as a function of pressing time. As a result of aggregation of VGCF, the networks facilitating electrical conduction were formed, and a percolation-like transition in conductivity was observed at a characteristic time, which was defined as the percolation time (tp). It was found that tp decreased with increasing VGCF content and molding temperature. The effect of molding time can be converted with that of molding temperature. From the plot of the logarithmic shift factor αt to the reciprocal temperature, a good linear relationship between them was observed, and the activation energy can be evaluated. Because the conductivity depended on the double percolation, i.e. the percolation of VGCF in HDPE phase and the continuity of this phase in the blends, the effect of molding time and temperature on the double percolation was also studied.