Chetan Sheth, B. R. Parekh, L. M. Manocha and Parul Sheth
This work presents an insight into the effect of conductive filler content on both electrical and thermal properties of a polymer composite system. The electrical conductivity of an insulating polymer can be achieved by dispersing conducting fillers (e.g., metal, graphite powder, carbon black, carbon fiber) in the polymer matrix. The resulting materials are referred to as conducting polymer composites. Electrical and thermal properties of epoxy/chopped carbon fiber composites were experimentally studied in this work. The composites are processed by hand mixing technique. The weight fraction of the chopped carbon fiber (CCF) ranged from 0 wt % (as such epoxy) up to 15 wt % with the epoxy resin. By discharging a high voltage (D.C.) through the composite it was found that the resistivity of the composite decreased. The conduction mechanism of composites was studied by means of exploring the current-time characteristics and frequency dependence of conductivity. The A.C. electrical conductivity (σ (ω) a.c.) for these composites have been measured over the frequency range (102 -106) Hz at room temperature. It is found that A.C. conductivity increased when increased conductive filler concentration and frequency. Epoxy/chopped carbon fiber composites show significant differences from the neat epoxy resin measured in the frequency range. The D.C. conductivity at room temperature, percolation threshold was found when CCF (chopped carbon fiber) is added in the range of 3 and 5 wt%. At 5 wt% of filler loading breakdown phenomena was observed. This effect was attributed to local dielectric breakdown of polymer layer between carbon fibers. The optical microscopy revealed the microstructure at critical filler concentration (fc). The thermal characterization done by Differential Scanning Calorimetry (DSC) for glass transition temperature (Tg) shows unpredictable results.
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