Effect of Carbon Fillers on Thermal and Electrical Conductivity of Highly Filled Natural Graphite-Phenolic Resin Composite Materials

In the present study, the effect of micro- and nano-sized carbon additives (multi-walled carbon nanotubes, chopped carbon fibers, carbon black with high specific surface area) on thermal and electrical conductivity of highly filled composites based on natural graphite/phenolic resin system was assessed. The influence of particle shape and additive content (within the range of 0.5–2.0 wt %) was analyzed. Thermal conductivity of the obtained materials was investigated along two main directions of particle orientation relative to the heat flux vector. Conclusions on possible mechanisms of the influence of dispersed carbon materials on heat and charge transfer in the system were drawn. It was shown that at total filler content in the composite of 85 wt %, even 2.0 wt % additive leads to a sharp decrease in thermal and electrophysical properties due to particle agglomeration. The maximum increase in thermal conductivity was established for 1 wt % carbon nanotube additive, while the maximum specific electrical conductivity was achieved at 1.5 wt % carbon black content.