THE EFFECT OF FIBER CONCENTRATION ON THE THERMAL-CONDUCTIVITY OF A POLYCARBONATE PITCH-BASED CARBON-FIBER COMPOSITE

Results of measurements of the thermal and electrical conductivities. of polycarbonate samples as a function of chopped pitch-based carbon fiber concentration are reported. The fibers, roughly 500 mum long, were found to be strongly oriented in the composite leading to a highly anisotropic thermal conductivity. Longitudinal thermal conductivities comparable to that of metallic alloys are obtained in the direction of the fibers, while in the transverse direction only a small increase in the thermal conductivity is observed. We proposed a new model which is a derivation of equations used for continuous fibers composites. This model is quite well in accordance with the linear dependence of the longitudinal thermal conductivity on the fiber concentration of our data. Taking into account the effect of the polymeric matrix, the importance Of contact resistances between fibers and their maximum packing as well as the qualitative differences between thermal and electrical conduction is discussed.