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 f iber concentration are reported. The fibers, roughly 500 mum long, wer e found to be strongly oriented in the composite leading to a highly a nisotropic thermal conductivity. Longitudinal thermal conductivities c omparable 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 i s a derivation of equations used for continuous fibers composites. Thi s model is quite well in accordance with the linear dependence of the longitudinal thermal conductivity on the fiber concentration of our da ta. Taking into account the effect of the polymeric matrix, the import ance Of contact resistances between fibers and their maximum packing a s well as the qualitative differences between thermal and electrical c onduction is discussed.