Factors affecting the magnitudes and anisotropies of the thermal and electrical conductivities of poly(l-lactic) acid composites with carbon fibers of various sizes

Investigation of the thermal and electrical conductivities of poly(l-lactic acid) composites containing carbon fibers (CFs) of various sizes has revealed that the thermal conductivity depends largely on the length of the CFs in the composites and that the electrical conductivity depends largely on the aspect ratio of the CFs. These different dependencies are due to the effect of the number of interfaces between the CFs in a percolation network formed in the composites, where electron transport is enhanced but phonon thermal conduction is limited by phonon scattering at the interfaces between the CFs. The anisotropy of each conductivity is also influenced by the length of the CFs, which could determine the alignment of the CFs in the molded composites.