Transport properties of graphite/epoxy composites: Thermal, permeability and dielectric characterization

In this study nanocomposites were prepared by dispersing three different grades of graphite particles, expanded graphite, commercial graphene nanoplatelets and natural graphite, in a commercial epoxy matrix. Dielectric properties, thermal conductivity and permeability to oxygen of the composites were studied and compared to those of the unfilled epoxy matrix. An increase of all properties is obtained using expanded graphite, suggesting the presence of a good dispersion of the filler in the matrix and a strong polar interactions of the filler with the matrix, attributed to the partially oxidised surfaces of the expanded graphite. All the measured transport properties were fitted with simple mathematical models obtaining good agreement between the experimental results and theoretical predictions. The model parameters were related to the aspect ratio of the filler, defined as the ratio between the in-plane average dimension and the thickness of the reinforcement. An aspect ratio between 1250 and 1550 indicates that graphite thin platelets (or graphene stacks), characterized by a thickness of the order of a few tens of nanometers, were dispersed in the epoxy matrix.