Modelling of effective thermal conductivity of polymer matrix composite foams with biaxially aligned filler networks

Recent research revealed potentials to develop polymer matrix composite foams filled with thermally conductive filler network as light-weight thermal management materials. Since polymeric foams are commonly used for thermal insulation, the concept of thermally conductive polymer matrix composite foams seems to be counter-intuitive, and the underlying factors that govern polymer matrix composite foam's effective thermal conductivity (k(eff)) were not clear. In this context, this paper develops new models to predict polymer matrix composite foams' k(eff) and to elucidate the dependence of k(eff) on their cellular morphology. Linear low density polyethylene-hexagonal boron nitride composite foams were used as case examples to verify the model. The model demonstrated that the composite foam's k(eff) would be promoted when the volume expansion was over a threshold percentage. At low hexagonal boron nitride loadings (e.g. 10vol.%) and fixed cell size, linear low density polyethylene-hexagonal boron nitride foams' k(eff) increased with volume expansion percent through an increase in cell population density. Constrained foaming with preferential expansion in the heat flow direction also enhanced their k(eff).