A composite foam consisting of foamed cross-linking polystyrene (c-PS) and boron nitride nanosheets (BNNSs) was synthesized, which shows a higher thermal conductivity (TC) than the corresponding solid counterparts. The BNNS fillers are found to be aligned along the cell wall as a result of the biaxial stress field from cell expansion during the formation of three-dimensional interconnectivity in the foams, resulting in an enhanced TC of 1.28 W/m K, nearly two and four times those of its solid counterpart and pure c-PS, respectively. It is found that the foaming-assisted formation of the filler network is an efficient strategy to improve the TC at low filler loadings in the composites. Furthermore, the composite foams exhibit low density, rather low dielectric constants and dissipation factors at wide frequency and temperature ranges. The present work provides a novel approach to design and prepare lightweight heat conductive polymers with low filler loadings as low-density heat management materials for potential applications in aeronautics and aerospace components.
Keywords: boron nitride nanosheets; dielectric properties; polymer composite; porous structure; thermal conductivity.