Effects of graphene concentration, relative density and cellular morphology on the thermal conductivity of polycarbonate–graphene nanocomposite foams

The thermal conductivity of polycarbonate–graphene nanocomposite foams was studied as a function of relative density, developed cellular structure and graphene concentration. Two types of supercritical CO2 foaming processes were employed to obtain foams with a wide range of relative densities and cellular morphologies. The thermal conductivity of unfoamed nanocomposites increased in more than two times upon addition of 5 wt% graphene. Foaming led to lowered thermal conductivity values, as low as 0.03 W/(m K), with thermal conductivity being mainly controlled by relative density and in a lower extent by graphene concentration. Higher thermal conductivities were obtained with increasing relative density and cell size, as well as with increasing graphene concentration, especially in those cases where improved graphene dispersion was achieved with foaming. Thermal conductivity values displayed a better fit when using a three-phase model when compared to the two-phase model previously proposed for polymer composite foams.