Thermal Insulation Foam of Polystyrene/Expanded Graphite Composite with Reduced Radiation and Conduction.

Expanded graphite (EG) with high infrared (IR) absorption is incorporated at low concentrations (≤2 wt%) into polystyrene (PS) foams to reduce radiative thermal conductivity and solid thermal conductivity, which account for 2040% and 1030% of total thermal conductivity, respectively. After systematically and quantitatively investigating thermal insulation behavior in PS/EG foams, it was found that the inclusion of 1 wt% EG in 25-fold expanded PS/EG foam blocks over 90% of the radiative thermal conductivity, with only a marginal increase in heat conduction. A great reduction in total thermal conductivity from 36.5 to 30.2 mW·m·K was then achieved. By further optimization using a co-blowing agent in the supercritical CO foaming process, superthermal insulating PS/EG foam with a total thermal conductivity of 19.6 mW·m·K was achieved for the first time. This significant result implies that the composite material design together with the foaming process design is capable of obtaining a superthermal insulating composite foam by using the following strategy: using additives with high IR absorption efficiency, a foam with a large expansion ratio, and a co-blowing agent with low gas conductivity.