Thermal Conductivity of Closed-cell Microcellular Ethylene-Octene Copolymer Foams

Abstract

The thermal conductivity of the unfilled as well as aluminium silicate, CaCO3 and silica filled systems have been studied by guarded hot plate method. It is observed that thermal conductivity of both unfilled and filled vulcanizates decreases with decrease in volume fraction of the solid, which is due to presence of air bubbles. The thermal conductivity values of both solid and microcellular vulcanizates varies in order of aluminium silicate filled > CaCO3filled >silica filled >unfilled. This can be attributed to the variation in thermal conductivity values of the fillers, which are in the order aluminium silicate > CaCO3> silica. The results reveal that the thermal conductivity (k) of microcellular ethylene-octene copolymers does not follow the theoretical model equation. The experimental values are found to be higher than that of the theoretical values for both unfilled and filled systems. This can be attributed to the stretching of polymer matrix during expansion. With increase in temperature, the thermal conductivity of both unfilled and filled vulcanizates decreases. This may be due to the increase in free volume with rise in temperature, which decreases the inter-chain coupling and hence, increases the resistance to energy transfer between the molecules resulting in the decrease of thermal conductivity.