Thermal properties of polymer foams

Abstract

Polymer foams are used as efficient thermal insulation materials owing to their poor thermal transport performance. Hence, it is highly desirable to study the thermal properties of polymer foams but, their disordered structure at the microscopic level with complex pore geometry makes it difficult to predict their effective thermal properties. Aiming at this problem, we studied the heat flow through a solid polymer cube, which is packed with a number of micro size spherical pores and solved the three-dimensional heat transport equation by using the finite difference method. Here, the number of pores of a given radius follows a Gaussian distribution. They can be distributed in the polymer phase in two ways: uniform size distribution and random size distribution. The uniform size distribution represents simulated foam whereas random size distribution of pores represents actual foam in which the pores are randomly arranged in the polymer phase. We have found thermal properties for both of the types of distribution and compared them, trying to correlate so as to validate our method. We have also discussed the effects of pore size distribution, porosity, temperature gradient, thermal conductivity ratio, temperature and the volume of the cubic system on the thermal properties of polymer foam. Initially, we have analyzed the thermal properties of randomly approximated polymer foam system and later of low-density polyethylene (LDPE) foam and Polyurethane (PU) foam. The effective thermal conductivity obtained is in fair agreement with the experimental results. The results have indicated that a denser filler material should be used in polymer foams for thermal insulation applications. We have proved that there is a strong dependence of pore size distribution, temperature gradient and volume of the cubic system on the thermal properties of polymer foams. Also, the results suggest that there is a negligible effect of change of porosity on the thermal properties. After considering the radiation effect, we obtained higher values of thermal properties and we have proved that radiation plays a significant role at a higher temperature.