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Dependence of Thermal Properties of Expandable Polystyrene Particle Foam on Cell Size and Density

An approach to improve the efficiency of the thermal insulation behavior of expandable polystyrene (EPS) particle foams by diminishing the thermal conductivity is the reduction of the radiation term of the thermal conductivity by an adjusted enlargement of the cell size of the particle foam. This correlation was investigated in detail by the determination of the dependences of cell size and thermal conductivity on the densities of the particle foam over a wider range using samples of expandable polystyrene particle foams showing conventional fine cell size as well as enlarged cell sizes. Based on the dependence of cell size on foam density of fine cell EPS foams, an equation is given also covering foams of larger cells. At the same mean diameter of the foam cells, the thermal conductivity of the EPS foam is increasing with a decrease in foam density in the whole range of diameters investigated from about 50—350 µm. At the same foam density, the thermal conductivity is in general independent of the mean cell diameter of the EPS foam at high foam densities, whereas at lower foam densities, the thermal conductivity is decreasing with increasing mean cell diameter of the foam, in a range of foam densities from about 10—35 g/L. Subsequently, a practical model to describe the dependence of thermal conductivity of expandable polystyrene particle foam on cell size and foam density is proposed and discussed.