An Evaluation of the Thermal Conductivity of Extruded Polystyrene Foam Blown with HFC-134a or HCFC-142b

Abstract

Insulation performance of extruded polystyrene (XPS) foams expanded with various halogenated blowing agents including HFC-134a or HCFC-142b was measured over time. Residual blowing agents were measured after aging up to 26 years. The diffusive transport properties of the blowing agents can be determined through the mathematical calculation of the heat transfer in the gas phase component of the foam thermal conductivity. These values are used in a Dow model which allows an accurate prediction of the long-term thermal resistance of extruded polystyrene foams blown with a variety of blowing agents including CFC-12, HCFC-142b, HCFC-22, HFC-134a, HFC-152a, and CO2. Excellent agreement was obtained between measured and predicted thermal conductivity values with samples stored in laboratory conditions, as well as samples extracted from field conditions, such as cellar and upside-down roof applications. The results confirm the slow diffusion rate of CFC-12, HCFC-142b and HFC-134a through extruded polystyrene foam, and demonstrate that HFC-134a or HCFC-142b-blown extruded polystyrene (XPS) foams meet the requirement for applications requiring excellent long-term insulation performance. HCFC-22 and HFC-152a are fugitive blowing agents in XPS foams, and the thermal performance of foams made with these blowing agents reach the thermal performance of CO2-blown foams after a short aging period.