Aging of Thin-Slices of PIR Foams Manufactured with Alternative Blowing Agents

Abstract

Chlorofluorocarbon compounds (CFCs) have historically been used to achieve superior thermal performance in closed-cell polymeric foams. The de terioration (aging) of thermal performance during the influx of gaseous components from the atmosphere, and the efflux of the insulating blowing agents usually takes place over a period of many years. The realization that atmospheric emissions of CFCs were having a detrimental effect on the environment increased the need for reliable and timely methods for the evaluation and selection of alternative insulating blowing agents for polymeric foam insulations. Accelerated aging at elevated temperatures has been suggested, but this method has practical limitations and often provides unreliable results. Thin-slice aging of closed-cell core at room temperature has achieved meaningful accelerations. In this paper, techniques which allow the required evaluation times to be reduced to acceptable values, without reduction of reliability will be discussed. A polyurethane modified isocyanurate (PIR) slabstock foam containing CFC-11, produced for a Joint Industry and Government Study was thin sliced to 1.3, 2.5 and 5.1 mm, and aged (at room temperature) for four months. Apparent thermal conduc tivities, k, were measured with a 100 × 100 mm heat flow meter (HFM) apparatus at Granville Research Center. The results were compared with k for slices of 10, 19 and 33 mm thickness of the same foam measured over a three-year period at the Oak Ridge National Laboratory (ORNL). The results confirm that (very) thin-slice accelerated aging can, in a timely manner, produce reliable parameters describing the long-term aging performance of closed- cell polymeric foams manufactured with alternative blowing agents.