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Rigid polyurethane foam originated in the World War II era. This material, the reaction product of polyisocyanates and hydroxyl-terminated polyols, was originally expanded by in situ generation of carbon dioxide during the polyurethane polymerization process. A major improvement in the insulation value of polyurethane foam was effected in the early 1950s by the development of technology to use chlorofluorocarbons (CFCs) as the blowing agent.
This paper presents a historical perspective on the development of rigid polyurethane foam as a superior insulation material. The role of CFC expansion agent will be examined with a review of the early concerns of aging of foam and the accompanying change in insulating property. The effects of blowing agent diffusion, humidity during foam aging, and the aging environment gas on the thermal conductivity of cellular material are detailed. Early attempts to explain heat transfer through rigid cellular structures in terms of conduction, convection and radiation factors are cited.
Attention is focused on problems outstanding to a complete understanding of foam aging. These factors include test methodology, the role of gas diffusion, polymer distribution in a cellular structure, effects of barrier materials, in-service moisture influences, foam structure features, and total insulation-containing structural design.
thermal conductivity, polyurethane foam, thermal insulation, chlorofluorocarbon, insulating gases, foam gas diffusion
Technical Supervisor, Allied-Signal Corporation, Buffalo, NY