Factors Affecting the Solubility of Gaseous HCFC and HFC Blowing Agents

Abstract

The majority of the current production of rigid polyurethane foams utilizes HCFC-141b (1,1-dichloro-1-fluoroethane) as either the blowing or co-blowing agent to expand the foam. With the phase-out of hydrochlorofluorocarbons (HCFCs) scheduled for the year 2003, the usage of HCFC-141b will need to be reduced or terminated at that time. The existing options for rigid polyurethane foam blowing agents after the phase-out will be hydrofluorocarbon (HFC), carbon dioxide, or hydrocarbon based compounds. One possible candidate for HFC blowing agents is HFC-134a (1,1,1,2-tetrafluoroethane). Reasons for its use include its commercial availability, zero ozone depletion potential, low toxicity, low foam k factors at low temperatures, better dimensional stability, and the lack of flammability limits in air [1,2]. The major challenge in the use of HFC-134a is the difficulty in foam processing due to its low boiling point and moderate solubility in rigid foam polyols. During foam production, the reacting mixture rapidly expands and froths. This expansion can lead to isolated large cells in a matrix of smaller cells (worm hole formation) and can adversely affect the k factor and quality of the foam. A slower expansion is desirable to achieve better processibility and the lowest k factor possible. One way to influence the expansion is to increase the intermolecular interactions between the blowing agent and the foaming mixture. It may be possible to increase these intermolecular forces through the judicious selection of polyols and additives. Moreover, if a good understanding of the intermolecular interactions is gained, an opportunity exists to design rigid foam polyols to meet processing difficulties.