Diffusion of CFC 11 and hydrofluorocarbons in polyurethane

• Published in: Journal of applied polymer science 1998-12, Vol.70 (10), p.2069-2073
• Main Authors: Hong, Seong-Uk, Duda, J. Larry
• Format: Article
• Language: English
• Subjects: Applied sciences; blowing agents; Cellular; diffusion; Exact sciences and technology; Forms of application and semi-finished materials; permeability; polymer foam; Polymer industry, paints, wood; Technology of polymers
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/(SICI)1097-4628(19981205)70:10<2069::AID-APP23>3.0.CO;2-4

Since Rowland and Molina first warned that the chlorine from chlorofluorocarbons (CFCs) could destroy ozone in the stratosphere, there has been extensive scientific and political controversy over the fate of these chemicals. Recent observations of ozone depletion over the Arctic supported the hypothesis that the ozone loss is owing to photochemical process. Because CFCs are so stable, they can reach the ozone layer before being destroyed by a natural process. As a result, in 1987, the nations of the world agreed in Montreal to implement regulatory controls by calling for a 50% cutback in yearly CFC production by the end of the century. The protocol was strengthened in 1992 in Copenhagen to cease CFC production after 1995 in developed countries. Therefore, hydrofluorocarbons (HCFCs) were developed to replace CFCs after the Montreal protocol, and can be used until 2030. Although HCFCs still contain chlorine, they are more environmentally benign than CFCs, owing to the presence of carbon-hydrogen bonds that can be easily broken before reaching the ozone layer. CFC 11 has been widely used in insulation foams because it is an easily handled liquid molecule that persists in the foam to maintain the foam's thermal resistance. However, the complete ban on CFC 11 necessitates the search for alternative blowing agents, which will produce foams having properties comparable to those made with CFC 11. During aging, the thermal resistance of insulating polymer foams decreases because of the counter-diffusion of the blowing agent and air. Consequently, information concerning loss of blowing agents from foams is a very important criterion in the selection of blowing agents. Models of blowing agent loss from insulating foams show that this aging phenomena is a complex function of the blowing agent's diffusivity and solubility. In this study, the solubilities of CFC 11 and three HCFCs in polyurethane are measured at room temperature at various blowing agent pressures. The purpose of this work is to evaluate the suitability of HCFCs as blowing agents for rigid polyurethane insulating foams.