Blowing Agent Alternatives for Sprayed Polyurethane Foam

Abstract

Trichlorofluoromethane, CFC-11, has been the predommant blow ing agent used in spray formulations for polyurethane systems. The low thermal con ductivity of this gas has provided polyurethane foam with its excellent msulation properties. However, due to environmental concerns over depletion of ozone in the upper atmosphere, regulations have been proposed limiting the production of CFC's in 1989, with further reductions in the 1990's. This limited supply situation will re quire a great deal of reformulation and testing by suppliers of polyurethane systems as they seek alternative blowing agents. This paper provides data on the performance of two hydrochlorofluorocarbons, HCFC-123 and HCFC-141b, which are currently being promoted as alternatives to CFC-11. The alternate materials differ from CFC- 11 in molecular weight, boiling point, latent heat of vaporization, flammability and thermal conductivity. Therefore, formulations must be modified to determine the total blowing agent required for foam density, catalyst levels required to achieve the proper reactivity and flame retardant loading needed to meet flammabihty require ments. In addition, the use of mcreased water levels, which reduces the total quantity of CFC required is discussed. The use of increased water levels will be required for the following two reasons. First, although using increased water levels has its limita tions, it is the most viable alternate method of blowing available for the short term since alternate materials are not currently in large scale production. Second, even when the alternative materials are readily available, the relatively high costs for these materials will certainly motivate the formulator to mimmize usage and therefore maximize the formulation economics. This paper presents data on the required quan tity of various blowing agent combinations, formulation modifications required, the physical properties and flammability test performance in sprayfoam applications.