Zero-ODP Rigid Insulation Foams Prepared with HFAs

Abstract

The industry is continuously being challenged by regulatory agencies to find alternatives to CFCs (chlorofluoro-carbons) for use in all applications. Two solutions investigated were to replace CFCs with HCFCs (hydrochloro-fluorocar-bons or PFAs (perfluoroalkanes). However, the contribution of HCFCs to the depletion of the ozone layer has been determined to be too high for them to be viewed as anything but an intermediate solution. PFAs have been getting attention for their high halogen global warming potential (HGWP) due to their long atmospheric lifetime and, thus, seem unlikely even as additives. At this time, it appears that both HCFCs and PFAs have a finite usage period in our industry.

In our search for alternatives, we have discovered that HFAs (hydrofluoroal-kanes or partially fluorinated alkanes) make fine, closed cell foams. As a result of this, HFA-blown rigid foams at 2.0 pcf density or lower have low initial k-factors (0.13 Btu in./hr ft²⁰F). Aged k-factors are excellent because of the relatively slow cell gas diffusion of HFAs. These insulation values are similar to or better than those of foams made with HCFCs and PFAs! The advantage to this technology is that HFAs have zero-ozone depletion potential (ODP) and relatively low HGWP, making HFAs viable long-term alternatives.

Processing of the alternatives evaluated is similar to HCFC-22 technology, because the HFAs used in this investigation are gases at room temperature and pressure. The HFAs examined in this study were HFA-32, 134a, 125, and 227. These HFAs all show the same characteristics of low solubility, low blowing efficiency, and higher working vapor pressures; therefore, emulsion technology was used (as with PFAs). Good quality foams were produced without utilizing special compatibilizers.