HFC-134a blended with Transcend? Additive Technology as a Replacement for HCFC-22 in Pour-in-Place Rigid Polyurethane Foams

摘要

Since the earlier phase out of CFC-11 in the mid 90's and the more recent phase out of HCFC-141b in the US in 2003, the use of HCFC-22 as a blowing agent in rigid polyurethane foams has become quite widespread in pressure/froth applications such as commercial refrigeration and marine flotation as well as in more typical pour-in-place applications including doors and building panels. The major reasons for this situation are its ease of blending into polyol blends, it is non-flammable, it provides a good overall balance of physical properties and it is cost effective. Unfortunately the use of HCFC-22, together with that of HCFC-141b in Canada, will be phased out across North America on January 1, 2010 and a big issue for remaining users is which alternative should they choose. The main alternative to HCFC-22 for pressure/froth applications is HFC-134a since it is non-flammable and has been shown to provide acceptable foam properties. However, HFC-134a is difficult to handle due to its low solubility in polyols and this can negatively influence foam quality. For pour-in-place applications, HFC-134a, HFC-245fa and blends of the pentane isomers are the obvious options to replace HCFC-22. Besides the problems noted above for HFC-134a, higher loadings can produce a thick “froth” when the foam is dispensed from machines and HFC-245fa is expensive to use not only because of its high raw material cost but also because of its lower blowing effectiveness. Hydrocarbons perform well overall but require significant modifications to existing production equipment and facilities to prevent unsafe situations. These modifications are expensive and may not always be feasible due to existing plant layouts. This study examines the use of a blend of HFC-134a and Transcend? additive technology (trans-1,2-dichloroethylene or TDCE) as a replacement for HCFC-22 in a generic pour-in-place formulation. Parameters examined include the ease of adding the gaseous blowing agent to the polyol blend, flow, thermal conductivity, dimensional stability and adhesion of the foam to thin steel. It is demonstrated that the use of a combination of TDCE and HFC-134a can produce foams having at least equivalent and in some cases superior overall performance compared to HCFC-22 and HFC-134a, and offers foam manufacturers a new, viable option.