Novel Processing of LBBA Appliance Systems

摘要

With the phase out of HCFC-141b, appliance manufacturers have had to decide on a zero Ozone Depletion Potential (ODP) blowing agent option. In North America, HFC-245fa and HFC-134a are the leading candidates, however there is a limited use of hydrocarbons. None of these options are an ideal drop in for HCFC-141b. Both HFC-245fa and HFC-134a are considered low boiling blowing agents (LBBA) and require additional handling measures. One of the hydrocarbons being used, isobutane, is also an LBBA. The much lower boiling points of these options lead to major challenges for the end user. Of these options, HFC-134a is the most difficult to work with. Polyol blends containing HFC-134a have an elevated vapor pressure that is significantly higher than current HCFC-141b systems. This is primarily due to the low boiling point in combination with the poor solubility of HFC-134a in polyol blends. Because of their high vapor pressure, blends containing HFC-134a need to be kept under pressure during every phase of their use. Blends containing HFC-245fa develop much lower vapor pressures because of the better polyol solubility of the blowing agent, and because its boiling point is much closer to ambient temperatures. Isobutane is typically used as a co-blowing agent with other hydrocarbons, so the effect of its low boiling point is somewhat diluted. However, in spite of their differences, any LBBA will present processing issues that can have a negative impact on foam quality.