The concern about the release of greenhouse
gases from PU foams has brought substantial changes in the type of
blowing agents used in foam. Hydrofluorocarbons with less potential of
forming ozone are replacing the fluorocarbon blowing agents. Other
blowing agents which are being used more are low boiling hydrocarbons
and gases such as carbon dioxide. The carbon dioxide can be generated
by reaction of water with the isocyanate. Carbon dioxide can
also be dissolved under pressure in the polyol.
