Urethane foam blowing agent

Methylene chloride is used in refrigeration, aerosol propellants, paint stripping, urethane foam-blowing agents, adhesive, and food extractants. It has low toxicity compared with other chlorinated hydrocarbons and has been show n lo be neither mutagenic nor carcinogenic toward humans. 

The main uses of methylene chloride are in paint remover, aerosols, chemical processing, urethane foam blowing agents, metal degreasing, and electronics. 

A different method of making foams is to generate the blowing agent at the same time as the polymer is being formed. Thus urethane polymers are prepared... 

Meeting the dead Line Urethane Foams Move from HCFCs to Cleaner Blowing Agents, PT, Jan. 2003. 

A search for alternate blowing agents for urethane foams became necessary in 1987 following the Montreal Protocol, which mandated the development of foams with substantially reduced CFC content by 1995. 

Chemical Blowing Agents. The conventional gas-generation reaction for flexible urethane foams is the water-isocyanate reaction which was first described in a German patent (122). Its chemical reaction is shown as follows ... 

CFCs. Table 6 shows major CFCs. CFC-11 has been the representative blowing agent for both flexible and rigid urethane foams (155). The use of CFCs brought significant advantages to both flexible and rigid polyurethane foams. However, ozone-depletion potential (ODP) in the stratosphere have led to the worldwide ban of the production and use of CFCs by 1995. 

Chloropropane as blowing agent for rigid urethane foams has been developed by Recticel (240). 

Preparation. Polyurethane foams (often referred to as urethane foams) are prepared by the reaction of a polyisocyanate with a polyol in the presence of a blowing agent, a surfactant, and a catalyst without external heating of the foaming system. The principle of preparation of urethane foams is based on the simultaneous occurrence of two reactions, i.e., polyurethane formation and gas generation in the presence of catalyst and surfactant, as shown below ... 

The blowing agent for microcellular elastomers is water. The amount of water should be accurate, and its accuracy can be obtained by a water-containing solution, such as liquid sodium sulfonate of vegetable oils containing a small amount of water. The catalysts to be used are those used in urethane foams, e.g., tertiary amines, and tin catalysts. The above ingredients are mixed and poured into a hot mold and cured in a defined period of time. After demolding, a post cure is applied to complete the polymer-formation reactions. 

In most cases semi-rigid urethane foams are produced by using two-component systems, that is component A (polyisocyanate component) and component B (blend of the remaining ingredients, i.e., polyol, blowing agent, catalyst and surfactant). 

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