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No. 5

No chemistry required (it would not hurt to know some)

 

Some chemistry or physics required


Blowing Agents  
Fluorine and chlorine containing blowing agents  
Polyurethane foams are generated by either blowing the isocyanate with water, the reaction of the isocyanate with water results in the formation of carbon dioxide or with a low boiling solvent or a gas. The gas or solvent is dissolved in the polyol before blending with the isocyanate. The heat of the reaction of the isocyanate with the polyol evaporates the solvent or releases the gas. The density of the foam depends on the amount of blowing agent, the boiling point, solubility in the foam and the molecular weight.  
CFC. Trichlorofluoromethane (CFC-11) and Dichlorodifluoromethane (CFC-21) were the largest volume blowing agents used in foams. The worldwide production reached a maximum in 1989. Because of the problem these compounds cause in the ozone layer their use was prohibited.    

CFC-11

CFC-12
HCFC's were developed as replacement for CFC's. These fluorocarbons have a reduced lifetime in the atmosphere and therefore a reduced ozone reduction potential. HCFC-123 2,2-Dichloro-1,1,1-Trifluoroethane is an example of an acceptable hydrochlorofluorocarbon. Please check the Federal Register for any updates on the regulations.  

HCFC-123


Hydrocarbons. Low boiling hydrocarbons are for some applications acceptable substitute for CFC blowing agents. Although these hydrocarbons present no problem with degradation of the ozone layer, their flammability and poor thermal conductivity do not make them ideal blowing agents.  

Saturated hydrocarbon , linear, branched and cyclic

Carbon dioxide.   Low cost and environmental acceptance are the main advantage of carbon dioxide as a blowing agent. Carbon dioxide can be generated in situe by reaction the isocyanate with water, or it can be added under pressure to the polyol  

Low toxicity, low cost, poor thermal properties. 

Acetone. A low boiling ketone solvent, low in toxicity has excellent solubility and compatibility with polyols and isocyanates. Mainly used in flexible foams. It is photochemically of low reactivity and is not considered a VOC.   




Last edited on:

November 20, 2006

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