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No chemistry required (it would not hurt to know some)
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Some chemistry or physics required
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| Blowing Agents |
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Fluorine and chlorine containing blowing agents
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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.
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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.
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CFC-11
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CFC-12
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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.
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HCFC-123
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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.
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Saturated hydrocarbon , linear, branched and cyclic
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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
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Low toxicity, low cost, poor thermal properties.
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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.
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