Insulation chlorofluorocarbons

F. Sherwood-Rowland, Chlorofluorocarbons and Depletion of Stratospheric O ne, Improved Thermal Insulation—Problems and Perspectives, D. A. Brandreth, ed., Technomic Puhlishing Co., Inc., Lancaster, Pa., 1991, pp. 5—25. 

Approximately 50% of the demand for tetrachloroethylene is in the dry-cleaning industry where about 80% of all dry cleaners use it as their primary cleaning agent. Use as a feedstock for chlorofluorocarbon production accounts for 30% of current demand. Metal cleaning and miscellaneous appHcations represent 12 and 8% of demand, respectively. The miscellaneous appHcations include such varied uses as transformer insulating fluid, chemical maskant formulations, and as a process solvent for desulfurizing coal. 

Chlorofluorocarbon-blown foam blocks are used to insulate the walls and roofs of some buildings, thus reducing heat losses and helping to conserve fossil fuels. In this area, polyurethane foam competes with polystyrene foam, which until recently was blown with dichlorodifluoromethane (CFC 12) but is now blown with a mixture of chlorodifluoromethane (HCFC 22) and 1 -chloro-l,l-difluoroethane (HCFC 142b). 

Rigid foams are based primarily on polyfunctional, low molecular weight alcohols and amines. Most global applications conventionally use polymeric isocyanates, TDI, or an undistilled grade of mixed TDI isomers. TDI prepolymers which have hydroxyl and isocyanate groups have been marketed as a low vapor pressure alternative to undistilled TDI. Density reduction is effected via the addition of chlorofluorocarbons, low molecular weight alkanes, or via the in situ generation of carbon dioxide. The resultant closed cell foams find applications as insulators in construction, appliance, transportation, pipeline, and tank end uses. 

Chlorofluorocarbons (CFCs) are widely used in refrigeration and air conditioning, insulation, and plastic foams. Although nontoxic and nonflammable, they are believed to deplete the ozone layer in the atmosphere which shields the earth from the sun s ultraviolet radiation. While action to control the production and use of CFCs was still being debated, McDonalds s Corporation announced it would no longer use foam food containers produced with the aid of CFC in its fast food outlets. 

Chlorofluorocarbons (CFCs) A family of inert, nontoxic, and easily liquefied chemicals used in refrigeration, air conditioning, packaging, insulation, or as solvents and aerosol propellants. Because CFCs are not destroyed in the lower atmosphere, they drift into the upper atmosphere where their chlorine components destroy the ozone. 

Flexible polyurethane foams are blown with water, methylene chloride, and chlorofluorocarbons (CFCs). Carbon dioxide from the water/isocyanate reaction functions as the blowing agent. The methylene chloride and CFCs assist in the blowing and contribute properties such as added softness and resilience. The CFCs also contribute to the insulation properties of rigid urethane foams. 

Chlorofluorocarbons were devised as nonflammable, nontoxic, noncorrosive alternatives to refrigerants, such as sulfur dioxide, ammonia, and chloromethane.130 Their uses grew to include blowing agents for foam insulation, aerosol propellants, and solvents for cleaning electronic parts.131 Typical compounds are the following ... 

In many applications, fluorocarbons are used because of their superior thermodynamic properties. Such is the case with polyurethane and polystyrene insulating foams. Two main fluorocarbons used for foams are chlorofluorocarbon 11 and chlorofluorocarbon 12. 

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