Chlorofluorocarbons polystyrene manufacture

In 1985 large holes were discovered in the ozone layer over Antarctica, Australasia and Europe (Figure 7.12). Scientists think that these holes have partly been produced by chemicals called chlorofluorocarbons or CFCs. CFCs were developed as refrigerants in fridges back in the 1950s. They have also been used in air conditioning systems, in aerosol cans (as propellants) and in the manufacture of expanded plastics such as polystyrene. CFCs are very unreactive molecules. They escape into the atmosphere and, because of their inertness, remain without further reaction until they reach the... 

Of particular relevance to this chapter is the use of CO2 in polymer synthesis, in the manufacture of polymethylmethacrylate and polystyrene (Xerox) and for the production of fluoropolymers (DuPont). One of the main drivers for the latter was the phasing out of the chlorofluorocarbons (CFCs) used in the original process. The main advantage to this application is not necessarily the avoidance of the use of CFCs (although this is important), but the superior polymer processing properties made possible by the relative volatility of CO2 and its ease of removal. 

In Table 1.1, the critical properties of some compounds which are commonly used as supercritical fluids are shown. Of these, carbon dioxide and water are the most frequently used in a wide range of applications. The production of polyethylene in supercritical propane is described in a loop reactor [13]. Supercritical ethylene and propylene are also apphed, where they usually act both as a solvent and as the reacting monomer. In the field of polymer processing, the Dow Chemical Company has developed a process in which carbon dioxide is used to replace chlorofluorocarbon as the blowing agent in the manufacture of polystyrene foam sheet [14, 15]. 

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