Polystyrene blowing agents

Polystyrene, blowing agent, foaming, pressirre, viscosity, Bagley... 

The use of CFCs as foam blowing agents has decreased 35% from 1986 levels. Polyurethanes, phenoHcs, extmded polystyrenes, and polyolefins are blown with CFCs, and in 1990 the building and appHance insulation markets represented about 88% of the 174,000 t of CFCs used in foams (see Foamed plastics). 

Plastics. Citric acid and bicarbonate are used as an effervescent blowing agent to foam polystyrene for insulated food and beverage containers replacing blowing agents such as chlorinated fluorocarbons (194—206). 

Incorporation of low boiling liquids which volatilise during processing. Such volatile blowing agents are important with polystyrene and polyurethanes and will be dealt with in the appropriate chapters. 

Figure 3.6 Sound velocity in polystyrene/HCFC 142b before phase separation as a function of temperature. The blowing agent concentrations (wt%) are indicated. After Sahnoune el al. [189]. Reproduced by permission of the Society of Plastic...

Foamed polystyrene, too, dates from the thirties. The method of adding blowing agents to polystyrene in an extruder so that the extrudate expands was developed by Dow (L5). It is still used today on a large scale. 

STYR0P0R, BASF - polymerization of styrene monomer in suspension in the presence of pentane as the blowing agent. Manufacture of new insulating packaging materials, etc. Suspension polymerization of crystal polystyrene in Ludwigshafen. 

The process is commonly used to mould expandable polystyrene (EPS) that is delivered containing some percentage of pentane as the blowing agent. The moulding needs three steps ... 

The use of CO as a blowing agent in polystyrene has now been developed by Dow Chemical Company, as a replacement for ozone depleting CFC-12. 

Uses Solvent blowing agent for polystyrene manufacturing chlorinated derivatives. 

Polystyrene s chief weakness is its image. There is a continuing effort to replace it with paper products. The prior use of CFCs as blowing agents in its foam products has contributed to this negative image. 

For the above-mentioned reasons the performance of this procedure is not quite simple in the context of a practical course.Therefore the following instruction is intended only to experimentally demonstrate two effects dissolving of pentane in solid polystyrene and foaming of the polystyrene, containing a blowing agent, in hot water. 

Until the late 1980s trichlorofluoromethane (CFC 11) was also used to blow flexible, open-celled polyurethane foams used in furniture upholstery however, the rapid loss of the blowing agent to the atmosphere meant that this CFC application was one of the first to be eliminated when concern over the possible effects of CFCs on stratospheric ozone increased. Similarly, dichlorodifluoromethane (CFC 12) in the relatively minor application of polystyrene hot-food containers was also rapidly replaced by hydrocarbon-blowing agents. 

Chloroethane is produced by the hydrochlorination of ethylene. It is used in the manufacture of tetraethyllead, as an industrial ethylating agent, as a blowing agent in the production of polystyrene foam and as a local anaesthetic. Occupational exposure occurs during the production of tetraethyllead, and industrial emissions have led to detectable levels of chloroethane in ambient air (lARC, 1991). 

---