Polystyrene is a lightweight transparent plastic derived from petroleum by-products and natural gas. It is widely used in the packaging industry, but most polystyrene is used to make durable goods such as television cabinets, appliances, and furniture. Polystyrene also has excellent insulating properties. As packaging, polystyrene is used both in foam and solid forms. Solid polystyrene is used in yogurt, sour cream, and cottage cheese containers, cutlery, clear clamshells used at salad bars, and video and audio cassette containers. As foam, polystyrene is used in cups, bowls, plates, trays, clamshell containers, meat trays, egg cartons, and packaging for electronics and other delicate items. Polystyrene foam is manufactured by processing solid polystyrene resin pellets with a gaseous expansion agent. In the past, about 30% of polystyrene foam products were made with chlorofluorocarbons (CFCs), which were identified as contributors to the deterioration of the ozone layer in the Earth's upper atmosphere. By 1990, manufacturers had phased out the use of CFCs as a polystyrene expansion agent. Some manufacturers switched to the use of hydrochlorofluorocarbon-22 (HCFC-22), which reduced ozone layer depletion potential by about 95% over CFCs. By 1994, as required by federal law, polystyrene foam manufacturers phased out the use of HCFC-22 and by 1997 were using alternative expansion agents, most commonly pentane gas. Pentane does not affect the ozone layer, but because it can contribute to smog formation some manufacturers recycle pentane emissions. Carbon dioxide (CO2) is also used by manufacturers as a polystyrene expansion agent. CO2 is nontoxic, nonflammable, does not contribute to smog, and has no atmospheric ozone depletion potential, but it has been implicated in global warming.
Polystyrene packaging accounts for about 1.2 % (by weight) of the total solid waste stream in the United States, and polystyrene makes up from about 2-10% of materials thrown away as litter. However, polystyrene can be recycled and used to make new polystyrene products such as wall insulation, packing filler, and cafeteria trays. Polystyrene has an energy content of 17,000 Btu/pound, about four times that of average municipal solid waste, and can be burned with other solid wastes in an incinerator that has appropriate emission controls to contain potentially toxic combustion products. Another potential environmental concern is the release of toxic metals such as cadmium and lead from combustion of inks used to tint the polystyrene. The polystyrene manufacturing industry is developing source reduction techniques, including improving resin properties to make stronger products with less material and making lighter-weight foam products.
Polystyrene is manufactured from styrene, which is a hazardous chemical. When styrene is heated to 392°F (198°C), it is converted into the polymer polystyrene. Health concerns have been raised about styrene residues remaining in polystyrene products, especially those that are used to contain food for consumption. Styrene is soluble in oil and in ethanol, substances commonly found in foods and alcoholic beverages. A U.S. EPA National Human Adipose Tissue Survey in 1986 identified styrene in 100% of the 46 human fat samples collected.
