Polystyrene

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Polystyrene

Overview

Polystyrene (pol-ee-STYE-reen) is a thermoplastic polymer made from styrene. A thermoplastic polymer is a material that can be repeatedly softened and hardened by alternately heating and cooling. Styrene is a hydrocarbon derived from petroleum with the formula C₆H₅CH=CH₂. The presence of the double bond in the styrene molecule makes it possible for styrene molecules to react with each other in long chains that constitute the polymer polystyrene.

Polystyrene is a hard, strong, transparent solid highly resistant to mechanical impact. It is an excellent thermal (heat) and electrical insulator, is easily shaped and molded in the liquid state, and takes dyes readily. It can be produced in a wide variety of shapes and forms, including sheets, plates, rods, beads, and foams.

Key Facts

Other Names:

Styrofoam

Formula:

-[-CH₂C₆H₅-]-_n

Elements:

Carbon, hydrogen

Compound Type:

Organic polymer

State:

Solid

Molecular Weight:

Varies g/mol

Melting Point:

Varies widely; ranges from 190°C-260°C (370°F-500°F)

Boiling Point:

Not applicable

Solubility:

Insoluble in water and inorganic acids and bases; soluble in many organic solvents, including ethylbenzene, chloroform, carbon tetrachloride, and tetrahydrofuran

The history of polystyrene dates to 1839 when a German apothecary (druggist) named Eduard Simon discovered styrene in petroleum. Later scientists attempted to incorporate styrene into some of the commercial products they made, such as rubber tires. But a polymer based on styrene was not actually produced until 1930 when researchers at the German chemical firm of I. G. Farben discovered how to make the material. Farber's parent company, BASF, shortly made the product commercially available and in 1937, Dow Chemical first made the compound available in the United States. During World War II, polystyrene was used for the manufacture of synthetic rubber products. After the war, the number of commercial and industrial uses expanded rapidly. Today, it is virtually impossible to avoid polystyrene products in one's daily life.

How It Is Made

Compounds like styrene with double bonds often polymerize easily. The double bond on a styrene molecule breaks open and a hydrogen atom from a second styrene molecule adds to one side of the double bond, while the rest of the second styrene molecule adds to the second side of the double bond. The product of this reaction still has a double bond. So the reaction can be repeated a second time; and a third time; and a fourth time; and so on. One goal of research on polystyrene has been to determine how the size of the polystyrene affects its properties (and, therefore, its uses) and how to stop the polymerization reaction at some desired point.

All that is needed to start the polymerization of styrene is a material that will cause the first double bond to break. Such materials are known as polymerization initiators. One of the most common initiators used in the polymerization of styrene is benzoyl peroxide (C₆H₅COOOCOC₆H₅). Once the polymerization reaction begins, it tends to release enough energy for the reaction to continue on its own.

An especially popular form of polystyrene is known as expanded polystyrene. It is made by blending air with molten polystyrene to make a lightweight foam sold under the trade name of Styrofoam®.

Interesting Facts

• Polystyrene is sold commercially under more than a hundred trade names, the most famous of which is probably Styrofoam®.
• Only about 5 percent of a styrofoam cup is polystyrene. The rest is air.
• One of the innovative uses for polystyrene is as a building material for the construction of new houses. Scientists suggest that it is perfect for the purpose: lightweight, inexpensive, strong, a good insulator, and available all over the world. One of the first applications suggested for polystyrene as a building material is in the construction of houses in Afghanistan, where many families have lost their homes after two decades of wars and earthquakes.

Common Uses and Potential Hazards

Polystyrene is the fourth largest thermoplastic polymer made in the United States by production volume. It is used in the manufacture of hundreds of commercial, industrial, household, and personal articles. Some examples include:

• Plastic model kits and toys;
• Containers with lids; disposable cups, plates, knives, forks, and spoons;
• "Jewel" cases for compact discs and cases for audiocassettes;
• Plastic coat hangers and plastic trays;
• Refrigerator doors and air conditioner cases;
• Housing for machines; and
• Cabinets for clocks, radios, and television sets.

Some uses of expanded polystyrene include:

• In all kinds of containers to keep foods either hot or cold (such as ice chests);
• Egg cartons;
• Fillers in shipping containers;
• Packages for carry-out foods;
• Insulation for buildings;
• In the construction of boats; and
• For the construction of some types of furniture.

Polystyrene dust and powder formed during production can be a mild irritant to the eyes, skin, and respiratory system. But even for workers in the field, the risk is regarded as being very low. A more serious problem posed by the compound is the risk it poses for the environment. About half of all the polystyrene produced in the United States is used for packaging and "one-time use" purposes. That is, someone uses the product and then throws it away. Since polystyrene does not readily decompose, it tends to accumulate in landfills and dumps. Some environmentalists point out that large volumes of discarded polystyrene contribute significantly to the nation's solid waste disposal problems. Industry spokespersons, however, point out that polystyrene accounts for less than one percent of all solid wastes. In any case, a number of industries and companies have attempted to reduce the amount of polystyrene used in their products in order to cut back on their contribution to the solid waste disposal problem.

Words to Know

HYDROCARBON

a compound consisting of carbon and hydrogen.

POLYMER

a compound consisting of very large molecules made of one or two small repeated units called monomers.

THERMOPLASTIC

can be repeatedly softened and hardened by alternately heating and cooling.

For Further Information

Boyd, Clark. "Polystyrene homes planned for Afghans." BBC News. http://news.bbc.co.uk/2/hi/technology/3528716.stm (accessed on October 26, 2005).

"Energy & Waste—Landfilling." Energy Information Administration, Department of Energy. http://www.eia.doe.gov/kids/energyfacts/saving/recycling/solidwaste/landfiller.html (accessed on October 26, 2005).

"Polystyrene." U.S. Environmental Protection Agency, Emissions Factors and Policy Applications Center. http://www.epa.gov/ttn/chief/ap42/ch06/final/c06s06-3.pdf (accessed on October 26, 2005).

"Polystyrene Packaging Delivers!" Polystyrene Packaging Council. http://www.polystyrene.org/ (accessed on October 26, 2005).

Sims, Judith. "Polystyrene." In Environmental Encyclopedia. 3rd ed. Edited by Marci Bortman and Peter Brimblecombe. Detroit, Mich.: Gale, 2003.

See Also

Styrene