There are several polymers, copolymers, and terpolymers based on the monomer styrene (C8H8), of which polystyrene (PS) is used in the highest volume. It is a linear homopolymer with amorphous structure that is generally noted for its brittleness. PS is transparent, easily colored, and readily molded, but degrades at elevated temperatures and dissolves in various solvents. Because of its brittleness, some PS grades contain 5% to 15% rubber and the term high-impact polystyrene (HIPS) is used for these types. They have higher toughness, but transparency and tensile strength are reduced. In addition to injection molding applications (e.g., molded toys, housewares), polystyrene also finds uses in packaging in the form of PS foams.
Polystyrene is abbreviated by PS. General-purpose polystyrene is the low-cost member of the family of styrenic plastics. Properties of the amorphous polymer include hardness, rigidity, optical clarity, and dimensional stability. Most crystal polystyrene is injection-molded. Oriented crystal PS sheet is thermoformed into trays and blister packaging, and foamed crystal PS is used in a wide variety of insulating and packaging applications.
Modified or impact polystyrene (with polybutadiene elastomers) extends the uses of polystyrenes into those areas where high impact strength and good elongation are required. Most products of this type have the rubber molecularly grafted to the polystyrenes; however, some are produced by mechanical mixing.
High-impact polystyrene is generally recognized as the best styrenic material for load-bearing applications. The other types of polystyrene offer various improvements in chemical, thermal, and optical performance, usually at the sacrifice of mechanical properties. High-impact polystyrene is a very rigid material, but it does not withstand long-term tensile loads as well as some other thermoplastics do.
Typical applications include food packaging (cups, lids, take-out containers), housewares, office products, and video and audio cassettes. Ignition-resistant grades are used in radio and TV housings.
Foamed crystal polystyrene has cushioning and insulation properties at very low densities. Extruded foam sheet is used as a protective wrapping material and is thermoformed into fast food packages, egg cartons, and meat and produce trays for supermarkets. Expandable polystyrene (EPS) is supplied in the form of small beads contianing a chemical blowing agent. The beads are pre-expanded with steam to establish the density of the finished product and then steam-chest-molded into lightweight products such as coffee cups, cooler chests, and protective package inserts.
Polystyrene is a glasslike, lightweight plastics material used in a variety of goods. Products made of polystyrene include food packaging, insulation, housewares, and automobile parts.
Polystyrene is a synthetic polymer. A polymer is a long, chainlike molecule. The "links" are repeating patterns of simple groups of atoms called monomers. Polystyrene is made from styrene monomers, each consisting of eight carbon atoms and eight hydrogen atoms. Polystyrene is a thermoplastic--that is, it softens and melts at high temperatures.
Polystyrene is fairly strong, easy to work, and inexpensive. A common way to make polystyrene is to heat styrene monomer to about 360 degrees F (180 degrees C). Manufacturers produce polystyrene plastics by adding fillers, colorings, and plasticizers (chemicals that help soften the material) to the polymer.
A number of methods are used to make products of the plastic. Extrusion (pushing melted plastic through an opening) makes a film used in wall coverings. A combination of extrusion and thermoforming (using a vacuum to draw hot plastic sheets into a mold) produces food containers and refrigerator parts. Injection molding (forcing melted plastic into a mold) creates auto parts and panels for cabinets. Blow molding (forcing air and plastic into a mold) produces polystyrene foam, a lightweight material containing tiny bubbles of air. This material is used in ice chests, disposable cups, packaging material, and building insulation.
Polystyrene plastics are difficult to break down into their basic ingredients for recycling. Instead, recyclers grind them into powders that are used as fillers.
Dow Chemical Company became the first producer of polystyrene in 1930. In the mid-1950's, the company introduced polystyrene foam under the registered trade name Styrofoam.