Polystyrene(PS) is a syntheticaromaticpolymermade from themonomerstyrene. Polystyrene can be solid or foamed. General purpose polystyrene is clear, hard, and rather brittle. It is an inexpensive resin per unit weight. It is a rather poor barrier to oxygen and water vapor and has a relatively low melting point. Polystyrene is one of the most widely usedplastics, the scale of its production being several billion kilograms per year.Polystyrene can be naturallytransparent, but can be colored with colorants. Uses include protective packaging (such as packing peanuts and CD andDVDcases), containers (such as "clamshells"), lids, bottles, trays, tumblers, and disposablecutlery. Polystyrene is very slow tobiodegradeand is therefore a focus of controversy. It is often abundant as a form oflitterin the outdoor environment, particularly along shores and waterways, especially in its foam form.Inchemicalterms, polystyrene is a long chain hydrocarbon wherein alternating carbon centers are attached tophenyl groups(the name given to the aromatic ringbenzene). Polystyrene's chemical formula is(C8H8)n; it contains thechemical elements which are carbonandhydrogen.The material's properties are determined by short-rangevan der Waalsattractions between polymers chains. Since the molecules are long hydrocarbon chains that consist of thousands of atoms, the total attractive force between the molecules is large. When heated (or deformed at a rapid rate, due to a combination of viscoelastic and thermal insulation properties), the chains are able to take on a higher degree of conformation and slide past each other. Thisintermolecularweakness (versus the highintramolecularstrength due to the hydrocarbon backbone) confers flexibility and elasticity.Extruded polystyrene is about as strong as an unalloyedaluminium, but much more flexible and much lighter (1.05 g/cm3vs. 2.70 g/cm3for aluminium)Polystyrene results when styrene monomers interconnect. In the polymerization, the carbon-carbon pi bond (in thevinylgroup) is broken and a new carbon-carbon single (sigma) bond is formed, attaching another styrene monomer to the chain. The newly formed sigma bond is much stronger than the pi bond that was broken, thus it is very difficult to depolymerize polystyrene. About a few thousand monomers typically comprise a chain of polystyrene, giving amolecular weightof 100,000400,000.Environmental issuesProductionPolystyrene foams are produced using blowing agents that form bubbles and expand the foam. In expanded polystyrene, these are usually hydrocarbons such aspentane, which may pose a flammability hazard in manufacturing or storage of newly manufactured material, but have relatively mild environmental impact. Extruded polystyrene is usually made withhydrofluorocarbons(HFC-134a), which have global warming potentials of approximately 10001300 times that of carbon dioxide.

Non-biodegradableDiscarded polystyrene does not biodegrade for hundreds of years and is resistant tophotolysis. LitterPolystyrene foam is a major component of plastic debris in the ocean, where it becomes hazardous to marine life and "could lead to the transfer [of] toxic chemicals to the food chain".Animals do not recognize this artificial material and may even mistake it for food. Polystyrene foam blows in the wind and floats on water, and is abundant in the outdoor environment. It can be lethal to any bird or sea creature that swallows significant quantities. ReducingRestricting the use of foamed polystyrene takeout food packaging is a priority of many solid wasteenvironmental organizations. Efforts have been made to find alternatives to polystyrene, especially foam in restaurant settings. The original impetus was to eliminatechlorofluorocarbons(CFC), which was a former component of foam.Recycling

Theresin identification codesymbol for polystyreneIn general, polystyrene is not accepted incurbside collectionrecycling programs, and is not separated and recycled where it is accepted. In Germany, polystyrene is collected, as a consequence of the packaging law (Verpackungsverordnung) that requires manufacturers to take responsibility for recycling or disposing of any packaging material they sell.Most polystyrene products are currently not recycled due to the lack of incentive to invest in the compactors and logistical systems required. Due to the low density of polystyrene foam, it is not economical to collect. However, if the waste material goes through an initial compaction process, the material changes density from typically 30kg/m3to 330kg/m3and becomes a recyclable commodity of high value for producers of recycled plastic pellets. Expanded polystyrene scrap can be easily added to products such as EPS insulation sheets and other EPS materials for construction applications; many manufacturers cannot obtain sufficient scrap because of collection issues. When it is not used to make more EPS, foam scrap can be turned into products such as clothes hangers, park benches, flower pots, toys, rulers, stapler bodies, seedling containers, picture frames, and architectural molding from recycled PS. Recycled EPS is also used in many metal casting operations.Rastrais made from EPS that is combined with cement to be used as an insulating amendment in the making of concrete foundations and walls. American manufacturers have produced insulating concrete forms made with approximately 80% recycled EPS since 1993.

IncinerationIf polystyrene is properly incinerated at high temperatures (up to 1000C) and with plenty of air (14 m3/kg), the chemicals generated are water, carbon dioxide, and possibly small amounts of residual halogen-compounds from flame-retardants.If only incomplete incineration is done, there will also be leftover carbon soot and a complex mixture of volatile compounds. According to theAmerican Chemistry Council, when polystyrene is incinerated in modern facilities, the final volume is 1% of the starting volume; most of the polystyrene is converted into carbon dioxide, water vapour, and heat. Because of the amount of heat released, it is sometimes used as a power source forsteamorelectricity generation. When polystyrene was burned at temperatures of 800900C (the typical range of a modern incinerator), the products of combustion consisted of "a complex mixture of polycyclic aromatic hydrocarbons(PAHs) from alkyl benzenes to benzoperylene. Over 90 different compounds were identified in combustion effluents from polystyrene.

Polystyrene

Names

IUPAC namePoly(1-phenylethene)

Other namesThermocole

Identifiers

CAS Registry Number9003-53-6

AbbreviationsPS

ChemSpider

Properties

Chemical formula(C8H8)n

Density0.961.04g/cm3

Melting point~240C (464F; 513K)[3](decomposes at lower temperature)

Thermal conductivity0.033 W/(mK) (foam, 0.05 g/cm3)[1]

Refractive index(nD)1.6;dielectric constant2.6 (1 KHz 1 GHz)[2]

Related compounds

Related compoundsStyrene(monomer)

Except where otherwise noted, data are given for materials in theirstandard state(at 25C [77F], 100kPa).

Infoboxreferences