Polystyrene
Overview
 
Polystyrene also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic
Aromaticity
In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...

 polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 made from the monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

 styrene, a liquid hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 that is manufactured from petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

 by the chemical industry
Chemical industry
The chemical industry comprises the companies that produce industrial chemicals. Central to the modern world economy, it converts raw materials into more than 70,000 different products.-Products:...

. Polystyrene is one of the most widely used plastics
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

, the scale being several billion kilograms per year.

Polystyrene is a thermoplastic
Thermoplastic
Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...

 substance, which is in solid (glassy) state at room temperature, but flows if heated above its glass transition temperature of about 100 °C (for molding
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....

 or extrusion), and becomes solid again when cooled.
Encyclopedia
Polystyrene also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic
Aromaticity
In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...

 polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 made from the monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

 styrene, a liquid hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 that is manufactured from petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

 by the chemical industry
Chemical industry
The chemical industry comprises the companies that produce industrial chemicals. Central to the modern world economy, it converts raw materials into more than 70,000 different products.-Products:...

. Polystyrene is one of the most widely used plastics
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

, the scale being several billion kilograms per year.

Polystyrene is a thermoplastic
Thermoplastic
Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...

 substance, which is in solid (glassy) state at room temperature, but flows if heated above its glass transition temperature of about 100 °C (for molding
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....

 or extrusion), and becomes solid again when cooled. Pure solid polystyrene is a colorless, hard plastic with limited flexibility. It can be cast into molds with fine detail. Polystyrene can be transparent or can be made to take on various colors.

Solid polystyrene is used, for example, in disposable cutlery
Cutlery
Cutlery refers to any hand implement used in preparing, serving, and especially eating food in the Western world. It is more usually known as silverware or flatware in the United States, where cutlery can have the more specific meaning of knives and other cutting instruments. This is probably the...

, plastic models, CD and DVD cases, and smoke detector housings. Products made from foamed polystyrene are nearly ubiquitous, for example packing materials, insulation, and foam drink cups.

Polystyrene can be recycled, and has the number "6" as its recycling symbol
Resin identification code
The SPI resin identification coding system is a set of symbols placed on plastics to identify the polymer type. It was developed by the Society of the Plastics Industry in 1988, and is used internationally....

. The increasing oil prices have increased the value of polystyrene for recycling. No known microorganism has yet been shown to biodegrade polystyrene, and it is often abundant as a form of pollution
Litter
Litter consists of waste products such as containers, papers, wrappers or faeces which have been disposed of without consent. Litter can also be used as a verb...

 in the outdoor environment
Environment (biophysical)
The biophysical environment is the combined modeling of the physical environment and the biological life forms within the environment, and includes all variables, parameters as well as conditions and modes inside the Earth's biosphere. The biophysical environment can be divided into two categories:...

, particularly along shores and waterways especially in its low density cellular form.

History

Polystyrene was discovered in 1839 by Eduard Simon
Eduard Simon
Eduard Simon, an apothecary in Berlin, Germany, accidentally discovered polystyrene in 1839. Simon distilled an oily substance from storax, the resin of the Sweetgum tree, Liquidambar orientalis, which he named "styrol"...

, an apothecary
Apothecary
Apothecary is a historical name for a medical professional who formulates and dispenses materia medica to physicians, surgeons and patients — a role now served by a pharmacist and some caregivers....

 in Berlin
Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...

. From storax
Storax
Storax is also a name for trees in the genus StyraxStorax is the resinous exudate of the tree Liquidambar orientalis , occasionally used in incense or as an aromatic fixative in perfumery....

, the resin of the Turkish sweetgum tree Liquidambar orientalis
Liquidambar orientalis
Liquidambar orientalis, commonly known as oriental sweetgum or Turkish sweetgum, is a deciduous tree in the genus Liquidambar, native to the eastern Mediterranean region, that occurs as pure stands mainly in the flood plains of southwestern Turkey and on the Greek island of Rhodes.-Biotope:The...

, he distilled an oily substance, a monomer that he named styrol. Several days later, Simon found that the styrol had thickened, presumably from oxidation, into a jelly he dubbed styrol oxide ("Styroloxyd"). By 1845 English chemist John Blyth and German chemist August Wilhelm von Hofmann
August Wilhelm von Hofmann
August Wilhelm von Hofmann was a German chemist.-Biography:Hofmann was born at Gießen, Grand Duchy of Hesse. Not intending originally to devote himself to physical science, he first took up the study of law and philology at Göttingen. But he then turned to chemistry, and studied under Justus von...

 showed that the same transformation of styrol took place in the absence of oxygen. They called their substance metastyrol. Analysis later showed that it was chemically identical to Styroloxyd. In 1866 Marcelin Berthelot correctly identified the formation of metastyrol from styrol as a polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

 process. About 80 years went by before it was realized that heating of styrol starts a chain reaction that produces macromolecule
Macromolecule
A macromolecule is a very large molecule commonly created by some form of polymerization. In biochemistry, the term is applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...

s, following the thesis of German organic chemist Hermann Staudinger
Hermann Staudinger
- External links :* Staudinger's * Staudinger's Nobel Lecture *....

 (1881–1965). This eventually led to the substance receiving its present name, polystyrene.

The company I. G. Farben
IG Farben
I.G. Farbenindustrie AG was a German chemical industry conglomerate. Its name is taken from Interessen-Gemeinschaft Farbenindustrie AG . The company was formed in 1925 from a number of major companies that had been working together closely since World War I...

 began manufacturing polystyrene in Ludwigshafen, Germany, about 1931, hoping it would be a suitable replacement for die-cast zinc in many applications. Success was achieved when they developed a reactor vessel that extruded polystyrene through a heated tube and cutter, producing polystyrene in pellet form.

Before 1949, the chemical engineer Fritz Stastny (1908–1985) developed pre-expanded PS beads by incorporating aliphatic hydrocarbons, such as pentane. These beads are the raw material for moulding parts or extruding sheets. BASF and Stastny applied for a patent that was issued in 1949. The moulding process was demonstrated at the Kunststoff Messe 1952 in Düsseldorf. Products were named Styropor.

The crystal structure of isotactice polystyrene was reported by Giulio Natta
Giulio Natta
Giulio Natta was an Italian chemist and Nobel laureate. He won a Nobel Prize in Chemistry in 1963 with Karl Ziegler for work on high polymers.-Early years:...

.

In 1959, the Koppers Company in Pittsburgh, Pennsylvania
Pittsburgh, Pennsylvania
Pittsburgh is the second-largest city in the US Commonwealth of Pennsylvania and the county seat of Allegheny County. Regionally, it anchors the largest urban area of Appalachia and the Ohio River Valley, and nationally, it is the 22nd-largest urban area in the United States...

, developed expanded polystyrene (EPS) foam.

Structure

In chemical terms, polystyrene is a long chain hydrocarbon wherein alternating carbon centers are attached to phenyl group
Phenyl group
In organic chemistry, the phenyl group or phenyl ring is a cyclic group of atoms with the formula C6H5. Phenyl groups are closely related to benzene. Phenyl groups have six carbon atoms bonded together in a hexagonal planar ring, five of which are bonded to individual hydrogen atoms, with the...

s (the name given to the aromatic ring benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....

. Polystyrene's chemical formula is (C8H8)n; it contains the chemical elements carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

.

The materials properties are determined by short range van der Waals
Van der Waals
-People:* Fransje van der Waals , Dutch medical physician* Johannes Diderik van der Waals , Dutch physicist-Physics:* the Van der Waals force, named after the physicist* the Van der Waals equation, named after the physicist...

 attractions 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. This intermolecular weakness (versus the high intramolecular
Intramolecular
Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule, a property or phenomenon limited to the extent of a single molecule.- Examples :...

strength due to the hydrocarbon backbone) confers flexibility and elasticity. The ability of the system to be readily deformed above its glass transition temperature allows polystyrene (and thermoplastic polymers in general) to be readily softened and molded upon heating.

Polymerization

Polystyrene results when styrene monomers interconnect. In the polymerization, one carbon-carbon double bond (in the vinyl
Vinyl
A vinyl compound is any organic compound that contains a vinyl group ,which are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group...

 group) is replaced by a much stronger carbon-carbon single bond, hence it is very difficult to depolymerize polystyrene. About a few thousand monomers typically comprise a chain of polystyrene, giving a molecular weight of 100,000–400,000.

A 3-D model would show that each of the chiral
Chirality (chemistry)
A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....

 backbone carbons lies at the center of a tetrahedron
Tetrahedron
In geometry, a tetrahedron is a polyhedron composed of four triangular faces, three of which meet at each vertex. A regular tetrahedron is one in which the four triangles are regular, or "equilateral", and is one of the Platonic solids...

, with its 4 bonds
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 pointing toward the vertices. Let's consider that the -C-C- bonds are rotated so that the backbone chain lies entirely in the plane of the diagram. From this flat schematic, it is not evident which of the phenyl (benzene) groups are angled toward us from the plane of the diagram, and which ones are angled away. The isomer
Isomer
In chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...

 where all of them are on the same side is called isotactic polystyrene, which is not produced commercially.


Atactic polystyrene

The only commercially important form of polystyrene is atactic, which means that the phenyl groups are randomly
Randomness
Randomness has somewhat differing meanings as used in various fields. It also has common meanings which are connected to the notion of predictability of events....

 distributed on both sides of the polymer chain. This random positioning prevents the chains from ever aligning with sufficient regularity to achieve any crystallinity
Crystallinity
Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a big influence on hardness, density, transparency and diffusion. In a gas, the relative positions of the atoms or...

. The plastic has a glass transition temperature Tg of ~90C. Polymerization is initiated with free radicals.

Isotactic and syndiotactic polystyrene

Ziegler-Natta polymerization can produce an ordered syndiotactic polystyrene with the phenyl groups positioned on alternating sides of the hydrocarbon backbone. This form is highly crystalline with a Tm of 270 °C (518 °F). Such materials are not commercially produced because the polymerization is slow.

Extruded polystyrene is about as strong as an unalloyed aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, but much more flexible and much lighter (1.05 g/cm3 vs. 2.70 g/cm3 for aluminium).

Degradation

Because it is an aromatic hydrocarbon
Aromatic hydrocarbon
An aromatic hydrocarbon or arene is a hydrocarbon with alternating double and single bonds between carbon atoms. The term 'aromatic' was assigned before the physical mechanism determining aromaticity was discovered, and was derived from the fact that many of the compounds have a sweet scent...

, it burns with an orange-yellow flame, giving off soot
Soot
Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...

, as is characteristic of materials containing aromatic rings. Complete oxidation of polystyrene produces carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and water vapor
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. Because of its chemical inertness, polystyrene is used to fabricate containers for chemicals, solvents, and foods.
Polystyrene contains traces of styrene monomer. When food is heated in polystyrene container the monomer is extracted and enter the digestive system of the consumer. Styrene is toxic and a known carcinogen. This causes additional concerns when used for food or beverage packaging.
Polystyrene is soluble in most of the organic solvents known and is not appropriate for such uses. Foamed polystyrene is used for packaging purposes of chemicals, but it does not come into contact with the actual solvents.

Forms produced

Properties
Density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

1.05 g/cm3
Density of EPS 16–640 kg/m3
Dielectric constant
Dielectric constant
The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...

2.4–2.7
Electrical conductivity (s) 10−16 S
Siemens (unit)
The siemens is the SI derived unit of electric conductance and electric admittance. Conductance and admittance are the reciprocals of resistance and impedance respectively, hence one siemens is equal to the reciprocal of one ohm, and is sometimes referred to as the mho. In English, the term...

/m
Thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

 (k)
0.08 W/(m·K)
Young's modulus
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...

 (E)
3000–3600 MPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...

Tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

 (st)
46–60 MPa
Elongation at break 3–4%
Notch
Charpy impact test
The Charpy impact test, also known as the Charpy v-notch test, is a standardized high strain-rate test which determines the amount of energy absorbed by a material during fracture. This absorbed energy is a measure of a given material's toughness and acts as a tool to study temperature-dependent...

 test
2–5 kJ/m2
Glass transition temperature 95 °C
Melting point 240 °C
Vicat B
Vicat softening point
Vicat softening point or Vicat hardness is the determination of the softening point for materials that have no definite melting point, such as plastics. It is taken as the temperature at which the specimen is penetrated to a depth of 1 mm by a flat-ended needle with a 1 square mm circular or...

90 °C
Linear expansion coefficient (a) 8×10−5 /K
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

Specific heat (c) 1.3 kJ/(kg·K)
Water absorption (ASTM) 0.03–0.1
Decomposition
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...

X years, still decaying


Polystyrene is commonly injection molded or extruded, while expanded polystyrene is either extruded or molded in a special process.
Polystyrene copolymers are also produced; these contain one or more other monomers in addition to styrene. In recent years the expanded polystyrene composites with cellulose and starch have also been produced.

Extruded closed-cell polystyrene foam is sold under the trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...

 Styrofoam
Styrofoam
Styrofoam is a trademark of The Dow Chemical Company for closed-cell currently made for thermal insulation and craft applications. In 1941, researchers in Dow's Chemical Physics Lab found a way to make foamed polystyrene...

 by Dow Chemical
Dow Chemical Company
The Dow Chemical Company is a multinational corporation headquartered in Midland, Michigan, United States. As of 2007, it is the second largest chemical manufacturer in the world by revenue and as of February 2009, the third-largest chemical company in the world by market capitalization .Dow...

. This term is often used informally for other foamed polystyrene products.

Polystyrene is used in some polymer-bonded explosive
Polymer-bonded explosive
A polymer-bonded explosive, also called PBX or plastic-bonded explosive, is an explosive material in which explosive powder is bound together in a matrix using small quantities of a synthetic polymer...

s:
Polystyrene PBX examples
Name Explosive ingredients Binder ingredients
PBX-9205 RDX
RDX
RDX, an initialism for Research Department Explosive, is an explosive nitroamine widely used in military and industrial applications. It was developed as an explosive which was more powerful than TNT, and it saw wide use in WWII. RDX is also known as cyclonite, hexogen , and T4...

 92%
Polystyrene 6%; DOP 2%
PBX-9007 RDX 90% Polystyrene 9.1%; DOP 0.5%; resin 0.4%

Sheet or molded polystyrene

Polystyrene (PS) is economical, and is used for producing plastic model
Plastic model
thumb|300px||4-year-old boy starts painting a plastic model he has assembled of the South Goodwin LightshipPlastic models, often called scale models, are models manufactured as kits which are assembled by hobbyists, and intended for static display....

 assembly kits, plastic cutlery, CD "jewel" cases
CD and DVD packaging
Optical disc packaging is the packaging that accompanies CDs, DVDs, and other formats of optical media. Most packaging is rigid or semi-rigid and designed to protect the media from scratches and other types of exposure damage.- Jewel case:...

, smoke detector
Smoke detector
A smoke detector is a device that detects smoke, typically as an indicator of fire. Commercial, industrial, and mass residential devices issue a signal to a fire alarm system, while household detectors, known as smoke alarms, generally issue a local audible and/or visual alarm from the detector...

 housings, license plate frames, and many other objects where a fairly rigid, economical plastic is desired. Production methods include thermoforming
Thermoforming
Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mold, and trimmed to create a usable product...

 and injection molding
Injection molding
Injection molding is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the cavity...

.

Polystyrene Petri dish
Petri dish
A Petri dish is a shallow glass or plastic cylindrical lidded dish that biologists use to culture cells or small moss plants. It was named after German bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch...

es and other laboratory
Laboratory
A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...

 containers such as test tubes and microplates play an important role in biomedical research and science. For these uses, articles are almost always made by injection molding, and often sterilized post-molding, either by irradiation or by treatment with ethylene oxide
Ethylene oxide
Ethylene oxide, also called oxirane, is the organic compound with the formula . It is a cyclic ether. This means that it is composed of two alkyl groups attached to an oxygen atom in a cyclic shape . This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered...

. Post-mold surface modification, usually with oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

-rich plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

s, is often done to introduce polar groups. Much of modern biomedical research relies on the use of such products; they therefore play a critical role in pharmaceutical research.

Foams

Polystyrene foams are good thermal insulators and are therefore often used as building insulation materials, such as in structural insulated panel building systems. They are also used for non-weight-bearing architectural structures (such as ornamental pillars
Column
A column or pillar in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces...

).
PS foams exhibit also good damping properties, therefore it is used widely in packaging.

Expanded polystyrene

Expanded polystyrene (EPS) is a rigid and tough, closed-cell foam. It is usually white and made of pre-expanded polystyrene beads. Familiar uses include molded sheets for building insulation and packing material ("peanuts"
Foam peanut
Foam peanuts, also known as packing peanuts or packing noodles, are a common loose-fill packaging and cushioning material used to prevent damage to fragile objects during shipping. They are shaped to interlock when compressed and free flow when not compressed...

) for cushioning fragile items inside boxes. Sheets are commonly packaged as rigid panels (size 4 by 8 or 2 by 8 feet in the United States), which are also known as "bead-board". Thermal resistivity is usually about 28 m·K/W
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

 (or R-4 per inch). Some EPS boards have a flame spread
Flame spread
Flame spread or surface burning characteristics rating is a ranking derived by laboratory standard test methodology of a material's propensity to burn rapidly and spread flames...

 of less than 25 and a smoke-developed index
Smoke-developed index
Smoke-developed index is a measure of the concentration of smoke a material emits as it burns. Like Flame Spread Index, it is based on an arbitrary scale in which asbestos-cement board has a value of 0, and red oak wood has 100....

 of less than 450, which means they can be used without a fire barrier (but require a 15-minute thermal barrier) according to US building codes. A growing use of EPS in construction is insulating concrete forms.
The density range is about 16–640 kg/m3. The most common processing method is thermal cutting with hot wires.

Extruded polystyrene foam

Extruded polystyrene foam (XPS) consists of closed cells, offers improved surface roughness and higher stiffness and reduced thermal conductivity. The density range is about 28 – 45 kg/m3.

Extruded polystyrene material is also used in craft
Craft
A craft is a branch of a profession that requires some particular kind of skilled work. In historical sense, particularly as pertinent to the Medieval history and earlier, the term is usually applied towards people occupied in small-scale production of goods.-Development from the past until...

s and model
Model (physical)
A physical model is a smaller or larger physical copy of an object...

 building, in particular architectural
Architecture
Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art...

 models. Because of the extrusion manufacturing process, XPS does not require facers to maintain its thermal or physical property performance. Thus, it makes a more uniform substitute for corrugated cardboard. Thermal resistivity is usually about 35 m·K/W (or R-5 per inch in American customary units).

Styrofoam is a trademarked name for XPS; however, it is often also used in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 as a generic name for all polystyrene foams.

Copolymers

Pure polystyrene is brittle
Toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing; Material toughness is defined as the amount of energy per volume that a material can absorb before rupturing...

, but hard enough that a fairly high-performance product can be made by giving it some of the properties of a stretchier material, such as polybutadiene
Polybutadiene
Polybutadiene is a synthetic rubber that is a polymer formed from the polymerization process of the monomer 1,3-butadiene.It has a high resistance to wear and is used especially in the manufacture of tires, which consumes about 70% of the production...

 rubber. The two such materials can never normally be mixed because of the amplified effect of intermolecular forces on polymer insolubility (see plastic recycling
Plastic recycling
Plastic recycling is the process of recovering scrap or waste plastics and reprocessing the material into useful products, sometimes completely different in form from their original state. For instance, this could mean melting down soft drink bottles and then casting them as plastic chairs and tables...

), but if polybutadiene is added during polymerization it can become chemically bonded to the polystyrene, forming a graft copolymer, which helps to incorporate normal polybutadiene into the final mix, resulting in high-impact polystyrene or HIPS, often called "high-impact plastic" in advertisements. One commercial name for HIPS is Bextrene. Common applications of HIPS include toys and product casings. HIPS is usually injection molded in production. Autoclaving polystyrene can compress and harden the material.

Several other copolymers are also used with styrene. Acrylonitrile butadiene styrene
Acrylonitrile butadiene styrene
Acrylonitrile butadiene styrene is a common thermoplastic. Its melting point is approximately 105 °C ....

 or ABS plastic is similar to HIPS: a copolymer of acrylonitrile and styrene, toughened with polybutadiene. Most electronics cases are made of this form of polystyrene, as are many sewer pipes. SAN
Styrene-acrylonitrile resin
Styrene acrylonitrile resin is a copolymer plastic consisting of styrene and acrylonitrile. It is also known as SAN. It is widely used in place of polystyrene owing to its greater thermal resistance...

 is a copolymer of styrene with acrylonitrile
Acrylonitrile
Acrylonitrile is the chemical compound with the formula C3H3N. This pungent-smelling colorless liquid often appears yellow due to impurities. It is an important monomer for the manufacture of useful plastics. In terms of its molecular structure, it consists of a vinyl group linked to a nitrile...

, and SMA
Styrene maleic anhydride
Styrene maleic anhydride, also known as SMA or SMAnh, is a synthetic polymer that is built-up of styrene and maleic anhydride monomers. The monomers are almost perfectly alternating, making it an alternating copolymer. It is formed by a radical polymerization, using an organic peroxide as the...

 one with maleic anhydride
Maleic anhydride
Maleic anhydride is an organic compound with the formula C2H22O. It is the acid anhydride of maleic acid and in its pure state it is a colourless or white solid with an acrid odour....

. Styrene can be copolymerized with other monomers; for example, divinylbenzene
Divinylbenzene
Divinylbenzene consists of a benzene ring bonded to two vinyl groups. It is related to styrene by the addition of a second vinyl group. Divinylbenzene, as it is usually encountered, is a 2:1 mixture of m- and p-divinylbenzene, containing also the corresponding ethylvinylbenzene isomers. It is...

 can be used for cross-linking the polystyrene chains to give the polymer used in Solid phase peptide synthesis.

Oriented polystyrene

Oriented polystyrene (OPS) is produced by stretching extruded PS film, improving visibility through the material by reducing haziness and increasing stiffness. This is often used in packaging where the manufacturer would like the consumer to see the enclosed product. Some benefits to OPS are that it is less expensive to produce than other clear plastics such as PP, PET, and HIPS, and it is less hazy than HIPS or PP. The main disadvantage to OPS is that it's brittle. It will crack or tear easily.

Disposal and environmental issues

Polystyrene is easily recycled. Due its light weight (especially if foamed), it is not economical to collect in its original form. However, if the waste material goes through an initial compaction process, the material changes density from typically 30 kg/m3 to 330 kg/m3 and becomes a recyclable commodity of high value for producers of recycled plastic pellets. In general, it is not accepted in curbside collection recycling programs. 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. In the US and many other countries, the interest in recycling polystyrene has led to the establishment of collection points. The producers of large quantities of polystyrene waste (50 tons per year or more) that have invested in the EPS compactors are able to sell the compacted blocks to plastic recyclers.

Environmental impact

Discarded polystyrene does not biodegrade for hundreds of years and is resistant to photolysis. Because of this stability, very little of the waste discarded in today's modern, highly engineered landfills biodegrades. Because degradation of materials creates potentially harmful liquid and gaseous by-products that could contaminate groundwater and air, today's landfills are designed to minimize contact with air and water required for degradation, thereby practically eliminating the degradation of waste.

Polystyrene foam is a major component of plastic debris in the ocean, where it becomes toxic to marine life. Foamed polystyrene blows in the wind and floats on water, and is abundant in the outdoor environment. Polystyrene foams are produced using blowing agents that form bubbles and expand the foam. In expanded polystyrene, these are usually hydrocarbons such as pentane
Pentane
Pentane is an organic compound with the formula C5H12 — that is, an alkane with five carbon atoms. The term may refer to any of three structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, pentane means exclusively the n-pentane isomer; the other two being called...

, which may pose a flammability hazard in manufacturing or storage of newly manufactured material, but have relatively mild environmental impact. However, extruded polystyrene is usually made with hydrochlorofluorocarbons (HCFC-22), which have a 1000-times greater 'greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...

' on global warming compared to carbon dioxide.

Recycling

Most polystyrene products are currently not recycled due to the lack of incentive to invest in the compactors and logistical systems required. Expanded polystyrene scrap can be easily added to products such as EPS insulation sheets and other EPS materials for construction applications. And many manufacturers cannot obtain sufficient scrap because of the aforementioned collection issues. When it is not used to make more EPS, foam scrap can be turned into 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. Rastra
Rastra
Rastra is an insulating concrete form used to make walls for buildings. It is composed of concrete and thastyron. Thastyron is a mixture of plastic foam and binder that is composed of eighty-five percent recycled post consumer polystyrene waste that are molded into blocks...

 is 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. However, polystyrene recycling is not a closed loop, producing more polystyrene; polystyrene cups and other packaging materials are instead usually used as fillers in other plastics, or in other items that cannot themselves be recycled and are thrown away.

Incineration

If polystyrene is properly incinerated at high temperatures, the chemicals generated are water, carbon dioxide, a complex mixture of volatile compounds, and carbon soot. According to the American Chemistry Council
American Chemistry Council
The American Chemistry Council , formerly known as the Manufacturing Chemists' Association and then as the Chemical Manufacturers' Association , is an industry trade association for American chemical companies, based in Washington, D.C.-Activities:The mission of the American Chemistry Council is...

, 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 vapor, and heat. Because of the amount of heat released, it is sometimes used as a power source for steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

 or electricity generation
Electricity generation
Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

.

When polystyrene was burned at temperatures of 800–900 °C (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."

When burned without enough oxygen or at lower temperatures (as in a campfire or a household fireplace), polystyrene can produce polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...

s, carbon black
Carbon black
Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...

, and carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

, as well as styrene monomers.

Burial

Foam cups and other polystyrene products can be safely buried in landfill
Landfill
A landfill site , is a site for the disposal of waste materials by burial and is the oldest form of waste treatment...

s, since it is as stable as concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 or brick
Brick
A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...

. No plastic film is required to protect the air and underground water.

Reducing

Some effort is being made to find alternatives to polystyrene foam, especially in restaurant settings. Restricting the use of foamed polystyrene takeout food packaging is a priority of many solid waste environmental organization
Environmental organization
An environmental organization is an organization that seeks to protect, analyze or monitor the environment against misuse or degradation or lobby for these goals....

s. However, the Plastics Foodservice Packaging Group counters that, in US, less than 1% by weight of solid waste disposed is polystyrene. A campaign to achieve the first ban of polystyrene foam from the food & beverage industry in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 was launched in Toronto
Toronto
Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...

 as of January 2007, by local non-profit organization NaturoPack
NaturoPack
NaturoPack is a Toronto-based not-for-profit organization that raises awareness, educates and advocates for the use and promotion of environmentally responsible packaging....

. Portland, Ore. and San Francisco are among about one hundred cities in the United States that currently have some sort of ban on polystyrene foam in restaurants. For instance, in 2007 restaurants in Oakland, California were required to switch to disposable food containers that will biodegrade if added to food compost.

Although polystyrene can be recycled at recycling facilities, most polystyrene is not recycled. The EPA (United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

) estimates that 25 billion polystyrene cups are tossed every year. Since polystyrene degrades very slowly - more than 500 years for a single cup – the EPA considers this a serious environmental problem. Several green leaders, from the Dutch Ministry of the Environment to Starbucks' Green Team, advise that individuals reduce their environmental impact by using reusable coffee cups.

Finishing

In the United States, environmental protection regulations prohibit the use of solvents on polystyrene (which would dissolve the polystyrene and de-foam most foams anyway).

Some acceptable finishing materials are
  • Water-based paint
    Paint
    Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...

     (artist
    Artist
    An artist is a person engaged in one or more of any of a broad spectrum of activities related to creating art, practicing the arts and/or demonstrating an art. The common usage in both everyday speech and academic discourse is a practitioner in the visual arts only...

    s have created painting
    Painting
    Painting is the practice of applying paint, pigment, color or other medium to a surface . The application of the medium is commonly applied to the base with a brush but other objects can be used. In art, the term painting describes both the act and the result of the action. However, painting is...

    s on polystyrene with gouache
    Gouache
    Gouache[p], also spelled guache, the name of which derives from the Italian guazzo, water paint, splash or bodycolor is a type of paint consisting of pigment suspended in water. A binding agent, usually gum arabic, is also present, just as in watercolor...

    )
  • Mortar
    Mortar (masonry)
    Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...

     or acrylic/cement render, often used in the building industry as a weather-hard overcoat that hides the foam completely after finishing the objects.
  • Cotton wool or other fabrics used in conjunction with a stapling implement.

Health

According to a plastic food service products website:
From 1999 to 2002, a comprehensive review of the potential health risks associated with exposure to styrene was conducted by a 12 member international expert panel selected by the Harvard Center for Risk Assessment. The scientists had expertise in toxicology, epidemiology, medicine, risk analysis, pharmacokinetics, and exposure assessment.
Styrene oligomers in polystyrene containers used for food packaging have been found to migrate into the food. Another Japanese study conducted on wild-type and AhR-null mice found that the styrene trimer, which the authors detected in cooked polystyrene container-packed instant foods, may increase thyroid hormone levels.

Fire hazards

Like other organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s, polystyrene is flammable. Polystyrene is classified according to DIN4102 as a "B3" product, meaning highly flammable or "easily ignited." As a consequence, although it is an efficient insulator at low temperatures, its use is prohibited in any exposed installations in building construction if the material is not flame-retardant
Flame retardant
Flame retardants are chemicals used in thermoplastics, thermosets, textiles and coatings that inhibit or resist the spread of fire. These can be separated into several different classes of chemicals:...

. It must be concealed behind drywall
Drywall
Drywall, also known as plasterboard, wallboard or gypsum board is a panel made of gypsum plaster pressed between two thick sheets of paper...

, sheet metal, or concrete. Foamed polystyrene plastic materials have been accidentally ignited and caused huge fires and losses, for example at the Düsseldorf International Airport
Düsseldorf International Airport
Düsseldorf International Airport is the largest airport in North Rhine-Westphalia, Germany, and the third largest airport in Germany, handling 18.99 million passengers in 2010....

, the Channel tunnel
Channel Tunnel
The Channel Tunnel is a undersea rail tunnel linking Folkestone, Kent in the United Kingdom with Coquelles, Pas-de-Calais near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is deep...

 (where polystyrene was inside a railcar that caught fire), and the Browns Ferry Nuclear Power Plant (where fire breached a fire retardant and reached the foamed plastic underneath, inside a firestop
Firestop
A firestop is a passive fire protection system of various components used to seal openings and joints in fire-resistance rated wall and/or floor assemblies, based on fire testing and certification listings....

that had not been tested and certified in accordance with the final installation).

External links

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