is a
Polymer made from the
Monomer Styrene , a
Liquid Hydrocarbon that is commercially
Manufacture d from
Petroleum . At room temperature, polystyrene is normally a solid
Thermoplastic , but can be melted at higher temperature for
Molding or extrusion, then resolidified. Styrene is an
Aromatic monomer, and polystyrene is an aromatic polymer.
Polystyrene was accidentally discovered in 1839 by
Eduard Simon , an apothecary in
Berlin, Germany . From
Storax , the resin of ''
Liquidambar Orientalis '', he distilled an oily substance, a monomer which he named styrol. Several days later Simon found that the styrol had thickened, presumably due to oxidation, into a jelly he dubbed styrol oxide ("Stryroloxyd"). By 1845 English chemist
John Blyth and German chemist
August Wilhelm Von Hofmann 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 process. About 80 years went by before it was realized that heating of styrol starts a chain reaction which produces
Macromolecule s, following the thesis of German organic chemist
Hermann Staudinger (1881 - 1965). This eventually led to the substance receiving its present name, polystyrene. The
I.G. Farben company 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.
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. It is economical and is used for producing
Plastic Model assembly kits, plastic cutlery,
CD "jewel" Cases , and many other objects where a fairly rigid, economical plastic of any of various colors is desired.
For architectural and engineering modelling, polystyrene is extruded into forms of standard modelling scale with the cross-sections of a miniature
I-beam as well as rods and tubes. It is also formed into sheets with various patterns for this purpose as well. The blank sheets of polystyrene are referred to as "plasticard" in Britain, after the vulgarization of a trademark, but are called "sheet styrene" in the US.
Polystyrene fabricated into a sheet can be stamped (formed) into economic, disposable cups, glasses, bowls, lids, and other items, especially when high strength, durability, and heat resistance are not essential. A thin layer of transparent polystyrene is often used as an
Infra-red Spectroscopy standard.
Polystyrene's most common use, however, is as expanded polystyrene (EPS). Expanded polystyrene is produced from a mixture of about 95% polystyrene and 5% gaseous blowing agent. The solid plastic is expanded into a foam through the use of heat, usually steam. Extruded polystyrene (XPS), which is different than expanded polystyrene, is commonly known by the trade name
Styrofoam® . Expandable polystyrene is the lightweight material of which coffee cups and takeaway food containers are made. The voids filled with trapped air give expanded polystyrene low
Thermal Conductivity . This makes it ideal as a construction material and it is used in
Structural Insulated Panel building systems. It is also used as
Insulation in building structures, as molded packing material for cushioning fragile equipment inside boxes, as packing "peanuts", as non-weight-bearing architectural structures (such as
Pillars ), and also in
Craft s and
Model building, particularly
Architectural models. Foamed between two sheets of paper, it makes a more-uniform substitute for
Corrugated Cardboard , tradenamed ''Fome-Cor''.
Expanded polystyrene used to contain
CFC s, but other, more environmentally-safe blowing agents are now used. Because it is an
Aromatic Hydrocarbon , it burns with an orange-yellow flame, giving off
Soot , as opposed to non-aromatic hydrocarbon polymers such as
Polyethylene , which burn with a light yellow flame (often with a blue tinge) and no soot.
Production methods include sheet stamping (PS) and
Injection Molding (both PS and HIPS).
The chemical makeup of polystyrene is a long chain hydrocarbon with every other carbon connected to a
Phenyl Group (an aromatic ring similar to
Benzene .
A 3-D model would show that each of the
Chiral backbone carbons lies at the center of a
Tetrahedron , with its 4
Bonds pointing toward the vertices. Say the -C-C- bonds are rotated so that the backbone chain lies entirely in the plane of the diagram. From this flat schematic, it isn't 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 where all of them are on the same side is called ''isotactic'' polystyrene, which isn't produced commercially. Ordinary ''atactic'' polystyrene has these large phenyl groups
Randomly distributed on both sides of the chain. This random positioning prevents the chains from ever aligning with sufficient regularity to achieve any
Crystallinity , so the plastic has no
Melting Temperature , ''T''
m. But
Metallocene -
Catalyzed Polymerization can produce an ordered ''syndiotactic'' polystyrene with the phenyl groups on alternating sides. This form is highly crystalline with a ''T''
m of 270°C.
The
Resin Identification Code symbol for polystyrene, developed by the
Society Of The Plastics Industry so that items can be labeled for easy recycling, is . Unfortunately, the majority of polystyrene products are currently not recycled due to a lack of suitable recycling facilities. Furthermore, when it is "recycled," it is not a closed loop — polystyrene cups and other packaging materials are usually recycled into fillers in other plastics, or other items that can not themselves be recycled and are thrown away.
The
Unicode character is ♸, which will appear here if you have a suitable font installed:
♸.
Pure polystyrene is
Brittle , 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 rubber. The two materials cannot normally be mixed due to the amplified effect of
Intermolecular Forces on polymer
Solubility (see
Plastic Recycling ), 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 or '''HIPS''', often called "high-impact plastic" in advertisements. Common applications include use in toys and product casings. HIPS is usually
Injection Molded in production.
Acrylonitrile Butadiene Styrene or
ABS plastic is similar to HIPS: a copolymer of crylonitrile and '''s'''tyrene, toughened with poly'''b'''utadiene. Most electronics cases are made of this form of polystyrene, as are many sewer pipes.
Styrene can be copolymerized with other monomers; for example, divinylbenzene for cross-linking the polystyrene chains.
Expanded polystyrene is very easily cut with a
Hot-wire Foam Cutter , which is easily made by a heated and taut length wire, usually
Nichrome due to nichrome's resistance to oxidation at high temperatures and its suitable
Electrical Conductivity . The hot wire foam cutter works by heating the wire to the point where it can vaporize foam immediately adjacent to it. The foam gets vaporized before actually touching the heated wire, which yields exceptionally smooth cuts. Polystyrene, shaped and cut with hot wire foam cutters, is used in architecture models, actual signage, amusement park and movie sets, airplane construction, and much more.
Polystyrene foam can easily be cut using a hot
Wire that melts the foam. Such cutters may cost just a few dollars (for a completely manual cutter) to tens of thousands of dollars for large
CNC machines that can be used in high-volume industrial production.
In the United States, environmental protection regulations prohibit the use of solvents on polystyrene (which would dissolve the polystyrene and de-foam most of foams anyway).
Some acceptable finishing materials are
- Water-based Paint ( Artist s have created Painting s on polystyrene with Gouache )
- Mortar 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.
