Polystyrene is a strong plastic created from erethylene and benzine that can be injected, extruded or blow molded, making it a very useful and versatile manufacturing material. Most of us recognize styrofoam a form of foam polystyrene packaging. Polystyrene is also used as a building material, with electrical appliances (light switches and plates), and in other household items.
Polystyrene has a long history of evolution behind it. In 1839, a German apothecary called Eduard Simon discovered polystyrene. Eduard Simon isolated a substance from natural resin, however, he did not know what he had discovered. It took another German, organic chemist, Hermann Staudinger, to realize that Simon's discovery, comprised of long chains of styrene molecules, was a plastic polymer.
In 1922, Staudinger published his theories on polymers, stating that natural rubbers were made up of long repetitive chains of monomers that gave rubber its elasticity. He went on to write that the materials manufactured by the thermal processing of styrene were similar to rubber. They were the high polymers including polystyrene. In 1953, Hermann Staudinger won the Nobel Prize for Chemistry for his research.
In 1930, the scientists at BASF developed a way to commercially manufacture polystyrene. Badische Anilin & Soda-Fabrik (BASF) was founded in 1861. BASF has invented synthetic coal tar dyes, ammonia, and nitrogenous fertilizers and developed polystyrene, PVC, magnetic tape, and synthetic rubber. (note: A company called I. G. Farben is often listed as the developer of polystyrene because BASF was under trust to I. G. Farben in 1930.) In 1937, Dow Chemical introduced polystyrene to the U.S. market.
Uses for Polystyrene
Polystyrene is a very strong material and will not fall apart or be dented easily by rough treatment. This ability to absorb shocks helps with the protection of the contents and prevents extra cost, replacing broken or damaged items.
The main benefit of polystyrene however is that it is extremely versatile as the properties it has allow it to be moulded into virtually any shape to match individual project specifications.
Some of the applications that Polystyrene can be used for are given below:
- Protection of Goods:By using polystyrene, goods will arrive at their destination in perfect condition. This is especially true for items such as televisions, video recorders, bottles and other products that can be easily broken.
- Mail Order:Useful for sending items through the post as few, if any, breakage’s will occur and because polystyrene is light in weight, the cost of postage will also be reduced.
- Climate Control: Keeps fresh produce cool during transportation so that it arrives at its destination in perfect condition.
- Strength: The strength of expanded polystyrene makes it suitable for supporting a great deal of weight.
- Energy Saving:Can be used for cavity wall, floor and loft insulation.
- Energy Source:When recycled, polystyrene gives out a high portion of heat that can be recovered through special heat recovery incinerators.
- Plant protection:This ensures that the perfect circumstances for nourishment of plants will be maintained and facilitate growth.
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.
Solid Foam:Polystyrene's most common use, however, is as expanded polystyrene, which is a mixture of about 5% polystyrene and 95% gaseous blowing agent. This 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 crafts and model building, particularly architectural models. Foamed between two sheets of paper, it makes a more-uniform substitute for corrugated cardboard, tradenamed Foamcore.
Expanded polystyrene used to contain CFCs, 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 benzene ring.
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, Tm. But metallocene-catalyzed polymerization can produce an ordered syndiotactic polystyrene with the phenyl groups on alternating sides. This form is highly crystalline with a Tm of 270°C.
Standard Markings: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 recycling facilities that recycle polystyrene. 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 item that can not be themselves recycled and are thrown away.
Toughening
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 high-impact polystyrene 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 acrylonitrile and styrene, toughened with polybutadiene. 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.
Cutting and Shaping: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.
Hot wire foam cutters are available for anywhere from under a hundred dollars to tens of thousands of dollars for large CNC machines.
Finishing: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
- Mortar, often used in the building industry as a weather-hard overcoat that makes the foam disappear completely after finishing the objects.
- Cotton wool or other fabrics used in conjunction with a stapling implement.