Polystyrene

Solid foam

  Polystyrene's most common use is as expanded polystyrene (EPS). Expanded polystyrene is produced from a mixture of about 90-95% polystyrene and 5-10% gaseous 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 Fome-Cor. A more unexpected use for the material is as a lightweight fill for embankments in the civil engineering industry ^[4].

Expanded polystyrene used to contain CFCs, but other, more environmentally-safe blowing agents are now used. Because it is an 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 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.

Standard markings

The Society of the Plastics Industry so that items can be labeled for easy recycling, is . However, the majority of polystyrene products are currently not recycled because of 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 cannot themselves be recycled and are thrown away.

Copolymers

  Pure polystyrene is brittle, but injection molded in production. Autoclaving polystyrene can compress and harden the material.

acrylonitrile.

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 taut length of wire, usually nichrome because of 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 parks, movie sets, airplane construction, and much more. 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.

Polystyrene can also be cut with a traditional cutter. In order to do this without ruining the sides of the blade one must first dip the blade in water and cut with the blade at an angle of about 30º. The procedure has to be repeated multiple times for best results.

Polystyrene can also be cut on 3 and 5-axis routers, enabling large-scale prototyping and model-making. Special polystyrene cutters are available that look more like large cylindrical rasps.

Use in biology

Petri dishes and other containers such as test tubes, made of polystyrene, play an important role in biomedical research and science. For these uses, articles are almost always made by ethylene oxide. Post mold surface modification, usually with oxygen rich plasmas, 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. Major manufacturers include Corning Incorporated/Costar, Nalgene/Nunc, Greiner and BD/Falcon. The web sites of these companies contain a wealth of information.

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 (artists have created paintings 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.

Dangers and Fire hazard

The health effects caused by consuming polystyrene when it migrates from food containers (primarily from a leaching caused by heat exchange)^{[citation needed]} into food is under serious investigation.^{[citation needed]} Benzene, a material used in the production of polystyrene, is a known human carcinogen. Moreover, butadiene and styrene (in ABS), when combined, become benzene-like in both form and function.^{[citation needed]}

The EPA claims

"Acute (short-term) exposure to styrene in humans results in mucous membrane and eye irritation, and gastrointestinal effects. Chronic (long-term) exposure to styrene in humans results in effects on the central nervous system (CNS), such as headache, fatigue, weakness, and depression, CSN dysfunction, hearing loss, and peripheral neuropathy. Human studies are inconclusive on the reproductive and developmental effects of styrene; several studies did not report an increase in developmental effects in women who worked in the plastics industry, while an increased frequency of spontaneous abortions and decreased frequency of births were reported in another study. Several epidemiologic studies suggest there may be an association between styrene exposure and an increased risk of leukemia and lymphoma. However, the evidence is inconclusive due to confounding factors. EPA has not given a formal carcinogen classification to styrene."

^[5]

Polystyrene is classified according to DIN4102 as a "B3" product, meaning highly flammable or "easily ignited". Consequently, though it is an efficient insulator at low temperatures, it is prohibited from being used in any exposed installations in building construction as long the material is not flame retarded e.g. with concrete. Foamed plastic materials have been accidentally ignited and caused huge fires and losses. Examples include the Düsseldorf International Airport, the Channel tunnel, where it was inside a railcar and caught on fire, and the Browns Ferry Nuclear Power Plant, where fire reached through a fire retardant, reached the foamed plastic underneath, inside a firestop that had not been tested and certified in accordance with the final installation.

In addition to fire hazard, substances that contain cyanoacrylate glues can dissolve polystyrene.

Environmental concerns and bans

Expanded polystyrene is not easily recyclable because of its light weight and low scrap value. It is generally not accepted in curbside programs. Expanded polystyrene foam takes a very long time to decompose in the environment and has been documented to cause starvation in birds and other marine wildlife. According to the California Coastal Commission, it is a principal component of marine debris. A CIWMB (California Integrated Waste Management Board) Report finds that “in the categories of energy consumption, greenhouse gas effect, and total environmental effect, EPS’s environmental impacts were second highest, behind aluminum.”^[6] Restricting the use of foamed polystyrene takeout food packaging is a priority of many solid waste environmentalist organizations, like Californians Against Waste.^[7]

The city of Berkeley, California was one of the first cities in the world to ban polystyrene food packaging (called Styrofoam in the media announcements).^[8][9] It was also banned in Portland, OR, and Suffolk County, NY in 1990.^[10] Now, over 20 US cities have banned polystyrene food packaging, including Oakland, CA on Jan 1st 2007.^[11] San Francisco introduced a ban on the packaging on June 1st 2007:^[12]

"This is a long time coming," Peskin said Monday. "Polystyrene foam products rely on nonrenewable sources for production, are nearly indestructible and leave a legacy of pollution on our urban and natural environments. If McDonald's could see the light and phase out polystyrene foam more than a decade ago, it's about time San Francisco got with the program." Board of Supervisors President, Aaron Peskin^[13]

The overall benefits of the ban in Portland have been questioned ^[14], as have the general environmental concepts of the use of paper versus polystyrene.^[15]

A campaign to achieve the first ban of polystyrene foam from the food & beverage industry in Canada has been launched in Toronto as of January 2007, by local non-profit organization NaturoPack.^[16]

Other cities that have banned expanded polystyrene include Portland, Oakland, and Santa Monica. Both the California and New York legislatures are currently considering bills which would effectively ban expanded polystyrene in all takeout food packaging state-wide.^[17].

Explosives

Polystyrene is used in some polymer-bonded explosives:

Some Polystyrene PBX Examples

Name	Explosive Ingredients	Binder Ingredients	Usage
PBX-9205	RDX 92%	Polystyrene 6%; DOP 2%
PBX-9007	RDX 90%	Polystyrene 9.1%; DOP 0.5%; resin 0.4%

It is also a component of Napalm and a component of most designs of hydrogen bombs.

Cleaning

Polystyrene can be dishwashed at 70 °C without deformation.

See also

• Structural insulated panel
• ThermaSAVE
• Greatpac Sdn. Bhd.

References

1. ^ International Labour Organisation chemical safety card for polystyrene
2. ^ A.K. vam der Vegt & L.E. Govaert, Polymeren, van keten tot kunstof, ISBN 90-407-2388-5
3. ^ The history of plastics
4. ^ http://www.vencel.co.uk/products/civil/design.htm
5. ^ http://www.epa.gov/ttn/atw/hlthef/styrene.html
6. ^ CIWMB Report
7. ^ "Business Gives Styrofoam a Rare Redemption.", Stockton Record, 21 September 2007. Retrieved on 2007-10-09. 
8. ^ The Berkeley Daily Planet
9. ^ Styrofoam food packaging banned in Oakland
10. ^ Californians Against Waste website
11. ^ San Francisco Chronical article, June 28, 2006
12. ^ San Francisco Chronical article, November 7, 2006
13. ^ San Francisco Chronical Article, June 27, 2006
14. ^ Eckhardt, Angela (November, 1998). Paper Waste: Why Portland's Ban on Polystyrene Foam Products Has Been a Costly Failure. Cascade Policy Institute. Retrieved on 2007-10-23.
15. ^ Thomas, Robert A. (March 8 2005). Where Might We Look for Environmental Heroes?. Center for Environmental Communications, Loyola University, New Orleans. Retrieved on 2007-10-23.
16. ^ Naturopack Campaign Page
17. ^ AB 904

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