Teflon

From Free net encyclopedia

Image:Teflon structure.PNG Teflon is the brand name of the polymer polytetrafluoroethylene (PTFE) discovered by Roy J. Plunkett (1910–1994) of DuPont in 1938 and introduced as a commercial product in 1946. It is a fluoropolymer but not a thermoplastic in the true sense.

PTFE has the lowest coefficient of friction of any known solid material. It is used as a non-stick coating for pans and other cookware. PTFE is very non-reactive, and so is often used in containers and pipework for reactive chemicals. Its melting point is 327 °C, but its properties degrade over 260 °C.

Other polymers with similar composition are known with the Teflon name: fluorinated ethylene-propylene (FEP) and perfluoroalkoxy polymer resin (PFA). They retain the useful properties of PTFE of low friction and non-reactivity, but are more easily formable. FEP is softer than PTFE and melts at 260 °C; it's highly transparent and resistant to sunlight.

PTFE is sometimes said to be a spin-off from the U.S. space program with more down-to-earth applications; this is an urban legend, as teflon cooking pans were commonplace before Yuri Gagarin's flight in 1961. PTFE was discovered serendipitously by Roy Plunkett of DuPont in 1938, while attempting to make a new CFC refrigerant, when the perfluorethylene polymerized in its storage container. DuPont patented it in 1941, and registered the Teflon trademark in 1944.

An early advanced use was in the Manhattan Project, as a material to coat valves and seals in the pipes holding highly-reactive uranium hexafluoride in the vast uranium enrichment plant at Oak Ridge, Tennessee, when it was known as K416.

Image:PFA structure.PNG It was first sold commercially in 1946 and by 1950, DuPont was producing over a million pounds (450 t) per year in Virginia.

Teflon has been supplemented with another DuPont product, Silverstone, a three-coat fluoropolymer system that produces a more durable finish than Teflon. Silverstone was released in 1976.

Amongst many other industrial applications, PTFE is used to coat certain types of hardened, armour-piercing bullets, so as to reduce the amount of wear on the firearm's rifling. These are often mistakenly referred to as "cop-killer" bullets on account of PTFE's supposed ability to ease a bullet's passage through body armour. Any armour-piercing effect is, however, purely a function of the bullet's velocity and rigidity rather than a property of PTFE.

PTFE has excellent dielectric properties. This is especially true at high radio frequencies, making it eminently suitable for use as an insulator in cables and connector assemblies and as a material for printed circuit boards used at microwave frequencies. Combined with its high melting temperature, this makes it the material of choice as a high performance substitute for the weaker and more meltable polyethylene that is commonly used in low-cost applications. Its extremely high bulk resistivity makes it an ideal material for fabricating long life electrets, useful devices that are the electrostatic analogues of magnets.

Due to its low friction, it is used for applications where sliding action of parts is needed: bearings, bushings, gears, slide plates, etc. In these applications it performs significantly better than nylon and acetal; it is comparable with UHMWPE, although UHMWPE is more resistant to wear than Teflon. For these applications, versions of teflon with mineral oil or molybdenum disulfide embedded as additional lubricants in its matrix are being manufactured.

Gore-Tex is a material incorporating teflon membrane with micropores.

Safety

Image:100 0783.JPG While Teflon itself is chemically inert and non-toxic, Teflon begins to deteriorate after the temperature of cookware reaches about 500 °F (260 °C), and begins to significantly decompose above 660 °F (350 °C). These degradation products can be lethal to birds, and can cause flu-like symptoms in humans. By comparison, cooking fats, oils and butter will begin to scorch and smoke at about 392 °F (200 °C), and meat is usually fried between 400–450 °F (200–230 °C), but empty cookware can exceed this temperature if left unattended on a hot burner. Inhalation of this byproduct can lead to hallucinations and in rare cases a 'high'. [1] Over the 40 years non-stick cookware has been in widespread use, there is only one published case of a minor, short-lasting health effect linked to overheating non-stick cookware.[2]

The EPA's scientific advisory board found in 2005 that perfluorooctanoic acid (PFOA), a chemical compound used to make Teflon, is a "likely carcinogen." This finding was part of a draft report [3] that has yet to be made final. DuPont settled for $300 million in 2004 a lawsuit filed by residents near its manufacturing plant in Ohio and West Virginia based on groundwater pollution from this chemical. Currently this chemical is not regulated by the EPA.

In January 2006, DuPont, the only company that manufactures PFOA in the US, has agreed to eliminate releases of the chemical from its manufacturing plants by 2015, but did not commit to completely phasing out its use of the chemical. This agreement is said to apply to not only Teflon used in cookware but in other products such as food packaging, clothing and carpeting. DuPont also stated that it cannot produce Teflon without the use of the chemical PFOA, although it is looking for a substitute.

It is noteworthy that PFOA is not part of the finished product of nonstick cookware or bakeware. It is only used during the manufacture of the product and only a trace amount of PFOA remains after the curing process. There should be no measurable amount of PFOA on a finished pan, provided that it has been properly cured.

External links

• Harmful Teflon Chemical To Be Eliminated by 2015 Washington Post Staff Writer Thursday, January 26, 2006; Page A01[4]
• The Chemical Heritage Foundation (2000). Roy J. Plunkett. Retrieved Oct 7, 2005.
• Adams, Cecil (1995). If Teflon is nonsticky, how do they get it to stick to the pan?. Retrieved Oct 7, 2005.
• DuPont (2005). Teflon News and Information. Retrieved Oct 7, 2005.
• DuPont (2005). Cooking Safety. Retrieved Oct 12, 2005.
• DuPont (2005). Information on PFOA. Retrieved Oct 12, 2005.
• Kopel, Dave (2004). Teflon Bullets. Retrieved Oct 7, 2005.
• Taconic (2005). Information on PTFE Laminates. Retrieved Nov 23, 2005.
• Environmental Issues:
  • Los Angeles Times (2005). DuPont Settles Charges That It Hid Toxic Risk Data. Retrieved Dec 15, 2005.
  • Washington Post (2005). Compound in Teflon A 'Likely Carcinogen'. Retrieved Oct 7, 2005
  • New York Times (2004). Dupont, Now in the Frying Pan. Retrieved Oct 7, 2005.
  • Environmental Working Group (2005). Canaries in the Kitchen - "Teflon Toxicosis" is deadly to pet birds. Are we at risk?. Retrieved Oct 7, 2005. More articles from EWG.
  • Nature Publishing Group (2001). Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the environment. Retrieved Oct 7, 2005.
  • ABC News (2006). Government Moves to Curb Use of Chemical in Teflon
  • PFOA Facts (2006). PFOA Facts

Harmful Teflon Chemical To Be Eliminated by 2015 Washington Post Staff Writer Thursday, January 26, 2006; Page A01[5]

References

• Ellis, D.A.; Mabury, S.A.; Martin, J.W.; Muir, D.C.G. "Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the environment." Nature 2001, 412 (6844), pp. 321-324.

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