Polytetrafluoroethylene

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Polytetrafluoroethylene
IUPAC name

poly(1,1,2,2-tetrafluoroethylene)[1]
Other names

Syncolon, Fluon, Poly(tetrafluoroethene), Poly(difluoromethylene), Poly(tetrafluoroethylene)
Identifiers
Abbreviations PTFE
CAS number 9002-84-0 YesY
KEGG D08974 N=
ChEBI CHEBI:53251 N
Properties
Molecular formula (C2F4)n
Density 2200 kg/m3
Melting point

600 K
Thermal conductivity 0.25 W/(m·K)
Hazards
MSDS External MSDS
NFPA 704
NFPA 704.svg
0
1
0
Supplementary data page
Structure and
properties		 n, εr, etc.
Thermodynamic
data		 Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best known brand name of PTFE is Teflon by DuPont Co.

PTFE is a fluorocarbon solid, as it is a high-molecular-weight compound consisting wholly of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine. PTFE has one of the lowest coefficients of friction against any solid.

PTFE is used as a non-stick coating for pans and other cookware. It is very non-reactive, partly because of the strength of carbon–fluorine bonds, and so it is often used in containers and pipework for reactive and corrosive chemicals. Where used as a lubricant, PTFE reduces friction, wear, and energy consumption of machinery. It is also commonly used as a graft material in surgical interventions.

It is commonly believed that Teflon is a spin-off product from the NASA space projects. Though it has been used by NASA, the assumption is incorrect.[2]

Contents

History[edit]

PTFE was accidentally discovered in 1938 by Roy Plunkett, in New Jersey while he was working for Kinetic Chemicals. As Plunkett was attempting to make a new chlorofluorocarbon refrigerant, the tetrafluoroethylene gas in its pressure bottle stopped flowing before the bottle's weight had dropped to the point signaling "empty." Since Plunkett was measuring the amount of gas used by weighing the bottle, he became curious as to the source of the weight, and finally resorted to sawing the bottle apart. Inside, he found it coated with a waxy white material which was oddly slippery. Analysis of the material showed that it was polymerized perfluoroethylene, with the iron from the inside of the container having acted as a catalyst at high pressure. Kinetic Chemicals patented the new fluorinated plastic (analogous to known polyethylene) in 1941,[3] and registered the Teflon trademark in 1945.[4][5]

DuPont, which founded Kinetic Chemicals in partnership with General Motors, was producing over two million pounds (900 tons) of Teflon brand PTFE per year in Parkersburg, West Virginia, by 1948.[6] 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 at the vast K-25 uranium enrichment plant at Oak Ridge, Tennessee.[7]

In 1954, French engineer Marc Grégoire created the first pan coated with Teflon non-stick resin under the brand name of Tefal after his wife Collete urged him to try the material he had been using on fishing tackle on her cooking pans.[8] In the United States, Kansas City, Missouri resident Marion A. Trozzolo, who had been using the substance on scientific utensils, marketed the first US-made Teflon coated frying pan, "The Happy Pan", in 1961.[9]

In the 1990's, it was found that PTFE can be radiation cross-linked above its melting point and in an oxygen free environment.[10] Electron beam processing is one example of radiation processing. Cross-linked PTFE has improved high temperature mechanical properties and radiation stability. This is significant because for many years irradiation at ambient conditions has been used to break down PTFE for recycling. [11] The radiation induced chain scissioning allows it to be more easily reground and reused.

Formation[edit]

It is formed by the polymerization of tetrafluoroethylene:

nF2C=CF2 → —{ F2C—CF2}—

Properties[edit]

PTFE is often used to coat non-stick frying pans as it is hydrophobic and possesses fairly high heat resistance.

PTFE is a thermoplastic polymer, which is a white solid at room temperature, with a density of about 2200 kg/m3. According to DuPont, its melting point is 600 K (327 °C; 620 °F).[12] Its mechanical properties degrade gradually at temperatures above 194 K (−79 °C; −110 °F).[13] PTFE gains its properties from the aggregate effect of carbon-fluorine bonds, as do all fluorocarbons. The only chemicals known to affect these carbon-fluorine bonds are certain alkali metals and most highly reactive fluorinating agents.[14]

Property Value
Density 2200 kg/m3
Melting point 600 K
Thermal expansion 135 · 10−6 K−1 [15]
Thermal diffusivity 0.124 mm²/s [16]
Young's modulus 0.5 GPa
Yield strength 23 MPa
Bulk resistivity 1016 Ω·m [17]
Coefficient of friction 0.05–0.10
Dielectric constant ε=2.1,tan(δ)<5(-4)
Dielectric constant (60 Hz) ε=2.1,tan(δ)<2(-4)
Dielectric strength (1 MHz) 60 MV/m

The coefficient of friction of plastics is usually measured against polished steel.[18] PTFE's coefficient of friction is 0.05 to 0.10,[12] which is the third-lowest of any known solid material (BAM being the first, with a coefficient of friction of 0.02; diamond-like carbon being second-lowest at 0.05). PTFE's resistance to van der Waals forces means that it is the only known surface to which a gecko cannot stick.[19]

PTFE has excellent dielectric properties. This is especially true at high radio frequencies, making it 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 lower melting point polyethylene that is commonly used in low-cost applications.

Because of its chemical inertness, PTFE cannot be cross-linked like an elastomer. Therefore, it has no "memory" and is subject to creep. This is advantageous when used as a seal, because the material creeps a small amount to conform to the mating surface. However, to keep the seal from creeping too much, fillers are used, which can also improve wear resistance and reduce friction. Sometimes, metal springs apply continuous force to PTFE seals to give good contact, while permitting a beneficially low percentage of creep.[citation needed]

Applications and uses[edit]

Owing to its low friction, it is used for applications where sliding action of parts is needed: plain bearings, gears, slide plates, etc. In these applications, it performs significantly better than nylon and acetal; it is comparable to ultra-high-molecular-weight polyethylene (UHMWPE), although UHMWPE is more resistant to wear than PTFE, for these applications, versions of PTFE with mineral oil or molybdenum disulfide embedded as additional lubricants in its matrix are being manufactured. Its extremely high bulk resistivity makes it an ideal material for fabricating long-life electrets, useful devices that are the electrostatic analogues of magnets.

Gore-Tex is a material incorporating a fluoropolymer membrane with micropores. The roof of the Hubert H. Humphrey Metrodome in Minneapolis, USA, is one of the largest applications of PTFE coatings, using 20 acres (81,000 m2) of the material in a double-layered, white dome, made using fiberglass with a PTFE coating.

PTFE is also used as a film interface patch for sports and medical applications, featuring a pressure-sensitive adhesive backing, which is installed in strategic high friction areas of footwear, insoles, ankle-foot orthosis, and other medical devices to prevent and relieve friction-induced blisters, calluses, and foot ulceration.

Powdered PTFE is used in pyrotechnic compositions as oxidizers together with powdered metals such as aluminium and magnesium. Upon ignition, these mixtures form carbonaceous soot and the corresponding metal fluoride, and release large amounts of heat. Hence they are used as infrared decoy flares and igniters for solid-fuel rocket propellants.[20]

In optical radiometry, sheets made from PTFE are used as measuring heads in spectroradiometers and broadband radiometers (e.g., illuminance meters and UV radiometers) due to its capability to diffuse a transmitting light nearly perfectly. Moreover, optical properties of PTFE stay constant over a wide range of wavelengths, from UV down to near infrared. In this region, the relation of its regular transmittance to diffuse transmittance is negligibly small, so light transmitted through a diffuser (PTFE sheet) radiates like Lambert's cosine law. Thus, PTFE enables cosinusoidal angular response for a detector measuring the power of optical radiation at a surface, e.g., in solar irradiance measurements.

PTFE is also used to coat certain types of hardened, armor-piercing bullets, so as to prevent the increased wear on the firearm's rifling that would result from the harder projectile, however it is not the PTFE itself that gives the bullet its armor-piercing property.[21]

High corrosion resistance favors the use of PTFE in laboratory environments as containers, as magnetic stirrer coatings, and as tubing for highly corrosive chemicals such as hydrofluoric acid, which will dissolve glass containers. It is used in containers for storing fluoroantimonic acid, a superacid.[citation needed]

PTFE tubes are used in gas-gas heat exchangers in gas cleaning of waste incinerators. Unit power capacity is typically several megawatts.

PTFE is also widely used as a thread seal tape in plumbing applications, largely replacing paste thread dope.

PTFE membrane filters are among the most efficient used in industrial air filtration applications. Filter coated with a PTFE membrane are often used within a dust collection system to collect particulate matter from air streams in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production, and steel foundries.

PTFE grafts can be used to bypass stenotic arteries in peripheral vascular disease, if a suitable autologous vein graft is not available.

PTFE can be used to prevent insects climbing up surfaces painted with the material. PTFE is so slippery that insects cannot get a grip and tend to fall off. For example, PTFE is used to prevent ants climbing out of formicaria. PTFE is also sometimes used as feet for computer mice, to reduce the friction with a mousepad or other tracking surface.[22]

Safety[edit]

The pyrolysis of PTFE is detectable at 200 °C (392 °F), and it evolves several fluorocarbon gases[23] and a sublimate. An animal study conducted in 1955 concluded that it is unlikely that these products would be generated in amounts significant to health at temperatures below 250 °C (482 °F).[24] More recently, however, a study documented birds having been killed by these decomposition products at 202 °C (396 °F), with unconfirmed reports of bird deaths as a result of non-stick cookware heated to as little as 163 °C (325 °F).[23][25]

While PTFE is stable and nontoxic, it begins to deteriorate after the temperature of cookware reaches about 533 K (260 °C; 500 °F), and decomposes above 623 K (350 °C; 662 °F).[26] These degradation by-products can be lethal to birds, and can cause flu-like symptoms in humans.[26] In May, 2003, the environmental research and advocacy organization Environmental Working Group filed a 14-page brief with the U.S. Consumer Product Safety Commission petitioning for a rule requiring that cookware and heated appliances bearing non-stick coatings carry a label warning of hazards to people and to birds.[27]

Meat is usually fried between 400 and 450 °F (204 and 232 °C), and most oils will start to smoke before a temperature of 500 °F (260 °C) is reached, but there are at least two cooking oils (refined safflower oil and avocado oil) that have a higher smoke point than 500 °F (260 °C). Empty cookware can also exceed this temperature upon heating.

PFOA[edit]

As of October 29, 2012, environmental exposure (i.e., via water and air) to perfluorooctanoic acid (PFOA or C8) has been linked to high cholesterol, ulcerative colitis, thyroid disease, testicular cancer, kidney cancer, and pregnancy-induced hypertension.[28] These correlative links were found as part of the C8 Science Panel research program, which was conducted by Brookmar, Inc., in order to determine PFOA's health effects on humans after it was released into the air and Ohio River by DuPont's West Virginia Washington Works Plant between 1950 and the early 21st century. From 2005 to 2006, information was gathered from members of the Mid-Ohio Valley community through interviews, questionnaires, and blood samples.[29]

In the form of an ammonium salt,[30] it is used as a surfactant in the emulsion polymerization of PTFE,[31] [32] and has been detected in some PTFE products. [33][34] The levels that have been measured in nonstick cookware range from not detectable to 75 parts per billion.[34] [35] These are lower than in PTFE products such as thread sealant tape (with 1800 parts per billion (1.8 parts per million) of PFOA detected) because nonstick cookware is heated to volatilize PFOA.[33]

A DuPont study on Teflon PTFE did not detect any PFOA above their detection limit of 9 parts per billion,[36] and DuPont says no PFOA is in Teflon brand cookware.[37] A 2009 USEPA study found levels of PFOA in nonstick cookware ranging from undetected (with a detection limit of 1.5 parts per billion) to 4.3 parts per billion.[34] DuPont says there should be no measurable amount on a finished pan provided it has been properly cured.[38] While PFOA has been detected in the low parts per billion range in the blood of people,[39] exposure from nonstick cookware is considered insignificant[40][41] —despite the marketing of other wares. However, at temperatures well above those encountered in cooking,[42] PTFE pyrolysis can form minor amounts of PFOA.[43][44]

In January 2006, DuPont, the only company that manufactures PFOA in the US, agreed to eliminate releases of the chemical from its manufacturing plants by 2015,[45] but did not commit to completely phasing out its use of the chemical. In the emulsion polymerization of PTFE, 3M subsidiary Dyneon has developed a replacement emulsifier[46] despite DuPont stating that PFOA is an "essential processing aid".[47] As of August 2008, the EPA's position was that it "has no information that routine use of household or other products using fluoropolymers, such as nonstick cookware or all weather clothing, poses a concern."[48]

Similar polymers[edit]

Teflon is also used as the trade name for a polymer with similar properties, perfluoroalkoxy polymer resin (PFA).

Other polymers with similar composition are also known by the Teflon trade name:

These retain the useful PTFE properties of low friction and nonreactivity, but are more easily formable. For example, FEP is softer than PTFE and melts at 533 K (260 °C; 500 °F); it is also highly transparent and resistant to sunlight.[49]

See also[edit]

References[edit]

  1. ^ "poly(tetrafluoroethylene) (CHEBI:53251)". Retrieved July 12, 2012. 
  2. ^ NASA Spinoff under Are Tang, Teflon, and Velcro NASA spinoffs?
  3. ^ US 2230654, Plunkett, Roy J, "Tetrafluoroethylene polymers", issued 4 February 1941 
  4. ^ "History Timeline 1930: The Fluorocarbon Boom". DuPont. Retrieved 10 June 2009. 
  5. ^ "Roy Plunkett: 1938". Retrieved 10 June 2009. 
  6. ^ American Heritage's Invention & Technology, Fall 2010, vol. 25, no. 3, p. 42
  7. ^ Rhodes, Richard (1986). The Making of the Atomic Bomb. New York, New York: Simon and Schuster. p. 494. ISBN 0-671-65719-4. Retrieved 31 October 2010. 
  8. ^ "Teflon History ", home.nycap.rr.com, Retrieved 25 January 2009.
  9. ^ Robbins, William (21 December 1986) "Teflon Maker: Out Of Frying Pan Into Fame ", New York Times, Retrieved 21 December 1986 (Subscription)
  10. ^ Modification of PTFE by radiation J.Z. Sun, Y.F. Zhang, X.G. Zhong, X.L. Zhu, Modification of polytetrafluoroethylene by radiation. 1. Improvement in high-temperature properties and radiation stability, Radiat. Phys. Chem. 44 (1994) 655–679.
  11. ^ Electron Beam Processing of PTFE E-BEAM Services website. Accessed May 21, 2013
  12. ^ a b Fluoropolymer Comparison – Typical Properties Retrieved 10 September 2006.
  13. ^ Teflon PTFE Properties Handbook Retrieved 11 October 2012.
  14. ^ DuPont Teflon® Coatings. plastechcoatings.com
  15. ^ "Reference Tables – Thermal Expansion Coefficients – Plastics". 
  16. ^ J. Blumm, A. Lindemann, M. Meyer, C. Strasser (2011). "Characterization of PTFE Using Advanced Thermal Analysis Technique". International Journal of Thermophysics 40 (3–4): 311. Bibcode:2010IJT....31.1919B. doi:10.1007/s10765-008-0512-z. 
  17. ^ "Microwaves101 – Polytetrafluoroethylene". 
  18. ^ Coefficient of Friction (COF) Testing of Plastics MatWeb Material Property Data Retrieved 1 January 2007.
  19. ^ "Research into Gecko Adhesion ", Berkeley, 2007-10-14, Retrieved 8 April 2010.
  20. ^ E.-C. Koch (2002). "Metal-Fluorocarbon Pyrolants:III. Development and Application of Magnesium/Teflon/Viton". Propellants Explosives Pyrotechnics 27 (5): 262–266. doi:10.1002/1521-4087(200211)27:5<262::AID-PREP262>3.0.CO;2-8. 
  21. ^ [1].
  22. ^ Mouse Feet Computer Hardware Buyers' Glossary, 20 April 2007. Retrieved 07 January 2012.
  23. ^ a b Teflon offgas studies|Environmental Working Group. Ewg.org. Retrieved on 2013-01-01.
  24. ^ Zapp JA, Limperos G, Brinker KC (26 April 1955). "Toxicity of pyrolysis products of 'Teflon' tetrafluoroethylene resin". Proceedings of the American Industrial Hygiene Association Annual Meeting. 
  25. ^ Can Nonstick Make You Sick?. ABC News. 14 November 2003
  26. ^ a b DuPont, Key Questions About Teflon, accessed on 3 December 2007.
  27. ^ Petition to Require Warning Labels|Environmental Working Group. (PDF) . Retrieved on 2013-01-01.
  28. ^ C8 Science Panel. "C8 Probable Link Reports". Retrieved 1 November 2012. 
  29. ^ About the C8 Science Panel. "About the C8 Science Panel". Retrieved 29 April 2013. 
  30. ^ Substance flow analysis for Switzerland ", (UW-0922-E), pp.40–41, 2009-12-03, 1787 kB, Swiss Federal Office for the Environment, Retrieved 8 April 2008
  31. ^ Sandy, Martha. "Petition for Expedited CIC Consideration of Perfluorooctanic Acid (PFOA)". The State of California, Office of Environmental Health Hazard Assessment, Cancer Toxicology and Epidemiology Section, Reproductive and Cancer Hazard Assessment Branch. Retrieved 27 September 2008. 
  32. ^ Lau C, Anitole K, Hodes C, Lai D, Pfahles-Hutchens A, Seed J (2007). "Perfluoroalkyl acids: a review of monitoring and toxicological findings". Toxicol. Sci. 99 (2): 366–94. doi:10.1093/toxsci/kfm128. PMID 17519394. 
  33. ^ a b "PFOA in Norway TA-2354/2007". Norwegian Pollution Control Authority. 2007. p. 18. Retrieved 29 August 2009. 
  34. ^ a b c Guo Z, Liu X, Krebs KA (March 2009). "Perfluorocarboxylic Acid Content in 116 Articles of Commerce" (PDF). USEPA. p. 40. 
  35. ^ Begley TH, White K, Honigfort P, Twaroski ML, Neches R, Walker RA (2005). "Perfluorochemicals: potential sources of and migration from food packaging". Food Addit. Contam. 22 (10): 1023–31. doi:10.1080/02652030500183474. PMID 16227186. 
  36. ^ Powley CR, Michalczyk MJ, Kaiser MA, Buxton LW (2005). "Determination of perfluorooctanoic acid (PFOA) extractable from the surface of commercial cookware under simulated cooking conditions by LC/MS/MS". Analyst 130 (9): 1299–302. Bibcode:2005Ana...130.1299P. doi:10.1039/b505377c. PMID 16096677. 
  37. ^ "Teflon firm faces fresh lawsuit". BBC News. 19 July 2005. Retrieved 24 January 2009. 
  38. ^ "About Teflon". DuPont. Archived from the original on 29 February 2008. Retrieved 9 February 2010. 
  39. ^ Houde M, Martin JW, Letcher RJ, Solomon KR, Muir DC (2006). "Biological monitoring of polyfluoroalkyl substances: A review". Environ. Sci. Technol. 40 (11): 3463–73. doi:10.1021/es052580b. PMID 16786681.  Supporting Information (PDF).
  40. ^ Trudel D, Horowitz L, Wormuth M, Scheringer M, Cousins IT, Hungerbühler K (2008). "Estimating consumer exposure to PFOS and PFOA". Risk Anal. 28 (2): 251–69. doi:10.1111/j.1539-6924.2008.01017.x. PMID 18419647. 
  41. ^ "Nonstick pans: Nonstick coating risks". Consumer Reports. Retrieved 4 July 2009. 
  42. ^ "Cooking up a storm in a frying pan ", Royal Society of Chemistry, Chemistry World, September 2005, Retrieved 8 April 2010
  43. ^ Ellis DA, Mabury SA, Martin JW, Muir DC (2001). "Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the environment". Nature 412 (6844): 321–4. doi:10.1038/35085548. PMID 11460160. 
  44. ^ Ellis DA, Martin JW, Muir DC, Mabury SA (2003). "The use of 19F NMR and mass spectrometry for the elucidation of novel fluorinated acids and atmospheric fluoroacid precursors evolved in the thermolysis of fluoropolymers". Analyst 128 (6): 756–64. Bibcode:2003Ana...128..756E. doi:10.1039/b212658c. PMID 12866900. 
  45. ^ Juliet Eilperin (26 January 2006). "Harmful PTFE chemical to be eliminated by 2015". Washington Post. Retrieved 10 September 2006. 
  46. ^ Michael McCoy (2008). "Dyneon Phasing Out Perfluorooctanoate". Chemical & Engineering News 86 (46): 26. doi:10.1021/cen-v086n033.p026. 
  47. ^ "Learn More About DuPont Teflon". DuPont. Retrieved 16 May 2009. 
  48. ^ "Failure to Report Chemical Risks Can Result in Major Fines, EPA Office of Civil Enforcement". Environmental Protection Agency. 2008-08. Retrieved 19 January 2009. 
  49. ^ FEP Detailed Properties, Parker-TexLoc, 13 April 2006. Retrieved 10 September 2006.

Further reading[edit]

  • Ellis, D.A.; Mabury, S.A.; Martin, J.W.; Muir, D.C.G.; Mabury, S.A.; Martin, J.W.; Muir, D.C.G. (2001). "Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the environment". Nature 412 (6844): 321–324. doi:10.1038/35085548. PMID 11460160. 

External links[edit]

Health issues of plastics and Polyhalogenated compounds (PHCs)
Plasticizers: Phthalates
Miscellaneous plasticizers
Monomers
Miscellaneous additives incl. PHCs
Health issues
Miscellanea
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