Polytetrafluoroethylene

OVERVIEW

Polytetrafluoroethylene (POL-ee-tet-ruh-FLUR-oh-ETH-eh-leen) is also known as polytetrafluoroethene, tetrafluoroethylene polymer, PTFE, and Teflon®. Polytetrafluoroethylenes are thermoplastic polymers made from the monomer tetrafluoroethylene (CF₂=CF₂). A thermoplastic polymer is a material that can be repeatedly softened and hardened by alternately heating and cooling. The polytetrafluoroethylenes are well known by the trade name of Teflon® although they are also available under more than a hundred other trade names, including Aflon®, Algloflon®, Ethicon®, Fluon®, Ftorlon®, Halon®, Molykote®, Polyflon®, Polytef®, and PTFE®. DuPont Chemical, one of the two largest manufacturers of polytetrafluoroethylene, makes at least ten grades of Teflon®. These products differ from each other in the physical form in which they are provided (powders, aqueous dispersions, yarn, or film, for example) and size (molecular weight) of the product (ranging from low-molecular weight to high-molecular weight).

KEY FACTS

OTHER NAMES:

See Overview.

FORMULA:

-[-CF₂-]-_n

ELEMENTS:

Carbon, fluorine

COMPOUND TYPE:

Organic polymer

STATE:

Solid

MOLECULAR WEIGHT:

Varies

MELTING POINT:

Varies; most common range: 302°-310°C (575°F-590°F)

BOILING POINT:

Not applicable

SOLUBILITY:

Insoluble in water, concentrated acids, other inorganic solvents and almost all organic solvents

Polytetrafluoroethylene has the lowest coefficient of friction of any known substance. The coefficient of friction is a measure of how easily one substance slides over the surface of a second substance. Polytetrafluoroethylene's low coefficient of friction means that nothing will stick very well to its surface, accounting for Teflon®'s primary use in the manufacture of non-stick products.

Polytetrafluoroethylene was invented in 1938 by Roy J. Plunkett (1910–1994) quite by accident. As a research chemist at DuPont's Jackson Laboratory, Plunkett was studying compounds that might be used for refrigerants. He kept the compounds in steel tanks and was surprised on one occasion to find that the gas he wanted did not leave the storage tank when the valve was opened. He cut the tank open to see what had happened to the gas and found a waxy white material. Upon analysis, the material turned out to be polytetrafluoroethylene. The gas stored in the tank, the potential refrigerant, was tetrafluoroethylene. It had undergone polymerization spontaneously within the tank, making it possible for Plunkett to discover one of the most remarkable synthetic products in the world.

HOW IT IS MADE

Molecules of tetrafluoroethylene contain double bonds. Any compound with double bonds has the ability to form polymers. Polymerization of tetrafluoroethylene occurs when the double bond in one molecule breaks apart. A fluorine atom from a second molecule of the monomer then adds on to one end of the broken double bond. The rest of the second molecule adds to the other end of the broken double bond. A "double-molecule," consisting of two monomers joined to each other forms: CF₂=CF₂ + CF₂=CF₂ → CF₃CF₂CF₂=CF₂. The product of this reaction also contains a double bond. So the process can be repeated to form another product consisting of three monomer molecules: CF₃CF₂CF₂=CF₂ + CF₂=CF₂ → CF₃CF₂CF₂CF₂CF₂=CF₂ The process is repeated hundreds or thousands of times producing a long chain of monomers with the general formula -[-CF₂-]-_n.

Interesting Facts

• Because Teflon® does not stick to anything else, cookware manufacturers must use a special process to get it to stay on pots and pans. They sometimes begin by blasting the pan with sand or grit to roughen the surface. Then they apply a special primer that makes the Teflon® adhere to the pan's surface.
• Teflon®'s non-stick quality has been compared to trying to make one piece of ice stick to another piece of ice.

COMMON USES AND POTENTIAL HAZARDS

Perhaps the best known application of polytetrafluoroethylene is in kitchen utensils with non-stick coatings, such as pots, pans, and spatulas. Polytetrafluoroethylene is also used to coat fibers to make them water-repellant and stain-resistant. Water will bead up and roll off the surface of clothing and other materials coated with polytetrafluoroethylene instead of penetrating the fabric and possibly leaving a stain. Polytetrafluoroethylene is available as a spray treatment for carpets and furniture, forming a molecular shield to prevent water or oil-based stains from penetrating the material. Some carpets come pre-treated with a polytetrafluoroethylene product to keep them clean and fresh. The compound can also be used on wood and plastic flooring to protect it from dirt, stains, and moisure.

Automobile manufacturers used polytetrafluoroethylene in a variety of ways. Windshield wiper blades coated with polytetrafluoroethylene are smoother and stronger than uncoated blades. Automobile paint can be coated with polytetrafluoroethylene to protect a car's finish from tree sap, insects, and other residues. Automobile upholstery is often treated with polytetrafluoroethylene to protect against stains caused by spilled drinks and dirty shoes. Polytetrafluoroethylene added to oil makes it flow through an engine more smoothly, reducing wear and tear on the engine.

Polytetrafluoroethylene is used widely for a number of industrial applications. Some armor-piercing bullets are coated with the compound to reduce friction when the bullet leaves the gun barrel and increases the ease with which it breaks through armor. Many electrical cables are insulated with polytetrafluoroethylene, which is not combustible or conductive. Food processing equipment made with polytetrafluoroethylene is easier to clean and more efficient for cooking and baking than non-polytetrafluoroethylene equipment. Industrial bakers often use equipment coated with some type of polytetrafluoroethylene. The product can also be used to coat stainless steel, carbon steel, aluminum, steel alloys, brass, magnesium, glass, fiberglass, plastics, and rubber. Outdoor signs are sometimes coated with polytetrafluoroethylene to make them last longer and resist stains.

Polytetrafluoroethylene has long been regarded as an essentially safe compound with no known health effects on humans or experimental animals. Recently, questions have been raised about possible health hazards of one of the compounds used in the manufacture of polytetrafluoroethylene, perfluorooctanoic acid (PFOA). Some studies suggest that PFOA may be responsible for birth defects and the development of cancer in people who have been exposed to the chemical. Other studies show that 96 percent of the children tested in 23 states and the District of Columbia in 2001 had detectable levels of PFOA in their blood. Federal agencies have not yet confirmed the level of risk that PFOA poses, if any, and have not listed any other chemicals used in the manufacture of polytetrafluoroethylene as hazardous to human health.

Words to Know

POLYMER

a compound consisting of very large molecules made of one or two small repeated units called monomers.

THERMOPLASTIC

Able to be repeatedly softened and hardened by alternately heating and cooling.

FOR FURTHER INFORMATION

"PTFE Specifications." Boedeker Plastics. http://www.boedeker.com/ptfe_p.htm (accessed on October 26, 2005).

Summer, Chris. "Teflon's Sticky Situation." BBC News Online (October 7, 2004). Available online at http://news.bbc.co.uk/1/hi/magazine/3697324.stm (accessed on October 26, 2005).

"Technical Information: Teflon® Fluorocarbon Resin." Omega. Stamford, Conn.: Omega Engineering, Inc. 2000. Available online at http://www.omega.com/pdf/tubing/technical_section/teflon_flourocarbon.asp (accessed on October 26, 2005).

"Teflon (PTFE: polytetrafluoroethylene)." Fluoride Action Network. http://www.fluoridealert.org/pesticides/polytetrafluoroethylenpage.htm (accessed on October 26, 2005).

See AlsoPolyethylene