Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene, also known as PTFE, is the chemical name for the product sold under the brand name Teflon. It is a slick, low friction substance that prevents other objects from sticking to those coated with PTFE. Since its discovery in the middle of the twentieth century, PTFE has played a key role in a number of industries, including manufacturing, aerospace, textiles, communications, and electronics. Although it has become an important part of projects as large as a space mission and as small as cooking an egg, PTFE has also been subject to some controversy over concerns of health risks.

Background

The accidental discovery of PTFE came in 1938 when Dr. Roy Plunkett, an American chemist working in DuPont's laboratories, was attempting to find a new refrigeration coolant. During his experiments, Plunkett inadvertently froze a sample of tetrafluoroethylene, a colorless, odorless, flammable, and slightly toxic gas. He discovered that his error caused the gas to turn into a powder that was polymerized—it had undergone a chemical change that resulted in long chains of connected molecules instead of individual molecules. The powder was very slippery and capable of withstanding a wide range of temperatures, from as high as 500 degrees Fahrenheit to as low as -400 degrees Fahrenheit. The newly discovered PTFE became a DuPont product and acquired the trade name Teflon.

It took a while for scientists to figure out applications for the new product. One of its earliest uses was as an insulator on the tubes and connectors used to contain the uranium when the United States built the first nuclear bombs during World War II in what was known as the Manhattan Project. PTFE's ability to resist corrosion helped to protect the valves, gaskets, and other parts of the mechanism from the effects of the uranium.

In 1954, scientists discovered that food did not stick to pots coated with PTFE. The manufacture of pots and pans with Teflon coatings became the first mass-market use of Plunkett's discovery. At the same time, industrial uses for PTFE continued to be discovered. It became an important part of the aerospace industry where it was used to help insulate and protect space suits and parts of the spacecraft from extreme conditions. By 1973, a way was found to treat fiberglass with PTFE, and it soon became a significant part of the building industry. PTFE-coated parts are found in many large structures because they are strong, long lasting, shed dirt, and are flame resistant.

Overview

Modern-day manufacturers have developed two different ways to make PTFE. The tetrafluoroethylene can be turned into a polymer with a free-radical catalyst. Free radicals have unpaired electrons that make them open to combining in a way that forms the long chains that characterize polymers. Another way PTFE can be formed is by substituting fluorine atoms for the hydrogen atoms present. This is done by applying fluorine and polyethylene gas at a temperature of 68 degrees Fahrenheit.

The resulting PTFE has a number of properties that make it unique. It has the lowest friction coefficient of any known product, explaining why almost nothing sticks to it. It does not absorb water, which also makes it resistant to sticking. The tendency to repel water and not collect any debris means that it weathers particularly well. It is also extremely resistant to chemical corrosion and has a limiting oxygen index (LOI) score of 95 percent, making it very fire retardant.

With all of these special properties, PTFE continues to be an important part of many products. Nearly all tubes and pipes used by the semiconductor industry include PTFE, as do parts of many computer chips. Its ability to shield against temperature change and tendency not to be affected by chemicals make it a good insulator for communication cables as well. In addition, fabric can be treated with a liquid version of PTFE to make it resist dirt and water without making the fabric stiff or uncomfortable to wear. One trade name for fabric made with this technique is Gore-Tex.

Power plants use PTFE to help shield corrodible parts such as steel tanks from damaging chemicals, and ball bearings in many motors are also coated with PTFE. It can be combined with magnesium and aluminum to form an igniter for explosives, or contain fuel sources in some types of fuel cells. In addition to its many industrial uses, PTFE is used as a coating in some medical tubing and catheters, and is present in some solid lubricant products, such as those used on bicycle chains.

Concerns have been raised about the safety of PTFE, particularly when used to coat pots and other cookware. During the 1990s, there were numerous news stories and accounts of people experiencing flu-like symptoms after PTFE exposure. In most cases, this exposure came after the person breathed the fumes from a PTFE-coated pan that was allowed to heat to at least 662 degrees Fahrenheit, which is the melting point for PTFE. People exposed to these fumes experienced short-term flu-like symptoms such as sore throat, coughing, fever, and shivering. Household birds exposed to these fumes sometimes died as a result.

Additional worries arose about ingesting food prepared in pots and pans containing PTFE. The concern stemmed from the discovery that the blood of nearly every person in the world contains the chemical perfluorooctanoic acid (PFOA), sometimes called C8. This chemical degrades very slowly and remains in the body for a long time, allowing for the possibility that toxic levels could cause hormonal imbalances and problems with the reproductive system. It is also a potential hazard for developing fetuses. PFOA was used in the manufacture of Teflon-coated products but is not in the coated pans themselves, according to the manufacturers. It is theorized that some of the PFOA may be contained in residual coatings on the pans from manufacture, or may be released when the pan is heated repeatedly or the coating is damaged by scratching.

While experts say there is a possibility of exposure to PFOA from using PTFE-coated cookware, they say it is more likely that people are exposed to the chemical from other sources. Other products that are manufactured with PTFE could be shedding PFOA, they believe, because while the products are durable, they are not indestructible and do break down. PFOA has since been removed from the PTFE manufacturing process by many makers of nonstick cookware, and research into the chemical's sources and impact continues.

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