|
 On this day in engineering history, Roy J. Plunkett discovered polytetrafluoroethylene (PTFE), a highly crystalline, perfluorinated polymer that is better known by its DuPont brand name and registered trademark, Teflon. Plunkett, a chemist at DuPont's Jackson Laboratory, discovered Teflon by accident while researching chlorofluorocarbons (CFCs), new refrigerants that would ultimately replace older compounds such as sulfur dioxide and ammonia. With the help of Jack Rebok, his technical assistant, the 27-year old Plunkett produced 100-pound cylinders of tetrafluoroethylene gas for storage at cryogenic temperatures. On April 6, 1938, the failure of a cylinder's release valve led to an amazing discovery. Although the container was emptied of gas, its weight remained the same. Ignoring the risk of explosion, Plunkett and Rebok opened the cylinder to find a white powder which, though not a refrigerant, had valuable properties.
Teflon has an extremely low coefficient of friction, exceptional chemical resistance, strong dielectric properties, and good heat resistance. With a coefficient of friction of 0.1 or less, Teflon is ideal for bearings, bushings, gears, and other sliding parts. PTFE is also used in Teflon seals because it exhibits sufficient creep to conform to surfaces, but not enough creep to compromise the seal itself. The chemical inertness that prevents elastomeric cross-linking makes Teflon a good choice for tubes, pipes, and containers that hold reactive or corrosive chemicals. PTFE's dielectric properties, especially at high radio frequencies (RF), makes Teflon an excellent insulator for cables and connector assemblies, and a good material for printed circuit boards (PCBs) used at microwave frequencies. Applications for Teflon include uses in World War II munitions and the Manhattan Project, and in the roofing material for Minneapolis' Hubert H. Humphrey Metrodome and London's Millennium Dome.
In terms of consumer applications, Teflon is best known for its use as a non-stick coating with pots and pans. In 1959, DuPont completed a study which concluded that the toxicity of fumes emitted by dry-heating a PTFE-coated pan was less than that of fumes from ordinary cooking oils. During the last 40 years, however, critics have noted that PTFE begins to deteriorate when Teflon-coated cookware reaches 450° F and decomposes significantly above 660° F. Humans who inhale the pyrolysis products of PTFE may experience the "Teflon flu", a condition which results in respiratory difficulties, headaches, and fevers. In 2005, a scientific advisory board from the U.S. Environmental Protection Agency (EPA) found that that perfluorooctanoic acid (PFOA), a chemical compound used to make Teflon, is a "likely carcinogen".
Resources:
http://heritage.dupont.com/touchpoints/tp_1938/depth.shtml
http://heritage.dupont.com/touchpoints/tp_1938/overview.shtml
http://en.wikipedia.org/wiki/Teflon#_note-4
http://www.medicalnewstoday.com/medicalnews.php?newsid=4716
| 
