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Teflon

Fall 2010 | Volume 25 |  Issue 3
Inventor:
Era:
1930s

One morning in April 1938, 27-year-old DuPont chemist Roy J. Plunkett cracked open the valve of a pressurized canister containing tetrafluoroethylene (TFE) gas in preparation for an experiment. Much to his irritation, the canister that he had filled the night before appeared to be empty. His assignment had been to find a replacement for the refrigerant Freon 114, on which Frigidaire currently held a monopoly. To conduct his scheduled experiment that morning, he needed to release some TFE into a heated chamber and then spray in hydrochloric acid. Had the gas somehow leaked out of the canister? Plunkett fiddled with the valve, but nothing happened. Finally he removed it completely, turned the canister upside down, and shook it. Some flecks of white powder floated out.

Two days of testing on the powder revealed that the material had intriguing characteristics. Plunkett wrote, “It is thermoplastic, melts at a temperature approaching red heat, and boils away. It burns without residue; the decompositive products etch glass.” It was also insoluble in cold and hot water, acetone, Freon 113, ether, petroleum ether, alcohol, pyridine, toluene, ethyl acetate, concentrated sulfuric acid, glacial acetic acid, nitrobenzene, isoamyl alcohol, ortho dichlorobenzene, sodium hydroxide, and concentrated nitric acid. Further tests showed that the substance did not char or melt when exposed to a soldering iron or an electric arc. Moisture did not cause it to rot or swell, prolonged exposure to sunlight did not degrade it, and it was impervious to mold and fungus. Plunkett didn’t realize it, but he had just inadvertently invented a material later called Teflon, one of the most versatile chemical products ever developed.

Plunkett’s next step was to duplicate the conditions that had produced the first batch of polymerized tetrafluoroethylene (PTFE). In his search for a new Freon chlorofluorocarbon (CFC), a hydrocarbon in which some or all of the hydrogen is replaced with chlorine or fluorine, he had synthesized it by reacting TFE—a gas at room conditions—with hydrochloric acid. He and his assistant, Jack Rebok, had prepared 100 pounds of TFE and stored it in pressure cylinders, to be dispensed as needed. To prevent an explosion or rupture of the cylinder, they had kept the canisters in dry ice. It was that combination of high pressure and low temperature that had forced the TFE molecules to join together in long chains to form a smooth, waxy white material, in essence a polymerized product, the first ever produced from chlorinated or fluorinated ethylene.

On July 1, 1939, he applied for a patent, which he assigned to Kinetic Chemicals (a joint venture of DuPont and General Motors), on tetrafluoroethylene polymers. The patent was granted in 1941, but soon after Plunkett was named chemical supervisor of DuPont’s tetraethyl lead plant.

For nearly three years DuPont’s organic chemicals department experimented with techniques to produce TFE (also known as TFE monomer), which was the raw material for PTFE, in industrial quantities. But the onset of World War II added a pressing nature to PTFE development.

In Arizona, Manhattan Project director Gen. Leslie Groves and his scientists, tasked with developing an atomic bomb, faced the challenge of separating the uranium isotope U-235 from the far more plentiful but inert U-238. The process of gaseous diffusion, in which a gas is forced through a porous material and separates heavy from light molecules, looked promising but required equipment that would stand up to highly corrosive materials. One of the essential ingredients—uranium hexafluoride gas—simply ate through conventional gaskets and seals. Those same items created out of PTFE, however, could withstand the corrosion. DuPont agreed to reserve its entire output for government use.

The PTFE not used ended up in other military applications such as the nose cones of proximity bombs, airplane engines, explosives manufacturing, and as a lining in liquid-fuel tanks. When the Army needed tape measuring only .002 of an inch thick to wrap copper wires in the radar systems of night bombers, scientists painstakingly shaved ultrathin slices of PTFE off a solid block.

DuPont registered the Teflon trademark in 1944. By 1948 DuPont’s first commercial plant, Washington Works near Parkersburg, West Virginia, was manufacturing 2 million pounds of Teflon a year. The material found hundreds of civilian applications in protective coating for machine parts, insulation sheets, gaskets, packings, valve components, pump components, bearings, sealer plates, and hoppers.

After Teflon cookware finally was introduced in the mid-1960s, it quickly made the transition from a low-volume specialty material used chiefly in industry to a mass-market consumer item. Today Teflon is used to insulate fabrics in tablecloths and carpets and to coat the surfaces of steam irons. Teflon plumbing pipes and valves can be found in many new homes; Teflon flakes add toughness to nail polish. In fiber form, it became part of the fabric Gore-Tex, beloved by campers and skiers for its ability to insulate while wicking moisture from the skin. It can also be found in pacemakers, dentures, medical sutures, artificial body parts, printed circuits, cables, space suits, and thousands of other manufactured products.

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