Briefly about the invention: The Teflon ® coating was accidentally discovered in 1938 by Dr Roy Plunkett, a young chemist at DuPont, who was then conducting experiments with refrigerant gases. This slippery material that doesn’t stick to anything is PTFE (polytetrafluoroethylene), which DuPont later gave the name Teflon ® .
Teflon ® is a registered trademark and may only be used by Chemours.
Dr Roy Plunkett’s note in his notebook
About the invention in detail: Excerpt from the Life and Science supplement
Author: Dr Árpád Máthé
Teflon ® and chance
In April 1938, Dr. Roy Plunkett, a chemist at the American company DuPont, used tetrafluoroethylene (C2F4) as an intermediate to produce a new refrigerant. The 45 kilograms of gas, hot at minus 76 degrees Celsius, was stored in a few dozen small steel bottles. Later, when they opened the shut-off valve, one of the bottles seemed to be empty… No gas came out of the bottle. The valve was removed. It turned out that a white powder from the tetrafluoroethylene gas was deposited on the wall of the bottle. To collect the dust, the bottle was sawn in half. The white powder was found to have the same chemical composition as tetrafluoroethylene gas. Poly(tetrafluoroethylene), in short: PTFE, was formed during storage, regardless of the researchers’ intentions.
Plunkett did not think that tetrafluoroethylene could polymerize during storage, since the polymerization of a similar monomer, vinyl chloride, required a catalyst, a radical initiator. The spontaneous polymerization was also surprising because the researchers were dealing with fluoro-chloro-hydrocarbons (freons) precisely because of their high stability.
Poly(tetrafluoroethylene) was given the name Teflon®. This thermoplastic polymer has a highly crystalline structure. It has the highest chemical resistance of all plastics: it has no solvents. It withstands both cold and heat well: it can be used permanently from minus 269 degrees Celsius to plus 260 degrees Celsius. The least flammable plastic. It meets the strictest food industry and medical requirements, and can even be incorporated into living organisms.
No material sticks to it, even at higher temperatures. That’s why we can bake in Teflon®-coated metal dishes without fat. It cannot be molded using traditional plastic processing methods: its density is higher (2.3 grams/cubic centimeter) than that of bulk plastics, and its price is much higher than theirs.
Thanks to its special application possibilities, more than 50,000 tons of Teflon® are produced worldwide every year.
Teflon ® is a product of radical polymerization of tetrafluoroethylene. It has a high average molecular weight (0.5–1 million), 90 percent crystalline structure and melts at 341 degrees Celsius. It is interesting that the bulked and then cooled polymer melts for the second time already at 327 degrees Celsius. It is stable above this temperature, but the viscosity of the melt is so high (1011 poise at 380 degrees Celsius) that it cannot be processed in the usual way (by extrusion or injection molding). The material consisting of porous particles of different shapes emerging from the suspension polymerization reactors is filtered, dried and ground depending on the needs. A typical PTFE granulate consists of particles with a diameter of 400-800 micrometers. This ground material is pressed into the desired shape at a low temperature, and then the semi-finished product is sintered in an oven (heat-treated at 380 degrees Celsius under pressure for a long time). This is how the particles are assembled into a pore-free, solid material that completely fills the space. This can then be shaped using processes known from the metal industry (drilling, turning, milling, etc.).
Teflon ® is suitable for the production of coatings and fibers in the form of an aqueous dispersion. The raw dispersion is first stabilized with surfactants and then thickened to a dry matter content of 50-60 percent. It is applied to the desired surface in a variety of ways: it is sprayed with propellant gas, it is applied with liquid, the material to be coated is dipped in it or in an electric field, as a result of which the coating is formed.
A Teflon® fiber can also be drawn from an aqueous dispersion. In this case, the dispersion is mixed with a matrix-forming plastic such as viscose. The auxiliary polymer providing the matrix is removed from the fiber bundle by heating, then the fibers are sintered and further stretched.