Polytetrafluoroethylene (PTFE)

By 1938 the American kitchen was being rewired. Mechanical refrigeration, a luxury a decade earlier, was going into ordinary homes by the millions, and the entire industry ran on a family of gases called chlorofluorocarbons that a General Motors team had introduced under the name Freon in 1930. DuPont had a stake in that business through a joint venture with GM, and it wanted refrigerants of its own that did not infringe anyone else’s patents. That commercial pressure is the reason a twenty-seven-year-old chemist named Roy J. Plunkett was at DuPont’s Jackson Laboratory in New Jersey that spring, manufacturing a hundred pounds of a candidate gas called tetrafluoroethylene and storing it in small cylinders on dry ice.

Plate I

Some four hundred miles away in Berlin that same year, Otto Hahn and Fritz Strassmann were bombarding uranium with neutrons and finding, to their own disbelief, that the atom itself would come apart. Nuclear fission would not be explained in print until January 1939, but 1938 was already the year physics discovered that matter could be split open. It is a strange coincidence that the same twelve months produced, in a New Jersey laboratory, a molecule that nothing on earth could split open at all.

Plate II

An Empty Cylinder That Was Not Empty

On the morning of 6 April 1938, Plunkett and his laboratory assistant, Jack Rebok, went to draw off gas from one of the stored cylinders and got nothing. The valve was open, the line was clear, and yet the cylinder had not lost any weight. Rather than write it off, Plunkett cut the cylinder open. Inside was a smooth, waxy white powder. The tetrafluoroethylene gas had polymerised on its own, catalysed by the iron of the cylinder’s own interior wall. That was something no theory of the day predicted a fluorocarbon would do. Instead of discarding a ruined experiment, Plunkett set the refrigerant work aside and spent the following weeks characterising the powder itself: testing its response to heat, solvents, acids and electrical fields. What he had was polytetrafluoroethylene, and almost every test came back the same way: nothing touched it.

A Backbone Nothing Can Reach

PTFE’s chain is carbon, two fluorines to a link, running on indefinitely. What makes the material remarkable is not the carbon backbone, which is common to half the plastics in this Atlas, but the sheath the fluorine builds around it. Fluorine is the most electronegative element there is, and the carbon-fluorine bond it forms is among the strongest single bonds in organic chemistry. Packed one after another down the chain, the fluorine atoms crowd out any possible approach to the carbon underneath, so that the backbone sits inside what is effectively a fully-fluorinated tube. Nothing gets past it to react.

A Material of Extremes

PTFE occupies a strange position among plastics: it is one of the densest of them, distinctly heavier than water though still far lighter than the metals whose jobs it eventually took, and it keeps its working properties across an enormous temperature span, from deep-freeze cold to well past the boiling point of water. It is soft and readily deforms under sustained load rather than snapping, which is part of why it can be skived into thin tape or machined into gaskets. Its most famous number is not really a number the reader needs; what matters is that it has the lowest coefficient of friction of any solid material known, low enough that almost nothing will adhere to a clean PTFE surface at all. That same fluorinated sheath makes it close to chemically inert: strong acids, strong bases, solvents and oils all pass over it without effect, and only a handful of the most aggressive reagents on earth (molten alkali metals, elemental fluorine gas) can touch it. It does not truly melt in the way most thermoplastics do, either; its molten state is so viscous that it cannot be pumped or injection moulded, and virtually all PTFE parts are formed by pressing the powder into shape and sintering it, the same principle a potter uses to fire clay.

From Powder to Product

Commercial production begins with tetrafluoroethylene made from chloroform and hydrogen fluoride, which is then polymerised in water using persulfate initiators under carefully controlled pressure and moderate heat; TFE is unstable enough in bulk that the reaction has to be respected rather than rushed. The resulting resin cannot be melt-processed, so parts are compression-moulded or ram-extruded as a powder compact and then sintered in an oven at several hundred degrees, after which the solid block or rod is skived, machined, or drawn into finished shapes. DuPont registered the Teflon trademark in 1945 and had commercial production running at industrial scale within a few years.

Plate III

Non-stick cookware, the application most people know PTFE by, did not come from DuPont at all. In 1954, a French engineer named Marc Grégoire (who had already been coating fishing tackle in Teflon to help his line run more freely off the rod) coated a frying pan for his wife Colette at her suggestion. Two years later the couple founded Tefal to sell the pans commercially, and non-stick cookware has carried some version of that chemistry ever since.

The War’s Quiet Passenger

PTFE’s first major industrial role, though, was one nobody could talk about for years. The Manhattan Project’s uranium enrichment plant at Oak Ridge, Tennessee, separated uranium isotopes by forcing uranium hexafluoride gas (ferociously corrosive, and reactive with almost every metal, rubber and plastic then in use) through miles of piping, valves and gaskets. PTFE was one of vanishingly few materials that simply did not react with it, and it went into seals and gasket linings throughout the plant. The work stayed classified long after the war ended, and PTFE’s reputation as an industrial material was already well established elsewhere before the public learned what it had quietly been holding together at Oak Ridge.

Plate IV

From there PTFE’s uses only widened: wire and cable insulation for aircraft and electronics, artificial blood vessels and joint liners in medicine, tank and pipe linings wherever a chemical plant needed to hold something nothing else could hold, and, laminated into a breathable membrane, the Gore-Tex fabric that keeps rain out while letting water vapour escape.

The Cost of Never Reacting

The same inertness that makes PTFE useful is what makes it a long-term environmental problem. The industry has taken to calling it, and the wider fluoropolymer family, “forever chemicals,” because the carbon-fluorine bonds that resist every solvent and acid also resist the microbes and sunlight that break down ordinary plastic waste. Manufacture of its precursor gas has historically involved potent greenhouse-gas byproducts, and processing aids once used in PTFE production (chiefly PFOA) have left a legacy of persistent environmental contamination that the industry has spent the past two decades phasing out. PTFE itself, once formed, is chemically stable and non-toxic in ordinary use; the environmental and health concerns attached to the “forever chemical” label mostly belong to the smaller, more mobile fluorinated molecules used in its manufacture or produced when it burns, not to the finished polymer sitting in a frying pan.

That distinction matters for cooks, too. PTFE cookware only begins to break down at temperatures well above anything a recipe calls for; ordinary frying, even on high heat, does not approach it. An empty pan left over a hot burner is the real risk, since with nothing in it to absorb the heat it can climb into the range where the coating starts to give off fumes and, at the higher end, can briefly cause a flu-like reaction in humans known as polymer fume fever. Used as directed (with food in the pan, and without scrubbing the coating away with metal tools), PTFE cookware is about as unremarkable, chemically, as kitchenware gets.