E&T marks the 100th anniversary of Roy Plunkett, the inventor of Teflon.
Lots of the best ideas in engineering come about through luck. That's not to say that engineers simply wander around bumping into things hoping that something will happen, but it is true that unintended consequence as often as intended ones can lead to a breakthrough. It is the job of the discoverer or inventor to be open to the possibility. As Louis Pasteur put it: 'Chance only favours the mind which is prepared.' A hundred years ago this June, a man with just such a mind was born in the town of New Carlisle, Ohio, and his story shows just how far an unintended consequence can go.
Roy Plunkett's contribution to the world could, were it not for one happy accident, have seemed to modern eyes rather environmentally unfriendly. In an era long before the dangers were fully understood, he took a leading role in the introduction of tetra-ethyl lead to petrol as an anti-knocking agent. He also tried to create novel CFC refrigerants, which we now know can leave a hole in the ozone layer.
But it was thanks to CFCs that Plunkett had his great moment of discovery and one which has made the lives of many an engineer, heart patient and cook much better. In 1938, Plunkett - a research chemist at the Du Pont Company, was investigating a toxic problem. Refrigerators then contained substances like ammonia, which were perfectly safe while enclosed in sealed systems but which had a nasty habit of leaking and poisoning anyone nearby. As poisoning chefs is generally considered poor form, Plunkett was charged with finding a safer alternative using chlorofluorocarbon compounds, work which would eventually lead to the synthesis of 'freon'. Had this been all, his contribution might have been hailed by refrigerator users and decried by environmentalists, but it was while working with CFCs that he made a more unusual discovery.
Plunkett produced a quantity of the gas tetrafluoroethylene (TFE), a simple fluorocarbon used in preparing polymers and, this being a shade volatile, he was sensibly keeping it in small steel cylinders cooled with solid carbon dioxide. The odd thing was that when he went to tap the TFE into some of the cylinders a few days later, nothing came out. Initially he assumed that the gas might have escaped, or the pressure valves on the cylinders had stuck shut? There was only one way to find out. Carefully taking one of the cylinders outside, he placed it behind a specially built shield and cut it open. Inside there appeared to be nothing, which was odd, as the cylinder weighed just as much as when it had first been filled.
Then he noticed a white powder lining the inside of the container. The TFE had accidentally polymerised to form polytetrafluoroethylene (PTFE), catalysed by the iron in the cylinder walls. This was worth a bit of investigation so he took away the powder for analysis. He recorded: 'It is thermoplastic, melts at a temperature approaching red heat, boils away without residue, is insoluble in hot and cold water, insoluble in all petroleum solvents, alcohols, ethers, all acids and alkalis...'
To put it another way, it was almost completely inert. It also had an extremely high electrical resistance but, more interestingly, it had an incredibly low coefficient of friction, in fact the second lowest of any known solid material, the lowest being 'diamond-like carbon'. This meant that nothing stuck to it.
What use is a substance that nothing reacts with and nothing sticks to? Du Pont, who christened it 'Teflon', could think of thousands of uses. Thanks to its inertness, it is today used to line valves and pipes carrying highly volatile substances, its dielectric properties make it an excellent insulator in cables and circuit boards, while in powdered form it can be used as a pyrotechnic oxidiser in decoy flares used to confuse heat-seeking missiles.
But it is its slipperiness that has really made its name. Sprayed on furnishing fabrics and carpets, it makes them highly resistant to dirt. On a larger scale, it helps to keep the Millennium dome a sparkling white(ish). The whole of the Sydney Opera House sits of Teflon pads, which allow it to respond to thermal expansion, and even Arctic expeditions benefit from its use on sledge runners. As a slippery coating, it eases the path of deadly armour-piercing bullets, but can also form vascular grafts, which prevent clots forming and hence save lives. Even pet shops have Teflon to thank as it makes an idea coating for insect cages, as even ants can't climb up it. It is also the only solid substance that can defeat a gecko.
The most famous application of this unexpected result came about in 1954 when French engineer Marc Grégoire was thinking about how Teflon might stop his fishing tackle getting tangled. His wife suggested that a more useful problem might be stopping food sticking to her cooking pans. So Grégoire created the first non-stick resin for cookery.
Serendipity affects writers just as much as it does scientists, so I was delighted when, as I was pondering what subject to choose next, Ian W Price sent E&T his researches on Roy Plunkett, who just happens to have been born 100 years ago this year. Ian's work provided invaluable research for the above.