PTFE (Polytetrafluoroethyl, aka Fluoroplastics)
Discovered in the 1930s by accident – which is the case with so many plastics – PTFE has become one of the most high-profile plastics in history. One of the easiest ways to remember PTFEs is to think of Teflon® from DuPont, a word that has become synonymous with non-stick, and a material that has become a household name and a part of common vocabulary. On that basis, it’s not hard to guess that its main property is that it is self-lubricating and super slippery and extremely good at resisting chemicals even at high temperatures.
Having said that, its main drawback is that, unlike most of the other materials featured in this book, it is extremely difficult to process by conventional plastic forming techniques. However, this has not stopped it from becoming widely used as a coating in all sorts of applications, including fabrics such a Gore-Tex® and as a major ingredient of the tent structure of the Millennium Dome.
To create solid shapes a processing method called ram extrusion is used, which allows the manufacture of tubes, rods and sections. PTFE powder is fed into an extrusion pipe, compressed by a ram and transported through the pipe, which is heated up to sintering temperature, so that it sinters together into a continuous extrudate.
Image: Dental floss
Key features
•Excellent heat resistance
•Non-stick
•Excellent chemical resistance
•Excellent UV resistance
•Non-flammable
•Difficult to form
•Food grade
Sources
Widely available from multiple global suppliers.
Cost
£10.25 ($16) per kg.
Sustainability issues
Recently there have been a number of claims and law suits on the basis that a key processing agent, perfluorooctanoic acid (PFOA), used in some PTFEs is a potential carcinogen and has been found in the environment and marine organisms.
Production
Unlike many other plastics, PTFEs cannot be injection moulded due to the high viscosity of the resin; as a result, solid shapes are difficult to form. However, it can be compression moulded from powder and ram extruded, although its main area of application is being sprayed as a thin layer.
Typical applications
Apart from the popular name of Teflon®, where it is applied to fabrics and cookware, it is also applied as a coating and lining for chemical equipment, tubes, films, sheets and tape, as a coating for the underside of irons, and infused in ski wax.
Derivatives
–Gore-Tex®
–Teflon®
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–Excellent heat resistance –Non-stick properties –Widely available |
–Difficult to process into solid shapes –Some PTFEs have been found to use carcinogens during processing |