Polytetrafluoroethylene (PTFE)

PTFE is a polymer of fluorinated ethylene. 3D model of a section of PTFE Polytetrafluoroethylene (PTFE) is a fluoropolymer discovered by Roy J. Plunkett (1910–1994) of DuPont in 1938. It was introduced as a commercial product in 1946 and (in an example of a genericized trademark) is generally known to the public by DuPont's brand name Teflon™.

The coefficient of friction of PTFE is 0.1 or less, which is the lowest of any known solid material. It is used as a non-stick coating for pans and other cookware. PTFE is very non-reactive, and so is often used in containers and pipework for reactive chemicals. According to DuPont its melting point is 327 °C, but its properties degrade above 260 °C.

Other polymers with similar composition are known with the PTFE name:: fluorinated ethylene-propylene (FEP) and perfluoroalkoxy polymer resin (PFA). They retain the useful properties of PTFE of low friction and non-reactivity, but are more easily formable. FEP is softer than PTFE and melts at 260 °C; it is highly transparent and resistant to sunlight.

Properties and applications
Amongst many other industrial applications, PTFE is used to coat certain types of hardened, armour-piercing bullets, so as to reduce the amount of wear on the firearm's rifling. These are often mistakenly referred to as "cop-killer" bullets by virtue of PTFE's supposed ability to ease a bullet's passage through body armour. Any armour-piercing effect is, however, purely a function of the bullet's velocity and rigidity rather than a property of PTFE.

PTFE has excellent dielectric properties. This is especially true at high radio frequencies, making it eminently suitable for use as an insulator in cables and connector assemblies and as a material for printed circuit boards used at microwave frequencies. Combined with its high melting temperature, this makes it the material of choice as a high performance substitute for the weaker and more meltable polyethylene that is commonly used in low-cost applications. Its extremely high bulk resistivity makes it an ideal material for fabricating long life electrets, useful devices that are the electrostatic analogues of magnets.

Due to its low friction, it is used for applications where sliding action of parts is needed:: bearings, bushings, gears, slide plates, etc. In these applications it performs significantly better than nylon and acetal; it is comparable with ultra high molecular weight polyethylene (UHMWPE), although UHMWPE is more resistant to wear than Teflon. For these applications, versions of PTFE with mineral oil or molybdenum disulfide embedded as additional lubricants in its matrix are being manufactured.

Because of its chemical inertness, PTFE cannot be cross-linked like an elastomer. Therefore it has no "memory", and is subject to creep (also known as cold flow and compression set). This can be both good and bad. A little bit of creep allows PTFE seals to conform to mating surfaces better than most other plastic seals. Too much creep, however, and the seal is compromised. Compounding fillers are used to control unwanted creep, as well as to improve wear, friction, and other properties.

Gore-Tex is a material incorporating PTFE membrane with micropores. The roof of the Hubert H. Humphrey Metrodome in Minneapolis is the largest application of PTFE on Earth, using 20 acres of the material in a double-layered white dome, made with PTFE-coated fiberglass, that gives the stadium its distinctive appearance.

It also, due to its flexibility and bio-compatibility is used in body piercing, such as in a Corset piercing.

Powdered PTFE is used in pyrotechnic compositions as oxidizer together with powdered metals such as aluminium and magnesium (see Magnesium/PTFE/Viton). Upon ignition these mixtures form carbonaceous soot and the corresponding metal fluoride and release large amounts of heat. Hence they are use as infrared decoy flares and igniters for solid fuel rocket propellant