Teflon

Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene and is a PFAS that has numerous applications. The commonly known brand name of PTFE-based composition is Teflon by Chemours,^[3] a spin-off from DuPont, which originally discovered the compound in 1938.^[3]

Polytetrafluoroethylene is a fluorocarbon solid, as it is a high-molecular-weight polymer consisting wholly of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons exhibit only small London dispersion forces due to the low electric polarizability of fluorine. PTFE has one of the lowest coefficients of friction of any solid.

Polytetrafluoroethylene is used as a non-stick coating for pans and other cookware. It is non-reactive, partly because of the strength of carbon–fluorine bonds, so it is often used in containers and pipework for reactive and corrosive chemicals. Where used as a lubricant, PTFE reduces friction, wear, and energy consumption of machinery. It is used as a graft material in surgery and as a coating on catheters.

PTFE is one of the best-known and widely applied PFAS commonly described as persistent organic pollutants or "forever chemicals". Only since the start of the 21st century has the environmental impact and toxicity to human and mammalian life been studied in depth.

History

Advertisement of the Happy Pan, a Teflon-coated pan from the 1960s

External audio
"From stove tops to outer space... Teflon touches every one of us some way almost every day.", Roy Plunkett, Science History Institute

Advertisement for Zepel, the trade name used to market Teflon as a fabric treatment

PTFE thermal cover showing impact craters, from NASA's Ultra Heavy Cosmic Ray Experiment (UHCRE) on the Long Duration Exposure Facility (LDEF)

Logo of Teflon, the commonly known brand name of PTFE-based compositions manufactured by Chemours

Polytetrafluoroethylene (PTFE) was accidentally discovered in 1938 by Roy J. Plunkett while he was working in New Jersey for DuPont. As Plunkett attempted to make a new chlorofluorocarbon refrigerant, the tetrafluoroethylene gas in its pressure bottle stopped flowing before the bottle's weight had dropped to the point signaling "empty".

Since Plunkett was measuring the amount of gas used by weighing the bottle, he became curious as to the source of the weight, and finally resorted to sawing the bottle apart. He found the bottle's interior coated with a waxy white material that was oddly slippery. Analysis showed that it was polymerized perfluoroethylene, with the iron from the inside of the container having acted as a catalyst at high pressure.^[4] Kinetic Chemicals patented the new fluorinated plastic (analogous to the already known polyethylene) in 1941,^[5] and registered the Teflon trademark in 1945.^[6][7]

By 1948, DuPont, which founded Kinetic Chemicals in partnership with General Motors, was producing over two million pounds (900 tons) of Teflon brand Polytetrafluoroethylene per year in Parkersburg, West Virginia.^[8] An early use was in the Manhattan Project as a material to coat valves and seals in the pipes holding highly reactive uranium hexafluoride at the vast K-25 uranium enrichment plant in Oak Ridge, Tennessee.^[9]

In 1954, Colette Grégoire urged her husband, the French engineer Marc Grégoire, to try the material he had been using on fishing tackle on her cooking pans. He subsequently created the first PTFE-coated, non-stick pans under the brand name Tefal (combining "Tef" from "Teflon" and "al" from aluminium).^[10] In the United States, Marion A. Trozzolo, who had been using the substance on scientific utensils, marketed the first US-made PTFE-coated pan, "The Happy Pan", in 1961.^[11] Non-stick cookware has since become a common household product, now offered by hundreds of manufacturers across the world.

The brand name Zepel was used for promoting its stain-resistance and water-resistance when applied to fabrics.^[12]

In the 1990s, it was found that PTFE could be radiation cross-linked above its melting point in an oxygen-free environment.^[13] Electron beam processing is one example of radiation processing. Cross-linked PTFE has improved high-temperature mechanical properties and radiation stability. This was significant because, for many years, irradiation at ambient conditions has been used to break down PTFE for recycling.^[14] This radiation-induced chain scission allows it to be more easily reground and reused.

Corona discharge treatment of the surface to increase the energy and improve adhesion has been reported.^[15]

Production

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Applications and uses|

Wire insulation, electronics

The major application of PTFE, consuming about 50% of production, is for the insulation of wiring in aerospace and computer applications (e.g. hookup wire, coaxial cables). This application exploits the fact that PTFE has excellent dielectric properties, specifically low group velocity dispersion,^[39] especially at high radio frequencies,^[39] making it suitable for use as an excellent insulator in connector assemblies and cables, and in 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, higher dispersion and lower-melting-point polyethylene commonly used in low-cost applications.

Bearings seals

In industrial applications, owing to its low friction, PTFE is used for plain bearings, gears, slide plates, seals, gaskets, bushings,^[40] and more applications with sliding action of parts, where it outperforms acetal and nylon.^[41]

Electrets

Its extremely high bulk resistivity makes it an ideal material for fabricating long-life electrets, the electrostatic analogues of permanent magnets.

Composites

PTFE film is also widely used in the production of carbon fiber composites as well as fiberglass composites, notably in the aerospace industry. PTFE film is used as a barrier between the carbon or fiberglass part being built, and breather and bagging materials used to incapsulate the bondment when debulking (vacuum removal of air from between layers of laid-up plies of material) and when curing the composite, usually in an autoclave. The PTFE, used here as a film, prevents the non-production materials from sticking to the part being built, which is sticky due to the carbon-graphite or fiberglass plies being pre-pregnated with bismaleimide resin. Non-production materials such as Teflon, Airweave Breather and the bag itself would be considered F.O.D. (foreign object debris/damage) if left in layup.

Gore-Tex is a brand of expanded PTFE (ePTFE), a material incorporating a fluoropolymer membrane with micropores. The roof of the Hubert H. Humphrey Metrodome in Minneapolis, US, was one of the largest applications of PTFE coatings. 20 acres (81,000 m²) of the material was used in the creation of the white double-layered PTFE-coated fiberglass dome.

Chemically inert liners

Because of its extreme non-reactivity and high temperature rating, PTFE is often used as the liner in hose assemblies, expansion joints, and in industrial pipe lines, particularly in applications using acids, alkalis, or other chemicals. Its frictionless qualities allow improved flow of highly viscous liquids, and for uses in applications such as brake hoses.

Tensioned Membrane Structures

PTFE architectural membranes are created by coating a woven glass-fibre base cloth with PTFE, forming one of the strongest and most durable materials used in Tensile structures. ^[42] Some notable structures featuring PTFE tensioned membranes include The O2 Arena in London, Moses Mabhida Stadium in South Africa, Metropolitano Stadium in Spain and the Sydney Football Stadium Roof in Australia.

Musical instruments

PTFE is often found in musical instrument lubrication products; most commonly, valve oil.

Lubricants

PTFE is used in some aerosol lubricant sprays, including in micronized and polarized form. It is notable for its extremely low coefficient of friction, its hydrophobia (which serves to inhibit rust), and for the dry film it forms after application, which allows it to resist collecting particles that might otherwise form an abrasive paste.^[43] Brands include GT85.^[44]

Two PTFE jars^{[clarification} ^needed]

Kitchen ware

PTFE is best known for its use in coating non-stick frying pans and other cookware, as it is hydrophobic and possesses fairly high heat resistance.

The sole plates of some clothes irons are coated with PTFE.^[45]

Others

Other niche applications include:

It is often found in ski bindings as a non-mechanical AFD (anti-friction device)
It can be stretched to contain small pores of varying sizes and is then placed between fabric layers to make a waterproof, breathable fabric in outdoor apparel.^[46]
It is used widely as a fabric protector to repel stains on formal school-wear, like uniform blazers.^[47]
It is frequently used as a lubricant to prevent captive insects and other arthropods from escaping.
It is used as a coating for medical and healthcare applications formulated to provide strength and heat resistance to surgical devices and other medical equipment. ^[48]
It is used as a film interface patch for sports and medical applications, featuring a pressure-sensitive adhesive backing, which is installed in strategic high friction areas of footwear, insoles, ankle-foot orthosis, and other medical devices to prevent and relieve friction-induced blisters, calluses and foot ulceration.^[49]
Expanded PTFE membranes have been used in trials to assist trabeculectomy surgery to treat glaucoma.^[50]
Powdered PTFE is used in pyrotechnic compositions as an oxidizer with powdered metals such as aluminium and magnesium. Upon ignition, these mixtures form carbonaceous soot and the corresponding metal fluoride, and release large amounts of heat. They are used in infrared decoy flares and as igniters for solid-fuel rocket propellants.^[51] Aluminium and PTFE is also used in some thermobaric fuel compositions.
Powdered PTFE is used in a suspension with a low-viscosity, azeotropic mixture of siloxane ethers to create a lubricant for use in twisty puzzles.^[52]
In optical radiometry, sheets of PTFE are used as measuring heads in spectroradiometers and broadband radiometers (e.g., illuminance meters and UV radiometers) due to PTFE's capability to diffuse a transmitting light nearly perfectly. Moreover, optical properties of PTFE stay constant over a wide range of wavelengths, from UV down to near infrared. In this region, the ratio of its regular transmittance to diffuse transmittance is negligibly small, so light transmitted through a diffuser (PTFE sheet) radiates like Lambert's cosine law. Thus PTFE enables cosinusoidal angular response for a detector measuring the power of optical radiation at a surface, e.g. in solar irradiance measurements.
Teflon-coated bullets are coated with PTFE to reduce wear on the rifling of firearms that uncoated projectiles would cause. PTFE itself does not give a projectile an armor-piercing property.^[53]
Its high corrosion resistance makes PTFE useful in laboratory environments, where it is used for lining containers, as a coating for magnetic stirrers, and as tubing for highly corrosive chemicals such as hydrofluoric acid, which will dissolve glass containers. It is used in containers for storing fluoroantimonic acid, a superacid.^[54]
PTFE tubes are used in gas-gas heat exchangers in gas cleaning of waste incinerators. Unit power capacity is typically several megawatts.
PTFE is widely used as a thread seal tape in plumbing applications, largely replacing paste thread dope.
PTFE membrane filters are among the most efficient industrial air filters. PTFE-coated filters are often used in dust collection systems to collect particulate matter from air streams in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production and steel foundries.^[55]
PTFE grafts can be used to bypass stenotic arteries in peripheral vascular disease if a suitable autologous vein graft is not available.
Many bicycle lubricants and greases contain PTFE and are used on chains and other moving parts subjected to frictional forces (such as hub bearings).
PTFE is used for some types of dental floss.
PTFE can also be used when placing dental fillings, to isolate the contacts of the adjacent tooth so the restorative materials will not stick to the adjacent tooth.^[56][57]
PTFE sheets are used in the production of butane hash oil due to its non-stick properties and resistance to non-polar solvents.^[58]
PTFE, associated with a slightly textured laminate, makes the plain bearing system of a Dobsonian telescope.
PTFE is widely used as a non-stick coating for food processing equipment;^[59] dough hoppers, mixing bowls, conveyor systems, rollers, and chutes. PTFE can also be reinforced where abrasion is present – for equipment processing seeded or grainy dough for example.^[60]
PTFE has been experimented with for electroless nickel plating.
PTFE tubing is used for Bowden tubing in 3D printers because its low friction allows the extruder stepper motor to push filament through it more easily.
PTFE is commonly used in aftermarket add-on mouse feet for gaming mice to reduce friction of the mouse against the mouse pad, resulting in a smoother glide.
PTFE foils are commonly used with laserprinters everywhere, in their fuser unit, wrapped around the heater element(s) and as well on the opposite pressure roller to prevent any kind of sticking to it (neither the printed paper nor toner waste)
PTFE is also used to make body jewellery as it's much safer to wear compared to materials like acrylic, that release toxics into the body at 26.6°C, unlike PTFE at 650–700°C.
PTFE is used to make bookbinding tools for folding, scoring and separating sheets of paper. These are typically referred to as Teflon bone folders.

Safety

While PTFE is stable and nontoxic at lower temperatures, it begins to deteriorate at temperatures of about 260 °C (500 °F), it decomposes above 350 °C (662 °F), and pyrolysis occurs at temperatures above 400 °C (752 °F).^[61] The main decomposition products are fluorocarbon gases and a sublimate, including tetrafluoroethylene (TFE) and difluorocarbene radicals (RCF2).^[61]

An animal study conducted in 1955 concluded that it is unlikely that these products would be generated in amounts significant to health at temperatures below 250 °C (482 °F).^[33] Above those temperatures the degradation by-products can be lethal to birds,^[62] and can cause flu-like symptoms in humans (polymer fume fever),^[63] although in humans those symptoms disappear within a day or two of being moved to fresh air.^[64]

Most cases of polymer fume fever in humans occur due to smoking PTFE-contaminated tobacco,^[64] although cases have occurred in people who have welded near PTFE components^[64] or heated PTFE-coated cookware at 390 °C (734 °F) for at least 4 hours.^[65] PTFE-coated cookware is unlikely to reach dangerous temperatures with normal use, as meat is usually fried between 204 and 232 °C (399 and 450 °F), and most cooking oils (except refined safflower and avocado oils) start to smoke before a temperature of 260 °C (500 °F) is reached. A 1973 study by DuPont's Haskell Laboratory found that a 4-hour exposure to the fumes emitted by PTFE cookware heated to 280 °C (536 °F) was lethal for parakeets, although that was a higher temperature than the 260 °C (500 °F) required for fumes from pyrolyzed butter to be lethal to the birds.^[66]

Perfluorooctanoic acid (PFOA), a chemical formerly used in the manufacture of PTFE products such as non-stick coated cookware, can be carcinogenic for people who are exposed to it (see Ecotoxicity).^[67] Concerning levels of PFOA have been found in the blood of people who work in or live near factories where the chemical is used, and in people regularly exposed to PFOA-containing products such as some ski waxes and stain-resistant fabric coatings, but non-stick cookware was not found to be a major source of exposure, as the PFOA is burned off during the manufacturing process and not present in the finished product.^[65][64] Non-stick coated cookware has not been manufactured using PFOA since 2013,^[68] and PFOA is no longer being made in the United States.^[67]