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Polytetrafluoroethylene (PTFE) is a synthetic
fluoropolymer A fluoropolymer is a fluorocarbon-based polymer with multiple carbon–fluorine bonds. It is characterized by a high resistance to solvents, acids, and bases. The best known fluoropolymer is polytetrafluoroethylene under the brand name "Teflon, ...
of
tetrafluoroethylene Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2 F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers. Properties Tetrafluoroethylene is a ...
that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chemours, a
spin-off Spin-off may refer to: *Spin-off (media), a media work derived from an existing work *Corporate spin-off, a type of corporate action that forms a new company or entity * Government spin-off, civilian goods which are the result of military or gove ...
from DuPont, which originally discovered the compound in 1938. Polytetrafluoroethylene is a
fluorocarbon Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often has distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Fluorocarbons and their derivatives are commerci ...
solid, as it is a high-
molecular-weight The molecular mass (''m'') is the mass of a given molecule: it is measured in daltons (Da or u). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The related quant ...
polymer consisting wholly of
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
and fluorine. PTFE is
hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, ...
: neither water nor water-containing substances wet PTFE, as fluorocarbons exhibit only small
London dispersion force London dispersion forces (LDF, also known as dispersion forces, London forces, instantaneous dipole–induced dipole forces, fluctuating induced dipole bonds or loosely as van der Waals forces) are a type of intermolecular force acting between at ...
s due to the low
electric polarizability Polarizability usually refers to the tendency of matter, when subjected to an electric field, to acquire an electric dipole moment in proportion to that applied field. It is a property of all matter, considering that matter is made up of elementar ...
of fluorine. PTFE has one of the lowest coefficients of
friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding (motion), sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative la ...
of any solid. Polytetrafluoroethylene is used as a
non-stick coating A non-stick surface is engineered to reduce the ability of other materials to stick to it. Non-stick cookware is a common application, where the non-stick coating allows food to brown without sticking to the pan. Non-stick is often used to refer ...
for pans and other cookware. It is non-reactive, partly because of the strength of
carbon–fluorine bond The carbon–fluorine bond is a polar covalent bond between carbon and fluorine that is a component of all organofluorine compounds. It is one of the strongest single bonds in chemistry (after the B–F single bond, Si–F single bond, and H– ...
s, so it is often used in containers and pipework for reactive and corrosive chemicals. Where used as a
lubricant A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...
, PTFE reduces friction, wear, and energy consumption of machinery. It is used as a graft material in surgery and as a coating on
catheter In medicine, a catheter (/ˈkæθətər/) is a thin tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. Cat ...
s.


History

Polytetrafluoroethylene 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 Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and pro ...
refrigerant, the
tetrafluoroethylene Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2 F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers. Properties Tetrafluoroethylene is a ...
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. Kinetic Chemicals patented the new fluorinated plastic (analogous to the already known
polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including ...
) in 1941, and registered the Teflon trademark in 1945. 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 Parkersburg is a city in and the county seat of Wood County, West Virginia. Located at the confluence of the Ohio and Little Kanawha rivers, it is the state's fourth-largest city and the largest city in the Parkersburg-Marietta-Vienna metrop ...
. An early use was in the
Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
as a material to coat valves and seals in the pipes holding highly reactive
uranium hexafluoride Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...
at the vast
K-25 K-25 was the codename given by the Manhattan Project to the program to produce enriched uranium for atomic bombs using the gaseous diffusion method. Originally the codename for the product, over time it came to refer to the project, the produ ...
uranium enrichment Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238 ...
plant in
Oak Ridge, Tennessee Oak Ridge is a city in Anderson and Roane counties in the eastern part of the U.S. state of Tennessee, about west of downtown Knoxville. Oak Ridge's population was 31,402 at the 2020 census. It is part of the Knoxville Metropolitan Area. O ...
. In 1954, Colette Grégoire, the wife of French engineer Marc Grégoire, urged him 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).Teflon History
, ''home.nycap.rr.com'', Retrieved 25 January 2009.
In the United States,
Marion A. Trozzolo Marion A. Trozzolo (1925 – June 30, 1992) was an innovator, inventor, entrepreneur, and professor of business at Rockhurst University in Kansas City, Missouri. He was the first manufacturer of teflon coated cookware in the United States, an ...
, who had been using the substance on scientific utensils, marketed the first US-made PTFE-coated pan, "The Happy Pan", in 1961.Robbins, William (21 December 1986)
Teflon Maker: Out Of Frying Pan Into Fame
, ''
New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...
'', Retrieved 21 December 1986 (Subscription)
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. In the 1990s, it was found that PTFE could be radiation cross-linked above its melting point in an oxygen-free environment. Electron beam processing is one example of radiation processing. Cross-linked Polytetrafluoroethylene 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 Polytetrafluoroethylene for recycling. 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.


Production

PTFE is produced by free-radical
polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
of
tetrafluoroethylene Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2 F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers. Properties Tetrafluoroethylene is a ...
. The net equation is : ''n'' F2C=CF2 → −(F2C−CF2)''n''− Because tetrafluoroethylene can explosively decompose to
tetrafluoromethane Tetrafluoromethane, also known as carbon tetrafluoride or R-14, is the simplest perfluorocarbon ( C F4). As its IUPAC name indicates, tetrafluoromethane is the perfluorinated counterpart to the hydrocarbon methane. It can also be classified as a h ...
(CF4) and carbon, special apparatus is required for the polymerization to prevent hot spots that might initiate this dangerous side reaction. The process is typically initiated with persulfate, which homolyzes to generate sulfate radicals: : 3SO−OSO3sup>2− ⇌ 2 The resulting polymer is terminated with
sulfate ester Organosulfates are a class of organic compounds sharing a common functional group with the structure R-O-SO3−. The SO4 core is a sulfate group and the R group is any organic residue. All organosulfates are formally esters derived from alcohols ...
groups, which can be hydrolyzed to give OH
end-group End groups are an important aspect of polymer synthesis and characterization. In polymer chemistry, they are functional groups that are at the very ends of a macromolecule or oligomer ( IUPAC). In polymer synthesis, like condensation polyme ...
s.Carlson, D. Peter and Schmiegel, Walter (2000) "Fluoropolymers, Organic" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim. Granular PTFE is produced via suspension polymerization, where PTFE is suspended in an aqueous medium primarily via agitation and sometimes with the use of a surfactant such as
perfluorooctanesulfonic acid Perfluorooctanesulfonic acid (PFOS) ( conjugate base perfluorooctanesulfonate) is a chemical compound having an eight-carbon fluorocarbon chain and a sulfonic acid functional group and thus a perfluorosulfonic acid. It is an anthropogenic (man ...
(PFOS) or FRD-903 (GenX). PTFE is also synthesized via emulsion polymerization, where a surfactant is the primary means of keeping PTFE in an aqueous medium.


Properties

PTFE is a
thermoplastic A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains associat ...
polymer A polymer (; Greek ''poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...
, which is a white solid at room temperature, with a density of about 2200 kg/m3 and a melting point of .Fluoroplastic Comparison – Typical Properties
Chemours.com, Retrieved 16 January 2018.
It maintains high strength, toughness and self-lubrication at low temperatures down to , and good flexibility at temperatures above .Teflon PTFE Properties Handbook
Retrieved 11 October 2012.
PTFE gains its properties from the aggregate effect of carbon-fluorine bonds, as do all fluorocarbons. The only chemicals known to affect these carbon-fluorine bonds are highly reactive metals like the alkali metals, and at higher temperatures also such metals as aluminum and magnesium, and fluorinating agents such as
xenon difluoride Xenon difluoride is a powerful fluorinating agent with the chemical formula , and one of the most stable xenon compounds. Like most covalent inorganic fluorides it is moisture-sensitive. It decomposes on contact with water vapor, but is otherwi ...
and cobalt(III) fluoride. At temperatures above PTFE undergoes depolymerization. The
coefficient of friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of tw ...
of plastics is usually measured against polished steel. PTFE's coefficient of friction is 0.05 to 0.10, which is the third-lowest of any known solid material ( aluminium magnesium boride (BAM) being the first, with a coefficient of friction of 0.02;
diamond-like carbon Diamond-like carbon (DLC) is a class of amorphous carbon material that displays some of the typical properties of diamond. DLC is usually applied as coatings to other materials that could benefit from such properties. DLC exists in seven diff ...
being second-lowest at 0.05). PTFE's resistance to
van der Waals force In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and t ...
s means that it is the only known surface to which a
gecko Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates throughout the world. They range from . Geckos ar ...
cannot stick.Research into Gecko Adhesion
, '' Berkeley'', 2007-10-14. Retrieved 8 April 2010.
In fact, PTFE can be used to prevent insects from climbing up surfaces painted with the material. PTFE is so slippery that insects cannot get a grip and tend to fall off. For example, PTFE is used to prevent ants from climbing out of formicaria. Because of its superior chemical and thermal properties, PTFE is often used as a gasket material within industries that require resistance to aggressive chemicals such as pharmaceuticals or chemical processing. However, until the 1990s, PTFE was not known to crosslink like an
elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic ...
, due to its chemical inertness. Therefore, it has no "memory" and is subject to
creep Creep, Creeps or CREEP may refer to: People * Creep, a creepy person Politics * Committee for the Re-Election of the President (CRP), mockingly abbreviated as CREEP, an fundraising organization for Richard Nixon's 1972 re-election campaign Art ...
. Because of the propensity to creep, the long-term performance of such seals is worse than for elastomers that exhibit zero, or near-zero, levels of creep. In critical applications, Belleville washers are often used to apply continuous force to PTFE gaskets, thereby ensuring a minimal loss of performance over the lifetime of the gasket. PTFE is an
Ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiati ...
(UV) transparent polymer. However, when exposed to an
excimer laser An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and micr ...
beam it severely degrades due to heterogeneous photothermal effect.


Processing

Processing PTFE can be difficult and expensive, because the high melting temperature, , is above the initial decomposition temperature, . Even when molten, PTFE does not flow due to its exceedingly high melt-viscosity. The viscosity and melting point can be decreased by inclusion of small amount of
comonomer In polymer chemistry, a comonomer refers to a polymerizable precursor to a copolymer aside from the principal monomer. In some cases, only small amounts of a comonomer are employed, in other cases substantial amounts of comonomers are used. Furthe ...
s such as perfluoro (propylvinyl ether) and hexafluoropropylene (HFP). These cause the otherwise perfectly linear PTFE chain to become branched, reducing its crystallinity. Some PTFE parts are made by cold-moulding, a form of
compression molding Compression molding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material int ...
. Here, fine powdered PTFE is forced into a mould under high pressure (10–100 MPa). After a settling period, lasting from minutes to days, the mould is heated at , allowing the fine particles to fuse (
sinter Sinter may refer to: * Sinter plant, in which iron-ore dust gets mixed with other fine materials at high temperature, to create a product – sinter – for use in a blast furnace * Sintering, a high temperature process for fusing powder together ...
) into a single mass.


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 In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the m ...
properties, specifically low
group velocity dispersion In optics, group velocity dispersion (GVD) is a characteristic of a dispersive medium, used most often to determine how the medium will affect the duration of an optical pulse traveling through it. Formally, GVD is defined as the derivative of the ...
,Extract of page 574
/ref> especially at high radio frequencies, making it suitable for use as an excellent insulator in
connector Connector may refer to: Hardware *Plumbing * Electrical connector, a device for joining electrical circuits together (sometimes known as ports, plugs, or interfaces) ** Gender of connectors and fasteners ** AC power plugs and sockets, devices tha ...
assemblies and cables, and in
printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich str ...
s used at
microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequency, frequencies between 300 MHz and 300 GHz respectively. Different sources define different fre ...
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 Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including ...
commonly used in low-cost applications.


Bearings seals

In industrial applications, owing to its low friction, PTFE is used for
plain bearing A plain bearing, or more commonly sliding contact bearing and slide bearing (in railroading sometimes called a solid bearing, journal bearing, or friction bearing), is the simplest type of bearing, comprising just a bearing surface and no roll ...
s,
gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic p ...
s, slide plates, seals, gaskets, bushings, and more applications with sliding action of parts, where it outperforms
acetal In organic chemistry, an acetal is a functional group with the connectivity . Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragment ...
and
nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic. Nylon is a silk-like thermoplastic, generally made from pet ...
.


Electrets

Its extremely high bulk
resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
makes it an ideal material for fabricating long-life
electret An electret (formed as a portmanteau of ''electr-'' from "electricity" and ''-et'' from "magnet") is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric f ...
s, the
electrostatic Electrostatics is a branch of physics that studies electric charges at rest (static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for am ...
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 The Hubert H. Humphrey Metrodome (commonly called the Metrodome) was a domed sports stadium located in downtown Minneapolis, Minnesota. It opened in 1982 as a replacement for Metropolitan Stadium, the former home of the National Football League' ...
in
Minneapolis Minneapolis () is the largest city in Minnesota, United States, and the county seat of Hennepin County. The city is abundant in water, with list of lakes in Minneapolis, thirteen lakes, wetlands, the Mississippi River, creeks and waterfalls. ...
, US, was one of the largest applications of PTFE coatings. 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 A hose is a flexible hollow tube designed to carry fluids from one location to another. Hoses are also sometimes called ''pipes'' (the word ''pipe'' usually refers to a rigid tube, whereas a hose is usually a flexible one), or more generally ' ...
assemblies,
expansion joint An expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials, and vibration, or to allow movement due to ground settlement or seis ...
s, 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.


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. Brands include GT85.


Kitchen ware

PTFE is best known for its use in coating non-stick
frying pan A frying pan, frypan, or skillet is a flat-bottomed pan used for frying, searing, and browning foods. It is typically in diameter with relatively low sides that flare outwards, a long handle, and no lid. Larger pans may have a small grab ha ...
s and other cookware, as it is
hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, ...
and possesses fairly high heat resistance. The sole plates of some clothes irons are coated with PTFE.


Others

Other niche applications include: *It is often found in
ski binding A ski binding is a device that connects a ski boot to the ski. Before the 1933 invention of ski lifts, skiers went uphill and down and cross-country on the same gear. As ski lifts became more prevalent, skis—and their bindings—became increasin ...
s 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. *It is used widely as a fabric protector to repel stains on formal school-wear, like uniform blazers. *It is frequently used as a lubricant to prevent captive insects and other
arthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, oft ...
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. *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. *Expanded PTFE membranes have been used in trials to assist
trabeculectomy Trabeculectomy is a surgical procedure used in the treatment of glaucoma to relieve intraocular pressure by removing part of the eye's trabecular meshwork and adjacent structures. It is the most common glaucoma surgery performed and allows drain ...
surgery to treat glaucoma. *Powdered PTFE is used in pyrotechnic compositions as an
oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...
with powdered metals such as
aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It h ...
and
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
. Upon ignition, these mixtures form carbonaceous
soot Soot ( ) is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyse ...
and the corresponding metal
fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts ...
, and release large amounts of heat. They are used in infrared decoy flares and as igniters for
solid-fuel rocket A solid-propellant rocket or solid rocket is a rocket with a rocket engine that uses solid propellants (fuel/ oxidizer). The earliest rockets were solid-fuel rockets powered by gunpowder; they were used in warfare by the Arabs, Chinese, Persi ...
propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or other motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the ...
s. Aluminum and PTFE is also used in some
thermobaric A thermobaric weapon, also called an aerosol bomb, a vacuum bomb or a fuel air explosive (FAE), is a type of explosive that uses oxygen from the surrounding air to generate a high-temperature explosion. The fuel–air explosive is one of the b ...
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. *In optical
radiometry Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which ch ...
, sheets of PTFE are used as measuring heads in spectroradiometers and broadband radiometers (e.g.,
illuminance In photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate with human brightn ...
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 Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from aroun ...
. 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 In optics, Lambert's cosine law says that the radiant intensity or luminous intensity observed from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to the cosine of the angle ''θ'' between the direction ...
. 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 In firearms, rifling is machining helical grooves into the internal (bore) surface of a gun's barrel for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting to stabilize ...
of firearms that uncoated projectiles would cause. PTFE itself does not give a projectile an armor-piercing property. *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 Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepr ...
, which will dissolve glass containers. It is used in containers for storing
fluoroantimonic acid Fluoroantimonic acid is a mixture of hydrogen fluoride and antimony pentafluoride, containing various cations and anions (the simplest being and ). This substance is a superacid that can be over a billion times stronger than 100% pure sulfuric ac ...
, a superacid. *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 Thread seal tape (also known as PTFE tape, Teflon tape, or plumber's tape) is a polytetrafluoroethylene (PTFE) film tape commonly used in plumbing for sealing pipe threads. The tape is sold cut to specific widths and wound on a spool, making it ...
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 system A dust collection system is an air quality improvement system used in industrial, commercial, and home production shops to improve breathable air quality and safety by removing particulate matter from the air and environment. Dust collection syste ...
s to collect
particulate matter Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The t ...
from air streams in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production and steel foundries. *PTFE grafts can be used to bypass
stenotic A stenosis (from Ancient Greek στενός, "narrow") is an abnormal narrowing in a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture). ''Stricture'' ...
arteries An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...
in peripheral vascular disease if a suitable autologous
vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenate ...
graft is not available. * Many bicycle lubricants and greases contain PTFE and are used on
chains A chain is a wikt:series#Noun, serial assembly of connected pieces, called links, typically made of metal, with an overall character similar to that of a rope in that it is flexible and curved in compression (physics), compression but line (g ...
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. * PTFE sheets are used in the production of
butane hash oil Hash oil or cannabis oil, is an oleoresin obtained by the extraction of cannabis or hashish. It is a cannabis concentrate containing many of its resins and terpenes – in particular, tetrahydrocannabinol (THC), cannabidiol (CBD), and other can ...
due to its non-stick properties and resistance to non-polar solvents. * 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; 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. *PTFE has been experimented with for electroless nickel plating. *PTFE tubing is used for Bowden tubing in
3D printers 3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer ...
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 , it decomposes above , and
pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''p ...
occurs at temperatures above . The main decomposition products are
fluorocarbon Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often has distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Fluorocarbons and their derivatives are commerci ...
gases and a sublimate, including
tetrafluoroethylene Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2 F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers. Properties Tetrafluoroethylene is a ...
(TFE) and difluorocarbene
radicals Radical may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...
(RCF2). 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 . Above those temperatures the degradation by-products can be lethal to
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s, and can cause flu-like symptoms in humans (
polymer fume fever __NOTOC__ Polymer fume fever or fluoropolymer fever, also informally called Teflon flu, is an inhalation fever caused by the fumes released when polytetrafluoroethylene (PTFE, known under the trade name Teflon) reaches temperatures of 300 ° ...
), although in humans those symptoms disappears within a day or two of being moved to fresh air. Most cases of polymer fume fever in humans occur due to smoking PTFE-contaminated tobacco, although cases have occurred in people who have welded near PTFE components or heated PTFE-coated cookware at for at least 4 hours. Teflon-coated cookware is unlikely to reach dangerous temperatures with normal use, as meat is usually fried between , and most
cooking oil Cooking oil is plant, animal, or synthetic liquid fat used in frying, baking, and other types of cooking. It is also used in food preparation and flavoring not involving heat, such as salad dressings and bread dips, and may be called edible oi ...
s (except refined
safflower Safflower (''Carthamus tinctorius'') is a highly branched, herbaceous, thistle-like annual plant in the family Asteraceae. It is commercially cultivated for vegetable oil extracted from the seeds and was used by the early Spanish colonies a ...
and
avocado The avocado (''Persea americana'') is a medium-sized, evergreen tree in the laurel family (Lauraceae). It is native to Americas, the Americas and was first domesticated by Mesoamerica, Mesoamerican tribes more than 5,000 years ago. Pre-Columb ...
oils) start to
smoke Smoke is a suspension of airborne particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrainment (engineering), entrained or otherwise mixed into the mass. It is commo ...
before a temperature of is reached. A 1973 study by DuPont's Haskell Laboratory found that a 4-hour exposure to the fumes emitted by teflon cookware heated to was lethal for
parakeets A parakeet is any one of many small to medium-sized species of parrot, in multiple genera, that generally has long tail feathers. Etymology and naming The name ''parakeet'' is derived from the French wor''perroquet'' which is reflected in ...
, although that was a higher temperature than the required for fumes from pyrolyzed butter to be lethal to the birds.
Perfluorooctanoic acid Perfluorooctanoic acid (PFOA; conjugate base perfluorooctanoate; also known colloquially as C8, for its 8 carbon chain structure) is a perfluorinated carboxylic acid produced and used worldwide as an industrial surfactant in chemical processes an ...
(PFOA), a chemical formerly used in the manufacture of PTFE products such as non-stick coated cookware, can be
carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subst ...
ic for people who are exposed to it (see Ecotoxicity). 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 wax Ski wax is a material applied to the bottom of snow runners, including skis, snowboards, and toboggans, to improve their coefficient of friction performance under varying snow conditions. The two main types of wax used on skis are glide waxes a ...
es and stain-resistant fabric coatings, but non-stick cookware was not found to be major sources of exposure as the PFOA is burned off during the manufacturing process and not present in the finished product. Non-stick coated cookware has not been manufactured using PFOA since 2013, and PFOA is no longer being made in the United States.


Ecotoxicity


Trifluoroacetate

Sodium trifluoroacetate and the similar compound chlorodifluoroacetate can both be generated when PTFE undergoes thermolysis, as well as producing longer chain polyfluoro- and/or polychlorofluoro- (C3-C14) carboxylic acids which may be equally persistent. These products can accumulate in evaporative
wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...
s and have been found in the roots and seeds of wetland plant species, but has not been observed to have an adverse impact on plant health or germination success.


PFOA

Perfluorooctanoic acid (PFOA, or C8) has been used as a
surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, fo ...
in the emulsion polymerization of PTFE, although several manufacturers have entirely discontinued its use. PFOA persists indefinitely in the environment. PFOA has been detected in the blood of many individuals of the general US population in the low and sub-
parts per billion In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, th ...
range, and levels are higher in chemical plant employees and surrounding subpopulations. PFOA and
perfluorooctanesulfonic acid Perfluorooctanesulfonic acid (PFOS) ( conjugate base perfluorooctanesulfonate) is a chemical compound having an eight-carbon fluorocarbon chain and a sulfonic acid functional group and thus a perfluorosulfonic acid. It is an anthropogenic (man ...
(PFOS) have been estimated to be in every American person’s blood stream in the parts per billion range, though those concentrations have decreased by 70% for PFOA and 84% for PFOS between 1999 and 2014, which coincides with the end of the production and phase out of PFOA and PFOS in the US. The general population has been exposed to PFOA through massive dumping of C8 waste into the ocean and near the Ohio River Valley. PFOA has been detected in industrial waste, stain-resistant carpets, carpet cleaning liquids, house dust, microwave popcorn bags, water, food and PTFE cookware. As a result of a class-action lawsuit and community settlement with DuPont, three
epidemiologists Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evide ...
conducted studies on the population surrounding a chemical plant that was exposed to PFOA at levels greater than in the general population. The studies concluded that there was an association between PFOA exposure and six health outcomes: kidney cancer, testicular cancer,
ulcerative colitis Ulcerative colitis (UC) is a long-term condition that results in inflammation and ulcers of the colon and rectum. The primary symptoms of active disease are abdominal pain and diarrhea mixed with blood ( hematochezia). Weight loss, fever, an ...
, thyroid disease,
hypercholesterolemia Hypercholesterolemia, also called high cholesterol, is the presence of high levels of cholesterol in the blood. It is a form of hyperlipidemia (high levels of lipids in the blood), hyperlipoproteinemia (high levels of lipoproteins in the bloo ...
(high cholesterol), and pregnancy-induced hypertension. Overall, PTFE cookware is considered a minor exposure pathway to PFOA.


GenX

As a result of the lawsuits concerning the PFOA class-action lawsuit, DuPont began to use GenX, a similarly fluorinated compound, as a replacement for perfluorooctanoic acid in the manufacture of
fluoropolymer A fluoropolymer is a fluorocarbon-based polymer with multiple carbon–fluorine bonds. It is characterized by a high resistance to solvents, acids, and bases. The best known fluoropolymer is polytetrafluoroethylene under the brand name "Teflon, ...
s, such as Teflon-brand PTFE. However, in lab tests on rats, GenX has been shown to cause many of the same health problems as PFOA. The chemicals are manufactured by Chemours, a corporate spin-off of DuPont, in
Fayetteville, North Carolina Fayetteville () is a city in and the county seat of Cumberland County, North Carolina, Cumberland County, North Carolina, United States. It is best known as the home of Fort Bragg, a major U.S. Army installation northwest of the city. Fayettev ...
. While PFOA was phased out by 2014, Chemours was already found to be dumping GenX into the
Cape Fear River The Cape Fear River is a long blackwater river in east central North Carolina. It flows into the Atlantic Ocean near Cape Fear, from which it takes its name. The river is formed at the confluence of the Haw River and the Deep River (North Ca ...
in 2017, with the North Carolina Department of Environmental Quality (NCDEQ) ordering Chemours to halt discharges of all fluorinated compounds on September 5, 2017.


Similar polymers

The Teflon trade name is also used for other polymers with similar compositions: * Perfluoroalkoxy alkane (PFA) *
Fluorinated ethylene propylene Fluorinated ethylene propylene (FEP) is a copolymer of hexafluoropropylene and tetrafluoroethylene. It differs from the polytetrafluoroethylene (PTFE) resins in that it is melt-processable using conventional injection molding and screw extrusion ...
(FEP) These retain the useful PTFE properties of low friction and nonreactivity, but are also more easily formable. For example, FEP is softer than PTFE and melts at ; it is also highly transparent and resistant to sunlight.FEP Detailed Properties
Parker-TexLoc, 13 April 2006. Retrieved 10 September 2006.


See also

* BS 4994, PTFE as a thermoplastic lining for dual laminate chemical process plant equipment * ''Dark Waters'', a film about litigation related to PFOA * ''The Devil We Know'', documentary on PFOA's health and environmental effects *
ETFE Ethylene tetrafluoroethylene (ETFE) is a fluorine-based plastic. It was designed to have high corrosion resistance and strength over a wide temperature range. ETFE is a polymer and its source-based name is poly(ethene-co-tetrafluoroethene). It i ...
* Gore-Tex waterproof fabric * Magnesium/Teflon/Viton, pyrolant thermite composition * Polymer adsorption * Superhydrophobic coating *
Surface treatment of PTFE Polytetrafluoroethylene (PTFE), better known by its trade name Teflon, has many desirable properties which make it an attractive material for numerous industries. It has good chemical resistance, a low dielectric constant, low dielectric loss, and a ...


Notes


References


Further reading

*


External links


Plasma Processes and Adhesive Bonding of Polytetrafluoroethylene

PTFE (polytetrafluoroethylene) (Properties) , Fluorotherm.com
{{DEFAULTSORT:Polytetrafluoroethylene American inventions Biomaterials Dielectrics Dry lubricants DuPont DuPont products Fluorocarbons Fluoropolymers Plastics Pyrotechnic oxidizers Roofing materials Engineering plastic