Everything about Ptfe totally explained
| Section2 =
}}
In
chemistry,
poly(tetrafluoroethene) or
poly(tetrafluoroethylene) (
PTFE) is a synthetic
fluoropolymer which finds numerous applications. PTFE's most well known trademark in the industry is the
DuPont brand name
Teflon.
Water and water-containing substances like most foods don't wet PTFE, therefore adhesion to PTFE surfaces is inhibited. Due to this property PTFE is used as a
non-stick coating for pans and other cookware. It is very non-reactive, and so 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.
History
PTFE was accidentally invented by
Roy Plunkett of
Kinetic Chemicals in 1938. While Plunkett was attempting to make a new
CFC refrigerant, the
perfluorethylene polymerized in its pressurized storage container. (In this original chemical reaction, iron from the inside of the container acted as a catalyst.) Kinetic Chemicals patented it in 1941 and registered the Teflon trademark in 1944. The original patent number is US2,230,654.
Teflon was first sold commercially in 1946. By 1950, DuPont had acquired full interest in Kinetic Chemicals and was producing over a million pounds (450 t) per year in
Parkersburg, West Virginia. In 1954, French engineer
Marc Grégoire created the first pan coated with Teflon non-stick resin under the brandname of Tefal after his wife urged him to try the material that he'd been using on fishing tackle on her cooking pans. In the United States, Kansas City, Missouri resident
Marion A. Trozzolo, who had been using the substance on scientific utensils, marketed the first frying pan, "The Happy Pan," in 1961.
An early advanced use was in the
Manhattan Project as a material to coat valves and seals in the pipes holding highly reactive
uranium hexafluoride in the vast
uranium enrichment plant at
Oak Ridge, Tennessee, when it was known as K-25.
Properties
PTFE is a white solid at room temperature, with a
density of about 2.2 g/cm³. According to DuPont its melting point is 327 °C (620.6 °F), but its properties degrade above 260 °C (500 °F).
The
coefficient of friction of plastics is usually measured against polished steel. PTFE's coefficient of friction is 0.1 or less
PTFE has excellent
dielectric properties. This is especially true at high
radio frequencies, making it 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 lower melting point
polyethylene that's 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.
Because of its chemical inertness, PTFE can't 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 control unwanted creep, as well as to improve wear, friction, and other properties. Sometimes metal springs apply continuous force to PTFE seals to give good contact, while permitting some creep.
Applications
Due to its low friction, it's 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's comparable to
ultra high-molecular weight polyethylene (UHMWPE), although UHMWPE is more resistant to wear than Teflon. For these applications, versions of teflon with mineral oil or
molybdenum disulfide embedded as additional
lubricants in its matrix are being manufactured.
Gore-Tex is a material incorporating fluoropolymer membrane with micropores. The roof of the
Hubert H. Humphrey Metrodome in
Minneapolis is one of the largest applications of Teflon PTFE coatings on Earth, using 20
acres (about 8
hectares) of the material in a double-layered, white dome, made with PTFE-coated fiberglass, that gives the stadium its distinctive appearance. The
Millennium Dome in
London is also substantially made of PTFE.
Powdered PTFE is used in
pyrotechnic compositions as
oxidizer together 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. Hence they're used as
infrared decoy flares and
igniters for
solid-fuel rocket propellants.
PTFE is also used in
body piercings, such as a sub-clavicle piercing, due to its flexibility and bio-compatibility.
In optical
radiometry, sheets made from PTFE are used as measuring heads in spectroradiometers and broadband radiometers (for example
illuminance meter and
UV radiometer) due to its capability to diffuse a transmitting light nearly perfectly. Moreover, optical properties of PTFE stay constant over a wide range of wavelengths, from UV up to near
infrared. In this region, the relation 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, for example, in solar
irradiance measurements.
PTFE is also used to coat certain types of hardened,
armor-piercing bullets, so as to reduce the amount of wear on the firearm's rifling. These are often referred to as
"cop-killer" bullets by virtue of PTFE's supposed ability to ease a bullet's passage through
body armor. However, this is simply an urban myth as PTFE has no effect in the bullet's ability to penetrate soft body armor.
PTFE's low frictional properties have also been utilized as
computer mice feet such as the
Logitech G5 and
Logitech G7 computer mice series from
Logitech. The low-friction provided by PTFE allows the mice to be moved and glide across surfaces smoothly and with less effort.
PTFE's high corrosion resistance makes it ideal for laboratory environments as containers, magnetic stirrers and tubing for highly corrosive chemicals such as Hydrofluoric Acid, which will dissolve glass containers.
PTFE can be used as a
thread seal tape in plumbing applications.
PTFE grafts can be used to bypass stenotic arteries in peripheral vascular disease, if a suitable autologous vein graft isn't available.
PTFE can be used to prevent insects climbing up surfaces painted with the material. PTFE is so slippery that insects can't get a grip and tend to fall off. For example PTFE is used to prevent ants climbing out of formicariums.
Production
PTFE is either synthesized by the
emulsion polymerization of
tetrafluoroethylene monomer under pressure, using free-radical catalysts, or it may be produced by the direct substitution of hydrogen atoms on
polyethylene with fluorine, using polyethylene and
fluorine gas at 20 °C.
Safety
While PTFE itself is chemically inert and non-toxic, it begins to deteriorate after the temperature of cookware reaches about 500 °F (260 °C), and decompose above 660 °F (350 °C). These degradation products can be lethal to
birds, and can cause flu-like symptoms in humans.
Carcinogens in production
The
United States Environmental Protection Agency's scientific advisory board found in 2005 that
perfluorooctanoic acid (PFOA), a chemical compound used to make Teflon, is a "likely
carcinogen." This finding was part of a draft report that has yet to be made final. DuPont settled for $300 million in a 2004 lawsuit filed by residents near its manufacturing plant in Ohio and West Virginia based on groundwater pollution from this chemical. Currently this chemical isn't regulated by the EPA.
In January 2006, DuPont, the only company that manufactures PFOA in the US, agreed to eliminate releases of the chemical from its manufacturing plants by 2015, but didn't commit to completely phasing out its use of the chemical. This agreement is said to apply to not only PTFE used in cookware but also other products such as food packaging, clothing, and carpeting. DuPont also stated that it can't produce PTFE without the use of the chemical PFOA, although it's looking for a substitute.
PFOA is used only during the manufacture of the product—only a trace amount of PFOA remains after the curing process. DuPont maintains that there should be no measurable amount of PFOA on a finished pan, provided that it has been properly cured.
Similar polymers
Other polymers with similar composition are also known by the
Teflon name:
Further Information
Get more info on 'Ptfe'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://polytetrafluoroethylene.totallyexplained.com">Polytetrafluoroethylene Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
