Polytetrafluoroethylene ( PTFE ) is a fluoropolymer synthetic tetrafluoroethylene having many applications. The most well known brand name of the PTFE-based formula is Teflon by Chemours. Congestion is a 2015 spin-off from DuPont Co., which discovered the compound in 1938.
PTFE is a fluorocarbon solid, because it is a high molecular weight compound consisting entirely of carbon and fluorine. PTFE is hydrophobic: neither water nor substance containing non-wet PTFE water, since fluorocarbons show the strength of the dispersion of London that is mitigated by the high fluorine electronegativity. PTFE has one of the lowest friction coefficients of any solid.
PTFE is used as a nonstick coating for pans and other cookware. It is non-reactive, partly due to the strength of the carbon-fluorized bond, and is therefore often used in containers and pipes for reactive and corrosive chemicals. Where used as a lubricant, PTFE reduces friction, wear and engine energy consumption. It is usually used as a graft material in surgical intervention. Also, it is often used as a coating on a catheter; this disrupts the ability of bacteria and other infectious agents to adhere to catheters and cause hospital-acquired infections.
Video Polytetrafluoroethylene
Histori
PTFE was accidentally discovered in 1938 by Roy Plunkett when he worked in New Jersey for DuPont. When Plunkett attempts to make a new chlorofluorocarbon refrigerant, the tetrafluoroethylene gas in the pressure bottle stops flowing before the bottle's weight falls to a point indicating "empty." Since Plunkett measured the amount of gas used by weighing the bottle, he became curious about the source of his weight, and eventually forced to saw off the bottle. He found the interior of the bottle coated with a waxy white waxy material. The analysis showed that it was polymerized perfluoroethylene, with iron from the inside of the container having acted as a catalyst at high pressure. Kinetic Chemicals patented new fluorinated plastic (analogous to known polyethylene) in 1941, and registered the Teflon trademark in 1945.
In 1948, DuPont, which established Kinetic Chemicals in partnership with General Motors, produces over two million pounds (900 tons) of PTFE Teflon brand per year in Parkersburg, West Virginia. The initial use is at the Manhattan Project as a material for coating valves and seals in pipelines that hold highly reactive uranium hexafluoride at the extensive K-25 uranium enrichment plant in Oak Ridge, Tennessee.
In 1954, the wife of French engineer Marc GrÃÆ' Â © goire urged him to try the material he used while fishing on his cooking pot. He then created the first Teflon-coated, non-stick pot under the Tefal brandname (combining "Tef" from "Teflon" and "al" from aluminum). In the United States, Marion A. Trozzolo, who has used substance in scientific equipment, marketed the first US-made Teflon pan, "The Happy Pan", in 1961.
However, Tefal is not the only company that uses PTFE in layers of nonstick cookware. In subsequent years, many cookware manufacturers developed proprietary PTFE-based formulas, including Swiss Diamond International, using a diamond reinforced PTFE formula; Scanpan, which uses a titanium-strengthened PTFE formula; and Calphalon All-Clad and Newell Rubbermaid, which use non-reinforced nonstick based nonstick. Other cookware companies, such as Anolon Meyer Corporation, use a Teflon nonstick coating purchased from DuPont.
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. Crosslinked PTFE has improved the mechanical properties of high temperature and radiation stability. This is important because, over the years, irradiation in ambient conditions has been used to break up PTFE for recycling. This radiation-induced chain cut allows it to be more easily rearranged and reused.
Maps Polytetrafluoroethylene
Production
PTFE is produced by the polymerization of tetrafluoroethylene free radicals. The net equation is
- n F 2 C = CF 2 -> - (F 2 C-CF 2 ) n -
Because tetrafluoroethylene can explosively decompose into tetrafluoromethane and carbon, special equipment is required for polymerization to prevent hot spots that may trigger these dangerous adverse reactions. This process usually begins with persulfate, which homolyzes to produce sulfate radicals:
- [O 3 SO-OSO 3 ] 2 - ? 2 SO 4 o -
The resulting polymer ends with a group of sulfate esters, which can be hydrolysed to produce OH end groups.
Because PTFE is not soluble in almost any solvent, the polymerization is carried out as an emulsion in water. This process provides the suspension of polymer particles. Alternatively, polymerization is carried out using surfactants such as PFOS.
Properties
PTFE is a thermoplastic polymer, which is a white solid at room temperature, with a density of about 2200 kg/m 3 . According to Chemours, the melting point is 600 Â ° K (327 Â ° C; 620 Â ° F). It retains its own high strength, toughness and lubrication at low temperatures of up to 5 ° K (-268.15 ° C; -450 ° F), and good flexibility at temperatures above 194 ° K (-79 Â ° C; -110 Â ° F). PTFE derives its properties from the aggregate effects of carbon-fluorine bonds, like all fluorocarbons. The only chemicals known to affect carbon-fluorine bonds are highly reactive metals such as alkali metals, and at higher temperatures as well as metals such as aluminum and magnesium, and fluorinated agents such as xenon difluoride and cobalt (III) fluoride.
The coefficient of plastic friction is usually measured against the polished steel. The friction coefficient of PTFE is 0.05 to 0.10, which is the third lowest of known solid materials (BAM being the first, with a friction coefficient of 0.02, carbon-like diamonds being the second lowest at 0.05). The resistance of PTFE to van der Waals forces means that this is the only known surface that the geckos can not penetrate. In fact, PTFE can be used to prevent insects from climbing surfaces that are painted with the material. PTFE is so slick that insects can not get a handle and tend to fall. For example, PTFE is used to prevent ants from climbing out formicaria.
Due to its inert nature, PTFE can not be cross-linked like elastomers. Therefore, it has no "memory" and is subject to creep. Due to superior chemical and thermal properties, PTFE is often used as a gasket material in industries that require resistance to aggressive chemicals such as pharmaceuticals or chemical processing. However, due to the tendency to crawl, the long-term performance of the seal is worse than elastomers that show zero, or near zero, creep levels. In critical applications, Belleville washing machines are often used to apply continuous force to PTFE gaskets, ensuring minimal performance loss during the lifetime of the gasket.
Processing
PTFE processing can be difficult and expensive, because the high melting temperature, 327 Â ° C (621 Â ° F), is above the initial decomposition temperature, 200 Â ° C (392 Â ° F). Even when melted, PTFE does not flow, but acts as a gel in the absence of high crystalline phases and high melt viscosity.
Some parts of PTFE are made with cold printing, a form of compression molding. Here, PTFE fine powder is forced into mold under high pressure (10 ~ 100 MPa). After a period of deposition, which lasts from minute to day, the mold is heated at 360 to 380 degrees Celsius (680 to 716 degrees Fahrenheit), allowing fine particles to merge into one mass.
Applications and usage
The main application of PTFE, consuming about 50% of production, is for wiring in aerospace and computer applications (eg wire hookup, coaxial cable). This application exploits the fact that PTFE has excellent dielectric properties, especially at high radio frequencies, making it suitable for use as an excellent insulator in connector and cable assemblies, and on printed circuit boards used in microwave frequencies. Combined with its high melting temperatures, this makes it an ingredient of choice in place of high performance for weaker and lower polyethylene, which is commonly used in low-cost applications.
In industrial applications, due to its low friction, PTFE is used for plain bearings, gears, shear plates, and more applications with shear action, where it exceeds the acetal and nylon.
Its very high bulk resistivity makes it an ideal material for fabrication of longevity, electrostatic analogs of magnets.
PTFE films are also widely used in the production of carbon fiber composites as well as fiberglass composites, especially in the aerospace industry. PTFE films are used as a barrier between carbon or fiberglass parts being built, and the breath and pockets used to wrap bonds when debulking and when curing composites, usually in an autoclave. PTFE, which is used here as a film, prevents non-production materials from sticking to the part being built, which is sticky due to carbon graphite or pre-pregnant fiberglass layers with bismaleimide resins. Non-production materials such as Teflon, Airweave Breather and the bag itself will be considered F.O.D. (foreign object debris/damage) if left in the layup.
Due to its extreme and high temperatures, PTFE is often used as a liner in hose assemblies, expansion joints, and in industrial pipelines, especially in applications using acid, alkali, or other chemicals. Its frictional qualities enable increased flow of highly viscous liquids, and for use in applications such as brake hoses.
Gore-Tex is a material that combines fluoropolymer membranes with micropores. Hubert H. Humphrey's roof Metrodome in Minneapolis, USA, is one of the largest applications of PTFE coatings. 20 acres (81,000 m 2 ) of the material was used in the manufacture of a multilayered layered fiberglass fiberglass dome.
PTFE is often found in the lubricant products of musical instruments; most often, oil valve.
PTFE (Teflon) is well known for its use in coating nonstick fryers and other cookware, because it is hydrophobic and has high heat resistance.
Single plates of several clothing irons are coated with PTFE (Teflon).
Other niche apps include:
- Often found in ski bindings as AFD non-mechanical (Anti-Friction Device)
- Can be stretched to contain small pores of various sizes and then placed between layers of fabric to make the fabric waterproof and breathe in outerwear.
- It's used extensively as a cloth shield to ward off stains on formal school attire, like a uniform blazer. It is used as a patch film interface for sports and medical applications, featuring pressure-sensitive adhesive support, installed in high-friction strategic areas of footwear, soles, ankle orthoses, and other medical devices to prevent and relieve blisters caused by friction, calluses and ulceration of the feet.
- The enlarged PTFE membrane has been used in trials to assist trabeculectomy surgery to treat glaucoma.
- PTFE powder is used in the pyrotechnic composition as an oxidizing agent with powdered metals such as aluminum and magnesium. After ignition, this mixture forms a corresponding carbon and metal fluoride soot, and releases a large amount of heat. They are used in infrared feed flares and as igniters for solid fuel rocket propellants. Aluminum and PTFE are also used in some thermobaric fuel compositions.
- PTFE powder is used in suspension with low viscosity, azeotropic mixture ether siloxane to create lubricant for use in puzzle winding.
- In optical radiometry, PTFE sheets are used as measuring heads in spektoradiometers and broadband radiometers (eg, UV lighting meters and radiometers) because of the ability of PTFE to spread the transmission light almost perfectly. In addition, the optical properties of PTFE remain constant at various wavelengths, from UV to near infrared. In this region, the regular transmittance relationship for diffuse transmission is very small, so the light transmitted through the diffuser (PTFE sheet) radiates like Lambert cosine law. Thus PTFE allows cosinusoidal angular response for detectors measuring the strength of optical radiation on the surface, for example in measurements of solar radiation.
- Several types of bullets are coated with PTFE to reduce wear and tear on firearm guns that will be caused by uncoated projectiles. PTFE itself does not provide projectile penetrating armor properties.
- High corrosion resistance makes PTFE useful in laboratory environments, where it is used to coat the container, as a coating for magnetic stirrer, and as a tube for highly corrosive chemicals such as hydrofluoric acid, which dissolves glass containers. These are used in containers to store fluoroantimonic acid, superacid.
- The PTFE tube is used in heat exchangers of gases in the cleaning of waste incinerator gases. The unit's power capacity is usually several megawatts.
- PTFE is widely used as yarn sealing tape in plumbing applications, mostly replacing dope yarn paste.
- PTFE membrane filter is one of the most efficient industrial air filters. PTFE lined filters are often used in dust collection systems to collect particles from airflow in applications involving high temperatures and high particulate loads such as coal-fired power plants, cement production and steel casting.
- PTFE graft can be used to bypass the arterial stenosis in peripheral vascular disease if a suitable venous venous veins are not available.
- Many lubricants and lubricating greases contain PTFE and are used on chains and other moving parts that experience frictional forces (such as hub bearings).
- PTFE can also be used for dental fillings, to isolate the anterior teeth contact so that the filler will not stick to adjacent teeth.
- PTFE sheets are used in the production of butane hash oil because of its nonstick properties and resistance to non-polar solvents.
- PTFE, associated with a slightly textured laminate, makes the plain bearing system of the Dobsonian telescope.
- PTFE is widely used as a nonstick coating for food processing equipment; dough wagons, mixing bowls, conveyor systems, rollers, and launches. PTFE can also be reinforced where abrasion is present - to process seeded equipment or rough dough eg
- Been experimenting with nickel plating without electricity
Security
PTFE pyrolysis was detected at 200 ° C (392 ° F), and it evolved several fluorocarbon and sublimate gases. An animal study conducted in 1955 concluded that it is unlikely that this product will be produced in significant amounts to health at temperatures below 250 Â ° C (482 Â ° F).
While PTFE is stable and non-toxic at lower temperatures, it begins to deteriorate after cooking equipment temperature reaches about 260 ° C (500 ° F), and decomposes above 350 ° C (662 ° F). Degradation of byproducts can kill birds, and can cause flu-like symptoms in humans - see polymer smoke fever. Meat is usually fried between 204 and 232 ° C (399 and 450 ° F), and most of the oil starts to smoke before the temperature of 260 ° C (500 ° F) is reached, but there are at least two cooking oils (processed safflower oil in 265Ã, Â ° C (510Ã, Â ° F) and avocado oil at 271Ã, Â ° C (520Ã, Â ° F)) which has a higher smoke point.
PFOA
Perfluorooctanoic acid (PFOA, or C8) has been used as a surfactant in PTFE emulsion polymerization, although some manufacturers have completely discontinued its use. PFOA continues indefinitely in the environment. These are toxins and carcinogens in animals. PFOA has been detected in the blood of more than 98% of the general US population in the low range and sub-parts per billion, and higher rates in plant chemical workers and surrounding subpopulations. The general population has been exposed to PFOA through the disposal of C8 waste into the ocean and near the Ohio River Valley. PFOA has been detected in industrial waste, stain-proof carpet, carpet cleaning fluid, house dust, microwave popcorn bag, water, food and Teflon cookware.
As a result of the class action lawsuits and community settlement with DuPont, three epidemiologists conducted research on populations around chemical plants affected by PFOA at a greater rate than in the general population. The study concluded that there may be a link between PFOA exposure and six health outcomes: kidney cancer, testicular cancer, ulcerative colitis, thyroid disease, hypercholesterolemia (high cholesterol), and pregnancy induced hypertension.
Overall, PTFE cookware is considered an insignificant exposure path to PFOA.
Similar polymers
The Teflon trade name is also used for other polymers with the same composition:
- Perfluoroalkoxy alkane (PFA)
- Fluorinated ethylene propylene (FEP)
It maintains the PTFE properties of low friction and non reactivity, but is easier to establish. For example, FEP is softer than PTFE and melts at 533 K (260 Â ° C; 500 Â ° F); it is also very transparent and resistant to sunlight.
See also
- Superhydrophobic layer
- ETFE
- Magnesium/Teflon/Viton pyrolant thermite composition
- Polymer absorption
- Polymer fume fever
- BS 4994 PTFE as a thermoplastic coating for double laminated process chemical plant equipment
References
Further reading
- Ellis, D.A.; Mabury, S.A.; Martin, J.W.; Muir, D.C.G.; Mabury, S.A.; Martin, J.W.; Muir, D.C.G. (2001). "Thermolysis fluoropolymers as a potential source of halogenated organic acids in the environment". Nature . 412 (6844): 321-324. doi: 10.1038/35085548. PMID 11460160.
External links
- EPA: Compounds in Teflon can cause cancer [1], Tom Costello, NBC News, June 29, 2005. (Flash video required)
- Plasma Process and Adhesive Ties of Polytetrafluoroethylene
- PTFE Tube Properties
Source of the article : Wikipedia
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