Поли(тетрафторэтилен)

Описание

Tetrafl uoroethylene (TFE), also known as perfl uoroethylene, is a colorless, fl ammable, toxic gas. It is the monomer used for polytetrafl uoroethylene (PTFE), which is sold under the DuPont tradename of Tefl on. TFE is co-polymerized with other compounds to produce a variety of Tefl ons. TFE is produced by heating chlorodifl uoromethane (CHClF2, Freon-22) or trifl uoromethane (CHF3, Freon-23). TFE is used almost exclusively as a monomer in the production of PTFE. PTFE is a vinyl polymer, which means it is made from a monomer with carbon-carbon double bonds. PTFE is made from TFE by free radical polymerization.
PTFE’s unique physical properties are due to its chemical structure. PTFE consists of long chains of carbon atoms surrounded by fluorine atoms. The fluorine atoms act as a protective barrier that shields the carbon-carbon bond from chemical attack. The fluorine atoms repel other atoms, making it diffi cult for anything to stick to PTFE. PTFE resins have very low coeffi cients of friction (< 0.1). The strong fluorine-to-carbon bonds and high electronegativity of fluorine make PTFE very stable. The long chains of PTFE pack closely together to give a dense crystalline solid. The packing, which can be compared to stacking boards, produces little cross-linking.

Химические свойства

white powder, or white solid with a slippery feel

История

The polymerized form of TFE was discovered accidentally by researchers at DuPont in 1938. During the mid-1930s, DuPont was investigating the development of new chlorofl uorocarbons (CFCs) for use as refrigerants. DuPont joined with General Motors to form a company called Kinetic Chemicals to combine their efforts in this area. Plunkett examined the properties of the substance. He discovered that the substance was inert to other chemicals, had a high melting point, and was very slippery. Plunkett also worked on duplicating the conditions necessary to produce it from TFE. He applied for a patent for polytetrafl uoroethylene polymers in 1939, which was granted in 1941 (U.S. Patent 2230654). He assigned the patent to Kinetic Chemicals. DuPont registered the term Tefl on in 1945 and introduced Tefl on products the next year.
Teflon is best known for its use in cookware, but its use in this area followed original industrial applications in gaskets, sealers, tape, and electrical insulation. Th ese applications were a direct result of the use of PTFE for military purposes during World War II.

Использование

Poly(tetrafluoroethylene) is used in hundreds of applications in addition to cookware. Poly(tetrafluoroethylene) is used in inks, plastics, coatings, and lubricants.Poly(tetrafluoroethylene) can be molded into gaskets, seals, bearings, gears, and other machine parts. Poly(tetrafluoroethylene) is used as liners, insulation, membranes, and adhesives. Tefl on tape is commonly used in plumbing work. Poly(tetrafluoroethylene) is used to produce rainproof garments.

Определение

ChEBI: A polymer composed of repeating tetrafluoroethyl groups.

Подготовка

The preferred commercial method of preparation of polytetrafluoroethylene (PTFE) is by suspension polymerization. The details of the procedures employed have not been disclosed but it appears that two main processes are in use. In the first process, the conventional techniques of suspension polymerization are used to produce a granular product suitable for moulding and extrusion. The tetrafluoroethylene is polymerized under pressure in stainless steel autoclaves with a free radical initiator such as ammonium persulphate. The reaction is rapid and exothermic and requires careful control. The polymer granules are collected, washed and dried. In the second process, conditions are adjusted to give a dispersion of polymer of much finer particle size and lower molecular weight. The product may be stabilized and employed in latex form in such uses as film casting, coating and impregnation of fibres. Alternatively, the product may be coagulated to give a powder (often called 'dispersion polymer') used mainly for the extrusion of thin flexible sections.

Методы производства

Polytetrafluoroethylene is generally made from tetrafluoroethylene gas by free-radical polymerization under pressure with oxygen, peroxides, or peroxydisulfates. The “granular resins” have medium-size particles that range from 30 to 600 mm. Colloidal aqueous dispersions, made by a different process, are concentrated to about 60% by weight of the polymer and have particles that average about 0.2 mm. Coagulated dispersions with agglomerates that average 450mm are also available .
The use of PTFE as a release agent in coatings and certain other food contact applications is permitted under FDA regulations .

Общее описание

Poly(tetrafluoroethylene) is a fluoropolymer that is commercially known as PTFE. Its properties include high thermal stability, excellent chemical resistance, low dielectric constant and low surface energy. It is a hydrophobic polymer that is majorly used as a protective coating on the metal surface.

Опасность

Evolves toxic fumes on heating. Question- able carcinogen.

Угроза здоровью

Fumes of heated polytetrafluoroethylene (PTFE) cause polymer fume fever, an influenza-like syndrome.

Промышленное использование

The polymer is insoluble, resistant to heat (upto 275°C) and chemical attack, and, in addition,has the lowest coefficient of friction of any solid.Because of its resistance to heat, the fabricationof polytetrafluoroethylene requires modificationof conventional methods. After molding thepowdered polymer using a cold press, the moldingsare sintered at 360 to 400°C by proceduressimilar to those used in powder metallurgy. Thesintered product can be machined or punched.Extrusion is possible if the powder is compoundedwith a lubricating material. Aqueoussuspensions of the polymer can also be used forcoating various articles. However, special surfacetreatments are required to ensure adhesionbecause polytetrafluoroethylene does not adherewell to anything.
Polytetrafluoroethylene (TFE resin) is usefulfor applications under extreme conditions ofheat and chemical activity. Polytetrafluoroethylenebearings, valve seats, packings, gaskets,coatings, and tubing can withstand relativelysevere conditions. Fillers such as carbon, inorganicfibers, and metal powders may be incorporatedto modify the mechanical and thermalproperties.
Because of its excellent electrical properties,polytetrafluoroethylene is useful when adielectric material is required for service at ahigh temperature. The nonadhesive quality isoften turned to advantage in the use of polytetrafluoroethyleneto coat articles such as rollsand cookware to which materials might otherwiseadhere.

Профиль безопасности

The finished polymerized compound is inert under ordinary condtions. There have been reports of “polymer fume fever” in humansexposed to pyrolysis products, whch also are irritants. Smohng should be prohibited in areas where ths material is being fabricated or, in general, where there may be dust from it. Exposure to pyrolysis or decomposition products appears to be the chief health-related problem. Questionable carcinogen with experimental tumorigenic data by implant. Incompatible with fluorine, sodmm potassium alloy. Under the proper conditions it undergoes hazardous reactions with boron, magnesium, or titanium. When heated to above 750°F it decomposes to yield highly toxic fumes of F-.

Канцерогенность

Animal studies have not demonstrated that this polymer is carcinogenic. No data are available in humans. The polymer is not classifiable as to its human carcinogenicity. However, the EPA found that perfluorooctanoic acid (PFOA), a chemical used to produce PTEE is a “likely carcinogen.

Экологическая судьба

PTFE is the most stable of all TFE polymers and under physiological conditions does not release any components (IARC Monograph 74, 1999). PTFE is very inert chemically; only alkali metals and fluorine under pressure attack PTFE (Hazardous Substances Data Bank (HSDB)). There are no known ecotoxicological effects for PTFE (DuPont MSDS, 2011).