Polytetrafluoroethylene
Polytetrafluoroethylene (Polytetrafluoroethene, generally known as "non-stick coating" or "easy to clean wok material"; is a use of fluorine to replace all the hydrogen atoms in the polyethylene It is a synthetic polymer material that uses fluorine to replace all hydrogen atoms in polyethylene. This material is resistant to acids, alkalis, and organic solvents, and is virtually insoluble in all solvents. At the same time, PTFE has the characteristics of high temperature resistance, its coefficient of friction is very low, so it can be used for lubrication, but also become an ideal coating for easy to clean woks and the inner layer of water pipes.
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Polytetrafluoroethylene (PTFE)
Advantages of Use
Chemical Properties
Physical PropertiesMechanical Properties
Chemical Resistance and Weathering Properties
Electrical Properties
Radiation Resistance
Polymerization
Coefficient of Expansion
These are the most important characteristics of PTFE.
Polytetrafluoroethylene products molding methods summary
Polytetrafluoroethylene sintering process material properties
Molding properties
Polytetrafluoroethylene applications
Polytetrafluoroethylene classification and its filler products general-purpose materials
Anti-corrosive
Sealing
Load-bearing
Insulation
Anti-sticky Anti-adhesive class
Temperature-resistant class
Other classes
Polytetrafluoroethylene (PTFE)
Advantages of use
Chemical properties
Physical properties Mechanical properties
Chemical corrosion resistance and weathering resistance
Electrical properties
Radiation resistance
Polymerization
Expansion coefficientPolytetrafluoroethylene products molding methods summary
Polytetrafluoroethylene sintering process Material properties
Molding properties
Polytetrafluoroethylene applications
Polytetrafluoroethylene classification and its filler products General-purpose materials
Anti-corrosive
Sealing
Load-bearing class
Insulation class
Anti-stick class
Temperature class
Other class
[Edit]Polytetrafluoroethylene (PTFE)
Polytetrafluoroethylene (abbreviated as Teflon or [PTFE,F4]), known as/commonly referred to as "King of Plastics", Chinese trade name: "Plastic King", is used in the manufacture of polytetrafluoroethylene. ", the Chinese trade name "Teflon", "Teflon" (teflon), "Teflon", "Teflon", "Teflon", "Teflon", "Teflon", "Teflon", "Teflon", "Teflon", "Teflon", "Teflon", "Teflon". Teflon", "Teflon", "Teflon", "Teflon", "Teflon", "Teflon", "Teflon", and so on. It is a polymerized polymer compound of tetrafluoroethylene, with excellent chemical stability, corrosion resistance (one of the best materials in the world today for corrosion resistance, in addition to molten metal sodium and liquid fluorine, resistant to all other chemicals, boiling in aqua regia does not change, and is widely used in a variety of needs to resist acids, alkalis and organic solvents), sealing, high lubrication and non-stickiness, electrical insulation and good anti-aging Endurance, excellent temperature resistance (can work for a long time under the temperature of +250℃ to -180℃). Polytetrafluoroethylene itself is not toxic to humans, but one of the raw materials used in the production process, Perfluorooctanoic acid ammonium (PFOA), is thought to have possible carcinogenic effects. Temperature -20 to 250°C (-4 to +482°F), allowing sudden cold and heat, or alternating hot and cold operation. Pressure -0.1～6.4Mpa (Full vacuum to 64kgf/cm2) Its creation solves many problems in the fields of chemical, petroleum and pharmaceutical in China. PTFE seals, gaskets, pads. PTFE seals, gaskets, sealing gaskets are made of suspension polymerized PTFE resin molding process. Polytetrafluoroethylene and other plastics compared with chemical resistance and characteristics, it has been widely used as sealing materials and filler materials. Used as engineering plastics, it can be made into PTFE tubes, rods, strips, plates, films and so on. Generally used in high performance requirements of corrosion-resistant pipes, containers, pumps, valves and system radar, high-frequency communication equipment, radio equipment. The dispersed liquid can be used as insulation impregnating liquid of various materials and anticorrosive layer on the surface of metal, glass and pottery. Various kinds of PTFE rings, PTFE gaskets, PTFE packing, etc. are widely used in all kinds of anticorrosive pipe flange sealing. In addition, it can also be used for drawing silk, polytetrafluoroethylene fiber - fluorine (foreign commodity name Teflon). At present, all kinds of PTFE products have been in the chemical industry, machinery, electronics, electrical appliances, military, aerospace, environmental protection and bridges and other areas of the national economy has played a pivotal role. Polytetrafluoroethylene (PTFE) conditions of use industry chemical, petrochemical, oil refining, chlor-alkali, acid, phosphate fertilizer, pharmaceuticals, pesticides, chemical fibers, dyeing, coking, gas, organic synthesis, non-ferrous smelting, iron and steel, atomic energy and the production of high-purity products (eg, ionic membrane electrolysis), viscous materials, transportation and operation of highly stringent hygiene requirements of the processing and production of food, beverages and other production sectors.
[Edit]Advantages of use
High-temperature resistance - the use of working temperature up to 250 ℃. Low temperature resistance - with good mechanical toughness; even if the temperature drops to -196 ℃, can maintain 5% elongation. Corrosion resistance - to most chemicals and solvents, showing inertia, resistance to strong acids and alkalis, water and a variety of organic solvents. Weather resistant - has the best aging life of any plastic. High lubricity - has the lowest coefficient of friction of any solid material. Non-adhesion - has the lowest surface tension of any solid material and does not adhere to any substance. Non-toxic - physiologically inert, as artificial blood vessels and organs implanted in the body for a long time without adverse reactions. Polytetrafluoroethylene relative molecular mass is large, the low hundreds of thousands, high up to 10 million or more, generally millions (degree of polymerization in the 104 order of magnitude, while polyethylene is only 103). General crystallinity of 90 ~ 95%, melting temperature of 327 ~ 342 ℃. Polytetrafluoroethylene molecule CF2 unit arranged in a sawtooth shape, due to fluorine atom radius is slightly larger than hydrogen, so adjacent CF2 unit can not be completely according to the trans cross orientation, but the formation of a helical twisted chain, fluorine atoms cover almost the entire surface of the polymer chain. This molecular structure explains the various properties of PTFE. At temperatures below 19°C, a 13/6 helix is formed; at 19°C a phase transition occurs and the molecules slightly unravel to form a 15/7 helix. Although in the perfluorocarbon compounds in the carbon-carbon bond and carbon-fluorine bond breaking need to absorb energy 346.94 and 484.88kJ/mol, but the polytetrafluoroethylene depolymerization to generate 1 mol tetrafluoroethylene only requires energy 171.38kJ. so in the high temperature cleavage, the polytetrafluoroethylene is mainly decomposition to tetrafluoroethylene. The weight loss rate (%) of PTFE at 260, 370 and 420°C is 1×10-4, 4×10-3 and 9×10-2 per hour, respectively, which shows that PTFE can be used for a long time at 260°C. The high temperature cracking also produces a dramatic increase in weight loss. Due to the high temperature cracking also produces highly toxic by-products such as fluorine gas and perfluoroisobutene, so special attention should be paid to the safety protection and to prevent PTFE from contacting with open flames.
[edit]Chemical properties
Atmospheric aging resistance: irradiation resistance and low permeability: long-term exposure to the atmosphere, the surface and properties remain unchanged. Incombustibility: limited oxygen index below 90. Acid and alkali resistance: insoluble in strong acids, alkalis and organic solvents. Oxidation resistance: resistant to corrosion by strong oxidizing agents. Acidity and alkalinity: neutral.
[edit]Physical Properties
Density: 2.1-2.3 g/cm? Polytetrafluoroethylene has soft mechanical properties. Has very low surface energy. Polytetrafluoroethylene (F4,PTFE) has a series of excellent use of performance: high temperature resistance - long-term use of 200 ~ 260 degrees, low temperature resistance - still soft at -100 degrees; corrosion resistance - resistant to aqua regia and all organic solvents; climate resistance - the best aging life in plastics. The best aging life among plastics; high lubrication - with the smallest coefficient of friction among plastics (0.04); non-sticky - with the smallest surface tension among solid materials without adhering to any substance; non-toxic - with physiological inertia; excellent electrical properties, is the ideal C-class insulating material. Polytetrafluoroethylene materials, widely used in the defense industry, atomic energy, petroleum, radio, electric machinery, chemical industry and other important sectors. Products: polytetrafluoroethylene rods, tubes, sheets, turned sheets. Polytetrafluoroethylene is a polymer of tetrafluoroethylene. The abbreviation is PTFE, and the structure formula is Discovered in the late 1930s and put into industrial production in the 1940s. Properties Polytetrafluoroethylene relative molecular mass is large, the low hundreds of thousands, high up to more than 10 million, generally millions (polymerization degree in the 104 order of magnitude, while the polyethylene is only 103). General crystallinity of 90 ~ 95%, melting temperature of 327 ~ 342 ℃. Polytetrafluoroethylene molecule CF2 unit arranged in a sawtooth shape, due to the fluorine atom radius is slightly larger than the hydrogen, so adjacent CF2 unit can not be completely according to the trans cross orientation, but the formation of a helical twisted chain, fluorine atoms cover almost the entire surface of the polymer chain. This molecular structure explains the various properties of PTFE. At temperatures below 19°C, a 13/6 helix is formed; at 19°C a phase transition occurs and the molecules slightly unravel to form a 15/7 helix. Although in the perfluorocarbon compounds in the carbon-carbon bond and carbon-fluorine bond breaking need to absorb energy 346.94 and 484.88kJ/mol, but the polytetrafluoroethylene depolymerization to generate 1 mol tetrafluoroethylene only requires energy 171.38kJ. so in the high temperature cleavage, the polytetrafluoroethylene is mainly decomposition to tetrafluoroethylene. The weight loss rate (%) of PTFE at 260, 370 and 420°C is 1×10-4, 4×10-3 and 9×10-2 per hour, respectively, which shows that PTFE can be used for a long time at 260°C. The high temperature cracking also produces a dramatic increase in weight loss. As high temperature cracking also produces highly toxic by-products such as fluorine gas and perfluoroisobutene, so special attention should be paid to the safety protection and to prevent PTFE from contacting with open flames.
Mechanical properties
Its coefficient of friction is very small, only 1/5 of that of polyethylene, which is an important feature of perfluorocarbon surface. And because of the fluorine - carbon chain intermolecular force is extremely low, so PTFE has non-sticky. Polytetrafluoroethylene in -196 ~ 260 ° C in a wide range of temperatures are to maintain excellent mechanical properties, perfluorocarbon polymer is characterized by one of the low temperature is not brittle.
Chemical resistance and weathering
Except for molten alkali metals, PTFE is not subject to corrosion by almost any chemical reagent. For example, in concentrated sulfuric acid, nitric acid, hydrochloric acid, and even boiled in aqua regia, its weight and performance are unchanged, and almost insoluble in all solvents, only slightly soluble in all-alkanes at 300 ℃ or more (about 0.1g / 100g). Polytetrafluoroethylene does not absorb moisture, non-combustible, extremely stable to oxygen, ultraviolet rays, so it has excellent weather resistance.
Electrical properties
Polytetrafluoroethylene in a wide frequency range of dielectric constant and dielectric loss are very low, and the breakdown voltage, volume resistivity and arc resistance are high.
Radiation resistance
Polytetrafluoroethylene radiation resistance is poor (104 rads), by high-energy radiation caused by the degradation of the polymer's electrical and mechanical properties are significantly reduced.
Polymerization
Polytetrafluoroethylene is produced by free radical polymerization of tetrafluoroethylene. Industrial polymerization reaction is carried out in the presence of a large number of water stirring, to disperse the reaction heat, and easy to control the temperature. Polymerization is generally carried out at 40 ~ 80 ℃, 3 ~ 26 kg force / cm 2 pressure, can be used inorganic persulfate, organic peroxide as initiator, can also be used in redox initiation system. Each mole of tetrafluoroethylene polymerization exothermic 171.38 kJ. Dispersive polymerization should add perfluorinated surfactants, such as perfluorooctanoic acid or its salts.
Expansion coefficient
(25～250℃)10～12×10-5/℃
[Edit]Summary of molding methods of PTFE products
1, molding method 2, pushing method 3, skin capsule method 4, spraying method 5, weaving method 6, winding method 7, rolling method 8, extruding method 9, bonding method 10, welding method 11, heat setting method 12、Machining method
[edit]PTFE sintering process
Molding shrinkage:3.1-5.0% Molding temperature:330-380 ℃ Sintering conditions: the best temperature should not exceed 385 degrees, otherwise the molecules will necrosis, affecting the quality.
Material properties
Long-term use temperature -200--260 degrees, excellent chemical resistance, corrosion resistance to all chemicals, the lowest coefficient of friction in plastics, and very good electrical properties, its electrical insulation is not affected by the temperature, the "king of plastics," said. 2. Transparent or semi-transparent state, the higher the crystallinity, the worse the transparency. Raw material is mostly powdered resin or concentrated dispersion, with very high molecular weight, high crystallinity thermoplastic polymer. 3, suitable for the production of corrosion-resistant parts, wear parts, seals, insulating parts and medical equipment parts1 K) 4,
Molding properties
1. Crystalline material, moisture absorption is small. 2. Poor fluidity, easy to decompose, decomposition of corrosive gases. It is desirable to strictly control the molding temperature, the mold should be heated, the pouring system should be small resistance to material flow. 3. Powdered resin is often molded by powder metallurgy, using the sintering method. Sintering temperature 360-375 degrees, not more than 410 degrees. Emulsion resin is usually processed by cold extrusion and then sintering process, which can form an anticorrosive layer on the surface of the article. If you need to require the transparency of the product, good toughness, should be taken to rapid cooling. Can also be taken to extrusion molding, can be extruded tube, rod, profile. 4, PTFE melt viscosity is very high, the bulk viscosity decreases with the increase of shear stress, showing its non-Newtonian fluid properties. 5、Secondary processing, can be hot pressing composite, welding, bonding, enhancement, machining, etc., in order to produce the final product. 6, preferably with curve sintering first step at 120 degrees for drying second step such as filled graphite or di- fluidized ink at 250 degrees to be temperature treatment. 3, the third step at 345 degrees to be processed once 4, the fourth step at 375 degrees to be processed 5, the fifth step to cool down do not be too fast
[edit]Polytetrafluoroethylene applications
Polytetrafluoroethylene can be molded by compression or extrusion processing; can also be made into a water-dispersed liquid for coating, impregnation or made of fiber. PTFE is widely used in atomic energy, national defense, aerospace, electronics, electrical, chemical, mechanical, instrumentation, instrumentation, construction, textile, metal surface treatment, pharmaceutical, medical, textile, food, metallurgy and refining industries as high and low temperature, corrosion-resistant materials, insulating materials, anti-adhesive coatings and so on, which makes it irreplaceable. Polytetrafluoroethylene has excellent comprehensive performance, high temperature resistance, corrosion resistance, non-stick, self-lubricating, excellent dielectric properties, very low coefficient of friction. Used as engineering plastics, it can be made into PTFE pipes, rods, strips, plates, films, etc.. Generally used in high performance requirements of corrosion-resistant pipes, containers, pumps, valves, and the system of radar, high-frequency communication equipment, radio equipment and so on. PTFE in any filler that can withstand the PTFE sintering temperature, its mechanical properties can be greatly improved. At the same time, to maintain the other excellent properties of PTFE. The filler varieties are glass fiber, metal, metallized oxides, graphite, molybdenum disulfide, carbon fiber fiber, polyimide, EKONOL...etc. The abrasion resistance and ultimate PV value can be increased by 1000 times. Teflon cloth PTFE tubing is made of suspension polymerized PTFE resin by plunger extrusion process. Among the known plastics PTFE has the best chemical resistance and dielectric properties. PTFE braided packing is a good dynamic sealing material. It is braided from strips of expanded polytetrachloroethylene tape. PTFE braided packing is a good dynamic sealing material. It is braided from strips of expanded polytetrachloroethylene. It has excellent properties such as low coefficient of friction, abrasion resistance, chemical resistance, good sealing, no hydrolysis, no hardening, etc. It is used as a liner for working in various media. It is used as liner seals and lubricating materials for working in various mediums, as well as electrical insulating parts used in various frequencies. Capacitor media, line insulation, electrical instrumentation insulation. PTFE film is suitable for capacitor media, special cable insulation, wire insulation, electrical instrumentation insulation and sealing gaskets, but also non-stick tape, sealing tape, mold release.
[edit]PTFE classification and its filler products
General-purpose materials
A variety of rods, tubes, sheets of film, tape, rope, packing, gaskets, and graphite, molybdenum disulfide, aluminum oxide, glass fibers, carbon fiber as a filler, to improve the mechanical properties of pure PTFE.
Anti-corrosion class
1. Pipes and fittings: pure PTFE pipes; PTFE lined pipes; outer wrapped fiberglass steel pipes; steel composite flanges; 2. Chemical vessel lining: PTFE lined kettles; PTFE lined tanks; PTFE lined towers; 3. Heat exchangers; 4. Corrugated expansion pipes; 5. Valves and pumps, the main components; 6. Steel wire reinforced full-pressure hose; 7. Filtering materials. PTFE membrane after longitudinal and transverse bi-directional stretching within a large number of pores, is a new material, it will be compounded with other fabrics, can be made of soot solid-phase anticorrosive filtration bags or good waterproof and breathable, wind and warm rain gear sportswear, cold weather clothing, special protective clothing and lightweight tents, pharmaceutical air compressed air, all kinds of solvents, sterile filtration and filtration of high-purity gases in the electronics industry.
Seals
1. Static seals: laminated gaskets; sitting material belt; elastic sealing tape; 2. Dynamic seals (preparation of packing, ring seals): V-type sealing body - for shafts, piston rods, valves; turbine pumps within the seals; PTFE and rubber composite sealing ring; with a bellows can be retractable Mechanical seals.
Load-bearing class
1. Filled PTFE bearings, used in food, chemical, paper, textile machinery; 2. Porous copper-impregnated fluoroplastic metal bearings, which can be used in high temperature and high pressure dry friction, vacuum conditions; 3. PTFE fiber bearings made of PTFE fibers blended with glass fibers or other fibers composite fabrics made of bearing liners, used for low-speed high-load; 4. Filled PTFE piston rings, guide rings, machine tool guides and bridge slides;
Insulation class
1. Class C insulating materials for wires and cables;
2. Sheaths for stator and rotor leadpipes of double-water internally cooled turbine generators and thermocouples;
Microwave insulating materials for high-frequency and ultra-high-frequency communication equipment and radar;
4. Printed-wire substrate and motors, transformers (including gas transformers) Insulating materials; 5. Insulating materials for air-conditioners, electronic furnaces, various heaters and sulfur hexafluoride circuit breakers;
Anti-sticking class
1. PTFE glass cloth covering layer on the hot roll of the sizing machine - it can exempt from the phenomenon of sticking to the rolls formed by the chemical slurry, and greatly improve the production rate and the quality of the blanks; 2. Microwave drying conveyor belts for the food industry - compared with other materials conveyor belts do not absorb microwave energy, non-stick objects due to which there are advantages of power saving, cleaning; 3. Polyethylene bagging sealing of the thermal laminating set of anti-adhesive materials; 4. Anti-adhesive coatings - used in kitchen pots, baking molds, frozen foods, bread, baking molds and other materials. Bread baking molds, frozen food storage trays, iron bottoms, photocopier pinch rollers;
Temperature class
1. Microwave ovens drive drive, such as microwave ovens couplings, rollers; 2. All kinds of refrigeration, air-conditioning, oxygen concentrator, compressor temperature accessories;
Other
1. The human body substitute arteries, veins, blood vessels, cardiac membranes; 2. Endoscopes, clamp catheters, trachea; 3. Other tubes, bottles, filter cloths and other medical equipment.