Polytetrafluoroethylene [PTFE, F4] is one of the best corrosion-resistant materials in the world today, so it is known as the "King of Plastics". It can be used in any kind of chemical media for a long time, and its production has solved many problems in my country's chemical industry, petroleum, pharmaceutical and other fields. PTFE seals, gaskets, and gaskets. PTFE seals, gaskets, and gaskets are molded from suspension polymerized PTFE resin. Compared with other plastics, PTFE has excellent chemical corrosion resistance and temperature resistance. It has been widely used as sealing material and filling material.
Polytetrafluoroethylene is a polymer of tetrafluoroethylene. The English abbreviation is PTFE. The trade name is "Teflon". Known as the "King of Plastics". The basic structure of polytetrafluoroethylene is. - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 - CF2 -. Polytetrafluoroethylene is widely used in various applications that require resistance to acids, alkalis and organic solvents. It is not toxic to humans, but perfluorooctanoate (PFOA), one of the raw materials used in the production process, is considered to be potentially carcinogenic.
Polytetrafluoroethylene (Teflon or PTFE), commonly known as the "King of Plastics", has Chinese trade names such as "Teflon", "Teflon", "Teflon", "Teflon", etc. It is a polymer compound made of tetrafluoroethylene and has excellent chemical stability, corrosion resistance, sealing, high lubrication and non-stickiness, electrical insulation and good anti-aging endurance. It can work for a long time at temperatures from +250°C to -180°C. Except for molten metal sodium and liquid fluorine, it is resistant to all other chemicals and does not change when boiled in aqua regia.
Used as engineering plastics, it can be made into polytetrafluoroethylene tubes, rods, strips, plates, films, etc. It is generally used in corrosion-resistant pipes, containers, pumps, valves, radars, high-frequency communication equipment, radio equipment, etc. that require high performance. The dispersion can be used as an insulating impregnation liquid for various materials and as an anti-corrosion coating on the surfaces of metal, glass, and ceramics. Various PTFE rings, PTFE gaskets, PTFE packing, etc. are widely used in various types of anti-corrosion pipeline flange seals. In addition, it can also be used for spinning polytetrafluoroethylene fiber - fluoron (foreign trade name is Teflon).
At present, various types of PTFE products have played a decisive role in the national economic fields such as chemical industry, machinery, electronics, electrical appliances, military industry, aerospace, environmental protection and bridges.
Polytetrafluoroethylene (PTFE) usage conditions industry chemical, petrochemical, oil refining, chlor-alkali, acid production, phosphate fertilizer, pharmaceuticals, pesticides, chemical fiber, dyeing, coking, gas, organic synthesis, non-ferrous smelting, steel , atomic energy and high-purity product production (such as ion membrane electrolysis), viscous material transportation and operation, food, beverage and other processing and production departments with highly strict hygiene requirements.
Media Hydrofluoric acid, phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, various organic acids, organic solvents, strong oxidants and other highly corrosive chemical media.
Temperature -20~250℃, allowing sudden cooling and heating, or alternating hot and cold operations.
-20～250℃ (-4～+482°F)
Pressure -0.1～6.4Mpa (full negative pressure to 64kgf/cm2)
- 0.1～6.4Mpa (Full vacuum to 64kgf/cm2)
High temperature resistance - the operating temperature reaches 250℃.
Low temperature resistance - has good mechanical toughness; even if the temperature drops to -196°C, it can maintain an elongation of 5%.
Corrosion resistance - It is inert to most chemicals and solvents, and can withstand strong acids and alkalis, water and various organic solvents.
Weather resistant - has the best aging life among plastics.
High lubrication - the lowest friction coefficient among solid materials.
Non-adhesion - It is the smallest surface tension in solid materials and does not adhere to anything.
Non-toxic - physiologically inert, it can be used as artificial blood vessels and organs for long-term implantation in the body without adverse reactions.
The relative molecular weight of polytetrafluoroethylene is relatively large, ranging from hundreds of thousands to more than 10 million, and generally millions (the degree of polymerization is in the order of 104, while polyethylene is only 103 ).
Generally, the crystallinity is 90 to 95%, and the melting temperature is 327 to 342°C. The CF2 units in the polytetrafluoroethylene molecule are arranged in a zigzag shape. Since the radius of the fluorine atom is slightly larger than that of hydrogen, the adjacent CF2 units cannot be completely trans-cross-oriented, but form a spiral twisted chain, which is almost covered by the fluorine atoms. on the surface of the entire polymer chain. This molecular structure explains PTFE's various properties. When the temperature is lower than 19°C, a 13/6 helix is ??formed; at 19°C, a phase change occurs, and the molecules unwind slightly to form a 15/7 helix.
Although the breaking of carbon-carbon bonds and carbon-fluorine bonds in perfluorocarbons requires energy absorption of 346.94 and 484.88kJ/mol respectively, the depolymerization of polytetrafluoroethylene to generate 1 mol of tetrafluoroethylene only requires Energy 171.38kJ. Therefore, during high-temperature cracking, polytetrafluoroethylene is mainly depolymerized into tetrafluoroethylene. The weight loss rates (%) of polytetrafluoroethylene at 260, 370 and 420°C are 1×10-4, 4×10-3 and 9×10-2 per hour respectively. It can be seen that PTFE can be used for a long time at 260℃. Since highly toxic by-products such as fluorophosgene and perfluoroisobutylene are also produced during high-temperature cracking, special attention must be paid to safety protection and to prevent polytetrafluoroethylene from coming into contact with open flames.
Mechanical properties Its friction coefficient is extremely small, only 1/5 of polyethylene, which is an important feature of perfluorocarbon surface. And because the fluorine-carbon chain intermolecular force is extremely low, PTFE is non-sticky.
It does not melt at a temperature of 250℃ and does not become brittle at an ultra-low temperature of -260℃. PTFE is extremely smooth, even ice cannot compare with it; its insulation properties are particularly good, a film as thick as newspaper is enough to withstand high voltage of 1500V.
Polytetrafluoroethylene maintains excellent mechanical properties in a wide temperature range of -196 to 260°C. One of the characteristics of perfluorocarbon polymers is that they are not brittle at low temperatures.
Chemical corrosion resistance and weather resistance Except for molten alkali metals, PTFE is almost not corroded by any chemical reagents. For example, when boiled in concentrated sulfuric acid, nitric acid, hydrochloric acid, or even aqua regia, its weight and performance remain unchanged. It is also almost insoluble in all solvents, and is only slightly soluble in all alkanes above 300°C (about 0.1g/100g). PTFE does not absorb moisture, is non-flammable, and is extremely stable to oxygen and ultraviolet rays, so it has excellent weather resistance.
Electrical properties PTFE has low dielectric constant and dielectric loss over a wide frequency range, and has high breakdown voltage, volume resistivity and arc resistance.
Radiation resistance: The radiation resistance of polytetrafluoroethylene is poor (104 rad). High-energy radiation causes degradation, and the electrical and mechanical properties of the polymer are significantly reduced.
Polymerization Polytetrafluoroethylene is produced by free radical polymerization of tetrafluoroethylene. Industrial polymerization reactions are carried out with stirring in the presence of a large amount of water to disperse the heat of reaction and facilitate temperature control. Polymerization is generally carried out at 40 to 80°C and a pressure of 3 to 26 kgf/cm2. Inorganic persulfates and organic peroxides can be used as initiators, or a redox initiating system can be used. Each mole of tetrafluoroethylene releases heat of 171.38kJ during polymerization. Dispersion polymerization requires the addition of perfluorinated surfactants, such as perfluorooctanoic acid or its salts.
Application PTFE can be formed by compression or extrusion; it can also be made into aqueous dispersion for coating, impregnation or fiber making. PTFE is widely used as high and low temperature resistant, corrosion resistant materials, insulation materials, anti-stick coatings, etc. in atomic energy, aerospace, electronics, electrical, chemical industry, machinery, instruments, meters, construction, textile, food and other industries.
Atmospheric aging resistance: radiation resistance and low permeability: the surface and performance remain unchanged after long-term exposure to the atmosphere.
Non-flammability: Oxygen limiting index is below 90.
Acid and alkali resistance: insoluble in strong acids, strong alkali and organic solvents.
Oxidation resistance: Resistant to corrosion by strong oxidants.
Acidity and alkalinity: neutral.
The mechanical properties of polytetrafluoroethylene are soft. Has very low surface energy.
Polytetrafluoroethylene (F4, PTFE) has a series of excellent performance properties: high temperature resistance - long-term use temperature of 200~260 degrees, low temperature resistance - still soft at -100 degrees; corrosion resistance - ability to withstand Aqua regia and all organic solvents; weather resistance - the best aging life among plastics; high lubrication - the smallest friction coefficient among plastics (0.04); non-stickiness - the smallest surface tension among solid materials without adhering to anything; Non-toxic - physiologically inert; excellent electrical properties, ideal C-class insulation material. PTFE materials are widely used in important sectors such as national defense industry, atomic energy, petroleum, radio, electric machinery, and chemical industry. Products: PTFE rods, pipes, plates, turned plates. PTFE is a polymer of tetrafluoroethylene. The English abbreviation is PTFE. The structural formula is . It was discovered in the late 1930s and put into industrial production in the 1940s. Properties: The relative molecular weight of polytetrafluoroethylene is relatively large, ranging from hundreds of thousands to more than 10 million, and generally millions (the degree of polymerization is on the order of 104, while polyethylene is only 103). Generally, the crystallinity is 90 to 95%, and the melting temperature is 327 to 342°C. The CF2 units in the polytetrafluoroethylene molecule are arranged in a zigzag shape. Since the radius of the fluorine atom is slightly larger than that of hydrogen, the adjacent CF2 units cannot be completely trans-cross-oriented, but form a spiral twisted chain, which is almost covered by the fluorine atoms. on the surface of the entire polymer chain. This molecular structure explains PTFE's various properties. When the temperature is lower than 19°C, a 13/6 helix is ??formed; at 19°C, a phase change occurs, and the molecules unwind slightly to form a 15/7 helix.
Although the breaking of carbon-carbon bonds and carbon-fluorine bonds in perfluorocarbons requires energy absorption of 346.94 and 484.88kJ/mol respectively, the depolymerization of polytetrafluoroethylene to generate 1 mol of tetrafluoroethylene only requires Energy 171.38kJ. Therefore, during high-temperature cracking, polytetrafluoroethylene is mainly depolymerized into tetrafluoroethylene. The weight loss rates (%) of polytetrafluoroethylene at 260, 370 and 420°C are 1×10-4, 4×10-3 and 9×10-2 per hour respectively. It can be seen that PTFE can be used for a long time at 260℃. Since highly toxic by-products such as fluorophosgene and perfluoroisobutylene are also produced during high-temperature cracking, special attention must be paid to safety protection and to prevent polytetrafluoroethylene from coming into contact with open flames.
Mechanical properties Its friction coefficient is extremely small, only 1/5 of polyethylene, which is an important feature of perfluorocarbon surface. And because the fluorine-carbon chain intermolecular force is extremely low, PTFE is non-sticky.
Polytetrafluoroethylene maintains excellent mechanical properties in a wide temperature range of -196 to 260°C. One of the characteristics of perfluorocarbon polymers is that they are not brittle at low temperatures.
Chemical corrosion resistance and weather resistance Except for molten alkali metals, PTFE is almost not corroded by any chemical reagents. For example, when boiled in concentrated sulfuric acid, nitric acid, hydrochloric acid, or even aqua regia, its weight and performance remain unchanged. It is also almost insoluble in all solvents, and is only slightly soluble in all alkanes above 300°C (about 0.1g/100g). PTFE does not absorb moisture, is non-flammable, and is extremely stable to oxygen and ultraviolet rays, so it has excellent weather resistance.
Electrical properties PTFE has low dielectric constant and dielectric loss over a wide frequency range, and has high breakdown voltage, volume resistivity and arc resistance.
Radiation resistance: The radiation resistance of polytetrafluoroethylene is poor (104 rad). High-energy radiation causes degradation, and the electrical and mechanical properties of the polymer are significantly reduced.
Polymerization Polytetrafluoroethylene is produced by free radical polymerization of tetrafluoroethylene. Industrial polymerization reactions are carried out with stirring in the presence of a large amount of water to disperse the heat of reaction and facilitate temperature control. Polymerization is generally carried out at 40 to 80°C and a pressure of 3 to 26 kgf/cm2. Inorganic persulfates and organic peroxides can be used as initiators, or a redox initiating system can be used. Each mole of tetrafluoroethylene releases heat of 171.38kJ during polymerization. Dispersion polymerization requires the addition of perfluorinated surfactants, such as perfluorooctanoic acid or its salts.
Expansion coefficient (25～250℃) 10～12×10-5/℃