What are the properties of PTFE?

You can find it with a search engine: High temperature resistance - the operating temperature reaches 250℃. Low temperature resistance - good mechanical toughness ； Even if the temperature drops to -196°C, the elongation of 5% can be maintained. Corrosion resistance - inert to most chemicals and solvents, resistant to strong acids and alkalis, water and various organic solvents. Weather resistant – has the best aging life among plastics. High lubrication - has the lowest friction coefficient among solid materials. Non-stick - is the smallest surface tension in a solid material and does not stick to anything. Non-toxic - physiologically inert, long-term implantation in the body as artificial blood vessels and organs 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 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. The fluorine atoms almost cover 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 spiral is formed ； A phase transition occurs at 19°C, and the molecule unwinds slightly to form a 15/7 helix. Although the cleavage 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 requires only 171.38kJ of energy. 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°C. 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 intermolecular force between fluorine and carbon chains is extremely low, polytetrafluoroethylene is non-sticky. It does not melt at a temperature of 250°C and does not become brittle at an ultra-low temperature of -260°C. PTFE is so smooth that not even ice can compare to it ； Its insulation performance is particularly good. A film as thick as a newspaper is enough to withstand high voltage of 1500V. PTFE 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 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 PTFE has poor radiation resistance (104 rad). It will be degraded after being exposed to high-energy radiation, and the electrical and mechanical properties of the polymer will be significantly reduced. 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 Polytetrafluoroethylene can be formed by compression or extrusion ； It can also be made into aqueous dispersions 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. Classification of polytetrafluoroethylene and its filling products: 1. General materials: various rods, tubes, plates, films, belts, ropes, packings, gaskets, and graphite, molybdenum disulfide, aluminum oxide, glass fiber, and carbon fiber as fillers to improve the mechanical properties of pure polytetrafluoroethylene. 2. Anti-corrosion 1. Pipes and accessories: Pure PTFE pipe ； PTFE lined pipe ； Outer wrapped fiberglass steel pipe ； Steel composite flange ； 2. Chemical container lining: PTFE lined kettle ； PTFE lined tank ； PTFE lined tower ； 3. Heat exchanger ； 4. Corrugated telescopic tube ； 5.Main components of valves and pumps ； 6. Steel wire reinforced full pressure hose ； 7. Filter materials. The polytetrafluoroethylene film has a large number of pores in it after being stretched vertically and horizontally. It is a new material. By combining it with other fabrics, it can be made into solid-phase anti-corrosion filter bags for smoke or good waterproof, breathable, windproof and warm rain gear, sportswear, cold-proof clothing, special protective clothing and lightweight tents, compressed air for pharmaceuticals, sterile filtration of various solvents and filtration of high-purity gases in the electronics industry. 3. Sealing category 1. Static sealing: Sandwich gasket ； Sitting belt ； Elastic sealing tape ； 2. Dynamic seal (braided packing, ring seal): V-shaped sealing body - used for shafts, piston rods, valves ； Turbo pump inner seals ； Composite sealing ring of PTFE and rubber ； Retractable mechanical seal with bellows. 4. Load-bearing category 1. Filled PTFE bearings, used in food, chemical, paper, and textile machinery ； 2. Porous copper-impregnated fluoroplastic metal bearings can be used normally under high temperature, high pressure, dry friction and vacuum conditions. ； 3. Bearing linings made of composite fabrics blended with polytetrafluoroethylene fiber and glass fiber or other fibers for PTFE fiber bearings, used for low speed and high load ； 4. Filled PTFE piston rings, guide rings, machine tool guide rails and bridge sliders ； 5. Insulation: 1. Class C insulation material for wires and cables ； 2. Sheaths for stator and rotor water pipes and thermocouples of double water internally cooled turbine generators ； 3. Microwave insulation materials for high-frequency and ultra-high-frequency communication equipment and radars ； 4. Printed circuit substrates and insulation materials for motors and transformers (including gas transformers) ； 5. Insulation materials for air conditioners, electronic furnaces, various heaters and sulfur hexafluoride circuit breakers ； 6. Anti-sticking type: 1. The PTFE glass cloth coating on the hot roller of the sizing machine can avoid the roller sticking phenomenon caused by chemical sizing. * * Improve production speed and gray fabric quality ； 2. Microwave drying conveyor belts in the food industry - Compared with conveyor belts made of other materials, they do not absorb microwave energy, and therefore non-stick materials have the advantages of energy saving and cleaning. ； 3. Anti-adhesive material for heat sealing sleeves sealed in polyethylene bags ； 4. Anti-stick coating - used in kitchen pots, bread baking molds, frozen food storage trays, electric iron bases, and copier rollers ； 7. Temperature resistance: 1. Microwave oven drive transmission device, such as microwave oven couplings and rollers ； 2. Temperature-resistant accessories for various refrigerators, air conditioners, oxygen generators, and compressors ； 8. Other categories: 1. Human body substitutes for arteries, veins, and cardiac membranes ； 2. Endoscope, clamp catheter, trachea ； 3. Other medical equipment such as tubes, bottles, filter cloths, etc.

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