Among fluoroplastics, polytetrafluoroethylene is the most consumed and widely used, and it is an important variety of fluoroplastics. The chemical structure of polytetrafluoroethylene is formed by replacing all hydrogen atoms in polyethylene with fluorine atoms.
Product Name: Polytetrafluoroethylene
English name: Polytetrafluoroethylene
Alias: PTFE; Teflon; Teflon; Teflon; Teflon; F4; The King of Plastics; Te フンン (Japanese) [English abbreviation is PTFE, trademark name Teflon®, Chinese translation varies from place to place: mainland is translated as Teflon®, Hong Kong is translated as Teflon®, and Taiwan is translated as Teflon®]
Molecular formula: [CF2CF2] n
Production method: Polytetrafluoroethylene is generated by free radical polymerization of tetrafluoroethylene. Industrial polymerization reactions are carried out by stirring in the presence of a large amount of water to disperse the reaction heat and facilitate temperature control. Polymerization is generally carried out at 40~80 ℃ and 3~26 kilogram-force/cm2 pressure. Inorganic persulfate and organic peroxide can be used as initiators, or redox initiation system can be used. 171.38 kJ of heat is released during the polymerization of tetrafluoroethylene per mole. Dispersion polymerization requires the addition of perfluorinated surfactants, such as perfluorooctanoic acid or its salts.
Usage: It can be made into rods, plates, pipes, films, and various shaped products, used in aerospace, chemical, electronic, mechanical, pharmaceutical and other fields.
Remarks:
Polytetrafluoroethylene [PTFE, F4] is one of the best corrosion-resistant materials in the world today, hence earning the nickname of "plastic king". It can be used for a long time in any type of chemical medium, and its emergence has solved many problems in China's chemical, petroleum, pharmaceutical and other fields. PTFE seals, gaskets, and gaskets. PTFE seals, gaskets, and sealing gaskets are made by using suspension polymerized PTFE resin molding. Compared with other plastics, polytetrafluoroethylene has excellent chemical corrosion resistance and temperature resistance, and it has been widely used as a sealing and filling material.
It has high chemical stability and excellent chemical corrosion resistance, such as strong acid, strong alkali, strong oxidant, outstanding heat resistance, cold resistance and friction resistance, long-term use temperature range of - 200 -+250 ℃, and excellent electrical insulation, which is not affected by temperature and frequency. In addition, it has the characteristics of non adhesion, non water absorption, and non combustion. Suspended resins are generally formed and processed by molding and sintering, and the resulting rods, plates, or other profiles can also be further processed by machining methods such as planing, drilling, and milling. The rod can be turned and drawn to form an oriented film.
Characteristics of polytetrafluoroethylene (PTFE):
1. Strength (high strength to weight ratio)
2. Chemical inertness
3. Biological adaptability
4. High thermal resistance
5. High chemical impedance in harsh environments
6. Low Flammability
7. Low friction coefficient
8. Low dielectric constant
9. Low water absorption
10. Good weathering properties
Detailed introduction:
Polytetrafluoroethylene is a polymer of tetrafluoroethylene. The English abbreviation is PTFE. The product 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-CF2-CF2-. Polytetrafluoroethylene is widely used in various materials that require resistance to acids, alkalis, and organic solvents. It is not toxic to humans, but one of the raw materials used in the production process, perfluorooctanoic acid ammonium (PFOA), is considered to have carcinogenic effects.
The relative molecular weight of polytetrafluoroethylene is relatively large, ranging from hundreds of thousands to over 10 million, usually in the millions (polymerization degree is in the order of 104, while polyethylene is only in 103). The general crystallinity is 90-95%, and the melting temperature is 327-342 ℃. CF2 units in polytetrafluoroethylene molecule are arranged in zigzag shape. Since the fluorine atomic radius is slightly larger than that of hydrogen, the adjacent CF2 units cannot be completely trans cross oriented, but form a helical twisted chain, and the fluorine atoms almost cover the surface of the entire polymer chain. This molecular structure explains the various properties of PTFE. When the temperature is below 19 ℃, a 13/6 helix is formed; At 19 ℃, a phase transition occurs, and the molecules slightly unravel, forming a 15/7 helix.
Chemical properties:
The chemical structure of polytetrafluoroethylene is formed by replacing all hydrogen atoms in polyethylene with fluorine atoms. Its molecular formula is:
The F atom in PTFE molecules covers the C-C bond and the C-F bond energy is high and particularly stable. It is not corroded by any chemical except for alkali metals and elemental fluorine.
The F atom in PTFE molecule is symmetrical, and the two elements in C-F are covalently bound. There are no free electrons in the molecule, and the entire molecule is neutral. It makes PTFE have excellent dielectric properties. Because there is no gram bond in the molecular structure of PTFE, its crystallinity is very high. Due to P
TFE molecules have an inert fluorinated outer shell, which gives them outstanding non stick properties and low friction coefficient.
Insulation: Not affected by environment and frequency, with a volume resistance of up to 1018 ohms • cm, low dielectric loss, and high breakdown voltage.
High and low temperature resistance: The impact on temperature is not significant, and the temperature range is wide. It can be used at temperatures of -190~260 ℃.
Self lubrication: With the smallest friction coefficient among plastics, it is an ideal oil-free lubricating material.
Surface non adhesion: Known solid materials cannot adhere to the surface and are the solid materials with the smallest surface energy.
Atmospheric aging resistance, radiation resistance, and low permeability: Long term exposure to the atmosphere, the surface and properties remain unchanged.
Non combustible: Oxygen limiting index below 90.
Chemical corrosion resistance and weather resistance: Except for molten alkali metals, polytetrafluoroethylene is hardly corroded by any chemical reagents. For example, when boiled in concentrated sulfuric acid, nitric acid, hydrochloric acid, or even aqua regia, its weight and properties remain unchanged, and it is almost insoluble in all solvents. It is only slightly soluble in total alkanes (about 0.1g/100g) above 300 ℃. Polytetrafluoroethylene does not absorb moisture, is non flammable, and is extremely stable to oxygen and ultraviolet rays, so it has excellent weather resistance.
Although the breaking of carbon carbon bonds and carbon fluorine bonds in perfluorocarbons requires energy absorption of 346.94 and 484.88kJ/mol, the depolymerization of polytetrafluoroethylene to produce 1mol of tetrafluoroethylene only requires energy of 171.38kJ. So during high-temperature cracking, polytetrafluoroethylene mainly depolymerizes to tetrafluoroethylene. The weight loss rates (%) of polytetrafluoroethylene at 260, 370, and 420 ℃ are 1% per hour, respectively × 10-4, 4 × 10-3 and 9 × 10-2. It can be seen that polytetrafluoroethylene can be used for a long time at 260 ℃. Due to the production of highly toxic by-products such as fluorophosgene and perfluoroisobutylene during high-temperature cracking, special attention should be paid to safety protection and prevent polytetrafluoroethylene from coming into contact with open flames.
It does not melt at a temperature of 250 ℃ and does not become brittle at ultra-low temperatures of -260 ℃. Polytetrafluoroethylene is exceptionally smooth, even ice cannot compare to it; It has excellent insulation performance, and a thick film of newspaper is enough to withstand high voltage of 1500V.
Physical properties:
The mechanical properties of polytetrafluoroethylene are relatively soft. Has very low surface energy.
Polytetrafluoroethylene (F4, PTFE) has a series of excellent performance: high temperature resistance - long-term use temperature 200-260 degrees Celsius, low temperature resistance - still soft at -100 degrees Celsius; Corrosion resistance - resistant to aqua regia and all organic solvents; Climate resistance - the best aging life in plastics; High lubrication - with the smallest friction coefficient in plastic (0.04); Non adhesive - having the minimum surface tension in a solid material without adhering to any substance; Non toxic - with physiological inertness; Excellent electrical performance, making it an ideal C-grade insulation material. PTFE materials are widely used in important sectors such as national defense and military industry, atomic energy, petroleum, radio, power machinery, chemical industry, etc.
Products: PTFE rods, tubes, plates, and turning plates. Polytetrafluoroethylene is a polymer of tetrafluoroethylene. The English abbreviation is PTFE. The structural formula is. In the late 1930s, it was discovered that it was put into industrial production in the 1940s. The relative molecular weight of polytetrafluoroethylene is relatively large, ranging from hundreds of thousands to over 10 million, usually in the millions (polymerization degree is in the order of 104, while polyethylene is only in 103). The general crystallinity is 90-95%, and the melting temperature is 327-342 ℃. CF2 units in polytetrafluoroethylene molecule are arranged in zigzag shape. Since the fluorine atomic radius is slightly larger than that of hydrogen, the adjacent CF2 units cannot be completely trans cross oriented, but form a helical twisted chain, and the fluorine atoms almost cover the surface of the entire polymer chain. This molecular structure explains the various properties of PTFE. When the temperature is below 19 ℃, a 13/6 helix is formed; At 19 ℃, a phase transition occurs, and the molecules slightly unravel, forming a 15/7 helix.