Structural characteristics and application fields of fluororubber
Since polyolefin-based fluororubber (26 type fluororubber, type 23 fluoroelastomer) and nitroso fluororubber have no unsaturated C=C bond structure in the main chain. It reduces the possibility of degradation and chain scission in the main chain due to oxidation and pyrolysis. The methylene group in vinylidene fluoride plays a very important role in the softness of the polymer chain. For example, fluororubber 23-21 and fluororubber 23-11 are respectively made of vinylidene fluoride and chlorotrifluoroethylene by 7:3. It is composed of a ratio of 5:5. Obviously, the former is softer than the latter.
Both vinylidene fluoride and chlorotrifluoroethylene, or a copolymer of the former and hexafluoropropylene, and a tetramer of tetrafluoroethylene, may be predominantly crystalline or amorphous. This depends on the amount of monomer intervening when one monomer is the major segment of the copolymer. Electron diffraction studies indicate that the two copolymers still have a hexafluoropropylene molar fraction of 7% in the vinylidene fluoride segment or a 16% molar fraction of vinylidene fluoride in the chlorotrifluoroethylene segment. Its equivalent homopolymer crystal structure. However, when the current hexafluoropropylene mole fraction is increased to more than 15%, or the latter's vinylidene fluoride mole fraction is increased to more than 25%, the crystal lattice is greatly destroyed, resulting in an amorphous property mainly composed of rubber properties. structure. This is due to the increase in the amount of introduction of the second monomer, which destroys the regularity of the original molecular chain. Fluororubber can be used in combination with nitrile rubber, acrylate rubber, ethylene propylene rubber, silicone rubber, fluorosilicone rubber, etc. to reduce cost and improve physical and mechanical properties and process performance.
The earliest fluororubber was poly-2-fluoro-1,3-butadiene which was produced by DuPont in the United States in 1948 and its copolymer with styrene and propylene. Its performance is no more prominent than that of neoprene or butyl rubber. And expensive, no actual industrial value. In the late 1950s, Thiokol Company of the United States developed a binary nitroso fluororubber with low temperature performance and strong oxidant resistance (N2O4). Fluororubbers are beginning to enter practical industrial applications. Since 1958, China has also developed a variety of fluororubbers, mainly polyolefin-based fluororubbers, such as type 23, type 26, type 246, and nitroso-based fluororubbers; subsequently developed a newer class of PTFE rubber. , perfluoroether rubber, fluorinated phosphorus rubber. These fluororubber varieties are first developed in the aviation, aerospace and other defense military supporting needs, and gradually applied to the civil industrial sector. They have been applied to cutting-edge technologies such as modern aviation, missiles, rockets, space navigation, ships, atomic energy, and automobiles, shipbuilding, and chemistry. , petroleum, telecommunications, instruments, machinery and other industrial fields.
Fluororubber is used in a wide range of applications in everyday life, such as in automotive parts, aerospace and aerospace, mechanical seals, pumps, reactors, mixers, compressor housings, valves, meters, and other equipment. Valve stem packing, diaphragms and gaskets, as well as in the rubber sheet industry, semiconductor manufacturing industry and food and pharmaceutical industries.
With the use of unleaded gasoline and EFI devices in automobiles, the structure and materials of the fuel hoses vary greatly. The inner rubber layer has replaced the nitrile rubber with fluororubber, in order to reduce fuel penetration and further improve heat resistance. The rubber layer is mostly composed of a composite structure, that is, a fluororubber and a chlorohydrin rubber or an acrylate rubber. Since the fluororubber is relatively expensive, the fluororubber layer is relatively thin and has a thickness of about 0.2 to 0.7 mm. This structure of fuel hose has become a mainstream product abroad. China has also developed this type of fluoro rubber as the inner layer of the hose, and used in Santana, Audi, Jetta, Fukang and other models of cars. In the automotive technology, gearbox and valve oil seals with high technical content, the materials selected are mainly fluorine rubber, hydrogenated nitrile rubber and so on. Fluororubber and silicone rubber composite oil seals have become the most commonly used engine crankshaft oil seals. The hydraulic system of the loading and unloading truck and the hydraulic system of the large loading and unloading truck have long working hours, the oil temperature and the temperature of the machine parts rise rapidly, the ordinary rubber can not meet the working requirements, and the fluororubber products can meet various harsh conditions due to their excellent temperature resistance. Technical requirements. With the continuous improvement of the reliability and safety requirements of the automotive industry, the demand for fluororubber in the automotive industry has also shown a rapid growth trend. In addition to automotive applications, fluororubber seals are used in drilling machinery, oil refining equipment, natural gas, and power plant desulfurization equipment to withstand harsh conditions such as high temperatures, high pressures, oils, and highly corrosive media; fluoroelastomer seals in chemical production The parts are used in pumps and equipment containers to seal chemicals such as inorganic acids and organic substances. Fluororubber seals are used in the petroleum and chemical industries for mechanical seals, pumps, reactors, mixers, compressor housings, valves, meters and other equipment, such as fillers commonly used as valve seats and stems, diaphragms. And gaskets. Fluororubber is one of the high-performance materials indispensable for cutting-edge science and technology such as modern aviation, missiles, rockets, space navigation, ships, and atomic energy. In recent years, new products of fluororubber have been continuously developed in the aerospace industry.