The advantages of polytetrafluoroethylene (PTFE) are as follows:
High temperature resistance – the working temperature is up to 250 ℃.
Low temperature resistance – good mechanical toughness; 5% elongation can be maintained even if the temperature drops to -196°C.
Corrosion resistance – for most chemicals and solvents, it is inert, resistant to strong acids and alkalis, water and various organic solvents.
Weather Resistant – Has the best aging life of any plastic.
High Lubrication – The lowest coefficient of friction among solid materials.
Non-stick – is the smallest surface tension in a solid material and does not stick to anything.
Non-toxic – It is physiologically inert, and it is implanted in the body as an artificial blood vessel and an organ for a long time without adverse reactions.
The relative molecular mass of PTFE is relatively large. Generally, the crystallinity is 90-95%, and the melting temperature is 327-342 °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 the hydrogen, the adjacent CF2 units cannot be completely oriented in trans, but form a helical twisted chain, which is almost covered by the fluorine atoms. the surface of the entire polymer chain. This molecular structure explains the various properties of PTFE. When the temperature is lower than 19°C, a 13/6 helix is formed; at 19°C, a phase transition occurs, and the molecules are slightly unwound, forming a 15/7 helix.
Although the breaking of carbon-carbon bonds and carbon-fluorine bonds in perfluorocarbons requires energy absorption of 346.94 and 484.88 kJ/mol, respectively, the depolymerization of PTFE to generate 1 mol of tetrafluoroethylene requires only 171.38 kJ of energy. Therefore, during high temperature cracking, PTFE is mainly depolymerized into tetrafluoroethylene. The weight loss rate (%) of polytetrafluoroethylene at 260, 370 and 420°C is 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 pyrolysis, special attention should be paid to safety protection and to prevent PTFE from contacting open flames.
Main applications of polytetrafluoroethylene (PTFE):
PTFE has a high melting point and a high melt viscosity, and is sensitive to shearing in an amorphous state, which is prone to melt fracture. Therefore, conventional thermoplastic molding processes such as melt extrusion and injection molding cannot be used, and only similar powders can be used. Metallurgical method for sintering.
The manufacture of filled PTFE is the same as the molding of PTFE. It can be processed by pre-forming, free sintering, or by plunger extrusion. The above processing technology is generally suitable for products with a certain wall thickness, not suitable for the processing of PTFE films. In recent years, a lot of research has been carried out in China. The more mature processing technologies are: calendering for disperse PTFE resin; metal turning processing using the characteristics of low hardness and good toughness of PTFE sintered products; in addition, there is a conventional extrusion method and In the extrusion processing of the calendering method, the resin is directly processed with raw materials without being melted and plasticized.
In addition to the primary processing technology introduced above, PTFE processing also has some newly developed secondary processing technologies worthy of attention, such as PTFE vacuum forming technology, hot press forming and hot blow molding technology, isobaric forming processing technology, etc. PTFE is the preferred material for corrosion-resistant lining of corrosion-resistant pipes, fittings, bellows, pump bodies, valves, kettles, tanks, towers and various standard equipment; as a sealing material, it is widely used in machinery, petrochemical, transportation, textile and construction industries. Wide range; PTFE 1.6 micron powder can also be used as valves, bearings, piston rings, guide rails and other parts requiring corrosion resistance and low friction;
According to the selective air permeability of PTFE film after treatment, it can be used as a separation material to selectively permeate gas or liquid, especially filter corrosive liquids; due to the excellent biocompatibility of PTFE, many people in recent years will It has been deeply studied as a biological material. In recent years, PTFE membrane has been developed and used as artificial organs at home and abroad, such as artificial blood vessels, heart valves, etc., for example, it is clinically used as artificial blood vessels and prosthesis stent materials in rhinoplasty. , have achieved good results.
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