Polytetrafluoroethylene (PTFE) has been excellent in high and low temperature resistance and chemical stability, good electrical insulation properties, non-adhesion, weather resistance, flame retardancy and good self-lubricating properties. , textile, electrical and electronic, medical, mechanical and other fields have been widely used.
Polytetrafluoroethylene (PTFE) is the most widely used in fluoroplastics and is the most widely used in fluoroplastics. PTFE has excellent high and low temperature resistance and chemical stability, good electrical insulation properties, non-adhesion, weather resistance, flame retardancy and good self-lubricating properties. It has the reputation of “Plastic King”. The material was first developed for the needs of national defense and cutting-edge technology, and then gradually extended to civilian use. Its use covers many aspects of aerospace and civil applications and is now an indispensable material in its application.
PTFE performance characteristics
PTFE is a polymer obtained by polymerizing a tetrafluoroethylene monomer. It is a transparent or opaque wax similar to PE. It has a density of 2.2 g/cm3 and a water absorption of less than 0.01%. Its chemical structure is similar to PE, except that all hydrogen atoms in the polyethylene are replaced by fluorine atoms. Due to its high CF bond energy and stable performance, it has excellent chemical resistance and can withstand all strong acids (including aqua regia) except molten alkali metal, fluorinated medium and sodium hydroxide above 300 °C. And the action of strong oxidants, reducing agents and various organic solvents; the F atoms in the PTFE molecule are symmetric, the two elements in the CF bond are covalently bonded, and there are no free electrons in the molecule, making the whole molecule neutral, so it has Excellent dielectric properties, and its electrical insulation is not affected by the environment and frequency. Its volume resistance is greater than 1017 m, low dielectric loss, high breakdown voltage, good arc resistance, long-term operation in an electrical environment of 250 ° C; due to the absence of hydrogen bonds in the molecular structure of PTFE, the structure is symmetrical, so its High crystallinity (generally 55%~75%, sometimes as high as 94%), making PTFE excellent heat resistance, melting temperature is 324 °C, decomposition temperature is 415 °C, maximum temperature is 250 °C, brittle The temperature was -190 ° C, and the heat distortion temperature (at 0.46 MPa) was 120 °C. The mechanical properties of PTFE are good, the tensile strength is 21~28MPa, the bending strength is 11~14MPa, the elongation is 250%~300%, and the dynamic and static friction coefficient of steel is 0.04, which is better than nylon, polyoxymethylene and polyester. The friction coefficient of plastic is small.
Use of PTFE
The unique properties of PTFE make it widely used in industrial and marine applications in the chemical, petroleum, textile, food, paper, medical, electronics and machinery industries.
1. Application of anti-corrosion performance
Since materials such as rubber, glass, and metal alloys have defects in corrosion resistance, it is difficult to meet the environment in which the temperature, pressure, and chemical medium coexist in a harsh condition, and the resulting loss is quite remarkable. PTFE materials have become the main corrosion-resistant materials in the petroleum, chemical, textile and other industries due to their excellent corrosion resistance. Specific applications include: conveying pipes for corrosive gases, exhaust pipes, steam pipes, high pressure oil pipes for rolling mills, high and low pressure pipes for aircraft hydraulic systems and cold press systems, rectification towers, heat exchangers, kettles, towers, tanks Lining, valves and other chemical equipment.
The performance of the seal has a great impact on the efficiency and performance of the entire machine. PTFE material has corrosion resistance, aging resistance, low friction coefficient and non-stickiness, wide temperature range and good elasticity. It is very suitable for the manufacture of seals with high corrosion resistance and temperature above 100 °C. Such as machines, heat exchangers, high pressure vessels, large diameter vessels, valves, seals for grooved flanges of pumps, glass reactors, flat flanges, seals for large diameter flanges, shafts, piston rods, valve stems, Worm gears, seals for tie rods, etc.
2, low friction performance in the application of load
Because some parts of the friction part of the equipment should not be lubricated, such as in the case where the lubricating grease will be dissolved by the solvent and the products in the papermaking, pharmaceutical, food, textile and other industrial fields need to avoid the contamination of the lubricating oil, which makes the filling of the PTFE material The most ideal material for mechanical parts without oil lubrication (direct load). This is because the coefficient of friction of the material is the lowest of the known solid materials. Its specific uses include bearings for chemical equipment, papermaking machinery, agricultural machinery, as piston rings, machine tool guides, guide rings; widely used in civil engineering construction as bridges, tunnels, steel roof trusses, large chemical pipelines, storage tanks Supports the slider and serves as a bridge support and bridge swivel.
3. Application in electrical and electronic applications
The inherent low loss and small dielectric constant of PTFE materials make it an enameled wire for use in micro motors, thermocouples, control devices, etc. PTFE films are ideal for capacitors, radio insulation gaskets, insulated cables, motors and transformers. Insulating material is also one of the indispensable materials for industrial electronic components such as aerospace; the oxygen sensor can be manufactured by using the fluoroplastic film with high oxygen permeability and low permeability to water vapor. The use of fluoroplastics to exhibit extreme charge deviation at high temperatures and pressures allows the manufacture of microphones, speakers, parts on robots, etc., and the use of low refractive index properties to produce optical fibers.
4. Application in medical and pharmaceutical fields
Expanded PTFE material is purely inert, has very strong biocompatibility, does not cause body rejection, has no physiological side effects on the human body, can be disinfected by any method, and has a microporous structure, which can be used for various rehabilitation solutions. Includes artificial blood vessels and patches for soft tissue regeneration and surgical sutures for blood vessels, heart, general surgery and orthopedics.
5, the application of anti-stick properties
The PTFE material has the smallest surface tension in solid materials, does not adhere to any substance, and has excellent properties of resistance to high and low temperatures, so that it is widely used in the anti-adhesion such as the manufacture of non-stick pans. The anti-sticking process mainly includes two types: mounting a PTFE member or a sheet on a substrate, and thermally shrinking the PTFE coating or the glass-bonded varnish onto the substrate.
With the continuous development of material application technology, the three major shortcomings of PTFE materials: cold flow, difficult weldability, and difficult melt processing are gradually being overcome, thus making it impervious to optical, electronic, medical, petrochemical oil transportation, etc. The application prospects in various fields are broader.
