Introduction of PTFE, PFA, ETFE, PCTFE, PVF, PVDF, Etc.

Basic properties of fluoroplastics

Fluoroplastics was founded in 1934, Schloffer, Scherer found polychlorotrifluoroethylene (PCTFE), in 1938 DuPont's R.J. P1unkett found Polytetrafluoroethylene (PTFE) and industrialized in 1949. Following the British ICI, Germany's Hoechst, Japan's Daikin Industries, Italy's Montefluos and other successive production. China's fluorine plastic was successfully developed in 1958, first industrialized in Shanghai, after the 80's countries have increased production capacity, new varieties continue to appear, the existing varieties of more than 20 kinds, the use is also increasingly expanding.

Fluoroplastics are produced by fluorine-containing monomers such as tetrafluoroethylene, hexafluoropropylene, trifluoroethylene chloride, vinylidene fluoride, fluoroethylene, hexafluoroisobutene, perfluoroalkyl vinyl ether and vinyl and other monomers through polymerization or copolymerization reaction.

Fluoroplastics is a general term for polymer compounds containing fluorine atoms in the main chain of the molecule. Fluoroplastics are heat-resistant, cold-resistant, weather-resistant, drug-resistant, solvent-resistant, and have excellent insulating properties and high-frequency electrical properties. And has no wither, self-lubrication, low friction coefficient and other characteristics.

Polytetrafluoroethylene, perfluoro (ethylene-propylene) copolymer (FEP) is composed entirely of carbon and fluorine atoms, while Polyvinylidene fluoride (PVDF), polyvinylidene fluoride (PVF) molecules also contain hydrogen atoms, and polytrifluoroethylene also contains chlorine atoms. The excellent performance of fluoroplastics is realized by the high binding energy between carbon and fluorine atoms. Polytetrafluoroethylene main chain skeleton is carbon atoms, and the surrounding completely surrounded by fluorine atoms, so its various properties are higher, while PFA, FEP, ETFE and other varieties due to the influence of the side group, the softening point of low sub-PTFE, and other properties have also changed.

1. Thermal properties: Fluoroplastics have flame retardant and excellent heat resistance, PTFE and PFA can be used continuously up to 260 ℃, short-term can be used at 300 ℃, the use of FEP temperature is 60 ℃ lower than them, PCTFE can be used at 120 ℃ higher. Fluorine plastic such as long-term use at high temperatures will cause changes in crystallinity, especially in the manufacture of equipment lining must be noted.

2. Drug resistance: Fluoroplastics have excellent drug resistance and solvent resistance, especially PTFE, PFA, FEP, etc., acid, alkali, solvents on them are not leaching. But the molten alkali metals, fluorine, CFCs have different degrees of influence on them, PCTFE, ETFE, PVDF, etc. in the fluorine plastics, drug resistance is slightly worse, but much better than the corrosion resistance of other plastics.

3. Electrical properties: the electrical properties of fluoroplastics, especially the high-frequency electrical properties of other materials is difficult to match. PTFE, FEP, PFA molecular polarity is very low, in a wide range of temperatures, frequency interval changes are very small, the relative dielectric constant is stable, the dielectric loss is very low, excellent electrical insulation. Among them, PVDF also has special piezoelectricity and pyroelectricity, can be used to manufacture piezoelectric materials.

4. Mechanical properties: fluorine plastic molecules containing hydrogen, chlorine atoms increase its tensile strength is also improved. PTFE and PCTFE brittleness temperature is very low, showing excellent low temperature performance. PTFE has a low coefficient of friction and special self-lubricating properties. But PTFE also has its own abrasion and cold flow and other shortcomings. Can be used to fill a variety of fillers to improve wear resistance, to overcome the cold flow.

5. Non-sticky: fluoroplastics have special non-stick. Especially like PTPE, FEP, PFA and other molecules with high fluorine content, the surface contact angle is very large, so that the liquid on the surface of fluoroplastic products into a ball. It is not easy to bond with resin, so it is often used to make cookware surface non-stick Xu layer.

6. Weather resistance: all varieties of fluoroplastics have excellent weather resistance, even in harsh temperatures under prolonged exposure to the sun, its various properties are unchanged.

7. Hydrophobicity: Fluorine plastic has a low water absorption rate, especially PTFE. It can be utilized to make air-impermeable composite fabrics and other equipment with its hydrophobicity.

Properties and uses of the main varieties of fluoroplastics

The main varieties of fluorine plastic introduction

Polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) density, 2.14 ~ 2.20g / cm3, almost non-absorbent, can be in -250 ~ 260 ℃ for long-term continuous use, not dissolved or dissolved in any known solvents, even at high temperatures, aqua regia, it does not play a role, there is a "king of plastics," the name. Table 2-1 lists the polytetrafluoroethylene (PTFE) materials. Table 2-1 lists the performance of polytetrafluoroethylene and modified varieties. PTFE has medium strength, low hardness, deformation under long-term stress, but high elongation at break.

The friction factor of PTFE is very small and has excellent lubricity. The friction factor of PTFE increases with the sliding rate and stabilizes when the linear velocity reaches 0.5-1.0m/s or more, and the static friction factor is smaller than the dynamic friction factor. In the high-speed, high load conditions, PTFE friction factor can be less than 0.01, and the friction factor does not change with temperature changes, from ultra-low temperature to the melting point of PTFE, the friction factor remains almost unchanged, only in the surface temperature is higher than the melting point, the friction factor increases dramatically. PTFE has excellent dielectric properties, above 0 ℃, the dielectric properties do not change with the frequency and temperature changes, also not subject to humidity and humidity. PTFE has excellent dielectric properties, above 0 ℃, the dielectric properties do not change with the frequency and temperature changes, and is not affected by humidity and corrosive gases.PTFE volume resistivity is greater than 1017Ω-cm, the surface resistivity is greater than 1016Ω, in all engineering plastics for the highest value.

PTFE's atmospheric aging resistance is very outstanding, even in the atmosphere for a long time exposure, the surface will not produce any changes, PTFE's flame retardant excellent, the surface has a non-stick, almost all solid materials can not stick to its surface.

PTFE crystallization melting point of 327 ℃, but the resin to be above 380 ℃ in order to be in a molten state, the melt viscosity of up to 1010Pa - s, and has a strong resistance to solvents, therefore, PTFE is usually used in cold press molding and then sintering molding methods.

PTFE's excellent performance makes it widely used in machinery, electronic and electrical appliances and chemical equipment, etc. PTFE's low friction factor and self-lubrication make it widely used in the manufacture of bearings, piston rings, machine tool guides and sealing materials. When PTFE is used to make bearings, glass fiber, bronze powder, graphite or molybdenum disulfide are added to fill the bearings to overcome creep and wear. The oil seal of rotating shaft made of PTFE can be used for a long time at 260℃, can resist various media, and can work in the absence or absence of oil.PTFE is mainly used in chemical equipment for lining, pipeline, valves, pumps, heat exchangers, etc. PTFE is also used as a sealing material of machine tool guide and sealing material of machine tool.

Tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) is developed to improve the molding properties of PTFE, its mechanical properties, electrical properties, chemical stability, lubricity, non-stick, flame retardant and atmospheric aging resistance and PTFE are basically the same (see Table 3-16), and its outstanding feature is that it has a good thermoplasticity, and can be used for injection, extrusion, blow molding and other methods of molding.

Tetrafluoroethylene - hexafluoropropylene copolymer (FEP) is a modified variety of PTFE, commonly known as fluorine resin 46 (F-46). Its melt viscosity is reduced to the point that it can be processed by general thermoplastic molding methods. Its main properties are similar to PTFE (see Table 3-16), but heat resistance is lower than PTFE, long-term use temperature is lower than PTFE about 50 ~ 60 ℃.

Ethylene - tetrafluoroethylene copolymer (E / TFE), also known as fluoroplastics 40, tensile strength, impact strength and creep resistance are better than PTFE (see Table 3-16). Low-temperature impact strength is the best of the existing fluoroplastics, its long-term use of the temperature of -60 ~ 180 ℃, a short period of time up to 230 ℃. E / TFE can be processed by general thermoplastic molding methods, but the molding temperature range is narrower, the fluidity of the mold is poorer, molding molds have strong adhesion, mold mold molds must be coated with mold releasing agent.

Other Fluoroplastics

Table 2-2 lists other fluoroplastics and their properties. The mechanical strength and modulus of elasticity of polychlorotrifluoroethylene (PCTFE) are higher than that of PTFE, the compression strength and creep resistance are obviously better than that of PTFE, the long-term continuous use temperature is 200℃, and the low-temperature performance is good, and it can be used for a long period of time at -200℃. PCTFE can be used to manufacture valve seats with high dimensional accuracy, self-lubricating gears, pulleys and brakes, sealing gaskets for liquid oxygen and liquid hydrogen devices, corrosion-resistant gaskets for chemical equipment, conduits, lined valves and corrosion-resistant pumps.

The mechanical strength of polyvinylidene fluoride (PVDF) is higher than that of PTFE, and it has excellent compressive properties and creep resistance. the melting point of PVDF is 165~185℃, and it has plasticity above the melting point, and the viscosity of the melt can satisfy the thermoplastic processing methods such as extrusion and injection when it is 240~260℃. the glass transition temperature of PVDF is -35℃, and the long-term continuous use temperature range is -70℃, and the temperature of PVDF is -40℃. PVDF glass transition temperature of -35 ℃, long-term continuous use temperature range of -70 ~ 150 ℃. PVDF dielectric constant is very high, the dielectric loss angle tangent value is larger, volume resistivity is lower than PTFE, dielectric strength is also lower, chemical resistance is not as good as PTFE and PCTFE, inorganic acids, alkalis have excellent resistance, but organic acids and organic solvents are less resistant. PVDF can be used in the manufacture of chemical pipelines, pumps, valves, storage tanks and other anti-corrosion lining, as well as corrosion-resistant gears, bearings, sealing gaskets and so on.

The outstanding features of polyvinyl fluoride (PVF) are excellent weather resistance and excellent mechanical properties. Among fluoroplastics, PVF has the highest tensile strength, the lowest gas permeability, good abrasion resistance, good chemical resistance, and is not subject to most acids and alkalis.PVF is mainly used for films and coatings, and the adhesion of PVF coatings to metals and plastics is good, so that it can form an ideal weatherproof protective layer of construction materials, which is used in the corners of houses, warehouses, factories, roofs, pipelines, and other surfaces, as well as in the inner panels of the airplane cabins and ship cabins, Greenhouse skylight, etc.