There are mainly two types of Teflon tape products: pure Teflon tape and Teflon coated fiberglass tape, which are very easily mixed. These two tapes have similar characteristics, but still some differences.
Teflon tape can be sorted into two categories according to the base material, one is the fiberglass fabric and the other one is Teflon film, customers are confusing when purchasing, the detailed difference is as follows:
Different surface: Teflon coated fiberglass tape is smooth with release liner or not, and the woven lines of fiberglass is visible ; Pure Teflon tape is smooth, without woven lines.
Different strength: the tensile strength of Teflon coated fiberglass tape is higher than pure Teflon tape.
Different specifications: Teflon coated fiberglass tape with the normal thickness of 0.13mm, 0.18mm, 0.25mm & 0.3mm, and the width of 1000mm, 1250mm are widely used; pure Teflon tapes are thinner with normal thickness 0.04mm, 0.06mm, 0.08mm, 0.13mm & 0.18mm, and the normal width of 300mm.
Polytetrafluoroethylene (PTFE) is considered the best solid lubricant, its friction coefficient is only 0.05 within 320 ℃ temperature, even smaller than the graphite friction factor 0.07. PTFE because its good lubricity and chemical stability, is widely used as industrial lubricants. Perfluoro surfactant is a type of fluorine-containing surfactant. Compared with the traditional surfactants, fluorosurfactants have high surface activity, high heat stability, high chemical stability, low surface tension, low use concentration and other excellent features. Most importantly, the fluorine-containing surfactant can be used as a dispersant, and the fluorine-containing surfactant can be used as a dispersant in the dispersion polymerization of various fluororesins.
Bonded solid lubricating film is organic and inorganic binder as the base material, the small friction coefficient solid as a solid lubricant, together with solvents and surfactants made of composite lubricating paint, by dip or spray to form coating.In this paper, epoxy resin as the base material, by adding polytetrafluoroethylene and perfluorinated surfactants (FC-400) made of self-lubricating friction-reducing coating. According to orthogonal experimental design to get different formulations of paint, and then coated on the polished iron which has been processed, at room temperature curing, get friction coating. After a series of tests, the best formula was screened out. The physical and chemical properties of the coatings were measured by a SpectrumOne infrared spectrometer, an MM-200 friction and wear tester, a Y-4Q X-ray diffractometer, a P / N2500052 SERIAL contact angle gage and a differential thermal analyzer.
Experimental method
The substrate used in the experiment is A4 steel sheet with size 20mm*20mm. The substrate was polished by model 200 #, 600 #, 800 #, 1500 # water-resistant sandpaper to remove the substrate surface oxide and impurities, with 15% hydrochloric acid and 15% sulfuric acid mixed solution pickling 2 min, with acetone and ethanol mixed solution in the beaker ultrasonic cleaning 10 min to remove the sample surface of organic matter, and then activated with 3% hydrochloric acid. According to orthogonal experiment design, select the amount of epoxy resin and curing agent are 3 g, the other reagents were tested according to a 4 factor 4 level orthogonal experiment table(see Table 1).
Table 1 4 factors 4 level orthogonal experiment table
According to the different formulations the orthogonal table, the weighed polytetrafluoroethylene powder and the graphite powder were mixed and shaken for 3 min in an ultrasonic oscillator, so that the polytetrafluoroethylene powder and the graphite powder are mixed uniformly. Take 4 mL of acetone, dissolve the dispersant FC-400, mix well, pay attention to slow stirring, to avoid excessive air bubbles. The mixed PTFE and graphite powder dissolved in acetone to dissolve the dispersant, the rapid mixing evenly. Pour the mixed mixture into a beaker with epoxy and EP curing agent, and mix well. The surface treatment of iron into the coating in the infiltration of 5 ~ 10 s, with the centrifuge to shake the sample, select the appropriate film thickness, that is the sample.
Results and discussion
Tribological properties
The friction coefficient of the coating was measured with a MM-200 friction and wear tester manufactured in Japan. The test was carried out at a load of 10 N at a speed of 180 r / min, the results of orthogonal experimental analysis are shown in Table 2.
Table 2 Friction factor analysis orthogonal table
In table 2, Kij is the i-th factor of the j-level test results and the value of the sum. For example, KA is the sum of the values of the first level of factor A for each test result, that is KA =0.144 +0.055 +0.122 +0.054 =0.375. ki is the ki value divided by the number of occurrences of that level, for example, KA means that the KA value is divided by the factor A factor of the first occurrence of the number of times, that is kA =KA/4 =0.375 /4 =0.094. Ri is the maximum difference between the ki values in the i-th factor, for example, the RA value is the difference between the maximum value of the kA value minus the minimum value, that is RA =kA -kA=0.12 -0.072 =0.048.
As can be seen from Table 2, the influence of each factor on the friction coefficient is small. We can see from RC
Table 3 is the contact angle of each factor and the impact of various factors on the contact angle, we can see from RB
Fig.1 X-ray diffraction spectrum of epoxy resin-PTFE composite coating
Infrared spectroscopy
The bond length and bond angle of the molecule can be determined by infrared spectroscopy, and thus infer the three-dimensional configuration of molecules. By infrared spectroscopy, which can determine the presence of organic functional groups in the sample, can determine the chemical structure of the coating.
Fig.2 Infrared spectrum of epoxy resin-PTFE composite coating
Fig.2 is infrared spectrum of epoxy resin-PTFE composite coating. The strongest band of PTFE appeared in the frequency range of 1 250 to 1 110 cm-1, the characteristic frequencies of 1 157 .2, 1 180 .3 and 1 245.9 cm-1 are in the strongest spectral band of PTFE, the characteristic absorption peak is mainly caused by the stretching vibration of C-F bond, which indicates the presence of PTFE in the composite coating. And an absorption peak at the frequency of 3 448.5 cm-1, the absorption peak is in the frequency range of 3000 ~ 4000 cm-1, which is caused by the absorption of O-H bond stretching vibration, indicating that the composite coating contains – O-H bond material, inferred that the epoxy resin curing agent in the curing chain by the chain generated. The characteristic frequencies of 1 245 cm-1 and 879.5 cm-1 are between 870 and 1 280 cm-1 of cyclic ether bond, from this inference that it contain ether bond. And the absorption peak appeared at the frequency of 829.3 cm-1, and these absorption peaks appeared in the frequency range of epoxy compound, which indicated the existence of epoxy compound in the coating.
Differential thermal analysis
Using the differential thermal analysis, the melting point, decomposition temperature and so on of the samples can be obtained, and the thermal stability of the samples in a certain temperature range can also be seen.
Figure 3 is the differential thermal analysis of the epoxy resin -PTFE composite coating at temperature below 600℃. As can be seen from Figure 3, there is an endothermic peak at 381.34℃, which may be caused by the decomposition of epoxy resin. There is also an endothermic peak at 541.60℃ which is due to the decomposition of PTFE. Indicating epoxy resin PTFE composite coating at 300℃ is a stable state, can work properly.
Figure 3 Differential thermal analysis of epoxy resin – PTFE composite coating
Scanning electron microscopy and energy spectrum analysis
The surface of the sample and the surface composition of the sample were analyzed by scanning electron microscopy. The results are shown in Table 4 and Fig.4.
Table 4 Relative proportions of coating surface composition
Figure 4 Epoxy resin – PTFE composite
It can be seen from Figure 4 that the surface of the epoxy resin- PTFE coating is relatively uniformly smooth and level. You can also see a small amount of white particles, it is caused by small amount of PTFE gathered. As can be seen from the relative proportions of the surface compositions of Table 4, the surface of the composite coating mainly contains F and C2 elements, and the mass ratio of F to C is 1: 7.15. The F element is one of the light elements, and the F element can be analyzed by electron microscopy. It is shown that the content of F in the composite coating is larger, that is, the content of PTFE is more.
Conclusion
Using the orthogonal experiment and the range analysis, the formula of epoxy resin- PTFE composite coating with the smallest friction factor was obtained, that is, epoxy resin and solid agent 3 g, PTFE 0.9 g, graphite 0.2 g, acetone 7 mL, dispersant FC-400 0.012 g, the minimum friction factor 0.037, the average thickness of about 300 micron. X-ray analysis showed that PTFE in coating is crystalline structure, epoxy resin is amorphous structure, the emergence of carbon peak shows the presence of graphite. FTIR and DTA showed that PTFE, graphite etc. are present as monomers in the coating, and in the stable below 300 ℃. Electron microscopy and energy dispersive X-ray spectroscopy (EDS) show that the surface of the composite coating is uniformly smooth and level, with a small amount of PTFE gathered, the mass ratio of F to C is 1: 7.15, indicating that the content of PTFE in the composite coating is higher, which plays a decisive role in reducing the friction. From the wetting properties of the coating and the medium water, due to the presence of PTFE in the coating, the contact angle is generally larger than without PTFE, indicating that the coating is more suitable for dry friction in the environment.
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Preparation and properties of PTFE anti-friction coating.pdf
Polytetrafluoroethylene (PTFE) resin was invented by Dr. Champlain Kate (Plankett) in 1938 and formally put into industrial production by Du Pont in 1950. PTFE as high crystallization of tetrafluoroethylene monomer polymer is a kind of thermoplastics of white waxy feeling. In PTFE, fluorine atoms to replace the hydrogen atoms in the polyethylene, due to the radius of the fluorine atoms (0.064 nm) is greater than the radius of the hydrogen atom (0.028 nm), makes carbon – carbon chain of polyethylene flat, at full stretch and conformation is reverse to the PTFE spiral conformation. The helical conformation is surrounded in the PTFE are susceptible to chemical attack skeleton of carbon chain, formed a close completely “fluorine generation” protective layer, makes the main chain of the PTFE is not affected by the outside world any reagent, make PTFE has unmatched by other materials in solvent resistance, chemical stability and low of cohesive energy density; At the same time, carbon – fluorine keys is extremely strong, the key can reach 460.2 kJ/mol, than carbon – hydrogen bonding (410 kJ/mol) and carbon – carbon bonds (372 kJ/mol) is high, the PTFE has good thermal stability and chemical inertness. In addition of fluorine atoms electro negativity is great, and tetrafluoroethylene monomer with perfect symmetry and make the PTFE intermolecular attraction and low surface energy, so that the PTFE has very low surface friction coefficient and good ductility when low temperature; At the same time also make PTFE creep resistant ability is bad, it’s easy to have a cold flow phenomenon. No branch of PTFE symmetrical main chain structure also makes it highly crystalline, so it is difficult to machining.
Pure PTFE is suitably modified, can improve the comprehensive performance, and expand its applications in various fields. at present, the modification of PTFE is mainly based on the principle of composite; it combined with other materials, to make up for the defects of PTFE. Modified methods mainly include: surface modification, filling modification and blending modification, etc.
The surface modification of PTFE
The extremely low surface activity and tackiness of PTFE limits its ability to combine with other materials, especially the adhesive of the PTFE film skeleton with other materials. At present, the solution of the PTFE adhesive, mainly through the surface of the PTFE activation to improve its surface tension, then choose the suitable adhesive for bonding. PTFE surface activation generally based on several methods such as the displacement, crosslinking, grafting, oxidation and recrystallization. Technology of surface modification of PTFE commonly used are: the method of reducing agent (sodium – naphthalene solution permutation method), high temperature melting method, plasma treatment, laser radiation chemical processing method, silicate modification method, force method, etc.
Reducing agent method (sodium – naphthalene solution permutation method)
Sodium – naphthalene solution permutation method in all the modification methods are now known to effect is better, is widely used. Its principle is: the Na to the outermost electron transfer to naphthalene empty orbit, form anion free radicals; With Na + ion pair formation, can release a lot of resonance, to generate the dark green metal mixture of organic compounds. These compounds of high reactivity, contact with PTFE, sodium can destroy C – F key, ripped the partial fluorine atoms on the surface of the PTFE, left on the surface of carbide layer and the – CH, CO and C = C, – COOH polar groups; The depth of carbonation layer is about 0.05 ~ 1 micron, the surface tension of the PTFE by 18.5 x 10-3 N/m increase to 50.0 x 10-3 N/m, the surface has high polarity and high surface energy.
With this method the activation of PTFE with epoxy – polyamide adhesive bonding, the shear strength can be more than 10.7 MPa. According to the data reported, it cannot reach many industrial requirements on bonding strength when PTFE shear strength of bonding under 10.7 MPa. Xu Baoguo by sodium naphthalene solution activation of PTFE surface, and form a complete set of J – 2021 adhesive is developed, the shear strength reach 13.7 MPa above, better meet the requirement of some of the applications of industrial sector.
This method also has some obvious disadvantages, such as: glued surfaces dark or black, under the environment of high temperature resistance is reduced, surface cementing performance under long-term exposure to the light will greatly decrease; Makes the method of application is limited by a lot. Also have reported, after adding carbon black PTFE and adhesive and hydroquinone, light resistance can be greatly improved.
Besides sodium -naphthalene tetrahydrofuran corrosion liquid sodium, sodium -biphenyl dioxane, sodium -naphthalene ethylene glycol dimethyl ether and other processing liquid also has a good effect.
High temperature melting method
The basic principle of this method is: under the high temperature, crystal morphology change, make the surface of the PTFE embedded some high surface energy, easy adhesive material such as SiO2, Al powder, etc.; After cooling will form a layer on the surface of PTFE modified layer can be sticky substances are embedded. Because of the easy sticky material has entered the PTFE surface molecules, destroy it equivalent to intermolecular destruction; so, the bonding strength is high. This method has the advantage of weatherability, wet and heat resistance than other methods, suitable for outdoor use for a long time; Shortcoming in high temperature sintered PTFE emit a kind of toxic substances, and PTFE membrane shape is not easy to maintain.
Plasma treatment
Plasma processing is exposed to the gas plasma polymerized to material, the use of plasma bombardment material surface, causing many changes the structure of the polymer material and the surface modification of polymer materials. The active substances in plasma can various interactions with polymer material surface; plasma processing mechanism of polymer surface is different. Has been reported with CF4 plasma gases, C2F6, CF3H, CF3Cl, CF3Br, NH3, N2, NO, O2 and H2O, CO2, SO2, H2 / N2 and CF4 / O2, O2 / He, air, He, Ar, Kr, Ne, etc. Badey J P disposes PTFE by microwave plasma downstream processing, makes it surface modification. PTFE is disposed With O2 / N2 / O2, surface without modification; Using NH3 plasma treatment, the PTFE surface polarity composition increase, the hydrophilic also increase.
Several parameters which easy to adjust such as operating gas pressure, electric field frequency, power and action time in plasma treatment process , can obtain the ideal control and produce good results. Such as under the condition of high electric/gas density ratio of PTFE surface modification, surface modification of PTFE can be compared with the usual process increased significantly.
PTFE and the adhesion about the aluminum metal were studied by Zhang E C and others. They first use argon plasma (frequency is 40 kHz, power is 35 W, argon gas pressure is 80 Pa) for preprocessing of PTFE and exposed to the atmosphere about 10 min to produce oxide and peroxide; Then conducted on the glycerin alcohol acrylate (GMA) grafted copolymerization, then thermal evaporation of aluminum, results make the adhesion force that PTFE with GMA grafted polymer and Al is 22 times as big as between PTFE and Al, it is also only three times after Ar plasma pretreatment.
Laser radiation method
Laser surface processing with high power density of laser beam, in the form of non-contact heating surface, with the help of the material surface itself conduction cooled, live up to its surface modification process. It has many advantages in material processing, the other surface treatment technology is difficult to match: (1) The energy transfer is convenient, can choose to be processed work piece surface is the local reinforcement; (2) The energy concentration, the processing time is short, small heat affected zone, laser processing, deformation is small; (3) Processing complicated shape of work piece surface, and easy to realize automatic production; (4) Modification effect is more significant: high speed, high efficiency, low cost; (5) Usually can handle only some sheet metal, not suitable for dealing with thicker plate; (6) Due to the laser damage to the human eye, affect the safety of the staff, so be committed to the development of safety facilities.
Steps of this method are as follows: put PTFE membrane in monomers of fumaric acid, methyl acrylate, styrene polymerization, such as with Co60 radiation, the monomer grafting polymerization on the PTFE membrane surface, thus in PTFE membrane surface to form a layer of adhesive of graft polymer easily. PTFE in three dimensional directions after grafting grew up, and keep shape, but lost the original luster and lubrication; Surface roughness increases with increasing the amount of grafted, but surface does not change color, and surface resistance in a wet environment change.
Silicate activation method
Porous PTFE with SiX4 after processing, then through hydrolysis, can achieve the purpose of make PTFE surface activation; this is “silicate modification method”.
As early as 1959, Herr has used SiCl4 processing and hydrolyzed to silicate surface treatment methods of PTFE and the formation mechanism of surface oxide layer are discussed in this paper. Thereafter Rossbach use SiF4 to activate PTFE surface, using ESCA (X-ray photoelectron spectroscopic analysis) to verify the modification result. On the basis of this, the modification technology by Mohammed step further. They think: traditional modification method can change the chemical structure of PTFE, thereby the influence of different degree of the inherent structure of PTFE; and this modification will not change the chemical structure of PTFE, and can achieve the goal that make its surface activation.
Force chemical treatment method
“Force chemical treatment” is glued on coated with adhesive friction material surface, by chemical action, the adhesive molecules combine with material surface chemical bond, thus greatly improve the bonding strength of joint. This is a new method used to glue stick plastic.
The principle is the polymer surface under the action of external force, strength degradation and form free radical chains, and adhesive molecules form covalent bond, produce strong interface bonding. This has been confirmed by the ESR (electron spin resonance spectroscopy) and ATRIR (internal reflection FTIR).Table 1 lists the joints Bonding strength contrast of PTFE after chemical treatment and processing of sand paper burnish, the bonding strength of contrast.
Table 1 Adhesive joint shear strength contrast of PTFE
Filling modification of PTFE
Suitable for filling PTFE packing must meet the following requirements: (1) under the condition of 380 ~ 400 ℃ sintering stability;(2) particle size is 150 microns or less;(3)not moisture absorption;(4) under the condition of sintering, itself not cluster;5. Do not react with PTFE. According to these requirements, the commonly used fillers are: glass fiber, carbon fiber, graphite, quartz sand, molybdenum disulfide, amorphous carbon, calcium fluoride, bronze powder, ceramic, polyimide, polystyrene, poly hydroxy acid ester, etc.
The application of filled PTFE products components according to fill products environment to decide, with single filler filling, also there are several kinds of filler composite filling. Such as: 20% SiO2 filled PTFE used as the oxygen compressor piston ring,10% polyimide，15% glass fiber, 5% graphite composite filled PTFE used as hydrogen booster piston ring, etc. The single packing of PTFE can improve some performance, but adverse influence on the performance of some other. Such as glass fiber filled PTFE resistance to wear life can increase 1 000 ~ 2 000 times, use the PV value of about 10 times; But the friction coefficient increases, load variables to reduce about 10%.Again, such as the addition of graphite improved PTFE dimension stability, drug resistance, resistant to compression creep and thermal conductivity; But abrasion resistance is poor. Therefore, usually adopt several packing composites filling to filled PTFE products with excellent properties. As applied to the injection molding machine of PTFE bearing consists of PTFE filled with glass fiber, graphite, carbon fiber, copper powder and Fe2O3, its mechanical properties, electrical conductivity, cold flow property and wear resistance are improved; Applied to the guide rail with boring machine is made of glass fiber, graphite, bronze powder, MoS2 filled PTFE composite materials; Used to import equipment accessories and high strength wear resistant filling PTFE seals, is made from 15% 10% glass fiber, carbon fiber filled PTFE, its friction coefficient is 0.17, the abrasion value is 0.000 1 mm, grinding crack width is 3.7 mm, reach imported equipment and more random accessories required.
The blending modification of PTFE
Liquid crystal polymer modification of PTFE
Liquid crystal polymer (LCP) is a unique member of the family of polymers; it refers to the liquid when some parts of the macromolecular chain can still each other are arranged orderly in the polymer. Polyphenylene ester is also called the poly hydroxy benzoic acid benzene ester, is a kind of liquid crystal polymer and the type of chain linear molecules, it has high crystallinity (greater than 90%), make it difficult to melt flow, generally uses the moulding. In 1970 the United States emery company first successful develop the product. Polyphenylene esters in larger temperature range has high rigidity, high compression creep resistance, high thermal stability, even if heated to 538 ℃ is not melting, at the same time both heat conduction and insulation as well as excellent solvent resistance and radiation resistance. Because of the special molding process of PTFE, so used for liquid crystal polymer modified PTFE must have very high heat resistance, and the molten state of viscosity is very big, can satisfy the PTFE sintering conditions. Meet the above conditions of liquid crystal polymer with all together p-hydroxy benzoic acid benzene ester is the most suitable. Began in the 1960 s, American Carborundum started manufacture of PTFE/polyphenylene ester material .In 1973, Japan Daikin company produced and sold the materials, the commodity was called “Polyflon 7060”.After 1979, Japan’s Sumitomo chemical industrial company from emery bought and modified polyphenyl ester production technology, to produce the blending materials and had a large number of listed, its brand has EkonolS200, EkonolS230, EkonolS300 and EkonolS330, etc. Since the 1980 s, the material market demand increased rapidly.
According to reports, to use type liquid crystal polymer as modifier of PTFE, the wear resistance of PTFE can be improved more than 100 times, significantly improved the wear resistance of PTFE, and maintained the characteristic of low friction coefficient.
Liquid crystal polymer modified PTFE abrasion mechanism is: the liquid crystal polymer melt after high temperature has excellent liquidity, formation heat transfer; the result of the heat transfer inside the liquid crystal polymer in PTFE matrix to move form the gap along the PTFE micro fiber. In alloy composition ratio and sintering temperature is appropriate, these micro fiber end are interconnected to form a dense and uniform in the PTFE matrix three-dimensional network; These networks tightly envelope PTFE matrix and reinforcement effect, greatly restricted and prevented the PTFE belt wear, the wear and tear of PTFE turned into tiny particles plough wear, thus improved the wear form of PTFE and course, raised the wear properties of PTFE.
Other plastic modification of PTFE
Thierry mix PTFE with copolymer (FEP) of tetrafluoroethylene and hexafluoropropylene after electronic radiation, through high heat sintering in nitrogen self-lubricating composite materials. Research shows that: when the filling amount of FEP were 35% and 50% respectively, the corresponding friction coefficient of the composite material is 0.09 and 0.11, are lower than the pure PTFE friction coefficient; When sliding speed reach 0.01 m/s and 0.05 m/s, the wear rate of the composite is 8.6 x 10-6 mm/(N, m) and 7.7 x 10-6 mm/(N, m), were far lower than the wear rate of pure PTFE [each 0.43 x 10-6 mm/(N, m) and 1.2 x 10-6 mm/(N, m)];Compared with the hard particles filled PTFE composites, no etching on the surface of side effects. When the blend contains 35% FEP, can significantly improve the tensile strength of the PTFE, explain these two kinds of polymer compatibility is good. Japan develop a PTFE/PFA (soluble PTFE) material, made ball valve sealing material, it not only improves durability but also products easy to hot welding. Abroad with PTFE and polyurethane block copolymer (FPV) making artificial heart blood and blood circulation of elastic material, this material is not only meet the durability, flexibility, strength, and molding requirements, but also in contact with the blood will not make bad blood, also won’t destroy blood components, the most important thing is not to form blood clots.
Polyphenylene Sulfide Modified PTFE Blend Materials(PTFE/PPS) has excellent creep resistance and dimensional stability. The blending material, PPS mass fraction is 20% ~ 40% commonly, in order to improve the mechanical properties of blend material, usually also filled with other inorganic materials, such as glass fiber, carbon fiber, etc.
PTFE emulsion used for metal spraying, the base material has poor adhesion and membrane is soft. In order to improve these properties, usually with other high polymer materials, such as phenolic resin, polypropylene resin, epoxy resin, polyimide, PPS, etc.) And its blending, can make the modified PTFE coating film hardness, abrasion resistance, and make the film at low temperature. for example, the coating of PTFE and PPS blending has strong adhesion to the metal, heat resistance and corrosion resistance, they can withstand oil, acid, can be used as the heat protective coating of organic matter, inorganic salt chemical industry equipment, can also be used on the cooker, pastry mould, rubber mould and film coating.
Nanomaterials are new materials with excellent performance which develop in recent years, it has good plasticity and toughness, its hardness and strength is 4 ~ 5 times higher than ordinary liquid crystal materials. It is essential to the wear and tear of PTFE in macromolecular slip or fracture under the action of external force, so that the material is pulling on the surface of the crystalline region and the slice to accidentally, caused by adhesive wear. After filling A12O3 in the PTFE, the hardness, compression strength, elastic modulus and creep performance can been improved to varying degrees, and this is because in its contact with the metal surface, packing plays a role of bearing .PTFE macromolecular implicated by filling at the same time, unlike in the filled PTFE as easily, and obviously improve the wear resistance.
It is important to note that although the nano Al2O3 can improve the wear resistance of PTFE, it can lead to severe plastic deformation; and not the content of nano filler is higher, the wear resistance of filled PTFE composite material is better. He Chunxia used to measure the filled PTFE wear mass loss and the relationship between load data; When the mass fraction of nano Al2O3 is 10%, material performance is better. So only in adding the right amount of nano Al2O3 in substrate, can make the hardness and strength of the PTFE increased, can not only improve the wear resistance of PTFE, but also will not lead to severe plastic deformation.
Expectation
Modified PTFE material is a promising new type of PTFE, should vigorously develop, and make its commercialization, variety series.
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Teflon (PTFE) because of its excellent chemical stability of high temperature resistance, known as the “plastic king”, it is often used as a membrane separation material. But because the material molecular structure is highly symmetrical, causing its surface hydrophobicity to be strong, this affects Teflon in the bonding and liquid filtration and other applications. This question had been troubled Teflon coated fabric suppliers for many years. In order to make up for these shortcomings, the major Teflon coated suppliers in the world spent a huge investment on the PTFE membrane modified.
At present, the major suppliers commonly used chemical method, high temperature method and plasma method and other methods to deal with PTFE membrane surface. But the surface of the Teflon film treated by the chemical method is obviously darkened and the ontology of the material is affected. PTFE will evaporate toxic substances.in high temperature melting process. And the plasma method has the effect of changing the surface properties of the material in a short time without affecting the inherent properties of the substrate, and the process is dry processing, saving energy protection environment.
In this paper, Ar is used as the treatment medium to treat the Teflon membrane, the grafted AA monomer further enhances its hydrophilicity to address the timeliness of plasma treatment. The effects of different plasma treatments and grafting processes on the hydrophilicity of Teflon films were investigated, and the contact angle was used to characterize the hydrophilicity of FTIR. The solution and the corresponding results in this paper, there have a huge reference value for the suppliers of Teflon coated fabric, Teflon adhesive tape and Teflon conveyor belt.
Experiment
Major reagents and equipment
Teflon hollow fiber membrane, Lab homemade; Argon (purity ≥99.99%), Acrylic acid, anhydrous ethanol (AR).
DSA25S contact angle measuring instrument, Germany Kruss company; BTF-1200C-S-SL plasma processing system; IR Affinity-1 Fourier transform infrared spectrometer.
Sample preparation
Ar plasma pretreatment
The Teflon membrane was ultrasonically cleaned with absolute ethanol for 30 min, after drying, put it in the reaction chamber of the quartz stent, Vacuum to 2 ~ 6Pa, through argon, draining the residual air in the reaction chamber, adjust the needle to control the gas flow in 10~60cm3·min-1, adjust the pressure to 20 ~ 100Pa, After stabilization, start the RF power source, the Teflon film was pretreated by plasma, processing power of 100 ~ 500W, processing time of 30 ~ 300s.
Surface graft polymerization
After the plasma pretreatment of the sample with air contact oxidation for a period of time, put in the concentration of 5% to 45% of the AA solution, heated to 3070, the processing time is 214h, After the reaction, remove it and wash it in 40 distilled water for 12 hours.
Performance test and structural characterization
Contact angle
The contact angle of the PTFE film surface was measured using a contact angle meter, and the measurement was carried out at a room temperature and humidity of 30% RH, using micro-injectors to control the droplets in about 2μL, the average of the five points measured on the same sample surface is taken as the final contact angle.
ATR-FTIR
The change of membrane surface structure before and after modification was analyzed by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), ATR-FTIR analysis of the scanning frequency is 30 times, scanning range is 600 ~ 4500cm-1, the minimum resolution is 2cm-1.
Results and discussion
Effect of Plasma Treatment Conditions on Surface Wettability of Teflon Membrane
By testing the plasma processing power time and the gas flow rate of PTFE membrane surface contact angle, explore the best conditions for plasma treatment.
Effect of Plasma Treatment Power on Surface Wettability of PTFE Membrane
The effect of the contact angle of the film surface on the treated power is shown in Table 1, Membrane surface wettability with power changes shown in Figure 1.
Table1 Effect of power in Ar plasma on PTFE membrane contact angle
Fig.1 Teflon membrane wettability change with different plasma powers
As can be seen from Table 1, The contact angle of the surface of the Teflon membrane is 125°. When the power increases from 0W to 300W, the contact angle decreases from 125°to 65°. When the power increases from 300W to 500W, the contact angle becomes 58°.As the power increases, the contact angle of the membrane surface initially decreases rapidly and then slowly and stabilizes. Figure 1 shows that the wettability of the membrane with the power increase gradually improved, and ultimately no longer significantly changed.
The reason is that the level of power represents the amount of energy that can be accepted on the surface of the membrane, and the power increases so that the energy obtained by the quantitative argon molecules also increases, the chemical bond of the membrane surface molecules is increased by the probability of being opened, and the number of hydrophilic groups formed by further combining the free radicals in the plasma increases, thereby reducing the contact angle of the film surface. However, when the power is too large, the plasma generated free radicals between the probability of binding will increase, can not effectively combine the free surface of the membrane surface.
Considering, the best processing power is 300W.
Effect of Plasma Treatment Time on Surface Wettability of Teflon Membrane
By changing the treatment time, to study its effect on the film surface wettability, the results shown in Figure 2
Fig. 2 Teflon membrane contact angle change with different plasma times
It can be seen from Fig. 2 that the contact angle of the membrane surface is different when the processing time is different, and the contact angle increases gradually with time, and then begins to rise and stabilize after a minimum value. The contact angle decreases rapidly in a short time and reaches a minimum of 52°at 120 s, and the contact angle increases after more than 120 s.
The reason may be related to the mechanism of plasma reaction. As shown in Figure 3. When the time is short, the active particles in the Ar plasma bombard the membrane surface, resulting in the membrane surface of the C-F bond fracture, generating peroxides, These free radicals formed by the destruction of the membrane matrix recombine with other free radicals in the plasma, forming a polar group on the membrane surface, thereby significantly improving the wettability of the film surface. When the time reaches a certain limit, the free radicals generated on the membrane surface also reach a critical value, and then extended the time will increase the probability of the new generation of free radicals between the cross-linking reaction until the membrane surface polarity The rate of increase to achieve dynamic equilibrium, contact angle is no longer significantly increased.
Fig. 3 The principle of plasma treatment on the hydrophilic modification of PTFE membrane
According to the above, both to ensure that the hydrophilic modification effect can improve the experimental efficiency of the best processing time is 120s.
Effect of Plasma Flow Rate on Surface Wettability of PTFE Membrane
Table 2 Effect of different plasma gas flows on PTFE membrane contact angle
The effect of the gas flow on the film surface wettability was investigated by changing the gas flow rate. The results are shown in Table 2.
It can be seen from Table 2 that when the gas flow rate is 30cm3·min-1, the contact angle of the membrane surface is at least 54°, which is 61° lower than that of the original film. When the flow rate is increased to 50cm3·min- The contact angle becomes 65°.
As the gas flow increases, the contact angle of the membrane surface decreases first. This is because as the gas flow increases, the concentration of argon ions in the plasma generator increases rapidly, but also accelerates the rate of regeneration of the ionized gas, Resulting in enhanced deflagration on the membrane surface, thus generating more free radicals, a large amount of hydrophilic groups are polymerized on the surface of the film so that the contact angle after treatment decreases first. But when the gas flow exceeds 40cm3·min-1, the contact angle of the membrane surface increases. This is due to the increase in gas flow, resulting in reduced vacuum in the plasma generator, shortening the activity of high-energy particles free path, and thus can not fully stimulate the gas molecules in the reactor.
Effect of Grafting Conditions on Surface Wettability of Teflon Membrane
Effect of Acrylic Acid Concentration on Surface Wettability of Teflon Membrane
The concentration of AA monomer has a great effect on the wettability of the membrane surface, as shown in Fig 4.
Fig. 4 PTFE membrane contact angle change with different AA volume concentrations
It can be seen from Fig. 4 that the wettability of the membrane surface increases with the increase of AA concentration, and the contact angle decreases to 52° when the AA concentration reaches 20%. This is because when the AA concentration is low, the solution viscosity in the reactor is low, the monomer is easy to approach the free radicals on the membrane surface, which can lead to the graft polymerization. When the AA concentration continues to increase, the contact angle is slightly increased. This is because when the AA concentration is too high, the AA monomer self-aggregation or homopolymerization rate is accelerated, so that the monomer can not react with the free radicals on the membrane surface.
Fig. 5 Infrared spectrogram of Teflon membrane with different AA volume concentrations
The ATR-FTIR test was performed on the membrane surface. The results are shown in Fig.5. It can be seen from Fig. 5 that the plasma treated membranes have peaks that characterize AA grafts, and the positions and shapes of the peaks are basically the same. When the AA concentration of 20%, the measured bands appear rich in bands near 3300 cm-1, should be -OH stretching vibration peak, the band at 2800-3000 cm-1 is the stretching vibration of saturated C-H, near 1730cm-1 appear the C = O stretching vibration peak, 1149cm-1 and 1210cm-1 are C-F stretching vibration peaks. These characteristic peaks demonstrate that AA is successfully grafted onto the membrane surface.
Effect of Grafting Reaction Time and Temperature on Surface Wettability of PTFE Membrane
The effect of graft reaction time and temperature on the contact angle of the membrane surface is shown in Fig.6.
Fig. 6 Effect of different grafting times and temperatures on PTFE membrane wettability
As can be seen from Figure 6, As the temperature increases, the contact angle of the membrane surface gradually decreases, and when the temperature is 50 ℃, the minimum contact angle is 58°. This is because the temperature rise makes the free radicals on the membrane surface and the AA monomer in the solution activated, the contact angle in the early reaction with the temperature rise and decreased. When the temperature is more than 50 ℃, the contact angle be increased. May be caused by high temperature self-polymerization of AA monomer, so that the solution becomes viscous and hinder the grafting rate.
Conclusion
The results of this paper show that, Teflon hollow fiber membrane by Ar plasma treatment and then grafted AA monomer, the number of hydrophilic groups on the membrane surface increased significantly, surface energy and surface activity increased, the hydrophilicity is greatly improved and the modification effect is long, Thus broadening the scope of application of Teflon hollow fiber membrane for membrane separation systems in the field of waste water treatment.
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Hydrophilic Modification of Teflon Hollow Fiber Membrane by Ar Plasma.pdf
Polytetrafluoroethylene (PTFE) has many excellent properties.
A. Excellent high and low temperature performance, widely use temperature range, from -190℃～260℃.
B. High chemical stability, it can withstand all strong acid and alkali except for molten alkali metal and fluorinated media, including aqua regia, strong oxidants, reducing agents and various organic solvents.
C. Outstanding non-stick and lubricity, all the known solid materials can not adhere to the surface, it is the smallest surface energy of solid material.
D. Excellent resistance to atmospheric aging, radiation resistance, low permeability.
E. Good noncombustibility, its limited oxygen index below 90.
F. Good waterproof performance.
PTFE has very good heat resistance and chemical resistance, but the physical terms, its strength is not very good, but from physical point of view, its strength is not very good, in high temperature conditions, the dimensional stability of the material is not stronger than other materials.
Glass fiber brittle easy to break, wear resistance is poor, not resistant to hydrolysis, for some chemical substances such as fluoride, the corrosion resistance is also poor, This makes it as a high temperature filter in the application with great limitations. However, the high strength, heat resistance and dimensional stability of fiberglass cloth is just complementary to PTFE. These two kinds of materials can be formed composite performance and superior strength of high temperature dust filter.
PTFE glass sintering high temperature filter material which used PTFE and fiberglass two materials of their own performance characteristics to research and develop, The principle is using imported PTFE polymer raw materials and other chemical additives, using a special sintering process, This makes the fiberglass cloth with good wear resistance, corrosion resistance and high temperature performance better than the glass fiber. Giving the filter material a good acid and alkali resistance, corrosion resistance, high temperature, abrasion resistance and resistance to flexing and other properties, and the surface is smooth, hydrophobic, dust can not adhere to the filter surface, it is suitable to high temperature, high humidity, high viscosity dust industry or with acid and alkali, corrosive chemical gas industrial dust purification and other conditions of the occasion.
The Technology Characteristics of PTFE Glass Fiber Sintered High Temperature Filter
The filter function and structural features
As the glass fiber brittle easy to break, wear resistance is poor, for some chemical substances such as fluoride, the corrosion resistance is also poor, this makes it as a high temperature filter in the application with great limitations; Another PTFE fiber composite material that has not been sintered is not sufficiently bonded to the glass fibers because of the low crystallinity of the PTFE molecules, PTFE in the glass on the protective layer is easy to fall off, the high temperature resistance, corrosion resistance, hydrolysis resistance, flexibility, wear resistance, bending and other properties are poor to made of filter materials, as a high temperature filter its life is very short.
Fiberglass cloth fiber surface treatment
Fiberglass cloth fibers are generally have pulp, grease and other impurities, if you do not clear the the pulp, self-lubricants, wetting agents, grease and other impurities of fiberglass cloth, or impurity removal is not complete, inadequate and directly impregnated with PTFE, it will affect the quality of the sintering of the filter material, so that the glass fiber cloth and PTFE bond firmness is not good, made of poor performance of the filter. So it should first through a non-physical wear and chemical erosion of the removal process, thoroughly remove the pulp lubricant, infiltrant, grease and other impurities in the fiberglass cloth, so that the glass fiber cloth fiber surface smooth, clean, can effectively improve the adhesion of PTFE and glass and firmness.
PTFE glass sintering process characteristics
After pre-treatment of fiberglass cloth and PTFE, using sintering process, after several times sintering, so that the fiberglass filter cloth in each fiber surface are wrapped in a layer of dense PTFE protective layer, and the preparation of the PTFE solution by adding other chemical additives, it has been control the appropriate sintering temperature, speed, pressure and other processes, enhanced the adhesion strength and softness of PTFE and fiberglass substrate. As the PTFE molecular with high crystallinity, fiberglass surface PTFE crystallize uniform, PTFE is very firmly bonded to the glass fiber, which greatly improves the filter of the folding, corrosion resistance, wear and strength properties. Equipment bag filter can not only broaden its scope of application, but also greatly extend its service life.
Laminating process and effect
In order to further improve the working life and filtration performance of the filter material, puffed PTFE microporous film can be used, with sintered glass fiber cloth through the high-temperature hot-pressing process melt composite, it is possible to connect the glass fiber cloth, the PTFE protective layer and the PTFE microporous film layer, to form a high degree of high temperature, corrosion-resistant PTFE glass sintered film filter, Its corrosion resistance, folding, wear resistance has been further improved, the service life is further extended.
The filter material after laminating has the following properties:
A. High filtration efficiency: Microporous films have unique cross-microporous properties, PTFE porous membrane porosity is more than 90%, it has a good filter performance for ultra-fine dust, for 0.3 ~ 1μm and above the fine dust up to 99.99% or more of the filtration efficiency, can achieve near zero emissions.
B. Low running resistance: As the PTFE film itself has non-sticky dust, hydrophobic, chemical stability and other characteristics. After laminating, filter work surface is very smooth, dust stripping performance is very good, especially for the moisture absorption, easy to bond hardening of the dust has a good peelability.
C. Corrosion resistance, folding, wear resistance to further improve: Microporous film and PTFE glass fiber sintered filter compound, with better acid and alkali resistance, high temperature, high humidity and other characteristics.
D. Long service life, large filter rate: Film filter resistance is small and stable, faster filter speed.
Performance of PTFE glass fiber sintered high temperature filter
PTFE glass sintered high temperature filter main components: it is glass fiber + PTFE chemical additives, the technical parameters after the test as shown in Table 1.
Characteristics of PTFE glass fiber sintered high temperature filter
A. High temperature resistance: The temperature resistance of this filter is mainly determined by the the temperature performance of glass and PTFE itself, the long-term use temperature is 260 ℃, short-term and instantaneous temperature is up to 300 ℃, and heat shrinkage <0.5%.
B. Good acid and alkali resistance: with good resistance for acid and alkaline and most of the organic matter, the resistance for the acidity and other corrosive gases, including hydrogen fluoride is significantly higher than ordinary glass fiber filter.
C. Good wear resistance and fatigue resistance, high tensile strength, and they are all better than ordinary glass fiber filter.
D. Good hydrophobicity: Filter material surface smooth, hydrophobic, any dust can not be attached to the filter surface and easy to clean, resistant to tar and water vapor, Therefore, the dust does not need to do outside insulation. It can be applied to the acid and alkali components, humidity fluctuations in large flue gas dust filter.
E. Good thermal stability: The heat shrinkage is less than 0.5% at 300 ℃, this feature determines the safety of its use at high temperatures.
F. High filter speed: The filter material is a smooth cylinder, clogging capacity is small, easy to clean, and also has good wear resistance and fatigue resistance. These characteristics determine that it has a high filtration wind speed, but also determines its competent cleaning method has a backflush cleaning, rotary anti-blowing dust, mechanical vibration cleaning, pulse cleaning and so on.
G. The sintered filter material can be combined with PTFE microporous film into a film filter.
With characteristics of high filtration efficiency, easy to clean, acid and alkali resistance, flexibility and so on.
Conclusion
PTFE glass sintered high temperature filter has very good acid and alkali resistance, corrosion resistance, high temperature, abrasion resistance and resistance to flexion and other properties, and the surface is smooth, hydrophobic, dust can not adhere to the filter surface, it is suitable for high temperature, high humidity, high viscosity dust industry or with acid and alkali, corrosive chemical gas industrial dust purification. PTFE glass sintered high temperature filter in the high temperature flue gas filtration industry has a wide range of uses, the mainly applications:
A. Waste incinerator high temperature, high viscosity dust flue gas purification. Especially waste medical supplies (such as disposable syringes, rubber gloves and so on) and the treatment of domestic waste, it can solve the high temperature burning bags, high viscosity dust paste bags, chemical gas corrosion bags and other issues.
B. Flue gas purification of the Iron and steel smelting blast furnace gas. It is main to solve the high temperature, high humidity, dew point paste bags and high temperature sulfur and other chemical gas corrosion bags and other issues.
C. Carbon black, coking furnace flue gas purification. It is main to solve the high temperature, high viscosity dust caused by cleaning difficulties, after the shutdown of the dew point of the following oxidation reaction to the early embrittlement of the filter and other issues.
D. Chemical industry, metallurgy, cement and other industries. It can solve the high temperature, high viscosity dust caused by the bag filter bag, equipment running resistance, filter early embrittlement damage and other issues.
E. Flue gas dry desulfurization of power plant coal fired boiler, compared with ordinary fiberglass bags. It has good performance of non-stick bag, easy to clean, low running resistance, long service life and so on.
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Development and Application of PTFE Teflon Glass Fiber Sintered High Temperature Filter.pdf
Currently,the handling of flue gas, dust mainly adopts bag dust removal, bag filter bag filter material mainly selects the aramid amine fiber, and d, PPS fiber, poly (aromatic phthalein imide fiber, etc. Although these have different optimal glass fiber bag filter, with different properties of flue gas, dust, there are also different, such as aromatic poly phthalein amine fiber with moisture and chemical composition point temperature will reduce operation, especially in the SOX exist, with moisture, will be corrosion, strength retention; PPS fiber is sensitive to oxidant; Poly (aromatic phthalein imide fiber resist to hydrolysis, and high prices; The glass fiber of hydrofluoric acid, strong alkali corrosion resistance is poor. These problems will be in practice to reduce the service life of the bag, and make the bag filter machine for the inefficiency of flue gas, dust processing, at the same time, the effect filter continuous normal work of the machine. Therefore, the project, on the basis of traditional bag filter with filter material, combine the company of PTFE membrane and to develop a high performance fiber production process of pure PTFE (PTFE) coated filter material manufacturing process, namely, the company produced PTFE film materials, process such as fiber, woven, composite filter material. Production of pure PTFE filter material, this method possesses short process flow, simple operation, low cost, easy to mass production, etc.
Experimental section
Materials and equipment
PTFE microporous membrane, PTFE fiber and PTFE needled felt all made for this project; Hydrogen peroxide, concentrated ammonia are analytically pure; Distilled water is homemade. Tectorial membrane unit is homemade.
Production process of PTFE coated filter material
PTFE staple fiber→PTFE fiber mesh（PTFE high strength and low stretch base fabric carding and laying）→High density acupuncture→High temperature heat setting→PTFE needle felt→PTFE film polymerize→PTFE acupuncture felt film filter material
Base fabric as skeleton of needled felt filter material, has an effect on enhancement ;In the process of needle, first will be through a certain process of PTFE with short fibers compressed into netting, then press base fabric in the middle with two fiber webs (upper 、 lower has a web respectively), and then through the two processes and the main acupuncture needle, after a certain thermal setting process, finally get needled felt; tectorial membrane divided into resin coated and hot laminating, its purpose is to combined with PTFE membrane on the surface of needled felt, to further improve the physical and chemical performance of needled felt, make its surface level off smooth, not easy to be blocked by dust, high chemical stability, with resistance to high temperature, high humidity, corrosion resistance, wear resistance, high filtration precision, easy to, etc.
The results and analysis
Component analysis of pure PTFE coated filter material
Figure 2 is the infrared spectra of pure PTFE coated filter material, figure 3, 4 respectively the base cloth of the filter material and the surface of the DSC analysis.
Figure 2 Infrared spectrum of pure PTFE coated filter material
Figure 3 DSC analysis of pure PTFE coated filter material base fabric
Figure 4 DSC analysis of pure PTFE coated filter material layer
Figure 2 shows that in 150 cm – 1 and 1200 cm – 1 has two strong bands, near for PTFE characteristic absorption peak, this is – CF2 stretching vibration peak; In the range of 500 ~ 850 cm – 1 a series of bands come from vibration peak PTFE amorphous area. After PTFE resin and fiber, and then with the base fabric needle punched felt, after laminating into filter material processing, the band was not found. Figure 3 and figure 4, with ir spectrum and DSC analysis, can know PTFE coated filter material is made of pure PTFE.
Electron microscopy of pure PTFE coated filter material
Figure 5 is pure PTFE coated filter material longitudinal section electron microscopic photograph.
Figure 5 100% PTFE coated filter material longitudinal section electron micrograph
Pure PTFE coated filter material is based on PTFE fabric as substrate (FIG. 5 longitudinal section electron micrograph middle coarser fiber is the Teflon long fiber), through the acupuncture of different fineness of PTFE staple fiber, and at the completion of needle-punched process on one side of the filter material, a layer of PTFE membranes made of compound. PTFE fiber and PTFE microporous membrane layer have good bonding properties, which in the mechanical properties of pure PTFE coated filter material can be well reflected. Figure 2 ~ 4 did not show a new absorption peak, it shows that it does not form new chemical bonds between PTFE microporous membrane and PTFE base fabric, just rely on the role of high temperature melt to produce high temperature thermal bonding effect.
Figure 6 is pure PTFE coated fiber filter material surface electron microscopic photograph.
Figure 6 pure PTFE coated fiber filter material surface electron microscopic photograph
Figure 6 shows that, due to the special structure of PTFE microporous membrane, made of pure PTFE coated filter material surface without the straight hole, the dust can’t through the membrane surface to the interior of the membrane or base material, the only through the dust and gas or withholding material on the surface of the membrane surface filtering approach is called filtering. In addition, the low surface tension of PTFE membrane which has the good non-stick performance for powder. Trapped and dust or material not like traditional filtering method in the filter material surface form thicker filter cake, don’t blow will not be able to continue to work, instead reaching a certain thickness fall off automatically from the surface of the filter material. So using PTFE coated filter material filter bag won’t cause the system pressure to rise continuously, instead the basic stable state of stress.
Performance metrics of pure PTFE coated filter material
Pure PTFE coated filter material performance is: the surface density is about 850 g/m2, thickness is about 1. 5 mm, 127 Pa pressure ventilation quantity is 25 ~ 40 L/m2 s., continuous working temperature 260 ℃, instantaneous temperature 280 ℃, and the breaking strength is 800 N / 5 cm or more, heat shrinkage rate < 1%, the shortest service life of four years or more, resistance to pH range of 0 ~ 14, no oxidation, no hydrolysis. Ultrafine PTFE fiber layer surface level off, the PTFE film plays a supporting role, make it not easy to damage, and can have quite good protection effect. PTFE crude fiber layer contained in crude fiber make the pore enlargement, increased ventilation volume, greatly reduce the filtering resistance PTFE base cloth for the skeleton, keep high strength making warp/weft to fiber, and guarantee the stability of the size of the filter material, to strengthen the role of filter material. High and low temperature resistance of pure PTFE gradient effect of filtering material, acid and alkali resistance, especially the resistance to high sulfur, high humidity, excellent chemical stability, and filtering channel to gradually form a gradient from small to large, therefore, in process of filtering and ash removal, gas flow rate of filter material increased significantly, the filtering efficiency, filtering speed, high dust removal ability, little resistance during operation, soot cleaning frequency is low, service life is long, not only make the energy consumption dropped substantially, also reduces the maintenance workload and the costs of spare parts and other investments.
Pure PTFE coated filter material performance comparison with ordinary filter material
Pure PTFE coated filter material compared with the performance of several kinds of filter material shows in table 1.
Table 1 pure PTFE coated filter material compared with the performance of several kinds of filter material
Table 1 shows that only the glass fiber and pure PTFE coated filter material of continuous operating temperature can reach 260 ℃, the instantaneous temperature reached 280 ℃.Due to the temperature tolerance is one of the important indicators; bag filter is expected to run as a result, the pure PTFE and glass fiber has more advantages. But because of work in the bag filter process, the need to repeatedly to injection of filter bag, stripping absorption in thin film on the surface of the particles, filter bag need wear and fold reciprocating back and forth, and glass fiber wear-resisting performance is poor, therefore, compared with the traditional effect of filter material, pure PTFE coated fabric more can satisfy the requirement of high temperature, high humidity and high corrosive flue gas dust removal.
The application prospect of pure PTFE coated filter material
Pure PTFE coated filter material because of its high temperature resistance, corrosion resistance and high filtration efficiency, excellent performance, fully competent control of PM2. 5 particulate matter .Compared with PTFE microporous membrane filter material, PTFE coated filter material can make the dust filter from conventional deep filter into a surface, thus to improve filtration efficiency by an order of magnitude, filtration efficiency of PM10 lab reaches 99. 999%, filtration efficiency of PM2.5 reaches 99. 95%, almost zero emissions, its service life can reach more than 10 years, has the high cost performance.
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The preparation and properties of high-performance PTFE coated membrane filter.pdf
Polytetrafluoroethylene (PTFE) has excellent heat resistance, corrosion resistance and good electrical insulating properties, it is a kind of important matrix composite materials for sliding friction parts. But due to low hardness, poor wear resistance of pure PTFE, the modification of PT FE in recent decades to a lot of researches, found in adding graphite, PTFE Mo S2, copper powder, glass fiber, carbon fiber, etc., can significantly improve the strength, hardness and wear resistance, etc. Many studies have shown that mixed filling materials than single filler material to improve the friction and wear properties of PT FE is better. Graphite is a good solid lubrication materials, filling in the PTFE graphite can further improve their tribological properties, graphite filled PT FE has become more widely in engineering application. Nanometer materials is the excellent performance of new materials developed in recent years, due to the nanometer material has good plasticity and toughness, its strength and hardness is higher than ordinary coarse grain materials 4 ~ 5 times. Current research on modification of polymer with nano materials much attention, in recent years the domestic existing unit to carry out this work. The author of SiO2, TiO2, Al2 O3 three different nano materials mixed with graphite filled PTFE composite material has carried on the friction and wear performance test, comparing their tribological performance, they wear mechanisms are also discussed.
Test method
The PTFE average particle size is 50 microns, graphite’s particle size is 1. 5 ~ 30 microns, the performance of three kinds nanometer materials of SiO2, TiO2, Al2 O3 are shown in table 1. The three kinds of nanometer materials respectively by 10% and 5% mass fraction of graphite join the PTFE, according to the following process to make different nanometer materials filled PTFE composite material specimen:
PTFE+ nano material – graphite→ mechanical stirring blending→compression molding→blank products→sawing→polish→specimen
Table 1 The performance of the nano materials
M M – 200 type friction and wear testing machine is adopted to improve the friction and wear test, the rotating speed of 200 r/min, the conditions of dry friction sliding, couple of 45 # steel ring, the surface roughness Ra to 0.08 ~0.12 microns. Wear mass loss of samples are measured under different loading (with one over ten thousand of the photoelectric analytical balance), and the coefficient of friction. Use JMS – 6300 scanning electron microscope to observe and analyze (SEM) of nanometer mixed with graphite filler composites wear surface morphology, and adopt Brinell hardness tester to measure hardness, load is 62. 5 N, loading time is 60 s.
Test results and discussion
Wear performance
Figure 1 shows the three kinds of nanometer materials and their mixed with graphite filler PT FE and the grinding quality of the pure PTFE under different load loss. Can be seen from figure 1, filled PTFE composites wear mass loss is much smaller than the pure PTFE, nanometer materials and their mixed with graphite filler PT FE wear resistance than pure graphite composite mixed filling PTFE composite material is much better than that of nanometer materials and their mixed with graphite filler PTFE composite material with high wear resistance, which can effectively improve the wear resistance of PTFE. Also suggests that single graphite filler of PTFE to improve the wear resistance of the result is bad, are not equal to its single nanometer material of PTFE mixed with graphite filled PTFE composite material, may be the graphite as nanometer materials can have the effect of effective support load, and graphite played a good lubricant and can form transfer film on the friction process to reduce wear materials, to make the nanometer materials and their mixed with graphite filler of PT FE composite material has good abrasion resistance. Can be seen from the figure 1 (b), three kinds of material mixed with graphite filler to PT FE abrasion resistance is different, the influence of the nanometer SiO2 nano TiO2 – graphite – graphite, the two materials on wear resistance of PTFE increased more, especially nano SiO2 – very effective to improve the wear resistance of PTFE and graphite materials and Al2 O3 – graphite material with nano SiO2 – graphite, TiO2 – graphite material, compared to the improve the wear resistance of PTFE is relatively less, and also can be seen from the figure 1 (a), a single nanometer SiO2 is very effective to improve the wear resistance of PTFE, but trials found that SiO2 / PTFE composite materials prone to cracking phenomenon, the reason is worth further exploration in the future.
Figure 1 The relationship between wear mass loss and the load of nanometer materials and its mixed with graphite filler material filling PTFE.
Figure 1 also shows that PTFE and three kinds of nano and its mixed with graphite filled PTFE wear mass loss increase with the increase of load, PTFE wear mass loss increased faster, and the wear mass loss of filled PTFE composites increase more gently, and three kinds of nanometer materials – graphite filling is far smaller than the pure PTFE composite materials, nano – graphite filled PTFE material can improve the wear resistance. That the essence of wear about PTFE under the action of external force, macromolecular chain will slip or rupture, so that the material is pulled out of the land of crystalline region and the slice on the surface of the transferred to accidentally, caused by adhesive wear. Due to the hardness of PTFE and the shear strength is lower than metal, with the steel mill, PTFE wear mainly in itself. After PTFE filled with nano – graphite composite material, its hardness, compressive strength, elastic modulus and creep performance are improved, when its contact with the metal surface, packing plays a role of bearing load, PTFE macromolecular implicated by padding at the same time, it is not as easy as in the filled PTFE relief, and obviously improve the wear resistance.
Figure 2 is the rigidity of PTFE and nano graphite filled composite materials, we can find that, nano materials and nano – graphite filled PTFE material can improve the hardness, the hardness of PTFE composites increase will make its wear resistance also increase. Nano material filling and its corresponding nano – hardness of mixed graphite filled PTFE composites were similar, three kinds of nano – graphite filler material, nano – SiO2 – graphite materials to improve the hardness of PT FE is more, so its corresponding wear ability is good, and nano – PT FE Al2 O3 – graphite composite materials is small, therefore, the hardness of the PTFE composite material has smaller, wear ability is poor, which further shows that nano – graphite is mixed filling materials have played a role in bearing load.
Figure 2 PTFE, nanometer material and its hardness with graphite filled PTFE composite material
Figure 3 shows three different nanometer materials and graphite filled PTFE samples under two load worn surface morphology of the SEM. It can be seen that different nano – almost the wear surface of graphite filled PTFE has different degree of furrows and plastic deformation, and furrows and plastic deformation degree and the filling material and the size of the load, the load is small (100 N), furrows and plastic deformation are relatively mild, and can see the wear and sliding in the same direction, their gall scratches relatively clear [figure 3 (a), 3 (c), 3 (e)];When load increases, furrows and plastic deformation are aggravating, especially nano Al2 O3 – graphite filled PTFE, when load increases, the sample the furrows of the SEM photos visible on the surface of the larger, and appeared surface flaking off, show the characteristics of fatigue wear. And nano SiO2 – graphite mixed filling materials, when the load increases (250 N), the surface is still visible, which is similar to those of low load and grinding crack, explain the material in the loading load range is not sensitive to loading, from the previous figure 1 also shows that load increase the added value of this kind of composite material the erosion rate is very small, showing good abrasion resistance. Also can be seen from the picture, in three groups of filling material, nano SiO2 – graphite mixed filling materials in load under the action of wear and tear, and the plough cut effect of plastic deformation is small, so the nano SiO2 – mixed graphite filled PTFE composites showed better resistance to wear, mixing of nano SiO2 – graphite filler material is one of the effective material of PTFE improve wear resistance.
Figure 3 SEM photographs of worn surfaces of PTFE filled with different nano – materials and graphite
Friction performance
Figure 4 shows the PTFE and different nanometer materials – graphite filler PT FE composite friction coefficient along with the change of load. It can be seen that different nano – graphite material for PTFE composite material with different friction coefficient, the influence of different nano – graphite filled PTFE composite material of the friction coefficient with the increase of load are different. Nano SiO2 – graphite filler PTFE composite materials and PTFE are basic same, friction coefficient and load increase slightly to reduce the friction coefficient, and nano TiO2 – graphite filled PTFE composites slightly bigger than a pure PTFE friction coefficient, and slightly increased along with the increase of load, nano Al2 O3 – graphite filled PTFE composite material is smaller than the pure PTFE, its relationship with load is more complicated. All in all, three kinds of nanometer materials – mixed graphite filled PTFE composite, the friction coefficient of nanometer Al2 O3 – graphite filling PTFE composite material is smaller than the others, nano TiO2 – graphite filled PTFE composite material of the friction coefficient is bigger, the corresponding relationship between the abrasion performance above, nano – SiO2 – wear resistance of graphite filled PTFE composites is much better than nano Al2 O3 – graphite filled PTFE composite material, it shows that SiO2 – graphite filler mixed filling materials for PTFE is a kind of good filling material, its wear resistance of PT FE increased significantly, and the coefficient of friction and pure PT FE are basic same. Although nano Al2 O3 – graphite mixed filling materials can reduce the friction coefficient of PT FE, to improve the wear resistance of PT FE is worse than SiO2 and TiO2 – graphite – graphite filled PTFE composite material performance.
Figure 4 The relationship between load and friction coefficient of different nanometer materials filling PTFE
Conclusions
(1) Nano- graphite mix packing and can improve the hardness and wear resistance of PTFE, they improve the wear resistance of the reason is because the filler material bearing load and graphite lubricant and the three kinds of nano – graphite filled PTFE composite material, mixed with SiO2 – graphite filling effect is best, its wear resistance of PTFE increased more.
(2) Different nano – graphite filled PTFE composite material is different, the friction coefficient of nano SiO2 – graphite friction coefficient of PTFE composites filled with PTFE is basically the same, the friction coefficient of nano TiO2 – graphite filled PTFE than pure PTFE increases slightly, and nano Al2 O3 – graphite filled PTFE composite material is smaller than the pure PTFE.
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As people on architectural form and beauty, as well as the safety, energy saving, membrane structure material (hereinafter referred to as the membrane material) as a new type of space structure material, with its light and beautiful, pervious to light the advantages of energy saving, safe and durable, widely used in all kinds of large construction projects. Architectural membrane material is called after the steel, cement, wood and glass of 5 kinds of building materials, it not only can be applied to the original application fields of building materials, but have trouble with the original building materials application areas, such as large span space structure with traditional building materials incomparable superiority.
Architectural membrane material refers to high strength fiber fabric, which is after a certain finishing process, the surface coating of high performance resin material to form a flexible composite. At present the most commonly used architectural membrane material mainly has three types: (1) polyvinyl chloride (PVC) architectural membrane material, with high strength polyester fabric, which is coated on the surface of PVC resin. In order to improve its aging resistance and self-cleaning surface physical and chemical modification of membrane materials for processing or in PVC coated on the surface of PVDF membrane materials, PVF surface and a series of various types of PVC membrane material.(2) the polytetrafluoroethylene (PTFE) membrane material, with super fine glass fiber fabric, which is coated on the surface of PTFE resin. The membrane material on various aspects performance is excellent, especially on the ageing resistance and self-cleaning performance is incomparable with PVC membrane material.
This article focuses on the membrane material. (3) – Tetrafluoroethylene ethylene membrane material (ETFE), made from – Tetrafluoroethylene ethylene copolymerization body directly, no fabric reinforced base cloth. This is a new kind of recyclable green membrane material, showed a larger advantage in environmental protection and good market prospects.
Development status of PTFE membrane
Membrane development and application originated in Europe and the United States, membrane material building all over the world is the world’s fair in 1970, Osaka, Japan on the USA pavilion, it used the PVC coated glass fiber cloth membrane material, but its service life is shorter. In order to overcome the PVC architectural membrane material aging resistance and self-cleaning bad and some shortcomings, under the leadership of the ford foundation support and Geiger company, in the United States Dupont, corning glass fiber company, Baird construction company, chemical fiber weaving company to jointly develop the better durability, anti-fouling strong of PTFE membrane material, make the permanent large span buildings become a reality. The membrane material used in the United States in 1973 Laverne college student activity center, 20 years later tracking test results show that the mechanical properties of membrane material and the physical performance index fell by less than 30%, it is enough to show the superiority of this kind of membrane material on the various performance.
PTFE membrane material development depends largely on the super fine glass fiber and the weaving processing technology, etc. Commonly used glass fiber monofilament diameter of about 4 microns non-alkali fiberglass (E -glass fiber), due to the poor wear resistance and percentage of elongation of glass fiber, in the weaving process, the effect of friction on the strength of the glass fiber has great influence on mechanical properties, can’t meet the requirements of membrane material base cloth weaving, so people choose a superfine glass fiber cloth as the membrane material base cloth. Along with the development of the processing and weaving technology, about 6 microns or more glass fiber applied in membrane material, but in terms of large span structure, 4 microns of glass fiber is more secure. Foreign superfine glass fiber industry and weaving technology development earlier, better product performance, low cost, satisfy the requirement of membrane material can produce a variety of the thickness of the glass fiber cloth, fabric width can be more than 4 m, can effectively reduce the splicing part of membrane material, improving the performance of membrane structure architecture.
With the development of the technology, PTFE membrane material is also toward diversification, high-performance and intelligent gradually. For now, manufacturing enterprise conclude the Chemfab of the United States, Taconic Company, Mehler of Germany, Duraskin Company, Saint – Gobain Company of France, TaiyoKogyo of Japan, etc.The United States is the earliest development of PTFE membrane material, the glass fiber and membrane material has greater advantage, has been in a leading position in the world; German film materials development is also in the top in the world, du company could produce the world’s most wide (4.7 m) of PTFE membrane material, and product diversification; saint-Gobain company of French is a large glass fiber and its products production enterprise, in regard to the development of PTFE membrane material has great advantages, is the world expo in Shanghai world expo axis of PTFE membrane material suppliers; Japan could produce the finest in the world of glass fibers, made from the fiber fabric as the base cloth of membrane material, can make the membrane material has more flexibility, more durable.
Production technology of PTFE membrane material
The process flow of PTFE membrane material
PTFE membrane material use dip coating method, the super fine glass fiber cloth (hereinafter referred to as the glass fiber cloth) on the coated PTFE resin and elaboration. Glass fiber cloth by dipping tank coated PTFE dispersion concentrate first, then after drying, baking, sintering process, will be escaping through the excess water and solvent, and make the resin particles evenly distributed on both sides of the glass fiber cloth. Need to repeatedly impregnated fiberglass cloth, and each time the amount of resin impregnated to appropriate control, it is prone to cracking phenomenon after sintering if it dip too much, whereas dipping too little, it cannot meet the performance requirements of the product. Impregnation process is divided into single slot and slot, as shown in figure 1, but generally to the continuity of production and efficiency, mostly adopts multiple slot impregnation process.
The base cloth weaving process and coating process is as follows:
(1) The weaving process: glass fiber – and twist – warping – weaving – glass fiber cloth.
(2) Coating process:
Fiberglass fabric- Heat cleaning- Dipping- Drying- Sintering- Cooling- Finished product
Key factors in PTFE membrane production
Glass fiber raw material
Because of the glass fiber elongation small and brittle, it is difficult to meet the requirements of the base fabric weaving process, so should choose superfine glass fiber (4 microns) to the weaving cloth, both can satisfy the requirement of cloth, and can meet the requirements of the mechanical properties of membrane material. In Japan b-grade yarn (around 3. 8 microns) and DE yarn (about 6 microns), for example, to illustrate the advantages of super fine glass fiber. Intensity is inversely proportional to the diameter of fiber, B grade yarn tensile strength of 3.1 GPa, and DE grade yarn tensile strength is 1.5 GPa, than B grade yarn fell more than 50%, and the bending strength also fell by 30%.So the class B yarn made of membrane material mechanics performance is better, use more secure.
Glass fiber base fabric and its weaving
In the impregnation of membrane materials and sintering process, the demand for glass fiber fabric is higher, especially the flatness and surface tension of the base fabric uniformity greatly influence on the formation and properties of membrane material. Generally, base fabric require surface smooth, uniform tension, yarn joint and yarn breaking, oil and other defects. Base fabric structure generally uses woven plain or panama, weft yarn density general control within 13 root/ cm.
Warping process is the key technology, generally uses the partial warping again and shaft or warping. In the wide weaving fabric, generally adopts the partial warping and shaft process, this kind of technology in the electronic grade fiberglass.LTD application more widely; In a narrow fabric weaving, adopt a warping can better guarantee the fabric smoothness, but exist in species is not convenient, the production efficiency is relatively low. Commonly used in weaving of rapier loom, telescopic rapier loom better rigidity, and warp no wear and tear is advantageous to the glass fiber cloth weaving.
Dip coating process
The key factors in the process of dip coating include PTFE dispersion concentration, drying, baking, sintering temperature and speed. The concentration of dispersion directly affects the thickness of the membrane material, resin content and roughness, etc. The higher the concentration, the greater the thickness of after impregnating resin, not too much, but each time the dipping thickness generally multiple impregnation process, dispersion concentration increasing. In addition, the dispersion of softening agent, surface active agent and other auxiliaries’ application is also very important. Generally within three vertical oven drying, baking and sintering process of resin, continuous gradient, temperature in the oven is divided into three main temperature area: dry area dry after dipping fiberglass cloth, remove the moisture in dispersion, is in commonly 80 ~ 100 ℃, the temperature too high may produce bubbles or flow mark; Baking area to remove residual moisture and surfactant on cloth, etc., is in commonly 260 ~ 290 ℃, low temperature may make the cloth cover sticky, etc.; High temperature sintering area make the resin melt, eliminate interface, with the glass fiber fabric has better bonding force, so that the membrane material plasticizing, usually in the temperature of 380 ~ 400 ℃.Dipping tank temperature is usually at room temperature (20 ~ 25 ℃).Speed directly affect the quality of the product’s drying sintering and the production efficiency, speed too fast, it influence impregnated resin content as well as the effect of drying and sintering, etc.; Speed is too slow, it influence the production efficiency, is not conducive to reduce the cost.
The performance and characteristics of PTFE membrane material
General coated fabric, enhanced lining fabric has decided to the mechanical properties of membrane material, the outer coating material decided to physical properties of the membrane material. PTFE membrane material can give full play to high strength about the mechanical properties such as glass fiber, and can play PTFE physical properties such as resistance to ageing, self-cleaning advantage. Table 1 is the performance of PTFE membrane material compared with PVC membrane material.
Table 1 performance comparison of PTFE membrane material with PVC membrane material
Good mechanical properties
Glass fiber has high tensile strength and elongation of small features, it make the membrane material has good tensile strength and tear strength, and also won’t appear obvious under long-term load stress relaxation and creep. Generally moderate intensity of PTFE membrane material, its thickness is less than 1 mm, weight 1 kg/m2 or so, its tensile strength has reached the level of steel. Sintering process make glass fiber cloth and combining PTFE resin good, the peel strength is very high, almost impossible to separate.
Good weather resistance
Weather resistance is mainly embodied in the aging resistance and self-cleaning .Because PTFE has the character of inertia, low friction and not sticky, almost without any chemical erosion, so PTFE membrane material in resistance to ultraviolet radiation, the erosion of acid rain, microbial damage has obvious advantages, its aging resistance of PVC membrane material is incomparable. On self-cleaning aspect, membrane material with hardly any adhesive material, even with a small amount of dust pollution, after the rain wash, can achieve natural clean. Therefore, PTFE membrane material suitable for permanent membrane material, its life can reach more than 30 years.
Good flame retardant fire prevention performance
PTFE has excellent high temperature resistance, can be continuous use between 240 ~ 260 ℃, has significant thermal stability, glass fiber also non-flammable, so the membrane material with flame retardant fire performance can meet the requirements of national building materials fire. PTFE membrane material also resist low temperature, can use for a long time under the conditions of -180 ~ 260 ℃.
Pervious to light energy
PTFE membrane material of sunlight transmission rate was 12% ~ 21%, generally related to the thickness and the weight of the membrane material, membrane material has well pervious to light quality. Transmitted light evenly diffuse light inside the structure, natural soft, no lighting during the day, can save energy, at night, under the light irradiation and interior lighting the appearance, the appearance of buildings that show a dreamy effect.
Sound absorption and sound insulation performance
Because the glass fabric has sound-absorbing sound insulation performance, PTFE membrane material has good reflectivity for 500 ~ 2 000 Hz audio generally, absorbing some low-frequency melody; high-frequency sound absorption is limited, but with other sound-absorbing material, it has good sound-absorbing sound insulation effect.
The application of PTFE membrane material
PTFE membrane material, as a permanent membrane material with light free, pervious to light energy saving, security, good shape, long life and other advantages, is widely used in various kinds of large buildings. Mainly divided into the outer membrane and lining, it has a big difference in performance.
PTFE membrane for outer membrane
PTFE membrane for outer membrane is mainly used a general roofing material, canopy material and external decoration, etc. As roof material commonly used in stadiums, exhibition halls, the airport hall, shopping centers, recreation centers and other large public facilities. Such as the one thousand in the Thames dome, membrane material covering area of over 180000 m2, is a single area of the membrane structure; Saudi Arabia Jeddah airport lounge suspension membrane structure, covers an area of 420000 m2.Eighty thousand Shanghai stadium in China, covering the area of 3. 60000 m2 is our country for the first application of membrane structure in large buildings, far-reaching influence. As the canopy material is commonly used in square, park green space, park, station and other facilities. As external decoration mainly using artistry and plasticity of membrane material, such as the Shanghai world expo axis, the expo axis of cable membrane structure is the world’s largest continuous tensioned membrane structure by far, every piece of membrane single chip area of 1800 m2, total an area of 70000 m2, there are six eye-catching inverted cones which distribute well-proportioned, it is a beautiful scenery line of the Expo Park..
PTFE membrane for inner membrane
PTFE membrane for inner membrane is mainly used as sound insulation material, its mechanical performance requirements is lower than the outer membrane. The most typical engineering is the national stadium, the main Olympic stadium the bird’s nest, the structure of PTFE + ETFE, upper is ETFE membrane structure, rain and snow prevention role; Bottom is 53000 m2 of PTFE membrane structure, main effect is acoustic ceiling , by PTFE membrane absorption which can guarantee the stadium sound clear.
Problems and prospect
Architectural membrane material as an emerging industry, has strong advantages and broad market prospects, but there are some problems in its development: (1) the flexibility of the PTFE membrane material needs to be improved, due to the brittle glass fiber and bending performance is bad, make the products in the process of PTFE membrane material in bending strength and other mechanical performance degradation is more, in the course of processing, transport, construction and other inconvenience, so package forms commonly used PTFE membrane material. Glass fiber strand should be strengthened, the processing technology and coating technology research, improve the flexibility of the PTFE membrane material, make it easy to processing and installation.(2) the high cost of PTFE membrane material, including raw material production, transportation, construction and maintenance cost, etc. Superfine glass fiber raw materials and its processing cost is higher, due to the flexibility of the membrane material is bad, the transport, construction more difficult, also lead to higher costs. Enhanced PTFE membrane material of raw materials and the production research, strengthen technological innovation, constantly improve the performance of the membrane material and reduce cost, make it in terms of performance, cost has a strong market competitiveness.(3) PTFE membrane material recycling and environmental protection. New ETFE materials with no fabric reinforced, to melt it into particles can be recycled， this is a kind of environmental protection material; And enhanced PTFE membrane material with glass fiber cloth, how the substrate with enhanced body separation or recycling, it is an environmental problem to be solved.
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Development of fiberglass PTFE membrane structure materials.pdf
PTTE (polytetrafluoroethylene) and its composites as excellent self-lubrication material both in industry and aerospace fields are widely used, the thermal expansion characteristics and linear expansion coefficient as a very important physical parameters on the products design and use effect is large. Application of PTFE material temperature range is very wide, but there are changes at room temperature, while accompanying changes in structure and size. Because PTFE material bigger than linear expansion coefficient of metal materials, and large temperature changes, it is generally only larger temperature ranges of average linear expansion coefficient. Considering the phase change process of PTFE and composites of precision mechanical structure clearance and the use of a larger impact performance, the author analyzes the pure PTFE and aramid fiber reinforced PTFE matrix composites in thermal expansion between the – 100 ℃~ + 250 ℃.
Room temperature phase transition of PTFE
PTFE material with special spiral chain structure, along the main chain of C – C plane trans position, reverse for about 17 ° Angle. Under normal pressure, there are two reversible transitions in PTFE crystals at about 19 ℃ and 30 ℃. Under 19 ℃, the repeat unit contains 13 CF2, repeat distance of 1. 68 nm, the repeat distance chain be reversed in 180 ℃, unit cell belongs to triclinic crystal system. As shown in figure 1 in 19 ℃ PTFE material part through a crystal phase diagram type transformation, in 19 ℃ above spiral slightly spread, repeat unit contains 15 CF2, repeat distance of 1. 95 nm, is within the repeat distance chain turn 180 ℃, molecular accumulation into nearly hexagonal cylinder, unit cell of hexagonal system. As shown in figure 1, PTFE material in normal temperature zone in the phase diagram to mutually Ⅱ under 19 ℃, mutually Ⅳ between 19 ~ 30 ℃, PTFE has other phase transformation under high pressure.
Figure 1 The partial phase diagram of PTFE material
PTFE crystals in triclinic crystal system into a crystal structure transition of hexagonal system, volume increased about 1. 2%. At 30 ℃, PTFE crystal crystallization relaxation, the helix of the chain becomes irregularly wound, when 30 ℃ volume change about 10% of the 19 ℃.Due to the crystal transformation and crystallization temperature point in common temperature range, the relaxation of almost all application condition will override this temperature range. In the process of crystal transformation and crystallization relaxation, PTFE volume changes obviously, corresponding to the application performance of PTFE and its composites have an impact.
The preparation of PTFE matrix composites
PTFE matrix composites using powder blending, cold pressing molding and sintering temperature control of preparation process. PTFE powder produced by light chemical industry research institute, the particle size of 20 ~ 40 microns, density of 2. 2 g/cm3.Enhancement for commercially available with aramid fiber, fiber diameter of 10 ~ 12 mu m, length is about 100 microns, the density of 1.45 g/cm3. Strengthening agent quality percentage adopts 15% and 15% respectively. Reinforcing fiber with PTFE matrix after mechanical mixture, under pressure from 60 M P a pressure maintaining 10 min molding, then in sintering furnace control of sintering temperature, sintering temperature of 380 ℃, 300 min sintering time, l/cooling rate of 20 ℃ / M in, along with the furnace cooling. The cooled sintered specimen is machined to produce the required test piece.
Measurement and Analysis of Linear Expansion
Linear expansion coefficient of characterization of objects caused by temperature rise 1 ℃ which affects the ratio of growth and its original length. Set an initial length of an object as L0, L is the length of the increment when the object temperature T, the cable expansion coefficient alpha αL is:
With German D IL 402 c type thermal expansion instrument measuring the linear expansion coefficient of PTFE matrix composites, measure the direction parallel to the direction of specimen molding pressure. Sample 5 mm in diameter, length of about 25 mm. Experimental analysis temperature range: – 100 ~ + 250 ℃, low temperature zone by liquid nitrogen for evaporative cooling way, after – 100 ℃ keep 3 min began to heat up. Adopted in 0 ~ + 50 ℃ temperature zone in the heating rate of 2 ℃ / m, other zones are used in the heating rate of 5 ℃ / m.
PTFE material and adding 15% and 25% respectively of aramid fiber thermal expansion of PTFE composites curves as shown in figure 2 ~ 4, respectively. Abscissa is temperature, ordinate is amount for sample linear expansion. According to the definition, the linear expansion coefficient curve 2 ~ 4 by differential and linear change corresponding linear expansion coefficient curve, as shown in figure 5 ~ 7, respectively.
From figure 2 ~ 4, aramid fiber reinforced PTFE matrix composites show almost consistent with pure PTFE material thermal expansion characteristics, below 0 ℃ and 50 ℃ above sample length increase are almost linearly with the temperature, the turning point between 0 ~ 50 ℃.After adding aramid fiber materials of the thermal expansion amount is reduced, and the reduction increases with the increase of additive content. Three kinds of material in different temperature range of the average linear expansion coefficient values as shown in table 1, in – 100 ~ 0 ℃ interval linear expansion coefficient of value only half of the 50 ~ 250 ℃ range value, within the range of the two interior expansion coefficient with the increase of the filler content reduced slightly, and within the range of 0 ~ 50 ℃ insider expansion coefficient increases slightly with increasing filler content.
Table 1 The average linear expansion coefficient of PTFE composite materials ×10 – 5K – 1
As can be seen from figure 5 ~ 7, linear expansion of aramid fiber reinforced PTFE matrix composites curve profile consistent with that of pure PTFE material. Under 0 ℃, three kinds of linear expansion coefficient of material all showed increasing trend with the increase of temperature, linear expansion coefficient of the material is pure PTFE under 10 x 11-5 K – 1, after adding 15% and 25% of aramid fiber linear expansion coefficient are reduced to 10 x 10-5 and 9 x 10 K – 1-5 K – 1 the following, and expansion curve flattens. In 50 ~ 250 ℃ range, linear expansion coefficient of the same with the temperature increasing, the pure PTFE for linear expansion coefficient (7. 4 ~ 27. 5) x 10 – K – 1, 5 and add respectively 15% and 25% after aramid fiber linear expansion coefficient (6. 3 ~ 26. 2) x 10-5 K – 1 and 6. 3 ~ 23. (1) x 10-5 K – 1.In 0 ~ 50 ℃ range, due to containing PTFE material phase transition point, linear expansion curve changes appear several twists and turns, but the 3 kinds of materials are at 25. 5 ℃ at its highest point, near a crystallization relaxation near 30 ℃.Crystal structure transition temperature point of the three kinds of materials have some deviation, pure PTFE material appeared in the vicinity of 17 ℃ crystal structure transformation, and transformation point after adding 15% and 25% of aramid fiber are reduced to around 13 ℃.And after adding filler PTFE material general tendency of lower linear expansion coefficient, high coefficient of linear expansion of PTFE material is from low to high in turn, PTFE + 15% aramid fiber composites, PTFE + 25% of aramid fiber composite materials. In the case of phase change can achieve maximum linear expansion coefficient average linear expansion coefficient of 3 ~ 5 times.
Generally, adding graphite in PTFE and inorganic fillers such as glass fiber filler does not participate in the crystallization of the PTFE molecular chains, crystal transition temperature of PTFE is not having an impact. Aramid fiber made of PTFE crystal transition temperature the temperature offset, peak temperature relaxation of crystallization temperature and expansion is essentially the same, description of aramid fiber in a certain degree of participation in the crystallization of the PTFE molecule chain, copolymer copolymer results makes grain size small, Crystal changes are more prone to swelling, and reflects the crystalline transition region line expansion coefficient becomes larger.
Conclusion
The linear expansion coefficient of PTFE matrix composites with the temperature change is bigger, linear expansion coefficient is far less than that of low temperature zone high value. With aramid fiber as reinforcing agent, the decrease of average linear expansion coefficient, the filler content is higher, the smaller the average linear expansion coefficient. After adding filler PTFE composites compared with pure PTFE material crystal structure transition temperature drift in the direction of low temperature, crystallization temperature relaxation has not big change, but in the crystal type of filler content in the transformation process, the more the linear expansion coefficient, the greater the maximum linear expansion coefficient is 3 ~ 5 times the average linear expansion coefficient.
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Analysis of thermal expansion properties of PTFE matrix composites.pdf
Organic wastewater containing halogen is difficult to degrade organics, the common characteristics of these pollutants is toxic, complex components, high chemical oxygen demand, the general microbial almost no degradation effect to its, if these substances without governance to environmental emissions, would seriously pollute the environment and endanger human health. Meanwhile, halogenated organic compounds are important chemical raw material; its recovery has important economic value. Process of pervaporation (PV) is a new type of membrane separation process, it is especially suitable for the separation of the small amounts of organic pollutants in wastewater, and it has obvious technical and economic advantages. Pervaporation process play a key role is the core element of film, from the point of view of literature retrieval condition, materials used in silicone rubber polydimethylsiloxane (PDMS). Chandak prepared silica zeolite modified PDMS composite pervaporation membrane , and used for separation of chlorinated organic aqueous solution; Salehi, etc were used in pervaporation PDMS – PES crosslinked composite membrane, investigated its removal from aqueous solution, toluene and chloroform pervaporation performance; Bennett preparation containing different organic functional groups such as side chain of the modified PDMS silicon rubber membrane, with chloroform solution system testing the pervaporation performance; Tadahiro prepared PDMS-PMMA composite film by dimethyl siloxane crosslinking methyl methacrylate (mma) , studied the pervaporation separation of VOC pervaporation properties of aqueous solution. And with strong hydrophobicity, high crystallinity and stability good polytetrafluoroethylene (PTFE) modified PDMS is relatively rare, this paper was prepared with poly (vinylidene fluoride) (PVDF) ultrafiltration membrane as the basement membrane, PTFE superfine powder filling PDMS membrane for pervaporation of active cortex (PTFE – PDMS/PVDF) composite membrane, taking chloroform solution as separation system composite membrane pervaporation performance was studied.
Experimental part
The preparation of PTFE-PDMS/PVDF composite membranes
According to take the right amount of silicon rubber PDMS, dissolved in hexane, in proportion to join the right amount of PTFE powder, TEOS crosslinking agent, mechanical stirring 2 h after ultrasonic dispersion of PTFE, join DBTL catalyst, fully stir until sticky solution, dumping on PVDF ultrafiltration membrane, extending into membrane, place 2 h at room temperature, vacuum drying oven crosslinking on 60 ℃ in the 4 h, quick PTFE – PDMS/PVDF composite films. In the process of preparation of PDMS: TEOS: DBTL, the mass ratio is 10:1:0. 5.By PTFE: PDMS the mass ratio prepare the five (0:20, 1.5:20, 6:20, 10:20, 15:20) different composite membrane.SEM analyze and adopt the Japanese JMS – 5600 LV scanning electron microscope, contact Angle measurement by Shanghai Calvin JC2000D1 type of contact Angle meter.
The Pervaporation experiments of PTFE-PDMS/PVDF composite membrane
Pervaporation separation experiment device see references. Sample analysis use UV spectrophotometer. Membrane separation factor alpha, permeate flux J and separation index PSI is the main parameter that characterization of pervaporation membrane separation performance, respectively defined as:
Mass transfer model
Pervaporation series of low concentration organic solution mass transfer process is generally used resistance model, the component i and flux Ji are proportional to across the membrane mass transfer driving force:
The results and discussion
SEM analysis
From figure 1 (a) can be seen, no modified silicone rubber membrane surface showed very good flatness, and no found holes and cracks. But after joining PTFE composite membrane surface is uneven structure, and a large number of PTFE particles distribution in PDMS surface, the edge between PDMS and no phase separation phenomenon, the rough surface morphology significantly increased the membrane surface and the surface hydrophobicity enhanced composite membrane (water contact Angle change as shown in figure 2), to strengthen the pervaporation performance, as shown in figure 1 (b – c).From figure 1 (c), ultrafiltration membrane surface is about 25 microns thickness of PTFE filled with PDMS active cortex.
Figure 1 SEM. a-PDMS membrane surface (magnification：×5000) ；b-PTFE-PDMS/PVDF membrane surface (magnification：×200) ；c-PTFE-PDMS/PVDF membrane section (magnification：×500)
Figure 2 The impact of PTFE content on contact angle of composite membrane
The impact of PTFE content on the composite membrane pervaporation performance
The figure 3 and figure 4 shows that filling amount of PTFE film 15:20, and to explain hydrophobic nano PTFE and PDMS compatibility are good, and the addition of PTFE significantly improves the pervaporation properties of PDMS composite membrane. Water flux showed a trend of increase gradually and far greater than chloroform; Chloroform flux, the separation factor and separate index showed a trend of decrease after the first increase. Shingjiang Jessie thought the aggregation particle filling PDMS membrane help water flux to improve. By section 3.1, PTFE particles are the state of aggregation. So its content is increased, the water flux increased, chloroform adsorption quantity increases, the flux increases; and, because of the large water impetus the chloroform water flux is greater than chloroform. when the content of PTFE more than10:20, and get a lot of PTFE will add destroy the PDMS membrane structure of continuous phase, lead to water at this time spread more likely , the water flux increases with chloroform flux decline and separation factor decrease.
Figure 3 The impact of PTFE content on the composite membrane flux, water flux and the flux of chloroform (feed liquid temperature 60 ℃ and permeate side pressure 2.2 mmHg, slurry concentration 660 mg L – 1, the material liquid flow 400 mL min – 1)
Figure 4 The impact of PTFE content on the composite membrane separation factor and the separation index (feed liquid temperature 60 ℃, permeate side pressure 2.2 mmHg, slurry concentration 660 mg L – 1, the material liquid flow 400 mL min – 1)
The impact of material liquid flow rate on pervaporation performance
The mass ratio is 10:20 PTFE PDMS/PVDF composite membrane pervaporation performance results under different flow rate as shown in figure 5, and 6.With the increase of feed liquid velocity, total flux, chloroform, water fluxes and separation factor in increased rapidly, while less than 200 mL min – 1 when the flow rate is greater than 200 mL min – 1 change is steady, the experimental results and Park using PDMS composite membrane pervaporation VOC aqueous solution, the conclusion is very similar. Due to the effect of dissolve of the composite membrane of chloroform strong, easily happened under the condition of low velocity phenomenon of concentration polarization, but with the increase of flow velocity and boundary layer thinning, concentration polarization effect weakened and is beneficial to chloroform and mass transfer process, so when the flow rate is less than 200 mL min – 1 flux and separation factor are increased with the increase of flow velocity; And when the flow rate is greater than 200 mL min – 1 flux and separation factor change steady, shows that the boundary layer and mass transfer resistance is small, the mass transfer resistance is controlled by membrane resistance.
Figure 5 The impact of material liquid on the composite membrane material total flow flux, the water flux and flux chloroform (150 mg L – 1 material liquid concentration, feed liquid temperature 50 ℃, permeate side pressure 2.2 mmHg)
Figure 6 The impact of material liquid flow on the composite membrane separation factor (150 mg · L 1 material liquid concentration, feed liquid temperature 50 ℃, permeate side pressure 2.2 mmHg)
The impact of material liquid concentration on the pervaporation performance
PTFE material liquid concentration on the mass ratio 10:20, and get – PDMS/PVDF composite membrane pervaporation performance impact is shown in figure 7, 8.With the increase of the concentration of slurry, the total flux and chloroform flux linear increase slowly, and the water flux changes smaller; Separation factor with the increase of the concentration of material liquid drop sharply. The material liquid flow 400 mL min – 1 eliminate the influence of concentration polarization (see section 3.3), the type, the water mass transfer driving force changes with the increase of concentration of chloroform, so the water flux change is very small and chloroform flux linear increase. When chloroform concentrations greater than 200 PPM, film inside a large amount of dissolved chloroform by membrane of the groups in law of organic affinity effect and make the transfer resistance increases, chloroform molecules of mass transfer rate is reduced, the separation factor is on the decline.
Figure 7 The impact of feed concentration on the composite membrane flux , water flux and the flux of chloroform (feed temperature 50 ℃, permeate side pressure 2.2 mmHg, material liquid flow rate, 400 ml min – 1)
Figure 8 The impact of feed concentration of composite membrane separation factor (feed temperature 50 ℃, permeate side pressure 2.2 mmHg, material liquid flow rate, 400 ml min – 1)
Process analysis of mass transfer
From figure 9, 10, with the increase of feed liquid velocity, boundary layer thickness gradually thinning, Kb increase gradually, Rb gradually decreased; When the flow rate is greater than 200 mL min – 1, Kt gradually close to Km, Rt gradually close to the Rm, illustrate the Rb, chloroform and mass transfer process is controlled by the Rm. When the flow is 10 mL min – 1, Rb is Rm 29 times, chloroform and mass transfer process is controlled by Rb, thus, phenomenon of concentration polarization in chloroform plays a considerable role in the process of mass transfer, so the pervaporation chloroform solution should be carried out under high flow velocity, in order to overcome the influence of the concentration polarization. From figure 10, flow under the condition of 400 mL min – 1 Kt basic equal to Km, so in figure 11, with the increase of the concentration of chloroform in the material liquid, the chloroform Kt increases linearly, and water Kt has linear decreasing trend, namely chloroform Km linear increase, and the water Km linear decrease. This suggests that a greater influence on the concentration of chloroform in the material liquid Km, this is mainly due to the strong hydrophilic organic composite film features generated by the results.
Figure 9 The impact of material liquid velocity of chloroform and total mass transfer coefficient, boundary layer and mass transfer coefficient and the membrane mass transfer coefficient (150 mg · L 1 material liquid concentration, feed liquid temperature 50 ℃, permeate side pressure 2.2 mmHg)
Figure 10 The impact of material liquid velocity on mass transfer resistance of chloroform (150 mg · L 1 material liquid concentration, feed liquid temperature 50 ℃, permeate side pressure 2.2 mmHg)
Figure 11 The impact of concentration of materials on total mass transfer coefficient of chloroform and water(feed temperature 50 ℃, permeate side pressure 2.2 mmHg, material liquid flow rate, 400 ml min – 1)
Conclusion
PTFE PDMS/PVDF composite membrane was prepared, and in chloroform solution system study of pervaporation properties of the composite membrane. Increased, PTFE filler in PDMS membrane showed a trend of increasing total flux and water flux, flux and chloroform, the separation factor and separate index showed a trend of decrease after the first increase, when PTFE: PDMS is 10:20 for mass ratio, PTFE PDMS/PVDF composite membrane pervaporation performance was the best; With the increase of feed liquid velocity, total flux, chloroform, water fluxes and separation factor in increased rapidly, while less than 200 mL min – 1 when the flow rate is greater than 200 mL min – 1 change to level off; With the increase of the concentration of slurry, the total permeation flux and chloroform flux increase slowly, and the water flux changes smaller; Separation factor dramatically reduced with the increase of concentration of feed solution.
Chloroform and mass transfer process was analyzed, when the flow is 10 mL min – 1, the boundary layer resistance Rb is 29 times the Rm of the membrane resistance and mass transfer process is controlled by boundary layer resistance; And when the flow rate is greater than 200 mL min – 1, chloroform and mass transfer process is controlled by the membrane mass transfer resistance, thus, phenomenon of concentration polarization in chloroform plays a considerable role in the process of mass transfer, so the pervaporation chloroform solution should be carried out under high flow velocity, in order to overcome the influence of the concentration polarization.
Symbol explanation:
A The effective area of membrane，m2
C Molarity，mol L−1
G Quality，g
JPermeate flux，g m−2 h−1
KMass transfer coefficient，m s−1
R Mass transfer resistance，s m−1 t Operating time，h
XRaw material liquid component mole fraction
Y Penetrating fluid component mole fraction Superscript
f Raw material liquid
p penetrating fluid Subscript
b boundary layer
i component
m membrane
t total
C chloroform
W water
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PTFE PDMS PVDF composite membrane preparation and pervaporation properties.pdf