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Manufacturing, application and development of PTFE/Teflon coated fiber glass fabric

PTFE/Teflon coated fiber glass fabric is made of glass fiber cloth as the substrate, impregnated with PTFE dispersion. Impregnated fiberglass cloth surface, coated with a thin layer of fluororesin small particles, and then through the drying, baking, sintering and other processes, the dispersion of volatile and leaving F4 tiny particles, tightly attached to the surface and pores of the fiber glass cloth, intensive continuous as a whole, to achieve the purpose of fiberglass cloth and F4 firm bonding, it become a new material which not only has the characteristics of fiber glass, but also has many excellent properties of fluorine plastic. According to different needs, in the dispersion can also be added inorganic or organic filler, to further improve its electrical properties, anti-aging properties and wear resistance, add a different pigment and then increase its excellent decorative performance.

Process Research
Raw material
A. PTFE commonly known as “plastic king”, it is one of the best performance varieties of plastic. It has excellent temperature resistance and corrosion resistance, excellent insulation properties, non-stick, non-toxic and odorless, harmless to the human body.
B. Fiberglass fabric
The substrate of the coated materials should have high temperature resistance and good tensile strength, glass fiber compared with natural fibers and chemical fiber, it has high strength, elongation is small, good chemical stability, etc., and it can make up for the lack of F4, to maintain the size of the stability.

Production process and key technology
A. Production process
Treated fiberglass fabric and F4 dispersion liquid→Impregnation→Drying→Take-up→Sintering→Take-up→Checking→Finished product pakcaging→ Storage
B. The main key technology of the processes of fiberglass impregnated with F4 dispersion are the following three aspects.
a. F4 dispersion concentration, impregnation temperature and velocity
The concentration of F4 dispersion directly affects the surface finish, flatness, thickness and resin content of the product. High concentration, the thickness is large after each impregnation, the number of times to complete the dipping can be reduced accordingly; But if the impregnated F4 is too thick, it is easy to produce products surface cracking after drying. In order to ensure product quality, should use low concentration of dispersion, after several times impregnation is better.

The temperature distribution of the impregnation furnace is divided into three zones according to the elevation. Respectively, to complete the impregnation, drying and baking three processes.

Low temperature zone: The temperature of the first section of the lower part of the impregnation unit, it is affect the surface temperature of the dipping tank directly, and related to the liquid surface bubble burst rate and and flow marks and other defects. The temperature of the area is too high, will make the glass cloth dispersion too fast drying, thus producing bubble and flow marks. At the same time, the higher temperature of the area to radiate the bottom, so that F4 liquid surface crust, the impregnated fiberglass cloth will remain on the surface of the F4 pimple, serious damage to the fabric quality.

Medium temperature zone: When the impregnated cloth enters the second section of the middle part of the unit, it is needs to gradually complete the evaporation of water, the temperature is too low will make water evaporation is not complete, impact the effect of the next process of impregnation; Excessive temperature is not conducive to the uniform escape of water, also hindered the next section of the temperature control.

High temperature zone: When entering the upper third section, the residual moisture, the surfactant and the low molecular weight in the resin should be completely volatilized to facilitate the effect of the next impregnation process. If the temperature of this area is too high, will cause local F4 sintering, impact the effect of the next process of impregnation; If the temperature is too low, it will make the fabric sticky, the cloth will be stick together when coiling.

Although the impregnation unit is divided to three temperature zones from the bottom to the top, but they are not completely separated, but continuous gradient, there is no significant deviation between the sections. According to the test results, the temperature distribution of the longitudinal section of the impregnation unit is shown in Fig.2.
Fig.2
Fig.2 Temperature distribution diagram

The transmission speed of glass fiber cloth is one of the key factors affecting production efficiency and product quality. If the speed is slow, disperse evenly through the fabric, to avoid the flow marks, reduce product defects, to get good quality cloth. But if the speed is too slow will reduce production efficiency and cost will be increased. If the speed is too fast, easy to produce bubbles, flow marks and other defects, and cause dry time is not enough, dry through, causing the fabric sticky.

b. Sintering temperature and velocity
F4 resin is different from thermosetting resin, it does not have “curing” stage, but must be sintered at high temperatures. Sintering furnace is divided into two layers, The lower layer further removes the low molecular weight of the surfactant and F4 resin, and the upper layer completes the “plasticization” process of the F4 resin, which is characterized by the cloth immediately discolor, white products from pure white to soil white, black products from grey-blue into pitch-black. The upper temperature is too high or too long time in the plasticization temperature, will make the fabric brittle and performance reduction.

The choice of sintering speed must meet the temperature requirements, sintering speed and temperature are two closely related factors, must meet the temperature requirements of the premise to choose the appropriate speed, If not reached the temperature required for plasticization, speed is slow and even pause is not possible to complete the sintering, and once the plasticizing temperature is reached, the sintering is completed in just a few seconds. So the transmission speed does not affect the plasticization. At the same time, impregnated F4 glass cloth thickness uniform, and relatively thin, so heat quickly, it is easy to sintering.

c. The quality requirements of glass fiber base fabric
The requirement of PTFE products on the quality of the base fabric is extremely high, the main factors affecting the quality of the product are the glass mattress material and the technical maturity of the impregnation process. The base fabric can not exist cloth wrinkles, yarn joints, broken yarn, oil and other serious defects, the fabric flatness, density and other quality requirements are higher than the general fabric.

Application research
Glass fiber coated with PTFE products with its excellent performance widely used in aviation, electronics, textiles, food, building materials, medicine, clothing and other fields.

Architectural membrane material
This is the most promising area of PTFE/Teflon coated fiber glass products. Since the glass fiber “silver top” come out in 1975, buildings with various woven fabrics for roofs are emerging in the United States and Western Europe. “Light roof” has become a new type of soft shell structure, the coating has become a new type of roofing materials. This new building with its simple design, easy installation, huge size, shape color changeable to get much attention. It has been widely used in large span buildings since 1980s, such as pontoon roof, inflatable dome, suspension structure hall, sports venues, amusement parks, exhibition centers, music halls and warehouses and other soft shell structure. The most widely used in this type of architectural membrane is PTFE/Teflon coated fiber glass fabric.

This kind of glass fiber is made of B grade superfine glass fiber yarn, its tensile strength is higher than steel, and has a high tear strength and elastic modulus, good dimensional stability, no combustion, and PTFE coating has long-term weather resistance, no adhesion, can be automatically cleaned. The hardness of such materials is about 10 times that of organic polymer textile fibers. The use of this new building film construction of the building has the following advantages:
A. The weight of the roof is very light
B. Good aging resistance
C. Translucent and high energy efficiency
D Safety.

Insulation Materials
The volume of glass fiber is higher than the resistance, it can be used for aviation, electrical and electronic industry in the high-frequency high-temperature conveyor belt; Because of its good air tightness, bursting high strength, can be used as a solenoid valve diaphragm to prevent the leakage of dielectric materials; Tetrafluoroethylene casing can be used as wire and cable; thin cloth can be used for printed circuit boards.

Microwave drying conveyor belt
Because it does not absorb microwave, non-stick, high temperature, good insulation properties, is the ideal material for microwave conveyor belt. The previous food machinery conveyor belt is made of canvas, but the canvas is not high temperature, not easy to clean; and than be changed into chemical fiber, but it is easy to deformation. Using PTFE/Teflon coated fiber glass anti-stick belt instead of canvas and chemical fiber, completely overcome the above disadvantages. PTFE/Teflon coated fiber glass belt is high temperature, no deformation, inert, non-toxic side effects, no-clean, can also be used as the microwave transport belt in medical machinery.

Clothing fusing machine conveyor belt
Previously, people used horse hair cloth and ironing to produce shirts and suits, but temperature uniformity is poor, not high temperature and easy to stick. Now, with the use of anti-adhesive belt, the horse hair cloth has been gradually replaced by resin lining.

Flexible compensator
Flexible compensator is a new species of compensator for the gas transport and other areas, also known as non-metallic compensator, expansion joints, bellows, etc., the market share is expanding. As the PTFE/Teflon coated glass fabric with corrosion resistance, high temperature and high pressure, it can be used as pipeline lining of compensator.

Friction material
PTFE wear, the friction coefficient is small, it can be used for oil-free lubrication.in high temperature environment.

If you need more information about our products, please contact us: system@corefrp.com ,our engineers will answer you and provide free samples.

pdfManufacturing, application and development of PTFE Teflon coated fiber glass fabric.pdf

Effect of Adhesive Teflon Emulsion on Properties of Gas Diffused Electrode Prepared by Ethanol Pretreatment

With manganese dioxide as catalyst, activated carbon as catalyst support, teflon as the binder of gas diffusion electrode is a three-phase reaction groove electrode interface. Mainly used in alkaline metal air batteries, for the reduction of oxygen to provide a reaction site. With the increased demand for high-power power battery, the nature of the gas diffusion electrode was also hit by the unprecedented challenges. Both require the use of gas diffusion electrode low cost, but also requires the electrode has a higher output power. Since the use of manganese dioxide as the oxygen reduction catalyst, the use of Pt, Au and other precious metals as a catalyst when the electrode cost.

In determining the catalyst, the main factor determining the performance of the gas diffusion electrode is the microstructure of the electrode. The ideal gas diffusion electrode structure on the one hand must have good gas permeability to meet the high power of the electrode when the gas reactant supply; On the other hand have a good porous system, and can form enough three-phase interface, improve the gas diffusion electrode chemical energy into electrical energy capacity. By increasing the effective porosity of gas diffusion electrode structure to increase electrochemical reaction sites become one of the method of improving electrode performance. Adding a certain amount of pore-forming agent in the electrode can increase the permeability of the electrode to the reaction gas and reduce the concentration polarization. The formation of the porous system of the gas diffusion electrode is related to the structure of the catalyst support used, Carbon nanotubes as a catalyst carrier can make the gas diffusion electrode to form a unique network structure, greatly reducing the transmission of reactive gas barriers, while increasing the electrode electrochemical reaction activation point. In addition, fiber, activated carbon, nickel fiber mixture, etc. through the sintering to form a unique highly efficient porous structure, and the thickness does not exceed 2/3 of the conventional electrode. This electrode not only has good electronic conductivity, but also has a high efficiency of electrochemical performance.

The structure of the gas diffusion electrode is divided into a gas diffusion layer and a reactive layer (catalyst layer). The gas diffusion layer mainly exercises the reaction gas transmission function, and the reactive layer is mainly the place where the electrochemical reaction is provided. teflon emulsion as adhesive of gas diffusion electrode, On the one hand with the function of adhesive electrode material, on the other hand with the microstructure of the electrode itself is closely linked. In this paper, the pretreatment of teflon is added to the production process of gas diffusion electrode, the influence of the properties of the diffusion electrode on the diffusion electrode and the microstructure characteristic parameters of the gas diffusion electrode were discussed. The effect of the teflon powder on the performance of the gas diffusion electrode was discussed.

The experiment
The manufacture of gas diffusion electrode
Production process of gas diffusion layer. The acetylene black, graphite, activated carbon by 6: 3: 4 mass ratio with 20000 r·min-1 mixer evenly mixed, a certain amount of 30% (w, mass fraction) of teflon emulsion is mixed with the corresponding amount of ethanol (anhydrous ethanol, analytically pure), and than the two mixtures were uniformly blended and applied to the side of the foamed nickel, bake in an oven at 150 ℃ for 30 min.

Production process of catalytic layer. First, acetylene black, graphite, activated carbon, manganese dioxide by 2: 7: 9: 54 mass ratio with the same speed mixer evenly mixed, then a certain amount of 30% teflon latex mixed with appropriate amount of ethanol, and than the two mixtures were uniformly blended and applied to the side of the foamed nickel, bake in an oven at 150 ℃ for 30 min.

The baked electrode is naturally cooled to room temperature, A 0.1 mm thick teflon film was attached to the gas diffusion layer side to prevent the electrolyte leakage. Finally, the electrode is rolled and the thickness is about 0.5 mm.

Gas diffusion electrode performance testing
Gas diffusion electrode effective area is 70 cm2, with zinc electrode assembled into zinc air battery, 7 mol·L-1 KOH solution as the electrolyte, at room temperature and atmospheric pressure in the air discharge performance test. Zinc-air batteries in the first 30 minutes before the start of work, zinc electrode can be considered no change. It is generally believed that the overpotential of the zinc air battery is mainly produced by the cathode, In the experiment with calomel reference electrode measurements that, when the current density in 200, mA at 2 cm – produced by zinc electrode overpotential was only about 0.02 V, compared with the overpotential of gas diffusion electrode is a very small amount, it can be ignored. When increasing battery working current density of overpotential can approximate thought is caused by a gas diffusion electrode. Compared with zinc air battery voltage value under same working current density can determine gas diffusion electrode discharge performance. Each kind of experiment to repeat more than three times at least, to ensure the reliability of the experimental results.

Through automatic microporous physical and chemical adsorption instrument (American Microm – eritics ASAP2020M + C) to a single point of gas diffusion electrode BET specific surface area, Langmuir specific surface area, pore distribution, and total pore volume and area of the test. By scanning electron microscope (SEM, American FEI, Sirion200) observe apparent morphology of electrode.

The pretreatment of ethanol
Teflon film teflon membrane immersed in ethanol solution, and then at 150 ℃ conditions, the ethanol completely volatile, observed throughout the process of teflon membrane morphology changes.

The results and discussion
Discharge performance of gas diffusion electrode
Only the diffusion layer side teflon emulsion is pretreated
From the battery discharge results (as shown in figure 1), only the gas diffusion layer of teflon adhesive emulsion after pretreatment, other things being equal, compared with the adhesive without pretreatment of electrode, the current density is 110 cm, mA – 2, gas diffusion electrode polarization overpotential reduced 23 mV. This indicates that the gas diffusion layer adhesive after ethanol pretreatment can improve the performance of the electrode, but the magnitude is very small.
Fig 1

Only the catalyst layer side teflon emulsion was pretreated
Fig.2 shows the polarization curves of the catalytic layer teflon before and after ethanol pretreatment. As can be seen from Fig. 2, only the catalytic layer of adhesive teflon emulsion after ethanol pretreatment it can also significantly improve the performance of gas diffusion electrode. At relatively low current density (less than 50 mA · cm-2), the adhesive of the catalyst layer was not significantly different from the pretreated one. When the working current density exceeds 100 mA · cm-2, the polarization overpotential of the pretreated gas diffusion electrode of teflon emulsion is obviously lower than that without pretreatment. When the working current density is about 140 mA · cm-2, compared with the conventional electrode, the catalytic layer of teflon emulsion after pretreatment of gas diffusion electrode polarization overpotential was reduced 47 mV. This shows that the relatively high current density at work, the catalytic layer adhesive after ethanol pretreatment can significantly improve the performance of gas diffusion electrode.
Fig 2

Changes of teflon Membrane Before and After Pretreatment with Ethanol
Fig.3 is a photograph of a teflon film in ethanol. As shown in fig.3, the white teflon film is translucent in ethanol and can be completely immersed in ethanol, hydrophobic teflon membranes are hydrophilic in nature. After 150 ° C baking to completely evaporate ethanol, teflon film change into the original white, and was curved (see Figure 4). After treated with ethanol, teflon membrane has a certain degree of contraction.
Fig 3

Fig 4

Discussion
Teflon film in ethanol will be water swelling, and the ethanol is completely evaporated, the teflon film will shrink and resume, but the chemical properties do not change. teflon membrane and teflon emulsion is the same kind of material of two different forms, with the same chemical properties. teflon emulsion as adhesive will swell when mixed with ethanol, and after the powdery electrode material is uniformly blended, the teflon emulsion and the electrode material form micelles. The micelles and micelles are bonded to each other to form a catalytic layer and a gas diffusion layer of the gas diffusion electrode, and then at the condition of 150 ℃ drying, ethanol and water evaporation, teflon shrinkage, to a certain extent, the gas diffusion electrode played a role in making holes. Microscopic observation on electrode proved, adhesive after pretreatment, far more than the pore structure of the gas diffusion electrode without pretreatment of electrode. Comparison of gas diffusion electrode SEM photos (see figure 5 and figure 6) can be concluded that the adhesive without pretreatment of gas diffusion electrode apparent morphology show flat shape, pore and fissure is not obvious. After pretreatment, the surface of the gas diffusion electrode catalytic layer is almost covered with fissures and pores, and particles with different sizes of particles appear.
Fig 5

Fig 6
Figure 7 is BET test results, the straight line is based on p/(Q (p0 – p)) as the ordinate and  (p/p0) as abscissa.  The BET equation can calculate the gas diffusion electrode single saturated adsorption amount, Vm and Vm characterization of specific surface area:
Fig h
Type p as adsorbate in partial pressure; P0 as the adsorbent of saturated vapor pressure; Q as actual amount adsorbed sample; The Vm as single sample saturated adsorption capacity; C as adsorption capacity related to the sample of constant, this type of value is 122.846875.

Fig 7
The calculated results show that the specific surface area of the electrode catalytic layer is 41.6962 m2 · g-1 after pretreatment; The diffusion layer was pretreated followed by 37.6578 m2 g-1; Untreated electrodes, specific surface area is 36.6563 m2 g – 1.. Figure 8 shows the Langmuir test results, with p/Q as the ordinate, p as the abscissa. By the Langmuir isotherm adsorption model equation calculates the Vm (m2 g – 1).
type 2
Fig 8

Value type b is adsorption coefficient, in this value is 3.453 x 10-4 Pa-1. After the pretreatment of the catalytic layer, the specific surface area of the electrode is the largest, which is 63.8552 m2 · g-1; after preprocessing the electrode diffusion layer, specific surface area is 57.4402 m2 g – 1; without pretreatment of electrode, specific surface area is 56.0801 m2 g – 1. This shows that the catalytic layer adhesive after ethanol pretreatment can significantly increase the specific surface of electrode, gas diffusion layer of specific surface area increased after pretreatment is not very obvious. The different diameter and contribution to the electrode surface as shown in figure 9, whether electrode after ethanol pretreatment, the aperture between 1-2 nm porous provided almost no change, specific surface area can be speculated that the number of microporous aperture is mainly related to the production of electrode materials used. The catalytic layer adhesive after alcohol pretreatment, the micropores with pore size between 2.5 and 10.0 nm increase significantly, and the specific surface area of micropores in pore size increases. The gas diffusion layer has no obvious change after pretreatment, performance compared with conventional electrodes in the aperture range of electrode surface have no obvious change. This shows that the binder after ethanol pretreatment, can increase the catalytic pore size between 2.5-10.0 nm between the number of micropores.
Fig 9

The main function of the gas diffusion layer is to adsorb and transfer the reaction gas. At the same time, the electrolyte is transferred from the catalytic layer to the diffusion layer, and a new electrochemical reaction site can be formed in the diffusion layer. Increasing the specific surface area of gas diffusion layer , on the one hand, reduce the reaction of gas transmission, on the other hand also can form more new reaction activation points, improving electrode performance. But the gas diffusion layer is thin, the thickness is about 1/10 the thickness of electrode, the electrode overall contribution to the surface is not big. So the gas diffusion layer adhesive after pretreatment, the specific surface area increases is not very obvious, showing a slight improvement in electrode discharge performance (see Fig.1).

The main function of the gas diffusion electrode catalytic layer is to provide a reaction site for electrochemical reactions (also known as reaction activation points). Generally, the number of effective reaction sites is used to define the ability of the gas diffusion electrode to convert chemical energy into electrical energy. The more effective reaction sites, the greater the total gas diffusion electrode current contributes. So in the same condition of discharge voltage, effective place more gas diffusion electrode output current. The purpose of the catalytic layer of porous gas diffusion electrode is for more effective reaction activation point. teflon adhesive emulsion after pretreatment, catalyst layers obviously increase the specific surface area and porosity, effective reaction sites will also be increased accordingly. So under the condition of high current density, polarization overpotential is lower than conventional gas diffusion electrode in the same conditions (see Fig. 2).

The best content of ethanol
As ethanol is first mixed with teflon emulsio, there should be an optimum ratio between the amount of teflon emulsion and the amount of ethanol added. Figure 10 is ethanol electrode discharge performance of teflon emulsion with different ratio. It can be seen from figure 10, teflon emulsion with ethanol ratio of 4:1, the quality of the work in the same current density of gas diffusion electrode polarization potential minimum. The reason is the amount of ethanol added is too low, teflon expansion is not sufficient, the gas diffusion electrode pore formation did not achieve the best condition; Ethanol added too much, may lead to the initial bonding between the electrode powder material is not borne by the teflon, but by the ethanol, after high temperature drying, the original particles temporarily bonded by ethanol will relax, or even fall off, to the opposite effect.
Fig 10

Conclusion
Teflon in ethanol can be water swelling, until the ethanol and water completely evaporate teflon will shrink. The teflon emulsion is pretreated when the gas diffusion electrode is made to increase the electrode pore structure and specific surface area. The catalytic layer after pretreatment, specific surface area and pore structure increase more obviously, the catalytic layer increased pore structure can increase the gas diffusion electrode electrochemical reaction effectively. When under the condition of high current density, electrode polarization potential is relatively small; the gas diffusion electrode performance improvement is relatively significant. The increase of the specific surface area and pore structure of the electrode after the pretreatment of the gas diffusion layer is not obvious, and the improvement of the electrode performance is also limited. When the ratio of the mass of the teflon emulsion to the ethanol is 4: 1, the electrode performance is the best.

If you need more information about our products, please contact us: system@corefrp.com ,our engineers will answer you and provide free samples.

pdfEffect of Adhesive Teflon Emulsion on Properties of Gas Diffused Electrode Prepared by Ethanol Pretreatment.pdf

Study on Modified Polytetrafluoroethylene Composites Filled with Inorganic Nanoparticles

Polytetrafluoroethylene (PTFE) has excellent antifriction and self lubrication, but dimension stability is poor, the poor wear resistance, usually adopts the micron grade graphite, molybdenum disulfide, copper powder, glass fiber and other inorganic particles are filled and modify PTFE. Micron structured particle filling modification of PTFE, however, there are still some limitations, such as the contradiction between products softness, toughness and wear resistance, the improvement of the performance of the products processing is also limited.

Nanometer material is the excellent performance new material and developed quickly in recent years, it has the good physical and chemical properties which many micron-grade materials do not have, such as high particle strength, high specific surface area and high surface energy, etc., composite with plastic, will produce very strong interface function and good modification effect. This paper studies modification effect of inorganic nanometer particle on PTFE, focuses on the nanometer SiO2 and Al2O3 effect on the improvement of PTFE wear-resistance, results obtained excellent comprehensive properties of modified PTFE composites, the material is very suitable for the preparation of automobile engine crankshaft oil seal and other seals.

The experiment part
Raw materials
PTFE: JF – 4TM suspended powder, particle size of 10 ~ 50 microns. Nanometer SiO2, Al2O3:30 ~ 40 nm particle size, specific surface area is equal or greater than 20 g/m2.

Modified PTFE material production process:
1

Main instrument
Universal testing machine: UH – I, Friction and wear testing machine: the MM – 200, Shaw hardness tester model: LX – D.

The performance test
The tensile strength and elongation at break: according to HG/T 2902-1997 to test; Abrasion and friction coefficient, according to GB/T 3960-1983 to test; Shaw hardness: according to GB/T 2411-2411 to test.

Results and discussion
The selection of dispersion mode of Inorganic Nanoparticles
The most important problem of nano-materials modified polymer is the nano-materials evenly dispersed in the polymer. For ordinary polymer, dispersion method includes solution blending method, melt blending method, melt intercalation method, etc. But PTFE almost has no solvent, the melt viscosity in the molten state is also high, the above dispersion method can not be used. Therefore, in this paper, the use of mechanical mixing, ultrasonic mixing and other decentralized way. The experimental results are shown in table 1. Table 1 shows that scattered in various ways, mechanical mixing and airflow crushing combination is the best way to disperse. In mechanical and ultrasonic mix combination way of dispersion, the modification effect is changed with the change of ultrasonic intensity, when the intensity of ultrasonic is 300 mA, the modification effect is better.
Table 1
Table 1 inorganic nanoparticles dispersion effect on the properties of modified PTFE material

Dispersing the inorganic nanopowders dispersed by mechanical mixing and airflow comminution of the modified PTFE composites, the state of the blended structure was measured by atomic force microscopy (AFM), the results are shown in figure 1. Figure 1 shows that inorganic nanoparticles is basically in the form of a single nanoparticles dispersion in the modified PTFE material, It is described that the dispersion effect of the dispersion method using the mechanical mixing and the airflow pulverization combination is good; and the dispersion method has the advantages of simple operation and stability and very conducive to industrial production.
Figure 1
Figure 1 Atomic Force Microscopic Morphology of Nano – particle Modified PTFE Composites

Effect of airflow crushing process on properties of PTFE modified by Inorganic Nanoparticles
The specific conditions were experimented on the dispersion process of mechanical mixing and airflow comminution, the results are shown in Table 2 and figure 2. Table 2 results show that when the air is pulverized, the choice of feed pressure 0.50 MPa, air crushing pressure of 0.75 MPa process conditions, which is advantageous for improving the performance of the modified PTFE material. If the feed pressure, airflow crushing pressure is too low, the mixing is not sufficient; If the feed pressure, air flow crushing pressure is too high, then PTFE will have a certain degradation, will result in modified products, tensile strength and hardness decreased too fast. Figure 2 shows that the wear amount of the modified PTFE material decreases with the increase of the number of times of air flow crushing, this is because with the increase of the number of airflow pulverization, nanoparticles with PTFE mixed more evenly, the effect of the nanoparticles modified is better, reflected in the wear of PTFE composite materials to further reduce.

Table 2 Effect of Airflow Crushing Pressure on Properties of Modified PTFE Material
tab 2

Figure 2
Figure 2 Effect of the number of times of airflow crushing on wear performance of PTFE composites

Effect of Inorganic Nanoparticles on Mechanical Properties of Modified PTFE Materials
Figure 3
Figure 3 Effect of Nanometer Particle Type and Dosage on Mechanical Properties of PTFE Composites

The effect of the kind and amount of inorganic nanoparticles on the properties of modified PTFE is shown in Figure 3. As can be seen from a and b of Fig. 3, the addition of nano-SiO2 reduces the mechanical properties of PTFE, The addition of nano-Al2O3 increases the tensile strength and elongation at break of PTFE in a certain range, but with the further increase in the amount of PTFE material, the mechanical properties of PTFE materials decreased, and the decrease is smaller than that of the nano-SiO2. Therefore, filling the modified PTFE with 0 ~ 3% nano-Al2O3 is beneficial to improve the mechanical properties of PTFE composites. It can be seen from Figure 3c, Adding nano-SiO2 and nano-Al2O3 into PTFE, have significantly improved the wear resistance of PTFE materials, especially a small amount (3%) of nano-SiO2 modification, the PTFE material on the wear resistance has greatly improved, further increase the amount, the improvement in abrasion resistance is not significant. When the amount of nano-Al2O3 is more than 7%, the same effect can be achieved by nano-SiO2 modification.

Single nano-particles filling modification of PTFE material has certain limitation, it can only improve the performance of PTFE material in one aspect. In order to get excellent properties of modified PTFE material, nanometer Al2O3 and nano – SiO2 composite filling modification of PTFE experiment, the experimental results are shown in table 3. Experimental results showed that nano Al2O3 tensile strength, elongation at break of PTFE material, nano – SiO2 significantly improve the abrasion resistance of PTFE material, two aspects to improve effectively together, add 2% SiO2 and 3% nano Al2O3, the modified PTFE composite having excellent tensile properties of tensile strength of 27.4 MPa, elongation at break of 306.7%, Shao D hardness of 60.0, abrasion of 0.001 g and coefficient of friction of 0.20.

Table 3 Effect of Nano – particle Composite Filling on Properties of PTFE
Table 3

Application test
After the nano-particles modified PTFE composite materials made of automotive oil seal, the bench durability tests have been carried out. Test condition: test oil 15w / 40; Test oil temperature (120 + 3) ℃; Shaft beating 0.38 mm; Sitting holes eccentric 0.38 mm; Shaft speed 3400 r/min; Test period 120 ℃ x 20 h x 3 400 r/min + x 4 h * 0 r/min at room temperature. The test results show that There was no leaking oil in any form in 240 hours, far more than 150 hours of time required by CES10599; After the test by the demolition, the oil seal on the axis almost no wear. In the ordinary PTFE oil seal test, found that the shaft has obvious wear; From test after two main oil seal lip piece of wear, wear resistance of PTFE is better than the ordinary contrast samples. Therefore, with the experimental nano-particles modified PTFE composite made of oil seal, can better meet the needs of the automotive industry.

Conclusions
A. The inorganic nanoparticles can be uniformly dispersed in PTFE by a combination of mechanical mixing and airflow comminution.
B. The tensile strength and elongation at break of modified PTFE were improved by the addition of 0 ~ 3% nano -Al2O3; When the dosage is increased, the mechanical properties of the modified PTFE are decreased, but the rate of decrease is slower.
C. 3% of the amount of nano-SiO2 significantly improved the wear resistance of modified PTFE materials.
D. Nano-Al2O3 and nano-SiO2 composite modified PTFE, obtained a comprehensive performance of PTFE wear-resistant materials; the tensile strength of 27.4 MPa, the elongation at break 306.7%, shao (D) 60.0 hardness, abrasion quantity 0.001 g, 0.20 friction coefficient, the modified material is very suitable for the preparation of automobile engine shaft oil seal.

If you need more information about our products, please contact us: system@corefrp.com ,our engineers will answer you and provide free samples.

pdfStudy on Modified Polytetrafluoroethylene Composites Filled with Inorganic Nanoparticles.pdf

The application of PTFE fiber

Filtering material

PTFE fiber has an important role in high temperature flue gas filtration. With PTFE fiber or PTFE fibers mixed with other high-temperature resistant fibers, can be made from high-temperature composite filter carpet, this filter has good corrosion resistance, heat resistance, friction-resistant properties, suitable for high temperature, high humidity, high viscous powder with acid or alkali, corrosive chemicals industrial fume purification, is unmatched by other filtering materials.

Medical materials
In recent years, PTFE fibers are widely used in medicine, such as can be used in artificial blood vessels, heart valves and artificial heart assist device, artificial ligaments and esophagus. In addition, PTFE fibers can also be used in general surgery and plastic surgery, surgical suture, such as the more common cosmetic surgery rhinoplasty and plastic jaw PTFE is used as fill material.

Textile industry
PTFE fibers used in the manufacture of high-performance sewing thread, heat resistance and chemical resistance and high performance requirements of other textile products, as well as bruising spelled resistance of medical textiles and wearing apparel. For example, with PTFE fibers rub sports socks in cycling and other sports, can prevent athlete’s foot, blisters.

Other applications
PTFE fibers also have a wide range of applications in other areas, such as can be used for bearings with low friction rate components, ion-exchange, packing, etc. In addition, due to their inherent low-loss dielectric constant, PTFE fibers can also be used to prepare the insulation of wires and cables, and so on.

PTFE due to its excellent performance in the fields of petrochemical and other widely used, its main carrier spinning, spinning o f cutting split method, paste extrusion spinning, melt spinning, and so on. Large manufacturers in the world such as the United States, DuPont Corporation, United Kingdom the ICI company, Japan Daikin company and Germany’s Hoechst company has mastered the technology of PTFE fibers.

pdfThe research progress of PTFE fiber preparation technology.pdf

Preparation technology of PTFE fiber

Carrier spinning method
Wet spinning
Wet spinning of PTFE usually in viscose or polyvinyl alcohol (PVA) as the carrier, mix with PTFE powder or emulsion dispersion, and add a small amount of boric acid, make spinning solution , perform wet spinning, spinning head placed in sodium sulfate and ammonium sulfate coagulation bath, dope from the nozzle in the coagulation bath solidified into fiber, fiber after leaching roller soft water leaching, again after oil roller and drying roller respectively, in 380 ~ 400 ℃ high temperature sintering, remove PVA carrier carbide, stretch to make PTFE fiber under 350 ℃. This method of spinning spend process cumbersome, high processing cost and energy consumption and time-consuming. Guo Yu-hai and others invented a highly efficient rapid method of preparation of PTFE fiber. This method will first evenly mix low relative molecular mass of volatile organic solvent with water, in under the condition of stir with PVA, continue to stir until completely dissolved, mixture of PVA water solution. Then the PVA water solution and persulfate, PTFE dispersion mixing uniformity, dope. Then borate or boric acid dissolved in water, with alkaline pH adjustment as alkaline, mixture coagulation bath. Finally adopt the wet spinning equipment of conventional , the spinning fluid conveying to the nozzle, through metering pump metering, direct spinning in the coagulation bath, then drying, sintering and stretch, the PTFE fiber is made.

Dry spinning

This method is PTFE gel realized by dry spinning. PTFE is first concentrated dispersion and PVA blended, add gel regulator boric acid or Borate salts and alkalis adjust the pH to alkaline, whisking to a sudden increase in the viscosity and gel formation, are spinning solution. And then dry them using conventional spinning equipment, gas pressure or screw spinning liquid to the spinning head, measured in metering pumps, dry spinning, and then dried, prepared mixture of PTFE and PVA fiber. Finally using conventional sintering and stretching equipment, will be mixed sintering to remove PVA fiber, finally after stretching process stretching, PTFE fiber preparation.

Carrier spinning method is the most mature method of preparing PTFE fiber, and has been one of the few companies to realize industrialization. Among them, Japan toray company USES mass fraction 60%, the average particle size was 0. 3 microns of PTFE, and the mass fraction of 2% sodium alginic acid aqueous solution of the emulsoid mixed spinning, the fiber by coagulation, bath again after washing, drying, and under 380 ℃ hot stretching, removal of alginic acid sodium, gain PTFE fiber, its monofilament linear density of 0. 67 dtex and fracture strength of l. 25 cN/dtex, elongation at break of up to 59%, the method of spinning dope spinnability better than with viscose as carrier of PTFE dope spinnability. Showa industries, the use of the 114 mass fraction of 60% PT – 100 FE dispersed emulsion and cellulose of mass fraction of 8.9% viscose spinning solution spinning, after solidification of the nascent fibers by water, squeeze liquid, with 0. 05 mol/L Na0H processing, and the fiber heat treatment under 280 ℃ and hot stretching under 320 ℃, the final heat treatment 72 h under 320 ℃, the fiber’s breaking strength for 1. 16 cN/dtex elongation at break was 16.1%. In addition, Beijing demonstration plant will be 60% mass fraction of PTFE emulsion and 10% mass fraction of PVA solution in proportion of 1:1.5 the spinning solution spinning, after solidification of the fiber by acetal, washing, drying, sintering and stretch to PTFE fiber system.

Cutting film splitting method
Cutting film crack method in the early 1970 s by the Austrian Lenzing company development and industrialization, in the preparation of PTFE fiber, need to make PTFE powder sinter cylindrical PTFE parison, cutting it up with a certain thickness of the film, and then by serrated tool divided into silk, above the melting point (327 ℃) sintering, then through stretching and end up with PTFE fiber heat treatment. This method can get the fiber with microporous structure, and high strength. Multifilament can be used as the sealing filler material, short fibers, can be used in the needle felt.

In addition, the PTFE film or sheet can also be cut into tiny width, and then direct tensile narrow fabric made of high strength PTFE fibers. But it is difficult to maintain uniform obtained by cutting along the longitudinal direction through the narrow width of the fabric, and narrow fabric tends to end part of fibril, so much stretch in narrow fabric PTFE fibers easily broken or through partial cutting in the longitudinal direction of the film are filament PTFE membrane orientation. Along the membranes of the longitudinal direction and in the transverse direction of the film with a z shape or linear-convex shape embossed and cut, the resulting filament including individual fibrils partially broken rule the network structure. PTFE fibers produced this way the individual fibrils with small average size and uniform size.

Japan Asahi of into Corporation through cutting film crack legal into has high stretch strength, and resistance chemical performance excellent of PTFE yarn. will containing hole rate 48% of PTFE film tear into 222 dtex of fiber, again on its added twist to 750 twist/m, in 440 ℃ and 1 000 m/min Xia stretch, get of fiber line density for 55 dtex, and containing hole rate 1%, modulus up to 294 cN/dtex.

Paste extrusion spinning method
Paste extrusion spinning usually PTFE powder 16% ~ 25% with mass fraction of volatile lubricants mixes, tune into a paste, made of shaped prefabricated embryos, and under certain pressure through a spinneret with a strip of die extrusion spinning, and then by drying, sintering, high stretch under high temperature, non-uniform white yarn. In addition, can also squeeze film extrusion equipment or thin strips, then by a rolling process to remove additives, and longitudinal cutting, drawing and fluffy after processing, are PTFE fibers were made by paste extrusion of thin wall, small diameter and permeability of PTFE hollow fiber. PTFE powder in conditions below its melting point made of PTFE hollow fiber, and then fired 10 min at 350 ℃, 250 ℃ under 400%, was 0.76 mm inner diameter and wall thickness of 0.10 mm, diameter of less than 0.15 mm hollow fibers.

In 1997, M. Shimizu proposes a method for preparing high strength and PTFE fibers by paste extrusion. Added to the PTFE powder mass fraction 20% of lubricants, embryo, extrusion, gained single wire, heated treatment and then 350 ℃ 1.5h, and 387 ℃ to 50 mm/min of speed stretching 10 times, received strength as much as 1.56 ~ 2.82 GPa PTFE fibers.

The PTFE powder was mixed with a lubricant (isoparaffin oil Isopar-E) to form a paste, standing at 0 ℃ 180 h at 40 ℃ cure 30 h, make the mix full wetting and swelling, then press embryo and extrusion , handle 2 h under 340 ℃, and then to 0. 5 c/min speed down to room temperature, finally stretching to get in a 370 c PTFE fiber, 3.5 ~ 4.0 cN/dtex the fracture strength, elongation at break is 22%.

Melt spinning method

Melt spinning is PTFE content to 4% ~5% of perfluorinated ethylene copolymer of perfluoro-n-propyl ether mixed spinning melt, after spinning by screw extrusion machines pump quantitative pressure injection hole, making it into a fine stream into the air, and cooling in the spinning channel into the wire. PTFE fibers high strength of this method, but PTFE supermolecular structure changes after melting, leading to its ductility disappeared and molecular chain orientation stretch is blocked, together with PTFE high viscosity and apparent flexibility, PTFE melt fiber prepared by screw extruder for direct comparison difficult, difficult to achieve industrialization. Plunger extrusion method can overcome this difficulty. The plunger in the extrusion process, due to extremely low surface energy of PTFE and wall-slip phenomenon, reduce unnecessary shear in the flow process, so they can be on PTFE melt spinning. Li Min and other person in Donghua university, are prepared by the PTFE fibre with high molecular weight. Tervoort by high relative molecular mass such as PTFE and PTFE mixed with low relative molecular mass, melt processing, preparing PTFE filament. Properties of PTFE fibers produced this way worse than that of pure PTFE fiber with high molecular weight.

Comparison of advantages and disadvantages of these different spinning methods are shown in table 1.
Table 1 Advantages and disadvantages of PTFE spinning method
Table 1

pdfThe research progress of PTFE fiber preparation technology.pdf

Structure and performance of PTFE fiber

PTFE is linear polymer fluoride, it is a kind of highly symmetric nonpolar polymer compound, its structure is linear macromolecule structure, spiral and molecular chain conformation. According to the apparent color different, PTFE fiber can be divided into the brown and white fiber two kinds. Brown PTFE fiber carrier usually in spinning, the fabric is very soft, and low friction factor, widely used in machinery industry, oil free, dynamic and static anti-wear areas. White PTFE fiber is generally by membrane crack cutting method, the fiber filter material can improve filtering section, so as to improve the accuracy of filtering.

The performance of PTFE fiber

Chemical resistance
The key of “C – F” in PTFE molecules has a very high bonding energy, molecular chain appear conformation which is spiral, nonpolar and crystal structure, This makes the PTFE has very excellent chemical resistance. In addition to the strong element fluoride and fluoride medium (such as trifluoride chloride), molten alkali metals and 300 ℃ of sodium hydroxide, corrosion of PTFE almost without any chemical reagent, all of the strong acid, strong alkali, strong oxidizing agents, salt for PTFE are no effect, even in aqua regia boil, its quality and performance are also don’t have any change. For organic compounds, in addition to aromatic hydrocarbons and halide amine on the slight swelling, other organic solvent has no effect on PTFE, so is known as “plastics king”.

Thermal properties

PTFE has very excellent high and low temperature resistance, can be used in – 190 ~ 260 ℃ temperature for long time. It can not only bear the instant high temperature of up to 290 ℃, but is not brittle below -260 ℃, still can keep a deflection. So in some poor conditions, PTFE products are often used.

Mechanical properties

Because PTFE is nonpolar molecular chain, the mutual attraction between macromolecules is very small; Combined with the molecular chain is not branched chain of high rigidity, entanglement is very small, leading to poor mechanical properties of PTFE. Under long-term load, PTFE will have large creep, prone to cold flow phenomenon. But its fatigue resistance is excellent, general won’t appear permanent fatigue damage.

In addition to the above excellent performance, PTFE also has a good flame retardant performance, excellent lubricity, water repellency and electrical insulating properties, resist ultraviolet ageing resistance, etc.

pdfThe research progress of PTFE fiber preparation technology.pdf

PTFE material in the application of high temperature resistant filter material

The development situation of filter material with PTFE material
PTFE material was put into commercial production in the 1940 s, named “Teflon”. Its products are diverse, used for high temperature filter material of PTFE fiber and microporous membrane, liquid impregnation. PTFE has three varieties of supply market, that is, concentrated dispersion, dispersion resins and resin suspension method, the enrichment dispersion is mainly used for impregnation and spinning fiber by emulsion method.

PTFE fiber
PTFE fiber developed by DuPont as early as 1953, in 1957, it realize industrial production. Silk method is emulsion spinning method, membrane crack spinning method, paste extrusion spinning, and melt spinning method. Emulsion spinning method makes the fiber denier lesser, but the strength is low and with a brown or black; the spinning method of Membrane crack get white fiber, strength slightly higher, the uneven thickness of defect is fibers; Paste extrusion spinning method, the fiber strength is higher, the larger the size; Melt spinning method, the fiber high strength, rarely used. PTFE fiber in the world major producers include the United States DuPont, Gore companies in the United States, Austrian Lenzing company, Japan Daikin and Toray company, such as commodity market with TEFLON, PROFILEN, TOYOFLON and RAS TEX, etc.

PTFE microporous membrane
Bulk PTFE microporous membranes by the Gore company developed in the late 1970 s, the thickness of 10 ~ 25 microns, the aperture size is adjustable according to the craft.

PTFE impregnated liquid
PTFE impregnated liquid is concentrated by PTFE dispersion according to certain proportion configuration and its dispersion particle average particle diameter 0. 18 ~ 0. 30 microns and is mainly used for filter material after finishing, ash removal performance of the filter, filter efficiency and mechanical properties.

The application of PTFE in the high temperature filter material
Filter material by filtering type can be divided into deep filter material (conventional needled felt, compound needled felt), surface filter material, such as gradient compound needled felt), surface filter material (microporous membrane, tectorial membrane filter material).PTFE material with fiber and microporous membrane filter material, a variety of forms such as impregnation liquid used in all kinds of base cloth, spread nets, laminating and finishing.

The application of the PTFE fiber in high temperature filter material
2 .1.1 PTFE fiber properties and advantages of currently used for high temperature filtration fiber are mainly of glass fiber, Nomex fiber, P84 fiber and PPS fiber, PTFE fiber. PTFE fiber and other fiber performance and price comparison as shown in table 1.
table-1
Table 1 Performance and price comparison of PTFE fiber and other fibers

High-performance fibers of E glass fiber, Nomex fiber, P84 fiber, PPS fiber etc. due to their own characteristics, which have been affected to serviceable range. Among them, E glass fiber is fragile, poor wear resistance and folding and friction are prone to electrostatic hitches in weaving, cause fiber splitting, napping, and even rupture, processing difficult. Glass fiber alkali resistance, generally not H F resistance; Nomex is hydrolyzed fiber; its oxidation resistance is poor, when high temperature smoke contains water and oxide, hydrolysis and damaged soon. It cannot be used for temperature over 190 ℃, containing water and oxide of high temperature flue gas filtration; PPS has general oxidation resistance , the higher oxygen content, using the lower the temperature, when the oxygen content of 12%, can only use under 140 ℃; P84 fiber hydrolytic stability, easy to hydrolyze aging; And PTFE fiber resistance to chemical corrosion, high temperature resistant, can be used in all kinds of bad environment and can obtain good effect, the service life of the other fiber filter bag is 1 year commonly, PTFE and the service life of the filtering material up to 3 years.

The application of PTFE fiber in high temperature resistant needled felt
Mónica Lupión and others studies the filter and cleaning properties about 100% PTFE filter under 235℃ that its thickness is 1. 4mm, poriness is 78%, vertical and horizontal elongation were 15% and 30%, and found that 100% PTFE has good filtration, to run stable at higher wind speeds. In the particle concentration 14g/Nm 3, size 0.43 ~ 47.39 μ m, cleaning pressure 14 ± 0.1×105 Pa condition, dust filtration efficiency of greater than 99.98, filtered particle concentration is less than 3mg/Nm3. PTFE filter is stable when pressure drop at wind speeds of 1.6cm/s, it is unstable when1. 9cm/s; 3M FB700 (glass fiber filter) pressure drop at wind speeds of 1.0CM/s steadily, 1.2cm/s is unstable.

Pure PTFE needled filter felt with good corrosion resistance, high temperature resistant, low friction, insulating combustion and insulating stays hard, can withstand all kinds of strong oxide oxidation corrosion, has a good filtering and ash removal performance, it is a deal filter material under the condition of high temperature, strong corrosion resistance, such as steel, electric power, municipal waste incineration flue gas. Pure PTFE filter material is expensive, however, compared with other high performance fiber filter material amount less.

DuPont developed Tefaire filter felt is PTFE fiber and super fine glass fiber blend of acupuncture of composite filter materials, of which 100% PTFE filament fabric as skeleton material, the whole Tefaire mat, PTFE occupy its 85%, the rest of super fine glass fiber. PTFE fiber is the main base material of Tefaire, so the filter material is the characteristics of PTFE filter material. From figure 1 you can see most of fine dust adsorption on the PTFE fiber. After joining the superfine glass fiber, the effective area is multiplied, and reduces the porosity of mat, thus improve the filtering efficiency. Cleaning Tefaire is better than 100% PTFE needled felt in 0. 375 microns particle filter, the efficiency increase nearly forty percent, it up to 88%.Tefaire is also better than 100% PTFE needled felt in air permeability, so under the same filtration velocity filtering resistance is much smaller. Because PTFE fiber has good lubricity, thereby reducing the mechanical damage of the glass fiber in the processing. But its alkali resistance is poor; this glass filter strength is almost zero after alkali treatment .Due to the glass fiber folding performance is poor, so Tefaire filter felt relatively pure glass fiber filter material has a better performance of folding. Tefaire filter felt under 250 ℃, harsh chemical environment for more than 4 years of continuous service life.
figure-1
Figure 1 electron microscopy of Tefaire filter felt after dust filtering

The HBT developed by one technology development center, used has surface superfine fiber layer, and by layer gradually used more CF of gradient structure; filter layer main used PTFE and PPS composite fiber, bottom used PTFE and amount glass fiber, fabric used PTFE and glass fiber mixed, on made of acupuncture filter material for overall impregnated processing, to its surface stick attached PTFE film, on non-PTFE fiber anti-corrosion resistance temperature water repellent has major meaning. Filter structure before the formation of narrow width, slowing filtration resistance in the late problem caused by long-term use. Microfiber surface for the formation of learned the advantage of surface filtration, filter media has better durability. Yan Changyong tested the HBT performance, filter the wind of 1.0~3mm/min. Under 0mm/min of PM1.0, PM2.5 and PM10 filtration efficiency at 88.3%~91.5%, 91.0%~ 93.4% and 92.4%~ 94.4%, 2 micron above the basic particle filtration efficiency is 100%. H BT filtration efficiency and Tefaire, under the same rate of filtration, filtration resistance is much lower. When the filtration speed is 3M/s, Tefaire resistance is about 1150Pa and HBT is only 33Pa.

Application of PTFE microporous membrane in high temperature filter media
PTFE microporous membrane can be alone used for high temperature flue gas filtration, it can also be used with other filter material composite coated filter material. PTFE microporous membrane has high efficiency for micro particle filter, high initial resistance, with the increase of soot cleaning frequency, filtration resistance is less than the other filter materials; Due to surface friction coefficient is small and stable chemical performance, not with dust, dust stripping ratio is high, the soot cleaning performance is good.

Through the study of PTFE microporous membrane, it was found that the filtration efficiency of small particles over 99.99%. Using the expansion of PTFE membrane with different structure parameters, choose different nature of the gas (H2, H e, N2, O2, CO2, water vapor) and study its through behavior. Found that the gas in the form of Knudsen diffusion and viscous flow through the membrane pores, and it is inverse proportion that through coefficient and gas molecular weight of 0. 5 times, and is inversely proportional to the film thickness, single span through coefficient and the hole radius into 3.6 to the power relationship. The greater the average pore size and pore size distribution is wider, gas permeability is better. As the gas diffuses through the membrane with molecular diffusion and Poiseuille flow, the elevated temperature contributes to gas permeation.

PTFE microporous membrane filtration efficiency is high, but the poor for mechanical properties, when filtration resistance is large, it easy to disable the rupture membrane. PTFE coated filter material is filter material which PTFE microporous membrane and deep filter material or surface of filter material composite, mechanical performance is very good to strengthen, able to withstand the high filtration resistance, using a wider range. It’s main by PTFE microporous membrane filter, particle entrapment in the thin film surface, rarely particles into the filter material inside. Compared with other filter material, the comprehensive performance of PTFE coated filter material is best, but the effect of filter material cost is higher, about ordinary filter material 2 ~ 6 times.

The deep filter media and its coated filter media were compared, found that the effect of filter material dust removal efficiency is high, the soot cleaning thoroughly, steady pressure loss and keep the low level, small abrasion of filter bag, dust the applicable range, long life, especially for PM 1. 0 of ultrafine particles of dust filter, coated filter material shows a greater advantage. We can see from figure 2 PTFE coated filter material with normal nonwoven filter material of filtering efficiency along with the change of particle size. Effect of filter material clean and dust resistance condition of filtration resistance is higher than H BT filter material is about 30%, to 10 PM, PM2. 5, 1 PM. 0 filtering efficiency is about 10% higher than our HBT filter material. In the process of studying the filtration resistance of the expanded PTFE microporous membrane composite filter media, it was found that the main factors influencing the filtration resistance at the initial stage of filtration are the thickness of the dust layer. After certain filtering time, the change of porosity on the influence of the resistance increase gradually increased, and finally become the dominant factor of increased resistance. The study on the formation of filter cake on the surface of expanded PTFE membrane filter shows that the concentration of dust-laden gas mainly affects the thickness of filter cake per unit time and does not affect the porosity of filter cake. Particle diameter size and its distribution on porosity of filter cake has a great influence, the smaller the particle size, particle size distribution, the greater the porosity of filter cake formed by the smaller; Impact force of the filter cake filtration direction, from the bottom up filter, fluid drag force to offset the gravity of the filter cake, formed by the filter cake porosity is small; By the filter down, the gravity of the fluid drag force and the particle exerts same direction on the filter cake, cake prone to compression movement, and has lower porosity. From experiment results, the dust removal rate of glass fiber membrane filter is 93.88%, while that of uncoated filter media is only 74.42%.
figure-2
Figure 2 Comparison of Filtration Efficiency between Membrane Filter and Conventional Media

Application of PTFE impregnating liquid in high temperature filter media
In order to improve the use of filter material performance, composite filter material in spine needle composite surface is bright and clean after processing. Due to the high temperature resistant fiber heat melt glue not easily, generally using PTFE impregnated method, can add graphite by PTFE impregnated liquid or silicone oil emulsion to improve the antistatic performance of filter material and condensation resistance. First, at the time of filter material of PTFE surface impregnating solution, drying and hot rolling make the solution to a film, the main process parameters are shown in table 2.
table-2
Filter material after treatment, fiber surface and fiber form discontinuous membrane, make among fibers, between fiber and fabric can’t relative sliding under certain stress range, increase the density of the structure of the fibers, not only improve the peel resistance, folding strength and wear-resisting performance, but also improve the performance of the filter, filtration precision, ash removal and chemical resistance. In concentration, temperature of 85 ℃ and 10% NaOH solution for 1 h under the condition that the 15% PTFE emulsion PSA/PTFE fiber impregnated, its strength retention never deal with 40% to 91. 4%.

By comparing the performance of PPS surface coated filter media and permeable membrane filter media, analyzes the advantage of PPS osmosis coated relative PPS filter material coated on the surface of filter material. Resistance of PPS coated on the surface filter material filtration is big; filtration wind speed cannot too much, commonly under 0. 8 m/min, at the same time there also exist problems such as ash which is not easily precoat, because ontology rising costs, energy consumption is large, this filter film is easy to fall off and hole, congestion at the same time, the filter material cannot use; PPS saturation effect of filter material using PTFE emulsion infiltration for filter material as a whole, the fiber surface coated PTFE membrane, can well protect the fiber, the filter material, acid-proof alkaline, hydrolysis resistance and wear resistance are better and more suitable acid and alkali in adverse environments. After processing the penetration effect of filter material type ventilation quantity still can reach 166. 7 ~ 200 mm/s, it is lower 30% resistance than coated on the surface of filter material early.

Using several high temperature resistant polyester mixtures combing with different proportion and glass fiber net, the two-layer fiber mesh and glass fiber cloth needle into the material, and then use PTFE additives made after the use of a variety of characteristics of a series of filtration products. Conditioning soaking by PTFE impregnated liquid processed fiberglass base cloth draping on PTFE microporous membrane filter material, focus on many advantages of the glass fiber, such as high strength low stretch, high temperature resistance, corrosion resistance and PTFE microporous membrane surface more smooth, hydrophobic, breathable, chemical stability is good wait for a characteristic, reduce the possibility of owing to fiberglass sharp prick membrane. The effect of filter material is almost can intercept all dust, dust in the air and can run without any increase in resistance to guarantee air flux, it has high strength, long use period, large amount of high temperature resistant, breathable and ash removal , etc.

Conclusion and prospect
100% PTFE fiber filter material relative to other fiber filter material has better heat resistance and chemical corrosion resistance, but it is expensive and filtration efficiency advantage; In PTFE fiber adding suitable amount of super fine glass fiber, does not affect its heat resistance performance, and can improve the efficiency of filter material of filtering and to lower the price of filter material. With PTFE impregnation liquid after processing, can improve other fiber filter material performance of resistant to chemical corrosion and ash removal, expanding the scope of the filter material used and prolong service life. In addition, in order to reach the goal of highly efficient, can cover PTFE microporous membrane on surface coated of needled felt to improve its filtration efficiency, makes it not only has good mechanical properties, but also has better filtering performance.At present, the pure PTFE filter material and the mixing PTFE filter material have been praised by users.

If you need more information about our products, please contact us: system@corefrp.com ,our engineers will answer you and provide free samples.

pdfPTFE material in the application of high temperature resistant filter material.pdf

The preparation and modification of Teflon film

Modification of Teflon film

For Teflon film which has been formed, the following methods can be used to change or increasing the some properties of thin films, in order to achieve the experiment or industrial demand.

(1) The PTFE impregnated in some metal hydroxide colloid solution, such as iron hydroxide and hydroxide tin hydroxide colloid, gel ion deposition in PTFE membrane surface, can increase the wetting Angle.

(2) Iron hydroxide colloid adsorbed to the PTFE membrane, and polymerization of acrylic acid (AA) hydrophilic monomers, hydrophilic strong PTFE microporous membrane can be obtained.

(3) With the inert gas such as argon, helium plasma processing PTFE membrane, cohesive force than before treatment increased 10 times. PTFE membrane after plasma treatment, and then AA chemical treatment, AA of strong hydrophilic is grafted to the surface of PTFE, and makes the PTFE film is of good surface infiltration characteristics.

This paper reviews laser pulse deposition, pyrolytic amorphous PTFE precipitation method and impregnated method of coated Teflon film. In addition to these three methods, method of spin coating is commonly used with Teflon film, which obtain the quickest method, it is not the limitation on the sedimentary materials without a substantial, the thickness of thin film gets below the dip coating method. Through the above analysis, in the laser pulse deposition method, using different membrane characteristics of target material to produce slightly different. Powder compacting of PTFE as a target material, the thin film in high resistivity, and high temperature of unpolarized light has high transparency; polished block of PTFE as a target material, the thin film is lower for visible light transparency, in the form of cohesion is very poor. Pyrolysis of PTFE amorphous precipitation, the thin film has many holes, but after condensation formed by light transparent film with amorphous structure, and no hole under high magnification. Method of dip coating can change the deposition of thin film microstructure, operation is easy, high cost performance is higher. These methods have their advantages and disadvantages, in practice, should according to different conditions and demand to choose different coating methods. For example, in the double liquid zoom lens experiments, choose the tantalum pentoxide zoom lens as a double liquid dielectric layer, dielectric layer outside should be coated with a layer of hydrophobic membrane. According to the above advantages and disadvantages of various coating method, considering the base is a special cylindrical, this study thinks that dip coating technique is more suitable for double liquid zoom lens.

pdfThe preparation and modification of Teflon film.pdf

The preparation method of Teflon film

Laser pulse deposition crystallization Teflon coating

Using 248 nm UV excimer lasers radiation, and use powder compacting PTFE and PTFE polished block as target material, under the high deposition temperature, laser via melt crystallization PTFE heat transfer the particles to substrate, forming continuous smooth surfaces. Polished block in PTFE cut out from the PTFE rods. PTFE powder compacting (pressure is 3.8×108N/m2) particles is 6 ~ 9 micron, PTFE powder pressing need under the (275 ±10 )℃ condition of annealing for 24 h.

The film thickness of PTFE deposited by powder pressing is in the same laser pulse condition (p (Ar) = 0.3 mbar, laser energy density of Φ = 4 J/cm2] is far more than the film deposited by polishing PTFE. Thin film deposits at temperature below 340 ℃, it can form many particles and pores of the rough surface. When the deposit more than 340 ℃, will be formed without the surface of the particles, and firmly adhere to the substrate, through the “tape pull off” experiment particles will not fall off. This method of unpolarized light generated film has high transparency, the resistivity is higher than 1012Ω.

Made of polished block in PTFE deposition film surface is very rough, and covers many particles. Under the condition of same deposition rate is much lower than by PTFE powder compacting. Membrane attached to the substrate well, but cohesion is poor, through particles in the “tape pulled off” the experiment will fall off. Film thickness decreases when high temperature deposition. The method of thin film is lower for visible light transparency. The resistivity is lower than the suppression of PTFE powder deposition of thin film.

Pyrolytic amorphous PTFE precipitates to form an amorphous fluoropolymer film
DuPont recently developed Similar to PTFE fluorinated copolymers, including Teflon AF 1600, tetrafluoroethylene polymers, which improve its transparency, strength and adhesion. Dielectric constant is also lower than the ordinary Teflon, achieve minimum of known plastic, under room temperature is 1.9.

Using Teflon AF 1600 respectively and ordinary Teflon (PTFE) as raw materials, pyrolysis precipitation form amorphous containing fluorine polymer film. Teflon AF is transparent, and is not pale yellow related to the unsaturated fluoride. Elliptic partial instrument measuring refractive index is between 1.15 ~ 1.3 results published values consistent with the manufacturer. Ordinary Teflon refractive index from 1.35 to 1.6 the result is consistent with previous. Under scanning electron microscope observation using Teflon as raw materials to precipitate AF 1600 film, found that produces grating hole under high magnification. In this area will produce belongs to the electronic breakdown gas emissions generated in the process of large cracks. These phenomena in the use of ordinary Teflon precipitation as raw materials and also found in the film, but might be a slight degree.

X-ray diffraction scan compared the use of Teflon AF 1600 and common Teflon (PTFE) as raw materials to precipitate the thickness of the film. Contrary to Teflon film, within the scope of the diffraction Angle of 5 ~ 85 ° Teflon AF film did not detect the crystallization. All AF film surface with thickness larger are observed low Angle rings, consistent with the irregular amorphous microstructure.

Pyrolysis Teflon AF 1600 precipitation has many holes on the surface of thin film, reduce sedimentation rate and greatly reduced the depth of the hole, more important is the cross section of the film become smooth and holes on the low magnification plane image is still visible, but will be small and less severe. Moreover, even if the temperature as high as melting point, small hole will not disappear after low temperature annealing treatment. Pyrolysis, by contrast, ordinary Teflon precipitation of thin film is without hole. Under the sufficient heat, Teflon AF raw materials are melted. When cooling, it starts with a white opaque powder material condenses into 1 ~ 3 mm thickness of smooth and transparent material. After thermal cooling light transparent solid, it produces polygonal cracks. They are amorphous when materials into powder and by X-ray scanning. Solidification solutes in the infrared radiation spectrum are similar to raw materials, and no hole under high magnification.

Dip coating method

Dip coating method using the basement from the fluid movement, gravity drainage and evaporation of the solvent, then through further condensation reaction to get solid film .This method compared with other coating technology is simple and saving. The main advantage is that can change the deposition film microstructure.

PTFE super hydrophobic film preparation experiment by using polystyrene (PS) and PTFE2 kind of emulsion mixture, high-temperature roasting to remove PS and other additives, super hydrophobic PTFE membrane was prepared successfully. 40 ml styrene , 160 ml deionized water and 3 g Tween – 80 (emulsifier T – 80) add to the three beakers, then quick stir to form oil-in-water emulsion, with 500 r/min rate continue to stir, and pumped in nitrogen to the three beakers, slowly add 10 ml ammonium persulfate solution, under the condition of 70 ℃ water bath get PS emulsion polymerization 7 h. According to the above method preparation of PS emulsion and PTFE emulsion by certain volume mixing at room temperature. At a speed of 2 ~ 3 cm/min with dipping pulling method coating, drying at room temperature after repeated the operation three times, dry in the oven to 80 ℃ for 1 h. Then, in the resistance furnace roasting, insulation at 330 ℃ and 420 ℃ for 30 min. Experiments have directly affects the ratio of PS and PTFE super hydrophobic PTFE film, by changing two emulsion mixture ratio to obtain  the thin film that static contact Angle is 152.4°with water.

Dip coating method can get the thicker film, more fluorescent, more suitable for the coating of large area. Can be used for coating with different materials and shapes of components, such as silicon, glass, aluminum, smooth surface, and glass tubes, can also be coated on the bending of the lateral wall.

pdfThe preparation and modification of Teflon film.pdf

The modification of PTFE/teflon

Proper modification of pure PTFE can improve its comprehensive performance and expand its application in various fields. At present, the modification of PTFE mainly uses the composite principle, which is combined with other materials to make up its own defects. The methods of modification include: surface modification, filling modification, blending modification and so on.

The surface modification
PTFE’s very low surface activity and non adhesion limit the bonding with other materials, especially the bond between PTFE thin film and other skeleton materials. Therefore, it is necessary to modify the surface of PTFE material to improve its surface activity. PTFE commonly used surface modification technology.

Surface activation technique
Radiation grafting method. By irradiation of high energy radiation, the surface of the film can be grafted with other materials under certain conditions, and a layer of PTFE film which is tightly combined with the framework material is formed.
Plasma activation method. With an inert gas such as argon, helium plasma treatment of PTFE material, the surface etching, and carbon fluorine bonds and carbon carbon bonds fracturing, generating a large number of free radicals, but also can be introduced into the active groups, greatly increase the surface free energy of PTFE, improve the wettability and adhesion, which can be formed the adhesive layer on the surface of the surface activation. In general, the stick relay can be 10 times larger than before treatment.
Potassium acetate activation method. Immersing the PTFE in the molten potassium acetate, and the active layer could be formed after a certain amount of time to be treated at a proper temperature.
Mixed liquor activation treatment. PTFE in a certain proportion of sodium hydroxide, two propylene based melamine mixture to heat treatment for a certain period of time can improve the surface activity.
Corona discharge activation. The PTFE can be formed into adhesive bonded active layer by the corona treatment of the proper time and a certain atmosphere.
Tesla transformer discharge activation treatment. The transformer is used to discharge the PTFE, and the surface of the transformer is activated.

Chemical modification
The surface corrosion of PTFE mainly includes
The ammonia solution of sodium metal can be treated with a certain concentration of sodium ammonia solution for a certain period of time, so that the contact angle of PTFE can be reduced from 108 to 52 degrees, which can be used as a composite of epoxy resin and other materials.
Sodium naphthalene solution in tetrahydrofuran. PTFE with a certain concentration of sodium, naphthalene, tetrahydrofuran solution processing can achieve the goal of modification.
Alkali metal amalgam .The use of alkali metal amalgam corrosion of PTFE, which makes the surface carbonized and easy to be wetted and bonded.
Osmic acid corrosion. The use of osmium acid corrosion can increase the hydrophilicity of PTFE, which contributes to the composite molding.
The corrosion of iron pentacarbonyl. Using iron pentacarbonyl solution impregnates PTFE, which can improve its the surface corrosion and activity.

Surface deposition modification
Impregnating the PTFE in the colloidal solution of some metal hydroxide, which makes the colloidal particles deposited on the surface of PTFE, increasing the wetting angle, and improving the surface activity, which is easy to be combined with other materials.
The above surface modification methods are mainly applied to PTFE thin films. Usually, when the PTFE film is treated properly, it can be combined with other materials, and can be widely used in the design and manufacture of chemical anti-corrosion lining, sealing products and lubricating device. The basic design ideas of these methods, such as the introduction of polar groups, increase the interface bonding force; or to eliminate the weak interface layer, forming a strengthened surface layer; or to adjust the surface roughness, to give anchor effect. In short, various methods have their advantages and disadvantages, reasonable application or to find a new surface activation treatment is the main way to expand the application of PTFE thin film.
Filling modification of PTFE
Filling modification is adding filler to the PTFE, so as to improve and overcome the defects of pure PTFE, while maintaining its original advantages on the basis of the composite effect, improve the comprehensive performance. The filler can make the PTFE wear resistance increased about 1000 times; creep resistance increased 1.5 ~ 4.5 times at room temperature, 1.5 times at high temperature; flexural modulus increased 2 ~ 3 times; the hardness increased by 10% ~ 30%; the highest thermal conductivity increased 2 times; linear expansion coefficient reduced by about 1/2.
The filling properties of PTFE are closely related with the filler’s properties, content and technology, the basic principle for the general choices of filler include.The filler can withstand the sintering temperature of PTFE. The filler can improve PTFE’s abrasion resistance, mechanical strength, or increase the thermal conductivity coefficient, reduce the linear expansion etc. When in use, the filler will not effect other contact metals or fluid. The current commonly used fillers can be divided into 3 categories: inorganic materials, organic materials and metal materials.
Inorganic filler materials. The commonly used inorganic filler are mainly glass fiber, graphite, MoS2, carbon fiber etc.
Filled PTFE glass fiber is generally no alkali glass fiber, the filling amount is generally 15% ~ 25%, the ratio of length to diameter of 5 ~ 10. The hardness of the PTFE composited by the glass fiber can be generally increased by 10%, wear resistance can be increased by more than 500 times, creep resistance and resistance to cold flow properties have a greater degree of improvement and improvement.
Adding MoS2 helps to increase the rigidity and hardness of PTFE products, reduce the wear of the early start. In general, there’s little dosage of MoS2 in filling PTFE, and it often combines with other fillers.
The graphite can be used alone, and can be used in conjunction with the glass fiber or carbon black. Graphite filled PTFE has excellent chemical resistance, compression creep and better thermal conductivity, but its wear resistance worse than glass fiber filled PTFE difference. Only a small amount of carbon fiber filled PTFE can achieve carbon and graphite filling efficiency, but also has a very superior tensile properties. The wear resistance of the products in air and water can be greatly improved, and it has good creep resistance at room temperature and high temperature, but the biggest limitation to the application of this kind of material is the high cost.
Metal filling material. In order to improve the mechanical properties, thermal conductivity and dimensional stability of PTFE, it’s common to fill PTFE with iron, copper, lead, molybdenum, tungsten, silver and other metals, especially with copper and its alloys.
The copper filled PTFE can improve the creep resistance, compressive strength, hardness and dimensional stability of products, but the corrosion resistance and dielectric properties decrease. The suitable dosage of copper powder is 60%, at the moment, the limit value of PV can reach 29000, higher than that of other general materials.

Blending modification of PTFE
The blending modification of PTFE are familiar with the basic principle of filling modification generally, often refers to blend with other organic polymers, in order to improve its processing performance and use performance. In the blending modification, the PTFE is usually used only as a filling agent, and the processing method of the main material is usually used as the processing method of the blending material. The use of blending modification with PTFE has the following advantages:(1)The existing material and the existing process can be used to develop new varieties, and the investment is small, and the effect is fast; (2) Many varieties can be developed and the range is wide, such as the thermoplastic plastics, rubber, thermosetting resins, coatings, sealant, etc.;(3) The method of injection, molding curing, coating solidification and other methods of the main body material can be processed more efficiently and less energy consumption than the PTFE molding and sintering process;(4) Other polymers can improve the processing performance and use performance, such as heat resistance, chemical resistance, in particular, friction, wear resistance can be greatly improved.
The basic principle of blending is the principle of similar compatibility, solubility parameter and surface tension. PTFE blending modification engineering plastics mainly have polycarbonate (PC), poly formaldehyde (POM), nylon 66 (PA6), etc.. Modified engineering plastics not only maintain its original characteristics, especially the processing performance, but also improve its wear resistance, and improve the critical value of PV.
The rubber of PTFE modification is mainly silicone rubber, fluorine rubber. The wear resistance of the modified rubber is greatly improved. In some synthetic rubber and its coating, the blending of PTFE will greatly improve the chemical stability, oil resistance and solvent resistance of the rubber.
PTFE modified thermosetting resins are less. Often using a small amount of low molecular weight PTFE modifies the resin, and its wear performance is greatly improved; in addition, adding PTFE in curing type sealant, without reducing the sealing characteristics, can improve the use of temperature and chemical stability, while increasing lubrication.
In addition to the above modification method, introducing a small amount of non fluorine group into the PTFE chain, and the block is grafted to destroy the symmetry, so the modified PTFE is obtained by the method of thermoplastic processing. The performance of this product is similar to that of PTFE, but the performance of this product is greatly improved, so it is being paid more and more attention.
In addition, PTFE dispersion, paste and PTFE powder and expanded PTFE (EPTFE) are widely used in various industries because of its good processing performance.

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