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Development and Application of PTFE Teflon Glass Fiber Sintered High Temperature Filter

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.
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. If you need more information about our products, please contact us: system@corefrp.com ,our engineers will answer you and provide free samples. pdfDevelopment and Application of PTFE Teflon Glass Fiber Sintered High Temperature Filter.pdf

Development of fiberglass/PTFE membrane structure materials

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
Table 1
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.

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

pdfDevelopment of fiberglass PTFE membrane structure materials.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

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.

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