Polytetrafluoroethylene tube as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of volatile organic compound standard gas, and particularly relates to a polytetrafluoroethylene tube as well as a preparation method and application thereof. The polytetrafluoroethylene tube provided by the invention comprises a first polytetrafluoroethylene tube or a second polytetrafluoroethylene tube, the first polytetrafluoroethylene tube is provided with a hole structure; the tube material of the second polytetrafluoroethylene tube is doped with aluminum oxide, and the average particle size of the aluminum oxide is 10-200 nm; the doping amount of aluminum oxide in the second polytetrafluoroethylene tube is larger than 0 and smaller than or equal to 5%. The polytetrafluoroethylene tube provided by the invention has a uniformly distributed pore structure, can be directly arranged in a standard gas generation system, is used for on-site standard gas generation, and has relatively high magnitude transmission accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of volatile organic standard gases, and in particular relates to a polytetrafluoroethylene tube and a preparation method and application thereof. Background Art

[0002] A reference substance is a substance or material with uniform characteristic values, which is used to calibrate measuring devices, evaluate measurement methods or assign values ​​to materials. It is an indispensable material for measurement process control and measurement result evaluation, and is widely used in many fields such as environment, health, and food.

[0003] Ideal on-site calibration standard materials should have the following characteristics: ensuring the accuracy of the value, being easy to carry and transport, easy to operate, and being able to provide a wide range of configurations from low concentrations to high concentrations to meet different on-site calibration needs. At present, volatile organic compound (VOCs) standard gases are usually prepared in the laboratory according to the weight method and stored in gas cylinders. However, this method has some inherent limitations. For example, the adsorption of volatile organic compounds on the inner wall of the gas cylinder may cause fluctuations in gas concentration, thereby affecting the stability of the concentration value of the prepared standard material; in addition, the accuracy of the standard gas is limited by the accuracy of the electronic balance, and the error is large at the trace and trace levels, which seriously restricts the on-site calibration accuracy of the online monitoring equipment. Summary of the invention

[0004] In view of this, the present invention provides a polytetrafluoroethylene tube and a preparation method and application thereof. The polytetrafluoroethylene tube provided by the present invention contains a uniformly distributed pore structure, can efficiently prepare low-concentration VOCs standard gas, and can reduce the adsorption of VOCs by the tube wall, thereby improving the stability of the standard gas concentration value.

[0005] In order to solve the above technical problems, the present invention provides a polytetrafluoroethylene tube, including a first polytetrafluoroethylene tube or a second polytetrafluoroethylene tube; The first polytetrafluoroethylene tube has a pore structure; The second polytetrafluoroethylene tube is doped with aluminum oxide, and the average particle size of the aluminum oxide is 10-200 nm; the doping amount of aluminum oxide in the second polytetrafluoroethylene tube is greater than 0 and less than or equal to 5%.

[0006] Preferably, polytetrafluoroethylene pipe plugs are provided inside the ports at both ends of the polytetrafluoroethylene tube, and metal fastening sleeves are provided outside the ports at both ends of the polytetrafluoroethylene tube.

[0007] Preferably, the outer diameter of the polytetrafluoroethylene tube is 5-7 mm, the length is 13-15 cm, and the wall thickness is 0.7-0.9 mm; The length of the metal fastening sleeve is 1.8 to 2.2 cm, and the length of the polytetrafluoroethylene pipe plug is 1.8 to 2.2 cm.

[0008] The present invention also provides a method for preparing the polytetrafluoroethylene tube described in the above technical solution, comprising the following steps: Add petroleum solvent oil dropwise to polytetrafluoroethylene powder, then add aluminum oxide powder in batches and mix to obtain a mixed material; the average particle size of the aluminum oxide powder is 10-200 nm; The mixed material is molded and then sintered to obtain the second polytetrafluoroethylene tube; The second polytetrafluoroethylene tube is acid-etched to obtain the first polytetrafluoroethylene tube.

[0009] Preferably, the average particle size of the polytetrafluoroethylene powder is less than 500 μm; The petroleum solvent oil includes 70-200 number petroleum solvent oil; The mass ratio of the petroleum solvent oil to the polytetrafluoroethylene powder is 15-25:100; The mass ratio of the aluminum oxide powder to the polytetrafluoroethylene powder is less than or equal to 2:100; The dropping process is accompanied by a first oscillation and a first ultrasound, wherein the rotation speed of the first oscillation is 400-800 r / min, and the time of the first oscillation is 55-65 min; the power of the first ultrasound is 450-550 W, and the time of the first ultrasound is 55-65 min; The process of adding aluminum oxide powder is accompanied by a second oscillation and a second ultrasound, the rotation speed of the second oscillation is 600-1000 r / min, and the time of the second oscillation is 110-130 min; the power of the second ultrasound is 650-750 W, and the time of the second ultrasound is 55-65 min.

[0010] Preferably, the molding method is extrusion molding; The extrusion molding temperature is 40-60° C., the extrusion molding pressure is 0.7-7.5 MPa, the pressure holding time of the extrusion molding is 30-120 s, and the extrusion molding extrusion speed is 0.5-6 m / min.

[0011] Preferably, the sintering temperature is 340-380° C., the heating rate to the desired sintering temperature is 58-62° C. / h, and the sintering holding time is 3-6h.

[0012] Preferably, the acid used for acid etching includes hydrochloric acid, and the time of the acid etching is 24 to 48 hours; The molar concentration of the hydrochloric acid is 5-7 mol / L.

[0013] Preferably, the method further comprises disposing polytetrafluoroethylene pipe plugs on the inner sides of both end ports of the first polytetrafluoroethylene pipe and the second polytetrafluoroethylene pipe respectively, and disposing metal fastening sleeves on the outer sides of both end ports of the first polytetrafluoroethylene pipe and the second polytetrafluoroethylene pipe respectively.

[0014] The present invention also provides the use of the polytetrafluoroethylene tube described in the above technical solution or the polytetrafluoroethylene tube prepared by the preparation method described in the above technical solution in the preparation of low-concentration volatile organic compound standard gas; the concentration of the low-concentration volatile organic compound standard gas is 1ppb~10ppm.

[0015] The present invention provides a polytetrafluoroethylene tube, including a first polytetrafluoroethylene tube or a second polytetrafluoroethylene tube; the first polytetrafluoroethylene tube has a pore structure; the second polytetrafluoroethylene tube is doped with aluminum oxide, and the average particle size of the aluminum oxide is 10-200nm; the doping amount of aluminum oxide in the second polytetrafluoroethylene tube is greater than 0 and less than or equal to 5%. The polytetrafluoroethylene tube provided by the present invention has excellent sealing performance, is easy to transport and can be easily carried to the calibration site; and the polytetrafluoroethylene tube provided by the present invention has a uniformly distributed pore structure, can be directly placed in a standard gas generation system, and is used for on-site standard gas generation; it can effectively avoid the common adsorption problem in traditional gas cylinders and the dumping and leakage problem of standard emanated liquid in the membrane diffusion method, ensure that the standard emanated liquid is directly diffused from the polytetrafluoroethylene tube (permeation tube), and has higher value transfer accuracy.

[0016] The present invention also provides a method for preparing the polytetrafluoroethylene tube described in the above technical solution, comprising the following steps: adding petroleum solvent oil to polytetrafluoroethylene powder and then adding aluminum oxide powder in batches to mix to obtain a mixture; the average particle size of the aluminum oxide powder is 10-200nm; the mixture is formed and sintered to obtain the second polytetrafluoroethylene tube; the second polytetrafluoroethylene tube is acid-etched to obtain the first polytetrafluoroethylene tube. The present invention effectively adjusts the porosity and pore size of the polytetrafluoroethylene tube by adding nano-Al2O3 particles to the polytetrafluoroethylene powder; after adding Al2O3 particles to the polytetrafluoroethylene body, due to the filling effect of Al2O3 particles, the porosity of the obtained polytetrafluoroethylene tube is reduced compared with that of the pure polytetrafluoroethylene permeable tube; the Al2O3-doped polytetrafluoroethylene is made into a permeable tube and placed in hydrochloric acid to dissolve the Al2O3 particles, thereby forming nano-scale pores in the tube body and improving the porosity of the permeable tube. The present invention achieves fine adjustment of the pore size of the polytetrafluoroethylene tube by precisely controlling the particle size, doping amount and whether or not to perform acid etching treatment of nano-Al2O3 particles, which not only improves the uniform penetration performance of the polytetrafluoroethylene tube (the penetration rate can be adjusted), but also broadens its scope of application in scientific research and field calibration applications. The present invention limits the mixing order of polytetrafluoroethylene powder, petroleum solvent oil and aluminum oxide powder so that aluminum oxide is uniformly dispersed in the polytetrafluoroethylene powder, thereby obtaining a polytetrafluoroethylene tube with uniform pore distribution and smaller pore size, which is conducive to the preparation of low-concentration VOCs standard gas. The polytetrafluoroethylene tube provided by the present invention solves the problems of high cost, low efficiency and poor stability in the traditional VOCs standard gas preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of the clamp in the cylindrical crimping die used in the embodiment; Figure 2 This is a schematic diagram of the polytetrafluoroethylene tube prepared in Example 1. DETAILED DESCRIPTION

[0018] The invention provides a polytetrafluoroethylene tube, comprising a first polytetrafluoroethylene tube or a second polytetrafluoroethylene tube.

[0019] As a specific embodiment of the present invention, the first polytetrafluoroethylene tube has a pore structure. As a specific embodiment of the present invention, the pore structure is evenly distributed on the surface of the first polytetrafluoroethylene tube.

[0020] As a specific embodiment of the present invention, the second polytetrafluoroethylene tube is doped with aluminum oxide, and the average particle size of the aluminum oxide is 10-200 nm, and can be specifically 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 130 nm, 160 nm, 190 nm or 200 nm; the doping amount of aluminum oxide in the second polytetrafluoroethylene tube is greater than 0 and less than or equal to 5%, and can be specifically 0.5%, 1%, 1.5%, 2%, 3%, 4% or 5%.

[0021] As a specific embodiment of the present invention, the outer diameter of the polytetrafluoroethylene tube can be 5-7 mm, specifically 5 mm, 6 mm or 7 mm; the length of the polytetrafluoroethylene tube can be 13-15 cm, specifically 13 cm, 14 cm or 15 cm; the wall thickness of the polytetrafluoroethylene tube can be 0.7-0.9 mm, specifically 0.7 mm, 0.8 mm or 0.9 mm.

[0022] As a specific embodiment of the present invention, a polytetrafluoroethylene pipe plug is provided inside the ports at both ends of the polytetrafluoroethylene pipe, and a metal fastening sleeve is provided outside the ports at both ends of the polytetrafluoroethylene pipe; the length of the metal fastening sleeve can be 1.8~2.2cm, and can be specifically 2cm; the length of the polytetrafluoroethylene pipe plug can be 1.8~2.2cm, and can be specifically 2cm. The present invention realizes the sealing of the polytetrafluoroethylene pipe by providing the polytetrafluoroethylene pipe plug and the metal fastening sleeve at the ports at both ends of the polytetrafluoroethylene pipe.

[0023] In the present invention, polytetrafluoroethylene has stable chemical properties and does not react with organic solvents. The present invention uses polytetrafluoroethylene as the matrix of the pipe to reduce the adsorption of VOCs on the pipe wall, thereby improving the stability of the concentration value of the VOCs standard substance.

[0024] The present invention also provides a method for preparing the polytetrafluoroethylene tube described in the above technical solution, comprising the following steps: Add petroleum solvent oil dropwise to polytetrafluoroethylene powder, then add aluminum oxide powder in batches and mix to obtain a mixed material; the average particle size of the aluminum oxide powder is 10-200 nm; The mixed material is molded and then sintered to obtain the second polytetrafluoroethylene tube; The second polytetrafluoroethylene tube is acid-etched to obtain the first polytetrafluoroethylene tube.

[0025] The present invention drips petroleum solvent oil into polytetrafluoroethylene powder, and then adds aluminum oxide powder in batches to mix, so as to obtain a mixed material. As a specific embodiment of the present invention, the average particle size of the polytetrafluoroethylene powder can be less than 500 μm, and can also be 200-300 μm, and can be specifically 200 μm, 250 μm or 300 μm; the petroleum solvent oil can include 70-200 petroleum solvent oil, and can be specifically 200 petroleum solvent oil; the average particle size of the aluminum oxide powder is 10-200 nm, and can be specifically 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100nm, 130nm, 160nm, 190nm or 200nm; the mass ratio of the petroleum solvent oil to the polytetrafluoroethylene powder can be 15-25:100, and can be specifically 15:100, 18:100, 20:100, 23:100 or 25:100; the mass ratio of the aluminum oxide powder to the polytetrafluoroethylene powder can be less than or equal to 2:100, and can be specifically 0.5:100, 1:100, 1.5:100 or 2:100.

[0026] The present invention uses petroleum solvent oil as a dispersant to effectively reduce the surface tension between the polytetrafluoroethylene powder and the medium, and reduce the van der Waals force between the particles, thereby eliminating the agglomeration phenomenon. In addition, the high flash point and low volatility of petroleum solvent oil ensure that it is safer and more stable during the treatment process. The present invention drips petroleum solvent oil into the polytetrafluoroethylene powder, improves the dispersing effect of aluminum oxide in the polytetrafluoroethylene powder, and improves the lubricity of the mixed material, which is beneficial to the subsequent molding, and simplifies the experimental operation steps and saves time.

[0027] As a specific embodiment of the present invention, before adding petroleum solvent oil to the polytetrafluoroethylene powder, the process may further include: sieving the polytetrafluoroethylene powder. The present invention can remove the agglomerated polytetrafluoroethylene powder through the sieving process. The present invention has no particular limitation on the aperture of the sieve used for the sieving process, as long as the agglomerated polytetrafluoroethylene powder can be removed.

[0028] The present invention has no special limitation on the speed of the dripping, as long as it is added dropwise. As a specific embodiment of the present invention, the dripping process may be accompanied by a first oscillation and a first ultrasound performed sequentially, the speed of the first oscillation may be 400-800 r / min, specifically 400 r / min, 500 r / min, 600 r / min, 700 r / min or 800 r / min; the time of the first oscillation may be 55-65 min, specifically 55 min, 60 min or 65 min; the power of the first ultrasound may be 450-550 W, specifically 450 W, 500 W or 550 W; the time of the first ultrasound may be 55-65 min, specifically 55 min, 60 min or 65 min.

[0029] As a specific embodiment of the present invention, before adding aluminum oxide powder to the mixture of polytetrafluoroethylene powder and petroleum solvent oil, the process may further include: sieving the aluminum oxide powder. The present invention can remove agglomerated aluminum oxide powder through the sieving process. The present invention has no particular limitation on the aperture of the mesh used for the sieving process, as long as the agglomerated aluminum oxide powder can be removed. As a specific embodiment of the present invention, the process of adding aluminum oxide powder may be accompanied by a second oscillation and a second ultrasound performed sequentially, the rotation speed of the second oscillation may be 600-1000r / min, specifically 600r / min, 700r / min, 800r / min, 900r / min or 1000r / min; the time of the second oscillation may be 110-130min, specifically 110min, 120min or 130min; the power of the second ultrasound may be 650-750W, specifically 650W, 700W or 750W; the time of the second ultrasound may be 55-65min, specifically 55min, 60min or 65min.

[0030] After obtaining the mixed material, the present invention shapes and then sinter the mixed material to obtain the second polytetrafluoroethylene tube. As a specific embodiment of the present invention, the molding process may also include: preforming the mixed material to obtain a hollow cylindrical blank. The present invention has no special limitation on the preforming process, as long as a blank of a desired shape can be obtained.

[0031] As a specific embodiment of the present invention, the molding method can be extrusion molding; the extrusion molding temperature can be 40~60℃, specifically 40℃, 45℃, 50℃, 55℃ or 60℃; the extrusion molding pressure can be 0.7~7.5MPa, specifically 0.7MPa, 1MPa, 2MPa, 3MPa, 4MPa, 5MPa, 6MPa, 7MPa or 7.5MPa; the pressure holding time of the extrusion molding can be 30~120s, specifically 30s, 40s, 60s, 80s, 100s or 120s; the extrusion molding extrusion speed can be 0.5~6m / min, specifically 0.5m / min, 0.8m / min, 1m / min, 2m / min, 3m / min, 4m / min, 5m / min or 6m / min. As a specific embodiment of the present invention, the extrusion molding device can be an extruder.

[0032] As a specific embodiment of the present invention, after the molding, the process may further include: drying the molded product; the drying temperature may be 120-300°C, and may be specifically 120°C, 150°C, 200°C, 250°C or 300°C; the drying time may be 0.5-3h, and may be specifically 0.5h, 1h, 1.5h, 2h, 2.5h or 3h.

[0033] As a specific embodiment of the present invention, the sintering temperature can be 340-380°C, specifically 340°C, 350°C, 360°C, 370 or 380°C; the heating rate to the required sintering temperature can be 50-70°C / h, specifically 50°C / h, 55°C / h, 60°C / h, 65°C / h or 70°C / h; the sintering holding time can be 3-6h, specifically 3h, 4h, 5h or 6h. As a specific embodiment of the present invention, the sintering can be carried out in an oven. The present invention limits the sintering temperature and time within the above range to avoid the reaction between alumina and polytetrafluoroethylene to produce by-products. The present invention can cross-link the molecular chains between polytetrafluoroethylene particles through sintering to enhance the bonding force between the particles, so that the pipe becomes a whole; at the same time, the polytetrafluoroethylene particles form a dense porous structure through diffusion and crystallization.

[0034] As a specific embodiment of the present invention, after sintering, the process may further include: cooling the sintered product to room temperature, the room temperature may be 20-35°C, or 25-30°C; the cooling may be furnace cooling. The present invention cools the sintered product to facilitate shaping of the pipe, and the present invention uses furnace cooling to achieve gradual cooling to maintain the stability of the pipe structure.

[0035] After obtaining the second polytetrafluoroethylene tube, the present invention performs acid etching on the second polytetrafluoroethylene tube to obtain the first polytetrafluoroethylene tube. As a specific embodiment of the present invention, the acid etching acid may include hydrochloric acid, and the molar concentration of the hydrochloric acid may be 5-7 mol / L, and may be specifically 5 mol / L, 6 mol / L or 7 mol / L; the acid etching time may be 24-48 hours, and may be specifically 24 hours, 26 hours, 30 hours, 35 hours, 40 hours, 45 hours or 48 hours. The present invention removes the aluminum oxide particles in the second polytetrafluoroethylene tube by acid etching to form a uniformly distributed pore structure.

[0036] As a specific embodiment of the present invention, the acid etching may further include: washing the acid-etched product with water and alcohol in sequence and then drying to obtain the first polytetrafluoroethylene tube. As a specific embodiment of the present invention, the water washing may be rinsing with clean water; the detergent for the alcohol washing may be anhydrous ethanol, and the alcohol washing may be ultrasonic washing with anhydrous ethanol as a detergent, and the ultrasonic washing time may be 8 to 12 minutes, and may be specifically 10 minutes. As a specific embodiment of the present invention, the drying temperature may be 75 to 85°C, and may be specifically 75°C, 80°C or 85°C. The present invention has no special requirements for the drying time, as long as the solvent on the surface of the pipe can be removed.

[0037] As a specific embodiment of the present invention, after obtaining the first polytetrafluoroethylene tube and the second polytetrafluoroethylene tube, the method further includes packaging the first polytetrafluoroethylene tube and the second polytetrafluoroethylene tube; the packaging may be to respectively set polytetrafluoroethylene tube plugs on the inner sides of the two end ports of the first polytetrafluoroethylene tube and the second polytetrafluoroethylene tube, and then set metal fastening sleeves on the outer sides of the two end ports of the first polytetrafluoroethylene tube and the second polytetrafluoroethylene tube. As a specific embodiment of the present invention, the outer end of the polytetrafluoroethylene tube plug may be flush with the outer end of the pipe mouth; the sealing end of the metal fastening sleeve may be flush with the outer end of the pipe mouth of the pipe; the present invention may use electric hydraulic pliers to pressurize and tighten the metal fastening sleeve, the pressurized pressure may be 50~100kPa, and the tightening position may be the third division of the metal fastening sleeve.

[0038] The present invention also provides the use of the polytetrafluoroethylene tube described in the above technical solution or the polytetrafluoroethylene tube prepared by the preparation method described in the above technical solution in the preparation of low-concentration volatile organic compound standard gas. As a specific embodiment of the present invention, the concentration of the low-concentration volatile organic compound standard gas can be 1ppb~10ppm. When the present invention uses the polytetrafluoroethylene tube to prepare low-concentration volatile organic compound standard gas, one end of the tube can be encapsulated first, then analytical pure volatile organic matter is injected, and finally the other end is encapsulated; the analytical pure volatile organic matter can be toluene, and the added volume of the analytical pure volatile organic matter can be 1~2.5mL. The present invention encapsulates analytical pure volatile organic matter in a polytetrafluoroethylene tube, and the gaseous molecules diffuse from the tube through the wall of the permeation tube (polytetrafluoroethylene tube) into the on-site standard material distribution cabin, and the standard gas with accurate value is prepared by setting the parameters such as temperature, humidity, and ventilation rate of the distribution cabin.

[0039] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0040] Example 1 4.0 g of 200# petroleum solvent oil as a dispersant was added dropwise to 20.0 g of polytetrafluoroethylene powder having an average particle size of 250 μm and Al2O3 powder having an average particle size of 80 nm after being sieved through a 40-mesh sieve respectively, and the addition process was accompanied by oscillation (oscillation in a shaking table at a speed of 600 r / min for 60 min) and ultrasound (ultrasound at a power of 500 W for 60 min) in sequence; 0.4 g of alumina powder was added in batches to the mixture of polytetrafluoroethylene powder and dispersant, and mixed under oscillation and ultrasound conditions to obtain a paste-like mixed material, wherein the oscillation speed during mixing was 800 r / min, the oscillation time was 120 min, the ultrasound power was 700 W, and the ultrasound time was 60 min; The paste-like mixture is preformed into a hollow cylindrical billet and then placed in the extruder barrel. The billet is slowly pushed forward and pressurized with a plunger under heating to extrude the billet into the desired tube shape for molding; the extrusion temperature is 40°C, the extrusion speed is 0.8m / min, and the extrusion pressure is maintained for 60s after reaching 3MPa; The formed product was dried at 200°C for 2.5 hours and then placed in an oven and heated to 360°C at a heating rate of 60°C / h for 4 hours for sintering. The sintered tube was cooled to room temperature (25°C) in the oven and then cut to obtain a second polytetrafluoroethylene tube with a length of 14 cm and a wall thickness of 0.8 mm. The second polytetrafluoroethylene tube was packaged as follows: a polytetrafluoroethylene tube plug with a length of 2 cm was pushed into one end of the tube until the tube plug was flush with the tube mouth; a metal fastening sleeve with a length of 2 cm was inserted into one end where the polytetrafluoroethylene tube plug had been assembled, ensuring that the metal fastening sleeve was flush with the tube mouth of the permeation tube; a cylindrical crimping die was surrounded by the metal sleeve, and pressure was applied using a Desili DLX-Y700 electric hydraulic pliers in the pressure range of 50~100 kPa, and the metal sleeve was tightened twice at three equal parts; one end of the sealed second polytetrafluoroethylene tube was placed vertically downward with the open end facing upward, 2.0 mL of analytical pure toluene solution was injected, and the open end was sealed with a polytetrafluoroethylene tube plug, and the metal fastening sleeve was tightened and sealed to obtain an Al2O3-doped polytetrafluoroethylene permeation tube.

[0041] The cylindrical crimping die used in Example 1 is composed of a symmetrical fixture with a through hole. The structural diagram of the fixture is shown in FIG. Figure 1 shown.

[0042] The schematic diagram of the polytetrafluoroethylene tube prepared in Example 1 is as follows Figure 2 shown.

[0043] Example 2 A second polytetrafluoroethylene tube was prepared according to the method of Example 1, and the second polytetrafluoroethylene tube was acid-etched with hydrochloric acid having a molar concentration of 6 mol / L for 48 hours, then rinsed with clean water, ultrasonically cleaned with anhydrous ethanol for 10 minutes, and dried in an oven at 80° C. to obtain a first polytetrafluoroethylene tube with a uniform pore structure distribution; The first polytetrafluoroethylene tube was packaged according to the packaging method of Example 1 to obtain a polytetrafluoroethylene permeation tube with uniformly distributed nanopores.

[0044] Comparative Example 1 A polytetrafluoroethylene permeation tube was prepared according to the method of Example 1, except that aluminum oxide was not added during the preparation of the tube. The specific steps are as follows: After passing polytetrafluoroethylene powder with an average particle size of 250 μm through a 40-mesh sieve, 4.0 g of a dispersant, No. 200 petroleum solvent oil, was added dropwise to 20.0 g of the polytetrafluoroethylene powder to obtain a paste-like mixed material, and the dropping process was accompanied by oscillation and ultrasound in sequence; the mixture was shaken in a shaking table at a speed of 600 r / min for 60 min, and ultrasound was performed at a power of 500 W for 60 min; The paste-like mixture is preformed into a hollow cylindrical billet and then placed in the extruder barrel. The billet is slowly pushed forward and pressurized with a plunger under heating to extrude the billet into the desired tube shape for molding; the extrusion temperature is 40°C, the extrusion speed is: 0.8m / min, and the extrusion pressure reaches 3MPa and the pressure is maintained for 60s; The formed product was dried at 200°C for 2.5 hours and then placed in an oven and heated to 360°C at a heating rate of 60°C / h for 4 hours for sintering. The sintered tube was cooled to room temperature (25°C) and then cut to obtain a tube with a length of 14 cm and a wall thickness of 0.8 mm. The polytetrafluoroethylene tube was packaged as follows: a polytetrafluoroethylene tube plug with a length of 2 cm was pushed into one end of the tube until the tube plug was flush with the tube mouth; a metal fastening sleeve with a length of 2 cm was inserted into one end where the polytetrafluoroethylene tube plug had been assembled, ensuring that the metal fastening sleeve was flush with the tube mouth of the permeation tube; a cylindrical crimping die was surrounded by the metal sleeve, and pressure was applied using a Desili DLX-Y700 electric hydraulic pliers with a pressure range of 50~100Kpa, and the metal sleeve was tightened twice at three equal parts; one end of the sealed polytetrafluoroethylene tube was placed vertically downward with the open end facing upward, 2.0 mL of analytical pure toluene solution was injected, and the open end was sealed with a polytetrafluoroethylene tube plug, and the metal fastening sleeve was tightened and sealed to obtain an Al2O30-doped polytetrafluoroethylene permeation tube.

[0045] Comparative Example 2 Using silica microspheres as pore-forming agent and hydrofluoric acid as etching solution, polytetrafluoroethylene pipes were prepared according to the following method: 0.2 g of nano-silicon dioxide microspheres with an average particle size of 100 nm and 20.0 g of polytetrafluoroethylene powder with an average particle size of 300 μm were mixed evenly to obtain a mixture.

[0046] Add 4.0g of No. 200 petroleum solvent oil (the amount added is 20% of the mass of the polytetrafluoroethylene powder) to the mixture. After mixing, store it at 25°C for 48h (to ensure that the lubricant is fully infiltrated and evenly distributed) and then preform it into a hollow cylindrical billet. Put the obtained billet into the extruder barrel, and slowly push and pressurize it with a plunger under heating to extrude the billet into the desired tube shape; the extrusion temperature is 40°C, the extrusion speed is 0.8m / min, and when the pressure reaches 3MPa, the pressure is maintained for 60s; The extruded material was dried at 200° C. for 2.5 hours and then sintered in an oven; the heating rate was 60° C. / h and the temperature was kept at 360° C. for 4 hours; the sintered tube was cooled to 25° C. in the furnace and then cut to obtain a polytetrafluoroethylene tube substrate with a length of 14 cm and a wall thickness of 0.8 mm; the polytetrafluoroethylene substrate was placed in a plastic container, etched with hydrofluoric acid having a mass concentration of 30%, and allowed to stand for 24 hours; the etched polytetrafluoroethylene tube was taken out, rinsed with water, placed in a beaker, ethanol was added, and ultrasonic cleaning was performed for 10 minutes, and then the polytetrafluoroethylene tube after ultrasonic cleaning was dried in an oven at 80° C. to obtain a polytetrafluoroethylene permeation tube body, which was packaged according to the method of Example 1.

[0047] The permeation tubes prepared in Examples 1-2 and Comparative Examples 1-2 were placed upright in a constant temperature diffusion chamber, the temperature was controlled at 40°C, high purity nitrogen was introduced into the diffusion chamber, the nitrogen flow rate was 0.5 L / min, the relative humidity was 50%, and the diffusion rate of toluene gas through the polytetrafluoroethylene permeation tube was tested within a certain period of time. The experimental results are shown in Table 1. The diffusion rate is the ratio of the difference between the weight of the sample bottle at the end of the test and the weight of the sample bottle at the beginning of the test and the test time.

[0048] Table 1 Emission data of the permeation tubes prepared in Examples 1-2 and Comparative Examples 1-2

[0049] It can be seen from Table 1 that the polytetrafluoroethylene tube provided by the present invention can be used to prepare ultra-low concentration VOCs standard gas with excellent stability.

[0050] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A polytetrafluoroethylene tube, characterized in that: including a first polytetrafluoroethylene tube or a second polytetrafluoroethylene tube; The first polytetrafluoroethylene tube has a pore structure; The second polytetrafluoroethylene tube is doped with aluminum oxide, and the average particle size of the aluminum oxide is 10-200 nm; the doping amount of aluminum oxide in the second polytetrafluoroethylene tube is greater than 0 and less than or equal to 5%.

2. The polytetrafluoroethylene tube according to claim 1, characterized in that: The inner sides of the ports at both ends of the polytetrafluoroethylene tube are provided with polytetrafluoroethylene tube plugs, and the outer sides of the ports at both ends of the polytetrafluoroethylene tube are provided with metal fastening sleeves.

3. The polytetrafluoroethylene tube according to claim 2, characterized in that: The outer diameter of the polytetrafluoroethylene tube is 5-7 mm, the length is 13-15 cm, and the wall thickness is 0.7-0.9 mm; The length of the metal fastening sleeve is 1.8 to 2.2 cm, and the length of the polytetrafluoroethylene pipe plug is 1.8 to 2.2 cm.

4. The method for preparing the polytetrafluoroethylene tube according to any one of claims 1 to 3, comprising the following steps: Add petroleum solvent oil dropwise to polytetrafluoroethylene powder, then add aluminum oxide powder in batches and mix to obtain a mixed material; the average particle size of the aluminum oxide powder is 10-200 nm; The mixed material is molded and then sintered to obtain the second polytetrafluoroethylene tube; The second polytetrafluoroethylene tube is acid-etched to obtain the first polytetrafluoroethylene tube.

5. The preparation method according to claim 4, characterized in that: The average particle size of the polytetrafluoroethylene powder is less than 500 μm; The petroleum solvent oil includes 70-200 number petroleum solvent oil; The mass ratio of the petroleum solvent oil to the polytetrafluoroethylene powder is 15-25:100; The mass ratio of the aluminum oxide powder to the polytetrafluoroethylene powder is less than or equal to 2:100; The dropping process is accompanied by a first oscillation and a first ultrasound, wherein the rotation speed of the first oscillation is 400-800 r / min, and the time of the first oscillation is 55-65 min; the power of the first ultrasound is 450-550 W, and the time of the first ultrasound is 55-65 min; The process of adding aluminum oxide powder is accompanied by a second oscillation and a second ultrasound, the rotation speed of the second oscillation is 600-1000 r / min, and the time of the second oscillation is 110-130 min; the power of the second ultrasound is 650-750 W, and the time of the second ultrasound is 55-65 min.

6. The preparation method according to claim 4, characterized in that: The molding method is extrusion molding; The extrusion molding temperature is 40-60° C., the extrusion molding pressure is 0.7-7.5 MPa, the pressure holding time of the extrusion molding is 30-120 s, and the extrusion molding extrusion speed is 0.5-6 m / min.

7. The preparation method according to claim 4, characterized in that: The sintering temperature is 340-380° C., the heating rate to the required sintering temperature is 58-62° C. / h, and the sintering heat preservation time is 3-6h.

8. The preparation method according to claim 5, characterized in that: The acid used for the acid etching includes hydrochloric acid, and the time of the acid etching is 24 to 48 hours; The molar concentration of the hydrochloric acid is 5-7 mol / L.

9. The preparation method according to claim 4, characterized in that: The method also includes respectively arranging polytetrafluoroethylene pipe plugs on the inner sides of the two end ports of the first polytetrafluoroethylene pipe and the second polytetrafluoroethylene pipe and arranging metal fastening sleeves on the outer sides of the two end ports of the first polytetrafluoroethylene pipe and the second polytetrafluoroethylene pipe.

10. Use of the polytetrafluoroethylene tube according to any one of claims 1 to 3 or the polytetrafluoroethylene tube prepared by the preparation method according to any one of claims 4 to 9 in preparing low-concentration volatile organic compound standard gas; the concentration of the low-concentration volatile organic compound standard gas is 1 ppb to 10 ppm.

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