A method for preparing a high-peeling-strength internally supported polyvinylidene fluoride hollow fiber membrane

Abstract

The application discloses a preparation method of a high-peeling-strength inner support polyvinylidene fluoride hollow fiber membrane, and comprises the following steps: (1) mixing polyvinylidene fluoride, a hydrophilic pore-forming agent and an organic solvent to obtain a casting solution; (2) coating the casting solution on a modified support tube through a spinning nozzle, then walking vertically downward in the air, and then entering a coagulation bath to be coagulated and formed into a formed piece; and (3) soaking the formed piece obtained in the step (2) in pure water, then placing the formed piece in a mixed liquid of water and glycerol, and then drying to obtain the high-peeling-strength inner support polyvinylidene fluoride hollow fiber membrane. The anti-hook type support tube prepared by using the anti-hook technology has an increased roughness of the surface of the support tube, the casting solution and the support tube can have more contact areas, the adhesion between the membrane layer and the support tube is greatly improved, and the peeling and peeling-off of the membrane layer caused by washing during the operation of a membrane module can be effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of hollow fiber membrane technology, specifically relating to a method for preparing a high peel strength internally supported polyvinylidene fluoride hollow fiber membrane. Background Technology

[0002] Membrane separation technology, as an effective way to solve water resource problems, is becoming an important technology for addressing energy, resource, and environmental pollution issues and a technological foundation for sustainable development. Hollow fiber membrane modules, with their advantages of high packing density, small footprint, low power consumption, good separation effect, and high recovery rate of individual membrane modules, are receiving increasing attention in the field of membrane technology. Advanced membrane material preparation and large-scale module application performance are key points in wastewater treatment. The performance of membrane modules includes two aspects: first, the performance of the membrane material itself, including the strength, hydrophilicity, and membrane layer bonding of the hollow fiber membrane; and second, the overall operational performance of the module, including operational stability, operating energy consumption (aeration), and antifouling performance.

[0003] The invention of internally supported hollow membranes has largely solved the problem of membrane fiber breakage during MBR operation. However, due to issues with the strength, flexibility, and interfacial compatibility of the support layer and membrane layer, the peel strength is not high. High-intensity shaking or backwashing during operation can cause the membrane layer to peel off from the support tube. Therefore, recent research on support membranes has focused on enhancing peel strength, but the results have not been ideal. The standard method uses burst strength to evaluate the peel strength of the membrane fibers; the higher the burst strength, the higher the peel strength. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of the prior art and provide a method for preparing a high peel strength internally supported polyvinylidene fluoride hollow fiber membrane.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing a high peel strength internally supported polyvinylidene fluoride hollow fiber membrane includes the following steps:

[0007] (1) Mix polyvinylidene fluoride, polyvinylpyrrolidone and organic solvent, stir evenly at 70-85℃ and let stand to remove bubbles to obtain casting solution.

[0008] (2) The above casting solution is coated onto the modified support tube through a spinning spinneret, and then travels vertically downwards in the air for 1-5 cm before entering a coagulation bath to solidify and form a molded part. The coagulation bath is water or a mixture of water and the organic solvent. The preparation of the modified support tube includes: immersing the hook-shaped support tube in a tert-butyl hydrogen peroxide solution at a temperature of 40°C and a concentration of 0.5-1 wt% for 1-2 h, then washing it with RO water, then immersing it in a polyvinylpyrrolidone solution at a temperature of 80-90°C and a concentration of 5-8 wt% for a grafting reaction for 0.5-1 h, and then vacuum drying.

[0009] (3) After soaking the molded part obtained in step (2) in pure water at 20-30℃ for 24h, it is then soaked in a mixture of water and glycerin for 0.1-0.5h, and then dried in an oven at 45-50℃ for 5-8h to obtain the high peel strength internally supported polyvinylidene fluoride hollow fiber membrane.

[0010] In a preferred embodiment of the present invention, the organic solvent is at least one of dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

[0011] In a preferred embodiment of the present invention, the formulation of the casting solution is as follows:

[0012] 15-25 wt% of polyvinylidene fluoride

[0013] Polyvinylpyrrolidone 5-15 wt%

[0014] Add organic solvent to 100 wt%.

[0015] More preferably, the formulation of the casting solution is as follows:

[0016] Polyvinylidene fluoride 20-24 wt%

[0017] Polyvinylpyrrolidone 10-15 wt%

[0018] Add organic solvent to 100 wt%.

[0019] In a preferred embodiment of the present invention, the reverse hook-shaped support tube has the opposite internal and external structure to that of a conventional support tube, with the internal structure of the conventional support tube woven onto the outside as a contact layer with the membrane layer. Its preparation method includes the following steps:

[0020] A. After twisting the ultrafine fibers with a fineness of 0.1-50 denier 1-5 times, the yarn is pulled out from the spool at a speed of 5-15 m / min and guided to the braiding head through the guide wheel of the high-speed braiding machine. The hook of the braiding head is reversed and the yarn is cross-braided into a reverse hook hollow braided tube.

[0021] B. The above-mentioned reverse hook hollow braided tube is heat-set at 220-230℃ to improve the hardness of the braided tube, and then guided out with guide rollers to obtain the reverse hook type support tube.

[0022] More preferably, the microfiber is made of at least one of polyester, polyethylene, polyester fiber, and nylon.

[0023] More preferably, the high-speed braiding machine has 15-40 spindles and a braiding mesh count of 20-30 mesh.

[0024] In a preferred embodiment of the present invention, the inner diameter of the hook-shaped support tube is 0.5-2.2 mm and the outer diameter is 1.2-3.2 mm.

[0025] More preferably, the inner diameter of the hook-shaped support tube is 0.8-1.0 mm and the outer diameter is 1.9-2.2 mm.

[0026] The beneficial effects of this invention are:

[0027] 1. This invention uses tert-butyl hydrogen peroxide to generate free radicals under heating conditions to initiate the chemical bonding of polyvinylpyrrolidone (PVP) onto the surface of a support tube. While improving the hydrophilicity of the support tube itself, PPVP is also an effective pore-forming agent in the casting solution. The PPVP in the casting solution and the PPVP in the support tube can effectively generate bonding force, improve the adhesion between the membrane layer and the support layer, and also improve the hydrophilicity of the membrane and enhance its antifouling ability.

[0028] 2. The reverse hook-shaped support tube prepared by the present invention has increased surface roughness, and the casting liquid and the support tube can have more contact area, which greatly improves the bonding force between the membrane layer and the support tube, and can effectively reduce membrane peeling and desquamation caused by scouring during the operation of the membrane module. Attached Figure Description

[0029] Figure 1 These are scanning electron microscope (SEM) images of the outer surface of the conventional internal support tube used in Comparative Examples 1 and 2 of this invention.

[0030] Figure 2 These are scanning electron microscope (SEM) images of the outer surface of the hook-shaped support tube used in Embodiments 1 to 3 and Comparative Example 3 of the present invention.

[0031] Figure 3 This is a scanning electron microscope image of the internally supported polyvinylidene fluoride hollow fiber membrane prepared in Comparative Example 1 of this invention.

[0032] Figure 4 This is a scanning electron microscope image of the high peel strength internally supported polyvinylidene fluoride hollow fiber membrane prepared in Example 2 of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0034] Example 1

[0035] (1) Mix 2400g of polyvinylidene fluoride powder, 1200g of polyvinylpyrrolidone K30 and 6400g of dimethylacetamide, stir at high speed at 70℃ until uniform and let stand for 24h to remove bubbles to obtain casting solution.

[0036] (2) The above casting liquid is coated onto the modified support tube through the spinning spinneret, then travels vertically downwards for 3cm in the air, enters water at 70°C to solidify and form, and is wound by a winding wheel to obtain the molded part.

[0037] The preparation of the modified support tube includes: immersing the hook-shaped support tube in a 1 wt% tert-butyl hydrogen peroxide solution at 40°C for 1 hour, then washing it with RO water for 5 minutes, followed by a grafting reaction in a 5 wt% polyvinylpyrrolidone K30 solution at 80°C for 0.5 hours, and then drying it in a vacuum drying oven at 50°C for 30 minutes to obtain the modified support tube with a contact angle of 24°.

[0038] This inverted hook-shaped support tube has the opposite internal and external structure to that of a conventional support tube. The internal structure of a conventional support tube is woven onto the outside as a contact layer with the membrane. Its preparation method includes the following steps:

[0039] A. After twisting the 5 denier ultrafine polyester fiber once, it is pulled out from the spool at a speed of 8 m / min and guided to the braiding head through the guide wheel of the high-speed braiding machine. The hook of the braiding head is reversed, and the yarn is cross-braided into a reverse hook hollow braided tube. The high-speed braiding machine has 24 spindles and a braiding mesh of 24.

[0040] B. The above-mentioned reverse-hook hollow braided tubing is heat-set at 220°C to increase its rigidity, and then guided out using guide rollers to obtain the desired shape. Figure 2 The hook-shaped support tube shown has an inner diameter of 0.8 mm and an outer diameter of 1.9 mm.

[0041] (3) After immersing the molded part obtained in step (2) in pure water at 25°C for 24 hours, it is then immersed in a mixture of water and glycerol (glycerol content 40wt%) for 0.5 hours, and then dried in an oven at 45°C for 5 hours to obtain the high peel strength internally supported polyvinylidene fluoride hollow fiber membrane, with an outer diameter of 2.2 mm, an inner diameter of 0.8 mm, and a pure water flux of 2946 L / m at 25°C. 2 •h(0.1MPa), the blasting strength is 0.6MPa.

[0042] Example 2

[0043] (1) Mix 2000g of polyvinylidene fluoride powder, 1000g of polyvinylpyrrolidone K90 and 7000g of dimethylacetamide, stir at high speed at 70℃ until uniform and let stand for 24h to remove bubbles to obtain casting solution.

[0044] (2) The above casting solution is coated onto the modified support tube through the spinning spinneret, then travels vertically downwards for 5cm in the air, enters water at 70°C to solidify and form, and is wound by a winding wheel to obtain the molded part.

[0045] The preparation of the modified support tube includes: immersing the hook-shaped support tube in a 0.5 wt% tert-butyl hydrogen peroxide solution at 40°C for 2 hours, washing it with RO water for 5 minutes, then immersing it in a polyvinylpyrrolidone K90 solution at 80°C for 0.5 hours for grafting reaction, and then drying it in a vacuum drying oven at 50°C for 30 minutes to obtain the modified support tube with a contact angle of 19°.

[0046] This inverted hook-shaped support tube has the opposite internal and external structure to that of a conventional support tube. The internal structure of a conventional support tube is woven onto the outside as a contact layer with the membrane. Its preparation method includes the following steps:

[0047] A. After twisting the 30 denier ultrafine polyester fiber once, it is pulled out from the spool at a speed of 10 m / min and guided to the braiding head through the guide wheel of the high-speed braiding machine. The hook of the braiding head is reversed, and the yarn is cross-braided into a reverse hook hollow braided tube. The high-speed braiding machine has 32 spindles and a braiding mesh of 30 mesh.

[0048] B. The above-mentioned reverse-hook hollow braided tubing is heat-set at 230°C to increase its rigidity, and then guided out using guide rollers to obtain the desired shape. Figure 2 The hook-shaped support tube shown has an inner diameter of 1.0 mm and an outer diameter of 2.2 mm.

[0049] (3) After immersing the molded part obtained in step (2) in pure water at 25°C for 24 hours, immerse it in a mixture of water and glycerin (glycerin content 40wt%) for 0.1 hours, and then dry it in a drying oven at 50°C for 5 hours to obtain the product shown in the figure. Figure 4 The high peel strength internally supported polyvinylidene fluoride hollow fiber membrane shown has an outer diameter of 2.6 mm, an inner diameter of 1.0 mm, and a pure water flux of 3035 L / m³ at 25°C. 2 •h(0.1MPa), the blasting strength is 0.7MPa.

[0050] Example 3

[0051] (1) Mix 2400g of polyvinylidene fluoride powder, 1500g of polyvinylpyrrolidone K30 and 6100g of dimethylacetamide, stir at high speed at 80℃ until uniform and let stand for 24h to remove bubbles to obtain casting solution.

[0052] (2) The above casting solution is coated onto the modified support tube through the spinning spinneret, then travels vertically downwards for 5cm in the air, enters water at 70°C to solidify and form, and is wound by a winding wheel to obtain the molded part.

[0053] The preparation of the modified support tube includes: immersing the hook-shaped support tube in a 0.8 wt% tert-butyl hydrogen peroxide solution at 50°C for 1 hour, then washing it with RO water for 5 minutes, followed by a grafting reaction in a 5 wt% polyvinylpyrrolidone K30 solution at 80°C for 0.5 hours, and then drying it in a vacuum drying oven at 50°C for 30 minutes to obtain the modified support tube with a contact angle of 23°.

[0054] This inverted hook-shaped support tube has the opposite internal and external structure to that of a conventional support tube. The internal structure of a conventional support tube is woven onto the outside as a contact layer with the membrane. Its preparation method includes the following steps:

[0055] A. After twisting the 50 denier ultrafine polyester fiber 5 times, it is pulled out from the spool at a speed of 5 m / min and guided to the braiding head through the guide wheel of the high-speed braiding machine. The hook of the braiding head is reversed, and the yarn is cross-braided into a reverse hook hollow braided tube. The high-speed braiding machine has 24 spindles and a braiding mesh of 30 mesh.

[0056] B. The above-mentioned reverse-hook hollow braided tubing is heat-set at 230°C to increase its rigidity, and then guided out using guide rollers to obtain the desired shape. Figure 2 The hook-shaped support tube shown has an inner diameter of 1.0 mm and an outer diameter of 2.2 mm.

[0057] (3) After immersing the molded part obtained in step (2) in pure water at 25°C for 24 hours, it is then immersed in a mixture of water and glycerol (glycerol content 50wt%) for 0.1 hours, and then dried in an oven at 45°C for 5 hours to obtain the high peel strength internally supported polyvinylidene fluoride hollow fiber membrane, with an outer diameter of 2.6 mm, an inner diameter of 1.0 mm, and a pure water flux of 2933 L / m at 25°C. 2 •h(0.1MPa), the blasting strength is 0.8MPa.

[0058] Comparative Example 1

[0059] Under high-speed stirring, 2400g of polyvinylidene fluoride powder, 1200g of polyvinylpyrrolidone K30, and 6400g of dimethylacetamide were added and stirred until uniformly dissolved. The stirring temperature was 70℃, and the mixture was allowed to stand for 24 hours to remove bubbles. The external coagulation bath was water at 70℃. After passing through a filter screen, the casting solution was extruded from a spinneret and coated onto a conventional internal support tube with an outer diameter of 1.9mm and an inner diameter of 0.8mm (e.g., ...). Figure 1 As shown, the conventional inner support tube has a contact angle of 76°. After traveling 5 cm in air, it enters the outer coagulation bath for molding and is wound by a winding wheel. The resulting inner-supported polyvinylidene fluoride hollow fiber membrane is then soaked in pure water (25°C) for 24 hours, followed by soaking in glycerol water (glycerol content 40wt%) for 12 hours. The resulting inner-supported polyvinylidene fluoride hollow fiber membrane (as shown) Figure 3 As shown, the hollow fiber membrane has an outer diameter of 2.2 mm and an inner diameter of 0.8 mm. At 25℃, the pure water flux of this membrane was measured to be 1237 L / m³. 2 •h(0.1MPa), the blasting strength is 0.3MPa.

[0060] Comparative Example 2

[0061] Under high-speed stirring, 2400g of polyvinylidene fluoride powder, 1200g of polyvinylpyrrolidone K30, and 6400g of dimethylacetamide were added and stirred until uniformly dissolved. The stirring temperature was 70℃, and the mixture was allowed to stand for 24 hours to remove bubbles. The external coagulation bath was water at 70℃. After passing through a filter screen, the casting solution was extruded from a spinneret and coated onto a conventional internal support tube with an outer diameter of 1.9mm and an inner diameter of 0.8mm (e.g., ...). Figure 1 As shown, before use, the conventional support tube was immersed in a solution containing 1% tert-butyl hydrogen peroxide at 40°C for 1 hour, then rinsed with RO water for 5 minutes. The rinsed hook-shaped support tube was then placed in a 5wt% polyvinylpyrrolidone K30 solution at 80°C for a grafting reaction for 0.5 hours, followed by drying in a 50°C vacuum drying oven for 30 minutes. The contact angle of the hydrophilized support tube was 24°. After traveling 8 cm in air, it was formed in an external coagulation bath and wound by a winding wheel. The resulting internally supported polyvinylidene fluoride hollow fiber membrane was then immersed in pure water (25°C) for 24 hours, followed by immersion in glycerol water (40wt% glycerol) for 12 hours. The resulting internally supported polyvinylidene fluoride hollow fiber membrane had an outer diameter of 2.2 mm and an inner diameter of 0.8 mm. At 25°C, the pure water flux of this hollow fiber membrane was measured to be 2633 L / m³. 2 •h(0.1MPa), the blasting strength is 0.4MPa.

[0062] Comparative Example 3

[0063] Under high-speed stirring, 2400g of polyvinylidene fluoride powder, 1200g of polyvinylpyrrolidone K30, and 6400g of dimethylacetamide were added and stirred until dissolved evenly. The stirring temperature was 70℃, and the mixture was allowed to stand for 24 hours to remove bubbles. The external coagulation bath was water at 70℃. After passing through a filter screen, the casting solution was extruded from the spindle and coated onto the yarn, which was made of ultra-fine polyester fiber that had been twisted once. The yarn was pulled out from the spool at a speed of 8m / min and passed through the guide wheel of a 24-spindle high-speed braiding machine. The yarn was then guided to the braiding machine head with reversed needles. The yarn was cross-woven and heat-set at 220℃ onto a 24-mesh reverse hook support tube with an outer diameter of 1.9mm and an inner diameter of 0.8mm. After traveling 5cm in the air, the yarn entered the external coagulation bath for molding and was wound by a winding wheel. The resulting internally supported polyvinylidene fluoride hollow fiber membrane was soaked in pure water (25℃) for 24 hours, then soaked in glycerol water (glycerol content 40wt%) for 0.5 hours, and finally dried in a drying oven at 45℃ for 5 hours. The resulting internally supported polyvinylidene fluoride hollow fiber membrane had an outer diameter of 2.2 mm and an inner diameter of 0.8 mm. At 25℃, the pure water flux of this hollow fiber membrane was measured to be 1892 L / m³. 2 •h(0.1MPa), the blasting strength is 0.5MPa.

[0064] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a high peel strength internally supported polyvinylidene fluoride hollow fiber membrane, characterized in that: Includes the following steps: (1) Mix 15-25 wt% polyvinylidene fluoride, 5-15 wt% polyvinylpyrrolidone and organic solvent to 100 wt%, stir evenly at 70-85℃ and let stand to remove bubbles to obtain casting solution, wherein the organic solvent is at least one of dimethylformamide, dimethylacetamide and N-methylpyrrolidone. (2) The above casting solution is coated onto the modified support tube through a spinning spinneret, and then travels vertically downward in the air for 1-5 cm before entering a coagulation bath to solidify and form a molded part. The coagulation bath is water or a mixture of water and the organic solvent. The preparation of the modified support tube includes: immersing the hook-shaped support tube in a tert-butyl hydrogen peroxide solution at a temperature of 40°C and a concentration of 0.5-1 wt% for 1-2 h, then washing it with RO water, then immersing it in a polyvinylpyrrolidone solution at a temperature of 80-90°C and a concentration of 5-8 wt% for a grafting reaction for 0.5-1 h, and then vacuum drying. (3) After soaking the molded part obtained in step (2) in pure water at 20-30℃ for 24h, it is then soaked in a mixture of water and glycerin for 0.1-0.5h, and then dried in an oven at 45-50℃ for 5-8h to obtain the high peel strength internally supported polyvinylidene fluoride hollow fiber membrane. The aforementioned inverted hook-shaped support tube has the opposite internal and external structure to that of a conventional support tube. The internal structure of a conventional support tube is woven onto the outside as a contact layer with the membrane. Its preparation method includes the following steps: A. After twisting the ultrafine fibers with a fineness of 0.1-50 denier 1-5 times, the yarn is pulled out from the spool at a speed of 5-15 m / min and guided to the braiding head through the guide wheel of the high-speed braiding machine. The hook of the braiding head is reversed and the yarn is cross-braided into a reverse hook hollow braided tube. B. Heat-set the above-mentioned reverse hook hollow braided tube at 220-230℃ to improve the hardness of the braided tube, and then use guide rollers to lead it out to obtain the reverse hook support tube.

2. The preparation method according to claim 1, characterized in that: The formulation of the casting solution is as follows: Polyvinylidene fluoride 20-24wt% Polyvinylpyrrolidone 10-15 wt% Add organic solvent to 100 wt%.

3. The preparation method according to claim 1, characterized in that: The microfiber is made of at least one of polyester, polyethylene, polyester fiber, and nylon.

4. The preparation method according to claim 3, characterized in that: The high-speed braiding machine has 15-40 spindles and a weaving mesh count of 20-30 mesh.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The inner diameter of the hook-shaped support tube is 0.5-2.2 mm, and the outer diameter is 1.2-3.2 mm.

6. The preparation method according to claim 5, characterized in that: The inner diameter of the hook-shaped support tube is 0.8-1.0 mm, and the outer diameter is 1.9-2.2 mm.

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