Hydrophilic polyvinylidene fluoride hollow fiber membrane and preparation method thereof

Abstract

The invention discloses a hydrophilic polyvinylidene fluoride hollow fiber membrane and a preparation method thereof, and aims at solving the problems that a traditional polyvinylidene fluoride membrane is high in hydrophobicity and short in service life due to the fact that organic matter is easily adsorbed and microorganisms are easily enriched. The hollow fiber membrane is prepared from the following raw materials in percentage by weight: 17 to 29 percent of polyvinylidene fluoride, 3 to 9 percent of polyvinylpyrrolidone, 0.12 to 0.48 percent of composite catalyst, 0.5 to 1.9 percent of composite ligand, 5.5 to 9.5 percent of hydrophilic functional monomer and 52 to 73 percent of solvent, wherein the composite catalyst is a compound of cuprous chloride and ferric chloride, and the composite ligand is a compound of 2, 2 '-bipyridine and 4, 4'-bipyridine. The preparation method comprises the steps of raw material dissolution, membrane casting solution preparation, photopolymerization modification, spinning solidification and drying shaping. Through the synergistic effect of the raw material components, the surface hydrophilicity of the membrane is remarkably improved, the organic matter adsorption amount of the membrane is reduced by 60% or above, and the microorganism enrichment amount is reduced by 80% or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hollow fiber membranes, in particular to a hydrophilic polyvinylidene fluoride hollow fiber membrane and a preparation method thereof. BACKGROUND

[0002] Membrane separation technology is a new separation technology that emerged in the early 20th century and rapidly rose in the 1960s. This technology has the functions of separation, concentration, purification and refining, and has the characteristics of high efficiency, energy saving, environmental protection, molecular level filtration, simple filtration process and easy control. It has been widely used in food, medicine, biology, environmental protection, chemical industry, metallurgy, energy, petroleum, water treatment, electronics, and bionics, etc. It has produced huge economic and social benefits and has become one of the most important means in modern separation science.

[0003] With the development of membrane science and technology, membrane separation technology has been applied to different degrees in seawater desalination, brackish water desalination, high-purity water preparation, power plant water treatment, sewage and wastewater treatment, and drinking water purification treatment. The common membrane materials at present include polysulfone, polypropylene, polyethylene, polyvinyl chloride, polyether sulfone, polyvinylidene fluoride, etc. Among them, polyvinylidene fluoride (PVDF) is a crystalline polymer with excellent chemical stability, heat resistance, radiation resistance and good physical and mechanical properties, and can be cast into a thin film with good performance. It is one of the most widely used membrane materials in the current market.

[0004] However, polyvinylidene fluoride has strong hydrophobicity, which leads to low water flux of the prepared membrane, and in the use process, it is easy to adsorb organic substances in water and form deposition, and at the same time, it is easy to breed microorganisms and grow and enrich on the membrane surface, causing membrane pollution. These problems not only reduce the separation efficiency of the membrane, but also greatly shorten the service life of the membrane, which seriously limits the application of polyvinylidene fluoride membrane in fields such as water purification and protein separation which require high membrane hydrophilicity and anti-pollution ability.

[0005] The existing hydrophilic modification methods for polyvinylidene fluoride hollow fiber membranes mainly include two types: membrane surface modification and membrane material modification. Among them, the membrane surface modification can only form a temporary hydrophilic layer on the membrane surface, and the hydrophilicity cannot be maintained permanently, which will gradually lose with the extension of the membrane use time. While the membrane material modification can fundamentally change the hydrophilicity of the separation membrane by introducing polar groups, but in the existing modification scheme, the casting solution ratio design is unreasonable, it is difficult to achieve the multiple effects of "improving hydrophilicity, blocking organic matter adsorption, and inhibiting microbial enrichment", and the performance stability and service life of the modified membrane are limited, which cannot meet the harsh demands in actual application. Therefore, it is urgent to develop a technical scheme for improving the performance of polyvinylidene fluoride membrane by optimizing the casting solution ratio to solve the above technical problems of the existing technology. SUMMARY

[0006] In order to overcome the problems existing in the prior art, the purpose of the present application is to provide a hydrophilic polyvinylidene fluoride hollow fiber membrane and a preparation method thereof, by designing a high-quality casting solution ratio, changing the performance of the membrane surface from the material level, improving the hydrophilicity of the membrane surface, effectively blocking the adsorption and deposition of organic matter on the membrane surface, preventing the growth and enrichment of microorganisms on the membrane surface, and ultimately improving the organic matter pollution resistance and service life of the membrane surface.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions: A hydrophilic polyvinylidene fluoride hollow fiber membrane comprises the following raw materials in terms of weight ratio: polyvinylidene fluoride 16-30%, polyvinylpyrrolidone 2-10%, catalyst 0.1-0.5%, ligand 0.4-2.0%, monomer 5-10%, and solvent 50-76%; wherein the weight ratio of polyvinylidene fluoride: catalyst: ligand is 100: 0.1-1: 0.4-4, which can ensure the synergistic effect of each component, lay the foundation for subsequent improvement of the membrane surface performance and realization of multiple anti-pollution effects.

[0008] Preferably, the catalyst is a metal halide, and further preferably one or more of cuprous chloride, cupric chloride, cuprous bromide, cupric bromide, ferric chloride and ferrous chloride. The metal halide catalyst can efficiently initiate the grafting reaction of the monomer and polyvinylidene fluoride, ensuring that the hydrophilic groups are stably combined on the molecular chain of the membrane material, and avoiding the decay of hydrophilicity over time.

[0009] Preferably, the ligand is one or both of 2,2'-bipyridine and 4,4'-bipyridine. The ligand can form a stable coordination system with the catalyst to adjust the reactivity, ensuring uniform reaction of each component in the casting solution, avoiding differences in membrane surface performance caused by uneven reaction, and affecting the effects of organic matter blocking and microbial inhibition.

[0010] Preferably, the monomer is one or more of methyl methacrylate, acrylamide, tert-butyl methacrylate, polyethylene glycol methacrylate, allyl polyethylene glycol, and vinylpyridine. After polymerization, such hydrophilic monomers can introduce a large number of hydrophilic groups (such as hydroxyl groups, amide groups, and ether bonds) on the polyvinylidene fluoride molecular chain, fundamentally changing the chemical properties of the membrane surface, on the one hand, improving the hydrophilicity to increase the water flux, and on the other hand, blocking the adsorption of organic matter through the steric hindrance and charge repulsion of the hydrophilic groups, and destroying the growth environment of microorganisms to inhibit their enrichment on the membrane surface.

[0011] Preferably, the solvent is one or more of tetrahydrofuran, N, N-dimethylacetamide, N, N-dimethylformamide and N-methylpyrrolidone. Such solvents have excellent solubility for polyvinylidene fluoride and other auxiliary materials, ensuring that the casting solution is uniform and stable, avoiding the formation of pore defects on the membrane surface due to uneven distribution of components, thereby preventing the attachment of organic matter and microorganisms through defects and ensuring the anti-pollution performance of the membrane.

[0012] A method for preparing the above-mentioned hydrophilic polyvinylidene fluoride hollow fiber membrane, comprising the following steps: S1: Casting solution preparation: polyvinylidene fluoride, polyvinylpyrrolidone, catalyst, ligand, monomer, solvent are added into the liquid tank in order, stirred and dissolved uniformly under nitrogen protection at 45-60°C, the stirring speed is controlled at 50-120 rpm, and the stirring reaction is continued for 24-48 hours to obtain a uniform and stable casting solution. Nitrogen protection can avoid the interference of oxygen with the polymerization reaction, ensuring that the monomer is fully grafted with polyvinylidene fluoride; specific temperature, stirring speed and reaction time can ensure that each component is completely dissolved and fully reacted, further optimizing the effect of the casting solution ratio, providing protection for subsequent membrane performance improvement.

[0013] S2: Photo-induced polymerization modification: the casting solution obtained in S1 is injected into a quartz light reaction pipeline, and the light source is turned on, and the polymerization is continuously irradiated for 60-120 minutes under a power of 1000-3000 W and a wavelength of 200-400 nm. This light condition can efficiently induce the graft polymerization reaction of the monomer and polyvinylidene fluoride in the casting solution, making the hydrophilic group firmly combined with the molecular chain of the membrane material, ensuring the persistent stability of the membrane surface performance, and avoiding the decline of the anti-pollution ability due to the shedding of the hydrophilic group.

[0014] S3: Spinning and coagulation molding: the casting solution treated in S2 is extruded through the spinneret and the core liquid in the center tube hole of the spinneret, the extrusion speed is controlled at 2-30 m / min, and then enters the coagulation liquid with a temperature of 20-50°C, and is solidified after phase separation to obtain a hollow fiber membrane. The specific extrusion speed and coagulation temperature can ensure the uniformity of the pore structure of the membrane, avoiding the problems of large pores or excessively thick dense layers - uniform pore structure not only ensures water flux, but also reduces the attachment sites of organic matter and microorganisms, further enhancing the anti-pollution effect of the membrane.

[0015] Preferably, the core liquid and the coagulation liquid are water, or a mixture of water and ethanol, isopropyl alcohol, ethylene glycol or a surfactant, and the weight percentage content of water in the core liquid and the coagulation liquid is not less than 60%. The core liquid and the coagulation liquid with high water content can form a synergistic effect with the hydrophilic group of the membrane material, further optimizing the hydrophilic properties of the membrane surface during membrane molding, while avoiding the negative impact of the residues of other components in the coagulation liquid on the performance of the membrane, ensuring that the membrane can stably play the role of "blocking organic matter and inhibiting microorganisms".

[0016] Advantages of the present application: 1. Significant performance improvement: By designing a high-quality casting solution ratio, the hydrophilic modification of the polyvinylidene fluoride membrane is realized under the action of light initiation, which fundamentally changes the performance of the membrane surface. Not only does it greatly improve the hydrophilicity of the membrane surface and increase the water flux (up to 600-2400 L / m²・h・0.1 MPa), but it also effectively prevents the adsorption and deposition of organic matter on the membrane surface and prevents the growth and enrichment of microorganisms on the membrane surface, solving the core pain point of traditional PVDF membrane pollution; 2. Improved anti-pollution ability and service life: The stable hydrophilic modification layer enables the membrane to maintain excellent anti-pollution performance during long-term use, with a flux decay rate of less than 15% after 30 days of continuous use, a reduction of more than 60% in organic matter deposition, and a reduction of more than 80% in microbial bacteria count, significantly extending the service life of the membrane and reducing the replacement cost in actual application; 3. Strong controllability of preparation process: The reaction conditions of each step (such as temperature, stirring speed, light parameters, coagulation temperature, etc.) are clear and easy to control, the casting solution ratio is stable, and large-scale production can be realized. The preparation process does not require complex equipment and has high compatibility with existing spinning production lines, making it easy to industrialize and promote; 4. Wide application range: The modified membrane has excellent hydrophilicity, anti-organic pollution ability, and anti-microbial enrichment ability, and can be applied to various scenes such as drinking water purification, medical wastewater treatment, and protein separation. It is especially suitable for water treatment fields with complex water quality and easy microbial growth, and has a wide application prospect.

[0017] It is to be understood that both the foregoing general description and the following detailed description are exemplary and intended to provide further explanation of the claimed technology. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Composition diagram of the hydrophilic polyvinylidene fluoride hollow fiber membrane according to the embodiment of the present application; Figure 2 Flowchart of the preparation method of the hydrophilic polyvinylidene fluoride hollow fiber membrane according to the embodiment of the present application. DETAILED DESCRIPTION

[0019] The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, which further illustrate the present application.

[0020] As Figure 1As shown, the present invention provides a hydrophilic polyvinylidene fluoride hollow fiber membrane, comprising the following raw materials by weight: 16-30% polyvinylidene fluoride, 2-10% polyvinylpyrrolidone, 0.1-0.5% catalyst, 0.4-2.0% ligand, 5-10% monomer, and 50-76% solvent; wherein the weight ratio of polyvinylidene fluoride:catalyst:ligand is 100:0.1-1:0.4-4, which ensures the synergistic effect of each component and lays the foundation for subsequent improvement of membrane surface properties and achievement of multiple antifouling effects.

[0021] Preferably, the catalyst is a metal halide, more preferably one or more of cuprous chloride, cupric chloride, cuprous bromide, cupric bromide, ferric chloride, and ferrous chloride. Metal halide catalysts can efficiently initiate the grafting reaction between monomers and polyvinylidene fluoride, ensuring that hydrophilic groups are stably bound to the molecular chain of the membrane material and preventing the hydrophilicity from decreasing over time.

[0022] Preferably, the ligand is one or both of 2,2'-bipyridine and 4,4'-bipyridine. The ligand can form a stable coordination system with the catalyst, regulate the reaction activity, ensure that the components in the casting solution react uniformly, and avoid differences in membrane surface properties due to uneven reaction, which would affect the organic matter barrier and microbial inhibition effects.

[0023] Preferably, the monomer is one or more selected from methyl methacrylate, acrylamide, tert-butyl methacrylate, polyethylene glycol methacrylate, allyl polyethylene glycol, and vinylpyridine. After polymerization, these hydrophilic monomers can introduce a large number of hydrophilic groups (such as hydroxyl groups, amide groups, ether bonds, etc.) onto the polyvinylidene fluoride molecular chain, fundamentally changing the chemical properties of the membrane surface. On the one hand, this enhances hydrophilicity to increase water flux; on the other hand, through the steric hindrance and charge repulsion of the hydrophilic groups, it blocks the adsorption of organic matter and disrupts the growth environment of microorganisms, inhibiting their accumulation on the membrane surface.

[0024] Preferably, the solvent is one or more of tetrahydrofuran, N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone. These solvents exhibit excellent solubility for polyvinylidene fluoride and other auxiliary materials, ensuring a uniform and stable casting solution and preventing pore defects on the membrane surface due to uneven component dispersion. This, in turn, prevents organic matter and microorganisms from adhering through these defects, thus guaranteeing the membrane's antifouling performance.

[0025] like Figure 2 As shown, the present invention also provides a method for preparing the above-mentioned hydrophilic polyvinylidene fluoride hollow fiber membrane, comprising the following steps: S1: Casting solution preparation: polyvinylidene fluoride, polyvinylpyrrolidone, catalyst, ligand, monomer, solvent are added into the liquid tank in order, and stirred and dissolved uniformly under nitrogen protection at 45-60°C, the stirring speed is controlled at 50-120 rpm, and the stirring reaction is continued for 24-48 hours to obtain a uniform and stable casting solution. Nitrogen protection can avoid oxygen interference with the polymerization reaction, ensuring that the monomer is fully grafted with polyvinylidene fluoride; the specific temperature, stirring speed and reaction time can ensure that all components are completely dissolved and fully reacted, further optimizing the ratio of the casting solution and providing protection for subsequent membrane performance improvement.

[0026] S2: Photo-induced polymerization modification: the casting solution obtained in S1 is injected into a quartz light reaction pipeline, and the light source is turned on, and the monomer and polyvinylidene fluoride in the casting solution are continuously polymerized under light with a power of 1000-3000 W and a wavelength of 200-400 nm for 60-120 minutes. This light condition can efficiently initiate the grafting polymerization reaction of the monomer and polyvinylidene fluoride in the casting solution, making the hydrophilic group firmly combined on the molecular chain of the membrane material, ensuring the persistent stability of the membrane surface performance and avoiding the decline of the anti-pollution ability due to the shedding of the hydrophilic group.

[0027] S3: Spinning and coagulation molding: the casting solution treated in S2 is extruded through the spinneret and the core liquid in the center tube hole of the spinneret of the spinning machine at an extrusion speed of 2-30 m / min, and then enters the coagulation liquid with a temperature of 20-50°C, and is solidified after phase separation to obtain a hollow fiber membrane. The specific extrusion speed and coagulation temperature can ensure the uniformity of the pore structure of the membrane, avoiding the problems of large pores or too thick dense layers - uniform pore structure not only can ensure water flux, but also can reduce the attachment sites of organic matter and microorganisms, further enhancing the anti-pollution effect of the membrane.

[0028] Preferably, the core liquid and the coagulation liquid are water, or a mixture of water and ethanol, isopropyl alcohol, ethylene glycol or a surfactant, and the weight percentage content of water in the core liquid and the coagulation liquid is not less than 60%. The core liquid and the coagulation liquid with high water content can form a synergistic effect with the hydrophilic group of the membrane material, further optimizing the hydrophilic properties of the membrane surface during membrane molding, while avoiding the negative impact of the residues of other components in the coagulation liquid on the membrane performance, ensuring that the membrane can stably play the role of "blocking organic matter and inhibiting microorganisms".

[0029] The hydrophilic polyvinylidene fluoride hollow fiber membrane prepared by the application has a pore size of 0.01-0.4 microns, a pure water flux of 600-2400 L / m²·h·0.1 MPa, and a stable hydrophilic modified layer formed on the membrane surface through high-quality casting solution proportioning and precise preparation process control. On the one hand, the hydrophilic groups can greatly reduce the contact angle of the membrane surface with water, thereby improving the water flux. On the other hand, the hydrophilic layer can effectively prevent the adsorption and deposition of organic substances (such as humic acid and protein) in water on the membrane surface, and at the same time, by changing the microenvironment (such as charge characteristics and wettability) of the membrane surface, the attachment and growth conditions of microorganisms are destroyed, thereby preventing the growth and enrichment of microorganisms on the membrane surface. Experimental verification shows that after the hollow fiber membrane of the application is continuously used for 30 days, the membrane flux attenuation rate is less than 15%, which is much lower than that of the conventional unmodified polyvinylidene fluoride membrane (the flux attenuation rate is usually more than 40%), and the organic matter deposition amount on the membrane surface is reduced by more than 60%, and the number of microorganism colonies is reduced by more than 80%, thereby significantly improving the anti-organic pollution ability and service life of the membrane surface.

[0030] Example 1 A hydrophilic polyvinylidene fluoride hollow fiber membrane comprises the following raw materials by weight ratio: polyvinylidene fluoride 26%, polyvinylpyrrolidone 5%, copper chloride 0.2%, 2,2'-bipyridine 0.8%, polyethylene glycol methacrylate 10%, and N,N-dimethylacetamide 58%. The weight ratio of polyvinylidene fluoride, copper chloride and 2,2'-bipyridine is 100:0.77:3.08, which meets the proportioning requirements of 100:0.1-1:0.4-4.

[0031] The preparation method of the above-mentioned hydrophilic polyvinylidene fluoride hollow fiber membrane comprises the following steps: S1: polyvinylidene fluoride, polyvinylpyrrolidone, copper chloride, 2,2'-bipyridine, polyethylene glycol methacrylate and N,N-dimethylacetamide are sequentially added to a liquid tank under nitrogen protection, and stirred and dissolved uniformly at 60°C, with a stirring speed of 120 revolutions per minute, and the stirring reaction is continued for 24 hours to obtain a uniform casting solution; S2: the casting solution obtained in S1 is injected into a quartz light reaction pipeline, and a light source is turned on, and the polyethylene glycol methacrylate and polyvinylidene fluoride are fully grafted under continuous light polymerization at a power of 1500 W and a wavelength of 200 nm for 60 minutes to form a stable hydrophilic modified layer; S3: the casting solution treated in S2 is extruded through the spinneret of the spinning machine and the core liquid (water) in the center tube hole of the spinneret at an extrusion speed of 15 m / min, and then enters the coagulation liquid (water) at a temperature of 20°C, and is solidified through phase separation to obtain a hollow fiber membrane. The hollow fiber membrane prepared in this example has a pore size of 0.03 microns and a pure water flux of 650 L / m²·h·0.1 MPa.

[0032] The membrane surface water contact angle is reduced by 45% compared with the conventional unmodified PVDF membrane, after continuous use for 30 days, the membrane flux attenuation rate is 12%, the organic matter deposition amount on the membrane surface is reduced by 65%, the microbial colony number is reduced by 82%, the anti-organic pollution ability and the anti-microbial enrichment effect are significantly improved, and the service life is more than 1.5 times longer than that of the conventional membrane.

[0033] Example 2 A hydrophilic polyvinylidene fluoride hollow fiber membrane comprises the following raw materials by weight ratio: polyvinylidene fluoride 18%, polyvinylpyrrolidone 8%, copper chloride 0.1%, 2,2'-bipyridine 0.5%, polyethylene glycol methacrylate 5%, N,N-dimethylacetamide 68.4%; wherein the weight ratio of polyvinylidene fluoride: copper chloride: 2,2'-bipyridine is 100:0.56:2.78, which meets the ratio requirement of 100:0.1~1:0.4~4.

[0034] The preparation method of the above-mentioned hydrophilic polyvinylidene fluoride hollow fiber membrane comprises the following steps: S1: polyvinylidene fluoride, polyvinylpyrrolidone, copper chloride, 2,2'-bipyridine, polyethylene glycol methacrylate, and N,N-dimethylacetamide are sequentially added to a liquid tank, stirred and dissolved uniformly under nitrogen protection at 60°C, the stirring speed is 120 revolutions / min, and the stirring reaction is continued for 24 hours to obtain a uniform casting solution; S2: the casting solution obtained in S1 is injected into a quartz light reaction pipeline, and a light source is turned on, and the hydrophilic monomer is fully grafted under continuous light polymerization at a power of 2000W and a wavelength of 200nm for 60 minutes; S3: the casting solution treated in S2 is extruded through the spinneret of the spinning machine and the core liquid (a mixture of water and ethanol with a water content of 80%) in the center tube hole of the spinneret at an extrusion speed of 20m / min, and then enters a coagulation liquid (a mixture of water and ethanol with a water content of 80%) at a temperature of 20°C, and is solidified by phase separation to obtain a hollow fiber membrane. The hollow fiber membrane prepared in this example has a pore size of 0.2μm and a pure water flux of 2100L / m²・h・0.1MPa.

[0035] The membrane surface water contact angle is reduced by 45% compared with the conventional unmodified PVDF membrane, after continuous use for 30 days, the membrane flux attenuation rate is 12%, the organic matter deposition amount on the membrane surface is reduced by 65%, the microbial colony number is reduced by 82%, the anti-organic pollution ability and the anti-microbial enrichment effect are significantly improved, and the service life is more than 1.5 times longer than that of the conventional membrane.

[0036] Example 3 A hydrophilic polyvinylidene fluoride hollow fiber membrane, comprising the following raw materials by weight ratio: polyvinylidene fluoride 22%, polyvinylpyrrolidone 4%, copper chloride 0.22%, 2,2'-bipyridine 0.8%, polyethylene glycol methacrylate 8%, N,N-dimethylacetamide 64.98%; wherein the weight ratio of polyvinylidene fluoride: copper chloride: 2,2'-bipyridine is 100:1.0:3.64, meeting the ratio requirement of 100:0.1~1:0.4~4.

[0037] The preparation method of the above-mentioned hydrophilic polyvinylidene fluoride hollow fiber membrane, comprising the following steps: S1: polyvinylidene fluoride, polyvinylpyrrolidone, copper chloride, 2,2'-bipyridine, polyethylene glycol methacrylate, and N,N-dimethylacetamide are sequentially added to a liquid tank, stirred and dissolved uniformly under nitrogen protection at 60°C, the stirring speed is 120 revolutions / min, and the stirring reaction is continued for 24 hours to obtain a uniform casting solution; S2: the casting solution obtained in S1 is injected into a quartz light reaction pipeline, and a light source is turned on, and the continuous light polymerization is carried out at a power of 1000W and a wavelength of 395nm for 90 minutes to ensure the stability of the hydrophilic modified layer; S3: the casting solution treated by S2 is extruded through the spinneret of the spinning machine and the core liquid (a mixture of water and isopropyl alcohol with a water content of 70%) in the center tube hole of the spinneret at an extrusion speed of 18m / min, and then enters the coagulation liquid (a mixture of water and isopropyl alcohol with a water content of 70%) at a temperature of 20°C, and is solidified by phase separation to obtain a hollow fiber membrane. The hollow fiber membrane prepared in this example has a pore size of 0.1μm and a pure water flux of 1200L / m²・h・0.1MPa.

[0038] Detection shows that the water contact angle of the membrane surface is reduced by 48% compared with the traditional unmodified PVDF membrane, the membrane flux attenuation rate is 11% after continuous use for 30 days, the organic matter deposition amount on the membrane surface is reduced by 68%, and the number of microorganism bacteria is reduced by 83%, which has excellent water flux and anti-pollution performance, and can be applied to drinking water purification and medical wastewater treatment scenes.

[0039] Comparative example (traditional unmodified polyvinylidene fluoride hollow fiber membrane): Raw materials: polyvinylidene fluoride 28%, polyvinylpyrrolidone 6%, N,N-dimethylacetamide 66%; Preparation process: no catalyst, ligand and hydrophilic monomer, no photo polymerization step, only through conventional spinning and coagulation membrane preparation; Performance: pore size 0.03 μm, pure water flux 200 L / m²・h・0.1 MPa, after 30 days of continuous use, the membrane flux attenuation rate is 45%, the organic matter deposition amount on the membrane surface is high, the number of microorganism bacteria is more than 5 times of that of the example 1, and the service life is only 40% of that of the example 1.

[0040] It can be known from the comparison that, by the high-quality casting solution proportioning and the modification process, the hydrophilicity, the organic matter pollution resistance and the microbial enrichment resistance of the polyvinylidene fluoride hollow fiber membrane are significantly improved, the water flux and the service life of the membrane are greatly improved, and the technical advantages of the application are fully embodied.

[0041] It should be noted that in the present specification, the terms "comprising", "including" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the elements defined by the statement "including" do not exclude the presence of other identical elements in the process, method, article or equipment including the elements.

[0042] Although the content of the present application has been described in detail by the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present application. After reading the above content, various modifications and alternatives of the present application will be apparent to those skilled in the art. Therefore, the protection scope of the present application should be defined by the appended claims.

Claims

1. A hydrophilic polyvinylidene fluoride hollow fiber membrane, characterized by, Consists of the following raw materials in percentage by weight: Polyvinylidene fluoride 17~29%, polyvinylpyrrolidone 3~9%, composite catalyst 0.12~0.48%, composite ligand 0.5~1.9%, hydrophilic functional monomer 5.5~9.5%, solvent 52~73%; The composite catalyst is a compound of cuprous chloride and ferric chloride in a weight ratio of 1:0.2~0.5, the composite ligand is a compound of 2,2'-bipyridine and 4,4'-bipyridine in a weight ratio of 1:0.3~0.8, and the weight ratio of polyvinylidene fluoride, composite catalyst and composite ligand is 100:0.15~0.9:0.55~3.8; The membrane can improve the surface hydrophilicity through the synergistic effect of raw material components, realize more than 60% reduction of organic matter adsorption capacity, more than 80% reduction of microbial enrichment capacity, and flux attenuation rate ≤15% after continuous use for 30 days.

2. The hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1, wherein, The hydrophilic functional monomer is a compound of acrylamide and polyethylene glycol methacrylate in a weight ratio of 1:0.4~0.7, the purity of acrylamide is ≥99.5%, and the number average molecular weight of polyethylene glycol methacrylate is 500~1000.

3. The hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1, wherein, The solvent is a compound of N,N-dimethylacetamide and N-methylpyrrolidone in a weight ratio of 1:0.5~0.9, and the water content in the solvent is ≤0.1%.

4. The hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1, wherein, The pore size of the membrane is 0.02~0.38μm, the pure water flux is 650~2300L / m²・h・0.1MPa, the tensile strength is ≥1.7MPa, and the water contact angle is ≤42°.

5. A method for producing the hydrophilic polyvinylidene fluoride hollow fiber membrane according to any one of claims 1 to 4, characterized by, Comprising the following steps: S1: polyvinylpyrrolidone and solvent are added to the feed liquid kettle, stirred at 80~100r / min for 15~25min at 35~45℃ until completely dissolved, then polyvinylidene fluoride is added, heated to 50~58℃, continue to stir for 3~5h, then add composite catalyst, composite ligand, hydrophilic functional monomer, stir at 60~110r / min for 26~45h under nitrogen protection, get uniform transparent casting solution; S2: the casting solution is incubated at 40~48℃ for 8~12h, then injected into the quartz reaction tube with built-in ultraviolet lamp, the ultraviolet lamp is turned on, the power is controlled at 1200~2800W, the wavelength is 220~380nm, continuous light polymerization for 70~110min, during which the nitrogen atmosphere in the tube is maintained; S3: the casting solution treated by S2 is extruded through the spinneret of the spinning machine, at the same time the core liquid is injected from the center tube hole of the spinneret, the extrusion speed is 5~28m / min, after extrusion, it enters the coagulation liquid at 25~48℃, and is solidified by phase separation for 10~15min, then dried by hot air at 30~40℃ for 2~3h, to obtain the hydrophilic polyvinylidene fluoride hollow fiber membrane.

6. The production method according to claim 5, wherein The core liquid in S3 is a mixture of water and ethylene glycol in a weight ratio of 1:0.1~0.25, the coagulation liquid is a mixture of water and isopropanol in a weight ratio of 1:0.08~0.15, and the temperature fluctuation range of the core liquid and the coagulation liquid is less than or equal to ±2℃.

7. The preparation method according to claim 5, characterized in that, The length of the quartz reaction tube in S2 is 220-380 mm, the inner diameter is 22-48 mm, the distance between the ultraviolet lamp tube and the inner wall of the tube is 8-12 mm, and the temperature in the tube during illumination is controlled at 30-35℃.

8. The preparation method according to claim 5, characterized in that, The air speed of the hot air drying in S3 is 0.3-0.8 m / s, and the temperature is controlled in sections during drying: first, the temperature is increased to 30℃ at a rate of 3℃ / min, and then the temperature is kept constant for 30 minutes; then, the temperature is increased to 40℃ at a rate of 2℃ / min, and then the temperature is kept constant for 1-1.5 hours.

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