PVDF ultrafiltration membrane, preparation method and application thereof

Abstract

The present application relates to the technical field of membrane separation, in particular to a PVDF ultrafiltration membrane, a preparation method and application thereof, wherein the PVDF is in-situ modified by copolymerization of vinylpyridine, hydroxy acrylate and vinylidene fluoride, so as to improve the hydrophilicity, heat resistance and flexibility of the PVDF; the dispersibility of titanium oxide and the compatibility with the modified PVDF are improved by multi-component modification of the titanium oxide; and then the modified PVDF, the modified titanium oxide and a pore-forming agent are used as raw materials to prepare the ultrafiltration membrane, so that the prepared PVDF ultrafiltration membrane has a high water treatment flux, and the mechanical property, anti-fouling property and stability of the PVDF ultrafiltration membrane are improved; the prepared PVDF ultrafiltration membrane has a good water treatment effect and a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a PVDF ultrafiltration membrane, its preparation method, and its application. Background Technology

[0002] Ultrafiltration is a pressure-driven membrane separation technology that falls between microfiltration and nanofiltration. Existing ultrafiltration membranes are typically made of various polymer materials, such as cellulose acetate, cellulose acetate esters, polyethylene, polysulfone, polyamide, aromatic polymers, and fluoropolymers.

[0003] Among fluoropolymer materials, PVDF ultrafiltration membranes have high removal rates for organic matter, bacteria, and viruses, and are widely used in water purification, wastewater treatment, and biomedicine. However, the hydrophobicity of PVDF itself makes it susceptible to membrane fouling during use, resulting in poor antifouling performance, which greatly reduces the membrane's lifespan and separation efficiency.

[0004] To address the issue of poor stain resistance, some studies have employed in-situ modification of PVDF, which has shown significant effectiveness in improving stain resistance. However, the introduction of other groups or segments into PVDF can disrupt its crystal structure, thereby affecting its chemical stability, mechanical properties, and heat resistance. Summary of the Invention

[0005] The purpose of this invention is to provide a PVDF ultrafiltration membrane, its preparation method, and its application, in order to solve the problems mentioned in the background art regarding the insufficient antifouling properties, thermal stability, and mechanical properties of PVDF ultrafiltration membranes. The PVDF ultrafiltration membrane provided has better antifouling properties, thermal stability, and mechanical properties.

[0006] In a first aspect, a method for preparing a PVDF ultrafiltration membrane is provided, comprising the following preparation steps:

[0007] Step 1: Preparation of modified PVDF: Vinylpyridine, hydroxy acrylate and vinylidene fluoride are mixed to obtain a mixed monomer. An initiator is added to the mixed monomer and a polymerization reaction is carried out under heating conditions.

[0008] Step 2, Preparation of modified titanium dioxide: Titanium dioxide powder is dispersed in an organic solvent to obtain a suspension. A silane coupling agent is added to the suspension and stirred under heating conditions. Then, silicone oil containing epoxy groups is added and stirred. Finally, a rare earth carboxylic acid complex is added and stirred.

[0009] Step 3: Preparation of casting solution: Mix modified PVDF and modified titanium dioxide and heat to react, then add pore-forming agent and organic solvent and mix well, then perform intensive mixing;

[0010] Step 4, extrusion film formation: The casting solution is extruded under pressure and heating conditions, and then immersed in the gel solution to separate the phases and form a film, thus obtaining the final product.

[0011] In some embodiments, in the mixed monomers described in step 1, the mass fraction of vinylpyridine is 3%-15%, the mass fraction of hydroxyacrylate is 5%-20%, and the balance is the vinylidene fluoride.

[0012] In some embodiments, the amount of initiator added in step 1 is 0.5%-2% of the total mass of the mixed monomers.

[0013] In some embodiments, the polymerization reaction in step 1 is carried out at a temperature of 60-80°C for 6-12 hours.

[0014] In some embodiments, the amount of silane coupling agent added in step 2 is 3%-12% of the mass of titanium oxide.

[0015] In some embodiments, the reaction temperature after adding the silane coupling agent in step 2 is 30-80°C, and the reaction time is 2-6 hours.

[0016] In some embodiments, the amount of epoxy-containing silicone oil added in step 2 is 4%-14% of the mass of titanium oxide.

[0017] In some embodiments, the reaction time after adding epoxy-containing silicone oil in step 2 is 2-6 hours.

[0018] In some embodiments, the amount of rare earth carboxylic acid complex added in step 2 is 0.1%-0.5% of the mass of titanium oxide.

[0019] In some embodiments, the reaction time after adding the rare earth carboxylic acid complex in step 2 is 1-3 hours.

[0020] In some embodiments, the rare earth carboxylic acid complex in step 2 is a rare earth citrate complex.

[0021] In some embodiments, the mass ratio of modified titanium oxide to modified PVDF in step 3 is 1:5-1:20.

[0022] In some embodiments, the pore-forming agent in step 3 is selected from at least one of PVP, PEG, NaCl, LiCl, methanol, ethanol, acetone and butanone.

[0023] In some embodiments, the pressurization and heating conditions in step 4 are 8-15 atm and 160-200°C.

[0024] Secondly, a PVDF ultrafiltration membrane prepared by the above preparation method is provided.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) In-situ modification of PVDF was achieved by copolymerizing vinylpyridine and hydroxy acrylate with vinylidene fluoride. Flexible, hydrophilic acrylate segments were introduced into PVDF, which enhanced the toughness and hydrophilicity of PVDF. Using it to prepare ultrafiltration membranes is beneficial to improving the antifouling performance and mechanical properties of ultrafiltration membranes. Rigid pyridine heterocycles were introduced into PVDF, which is beneficial to adjusting the hydrophilicity-reactivity balance and initially improving the problem of decreased mechanical strength caused by the introduction of acrylate segments.

[0027] (2) By modifying titanium dioxide with multiple components and adding silicone oil containing epoxy groups, the hydrophilicity of titanium dioxide and its compatibility with modified PVDF are improved, so that the prepared PVDF ultrafiltration membrane has good consistency and avoids the problem of uneven dispersion and mechanical properties caused by directly adding titanium dioxide powder.

[0028] (3) Adding epoxy-containing silicone oil to modify the epoxy groups introduced on the obtained modified titanium dioxide facilitates the reaction with the active hydroxyl groups introduced in the modified PVDF, further improving the uniformity of the mixture and increasing crosslinking, which is beneficial to further improving the structural stability, heat resistance and mechanical properties of the prepared ultrafiltration membrane.

[0029] (4) Adding rare earth carboxylic acid complexes helps to build a more stable microstructure inside the membrane, enhances the binding force between the components, and improves the heat resistance, stability and mechanical properties of the prepared ultrafiltration membrane. At the same time, due to the catalytic effect of rare earth carboxylic acid complexes, in combination with the catalytic effect of titanium dioxide, the antifouling property of the prepared ultrafiltration membrane is further improved. Attached Figure Description

[0030] Figure 1 This is a cross-sectional view of the ultrafiltration membrane prepared in Example 1 of the present invention;

[0031] Figure 2 This is a SEM image of the surface of the ultrafiltration membrane prepared in Example 1 of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In a first aspect, a method for preparing a PVDF ultrafiltration membrane is provided, comprising the following preparation steps:

[0034] Step 1: Preparation of modified PVDF: Vinylpyridine, hydroxy acrylate, and vinylidene fluoride are mixed to obtain a mixed monomer. An initiator is added to the mixed monomer and a polymerization reaction is carried out under heating conditions. By copolymerizing vinylpyridine and hydroxy acrylate with vinylidene fluoride, PVDF is modified in situ. The flexible, hydrophilic acrylate segments, active hydroxyl groups, and rigid pyridine heterocycles introduced into PVDF not only increase the water treatment flux but also enhance the toughness, hydrophilicity, and mechanical strength of PVDF. Using it to prepare ultrafiltration membranes is beneficial for improving antifouling performance and mechanical strength.

[0035] Step 2: Preparation of modified titanium dioxide: Titanium dioxide powder is dispersed in an organic solvent to obtain a suspension. A silane coupling agent is added to the suspension and stirred under heating conditions. Then, epoxy-containing silicone oil is added and stirred. Finally, rare earth carboxylic acid complexes are added and stirred. Through multi-component modification of titanium dioxide, the addition of epoxy-containing silicone oil improves the hydrophilicity, antifouling properties, and compatibility with modified PVDF, and introduces active epoxy groups. The addition of rare earth carboxylic acid complexes helps to build a more stable microstructure inside the membrane, enhances the binding force between components, and increases mechanical strength and heat resistance. This is beneficial for improving the antifouling properties, consistency, stability, and mechanical properties of the ultrafiltration membrane prepared using it.

[0036] Step 3: Preparation of casting solution: The modified PVDF and modified titanium dioxide are mixed and heated to react. Then, a pore-forming agent and organic solvent are added and mixed. Then, the mixture is kneaded. The hydroxyl groups introduced on the modified PVDF and the epoxy groups introduced on the modified titanium dioxide react under heating conditions, which increases cross-linking and further improves the mechanical properties and stability of the ultrafiltration membrane.

[0037] Step 4, extrusion film formation: The casting solution is extruded under pressure and heating conditions, and then immersed in the gel solution to separate the phases and form a film, thus obtaining the final product.

[0038] In the preparation process of the PVDF ultrafiltration membrane of this invention, the added modified PVDF and modified titanium dioxide work together to prepare a PVDF ultrafiltration membrane that not only has a large water treatment flux, but also has good antifouling properties, mechanical properties and stability.

[0039] In some embodiments, in the mixed monomers described in step 1, the mass percentage of vinylpyridine is 3%-15%, and the mass percentage of hydroxyacrylate is 5%-20%. The amount of hydroxyacrylate is controlled within this range; if the amount added is too low, insufficient polar groups are introduced, and the improvement in hydrophilicity is not significant; if the amount added is too high, it may affect the crystallization and mechanical properties of PVDF. Similarly, the amount of vinylpyridine is controlled within this range; if too little is added, it is difficult to regulate surface charge and improve stability; if too much is added, it may lead to excessive hydrophilicity of the membrane, affecting retention performance.

[0040] In addition, hydroxy acrylate is a flexible segment, and the introduction of hydroxy acrylate gives the ultrafiltration membrane good flexibility. However, the introduction will destroy the crystallization properties of PVDF, resulting in insufficient strength and poor mechanical properties. The pyridine group in vinylpyridine is rigid, and its introduction can improve the strength. At the same time, it has a certain degree of torsional bending, so the flexibility will not be greatly affected.

[0041] In some embodiments, the amount of initiator added in step 1 is 0.5%-2% of the total mass of the mixed monomers, for example, 0.5%, 0.6%, 0.7%, 0.9%, 1.2%, 1.5%, 1.8%, or 2%.

[0042] In some embodiments, the polymerization reaction in step 1 is carried out at a temperature of 60-80°C for 6-12 hours, for example, at temperatures of 60°C, 65°C, 70°C, 75°C, or 80°C; and for example, at times of 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 10 hours, 11 hours, or 12 hours.

[0043] In some embodiments, the amount of silane coupling agent added in step 2 is 3%-12% of the mass of titanium dioxide, for example, 3%, 3.5%, 4%, 5%, 6%, 6.5%, 7%, 7.5%, 8%, 10%, or 12%. The silane coupling agent is selected from those whose molecular structure contains both inorganic and organic functional groups. Examples include KH-570, KH-560, and vinyltrimethoxysilane. The silane coupling agent can act as a bridge to chemically connect epoxy-containing silicone oil and titanium dioxide particles and coat the surface of the titanium dioxide particles, thereby improving the dispersibility of titanium dioxide and its compatibility with modified PVDF.

[0044] In some embodiments, the reaction temperature after adding the silane coupling agent in step 2 is 30-80°C, and the reaction time is 2-6 hours. For example, the temperature is 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C; and the time is 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours.

[0045] In some embodiments, the amount of epoxy-containing silicone oil added in step 2 is 4%-14% of the mass of titanium dioxide, for example, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, or 14%. Controlling the addition amount within this range is crucial; excessive addition will affect heat resistance, while insufficient addition will affect the modification effect and prevent adequate improvement in antifouling performance.

[0046] In some embodiments, the reaction time after adding the epoxy-containing silicone oil in step 2 is 2-5 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours.

[0047] In some embodiments, the epoxy-containing silicone oil in step 2 serves to improve antifouling performance and introduce active epoxy groups to facilitate subsequent reactions. Examples of epoxy-containing silicone oils include terminal epoxy silicone oils and single-terminal epoxy silicone oils. The structural formula of the terminal epoxy silicone oil is: ; The structural formula of single-ended epoxy silicone oil is: .

[0048] In some embodiments, the amount of rare earth carboxylic acid complex added in step 2 is 0.1%-0.5% of the mass of titanium dioxide, for example, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%. The rare earth carboxylic acid complex can interact with titanium dioxide and modified PVDF to optimize the microstructure of the ultrafiltration membrane and improve its mechanical properties. When the amount added is too small, the microstructure of the ultrafiltration membrane cannot be effectively optimized, resulting in limited improvement in mechanical strength and stability. In practical use, the membrane is more susceptible to damage from pressure and external impacts. When the amount added is too large, in addition to higher costs, it is difficult to disperse uniformly in the reaction system, easily forming agglomerates. These agglomerates not only affect the performance of the modified titanium dioxide but also cause uneven dispersion when blended with modified PVDF, leading to local defects in the ultrafiltration membrane, such as uneven pore size distribution. This reduces the membrane's retention performance, causing some pollutants that should be retained to permeate through the membrane, and also affects the water flux.

[0049] In some embodiments, the reaction time after adding the rare earth carboxylic acid complex in step 2 is 1-3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours.

[0050] In some embodiments, the rare earth carboxylic acid complex in step 2 is a rare earth citrate complex, which is at least one of cerium citrate, yttrium citrate, and lanthanum citrate. The rare earth citrate complex can interact with titanium dioxide, which is more conducive to enhancing the interfacial bonding between the inorganic and organic phases.

[0051] In some embodiments, the rare earth citrate complex is preferably cerium citrate. Cerium citrate can also be used as a functional additive for ultrafiltration membranes, endowing them with the ability to photocatalytically decompose organic pollutants. Under light irradiation, cerium citrate can generate free radicals with strong oxidizing properties, decomposing organic pollutants adsorbed on the membrane surface into carbon dioxide and water, slowing down membrane fouling and extending the membrane's lifespan.

[0052] In some embodiments, the mass ratio of modified titanium oxide to modified PVDF in step 3 is 1:5-1:20, for example, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:12, 1:14, 1:16, 1:18, or 1:20.

[0053] In some embodiments, the pressurization and heating conditions described in step 4 include a pressure of 8-15 atm and a temperature of 160-200°C, for example, pressures of 8 atm, 9 atm, 10 atm, 11 atm, 12 atm, 13 atm, 14 atm, and 15 atm; and temperatures of 160°C, 165°C, 170°C, 175°C, 180°C, 190°C, and 200°C.

[0054] Secondly, a PVDF ultrafiltration membrane prepared by the above preparation method is provided.

[0055] Thirdly, an application of the above-mentioned PVDF ultrafiltration membrane in water treatment is provided.

[0056] Example

[0057] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0058] The structural formulas of the epoxy-containing silicone oils used in Examples 1-4 and Comparative Examples 1-7 are as follows: .

[0059] The structural formula of the epoxy-containing silicone oil used in Example 5 is:

[0060]

[0061] Example 1

[0062] Preparation of PVDF ultrafiltration membrane:

[0063] Step 1: Preparation of modified PVDF: 2-vinylpyridine, 2-hydroxyethyl methacrylate and vinylidene fluoride are mixed to obtain a mixed monomer, wherein the mass fraction of 2-vinylpyridine in the mixed monomer is 5% and the mass fraction of 2-hydroxyethyl methacrylate is 12%. Benzoyl peroxide of 1% of the total mass of the mixed monomer is added to the mixed monomer and the polymerization reaction is carried out at 60°C for 8 hours.

[0064] Step 2: Preparation of modified titanium dioxide: Titanium dioxide powder was dispersed in N,N-dimethylformamide to obtain a suspension with a titanium dioxide powder content of 10% by mass. 3% (by mass) of KH-570 (by mass) of titanium dioxide was added to the suspension, and the mixture was stirred at 80℃ for 3 hours. Maintaining the solution temperature, 5% (by mass) of epoxy-containing silicone oil (by mass) of titanium dioxide was added, and the mixture was stirred for 5 hours. Then, 0.4% (by mass) of cerium citrate (by mass) of titanium dioxide was added, and the mixture was stirred for another 1 hour. The mixture was then filtered and washed with water to obtain modified titanium dioxide.

[0065] Step 3: Preparation of casting solution: Mix the modified titanium dioxide and modified PVDF at a mass ratio of 1:15 and react at 100°C for 4 hours. Then add 40% PVP of the modified PVDF and a dimethylacetamide solution to make the modified PVDF content 20% after the addition of the solution. Mix well and then internally mix at 80°C for 6 hours in an internal mixer.

[0066] Step 4, extrusion film formation: The casting solution is extruded at a pressure of 10 atm and 160°C, and then soaked in a 20% (v / v) ethanol-water solution at 40°C for 24 hours to undergo phase inversion, thus obtaining the film.

[0067] Example 2

[0068] Preparation of PVDF ultrafiltration membrane:

[0069] Step 1: Preparation of modified PVDF: 4-vinylpyridine, 2-hydroxyethyl acrylate and vinylidene fluoride are mixed to obtain a mixed monomer, wherein the mass fraction of 4-vinylpyridine in the mixed monomer is 15% and the mass fraction of 2-hydroxyethyl acrylate is 5%. 0.5% of azobisisobutyronitrile by mass of the total mass of the mixed monomer is added to the mixed monomer and the polymerization reaction is carried out at 80℃ for 12h.

[0070] Step 2: Preparation of modified titanium dioxide: Titanium dioxide powder was dispersed in N,N-dimethylformamide to obtain a suspension with a titanium dioxide powder content of 10% by mass. 6% KH-560 (by mass of titanium dioxide) was added to the suspension, and the mixture was stirred at 80℃ for 6 hours. Maintaining the solution temperature, 10% epoxy-containing silicone oil (by mass of titanium dioxide) was added, and the mixture was stirred for 2 hours. Then, 0.1% yttrium citrate (by mass of titanium dioxide) was added, and the mixture was stirred for another 2 hours. The mixture was then filtered and washed with water to obtain modified titanium dioxide.

[0071] Step 3: Preparation of casting solution: Mix the modified titanium dioxide and modified PVDF at a mass ratio of 1:10 and react at 80°C for 8 hours. Then add PEG (50% by mass of modified PVDF) and dimethylacetamide (20% by mass of modified PVDF after adding the solution), mix well, and then internally mix at 80°C for 12 hours.

[0072] Step 4, extrusion film formation: The casting solution is extruded at a pressure of 15 atm and 200°C, and then soaked in a 20% (v / v) ethanol-water solution at 40°C for 24 hours to undergo phase inversion, thus obtaining the film.

[0073] Example 3

[0074] Preparation of PVDF ultrafiltration membrane:

[0075] Step 1: Preparation of modified PVDF: 2-vinylpyridine, hydroxypropyl acrylate and vinylidene fluoride are mixed to obtain a mixed monomer, wherein the mass fraction of 2-vinylpyridine in the mixed monomer is 10% and the mass fraction of hydroxypropyl acrylate is 15%. Benzoyl peroxide of 2% of the total mass of the mixed monomer is added to the mixed monomer and the polymerization reaction is carried out at 60°C for 12 hours.

[0076] Step 2: Preparation of modified titanium dioxide: Titanium dioxide powder was dispersed in N,N-dimethylformamide to obtain a suspension with a titanium dioxide powder content of 10% by mass. 12% (by mass of titanium dioxide) of vinyltrimethoxysilane, a silane coupling agent, was added to the suspension and the mixture was stirred at 30°C for 2 hours. Maintaining the solution temperature, 14% (by mass of titanium dioxide) of epoxy-containing silicone oil was added and the mixture was stirred for 4 hours. Then, 0.3% (by mass of titanium dioxide) of lanthanum citrate was added and the mixture was stirred for another 3 hours. The mixture was then filtered and washed with water to obtain modified titanium dioxide.

[0077] Step 3: Preparation of casting solution: Mix the modified titanium dioxide and modified PVDF at a mass ratio of 1:5 and react at 120°C for 5 hours. Then add 40% PVP of the modified PVDF and dimethylacetamide to make the modified PVDF content 20% after the solution is added. Mix well and then internally mix at 80°C for 8 hours in an internal mixer.

[0078] Step 4, extrusion film formation: The casting solution is extruded at a pressure of 8 atm and 180°C, and then soaked in a 20% (v / v) ethanol-water solution at 40°C for 24 hours to undergo phase inversion, thus obtaining the film.

[0079] Example 4

[0080] Preparation of PVDF ultrafiltration membrane:

[0081] Step 1: Preparation of modified PVDF: 2-vinylpyridine, hydroxypropyl acrylate and vinylidene fluoride are mixed to obtain a mixed monomer, wherein the mass fraction of 2-vinylpyridine in the mixed monomer is 3% and the mass fraction of hydroxypropyl acrylate is 20%. Benzoyl peroxide of 1.6% of the total mass of the mixed monomer is added to the mixed monomer and the polymerization reaction is carried out at 80°C for 6 hours.

[0082] Step 2: Preparation of modified titanium dioxide: Titanium dioxide powder was dispersed in N,N-dimethylformamide to obtain a suspension with a titanium dioxide powder content of 10% by mass. 8% (by mass) of KH-560 (by mass) of titanium dioxide was added to the suspension, and the mixture was stirred at 30°C for 6 hours. Maintaining the solution temperature, 4% (by mass) of epoxy-containing silicone oil (by mass) of titanium dioxide was added, and the mixture was stirred for 3 hours. Then, 0.5% (by mass) of cerium citrate (by mass) of titanium dioxide was added, and the mixture was stirred for another 2 hours. The mixture was then filtered and washed with water to obtain modified titanium dioxide.

[0083] Step 3, Preparation of casting solution: Mix the above modified titanium dioxide and modified PVDF at a mass ratio of 1:20 and react at 100℃ for 5h. Then add 30% PEG of modified PVDF and dimethylacetamide to make the mass content of modified PVDF 20% after the solution is added. Mix well and then internally mix at 80℃ for 5h in an internal mixer.

[0084] Step 4, extrusion film formation: The casting solution is extruded at a pressure of 12 atm and 160°C, and then soaked in a 20% (v / v) ethanol-water solution at 40°C for 24 hours to undergo phase inversion, thus obtaining the film.

[0085] Example 5

[0086] Preparation of PVDF ultrafiltration membrane:

[0087] Step 1: Preparation of modified PVDF: 4-vinylpyridine, hydroxypropyl acrylate and vinylidene fluoride are mixed to obtain a mixed monomer, wherein the mass fraction of 4-vinylpyridine in the mixed monomer is 8% and the mass fraction of hydroxypropyl acrylate is 18%. 0.8% of benzoyl peroxide by mass of the total mass of the mixed monomer is added to the mixed monomer and the polymerization reaction is carried out at 70°C for 8 hours.

[0088] Step 2: Preparation of modified titanium dioxide: Titanium dioxide powder was dispersed in N,N-dimethylformamide to obtain a suspension with a titanium dioxide powder content of 10% by mass. 10% (by mass) of KH-560 (by mass) of titanium dioxide was added to the suspension, and the mixture was stirred at 50°C for 4 hours. Maintaining the solution temperature, 8% (by mass) of epoxy-containing silicone oil (by mass) of titanium dioxide was added, and the mixture was stirred for 2 hours. Then, 0.3% (by mass) of cerium citrate (by mass) of titanium dioxide was added, and the mixture was stirred for another 2 hours. The mixture was then filtered and washed with water to obtain modified titanium dioxide.

[0089] Step 3: Preparation of casting solution: Mix the modified titanium dioxide and modified PVDF at a mass ratio of 1:15 and react at 80°C for 5 hours. Then add 60% PVP of the modified PVDF and dimethylacetamide to make the modified PVDF content 20% after the solution is added. Mix well and then internally mix at 80°C for 8 hours in an internal mixer.

[0090] Step 4, extrusion film formation: The casting solution is extruded at a pressure of 8 atm and 160°C, and then soaked in a 20% (v / v) ethanol-water solution at 40°C for 24 hours to undergo phase inversion, thus obtaining the film.

[0091] Comparative Example 1

[0092] The difference between the preparation method of the PVDF ultrafiltration membrane in Comparative Example 1 and Example 1 is that vinylpyridine is not added in Comparative Example 1.

[0093] Comparative Example 2

[0094] The difference between the preparation method of the PVDF ultrafiltration membrane in Comparative Example 2 and that in Example 1 is that hydroxy acrylate is not added in Comparative Example 2.

[0095] Comparative Example 3

[0096] The difference between the preparation method of the PVDF ultrafiltration membrane in Comparative Example 3 and Example 1 is that 2-hydroxyethyl methacrylate is replaced with methyl methacrylate in Comparative Example 3.

[0097] Comparative Example 4

[0098] The difference between the preparation method of the PVDF ultrafiltration membrane in Comparative Example 4 and that in Example 1 is that no epoxy-containing silicone oil is added in Comparative Example 4.

[0099] Comparative Example 5

[0100] The difference between the preparation method of the PVDF ultrafiltration membrane in Comparative Example 5 and Example 1 is that the epoxy-containing silicone oil added in Example 1 is replaced with vinyl silicone oil in Comparative Example 5.

[0101] Comparative Example 6

[0102] The difference between the preparation method of the PVDF ultrafiltration membrane in Comparative Example 6 and that in Example 1 is that no rare earth carboxylic acid complex is added in Comparative Example 6.

[0103] Comparative Example 7

[0104] The difference between the preparation method of the PVDF ultrafiltration membrane in Comparative Example 7 and Example 1 is that cerium citrate is replaced with cerium oxide in Comparative Example 7.

[0105] Performance testing

[0106] (1) Membrane water purification performance test

[0107] Humic acid solutions with a concentration of 5 mg / L were prepared, and the filtration pressure was adjusted to 0.05 MPa. The PVDF ultrafiltration membranes prepared in the examples and comparative examples were subjected to filtration tests to determine the removal effect of the ultrafiltration membranes on humic acid. The flux of the ultrafiltration membrane was calculated by measuring the mass of the permeate and using F = J / A*t (where F is the membrane flux, J is the sampling volume, A is the effective membrane area, and t is the time).

[0108] (2) Organic pollutant removal performance test

[0109] The organic pollutant removal performance of the ultrafiltration membranes prepared by the examples and comparative examples was tested using an ultrafiltration cup. The tests were performed in three parallel trials, and the removal rates were recorded and averaged.

[0110] (3) Mechanical strength test

[0111] The mechanical strength of the ultrafiltration membrane was tested using a tensile test method to determine the mechanical strength of the ultrafiltration membrane, including the tensile strength and elongation at break of the ultrafiltration membrane; in addition, the thickness of the ultrafiltration membranes prepared in each embodiment and comparative example is 200 μm.

[0112] Testing instrument: W56 universal electronic testing machine.

[0113] Test conditions: The test temperature was room temperature (around 25℃), the tensile rate was 5 mm / min, and the tensile strength and elongation at break were the average of 5 test data.

[0114] (4) Anti-pollution ability test

[0115] The ultrafiltration membranes prepared in each embodiment and comparative example have a thickness of 200 μm.

[0116] The ultrafiltration membrane, used 10 times, was stirred and washed for 20 minutes, then backwashed for 10 minutes. A water purification membrane flux test was then conducted at 0.1 MPa. The formula for calculating the antifouling ability is as follows:

[0117] R = F2 / F1 × 100%; F1 is the membrane flux before filtration, mg / L; F2 is the membrane flux after filtration, mg / L; R is the antifouling ability of the ultrafiltration membrane, %.

[0118] (5) Chemical stability test

[0119] The ultrafiltration membranes prepared in the examples and comparative examples were immersed in 1 mol / L hydrochloric acid solution and 1 mol / L sodium hydroxide solution, respectively, for 24 hours at room temperature. After treatment, each ultrafiltration membrane was removed and repeatedly rinsed with deionized water to remove residual reagents on the surface. The change in water flux of the ultrafiltration membranes before and after treatment was measured.

[0120] (6) Test results

[0121] The test results are shown in Table 1.

[0122] Table 1

[0123]

[0124] Depend on Figure 1 and Figure 2 It can be seen that the ultrafiltration membrane prepared by this invention has a rich pore structure and good uniformity. Furthermore, as shown in Table 1, the ultrafiltration membranes prepared in Examples 1-5 of this invention have high humic acid removal rates and high filtration fluxes, with the highest filtration flux reaching 1911 L / m³. 2 The highest removal rate can reach 93%; it also has high tensile strength and elongation at break, indicating good mechanical properties; the antifouling ability of the ultrafiltration membrane prepared by this invention can reach 71%, indicating good antifouling performance; stability tests show that its temperature resistance is above 85℃, and the flux change is small after immersion in acid and alkali solutions, indicating that the ultrafiltration membrane prepared by the method of this invention has good mechanical properties and chemical stability. Furthermore, comparing Example 1 and Comparative Examples 1-7, it can be seen that changing the modifying raw materials of modified PVDF and modified titanium dioxide will lead to insufficient modification, resulting in a decrease in material performance, and thus affecting the performance of the prepared PVDF ultrafiltration membrane.

[0125] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a PVDF ultrafiltration membrane, characterized in that, The preparation steps include the following: Step 1: Preparation of modified PVDF: Vinylpyridine, hydroxy acrylate and vinylidene fluoride are mixed to obtain a mixed monomer. An initiator is added to the mixed monomer and a polymerization reaction is carried out under heating conditions. Step 2: Preparation of modified titanium dioxide: Titanium dioxide powder is dispersed in an organic solvent to obtain a suspension. A silane coupling agent is added to the suspension, and the mixture is stirred under heating conditions. Then, an epoxy-containing silicone oil is added and stirred, followed by the addition of a rare earth carboxylic acid complex and continued stirring. The silane coupling agent is at least one of KH-570, KH-560, and vinyltrimethoxysilane. The rare earth carboxylic acid complex is a rare earth citrate complex, which is at least one of cerium citrate, yttrium citrate, and lanthanum citrate. Step 3: Preparation of casting solution: Mix modified PVDF and modified titanium dioxide and heat to react, then add pore-forming agent and organic solvent and mix well, then perform intensive mixing; Step 4, extrusion film formation: The casting solution is extruded under pressure and heating conditions, and then immersed in the gel solution to separate the phases and form a film, thus obtaining the final product.

2. The method for preparing the PVDF ultrafiltration membrane according to claim 1, characterized in that, In step 1, the mass fraction of vinylpyridine in the mixed monomers is 3%-15% or / and the mass fraction of hydroxyacrylate is 5%-20%.

3. The method for preparing the PVDF ultrafiltration membrane according to claim 1, characterized in that, In step 2, the amount of silane coupling agent added is 3%-12% of the mass of titanium oxide or / and the amount of epoxy-containing silicone oil added is 4%-14% of the mass of titanium oxide or / and the amount of rare earth carboxylic acid complex added is 0.1%-0.5% of the mass of titanium oxide.

4. The method for preparing the PVDF ultrafiltration membrane according to claim 1, characterized in that, In step 2, after adding the silane coupling agent, the reaction temperature is 30-80℃ and the reaction time is 2-6h.

5. The method for preparing the PVDF ultrafiltration membrane according to claim 1, characterized in that, The mass ratio of modified titanium dioxide to modified PVDF in step 3 is 1:5-1:

20.

6. The method for preparing the PVDF ultrafiltration membrane according to claim 1, characterized in that, The pore-forming agent mentioned in step 3 is selected from at least one of PVP, PEG, NaCl, LiCl, methanol, ethanol, acetone and butanone.

7. The method for preparing the PVDF ultrafiltration membrane according to claim 1, characterized in that, The gel solution mentioned in step 4 is water, an organic solvent, or a composite solution of water and an organic solvent, and the soaking time is 10 min to 24 h.

8. A PVDF ultrafiltration membrane prepared by the method according to any one of claims 1-7.

9. An application of the PVDF ultrafiltration membrane according to claim 8 in water treatment.

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