A method for preparing a copolymer ultrafiltration membrane

Abstract

This invention discloses a method for preparing a copolymer ultrafiltration membrane. This method combines in-situ suspension polymerization, polyaddition reaction, sol-gel method, and non-solvent-induced phase separation to prepare a copolymer ultrafiltration membrane. Excellent hydrophilicity and component stability of the ultrafiltration membrane are achieved through stable covalent bonding between tannic acid and the copolymer. Furthermore, the in-situ polyaddition reaction and sol-gel reaction are combined to stably introduce high-performance tannic acid into the polymer membrane. Stable bonding of each component is achieved through co-hydrolysis and condensation polymerization of the copolymer and the siloxane on the modified tannic acid during the film formation process. The polymerization process of this invention is simple and the structure is tunable. The prepared material not only has excellent hydrophilicity and antifouling ability but also a stable structure, making it a cross-linked copolymer ultrafiltration membrane with antifouling and antibacterial adhesion properties.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, to copolymer ultrafiltration membranes, and particularly to a method for preparing copolymer ultrafiltration membranes by in-situ suspension polymerization and in-situ hydrolysis-condensation reaction. Background Technology

[0002] Ultrafiltration membrane technology, as a highly efficient water treatment method, has attracted widespread attention due to its excellent separation efficiency, low energy consumption, and environmental friendliness. This technology effectively removes impurities from water through semi-permeable membranes, making it an important approach to solving water pollution problems. However, ultrafiltration membrane technology also faces certain challenges in its application. Membrane fouling is the main reason for decreased separation efficiency and reduced lifespan. During treatment, the membrane surface is easily clogged by pollutants such as organic matter, microorganisms, and suspended particles in the water, thus affecting membrane performance. Therefore, developing ultrafiltration membrane materials with excellent antifouling properties has become a key research focus.

[0003] Currently, methods to improve the antifouling performance of ultrafiltration membranes mainly include surface modification and material innovation. Surface modification techniques, such as surface coating and chemical grafting, enhance antifouling capabilities by altering the chemical composition and physical structure of the membrane surface. A representative example is Chinese patent (CN101402701A), which discloses a method for producing a vinyl chloride-vinyl acetate-maleic anhydride terpolymer. This PVC copolymer exhibits good hydrophilicity and can be used to produce the hydrophilic component of PVC filter membranes. However, existing vinyl chloride copolymers primarily use oil-soluble monomers (such as vinyl acetate and acrylates), resulting in copolymers with poor hydrophilicity. When water-soluble monomers (such as maleic anhydride and acrylic acid) are used as comonomers, copolymerization with vinyl chloride monomers is difficult, and additional functionality is lacking. The inventors of this invention previously disclosed a method for preparing an amphiphilic ternary copolymer ultrafiltration membrane in CN109705286B. This method employs in-situ suspension copolymerization, utilizing a free radical polymerization mechanism and the bridging effect of acrylonitrile to ensure that all polymeric components are located on the polymer backbone, thus preparing the ultrafiltration membrane from the copolymer. This copolymer membrane exhibits excellent hydrophilicity and functionality, but its mechanical strength is low, preventing long-term use under complex environmental conditions. Furthermore, these methods often suffer from problems such as easy coating detachment and low grafting efficiency. Therefore, developing a novel copolymer ultrafiltration membrane can overcome the shortcomings of existing technologies, providing a more efficient, stable, and economical water treatment solution, which is of great significance for environmental protection and the sustainable use of water resources. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of current ultrafiltration membrane modification technologies by providing a method for preparing copolymer ultrafiltration membranes. This method combines in-situ suspension polymerization, polyaddition reaction, sol-gel method, and non-solvent-induced phase separation to prepare copolymer ultrafiltration membranes. Excellent hydrophilicity and component stability of the ultrafiltration membrane are achieved through stable covalent bonding between tannic acid and the copolymer. Furthermore, the in-situ polyaddition reaction and sol-gel reaction are combined to stably introduce high-performance tannic acid into the polymer membrane. Stable bonding of each component is achieved through co-hydrolysis and polycondensation of the copolymer and the siloxane on the modified tannic acid during film formation. This invention features a simple polymerization process and tunable structure. The prepared material not only possesses excellent hydrophilicity and antifouling capabilities but also exhibits structural stability, making it a cross-linked copolymer ultrafiltration membrane with antifouling and antibacterial adhesion properties.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a copolymer ultrafiltration membrane, the method comprising the following steps:

[0007] (1) Stir deionized water, dispersant and initiator for 0.3-0.5 h to obtain a mixed solution;

[0008] The mass ratio of the deionized water, dispersant, and initiator is (500-800):(15-25):(4-6);

[0009] The dispersant is polyvinyl alcohol, hydroxymethyl propyl cellulose, or a combination thereof; the initiator is tert-butyl peroxynedecanoate, cumyl peroxynedecanoate, or tert-amyl peroxynedecanoate.

[0010] The stirring speed is 100-500 r / min;

[0011] (2) After stirring the mixed solution obtained in step (1), vinyltriethoxysilane and vinyl chloride, the polymerization reaction was carried out at 50-70℃ for 5-9h to obtain the copolymer;

[0012] The mass ratio of the mixed solution, vinyl chloride, and vinyltriethoxysilane is (519-831):(300-500):(10-20).

[0013] The polymerization stirring speed is 600-800 r / min.

[0014] (3) The copolymer obtained in step (2), solvent, tannic acid, isocyanate propyltriethoxysilane and catalyst are mixed, sealed and stirred, and in-situ polymerized at 40-60°C for 10-15 h. Then the additives are added and stirring is continued for 0.3-0.6 h. Then the mixture is allowed to stand for 24-48 h to obtain the casting solution.

[0015] The mass ratio of the copolymer, solvent, tannic acid, isocyanate propyltriethoxysilane, catalyst, and additive is (10-20): (60-80): (0.15-0.45): (0.1-0.3): (0.001-0.003): (5-15).

[0016] The catalyst is one or more of dibutyltin dilaurate, tetrabutyltin, dibutyltin dodecanoate, and dioctyltin octaate;

[0017] The additive is one or more of PEG400, PEG800, PEG1000, and PVP(K30);

[0018] The solvent is one or more of DMAc, DMF, and NMP.

[0019] The stirring speed is 100-200 r / min; after adding the additive, the stirring speed is 100-200 r / min.

[0020] (4) The casting solution obtained in step (3) is scraped and cast into a membrane, and then immersed in alkaline deionized water for 1.0-3.0 min to obtain a copolymer ultrafiltration membrane;

[0021] The thickness of the scraped casting is 100-300 μm; the pH value of the alkaline deionized water is 8-12.

[0022] The essential features of this invention are:

[0023] In the current technology, the reactive sites of the sol-gel are first embedded into the polyvinyl chloride (PVC) backbone through copolymerization with vinyltriethoxysilane for subsequent sol-gel reactions. The copolymer is then dissolved in a solvent to form a casting solution, and tannic acid, isocyanate propyltriethoxysilane, and a catalyst are added. Under the action of the catalyst, tannic acid and isocyanate propyltriethoxysilane undergo a polyaddition reaction, providing reactive sites for tannic acid to undergo sol-gel formation. The casting solution is then cast onto a smooth glass plate, which is then placed in alkaline deionized water to form a film. In an alkaline coagulation bath, the active sites on the copolymer and the active sites on the tannic acid undergo a co-hydrolysis and condensation reaction, thereby stably bonding and crosslinking the tannic acid with the copolymer.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention uses a copolymer ultrafiltration membrane prepared by combining suspension copolymerization, polyaddition reaction, sol-gel method and non-solvent induced phase separation method to make tannic acid stably bonded to the copolymer matrix through covalent bonds.

[0026] (2) The copolymer ultrafiltration membrane prepared by the present invention has a stable cross-linked structure, which can avoid the problem of poor compatibility between the modifier and the matrix, and effectively prevent the leakage of effective components in the membrane.

[0027] (3) The copolymer ultrafiltration membrane prepared by the present invention has excellent antifouling and antibacterial adhesion properties (the flux recovery rate of bovine serum albumin rejection rate is higher than 94%, and the bacterial removal rate can reach more than 96%), which has broad application prospects in the field of treating complex wastewater. Detailed Implementation

[0028] The present invention will be described below with reference to examples. These descriptions are only for further illustrating the features and advantages of the present invention and are not intended to limit the scope of the claims of the present invention.

[0029] Example 1

[0030] This embodiment provides a method for preparing a structurally stable copolymer ultrafiltration membrane, the method comprising the following steps:

[0031] (1) Mix 500g of deionized water, 15g of polyvinyl alcohol and 4g of tert-butyl peroxydecanoate, and stir at 100r / min for 0.3h to obtain a mixed solution;

[0032] (2) The entire mixed solution obtained in step (1), 10g of vinyltriethoxysilane and 300g of vinyl chloride were added to the reaction vessel and sealed. Then, the polymerization reaction was carried out at 50°C (with a co-current pressure of 0.60 MPa) with a stirring speed of 600r / min for 5h to obtain the copolymer. The copolymer was then washed with deionized water and dried.

[0033] (3) Mix 10g of the copolymer obtained in step (2), 60g of N,N-dimethylacetamide (DMAc), 0.15g of tannic acid, 0.1g of propyltriethoxysilane isocyanate, and 0.001g of dibutyltin dilaurate, stir at 100r / min, heat to 40℃ and react for 10h, then add 5g of PEG400, stir at 100r / min for 0.3h, and then let stand for 24h to obtain the casting solution;

[0034] (4) The casting solution obtained in step (3) is used to cast a membrane using a 100 μm coating tool, and then immersed in deionized water at pH 8 for 1.0 min to obtain an 89 μm copolymer ultrafiltration membrane.

[0035] Example 2

[0036] This embodiment provides a method for preparing a structurally stable copolymer ultrafiltration membrane, the method comprising the following steps:

[0037] (1) Mix 600g of deionized water, 20g of polyvinyl alcohol and 5g of tert-butyl peroxydecanoate, and stir at 200r / min for 0.4h to obtain a mixed solution;

[0038] (2) The entire mixed solution obtained in step (1), 15g of vinyltriethoxysilane and 400g of vinyl chloride were added to the reaction vessel and sealed. Then, the polymerization reaction was carried out at 60°C (with a co-current pressure of 1.10 MPa) with a stirring speed of 700r / min for 7h to obtain the copolymer. The copolymer was then washed with deionized water.

[0039] (3) Take 15g of the copolymer obtained in step (2), 70g of DMAc, 0.30g of tannic acid, 0.2g of isocyanate propyltriethoxysilane, and 0.002g of tetrabutyltin, stir at 100r / min, heat to 50℃ and react for 13h, then add 10g of PEG400, stir at 150r / min for 0.4h, and then let stand for 36h to obtain the casting solution;

[0040] (4) The casting solution obtained in step (3) is used to cast a membrane using a 200 μm coating tool, and then immersed in deionized water at pH 10 for 1.5 min to obtain a 120 μm copolymer ultrafiltration membrane.

[0041] Example 3

[0042] This embodiment provides a method for preparing a structurally stable copolymer ultrafiltration membrane, the method comprising the following steps:

[0043] (1) Mix 800g of deionized water, 25g of polyvinyl alcohol and 6g of tert-butyl peroxydecanoate, and stir at 500r / min for 0.5h to obtain a mixed solution;

[0044] (2) The entire mixed solution obtained in step (1), 20g of vinyltriethoxysilane and 500g of vinyl chloride were added to the reaction vessel and sealed. Then, the polymerization reaction was carried out at 70℃ (with a pressure of 1.30Mpa) for 9h with a stirring speed of 800r / min to obtain the copolymer. The copolymer was then washed with deionized water.

[0045] (3) Take 20g of the copolymer obtained in step (2), 80g of DMAc, 0.450g of tannic acid, 0.3g of isocyanate propyltriethoxysilane, and 0.003g of dibutyltin dodecanoate, stir at 200r / min, heat to 60℃, react for 15h, then add 15g of PEG400, stir at 200r / min for 0.3h, and then let stand for 24h to obtain the casting solution;

[0046] (4) The casting solution obtained in step (3) is used to cast a membrane using a 300 μm coating tool, and then immersed in deionized water at pH 10 for 1.5 min to obtain a 210 μm copolymer ultrafiltration membrane.

[0047] Comparative Example 1

[0048] This comparative example provides a method for preparing a PVC ultrafiltration membrane, the method comprising the following steps:

[0049] Weigh out 20g of polyvinyl alcohol, 4g of tert-butyl peroxyneodecanate and 800g of deionized water, add them to the reaction vessel, and mix and stir at 200r / min for 0.3h to obtain a homogeneous aqueous solution.

[0050] 300g of vinyl chloride was weighed and added to a sealed reactor. The mixture was stirred at 500r / min for 0.3h, heated to 60℃, and reacted for 5h. Unreacted monomers were discharged, and the product was repeatedly washed with deionized water to obtain the copolymer.

[0051] Weigh out 10g of PVC, 60g of DMAc and 5g of PEG400 and put them into flasks respectively. Stir at 200r / min at 50℃ for 10h. After the reaction is complete, let stand for 24h to obtain the casting solution.

[0052] The casting solution was coated into a membrane using a 200μm coating tool, and after standing, it was immersed in deionized water to obtain an 85μm PVC ultrafiltration membrane.

[0053] The membranes obtained in Examples 1-3 and Comparative Example 1 were subjected to performance tests, including the following tests:

[0054] Tensile strength, which is the tensile strength tested when the membrane breaks.

[0055] Heat resistance, which is measured by the glass transition temperature and initial decomposition temperature of the membrane.

[0056] Solubility refers to whether the test membrane completely dissolves in DMAc solution.

[0057] Water contact angle, which measures the hydrophilicity of the membrane.

[0058] Hydrophilic stability, which is the water contact angle after 20 days of immersion in deionized water.

[0059] Pure water flux was measured by filtration at 0.1 MPa (25°C) for 30 min to evaluate the membrane's pure water flux. Before the experiment, the membrane was pre-pressurized at 0.15 MPa (25°C) for 30 min.

[0060] Pure water flux calculation formula: In the formula, Jw is the pure water flux, V(L) is the permeate flow rate, and A(m) is the permeate flow rate. 2 ) represents the effective area of ​​the membrane, and (t(h) represents the test time.

[0061] Antifouling ability was assessed by continuously filtering a 1 g / L bovine serum albumin solution at 0.1 MPa for 1 hour, and then measuring the membrane's rejection rate and flux reduction rate. The bovine serum albumin concentration before and after filtration was measured at 286 nm using a UV spectrophotometer, and the membrane rejection rate was calculated. The flux reduction rate was calculated by comparing the flux after filtering the bovine serum albumin solution with the flux of pure water before the measurement.

[0062] Retention rate calculation formula: In the formula, r is the rejection rate, Cp and Cf (mg·L) -1 The concentrations of bovine serum albumin solution in the filtrate and feed liquid are respectively.

[0063] Formula for calculating flux recovery rate: In the formula, FRR is the flux recovery rate, J w2 Jw represents the flux when the feed solution is bovine serum albumin solution, and Jw represents the pure water flux of the membrane.

[0064] The antibacterial adhesion test, using the traditional plate count method, evaluated the anti-adhesion effect of the copolymer ultrafiltration membrane against Staphylococcus aureus and Escherichia coli. All experimental procedures were performed under aseptic conditions. 10 μL of a 1.0 × 10⁷ CFU / mL solution was used. -1 A bacterial suspension was spread onto a sterile membrane with a diameter of 4 cm and incubated at 37°C for 2 h. The membrane was then thoroughly rinsed with PBS solution, and any remaining bacteria were collected using sonication and placed back into PBS solution. The collected bacteria were spread onto agar plates and incubated at 37°C for 12 h. Colony counts were then performed to assess the membrane's anti-adhesion properties.

[0065] Finally, the number of colonies on the agar plates was determined, and the bacterial removal rate (E) was calculated. b (%,%), the calculation formula 3.1 is as follows:

[0066]

[0067] In the formula N t For the colony count of the membrane in the example, N c This is for colony counting on the comparative membrane.

[0068] The results of tensile strength, water contact angle, heat resistance, solvent resistance, pure water flux, rejection rate, flux reduction rate and bacterial removal rate of the above membranes are shown in Table 1.

[0069] Table 1. Effect of different embodiments on the performance of copolymer ultrafiltration membranes

[0070]

[0071] As shown in the table, the copolymer ultrafiltration membrane exhibits significant improvements in tensile strength, hydrophilicity, pure water flux, rejection rate, flux recovery rate, and heat resistance. More importantly, after 20 days of soaking, the copolymer ultrafiltration membrane maintains stable hydrophilicity and remains stable in DMAc solution, without complete dissolution. The copolymer ultrafiltration membrane also demonstrates excellent bacterial removal rates, removing up to 98.47% of Staphylococcus aureus and 99.42% of Escherichia coli. Furthermore, the performance of the copolymer membrane increases with the addition of vinyltriethoxysilane, tannic acid, and 3-isocyanate propyltriethoxysilane. In contrast, the pure PVC membrane in Comparative Example 1, due to its inherent hydrophobic properties and the lack of stable bonding with the hydrophilic modifier, allows residual hydrophilic polymers (additives) to leak into the water, preventing it from maintaining long-term stability. Secondly, pure PVC lacks active sites for sol-gel reactions and contains no tannic acid or isocyanate propyltriethoxysilane, so it cannot form cross-linked structures. Therefore, it is easily soluble in solvents and has poor heat resistance, anti-fouling properties, and antibacterial adhesion properties.

[0072] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a copolymer ultrafiltration membrane, characterized in that the method comprises the following steps: (1) Stir deionized water, dispersant and initiator for 0.3-0.5 h to obtain a mixed solution; The mass ratio of the deionized water, dispersant and initiator is (500-800):(15-25):(4-6). The dispersant is polyvinyl alcohol, hydroxymethyl propyl cellulose, or a combination thereof; the initiator is tert-butyl peroxynedecanoate, cumyl peroxynedecanoate, or tert-amyl peroxynedecanoate. (2) After stirring the mixed solution obtained in step (1), vinyltriethoxysilane and vinyl chloride, the polymerization reaction was carried out at 50-70℃ for 5-9h to obtain the copolymer; The mass ratio of the mixed solution, vinyl chloride, and vinyltriethoxysilane is (519-831):(300-500):(10-20). (3) The copolymer, solvent, tannic acid, isocyanate propyltriethoxysilane and catalyst obtained in step (2) are mixed, sealed and stirred, and in situ polymerized at 40-60°C for 10-15 h. Then the additives are added and stirring is continued for 0.3-0.6 h. Then the mixture is allowed to stand for 24-48 h to obtain the casting solution. The mass ratio of the copolymer, solvent, tannic acid, isocyanate propyltriethoxysilane, catalyst, and additive is (10-20): (60-80): (0.15-0.45): (0.1-0.3): (0.001-0.003): (5-15). (4) The casting solution obtained in step (3) is scraped and cast into a membrane, and then immersed in alkaline water for 1.0-3.0 min to obtain a copolymer ultrafiltration membrane.

2. The method for preparing the copolymer ultrafiltration membrane according to claim 1, characterized in that the catalyst is one or more of dibutyltin dilaurate, tetrabutyltin, dibutyltin dodecanoate, and dioctyltin octaate.

3. The method for preparing the copolymer ultrafiltration membrane according to claim 1, characterized in that the additive is one or more of PEG400, PEG800, PEG1000, and PVP (K30).

4. The method for preparing the copolymer ultrafiltration membrane according to claim 1, characterized in that the solvent is one or more of DMAc, DMF, and NMP.

5. The method for preparing the copolymer ultrafiltration membrane according to claim 1, characterized in that the coating thickness is 100~300μm; and the pH value of the alkaline water is 8-12.

6. The method for preparing the copolymer ultrafiltration membrane as described in claim 1, characterized in that: The stirring speed in step (1) is 100-500 r / min; the stirring speed in step (2) is 600-800 r / min; the stirring speed in step (3) is 100-200 r / min, and the stirring speed after adding the additive is 100-200 r / min.

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