A method for preparing a copolymer ultrafiltration membrane with a bonded structure

Abstract

This invention discloses a method for preparing a copolymer ultrafiltration membrane with a bonded structure. This method combines in-situ suspension polymerization, click reaction, sol-gel method, and solvent-inducible phase separation to prepare the copolymer ultrafiltration membrane. Excellent hydrophilicity and component stability of the ultrafiltration membrane are achieved through stable covalent bonding between tannic acid and the copolymer. This invention also combines in-situ click reaction and sol-gel reaction to stably introduce high-performance resveratrol into the polymer membrane. Stable bonding of the components is achieved through co-hydrolysis and condensation of the copolymer and the siloxane on the modified resveratrol during the film formation process. The polymerization process of this invention is simple and the structure is tunable. The prepared copolymer ultrafiltration membrane not only has excellent hydrophilicity and antifouling ability but also a stable structure.

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] In the field of water treatment technology, polymer ultrafiltration membrane technology has attracted much attention due to its high efficiency, energy-saving advantages, and excellent separation performance. Compared with traditional methods, this technology has higher separation efficiency and environmental protection characteristics. However, one of the main challenges facing membrane technology is membrane surface fouling. During use, organic matter, bacteria, and other particles in the water easily adhere to the membrane surface, leading to decreased flux, increased energy consumption, and even shortened membrane lifespan. Therefore, developing novel ultrafiltration membrane materials with high anti-fouling properties has become a research hotspot in the water treatment field. The development of these new materials can not only improve membrane separation efficiency but also help reduce operating costs, thus having a positive impact on environmental protection.

[0003] Currently, common methods for addressing polymer ultrafiltration membrane fouling include surface coating, surface grafting, and physical blending. Coating the membrane with hydrophilic inorganic materials or polymers can significantly improve its antifouling properties; however, the antifouling coating has weak interaction with the membrane substrate and is prone to detachment. Surface grafting improves membrane antifouling by grafting hydrophilic segments onto the membrane surface or the film-forming material; however, this is achieved by sacrificing the structural stability of the film-forming polymer or the membrane itself. Physical blending typically involves mechanically blending hydrophilic additives (such as inorganic nanoparticles or amphiphilic polymers) with a casting solution before membrane formation. However, physical blending still suffers from uneven additive distribution, poor compatibility with the matrix, and easy detachment.

[0004] 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 prepare the hydrophilic component of PVC filter membranes. However, existing vinyl chloride copolymers often 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 further functionalities are lacking. The inventors of this invention previously disclosed a method for preparing an amphiphilic terpolymer ultrafiltration membrane using in-situ suspension copolymerization. Through free radical polymerization and the bridging effect of acrylonitrile, all polymeric components are located on the polymer backbone, and the copolymer is then prepared into an ultrafiltration membrane. This copolymer membrane possesses excellent hydrophilicity and functionality, but its mechanical strength is low, preventing long-term use under complex environmental conditions. Therefore, it is of great significance to develop a copolymer ultrafiltration membrane with a stable cross-linked novel structure that can operate for a long time in complex environments. Summary of the Invention

[0005] 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 with bonded structures. This method combines in-situ suspension polymerization, click reaction, sol-gel method, and solvent-inducible phase separation to prepare copolymer ultrafiltration membranes. Excellent hydrophilicity and component stability of the ultrafiltration membrane are achieved through stable covalent bonding between resveratrol and the copolymer. This invention also combines in-situ click reaction and sol-gel reaction to stably introduce high-performance resveratrol into the polymer membrane. Stable bonding of the components is achieved through co-hydrolysis and condensation of the copolymer and the siloxane on the modified resveratrol during the film formation process. The polymerization process of this invention is simple and the structure is tunable. The prepared copolymer ultrafiltration membrane not only has excellent hydrophilicity and antifouling ability but also structural stability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a copolymer ultrafiltration membrane with a bonded structure, the method comprising the following steps:

[0008] (1) Add deionized water, dispersant and initiator into the reactor and stir for 0.1-0.5 h to obtain a mixed solution;

[0009] The mass ratio of deionized water, dispersant, and initiator is (600-800):(10-20):(2-5);

[0010] The dispersant is polyvinyl alcohol, hydroxymethylpropyl cellulose, or a combination of the two.

[0011] The initiator is tert-butyl peroxynedecanoate, cumyl peroxynedecanoate, or tert-amyl peroxynedecanoate.

[0012] (2) Stir the mixed solution obtained in step (1), vinyltriethoxysilane and vinyl chloride for 0.3-0.5 h, then seal and polymerize at 50-70 °C for 4-8 h to obtain the copolymer;

[0013] The mass ratio of the mixed solution, vinyl chloride, and vinyltriethoxysilane is (612-825):(200-300):(5-15);

[0014] (3) The copolymer, solvent, resveratrol, 3-mercaptopropyltrimethoxysilane, photoinitiator and additives obtained in step (2) are mixed and stirred at 50-70°C for 10-18 hours, and then allowed to stand for 12-24 hours to obtain casting solution.

[0015] The mass ratio of copolymer, solvent, resveratrol, 3-mercaptopropyltrimethoxysilane, photoinitiator and additive is (10-20): (60-80): (0.3-0.9): (0.3-0.9): (0.003-0.009): (5-15).

[0016] (4) The casting solution obtained in step (3) is scraped and cast into a film, then irradiated with ultraviolet light for 0.5-1.5 min, and then immersed in alkaline deionized water for 0.5-1.5 min to obtain a copolymer ultrafiltration membrane with a bonded structure.

[0017] The thickness of the coating is 150-250 μm; the wavelength of the ultraviolet light is 365 nm; and the light intensity is 3-10 mw / cm². 2 ;

[0018] The stirring rate in step (1) is 100-500 r / min. The stirring rate in step (2) is 500-800 r / min.

[0019] The solvent in step (3) includes one or a mixture of several of DMAc, DMF, and NMP.

[0020] The additives in step (3) include one or more of PEG400, PEG800, PEG1000, and PVP(K30).

[0021] The photoinitiator in step (3) includes one or more of benzoin dimethyl ether, 2-hydroxy-2-methyl-1-1-phenyl-1-propanone, 1-hydroxy-cyclohexyl-phenyl ketone, and 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide.

[0022] In step (4), the pH value of the alkaline deionized water is 8-13.

[0023] The essential features of this invention are:

[0024] 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. Then, the copolymer is dissolved in a solvent to form a casting solution, followed by the addition of resveratrol, 3-mercaptopropyltrimethoxysilane, and a photoinitiator. After coating on a smooth glass plate, rapid ultraviolet irradiation initiates a click reaction between resveratrol and 3-mercaptopropyltrimethoxysilane, methoxylating the resveratrol and allowing for the next sol-gel reaction. Finally, the glass plate is placed in alkaline deionized water to form a film. In an alkaline coagulation bath, the reactive sites on the copolymer undergo a co-hydrolysis and condensation reaction with the methoxylated resveratrol, resulting in stable bonding and cross-linking of the components within the film.

[0025] The present invention has the following beneficial effects:

[0026] (1) The present invention uses a copolymer ultrafiltration membrane prepared by combining suspension copolymerization, click reaction, sol-gel method and non-solvent induced phase separation method, so that the components in the membrane are bonded together by covalent bonds.

[0027] (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.

[0028] (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 93%, and the bacterial removal rate can reach more than 90%, which has broad application prospects in the field of treating complex sewage). Detailed Implementation

[0029] 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.

[0030] Example 1

[0031] This embodiment provides a method for preparing a copolymer ultrafiltration membrane, the method comprising the following steps:

[0032] (1) Mix 800g of deionized water, 20g of polyvinyl alcohol and 5g of tert-butyl peroxynedecanoate, and stir at 200r / min for 0.3h to obtain a mixed solution;

[0033] (2) The entire mixed solution obtained in step (1), 5g of vinyltriethoxysilane and 300g of vinyl chloride were added to the reaction vessel and sealed. The mixture was stirred at 800r / min for 0.4h and then subjected to polymerization at 60℃ (with a pressure of 0.75Mpa) for 5h to obtain the copolymer. The copolymer was then washed with deionized water and dried.

[0034] (3) Mix 10g of the copolymer obtained in step (2), 60g of N,N-dimethylacetamide (DMAc), 0.3g of resveratrol, 0.3g of 3-mercaptopropyltrimethoxysilane, 0.003g of benzoin dimethyl ether and 5g of PEG400, heat to 60°C, stir for 10h under heat preservation conditions, and then let stand for 12h to obtain the casting solution;

[0035] (4) The casting solution obtained in step (3) is used to cast a film using a 200 μm coating tool, and then the film is cast with a wavelength of 365 nm and an irradiation intensity of 5 mw / cm². 2 Irradiate with ultraviolet light for 0.5 min, then immerse in deionized water at pH 9 for 0.5 min to obtain a 115 μm copolymer ultrafiltration membrane;

[0036] Example 2

[0037] This embodiment provides a method for preparing a copolymer ultrafiltration membrane, the method comprising the following steps:

[0038] (1) Mix 700g of deionized water, 15g of polyvinyl alcohol and 3g of cumyl peroxynedecanoate, and stir at 150r / min for 0.5h to obtain a mixed solution;

[0039] (2) The entire mixed solution obtained in step (1), 10g of vinyltriethoxysilane and 250g of vinyl chloride were added to the reaction vessel and sealed. The mixture was stirred at 700r / min for 0.4h and then subjected to polymerization at 70℃ (with a pressure of 1.23Mpa) for 6h to obtain the copolymer. The copolymer was then washed with deionized water.

[0040] (3) Heat 20g of the copolymer obtained in step (2), 80g of DMAc, 0.6g of resveratrol, 0.6g of 3-mercaptopropyltrimethoxysilane, 0.006g of 2-hydroxy-2-methyl-1-1-phenyl-1-propanone and 10g of PEG800 to 70°C, then stir for 15h under heat preservation conditions, and then let stand for 18h to obtain the casting solution;

[0041] (4) The casting solution obtained in step (3) is used to cast a film using a 200 μm coating tool, then irradiated with ultraviolet light for 0.5 min, and then immersed in deionized water at pH 10 for 1.0 min to obtain a 121 μm copolymer ultrafiltration membrane.

[0042] Example 3

[0043] This embodiment provides a method for preparing a copolymer ultrafiltration membrane, the method comprising the following steps:

[0044] (1) Mix 600g of deionized water, 10g of hydroxymethylpropyl cellulose and 3g of tert-pentyl peroxide, and stir at 250r / min for 0.5h to obtain a mixed solution;

[0045] (2) The entire mixed solution obtained in step (1), 15g of vinyltriethoxysilane and 200g of vinyl chloride were added to the reaction vessel and sealed. The mixture was stirred at 600r / min for 0.4h and then subjected to polymerization at 50℃ (with associated pressure of 0.7Mpa) for 7h to obtain the copolymer. The copolymer was then washed with deionized water.

[0046] (3) Heat 15g of the copolymer obtained in step (2), 60g of DMAc, 0.6g of resveratrol, 0.6g of 3-mercaptopropyltrimethoxysilane, 0.006g of 2-hydroxy-2-methyl-1-1-phenyl-1-propanone and 5g of PEG400 to 60°C, then stir for 18h under heat preservation conditions, and then let stand for 24h to obtain the casting solution;

[0047] (4) The casting solution obtained in step (3) is used to cast a film using a 200 μm coating tool, then irradiated with ultraviolet light for 0.5 min, and then immersed in deionized water at pH 11 for 1.5 min to obtain a 118 μm copolymer ultrafiltration membrane.

[0048] Comparative Example 1

[0049] This comparative example provides a method for preparing a PVC ultrafiltration membrane, the method comprising the following steps:

[0050] Weigh out 20g of polyvinyl alcohol, 2g of tert-butyl peroxyneodecanate and 800g of deionized water respectively, add them to the reaction vessel, and mix and stir at 200r / min for 6min to obtain a homogeneous aqueous solution.

[0051] 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 4h. Unreacted monomers were discharged, and the product was repeatedly washed with deionized water to obtain the copolymer.

[0052] Weigh out 10g of PVC, 60g of DMAc and 5g of PEG400, and put them into flasks respectively. Stir at 50℃ for 10h. After the reaction is complete, let stand for 12h to obtain the casting solution.

[0053] 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 86μm PVC ultrafiltration membrane.

[0054] The membranes obtained in Examples 1-3 and Comparative Example 1 were subjected to performance tests, including the following tests:

[0055] Tensile strength, which is the tensile strength tested when the membrane breaks.

[0056] Heat resistance, which is measured by the glass transition temperature and initial decomposition temperature of the membrane.

[0057] Solubility refers to whether the test membrane completely dissolves in DMAc solution.

[0058] Water contact angle, which measures the hydrophilicity of the membrane.

[0059] Hydrophilic stability, which is the water contact angle after 20 days of immersion in deionized water.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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:

[0067]

[0068] 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.

[0069] 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.

[0070] Table 1. Effect of different embodiments on the performance of structurally stable copolymer ultrafiltration membranes

[0071]

[0072] As shown in the table, the tensile strength, hydrophilicity, pure water flux, rejection rate, flux recovery rate, and heat resistance of the structurally stable copolymer ultrafiltration membrane are significantly improved. More importantly, after soaking for 20 days, the structurally stable copolymer ultrafiltration membrane still maintains stable hydrophilicity and remains stable in DMAc solution, without complete dissolution. The copolymer ultrafiltration membrane also exhibits excellent bacterial removal rates, removing up to 87.56% of Staphylococcus aureus and 88.34% of Escherichia coli. Furthermore, with the increase of vinyltriethoxysilane, resveratrol, and 3-mercaptopropyltrimethoxysilane in the copolymer, the performance of the copolymer membrane shows an increasing trend. In contrast, the pure PVC membrane of Comparative Example 1, due to its inherent hydrophobic properties and the lack of stable bonding with the hydrophilic modifier, allows residual hydrophilic polymers (additives) within the membrane to leak into the water, thus failing to maintain 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.

[0073] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a copolymer ultrafiltration membrane with a bonded structure, characterized in that the method comprises the following steps: (1) Add deionized water, dispersant and initiator into the reactor and stir for 0.1-0.5 h to obtain a mixed solution; The mass ratio of deionized water, dispersant, and initiator is (600-800):(10-20):(2-5). The dispersant is polyvinyl alcohol, hydroxymethylpropyl cellulose, or a combination of the two; The initiator is tert-butyl peroxynedecanoate, cumyl peroxynedecanoate, or tert-amyl peroxynedecanoate. (2) Stir the mixed solution obtained in step (1), vinyltriethoxysilane and vinyl chloride for 0.3-0.5 h, then seal and polymerize at 50-70 °C for 4-8 h to obtain the copolymer; The mass ratio of the mixed solution, vinyl chloride, and vinyltriethoxysilane is (612-825):(200-300):(5-15). (3) The copolymer, solvent, resveratrol, 3-mercaptopropyltrimethoxysilane, photoinitiator and additives obtained in step (2) are mixed and stirred at 50-70°C for 10-18 hours, and then allowed to stand for 12-24 hours to obtain casting solution. The mass ratio of copolymer, solvent, resveratrol, 3-mercaptopropyltrimethoxysilane, photoinitiator and additive is (10-20): (60-80): (0.3-0.9): (0.3-0.9): (0.003-0.009): (5-15). (4) The casting solution obtained in step (3) is scraped and cast into a film, then irradiated with ultraviolet light for 0.5-1.5 min, and then immersed in alkaline water for 0.5-1.5 min to obtain a copolymer ultrafiltration membrane with a bonded structure.

2. The method for preparing a copolymer ultrafiltration membrane with a bonded structure as described in claim 1, characterized in that: The stirring rate in step (1) is 100-500 r / min; the stirring rate in step (2) is 500-800 r / min.

3. The method for preparing a copolymer ultrafiltration membrane with a bonded structure as described in claim 1, characterized in that: The solvent in step (3) includes one or a mixture of several of DMAc, DMF, and NMP.

4. The method for preparing a copolymer ultrafiltration membrane with a bonded structure as described in claim 1, characterized in that: The additives in step (3) include one or more of PEG400, PEG800, PEG1000, and PVP (K30).

5. The method for preparing a copolymer ultrafiltration membrane with a bonded structure as described in claim 1, characterized in that: The photoinitiator in step (3) includes one or more of benzoin dimethyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxy-cyclohexyl-phenyl ketone, and 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide.

6. The method for preparing a copolymer ultrafiltration membrane with a bonded structure as described in claim 1, characterized in that: In step (4), the pH value of the alkaline deionized water is 8-13.

7. The method for preparing a copolymer ultrafiltration membrane with a bonded structure as described in claim 1, characterized in that: The thickness of the doctor-blade film in step (4) is 150-250 μm; the wavelength of the ultraviolet light is 365 nm; and the light intensity is 3-10 mw / cm 2 .

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