Ultrafiltration composite membrane and preparation method thereof

Abstract

The invention relates to an ultrafiltration composite membrane and a preparation method thereof. The ultrafiltration composite membrane comprises a base membrane and a pre-filtration antibacterial layer which are laminated, the base membrane comprises a support body and a heat-resistant polymer separation layer, and the heat-resistant polymer separation layer is located on one side of the support body and at least partially permeates into the support body; the pre-filtering antibacterial layer is made of a composite chitosan layer which is chemically cross-linked and has a three-dimensional network structure. According to the ultrafiltration composite membrane disclosed by the invention, the heat-resistant polymer separation layer and the chemically crosslinked chitosan three-dimensional network antibacterial layer are compounded, so that the ultrafiltration composite membrane has excellent heat-resistant stability and efficient and lasting antibacterial performance. The heat-resistant high polymer material ensures the structural integrity and separation efficiency of the membrane at high temperature, and the chemically cross-linked chitosan layer not only provides a broad-spectrum antibacterial effect, but also improves the membrane flux and enhances the anti-pollution capacity through hydrophilic modification. Due to the double-layer structural design, the membrane has good comprehensive performance and long service life in high-temperature sterilization and filtration application.

Description

Technical Field

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

[0002] Membrane separation technology is widely used in water treatment, food, and biomedicine due to its advantages such as ease of operation, high efficiency, energy saving, and environmental friendliness. Ultrafiltration membranes, as an important component of this technology, rely heavily on the physicochemical properties of the membrane material for their separation performance.

[0003] In practical applications, especially under conditions requiring high temperatures or suppression of microbial growth (such as hot water sterilization systems and high-temperature material separation), higher demands are placed on the heat resistance and antibacterial properties of ultrafiltration membranes. Currently used polymer membrane materials (such as polysulfone, polyethersulfone, and cellulose esters) are prone to hydrolysis, oxidation, or structural relaxation under prolonged high temperatures, leading to performance degradation. While special engineering plastics such as polyetheretherketone (PEEK) and polyvinylidene fluoride (PVDF) possess excellent heat resistance, chemical stability, and mechanical strength, their surfaces are typically hydrophobic or electrically neutral, resulting in insufficient antibacterial properties. When processing fluids containing bacteria, these materials are prone to membrane fouling and biofouling, affecting flux and lifespan. Summary of the Invention

[0004] Therefore, it is necessary to provide an ultrafiltration composite membrane and its preparation method. The ultrafiltration composite membrane has excellent heat resistance and high efficiency antibacterial properties, and is particularly suitable for sterilization filtration of high-temperature fluids.

[0005] An ultrafiltration composite membrane, the ultrafiltration composite membrane comprising a stacked base membrane and a pre-filtration antibacterial layer; The base film includes a support and a heat-resistant polymer separation layer, wherein the heat-resistant polymer separation layer is located on one side of the support and at least partially penetrates into the interior of the support; The pre-filtered antibacterial layer is a composite chitosan layer with a three-dimensional network structure that is chemically cross-linked.

[0006] The ultrafiltration composite membrane of this invention combines a heat-resistant polymer separation layer with a chemically cross-linked chitosan three-dimensional network antibacterial layer, achieving both excellent heat resistance and highly efficient and long-lasting antibacterial properties. The heat-resistant polymer material (such as PEEK and PVDF) ensures the membrane's structural integrity and separation efficiency at high temperatures, while the chemically cross-linked chitosan layer not only provides broad-spectrum antibacterial activity (antibacterial inhibition rate > 98%) but also enhances membrane flux and antifouling capabilities through hydrophilic modification. This dual-layer structure design enables the membrane to exhibit excellent overall performance and service life in high-temperature sterilization filtration applications.

[0007] In one embodiment, the thickness of the pre-filtered antibacterial layer is 20 μm to 100 μm.

[0008] In one embodiment, the polymer material of the heat-resistant polymer separation layer is selected from at least one of polyetheretherketone, polyvinylidene fluoride, polyethersulfone ketone, and polyarylsulfone; and / or The thickness of the heat-resistant polymer separation layer is 100μm~200μm.

[0009] In one embodiment, the support is a nonwoven fabric.

[0010] A method for preparing any of the above-mentioned ultrafiltration composite membranes includes the following steps: A heat-resistant polymer material is dissolved in an organic solvent to form a casting solution; the casting solution is coated onto one side of a support, and a heat-resistant polymer separation layer is formed through non-solvent-induced phase separation to obtain a base film; and Chitosan is dissolved in a dilute acid solution to form a chitosan coating solution; the chitosan coating solution is then coated onto the surface of the heat-resistant polymer separation layer of the base film to form a first chitosan wet layer. The first chitosan wet layer is subjected to a first curing treatment, and then immersed in a crosslinking agent aqueous solution for crosslinking treatment; The chitosan coating solution is coated again on the cross-linked surface to form a second chitosan wet layer, followed by a second curing process to obtain an ultrafiltration composite membrane with the pre-filtered antibacterial layer.

[0011] The ultrafiltration composite membrane preparation method of this invention adopts a "two-step coating-intermediate crosslinking" process. First, a base membrane is formed through non-solvent-induced phase separation. Then, an antibacterial layer is constructed through chitosan coating, crosslinking, secondary coating, and curing. This process is mild, simple, and highly controllable, requiring no complex post-processing and facilitating large-scale production. The resulting composite membrane exhibits strong interlayer bonding, with the chitosan layer forming a stable three-dimensional network. This maintains antibacterial activity while significantly improving the coating's durability and adhesion under high temperatures and fluid shear.

[0012] In one embodiment, the dissolution temperature of the heat-resistant polymer material in the organic solvent is 60°C to 80°C, and the dissolution time is 10 hours to 24 hours; and / or The heat-resistant polymer material has a mass percentage concentration of 15%~18% in the casting solution; and / or The organic solvent includes one or more of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.

[0013] In one embodiment, the chitosan is dissolved in a dilute acid solution at a temperature of 50°C to 70°C for a time of 1 hour to 5 hours; and / or The chitosan coating solution contains chitosan at a mass concentration of 0.2% to 0.5%; and / or The dilute acid solution is an aqueous solution of acetic acid with a volume concentration of 2% to 3%.

[0014] In one embodiment, the first curing process is performed by drying at 50°C to 70°C for 2 to 5 minutes.

[0015] In one embodiment, the crosslinking agent aqueous solution has a mass concentration of 2% to 4%; and / or The crosslinking agent includes one or more of glutaraldehyde, terephthalaldehyde, tannic acid, and sodium tripolyphosphate.

[0016] In one embodiment, the second curing process is performed by drying at 50°C to 70°C for 5 to 10 minutes. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing an ultrafiltration composite membrane according to an embodiment of the present invention. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] One embodiment of the ultrafiltration composite membrane includes a stacked base membrane and a pre-filtered antibacterial layer.

[0021] The base membrane comprises a support and a heat-resistant polymer separation layer. The heat-resistant polymer separation layer is located on one side of the support and at least partially penetrates into the interior of the support. The heat-resistant polymer separation layer is prepared by a non-solvent-induced phase separation method.

[0022] The pre-filtered antibacterial layer is a composite chitosan layer with a three-dimensional network structure that is chemically cross-linked.

[0023] In this invention, the "pre-filter antibacterial layer" refers to the functional layer that first contacts the feed liquid during the filtration process. Its core function is to utilize the properties of chitosan to initially intercept and kill / inhibit microorganisms. Through a chemically cross-linked three-dimensional chitosan network, not only is the membrane layer endowed with durable, highly efficient, and broad-spectrum antibacterial properties (inhibition rate > 98%), but the structural stability of the antibacterial layer itself and its bonding strength with the heat-resistant polymer separation layer are also significantly enhanced. The "heat-resistant polymer separation layer" undertakes the main physical sieving function and maintains structural integrity at high temperatures.

[0024] Based on the aforementioned embodiments, the thickness of the pre-filter antibacterial layer is 20 μm to 100 μm. Within this thickness range, the chitosan layer can form an effective antibacterial barrier without excessively negatively impacting the overall flux of the membrane. If the thickness is too thin, the antibacterial capacity and durability are insufficient; if it is too thick, the mass transfer resistance is too high. Furthermore, the thickness of the pre-filter antibacterial layer can be, but is not limited to, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.

[0025] Based on the aforementioned embodiments, the polymer material of the heat-resistant polymer separation layer is selected from at least one of polyetheretherketone (PEEK), polyvinylidene fluoride (PVDF), polyethersulfone ketone, and polyarylsulfone. These materials all possess excellent high-temperature resistance, chemical stability, and mechanical strength.

[0026] Based on the aforementioned embodiments, the thickness of the heat-resistant polymer separation layer is 100μm to 200μm. This thickness range ensures that the separation layer possesses sufficient mechanical strength and suitable separation accuracy. Furthermore, the thickness of the heat-resistant polymer separation layer can be, but is not limited to, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, or 200μm.

[0027] Based on the aforementioned embodiments, the support is a non-woven fabric. Non-woven fabric has good porosity and mechanical support, which is beneficial for the penetration of the casting solution and the formation of the composite membrane.

[0028] The ultrafiltration composite membrane of this invention combines a heat-resistant polymer separation layer with a chemically cross-linked chitosan three-dimensional network antibacterial layer, achieving both excellent heat resistance and highly efficient and long-lasting antibacterial properties. The heat-resistant polymer material (such as PEEK and PVDF) ensures the membrane's structural integrity and separation efficiency at high temperatures, while the chemically cross-linked chitosan layer not only provides broad-spectrum antibacterial activity (antibacterial inhibition rate > 98%) but also enhances membrane flux and antifouling ability through hydrophilic modification. This dual-layer structure design enables the membrane to exhibit excellent overall performance and service life in high-temperature sterilization filtration applications. Please refer to [link to relevant documentation]. Figure 1 The preparation method of the ultrafiltration composite membrane according to one embodiment of the present invention includes the following steps: S10. Dissolve the heat-resistant polymer material in an organic solvent to form a casting solution; coat the casting solution onto one side of the support, and form a heat-resistant polymer separation layer through non-solvent-induced phase separation to obtain the base film.

[0029] In step S10, the casting liquid can be coated onto one side of the support by scraping, and at the same time, the scraping speed can be controlled to allow some of the casting liquid to penetrate into the interior of the support.

[0030] In one embodiment, the mass percentage concentration of the heat-resistant polymer material in the casting solution is 15% to 18%. This concentration range is beneficial for forming a heat-resistant polymer separation layer with ideal pore structure and mechanical strength. Further, the mass percentage concentration of the heat-resistant polymer material in the casting solution may be, but is not limited to, 15%, 16%, 17%, or 18%.

[0031] In one embodiment, the organic solvent includes N-methylpyrrolidone.

[0032] In one embodiment, the heat-resistant polymer material is dissolved in an organic solvent at a temperature of 60°C to 80°C for a time of 10 to 24 hours. This helps ensure complete dissolution of the polymer, forming a uniform and stable casting solution. Furthermore, the dissolution temperature can be, but is not limited to, 60°C, 65°C, 70°C, 75°C, or 80°C, and the dissolution time can be, but is not limited to, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, or 24 hours.

[0033] In one embodiment, the non-solvent coagulation bath is a water bath. Water is a green, inexpensive, and effective coagulant.

[0034] S20. Dissolve chitosan in a dilute acid solution to form a chitosan coating solution; coat the chitosan coating solution onto the surface of the heat-resistant polymer separation layer of the base film to form a first chitosan wet layer.

[0035] Step S20 mainly involves the dissolution and protonation of chitosan. When chitosan is added to a dilute acid solution (such as acetic acid), the free amino groups (-NH2) on the chitosan molecular chains react with hydrogen ions (H+) in the solution. + They combine to form positively charged ammonium ions (-NH3). + This chemical reaction transforms chitosan, which is originally insoluble in water, into a soluble polyelectrolyte, forming a homogeneous, viscous chitosan coating solution. This solution is then coated onto the surface of the base film to form the first chitosan wet layer. This step not only dissolves the functional material but, more importantly, activates the antibacterial and reactive sites (-NH3) of chitosan.+ This laid the foundation for subsequent chemical cross-linking.

[0036] In one embodiment, the chitosan is dissolved in a dilute acid solution at a temperature of 50°C to 70°C for 1 hour to 5 hours. This helps ensure complete dissolution of the chitosan. Furthermore, the dissolution temperature can be, but is not limited to, 50°C, 55°C, 60°C, 65°C, or 70°C, and the dissolution time can be, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours.

[0037] In one embodiment, the chitosan concentration in the chitosan coating solution is 0.2% to 0.5%. At this concentration, the resulting coating thickness is suitable, the solution viscosity is moderate, and the coating operation is convenient. Further, the chitosan concentration in the chitosan coating solution can be, but is not limited to, 0.2%, 0.3%, 0.4%, or 0.5%.

[0038] In one embodiment, the dilute acid solution is an aqueous solution of acetic acid with a volume concentration of 2% to 3%.

[0039] S30. The first chitosan wet layer obtained in step S20 is subjected to a first curing treatment, and then immersed in a crosslinking agent aqueous solution for crosslinking treatment.

[0040] Step S30 is the crucial chemical cross-linking reaction step. A gentle first curing treatment is applied to the first wet chitosan layer. The main purpose of this treatment is to remove most of the solvent, allowing the chitosan molecular chains to initially aggregate and stabilize, preventing dissolution and loss in subsequent aqueous solutions. Subsequently, the layer is immersed in an aqueous solution of a cross-linking agent such as glutaraldehyde. The cross-linking agent molecules (e.g., the aldehyde group -CHO of glutaraldehyde) undergo a nucleophilic addition-elimination reaction with the amino groups (-NH2) on the chitosan chains, i.e., a Schiff base reaction, forming stable imine bonds (-C=N-). This reaction constructs a three-dimensional network structure with covalent bonds between chitosan molecular chains and between chitosan and any active groups that may exist on the base film surface, thereby greatly enhancing the coating's mechanical strength, water resistance, and adhesion to the film surface.

[0041] In one embodiment, the first curing process involves drying at 50°C to 70°C for 2 to 5 minutes. Further, the curing time can be, but is not limited to, 50°C, 55°C, 60°C, 65°C, or 70°C, and the drying time can be, but is not limited to, 2 minutes, 3 minutes, 4 minutes, or 5 minutes.

[0042] In one embodiment, the mass concentration of the crosslinking agent in the aqueous crosslinking agent solution is 2% to 4%. Further, the mass concentration of the crosslinking agent in the aqueous crosslinking agent solution may be, but is not limited to, 2%, 3%, or 4%.

[0043] In one embodiment, the crosslinking agent includes one or more of glutaraldehyde, terephthalaldehyde, tannic acid, and sodium tripolyphosphate.

[0044] S40. A chitosan coating solution is applied again to the cross-linked surface to form a second chitosan wet layer. Then, a second curing process is performed to obtain an ultrafiltration composite membrane with a pre-filtered antibacterial layer.

[0045] Step S40 primarily involves the physical fixation and network reinforcement of the secondary coating layer. A second chitosan coating solution is applied to the already cross-linked, stable three-dimensional network substrate. This second chitosan solution effectively wets the surface of the cross-linked network. The subsequent second curing process (e.g., drying at 60°C) causes solvent evaporation and allows the second layer of chitosan molecules to bind tightly to and fix on the underlying network through hydrogen bonds, van der Waals forces, and possible further cross-linking with residual aldehyde groups in the underlying network. The final cleaning step removes any remaining unreacted cross-linking agents and acids, ensuring the coating's purity and biocompatibility. This step thickens the overall antibacterial layer, making its structure more uniform and dense, ultimately forming a robust and fully functional composite antibacterial layer.

[0046] In one embodiment, the second curing process involves drying at 50°C to 70°C for 5 to 10 minutes. Further, the curing time can be, but is not limited to, 50°C, 55°C, 60°C, 65°C, or 70°C, and the drying time can be, but is not limited to, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes.

[0047] In addition, after the second curing process, it can be rinsed with deionized water 3 to 4 times.

[0048] The ultrafiltration composite membrane preparation method of this invention adopts a "two-step coating-intermediate crosslinking" process. First, a base membrane is formed through non-solvent-induced phase separation. Then, an antibacterial layer is constructed through chitosan coating, crosslinking, secondary coating, and curing. This process is mild, simple, and highly controllable, requiring no complex post-processing and facilitating large-scale production. The resulting composite membrane exhibits strong interlayer bonding, with the chitosan layer forming a stable three-dimensional network. This maintains antibacterial activity while significantly improving the coating's durability and adhesion under high temperatures and fluid shear.

[0049] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0050] Example 1 16g of polyetheretherketone (PEEK) was dissolved in 84g of N-methylpyrrolidone (NMP) solvent and stirred at 70℃ for 10h until the PEEK was completely dissolved, resulting in a homogeneous and transparent casting solution. The casting solution was poured onto a nonwoven fabric, and a 150μm layer was slowly scraped onto the fabric using a doctor blade. The membrane was then placed in a room-temperature water coagulation bath, where the casting solution and water underwent non-solvent-induced phase separation (NIPS), and the PEEK gradually solidified and precipitated, forming a porous separation layer. After complete solidification, the base membrane was obtained and stored in deionized water.

[0051] Dissolve 0.3g of chitosan in 100g of 3% (volume concentration) acetic acid solution and stir at 50℃ for 1h to completely dissolve it, forming a chitosan coating solution; pour the chitosan coating solution onto the surface of the base film and scrape a 50μm thick first chitosan wet layer with a scraper.

[0052] The coated chitosan ultrafiltration membrane was dried in a 60°C oven for 2 minutes, then the entire composite membrane was immersed in a 3% glutaraldehyde aqueous solution for 3 minutes, and finally dried at 60°C for 5 minutes.

[0053] A second chitosan wet layer was formed by coating the dried chitosan / ultrafiltration membrane with a chitosan coating solution. The composite membrane was then dried at 60°C for 10 minutes. Finally, it was washed three times with deionized water. Once the chitosan layer was completely dry and cured, a pre-filtration antibacterial layer was formed, yielding the ultrafiltration composite membrane of Example 1.

[0054] Example 2 16g of polyvinylidene fluoride (PVDF) was dissolved in 84g of N-methylpyrrolidone (NMP) solvent and stirred at 70°C for 10 hours until the PEEK was completely dissolved, resulting in a homogeneous and transparent casting solution. The casting solution was poured onto a nonwoven fabric, and a 150μm layer was slowly scraped onto the fabric using a doctor blade. The membrane was then placed in a room-temperature water coagulation bath, where the casting solution and water underwent non-solvent-induced phase separation (NIPS), and PEEK gradually solidified and precipitated, forming a porous separation layer. After complete solidification, the base membrane was obtained and stored in deionized water.

[0055] Dissolve 0.3g of chitosan in 100g of 3% acetic acid solution and stir at 50℃ for 1h to completely dissolve it, forming a chitosan coating solution; pour the chitosan coating solution onto the surface of the base film and scrape a 50μm thick first chitosan wet layer with a doctor blade.

[0056] The coated chitosan ultrafiltration membrane was dried in a 60°C oven for 2 minutes, then the entire composite membrane was immersed in a 3% glutaraldehyde aqueous solution for 3 minutes, and finally dried at 60°C for 5 minutes.

[0057] A second chitosan wet layer was formed by coating the dried chitosan / ultrafiltration membrane with a chitosan coating solution. The composite membrane was then dried at 60°C for 10 minutes. Finally, it was washed three times with deionized water until the chitosan layer was completely dried and cured to form a pre-filtration antibacterial layer, thus obtaining the ultrafiltration composite membrane of Example 2.

[0058] Example 3 16g of polyethersulfone ketone (PEEK) was dissolved in 82g of N-methylpyrrolidone (NMP) solvent and stirred at 70℃ for 10h until the PEEK was completely dissolved, resulting in a homogeneous and transparent casting solution. The casting solution was poured onto a nonwoven fabric, and a 150μm layer was slowly scraped onto the fabric using a doctor blade. The membrane was then placed in a room-temperature water coagulation bath, where the casting solution and water underwent non-solvent-induced phase separation (NIPS), and PEEK gradually solidified and precipitated, forming a porous separation layer. After complete solidification, the base membrane was obtained and stored in deionized water.

[0059] Dissolve 0.3g of chitosan in 100g of 3% acetic acid solution and stir at 50℃ for 1h to completely dissolve it, forming a chitosan coating solution; pour the chitosan coating solution onto the surface of the base film and scrape a 50μm thick first chitosan wet layer with a doctor blade.

[0060] The coated chitosan ultrafiltration membrane was dried in a 60°C oven for 2 minutes, then the entire composite membrane was immersed in a 3% glutaraldehyde aqueous solution for 3 minutes, and finally dried at 60°C for 5 minutes.

[0061] A second chitosan wet layer was formed by coating the dried chitosan / ultrafiltration membrane with a chitosan coating solution. The composite membrane was then dried at 60°C for 10 minutes. Finally, it was washed three times with deionized water until the chitosan layer was completely dried and cured to form a pre-filtration antibacterial layer, thus obtaining the ultrafiltration composite membrane of Example 3.

[0062] Example 4 16g of polyarylsulfone was dissolved in 82g of N-methylpyrrolidone (NMP) solvent and stirred at 70℃ for 10h until the polyether ether ketone was completely dissolved, resulting in a homogeneous and transparent casting solution. The casting solution was poured onto a nonwoven fabric, and a 150μm layer was slowly scraped onto the fabric using a doctor blade. The membrane was then placed in a room-temperature water coagulation bath, where the casting solution and water underwent non-solvent-induced phase separation (NIPS), and PEEK gradually solidified and precipitated, forming a porous separation layer. After complete solidification, the base membrane was obtained and stored in deionized water.

[0063] Dissolve 0.3g of chitosan in 100g of 3% acetic acid solution and stir at 50℃ for 1h to completely dissolve it, forming a chitosan coating solution; pour the chitosan coating solution onto the surface of the base film and scrape a 50μm thick first chitosan wet layer with a doctor blade.

[0064] The coated chitosan ultrafiltration membrane was dried in a 60°C oven for 2 minutes, then the entire composite membrane was immersed in a 3% glutaraldehyde aqueous solution for 3 minutes, and finally dried at 60°C for 5 minutes.

[0065] A second chitosan wet layer was formed by coating the dried chitosan / ultrafiltration membrane with a chitosan coating solution. The composite membrane was then dried at 60°C for 10 minutes. Finally, it was washed three times with deionized water until the chitosan layer was completely dried and cured to form a pre-filtration antibacterial layer, thus obtaining the ultrafiltration composite membrane of Example 4.

[0066] Comparative Example 1 16g of polyetheretherketone (PEEK) was dissolved in 84g of N-methylpyrrolidone (NMP) solvent and stirred at 70℃ for 10h until the PEEK was completely dissolved, resulting in a homogeneous and transparent casting solution. The casting solution was poured onto a nonwoven fabric, and a 150μm layer was slowly scraped onto the fabric using a doctor blade. The membrane was then placed in a room-temperature water coagulation bath, where the casting solution and water underwent non-solvent-induced phase separation (NIPS). PEEK gradually solidified and precipitated, forming a porous separation layer. After complete solidification, the ultrafiltration membrane of Comparative Example 1 was obtained and stored in deionized water.

[0067] Performance testing: The antibacterial properties and water flux of the composite ultrafiltration membranes of Examples 1-4 and the ultrafiltration membrane of Comparative Example 1 were tested respectively. The test methods are as follows, and the results are shown in Tables 1 and 2.

[0068] (1) Antibacterial test: Escherichia coli was used as a representative bacterium to test the antibacterial properties of the membrane. The composite membranes of Examples 1-4 and Comparative Example 1 were laid flat in a sterile culture dish, and the same amount of Escherichia coli was added. The membranes were incubated at 37°C for 24 hours, and the colonies were counted on a counting plate.

[0069] Table 1. Antibacterial performance test results of the composite ultrafiltration membranes of Examples 1-4 and the ultrafiltration membrane of Comparative Example 1. As shown in Table 1, all embodiments (1-4) employing the structure of this invention exhibit a perfect combination of high water flux (>590 LMH) and high antibacterial rate (>98%). Comparative Example 1 (pure PEEK membrane) showed a lower flux and almost no antibacterial activity (5.2%). This demonstrates the decisive role of the chitosan pre-filtration layer in achieving highly efficient antibacterial activity. The higher flux of the structure of this invention compared to the pure PEEK membrane is presumably due to the hydrophilic chitosan layer improving the wettability of the membrane surface and reducing the initial filtration resistance.

[0070] (2) Water flux test: Water flux was tested at 25℃, 60℃, 90℃ and 25℃ in sequence.

[0071] Water flux testing method: The water flux of the composite membrane was tested at 1 bar using a cross-flow apparatus. The formula for calculating pure water flux Jw (LMH) is as follows: ; Where M represents the mass of permeated water (kg), A represents the effective area of ​​the membrane (m2), and Δt represents the permeation time (h).

[0072] Table 2. Test results of heat resistance of the composite ultrafiltration membranes of Examples 1-4 and the ultrafiltration membrane of Comparative Example 1. As shown in Table 2, the ultrafiltration composite membranes prepared in this invention (Examples 1-4) exhibit excellent thermal stability. After undergoing a complete thermal cycle from 25°C to 90°C and then back to 25°C, the flux recovery rate of the membranes in each example was close to 99% (e.g., Example 1 recovered from 621.6 LMH to 619.3 LMH). This data strongly demonstrates that the overall structure of the composite membrane (including the heat-resistant polymer separation layer and the chemically cross-linked chitosan antibacterial layer) did not undergo irreversible damage, shrinkage, or interlayer delamination at high temperatures. Particularly noteworthy is that at 90°C, the flux of Examples 1-4 (1688.9 LMH~1750.3 LMH) was significantly higher than that of Comparative Example 1 (1175.9 LMH), indicating that it not only has a stable structure but also superior separation efficiency at high temperatures. This stable thermal recovery performance is the key reason why the membranes of this invention are suitable for high-temperature fluid processing conditions (such as hot water sterilization).

[0073] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0074] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An ultrafiltration composite membrane, characterized in that, The ultrafiltration composite membrane includes a stacked base membrane and a pre-filtration antibacterial layer; The base film includes a support and a heat-resistant polymer separation layer, wherein the heat-resistant polymer separation layer is located on one side of the support and at least partially penetrates into the interior of the support; The pre-filtered antibacterial layer is a composite chitosan layer with a three-dimensional network structure that is chemically cross-linked.

2. The ultrafiltration composite membrane according to claim 1, characterized in that, The thickness of the pre-filtered antibacterial layer is 20μm~100μm.

3. The ultrafiltration composite membrane according to claim 1, characterized in that, The polymer material of the heat-resistant polymer separation layer is selected from at least one of polyetheretherketone, polyvinylidene fluoride, polyethersulfone ketone, and polyarylsulfone; and / or The thickness of the heat-resistant polymer separation layer is 100μm~200μm.

4. The ultrafiltration composite membrane according to claim 1, characterized in that, The support is made of non-woven fabric.

5. A method for preparing an ultrafiltration composite membrane according to any one of claims 1 to 4, characterized in that, Includes the following steps: A heat-resistant polymer material is dissolved in an organic solvent to form a casting solution; the casting solution is coated onto one side of a support, and a heat-resistant polymer separation layer is formed through non-solvent-induced phase separation to obtain a base film; and Chitosan is dissolved in a dilute acid solution to form a chitosan coating solution; the chitosan coating solution is then coated onto the surface of the heat-resistant polymer separation layer of the base film to form a first chitosan wet layer. The first chitosan wet layer is subjected to a first curing treatment, and then immersed in a crosslinking agent aqueous solution for crosslinking treatment; The chitosan coating solution is coated again on the cross-linked surface to form a second chitosan wet layer, followed by a second curing process to obtain an ultrafiltration composite membrane with the pre-filtered antibacterial layer.

6. The method for preparing the ultrafiltration composite membrane according to claim 5, characterized in that, The dissolution temperature of the heat-resistant polymer material in the organic solvent is 60℃~80℃, and the dissolution time is 10 hours~24 hours; and / or The heat-resistant polymer material has a mass percentage concentration of 15%~18% in the casting solution; and / or The organic solvent includes one or more of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.

7. The method for preparing the ultrafiltration composite membrane according to claim 5, characterized in that, The dissolution temperature of chitosan in dilute acid solution is 50℃~70℃, and the dissolution time is 1 hour~5 hours; and / or The chitosan coating solution contains chitosan at a mass concentration of 0.2% to 0.5%; and / or The dilute acid solution is an aqueous solution of acetic acid with a volume concentration of 2% to 3%.

8. The method for preparing the ultrafiltration composite membrane according to claim 6, characterized in that, The first curing process involves drying at 50°C to 70°C for 2 to 5 minutes.

9. The method for preparing the ultrafiltration composite membrane according to claim 6, characterized in that, The crosslinking agent aqueous solution has a mass concentration of 2% to 4%; and / or The crosslinking agent includes one or more of glutaraldehyde, terephthalaldehyde, tannic acid, and sodium tripolyphosphate.

10. The method for preparing the ultrafiltration composite membrane according to claim 6, characterized in that, The second curing process involves drying at 50°C to 70°C for 5 to 10 minutes.

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