Hydrophilic polyvinylidene fluoride hollow fiber membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of membrane separation, and discloses a hydrophilic polyvinylidene fluoride hollow fiber membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, mixing polyvinylidene fluoride and a composite diluent, and melting to obtain a spinning solution; s2, spinning by using the spinning solution to obtain a polyvinylidene fluoride hollow fiber original membrane; s3, extracting the polyvinylidene fluoride hollow fiber original membrane to obtain a polyvinylidene fluoride hollow fiber base membrane; and S4, placing the polyvinylidene fluoride hollow fiber base membrane in a hydrophilic modified monomer solution, and performing irradiation to obtain the hydrophilic polyvinylidene fluoride hollow fiber membrane. The hydrophilic polyvinylidene fluoride hollow fiber membrane disclosed by the invention has excellent mechanical property and separation property, and can be used as a membrane material which has enough strength and flexibility and can efficiently separate and intercept target substances in the fields of water treatment, biological pharmacy or food processing and the like; and a reliable material basis is provided for technology development and efficiency improvement of related industries.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and discloses a hydrophilic polyvinylidene fluoride hollow fiber membrane, its preparation method, and its application. Background Technology

[0002] In the biopharmaceutical field, virus clearance is a core step in ensuring the safety of biological products, directly impacting patient medication safety and product quality stability. Virus-removing membranes, as a key means of physical virus removal, have their material properties that decisively influence filtration efficiency, protein recovery rate, and process economics. Currently, mainstream virus-removing membrane materials include cellulose and its derivatives, polyethersulfone (PES), and polyvinylidene fluoride (PVDF).

[0003] Cellulose membranes are prone to irreversible shrinkage after drying, requiring storage and transportation in a moist state. This not only increases storage and transportation costs and operational complexity but also limits their large-scale application in industrial production. For example, while the regenerated cellulose virus-removing membrane disclosed in Japanese Patent JP1984204911A exhibits good clearance effects against HIV (approximately 100 nm), its clearance capacity for small viruses in the 20 nm-100 nm range (such as hepatitis B virus, nAnB hepatitis virus, and mouse parvovirus) is insufficient, failing to meet current stringent viral safety standards. Furthermore, its complex storage and transportation conditions further restrict the industrial-scale promotion of this technology.

[0004] While polyethersulfone (PES) membrane materials can achieve highly efficient virus removal through their composite structure design, their inherent defects are difficult to overcome. For example, Chinese patent CN113842792A discloses an asymmetric PES virus removal filter membrane, which achieves effective virus retention through a composite structure of a pre-filtration layer and a separation layer, resulting in a high logarithmic virus removal rate. However, PES materials themselves have poor hydrophilicity, leading to high protein adsorption and low recovery rates, which cannot meet the urgent needs of the biopharmaceutical industry for high protein yields. Especially in the production of high-cost biopharmaceuticals such as monoclonal antibodies and vaccines, protein loss directly increases manufacturing costs, limiting the economic feasibility of the technology.

[0005] Despite the comprehensive advantages of PVDF in terms of material properties, its preparation process still faces the following challenges: (1) The preparation process of PVDF membranes involves various additives (such as pore-forming agents, surfactants, modifiers, solubilizers, etc.), which will gradually dissolve and enter the product stream during subsequent cleaning and filtration, posing a potential safety risk to biological products (such as vaccines, antibodies, cell therapy products, etc.). (2) PVDF material itself has strong hydrophobicity, which will lead to severe protein adsorption and low protein recovery rate during filtration, and will also increase the membrane's tendency to foul and shorten its service life. (3) PVDF virus removal membranes not only need to have good filtration performance, but also need to have good biocompatibility to ensure that they do not have adverse effects on the active ingredients in biological products. However, the chemical substances introduced during the existing PVDF membrane surface modification process usually change the surface properties of the membrane and affect its biocompatibility (generating toxic byproducts or adsorbing biomolecules, leading to reduced biological activity).

[0006] Therefore, developing a PVDF hollow fiber virus removal membrane that is simple to process, uses readily available raw materials, is safe to modify and has low dissolution, combines high virus retention capacity and high protein yield, and meets the requirements of biomedical applications is a key challenge to overcome the application bottleneck of virus removal filter membrane materials and promote their large-scale application in the field of virus removal in high-value biological products. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a hydrophilic polyvinylidene fluoride hollow fiber membrane, its preparation method, and its application.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a hydrophilic polyvinylidene fluoride hollow fiber membrane, comprising the following steps: S1. Polyvinylidene fluoride and a composite diluent are mixed and melted to obtain a spinning solution; the composite diluent includes a first diluent, a second diluent, and a third diluent in a mass ratio of (0.5-5):(1.5-4):1; the first diluent includes at least one of acetylacetonate tributyl citrate, tributyl citrate, triethyl citrate, dibutyl phthalate, diethyl phthalate, dimethyl phthalate, triacetin, methyl salicylate, and tributyl phosphate; the second diluent includes at least one of benzophenone, diphenyl ether, and diphenyl carbonate; the third diluent includes at least one of propylene carbonate, hydroxyethoxymethyl, caprolactam, and γ-butyrolactone. S2. Spinning is performed using the spinning solution to obtain a polyvinylidene fluoride hollow fiber membrane; S3. Extract the polyvinylidene fluoride hollow fiber original membrane to obtain a polyvinylidene fluoride hollow fiber base membrane; S4. The polyvinylidene fluoride hollow fiber base membrane is placed in a hydrophilic modified monomer solution and irradiated to obtain the hydrophilic polyvinylidene fluoride hollow fiber membrane; the hydrophilic modified monomer is a vinyl monomer containing hydrophilic groups.

[0009] This invention discloses a method for preparing hydrophilic polyvinylidene fluoride hollow fiber membranes. Through a synergistic process combining precise control of raw material composition, thermally induced phase separation (TIPS), and irradiation grafting modification, the method achieves efficient conversion from raw materials to asymmetric (three-layer porous structure) high-performance hydrophilic polyvinylidene fluoride hollow fiber membranes. This ensures the excellent mechanical and separation properties of the hydrophilic polyvinylidene fluoride hollow fiber membranes, making them suitable as membrane materials with sufficient strength and flexibility, as well as efficient separation and retention of target substances, for applications in water treatment, biopharmaceuticals, or food processing. This provides a reliable material basis for the technological development and efficiency improvement of related industries. First, the preparation method of the hydrophilic polyvinylidene fluoride hollow fiber membrane of this invention, through the synergistic effect of a ternary composite diluent system, induces more refined and controllable phase separation behavior during melt blending and subsequent cooling, jointly regulating the microstructure of the membrane and achieving the formation of an asymmetric three-layer porous structure. The first diluent, as the main diluent, exhibits good compatibility with polyvinylidene fluoride at high temperatures and separates from it in a liquid-solid (LS) mode during cooling, ensuring the full dissolution and plasticization of the polyvinylidene fluoride polymer. The second and third diluents, as synergistic diluents and solid-liquid phase separation diluents, regulate the phase separation rate and nucleation process, contributing to the formation of a bicontinuous, interconnected microporous framework, providing the membrane with high specific surface area and porosity, while ensuring the nascent membrane has good operational strength. Second, the composite diluent system also solidifies the polymer-rich phase during the spinning and phase separation stages to form the main structure of the membrane, precisely forming the macroscopic hollow fiber morphology and microscopic porous structure of the nascent membrane, giving it high virus retention capacity and high protein yield. Furthermore, the preparation method of the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention also performs chemical grafting hydrophilic modification on the membrane surface and the inner wall of the membrane pores. By covalently introducing hydrophilic molecular chain segments, it is ensured that the hydrophilic layer not only exists on the membrane surface, but also penetrates into the internal pores of the membrane, realizing bulk phase modification, significantly reducing the water contact angle of the membrane, endowing the membrane with antifouling properties, and because it is chemically grafted, the hydrophilic effect is long-lasting and stable, and is not easily lost due to use or cleaning, which greatly extends the service life of the membrane.

[0010] In a preferred embodiment of the method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention, the mass ratio of the first diluent, the second diluent, and the third diluent is (1.5-2):(2-2.5):1.

[0011] Preferably, the mass ratio of the first diluent, the second diluent, and the third diluent is 1.5:2.5:1.

[0012] In a preferred embodiment of the method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention, the mass percentage of polyvinylidene fluoride in the spinning solution is 25wt%-50wt%.

[0013] Preferably, the mass percentage of polyvinylidene fluoride in the spinning solution is 30wt%-45wt%.

[0014] In a preferred embodiment of the method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention, the melt viscosity of the polyvinylidene fluoride is 2500 Pa·s-8500 Pa·s.

[0015] Preferably, the melt viscosity of the polyvinylidene fluoride is 4500 Pa·s-8500 Pa·s.

[0016] In a preferred embodiment of the method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention, the first diluent includes at least one of dibutyl phthalate, diethyl phthalate, dimethyl phthalate, and triacetin; the second diluent is diphenyl carbonate; and the third diluent is propylene carbonate and / or hydroxyethoxymethyl ester.

[0017] In a preferred embodiment of the method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention, in step S1, the instrument used for melting is a twin-screw extruder; the temperature of the twin-screw extruder is as follows: zone 1 100℃-150℃, zone 2 150℃-190℃, zone 3 160℃-220℃, zone 4 180℃-260℃, zone 5 180℃-260℃, zone 6 180℃-250℃, zone 7 180℃-250℃, screen changing temperature control zone 180℃-250℃, and gear pump 180℃-250℃.

[0018] Preferably, the temperatures of the twin-screw extruder are as follows: Zone 1 130℃-140℃, Zone 2 170℃-180℃, Zone 3 190℃-200℃, Zone 4 200℃-210℃, Zone 5 200℃-210℃, Zone 6 195℃-205℃, Zone 7 190℃-195℃, screen changing temperature control zone 190℃-195℃, and gear pump 190℃-195℃. As a preferred embodiment of the preparation method of the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention, in step S2, the spinning method is as follows: the spinning solution is extruded through a spinneret and the core liquid is injected into the inner cavity of the extruded fiber, and then solidified in a coagulation bath.

[0019] Preferably, the core fluid includes at least one of acetylated tributyl citrate, tributyl citrate, triethyl citrate, dibutyl phthalate, diethyl phthalate, dimethyl phthalate, triacetin, methyl salicylate, and tributyl phosphate.

[0020] Preferably, the solute in the coagulation bath includes at least one of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; the concentration of the solute is 20wt%-60wt%.

[0021] Preferably, the temperature of the spinneret is 190℃-230℃.

[0022] Preferably, the temperature of the core fluid is 25℃-190℃.

[0023] Preferably, the temperature of the coagulation bath is 25℃-40℃.

[0024] As a preferred embodiment of the preparation method of the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention, in step S3, the extractant used for extraction is any one of methanol, ethanol, isopropanol, and petroleum ether, the extraction method is distillation and cyclic soaking, and the extraction endpoint is when the absorbance of the soaking solution is ≤0.03 as measured by ultraviolet spectrophotometer.

[0025] Preferably, the extractant used in the extraction is ethanol.

[0026] In a preferred embodiment of the method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention, in step S4, the hydrophilic modifying monomer includes at least one of hydroxyethyl methacrylate, acrylic acid, methacrylic acid, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, glycidyl methacrylate, sodium styrene sulfonate, N-(3-dimethylaminopropyl)methacrylamide, 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate, and 2-methacryloyloxyethylphosphorylcholine; the concentration of the hydrophilic modifying monomer is 0.5wt%-3wt%; and the solvent of the hydrophilic modifying monomer solution includes water and alcohol.

[0027] Preferably, the concentration of the hydrophilic modified monomer is 1wt%-2wt%.

[0028] Preferably, the solvent of the hydrophilic modified monomer solution comprises water and alcohol in a mass ratio of (1-6):1.

[0029] Preferably, the alcohol includes at least one of methanol, ethanol, and isopropanol.

[0030] More preferably, the alcohol is isopropanol.

[0031] In a preferred embodiment of the method for preparing polyvinylidene fluoride hollow fiber membrane according to the present invention, in step S4, the irradiation used is gamma ray; the irradiation dose is 10kGy-30kGy.

[0032] Preferably, the γ-rays are cobalt-60 γ-rays.

[0033] Preferably, the irradiation dose is 20kGy-30kGy.

[0034] More preferably, the irradiation dose is 25kGy-27kGy.

[0035] Secondly, the present invention provides a hydrophilic polyvinylidene fluoride hollow fiber membrane prepared by the preparation method described above.

[0036] In a preferred embodiment of the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention, the hydrophilic polyvinylidene fluoride hollow fiber membrane comprises, from the inside out, a loose layer, an intermediate layer, and a dense layer; the pore size of the loose layer is 150nm-200nm and the thickness is 10μm-20μm; the pore size of the intermediate layer is 80nm-120nm and the thickness is 20μm-40μm; the pore size of the dense layer is 20nm-60nm and the thickness is 5μm-10μm.

[0037] The hydrophilic polyvinylidene fluoride hollow fiber membrane of this invention comprises, from the inside out, a loose layer, an intermediate layer, and a dense layer. The loose layer effectively removes polymeric proteins and protects the dense separation layer from fouling. The intermediate layer serves as a pre-separation layer, gradually adsorbing and retaining some viruses while maintaining high throughput. The dense layer is a small virus retention zone, achieving efficient size exclusion of small viruses while keeping mass transfer resistance at a low level. Furthermore, this hydrophilic polyvinylidene fluoride hollow fiber membrane undergoes hydrophilic modification, chemically grafting hydrophilicity onto both the membrane surface and the inner walls of the pores. This results in a larger specific surface area, leading to lower protein adsorption and extremely high protein recovery. Moreover, the pore size and membrane thickness remain essentially unchanged after hydrophilic modification. This asymmetric structural design constructs a three-level protection system of "pre-filtration-pre-separation-fine retention" through functional stratification and pore size gradient. While ensuring high retention performance of small viruses, it significantly improves the membrane's anti-fouling ability and operational stability, making it particularly suitable for high-value-added bioseparation fields such as vaccine purification and blood product virus filtration.

[0038] Thirdly, the present invention provides the application of the hydrophilic polyvinylidene fluoride hollow fiber membrane in wastewater treatment, gas separation, drug purification, and food processing.

[0039] Compared with existing technologies, the beneficial effects of this invention are as follows: First, by leveraging the synergistic effect of a ternary composite diluent system and thermally induced phase separation (TIPS) technology, this invention effectively regulates the asymmetric structure formation process of the membrane, precisely controls the phase separation kinetic path, and successfully induces the formation of an asymmetric three-layer porous structure with a loose layer, an intermediate layer, and a dense layer. This results in a final product that simultaneously possesses high mechanical strength, high porosity, and excellent permeability, achieving a balance between high throughput and high rejection rate (such as efficient virus rejection and high protein yield). Second, this invention employs irradiation grafting technology to modify the bulk phase of the base membrane, firmly grafting hydrophilic functional groups onto the membrane surface and internal pores via covalent bonds. This significantly enhances the membrane's hydrophilicity and antifouling properties. Furthermore, due to the stability of its chemical bonds, the hydrophilic effect is durable and not easily lost during use or cleaning, greatly extending the membrane's service life and operational stability. Furthermore, the preparation method provided by this invention is simple, the conditions are controllable, and it is easy to scale up production. The resulting hydrophilic polyvinylidene fluoride hollow fiber membrane has excellent comprehensive performance. While maintaining the inherent excellent mechanical properties and chemical stability of PVDF materials, it also has high efficiency separation capability and long-term anti-fouling characteristics, making it suitable for long-term operation in harsh environments. It provides a high-performance, long-life membrane material solution for separation processes in water treatment, biopharmaceuticals, and food processing. Attached Figure Description

[0040] Figure 1 This is an electron microscope image of the cross-section of the PVDF hollow fiber base membrane obtained in step S5 of Example 1 of the present invention; Figure 2 This is an electron microscope image of the pore structure of the PVDF hollow fiber base membrane obtained in step S5 of Example 1 of the present invention. Figure 3 The images shown are electron microscope images of the intermediate layer and the dense layer of the PVDF hollow fiber base membrane obtained in step S5 of Example 1 of the present invention. Figure 4 The image shows an electron microscope image of the intermediate layer and the porous layer of the PVDF hollow fiber base membrane obtained in step S5 of Example 1 of the present invention. Figure 5 This is an electron microscope image of the outer surface of the PVDF hollow fiber base membrane obtained in step S5 of Embodiment 1 of the present invention. Detailed Implementation

[0041] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0042] The following description, in conjunction with specific embodiments, illustrates the practical effects of the present invention.

[0043] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials, reagents, equipment, etc. used are all commercially available unless otherwise specified.

[0044] Example 1: This embodiment prepares a hydrophilic polyvinylidene fluoride hollow fiber membrane. The preparation method includes the following steps: S1. Polyvinylidene fluoride, triacetin, diphenyl carbonate, and propylene carbonate are crushed and mixed evenly at high speed. The mass fraction of polyvinylidene fluoride is 40 parts, and the mass ratio of triacetin, diphenyl carbonate, and propylene carbonate is 2:2:1 (the mass fraction of triacetin is 24 parts, the mass fraction of diphenyl carbonate is 24 parts, and the mass fraction of propylene carbonate is 12 parts). Then, the mixture is transferred to the feed hopper of a twin-screw extruder.

[0045] S2. Set the temperature of the twin-screw extruder. The temperatures of each zone are 140℃, 180℃, 200℃, 210℃, 210℃, 205℃, and 195℃ respectively. The temperature of the screen changing temperature control zone is 195℃, and the temperature of the gear pump is 195℃.

[0046] S3. When the discharge port of the spinneret is stable, transparent, and free of bubbles, stop the machine and install the spinneret and core liquid pipeline. Set the spinneret temperature to 195℃, the core liquid to triacetin, and the core liquid tank temperature to room temperature (25℃). The coagulation bath is a dimethylacetamide aqueous solution (the mass percentage of dimethylacetamide in the dimethylacetamide aqueous solution is 20wt%), the coagulation bath temperature is 30℃, and the cleaning tank water temperature is 70℃.

[0047] S4. Once the temperature reaches the set value, spinning will begin.

[0048] S5. After winding the fibers, cut them and extract them with distilled circulating ethanol for 3 hours each time. The ethanol temperature should not exceed 70℃. Replace with fresh ethanol and repeat three times until the absorbance is measured to be ≤0.03 by UV spectrophotometer to obtain PVDF hollow fiber base film.

[0049] S6. Immerse the extracted PVDF hollow fiber membrane in water for complete displacement. Prepare a 1 wt% sodium styrene sulfonate modified solution, wherein the solute is sodium styrene sulfonate and the solvent is an aqueous isopropanol solution (isopropanol and water mass ratio is 1:1); add 0.05m 2 The membrane fibers were packed into a PE / PET composite bag, 200 mL of sodium styrene sulfonate modified solution was added, and after sealing, it was sent for γ-ray irradiation with an absorbed dose of 25 kGy.

[0050] S7. After irradiation, the membrane fibers are removed and washed repeatedly three times in pure water at 50°C to obtain a hydrophilic PVDF hollow fiber membrane for virus removal.

[0051] The morphology of the PVDF hollow fiber base membrane obtained in step S5 was characterized using scanning electron microscopy.

[0052] like Figure 1-5 As shown, the PVDF hollow fiber membrane obtained in this embodiment has an asymmetric cross-sectional structure, consisting of a loose layer, an intermediate separation layer, and a dense separation layer on the outer surface, from the inside out. The loose layer serves as a pre-filtration layer with a relatively large pore size of approximately 150nm-200nm and a thickness of 10μm-20μm. The intermediate layer is the pre-separation layer with a pore size distribution of 80nm-150nm and a thickness of 20μm-40μm. The dense separation layer is a small virus trapping zone with a pore size distribution of 20nm-60nm and a thickness of 5μm-10μm.

[0053] Meanwhile, this embodiment uses a hydrophilic modification method to not only chemically graft hydrophilic modification onto the membrane surface, but also chemically graft hydrophilic modification onto the inner wall of the membrane pores. The hydrophilic specific surface area is larger, resulting in lower protein adsorption and extremely high protein recovery rate. Moreover, after hydrophilic modification, the membrane pore size and membrane thickness remain basically unchanged.

[0054] Example 2: This embodiment prepares a hydrophilic polyvinylidene fluoride hollow fiber membrane. The preparation method includes the following steps: S1. Polyvinylidene fluoride, diethyl phthalate, diphenyl carbonate, and hydroxyethoxymethyl are crushed and mixed evenly at high speed. The mass fraction of polyvinylidene fluoride is 35 parts, and the mass ratio of diethyl phthalate, diphenyl carbonate, and hydroxyethoxymethyl is 1.5:2.5:1 (the mass fraction of diethyl phthalate is 19.5 parts, the mass fraction of diphenyl carbonate is 32.5 parts, and the mass fraction of hydroxyethoxymethyl is 13 parts). Then, the mixture is transferred to the feed hopper of a twin-screw extruder.

[0055] S2. Set the temperature of the twin-screw extruder. The temperatures of each zone are 130℃, 170℃, 190℃, 200℃, 200℃, 195℃, and 190℃ respectively. The temperature of the screen changing temperature control zone is 190℃, and the temperature of the gear pump is 190℃.

[0056] S3. When the discharge port of the spinneret head is stable, transparent, and free of bubbles, stop the machine and install the spinneret and core liquid pipeline. Set the spinneret temperature to 190℃, the core liquid to dibutyl phthalate, and the core liquid tank temperature to room temperature (25℃). The coagulation bath is an aqueous solution of N-methylpyrrolidone (20wt% N-methylpyrrolidone by mass), the coagulation bath temperature is 30℃, and the cleaning tank water temperature is 70℃.

[0057] S4. Once the temperature reaches the set value, spinning will begin.

[0058] S5. After winding the fibers, cut them and extract them with distilled circulating ethanol for 3 hours each time. The ethanol temperature should not exceed 70℃. Replace with fresh ethanol and repeat three times until the absorbance is measured to be ≤0.03 by UV spectrophotometer to obtain PVDF hollow fiber base film.

[0059] S6. Immerse the extracted PVDF hollow fiber membrane in water to fully displace it. Prepare a 1.5 wt% 2-methacryloyloxyethyl phosphorylcholine (MPC) modified solution, wherein the solute is 2-methacryloyloxyethyl phosphorylcholine and the solvent is an aqueous isopropanol solution (isopropanol to water mass ratio of 7:13); Add 0.05 m 2 The membrane fibers were packed into a PE / PET composite bag, 200 mL of 2-methacryloyloxyethyl phosphorylcholine (MPC) modified solution was added, and after sealing, it was sent for γ-ray irradiation with an absorbed dose of 26 kGy.

[0060] S7. After irradiation, the membrane fibers are removed and washed repeatedly three times in pure water at 50°C to obtain a hydrophilic PVDF hollow fiber membrane for virus removal.

[0061] Test Example: Performance Testing The performance of the hydrophilic antiviral PVDF hollow fiber membranes of the above comparative examples and embodiments was characterized by the following test methods: (1) Mechanical strength test Test method: A 100mm long hydrophilic PVDF hollow fiber virus-removing membrane was fixed at both ends on a tensile testing machine and tested using an electronic universal testing machine. The tensile speed used was 200mm / min, and the tensile strength and elongation at break were measured.

[0062] (2) Pure water flux test Test method: A hydrophilic PVDF hollow fiber virus-removing membrane and a membrane shell are encapsulated into a small component. The membrane component is used as a filter element. The pure water flux is tested using the internal pressure method (i.e., pure water enters the inner side of the hollow fiber membrane under a certain pressure, and the filtrate flows out on the outer side of the membrane). The test pressure is adjusted to 3 bar, the pure water temperature is 25℃, and after stabilizing for 30 minutes, the permeate volume (V) is collected for a certain time (t). The effective membrane area of ​​the membrane component is A.

[0063] Pure water flux: Calculate the pure water flux (L·m) corresponding to the virus-free membrane using the formula J=V / (t×A). -2 ·h -1 ).

[0064] (3) Membrane protein flux and protein permeability test Test method: The hydrophilic PVDF hollow fiber virus removal membrane and membrane shell were encapsulated into a small component. The membrane component was used as the filter element. The internal pressure method was used, and intravenous human immunoglobulin (ivig, 50g / L) was used as the stock solution for testing. The test pressure was adjusted to 3 bar, and the stock solution temperature was 25℃. After the system was running stably, the permeate was collected for 30 minutes and the volume of the permeate was measured.

[0065] The calculation method for protein flux is the same as that for pure water flux. The protein flux (L·m³) corresponding to the viral membrane is calculated using the formula J = V / (t × A). -2 ·h -1 ).

[0066] Protein transmittance: Using a UV-Vis spectrophotometer with distilled water as a reference, the absorbance of the stock protein solution and the collected permeate solution after a 250-fold dilution was measured at a wavelength of 280 nm. The protein transmittance was then calculated using the following formula: Protein permeability (%) = Cp / Cf × 100%, where Cp is the concentration of protein (ivig) in the permeate and Cf is the concentration of protein (ivig) in the original solution, in mg / ml.

[0067] (4) Gold nanoparticle retention rate test Test method: A hydrophilic PVDF hollow fiber virus-removing membrane and a membrane shell were encapsulated into a small component. The membrane component was used as the filter element. The internal pressure method was used to simulate parvovirus with gold nanoparticles (15nm). The gold nanoparticle solution was diluted 50 times and used as the feed liquid for testing. The test pressure was adjusted to 3 bar and the original solution temperature was 25℃. After the system ran stably for 5 minutes, about 3 ml of filtrate was collected to test the gold nanoparticle solution.

[0068] The absorbance of the feed liquid and the permeate was measured at a wavelength of 521 nm using a UV-Vis spectrophotometer with distilled water as a reference.

[0069] Retention rate R = (C1-C2) / C1×100%, where C1 is the concentration of gold nanoparticles in the feed liquid in mg / L, and C2 is the concentration of gold nanoparticles in the filtrate in mg / L.

[0070] Table 1 shows the performance test results of the hydrophilic PVDF hollow fiber membranes in the examples and comparative examples. As can be seen from the data in the table, the polyvinylidene fluoride (PVDF) hollow fiber membrane of this invention exhibits excellent mechanical and separation properties. It can be used as a membrane material with sufficient strength and flexibility, capable of efficiently separating and retaining target substances, in industries such as water treatment, biopharmaceuticals, and food processing, thus promoting industry development and progress. Firstly, the PVDF hollow fiber membrane of this invention possesses high tensile strength and good elongation at break, meaning it can withstand greater external forces in practical applications without breaking. Furthermore, it can undergo significant deformation without rupture when subjected to tension or deformation. This characteristic makes the PVDF hollow fiber membrane of this invention more adaptable to complex water flow environments or potential localized stress concentrations, maintaining structural integrity, reducing the risk of membrane damage, and further enhancing the membrane's reliability and stability. Secondly, the polyvinylidene fluoride (PVDF) hollow fiber membrane of this invention has strong water permeability, enabling it to process more water in the same amount of time, thus improving water treatment efficiency. It can also effectively retain proteins while ensuring a certain protein flux, achieving a good balance between flux and retention performance, meeting the requirements for efficient protein separation and recovery in production processes. Furthermore, the PVDF hollow fiber membrane of this invention has extremely strong retention capacity for small particles, effectively blocking the passage of viruses. This ensures that the virus content in treated water or liquid products is extremely low, meeting safety standards and providing strong protection for public health safety. Therefore, the PVDF hollow fiber membrane of this invention, with its superior mechanical and separation performance, demonstrates enormous application potential and market value. It can not only meet the diverse needs of different industries for membrane materials but also bring higher efficiency, lower costs, and better product quality to the production processes of various industries.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a hydrophilic polyvinylidene fluoride hollow fiber membrane, characterized in that, Includes the following steps: S1. Polyvinylidene fluoride and a composite diluent are mixed and melted to obtain a spinning solution; the composite diluent includes a first diluent, a second diluent, and a third diluent in a mass ratio of (0.5-5):(1.5-4):1; the first diluent includes at least one of acetylacetonate tributyl citrate, tributyl citrate, triethyl citrate, dibutyl phthalate, diethyl phthalate, dimethyl phthalate, triacetin, methyl salicylate, and tributyl phosphate; the second diluent includes at least one of benzophenone, diphenyl ether, and diphenyl carbonate; the third diluent includes at least one of propylene carbonate, hydroxyethoxymethyl, caprolactam, and γ-butyrolactone. S2. Spinning is performed using the spinning solution to obtain a polyvinylidene fluoride hollow fiber membrane; S3. Extract the polyvinylidene fluoride hollow fiber original membrane to obtain a polyvinylidene fluoride hollow fiber base membrane; S4. The polyvinylidene fluoride hollow fiber base membrane is placed in a hydrophilic modified monomer solution and irradiated to obtain the hydrophilic polyvinylidene fluoride hollow fiber membrane; the hydrophilic modified monomer is a vinyl monomer containing hydrophilic groups.

2. The method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane as described in claim 1, characterized in that, The mass ratio of the first diluent, the second diluent, and the third diluent is (1.5-2):(2-2.5):

1.

3. The method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane as described in claim 1, characterized in that, The mass percentage of polyvinylidene fluoride in the spinning solution is 25wt%-50wt%.

4. The method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane as described in claim 1, characterized in that, The first diluent includes at least one of dibutyl phthalate, diethyl phthalate, dimethyl phthalate, and triacetin; the second diluent is diphenyl carbonate; and the third diluent is propylene carbonate and / or hydroxyethoxymethyl ester.

5. The method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane as described in claim 1, characterized in that, In step S1, the instrument used for melting is a twin-screw extruder; the temperature of the twin-screw extruder is as follows: Zone 1 100℃-150℃, Zone 2 150℃-190℃, Zone 3 160℃-220℃, Zone 4 180℃-260℃, Zone 5 180℃-260℃, Zone 6 180℃-250℃, Zone 7 180℃-250℃, screen changing temperature control zone 180℃-250℃, gear pump 180℃-250℃.

6. The method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane as described in claim 5, characterized in that, The temperatures of the twin-screw extruder are as follows: Zone 1 130℃-140℃, Zone 2 170℃-180℃, Zone 3 190℃-200℃, Zone 4 200℃-210℃, Zone 5 200℃-210℃, Zone 6 195℃-205℃, Zone 7 190℃-195℃, screen changing temperature control zone 190℃-195℃, and gear pump 190℃-195℃.

7. The method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane as described in claim 1, characterized in that, In step S4, the hydrophilic modifying monomer includes at least one of hydroxyethyl methacrylate, acrylic acid, methacrylic acid, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, glycidyl methacrylate, sodium styrene sulfonate, N-(3-dimethylaminopropyl)methacrylamide, 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate, and 2-methacryloyloxyethylphosphorylcholine; the concentration of the hydrophilic modifying monomer is 0.5wt%-3wt%; and the solvent of the hydrophilic modifying monomer solution includes water and alcohol.

8. The method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane as described in claim 1, characterized in that, In step S4, the radiation used for irradiation is gamma rays; the irradiation dose is 10 kGy-30 kGy.

9. The hydrophilic polyvinylidene fluoride hollow fiber membrane prepared by the preparation method according to any one of claims 1-8.

10. The application of the hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 9 in wastewater treatment, gas separation, drug purification, and food processing.

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