Hydrophilic polyvinylidene fluoride hollow fiber membranes, methods of making the same, and uses thereof

Abstract

This invention relates to a method for preparing hydrophilic polyvinylidene fluoride (PVDF) hollow fiber membranes, comprising the following steps: (1) melt-blending PVDF with a diluent to form a homogeneous PVDF-diluent solution, wherein the diluent contains at least one photoinitiator; (2) molding the PVDF-diluent solution from step (1) into a PVDF hollow fiber precursor membrane; (3) partially removing the diluent from the PVDF hollow fiber precursor membrane obtained in step (2) by extraction, followed by removal of the extractant; (4) immersing the PVDF hollow fiber precursor membrane obtained in step (3) in a hydrophilic monomer solution, and initiating a photopolymerization reaction of the hydrophilic monomer by ultraviolet light irradiation to obtain a hydrophilically modified PVDF hollow fiber membrane. This invention also relates to the hydrophilic PVDF hollow fiber membrane obtained by this method and its use in biopharmaceutical separation processes.

Description

Technical Field

[0001] This invention relates to a technique for preparing a hydrophilic polyvinylidene fluoride hollow fiber membrane, and more specifically, to a method for preparing a hydrophilic polyvinylidene fluoride hollow fiber membrane by combining thermally induced phase separation with free radical polymerization graft copolymerization, as well as the polyvinylidene fluoride hollow fiber membrane prepared therefrom and its use in biopharmaceutical separation processes. Background Technology

[0002] Membrane separation technology is a highly efficient separation process that combines concentration, purification, and refining functions, offering advantages such as low energy consumption, high efficiency, no phase change, and mild operating conditions. Hollow fiber membranes are one of the main types of separation membranes due to their self-supporting nature, high packing density, strong fouling resistance, high recovery rate, and low replacement cost. They are widely used in wastewater treatment, water purification, and material separation, concentration, and recovery in environmental protection, food industry, medical, and electronics industries. Currently, the main methods for preparing hollow fiber membranes include non-solvent-induced phase separation (NIPS), thermally induced phase separation (TIPS), and melt-spinning / cold-stretching (MSCS). The TIPS method for preparing hollow fiber membranes offers high controllability, film-forming stability, structural regularity, and mechanical strength. Furthermore, it allows for precise control of the pore size, enabling the fabrication of membranes suitable for precise separation processes in the food, biopharmaceutical, and medical industries. However, hollow fiber membranes prepared using the TIPS method are typically highly hydrophobic, making them prone to interaction and adsorption with proteins, polysaccharides, and other substances during use. This can lead to performance degradation or low product yield. Therefore, hollow fiber membranes prepared by the TIPS method require hydrophilic modification to enhance their hydrophilicity and reduce the adsorption of products or pollutants, thereby further improving the potential of this type of hollow fiber membrane in practical applications.

[0003] Existing TIPS hollow fiber membrane preparation processes struggle to incorporate hydrophilic substances into the production formulation to achieve hydrophilicity in the hollow fiber membrane. Therefore, post-treatment methods such as chemical grafting or physical coating are commonly used for modification. While physical coating is simple, the binding force between the hydrophilic substance and the hollow fiber membrane is weak, and the coated hydrophilic substance can be washed off by the feed solution, leading to feed product contamination and membrane performance degradation. Therefore, covalent bonding-based chemical grafting is the preferred method for addressing the hydrophilicity of hollow fiber membranes used in biopharmaceuticals. Chemical grafting involves pretreating the TIPS-prepared hollow fiber membrane with free radicals or active groups through methods such as gamma-ray or beta-ray irradiation, low-temperature plasma treatment, or acid-base treatment. Modification is then achieved through graft polymerization or direct grafting of hydrophilic substances. However, the pretreatment process often leads to the breakage of polymer molecular chains, resulting in a decrease in the overall mechanical properties of the hollow fiber membrane, affecting product performance and service life. Furthermore, this strategy of producing hollow fiber membranes first and then performing pretreatment and hydrophilic modification results in a discontinuity between the membrane fiber production and modification processes. This leads to a longer overall production cycle for hydrophilic modified hollow fiber membranes, increases uncontrollable factors in the production process, and raises the risk of unstable performance in the resulting membranes. In addition, too many processes can cause problems such as hollow fiber membrane entanglement and breakage, increasing the production cost of hollow fiber membranes. Summary of the Invention

[0004] To address the above problems, this invention provides a method for preparing hydrophilic polyvinylidene fluoride hollow fiber membranes, the method comprising the following steps:

[0005] (1) 20-60% by weight, preferably 40-50% by weight, of polyvinylidene fluoride (PVDF) and 40-80% by weight, preferably 50-60% by weight, of a diluent are melt-blended at a temperature of 180-240°C, preferably 220-240°C, to form a homogeneous PVDF-diluent solution, wherein the diluent contains at least one photoinitiator, and the weight percentages are based on the weight of the PVDF-diluent solution.

[0006] (2) The polyvinylidene fluoride-diluent solution from step (1) is molded into a polyvinylidene fluoride hollow fiber membrane.

[0007] (3) The diluent in the polyvinylidene fluoride hollow fiber membrane obtained in step (2) is partially removed by extraction, and then the extractant is removed.

[0008] (4) The polyvinylidene fluoride hollow fiber membrane obtained in step (3) is immersed in a hydrophilic monomer solution, and then the photopolymerization reaction of the hydrophilic monomer is initiated by ultraviolet light irradiation to obtain a hydrophilic modified polyvinylidene fluoride hollow fiber membrane.

[0009] On the other hand, the present invention also provides a hydrophilic polyvinylidene fluoride hollow fiber membrane obtained by the method of the present invention.

[0010] In another aspect, the present invention also provides the use of polyvinylidene fluoride hollow fiber membranes in biopharmaceutical separation processes.

[0011] The method of the present invention has the following advantages over the prior art:

[0012] 1. This method involves pre-mixing a free radical polymerization initiator into the casting solution, so that the free radical polymerization initiator is uniformly distributed in the polyvinylidene fluoride hollow fiber original membrane prepared by thermally induced phase separation. In other words, the free radical polymerization initiator is implanted into the polyvinylidene fluoride hollow fiber membrane, and then the free radical polymerization of aqueous monomers is initiated, so that the aqueous polymer is grafted onto the surface of the hollow fiber membrane through covalent bonds. This results in the modified polyvinylidene fluoride hollow fiber membrane having good hydrophilicity and low protein adsorption.

[0013] 2. Compared with the NIPS method, TIPS has many advantages: it promotes phase separation of the polymer solution through relatively rapid heat exchange, rather than slow solvent-non-solvent exchange, thus avoiding the disadvantage of low porosity caused by the partial participation of solvent in the polymer gelation in the film-forming solution due to solvent-non-solvent exchange in the NIPS method; the TIPS method can be used to prepare crystalline polymer microporous filter membranes that are difficult to prepare using the NIPS method, and the influencing factors of the TIPS method are fewer and easier to control than those of the NIPS method; moreover, the TIPS method can obtain a variety of microstructures, such as open pores, closed pores, isotropic, anisotropic, and asymmetric pores. The polyvinylidene fluoride hollow fiber membrane prepared by the method of this invention has a uniform pore size and uniform pore distribution.

[0014] 3. The hydrophilic modified polyvinylidene fluoride hollow fiber membrane can maintain the mechanical properties before modification, such as the tensile strength and elongation at break.

[0015] 4. This invention uses a continuous method to prepare hydrophilic polyvinylidene fluoride hollow fiber membranes, which is simple to operate and saves costs.

[0016] 5. The hydrophilic polyvinylidene fluoride hollow fiber membrane prepared by this invention remains stable in performance after a long operating time. Attached Figure Description

[0017] Figure 1 This is a SEM image of the outer surface of the polyvinylidene fluoride hollow fiber membrane prepared in Example 1.

[0018] Figure 2 This is a SEM image of the outer surface of the polyvinylidene fluoride hollow fiber membrane prepared in Comparative Example 4.

[0019] Figure 3 This is a SEM image of the outer surface of the polyvinylidene fluoride hollow fiber membrane prepared in Comparative Example 3.

[0020] Figure 4 The graph shows the relationship between protein flux and operating time for the polyvinylidene fluoride hollow fiber membranes prepared in Examples 1, 3, and 4.

[0021] Figure 5 The graph shows the relationship between protein throughput and operating time for the polyvinylidene fluoride hollow fiber membranes prepared in Examples 1, 3, and 4.

[0022] Figure 6 This is a graph showing the relationship between the residual amount of diluent in the original polyvinylidene fluoride hollow fiber membrane and the extraction time. Detailed Implementation

[0023] In this invention, unless otherwise stated, the content ratio refers to the weight ratio.

[0024] The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membranes according to the present invention includes the following steps:

[0025] (1) 20-60% by weight, preferably 40-50% by weight, of polyvinylidene fluoride (PVDF) and 40-80% by weight, preferably 50-60% by weight, of a diluent are melt-blended at a temperature of 180-240°C, preferably 220-240°C, to form a homogeneous PVDF-diluent solution, wherein the diluent contains at least one photoinitiator, and the weight percentages are based on the weight of the PVDF-diluent solution.

[0026] (2) The polyvinylidene fluoride-diluent solution from step (1) is molded into a polyvinylidene fluoride hollow fiber membrane.

[0027] (3) The diluent in the polyvinylidene fluoride hollow fiber membrane obtained in step (2) is partially removed by extraction, and then the extractant is removed.

[0028] (4) Immerse the polyvinylidene fluoride hollow fiber membrane obtained in step (3) into a hydrophilic monomer solution, and then place it under ultraviolet light, for example in an ultraviolet irradiation chamber, to initiate the photopolymerization reaction of the hydrophilic monomer and obtain a hydrophilic modified polyvinylidene fluoride hollow fiber membrane.

[0029] In a preferred embodiment of the present invention, the melt index (MFR, 230°C, 5kg) of the polyvinylidene fluoride used in the present invention is preferably 1-20g / 10min, obtained by means of the ASTM D1238 method.

[0030] The diluent is an organic solvent that can form a homogeneous solution with polyvinylidene fluoride at temperatures above 150°C and is immiscible with each other at temperatures below 100°C. Preferably, the diluent is composed of two or more organic solvents, provided that the boiling point of each organic solvent is not lower than 240°C.

[0031] More preferably, the diluent may be a high-temperature solvent for polyvinylidene fluoride (PVDF), or a mixture of a high-temperature solvent for PVDF and a non-solvent. Preferably, the content of the high-temperature solvent in the mixture is 70-90% by weight, preferably 75-85% by weight; the content of the non-solvent is 10-30% by weight, preferably 15-25% by weight, both based on the total weight of the mixture of the high-temperature solvent and the non-solvent. A high-temperature solvent refers to a solvent that can form a homogeneous solution with PVDF in a temperature range of 170-250°C, and that this homogeneous solution undergoes phase separation in a temperature range of 0-90°C. A non-solvent refers to a solvent that cannot form a homogeneous solution with PVDF in any temperature range.

[0032] Preferably, the high-temperature solvent is a photoinitiator, which can generate active free radicals capable of initiating free radical polymerization under ultraviolet light irradiation at a wavelength of 320-400 nm. The photoinitiator is preferably selected from one or a mixture of more than one of the following: benzoin dimethyl ether, 4-phenylbenzophenone, 4-chlorobenzophenone, 4-methylbenzophenone, 1-hydroxycyclohexylbenzophenone, 2-hydroxy-2-methylacetophenone, ethyl 4-dimethylaminobenzoate, methyl o-benzoylbenzoate, 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide, and ethyl 2,4,6-trimethylbenzoylphenylphosphonate, preferably 4-methylbenzophenone or 4-chlorobenzophenone; wherein the non-solvent is selected from C 10 -C 20 - Alkanoic acid or alkanoic alcohol, preferably C 12 -C 16 - Alkanoic acid or alkanoic alcohol, more preferably C 14 -C 16 - Alkyl acids or alkyl alcohols.

[0033] Preferably, in step (1), polyvinylidene fluoride and diluent are melt-blended by mechanical stirring, extrusion mixing or other methods to form a uniform polyvinylidene fluoride-diluent high-temperature solution.

[0034] Preferably, in step (2), after the polyvinylidene fluoride-diluent high-temperature solution in step (1) is degassed, it is driven by pressure through a spinneret with an annular die, and then pulled into a cooling liquid at 0-50°C for 0.1-10s to form a polyvinylidene fluoride hollow fiber original membrane.

[0035] The driving pressure is preferably provided by an extruder or compressed gas. The compressed gas is preferably nitrogen.

[0036] The extruder can be any extruder known in the art for preparing hollow fiber membranes, such as a twin-screw extruder. The air section temperature after the spinneret is preferably 5-30°C, for example, 25°C. The air section residence time can be arbitrarily selected, typically 10-300 ms, and the extrusion speed of the polyvinylidene fluoride hollow fiber membrane is preferably 20-80 m / min. The cooling water bath temperature is preferably 5-50°C, for example, 30°C.

[0037] The coolant is a non-solvent mixture of polyvinylidene fluoride and a diluent, preferably water or a mixture of water with ethanol, n-propanol, isopropanol, and glycerol.

[0038] Preferably, in step (3), the residual amount of the diluent is 0.5 to 30% by weight, preferably 0.5 to 5.5% by weight, more preferably 0.5 to 1.5% by weight, and most preferably 0.9 to 1.3% by weight, based on the total weight of the polyvinylidene fluoride hollow fiber original membrane.

[0039] Preferably, in step (3), the extractant is a good solvent that is not a solvent for polyvinylidene fluoride and is also a diluent, preferably ethanol, n-propanol, or isopropanol. To ensure the extraction rate, the extraction temperature should be as high as possible, but needs to be at least 10°C lower than the boiling point of the extractant.

[0040] Preferably, in step (3), the extraction time is 5-25 min, more preferably 12-15 min.

[0041] Preferably, in step (3), the extractant can be removed by, for example, drying, at a temperature not exceeding 60°C.

[0042] Preferably, the polyvinylidene fluoride hollow fiber membrane obtained in step (3) is hydrophilically modified by the following steps:

[0043] a) The unmodified polyvinylidene fluoride hollow fiber membrane from step (3) is drawn into a monomer solution at a constant temperature of 20-80℃ and immersed for 1-20 minutes to allow the monomer solution to fully immerse the unmodified polyvinylidene fluoride hollow fiber membrane pores. Then, the unmodified polyvinylidene fluoride hollow fiber membrane is drawn through an annular air knife to remove excess liquid from its surface.

[0044] b) Graft polymerization: Unmodified polyvinylidene fluoride hollow fiber membranes impregnated with monomer solutions are pulled through an ultraviolet irradiation chamber to undergo photo-initiated polymerization, thereby completing the hydrophilic modification of the polyvinylidene fluoride hollow fiber membranes.

[0045] c) Post-treatment: The polyvinylidene fluoride hollow fiber membrane is drawn into a water washing tank to clean the unreacted monomers and diluents. The cleaned polyvinylidene fluoride hollow fiber membrane is then drawn into an oven, preferably an infrared oven, to dry it, thereby obtaining a hydrophilic polyvinylidene fluoride hollow fiber membrane. The solution in the water washing tank is preferably a 10-75% by weight ethanol aqueous solution.

[0046] Preferably, in step (4), the hydrophilic monomer is a compound containing hydroxyl, ester, carboxylic acid, epoxy groups and double bonds capable of free radical polymerization, preferably selected from one or more of hydroxybutyl acrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, glycidyl acrylate, 2-methoxyethyl acrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and glycidyl methacrylate, with hydroxyethyl methacrylate being the most preferred.

[0047] Preferably, the concentration of the hydrophilic monomer is 1-50% by weight, more preferably 4-45% by weight, even more preferably 4-30% by weight, and most preferably 10-30% by weight, based on the total weight of the hydrophilic monomer solution; preferably, the solvent of the hydrophilic monomer solution is a mixed solution of water and alcohol, preferably with a weight ratio of water:alcohol = 20:80 to 80:20, and preferably, the alcohol is ethanol, n-propanol, isopropanol, or isobutanol.

[0048] The aforementioned ultraviolet irradiation chamber can achieve annular irradiation of hollow fibers, using a power of 12000 MW / cm². 2 The UV LED lamp has an irradiation time of 0.1-5 minutes.

[0049] Preferably, in the post-processing step c), the cleaned polyvinylidene fluoride hollow fiber membrane is drawn into an infrared oven for drying at a temperature of 60 to 100°C for a duration of 5 to 30 minutes.

[0050] The membrane fiber traction is controlled by a traction system, which includes multiple tension sensors, a drive wheel, and a final take-up hub. Traction is achieved through the drive wheel and the take-up hub, tension is sensed by the tension sensors, and the rotation speed of the drive wheel and the take-up hub is controlled by an electronic control system to ensure that the tension of each part of the hollow fiber membrane during the traction process is below 20 cN.

[0051] In a preferred embodiment of the present invention, the method for preparing the hydrophilic polyvinylidene fluoride hollow fiber membrane is a continuous method.

[0052] The present invention also relates to a hydrophilic polyvinylidene fluoride hollow fiber membrane obtained by the above method.

[0053] The present invention also relates to the use of hydrophilic polyvinylidene fluoride hollow fiber membranes in biopharmaceutical separation processes.

[0054] In this invention, the hydrophilicity of the hydrophilically modified polyvinylidene fluoride hollow fiber membrane is controlled by adjusting the residual amount of diluent (i.e., by changing the extraction time), the concentration of aqueous monomers, and the UV irradiation time, thereby affecting the water and protein permeability of the hydrophilically modified polyvinylidene fluoride hollow fiber membrane.

[0055] The hydrophilic modified polyvinylidene fluoride hollow fiber membrane obtained by the method of the present invention has better mechanical properties. Moreover, the modified membrane has enhanced hydrophilicity, lower protein adsorption, and improved protein flux and / or protein permeability. Therefore, the polyvinylidene fluoride hollow fiber membrane obtained by the present invention is better suited for the separation of protein product systems.

[0056] The following examples are intended to illustrate the invention but not to limit it.

[0057] In this invention, unless otherwise stated, all operations are performed at room temperature and normal pressure.

[0058] Example

[0059] Example 1:

[0060] Step (1): Blending of raw materials.

[0061] 45 wt.% polyvinylidene fluoride (MFR (230℃, 5 kg) = 4-8 g / 10 min) was blended with 45 wt.% 4-methylbenzophenone and 10 wt.% tetradecanoic acid. The mixture was then fed into a twin-screw extruder at a feed rate of 0.8 kg / h. The mixture was heated to 230℃ in the twin-screw extruder for melt blending for approximately 2 min, resulting in a homogeneous high-temperature solution of polyvinylidene fluoride, 4-methylbenzophenone, and tetradecanoic acid.

[0062] Step (2): Preparation of the original membrane.

[0063] After the polyvinylidene fluoride-diluent high-temperature solution in step (1) is degassed by the degassing section of a twin-screw extruder, it is drawn through a spinneret with an annular die at a speed of 30 m / min through a 20 ms room temperature air section and then cooled in a 50°C water bath for 10 s to form a polyvinylidene fluoride hollow fiber original film.

[0064] Step (3): Extraction.

[0065] The polyvinylidene fluoride hollow fiber membrane from step (2) is drawn into ethanol at 60°C and 99% of the diluent is removed from the polyvinylidene fluoride hollow fiber membrane by extraction for 15 min. The ethanol is then removed by drying (temperature 60°C, time 30 min) to obtain the polyvinylidene fluoride hollow fiber membrane.

[0066] Step (4): Photoinitiated modification.

[0067] Photoinitiation is performed according to the following steps:

[0068] (a) Monomer coating: The unmodified polyvinylidene fluoride hollow fiber membrane from step (3) is drawn into a 10 wt.% hydroxyethyl methacrylate ethanol / water (weight ratio ethanol / water = 1 / 2) solution at a constant temperature of 40°C and immersed for 5 min to allow the hydroxyethyl methacrylate solution to fully penetrate the pores of the unmodified polyvinylidene fluoride hollow fiber membrane. Then, the original polyvinylidene fluoride hollow fiber membrane is drawn through an annular air knife to remove excess liquid from the surface.

[0069] (b) Graft polymerization: Unmodified polyvinylidene fluoride hollow fiber membranes impregnated with hydroxyethyl methacrylate solution are drawn through an ultraviolet irradiation chamber (using a power of 12000 MW / cm²). 2 The UV LED lamp was used to treat the polyvinylidene fluoride hollow fiber membrane at a constant temperature of 80℃ for 1 minute, which caused photo-initiated polymerization and completed the hydrophilic modification of the membrane.

[0070] (c) Post-processing: The polyvinylidene fluoride hollow fiber membrane is drawn into a water tank to clean the unreacted monomers. Then, the cleaned polyvinylidene fluoride hollow fiber membrane is drawn into an infrared oven to dry (temperature 80℃, time 15min) to obtain a hydrophilic polyvinylidene fluoride hollow fiber membrane.

[0071] Example 2:

[0072] The concentration of the ethanol / water (ethanol / water = 1 / 2) solution of hydroxyethyl methacrylate in step (4)(a) of Example 1 was reduced to 1 wt., while other conditions remained unchanged.

[0073] Example 3

[0074] The concentration of hydroxyethyl methacrylate in the ethanol / water (ethanol / water = 1 / 2) solution of hydroxyethyl methacrylate in step (4)(a) of Example 1 was reduced to 4 wt.%, while other conditions remained unchanged.

[0075] Example 4

[0076] The concentration of hydroxyethyl methacrylate in the ethanol / water (ethanol / water = 1 / 2) solution of hydroxyethyl methacrylate in step (4)(a) of Example 1 was increased to 30 wt.%, while other conditions remained unchanged.

[0077] Example 5

[0078] The ultraviolet irradiation time in step (4)(b) of Example 1 was extended to 2 minutes, while other conditions remained unchanged.

[0079] Example 6

[0080] In Example 1, step (1), 45 wt.% of 4-methylbenzophenone and 10 wt.% of tetradecanoic acid were replaced with 42 wt.% of 4-chlorobenzophenone and 13 wt.% of hexadecyl alcohol, while other conditions remained unchanged.

[0081] Example 7

[0082] In Example 1, the concentration of hydroxyethyl methacrylate in the ethanol / water (ethanol / water = 1 / 2) solution of hydroxyethyl methacrylate in step (4)(a) of Example 1 was increased to 45 wt.%, while other conditions remained unchanged.

[0083] Example 8

[0084] The extraction time in step (3) of Example 1 was set to 12 minutes, while other conditions remained unchanged.

[0085] Example 9

[0086] The extraction time in step (3) of Example 1 was set to 5 minutes, while other conditions remained unchanged.

[0087] Comparative Example 1

[0088] In Example 1, step (1) was performed by replacing 45 wt.% of 4-methylbenzophenone and 10 wt.% of tetradecanoic acid with 52 wt.% of diphenyl carbonate and 3 wt.% of hexadecyl alcohol, which do not have photoinitiating polymerization properties, while keeping other conditions unchanged.

[0089] Comparative Example 2

[0090] The extraction time in step (3) of Example 1 was extended to 50 minutes until the diluent was completely extracted. The residual amount of diluent was determined according to the method described below, with other conditions remaining unchanged.

[0091] Comparative Example 3

[0092] The extraction time in step (3) of Example 1 was extended to 50 minutes until the diluent was completely extracted. The prepared membrane was then immersed in a 2 wt.% 4-methylbenzophenone ethanol solution for 5 minutes, and then the subsequent photoinitiation modification step was carried out, with other conditions remaining unchanged.

[0093] Comparative Example 4

[0094] The extraction time in step (3) of Example 1 was extended to 50 minutes until the diluent was completely extracted and the photoinitiation modification in step (4) was not performed, thus obtaining the unmodified polyvinylidene fluoride hollow fiber original membrane.

[0095] Comparative Example 5

[0096] Preparation of polyvinylidene fluoride hollow fiber membranes by NIPS method

[0097] 1) Polyvinylidene fluoride (MFR (230℃, 5kg) = 4-8g / 10min), 4-methylbenzophenone, polyvinylpyrrolidone, and N,N-dimethylacetamide are prepared in a weight ratio of 30:1:9:60. After preliminary mixing to obtain a slurry, it is fed into a twin-screw extruder at a feeding rate of 0.8kg / h. The slurry is then heated to 90℃ by the twin-screw extruder for melt blending to form a uniform polyvinylidene fluoride solution.

[0098] 2) Preparation of the original membrane. After the polyvinylidene fluoride solution in step 1) is degassed by the degassing section of a twin-screw extruder, it is drawn into a 50°C water bath at a speed of 30 m / min through a spinneret with an annular die to gel and form a polyvinylidene fluoride hollow fiber membrane.

[0099] 3) Water washing. The polyvinylidene fluoride hollow fiber membrane from step 2) is drawn into pure water at 60°C and washed for 15 minutes to remove polyvinylpyrrolidone and N,N-dimethylacetamide from the polyvinylidene fluoride hollow fiber membrane. Then, the water is removed by drying to obtain the unmodified polyvinylidene fluoride hollow fiber membrane prepared by the NIPS method.

[0100] Comparative Example 6

[0101] Preparation of hydrophilic polyvinylidene fluoride hollow fiber membranes by NIPS method

[0102] The unmodified polyvinylidene fluoride hollow fiber membrane obtained in Comparative Example 5 was subjected to hydrophilic modification through the following steps:

[0103] a) Monomer coating: The unmodified polyvinylidene fluoride hollow fiber membrane prepared by the NIPS method in step 3) of Comparative Example 5 was drawn into a 10 wt.% hydroxyethyl methacrylate ethanol / water (weight ratio ethanol / water = 1 / 2) solution at a constant temperature of 40°C and immersed for 5 min to allow the hydroxyethyl methacrylate solution to fully penetrate the pores of the unmodified polyvinylidene fluoride hollow fiber membrane. Then, the unmodified polyvinylidene fluoride hollow fiber membrane was drawn through an annular air knife to remove excess liquid from the surface.

[0104] b) Graft polymerization: Unmodified polyvinylidene fluoride hollow fiber membrane impregnated with hydroxyethyl methacrylate solution is pulled through an ultraviolet irradiation chamber and treated with light at a constant temperature of 80°C for 1 min to initiate polymerization and complete the hydrophilic modification of polyvinylidene fluoride hollow fiber membrane.

[0105] c) Post-processing: The polyvinylidene fluoride hollow fiber membrane is drawn into a water tank to clean the unreacted monomers. The cleaned polyvinylidene fluoride hollow fiber membrane is then drawn into an infrared oven to dry, thus obtaining a hydrophilic polyvinylidene fluoride hollow fiber membrane.

[0106] The properties of the modified hollow fiber membranes in the examples and comparative examples were characterized using the following test methods:

[0107] 1. Method for determining the residual amount of diluent after extraction

[0108] After preparing the polyvinylidene fluoride hollow fiber original membrane in step (3), take 50 cm of the original membrane fiber sample after extraction and drying, weigh it, and record its weight as M1. Then place the membrane fiber sample in a Soxhlet extractor and extract it repeatedly with ethanol for at least 1 hour. After removing the membrane fiber and drying it to constant weight, weigh it and record its weight as M0. The residual amount of diluent (the percentage of diluent relative to the weight of the polyvinylidene fluoride hollow fiber original membrane) can be calculated by the following formula:

[0109] Diluent residual amount % = (M1 - M0) / M0 × 100%

[0110] For example, the relationship between the residual amount of diluent and the extraction time after extraction of the polyvinylidene fluoride hollow fiber membrane obtained in step (2) of Comparative Example 2 was studied, and the relationship between the residual amount of diluent and the extraction time was recorded in [the relevant document / document / etc.]. Figure 6 middle.

[0111] 2. Average pore size and pore size distribution

[0112] At room temperature of 25℃, a 5cm sample of polyvinylidene fluoride hollow fiber membrane was taken and analyzed using a pore size analyzer (full-function membrane pore size analyzer, BSD-PBL, Beijing Best Instruments).

[0113] 3. Grafting rate

[0114] The diluent in the polyvinylidene fluoride hollow fiber membrane obtained in step (2) of the examples or comparative examples was completely extracted. A 10-meter-long section of the polyvinylidene fluoride hollow fiber membrane was selected, completely dried, and weighed. The mass was repeated three times and the average value was taken to obtain the mass M2 of the unmodified polyvinylidene fluoride hollow fiber membrane. A 10-meter-long section of the modified polyvinylidene fluoride hollow fiber membrane from the examples or comparative examples was selected, completely dried, and weighed. The mass was repeated three times and the average value was taken to obtain the mass M3 of the modified polyvinylidene fluoride hollow fiber membrane. The grafting rate (%) of the prepared modified polyvinylidene fluoride hollow fiber membrane was calculated using the following formula:

[0115] Grafting rate (%) = (M3 - M2) / M2 × 100%

[0116] 4. Measurement of water contact angle

[0117] Select membrane products with uniform inner and outer diameters of approximately 2 cm and dry them in a 60℃ oven for 1 hour. Use double-sided tape to smoothly attach the dried membrane products to the surface of a glass slide. Then, place the slide on the platform of a contact angle meter and measure the static contact angle using approximately 0.1 μL of pure water via the droplet method on a KRUSS-DSA100 contact angle meter to obtain the water contact angle of the membrane product. Measure the contact angles at three different locations for each membrane product and take the arithmetic mean of the contact angles to obtain the average contact angle of the membrane product.

[0118] 5. Testing of pure water flux

[0119] The hollow fiber membrane to be tested was encapsulated into a module and then placed in a membrane performance evaluation device (low-pressure membrane flux tester, model SF-SA, Hangzhou Saifei Membrane Separation Technology Co., Ltd.) for testing. The operating pressure was 0.2 MPa, the water temperature was 25℃, and pure water was pre-pressurized for more than half an hour until the flux stabilized. The permeate flow rate per unit time was then collected and measured. The pure water flux can be calculated using the following formula:

[0120] Jw=V / (A×ΔT)

[0121] In the formula, Jw is the pure water flux, in L·m -2 ·h -1 V represents the volume of water produced during the test time ΔT, in liters (L); A represents the effective filtration membrane area, in m². 2 ΔT represents the test time, in hours (h).

[0122] 6. Determination of protein adsorption properties

[0123] The hollow fiber membrane to be tested was dried at a constant temperature to a constant weight, and this weight was taken as its initial mass. After being successively soaked and washed with ethanol and deionized water, it was placed in a simulated protein-containing solution prepared with bovine serum albumin (BSA) (isoelectric point 4.7, negatively charged) (BSA concentration 1 mg / mL, solvent: deionized water). The membrane was immersed at 25°C for 24 hours to allow sufficient adsorption of BSA on the membrane surface and within the pores. After rinsing with deionized water and drying, its mass was measured. The protein adsorption capacity was obtained using the following formula:

[0124] Protein adsorption capacity = (M p -M0) / A

[0125] In the formula, protein adsorption capacity is expressed in μg / cm³. 2 M p M0 represents the mass of the hollow fiber membrane after protein adsorption, in μg; M0 represents the initial mass of the hollow fiber membrane, in μg; A represents the effective surface area of ​​the membrane, in cm². 2 .

[0126] 7. Determination of membrane protein flux and protein permeability

[0127] The protein flux was determined using a protein solution permeation experiment, specifically including the following steps: The hollow fiber membrane to be tested was encapsulated into a module and placed in a membrane performance evaluation device for testing (low-pressure membrane flux analyzer, model SF-SA, Hangzhou Saifei Membrane Separation Technology Co., Ltd.). Immunoglobulin (IgG) was prepared into a solution of approximately 10 mg / mL using PBS buffer as the stock solution for testing. The operating pressure was 0.2 MPa, and the operating temperature was 25°C. The permeate was collected for 20 minutes, and the permeate volume was measured. The membrane protein flux was calculated using the following formula:

[0128] J = V / (A × ΔT)

[0129] In the formula, J is the protein flux, L·m -2 ·h -1 V represents the volume of permeate collected within the test time ΔT, in L; A represents the effective filtration membrane area, in m². 2 ΔT is the test time, in hours.

[0130] The concentration of IgG protein in the stock solution and the collected permeate was determined using the Coomassie brilliant blue (G250, purchased from Beyotime Biotechnology) method. The protein permeability was calculated using the following formula:

[0131] Protein permeability (%) = C p / C f ×100%

[0132] In the formula, C p and C f The values ​​represent the concentrations of IgG in the permeate and stock solutions, respectively, in mg / mL.

[0133] The test results of the above embodiments and comparative examples are recorded in Table 1.

[0134] 8. Mechanical performance testing

[0135] Using the unmodified hollow fiber membrane from Comparative Example 4 as a sample, different pretreatments were applied, and the mechanical properties were tested. The specific pretreatment methods are as follows:

[0136] 1) Plasma treatment: Place the membrane fiber sample into the cavity of the plasma treatment equipment (CIF laboratory plasma cleaner CPC-F, CIF Corporation, USA), and treat it at a power of 50W for 30s or 60s in an oxygen atmosphere before taking it out.

[0137] 2) Irradiation treatment: The membrane fiber sample was placed in the cavity of the electron accelerator equipment (Jiangsu Leida Irradiation, 10MeV / 20-25KW high-energy electron accelerator irradiation device) and irradiated with a dose of 10kGy or 30kGy respectively before being taken out.

[0138] 3) Chemical treatment: After wetting the membrane fiber sample with ethanol and then with pure water, place it in 2 mol / L sodium hydroxide and place it at 60℃ for 15 min or 30 min respectively. After taking it out, rinse it with pure water.

[0139] The specific operating procedures for mechanical performance testing are as follows:

[0140] The dried hollow fiber membrane fibers were placed in the fixture of a tensile testing machine (electronic universal testing machine, model AGS-J 20N, Shimadzu Corporation, Japan). The gauge length of the hollow fiber membrane was set to 50 mm, and the membrane was stretched at a tensile speed of 250 mm / min until the fibers broke. The tensile force at which the membrane fibers broke is the breaking strength. The breaking strength and elongation at break of the hollow fiber membrane are obtained using the following formulas:

[0141] Tensile strength = Tensile force / Cross-sectional area of ​​membrane fiber

[0142] (The cross-sectional area of ​​the membrane fiber is the cross-sectional area of ​​the membrane fiber before the tensile test. The radial cross-section of the membrane fiber is observed by scanning electron microscopy, and the inner and outer diameters of the membrane fiber are measured from the electron microscope image, thereby calculating the cross-sectional area of ​​the membrane fiber.)

[0143] Elongation at break = (Tension distance at break / Gauge length) × 100%

[0144] The mechanical properties of the polyvinylidene fluoride hollow fiber membranes prepared in Example 1 and Comparative Examples 5 and 6 were determined, and the results are recorded in Table 2.

[0145] Table 1. Performance characterization results and main preparation parameters of hollow fiber membranes in the examples and comparative examples.

[0146]

[0147] According to Table 1:

[0148] 1. Comparing the modified polyvinylidene fluoride hollow fiber membranes in Examples 1-9 with the original polyvinylidene fluoride hollow fiber membrane in Comparative Example 4, it can be seen that the method of the present invention can achieve hydrophilic modification of the hollow fiber membrane. The water contact angle of the modified membrane decreases, indicating enhanced hydrophilicity. The modified membrane exhibits lower protein adsorption capacity, and improved protein flux and / or protein permeability, demonstrating that the modification method provided by the present invention can effectively improve the hydrophilicity of the polyvinylidene fluoride hollow fiber membrane, making it more suitable for the separation of protein product systems.

[0149] 2. Comparing the polyvinylidene fluoride hollow fiber membranes in Examples 1-9 with those in Comparative Example 1 or Comparative Example 2, it can be seen that when a photoinitiator is not used as a diluent or the photoinitiator diluent is completely cleaned from the membrane, the obtained polyvinylidene fluoride hollow fiber membrane is not effective. This indicates that the photoinitiator as a diluent and the subsequent modification steps provided by the present invention can achieve significant modification effects.

[0150] 3. The extraction time also affects the hydrophilicity of the obtained polyvinylidene fluoride hollow fiber membrane. For example, when the diluent / photoinitiator content in the original polyvinylidene fluoride hollow fiber membrane is very high, such as in Example 9 (extraction time 5 min), the water contact angle of the modified polyvinylidene fluoride hollow fiber membrane is larger than that in Example 1, that is, the hydrophilicity is poor.

[0151] Table 2. Mechanical performance test results

[0152] Example 1 163 7.78 290 Comparative Example 4 164 7.73 300 Plasma treatment for 30 seconds 148 6.98 190 Plasma treatment for 60 seconds 119 5.61 110 Irradiation treatment 10kGy 139 6.55 187 30kGy irradiation treatment 108 5.09 119 Chemical treatment for 15 min 154 7.26 210 Chemical treatment for 30 min 131 6.18 167 Comparative Example 5 110 5.19 149 Comparative Example 6 108 5.09 137

[0153] As shown in Table 2, compared with hydrophilic hollow fiber membranes obtained through other modification methods (plasma treatment, irradiation treatment, and chemical treatment), the hydrophilic polyvinylidene fluoride hollow fiber membrane of the present invention maintains better mechanical properties. Furthermore, the mechanical properties of the polyvinylidene fluoride hollow fiber membranes prepared by the NIPS method (Comparative Examples 5 and 6) are significantly worse.

[0154] according to Figure 1-3 It can be seen that the modified hollow fiber membrane prepared by the method of the present invention has a more uniform pore size and a more uniform pore distribution, which can minimize the influence of the grafted modified molecules on the pore size distribution of the membrane itself. Figure 3 In Comparative Example 3, the polyvinylidene fluoride hollow fiber membrane almost completely lost its pore structure.

[0155] In addition, the membranes from Example 1, Comparative Example 3, and Comparative Example 4 were subjected to long-term protein permeation tests to examine their operational stability. Samples were taken every 20 minutes to measure the mass of the permeate and the protein concentration, and the protein flux and permeation rate were calculated. The results are as follows: Figure 4 and Figure 5As shown in the figure, the polyvinylidene fluoride hollow fiber membrane of the present invention exhibits high stability in protein flux during long-term operation. This is presumably because by using a photoinitiator as a diluent, dispersing the photoinitiator in the polymer matrix of the membrane before hydrophilic modification, the interaction between the hydrophilic substance and the polymer matrix can be effectively enhanced, increasing the stability of the prepared membrane and ensuring high protein permeability and flux during long-term operation. In Comparative Example 3, a polyvinylidene fluoride hollow fiber primary membrane was first prepared, then immersed in an initiator solution, and subsequently graft copolymerized using hydrophilic monomers. The resulting hollow fiber membrane showed a decrease in protein flux over time in the protein flux test, indicating unstable performance.

[0156] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing hydrophilic polyvinylidene fluoride hollow fiber membranes, comprising the following steps: (1) 20-60% by weight of polyvinylidene fluoride (PVDF) and 40-80% by weight of diluent are melt-blended at a temperature of 180-240°C to form a homogeneous PVDF-diluent solution, wherein the weight percentage is based on the weight of the PVDF-diluent solution; wherein the diluent is a high-temperature solvent of PVDF, or a mixture of a high-temperature solvent of PVDF and a non-solvent, wherein the content of the high-temperature solvent in the mixture of the high-temperature solvent and the non-solvent is 70-90% by weight and the content of the non-solvent is 10-30% by weight, based on the total weight of the mixture of the high-temperature solvent and the non-solvent, wherein the high-temperature solvent is a photoinitiator selected from 4-chlorobenzophenone or 4-methylbenzophenone, and wherein the non-solvent is selected from C10-C20-alkanoic acid or alkanol. (2) The polyvinylidene fluoride-diluent solution from step (1) is molded into a polyvinylidene fluoride hollow fiber membrane. (3) The diluent in the polyvinylidene fluoride hollow fiber membrane obtained in step (2) is partially removed by extraction, and then the extractant is removed. The residual amount of the diluent is 0.5-30% by weight, based on the total weight of the polyvinylidene fluoride hollow fiber membrane. (4) The polyvinylidene fluoride hollow fiber membrane obtained in step (3) is immersed in a hydrophilic monomer solution, and the photopolymerization reaction of the hydrophilic monomer is initiated by ultraviolet light irradiation to obtain a hydrophilic modified polyvinylidene fluoride hollow fiber membrane.

2. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1, wherein in step (1), 40-50% by weight of polyvinylidene fluoride and 50-60% by weight of diluent are melt-blended at a temperature of 180-240°C to form a uniform polyvinylidene fluoride-diluent solution.

3. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1 or 2, wherein in step (1), polyvinylidene fluoride and diluent are melt-blended at a temperature of 220-240°C.

4. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1 or 2, wherein the content of high-temperature solvent in the mixture of high-temperature solvent and non-solvent is 75-85% by weight; and the content of non-solvent is 15-25% by weight, both based on the total weight of the mixture of high-temperature solvent and non-solvent.

5. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1 or 2, wherein the non-solvent is selected from C12-C16-alkanoic acids or alkanols.

6. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 5, wherein the non-solvent is selected from C14-C16-alkanoic acids or alkanols.

7. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1 or 2, wherein the residual amount of the diluent in step (3) is 0.5-5.5% by weight, based on the total weight of the original polyvinylidene fluoride hollow fiber membrane.

8. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 7, wherein the residual amount of the diluent in step (3) is 0.5-1.5% by weight, based on the total weight of the original polyvinylidene fluoride hollow fiber membrane.

9. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 8, wherein the residual amount of the diluent in step (3) is 0.9-1.3% by weight, based on the total weight of the original polyvinylidene fluoride hollow fiber membrane.

10. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1 or 2, wherein the hydrophilic monomer is selected from one or a mixture of more than one of hydroxybutyl acrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, glycidyl acrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and glycidyl methacrylate.

11. The method for preparing a hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1 or 2, wherein the concentration of the hydrophilic monomer solution is 1-50% by weight, based on the total weight of the hydrophilic monomer solution.

12. The method for preparing a hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 11, wherein the concentration of the hydrophilic monomer solution is 4-45% by weight, based on the total weight of the hydrophilic monomer solution.

13. The method for preparing a hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 12, wherein the concentration of the hydrophilic monomer solution is 4-30% by weight, based on the total weight of the hydrophilic monomer solution.

14. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 1 or 2, wherein the solvent of the hydrophilic monomer solution is a mixed solution of water and alcohol.

15. The method for preparing a hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 14, wherein the weight ratio of water to alcohol is 20:80 to 80:

20.

16. The method for preparing a hydrophilic polyvinylidene fluoride hollow fiber membrane according to claim 15, wherein the alcohol is ethanol, n-propanol, isopropanol or isobutanol.

17. The method for preparing hydrophilic polyvinylidene fluoride hollow fiber membranes according to claim 1 or 2, characterized in that... It is a continuous method.

18. A hydrophilic polyvinylidene fluoride hollow fiber membrane, obtained by the method according to any one of claims 1-17.

19. Use of the polyvinylidene fluoride hollow fiber membrane according to claim 18 in a biopharmaceutical separation process.

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