Hollow fiber membrane and method for producing the same

Abstract

The application discloses a preparation method of a hollow fiber membrane, comprising the following steps: co-extruding a spinning solution and a core liquid through a hollow fiber spinning spinneret, and obtaining primary membrane filaments through an air gap in sequence; and obtaining the hollow fiber membrane after the primary membrane filaments pass through a coagulation bath and are washed; wherein the core liquid comprises nanomaterials, pure water and a solvent; and the coagulation bath comprises a crosslinking agent and a solvent; the nanomaterials in the core liquid are driven to produce interface segregation and are enriched on the inner surface of the membrane by the difference in interfacial tension between the spinning solution and the core liquid; meanwhile, the crosslinking agent in the coagulation bath diffuses to the inner surface of the membrane through the support layer of the primary membrane filaments and forms a stable chemical bonding network with the nanomaterials on the inner surface of the membrane; and then, directional and stable loading of the nanomaterials on the inner surface of the membrane is realized, invalid dispersion and waste of the materials in the membrane matrix are avoided, and dissolution and loss of the nanomaterials in the process of washing and long-term use are effectively inhibited; meanwhile, the pure water flux and the anti-pollution performance of the membrane are improved, and the integrity of the membrane structure is maintained.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a hollow fiber membrane and its preparation method. Background Technology

[0002] Membrane separation technology, due to its advantages such as high separation efficiency, mild operating conditions, energy saving, and environmental friendliness, has been widely used in fields such as biopharmaceutical purification, pharmaceutical production, food processing, and industrial wastewater and drinking water purification. Among the many membrane materials, hollow fiber membranes have become the mainstream product in the fields of ultrafiltration and microfiltration due to their high packing density, large specific surface area, and good self-support.

[0003] Currently, the mainstream method for industrial-scale preparation of hollow fiber membranes made of polymers such as polysulfone (PSF), polyethersulfone (PES), and polyvinylidene fluoride (PVDF) is non-solvent-induced phase separation (NIPS). However, during the membrane formation process, the rapid evaporation of solvents on the membrane surface can easily lead to densification of the membrane skin and low porosity. As a result, the hollow fiber membranes produced generally suffer from insufficient pure water flux and poor surface hydrophilicity, which in turn leads to serious membrane fouling and shortens the membrane's service life.

[0004] To improve membrane surface properties, the industry typically adds hydrophilic additives to spinning solutions. Among these, nano-hydrophilic materials are considered highly promising modifiers due to their combination of superhydrophilic properties and nucleation-inducing effects. Current technologies often employ a method of directly physical blending nanomaterials with polymer spinning solutions for modification; however, this method has significant drawbacks: the nanomaterials are only physically bonded to the membrane substrate, lacking chemical anchoring, making them highly susceptible to loss during membrane preparation washing, long-term operation, and cleaning. This leads to rapid degradation of hydrophilicity, collapse of the membrane pore structure, and decreased mechanical strength. Furthermore, the nanomaterials are distributed throughout the entire membrane substrate, failing to act directionally on the inner surface of the membrane directly involved in separation, resulting in low modification efficiency and poor material utilization.

[0005] Therefore, developing a modification technology that enables the directional enrichment, strong bonding, and long-term stability of hydrophilic nanomaterials on the inner surface of hollow fiber membranes, and is suitable for industrial mass production, has become an urgent need in the field of high-performance hollow fiber membranes. Summary of the Invention

[0006] In view of this, this application provides a hollow fiber membrane and its preparation method. The preparation method provided by this application utilizes the interfacial tension difference between the spinning solution and the core solution to drive the interfacial segregation of nanomaterials in the core solution and enrichment on the inner surface of the membrane. At the same time, a crosslinking agent is introduced into the coagulation bath. The crosslinking agent diffuses through the primary membrane support layer to the inner surface of the membrane and undergoes an in-situ chemical reaction with the surface active groups of the nanomaterials. While achieving the orientation and firm loading of nanomaterials, it effectively inhibits the leaching loss during water washing and long-term operation. It can significantly improve the hydrophilicity, pure water flux and antifouling performance of the hollow fiber membrane while maintaining the integrity of the membrane's pore structure.

[0007] This application provides a method for preparing a hollow fiber membrane, comprising the following steps: The spinning solution and core solution are co-extruded through a hollow fiber spinning spinneret and passed through an air gap to obtain nascent membrane fibers. The nascent membrane fibers are then subjected to a coagulation bath and washed with water to obtain a hollow fiber membrane. The core fluid comprises 0.5wt%~2wt% nanomaterials, 38wt%~49.5wt% pure water and 48.5wt%~61.5wt% solvent; The coagulation bath comprises 0.5wt% to 2wt% of a crosslinking agent and 98wt% to 99.5wt% of a solvent.

[0008] In some specific implementations, the nanomaterials in the core fluid are selected from one or more of carbon-based nanomaterials, inorganic hydrophilic nanomaterials, and organic hydrophilic nanomaterials; The nanomaterials in the core fluid have a particle size of 10nm to 50nm.

[0009] In some specific implementations, the carbon-based nanomaterial is selected from one or more of hydroxylated carbon nanotubes, carboxylated carbon nanotubes, aminated carbon nanotubes, graphene oxide, and reduced graphene oxide. The inorganic hydrophilic nanomaterials are selected from one or more of silica nanoparticles, titanium dioxide nanoparticles, nano-alumina, nano-zinc oxide, and hydroxyapatite nanorods. The organic hydrophilic nanomaterial is selected from one or more of chitosan nanoparticles and cellulose nanocrystals.

[0010] In some specific implementations, the solvent in the core fluid is selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0011] In some specific implementations, the crosslinking agent in the coagulation bath is selected from one or more of the following: polyaldehyde crosslinking agents, epoxy crosslinking agents, dicarboxylic acid active derivative crosslinking agents, isocyanate crosslinking agents, and silane coupling agents; The solvent in the coagulation bath is selected from one or more of water, methanol, ethanol and isopropanol.

[0012] In some specific implementations, the multialdehyde crosslinking agent is selected from one or more of glutaraldehyde, glyoxal, and adipaldehyde; The epoxy crosslinking agent is selected from one or more of polyethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glyceryl triglycidyl ether, sorbitol polyglycidyl ether, and pentaerythritol tetraglycidyl ether. The dicarboxylic acid active derivative crosslinking agent is selected from one or more of the following: succinic acid dihydrazide, succinic acid dihydrazide, succinic acid chloride, and adipic acid chloride; The isocyanate crosslinking agent is selected from one or more of diphenylmethane diisocyanate, toluene diisocyanate, and polymethylene polyphenyl polyisocyanate; The silane coupling agent is selected from one or more of KH-550 and KH-560.

[0013] In some specific implementations, the spinning solution comprises 15wt% to 20wt% of a polymer and 80wt% to 85wt% of a solvent; The polymer is selected from one or more of polysulfone, polyethersulfone, and polyvinylidene fluoride; The molecular weight of the polymer is 70,000 to 150,000; The solvent in the spinning solution is selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.

[0014] In some specific implementations, the height of the air gap is 100mm~400mm; The temperature of the air gap is 50℃~70℃.

[0015] In some specific implementations, the residence time of the nascent membrane filaments in the coagulation bath is 4s to 10s; The temperature of the coagulation bath is 50℃~65℃.

[0016] Furthermore, this application also provides a hollow fiber membrane, including a hollow fiber membrane body and nanomaterials formed on the inner surface of the hollow fiber membrane.

[0017] In some specific implementations, the nanomaterials are fixed to the inner surface of the hollow fiber membrane by a crosslinking agent.

[0018] This application provides a method for preparing a hollow fiber membrane, comprising the following steps: co-extruding a spinning solution and a core solution through a hollow fiber spinning spinneret, and sequentially passing them through an air gap to obtain nascent membrane fibers; subjecting the nascent membrane fibers to a coagulation bath and washing with water to obtain a hollow fiber membrane; wherein the core solution comprises 0.5wt%~2wt% nanomaterials, 38wt%~49.5wt% pure water, and 48.5wt%~61.5wt% solvent; and the coagulation bath comprises 0.5wt%~2wt% crosslinking agent and 98wt%~99.5wt% solvent; this application utilizes the spinning solution to confine hydrophilic nanomaterials within the core solution system. The interfacial tension difference between the core fluid and the core fluid drives the interfacial segregation of nanomaterials within the core fluid and their enrichment on the inner surface of the membrane. Simultaneously, a crosslinking agent is introduced into the coagulation bath. This crosslinking agent diffuses through the primary membrane support layer to the inner surface of the membrane, where it undergoes an in-situ chemical reaction with the surface-active groups of the nanomaterials, thereby constructing a stable chemical bonding network on the inner surface of the membrane. This achieves directional and stable loading of hydrophilic nanomaterials on the inner surface of the membrane, avoiding ineffective dispersion and waste of materials within the membrane matrix. Furthermore, it effectively inhibits the dissolution and loss of nanomaterials during water washing and long-term use, significantly improving the membrane's pure water flux and antifouling performance while maintaining the integrity of the membrane structure.

[0019] Experimental results show that the hollow fiber membrane prepared in this application can achieve a pure water flux of up to 875 LMH / bar and a flux attenuation rate of up to 35%. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the hollow fiber membrane preparation process in this application; Figures 2-7 These are scanning electron microscope images of the inner and outer surfaces of the hollow fiber membranes prepared in Examples 1 to 6; Figure 8 This is a scanning electron microscope image of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 1. Figure 9 These are scanning electron microscope images of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 2. Figure 10 These are scanning electron microscope images of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 3. Figure 11 This is a scanning electron microscope image of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 4. Figure 12 This is a scanning electron microscope image of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 5. Figure 13 This is a scanning electron microscope image of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 6. Detailed Implementation

[0021] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0022] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0023] It should be understood that the order of steps or the sequence of actions is not important as long as this application remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0024] This application provides a method for preparing a hollow fiber membrane, comprising the following steps: co-extruding a spinning solution and a core solution through a hollow fiber spinning spinneret, and sequentially passing them through an air gap to obtain nascent membrane fibers; subjecting the nascent membrane fibers to a coagulation bath and washing them with water to obtain a hollow fiber membrane; wherein the core solution comprises 0.5wt%~2wt% of nanomaterials, 38wt%~49.5wt% of pure water and 48.5wt%~61.5wt% of solvent; and wherein the coagulation bath comprises 0.5wt%~2wt% of a crosslinking agent and 98wt%~99.5wt% of solvent.

[0025] This application involves co-extruding the spinning solution and core solution through a hollow fiber spinning spinneret, followed by a preliminary phase inversion via an air gap to obtain nascent membrane filaments. The spinning solution comprises 15wt%~20wt% of a polymer and 80wt%~85wt% of a solvent; in some specific implementations, the preferred mass percentage of the polymer in the spinning solution is 15wt%, 18wt%, or 20wt%; the preferred mass percentage of the solvent in the spinning solution is 80wt%, 82wt%, or 85wt%; the polymer is selected from one or more of polysulfone, polyethersulfone, and polyvinylidene fluoride, preferably polysulfone, polyethersulfone, or polyvinylidene fluoride; the molecular weight of the polymer is 70,000~150,000, preferably 80,000~150,000, more preferably 80,000, 120,000, or 150,000; the solvent in the spinning solution is selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide, preferably N-methylpyrrolidone, N,N-dimethylacetamide, or N,N-dimethylformamide.

[0026] This application does not specifically limit the preparation method of the spinning solution. Specifically, the preparation steps are to add the polymer to the solvent and stir to obtain the spinning solution. In some specific implementations, the stirring temperature is 50℃~100℃, preferably 60℃~90℃, more preferably 60℃, 80℃ or 90℃; the stirring time is 5h~15h, preferably 8h~12h, more preferably 8h, 10h or 12h.

[0027] The core fluid described in this application comprises 0.5wt% to 2wt% nanomaterials, 38wt% to 49.5wt% pure water, and 48.5wt% to 61.5wt% solvent. In some specific implementations, the mass percentage of the nanomaterials is preferably 0.5wt%, 1.2wt%, or 2wt%; the mass percentage of the pure water is preferably 38wt%, 43.8wt%, or 49.5wt%; and the mass percentage of the solvent is preferably 50wt%, 55wt%, or 60wt%.

[0028] In this application, the mass percentage of nanomaterials in the core fluid is less than 0.5 wt%, which is too low and does not significantly improve hydrophilicity and antifouling properties; if it is higher than 2 wt%, the concentration of nanoparticles is too high, which makes them prone to aggregation and sedimentation. The nanomaterials migrate to the membrane pores, clogging the micropores and reducing the flux, increasing costs and easily causing membrane defects.

[0029] In some specific implementations, the nanomaterial is selected from one or more of carbon-based nanomaterials, inorganic hydrophilic nanomaterials, and organic hydrophilic nanomaterials, preferably carbon-based nanomaterials, inorganic hydrophilic nanomaterials, or organic hydrophilic nanomaterials; the particle size of the nanomaterial is 10 nm to 50 nm, preferably 20 nm to 50 nm, more preferably 20 nm, 30 nm, or 50 nm; the solvent in the core liquid is selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide, preferably N-methylpyrrolidone, N,N-dimethylacetamide, or N,N-dimethylformamide; in this application, if the particle size of the nanomaterial is less than 10 nm, the nanoparticles easily penetrate the membrane pores and diffuse into the coagulation bath and are very prone to agglomeration, clumping in the core liquid and resulting in poor dispersion; if the particle size of the nanomaterial is greater than 50 nm, it easily causes membrane pore blockage, membrane surface defects, and sedimentation and stratification in the core liquid.

[0030] In some specific implementations, the carbon-based nanomaterial is selected from one or more of hydroxylated carbon nanotubes, carboxylated carbon nanotubes, aminated carbon nanotubes, graphene oxide, and reduced graphene oxide, preferably one or more of hydroxylated carbon nanotubes, carboxylated carbon nanotubes, and aminated carbon nanotubes, and more preferably hydroxylated carbon nanotubes; the inorganic hydrophilic nanomaterial is selected from one or more of silica nanoparticles, titanium dioxide nanoparticles, nano-alumina, nano-zinc oxide, and hydroxyapatite nanorods, preferably one or more of silica nanoparticles and titanium dioxide nanoparticles, and more preferably silica nanoparticles; the organic hydrophilic nanomaterial is selected from one or more of chitosan nanoparticles and cellulose nanocrystals, preferably... Chitosan nanoparticles were selected. In this application, the nanomaterials in the core solution undergo interfacial segregation and enrichment on the inner surface of the membrane under the influence of the interfacial tension difference between the spinning solution and the core solution. After chemical bonding with a crosslinking agent in the coagulation bath, a stable hydrophilic inner surface layer is constructed, significantly increasing the membrane's pure water flux while endowing it with excellent antifouling and antiprotein adsorption properties. Furthermore, it avoids the defects of ineffective dispersion and easy leaching of nanomaterials in the membrane matrix in traditional blending processes, achieving efficient utilization and long-term stability of the modifier, structurally ensuring the durability of membrane separation performance. This application does not specifically limit the preparation method of the core solution. Specifically, it is prepared according to the following steps: mixing the nanomaterials with water, then adding a solvent and stirring to obtain the core solution.

[0031] This application, after preparing the spinning solution and core solution, co-extrudes the spinning solution and core solution through a spinneret, and performs a preliminary phase inversion after passing through an air gap to obtain nascent membrane fibers. In some specific implementations, the co-extrusion step specifically involves extruding the core solution from inside the spinneret needle core and the spinning solution from outside the spinneret needle core. The flow rate of the core solution is 10 mL / min to 20 mL / min, preferably 10 mL / min to 15 mL / min, more preferably 10 mL / min, 12 mL / min, or 15 mL / min; the flow rate of the spinning solution is 5 mL / min to 10 mL / min, preferably 6 mL / min to 10 mL / min, more preferably 6 mL / min or 8 mL / min. Or 10 mL / min; the height of the air gap is 100 mm to 400 mm, preferably 150 mm to 400 mm, more preferably 150 mm, 300 mm or 400 mm; the temperature of the air gap is 50℃ to 70℃, preferably 50℃ to 65℃, more preferably 50℃, 60℃ or 65℃.

[0032] After the nascent membrane fibers are prepared, they enter a coagulation bath through an air gap, are washed with water, dried, and collected to obtain the hollow fiber membrane. The coagulation bath comprises 0.5wt%~2wt% of a crosslinking agent and 98wt%~99.5wt% of a solvent. In some specific implementations, the mass percentage of the crosslinking agent is preferably 0.5wt%, 0.8wt%, or 1.5wt%; the mass percentage of the solvent is preferably 98.5wt%, 99.2wt%, or 99.5wt%. In some specific implementations, the crosslinking agent is selected from one or more of polyaldehydes, epoxy crosslinking agents, dicarboxylic acid active derivative crosslinking agents, isocyanate crosslinking agents, and silane coupling agents. The solvent of the coagulation bath is selected from one or more of water, methanol, ethanol, and isopropanol. The nascent membrane fibers are placed in the coagulation bath... The retention time is 4s~10s, preferably 5s~10s, more preferably 5s, 8s or 10s; the temperature of the coagulation bath is 50℃~65℃, preferably 50℃, 60℃ or 65℃; this application does not have specific restrictions on the washing conditions, but it is preferred to wash at 60℃~90℃ for 40s~60s; in this application, the selection of the crosslinking agent is matched with the functional groups on the surface of the nanomaterial to achieve efficient crosslinking; specifically, for nanomaterials with a surface rich in hydroxyl and / or carboxyl groups, the crosslinking agent is preferably a polyaldehyde crosslinking agent; for nanomaterials with a surface rich in amino groups, the crosslinking agent is preferably an epoxy crosslinking agent and / or a dicarboxylic acid active derivative crosslinking agent; in addition, all of the above types of nanomaterials can use multifunctional crosslinking agents, and the multifunctional crosslinking agent is preferably an isocyanate crosslinking agent or a silane coupling agent.

[0033] In some specific implementations, the multialdehyde crosslinking agent is selected from one or more of glutaraldehyde, glyoxal, and hexamethylenedialdehyde, preferably glutaraldehyde; the epoxy crosslinking agent is selected from one or more of polyethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glyceryl triglycidyl ether, sorbitol polyglycidyl ether, and pentaerythritol tetraglycidyl ether, preferably polyethylene glycol diglycidyl ether; the dicarboxylic acid active derivative crosslinking agent is selected from one or more of succinic acid dihydrazide, succinic acid dihydrazide, succinyl chloride, and adipic acid chloride. The isocyanate crosslinking agent is selected from one or more of diphenylmethane diisocyanate, toluene diisocyanate, and polymethylene polyphenyl polyisocyanate; the silane coupling agent is selected from one or more of KH-550 and KH-560, preferably KH-550; this application does not specifically limit the preparation method of the coagulation bath. Specifically, the preparation step is to mix the crosslinking agent with pure water and stir evenly to obtain the coagulation bath; in some specific implementations, the stirring temperature is 50℃~70℃, preferably 50℃~65℃, more preferably 50℃, 60℃ or 65℃.

[0034] In this application, the crosslinking agent in the coagulation bath diffuses to the inner surface of the membrane through the primary membrane filament support layer. At the interface between the inner surface of the membrane and the core liquid, the crosslinking molecules contact the surface active functional groups of the nanomaterials and undergo covalent crosslinking, condensation reaction, coordination crosslinking, or hydrogen bond network crosslinking. Chemical bonding enables the nanoparticles to no longer rely solely on physical adsorption, effectively inhibiting the dissolution, shedding, and loss of nanomaterials during water flow, cleaning, and use. Furthermore, the hydrophilic nanolayer enriched on the inner surface continuously provides high hydrophilicity, high water flux, anti-fouling, and anti-protein adsorption properties.

[0035] Furthermore, this application also provides a hollow fiber membrane, including a hollow fiber membrane body and nanomaterials formed on the inner surface of the hollow fiber membrane; in some specific implementations, the nanomaterials are fixed to the inner surface of the hollow fiber membrane by a crosslinking agent.

[0036] See Figure 1 , Figure 1 This is a flow chart of the preparation process of the hollow fiber membrane in this application. After the spinning solution and core solution are co-extruded through a spinneret, they pass through an air gap. Driven by the interfacial tension difference between the spinning solution and the core solution, the nanomaterials in the core solution undergo interfacial segregation and are directionally enriched on the inner surface of the nascent membrane fibers. Subsequently, the nascent membrane fibers enter a coagulation bath. The crosslinking agent in the coagulation bath diffuses through the nascent membrane fiber support layer to the inner surface of the membrane and undergoes an in-situ chemical crosslinking reaction with the nanomaterials enriched on the inner surface of the membrane fibers, thereby achieving a firm anchoring of the nanomaterials on the inner surface of the membrane. After the crosslinked and cured membrane fibers are drawn out, they are sequentially washed through a multi-stage water washing tank to remove residual solvent. Finally, they are dried and collected to obtain the hollow fiber membrane.

[0037] This application provides a method for preparing a hollow fiber membrane, comprising the following steps: co-extruding a spinning solution and a core solution through a hollow fiber spinning spinneret, and sequentially passing them through an air gap to obtain nascent membrane fibers; subjecting the nascent membrane fibers to a coagulation bath and washing with water to obtain a hollow fiber membrane; wherein the core solution comprises 0.5wt%~2wt% nanomaterials, 38wt%~49.5wt% pure water, and 48.5wt%~61.5wt% solvent; and the coagulation bath comprises 0.5wt%~2wt% crosslinking agent and 98wt%~99.5wt% solvent; this application utilizes the spinning solution to confine hydrophilic nanomaterials within the core solution system. The interfacial tension difference between the core fluid and the core fluid drives the interfacial segregation of nanomaterials within the core fluid and their enrichment on the inner surface of the membrane. Simultaneously, a crosslinking agent is introduced into the coagulation bath. This crosslinking agent diffuses through the primary membrane support layer to the inner surface of the membrane, where it undergoes an in-situ chemical reaction with the surface-active groups of the nanomaterials, thereby constructing a stable chemical bonding network on the inner surface of the membrane. This achieves directional and stable loading of hydrophilic nanomaterials on the inner surface of the membrane, avoiding ineffective dispersion and waste of materials within the membrane matrix. Furthermore, it effectively inhibits the dissolution and loss of nanomaterials during water washing and long-term use, significantly improving the membrane's pure water flux and antifouling performance while maintaining the integrity of the membrane structure.

[0038] Experimental results show that the hollow fiber membrane prepared in this application can achieve a pure water flux of up to 875 LMH / bar and a flux attenuation rate of up to 35%.

[0039] The present application is further illustrated below with reference to embodiments. The scope of protection of the present application is not limited to the following embodiments.

[0040] Example 1

[0041] 1. Raw material composition: The spinning solution consists of 15 wt% polysulfone and 85 wt% N,N-dimethylacetamide. The molecular weight of the polysulfone is 150,000. The core fluid consists of 0.5 wt% hydroxyl carbon nanotubes, 49.5 wt% pure water, and 50 wt% N,N-dimethylacetamide. The hydroxyl carbon nanotubes have a particle size of 20 nm. The coagulation bath consists of 0.5 wt% glutaraldehyde and 99.5 wt% pure water.

[0042] 2. A method for preparing a hollow fiber membrane: 1) Add 1500g of polysulfone to 8500g of N,N-dimethylacetamide and stir at 60℃ for 8h to obtain spinning solution; dissolve 50g of hydroxyl carbon nanotubes in 4950g of pure water, stir evenly at room temperature, add 5000g of N,N-dimethylacetamide, stir evenly at room temperature to obtain core solution; add 250g of glutaraldehyde to 49750g of pure water, stir evenly at 50℃ to obtain coagulation bath.

[0043] 2) The spinning solution and core solution are extruded together from the spinneret, with the core solution being extruded from the inside of the spinneret needle core and the spinning solution being extruded from the outside of the spinneret needle core. The flow rate of the core solution is 10 mL / min, and the flow rate of the spinning solution is 6 mL / min.

[0044] 3) The spinning solution is extruded from the spinneret into the air gap, where the initial phase transformation from spinning solution to nascent membrane filaments is completed; the height of the air gap is 150 mm and the temperature of the air gap is 50 °C.

[0045] 4) The nascent membrane fibers enter the coagulation bath through the air gap, then enter the water washing tank, and after washing, enter the drying oven to collect the fibers and obtain the hollow fiber membrane; the residence time of the membrane fibers in the coagulation bath is 5s.

[0046] Example 2

[0047] The difference between this embodiment and Example 1 is that 0.8 wt% glutaraldehyde and 99.2 wt% pure water are added to the coagulation bath, while the other raw materials and preparation methods are exactly the same.

[0048] Example 3

[0049] 1. Raw material composition: The spinning solution consists of 18 wt% polyvinylidene fluoride and 82 wt% N,N-dimethylformamide. The molecular weight of polyvinylidene fluoride is 120,000. The composition of the core fluid is: 1.2 wt% silica nanoparticles, 43.8 wt% pure water, and 55 wt% N,N-dimethylformamide. The particle size of the silica nanoparticles is 50 nm. The coagulation bath consists of 0.8 wt% KH-550 and 99.2 wt% isopropanol.

[0050] 2. A method for preparing a hollow fiber membrane: 1) Add 1800g of polyvinylidene fluoride to 8200g of N,N-dimethylformamide and stir at 80℃ for 10h to obtain a spinning solution; dissolve 120g of silica nanoparticles in 4380g of pure water, stir evenly, add 5500g of N,N-dimethylformamide, and stir evenly at room temperature to obtain a core solution; add 400g of KH-550 to 49600g of isopropanol and stir evenly at 60℃ to obtain a coagulation bath.

[0051] 2) The spinning solution and core solution are extruded together from the spinneret, with the core solution being extruded from the inside of the spinneret needle core and the spinning solution being extruded from the outside of the spinneret needle core. The flow rate of the core solution is 12 mL / min, and the flow rate of the spinning solution is 8 mL / min.

[0052] 3) The spinning solution is extruded from the spinneret into the air gap, where the initial phase transformation from spinning solution to nascent membrane filaments is completed; the height of the air gap is 300 mm and the temperature of the air gap is 60 °C.

[0053] 4) The nascent membrane fibers enter the coagulation bath through the air gap, then enter the water washing tank, and after washing, enter the drying oven to collect the fibers and obtain the hollow fiber membrane; the residence time of the membrane fibers in the coagulation bath is 8s.

[0054] Example 4

[0055] The difference between this embodiment and Example 3 is that 1.5 wt% KH-550 and 98.5 wt% isopropanol are added to the coagulation bath; the other raw materials and preparation methods are exactly the same.

[0056] Example 5

[0057] 1. Raw material composition: The spinning solution consists of 20 wt% polyethersulfone and 80 wt% N-methylpyrrolidone, with a molecular weight of 80,000 for the polyethersulfone. The core fluid consists of 2 wt% chitosan nanoparticles, 38 wt% pure water, and 60 wt% N-methylpyrrolidone. The particle size of the chitosan nanoparticles is 30 nm. The coagulation bath consists of 1.5 wt% polyethylene glycol diglycidyl ether and 98.5 wt% pure water.

[0058] 2. A method for preparing a hollow fiber membrane: 1) Add 2000g of polyethersulfone to 8000g of N-methylpyrrolidone and stir at 90℃ for 12h to obtain a spinning solution; dissolve 200g of chitosan nanoparticles in 3800g of pure water, stir evenly, add 6000g of N-methylpyrrolidone, and stir evenly at room temperature to obtain a core solution; add 750g of polyethylene glycol diglycidyl ether to 49250g of pure water and stir evenly at 65℃ to obtain a coagulation bath.

[0059] 2) The spinning solution and core solution are extruded together from the spinneret, with the core solution being extruded from the inside of the spinneret needle core and the spinning solution being extruded from the outside of the spinneret needle core. The flow rate of the core solution is 15 mL / min, and the flow rate of the spinning solution is 10 mL / min.

[0060] 3) The spinning solution is extruded from the spinneret into the air gap, where the initial phase transformation from spinning solution to nascent membrane filaments is completed; the height of the air gap is 400 mm and the temperature of the air gap is 65 ℃.

[0061] 4) The nascent membrane fibers enter the coagulation bath through the air gap, then enter the water washing tank, and after washing, enter the drying oven to collect the fibers and obtain the hollow fiber membrane; the residence time of the membrane fibers in the coagulation bath is 10s.

[0062] Example 6

[0063] The difference between this embodiment and Example 5 is that 2 wt% polyethylene glycol diglycidyl ether and 98 wt% pure water are added to the coagulation bath; the other raw materials and preparation methods are exactly the same.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 1 is that glutaraldehyde is not added to the coagulation bath, while the other raw materials and preparation methods are exactly the same.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 3 is that no silica nanoparticles are added to the core fluid, and 45wt% pure water is added. The other raw materials and preparation methods are exactly the same.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 5 is that chitosan nanoparticles are not added to the core liquid, 40wt% pure water is added, and polyethylene glycol diglycidyl ether is not added to the coagulation bath. All other raw materials and preparation methods are exactly the same.

[0070] Comparative Example 4

[0071] The difference between this comparative example and Example 1 is that 0.2 wt% hydroxyl carbon nanotubes and 49.8 wt% pure water were added to the core fluid, while the other raw materials and preparation methods were exactly the same.

[0072] Comparative Example 5

[0073] The difference between this comparative example and Example 5 is that 3 wt% polyethylene glycol diglycidyl ether and 97 wt% pure water were added to the coagulation bath; the other raw materials and preparation methods were exactly the same.

[0074] Comparative Example 6

[0075] 1. Raw material composition: The spinning solution consists of 20 wt% polyethersulfone, 2 wt% chitosan nanoparticles, and 78 wt% N-methylpyrrolidone. The molecular weight of the polyethersulfone is 80,000, and the particle size of the chitosan nanoparticles is 30 nm. Core fluid composition: 40wt% pure water, 60wt% N-methylpyrrolidone; Composition of the coagulation bath: 100wt% pure water.

[0076] 2. A method for preparing a hollow fiber membrane: 1) Add 200g of chitosan nanoparticles to 7800g of N-methylpyrrolidone, stir evenly, then add 2000g of polyethersulfone, and stir at 90℃ for 12h to obtain spinning solution; add 4000g of pure water to 6000g of N-methylpyrrolidone, stir evenly at room temperature to obtain core solution.

[0077] 2) The spinning solution and core solution are extruded together from the spinneret, with the core solution being extruded from the inside of the spinneret needle core and the spinning solution being extruded from the outside of the spinneret needle core. The flow rate of the core solution is 15 mL / min, and the flow rate of the spinning solution is 10 mL / min.

[0078] 3) The spinning solution is extruded from the spinneret into the air gap, where the initial phase transformation from spinning solution to nascent membrane filaments is completed; the height of the air gap is 400 mm and the temperature of the air gap is 65 ℃.

[0079] 4) The nascent membrane fibers enter the coagulation bath through the air gap, then enter the water washing tank, and after washing, enter the drying oven to collect the fibers and obtain the hollow fiber membrane; the residence time of the membrane fibers in the coagulation bath is 10s.

[0080] Performance testing: 1. Scanning Electron Microscopy (SEM): A Hitachi TM4000 desktop scanning electron microscope was used to observe the pore structure, distribution and adhesion of nanomaterials on the inner and outer surfaces of the membrane.

[0081] 2. Hydrophilicity (contact angle): The static water contact angle was measured using a German dataphysics OCA25 video optical contact angle meter. The smaller the contact angle, the better the hydrophilicity.

[0082] 3. Pure water flux: The membrane module was tested using internal pressure and cross-flow filtration. The test water temperature was adjusted to be stable at 25±0.5℃, and the pure water permeation was measured under 1 bar conditions. The higher the value, the better the permeation performance.

[0083] 4. Fouling Performance (Fluorescence Decay Rate): To evaluate the flux decay rate of hollow fiber membranes, the test procedures are as follows: Using the assembled hollow fiber membrane module, under constant operating pressure of 0.1 MPa and 25°C, the module was first pre-pressurized with pure water until the flux stabilized using internal pressure and cross-flow filtration. The initial pure water flux J0 was measured. Subsequently, the solution was replaced with 1 g / L BSA simulated pollutant, and continuous filtration was performed at constant temperature and pressure for 120 min. The flux J at this point was measured. t Calculate the membrane flux decay rate using the following formula. The smaller the flux decay rate, the stronger the membrane's antifouling performance.

[0084]

[0085] Where: J0 - initial stable pure water flux, LMH / bar; J t - Flux after 120 minutes of operation, LMH / bar; The test results are shown in Table 1.

[0086]

[0087] Figures 2-7 These are scanning electron microscope images of the inner and outer surfaces of the hollow fiber membranes prepared in Examples 1 to 6. The results show that nanomaterials are uniformly attached to the inner surface of the membranes in Examples 1 to 6, while no nanomaterials are distributed on the outer surface. This confirms that hydrophilic nanomaterials can be directionally enriched on the inner surface of the hollow fiber membrane without migrating into the membrane interior or to the outer surface, demonstrating precise modification and high utilization. As the concentration of the crosslinking agent in the coagulation bath increases, the loading of nanomaterials on the inner surface of the membrane gradually increases, indicating that the crosslinking agent can effectively promote the chemical bonding and fixation between the nanomaterials and the membrane substrate. Figure 8The images show scanning electron microscope images of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 1. In Comparative Example 1, no crosslinking agent was added, and only a very small amount of nanomaterials were attached to the inner surface of the membrane. This indicates that without a crosslinking agent, the nanomaterials are only attached to the inner surface of the membrane by weak physical adsorption, and the binding force is extremely poor. They are easily washed away by the coagulation bath during the membrane forming phase separation process and are difficult to be stably loaded on the inner wall of the membrane. This further confirms that the crosslinking agent is the key component for achieving efficient and firm directional fixation of nanomaterials. Figure 9 These are scanning electron microscope images of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 2. Figure 10 The images are scanning electron microscope images of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 3. No nanomaterials were added to Comparative Examples 2 and 3, and no nanomaterials were attached to the inner surface of the membrane, which only showed the original pore morphology of the pure membrane substrate itself. Figure 11 The images are scanning electron microscope images of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 4. Due to the low amount of nanomaterials added in the core liquid, the nano-load on the inner surface of the membrane in Comparative Example 4 is significantly reduced. The nanoparticles are sparsely distributed and the coverage area is much lower than that in Examples 1-6. Some areas are even exposed on the inner wall of the substrate. This shows that the supply of hydrophilic nanomaterials in the core liquid directly determines the load on the inner wall of the membrane. Sufficient nanomaterials are the basis for achieving a complete and uniform modified layer. This also indirectly confirms the mechanism of action of this system in relying on the core liquid to supply nanomaterials and achieve directional modification of the inner surface. Figure 12 The images show scanning electron microscope images of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 5. Due to excessive addition of crosslinking agent, the inner surface of the membrane in Comparative Example 5 showed pore shrinkage, densification and local blockage, the loading of nanomaterials was not further improved and the water permeability channels were damaged. Figure 13 The images show scanning electron microscope images of the inner and outer surfaces of the hollow fiber membrane prepared in Comparative Example 6. As can be seen from the images, when nanomaterials are added to the spinning solution, they tend to spontaneously aggregate due to their large specific surface area. They are then embedded in the pores by the membrane matrix, reducing or even completely blocking the membrane pores.

[0088] The experimental data in Table 1 show that, with a fixed amount of core liquid nanomaterials added, the hydrophilicity, water permeability, and antifouling properties of the membrane are significantly improved with increasing concentration of crosslinking agent in the coagulation bath. Taking Examples 1 and 2 as examples: when the crosslinking agent was increased from 0.5 wt% to 0.8 wt%, the contact angle of the membrane inner surface decreased from 82.5° to 75.8°, the pure water flux increased from 455 LMH / bar to 527 LMH / bar, and the flux decay rate decreased from 65% to 60%. Similarly, comparing Examples 3 and 4, it was found that when the crosslinking agent was increased from 0.8 wt% to 1.5 wt%, the contact angle decreased from 68.4° to 60.2°, the pure water flux increased from 610 LMH / bar to 667 LMH / bar, and the flux decay rate decreased from 54% to 49%. In the comparison of Examples 5 and 6, when the crosslinking agent was increased from 1.5 wt% to 2.0 wt%, the contact angle further decreased to 48.8°, the pure water flux jumped to 875 LMH / bar, and the flux decay rate was optimized to 35%. This is because higher concentrations of crosslinking agents can provide more active reaction sites, strengthen the covalent bonding between hydrophilic nanomaterials and membrane substrates, and significantly improve the loading capacity and adhesion of nanomaterials on the inner wall of the membrane; the membrane surface is enriched with a large number of hydrophilic groups containing hydroxyl and carboxyl groups, which enhances the affinity between water molecules and the membrane interface, continuously reduces the water contact angle, and significantly improves the pure water permeate flux; at the same time, the high-density stable hydrophilic modification layer can form a hydration barrier on the membrane surface, effectively blocking the adsorption and accumulation of pollutants, reducing the generation of filter cake layer and irreversible adsorption pollution during filtration, ultimately resulting in a continuous reduction in flux attenuation and a significant improvement in membrane antifouling performance.

[0089] Comparative Example 1 added nanomaterials only to the core liquid without crosslinking agent in the coagulation bath, resulting in a membrane contact angle of 90.6°, a pure water flux of 385 LMH / bar, and a flux decay rate as high as 76%. The hydrophilicity and antifouling properties were significantly deteriorated. The nanomaterials were bound only by weak physical adsorption and were easily washed away by the coagulation bath during the molding process. The hydrophilic filler loading on the inner wall was low, the hydrophilic modification effect was limited, and the hydration protective layer was difficult to construct completely. Therefore, the water permeability and antifouling performance were poor, which further confirmed the key role of crosslinking agent in anchoring the surface of nanomaterials. In Comparative Examples 2 and 3, no nanomaterials were introduced into the core solution. Regardless of whether the coagulation bath contained a crosslinking agent, the membrane contact angle was higher than 89°, and the pure water flux was only 276 LMH / bar to 305 LMH / bar, with a flux decay rate of 80% to 82%. The hydrophilic modification effect was almost ineffective, which fully demonstrates that the improvement of membrane performance depends on the synergistic effect of the core solution nanomaterial loading and the coagulation bath crosslinking agent fixation. Comparative Examples 4 and 5 show that the amount of nanomaterials and crosslinking agents added is crucial. When the mass percentage of nanomaterials in Comparative Example 4 was reduced to 0.2 wt%, the hydrophilic modification failed due to insufficient active sites, and the flux was only 421 LMH / bar. When the mass percentage of crosslinking agent in Comparative Example 5 was increased to 3.0 wt%, although the hydrophilicity was good, excessive crosslinking caused pore blockage, and the flux dropped back to 720 LMH / bar. In Comparative Example 6, with the addition of nanomaterials in the spinning solution, the membrane surface contact angle reached as high as 90.2°, and the pure water flux dropped to 243 LMH / bar. With a flux decay rate of 86% at LMH / bar, the addition of nanomaterials to the spinning solution caused nanomaterial aggregates to easily become embedded in the hollow fiber membrane matrix, blocking the internal pores of the membrane and resulting in a significant decrease in the pure water flux and reduced performance.

[0090] In summary, the preparation method provided in this application achieves the directional construction and chemical anchoring of hydrophilic nanomaterials on the inner surface of hollow fiber membranes. Thanks to the robust chemical bonding network formed between the nanomaterials and the membrane substrate, the modified layer is resistant to erosion and leaching, endowing the membrane material with long-lasting and stable ultra-high hydrophilicity and antifouling properties. By precisely controlling the ratio of the core liquid nanomaterials to the coagulation bath crosslinking agent, the properties of the inner surface of the membrane can be controllably optimized without damaging the membrane's pore structure and mechanical properties. This process route is simple, environmentally friendly, and easily compatible with existing spinning production lines, making it suitable for large-scale mass production. The resulting hollow fiber membranes exhibit extremely high application value and market potential in high-end fields such as biopharmaceutical purification, food processing separation, and water treatment purification.

[0091] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this application, based on the technical solution and application concept of this application, should be included within the scope of protection of this application.

Claims

1. A method for preparing a hollow fiber membrane, characterized in that, Includes the following steps: The spinning solution and core solution are co-extruded through a hollow fiber spinning spinneret and passed through an air gap to obtain nascent membrane fibers. The nascent membrane fibers are then subjected to a coagulation bath and washed with water to obtain a hollow fiber membrane. The core fluid comprises 0.5wt%~2wt% nanomaterials, 38wt%~49.5wt% pure water and 48.5wt%~61.5wt% solvent; The coagulation bath comprises 0.5wt% to 2wt% of a crosslinking agent and 98wt% to 99.5wt% of a solvent.

2. The preparation method according to claim 1, characterized in that, The nanomaterials in the core fluid are selected from one or more of carbon-based nanomaterials, inorganic hydrophilic nanomaterials, and organic hydrophilic nanomaterials. The particle size of the nanomaterials in the core fluid is 10nm~50nm.

3. The preparation method according to claim 2, characterized in that, The carbon-based nanomaterials are selected from one or more of hydroxylated carbon nanotubes, carboxylated carbon nanotubes, aminated carbon nanotubes, graphene oxide, and reduced graphene oxide. The inorganic hydrophilic nanomaterials are selected from one or more of silica nanoparticles, titanium dioxide nanoparticles, nano-alumina, nano-zinc oxide, and hydroxyapatite nanorods. The organic hydrophilic nanomaterial is selected from one or more of chitosan nanoparticles and cellulose nanocrystals.

4. The preparation method according to claim 1, characterized in that, The solvent in the core fluid is selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.

5. The preparation method according to claim 1, characterized in that, The crosslinking agent in the coagulation bath is selected from one or more of the following: polyaldehyde crosslinking agents, epoxy crosslinking agents, dicarboxylic acid active derivative crosslinking agents, isocyanate crosslinking agents, and silane coupling agents; The solvent in the coagulation bath is selected from one or more of water, methanol, ethanol and isopropanol.

6. The preparation method according to claim 5, characterized in that, The multi-aldehyde crosslinking agent is selected from one or more of glutaraldehyde, glyoxal, and adipaldehyde; The epoxy crosslinking agent is selected from one or more of polyethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glyceryl triglycidyl ether, sorbitol polyglycidyl ether, and pentaerythritol tetraglycidyl ether. The dicarboxylic acid active derivative crosslinking agent is selected from one or more of the following: succinic acid dihydrazide, succinic acid dihydrazide, succinic acid chloride, and adipic acid chloride; The isocyanate crosslinking agent is selected from one or more of diphenylmethane diisocyanate, toluene diisocyanate, and polymethylene polyphenyl polyisocyanate; The silane coupling agent is selected from one or more of KH-550 and KH-560.

7. The preparation method according to claim 1, characterized in that, The spinning solution comprises 15wt%~20wt% polymer and 80wt%~85wt% solvent; The polymer is selected from one or more of polysulfone, polyethersulfone, and polyvinylidene fluoride; The molecular weight of the polymer is 70,000 to 150,000; The solvent in the spinning solution is selected from one or more of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.

8. The preparation method according to claim 1, characterized in that, The height of the air gap is 100mm~400mm; The temperature of the air gap is 50℃~70℃; The residence time of the nascent membrane filaments in the coagulation bath is 4s to 10s; The temperature of the coagulation bath is 50℃~65℃.

9. A hollow fiber membrane, characterized in that, It includes the hollow fiber membrane body and the nanomaterials formed on the inner surface of the hollow fiber membrane.

10. The hollow fiber membrane according to claim 9, characterized in that, The nanomaterials are fixed to the inner surface of the hollow fiber membrane by a crosslinking agent.

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