Multi-level pore structure porous fiber membrane and preparation method thereof

Abstract

The present invention provides a porous fiber membrane with a multi-level pore structure and a preparation method thereof. The preparation method comprises dissolving a soluble polymer in a corresponding solvent, then adding dispersed EVOH nanofibers to obtain a solution of the polymer solution and the EVOH nanofibers; then injecting the mixed solution into a rotating and stirring non-solvent coagulation bath containing a cross-linking agent using a syringe at a certain rate, causing the mixed solution to undergo phase separation and form porous fibers dispersed in the non-solvent under the action of centrifugal force, thereby obtaining a porous fiber dispersion; finally, coating the aforementioned porous fiber dispersion on a non-woven substrate, assisting film formation under the action of negative pressure, and obtaining a porous fiber membrane with a multi-level pore structure after drying. The prepared porous fiber membrane with a multi-level pore structure not only has micron-scale pores, but also has nano-scale pores of varying sizes on the surface of the porous fibers constituting the membrane pores, exhibiting higher load capacity and lower mass transfer resistance, and is suitable for the field of adsorption separation.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber membrane material preparation, and in particular to a porous fiber membrane with a multi-level pore structure and a preparation method thereof. Background Art

[0002] Porous fiber membrane filtration materials have the advantages of large specific surface area, high porosity, small pore size, and good internal pore connectivity, which give them excellent adsorption and separation performance. Currently, ordinary fiber membrane materials have a simple structure, and the specific surface area and porosity cannot meet the application requirements of high-efficiency adsorption and separation.

[0003] An invention patent (CN 116791225 A) discloses an ultra-tough cellulose aerogel fiber, its preparation method, and its application. The preparation method involves using wet spinning technology to prepare a cellulose molecular solution using cellulose polymer as the raw material. The cellulose molecular solution is then used as the spinning solution. During the spinning process, the cellulose polymer undergoes in-situ self-assembly and hydrogen-bonding cross-linking reactions, forming a multi-layered nanofiber structure. The nanofiber structure is a continuous three-dimensional, multi-level pore network. The cellulose aerogel fiber prepared using this method not only exhibits excellent physical properties such as high strength and toughness, but also, due to its multi-level pore structure, possesses excellent adsorption and thermal insulation properties. This makes it suitable for use not only in weaving technology, but also in air purification, heavy metal adsorption, atmospheric inhalable particulate adsorption, indoor harmful gas adsorption, filtration materials, or thermal insulation materials, and is therefore widely applicable. However, the porous fibers prepared by this method are relatively coarse, making them difficult to use alone and requiring further processing into textile materials.

[0004] An invention patent (CN 111676591 A) discloses a graphene oxide aerogel fiber fabric, its preparation method, and application. The preparation method comprises the following steps: dispersing graphene oxide in a solvent, oscillating and mixing, and ultrasonically obtaining a graphene oxide solution; injecting the obtained graphene oxide solution into a rotating coagulation bath through a spinning head, and washing with deionized water after coagulation to obtain graphene oxide gel fibers; filtering the obtained graphene oxide gel fibers to obtain a gel fiber fabric, and then freeze-drying to obtain a graphene oxide aerogel fiber fabric. The product obtained by this method has a multi-level pore structure formed by nano-scale voids and micron-scale holes, high filtration efficiency, and good PM2.5 capture performance, and has broad application prospects in the field of air filtration. However, the above method has a complex preparation process and requires freeze-drying, which makes it difficult to achieve large-scale production.

[0005] In view of this, it is necessary to design an improved multi-level pore structure porous fiber membrane and its preparation method to solve the above problems. Summary of the Invention

[0006] The object of the present invention is to provide a porous fiber membrane with a multi-level pore structure and a preparation method thereof. The preparation method comprises the following steps: dissolving a soluble polymer in a corresponding solvent, and then adding dispersed EVOH nanofibers to obtain a polymer solution; injecting the polymer solution into a rotating and stirring non-solvent coagulation bath containing a cross-linking agent using a syringe at a certain rate, causing the mixed solution to undergo phase separation and form porous fibers dispersed in the non-solvent under the action of centrifugal force to obtain a porous fiber dispersion; finally, coating the aforementioned porous fiber dispersion on a non-woven substrate, assisting film formation under the action of negative pressure, and obtaining a porous fiber membrane with a multi-level pore structure after drying.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing a porous fiber membrane with a multi-level pore structure, comprising the following steps:

[0008] S1, dissolving a soluble polymer in a corresponding solvent to obtain a polymer solution with a mass fraction of 1-10%;

[0009] S2, adding the dispersed EVOH nanofibers to the polymer solution obtained in step S1, and stirring with an emulsifier for 10-30 minutes to obtain a uniformly dispersed mixed solution;

[0010] S3, injecting the mixed solution obtained in step S2 into a rotating and stirring non-solvent coagulation bath containing a cross-linking agent at a certain rate using a syringe, so that the mixed solution undergoes phase separation and forms porous fibers dispersed in the non-solvent under the action of centrifugal force, thereby obtaining a porous fiber dispersion;

[0011] S4, coating the porous fiber dispersion obtained in step S3 on a non-woven substrate, assisting film formation under negative pressure, and drying to obtain a porous fiber membrane with a multi-level pore structure.

[0012] Furthermore, in step S3, the injection rate of the syringe is 10-100 mm / min, and the stirring rate of the coagulation bath is 100-1000 rpm.

[0013] Furthermore, in step S3, the non-solvent coagulation bath is one of ethanol and isopropanol, and the cross-linking agent is glutaraldehyde.

[0014] Furthermore, in step S2, the EVOH nanofibers have a diameter distribution of 50-500 nm and an average diameter of 100 nm.

[0015] Furthermore, in step S2, the EVOH nanofiber content is 0.1%-5%.

[0016] Furthermore, in step S3, the solid content of the fibers in the porous fiber dispersion is 0.5% to 10%.

[0017] Furthermore, in step S1, the soluble polymer is one of polyethersulfone, polyvinyl alcohol, nylon, cellulose ester, chitosan, quaternized chitosan, and sodium alginate; and the solvent is one of acetone, water, and dimethylformamide.

[0018] The present invention also provides a multi-level pore structure porous fiber membrane, prepared by any of the above-described methods for preparing a multi-level pore structure porous fiber membrane. The multi-level pore structure porous fiber membrane is composed of a stack of porous fibers with a diameter of 10-100 μm, wherein the porous fibers are composed of nanofibers and porous polymer fibers intertwined. The fiber membrane has micrometer-scale pores within, and the porous fibers have nanometer-scale pores on their surfaces.

[0019] Furthermore, the pores inside the fiber membrane are formed by stacking wet-laid porous fibers, with a pore diameter ranging from 1 to 100 μm, and the pores on the surface of the wet-laid porous fibers are composed of porous polymers and nanofibers, with a pore diameter ranging from 100 to 500 nm.

[0020] Furthermore, the thickness of the multi-level pore structure porous fiber membrane is 10-100 μm; the diameter of the nanofiber is in the range of 50-500 nm.

[0021] The prepared multi-level pore structure porous fiber membrane not only has micron-scale pores (1-100μm), but also the porous fiber surface that constitutes the membrane pores has nano-scale pores of varying sizes (100-500nm), which effectively reduces the mass transfer resistance of molecules, ions, particles and other substances therein. This multi-level pore structure exhibits higher load capacity and lower mass transfer resistance, and is suitable for the field of adsorption and separation, realizing stable and efficient adsorption and separation of biological macromolecules.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention relates to a method for preparing a porous fiber membrane with a multi-level pore structure. The method comprises first dissolving a soluble polymer in a corresponding solvent, then adding the dispersed EVOH nanofibers to obtain a polymer solution. The polymer solution is then injected into a rotating, stirred non-solvent coagulation bath containing a crosslinker using a syringe at a certain rate. The mixed solution undergoes phase separation, and under the action of centrifugal force, porous fibers are formed and dispersed in the non-solvent to obtain a porous fiber dispersion. Finally, the porous fiber dispersion is coated on a non-woven substrate, and negative pressure is applied to assist film formation. After drying, a porous fiber membrane with a multi-level pore structure is obtained. This preparation method is simple, without tedious preparation processes or complex chemical reactions. It simply requires injecting the mixture of polymer and EVOH nanofibers into a coagulation bath, where porous fibers are formed under the action of centrifugal force. The porous fiber membrane is then obtained after filtration.

[0024] 2. The multi-level pore structure of the porous fiber membrane produced by the present invention not only possesses micron-scale pores (1-100 μm) within the fiber membrane, formed by the accumulation of fibers, but also features numerous nanoscale pores (100-500 nm) of varying sizes on the surface of the fibers that make up the membrane pores. This multi-level pore structure effectively reduces the mass transfer resistance of molecules, ions, particles, and other substances within the membrane. This multi-level pore structure exhibits a higher load capacity and lower mass transfer resistance, making it suitable for separation, purification, and adsorption of biomacromolecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The surface and cross-sectional morphologies of the CAB+EVOH nanofiber porous fibers obtained in step S3 of Example 1.

[0026] Figure 2 The surface and cross-sectional morphologies of the CAB+EVOH nanofiber porous fiber membrane prepared in Example 1.

[0027] Figure 3 The surface and cross-sectional morphology of the porous PES+EVOH nanofiber obtained in step S3 of Example 2.

[0028] Figure 4 The surface and cross-sectional morphology of the PA6+EVOH nanofiber porous fiber obtained in step S3 of Example 4.

[0029] Figure 5 The surface and cross-sectional morphologies of the chitosan+EVOH nanofiber porous fibers obtained in step S3 of Example 5.

[0030] Figure 6 The surface and cross-sectional morphologies of the porous sodium alginate + EVOH nanofibers obtained in step S3 of Example 7.

[0031] Figure 7 This is the surface morphology of the CAB+EVOH nanofiber porous fiber obtained in step S3 of Comparative Example 1.

[0032] Figure 8 This is the surface morphology of the CAB porous fiber obtained in Comparative Example 2.

[0033] Figure 9 This is the surface morphology of the CAB+EVOH nanofiber porous membrane (without coagulation bath) obtained in Comparative Example 3. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] It should also be noted here that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0036] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0037] The present invention provides a method for preparing a porous fiber membrane with a multi-level pore structure, comprising the following steps:

[0038] S1, dissolving a soluble polymer in a corresponding solvent to obtain a polymer solution with a mass fraction of 1-10%;

[0039] Specifically, the soluble polymer is one of polyethersulfone, polyvinyl alcohol, nylon, cellulose ester, chitosan, quaternized chitosan, and sodium alginate. Cellulose ester can be cellulose acetate butyrate, cellulose acetate propionate, and cellulose acetate.

[0040] The solvent is one of acetone, water and dimethylformamide.

[0041] S2, adding the dispersed EVOH nanofibers to the polymer solution obtained in step S1, and stirring with an emulsifier for 10-30 minutes to obtain a uniformly dispersed mixed solution;

[0042] Specifically, the diameter distribution of the EVOH nanofibers is 50-500 nm, and the average diameter is 100 nm.

[0043] The content of the EVOH nanofiber is 0.1%-5% of the mass fraction of the polymer solution.

[0044] S3, injecting the mixed solution obtained in step S2 into a rotating and stirring non-solvent coagulation bath containing a cross-linking agent at a certain rate using a syringe, so that the mixed solution undergoes phase separation and forms porous fibers dispersed in the non-solvent under the action of centrifugal force, thereby obtaining a porous fiber dispersion;

[0045] Specifically, the non-solvent coagulation bath is one of ethanol and isopropanol, and the cross-linking agent is glutaraldehyde.

[0046] The injection rate of the syringe was 10-100 mm / min, and the stirring rate of the coagulation bath was 100-1000 rpm.

[0047] The solid content of the fibers in the porous fiber dispersion is 0.5% to 10%.

[0048] During this process, when the mixed solution is injected into the coagulation bath, it is stretched under the action of centrifugal force to form fibers. At the same time, the solvent in the mixed solution and the non-solvent in the coagulation bath undergo double diffusion, the polymer phase is separated, and a large number of through-holes are formed inside and on the surface. EVOH nanofibers are interspersed in the porous fibers to form a skeleton structure, and together with the polymer, they constitute porous fibers.

[0049] S4, coating the porous fiber dispersion obtained in step S3 on a non-woven substrate, assisting film formation under negative pressure, and drying to obtain a fiber membrane with a multi-level pore structure.

[0050] The present invention also provides a multi-level porous fiber membrane with a hierarchical pore structure, prepared by the aforementioned method for preparing a multi-level porous fiber membrane. The multi-level porous fiber membrane is composed of a stack of porous fibers with a diameter of 10-100 μm, wherein the porous fibers are composed of nanofibers intertwined with porous polymer fibers. The fiber membrane has micrometer-scale pores within it, and nanometer-scale pores on the surface of the porous fibers.

[0051] The pores inside the fiber membrane are formed by the accumulation of wet-laid porous fibers, with a pore diameter ranging from 1 to 100 μm. The pores on the surface of the wet-laid porous fibers are composed of porous polymers and nanofibers, with a pore diameter ranging from 100 to 500 nm.

[0052] The thickness of the multi-level pore structure porous fiber membrane is 10-100 μm.

[0053] The nonwoven substrate is polypropylene nonwoven fabric.

[0054] The porous fiber membrane material has a multi-level pore structure and high porosity and specific surface area, which are beneficial to its adsorption and separation performance. This multi-level pore structure porous fiber membrane can be used for the adsorption and separation of biomacromolecules.

[0055] The multi-level pore structure porous fiber membrane and its preparation method provided by the present invention are described below with reference to specific embodiments.

[0056] Example 1

[0057] This embodiment provides a method for preparing a porous fiber membrane with a multi-level pore structure, comprising the following steps:

[0058] S1, dissolving cellulose acetate butyrate (CAB) in acetone to obtain a CAB solution with a mass fraction of 5%;

[0059] S2, placing monodispersed EVOH nanofibers in the CAB solution obtained in step S1, and stirring with an emulsifier for 30 minutes to uniformly disperse the EVOH nanofibers in the CAB solution to obtain a mixed solution; wherein the mass fraction of the EVOH nanofibers is 0.5%;

[0060] The preparation method of monodisperse EVOH nanofibers is as follows:

[0061] EVOH nanofibers are prepared by a melt extrusion phase separation method; then, the EVOH nanofibers are dispersed in a mixed solvent to obtain an EVOH nanofiber dispersion; after removing the mixed solvent, monodispersed EVOH nanofibers are obtained.

[0062] The mixed solvent is ethanol and water in a mass ratio of 1:1; the diameter of the EVOH nanofiber is 100 nm.

[0063] S3, using a syringe (the syringe needle is 0.2 mm), injecting the mixed solution obtained in step S2 into the isopropanol solution at a rate of 5 mm / min;

[0064] The stirring rate of the isopropanol solution was 200 r / min. At this time, CAB phase separated in the isopropanol and formed fibers dispersed in the isopropanol under the action of centrifugal force to obtain a porous fiber dispersion.

[0065] S4, coating the porous fiber dispersion obtained in step S3 on a non-woven substrate, assisting film formation under the action of negative pressure, and peeling it off from the non-woven substrate after drying to obtain a fiber membrane with a multi-level pore structure.

[0066] See also Figure 1 The following are the surface and cross-sectional morphologies of the porous CAB+EVOH nanofibers obtained in step S3 of Example 1. Figure 1 (a) and (b) are SEM images of the fiber surface. Figure 1 (c) and (d) are SEM images of fiber cross sections. The fiber diameter ranges from 10 to 100 μm.

[0067] It can be seen that there are many small holes (20-100nm) of varying sizes on the fiber surface. In addition, from the cross-section of the fiber, it can be seen that these channels are not only present on the fiber surface, but also penetrate and connect the entire fiber.

[0068] See also Figure 2 The surface and cross-sectional morphologies of the CAB+EVOH nanofiber porous membrane obtained in step S4 of Example 1 are shown. Figure 2 (a) and (b) are SEM images of the fiber membrane surface. Figure 2(c) and (d) are SEM images of the cross section of the fiber membrane.

[0069] The membrane is composed of a stack of fibers of varying thicknesses, exhibiting a typical nonwoven structure. Furthermore, the surface and cross-sectional morphologies reveal that the fibers are stacked to form pores measuring 10-100 μm, with pores of 20-100 nm existing within the fibers, forming a multi-level pore structure.

[0070] Examples 2-5 and Comparative Example 1

[0071] Examples 2-5 and Comparative Example 1 provide a method for preparing a porous fiber membrane with a multi-level pore structure. Compared with Example 1, the difference is that the type of soluble polymer and the corresponding solvent and the concentration of the corresponding polymer solution in step S1 are changed, as shown in the table below. The rest is roughly the same as Example 1 and will not be repeated here.

[0072] Types of soluble polymers solvent Concentration of polymer solution Example 1 CAB acetone 5％ Example 2 polyethersulfone DMF 5％ Example 3 polyvinyl alcohol 80℃ water 10％ Example 4 Nylon 6 Formic acid 10％ Example 5 Chitosan 1% hydrochloric acid 1.5％ Example 6 Quaternized chitosan water 2％ Example 7 Sodium alginate water 1％ Comparative Example 1 CAB acetone 15％

[0073] Experiments show that Examples 2-7 can all produce porous fiber membranes with multi-level pore structures. Figure 3-6 shown.

[0074] Figure 7 The surface morphology of the porous CAB+EVOH nanofibers obtained in step S3 of Comparative Example 1 is shown. It can be seen that when the concentration of the polymer solution exceeds a certain range, the mixture of high-concentration CAB and EVOH nanofibers has difficulty forming a fibrous, multi-level pore structure. Instead, a porous structure with docked CAB particles forms, with a lower specific surface area and porosity than the fibrous pore structure.

[0075] Comparative Example 2

[0076] Comparative Example 2 provides a method for preparing a porous fiber membrane with a multi-level pore structure. Compared with Example 1, the difference is that step S2 is not performed, that is, EVOH nanofibers are not added. The rest is roughly the same as Example 1 and will not be repeated here.

[0077] like Figure 8 As shown, without the addition of EVOH nanofibers, the polymer solution forms a conventional porous structure under the action of non-solvent phase separation, and without the support of the fiber skeleton, its strength is poor and the stability of the structure cannot be maintained.

[0078] Comparative Example 3

[0079] Comparative Example 3 provides a multi-level pore structure porous fiber membrane and its preparation method. Compared with Example 1, the difference is that the coagulation bath treatment in step S3 is not performed, that is, the mixed solution is directly coated on the non-woven substrate. The rest is roughly the same as Example 1 and will not be repeated here.

[0080] like Figure 9 Figure 2 shows the surface morphology of the CAB+EVOH nanofiber porous membrane obtained in this comparative example. Without the bidirectional diffusion effect of the coagulation bath, the CAB solution and EVOH nanofiber mixed solution cannot form a porous structure during the natural drying process. Instead, it forms a flat structure with extremely low specific surface area and porosity and no through-hole network, resulting in no fibrous membrane material composed of porous fibers.

[0081] Comparative Example 4

[0082] Comparative Example 4 provides a method for preparing a porous fiber membrane with a multi-level pore structure. Compared with Example 1, the difference is that in step S3, the non-solvent coagulation bath is not stirred. The rest is roughly the same as Example 1 and will not be repeated here.

[0083] Experiments show that when the mixed solution is injected into the coagulation bath without stirring, it cannot be stretched and thinned under the action of centrifugal force. The formed fibers are coarse and difficult to disperse in the coagulation bath, and the film material cannot be prepared by the non-woven method.

[0084] Comparative Example 5

[0085] Comparative Example 5 provides a multi-level pore structure porous fiber membrane and its preparation method. Compared with Example 1, the difference is that in step S3, the cross-linking agent is changed from glutaraldehyde to citric acid. The rest is basically the same as Example 1 and will not be repeated here.

[0086] Experiments show that without the cross-linking effect of glutaraldehyde, the fiber strength is poor, it is very easy to break, and it is difficult to maintain integrity.

[0087] Comparative Example 6

[0088] Comparative Example 6 provides a multi-level pore structure porous fiber membrane and a preparation method thereof. Compared with Example 1, the difference is that in step S3, no cross-linking agent is added. The rest is roughly the same as Example 1 and will not be repeated here.

[0089] Experiments show that without the cross-linking effect of glutaraldehyde, the fiber strength is poor, it is very easy to break, and it is difficult to maintain integrity.

[0090] Comparative Example 7

[0091] Comparative Example 7 provides a multi-level pore structure porous fiber membrane and a preparation method thereof. Compared with Example 1, the difference is that in step S3, the injection rate of the syringe is 200 mm / min, and the rest is roughly the same as Example 1 and will not be repeated here.

[0092] Experiments show that when the injection rate is too fast, the mixed solution forms irregularly shaped substances in the coagulation bath and cannot form fibers.

[0093] The fiber membranes prepared in Examples 1-7 and Comparative Examples 1-7 were tested for pore size statistics, mechanical properties, and filtration performance, and the results are shown in the following table.

[0094] The test procedure is as follows: 0.05g of membrane sample is placed in 100ml (2g / L) protein solution and shaken at 150 rpm at room temperature for 24 hours. After shaking, the membrane is removed. The concentration change of the protein solution before and after adsorption is measured. The adsorption capacity of the membrane is calculated using the following formula:

[0095]

[0096] Where q t is the protein adsorption capacity of the membrane in time t;

[0097] C0 is the concentration of protein in the solution before adsorption;

[0098] C t is the concentration of protein in the solution after adsorption;

[0099] m is the mass of the membrane sample.

[0100] The test results are as follows:

[0101]

[0102]

[0103] As shown in the table above, it can be seen from Examples 1-7 that different polymers can be used to prepare multi-level porous fibers with high specific surface area and high porosity under this method, and can adsorb corresponding biomacromolecules according to the functional groups carried by the polymer itself.

[0104] It can be seen from Comparative Example 1 that when the concentration of the polymer (CAB) is too high, the multi-level pores formed are not composed of fibers but of particles, and their specific surface area and porosity are reduced, resulting in a decrease in their adsorption capacity for biomacromolecules.

[0105] It can be seen from Comparative Example 2 that a porous fiber membrane can still be prepared without EVOH nanofibers. However, due to the lack of nanofibers to provide a cross-linked network skeleton, the strength of the fiber membrane is poor, and it is difficult to maintain its structural integrity in water, making it difficult to perform adsorption applications.

[0106] It can be seen from Comparative Example 3 that the mixed solution is directly coated on the non-woven substrate without the action of a coagulation bath to form a flat membrane without any void structure, and its adsorption capacity is very poor.

[0107] It can be seen from Comparative Example 4 that the mixed solution is injected into the coagulation bath without stirring, and cannot be stretched and thinned under the action of centrifugal force. The formed fibers are relatively coarse, and the specific surface area and porosity of the prepared fiber membrane are lower than those of the fiber membrane in Example 1, and therefore exhibit relatively poor adsorption capacity.

[0108] It can be seen from Comparative Example 5 that after the cross-linking agent is replaced by citric acid from glutaraldehyde, the strength of the prepared fiber membrane is relatively poor, and due to the effect of the carboxyl group of citric acid, it has a certain adsorption effect on lysozyme.

[0109] It can be seen from Comparative Example 6 that without the action of a cross-linking agent, the fiber membrane has low strength and cannot maintain structural integrity.

[0110] It can be seen from Comparative Example 7 that when the injection rate of the mixed solution is too fast, the mixed solution forms irregularly shaped substances in the coagulation bath, and a fiber membrane cannot be prepared.

[0111] In summary, the present invention provides a multi-level porous fiber membrane and its preparation method. The preparation method comprises dissolving a soluble polymer in a corresponding solvent, then adding the dispersed polymer nanofibers to obtain a polymer solution. The polymer solution is then injected into a rotating, stirred non-solvent coagulation bath containing a crosslinker using a syringe at a certain rate. The mixed solution undergoes phase separation and, under the action of centrifugal force, forms fibers dispersed in the non-solvent to obtain a fiber dispersion. Finally, the fiber dispersion is coated on a non-woven substrate, and negative pressure is applied to assist film formation. After drying, a fiber membrane with a multi-level porous structure is obtained. The prepared multi-level porous fiber membrane not only has micron-scale pores (1-100 μm) inside the fiber membrane, but also has numerous nano-scale pores (100-500 nm) of varying sizes on the surface of the fibers that constitute the membrane pores, effectively reducing the mass transfer resistance of molecules, ions, particles, and other substances therein. This multi-level porous structure exhibits higher load capacity and lower mass transfer resistance, making it suitable for the separation, purification, adsorption, and separation of biomacromolecules.

[0112] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a porous fiber membrane with a multi-level pore structure, characterized in that: The following steps are involved: S1, dissolving a soluble polymer in a corresponding solvent to obtain a polymer solution with a mass fraction of 1-10%; S2, adding the dispersed EVOH nanofibers to the polymer solution obtained in step S1, and stirring with an emulsifier for 10-30 minutes to obtain a uniformly dispersed mixed solution; S3, injecting the mixed solution obtained in step S2 into a rotating and stirring non-solvent coagulation bath containing a cross-linking agent using a syringe at a rate of 10-100 mm / min, causing the mixed solution to phase separate and form porous fibers dispersed in the non-solvent under the action of centrifugal force, thereby obtaining a porous fiber dispersion; the cross-linking agent is glutaraldehyde; S4, coating the porous fiber dispersion obtained in step S3 on a non-woven substrate, assisting film formation under negative pressure, and drying to obtain a porous fiber membrane with a multi-level pore structure.

2. The method for preparing a porous fiber membrane with a multi-level pore structure according to claim 1, characterized in that: In step S3, the stirring rate of the coagulation bath is 100-1000 rpm.

3. The method for preparing a porous fiber membrane with a multi-level pore structure according to claim 1, characterized in that: In step S3, the non-solvent coagulation bath is one of ethanol and isopropanol.

4. The method for preparing a porous fiber membrane with a multi-level pore structure according to claim 1, characterized in that: In step S2, the EVOH nanofibers have a diameter distribution of 50-500 nm and an average diameter of 100 nm.

5. The method for preparing a porous fiber membrane with a multi-level pore structure according to claim 4, characterized in that: In step S2, the EVOH nanofiber content is 0.1-5 wt%.

6. The method for preparing a porous fiber membrane with a multi-level pore structure according to claim 1, characterized in that: In step S3, the solid content of the fibers in the porous fiber dispersion is 0.5% to 10%.

7. The method for preparing a porous fiber membrane with a multi-level pore structure according to claim 1, characterized in that: In step S1, the soluble polymer is one of polyethersulfone, polyvinyl alcohol, nylon, cellulose ester, chitosan, quaternized chitosan, and sodium alginate; and the solvent is one of acetone, water, and dimethylformamide.

8. A porous fiber membrane with a multi-level pore structure, characterized in that: Prepared by the preparation method described in any one of claims 1-7; the multi-level pore structure porous fiber membrane is composed of a stack of porous fibers with a diameter of 10-100μm, and the porous fibers are composed of nanofibers and porous polymer fibers intertwined with each other; the fiber membrane has micron-scale pores inside, and the porous fiber surface has nanoscale pores.

9. The porous fiber membrane with a multi-level pore structure according to claim 8, characterized in that: The pores inside the fiber membrane are formed by the accumulation of wet-laid porous fibers, and the pore diameter ranges from 1 to 100 μm. The pores on the surface of the wet-laid porous fibers are composed of porous polymers and nanofibers, and the pore diameter ranges from 100 to 500 nm.

10. The porous fiber membrane with a multi-level pore structure according to claim 8, characterized in that: The thickness of the multi-level pore structure porous fiber membrane is 10-100 μm; the diameter of the nanofiber is in the range of 50-500 nm.

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