Strong cationic nanofiber membrane and method of making same

Abstract

The application provides a strong cationic nanofiber membrane and a preparation method thereof, and belongs to the field of protein separation and purification. EVOH is mixed with CAB, a nanofiber with a rough surface and a nano-protrusion structure is prepared by using a melting method, and a nanofiber suspension is obtained by dispersion; then, 3-hydroxypropanesulfonic acid, an alkali agent and glutaraldehyde are added to the nanofiber suspension obtained in step S1 to simultaneously perform cross-linking and grafting modification, and a modified nanofiber suspension is obtained by stirring reaction; finally, the modified nanofiber suspension is uniformly coated on a non-woven fabric substrate, washed after first drying, and secondly dried to obtain a strong cationic nanofiber membrane. The application is favorable for improving the grafting rate of sulfonic acid groups on the nanofiber membrane, obtaining a strong cationic nanofiber membrane, and further improving the adsorption separation efficiency and adsorption capacity of proteins.

Description

Technical Field

[0001] This invention relates to the field of protein separation and purification technology, specifically to a strongly cationic nanofiber membrane and its preparation method. Background Technology

[0002] With the rapid development of biotechnology, proteins are widely used in biomedicine, food engineering, and other fields, leading to a significant increase in market demand. In the production of protein products, separation and purification costs exceed 80% of the total production cost, making it one of the key steps determining whether large-scale protein production is possible. Traditional protein separation and purification methods include centrifugation, precipitation, gel filtration chromatography, hydrophobic chromatography, affinity chromatography, and ion exchange chromatography. Among these, ion exchange chromatography primarily utilizes the difference in reversible binding forces between proteins and the charged groups on ion exchange resins for adsorption and separation. Ion exchange resins are divided into cation exchange resins and anion exchange resins; cation exchange resins carry a negative charge and can exchange cations. However, existing cation exchange resins have weak interactions with proteins, resulting in slow mass transfer rates, which fails to meet the demands for efficient and rapid separation and purification.

[0003] In existing technologies, researchers have used electrospinning to prepare nanofiber membranes with high specific surface area and wide pore size. These nanofiber membranes exhibit excellent adsorption properties and are widely used in protein separation and purification. However, the electrospinning process for preparing nanofiber membranes is complex and costly, making large-scale production difficult. To enhance the interaction between the nanofiber membrane and proteins, grafting modifications such as coating, light irradiation, and impregnation are often required during the preparation process. However, these methods often result in low grafting rates, typically yielding only weakly cationic nanofiber membranes, which still have limitations in protein adsorption and separation applications.

[0004] In view of this, it is necessary to design a strongly cationic nanofiber membrane and its preparation method to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a strong cationic nanofiber membrane and its preparation method, aiming to solve the technical problems of complex process, high cost and difficulty in large-scale production of nanofiber membrane in the prior art, as well as low grafting rate of modified nanofiber membrane and difficulty in preparing strong cationic nanofiber membrane.

[0006] In a first aspect, embodiments of this application provide a method for preparing a strongly cationic nanofiber membrane, specifically including the following steps:

[0007] S1, Polyvinyl alcohol-ethylene copolymer (EVOH) and cellulose acetate (CAB) are mixed and nanofibers with rough surface and nano-protrusion structure are prepared by melt method. The nanofibers are dispersed in a mixed solvent to obtain a nanofiber suspension.

[0008] S2, 3-hydroxypropanesulfonic acid, alkali and glutaraldehyde are added to the nanofiber suspension obtained in step S1 to simultaneously carry out cross-linking and grafting modification. The mixture is stirred and reacted for a certain time to obtain the modified nanofiber suspension.

[0009] S3, the modified nanofiber suspension obtained in step S2 is uniformly coated onto a nonwoven fabric substrate, dried for the first time, washed, and dried a second time to obtain a strongly cationic nanofiber membrane.

[0010] In the technical solution of this application embodiment, by directly adding 3-hydroxypropanesulfonic acid, alkali agent and glutaraldehyde to the nanofiber suspension, the nanofibers are simultaneously crosslinked and grafted, which significantly improves the grafting rate and mechanical properties of the strong cationic nanofiber membrane.

[0011] In some embodiments, the preparation of nanofibers by melt method specifically includes the following steps: mixing EVOH and CAB to obtain a mixture, adding the mixture to a twin-screw extruder, heating the mixture to a molten state, then stretching and molding, and extracting with acetone to remove CAB from the surface of the nanofibers to obtain nanofibers with a rough surface and a nano-protrusion structure.

[0012] In this embodiment, fibers are prepared by first mixing EVOH and CAB using a melt method, and then extracting with acetone to remove CAB from the surface of the nanofibers (CAB is easily soluble in acetone). This makes the surface of the nanofibers rough and uneven, with nano-protrusions composed of EVOH. EVOH molecules contain abundant hydroxyl groups, which can provide sufficient active sites for cross-linking and grafting. Combined with the nano-protrusion structure, it is beneficial to improve the reaction efficiency and reaction amount in the subsequent grafting and cross-linking processes, as well as the binding force between the nanofibers after cross-linking, thereby improving the grafting rate and the mechanical properties of the nanofiber membrane.

[0013] In some embodiments, the mass ratio of EVOH to CAB is 1:2 to 1:4; and the concentration of the nanofiber suspension is 1-5%.

[0014] In this embodiment, the mass ratio of EVOH to CAB determines the porosity of the nanofibers prepared in step S1. A higher CAB ratio results in higher porosity. Higher porosity is beneficial for sufficient cross-linking and grafting, and also helps to increase the specific surface area of ​​the nanofiber membrane. However, excessively high porosity will affect the mechanical properties of the fibers, and thus the mechanical properties of the nanofiber membrane. The concentration of the nanofiber suspension should not be too high or too low. Too high a concentration will lead to uneven reaction and excessively high viscosity of the solution after the reaction, making it difficult to coat evenly onto the nonwoven fabric substrate. Too low a concentration will reduce the grafting rate and the degree of cross-linking, and the nanofiber membrane formed after coating will be too thin.

[0015] In some embodiments, in step S2, the amount of 3-hydroxypropanesulfonic acid is 2.5-15% of the volume of the nanofiber suspension; the amount of glutaraldehyde is 1-5% of the volume of the nanofiber suspension.

[0016] In this embodiment, the amount of 3-hydroxypropanesulfonic acid was positively correlated with the hydrophilicity and adsorption capacity of the nanofiber membrane, indicating that the grafting rate increased with the increase of the amount of 3-hydroxypropanesulfonic acid.

[0017] In some embodiments, in step S2, the alkali is used to adjust the pH of the nanofiber suspension to 5-5.5; the alkali is one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, and potassium carbonate aqueous solution; the concentration of the alkali is 2-4 mol / L.

[0018] In this embodiment, the alkali agent activates the hydroxyl groups, promoting the forward progress of the grafting and cross-linking reactions.

[0019] In some embodiments, the stirring reaction time in step S2 is 12-36 hours.

[0020] In some embodiments, in step S1, the mixed solvent is obtained by mixing deionized water and isopropanol at a volume ratio of (0.7-1):1.

[0021] In this embodiment, mixing deionized water and isopropanol in a specific ratio can adjust the polarity of the mixed solvent, ensuring that the nanofibers are uniformly dispersed in the mixed solvent.

[0022] In some embodiments, in step S1, the diameter of the nanofiber is 250-750 nm.

[0023] In some embodiments, in step S3, the solvent used for washing is ethanol and deionized water; the temperature of the first drying is 40-60°C; and the temperature of the second drying is room temperature.

[0024] Secondly, embodiments of this application provide a strongly cationic nanofiber membrane prepared according to the aforementioned technical solution, wherein the grafting rate of the strongly cationic nanofiber membrane is greater than 5% and the average pore size is 400-500 nm; the strongly cationic nanofiber membrane is used for the adsorption and separation of proteins.

[0025] In the technical solution of this application embodiment, the strongly cationic nanofiber membrane provided by this application carries a large number of hydrophilic groups (hydroxyl and sulfonic acid groups) on its surface, which enhances the interaction with proteins while preventing non-specific adsorption. Specifically, a large number of sulfonic acid groups are uniformly grafted onto the scaffold surface of the strongly cationic nanofiber membrane, providing numerous adsorption sites for proteins. By increasing the grafting rate of sulfonic acid groups, a strong electrostatic adsorption effect exists between the nanofiber membrane and the positively charged groups carried by the proteins, significantly improving the adsorption efficiency and adsorption capacity of the nanofiber membrane for proteins.

[0026] The beneficial effects of this application are as follows:

[0027] This application provides a strongly cationic nanofiber membrane and its preparation method. Porous nanofibers are prepared by mixing EVOH and CAB. The porous nanofibers are then dispersed in a solvent to obtain a nanofiber suspension. 3-hydroxypropanesulfonic acid, an alkali, and glutaraldehyde are directly added to the nanofiber suspension. By simultaneously crosslinking and grafting the nanofibers, the grafting rate and mechanical properties of the strongly cationic nanofiber membrane are significantly improved. Specifically, glutaraldehyde can react with the alkali-activated hydroxyl groups on 3-hydroxypropanesulfonic acid to generate derivatives with sulfonic acid groups. These derivatives further undergo acetalization with the hydroxyl groups on the nanofibers, thereby grafting the sulfonic acid groups onto the nanofibers. Glutaraldehyde can also react with the hydroxyl groups on the nanofibers, causing crosslinking between the nanofibers to form a three-dimensional crosslinked network.

[0028] On the one hand, grafting and cross-linking in nanofiber suspension ensures that the fibers are fully wetted and their active sites are fully exposed, increasing the grafting rate and cross-linking degree. This, in turn, increases the number of sulfonic acid groups on and inside the nanofiber membrane, as well as the mechanical properties of the nanofiber membrane. On the other hand, the simultaneous cross-linking and grafting processes mutually promote each other. The increased hydrophilicity and volume of the fibers after grafting sulfonic acid groups facilitates full fiber wetting and increases intermolecular motion through the interaction forces between fibers and water molecules, promoting the diffusion of glutaraldehyde. This improves the efficiency and uniformity of the cross-linking reaction, forming a stable three-dimensional cross-linked network and enhancing the mechanical properties and stability of the nanofiber membrane. Simultaneously, this three-dimensional cross-linked network provides a stable framework for the grafting reaction. By fixing and encapsulating the sulfonic acid groups within the framework through the simultaneous grafting and cross-linking reactions, the grafting rate and the stability of the nanofiber membrane's adsorption performance are further enhanced.

[0029] The strongly cationic nanofiber membrane provided in this application carries a large number of hydrophilic groups (hydroxyl and sulfonic acid groups) on its surface, which enhances the interaction with proteins while preventing non-specific adsorption. The grafting rate of the sulfonic acid groups is greater than 5%. The uniform grafting of numerous sulfonic acid groups onto the scaffold surface of the strongly cationic nanofiber membrane provides a large number of adsorption sites for proteins. By increasing the grafting rate of sulfonic acid groups, this application creates a strong electrostatic adsorption relationship between the nanofiber membrane and the positively charged groups carried by proteins, significantly improving the adsorption efficiency and capacity of the nanofiber membrane for proteins.

[0030] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0032] Figure 1 This is a SEM image of the strongly cationic nanofiber membrane prepared in Example 1 of this application;

[0033] Figure 2 This is a SEM image of the modified nanofiber membrane A prepared in Comparative Example 1 of this application;

[0034] Figure 3This is a SEM image of the modified nanofiber membrane B prepared in Comparative Example 2 of this application. Detailed Implementation

[0035] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0037] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0038] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0039] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0040] In existing technologies, researchers have used electrospinning to prepare nanofiber membranes with high specific surface area and wide pore size. These nanofiber membranes exhibit excellent adsorption properties and are widely used in protein separation and purification. However, the electrospinning process for preparing nanofiber membranes is complex and costly, making large-scale production difficult. To enhance the interaction between the nanofiber membrane and proteins, grafting modifications such as coating, light irradiation, and impregnation are often required during the preparation process. However, these methods often result in low grafting rates, typically yielding only weakly cationic nanofiber membranes, which still have limitations in protein adsorption and separation applications.

[0041] To address the technical problems of complex processes, high costs, and difficulty in large-scale production of nanofiber membranes in existing technologies, as well as the low grafting rate of modified nanofiber membranes and the difficulty in preparing strongly cationic nanofiber membranes, this application provides a strongly cationic nanofiber membrane and its preparation method. The method involves a one-step crosslinking grafting process, where 3-hydroxypropanesulfonic acid, an alkali agent, and glutaraldehyde are directly added to the nanofiber suspension to simultaneously crosslink and graft the nanofibers. This significantly improves the grafting rate and crosslinking degree of the strongly cationic nanofiber membrane, thereby enhancing the adsorption efficiency and capacity of the nanofiber membrane for proteins, as well as its mechanical properties.

[0042] In a first aspect, embodiments of this application provide a method for preparing a strongly cationic nanofiber membrane, specifically including the following steps:

[0043] S1, Polyvinyl alcohol-ethylene copolymer (EVOH) and cellulose acetate (CAB) are mixed and nanofibers with rough surface and nano-protrusion structure are prepared by melt method. The nanofibers are dispersed in mixed solvent to obtain nanofiber suspension.

[0044] S2, 3-hydroxypropanesulfonic acid, alkali and glutaraldehyde are added to the nanofiber suspension obtained in step S1 to simultaneously carry out cross-linking and grafting modification. The mixture is stirred and reacted for a certain time to obtain the modified nanofiber suspension.

[0045] S3, the modified nanofiber suspension obtained in step S2 is uniformly coated onto a nonwoven fabric substrate, dried for the first time, washed, and dried a second time to obtain a strongly cationic nanofiber membrane.

[0046] In the technical solution of this application embodiment, porous nanofibers are prepared by mixing EVOH and CAB. The porous nanofibers are then dispersed in a solvent to obtain a nanofiber suspension. 3-hydroxypropanesulfonic acid, an alkali, and glutaraldehyde are directly added to the nanofiber suspension. By simultaneously crosslinking and grafting the nanofibers, the grafting rate and mechanical properties of the strongly cationic nanofiber membrane are significantly improved. Specifically, glutaraldehyde can react with the alkali-activated hydroxyl groups on 3-hydroxypropanesulfonic acid to generate derivatives with sulfonic acid groups. These derivatives further undergo acetalization with the hydroxyl groups on the nanofibers, thereby grafting the sulfonic acid groups onto the nanofibers. Glutaraldehyde can also react with the hydroxyl groups on the nanofibers, causing crosslinking between the nanofibers to form a three-dimensional crosslinked network.

[0047] On the one hand, grafting and cross-linking in nanofiber suspension ensures that the fibers are fully wetted and their active sites are fully exposed, increasing the grafting rate and cross-linking degree. This, in turn, increases the number of sulfonic acid groups on and inside the nanofiber membrane, as well as the mechanical properties of the nanofiber membrane. On the other hand, the simultaneous cross-linking and grafting processes mutually promote each other. The increased hydrophilicity and volume of the fibers after grafting sulfonic acid groups facilitates full fiber wetting and increases intermolecular motion through the interaction forces between fibers and water molecules, promoting the diffusion of glutaraldehyde. This improves the efficiency and uniformity of the cross-linking reaction, forming a stable three-dimensional cross-linked network and enhancing the mechanical properties and stability of the nanofiber membrane. Simultaneously, this three-dimensional cross-linked network provides a stable framework for the grafting reaction. By fixing and encapsulating the sulfonic acid groups within the framework through the simultaneous grafting and cross-linking reactions, the grafting rate and the stability of the nanofiber membrane's adsorption performance are further enhanced.

[0048] Furthermore, the preparation of nanofibers by the melt method specifically includes the following steps: mixing EVOH and CAB and adding them into a twin-screw extruder, heating the mixture to a molten state, then stretching and molding, and extracting with acetone to remove CAB, thereby obtaining porous nanofibers.

[0049] In the technical solution of this application embodiment, EVOH and CAB are first mixed and then the fibers are prepared by melt method. Then, acetone is used for extraction to remove CAB (CAB is easily soluble in acetone) from the surface of the nanofibers, thereby making the surface of the nanofibers rough and uneven, with nano-protrusion structures composed of EVOH. EVOH molecules contain abundant hydroxyl groups, which can provide sufficient active sites for cross-linking and grafting. Combined with the nano-protrusion structure, it is beneficial to improve the reaction efficiency and reaction amount in the subsequent grafting and cross-linking process, as well as the binding force between the nanofibers after cross-linking, thereby improving the grafting rate and the mechanical properties of the nanofiber membrane.

[0050] Furthermore, the mass ratio of EVOH to CAB is 1:2 to 1:4. The concentration of the nanofiber suspension is 1-7.5%.

[0051] In the technical solution of this application embodiment, the mass ratio of EVOH to CAB determines the porosity of the nanofibers prepared in step S1. The higher the proportion of CAB, the higher the porosity. Higher porosity is beneficial for sufficient cross-linking and grafting, and also beneficial for increasing the specific surface area of ​​the nanofiber membrane. However, excessively high porosity will affect the mechanical properties of the fibers, and thus the mechanical properties of the nanofiber membrane. The concentration of the nanofiber suspension should not be too high or too low. Too high a concentration will lead to uneven reaction, and the viscosity of the solution after the reaction will be too high, making it difficult to coat evenly on the nonwoven fabric substrate. Too low a concentration will lead to a decrease in grafting rate and cross-linking degree, and the nanofiber membrane formed after coating will be too thin.

[0052] Furthermore, step S1 also includes dispersing the nanofibers in a mixed solvent and then dispersing them for 10-30 seconds using an ultra-high-speed shearing machine.

[0053] In the technical solution of this application embodiment, the use of an ultra-high-speed shearing machine to disperse the fibers during the preparation of the nanofiber suspension can further refine the fibers, reduce the fiber diameter, and increase the specific surface area of ​​the fibers.

[0054] Furthermore, in step S2, the amount of 3-hydroxypropanesulfonic acid accounts for 2.5-15% of the volume of the nanofiber suspension; the amount of glutaraldehyde accounts for 1-5% of the volume of the nanofiber suspension.

[0055] In the technical solution of this application embodiment, the amount of 3-hydroxypropanesulfonic acid is positively correlated with the hydrophilicity and adsorption capacity of the nanofiber membrane, indicating that the grafting rate increases with the increase of the amount of 3-hydroxypropanesulfonic acid.

[0056] Further, in step S2, the alkali is used to adjust the pH of the nanofiber suspension to 5-5.5; the alkali is one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, and potassium carbonate aqueous solution; the concentration of the alkali is 2-4 mol / L.

[0057] In the technical solution of this application embodiment, the alkali agent plays the role of activating hydroxyl groups and promoting the forward progress of grafting and cross-linking reactions.

[0058] Furthermore, in step S2, the stirring reaction time is 12-36 hours.

[0059] Further, in step S1, the mixed solvent is obtained by mixing deionized water and isopropanol at a volume ratio of (0.7-1):1.

[0060] In the technical solution of this application embodiment, mixing deionized water and isopropanol in a specific ratio can adjust the polarity of the mixed solvent and ensure that the nanofibers are uniformly dispersed in the mixed solvent.

[0061] Furthermore, in step S1, the diameter of the nanofibers is 50-750 nm.

[0062] Furthermore, in step S3, the solvents used for washing are ethanol and deionized water; the temperature for the first drying is 40-60℃; and the temperature for the second drying is room temperature.

[0063] Secondly, embodiments of this application provide a strongly cationic nanofiber membrane prepared according to the aforementioned technical solution. The grafting rate of the strongly cationic nanofiber membrane is greater than 5%, and the average pore size is 400-500 nm. The strongly cationic nanofiber membrane is used for the adsorption and separation of proteins.

[0064] The strongly cationic nanofiber membrane provided in this application carries a large number of hydrophilic groups (hydroxyl and sulfonic acid groups) on its surface, which enhances the interaction with proteins while preventing non-specific adsorption. The numerous sulfonic acid groups uniformly grafted onto the scaffold surface of the strongly cationic nanofiber membrane provide a large number of adsorption sites for proteins. By increasing the grafting rate of sulfonic acid groups, a strong electrostatic adsorption effect exists between the nanofiber membrane and the positively charged groups carried by proteins, significantly improving the adsorption efficiency and capacity of the nanofiber membrane for proteins.

[0065] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0066] I. Preparation Method

[0067] Example 1

[0068] Example 1 provides a method for preparing a strongly cationic nanofiber membrane, which specifically includes the following steps:

[0069] S1, EVOH (after removing moisture) and CAB are mixed at a mass ratio of 1:4 and added to a twin-screw extruder. The mixture is heated to a molten state, then stretched and shaped. CAB is removed by extraction with acetone to obtain nanofibers with a rough surface and nano-protrusion structure, with a diameter of 50-750 nm. The nanofibers are dispersed in a mixed solvent (V... 去离子水 V 异丙醇 In a ratio of 1:1, a nanofiber suspension with a concentration of 4% was obtained.

[0070] In step S2, 3-hydroxypropanesulfonic acid, a 3 mol / L sodium hydroxide aqueous solution, and glutaraldehyde were added to the nanofiber suspension obtained in step S1 to simultaneously perform crosslinking and grafting modification. The reaction was magnetically stirred for 24 hours to obtain a modified nanofiber suspension. The amount of 3-hydroxypropanesulfonic acid was 15% of the volume of the nanofiber suspension, and the amount of glutaraldehyde was 4% of the volume. The 3 mol / L sodium hydroxide aqueous solution was used to adjust the pH of the nanofiber suspension to 5.

[0071] S3. The modified nanofiber suspension obtained in step S2 is uniformly coated onto a polypropylene (PP) nonwoven fabric substrate, dried at 50°C, washed with ethanol and deionized water, and then dried at room temperature to obtain a strongly cationic nanofiber membrane.

[0072] The average pore size of the strongly cationic nanofiber membrane prepared in Example 1 is 450 nm.

[0073] Example 2

[0074] The difference between Example 2 and Example 1 is that the amount of 3-hydroxypropanesulfonic acid used accounts for 10% of the volume of the nanofiber suspension. The rest is the same as in Example 1, and will not be repeated here.

[0075] Example 3

[0076] The difference between Example 3 and Example 1 is that the amount of 3-hydroxypropanesulfonic acid used accounts for 7.5% of the volume of the nanofiber suspension. The rest is the same as in Example 1, and will not be repeated here.

[0077] Example 4

[0078] The difference between Example 4 and Example 1 is that the amount of 3-hydroxypropanesulfonic acid used accounts for 5% of the volume of the nanofiber suspension. The rest is the same as in Example 1, and will not be repeated here.

[0079] Example 5

[0080] The difference between Example 5 and Example 1 is that the amount of 3-hydroxypropanesulfonic acid used accounts for 2.5% of the volume of the nanofiber suspension. The rest is the same as in Example 1 and will not be repeated here.

[0081] Comparative Example 1

[0082] The difference between Comparative Example 1 and Example 1 is that the cross-linked nanofiber suspension was coated onto a PP nonwoven fabric substrate, and after film formation, 3-hydroxypropanesulfonic acid was sprayed on for grafting to obtain modified nanofiber membrane A. Specifically, the steps are as follows:

[0083] S1, EVOH (after removing moisture) and CAB are mixed at a mass ratio of 1:4 and added to a twin-screw extruder. The mixture is heated to a molten state, then stretched and shaped. CAB is removed by extraction with acetone to obtain porous nanofibers with a diameter of 50-750 nm. The nanofibers are dispersed in a mixed solvent (V... 去离子水 V 异丙醇 In a ratio of 1:1, a nanofiber suspension with a concentration of 4% was obtained.

[0084] S2, a 3 mol / L sodium hydroxide aqueous solution and glutaraldehyde are added to the nanofiber suspension obtained in step S1 to perform cross-linking. The reaction is carried out with magnetic stirring for 24 hours to obtain a modified nanofiber suspension. The amount of glutaraldehyde used accounts for 4% of the volume of the nanofiber suspension; the 3 mol / L sodium hydroxide aqueous solution is used to adjust the pH of the nanofiber suspension to 5.

[0085] S3, the modified nanofiber suspension obtained in step S2 is uniformly coated onto a PP nonwoven fabric substrate and dried at 50°C to form a film. Then, a 10% aqueous solution of 3-hydroxypropanesulfonic acid is sprayed onto the film surface. After reacting for 24 hours, the film is washed with ethanol and deionized water, and then dried at room temperature to obtain modified nanofiber membrane A. The amount of 3-hydroxypropanesulfonic acid used accounts for 15% of the volume of the modified nanofiber suspension.

[0086] Comparative Example 2

[0087] The difference between Comparative Example 2 and Example 1 is that the nanofiber suspension obtained in step S1 was directly and uniformly coated onto a PP nonwoven fabric substrate, dried at 50°C to form a film, and then a 5% aqueous solution of 3-hydroxypropanesulfonic acid, a 3 mol / L aqueous solution of sodium hydroxide, and a 2% aqueous solution of glutaraldehyde were sequentially sprayed onto the film surface. After reacting for 24 hours, the film was washed with ethanol and deionized water, and then dried at room temperature to obtain modified nanofiber membrane B. The amount of 3-hydroxypropanesulfonic acid accounted for 15% of the volume of the modified nanofiber suspension; the amount of glutaraldehyde accounted for 4% of the volume of the modified nanofiber suspension; and the amount of sodium hydroxide aqueous solution accounted for 15% of the volume of the modified nanofiber suspension. Other aspects were the same as in Example 1 and will not be repeated here.

[0088] II. Testing Methods

[0089] 1. Surface morphology testing of nanofiber membranes

[0090] The morphology of the nanofibers prepared in Example 1, the nanofiber membranes prepared in Example 1 and Comparative Examples 1-2 was characterized by scanning electron microscopy (SEM).

[0091] 2. Grafting rate of nanofiber membranes

[0092] The grafting rates of the nanofiber membranes prepared in Examples 1-5 and Comparative Examples 1-2 were calculated using the formula: Grafting rate (%) = (Mass of grafted functional groups / Total mass of polymer) × 100%.

[0093] 3. Water contact angle of nanofiber membranes

[0094] The water contact angles of the nanofiber membranes prepared in Examples 1-5 and Comparative Examples 1-2 were tested according to the test methods in standard GB / T 30693-2014.

[0095] 4. Adsorption performance of nanofiber membranes for proteins (adsorption capacity and adsorption efficiency)

[0096] The adsorption performance of the nanofiber membranes prepared in Examples 1-5 and Comparative Examples 1-2 on proteins was tested, and the test steps are as follows:

[0097] The nanofiber membrane was first pretreated with a 1 mol / L NaOH and NaCl solution, then rinsed thoroughly with deionized water and dried. Next, a phosphate buffer solution was prepared by mixing 0.2 mol / L NaH₂PO₄ and 0.2 mol / L Na₂HPO₄ and adjusting the pH to 5. Lysozyme was added to the phosphate buffer solution and stirred slowly to obtain a 2 mg / mL lysozyme solution. Then, 50 mg of the nanofiber membrane was added to 15 mL of the lysozyme solution. After shaking for a period of time, the lysozyme non-specifically adsorbed on the nanofiber membrane was removed with the phosphate buffer solution. The absorbance of the lysozyme solution at 280 nm was measured at different preset time points (e.g., 60 min, 120 min, 180 min).

[0098] The absorbance A is calculated using formula (1), and the adsorption amount of lysozyme (mg / g) is calculated using formula (2).

[0099] (1)

[0100] Where k is the absorption coefficient; l is the optical path length; and c is the lysozyme concentration.

[0101] (2)

[0102] Where C0 is the initial concentration of the lysozyme solution; C1 is the concentration of the lysozyme after adsorption; V is the volume of the lysozyme solution; and m0 is the mass of the nanofiber membrane.

[0103] 5. Mechanical properties of nanofiber membranes

[0104] The tensile strength of the nanofiber membranes prepared in Examples 1-5 and Comparative Examples 1-2 was tested using the following method:

[0105] Cut the nanofiber membrane into rectangular samples, clamp the rectangular samples on the Instron universal testing machine with appropriate clamps, ensuring that the clamping surfaces are flat and can firmly hold the samples without slipping or damaging the nanofiber membrane, and then apply tension until the nanofiber membrane completely breaks, and record the breaking strength.

[0106] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0107] Please see Figures 1 to 3 The image shows SEM images of the nanofiber membranes prepared in Example 1 and Comparative Examples 1-2. It can be seen that the strong cationic nanofiber membrane prepared in Example 1 has dense particles uniformly attached to its fiber skeleton and membrane surface. These particles are derivatives containing sulfonic acid groups obtained through grafting. In contrast, the nanofiber membranes prepared in Comparative Examples 1-2 have significantly fewer particles attached to their fiber skeleton and membrane surface, and these particles are unevenly distributed.

[0108] Table 1 Performance test results of nanofiber membranes prepared in Examples 1-5 and Comparative Examples 1-2

[0109]

[0110] Please refer to Table 1 for the test results of the nanofiber membranes prepared in Examples 1-5 and Comparative Examples 1-2. It can be seen that the amount of 3-hydroxypropanesulfonic acid is directly proportional to the grafting rate, hydrophilicity, adsorption capacity, and tensile strength of the nanofiber membrane. The nanofiber membrane obtained by the method of simultaneous cross-linking grafting followed by membrane formation (Example 1) exhibits good adsorption capacity for lysozyme, reaching adsorption equilibrium in 180 min, with a maximum adsorption capacity of 490 mg / g. Simultaneously, the grafted nanofiber membrane also possesses good hydrophilicity, with a minimum water contact angle of 21°.

[0111] Further comparison reveals that, compared to simultaneous crosslinking and grafting followed by film formation (Example 1), both crosslinking followed by film formation and then grafting (Comparative Example 1) and film formation followed by crosslinking and then grafting (Comparative Example 2) result in a significant decrease in grafting rate, leading to a significant reduction in the hydrophilicity and adsorption capacity of the nanofiber membrane, as well as a decrease in tensile strength. This is because, on the one hand, grafting and crosslinking in a nanofiber suspension ensures that the fibers are fully wetted and their active sites are fully exposed, increasing the grafting rate and the degree of crosslinking, thereby increasing the number of sulfonic acid groups on the surface and inside the nanofiber membrane, as well as the mechanical properties of the nanofiber membrane. On the other hand, during simultaneous crosslinking and grafting, crosslinking and grafting have a mutually promoting effect. The increased hydrophilicity and volume of the fibers after grafting sulfonic acid groups are beneficial for both full fiber wetting and increased intermolecular movement through the interaction forces between fibers and water molecules, promoting the diffusion of glutaraldehyde, improving the efficiency and uniformity of the crosslinking reaction, forming a stable three-dimensional crosslinked network, and enhancing the mechanical properties and stability of the nanofiber membrane after formation. Crosslinking first, then film formation, and finally grafting (Comparative Example 1) or film formation first, then crosslinking, and finally grafting (Comparative Example 2) cannot promote the crosslinking and grafting processes, nor can they achieve the other technical effects mentioned above. As a result, the grafting rate, hydrophilicity, and adsorption capacity are significantly reduced, and the fracture strength is reduced.

[0112] In summary, this application provides a strongly cationic nanofiber membrane and its preparation method. Porous nanofibers are prepared by mixing EVOH and CAB. These porous nanofibers are then dispersed in a solvent to obtain a nanofiber suspension. 3-hydroxypropanesulfonic acid, an alkali, and glutaraldehyde are directly added to the nanofiber suspension. By simultaneously crosslinking and grafting the nanofibers, the grafting rate and mechanical properties of the strongly cationic nanofiber membrane are significantly improved. The strongly cationic nanofiber membrane provided by this application has a sulfonic acid group grafting rate greater than 5%.

[0113] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a strongly cationic nanofiber membrane, characterized in that, Specifically, the steps include the following: S1, Polyvinyl alcohol-ethylene copolymer is mixed with cellulose acetate and nanofibers with rough surface and nano-protrusion structure are prepared by melt method. The nanofibers are dispersed in mixed solvent to obtain nanofiber suspension. S2, 3-hydroxypropanesulfonic acid, alkali and glutaraldehyde are added to the nanofiber suspension obtained in step S1 to simultaneously carry out cross-linking and grafting modification. The mixture is stirred and reacted for a certain time to obtain the modified nanofiber suspension. S3, the modified nanofiber suspension obtained in step S2 is uniformly coated onto a nonwoven fabric substrate, dried for the first time, washed, and dried a second time to obtain a strongly cationic nanofiber membrane.

2. The method for preparing a strongly cationic nanofiber membrane according to claim 1, characterized in that, The preparation of nanofibers by the melt method specifically includes the following steps: mixing the polyvinyl alcohol-ethylene copolymer with the cellulose acetate to obtain a mixture, adding the mixture to a twin-screw extruder, heating the mixture to a molten state, then stretching and molding, and extracting with acetone to remove CAB from the surface of the nanofibers to obtain nanofibers with a rough surface and a nano-protrusion structure.

3. The method for preparing a strongly cationic nanofiber membrane according to claim 1, characterized in that, The mass ratio of the polyvinyl alcohol-ethylene copolymer to the cellulose acetate is 1:2 to 1:4; the concentration of the nanofiber suspension is 1-5%.

4. The method for preparing a strongly cationic nanofiber membrane according to claim 1, characterized in that, In step S2, the amount of 3-hydroxypropanesulfonic acid is 2.5-15% of the volume of the nanofiber suspension; the amount of glutaraldehyde is 1-5% of the volume of the nanofiber suspension.

5. The method for preparing a strongly cationic nanofiber membrane according to claim 1, characterized in that, In step S2, the alkali is used to adjust the pH of the nanofiber suspension to 5-5.5; the alkali is one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, and potassium carbonate aqueous solution; the concentration of the alkali is 2-4 mol / L.

6. The method for preparing a strongly cationic nanofiber membrane according to claim 1, characterized in that, In step S2, the stirring reaction takes 12-36 hours.

7. The method for preparing a strongly cationic nanofiber membrane according to claim 1, characterized in that, In step S1, the mixed solvent is obtained by mixing deionized water and isopropanol at a volume ratio of (0.7-1):

1.

8. The method for preparing a strongly cationic nanofiber membrane according to claim 1, characterized in that, In step S1, the diameter of the nanofiber is 250-750 nm.

9. The method for preparing a strongly cationic nanofiber membrane according to claim 1, characterized in that, In step S3, the solvents used for washing are ethanol and deionized water; the temperature of the first drying is 40-60℃; and the temperature of the second drying is room temperature.

10. A strongly cationic nanofiber membrane prepared by the method according to any one of claims 1-9, characterized in that, The strong cationic nanofiber membrane has a grafting rate of greater than 5% and an average pore size of 400-500 nm; the strong cationic nanofiber membrane is used for the adsorption and separation of proteins.

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