A polybenzimidazole nanofiber membrane for medical mask filter material and its preparation method and modification method

Abstract

The present invention discloses a polybenzimidazole nanofiber membrane for use as a filter material for medical masks, as well as its preparation and modification methods. The polybenzimidazole nanofiber membrane is composed of cross-linked polybenzimidazole nanofibers, with the cross-links formed by polybenzimidazole bonding. The nanofiber membrane has a dumbbell-shaped pore size distribution. The preparation method comprises the following steps: preparing a spinning solution, preparing a bonding solution, preparing a nanofiber membrane layer, performing impregnation bonding, and post-processing. The polybenzimidazole nanofiber membrane obtained using the preparation method of the present invention has a tensile strength of 10 to 95 MPa and a filtration efficiency of 90% to 99.95% for particles ≥50 nm. It maintains its original stable structure and filtration performance after ultraviolet or dry heat sterilization, and maintains a filtration efficiency greater than 90% after 50 washes. It is reusable, has high economic and environmental benefits, and is simple to prepare, making it suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiber membranes, and in particular to a polybenzimidazole nanofiber membrane used as a filter material for medical masks, and a preparation method and a modification method thereof. Background Art

[0002] Nanofiber membrane is prepared by electrospinning and has unique characteristics and properties, such as high specific surface area, high porosity, and small pore size distribution. It is an ideal high-efficiency filtration material and provides a new direction for the development of filtration technology.

[0003] Existing nanofiber membranes are mostly produced through electrospinning using polymers such as polyvinylidene fluoride, polyacrylonitrile, polylactic acid, and polycaprolactone. While each possesses its own performance advantages, they often suffer from low tensile strength, high temperature resistance, inability to be sterilized with UV light, inability to be washed with water, high air resistance, and low filtration efficiency, limiting their reuse. This is particularly true when used as filter media for medical masks, resulting in a waste of polymer resources.

[0004] Therefore, it is necessary to develop a nanofiber membrane for medical mask filter material that can be ultraviolet disinfected or dry heat sterilized, can be washed multiple times, has high tensile strength, low air permeability resistance, and high filtration efficiency, as well as a preparation method and modification method thereof. Summary of the Invention

[0005] The purpose of the present invention is to provide a polybenzimidazole nanofiber membrane for medical mask filter material, and a preparation method and modification method thereof. Using polybenzimidazole (PBI) as a raw material and the preparation method can make the prepared nanofiber membrane have high tensile strength, low filtration resistance, and can be sterilized by ultraviolet and dry heat. After multiple water washings, it can still maintain a high filtration efficiency, thereby realizing the reuse of the nanofiber membrane and reducing the waste of polymer resources.

[0006] In order to solve the above technical problems, the present invention provides a polybenzimidazole nanofiber membrane for medical mask filter material, wherein the polybenzimidazole nanofiber membrane is composed of polybenzimidazole nanofibers, the polybenzimidazole nanofibers are in a cross-linked state, and the intersections between the polybenzimidazole nanofibers are bonded by polybenzimidazole to form a bonding structure, and the polybenzimidazole nanofiber membrane has a dumbbell-shaped pore size distribution structure.

[0007] The diameter of the polybenzimidazole nanofiber used for the medical mask filter material is 0.05 to 0.8 μm.

[0008] The dumbbell-shaped pore size distribution structure of the polybenzimidazole nanofiber membrane means that the average pore size of each membrane layer gradually decreases and then gradually increases in the thickness direction thereof, and the dumbbell-shaped pore size distribution structure is an adjustable dumbbell-shaped pore size distribution structure.

[0009] The present invention uses polybenzimidazole as a raw material for preparing the nanofiber membrane, which enables the nanofiber membrane to withstand long-term high-temperature use, for example, at 300-370°C. PBI also has excellent flame retardancy, a bactericidal effect, and resistance to radiation, boiling water, solvents, and chemicals.

[0010] The adjustability of the dumbbell-shaped pore size distribution structure is achieved through the synergistic effect of factors such as the inner diameter of the spinning needle, the concentration of the spinning solution, the concentration of the impregnation adhesive solution, the impregnation time, and the number of impregnations. By changing the inner diameter of the spinning needle and the concentration of the spinning solution, the average pore size of the different membrane layers and the average pore size change rate between the membrane layers can be adjusted. By changing the concentration of the impregnation adhesive solution, the impregnation time, and the number of impregnations, the average pore size of each membrane layer of the nanofiber membrane can be reduced by an equal amount. Multiple factors jointly determine the absolute average pore size of each membrane layer of the nanofiber membrane and the relative average pore size between the membrane layers, thereby achieving the adjustability of the dumbbell-shaped pore size distribution structure.

[0011] The polybenzimidazole nanofiber membrane has a thickness of 3 to 20 μm, a pore size distribution of 0.01 to 10 μm, and a tensile strength of 20 to 90 MPa.

[0012] The polybenzimidazole nanofiber membrane is used as a reusable medical mask filter material.

[0013] The polybenzimidazole nanofiber membrane has a filtration efficiency of 90% to 99.95% for particles ≥50nm, with a resistance of 5 to 250 Pa. The PBI nanofiber membrane can withstand UV and dry heat sterilization. After UV and dry heat sterilization, the filtration efficiency for particles ≥50nm remains at 90% to 99.95%, with a resistance of 5 to 250 Pa, and is reusable. After 50 washes, the filtration efficiency remains greater than 90%.

[0014] To solve the above technical problems, the present invention also provides a method for preparing a polybenzimidazole nanofiber membrane for a medical mask filter material, comprising the following steps:

[0015] Step A) preparing a spinning solution: dissolving polybenzimidazole in N,N-dimethylacetamide to obtain a spinning solution with a polybenzimidazole mass concentration of 5% to 30%;

[0016] Step B) preparing an adhesive solution: heating and dissolving polybenzimidazole in N,N-dimethylacetamide, dimethylformamide, or N-methylpyrrolidone to obtain a polybenzimidazole dilute solution with a mass concentration of 0.05% to 5%;

[0017] Step C) preparing a nanofiber membrane layer: electrospinning the spinning solution obtained in step A) to prepare a polybenzimidazole nanofiber membrane layer, and adjusting the dumbbell-shaped pore size distribution of the polybenzimidazole nanofiber membrane layer by adjusting the inner diameter of the spinning needle and the concentration of the spinning solution;

[0018] Step D) impregnation and bonding: the polybenzimidazole nanofiber membrane layer obtained in step C) is immersed in the polybenzimidazole dilute solution obtained in step B) for bonding, crosslinking, and pore size control to obtain a bonded and crosslinked polybenzimidazole nanofiber membrane layer;

[0019] Step E) post-treatment: subjecting the bonded and cross-linked polybenzimidazole nanofiber membrane obtained in step D) to a gradient temperature treatment to obtain an in-situ bonded and cross-linked polybenzimidazole nanofiber membrane.

[0020] The diacid monomers used in the polybenzimidazole polymerization in step A) are isophthalic acid, terephthalic acid, pyridinedicarboxylic acid, and 4,4-diphenyl ether dicarboxylic acid; the diester monomers are dimethyl isophthalate and dimethyl terephthalate; and the tetraamine monomers are one of 3,3′-diaminobenzidine, benzene-1,2,4,5-tetramine, and 2,3,5,6-pyridinetetramine.

[0021] A polymerization method for the polybenzimidazole in step A) is as follows: under nitrogen protection, polyphosphoric acid is heated at 60-150° C. in a reaction vessel for 0.5-2 h for degassing; then, a diacid and a tetraamine monomer, or a diester monomer and a tetraamine monomer, and phosphorus pentoxide are sequentially added to the reaction vessel, with the diacid and tetraamine monomer or the diester and tetraamine monomer being in a total molar ratio of 1:0.85-1:1.15; the reaction system is prepolymerized at 140-180° C. for 0.5-5 h to obtain a prepolymerized material; a heating device (the heating device can be a microwave reactor or other heating methods such as an oil bath) is set to a temperature of 200-250° C. for polymerization, the reaction time being 0.5-20 h, and phosphorus pentoxide is added 1-5 times during the polymerization process to obtain a polybenzimidazole (PBI) material having a solid content of 3%-20% and polyphosphoric acid as the solvent; then, the material is poured into deionized water to precipitate a polybenzimidazole polymer.

[0022] The solvent for dissolving the polybenzimidazole in step B) is preferably N,N-dimethylacetamide.

[0023] It should be noted that the concentration of the spinning solution directly affects the pore size of the PBI nanofiber membrane. The smaller the spinning solution concentration, the smaller the diameter of the nanofiber prepared by electrospinning, and the smaller the pore size.

[0024] The heating temperature in step B) is 100-200° C., which can accelerate the dissolution rate of polybenzimidazole.

[0025] Further preferably, in step B), a crosslinking agent is added in an amount of 1%-20% (this content is based on the polybenzimidazole content in the dilute solution), and the crosslinking agent includes 1,4-di(bromomethyl)benzene or 4,4'-di(bromomethyl)diphenyl ether or 4,4'-dibromomethylbiphenyl. After the prepared fiber membrane is immersed in the above solution, first, there is an adhesive cross-linking structure between the fibers, and secondly, there is a cross-linking structure between the main chains of the polybenzimidazole. This can significantly improve the mechanical properties of the membrane. It can be called a high-strength double-crosslinked polybenzimidazole nanofiber membrane. The first crosslinking is the crosslinking bonding between the nanofibers; the second crosslinking is the crosslinking between the polybenzimidazole main chain structures on the surface of the polybenzimidazole fibers.

[0026] In step C), the inner diameter of the spinning needle is 0.1 to 1.5 mm, and the order of using the spinning needle is that the inner diameter of the needle gradually decreases and then gradually increases.

[0027] It should be noted that the present application regulates the dumbbell-shaped pore size distribution of the polybenzimidazole nanofiber membrane layer by adjusting the inner diameter of the spinning needle and the concentration of the spinning solution. This dumbbell-shaped pore size distribution is primarily achieved during the fiber membrane spinning process. The smaller the inner diameter of the needle and the lower the spinning solution concentration, the smaller the diameter of the resulting fiber membrane. The larger the inner diameter of the needle and the higher the spinning solution concentration, the larger the diameter of the resulting fiber membrane. Therefore, by adjusting both the inner diameter of the spinning needle and the concentration of the spinning solution, the fiber diameter can be achieved over a wide range, and the two factors have a synergistic effect.

[0028] The dipping times in step D) are 1 to 5 times, and the dipping time for each time is 0.1 to 30 minutes.

[0029] The step D) of impregnation and bonding is an integrated impregnation and bonding process, which means that the prepared PBI nanofiber membrane is immersed in a dilute PBI solution, which is similar to the sizing treatment. The slurry can effectively bond the nanofibers together. Multiple immersion sizing can achieve pore size regulation. The more times it is immersed in the liquid, the smaller the pore size will be.

[0030] Preferably, the immersion temperature in step D) is 25° C. to 80° C. The immersion process can be carried out under ultrasonic conditions. The presence of ultrasound is conducive to the immersion liquid fully entering the fiber membrane. The immersion time is 10 seconds to 5 minutes.

[0031] The gradient heating in step E refers to a gradual increase in temperature, the purpose of which is to allow the solvent after impregnation to evaporate. The polymer dissolved in the impregnation adhesive liquid adheres to the fiber like glue. The gradient heating is to allow the solvent to evaporate smoothly, which can ensure that the solvent is completely removed.

[0032] The method for preparing the polybenzimidazole nanofiber membrane for medical mask filter material specifically comprises the following steps:

[0033] Step A) preparing a spinning solution: heating and dissolving polybenzimidazole with a molecular weight of 20,000 to 800,000 g / mol in N,N-dimethylacetamide to obtain a spinning solution with a polybenzimidazole mass concentration of 5% to 30%;

[0034] Step B) preparing an adhesive solution: dissolving polybenzimidazole having a molecular weight of 20,000 to 800,000 g / mol and a crosslinking agent in N,N-dimethylacetamide, dimethylformamide, or N-methylpyrrolidone by heating to obtain a polybenzimidazole dilute solution having a mass concentration of 0.05% to 5%, wherein the amount of the crosslinking agent added is 1% to 20% of the amount of the polybenzimidazole added;

[0035] Step C) preparing a nanofiber membrane layer: electrospinning the spinning solution obtained in step A) to prepare a polybenzimidazole nanofiber membrane layer, and regulating the dumbbell-shaped pore size distribution of the polybenzimidazole nanofiber membrane layer by adjusting the inner diameter of the spinning needle and the concentration of the spinning solution, wherein the inner diameter of the spinning needle is 0.1 to 1.5 mm, and the dumbbell-shaped pore size distribution is that the pore size of the nanofiber membrane layer gradually decreases from 1.5 μm to 0.03 μm along the thickness direction, and then gradually increases from 0.03 μm to 1.5 μm;

[0036] Step D) impregnation and bonding: the polybenzimidazole nanofiber membrane layer obtained in step C) is immersed in the polybenzimidazole dilute solution obtained in step B) for bonding, crosslinking, and pore size control, the number of immersions being 1 to 5 times, and the time of each immersion being 0.1 to 30 minutes, to obtain a bonded and cross-linked polybenzimidazole nanofiber membrane layer;

[0037] Step E) post-treatment: The bonded and cross-linked polybenzimidazole nanofiber membrane layer obtained in step D) is subjected to a gradient temperature increase treatment to obtain an in-situ bonded and cross-linked polybenzimidazole nanofiber membrane, wherein the gradient temperature increase process is first heated to 25-150°C and maintained for 1-15 hours, and then heated to 50-200°C and maintained for 0.5-6 hours, with a heating rate of 1-15°C / min.

[0038] It should be noted that the higher the molecular weight of polybenzimidazole, the better the mechanical properties of the nanofibers prepared therefrom, and the better the bonding effect when used as an adhesive.

[0039] The dumbbell-shaped pore size distribution means that the pore size of the nanofiber membrane layer gradually decreases from 1.5 μm to 0.03 μm along the thickness direction, and then gradually increases from 0.03 μm to 1.5 μm, and the pore size changes continuously.

[0040] The heating device used in the spinning solution preparation process in step A) is a microwave reaction heating device, a heat collecting constant temperature heating device or a digital display constant temperature electric heating jacket.

[0041] In step C), the spinning needles are replaced 1 to 5 times, and the order of using the spinning needles is from large to small inner diameter, and then from small to large inner diameter.

[0042] Preferably, the spinning solution in step A) is prepared using polybenzimidazole with a molecular weight of 200,000 to 800,000 g / mol;

[0043] The bonding liquid in step B) is prepared using polybenzimidazole with a molecular weight of 80,000 to 600,000 g / mol;

[0044] The gradient heating condition in step E) is to heat to 25-120° C. and maintain for 1-12 hours, then heat to 60-180° C. and maintain for 1-5 hours, with a heating rate of 2-12° C. / min.

[0045] In order to solve the above technical problems, the present invention also provides a method for modifying a polybenzimidazole nanofiber membrane for a mask filter material, which is characterized by comprising the following steps:

[0046] First, polybenzimidazole is dissolved in dimethyl sulfoxide, and KOH is added and refluxed for 5 to 10 hours, and then cooled to room temperature to obtain solution a;

[0047] Adding iodomethane dropwise and in batches to the solution a to obtain solution b;

[0048] Then, the solution b is placed in deionized water to precipitate to obtain a quaternized polyimidazole salt;

[0049] The quaternized polyimidazole salt is prepared into a 0.01% to 1% dilute solution to obtain solution c;

[0050] Then, the polybenzimidazole nanofiber membrane is immersed in solution c to obtain a nanofiber membrane with a surface layer of quaternized polybenzimidazole salt. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is one of the electron micrographs of the polybenzimidazole nanofiber membrane used as a medical mask filter material of the present invention;

[0052] Figure 2 This is the second electron micrograph of the polybenzimidazole nanofiber membrane used as a medical mask filter material of the present invention;

[0053] Figure 3 This is the third electron micrograph of the polybenzimidazole nanofiber membrane used as a medical mask filter material of the present invention;

[0054] Figure 4 This is an electron micrograph of the polybenzimidazole nanofiber membrane used as a medical mask filter material after being heated at 350° C. of the present invention;

[0055] Figure 5 The thermal stability diagram of polybenzimidazole used in the present invention;

[0056] Figure 6 Quaternized polyimidazole salt 1 H NMR spectrum;

[0057] Figure 7 This is a schematic diagram of the antibacterial results of the modified nanofiber composite membrane of the present invention:

[0058] Figure 8 Schematic diagram of the antibacterial results of unmodified nanofiber membrane.

[0059] Effects of the present invention

[0060] The beneficial effects of the polybenzimidazole nanofiber membrane for medical mask filter material and the preparation method of the present invention are as follows: ① The intersections between the polybenzimidazole nanofibers are bonded by polybenzimidazole impregnation to form a bonding structure, which greatly improves the tensile strength of the nanofiber membrane to 10-95 MPa, laying the foundation for its service life extension; ② It has a dumbbell-shaped pore size distribution structure, and the filtration efficiency of particles ≥50 nm reaches 90%-99.95%, with a resistance of only 5-250 Pa; ③ The PBI nanofiber filter material can still maintain its original stability after ultraviolet or dry heat sterilization. The structure and filtration performance are fixed. After washing 50 times, the filtration efficiency is still greater than 90%. It can be reused many times, which greatly reduces the consumption of membrane polymers and the generation of corresponding waste, and has high economic and environmental benefits. ④ Based on the self-adhesion technology in the spinning integration and impregnation bonding process, the dumbbell-shaped PBI nanofiber filter material with adjustable pore size distribution is prepared, which can realize the regulation of mechanical properties, bonding degree and cross-linking morphology. The preparation process is simple and suitable for industrial production. ⑤ It can be modified by quaternization, and the modified nanofiber membrane has excellent antibacterial properties. DETAILED DESCRIPTION

[0061] In order to further understand the present invention, the technical solutions of the present invention are described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0062] Example

[0063] The polybenzimidazole nanofiber membrane was prepared by the following method:

[0064] Step A) preparing a spinning solution: dissolving polybenzimidazole (PBI) of a certain molecular weight in N,N-dimethylacetamide to obtain a polybenzimidazole solution (spinning solution). The changes in PBI molecular weight and spinning solution concentration are shown in Table 1.

[0065] Step B) preparing an adhesive solution: heating and dissolving polybenzimidazole of a certain molecular weight in a solvent to obtain a polybenzimidazole dilute solution. The molecular weight of PBI, type of solvent, dissolution temperature, and mass concentration of the polybenzimidazole dilute solution are shown in Table 2;

[0066] Step C) Preparing a nanofiber membrane layer: The spinning solution obtained in step A) was subjected to electrospinning to prepare a polybenzimidazole nanofiber membrane layer. The dumbbell-shaped pore size distribution of the polybenzimidazole nanofiber membrane layer was regulated by the inner diameter of the spinning needle and the concentration of the spinning solution. The changes in the electrospinning voltage and the inner diameter of the spinning needle are shown in Table 2.

[0067] Step D) Impregnation and bonding: The polybenzimidazole nanofiber membrane layer obtained in step C) is immersed in the polybenzimidazole dilute solution obtained in step B) for bonding, crosslinking, and pore size control to obtain a bonded and crosslinked polybenzimidazole nanofiber membrane layer. The number of immersions and the time of each immersion are shown in Table 3.

[0068] Step E) Post-treatment: The bonded and cross-linked polybenzimidazole nanofiber membrane layer obtained in step D) was subjected to a gradient temperature increase treatment to obtain an in-situ bonded and cross-linked polybenzimidazole nanofiber membrane. The temperature before heating, the end temperature of the first stage heating, the first stage heating holding time, the end temperature of the second stage heating, the second stage heating holding time, and the heating rate are shown in Table 4.

[0069] Among them, the adhesive liquid of Example 1 contains the cross-linking agent 1,4-di(bromomethyl)benzene, and its content is 20% of the mass of the polybenzimidazole therein; the adhesive liquid of Example 5 contains the cross-linking agent 4,4'-di(bromomethyl)diphenyl ether, and its content is 1% of the mass of the polybenzimidazole therein; the adhesive liquid of Example 8 contains the cross-linking agent 4,4'-dibromomethylbiphenyl phenyl, and its content is 10% of the mass of the polybenzimidazole therein.

[0070] Example 6 also includes a step of modifying the nanofiber membrane, including the following steps:

[0071] First, polybenzimidazole is dissolved in dimethyl sulfoxide, and KOH is added and refluxed for 5 to 10 hours, and then cooled to room temperature to obtain solution a;

[0072] Add iodomethane dropwise in batches to solution a to obtain solution b;

[0073] Then, solution b was placed in deionized water to precipitate the quaternized polyimidazolium salt. The mass spectrum of the quaternized polyimidazolium salt is as follows: Figure 6 As shown;

[0074] The quaternized polyimidazole salt is prepared into a 0.01% to 1% dilute solution to obtain solution c;

[0075] Then, the polybenzimidazole nanofiber membrane is immersed in solution c to obtain a nanofiber membrane with a surface layer of quaternized polybenzimidazole salt.

[0076] Table 1 Main parameters of the method for preparing polybenzimidazole nanofiber membrane in the embodiment of the present invention (I)

[0077]

[0078] Table 2 Main parameters of the method for preparing polybenzimidazole nanofiber membrane in the embodiment of the present invention (II)

[0079]

[0080]

[0081] Table 3 Main parameters of the method for preparing polybenzimidazole nanofiber membrane in the embodiment of the present invention (III)

[0082]

[0083] Table 4 Main parameters of the method for preparing polybenzimidazole nanofiber membrane according to the embodiment of the present invention (IV)

[0084]

[0085]

[0086] The polybenzimidazole nanofiber membrane obtained in the above embodiment has a dumbbell-shaped pore size distribution structure, and other performance parameters are shown in Table 5.

[0087] Table 5 Main properties of polybenzimidazole nanofiber membranes obtained in the examples of the present invention

[0088]

[0089] The above-mentioned example conditions were used to prepare Figure 1 、 Figure 2 、 Figure 3 The polybenzimidazole nanofiber membrane layer shown is used for medical mask filter material.

[0090] The polybenzimidazole nanofiber membrane prepared in Example 4 was sterilized at 300°C for 2 hours. Figure 4 As shown in the figure, no obvious changes have occurred, its structure is still stable, the filtration efficiency for particles ≥50nm can still reach 95%, and the resistance is 145Pa, indicating that it can still be reused after dry heat sterilization. Figure 5 This is the thermal stability diagram of the polybenzimidazole used in the present invention. It can be seen that the PBI material can be used for a long time at 300°C, and the membrane material will not degrade until it is above 500°C.

[0091] After the polybenzimidazole nanofiber membrane prepared in Example 4 was sterilized by ultraviolet light, the filtration efficiency for particles ≥50 nm was still able to reach 95%, and the resistance was 140 Pa, indicating that it can be reused after ultraviolet sterilization.

[0092] The polybenzimidazole nanofiber membrane prepared in Example 4 was washed with water for many times. After 50 washes, the filtration efficiency for particles ≥50 nm was still greater than 94.5%, and the resistance was 140 Pa, indicating that it can be reused after multiple washes.

[0093] The filtration efficiency and filtration resistance of the above embodiments were measured in accordance with the standard GB19083-2010 "Technical Requirements for Medical Protective Masks".

[0094] The modified polybenzimidazole nanofiber membrane of Example 6 was tested for antibacterial properties according to the following method. The antibacterial results are shown in FIG. Figure 7 shown.

[0095] The bacteria selected for testing were Gram-positive Staphylococcus aureus (ATCC 6538). All instruments to be used were sterilized before testing.

[0096] Prepare the bacterial solution to be inoculated: add 0.5wt% beef extract, 0.5wt% sodium chloride, 1wt% peptone and distilled water to a beaker, ultrasonically dissolve, and adjust the pH value to 7.0-7.2 with a dilute alkaline solution to obtain a nutrient broth. Take 20mL of the liquid into two 50mL conical flasks respectively. Then place the conical flask in a pressure steam sterilizer and sterilize it at 121°C for 20 minutes. After sterilization, wait for the solution to cool to room temperature, use a sterilized pipette in a clean bench to draw 0.2mL of Staphylococcus aureus into the above-mentioned sterilized nutrient broth, and then culture the bacteria at 37°C in a constant temperature oscillator for 24 hours. The obtained liquid is the mother liquor. In the clean bench, use a pipette to draw 0.2mL of the mother liquor into a test tube with 1.8mL of sterilized water and shake well. Repeat this method. Select a dilution factor of 10 -5 or 10 -6 The test tube is used as the inoculum.

[0097] Preparation of solid agar medium: Prepare nutrient broth using the same method as above, add 1.5-2.0 wt% agar, and heat to dissolve. Sterilize the agar medium in a pressure steam autoclave at 121°C for 20 minutes. In a laminar flow hood, quickly pour the sterilized liquid agar medium into a sterilized Petri dish and allow to cool to obtain a solid agar medium.

[0098] Test: Select the prepared fiber membrane and, according to the national standard GB / T4789.2-2003, take 0.4 mL of the bacterial solution to be inoculated and evenly add it to the blank control group and the antibacterial fiber membrane group. Then, cover the sample with a 40 mm × 40 mm polyethylene film to ensure that the bacterial solution can fully contact the coating and no bubbles appear. Then place it in a blank culture dish and incubate it in a clean bench for 3 hours. After that, wash the coating surface and polyethylene film with 5 mL of sterile water several times. Collect the washed liquid and shake it well. Take 0.2 mL of the liquid and evenly spread it on the prepared solid agar medium. Place it in a biochemical incubator. After incubation at 37 ° C for 24 hours, count the colonies on the solid agar medium to verify the antibacterial properties of the fiber membrane.

[0099] Comparative Example 1-No dumbbell-shaped pore size distribution structure

[0100] The polybenzimidazole nanofiber membrane was prepared by the following method:

[0101] Step A) preparing a spinning solution: dissolving polybenzimidazole in N,N-dimethylacetamide to obtain a spinning solution with a polybenzimidazole mass concentration of 20%;

[0102] Step B) preparing an adhesive solution: heating and dissolving polybenzimidazole in N,N-dimethylacetamide to obtain a polybenzimidazole dilute solution with a mass concentration of 2%;

[0103] Step C) preparing a nanofiber membrane layer: electrospinning the spinning solution obtained in step A) to prepare a polybenzimidazole nanofiber membrane layer, with an inner diameter of the spinning needle being 1.0 mm;

[0104] Step D) impregnation and bonding: the polybenzimidazole nanofiber membrane layer obtained in step C) is impregnated with the polybenzimidazole dilute solution obtained in step B) for bonding and crosslinking to obtain a bonded and crosslinked polybenzimidazole nanofiber membrane layer;

[0105] Step E) post-treatment: subjecting the bonded and cross-linked polybenzimidazole nanofiber membrane obtained in step D) to a gradient temperature treatment to obtain an in-situ bonded and cross-linked polybenzimidazole nanofiber membrane.

[0106] The obtained polybenzimidazole nanofiber membrane has a thickness of 12μm, a pore size of 0.1μm, and a tensile strength of 63MPa. Due to the lack of a dumbbell-shaped pore size distribution structure, it is very easy to get clogged during the filtration of solid particles. After only 1 hour of use, the resistance increased from 80Pa to more than 500Pa, and the resistance increased rapidly.

[0107] Comparative Example 2 - No Dipping Adhesion and Post-Processing Steps

[0108] The polybenzimidazole nanofiber membrane was prepared by the following method:

[0109] Step A) preparing a spinning solution: dissolving polybenzimidazole in N,N-dimethylacetamide to obtain a spinning solution with a polybenzimidazole mass concentration of 20%;

[0110] Step C) preparing a nanofiber membrane layer: electrospinning the spinning solution obtained in step A) to prepare a polybenzimidazole nanofiber membrane layer, with an inner diameter of the spinning needle being 1.0 mm;

[0111] The obtained polybenzimidazole nanofiber membrane has a thickness of 12 μm, a pore size of 0.1 μm, and a tensile strength of only 15 MPa. Due to the lack of impregnation, bonding, and post-processing steps, the tensile strength of the membrane is greatly reduced.

[0112] Comparative Example 3-No Modification Step

[0113] The antibacterial performance of the unmodified nanofiber membrane is shown in the figure. Figure 8 shown.

[0114] In summary, the nanofiber membrane prepared by the polybenzimidazole nanofiber membrane preparation method of the present invention has a bonding structure at the fiber intersection, which greatly improves the tensile strength of the nanofiber membrane; it has a dumbbell-shaped pore size distribution structure, and the filtration efficiency for particles ≥50nm reaches 90% to 99.95%, and the resistance is only 5 to 250Pa; the PBI nanofiber filter material can still maintain its original stable structure and filtration performance after ultraviolet or dry heat sterilization, and the filtration efficiency is still greater than 90% after washing 50 times, and it can be quaternized and surface modified to have excellent antibacterial properties, and can be reused many times, greatly reducing the consumption of polymers used in medical mask filter materials and the generation of corresponding waste, and has high economic and environmental benefits.

Claims

1. A polybenzimidazole nanofiber membrane for medical mask filter material, characterized in that: The polybenzimidazole nanofiber membrane is composed of polybenzimidazole nanofibers, which are in a cross-linked state. The intersections between the polybenzimidazole nanofibers are bonded by polybenzimidazole to form a bonding structure. The polybenzimidazole nanofiber membrane has a dumbbell-shaped pore size distribution structure. The dumbbell-shaped pore size distribution structure of the polybenzimidazole nanofiber membrane means that the average pore size of each membrane layer gradually decreases and then gradually increases in its thickness direction; the diameter of the polybenzimidazole nanofiber is 0.05~0.8 μm; the thickness of the polybenzimidazole nanofiber membrane is 3~20 μm, the pore size distribution is 0.01~10 μm, and the tensile strength is 20~90 MPa; by changing the inner diameter of the spinning needle and the concentration of the spinning solution, the average pore size of different membrane layers and the average pore size change rate between membrane layers are regulated.

2. The polybenzimidazole nanofiber membrane for medical mask filter material according to claim 1, wherein The dumbbell-shaped pore size distribution structure is an adjustable dumbbell-shaped pore size distribution structure.

3. The polybenzimidazole nanofiber membrane for medical mask filter material according to claim 1, wherein The polybenzimidazole nanofiber membrane is used as a reusable medical mask filter material.

4. A method for preparing a polybenzimidazole nanofiber membrane for a medical mask filter material as claimed in claim 1, characterized in that: The following steps are involved: Step A) preparing a spinning solution: dissolving polybenzimidazole in N,N-dimethylacetamide to obtain a spinning solution having a polybenzimidazole mass concentration of 5% to 30%; Step B) preparing an adhesive solution: dissolving polybenzimidazole in N,N-dimethylacetamide, dimethylformamide, or N-methylpyrrolidone by heating to obtain a polybenzimidazole dilute solution with a mass concentration of 0.05% to 5%; Step C) preparing a nanofiber membrane layer: electrospinning the spinning solution obtained in step A) to prepare a polybenzimidazole nanofiber membrane layer, and adjusting the dumbbell-shaped pore size distribution of the polybenzimidazole nanofiber membrane layer by adjusting the inner diameter of the spinning needle and the concentration of the spinning solution; Step D) impregnation and bonding: the polybenzimidazole nanofiber membrane layer obtained in step C) is immersed in the polybenzimidazole dilute solution obtained in step B) for bonding, crosslinking, and pore size regulation to obtain a bonded and crosslinked polybenzimidazole nanofiber membrane layer; Step E) post-treatment: subjecting the bonded and cross-linked polybenzimidazole nanofiber membrane obtained in step D) to a gradient temperature treatment to obtain an in-situ bonded and cross-linked polybenzimidazole nanofiber membrane.

5. The method for preparing a polybenzimidazole nanofiber membrane for a medical mask filter material according to claim 4, wherein: The polybenzimidazole in step A) is prepared by polymerizing a diacid monomer and a tetramine monomer, or by polymerizing a diester monomer and a tetramine monomer, wherein the diacid monomer is one of isophthalic acid, terephthalic acid, pyridinedicarboxylic acid, and 4,4-diphenyl ether dicarboxylic acid; the diester monomer is dimethyl isophthalate or dimethyl terephthalate; and the tetramine monomer is one of 3,3′-diaminobenzidine, benzene-1,2,4,5-tetramine, and 2,3,5,6-pyridinetetramine.

6. The method for preparing a polybenzimidazole nanofiber membrane for a medical mask filter material according to claim 4, wherein In step C), the inner diameter of the spinning needle is 0.1-1.5 mm, and the order of using the spinning needle is that the inner diameter of the needle gradually decreases and then gradually increases.

7. The method for preparing a polybenzimidazole nanofiber membrane for a mask filter according to any one of claims 4 to 6, characterized in that: The following steps are involved: Step A) preparing a spinning solution: dissolving polybenzimidazole having a molecular weight of 20,000 to 800,000 g / mol in N,N-dimethylacetamide by heating to obtain a spinning solution having a polybenzimidazole concentration of 5% to 30%; Step B) preparing an adhesive solution: dissolving polybenzimidazole (PBZ) having a molecular weight of 20,000 to 800,000 g / mol and a crosslinking agent in N,N-dimethylacetamide, dimethylformamide, or N-methylpyrrolidone by heating to obtain a polybenzimidazole dilute solution having a mass concentration of 0.05% to 5%, wherein the amount of crosslinking agent added is 1% to 20% of the amount of the polybenzimidazole added; Step C) preparing a nanofiber membrane layer: electrospinning the spinning solution obtained in step A) to prepare a polybenzimidazole nanofiber membrane layer, and regulating the dumbbell-shaped pore size distribution of the polybenzimidazole nanofiber membrane layer by adjusting the inner diameter of the spinning needle and the concentration of the spinning solution. The inner diameter of the spinning needle is 0.1 to 1.5 mm. The dumbbell-shaped pore size distribution is that the pore size of the nanofiber membrane layer gradually decreases from 1.5 μm to 0.03 μm along the thickness direction, and then gradually increases from 0.03 μm to 1.5 μm. Step D) impregnation and bonding: the polybenzimidazole nanofiber membrane layer obtained in step C) is immersed in the polybenzimidazole dilute solution obtained in step B) for bonding, crosslinking, and pore size control. The number of immersions is 1 to 5 times, and each immersion time is 0.1 to 30 minutes, to obtain a bonded and cross-linked polybenzimidazole nanofiber membrane layer. Step E) post-treatment: The bonded and cross-linked polybenzimidazole nanofiber membrane layer obtained in step D) is subjected to a gradient temperature increase treatment to obtain an in-situ bonded and cross-linked polybenzimidazole nanofiber membrane, wherein the gradient temperature increase process is first heated to 25-150°C and maintained for 1-15 hours, then heated to 50-200°C and maintained for 0.5-6 hours, with a heating rate of 1-15°C / min.

8. A method for modifying a polybenzimidazole nanofiber membrane for a mask filter material according to any one of claims 1 to 3, characterized in that: The following steps are involved: First, polybenzimidazole is dissolved in dimethyl sulfoxide, and KOH is added and refluxed for 5 to 10 hours, and then cooled to room temperature to obtain solution a; Adding iodomethane dropwise and in batches to the solution a to obtain solution b; Then, the solution b is placed in deionized water to precipitate to obtain a quaternized polyimidazole salt; The quaternized polyimidazole salt is prepared into a 0.01% to 1% dilute solution to obtain solution c; Then, the polybenzimidazole nanofiber membrane is immersed in solution c to obtain a nanofiber membrane with a surface layer of quaternized polybenzimidazole salt.

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