Nanofiber composite filter material and preparation process thereof

Abstract

The invention relates to the technical field of non-woven fiber filter materials, and discloses a nanofiber composite filter material and a preparation process thereof, the preparation process comprises the following steps: synthesizing a composite antibacterial epoxy group cross-linking agent, taking chitosan and polyvinyl alcohol as raw materials, and adopting an electrostatic spinning process to prepare a chitosan-polyvinyl alcohol nanofiber membrane; on the basis of an epoxy ring-opening mechanism, an epoxy functional group of a composite antibacterial epoxy cross-linking agent and hydroxyl and amino functional groups contained in the chitosan-polyvinyl alcohol nanofiber membrane are subjected to a ring-opening reaction, so that the cross-linking modification effect of the chitosan-polyvinyl alcohol nanofiber membrane is realized; the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane is prepared; the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane is used as a middle filtering medium layer to be compounded with a PP non-woven fabric base layer, the nanofiber composite filter material is prepared, the air filtering efficiency of the composite filter material is larger than 98%, the antibacterial rate of the composite filter material is larger than 96%, and the composite filter material shows very excellent filtering effect and antibacterial effect.

Description

Technical Field

[0001] The invention relates to the technical field of non-woven fiber filter materials, in particular to a nanofiber composite filter material and a preparation process thereof. Background Art

[0002] Preparation of high performance air filter materials is the key to reducing PM 2.5 Particulate matter is an important way to endanger human health, and the development of green air filtration materials is a new direction of industrial development.

[0003] Chitosan is a biodegradable natural polymer material that not only has the physical adsorption and filtration functions required by nanofibers, but also has unique chemical adsorption and excellent antibacterial properties, and can be used in the field of functional nanofiber filter materials.

[0004] However, chitosan has low strength, high viscosity and cationic polyelectrolyte characteristics after dissolution, which makes it difficult to carry out electrospinning smoothly, thus limiting the application range of chitosan as a functional fiber. Polyvinyl alcohol is a biocompatible, biodegradable, non-toxic soluble polymer. Blending chitosan with polyvinyl alcohol, which has excellent spinnability, is an effective way to improve the spinnability and mechanical properties of chitosan.

[0005] Since chitosan and polyvinyl alcohol are both water-soluble materials, the nanofiber membrane obtained by electrospinning is unstable when exposed to water and needs to be cross-linked. Glutaraldehyde is the most widely used cross-linking agent, but related studies have confirmed that it is cytotoxic. Summary of the invention

[0006] The present invention utilizes fiber raw materials that are widely available, low in price, and green and renewable, and prepares chitosan-polyvinyl alcohol nanofiber membranes with antibacterial function and stable performance based on an electrospinning method, and uses the chitosan-polyvinyl alcohol nanofiber membranes as filter media to be composited with a non-woven fabric substrate to prepare nanofiber composite filter materials.

[0007] A preparation process of a nanofiber composite filter material comprises the following steps: Step 1: synthesizing a composite antibacterial epoxy crosslinking agent, wherein the composite antibacterial epoxy crosslinking agent is composite antibacterial epoxy crosslinking agent I or composite antibacterial epoxy crosslinking agent II; Step 2: using chitosan and polyvinyl alcohol as raw materials, adopting electrospinning process to prepare chitosan-polyvinyl alcohol nanofiber membrane; Step 3: Based on the epoxy ring-opening mechanism, the epoxy functional groups of the composite antibacterial epoxy crosslinking agent react with the hydroxyl and amino functional groups contained in the chitosan-polyvinyl alcohol nanofiber membrane to undergo a ring-opening reaction, thereby achieving the cross-linking modification of the chitosan-polyvinyl alcohol nanofiber membrane and preparing a cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane; Step 4: Compounding the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane as the intermediate filter medium layer with the PP non-woven fabric base layer to prepare a nanofiber composite filter material.

[0008] Preferably, the chemical structural formula of the composite antibacterial epoxy crosslinking agent I is: .

[0009] Preferably, the preparation method of the composite antibacterial epoxy crosslinking agent I is: The Schiff base reaction mechanism is used to generate a di-Schiff base tertiary phosphine monomer through a condensation reaction between the carbonyl functional group of 4,4'-biphenyldicarboxaldehyde and the amino functional group of 3-(diphenylphosphino)propylamine. The composite antibacterial epoxy crosslinking agent I is generated by utilizing the nucleophilic substitution reaction mechanism, through the quaternary phosphine group of the di-Schiff base tertiary phosphine monomer and the chlorine functional group of epichlorohydrin.

[0010] Preferably, the chemical structural formula of the composite antibacterial epoxy crosslinking agent II is: .

[0011] Preferably, the preparation method of the composite antibacterial epoxy crosslinking agent II is: Using the Schiff base reaction mechanism, the carbonyl functional group of 3,3',5,5'-tetraaldehyde biphenyl reacts with the amino functional group of 3-(diphenylphosphino)propylamine to generate tetra-Schiff base tertiary phosphine monomers; Utilizing the nucleophilic substitution reaction mechanism, the tertiary phosphine group of the tetra-Schiff base tertiary phosphine monomer reacts with the chlorine functional group of epichlorohydrin to undergo quaternary phosphination reaction to generate a composite antibacterial epoxy crosslinker II.

[0012] Preferably, the mass ratio of chitosan to polyvinyl alcohol in the chitosan-polyvinyl alcohol nanofiber membrane of step 2 is 1:(0.8-2).

[0013] Preferably, the preparation method of the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane is: mix a composite antibacterial epoxy cross-linking agent, acetone and deionized water to prepare a composite antibacterial epoxy cross-linking agent solution with a mass fraction of 1-10wt%, completely immerse the chitosan-polyvinyl alcohol nanofiber membrane in the composite antibacterial epoxy cross-linking agent solution, keep it for 1-5 hours to carry out the cross-linking reaction, take it out, wash and dry it to obtain a cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane.

[0014] The air filtration efficiency of a nanofiber composite filter material prepared according to the above process is greater than 98%.

[0015] The antibacterial rate of a nanofiber composite filter material prepared according to the above process is greater than 96%, and the bacteria are Escherichia coli or Staphylococcus aureus.

[0016] The application of a nanofiber composite filter material prepared according to the above process in medical masks.

[0017] Beneficial effects:

[0018] The present invention firstly uses chitosan, which has excellent properties such as biocompatibility, biodegradability, antibacterial and adsorption, as a raw material for nanofiber filter material, and polyvinyl alcohol, which has biocompatibility and biodegradability, as a spinning aid, to prepare chitosan-polyvinyl alcohol nanofiber membrane through an electrospinning process; Then, based on the epoxy ring-opening reaction, the chitosan-polyvinyl alcohol nanofiber membrane was cross-linked and modified using a composite antibacterial epoxy cross-linking agent synthesized independently to prepare a cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane; The experimental results show that the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane prepared by the present invention has achieved significant improvement in water resistance, antibacterial properties and mechanical properties compared with the chitosan-polyvinyl alcohol nanofiber membrane that has not been cross-linked and modified and the chitosan-polyvinyl alcohol nanofiber membrane that has been conventionally cross-linked and modified using glutaraldehyde. Finally, the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane was used as the intermediate filter medium layer and composited with the PP non-woven fabric base layer to prepare a nanofiber composite filter material; The experimental results show that the air filtration efficiency of the nanofiber composite filter material prepared by the present invention is greater than 98%, and the antibacterial rate is greater than 96%, showing very excellent filtration effect and antibacterial effect. DETAILED DESCRIPTION

[0019] Experimental Example 1:

[0020] The synthetic route of composite antibacterial epoxy crosslinking agent I is as follows: ; The synthesis process of composite antibacterial epoxy crosslinker Ⅰ is as follows: (1) Synthesizing a di-Schiff base tertiary phosphine monomer, wherein the specific synthesis method is as follows: utilizing the Schiff base reaction mechanism, a condensation reaction occurs between the carbonyl functional group of 4,4'-biphenyldicarboxaldehyde and the amino functional group of 3-(diphenylphosphino)propylamine to generate a di-Schiff base tertiary phosphine monomer, wherein the specific experimental steps are as follows: adding 2.1 g of 4,4'-biphenyldicarboxaldehyde and 30 mL of N,N-dimethylformamide to a three-necked flask, heating to 40°C and stirring for 20 min to completely dissolve the monomer under mechanical stirring, cooling to room temperature, sequentially adding 50 mL of an N,N-dimethylformamide solution containing 4.9 g of 3-(diphenylphosphino)propylamine and 2 mL of glacial acetic acid to the three-necked flask, heating to 80°C and stirring for 4 h, cooling to room temperature, removing the solvent by rotary evaporation, repeatedly washing with ethanol, and vacuum drying to obtain a di-Schiff base tertiary phosphine monomer; (2) Synthesis of composite antibacterial epoxy crosslinker I, the specific synthesis method of which is: using the nucleophilic substitution reaction mechanism, the tertiary phosphine group of the di-Schiff base tertiary phosphine monomer reacts with the chlorine functional group of epichlorohydrin to produce a quaternary phosphine reaction to generate a composite antibacterial epoxy crosslinker I, the specific experimental steps are: under the protection of nitrogen, 3.3g of di-Schiff base tertiary phosphine monomer and 40mL of N,N-dimethylformamide are added to a three-necked flask, stirred at room temperature until completely dissolved, then 1.5mL of epichlorohydrin is added dropwise to the three-necked flask, the temperature is raised to 60°C and stirred for reaction for 8h, cooled to room temperature, the solvent is removed by rotary evaporation, repeatedly washed with ethanol, and vacuum dried to obtain a composite antibacterial epoxy crosslinker I; The nuclear magnetic resonance hydrogen spectrum of the composite antibacterial epoxy crosslinker Ⅰ is characterized as follows: 1 H NMR (CDCl3, 400MHz) δ: 1.90-1.97 (m, 4H), 3.43-3.44 (d, 4H), 3.73-4.03 (m, 14H), 7.41-7.74 (m, 28H), 8.49 (s, 2H).

[0021] Experimental Example 2:

[0022] Synthesized composite antibacterial epoxy crosslinker II, its chemical structure is: ; The synthesis process of composite antibacterial epoxy crosslinker II is as follows: (1) Synthesizing tetra-Schiff base tertiary phosphine monomers, the specific synthesis method of which is: utilizing the Schiff base reaction mechanism, the carbonyl functional group of 3,3',5,5'-tetraaldehyde biphenyl and the amino functional group of 3-(diphenylphosphino)propylamine undergo condensation reaction to generate tetra-Schiff base tertiary phosphine monomers, the specific experimental steps of which refer to the preparation experiment of di-Schiff base tertiary phosphine monomers, the only difference being that 1.3 g of 3,3',5,5'-tetraaldehyde biphenyl is used to replace 2.1 g of 4,4'-biphenyl dicarboxaldehyde; (2) Synthesizing a composite antibacterial epoxy crosslinker II, wherein the specific synthesis method is as follows: utilizing a nucleophilic substitution reaction mechanism, the tertiary phosphine group of a tetra-Schiff base tertiary phosphine monomer reacts with the chlorine functional group of epichlorohydrin to produce a quaternary phosphine reaction to generate a composite antibacterial epoxy crosslinker II. The specific experimental steps refer to the preparation experiment of the composite antibacterial epoxy crosslinker I, and the only difference is that 2.9 g of the tetra-Schiff base tertiary phosphine monomer is used to replace 3.3 g of the di-Schiff base tertiary phosphine monomer; The nuclear magnetic resonance hydrogen spectrum of the composite antibacterial epoxy crosslinker II is characterized as follows: 1 H NMR (CDCl3, 400MHz) δ: 1.92-1.99 (m, 8H), 3.49-3.51 (d, 8H), 3.72-4.02 (m, 28H), 7.40-7.81 (m, 46H), 8.42 (s, 4H).

[0023] Embodiment 1:

[0024] The cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane I was prepared, and the preparation steps were as follows: Step 1, prepare chitosan / polyvinyl alcohol / acetic acid aqueous solution: first, add 0.8g chitosan (purchased from Shanghai McLean Biochemical Technology Co., Ltd., with a relative molecular mass of 1000000) to 10g acetic acid aqueous solution (the mass ratio of acetic acid to deionized water is 7:3), stir at room temperature for 12h until completely dissolved, and prepare chitosan / acetic acid aqueous solution with a mass fraction of 8.0wt%, then add 0.8g polyvinyl alcohol (purchased from Shanghai McLean Biochemical Technology Co., Ltd., with a relative molecular mass of 250000) to 10g deionized water, stir at 70°C for 12h until completely dissolved, and prepare polyvinyl alcohol aqueous solution with a mass fraction of 8.0wt%, finally mix the prepared chitosan / acetic acid aqueous solution and polyvinyl alcohol aqueous solution, stir at room temperature for 2h until mixed evenly, and stand for 5h to degas, to obtain chitosan / polyvinyl alcohol / acetic acid aqueous solution; Step 2: Prepare chitosan-polyvinyl alcohol nanofiber membrane: Inject the chitosan / polyvinyl alcohol / acetic acid aqueous solution prepared in step 1 into the propulsion pump of a DXES-3 electrospinning machine for electrospinning. The spinning voltage is 25 kV, the spinning distance is 20 cm, the infusion rate is 0.5 mL / h, the temperature is 25 ° C, and the humidity is 60% RH. Place a non-woven fabric substrate on the receiving device to collect the nanofiber membrane. After the electrospinning is completed, place the nanofiber membrane collected on the receiving substrate in a vacuum oven at 30 ° C for 1 hour to remove the residual solvent to obtain a nanofiber membrane with a thickness of 50 μm and a surface density of 4.5 g / m 2 Chitosan-polyvinyl alcohol nanofiber membrane; Step 3, preparing a cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane I: based on the epoxy ring-opening mechanism, the epoxy functional group of the composite antibacterial epoxy cross-linking agent I reacts with the hydroxyl and amino functional groups contained in the chitosan-polyvinyl alcohol nanofiber membrane to achieve a cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane, thereby preparing a cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane I; The specific experimental steps for preparing the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane I are as follows: 0.5 g of composite antibacterial epoxy cross-linker I, 4 g of acetone and 6 g of deionized water are mixed evenly to prepare a composite antibacterial epoxy cross-linker I solution with a mass fraction of 5.0 wt%. Then, the chitosan-polyvinyl alcohol nanofiber membrane prepared in step 2 is completely immersed in the composite antibacterial epoxy cross-linker I solution for 2 hours for cross-linking reaction. After taking it out, it is repeatedly washed with acetone and deionized water in turn, fully infiltrated with ethanol, air-dried at room temperature, and then placed in a vacuum oven at 30°C for 1 hour to obtain a cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane I.

[0025] Embodiment 2:

[0026] Preparation of cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane II: Based on the epoxy ring-opening mechanism, the epoxy functional groups of the composite antibacterial epoxy crosslinker II react with the hydroxyl and amino functional groups contained in the chitosan-polyvinyl alcohol nanofiber membrane to undergo a ring-opening reaction to achieve the cross-linking modification of the chitosan-polyvinyl alcohol nanofiber membrane, and prepare the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane II. The specific experimental steps refer to the preparation experiment of the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane I, and the only difference is that the composite antibacterial epoxy crosslinker II is used to replace the composite antibacterial epoxy crosslinker I.

[0027] Embodiment three:

[0028] The nanofiber composite filter material I is prepared in the following steps: Step 1: Preparation of non-woven fabric / cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane composite structure I: Referring to the preparation experiment of cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane I in Example 1, the only difference is that in the process of preparing chitosan-polyvinyl alcohol nanofiber membrane by electrospinning process, PP non-woven fabric (purchased from Zhejiang Runjiang New Materials Technology Co., Ltd., with a thickness of 100 μm and a surface density of 40 g / m 2 ) as a receiving substrate, the PP non-woven fabric substrate and the chitosan-polyvinyl alcohol nanofiber membrane deposited thereon are peeled off together, and are immersed in a composite antibacterial epoxy crosslinking agent I solution for crosslinking modification treatment to obtain a non-woven fabric / crosslinked modified chitosan-polyvinyl alcohol nanofiber membrane composite structure I; Step 2, preparing nanofiber composite filter material I: covering the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane in the non-woven fabric / cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane composite structure I with a layer of PP non-woven fabric to obtain nanofiber composite filter material I.

[0029] Embodiment 4:

[0030] The specific experimental steps for preparing nanofiber composite filter material II refer to the preparation experiment of nanofiber composite filter material I, and the only difference is that the composite antibacterial epoxy crosslinking agent II solution is used to replace the composite antibacterial epoxy crosslinking agent I solution.

[0031] Comparative Example 1:

[0032] The conventional cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane was prepared. The specific preparation steps were based on the preparation experiment of the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane Ⅰ. The only difference was that the conventional glutaraldehyde cross-linking agent was used to replace the composite antibacterial epoxy cross-linking agent Ⅰ. The specific preparation steps of the nanofiber composite filter material a are referred to the preparation experiment of the nanofiber composite filter material I, and the only difference is that the conventional glutaraldehyde crosslinking agent solution is used to replace the composite antibacterial epoxy crosslinking agent I solution.

[0033] Comparative Example 2:

[0034] The specific preparation steps of nanofiber composite filter material b are referred to the preparation experiment of nanofiber composite filter material I, and the only difference is that the PP non-woven fabric substrate and the chitosan-polyvinyl alcohol nanofiber membrane deposited thereon are peeled off together, but not immersed in the composite antibacterial epoxy crosslinker I solution for crosslinking modification treatment (i.e., the chitosan-polyvinyl alcohol nanofiber membrane is not crosslinked).

[0035] Performance Test:

[0036] The following performance tests were performed on the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane: (1) Water resistance test: The fiber membrane sample was placed in an atmosphere of 25°C and 60% RH for 24 h. Then, the fiber membrane sample (m0g) was placed in 100 mL of deionized water and soaked for 1 h to ensure complete water absorption. The sample was taken out and filter paper was placed on the surface of the sample to absorb the surface moisture. The sample was dried to a constant weight and the mass of the fiber membrane sample (m1g) was recorded. The mass loss rate was calculated and the water resistance of the material was characterized by the mass loss rate of the fiber membrane sample. The lower the mass loss rate, the better the water resistance of the material. The specific method is as follows: Mass loss rate (%) = (m0-m1) / m0×100%; (2) Mechanical properties test: A YM-06E electronic single fiber strength tester was used to perform a tensile test on a fiber membrane sample with a size of 10 mm × 40 mm at a tensile speed of 5 mm / min under the conditions of 25°C and 60% RH. The gauge length was set to 20 mm, and the tensile strength of the sample was recorded. (3) Antibacterial performance test: 200 μL of bacterial solution was transferred to 500 mL of LB broth culture medium sterilized at 120°C, and cultured in a shaker (37°C, 120 r / min) for 24 h as the test bacterial solution. The test bacterial solution was gradient diluted using sterilized test tubes on a clean bench to obtain the test bacterial solution. 100 μL of the solution with a concentration of 10 8 CFU / mL of test bacterial solution was added to LB broth solid culture medium, and the coating was evenly spread using a coating rod. Then, a 6 mm circular fiber membrane sample was attached to the surface of the LB broth solid culture medium. The LB broth solid culture medium was inverted and cultured in a 37°C biological incubator for 24 h. The diameter of the inhibition zone around the sample (including the diameter of the sample disc) was recorded. The bacterial liquid was ATCC6538 Staphylococcus aureus and ATCC25922 Escherichia coli purchased from Shanghai Luwei Technology Co., Ltd. The above experimental results are shown in Table 1 below.

[0037]

[0038] The following performance tests were performed on the nanofiber composite filter material: (1) Air filtration performance test: The air filtration performance of the sample was tested using the 8130 automatic filter material tester produced by TSI, USA. During the test, compressed air entered the device in three ways: the first way entered the aerosol generator containing 2wt% NaCl aqueous solution to produce NaCl aerosol with an average particle size of 0.26µm; this aerosol was mixed with the second way compressed air in the mixer and the dilution concentration was 20mg / m by controlling the flow control valve. 3 The test concentration is then passed through the filter element to be tested; the third compressed air provides a pressing force to ensure that the upper and lower clamps are tightened during the test; when the NaCl aerosol passes through the filter element to be tested, the upstream and downstream photometers respectively detect the NaCl aerosol concentration before and after passing through the filter element. The gas flow rate is 85L / min, and the filtration efficiency of the sample is calculated. The specific method is as follows: Filtration efficiency (%) = (upstream NaCl concentration - downstream NaCl concentration) × 100%; (2) Antibacterial performance test: The antibacterial performance of the samples was evaluated with reference to GB / T 20944-2008. The specific test steps were as follows: a sample with a diameter of 6 mm was placed in a well plate, and 0.1 mL of a 2×10 8CFU / mL of bacterial solution (phosphate buffered saline as buffer) was placed in an MJ-250I mold incubator for 30 min, then 0.9 mL of phosphate buffered saline was dripped into the well plate to which the bacterial solution had been added before, and after shaking, 0.1 mL of phosphate buffered saline was taken from the well plate and dripped into a centrifuge tube (volume 1.5 mL) containing 0.9 mL of phosphate buffered saline, and then 1×10 6 times, take 10 μL from each dilution gradient solution and drop it on the culture medium plate, culture for 24 hours, record the number of bacterial colonies and calculate the antibacterial rate of the sample. The specific method is as follows: Antibacterial rate (%) = {(average colony count of the original bacterial solution series - average colony count of the sample treated with antibacterial treatment and the original bacterial solution at the corresponding gradient) / average colony count of the original bacterial solution series} × 100%; The bacterial liquid was ATCC6538 Staphylococcus aureus and ATCC25922 Escherichia coli purchased from Shanghai Luwei Technology Co., Ltd. The above experimental results are shown in Table 2 below.

[0039]

[0040] By comprehensively analyzing the above experimental results, the following conclusions can be drawn: (1) The present invention uses a self-developed composite antibacterial epoxy crosslinking agent to crosslink and modify chitosan-polyvinyl alcohol nanofiber membranes. The crosslinked modified chitosan-polyvinyl alcohol nanofiber membranes prepared thereby have achieved significant improvements in water resistance, antibacterial properties and mechanical properties compared with chitosan-polyvinyl alcohol nanofiber membranes that have not been crosslinked and modified and chitosan-polyvinyl alcohol nanofiber membranes that have been conventionally crosslinked and modified using glutaraldehyde. Among them, the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane II prepared by using composite antibacterial epoxy cross-linking agent II has better comprehensive performance; (2) The air filtration efficiency of the nanofiber composite filter material prepared by the present invention is greater than 97%, and the antibacterial rate is greater than 95%, showing very excellent filtration effect and antibacterial effect.

Claims

1. A process for preparing a nanofiber composite filter material, characterized in that: The following steps are involved: Step 1: synthesizing a composite antibacterial epoxy crosslinking agent, wherein the composite antibacterial epoxy crosslinking agent is composite antibacterial epoxy crosslinking agent I or composite antibacterial epoxy crosslinking agent II; Step 2: using chitosan and polyvinyl alcohol as raw materials, adopting electrospinning process to prepare chitosan-polyvinyl alcohol nanofiber membrane; Step 3: Based on the epoxy ring-opening mechanism, the epoxy functional groups of the composite antibacterial epoxy crosslinking agent react with the hydroxyl and amino functional groups contained in the chitosan-polyvinyl alcohol nanofiber membrane to undergo a ring-opening reaction, thereby achieving the cross-linking modification of the chitosan-polyvinyl alcohol nanofiber membrane and preparing a cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane; Step 4: Compounding the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane as the intermediate filter medium layer with the PP non-woven fabric base layer to prepare a nanofiber composite filter material.

2. The preparation process of a nanofiber composite filter material according to claim 1, characterized in that: The chemical structural formula of the composite antibacterial epoxy crosslinking agent I is: 。 3. The preparation process of a nanofiber composite filter material according to claim 2, characterized in that: The preparation method of the composite antibacterial epoxy crosslinking agent I is: The Schiff base reaction mechanism is used to generate a di-Schiff base tertiary phosphine monomer through a condensation reaction between the carbonyl functional group of 4,4'-biphenyldicarboxaldehyde and the amino functional group of 3-(diphenylphosphino)propylamine. The composite antibacterial epoxy crosslinking agent I is generated by utilizing the nucleophilic substitution reaction mechanism, through the quaternary phosphine group of the di-Schiff base tertiary phosphine monomer and the chlorine functional group of epichlorohydrin.

4. The preparation process of a nanofiber composite filter material according to claim 1, characterized in that: The chemical structural formula of the composite antibacterial epoxy crosslinking agent II is: 。 5. The preparation process of a nanofiber composite filter material according to claim 4, characterized in that: The preparation method of the composite antibacterial epoxy crosslinking agent II is as follows: Using the Schiff base reaction mechanism, the carbonyl functional group of 3,3',5,5'-tetraaldehyde biphenyl reacts with the amino functional group of 3-(diphenylphosphino)propylamine to generate tetra-Schiff base tertiary phosphine monomers; Utilizing the nucleophilic substitution reaction mechanism, the tertiary phosphine group of the tetra-Schiff base tertiary phosphine monomer reacts with the chlorine functional group of epichlorohydrin to undergo quaternary phosphination reaction to generate a composite antibacterial epoxy crosslinker II.

6. The process for preparing a nanofiber composite filter material according to claim 1, characterized in that: The mass ratio of chitosan to polyvinyl alcohol in the chitosan-polyvinyl alcohol nanofiber membrane of step 2 is 1:(0.8-2).

7. The process for preparing a nanofiber composite filter material according to claim 1, characterized in that: The preparation method of the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane is as follows: a composite antibacterial epoxy cross-linking agent, acetone and deionized water are mixed to prepare a composite antibacterial epoxy cross-linking agent solution with a mass fraction of 1-10wt%, the chitosan-polyvinyl alcohol nanofiber membrane is completely immersed in the composite antibacterial epoxy cross-linking agent solution, and the cross-linking reaction is maintained for 1-5 hours, and the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane is taken out, washed and dried to obtain the cross-linked modified chitosan-polyvinyl alcohol nanofiber membrane.

8. A nanofiber composite filter material prepared by the process according to any one of claims 1 to 7, characterized in that: The air filtration efficiency of the nanofiber composite filter material is greater than 98%.

9. A nanofiber composite filter material prepared by the process according to any one of claims 1 to 7, characterized in that: The antibacterial rate of the nanofiber composite filter material is greater than 96%, and the bacteria are Escherichia coli or Staphylococcus aureus.

10. Use of a nanofiber composite filter material prepared according to the process according to any one of claims 1 to 7 in a medical mask.

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