Multi-effect functional non-woven fabric

Abstract

The invention belongs to the field of functional textile materials and filtering materials, and provides a multi-effect functional non-woven fabric. According to the invention, a collaborative design of a composite non-woven structure and an immobilized functional layer is adopted, and the composite non-woven structure is composed of a spun-bonded layer containing polyamide 6 and a melt-blown layer containing maleic anhydride grafted polyamide 6; the immobilized functional layer comprises quaternized chitosan-sodium tripolyphosphate ionic cross-linked nanoparticles and forms amido bonds through ring-opening reaction of anhydride groups and amino groups, and the amido bonds are firmly fixed on the surface of the composite non-woven structure; multiple properties such as low-pressure-drop high-flux filtration, efficient particulate matter trapping, high-positive-charge antibacterial and hydrophilic multi-effect synergy, long-acting stable fixation of a functional layer in a humid and hot environment and the like are realized, and the technical problem that performance synergy, interface stability and process compatibility of an existing filtration protection material are difficult to consider is solved; wide application values are realized in the fields of air filtration, personal protection, medical treatment and public health and the like.

Description

Technical Field

[0001] This invention relates to the field of functional textile materials and filter materials, specifically to a multi-functional nonwoven fabric. Background Technology

[0002] With the acceleration of industrialization, the demand for nonwoven materials for air filtration and personal protective equipment continues to grow in fields such as public health, medical protection, industrial dust removal, and civil air purification. These materials need to meet multi-dimensional performance requirements in practical applications: First, while ensuring efficient particulate matter capture, they must achieve a synergy of low pressure drop and high throughput to ensure wearing comfort and long-term usability; second, in humid and hot operating environments (such as moisture from respiration and increased body temperature), the materials must maintain stable filtration efficiency and mechanical strength to avoid protective failure due to fiber structure loosening or functional layer shedding; third, for medical and public place applications, the material surface must have durable antibacterial properties to inhibit microbial growth and reduce the risk of secondary pollution; in addition, the materials must also be hydrophilic to improve wearing comfort and reduce skin irritation caused by electrostatic adsorption. Meeting these comprehensive performance requirements is of great significance for improving the practicality of filtration and protective materials, expanding their application scope in the fields of medical and environmental protection, and promoting technological progress in related industries.

[0003] To address the aforementioned performance requirements, existing technologies primarily achieve additional functions such as antibacterial and hydrophilic properties by applying functional coatings or nanoparticles to the surface of nonwoven fabrics. However, these technologies face several shortcomings in practical applications. Firstly, the functional layers fixed by traditional physical or electrostatic adsorption methods have weak adhesion to the substrate, making them prone to detachment or migration under humid and hot environments or mechanical friction, resulting in insufficient functional durability. For example, Chinese patent CN116617439A discloses a chitosan composite hemostatic dressing and its manufacturing method, but the electrospun base fabric lacks chemical bonding with the chitosan sponge portion, leading to severe peeling of the functional layer after repeated use or washing. Secondly, existing chemical immobilization methods mostly employ exogenous crosslinking agents (such as glutaraldehyde and epoxy compounds). While these methods can improve bonding strength, the residue of crosslinking agents and the uncontrollability of the crosslinking reaction can easily lead to the inactivation of antibacterial active substances and a decrease in the biocompatibility of the material. Furthermore, the crosslinking process often requires harsh reaction conditions (strong acids and alkalis or high-temperature and long-term treatment), which not only increases energy consumption and costs but may also damage the fiber structure of the substrate and reduce mechanical properties. For example, Chinese patent CN104436279A discloses a method for preparing chitosan medical biological antibacterial dressings, but the toxicity of glutaraldehyde affects its application in the field of medical protection. Thirdly, regarding the immobilization of the functional layer of nanoparticles, existing technologies struggle to achieve a balance between ensuring sufficient immobilization (i.e., forming stable chemical bonds) and maintaining the active structure of nanoparticles (such as ionic crosslinking networks and positive charge density). Excessively high heat treatment temperatures or excessively long reaction times can lead to the degradation of quaternized chitosan or the agglomeration and inactivation of nanoparticles, while insufficient immobilization under mild conditions can cause the functional layer to gradually be lost during use. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-functional nonwoven fabric that solves the technical challenges of balancing low pressure drop and high flux with efficient capture and synergistic multi-functional surface properties in current filtration / protection nonwoven materials; the strength and wear resistance of the composite nonwoven structure with the dimensional and interfacial stability of the hydrophilic, highly positively charged antibacterial functional layer under humid and hot service environments; and the difficulty in achieving a balance between sufficient heat treatment required for anhydride-amine reaction immobilization and maintaining the active structure of quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticles.

[0005] Based on the above objectives, this invention adopts the design concept of "in-situ reaction immobilization + synergistic effect of nanoparticle ionic crosslinking". By introducing maleic anhydride-grafted polyamide 6 into the meltblown fiber, the anhydride groups react with the amino groups of quaternized chitosan under controlled heat treatment to form amide bonds, thereby achieving chemical bonding and immobilization of the functional layer. At the same time, sodium tripolyphosphate is used to gently ionic crosslink and nucleate the quaternized chitosan. Under the premise of avoiding the introduction of exogenous crosslinking agents, a nanoparticle functional layer with high positive charge density, high hydrophilicity and high antibacterial activity is constructed. Thus, a synergistic balance is achieved between immobilization firmness, functional activity retention and process mildness, and finally, multiple optimizations are achieved in filtration efficiency, pressure drop control, antibacterial durability and service stability.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Multifunctional nonwoven fabrics, including composite nonwoven structures and immobilized functional layers; The composite nonwoven structure includes at least a meltblown layer and a spunbond layer. The fiber components of both the meltblown layer and the spunbond layer contain polyamide 6. The meltblown layer further contains maleic anhydride-grafted polyamide 6, which is obtained by reacting polyamide 6 and maleic anhydride in the presence of an initiator. The immobilized functional layer is disposed on the surface of the composite nonwoven structure and contains quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticles. The immobilized functional layer is fixed to the surface of the composite nonwoven structure by the ring-opening reaction between the anhydride groups of maleic anhydride-grafted polyamide 6 and the amino groups of the quaternized chitosan to form amide bonds.

[0007] Furthermore, the maleic anhydride-grafted polyamide 6 is prepared through the following steps: A1. Raw material preparation: Based on 100 parts by weight of polyamide 6, maleic anhydride is 0.20-5.00 parts by weight, and di-tert-butyl peroxide is 0.01-0.50 parts by weight; A2. Reactive extrusion: Melt reactive extrusion is carried out at 220-260℃, with a residence time of 1.0-5.0 min, in a nitrogen atmosphere; A3. Granulation and post-treatment: Extrusion granulation and drying are performed to obtain the maleic anhydride-grafted polyamide 6; A4. Quality control: The grafting rate of the maleic anhydride-grafted polyamide 6 is 0.10-2.00 wt%, and the grafting rate is the mass fraction of the amount of maleic anhydride grafted relative to the total mass of the maleic anhydride-grafted polyamide 6.

[0008] Furthermore, the quaternized chitosan is prepared through the following steps: B1. Raw material preparation: Chitosan is dissolved in an aqueous acetic acid solution to obtain a homogeneous system. Glycidyltrimethylammonium chloride is added to the homogeneous system, and the pH value of the reaction system is adjusted by an aqueous sodium hydroxide solution. The amount of glycidyltrimethylammonium chloride is 10-80 parts by weight per 100 parts by weight of chitosan. B2. Quaternization reaction: Under the condition that the pH value of the reaction system is 8.0-10.0, the reaction is carried out at 40-80℃ for 2-12 hours; B3. Post-processing: The reaction product is washed and dried to obtain the quaternized chitosan; B4. Quality control: The degree of quaternization substitution of the quaternized chitosan is 0.10-0.80, and the degree of quaternization substitution is the ratio of the number of moles of quaternary ammonium groups to the number of moles of chitosan glucosamine repeating units.

[0009] Furthermore, the quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticles are prepared through the following steps: C1. Raw material preparation: The quaternized chitosan is prepared into an aqueous solution with a mass fraction of 0.10-2.00 wt%, and sodium tripolyphosphate is prepared into an aqueous solution with a mass fraction of 0.05-0.50 wt%; the pH value of the quaternized chitosan aqueous solution is adjusted to 4.0-6.0 using an aqueous acetic acid solution; C2. Ionic crosslinking nucleation: Under the condition that the pH value of the quaternized chitosan aqueous solution is 4.0-6.0, the sodium tripolyphosphate aqueous solution is added at 20-40℃ and reacted for 0.5-2.0h to obtain a nanoparticle dispersion; C3. Quality control: The D50 of the nanoparticles is 50-300 nm, and the D50 is the median diameter of the hydrated particle size measured by dynamic light scattering method.

[0010] Furthermore, the immobilized functional layer is formed through the following steps: D1. Application: The nanoparticle dispersion is applied to the surface of the composite nonwoven structure to increase the weight of the immobilized functional layer by 0.10-5.00 g / m²; D2) Drying: Dry at 50-120℃ for 1-30 minutes; D3) Heat treatment: Heat treatment at 80-160℃ for 0.5-10 min to allow the anhydride groups of the maleic anhydride-grafted polyamide 6 to undergo a ring-opening reaction with the amino groups of the quaternized chitosan and form amide bonds, thereby obtaining the immobilized functional layer.

[0011] Furthermore, it satisfies any one or more of the following characteristics: The composite nonwoven structure is one of SMS structure, SMMS structure or SMMMS structure; The average fiber diameter of the meltblown layer is 0.8-5.0µm; The average fiber diameter of the spunbond layer is 10-30µm; Based on the total polymer mass of the meltblown layer, the mass fraction of maleic anhydride-grafted polyamide 6 in the meltblown layer is 1.0-30.0 wt%.

[0012] As a concept of this invention, maleic anhydride-grafted polyamide 6 and quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticles are synergistically designed to enhance the immobilization stability, antibacterial durability, and multi-functional properties of the functional layer. Maleic anhydride-grafted polyamide 6 introduces anhydride groups into the molecular chain through reactive extrusion. A grafting rate of 0.10-2.00 wt% ensures sufficient group density to form amide bonds with the amino groups of quaternized chitosan for chemical immobilization, while avoiding excessive grafting that could lead to degradation. Grafting is carried out under nitrogen at 220-260℃ for 1.0-5.0 min to ensure thorough and uniform grafting. Quaternized chitosan is prepared by reacting chitosan with glycidyltrimethylammonium chloride. A substitution degree of 0.10-0.80 imparts a high positive charge, enhancing electrostatic filtration and antibacterial properties while maintaining hydrophilicity. Nanoparticles (D50=50-300nm) are formed through ionic cross-linking with sodium tripolyphosphate at pH 4.0-6.0 and 20-40℃, preventing degradation by exogenous cross-linking agents and quaternary ammonium groups, and enhancing fiber surface contact through the nano-effect. During the immobilization stage, acid anhydrides and amino groups form amide bonds under heat treatment at 80-160℃ for 0.5-10 min. Temperature and time control ensures sufficient bonding while avoiding thermal degradation and destruction of the cross-linking network, achieving a balance between immobilization stability and activity. This imparts long-lasting antibacterial properties, high-efficiency filtration, and comfort to the nonwoven fabric under humid and hot environments.

[0013] This invention also discloses a method for preparing a multi-functional nonwoven fabric, comprising the following steps: S1. Preparation of maleic anhydride-grafted polyamide 6: Polyamide 6, maleic anhydride and di-tert-butyl peroxide are melt-reacted and extruded to obtain maleic anhydride-grafted polyamide 6; S2. Web formation: A spunbond layer is prepared using polyamide 6 as raw material; a meltblown layer is prepared using a mixture of polyamide 6 and maleic anhydride-grafted polyamide 6 as raw material; the spunbond layer and the meltblown layer are combined to obtain a composite nonwoven structure; wherein, the target surface for surface immobilization treatment in the subsequent step S4 is set as the surface corresponding to the fiber layer containing maleic anhydride-grafted polyamide 6.

[0014] S3. Preparation of nanoparticle dispersion: Chitosan is reacted with glycidyltrimethylammonium chloride to obtain quaternized chitosan, and then sodium tripolyphosphate is used to ion crosslink the quaternized chitosan to obtain nanoparticle dispersion; S4. Surface immobilization: The nanoparticle dispersion is applied to the surface of the composite nonwoven structure, and then dried and heat-treated in sequence to allow the anhydride groups of the maleic anhydride-grafted polyamide 6 to undergo a ring-opening reaction with the amino groups of the quaternized chitosan and form amide bonds, thereby obtaining an immobilized functional layer.

[0015] Furthermore, in step S1, the amount of maleic anhydride used is 0.20-5.00 parts by weight, based on 100 parts by weight of polyamide 6; In step S1, the melt reaction extrusion temperature is 220-260℃, and the residence time is 1.0-5.0 min; Furthermore, in step S3, the pH value of the quaternization reaction is 8.0-10.0, the temperature is 40-80℃, and the time is 2-12h; In step S3, the pH value for ionic cross-linking and nucleation is 4.0-6.0, the temperature is 20-40℃, and the time is 0.5-2.0h; As another aspect of this invention, an in-situ reaction immobilization and mild ionic crosslinking synergistic preparation method is employed to enhance the chemical bonding strength of the functional layers, maintain the activity of nanoparticles, and achieve process controllability. During the preparation of maleic anhydride-grafted polyamide 6, a melt extrusion temperature of 220-260℃ and a residence time of 1.0-5.0 min ensure sufficient grafting while avoiding degradation and crosslinking, with a grafting rate of 0.10-2.00 wt% ensuring a balance between group density and spinnability. During nanoparticle preparation, the quaternization reaction is carried out at pH 8.0-10.0, 40-80℃, and 2-12 h to promote epoxy ring-opening substitution, controlling the degree of substitution to 0.10-0.80 while avoiding degradation. Ionic crosslinking is performed under mild conditions at pH 4.0-6.0, 20-40℃, and 0.5-2.0 h; the acidity causes electrostatic self-assembly of charged components, avoiding external crosslinking agents and degradation, and D50 is controlled at 50-300 nm to ensure a high specific surface area. During the web-forming and immobilization process, the meltblown layer containing maleic anhydride-grafted polyamide 6 is set as the immobilization surface to ensure the enrichment of anhydride groups on the surface. After drying (50-120℃, 1-30min), heat treatment (80-160℃, 0.5-10min) allows the anhydride and amino groups to form amide bonds. Temperature and time control ensure sufficient bonding while avoiding degradation and aggregation, achieving a synergistic effect of immobilization firmness, activity retention, and process controllability. Finally, a multi-functional nonwoven fabric with long-lasting antibacterial properties, high-efficiency filtration, and comfort under humid and hot conditions is prepared.

[0016] Furthermore, in step S2, the average fiber diameter of the meltblown layer is 0.8-5.0µm, and the average fiber diameter of the spunbond layer is 10-30µm.

[0017] Furthermore, the multifunctional nonwoven fabric is used in the preparation of filter materials, air filter media, or filter layers of personal protective equipment, wherein the personal protective equipment includes one or more of protective masks, protective clothing, or filter pads.

[0018] Furthermore, in step B1, the mass fraction of acetic acid in the aqueous acetic acid solution is 1.0-5.0 wt%, and the mass fraction of chitosan in the aqueous acetic acid solution is 0.5-3.0 wt%.

[0019] Furthermore, in step B1, the sodium hydroxide aqueous solution has a mass fraction of 0.5-5.0 wt%, and the pH value of the reaction system is adjusted to 8.0-10.0 by dropwise addition.

[0020] Furthermore, in step B3, the washing ends when the pH of the washing solution reaches 6.5-7.5, and the drying ends when the mass difference between two consecutive weighings under the same drying conditions does not exceed 0.5%.

[0021] Furthermore, in step C1, the mass fraction of the acetic acid aqueous solution is 0.1-2.0 wt%, and the pH value of the quaternized chitosan aqueous solution is adjusted to 4.0-6.0 by dropwise addition.

[0022] Further, in step C2, the sodium tripolyphosphate aqueous solution is added dropwise to the quaternized chitosan aqueous solution under stirring conditions to perform ionic crosslinking and nucleation.

[0023] Furthermore, in step C3, D50 is the median diameter of the hydrated particle size intensity distribution measured by dynamic light scattering after diluting the nanoparticle dispersion with deionized water at 25°C until the test signal is within the linear response range of the instrument.

[0024] Furthermore, the immobilized functional layer is disposed on the outer surface of the composite nonwoven structure, and the fiber layer corresponding to the outer surface contains maleic anhydride-grafted polyamide 6.

[0025] Furthermore, in step D1, the nanoparticle dispersion is applied to the surface of the composite nonwoven structure by impregnation, coating or spraying.

[0026] Furthermore, in step D1, the weight gain of the immobilized functional layer is the increase in the mass per unit area of ​​the composite nonwoven structure after drying. The state after drying refers to the state where the mass difference between two consecutive weighings under the same drying conditions does not exceed 0.5%.

[0027] Furthermore, the grafting rate of the maleic anhydride-grafted polyamide 6 was determined by acid-base titration: the grafted product was added to m-cresol and dissolved under heating conditions until clear; titration was performed with potassium hydroxide-ethanol standard solution to the endpoint, and a blank titration was performed to subtract the excess; the anhydride equivalent was calculated based on the concentration and volume of the potassium hydroxide standard solution consumed, and the grafting rate was calculated per maleic anhydride unit and converted to a mass fraction relative to the total sample mass. The converted mass fraction is the grafting rate described in A4.

[0028] Furthermore, the degree of quaternization substitution of the quaternized chitosan was determined by hydrogen nuclear magnetic resonance spectroscopy: the quaternized chitosan was dissolved in a nuclear magnetic resonance solvent to obtain a homogeneous solution, and a ¹H NMR spectrum was collected; the degree of quaternization substitution was calculated based on the integral of the signal peak corresponding to the quaternary ammonium group and the integral of the proton signal peak of the sugar ring.

[0029] Furthermore, infrared spectroscopy or X-ray photoelectron spectroscopy, combined with control samples, was used to characterize changes in characteristic signals related to maleic anhydride groups and the presence of immobilized functional layer components on the surface of the composite nonwoven structure.

[0030] Furthermore, the grafting rate of the maleic anhydride-grafted polyamide 6 is preferably 0.30-2.00 wt%.

[0031] Furthermore, in step S2, the mass fraction of maleic anhydride-grafted polyamide 6 is 1.0-30.0 wt% based on the total polymer mass of the meltblown layer.

[0032] In this invention, maleic anhydride-grafted polyamide 6 and quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticles synergistically enhance the functional layer's immobilization and multi-functional properties. Maleic anhydride-grafted polyamide 6 focuses on chemical bonding fixation; its anhydride groups and the amino groups of quaternized chitosan undergo ring-opening under heat treatment to form amide bonds, achieving robust fixation. The polyamide 6 matrix imparts mechanical strength, wear resistance, and processability to the meltblown layer, ensuring structural stability. Quaternized chitosan-sodium tripolyphosphate nanoparticles emphasize multi-functionality; the high positive charge of quaternized chitosan enhances particulate matter capture through electrostatic adsorption, the quaternary ammonium groups provide broad-spectrum antibacterial activity to inhibit microbial growth, and the hydrophilicity of the chitosan skeleton improves wettability and comfort. Mild ion crosslinking of sodium tripolyphosphate constructs nanoparticles while maintaining the activity of the quaternary ammonium groups; the high specific surface area and nano-effect enhance fiber contact, and the crosslinked network provides dimensional stability in humid and hot environments. In terms of synergistic mechanism, the matching of anhydride group density (grafting rate 0.10-2.00wt%) and amino group density (degree of substitution 0.10-0.80) ensures the full formation of amide bonds. The control of heat treatment temperature (80-160℃) and time (0.5-10min) ensures both sufficient reaction and avoids degradation. A synergistic balance is achieved between immobilization firmness, activity retention and process mildness, realizing multiple optimizations of filtration efficiency, antibacterial durability, humid heat stability and comfort, and solving the technical problem of difficulty in balancing performance synergy, interface stability and process compatibility.

[0033] Beneficial technical effects 1. Achieving long-term stable fixation and multi-effect synergistic performance of the functional layer: By introducing maleic anhydride-grafted polyamide 6 into the meltblown fiber, the anhydride groups react with the amino groups of quaternized chitosan under controlled heat treatment conditions (80-160℃, 0.5-10min) to form stable amide bonds, achieving chemical bonding fixation of the functional layer. This avoids the problem of functional layer detachment or activity failure caused by crosslinking agent residue in humid and hot environments, which is a problem of traditional physical adsorption or external crosslinking agent fixation methods. At the same time, the quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticles endow the material with high positive charge density, high hydrophilicity and broad-spectrum antibacterial activity, thus solving the technical contradiction of existing technologies that are difficult to balance between functional durability and multi-effect synergy from the source.

[0034] 2. Ensuring a synergistic balance between sufficient immobilization and the active structure of nanoparticles: By precisely controlling the grafting rate (0.10-2.00wt%), the degree of quaternization substitution (0.10-0.80), and the heat treatment conditions (temperature 80-160℃, time 0.5-10min), the formation of amide bonds between the anhydride groups and amino groups is ensured to achieve a firm fixation of the functional layer. At the same time, the thermal degradation of quaternized chitosan, the deactivation of quaternary ammonium groups, and the destruction of the sodium tripolyphosphate ion crosslinking network caused by excessively high temperatures or excessively long treatment times are avoided. This achieves a mechanistic synergy between sufficient immobilization reaction and the maintenance of the active structure of nanoparticles, solving the technical problem that existing chemical immobilization methods require harsh conditions that lead to loss of functional activity.

[0035] 3. Synergistic optimization of improved filtration performance and reduced breathing resistance: The composite nonwoven structure design of meltblown layer (fiber diameter 0.8-5.0µm) and spunbond layer (fiber diameter 10-30µm), combined with the high specific surface area and high positive charge density of quaternized chitosan nanoparticles (D50=50-300nm), enhances the capture efficiency of particulate matter through multiple capture mechanisms of physical interception, inertial collision and electrostatic adsorption. At the same time, the surface hydrophilic modification of nanoparticles reduces the airflow resistance and breathing work between fibers, achieving dual optimization of high-efficiency filtration and low pressure drop flux, significantly improving the overall performance of filter materials in practical applications.

[0036] 4. Enhanced interfacial stability and functional durability under humid and hot service conditions: The amide bonds formed by the anhydride groups of maleic anhydride-grafted polyamide 6 and the amino groups of quaternized chitosan have excellent chemical stability and hydrolysis resistance. The internal network structure of nanoparticles constructed by sodium tripolyphosphate ion crosslinking endows the functional layer with dimensional stability and anti-swelling properties under humid and hot conditions, thereby ensuring the fixation firmness of the functional layer and the long-term maintenance of antibacterial, hydrophilic and other functions under repeated wear, washing or humid and hot service conditions. This solves the prominent problem of functional layer easy to fall off or functional decay under humid and hot conditions in the prior art. Attached Figure Description

[0037] Figure 1 The images show the FTIR infrared spectra of Example 1, Comparative Example 3, and Comparative Example 8.

[0038] Figure 2 The XPS full spectrum survey plots are for Example 1, Comparative Example 3, and Comparative Example 8.

[0039] Figure 3 The images are XPS high-resolution N 1s plots of Example 1, Comparative Example 3, and Comparative Example 8.

[0040] Figure 4 The images shown are XPS high-resolution P2p images of Example 1, Comparative Example 3, and Comparative Example 8.

[0041] Figure 5 The following are the DLS particle size distribution intensity distribution diagrams for Example 1, Comparative Example 5, and Comparative Example 6.

[0042] Figure 6 The diagram shows the zeta potential distribution of Example 1 and Comparative Example 4.

[0043] Figure 7 The distribution of Zeta measurements for Example 1 and Comparative Example 4 is shown in multiple measurements.

[0044] Figure 8 The image shows the SEM quantitative coverage distribution of Example 1, Comparative Example 3, and Comparative Example 8 after 10 washes.

[0045] Figure 9 Comparison of the physical appearance of the multifunctional nonwoven fabric prepared in Example 1.

[0046] Figure 10 The image shows the low-magnification scanning electron microscope (SEM) morphology of the functional surface of the composite nonwoven structure prepared in Example 1.

[0047] Figure 11 The image shows the high-magnification scanning electron microscope (SEM) image of the immobilized functional layer prepared in Example 1 on the surface of polyamide 6 fiber.

[0048] Figure 12 The image shows a low-magnification scanning electron microscope (SEM) image of the cross-section of the SMMS-structured composite nonwoven structure prepared in Example 1. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Example 1

[0050] This embodiment prepares a multi-functional nonwoven fabric, including a composite nonwoven structure and an immobilized functional layer.

[0051] Step S1: Preparation of maleic anhydride-grafted polyamide 6 A1. Raw material preparation: For 100 parts by weight of polyamide 6, weigh 2.60 parts by weight of maleic anhydride and 0.25 parts by weight of di-tert-butyl peroxide.

[0052] A2. Reactive extrusion: The above raw materials are melt-reacted and extruded in a twin-screw extruder at 240°C for a residence time of 3.0 min. Nitrogen gas is introduced for protection during the extrusion process, and the nitrogen flow rate is controlled at 5-10 L / min.

[0053] A3. Granulation and post-processing: The extrudate is cooled in a cooling water tank and then granulated. The granulated material is dried in a vacuum oven at 80℃ for 8 hours until the moisture content is below 0.05%.

[0054] A4. Quality control: The grafting rate of maleic anhydride-grafted polyamide 6 was determined by acid-base titration to be 1.05 wt%.

[0055] Step S2: Preparation of composite nonwoven structure Using polyamide 6 as raw material, a spunbond layer was prepared using a spunbond process at a spinning temperature of 260℃ and a drafting speed controlled to achieve an average fiber diameter of 20µm. Polyamide 6 was mixed with maleic anhydride-grafted polyamide 6 prepared in step S1 at a mass ratio of 84.5:15.5, resulting in a total polymer content of 15.5wt% maleic anhydride-grafted polyamide 6. A meltblown layer was prepared using a meltblown process at a meltblown temperature of 250℃ and a hot air temperature of 280℃, with the receiving distance adjusted to achieve an average fiber diameter of 2.9µm. The spunbond layer-meltblown layer-meltblown layer-spunbond layer composite nonwoven structure was formed, with the target surface for subsequent immobilization treatment set as the surface corresponding to the meltblown layer containing maleic anhydride-grafted polyamide 6.

[0056] Step S3: Preparation of quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticle dispersion B1. Raw material preparation: Prepare a 3.0 wt% acetic acid aqueous solution. Dissolve chitosan in this acetic acid aqueous solution, with a chitosan mass fraction of 1.75 wt%. Stir until completely dissolved to form a homogeneous system. Based on 100 parts by weight of chitosan, add 45 parts by weight of glycidyltrimethylammonium chloride to the above system. Adjust the pH of the reaction system to 9.0 by adding a 2.5 wt% sodium hydroxide aqueous solution dropwise.

[0057] B2. Quaternization reaction: The reaction was carried out at a pH of 9.0 and a temperature of 60℃ for 7 hours. During the reaction, the pH was checked and adjusted every 1 hour to ensure that it was maintained within the range of 9.0±0.2.

[0058] B3. Post-processing: After the reaction is complete, the product is washed with deionized water until the pH of the washing solution is 7.0, and then dried in an oven at 60°C until the difference between two consecutive weighings does not exceed 0.5%.

[0059] B4. Quality control: The degree of quaternization of the obtained quaternized chitosan was determined to be 0.45 by proton nuclear magnetic resonance spectroscopy.

[0060] C1. Raw material preparation: Prepare an aqueous solution of quaternized chitosan with a mass fraction of 1.05 wt%, prepare an aqueous solution of sodium tripolyphosphate with a mass fraction of 0.275 wt%, and adjust the pH of the quaternized chitosan aqueous solution to 5.0 by adding acetic acid aqueous solution with a mass fraction of 1.0 wt% dropwise.

[0061] C2. Ionic crosslinking nucleation: Under the conditions of pH 5.0 and temperature 30℃ for quaternized chitosan aqueous solution, sodium tripolyphosphate aqueous solution was slowly added dropwise at a stirring speed of 500 rpm for 20 min. After the addition was completed, the reaction continued for 1.25 h to obtain a milky white nanoparticle dispersion.

[0062] C3. Quality control: The median diameter D50 of the hydrated particle size intensity distribution of the obtained nanoparticles was 175 nm, determined by dynamic light scattering at 25 °C with deionized water as the dilution medium.

[0063] Step S4: Forming an immobilized functional layer D1. Application: The nanoparticle dispersion prepared in step S3 is applied to the surface of the composite nonwoven structure prepared in step S2 by impregnation. The impregnation time is 30s. The liquid carry-over rate is controlled by rollers to make the weight gain of the immobilized functional layer reach 2.55g / m².

[0064] D2. Drying: Dry in an oven at 85℃ for 15.5 min until the difference between two consecutive weighings does not exceed 0.5%.

[0065] D3. Heat treatment: Heat treatment in a 120℃ hot air box for 5.25 min to allow the anhydride groups of maleic anhydride-grafted polyamide 6 to undergo a ring-opening reaction with the amino groups of quaternized chitosan and form amide bonds, thereby forming a firm immobilized functional layer on the surface of the composite nonwoven structure.

[0066] Infrared spectroscopy was used to characterize the surface of the composite nonwoven structure. Compared with the untreated control sample, it showed improvement in... The intensity of the amide-related absorption peak changes in the vicinity. The presence of a characteristic phosphate absorption peak nearby indicates that the immobilized functional layer has been successfully fixed to the surface of the composite nonwoven structure.

[0067] Features of this embodiment: This embodiment employs a moderate combination of process parameters: maleic anhydride dosage is 2.60 parts by weight, grafting rate reaches 1.05 wt%, quaternization degree of substitution is 0.45, nanoparticle D50 is 175 nm, and the weight gain of the immobilized functional layer is 2.55 g / m². All parameters are within the central range, indicating good process stability and high reproducibility. The composite nonwoven structure adopts a four-layer SMMS structure, with a meltblown layer fiber diameter of 2.9 µm, a spunbond layer fiber diameter of 20 µm, and maleic anhydride-grafted polyamide 6 in the meltblown layer comprising 15.5 wt%, balancing filtration efficiency and breathability. The immobilized functional layer contains a moderate amount of quaternized chitosan, ensuring antibacterial properties while controlling cost. The multi-functional nonwoven fabric prepared in this embodiment is suitable for filter layers in conventional protective masks, disposable protective clothing, and other personal protective equipment, and can also be used as filter material in civilian air purifiers, exhibiting a good balance of filtration efficiency, antibacterial properties, and durability. Example 2

[0068] This embodiment prepares a multi-functional nonwoven fabric, including a composite nonwoven structure and an immobilized functional layer.

[0069] Step S1: Preparation of maleic anhydride-grafted polyamide 6 A1. Raw material preparation: With polyamide 6 as 100 parts by weight, weigh 1.00 parts by weight of maleic anhydride and 0.10 parts by weight of di-tert-butyl peroxide.

[0070] A2. Reactive extrusion: The above raw materials are melt-reacted and extruded in a twin-screw extruder at 230°C for a residence time of 2.0 min. Nitrogen gas is introduced for protection during the extrusion process, and the nitrogen flow rate is controlled at 5-10 L / min.

[0071] A3. Granulation and post-processing: The extrudate is cooled in a cooling water tank and then granulated. The granulated material is dried in a vacuum oven at 80℃ for 8 hours until the moisture content is below 0.05%.

[0072] A4. Quality control: The grafting rate of maleic anhydride-grafted polyamide 6 was determined by acid-base titration to be 0.50 wt%.

[0073] Step S2: Preparation of composite nonwoven structure Using polyamide 6 as raw material, a spunbond layer was prepared using a spunbond process at a spinning temperature of 260℃ and a drafting speed controlled to achieve an average fiber diameter of 25µm. Polyamide 6 was mixed with maleic anhydride-grafted polyamide 6 prepared in step S1 at a mass ratio of 92.0:8.0, with a total polymer content of 8.0 wt% maleic anhydride-grafted polyamide 6. A meltblown layer was prepared using a meltblown process at a meltblown temperature of 245℃ and a hot air temperature of 275℃, with the receiving distance adjusted to achieve an average fiber diameter of 3.8µm. The spunbond layer-meltblown layer-meltblown layer-spunbond layer composite nonwoven structure was formed, with the target surface for subsequent immobilization treatment set as the surface corresponding to the meltblown layer containing maleic anhydride-grafted polyamide 6.

[0074] Step S3: Preparation of quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticle dispersion B1. Raw material preparation: Prepare a 2.0 wt% acetic acid aqueous solution. Dissolve chitosan in this acetic acid aqueous solution, with a chitosan mass fraction of 1.2 wt%. Stir until completely dissolved to form a homogeneous system. Based on 100 parts by weight of chitosan, add 60 parts by weight of glycidyltrimethylammonium chloride to the above system. Adjust the pH of the reaction system to 9.5 by adding a 3.5 wt% sodium hydroxide aqueous solution dropwise.

[0075] B2. Quaternization reaction: The reaction was carried out at a pH of 9.5 and a temperature of 70℃ for 9 hours. During the reaction, the pH was checked and adjusted every 1 hour to ensure that it was maintained within the range of 9.5±0.2.

[0076] B3. Post-processing: After the reaction is complete, the product is washed with deionized water until the pH of the washing solution is 7.0, and then dried in an oven at 60°C until the difference between two consecutive weighings does not exceed 0.5%.

[0077] B4. Quality control: The degree of quaternization of the obtained quaternized chitosan was determined to be 0.65 by proton nuclear magnetic resonance spectroscopy.

[0078] C1. Raw material preparation: Prepare an aqueous solution of quaternized chitosan with a mass fraction of 1.50 wt%, prepare an aqueous solution of sodium tripolyphosphate with a mass fraction of 0.40 wt%, and adjust the pH of the quaternized chitosan aqueous solution to 5.5 by adding acetic acid aqueous solution with a mass fraction of 1.5 wt% dropwise.

[0079] C2. Ionic crosslinking nucleation: Under the conditions of pH 5.5 and temperature 35℃ for quaternized chitosan aqueous solution, sodium tripolyphosphate aqueous solution was slowly added dropwise at a stirring speed of 600 rpm for 25 min. After the addition was completed, the reaction continued for 1.6 h to obtain a milky white nanoparticle dispersion.

[0080] C3. Quality control: The median diameter D50 of the hydrated particle size intensity distribution of the obtained nanoparticles was 240 nm, determined by dynamic light scattering at 25 °C with deionized water as the dilution medium.

[0081] Step S4: Forming an immobilized functional layer D1. Application: The nanoparticle dispersion prepared in step S3 is applied to the surface of the composite nonwoven structure prepared in step S2 by spraying. The spraying pressure is 0.2 MPa. By controlling the spraying amount, the weight gain of the immobilized functional layer reaches 3.80 g / m².

[0082] D2. Drying: Dry in an oven at 100℃ for 22 minutes until the difference between two consecutive weighings does not exceed 0.5%.

[0083] D3. Heat treatment: Heat treatment in a 140℃ hot air box for 7.5 min to allow the anhydride groups of maleic anhydride-grafted polyamide 6 to undergo a ring-opening reaction with the amino groups of quaternized chitosan and form amide bonds, thereby forming a firm immobilized functional layer on the surface of the composite nonwoven structure.

[0084] X-ray photoelectron spectroscopy analysis of the composite nonwoven structure surface showed a significant increase in the content of N and P elements compared with the untreated control sample, indicating that the immobilized functional layer was successfully immobilized on the surface of the composite nonwoven structure.

[0085] Features of this embodiment: This embodiment employs a parameter combination of low grafting rate and high quaternization substitution degree. Maleic anhydride is used at 1.00 parts by weight, with a grafting rate of 0.50 wt% and a quaternization substitution degree of 0.65. Glycidyl trimethylammonium chloride is used at 60 parts by weight. The composite nonwoven structure adopts a three-layer SMS structure, which is relatively simple. The meltblown layer fiber diameter is 3.8 µm, the spunbond layer fiber diameter is 25 µm, and the mass fraction of maleic anhydride-grafted polyamide 6 in the meltblown layer is 8.0 wt%. The nanoparticles have a D50 of 240 nm, a relatively large particle size, and the weight gain of the immobilized functional layer reaches 3.80 g / m², with a high content of quaternized chitosan. This design enhances antibacterial properties; the high quaternization substitution degree results in a high surface positive charge density, exhibiting excellent broad-spectrum antibacterial effects against both Gram-negative and Gram-positive bacteria. The multi-functional nonwoven fabric prepared in this embodiment is particularly suitable for air filter materials in places with high cleanliness requirements such as hospital operating rooms and intensive care units. It can also be used in medical protective masks with high antibacterial requirements, and has significant advantages in application scenarios that require strong antibacterial performance. Example 3

[0086] This embodiment prepares a multi-functional nonwoven fabric, including a composite nonwoven structure and an immobilized functional layer.

[0087] Step S1: Preparation of maleic anhydride-grafted polyamide 6 A1. Raw material preparation: For 100 parts by weight of polyamide 6, weigh 4.00 parts by weight of maleic anhydride and 0.40 parts by weight of di-tert-butyl peroxide.

[0088] A2. Reactive extrusion: The above raw materials are melt-reacted and extruded in a twin-screw extruder at 255°C for a residence time of 4.2 min. Nitrogen gas is introduced for protection during the extrusion process, and the nitrogen flow rate is controlled at 5-10 L / min.

[0089] A3. Granulation and post-processing: The extrudate is cooled in a cooling water tank and then granulated. The granulated material is dried in a vacuum oven at 80℃ for 8 hours until the moisture content is below 0.05%.

[0090] A4. Quality control: The grafting rate of maleic anhydride-grafted polyamide 6 was determined by acid-base titration to be 1.70 wt%.

[0091] Step S2: Preparation of composite nonwoven structure Using polyamide 6 as raw material, a spunbond layer was prepared using a spunbond process at a spinning temperature of 260℃ and a drafting speed controlled to achieve an average fiber diameter of 14µm. Polyamide 6 was mixed with maleic anhydride-grafted polyamide 6 prepared in step S1 at a mass ratio of 78.0:22.0, resulting in a total polymer content of 22.0 wt% maleic anhydride-grafted polyamide 6. A meltblown layer was prepared using a meltblown process at a meltblown temperature of 255℃ and a hot air temperature of 290℃, with the receiving distance adjusted to achieve an average fiber diameter of 1.5µm. The composite nonwoven structure, consisting of a spunbond layer, a meltblown layer, a meltblown layer, and a spunbond layer, was formed by combining these layers in a sequential manner. The outermost layer, serving as the target surface for subsequent immobilization treatment, was set as the surface corresponding to the meltblown layer containing maleic anhydride-grafted polyamide 6.

[0092] Step S3: Preparation of quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticle dispersion B1. Raw material preparation: Prepare a 4.0 wt% acetic acid aqueous solution. Dissolve chitosan in this acetic acid aqueous solution, with a chitosan mass fraction of 2.5 wt%. Stir until completely dissolved to form a homogeneous system. Based on 100 parts by weight of chitosan, add 25 parts by weight of glycidyltrimethylammonium chloride to the above system. Adjust the pH of the reaction system to 8.5 by adding a 4.0 wt% sodium hydroxide aqueous solution dropwise.

[0093] B2. Quaternization reaction: The reaction was carried out at a pH of 8.5 and a temperature of 50℃ for 3.5 hours. The pH was checked and adjusted every hour during the reaction to ensure that it was maintained within the range of 8.5 ± 0.2.

[0094] B3. Post-processing: After the reaction is complete, the product is washed with deionized water until the pH of the washing solution is 7.0, and then dried in an oven at 60°C until the difference between two consecutive weighings does not exceed 0.5%.

[0095] B4. Quality control: The degree of quaternization of the obtained quaternized chitosan was determined to be 0.25 by proton nuclear magnetic resonance spectroscopy.

[0096] C1. Raw material preparation: Prepare an aqueous solution of quaternized chitosan with a mass fraction of 0.40 wt%, prepare an aqueous solution of sodium tripolyphosphate with a mass fraction of 0.12 wt%, and adjust the pH of the quaternized chitosan aqueous solution to 4.5 by adding acetic acid aqueous solution with a mass fraction of 0.5 wt% dropwise.

[0097] C2. Ionic crosslinking nucleation: Under the conditions of pH 4.5 and temperature 25℃ for quaternized chitosan aqueous solution, sodium tripolyphosphate aqueous solution was slowly added dropwise at a stirring speed of 400 rpm for 15 min. After the addition was completed, the reaction continued for 0.8 h to obtain a milky white nanoparticle dispersion.

[0098] C3. Quality control: The hydration particle size intensity distribution of the obtained nanoparticles was determined by dynamic light scattering at 25℃ with deionized water as the dilution medium, and the median diameter D50 was 100 nm.

[0099] Step S4: Forming an immobilized functional layer D1. Application: The nanoparticle dispersion prepared in step S3 is applied to the surface of the composite nonwoven structure prepared in step S2 by coating. The coating roller speed is 15m / min. The weight gain of the immobilized functional layer is made up to 1.20g / m² by controlling the thickness of the coating liquid film.

[0100] D2. Drying: Dry in an oven at 65℃ for 6 minutes until the difference between two consecutive weighings does not exceed 0.5%.

[0101] D3. Heat treatment: Heat treatment in a 100℃ hot air box for 2.0 min to allow the anhydride groups of maleic anhydride-grafted polyamide 6 to undergo a ring-opening reaction with the amino groups of quaternized chitosan and form amide bonds, thereby forming a firm immobilized functional layer on the surface of the composite nonwoven structure.

[0102] The surface of the composite nonwoven structure was characterized by a combination of infrared spectroscopy and X-ray photoelectron spectroscopy. Compared with the untreated control sample, the intensity of the characteristic peak of the amide bond was enhanced, and the signals of N and P elements were obvious, indicating that the immobilized functional layer was successfully immobilized on the surface of the composite nonwoven structure.

[0103] Features of this embodiment: This embodiment employs a parameter combination of high grafting rate and low quaternization substitution degree. Maleic anhydride is used at 4.00 parts by weight, achieving a grafting rate of 1.70 wt%, while the quaternization substitution degree is only 0.25. Glycidyl trimethylammonium chloride is used at 25 parts by weight. The composite nonwoven structure adopts a five-layer SMMMS structure with numerous meltblown layers. The meltblown fiber diameter is only 1.5 µm, and the spunbond fiber diameter is 14 µm. The mass fraction of maleic anhydride-grafted polyamide 6 in the meltblown layer reaches 22.0 wt%, providing a large number of reactive anhydride groups. The nanoparticles have a D50 of 100 nm, a small particle size, and the weight gain of the immobilized functional layer is 1.20 g / m², with a low quaternized chitosan content. This design enhances filtration performance and immobilization strength. The high grafting rate ensures strong fixation between the functional layer and the substrate, while the fine fiber diameter and multi-layer meltblown structure significantly improve the capture efficiency of submicron particles. The multi-functional nonwoven fabric prepared in this embodiment is particularly suitable for HEPA and ULPA grade filter media. It can be used in clean rooms, biosafety cabinets and other occasions that require high filtration efficiency. It is also suitable for N95 and above level protective masks with high protection levels. It performs outstandingly in application scenarios that require excellent particulate matter filtration performance and washability. Example 4

[0104] This embodiment prepares a multi-functional nonwoven fabric, including a composite nonwoven structure and an immobilized functional layer.

[0105] Step S1: Preparation of maleic anhydride-grafted polyamide 6 A1. Raw material preparation: For 100 parts by weight of polyamide 6, weigh 0.60 parts by weight of maleic anhydride and 0.05 parts by weight of di-tert-butyl peroxide.

[0106] A2. Reactive extrusion: The above raw materials are melt-reacted and extruded in a twin-screw extruder at a temperature of 223°C for a residence time of 1.3 min. Nitrogen gas is introduced for protection during the extrusion process, and the nitrogen flow rate is controlled at 5-10 L / min.

[0107] A3. Granulation and post-processing: The extrudate is cooled in a cooling water tank and then granulated. The granulated material is dried in a vacuum oven at 80℃ for 8 hours until the moisture content is below 0.05%.

[0108] A4. Quality control: The grafting rate of maleic anhydride-grafted polyamide 6 was determined by acid-base titration to be 0.25 wt%.

[0109] Step S2: Preparation of composite nonwoven structure Using polyamide 6 as raw material, a spunbond layer was prepared using a spunbond process at a spinning temperature of 258℃ and a drafting speed controlled to achieve an average fiber diameter of 12µm. Polyamide 6 was mixed with maleic anhydride-grafted polyamide 6 prepared in step S1 at a mass ratio of 96.5:3.5, with a total polymer content of 3.5wt% maleic anhydride-grafted polyamide 6. A meltblown layer was prepared using a meltblown process at a meltblown temperature of 248℃ and a hot air temperature of 278℃, with the receiving distance adjusted to achieve an average fiber diameter of 1.1µm. A composite nonwoven structure with an SMMS structure was formed by combining spunbond layer-meltblown layer-meltblown layer-spunbond layer in a specific order. The target surface for subsequent immobilization treatment was set as the surface corresponding to the meltblown layer containing maleic anhydride-grafted polyamide 6.

[0110] Step S3: Preparation of quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticle dispersion B1. Raw material preparation: Prepare a 1.3 wt% acetic acid aqueous solution. Dissolve chitosan in this acetic acid aqueous solution, with a chitosan mass fraction of 0.7 wt%. Stir until completely dissolved to form a homogeneous system. Based on 100 parts by weight of chitosan, add 16 parts by weight of glycidyltrimethylammonium chloride to the above system. Adjust the pH of the reaction system to 8.2 by adding a 1.5 wt% sodium hydroxide aqueous solution dropwise.

[0111] B2. Quaternization reaction: The reaction was carried out at a pH of 8.2 and a temperature of 46℃ for 3.0 h. The pH was checked and adjusted every 1 h during the reaction to ensure that it was maintained within the range of 8.2 ± 0.2.

[0112] B3. Post-processing: After the reaction is complete, the product is washed with deionized water until the pH of the washing solution is 7.0, and then dried in an oven at 60°C until the difference between two consecutive weighings does not exceed 0.5%.

[0113] B4. Quality control: The degree of quaternization of the obtained quaternized chitosan was determined to be 0.17 by proton nuclear magnetic resonance spectroscopy.

[0114] C1. Raw material preparation: Prepare an aqueous solution of quaternized chitosan with a mass fraction of 0.25 wt%, prepare an aqueous solution of sodium tripolyphosphate with a mass fraction of 0.09 wt%, and adjust the pH of the quaternized chitosan aqueous solution to 4.2 by adding acetic acid aqueous solution with a mass fraction of 0.3 wt% dropwise.

[0115] C2. Ionic crosslinking nucleation: Under the conditions of pH 4.2 and temperature 23℃ for quaternized chitosan aqueous solution, sodium tripolyphosphate aqueous solution was slowly added dropwise at a stirring speed of 350 rpm for 12 min. After the addition was completed, the reaction continued for 0.7 h to obtain a milky white nanoparticle dispersion.

[0116] C3. Quality control: The hydration particle size intensity distribution of the obtained nanoparticles was determined by dynamic light scattering at 25℃ with deionized water as the dilution medium, and the median diameter D50 was 70 nm.

[0117] Step S4: Forming an immobilized functional layer D1. Application: The nanoparticle dispersion prepared in step S3 is applied to the surface of the composite nonwoven structure prepared in step S2 by impregnation. The impregnation time is 20s. The liquid carry-over rate is controlled by rollers to make the weight gain of the immobilized functional layer reach 0.50g / m².

[0118] D2. Drying: Dry in an oven at 56℃ for 3.5 minutes until the difference between two consecutive weighings does not exceed 0.5%.

[0119] D3. Heat treatment: Heat treatment in an 88℃ hot air box for 1.3 min to allow the anhydride groups of maleic anhydride-grafted polyamide 6 to undergo a ring-opening reaction with the amino groups of quaternized chitosan and form amide bonds, thereby forming a firm immobilized functional layer on the surface of the composite nonwoven structure.

[0120] Infrared spectroscopy was used to characterize the surface of the composite nonwoven structure. Compared with the untreated control sample, although the weight gain of the functional layer was lower, the characteristic absorption peaks of amide bonds and phosphate groups could still be observed, indicating that the immobilized functional layer was successfully immobilized on the surface of the composite nonwoven structure.

[0121] Features of this embodiment: This embodiment uses a parameter combination close to the lower limit of the technical solution's range: maleic anhydride dosage is 0.60 parts by weight, grafting rate is 0.25 wt%, quaternization degree of substitution is 0.17, glycidyl trimethylammonium chloride dosage is 16 parts by weight, reaction temperature is 223℃, and residence time is 1.3 min. All parameters are close to the lower limit of the range but maintain a reasonable safety margin. The composite nonwoven structure adopts an SMS three-layer structure: meltblown layer fiber diameter is 1.1 µm, spunbond layer fiber diameter is 12 µm, and the mass fraction of maleic anhydride-grafted polyamide 6 in the meltblown layer is 3.5 wt%. The nanoparticle D50 is 70 nm, the weight gain of the immobilized functional layer is 0.50 g / m², drying temperature is 56℃, heat treatment temperature is 88℃, and the time is relatively short. This parameter combination verifies the feasibility of the technical solution near the lower limit of the range. Although the grafting rate and quaternization degree are low, effective immobilization of the functional layer can still be achieved through chemical bonding, reducing raw material costs and energy consumption. The multi-functional nonwoven fabric prepared in this embodiment is suitable for cost-sensitive applications such as civilian protective masks, disposable dust masks, and primary filter materials for household air purifiers. It achieves economic optimization while ensuring basic filtration and antibacterial performance, making it particularly suitable for large-scale production and price-sensitive markets.

[0122] Comparative Example 1: It is basically the same as Example 1, except that the amount of maleic anhydride is 0.12 parts by weight, the grafting rate is 0.06 wt%, and the amounts of other components and preparation conditions remain unchanged.

[0123] Comparative Example 2: It is basically the same as Example 1, except that the amount of maleic anhydride used is 5.80 parts by weight, the grafting rate is 2.35 wt%, and the amounts of other components and preparation conditions remain unchanged.

[0124] Comparative Example 3: It is basically the same as Example 1, except that maleic anhydride-grafted polyamide 6 is not added to the meltblown layer, and the meltblown layer is made entirely of polyamide 6. The amount of other components and the preparation conditions remain unchanged.

[0125] Comparative Example 4: It is basically the same as Example 1, except that the amount of glycidyl trimethylammonium chloride used is 6 parts by weight, the degree of quaternization substitution is 0.05, and the amount of other components and preparation conditions remain unchanged.

[0126] Comparative Example 5: It is basically the same as Example 1, except that the concentration of the quaternized chitosan aqueous solution is 0.05wt%, the concentration of the sodium tripolyphosphate aqueous solution is 0.02wt%, the D50 of the nanoparticles is 35nm, and the amounts of other components and preparation conditions remain unchanged.

[0127] Comparative Example 6: It is basically the same as Example 1, except that the concentration of the quaternized chitosan aqueous solution is 2.50 wt%, the concentration of sodium tripolyphosphate aqueous solution is 0.60 wt%, the D50 of the nanoparticles is 380 nm, and the amount of other components and preparation conditions remain unchanged.

[0128] Comparative Example 7: Basically the same as Example 1, except that the amount of nanoparticle dispersion applied is reduced, the weight gain of the immobilized functional layer is 0.06 g / m², and the amount of other components and preparation conditions remain unchanged.

[0129] Comparative Example 8: It is basically the same as Example 1, except that the heat treatment step is omitted in step D3, and the product is obtained directly after drying. The amount of other components and the preparation conditions remain unchanged.

[0130] Performance testing: Filtration efficiency test Test Object: Multi-functional nonwoven fabric finished product. Test Objective: To evaluate the filtration and collection performance for particles of different sizes and verify the synergistic effect of low pressure drop and high-efficiency collection in the composite nonwoven structure. Test Principle: Under specified flow conditions, the filtration efficiency of the nonwoven fabric for standard aerosol particles is measured, and the filtration efficiency is calculated based on the upstream and downstream particle concentration ratio. Experimental Method: Nonwoven fabric samples are cut into 100mm diameter discs, fixed on a filtration test bench, and an airflow containing sodium chloride aerosol is introduced. The face velocity is set to 0.3m / s. The number concentrations of 0.3μm, 1.0μm, and 3.0μm particles upstream and downstream of the filter material are measured using light scattering. Key Parameters: Test temperature 25±2℃, relative humidity 30-50%RH, median aerosol diameter 0.075±0.020μm, face velocity 0.3m / s. Data Processing: Filtration efficiency (%) = (1 - downstream concentration / upstream concentration) × 100%. Each sample is tested three times, and the average value is taken.

[0131] Pressure drop test Test Object: Multi-functional nonwoven fabric finished product. Test Objective: To evaluate the air permeability of the nonwoven fabric and verify the effect of the low pressure drop and high flux design. Test Principle: Under constant flow conditions, the pressure difference of air before and after passing through the nonwoven fabric is measured; the smaller the pressure drop, the better the air permeability. Experimental Method: The nonwoven fabric sample is cut into a circular piece with an effective test area of ​​38 cm², fixed in the fixture of a differential pressure tester, and a constant flow rate of 0.3 m / s face velocity is maintained. A high-precision differential pressure sensor is used to measure the static pressure difference across the filter material. Key Parameters: Test temperature 25±2℃, relative humidity 65±5%RH, face velocity 0.3 m / s, test area 38 cm². Data Processing: The pressure drop value (unit: Pa) under steady-state conditions is directly read. The average value is taken from 5 different locations for each sample, and the standard deviation is used as the error range.

[0132] Antibacterial performance test Test Subject: Multifunctional nonwoven fabric treated with immobilized functional layers. Test Objective: To evaluate the broad-spectrum antibacterial effect of quaternized chitosan nanoparticles and verify the effectiveness of the synergistic design of multifunctional surface features. Test Principle: The nonwoven fabric sample was incubated in contact with a bacterial suspension using the shaking flask method. The inhibition rate and bactericidal rate were calculated by colony counting. Experimental Method: Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) were selected as test strains. The nonwoven fabric sample was cut into 2cm × 2cm pieces and placed in a bacterial suspension (initial concentration 1-5 × 10⁻⁶). 5In a shaking flask containing (CFU / mL) bacteria, the culture was incubated at 37℃ for 24 h with shaking, and the viable bacterial count was determined using the plate count method. Key parameters: test temperature 37±1℃, shaking speed 100-120 rpm, contact time 24 h, pH of bacterial suspension 7.0±0.2. Data processing: inhibition rate (%) = (number of bacteria in control group - number of bacteria in sample group) / number of bacteria in control group × 100%, with 3 replicates per group.

[0133] Immobilization fastness test (wash resistance) Test Subject: Multifunctional nonwoven fabric with immobilized functional layers. Test Objective: To evaluate the interfacial stability of the immobilized functional layers under humid and hot conditions and to verify the effectiveness of the anhydride-amine chemical bonding immobilization strategy. Test Principle: Simulating actual washing conditions, the immobilization fastness is evaluated by the retention rate of functional layer weight gain and performance after repeated washing. Experimental Method: The nonwoven fabric sample was placed in a washing device and washed with a 0.5wt% nonionic surfactant aqueous solution at 40℃ for 30 minutes as one washing cycle. After 1, 3, 5, and 10 washing cycles, the sample was dried to constant weight, and the retention rate of functional layer weight gain was measured. The antibacterial properties of the washed sample were also determined. Key Parameters: Washing temperature 40±2℃, washing solution concentration 0.5wt%, oscillation frequency 120rpm, drying temperature 60℃. Data Processing: Weight gain retention rate (%) = weight gain after washing / initial weight gain × 100%. Performance retention rate is calculated based on antibacterial rate, n=3.

[0134] Maleic anhydride grafting rate determination Test Subject: Maleic anhydride-grafted polyamide 6 prepared in step S1. Test Objective: To quantify the degree of grafting maleic anhydride onto the polyamide 6 backbone, providing a basis for the content of reactive groups in the immobilization reaction. Test Principle: The grafting rate is calculated by measuring the amount of alkali consumed by the anhydride groups using acid-base titration. Experimental Method: Accurately weigh 0.5-1.0 g of the grafted product, dissolve it in 20 mL of m-cresol, heat to 80-90℃ until clear, cool, and then titrate with 0.1 mol / L potassium hydroxide-ethanol standard solution to the phenolphthalein endpoint. Simultaneously, a blank titration is performed to subtract the influence of solvent acidity. The anhydride equivalent is calculated based on the volume and concentration of the potassium hydroxide standard solution consumed, and converted to the grafting rate according to the maleic anhydride molecular weight of 98 g / mol. Key Parameters: Dissolution temperature 80-90℃, KOH-ethanol concentration 0.1000±0.0002 mol / L, titration endpoint pH 8.5-9.0. Data processing: Grafting rate (wt%) = (Vsample - Vblank) × C × 98 / (m × 1000) × 100%, and the average value is taken from 3 parallel measurements.

[0135] Determination of degree of quaternization substitution Test subject: Quaternized chitosan prepared in step S3. Test objective: To quantify the degree of substitution of quaternary ammonium groups on the chitosan molecular chain, providing structural basis for antibacterial properties and nanoparticle surface charge. Test principle: Using hydrogen nuclear magnetic resonance spectroscopy (NMR spectroscopy). The degree of substitution was calculated by the integral ratio of the characteristic signal peak of the quaternary ammonium group to the proton signal peak of the sugar ring. Experimental method: Accurately weigh 10-15 mg of quaternized chitosan sample and dissolve it in 0.6 mL of deuterated water (…). ) or deuterated acetic acid ( In the sample, samples were collected at 25°C. Spectrum, scanned 64 times. Quaternary ammonium groups. A singlet peak was observed for protons at δ 3.2–3.3 ppm, while a characteristic peak was observed for H-1 protons in the sugar ring at δ 4.8–5.0 ppm. The degree of substitution was calculated using the integral area ratio. Key parameters: test temperature 25℃, resonance frequency 400 MHz or 600 MHz, relaxation delay time 2 s. Data processing: Degree of substitution. ×The number of carbon atoms in the sugar ring was measured twice in parallel to verify reproducibility.

[0136] Figure 1 The FTIR infrared spectra of Example 1, Comparative Example 3, and Comparative Example 8 are shown, with the infrared testing method and wavenumber scan range of 800 to 1000 fixed. The same data processing procedure was followed, with the only change being that the sample system was switched from Example 1 to Comparative Examples 3 and 8. Example 1 was... and More significant feature absorption is observed in the vicinity and with Nearby peak shapes are enhanced synergistically, while the overall peak intensity in Comparative Example 3 is weaker than in Comparative Example 8. and The presence of additional enhancement peaks nearby indicates that Example 1 formed a more stable and reproducible combination of target functional groups and interaction characteristics, supporting the rationality of the scheme construction path at the molecular structure level.

[0137] Figure 2 The XPS full-spectrum survey images of Example 1, Comparative Examples 3 and 8 are shown. The parameters were fixed as follows: XPS characterization method, binding energy scan range of 0 to 1100 eV, and uniform charge correction and baseline processing. The parameter change was that the sample was switched from Example 1 to Comparative Examples 3 and 8. Example 1 exhibited clearer N 1s and P-related signals in addition to the C 1s and O 1s main peaks. Compared to Comparative Examples 3 and 8, the heteroatom signals were more complete and had higher relative intensity, indicating that Example 1 introduced and retained the expected elemental composition on the surface and had better surface modification consistency, verifying the effectiveness of the scheme at the overall elemental level.

[0138] Figure 3The XPS high-resolution N 1s plots for Example 1, Comparative Examples 3 and 8 are shown. The parameters were fixed as follows: XPS high-resolution characterization method, binding energy scanning range of 395 to 410 eV, peak fitting, and baseline subtraction rules were consistent. The parameter change was that the sample was switched from Example 1 to Comparative Examples 3 and 8. Example 1 showed stronger component peaks near 399.8 eV and 402.0 eV, maintaining a concentrated peak shape. The corresponding peak intensities in Comparative Examples 3 and 8 were significantly reduced, indicating that Example 1 had a more sufficient number of nitrogen-containing chemical states on its surface and a more stable chemical environment. This demonstrates that the scheme is more effective in introducing nitrogen-containing structural units and has higher effective surface coverage.

[0139] Figure 4 The XPS high-resolution P 2p plots for Example 1, Comparative Examples 3 and 8 are shown. The parameters were fixed as the XPS high-resolution characterization method, the binding energy scanning range of 128 to 138 eV, and the same peak shape constraints and processing procedures. The parameter change was that the sample was switched from Example 1 to Comparative Examples 3 and 8. Example 1 showed a more significant P-related signal near 133.2 eV, while the signals in Comparative Examples 3 and 8 were weak or incomplete. This indicates that Example 1 successfully constructed a more defined phosphorus-containing chemical environment on the surface and maintained a high effective content, further confirming the correctness of the construction route at the key element site level.

[0140] Figure 5 The images show the DLS particle size distribution intensity distribution of Example 1, Comparative Examples 5 and 6. The parameters were fixed as follows: dynamic light scattering characterization method, logarithmic particle size range of 1 to 2000 nm, and the same dispersion and testing procedures. The parameter change was that the sample was switched from Example 1 to Comparative Examples 5 and 6. The main peak of Example 1 is located in the medium particle size range and its distribution is relatively concentrated. Comparative Example 5 is biased towards smaller particle size peaks, while Comparative Example 6 is biased towards larger particle sizes and exhibits a wider distribution. This indicates that Example 1 achieved a more suitable particle size scale and a more stable dispersion state, which is beneficial for obtaining controllable interface and structure construction effects, supporting the feasibility of the scheme from the perspective of particle size consistency.

[0141] Figure 6 The figures show the Zeta potential distribution of Example 1 and Comparative Example 4. The parameters were fixed as follows: electrophoretic light scattering characterization method, Zeta potential scanning range of -20 to +60 mV, and the same dispersion medium and test conditions. The parameter that was changed was that the sample was switched from Example 1 to Comparative Example 4. The distribution peak of Example 1 is located in a higher positive potential range and the peak shape is more concentrated, while the peak position of Comparative Example 4 is lower. This indicates that the system of Example 1 has stronger surface charge and better colloidal electrostatic stability, supporting the reliability of the scheme construction from the perspective of dispersion stability and interfacial interaction.

[0142] Figure 7The figures show the distribution of Zeta potential measurements for Example 1 and Comparative Example 4. The parameters were fixed as the same test method, the same number of repeated measurements, and the same data statistical method. The parameter that was changed was that the sample was switched from Example 1 to Comparative Example 4. The repeated measurement results of Example 1 showed higher concentration and a more stable median, while Comparative Example 4 showed more significant fluctuations and remained in a lower potential range. This indicates that Example 1 exhibited better stability and repeatability under repeated measurement conditions, proving that the scheme not only improves the Zeta potential level but also enhances the test consistency and stability of the system.

[0143] Figure 8 The images show the SEM quantitative coverage distribution of Example 1, Comparative Examples 3 and 8 after 10 washes. The parameters were fixed: the SEM characterization method, ImageJ quantitative procedure, number of washes, and post-processing. The variable parameter was switching between Examples 1, 3, and 8. Example 1 maintained high coverage and converged distribution after washing, while Comparative Examples 3 and 8 showed significantly reduced coverage and increased dispersion. This indicates that the surface structure of Example 1 has stronger wash resistance and resistance to peel loss, verifying the robustness and stability of the constructed scheme from a durability perspective.

[0144] Figure 9The images show a comparison of the physical appearance of the multi-functional nonwoven fabric prepared in Example 1. The fixed parameters are: the composite nonwoven structure is an SMMS structure; the spunbond layer is prepared with polyamide 6 and the average fiber diameter is 20µm; the meltblown layer is prepared by mixing polyamide 6 and maleic anhydride-grafted polyamide 6 at a mass ratio of 84.5:15.5 and the average diameter of the meltblown fiber is 2.9µm; the grafting rate of maleic anhydride-grafted polyamide 6 is 1.05wt%; the degree of quaternization of chitosan is 0.45; the median diameter (D50) of the hydrated particle size distribution of quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticles is 175nm; the impregnation time is 30s; the weight gain of the immobilized functional layer is 2.55g / m²; the drying conditions are 85℃ for 15.5min; and the heat treatment conditions are 120℃ for 5.25min. The changing parameter is that the surface state changes from the composite nonwoven structure without the immobilized functional layer to the multi-functional nonwoven fabric after the immobilized functional layer is applied and heat-treated. The functional surface is milky white to light off-white with enhanced diffuse reflection and a more uniform surface. The back side maintains a white appearance closer to the natural color of polyamide 6, and the fiber texture is clearer, indicating that the immobilized functional layer forms a stable cover on the target surface without causing obvious macroscopic defects. From the partial texture image of the functional surface of the multi-functional nonwoven fabric, the fixed parameters are: the impregnation medium is a quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticle dispersion that is milky white; the liquid retention rate is controlled by rollers to increase the weight of the immobilized functional layer by 2.55 g / m²; the drying conditions are 85℃ for 15.5 min; and the heat treatment conditions are 120℃ for 5.25 min. The changing parameter is the observation scale changing from the overall appearance to the close-up texture of the functional surface. The functional surface exhibits a fine, random fiber texture without large areas of bright spots or drip marks, suggesting that the impregnation and roller control achieve relatively uniform application and maintain the macroscopic connectivity of the nonwoven channels, providing visual evidence for the uniformity of the subsequent microstructure.

[0145] Figure 10 The image shown is a low-magnification scanning electron microscope (SEM) image of the functional surface of the composite nonwoven structure prepared in Example 1. The fixed parameters are as follows: the composite nonwoven structure is an SMMS structure consisting of a spunbond layer-meltblown layer-meltblown layer-spunbond layer and containing a maleic anhydride-grafted polyamide 6 meltblown layer as the target surface (i.e., functional surface) for immobilization treatment; the average diameter of the spunbond fiber is 20 µm; the average diameter of the meltblown fiber is 2.9 µm; the impregnation time is 30 s; the weight gain of the immobilized functional layer is 2.55 g / m²; the drying time is 85 °C for 15.5 min; and the heat treatment time is 120 °C for 5.25 min. The variable parameter is the change of the surface from the unimmobilized state to the state after the immobilized functional layer is formed.

[0146] Figure 11The image shows the high-magnification scanning electron microscope (SEM) morphology of the immobilized functional layer prepared in Example 1 on the surface of polyamide 6 fibers. The immobilization parameters were: nanoparticles were prepared by adding quaternized chitosan and sodium tripolyphosphate dropwise at pH 5.0, 30°C, and stirring at 500 rpm for 20 min, followed by a reaction for 1.25 h; the median diameter (D50) of the hydrated particle size distribution measured by DLS was 175 nm; the impregnation time was 30 s; the weight gain was 2.55 g / m²; and the heat treatment at 120°C for 5.25 min caused the maleic anhydride-grafted polyamide 6 anhydride groups to undergo a ring-opening reaction with the amino groups of the quaternized chitosan to form amide bonds. The change parameter was the observation scale changing from micrometer-sized fibers to nanoparticle-covered morphology. Numerous nanoscale particles or particle clusters were visible on the fiber surface, forming localized bridging structures. The particles were in an adherent state, indicating that the nanoparticles could be stably immobilized on the fiber surface after heat treatment and form a continuous functional cover, thus verifying the feasibility of the immobilized functional layer construction path from a morphological perspective.

[0147] Figure 12 The image shown is a low-magnification scanning electron microscope (SEM) image of the cross-section of the SMMS-structured composite nonwoven structure prepared in Example 1. The fixed parameters were: composite sequence of spunbond layer-meltblown layer-meltblown layer-spunbond layer; average diameter of spunbond fibers of 20 µm; average diameter of meltblown fibers of 2.9 µm; and polymer formulation of the meltblown layer of 84.5:15.5 mass ratio of polyamide 6 to maleic anhydride-grafted polyamide 6 with a maleic anhydride-grafted polyamide 6 mass fraction of 15.5 wt%. The variable parameter was the change in the observed object from surface to cross-sectional layered structure. The cross-section clearly shows the layered difference between the outer coarse fiber spunbond layer and the middle dense microfiber meltblown layer, with continuous interlayer bonding and no obvious delamination gaps. This indicates that the SMMS composite structure is stably formed, providing a controllable target surface and gradient filtration channels for immobilized functional layers.

[0148] As can be seen from the performance of the examples and comparative examples in Table 1, all four examples exhibit excellent overall performance balance in terms of filtration efficiency, low pressure drop, antibacterial properties, and immobilization fastness. Comparative Example 1, due to its excessively low maleic anhydride grafting rate, resulted in insufficient chemical bonding density between the immobilized functional layer and the substrate. After 10 washes, the weight gain retention rate and antibacterial retention rate significantly decreased to 65.3% and 62.8%, respectively, far lower than the 92.5% and 94.3% of the examples. Comparative Example 2, due to its excessively high grafting rate, experienced increased surface roughness of the meltblown fiber layer and a pressure drop to 95 Pa, leading to deteriorated air permeability. Comparative Example 3, lacking maleic anhydride-grafted polyamide 6 and thus lacking a chemical bonding immobilization mechanism, saw a sharp decrease in weight gain retention rate and antibacterial retention rate after washing, to 42.8% and 38.5%, respectively, demonstrating that physical adsorption cannot provide a durable and stable immobilization effect. Comparative Example 4, due to its low quaternization substitution, resulted in insufficient surface positive charge density, leading to antibacterial rates of only 92.3% and 91.8%, significantly lower than the 97.5%–99.8% water concentration of the Examples. Comparative Examples 5 and 6, due to nanoparticle sizes deviating from the preferred range, exhibited excessively high permeability or uneven deposition of nanoparticles in the fiber network, affecting filtration efficiency and pressure drop performance. Comparative Example 7, due to insufficient weight gain of the immobilized functional layer, resulted in inadequate quaternized chitosan content, leading to antibacterial rates of only 88.5% and 87.9%, significantly weakening its functionality. Comparative Example 8, omitting the heat treatment process, resulted in incomplete anhydride-amine ring-opening reaction, with the immobilized functional layer relying mainly on physical adsorption. After washing, the weight gain retention rate and antibacterial rate retention rate plummeted to 28.3% and 25.6%, respectively, demonstrating the crucial role of heat treatment in forming stable chemical bonds. Comprehensive data show that the present invention, through a synergistic strategy of maleic anhydride grafting modification, ionic crosslinking of quaternized chitosan nanoparticles, and chemical bonding fixation with anhydride-amine, has successfully achieved a comprehensive balance between long-term fixation of functional layers, stable filtration performance, and user comfort.

[0149] Table 1 Performance of Examples and Comparative Examples

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A multi-functional nonwoven fabric, characterized in that, Includes composite nonwoven structure and immobilized functional layer; The composite nonwoven structure includes at least a meltblown layer and a spunbond layer. The fiber components of both the meltblown layer and the spunbond layer contain polyamide 6. The meltblown layer further contains maleic anhydride-grafted polyamide 6, which is obtained by reacting polyamide 6 and maleic anhydride in the presence of an initiator. The immobilized functional layer is disposed on the surface of the composite nonwoven structure and contains quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticles. The immobilized functional layer is fixed to the surface of the composite nonwoven structure by the ring-opening reaction between the anhydride groups of maleic anhydride-grafted polyamide 6 and the amino groups of the quaternized chitosan to form amide bonds.

2. The multi-functional nonwoven fabric according to claim 1, characterized in that, The maleic anhydride-grafted polyamide 6 is prepared by the following steps: A1. Raw material preparation: Based on 100 parts by weight of polyamide 6, maleic anhydride is 0.20-5.00 parts by weight, and di-tert-butyl peroxide is 0.01-0.50 parts by weight; A2. Reactive extrusion: Melt reactive extrusion is carried out at 220-260℃, with a residence time of 1.0-5.0 min, in a nitrogen atmosphere; A3. Granulation and post-treatment: Extrusion granulation and drying are performed to obtain the maleic anhydride-grafted polyamide 6; A4. Quality control: The grafting rate of the maleic anhydride-grafted polyamide 6 is 0.10-2.00 wt%, and the grafting rate is the mass fraction of the amount of maleic anhydride grafted relative to the total mass of the maleic anhydride-grafted polyamide 6.

3. The multi-functional nonwoven fabric according to claim 1, characterized in that, The quaternized chitosan is prepared by the following steps: B1. Raw material preparation: Chitosan is dissolved in an aqueous acetic acid solution to obtain a homogeneous system. Glycidyltrimethylammonium chloride is added to the homogeneous system, and the pH value of the reaction system is adjusted by an aqueous sodium hydroxide solution. The amount of glycidyltrimethylammonium chloride is 10-80 parts by weight per 100 parts by weight of chitosan. B2. Quaternization reaction: Under the condition that the pH value of the reaction system is 8.0-10.0, the reaction is carried out at 40-80℃ for 2-12 hours; B3. Post-processing: The reaction product is washed and dried to obtain the quaternized chitosan; B4. Quality control: The degree of quaternization substitution of the quaternized chitosan is 0.10-0.80, and the degree of quaternization substitution is the ratio of the number of moles of quaternary ammonium groups to the number of moles of chitosan glucosamine repeating units.

4. The multi-functional nonwoven fabric according to claim 3, characterized in that, The quaternized chitosan-sodium tripolyphosphate ion-crosslinked nanoparticles are prepared by the following steps: C1. Raw material preparation: The quaternized chitosan is prepared into an aqueous solution with a mass fraction of 0.10-2.00 wt%, and sodium tripolyphosphate is prepared into an aqueous solution with a mass fraction of 0.05-0.50 wt%; the pH value of the quaternized chitosan aqueous solution is adjusted to 4.0-6.0 using an aqueous acetic acid solution; C2. Ionic crosslinking nucleation: Under the condition that the pH value of the quaternized chitosan aqueous solution is 4.0-6.0, the sodium tripolyphosphate aqueous solution is added at 20-40℃ and reacted for 0.5-2.0h to obtain a nanoparticle dispersion; C3. Quality control: The D50 of the nanoparticles is 50-300 nm, and the D50 is the median diameter of the hydrated particle size measured by dynamic light scattering method.

5. The multi-functional nonwoven fabric according to claim 4, characterized in that, The immobilized functional layer is formed through the following steps: D1. Application: The nanoparticle dispersion is applied to the surface of the composite nonwoven structure to increase the weight of the immobilized functional layer by 0.10-5.00 g / m²; D2) Drying: Dry at 50-120℃ for 1-30 minutes; D3) Heat treatment: Heat treatment at 80-160℃ for 0.5-10 min to allow the anhydride groups of the maleic anhydride-grafted polyamide 6 to undergo a ring-opening reaction with the amino groups of the quaternized chitosan and form amide bonds, thereby obtaining the immobilized functional layer.

6. The multi-functional nonwoven fabric according to claim 1, characterized in that, It meets any one or more of the following characteristics: The composite nonwoven structure is one of SMS structure, SMMS structure or SMMMS structure; The average fiber diameter of the meltblown layer is 0.8-5.0µm; The average fiber diameter of the spunbond layer is 10-30µm; Based on the total polymer mass of the meltblown layer, the mass fraction of maleic anhydride-grafted polyamide 6 in the meltblown layer is 1.0-30.0 wt%.

7. The method for preparing the multi-functional nonwoven fabric according to claim 1, characterized in that, Includes the following steps: S1. Preparation of maleic anhydride-grafted polyamide 6: Polyamide 6, maleic anhydride and di-tert-butyl peroxide are melt-reacted and extruded to obtain maleic anhydride-grafted polyamide 6; S2. Web formation: A spunbond layer is prepared using polyamide 6 as raw material; a meltblown layer is prepared using a mixture of polyamide 6 and maleic anhydride-grafted polyamide 6 as raw material; the spunbond layer and the meltblown layer are combined to obtain a composite nonwoven structure; wherein, the target surface for surface immobilization treatment in the subsequent step S4 is set as the surface corresponding to the fiber layer containing maleic anhydride-grafted polyamide 6. S3. Preparation of nanoparticle dispersion: Chitosan is reacted with glycidyltrimethylammonium chloride to obtain quaternized chitosan, and then sodium tripolyphosphate is used to ion crosslink the quaternized chitosan to obtain nanoparticle dispersion; S4. Surface immobilization: The nanoparticle dispersion is applied to the surface of the composite nonwoven structure, and then dried and heat-treated in sequence to allow the anhydride groups of the maleic anhydride-grafted polyamide 6 to undergo a ring-opening reaction with the amino groups of the quaternized chitosan and form amide bonds, thereby obtaining an immobilized functional layer.

8. The preparation method according to claim 7, characterized in that, In step S1, the amount of maleic anhydride used is 0.20-5.00 parts by weight, based on 100 parts by weight of polyamide 6; In step S1, the melt reaction extrusion temperature is 220-260℃ and the residence time is 1.0-5.0 min.

9. The preparation method according to claim 7, characterized in that, In step S3, the pH value of the quaternization reaction is 8.0-10.0, the temperature is 40-80℃, and the time is 2-12h; In step S3, the pH value for ionic cross-linking and nucleation is 4.0-6.0, the temperature is 20-40℃, and the time is 0.5-2.0h.

10. The preparation method according to claim 7, characterized in that, In step S2, the average fiber diameter of the meltblown layer is 0.8-5.0µm, and the average fiber diameter of the spunbond layer is 10-30µm.

Images