Self-repairing multifunctional meta-modified aramid fiber composite paper, preparation method and application

Abstract

This invention provides a self-healing, multifunctional meta-modified aramid composite paper, its preparation method, and its applications. This meta-modified aramid composite paper is composed of meta-aramid precipitated fibers, a bio-based modifier, in-situ biomineralized hydroxyapatite nanoparticles, and a dynamic coordination bond cross-linking network. Its dry tensile strength is ≥80 MPa, wet tensile strength is ≥30 MPa, the repair rate of 1-2 mm cracks after heating at 250℃ for 10 min is ≥85%, the long-term service temperature is ≥200℃, the antibacterial rate is ≥90%, the oxygen index (LOI) is ≥32%, and the smoke density rating (SDR) is ≤50. Advantages: (1) The problem of weak inter-fiber bonding force is solved by the "physical bridge" of hydroxyapatite nanoparticles and the "chemical cross-linking" of dynamic coordination bonds through in-situ biomineralization, and the interface bonding performance is optimized; (2) Meta-aramid paper achieves "high temperature resistance + self-healing + antibacterial + low smoke flame retardancy", and its comprehensive performance far exceeds that of existing aramid paper; (3) The "one-step papermaking" process is adopted to simultaneously complete in-situ mineralization, dynamic cross-linking and molding, which simplifies the process and reduces energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of high-performance materials technology and relates to a meta-aramid (PMIA) composite paper material and its preparation method. Specifically, it relates to a meta-aramid composite paper modified by in-situ biomineralization and dynamic coordination bonds. This composite paper is self-healing and also has functions such as high temperature resistance, low smoke flame retardancy, and antibacterial properties. It is prepared by a one-step papermaking process. Background Technology

[0002] Meta-aramid (PMIA) precipitated fibers have excellent high-temperature resistance, flame retardancy and insulation properties. Aramid paper made from them is widely used in high-end fields such as aerospace, electronics and electrical, and new energy. However, the existing PMIA precipitated fiber papermaking technology has the following problems: (1) PMIA fibers are chemically inert and have low surface hydroxyl content, resulting in weak inter-fiber bonding force. The dry / wet mechanical properties of the prepared aramid paper are insufficient, which limits its application in complex stress scenarios; (2) In order to improve the inter-fiber bonding force, chemical additives such as PAE and epoxy are usually added during the preparation of aramid paper. However, these additives are easy to decompose at high temperatures, destroying the high-temperature resistance of aramid paper. Moreover, pollutants are easily generated during the preparation process, which does not meet environmental protection requirements; (3) Existing aramid paper has a single function, focusing only on high-temperature resistance and flame retardancy. It lacks extended functions such as self-repair and antibacterial properties, which makes it difficult to meet the multi-functional needs of high-end scenarios such as aerospace interiors and medical protection; (4) PMIA precipitated fibers have poor dispersibility in aqueous systems and are easy to agglomerate, resulting in poor uniformity of the prepared aramid paper and affecting the overall performance stability of the material.

[0003] Existing technologies mostly employ single modification to solve the above-mentioned technical problems: (1) Improving mechanical properties by adding inorganic reinforcing agents through physical mixing. However, this method suffers from weak interfacial bonding between the inorganic phase and organic fibers. (2) Introducing functional groups through chemical grafting to impart specific functions. However, this method requires multiple post-processing steps, which are complex and easily damage the fiber structure. In addition, existing self-healing polymer materials mostly rely on dynamic bonds such as Schiff bases and disulfide bonds, which have poor high-temperature resistance and are prone to failure above 200°C, making them unsuitable for the high-temperature service environment of PMIA aramid paper.

[0004] Therefore, there is an urgent need to provide a meta-modified aramid composite paper with multiple functions such as self-healing, high temperature resistance, antibacterial properties, low smoke, and flame retardancy, as well as a method for preparing the above-mentioned meta-modified aramid composite paper in one-step papermaking. Summary of the Invention

[0005] In order to overcome the above-mentioned technical problems, the present invention aims to: (1) provide a meta-modified aramid composite paper that has multiple functions such as self-healing, high temperature resistance, antibacterial properties, low smoke flame retardancy, etc.; (2) provide a one-step method for preparing the above-mentioned self-healing multifunctional meta-modified aramid composite paper; and (3) provide the uses of the above-mentioned self-healing multifunctional meta-modified aramid composite paper.

[0006] The inventive concept of this invention is as follows: using meta-aramid (PMIA) precipitated fibers as the base material, combined with bio-based modifiers, biomineralization precursors, and dynamic coordination bond regulators, the modification of meta-aramid precipitated fibers and paper forming are completed simultaneously during the papermaking process; through the triple synergistic effect of constructing inorganic nanobridges by biomineralization, achieving reversible cross-linking by dynamic coordination bonds, and improving interfacial compatibility by bio-based modifiers, meta-modified aramid composite paper with functions such as high temperature resistance, self-healing, antibacterial, low smoke flame retardancy, and high strength is developed.

[0007] To achieve the above-mentioned objectives, this invention provides a self-healing multifunctional meta-modified aramid composite paper. The meta-modified aramid composite paper is composed of meta-aramid precipitated fibers, a bio-based modifier, in-situ biomineralized hydroxyapatite nanoparticles, and a dynamic coordination bond cross-linking network. The meta-modified aramid composite paper possesses a multi-level composite structure of "precipitated fibers forming the skeleton - nanoparticles bridging the fibers - dynamic coordination network coating and reinforcement." The meta-modified aramid composite paper exhibits a dry tensile strength ≥80 MPa, a wet tensile strength ≥30 MPa, a 1-2 mm crack repair rate ≥85% after heating at 250℃ for 10 min, a long-term service temperature ≥200℃, an antibacterial rate of ≥90% against Escherichia coli and Staphylococcus aureus, an oxygen index (LOI) ≥32%, and a smoke density rating (SDR) ≤50.

[0008] Furthermore, in the self-healing multifunctional meta-modified aramid composite paper provided by the present invention, the mass ratio of meta-aramid precipitated fibers, bio-based modifier and in-situ biomineralized hydroxyapatite nanoparticles is 100:(5~15):(3~10).

[0009] Furthermore, in the self-healing multifunctional meta-modified aramid composite paper provided by this invention, the in-situ biomineralized hydroxyapatite nanoparticles are generated in situ from a mixed solution of diammonium hydrogen phosphate and calcium nitrate; the molar ratio of diammonium hydrogen phosphate to calcium nitrate is 1.67:1; the total amount of the mixed solution of diammonium hydrogen phosphate and calcium nitrate added is 5% to 8% of the mass of PMIA precipitated fibers.

[0010] Furthermore, in the self-healing multifunctional meta-modified aramid composite paper provided by the present invention, the bio-based modifier is a mixture of aldehyde-modified sodium alginate and amino-modified chitosan; the amount of amino-modified chitosan added is 2%~4% of the meta-aramid precipitated fiber, and the degree of substitution of amino-modified chitosan is ≥85%; the amount of aldehyde-modified sodium alginate added is 3%~5% of the meta-aramid precipitated fiber, and the degree of oxidation of aldehyde-modified sodium alginate is 20%~30%.

[0011] Furthermore, in the self-healing multifunctional meta-modified aramid composite paper provided by this invention, the dynamic coordination bond is COO-Fe³⁺-NH-; the dynamic coordination bond can be reversibly broken and recombined at 250~300℃.

[0012] Furthermore, in the self-healing multifunctional meta-modified aramid composite paper provided by this invention, the dynamic coordination bond regulator used for the dynamic coordination bonds is a Fe³⁺ solution with a concentration of 0.5~1mmol / L.

[0013] To achieve the above-mentioned objectives, this invention also provides a method for preparing any of the above-mentioned self-healing multifunctional meta-modified aramid composite papers, comprising the following steps:

[0014] S1. Preparation of pulp suspension: Add meta-aramid precipitated fibers to deionized water and disperse them using a high-speed stirrer to obtain a uniform pulp suspension with a concentration of 0.5wt%~1wt%.

[0015] S2. Add and disperse bio-based modifiers: Add aldehyde-modified sodium alginate and amino-modified chitosan to the pulp suspension, and ultrasonically disperse for 10 minutes to ensure uniform adsorption of the modifiers onto the fiber surface; the amount of aldehyde-modified sodium alginate added is 3%~5% of the meta-aramid precipitated fiber, and the oxidation degree of aldehyde-modified sodium alginate is 20%~30%; the amount of amino-modified chitosan added is 2%~4% of the meta-aramid precipitated fiber, and the substitution degree of amino-modified chitosan is ≥85%;

[0016] S3. In-situ biomineralization: The pH of the mixed system was adjusted to 7.5-8.0 using a weakly alkaline buffer solution. A mixed solution of diammonium hydrogen phosphate and calcium nitrate was added, and the mixture was stirred at room temperature until completely dispersed and homogeneous, resulting in the in-situ formation of hydroxyapatite nanoparticles. The molar ratio of diammonium hydrogen phosphate to calcium nitrate was 1.67:1. The total amount of diammonium hydrogen phosphate and calcium nitrate mixed solution added was 5%-8% of the mass of the meta-aramid precipitated fiber.

[0017] S4. Constructing dynamic coordination bonds: Fe³⁺ solution is added dropwise to the system. After the solution is stirred evenly, a dynamic coordination cross-linking network is formed to obtain the composite slurry; the concentration of Fe³⁺ solution is 0.5~1mmol / L.

[0018] S5. Papermaking and Drying: The composite pulp is formed into paper, then vacuum dewatered, pressed, and dried to obtain self-healing multifunctional meta-modified aramid composite paper.

[0019] Furthermore, in the method for preparing a self-healing multifunctional meta-modified aramid composite paper provided by the present invention, the mass ratio of meta-aramid precipitated fibers, bio-based modifier and in-situ biomineralized hydroxyapatite nanoparticles is 100:(5~15):(3~10).

[0020] Furthermore, in the method for preparing a self-healing multifunctional meta-modified aramid composite paper provided by the present invention, Fe³⁺ forms a -COO-Fe³⁺-NH- dynamic coordination bond with the carboxyl and amino groups in the bio-based modifier; the dynamic coordination bond can be reversibly broken and recombined at 250~300℃.

[0021] Furthermore, in the method for preparing a self-healing multifunctional meta-modified aramid composite paper provided by the present invention, in step S5, the vacuum degree during vacuum dehydration is 0.06~0.08MPa; the pressing pressure is 0.3~0.5MPa; the drying temperature is 120℃; and the drying time is 30min.

[0022] To achieve the purpose of the invention, the present invention also provides the application of any of the above-mentioned self-healing multifunctional meta-modified aramid composite paper or the self-healing multifunctional meta-modified aramid composite paper prepared according to any of the above-mentioned self-healing multifunctional meta-modified aramid composite paper preparation methods, for use in any of the following fields: aerospace interiors, new energy vehicle battery separator substrates, high-temperature disinfection medical protective paper, and industrial high-temperature bacterial fluid filtration materials.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The composite paper of the present invention effectively solves the technical pain point of weak bonding force between meta-aramid fibers through the synergistic effect of the "physical bridge" of in-situ biomineralized hydroxyapatite nanoparticles and the "chemical cross-linking" of dynamic coordination bonds. The dry tensile strength is ≥80MPa, which is more than 50% higher than that of unmodified meta-aramid paper; the wet tensile strength is ≥30MPa, which is more than 100% higher than that of unmodified meta-aramid paper; the interface bonding performance is significantly optimized; (2) The present invention achieves the first synergistic effect of four functions of meta-aramid paper: "high temperature resistance + self-repair + antibacterial + low smoke flame retardancy". The long-term use temperature is ≥200℃, the thermal decomposition temperature is ≥400℃, and the repair efficiency of 1~2mm cracks after heating at 250℃ for 10min is ≥85% (can be repaired more than 3 times). The antibacterial rate of Enterobacteriaceae and Staphylococcus aureus is ≥90%, the oxygen index (LOI) is ≥32%, and the smoke density grade (SDR) is ≤50. The overall performance is far superior to that of existing aramid paper; (3) The present invention adopts the "one-step papermaking" process, which simultaneously completes in-situ mineralization, dynamic cross-linking and molding. No additional post-processing modification is required, the process is simplified and energy consumption is reduced; the modifiers used are all bio-based / inorganic materials, and the papermaking wastewater COD≤80mg / L can be directly discharged in compliance with the standard, which completely solves the pollution problem of traditional processes relying on chemical additives. The process is green and efficient; (4) The composite paper of the present invention, with its multi-functional synergistic characteristics, can meet the usage needs of high-end scenarios such as aerospace interiors, new energy vehicle battery separator substrates, high-temperature disinfection medical protective paper, and industrial high-temperature bacterial fluid filtration materials. It has a wide range of applications and huge market potential. Detailed Implementation

[0024] This invention aims to solve the problems of weak inter-fiber bonding, single function, reliance on chemical additives to pollute the environment, and complex preparation process with multiple post-processing steps in traditional meta-aramid (PMIA) precipitated fiber papermaking. The innovations of this invention are: (1) providing a novel modification system of "biomineralization-dynamic coordination bond synergistic modification", which simultaneously improves the interfacial bonding force and multifunctionality of fibers through the dual effects of inorganic nanobridges and reversible chemical cross-linking; (2) innovatively adopting a "one-step papermaking" process, which simultaneously completes in-situ mineralization, dynamic bond cross-linking and functional integration during the forming process, without the need for additional post-processing, simplifying the process and being green and environmentally friendly; (3) realizing the synergistic four functions of PMIA paper: "high temperature resistance + self-healing + antibacterial + low smoke flame retardancy", breaking through the limitations of the single function of existing aramid paper and adapting to the multi-dimensional needs of high-end scenarios.

[0025] The preparation method provided by this invention is mainly divided into two modules: raw material system optimization and one-step papermaking process control. The raw material system lays the foundation for the performance of composite paper, and the one-step papermaking process achieves the simultaneous completion of modification and molding through precise parameter control, ultimately obtaining multifunctional meta-aramid composite paper.

[0026] Regarding the optimization and selection of raw material system: The composite paper of this invention uses PMIA precipitated fibers as the base material, combined with bio-based modifiers, biomineralization precursors, and dynamic coordination bond regulators. The parameter selection and principles of each raw material are as follows:

[0027] Regarding meta-aramid (PMIA) precipitated fibers: As a skeleton material for meta-modified aramid composite paper, its concentration in pulp is preferably 0.5% to 1%. Through extensive practical experience, the inventors discovered that: when the concentration is below 0.5%, the fiber dispersion in the pulp is too sparse, resulting in insufficient physical entanglement and hydrogen bonding sites between fibers. This leads to discontinuous mechanical support structure in the formed composite paper, making it prone to defects such as breakage and porosity. When the concentration is above 1%, the van der Waals forces between fibers increase, making agglomeration more likely. Ultrasonic and stirring methods are insufficient to fully disperse these agglomerates, resulting in poor uniformity and reduced performance stability in the produced composite paper. Simultaneously, PMIA precipitated fibers themselves possess excellent high-temperature resistance and flame-retardant properties, ensuring the fundamental performance of the composite paper.

[0028] Regarding bio-based modifiers: A combination of aldehyde-modified sodium alginate and amino-modified chitosan was selected. The amount of aldehyde-modified sodium alginate added was 3%~5% of the mass of PMIA precipitated fibers, with an oxidation degree of 20%~30%; the amount of amino-modified chitosan added was 2%~4% of the mass of PMIA precipitated fibers, with a substitution degree ≥85%. The inventors found that when the oxidation degree of aldehyde-modified sodium alginate was below 20%, the number of surface carboxyl groups (-COOH) was insufficient, making it difficult to form effective interaction sites with Fe³⁺ and in-situ biomineralized hydroxyapatite (HAP) nanoparticles. The dynamic coordination bond construction was insufficient, and the improvement in the compatibility between the fiber and the inorganic phase was limited. When the oxidation degree was above 30%, the degradation of the sodium alginate molecular chain intensified, the mechanical properties decreased, and it could not provide stable support for the cross-linking network. When the degree of substitution of aminated chitosan is less than 85%, the amino content is insufficient, which not only affects the efficiency of dynamic coordination bond formation but also significantly reduces its antibacterial activity. When the degree of substitution is ≥85%, the amino density is moderate, which can simultaneously meet the requirements of coordination bond formation and antibacterial function. In terms of addition amount, if the aldehyde-modified sodium alginate is less than 3% and the aminated chitosan is less than 2%, the modification effect is insufficient and cannot effectively improve the interfiber bonding force. If the aldehyde-modified sodium alginate is more than 5% and the aminated chitosan is more than 4%, the modifier is excessive and easily agglomerates on the fiber surface, resulting in a decrease in the porosity of the composite paper and affecting auxiliary properties such as air permeability and heat insulation.

[0029] Regarding biomineralization precursors: Diammonium hydrogen phosphate and calcium nitrate were selected as precursors, with a fixed molar ratio of 1.67:1. The total addition amount was 5%~8% of the mass of PMIA precipitated fibers, and the reaction required an aqueous environment with a pH of 7.5~8.0. The inventors found that when the molar ratio deviated from 1.67:1, hydroxyapatite (HAP) nanoparticles could not be stably generated, and impurity phases such as calcium phosphate and calcium hydrogen phosphate were easily formed. These impurity phases have poor high-temperature resistance and small specific surface area, and cannot play the role of "physical bridge," instead reducing the mechanical properties and flame retardancy of the composite paper. When the total addition amount was less than 5%, the number of HAP nanoparticles was insufficient, the density of "physical bridges" between fibers was insufficient, and the effect of improving interfacial bonding was not obvious; when it was higher than 8%, the nanoparticles were prone to agglomeration, and the formed agglomerates became stress concentration points in the composite paper, leading to increased paper brittleness and decreased folding resistance. When the pH value is below 7.5, the precursor reaction is incomplete, resulting in a small amount of HAP nanoparticles and uneven particle size. When the pH value is above 8.0, the nanoparticles tend to grow rapidly, with a particle size exceeding 20 nm. This reduces the specific surface area and weakens the interaction with fibers and modifiers, making it impossible to fully exert the synergistic effect.

[0030] Regarding the dynamic coordination bond regulator: A Fe³⁺ solution with a concentration of 0.5–1 mmol / L was selected. The inventors discovered that when the Fe³⁺ concentration is below 0.5 mmol / L, its coordination reaction with the carboxyl groups of aldehyde-modified sodium alginate and the amino groups of amino-modified chitosan is insufficient, resulting in an incomplete reversible cross-linking network and the self-healing performance of the composite paper failing to meet design requirements. When the concentration is above 1 mmol / L, excessive Fe³⁺ leads to over-cross-linking of coordination bonds, reducing the flexibility of the composite paper. Furthermore, excess Fe³⁺ forms impurities in the paper, affecting its high-temperature stability and causing performance degradation after aging at 200°C. Simultaneously, the -COO-Fe³⁺-NH⁻ dynamic coordination bonds formed within this concentration range remain stable below 200°C and undergo reversible breakage and recombination at 250–300°C, perfectly suited to the high-temperature service environment of PMIA.

[0031] Regarding the control of key process parameters in one-step papermaking. This invention achieves simultaneous modification and forming by precisely controlling the parameters of each process step. The specific parameter selection and principles are as follows:

[0032] Regarding the preparation of the pulp suspension: PMIA precipitated fibers were added to deionized water and dispersed using a high-speed stirrer to obtain a homogeneous pulp suspension with a concentration of 0.5%~1%. The key to the stirring process is to ensure sufficient dispersion of the fibers and prevent agglomeration, thus providing a uniform reaction environment for subsequent modifier adsorption and mineralization reactions. If stirring is insufficient, fiber agglomerates cannot be completely broken up in subsequent steps, leading to uneven properties of the composite paper.

[0033] Regarding the addition and dispersion of bio-based modifiers: Aldehyde-modified sodium alginate and amino-modified chitosan were added to the pulp suspension in a specific ratio, followed by ultrasonic dispersion for 10 minutes. The inventors discovered that when the ultrasonic time was less than 10 minutes, the modifier could not be uniformly adsorbed onto the fiber surface; some areas had excessively high modifier concentrations, leading to agglomeration, while other areas lacked modifier, resulting in insufficient modification. When the ultrasonic time exceeded 10 minutes, excessive ultrasonic action damaged the molecular chain structure of PMIA fibers, reducing the fiber's mechanical properties and high-temperature resistance, thus affecting the overall quality of the composite paper. The core of ultrasonic dispersion is to use vibration to break up fiber agglomerates while simultaneously ensuring sufficient contact between the modifier and the fiber surface, laying the foundation for the subsequent formation of dynamic coordination bonds.

[0034] Regarding in-situ biomineralization: A weakly alkaline buffer solution was used to adjust the pH of the mixed system to 7.5–8.0. The use of a weakly alkaline buffer solution to adjust the pH was to avoid drastic pH fluctuations and ensure uniform formation of HAP nanoparticles. Direct use of strong acids or bases would cause sudden pH changes, leading to rapid agglomeration of nanoparticles and uncontrolled particle size.

[0035] Regarding the construction of dynamic coordination bonds: Fe³⁺ solution was slowly added dropwise to the mineralization system. The slow addition of Fe³⁺ solution was to ensure sufficient contact and coordination between Fe³⁺ and the carboxyl and amino groups, avoiding excessive concentration in certain areas that could lead to over-concentration of coordination bonds.

[0036] Regarding paper forming and drying: The composite system is transferred to the surface of a paper machine filter screen and filtered and dehydrated under a vacuum of 0.06~0.08MPa, followed by pressing under a pressure of 0.3~0.5MPa, and finally dried at 120℃ for 30 minutes. The inventors found that: when the vacuum is below 0.06MPa, the filtration and dehydration efficiency is low, the bonding between fibers and modifiers and HAP nanoparticles is not tight, and the structure of the formed composite paper is loose; when the pressure is above 0.08MPa, excessive pressure can easily cause the fiber network to be compacted, resulting in too low porosity and affecting the air permeability, heat insulation and other properties of the composite paper. When the pressing pressure is below 0.3MPa, dehydration is insufficient, and there is too much residual moisture in the composite paper, which is prone to shrinkage and deformation after drying; when the pressure is above 0.5MPa, excessive pressing will destroy the cross-linked structure formed by the fibers and nanoparticles and coordination bonds, leading to a decrease in mechanical properties. When the drying temperature is below 120℃, the drying time needs to be extended, and the residual moisture is difficult to remove completely, affecting the stability of the composite paper. When the temperature is above 120℃, although the drying time can be shortened, the excessively high temperature may cause slight degradation of the bio-based modifier, affecting the self-repair and antibacterial properties. Therefore, drying at 120℃ for 30 minutes is the optimal parameter, which can ensure sufficient drying while retaining the functional characteristics of each component.

[0037] The prepared meta-aramid composite paper, synergistically modified by in-situ biomineralization and dynamic coordination bonds, is composed of PMIA precipitated fibers, bio-based modifiers, HAP nanoparticles, and dynamic coordination bonds, exhibiting a three-dimensional cross-linked structure of "PMIA fiber-HAP nanobridge-dynamic coordination bonds". The composite paper has a dry tensile strength ≥80MPa, a wet tensile strength ≥30MPa, a long-term service temperature ≥200℃, and a thermal decomposition temperature ≥400℃. A 1-2mm crack can be repaired at 250℃ for 10 minutes with a repair efficiency ≥85%, and can be cyclically repaired more than 3 times. It exhibits an antibacterial rate of ≥90% against Escherichia coli and Staphylococcus aureus, an oxygen index (LOI) ≥32%, and a smoke density rating (SDR) ≤50, demonstrating excellent overall performance and meeting the needs of various high-end applications.

[0038] The properties of the meta-modified aramid composite paper provided by this invention were characterized by multiple standard methods: tensile strength was tested according to ASTM D828 (tensile method); antibacterial rate was tested according to GB / T 20944.2 (oscillation contact method); limiting oxygen index was tested according to GB / T 2406.2 (oxygen index method).

[0039] Example 1

[0040] The meta-aramid precipitated fibers, aldehyde-modified sodium alginate, amino-modified chitosan, diammonium hydrogen phosphate, calcium nitrate, and ferric chloride used in this embodiment were all purchased commercially. The in-situ biomineralization-dynamic coordination bond synergistic modification of meta-aramid composite paper was prepared according to the following steps:

[0041] (1) Preparation of pulp suspension: 100g of meta-aramid precipitated fiber was added to 20L of deionized water and stirred with a high-speed stirrer to obtain a uniform pulp suspension with a concentration of 0.5wt%.

[0042] (2) Adding and dispersing bio-based modifiers: Add 3g of aldehyde-modified sodium alginate and 2g of amino-modified chitosan to the pulp suspension, and ultrasonically disperse for 10min to allow the modifiers to be uniformly adsorbed on the fiber surface; wherein, the degree of oxidation of aldehyde-modified sodium alginate is 20% and the degree of substitution of amino-modified chitosan is 85%;

[0043] (3) In-situ biomineralization: The pH of the mixed system was adjusted to 7.5 using a weak alkaline buffer solution, and 5g of a mixed solution of diammonium hydrogen phosphate and calcium nitrate was added. The molar ratio of diammonium hydrogen phosphate to calcium nitrate in the mixed solution was 1.67:1. The mixture was stirred at room temperature until it was completely dispersed and uniform, and hydroxyapatite nanoparticles were generated in situ.

[0044] (4) Construction of dynamic coordination bonds: 0.5 mmol / L Fe³⁺ solution was slowly added to the system and the solution was stirred evenly at room temperature to form a dynamic coordination cross-linking network;

[0045] (5) Paper forming and drying: The composite pulp is transferred to the filter screen of the paper machine, filtered and dewatered under a vacuum of 0.06 MPa, then pressed under a pressure of 0.3 MPa, and finally dried in an oven at 120°C for 30 min to obtain composite paper.

[0046] The prepared composite paper has a basis weight of 65 g / m² and a thickness of 100 μm. Its dry tensile strength is 82 MPa and its wet tensile strength is 31 MPa. After heating at 250℃ for 10 min, the repair efficiency for a 1 mm wide crack can reach 86%. The composite paper has an antibacterial rate of 91% against Escherichia coli and 90% against Staphylococcus aureus. The limiting oxygen index is 32% and the smoke density grade is 48. After aging at 200℃ for 100 h, its tensile strength retention rate is 92%.

[0047] Example 2

[0048] The meta-aramid (PMIA) precipitated fiber used in this embodiment is a conventional commercial product. Reagents such as aldehyde-modified sodium alginate, amino-modified chitosan, diammonium hydrogen phosphate, calcium nitrate, Fe³⁺ salt (ferric nitrate), and weakly alkaline buffer solution were all purchased commercially. The in-situ biomineralization-dynamic coordination bond synergistic modification of meta-aramid composite paper was prepared according to the following steps:

[0049] (1) Preparation of pulp suspension: Take 160g of meta-aramid precipitated fiber, add 20L of deionized water, stir at high speed to obtain a uniform pulp suspension with a concentration of 0.8%;

[0050] (2) Addition and dispersion of bio-based modifier: Add 6.4g of aldehyde-modified sodium alginate with an oxidation degree of 25% and 4.8g of amino-modified chitosan with a substitution degree of 90% to the pulp suspension in step (1), and place it in an ultrasonic device for ultrasonic dispersion for 10min so that the modifier is uniformly adsorbed on the fiber surface.

[0051] (3) In-situ biomineralization: The pH of the mixed system in step (2) was adjusted to 7.8 with a weak alkaline buffer solution, and 9.6g of a mixed solution of diammonium hydrogen phosphate and calcium nitrate (molar ratio of the two is 1.67:1) was added. The mixture was stirred at room temperature until it was completely dispersed and uniform, and hydroxyapatite (HAP) nanoparticles were generated in situ.

[0052] (4) Construction of dynamic coordination bonds: Slowly add 0.8 mmol / L Fe³⁺ solution to the mineralization system in step (3) and stir the solution evenly so that Fe³⁺ forms dynamic coordination bonds with the carboxyl group of aldehyde-modified sodium alginate and the amino group of amino-modified chitosan to construct a three-dimensional cross-linked network.

[0053] (5) Paper forming and drying: The composite system of step (4) is transferred to the paper machine, filtered and dehydrated under a vacuum of 0.07 MPa, then pressed and dehydrated under a pressure of 0.4 MPa, and finally placed in an oven to dry at 120°C for 30 min to obtain meta-aramid composite paper with in-situ biomineralization-dynamic coordination bond synergistic modification.

[0054] The prepared meta-aramid composite paper exhibits a dry tensile strength of 88 MPa and a wet tensile strength of 35 MPa. After heating at 250℃ for 10 min, it achieves an 88% repair efficiency for a 1.5 mm crack. It demonstrates a 93% inhibition rate against Escherichia coli and a 92% inhibition rate against Staphylococcus aureus. The oxygen index (LOI) is 33%, and the smoke density rating (SDR) is 45. After aging at 200℃ for 100 h, the tensile strength retention rate is 93%. The composite paper combines excellent high-temperature stability, self-healing properties, antibacterial effects, and low-smoke flame retardant characteristics.

[0055] Example 3

[0056] The meta-aramid (PMIA) precipitated fiber used in this embodiment is a conventional commercial product. Reagents such as aldehyde-modified sodium alginate, amino-modified chitosan, diammonium hydrogen phosphate, calcium nitrate, Fe³⁺ salt (ferric nitrate), and weakly alkaline buffer solution were all purchased commercially. The in-situ biomineralization-dynamic coordination bond synergistic modification of meta-aramid composite paper was prepared according to the following steps:

[0057] (1) Preparation of pulp suspension: Take 200g of meta-aramid precipitated fiber, add 20L of deionized water, stir at high speed to obtain a uniform pulp suspension with a concentration of 1%;

[0058] (2) Addition and dispersion of bio-based modifier: Add 10g of aldehyde-modified sodium alginate with an oxidation degree of 30% and 8g of amino-modified chitosan with a substitution degree of 95% to the pulp suspension in step (1), and place it in an ultrasonic device for ultrasonic dispersion for 10min so that the modifier is uniformly adsorbed on the fiber surface.

[0059] (3) In-situ biomineralization: The pH of the mixed system in step (2) was adjusted to 8.0 with a weak alkaline buffer solution, and 16g of a mixed solution of diammonium hydrogen phosphate and calcium nitrate (molar ratio of the two is 1.67:1) was added. The mixture was stirred at room temperature until it was completely dispersed and uniform, and hydroxyapatite (HAP) nanoparticles were generated in situ.

[0060] (4) Construction of dynamic coordination bonds: Add 1 mmol / L Fe³⁺ solution to the mineralization system in step (3) and stir the solution evenly so that Fe³⁺ forms dynamic coordination bonds with the carboxyl group of aldehyde-modified sodium alginate and the amino group of amino-modified chitosan to construct a three-dimensional cross-linked network.

[0061] (5) Paper forming and drying: The composite system of step (4) is transferred to the paper machine, filtered and dehydrated under a vacuum of 0.08 MPa, then pressed and dehydrated under a pressure of 0.5 MPa, and finally placed in an oven at 120°C for 30 min to obtain meta-aramid composite paper with in-situ biomineralization-dynamic coordination bond synergistic modification.

[0062] The prepared meta-aramid composite paper exhibited a dry tensile strength of 92 MPa and a wet tensile strength of 38 MPa. After heating at 250℃ for 10 min, it showed a 90% repair efficiency for a 2 mm crack. It also demonstrated a 95% inhibition rate against Escherichia coli and a 94% inhibition rate against Staphylococcus aureus. The oxygen index (LOI) was 34%, and the smoke density rating (SDR) was 42. After aging at 200℃ for 100 h, the tensile strength retention rate was 95%. The composite paper achieved optimal synergistic effects in high-temperature stability, self-healing efficiency, antibacterial activity, and low-smoke flame retardant properties.

Claims

1. A self-healing, multifunctional meta-modified aramid composite paper, characterized in that, The meta-modified aramid composite paper is composed of meta-aramid precipitated fibers, bio-based modifiers, in-situ biomineralized hydroxyapatite nanoparticles, and a dynamic coordination bond cross-linking network. The meta-modified aramid composite paper has a multi-level composite structure of "precipitated fibers forming the skeleton - nanoparticles bridging the fibers - dynamic coordination network coating and reinforcement". The dry tensile strength of the meta-modified aramid composite paper is ≥80MPa, the wet tensile strength is ≥30MPa, the repair rate of 1~2mm cracks after heating at 250℃ for 10min is ≥85%, the long-term use temperature is ≥200℃, the antibacterial rate against Escherichia coli and Staphylococcus aureus is ≥90%, the oxygen index (LOI) is ≥32%, and the smoke density rating (SDR) is ≤50.

2. The self-healing multifunctional meta-modified aramid composite paper as described in claim 1, characterized in that, The mass ratio of the meta-aramid precipitated fiber, the bio-based modifier, and the in-situ biomineralized hydroxyapatite nanoparticles is 100:(5~15):(3~10).

3. The self-healing multifunctional meta-modified aramid composite paper as described in claim 2, characterized in that, The in-situ biomineralized hydroxyapatite nanoparticles are generated in situ from a mixed solution of diammonium hydrogen phosphate and calcium nitrate; the molar ratio of diammonium hydrogen phosphate to calcium nitrate is 1.67:1; the total amount of the mixed solution of diammonium hydrogen phosphate and calcium nitrate added is 5% to 8% of the mass of the meta-aramid precipitated fiber.

4. The self-healing multifunctional meta-modified aramid composite paper as described in claim 1, characterized in that, The bio-based modifier is a mixture of aldehyde-modified sodium alginate and amino-modified chitosan; the amount of amino-modified chitosan added is 2% to 4% of the meta-aramid precipitated fiber, and the degree of substitution of the amino-modified chitosan is ≥85%; the amount of aldehyde-modified sodium alginate added is 3% to 5% of the meta-aramid precipitated fiber, and the degree of oxidation of the aldehyde-modified sodium alginate is 20% to 30%.

5. The self-healing multifunctional meta-modified aramid composite paper as described in claim 1, characterized in that, The dynamic coordination bond is COO-Fe³⁺-NH-; the dynamic coordination bond can be reversibly broken and reformed at 250~300℃.

6. The self-healing multifunctional meta-modified aramid composite paper as described in claim 5, characterized in that, The dynamic coordination bond modifier used in the dynamic coordination bond is a Fe³⁺ solution with a concentration of 0.5~1 mmol / L.

7. A method for preparing a self-healing multifunctional meta-modified aramid composite paper as described in any one of claims 1 to 6, characterized in that, Including the following steps: S1. Preparation of pulp suspension: Add meta-aramid precipitated fibers to deionized water and disperse them using a high-speed stirrer to obtain a uniform pulp suspension with a concentration of 0.5wt%~1wt%. S2. Adding and dispersing bio-based modifiers: Add aldehyde-modified sodium alginate and amino-modified chitosan to the pulp suspension, and ultrasonically disperse for 10 minutes to ensure uniform adsorption of the modifiers onto the fiber surface; the amount of amino-modified chitosan added is 2%~4% of the meta-aramid precipitated fiber, and the degree of substitution of the amino-modified chitosan is ≥85%; the amount of aldehyde-modified sodium alginate added is 3%~5% of the meta-aramid precipitated fiber; the degree of oxidation of the aldehyde-modified sodium alginate is 20%~30%. S3. In-situ biomineralization: The pH of the mixed system was adjusted to 7.5-8.0 using a weakly alkaline buffer solution. A mixed solution of diammonium hydrogen phosphate and calcium nitrate was added, and the mixture was stirred at room temperature until completely dispersed and homogeneous, resulting in the in-situ formation of hydroxyapatite nanoparticles. The molar ratio of diammonium hydrogen phosphate to calcium nitrate was 1.67:

1. The total amount of the mixed solution of diammonium hydrogen phosphate and calcium nitrate added was 5%-8% of the mass of the meta-aramid precipitated fiber. S4. Constructing dynamic coordination bonds: Fe³⁺ solution is added dropwise to the system. After the solution is stirred evenly, a dynamic coordination cross-linking network is formed to obtain a composite slurry; the concentration of the Fe³⁺ solution is 0.5~1mmol / L. S5. Papermaking and Drying: The composite pulp is formed into paper, then vacuum dewatered, pressed, and dried to obtain self-healing multifunctional meta-modified aramid composite paper.

8. The method for preparing a self-healing multifunctional meta-modified aramid composite paper as described in claim 7, characterized in that, The mass ratio of the meta-aramid precipitated fiber, the bio-based modifier, and the in-situ biomineralized hydroxyapatite nanoparticles is 100:(5~15):(3~10).

9. The method for preparing a self-healing multifunctional meta-modified aramid composite paper as described in claim 7, characterized in that, The Fe³⁺ forms a -COO-Fe³⁺-NH- dynamic coordination bond with the carboxyl and amino groups in the bio-based modifier; the dynamic coordination bond can be reversibly broken and recombined at 250~300℃.

10. The method for preparing a self-healing multifunctional meta-modified aramid composite paper as described in claim 7, characterized in that, In step S5, the vacuum degree during vacuum dehydration is 0.06~0.08MPa; the pressing pressure is 0.3~0.5MPa; the drying temperature is 120℃; and the drying time is 30min.

11. The application of the self-healing multifunctional meta-modified aramid composite paper according to any one of claims 1 to 6 or the self-healing multifunctional meta-modified aramid composite paper prepared according to any one of claims 7 to 10, characterized in that, It can be used in any of the following fields: aerospace interiors, new energy vehicle battery separator substrates, high-temperature sterilization medical protective paper, and industrial high-temperature bacterial fluid filtration materials.