Polyamide modified aerogel powder and preparation method and application thereof

Abstract

The present application belongs to aerogel technical field, and particularly relates to a kind of polyamide modified aerogel powder and its preparation method and application.The aerogel composite material prepared by the present application is the porous solid material formed by one-dimensional composite fiber of aramid nanofiber and polyaniline and polyimide resin combination.In the aerogel nanocomposite material, polyimide resin is continuous phase, and nanoscale polyaniline coated aramid nanofiber is dispersed phase and reinforcing phase.Each phase in the aerogel composite material maintains its independent characteristics, but takes advantage of each other and produces synergistic effect, so that the comprehensive performance of the composite material is better than each combination phase, thereby meeting the use requirements of polyamide mechanical properties and antistatic performance, and can be widely applied in pipe, plate, grouting equipment parts and grouting bag and other fields.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aerogels, and particularly relates to a polyamide modified aerogel powder and a preparation method and application thereof. BACKGROUND

[0002] Polyamide is a general term for high polymers containing amide groups in the repeating units of the macromolecular chain. Polyamide can be prepared by ring-opening polymerization reaction with lactam as raw material, or by condensation polymerization with diamine and diacid as raw material. The most common polyamide varieties include polyamide 6, polyamide 66, polyamide 12, polyamide 1010, etc. In order to solve the problems of large density and high cost of metal materials, polyamide is applied to injection molding and other industrial products. Polyamide has good comprehensive performance, including mechanical properties, heat resistance, wear resistance, chemical resistance and self-lubricity, low friction coefficient, certain flame retardancy, easy processing, and can expand its application range by adding fibers or carbon nanomaterials. As a kind of thermoplastic industrial plastic, polyamide has good elasticity, self-lubricity, wear resistance, corrosion resistance and easy molding, and is widely used in industry, textile, automobile, machinery manufacturing and other fields. Although the comprehensive performance of polyamide is excellent, due to the easy formation of ammonia bond between amide bond and water molecules, the water absorption of polyamide is large, which causes low dimensional stability, easy deterioration at high temperature, and not ideal strength and modulus, etc. These factors limit the application of polyamide.

[0003] In addition, the antistatic property and fire safety of polyamide products have attracted widespread attention in the application of automobiles, railway transportation equipment, household appliances and other public facilities. It is well known that polyamide material is a kind of insulating material with very poor conductivity, which makes it easy to accumulate static electricity when the air is dry and the environmental humidity is low. When the electric charge accumulates to a certain extent, it will break the air insulation and produce sparks, forming a fire source, thereby causing a fire. At the same time, since polyamide material is composed of carbon, hydrogen, oxygen and nitrogen elements in the form of weak covalent bond. When it is burned by flame to obtain energy, these covalent bonds will be broken to generate free radicals, and the polymer will continue to burn. Therefore, in order to ensure the safety of the material, it is necessary to modify the polymer with flame retardant and antistatic properties, and prepare safe and effective polymer-based antistatic composite materials. In order to expand the application range of polyamide more widely, the modification of polyamide has always been a research hotspot.

[0004] CN120174504A discloses an antistatic modified nylon fiber and its preparation method. In preparing the antistatic modified nylon fiber, halloysite nanotubes are in-situ loaded with silver nanoparticles to obtain pre-modified halloysite nanotubes; chitosan grafted with 9H-carbazole-9-formaldehyde is mixed with the pre-modified halloysite nanotubes and silver nitrate to obtain modified halloysite nanotubes; diethyl (hydroxymethyl) phosphate and carbazole-N-formyl chloride are reacted to obtain a functional monomer; hexamethylenediamine, adipic acid, pyromellitic anhydride, and the functional monomer are reacted to obtain modified polyamide chips; the modified polyamide chips, modified halloysite nanotubes, carbazole, and ferric chloride are mixed, spun, and then grafted with 4-aminomethyl-2,2,6,6-tetramethylpiperidine to obtain the antistatic modified nylon fiber, which has excellent antistatic, antibacterial, flame retardant, and anti-aging properties. CN120462767A relates to the field of packaging bag technology. This packaging bag achieves a balance between flexibility and rigidity through optimized material formulation and manufacturing process, significantly enhancing wear resistance and water resistance, improving aging stability, ensuring performance through precise processing, and reducing potential risks through efficient adhesion and antistatic design. While the aforementioned patented technologies improve the mechanical properties and antistatic capabilities of polyamide composites to some extent, they all rely on simple filler additions to improve the properties of the polyamide resin. The addition of large amounts of inorganic fillers can lead to poor compatibility with polyamide, resulting in reduced mechanical strength and making it difficult to meet application requirements. Summary of the Invention

[0005] To address the issues of low mechanical strength and poor antistatic properties in polyamide materials prepared using existing technologies, this invention provides an aerogel powder for polyamide modification. This aerogel powder improves the aforementioned properties of polyamide, thereby meeting the application requirements of polyamide materials in pipes, sheets, grouting equipment parts, and grouting bags.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0008] (1) Using aramid fiber as raw material, aramid nanofiber solution was prepared by alkaline etching method, and then long-chain alkyl quaternary ammonium salt was added to obtain aramid nanofiber dispersion;

[0009] (2) Add acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After the reaction, a polyaniline-coated aramid nanofiber dispersion is obtained; the mass ratio of aniline monomer to aramid fiber is (0.1-0.6):1.

[0010] (3) Mix the polyamic acid solution with the polyaniline-coated aramid nanofiber dispersion, add a chemical imidizing agent to perform partial imidization; let stand, and then exchange solvent with deionized water to prepare a hydrogel;

[0011] (4) The hydrogel was freeze-dried, thermally imidized, and pulverized to obtain polyamide-modified aerogel powder.

[0012] Polyamide materials alone have low mechanical strength and poor antistatic properties. Current technologies generally improve the mechanical properties and antistatic capabilities of polyamide composites by adding reinforcing fillers and conductive substances respectively.

[0013] The most common reinforcing fillers for polyamides are various organic or inorganic fiber materials. Aramid nanofibers, as nanoscale products of aramid fibers, possess high aspect ratios, large specific surface areas, and good dispersibility. Compared to aramid fibers, aramid nanofibers retain the high mechanical properties and excellent thermal stability of aramid fibers. Furthermore, due to their unique nanoscale structure, they can serve as nanobuilding units, introduced into nanomaterial preparation methods for bottom-up assembly of advanced structures. In previous work, the inventors used aramid nanofiber / inorganic filler blends to prepare various forms of aerogel materials (CN118878287A, CN118851649A, CN118812184A, CN118702437A) to enhance the stability of concrete. However, aramid nanofiber / inorganic filler aerogels are only suitable for modifying inorganic materials such as concrete. When directly applied to organic polymer materials such as polyamides, they are difficult to disperse uniformly in polyamides, easily causing stress concentration problems, which may actually reduce the performance of the composite material.

[0014] To improve the antistatic properties of polyamide resins, conductive fillers are generally added. Conductive materials can include conductive carbon black, carbon fibers, carbon nanotubes, graphite, conductive polymers, metal powders, and various conductive metal oxides and salts. Composite conductive polyamide resins combine the processing characteristics of polymer materials with the conductivity of metals. Compared to metals, composite conductive polyamide resins offer advantages such as good processability, simple processing, corrosion resistance, a wide adjustable resistivity range, and low cost. Currently, the conductive materials added to composite conductive polyamide resins fall into two categories: small-molecule antistatic agents and conductive fillers. Adding antistatic agents is the most common antistatic method for polymer materials. These agents form a conductive layer on the material surface, reducing surface resistivity and allowing static charges to dissipate quickly; they also impart a certain degree of lubrication to the material surface, reducing the coefficient of friction and inhibiting and reducing the generation of static charges. However, the reduction in resistivity from adding small-molecule antistatic agents is limited, their durability is poor, and they can reduce the mechanical properties of the composite material. Therefore, current composite polyamide resin materials primarily rely on the addition of conductive fillers. Polyaniline, a common conductive polymer, can improve the antistatic properties of polyamide resins to some extent when added. In previous work, the inventors used polypyrrole-coated aramid nanofibers as a reinforcing phase for polyimide aerogels; however, polypyrrole's poor thermal stability made it difficult to meet the high-temperature processing requirements of polyamides. Compared to conductive polymers like polypyrrole, polyaniline has higher thermal stability, which meets the processing requirements of polyamide resins.

[0015] However, the addition of large amounts of reinforcing fillers and conductive materials can lead to reduced processing performance and poor component compatibility in composite materials, making it difficult to simultaneously improve mechanical properties and antistatic capabilities. To address this issue, this invention creatively prepares a polyaniline-coated aramid nanofiber-polyimide aerogel composite material. Using aerogel as the addition method for polyamide modification solves the problem of poor compatibility associated with conventional fillers. Aerogels possess abundant porous structures; by adding the modifying material to polyamide in aerogel form, the high porosity or interpenetrating network structure of the aerogel material allows the polyamide melt to be adsorbed into its porous structure through physical interactions such as capillary forces, surface tension, and hydrogen bonds. This enhances the interaction between the filler and the polyamide, thereby improving the compatibility between the materials.

[0016] Using polyaniline-coated aramid nanofibers as a reinforcing and conductive material can significantly improve the mechanical strength and antistatic properties of polyamide composites. However, directly adding aramid nanofibers as nanoscale fillers not only easily causes compatibility issues with polyimide or polyamide, but also, due to the numerous surface defects and strong interactions of aramid nanofibers, they are prone to agglomeration during processing, losing their nanoscale size and reducing their modifying effect. Coating aramid nanofibers with polyaniline not only improves the fiber dispersion properties but also enhances the compatibility between the aramid nanofibers and the aerogel matrix, i.e., the polyimide resin, through the coating effect. This allows the aramid nanofibers to be uniformly dispersed in the polyimide precursor, forming a polyimide aerogel material with the coated aramid nanofibers as the reinforcing skeleton. Conversely, aramid nanofibers, as the core matrix of polyaniline, can also promote the dispersion of polyaniline, enabling it to form a network structure, which is beneficial for the formation of conductive pathways. With less polyaniline, the conductivity of polyimide aerogels and polyamide composites can be significantly improved, avoiding the technical problem of reduced mechanical properties caused by adding large amounts of polyaniline.

[0017] The reason polyimide was chosen as the matrix resin for the aerogel in this invention is twofold. Firstly, polyamic acid, the precursor of polyimide, has good solubility and is easy to process. Secondly, the polyimide formed after imidization has high mechanical strength and a high melting point, which meets the processing requirements of polyamide materials. Specifically, during melt processing, the polyamide melt exhibits high fluidity, and the porous aerogel powder is uniformly dispersed within the polyamide melt, facilitating thorough wetting of the melt, increasing the interfacial force between the aerogel powder and the polyamide resin, and improving the mechanical properties of the polyamide composite material. Furthermore, polyamide and polyimide have similar structures, and the polyimide-based aerogel has good compatibility with the polyamide resin, which is beneficial for the wetting of the polyamide melt.

[0018] Overall, the aerogel composite material prepared by this invention is a porous solid material formed by combining aramid nanofibers and polyaniline into a one-dimensional composite fiber with polyimide resin. In the aerogel nanocomposite material, the polyimide resin is the continuous phase, referred to as the matrix, while the nanoscale polyaniline-coated aramid nanofibers are the dispersed and reinforcing phases. The dispersed and reinforcing phases are distributed independently in the polyimide resin matrix. Due to the presence of the polyaniline coating layer, there is a high interfacial force between the fibers and the polyimide resin. At the same time, each phase in the aerogel composite material retains some independent properties, but they complement each other, producing a synergistic effect, making the overall performance of the composite material superior to that of each combined phase, thus meeting the requirements for the mechanical and antistatic properties of polyamide. In addition, in this aerogel structure, the polyimide, as the matrix resin, forms a bonding structure with the polyaniline, further improving the thermal stability of the polyaniline and facilitating the melt processing of the polyamide resin. By combining aerogel powder with different polyamide resins, the synergistic effect between the different components at the molecular level in the composite material forms a resin composite with novel structure and function. This resin composite exhibits synergistic benefits: the properties of the matrix and reinforcement are superimposed and complementary; its properties are designable, and the performance of the composite can be controlled by adjusting the components, structure, and process. The emergence of this aerogel material structure integrates the properties of different materials, resulting in a polyamide resin composite with high strength and antistatic properties.

[0019] Furthermore, the specific process of step (1) is as follows: aramid fibers are placed in a reaction vessel containing alkali and dimethyl sulfoxide to prepare aramid nanofibers, and then long-chain alkyl quaternary ammonium salts are added to obtain aramid nanofiber dispersion.

[0020] Furthermore, in step (1), the alkali is sodium hydroxide or potassium hydroxide.

[0021] Furthermore, in step (1), the ratio of aramid fiber, alkali, and dimethyl sulfoxide is 1g:(1-2)g:(350-500)ml. Specifically, the preparation of aramid nanofibers involves stirring in a reactor at room temperature for 4-8 days. Furthermore, commercially available aramid fiber is used. During the preparation of commercial aramid fiber, various greases generally remain on the fiber surface, which can be removed by cleaning. Specifically, acetone solvent, sodium dodecylbenzenesulfonate solution, and deionized water can be used sequentially to remove grease and other impurities from the fiber surface.

[0022] Furthermore, in step (1), the long-chain alkyl quaternary ammonium salt is at least one of dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, and octadecyltrimethylammonium chloride. In particular, hexadecyltrimethylammonium bromide can be selected. By adding the long-chain alkyl quaternary ammonium salt to the aramid nanofiber dispersion in advance, the dispersibility of the aramid nanofiber can be improved, and it can act as a template. This is because the aramid nanofiber prepared by the alkali / DMSO soaking method has a large number of reactive oxygen-containing functional groups such as carboxyl groups and hydroxyl groups on its surface, which are electronegative. Although it has a large aspect ratio and excellent mechanical properties, the mixed solution after soaking is extremely unstable. When new polar substances (acids, aniline monomers, initiators, etc.) are added, the equilibrium of the solution will be disrupted, leading to the merging of fiber bundles and fiber agglomeration, which affects the dispersion of aramid nanofiber. As a cationic surface modifier, long-chain alkyl quaternary ammonium salts possess excellent surface modification capabilities. The presence of ammonium ions facilitates their binding with aramid nanofibers, improving their dispersibility. Simultaneously, the long-chain alkyl quaternary ammonium salts, with their relatively long alkyl chains, can improve the hydrophilic / hydrophobic properties of the aramid nanofiber surface, promoting the adhesion of aniline monomers and forming a coating structure through in-situ polymerization. Furthermore, the presence of long-chain alkyl groups can hinder fiber aggregation and promote fiber dispersion. In previous work, the inventors corroded aramid fibers with a 1wt% sodium hydroxide aqueous solution for several hours, then directly polymerized conductive monomers on their surface to prepare polymer-coated aramid fibers. The main morphology of the aramid fibers in this structure remained unchanged; it was not a nanostructure, only the fiber surface was corroded. Although the thicker fibers did not agglomerate, and this process did not require the addition of long-chain alkyl quaternary ammonium salts, the relatively large fiber diameter prevented its application in modification fields such as polyamides, limiting its suitability to reinforcement applications in inorganic materials such as concrete and cement paste.

[0023] Furthermore, the mass ratio of the long-chain alkyl quaternary ammonium salt to the aramid fiber is (0.1-0.5):1. Specifically, it can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, or 0.5:1; particularly, it is (0.2-0.4):1. An appropriate amount of long-chain alkyl quaternary ammonium salt can not only fully disperse the aramid nanofibers and serve as a template for aniline polymerization, but also avoid excessive long-chain alkyl quaternary ammonium salt leading to entanglement between the long chains of the salt itself.

[0024] Furthermore, in step (2), the acid is one or more of formic acid, acetic acid, hydrochloric acid, sulfuric acid, and nitric acid. The molar ratio of the acid to the alkali in step (1) is (0.5-2):1, and more specifically, (1-2):1. In particular, concentrated hydrochloric acid, concentrated sulfuric acid, and concentrated nitric acid can be selected. Even further, high-concentration concentrated nitric acid can be selected. Furthermore, in step (2), the initiator is at least one of ammonium persulfate, potassium persulfate, ferric chloride, azobisisobutyronitrile, and benzoyl peroxide. In particular, ferric chloride with doping effect can be selected. Since the aramid nanofibers are modified with long-chain alkyl quaternary ammonium salts, the addition of polar compounds such as acids, aniline monomers, and initiators will not lead to the merging of fiber bundles; at the same time, the formation of polar compounds can play an ionic cross-linking role, which is beneficial to the formation of hydrogel structures. If polar compounds such as acids, aniline monomers, or initiators are added first, and then long-chain alkyl quaternary ammonium salts are added, not only will the fiber bundles merge, but the long-chain alkyl quaternary ammonium salts will also fail to adsorb onto the fiber surface, lose their template function, and fail to form the polyaniline coating structure.

[0025] Furthermore, in step (2), the reaction temperature is 0-30℃ and the reaction time is 8-12h.

[0026] Furthermore, in step (2), the mass ratio of the initiator to the aniline monomer is (1-5):1.

[0027] Furthermore, in step (3), the polyamic acid solution is prepared using dianhydride and diamine as raw materials in an organic solvent.

[0028] Furthermore, in step (3), the molar ratio of dianhydride monomer to diamine monomer is (1-1.04):1.

[0029] Furthermore, the temperature for preparing polyamic acid in step (3) is 25-35℃ and the time is 6-12h.

[0030] Furthermore, in step (3), the mass ratio of the sum of the dianhydride monomers and diamine monomers to the mass of the aramid fiber is (1-5):1. Specifically, it can be any value among 1:1, 2:1, 3:1, 4:1, and 5:1. Further, the mass ratio of the sum of the dianhydride monomers and diamine monomers to the mass of the aramid fiber is (2-3):1. Polyimide, as the matrix resin of the aerogel, plays a binding role; at the same time, the amount of polyimide used should not be excessive, otherwise it will easily lead to a decrease in the porosity of the aerogel, which is not conducive to the wetting of the polyamide melt.

[0031] Furthermore, in step (3), the imidizing agent is a mixture of acetic anhydride and pyridine in a molar ratio of (1-3):1, and the mass of the mixture is 1-4 times the sum of the masses of the dianhydride monomer and the diamine monomer; specifically, the mass of the mixture is 2-3 times the sum of the masses of the dianhydride monomer and the diamine monomer, as a larger amount of chemical imidizing agent can better promote the imidization process; specifically, the degree of partial imidization of polyamic acid can be 20%-60%. Furthermore, the partial imidization time is 2-5 hours. The partial chemical imidization process can not only promote the formation of the gel structure, but also effectively reduce the temperature of thermal imidization, preventing high temperature from damaging the coating structure.

[0032] Further, in step (3), the diamine monomer is p-phenylenediamine, 2-trifluoromethyl-1,4-diaminobenzene, 5-methyl-1,3-diaminobenzene, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4'-diamino-3,3'-bis(trifluoromethyl)diphenylmethane, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenylmethane, etc. One or more of diphenyl sulfone, 4,4'-bis(4-aminophenoxy)benzene, 4,4'-bis(3-aminophenoxy)benzene, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3'-bis(trifluoromethyl)biphenyl or 4,4'-bis(4-aminophenoxy)biphenyl.

[0033] Further, in step (3), the dianhydride monomer is pyromellitic dianhydride, oxydiphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, diphenyl sulfone-3,4,3',4'-tetracarboxylic dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2'-bis(3,4) One or more of the following: (-dicarboxylic acid) hexafluoropropane dianhydride, m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)phenyl dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride.

[0034] Furthermore, the organic solvent in step (3) is one or more of N,N-dimethylacetamide, acetone, acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0035] Furthermore, in step (4), the thermal imidization temperature is 150-200℃ and the time is 2-6h.

[0036] Furthermore, the present invention also provides a polyamide-modified aerogel powder and its application in the preparation of high-strength pipes, plates, grouting equipment parts and grouting bags.

[0037] On the other hand, the present invention provides a polyamide composite material comprising the following components in parts by weight: 50-150 parts of polyamide resin, 1-30 parts of the aforementioned polyamide-modified aerogel powder, 1-10 parts of fiber-reinforcing filler, and 1-5 parts of processing aids. Specifically, the composite material can be granulated using an extruder at an extrusion temperature of 200-280°C, particularly 220-260°C. This high-temperature melt processing not only further improves the polyimide structure but also facilitates the full wetting of the aerogel by the polyamide melt. The type of polyamide resin is not particularly limited; commonly used polyamides in the art, such as polyamide 6, polyamide 66, polyamide 610, and polyamide 12, are all acceptable. Furthermore, the polyamide composite material may also include glass fibers, carbon fibers, flame retardants, lubricants, flow modifiers, colorants, anti-aging agents, antioxidants, anti-hydrolysis agents, coupling agents, and other additives. In particular, conductive fibrous fillers may be added to promote the formation of a conductive network.

[0038] The raw materials used in this invention are all common types that can be prepared in-house or purchased and recycled. For example, aramid fibers can be selected from DuPont K-series fibers, polyamide 6 can be selected from Xinhui Meda M-series polyamide 6, carbon fibers can be selected from Toray T-series carbon fibers, antioxidants can be selected from Xindongyi Chemical 1010 series, coupling agents can be selected from Hairui New Materials KH570 series, etc. In particular, this invention uses recycled amide 6 as a base material to save costs.

[0039] This aerogel powder is a porous solid material formed by combining aramid nanofibers and polyaniline into a one-dimensional composite fiber with polyimide resin. By combining the aerogel powder with different polyamide resin materials, the synergistic effect between the different components at the molecular level in the composite material results in a resin composite material with novel structure and function.

[0040] Beneficial effects

[0041] (1) Adding long-chain alkyl quaternary ammonium salts to the aramid nanofiber dispersion in advance can improve the dispersibility of aramid nanofibers and act as a template. Long-chain alkyl quaternary ammonium salts have good surface modification functions and can combine with aramid nanofibers to improve their dispersibility; long-chain alkyl quaternary ammonium salts have long alkyl chains, which can improve the hydrophilic and hydrophobic properties of the aramid nanofiber surface, which is conducive to the adhesion of aniline monomers and the formation of a coating structure through in-situ polymerization; in addition, the presence of long-chain alkyl groups can hinder the merging between fibers.

[0042] (2) Using polyaniline-coated aramid nanofibers as a reinforcing and conductive material can greatly improve the mechanical strength and antistatic properties of polyamide composites.

[0043] (3) Polyamic acid, the precursor of polyimide, has good solubility and is easy to process; the polyimide formed after imidization has high mechanical strength and high melting point, which can meet the processing requirements of polyamide materials, facilitate the full wetting of polyamide melt, improve the interfacial force between aerogel powder and polyamide resin, and improve the mechanical properties of polyamide composite materials.

[0044] (4) The aerogel composite material prepared by this invention is a porous solid material formed by combining aramid nanofibers and polyaniline into a one-dimensional composite fiber and then bonding it with polyimide resin. In the aerogel nanocomposite material, the polyimide resin is the continuous phase, and the nanoscale polyaniline-coated aramid nanofibers are the dispersed and reinforcing phases. Each phase in the aerogel composite material retains some independent properties, but they complement each other and produce a synergistic effect, making the overall performance of the composite material superior to that of each combined phase, thereby meeting the requirements for the mechanical and antistatic properties of polyamide. Attached Figure Description

[0045] Figure 1 This is a transmission electron microscope image of the polyaniline-coated aramid nanofibers prepared in Example 10.

[0046] Figure 2 Transmission electron microscopy (TEM) image of the modified aramid nanofibers prepared for Comparative Example 1. Detailed Implementation

[0047] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The raw materials used in the embodiments are all commercially available or prepared by conventional methods.

[0048] Unless otherwise specified, the raw materials and specific process steps used in the following examples and comparative examples are the same. The aramid fiber used in this invention is DuPont Kevlar fiber after cleaning and degreasing. The cleaning process involves first ultrasonically treating the aramid fiber in an acetone solution, then cleaning it with deionized water; next, ultrasonically treating it again with a 5wt% sodium dodecyl sulfonate aqueous solution; finally, repeatedly rinsing with flowing deionized water to remove the grease from the surface of the aramid fiber.

[0049] Performance Testing: A polyamide 6 composite material comprises the following components in parts by weight: 105 parts polyamide 6 resin, 20 parts polyamide-modified aerogel powder (prepared in Examples 1-10 and Comparative Examples 1-2, respectively), 4 parts carbon fiber, 2 parts antioxidant 1010, and 2 parts zinc stearate lubricant. The above components are added to a twin-screw extruder and melt-extruded into granules (extruder temperature 230°C). Standard samples are then prepared, and their mechanical and antistatic properties are tested. Tensile strength is measured according to ISO 527-2, flexural strength according to ISO 178, and the volume resistivity of the samples is measured using a ohmmeter.

[0050] Example 1

[0051] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0052] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 7 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.35:1.

[0053] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 11 h, a polyaniline-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of aniline monomer to aramid fiber is 0.5:1. The mass ratio of initiator to aniline monomer is 3.1:1.

[0054] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 9 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The mass ratio of the sum of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 2.4:1. The dianhydride monomer was a mixture of pyromellitic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride in a molar ratio of 1:3. The diamine monomer was 4,4'-diaminodiphenyl sulfone. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 2.1 times the mass of the sum of the dianhydride monomer and the diamine monomer.

[0055] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 91.6 MPa, a flexural strength of 113.1 MPa, and a volume resistivity of 2.1 × 10⁻⁶ MPa. 6 Ω·m.

[0056] Example 2

[0057] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0058] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 5.5 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.35:1.

[0059] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 8 hours, a polyaniline-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of aniline monomer to aramid fiber is 0.45:1. The mass ratio of initiator to aniline monomer is 3.4:1.

[0060] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8.5 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The mass ratio of the sum of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 2.2:1. The dianhydride monomer was 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride. The diamine monomer was a mixture of 4,4'-diaminodiphenylmethane and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 1.6 times the mass of the sum of the dianhydride monomer and the diamine monomer.

[0061] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 89.8 MPa, a flexural strength of 108.5 MPa, and a volume resistivity of 3.7 × 10⁻⁶. 6 Ω·m.

[0062] Example 3

[0063] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0064] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 5.5 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1 g: 1.2 g: 460 ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.5: 1.

[0065] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 10 h, a polyaniline-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of aniline monomer to aramid fiber is 0.4:1; the mass ratio of initiator to aniline monomer is 2.8:1;

[0066] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The ratio of the sum of the masses of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 2:1. The dianhydride monomer was 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The diamine monomer was a mixture of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 2.1 times the sum of the masses of the dianhydride monomer and the diamine monomer.

[0067] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 87.6 MPa, a flexural strength of 105.4 MPa, and a volume resistivity of 3.1 × 10⁻⁶. 7 Ω·m.

[0068] Example 4

[0069] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0070] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 8 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.15:1.

[0071] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 9 hours, a polyaniline-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of aniline monomer to aramid fiber is 0.3:1. The mass ratio of initiator to aniline monomer is 2.7:1.

[0072] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 9 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The mass ratio of the sum of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 1.7:1. The dianhydride monomer was a mixture of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride in a molar ratio of 4:1. The diamine monomer was 3,3'-diaminobenzophenone. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 1.9 times the mass of the sum of the dianhydride monomer and the diamine monomer.

[0073] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 93.1 MPa, a flexural strength of 114.5 MPa, and a volume resistivity of 6.2 × 10⁻⁶. 6 Ω·m.

[0074] Example 5

[0075] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0076] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 5.5 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.25:1.

[0077] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 10 h, a polyaniline-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of aniline monomer to aramid fiber is 0.4:1; the mass ratio of initiator to aniline monomer is 2.8:1;

[0078] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The ratio of the sum of the masses of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 1:1. The dianhydride monomer was 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The diamine monomer was a mixture of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 2.1 times the sum of the masses of the dianhydride monomer and the diamine monomer.

[0079] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 86.1 MPa, a flexural strength of 103.8 MPa, and a volume resistivity of 9.5 × 10⁻⁶. 6 Ω·m.

[0080] Example 6

[0081] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0082] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 5 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.2:1.

[0083] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 10 h, a polyaniline-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of aniline monomer to aramid fiber is 0.4:1. The mass ratio of initiator to aniline monomer is 3:1.

[0084] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 7 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The mass ratio of the sum of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 1.9:1. The dianhydride monomer was 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The diamine monomer was a mixture of 4,4'-diaminobenzophenone and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 1.7 times the mass of the sum of the dianhydride monomer and the diamine monomer.

[0085] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 95.3 MPa, a flexural strength of 114.2 MPa, and a volume resistivity of 3.9 × 10⁻⁶. 7 Ω·m.

[0086] Example 7

[0087] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0088] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 5.5 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.25:1.

[0089] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 10 h, a polyaniline-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of aniline monomer to aramid fiber is 0.4:1; the mass ratio of initiator to aniline monomer is 2.8:1;

[0090] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The ratio of the sum of the masses of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 5:1. The dianhydride monomer was 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The diamine monomer was a mixture of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 2.1 times the sum of the masses of the dianhydride monomer and the diamine monomer.

[0091] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 90.2 MPa, a flexural strength of 109.8 MPa, and a volume resistivity of 3.8 × 10⁻⁶. 7 Ω·m.

[0092] Example 8

[0093] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0094] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 4 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.1:1.

[0095] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 8 hours, a polyaniline-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of aniline monomer to aramid fiber is 0.1:1. The mass ratio of initiator to aniline monomer is 2.3:1.

[0096] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 6 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The mass ratio of the sum of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 1.5:1. The dianhydride monomer was a mixture of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride in a molar ratio of 1:2. The diamine monomer was 4,4'-diaminodiphenylmethane. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 1.6 times the mass of the sum of the dianhydride monomer and the diamine monomer.

[0097] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 81.2 MPa, a flexural strength of 102.3 MPa, and a volume resistivity of 7.6 × 10⁻⁶. 7 Ω·m.

[0098] Example 9

[0099] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0100] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 8 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1 g: 1.2 g: 460 ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.4: 1.

[0101] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 12 h, a polyaniline-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of aniline monomer to aramid fiber is 0.6:1; the mass ratio of initiator to aniline monomer is 3.1:1;

[0102] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 10 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added to react for 3.5 h for partial imidization. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The mass ratio of the sum of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 2.8:1. The dianhydride monomer was 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The diamine monomer was a mixture of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenylmethane in a molar ratio of 1:1. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was twice the sum of the masses of the dianhydride monomer and the diamine monomer.

[0103] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 94.2 MPa, a flexural strength of 111.5 MPa, and a volume resistivity of 1.0 × 10⁻⁶ MPa. 6 Ω·m.

[0104] Example 10

[0105] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0106] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 5.5 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.25:1.

[0107] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 10 h, a polyaniline-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of aniline monomer to aramid fiber is 0.4:1; the mass ratio of initiator to aniline monomer is 2.8:1;

[0108] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The ratio of the sum of the masses of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 2:1. The dianhydride monomer was 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The diamine monomer was a mixture of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 2.1 times the sum of the masses of the dianhydride monomer and the diamine monomer.

[0109] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 97.8 MPa, a flexural strength of 117.2 MPa, and a volume resistivity of 1.3 × 10⁻⁶. 6 Ω·m.

[0110] Comparative Example 1

[0111] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0112] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 5.5 days to prepare an aramid nanofiber dispersion; the alkali was potassium hydroxide; the ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml;

[0113] (2) First, concentrated nitric acid is added to the aramid nanofiber dispersion, and then long-chain alkyl quaternary ammonium salt hexadecyltrimethylammonium bromide, aniline monomer and initiator are added to the dispersion in sequence. After reacting at 20°C for 10 h, a modified aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of aniline monomer to aramid fiber is 0.4:1. The mass ratio of initiator to aniline monomer is 2.8:1. The mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.25:1.

[0114] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 h to obtain a polyamic acid solution. Then, the solution was mixed with the modified aramid nanofiber dispersion and a chemical imidizing agent was added and reacted for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The ratio of the sum of the masses of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 2:1. The dianhydride monomer was 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The diamine monomer was a mixture of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 2.1 times the sum of the masses of the dianhydride monomer and the diamine monomer.

[0115] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 67.5 MPa, a flexural strength of 83.3 MPa, and a volume resistivity of 3.9 × 10⁻⁶. 9 Ω·m.

[0116] Comparative Example 2

[0117] A method for preparing polyamide-modified aerogel powder includes the following steps:

[0118] (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 5.5 days to prepare aramid nanofibers. Then, a long-chain alkyl quaternary ammonium salt, hexadecyltrimethylammonium bromide, was added and stirred evenly to obtain an aramid nanofiber dispersion. The alkali was potassium hydroxide. The ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.2g:460ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.25:1.

[0119] (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add aniline monomer and initiator to the dispersion. After reacting at 20°C for 10 h, a polyaniline-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of aniline monomer to aramid fiber is 1:1. The mass ratio of initiator to aniline monomer is 2.8:1.

[0120] (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 h to obtain a polyamic acid solution. Then, the solution was mixed with the polyaniline-coated aramid nanofiber dispersion and a chemical imidizing agent was added for 3.5 h to partially imidize the solution. After standing, the solution was exchanged with deionized water to prepare a hydrogel. The molar ratio of the dianhydride monomer to the diamine monomer was 1.02:1. The ratio of the sum of the masses of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber was 2:1. The dianhydride monomer was 3,3',4,4'-benzophenone tetracarboxylic dianhydride. The diamine monomer was a mixture of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1. The imidizing agent was a mixture of acetic anhydride and pyridine in a molar ratio of 2:1. The mass of the mixture was 2.1 times the sum of the masses of the dianhydride monomer and the diamine monomer.

[0121] (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 170℃ / 1h and 200℃ / 2h. After pulverization, aerogel powder for polyamide modification was obtained. The corresponding polyamide composite material was tested and found to have a tensile strength of 72.5 MPa, a flexural strength of 88.3 MPa, and a volume resistivity of 8.8 × 10⁻⁶. 6 Ω·m.

[0122] Figure 1 This is a transmission electron microscope image of the polyaniline-coated aramid nanofibers prepared in Example 10. Figure 2 The image shown is a transmission electron microscope (TEM) image of the modified aramid nanofibers prepared in Comparative Example 1. The test samples were prepared by repeatedly ultrasonically washing and filtering the corresponding polyaniline-coated aramid nanofibers and modified aramid nanofibers with deionized water before testing. Figure 1 As can be seen, a distinct polyaniline coating structure forms on the surface of the aramid nanofibers, and the coating structure is relatively uniform, which promotes the dispersion of aramid nanofibers in polyimide resin and is beneficial for constructing fiber-reinforced networks and conductive networks. Figure 2 As can be seen, no coating structure was formed on the surface of the aramid nanofibers. This indicates that adding long-chain alkyl quaternary ammonium salts to the aramid nanofiber dispersion in advance can improve the dispersibility of the aramid nanofibers and act as a template, which is conducive to the formation of polyaniline coating structures. However, adding polar substances such as acids, aniline monomers, and initiators in advance will disrupt the solution equilibrium, affect the surface modification function of the long-chain alkyl quaternary ammonium salts, and hinder the adhesion of aniline monomers to the fiber surface, thus preventing in-situ polymerization to form a coating structure.

[0123] As can be seen from the above figures and data, the composite material of aerogel and polyamide resin exhibits synergistic effects at the molecular level, resulting in a resin composite material with novel structure and function. This aerogel material combines the properties of different materials, yielding a polyamide resin composite material with high strength and antistatic properties. Specifically, compared to Example 10, Comparative Example 1 did not add hexadecyltrimethylammonium bromide beforehand, which failed to act as a dispersant and template, thus failing to form a coating structure. This affected the dispersion of aramid nanofibers and hindered the formation of reinforcing and conductive networks, resulting in reduced mechanical properties and conductivity of the prepared polyamide composite material. Furthermore, compared to Example 10, Comparative Example 2 added excessive amounts of polyaniline, which did not further improve conductivity but instead caused a significant decrease in mechanical properties. This is because polyaniline, as a conductive polymer, has low mechanical strength. When its dosage is too high, it can easily cause excessive coating of polyaniline, which is not only detrimental to the dispersion of fibers and the formation of conductive pathways, but also affects the improvement of the mechanical properties of polyimide-based aerogel powder. It can easily lead to cracking during the melt processing of polyamide, resulting in a decrease in the strength and toughness of polyamide composite materials.

[0124] The above embodiments are not intended to limit the content of the composition of the present invention. Any minor modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention or the composition or content of the composition shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for producing an aerogel powder for polyamide modification, characterized by, The method comprises the following steps: (1) using aramid fiber as raw material, alkali etching method is used to prepare aramid nanofiber solution, then long chain alkyl quaternary ammonium salt is added to obtain aramid nanofiber dispersion liquid; (2) adding acid to the aramid nanofiber dispersion liquid, then adding aniline monomer and initiator to the dispersion liquid, and obtaining poly aniline coated aramid nanofiber dispersion liquid after reaction; the mass ratio of aniline monomer to aramid fiber is (0.1-0.6):1; (3) mixing polyamide acid solution and poly aniline coated aramid nanofiber dispersion liquid, adding chemical imidization reagent for partial imidization; standing, then solvent exchanging with deionized water to prepare hydrogel; (4) freezing drying, thermal imidization, and crushing the hydrogel to obtain polyamide modified aerogel powder.

2. The method for preparing a polyamide-modifying aerogel powder according to claim 1, characterized by, The long chain alkyl quaternary ammonium salt in step (1) is at least one of dodecyl trimethyl ammonium bromide, dodecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium chloride, octadecyl trimethyl ammonium bromide, and octadecyl trimethyl ammonium chloride.

3. The method for preparing polyamide-modified aerogel powder as described in claim 1, characterized in that, The mass ratio of long chain alkyl quaternary ammonium salt to aramid fiber in step (1) is (0.1-0.5):

1.

4. The method for preparing polyamide-modified aerogel powder as described in claim 1, characterized in that, The polyamide acid in step (3) is prepared by polymerization of dianhydride monomer and diamine monomer; the dianhydride monomer is one or more of pyromellitic dianhydride, oxydiphthalic anhydride, 3,3',4,4'-diphenyltetracarboxylic dianhydride, 2,3,3',4'-diphenyltetracarboxylic dianhydride, diphenyl sulfone-3,4,3',4'-tetracarboxylic dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, m-triphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-triphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis-[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, and 1,4,5,8-naphthalene tetracarboxylic dianhydride.

5. The method for preparing polyamide-modified aerogel powder as described in claim 1, characterized in that, The polyamide acid in the step (3) is prepared by polymerization of dianhydride monomers and diamine monomers; the diamine monomers are one or more of p-phenylenediamine, 2-trifluoromethyl-1,4-diaminobenzene, 5-methyl-1,3-diaminobenzene, 4,4'-oxydianiline, 4,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4'-diamino-3,3'-bis(trifluoromethyl)diphenylmethane, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenylsulfone, 4,4'-bis(4-aminophenoxy)benzene, 4,4'-bis(3-aminophenoxy)benzene, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3'-bis(trifluoromethyl)biphenyl, or 4,4'-bis(4-aminophenoxy)biphenyl.

6. The method for preparing aerogel powder for polyamide modification as described in claim 1, characterized in that, The imidization reagent in the step (3) is a mixture of acetic anhydride and pyridine in a molar ratio of (1-3):

1.

7. The method for preparing polyamide-modified aerogel powder according to claim 1, characterized in that, The thermal imidization temperature in the step (4) is 150-200°C, and the time is 2-6h.

8. An aerogel powder for polyamide modification, characterized by, A polyamide modified aerogel powder prepared by the method of any one of claims 1-7.

9. Use of the polyamide modified aerogel powder of claim 8 in the preparation of pipes, plates, grouting equipment parts, and grouting bags.

10. A polyamide composite, characterized in that, The polyamide modified aerogel powder of claim 8 is used in the preparation of pipes, plates, grouting equipment parts, and grouting bags. The polyamide modified aerogel powder of claim 8 is used in the preparation of pipes, plates, grouting equipment parts, and grouting bags.

Images