Aerogel powder for polyolefin modification and preparation method and application thereof

Abstract

The invention belongs to the technical field of gel materials, and particularly relates to aerogel powder for polyolefin modification and a preparation method and application thereof. The preparation method of the aerogel powder comprises the following steps: (1) preparing aramid nanofiber dispersion liquid; (2) preparing a polypyrrole coated aramid nanofiber dispersion liquid; (3) mixing polyamide acid and the polypyrrole coated aramid nanofiber dispersion liquid, and then carrying out partial imidization and solvent exchange to prepare hydrogel; and (4) carrying out freeze drying, thermal imidization and crushing to obtain the aerogel powder for polyolefin modification. The aerogel powder is a porous solid material formed by forming one-dimensional composite fibers from aramid nanofibers and polypyrrole and combining the one-dimensional composite fibers with polyimide resin. The aerogel powder and polyolefin resin are compounded to obtain the polyolefin resin composite material with high strength and antistatic property, and the polyolefin resin composite material can be widely applied to the fields of pipes, plates, grouting equipment parts, grouting bags and the like.

Description

Technical Field

[0001] This invention belongs to the field of gel materials technology, specifically relating to an aerogel powder for polyolefin modification, its preparation method, and its application. Background Technology

[0002] Polyolefin resin is not a single type of resin, but a general term for thermoplastic resins such as polypropylene, polyethylene, EPDM rubber, and polyolefin elastomers. Among all polyolefin materials, polypropylene and polyethylene are the most widely used, and they share many similarities in properties and applications. Polypropylene and polyethylene are among the lowest density plastics available, with a milky-white appearance, and are non-toxic, odorless, and general-purpose thermoplastics. Furthermore, polyolefin resins such as polypropylene and polyethylene have excellent chemical resistance, are easy to process and mold, and can be used in various methods such as extrusion, injection molding, blow molding, and thermoforming. However, due to the relatively large shrinkage rate of molded products, the surface of the products is prone to warping and deformation, making it difficult to achieve high dimensional accuracy. They also exhibit poor toughness and poor aging resistance at lower temperatures. Polyolefin resins generally have strong crystallinity and regular structure, thus exhibiting excellent mechanical strength and thermal stability. In addition, polyolefin resins have good rigidity and hardness, as well as excellent wear resistance and flexural fatigue resistance. The impact strength of their products decreases with increasing crystallinity. Generally, the initial properties of polyolefin resins are related to the ambient temperature and the rate of loading. When the ambient temperature is higher than the glass transition temperature of a material, the material mostly undergoes ductile fracture; when the temperature is lower than the glass transition temperature, the material mostly undergoes brittle fracture, and the impact strength value will decrease significantly. Polyolefin resins have low surface energy, which makes them less permeable to air and water vapor, and less hygroscopic, resulting in better electrical insulation properties, weaker intermolecular forces, and stronger impact resistance.

[0003] However, polyolefin resin products also have performance defects: for example, compared with some engineering plastics such as polyamide, they have lower tensile strength and lower hardness; compared with rubber products, their molding shrinkage rate is larger, which easily causes warping and bending, and obvious brittle fracture at lower temperatures; their antistatic properties are poor, which easily leads to static damage. In order to further expand the application fields of polyolefin resin products, many researchers have modified polyolefin resins to address their shortcomings. CN120040874A discloses a polypropylene composition. The polypropylene composition includes polypropylene: 100 parts by weight; antioxidant: 0.1-0.8 parts by weight; nucleating agent: 0.01-0.3 parts by weight; acid scavenger: 0.01-0.1 parts by weight; antistatic agent: 0.01-0.1 parts by weight. Through the combined action of nucleating agent, antistatic agent and other components (polypropylene, antioxidant, acid scavenger), the polypropylene composition has good high temperature resistance, impact resistance and stiffness, and is suitable for preparing thermoforming packaging materials, especially hot-fill bottles under ultra-high temperature (121°C) sterilization conditions. CN120025630A also discloses a high-performance polypropylene plastic woven bag and its production method, relating to the field of plastic products technology. It includes the following specific components: polypropylene, talc, UV stabilizer, antistatic agent, toughening agent, and additives, including superconducting nano-graphene oxide, micron-sized composite materials, photocatalysts, composite microcapsules, and silicon nitride microparticles. The woven bag is produced using these materials. This high-performance polypropylene plastic woven bag and its production method, by introducing multiple additives into the production of the polypropylene plastic woven bag, can significantly improve its comprehensive properties such as UV resistance, antistatic properties, antibacterial properties, high-temperature resistance, and wear resistance. It not only greatly extends the service life of the polypropylene woven bag but also effectively protects the contents from electrostatic damage and microbial contamination, thereby improving the overall safety and applicability of the product. It is particularly suitable for fields such as electronics, food, and pharmaceuticals where packaging materials have strict requirements. While the above-mentioned patented technologies improve the mechanical properties and antistatic capabilities of polyolefin composite materials to a certain extent, they all improve the properties of polyolefin resins through simple filler additions. The addition of large amounts of fillers can lead to poor compatibility with polyolefins, resulting in reduced mechanical strength and making it difficult to meet usage requirements. Summary of the Invention

[0004] To address the issues of low mechanical strength and poor antistatic properties in polyolefin materials prepared by existing technologies, this invention provides an aerogel powder for polyolefin modification, which improves the aforementioned properties of polyolefins.

[0005] To achieve the above objectives, the present invention provides the following solution: A method for preparing aerogel powder for polyolefin modification includes the following steps: (1) Arand 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; (2) Add acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After the reaction, a polypyrrole-coated aramid nanofiber dispersion is obtained; the mass ratio of the pyrrole monomer to the aramid fiber is (0.1-0.6):1. (3) Polyamic acid was prepared in an organic solvent using dianhydride and diamine as raw materials, and then mixed with a dispersion of polypyrrole-coated aramid nanofibers. A chemical imidizing agent was added to perform partial imidization. After standing, the mixture was then exchanged with deionized water to prepare a hydrogel. (4) The hydrogel was freeze-dried, thermally imidized, and pulverized to obtain polyolefin modified aerogel powder.

[0006] Polyolefin materials have low mechanical strength and poor antistatic properties. Current technologies generally improve the mechanical properties and antistatic ability of polyolefin composites by adding reinforcing fillers and conductive substances respectively.

[0007] The most common reinforcing fillers for polyolefins 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 polyolefins, compatibility issues make uniform dispersion in polyolefins difficult, easily causing stress concentration problems and potentially reducing the performance of the composite material.

[0008] To improve the antistatic properties of polyolefin 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 polyolefin resins combine the processing characteristics of polymer materials with the conductivity of metals. Compared to metals, composite conductive polyolefin 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 polyolefin 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 or 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 polyolefin resin materials primarily rely on the addition of conductive fillers. Among them, polypyrrole, as a common conductive polymer material, can improve the antistatic properties of polyolefin resins to a certain extent when added.

[0009] 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 polypyrrole-coated aramid nanofiber-polyimide aerogel composite material. Using aerogel as the addition method for polyolefin modification solves the problem of poor compatibility associated with conventional fillers. Aerogels possess abundant pore structures; by adding the modifying material to the polyolefin in aerogel form, the high porosity or interpenetrating network structure of the aerogel material allows the polyolefin melt to be adsorbed into its pore structure through physical interactions such as capillary forces, surface tension, and hydrogen bonds. This enhances the interaction force between the filler and the polyolefin, thereby improving the compatibility between the materials.

[0010] Using polypyrrole-coated aramid nanofibers as a reinforcing and conductive material can significantly improve the mechanical strength and antistatic properties of polyolefin composites. However, directly adding aramid nanofibers as nanoscale fillers not only easily causes compatibility issues with polyimide or polyolefins, 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. By using polypyrrole-coated aramid nanofibers, not only is the fiber dispersion improved, but the coating also enhances the compatibility between the aramid nanofibers and the aerogel matrix, i.e., the polyimide resin. 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 polypyrrole, can also promote the dispersion of polypyrrole, enabling it to form a network structure, which is beneficial for the formation of conductive pathways. With less polypyrrole, the conductivity of polyimide aerogels and polyolefin composites can be significantly improved, avoiding the technical problem of reduced mechanical properties caused by the addition of large amounts of polypyrrole.

[0011] The reason for choosing polyimide 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 (generally above 350°C), which can meet the processing requirements of polyolefin materials (polyolefin materials have lower melting points, generally below 200°C). Specifically, during melt processing, the polyolefin melt has high fluidity, and the porous aerogel powder is uniformly dispersed in the polyolefin melt, which is conducive to the full wetting of the melt, improves the interfacial force between the aerogel powder and the polyolefin resin, and improves the mechanical properties of the polyolefin composite material.

[0012] Overall, the aerogel composite material prepared by this invention is a porous solid material formed by combining aramid nanofibers and polypyrrole 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, referred to as the matrix, while the nanoscale polypyrrole-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 polypyrrole 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. This makes 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 polyolefins. Furthermore, in this aerogel structure, the polyimide, as the matrix resin, forms a bonding structure with the polypyrrole, further improving the thermal stability of the polypyrrole, which is beneficial for the melt processing of polyolefin resins. By combining aerogel powder with different polyolefin resins, the synergistic effect of different components at the molecular level in the composite material results in 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 polyolefin resin composite with high strength and antistatic properties.

[0013] Furthermore, in step (1), the alkali is sodium hydroxide or potassium hydroxide.

[0014] 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.

[0015] 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, pyrrole monomers, initiators, etc.) are added, the equilibrium of the solution will be disrupted, resulting in 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 pyrrole 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 polyolefins, limiting its suitability to reinforcement of inorganic materials such as concrete and cement paste.

[0016] 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 pyrrole polymerization, but also avoid excessive long-chain alkyl quaternary ammonium salt leading to entanglement between the long chains of the salt itself.

[0017] 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, and azobisisobutyronitrile. 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, pyrrole 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, pyrrole 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 a polypyrrole coating structure.

[0018] Furthermore, in step (2), the reaction temperature is 0-30℃ and the reaction time is 8-12h.

[0019] Furthermore, in step (2), the mass ratio of the initiator to the pyrrole monomer is (1-5):1.

[0020] Furthermore, in step (3), the molar ratio of dianhydride monomer to diamine monomer is (1-1.04):1.

[0021] Furthermore, the temperature for preparing polyamic acid in step (3) is 25-35℃ and the time is 6-12h.

[0022] 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 polyolefin melt.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Furthermore, in step (4), the thermal imidization temperature is 150-200℃ and the time is 2-6h.

[0028] Furthermore, the present invention also provides an aerogel powder for polyolefin modification and its application in the preparation of high-strength pipes, plates, grouting equipment parts and grouting bags.

[0029] On the other hand, the present invention provides a polyolefin composite material comprising the following components in parts by weight: 50-150 parts polyolefin resin, 1-30 parts polyolefin-modified aerogel powder, 1-10 parts fiber-reinforcing filler, and 1-5 parts processing aids. Specifically, the composite material can be granulated using an extruder at an extrusion temperature of 160-200°C, particularly 170-190°C. This high-temperature melt processing not only further promotes the improvement of the polyimide structure but also facilitates the full wetting of the aerogel by the polyolefin melt. The type of polyolefin resin is not particularly limited; common types in the art such as polyethylene, polypropylene, polybutene, and polystyrene are all acceptable. Furthermore, the polyolefin composite material may also include glass fiber, carbon fiber, flame retardant, lubricant, flow modifier, colorant, anti-aging agent, antioxidant, anti-hydrolysis agent, coupling agent, and other additives. In particular, conductive fibrous filler can be added to promote the formation of a conductive network. The raw materials used in this invention are all common types and can be prepared independently or purchased and recycled. For example, aramid fibers can be selected from DuPont's K-series fibers, polyolefins can be selected from Sinopec's PPH series polypropylene, carbon fibers can be selected from Toray Industries' T-series carbon fibers, antioxidants can be selected from Xindongyi Chemical's 1010 series, coupling agents can be selected from Hairui New Materials' KH570 series, and so on. In particular, this invention uses recycled polypropylene as a base material to save costs.

[0030] This aerogel powder is a porous solid material formed by combining aramid nanofibers and polypyrrole into a one-dimensional composite fiber and then bonding it with polyimide resin. By combining the aerogel powder with different polyolefin resins, 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.

[0031] Beneficial effects (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 function 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 pyrrole monomers to form a coating structure through in-situ polymerization; and the presence of long-chain alkyl groups can hinder the merging between fibers.

[0032] (2) Using polypyrrole-coated aramid nanofibers as a reinforcing and conductive material can greatly improve the mechanical strength and antistatic properties of polyolefin composites.

[0033] (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 polyolefin materials, facilitate the full wetting of polyolefin melt, improve the interfacial force between aerogel powder and polyolefin resin, and improve the mechanical properties of polyolefin composite materials.

[0034] (4) The aerogel composite material prepared by this invention is a porous solid material formed by combining aramid nanofibers and polypyrrole 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 polypyrrole-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 polyolefins. Attached Figure Description

[0035] Figure 1 Transmission electron microscopy image of polypyrrole-coated aramid nanofibers prepared in Example 10.

[0036] Figure 2 Transmission electron microscopy (TEM) image of the modified aramid nanofibers prepared for Comparative Example 1. Detailed Implementation

[0037] 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.

[0038] It should be specifically noted that the types of raw materials and specific process steps used in the following embodiments 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.

[0039] Performance Testing: A polypropylene composite material comprises the following components in parts by weight: 100 parts polypropylene resin, 20 parts polyolefin-modified aerogel powder (prepared in Examples 1-10 and Comparative Examples 1-2, respectively), 5 parts carbon fiber, 1 part antioxidant 1010, and 1 part paraffin lubricant. The above components are added to a twin-screw extruder and melt-extruded into granules (extruder temperature 190°C). Standard samples are then prepared, and their mechanical and antistatic properties are tested. Tensile strength is measured according to ASTM D638, flexural strength according to ASTM D790, and the volume resistivity of the samples is measured using a ohmmeter.

[0040] Example 1 A method for preparing aerogel powder for polyolefin modification includes the following steps: (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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.1:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 8 hours, a polypyrrole-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of pyrrole monomer to aramid fiber is 0.1:1. The mass ratio of initiator to pyrrole monomer is 2.5:1. (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 polypyrrole-coated aramid nanofiber dispersion and a chemical imidizing agent was added to react for 3 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 39.1 MPa, a flexural strength of 48.6 MPa, and a volume resistivity of 9.3 × 10⁻⁶ MPa. 7 Ω·m.

[0041] Example 2 A method for preparing aerogel powder for polyolefin modification includes the following steps: (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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.4:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 12 hours, a polypyrrole-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of pyrrole monomer to aramid fiber is 0.6:1. The mass ratio of initiator to pyrrole monomer is 3.5:1. (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 a dispersion of polypyrrole-coated aramid nanofibers and a chemical imidizing agent was added to react for 3 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 2.8:1. 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 46.1 MPa, a flexural strength of 57.6 MPa, and a volume resistivity of 1.9 × 10⁻⁶. 6 Ω·m.

[0042] Example 3 A method for preparing aerogel powder for polyolefin modification includes the following steps: (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 6 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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.5:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 10 h, a polypyrrole-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of pyrrole monomer to aramid fiber is 0.4:1; the mass ratio of initiator to pyrrole monomer is 3:1. (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 hours to obtain a polyamic acid solution. Then, the solution was mixed with the polypyrrole-coated aramid nanofiber dispersion and a chemical imidizing agent was added to react for 3 hours 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 42.5 MPa, a flexural strength of 51.6 MPa, and a volume resistivity of 6.4 × 10⁻⁶. 7 Ω·m.

[0043] Example 4 A method for preparing aerogel powder for polyolefin modification includes the following steps: (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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.15:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 9 hours, a polypyrrole-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of pyrrole monomer to aramid fiber is 0.3:1; the mass ratio of initiator to pyrrole monomer is 2.8:1; (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 polypyrrole-coated aramid nanofiber dispersion and a chemical imidizing agent was added to react for 3 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 44.7 MPa, a flexural strength of 54.2 MPa, and a volume resistivity of 8.5 × 10⁻⁶. 6 Ω·m.

[0044] Example 5 A method for preparing aerogel powder for polyolefin modification includes the following steps: (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 6 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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.25:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 10 h, a polypyrrole-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of pyrrole monomer to aramid fiber is 0.4:1; the mass ratio of initiator to pyrrole monomer is 3:1. (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 hours to obtain a polyamic acid solution. Then, the solution was mixed with a dispersion of polypyrrole-coated aramid nanofibers and a chemical imidizing agent was added to react for 3 hours 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 41.6 MPa, a flexural strength of 51.9 MPa, and a volume resistivity of 5.1 × 10⁻⁶. 7 Ω·m.

[0045] Example 6 A method for preparing aerogel powder for polyolefin modification includes the following steps: (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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.2:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 10 h, a polypyrrole-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of pyrrole monomer to aramid fiber is 0.4:1; the mass ratio of initiator to pyrrole monomer is 2.8:1; (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 polypyrrole-coated aramid nanofiber dispersion and a chemical imidizing agent was added to react for 3 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 46.8 MPa, a flexural strength of 57.1 MPa, and a volume resistivity of 8.6 × 10⁻⁶. 7 Ω·m.

[0046] Example 7 A method for preparing aerogel powder for polyolefin modification includes the following steps: (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 6 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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.25:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 10 h, a polypyrrole-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of pyrrole monomer to aramid fiber is 0.4:1; the mass ratio of initiator to pyrrole monomer is 3:1. (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 hours to obtain a polyamic acid solution. Then, the solution was mixed with a dispersion of polypyrrole-coated aramid nanofibers and a chemical imidizing agent was added to react for 3 hours 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 43.7 MPa, a flexural strength of 54.3 MPa, and a volume resistivity of 8.3 × 10⁻⁶. 7 Ω·m.

[0047] Example 8 A method for preparing aerogel powder for polyolefin modification includes the following steps: (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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.35:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 11 h, a polypyrrole-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of pyrrole monomer to aramid fiber is 0.5:1. The mass ratio of initiator to pyrrole monomer is 3.2:1. (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 a dispersion of polypyrrole-coated aramid nanofibers and a chemical imidizing agent was added and reacted for 3 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 44.2 MPa, a flexural strength of 55.7 MPa, and a volume resistivity of 7.3 × 10⁻⁶. 6 Ω·m.

[0048] Example 9 A method for preparing aerogel powder for polyolefin modification includes the following steps: (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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.35:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 8 hours, a polypyrrole-coated aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of pyrrole monomer to aramid fiber is 0.45:1. The mass ratio of initiator to pyrrole monomer is 3.8:1. (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 polypyrrole-coated aramid nanofiber dispersion and a chemical imidizing agent was added to react for 3 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 44.3 MPa, a flexural strength of 52.9 MPa, and a volume resistivity of 4.8 × 10⁻⁶. 6 Ω·m.

[0049] Example 10 A method for preparing aerogel powder for polyolefin modification includes the following steps: (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 6 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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.25:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 10 h, a polypyrrole-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of pyrrole monomer to aramid fiber is 0.4:1; the mass ratio of initiator to pyrrole monomer is 3:1. (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 hours to obtain a polyamic acid solution. Then, the solution was mixed with the polypyrrole-coated aramid nanofiber dispersion and a chemical imidizing agent was added to react for 3 hours 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 47.4 MPa, a flexural strength of 56.3 MPa, and a volume resistivity of 3.1 × 10⁻⁶ MPa. 6 Ω·m.

[0050] Comparative Example 1 A method for preparing aerogel powder for polyolefin modification includes the following steps: (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 6 days to prepare an aramid nanofiber dispersion; the alkali was potassium hydroxide; the ratio of aramid fibers, alkali and dimethyl sulfoxide was 1g:1.3g:450ml; (2) First, concentrated nitric acid is added to the aramid nanofiber dispersion, and then long-chain alkyl quaternary ammonium salt hexadecyltrimethylammonium bromide, pyrrole monomer and initiator are added to the dispersion in sequence. After reacting at 15°C for 10 h, a modified aramid nanofiber dispersion is obtained. The initiator is ferric chloride. The molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1. The mass ratio of pyrrole monomer to aramid fiber is 0.4:1. The mass ratio of initiator to pyrrole monomer is 3:1. The mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.25:1. (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 hours 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 hours 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 2:1. 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 mass of the sum of the dianhydride monomer and the diamine monomer. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 30.4 MPa, a flexural strength of 39.2 MPa, and a volume resistivity of 7.5 × 10⁻⁶. 9 Ω·m.

[0051] Comparative Example 2 A method for preparing aerogel powder for polyolefin modification includes the following steps: (1) Aramid fibers were placed in a reaction vessel containing alkali and dimethyl sulfoxide and stirred at room temperature for 6 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:1.3g:450ml. The mass ratio of the long-chain alkyl quaternary ammonium salt to aramid fibers was 0.25:1. (2) Add concentrated nitric acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After reacting at 15°C for 10 h, a polypyrrole-coated aramid nanofiber dispersion is obtained; the initiator is ferric chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of pyrrole monomer to aramid fiber is 1:1; the mass ratio of initiator to pyrrole monomer is 3:1; (3) The dianhydride monomer and diamine monomer were dispersed in the organic solvent N,N-dimethylacetamide and reacted at 30°C for 8 hours to obtain a polyamic acid solution. Then, the solution was mixed with the polypyrrole-coated aramid nanofiber dispersion and a chemical imidizing agent was added to react for 3 hours 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. (4) The hydrogel was freeze-dried and then subjected to thermal imidization at 160℃ / 1h and 180℃ / 2h. After pulverization, aerogel powder for polyolefin modification was obtained. The corresponding polypropylene composite material was tested and found to have a tensile strength of 32.3 MPa, a flexural strength of 41.6 MPa, and a volume resistivity of 2.8 × 10⁻⁶. 7 Ω·m.

[0052] Figure 1 This is a transmission electron microscope image of the polypyrrole-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 polypyrrole-coated aramid nanofibers and modified aramid nanofibers with deionized water before testing. Figure 1 As can be seen, a distinct polypyrrole coating structure forms on the surface of the aramid nanofibers, promoting their dispersion in the polyimide resin and facilitating the formation of the gel structure, which 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 polypyrrole coating structures. However, adding polar substances such as acids, pyrrole monomers, and initiators in advance will disrupt the solution equilibrium, affect the surface modification function of long-chain alkyl quaternary ammonium salts, and hinder the adhesion of pyrrole monomers to the fiber surface, thus preventing in-situ polymerization to form a coating structure.

[0053] As can be seen from the above figures and data, the aerogel composite material prepared by this invention is a porous solid material formed by combining aramid nanofibers and polypyrrole into a one-dimensional composite fiber and then bonding it with polyimide resin. By combining the aerogel material with the polyolefin resin material, the synergistic effect between different components at the molecular level in the composite material results in a resin composite material with a novel structure and function. The emergence of this aerogel material structure integrates the properties of different materials, resulting in a polyolefin resin composite material with high strength and antistatic properties. Specifically, compared with Example 10, Comparative Example 1 did not add hexadecyltrimethylammonium bromide in advance, which could not act as a dispersant or template, and could not form a coating structure, affecting the dispersion of aramid nanofibers and hindering the formation of reinforcing and conductive networks. The mechanical properties and conductivity of the prepared polypropylene composite material were both reduced. Compared with Example 10, Comparative Example 2 added too much polypyrrole, and its conductivity was not further improved; instead, its mechanical properties decreased significantly. This is because polypyrrole, as a conductive polymer, has low mechanical strength. When its dosage is too high, it can easily cause excessive coating of polypyrrole, 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. This can easily lead to cracking during the melt processing of polyolefins, resulting in a reduction in the strength and toughness of polyolefin composites.

[0054] 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 preparing aerogel powder for polyolefin modification, characterized in that, Includes the following steps: (1) Arand 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; (2) Add acid to the aramid nanofiber dispersion, and then add pyrrole monomer and initiator to the dispersion. After the reaction, a polypyrrole-coated aramid nanofiber dispersion is obtained; the mass ratio of the pyrrole monomer to the aramid fiber is (0.1-0.6):

1. (3) Polyamic acid was prepared in an organic solvent using dianhydride and diamine as raw materials, and then mixed with a dispersion of polypyrrole-coated aramid nanofibers. A chemical imidizing agent was added to perform partial imidization. After standing, the mixture was then exchanged with deionized water to prepare a hydrogel. (4) The hydrogel was freeze-dried, thermally imidized, and pulverized to obtain polyolefin modified aerogel powder.

2. The method for preparing aerogel powder for polyolefin modification as described in claim 1, characterized in that, In step (1), the alkali is sodium hydroxide or potassium hydroxide.

3. The method for preparing aerogel powder for polyolefin modification as described in claim 1, characterized in that, In step (1), the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:(1-2)g:(350-500)ml.

4. The method for preparing aerogel powder for polyolefin modification as described in claim 1, characterized in that, 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.

5. The method for preparing aerogel powder for polyolefin modification as described in claim 1, characterized in that, In step (2), the initiator is at least one of ammonium persulfate, potassium persulfate, ferric chloride, and azobisisobutyronitrile.

6. The method for preparing aerogel powder for polyolefin modification as described in claim 1, characterized in that, The reaction temperature in step (2) is 0-30℃ and the reaction time is 8-12h.

7. The method for preparing aerogel powder for polyolefin modification as described in claim 1, characterized in that, In step (3), the mass ratio of the sum of the masses of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber is (1-5):

1.

8. An aerogel powder for modifying polyolefins, characterized in that, It is prepared by the method for preparing a polyolefin modified aerogel powder according to any one of claims 1-7.

9. The application of the polyolefin modified aerogel powder as described in claim 8 in the preparation of pipes, plates, grouting equipment parts and grouting bags.

10. A polyolefin composite material, characterized in that, The product comprises the following components in parts by weight: 50-150 parts of polyolefin resin, 1-30 parts of the polyolefin-modified aerogel powder as described in claim 8, 1-10 parts of fiber-reinforced filler, and 1-5 parts of processing aid.

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