Aerogel powder for polyolefin modification and preparation method and application thereof

Abstract

The application 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 aramid nanofiber dispersion liquid coated with polypyrrole; (3) mixing polyamide acid with the aramid nanofiber dispersion liquid coated with polypyrrole, then performing partial imidization and solvent exchange to prepare hydrogel; (4) freeze-drying, thermal imidization, and crushing to obtain the aerogel powder for polyolefin modification. The aerogel powder is a porous solid material formed by combining aramid nanofiber and polypyrrole into one-dimensional composite fibers and combining with polyimide resin. The aerogel powder is compounded with polyolefin resin to obtain polyolefin resin composite material with high strength and antistatic performance, which can be widely applied in the fields of pipe, plate, grouting equipment parts, and grouting bag, etc.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gel materials, and particularly relates to aerogel powder for polyolefin modification and a preparation method and application thereof. BACKGROUND

[0002] Polyolefin resin is not a simple resin, but a general term of thermoplastic resins such as polypropylene, polyethylene, ethylene-propylene-diene rubber and polyolefin elastomer. Among all polyolefin materials, polypropylene and polyethylene are most widely used, and their properties and application fields have many similarities. Polypropylene and polyethylene are the less dense types of existing plastics, and their appearance is milky white, which is a non-toxic, odorless thermoplastic general-purpose plastic. Moreover, polyolefin resins such as polypropylene and polyethylene have excellent chemical resistance and are easy to process into various shapes such as extrusion, injection molding, blow molding and thermoforming. However, due to the large shrinkage of the molded products, the product surface is prone to warping and deformation, and it is difficult to achieve high precision size requirements. At low temperatures, the toughness and aging resistance are poor. Polyolefin resins generally have strong crystallization ability and structural regularity, so they exhibit excellent mechanical strength and thermal stability. In addition, polyolefin resins have good rigidity and hardness, and also have excellent wear resistance and bending fatigue resistance. The impact strength of the products will decrease with the increase of crystallinity. Generally, the initial properties of polyolefin resins are related to the environmental temperature and the rate of loading load. When the external temperature is higher than the glass transition temperature of the material, the material is mostly ductile fracture; when the temperature is lower than the glass transition temperature, the material is mostly brittle fracture, and the impact strength value will decrease significantly. The surface energy of polyolefin resin is low, and the low surface energy makes the material have small air and water vapor permeability and low hygroscopicity, so the electrical insulation performance is better, the intermolecular force is weak, and the impact strength is strong.

[0003] However, polyolefin resin products also have defects in terms of product performance: for example, compared with some engineering plastics such as polyamide, the tensile strength is low and the hardness is small; compared with rubber products, the product has a large molding shrinkage, is prone to warping and bending, and has obvious brittle fracture at a low temperature; and the antistatic performance is poor, which is prone to cause static damage. In order to further expand the application field of polyolefin resin products, many researchers modify polyolefin resin in view of the shortcomings of polyolefin resin. CN120040874A discloses a polypropylene composition. The polypropylene composition comprises polypropylene: 100 parts by weight; antioxidant: 0.1-0.8 parts by weight; nucleating agent: 0.01-0.3 parts by weight; acid absorbent: 0.01-0.1 parts by weight; antistatic agent: 0.01-0.1 parts by weight. Through the combined action of the nucleating agent, the antistatic agent and other components (polypropylene, antioxidant, acid absorbent), the polypropylene composition has good high-temperature resistance, impact resistance and stiffness, and is suitable for preparing thermoforming packaging materials, especially hot-filling bottles under ultrahigh-temperature (121℃) sterilization conditions. CN120025630A also discloses a high-performance polypropylene plastic woven bag and a production method, relating to the technical field of plastic products, comprising the following specific components: polypropylene, talcum powder, ultraviolet resistance agent, antistatic agent, toughening agent, and additives, wherein the additives comprise superconducting nanometer graphene oxide, micron-level composite material, photocatalyst, composite microcapsule and silicon nitride microparticle, and the woven bag is produced by using the above materials. The high-performance polypropylene plastic woven bag and the production method can significantly improve the comprehensive performance of ultraviolet resistance, antistatic property, antibacterial property, high-temperature resistance and wear resistance of the polypropylene plastic woven bag by introducing various additives in the production of the polypropylene plastic woven bag, thereby greatly improving the service life of the polypropylene woven bag, effectively protecting the contents from static damage and microbial pollution, and improving the overall safety and applicability of the product, and the method is especially suitable for fields such as electronics, food and medicine that have strict requirements on packaging materials. Although the above-mentioned patent technologies improve the mechanical properties and antistatic ability of polyolefin composite materials to some extent, they are all simple filler addition to improve the performance of polyolefin resin, and a large amount of filler addition will lead to poor compatibility of the filler with polyolefin, resulting in a decrease in mechanical strength and difficulty in meeting the use requirements. SUMMARY

[0004] In order to solve the problems of low mechanical strength and poor antistatic performance of the polyolefin materials prepared by the prior art, the present application provides a kind of aerogel powder for polyolefin modification, which improves the above-mentioned performance of polyolefin through the aerogel powder.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0006] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0007] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt to obtain aramid nanofiber dispersion;

[0008] (2) Add acid to the aramid nanofiber dispersion, then add pyrrole monomer and initiator to the dispersion, and obtain poly-pyrrole coated aramid nanofiber dispersion after reaction; the mass ratio of pyrrole monomer to aramid fiber is (0.1-0.6):1;

[0009] (3) Prepare polyamide acid from dianhydride and diamine in an organic solvent, then mix with poly-pyrrole coated aramid nanofiber dispersion, add chemical imidization reagent for partial imidization; stand, then perform solvent exchange with deionized water to prepare hydrogel;

[0010] (4) Freeze-dry the hydrogel, heat imidize, crush to obtain aerogel powder for polyolefin modification.

[0011] Polyolefin materials have low mechanical strength and poor antistatic performance. The existing technology generally improves the mechanical properties and antistatic ability of polyolefin composite materials by adding reinforcing fillers and conductive substances respectively.

[0012] The most common reinforcing filler for polyolefin is various organic or inorganic fiber materials. Aramid nanofiber, as a nanoscale product of aramid fiber, has high aspect ratio, large specific surface area and good dispersibility. Compared with aramid fiber, aramid nanofiber not only retains the high mechanical properties and excellent thermal stability of aramid fiber, but also can be used as a nanoscale building block to introduce nanomaterials and prepare high-level structures from bottom to top. In previous work, the inventors prepared various forms of aerogel materials (CN118878287A, CN118851649A, CN118812184A, CN118702437A) by compounding aramid nanofiber / inorganic filler to enhance the stability of concrete. However, aramid nanofiber / inorganic filler aerogel is only suitable for modifying inorganic materials such as concrete. When it is directly applied to organic polymer materials such as polyolefin, it is difficult to disperse uniformly in polyolefin due to compatibility problems, which may cause stress concentration and even reduce the performance of the composite material.

[0013] In order to improve the antistatic property of the polyolefin resin, generally, a conductive filler needs to be added. The conductive material can be conductive carbon black, carbon fiber, carbon nanotube, graphite, conductive polymer, metal powder, and various conductive metal oxides and metal salts. The composite conductive polyolefin resin has the processing characteristics of the polymer material and the conductivity of the metal. Compared with the metal, the composite conductive polyolefin resin material has the advantages of good processability, simple process, corrosion resistance, large adjustable range of resistivity, low price, etc. At present, the conductive material added in the composite conductive polyolefin resin material is one kind of small molecule antistatic agent and the other kind of conductive filler. Adding the antistatic agent is the most common antistatic method for the polymer material, which forms a conductive layer on the surface of the material, reduces the surface resistivity, makes the generated static charge leak out quickly, and at the same time, gives the material surface certain lubricity, reduces the friction coefficient, and inhibits and reduces the generation of static charge. However, the reduction of the resistivity of the small molecule antistatic agent is limited, the durability is poor, and the mechanical properties of the composite material are reduced. Therefore, at present, the composite polyolefin resin material mainly adds the conductive filler. Among them, the polypyrrole as a common conductive polymer material, adding the polypyrrole can improve the antistatic property of the polyolefin resin to a certain extent.

[0014] However, a large amount of reinforcing fillers and conductive substances will cause the processing performance of the composite material to be reduced, the compatibility of the components to be poor, and it is difficult to simultaneously improve the mechanical properties and the antistatic ability. In order to solve the problem, the polypropylene-coated aramid nanofiber-polyimide aerogel composite material is prepared creatively. The aerogel form is used as the adding method of the polyolefin modification material, and the problem of poor compatibility of the general filler is solved. The aerogel has a rich pore structure, and the modified substance is added to the polyolefin in the form of aerogel. The high porosity or interpenetrating network structure of the aerogel material is used to adsorb the polyolefin melt into the pore structure through capillary force, surface tension and hydrogen bond physical interaction, improve the interaction force between the filler and the polyolefin, and improve the compatibility between the materials.

[0015] The polyacrylonitrile nanofiber coated with polypyrrole can greatly improve the mechanical strength and antistatic property of the polyolefin composite material. As a nanoscale filler, the direct addition of the polyacrylonitrile nanofiber can easily cause the compatibility problem with the polyimide or the polyolefin, and the polyacrylonitrile nanofiber can easily agglomerate in the processing process due to the strong interaction force caused by the many surface defects of the polyacrylonitrile nanofiber, so that the nanoscale size is lost and the modification effect is reduced. After the polyacrylonitrile nanofiber is coated with polypyrrole, the dispersion performance of the fiber is improved, and the compatibility between the polyacrylonitrile nanofiber and the aerogel matrix, i.e. the polyimide resin, is improved through the coating effect, so that the polyacrylonitrile nanofiber is uniformly dispersed in the polyimide precursor to form a polyimide aerogel material with the coated polyacrylonitrile nanofiber as the reinforcing skeleton. In turn, the polyacrylonitrile nanofiber as the core layer substrate of polypyrrole can also promote the dispersion of polypyrrole, so that the polypyrrole forms a network structure, which is beneficial to the formation of a conductive path; a small amount of polypyrrole can greatly improve the conductive property of the polyimide aerogel and the polyolefin composite material, and the technical problem of the reduction of the mechanical property caused by the large amount of polypyrrole is avoided.

[0016] The polyimide is selected as the matrix resin of the aerogel in the present application, on the one hand, because the polyamide acid, the precursor of the polyimide, has good solubility and is easy to process. On the other hand, the polyimide formed after imidization has high mechanical strength and high melting point (generally above 350℃), which can meet the processing requirements of the polyolefin material (the melting point of the polyolefin material is generally below 200℃). Specifically, in the melt processing process, the polyolefin melt has high fluidity, and the aerogel powder with a porous structure is uniformly dispersed in the polyolefin melt, which is beneficial to the full infiltration of the melt, improves the interfacial force between the aerogel powder and the polyolefin resin, and improves the mechanical property of the polyolefin composite material.

[0017] In general, the aerogel composite material prepared by the present application is a porous solid material formed by combining one-dimensional composite fibers of aramid nanofibers and polypyrrole with a polyimide resin. In the aerogel nanocomposite material, the polyimide resin is the continuous phase, referred to as the matrix, and the aramid nanofiber coated with nanoscale polypyrrole is the dispersed phase and the reinforcing phase. The dispersed phase and the reinforcing phase are distributed in the polyimide resin matrix in an independent form. 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, the phases in the aerogel composite material retain some independent properties of each phase, but complement each other and produce a synergistic effect, so that the comprehensive performance of the composite material is better than that of each combined phase, thereby meeting the use requirements of the polyolefin mechanical properties and antistatic properties. In addition, in the 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 to meet the melt processing process of the polyolefin resin. The aerogel powder is compounded with different polyolefin resin materials, and the synergistic effect between different components in the composite material at the molecular level forms a resin composite material with a new structure and function. The resin composite material has a stacking benefit: the stacking and complementation of the performance of the matrix and the reinforcing body; the performance has designability, and the performance of the composite material is adjusted by adjusting the components, structure and process. The emergence of the aerogel material with this structure integrates the properties of different materials, and a polyolefin resin composite material with high strength and antistatic performance is obtained.

[0018] Further, the base in step (1) is sodium hydroxide or potassium hydroxide.

[0019] Further, the ratio of aramid fiber, base and dimethyl sulfoxide in step (1) is 1 g: (1-2) g: (350-500) ml. In particular, the preparation of aramid nanofiber is a stirring reaction in a reaction kettle at room temperature for 4-8 days. Further, a commercial aramid fiber is used. In the preparation process of the commercial aramid fiber, various oils are generally left on the surface of the fiber, which can be cleaned. Specifically, acetone solvent, sodium dodecyl benzene sulfonate solution and deionized water can be used in sequence to remove oil and other impurities on the surface of the fiber.

[0020] Further, 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. In particular, hexadecyl trimethyl ammonium bromide can be selected. The long-chain alkyl quaternary ammonium salt added in advance to the aramid nanofiber dispersion liquid can improve the dispersibility of the aramid nanofiber and play a template role. This is because the aramid nanofiber prepared by the alkali / DMSO soaking method contains a large number of reactive oxygen-containing functional groups such as carboxyl and hydroxyl groups on the surface, which are electronegative. Although the aspect ratio is large and the mechanical properties are excellent, the mixed solution after soaking is extremely unstable. When new polar substances (acid, pyrrole monomer, initiator, etc.) are added, the balance of the solution is destroyed, the fiber bundles between the fibers are combined, and the fiber aggregation phenomenon occurs, which affects the dispersion of the aramid nanofiber. As a cationic surface modifier, the long-chain alkyl quaternary ammonium salt has good surface modification function, and the presence of ammonium ions is conducive to the combination of the aramid nanofiber and the improvement of the dispersibility. At the same time, the long-chain alkyl quaternary ammonium salt has a long alkyl chain, which can improve the hydrophilic and hydrophobic properties of the surface of the aramid nanofiber, and is conducive to the attachment of the pyrrole monomer to form a coating structure by in-situ polymerization. Moreover, the presence of the long-chain alkyl group can hinder the combination between the fibers and promote the dispersion of the fibers. In the previous work of the inventors, 1wt% sodium hydroxide aqueous solution was used to corrode aramid fibers for several hours, and then conductive monomers were directly polymerized on the surface of the fibers to prepare polymer-coated aramid fibers. The main form of the aramid fiber of this structure has not changed, which is not a nano structure, but only the surface of the fiber has been corroded. Although the relatively thick fiber will not aggregate, this process does not need to add long-chain alkyl quaternary ammonium salt. However, due to the relatively thick diameter of the fiber, it cannot be used in the modification field of polyolefins, but only in the reinforcement field of inorganic materials such as concrete and cement grout.

[0021] Further, 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, 0.5:1; in particular, it is (0.2-0.4):1. An appropriate amount of long-chain alkyl quaternary ammonium salt can not only fully play the role of dispersing aramid nanofiber and serving as a template for pyrrole polymerization, but also avoid the mutual entanglement between the long chains of the long-chain alkyl quaternary ammonium salt due to too much long-chain alkyl quaternary ammonium salt.

[0022] Further, the acid in step (2) is one or more of formic acid, acetic acid, hydrochloric acid, sulfuric acid, nitric acid. The molar ratio of the acid to the base in step (1) is (0.5-2):1, further (1-2):1. In particular, one of concentrated hydrochloric acid, concentrated sulfuric acid, concentrated nitric acid can be selected. Further, high-concentration concentrated nitric acid can be selected. Further, the initiator in step (2) is at least one of ammonium persulfate, potassium persulfate, ferric chloride, azobisisobutyronitrile. In particular, ferric chloride with doping effect can be selected. Since the aramid nanofiber is modified by long-chain alkyl quaternary ammonium salt, the addition of polar compounds such as acid, pyrrole monomer and initiator will not cause the merging of fiber bundles; at the same time, the formation of polar compounds can play an ionic crosslinking role, which is conducive to the formation of hydrogel structure. If polar compounds such as acid, pyrrole monomer or initiator are added first, and then long-chain alkyl quaternary ammonium salt is added, not only will the fiber bundles merge, but also the long-chain alkyl quaternary ammonium salt will not be able to be absorbed on the fiber surface, losing the template effect and being unable to form a poly-pyrrole coating structure.

[0023] Further, the reaction temperature in step (2) is 0-30℃, and the reaction time is 8-12h.

[0024] Further, the mass ratio of the initiator to the pyrrole monomer in step (2) is (1-5):1.

[0025] Further, the molar ratio of the dianhydride monomer to the diamine monomer in step (3) is (1-1.04):1.

[0026] Further, the temperature of the polyamide acid preparation process in step (3) is 25-35℃, and the time is 6-12h.

[0027] Further, the mass ratio of the sum of the mass of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber in step (3) is (1-5):1. Specifically, it can be any value of 1:1, 2:1, 3:1, 4:1, 5:1. Further, the mass ratio of the sum of the mass of the dianhydride monomer and the diamine monomer to the mass of the aramid fiber is (2-3):1. Polyimide as the matrix resin of aerogel plays a bonding role; at the same time, the amount of polyimide cannot be too much, otherwise it is easy to cause the porosity of the aerogel to decrease, which is not conducive to the infiltration of the polyolefin melt.

[0028] Further, the imidization reagent in step (3) is a mixture of acetic anhydride and pyridine with a molar ratio of (1-3):1, and the mass of the mixture is 1-4 times the sum of the mass of the dianhydride monomer and the mass of the diamine monomer; in particular, the mass of the mixture is 2-3 times the sum of the mass of the dianhydride monomer and the mass of the diamine monomer, and more chemical imidization reagent can better promote the imidization process; in particular, the degree of partial imidization of the polyamic acid can be 20%-60%. Further, the partial imidization time is 2-5h. Through the partial chemical imidization process, not only can the formation of the gel structure be promoted, but also the temperature of the thermal imidization can be effectively reduced to prevent the destruction of the coating structure by high temperature.

[0029] Further, the diamine monomer in step (3) is 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'-diaminodiphenyl 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.

[0030] Further, the dianhydride monomer in step (3) 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-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-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, 1,4,5,8-naphthalene tetracarboxylic dianhydride.

[0031] Further, the organic solvent in step (3) is one or more of N,N-dimethylacetamide, acetone, acetonitrile, dimethyl sulfoxide, N,N-dimethylformamide, and N-methyl pyrrolidone.

[0032] Further, the heat imidization temperature in step (4) is 150-200℃, and the time is 2-6h.

[0033] Further, the present application also provides an aerogel powder for polyolefin modification and its application in preparing high-strength pipes, plates, grouting equipment parts, and grouting bags.

[0034] In another aspect, the present application provides a polyolefin composite material, which comprises the following components by weight: 50-150 parts of polyolefin resin, 1-30 parts of aerogel powder for polyolefin modification, 1-10 parts of fiber-reinforced filler, and 1-5 parts of processing aid. In particular, the composite material can be granulated and formed by an extruder, and the extrusion temperature is 160-200℃, in particular 170-190℃. Through the high-temperature melt processing process, not only can the perfection of the polyimide structure be further promoted, but also the polyolefin melt can be fully infiltrated into the aerogel. The type of the polyolefin resin is not particularly limited, and common types in the art such as polyethylene, polypropylene, polybutylene, and polystyrene can be used. Further, the polyolefin composite material can also include glass fibers, carbon fibers, flame retardants, lubricants, flow modifiers, toners, anti-aging agents, antioxidants, anti-hydrolysis agents, coupling agents, and other aids. In particular, electrically conductive fibrous fillers can be added to promote the formation of an electrically conductive network. The raw materials used in the present application all belong to common types and can be prepared, purchased, or recycled. For example, aramid fibers can be selected from the K series fibers of DuPont, polyolefins can be selected from the PPH series polypropylenes of Sinopec, carbon fibers can be selected from the T series carbon fibers of Toray, antioxidants can be selected from the 1010 series of Xindongyi Chemicals, and coupling agents can be selected from the KH570 series of Hairex Materials, and the like. In particular, recycled polypropylene is used as the base material in the present application to save costs.

[0035] The aerogel powder is a porous solid material formed by combining aramid nanofibers and polypyrrole into one-dimensional composite fibers and combining with polyimide resin. The aerogel powder is compounded with different polyolefin resin materials, and the synergistic effect between different components in the composite material at the molecular level forms a resin composite material with new structure and function.

[0036] Advantages

[0037] (1) The dispersibility of aramid nanofiber can be improved by adding long-chain alkyl quaternary ammonium salt in advance into aramid nanofiber dispersion, and the long-chain alkyl quaternary ammonium salt can play a role of template. The long-chain alkyl quaternary ammonium salt has good surface modification function, and can be combined with aramid nanofiber to improve the dispersibility thereof; the long-chain alkyl quaternary ammonium salt has a long alkyl chain, which can improve the hydrophilic and hydrophobic properties of the surface of aramid nanofiber, and is conducive to the attachment of pyrrole monomer to form a coating structure by in-situ polymerization; and the presence of long-chain alkyl can hinder the combination between fibers.

[0038] (2) The aramid nanofiber coated with polypyrrole as reinforcing and conductive material can greatly improve the mechanical strength and antistatic property of polyolefin composite material.

[0039] (3) The polyamide acid, which is a polyimide precursor, has good solubility and is easy to process; the polyimide formed after imidization has high mechanical strength and high melting point, and can meet the processing requirements of polyolefin material, which is conducive to the full infiltration of polyolefin melt, improves the interfacial force between aerogel powder and polyolefin resin, and improves the mechanical properties of polyolefin composite material.

[0040] (4) The aerogel composite material prepared by the present application is a porous solid material formed by combining one-dimensional composite fibers of aramid nanofiber and polypyrrole with polyimide resin. In the aerogel nanocomposite material, the polyimide resin is the continuous phase, and the aramid nanofiber coated with nanoscale polypyrrole is the dispersed phase and the reinforcing phase. Each phase in the aerogel composite material retains some independent characteristics, but also takes advantage of each other's strengths and makes up for each other's weaknesses, and produces a synergistic effect, so that the comprehensive performance of the composite material is better than that of each combined phase, thereby meeting the use requirements of polyolefin mechanical properties and antistatic properties. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The transmission electron microscope image of polypyrrole-coated aramid nanofiber prepared for Example 10.

[0042] Figure 2 The transmission electron microscope image of modified aramid nanofiber prepared for Comparative Example 1. DETAILED DESCRIPTION

[0043] The present application will be further described in detail by the following examples and drawings, and the raw materials used in the examples can be purchased or prepared by conventional methods.

[0044] The raw material types and specific process steps used in the following examples and comparative examples are the same as described above. The aramid fiber used in the present application is cleaned and deoiled Kevlar fiber from DuPont. The cleaning process is as follows: first, the aramid fiber is placed in an acetone solution and ultrasonically treated, then taken out and washed with deionized water; then placed in a sodium dodecyl sulfonate aqueous solution (5 wt%) and ultrasonically treated again; finally, repeatedly washed with flowing deionized water to remove the oil on the surface of the aramid fiber.

[0045] Performance test: a polypropylene composite material containing the following components by weight: 100 parts of polypropylene resin, 20 parts of aerogel powder for polyolefin modification (prepared in Examples 1-10 and Comparative Examples 1-2, respectively), 5 parts of carbon fiber, 1 part of antioxidant 1010, and 1 part of paraffin lubricant. The above components are added to a twin-screw extruder and melt-extruded and pelletized (extruder temperature is 190°C). Then standard samples are prepared and their mechanical properties and antistatic properties are tested. The tensile strength is tested according to ASTM D638, the bending strength is tested according to ASTM D790, and the volume resistivity of the sample is tested using a resistance meter.

[0046] Example 1

[0047] A method for preparing an aerogel powder for polyolefin modification, comprising the following steps:

[0048] (1) The aramid fiber is placed in a reaction kettle containing alkali and dimethyl sulfoxide and stirred at room temperature for 4 days to prepare aramid nanofiber, then a long-chain alkyl quaternary ammonium salt, hexadecyl trimethyl ammonium bromide, is added and stirred uniformly to obtain an aramid nanofiber dispersion; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1 g:1.3 g:450 ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.1:1;

[0049] (2) Concentrated nitric acid is added to the aramid nanofiber dispersion, then pyrrole monomer and initiator are added to the dispersion, and the mixture is reacted at 15°C for 8h to obtain a poly-pyrrole coated aramid nanofiber dispersion; 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;

[0050] (3) dispersing dianhydride monomer and diamine monomer in organic solvent N, N-dimethylacetamide, obtaining polyamide acid solution after 6h reaction at 30℃, then mixing with polyazole coated aramid nanofiber dispersion liquid, adding chemical imidization reagent to react for 3h to carry out partial imidization; after standing, solvent exchanging with deionized water to prepare hydrogel; the molar ratio of dianhydride monomer to diamine monomer is 1.02:1; the mass ratio of the sum of dianhydride monomer and diamine monomer to aramid fiber is 1.5:1; the dianhydride monomer is a mixture of pyromellitic dianhydride and 3, 3', 4, 4'-diphenyl tetracarboxylic dianhydride with a molar ratio of 1:2; the diamine monomer is 4, 4'-diaminodiphenyl methane; the imidization reagent is a mixture of acetic anhydride and pyridine with a molar ratio of 2:1, and the mass of the mixture is 1.6 times the sum of the mass of dianhydride monomer and diamine monomer;

[0051] (4) freeze-drying the hydrogel, carrying out thermal imidization under the condition of 160℃ / 1h, 180℃ / 2h, crushing to obtain aerogel powder for polyolefin modification. The corresponding tensile strength of polypropylene composite material is 39.1MPa, the bending strength is 48.6MPa, and the volume resistivity is 9.3×10 7 Ω·m.

[0052] Example 2

[0053] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0054] (1) placing aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stirring at room temperature for 8 days to prepare aramid nanofiber, then adding long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide, stirring uniformly to obtain aramid nanofiber dispersion liquid; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.4:1;

[0055] (2) adding concentrated nitric acid to the aramid nanofiber dispersion liquid, then adding pyrrole monomer and initiator to the dispersion liquid, obtaining polyazole coated aramid nanofiber dispersion liquid after 12h reaction at 15℃; the initiator is ferric chloride; the molar ratio of nitric acid to potassium hydroxide in 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;

[0056] (3) the dianhydride monomer and the diamine monomer are dispersed in an organic solvent N,N-dimethylacetamide, a polyamide acid solution is obtained after reaction at 30℃ for 10h, then mixed with the polyazole-coated aramid nanofiber dispersion liquid, and a chemical imidization reagent is added to react for 3h to perform partial imidization; after standing, solvent exchange is performed with deionized water to prepare a hydrogel; the molar ratio of the dianhydride monomer to the diamine monomer is 1.02:1; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is 2.8:1; the dianhydride monomer is 3,3',4,4'-benzophenonetetracarboxylic dianhydride; the diamine monomer is a mixture of 4,4'-oxydianiline and 4,4'-diaminodiphenylmethane at a molar ratio of 1:1; the imidization reagent is a mixture of acetic anhydride and pyridine at a molar ratio of 2:1, and the mass of the mixture is 2 times the sum of the mass of the dianhydride monomer and the diamine monomer;

[0057] (4) the hydrogel is freeze-dried, heat imidized under the condition of 160℃ / 1h, 180℃ / 2h, and after crushing, an aerogel powder for polyolefin modification is obtained. The corresponding polypropylene composite material has a tensile strength of 46.1MPa, a bending strength of 57.6MPa, and a volume resistivity of 1.9×10 6 Ω·m.

[0058] Example 3

[0059] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0060] (1) aramid fibers are put into a reaction kettle containing alkali and dimethyl sulfoxide, stirred at room temperature for 6 days to prepare aramid nanofibers, then a long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide is added, and after uniform stirring, an aramid nanofiber dispersion liquid is obtained; the alkali is potassium hydroxide; the ratio of the aramid fiber, the alkali and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of the long-chain alkyl quaternary ammonium salt to the aramid fiber is 0.5:1;

[0061] (2) concentrated nitric acid is added to the aramid nanofiber dispersion liquid, then pyrrole monomer and an initiator are added to the dispersion liquid, and after reaction at 15℃ for 10h, a polyazole-coated aramid nanofiber dispersion liquid is obtained; the initiator is iron chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of the pyrrole monomer to the aramid fiber is 0.4:1; the mass ratio of the initiator to the pyrrole monomer is 3:1;

[0062] (3) the dianhydride monomer and the diamine monomer are dispersed in an organic solvent N,N-dimethylacetamide, a polyamide acid solution is obtained after reaction at 30℃ for 8h, then mixed with the polyazole-coated aramid nanofiber dispersion liquid, and a chemical imidization reagent is added to react for 3h to perform partial imidization; after standing, solvent exchange is performed with deionized water to prepare a hydrogel; the molar ratio of the dianhydride monomer to the diamine monomer is 1.02:1; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is 2:1; the dianhydride monomer is 3,3',4,4'-benzophenonetetracarboxylic dianhydride; the diamine monomer is a mixture of 4,4'-oxydianiline and 4,4'-diamino diphenyl sulfone in a molar ratio of 1:1; the imidization reagent is a mixture of acetic anhydride and pyridine in a molar ratio of 2:1, and the mass of the mixture is 2.1 times the sum of the mass of the dianhydride monomer and the diamine monomer;

[0063] (4) the hydrogel is freeze-dried, heat imidized under the condition of 160℃ / 1h, 180℃ / 2h, and after crushing, an aerogel powder for polyolefin modification is obtained. The corresponding polypropylene composite material has a tensile strength of 42.5MPa, a bending strength of 51.6MPa, and a volume resistivity of 6.4×10 7 Ω·m.

[0064] Example 4

[0065] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0066] (1) aramid fibers are put into a reaction kettle containing alkali and dimethyl sulfoxide, stirred at room temperature for 8 days to prepare aramid nanofibers, then a long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide is added, and after uniform stirring, an aramid nanofiber dispersion liquid is obtained; the alkali is potassium hydroxide; the ratio of the aramid fiber, the alkali and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of the long-chain alkyl quaternary ammonium salt to the aramid fiber is 0.15:1;

[0067] (2) concentrated nitric acid is added to the aramid nanofiber dispersion liquid, then pyrrole monomer and an initiator are added to the dispersion liquid, and after reaction at 15℃ for 9h, a polyazole-coated aramid nanofiber dispersion liquid is obtained; the initiator is iron chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of the pyrrole monomer to the aramid fiber is 0.3:1; the mass ratio of the initiator to the pyrrole monomer is 2.8:1;

[0068] (3) dispersing dianhydride monomer and diamine monomer in organic solvent N, N-dimethylacetamide, obtaining polyamide acid solution after 9h reaction at 30℃, then mixing with polyazole coated aramid nanofiber dispersion liquid, adding chemical imidization reagent to react for 3h to carry out partial imidization; after standing, solvent exchange with deionized water to prepare hydrogel; the molar ratio of dianhydride monomer to diamine monomer is 1.02:1; the mass ratio of the sum of dianhydride monomer and diamine monomer to aramid fiber is 1.7:1; the dianhydride monomer is a mixture of 3, 3', 4, 4'-benzophenone tetracarboxylic dianhydride and 2, 2'-bis (3, 4-dicarboxylic acid) hexafluoropropane dianhydride with a molar ratio of 4:1; the diamine monomer is 3, 3'-diaminobenzophenone; the imidization reagent is a mixture of acetic anhydride and pyridine with a molar ratio of 2:1, and the mass of the mixture is 1.9 times the sum of the mass of dianhydride monomer and diamine monomer;

[0069] (4) freeze-drying the hydrogel, carrying out thermal imidization under the condition of 160℃ / 1h, 180℃ / 2h, crushing to obtain aerogel powder for polyolefin modification. The corresponding tensile strength of polypropylene composite material is 44.7MPa, the bending strength is 54.2MPa, and the volume resistivity is 8.5×10 6 Ω·m.

[0070] Example 5

[0071] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0072] (1) placing aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stirring at room temperature for 6 days to prepare aramid nanofiber, then adding long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide, and stirring uniformly to obtain aramid nanofiber dispersion liquid; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.25:1;

[0073] (2) adding concentrated nitric acid to the aramid nanofiber dispersion liquid, then adding pyrrole monomer and initiator to the dispersion liquid, obtaining polyazole coated aramid nanofiber dispersion liquid after 10h reaction at 15℃; the initiator is iron chloride; the molar ratio of nitric acid to potassium hydroxide in 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;

[0074] (3) the dianhydride monomer and the diamine monomer are dispersed in an organic solvent N,N-dimethylacetamide, a polyamide acid solution is obtained after reaction at 30℃ for 8h, then mixed with the polyazole-coated aramid nanofiber dispersion liquid, and a chemical imidization reagent is added to react for 3h to perform partial imidization; after standing, solvent exchange is performed with deionized water to prepare a hydrogel; the molar ratio of the dianhydride monomer to the diamine monomer is 1.02:1; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is 1:1; the dianhydride monomer is 3,3',4,4'-benzophenonetetracarboxylic dianhydride; the diamine monomer is a mixture of 4,4'-oxydianiline and 4,4'-diamino diphenyl sulfone in a molar ratio of 1:1; the imidization reagent is a mixture of acetic anhydride and pyridine in a molar ratio of 2:1, and the mass of the mixture is 2.1 times the sum of the mass of the dianhydride monomer and the diamine monomer;

[0075] (4) the hydrogel is freeze-dried, heat imidized under the condition of 160℃ / 1h, 180℃ / 2h, and after crushing, an aerogel powder for polyolefin modification is obtained. The corresponding polypropylene composite material has a tensile strength of 41.6MPa, a bending strength of 51.9MPa, and a volume resistivity of 5.1×10 7 Ω·m.

[0076] Example 6

[0077] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0078] (1) aramid fibers are put into a reaction kettle containing alkali and dimethyl sulfoxide, stirred at room temperature for 5 days to prepare aramid nanofibers, then a long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide is added, and after uniform stirring, an aramid nanofiber dispersion liquid is obtained; the alkali is potassium hydroxide; the ratio of the aramid fiber, the alkali and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of the long-chain alkyl quaternary ammonium salt to the aramid fiber is 0.2:1;

[0079] (2) concentrated nitric acid is added to the aramid nanofiber dispersion liquid, then pyrrole monomer and an initiator are added to the dispersion liquid, and after reaction at 15℃ for 10h, a polyazole-coated aramid nanofiber dispersion liquid is obtained; the initiator is iron chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of the pyrrole monomer to the aramid fiber is 0.4:1; the mass ratio of the initiator to the pyrrole monomer is 2.8:1;

[0080] (3) the dianhydride monomer and the diamine monomer are dispersed in an organic solvent N,N-dimethylacetamide, a polyamide acid solution is obtained after reaction at 30℃ for 7h, then mixed with the polyazole-coated aramid nanofiber dispersion liquid, and a chemical imidization reagent is added to react for 3h to perform partial imidization; after standing, solvent exchange is performed with deionized water to prepare a hydrogel; the molar ratio of the dianhydride monomer to the diamine monomer is 1.02:1; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is 1.9:1; the dianhydride monomer is 3,3',4,4'-benzophenonetetracarboxylic dianhydride; the diamine monomer is a mixture of 4,4'-diaminobenzophenone and 4,4'-diaminodiphenyl sulfone at a molar ratio of 1:1; the imidization reagent is a mixture of acetic anhydride and pyridine at a molar ratio of 2:1, and the mass of the mixture is 1.7 times the sum of the mass of the dianhydride monomer and the diamine monomer;

[0081] (4) the hydrogel is freeze-dried, heat imidization is performed at 160℃ / 1h, 180℃ / 2h, and after crushing, a aerogel powder for polyolefin modification is obtained. The corresponding tensile strength of the polypropylene composite material is 46.8MPa, the bending strength is 57.1MPa, and the volume resistivity is 8.6×10 7 Ω·m.

[0082] Example 7

[0083] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0084] (1) aramid fibers are placed in a reaction kettle containing alkali and dimethyl sulfoxide, stirred at room temperature for 6 days to prepare aramid nanofibers, then long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide is added, and after uniform stirring, an aramid nanofiber dispersion liquid is obtained; the alkali is potassium hydroxide; the ratio of the aramid fiber, the alkali and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of the long-chain alkyl quaternary ammonium salt to the aramid fiber is 0.25:1;

[0085] (2) concentrated nitric acid is added to the aramid nanofiber dispersion liquid, then pyrrole monomer and an initiator are added to the dispersion liquid, and after reaction at 15℃ for 10h, a polyazole-coated aramid nanofiber dispersion liquid is obtained; the initiator is iron chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of the pyrrole monomer to the aramid fiber is 0.4:1; the mass ratio of the initiator to the pyrrole monomer is 3:1;

[0086] (3) the dianhydride monomer and the diamine monomer are dispersed in an organic solvent N,N-dimethylacetamide, a polyamide acid solution is obtained after reaction at 30℃ for 8h, then mixed with the polyazole-coated aramid nanofiber dispersion liquid, and a chemical imidization reagent is added to react for 3h to perform partial imidization; after standing, solvent exchange is performed with deionized water to prepare a hydrogel; the molar ratio of the dianhydride monomer to the diamine monomer is 1.02:1; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is 5:1; the dianhydride monomer is 3,3',4,4'-benzophenonetetracarboxylic dianhydride; the diamine monomer is a mixture of 4,4'-oxydianiline and 4,4'-diamino diphenyl sulfone in a molar ratio of 1:1; the imidization reagent is a mixture of acetic anhydride and pyridine in a molar ratio of 2:1, and the mass of the mixture is 2.1 times the sum of the mass of the dianhydride monomer and the diamine monomer;

[0087] (4) the hydrogel is freeze-dried, heat imidized under the condition of 160℃ / 1h, 180℃ / 2h, and after crushing, an aerogel powder for polyolefin modification is obtained. The corresponding polypropylene composite material has a tensile strength of 43.7MPa, a bending strength of 54.3MPa, and a volume resistivity of 8.3×10 7 Ω·m.

[0088] Example 8

[0089] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0090] (1) aramid fibers are put into a reaction kettle containing alkali and dimethyl sulfoxide, stirred at room temperature for 7 days to prepare aramid nanofibers, then a long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide is added, and after uniform stirring, an aramid nanofiber dispersion liquid is obtained; the alkali is potassium hydroxide; the ratio of the aramid fiber, the alkali and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of the long-chain alkyl quaternary ammonium salt to the aramid fiber is 0.35:1;

[0091] (2) concentrated nitric acid is added to the aramid nanofiber dispersion liquid, then pyrrole monomer and an initiator are added to the dispersion liquid, and after reaction at 15℃ for 11h, a polyazole-coated aramid nanofiber dispersion liquid is obtained; the initiator is iron chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of the pyrrole monomer to the aramid fiber is 0.5:1; the mass ratio of the initiator to the pyrrole monomer is 3.2:1;

[0092] (3) dispersing dianhydride monomer and diamine monomer in organic solvent N, N-dimethylacetamide, obtaining polyamide acid solution after 9h reaction at 30℃, then mixing with polyazole coated aramid nanofiber dispersion liquid, adding chemical imidization reagent to react for 3h to carry out partial imidization; after standing, solvent exchange with deionized water to prepare hydrogel; the molar ratio of the dianhydride monomer to the diamine monomer is 1.02:1; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is 2.4:1; the dianhydride monomer is a mixture of pyromellitic dianhydride and 3, 3', 4, 4'-benzophenone tetracarboxylic dianhydride with a molar ratio of 1:3; the diamine monomer is 4, 4'-diamino diphenyl sulfone; the imidization reagent is a mixture of acetic anhydride and pyridine with a molar ratio of 2:1, and the mass of the mixture is 2.1 times the sum of the mass of the dianhydride monomer and the diamine monomer;

[0093] (4) freeze-drying the hydrogel, carrying out thermal imidization under the condition of 160℃ / 1h, 180℃ / 2h, crushing to obtain aerogel powder for polyolefin modification. The corresponding tensile strength of the polypropylene composite material is 44.2MPa, the bending strength is 55.7MPa, and the volume resistivity is 7.3×10 6 Ω·m.

[0094] Example 9

[0095] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0096] (1) placing aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stirring at room temperature for 5.5 days to prepare aramid nanofiber, then adding long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide, and stirring uniformly to obtain aramid nanofiber dispersion liquid; the alkali is potassium hydroxide; the ratio of the aramid fiber, the alkali and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of the long-chain alkyl quaternary ammonium salt to the aramid fiber is 0.35:1;

[0097] (2) adding concentrated nitric acid to the aramid nanofiber dispersion liquid, then adding pyrrole monomer and initiator to the dispersion liquid, obtaining polyazole coated aramid nanofiber dispersion liquid after 8h reaction at 15℃; 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 the pyrrole monomer to the aramid fiber is 0.45:1; the mass ratio of the initiator to the pyrrole monomer is 3.8:1;

[0098] (3) dispersing dianhydride monomer and diamine monomer in organic solvent N, N-dimethylacetamide, obtaining polyamide acid solution after 8.5h reaction at 30℃, then mixing with polyazole coated aramid nanofiber dispersion liquid, adding chemical imidization reagent to react for 3h to carry out partial imidization; after standing, solvent exchange with deionized water to prepare hydrogel; the molar ratio of the dianhydride monomer to the diamine monomer is 1.02:1; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is 2.2:1; the dianhydride monomer is 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride; the diamine monomer is a mixture of 4,4'-diaminodiphenyl methane and 4,4'-diaminodiphenyl sulfone with a molar ratio of 1:1; the imidization reagent is a mixture of acetic anhydride and pyridine with a molar ratio of 2:1, and the mass of the mixture is 1.6 times the sum of the mass of the dianhydride monomer and the diamine monomer;

[0099] (4) freeze-drying the hydrogel, carrying out thermal imidization under the condition of 160℃ / 1h, 180℃ / 2h, crushing to obtain aerogel powder for polyolefin modification. The corresponding tensile strength of the polypropylene composite material is 44.3MPa, the bending strength is 52.9MPa, and the volume resistivity is 4.8×10 6 Ω·m.

[0100] Example 10

[0101] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0102] (1) placing aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stirring at room temperature for 6 days to prepare aramid nanofiber, then adding long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide, and stirring uniformly to obtain aramid nanofiber dispersion liquid; the alkali is potassium hydroxide; the ratio of the aramid fiber, the alkali and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of the long-chain alkyl quaternary ammonium salt to the aramid fiber is 0.25:1;

[0103] (2) adding concentrated nitric acid to the aramid nanofiber dispersion liquid, then adding pyrrole monomer and initiator to the dispersion liquid, obtaining polyazole coated aramid nanofiber dispersion liquid after 10h reaction at 15℃; 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 the pyrrole monomer to the aramid fiber is 0.4:1; the mass ratio of the initiator to the pyrrole monomer is 3:1;

[0104] (3) dispersing dianhydride monomer and diamine monomer in organic solvent N, N-dimethylacetamide, obtaining polyamide acid solution after 8h reaction at 30℃, then mixing with polyazole coated aramid nanofiber dispersion liquid, adding chemical imidization reagent to react for 3h to carry out partial imidization; after standing, solvent exchange with deionized water to prepare hydrogel; the molar ratio of dianhydride monomer to diamine monomer is 1.02:1; the mass ratio of the sum of dianhydride monomer and diamine monomer to aramid fiber is 2:1; the dianhydride monomer is 3,3',4,4'-benzophenone tetracarboxylic dianhydride; the diamine monomer is a mixture of 4,4'-oxydianiline and 4,4'-diamino diphenyl sulfone with a molar ratio of 1:1; the imidization reagent is a mixture of acetic anhydride and pyridine with a molar ratio of 2:1, and the mass of the mixture is 2.1 times the sum of the mass of dianhydride monomer and diamine monomer;

[0105] (4) freeze-drying the hydrogel, carrying out thermal imidization under the condition of 160℃ / 1h, 180℃ / 2h, crushing to obtain aerogel powder for polyolefin modification. The corresponding tensile strength of polypropylene composite material is 47.4MPa, the bending strength is 56.3MPa, and the volume resistivity is 3.1×10 6 Ω·m.

[0106] Comparative Example 1

[0107] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0108] (1) placing aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stirring at room temperature for 6 days to prepare aramid nanofiber dispersion liquid; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.3g:450ml;

[0109] (2) adding concentrated nitric acid to the aramid nanofiber dispersion liquid first, then adding long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide, pyrrole monomer and initiator to the dispersion liquid in sequence, and obtaining modified aramid nanofiber dispersion liquid after 10h reaction at 15℃; the initiator is ferric chloride; the molar ratio of nitric acid to potassium hydroxide in 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;

[0110] (3) the dianhydride monomer and the diamine monomer are dispersed in an organic solvent N,N-dimethylacetamide, a polyamide acid solution is obtained after reaction at 30 DEG C for 8h, then mixed with the modified aramid nanofiber dispersion liquid, and a chemical imidization reagent is added to react for 3h to perform partial imidization; after standing, solvent exchange is performed with deionized water to prepare a hydrogel; the molar ratio of the dianhydride monomer to the diamine monomer is 1.02:1; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is 2:1; the dianhydride monomer is 3,3',4,4'-benzophenonetetracarboxylic dianhydride; the diamine monomer is a mixture of 4,4'-oxydianiline and 4,4'-diaminodiphenyl sulfone at a molar ratio of 1:1; the imidization reagent is a mixture of acetic anhydride and pyridine at a molar ratio of 2:1, and the mass of the mixture is 2.1 times the sum of the mass of the dianhydride monomer and the diamine monomer;

[0111] (4) the hydrogel is freeze-dried, heat imidization is performed at 160 DEG C / 1h, 180 DEG C / 2h, and after crushing, an aerogel powder for polyolefin modification is obtained. The corresponding polypropylene composite material has a tensile strength of 30.4 MPa, a bending strength of 39.2 MPa, and a volume resistivity of 7.5 x 10 9 Ω·m.

[0112] Comparative Example 2

[0113] A preparation method of an aerogel powder for polyolefin modification, comprising the following steps:

[0114] (1) aramid fibers are placed in a reaction kettle containing alkali and dimethyl sulfoxide, stirred at room temperature for 6 days to prepare aramid nanofibers, then a long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide is added, and after uniform stirring, an aramid nanofiber dispersion liquid is obtained; the alkali is potassium hydroxide; the ratio of the aramid fiber, the alkali, and dimethyl sulfoxide is 1g:1.3g:450ml; the mass ratio of the long-chain alkyl quaternary ammonium salt to the aramid fiber is 0.25:1;

[0115] (2) concentrated nitric acid is added to the aramid nanofiber dispersion liquid, then pyrrole monomer and an initiator are added to the dispersion liquid, and after reaction at 15 DEG C for 10h, a poly-pyrrole-coated aramid nanofiber dispersion liquid is obtained; the initiator is iron chloride; the molar ratio of nitric acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of the pyrrole monomer to the aramid fiber is 1:1; the mass ratio of the initiator to the pyrrole monomer is 3:1;

[0116] (3) dispersing the dianhydride monomer and the diamine monomer in an organic solvent N,N-dimethylacetamide, obtaining a polyamide acid solution after reacting at 30℃ for 8h, then mixing with the polyacrylonitrile coated aramid nanofiber dispersion liquid, adding a chemical imidization reagent to react for 3h to perform partial imidization; after standing, solvent exchange with deionized water to prepare a hydrogel; the molar ratio of the dianhydride monomer to the diamine monomer is 1.02:1; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is 2:1; the dianhydride monomer is 3,3',4,4'-benzophenonetetracarboxylic dianhydride; the diamine monomer is a mixture of 4,4'-oxydianiline and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1:1; the imidization reagent is a mixture of acetic anhydride and pyridine in a molar ratio of 2:1, and the mass of the mixture is 2.1 times the sum of the mass of the dianhydride monomer and the diamine monomer;

[0117] (4) freeze-drying the hydrogel, performing thermal imidization at 160℃ / 1h, 180℃ / 2h, crushing to obtain aerogel powder for polyolefin modification. The corresponding polypropylene composite material has a tensile strength of 32.3MPa, a bending strength of 41.6MPa, and a volume resistivity of 2.8×10 7 Ω·m.

[0118] Figure 1 The transmission electron microscope image of the polyacrylonitrile coated aramid nanofiber prepared for Example 10, Figure 2 The transmission electron microscope image of the modified aramid nanofiber prepared for Comparative Example 1; the test sample is the corresponding polyacrylonitrile coated aramid nanofiber and modified aramid nanofiber repeatedly washed and filtered with deionized water. From Figure 1 It can be seen from the figure that a clear polyacrylonitrile coating structure is formed on the surface of the aramid nanofiber, which promotes the dispersion of the aramid nanofiber in the polyimide resin, promotes the formation of a gel structure, and is conducive to the construction of a fiber reinforced network and a conductive network. From Figure 2 It can be seen from the figure that no coating structure is formed on the surface of the aramid nanofiber. This shows that the addition of long-chain alkyl quaternary ammonium salt in advance to the aramid nanofiber dispersion liquid can improve the dispersibility of the aramid nanofiber and play a template role, which is conducive to the formation of a polyacrylonitrile coating structure. However, the addition of polar substances such as acid, pyrrole monomer and initiator in advance will destroy the balance of the solution, affect the surface modification function of the long-chain alkyl quaternary ammonium salt, and is not conducive to the attachment of the pyrrole monomer on the fiber surface, and cannot form a coating structure by in-situ polymerization.

[0119] It can be seen from the above figures and data that the aerogel composite prepared by the present application is a porous solid material formed by combining aramid nanofibers and polypyrrole into one-dimensional composite fibers and combining with polyimide resin. The aerogel material is compounded with polyolefin resin material, and the synergistic effect between different components in the composite material at the molecular level forms a resin composite material with new structure and function. The emergence of this structure of aerogel material, which integrates the properties of different materials, has obtained a polyolefin resin composite material with high strength and antistatic performance. Specifically, compared with Example 10, Comparative Example 1 does not add cetyltrimethylammonium bromide in advance, which cannot play the role of dispersion and template, cannot form a coating structure, affects the dispersion of aramid nanofibers, and is not conducive to the formation of the reinforcing network and the conductive network, so the mechanical properties and conductivity of the prepared polypropylene composite material are reduced. Compared with Example 10, Comparative Example 2 adds too much polypyrrole, which does not further improve the conductivity, but the mechanical properties decrease significantly. This is because polypyrrole as a conductive polymer has low mechanical strength, and when its amount is too much, it is easy to cause excessive coating of polypyrrole, which is not conducive to the dispersion of fibers and the formation of conductive paths, and affects the improvement of the mechanical properties of the polyimide-based aerogel powder, and is easy to cause rupture during the polyolefin melt processing process, resulting in a decrease in the strength and toughness of the polyolefin composite material.

[0120] The above examples do not limit the content of the composition of the present application in any way, and any slight modification, equivalent change and modification of the above examples according to the technical essence or composition components or content of the present application still belong to the scope of the technical scheme of the present application.

Claims

1. A method for producing an aerogel powder for polyolefin modification, characterized by, The method comprises the following steps: (1) putting aramid fibers into a reaction kettle containing alkali and dimethyl sulfoxide to prepare aramid nanofiber, then adding long-chain alkyl quaternary ammonium salt to obtain aramid nanofiber dispersion liquid; (2) adding acid to the aramid nanofiber dispersion liquid, then adding pyrrole monomer and initiator to the dispersion liquid, and obtaining poly-pyrrole coated aramid nanofiber dispersion liquid after reaction; the mass ratio of the pyrrole monomer to the aramid fiber is (0.1-0.6):1; (3) preparing polyamide acid from dianhydride and diamine in an organic solvent, then mixing the polyamide acid with the poly-pyrrole coated aramid nanofiber dispersion liquid, adding chemical imidization reagent for partial imidization; standing, then performing solvent exchange with deionized water to prepare hydrogel; the mass ratio of the sum of the dianhydride monomer and the diamine monomer to the aramid fiber is (1-5):1; (4) obtaining aerogel powder for polyolefin modification by freeze-drying, thermal imidization, and crushing the hydrogel.

2. The method for preparing an aerogel powder for polyolefin modification according to claim 1, characterized by, The alkali in the step (1) is sodium hydroxide or potassium hydroxide.

3. The method for preparing aerogel powder for polyolefin modification as described in claim 1, characterized in that, The ratio of the aramid fiber, the alkali, and the dimethyl sulfoxide in the step (1) 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, The long-chain alkyl quaternary ammonium salt in the 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.

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

7. An aerogel powder for polyolefin modification, characterized by, The method is prepared by the method of any one of claims 1-6.

8. The use of the aerogel powder for polyolefin modification in claim 7 in the preparation of pipe, plate, grouting equipment parts, and grouting bag.

9. A polyolefin composite material, characterized by, The composition comprises the following components by weight: 50-150 parts of polyolefin resin, 1-30 parts of the aerogel powder for polyolefin modification in claim 7, 1-10 parts of fiber reinforced filler, and 1-5 parts of processing aid.

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