High-strength modified aramid nanofiber, and preparation method and application thereof

Abstract

The application belongs to the technical field of fiber materials, and particularly relates to high-strength modified aramid nanofiber as well as a preparation method and application thereof. The high-strength modified aramid nanofiber prepared by the application is a composite fiber with a rough surface in a one-dimensional form formed by aramid nanofiber and polyaniline, which can be directly used as a conductive and reinforcing filler of a polyamide resin. Due to the existence of the rough structure polyaniline coating layer, high interfacial force exists between the fiber and the polyamide resin, and the use requirements of the polyamide mechanical properties and antistatic properties are met. The aramid nanofiber coated with the polyaniline with the rough structure is used as the modified material of the polyamide, the problem of low interfacial force existing in general fillers is solved, the polyamide resin composite material with high strength and antistatic properties is obtained, and the polyamide resin composite material can be widely applied in the fields of pipe materials, plate materials, grouting equipment parts and grouting bags.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fiber materials, and particularly relates to a high-strength modified aramid nanofiber as well as a preparation method and application thereof. BACKGROUND

[0002] Aramid fiber is a general term for aromatic polyamide fibers, which is divided into poly-p-phenylene terephthalamide and poly-m-phenylene isophthalamide according to the molecular structure. Among them, poly-p-phenylene terephthalamide is obtained by condensation polymerization of p-terephthaloyl chloride and p-phenylenediamine. Aramid fiber based on poly-p-phenylene terephthalamide is also called aramid 1414 or para-aramid, which was invented by DuPont Company in the 1960s and realized industrialization, and the trade name is Kevlar. It is prepared by dry-jet wet spinning of poly-p-phenylene terephthalamide liquid crystal solution. In the fiber, the rigid conjugated main chain of poly-p-phenylene terephthalamide shows high orientation order, and strong intermolecular forces are formed through ordered hydrogen bonds and π-π interactions, which is the source of high performance of para-aramid. Due to the characteristics of light weight, high strength, high modulus, heat resistance and flame resistance of para-aramid, aramid products directly processed therefrom or high-performance resin composites prepared by using para-aramid as a reinforcing body have important applications in the fields of aerospace, transportation, national defense equipment, special protection, sound absorption and vibration reduction, insulation and the like. However, para-aramid is difficult to be dissolved in conventional solvents and will not soften before thermal decomposition temperature, and the fiber surface has high chemical inertness, which greatly increases the difficulty of processing and compounding with other resin materials. In order to form effective interfacial bonding with resin, various methods of physical and chemical treatment of fiber surface are proposed in the prior art, such as ion plasma modification, ultrasonic immersion, surface coating and solid solution immersion. As a nanoscale product of aramid fiber, aramid nanofiber 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, self-assembly of high-level structures from bottom to top, and has become one of the materials with great application potential for building high-performance composites. However, aramid nanofiber also faces the technical problem of poor compatibility with resin.

[0003] Among them, polyamide is a thermoplastic industrial plastic with good elasticity, self-lubricity, wear resistance, corrosion resistance and easy molding, and is widely used in industry, textile, automobile, machinery manufacturing and other aspects. Although the comprehensive performance of polyamide is excellent, due to the easy formation of amide bond between amide bond and water molecules, the water absorption of polyamide is large, which causes low dimensional stability, poor antistatic property, easy deterioration at high temperature, and not ideal strength and modulus, etc. These factors limit the application of polyamide.

[0004] Aramid nanofiber has high aspect ratio, large specific surface area, and is expected to solve the problem of low mechanical properties of polyamide resin. CN120518993A discloses a preparation method of aramid nanofiber / polyurethane composite material: (1) preparing an organosilicon modified polyurethane prepolymer; (2) preparing fluorinated modified aramid nanofiber; (3) uniformly dispersing FANF in a solvent to form a dispersion liquid, adding a chain extender to the organosilicon modified polyurethane prepolymer according to a preset chain extension coefficient, and then adding the FANF dispersion liquid, mixing and curing to form a high-performance polyurethane elastomer. Through the synergistic effect of the rigid reinforcing effect of aramid nanofiber and the interfacial lubrication properties of polydimethylsiloxane, the wear resistance and mechanical strength of the material are significantly improved. CN118374023A provides a preparation method of modified aramid nanofiber, a composite material thereof and an application thereof. First, aramid nanofiber hydrogel is added to solvent A, then alkoxysilane compounds and silicate compounds are added respectively to obtain primary modified aramid nanofiber hydrogel; and then a silane coupling agent is added to heat and react to form secondary modified aramid nanofiber hydrogel. The primary modified aramid nanofiber has flocculation function for synthetic latex, and the secondary modified aramid nanofiber has flocculation function for synthetic latex and natural latex, so that the modified aramid nanofiber can be used to improve the performance of high polymer materials. The patents CN120574422A, CN120504961A, CN120607742A, CN120310019A, CN120589733A, CN119431944A and CN112029272A all use conductive polymers as conductive fillers to improve the antistatic performance of the composite material, but they do not fundamentally solve the problem of poor dispersion of polyaniline in the resin. SUMMARY

[0005] In order to solve the technical problems of easy agglomeration of aramid nanofiber and poor compatibility with polyamide resin, the present application provides a high-strength modified aramid nanofiber. The aramid nanofiber is modified by polyaniline coating to form a micro-rough structure on its surface, increase the interaction area with the matrix resin, and thus improve the interfacial energy, the mechanical strength and the antistatic ability of the polyamide resin.

[0006] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0007] A preparation method of high-strength modified aramid nanofiber, comprising the following steps:

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

[0009] (2) adding acid to the aramid nanofiber dispersion liquid and stirring uniformly, then adding active group-containing POSS to the dispersion liquid, heating and stirring for a certain time to obtain a POSS modified aramid nanofiber dispersion liquid;

[0010] (3) adding aniline monomer and initiator to the POSS modified aramid nanofiber dispersion liquid, and reacting for a certain time to obtain high-strength modified aramid nanofiber.

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

[0012] The most common reinforcing filler for polyamide is various organic or inorganic fiber materials. Aramid nanofiber, as a nanoscale product of aramid fiber, has a 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, which were used to enhance the stability of concrete. However, aramid nanofiber / inorganic filler aerogel is only suitable for the modification of inorganic materials such as concrete. When it is directly applied to organic polymer materials such as polyamide, it is difficult to disperse uniformly in polyamide due to compatibility problems, which may cause stress concentration and even reduce the performance of the composite material.

[0013] To improve the antistatic property of polyamide resin, conductive fillers are generally added. The conductive substances 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 polyamide resin has both the processing characteristics of polymer materials and the conductivity of metal. Compared with metal, the composite conductive polyamide resin material has the advantages of good processability, simple process, corrosion resistance, large adjustable range of resistivity, and low price. At present, the conductive materials added to the composite conductive polyamide resin material are small molecule antistatic agents and conductive fillers. Adding antistatic agents is the most common antistatic method for polymer materials, which forms a conductive layer on the surface of the material, reduces the surface resistivity, and makes the generated static charge quickly leak out; at the same time, it gives the material surface certain lubricity, reduces the friction coefficient, and inhibits and reduces the generation of static charge. However, the reduction of resistivity by adding small molecule antistatic agents is limited, the durability is poor, and the mechanical properties of the composite material are reduced. Therefore, at present, the composite polyamide resin material mainly adds conductive fillers. Among them, polyaniline as a common conductive polymer material can improve the antistatic property of polyamide resin to a certain extent. In the inventors' previous work, aramid nanofiber with rough polypyrrole coating structure was directly used as the reinforcing phase of olefin, but polypyrrole has poor thermal stability and is difficult to meet the high temperature processing requirements of polyamide. Compared with polypyrrole and other conductive polymers, polyaniline has higher thermal stability and can meet the processing requirements of polyamide resin.

[0014] However, a large amount of reinforcing fillers and conductive substances will cause the processing performance of the composite material to decrease, the compatibility of the components to become poor, and it is difficult to simultaneously improve the mechanical properties and antistatic ability. The inventors prepared aramid nanofiber with polyaniline coating structure in previous work. However, the surface of the fiber is smooth, and the interaction force with polyamide is low, which is easy to cause interface separation under the action of pulling force, so it is necessary to prepare it into composite aerogel to increase the interface area with polyamide resin, which increases the process complexity and cost.

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

[0016] More importantly, the polyacrylonitrile nanofiber coated with polyaniline with rough structure is used as the additive of the polyamide material, and the compatibility problem existing in the general filler is solved. By improving the roughness of the surface of the polyacrylonitrile nanofiber coated with polyaniline, the polyamide resin can be filled in the groove on the fiber surface, and the interface bonding degree between the fiber and the polyamide resin is enhanced through physical entanglement. Compared with the polyacrylonitrile nanofiber coated with polyaniline with smooth structure prepared by the inventor before, the polyamide resin can be better filled in the groove on the rough fiber surface, so that the contact area between the fiber and the polyamide resin is improved; at the same time, the polyamide resin can be better physically entangled on the fiber surface, and the fiber and the polyamide can be mechanically locked together after curing, so that the interface bonding force and the mechanical bonding strength between the polyacrylonitrile nanofiber coated with polyaniline and the polyamide resin are enhanced.

[0017] Overall, the high-strength modified polyacrylonitrile nanofiber prepared by the application is a composite fiber with rough surface formed by the polyacrylonitrile nanofiber and polyaniline in one-dimensional form, which can be directly used as the conductive and reinforcing filler of the polyamide resin. Due to the existence of the rough structure polyaniline coating layer, the interface interaction force between the fiber and the polyamide resin is high, which meets the use requirements of the mechanical property and the antistatic property of the polyamide. The high-strength modified polyacrylonitrile nanofiber is compounded with different polyamide resin materials, and the different components in the composite material synergistically act at the molecular level, so that a resin composite material with new structure and function is formed.

[0018] Further, the step (1) is specifically: putting aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide to prepare aramid nanofiber, and then adding long-chain alkyl quaternary ammonium salt to obtain aramid nanofiber dispersion liquid.

[0019] Further, the alkali in the step (1) is sodium hydroxide or potassium hydroxide.

[0020] Further, the ratio of aramid fiber, alkali and dimethyl sulfoxide in the step (1) is 1g: (1-2) g: (350-500) ml. In particular, the preparation process of aramid nanofiber is stirring reaction at room temperature in the reaction kettle for 4-8 days. Further, commercial aramid fiber is used. In the preparation process of commercial aramid fiber, various oils are generally left on the surface of the fiber, which can be cleaned. Specifically, the fiber surface oil and other impurities can be removed by cleaning with acetone solvent, sodium dodecyl benzene sulfonate solution and deionized water in turn.

[0021] Further, 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. In particular, hexadecyl trimethyl ammonium bromide can be selected. By adding long-chain alkyl quaternary ammonium salt to aramid nanofiber dispersion liquid in advance, the dispersibility of aramid nanofiber can be improved, and the long-chain alkyl quaternary ammonium salt can also play a role as a template. This is because the aramid nanofiber prepared by alkali / DMSO soaking method contains a large number of carboxyl, hydroxyl and other reactive oxygen-containing functional groups on the surface, which is electronegative. Although the aramid nanofiber has large aspect ratio and excellent mechanical properties, the mixed solution after soaking is extremely unstable. When new polar substances (acid, aniline monomer, initiator, etc.) are added, the balance of the solution will be destroyed, the fiber bundles will be combined, and the fiber agglomeration phenomenon will occur, which will affect the dispersion of aramid nanofiber. As a cationic surface modifier, long-chain alkyl quaternary ammonium salt has good surface modification function. The presence of ammonium ion is conducive to the combination of long-chain alkyl quaternary ammonium salt with aramid nanofiber, and improves the dispersibility of aramid nanofiber. At the same time, 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 adhesion of aniline monomer to form a coating structure by in-situ polymerization. In addition, the presence of long-chain alkyl can hinder the combination of fibers and promote the dispersion of fibers. In the previous work of the inventors, 1wt% sodium hydroxide aqueous solution was used to corrode aramid fiber for several hours, and then conductive monomer was directly polymerized on the surface of the aramid fiber to prepare polymer-coated aramid fiber. The main form of the aramid fiber with this structure has not changed, which is not a nano structure, but only the surface of the fiber is corroded. Although the relatively thick fiber will not agglomerate, 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 field of polyamide modification, but only in the field of reinforcing inorganic materials such as concrete and cement paste.

[0022] Further, the mass ratio of the long-chain alkyl quaternary ammonium salt to 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; particularly, (0.2-0.4):1. The appropriate amount of long-chain alkyl quaternary ammonium salt not only can fully play the role of dispersing aramid nanofiber and as a template for aniline polymerization, but also can 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, which is not conducive to the dispersion of the fiber.

[0023] Further, the acid in step (2) is one or more of hydrochloric acid, sulfuric acid, nitric acid, acetic acid, propionic acid, formic acid, malic acid, and phosphoric acid. The molar ratio of the acid to the base in step (1) is (0.5-2):1, and further (1-2):1. In particular, one of concentrated hydrochloric acid, concentrated sulfuric acid, and concentrated nitric acid can be selected. Further, high-concentration concentrated nitric acid can be selected.

[0024] Further, the mass ratio of the POSS to the long-chain alkyl quaternary ammonium salt in step (2) is (0.01-0.3):1.

[0025] Further, the active group-containing POSS in step (2) is at least one of amino-containing POSS, hydroxyl-containing POSS, epoxy-containing POSS, carboxyl-containing POSS, and mercapto-containing POSS. Specifically, it can be at least one of aminopropyl heptaphenyl POSS, aminopropyl heptaisobutyl POSS, octaaminophenyl POSS, octaaminopropyl POSS, heptaisooctyl epoxy POSS, heptaisobutyl epoxy POSS, octahydroxybutyl POSS, octa mercapto propyl POSS, mercapto propyl isobutyl POSS, octa methyl carboxyl POSS, octa ethyl carboxyl POSS, and octa propyl carboxyl POSS. In particular, amino-functionalized POSS can be selected. Further, octaaminophenyl POSS or octaaminopropyl POSS with eight functional groups can be selected. Amino has a higher activity and is more likely to form a chemical bond with oxygen-containing functional groups such as carboxyl groups, which can better promote the combination of POSS and aramid nanofiber. In particular, the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is (0.05-0.2):1. Since POSS has a large volume and hydrophobic effect, the amount of POSS should not be too much, otherwise its large structure will hinder the attachment of polyaniline, affecting the modification of aramid nanofiber.

[0026] POSS plays a role of surface modification and dispersion polymerization in the present application. POSS (polyhedral oligomeric silsesquioxane) is a kind of organic-inorganic hybrid material, which is externally connected with organic groups and exhibits a three-dimensional structure system at the nanoscale. Compared with general polysiloxanes, POSS has better heat resistance and lower surface energy. The POSS molecule has a closed cubic structure in macroscopic. The alkane substituents or active reaction groups are externally connected to the POSS molecule, wherein the active groups can not only improve the compatibility between POSS and the polymer, but also realize the chemical bonding between POSS and the polymer. Therefore, the POSS is used to modify aramid nanofiber to improve the interfacial performance of aramid nanofiber and polyaniline. Specifically, there are a large number of oxygen-containing functional groups such as hydroxyl and carboxyl on the surface of aramid nanofiber prepared by alkali splitting method, and the active groups on the POSS containing active groups are easy to form strong chemical bonds such as hydrogen bonds with the oxygen-containing functional groups on the surface of aramid nanofiber. The scattering attachment of POSS on the surface of aramid nanofiber will affect the template effect of long-chain alkyl quaternary ammonium salt and affect the polymerization process of aniline monomer, and the uneven polymerization of aniline monomer on the surface of aramid nanofiber leads to the formation of rough structure on the surface of aramid nanofiber.

[0027] Further, the temperature of heating and stirring in the step (2) is 80-100℃, and the time is 3-5h. Through the process of heating and stirring, not only the uniform dispersion of the POSS containing active groups can be promoted, but also the chemical bonds between the POSS and the oxygen-containing functional groups on the surface of aramid nanofiber can be formed better.

[0028] Further, the initiator in the step (3) 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 nanofiber is modified by long-chain alkyl quaternary ammonium salt, the addition of polar compounds such as acid, aniline monomer and initiator will not cause the merging of fiber bundles. If the polar compounds such as acid, aniline monomer or initiator are added first, and then the long-chain alkyl quaternary ammonium salt is added, not only the fiber bundles will merge, but also the long-chain alkyl quaternary ammonium salt will not be adsorbed on the surface of the fiber, losing the template effect and not easy to form the coating structure of polyaniline.

[0029] Further, the reaction temperature in the step (3) is 0-30℃, and the reaction time is 8-12h.

[0030] Further, the mass ratio of initiator to aniline monomer in the step (3) is (1-5):1.

[0031] Further, the mass ratio of the aniline monomer to the aramid fiber in step (3) is (0.1-1):1. The introduction of the POSS modifier improves the dispersibility of the aramid nanofiber and can better promote the in-situ polymerization of the aniline monomer and increase the loading of polyaniline. Further, the mass ratio of the aniline monomer to the aramid fiber is (0.2-0.8):1 or (0.3-0.7):1. The aramid nanofiber is coated with an appropriate amount of polyaniline, which is conducive to the formation of a rough structure and can avoid the problem of excessive polyaniline falling off.

[0032] Further, the reaction in step (3) further includes a filtration, washing, and drying process. The washing is performed using deionized water, and the drying is performed by placing in an oven.

[0033] Further, the application also provides a high-strength modified aramid nanofiber and its application in the preparation of high-strength pipe materials, plate materials, grouting equipment parts, and grouting bags.

[0034] On the other hand, the application provides a polyamide composite material, which comprises the following components by weight: 50-150 parts of a polyamide resin, 1-30 parts of a high-strength modified aramid nanofiber, 1-30 parts of an inorganic fiber reinforcing filler, and 1-10 parts of a processing aid. In particular, the composite material can be granulated and formed by an extruder, and the extrusion temperature is 200-300 DEG C, in particular 220-260 DEG C. Through the high-temperature melting process, it is beneficial for the polyamide melt to fully infiltrate the rough structure on the surface of the aramid nanofiber. The type of the polyamide resin is not particularly limited, and the types commonly used in the art, such as polyamide 6, polyamide 66, polyamide 610, and polyamide 12, can be used. Further, the polyamide 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.

[0035] The raw materials used in the application all belong to common types and can be prepared, purchased, or recycled. For example, the aramid fiber can be selected from the K series fibers of DuPont, the polyamide can be selected from the M series polyamides of Xinhui Meida, the carbon fiber can be selected from the T series carbon fibers of Toray, the antioxidant can be selected from the 1010 series of Xindongyi Chemical, and the coupling agent can be selected from the KH570 series of Hairexin Material, and the like. Further, the application uses recycled polyamide 6 as a base material, which not only saves costs but also solves the technical problem of poor mechanical properties of recycled polyamide.

[0036] Advantages

[0037] (1) The POSS has a large volume exclusion effect and hydrophobic property. The random attachment of the POSS on the surface of the aramid nanofiber can affect the template effect of the long-chain alkyl quaternary ammonium salt and the polymerization process of the aniline monomer. The uneven polymerization of the aniline monomer on the surface of the aramid nanofiber leads to the formation of a rough structure on the surface of the aramid nanofiber.

[0038] (2) 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, facilitate the attachment of the aniline monomer, and form a coating structure by in-situ polymerization. In addition, the presence of the long-chain alkyl group can hinder the merging of the fibers and promote the dispersion of the fibers.

[0039] (3) After the aramid nanofiber is coated with polyaniline, not only the dispersion performance of the fiber is improved, but also the compatibility of the aramid nanofiber and the polyamide resin is improved through the rough coating interface, so that the aramid nanofiber is uniformly dispersed in the matrix resin. In turn, the aramid nanofiber as the core layer substrate of polyaniline can also promote the dispersion of polyaniline, so that polyaniline forms a network structure, which is conducive to the formation of a conductive path. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A scanning electron microscope image of the aramid nanofiber prepared in step (1) of Example 10.

[0041] Figure 2 A scanning electron microscope image of the high-strength modified aramid nanofiber prepared in Example 10.

[0042] Figure 3 A scanning electron microscope image of the high-strength modified aramid nanofiber prepared in Comparative Example 1. DETAILED DESCRIPTION

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

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

[0045] Performance test: a kind of polyamide 6 composite material, comprising the following components by weight: polyamide 6 resin 110 parts, 12 parts of high-strength modified aramid nanofiber (prepared in examples 1-10 and comparative examples 1-2, respectively), 4 parts of carbon fiber, 1.8 parts of antioxidant 168, 3.5 parts of polytetrafluoroethylene lubricant. The above components are added to a twin-screw extruder, and melt extrusion granulation is carried out (the temperature of the extruder is 230 DEG C). Then standard samples are prepared, and their mechanical properties and antistatic properties are tested respectively. Among them, the tensile strength refers to ISO 527-2, the bending strength refers to ISO 178; and the volume resistivity of the sample is tested by using a resistance meter.

[0046] Example 1

[0047] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0048] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stir at room temperature for 6 days to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide, and stir uniformly to obtain aramid nanofiber dispersion; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.2g:430ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.33:1;

[0049] (2) Add concentrated nitric acid to the aramid nanofiber dispersion and stir uniformly, then add active group-containing POSS octaaminophenyl POSS, and stir at 80 DEG C for 3h to obtain POSS modified aramid nanofiber dispersion; the molar ratio of acid to potassium hydroxide in concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.17:1;

[0050] (3) Add aniline monomer and initiator ferric chloride to the POSS modified aramid nanofiber dispersion, react at 15 DEG C for 8h, filter, wash with deionized water, and dry in an oven to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.22:1; the mass ratio of initiator to aniline monomer is 3.6:1. After testing, the corresponding polyamide composite material has a tensile strength of 93.2 MPa, a bending strength of 109.7 MPa, and a volume resistivity of 8.7 x 10 6 Ω·m.

[0051] Example 2

[0052] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0053] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stir at room temperature for 5.5 days to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt cetyltrimethyl ammonium bromide, and stir uniformly to obtain aramid nanofiber dispersion; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.7g:440ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.18:1;

[0054] (2) Add concentrated nitric acid to the aramid nanofiber dispersion and stir uniformly, then add active group-containing POSS octaaminophenyl POSS, and stir at 83℃ for 4.5h to obtain POSS modified aramid nanofiber dispersion; the molar ratio of acid to potassium hydroxide in concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.06:1;

[0055] (3) Add aniline monomer and initiator ferric chloride to the POSS modified aramid nanofiber dispersion, react at 17℃ for 11h, filter, wash with deionized water, and dry in an oven to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.32:1; the mass ratio of initiator to aniline monomer is 2.8:1. The corresponding polyamide composite material has a tensile strength of 91.1MPa, a bending strength of 110.5MPa, and a volume resistivity of 5.3x10 6 Ω·m.

[0056] Example 3

[0057] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0058] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stir at room temperature for 4.5 days to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt cetyltrimethyl ammonium bromide, and stir uniformly to obtain aramid nanofiber dispersion; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.3g:500ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.5:1;

[0059] (2) Add concentrated nitric acid to the aramid nanofiber dispersion and stir uniformly, then add active group-containing POSS octaaminophenyl POSS, and stir at 90℃ for 4h to obtain POSS modified aramid nanofiber dispersion; the molar ratio of acid to potassium hydroxide in concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.12:1;

[0060] (3) adding aniline monomer and initiator ferric chloride into the POSS modified aramid nanofiber dispersion liquid, reacting at 18℃ for 10h, filtering, washing with deionized water, drying in an oven, to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.46:1; the mass ratio of initiator to aniline monomer is 3.1:1. The corresponding polyamide composite material has a tensile strength of 90.3MPa, a bending strength of 108.7MPa, and a volume resistivity of 3.4×10 6 Ω·m.

[0061] Example 4

[0062] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0063] (1) placing aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stirring at room temperature for 4 days to prepare aramid nanofiber, then adding long-chain alkyl quaternary ammonium salt hexadecyl trimethyl ammonium 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:2g:400ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.1:1;

[0064] (2) adding concentrated nitric acid into the aramid nanofiber dispersion liquid and stirring uniformly, then adding active group-containing POSS octaamino phenyl POSS, stirring at 80℃ for 5h, to obtain POSS modified aramid nanofiber dispersion liquid; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.01:1;

[0065] (3) adding aniline monomer and initiator ferric chloride into the POSS modified aramid nanofiber dispersion liquid, reacting at 15℃ for 12h, filtering, washing with deionized water, drying in an oven, to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.1:1; the mass ratio of initiator to aniline monomer is 2.4:1. The corresponding polyamide composite material has a tensile strength of 95.8MPa, a bending strength of 116.1MPa, and a volume resistivity of 8.3×10 6 Ω·m.

[0066] Example 5

[0067] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0068] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stir at room temperature for 4.5 days to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt cetyltrimethyl ammonium bromide, and stir uniformly to obtain aramid nanofiber dispersion; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.3g:500ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.22:1;

[0069] (2) Add concentrated nitric acid to the aramid nanofiber dispersion and stir uniformly, then add active group-containing POSS octaaminophenyl POSS, and stir at 90°C for 4h to obtain POSS modified aramid nanofiber dispersion; the molar ratio of acid to potassium hydroxide in concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.3:1;

[0070] (3) Add aniline monomer and initiator ferric chloride to the POSS modified aramid nanofiber dispersion, react at 18°C for 10h, filter, wash with deionized water, and dry in an oven to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.46:1; the mass ratio of initiator to aniline monomer is 3.1:1. The corresponding polyamide composite material has a tensile strength of 88.5MPa, a bending strength of 107.3MPa, and a volume resistivity of 6.4x10 6 Ω·m.

[0071] Example 6

[0072] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0073] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stir at room temperature for 6.5 days to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt cetyltrimethyl ammonium bromide, and stir uniformly to obtain aramid nanofiber dispersion; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1g:480ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.35:1;

[0074] (2) Add concentrated nitric acid to the aramid nanofiber dispersion and stir uniformly, then add active group-containing POSS octaaminophenyl POSS, and stir at 95°C for 5h to obtain POSS modified aramid nanofiber dispersion; the molar ratio of acid to potassium hydroxide in concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.2:1;

[0075] (3) adding aniline monomer and initiator ferric chloride into the POSS modified aramid nanofiber dispersion liquid, reacting at 23℃ for 8h, filtering, washing with deionized water, drying in an oven, to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.72:1; the mass ratio of initiator to aniline monomer is 3.6:1. The corresponding polyamide composite material has a tensile strength of 84.1 MPa, a bending strength of 101.3 MPa, and a volume resistivity of 7.9 x 10 5 Ω·m.

[0076] Example 7

[0077] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0078] (1) placing aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stirring at room temperature for 4.5 days to prepare aramid nanofiber, then adding long-chain alkyl quaternary ammonium salt hexadecyl trimethyl ammonium 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:500ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.22:1;

[0079] (2) adding concentrated nitric acid into the aramid nanofiber dispersion liquid and stirring uniformly, then adding active group-containing POSS octaamino phenyl POSS, stirring at 90℃ for 4h, to obtain POSS modified aramid nanofiber dispersion liquid; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.12:1;

[0080] (3) adding aniline monomer and initiator ferric chloride into the POSS modified aramid nanofiber dispersion liquid, reacting at 18℃ for 10h, filtering, washing with deionized water, drying in an oven, to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 1:1; the mass ratio of initiator to aniline monomer is 3.1:1. The corresponding polyamide composite material has a tensile strength of 80.3 MPa, a bending strength of 95.6 MPa, and a volume resistivity of 6.2 x 10 5 Ω·m.

[0081] Example 8

[0082] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0083] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stir at room temperature for 5.5 days to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt cetyltrimethyl ammonium bromide, and stir uniformly to obtain aramid nanofiber dispersion liquid; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.5g:380ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.3:1;

[0084] (2) Add concentrated nitric acid to the aramid nanofiber dispersion liquid and stir uniformly, then add active group-containing POSS octaaminophenyl POSS, and stir at 90°C for 3.5h to obtain POSS modified aramid nanofiber dispersion liquid; the molar ratio of acid to potassium hydroxide in concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.15:1;

[0085] (3) Add aniline monomer and initiator ferric chloride to the POSS modified aramid nanofiber dispersion liquid, react at 21°C for 9h, filter, wash with deionized water, and dry in an oven to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.62:1; the mass ratio of initiator to aniline monomer is 3.3:1. The corresponding polyamide composite material has a tensile strength of 85.6MPa, a bending strength of 104.6MPa, and a volume resistivity of 7.7x10 5 Ω·m.

[0086] Example 9

[0087] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0088] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stir at room temperature for 5.5 days to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt cetyltrimethyl ammonium bromide, and stir uniformly to obtain aramid nanofiber dispersion liquid; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.6g:420ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.27:1;

[0089] (2) Add concentrated nitric acid to the aramid nanofiber dispersion liquid and stir uniformly, then add active group-containing POSS octaaminophenyl POSS, and stir at 88°C for 4.2h to obtain POSS modified aramid nanofiber dispersion liquid; the molar ratio of acid to potassium hydroxide in concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.13:1;

[0090] (3) adding aniline monomer and initiator ferric chloride into the POSS modified aramid nanofiber dispersion liquid, reacting at 19℃ for 9h, filtering, washing with deionized water, drying in an oven, to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.52:1; the mass ratio of initiator to aniline monomer is 3.1:1. After testing, the corresponding polyamide composite material has a tensile strength of 91.2MPa, a bending strength of 110.4MPa, and a volume resistivity of 9.6×10 5 Ω·m.

[0091] Example 10

[0092] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0093] (1) placing aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stirring at room temperature for 4.5 days to prepare aramid nanofiber, then adding long-chain alkyl quaternary ammonium salt hexadecyl trimethyl ammonium 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:500ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.22:1;

[0094] (2) adding concentrated nitric acid into the aramid nanofiber dispersion liquid and stirring uniformly, then adding active group-containing POSS octaamino phenyl POSS, stirring at 90℃ for 4h, to obtain POSS modified aramid nanofiber dispersion liquid; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.12:1;

[0095] (3) adding aniline monomer and initiator ferric chloride into the POSS modified aramid nanofiber dispersion liquid, reacting at 18℃ for 10h, filtering, washing with deionized water, drying in an oven, to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.46:1; the mass ratio of initiator to aniline monomer is 3.1:1. After testing, the corresponding polyamide composite material has a tensile strength of 93.7MPa, a bending strength of 116.5MPa, and a volume resistivity of 6.8×10 5 Ω·m.

[0096] Comparative Example 1

[0097] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0098] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stir at room temperature for 4.5 days to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide, and stir uniformly to obtain aramid nanofiber dispersion; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.3g:500ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.22:1;

[0099] (2) Add concentrated nitric acid to the aramid nanofiber dispersion and stir uniformly to obtain modified aramid nanofiber dispersion; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1;

[0100] (3) Add aniline monomer and initiator ferric chloride to the modified aramid nanofiber dispersion, react at 18℃ for 10h, filter, wash with deionized water, and dry in an oven to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.46:1; the mass ratio of initiator to aniline monomer is 3.1:1. The corresponding polyamide composite material has a tensile strength of 73.6MPa, a bending strength of 91.2MPa, and a volume resistivity of 1.5x10 7 Ω·m.

[0101] Comparative Example 2

[0102] A method for preparing high-strength modified aramid nanofiber, comprising the following steps:

[0103] (1) Put aramid fiber into a reaction kettle containing alkali and dimethyl sulfoxide, stir at room temperature for 4.5 days to prepare aramid nanofiber, then add long-chain alkyl quaternary ammonium salt cetyltrimethylammonium bromide, and stir uniformly to obtain aramid nanofiber dispersion; the alkali is potassium hydroxide; the ratio of aramid fiber, alkali and dimethyl sulfoxide is 1g:1.3g:500ml; the mass ratio of long-chain alkyl quaternary ammonium salt to aramid fiber is 0.22:1; the molar ratio of acid to potassium hydroxide in the concentrated nitric acid is 1:1;

[0104] (2) Add active group-containing POSS octaaminophenyl POSS to the aramid nanofiber dispersion, stir at 90℃ for 4h to obtain POSS-modified aramid nanofiber dispersion; the mass ratio of POSS to long-chain alkyl quaternary ammonium salt is 0.12:1;

[0105] (3) adding aniline monomer and initiator ferric chloride into the POSS modified aramid nanofiber dispersion liquid, reacting at 18℃ for 10h, filtering, washing with deionized water, drying in an oven to obtain high-strength modified aramid nanofiber; the mass ratio of aniline monomer to aramid fiber is 0.46:1; the mass ratio of initiator to aniline monomer is 3.1:1. After testing, the corresponding tensile strength of the polyamide composite material is 63.6MPa, the bending strength is 81.4MPa, and the volume resistivity is 9.9x10 7 Ω·m.

[0106] Figure 1 、 Figure 2 are scanning electron microscope images and local enlarged images of aramid nanofiber and high-strength modified aramid nanofiber prepared in Example 10, respectively, Figure 3 is a scanning electron microscope image and a local enlarged image of high-strength modified aramid nanofiber prepared in Comparative Example 1. The electron microscope image test sample is obtained by repeatedly ultrasonicating, washing, and filtering the corresponding aramid nanofiber and high-strength modified aramid nanofiber with deionized water to remove impurities therefrom. Figure 1 Compared with Figure 2 and Figure 3 , the fiber diameter is obviously thickened, indicating that in-situ polymerization of aniline monomer occurs on the surface of aramid nanofiber, increasing the fiber diameter. Among them, the high-strength modified aramid nanofiber in Figure 2 presents a rough structure, which indicates that POSS has a large volume exclusion effect, and the random attachment of POSS on the surface of aramid nanofiber will affect the templating effect of long-chain alkyl quaternary ammonium salt, affecting the polymerization process of aniline monomer. The uneven polymerization of aniline monomer on the surface of aramid nanofiber leads to the formation of a rough structure on the surface thereof. The rough structure on the surface of aramid nanofiber improves the interaction force between the fiber and the matrix resin, which not only effectively prevents the shedding of polyaniline during processing, but also is conducive to the formation of a conductive network, and can better improve the mechanical strength and conductive properties of the composite material. Compared with Example 10, Comparative Example 1 does not use POSS modification, and the corresponding Figure 3The fiber surface is relatively smooth and no rough structure is formed. It can also be seen from the data of the examples and comparative examples that after the aramid nanofiber is coated with polyaniline in Examples 1-10, the dispersion performance of the fiber is improved, and the compatibility between the aramid nanofiber and the polyamide resin is improved through the coating interface with a rough structure, so that the aramid nanofiber is uniformly dispersed in the base resin. In turn, the aramid nanofiber as the core layer substrate of polyaniline can also promote the dispersion of polyaniline, so that polyaniline forms a network structure, which is conducive to the formation of a conductive path. The smooth fiber prepared in Comparative Example 1 has a weak interface bonding force with the polyamide resin, and the aramid nanofiber cannot be well dispersed in the base resin, which not only affects the formation of a conductive path, but also leads to a decrease in mechanical properties. Compared with Example 10, no cetyltrimethylammonium bromide is added in advance in Comparative Example 2, which cannot fully play a role in dispersion and templating, cannot form a stable coating structure, affects the dispersion of the aramid nanofiber, is not conducive to the formation of a reinforcing network and a conductive network, and the mechanical properties and conductivity of the prepared polyamide composite material are both reduced.

[0107] 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 made to 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 solution of the present application.

Claims

1. A method for preparing high-strength modified aramid nanofiber, characterized in that, The method comprises the following steps: (1) using aramid fiber as raw material, alkali etching method is used to prepare aramid nanofiber solution, then long chain alkyl quaternary ammonium salt is added to obtain aramid nanofiber dispersion liquid; (2) acid is added to the aramid nanofiber dispersion liquid and stirred uniformly, then active group-containing POSS is added to the dispersion liquid, heated and stirred for a certain time to obtain POSS modified aramid nanofiber dispersion liquid; the active group-containing POSS is at least one of amino-containing POSS, hydroxyl-containing POSS, epoxy-containing POSS, carboxyl-containing POSS and mercapto-containing POSS; (3) aniline monomer and initiator are added to the POSS modified aramid nanofiber dispersion liquid, and reacted for a certain time to obtain high-strength modified aramid nanofiber.

2. The method for preparing high-strength modified aramid nanofibers as described in claim 1, characterized in that, The alkali in the step (1) is sodium hydroxide or potassium hydroxide.

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

1.

4. The method for preparing high-strength modified aramid nanofibers as described in claim 1, characterized in that, The active group-containing POSS in the step (2) is at least one of aminopropyl heptaphenyl POSS, aminopropyl heptaisobutyl POSS, octylaminophenyl POSS, octylaminopropyl POSS, heptaisooctyl epoxy POSS, heptaisobutyl epoxy POSS, octylhydroxybutyl POSS, octylmercapto propyl POSS, mercapto propyl isobutyl POSS, octylcarboxymethyl POSS, octylcarboxyethyl POSS and octylcarboxypropyl POSS.

5. The method for preparing high-strength modified aramid nanofibers as described in claim 1, characterized in that, The mass ratio of POSS to long chain alkyl quaternary ammonium salt in the step (2) is (0.01-0.3):

1.

6. The method for preparing high-strength modified aramid nanofibers as described in claim 1, characterized in that, The initiator in the step (3) is at least one of ammonium persulfate, potassium persulfate, ferric chloride and azobis isobutyronitrile.

7. A high-strength modified aramid nanofiber, characterized by, The high-strength modified aramid nanofiber is prepared by the method of any one of claims 1-6.

8. The use of the high-strength modified aramid nanofiber of claim 7 in the preparation of pipe, plate, grouting equipment parts and grouting bag.

9. A polyamide composite, characterized in that The composition comprises the following components by weight: 50-150 parts of polyamide resin, 1-30 parts of the high-strength modified aramid nanofiber of claim 7, 1-30 parts of inorganic fiber reinforced filler and 1-10 parts of processing aid.

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