Composite material based on multiple synergistic modification and gradient nanostructure and preparation method thereof

Abstract

The invention discloses a composite material based on multiple synergistic modification and a gradient nanostructure and a preparation method of the composite material, and relates to the technical field of high-performance composite materials. The problems of weak interface bonding and insufficient load transmission efficiency of the composite material in the prior art are solved, the cohesiveness of the fiber surface and the matrix is greatly enhanced, the problem of high-temperature long-time curing of PAN / CNT grafting is avoided through microwave curing of the nano structure, rapid low-temperature curing is realized, the process period is shortened, and the production cost is reduced. The interface shear strength, the tensile strength and the bending strength of the composite material are obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-performance composite materials, and in particular to a composite material based on multiple synergistic modifications and gradient nanostructures and a preparation method thereof. Background Art

[0002] With the rapid adoption of high-performance composites in aerospace, rail transit, construction, and other fields, the interface structure between reinforcing fibers and the resin matrix has become a key factor in determining the overall performance of composites. In particular, improving the bond strength of inorganic reinforcing materials such as glass fiber and carbon fiber with thermoplastic or thermosetting resins through surface modification is a core research issue in materials engineering.

[0003] In existing technologies, silane coupling agents, oxidation treatments, and nanoparticle coatings are commonly used to improve the adhesion between the fiber surface and the matrix. While these traditional fiber surface modification methods improve fiber-matrix adhesion, they generally face technical bottlenecks that limit their application in high-performance composites. For example, silane coupling agent modification can lead to insufficient interfacial stability (chemical sensitivity and poor adaptability to non-polar fibers) and uneven adsorption layer thickness; oxidation damages the fiber itself, degrading material properties and causing environmental pollution; and nanoparticle coating can lead to severe nanoparticle agglomeration and weak interfacial bonding. These methods also suffer from poor stability or uneven dispersion of the modified layer.

[0004] In recent years, polymer grafting (such as polyacrylonitrile and polyaniline) has gradually become an effective modification method. By introducing active groups on the fiber surface and then compounding with functional materials such as carbon nanotubes (CNTs), polyacrylonitrile (PAN) grafted carbon nanotubes (CNTs) have been reported to enhance interfacial reactivity and micromechanical interlocking structure, thereby improving interfacial stress transmission.

[0005] Existing methods only improve adhesion through a single mechanism (chemical adsorption, physical roughening or filler filling), lack multi-dimensional synergy, resulting in limited improvement in interface performance. These methods can often only provide chemical bonds or mechanical engagement in a single way, the modified layer has poor stability and uneven dispersion, and lacks a layered gradient design. In addition, existing PAN / CNT grafting mostly relies on high-temperature and long-term curing, making it difficult to simultaneously take into account nanotube dispersion, interface adhesion and process efficiency. Summary of the Invention

[0006] One object of the present invention is to provide a method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures. Through gradient spraying, triple synergistic chemical modification of silane coupling, PDA self-polymerization and imidazole additives, and microwave curing, the problems of weak interface bonding and insufficient load transfer efficiency in the composite material in the prior art are solved. At the same time, the problem of high-temperature and long-term curing of PAN / CNT grafting is avoided, rapid low-temperature curing is achieved, and the fiber / matrix interface bonding strength, interlayer shear strength and tensile / bending properties are significantly improved.

[0007] Another object of the present invention is to provide a composite material based on multiple synergistic modifications and gradient nanostructures, which further improves the bonding strength and interface toughness of the composite material by optimizing the modification process and the curing process.

[0008] The first object of the invention comprises the following steps:

[0009] soaking the fiber in a silane coupling agent to prepare a silane-coupled fiber;

[0010] The silane-coupled fibers are immersed in a dopamine self-polymerization solution to prepare fibers with active sites on the surface;

[0011] The fibers covered with active sites on the surface were sprayed with different concentrations of imidazole-functionalized PAN / MWCNT dispersions three times to prepare fibers covered with a concentration gradient nanolayer.

[0012] performing heat stabilization treatment on the fiber covered with the concentration gradient nanolayer to obtain heat-treated fiber;

[0013] The cured fibers are stacked alternately with thermoplastic films and then hot-pressed and cured to obtain a composite material.

[0014] Among them, imidazole-functionalized PAN / MWCNT dispersions of different concentrations were sprayed three times to prepare fibers covered with a concentration gradient nanolayer. Through concentration gradient spraying, a nanolayer structure with gradually increasing strength from the outside to the inside was established, which could generate a stress gradient in the interface area, alleviate load concentration and promote crack pinning effect. The gradient structure improved the interface shear resistance, delayed the delamination of the inner layer matrix and fiber, and improved the comprehensive mechanical properties.

[0015] Among them, the alkoxy group (-OR) of the silane coupling agent γ-aminopropyltriethoxysilane molecule hydrolyzes in water (or a humid environment) to generate silanol (-Si-OH). The hydrolyzed silanol (-Si-OH) reacts with the hydroxyl group on the fiber surface (such as (-OH) on the surface of glass fiber and silica fiber) to form a silicon-oxygen bond (-Si-O-fiber), forming a strong molecular bridge. The amino group at the other end of the γ-aminopropyltriethoxysilane molecule can form a hydrogen bond or covalent bond with the subsequent PDA coating, significantly improving the stability of the interfacial chemical bonding, improving the fiber / matrix wettability, and reducing the interfacial porosity, thereby enhancing the tensile and flexural strength of the composite material.

[0016] Dopamine will spontaneously oxidize and self-polymerize to form polydopamine under weak alkaline conditions (such as Tris-HCl buffer at pH 8.5). PDA has strong adhesion and can be adsorbed on the surface of almost all materials, such as polymers and fibers, through hydrogen bonds, π-π interactions, and metal coordination. The active functional groups on the surface of silane-coupled fibers act as nucleation sites, promoting the preferential deposition of PDA on the fiber surface to form a uniform and compact polymer coating. This coating is not only fixed to the fiber surface through chemical bonds and physical effects, but also forms a tough film through the cross-linking structure of PDA itself. This film is rich in amine and hydroxyl functional groups, which can provide more active binding sites for the subsequent PAN / MWCNT layer, enhance the roughness and hydrophilicity of the fiber surface, significantly improve the adhesion uniformity of the additive and nanotube dispersion, and enhance the processing controllability and stability.

[0017] Imidazole-functionalized PAN / MWCNT dispersion, the imidazole polar group and the surface functional group of MWCNT (multi-walled carbon nanotube) are combined through covalent bonds or π-π interactions to form a stable dispersion system. The cyano group (-CN) of PAN acts as a dipole, forming hydrogen bonds or dipole-dipole interactions with the hydroxyl (-OH) and amino (-NH2) groups on the active sites of the fiber surface. The PAN molecular chains in the PAN / MWCNT dispersion can penetrate into these structures, forming mechanical anchors after curing, and building a "molecular bridge" between the fiber and the nanotube, thereby improving the interfacial shear strength. The MWCNT has a high aspect ratio and is easily cross-entangled on the fiber surface, forming a three-dimensional network coating together with the PAN molecular chain, thereby improving the firmness of the grafting.

[0018] The fibers are treated with silane coupling to enhance their strength and transform their surface from hydrophobic / inert to hydrophilic / active, providing sites for subsequent chemical reactions. After soaking in a dopamine self-polymerization solution, PDA is fixed to the fibers through chemical bonds and physical interactions, increasing the roughness, hydrophilicity, and reactivity of the fiber surface, providing more active binding sites for the subsequent PAN / MWCNT layer. Subsequently, an imidazole-functionalized PAN / MWCNT dispersion is sprayed on the fibers to construct a multi-level interaction network within the material. This triple synergistic modification breaks the limitations of traditional modification methods and significantly improves the interfacial adhesion between the reinforced fibers and the matrix, as well as the overall tensile and bending properties, through the deep coupling of multi-dimensional action mechanisms.

[0019] The preparation of existing high-performance fiber / resin composites is often done through a uniform coating process or a single chemical modification, resulting in homogeneous interface layer structure and low stress transfer efficiency, which leads to sudden changes in interface stress and prone to brittle fracture. Secondly, the single chemical modification lacks multi-dimensional synergy, resulting in limited improvement in interface performance. These methods can often only provide a single chemical bond engagement, resulting in poor stability and uneven dispersion of the modified layer. In addition, the existing PAN / CNT grafting heat treatment time is long and the temperature is high, which makes the process time-consuming and causes thermal damage to the fiber.

[0020] Therefore, the present invention significantly improves the interfacial shear strength, tensile strength and flexural strength of the composite material through gradient spraying of nanolayers, triple synergistic chemical modification and microwave rapid curing process, while achieving low-temperature short-time curing, and giving the material excellent thermal stability and functionalization potential. It is suitable for a variety of continuous fiber substrates and has important application value for the preparation of high-performance composite materials in the fields of aerospace, rail transportation and high-end manufacturing.

[0021] The fibers covering the active sites were sequentially sprayed with a first solution, a second solution, and a third solution. Each solution was an imidazole-functionalized PAN / MWCNT dispersion. After each spraying, the solution was dried at 60-80°C for 8-12 minutes. The concentrations of the first, second, and third solutions increased in a gradient. The concentration of the first solution was 0.1-0.3 wt%, the concentration of the second solution was 0.4-0.6 wt%, and the concentration of the third solution was 0.9-1.1 wt%. The first solution has a low concentration, low viscosity, and strong diffusion ability, and can easily diffuse into the deep fibers, as well as the fiber gaps or nano-scale grooves; the second solution has a moderate concentration, and has both certain diffusion and accumulation abilities. Part of it penetrates into the bottom gaps, and part of it is deposited on the surface, forming a transitional structure that connects the upper and lower layers. The modulus of the medium-concentration layer is between the bottom layer and the outer layer, forming a gradient to reduce interfacial stress concentration; the third solution has a relatively high concentration and strong interaction between particles. It can quickly accumulate on the surface to form a dense layer, blocking external invasions such as corrosive media and wear particles, and adapting to deformation coordination under dynamic loads. Through three concentration gradients, a nanolayer structure with gradually increasing strength from the outside to the inside is established, which can generate a stress gradient in the interface area, alleviate load concentration and promote crack pinning effect. The gradient structure improves the interface shear resistance, delays the delamination of the inner layer matrix and fiber, and improves the comprehensive mechanical properties.

[0022] The thermal stabilization treatment involves microwave field curing, specifically placing the fibers covered with a concentration gradient nanolayer in a microwave field and curing them in three batches of intermittent cooling, with each batch curing for 3 to 7 minutes. Because MWCNTs and ionic liquids exhibit high dielectric loss to microwaves, they can generate localized high temperatures within a short period of time, achieving cross-linking and curing of the PAN chains and covalent or physical anchoring of the CNTs. This short curing time (3 x 5 minutes) significantly shortens the process cycle. The efficient local heating reduces the overall temperature requirement (≤180°C), avoids thermal damage to the fibers, and improves interfacial attachment efficiency.

[0023] The imidazole-functionalized PAN / MWCNT dispersion is prepared by dissolving polyacrylonitrile, carboxylated multi-walled carbon nanotubes, and 1-ethyl-3-methylimidazolium tetrafluoroborate in N,N-dimethylformamide and ultrasonically dispersing the mixture at 40-60°C for 50-70 minutes. The imidazole-functionalized ionic liquid (EMIMBF4) forms electrostatic and π-π conjugated interactions with the PAN molecular chains and carboxylated MWCNTs, improving the dispersion and stability of the nanotubes in DMF.

[0024] Furthermore, the concentration of the dopamine self-polymerization solution is 1-3 mg / ml, and the silane-coupled fiber is immersed in the dopamine self-polymerization solution at room temperature for 3-5 hours.

[0025] Furthermore, the concentration of the silane coupling agent is 1-3 wt %.

[0026] Furthermore, the present invention also proposes a second invention purpose, which is to prepare a composite material based on multiple synergistic modifications and gradient nanostructures using the above preparation method.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] 1. The present invention provides a composite material based on multiple synergistic modifications and gradient nanostructures and a preparation method thereof. A nano-reinforced layer that increases from the outside to the inside is constructed on the fiber by spraying three levels of concentration gradient, which can generate a stress gradient in the interface area, alleviate load concentration and promote crack pinning effect, avoid interface stress concentration, and the gradient structure improves the interface shear resistance and enhances the overall mechanical properties.

[0029] 2. The present invention provides a composite material based on multiple synergistic modifications and gradient nanostructures and a preparation method thereof. A multi-level interaction network is constructed on the material through triple synergistic modifications, which significantly improves the interfacial bonding force between the reinforcing fibers and the matrix as well as the overall tensile and bending properties.

[0030] 3. The composite material based on multiple synergistic modifications and gradient nanostructure and its preparation method of the present invention achieves short-time curing through a microwave rapid curing process, greatly shortening the process cycle. The efficient heating of the microwave field reduces the overall temperature requirement, avoids thermal damage to the fiber and improves the interface adhesion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0032] Figure 1 This is a flow chart of the method for preparing the composite material of Example 1 of the present application;

[0033] Figure 2 a is a SEM image of the fiber with active sites covered on the surface in Example 1 of the present application;

[0034] Figure 2 b is a SEM image of the fiber covered with the concentration gradient nanolayer according to Example 1 of the present application;

[0035] Figure 2 c is an SEM image of the fiber covered with the concentration gradient nanolayer in Example 3 of the present application. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the following examples and accompanying drawings. However, the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions or selected according to the product specifications.

[0037] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. Example 1

[0038] Step 1, preparing a silane-coupled fiber fabric;

[0039] Step 11, ultrasonically cleaning the desized basalt fiber fabric with deionized water for 30 minutes, and drying it at 80° C. for 12 hours to obtain a dried fiber fabric;

[0040] Step 12, preparing a 2 wt % γ-aminopropyltriethoxysilane solution with a pH of 4.5; the γ-aminopropyltriethoxysilane solution is prepared by dissolving γ-aminopropyltriethoxysilane in a mixed solution of ethanol and water, wherein the volume ratio of ethanol to water is 9:1;

[0041] Step 13: Place the dried fiber fabric in a 2 wt % γ-aminopropyltriethoxysilane solution, soak it at room temperature for 2 hours, and then cure it at 110° C. for 2 hours to obtain a silane-coupled fiber fabric.

[0042] Step 2: The silane-coupled fiber fabric was immersed in a 2 mg / mL dopamine self-polymerization solution (prepared by dissolving dopamine in Tris-HCl buffer at pH 8.5), self-polymerized at room temperature for 4 hours, washed, and then dried at 80°C for 4 hours to obtain a uniform PDA layer, thereby obtaining a fiber fabric with active sites covered on the surface.

[0043] Step 3, preparing a fiber fabric covered with a concentration gradient nanolayer;

[0044] Step 31, dissolving PAN, carboxylated MWCNTs, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) in N,N-dimethylformamide (DMF) at a mass ratio of PAN:carboxylated MWCNTs:EMIMBF4 = 0.5:0.5:0.1, and then sonicating at 50°C for 60 minutes to obtain an imidazole-functionalized PAN / MWCNT dispersion;

[0045] Step 32: spray 30 mL (0.2 wt%), 20 mL (0.5 wt%), and 10 mL (1.0 wt%) of imidazole-functionalized PAN / MWCNT dispersion onto the fiber fabric with active sites on its surface, and dry at 80°C for 10 min after each spraying to obtain a fiber fabric covered with a concentration gradient nanolayer.

[0046] Step 4: Place the fiber fabric covered with the concentration gradient nanolayer in a microwave field (2.45 GHz, 200 W) and perform intermittent cooling and curing in three steps. Each microwave irradiation time is 5 minutes. After a 5-minute curing stage, enter the cooling stage to obtain the heat-treated fiber fabric.

[0047] Step 5: The heat-treated fiber fabric and PLA film are staggered in the direction of ±45°, with 8 layers of heat-treated fiber fabric and PLA film respectively. The stacked blanks are hot-pressed and solidified. The temperature is raised to 120°C at a rate of 3°C / min, and pre-pressed at a pressure of 50 bar for 5 minutes; then the temperature is raised to 180°C, and the pressure is maintained at 100 bar for 15 minutes. The composite material is cooled and demolded to obtain the composite material. Example 2

[0048] Step 1, preparing a silane-coupled fiber fabric;

[0049] Step 11, ultrasonically cleaning the desized basalt fiber fabric with deionized water for 30 minutes, and drying it at 80° C. for 12 hours to obtain a dried fiber fabric;

[0050] Step 12, preparing a 2 wt % γ-aminopropyltriethoxysilane solution with a pH of 4.5; the γ-aminopropyltriethoxysilane solution is prepared by dissolving γ-aminopropyltriethoxysilane in a mixed solution of ethanol and water, wherein the volume ratio of ethanol to water is 9:1;

[0051] Step 13: Place the dried fiber fabric in a 2 wt % γ-aminopropyltriethoxysilane solution, soak it at room temperature for 2 hours, and then cure it at 110° C. for 2 hours to obtain a silane-coupled fiber fabric.

[0052] Step 2: The silane-coupled fiber fabric was immersed in a 2 mg / mL dopamine self-polymerization solution (prepared by dissolving dopamine in Tris-HCl buffer at pH 8.5), self-polymerized at room temperature for 4 hours, washed, and then dried at 80°C for 4 hours to obtain a uniform PDA layer, thereby obtaining a fiber fabric with active sites covered on the surface.

[0053] Step 3, preparing a fiber fabric covered with a nanolayer;

[0054] Step 31, dissolving PAN, carboxylated MWCNTs, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) in N,N-dimethylformamide (DMF) at a mass ratio of PAN:carboxylated MWCNTs:EMIMBF4 = 0.5:0.5:0.1, and then sonicating at 50°C for 60 minutes to obtain an imidazole-functionalized PAN / MWCNT dispersion;

[0055] Step 32: spray 50 mL (0.5 wt %) of imidazole-functionalized PAN / MWCNT dispersion onto the fiber fabric with active sites on its surface, and dry at 80° C. for 10 min after each spraying to obtain a fiber fabric covered with a nanolayer.

[0056] Step 4: Place the fiber fabric covered with the nanolayer in a microwave field (2.45 GHz, 200 W) and perform intermittent cooling and curing in three steps. Each microwave irradiation time is 5 minutes. After a 5-minute curing stage, enter the cooling stage to obtain the heat-treated fiber fabric.

[0057] Step 5: The heat-treated fiber fabric and PLA film are staggered in the direction of ±45°, with 8 layers of heat-treated fiber fabric and PLA film respectively. The stacked blanks are hot-pressed and solidified. The temperature is raised to 120°C at a rate of 3°C / min, and pre-pressed at a pressure of 50 bar for 5 minutes; then the temperature is raised to 180°C, and the pressure is maintained at 100 bar for 15 minutes. The composite material is cooled and demolded to obtain the composite material. Example 3

[0058] Step 1, preparing a silane-coupled fiber fabric;

[0059] Step 11, ultrasonically cleaning the desized basalt fiber fabric with deionized water for 30 minutes, and drying it at 80° C. for 12 hours to obtain a dried fiber fabric;

[0060] Step 12, preparing a 2 wt % γ-aminopropyltriethoxysilane solution with a pH of 4.5; the γ-aminopropyltriethoxysilane solution is prepared by dissolving γ-aminopropyltriethoxysilane in a mixed solution of ethanol and water, wherein the volume ratio of ethanol to water is 9:1;

[0061] Step 13: Place the dried fiber fabric in a 2 wt % γ-aminopropyltriethoxysilane solution, soak it at room temperature for 2 hours, and then cure it at 110° C. for 2 hours to obtain a silane-coupled fiber fabric.

[0062] Step 2: The silane-coupled fiber fabric was immersed in a 2 mg / mL dopamine self-polymerization solution (prepared by dissolving dopamine in Tris-HCl buffer at pH 8.5), self-polymerized at room temperature for 4 hours, washed, and then dried at 80°C for 4 hours to obtain a uniform PDA layer, thereby obtaining a fiber fabric with active sites covered on the surface.

[0063] Step 3, preparing a fiber fabric covered with a concentration gradient nanolayer;

[0064] Step 31, dissolving PAN, carboxylated MWCNTs, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) in N,N-dimethylformamide (DMF) at a mass ratio of PAN:carboxylated MWCNTs:EMIMBF4 = 0.5:0.5:0.1, and then sonicating at 50°C for 60 minutes to obtain an imidazole-functionalized PAN / MWCNT dispersion;

[0065] Step 32: The fiber fabric with active sites on its surface is sprayed with 30 mL (1.0 wt%), 20 mL (3 wt%), and 10 mL (5 wt%) of imidazole-functionalized PAN / MWCNT dispersion in sequence, and dried at 80°C for 10 min after each spraying to obtain a fiber fabric covered with a concentration gradient nanolayer.

[0066] Step 4: Place the fiber fabric covered with the concentration gradient nanolayer in a microwave field (2.45 GHz, 200 W) and perform intermittent cooling and curing in three steps. Each microwave irradiation time is 5 minutes. After a 5-minute curing stage, enter the cooling stage to obtain the heat-treated fiber fabric.

[0067] Step 5: The heat-treated fiber fabric and PLA film are staggered in the direction of ±45°, with 8 layers of heat-treated fiber fabric and PLA film respectively. The stacked blanks are hot-pressed and solidified. The temperature is raised to 120°C at a rate of 3°C / min, and pre-pressed at a pressure of 50 bar for 5 minutes; then the temperature is raised to 180°C, and the pressure is maintained at 100 bar for 15 minutes. The composite material is cooled and demolded to obtain the composite material. Example 4

[0068] Step 1, preparing a silane-coupled fiber fabric;

[0069] Step 11, ultrasonically cleaning the desized basalt fiber fabric with deionized water for 30 minutes, and drying it at 80° C. for 12 hours to obtain a dried fiber fabric;

[0070] Step 12, preparing a 2 wt % γ-aminopropyltriethoxysilane solution with a pH of 4.5; the γ-aminopropyltriethoxysilane solution is prepared by dissolving γ-aminopropyltriethoxysilane in a mixed solution of ethanol and water, wherein the volume ratio of ethanol to water is 9:1;

[0071] Step 13: Place the dried fiber fabric in a 2 wt % γ-aminopropyltriethoxysilane solution, soak it at room temperature for 2 hours, and then cure it at 110° C. for 2 hours to obtain a silane-coupled fiber fabric.

[0072] Step 2: The silane-coupled fiber fabric was immersed in a 2 mg / mL dopamine self-polymerization solution (prepared by dissolving dopamine in Tris-HCl buffer at pH 8.5), self-polymerized at room temperature for 4 hours, washed, and then dried at 80°C for 4 hours to obtain a uniform PDA layer, thereby obtaining a fiber fabric with active sites covered on the surface.

[0073] Step 3, preparing a fiber fabric covered with a concentration gradient nanolayer;

[0074] Step 31, dissolving PAN, carboxylated MWCNTs, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) in N,N-dimethylformamide (DMF) at a mass ratio of PAN:carboxylated MWCNTs:EMIMBF4 = 0.5:0.5:0.1, and then sonicating at 50°C for 60 minutes to obtain an imidazole-functionalized PAN / MWCNT dispersion;

[0075] Step 32: Spray 30 mL (1.0 wt%), 20 mL (0.5 wt%), and 10 mL (0.2 wt%) of imidazole-functionalized PAN / MWCNT dispersion onto the fiber fabric with active sites on its surface. Dry at 80°C for 10 min after each spraying to obtain a fiber fabric covered with a concentration gradient nanolayer.

[0076] Step 4: Place the fiber fabric covered with the concentration gradient nanolayer in a microwave field (2.45 GHz, 200 W) and perform intermittent cooling and curing in three steps. Each microwave irradiation time is 5 minutes. After a 5-minute curing stage, enter the cooling stage to obtain the heat-treated fiber fabric.

[0077] Step 5: The heat-treated fiber fabric and PLA film are staggered in the direction of ±45°, with 8 layers of heat-treated fiber fabric and PLA film respectively. The stacked blanks are hot-pressed and solidified. The temperature is raised to 120°C at a rate of 3°C / min, and pre-pressed at a pressure of 50 bar for 5 minutes; then the temperature is raised to 180°C, and the pressure is maintained at 100 bar for 15 minutes. The composite material is cooled and demolded to obtain the composite material. Example 5

[0078] Step 1, preparing a silane-coupled fiber fabric;

[0079] Step 11, ultrasonically cleaning the desized basalt fiber fabric with deionized water for 30 minutes, and drying it at 80° C. for 12 hours to obtain a dried fiber fabric;

[0080] Step 12, preparing a 2 wt % γ-aminopropyltriethoxysilane solution with a pH of 4.5; the γ-aminopropyltriethoxysilane solution is prepared by dissolving γ-aminopropyltriethoxysilane in a mixed solution of ethanol and water, wherein the volume ratio of ethanol to water is 9:1;

[0081] Step 13: Place the dried fiber fabric in a 2 wt % γ-aminopropyltriethoxysilane solution, soak it at room temperature for 2 hours, and then cure it at 110° C. for 2 hours to obtain a silane-coupled fiber fabric.

[0082] Step 2, preparing a fiber fabric covered with a concentration gradient nanolayer;

[0083] Step 21, dissolving PAN, carboxylated MWCNTs, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) in N,N-dimethylformamide (DMF) at a mass ratio of PAN:carboxylated MWCNTs:EMIMBF4 = 0.5:0.5:0.1, and then sonicating at 50°C for 60 minutes to obtain an imidazole-functionalized PAN / MWCNT dispersion;

[0084] Step 22: Spray 30 mL (0.2 wt%), 20 mL (0.5 wt%), and 10 mL (1.0 wt%) of imidazole-functionalized PAN / MWCNT dispersion onto the silane-coupled fiber fabric in sequence. Dry at 80°C for 10 min after each spraying to obtain a fiber fabric covered with a concentration gradient nanolayer.

[0085] Step 3: Place the fiber fabric covered with the concentration gradient nanolayer in a microwave field (2.45 GHz, 200 W) and perform intermittent cooling and curing in three steps. Each microwave irradiation time is 5 minutes. After a 5-minute curing stage, enter the cooling stage to obtain the heat-treated fiber fabric.

[0086] Step 4: The heat-treated fiber fabric and PLA film are staggered in the direction of ±45°, with 8 layers of heat-treated fiber fabric and PLA film respectively. The stacked blanks are hot-pressed and solidified. The temperature is raised to 120°C at a rate of 3°C / min, and pre-pressed at a pressure of 50 bar for 5 minutes; then the temperature is raised to 180°C, and the pressure is maintained at 100 bar for 15 minutes. The composite material is cooled and demolded to obtain the composite material. Example 6

[0087] Step 1, preparing a dried fiber fabric;

[0088] Step 11, ultrasonically cleaning the desized basalt fiber fabric with deionized water for 30 minutes, and drying it at 80° C. for 12 hours to obtain a dried fiber fabric;

[0089] Step 2: The dried fiber fabric is immersed in a 2 mg / mL dopamine self-polymerization solution (prepared by dissolving dopamine in Tris-HCl buffer at pH = 8.5), self-polymerized at room temperature for 4 hours, washed, and then dried at 80°C for 4 hours to obtain a uniform PDA layer, thereby obtaining a fiber fabric with active sites covered on the surface.

[0090] Step 3, preparing a fiber fabric covered with a concentration gradient nanolayer;

[0091] Step 31, preparing an imidazole-functionalized PAN / MWCNT dispersion; dissolving PAN, carboxylated MWCNT, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) in N,N-dimethylformamide (DMF) at a mass ratio of PAN:carboxylated MWCNT:EMIMBF4 = 0.5:0.5:0.1, and then sonicating at 50°C for 60 minutes to obtain an imidazole-functionalized PAN / MWCNT dispersion;

[0092] Step 32: spray 30 mL (0.2 wt%), 20 mL (0.5 wt%), and 10 mL (1.0 wt%) of imidazole-functionalized PAN / MWCNT dispersion onto the fiber fabric with active sites on its surface, and dry at 80°C for 10 min after each spraying to obtain a fiber fabric covered with a concentration gradient nanolayer.

[0093] Step 4: Place the fiber fabric covered with the concentration gradient nanolayer in a microwave field (2.45 GHz, 200 W) and perform intermittent cooling and curing in three steps. Each microwave irradiation time is 5 minutes. After a 5-minute curing stage, enter the cooling stage to obtain the heat-treated fiber fabric.

[0094] Step 5: The heat-treated fiber fabric and PLA film are staggered in the direction of ±45°, with 8 layers of heat-treated fiber fabric and PLA film respectively. The stacked blanks are hot-pressed and solidified. The temperature is raised to 120°C at a rate of 3°C / min, and pre-pressed at a pressure of 50 bar for 5 minutes; then the temperature is raised to 180°C, and the pressure is maintained at 100 bar for 15 minutes. The composite material is cooled and demolded to obtain the composite material. Example 7

[0095] Step 1, preparing a silane-coupled fiber fabric;

[0096] Step 11, ultrasonically cleaning the desized basalt fiber fabric with deionized water for 30 minutes, and drying it at 80° C. for 12 hours to obtain a dried fiber fabric;

[0097] Step 12, preparing a 2 wt % γ-aminopropyltriethoxysilane solution with a pH of 4.5; the γ-aminopropyltriethoxysilane solution is prepared by dissolving γ-aminopropyltriethoxysilane in a mixed solution of ethanol and water, wherein the volume ratio of ethanol to water is 9:1;

[0098] Step 13: Place the dried fiber fabric in a 2 wt % γ-aminopropyltriethoxysilane solution, soak it at room temperature for 2 hours, and then cure it at 110° C. for 2 hours to obtain a silane-coupled fiber fabric.

[0099] Step 2: The silane-coupled fiber fabric was immersed in a 2 mg / mL dopamine self-polymerization solution (prepared by dissolving dopamine in Tris-HCl buffer at pH 8.5), self-polymerized at room temperature for 4 hours, washed, and then dried at 80°C for 4 hours to obtain a uniform PDA layer, thereby obtaining a fiber fabric with active sites covered on the surface.

[0100] Step 3, preparing a fiber fabric covered with a concentration gradient nanolayer;

[0101] Step 31, dissolving PAN, carboxylated MWCNTs, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) in N,N-dimethylformamide (DMF) at a mass ratio of PAN:carboxylated MWCNTs:EMIMBF4 = 0.5:0.5:0.1, and then sonicating at 50°C for 60 minutes to obtain an imidazole-functionalized PAN / MWCNT dispersion;

[0102] Step 32: spray 30 mL (0.2 wt%), 20 mL (0.5 wt%), and 10 mL (1.0 wt%) of imidazole-functionalized PAN / MWCNT dispersion onto the fiber fabric with active sites on its surface in sequence; dry at 80°C for 10 min after each spraying to obtain a fiber fabric covered with a concentration gradient nanolayer.

[0103] Step 4: Curing the fiber fabric covered with the concentration gradient nanolayer in an oven at 120° C. for 12 hours to obtain a heat-treated fiber fabric.

[0104] Step 5: The heat-treated fiber fabric and PLA film are staggered in the direction of ±45°, with 8 layers of heat-treated fiber fabric and PLA film respectively. The stacked blanks are hot-pressed and solidified. The temperature is raised to 120°C at a rate of 3°C / min, and pre-pressed at a pressure of 50 bar for 5 minutes; then the temperature is raised to 180°C, and the pressure is maintained at 100 bar for 15 minutes. The composite material is cooled and demolded to obtain the composite material. Example 8

[0105] The composite materials prepared in Examples 1-7 were subjected to a short beam shear test (SBS) to determine the interlaminar shear strength, and a universal testing machine was used to perform tensile and bending property tests. The results are shown in Table 1.

[0106] Table 1

[0107] Among them, electron microscopy was used to observe the microscopic morphology of the fiber surface, such as Figure 2 (a) shows the fiber with active sites on the surface obtained in Example 1. It can be seen that the surface roughness of the activated fiber is significantly increased, and tiny particles are attached to the fiber surface, making the fiber microstructure more complex, providing more active sites for subsequent PAN / MWCNT grafting, as shown in FIG. Figure 2 (b) shows the fiber coated with the concentration gradient nanolayer obtained in Example 1. It can be seen that through the synergistic effects of batch gradient spraying of the PAN / MWCNT dispersion, silane coupling, and PDA self-polymerization, PAN and MWCNT have been continuously and evenly coated on the fiber surface, forming a dense modified layer. This structure significantly improves the adhesion between the fiber and the polymer matrix, making the interface bond more secure. Figure 2 (c) shows the fiber covered with the concentration gradient nanolayer obtained in Example 3. It can be observed that due to the high concentration of the PAN / MWCNT dispersion, the modified layer is obviously piled up and uneven. This excessive accumulation will reduce the interfacial bonding performance and may cause stress concentration.

[0108] Interlaminar shear strength reflects the quality of the interfacial bonding. The higher the value, the stronger the chemical bonding (e.g., covalent bonds) and physical interlocking (e.g., surface roughness) between the fiber and the matrix, and between the layers, resulting in higher load transfer efficiency and greater resistance to delamination. Tensile strength, flexural strength, and elastic modulus also reflect the composite material's interfacial load transfer efficiency and the matrix's overall load-bearing capacity, including toughness, stiffness, and resistance to deformation. As can be seen in Table 1, the composite material prepared in Example 1 exhibits optimal mechanical properties and interfacial bonding strength, due to the present invention's use of a gradient sprayed nanolayer, triple synergistic chemical modification, and microwave rapid curing process.

[0109] From the comparison of Example 1 with Examples 2, 3 and 4 in Table 1, it can be seen that the gradient sprayed nanolayer establishes a nanolayer structure with gradually increasing strength from the outside to the inside, which can generate a stress gradient in the interface area, alleviate load concentration and promote crack pinning effect. The gradient structure improves the interface shear resistance.

[0110] From the comparison of Example 1 with Examples 5 and 6, it can be seen that the triple synergistic chemical modification treats the surface of the fiber through silane coupling, strengthens the strength of the fiber, and changes the fiber surface from hydrophobic / inert to hydrophilic / active, providing sites for subsequent chemical reactions. After soaking in dopamine self-polymerization solution, PDA is fixed to the fiber surface through chemical bonds and physical effects, which improves the roughness, hydrophilicity and reactivity of the fiber surface, and provides more active binding sites for the subsequent PAN / MWCNT layer. Then, after spraying with imidazole-functionalized PAN / MWCNT dispersion, a multi-level interaction network is constructed inside the material. Through the deep coupling of multi-dimensional action mechanisms, the performance upper limit of a single mechanism is broken, and the interfacial adhesion between the reinforced fiber and the matrix and the overall tensile and bending properties are improved.

[0111] Comparing Example 1 with Example 7 demonstrates that the microwave rapid curing process, due to the high dielectric loss of MWCNTs and ionic liquids to microwaves, can generate localized high temperatures in a short period of time, achieving cross-linking and curing of PAN chains and covalent or physical anchoring of CNTs for short periods of time, significantly shortening the process cycle while avoiding thermal damage to the fibers and improving interfacial adhesion efficiency. This invention improves the adhesion between the fiber surface and the matrix, significantly enhancing fiber / matrix interfacial bond strength, interlaminar shear strength, and tensile / flexural properties while maintaining rapid, low-temperature curing.

[0112] The above descriptions are only some specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures, characterized in that: The following steps are involved: soaking the fiber in a silane coupling agent to prepare a silane-coupled fiber; The silane-coupled fibers are immersed in a dopamine self-polymerization solution to prepare fibers with active sites on the surface; The fibers covered with active sites on the surface were sprayed with different concentrations of imidazole-functionalized PAN / MWCNT dispersions three times to prepare fibers covered with a concentration gradient nanolayer. performing heat stabilization treatment on the fiber covered with the concentration gradient nanolayer to obtain heat-treated fiber; The cured fibers are stacked alternately with thermoplastic films and then hot-pressed and cured to obtain a composite material.

2. The method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures according to claim 1, characterized in that: Preparation of fibers covered with a concentration gradient nanolayer, specifically comprising: The first solution, the second solution and the third solution are sprayed sequentially on the fibers covering the active sites. The first solution, the second solution and the third solution are all imidazole-functionalized PAN / MWCNT dispersions. After each spraying, the solution is dried at 60-80°C for 8-12 minutes. The concentration gradients of the first solution, the second solution and the third solution are increased.

3. The method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures according to claim 2, characterized in that: The concentration of the first solution is 0.1-0.3 wt %, the concentration of the second solution is 0.4-0.6 wt %, and the concentration of the third solution is 0.9-1.1 wt %.

4. The method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures according to claim 1, characterized in that: The thermal stabilization treatment is microwave field curing, which specifically includes: The fibers covered with the concentration gradient nanolayer were placed in a microwave field and intermittently cooled and solidified in three batches, with each batch solidifying for 3 to 7 minutes.

5. The method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures according to claim 1, characterized in that: The temperature of the hot pressing curing is first raised to 110-130° C. for pre-pressing, and then raised to 170-190° C. for hot pressing.

6. The method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures according to claim 1, characterized in that: The preparation of the imidazole-functionalized PAN / MWCNT dispersion specifically includes: Polyacrylonitrile, carboxylated multi-walled carbon nanotubes and 1-ethyl-3-methylimidazolium tetrafluoroborate were dissolved in N,N-dimethylformamide and ultrasonically dispersed at 40-60°C for 50-70 min.

7. The method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures according to claim 1, characterized in that: The concentration of the dopamine self-polymerization solution is 1-3 mg / ml, and the silane-coupled fiber is immersed in the dopamine self-polymerization solution at room temperature for 3-5 hours.

8. The method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures according to claim 1, characterized in that: The silane coupling agent is γ-aminopropyltriethoxysilane.

9. The method for preparing a composite material based on multiple synergistic modifications and gradient nanostructures according to claim 8, characterized in that: The concentration of the silane coupling agent is 1-3 wt %.

10. A composite material prepared according to the preparation method according to any one of claims 1 to 9.

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