A carbon fiber / epoxy resin composite material synergistically enhanced interface bonding by rigid-flexible mechanical interlocking and covalent cross-linking and a preparation method thereof

Abstract

The application belongs to the technical field of polymer composites, and provides a carbon fiber / epoxy resin composite material with rigid-flexible mechanical interlocking and covalent cross-linking synergistic reinforced interface bonding and a preparation method thereof. Polydopamine PDA and polyethylene imine PEI are deposited on the surface of carbon fiber CF, polyacrylic acid PAA is grafted in situ through amide cross-linking reaction, an active coating layer of PAA-PEI-PDA is formed on the surface of the carbon fiber CF, amino carbon nanotubes CNTs are grafted on the surface of the coating layer, and modified carbon fiber CNTs-PAA-PEI-PDA-CF with a nano-scale rod-like surface structure is formed. The modified carbon fiber is combined with an epoxy resin matrix to form a mechanical interlocking structure, and a high-strength fatigue-resistant carbon fiber / epoxy resin composite material is prepared. The application avoids damage to the mechanical properties of the fiber body caused by traditional oxidation methods, the modification preparation conditions are mild, the operation is simple, and the industrial scale production can be easily realized. The obtained material is high-strength fatigue-resistant, all components are non-toxic and harmless, and the application range is not limited.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, specifically relating to a carbon fiber / epoxy resin composite material with rigid-flexible mechanical interlocking and covalent crosslinking synergistic reinforcement of interfacial bonding and its preparation method; the resulting composite material is a high-strength fatigue-resistant carbon fiber composite material. Background Technology

[0002] Carbon fiber reinforced resin matrix composites are composite materials formed by bonding high-strength carbon fibers with a resin matrix. The resin matrix, acting as a binder for the carbon fiber reinforcement, is responsible for transferring loads. The carbon fibers, as the reinforcement within the matrix, are the primary load-bearing component of the composite material. Carbon fiber / epoxy resin composites are widely used in aerospace, medical device, automotive, and energy industries due to their advantages such as high specific strength, high modulus, and corrosion resistance.

[0003] However, the strong chemical inertness of carbon fiber surfaces limits the bonding strength with epoxy resin, making interfacial debonding a common problem. This inability to prevent crack propagation within the epoxy matrix limits the overall mechanical properties of carbon fiber / epoxy resin composites. Polyacrylic acid, with its flexible long chains and numerous carboxyl groups, is an excellent choice for constructing flexible networks in the interfacial layer of composite materials. Carbon nanotubes, with their extremely high modulus, are commonly used reinforcing materials in the modification of carbon fibers and epoxy matrixes, and numerous studies have confirmed their role in hindering crack propagation within the epoxy matrix.

[0004] Addressing the challenges in improving the mechanical properties of carbon fiber / epoxy resin composites, constructing a robust rigid-flexible mechanical interlocking structure within the composite's interfacial layer is a major research direction. A novel modification scheme that balances both rigidity and flexibility is of significant importance to current research and holds broad commercial potential. Summary of the Invention

[0005] To address the problem of insufficient interfacial bonding in carbon fiber / epoxy resin composites, this invention provides a carbon fiber / epoxy resin composite material with synergistic reinforcement of interfacial bonding through rigid-flexible mechanical interlocking and covalent crosslinking, and its preparation method.

[0006] The present invention is implemented using the following technical solutions: A method for preparing a carbon fiber / epoxy resin composite material with synergistic reinforcement of interfacial bonding through rigid-flexible mechanical interlocking and covalent crosslinking is disclosed. First, polydopamine (PDA) and polyethyleneimine (PEI) are deposited on the surface of carbon fiber (CF). Then, polyacrylic acid (PAA) is grafted in situ via an amide crosslinking reaction, forming a PAA-PEI-PDA active coating on the carbon fiber (CF) surface. Aminated carbon nanotubes (CNTs) are then grafted onto the coating surface, forming a modified carbon fiber CNTs-PAA-PEI-PDA-CF with a nanoscale barbed surface structure. During the composite process between CNTs-PAA-PEI-PDA-CF and the epoxy resin matrix, a mechanical interlocking structure is formed, resulting in a high-strength, fatigue-resistant carbon fiber / epoxy resin composite material.

[0007] Specifically, the steps include the following: (1) Carbon fiber pretreatment: Soak carbon fiber in acetone for 24 hours to remove the sizing agent on the surface of carbon fiber; (2) Preparation of PAA-PEI-PDA-CF: PDA and PEI are deposited on the surface of the carbon fiber prepared in step (1) by Schiff base reaction and Michael addition reaction. Amino groups are introduced on the carbon fiber surface to obtain PEI-PDA-CF. 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride EDC and N-hydroxysuccinimide NHS are added to the PAA aqueous solution. PEI-PDA-CF is immersed in the solution to activate the carboxyl groups of PAA to carry out amide crosslinking reaction. An active coating with a large number of carboxyl groups is formed on the surface of the carbon fiber, and PAA-PEI-PDA-CF is generated. (3) Preparation of CNTs-PAA-PEI-PDA-CF: Polypyrrolidone (PVP) was added to the aqueous solution of carbon nanotubes (CNTs) and ultrasonically treated for 1 h to stabilize the dispersion of carbon nanotubes. The PAA-PEI-PDA-CF prepared in step (2) was immersed in the solution and oscillated to graft amino-terminated carbon nanotubes to form a nanoscale bar-like structure. The carbon fibers were taken out of the solution, washed, and dried to obtain CNTs-PAA-PEI-PDA-CF, abbreviated as CNTs-PPP-CF. (4) Preparation of carbon fiber / epoxy resin composite material: epoxy resin E51 and curing agent polyamide 651 are mixed at room temperature and stirred for 5 minutes to achieve uniform mixing. The mixture is then uniformly coated onto the surface of CNTs-PPP-CF prepared in step (3), placed in a mold, and heated to cure to obtain carbon fiber / epoxy resin composite material, abbreviated as CNTs-PPP-CF / EP.

[0008] The specific preparation method of PEI-PDA-CF in step (2) is as follows: prepare a mixed aqueous solution of dopamine and PEI, both with a concentration of 2 mg / ml; add 1.2 mg / ml of tris(hydroxymethyl)aminomethane (Tris) to adjust the pH of the solution to 8-9, and stir magnetically for 1 hour until the solution turns orange-yellow; immerse the acetone-treated carbon fiber in the above solution, shake for 12 hours, then remove, wash, and dry it, and record it as PEI-PDA-CF.

[0009] In the amide crosslinking reaction system in step (2): the concentration of PAA aqueous solution is 20 mg / ml, the concentration of EDC is 4.8 mg / ml, and the concentration of NHS is 1.2 mg / ml. The specific reaction method is as follows: EDC and NHS are added to PAA aqueous solution as activators to activate the carboxyl group. At the same time, 2.5 mg / ml of phosphoric acid is added to adjust the pH of the solution to 5. After magnetic stirring for 1 hour, the solution becomes clear. PEI-PDA-CF is immersed in PAA aqueous solution, with 5g of PEI-PDA-CF immersed in each 100ml solution. After shaking for 12 hours, the carboxyl group of PAA is activated to carry out the amide crosslinking reaction. Then, it is taken out, washed, and dried. The sample obtained is PAA-PEI-PDA-CF, abbreviated as PPP-CF.

[0010] In step (3), the mass fraction of carbon nanotubes is 0.05-0.15%, PVP assists in dispersing carbon nanotubes, the mass ratio of carbon nanotubes to PVP is 1:8, and 2g of PAA-PEI-PDA-CF is immersed in every 100ml of solution.

[0011] In step (4), epoxy resin E51 and polyamide 651 are mixed in a ratio of 100g: 25-30g. The curing conditions are pre-curing at room temperature for 2 hours, curing at 90℃ for 2 hours, and curing at 125℃ for 1-3 hours.

[0012] The present invention also provides a carbon fiber / epoxy resin composite material prepared by the method described above, which features synergistic reinforcement of interfacial bonding through rigid-flexible mechanical interlocking and covalent crosslinking.

[0013] The carbon fiber / epoxy resin composite material prepared by this invention has a tensile strength of 1324 MPa, which is 49.4% higher than that of the unmodified carbon fiber composite material; a flexural strength of 1176 MPa, which is 71.7% higher; and an interlaminar shear strength of 73.83 MPa, which is 39.2% higher. Under stress levels of 850 MPa, 800 MPa, and 750 MPa, the fatigue life of the modified carbon fiber / epoxy resin composite material is extended by 38 times, 29 times, and 26 times respectively compared with the unmodified material. Under a stress level of 700 MPa, the modified carbon fiber / epoxy resin composite material does not fracture even after 1 million tensile cycles, which is at least 14 times longer than the average fatigue life of 67,000 cycles before modification.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention constructs an active coating by depositing PEI-PDA and grafting PAA with amide crosslinking, avoiding the damage to the fiber's mechanical properties caused by traditional oxidation methods. Furthermore, the modification preparation conditions are mild, the operation is simple, and it is easy to achieve large-scale industrial production.

[0015] The polymer molecular chains of PAA and PEI in this invention enable the flexible coating formed by PAA-PEI-PDA through amide crosslinking to have excellent toughness. The active groups of PAA create conditions for its covalent crosslinking with the matrix and curing agent, eliminating the weak boundary layer at the interface between carbon fiber and epoxy matrix.

[0016] In this invention, the high modulus of carbon nanotubes leads to strong mechanical interlocking in the interface layer, which can hinder the propagation of intramolecular cracks in epoxy groups. At the same time, the flexible network based on PAA also compensates for the stress shielding shortcomings that occur when high-modulus materials are mixed with low-modulus materials, truly realizing an interface structure that is synergistically enhanced by rigid-flexible interlocking and covalent cross-linking.

[0017] All components in the carbon fiber / epoxy resin composite material with rigid-flexible mechanical interlocking and covalent crosslinking synergistic reinforcement of interfacial bonding prepared by the method described in this invention are non-toxic and harmless, and its application scope will not be limited as a result. Attached Figure Description

[0018] Figure 1 The FI-TR spectra of CF, PDA-CF, PAA-CF, and PAA-PDA-CF proposed in this invention; Figure 2 XPS test C1s fitting for (a) PPP-CF and (b) CNTs-PPP-CF proposed in this invention; Figure 3 The images show SEM images of the CNTs-PPP-CF proposed in this invention, with different CNT concentrations: (a) 0.5%, (b) 1.0%, (c) 1.5%. Figure 4 (a) Tensile stress-strain curves and (b) tensile strength and Young's modulus of CF / EP, PPP-CF / EP and CNTs-PPP-CF / EP proposed in this invention; Figure 5 (a) Bending stress-strain curves and (b) Bending strength and flexural modulus of elasticity for CF / EP, PPP-CF / EP and CNTs-PPP-CF / EP proposed in this invention; Figure 6 (a) Interlaminar shear stress-strain curves and (b) interlaminar shear strength of CF / EP, PPP-CF / EP and CNTs-PPP-CF / EP proposed in this invention; Figure 7 The fatigue life test results of CF / EP, PPP-CF / EP and CNTs-PPP-CF / EP proposed in this invention are shown. Figure 8 This is a diagram illustrating the mechanism by which the interface modification scheme of the present invention improves the interface layer damage process. Figure 9 SEM images of the cross-section of a CF / EP interlaminar shear test sample; Figure 10 SEM images of the cross-section of a CNTs-PPP-CF / EP interlaminar shear test sample. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and all materials publicly cited herein and cited by them are incorporated herein by reference.

[0021] Equivalent technologies of the specific embodiments described herein that are readily apparent to those skilled in the art through routine experimentation are included in this application.

[0022] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the instruments and equipment used in the following examples are all standard laboratory instruments and equipment; unless otherwise specified, the experimental materials used in the following examples were all purchased from regular biochemical reagent stores.

[0023] Example 1: Preparation, testing, and characterization of a carbon nanotube-polyacrylic acid-polyethyleneimine-polydopamine modified carbon fiber / epoxy resin composite material, the details of which are as follows: (1) Soak the carbon fiber in acetone for 24 hours to remove the sizing agent on the surface of the carbon fiber.

[0024] (2) Take 0.2g of dopamine hydrochloride and 0.2g of PEI and add them to 100ml of deionized water. Then add 0.12g of Tris to adjust the pH of the solution to 8-9. After stirring magnetically for 1h, the solution turns orange-yellow. Immerse the carbon fiber in the above solution, shake for 12h, then take it out, wash and dry it. The obtained sample is named PEI-PDA-CF. All the above operations are carried out at room temperature.

[0025] (3) Add 2g of PAA to 100ml of deionized water, add 0.48g of EDC and 0.12g of NHS to activate the carboxyl group, add 2.5ml of phosphoric acid to adjust the pH of the solution to 5, and stir magnetically for 1h until the solution becomes clear. Immerse 5g of PEI-PDA-CF in the solution, shake for 12h, then remove, wash, and dry. The obtained sample is named PAA-PEI-PDA-CF, or simply PPP-CF. All the above operations were performed at room temperature.

[0026] (4) Take 0.10g of aminated carbon nanotubes and add them to 100ml of deionized water, then add 0.8g of PVP and sonicate for 1h to disperse the carbon nanotubes evenly. Immerse 2g of PPP-CF in the solution and shake for 12h, then take it out, wash and dry it. The obtained sample is named CNTs-PPP-CF. All the above operations are carried out at room temperature.

[0027] (5) Mix epoxy resin E51 and polyamide 651 evenly at a mass ratio of 10g:2.5g. Apply the mixture evenly to the surface of CNTs-PPP-CF, place it in a mold, apply a pressure of 4MPa, and cure according to the conditions of "pre-curing at room temperature for 2 hours, curing at 90℃ for 2 hours, and curing at 125℃ for 1 hour". After curing, allow it to cool naturally to room temperature and then demold to obtain the CNTs-PPP-CF / EP composite material. Cut the obtained sample to an appropriate size according to the test requirements for testing.

[0028] (6) The tensile strength of the CNTs-PPP-CF / EP composite material is 1324 MPa, the flexural strength is 1176 MPa, and the interlaminar shear strength is 73.83 MPa. Under stress levels of 850 MPa, 800 MPa, 750 MPa, and 700 MPa, the average fatigue life of the composite material is 2142 cycles, 26710 cycles, 202000 cycles, and 1 million cycles without fracture, respectively.

[0029] Example 2: This example provides the preparation, testing, and characterization of a carbon nanotube-polyacrylic acid-polyethyleneimine-polydopamine modified carbon fiber / epoxy resin composite material. The difference between this example and Example 1 is that the CNT content is 0.05 g and the PVP content is 0.4 g. The tensile strength of the CNTs-PPP-CF / EP composite material is 1182 MPa, the flexural strength is 984 MPa, and the interlaminar shear strength is 67.82 MPa.

[0030] Example 3: This example provides the preparation, testing, and characterization of a carbon nanotube-polyacrylic acid-polyethyleneimine-polydopamine modified carbon fiber / epoxy resin composite material. The difference between this example and Example 1 is that the CNT content is 0.15 g and the PVP content is 1.2 g. The tensile strength of the CNTs-PPP-CF / EP composite material is 1103 MPa, the flexural strength is 949 MPa, and the interlaminar shear strength is 69.30 MPa.

[0031] Comparative Example 1: This example provides a method for preparing, testing, and characterizing a polyacrylic acid-polyethyleneimine-polydopamine modified carbon fiber / epoxy resin composite material. The specific details are as follows: (1) Soak carbon fiber in acetone for 24 hours to remove the sizing agent from the surface of carbon fiber.

[0032] (2) Take 0.2g of dopamine hydrochloride and 0.2g of PEI and add them to 100ml of deionized water. Add 0.12g of Tris to adjust the pH of the solution to 8-9. After stirring magnetically for 1h, the solution turns orange-yellow. Immerse the carbon fiber in the solution, shake for 12h, then take it out, wash and dry it. The obtained sample is named PEI-PDA-CF. All the above operations are carried out at room temperature.

[0033] (3) Take 2g of PAA and add it to 100ml of deionized water. Add 0.48g of EDC and 0.12g of NHS to activate the carboxyl group. Add 2.5ml of phosphoric acid to adjust the pH of the solution to 5. After stirring magnetically for 1h, the solution becomes clear. Immerse PEI-PDA-CF in the solution, shake for 12h, then take it out, wash, and dry it. The obtained sample is recorded as PAA-PEI-PDA-CF, also known as PPP-CF. All the above operations are carried out at room temperature.

[0034] (4) Mix epoxy resin E51 and polyamide 651 evenly at a mass ratio of 10g:2.5g. Apply the mixture evenly to the surface of PPP-CF, place it in a mold, apply a pressure of 4MPa, and cure according to the conditions of "pre-curing at room temperature for 2 hours, curing at 90℃ for 2 hours, and curing at 125℃ for 1 hour". After curing, allow it to cool naturally to room temperature and then demold to obtain the PPP-CF / EP composite material. Cut the obtained sample to an appropriate size according to the test requirements for testing.

[0035] (5) The tensile strength of the PPP-CF / EP composite material is 1092 MPa, the flexural strength is 854 MPa, and the interlaminar shear strength is 62.09 MPa. Under stress levels of 850 MPa, 800 MPa, 750 MPa, and 700 MPa, the average fatigue life of the PPP-CF / EP composite material is 1090 cycles, 8200 cycles, 58900 cycles, and 383000 cycles, respectively.

[0036] Comparative Example 2: This example provides a method for preparing, testing, and characterizing a carbon fiber / epoxy resin composite material, as detailed below: (1) Soak carbon fiber in acetone for 24 hours to remove the sizing agent from the surface of carbon fiber.

[0037] (2) Mix epoxy resin E51 and polyamide 651 evenly at a mass ratio of 10 g: 2.5 g. Take acetone-treated carbon fiber, apply the epoxy resin mixed with curing agent evenly to the surface of the carbon fiber, place it in a mold and apply a pressure of 4 MPa. After curing according to the conditions of "pre-curing at room temperature for 2 hours, curing at 90 ℃ for 2 hours, and curing at 125 ℃ for 1 hour", let it cool naturally to room temperature and then demold to obtain CF / EP composite material. Cut the obtained sample to an appropriate size according to the test requirements for testing.

[0038] (3) The tensile strength of the CF / EP composite material is 886 MPa, the flexural strength is 685 MPa, and the interlaminar shear strength is 53.02 MPa. Under stress levels of 850 MPa, 800 MPa, 750 MPa, and 700 MPa, the average fatigue life of CF / EP is 55 cycles, 890 cycles, 7400 cycles, and 67000 cycles, respectively.

[0039] Table 1 shows the performance comparison results of the CNTs-PPP-CF / EP obtained in Examples 1-3 and the composite materials obtained in Comparative Examples 1 and 2.

[0040] Table 1: Performance Comparison of Carbon Nanotube-Polyacrylic Acid-Polyethyleneimine-Polydopamine Modified Carbon Fiber / Epoxy Resin Composites and Unmodified Carbon Fiber / Epoxy Resin (CF / EP) Composites Figure 1 Infrared characterization was performed to establish the covalent crosslinking mechanism of PAA and PDA on the carbon fiber surface, with CF, PDA-CF, and PAA-CF serving as control groups. Based on the characteristic peak values, it can be seen that the bonding mode within the modified coating on the carbon fiber surface is covalent crosslinking through the formation of amide bonds. PEI, CNTs, and PDA also provide amino sites, exhibiting the same crosslinking mechanism.

[0041] Figure 2 a and 2b are the C1s peak fittings of the XPS spectra of PPP-CF and CNTs-PPP-CF, respectively, which indicate that the carboxyl groups introduced by PAA are excessive. Therefore, after amide crosslinking, there are still a large number of carboxyl groups on the outer surface of the PPP coating. After grafting carbon nanotubes, the outer surface of the coating still carries carboxyl groups, which provides reaction sites for the interface layer to form chemical bonds with the matrix.

[0042] Figure 3 The images are SEM images of the CNTs-PPP-CF samples prepared in Examples 1 to 3, respectively. It can be seen that the morphological features of coating and carbon nanotubes intertwined appear on the fiber surface. Among them, the morphological features of the sample in Example 1 are most consistent with the barbed structure, forming the largest steric hindrance on the fiber surface.

[0043] Figure 4 The tensile properties of the carbon fiber / epoxy resin composites in Examples 1-3 and Comparative Examples 1 and 2 are shown in the table. It can be seen that, compared to the unmodified CF / EP in Comparative Example 2, the tensile strength of the modified carbon fiber / epoxy resin composites in Examples 1-3 and Comparative Example 1 increased by 49.4%, 33.4%, 24.5%, and 22.3%, respectively.

[0044] Figure 5 The results show the flexural properties of the carbon fiber / epoxy resin composites in Examples 1-3 and Comparative Examples 1 and 2. It can be seen that, compared to the unmodified CF / EP in Comparative Example 2, the flexural strength of the modified carbon fiber / epoxy resin composites in Examples 1-3 and Comparative Example 1 increased by 71.7%, 43.6%, 38.5%, and 24.7%, respectively.

[0045] Figure 6 The interlaminar shear properties of the carbon fiber / epoxy resin composites in Examples 1-3 and Comparative Examples 1 and 2 are shown in the test results. It can be seen that, compared to the unmodified CF / EP in Comparative Example 2, the shear strength of the modified carbon fiber / epoxy resin composites in Examples 1-3 and Comparative Example 1 increased by 39.2%, 27.9%, 30.7%, and 17.1%, respectively.

[0046] Figure 7 The tensile cyclic fatigue life test results (R=0.1, 5 Hz) of the carbon fiber / epoxy resin composites in Example 1, Comparative Example 1, and Comparative Example 2 are shown. It can be seen that, compared to the unmodified CF / EP in Comparative Example 2, the fatigue life of the modified carbon fiber / epoxy resin composites in Comparative Example 1 and Example 1 is extended by 5–19 times and 14–38 times, respectively.

[0047] Figure 8 This diagram illustrates the mechanism by which the interface modification scheme of the present invention improves the interface layer damage process. Cracks at the CF / EP interface can propagate rapidly along the interface layer, leading to material failure. In CNTs-PPP-CF / EP, CNTs form a mechanical interlock with the matrix, effectively hindering crack propagation. Material failure only occurs when more cracks form in other parts of the material, eventually merging together. Therefore, the interface modification scheme of the present invention delays interface failure in carbon fiber / epoxy resin materials, significantly improving the overall performance of the composite material.

[0048] Figure 9 This is a SEM image of the cross-section of a CF / EP interlaminar shear test sample. It can be seen that there is relatively little resin residue on the fiber surface, which is consistent with... Figure 8 The analysis results are consistent with those of the mechanism diagram.

[0049] Figure 10 SEM images of the cross-section of a CNTs-PPP-CF / EP interlaminar shear test sample. A large amount of resin residue is visible on the fiber surface, which is consistent with... Figure 8 The results of the analysis of the mechanism diagram are consistent with those of the modified scheme, confirming the enhancement mechanism.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a carbon fiber / epoxy resin composite material with synergistic interlocking of rigid and flexible mechanical interlocking and covalent crosslinking, characterized in that: First, polydopamine (PDA) and polyethyleneimine (PEI) are deposited on the surface of carbon fiber (CF). Then, polyacrylic acid (PAA) is grafted in situ through an amide crosslinking reaction to form an active coating of PAA-PEI-PDA on the surface of carbon fiber (CF). Aminated carbon nanotubes (CNTs) are then grafted onto the coating surface to form a modified carbon fiber CNTs-PAA-PEI-PDA-CF with a nanoscale barbed surface structure. During the composite process of CNTs-PAA-PEI-PDA-CF and epoxy resin matrix, a mechanical interlocking structure is formed to prepare a high-strength fatigue-resistant carbon fiber / epoxy resin composite material, abbreviated as CNTs-PPP-CF / EP.

2. The preparation method according to claim 1, characterized in that: Specifically, the steps include the following: (1) Carbon fiber pretreatment: Soak carbon fiber in acetone for 24 hours to remove the sizing agent on the surface of carbon fiber; (2) Preparation of PAA-PEI-PDA-CF: PDA and PEI are deposited on the surface of the carbon fiber prepared in step (1) by Schiff base reaction and Michael addition reaction. Amino groups are introduced on the carbon fiber surface to obtain PEI-PDA-CF. 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride EDC and N-hydroxysuccinimide NHS are added to the PAA aqueous solution. PEI-PDA-CF is immersed in the solution to activate the carboxyl groups of PAA to carry out amide crosslinking reaction. An active coating with a large number of carboxyl groups is formed on the surface of the carbon fiber, and PAA-PEI-PDA-CF is generated. (3) Preparation of CNTs-PAA-PEI-PDA-CF: Polypyrrolidone (PVP) was added to the aqueous solution of carbon nanotubes (CNTs) and ultrasonically treated for 1 h to stabilize the dispersion of carbon nanotubes. The PAA-PEI-PDA-CF prepared in step (2) was immersed in the solution and oscillated to graft amino-terminated carbon nanotubes to form a nanoscale bar-like structure. The carbon fibers were taken out of the solution, washed, and dried to obtain CNTs-PAA-PEI-PDA-CF, abbreviated as CNTs-PPP-CF. (4) Preparation of carbon fiber / epoxy resin composite material: epoxy resin E51 and curing agent polyamide 651 are mixed at room temperature and stirred for 5 minutes to achieve uniform mixing. The mixture is then uniformly coated onto the surface of CNTs-PPP-CF prepared in step (3), placed in a mold, and heated to cure to obtain carbon fiber / epoxy resin composite material.

3. The preparation method according to claim 2, characterized in that: The specific preparation method of PEI-PDA-CF in step (2) is as follows: prepare a mixed aqueous solution of dopamine and PEI, both with a concentration of 2 mg / ml; add 1.2 mg / ml of tris(hydroxymethyl)aminomethane (Tris) to adjust the pH of the solution to 8-9, and stir magnetically for 1 hour until the solution turns orange-yellow; immerse the acetone-treated carbon fiber in the above solution, shake for 12 hours, then remove, wash, and dry it, and record it as PEI-PDA-CF.

4. The preparation method according to claim 2, characterized in that: In the amide crosslinking reaction system in step (2): the concentration of PAA aqueous solution is 20 mg / ml, the concentration of EDC is 4.8 mg / ml, and the concentration of NHS is 1.2 mg / ml. The specific reaction method is as follows: EDC and NHS are added to PAA aqueous solution as activators to activate the carboxyl group. At the same time, 2.5 mg / ml of phosphoric acid is added to adjust the pH of the solution to 5. After magnetic stirring for 1 hour, the solution becomes clear. PEI-PDA-CF is immersed in PAA aqueous solution, with 5g of PEI-PDA-CF immersed in each 100ml solution. After shaking for 12 hours, the carboxyl group of PAA is activated to carry out the amide crosslinking reaction. Then, it is taken out, washed, and dried. The sample obtained is PAA-PEI-PDA-CF, abbreviated as PPP-CF.

5. The preparation method according to claim 2, characterized in that: In step (3), the mass fraction of carbon nanotubes in the solution is 0.05-0.15%, PVP assists in dispersing carbon nanotubes, the mass ratio of carbon nanotubes to PVP is 1:8, and 2g of PAA-PEI-PDA-CF is immersed in every 100ml of solution.

6. The preparation method according to claim 2, characterized in that: In step (4), epoxy resin E51 and polyamide 651 are mixed in a ratio of 100g: 25-30g. The curing conditions are pre-curing at room temperature for 2 hours, curing at 90℃ for 2 hours, and curing at 125℃ for 1-3 hours.

7. A carbon fiber / epoxy resin composite material with synergistic reinforcement of interfacial bonding by rigid-flexible mechanical interlocking and covalent crosslinking, prepared by any one of the methods described in claims 1-6.

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