Method for enhancing interface performance of carbon fiber resin-based composite material by using rigid-flexible structure

Abstract

The invention belongs to the technical field of carbon fibers, and relates to a surface modification method of carbon fibers, in particular to a method for enhancing the interface performance of a carbon fiber resin-based composite material by using a rigid-flexible structure, which comprises the following steps: (1) desizing and acidizing carbon fibers to obtain acidized carbon fibers with oxygen-containing functional groups on the surfaces; (2) carrying out an electropolymerization reaction in an electrolyte containing acrylic acid by taking the obtained acidified carbon fiber as a cathode, and forming a polyacrylic acid layer on the surface of the carbon fiber to obtain a flexible component modified carbon fiber; (3) putting the obtained flexible component modified carbon fiber into a reaction system containing a zirconium source, an organic ligand and a solvent, and carrying out solvothermal reaction; and growing a UiO-66-NH2 metal organic framework material on the surface of the polyacrylic acid layer in situ. The gradient interface layer with the characteristic of'soft inside and rigid outside 'is constructed on the surface of the carbon fiber through an efficient and controllable process, and the interface strength and toughness of the composite material are improved.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber technology and relates to a method for surface modification of carbon fiber, particularly a method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure. Background Technology

[0002] Carbon fiber reinforced resin matrix composites, with their high specific strength, high specific modulus, corrosion resistance, and excellent fatigue performance, have become key structural materials in aerospace, automotive, wind turbine blades, and high-end sporting goods. In carbon fiber composites, the primary role of the fiber is to bear the load, while the resin's main role is to distribute the load, protect the carbon fibers, and maintain the material's shape. The interface between the fiber and resin plays a crucial role in transferring and dispersing the applied load. Changes in the interface composition and structure can cause gradual or even abrupt changes in the composite's physicochemical properties, especially under high loads and complex stresses, and are a major factor affecting the overall performance of carbon fiber composites. Therefore, improving the overall performance of composites through the design and control of interface properties has become a fundamental and common research topic in carbon fiber composite surface and interface studies. Typically, the design and control of carbon fiber composite interfaces can be achieved by altering the surface activity, morphology, structure, and wettability with the resin matrix. However, a major problem with traditional research on carbon fiber composite interface modification is that increased interfacial bonding strength is often accompanied by decreased toughness, which prevents the strengthening effect of interface modification from being fully realized, thus limiting its application in some fields.

[0003] In recent years, constructing rigid-flexible synergistic interface structures has become a research hotspot for improving the interfacial properties of carbon fibers / resins. The flexible component, through chemical grafting of polymeric segments such as polyetheramine, polyethyleneimine, and dopamine onto the carbon fiber surface, not only introduces a large number of amino groups, improving the surface polarity and wettability of the fiber, but also absorbs energy and buffers stress concentration at the interface. The rigid component, by introducing rigid particles such as carbon nanotubes, graphene, metal oxides, and titanium carbide onto the carbon fiber surface, significantly enhances load transfer efficiency and interfacial stability. Rigid nanoporous materials (MOFs) have attracted considerable attention in recent years due to their high designability and structural diversity. The large number of active surface atoms and the resulting enhanced surface functionalization modification capabilities endow them with many novel physical, chemical, and mechanical properties, allowing for the design and control of their structures at the molecular scale.

[0004] However, there are still challenges in how to accurately control the interface distribution, bonding strength and process simplicity of rigid-flexible structures: (1) Chemical grafting of flexible polymers is inefficient and the flexible molecular chains are very easy to curl and entangle; (2) In the control of UiO-66-NH2 structure, excessively large pore size and pore connectivity can easily reduce the stability of MOF structure, and conversely, restrict the flow of resin molecules in it; (3) The operation process is time-consuming and energy-intensive, which is not conducive to large-scale production.

[0005] Therefore, a simplified and efficient carbon fiber modification method was developed, which involves electropolymerizing a flexible PAA portion on the carbon fiber surface for 5 minutes, followed by in-situ growth of a rigid UiO-66-NH2 portion with tunable pore structure. The amino-containing and structurally stable UiO-66-NH2 can form a rigid pore structure on the carbon fiber surface, allowing resin molecules to pass through and react with the functional groups on the inner wall to form an interpenetrating network structure, reducing the resin crosslinking density and thus providing toughening. Constructing flexible and rigid structures layer by layer on the carbon fiber surface to synergistically enhance the interfacial properties of the composite material allows for precise control of the interfacial distribution and interaction between PAA and UiO-66-NH2, while also offering process controllability, facilitating industrial scale-up, and improving the reliability and safety of carbon fiber composites. Therefore, this method has significant practical implications. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure. This method utilizes an efficient and controllable process to construct a gradient interfacial layer with "inner flexibility and outer rigidity" characteristics on the carbon fiber surface, aiming to simultaneously improve the interfacial strength and toughness of the composite material.

[0007] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0008] A method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure includes the following steps:

[0009] (1) Pretreatment of carbon fiber: carbon fiber is desizing and acidification to obtain acidified carbon fiber with oxygen-containing functional groups on the surface.

[0010] (2) Construction of flexible surface components: The acidified carbon fiber obtained in step (1) is used as the cathode and electropolymerization reaction is carried out in an electrolyte containing acrylic acid to form a polyacrylic acid layer on the surface of the carbon fiber, thereby obtaining carbon fiber modified with flexible components.

[0011] (3) Construction of surface rigid component: The carbon fiber modified with flexible component obtained in step (2) is placed in a reaction system containing zirconium source, organic ligand and solvent and subjected to solvothermal reaction; UiO-66-NH2 metal-organic framework material is grown in situ on the surface of the polyacrylic acid layer to form a rigid-flexible structure composed of flexible polyacrylic acid inner layer and rigid UiO-66-NH2 outer layer, thus obtaining carbon fiber reinforced with rigid-flexible structure.

[0012] Further, the desizing treatment in step (1) is as follows: the carbon fiber is placed in acetone and extracted by refluxing at 70-90°C for 36-60 hours using a Soxhlet extractor; the acidification treatment is as follows: the desizing carbon fiber is immersed in concentrated nitric acid and treated at 70-90°C for 3-5 hours, then washed until neutral and dried.

[0013] Furthermore, in the electropolymerization reaction described in step (2), the electrolyte is an aqueous solution containing acrylic acid and zinc chloride, wherein the concentration of acrylic acid is 0.3 to 0.5 mol / L and the concentration of zinc chloride is 0.02 to 0.04 mol / L.

[0014] Furthermore, the electropolymerization reaction described in step (2) is carried out under nitrogen protection, with a current of 0.016 to 0.020 A and a reaction time of 3 to 10 minutes.

[0015] Further, the zirconium source mentioned in step (3) is zirconium tetrachloride; the organic ligand is 2-aminoterephthalic acid; and the solvent includes N,N-dimethylformamide and concentrated hydrochloric acid.

[0016] Further, in the reaction system described in step (3), the concentration of 2-aminoterephthalic acid is 0.06-0.09 mol / L; the concentration of zirconium tetrachloride is 0.08-0.11 mol / L; and the volume ratio of N,N-dimethylformamide to concentrated hydrochloric acid is 4-6:1.

[0017] Furthermore, the solvothermal reaction described in step (3) is carried out under vacuum conditions, with a reaction temperature of 80-90°C and a reaction time of 6-10 hours.

[0018] Furthermore, after the reaction in step (3) is completed, the product is further subjected to ultrasonic treatment with N,N-dimethylformamide; the ultrasonic treatment power is 280-350W, the ultrasonic treatment time is 0.4-0.6h, and the product is dried under vacuum conditions; the drying temperature is 80-90℃, and the drying time is 10-12h.

[0019] A rigid-flexible reinforced carbon fiber prepared by the above method, wherein the surface of the rigid-flexible reinforced carbon fiber is sequentially coated with a polyacrylic acid layer and a UiO-66-NH2 layer from the inside to the outside.

[0020] A carbon fiber resin-based composite material comprising the aforementioned rigid-flexible reinforced carbon fibers and a resin matrix.

[0021] By employing a simplified and efficient carbon fiber modification method, the flexible PAA portion can be electropolymerized on the carbon fiber surface in 5 minutes, followed by the in-situ growth of a rigid UiO-66-NH2 portion with tunable pore structure. The amino-containing and structurally stable UiO-66-NH2 can form a rigid pore structure on the carbon fiber surface, allowing resin molecules to pass through and react with the functional groups on the inner wall to form an interpenetrating network structure. This reduces the resin crosslinking density and provides a toughening effect. The layer-by-layer construction of flexible and rigid structures on the carbon fiber surface synergistically enhances the interfacial properties of the composite material. This approach allows for precise control of the interfacial distribution and interaction between PAA and UiO-66-NH2, while also offering process controllability, facilitating industrial scale-up production, and improving the reliability and safety of carbon fiber composites. Therefore, it has significant practical implications.

[0022] The core technology of this invention lies in firstly, uniformly coating a flexible polyacrylic acid (PAA) layer onto the surface of carbon fibers using rapid electropolymerization technology. This layer is rich in carboxyl groups, which can serve as a reactive "bridge." Then, utilizing the carboxyl groups on the surface of this flexible layer as nucleation sites, a rigid and porous UiO-66-NH2 metal-organic framework material is firmly and uniformly constructed on the PAA layer through in-situ growth. The resulting "flexible PAA-rigid UiO-66-NH2" composite structure can form a gradient modulus interface region with synergistic physicochemical effects between the fiber and the resin, thereby effectively transferring stress, absorbing energy, and enhancing the bond.

[0023] This invention achieves surface polymerization of carbon fibers through covalent interactions. The rigid-flexible structure enhances the surface roughness and specific surface area of ​​the fibers, thereby strengthening the mechanical interlocking with epoxy resin. The amino groups on the UiO-66-NH2 surface can form CN covalent bonds with the epoxy resin, making the physicochemical interaction in the interfacial region more complete. The polyacrylic acid chains penetrate into the matrix, forming a wider and thicker interfacial transition layer, increasing the crack propagation path, and thus achieving the purpose of enhancing the interfacial properties of the composite material.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention achieves comprehensive optimization of interfacial properties by constructing a gradient interfacial layer with a "flexible interior and rigid exterior" structure on the surface of carbon fibers. The flexible PAA layer penetrates deep into the resin matrix, buffering stress concentration, increasing crack propagation paths, and improving toughness; the rigid UiO-66-NH2 layer achieves mechanical interlocking by increasing surface roughness, utilizes its porous structure to form an interpenetrating network with the resin, and chemically bonds with the epoxy resin through amino groups, significantly enhancing the interfacial bonding strength. Experiments show that the interlaminar shear strength and impact strength of the resulting composite material are significantly improved, solving the problem of difficulty in achieving both strength and toughness in traditional modifications.

[0026] 2. This invention employs electropolymerization technology to construct flexible layers, which results in rapid reaction, uniform film thickness, and significantly higher efficiency than traditional chemical grafting. Utilizing the carboxyl groups on the PAA surface as nucleation sites for in-situ growth guides the uniform and robust growth of UiO-66-NH2, preventing MOF aggregation and achieving effective control over the morphology and distribution of the rigid layer.

[0027] 3. The process of this invention is simple, the conditions are mild, and it is easy to operate and control. Each step has good potential for scale-up production, providing a feasible technical option for the preparation of high-performance carbon fiber composite materials. Attached Figure Description

[0028] Figure 1 The above are XPS full spectra of the carbon fibers obtained in Example 1 of this invention, where (a) is acidified carbon fiber, (b) is CF / PAA, and (c) is CF / PAA / UiO-66-NH2.

[0029] Figure 2 This is the C1s XPS peak spectrum of the acidified carbon fiber in Example 1 of the present invention.

[0030] Figure 3 This is the C1s XPS peak spectrum of CF / PAA in Embodiment 1 of the present invention.

[0031] Figure 4 The XPS peak spectra of C1s and Zr 3d of CF / PAA / UiO-66-NH2 in Example 1 of this invention are shown.

[0032] Figure 5 The images are scanning electron microscope images of different carbon fiber samples in Example 1 of the present invention: (a) acidified carbon fiber, (b) CF / PAA, and (c) CF / PAA / UiO-66-NH2.

[0033] Figure 6 These are EDS line scan images of the interface regions of different carbon fiber composite materials in Example 1 of the present invention.

[0034] Figure 7This is a comparison diagram of the monofilament tensile strength and interlaminar shear strength of different carbon fiber composite materials in Example 1 of the present invention.

[0035] Figure 8 This is a comparison chart of the impact strength of different carbon fiber composite materials in Example 1 of the present invention. Detailed Implementation

[0036] The present invention will now be described in detail through specific embodiments. These embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. As used throughout the specification and claims, "comprising" or "including" is an open-ended term and is interpreted as "comprising but not limited to". The following description is a preferred embodiment for carrying out the invention; however, this description is intended to illustrate the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the present invention is defined by the appended claims. Unless otherwise specified, all reagents and materials used in the present invention are commercially available. In the present invention, unless otherwise specified, all percentages are by mass.

[0037] Example 1

[0038] This embodiment describes a method for preparing carbon fiber resin matrix composites with enhanced interfacial properties through the construction of a rigid-flexible structure, implemented according to the following steps:

[0039] (1) Extraction treatment of carbon fiber: 2.3g of carbon fiber is placed in a Soxhlet extractor containing acetone, and the acetone is heated to 80°C. The acetone is continuously distilled out and condensed in the Soxhlet extractor, so that the impurities on the surface of the carbon fiber are cleaned in the distilled acetone. The cleaning time is 48h, and carbon fiber with the epoxy coating removed is obtained.

[0040] (2) Acidification treatment of carbon fibers: The carbon fibers with the epoxy coating removed were placed at the bottom of a beaker, and concentrated nitric acid was added until the carbon fibers were completely submerged. The beaker was then fixed in a water bath, and the temperature was set to 80℃ for 4 hours. After cooling to room temperature, the beaker was removed and rinsed repeatedly with deionized water. During this process, the pH of the rinsing solution was continuously tested with pH test paper until the result was neutral. Subsequently, the carbon fibers were placed in a drying oven and dried at 60℃ for 24 hours to obtain acidified carbon fibers.

[0041] (3) Electropolymerized acrylic acid on carbon fiber surface

[0042] ① Preparation of acrylic electrolyte

[0043] Accurately weigh 0.4 mol of acrylic acid and 0.03 mol of zinc chloride into a beaker, and add deionized water to prepare 200 mL of electrolyte. Sonicate the solution for 10 min to ensure uniform dispersion.

[0044] ② Electropolymerized acrylic acid

[0045] A section of acidified carbon fiber was cut and bound to a glass frame, placed in an electrolytic cell to act as the cathode, and a graphite plate as the anode, with a spacing of 1.0 cm between them. A constant current and constant voltage power supply was connected to the cathode and anode of the acidified carbon fiber and the graphite plate, respectively, to form an electropolymerization system. The prepared acrylic acid solution was slowly poured into the electrolytic cell until the acidified carbon fiber was submerged, and nitrogen gas was purged for 10 minutes to remove air from the cell. The current was set to 0.018 A, and electropolymerization was carried out for 5 minutes in a nitrogen atmosphere. After completion, the sample was repeatedly washed with ethanol and distilled water and dried in a 60℃ drying oven for 12 hours. The resulting sample was electropolymerized flexible polyacrylic acid carbon fiber.

[0046] (4) In-situ growth of UiO-66-NH2 on carbon fiber surface

[0047] Solution 1: Weigh 7.5 mmol of 2-aminoterephthalic acid and add it to 100 mL of DMF. Sonicate for 20 min.

[0048] Solution 2: Weigh 5.4 mmol of zirconium tetrachloride and add it to 50 mL of DMF. Then slowly add 10 mL of HCl and sonicate for 20 min.

[0049] Solution 1 and Solution 2 were mixed and poured into a hydrothermal reactor. After mixing, the prepared electropolymerized flexible polyacrylic acid carbon fibers were placed into the hydrothermal reactor. The reaction was carried out under vacuum heating at 80°C for 8 hours. After cooling to room temperature, the obtained carbon fibers were washed three times with DMF and then dried in a drying oven at 60°C for 12 hours. The obtained sample was a reinforced carbon fiber with a surface-constructed rigid-flexible structure.

[0050] Example 2

[0051] The method for enhancing the interfacial properties of carbon fiber resin matrix composites using rigid-flexible structures is implemented according to the following steps:

[0052] (1) Extraction treatment of carbon fiber: 2.3g of carbon fiber is placed in a Soxhlet extractor containing acetone, and the acetone is heated to 80°C. The acetone is continuously distilled out and condensed in the Soxhlet extractor, so that the impurities on the surface of the carbon fiber are cleaned in the distilled acetone. The cleaning time is 48 h, and carbon fiber with the epoxy coating removed is obtained.

[0053] (2) Acidification treatment of carbon fibers: The carbon fibers with the epoxy coating removed were placed at the bottom of a beaker, and concentrated nitric acid was added until the carbon fibers were completely submerged. The beaker was then fixed in a water bath, and the temperature was set to 80℃ for 4 hours. After cooling to room temperature, the beaker was removed and rinsed repeatedly with deionized water. During this process, the pH of the rinsing solution was continuously tested with pH test paper until the result was neutral. Subsequently, the carbon fibers were placed in a drying oven and dried at 60℃ for 24 hours to obtain acidified carbon fibers.

[0054] (3) Electropolymerized acrylic acid on carbon fiber surface

[0055] ① Preparation of acrylic electrolyte

[0056] Accurately weigh 0.4 mol of acrylic acid and 0.03 mol of zinc chloride into a beaker, and add deionized water to prepare 200 mL of electrolyte. Sonicate for 10 min to ensure uniform dispersion of the two in the aqueous solution.

[0057] ② Electropolymerized acrylic acid

[0058] A section of acidified carbon fiber was cut and bound to a glass frame, placed in an electrolytic cell to act as the cathode, and a graphite plate as the anode, with a spacing of 1.0 cm between them. A constant current and constant voltage power supply was connected to the cathode and anode of the acidified carbon fiber and the graphite plate, respectively, to form an electropolymerization system. The prepared acrylic acid solution was slowly poured into the electrolytic cell until the acidified carbon fiber was submerged, and nitrogen gas was purged for 10 minutes to remove air from the cell. The current was set to 0.018 A, and electropolymerization was carried out for 3 minutes in a nitrogen atmosphere. After completion, the sample was repeatedly washed with ethanol and distilled water and dried in a 60℃ drying oven for 12 hours. The resulting sample was electropolymerized flexible polyacrylic acid carbon fiber.

[0059] (4) In-situ growth of UiO-66-NH2 on carbon fiber surface

[0060] Solution 1: Weigh 7.5 mmol of 2-aminoterephthalic acid and add it to 100 mL of DMF. Sonicate for 20 min.

[0061] Solution 2: Weigh 5.4 mmol of zirconium tetrachloride and add it to 50 mL of DMF, then slowly add 10 mL of HCl. Sonicate for 20 min.

[0062] Solution 1 and Solution 2 were mixed and poured into a hydrothermal reactor. After mixing, the prepared electropolymerized flexible polyacrylic acid carbon fibers were placed into the hydrothermal reactor. The reaction was carried out at 80°C for 6 hours. After cooling to room temperature, the obtained carbon fibers were washed three times with DMF and then placed in a vacuum drying oven for 12 hours. The obtained sample was a reinforced carbon fiber with a surface-constructed rigid-flexible structure.

[0063] Performance testing and characterization:

[0064] The samples prepared in Example 1 were characterized and their performance was tested.

[0065] 1. XPS Analysis: Figure 1 The image shows the full XPS spectrum of the carbon fibers obtained in Example 1 of this invention, where (a) is acidified carbon fiber, (b) is carbon fiber with surface electropolymerized flexible polyacrylic acid, and (c) is carbon fiber after in-situ growth of UiO-66-NH2. Figure 1 As can be seen, the main elements on the carbon fiber surface are carbon (C) and oxygen (O). Due to the electropolymerization of acrylic acid, the O content of CF / PAA is significantly increased. Furthermore, the CF / PAA / UiO-66-NH2 surface contains nitrogen (N) and zirconium (Zr), indicating that the carbon fiber was covered by UiO-66-NH2 during in-situ growth. Figure 1 The full spectrum shows that the oxygen content of CF / PAA is significantly higher than that of acidified carbon fiber, and N and Zr elements appear on the surface of CF / PAA / UiO-66-NH2, which preliminarily proves that the modification steps were successful. Figure 2 The image shows the C 1s peak fitting spectrum of acidified carbon fibers. The characteristic peak of -COO can be observed in the figure, with a content of only 3.91%, indicating low surface activity. After electropolymerization of PAA on the carbon fiber surface (… Figure 3 The presence of numerous carboxyl groups in PAA led to a sharp increase in the -COO content, reaching 10.30%, significantly improving the surface activity of the carbon fiber. Furthermore, the specific potential where CO (286.2 eV) was originally located shifted to the right to 286.02 eV. This indicates the simultaneous presence of CN characteristic peaks within the CO characteristic peak, proving the introduction of amino groups onto the carbon fiber surface. Peak fitting of Zr 3d was then performed to obtain… Figure 4 (b) It can be clearly observed that Zr 3d is present at 182.98 eV and 185.34 eV. 3 / 2 and Zr 3d 5 / 2 The characteristic peaks indicate that UiO-66-NH2 was successfully deposited on the CF / PAA surface. Figures 2-4 The peak fitting spectrum further confirms that the introduction of PAA significantly increases the surface-COO content ( Figure 3 The growth of UiO-66-NH2 brings characteristic peaks of CN bonds and Zr3d. Figure 4 This proves the successful construction of the target structure.

[0066] 2. SEM observation: Figure 5The images show scanning electron microscope (SEM) images of different carbon fiber samples from Example 1 of this invention. (a) shows acidified carbon fiber, (b) shows carbon fiber after surface electropolymerization with acrylic acid, and (c) shows carbon fiber after in-situ growth of UiO-66-NH2. The images show that the acidified carbon fiber has a smooth surface with obvious grooves. The carbon fiber after electropolymerization with acrylic acid has a suitable and uniform polyacrylic acid film attached to its surface, which fills the defects of the grooves in the acidified carbon fiber without affecting the dispersion of the carbon fiber bundles. The carbon fiber after in-situ growth of UiO-66-NH2 has uniformly distributed nanoparticles on its surface, which increases the roughness of the fiber to a certain extent. Figure 5 SEM images show that the acidified carbon fiber (a) has a smooth surface with grooves; after electropolymerization of PAA (b), the surface is covered with a uniform thin film; after in-situ growth of MOFs (c), nanoparticles are uniformly distributed on the fiber surface, and the roughness is significantly increased.

[0067] 3. Interface thickness analysis: Figure 6 The images show EDS line scans of carbon elements in different carbon fiber samples from Example 1 of this invention. (a, d) represent carbon fibers, (b, e) represent carbon fibers after surface electropolymerization with acrylic acid, and (c, f) represent carbon fibers after in-situ growth of UiO-66-NH2. The carbon content of the composite material decreases significantly along the direction of the yellow arrow in the figure, and the interface thickness of the carbon fiber composite material is approximately 0.96 μm. The interface thicknesses of the CF / PAA and CF / PAA / UiO-66-NH2 composite materials are 1.12 μm and 1.98 μm, respectively. The results indicate that the carbon fiber composite material forms a thicker interface transition layer through a rigid-flexible structural design, which is beneficial for the smooth transition of fiber modulus to resin modulus and effective stress transfer, thereby improving interface properties. Furthermore, the reduction in the carbon element gap between the resin and the fiber further demonstrates the reduction in the modulus gap, which means that the synchronous structural design on the carbon fiber surface balances the modulus of the fiber and the resin.

[0068] 4. Mechanical property testing: Figure 7(a) The tensile strength of the single filaments of different carbon fiber composites in Example 1 of this invention. Compared with the 3.56 GPa of carbon fiber, the tensile strength of CF / PAA increased to 3.87 GPa. The results show that electropolymerization of PAA can not only compensate for the tensile strength loss caused by the chemical corrosion effect during the reaction, but also slightly improve the tensile strength of carbon fiber. For CF / PAA / UiO-66-NH2, the tensile strength of the single filament was further improved by 20.5% to 4.29 GPa because the UiO-66-NH2 nanoparticles filled the surface defects of carbon fiber. The rigid-flexible structure formed by the two layers of PAA and UiO-66-NH2 further filled more defects on the surface of carbon fiber, prevented the diffusion of fiber surface defects, and effectively reduced stress concentration. The ILSS results of carbon fiber, CF / PAA, and CF / PAA / UiO-66-NH2 composites are as follows. Figure 7 As shown in (b), it is clear that the polymerization of PAA and the growth of UiO-66-NH2 significantly enhanced the ILSS of the composite material. After electropolymerization of PAA, the ILSS of the composite material increased from 53.2 MPa to 67.8 MPa, mainly due to the enhanced resin compatibility of PAA and the increased wettability of the large number of carboxyl groups. The ILSS of the CF / PAA / UiO-66-NH2 composite material was significantly increased to 80.2 MPa, a 50.2% improvement compared to the carbon fiber composite material. The impact strength results of the reinforced composite material are as follows: Figure 8 As shown, it is clear that the presence of PAA and UiO-66-NH2 significantly enhances the impact strength of the composite material. After electropolymerization of PAA, the impact strength of the composite material increases from 119.5 KJ / m². 2 Increased to 127.3 KJ / m 2 The impact strength of the CF / PAA / UiO-66-NH2 composite material was significantly improved to 152.2 KJ / m. 2 This represents a 27.4% improvement over carbon fiber composites. This is because PAA and UiO-66-NH2 form a rigid-flexible interfacial layer in the interface region. This intermediate layer prevents cracks from propagating directly from the matrix to the carbon fiber surface, effectively absorbing fracture energy and enhancing the impact resistance of the carbon fiber composite. This rigid-flexible modified carbon fiber composite exhibits the synergistic effect of the PAA and UiO-66-NH2 layers, improving the mechanical interlocking, wettability, and interfacial bonding properties between the fiber and resin. Figure 7 and Figure 8 The results showed that, compared with the unmodified carbon fiber composite, the CF / PAA / UiO-66-NH2 composite exhibited a 20.5% increase in monofilament tensile strength (reaching 4.29 GPa), a 50.2% increase in interlaminar shear strength (reaching 80.2 MPa), and a 27.4% increase in impact strength (reaching 152.2 KJ / m²).2 This fully demonstrates that the rigid-flexible structure constructed in this invention can effectively enhance both the interfacial strength and toughness of composite materials.

[0069] It is understood that the above specific description of the present invention is only for illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the present invention.

Claims

1. A method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure, characterized in that, Includes the following steps: (1) Pretreatment of carbon fiber: carbon fiber is desizing and acidification to obtain acidified carbon fiber with oxygen-containing functional groups on the surface. (2) Construction of flexible surface components: The acidified carbon fiber obtained in step (1) is used as the cathode and electropolymerization reaction is carried out in an electrolyte containing acrylic acid to form a polyacrylic acid layer on the surface of the carbon fiber, thereby obtaining carbon fiber modified with flexible components. (3) Construction of surface rigid component: The carbon fiber modified with flexible component obtained in step (2) is placed in a reaction system containing zirconium source, organic ligand and solvent and subjected to solvothermal reaction; UiO-66-NH2 metal-organic framework material is grown in situ on the surface of the polyacrylic acid layer to form a rigid-flexible structure composed of flexible polyacrylic acid inner layer and rigid UiO-66-NH2 outer layer, thus obtaining carbon fiber reinforced with rigid-flexible structure.

2. The method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure according to claim 1, characterized in that, The desizing treatment in step (1) is as follows: the carbon fiber is placed in acetone and extracted by refluxing at 70-90°C for 36-60 hours using a Soxhlet extractor; the acidification treatment is as follows: the desizing carbon fiber is immersed in concentrated nitric acid and treated at 70-90°C for 3-5 hours, then washed until neutral and dried.

3. The method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure according to claim 2, characterized in that, The electropolymerization reaction described in step (2) uses an electrolyte that is an aqueous solution containing acrylic acid and zinc chloride, wherein the concentration of acrylic acid is 0.3 to 0.5 mol / L and the concentration of zinc chloride is 0.02 to 0.04 mol / L.

4. The method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure according to claim 3, characterized in that, The electropolymerization reaction described in step (2) is carried out under nitrogen protection, with a current of 0.016 to 0.020 A and a reaction time of 3 to 10 minutes.

5. The method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure according to claim 4, characterized in that, The zirconium source mentioned in step (3) is zirconium tetrachloride; the organic ligand is 2-aminoterephthalic acid; and the solvent includes N,N-dimethylformamide and concentrated hydrochloric acid.

6. The method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure according to claim 5, characterized in that, In the reaction system described in step (3), the concentration of 2-aminoterephthalic acid is 0.06-0.09 mol / L; the concentration of zirconium tetrachloride is 0.08-0.11 mol / L; and the volume ratio of N,N-dimethylformamide to concentrated hydrochloric acid is 4-6:

1.

7. The method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure according to claim 6, characterized in that, The solvothermal reaction described in step (3) is carried out under vacuum conditions, with a reaction temperature of 80-90°C and a reaction time of 6-10 hours.

8. The method for enhancing the interfacial properties of carbon fiber resin matrix composites using a rigid-flexible structure according to claim 7, characterized in that, After the reaction in step (3) is completed, the product is further subjected to ultrasonic treatment with N,N-dimethylformamide; the ultrasonic treatment power is 280-350W, the ultrasonic treatment time is 0.4-0.6h, and the product is dried under vacuum conditions; the drying temperature is 80-90℃, and the drying time is 10-12h.

9. A rigid-flexible reinforced carbon fiber prepared by the method according to any one of claims 1 to 8, characterized in that, The surface of the rigid-flexible reinforced carbon fiber is coated with a polyacrylic acid layer and a UiO-66-NH2 layer from the inside out.

10. A carbon fiber resin-based composite material, characterized in that, The composite material comprises carbon fibers and a resin matrix reinforced with a rigid-flexible structure as described in claim 9.

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