An epoxy composite material that can be repaired and reworked at sub-glass transition temperature conditions and methods of making and use thereof

Abstract

The application provides an epoxy composite material which can be repaired and reprocessed under conditions below the glass transition temperature, a preparation method and application thereof, and belongs to the field of advanced materials. The epoxy resin containing imine bonds and VU dynamic covalent bonds is used as a matrix, and a shaped composite material is prepared through continuous fiber reinforcement. The composite material has good initial interlaminar shear strength and repair capacity, can be hot-pressed and repaired under conditions below the glass transition temperature, and the fibers can be recycled without damage. The composite material prepared by the application has significant advantages in composite material repair, service life extension, secondary processing, recycling and reprocessing, recycling, and resource saving and environmental protection, and has great potential and broad application prospects in the field of composite materials.

Description

Technical Field

[0001] This invention belongs to the field of advanced materials, specifically relating to an epoxy composite material that can be repaired and reprocessed under conditions below the glass transition temperature, its preparation method, and its uses. Background Technology

[0002] Epoxy resin-based composites are high-performance composite materials with advantages including: the combination of continuous fibers and epoxy resin can create high-strength and lightweight materials; the epoxy resin matrix provides excellent chemical resistance, protecting the fiber materials from environmental impacts; these materials exhibit good fatigue and impact resistance, making them suitable for high-stress and high-impact environments; and they can withstand ambient light, making them suitable for long-term outdoor applications. They are widely used in various fields, including aerospace, automotive parts manufacturing, shipbuilding and marine applications, consumer goods, industrial equipment, military and defense, oil and gas processing, sporting goods, and transportation. Due to their high strength, lightweight, and excellent chemical resistance, these materials are particularly suitable for applications requiring high performance.

[0003] Despite the many advantages of epoxy resin-based composite materials, the following problems exist in their application: (1) Because epoxy resin-based composite materials have a three-dimensional covalent cross-linked network after curing and molding, they are in a state of insolubility and infusibility. It is difficult to repair them after surface or internal damage, which leads to a decrease in the service life of the material. (2) The shape of epoxy resin-based composite materials is fixed after molding and cannot be reshaped or processed again. (3) The resin matrix in the composite material is difficult to degrade, which makes it impossible for the fiber to be separated from the resin and recycled, which easily causes environmental pollution and waste of resources.

[0004] In summary, epoxy resin-based fiber-reinforced composites offer significant advantages; however, the insolubility of the resin itself limits their development in areas such as repair and recycling. Furthermore, current research indicates that repairing thermosetting resins often requires temperatures exceeding the glass transition temperature, increasing the complexity of the repair process and exposing the material to the risks of oxidation and degradation, thus restricting the development of self-healing composites. Therefore, developing epoxy resin-based continuous fiber-reinforced composites that can be reprocessed below the glass transition temperature and possess fiber-free recycling capabilities is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide an epoxy composite material that can be repaired under conditions below the glass transition temperature, as well as its preparation method and applications.

[0006] This invention provides a composite material, which is prepared by using an epoxy resin containing imine bonds and VU dynamic covalent bonds as the matrix and continuous fibers as the reinforcement.

[0007] Furthermore, the continuous fiber is carbon fiber, aramid fiber, or glass fiber.

[0008] Further, the epoxy resin is prepared from epoxy resin containing imine dynamic bonds and curing agent containing VU dynamic covalent bonds as raw materials; the mass ratio of the epoxy resin containing imine dynamic bonds to the curing agent containing VU dynamic covalent bonds is 1:0.5-5; the imine dynamic bonds are... The VU dynamic covalent bond is

[0009] Furthermore, the epoxy resin is selected from glycidyl ether type epoxy resin, glycidyl ester type epoxy resin, glycidyl amine type epoxy resin, alicyclic epoxide, aromatic epoxy resin, linear aliphatic epoxide, bisphenol A type epoxy resin, phenolic epoxy resin, and polyol glycidyl ether type epoxy resin.

[0010] The curing agent containing VU dynamic covalent bonds is prepared from difunctional amines, trifunctional amines and EGAA as raw materials.

[0011] Furthermore, the epoxy resin containing imine dynamic bonds has the following structure:

[0012]

[0013] Furthermore, the preparation method of the curing agent containing VU dynamic covalent bonds includes the following steps:

[0014] (1) Mix the difunctional amine and the trifunctional amine;

[0015] (2) Add EGAA to the mixture in step (1) to react and obtain a curing agent containing VU dynamic covalent bonds.

[0016] The molar ratio of the difunctional amine, trifunctional amine, and EGAA is 1–5:0.1–0.5:1;

[0017] The structure of the EGAA is as follows:

[0018] Furthermore, the molar ratio of the difunctional amine, the trifunctional amine, and EGAA is 1–2:0.4–0.5:1;

[0019] The difunctional and trifunctional amines are selected from aromatic amines, aliphatic amines, or alicyclic amines. The difunctional amine is further preferably isophorone diamine, m-phenylenediamine, or bis(4-amino-3-methylcyclohexyl)methane; the trifunctional amine is tris(2-aminoethyl)amine.

[0020] Furthermore, the mass ratio of the epoxy resin containing imine dynamic bonds to the curing agent containing VU dynamic covalent bonds is 1:1 to 1.2.

[0021] The present invention also provides a method for preparing the above-mentioned composite material, wherein the method uses an epoxy resin containing imine bonds and VU dynamic covalent bonds as a matrix and continuous fibers as reinforcement to prepare the composite material; the method is a solution method, a melt method, a powder impregnation method, a slurry resin deposition method, a blending method, a thin film lamination method, or a reactive impregnation method.

[0022] Furthermore, the melt method, also known as the dry method, is a method of preparing composite materials by heating epoxy resin into a liquid state, coating it onto the surface of continuous fibers, and then hot-pressing and curing it.

[0023] The solution method, also known as the wet method, is a method of preparing composite materials by dissolving epoxy resin in a solvent, coating it onto the surface of continuous fibers, evaporating the solvent, hot-pressing for curing, and molding.

[0024] Further, the method includes the following steps: dissolving an epoxy resin containing imine dynamic bonds and VU dynamic covalent bonds in a solvent to obtain an epoxy resin solution; coating the epoxy resin solution onto the surface of a continuous fiber, drying, and molding to obtain the final product; preferably, the solvent is an organic solvent; the molding conditions are: first maintaining at 5-15 MPa and 60-100°C for 1-4 hours, and then maintaining at 5-15 MPa and 100-140°C for 1-4 hours.

[0025] Further, the solvent is dichloromethane; the molding conditions are: first, maintain at 10 MPa and 80°C for 2 hours, and then maintain at 10 MPa and 120°C for 2 hours.

[0026] Furthermore, the epoxy resin solution contains an epoxy resin mass concentration of 30-70%, preferably 50%.

[0027] The present invention also provides the use of the above-mentioned composite material in the preparation of materials for aerospace, military defense, industrial and daily life applications.

[0028] In this invention, a difunctional amine refers to a small molecule that simultaneously possesses two amino (-NH2) functional groups.

[0029] This invention uses epoxy resin containing imine bonds and VU dynamic covalent bonds as a matrix to prepare a molded composite material through continuous fiber reinforcement. This composite material exhibits good initial interlaminar shear strength and hot-press repair capability, allowing for hot-press repair below the glass transition temperature, and its fibers can be recycled without damage. The composite material prepared by this invention demonstrates significant advantages in composite material repair, extended service life, secondary processing, recycling and reprocessing, as well as resource conservation and environmental protection, showing great potential and broad application prospects in the field of composite materials.

[0030] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0031] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following embodiments. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0032] Figure 1 A schematic diagram of the synthesis of EDT curing agent containing VU dynamic covalent bonds (a), chemical shift characterization of EGAA (b), and infrared spectral changes of EGAA and EDT (c).

[0033] Figure 2 The thermogravimetric analysis curves of the composite material are shown.

[0034] Figure 3 Electron micrographs of interlaminar shear strips of composite materials: (a,b) images of the side of the interlaminar shear strip after damage and repair; (c,d) images of the cross section of the interlaminar shear strip after damage and repair.

[0035] Figure 4 For the original composite material sample, after one repair, and after two repairs: (a) interlaminar shear test curve; (b) statistical bar chart of interlaminar shear strength.

[0036] Figure 5 DMA testing was conducted on the original composite material sample, after one repair, and after two repairs.

[0037] Figure 6 For laser Raman testing: (a) Raman test of commercial T700 carbon fiber; (b) Raman test of carbon fiber after 24 hours of chemical recycling. Detailed Implementation

[0038] The raw materials and equipment used in this invention are all known products, obtained by purchasing commercially available products.

[0039] The "room temperature" condition of this invention is 25±5℃.

[0040] Example 1: Preparation of composite materials containing double dynamic exchange bonds

[0041] 1. Preparation of imine-containing dynamic bond intermediates

[0042] 40 mmol of vanillin and 40 mmol of p-aminophenol were mixed and added to a round-bottom flask, followed by 125 mL of water. The mixture was stirred at room temperature for 4 hours. After filtration, a yellow powder was collected, washed with water, and dried to obtain a pale yellow powder (9.32 g), which was named VAN-AP powder. The NMR data of VAN-AP are as follows: 1 H NMR(DMSO-d6,400MHz)δ:9.69(s,1H,-OH),9.44(s,1H,-OH),8.43(s,1H,-CH=N-),7.49(d,1H,Ar-H),7.2 7(dd,1H,Ar-H),7.10-7.13(m,2H,Ar-H),6.86(d,1H,Ar-H),6.75-6.79(m,2H,Ar-H),3.84(s,3H,-OCH3).

[0043] 2. Preparation of epoxy resins containing imine dynamic bonds

[0044] 40 mmol of VAN-AP powder was mixed with 1081 mmol of epichlorohydrin and added to a round-bottom flask. Then, 1.7 mmol of tetrabutylammonium bromide was added. The flask was heated at 80 °C and stirred for 4 hours. Then, 12.5 g of 50% NaOH aqueous solution was added, and the reaction was continued for 1 hour, followed by 1 hour at room temperature. Excess ethyl acetate was added, and the resulting NaCl solid particles were removed by filtration. The mixture was washed three times with deionized water, concentrated, and transferred to a vacuum oven for dehydration at 60 °C. The final product was an imine-containing epoxy resin, a pale yellow solid, which was named GE-VAN-AP resin. The NMR data of GE-VAN-AP resin are as follows: 1H NMR(DMSO-d6,400MHz)δ:8.52(s,1H,-CH=N-),7.56(d,1H,Ar-H),7.39-7.41(dd, 1H,Ar-H),7.26-7.24(m,2H,Ar-H),7.08-7.10(d,1H,Ar-H),6.99-7.01(m,2H,Ar -H),4.37-4.40(dd,1H,Ar-H),4.33-4.37(dd,1H,Ar-H),3.87-3.92(dd,1H,-O-C H2-),3.86(s,3H,-OCH3),3.83-3.87(dd,1H,-O-CH2-),3.34-3.39(m,2H,-CH-in oxirane),2.85-2.86(m,2H,-CH2-in oxirane),2.71-2.73(m,2H,-CH2-in oxirane).

[0045] 3. Preparation of ethylene glycol diacetate

[0046] Ethylene diacetate (EGAA) was prepared according to Example 1 of patent application document (CN116333268A). The structure of the EGAA is as follows:

[0047] 4. Preparation of curing agents containing VU dynamic covalent bonds

[0048] Referring to Example 1 of patent application (CN116333268A), a curing agent containing VU dynamic covalent bonds was prepared. The primary amine content in the curing agent was calculated to be 0.005311 mol / g.

[0049] 5. Preparation of epoxy resin systems containing double dynamic exchange bonds

[0050] Take 10g of GE-VAN-AP resin and 11.65g of EDT curing agent, stir and mix them at 80℃, then transfer them to a vacuum oven to remove air bubbles. Then transfer the mixed sample to a flat vulcanizing machine, pour it into a steel plate mold, heat it to 80℃ under 5MPa pressure, hold it for two hours, then heat it to 120℃ and hold it for two hours. Demold the obtained sample at high temperature, then anneal and cool it in a forced-air oven to obtain a sheet sample, which is named the Dual dynamic exchange mechanism resin system (DDEM resin).

[0051] 6. Preparation of composite materials containing double dynamic exchange bonds

[0052] 10 grams of DDEM resin were dissolved in dichloromethane to prepare a 50 wt% epoxy resin solution. The T700 carbon fiber surface was then fully coated with the epoxy resin solution and transferred to a 60°C vacuum oven, where a vacuum was applied for 10 minutes. The treated carbon fiber was then transferred to a mold, heated to 80°C under 10 MPa pressure, held for two hours, and then heated to 120°C and held for another two hours, ultimately yielding the epoxy / carbon fiber composite material.

[0053] The following experimental examples demonstrate the beneficial effects of the present invention.

[0054] Experimental Example 1: Performance Testing of Composite Materials Containing Double Dynamic Exchange Bonds at Temperatures Below the Glass Transition Temperature

[0055] 1. Experimental Methods

[0056] (1) Dynamic thermomechanical property test (DMA): The Q800 dynamic thermomechanical analyzer manufactured by TA Company of the United States was used. Tensile fixture was selected for testing. The test frequency was 1Hz, the amplitude was 15um, the heating rate was 3℃ / min, and the test temperature range was 0℃~200℃.

[0057] (2) Differential Scanning Calorimetry (DSC) Testing: For uncured samples, a differential scanning calorimeter (Mettler-Toledo, Switzerland) was used to investigate the curing temperature of the curing agent and resin. The test atmosphere was N2, and the test temperature range was 30–200℃, with heating rates of 5 K / min, 10 K / min, 15 K / min, and 20 K / min, respectively. For cured samples, a temperature range of 30–200℃ and a heating rate of 10 K / min were selected to characterize the curing process and glass transition temperature of the material.

[0058] (3) Mechanical property test: The tensile properties were tested using an Instron universal testing machine in accordance with the GB / T1040-2006 standard. The test size used a 5B type tensile specimen, and the tensile speed was 1 mm / min.

[0059] (4) Reprocessing Experiment: 20 grams of the cured sample from Example 1 were placed in a crusher and continuously crushed for 10 seconds. The crushed particles were then evenly placed into a hot press mold and hot-pressed at 120°C and 5MPa for 30 minutes. After natural cooling, the mold was opened. The reprocessed hot-pressed repaired sample was cut into target strips using a cutter. The repair efficiency was calculated using the following formula:

[0060]

[0061] (5) Stress relaxation test: An Anton Paar rheometer was used to conduct stress relaxation test, with a constant shear strain of 1% and a normal force of 5N.

[0062] (6) Nuclear Magnetic Resonance Spectroscopy (NMR) Testing: The NMR testing of the modified curing agent was performed using a Bruker AV II (Bruker, Germany) NMR spectrometer. 1 The H spectrum was obtained using deuterated DMSO as the test solvent at a frequency of 400 Hz.

[0063] (7) Thermogravimetric analysis (TGA): Thermogravimetric analysis of the elastomer sample was performed using a TG209F1 thermogravimetric analyzer from Netzsch GmbH, Germany. 5 mg of sample was weighed and placed in a crucible. The test conditions were: nitrogen and air atmosphere, gas flow rate of 60 mL / min, temperature range of room temperature to 800 °C, and heating rate of 10 °C / min.

[0064] (8) Interlaminar Shear Performance Test: The interlaminar mechanical properties of GO-reinforced epoxy / carbon fiber composites of different sizes were characterized according to ASTM D2344. The tests were conducted on an Instron 5567 universal testing machine at a test rate of 1 mm / min. The ILSS value of the composite material was calculated using the following formula:

[0065]

[0066] In the formula, P max (N) represents the maximum force at which interlaminar failure occurs, and b (mm) and h (mm) represent the width and thickness of the specimen, respectively. At least 6 valid values ​​should be tested for each group of samples and the average value should be calculated.

[0067] (9) Composite material repair process: Place the completely damaged interlaminar shear strip in a hot press mold, hold it at 10 MPa pressure at 120°C for 10 minutes, and then cool and remove it.

[0068] (10) Degradation and recycling effect test: Under room temperature conditions, carbon fiber composite material was immersed in ethylenediamine solution, and then carbon fiber samples were taken out sequentially at different time points. After rinsing in anhydrous ethanol, the surface and morphology of the samples were observed.

[0069] (11) Raman spectroscopy analysis: The Raman spectra of the original carbon fibers and the recycled carbon fibers were scanned using a confocal Raman microscope, with a scanning range of 400 cm⁻¹. -1 -2500cm -1 The wavelength of the excitation laser is 785nm.

[0070] 2. Experimental Results

[0071] Experimental results ( Figure 1 (ac) indicates that this study successfully synthesized EGAA and EDT containing VU dynamic covalent bonds, wherein the structure of the VU dynamic covalent bonds is as follows: Figure 1 As shown in a.

[0072] (1) Characterization and mechanical property testing of composite materials

[0073] Figure 2 The thermogravimetric analysis curves of the composite material are shown. For example... Figure 2 As shown, the highest thermal weight loss rate peak temperature is 309.7℃, and the maximum thermal weight loss rate is 4.20% / min; the composite material prepared by dual-mechanism dynamic exchange resin has a thermal residual weight of 52.79% at 800℃. This indicates that the total thermal residual weight of fiber and resin in the composite material is between 50% and 60%, while the resin content is around 40%, indicating that the composite material has a high fiber content.

[0074] This invention also tested the initial appearance of the composite material interlaminar shear test specimens and their morphology before and after damage and repair following the interlaminar shear test. Before the interlaminar shear test, the front, side, and cross-sections of the composite material specimens showed uniform surfaces, good fiber-resin integration, and no significant defects. After the interlaminar shear test, a significant bending crack appeared on the front of the composite material specimen; simultaneously, interlaminar delamination caused by the interlaminar shear was observed on the side and cross-sections, indicating that the upper and lower layers of the specimen had completely delaminated and separated, confirming that the specimen had been completely destroyed after the interlaminar shear test. After hot-press repair, the crack on the front of the specimen was faded, and the detached parts of the specimen were bonded together in the side and cross-section photographs, macroscopically indicating that they had fused into a whole.

[0075] Figure 3 Microscopic images of the failure and repair of interlaminar shear splines observed using scanning electron microscopy are presented. Figure 3 As shown in figure a, under 50x electron microscopy, a groove is visible on the side of the sample, corresponding to interlayer delamination of the material; and Figure 3 As shown in Figure b, the microscopic interlayer separation phenomenon has completely disappeared after hot pressing repair, and there are no significant repair traces. Figure 3 c demonstrates the interlaminar delamination phenomenon in the cross-section, while... Figure 3 As shown in Figure d, the interlayer cracks in the repaired section have completely disappeared; compared to Figure 3 The repaired morphology of d Figure 3 b appears to have a smoother surface.

[0076] (2) Comparison of mechanical properties of composite materials before and after repair

[0077] Figure 4 The diagram shows the interlaminar shear test curves and their statistical bar charts of interlaminar shear strength after primary and secondary repairs of the composite material. Figure 4As shown in Figure b, the original interlaminar shear strength of the composite material was approximately 56.05 MPa, and the tensile strength after the first recycling was approximately 39.00 MPa, recovering 69% of the initial strength; after the second repair, the interlaminar shear strength was 28.93 MPa, representing 51% of the initial strength. Figure 4 The test curves show a sharp drop in strength at the end of each interlaminar shear test, indicating severe and complete damage after the test. This damage mainly consists of two parts: fiber breakage and interlaminar delamination. During hot-press repair, broken fibers cannot be repaired, while the delamination, primarily caused by resin-reinforced bonding, can be repaired under hot-press conditions. Therefore, the interlaminar shear strength decreases significantly after multiple repairs. Furthermore, in... Figure 4 As can be seen in Figure a, the strength decreases in the test curves after one and two repairs exhibit a "sawtooth" pattern. This is mainly because the hot-pressing process can only repair the resin portion, while the broken fiber portion cannot be repaired. Consequently, during the test, the repaired broken fiber portion fails first, resulting in the "sawtooth" phenomenon on the strength curve. After two repairs, a portion of the test specimen has completely detached, making a third repair process impossible.

[0078] Figure 5 The DMA test results for the original composite material sample and the two reprocessing processes are presented. Figure 5 As shown, the storage modulus of the original sample was approximately 40,000 MPa. The storage modulus of the sample after one repair was slightly lower than that of the original sample, approximately 37,000 MPa. The storage modulus of the sample after two repairs was significantly lower, approximately 29,000 MPa. With repeated shear failure and hot-press repair processes, the storage modulus of the material showed a decreasing trend. This indicates that during shear failure, some fibers break. The hot-press process cannot repair the broken fibers, but can only repair the resin attached to the fibers. With repeated failures, the breakage of some fibers leads to a gradual decrease in the storage modulus. The Tanδ temperature position shows that the glass transition temperature of the initial composite material was approximately 127℃. After repair, the glass transition temperature increased significantly, and the Tanδ peak showed a wider temperature range. This is because after multiple repairs, there were more broken fibers in the sample, and the structural difference between the fiber-containing part and the broken fiber part of the composite material was too large, resulting in a large difference in the molecular chain segment mobility. This indicates that after the composite material undergoes the interlaminar shear failure repair process, the sample can retain a certain storage modulus and a higher glass transition temperature; at the same time, the Tanδ peak also reflects the large structural differences of the composite material, confirming the phenomenon that some broken fibers cannot be repaired.

[0079] (3) Non-destructive recycling of carbon fiber

[0080] This invention also investigated the morphological changes of carbon fiber composite materials after immersion in ethylenediamine for different times. It was found that as the immersion time of the carbon fiber composite material in the ethylenediamine solution increased, the color of the solution gradually changed from colorless to yellow, and the color gradually deepened with increasing time. When the carbon fiber composite material was immersed in ethylenediamine for 0 to 6 hours, the surface of the carbon fibers gradually became rougher; however, as the immersion time increased to 24 hours, the fibers gradually delaminated and separated, becoming a loose state completely unconstrained by resin, indicating that the internal resin was fully degraded.

[0081] This invention also investigated the changes in carbon fibers after resin degradation in the composite material by immersing the original T700 carbon fibers for 16 hours and 24 hours. Before chemical degradation, the microscopic surface of the original T700 sample was very smooth. After 16 hours of chemical degradation, the carbon fiber surface of the composite material of this invention was rough and uneven, with a large amount of undegraded epoxy resin adhering to the fiber surface. After 24 hours of chemical degradation, the carbon fiber surface of the composite material of this invention was smooth and clean, without any adhering substances, and its morphology was basically no different from that of the T700 carbon fiber. This indicates that the composite material can completely degrade the adhering resin on the carbon fiber surface by immersing it in ethylenediamine solution at room temperature for 24 hours.

[0082] Figure 6 Figures a and b show the laser Raman spectroscopy results of pristine T700 carbon fiber and T700 carbon fiber after 24 hours of chemical recycling. Raman spectroscopy can be used to analyze changes in the surface structure of carbon fibers. Figure 6 As can be seen, both unused commercial carbon fiber T700 and chemically degraded and recycled carbon fiber exhibit two distinct spectral lines in their Raman spectra: the D line (disordered carbon structure: 1360 cm⁻¹). -1 ) and G line (graphite crystal structure: 1580cm) -1 R(R=I) D / I G The ratio of the integral intensity of the D peak (disordered structure) to the G peak (graphite structure) can be used to measure changes in surface defects and low-symmetry structures of carbon fibers.

[0083] Table 1 Comparison of D / G peaks in Raman spectra

[0084]

[0085] Table 1 lists the Raman spectral analysis values ​​for each sample. As can be seen from the table, compared to unused commercial carbon fiber T700, the positions of the D and G peaks in the recycled carbon fiber remained almost unchanged, and the original T700 carbon fiber Rorigin (I D / I G The value is 2.529, and the recycled carbon fiber Rrecycle(I) is 2.529. D / I GThe value was 2.592, with a difference of 0.063 between the two. The difference in the ordered graphite structure on the surface of the two is small, meaning that the recycled carbon fiber did not suffer significant damage compared to the unused carbon fiber.

[0086] The experimental results above show that the glass transition temperature of the composite material containing double dynamic exchange bonds in this invention is 127℃. This composite material can be reprocessed at temperatures below the glass transition temperature, and the reprocessed sample still retains good mechanical properties. Furthermore, this composite material exhibits good initial interlaminar shear strength and hot-press repair capability, and also enables the non-destructive recycling of carbon fibers.

[0087] In summary, this invention provides an epoxy composite material that can be repaired and reprocessed under conditions below the glass transition temperature, along with its preparation method and applications. This invention uses an epoxy resin containing imine bonds and VU dynamic covalent bonds as a matrix, and prepares a molded composite material through continuous fiber reinforcement. This composite material exhibits good initial interlaminar shear strength and hot-press repair capability, allowing for hot-press repair under conditions below the glass transition temperature, and its fibers can be recycled without damage. The composite material prepared by this invention demonstrates significant advantages in composite material repair, extended service life, secondary processing, recycling and reprocessing, as well as resource conservation and environmental protection, showing great potential and broad application prospects in the field of composite materials.

Claims

1. A composite material, characterized in that, It is a product prepared by using epoxy resin containing imine dynamic bonds and curing agent containing VU dynamic covalent bonds as raw materials as the matrix and continuous fibers as the reinforcement. The VU dynamic covalent bond is .

2. The composite material according to claim 1, characterized in that, The continuous fiber is carbon fiber, aramid fiber, or glass fiber.

3. The composite material according to claim 1, characterized in that, The mass ratio of the epoxy resin containing imine dynamic bonds to the curing agent containing VU dynamic covalent bonds is 1:0.5~5; the imine dynamic bonds are... .

4. The composite material according to claim 3, characterized in that, The curing agent containing VU dynamic covalent bonds is prepared from difunctional amines, trifunctional amines and EGAA as raw materials.

5. The composite material according to claim 3, characterized in that, The epoxy resin containing imine dynamic bonds has the following structure: ； The preparation method of the curing agent containing VU dynamic covalent bonds includes the following steps: (1) Mix difunctional amines and trifunctional amines; (2) Add EGAA to the mixture in step (1) to react and obtain a curing agent containing VU dynamic covalent bonds; The molar ratio of the difunctional amine, trifunctional amine, and EGAA is 1–5:0.1–0.5:1; The structure of the EGAA is as follows: .

6. The composite material according to claim 5, characterized in that, The molar ratio of the difunctional amine, trifunctional amine, and EGAA is 1–2:0.4–0.5:1; The difunctional and trifunctional amines are selected from aromatic amines, aliphatic amines, or alicyclic amines.

7. The composite material according to any one of claims 3-6, characterized in that, The mass ratio of the epoxy resin containing imine dynamic bonds to the curing agent containing VU dynamic covalent bonds is 1:1 to 1.

2.

8. A method for preparing the composite material according to any one of claims 1-7, characterized in that, The method uses epoxy resin containing imine bonds and VU dynamic covalent bonds as the matrix and continuous fibers as the reinforcement to prepare composite materials; the method can be solution method, melt method, powder impregnation method, slurry resin deposition method, blending method, thin film lamination method or reactive impregnation method.

9. The method according to claim 8, characterized in that, The method includes the following steps: dissolving an epoxy resin containing imine dynamic bonds and VU dynamic covalent bonds in a solvent to obtain an epoxy resin solution; coating the epoxy resin solution onto the surface of a continuous fiber, drying, and molding to obtain the final product.

10. The method according to claim 9, characterized in that, The solvent is an organic solvent; the molding conditions are: first, maintain at 5~15MPa and 60~100℃ for 1~4 hours, and then maintain at 5~15MPa and 100~140℃ for 1~4 hours.

11. Use of the composite material according to any one of claims 1-7 in the preparation of materials for aerospace, military defense, industrial and civilian applications.

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