Epoxy composite material capable of being repaired and reprocessed under condition lower than glass transition temperature and preparation method and application thereof

Abstract

The invention provides an epoxy composite material capable of being repaired and reprocessed under the condition of being lower than the glass-transition temperature as well as a preparation method and application of the epoxy composite material, and belongs to the field of advanced materials. Epoxy resin containing imine bonds and VU dynamic covalent bonds is used as a matrix, and the molded composite material is prepared through continuous fiber reinforcement. The composite material has good initial interlaminar shear strength and repairing capacity, hot-pressing repairing can be carried out under the condition that the temperature is lower than the glass-transition temperature, and the fibers of the composite material can be recycled in a lossless mode. The composite material prepared by the invention shows remarkable advantages in the aspects of composite material repairing, service life prolonging, secondary processing, recycling, reprocessing, recycling, resource saving, environmental protection and the like, and has huge potential and wide application prospects in the field of composite materials.

Description

Technical Field

[0001] The present invention belongs to the field of advanced materials, and particularly relates to an epoxy composite material that can be repaired and reprocessed under conditions below the glass transition temperature, and a preparation method and use thereof. Background Art

[0002] Epoxy resin-based composite materials belong to high-performance composite materials, and their advantages include: after continuous fibers are combined with epoxy resin, high-strength and lightweight materials can be manufactured; the epoxy resin matrix provides excellent chemical corrosion resistance to protect fiber materials from environmental impacts; this material has good fatigue and impact resistance and is suitable for high-stress and high-impact environments; it can withstand environmental light and is suitable for long-term outdoor applications, etc. It is widely used in multiple fields, including aerospace, automotive parts manufacturing, ship and marine applications, consumer goods, industrial equipment, military and national defense, oil and gas processing, sports goods, and transportation. Due to its high strength, lightweight, and excellent chemical corrosion resistance, this material is particularly suitable for applications that require high performance.

[0003] Although epoxy resin-based composite materials have the above-mentioned multiple advantages, the following problems exist in the application process: (1) Since there is a three-dimensional covalent cross-linking network in the epoxy resin-based composite materials after curing and forming, they are in an insoluble and infusible state, and it is difficult to repair the surface or internal damage, resulting in a decrease in the service life of the materials; (2) The shape of the epoxy resin-based composite materials after forming is fixed and cannot be reshaped and reprocessed; (3) The resin matrix in the composite materials is difficult to degrade, resulting in the fibers being unable to be separated from the resin and recycled, which is likely to cause environmental pollution and waste of resources.

[0004] In summary, epoxy resin-based fiber-reinforced composite materials have prominent advantages, but due to the insoluble characteristics of the resin itself, the development of their repair, recycling, and reuse is restricted. At the same time, under the current research background, the repair of thermosetting resins often requires a temperature higher than the glass transition temperature, which increases the construction difficulty in the material repair process, makes the material bear the risk of oxidation and degradation, and restricts the development of composite materials in the field of self-repair. Therefore, it is of great significance to develop an epoxy resin-based continuous fiber-reinforced composite material that can be reprocessed under conditions below the glass transition temperature and has the ability to recover fibers without damage. Summary of the Invention

[0005] The purpose of the present invention is to provide an epoxy composite material that can be repaired under conditions below the glass transition temperature, and a preparation method and use thereof.

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

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

[0008] Further, the epoxy resin is prepared from an epoxy resin containing imine dynamic bonds and a curing agent containing VU dynamic covalent bonds; 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 bond is The VU dynamic covalent bond is

[0009] Further, 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, polyol glycidyl ether type epoxy resin;

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

[0011] Further, the structure of the epoxy resin containing imine dynamic bonds is:

[0012]

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

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

[0015] (2) Add EGAA to the mixture in step (1) for reaction to obtain the 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

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

[0019] The difunctional amine and trifunctional amine are selected from aromatic amine, aliphatic amine or alicyclic amine. The difunctional amine is further preferably isophorone diamine, m - xylylenediamine 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 composite material. The method uses an epoxy resin containing imine bonds and VU dynamic covalent bonds as the matrix and continuous fibers as the reinforcing body to prepare the composite material; the method is a solution method, a melting method, a powder impregnation method, a slurry resin deposition method, a co-weaving method, a film lamination method or a reaction impregnation method.

[0022] Furthermore, the melting method, also known as the dry method, is a method for preparing a composite material by heating the epoxy resin to a liquid state, coating it on the surface of continuous fibers and hot pressing and curing.

[0023] The solution method, also known as the wet method, is a method for preparing a composite material by dissolving the epoxy resin in a solvent, then coating it on the surface of continuous fibers, and then volatilizing the solvent, followed by hot pressing and curing and shaping.

[0024] Furthermore, the method includes the following steps: dissolving the 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 on the surface of continuous fibers, drying, and shaping to obtain the product; preferably, the solvent is an organic solvent; the shaping 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] Furthermore, the solvent is dichloromethane; the shaping conditions are: first maintaining at 10 MPa and 80 °C for 2 hours, and then maintaining at 10 MPa and 120 °C for 2 hours.

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

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

[0028] In the present invention, a bifunctional amine refers to a small molecule having two amino (-NH2) functional groups.

[0029] The present invention uses an epoxy resin containing imine bonds and VU dynamic covalent bonds as the matrix, and prepares and forms a composite material through continuous fiber reinforcement. This composite material has good initial interlaminar shear strength and hot pressing repair ability, can be hot pressed and repaired under conditions below the glass transition temperature, and its fibers can be recycled without damage. The composite material prepared by the present invention shows significant advantages in aspects such as composite material repair, extending service life, secondary processing, recycling and reprocessing, and saving resources and environmental protection, and has great potential and broad application prospects in the field of composite materials.

[0030] Obviously, based on the above content of the present invention, according to the common general knowledge and customary means in the art, without departing from the above basic technical idea of the present invention, various other forms of modifications, substitutions or changes can be made.

[0031] The following is a further detailed description of the above content of the present invention through specific embodiments in the form of examples. However, this should not be construed as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above content of the present invention belong to the scope of the present invention. Brief Description of the Drawings

[0032] Figure 1 Schematic diagram for synthesizing EDT curing agent containing VU dynamic covalent bond (a), chemical shift characterization of EGAA (b), and infrared spectrum changes of EGAA and EDT (c).

[0033] Figure 2 Thermogravimetric test curve of the composite material.

[0034] Figure 3 SEM photos of the interlaminar shear spline of the composite material: (a, b) photos of the side damage and repair of the interlaminar shear spline; (c, d) photos of the cross-section damage and repair of the interlaminar shear spline.

[0035] Figure 4 For the original sample of the composite material, after the first repair and the second repair: (a) interlaminar shear test curve; (b) statistical histogram of interlaminar shear strength.

[0036] Figure 5 DMA test of the original sample of the composite material, after the first repair and the second repair.

[0037] Figure 6 Laser Raman test: (a) Raman test of commercial T700 carbon fiber; (b) Raman test of carbon fiber after 24-hour chemical recycling. Detailed Description of the Invention

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

[0039] The "room temperature" condition of the present invention is 25 ± 5 °C.

[0040] Example 1. Preparation of a composite material containing dual dynamic exchange bonds

[0041] 1. Preparation of an intermediate containing imine dynamic bonds

[0042] Mix 40 mmol of vanillin and 40 mmol of p-aminophenol and add them to a round-bottom flask. Then add 125 mL of water and stir at room temperature for 4 hours. After filtration, collect the obtained yellow powder, wash it with water and dry it to obtain a pale yellow powder (9.32 g), which is named VAN-AP powder. The NMR data of VAN-AP are as follows: 1 H NMR (DMSO-d6, 400 MHz) δ: 9.69 (s, 1H, -OH), 9.44 (s, 1H, -OH), 8.43 (s, 1H, -CH=N-), 7.49 (d, 1H, Ar-H), 7.27 (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 an epoxy resin containing imine dynamic bonds

[0044] Take 40 mmol of VAN-AP powder and mix it with 1081 mmol of epichlorohydrin, add them to a round-bottom flask, and then add 1.7 mmol of tetrabutylammonium bromide. Place the round-bottom flask in an 80 °C water bath and stir for 4 hours. Then add 12.5 g of a 50% NaOH aqueous solution by weight, continue the reaction for 1 hour, and then react at room temperature for 1 hour. Add an excess of ethyl acetate, filter to remove the formed NaCl solid particles. Wash three times with deionized water, concentrate and transfer to a vacuum oven to remove water at 60 °C. Finally, an epoxy resin containing imine bonds is obtained, which is a pale yellow solid and is named GE-VAN-AP resin. The NMR data of GE-VAN-AP resin are as follows: 11H NMR (DMSO-d6, 400 MHz) 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-CH2-), 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 Diacetoacetate

[0046] Refer to Example 1 of the patent application document (CN116333268A) to prepare ethylene glycol diacetoacetate (EGAA). The structure of the EGAA is

[0047] 4. Preparation of Curing Agent Containing VU Dynamic Covalent Bonds

[0048] Refer to Example 1 of the patent application document (CN116333268A) to prepare a curing agent containing VU dynamic covalent bonds. After calculation, the primary amine content in the curing agent is 0.005311 mol / g.

[0049] 5. Preparation of Epoxy Resin System Containing Dual Dynamic Exchange Bonds

[0050] Take 10 g of GE-VAN-AP resin and 11.65 g of EDT curing agent, stir and mix them evenly at 80 °C, then transfer them to a vacuum oven to remove air bubbles. Then transfer the mixed sample to a flat vulcanizer, pour it into a steel plate mold, raise the temperature to 80 °C under a pressure of 5 MPa, keep it for two hours and then raise the temperature to 120 °C and keep it for two hours. Demold the sample at high temperature, then anneal and cool it in a blast drying oven to obtain a flaky sample, and name it resin system containing dual dynamic exchange bonds (Dual dynamic exchange mechanism resin system), abbreviated as DDEM resin.

[0051] 6. Preparation of Composite Material Containing Dual Dynamic Exchange Bonds

[0052] Dissolve 10 g of DDEM resin in dichloromethane to prepare a 50 wt% epoxy resin solution. Then, fully coat the surface of T700 carbon fiber with the epoxy resin solution, and transfer it to a vacuum oven at 60 °C. Evacuate the air within 10 minutes. Then, transfer the treated carbon fiber to a mold, heat it to 80 °C under a pressure of 10 MPa, hold for two hours, then heat it to 120 °C and hold for another two hours to finally prepare the epoxy / carbon fiber composite material.

[0053] The beneficial effects of the present invention are demonstrated by the following experimental examples.

[0054] Experimental Example 1: Performance test of the composite material containing dual dynamic exchange bonds at a temperature below the glass transition temperature

[0055] 1. Experimental method

[0056] (1) Dynamic thermomechanical property test (DMA): Use a Q800 type dynamic thermomechanical analyzer produced by TA Instruments, USA. Select a tensile fixture for testing, with a test frequency of 1 Hz, an amplitude of 15 μm, a heating rate of 3 °C / min, and a test temperature range of 0 °C to 200 °C.

[0057] (2) Differential scanning calorimeter (DSC) test: For uncured samples, use a differential scanning calorimeter (Mettler Toledo, Switzerland) to explore the curing temperature of the curing agent and the resin. The test atmosphere is N2, the test temperature range is 30 - 200 °C, and the heating rates are 5 K / min, 10 K / min, 15 K / min, and 20 K / min respectively. For cured samples, select a test temperature range of 30 - 200 °C and a heating rate of 10 K / min to characterize the curing situation and glass transition temperature of the material.

[0058] (3) Mechanical property test: Tensile properties are tested using an Instron universal testing machine according to the GB / T1040 - 2006 standard. Use a 5B type tensile spline for the test size, and the tensile speed is 1 mm / min.

[0059] (4) Remanufacturing experiment: Put 20 g of the cured sample of Example 1 into a crushing mixer and continuously crush it for 10 seconds. Level the crushed particles into a hot pressing mold, hot press at 120 °C and 5 MPa for 30 min, and open the mold after natural cooling. Cut the remanufactured and hot - pressed repaired sample sheet into target splines using a cutter. Calculate the repair efficiency through the following formula:

[0060]

[0061] (5) Stress relaxation test: Use an Anton Paar rheometer to conduct stress relaxation experiment tests, select a constant shear strain of 1% and a normal force of 5 N.

[0062] (6) Nuclear magnetic resonance spectroscopy test: The nuclear magnetic resonance test of the modified curing agent was carried out using a Bruker AV II (Bruker, Germany) nuclear magnetic resonance spectrometer to test the 1 1H spectrum. The test solvent was deuterated DMSO, and the test frequency was 400 Hz.

[0063] (7) Thermogravimetric test (TGA): The thermogravimetric analysis of the elastomer specimen was carried out using a TG209F1 thermogravimetric analyzer from Netzsch, Germany. Weigh 5 mg of the sample and place it in a crucible. The test conditions were as follows: under nitrogen and air atmospheres, the gas flow rate was 60 mL / min, the temperature range was from room temperature to 800 °C, and the heating rate was 10 °C / min.

[0064] (8) Interlaminar shear performance test: Referring to ASTM D2344, the interlaminar mechanical properties of GO-reinforced epoxy / carbon fiber composites with different scales were characterized. The test was carried out on an Instron 5567 universal testing machine at a test rate of 1 mm / min. The ILSS value of the composite material was calculated according to the following formula:

[0065]

[0066] where P max (N) is the maximum force at the time of interlaminar failure, and b (mm) and h (mm) are the width and thickness of the specimen, respectively. At least 6 valid values were tested for each group of samples and the average value was calculated.

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

[0068] (10) Degradation and recycling effect test: At room temperature, immerse the carbon fiber composite material in an ethylenediamine solution, and then take out the carbon fiber samples at different time points. After rinsing in absolute ethanol, observe the surface and morphology of the samples.

[0069] (11) Raman spectroscopy analysis: Use a confocal Raman microscope to scan the Raman spectra of the original carbon fiber and the recycled carbon fiber. The scanning ranges are 400 cm -1 -2500 cm -1 respectively, and the wavelength of the excitation laser is 785 nm.

[0070] 2. Experimental results

[0071] The experimental results ( Figure 1 a-c) show that EGAA and EDT containing VU dynamic covalent bonds were successfully synthesized in this study, and the structure of the VU dynamic covalent bond is as shown in Figure 1 a.

[0072] (1) Characterization and Mechanical Property Testing of Composite Materials

[0073] Figure 2 The thermogravimetric test curve of the composite material is shown. As Figure 2 shown, the temperature at the peak of the highest thermogravimetric rate is 309.7 °C, and the maximum thermogravimetric rate is 4.20% / min; the composite material prepared by the double-mechanism dynamic exchange resin has a thermal residue of 52.79% at 800 °C. It shows that the total thermal residue of the fiber and resin in the composite material is between 50% and 60%, and the resin content is about 40%, indicating that the composite material has a relatively high fiber content.

[0074] The present invention also tested the initial appearance of the interlaminar shear spline of the composite material and the appearance before and after damage and repair through interlaminar shear testing. Before the interlaminar shear test, the front, side, and cross-section of the composite material spline had a uniform surface, and the fiber and resin were well integrated as a whole without significant defects. After the composite material spline underwent the interlaminar shear test, there was a significant bending crack on the front; at the same time, interlaminar delamination caused by interlaminar shear could be observed on both the side and the cross-section, and the upper part and the lower part of the spline had completely delaminated and separated, confirming that the spline had been completely damaged after the interlaminar shear test. It can be seen that after the damaged interlaminar shear spline was repaired by hot pressing, the crack on the front of the spline after hot pressing repair had faded, and it could be seen from the side and cross-section photos that the separated part of the spline had been bonded and macroscopically integrated into a whole.

[0075] Figure 3 The microscopic photos of the damage and repair of the interlaminar shear spline observed using a scanning electron microscope are shown. As Figure 3 shown in a, at a magnification of 50 times by the electron microscope, there was a gully on the side of the spline, corresponding to the interlaminar delamination phenomenon of the material; while Figure 3 the microscopic interlaminar delamination phenomenon shown in b had completely disappeared after hot pressing repair, and there were no significant repair marks. Figure 3 c shows the interlaminar delamination phenomenon of the cross-section, and as Figure 3 shown in d, the interlaminar crack on the cross-section had completely disappeared after repair; compared with the repair morphology of Figure 3 d, Figure 3 b had a smoother surface.

[0076] (2) Comparison of Mechanical Properties of Composite Materials before and after Repair

[0077] Figure 4 The interlaminar shear test curves of the composite material and after the first and second repairs and the statistical bar chart of their interlaminar shear strength are shown. As Figure 4As shown in Fig. b, the original interlaminar shear strength of the composite material was approximately 56.05 MPa, the tensile strength after the first recycling was approximately 39.00 MPa, recovering 69% of the initial strength; the interlaminar shear strength after the second repair was 28.93 MPa, which was 51% of the initial strength. From Figure 4 Looking at the test curve in Fig. a, there is a cliff-like strength drop at the end of each interlaminar shear test, which indicates that serious and complete damage has occurred after each interlaminar shear test; it is mainly divided into two parts, one part is the damage caused by fiber fracture, and the other part is the interlayer delamination damage; during the hot pressing repair process, the broken fibers cannot be repaired, and since the interlayer delamination part is mainly the damage between resins, this part can be repaired under hot pressing conditions, so the interlaminar shear strength decreases significantly after multiple repairs. In addition, in Figure 4 Fig. a, it can be seen that there is a "saw-tooth" drop in strength in the test curves of the first and second repairs. This is mainly because only the resin part can be repaired during the hot pressing process, and the broken fiber part cannot be repaired. As a result, during the test, the broken fiber part after repair fails first, resulting in the "saw-tooth" phenomenon of strength drop on the curve. After two repairs, a part of the test specimen has completely detached and cannot be repaired for the third time.

[0078] Figure 5 The DMA test results of the original composite material sample and the two reprocessing processes are shown. As Figure 5 shown, the storage modulus of the original sample was about 40000 Mpa. The storage modulus of the sample after the first repair decreased slightly compared to the original sample, about 37000 MPa, while the storage modulus of the sample after the second repair decreased significantly, about 29000 Mpa. With the multiple shear failure hot pressing repair process, the storage modulus of the material shows a downward trend. This indicates that during the shear failure process, some fibers will break, and the hot pressing process cannot repair the broken fibers, but can only repair the resin part attached to the fibers through hot pressing; with multiple damages, the breakage of some fibers leads to a gradual decrease in the storage modulus. From the temperature position of Tanδ, it can be seen that the glass transition temperature of the initial composite material was about 127 °C, while the glass transition temperature after repair increased significantly and the temperature range where Tanδ peaks became wider. This is because there are more broken fibers in the sample after multiple repairs, and the structural differences between the fiber-containing part and the broken fiber part of the composite material are too large, resulting in too large differences in the molecular chain segment movement ability. This indicates that after the interlaminar shear failure repair process of the composite material, the sample can retain a certain storage modulus and a higher glass transition temperature; at the same time, the peak of Tanδ also reflects the large structural differences in the composite material, verifying the phenomenon that some broken fiber parts cannot be repaired.

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

[0080] The present invention also studied the morphological changes of carbon fiber composites after being immersed in ethylenediamine for different periods of time. It was found that as the immersion time of the carbon fiber composites in the ethylenediamine solution increased, the color of the solution gradually changed from colorless to yellow, and the color became darker with the increase of time. When the carbon fiber composites were immersed in ethylenediamine for 0 to 6 hours, the surface of the carbon fibers gradually became rough; as the immersion time increased to 24 hours, the fibers gradually delaminated and separated, becoming a loose state without any resin constraint, indicating that the internal resin was fully degraded.

[0081] The present invention also studied the changes of carbon fibers after the resin of the composites made of the original T700 carbon fibers immersed for 16 hours and 24 hours was degraded. Before chemical degradation, the microscopic surface of the original T700 sample was very smooth. After 16 hours of chemical degradation, the surface of the carbon fibers of the composites of the present invention was rough, and a large amount of undegraded epoxy resin adhered to the fiber surface. After 24 hours of chemical degradation, the surface of the carbon fibers of the composites of the present invention was smooth and clean, without any attachments, and there was basically no difference in the surface morphology from that of the T700 carbon fibers. This indicates that the composites can be immersed in an ethylenediamine solution at room temperature for 24 hours to completely degrade the resin adhering to the carbon fiber surface.

[0082] Figure 6 a and b show the laser Raman test results of the original T700 carbon fibers and the T700 carbon fibers after 24-hour chemical recycling. Raman spectroscopy can be used to analyze the changes in the surface structure of carbon fibers. From Figure 6 it can be seen that there are two obvious spectral lines in the Raman spectral regions of the unused commercial carbon fiber T700 and the carbon fibers after chemical degradation and recycling: the D line (disordered carbon structure: 1360 cm -1 ) and the G line (graphite crystal structure: 1580 cm -1 ). R (R = I D / I G ) is the integral intensity ratio of the D peak (disordered structure) to the G peak (graphite structure), which can be used to measure the changes in surface defects and the low-symmetry structure of carbon fibers.

[0083] Table 1 Comparison of various items of the D / G peak in the Raman spectrum table

[0084]

[0085] Table 1 lists the Raman spectrum analysis values of each sample. It can be seen from the table that compared with the unused commercial carbon fiber T700, the positions of the D peak and the G peak of the recycled carbon fibers hardly changed, and the Rorigin (I D / I G ) of the original T700 carbon fibers was 2.529, and the Rrecycle (I D / I G) is 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, indicating that the recycled carbon fiber has not been significantly damaged compared to the unused carbon fiber.

[0086] As can be seen from the above experimental results, the glass transition temperature of the composite material with dual dynamic exchange bonds in the present invention is 127 °C. This composite material can be reprocessed at a temperature below the glass transition temperature, and the reprocessed sample still retains good mechanical properties. At the same time, this composite material has good initial interlaminar shear strength and hot pressing repair ability, and can also achieve non-destructive recycling of carbon fibers.

[0087] In summary, the present invention provides an epoxy composite material that can be repaired and reprocessed under conditions below the glass transition temperature, and its preparation method and uses. The present invention uses an epoxy resin containing imine bonds and VU dynamic covalent bonds as the matrix, and prepares a composite material by continuous fiber reinforcement. This composite material has good initial interlaminar shear strength and hot pressing repair ability, can be hot pressed and repaired under conditions below the glass transition temperature, and its fibers can be recycled without damage. The composite material prepared by the present invention shows significant advantages in aspects such as composite material repair, extending service life, secondary processing, recycling and reprocessing for circular reuse, and saving resources and environmental protection, and has great potential and broad application prospects in the field of composite materials.

Claims

1. A composite material, characterized in that: The product is prepared by using epoxy resin containing imine bonds and VU dynamic covalent bonds as a matrix and continuous fibers as a reinforcement.

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

3. The composite material according to claim 1, characterized in that 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 4. The composite material according to claim 3, characterized in that The epoxy resin is selected from the group consisting of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, alicyclic epoxide, aromatic epoxy resin, linear aliphatic epoxide, bisphenol A epoxy resin, phenolic epoxy resin, polyol glycidyl ether epoxy resin; The curing agent containing VU dynamic covalent bonds is prepared from difunctional amine, trifunctional amine and EGAA as raw materials.

5. The composite material according to claim 3, characterized in that The epoxy resin structure containing imine dynamic bonds is: The preparation method of the curing agent containing VU dynamic covalent bonds comprises the following steps: (1) mixing a difunctional amine and a trifunctional amine; (2) adding EGAA to the mixture of step (1) to react, thereby obtaining a curing agent containing a VU dynamic covalent bond; The molar ratio of the difunctional amine, the trifunctional amine and EGAA is 1-5:0.1-0.5:1; The structure of EGAA is 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 amine and trifunctional amine are selected from aromatic amines, aliphatic amines or alicyclic amines.

7. The composite material according to any one of claims 3 to 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 1:1-1.

2.

8. A method for preparing the composite material according to any one of claims 1 to 7, characterized in that: The method uses epoxy resin containing imine bonds and VU dynamic covalent bonds as a matrix and continuous fibers as a reinforcement to prepare a composite material; the method is a solution method, a melting method, a powder impregnation method, a slurry resin deposition method, a mixed knitting method, a film lamination method or a reaction impregnation method.

9. The method according to claim 8, characterized in that The method comprises 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 on the surface of a continuous fiber, drying, and molding; preferably, the solvent is an organic solvent; the molding conditions are: first maintaining at 5-15MPa and 60-100°C for 1-4 hours, and then maintaining at 5-15MPa and 100-140°C for 1-4 hours.

10. Use of the composite material according to any one of claims 1 to 7 in preparing materials for aerospace, military defense, industry and life applications.

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