Preparation method of Mg(OH)2 / polydopamine multi-scale synergistic modified carbon fiber / epoxy resin composite material

Abstract

The present invention discloses a method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material, which relates to the technical field of composite material preparation and includes the following steps: S1, preparation of material solution and equipment; S2, preparation of polydopamine modified carbon fiber; S3, preparation of Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber; S4, preparation of Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material. The present invention introduces nano-Mg(OH)2 on the surface of polydopamine modified carbon fiber with a coordination bond as a force, thereby forming an organic-inorganic combined three-dimensional structure interface layer. At the same time, the method improves the wettability and bonding effect between the carbon fiber and the matrix, making the bending performance of the composite material more excellent. Moreover, the method of introducing nano-Mg(OH)2 with a coordination bond is simple, fast and efficient, does not destroy the original structure of the carbon fiber, and avoids complex operations such as chemical grafting and oxidation treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material preparation, and in particular to a method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material. Background Art

[0002] Carbon fiber / epoxy resin composites have the characteristics of high specific strength and specific modulus and are often used as structural materials. Most of them are made of carbon fiber composites with resin, metal and other matrices. They are widely used in aerospace, automobile, sports equipment and other fields. However, due to the smooth surface and high inertness of carbon fiber, its wettability and bonding with the resin matrix are poor, and the interface phase often becomes the weak link of the composite material.

[0003] Surface modification technology can improve the surface activity of carbon fiber and strengthen the interfacial properties between carbon fiber and resin matrix. At present, there are many methods for modifying the surface of carbon fiber to enhance the interfacial strength of carbon fiber resin composites. Traditional modification methods mainly include nano-modification and sizing modification. In recent years, the use of nanoparticles combined with other polymers to perform multi-scale modification of the carbon fiber surface can avoid some of the shortcomings of single modification and has become a hot topic of research at home and abroad. The commonly used nanomaterials in multi-scale modification are mainly metal oxides and metal hydroxides (such as nickel hydroxide, iron hydroxide, copper hydroxide, etc.), and the commonly used polymers are polyetheramine, polyethyleneimine and polydopamine. Among them, polydopamine is a biomimetic mussel material that can be adsorbed to the carbon fiber surface through ππ bonds to form a layer of polydopamine film, thereby improving the adhesion of carbon fiber to nanoparticles. Jin L et al. (Jin L, He Y, Shang L, et al. Superior and versatile interface transition layer with a sandwich-like multiscale rigid-soft dual-locked structure for high performance composites [J]. Applied Surface Science, 2020, 508: 145238.) proposed using an ultrasonic method to load nickel hydroxide nanoparticles on the surface of polydopamine-modified carbon fibers. However, due to the lack of chemical bonds between nickel hydroxide nanoparticles and polydopamine, phenomena such as loose loading, uneven loading, and nanoparticle agglomeration are prone to occur; the patent with announcement number CN118345632A discloses a carbon fiber modified based on polydopamine-iron complex nanospheres and its preparation method. Polydopamine contains a large amount of catechol in its structure, and iron ions have strong electron-withdrawing ability. This invention first combines the two, forming a coordination bond between catechol and iron ions to produce polydopamine-iron complex aggregates. These complex nanospheres are then loaded onto the surface of carbon fibers to achieve the purpose of modifying the carbon fibers. Although this method increases the chemical bond strength between the metal particles and polydopamine, the contact area between the polydopamine-iron complex aggregates and the carbon fibers is small, resulting in their adsorption force on the carbon fiber surface being less than that of the polydopamine film, and the nanospheres are prone to agglomeration.

[0004] In summary, the present invention proposes a method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material. Summary of the Invention

[0005] The present invention discloses a preparation method of a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material, aiming to solve the technical problems in the background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material comprises the following steps:

[0008] S1. Preparation of material solutions and equipment:

[0009] (1) Preparation of material solution: carbon fiber, dopamine hydrochloride solution, tris (hydroxymethyl)aminomethane (Tris) solution, magnesium source solution, alkaline solution, epoxy resin, curing agent, accelerator and deionized water;

[0010] (2) Equipment preparation: oven, constant temperature digital display heating table, vacuum drying oven and infrared tablet press;

[0011] S2. Preparation of polydopamine modified carbon fiber: The unsized carbon fiber was fully washed and dried, and then completely immersed in a solution containing 2gL -1 of dopamine hydrochloride solution, and then 2gL -1 The solution pH was adjusted to 8.5 with a Tris buffer solution, and the solution was allowed to stand at room temperature for 4 h. After being fully washed, the solution was dried in an oven to obtain polydopamine-modified carbon fibers.

[0012] S3. Preparation of Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber: completely immersing the polydopamine-modified carbon fiber obtained in S2 in a magnesium source solution, drying it after the impregnation, and then completely immersing it in an alkaline solution. After the immersion in the alkaline solution, washing it is performed, and then drying it in an oven to obtain a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber tow;

[0013] Preparation of S4, Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material: After the epoxy resin, curing agent and accelerator are stirred evenly and the bubbles are removed, a resin matrix glue solution is obtained, which is evenly coated on the surface of the Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber tow in S3 on a constant temperature digital display heating table, and then placed in a vacuum drying oven and impregnated at 55°C for 30-45 minutes to obtain a modified carbon fiber prepreg;

[0014] The prepreg is placed in a metal mold on an infrared sheet press, the molding pressure on the infrared sheet press is set to 15 MPa, and the pressure is maintained for 30 minutes; then, the metal mold is fixed with a heavy G-clamp, and cured at 90°C for 1 hour, at 130°C for 2 hours, and at 150°C for 2-3 hours to obtain a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material.

[0015] In a preferred embodiment, the magnesium source solution in step S3 is one or two of magnesium nitrate solution, magnesium chloride solution, and magnesium sulfate solution.

[0016] In a preferred embodiment, in step S3, the polydopamine-modified carbon fiber is immersed in the magnesium source solution at a temperature of 20-80° C. for a time of 1-60 min.

[0017] In a preferred embodiment, in step S3, after the polydopamine-modified carbon fiber is immersed in the magnesium source solution, it is placed in a vacuum oven and dried at 60° C. for 30 minutes.

[0018] In a preferred embodiment, the alkaline solution in step S3 is one or two of ammonium hydroxide solution, urea solution, and sodium hydroxide solution.

[0019] In a preferred embodiment, the polydopamine-modified carbon fiber is immersed in the alkaline solution at a temperature of 20-80° C. and a time of 1-120 min in step S3.

[0020] In a preferred embodiment, after the polydopamine-modified carbon fiber is immersed in the alkaline solution and fully washed in step S3, it is placed in a vacuum oven and dried at 60° C. for 8 hours.

[0021] In a preferred embodiment, the epoxy resin matrix glue in step S4 includes the following raw materials in mass fractions: 1000 parts of epoxy resin, 700 parts of curing agent, and 1-5 parts of accelerator.

[0022] In a preferred embodiment, the epoxy resin in step S4 is E51 epoxy resin, the curing agent is methyltetrahydrophthalic anhydride, and the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.

[0023] In a preferred embodiment, the epoxy resin, curing agent and accelerator are stirred in step S4 by magnetic stirring in a 40°C water bath for 15-30 minutes; the bubble removal method is ultrasonic removal, with an ultrasonic frequency of 40-50KHz, an ultrasonic power of 360-480W, and an ultrasonic time of 15-45 minutes.

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

[0025] First: This invention is the first to use Mg(OH)2 / polydopamine multi-scale synergistic modification of carbon fibers to improve the interface performance of composite materials. This strategy expands the application of Mg(OH)2 in composite interface engineering. The modification method is green, environmentally friendly, simple, fast and efficient.

[0026] Second, the Mg(OH)2 grown in situ on the polydopamine layer exhibits excellent dispersibility and robustness. The polydopamine layer contains a large amount of catechol. Furthermore, magnesium ions have a smaller diameter and lower electron affinity than iron and nickel ions. Therefore, magnesium ions and catechol can undergo a coordination reaction to form a chelate without forming complex aggregates. This characteristic of magnesium ions does not destroy the polydopamine film adsorbed on the carbon fiber surface. Furthermore, the magnesium ions firmly chelated on the polydopamine film inhibit subsequent Mg(OH)2 aggregation, resulting in interlaced Mg(OH)2 nanosheets that form a robust three-dimensional structure.

[0027] Thirdly, the rich functional groups of polydopamine improve the chemical activity of the carbon fiber surface, and enhance the wettability and chemical bonding ability of the carbon fiber with the resin matrix. Nano-Mg(OH)2 is introduced into the surface of the polydopamine-modified carbon fiber with coordination bonds as the force. The three-dimensional structure interface layer of organic-inorganic combination increases the roughness of the carbon fiber surface, improves the wettability and mechanical interlocking effect of the carbon fiber with the resin matrix, and makes the bending performance of the composite material even better. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a step diagram of a method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material of the present invention.

[0029] Figure 2 This is a scanning electron microscope image of the polydopamine-modified carbon fiber obtained in Comparative Example 1 of the present invention.

[0030] Figure 3 This is a scanning electron microscope image of the Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber obtained in Example 1 of the present invention.

[0031] Figure 4 This is a scanning electron microscope image of the Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber obtained in Example 3 of the present invention.

[0032] Figure 5 This is a macroscopic morphology diagram of the composite material sample of Example 3 of the present invention after a three-point bending test.

[0033] Figure 6 1 is a graph showing the bending performance data of the samples of Comparative Example 1 and Examples 1 to 4 of the present invention. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0035] Reference Figure 1 A method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material comprises the following steps:

[0036] S1. Preparation of material solutions and equipment:

[0037] (1) Preparation of material solution: carbon fiber, dopamine hydrochloride solution, tris (hydroxymethyl)aminomethane (Tris) solution, magnesium source solution, alkaline solution, epoxy resin, curing agent, accelerator and deionized water;

[0038] (2) Equipment preparation: oven, constant temperature digital display heating table, vacuum drying oven and infrared tablet press;

[0039] S2. Preparation of polydopamine modified carbon fiber: The unsized carbon fiber was fully washed and dried, and then completely immersed in a solution containing 2gL -1 of dopamine hydrochloride solution, and then 2gL -1 The solution pH was adjusted to 8.5 with a Tris buffer solution, and the solution was allowed to stand at room temperature for 4 h. After being fully washed, the solution was dried in an oven to obtain polydopamine-modified carbon fibers.

[0040] S3. Preparation of Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fibers: The polydopamine-modified carbon fibers obtained in S2 are completely immersed in a magnesium source solution.

[0041] In a preferred embodiment, the magnesium source solution is one or two of magnesium nitrate solution, magnesium chloride solution, and magnesium sulfate solution;

[0042] In a preferred embodiment, the polydopamine-modified carbon fiber is immersed in the magnesium source solution at a temperature of 20-80° C. for a time of 1-60 min;

[0043] After the dipping is completed, it is dried;

[0044] In a preferred embodiment, after the polydopamine-modified carbon fiber is impregnated with the magnesium source solution, it is placed in a vacuum oven and dried at 60° C. for 30 minutes.

[0045] After drying, completely immerse in alkaline solution;

[0046] In a preferred embodiment, the alkaline solution is one or two of ammonium hydroxide solution, urea solution, and sodium hydroxide solution.

[0047] In a preferred embodiment, the polydopamine-modified carbon fiber is immersed in the alkaline solution at a temperature of 20-80° C. and a time of 1-120 min.

[0048] After the immersion in the alkaline solution, washing is performed;

[0049] Then it was placed in an oven for drying to obtain a carbon fiber tow with multi-scale synergistic modification of Mg(OH)2 / polydopamine;

[0050] In a preferred embodiment, after the polydopamine-modified carbon fiber is immersed in the alkaline solution and fully washed, it is placed in a vacuum oven and dried at 60° C. for 8 hours.

[0051] S4. Preparation of Mg(OH)2 / polydopamine multi-scale synergistic modified carbon fiber / epoxy resin composite material: epoxy resin, curing agent and accelerator were stirred evenly and then bubbles were removed;

[0052] In a preferred embodiment, the epoxy resin is E51 epoxy resin, the curing agent is methyltetrahydrophthalic anhydride, and the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.

[0053] Obtaining a resin matrix glue solution;

[0054] In a preferred embodiment, the epoxy resin matrix glue comprises the following raw materials in mass fractions: 1000 parts of epoxy resin, 700 parts of curing agent, and 1-5 parts of accelerator.

[0055] In a preferred embodiment, the epoxy resin, curing agent and accelerator are stirred by magnetic stirring in a 40°C water bath for 15-30 minutes; the bubble removal method is ultrasonic removal, with an ultrasonic frequency of 40-50KHz, an ultrasonic power of 360-480W, and an ultrasonic time of 15-45 minutes.

[0056] It was evenly coated on the surface of the carbon fiber tow modified by Mg(OH)2 / polydopamine multi-scale synergistically in S3 on a constant temperature digital display heating table, and then placed in a vacuum drying oven and immersed at 55°C for 30-45 minutes to obtain a modified carbon fiber prepreg.

[0057] The prepreg was placed in a metal mold on an infrared sheet press, and the molding pressure on the infrared sheet press was set to 15 MPa and maintained at pressure for 30 minutes. Subsequently, the metal mold was fixed with a heavy G-clamp and cured at 90°C for 1 hour, 130°C for 2 hours, and 150°C for 2-3 hours to obtain a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material.

[0058] Comparative Example 1:

[0059] Preparation of a polydopamine modified carbon fiber / epoxy resin composite material;

[0060] S1. Preparation of polydopamine modified carbon fiber: The unsized carbon fiber was placed in anhydrous ethanol and ultrasonicated for 30 minutes, then dried in a 60°C oven to remove impurities on the surface of the carbon fiber, and then completely immersed in 2gL -1 of dopamine hydrochloride solution, and then 2gL -1 Adjust the pH value of the solution to 8.5 with Tris buffer solution, keep it still at room temperature for 4 h, wash it thoroughly and then dry it in an oven;

[0061] S2, preparation of polydopamine modified carbon fiber / epoxy resin composite material: after the epoxy resin, curing agent and accelerator are stirred evenly and the bubbles are removed, a resin matrix glue is obtained, which is evenly coated on the surface of the polydopamine modified carbon fiber tow obtained in S1 on a constant temperature digital display heating table, and then placed in a vacuum drying oven and impregnated at 55 ° C for 30-45 minutes to obtain a modified carbon fiber prepreg; the prepreg is placed in a metal mold, and the molding pressure is set to 15 MPa on the infrared sheet press, and the pressure is maintained for 30 minutes. Subsequently, the metal mold is fixed with a heavy G-shaped clamp, and then cured at 90 ° C for 1 hour, 130 ° C for 2 hours, and 150 ° C for 2-3 hours to obtain a polydopamine modified carbon fiber / epoxy resin composite material. In order to reduce experimental errors, at least 3 parallel samples are prepared for each group for subsequent bending performance tests, and the results are averaged. The average bending strength of the polydopamine modified carbon fiber / epoxy resin composite material obtained in this comparative example 1 is 871.0 MPa.

[0062] Among them, the scanning electron microscope image of polydopamine modified carbon fiber is as follows Figure 2 As shown, from Figure 2 It can be seen that there is a thin film on the surface of the polydopamine-modified carbon fiber, and the grooves on the surface of the carbon fiber can be clearly seen.

[0063] Example 1:

[0064] This embodiment provides a method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material in which Mg(OH)2 is in situ grown on the surface of polydopamine-modified carbon fiber in an alkaline solution at 20°C, comprising the following steps:

[0065] S1. Preparation of polydopamine modified carbon fiber: The unsized carbon fiber was placed in anhydrous ethanol for 30 minutes and then placed in a 60°C oven to dry to remove impurities on the carbon fiber surface. -1 of dopamine hydrochloride solution, and then 2gL -1 The pH value of the solution was adjusted to 8.5 with Tris buffer solution, and the solution was allowed to stand at room temperature for 4 h. After thorough washing, the solution was dried in an oven.

[0066] S2, preparation of Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber: The polydopamine modified carbon fiber obtained in S1 was completely immersed in a solution providing a magnesium source at 20°C for 5 minutes. After the impregnation, it was placed in a vacuum oven at 60°C for drying for 30 minutes. Then it was completely immersed in an alkaline solution at 20°C for 5 minutes. After the impregnation, it was fully washed and then placed in a vacuum oven at 60°C for drying for 8 hours to obtain a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber bundle with Mg(OH)2 in situ grown in an alkaline solution at 20°C.

[0067] Preparation of S3, Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite: Epoxy resin, curing agent, and accelerator were stirred uniformly and then air bubbles were removed to obtain a resin matrix adhesive. This was then evenly coated on the surface of the Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber tow obtained in S2 on a constant temperature digital heating table. The prepreg was then placed in a vacuum drying oven and impregnated at 55°C for 30-45 minutes to obtain a modified carbon fiber prepreg. The prepreg was placed in a metal mold, and the molding pressure on an infrared sheet press was set to 15 MPa and maintained for 30 minutes. The mold was then secured with a heavy-duty G-clamp and cured at 90°C for 1 hour, 130°C for 2 hours, and 150°C for 2-3 hours to obtain the Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite. To reduce experimental error, at least three replicate samples were prepared for each group for subsequent flexural properties testing, and the results were averaged. The average flexural strength of the modified carbon fiber / epoxy resin composite material obtained in this example is 925.3 MPa.

[0068] Among them, the scanning electron microscope images of Mg(OH)2 / polydopamine multi-scale synergistic modified carbon fibers are shown in Figure 2. Figure 3 As shown, from Figure 3 It can be seen that the flake-like Mg(OH)2 is in situ grown on the surface of the polydopamine-modified carbon fiber. Figure 2 In comparison, the roughness of the carbon fiber surface is effectively increased, but the growth of Mg(OH)2 is not uniform enough.

[0069] Example 2:

[0070] This example provides a method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber epoxy resin composite material, in which Mg(OH)2 is in situ grown on the surface of polydopamine-modified carbon fibers in an alkaline solution at 40°C. The method differs from Comparative Example 1 in that the alkaline solution immersion temperature in step S2 is changed to 40°C. The average flexural strength of the modified carbon fiber / epoxy resin composite material obtained in this example is 997.8 MPa.

[0071] Example 3:

[0072] This example provides a method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber epoxy resin composite material, in which Mg(OH)2 is in situ grown on the surface of polydopamine-modified carbon fibers in an alkaline solution at 60°C. The method differs from Comparative Example 1 in that the alkaline solution immersion temperature in step S2 is changed to 60°C. The average flexural strength of the modified carbon fiber / epoxy resin composite material obtained in this example is 1044.3 MPa.

[0073] Among them, the scanning electron microscope images of Mg(OH)2 / polydopamine multi-scale synergistic modified carbon fibers are shown in Figure 2. Figure 4 As shown, from Figure 4 It can be seen that the flake-like Mg(OH)2 is in situ grown on the surface of the polydopamine-modified carbon fiber. Figure 3 In comparison, the surface of carbon fiber is evenly covered with Mg(OH)2 nanosheets. Its unique sheet structure and staggered arrangement form a three-dimensional structure, which effectively increases the roughness of the carbon fiber surface and can be firmly embedded in the resin matrix, increasing the interface bonding force, thereby achieving the purpose of enhancing the mechanical properties of the composite material.

[0074] in, Figure 5 This is a macroscopic morphology of the composite material sample of Example 3 of the present invention after the three-point bending test; Figure 5 It can be seen that the composite material did not completely break after the bending test, indicating that the carbon fiber plays a full role as a stress carrier. It also proves that the carbon fiber / epoxy resin composite material prepared by the present invention can play a role of toughening modification.

[0075] Example 4:

[0076] This example provides a method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber epoxy resin composite material, in which Mg(OH)2 is in situ grown on the surface of polydopamine-modified carbon fibers in an alkaline solution at 80°C. The method differs from Comparative Example 1 in that the alkaline solution immersion temperature in step S2 is changed to 80°C. The average flexural strength of the modified carbon fiber / epoxy resin composite material obtained in this example is 932.1 MPa.

[0077] Among them, in the above-mentioned comparative example 1 and embodiment 1, embodiment 2, embodiment 3 and embodiment 4, when the bending strength of the material was tested, according to the GB / T1449-2005 test standard, the bending performance test samples of Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite materials were measured on a German Zwick Z100 universal testing machine.

[0078] in, Figure 6 The bending performance data of the samples of Comparative Example 1 and Examples 1 to 4 of the present invention are shown in FIG. Figure 6 It can be seen that the flexural strength of the composite material in Comparative Example 1 is the lowest, at 871.0 MPa. The flexural strengths of the composite materials in Examples 1 to 4 are all higher than that in Comparative Example 1, and their variation trends show an increase first and then a decrease. When the temperature of the alkaline solution is 20°C, the flexural strength of the sample is the lowest, at 925.3 MPa. In comparison, when the temperature of the alkaline solution is 60°C, the flexural strength of the sample reaches the maximum, at 1044.3 MPa, which is 12.86% higher than that of the composite material in Example 1 and 19.90% higher than that of the composite material in Comparative Example 1.

[0079] It can be seen that the in-situ growth of Mg(OH)2 on the surface of polydopamine modified carbon fibers significantly improves the flexural strength of the composite material. Moreover, under the same reaction time, the amount of Mg(OH)2 grown in situ on the surface of polydopamine modified carbon fibers can be changed by changing the temperature of the immersion alkaline solution, thereby changing the roughness of the carbon fiber surface. Of course, the higher the temperature of the immersion alkaline solution, the better. This is because too high a temperature of the alkaline solution will weaken the chelating force between magnesium ions and catechol, causing magnesium ions to fall off from the polydopamine film, which in turn causes the generated Mg(OH)2 to agglomerate and fall off, reducing the interfacial bonding force between the carbon fibers and the resin matrix, and ultimately leading to a decrease in the bending performance of the Mg(OH)2 / polydopamine multi-scale synergistic modified carbon fiber epoxy resin composite material. Therefore, nano-Mg(OH)2 is introduced on the surface of polydopamine modified carbon fibers with coordination bonds as the acting force. This method can effectively control the nucleation and growth of Mg(OH)2. Of course, only the appropriate immersion alkaline solution temperature can fully cover the surface of the polydopamine-modified carbon fiber with a uniform, interlaced layer of Mg(OH)2 nanosheets, thereby forming a strong mechanical meshing force between the carbon fiber and the resin matrix, and ultimately improving the bending properties of the composite material.

[0080] In summary, the method for modifying the carbon fiber surface proposed in the present invention is a multi-scale modification method. First, a layer of polydopamine film is in situ polymerized on the carbon fiber surface. The polydopamine layer can improve the chemical activity of the carbon fiber surface, and can also serve as a functional platform for providing nucleation points for Mg(OH)2, using coordination bonds as a force to firmly chelate magnesium ions on the polydopamine film. The magnesium ions will not destroy the polydopamine film adsorbed on the carbon fiber surface, and can effectively inhibit the agglomeration of Mg(OH)2. The obtained Mg(OH)2 nanosheets arranged in an interlaced manner can evenly form a layer of a firm three-dimensional structure on the surface of the polydopamine-modified carbon fiber. This structure can be firmly embedded in the resin matrix, and the sheet-like nanomaterial is more beneficial to improving the interfacial properties of carbon fiber composites.

[0081] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Without departing from the principles of the present invention, any improvements, modifications, or equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material, characterized in that: The following steps are involved: S1. Preparation of material solutions and equipment: (1) Preparation of material solution: carbon fiber, dopamine hydrochloride solution, tris (hydroxymethyl)aminomethane (Tris) solution, magnesium source solution, alkaline solution, epoxy resin, curing agent, accelerator and deionized water; (2) Equipment preparation: oven, constant temperature digital display heating table, vacuum drying oven and infrared tablet press; S2. Preparation of polydopamine modified carbon fiber: The unsized carbon fiber was fully washed and dried, and then completely immersed in a solution containing 2gL -1 of dopamine hydrochloride solution, and then 2gL -1 The solution pH was adjusted to 8.5 with a Tris buffer solution, and the solution was allowed to stand at room temperature for 4 h. After being fully washed, the solution was dried in an oven to obtain polydopamine-modified carbon fibers. S3. Preparation of Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber: completely immersing the polydopamine-modified carbon fiber obtained in S2 in a magnesium source solution, drying it after the impregnation, and then completely immersing it in an alkaline solution. After the immersion in the alkaline solution, washing it is performed, and then drying it in an oven to obtain a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber tow; Preparation of S4, Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material: After the epoxy resin, curing agent and accelerator are stirred evenly and the bubbles are removed, a resin matrix glue solution is obtained, which is evenly coated on the surface of the Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber tow in S3 on a constant temperature digital display heating table, and then placed in a vacuum drying oven and impregnated at 55°C for 30-45 minutes to obtain a modified carbon fiber prepreg; The prepreg is placed in a metal mold on an infrared sheet press, the molding pressure on the infrared sheet press is set to 15 MPa, and the pressure is maintained for 30 minutes; then, the metal mold is fixed with a heavy G-clamp, and cured at 90°C for 1 hour, at 130°C for 2 hours, and at 150°C for 2-3 hours to obtain a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material.

2. The method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material according to claim 1, characterized in that: The magnesium source solution in step S3 is one or two of magnesium nitrate solution, magnesium chloride solution, and magnesium sulfate solution.

3. The method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material according to claim 1, characterized in that: In step S3, the polydopamine-modified carbon fiber is immersed in the magnesium source solution at a temperature of 20-80° C. for a time of 1-60 minutes.

4. The method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material according to claim 1, characterized in that: In step S3, after the polydopamine-modified carbon fiber is immersed in the magnesium source solution, it is placed in a vacuum oven and dried at 60° C. for 30 minutes.

5. The method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material according to claim 1, characterized in that: The alkaline solution in step S3 is one or two of ammonium hydroxide solution, urea solution, and sodium hydroxide solution.

6. The method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material according to claim 1, characterized in that: In step S3, the polydopamine-modified carbon fiber is immersed in the alkaline solution at a temperature of 20-80° C. and a time of 1-120 min.

7. The method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material according to claim 1, characterized in that: In step S3, the polydopamine-modified carbon fiber is immersed in the alkaline solution and fully washed, and then placed in a vacuum oven and dried at 60° C. for 8 hours.

8. The method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material according to claim 1, characterized in that: The epoxy resin matrix glue in step S4 includes the following raw materials in mass fractions: 1000 parts of epoxy resin, 700 parts of curing agent, and 1-5 parts of accelerator.

9. The method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material according to claim 1, characterized in that: The epoxy resin in step S4 is E51 epoxy resin, the curing agent is methyltetrahydrophthalic anhydride, and the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.

10. The method for preparing a Mg(OH)2 / polydopamine multi-scale synergistically modified carbon fiber / epoxy resin composite material according to claim 1, characterized in that: In step S4, the epoxy resin, curing agent and accelerator are stirred by magnetic stirring in a 40° C. water bath for 15-30 minutes; the bubble removal method is ultrasonic removal, with an ultrasonic frequency of 40-50 KHz, an ultrasonic power of 360-480 W, and an ultrasonic time of 15-45 minutes.

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