Method for improving interface bonding performance of carbon fiber reinforced epoxy resin-based composite material

Abstract

The invention provides a method for improving the interface bonding performance of a carbon fiber reinforced epoxy resin-based composite material, and belongs to the technical field of carbon fiber surface modification. The preparation method of the modified carbon fiber comprises the following steps: carrying out plasma treatment on carbon fiber by using air as a plasma gas medium to obtain plasma surface modified carbon fiber; the plasma surface modified carbon fiber is soaked in a polyamide-amine dendrimer (PAMAM) solution for a reaction, and the modified carbon fiber is obtained. The modified carbon fiber is prepared through a method of combining plasma treatment and surface grafting treatment, so that the interface bonding strength of the carbon fiber reinforced epoxy resin-based composite material is improved, and meanwhile, the original tensile property of the carbon fiber can be kept stable.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber surface modification, and in particular to a method for improving the interface bonding performance of a carbon fiber reinforced epoxy resin-based composite material. Background Art

[0002] Carbon fiber is a high-performance material with a carbon content of more than 90%, and its molecular structure is similar to that of turbostratic graphite. As a commonly used reinforcing material, carbon fiber has high strength, high stiffness, low density and excellent corrosion resistance, and also performs well in thermal, electrical and chemical properties. The composite material formed by it combined with epoxy resin is light and high-strength, has good design flexibility, strong fatigue resistance, good corrosion resistance, and is suitable for large-area integral molding. Therefore, carbon fiber has received more and more attention and application in many fields such as aerospace, electronic information, transportation, metallurgy and chemical industry, and medical and health care.

[0003] During the production process of carbon fiber, it undergoes a high-temperature carbonization treatment of over 1000°C in an inert gas environment. This process releases non-carbon elements (such as oxygen and nitrogen) from the fiber and causes the lattice structure of carbon atoms to transform into a turbostratic graphite state. As a result, the surface of the carbon fiber becomes relatively smooth and lacks active functional groups, so the surface is inert and less reactive. This characteristic results in poor bonding between carbon fiber and resin and insufficient interfacial bonding force, thereby reducing the interlaminar shear strength of carbon fiber reinforced resin-based composites and affecting their performance. Therefore, before the carbon fiber is combined with the resin, the surface of the carbon fiber needs to be treated to improve its surface roughness and chemical activity, thereby improving its bonding with the epoxy resin.

[0004] Plasma treatment is an emerging carbon fiber modification technology that has attracted much attention in recent years. Plasma is an ionized mixed substance containing ions, electrons, free radicals, and excited molecules and atoms, which can interact with the surface of carbon fibers to produce highly active substances. When plasma treats carbon fibers, due to the different properties of the gas used, free radicals, ions, and metastable substances may be produced, thereby inducing ablation, crosslinking, or oxidation reactions. During the treatment process, the plasma etches the surface of the carbon fiber to change its surface morphology, thereby increasing the roughness of the fiber surface, and an oxidation reaction occurs to produce active oxygen-containing functional groups to increase the surface activity of the fiber, thereby improving the physical intercalation and chemical bonding between the fiber and the resin, and enhancing the bonding performance between the interfaces. At the same time, plasma-treated carbon fibers only react on the fiber surface, which will not significantly change the overall properties and can maintain the original properties inside the fiber. Therefore, plasma treatment has become a carbon fiber surface modification method with very obvious treatment effects and is widely used.

[0005] However, the carbon fiber treated with plasma has a time-limited effect, and the treated surface may gradually lose its activity over time. Therefore, in order to prevent the failure of the carbon fiber treated with plasma, an additional surface treatment is required. Summary of the invention

[0006] Based on the above content, the purpose of the present invention is to provide a method for improving the interfacial bonding performance of carbon fiber reinforced epoxy resin-based composite materials. The present invention combines plasma treatment and surface grafting treatment to enhance the interfacial bonding strength of carbon fiber and epoxy resin-based composite materials, while maintaining the original tensile properties of carbon fiber.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] One of the technical solutions of the present invention is a method for preparing modified carbon fiber, comprising the following steps:

[0009] Using air as a plasma gas medium, the carbon fiber is subjected to plasma treatment to obtain a plasma surface-modified carbon fiber;

[0010] The plasma surface modified carbon fiber is immersed in a PAMAM solution for reaction to obtain the modified carbon fiber.

[0011] A second technical solution of the present invention is to prepare modified carbon fiber using the above preparation method.

[0012] A third technical solution of the present invention is a method for improving the interfacial bonding performance of carbon fiber reinforced epoxy resin-based composite materials, wherein the carbon fiber is modified by the above-mentioned preparation method.

[0013] A fourth technical solution of the present invention is a carbon fiber reinforced epoxy resin-based composite material, the raw materials of which include the above-mentioned modified carbon fiber and epoxy resin.

[0014] The principle of the present invention is:

[0015] First, vacuum plasma is used to modify the surface of carbon fiber. The modified carbon fiber surface is rich in oxygen-containing functional groups such as -OH, -COOH, C=O, and the surface roughness is increased. The chemical bonding and mechanical meshing between the fiber and the epoxy resin are enhanced, which increases the interfacial shear strength of the carbon fiber reinforced epoxy resin-based composite material and improves the interfacial bonding performance. At the same time, plasma treatment can keep the original tensile properties of the carbon fiber unaffected and does not affect the overall performance of the carbon fiber.

[0016] After that, the carbon fiber surface was modified by PAMAM solution. The surface of the modified carbon fiber added nitrogen-containing functional groups rich in -C-NH2 on the original basis, and oxygen-containing functional groups rich in -OH, -COOH, C=O, etc. were further increased. PAMAM molecules will be adsorbed on the surface of the carbon fiber during the treatment process, resulting in a slight decrease in the surface roughness of the carbon fiber, but overall it remains the same as before the surface grafting treatment.

[0017] The present invention discloses the following technical effects:

[0018] The present invention uses vacuum plasma to perform surface modification on carbon fiber, which has the characteristics of both physical modification and chemical modification. It can not only generate oxygen-containing functional groups on the surface of carbon fiber, but also increase the surface roughness of the fiber, thereby strengthening the bonding ability between the fiber and epoxy resin, and further enhancing the interface performance.

[0019] The present invention adopts surface grafting treatment to fill the fine grooves on the surface of the carbon fiber, and can generate nitrogen-containing functional groups and oxygen-containing functional groups on the surface of the carbon fiber, further improve the surface activity of the carbon fiber on the basis of plasma treatment, make up for the timeliness of vacuum plasma treatment, thereby further strengthening the bonding ability of the carbon fiber and the epoxy resin, and enhancing the interface performance of the composite material.

[0020] After the fiber is modified by the method of the present invention, not only the interface strength of the carbon fiber reinforced epoxy resin-based composite material is improved, but also the original overall properties of the carbon fiber, such as tensile properties, are not affected.

[0021] The method provided by the present invention is simple and efficient, can introduce more active functional groups on the surface of carbon fiber, and can avoid the problem of short aging of carbon fiber after plasma treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 Schematic diagram of the preparation of modified carbon fiber of the present invention;

[0024] Figure 2 Schematic diagram for the preparation of PAMAM solution;

[0025] Figure 3 This is the macroscopic morphology of the modified carbon fiber and the unmodified carbon fiber in Example 1. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] Among the methods of carbon fiber surface modification, surface grafting is also a commonly used method, and surface grafting (such as grafting macromolecules, polymers or functional molecules) can add stable chemical structures to these active groups. These structures can not only reduce the exposure of surface active groups and prevent them from being further oxidized or hydrolyzed by molecules in the air, but also "close" or "protect" surface active groups through chemical reactions to a certain extent, thereby enhancing the stability of the carbon fiber surface and delaying the degradation of surface active groups over time, thereby slowing down or solving the timeliness problem. Surface grafting refers to modifying the surface of carbon fiber so that it can be grafted or in situ grown with compounds or polymers with specific functional groups, and can also connect nanoparticles to form an effective interface transition layer, thereby enhancing the interfacial adhesion of carbon fiber reinforced polymer-based composites. This treatment method can not only introduce functional groups, improve surface roughness and wettability, but also avoid damage to carbon fiber, and even enhance its strength to a certain extent. Therefore, like plasma treatment, it will not have a negative impact on the tensile properties of carbon fiber and can effectively improve the interfacial bonding force.

[0032] A first aspect of the present invention provides a method for preparing modified carbon fiber, comprising the following steps:

[0033] Using air as a plasma gas medium, the carbon fiber is subjected to plasma treatment to obtain a plasma surface-modified carbon fiber;

[0034] The plasma surface modified carbon fiber is immersed in a PAMAM solution for reaction to obtain the modified carbon fiber.

[0035] In some embodiments of the present invention, the plasma treatment is specifically: placing the carbon fiber in a vacuum plasma vacuum chamber, evacuating the vacuum chamber to a pressure of 0.2-0.5 mbar, a processing power of 100-300 W, a gas flow rate of 5-10 sccm, and a processing time of 0.5-10 min.

[0036] In some embodiments of the present invention, the concentration of the PAMAM solution is 2×10 -4 mol / L—20×10 -4 The preparation method of the PAMAM solution in the present invention is as follows: PAMAM is dissolved in DMF, ultrasonicated, and then condensation agent HATU is added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated.

[0037] In some embodiments of the present invention, the concentration of the PAMAM solution is 2×10 -4 mol / L—15×10 -4 mol / L.

[0038] In some embodiments of the present invention, the concentration of the PAMAM solution is 10×10 -4 mol / L—15×10 - 4 mol / L.

[0039] The present invention does not impose any particular limitation on the amount of the PAMAM solution used, as long as it can completely immerse the carbon fibers.

[0040] In some embodiments of the present invention, the reaction temperature is room temperature and the reaction time is 4 hours.

[0041] In some embodiments of the present invention, after the reaction is completed, a cleaning and drying step is further included; the drying is vacuum drying, and the vacuum drying temperature is 50° C. and the time is 24 hours.

[0042] A second aspect of the present invention provides a modified carbon fiber prepared by the above preparation method.

[0043] A third aspect of the present invention provides a method for improving the interface bonding performance of a carbon fiber reinforced epoxy resin-based composite material, wherein the carbon fiber is modified using the above-mentioned preparation method.

[0044] A fourth aspect of the present invention provides a carbon fiber reinforced epoxy resin-based composite material, the raw materials of which include the above-mentioned modified carbon fiber and epoxy resin.

[0045] The technical solutions described in the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0046] In order to better understand the present invention, the content of the present invention is further explained in conjunction with the following examples, but the content of the present invention is not limited to the following examples. Figure 1 .

[0047] In the embodiment, the epoxy resin used is E54 epoxy resin, and the curing temperature when the epoxy resin is composited with the modified carbon fiber is 180° C., and the curing time is 3 hours.

[0048] In the following examples and comparative examples, the mass ratio of epoxy resin to modified carbon fiber = the mass ratio of epoxy resin to unmodified carbon fiber = 1:3.

[0049] Example 1

[0050] The preparation steps of modified carbon fiber are as follows:

[0051] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Air is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 0.5 min.

[0052] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 2×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0053] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution, and then placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF, rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0054] After the epoxy resin and the modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 106.54 MPa, which was 23.85% higher than that of the unmodified interface shear strength of Comparative Example 1.

[0055] Example 2

[0056] The preparation steps of modified carbon fiber are as follows:

[0057] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Air is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 3 min.

[0058] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 6×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0059] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF and rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0060] After the epoxy resin and the modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 118.23 MPa, which was 37.44% higher than that of the unmodified interface shear strength of Comparative Example 1.

[0061] Example 3

[0062] The preparation steps of modified carbon fiber are as follows:

[0063] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Air is used as the plasma gas medium, the gas flow rate is 8 sccm, the processing power is 300 W, and the processing time is 3 min.

[0064] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 10×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0065] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF and rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0066] After the epoxy resin and the modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 128.53 MPa, which was 49.42% higher than that of the unmodified interface shear strength of Comparative Example 1.

[0067] Example 4

[0068] The preparation steps of modified carbon fiber are as follows:

[0069] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.3 mbar. Air is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 3 min.

[0070] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 15×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0071] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF and rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0072] After the epoxy resin and the modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 124.21 MPa, which was 44.40% higher than that of the unmodified interface shear strength of Comparative Example 1.

[0073] Example 5

[0074] The preparation steps of modified carbon fiber are as follows:

[0075] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Air is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 5 min.

[0076] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 10×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0077] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF and rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0078] After the epoxy resin and the modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 116.46 MPa, which was 35.39% higher than that of the unmodified interface shear strength of Comparative Example 1.

[0079] Example 6

[0080] The preparation steps of modified carbon fiber are as follows:

[0081] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Air is used as the plasma gas medium, the gas flow rate is 8 sccm, the processing power is 300 W, and the processing time is 9 min.

[0082] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 6×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0083] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF and rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0084] After the epoxy resin and the modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 135.63 MPa, which was 57.67% higher than that of the unmodified interface shear strength of Comparative Example 1.

[0085] Example 7

[0086] The preparation steps of modified carbon fiber are as follows:

[0087] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Air is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 9 min.

[0088] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 10×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0089] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF and rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0090] After the epoxy resin and the modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 140.73 MPa, which was 63.60% higher than that of the unmodified interface shear strength of Comparative Example 1.

[0091] Example 8

[0092] The preparation steps of modified carbon fiber are as follows:

[0093] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.3 mbar. Air is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 9 min.

[0094] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 15×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0095] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF and rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0096] After the epoxy resin and the modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 137.85 MPa, which was 60.25% higher than that of the unmodified interface shear strength of Comparative Example 1.

[0097] Comparative Example 1

[0098] The unmodified carbon fiber and epoxy resin were heated and cured and then subjected to a micro-debonding test, and the interface shear strength was found to be 86.02 MPa.

[0099] The carbon fiber obtained above has not been modified, and its interface bonding performance with epoxy resin is poor.

[0100] Comparative Example 2

[0101] (1) Carbon fiber surface plasma treatment. The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Air is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 1 min. The plasma-modified carbon fiber is obtained.

[0102] The plasma-modified carbon fiber and epoxy resin were heated and cured and then subjected to a micro-debonding test, and the interface shear strength was found to be 95.09 MPa, which was 10.54% higher than that of the unmodified carbon fiber in comparative example 1.

[0103] The carbon fibers obtained above have not been subjected to surface grafting treatment, and only have limited improvement in the interface bonding performance between the fibers and the epoxy resin after being subjected to plasma treatment.

[0104] Comparative Example 3

[0105] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Air is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 15 min.

[0106] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 10×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0107] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF and rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0108] After the epoxy resin and modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 95.68MPa, which was 11.23% higher than that of the unmodified interface shear strength.

[0109] The carbon fibers obtained above are severely damaged due to the long plasma treatment time and are therefore not suitable as reinforcing materials.

[0110] Comparative Example 4

[0111] (1) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 2×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0112] (2) Carbon fiber surface grafting treatment. The carbon fiber was placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction, it was rinsed once with solvent DMF and three times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain the modified carbon fiber.

[0113] The modified carbon fiber and epoxy resin were heated and cured and then subjected to a micro-debonding test, and the interface shear strength was found to be 96.53 MPa, which was 12.22% higher than that of the unmodified carbon fiber.

[0114] The carbon fiber obtained above has not been subjected to plasma treatment, and only has been subjected to surface grafting treatment, which results in limited improvement in the interface bonding performance between the fiber and the epoxy resin.

[0115] Comparative Example 5

[0116] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Argon is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 0.5 min.

[0117] (2) Prepare PAMAM / DMF solution. Dissolve PAMAM in DMF to a concentration of 2×10 -4 mol / L PAMAM / DMF solution was ultrasonicated for 5 min, and then condensation agent HATU was added at a ratio of 45 mg per 270 mL of solution, and ultrasonicated for 5 min.

[0118] (3) Carbon fiber surface grafting treatment. The carbon fiber treated with plasma in step (1) is placed in the prepared PAMAM / DMF solution and placed in a dryer to react for 4 hours at room temperature. After the reaction is completed, it is rinsed once with solvent DMF and rinsed 3 times with deionized water, and then placed in a vacuum drying oven at 50°C for 24 hours to obtain modified carbon fiber.

[0119] After the epoxy resin and modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 98.45 MPa, which was 14.45% higher than that of the unmodified interface shear strength.

[0120] The carbon fiber obtained above uses argon as the plasma gas medium, and the improvement of the interface bonding performance is limited.

[0121] Comparative Example 6

[0122] (1) Carbon fiber surface plasma treatment: The carbon fiber is placed in a plasma chamber, and the chamber is evacuated to a vacuum pressure of 0.25 mbar. Air is used as the plasma gas medium, the gas flow rate is 7 sccm, the processing power is 300 W, and the processing time is 0.5 min.

[0123] (2) Preparation of a xylene solution of maleic anhydride: Dissolve 7 g of maleic anhydride in 100 mL of xylene in a 60° C. water bath to obtain a xylene solution of maleic anhydride.

[0124] (3) Carbon fiber surface grafting treatment. Place the carbon fiber treated with plasma in step (1) in a prepared maleic anhydride xylene solution, ultrasonicate for 30 minutes, then wrap the carbon fiber with tin foil, place it in a high-temperature oven at 170°C, react for 7 minutes and then cool to obtain a crude carbon fiber grafted with maleic anhydride on the plasma treatment. Add the obtained crude carbon fiber to the precipitant acetone and let it stand for 24 hours, pour off the solvent, dissolve it with xylene, and pour it into acetone for precipitation after dissolution, repeat twice; then, evaporate most of the solvent under an infrared lamp, and then vacuum dry it at 50°C to constant weight to obtain grafted maleic anhydride carbon fiber.

[0125] After the epoxy resin and modified carbon fiber were heated and cured, a micro-debonding test was performed, and the interface shear strength was 100.45 MPa, which was 16.78% higher than that of the unmodified interface shear strength.

[0126] The carbon fiber obtained above is surface-grafted with maleic anhydride, and the improvement of the interface bonding performance is limited.

[0127] It is found from Examples 1 to 8 that when the plasma treatment time of the carbon fiber is 9 min, the concentration of the PAMAM / DMF solution in the surface grafting treatment is 10×10 -4 mol / L, the interface shear strength of carbon fiber reinforced epoxy resin composite material is the highest, which is 140.73MPa, which is 63.60% higher than the interface shear strength of untreated carbon fiber of 86.02MPa. The composite board made by compression molding of treated carbon fiber and epoxy resin has the best interface bonding performance and the most obvious improvement in interface performance.

[0128] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing modified carbon fiber, characterized in that: The following steps are involved: Using air as a plasma gas medium, the carbon fiber is subjected to plasma treatment to obtain a plasma surface-modified carbon fiber; The plasma surface modified carbon fiber is immersed in a polyamide-amine dendritic macromolecule PAMAM solution for reaction to obtain the modified carbon fiber.

2. The method for preparing modified carbon fiber according to claim 1, characterized in that: The plasma treatment is specifically as follows: placing the carbon fiber in a vacuum plasma vacuum chamber, evacuating the vacuum chamber to a pressure of 0.2-0.5 mbar, with a treatment power of 100-300 W, a gas flow rate of 5-10 sccm, and a treatment time of 0.5-10 min.

3. The method for preparing modified carbon fiber according to claim 1, characterized in that: The concentration of the PAMAM solution is 2×10 -4 mol / L—20×10 -4 mol / L.

4. The method for preparing modified carbon fiber according to claim 1, characterized in that: The reaction temperature is room temperature and the reaction time is 4 hours.

5. The method for preparing modified carbon fiber according to claim 1, characterized in that: After the reaction is completed, the steps of washing and drying are also included.

6. A modified carbon fiber prepared by the preparation method according to any one of claims 1 to 5.

7. A method for improving the interfacial bonding performance of carbon fiber reinforced epoxy resin-based composite materials, characterized in that: The carbon fiber is modified by the preparation method described in any one of claims 1 to 5.

8. A carbon fiber reinforced epoxy resin-based composite material, characterized in that: The raw materials include the modified carbon fiber according to claim 6 and epoxy resin.

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