Microwave-assisted nanowelding modification method, modified carbon fiber and application thereof

Abstract

The application discloses a microwave-assisted nano welding modification method, modified carbon fibers and application thereof, and relates to the field of composite material surface modification.The microwave-assisted nano welding modification method provided by the application firstly constructs a three-layer structure of carbon fiber-polymer coating-conductive nano material layer on the surface of the carbon fiber from inside to outside, and then the carbon fiber is treated by microwave irradiation, so that the polymer coating in the middle of the three-layer structure is firstly melted and then carbonized, the conductive nano material is firstly embedded into the molten polymer coating, then the polymer coating is carbonized to form amorphous carbon, the surface of the carbon fiber can be epitaxially grown, and the conductive nano material is firmly welded on the surface of the carbon fiber, and the activation of the surface of the carbon fiber is realized.

Description

Technical Field

[0001] This invention relates to the field of surface modification of composite materials, specifically to a microwave-assisted nano-welding modification method, modified carbon fibers, and their applications. Background Technology

[0002] Carbon fiber (CF) is a high-performance carbon fiber widely used as a reinforcing material for polymer matrices. Carbon fiber reinforced polymer (CFRP) composites, composed of carbon fibers and a polymer matrix, possess high strength, high specific modulus, and high thermal stability, thus showing broad application prospects in aerospace, automotive, military, and concrete industries. However, the surface of carbon fibers has almost no active groups, resulting in high surface inertness and poor wettability. This leads to poor bonding ability with the polymer matrix when used for reinforcement, limiting the application of carbon fibers in reinforced composites and hindering its development.

[0003] Doping the surface of carbon fibers with heteroatoms is a feasible method to activate carbon fibers and improve the compatibility between carbon fibers and polymer matrices. This is because introducing heteroatoms can generate polar modified groups on the carbon fiber surface, which, according to the principle of like compatibility, can improve the bonding ability between carbon fibers and polymer matrices. However, carbon fiber is a fibrous material composed of carbon elements, with a carbon content generally exceeding 90%. Furthermore, the surface of carbon fibers is mostly composed of amorphous carbon and graphitic carbon, which have poor reactivity, making surface activation of carbon fibers extremely difficult.

[0004] Existing technology discloses a method for preparing carbon fiber reinforced 17-4PH high-strength steel composites using SLM molding. First, the carbon fibers are etched using a strong oxidant KClO3 and a strong acid NH3SO3H. Then, the carbon fibers are immersed in aminosilane, ensuring the etched carbon fiber surface is wetted with aminosilane. Finally, the carbon fibers are subjected to microwave treatment at 850W for 30–50 minutes, which supposedly improves the bonding ability between the carbon fibers and the 17-4PH high-strength steel matrix. However, the aminosilane used in this prior art actually acts as an adhesive and cannot activate the carbon fibers or increase the number of active groups on the carbon fiber surface. Summary of the Invention

[0005] To address the challenge of activating carbon fiber surfaces using existing technologies, this invention provides a microwave-assisted nano-welding modification method. First, a three-layer structure is constructed on the carbon fiber surface, consisting of carbon fiber, a polymer coating, and a conductive nanomaterial coating, arranged sequentially from the inside out. Then, microwave irradiation is applied to the carbon fiber, causing the polymer coating in the middle of the three layers to melt and then carbonize, firmly welding the conductive nanomaterials to the carbon fiber surface and thus activating the carbon fiber surface.

[0006] Another object of the present invention is to provide a modified carbon fiber.

[0007] Another object of the present invention is to provide an application of modified carbon fiber in the preparation of carbon fiber reinforced composite materials.

[0008] Another object of the present invention is to provide a carbon fiber reinforced composite material.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution:

[0010] A microwave-assisted nano-welding modification method includes the following steps:

[0011] S1. Preparation of microwave-modified carbon fiber precursor:

[0012] A polymer layer is formed on the surface of carbon fiber, and then conductive nanomaterials are loaded on the surface of the polymer layer to obtain a microwave-modified carbon fiber precursor.

[0013] The polymer layer has a lower melting point than the carbon fiber and the conductive nanomaterial, wherein the conductive nanomaterial is arbitrarily selected from one or more of MXene, carbon nanotubes, graphene, and carbon black;

[0014] S2. Microwave surface modification:

[0015] The carbon fiber precursor before microwave modification is subjected to microwave irradiation, which embeds the conductive nanomaterial into the polymer layer and completely carbonizes the polymer layer. After the microwave irradiation is stopped, surface-modified carbon fiber can be obtained.

[0016] In a specific embodiment of the present invention, the polymer in step S1 can be arbitrarily selected from one or more of polydopamine, polypyrrole, polyaniline, polyacrylonitrile, and polyacrylate, and the melting point of the above polymers is lower than that of carbon fiber and conductive nanomaterials.

[0017] After forming a polymer layer on the surface of carbon fiber, and then loading conductive nanomaterials onto the surface of the polymer layer, the resulting carbon fiber can have a three-layer structure from the inside out, consisting of carbon fiber-polymer coating-conductive nanomaterial layer.

[0018] Both carbon fiber and the conductive nanomaterials used in this invention are excellent microwave absorbing materials. Therefore, when the carbon fiber with the above-mentioned three-layer structure is irradiated with microwaves, both the carbon fiber and the conductive nanomaterials can quickly absorb microwaves and generate a large amount of heat in a short time, causing their own temperature to rise rapidly. In particular, the temperature of the carbon fiber body can reach over 1000°C within 5 seconds. During the heating process of the carbon fiber body and the conductive nanomaterials, the polymer coating sandwiched between the two undergoes a process of melting followed by carbonization. During melting, the conductive nanomaterials are encapsulated and embedded into the molten and liquefied polymer coating. Then, during carbonization, the polymer coating is transformed into amorphous carbon in situ. Since the surface of the carbon fiber is also mainly composed of amorphous carbon, the carbonization process of the polymer coating can also be regarded as an epitaxial growth process on the carbon fiber surface. At this time, the conductive nanomaterials that have already been embedded in the previously molten polymer coating are firmly welded to the carbon fiber surface.

[0019] One or more of MXene, carbon nanotubes, graphene, and carbon black are used as conductive nanomaterials because these materials possess excellent wave absorption properties, capable of absorbing electromagnetic waves and converting them into heat energy, while also being resistant to decomposition. Therefore, using these conductive nanomaterials to prepare a coating allows for a "sandwich" heating of the polymer coating on the carbon fiber surface; that is, the carbon fiber and the conductive nanomaterial coating simultaneously heat the polymer coating from both sides, allowing the polymer coating to melt first and then carbonize. Simultaneously, the surfaces of these conductive nanomaterials possess abundant active groups (e.g., MXene has -OH, -F, and -O groups). Welding these conductive nanomaterials onto the carbon fiber surface introduces these active groups, thus activating and modifying the carbon fiber. Furthermore, the introduction of these conductive nanomaterials increases the surface roughness of the carbon fiber. This increased roughness, along with the increased active groups on the carbon fiber surface, enhances the bond strength between the carbon fiber and the polymer matrix when used to prepare carbon fiber reinforcement materials.

[0020] Preferably, the power of the microwave irradiation in step S2 is 700-900W.

[0021] If the microwave power is too low, the heating rate will be slow, making it difficult to carry out the above-mentioned melting-carbonization process; if the microwave power is too high, the heating rate will be too fast, preventing the polymer coating from melting and carbonizing directly, thus affecting the processing effect. If the polymer coating is carbonized directly, the step of embedding conductive nanomaterials into the molten polymer coating is omitted. The conductive nanomaterials are merely coated on the carbon fiber surface and cannot be firmly welded, thus making it impossible to carry out efficient modification treatment on the carbon fiber surface.

[0022] Preferably, the microwave irradiation time in step S2 is 5 to 12 seconds.

[0023] If the microwave treatment time is too short, the heating process of the carbon fiber body and conductive nanomaterials is limited, and the polymer coating cannot be completely carbonized; if the microwave treatment time is too long, the entire system will be in a high-temperature state for too long, causing the thermally unstable conductive nanomaterials, especially MXene, to decompose.

[0024] Preferably, the polymer layer formed on the carbon fiber surface in step S1 is formed by in-situ polymerization.

[0025] A polymer layer is formed on the surface of carbon fibers using in-situ polymerization. Specifically, the operation can involve immersing the carbon fibers in a monomer solution, adding an initiator to initiate the polymerization reaction of the monomers on the carbon fiber surface (e.g., to form a polydopamine layer on the carbon fiber surface via in-situ polymerization, the carbon fibers can be immersed in a dopamine solution, and an initiator can be added to polymerize the dopamine on the carbon fiber surface to form a polydopamine layer). In a specific embodiment of the invention, before immersing the carbon fibers in the polymer monomer solution, the carbon fibers can be washed in a Soxhlet extractor containing acetone and then dried after washing; after the reaction, the carbon fibers can also be washed and dried to remove unreacted polymer monomers and initiators from the carbon fiber surface; the polymer monomers in the monomer solution can be arbitrarily selected from one or more of dopamine, pyrrole, aniline, acrylonitrile, and acrylates, and when the polymer monomer is dopamine, the pH of the system needs to be adjusted to 8-10 before the reaction; the initiator in the reaction system can be arbitrarily selected from one or more of oxygen, ammonium persulfate, hydrogen peroxide, and benzoyl peroxide.

[0026] In-situ polymerization is used to form a polymer layer on the surface of carbon fiber. Compared with the method of directly coating a polymer layer on the surface of carbon fiber, the polymer coating has the advantages of being more uniform and firm.

[0027] More preferably, the reaction time for the in-situ polymerization is 2 to 48 hours.

[0028] Controlling the in-situ polymerization time of monomers on the carbon fiber surface is crucial for obtaining a polymer coating that completely covers the fiber surface and is of moderate and uniform thickness. Too short a reaction time results in incomplete coating coverage of the fiber surface; too long a reaction time leads to an excessively thick polymer layer, which is detrimental to improving the interfacial properties of carbon fiber reinforced composites.

[0029] More preferably, the concentration of the monomer solution is 1–15 mg / mL.

[0030] More preferably, the reaction temperature for in-situ polymerization is 0–50°C.

[0031] By controlling the reaction temperature within the above range, the polymerization reaction of the monomers can proceed at a suitable rate, and a sufficiently uniform polymer coating can be formed on the carbon fiber surface.

[0032] Preferably, in step S1, the conductive nanomaterials are loaded onto the surface of the polymer layer by impregnation, and the impregnation time is 0.5 to 1 hour.

[0033] A layer of conductive nanomaterials is loaded onto the polymer layer surface of carbon fibers using an impregnation method. The loading amount of conductive nanomaterials on the carbon fibers can be controlled by adjusting the impregnation time. The impregnation time is controlled to 0.5–1 hour because if the reaction time is too short, the conductive nanomaterial slurry cannot fully penetrate into the interior of the carbon fiber bundle, resulting in insufficient adhesion of conductive nanomaterials to the fiber surface inside the bundle and an uneven coating. When the reaction time is 1 hour, the conductive nanomaterials can completely penetrate and submerge the fibers; extending the impregnation time further will not significantly improve the loading effect of the nanomaterials.

[0034] In a specific embodiment of the present invention, to load conductive nanomaterials onto the polymer layer on the surface of carbon fibers using an impregnation method, it is necessary to first prepare a conductive nanomaterial slurry. This slurry is obtained by dissolving the conductive nanomaterials in a dispersant and then sonicating it at a power of 0-500W for 30 minutes to 2 hours. The dispersant can be any one or more of water, ethanol, or acetone. The specific operation of uniformly dispersing the carbon fibers with the polymer layer on their surface in the conductive nanomaterial slurry can be as follows: after adding the carbon fibers to the slurry, sonicate them for 1-3 minutes. After impregnation, the carbon fibers can be dried, and then re-impregnated into the conductive nanomaterial slurry. Repeating this impregnation and drying process yields carbon fibers with a uniform conductive nanomaterial coating on their surface.

[0035] More preferably, the concentration of the conductive nanomaterial slurry is 1–10 mg / mL.

[0036] More preferably, the temperature of the impregnation reaction is 0–50°C.

[0037] By controlling the temperature of the carbon fiber impregnation reaction in the conductive nanomaterial slurry to be between 0 and 50°C, the loading of the conductive nanomaterial can proceed at a suitable rate, forming a sufficiently uniform layer of conductive nanomaterial.

[0038] Preferably, when the conductive nanomaterial is a carbon nanotube, the diameter of the carbon nanotube is 8–15 μm.

[0039] Preferably, when the conductive nanomaterial is MXene and / or graphene, the sheet diameter of the MXene and graphene is 1 to 5 μm.

[0040] This invention also protects a carbon fiber modified by the above-described microwave-assisted nano-welding modification method.

[0041] This invention also protects the use of the above-mentioned modified carbon fibers in the preparation of carbon fiber reinforced composite materials.

[0042] The present invention also protects a carbon fiber reinforced composite material comprising a polymer matrix and the aforementioned modified carbon fibers.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] After modifying carbon fibers using the microwave-assisted nano-welding modification method provided by this invention, the carbon fiber reinforced material prepared from the obtained carbon fibers has an ILSS that is at least 18 MPa higher than that prepared from carbon fibers coated only with polymers and conductive nanomaterials. Furthermore, after ultrasonic treatment for 30 minutes, the conductive nanomaterials on the surface of the obtained carbon fibers remain firmly attached to the carbon fiber surface, indicating that the modification method provided by this invention can indeed activate and modify the surface of carbon fibers, and the activation effect is excellent and stable. Attached Figure Description

[0045] Figure 1 This is a SEM image of the modified carbon fiber obtained in Example 1 of the present invention.

[0046] Figure 2 The images show SEM images of the modified carbon fibers obtained in Example 1 and Comparative Example 1 after 30 minutes of ultrasonication. The left image corresponds to Comparative Example 1, and the right image corresponds to Example 1. Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0048] Example 1

[0049] A microwave-assisted nano-welding modification method includes the following steps:

[0050] S1. Preparation of microwave-modified carbon fiber precursor:

[0051] A polydopamine layer was formed on the surface of carbon fibers: carbon fibers were immersed in a dopamine monomer solution with a concentration of 2 mg / mL, the pH of the system was controlled at 8, oxygen was introduced as an initiator, and the reaction was carried out at room temperature for 24 h, so that the dopamine monomer was polymerized in situ on the carbon fiber surface to form a polydopamine layer; then conductive nanomaterials were loaded on the surface of the polydopamine layer: carbon fibers with a polydopamine coating were uniformly dispersed in an MXene slurry with a concentration of 2 mg / mL at room temperature and impregnated for 1 h to obtain a carbon fiber precursor before microwave modification; the melting point of the polydopamine layer was lower than that of carbon fibers and MXene.

[0052] S2. The microwave-modified carbon fiber precursor obtained in step S1 is irradiated with a microwave power of 800W for 10s to obtain modified carbon fiber.

[0053] The MXene in step S1 has a sheet diameter of 2.5 μm.

[0054] Example 2

[0055] A microwave-assisted nano-welding modification method, which differs from Example 1 in that:

[0056] S1. Preparation of microwave-modified carbon fiber precursor:

[0057] A polyaniline layer is formed on the surface of carbon fibers: carbon fibers are immersed in a 9 mg / mL aniline monomer solution, ammonium persulfate is added as an initiator, and the reaction is carried out at 0°C for 6 h to allow the aniline monomer to polymerize in situ on the carbon fiber surface to form a polyaniline layer; then conductive nanomaterials are loaded onto the surface of the polyaniline layer: carbon fibers with a polyaniline coating are uniformly dispersed in a 0.2 mg / mL carbon nanotube slurry at room temperature;

[0058] The carbon nanotubes described in step S2 have a diameter of 12 μm.

[0059] Example 3

[0060] A microwave-assisted nano-welding modification method, which differs from Example 1 in that:

[0061] S2. Irradiation is performed using microwaves with a power of 700W.

[0062] Example 4

[0063] A microwave-assisted nano-welding modification method, which differs from Example 1 in that:

[0064] S2. Irradiation is performed using microwaves with a power of 900W.

[0065] Example 5

[0066] A microwave-assisted nano-welding modification method, which differs from Example 1 in that:

[0067] S2. The microwave irradiation treatment time is 5 seconds.

[0068] Example 6

[0069] A microwave-assisted nano-welding modification method, which differs from Example 1 in that:

[0070] S2. The microwave irradiation treatment time is 12s.

[0071] Comparative Example 1

[0072] A method for modifying the surface of carbon fibers, wherein the difference from Example 1 is:

[0073] S2 is not performed.

[0074] Performance testing

[0075] ILSS (Interlaminar Shear Strength) Test: The modified carbon fibers obtained in Examples 1-6 of this invention and Comparative Example 1 were mixed with a polymer matrix to prepare carbon fiber reinforced composite materials, and the ILSS data of the composite materials were measured.

[0076] Performance test data are shown in Table 1 below. Figures 1-2 As shown:

[0077] Table 1. ILSS data of the examples and comparative examples

[0078] Example ILSS (MPa) Example 1 50.26 Example 2 54.23 Comparative Example 1 32.33

[0079] Note: The ILSS data of Examples 3 to 6 are similar to those of Example 1 in Table 1 above.

[0080] As shown in Table 1, the carbon fiber reinforced composite material obtained by reinforcing the polymer matrix with the modified carbon fiber obtained by the modification method provided in this invention has an ILSS that is at least 18 MPa higher than that prepared from carbon fiber reinforced composite material prepared from carbon fiber without modification by this method (reaching 50.26 MPa in Example 1). This indicates that the modified carbon fiber provided in this invention has a stronger bonding force with the polymer matrix, thus proving that the modified carbon fiber provided in this invention has more active groups on its surface and that the carbon fiber surface can be successfully activated. Data from Examples 1, 3-6 show that when the carbon fiber is modified using the microwave-assisted nano-welding modification method provided in this invention, and the microwave irradiation power and time are within the preferred ranges of 700-900 W and 5-12 s respectively, the finally modified carbon fiber, when used to make carbon fiber reinforced composite material, exhibits excellent bonding ability with the polymer matrix, with ILSS data around 50.26 MPa. This indicates that modifying the carbon fiber surface using the method provided in this invention can activate the carbon fiber surface, thus improving the bonding ability between the carbon fiber and the polymer matrix. When the microwave power is below 700W, the heating rate during microwave irradiation is slow, making it difficult for the polymer layer on the carbon fiber surface to melt and carbonize. Even with extended microwave irradiation time, the polymer layer is difficult to completely carbonize, resulting in low activation of the carbon fiber. This has very limited effect on improving ILSS when used to prepare carbon fiber reinforced composites. When the microwave power is above 900W, the heating rate is too fast, and the polymer layer does not have enough time to melt and carbonize directly. This results in the omission of the step of embedding conductive nanomaterials into the molten polymer coating. The conductive nanomaterials are merely coated on the carbon fiber surface and cannot be firmly welded, which can easily lead to a decrease in the bonding ability between the carbon fiber and the polymer matrix (manifested as a decrease in ILSS). When the microwave treatment time is less than 5s, the heating process of the carbon fiber body and conductive nanomaterials is not complete, resulting in incomplete carbonization of the polymer layer and a decrease in the activation of the carbon fiber surface. When the microwave treatment time is more than 12s, the entire system remains at a high temperature for too long, making the conductive nanomaterials prone to decomposition, and the activation of the carbon fiber surface also decreases.

[0081] Figure 1 This is a SEM image of the modified carbon fiber obtained in Example 1 of the present invention. From... Figure 1 As can be seen from the above, the microwave-assisted nano-welding modification method provided by this invention can be used to modify carbon fibers, resulting in a structure in which conductive nanomaterial MXene coats the carbon fibers, indicating that this invention can successfully activate carbon fibers.

[0082] Figure 2The images show SEM images of the modified carbon fibers obtained in Example 1 and Comparative Example 1 after 30 minutes of ultrasonication, with the left image corresponding to Comparative Example 1 and the right image corresponding to Example 1. Figure 2 As can be seen, the conductive nanomaterials successfully embedded in the carbon fiber surface by the microwave-assisted nano-welding modification method provided by this invention remain firmly attached to the carbon fiber surface after 30 minutes of ultrasonication. This indicates that the modification method provided by this invention can not only successfully activate carbon fiber, but also achieve a strong and stable activation effect.

[0083] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A microwave-assisted nano-welding modification method, characterized in that, Includes the following steps: S1. Preparation of microwave-modified carbon fiber precursor: A polymer layer is formed on the surface of carbon fiber, and then conductive nanomaterials are loaded on the surface of the polymer layer to obtain a microwave-modified carbon fiber precursor. The polymer layer has a lower melting point than the carbon fiber and the conductive nanomaterial, wherein the conductive nanomaterial is arbitrarily selected from one or more of MXene, carbon nanotubes, graphene, and carbon black; S2. Microwave surface modification: Microwave irradiation is performed on the carbon fiber precursor before microwave modification to embed the conductive nanomaterial into the polymer layer and completely carbonize the polymer layer. After microwave irradiation is stopped, modified carbon fiber can be obtained. The power of microwave irradiation in step S2 is 700~900 W; the duration of microwave irradiation in step S2 is 5~12 s.

2. The microwave-assisted nano-welding modification method as described in claim 1, characterized in that, The polymer layer formed on the carbon fiber surface in step S1 is produced by in-situ polymerization.

3. The microwave-assisted nano-welding modification method as described in claim 1, characterized in that, In step S1, the conductive nanomaterials are loaded onto the surface of the polymer layer by impregnation, and the impregnation time is 0.5 to 1 h.

4. The microwave-assisted nano-welding modification method as described in claim 1, characterized in that, When the conductive nanomaterial is a carbon nanotube, the diameter of the carbon nanotube is 8~15μm.

5. The microwave-assisted nano-welding modification method as described in claim 1, characterized in that, When the conductive nanomaterial is MXene and / or graphene, the sheet diameter of MXene and graphene is 1~5μm.

6. A modified carbon fiber obtained by the microwave-assisted nano-welding modification method according to any one of claims 1 to 5.

7. The use of the modified carbon fiber according to claim 6 in the preparation of carbon fiber reinforced composite materials.

8. A carbon fiber reinforced composite material, characterized in that, It includes a polymer matrix and the modified carbon fiber as described in claim 6.

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