A modified carbon fiber, a carbon fiber-reinforced thermoplastic resin composite material, and a method for producing the same

Abstract

The application belongs to the field of carbon fiber surface modification and carbon fiber composite material preparation, and discloses a modified carbon fiber, a carbon fiber reinforced thermoplastic resin composite material and a preparation method thereof. The modified carbon fiber is wrapped with a polydopamine carbon layer, a metal nanoparticle layer with magnetic loss or dielectric loss to electromagnetic waves and an ANF layer from inside to outside on the surface of the carbon fiber. The preparation method comprises the following steps: (1) fully immersing the carbon fiber in a weak alkaline dopamine / Tris-HCl aqueous solution; (2) fully immersing the carbon fiber in a metal salt solution, drying after taking out, and then calcining at 400-900 DEG C for 1-4 h in an inert or protective atmosphere to obtain a modified carbon fiber intermediate; (3) using aramid nanofiber as raw material, preparing an ANF / DMSO dispersion liquid by alkali solution deprotonation method; fully immersing the modified carbon fiber intermediate in the ANF / DMSO dispersion liquid, drying after taking out, and then obtaining the modified carbon fiber. The application improves the interfacial compatibility between the CF and the thermoplastic resin, and effectively improves the electromagnetic stealth performance of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber surface modification and carbon fiber composite material preparation, specifically relating to a modified carbon fiber, a carbon fiber reinforced thermoplastic resin composite material and its preparation method. Background Technology

[0002] Carbon fiber (CF), due to its lightweight and high strength, is widely used as a reinforcement in aerospace, automotive lightweighting, and sporting equipment. In recent years, compared to traditional thermosetting resins, CF-reinforced thermoplastic resin (CFRTP) composites have attracted considerable attention due to their short processing cycle and reusability. Simultaneously, given the complexity of high-performance composite material applications, in addition to requiring high mechanical properties, higher demands are placed on the structural-functional integration of CFRTP composites. Especially in the military field, the low surface chemical activity of CF leads to poor interfacial compatibility and impedance mismatch in CFRTP composites, resulting in weak electromagnetic wave absorption performance. Furthermore, the high conductivity of CF leads to strong electromagnetic wave reflection, resulting in poor electromagnetic stealth performance. Therefore, exploring the interfacial electromagnetic modification mechanism of CF to improve the combat performance of weaponry and equipment, and thus enhancing the electromagnetic stealth performance of CFRTP composites, is an urgent requirement. Summary of the Invention

[0003] To address the problems of poor interfacial compatibility, impedance mismatch, and poor electromagnetic stealth performance in existing CFRTP composite materials, the present invention aims to provide a modified carbon fiber, a carbon fiber reinforced thermoplastic resin composite material, and a method for preparing the same.

[0004] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows: A modified carbon fiber, wherein the surface of the carbon fiber is sequentially coated from the inside out with a polydopamine carbon layer, a metal nanoparticle layer with magnetic or dielectric loss to electromagnetic waves, and an ANF (aramid nanofiber) layer; the metal nanoparticle layer is one or more of elemental metals, metal oxides, and metal alloys. The polydopamine carbon layer is formed by carbonizing polydopamine.

[0005] Preferably, the metal nanoparticle layer that has magnetic or dielectric loss to electromagnetic waves is one or more of Fe, Ni, Co, NiCo alloy, FeNiCo alloy, Fe3O4, NiFe2O4, MnFe2O4, MnO, ZnO, and TiO2.

[0006] A method for preparing modified carbon fiber, comprising the following steps: (1) The desized or unsized carbon fiber is fully impregnated in a weakly alkaline dopamine / Tris-HCl aqueous solution; wherein, the concentration of dopamine in the weakly alkaline dopamine / Tris-HCl aqueous solution is 0.5~3mg / mL; (2) The carbon fibers obtained after impregnation in step (1) are fully impregnated in a metal salt solution, taken out and dried, and then calcined at 400~900℃ for 1~4h under an inert or protective atmosphere to obtain a modified carbon fiber intermediate; wherein, the metal salt is a water-soluble metal salt corresponding to the metal element in the metal particle layer that has magnetic loss or dielectric loss of electromagnetic waves, and the total metal concentration of the metal salt solution is 0.05~1mol / L based on the metal element provided by it. (3) Using aramid nanofibers as raw materials, an ANF / DMSO dispersion was prepared by alkaline dissolution and deprotonation method; the modified carbon fiber intermediate obtained in step (2) was fully impregnated in the ANF / DMSO dispersion, and then dried to obtain the modified carbon fiber; wherein the concentration of the ANF / DMSO dispersion was 2~5 mg / mL.

[0007] Preferably, in step (1), the pH of the weakly alkaline dopamine / Tris-HCl aqueous solution is 8 to 9.

[0008] Preferably, in step (1), the weakly alkaline dopamine / Tris-HCl aqueous solution is prepared according to the following process: first, a Tris-HCl aqueous solution with a concentration of 0.5~5 mg / mL is prepared, then dopamine is gradually added to the Tris-HCl aqueous solution until the dopamine concentration is 0.5~5 mg / mL, and then a NaOH solution with a concentration of 20~200 mg / mL is added to adjust the pH of the system to weakly alkaline.

[0009] Preferably, in step (2), the metal salt is one or more of metal chlorides, nitrates, and sulfates.

[0010] Preferably, in step (3), the ANF / DMSO dispersion is prepared according to the following process: aramid nanofibers, DMSO solution and strong alkali solution are mixed evenly and then ball-milled to obtain the ANF / DMSO dispersion; wherein, the raw material ratio is aramid nanofibers∶DMSO∶strong alkali solution = (0.2~0.5)g∶100mL∶(5~10)mL; the concentration of the strong alkali solution is 0.2~0.4mmol / L, and the strong alkali solution is NaOH solution or KOH solution.

[0011] Preferably, in step (1), the carbon fibers in the desized carbon fibers and unsized carbon fibers are continuous carbon fibers or short-cut carbon fibers; when the carbon fibers in the desized carbon fibers and unsized carbon fibers are continuous carbon fibers, the impregnation methods involved in steps (1), (2) and (3) are all static impregnation; when the carbon fibers in the desized carbon fibers and unsized carbon fibers are short-cut carbon fibers, the impregnation method in step (1) is to first ultrasonically treat for 10~20 min, and then stir at low speed of 20~100 rpm for 6~12 h, the impregnation method in step (2) is to stir at low speed of 20~100 rpm for 1~2 h, and the impregnation method in step (3) is to stir at low speed of 20~100 rpm for 5~10 min.

[0012] A method for preparing carbon fiber reinforced thermoplastic resin composite material using the modified carbon fiber, comprising the following steps: (1) When the modified carbon fiber is obtained by modifying short carbon fiber, the modified carbon fiber is directly melt-blended with thermoplastic resin and extruded into granules to obtain composite granules; When the modified carbon fiber is obtained based on continuous carbon fiber modification, the modified carbon fiber is first cut, and then melt-blended and extruded with thermoplastic resin to obtain composite granules. (2) The composite granules obtained in step (1) are injection molded or hot-pressed to obtain carbon fiber reinforced thermoplastic resin composite material; wherein, by mass ratio, the raw material ratio is modified carbon fiber: thermoplastic resin = a: (100-a), and the value of a ranges from 5 to 30.

[0013] Preferably, the thermoplastic resin is one or more of nylon, polyimide, and polycarbonate; during melt blending extrusion granulation, the screw speed is 40~60 r / min; the conditions for injection molding or hot pressing are: holding temperature of 200~300℃, holding time of 5~60 min, and holding pressure of 30~100 bar.

[0014] In this invention, the presence of ANF not only effectively compensates for the negative effects of reduced mechanical properties of the composite material caused by the thermal reduction process, but also further improves the interfacial compatibility between the modified CF and the thermoplastic resin. Therefore, the addition of ANF and the selection of the ANF / DMSO dispersion concentration have a significant impact on the performance of the composite material: when the ANF concentration in the ANF / DMSO dispersion is too low, ANF cannot form a complete coating on the CF surface, thus failing to fully exert its function; while when the ANF concentration in the ANF / DMSO dispersion is too high, it will cause CF agglomeration and entanglement, affecting the uniformity of CF dispersion in the thermoplastic resin in the later stages, thereby further affecting the mechanical properties and electromagnetic shielding performance of the resulting composite material. Therefore, selecting an ANF / DMSO dispersion of appropriate concentration is crucial for the modification effect of CF.

[0015] Beneficial Effects: This invention successfully loads metal particles with magnetic or dielectric losses to electromagnetic waves onto the surface of a thermoplastic composite (CF) through high-temperature thermal reduction. The modified CF is then coated with an aramid nanofiber film, effectively improving the stability of the metal particles on the CF surface during processing. This heterogeneous structure, where the aramid nanofiber film encapsulates the metal particles, not only effectively improves the interfacial compatibility between the CF and the thermoplastic resin but also enhances the impedance properties and attenuation ability of the composite material, thus significantly improving its electromagnetic wave absorption performance (electromagnetic stealth performance). The modified CF preparation method of this invention effectively ensures the structural stability of the modified structure under composite material processing conditions, providing an improved approach for preparing CF electromagnetic stealth composite materials with high interfacial compatibility. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the preparation process of modified CF.

[0017] Figure 2 The following are microscopic images of the original carbon fiber and the modified intermediate in Example 1: (a) SEM image of the original carbon fiber; (b) SEM image of polydopamine modified carbon fiber; (c) SEM image of NiCo alloy modified carbon fiber; (d) EDS energy spectrum corresponding to image (c).

[0018] Figure 3 The XPS C 1s spectra of the original CF(a) and ANF@NiCo-CF(b) in Example 1 are shown.

[0019] Figure 4 Microscopic morphology images of the products obtained under different conditions: (a~b) SEM images of ANF@NiCo-CF prepared in Example 1; (c) SEM images of ANF@NiCo-CF prepared in Comparative Example 3; (d) One of the SEM images of ANF@NiCo-CF prepared in Comparative Example 4; (e) Tensile fracture section morphology of the unmodified CF / PA6 composite plate prepared in Comparative Example 5; (f) Tensile fracture section morphology of the modified CF / PA6 composite plate prepared in Example 1.

[0020] Figure 5 The second image (SEM image) shows the microstructure of ANF@NiCo-CF prepared in Comparative Example 4.

[0021] Figure 6 Electromagnetic wave absorption performance diagrams: (a) Unmodified CF / PA6 composite plate prepared in Comparative Example 5; (b) Modified CF / PA6 composite plate prepared in Comparative Example 2; (c) Modified CF / PA6 composite plate prepared in Example 1. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0023] In the following examples and comparative examples, carbon fiber is abbreviated as CF, aramid nanofiber is abbreviated as ANF, and polydopamine is abbreviated as PDA.

[0024] Example 1 A method for preparing modified CF, such as Figure 1 As shown, the steps are as follows: (1) Commercially purchased short-cut carbon fibers were desizing using existing conventional techniques and marked as raw CF. The raw CF was immersed in a dopamine / Tris-HCl aqueous solution with pH 8.5, ultrasonically treated for 15 min, and then stirred and impregnated at a rate of 50 rpm for 12 h. After impregnation, it was taken out to obtain modified CF intermediate 1, which was marked as polydopamine modified CF. The dopamine / Tris-HCl aqueous solution with pH 8.5 was prepared according to the following process: first, a Tris-HCl aqueous solution with a concentration of 2 mg / mL was prepared, then dopamine was gradually added to the Tris-HCl aqueous solution until the dopamine concentration was 2 mg / mL, and then NaOH solution with a concentration of 80 mg / mL was added to adjust the pH of the system to 8.5. (2) The polydopamine-modified CF was immersed in a mixed aqueous solution of NiCl2·6H2O and CoCl2·6H2O (where the molar concentration of NiCl2·6H2O and CoCl2·6H2O was 0.05 mol / L), stirred at 50 rpm for 2 h, removed and placed in an oven to dry, and the dried sample was placed in a tube furnace under an argon atmosphere and calcined at 700 °C for 2 h to obtain modified CF intermediate 2, labeled as NiCo alloy modified CF; (3) Add 200 mL of DMSO solution and 0.6 g of para-ANF to a ball mill jar, then add 12 mL of 0.3 mmol / L NaOH solution. After mixing evenly, ball mill the mixture at 500 rpm for 2 h to obtain an ANF / DMSO dispersion (concentration of 3 mg / mL). Immerse the modified CF intermediate 2 in the ANF / DMSO dispersion and stir at 50 rpm for 5 min. After removing it, place it in an oven to dry to obtain the modified CF, labeled as ANF@NiCo-CF.

[0025] A method for preparing a carbon fiber reinforced thermoplastic resin composite material: The modified CF and PA6 resin prepared in this embodiment are mixed at a mass ratio of 20:80 and then melt-blended and extruded to obtain CF / PA6 composite granules (melt temperature 230℃, screw speed 40rpm, mixing time 10min). The CF / PA6 composite granules are then subjected to a hot pressing process (holding temperature 230℃, holding time 10min, holding pressure 50bar) to obtain a modified CF / PA6 composite board.

[0026] Example 2 The difference from Example 1 is that the calcination temperature in step (2) of the preparation method of modified CF is 600℃; all other aspects are the same as in Example 1.

[0027] Example 3 The difference from Example 1 is that the calcination temperature in step (2) of the preparation method of modified CF is 800℃; all other aspects are the same as in Example 1.

[0028] Comparative Example 1 A method for preparing modified CF, which differs from Example 1 in that no metal layer coating is performed, and the specific steps are as follows: (1) After the commercially available short-cut CF was deslurried using existing conventional technology, it was immersed in a dopamine / Tris-HCl aqueous solution with pH 8.5, ultrasonically treated for 15 min, and then stirred at a rate of 50 rpm for 12 h to obtain modified CF intermediate 1. The dopamine / Tris-HCl aqueous solution with pH 8.5 was prepared according to the following process: first, a Tris-HCl aqueous solution with a concentration of 2 mg / mL was prepared, then dopamine was gradually added to the Tris-HCl aqueous solution until the dopamine concentration was 2 mg / mL, and then NaOH solution with a concentration of 80 mg / mL was added to adjust the pH of the system to 8.5. (2) The CF obtained by modifying CF intermediate 1 is placed in a tube furnace under an argon atmosphere and calcined at 700°C for 2 hours to obtain modified CF intermediate 2. (3) Add 200 mL of DMSO solution and 0.6 g of para-ANF to a ball mill jar, then add 12 mL of 0.3 mmol / L NaOH solution. After mixing evenly, ball mill the mixture at 500 rpm for 2 h to obtain an ANF / DMSO dispersion (concentration of 3 mg / mL). Immerse the modified CF intermediate 2 in the ANF / DMSO dispersion and stir at 50 rpm for 5 min. After removing it, place it in an oven to dry to obtain the modified CF.

[0029] A method for preparing a carbon fiber reinforced thermoplastic resin composite material: The modified CF and PA6 resin prepared in this comparative example are melt-blended and extruded into granules at a mass ratio of 20:80 (melt temperature 230℃, screw speed 40rpm, mixing time 10min) to obtain CF / PA6 composite granules. The CF / PA6 composite granules are then processed by hot pressing (holding temperature 230℃, holding time 10min, holding pressure 50bar) to obtain a modified CF / PA6 composite board.

[0030] Comparative Example 2 A method for preparing modified CF, which differs from Example 1 in that ANF coating is not performed, and the specific steps are as follows; (1) After the commercially available short-cut carbon fibers were desizing using conventional techniques, they were immersed in a pH 8.5 dopamine / Tris-HCl aqueous solution, ultrasonically treated for 15 min, and then stirred at 50 rpm for 12 h to obtain modified CF intermediate 1. The dopamine / Tris-HCl aqueous solution with pH 8.5 was prepared according to the following process: first, a Tris-HCl aqueous solution with a concentration of 2 mg / mL was prepared, then dopamine was gradually added to the Tris-HCl aqueous solution until the dopamine concentration was 2 mg / mL, and then NaOH solution with a concentration of 80 mg / mL was added to adjust the pH of the system to 8.5. (2) The modified CF intermediate 1 was immersed in a mixed aqueous solution of NiCl2·6H2O and CoCl2·6H2O (the molar concentration of NiCl2·6H2O and CoCl2·6H2O was 0.05 mol / L), stirred at 50 rpm for 2 h, removed and placed in an oven to dry, and the dried sample was placed in a tube furnace under an argon atmosphere and calcined at 700℃ for 2 h to obtain the modified CF.

[0031] A method for preparing a carbon fiber reinforced thermoplastic resin composite material: The modified CF and PA6 resin prepared in this comparative example are melt-blended and extruded into granules at a mass ratio of 20:80 (melt temperature 230℃, screw speed 40rpm, mixing time 10min) to obtain CF / PA6 composite granules. The CF / PA6 composite granules are then processed by hot pressing (holding temperature 230℃, holding time 10min, holding pressure 50bar) to obtain a modified CF / PA6 composite board.

[0032] Comparative Example 3 A method for preparing modified CF differs from Example 1 in that: in step (3), the amount of ANF is adjusted to 0.2g, and the concentration of the prepared ANF / DMSO dispersion is 1mg / mL; all other steps are the same as in Example 1.

[0033] A method for preparing a carbon fiber reinforced thermoplastic resin composite material: The modified CF and PA6 resin prepared in this comparative example are melt-blended and extruded into granules at a mass ratio of 20:80 (melt temperature 230℃, screw speed 40rpm, mixing time 10min) to obtain CF / PA6 composite granules. The CF / PA6 composite granules are then processed by hot pressing (holding temperature 230℃, holding time 10min, holding pressure 50bar) to obtain a modified CF / PA6 composite board.

[0034] Comparative Example 4 A method for preparing modified CF differs from Example 1 in that: in step (3), the amount of ANF is adjusted to 2g, and the concentration of the prepared ANF / DMSO dispersion is 10mg / mL; all other aspects are the same as in Example 1.

[0035] This comparative example did not involve the preparation of carbon fiber reinforced thermoplastic resin composites.

[0036] Comparative Example 5 This comparative example did not modify CF.

[0037] A method for preparing a carbon fiber reinforced thermoplastic resin composite material: Commercially available short-cut carbon fiber (CF) is deslurried using conventional techniques, and then mixed with PA6 resin at a mass ratio of 20:80 by melt blending and extrusion granulation (melt temperature 230℃, screw speed 40rpm, mixing time 10min) to obtain CF / PA6 composite granules. The CF / PA6 composite granules are then subjected to a hot pressing process (holding temperature 230℃, holding time 10min, holding pressure 50bar) to obtain an unmodified CF / PA6 composite board.

[0038] Product structure characterization Figure 2 The following are microscopic images of the original carbon fiber and the modified intermediate in Example 1: (a) SEM image of the original carbon fiber; (b) SEM image of polydopamine modified carbon fiber; (c) SEM image of NiCo alloy modified carbon fiber; (d) EDS energy spectrum corresponding to image (c). Figure 2 Display: The original CF surface is smooth and free of material load. Figure 2 a); Due to the low inertness of the original CF surface, metal ions are difficult to uniformly adhere to its surface. To overcome this limitation, this invention utilizes the property that the catechol and amino functional groups rich in polydopamine can coordinate and bind with various metal ions to deposit a polydopamine coating in situ on the carbon fiber surface. Figure 2 b), thus creating favorable conditions for the uniform adhesion of cobalt and nickel ions. After high-temperature reduction treatment, uniformly distributed NiCo alloy nanoparticles can be observed on the carbon fiber surface. Figure 2 c); EDS energy dispersive spectroscopy analysis further indicated that these nanoparticles correspond to cobalt and nickel elements ( Figure 2 (d) indicates that the metal ions were reduced at high temperature.

[0039] Figure 3 The XPS C 1s spectra of the original CF(a) and ANF@NiCo-CF(b) in Example 1 are shown. Figure 3 As shown, after modification, the number of active functional groups on the carbon fiber surface increases significantly, which helps to form stronger interfacial bonding in the composite material.

[0040] Figure 4 Microscopic morphology images of the products obtained under different conditions: (a-b) SEM images of ANF@NiCo-CF prepared in Example 1; (c) SEM image of ANF@NiCo-CF prepared in Comparative Example 3; (d) One of the SEM images of ANF@NiCo-CF prepared in Comparative Example 4; (e) Tensile fracture section morphology of the unmodified CF / PA6 composite plate prepared in Comparative Example 5; (f) Tensile fracture section morphology of the modified CF / PA6 composite plate prepared in Example 1. Figure 4 As shown in (a~b), combined with Figure 2 The characterization results show that the present invention sequentially coats the original carbon fiber (CF) surface with a polydopamine carbon layer (nitrogen-doped carbon), a NiCo alloy nanoparticle layer, and an ANF layer. The ANF layer and the NiCo alloy nanoparticles together construct a complete surface functional structure. The heterogeneous interface structure formed by the ANF film coating the NiCo alloy nanoparticles significantly enhances the interfacial compatibility between the carbon fiber and the thermoplastic resin. Figure 4 As shown in (c~d), different concentrations of ANF / DMSO dispersions affect the coating effect of ANF on the modified CF intermediates: lower concentrations of ANF / DMSO dispersions prevent ANF from forming a complete coating on the carbon fiber surface, leaving the magnetic particles on the carbon fiber surface directly exposed. This is expected to cause some of the modified CF to detach during mixing with the thermoplastic resin, increasing surface defects and reducing mechanical and electromagnetic stealth properties. Higher concentrations of ANF / DMSO dispersions, due to the higher viscosity of the ANF solution, make it difficult for the carbon fibers to separate, causing them to entangle. ANF cannot completely coat the fibers either. It is expected that carbon fibers modified with high-concentration ANF / DMSO dispersions will be difficult to distribute uniformly in the thermoplastic resin, thus affecting the material's mechanical and electromagnetic stealth properties. Furthermore, as... Figure 4As shown in (e~f), after tensile fracture, the carbon fibers pulled from the resin in the unmodified CF / PA6 composite plate have a relatively smooth surface with little residual resin, indicating poor interfacial bonding between the carbon fibers and the resin. This also suggests that the interfacial strength of the composite material is low. In contrast, after tensile fracture, the modified carbon fibers pulled from the resin in the modified CF / PA6 composite plate have a large amount of resin residue on their surface, indicating improved interfacial bonding. This is mainly due to the effective enhancement of surface activity by the presence of the ANF layer. Figure 3 As can be seen, the ANF coating on the carbon fiber surface enhances the structural stability of NiCo alloy nanoparticles on the carbon fiber surface, effectively increasing the surface roughness of the carbon fiber. This is beneficial for enhancing the mechanical interlocking effect between the carbon fiber and PA6, and for improving the interfacial strength of the composite material.

[0041] Figure 5 This is the second SEM image showing the microstructure of ANF@NiCo-CF prepared in Comparative Example 4. Combined with... Figure 4 (d) The results fully confirm that a high ANF / DMSO dispersion will cause ANF to coat all the CF together, resulting in poor dispersibility. Therefore, Comparative Example 4 of this invention did not proceed with the preparation of the composite material.

[0042] Product performance testing To test the electromagnetic absorption of the composite materials, test strips were machined from the modified CF / PA6 composite plates obtained in Examples 1-3, the modified CF / PA6 composite plates obtained in Comparative Examples 1-3, and the unmodified CF / PA6 composite plate obtained in Comparative Example 5. A biaxial engraving machine was used to machine the unmodified / unmodified CF / PA6 composite plates into concentric rings with an inner diameter of 3.02 mm and an outer diameter of 7 mm. The relative complex permittivity and relative complex permeability of the carbon fiber reinforced thermoplastic resin composites were determined using an Agilent N5230C network analyzer in the frequency range of 2-18 GHz. The tensile strength of the carbon fiber reinforced thermoplastic resin composite specimens was tested on a general-purpose testing machine (AG-X plus, 10 KN, SHIMADZD, Japan) according to ASTM D3039 standard.

[0043] The specific results are shown in Table 1.

[0044]

[0045] The experimental results of Examples 1-3 in Table 1 show that, within the process parameters of this invention, the prepared carbon fiber reinforced thermoplastic resin composite material maintains a high level in both mechanical properties and electromagnetic wave absorption performance. Comparing the data of Example 1 and Comparative Example 1 in Table 1, the experimental results show that the original CF has a high dielectric constant, which is unfavorable for electromagnetic wave absorption, and its permeability is almost nonexistent, making it unable to attenuate electromagnetic waves through changes in the magnetic field. In Example 1, the introduction of magnetic particles improves its dielectric constant and also increases magnetic loss, thereby achieving the goal of enhanced wave absorption performance. Comparing the data of Example 1 and Comparative Example 2 in Table 1, the experimental results show that the presence of ANF also affects electromagnetic wave absorption and mechanical properties. In Example 1, the introduction of an ANF coating layer not only increases the number of heterogeneous interfaces, causing multiple reflections of electromagnetic waves internally, and correspondingly increasing polarization loss, but also demonstrates that the bonding force between the resin and ANF is superior to that between the fiber and resin alone, resulting in a significant enhancement of mechanical properties. By comparing the data from Example 1 and Comparative Example 3 in Table 1, the experimental results show that the introduced magnetic particles achieved the goal of optimizing the microwave absorption performance. However, due to the damage to the carbon fibers caused by high temperature, the increase in defects and the reduction in mechanical properties are inevitable. Furthermore, the ANF coating layer of the low-concentration ANF / DMSO dispersion is insufficient to completely coat all CF fibers, failing to form an effective mechanical interlocking structure and interfacial bonding. Compared to the fiber with ANF coating in Example 1, the decrease in mechanical properties is more significant. Figure 4 (d) and Figure 5 The results show that high-concentration ANF / DMSO dispersions lead to CF agglomeration and entanglement, resulting in poor dispersibility. This is detrimental to the blending of CF and thermoplastic resin, causing uneven mixing within the composite material, inconsistent CF content, and failure to achieve the expected microwave absorption and mechanical properties. Comparing the data from Example 1 and Comparative Example 5 in Table 1, the experimental results indicate that the poor interfacial compatibility and impedance mismatch between unmodified CF and thermoplastic resin result in weak electromagnetic absorption performance in the prepared composite material.

[0046] In summary, by adjusting the appropriate loading of NiCo alloy nanoparticles and the ANF coating concentration, carbon fiber composite materials with stable heterogeneous interfaces, uniform dispersion structures, and multiple electromagnetic loss mechanisms can be effectively constructed while preserving the mechanical properties of carbon fibers as much as possible, thereby achieving synergistic optimization of mechanical properties and electromagnetic wave absorption performance.

[0047] Figure 6 Electromagnetic wave absorption performance diagrams: (a) Unmodified CF / PA6 composite plate prepared in Comparative Example 5; (b) Modified CF / PA6 composite plate prepared in Comparative Example 2; (c) Modified CF / PA6 composite plate prepared in Example 1. Figure 6As shown, compared with the unmodified CF / PA6 and the modified CF / PA6 composite material prepared in Comparative Example 2 (without ANF coating modification), the modified CF / PA6 composite material prepared in Example 1 exhibits the best electromagnetic wave absorption characteristics. With a thickness of only 1.5 mm, the minimum RL is -60.73 dB, and the EAB reaches 4.90 GHz with a thickness of 1.3 mm. The main reason is the enhanced interfacial compatibility between the modified CF and PA6, which promotes a more uniform distribution of CF in the resin and facilitates the formation of a more developed conductive network, thus improving the material's conductivity loss and multiple reflection capability. Secondly, the PDA carbon layer (polydopamine carbon layer), NiCo alloy nanoparticles, and ANF layer form a highly active multilayer heterostructure, generating interfacial heteropolarization and dipole polarization. Furthermore, the ANF structure on the CF surface maintains the stability of the magnetic NiCo alloy nanoparticles during processing. These magnetic nanoparticles induce magnetic loss under the influence of EMW through mechanisms such as resonance and eddy current loss. Finally, charge rearrangement under the influence of an external oscillating electromagnetic field also leads to energy dissipation in the form of heat.

[0048] The main criterion for judging electromagnetic stealth performance is the electromagnetic wave absorption capacity. The better the electromagnetic wave absorption performance, the better the electromagnetic stealth performance. Therefore, the performance test results of this invention show that the technical solution adopted in this invention can greatly improve the electromagnetic stealth performance of composite materials.

Claims

1. A modified carbon fiber, characterized in that: The carbon fiber surface is sequentially coated from the inside out with a polydopamine carbon layer, a metal nanoparticle layer that has magnetic or dielectric loss to electromagnetic waves, and an ANF layer; the metal nanoparticle layer is one or more of elemental metals, metal oxides, and metal alloys.

2. The modified carbon fiber as described in claim 1, characterized in that: The metal nanoparticle layer that has magnetic or dielectric loss to electromagnetic waves is one or more of Fe, Ni, Co, NiCo alloy, FeNiCo alloy, Fe3O4, NiFe2O4, MnFe2O4, MnO, ZnO, and TiO2.

3. A method for preparing modified carbon fiber as described in claim 1 or 2, characterized in that, The steps are as follows: (1) The desized or unsized carbon fiber is fully impregnated in a weakly alkaline dopamine / Tris-HCl aqueous solution; wherein, the concentration of dopamine in the weakly alkaline dopamine / Tris-HCl aqueous solution is 0.5~3mg / mL; (2) The carbon fibers obtained after impregnation in step (1) are fully impregnated in a metal salt solution, taken out and dried, and then calcined at 400~900℃ for 1~4h under an inert or protective atmosphere to obtain a modified carbon fiber intermediate; wherein, the metal salt is a water-soluble metal salt corresponding to the metal element in the metal particle layer that has magnetic loss or dielectric loss of electromagnetic waves, and the total metal concentration of the metal salt solution is 0.05~1mol / L based on the metal element provided by it. (3) Using aramid nanofibers as raw materials, an ANF / DMSO dispersion was prepared by alkaline dissolution and deprotonation method; the modified carbon fiber intermediate obtained in step (2) was fully impregnated in the ANF / DMSO dispersion, and then dried to obtain the modified carbon fiber; wherein the concentration of the ANF / DMSO dispersion was 2~5 mg / mL.

4. The method for preparing modified carbon fiber as described in claim 3, characterized in that: In step (1), the pH of the weakly alkaline dopamine / Tris-HCl aqueous solution is 8~9.

5. The method for preparing modified carbon fiber as described in claim 3, characterized in that, In step (1), the weakly alkaline dopamine / Tris-HCl aqueous solution is prepared according to the following process: first, prepare a Tris-HCl aqueous solution with a concentration of 0.5~5 mg / mL, then gradually add dopamine to the Tris-HCl aqueous solution until the dopamine concentration is 0.5~5 mg / mL, and then add NaOH solution with a concentration of 20~200 mg / mL to adjust the pH of the system to weakly alkaline.

6. The method for preparing modified carbon fiber as described in claim 3, characterized in that, In step (2), the metal salt is one or more of the following: metal chloride, nitrate, and sulfate.

7. The method for preparing modified carbon fiber as described in claim 3, characterized in that, In step (3), the ANF / DMSO dispersion is prepared according to the following process: aramid nanofibers, DMSO solution and strong alkali solution are mixed evenly and then ball-milled to obtain the ANF / DMSO dispersion; wherein, the raw material ratio is aramid nanofibers∶DMSO∶strong alkali solution = (0.2~0.5)g∶100mL∶(5~10)mL; the concentration of the strong alkali solution is 0.2~0.4mmol / L, and the strong alkali solution is NaOH solution or KOH solution.

8. The method for preparing modified carbon fiber as described in claim 3, characterized in that, In step (1), the carbon fibers in the desized carbon fibers and unsized carbon fibers are continuous carbon fibers or short-cut carbon fibers. When the carbon fibers in the desized carbon fibers and unsized carbon fibers are continuous carbon fibers, the impregnation methods involved in steps (1), (2) and (3) are all static impregnation. When the carbon fibers in the desized carbon fibers and unsized carbon fibers are short-cut carbon fibers, the impregnation method in step (1) is to first ultrasonically treat for 10~20 min, and then stir at low speed of 20~100 rpm for 6~12 h. The impregnation method in step (2) is to stir at low speed of 20~100 rpm for 1~2 h. The impregnation method in step (3) is to stir at low speed of 20~100 rpm for 5~10 min.

9. A method for preparing carbon fiber reinforced thermoplastic resin composite materials using the modified carbon fiber as described in claim 1 or 2, characterized in that, The steps are as follows: (1) When the modified carbon fiber is obtained by modifying short carbon fiber, the modified carbon fiber is directly melt-blended with thermoplastic resin and extruded into granules to obtain composite granules; When the modified carbon fiber is obtained based on continuous carbon fiber modification, the modified carbon fiber is first cut, and then melt-blended and extruded with thermoplastic resin to obtain composite granules. (2) The composite granules obtained in step (1) are injection molded or hot-pressed to obtain carbon fiber reinforced thermoplastic resin composite material; wherein, by mass ratio, the raw material ratio is modified carbon fiber: thermoplastic resin = a: (100-a), and the value of a ranges from 5 to 30.

10. The method for preparing the carbon fiber reinforced thermoplastic resin composite material as described in claim 9, characterized in that: The thermoplastic resin is one or more of nylon, polyimide, and polycarbonate; during melt blending extrusion granulation, the screw speed is 40~60 r / min; the conditions for injection molding or hot pressing are: holding temperature of 200~300℃, holding time of 5~60 min, and holding pressure of 30~100 bar.

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