Surface-modified carbon fiber, modification method and epoxy composite material thereof

Abstract

This invention discloses a surface-modified carbon fiber, a modification method, and an epoxy composite material thereof, belonging to the field of carbon fiber modification technology. This invention uses a hydrothermal method to synthesize MnO2 on the surface of carbon fiber. Manganese dioxide nanosheets have advantages such as low cost, simple preparation process, high environmental compatibility, and controllable morphology. Due to their excellent catalytic activity and physical barrier effect, this material also has good applications in the flame retardant field. Metal-organic frameworks (MOFs) possess excellent physical and chemical properties, including superior structural designability, large specific surface area, and high porosity. UiO66-NH2 is particularly prominent due to its excellent mechanical properties, good structural stability, and thermal stability. This application introduces UiO66-NH2 through in-situ generation, combining the barrier effect of nano-flame retardants with the catalytic effect of metals in MOFs to synergistically improve the flame retardant performance of CFRP. Simultaneously, it improves the mechanical properties of the carbon fiber composite material.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber modification technology, specifically relating to a surface-modified carbon fiber, a modification method, and an epoxy composite material thereof. Background Technology

[0002] Carbon fiber reinforced resin matrix composites, with their outstanding properties such as low density, high specific strength, and light weight, have been widely used in rail transportation, wind power generation, aerospace, and other fields. However, the inherent flammability of composite materials in fires poses a potential danger, as high-temperature, dense smoke can lead to significant property damage and personal injury. These phenomena severely limit the application of carbon fiber reinforced resin matrix composites in fire safety and other fields. Therefore, improving the flame-retardant properties of composite materials has become a key research focus.

[0003] Adding flame retardants to carbon fiber reinforced polymer (CFRP) is a rapid way to improve the flame retardant performance of the material. Generally, based on the relationship between the flame retardant and the substrate being flame-retarded, flame retardants can be divided into two main categories: intrinsic and additive. Intrinsic flame retardants contain flame-retardant molecular structures in their main chain, and the material itself has a flame-retardant effect. Additive flame retardants are directly applied to the surface of the material to improve its flame retardant effect. Balancing cost and performance, additive flame retardants have become the more widely used approach. To date, common flame retardants include halogen-based, phosphorus-based, nitrogen-based, silicon-based, novel nano-flame retardants, and metal-containing compound flame retardants. Generally, flame retardant mechanisms can be divided into condensed-phase flame retardancy, gas-phase flame retardancy, and heat exchange interruption flame retardancy mechanisms. Condensed-phase flame retardancy mainly works by acting as a barrier, hindering the conduction of heat and flammable gases. Gas-phase flame retardancy mainly involves the flame retardant interfering with the flammable gases released during the combustion process of the polymer. Some flame retardants can cause dehydration, physical transformation, or other endothermic reactions, thereby lowering the temperature of the combustion system and slowing down the combustion rate of the polymer. However, the actual combustion and flame retardant process is very complex, involving very complex flame retardant mechanisms. It is generally not entirely due to a single flame retardant mechanism, but rather multiple flame retardant mechanisms working together. Furthermore, the addition of traditional flame retardants can significantly affect the mechanical strength of the material.

[0004] Therefore, existing technologies for carbon fiber suffer from technical problems such as low flame retardancy or poor mechanical strength. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a surface-modified carbon fiber, a modification method and an epoxy composite material thereof, so as to solve the technical problems of low flame retardant properties or poor mechanical strength of carbon fiber in the prior art.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A method for modifying the surface of carbon fiber, comprising:

[0008] S1: Manganese dioxide nanosheets were uniformly grown on the surface of carbon fibers using a hydrothermal method to obtain CF / MnO2.

[0009] S2: UiO66-NH2 was modified on the surface of CF / MnO2 using an in-situ growth method to obtain CF / MnO2 / UiO66-NH2.

[0010] Preferably, in step S1, the carbon fiber is cleaned in acetone and dried before use. The cleaning time is 20-48 hours, and the drying environment is vacuum drying at 75-85°C.

[0011] Preferably, in step S1, manganese dioxide nanosheets are uniformly grown on the surface of carbon fibers using a hydrothermal method. Specifically, potassium permanganate is dissolved in deionized water to obtain a mixed solution A, and then the carbon fibers are placed in the mixed solution A for a hydrothermal reaction. After washing and drying, CF / MnO2 is obtained.

[0012] Preferably, the ratio of potassium permanganate, deionized water and carbon fiber is (0.0226~0.113)g∶(50~250)mL∶(1~3)g.

[0013] Preferably, in step S2, UiO66-NH2 is modified onto the CF / MnO2 surface using an in-situ growth method, comprising the following steps:

[0014] ZrCl4 and 2-aminoterephthalic acid were dissolved in DMF to form mixed solution B. Glacial acetic acid was added to mixed solution B to obtain mixed solution C.

[0015] CF / MnO2 is placed in mixed solution C, heated and reacted to obtain CF / MnO2 / UiO66-NH2.

[0016] Preferably, the ratio of ZrCl4 to DMF is (0.0899–0.2339) g : (5–13) mL; the ratio of 2-aminoterephthalic acid to DMF is (0.0362–0.181) g : (5–25) mL; the ratio of glacial acetic acid to mixed solution B is (1–9) mL : (10–38) mL; and the ratio of CF / MnO2 to mixed solution C is (1–3) g : (15–47) mL.

[0017] Preferably, the heating temperature for placing CF / MnO2 into the mixed solution C and heating and reacting is 60℃~80℃.

[0018] Preferably, after obtaining CF / MnO2 / UiO66-NH2, it is washed by centrifugation with DMF and acetone, and then vacuum dried at 60℃~80℃ for 24h~36h.

[0019] The present invention also discloses a surface-modified carbon fiber, characterized in that it is prepared by any one of the carbon fiber surface modification methods described above.

[0020] The present invention also discloses an epoxy composite material of surface-modified carbon fiber, wherein an epoxy resin system is coated on CF / MnO2 / UiO66-NH2.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention utilizes a hydrothermal method to synthesize MnO2 on the surface of carbon fibers. Manganese dioxide nanosheets possess advantages such as low cost, simple preparation process, high environmental compatibility, and controllable morphology, and have been widely applied in fields such as batteries, supercapacitors, and biosensors. Notably, due to its excellent catalytic activity and physical barrier properties, this material also shows great promise in the field of flame retardancy. Metal-organic frameworks (MOFs) possess excellent physical and chemical properties, including superior structural designability, large specific surface area, and high porosity, and have been widely used in fields such as supercapacitors, lithium-ion batteries, nanogenerators, gas sensors, electrocatalysts, and photocatalysts. In recent years, this material has gradually shown potential value as an excellent flame retardant for enhancing the flame retardancy, smoke suppression, and mechanical properties of polymer matrices. Among these MOF materials, UiO66-NH2 has attracted widespread attention due to its excellent mechanical properties, good structural stability, and thermal stability. This application introduces UiO66-NH2 in situ, and the most significant feature of this nanoflame retardant is that it can significantly improve the flame retardant performance of the material with a very small amount added, while also improving the mechanical properties. This method combines the barrier effect of nano-flame retardants with the catalytic effect of metals in MOFs to synergistically improve the flame retardant properties of carbon fibers. It also enhances the mechanical properties of carbon fibers.

[0023] Furthermore, a hydrothermal method is used to uniformly grow manganese dioxide nanosheets on the surface of carbon fibers. The hydrothermal method is simple to operate, has good dispersibility, and can be used on a large scale.

[0024] Furthermore, UiO66-NH2 was modified on the CF / MnO2 surface using an in-situ growth method. The material prepared by the in-situ growth method has a core formed within the metal matrix, the surface of the reinforcement is free from contamination, the matrix and the reinforcement have good compatibility, and the interfacial bonding strength is high.

[0025] Furthermore, the ratio of potassium permanganate, deionized water, and carbon fiber is (0.0226–0.113) g : (50–250) mL : (1–3) g; too much potassium permanganate will prevent it from reacting completely; too little will result in an undesirable MnO2 morphology.

[0026] Furthermore, the ratio of ZrCl4 to DMF is (0.0899–0.2339) g : (5–13) mL; the ratio of 2-aminoterephthalic acid to DMF is (0.0362–0.181) g : (5–25) mL; the ratio of glacial acetic acid to mixed solution B is (1–9) mL : (10–38) mL; the ratio of CF / MnO2 to mixed solution C is (1–3) g : (15–47) mL; and the generated UiO66-NH2 is uniform in size and regular in morphology.

[0027] This invention also discloses a surface-modified carbon fiber, prepared using any of the above-mentioned carbon fiber surface modification methods. Manganese dioxide nanosheets have advantages such as low cost, simple preparation process, high environmental compatibility, and controllable morphology, and possess excellent catalytic activity and physical barrier properties. UiO66-NH2 exhibits excellent mechanical properties, good structural stability, and thermal stability. With the addition of a very small amount of nano-flame retardant, the flame retardant properties of carbon fiber are significantly improved, while also enhancing the mechanical properties of the carbon fiber.

[0028] This invention also discloses a surface-modified carbon fiber epoxy composite material, which is an epoxy resin system coated on CF / MnO2 / UiO66-NH2. Traditional thermosetting resins are mainly composed of carbon, hydrogen, and oxygen. Like other polymer materials, their organic properties make epoxy resins highly flammable. The combustion process releases high heat, produces a large amount of flammable gases and smoke, and generates molten drips. These combustion characteristics indicate that the widespread use of epoxy resins poses significant safety hazards, and their flammability greatly limits their practical application. In general, the flame-retardant mechanism of polymers is based on combustion; understanding the combustion mechanism is fundamental to achieving effective flame retardancy. The combustion process consists of five stages: heating, decomposition, ignition, combustion, and propagation. The key factors in combustion are fuel, oxygen, heat source, and chain reaction. Flame retardancy involves inhibiting one or more processes in the polymer's combustion process, thus disrupting the combustion factors. The heat and smoke generated during the combustion of unmodified epoxy resin (EP) can break through the surface of the char residue, forming pores and cracks. This reduces the char residue's ability to impede heat, combustible gases, and smoke, creating a vicious cycle and accelerating the material's combustion process. Nano-flame retardants, due to their high thermal stability and physical barrier properties, can form an effective barrier preventing the escape of combustible gases and smoke. Attached Figure Description

[0029] Figure 1 Infrared spectra of untreated CF, CF / MnO2, and CF / MnO2 / UiO66-NH2;

[0030] Figure 2 XRD patterns of untreated CF, CF / MnO2, and CF / MnO2 / UiO66-NH2;

[0031] Figure 3 The maximum heat release rate test graphs are for Untreated CF, CF / MnO2, and CF / MnO2 / UiO66-NH2. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0033] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0034] The present invention will now be described in further detail with reference to the accompanying drawings:

[0035] In recent years, carbon fiber composites have been widely used in various fields such as automobiles, sports, and aerospace due to their advantages such as high strength, high modulus, wear resistance, and high load-bearing capacity. However, the poor compatibility between carbon fiber and polymer matrix, weak adhesion, and flammability and explosiveness have limited the further application of carbon fiber composites to some extent. This invention aims to enhance the bonding ability between carbon fiber and epoxy resin and improve the flame retardant properties of the composite material without sacrificing the original properties of carbon fiber. A carbon fiber reinforced resin composite material with manganese dioxide nanosheets as the interface phase was designed and prepared. Manganese dioxide nanosheets were uniformly grown on carbon fibers using a hydrothermal method, and then UiO66-NH2 was modified on the fiber surface using an in-situ growth method. A multi-scale carbon fiber reinforcement was successfully prepared. The changes in morphology, thermal stability, and flame retardant properties of the composite material when UiO66-NH2 and MnO2 synergistically act on the carbon fiber epoxy matrix were also studied.

[0036] The technical solution adopted in this invention is:

[0037] This invention discloses a method for modifying the surface of carbon fibers, comprising:

[0038] S1: Manganese dioxide nanosheets were uniformly grown on the surface of carbon fibers using a hydrothermal method to obtain CF / MnO2.

[0039] S2: UiO66-NH2 was modified on the surface of CF / MnO2 using an in-situ growth method to obtain CF / MnO2 / UiO66-NH2.

[0040] Manganese dioxide nanosheets were uniformly grown on carbon fibers using a hydrothermal method, and UiO66-NH2 was modified onto the fiber surface using an in-situ growth method. Manganese dioxide (MnO2), as a transition metal oxide, is widely used in batteries, supercapacitors, and biosensors due to its advantages such as low cost, simple preparation process, high environmental compatibility, and controllable morphology. Notably, due to its excellent catalytic activity and physical barrier effect, this material also has broad application prospects in the field of flame retardancy. Compared with traditional flame retardants, the most significant feature of nano-flame retardants is that only a very small amount needs to be added to significantly improve the flame retardant performance of the material, and the addition of nano-flame retardants also improves the mechanical properties of the material.

[0041] Metal-organic frameworks (MOFs) are a class of crystalline porous materials with a periodic network structure, formed by the self-assembly of inorganic metal centers (metal ions or metal clusters) and bridging organic ligands. They possess excellent physical and chemical properties, such as rich structure, large specific surface area, high porosity, numerous metal sites, and strong catalytic activity. Thanks to these superior properties, MOFs and their composites have been widely used in energy storage and conversion systems.

[0042] In some embodiments, the carbon fibers are cleaned in acetone and dried before use for 20–28 hours, and then vacuum dried at 75–85°C. Since the carbon fibers undergo sizing before leaving the factory, and sizing agents typically affect fiber surface modification and bulk characterization results, the carbon fibers need to be cleaned before use to remove sizing agents and other impurities.

[0043] In some embodiments, a hydrothermal method is used to uniformly grow manganese dioxide nanosheets on the surface of carbon fibers. Specifically, potassium permanganate is dissolved in deionized water to obtain a mixed solution A, and then the carbon fibers are placed in mixed solution A for a hydrothermal reaction. After washing and drying, CF / MnO2 is obtained. The hydrothermal method is simple to operate, has good dispersibility, and can be used on a large scale. In contrast, the fiber surface oxidation method is more difficult to control. If excessive oxidation occurs, it will inevitably induce the generation of cracks, micropores, and pits, thereby reducing the mechanical strength of the fiber.

[0044] More preferably, the ratio of potassium permanganate, deionized water, and carbon fiber is (0.0226–0.113) g : (50–250) mL : (1–3) g. Too much potassium permanganate will prevent it from reacting completely; too little will result in an undesirable MnO2 morphology.

[0045] In some embodiments, UiO66-NH2 is modified on the CF / MnO2 surface using an in-situ growth method, including the following steps:

[0046] ZrCl4 and 2-aminoterephthalic acid were dissolved in DMF to form mixed solution B. Glacial acetic acid was added to mixed solution B to obtain mixed solution C.

[0047] CF / MnO2 is placed in mixed solution C, heated and reacted to obtain CF / MnO2 / UiO66-NH2.

[0048] The material was prepared using an in-situ growth method. The reinforcement forms a nucleus within the metal matrix, the surface of the reinforcement is free of contamination, the matrix and reinforcement have good compatibility, and the interfacial bonding strength is high.

[0049] As a preferred embodiment, the ratio of ZrCl4 to DMF is (0.0899–0.2339) g : (5–13) mL; the ratio of 2-aminoterephthalic acid to DMF is (0.0362–0.181) g : (5–25) mL; the ratio of glacial acetic acid to mixed solution B is (1–9) mL : (10–38) mL; and the ratio of CF / MnO2 to mixed solution C is (1–3) g : (15–47) mL. The resulting UiO66-NH2 is uniform in size and has a regular morphology. The effect is better when the molar ratio of ZrCl4 to 2-aminoterephthalic acid is 1:1.

[0050] As a preferred embodiment, the heating temperature for placing CF / MnO2 into the mixed solution C and heating and reacting is 60°C to 80°C.

[0051] As a preferred embodiment, after obtaining CF / MnO2 / UiO66-NH2, it is washed by centrifugation with DMF and acetone, and then vacuum dried at 60℃~80℃ for 24h~36h.

[0052] This invention also discloses a surface-modified carbon fiber, prepared using any of the above-mentioned carbon fiber surface modification methods. Manganese dioxide nanosheets have advantages such as low cost, simple preparation process, high environmental compatibility, and controllable morphology, and possess excellent catalytic activity and physical barrier properties. UiO66-NH2 exhibits excellent mechanical properties, good structural stability, and thermal stability. With the addition of a very small amount of nano-flame retardant, the flame retardant properties of carbon fiber are significantly improved, while also enhancing the mechanical properties of the carbon fiber.

[0053] This invention also discloses a surface-modified carbon fiber epoxy composite material, which is an epoxy resin system coated on CF / MnO2 / UiO66-NH2. Traditional thermosetting resins are mainly composed of carbon, hydrogen, and oxygen. Like other polymer materials, their organic properties make epoxy resins highly flammable. The combustion process releases high heat, produces a large amount of flammable gases and smoke, and generates molten drips. These combustion characteristics indicate that the widespread use of epoxy resins poses significant safety hazards, and their flammability greatly limits their practical application. In general, the flame-retardant mechanism of polymers is based on combustion; understanding the combustion mechanism is fundamental to achieving effective flame retardancy. The combustion process consists of five stages: heating, decomposition, ignition, combustion, and propagation. The key factors in combustion are fuel, oxygen, heat source, and chain reaction. Flame retardancy involves inhibiting one or more processes in the polymer's combustion process, thus disrupting the combustion factors. The heat and smoke generated during the combustion of unmodified epoxy resin (EP) can break through the surface of the char residue, forming pores and cracks. This reduces the char residue's ability to impede heat, combustible gases, and smoke, creating a vicious cycle and accelerating the material's combustion process. Nano-flame retardants, due to their high thermal stability and physical barrier properties, can form an effective barrier preventing the escape of combustible gases and smoke.

[0054] This invention employs a hydrothermal method to synthesize MnO2 on the surface of carbon fibers and introduces UiO66-NH2 through in-situ generation. This strategy combines the barrier effect of nano-flame retardants with the catalytic effect of metals in MOFs, synergistically improving the flame retardant properties of CFRP. Simultaneously, it enhances the mechanical properties of the carbon fiber composite material, improves the interfacial properties of the carbon fiber composite material, and elevates the overall performance of the composite material.

[0055] The following specific embodiments illustrate the effects of this application by using the carbon fiber surface modification method disclosed in this invention to prepare surface-modified carbon fibers and fabricating epoxy composite materials of surface-modified carbon fibers:

[0056] Example 1

[0057] (1) Carbon fibers undergo sizing before leaving the factory. Sizing agents typically affect fiber surface modification and bulk characterization results; therefore, the carbon fibers must be cleaned before use to remove sizing agents and other impurities. The specific procedure is as follows: Place an appropriate amount of carbon fiber in a Soxhlet extractor containing acetone, reflux for 48 hours, and vacuum dry at 80°C for 24 hours. The cleaned carbon fiber is marked as Untreated CF.

[0058] (2) A simple one-step hydrothermal method was used to prepare carbon fiber manganese dioxide nanosheets multiscale reinforcements.

[0059] Specific procedures: First, weigh 0.113 g of potassium permanganate and dissolve it in 250 mL of deionized water. Stir with a magnetic stirrer for 60 min until the solution is completely dissolved. Add untreated carbon fiber to the solution and stir at 120 rpm for 1 h in a water bath. Then, transfer the reaction solution and carbon fiber to a hydrothermal reactor and react hydrothermally at 100 °C for 2 h. After the reaction, thoroughly wash and dry the carbon fiber to obtain a CF / MnO2 multiscale reinforcement, labeled as CF / MnO2.

[0060] (3) Dissolve 0.2339 g of ZrCl4 in 13 mL of DMF and sonicate for 30 min. Then dissolve 0.181 g of 2-aminoterephthalic acid in 25 mL of DMF and sonicate for 1 h. Mix the solution with the ZrCl4 solution, and then add 9 mL of glacial acetic acid dropwise to the ZrCl4 mixture and sonicate for 5 min. Add CF / MnO2 to the above solution, and finally add the solution to a 100 mL reactor and heat to 80 °C for 24 h. After the reaction cools to room temperature, wash the carbon fiber twice with DMF and acetone by sonication, and then vacuum dry at 80 °C for 24 h to obtain CF / MnO2 / UiO66-NH2.

[0061] (4) First, the carbon fiber and epoxy resin system are thoroughly impregnated. The mass ratio of resin to curing agent in the epoxy resin system is 100:32. Then, the mixture is heated in a water bath to make it flowable and evenly coated onto the carbon fiber. Next, the resin-impregnated reinforcement is placed into a mold preheated to 70°C, and the mold is placed in a hot press. The composite material preparation process adopts a three-stage heating process: after holding at 90°C under normal pressure for 2 hours, the pressure is increased to 5MPa, then the temperature is increased to 120°C and held for 2 hours, and then the temperature is increased to 150°C and held under pressure for 3 hours. After the process is completed, the press is turned off, and the pressure is maintained until the mold cools down and the sample is demolded. The obtained sample is cut to an appropriate size according to the test requirements for testing.

[0062] Example 2

[0063] (1) Carbon fibers undergo sizing before leaving the factory. Sizing agents typically affect fiber surface modification and bulk characterization results; therefore, the carbon fibers must be cleaned before use to remove sizing agents and other impurities. The specific procedure is as follows: Place 3g of carbon fiber in a Soxhlet extractor containing acetone, reflux for 48 hours, and vacuum dry at 80℃ for 24 hours. The cleaned carbon fiber is marked as Untreated CF.

[0064] (2) A simple one-step hydrothermal method was used to prepare carbon fiber manganese dioxide nanosheets multiscale reinforcements.

[0065] Specific procedures: First, weigh 0.113 g of potassium permanganate and dissolve it in 250 mL of deionized water. Stir with a magnetic stirrer for 60 min until the solution is completely dissolved. Add untreated carbon fiber to the solution and stir at 120 rpm for 1 h in a water bath. Then, transfer the reaction solution and carbon fiber to a hydrothermal reactor and react hydrothermally at 120 °C for 2 h. After the reaction, thoroughly wash and dry the carbon fiber to obtain a CF / MnO2 multiscale reinforcement, labeled as CF / MnO2.

[0066] (3) Dissolve 0.2339 g of ZrCl4 in 13 mL of DMF and sonicate for 30 min. Then dissolve 0.181 g of 2-aminoterephthalic acid in 25 mL of DMF and sonicate for 1 h. Mix the solution with the ZrCl4 solution, and then add 9 mL of glacial acetic acid dropwise to the ZrCl4 mixture and sonicate for 5 min. Add CF / MnO2 to the above solution, and finally add the solution to a 100 mL reactor and heat to 80 °C for 24 h. After the reaction cools to room temperature, wash the carbon fiber twice with DMF and acetone by sonication, and then vacuum dry at 80 °C for 24 h to obtain CF / MnO2 / UiO66-NH2.

[0067] (4) First, the carbon fiber and epoxy resin system are thoroughly impregnated. The mass ratio of resin to curing agent in the epoxy resin system is 100:32. Then, the mixture is heated in a water bath to make it flowable and evenly coated onto the carbon fiber. Next, the resin-impregnated reinforcement is placed into a mold preheated to 70°C, and the mold is placed in a hot press. The composite material preparation process adopts a three-stage heating process: after holding at 90°C under normal pressure for 2 hours, the pressure is increased to 5MPa, then the temperature is increased to 120°C and held for 2 hours, and then the temperature is increased to 150°C and held under pressure for 3 hours. After the process is completed, the press is turned off, and the pressure is maintained until the mold cools down and the sample is demolded. The obtained sample is cut to an appropriate size according to the test requirements for testing.

[0068] Example 3

[0069] (1) Carbon fibers undergo sizing before leaving the factory. Sizing agents typically affect fiber surface modification and bulk characterization results; therefore, the carbon fibers must be cleaned before use to remove sizing agents and other impurities. The specific procedure is as follows: Place 3g of carbon fiber in a Soxhlet extractor containing acetone, reflux for 48 hours, and vacuum dry at 80℃ for 24 hours. The cleaned carbon fiber is marked as Untreated CF.

[0070] (2) A simple one-step hydrothermal method was used to prepare carbon fiber manganese dioxide nanosheets multiscale reinforcements.

[0071] Specific procedures: First, weigh 0.113 g of potassium permanganate and dissolve it in 250 mL of deionized water. Stir with a magnetic stirrer for 60 min until the solution is completely dissolved. Add untreated carbon fiber to the solution and stir at 120 rpm for 1 h in a water bath. Then, transfer the reaction solution and carbon fiber to a hydrothermal reactor and react hydrothermally at 140 °C for 2 h. After the reaction, thoroughly wash and dry the carbon fiber to obtain a CF / MnO2 multiscale reinforcement, labeled as CF / MnO2.

[0072] (3) Dissolve 0.2339 g of ZrCl4 in 13 mL of DMF and sonicate for 30 min. Then dissolve 0.181 g of 2-aminoterephthalic acid in 25 mL of DMF and sonicate for 1 h. Then add 9 mL of glacial acetic acid dropwise to the ZrCl4 solution and sonicate for 5 min. Add CF / MnO2 to the above solution, and finally add the solution to a 100 mL reaction vessel and heat to 80 °C for 24 h. After the reaction cools to room temperature, wash the carbon fiber twice with DMF and acetone by sonication, and then vacuum dry at 80 °C for 24 h to obtain CF / MnO2 / UiO66-NH2.

[0073] (4) First, the carbon fiber and epoxy resin system are thoroughly impregnated. The mass ratio of resin to curing agent in the epoxy resin system is 100:32. Then, the mixture is heated in a water bath to make it flowable and evenly coated onto the carbon fiber. Next, the resin-impregnated reinforcement is placed into a mold preheated to 70°C, and the mold is placed in a hot press. The composite material preparation process adopts a three-stage heating process: after holding at 90°C under normal pressure for 2 hours, the pressure is increased to 5MPa, then the temperature is increased to 120°C and held for 2 hours, and then the temperature is increased to 150°C and held under pressure for 3 hours. After the process is completed, the press is turned off, and the pressure is maintained until the mold cools down and the sample is demolded. The obtained sample is cut to an appropriate size according to the test requirements for testing.

[0074] Example 4

[0075] (1) Carbon fibers undergo sizing before leaving the factory. Sizing agents typically affect fiber surface modification and bulk characterization results; therefore, the carbon fibers must be cleaned before use to remove sizing agents and other impurities. The specific procedure is as follows: Place 3g of carbon fiber in a Soxhlet extractor containing acetone, reflux for 48 hours, and vacuum dry at 80℃ for 24 hours. The cleaned carbon fiber is marked as Untreated CF.

[0076] (2) A simple one-step hydrothermal method was used to prepare carbon fiber manganese dioxide nanosheets multiscale reinforcements.

[0077] Specific procedures: First, weigh 0.113 g of potassium permanganate and dissolve it in 250 mL of deionized water. Stir with a magnetic stirrer for 60 min until the solution is completely dissolved. Add untreated carbon fiber to the solution and stir at 120 rpm for 1 h in a water bath. Then, transfer the reaction solution and carbon fiber to a hydrothermal reactor and react hydrothermally at 160 °C for 2 h. After the reaction, thoroughly wash and dry the carbon fiber to obtain a CF / MnO2 multiscale reinforcement, labeled as CF / MnO2.

[0078] (3) Dissolve 0.2339 g of ZrCl4 in 13 mL of DMF and sonicate for 30 min. Then dissolve 0.181 g of 2-aminoterephthalic acid in 25 mL of DMF and sonicate for 1 h. Then add 9 mL of glacial acetic acid dropwise to the ZrCl4 solution and sonicate for 5 min. Add CF / MnO2 to the above solution, and finally add the solution to a 100 mL reaction vessel and heat to 80 °C for 24 h. After the reaction cools to room temperature, wash the carbon fiber twice with DMF and acetone by sonication, and then vacuum dry at 80 °C for 24 h to obtain CF / MnO2 / UiO66-NH2.

[0079] (4) First, the carbon fiber and epoxy resin system are thoroughly impregnated. The mass ratio of resin to curing agent in the epoxy resin system is 100:32. Then, the mixture is heated in a water bath to make it flowable and evenly coated onto the carbon fiber. Next, the resin-impregnated reinforcement is placed into a mold preheated to 70°C, and the mold is placed in a hot press. The composite material preparation process adopts a three-stage heating process: after holding at 90°C under normal pressure for 2 hours, the pressure is increased to 5MPa, then the temperature is increased to 120°C and held for 2 hours, and then the temperature is increased to 150°C and held under pressure for 3 hours. After the process is completed, the press is turned off, and the pressure is maintained until the mold cools down and the sample is demolded. The obtained sample is cut to an appropriate size according to the test requirements for testing.

[0080] Example 5

[0081] (1) Carbon fibers undergo sizing before leaving the factory. Sizing agents typically affect fiber surface modification and bulk characterization results; therefore, the carbon fibers must be cleaned before use to remove sizing agents and other impurities. The specific procedure is as follows: Place an appropriate amount of carbon fiber in a Soxhlet extractor containing acetone, reflux for 24 hours, and vacuum dry at 75°C for 24 hours. The cleaned carbon fiber is marked as Untreated CF.

[0082] (2) A simple one-step hydrothermal method was used to prepare carbon fiber manganese dioxide nanosheets multiscale reinforcements.

[0083] Specific procedures: First, weigh 0.0226 g of potassium permanganate and dissolve it in 50 mL of deionized water. Stir with a magnetic stirrer for 60 min until the solution is completely dissolved. Add 1 g of untreated carbon fiber to the solution and stir at 120 rpm for 1 h in a water bath. Then, transfer the reaction solution and carbon fiber to a hydrothermal reactor and react hydrothermally at 100 °C for 2 h. After the reaction, thoroughly wash and dry the carbon fiber to obtain a CF / MnO2 multiscale reinforced composite, labeled as CF / MnO2.

[0084] (3) Dissolve 0.0899 g of ZrCl4 in 5 mL of DMF and sonicate for 30 min. Then dissolve 0.0362 g of 2-aminoterephthalic acid in 25 mL of DMF and sonicate for 1 h. Mix the solution with the ZrCl4 solution, and then add 1 mL of glacial acetic acid dropwise to the ZrCl4 mixture and sonicate for 5 min. Add CF / MnO2 to the above solution, and finally add the solution to a 100 mL reactor and heat to 80 °C for 24 h. After the reaction cools to room temperature, wash the carbon fiber twice with DMF and acetone by sonication, and then vacuum dry at 80 °C for 24 h to obtain CF / MnO2 / UiO66-NH2.

[0085] (4) First, the carbon fiber and epoxy resin system are thoroughly impregnated. The mass ratio of resin to curing agent in the epoxy resin system is 100:32. Then, the mixture is heated in a water bath to make it flowable and evenly coated onto the carbon fiber. Next, the resin-impregnated reinforcement is placed into a mold preheated to 70°C, and the mold is placed in a hot press. The composite material preparation process adopts a three-stage heating process: after holding at 90°C under normal pressure for 2 hours, the pressure is increased to 5MPa, then the temperature is increased to 120°C and held for 2 hours, and then the temperature is increased to 150°C and held under pressure for 3 hours. After the process is completed, the press is turned off, and the pressure is maintained until the mold cools down and the sample is demolded. The obtained sample is cut to an appropriate size according to the test requirements for testing.

[0086] Example 6

[0087] (1) Carbon fibers undergo sizing before leaving the factory. Sizing agents typically affect fiber surface modification and bulk characterization results; therefore, the carbon fibers must be cleaned before use to remove sizing agents and other impurities. The specific procedure is as follows: Place an appropriate amount of carbon fiber in a Soxhlet extractor containing acetone, reflux for 36 hours, and vacuum dry at 85°C for 24 hours. The cleaned carbon fiber is marked as Untreated CF.

[0088] (2) A simple one-step hydrothermal method was used to prepare carbon fiber manganese dioxide nanosheets multiscale reinforcements.

[0089] Specific procedures: First, weigh 0.5g of potassium permanganate and dissolve it in 150mL of deionized water. Stir with a magnetic stirrer for 60 minutes until the solution is completely dissolved. Add 2g of untreated carbon fiber to the solution and stir at 120rpm for 1 hour in a water bath. Then, transfer the reaction solution and carbon fiber to a hydrothermal reactor and react hydrothermally at 100℃ for 2 hours. After the reaction, thoroughly wash and dry the carbon fiber to obtain a CF / MnO2 multiscale reinforcement, labeled as CF / MnO2.

[0090] (3) Dissolve 0.145 g of ZrCl4 in 5 mL of DMF and sonicate for 30 min. Then dissolve 0.0546 g of 2-aminoterephthalic acid in 15 mL of DMF and sonicate for 1 h. Mix the solution with the ZrCl4 solution, and then add 5 mL of glacial acetic acid dropwise to the ZrCl4 mixture and sonicate for 5 min. Add CF / MnO2 to the above solution, and finally add the solution to a 100 mL reactor and heat to 80 °C for 24 h. After the reaction cools to room temperature, wash the carbon fibers twice with DMF and acetone by sonication, and then vacuum dry at 80 °C for 24 h to obtain CF / MnO2 / UiO66-NH2.

[0091] (4) First, the carbon fiber and epoxy resin system are thoroughly impregnated. The mass ratio of resin to curing agent in the epoxy resin system is 100:32. Then, the mixture is heated in a water bath to make it flowable and evenly coated onto the carbon fiber. Next, the resin-impregnated reinforcement is placed into a mold preheated to 70°C, and the mold is placed in a hot press. The composite material preparation process adopts a three-stage heating process: after holding at 90°C under normal pressure for 2 hours, the pressure is increased to 5MPa, then the temperature is increased to 120°C and held for 2 hours, and then the temperature is increased to 150°C and held under pressure for 3 hours. After the process is completed, the press is turned off, and the pressure is maintained until the mold cools down and the sample is demolded. The obtained sample is cut to an appropriate size according to the test requirements for testing.

[0092] To characterize the morphological features, Fourier transform infrared spectroscopy (FTIR) was performed on the target product, and the results are as follows: Figure 1 As shown. Figure 1 Infrared spectra of untreated CF, CF / MnO2, and CF / MnO2 / UiO66-NH2. For untreated CF, 3436 cm⁻¹ -1 The peak is the stretching vibration peak of intermolecular hydrogen bonds (OH), at 1700 cm⁻¹. -1 This refers to the C=C stretching vibration in the benzene ring structure of carbon fibers. The framework structure of manganese dioxide is MnO6 octahedral, with oxygen atoms at the vertices and manganese atoms within the octahedrons. Compared to untreated carbon dioxide (CF), the CF / MnO2 ratio is 520-440 cm⁻¹. -1 A new absorption peak appeared, attributed to the Mn-O stretching vibration, confirming the successful growth of manganese dioxide on the carbon fiber surface. In the CF / MnO2 / UiO66-NH2 infrared spectrum, in addition to the Mn-O bond absorption peak, many new characteristic absorption peaks appeared, including those at 3460 and 3300 cm⁻¹. -1 There is an NH stretching vibration peak at 1620 cm⁻¹. -1 There are C=O stretching vibration peaks at 1379 and 1250 cm⁻¹. -1 The presence of a CN stretching vibration peak indicates successful growth of UiO66-NH2 on the CF / MnO2 multiscale reinforced substrate.

[0093] To verify the crystal structure characteristics of the material, X-ray powder diffraction (XRD) tests were performed on the product, and the results are as follows: Figure 2 As shown. Figure 2The XRD patterns before and after carbon fiber modification are shown. In the untreated CF, a broad diffraction peak appears at 2θ = 25°, which is generated by the (002) plane of a typical graphite crystal structure. After MnO2 nanosheets are grown on the fiber surface, a new diffraction peak appears at 12.75°. Comparing with the standard card JCPDS 44-0141, this diffraction peak corresponds to the (110) crystal plane of MnO2. The introduction of UiO66-NH2 results in two distinct characteristic peaks at 2θ = 7.4° and 8.4°, representing the (111) and (002) crystal plane diffraction of UiO66-NH2, respectively. This demonstrates the successful growth of MnO2 and UiO66-NH2 on the fiber surface.

[0094] Traditional thermosetting resins are mainly composed of carbon, hydrogen, and oxygen. Like other polymer materials, their organic properties make epoxy resins highly flammable. The combustion process releases high amounts of heat, flammable gases, and smoke, and produces molten drippings. These combustion characteristics indicate that the widespread use of epoxy resins poses significant safety hazards, and their flammability greatly limits their practical applications. Generally speaking, the flame-retardant mechanism of polymers is based on combustion; understanding the combustion mechanism is fundamental to achieving effective flame retardancy. The combustion process consists of five stages: heating, decomposition, ignition, combustion, and propagation. The key factors in combustion are fuel, oxygen, heat source, and chain reaction. Flame retardancy involves inhibiting one or more of these processes, disrupting the combustion factors. The heat and smoke generated during the combustion of unmodified epoxy resin (EP) can break through the surface of the char residue, forming pores and cracks. This reduces the char residue's ability to impede heat, flammable gases, and smoke, further creating a vicious cycle and accelerating the material's combustion process. Because nano flame retardants have high thermal stability and physical barrier properties, they can form an effective barrier that prevents flammable gases and smoke from escaping.

[0095] See performance test Figure 3 The maximum heat release rates of untreated CF, CF / MnO2, and CF / MnO2 / UiO66-NH2

[0096] The maximum heat release rate of untreated CF was 349.077 kW / m³. 2 The THR is 30.388 MJ / m³. 2 After introducing MnO2, the PHRR and HRR decreased to 82.947 KW / m. 2 and 14.729 MJ / m 2 Compared to untreated CF, the PHRR and HRR decreased by 76.23% and 51.53%, respectively. Further introduction of UiO66-NH2 reduced the PHRR and HRR to 74.537 KW / m³. 2and 13.678 MJ / m 2 Compared to untreated CF, the levels were reduced by 78.65% and 54.99%, respectively.

[0097] In summary, this invention discloses a surface-modified carbon fiber, a modification method, and an epoxy composite material thereof. MnO2 is synthesized on the surface of carbon fiber using a hydrothermal method. Manganese dioxide nanosheets offer advantages such as low cost, simple preparation process, high environmental compatibility, and controllable morphology. Due to their excellent catalytic activity and physical barrier effect, this material also has promising applications in the flame retardant field. Metal-organic frameworks (MOFs) possess excellent physical and chemical properties, including superior structural designability, large specific surface area, and high porosity. UiO66-NH2 is particularly prominent due to its excellent mechanical properties, good structural stability, and thermal stability. This application introduces UiO66-NH2 through in-situ generation, combining the barrier effect of nano-flame retardants with the catalytic effect of metals in MOFs to synergistically improve the flame retardant performance of CFRP. Simultaneously, it enhances the mechanical properties of the carbon fiber composite material.

[0098] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for modifying the surface of carbon fiber, characterized in that, include: S1: Manganese dioxide nanosheets were uniformly grown on the surface of carbon fibers using a hydrothermal method to obtain CF / MnO2. S2: UiO66-NH2 is modified onto the CF / MnO2 surface using an in-situ growth method to obtain CF / MnO2 / UiO66-NH2; specifically including the following steps: ZrCl4 and 2-aminoterephthalic acid were dissolved in DMF to form mixed solution B. Glacial acetic acid was added to mixed solution B to obtain mixed solution C. CF / MnO2 was placed in mixed solution C, heated and reacted to obtain CF / MnO2 / UiO66-NH2; The ratio of ZrCl4 to DMF is (0.0899~0.2339) g : (5-13) mL; the ratio of 2-aminoterephthalic acid to DMF is (0.0362~0.181) g : (5~25) mL; the ratio of glacial acetic acid to mixed solution B is (1~9) mL : (10~38) mL; and the ratio of CF / MnO2 to mixed solution C is (1~3) g : (15~47) mL.

2. The carbon fiber surface modification method according to claim 1, characterized in that, In step S1, the carbon fiber is cleaned in acetone and dried before use. The cleaning time is 20-48 hours, and the drying environment is vacuum drying at 75-85 ℃.

3. The carbon fiber surface modification method according to claim 1, characterized in that, In step S1, manganese dioxide nanosheets are uniformly grown on the surface of carbon fibers using a hydrothermal method, specifically including the following steps: Dissolve potassium permanganate in deionized water to obtain mixed solution A; Carbon fibers were placed in a mixed solution A for hydrothermal reaction, washed and dried to obtain CF / MnO2.

4. The carbon fiber surface modification method according to claim 3, characterized in that, The ratio of potassium permanganate, deionized water and carbon fiber is (0.0226~0.113)g∶(50~250)mL∶(1~3)g; the hydrothermal reaction temperature is 100~160℃.

5. The carbon fiber surface modification method according to claim 1, characterized in that, The heating temperature for placing CF / MnO2 into the mixed solution C and heating and reacting is 60℃~80℃.

6. The carbon fiber surface modification method according to claim 1, characterized in that, After obtaining CF / MnO2 / UiO66-NH2, it was washed by centrifugation with DMF and acetone, and then vacuum dried at 60℃~80℃ for 24 h~36 h.

7. A surface-modified carbon fiber, characterized in that, It is prepared by the carbon fiber surface modification method according to any one of claims 1 to 6.

8. An epoxy composite material based on surface-modified carbon fiber as described in claim 7, characterized in that, An epoxy resin system was coated onto CF / MnO2 / UiO66-NH2.

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