Method for synergistically modifying interface performance of carbon fiber composite coating by two-step chemical reaction, modified carbon fiber and application

Abstract

The application discloses a method for modifying the interface performance of a carbon fiber composite coating through two-step chemical reactions, modified carbon fiber and application. The method comprises the following steps: performing silanization modification treatment and hyperbranched modification treatment on the carbon fiber after oxidation treatment to obtain the modified carbon fiber. The method for modifying the interface performance of the carbon fiber composite coating through two-step chemical reactions is suitable for improving the interface performance of the carbon fiber composite coating. After the modified carbon fiber is mixed with a resin and a curing agent and is cured, the obtained carbon fiber reinforced composite coating has excellent mechanical properties, wear resistance and erosion and impact wear resistance, and can effectively reduce the corrosion, erosion and wear and tear of a steel structure facility in a complex and harsh marine environment such as a splash area.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber reinforced anti-erosion composite coating technology for use in complex and harsh marine environments such as splash zones. It relates to a method for modifying carbon fibers, specifically a two-step chemical reaction method for synergistically modifying and enhancing the interfacial properties of carbon fiber composite coatings, the obtained modified carbon fibers, and their applications. Background Technology

[0002] In the splash zone, steel structures are subjected to periodic wetting by seawater, resulting in a constant alternating wet and dry state. Combined with the effects of wave impact, sunlight, and abundant oxygen, the corrosion rate is fastest and most severe in this area. Furthermore, seawater carrying air and sediment continuously and rapidly erodes and wears down the steel structure. This coupled effect of multiple corrosive factors significantly accelerates the damage rate, leading to structural fracture and failure, and drastically shortening its service life.

[0003] Carbon fiber reinforced composite coatings, with their excellent mechanical strength, heat resistance, corrosion resistance, friction resistance, and impact resistance, have shown great application potential in the corrosion protection of metallic materials in marine environments. However, the smooth surface of untreated carbon fibers and the limited number of active functional groups prevent them from effectively wetting the resin matrix. The bonding strength between the two is insufficient to support the heavy load required for metal corrosion protection using composite coatings. Due to poor interfacial compatibility between the carbon fiber and the resin matrix, the load cannot be effectively transferred from the matrix to the carbon fiber, leading to interfacial failure at the carbon fiber / resin interface. Stress concentration occurs at interfacial defects, resulting in microcracks. Further propagation of these microcracks leads to complete failure of the composite coating, severely limiting its high performance. Therefore, interfacial failure is a key scientific issue for the service of carbon fiber composite coatings in marine environments. Designing and developing carbon fiber composite coatings that synergistically enhance interfacial properties through mechanical interlocking and chemical bonding has become an important research topic in the interfacial studies of carbon fiber reinforced composite coatings.

[0004] Currently, the main strategies for strengthening the carbon fiber-resin interface in carbon fiber reinforced composite coatings are oxidation treatment, surface chemical modification, and nanoparticle grafting. Oxidation treatment involves etching carbon fibers using methods such as electrochemical etching or plasma bombardment to improve the surface roughness and active functional groups of the carbon fibers, thereby enhancing compatibility with the resin. However, this can damage the carbon fibers and reduce their original mechanical strength. Nanoparticle grafting involves assembling carbon nanotubes, graphene, and other nanomaterials on the carbon fiber surface to improve surface roughness, surface energy, wettability, and other properties, thus enhancing the interfacial bonding strength with the matrix. However, due to high cost and demanding production conditions, mass production is difficult. Therefore, there is an urgent need to develop milder and more efficient carbon fiber surface modification methods to prepare carbon fiber reinforced composite coatings with strong interfacial bonding to meet the required mechanical properties, erosion resistance, and friction and wear resistance in harsh environments such as marine splash zones. Summary of the Invention

[0005] The main objective of this invention is to provide a method for synergistic modification and enhancement of the interfacial properties of carbon fiber composite coatings through a two-step chemical reaction, in order to overcome the shortcomings of the prior art.

[0006] Another object of the present invention is to provide modified carbon fibers obtained by the method.

[0007] Another objective of this invention is to provide a carbon fiber reinforced composite coating, its preparation method, and its application.

[0008] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0009] This invention provides a method for synergistic modification and enhancement of the interfacial properties of carbon fiber composite coatings through a two-step chemical reaction, comprising: performing silanization modification and hyperbranching modification on carbon fibers after oxidation treatment to obtain modified carbon fibers.

[0010] In some embodiments, a pretreatment of the hyperbranching modification is performed before the hyperbranching modification treatment; the pretreatment includes: grafting polyisocyanate onto the surface of carbon fibers to obtain carbon fibers grafted with isocyanate.

[0011] The hyperbranching modification process includes: in a protective atmosphere, imidazole and isocyanate-grafted carbon fibers undergoing a hyperbranching polymerization reaction to obtain carbon fibers grafted with hyperbranched polyimide.

[0012] In some embodiments, the silanization modification treatment includes:

[0013] A silane coupling agent, water, and a second organic solvent are mixed to carry out a hydrolysis pre-reaction to form a pre-reaction solution.

[0014] Carbon fibers are brought into full contact with a pre-reaction solution and subjected to reactive grafting to obtain silanized modified carbon fibers grafted with polysiloxane.

[0015] This invention also provides modified carbon fibers prepared by the aforementioned method, the surface of which has a modulus gradient transition layer.

[0016] This invention also provides a method for preparing a carbon fiber reinforced composite coating, comprising:

[0017] The modified carbon fiber is mixed evenly with the resin matrix to form a first mixture;

[0018] Add the curing agent and defoamer to the first mixture and mix them evenly to obtain the second mixture;

[0019] The second mixture is applied to the surface of a metal substrate and cured to obtain a carbon fiber reinforced composite coating.

[0020] This invention also provides a carbon fiber reinforced composite coating prepared by the aforementioned method.

[0021] Accordingly, embodiments of the present invention also provide the application of the carbon fiber reinforced composite coating in the field of substrate protection.

[0022] Furthermore, the application includes the application of the carbon fiber reinforced composite coating on steel structures serving in marine splash zones.

[0023] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0024] (1) The modified carbon fiber prepared by the present invention has uniform polymer grafting on the surface, the number of polar functional groups is greatly increased, the wettability and adhesion between the resin and the carbon fiber are significantly improved, thereby greatly improving the interface performance of the composite coating; and a modulus gradient transition layer is constructed between the carbon fiber and the resin with unbalanced modulus difference, so that the load can be effectively transferred from the resin to the carbon fiber, avoiding stress concentration and thus extending the service life of the composite coating.

[0025] (2) The carbon fiber reinforced composite coating prepared by the method provided by the present invention has excellent mechanical properties, friction and wear resistance and erosion wear resistance, and can effectively inhibit the corrosion damage of steel structures in marine environments for a long time. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart of a two-step chemical reaction synergistic modification method for enhancing the interfacial properties of carbon fiber composite coatings in a typical embodiment of the present invention.

[0028] Figure 2 This is a SEM image of the modified carbon fiber prepared by hyperbranching followed by silanization in Example 1 of the present invention.

[0029] Figures 3a-3b Digital photographs of the composite coating prepared in Example 1 of the present invention before and after erosion tests;

[0030] Figure 4 This is a SEM image of the carbon fiber modified by first silanization and then hyperbranching as described in Example 2 of the present invention;

[0031] Figure 5 This is a SEM image of the carbon fiber modified by first silanization and then hyperbranching as described in Example 3 of the present invention;

[0032] Figure 6 This is a SEM image of the carbon fiber modified by first hyperbranching and then silanization as described in Example 4 of the present invention.

[0033] Figure 7 This is a SEM image of the hyperbranched and then silanized modified carbon fiber described in Example 5 of the present invention.

[0034] Figure 8 This is a SEM image of the carbon fiber modified by first silanization and then hyperbranching as described in Example 7 of the present invention;

[0035] Figure 9 This is a SEM image of the oxidized carbon fiber described in Comparative Example 1 of the present invention;

[0036] Figures 10a-10b Digital photographs of the composite coating prepared in Comparative Example 1 of this invention before and after erosion tests.

[0037] Figure 11 This is a SEM image of the silanized modified carbon fiber described in Comparative Example 2 of the present invention.

[0038] Figure 12 This is a SEM image of the hyperbranched modified carbon fiber described in Comparative Example 3 of the present invention.

[0039] Figure 13This is a comparison diagram of the average interfacial shear strength between the modified carbon fibers and epoxy resins described in Examples 1-2 and Comparative Examples 1-3 of the present invention.

[0040] Figure 14 This is a comparison chart of the average mass loss and average volume loss of each carbon fiber composite coating described in Examples 1-2 and Comparative Examples 1-3 of the present invention after erosion tests.

[0041] Figure 15 This is a SEM image of the hyperbranched and then silanized modified carbon fiber in Comparative Example 4 of this invention, which was not subjected to oxidation treatment. Detailed Implementation

[0042] In view of the deficiencies of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. This method for synergistically modifying and enhancing the interfacial properties of carbon fiber composite coatings using a two-step chemical reaction includes: dust removal and desizing treatment of the carbon fiber, oxidation treatment, and a two-step chemical modification treatment. The technical solution of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0044] Specifically, as one aspect of the technical solution of this invention, a method for synergistic modification and enhancement of the interface properties of carbon fiber composite coatings through a two-step chemical reaction includes: performing silanization modification and hyperbranching modification on carbon fibers after oxidation treatment to obtain modified carbon fibers.

[0045] In some embodiments, a pretreatment of the hyperbranching modification is performed before the hyperbranching modification treatment; the pretreatment includes grafting polyisocyanate onto the surface of carbon fibers to obtain carbon fibers grafted with isocyanate.

[0046] In some preferred embodiments, the temperature for grafting polyisocyanate onto the carbon fiber surface is 20°C to 120°C, and the time is 30 min to 24 h.

[0047] In some more specific embodiments, the pretreatment specifically includes: mixing a polyisocyanate with a first organic solvent to form a polyisocyanate solution, adding carbon fibers and a catalyst, and reacting in a protective atmosphere to obtain carbon fibers grafted with isocyanate.

[0048] Furthermore, the concentration of polyisocyanate in the polyisocyanate solution is 0.05 mol / L to 5 mol / L.

[0049] Furthermore, the mass-to-volume ratio of the catalyst to the first organic solvent is (0g~0.5g):(2ml~200ml).

[0050] In some preferred embodiments, the polyisocyanate includes any one or a combination of two or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, dicyclohexylmethane diisocyanate, etc., and is not limited thereto.

[0051] In some preferred embodiments, the first organic solvent includes any one or a combination of two or more of benzene, xylene, cyclohexanone, acetone, butyl acetate, etc., and is not limited thereto.

[0052] In some preferred embodiments, the catalyst includes any one or a combination of two or more of dibutyltin dilaurate, stannous octoate, tin oleate, etc., and is not limited thereto.

[0053] In some preferred embodiments, the protective atmosphere is composed of a protective gas, which includes any one or a combination of two or more of nitrogen, carbon dioxide, helium, argon, etc., and is not limited thereto.

[0054] In some embodiments, the hyperbranching modification treatment includes: subjecting imidazole to hyperbranching polymerization of isocyanate-grafted carbon fibers in a protective atmosphere to obtain carbon fibers grafted with hyperbranched polyimide.

[0055] In some preferred embodiments, the hyperbranching polymerization reaction is carried out at a temperature of 30°C to 100°C for a time of 30 min to 72 h.

[0056] In some preferred embodiments, the hyperbranching modification treatment specifically includes: mixing imidazole with a first organic solvent to form an imidazole solution, and performing a hyperbranching polymerization reaction with isocyanate-grafted carbon fibers in a protective atmosphere to obtain carbon fibers grafted with hyperbranched polyimidazole.

[0057] Furthermore, the concentration of imidazole in the imidazole solution is 0.05 mol / L to 5 mol / L.

[0058] Furthermore, the protective atmosphere used in the hyperbranching modification treatment is the same as that used in the pretreatment.

[0059] In some embodiments, the silanization modification treatment includes:

[0060] A silane coupling agent, water, and a second organic solvent are mixed to carry out a hydrolysis pre-reaction to form a pre-reaction solution.

[0061] Carbon fibers are brought into full contact with a pre-reaction solution and subjected to reaction grafting to obtain carbon fibers grafted with polysiloxane.

[0062] In some preferred embodiments, the hydrolysis pre-reaction time of the silane coupling agent is 5 min to 4 h, and the temperature is 10 °C to 50 °C.

[0063] Furthermore, the volume ratio of the silane coupling agent to water is 13:(1-20).

[0064] In some preferred embodiments, the pH of the pre-reaction solution is 8 to 13 when the carbon fibers are added.

[0065] In some preferred embodiments, the silane coupling agent includes any one or a combination of two or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-isocyanate propyltriethoxysilane, and 3-isocyanate propyltrimethoxysilane, and is not limited thereto.

[0066] Furthermore, the second organic solvent includes, but is not limited to, methanol and / or ethanol, etc.

[0067] In some preferred embodiments, the reaction grafting time of the silanized modified carbon fiber is 10 min to 12 h, and the reaction grafting temperature is 20 °C to 70 °C.

[0068] In some implementations, in the method of synergistic modification and enhancement of the interfacial properties of carbon fiber composite coatings through two-step chemical reactions, the order of hyperbranching modification and silanization modification of the carbon fiber can be arbitrarily changed.

[0069] For example, such as Figure 1 As shown, in some more preferred embodiments, the method includes: first performing the hyperbranching modification treatment, and then performing the silanization modification treatment, specifically including:

[0070] Carbon fibers are oxidized to obtain oxidized carbon fibers;

[0071] Polyisocyanate is mixed with a first organic solvent to form a polyisocyanate solution, and carbon fiber oxide and a catalyst are added. The reaction is carried out in a protective atmosphere to obtain carbon fiber grafted with isocyanate.

[0072] Imidazole is mixed with a first organic solvent to form an imidazole solution, which is then subjected to hyperbranching polymerization of isocyanate-grafted carbon fibers in a protective atmosphere to obtain carbon fibers grafted with hyperbranched polyimide.

[0073] A silane coupling agent, water, and a second organic solvent are mixed to carry out a hydrolysis pre-reaction to form a pre-reaction solution.

[0074] The grafted hyperbranched polyimide carbon fiber was placed in a pre-reaction solution for reaction grafting to obtain hyperbranched polyimide modified carbon fiber grafted with polysiloxane.

[0075] For example, in some other, more preferred embodiments, the method includes: first performing the silanization modification treatment, and then performing the hyperbranching modification treatment, specifically including:

[0076] Carbon fibers are oxidized to obtain oxidized carbon fibers;

[0077] A silane coupling agent, water, and a second organic solvent are mixed to carry out a hydrolysis pre-reaction to form a pre-reaction solution.

[0078] The oxidized carbon fiber was placed in a pre-reaction solution for reaction grafting to obtain oxidized carbon fiber grafted with polysiloxane.

[0079] Polyisocyanate is mixed with a first organic solvent to form a polyisocyanate solution, and then grafted polysiloxane-coated carbon fibers and a catalyst are added. The reaction is carried out in a protective atmosphere to obtain grafted isocyanate and polysiloxane-coated carbon fibers.

[0080] Imidazole is mixed with a first organic solvent to form an imidazole solution, which is then subjected to hyperbranching polymerization with oxidized carbon fibers grafted with isocyanate and polysiloxane in a protective atmosphere to obtain polysiloxane-modified carbon fibers grafted with hyperbranched polyimide.

[0081] In some preferred embodiments, the oxidation treatment includes: oxidizing the carbon fiber with an oxidizing agent to give the carbon fiber surface polar functional groups, the polar functional groups including at least one of hydroxyl, ketone, carboxyl, etc.; the oxidizing agent may include any one or a combination of two or more of fluorine, oxygen, ozone, nitric acid, concentrated sulfuric acid, hypochlorous acid, hydrogen peroxide, potassium permanganate, potassium dichromate, potassium persulfate, etc., and is not limited thereto.

[0082] In some preferred embodiments, the method further includes: treating the carbon fibers with an alkaline solution or an organic solvent to remove dust and slurry before oxidizing them.

[0083] The organic solvent may include any one or a combination of two or more of acetone, ethanol, cyclohexanone, tetrahydrofuran, toluene, petroleum ether, etc., and is not limited thereto.

[0084] In some preferred embodiments, the carbon fiber includes any one or a combination of two or more of carbon fiber powder, chopped carbon fiber, and carbon fiber cloth, but is not limited thereto.

[0085] In some preferred embodiments, the method for synergistic modification and enhancement of the interfacial properties of the carbon fiber composite coating through two-step chemical reaction is completed in four steps: dust removal and desizing treatment of carbon fiber, oxidation treatment, silanization modification treatment, and hyperbranching modification treatment. The specific steps are as follows:

[0086] Dust removal and slurry removal treatment: Untreated carbon fibers are washed in an alkaline solution (such as sodium hydroxide solution), separated and dried to obtain dust-removed carbon fibers; then the dust-removed carbon fibers are washed in an organic solvent (such as acetone), separated and dried to obtain carbon fibers with no dust and slurry on the surface.

[0087] Oxidation treatment (i.e. activation): Oxidizing desizing carbon fibers with an oxidizing agent (such as a mixed aqueous solution of potassium persulfate / silver nitrate) will give the carbon fibers a polar functional group such as hydroxyl, ketone, and carboxyl groups on their surface after oxidation.

[0088] Two-step chemical modification:

[0089] (1) Hyperbranching modification treatment

[0090] Pretreatment before hyperbranching modification: Polyisocyanate is added to the first organic solvent and dispersed evenly, then dry carbon oxide carbon fiber and catalyst are added, and after the protective gas is introduced to remove air and moisture, the reaction is carried out to obtain carbon fiber grafted with isocyanate.

[0091] Hyperbranching polymerization reaction: Imidazole is dissolved in a first organic solvent to obtain an imidazole solution, which is then added to the reaction system. Under a protective atmosphere, it undergoes a hyperbranching polymerization reaction with isocyanate-grafted carbon fibers. After separation, carbon fibers grafted with hyperbranched polyimide are obtained.

[0092] (2) Silanization modification treatment

[0093] A silane coupling agent and water are added to a second organic solvent for hydrolysis pre-reaction;

[0094] Hyperbranched polyimidazolium-modified carbon fibers were placed in a pre-reaction solution for further reaction, and after separation, hyperbranched polyimidazolium-modified carbon fibers grafted with polysiloxane were obtained.

[0095] As another aspect of the technical solution of the present invention, it relates to modified carbon fibers obtained by the aforementioned method.

[0096] In some embodiments, the modified carbon fiber surface has a modulus gradient transition layer, which includes any one of a hyperbranched polyimidazolium layer, a polysiloxane layer, or a superposition layer of hyperbranched polyimidazolium and polysiloxane.

[0097] In some embodiments, the thickness of the modulus gradient transition layer is 20 nm to 2 μm. The thickness of the modulus gradient transition layer on the carbon fiber surface can be controlled by changing the time of the two-step chemical modification of the carbon fiber.

[0098] Specifically, the modified carbon fiber exhibits an interfacial shear strength of 44.1 MPa to 75.3 MPa between the modified carbon fiber monofilament and resin droplets of 30 μm to 50 μm.

[0099] The polymer grafting on the carbon fiber surface prepared by the above modification method is uniform, the number of polar functional groups is greatly increased, and the wettability and adhesion between the resin and the carbon fiber are significantly improved, thereby greatly improving the interfacial performance of the composite coating. Furthermore, a modulus gradient transition layer is constructed between the carbon fiber and the resin with unbalanced modulus difference, so that the load can be effectively transferred from the resin to the carbon fiber, avoiding stress concentration and thus extending the service life of the composite coating.

[0100] As another aspect of the technical solution of the present invention, a method for preparing a carbon fiber reinforced composite coating includes:

[0101] The modified carbon fiber is mixed evenly with the resin matrix to form a first mixture;

[0102] Add the curing agent and defoamer to the first mixture and mix them evenly to obtain the second mixture;

[0103] The second mixture is applied to the surface of a metal substrate and cured to obtain a carbon fiber reinforced composite coating.

[0104] In some preferred embodiments, the mass ratio of the modified carbon fiber to the resin matrix is ​​1:(14.5 to 76.5).

[0105] In some preferred embodiments, the mass ratio of the modified carbon fiber to the curing agent is 1:(4-23).

[0106] In some preferred embodiments, the mass ratio of the defoamer to the total mass of the modified carbon fiber, resin matrix, and curing agent is (0.001 to 0.005):1.

[0107] In some preferred embodiments, the composite coating is made from modified carbon fibers, a resin matrix, and a curing agent.

[0108] In some preferred embodiments, the resin matrix may include any one or a combination of two or more of epoxy resin, phenolic resin, acrylic resin, polyurethane, unsaturated polyester resin, etc., and is not limited thereto.

[0109] Furthermore, the curing agent may include any one or a combination of two or more of amine curing agents, acid anhydride curing agents, isocyanate curing agents, and thiol curing agents, and is not limited thereto.

[0110] Furthermore, the defoamer may include any one or a combination of two or more of alcohol-based defoamers, polyether-based defoamers, and silicone-based defoamers, and is not limited thereto.

[0111] In some preferred embodiments, the preparation method includes: mixing the modified carbon fiber with a resin matrix to form a first mixture, and degassing it in a vacuum environment for 10 min to 30 min.

[0112] In some preferred embodiments, the preparation method includes: adding a curing agent and a defoamer to the first mixture, and placing it in a vacuum environment to degas for 10 min to 30 min to obtain a uniformly dispersed second mixture.

[0113] In some preferred embodiments, the preparation method includes: coating the second mixture onto the surface of a metal substrate, allowing the coating to cure once at room temperature for 12h to 48h, and then placing it in a high-temperature environment of 60℃ to 100℃ for a second curing for 12h to 48h to obtain a carbon fiber reinforced composite coating.

[0114] In some preferred embodiments, a method for preparing a carbon fiber reinforced composite coating specifically includes the following steps:

[0115] ① The modified carbon fiber and resin matrix are mixed evenly to form a first mixture, and then placed in a vacuum environment for degassing for 10 min to 30 min;

[0116] ② Add the curing agent and defoamer to the first mixture, mix them evenly to obtain the second mixture, and place it in a vacuum environment to degas for 10 min to 30 min to obtain a uniformly dispersed carbon fiber reinforced composite coating precursor;

[0117] ③ The carbon fiber reinforced composite coating precursor is coated on the surface of the metal substrate and placed horizontally at room temperature for 12h to 48h to allow the coating to basically cure. Then, it is placed in a high temperature environment of 60℃ to 100℃ for 12h to 48h to obtain the carbon fiber reinforced composite coating.

[0118] As another aspect of the technical solution of this invention, it also relates to a carbon fiber reinforced composite coating prepared by the aforementioned method. The carbon fiber reinforced composite coating prepared by this invention has excellent mechanical properties, friction and wear resistance, and erosion wear resistance, and can effectively inhibit corrosion damage to steel structures in marine environments for a long period of time.

[0119] Furthermore, when the thickness of the carbon fiber reinforced composite coating is 3.25 mm to 3.88 mm, its tensile strength is 68.3 MPa to 86.6 MPa.

[0120] Furthermore, the wear rate of the carbon fiber reinforced composite coating after the friction test was 4.4 × 10⁻⁶. -5 (mm 3 / Nm)~8.0×10 -5 (mm 3 / Nm).

[0121] Furthermore, the carbon fiber reinforced composite coating experiences a mass loss of 0.60g to 0.83g after an erosion test when the mass is between 21.99g and 23.61g.

[0122] As another aspect of the technical solution of the present invention, it also relates to the application of the carbon fiber reinforced composite coating in the field of substrate protection.

[0123] The substrate includes steel structure facilities.

[0124] Specifically, the applications include the application of the carbon fiber reinforced composite coating on steel structures serving in marine splash zones.

[0125] In summary, the method provided by this invention is suitable for improving the interfacial properties of carbon fiber composite coatings. After the modified carbon fiber is mixed with resin and curing agent and cured, the resulting carbon fiber composite coating has excellent mechanical properties, wear resistance, and erosion resistance, which can effectively reduce the corrosion, erosion and wear damage to steel structures caused by complex and harsh marine environments such as the splash zone.

[0126] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0127] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0128] Example 1

[0129] I. Dust and Slurry Removal Treatment for Carbon Fiber

[0130] ① Add 16g of sodium hydroxide and 200ml of deionized water to a glass container and sonicate for 3 minutes to obtain a 2M sodium hydroxide solution.

[0131] ② Add 5g of carbon fiber to the sodium hydroxide solution, and then place the glass container containing the mixture of carbon fiber and sodium hydroxide solution in a heating device at 85℃.

[0132] ③ Heat and stir the mixture of carbon fiber and sodium hydroxide solution from process ②, control the stirring speed at 400 r / min for 2 hours, then stop heating and let it cool to room temperature before filtering the mixture to obtain dust removal carbon fiber;

[0133] ④ Use deionized water to stir and wash the treated carbon fiber, then filter it. Repeat this process 3 times. Place the obtained carbon fiber in a constant temperature drying oven and dry it at 100℃ for 12 hours to obtain dried dust removal carbon fiber.

[0134] ⑤ Add 5g of dust-removing carbon fiber to a glass container containing 200ml of acetone. Place the glass container on a heating device and set up a reflux device. Control the heating temperature to 65℃ and stir at a stirring speed of 400r / min for 6 hours. Then filter the mixture to obtain desizing carbon fiber.

[0135] ⑥ Immerse the desizing carbon fiber obtained in step ⑤ in deionized water at room temperature, control the stirring speed at 200 r / min, stir for 1 min and let stand for 3 min to allow the carbon fiber to settle, then remove the impurities floating on the water surface and pour out for filtration.

[0136] ⑦ Repeat process ⑥ 3 times to obtain desizing carbon fiber after being cleaned with deionized water. Then place it in a constant temperature drying oven and dry it continuously at 100℃ for 12 hours to obtain dried desizing carbon fiber.

[0137] II. Carbon Fiber Oxidation Treatment

[0138] ① Add 20.65g potassium persulfate, 0.14g silver nitrate and 400ml deionized water to a glass container, then place the glass container in a heating device at 85℃ and stir to dissolve for 15min. Set the stirring speed to 700r / min to obtain a potassium persulfate / silver nitrate mixed aqueous solution.

[0139] ② Add 3g of dried desizing carbon fiber to a mixed aqueous solution of potassium persulfate / silver nitrate, maintain the temperature at 85℃, adjust the stirring speed to 400r / min, and continue stirring for 4h. After the reaction is completed, filter while hot to obtain oxidized carbon fiber.

[0140] ③ Soak the obtained oxidized carbon fiber in deionized water and stir at a stirring speed of 200 r / min for 5 min, then pour it out and filter it for separation;

[0141] ④ Repeat process ③ 3 times to obtain carbon dioxide carbon fiber after being cleaned with deionized water. Place it in a constant temperature drying oven and dry it at 100℃ for 12 hours to obtain dried carbon dioxide carbon fiber.

[0142] III. Hyperbranching Modification Treatment of Carbon Fiber

[0143] ① Add 4.95g of isophorone diisocyanate to a glass container containing 30ml of acetone, disperse by ultrasonic vibration for 3min, then add 0.5g of dry carbon dioxide and 0.02g of dibutyltin dilaurate, purge the air and moisture from the glass container with nitrogen, and react in a closed environment at a heating temperature of 55℃ and a stirring speed of 600r / min for 6h to obtain reaction product I;

[0144] ② Add 1.65g of imidazole to 30ml of acetone and vortex for 2min to obtain an imidazole-acetone solution;

[0145] ③ Add the imidazole acetone solution dropwise to the reaction product I in process ① at a rate of 3 drops / second, and react for 24 hours at a temperature of 60℃, a stirring speed of 800 r / min and a closed environment to obtain a uniformly dispersed reaction product II;

[0146] ④ The reaction product II obtained in process ③ is filtered to obtain hyperbranched polyimide-modified carbon fiber. Then, the carbon fiber is soaked and washed for 5 minutes at room temperature with 50 ml of methanol and 50 ml of anhydrous ethanol at a stirring speed of 200 r / min. The washing is repeated twice. After separation by filtration, the carbon fiber is placed in a constant temperature drying oven at 90℃ and dried for 24 hours to obtain dried hyperbranched modified carbon fiber.

[0147] IV. Silanization Modification Treatment of Carbon Fibers

[0148] ① Add 5 ml of 3-aminopropyltriethoxysilane and 90 ml of anhydrous ethanol to a glass container and stir vigorously at 800 r / min for 5 min to obtain a 3-aminopropyltriethoxysilane solution.

[0149] ② Add 5 ml of deionized water to the 3-aminopropyltriethoxysilane solution under vigorous stirring, then adjust the stirring speed to 500 r / min and react at room temperature for 1 h to obtain reaction product III;

[0150] ③ Adjust the pH of reaction product III to 10, then add 0.5g of hyperbranched modified carbon fiber to reaction product III, and stir at 400r / min for 2h at room temperature to obtain reaction product IV;

[0151] ④ The reaction product IV was filtered, and the resulting carbon fiber was soaked in 100ml of anhydrous ethanol for 5min and then filtered again. After repeated washing and filtration twice, it was placed in a constant temperature drying oven at 90℃ for 8h to obtain the dried modified carbon fiber that was first hyperbranched and then silanized.

[0152] V. Preparation of Carbon Fiber Composite Coating

[0153] ① Mix 0.975g of dried, hyperbranched and then silanized modified carbon fiber with 29.25g of GCC135 epoxy resin to form mixture I, and place it in a -0.1MPa vacuum environment for degassing for 20min.

[0154] ② Add 8.775g of GCC137 curing agent and 0.08g of defoamer to mixture I, mix evenly to obtain mixture II, and degas in a -0.1MPa vacuum environment for 15 minutes to obtain a uniformly dispersed carbon fiber reinforced composite coating;

[0155] ③ Apply the carbon fiber reinforced composite coating described in step ② to the surface of the metal substrate, keep it horizontal at room temperature for 24 hours to allow the coating to basically cure, and then place it in a high temperature environment of 80℃ for 24 hours to cure to obtain the carbon fiber reinforced composite coating.

[0156] Figure 2 The image shown is an SEM image of the modified carbon fiber prepared in this embodiment, which was first hyperbranched and then silanized. It can be seen that the protruding particles are hyperbranched polyimide macromolecules grafted onto the carbon fiber surface through the first chemical reaction, increasing the surface roughness of the carbon fiber and providing more mechanical interlocking physical anchor points for the interfacial bonding between the fiber and the resin. Encasing the carbon fiber and protruding particles is a uniform layer of aminopropyl polysiloxane grafted onto the carbon fiber surface through the second chemical reaction. The amino groups on the side chains of the polysiloxane greatly enhance the surface energy of the carbon fiber, providing abundant chemical bonding reaction sites. Therefore, the two-step chemical reaction synergistic modification method significantly improves the bonding between the carbon fiber and the epoxy resin, enhancing interfacial properties. Compared to comparative examples 1-3, the composite coating prepared in this embodiment exhibits superior mechanical properties, erosion resistance, and friction and wear resistance.

[0157] Microbead debonding tests showed that the carbon fiber composite coating prepared in this embodiment has excellent interfacial adhesion. The interfacial shear strength between the fiber and the resin was 66.23 MPa, which was 58.7% higher than that of Comparative Example 1 without two-step chemical reaction modification treatment. Similarly, it was also higher than the interfacial shear strength of all other comparative examples (e.g., ...). Figure 13 As shown in the figure, the data are the average values ​​after 20 experiments, indicating that the two-step chemical reaction synergistically enhances the interfacial properties between carbon fiber and resin, thereby improving the mechanical properties of the composite coating.

[0158] The parameters selected for the erosion test were as follows: the erosion material was a mixture of silicon carbide and water with a mass concentration of 10 wt%, the solid-liquid two-phase flow ejection pressure was 0.2 MPa, the impact time was 15 min, and the impact direction was perpendicular to the coating surface.

[0159] Erosion tests show that the carbon fiber composite coating prepared in this embodiment has excellent resistance to erosion and wear. Figure 3a and Figure 3b , Figure 10a and Figure 10b As can be seen, the area of ​​the erosion pits formed on the surface of the composite coating prepared in this embodiment is significantly smaller than that of the erosion pits in Comparative Example 1. After 15 minutes of high-speed rinsing with silicon carbide and water, the composite coating of this embodiment experienced a mass loss of 629.6 mg and a volume loss of 380.38 mm. 3 The values ​​are all lower than those of the comparative composite coating (such as...). Figure 14 As shown in the figure, the data are the average values ​​after 5 experiments. The carbon fiber composite coating prepared in Comparative Example 1 suffered the greatest loss in both mass and volume: a mass loss of 893.4 mg and a volume loss of 575.97 mm². 3 Compared to this, the carbon fiber composite coating in this embodiment reduces mass loss by 29.5% and volume loss by 34%.

[0160] This embodiment illustrates that by synergistically modifying carbon fibers through a two-step chemical reaction of hyperbranching followed by silanization, a modulus gradient transition layer can be constructed on the surface of the carbon fibers, reducing the huge modulus difference between the fibers and the resin, improving load transfer efficiency, and enhancing the interfacial properties of the carbon fiber composite coating.

[0161] Example 2

[0162] This embodiment is basically the same as Embodiment 1, except that: in this embodiment, step three is carbon fiber silanization modification treatment, and step four is carbon fiber hyperbranching modification treatment, which is the reverse of the order in Embodiment 1.

[0163] like Figure 4 The image shown is a SEM image of the modified carbon fiber prepared in this embodiment, which was first silanized and then hyperbranched. First, the first step of chemical modification grafted a layer of polysiloxane onto the carbon fiber surface. The abundant side-chain amino groups of the polysiloxane greatly improved the surface energy of the carbon fiber and laid the foundation for the subsequent uniform grafting of hyperbranched polyimide. In the second step of the chemical reaction, hyperbranched polyimide grew in situ using amino groups as reaction sites, grafting a layer of dense nanoparticles onto the carbon fiber surface. This significantly improved the surface roughness and wettability of the carbon fiber and provided numerous mechanical interlocking anchor points for subsequent bonding with the resin.

[0164] The microsphere debonding test showed that the interfacial shear strength between the modified carbon fiber and epoxy resin obtained according to this example was 65.97 MPa, which was 58.1% higher than that of Comparative Example 1 without two-step chemical modification (e.g., ...). Figure 13 (As shown).

[0165] Erosion tests showed that the carbon fiber composite coating suffered a mass loss of 663.9 mg and a volume loss of 419.66 mm after the erosion test. 3 Compared with the comparative example, its mechanical properties, erosion resistance, and friction and wear resistance are superior (e.g., Figure 14 (As shown).

[0166] This embodiment illustrates that by changing the order of the two-step chemical reaction, a modulus gradient transition layer can also be constructed on the carbon fiber surface, improving load transfer efficiency. At the same time, it greatly improves the bonding between carbon fiber and epoxy resin, enhances interfacial properties, and thus improves the overall performance of the composite coating.

[0167] Example 3

[0168] This embodiment is basically the same as Embodiment 2, except that the time for the hyperbranching polymerization reaction of carbon fibers in this embodiment is extended from 24h to 48h.

[0169] like Figure 5 The image shown is a SEM image of the modified carbon fiber prepared by first silanization and then hyperbranching in this embodiment.

[0170] This embodiment illustrates that by changing the time of the hyperbranching polymerization reaction, the thickness of the modulus gradient transition layer on the carbon fiber surface can be altered, thereby affecting the overall performance of the composite coating.

[0171] Example 4

[0172] This embodiment is basically the same as Embodiment 1, except that the polyisocyanate selected in the carbon fiber hyperbranching modification step in this embodiment is hexamethylene diisocyanate instead of isophorone diisocyanate.

[0173] like Figure 6 The image shown is a SEM image of the modified carbon fiber prepared in this embodiment, which was first hyperbranched and then silanized. Comparison with the surface morphology of the carbon fiber prepared in Example 1 reveals that their morphologies and structures are highly similar. Furthermore, erosion tests show that the composite coating prepared in this embodiment exhibits a mass loss of 655.4 mg after erosion testing, demonstrating superior erosion resistance compared to Example 2.

[0174] This embodiment illustrates that grafting other polyisocyanates as described in claim 4 onto the surface of carbon fibers and then reacting them with imidazole to undergo hyperbranching can also effectively improve the surface energy and roughness of carbon fibers, enhance the interfacial bonding between carbon fibers and the resin matrix, and improve the erosion resistance of the composite coating.

[0175] Example 5

[0176] This embodiment is basically the same as Embodiment 1, except that the silane coupling agent selected in the carbon fiber silanization modification step in this embodiment is 3-aminopropyltrimethoxysilane, rather than 3-aminopropyltriethoxysilane.

[0177] like Figure 7 The image shown is a SEM image of the modified carbon fibers prepared in this embodiment, which were first hyperbranched and then silanized. (Observation and comparison) Figure 2 and Figure 7 It was found that the polysiloxane layer on the surface of the hyperbranched and then silanized modified carbon fibers prepared using 3-aminopropyltrimethoxysilane was relatively thin, resulting in greater surface roughness. Erosion tests showed that the composite coating prepared in this example had a mass loss of 614.5 mg after erosion testing, exhibiting superior erosion resistance compared to Example 1. Grafting 3-aminopropyltrimethoxysilane not only increased the number of active groups on the carbon fiber surface but also improved the roughness, enhancing the mechanical interlocking between the carbon fiber and the resin matrix.

[0178] This embodiment illustrates that modifying carbon fibers with other silane coupling agents as described in claim 5 can also significantly increase the number of active groups on the surface of carbon fibers, enhance the mechanical interlocking and chemical bonding between carbon fibers and the resin matrix, thereby improving the erosion resistance of the composite coating.

[0179] Example 6

[0180] The processing steps for the modified carbon fiber in this embodiment are completely consistent with those in Example 1, except for the preparation steps of the carbon fiber composite coating. In this embodiment, the resin matrix selected is type 191 unsaturated polyester resin, and methyl ethyl ketone peroxide is selected as the curing agent, with cobalt isooctanoate as the accelerator. The ratio of unsaturated polyester resin to curing agent is 100:0.8-1.5, and the ratio of unsaturated polyester resin to accelerator is 100:0.5-1. The preparation process of the carbon fiber composite coating is as follows:

[0181] ① Mix 1g of dried, hyperbranched and then silanized modified carbon fiber, 38.42g of type 191 unsaturated polyester resin and 0.19g of accelerator evenly to form mixture I, and place it in a -0.1MPa vacuum environment for degassing for 10min;

[0182] ② Add 0.38g of V388 curing agent to mixture I, mix evenly to obtain mixture II, and then obtain a uniformly dispersed carbon fiber reinforced composite coating;

[0183] ③ Pour the carbon fiber reinforced composite coating described in step ② into the mold, keep it horizontal at room temperature for 24 hours to allow the coating to cure, and then demold to obtain the carbon fiber reinforced composite coating.

[0184] Tensile tests showed that the composite coating prepared in this embodiment had a tensile strength of 72.1 MPa, while the composite coating prepared with oxidized carbon fiber as filler had a tensile strength of 56.8 MPa. Compared with the latter, the tensile strength of the composite coating in this embodiment was increased by 26.94%. After erosion testing, the composite coating prepared in this embodiment had a mass loss of 726.3 mg, while the composite coating with oxidized carbon fiber as filler had a mass loss of 1218.4 mg. In comparison, the mass loss of the composite coating in this embodiment was reduced by 40.39%. This indicates that a modulus gradient transition layer was constructed between the carbon fiber and the resin matrix through two-step chemical modification, which can effectively transfer the load from the resin matrix to the fiber. Furthermore, the interfacial bonding between the two is better, thereby significantly improving the mechanical properties and erosion resistance of the composite coating.

[0185] This embodiment illustrates that composite coatings with excellent performance can also be obtained by combining other resin matrices as described in claim 9 with carbon fibers modified by the two-step chemical reaction described in this invention.

[0186] Example 7

[0187] This embodiment is basically the same as Embodiment 2, except that the amount of isophorone diisocyanate added in the carbon fiber hyperbranching modification step is 0.495g.

[0188] like Figure 8 The image shown is a SEM image of the modified carbon fibers prepared in this embodiment, which were first silanized and then hyperbranched. Because the concentration of isophorone diisocyanate was reduced by a factor of 10 compared to Example 2, in conjunction with... Figure 4 At the same magnification, almost no spherical hyperbranched polyimide particles can be observed on the surface of carbon fibers. When the magnification is 7×10⁻⁶, however, spherical hyperbranched polyimide particles are not visible. 4 When doubled, it was observed that... Figure 4 Same surface structure.

[0189] This embodiment illustrates that changing the concentration of reactants alters the growth size of the polymer, the degree of grafting on the carbon fiber surface, and the morphology of the carbon fiber surface, thereby affecting the interfacial bonding between the carbon fiber and the resin matrix, as well as the overall performance of the composite coating.

[0190] Example 8

[0191] This embodiment is basically the same as Example 1, except that: the polyisocyanate is lysine diisocyanate, the temperature for grafting the polyisocyanate onto the carbon fiber surface is 20°C and the time is 24h; the concentration of the polyisocyanate is 0.05mol / L, and the temperature for the hyperbranching polymerization reaction is 30°C and the time is 72h.

[0192] The hydrolysis pre-reaction temperature was 10℃, the time was 4h, and the pH value of the pre-reaction solution was 8; the reaction grafting time of the silanized modified carbon fiber was 10min, and the reaction grafting temperature was 70℃.

[0193] The mass ratio of the modified carbon fiber to the resin matrix is ​​1:14.5; the mass ratio of the modified carbon fiber to the curing agent is 1:4.

[0194] The coating preparation method includes: coating the second mixture onto the surface of a metal substrate, allowing the coating to cure at room temperature for 12 hours, and then curing it a second time at 60°C for 48 hours to obtain a carbon fiber reinforced composite coating.

[0195] Example 9

[0196] This embodiment is basically the same as Example 1, except that: the polyisocyanate is dicyclohexylmethane diisocyanate, the temperature used to graft the polyisocyanate onto the carbon fiber surface is 120°C and the time is 30 min; the concentration of the polyisocyanate is 5 mol / L, and the temperature of the hyperbranching polymerization reaction is 100°C and the time is 30 min.

[0197] The hydrolysis pre-reaction temperature was 50℃, the time was 5 min, and the pH value of the pre-reaction solution was 13; the reaction grafting time of the silanized modified carbon fiber was 12 h, and the reaction grafting temperature was 20℃.

[0198] The mass ratio of the modified carbon fiber to the resin matrix is ​​1:76.5; the mass ratio of the modified carbon fiber to the curing agent is 1:23.

[0199] The coating preparation method includes: coating the second mixture onto the surface of a metal substrate, allowing the coating to cure at room temperature for 48 hours, and then placing it in a high-temperature environment of 100°C for a second curing for 12 hours to obtain a carbon fiber reinforced composite coating.

[0200] Example 8N9 illustrates that using different reaction temperatures, reaction times, reaction concentrations, and pH values ​​to perform hyperbranching and silanization modifications on fibers can effectively improve the surface roughness and interfacial compatibility of the fibers, improve the interfacial bonding with the resin matrix, and construct a modulus gradient transition layer on the carbon fiber surface, thereby promoting the transfer of stress concentration, effectively inhibiting the initiation and propagation of cracks at the interface, and thus improving the overall performance and service life of the composite coating.

[0201] Comparative Example 1

[0202] This comparative example is basically the same as Example 1, except that the carbon fibers in this comparative example were not subjected to silanization and hyperbranching modification after oxidation treatment.

[0203] like Figure 9The image shown is a SEM image of the oxidized carbon fiber in this comparative example. Figures 10a-10b Digital photographs of the composite coating prepared in this comparative example before and after erosion tests. The interfacial shear strength between carbon fiber and epoxy resin is shown. Figure 13 The comparison chart of mass loss and volume loss of the composite coating after erosion test is shown in the figure. Figure 14 .

[0204] Comparative Example 2

[0205] This comparative example is basically the same as Example 1, except that the carbon fibers in this comparative example were silanized after oxidation treatment, but not hyperbranched.

[0206] like Figure 11 The image shown is a SEM image of the silanized modified carbon fiber prepared in this comparative example. The interfacial shear strength between the carbon fiber and epoxy resin is shown in [reference needed]. Figure 13 For a comparison of mass loss and volume loss after erosion testing of the composite coating, please refer to the graph. Figure 14 .

[0207] Comparative Example 3

[0208] This comparative example is basically the same as Example 1, except that the carbon fibers in this comparative example were hyperbranched after oxidation treatment, but were not silanized.

[0209] like Figure 12 The image shown is a SEM image of the hyperbranched modified carbon fiber prepared in this comparative example. The interfacial shear strength between the carbon fiber and epoxy resin is shown in [reference needed]. Figure 13 For a comparison of mass loss and volume loss after erosion testing of the composite coating, please refer to the graph. Figure 14 .

[0210] Comparative Examples 1-3 demonstrate that the interfacial properties between carbon fibers and resin are inferior to those obtained by performing two-step modification or only performing two-step chemical modification in either step. Furthermore, the mechanical strength, wear resistance, and erosion resistance of the resulting composite coating cannot be significantly improved.

[0211] Comparative Example 4

[0212] This comparative example is basically the same as Example 1, except that the carbon fiber in this comparative example was not oxidized.

[0213] like Figure 15 The image shown is a SEM image of the surface morphology of the carbon fiber prepared in this comparative example. (Comparison) Figure 2 and Figure 15It was found that the carbon fiber surface did not exhibit the morphology of a polysiloxane layer encapsulating large hyperbranched polyimide particles as seen in Example 1. Instead, a thin polysiloxane layer covered the carbon fiber with small, protruding polysiloxane particles. This is because oxidation treatment activates the carbon fiber surface, introducing hydroxyl and carboxyl functional groups, providing reaction sites for subsequent hyperbranching modification. Without oxidation treatment, polyisocyanate cannot be chemically bonded to the fiber surface, and hyperbranched polyimide cannot grow in situ on the fiber surface, resulting in the absence of a hyperbranched polyimide layer. Only a small number of hyperbranched polyimide particles are deposited on the fiber surface, weakening the modulus gradient transition layer between the carbon fiber and the resin matrix.

[0214] Friction and wear tests showed that the composite coating prepared in this comparative example had a wear rate of 7.94 × 10⁻⁶ after the friction and wear test. -5 (mm 3 / Nm), compared to the composite coating prepared in Comparative Example 2 (7.99×10). -5 (mm 3 The wear rate ( / Nm) is close to, but much higher than, that of the composite coating prepared in Example 1 (5.77 × 10⁻⁶). -5 (mm 3 The wear rate of / Nm indicates that the lack of oxidation treatment reduces the wear resistance of the two-step chemically modified carbon fiber composite coating.

[0215] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0216] It should be understood that the technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made to the technical solutions of the present invention without departing from the spirit and scope of the claims are within the scope of protection of the present invention.

Claims

1. A method for synergistic modification and enhancement of the interfacial properties of carbon fiber composite coatings through a two-step chemical reaction, characterized in that, include: Carbon fibers are oxidized using an oxidizing agent to give the carbon fiber surface polar functional groups, wherein the polar functional groups are selected from at least one of hydroxyl, ketone, and carboxyl groups. The carbon fibers after oxidation treatment are first subjected to hyperbranching modification, and then to silanization modification. Before performing the hyperbranching modification treatment, a pretreatment for hyperbranching modification is performed first; The pretreatment includes: grafting polyisocyanate onto the surface of carbon fibers to obtain carbon fibers grafted with isocyanate; The hyperbranching modification treatment includes: in a protective atmosphere, imidazole and isocyanate-grafted carbon fibers undergo a hyperbranching polymerization reaction to obtain carbon fibers grafted with hyperbranched polyimide; the temperature of the hyperbranching polymerization reaction is 30℃~100℃, and the time is 30min~72h. The silanization modification treatment includes: A silane coupling agent, water, and a second organic solvent are mixed and subjected to a hydrolysis pre-reaction to form a pre-reaction solution; the temperature of the hydrolysis pre-reaction is 10℃~50℃, and the time is 5min~4h. Carbon fibers are brought into full contact with a pre-reaction solution and subjected to reaction grafting to obtain silanized modified carbon fibers grafted with polysiloxane. The reaction grafting time of the silanized modified carbon fibers is 10 min to 12 h, and the reaction grafting temperature is 20 ℃ to 70 ℃.

2. The method according to claim 1, characterized in that: The temperature for grafting polyisocyanate onto the carbon fiber surface is 20℃~120℃, and the time is 30min~24h.

3. The method according to claim 1, characterized in that, The pretreatment includes: mixing polyisocyanate with a first organic solvent to form a polyisocyanate solution, adding carbon fibers and a catalyst, and reacting in a protective atmosphere to obtain carbon fibers grafted with isocyanate.

4. The method according to claim 1, characterized in that, The hyperbranching modification process includes: mixing imidazole with a first organic solvent to form an imidazole solution, and then performing a hyperbranching polymerization reaction with isocyanate-grafted carbon fibers in a protective atmosphere to obtain carbon fibers grafted with hyperbranched polyimidazole.

5. The method according to claim 3, characterized in that: The concentration of polyisocyanate in the polyisocyanate solution is 0.05 mol / L to 5 mol / L.

6. The method according to claim 3, characterized in that: The mass-to-volume ratio of the catalyst to the first organic solvent is (0g~0.5g):(2ml~200ml).

7. The method according to claim 3, characterized in that: The polyisocyanate is selected from any one or a combination of two or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, and dicyclohexylmethane diisocyanate.

8. The method according to claim 3, characterized in that: The first organic solvent is selected from any one or a combination of two or more of benzene, xylene, cyclohexanone, acetone, and butyl acetate.

9. The method according to claim 3, characterized in that: The catalyst is selected from any one or a combination of two of dibutyltin dilaurate and stannous octoate.

10. The method according to claim 4, characterized in that: The concentration of imidazole in the imidazole solution is 0.05 mol / L to 5 mol / L.

11. The method according to claim 4, characterized in that: The protective atmosphere is composed of a protective gas, which is selected from any one or a combination of two or more of nitrogen, carbon dioxide, helium, and argon.

12. The method according to claim 1, characterized in that: The silane coupling agent is selected from any one or a combination of two or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-isocyanate propyltriethoxysilane, and 3-isocyanate propyltrimethoxysilane.

13. The method according to claim 1, characterized in that: The second organic solvent is selected from methanol and / or ethanol.

14. The method according to claim 1, characterized in that: The volume ratio of the silane coupling agent to water is 13:(1~20).

15. The method according to claim 1, characterized in that: The pH value of the pre-reaction solution is 8-13.

16. The method according to claim 1, characterized in that, include: The process involves first performing the hyperbranching modification treatment, followed by the silanization modification treatment, specifically including: Carbon fibers are oxidized to obtain oxidized carbon fibers; Polyisocyanate is mixed with a first organic solvent to form a polyisocyanate solution, and carbon fiber oxide and a catalyst are added. The reaction is carried out in a protective atmosphere to obtain carbon fiber grafted with isocyanate. Imidazole is mixed with a first organic solvent to form an imidazole solution, which is then subjected to hyperbranching polymerization of isocyanate-grafted carbon fibers in a protective atmosphere to obtain carbon fibers grafted with hyperbranched polyimide. A silane coupling agent, water, and a second organic solvent are mixed to carry out a hydrolysis pre-reaction to form a pre-reaction solution. The grafted hyperbranched polyimide carbon fiber was placed in a pre-reaction solution for reaction grafting to obtain hyperbranched polyimide modified carbon fiber grafted with polysiloxane.

17. The method according to claim 1, characterized in that: The oxidant is selected from any one or a combination of two or more of the following: fluorine, oxygen, ozone, nitric acid, concentrated sulfuric acid, hypochlorous acid, hydrogen peroxide, potassium permanganate, potassium dichromate, and potassium persulfate.

18. The method according to claim 17, characterized in that, The method further includes: before oxidizing the carbon fiber, treating the carbon fiber with an alkaline solution and an organic solvent to remove dust and slurry, wherein the organic solvent is selected from any one or a combination of two or more of acetone, ethanol, cyclohexanone, tetrahydrofuran, toluene, and petroleum ether.

19. The method according to claim 17, characterized in that: The carbon fiber is selected from any one or a combination of two or more of carbon fiber powder, chopped carbon fiber, and carbon fiber cloth.

20. The modified carbon fiber prepared by the method according to any one of claims 1-19, characterized in that, The modified carbon fiber surface has a modulus gradient transition layer, which is a superposition layer of hyperbranched polyimide and polysiloxane, and the thickness of the modulus gradient transition layer is 20nm~2μm. The interfacial shear strength between the modified carbon fiber monofilament and the resin droplets of 30μm~50μm is 44.1MPa~75.3MPa.

21. A method for preparing a carbon fiber reinforced composite coating, characterized in that, include: The modified carbon fiber of claim 20 is mixed evenly with the resin matrix to form a first mixture; Add the curing agent and defoamer to the first mixture and mix them evenly to obtain the second mixture; The second mixture is applied to the surface of a metal substrate and cured to obtain a carbon fiber reinforced composite coating.

22. The preparation method according to claim 21, characterized in that: The mass ratio of the modified carbon fiber to the resin matrix is ​​1:(14.5~76.5).

23. The preparation method according to claim 21, characterized in that: The mass ratio of the modified carbon fiber to the curing agent is 1:(4~23).

24. The preparation method according to claim 21, characterized in that: The ratio of the mass of the defoamer to the total mass of the modified carbon fiber, resin matrix, and curing agent is (0.001~0.005):

1.

25. The preparation method according to claim 21, characterized in that: The resin matrix is ​​selected from any one or a combination of two or more of epoxy resin, phenolic resin, acrylic resin, polyurethane, and unsaturated polyester resin.

26. The preparation method according to claim 21, characterized in that: The curing agent is selected from any one or a combination of two or more of the following: amine curing agents, acid anhydride curing agents, isocyanate curing agents, and thiol curing agents.

27. The preparation method according to claim 21, characterized in that: The defoamer is selected from any one or a combination of two or more of alcohol-based defoamers, polyether-based defoamers, and silicone-based defoamers.

28. The preparation method according to claim 21, characterized in that... include: The modified carbon fiber is mixed evenly with the resin matrix to form a first mixture, and then placed in a vacuum environment for degassing for 10 min to 30 min.

29. The preparation method according to claim 21, characterized in that... include: Add the curing agent and defoamer to the first mixture, and place it in a vacuum environment to degas for 10 min to 30 min to obtain a uniformly dispersed second mixture.

30. The preparation method according to claim 21, characterized in that... include: The second mixture is coated onto the surface of a metal substrate and left at room temperature for 12-48 hours to allow the coating to cure once. Then, it is placed in a high-temperature environment of 60-100°C for a second curing of 12-48 hours to obtain a carbon fiber reinforced composite coating.

31. A carbon fiber reinforced composite coating prepared by any one of claims 21-30, characterized in that: When the thickness of the carbon fiber reinforced composite coating is 3.25 mm to 3.88 mm, the tensile strength is 68.3 MPa to 86.6 MPa; The carbon fiber reinforced composite coating has a wear rate of 4.4 x 10 -5 (mm 3 / Nm)~8.0 x 10 -5 (mm 3 / Nm) after the friction test. The mass loss of the carbon fiber reinforced composite coating, which weighs 21.99g to 23.61g, after the erosion test is 0.60g to 0.83g.

32. The application of the carbon fiber reinforced composite coating of claim 31 in the field of substrate protection.

33. The application according to claim 32, characterized in that: The base material is a steel structure facility.

34. The application according to claim 32, characterized in that, The applications include the application of the carbon fiber reinforced composite coating on steel structures serving in marine splash zones.

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