Preparation method of heat insulation carbon fiber heat preservation material

Abstract

The invention discloses a preparation method of a heat insulation carbon fiber heat preservation material, and belongs to the technical field of carbon fiber modification. Dipping and oxidizing carbon fibers in a nitric acid solution to obtain surface-pretreated carbon fibers; the tetrapropyl orthosilicate hydrolysate and the activated levodopa dispersion liquid are mixed and then subjected to reduced pressure evaporation to remove solvent water, and then the mixture reacts for 18 h to 22 h in the temperature environment of 20 DEG C to 25 DEG C to obtain organic silicon modified levodopa composite liquid; adjusting the pH value of the organic silicon modified levodopa composite liquid to 8.0-9.0, then coating the surface of the surface pretreated carbon fiber with the organic silicon modified levodopa composite liquid, carrying out ultrasonic treatment, and then standing, adsorbing and cross-linking to obtain modified carbon fiber; the modified carbon fiber is subjected to high-temperature pyrolysis to obtain the heat-insulation carbon fiber heat-preservation material. Through the treatment of the invention, the modified carbon fiber has good high-temperature oxidation resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon fiber modification, and particularly relates to a preparation method of a heat-insulating carbon fiber thermal insulation material. Background Art

[0002] With the rapid development of technology, people's requirements for the special properties of materials have gradually increased. Carbon fiber has been widely used in many fields such as biology, chemical industry, automobiles, machinery, aviation, and aerospace due to its excellent mechanical properties, high specific modulus, high specific strength, low coefficient of thermal expansion, and good toughness. By selecting different substrate materials for compounding, carbon fiber reinforced composites with specific functions can be prepared. For example, carbon / carbon composites with a carbon-based substrate are used in high mechanical performance fields due to their small coefficient of thermal expansion, high elasticity, and high strength; and they are also important tools in metal heat treatment due to their excellent heat resistance and low weight. However, carbon fiber reinforced composites need to be protected by an inert gas to exhibit these important properties. This is mainly because the high-temperature oxidation resistance of carbon fiber is weak. In a high-temperature environment, there are a series of active sites on the surface of carbon fiber. Oxygen diffuses to the fiber surface and combines with the active sites to react and form carbon oxides, resulting in weight loss of the fiber. This is the essence of carbon fiber oxidation, which causes the performance of the prepared matrix composite to fail to meet the expected effect, or even leads to the failure of preparation. Such characteristics limit the application of carbon fiber. Therefore, on the premise of ensuring the performance of carbon fiber, improving the antioxidant ability of carbon fiber in an aerobic environment can greatly expand the application of carbon fiber in various fields and improve the stability of carbon fiber as a high-temperature protection material and an ablative material reinforcement.

[0003] Currently, the research on improving the antioxidant performance of carbon fiber mainly focuses on two aspects: (1) Matrix modification technology: improving the antioxidant performance of carbon fiber itself, such as graphitization; (2) Coating modification of the carbon fiber surface to improve the antioxidant performance. Currently, common surface coating treatments for carbon fiber include methods such as oxidation method, electroplating method, electroless plating, chemical vapor deposition method, and ion spraying sputtering method; common coating materials include metal coatings such as Ni, Cu, Fe, Co, Al, Ag, and non-metal coatings such as SiC, Si, B. However, before the carbon fiber undergoes surface treatment, there is a gelatinous layer on the surface of the carbon fiber, the surface is smooth, lacking active functional groups, and the surface is very inert. When compounding with the surface coating matrix, the wettability is poor, there are many interface defects, and the interface bonding strength is insufficient, affecting many properties of the modified carbon fiber.

[0004] Due to its excellent low coefficient of thermal expansion, carbon fiber has good application prospects in the field of thermal insulation. Therefore, how to improve the antioxidant performance of carbon fiber in a high-temperature environment is of great significance for improving the application of carbon fiber in the field of thermal insulation in a high-temperature environment. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention constructs a weakly alkaline organosilicon-modified levodopa composite solution, and then coats it on the surface of surface-pretreated carbon fibers for polymerization adhesion to obtain modified carbon fibers. Subsequently, heat treatment at high temperature is carried out to obtain a heat-insulating carbon fiber thermal insulation material, thereby solving the technical problems raised in the background art. Specifically, the technical solution of the present invention includes the following contents: A preparation method of a heat-insulating carbon fiber thermal insulation material, the preparation method comprising the following steps: The carbon fibers are impregnated and oxidized with a nitric acid solution to obtain surface-pretreated carbon fibers; The tetrapropyl orthosilicate hydrolysis solution and the activated levodopa dispersion solution are mixed and then the solvent water is removed by reduced pressure evaporation. Subsequently, the reaction is carried out for 18 h to 22 h at a temperature of 20 °C to 25 °C to obtain an organosilicon-modified levodopa composite solution; The pH of the organosilicon-modified levodopa composite solution is adjusted to 8.0 to 9.0, and then it is coated on the surface of the surface-pretreated carbon fibers and treated with an ultrasonic power of 300 W to 400 W for 10 min to 15 min. Subsequently, it is left standing for adsorption crosslinking for 20 h to 30 h to obtain modified carbon fibers; The modified carbon fibers are pyrolyzed at high temperature to obtain the heat-insulating carbon fiber thermal insulation material.

[0006] Further, the mass concentration of the nitric acid solution is 40% to 45%. The purpose of nitric acid impregnation is to obtain oxygen-containing groups with reactive activity on the inert surface of the carbon fibers, so that when the organosilicon-modified levodopa composite solution is coated later, the organosilicon-modified levodopa composite solution loaded with organosilicon can be fixed on the surface of the modified carbon fibers through the synergistic cooperation of hydrogen bond adsorption and covalent bond crosslinking.

[0007] Further, the conditions of the impregnation oxidation treatment include a treatment temperature of 40 °C to 50 °C and a treatment time of 50 min to 55 min.

[0008] Further, the preparation method of the tetrapropyl orthosilicate hydrolysis solution includes the following steps: After tetrapropyl orthosilicate is dispersed in deionized water, the pH is adjusted to 2.5 to 3.0 with acid, and then the temperature is raised to 50 °C to 60 °C and the reaction is carried out for 2 h to 3 h to obtain the tetrapropyl orthosilicate hydrolysis solution.

[0009] Further, the preparation method of the activated levodopa dispersion solution includes the following steps: Levodopa and a carboxyl activator are dispersed in anhydrous dichloromethane and pre-activated at 0 °C for 15 min to 20 min to obtain the activated levodopa dispersion solution.

[0010] Further, the molar ratio of levodopa to the carboxyl activator is 1:1.5 to 2.

[0011] Further, the carboxyl activator consists of EDC hydrochloride and DMAP in a molar ratio of 1:0.5 - 1.

[0012] Further, the weight ratio of the tetrapropyl orthosilicate hydrolysis solution to the activated levodopa dispersion is 1:5 - 10.

[0013] Further, the conditions for high-temperature pyrolysis include a pyrolysis temperature of 1100°C - 1300°C and a pyrolysis time of 60 min - 80 min.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses levodopa as one of the raw materials. After self-polymerization, poly-levodopa with good adhesion can be formed. First, the functional group carboxyl on levodopa is activated, and then covalently condensed and esterified cross-linked with the hydrolysis solution containing silanol groups obtained after acid hydrolysis of tetrapropyl orthosilicate to form an organosilicon-modified levodopa composite solution. Then, the surface of carbon fiber is oxidized by nitric acid with a specific concentration under specific conditions, so that the inertness of the carbon fiber surface is changed, and active oxygen-containing groups (such as hydroxyl and carboxyl groups) are obtained, and then surface-pretreated carbon fiber is obtained. Subsequently, the organosilicon-modified levodopa composite solution is adjusted to a weakly alkaline environment and then coated on the surface of the surface-pretreated carbon fiber, promoting the self-polymerization of the organosilicon-modified levodopa composite solution. Through physical and chemical adsorption with the active oxygen-containing groups on the surface-pretreated carbon fiber, it adheres to the surface of the surface-pretreated carbon fiber to obtain modified carbon fiber. Subsequently, the modified carbon fiber is taken out and dried, and then treated at high temperature to remove the poly-levodopa on the surface of the modified carbon fiber, while retaining silica on the surface of the modified carbon fiber to obtain a heat-insulating carbon fiber thermal insulation material. Silica has good high-temperature oxidation resistance, so that the prepared heat-insulating carbon fiber thermal insulation material has good high-temperature oxidation resistance. Specific Embodiments

[0015] The technical solutions of the present invention will be clearly and completely described below through the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0016] Unless otherwise specified, the raw materials and reagents used in the present invention below are all commercially available products or can be prepared by known methods.

[0017] The carbon fiber was purchased from Weihai Guangwei Composite Materials Co., Ltd.

[0018] Preparation Example 1: The preparation method of the tetrapropyl orthosilicate hydrolysis solution specifically includes the following process: Mix tetrapropyl orthosilicate and deionized water in a flask at a weight ratio of 1:0.5, and then place it in an ultrasonic disperser. Disperse it for 20 min at an ultrasonic power of 200 W to obtain a tetrapropyl orthosilicate dispersion. After adjusting the pH of the tetrapropyl orthosilicate dispersion to 2.5 with hydrochloric acid, heat it to 50 °C for hydrolysis for 2 h, and then adjust the pH to neutral for storage to obtain a hydrolyzed solution of tetrapropyl orthosilicate.

[0019] Preparation Example 2: A method for preparing a hydrolyzed solution of tetrapropyl orthosilicate specifically includes the following process: Mix tetrapropyl orthosilicate and deionized water in a flask at a weight ratio of 1:0.7, and then place it in an ultrasonic disperser. Disperse it for 20 min at an ultrasonic power of 200 W to obtain a tetrapropyl orthosilicate dispersion. After adjusting the pH of the tetrapropyl orthosilicate dispersion to 2.5 with hydrochloric acid, heat it to 55 °C for hydrolysis for 2.5 h, and then adjust the pH to neutral for storage to obtain a hydrolyzed solution of tetrapropyl orthosilicate.

[0020] Preparation Example 3: A method for preparing a hydrolyzed solution of tetrapropyl orthosilicate specifically includes the following process: Mix tetrapropyl orthosilicate and deionized water in a flask at a weight ratio of 1:0.9, and then place it in an ultrasonic disperser. Disperse it for 20 min at an ultrasonic power of 200 W to obtain a tetrapropyl orthosilicate dispersion. After adjusting the pH of the tetrapropyl orthosilicate dispersion to 3.0 with hydrochloric acid, heat it to 60 °C for hydrolysis for 3 h, and then adjust the pH to neutral for storage to obtain a hydrolyzed solution of tetrapropyl orthosilicate.

[0021] Preparation Example 4: A method for preparing a hydrolyzed solution of tetraethyl orthosilicate specifically includes the following process: Mix tetraethyl orthosilicate and deionized water in a flask at a weight ratio of 1:0.9, and then place it in an ultrasonic disperser. Disperse it for 20 min at an ultrasonic power of 200 W to obtain a tetraethyl orthosilicate dispersion. After adjusting the pH of the tetraethyl orthosilicate dispersion to 3.0 with hydrochloric acid, heat it to 60 °C for hydrolysis for 3 h, and then adjust the pH to neutral for storage to obtain a hydrolyzed solution of tetraethyl orthosilicate.

[0022] Preparation Example 5: A method for preparing a hydrolyzed solution of tetrabutyl orthosilicate specifically includes the following process: Tetrabutyl orthosilicate and deionized water were mixed in a flask at a weight ratio of 1:0.9, and then placed in an ultrasonic disperser. They were dispersed for 20 min at an ultrasonic power of 200 W to obtain a tetrabutyl orthosilicate dispersion. After adjusting the pH of the tetrabutyl orthosilicate dispersion to 3.0 with hydrochloric acid, it was heated to 60 °C for hydrolysis treatment for 3 h, and then the pH was adjusted to neutral for storage to obtain a tetrabutyl orthosilicate hydrolysis solution.

[0023] Preparation Example 6: A method for preparing an activated levodopa dispersion specifically includes the following process: Weigh 0.1 mol of levodopa and add it to 400 ml of anhydrous dichloromethane. Then, with the aid of an ultrasonic disperser, disperse it at an ultrasonic power of 400 W for 15 min to obtain a levodopa dispersion. Add a carboxyl activator composed of 0.1 mol of EDC hydrochloride and 0.05 mol of DMAP to the levodopa dispersion, and then place it in a temperature environment of 0 °C and stir for pre-activation treatment for 15 min to obtain an activated levodopa dispersion.

[0024] Preparation Example 7: A method for preparing an activated levodopa dispersion specifically includes the following process: Weigh 0.1 mol of levodopa and add it to 400 ml of anhydrous dichloromethane. Then, with the aid of an ultrasonic disperser, disperse it at an ultrasonic power of 400 W for 15 min to obtain a levodopa dispersion. Add a carboxyl activator composed of 0.1 mol of EDC hydrochloride and 0.08 mol of DMAP to the levodopa dispersion, and then place it in a temperature environment of 0 °C and stir for pre-activation treatment for 17 min to obtain an activated levodopa dispersion.

[0025] Preparation Example 8: A method for preparing an activated levodopa dispersion specifically includes the following process: Weigh 0.1 mol of levodopa and add it to 400 ml of anhydrous dichloromethane. Then, with the aid of an ultrasonic disperser, disperse it at an ultrasonic power of 400 W for 15 min to obtain a levodopa dispersion. Add a carboxyl activator composed of 0.1 mol of EDC hydrochloride and 0.1 mol of DMAP to the levodopa dispersion, and then place it in a temperature environment of 0 °C and stir for pre-activation treatment for 20 min to obtain an activated levodopa dispersion.

[0026] Preparation Example 9: A method for preparing an activated dopamine hydrochloride dispersion specifically includes the following process: Weigh 0.1 mol of dopamine hydrochloride and add it to 400 ml of anhydrous dichloromethane. Subsequently, with the aid of an ultrasonic disperser, disperse it for 15 min at an ultrasonic power of 400 W to obtain a dopamine hydrochloride dispersion. Add the carboxyl activator composed of 0.1 mol of EDC hydrochloride and 0.1 mol of DMAP to the dopamine hydrochloride dispersion, and then place it in a temperature environment of 0 °C and stir for pre-activation treatment for 20 min to obtain an activated dopamine hydrochloride dispersion.

[0027] Example 1: A preparation method of a heat-insulating carbon fiber thermal insulation material specifically includes the following process: Completely immerse the carbon fiber in a nitric acid solution with a mass concentration of 40%, and then place it in a water bath at a temperature of 40 °C for heat oxidation treatment for 50 min. After the oxidation treatment is completed, take out the carbon fiber and rinse the surface nitric acid solution with a large amount of distilled water until the pH of the rinsing water is neutral. Subsequently, place it in a vacuum drying oven at 70 °C and dry it to constant weight to obtain surface-pretreated carbon fiber; Mix and stir 1 part by weight of the tetrapropyl orthosilicate hydrolysis solution obtained in Preparation Example 1 and 5 parts by weight of the activated levodopa dispersion obtained in Preparation Example 6 to obtain a mixed system, and then remove the water in the mixed system by a vacuum evaporator. Subsequently, control the reaction at a temperature environment of 20 °C for 18 h to obtain an organosilicon-modified levodopa composite solution; adjust the pH of the organosilicon-modified levodopa composite solution to 8.0 with ammonia water, and then coat it on the surface of the surface-pretreated carbon fiber. After the coating is completed, place it in an ultrasonic power environment of 300 W and process it for 10 min, and then let it stand for adsorption crosslinking at room temperature for 20 h to obtain modified carbon fiber; After the static adsorption is completed, place the modified carbon fiber in an oven at 80 °C and dry it until the surface hardens. Subsequently, put it into a tube furnace and heat it at a heating rate of 10 °C / min to 1100 °C. Pyrolyze it for 60 min in this temperature environment, and then naturally cool it to room temperature to obtain a heat-insulating carbon fiber thermal insulation material.

[0028] Example 2: A preparation method of a heat-insulating carbon fiber thermal insulation material specifically includes the following process: Completely immerse the carbon fiber in a nitric acid solution with a mass concentration of 40%, and then place it in a water bath at a temperature of 45 °C for heat oxidation treatment for 50 min. After the oxidation treatment is completed, take out the carbon fiber and rinse the surface nitric acid solution with a large amount of distilled water until the pH of the rinsing water is neutral. Subsequently, place it in a vacuum drying oven at 70 °C and dry it to constant weight to obtain surface-pretreated carbon fiber; Mix 1 part by weight of the tetrapropyl orthosilicate hydrolysis solution obtained in Preparation Example 2 and 6 parts by weight of the activated levodopa dispersion obtained in Preparation Example 7, and stir to obtain a mixed system. Then, remove the water in the mixed system using a vacuum evaporator. Subsequently, control the reaction at a temperature of 20 °C for 19 h to obtain an organosilicon-modified levodopa composite solution; adjust the pH of the organosilicon-modified levodopa composite solution to 8.0 with ammonia water. Subsequently, coat it on the surface of the surface-pretreated carbon fiber. After coating, place it in an ultrasonic power environment of 350 W and treat for 10 min, and then let it stand for adsorption crosslinking in a room-temperature environment for 24 h to obtain a modified carbon fiber; After the static adsorption is completed, place the modified carbon fiber in an oven at 80 °C and dry it until the surface hardens. Subsequently, put it into a tube furnace and heat it to 1200 °C at a heating rate of 10 °C / min. Pyrolyze it in this temperature environment for 70 min, and then naturally cool it to room temperature to obtain a heat-insulating carbon fiber thermal insulation material.

[0029] Example 3: A preparation method of a heat-insulating carbon fiber thermal insulation material specifically includes the following process: Completely immerse the carbon fiber in a nitric acid solution with a mass concentration of 45%, and then place it in a water bath at a temperature of 45 °C and heat it for oxidation treatment for 55 min. After the oxidation treatment is completed, take out the carbon fiber and rinse the surface nitric acid solution with a large amount of distilled water until the pH of the rinsing water is neutral. Subsequently, place it in a vacuum drying oven at 70 °C and dry it to constant weight to obtain a surface-pretreated carbon fiber; Mix 1 part by weight of the tetrapropyl orthosilicate hydrolysis solution obtained in Preparation Example 3 and 8 parts by weight of the activated levodopa dispersion obtained in Preparation Example 8, and stir to obtain a mixed system. Then, remove the water in the mixed system using a vacuum evaporator. Subsequently, control the reaction at a temperature of 25 °C for 20 h to obtain an organosilicon-modified levodopa composite solution; adjust the pH of the organosilicon-modified levodopa composite solution to 8.5 with ammonia water. Subsequently, coat it on the surface of the surface-pretreated carbon fiber. After coating, place it in an ultrasonic power environment of 350 W and treat for 15 min, and then let it stand for adsorption crosslinking in a room-temperature environment for 28 h to obtain a modified carbon fiber; After the static adsorption is completed, place the modified carbon fiber in an oven at 80 °C and dry it until the surface hardens. Subsequently, put it into a tube furnace and heat it to 1300 °C at a heating rate of 10 °C / min. Pyrolyze it in this temperature environment for 80 min, and then naturally cool it to room temperature to obtain a heat-insulating carbon fiber thermal insulation material.

[0030] Example 4: A preparation method of a heat-insulating carbon fiber thermal insulation material specifically includes the following process: The carbon fiber is completely immersed in a nitric acid solution with a mass concentration of 45%, and then placed in a water bath at a temperature of 50 °C for heat oxidation treatment for 55 min. After the oxidation treatment is completed, the carbon fiber is taken out and the surface nitric acid solution is rinsed with a large amount of distilled water until the pH of the rinsing water is neutral. Subsequently, it is placed in a vacuum drying oven at 70 °C and dried to a constant weight to obtain surface-pretreated carbon fiber; Mix 1 part by weight of the tetrapropyl orthosilicate hydrolysis solution obtained in Preparation Example 3 and 10 parts by weight of the activated levodopa dispersion obtained in Preparation Example 8 and stir to obtain a mixed system. Then, the water in the mixed system is removed by a vacuum evaporator. Subsequently, the reaction is carried out for 22 h under a temperature environment of 25 °C to obtain an organosilicon-modified levodopa composite solution; adjust the pH of the organosilicon-modified levodopa composite solution to 9.0 with ammonia water. Subsequently, it is coated on the surface of the surface-pretreated carbon fiber. After the coating is completed, it is placed in an ultrasonic power environment of 400 W and treated for 15 min, and then left to stand for adsorption crosslinking for 30 h at room temperature to obtain modified carbon fiber; After the static adsorption is completed, the modified carbon fiber is placed in an oven at 80 °C and dried until the surface hardens. Subsequently, it is put into a tubular furnace and heated to 1300 °C at a heating rate of 10 °C / min. Pyrolysis is carried out for 80 min in this temperature environment, and then it is naturally cooled to room temperature to obtain a heat-insulating carbon fiber thermal insulation material.

[0031] Comparative Example 1: A preparation method of a heat-insulating carbon fiber thermal insulation material specifically includes the following process: The carbon fiber is completely immersed in a nitric acid solution with a mass concentration of 45%, and then placed in a water bath at a temperature of 50 °C for heat oxidation treatment for 55 min. After the oxidation treatment is completed, the carbon fiber is taken out and the surface nitric acid solution is rinsed with a large amount of distilled water until the pH of the rinsing water is neutral. Subsequently, it is placed in a vacuum drying oven at 70 °C and dried to a constant weight to obtain surface-pretreated carbon fiber; Mix 1 part by weight of the tetraethyl orthosilicate hydrolysis solution obtained in Preparation Example 4 and 10 parts by weight of the activated levodopa dispersion obtained in Preparation Example 8 and stir to obtain a mixed system. Then, the water in the mixed system is removed by a vacuum evaporator. Subsequently, the reaction is carried out for 22 h under a temperature environment of 25 °C to obtain an organosilicon-modified levodopa composite solution; adjust the pH of the organosilicon-modified levodopa composite solution to 9.0 with ammonia water. Subsequently, it is coated on the surface of the surface-pretreated carbon fiber. After the coating is completed, it is placed in an ultrasonic power environment of 400 W and treated for 15 min, and then left to stand for adsorption crosslinking for 30 h at room temperature to obtain modified carbon fiber; After the static adsorption is completed, the modified carbon fiber is placed in an oven at 80 °C and dried until the surface hardens. Subsequently, it is put into a tubular furnace and heated to 1300 °C at a heating rate of 10 °C / min. Pyrolysis is carried out for 80 min in this temperature environment, and then it is naturally cooled to room temperature to obtain a heat-insulating carbon fiber thermal insulation material.

[0032] Comparative Example 2: A preparation method of a heat-insulating carbon fiber thermal insulation material, specifically including the following process: Completely immerse carbon fibers in a nitric acid solution with a mass concentration of 45%, and then place them in a water bath at a temperature of 50 °C for heat oxidation treatment for 55 minutes. After the oxidation treatment is completed, take out the carbon fibers and rinse the surface nitric acid solution with a large amount of distilled water until the pH of the rinsing water is neutral. Subsequently, place them in a vacuum drying oven at 70 °C and dry to constant weight to obtain surface-pretreated carbon fibers; Mix and stir 1 part by weight of the tetrabutyl orthosilicate hydrolysis solution obtained in Preparation Example 5 and 10 parts by weight of the activated levodopa dispersion solution obtained in Preparation Example 8 to obtain a mixed system. Then, use a vacuum evaporator to remove the water in the mixed system. Subsequently, control the reaction at a temperature of 25 °C for 22 hours to obtain an organosilicon-modified levodopa composite solution; adjust the pH of the organosilicon-modified levodopa composite solution to 9.0 with ammonia water. Subsequently, coat it on the surface of the surface-pretreated carbon fibers. After the coating is completed, place it in an ultrasonic power environment of 400 W and process for 15 minutes, and then let it stand for adsorption crosslinking at room temperature for 30 hours to obtain modified carbon fibers; After the static adsorption is completed, place the modified carbon fibers in an oven at 80 °C and dry until the surface hardens. Subsequently, put them into a tubular furnace and heat up to 1300 °C at a heating rate of 10 °C / min. Pyrolyze at this temperature for 80 minutes, and then naturally cool to room temperature to obtain a heat-insulating carbon fiber thermal insulation material.

[0033] Comparative Example 3: A preparation method of a heat-insulating carbon fiber thermal insulation material, specifically including the following process: Completely immerse carbon fibers in a nitric acid solution with a mass concentration of 45%, and then place them in a water bath at a temperature of 50 °C for heat oxidation treatment for 55 minutes. After the oxidation treatment is completed, take out the carbon fibers and rinse the surface nitric acid solution with a large amount of distilled water until the pH of the rinsing water is neutral. Subsequently, place them in a vacuum drying oven at 70 °C and dry to constant weight to obtain surface-pretreated carbon fibers; Mix and stir 1 part by weight of the tetrapropyl orthosilicate hydrolysis solution obtained in Preparation Example 3 and 10 parts by weight of the activated hydrochloric acid dopamine dispersion solution obtained in Preparation Example 9 to obtain a mixed system. Then, use a vacuum evaporator to remove the water in the mixed system. Subsequently, control the reaction at a temperature of 25 °C for 22 hours to obtain an organosilicon-modified levodopa composite solution; adjust the pH of the organosilicon-modified levodopa composite solution to 9.0 with ammonia water. Subsequently, coat it on the surface of the surface-pretreated carbon fibers. After the coating is completed, place it in an ultrasonic power environment of 400 W and process for 15 minutes, and then let it stand for adsorption crosslinking at room temperature for 30 hours to obtain modified carbon fibers; After the static adsorption is completed, place the modified carbon fiber in an oven at 80 °C and dry it until the surface hardens. Then, put it into a tubular furnace and heat it to 1300 °C at a heating rate of 10 °C / min. Pyrolyze it for 80 min in this temperature environment, and then naturally cool it to room temperature to obtain the heat-insulating carbon fiber thermal insulation material.

[0034] Comparative Example 4: A preparation method of a heat-insulating carbon fiber thermal insulation material specifically includes the following process: Mix 1 part by weight of the tetrapropyl orthosilicate hydrolysis solution obtained in Preparation Example 3 and 10 parts by weight of the activated levodopa dispersion solution obtained in Preparation Example 8 and stir to obtain a mixed system. Then, use a vacuum evaporator to remove the water in the mixed system. Subsequently, control the reaction at 25 °C for 22 h to obtain an organosilicon-modified levodopa composite solution; adjust the pH of the organosilicon-modified levodopa composite solution to 9.0 with ammonia water. Then, coat it on the surface of the carbon fiber. After the coating is completed, place it in an ultrasonic power environment of 400 W and process it for 15 min. Then, let it stand for adsorption and crosslinking at room temperature for 30 h to obtain the modified carbon fiber; After the static adsorption is completed, place the modified carbon fiber in an oven at 80 °C and dry it until the surface hardens. Then, put it into a tubular furnace and heat it to 1300 °C at a heating rate of 10 °C / min. Pyrolyze it for 80 min in this temperature environment, and then naturally cool it to room temperature to obtain the heat-insulating carbon fiber thermal insulation material.

[0035] Comparative Example 5: A preparation method of a heat-insulating carbon fiber thermal insulation material specifically includes the following process: Completely immerse the carbon fiber in a nitric acid solution with a mass concentration of 60%, and then place it in a water bath at 60 °C for heat oxidation treatment for 70 min. After the oxidation treatment is completed, take out the carbon fiber and rinse the surface nitric acid solution with a large amount of distilled water until the pH of the rinsing water is neutral. Then, place it in a vacuum drying oven at 70 °C and dry it to a constant weight to obtain the surface-pretreated carbon fiber; Mix 1 part by weight of the tetrapropyl orthosilicate hydrolysis solution obtained in Preparation Example 3 and 10 parts by weight of the activated levodopa dispersion solution obtained in Preparation Example 8 and stir to obtain a mixed system. Then, use a vacuum evaporator to remove the water in the mixed system. Subsequently, control the reaction at 25 °C for 22 h to obtain an organosilicon-modified levodopa composite solution; adjust the pH of the organosilicon-modified levodopa composite solution to 9.0 with ammonia water. Then, coat it on the surface of the surface-pretreated carbon fiber. After the coating is completed, place it in an ultrasonic power environment of 400 W and process it for 15 min. Then, let it stand for adsorption and crosslinking at room temperature for 30 h to obtain the modified carbon fiber; After static adsorption is completed, the modified carbon fiber is placed in an oven at 80 °C and dried until the surface hardens. Subsequently, it is placed in a tube furnace and heated to 1300 °C at a heating rate of 10 °C / min. Pyrolysis is carried out at this temperature for 80 min, and then it is naturally cooled to room temperature to obtain the heat-insulating carbon fiber thermal insulation material.

[0036] Comparative Example 6: A preparation method of a heat-insulating carbon fiber thermal insulation material specifically includes the following process: The carbon fiber is completely immersed in a nitric acid solution with a mass concentration of 45%, and then placed in a water bath at 50 °C for heat oxidation treatment for 55 min. After the oxidation treatment is completed, the carbon fiber is taken out and the surface nitric acid solution is rinsed with a large amount of distilled water until the pH of the rinsing water is neutral. Subsequently, it is placed in a vacuum drying oven at 70 °C and dried to constant weight to obtain the surface-pretreated carbon fiber; 11 parts by weight of the tetrapropyl orthosilicate hydrolysis solution obtained in Preparation Example 3 is coated on the surface of the surface-pretreated carbon fiber. After the coating is completed, it is placed in an environment with an ultrasonic power of 400 W and treated for 15 min, and then statically adsorbed and crosslinked at room temperature for 30 h to obtain the modified carbon fiber; After static adsorption is completed, the modified carbon fiber is placed in an oven at 80 °C and dried until the surface hardens. Subsequently, it is placed in a tube furnace and heated to 1300 °C at a heating rate of 10 °C / min. Pyrolysis is carried out at this temperature for 80 min, and then it is naturally cooled to room temperature to obtain the heat-insulating carbon fiber thermal insulation material.

[0037] High-temperature oxidation resistance test: The heat-insulating carbon fiber thermal insulation materials prepared in Examples 1 to 4 and Comparative Examples 1 to 6 are heated to 1000 °C at a heating rate of 5 °C / min, and the initial oxidation temperature is measured by a thermogravimetric analyzer. The results are shown in Table 1 below.

[0038] Table 1 Initial oxidation temperature The following conclusions can be drawn from the test results in Table 1 above: (1) It can be found from Examples 1 to 4 that the present invention constructs a weakly alkaline organosilicon-modified levodopa composite solution, then coats it on the surface of the surface-pretreated carbon fiber and polymerizes and adheres to obtain the modified carbon fiber. Subsequently, the heat-insulating carbon fiber thermal insulation material is obtained by high-temperature treatment, which has good high-temperature oxidation resistance.

[0039] (2)It can be found from Comparative Example 1 that although tetraethyl orthosilicate can be hydrolyzed to prepare a hydrolyzate containing silanol groups, in this system, the prepared heat-insulating carbon fiber thermal insulation material shows poor high-temperature antioxidant stability. This may be because the ethyl carbon chain in tetraethyl orthosilicate hydrolyzes faster than the propyl carbon chain in tetrapropyl orthosilicate in this system, resulting in a relatively high viscosity of the tetraethyl orthosilicate hydrolyzate prepared by the cross-linking between silanol groups after hydrolysis. Although a larger viscosity is beneficial for adhering to the surface-pretreated carbon fiber, the large viscosity makes it difficult to uniformly infiltrate the surface-pretreated carbon fiber, thus resulting in poor high-temperature antioxidant stability.

[0040] (3)It can be found from Comparative Example 2 that although tetrabutyl orthosilicate can be hydrolyzed to prepare a hydrolyzate containing silanol groups, in this system, the prepared heat-insulating carbon fiber thermal insulation material shows poor high-temperature antioxidant stability. This may be because the butyl carbon chain in tetrabutyl orthosilicate is relatively long compared to the propyl carbon chain, with a large steric hindrance, resulting in a slower hydrolysis of tetrabutyl orthosilicate in this system. The slower hydrolysis will lead to a poor adhesion of the tetrabutyl orthosilicate hydrolyzate obtained by hydrolysis. Merely relying on polydopamine in the formulation of this system is not sufficient to achieve good adhesion to the surface-pretreated carbon fiber, which may result in a relatively thin and easily detachable silica protective layer after high-temperature pyrolysis, thus leading to poor high-temperature antioxidant stability.

[0041] (4)It can be found from Comparative Example 3 that although dopamine hydrochloride can also undergo oxidative self-polymerization to produce an adhesive polydopamine structure, in this system, the prepared heat-insulating carbon fiber thermal insulation material shows poor high-temperature antioxidant stability. This may be because there is no functional group carboxyl on dopamine hydrochloride, which makes it difficult for the hydrolyzate of tetrapropyl orthosilicate containing silanol groups to effectively combine with dopamine hydrochloride through covalent esterification condensation between carboxyl and silanol groups. As a result, it is difficult for the prepared organosilicon-modified levodopa composite solution to effectively load organosilicon. Furthermore, after the polydopamine structure is removed by high-temperature pyrolysis, the silica protective layer is relatively thin, resulting in poor high-temperature antioxidant stability of the prepared heat-insulating carbon fiber thermal insulation material.

[0042] (5)It can be found from Comparative Example 4 that in this system, the prepared heat-insulating carbon fiber thermal insulation material shows poor high-temperature antioxidant stability. This may be because the main component of carbon fiber is carbon atoms, and the formed graphite-like structure has high chemical stability and low surface energy. This results in the carbon fiber showing low reactivity in many environments and being difficult to effectively adhere to the organosilicon-modified levodopa composite solution, thus resulting in poor high-temperature antioxidant stability of the finally prepared heat-insulating carbon fiber thermal insulation material.

[0043] (6)It can be found from Comparative Example 5 that in this system, the prepared heat-insulating carbon fiber thermal insulation material shows poor high-temperature oxidation stability. This may be because although nitric acid oxidation treatment can increase the oxygen-containing active groups on the carbon fiber surface, the increase in oxygen-containing active groups helps to further contact and react with the coating liquid to improve the adhesion effect. However, too high nitric acid concentration and too long oxidation treatment time may cause damage to the carbon fiber matrix structure, resulting in the poor high-temperature oxidation stability of the prepared heat-insulating carbon fiber thermal insulation material.

[0044] (7)It can be found from Comparative Example 6 that although the tetrapropyl orthosilicate hydrolysis solution can generate adhesion through the cross-linking and condensation between silanol groups, in the formulation of this system, it is not sufficient to achieve good adhesion performance to the surface-pretreated carbon fiber, resulting in the easy detachment of the silica protective layer after high-temperature pyrolysis and making it difficult to achieve high-temperature oxidation protection of the carbon fiber.

[0045] The above-described embodiments have detailed the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A preparation method of a heat-insulating carbon fiber thermal insulation material, characterized in that, The preparation method includes the following steps: The carbon fiber is impregnated and oxidized with a nitric acid solution to obtain a surface-pretreated carbon fiber; The hydrolyzate of tetrapropyl orthosilicate and the activated levodopa dispersion are mixed and the solvent water is removed by evaporation under reduced pressure. Subsequently, a reaction is carried out for 18 h to 22 h in a temperature environment of 20 °C to 25 °C to obtain an organosilicon-modified levodopa composite solution; The pH of the organosilicon-modified levodopa composite solution is adjusted to 8.0 to 9.0, and then it is coated on the surface of the surface-pretreated carbon fiber and treated with an ultrasonic power of 300 W to 400 W for 10 min to 15 min. Subsequently, it is left standing for adsorption crosslinking for 20 h to 30 h to obtain a modified carbon fiber; The modified carbon fiber is pyrolyzed at high temperature to obtain the heat-insulating carbon fiber thermal insulation material.

2. The preparation method of a heat-insulating carbon fiber thermal insulation material according to claim 1, wherein The mass concentration of the nitric acid solution is 40% to 45%.

3. The preparation method of a heat-insulating carbon fiber thermal insulation material according to claim 1, wherein, The conditions for the impregnation oxidation treatment include a treatment temperature of 40 °C to 50 °C and a treatment time of 50 min to 55 min.

4. The preparation method of a heat-insulating carbon fiber thermal insulation material according to claim 1, characterized in that The preparation method of the hydrolyzate of tetrapropyl orthosilicate includes the following steps: After tetrapropyl orthosilicate is dispersed in deionized water, the pH is adjusted to 2.5 to 3.0 by adding acid, and then the temperature is raised to 50 °C to 60 °C and the reaction is carried out for 2 h to 3 h to obtain the hydrolyzate of tetrapropyl orthosilicate; 5. The preparation method of a heat-insulating carbon fiber thermal insulation material according to claim 1, wherein, The preparation method of the activated levodopa dispersion includes the following steps: Levodopa and a carboxyl activator are dispersed in anhydrous dichloromethane and pre-activated in an environment of 0 °C for 15 min to 20 min to obtain the activated levodopa dispersion; 6. The preparation method of a heat-insulating carbon fiber thermal insulation material according to claim 5, characterized in that, The molar ratio of levodopa to the carboxyl activator is 1:1.5 to 2.

7. The preparation method of a heat-insulating carbon fiber thermal insulation material according to claim 1, characterized in that, The weight part ratio of the hydrolyzate of tetrapropyl orthosilicate to the activated levodopa dispersion is 1:5 to 10.

8. The preparation method of a heat-insulating carbon fiber thermal insulation material according to claim 1, characterized in that, The conditions for the high-temperature pyrolysis include a pyrolysis temperature of 1100 °C to 1300 °C and a pyrolysis time of 60 min to 80 min.

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