Asphalt carbon fiber and method for producing the same

Abstract

The application discloses asphalt carbon fiber and a preparation method thereof, relates to the technical field of fiber reinforced composite materials, and specifically belongs to the patent classification D01F9 / 145. The specific preparation method is as follows: first, active asphalt is crosslinked by a 4,4'-diphenyl methane diisocyanate crosslinking agent, and then, three-dimensional crosslinked modified asphalt is obtained through a melting reaction; then, the three-dimensional crosslinked modified asphalt is blended with hydroxylated graphene quantum dots to be spun; and finally, carboxylated carbon nanofibers and silicon carbide are sequentially combined to obtain asphalt carbon fiber. The asphalt carbon fiber prepared by the method has excellent mechanical strength and can meet the requirements of high-end application scenarios with high requirements on mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of fiber-reinforced composite materials technology, specifically to patent classification number D01F9 / 145, and specifically to pitch-carbon fiber and its preparation method. Background Technology

[0002] Carbon fiber, a high-molecular fiber material with a carbon content exceeding 90%, boasts a series of excellent properties, including high specific strength, high specific modulus, low density, resistance to chemical corrosion, thermal shock, and ablation. It has been widely used in industries such as chemical engineering, electromechanical engineering, shipbuilding, and aircraft manufacturing, and is an indispensable new material in aerospace, artificial satellites, rockets, missiles, and atomic energy. Currently, industrialized carbon fibers mainly fall into three categories: polyacrylonitrile-based carbon fiber, viscose-based carbon fiber, and pitch-based carbon fiber. Among these, polyacrylonitrile-based carbon fiber has the highest production volume, the most varieties, the fastest development speed, and the most mature technology. However, it suffers from high energy consumption and high costs during production, and its precursor, acrylonitrile, is mostly derived from petrochemicals, resulting in a relatively large carbon footprint. Although viscose-based carbon fiber has advantages such as low density, low graphitization (low thermal conductivity, making it an ideal thermal insulation material), and low content of alkali metals and alkaline earth metals (the sodium light produced during combustion during flight is weak and not easily detected by radar), in actual production, due to the difficulty in precisely controlling operating conditions, it is easy to generate byproducts such as L-glucose, resulting in a low actual carbon yield and unsatisfactory carbon fiber strength. Currently, it is mainly used in non-pressure-bearing components for aerospace and civilian applications.

[0003] Pitch-based carbon fiber is made from pitch, which has a wide range of sources, including petroleum pitch and coal tar pitch, and is relatively inexpensive. However, there are some problems to be solved in the production process of pitch-based carbon fiber. Defects can easily occur in its internal structure during the preparation process, making it difficult to meet the requirements of some high-end applications in terms of mechanical properties, especially tensile strength and modulus. Summary of the Invention

[0004] The purpose of this invention is to provide pitch-coated carbon fiber and its preparation method, thereby solving the technical problems mentioned in the background section. The pitch-coated carbon fiber prepared by this invention has excellent mechanical strength, which can meet the requirements of high-end applications with high mechanical performance requirements.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing pitch-carbon fiber includes the following steps:

[0007] a) Isotropic asphalt that has been oxidized by air is mixed with anisotropic asphalt modified by hydrogenated anthracene oil, and 4,4'-diphenylmethane diisocyanate crosslinking agent is added. The mixture is then melted to obtain three-dimensional crosslinked modified asphalt.

[0008] b) Prepare hydroxylated graphene quantum dots, then disperse the hydroxylated graphene quantum dots in N,N-dimethylformamide, then add three-dimensional cross-linked modified pitch, blend in the molten state, and spin through a spinneret to obtain pitch precursor containing hydroxylated graphene quantum dots;

[0009] c) Carbon nanofibers are treated with concentrated nitric acid to obtain carboxylated carbon nanofibers. The carboxylated carbon nanofibers are dispersed in N,N-dimethylformamide to obtain a carboxylated carbon nanofiber dispersion. The carboxylated carbon nanofiber dispersion is sprayed onto the surface of asphalt precursor fibers by electrostatic spraying to allow the carboxylated carbon nanofibers to adhere to the surface of the asphalt precursor fibers. Subsequently, air oxidation treatment is performed to obtain oxidized asphalt fibers.

[0010] d) Carbonize the oxidized pitch fibers, and then chemically vapor deposit a nano-silicon carbide coating in a mixed atmosphere of methyltrichlorosilane and hydrogen to obtain pitch carbon fibers.

[0011] In this invention, isotropic asphalt modified with air oxidation and anisotropic asphalt modified with hydrogenated anthracene oil are first used to load the asphalt with active groups. A 4,4'-diphenylmethane diisocyanate crosslinking agent then crosslinks with these active groups, forming a three-dimensional network structure. This three-dimensional crosslinked structure enhances intermolecular forces and reduces chain slippage, improving the overall structural stability of the asphalt and laying the foundation for subsequent fiber mechanical properties. Then, hydroxyl groups on the surface of hydroxylated graphene quantum dots form hydrogen bonds with the polar groups in the three-dimensional crosslinked modified asphalt, promoting uniform dispersion in the molten asphalt. The excellent mechanical properties of graphene quantum dots themselves allow them to act as a nano-reinforcing phase, effectively transferring stress and inhibiting crack initiation and propagation, thereby improving the mechanical strength of the precursor fiber. Finally, concentrated nitric acid treatment generates carboxyl groups on the surface of the carbon nanofibers. Electrostatic spraying utilizes electrostatic adsorption to attach the carboxylated carbon nanofibers to the surface of the asphalt precursor fiber. The attached carbon nanofibers can bridge potential cracks, significantly improving the fiber surface strength and damage resistance. Finally, the carbonization process removes non-carbon elements from the fiber, promoting the orderly arrangement of carbon atoms to form a graphite-like structure, thus improving the fiber's inherent strength. Meanwhile, silicon carbide, generated by the decomposition of methyltrichlorosilane in a hydrogen atmosphere, is deposited onto the fiber surface via chemical vapor deposition to form a nano-coating. This coating has high hardness and a tight bond with the fiber, protecting it from direct external damage and further enhancing its overall mechanical properties and bonding strength with other materials through synergistic effects. Figure 1The image shows a SEM image of the surface of the pitch-carbon fiber prepared in this invention. The electron microscope image clearly shows that a layer of material is bonded to the surface of the pitch-carbon fiber and exhibits an uneven structure.

[0012] Preferably, in step a), the melting reaction temperature is 180–200°C and the reaction time is 2–3 h.

[0013] Preferably, in step b), the mass ratio of three-dimensional cross-linked modified bitumen to hydroxylated graphene quantum dots is 100:2 to 6.

[0014] Preferably, in step c), the length of the carbon nanofibers is 20–50 μm.

[0015] Preferably, in step c), the mass ratio of pitch precursor to carboxylated carbon nanofibers is 10:0.5 to 1.5.

[0016] Preferably, in step c), the oxidation temperature is 280–290°C and the oxidation time is 1–3 h.

[0017] Preferably, in step d), the volume ratio of methyltrichlorosilane to hydrogen is 1:2 to 4.

[0018] Preferably, in step d), the chemical vapor deposition time is 1 to 2 hours.

[0019] Preferably, in step b), the hydroxylated graphene quantum dots undergo modification treatment, including the following steps:

[0020] Hydroxylated graphene quantum dots were added to deionized water and stirred to disperse them, resulting in a dispersion.

[0021] Add ferric chloride to deionized water and stir to dissolve. Add hydrochloric acid dropwise to adjust the pH to 3-4 to obtain a ferric chloride solution.

[0022] Ferric chloride solution is slowly added dropwise to the dispersion, the mixture is stirred and reacted, and then centrifuged, washed and dried to obtain the final product.

[0023] In the technical solution of this invention, as described above, by attaching carboxylated carbon nanofibers to the surface of pitch precursor fibers, the attached carbon nanofibers can bridge potential cracks, improving the surface strength and damage resistance of the fibers. However, a further problem encountered by the research and development team during the invention process was that carboxylated carbon nanofibers were difficult to stably bond to the surface of pitch precursor fibers, thereby reducing their effect on improving the mechanical strength of carbon fibers. To further solve this problem, this invention modifies hydroxylated graphene quantum dots, so that the hydroxyl groups on the hydroxylated graphene quantum dots react with Fe... 3+ Coordination is formed to form GQDs-Fe 3+ Complex. GQDs-Fe3+ The complex is dispersed inside and on the surface of the bitumen fiber, wherein the GQDs-Fe on the surface of the bitumen fiber 3+ Fe in the complex 3+ The carboxyl groups on the carboxylated carbon nanofibers coordinate with each other, thereby improving the stability of the bond between the carboxylated carbon nanofibers and the pitch precursor. This allows more carbon nanofibers to be stably bonded to the surface of the pitch precursor, thus significantly improving the mechanical strength of the carbon fiber.

[0024] A pitch-carbon fiber is prepared by the above method.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. The prepared pitch carbon fiber has excellent mechanical strength. Through the three-dimensional cross-linked structure to enhance the basic stability, the graphene quantum dots to transfer stress and suppress cracks, the carbon nanofibers to bridge cracks, and the silicon carbide coating for synergistic protection, it can meet the high requirements of mechanical performance in high-end scenarios.

[0027] 2. Modified hydroxylated graphene quantum dots can improve the stability of the bond between carboxylated carbon nanofibers and pitch precursor fibers through coordination, enhance their effect on improving the mechanical strength of carbon fibers, and improve the reliability of product performance. Attached Figure Description

[0028] Figure 1 This is a SEM image of the surface of the pitch-carbon fiber prepared according to the present invention. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] A method for preparing pitch-carbon fiber includes the following steps:

[0032] Step a) Weigh 60g of isotropic asphalt that has been oxidized in air (pre-oxidized at 300℃ and an air flow rate of 0.5L / min for 2h) and 40g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt-blended at 200℃ for 30min). Add the mixture to a mechanically stirred reactor, purge with nitrogen (flow rate 0.3L / min), and heat to 120℃ to melt the material. Add 3g of 4,4'-diphenylmethane diisocyanate, adjust the stirring speed to 300r / min, heat to 190℃, and maintain the temperature for 2.5h. After the reaction is complete, allow it to cool naturally to room temperature to obtain three-dimensional cross-linked modified asphalt.

[0033] Step b) Mix 5g graphite powder, 2g sodium nitrate and 200mL concentrated sulfuric acid, slowly add 10g potassium permanganate under ice bath, stir at 35℃ for 2h, add 200mL deionized water, heat to 98℃ and react for 15min, add 50mL hydrogen peroxide dropwise until the solution turns bright yellow, centrifuge and wash until neutral, freeze dry to obtain hydroxylated graphene quantum dots;

[0034] Weigh 2g of hydroxylated graphene quantum dots and add them to 100mL of deionized water. Sonicate the mixture for 30min to obtain a dispersion. Separately, add 0.5g of ferric chloride to 50mL of deionized water, stir to dissolve, and then add hydrochloric acid to adjust the pH to 3-4 to obtain a ferric chloride solution. Add the ferric chloride solution dropwise to the dispersion at a rate of 1mL / min, stir and react at 30℃ for 2h, then centrifuge at 8000r / min for 10min. Wash the precipitate three times with deionized water and vacuum dry at 60℃ for 12h to obtain modified hydroxylated graphene quantum dots.

[0035] 100g of three-dimensional cross-linked modified bitumen was weighed and added to the barrel of a melt spinning machine, and heated to 280℃ to melt it. 5g of modified hydroxyl graphene quantum dots were weighed and added to 100mL of N-methylpyrrolidone, and ultrasonically dispersed for 40min to obtain a uniform dispersion. The dispersion was injected into the melting section of the melt spinning machine through a metering pump and mixed with the molten bitumen for 1h. The spinning temperature was set to 300℃, the spinneret orifice diameter to 80μm, and the draw rate to 120m / min to spin bitumen precursor containing modified hydroxyl graphene quantum dots.

[0036] Step c) Weigh 10g of carbon nanofibers (20-50μm in length) and place them in a 250mL three-necked flask. Add 100mL of concentrated nitric acid (68wt%) and reflux at 80℃ for 3h. After cooling, centrifuge and wash with deionized water until the pH of the filtrate is 7. Dry under vacuum at 60℃ for 8h to obtain carboxylated carbon nanofibers. Weigh 1.2g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide. Disperse the dispersion by ultrasonication for 1h to obtain a dispersion. Fix 10g of pitch precursor fibers on a stage and use an electrostatic spraying device (voltage 30kV, spraying distance 15cm) to uniformly spray the dispersion onto the surface of the precursor fibers. Place the sprayed precursor fibers into a high-temperature tube furnace, introduce air (flow rate 0.3L / min), heat to 285℃, and maintain the temperature for 2h. After natural cooling, obtain oxidized pitch fibers.

[0037] Step d) Place the oxidized asphalt fiber into a high-temperature tubular furnace, introduce argon gas for protection (flow rate 0.5 L / min), heat to 1200 °C at a rate of 5 °C / min, and hold for 2 h to complete carbonization; after cooling to 1000 °C, switch to a mixed gas of methyltrichlorosilane and hydrogen (volume ratio 1:3), with a total flow rate of 0.5 L / min, and perform chemical vapor deposition for 1.8 h; after deposition, turn off the gas source and continue to introduce argon gas until cooled to room temperature, thus obtaining the final product.

[0038] Example 2

[0039] A method for preparing pitch-carbon fiber includes the following steps:

[0040] Step a) Weigh 60g of isotropic asphalt that has been oxidized in air (pre-oxidized at 300℃ and an air flow rate of 0.5L / min for 2h) and 40g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt-blended at 200℃ for 30min). Add the mixture to a mechanically stirred reactor, purge with nitrogen (flow rate 0.3L / min), and heat to 120℃ to melt the material. Add 3g of 4,4'-diphenylmethane diisocyanate, adjust the stirring speed to 300r / min, heat to 190℃, and maintain the temperature for 2.5h. After the reaction is complete, allow it to cool naturally to room temperature to obtain three-dimensional cross-linked modified asphalt.

[0041] Step b) Mix 5g graphite powder, 2g sodium nitrate and 200mL concentrated sulfuric acid, slowly add 10g potassium permanganate under ice bath, stir at 35℃ for 2h, add 200mL deionized water, heat to 98℃ and react for 15min, add 50mL hydrogen peroxide dropwise until the solution turns bright yellow, centrifuge and wash until neutral, freeze dry to obtain hydroxylated graphene quantum dots;

[0042] Weigh 2g of hydroxylated graphene quantum dots and add them to 100mL of deionized water. Sonicate the mixture for 30min to obtain a dispersion. Separately, add 0.5g of ferric chloride to 50mL of deionized water, stir to dissolve, and then add hydrochloric acid to adjust the pH to 3-4 to obtain a ferric chloride solution. Add the ferric chloride solution dropwise to the dispersion at a rate of 1mL / min, stir and react at 30℃ for 2h, then centrifuge at 8000r / min for 10min. Wash the precipitate three times with deionized water and vacuum dry at 60℃ for 12h to obtain modified hydroxylated graphene quantum dots.

[0043] 100g of three-dimensional cross-linked modified bitumen was weighed and added to the barrel of a melt spinning machine, and heated to 280℃ to melt it. 3g of modified hydroxyl graphene quantum dots were weighed and added to 100mL of N-methylpyrrolidone, and ultrasonically dispersed for 40min to obtain a uniform dispersion. The dispersion was injected into the melting section of the melt spinning machine through a metering pump and mixed with the molten bitumen for 1h. The spinning temperature was set to 300℃, the spinneret orifice diameter to 80μm, and the draw rate to 120m / min to spin bitumen precursor containing modified hydroxyl graphene quantum dots.

[0044] Step c) Weigh 10g of carbon nanofibers (20-50μm in length) and place them in a 250mL three-necked flask. Add 100mL of concentrated nitric acid (68wt%) and reflux at 80℃ for 3h. After cooling, centrifuge and wash with deionized water until the pH of the filtrate is 7. Dry under vacuum at 60℃ for 8h to obtain carboxylated carbon nanofibers. Weigh 0.8g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide. Disperse the dispersion by ultrasonication for 1h to obtain a dispersion. Fix 10g of pitch precursor fibers on a stage and use an electrostatic spraying device (voltage 30kV, spraying distance 15cm) to uniformly spray the dispersion onto the surface of the precursor fibers. Place the sprayed precursor fibers into a high-temperature tube furnace, introduce air (flow rate 0.3L / min), heat to 285℃, and maintain the temperature for 2h. After natural cooling, obtain oxidized pitch fibers.

[0045] Step d) Place the oxidized asphalt fiber into a high-temperature tubular furnace, and purge it with argon gas for protection (flow rate 0.5 L / min). Heat the furnace to 1200 °C at a rate of 5 °C / min and hold for 2 hours to complete carbonization. After cooling to 1000 °C, switch to a mixed gas of methyltrichlorosilane and hydrogen (volume ratio 1:3) at a total flow rate of 0.5 L / min, and perform chemical vapor deposition for 1.2 hours. After deposition, turn off the gas source and continue to purge with argon gas until the furnace cools to room temperature to obtain the final product.

[0046] Example 3

[0047] A method for preparing pitch-carbon fiber includes the following steps:

[0048] Step a) Weigh 60g of isotropic asphalt that has been oxidized in air (pre-oxidized at 300℃ and an air flow rate of 0.5L / min for 2h) and 40g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt-blended at 200℃ for 30min). Add the mixture to a mechanically stirred reactor, purge with nitrogen (flow rate 0.3L / min), and heat to 120℃ to melt the material. Add 3g of 4,4'-diphenylmethane diisocyanate, adjust the stirring speed to 300r / min, heat to 190℃, and maintain the temperature for 2.5h. After the reaction is complete, allow it to cool naturally to room temperature to obtain three-dimensional cross-linked modified asphalt.

[0049] Step b) Mix 5g graphite powder, 2g sodium nitrate and 200mL concentrated sulfuric acid, slowly add 10g potassium permanganate under ice bath, stir at 35℃ for 2h, add 200mL deionized water, heat to 98℃ and react for 15min, add 50mL hydrogen peroxide dropwise until the solution turns bright yellow, centrifuge and wash until neutral, freeze dry to obtain hydroxylated graphene quantum dots;

[0050] Weigh 2g of hydroxylated graphene quantum dots and add them to 100mL of deionized water. Sonicate the mixture for 30min to obtain a dispersion. Separately, add 0.5g of ferric chloride to 50mL of deionized water, stir to dissolve, and then add hydrochloric acid to adjust the pH to 3-4 to obtain a ferric chloride solution. Add the ferric chloride solution dropwise to the dispersion at a rate of 1mL / min, stir and react at 30℃ for 2h, then centrifuge at 8000r / min for 10min. Wash the precipitate three times with deionized water and vacuum dry at 60℃ for 12h to obtain modified hydroxylated graphene quantum dots.

[0051] 100g of three-dimensional cross-linked modified bitumen was weighed and added to the barrel of a melt spinning machine, and heated to 280℃ to melt it. 4g of modified hydroxyl graphene quantum dots were weighed and added to 100mL of N-methylpyrrolidone, and ultrasonically dispersed for 40min to obtain a uniform dispersion. The dispersion was injected into the melting section of the melt spinning machine through a metering pump and mixed with the molten bitumen for 1h. The spinning temperature was set to 300℃, the spinneret orifice diameter to 80μm, and the draw rate to 120m / min to spin bitumen precursor containing modified hydroxyl graphene quantum dots.

[0052] Step c) Weigh 10g of carbon nanofibers (20-50μm in length) and place them in a 250mL three-necked flask. Add 100mL of concentrated nitric acid (68wt%) and reflux at 80℃ for 3h. After cooling, centrifuge and wash with deionized water until the pH of the filtrate is 7. Dry under vacuum at 60℃ for 8h to obtain carboxylated carbon nanofibers. Weigh 1.0g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide. Disperse the dispersion by ultrasonication for 1h to obtain a dispersion. Fix 10g of pitch precursor fibers on a stage and use an electrostatic spraying device (voltage 30kV, spraying distance 15cm) to uniformly spray the dispersion onto the surface of the precursor fibers. Place the sprayed precursor fibers into a high-temperature tube furnace, introduce air (flow rate 0.3L / min), heat to 285℃, and maintain the temperature for 2h. After natural cooling, obtain oxidized pitch fibers.

[0053] Step d) Place the oxidized asphalt fiber into a high-temperature tubular furnace, and purge it with argon gas for protection (flow rate 0.5 L / min). Heat the furnace to 1200 °C at a rate of 5 °C / min and hold for 2 hours to complete carbonization. After cooling to 1000 °C, switch to a mixed gas of methyltrichlorosilane and hydrogen (volume ratio 1:3) at a total flow rate of 0.5 L / min and perform chemical vapor deposition for 1.5 hours. After deposition, turn off the gas source and continue to purge with argon gas until the furnace cools to room temperature to obtain the final product.

[0054] Example 4

[0055] A method for preparing pitch-carbon fiber includes the following steps:

[0056] Step a) Weigh 60g of isotropic asphalt that has been oxidized in air (pre-oxidized at 300℃ and an air flow rate of 0.5L / min for 2h) and 40g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt-blended at 200℃ for 30min). Add the mixture to a mechanically stirred reactor, purge with nitrogen (flow rate 0.3L / min), and heat to 120℃ to melt the material. Add 3g of 4,4'-diphenylmethane diisocyanate, adjust the stirring speed to 300r / min, heat to 200℃, and maintain the temperature for 3h. After the reaction is complete, allow it to cool naturally to room temperature to obtain three-dimensional cross-linked modified asphalt.

[0057] Step b) Mix 5g graphite powder, 2g sodium nitrate and 200mL concentrated sulfuric acid, slowly add 10g potassium permanganate under ice bath, stir at 35℃ for 2h, add 200mL deionized water, heat to 98℃ and react for 15min, add 50mL hydrogen peroxide dropwise until the solution turns bright yellow, centrifuge and wash until neutral, freeze dry to obtain hydroxylated graphene quantum dots;

[0058] Weigh 2g of hydroxylated graphene quantum dots and add them to 100mL of deionized water. Sonicate the mixture for 30min to obtain a dispersion. Separately, add 0.5g of ferric chloride to 50mL of deionized water, stir to dissolve, and then add hydrochloric acid to adjust the pH to 3-4 to obtain a ferric chloride solution. Add the ferric chloride solution dropwise to the dispersion at a rate of 1mL / min, stir and react at 30℃ for 2h, then centrifuge at 8000r / min for 10min. Wash the precipitate three times with deionized water and vacuum dry at 60℃ for 12h to obtain modified hydroxylated graphene quantum dots.

[0059] 100g of three-dimensional cross-linked modified bitumen was weighed and added to the barrel of a melt spinning machine, and heated to 280℃ to melt it. 6g of modified hydroxyl graphene quantum dots were weighed and added to 100mL of N-methylpyrrolidone, and ultrasonically dispersed for 40min to obtain a uniform dispersion. The dispersion was injected into the melting section of the melt spinning machine through a metering pump and mixed with the molten bitumen for 1h. The spinning temperature was set to 300℃, the spinneret orifice diameter to 80μm, and the draw rate to 120m / min to spin bitumen precursor containing modified hydroxyl graphene quantum dots.

[0060] Step c) Weigh 10g of carbon nanofibers (20-50μm in length) and place them in a 250mL three-necked flask. Add 100mL of concentrated nitric acid (68wt%) and reflux at 80℃ for 3h. After cooling, centrifuge and wash with deionized water until the pH of the filtrate is 7. Dry the filtrate under vacuum at 60℃ for 8h to obtain carboxylated carbon nanofibers. Weigh 1.5g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide. Disperse the filtrate by ultrasonication for 1h to obtain a dispersion. Fix 10g of pitch precursor fibers on a stage and use an electrostatic spraying device (voltage 30kV, spraying distance 15cm) to uniformly spray the dispersion onto the surface of the precursor fibers. Place the sprayed precursor fibers into a high-temperature tube furnace, introduce air (flow rate 0.3L / min), heat to 290℃, and maintain the temperature for 3h. After natural cooling, obtain oxidized pitch fibers.

[0061] Step d) Place the oxidized asphalt fiber into a high-temperature tubular furnace, introduce argon gas for protection (flow rate 0.5 L / min), heat to 1200 °C at a rate of 5 °C / min, and hold for 2 hours to complete carbonization; after cooling to 1000 °C, switch to a mixed gas of methyltrichlorosilane and hydrogen (volume ratio 1:4), with a total flow rate of 0.5 L / min, and perform chemical vapor deposition for 2 hours; after deposition, turn off the gas source and continue to introduce argon gas until cooled to room temperature, thus obtaining the final product.

[0062] Example 5

[0063] A method for preparing pitch-carbon fiber includes the following steps:

[0064] Step a) Weigh 60g of isotropic asphalt that has been oxidized in air (pre-oxidized at 300℃ and an air flow rate of 0.5L / min for 2h) and 40g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt-blended at 200℃ for 30min). Add the mixture to a mechanically stirred reactor, purge with nitrogen (flow rate 0.3L / min), and heat to 120℃ to melt the material. Add 3g of 4,4'-diphenylmethane diisocyanate, adjust the stirring speed to 300r / min, heat to 180℃, and maintain the temperature for 2h. After the reaction is complete, allow it to cool naturally to room temperature to obtain three-dimensional cross-linked modified asphalt.

[0065] Step b) Mix 5g graphite powder, 2g sodium nitrate and 200mL concentrated sulfuric acid, slowly add 10g potassium permanganate under ice bath, stir at 35℃ for 2h, add 200mL deionized water, heat to 98℃ and react for 15min, add 50mL hydrogen peroxide dropwise until the solution turns bright yellow, centrifuge and wash until neutral, freeze dry to obtain hydroxylated graphene quantum dots;

[0066] Weigh 2g of hydroxylated graphene quantum dots and add them to 100mL of deionized water. Sonicate the mixture for 30min to obtain a dispersion. Separately, add 0.5g of ferric chloride to 50mL of deionized water, stir to dissolve, and then add hydrochloric acid to adjust the pH to 3-4 to obtain a ferric chloride solution. Add the ferric chloride solution dropwise to the dispersion at a rate of 1mL / min, stir and react at 30℃ for 2h, then centrifuge at 8000r / min for 10min. Wash the precipitate three times with deionized water and vacuum dry at 60℃ for 12h to obtain modified hydroxylated graphene quantum dots.

[0067] 100g of three-dimensional cross-linked modified bitumen was weighed and added to the barrel of a melt spinning machine, and heated to 280℃ to melt it. 2g of modified hydroxyl graphene quantum dots were weighed and added to 100mL of N-methylpyrrolidone, and ultrasonically dispersed for 40min to obtain a uniform dispersion. The dispersion was injected into the melting section of the melt spinning machine through a metering pump and mixed with the molten bitumen for 1h. The spinning temperature was set to 300℃, the spinneret orifice diameter to 80μm, and the draw rate to 120m / min to spin bitumen precursor containing modified hydroxyl graphene quantum dots.

[0068] Step c) Weigh 10g of carbon nanofibers (20-50μm in length) and place them in a 250mL three-necked flask. Add 100mL of concentrated nitric acid (68wt%) and reflux at 80℃ for 3h. After cooling, centrifuge and wash with deionized water until the pH of the filtrate is 7. Dry under vacuum at 60℃ for 8h to obtain carboxylated carbon nanofibers. Weigh 0.5g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide. Disperse the dispersion by ultrasonication for 1h to obtain a dispersion. Fix 10g of pitch precursor fibers on a stage and use an electrostatic spraying device (voltage 30kV, spraying distance 15cm) to uniformly spray the dispersion onto the surface of the precursor fibers. Place the sprayed precursor fibers into a high-temperature tube furnace, introduce air (flow rate 0.3L / min), heat to 280℃, and maintain the temperature for 1h for oxidation. After natural cooling, obtain oxidized pitch fibers.

[0069] Step d) Place the oxidized asphalt fiber into a high-temperature tubular furnace, introduce argon gas for protection (flow rate 0.5 L / min), heat to 1200 °C at a rate of 5 °C / min, and hold for 2 hours to complete carbonization; after cooling to 1000 °C, switch to a mixed gas of methyltrichlorosilane and hydrogen (volume ratio 1:2), with a total flow rate of 0.5 L / min, and perform chemical vapor deposition for 1 hour; after deposition, turn off the gas source and continue to introduce argon gas until cooled to room temperature, thus obtaining the final product.

[0070] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that the asphalt in step a) is not subjected to the 4,4'-diphenylmethane diisocyanate crosslinking reaction.

[0071] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that in step b), the three-dimensional cross-linked modified pitch does not contain modified hydroxyl graphene quantum dots during the spinning process.

[0072] Comparative Example 3: The difference between Comparative Example 2 and Example 1 is that in step b), the modified hydroxyl graphene quantum dots are replaced with hydroxyl graphene quantum dots during the spinning process of the three-dimensional cross-linked modified pitch.

[0073] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that in step c), the surface of the pitch fiber is not coated with carboxylated carbon nanofibers by electrostatic spraying.

[0074] Comparative Example 5: The difference between Comparative Example 5 and Example 1 is that in step d), the carbonized oxidized asphalt fiber does not have a silicon carbide nano-coating bonded to its surface.

[0075] Comparison with Example 1: Ordinary pitch carbon fiber purchased from the market.

[0076] Performance testing:

[0077] 1. Tensile property testing: A universal testing machine was used, and the test was conducted according to the national standard GB / T 3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament". Before testing, the two ends of the carbon fiber were fixed to aluminum clamps with epoxy resin (clamping length 50mm) to ensure that the fiber axis was aligned with the tensile direction and to avoid eccentric force. The gauge length was set to 20mm, and the tensile rate was 1mm / min. The load-displacement curve was recorded in real time during the loading process. Ten fibers of uniform length (approximately 150mm) without obvious defects were selected for each test group. After the test, abnormal data (usually the maximum and minimum values) caused by improper clamping or obvious defects were removed. The average value of the remaining 8 sets of data was taken, and the tensile strength (unit: GPa, formula: strength = maximum load / fiber cross-sectional area), tensile modulus (unit: GPa, formula: modulus = slope of the linear segment of the stress-strain curve), and elongation at break (unit: %, formula: elongation = elongation within the gauge length at break / initial gauge length × 100%) were calculated. The test results are shown in Table 1.

[0078] 2. Interfacial Bond Strength Test: The interfacial bonding performance between carbon fiber and the matrix was evaluated using the single-filament pull-out method. First, an epoxy resin matrix (E-51 epoxy resin and curing agent mixed at a mass ratio of 5:1) was prepared and injected into a custom-made PTFE mold (groove depth 50 μm, width 100 μm). Using a microscope, a single pitch-coated carbon fiber was embedded along the groove axis into the uncured epoxy resin, ensuring the embedding length was precisely controlled at 50 μm to avoid fiber bending or tilting. After curing in a 60℃ oven for 24 h, the fiber was demolded to obtain the single-filament embedded sample. During testing, a micro-mechanical testing system was used to slowly pull the fiber along the fiber axis at a rate of 0.05 mm / min, recording the maximum pull-out force (F). The force was calculated using the formula "Interfacial Shear Strength (MPa) = F / (π×d×L)" (where d is the fiber diameter and L is the embedding length). Twenty single filaments were tested in each group, and the average value was taken after removing the three maximum and three minimum values ​​to ensure data stability. The test results are shown in Table 1.

[0079]

[0080] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing pitch-carbon fiber, characterized in that, Includes the following steps: a) Isotropic asphalt that has been oxidized by air is mixed with anisotropic asphalt modified by hydrogenated anthracene oil, and 4,4'-diphenylmethane diisocyanate crosslinking agent is added. The mixture is then melted to obtain three-dimensional crosslinked modified asphalt. b) Prepare hydroxylated graphene quantum dots, then modify the hydroxylated graphene quantum dots, disperse the modified hydroxylated graphene quantum dots in N,N-dimethylformamide, and then add three-dimensional cross-linked modified asphalt. The mass ratio of the three-dimensional cross-linked modified asphalt to the hydroxylated graphene quantum dots is 100:2-6. Blend in the molten state and spin through a spinneret to obtain asphalt precursor containing hydroxylated graphene quantum dots. The method for modifying hydroxylated graphene quantum dots includes the following steps: Hydroxylated graphene quantum dots were added to deionized water and stirred to disperse them, resulting in a dispersion. Add ferric chloride to deionized water and stir to dissolve. Add hydrochloric acid dropwise to adjust the pH to 3-4 to obtain a ferric chloride solution. Ferric chloride solution was slowly added dropwise to the dispersion, and the reaction was stirred. After centrifugation, washing and drying, modified hydroxylated graphene quantum dots were obtained. c) Carbon nanofibers are treated with concentrated nitric acid to obtain carboxylated carbon nanofibers. The carboxylated carbon nanofibers are dispersed in N,N-dimethylformamide to obtain a carboxylated carbon nanofiber dispersion. The carboxylated carbon nanofiber dispersion is sprayed onto the surface of asphalt precursor fibers by electrostatic spraying to allow the carboxylated carbon nanofibers to adhere to the surface of the asphalt precursor fibers. Subsequently, air oxidation treatment is performed to obtain oxidized asphalt fibers. d) Carbonize the oxidized pitch fibers, and then chemically vapor deposit a nano-silicon carbide coating in a mixed atmosphere of methyltrichlorosilane and hydrogen to obtain pitch carbon fibers.

2. The method for preparing pitch-carbon fiber according to claim 1, characterized in that, In step a), the melting reaction temperature is 180–200°C and the reaction time is 2–3 h.

3. The method for preparing pitch-carbon fiber according to claim 1, characterized in that, In step c), the length of the carbon nanofibers is 20–50 μm.

4. The method for preparing pitch-carbon fiber according to claim 1, characterized in that, In step c), the mass ratio of pitch precursor to carboxylated carbon nanofibers is 10:0.5 to 1.

5.

5. The method for preparing pitch-carbon fiber according to claim 1, characterized in that, In step c), the oxidation temperature is 280–290°C and the oxidation time is 1–3 hours.

6. The method for preparing pitch-carbon fiber according to claim 1, characterized in that, In step d), the volume ratio of methyltrichlorosilane to hydrogen is 1:2 to 4.

7. The method for preparing pitch-carbon fiber according to claim 1, characterized in that, In step d), the chemical vapor deposition time is 1 to 2 hours.

8. A pitch-carbon fiber, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

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