Asphalt carbon fiber and preparation method thereof

Abstract

The invention discloses an asphalt carbon fiber and a preparation method thereof, relates to the technical field of fiber reinforced composite materials, and particularly belongs to the patent classification number D01F9 / 145. The specific preparation method comprises the following steps: firstly, enabling active asphalt to pass through a 4, 4 '-diphenylmethane diisocyanate cross-linking agent, carrying out a melting reaction to obtain three-dimensional cross-linked modified asphalt, then carrying out blended spinning on the three-dimensional cross-linked modified asphalt and hydroxylated graphene quantum dots, and then sequentially combining carboxylated carbon nanofibers and silicon carbide to obtain the asphalt carbon fibers. The asphalt carbon fiber prepared by the invention has excellent mechanical strength, and can meet the requirements of high-end application scenarios with relatively high requirements on mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber-reinforced composite materials, specifically belonging to patent classification number D01F9 / 145, and specifically relates to a pitch carbon fiber and a preparation method thereof. Background Art

[0002] As a polymer fiber material with a carbon content of more than 90%, carbon fiber has been widely used in chemical, electromechanical, shipbuilding, aircraft manufacturing and other industrial sectors due to its high specific strength, high specific modulus, low density, chemical corrosion resistance, thermal shock resistance and ablation resistance. It is also an indispensable new material in the fields of space, artificial satellites, rockets and missiles, and atomic energy. At present, the industrialized carbon fibers mainly include three categories: polyacrylonitrile-based carbon fibers, viscose-based carbon fibers and asphalt-based carbon fibers. Among them, polyacrylonitrile-based carbon fibers have the highest output, the most varieties, the fastest development speed and the most mature process technology. However, there are problems with high energy consumption and high cost in the production process. In addition, its precursor acrylonitrile is mostly derived from petrochemicals, and its carbon footprint is relatively large. Although viscose-based carbon fiber has advantages such as low density, low degree of 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 by combustion during flight is weak and not easily detected by radar), in actual production, due to the difficulty in precisely controlling operating conditions, by-products such as L-glucose are easily generated, resulting in a low actual carbon yield and unsatisfactory carbon fiber strength. It is currently mainly used in non-pressure-bearing components in aerospace and civilian fields.

[0003] Pitch-based carbon fibers are made from asphalt, a relatively low-cost material sourced from a wide range of sources, including petroleum asphalt and coal tar pitch. However, during production, asphalt-based carbon fibers face several pressing challenges. Defects can easily develop in their internal structure during the manufacturing process, hindering mechanical properties, particularly tensile strength and modulus, from meeting the requirements of high-end applications. Summary of the Invention

[0004] The purpose of the present invention is to provide a pitch carbon fiber and a preparation method thereof to solve the technical problems raised by the above background technology. The pitch carbon fiber prepared by the present invention has excellent mechanical strength and can meet the needs of high-end application scenarios with high mechanical performance requirements.

[0005] To achieve the above object, the present invention provides the following technical solutions:

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

[0007] a) mixing the air-oxidized isotropic pitch with the anisotropic pitch modified by hydrogenated anthracene oil, adding 4,4'-diphenyl methane diisocyanate crosslinking agent, and obtaining three-dimensional cross-linked modified pitch through melt reaction;

[0008] b) preparing hydroxylated graphene quantum dots, then dispersing the hydroxylated graphene quantum dots in N,N-dimethylformamide, then adding the three-dimensional cross-linked modified pitch, and obtaining hydroxylated graphene quantum dot-containing pitch precursor through melt blending and spinning through a spinneret;

[0009] c) treating carbon nanofibers with concentrated nitric acid to obtain carboxylated carbon nanofibers, dispersing the carboxylated carbon nanofibers in N,N-dimethylformamide to obtain a carboxylated carbon nanofiber dispersion, spraying the carboxylated carbon nanofiber dispersion on the surface of the pitch precursor through electrostatic spraying, and making the carboxylated carbon nanofibers adhere to the surface of the pitch precursor, and then performing air oxidation treatment to obtain oxidized pitch fibers;

[0010] d) carbonizing the oxidized pitch fibers, and then chemical vapor depositing a nanometer silicon carbide coating in a mixed atmosphere of methyltrichlorosilane and hydrogen to obtain pitch carbon fibers.

[0011] In the technical scheme of the present application, the air-oxidized isotropic pitch is mixed with the anisotropic pitch modified by hydrogenated anthracene oil to load active groups on the pitch, and the active groups in the pitch react with the 4,4'-diphenyl methane diisocyanate crosslinking agent to form a three-dimensional network structure of the modified pitch, which enhances the intermolecular forces and reduces the molecular chain slip, thereby improving the overall structural stability of the pitch and laying a foundation for the subsequent mechanical properties of the fibers. Then, the hydroxyl groups on the surface of the hydroxylated graphene quantum dots form hydrogen bonds with the polar groups in the three-dimensional cross-linked modified pitch, promoting the uniform dispersion of the graphene quantum dots in the molten pitch. The excellent mechanical properties of the graphene quantum dots make them effective stress transmitters and crack inhibitors, thereby improving the mechanical strength of the precursor. The carboxyl groups are generated on the surface of the carbon nanofibers through concentrated nitric acid treatment, and the electrostatic spraying utilizes the electrostatic adsorption effect to make the carboxylated carbon nanofibers adhere to the surface of the pitch precursor. The carbon nanofibers attached to the surface of the pitch precursor can bridge potential cracks, significantly improving the surface strength and damage resistance of the fibers. Finally, the carbonization process removes non-carbon elements in the fibers, promotes the ordered arrangement of carbon atoms to form a graphite-like structure, and improves the overall strength of the fibers. The silicon carbide generated by the decomposition of methyltrichlorosilane in a hydrogen atmosphere is deposited on the surface of the fibers through chemical vapor deposition to form a nanometer coating. The coating has high hardness and is tightly combined with the fibers, which can protect the fibers from direct damage by external forces and further improve the overall mechanical properties of the fibers and the bonding strength with other materials. Figure 1This is a SEM image of the surface of the pitch carbon fiber prepared in the present invention. From the electron microscope image, it can be clearly observed that a layer of substance is combined on the surface of the pitch carbon fiber and the surface presents 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 the three-dimensional cross-linked modified asphalt to the hydroxylated graphene quantum dots is 100:2-6.

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

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

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

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

[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 are subjected to a modification treatment, comprising the following steps:

[0020] adding hydroxylated graphene quantum dots into deionized water and stirring to disperse them to obtain a dispersion;

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

[0022] The ferric chloride solution is slowly added dropwise to the dispersion, stirred for reaction, and then centrifuged, washed and dried to obtain the product.

[0023] In the technical solution of the present invention, as mentioned above, by attaching carboxylated carbon nanofibers to the surface of asphalt precursor, the carbon nanofibers attached to the surface can bridge potential cracks and improve the surface strength and damage resistance of the fiber. However, a further problem encountered by the team of the present invention during the research and development process is that it is difficult for the carboxylated carbon nanofibers to be stably attached to the surface of asphalt precursor, thereby reducing its effect on improving the mechanical strength of carbon fiber. In order to further solve this problem, the present invention modifies the hydroxylated graphene quantum dots so that the hydroxyl groups on the hydroxylated graphene quantum dots can be bound to the Fe 3+ Coordination to form GQDs-Fe 3+ GQDs-Fe composite3+ The composites are dispersed inside and on the surface of the asphalt precursor, where the GQDs-Fe 3+ Fe in the complex 3+ It forms a coordination effect with the carboxyl groups on the carboxylated carbon nanofibers, thereby improving the stability of the combination of the carboxylated carbon nanofibers and the asphalt precursor, that is, more carbon nanofibers are stably bound to the surface of the asphalt precursor, thereby significantly improving the improvement effect of the carboxylated carbon nanofibers on the mechanical strength of the carbon fibers.

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

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The prepared asphalt carbon fiber has excellent mechanical strength. It can meet the high requirements of mechanical properties in high-end scenarios by enhancing basic stability through three-dimensional cross-linking structure, suppressing cracks through stress transfer by graphene quantum dots, bridging cracks by carbon nanofibers and synergistic protection by silicon carbide coating.

[0027] 2. The modified hydroxylated graphene quantum dots can improve the stability of the combination between carboxylated carbon nanofibers and asphalt precursors through coordination, enhance their effect on improving the mechanical strength of carbon fibers, and improve product performance reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an SEM image of the surface of the pitch carbon fiber prepared in the present invention. DETAILED DESCRIPTION

[0029] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the implementation regulations described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0030] Example 1

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

[0032] Step a) 60 g of air-oxidized isotropic asphalt (preliminarily oxidized at 300° C. and an air flow rate of 0.5 L / min for 2 h) and 40 g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt blending at 200° C. for 30 min) are weighed and added to a mechanically stirred reactor, nitrogen protection is introduced (flow rate 0.3 L / min), and the temperature is raised to 120° C. to melt the materials; 3 g of 4,4'-diphenylmethane diisocyanate is added, the stirring rate is adjusted to 300 r / min, the temperature is raised to 190° C., and the reaction is kept at this temperature for 2.5 h; after the reaction is completed, the mixture is naturally cooled to room temperature to obtain a three-dimensional cross-linked modified asphalt.

[0033] Step b) 5 g of graphite powder, 2 g of sodium nitrate and 200 mL of concentrated sulfuric acid were mixed, 10 g of potassium permanganate was slowly added under ice bath, the mixture was stirred at 35° C. for 2 h, 200 mL of deionized water was added, the mixture was heated to 98° C. and reacted for 15 min, 50 mL of hydrogen peroxide was added dropwise until the solution turned bright yellow, the mixture was centrifuged and washed until neutral, and freeze-dried to obtain hydroxylated graphene quantum dots;

[0034] 2 g of hydroxylated graphene quantum dots were weighed and added to 100 mL of deionized water, and ultrasonic dispersion was performed for 30 min to obtain a dispersion; another 0.5 g of ferric chloride was added to 50 mL of deionized water, stirred to dissolve, and then hydrochloric acid was added dropwise to adjust the pH to 3-4 to obtain a ferric chloride solution; the ferric chloride solution was dropped into the dispersion at a rate of 1 mL / min, stirred and reacted at 30°C for 2 h, and then centrifuged at 8000 r / min for 10 min. The precipitate was washed three times with deionized water and vacuum dried at 60°C for 12 h to obtain modified hydroxylated graphene quantum dots.

[0035] 100 g of three-dimensional cross-linked modified asphalt was weighed and added to the barrel of a melt spinning machine, and the temperature was raised to 280°C to melt it; 5 g of modified hydroxylated graphene quantum dots were weighed and added to 100 mL of N-methylpyrrolidone, and ultrasonic dispersion was performed for 40 minutes 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 asphalt for 1 hour; the spinning temperature was set to 300°C, the spinneret aperture was 80 μm, and the drawing rate was set to 120 m / min to spin asphalt filaments containing modified hydroxylated graphene quantum dots.

[0036] Step c) Weigh 10g of carbon nanofibers (length 20-50μm) and place them in a 250mL three-necked flask, add 100mL of concentrated nitric acid (68wt%), reflux and oxidize at 80℃ for 3h, cool and centrifuge, wash with deionized water until the filtrate pH = 7, and vacuum dry at 60℃ for 8h to obtain carboxylated carbon nanofibers; weigh 1.2g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide, ultrasonically disperse for 1h to obtain a dispersion; take 10g of asphalt precursor and fix it on the stage, and use electrostatic spraying equipment (voltage 30kV, spraying distance 15cm) to evenly spray the dispersion on the surface of the precursor; put the sprayed precursor into a high-temperature tubular furnace, introduce air (flow rate 0.3L / min), heat to 285℃, keep warm and oxidize for 2h, and obtain oxidized asphalt fiber after natural cooling.

[0037] Step d) Place the oxidized asphalt fiber in a high-temperature tubular furnace, introduce argon protection (flow rate 0.5 L / min), raise the temperature to 1200°C at a rate of 5°C / min, and keep it at that temperature for 2 hours 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 hours; after the deposition is completed, turn off the gas source and continue to pass argon until it cools to room temperature.

[0038] Example 2

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

[0040] Step a) 60 g of air-oxidized isotropic asphalt (preliminarily oxidized at 300° C. and an air flow rate of 0.5 L / min for 2 h) and 40 g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt blending at 200° C. for 30 min) are weighed and added to a mechanically stirred reactor, nitrogen protection is introduced (flow rate 0.3 L / min), and the temperature is raised to 120° C. to melt the materials; 3 g of 4,4'-diphenylmethane diisocyanate is added, the stirring rate is adjusted to 300 r / min, the temperature is raised to 190° C., and the reaction is kept at this temperature for 2.5 h; after the reaction is completed, the mixture is naturally cooled to room temperature to obtain a three-dimensional cross-linked modified asphalt.

[0041] Step b) 5 g of graphite powder, 2 g of sodium nitrate and 200 mL of concentrated sulfuric acid were mixed, 10 g of potassium permanganate was slowly added under ice bath, the mixture was stirred at 35° C. for 2 h, 200 mL of deionized water was added, the mixture was heated to 98° C. and reacted for 15 min, 50 mL of hydrogen peroxide was added dropwise until the solution turned bright yellow, the mixture was centrifuged and washed until neutral, and freeze-dried to obtain hydroxylated graphene quantum dots;

[0042] 2 g of hydroxylated graphene quantum dots were weighed and added to 100 mL of deionized water, and ultrasonic dispersion was performed for 30 min to obtain a dispersion; another 0.5 g of ferric chloride was added to 50 mL of deionized water, stirred to dissolve, and then hydrochloric acid was added dropwise to adjust the pH to 3-4 to obtain a ferric chloride solution; the ferric chloride solution was dropped into the dispersion at a rate of 1 mL / min, stirred and reacted at 30°C for 2 h, and then centrifuged at 8000 r / min for 10 min. The precipitate was washed three times with deionized water and vacuum dried at 60°C for 12 h to obtain modified hydroxylated graphene quantum dots.

[0043] 100 g of three-dimensional cross-linked modified asphalt was weighed and added to the barrel of a melt spinning machine, and the temperature was raised to 280°C to melt it; 3 g of modified hydroxylated graphene quantum dots were weighed and added to 100 mL of N-methylpyrrolidone, and ultrasonic dispersion was performed for 40 minutes 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 asphalt for 1 hour; the spinning temperature was set to 300°C, the spinneret aperture to 80 μm, and the drawing rate to 120 m / min to spin asphalt filaments containing modified hydroxylated graphene quantum dots.

[0044] Step c) Weigh 10g of carbon nanofibers (length 20-50μm) and place them in a 250mL three-necked flask, add 100mL of concentrated nitric acid (68wt%), reflux and oxidize at 80℃ for 3h, cool and centrifuge, wash with deionized water until the filtrate pH = 7, and vacuum dry at 60℃ for 8h to obtain carboxylated carbon nanofibers; weigh 0.8g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide, ultrasonically disperse for 1h to obtain a dispersion; take 10g of asphalt precursor and fix it on the stage, and use electrostatic spraying equipment (voltage 30kV, spraying distance 15cm) to evenly spray the dispersion on the surface of the precursor; put the sprayed precursor into a high-temperature tubular furnace, introduce air (flow rate 0.3L / min), heat to 285℃, keep warm and oxidize for 2h, and obtain oxidized asphalt fiber after natural cooling.

[0045] Step d) Place the oxidized asphalt fiber in a high-temperature tubular furnace, introduce argon protection (flow rate 0.5 L / min), raise the temperature to 1200°C at a rate of 5°C / min, and keep it at that temperature for 2 hours 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 1.2 hours; after the deposition is completed, turn off the gas source and continue to pass argon until it cools to room temperature.

[0046] Example 3

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

[0048] Step a) 60 g of air-oxidized isotropic asphalt (preliminarily oxidized at 300° C. and an air flow rate of 0.5 L / min for 2 h) and 40 g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt blending at 200° C. for 30 min) are weighed and added to a mechanically stirred reactor, nitrogen protection is introduced (flow rate 0.3 L / min), and the temperature is raised to 120° C. to melt the materials; 3 g of 4,4'-diphenylmethane diisocyanate is added, the stirring rate is adjusted to 300 r / min, the temperature is raised to 190° C., and the reaction is kept at this temperature for 2.5 h; after the reaction is completed, the mixture is naturally cooled to room temperature to obtain a three-dimensional cross-linked modified asphalt.

[0049] Step b) 5 g of graphite powder, 2 g of sodium nitrate and 200 mL of concentrated sulfuric acid were mixed, 10 g of potassium permanganate was slowly added under ice bath, the mixture was stirred at 35° C. for 2 h, 200 mL of deionized water was added, the mixture was heated to 98° C. and reacted for 15 min, 50 mL of hydrogen peroxide was added dropwise until the solution turned bright yellow, the mixture was centrifuged and washed until neutral, and freeze-dried to obtain hydroxylated graphene quantum dots;

[0050] 2 g of hydroxylated graphene quantum dots were weighed and added to 100 mL of deionized water, and ultrasonic dispersion was performed for 30 min to obtain a dispersion; another 0.5 g of ferric chloride was added to 50 mL of deionized water, stirred to dissolve, and then hydrochloric acid was added dropwise to adjust the pH to 3-4 to obtain a ferric chloride solution; the ferric chloride solution was dropped into the dispersion at a rate of 1 mL / min, stirred and reacted at 30°C for 2 h, and then centrifuged at 8000 r / min for 10 min. The precipitate was washed three times with deionized water and vacuum dried at 60°C for 12 h to obtain modified hydroxylated graphene quantum dots.

[0051] 100 g of three-dimensional cross-linked modified asphalt was weighed and added to the barrel of a melt spinning machine, and the temperature was raised to 280°C to melt it; 4 g of modified hydroxylated graphene quantum dots were weighed and added to 100 mL of N-methylpyrrolidone, and ultrasonic dispersion was performed for 40 minutes 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 asphalt for 1 hour; the spinning temperature was set to 300°C, the spinneret aperture to 80 μm, and the drawing rate to 120 m / min to spin asphalt filaments containing modified hydroxylated graphene quantum dots.

[0052] Step c) Weigh 10g of carbon nanofibers (length 20-50μm) and place them in a 250mL three-necked flask, add 100mL of concentrated nitric acid (68wt%), reflux and oxidize at 80℃ for 3h, cool and centrifuge, wash with deionized water until the filtrate pH = 7, and vacuum dry at 60℃ for 8h to obtain carboxylated carbon nanofibers; weigh 1.0g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide, ultrasonically disperse for 1h to obtain a dispersion; take 10g of asphalt precursor and fix it on the stage, and use electrostatic spraying equipment (voltage 30kV, spraying distance 15cm) to evenly spray the dispersion on the surface of the precursor; put the sprayed precursor into a high-temperature tubular furnace, introduce air (flow rate 0.3L / min), heat to 285℃, keep warm and oxidize for 2h, and obtain oxidized asphalt fiber after natural cooling.

[0053] Step d) Place the oxidized asphalt fiber into a high-temperature tubular furnace, introduce argon protection (flow rate 0.5 L / min), raise the temperature to 1200°C at a rate of 5°C / min, and keep it at that temperature for 2 hours 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 1.5 hours; after the deposition is completed, turn off the gas source and continue to pass argon until it cools to room temperature.

[0054] Example 4

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

[0056] Step a) 60 g of air-oxidized isotropic asphalt (preliminarily oxidized at 300° C. and an air flow rate of 0.5 L / min for 2 h) and 40 g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt blending at 200° C. for 30 min) are weighed and added to a mechanically stirred reactor, nitrogen protection (flow rate 0.3 L / min) is introduced, and the temperature is raised to 120° C. to melt the materials; 3 g of 4,4'-diphenylmethane diisocyanate is added, the stirring rate is adjusted to 300 r / min, the temperature is raised to 200° C., and the reaction is maintained at this temperature for 3 h; after the reaction is completed, the mixture is naturally cooled to room temperature to obtain a three-dimensional cross-linked modified asphalt.

[0057] Step b) 5 g of graphite powder, 2 g of sodium nitrate and 200 mL of concentrated sulfuric acid were mixed, 10 g of potassium permanganate was slowly added under ice bath, the mixture was stirred at 35° C. for 2 h, 200 mL of deionized water was added, the mixture was heated to 98° C. and reacted for 15 min, 50 mL of hydrogen peroxide was added dropwise until the solution turned bright yellow, the mixture was centrifuged and washed until neutral, and freeze-dried to obtain hydroxylated graphene quantum dots;

[0058] 2 g of hydroxylated graphene quantum dots were weighed and added to 100 mL of deionized water, and ultrasonic dispersion was performed for 30 min to obtain a dispersion; another 0.5 g of ferric chloride was added to 50 mL of deionized water, stirred to dissolve, and then hydrochloric acid was added dropwise to adjust the pH to 3-4 to obtain a ferric chloride solution; the ferric chloride solution was dropped into the dispersion at a rate of 1 mL / min, stirred and reacted at 30°C for 2 h, and then centrifuged at 8000 r / min for 10 min. The precipitate was washed three times with deionized water and vacuum dried at 60°C for 12 h to obtain modified hydroxylated graphene quantum dots.

[0059] 100 g of three-dimensional cross-linked modified asphalt was weighed and added to the barrel of a melt spinning machine, and the temperature was raised to 280°C to melt it; 6 g of modified hydroxylated graphene quantum dots were weighed and added to 100 mL of N-methylpyrrolidone, and ultrasonic dispersion was performed for 40 minutes 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 asphalt for 1 hour; the spinning temperature was set to 300°C, the spinneret aperture to 80 μm, and the drawing rate to 120 m / min to spin asphalt filaments containing modified hydroxylated graphene quantum dots.

[0060] Step c) Weigh 10g of carbon nanofibers (length 20-50μm) and place them in a 250mL three-necked flask, add 100mL of concentrated nitric acid (68wt%), reflux and oxidize at 80℃ for 3h, cool and centrifuge, wash with deionized water until the filtrate pH = 7, and vacuum dry at 60℃ for 8h to obtain carboxylated carbon nanofibers; weigh 1.5g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide, ultrasonically disperse for 1h to obtain a dispersion; take 10g of asphalt precursor and fix it on the stage, and use electrostatic spraying equipment (voltage 30kV, spraying distance 15cm) to evenly spray the dispersion on the surface of the precursor; put the sprayed precursor into a high-temperature tubular furnace, introduce air (flow rate 0.3L / min), heat to 290℃, keep warm for oxidation for 3h, and obtain oxidized asphalt fiber after natural cooling.

[0061] Step d) Place the oxidized asphalt fiber in a high-temperature tubular furnace, introduce argon protection (flow rate 0.5 L / min), raise the temperature to 1200°C at a rate of 5°C / min, and keep it at that temperature 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 the deposition is completed, turn off the gas source and continue to pass argon until it cools to room temperature.

[0062] Example 5

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

[0064] Step a) 60 g of air-oxidized isotropic asphalt (preliminarily oxidized at 300° C. and an air flow rate of 0.5 L / min for 2 h) and 40 g of anisotropic asphalt modified by blending with hydrogenated anthracene oil (anisotropic asphalt to hydrogenated anthracene oil mass ratio of 95:5, melt blending at 200° C. for 30 min) are weighed and added to a mechanically stirred reactor, nitrogen protection (flow rate 0.3 L / min) is introduced, and the temperature is raised to 120° C. to melt the materials; 3 g of 4,4'-diphenylmethane diisocyanate is added, the stirring rate is adjusted to 300 r / min, the temperature is raised to 180° C., and the reaction is maintained at this temperature for 2 h; after the reaction is completed, the mixture is naturally cooled to room temperature to obtain a three-dimensional cross-linked modified asphalt.

[0065] Step b) 5 g of graphite powder, 2 g of sodium nitrate and 200 mL of concentrated sulfuric acid were mixed, 10 g of potassium permanganate was slowly added under ice bath, the mixture was stirred at 35° C. for 2 h, 200 mL of deionized water was added, the mixture was heated to 98° C. and reacted for 15 min, 50 mL of hydrogen peroxide was added dropwise until the solution turned bright yellow, the mixture was centrifuged and washed until neutral, and freeze-dried to obtain hydroxylated graphene quantum dots;

[0066] 2 g of hydroxylated graphene quantum dots were weighed and added to 100 mL of deionized water, and ultrasonic dispersion was performed for 30 min to obtain a dispersion; another 0.5 g of ferric chloride was added to 50 mL of deionized water, stirred to dissolve, and then hydrochloric acid was added dropwise to adjust the pH to 3-4 to obtain a ferric chloride solution; the ferric chloride solution was dropped into the dispersion at a rate of 1 mL / min, stirred and reacted at 30°C for 2 h, and then centrifuged at 8000 r / min for 10 min. The precipitate was washed three times with deionized water and vacuum dried at 60°C for 12 h to obtain modified hydroxylated graphene quantum dots.

[0067] 100 g of three-dimensional cross-linked modified asphalt was weighed and added to the barrel of a melt spinning machine, and the temperature was raised to 280°C to melt it; 2 g of modified hydroxylated graphene quantum dots were weighed and added to 100 mL of N-methylpyrrolidone, and ultrasonic dispersion was performed for 40 minutes 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 asphalt for 1 hour; the spinning temperature was set to 300°C, the spinneret aperture to 80 μm, and the drawing rate to 120 m / min to spin asphalt filaments containing modified hydroxylated graphene quantum dots.

[0068] Step c) Weigh 10g of carbon nanofibers (length 20-50μm) and place them in a 250mL three-necked flask, add 100mL of concentrated nitric acid (68wt%), reflux and oxidize at 80℃ for 3h, cool and centrifuge, wash with deionized water until the filtrate pH = 7, and vacuum dry at 60℃ for 8h to obtain carboxylated carbon nanofibers; weigh 0.5g of carboxylated carbon nanofibers and add 100mL of N,N-dimethylformamide, ultrasonically disperse for 1h to obtain a dispersion; take 10g of asphalt precursor and fix it on the stage, and use electrostatic spraying equipment (voltage 30kV, spraying distance 15cm) to evenly spray the dispersion on the surface of the precursor; put the sprayed precursor into a high-temperature tubular furnace, introduce air (flow rate 0.3L / min), heat to 280℃, keep warm for oxidation for 1h, and obtain oxidized asphalt fiber after natural cooling.

[0069] Step d) Place the oxidized asphalt fiber in a high-temperature tubular furnace, introduce argon protection (flow rate 0.5 L / min), raise the temperature to 1200°C at a rate of 5°C / min, and keep it at that temperature 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 the deposition is completed, turn off the gas source and continue to pass argon until it cools to room temperature.

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

[0071] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that in step b), no modified hydroxylated graphene quantum dots are added to the three-dimensional cross-linked modified asphalt during the spinning process.

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

[0073] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that in step c), the surface of the asphalt precursor is not bonded with the 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 silicon carbide nanocoating is not bonded to the surface of the oxidized pitch fibers after carbonization.

[0075] Comparative Example 1: Ordinary pitch carbon fiber purchased on the market.

[0076] Performance testing:

[0077] 1. Tensile Properties: A universal materials testing machine was used in accordance with the national standard GB / T 3362-2017, "Test Method for Tensile Properties of Carbon Fiber Multifilaments." Before testing, the carbon fibers were fixed to an aluminum fixture (clamping length 50 mm) using epoxy resin at both ends to ensure that the fiber axis was aligned with the tensile direction and to avoid eccentric loading. The test gauge length was set at 20 mm, and the tensile rate was 1 mm / min. Load-displacement curves were recorded in real time during loading. Ten fibers of uniform length (approximately 150 mm) and without obvious defects were selected for each test. After testing, abnormal data (typically the maximum and minimum values) due to improper clamping or obvious defects were eliminated. The remaining eight data sets were averaged to calculate 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%). The test results are shown in Table 1.

[0078] 2. Interface Bonding Strength Test: The interfacial bonding performance between carbon fiber and matrix was evaluated using the single-filament pullout method. An epoxy resin matrix (E-51 epoxy resin and curing agent mixed in a mass ratio of 5:1) was prepared and injected into a custom polytetrafluoroethylene mold (groove depth 50 μm, width 100 μm). Using a microscope, a single pitch carbon fiber was embedded in the uncured epoxy resin along the groove axis, ensuring a precise embedment length of 50 μm to avoid fiber bending or tilting. After curing in a 60°C oven for 24 hours, the fiber was removed from the mold to obtain the embedded single-filament specimen. During the test, a micromechanical testing system was used to slowly pull out the fiber along the axial direction at a rate of 0.05 mm / min. The maximum pullout force (F) was recorded and calculated using the formula "Interfacial shear strength (MPa) = F / (π × d × L)" (where d is the fiber diameter and L is the embedment length). Twenty single-filaments were tested in each group, and the average value was calculated 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 aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing pitch carbon fiber, characterized in that: The following steps are involved: a) mixing air-oxidized isotropic asphalt with hydrogenated anthracene oil-modified anisotropic asphalt, adding 4,4'-diphenylmethane diisocyanate as a crosslinking agent, and performing a melt reaction to obtain a three-dimensional crosslinked modified asphalt; b) preparing hydroxylated graphene quantum dots, dispersing the hydroxylated graphene quantum dots in N,N-dimethylformamide, adding three-dimensional cross-linked modified asphalt, blending in a molten state, and spinning through a spinneret to obtain asphalt precursor fibers containing hydroxylated graphene quantum dots; c) treating the carbon nanofibers with concentrated nitric acid to obtain carboxylated carbon nanofibers, dispersing the carboxylated carbon nanofibers in N,N-dimethylformamide to obtain a carboxylated carbon nanofiber dispersion, spraying the carboxylated carbon nanofiber dispersion onto the surface of asphalt precursor fibers by electrostatic spraying to adhere the carboxylated carbon nanofibers to the surface of the asphalt precursor fibers, and then performing air oxidation treatment to obtain oxidized asphalt fibers; d) The oxidized pitch fibers are carbonized, and then a nano-silicon carbide coating is chemically vapor deposited in a mixed atmosphere of methyltrichlorosilane and hydrogen to obtain pitch carbon fibers.

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

3. The method for preparing a pitch carbon fiber according to claim 1, characterized in that: In the step b), the mass ratio of the three-dimensional cross-linked modified asphalt to the hydroxylated graphene quantum dots is 100:2-6.

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

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

5.

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

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

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

9. The method for preparing pitch carbon fiber according to claim 1, characterized in that: In the step b), the hydroxylated graphene quantum dots are subjected to a modification treatment, comprising the following steps: adding hydroxylated graphene quantum dots into deionized water and stirring to disperse them to obtain a dispersion; Add ferric chloride to deionized water, stir and dissolve, and add hydrochloric acid dropwise to adjust the pH to 3-4 to obtain a ferric chloride solution; The ferric chloride solution is slowly added dropwise to the dispersion, stirred for reaction, and then centrifuged, washed and dried to obtain the product.

10. A pitch carbon fiber, characterized in that: The product is prepared by the method described in any one of claims 1 to 9 above.

Images