SUGAR-BASED HIGH-STRENGTH CARBON FIBER AND PREPARATION METHOD THEREOF

[0001] This application claims priority to Chinese Patent Application No. 202510082229.2, filed on Jan. 20, 2025, the contents of which are hereby incorporated by reference.

[0002] The present disclosure belongs to the technical field of carbon fiber production, and in particular to relates to a sugar-based high-strength carbon fiber and a preparation method thereof.

[0003] Carbon fibers, with their excellent properties such as high strength, high modulus, light weight, high temperature resistance and corrosion resistance, are widely used in fields like automobile manufacturing, wind turbine blades, sports equipment, aerospace and so on. With the high specific strength and high specific modulus, carbon fibers perform excellently as reinforcements in composite materials, and are often used in carbon fiber reinforced resins and ceramic composites. Meanwhile, the high temperature resistance in extreme environments endows carbon fibers with unique application advantages, showing broad development prospects.

[0004] Currently, traditional carbon fibers are mainly classified into polyacrylonitrile (PAN)-based, pitch-based, and viscose-based carbon fibers. The preparation process of the carbon fiber precursor fibers is complex and costly, often involving the use of toxic or harmful substances. The precursor fibers require multiple steps of treatment such as long-term pre-oxidation and high-temperature carbonization, resulting in significant energy consumption. Particularly in the preparation of PAN and pitch-based carbon fiber production, high-temperature multi-step treatment process severely limits further improvements in yield and cost reduction. In addition, these traditional methods rely on non-renewable fossil resources, and the emission of toxic and harmful gases during production adversely impacts the environment. Although viscose-based carbon fibers are derived from natural cellulose, the alkalization and vulcanization processes are complex, still generating harmful waste; moreover, after decades of efforts, the strength improvement has been limited, reaching a maximum of 1 gigapascal (GPa). Traditional carbon fiber production faces issues such as high costs, long preparation cycles, complex processes, high energy consumption, severe pollution, and strong dependence on non-renewable fossil resources. To achieve green and sustainable carbon fiber production, a more environmentally friendly and low-cost alternative scheme is urgently needed.

[0005] The objective of the present disclosure is to provide a sugar-based high-strength carbon fiber and a preparation method thereof. Using renewable water-soluble sugars as the carbon source and water as the solvent, the carbon fiber precursor fibers are prepared through wet spinning, followed by pre-carbonization and carbonization treatments to achieve efficient synthesis of carbon fiber. This method significantly reduces raw material and production costs, features simple processes and short cycles, and avoids the emission of toxic and harmful substances. The produced carbon fibers have uniform and dense structures, excellent mechanical properties, and the surface with abundant groove structures may effectively enhance the bonding force with the composite material matrices. The prepared carbon fiber is not only environmentally friendly but also holds great market potential, with prospects for widespread application in automotive and sports equipment fields.

[0006] To achieve the above objectives, the disclosure provides the following technical schemes:

• • [0007] the first technical scheme of the present disclosure provides a method for preparing a sugar-based high-strength carbon fiber, including following steps:
  • [0008] dissolving gel monomers, water-soluble sugars, and crosslinking agents in water to obtain solution A; and adding spinning aids, initiators, and catalysts to the solution A to serve as spinning dope;
  • [0009] preparing a solution identical to the solution A, and adding ionic gel aids to serve as coagulation bath;
  • [0010] using a solution obtained by omitting the gel monomers, the crosslinking agents, and the spinning aids from the spinning dope as water bath solution;
  • [0011] obtaining carbon fiber precursor fibers through wet spinning by using the spinning dope, the coagulation bath, and the water bath solution; and
  • [0012] performing pre-carbonization on the carbon fiber precursor fibers to obtain pre-carbonized fiber; then performing carbonization on the pre-carbonized fiber to obtain the sugar-based high-strength carbon fiber.

[0013] The present disclosure uses water-soluble sugars as the carbon source to prepare carbon fiber precursor fibers through wet spinning process; the coagulation bath and water bath solution prepared in the wet spinning process may be recycled for multiple times; then volatile substances and moisture are removed through pre-carbonization, to promote caramelization reaction, reduce internal stress, avoid cracking and breaking, complete stabilization treatment, and ensure fiber uniformity and strength; finally, high-strength carbon fibers are obtained through carbonization.

[0014] Optionally, the gel monomers include one or more of acrylic acid, methacrylic acid, acrylamide, and N-isopropylacrylamide.

[0015] Optionally, the water-soluble sugars include one or more of glucose, fructose, galactose, maltose, sucrose, lactose, and fructooligosaccharides.

[0016] Optionally, the crosslinking agents include one or more of ethylene glycol diacrylate, sodium acrylate, N,N′-methylenebisacrylamide, ethylene glycol dimethacrylate, diacrylamide ethylenediamine, and N,N′-ethylenebisacrylamide.

[0017] Optionally, a mass ratio of the gel monomers, the water-soluble sugars, the crosslinking agents to the water in the solution A is 1-30:10-80:0.05-2:100.

[0018] Optionally, the spinning aids include one or more of sodium alginate, sodium polyacrylate, and sodium carboxymethyl cellulose.

[0019] Optionally, the initiators include one or more of azobisisobutyronitrile, ammonium persulfate, potassium persulfate, and hydrogen peroxide.

[0020] Optionally, the catalysts include one or more of sodium sulfite, triethanolamine, and tetramethylethylenediamine.

[0021] Optionally, in the spinning dope, the spinning aids, the initiators, and the catalysts are added in forms of aqueous solutions; where a concentration of spinning aid aqueous solution is 1-10 weight percent (wt. %), a concentration of initiator aqueous solution is 0.5-20 wt. %, and a concentration of catalyst aqueous solution is 0.5-20 wt. %.

[0022] Optionally, in the spinning dope, a mass ratio of the spinning aids to the water in the solution A is 0.5-10:100.

[0023] In the spinning dope, the amounts of the initiators and catalysts are determined based on the gel monomer content and may be added according to conventional practices in the field.

[0024] Optionally, the ionic gel aids include calcium chloride and/or calcium acetate.

[0025] Optionally, the ionic gel aids account for 1-20 percent (%) of a mass of the coagulation bath.

[0026] Optionally, the temperature of the water bath solution during wet spinning is 25-90 degrees Celsius (° C.).

[0027] Optionally, in a process of the wet spinning, process parameters are: a diameter of an inner hole of a spinning needle is 30-200 micrometers (μm), a spinning speed is 50-2000 microliters per minute (μL/min), a drawing machine speed is 1-20 meters per minute (m/min), drying temperature is 50-300° C., and duration of drying is 1-30 minutes (min).

[0028] Optionally, the pre-carbonization is performed with gradient heating, with a maximum temperature not exceeding 350° C.

[0029] More specifically, the operation steps are as follow: the carbon fiber precursor fibers are gradually heated in a continuous pre-carbonization furnace and uniformly drawn through various temperature zones to achieve stable pre-carbonization and obtain pre-carbonized fibers with consistent quality; the fiber running speed is optionally 0.02-1 m/min to ensure that the fibers gradual adapt to the heating process, avoid damage to the internal structure, and allow sufficient residence time of the precursor fibers in each temperature zone for reactions to form ideal micro-nano structures.

[0030] Optionally, the carbonization is conducted under an oxygen-free condition, with direct or gradient heating to 800-2000° C., a heating rate of 1-20 degrees Celsius per minute (° C./min), and a holding duration of 0.5-6 hours (h) for each gradient.

[0031] The second technical scheme of the present disclosure provides a sugar-based high-strength carbon fiber prepared by the method for preparing a sugar-based high-strength carbon fiber described above.

[0032] The third technical scheme of the present disclosure provides a graphite fiber, which is obtained by graphitizing of a pre-carbonized fiber or a sugar-based high-strength carbon fiber prepared by the method described above.

[0033] Optionally, the graphitization is performed at 2000-3000° C., with a heating rate of 0.5-20° C./min and a holding duration of 0.5-6 h.

[0034] The beneficial effects of the present disclosure are as follows.

[0035] Aiming at the issues of traditional carbon fiber production such as high cost, long cycles, complex processes, high energy consumption, serious pollution and strong dependence on non-renewable fossil resources, the present disclosure innovatively proposes a method for preparing a green and low-cost of sugar-based high-strength carbon fiber. The method uses inexpensive, green and renewable water-soluble sugars as the carbon source and water as the solvent, significantly reducing raw material and production costs, and avoiding the emission of toxic and harmful substances. The preparation process is simple with a short cycle; the obtained carbon fibers have a uniform and dense structure, excellent mechanical properties, and grooves on the surface, which enable good bonding with other materials when compounded. Due to low raw material cost and environmentally friendly manufacturing processes, the carbon fibers provided by the present disclosure have broad market application prospects and are expected to be widely used in fields such as automobiles and sporting goods.

[0042] Various exemplary embodiments of the present disclosure are described in detail below. This detailed description should not be construed as limiting the disclosure but rather as providing a more detailed explanation of certain aspects, features, and embodiments. The terms used herein are intended to describe specific embodiments and are not meant to limit the disclosure.

[0043] Additionally, for numerical ranges in the disclosure, each intermediate value between the upper and lower limits is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as any smaller range formed by intermediate values, is included in the disclosure. The upper and lower limits of these smaller ranges may be independently included or excluded.

[0044] Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art. Although only optional methods and materials are described herein, any methods and materials similar or equivalent to those described may be used in the practice or testing of the disclosure.

[0045] The terms “comprising,” “including,” “having,” “containing,” etc., are open-ended and mean “including but not limited to.”

[0046] (1) Preparation of the spinning dope: firstly, 42 grams (g) of acrylic acid, 140 g of glucose and 2.3 g of ethylene glycol diacrylate are mixed and dissolved in 385 milliliters (mL) of deionized water, and stirred to form a uniform and transparent solution. Then, 175 mL of sodium alginate aqueous solution with mass fraction of 4 percent (%), 14 mL of ammonium persulfate aqueous solution with mass fraction of 10% and 14 mL of tetramethylethylene diamine aqueous solution with mass fraction of 10% are added, ultrasonic and stirring are carried out to form a uniform solution, and bubbles in the spinning solution are removed by a defoamer to obtain the spinning dope for later use.

[0047] (2) Preparation of the coagulation bath: 1800 g of acrylic acid, 6000 g of glucose, 150 g of ethylene glycol diacrylate and 1800 g of calcium chloride are mixed and dissolved in 16500 mL of deionized water, stirred in the coagulation bath tank to form a uniform and transparent solution, and the circulating pump of the coagulation bath is turned on during the spinning operation, so that the coagulation bath circulates directionally in the coagulation bath tank. In addition, the coagulation bath may be recycled for many times after preparation.

[0048] (3) Preparation of the water bath solution: 6000 g of glucose, 600 mL of ammonium persulfate aqueous solution with mass fraction of 10% and 600 mL of tetramethylethylene diamine aqueous solution with mass fraction of 10% are mixed and dissolved in 16500 mL of deionized water, stirred in a constant temperature water bath to form a uniform and transparent solution, and the heating device of the constant temperature water bath is turned on during spinning operation to stabilize the temperature of the water bath at 70 degrees Celsius (° C.). In addition, the water bath solution may be recycled for many times after preparation.

[0049] (4) Preparation of the carbon fiber precursor fibers: the prepared spin solution is sucked by a syringe and connected with a spinning needle, and the diameter of the inner hole of the spin needle is 80 micrometers (μm). Then the spinning dope is injected into the coagulation bath through the spinning needle at a speed of 500 microliters per minute (μL/min) by using a high-precision injection pump to generate gel precursor fibers.

[0050] After the gel precursor fibers passes through a constant temperature water washing tank at 70° C. under the traction of a drawing machine, with the drawing machine speed of 8 meters per minute (m/min), and the gel precursor fibers enter a blower dryer at 120° C. for drying. Finally, the gel precursor fibers are collected into bundles by a wire collecting rod to obtain carbon fiber precursor fibers.

[0051] (5) Pre-carbonization: the carbon fiber precursor fibers are passed through the continuous pre-carbonization furnace at a speed of 0.05 m/min by a pay-off machine and a tractor, and the precursor fibers pass through various temperature zones in a uniform traction way, thus realizing stable pre-carbonization and obtaining pre-carbonized fibers with uniform quality. The pre-carbonization production line adopts a 5-section furnace design, each section of the furnace is provided with five temperature zones, totaling 25 temperature zones, which are gradually increases from 25° C. to 220° C. The temperature zones are distributed from low temperature, medium temperature to high temperature, to gradually remove volatile substances and moisture, promote caramelization reaction, and complete the final stabilization treatment to ensure fiber uniformity and strength. The temperature zone settings of the continuous pre-carbonization furnace are shown in Table 1.

TABLE 1
Temperature parameter setting for continuous
pre-carbonization furnace (° C.)
		Temperature zone
		1	2	3	4	5
	Furnace A	40	60	80	100	120
	Furnace B	145	145	145	145	165
	Furnace C	185	185	185	185	185
	Furnace D	185	185	185	200	220
	Furnace E	220	220	220	220	220
	Note:
	the five sections of the furnace from unwinding to winding are respectively Furnace A/B/C/D/E, and each section of the furnace has five temperature zones 1/2/3/4/5 from fiber feeding to fiber discharging.

[0052] (6) Carbonization: a carbonization furnace is used to carbonize the pre-carbonized fibers, and the temperature is raised to 360° C., 920° C., 1050° C. and 1400° C. respectively at the heating rate of 4 degrees Celsius per minute (° C./min) under vacuum conditions, held for 2 hours (h) at each temperature, then the carbon fibers are cooled to room temperature in the furnace, and the carbon fibers are obtained.

[0053] (7) Graphitization: the pre-carbonized fiber or carbon fiber are graphitized in a graphitizing furnace, heated to 1800° C. at a heating rate of 2° C./min under vacuum conditions, then heated to 2800° C. at a heating rate of 2° C./min, the temperature is held for 2 h, and cooled the furnace to room temperature to obtain graphite fibers.

[0054] The scanning electron microscope (SEM) images of the carbon fiber prepared in Embodiment 1 are shown in FIG. 1A and FIG. 1B; where FIG. 1A is the image of the surface morphology, and FIG. 1B is the image of the cross-sectional morphology.

[0055] FIG. 1A shows the scanning electron microscope image of the carbon fiber surface, and groove structures distributed along the fiber axis may be clearly observed; such surface roughness helps carbon fibers form stronger mechanical interlocking with the matrix in composites, thereby significantly improving the interface bonding strength. FIG. 1B is a scanning electron microscope image of the carbon fiber cross-section, which is regularly circular with a dense interior, and no obvious defects such as cracks or holes are found, indicating that the carbon fiber has high structural integrity and excellent mechanical properties. Combining the characteristics of the two images, it may be inferred that the groove structures and dense cross-section of the carbon fiber work together to improve the overall mechanical properties of the composite, making it have great application potential in reinforcing phase materials.

[0056] The transmission electron microscope (TEM) images of the carbon fiber prepared in Embodiment 1 are shown in FIG. 2A, FIG. 2B and FIG. 2C; where FIG. 2A is a high-resolution TEM (HRTEM) image, FIG. 2B is a selected area electron diffraction (SAED) image, and FIG. 2C is a partial enlarged view of FIG. 2A.

[0057] It may be seen from FIG. 2A, FIG. 2B and FIG. 2C that the TEM image of the carbonized carbon fiber treated at 1400° C. shows the mixed structural characteristics of amorphous carbon and microcrystalline graphite. In the HRTEM image of FIG. 2A, the amorphous carbon regions are uniformly distributed and disordered without clear lattice fringes, while the microcrystalline graphite regions show a lattice structure with bright and dark fringes, and the lattice is distorted to a certain extent at the microcrystalline scale. The image shows that microcrystalline graphite is embedded in the amorphous carbon matrix, forming a composite microstructure. The SAED pattern in FIG. 2B shows bright rings, indicating that the sample has a certain degree of crystallinity. The discrete bright spots on the rings correspond to microcrystalline graphite regions, while the continuous rings reflect the existence of amorphous carbon. The inverse Fourier transform (IFFT) image in FIG. 2C further highlights the bright and dark fringes of the lattice structure, which may more clearly identify the shape and distribution of microcrystalline graphite. It may be inferred from the performance that the mixed structure of the carbon fiber has excellent mechanical properties.

[0058] The tensile strength diagram of the carbon fiber prepared in Embodiment 1 is shown in FIG. 8, where 1 #, 2 #, 3 #are the tensile strengths of different sections of the carbon fiber prepared in Embodiment 1, respectively.

[0059] (1) Preparation of the spinning dope: firstly, 36 g of methacrylic acid, 120 g of sucrose and 3 g of N,N′-methylenebisacrylamide are mixed and dissolved in 330 mL of deionized water, and stirred to form a uniform and transparent solution. Then, 120 mL of sodium alginate aqueous solution with mass fraction of 5%, 12 mL of azobisisobutyronitrile aqueous solution with mass fraction of 10% and 12 mL of sodium sulfite aqueous solution with mass fraction of 10% are added, ultrasonic and stirring are carried out to form a uniform solution, and bubbles in the spinning solution are removed by a defoamer to obtain the spinning dope for later use.

[0060] (2) Preparation of the coagulation bath: 1800 g of acrylic acid, 6000 g of sucrose, 150 g of N,N′-methylenebisacrylamide and 1800 g of calcium chloride are mixed and dissolved in 16500 mL of deionized water, stirred in the coagulation bath tank to form a uniform and transparent solution, and the circulating pump of the coagulation bath is turned on during the spinning operation, so that the coagulation bath circulates directionally in the coagulation bath tank. In addition, the coagulation bath may be recycled for many times after preparation.

[0061] (3) Preparation of the water bath solution: 6000 g of glucose, 600 mL of azobisisobutyronitrile aqueous solution with mass fraction of 10% and 600 mL of sodium sulfite aqueous solution with mass fraction of 10% are mixed and dissolved in 16500 mL of deionized water, stirred in a constant temperature water bath to form a uniform and transparent solution, and the heating device of the constant temperature water bath is turned on during spinning operation to stabilize the temperature of the water bath at 60° C. In addition, the water bath solution may be recycled for many times after preparation.

[0062] (4) Preparation of the carbon fiber precursor fibers: the prepared spin solution is sucked by a syringe and connected with a spinning needle, and the diameter of the inner hole of the spin needle is 60 μm. Then the spinning dope is injected into the coagulation bath through the spinning needle at a speed of 400 μL/min by using a high-precision injection pump to generate gel precursor fibers. After the gel precursor fibers passes through a constant temperature water washing tank at 60° C. under the traction of a drawing machine, with the drawing machine speed of 8 m/min, and the gel precursor fibers enter a blower dryer at 90° C. for drying. Finally, the gel precursor fibers are collected into bundles by a wire collecting rod to obtain carbon fiber precursor fibers.

[0063] (5) Pre-carbonization: the carbon fiber precursor fibers are passed through the continuous pre-carbonization furnace at a speed of 0.01 m/min by a pay-off machine and a tractor, and the precursor fibers pass through various temperature zones in a uniform traction way, thus realizing stable pre-carbonization and obtaining pre-carbonized fibers with uniform quality. The pre-carbonization production line adopts a 5-section furnace design, each section of the furnace is provided with five temperature zones, totaling 25 temperature zones, which are gradually increases from 25° C. to 220° C. The temperature zones are distributed from low temperature, medium temperature to high temperature, to gradually remove volatile substances and moisture, promote caramelization reaction, and complete the final stabilization treatment to ensure fiber uniformity and strength. The temperature zone settings of the continuous pre-carbonization furnace are shown in Table 2.

TABLE 2
Temperature parameter setting for continuous
pre-carbonization furnace (° C.)
		Temperature zone
		1	2	3	4	5
	Furnace A	33	46	60	60	60
	Furnace B	74	88	102	116	130
	Furnace C	145	158	171	185	185
	Furnace D	185	185	185	185	185
	Furnace E	197	209	220	220	220
	Note:
	the five sections of the furnace from unwinding to winding are respectively Furnace A/B/C/D/E, and each section of the furnace has five temperature zones 1/2/3/4/5 from fiber feeding to fiber discharging.

[0064] (6) Carbonization: a carbonization furnace is used to carbonize the pre-carbonized fibers, and the temperature is raised to 1100° C. respectively at the heating rate of 2° C./min under argon conditions, held for 2 h at each temperature, then the carbon fibers are cooled to room temperature in the furnace, and the carbon fibers are obtained.

[0065] (7) Graphitization: the pre-carbonized fiber or carbon fiber are graphitized in a graphitizing furnace, heated to 1800° C. at a heating rate of 8° C./min under argon conditions, then heated to 2600° C. at a heating rate of 4° C./min, the temperature is held for 3 h, and cooled the furnace to room temperature to obtain graphite fibers.

[0066] The SEM images of the carbon fiber prepared in Embodiment 2 are shown in FIG. 4A and FIG. 4B; where FIG. 4A is the surface morphology image, and FIG. 4B is the cross-sectional morphology image.

[0067] FIG. 4A shows the SEM image of the carbon fiber surface, revealing obvious groove structures distributed along the axial direction of the fiber. These grooves not only increase the surface roughness of the fiber but also provide a larger specific surface area, which significantly enhances the mechanical interlocking effect between the carbon fiber and the composite matrix, thereby improving the interface bonding strength. FIG. 4B presents the SEM image of the carbon fiber cross-section. The cross-section is regularly circular with a dense interior, and no significant defects such as cracks or holes are observed, indicating that the fiber has good structural integrity during the preparation process. This type of carbon fiber may effectively improve the interface performance of composites due to the presence of surface groove structures, while the compactness of the cross-section indicates that the fiber itself has high mechanical properties, such as high strength and modulus. Such carbon fibers have important application potential in reinforced composites, especially in fields with high requirements for mechanical properties.

[0068] (1) Preparation of the spinning dope: firstly, 42 g of acrylamide, 140 g of maltose and 2.3 g of polyethylene glycol diacrylate are mixed and dissolved in 385 mL of deionized water, and stirred to form a uniform and transparent solution. Then, 175 mL of sodium alginate aqueous solution with mass fraction of 6%, 14 mL of azobisisobutyronitrile aqueous solution with mass fraction of 10% and 14 mL of hydrogen peroxide aqueous solution with mass fraction of 10% are added, ultrasonic and stirring are carried out to form a uniform solution, and bubbles in the spinning solution are removed by a defoamer to obtain the spinning dope for later use.

[0069] (2) Preparation of the coagulation bath: 1800 g of acrylamide, 6000 g of maltose, 150 g of ethylene glycol diacrylate and 1800 g of calcium chloride are mixed and dissolved in 16500 mL of deionized water, stirred in the coagulation bath tank to form a uniform and transparent solution, and the circulating pump of the coagulation bath is turned on during the spinning operation, so that the coagulation bath circulates directionally in the coagulation bath tank. In addition, the coagulation bath may be recycled for many times after preparation.

[0070] (3) Preparation of the water bath solution: 6000 g of maltose, 600 mL of hydrogen peroxide aqueous solution with mass fraction of 10% and 600 mL of sodium sulfite aqueous solution with mass fraction of 10% are mixed and dissolved in 16500 mL of deionized water, stirred in a constant temperature water bath to form a uniform and transparent solution, and the heating device of the constant temperature water bath is turned on during spinning operation to stabilize the temperature of the water bath at 60° C. In addition, the water bath solution may be recycled for many times after preparation.

[0071] (4) Preparation of the carbon fiber precursor fibers: the prepared spin solution is sucked by a syringe and connected with a spinning needle, and the diameter of the inner hole of the spin needle is 80 μm. Then the spinning dope is injected into the coagulation bath through the spinning needle at a speed of 600 μL/min by using a high-precision injection pump to generate gel precursor fibers. After the gel precursor fibers passes through a constant temperature water washing tank at 60° C. under the traction of a drawing machine, with the drawing machine speed of 9 m/min, and the gel precursor fibers enter a blower dryer at 140° C. for drying. Finally, the gel precursor fibers are collected into bundles by a wire collecting rod to obtain carbon fiber precursor fibers.

[0072] (5) Pre-carbonization: the carbon fiber precursor fibers are passed through the continuous pre-carbonization furnace at a speed of 0.2 m/min by a pay-off machine and a tractor, and the precursor fibers pass through various temperature zones in a uniform traction way, thus realizing stable pre-carbonization and obtaining pre-carbonized fibers with uniform quality. The pre-carbonization production line adopts a 5-section furnace design, each section of the furnace is provided with five temperature zones, totaling 25 temperature zones, which are gradually increases from 25° C. to 220° C. The temperature zones are distributed from low temperature, medium temperature to high temperature, to gradually remove volatile substances and moisture, promote caramelization reaction, and complete the final stabilization treatment to ensure fiber uniformity and strength. The temperature zone settings of the continuous pre-carbonization furnace are shown in Table 2.

[0073] (6) Carbonization: a carbonization furnace is used to carbonize the pre-carbonized fibers, and the temperature is raised to 1500° C. respectively at the heating rate of 5° C./min under argon conditions, held for 3 h at each temperature, then the carbon fibers are cooled to room temperature in the furnace, and the carbon fibers are obtained.

[0074] (7) Graphitization: the pre-carbonized fiber or carbon fiber are graphitized in a graphitizing furnace, heated to 2800° C. at a heating rate of 2° C./min under vacuum conditions, the temperature is held for 1 h, and cooled the furnace to room temperature to obtain graphite fibers.

[0075] FIG. 5A and FIG. 5B are the SEM images of the graphite fiber prepared in Embodiment 3; where FIG. 5A is the surface morphology image, and FIG. 5B is the cross-sectional morphology image.

[0076] The SEM images of the graphite fiber prepared in Embodiment 3 are shown in FIG. 5A and FIG. 5B; where FIG. 5A is the surface morphology image, and FIG. 5B is the cross-sectional morphology image.

[0077] FIG. 5A is a scanning electron microscope (SEM) image of the graphite fiber surface, from which groove structures distributed along the axial direction of the fiber may be observed. These grooves provide surface roughness for the fiber, which helps to enhance the mechanical interlocking effect between the fiber and the composite matrix, thereby significantly improving the interface bonding strength. FIG. 5B is an SEM image of the graphite fiber cross-section, which is regularly circular with a dense internal structure. No obvious defects such as cracks or holes are observed, indicating that the fiber has high structural integrity and excellent mechanical properties. Based on the characteristics shown in these two images, it may be inferred that graphite fibers may exhibit excellent performance in composites due to their surface grooves and dense cross-sectional structure. The surface grooves not only improve the interface bonding strength but also enhance the shear resistance of the material, while the dense cross-section ensures high strength and high modulus of the fiber itself. Such graphite fibers have broad application potential in high-performance composites, especially suitable for use in fields requiring high strength and high reliability.

[0078] The above-described embodiments only describe the optional modes of the present disclosure and do not limit the scope of the present disclosure. Without departing from the design spirit of the present disclosure, various modifications and improvements made to the technical schemes of the present disclosure by those of ordinary skill in the art shall fall within the protection scope defined by the claims of the present disclosure.