A graphite fiber and a method for producing the same

Abstract

This invention belongs to the field of new materials. It provides a graphite fiber and its preparation method. The preparation method includes mixing exfoliated graphene, a cellulose dispersion, and an alginate dispersion to obtain a spinning solution; then, the spinning solution is extruded into a coagulation bath and dried to obtain the graphite fiber. Cellulose can effectively disperse and exfoliate graphite sheets and has a natural network structure, which can modify exfoliated graphene to obtain a preliminary fiber structure. Alginate is used as a liquid crystal inducer to generate exfoliated graphene / sodium alginate nematic liquid crystal, which can effectively improve the orientation and density of the graphene sheets. Introducing a wet coagulation bath causes crosslinking of the exfoliated graphene / sodium alginate to obtain graphite fiber. This preparation method effectively solves the problem of the contradiction between strength and toughness in artificial fiber structural materials. The resulting exfoliated graphene-cellulose-alginate composite large fiber combines good mechanical properties and thermal conductivity.

Description

Technical Field

[0001] This invention belongs to the field of new materials and relates to a graphite fiber and its preparation method. Background Technology

[0002] In the field of emerging materials, continuous long fibers with diameters ranging from tens to hundreds of micrometers have shown broad application potential in many high-tech and traditional industrial fields due to their excellent mechanical properties.

[0003] For a long time, long fibers with exceptional mechanical properties have primarily relied on synthetic polymer fibers, such as polyacrylonitrile (PA) and Kevlar. These synthetic fibers, through precise chemical synthesis and complex processing, achieve high strength and high modulus, thus meeting the demands of various high-end applications. However, with increasing environmental awareness, the difficulty in degrading synthetic polymer fibers at the end of their life cycle has become increasingly prominent, causing significant negative impacts on the environment. In contrast, bio-derived fibers possess better biodegradability, renewability, low density, and wide availability, offering more possibilities for customized and diversified applications. However, currently, bio-derived fibers are still limited by their relatively weaker mechanical properties.

[0004] In addition to the issues mentioned above, strength and toughness, two properties of long fibers, often exhibit a mutually exclusive tendency. Generally, achieving sufficiently high strength often requires sacrificing elongation and toughness. Therefore, how to resolve the contradiction between strength and toughness to better balance high tensile strength, large elongation, and toughness is also a key focus for researchers.

[0005] Graphite fiber, as a novel high-performance fiber material, has received widespread attention and research in recent years. With its unique graphite structure and properties such as high electrical and thermal conductivity, graphite fiber shows great application potential in electronics, energy, aerospace, and other fields. Particularly in terms of mechanical properties, graphite fiber possesses the potential to balance high strength and high toughness, primarily due to the arrangement and orientation of its internal graphite materials (such as graphene and graphene oxide), factors that are directly related to the preparation process of graphite fiber.

[0006] Currently, various effective preparation methods have been developed in the industry. Among them, wet spinning, with its advantages of simple process, low cost, and ease of large-scale production, has become one of the more widely used methods for large-scale practical applications. The general process of preparing graphene fibers by wet spinning includes the preparation of graphene oxide dispersion, the formulation of spinning solution, the spinning process, the coagulation and washing of nascent fibers, and subsequent heat treatment or chemical reduction steps. Through these steps, graphene fibers with a certain length and diameter can be prepared.

[0007] However, several problems remain to be solved in the wet spinning process for preparing graphene fibers. First, due to the irregular size and shape of graphene oxide and the weak interlayer forces, the double diffusion process during coagulation of the spinning solution in the coagulation bath is slow, easily introducing numerous defects and voids. These defects and voids severely affect the mechanical and electrical properties of the macroscopic fibers, causing significant differences in performance compared to monolithic graphene materials. Second, although external stretching can improve the orientation and density of graphene units in the fiber, thereby enhancing its mechanical and electrochemical properties, it is difficult to precisely control the stretching force on each graphene sheet for one-dimensional graphene fibers. Furthermore, graphene sheets are prone to wrinkling and slippage during stretching, leading to uneven fiber thickness and making it difficult to achieve a regular arrangement and high density of graphene sheets. These problems greatly hinder the transfer of the superior microscopic properties of graphene to macroscopic fiber materials, limiting the practical applications of graphene fibers.

[0008] Therefore, further research and development of graphite fibers and their preparation methods are needed to address the problems encountered in the wet spinning process for preparing graphene fibers. This will allow for a better balance between high strength and high toughness, providing support for the application and development of graphite fibers in more fields. Summary of the Invention

[0009] In view of the problems existing in the prior art, the purpose of this invention is to provide a graphite fiber and its preparation method. The preparation method includes mixing exfoliated graphene, a cellulose dispersion, and an alginate dispersion to obtain a spinning solution; then, the spinning solution is extruded into a coagulation bath and dried to obtain the graphite fiber. By using a cellulose dispersion to stabilize the exfoliated graphene, the graphite sheets are effectively dispersed and exfoliated; simultaneously, cellulose has a natural network structure, which can modify the exfoliated graphene to obtain a preliminary fiber structure; alginate is used as a liquid crystal inducer to generate an exfoliated graphene / sodium alginate nematic liquid crystal, which can effectively improve the orientation and density of the graphene sheets; at the same time, the introduction of a coagulation bath in wet spinning causes crosslinking of the exfoliated graphene / sodium alginate to obtain the graphite fiber. This preparation method can effectively solve the problem of the contradiction between strength and toughness in artificial fiber structural materials, and the resulting exfoliated graphene-cellulose-alginate composite large fiber has both good mechanical properties and thermal conductivity.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for preparing graphite fibers, comprising:

[0012] (1) The exfoliated graphene, cellulose dispersion and alginate dispersion are mixed to obtain the spinning solution;

[0013] (2) The spinning solution is squeezed into a coagulation bath and then dried to obtain the graphite fiber.

[0014] This invention discovers that adding a cellulose dispersion can effectively stabilize exfoliated graphene. The interaction between cellulose and graphite sheets effectively disperses and exfoliates the graphite sheets. Simultaneously, cellulose possesses a natural network structure; by adding cellulose, the exfoliated graphene can be modified using cellulose as a matrix to obtain a preliminary fiber structure. Then, using alginate, a natural polysaccharide, as a liquid crystal inducer, only a small amount of alginate is needed to generate an exfoliated graphene / alginate nematic liquid crystal, effectively improving the orientation and density of the graphene sheets. Finally, by introducing a coagulation bath during wet spinning, a cross-linking reaction occurs between the exfoliated graphene and sodium alginate, forming a stable system to cross-link and fix the graphene sheets, resulting in a graphite fiber product. The graphite fiber obtained by the described preparation and method is a large composite fiber of exfoliated graphene-cellulose-alginate, possessing both excellent mechanical properties and thermal conductivity. The "wet orientation method" of this invention can reduce the surface roughness and porosity of the obtained graphite fibers, improve the orientation of the layers, and enhance the electrical and mechanical properties of the graphite fibers. This can solve the defect of the contradiction between strength and toughness in current artificial fiber structural materials.

[0015] It should be further explained that the cellulose dispersion in this invention refers to the substance obtained by dispersing cellulose in a solvent, such as water or ethanol. The type of solvent is not limited, as long as it can disperse cellulose.

[0016] It should be further explained that the alginate dispersion in this invention refers to the substance obtained by dispersing alginate in a solvent, such as water or ethanol. The type of solvent is not limited, as long as it can disperse cellulose.

[0017] It should be further explained that in this invention, the exfoliated graphene / alginate nematic liquid crystal refers to the nematic liquid crystal being formed by the growth and arrangement of graphite sheets induced by sodium alginate along the direction perpendicular to the cross section under the action of extrusion pressure in the spinning solution.

[0018] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0019] As a preferred embodiment of the present invention, the method for preparing the exfoliated graphene includes:

[0020] (1) The graphite raw material is subjected to pre-oxidation heat treatment to obtain graphite oxide;

[0021] (2) After mixing the graphene oxide with the stripping agent dispersion, the mixture is sand-milled and centrifuged to obtain stripped graphene.

[0022] As a preferred technical solution of the present invention, in step (1), the total mass of the exfoliated graphene, cellulose, and alginate in the spinning solution is 100%, and the mass of the exfoliated graphene accounts for 49% to 80%, for example, 49%, 50%, 53%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 75%, 78%, or 80%, etc.; the mass of cellulose accounts for 1% to 2%, for example, 1%. The percentages are 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%, etc.; the mass percentage of alginate is 19% to 49%, for example, it can be 19%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, or 49%, etc., but it is not limited to the values ​​listed. Other unlisted values ​​within the above range also apply.

[0023] Preferably, the alginate in the alginate dispersion includes at least one of sodium alginate, potassium alginate, calcium alginate, or ammonium alginate.

[0024] Preferably, the cellulose in the cellulose dispersion includes at least one of carboxymethyl cellulose and hydroxymethyl cellulose.

[0025] Preferably, the preparation method includes first mixing exfoliated graphene with the cellulose dispersion to obtain a suspension; then mixing the suspension with the alginate dispersion to obtain a spinning solution.

[0026] As a preferred technical solution of the present invention, in step (2), a crosslinking aid dispersion is used in the coagulation bath.

[0027] Preferably, the concentration of the crosslinking aid in the crosslinking aid dispersion is 0.1 to 2.0 mol / L, such as 0.1 mol / L, 0.3 mol / L, 0.50 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, or 2 mol / L, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0028] Preferably, the crosslinking aid comprises a soluble calcium salt.

[0029] Preferably, the soluble calcium salt includes CaCl2.

[0030] In this invention, calcium ions in the crosslinking aid can undergo ionic crosslinking with alginate, thereby causing the exfoliated graphene / alginate to crosslink and form a stable system to fix the exfoliated graphene, thus obtaining graphite fibers.

[0031] Preferably, the solvent of the crosslinking aid dispersion includes ethanol and water.

[0032] Preferably, the volume ratio of ethanol to water is 1:(2-4), such as 1:2, 1:2.3, 1:2.5, 1:2.8, 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8 or 1:4, etc., but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0033] As a preferred technical solution of the present invention, in step (2), the coagulation bath is used to squeeze the spinning solution into the crosslinking aid dispersion to obtain the raw yarn, and then the obtained raw yarn is dried.

[0034] Preferably, the drying process includes fixing both ends of the raw filament and performing directional low-temperature drying at a temperature ≤60℃ to obtain dried filament, such as 60℃, 58℃, 55℃, 52℃, 50℃, 48℃, 45℃, 42℃, 40℃, 38℃, 35℃, 32℃, 30℃, 28℃, or 25℃, but is not limited to the listed values; other unlisted values ​​within the above range are also applicable.

[0035] As a preferred technical solution of the present invention, the preparation method further includes washing the raw yarn or the dried yarn to remove the crosslinking aid.

[0036] In this invention, after the graphite fibers are prepared, they are washed to remove the crosslinking aids. Therefore, the content of crosslinking aids in the final graphite fiber product is negligible.

[0037] As a preferred technical solution of the present invention, in step S1, the graphite raw material includes at least one of recycled graphite, expanded graphite, graphite oxide, or natural flake graphite.

[0038] Preferably, the graphite raw material is an ultrafine powder with a particle size Dv50 of 4 to 5 μm, such as 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm or 5 μm, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0039] As a preferred technical solution of the present invention, in step S1, the temperature of the pre-oxidation heat treatment is 400-500℃, such as 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, or 500℃, and the time is 3-7h, such as 3h, 3.3h, 3.5h, 3.7h, 4h, 4.2h, 4.5h, 4.8h, 5h, 5.3h, 5.5h, 5.8h, 6h, 6.3h, 6.5h, 6.8h, or 7h, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0040] Preferably, the pre-oxidation heat treatment is carried out in an air or oxygen atmosphere.

[0041] In this invention, it is preferable to pre-oxidize the graphite raw material with heat treatment, which can expand the graphite and facilitate the subsequent intercalation and stripping of it by the stripping agent.

[0042] As a preferred technical solution of the present invention, in step S2, the stripping agent in the stripping agent dispersion includes cellulose.

[0043] Preferably, the cellulose includes at least one of carboxymethyl cellulose and hydroxymethyl cellulose.

[0044] This invention utilizes the non-covalent interaction between cellulose and graphene nanosheets. This interaction can effectively disperse and exfoliate graphite sheets, meaning that cellulose can both exfoliate graphite raw materials to obtain exfoliated graphene material and stabilize the exfoliated graphene sheets. Simultaneously, cellulose has a natural network structure; when mixed with exfoliated graphene, cellulose can act as a matrix to modify the exfoliated graphene, giving it a preliminary fibrous structure, which is beneficial for subsequent induction of nematic liquid crystals by liquid crystal template agents. It should be noted that when using cellulose as an exfoliating agent to exfoliate graphite raw materials, the amount of cellulose is not limited. It should be adjusted reasonably to achieve the desired exfoliation effect. Since the exfoliated graphene undergoes solid-liquid separation and washing, the exfoliating agent is easily removed. Therefore, the amount of cellulose used as an exfoliating agent does not affect the final graphite fiber content.

[0045] As a preferred technical solution of the present invention, in step S2, the grinding time is 10 to 180 minutes, such as 10 minutes, 20 minutes, 35 minutes, 50 minutes, 75 minutes, 90 minutes, 110 minutes, 130 minutes, 150 minutes or 180 minutes, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0046] Preferably, the grinding balls used in the sand mill include zirconium balls with a particle size of 0.1 to 3 μm, such as 0.1 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm or 3 μm, but are not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0047] As a preferred technical solution of the present invention, in step S2, the centrifugation speed is 3000-5000 rpm, such as 3000 rpm, 3200 rpm, 3500 rpm, 3800 rpm, 4000 rpm, 4200 rpm, 4500 rpm, 4800 rpm or 5000 rpm, and the time is 15-25 min, such as 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min or 25 min, but it is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0048] Preferably, the method for preparing the exfoliated graphene further includes collecting the supernatant containing the exfoliated graphene after centrifugation, and then centrifuging the supernatant at high speed to obtain the precipitate of exfoliated graphene; the high-speed centrifugation speed is 12000-18000 rpm, such as 12000 rpm, 13000 rpm, 14000 rpm, 15000 rpm, 16000 rpm, 17000 rpm or 18000 rpm, etc., and the time is 30-60 min, such as 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0049] In a second aspect, the present invention provides a graphite fiber, which is prepared by the preparation method described in the first aspect.

[0050] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0051] The preparation method of this invention uses a cellulose dispersion to stabilize exfoliated graphene, effectively dispersing and exfoliating graphite sheets. Simultaneously, cellulose, with its natural network structure, can modify the exfoliated graphene to obtain a preliminary fiber structure. Alginate is used as a liquid crystal inducer to generate an exfoliated graphene / sodium alginate nematic liquid crystal, effectively improving the orientation and density of the graphene sheets. Furthermore, the introduction of a coagulation bath during wet spinning causes cross-linking of the exfoliated graphene / sodium alginate, resulting in graphite fibers. This preparation method effectively solves the problem of the contradiction between strength and toughness in man-made fiber structural materials. The resulting exfoliated graphene-cellulose-alginate composite large fiber combines good mechanical properties and thermal conductivity, making it a low-cost, environmentally friendly graphite fiber. Attached Figure Description

[0052] Figure 1 This is a SEM image of the exfoliated graphene from Example 1.

[0053] Figure 2 This is an SEM image of the ultrafine powder of natural flake graphite, the raw material of Example 1.

[0054] Figure 3 This is a SEM image of the graphite fiber from Example 1.

[0055] Figure 4 This is a photograph of the graphite fibers obtained in Example 1.

[0056] Figure 5 This is a schematic diagram of the graphite fiber obtained in Example 1 undergoing a load-bearing tensile test. Detailed Implementation

[0057] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0058] Those skilled in the art will understand that the embodiments described are merely illustrative of the invention and should not be construed as limiting the invention.

[0059] Example 1

[0060] This embodiment provides a method for preparing graphite fibers, the method comprising:

[0061] Step S1: Take ultrafine powder of natural flake graphite with a particle size of 4-5 μm as graphite raw material, put it into CVD furnace, and perform pre-oxidation heat treatment at 450℃ in air atmosphere for 6 hours to obtain graphite oxide.

[0062] Weigh 30g of carboxymethyl cellulose (CMC) nanocrystals as a stripping agent, dissolve them in deionized water by ultrasonication, and bring the volume to 1000mL to obtain a stripping agent dispersion.

[0063] Step S2: Add 10g of graphite oxide to the stripping agent dispersion and stir and sonicate at high speed at 25°C for 6 hours. Then, transfer 1kg of the solution to a sand mill, add zirconium balls with a particle size of 1-2μm, and sand mill at 25°C for 60 minutes to obtain a suspension.

[0064] The treated suspension was subjected to primary centrifugation for 20 minutes at 4000 rpm to remove unexfoliated graphite material. After primary centrifugation, the supernatant (i.e., the aqueous dispersion containing exfoliated graphene) was collected using a pipette and set aside. The supernatant after multiple primary centrifugations was collected and then subjected to high-speed centrifugation at 15000 rpm for 60 minutes to collect the precipitate (i.e., the exfoliated graphene).

[0065] Step (1): Weigh 1g of CMC as a dispersant and dissolve it in 78g of water to obtain a cellulose dispersion. Then weigh 30g of the obtained exfoliated graphene and add it to the dispersion to obtain a suspension.

[0066] 37.5g of sodium alginate was weighed as a liquid crystal template agent and dissolved in 600mL of water in four portions to obtain an alginate dispersion.

[0067] The obtained suspension is mixed with the alginate dispersion to obtain a spinning solution; in the spinning solution, based on the total mass of exfoliated graphene, cellulose and sodium alginate as 100%, the mass of exfoliated graphene accounts for 43.80%, the mass of cellulose accounts for 1.46%, and the mass of sodium alginate accounts for 54.74%.

[0068] Step (2): Weigh 11.1g of calcium chloride as a crosslinking aid, dissolve it in 1000mL of water to obtain a crosslinking aid dispersion with a concentration of 0.1mol / L.

[0069] The spinning solution is squeezed into a crosslinking agent dispersion to carry out a crosslinking reaction, and the precursor fiber is obtained. The two ends of the obtained precursor fiber are fixed and directionally dried at 55°C to obtain dry graphite fiber.

[0070] Example 2

[0071] This embodiment provides a method for preparing graphite fibers. In step (1), the amount of exfoliated graphene is adjusted from 30g to 25g, and the amount of sodium alginate is adjusted from 37.5g to 42.5g, so that the mass percentage of exfoliated graphene in the spinning solution is adjusted from 43.80% to 36.50%, and the mass percentage of sodium alginate is adjusted from 54.74% to 62.04%. Except for the above, the other conditions are exactly the same as in Example 1.

[0072] Example 3

[0073] This embodiment provides a method for preparing graphite fibers. In step (1), the amount of exfoliated graphene is adjusted from 30g to 42g, and the amount of sodium alginate is adjusted from 37.5g to 25.5g, so that the mass percentage of exfoliated graphene in the spinning solution is adjusted from 43.80% to 61.31%, and the mass percentage of sodium alginate is adjusted from 54.74% to 37.23%. Except for the above, the other conditions are exactly the same as in Example 1.

[0074] Example 4

[0075] This embodiment provides a method for preparing graphite fibers. In step (1), the amount of exfoliated graphene is adjusted from 30g to 54g, and the amount of sodium alginate is adjusted from 37.5g to 13.5g, so that the mass percentage of exfoliated graphene in the spinning solution is adjusted from 43.80% to 78.83%, and the mass percentage of sodium alginate is adjusted from 54.74% to 19.71%. Except for the above, the other conditions are exactly the same as in Example 1.

[0076] Example 5

[0077] This embodiment provides a method for preparing graphite fibers. In step (1), the amount of exfoliated graphene is adjusted from 30g to 60g, and the amount of sodium alginate is adjusted from 37.5g to 7.5g, so that the mass percentage of exfoliated graphene in the spinning solution is adjusted from 43.80% to 87.59%, and the mass percentage of sodium alginate is adjusted from 54.74% to 10.95%. Except for the above, the other conditions are exactly the same as in Example 1.

[0078] Comparative Example 1

[0079] This comparative example provides a method for preparing graphite fibers, wherein sodium alginate is replaced with PVP, and all other conditions are exactly the same as in Example 1.

[0080] Comparative Example 2

[0081] This comparative example provides a method for preparing graphite fibers. In step (1) of the preparation method, CMC is not used as a dispersant. That is, the amount of dispersant CMC is adjusted from 1g to 0g. Except for the above, the other conditions are exactly the same as those in Example 1.

[0082] Comparative Example 3

[0083] This comparative example provides a method for preparing graphite fibers. In step (2) of the preparation method, there is no extrusion process. Instead, the crosslinking aid dispersion is added to the spinning solution. Other conditions are exactly the same as in Example 1.

[0084] Characterization and Testing

[0085] I. Morphological characteristics:

[0086] Figure 1 This is a SEM image of the exfoliated graphene from Example 1. Figure 2 This is a SEM image of the ultrafine powder of natural flake graphite, the raw material from Example 1. (By...) Figure 1 and Figure 2 It can be seen that the graphite changed from a block shape to a uniform sheet shape, indicating that the graphite was peeled off. Figure 3 This is a SEM image of the graphite fiber from Example 1. Figure 3 It can be seen that the graphite sheets are arranged radially in the sodium alginate liquid crystal.

[0087] Figure 4 This is a photograph of the graphite fibers obtained in Example 1. Figure 4 It can be seen that the obtained graphite can be wound around objects and has a certain degree of toughness. The obtained graphite fibers are composite large fibers, as shown in the following figure. Figure 5 As shown.

[0088] II. Mechanical property testing:

[0089] The tensile properties of the samples were tested using a biomechanical testing machine (23MTSInsight, USA), and stress-strain curves were obtained. Tensile strength, strain at fracture, modulus, and toughness were calculated. Tests were conducted at room temperature and relative humidity (50% RH), with a tensile rate of 5 mm / min, a sample length of approximately 50 mm, and a gauge length of 20 mm. The cross-sectional area of ​​the fibers was calculated using an optical microscope. Each sample group was tested three times, and the average value was taken to ensure the repeatability of the experimental results.

[0090] The results are recorded in Table 1.

[0091] Table 1

[0092] Group Tensile strength (MPa) Fiber diameter (μm) Example 1 460 56 Example 2 393 49 Example 3 367 48 Example 4 355 57 Example 5 342 62 Comparative Example 1 336 59 Comparative Example 2 322 71 Comparative Example 3 Unable to obtain fibers 200

[0093] As shown in Table 1, exfoliated graphite effectively enhances the tensile strength of graphite fibers. A high exfoliated graphite content leads to insufficient toughness and easy breakage of the graphite fibers, while a low exfoliated graphite content results in inconsistent mechanical strength and easy breakage. Uniform dispersion of exfoliated graphite allows for better utilization of its lamellar structure to enhance mechanical strength. Directly adding the coagulation bath to the spinning solution generates flocculent floating matter, preventing fiber formation.

[0094] In summary, the graphite fiber of the present invention, by adding the liquid crystal template agent, induces the exfoliation of graphene, and together with the exfoliated graphene, forms an exfoliated graphene / liquid crystal template agent nematic liquid crystal, effectively improving the orientation density of the graphene sheets. By adding a crosslinking aid that can crosslink with the liquid crystal template agent, the crosslinking aid and the nematic liquid crystal form a crosslinked body, thereby obtaining a stable graphite fiber. The graphite fiber has low surface roughness and low porosity, and balances strength and toughness, making it a composite large fiber material with excellent mechanical properties and thermal conductivity.

[0095] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0096] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0097] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing graphite fibers, characterized in that, include: (1) First, the exfoliated graphene is mixed with the cellulose dispersion to obtain a suspension; then the suspension is mixed with an aqueous solution of sodium alginate to obtain a spinning solution; in the spinning solution, based on the total mass of the exfoliated graphene, cellulose and sodium alginate as 100%, the mass of the exfoliated graphene accounts for 49% to 80%, the mass of the cellulose accounts for 1% to 2%, and the mass of the sodium alginate accounts for 19% to 49%; the cellulose in the cellulose dispersion includes at least one of carboxymethyl cellulose and hydroxymethyl cellulose; The method for preparing the exfoliated graphene includes: S1. Under an air or oxygen atmosphere, graphite raw material is subjected to pre-oxidation heat treatment at 400~500℃ to obtain graphite oxide; S2. After mixing the graphene oxide with the stripping agent dispersion, the mixture is milled and centrifuged to obtain stripped graphene. (2) The spinning solution is squeezed into a calcium chloride aqueous solution to obtain a raw filament. The two ends of the raw filament are then fixed and directionally dried at a temperature ≤60℃ to obtain the graphite fiber.

2. The preparation method according to claim 1, characterized in that, In step S1, the graphite raw material includes at least one of recycled graphite, expanded graphite, graphite oxide, or natural flake graphite.

3. The preparation method according to claim 1, characterized in that, The graphite raw material is an ultrafine powder with a particle size Dv50 of 4~5μm.

4. The preparation method according to claim 1, characterized in that, In step S1, the pre-oxidation heat treatment takes 3 to 7 hours.

5. The preparation method according to claim 1, characterized in that, In step S2, the stripping agent in the stripping agent dispersion includes cellulose.

6. The preparation method according to claim 5, wherein the cellulose comprises at least one of carboxymethyl cellulose and hydroxymethyl cellulose.

7. The preparation method according to claim 1, characterized in that, In step S2, the grinding time is 10~180 min.

8. The preparation method according to claim 1, characterized in that, The grinding balls used in the sand mill include zirconium balls with a particle size of 0.1~3μm.

9. The preparation method according to claim 1, characterized in that, In step S2, the centrifugation speed is 3000~5000 rpm and the time is 15~25 min.

10. A graphite fiber, characterized in that, The graphite fiber is prepared by the preparation method according to any one of claims 1-9.

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