A kind of uniform high-rigidity graphene fiber and preparation method thereof

Abstract

The present invention discloses a uniform, high-rigidity graphene fiber and a continuous preparation method thereof. A graphene oxide dispersion is squeezed into a coagulation bath using a porous spinning head, pulled out and dried to produce a primary graphene oxide tow. The tow is then fed sequentially into three or more swelling baths via rollers to produce uniform, high-rigidity graphene fibers. The standard deviation of tensile strength for fibers of varying diameters and test lengths is ≤0.095, and the bending stiffness is as high as 1.02 N mm². During the continuous preparation process, repeated wet-melting and splitting of the fibers optimizes the uniformity and density of the axial and radial structures, increases the fiber's stiffness, and avoids the loss of skin-core structure and stiffness associated with direct wet-spinning of large-diameter fibers.

Description

Technical Field

[0001] The present invention relates to the field of graphene preparation, and in particular to a uniform high-rigidity graphene fiber and a preparation method thereof. Background Art

[0002] Graphene is a new material composed of carbon atoms tightly packed into a single-layer two-dimensional honeycomb lattice structure connected by sp² hybridization. It possesses excellent mechanical, electrical, thermal, and optical properties. By tightly and orderly arranging graphene sheets along one dimension, macroscopic high-performance graphene fibers can be prepared, which have important application prospects in aerospace, biosensing, smart fabrics, and other fields. Although the mechanical strength of small-diameter graphene fibers (≤10 μm) can reach 3.2 GPa, the small diameter results in a bending stiffness of the fibers of ≤2×10 -5 N mm², it is not resistant to bending and compression, and is difficult to apply in complex actual stress environments. One effective way to improve the bending stiffness of graphene fibers is to increase the fiber diameter while ensuring the density and high orientation of the internal sheets. Currently, the main way to increase the fiber diameter is to increase the diameter of the spinning head. However, this method faces many problems. For example, the double diffusion process of the gel fiber in the coagulation bath and the subsequent carbonization treatment will form a serious skin-core structure, and the internal sheets are looser and less dense than the skin. Because the core graphene oxide sheets are subjected to weak shear force from the tube wall, the core sheets have poor orientation and the bending stiffness is less than 6×10 -4 N mm²; Furthermore, the fiber's radial and axial structures are non-uniform, resulting in a significant size effect. This means that as the axial and radial dimensions of the fiber increase, its performance rapidly decreases. Although coarse fibers assembled through tow drawing are currently available, they still suffer from issues such as uneven cross-sections and insufficient internal density, which severely impact the performance of large-diameter fibers. Summary of the Invention

[0003] The present invention aims to solve the problems in the prior art of uneven cross-section and insufficient density of the coarse fibers integrated by tow stretching, and provides a method for preparing graphene fibers.

[0004] The present invention proposes for the first time to perform swelling on spun silk that has not been completely dried, solving the problem that the tight stacking between the fully dehydrated and dried lamellae in the swelling bath of the finished silk leads to the inability of the lamellae to fully swell and separate, the lamellae rearrangement plasticity is poor, and there are still many wrinkles on the fiber surface, resulting in the inability to achieve complete adaptive bonding between the fibers. After the spun silk that has not been completely dried is immersed in the swelling bath, since the lamellae are in an incompletely stacked state, the graphene oxide sheets can achieve better solvent immersion between the sheets, which can induce sheet rearrangement to the greatest extent. The sufficient immersion of the solvent causes the fibers to fully swell into a wrinkle-free state on the surface, and the surfaces between the fibers can fully bond, regenerating the π-π stacking under the action of van der Waals forces during the drying process to obtain large-diameter graphene oxide fibers with overall density and high orientation.

[0005] Secondly, by adjusting the polarity of the swelling bath solution and establishing a multi-stage progressive weakening process, the axial and radial structural uniformity and density of the fiber bundle are optimized during repeated wet-melt splitting, avoiding the degradation of the skin-core structure and stiffness associated with direct wet spinning. A high reduction of the carbon-oxygen ratio (C / O) of ≥25 is achieved through stretching in a chemical reduction bath and a specialized microwave-assisted thermal reduction method. The graphene fibers prepared by this method have a diameter greater than 20 μm, a regular circular cross-section, uniform density, high orientation, and high stiffness. The standard deviation of tensile strength across different diameters and test lengths is ≤0.095, and the flexural stiffness reaches 1.02 N mm². Furthermore, the preparation process is continuous and the yarn collection efficiency is high. The resulting graphene fibers exhibit large diameter, axial and radial uniformity, density, and high flexural stiffness, making them extremely valuable for applications in spacecraft frameworks, bioelectrodes, and building materials.

[0006] One of the technical solutions of the present invention is to provide a method for preparing uniform high-rigidity graphene fibers, comprising the following steps:

[0007] (1) extruding a graphene oxide dispersion into a coagulation bath through a porous spinning head to obtain a primary graphene oxide filament bundle;

[0008] (2) feeding the primary graphene oxide tow into a first swelling bath for swelling, pulling out and drying, and obtaining primary wet-melt graphene oxide fibers;

[0009] (3) continuing to perform two or more swelling baths, performing swelling rearrangement, pulling out and drying, and obtaining uniform and dense graphene oxide fibers with sufficient lamellar orientation; the polarity of the swelling bath solvent is gradually weakened to adjust the degree of fiber swelling;

[0010] (4) The graphene oxide fibers with sufficient lamellae orientation are continuously fed into a chemical reduction bath and a microwave-assisted thermal reduction drum through rollers to obtain uniform high-rigidity graphene fibers.

[0011] Furthermore, the porous spinning head in step 1 has ≥10 holes, and the hole diameter is 60 μm-240 μm.

[0012] Furthermore, the coagulation bath described in step 1 is a poor solvent for graphene oxide and is miscible with the graphene oxide dispersion.

[0013] Furthermore, the swelling bath includes one or more of ethanol, acetone, isopropanol, ethyl acetate, methanol, water, glycerol, propylene glycol, ethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, succinic acid, and acrylic acid.

[0014] Furthermore, the chemical reduction bath in step 4 includes one or more of acetic acid, trifluoroacetic acid, vitamin C, hydroiodic acid, and hydrazine hydrate.

[0015] Furthermore, the chemical reduction bath in step 4 is carried out in a chemical reduction tank, which is equipped with side-by-side multi-stage rollers to fully improve the stretching ratio and reduction time of the fiber. The stretching ratio is as high as 10%, and the carbon-oxygen ratio of the reduced fiber is ≥12, ensuring the high bending stiffness of the reduced fiber.

[0016] Furthermore, in the microwave-assisted thermal reduction cylinder described in step 4, the temperature is 100°C-350°C, and the microwave power is 100W-800W. The dual reducing effects of high temperature and microwaves further improve the reduction degree of the fiber. After reduction, the carbon-oxygen ratio of the fiber is ≥25, which further improves the bending stiffness.

[0017] Furthermore, the repeated wet-melt splitting process described in step 3 can gradually increase the drafting speed of the roller, so that the fiber bundle can achieve a certain degree of stretching during the densification process, thereby improving the orientation degree.

[0018] The second technical solution of the present invention is to provide a uniform high-rigidity graphene fiber prepared by the above preparation method.

[0019] The graphene fibers prepared by the present invention have a diameter of ≥20 μm, a standard deviation of tensile strength of ≤0.095 for different diameters and test lengths, a bending stiffness of up to 1.02 N mm², a tensile strength greater than 2.5 GPa, an elongation at break of 1%-2.5%, and a density of greater than 1.8 g cm for different diameters. -3 , the orientation degree is greater than 8.5.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1) Utilize a gradual weakening swelling process and repeated wet-melt splitting. Through the splitting and rearrangement process, the internal lamella orientation is optimized, and the uniformity and density are improved.

[0022] 2) Immediately swelling the partially dried spun fibers on the continuous spinning line. After immersion in the swelling bath, the graphene oxide sheets are not fully stacked, allowing for better solvent penetration between them, maximizing sheet rearrangement. This complete solvent penetration allows the fibers to fully swell to a wrinkle-free surface, allowing for full fiber adhesion. During the drying process, π-π stacking, driven by van der Waals forces, is reestablished, resulting in dense, highly oriented, large-diameter graphene oxide fibers.

[0023] 3) Utilizing a chemical reduction bath equipped with parallel multi-stage rollers and a specially designed microwave-assisted thermal reduction drum, continuous fiber reduction with a carbon-oxygen ratio of ≥25 is achieved. The continuous and integrated preparation and reduction process facilitates large-scale production.

[0024] 4) The prepared fibers can ensure high orientation and density of the internal layers when the diameter is arbitrarily increased. The fiber cross-section is regular and circular, and is uniform in the axial and radial directions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the continuous preparation process.

[0026] Figure 2 This is the SEM image of the fiber cross section prepared in Example 1.

[0027] Figure 3 The strength of the fibers prepared in Example 1 varies with the length tested.

[0028] Figure 4 The fiber strength prepared in Example 1 varies with fiber diameter. DETAILED DESCRIPTION

[0029] The following examples are used to further illustrate the present invention. Their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all references are by weight and weight percentage.

[0030] Unless otherwise specified, the raw materials used in the present invention are conventional commercial products; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0031] The embodiments of the present invention are further described below with reference to a number of embodiments.

[0032] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0033] The wet fusion mentioned in the present invention refers to wet spinning fusion.

[0034] The swelling degree mentioned in the present invention refers to the ratio of the equivalent diameter of the graphene fiber after swelling in a solvent to the equivalent diameter of the fiber before swelling.

[0035] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0036] Example 1:

[0037] 1. 8 mg g -1 The DMF-phase graphene oxide spinning solution was loaded into a 100 ml syringe and stirred at a rate of 1 ml min -1 The graphene oxide filaments were pushed forward at a speed of 100 μm and squeezed into an ethyl acetate coagulation bath through a 100-hole multi-porous spinning head with a pore size of 100 μm. The coagulation time was 30 s. After being pulled out, they were fully dried in situ to obtain graphene oxide filaments.

[0038] 2. The graphene oxide tow was fed via rollers into the first strong swelling bath, a mixture of ethanol and water in a ratio of 2:1, with a swelling degree of 250%. The tow was then pulled out of the swelling bath and dried to obtain the initially wet-melted graphene oxide fibers.

[0039] 3. The initially melted graphene oxide fibers were fed via rollers into a second, slightly swellable bath consisting of a 3:1 mixture of ethanol and water, achieving a swelling degree of 190%. The drafting rate was increased to 1.05 times. The fibers split to a certain extent in this swelling bath, optimizing their orientation and uniformity. The fibers were then pulled out and dried to achieve secondary wet melting.

[0040] 4. The fiber obtained in step 3 was fed into the third micro-swelling bath through a roller, and the ratio of ethanol to water was increased to 4:1, the swelling degree was 130%, and the drawing speed was increased to 1.1 times to further improve the fiber orientation and density.

[0041] 5. The fiber obtained in step 4 is continued to be fed into the fourth micro-swelling bath through a roller, the ratio of ethanol and water is increased to 5:1, the swelling degree is 90%, and the drawing speed is increased to 1.2 times to obtain highly oriented and high-density wet-melt graphene oxide fibers.

[0042] 6. The wet melt graphene oxide fiber obtained in step 5 was fed into a mixed chemical reduction bath of acetic acid and trifluoroacetic acid in a ratio of 3:1 via a roller for continuous room temperature chemical reduction to obtain reduced graphene oxide fiber with a stretching ratio of up to 10% and a carbon-oxygen ratio of 12 after reduction.

[0043] 7. The reduced graphene oxide fibers were fed through rollers into a microwave-assisted thermal reduction drum for thermal reduction under tension. The drum temperature was 100°C and the microwave power was 100 W. Finally, uniform and dense graphene fibers with a diameter of 124 μm were collected on a roller with a diameter of 15 cm. The fibers had a carbon-oxygen ratio of 25 and a density of 1.87 g cm -3 .like Figure 3 As shown in the figure, the mechanical strength of the obtained fiber can always be maintained above 2.5GPa with the test length increasing from 0.5 cm to 10 cm, and there is no obvious downward trend. The elongation at break is 2.5%, and the conductivity is 6.28×10 4 S m -1 , with a bending stiffness of 1.02 N mm².

[0044] 8. By changing the number of holes in the multi-hole spinning head in step 1 to 20, 40, 60, and 80, and keeping the other steps unchanged, uniform high-stiffness graphene fibers with different diameters can be obtained, with diameters of 26 μm, 52 μm, 73 μm, and 101 μm, respectively. The strength does not show a significant downward trend with increasing diameter, and remains above 2.5 GPa. Figure 4 As shown, the density is basically the same; the conductivity is maintained at 6×10 4 S m -1 The bending stiffness increases with the increase of diameter. And with the increase of diameter, the orientation degree remains above 8.5.

[0045] Comparative Example 1

[0046] This comparative example is the same as Example 1, except that a large-aperture single-hole spinning head with pore sizes of 610 μm, 840 μm, 1000 μm, 1100 μm, and 1250 μm is directly used for spinning.

[0047] 1. 8 mg g -1 The DMF phase graphene oxide dispersion is squeezed into an ethyl acetate coagulation bath from a large-diameter single-hole spinning head, and is pulled out and fully dried to obtain primary graphene oxide coarse fibers.

[0048] 2. The graphene oxide crude fibers obtained in step 1 were fed into a swelling bath of ethanol and water in a ratio of 3:1 via a roller, with a stretching ratio of 1.05, which was consistent with step 3 of example 1.

[0049] 3. The fiber obtained in step 2 is further fed into a swelling bath of ethanol and water in a ratio of 4:1 through a roller, with a stretching ratio of 1.1, which is consistent with step 2 of example 1.

[0050] 4. The chemical reduction treatment process is the same as step 5 of Example 1.

[0051] 5. Similarly, the chemically reduced fibers were placed in a microwave-assisted thermal reduction chamber at 300°C and a microwave power of 500 W. The resulting fibers had irregular cross-sectional morphology, with equivalent diameters of 23 μm, 49 μm, 82 μm, and 106 μm. The density was only 1.56 g cm -3 The maximum orientation degree is only 7.2, the maximum strength is only 560 MPa, the elongation at break is 3%-6%, and the electrical conductivity is only 2.2×10 3 S m -1 , bending stiffness ≤3.9×10 -3 N mm², the various performance indicators show a sharp decrease trend with the increase of diameter, and the various performance indicators are significantly lower than those in Example 1.

[0052] Comparative Example 2

[0053] This comparative example is the same as Example 1, except that there is no repeated wet-melt splitting process.

[0054] 1. Same as step 1 in example 1.

[0055] 2. The obtained graphene oxide filament bundle is fed into a swelling bath of ethanol and water in a ratio of 2:1 through a roller, with a drafting ratio of 1.1 times, and graphene oxide crude fibers are obtained after drying and wet melting.

[0056] 3. The chemical reduction and thermal reduction processes were the same as step 6 of Example 1. The resulting fiber had an irregular cross-section, many voids, poor density, and a density of 1.71 g cm -3 , the orientation degree is 7.9, the strength is only 832 MPa, the elongation at break is 3%, and the electrical conductivity is 0.97×10 4 S m -1 , with a bending stiffness of 0.11 N mm².

[0057] Example 2:

[0058] 1. Add 5 mg g -1 The DMSO phase graphene oxide spinning solution was loaded into a 50 ml syringe and stirred at a speed of 0.8 ml min -1 The filaments were pushed forward at a speed of 1000 nm and squeezed into an acetone coagulation bath through a 50-hole porous spinning head with a pore size of 120 μm. The time in the coagulation bath was 25 s. The filaments were pulled out from the coagulation bath and fully dried in situ to obtain primary graphene oxide filament bundles.

[0059] 2. The obtained graphene oxide filaments were fed into a swelling bath consisting of a mixed solution of acetic acid and ethylene glycol via rollers in a ratio of 3:1, with a swelling degree of 210%, and then pulled out of the swelling bath and dried.

[0060] 3. The film is fed into the second swelling bath via rollers. The ratio of acetic acid to water is 4:1, and the swelling degree is 175%. The stretching ratio during this process is 1.15 times. The film is pulled out of the second swelling bath and dried to achieve the second wet-melt process.

[0061] 4. Continuing through the third swelling bath, the ratio of acetic acid to water is increased to 5:1, the swelling degree is 110%, and the stretching ratio is further increased to 1.25 times. The fiber is pulled out of the third swelling bath and dried, achieving the third wet-melt process. The fiber orientation and density are further increased.

[0062] 5. Finally, the obtained wet-melt fiber is sent into a pure acetic acid solvent through a roller for pure plasticization stretching, and the stretching ratio is increased to 1.3 times. After drying, highly oriented and highly densified graphene oxide coarse fibers are obtained.

[0063] 6. The fiber obtained in step 5 is further fed into hydrazine hydrate through a roller, and after being pulled out and dried, chemically reduced graphene fiber is obtained. The graphene fiber stretching ratio is as high as 10%, and the carbon-oxygen ratio of the reduced fiber is 12.

[0064] 7. The chemically reduced graphene fibers were fed into a microwave-assisted thermal reduction drum at a reduction temperature of 280°C and a microwave power of 800 W, where they were thermally reduced under tension. The resulting fibers were uniform, crude graphene fibers with a carbon-oxygen ratio of 31, a diameter of 82 μm, and a density of 1.89 g cm. -3 The orientation degree is 8.8. In the test length range of 0.5 cm-10 cm, the strength standard deviation is ≤0.082, and all are above 2.5 GPa. The elongation at break is 2.1%, and the conductivity is 9.73×10 4 S m -1 , with a bending stiffness of 0.2 N mm².

[0065] Example 3:

[0066] 1. Add 15 mg g -1 The NMP phase graphene oxide spinning solution was loaded into a 100 ml syringe and stirred at a rate of 0.5 ml min -1 The fiber was pushed forward at a speed of 200 μm through a porous spinning head with 20 holes and an aperture of 200 μm and squeezed into a n-hexane coagulation bath. The time in the coagulation bath was 20 s. The fiber was pulled out from the coagulation bath and fully dried in situ to obtain a primary graphene oxide filament bundle.

[0067] 2. The obtained graphene oxide filaments were fed into a swelling bath consisting of a mixed solution of ethanol and ethylene glycol with a ratio of 4:1 and a swelling degree of 180% via rollers, and then pulled out of the swelling bath and dried.

[0068] 3. The film is fed into the second swelling bath via rollers. The ratio of ethanol to ethylene glycol is 5:1, and the swelling degree is 160%. The stretching ratio during this process is 1.15 times. The film is pulled out of the second swelling bath and dried to achieve the second wet-melt process.

[0069] 4. Continuing through the third swelling bath, the ratio of ethanol to ethylene glycol is increased to 6:1, the swelling degree is 130%, and the stretching ratio is further increased to 1.25 times. The fiber is pulled out of the third swelling bath and dried, achieving the third wet-melt process. The fiber orientation and density are further increased.

[0070] 5. Finally, the obtained wet-melt fibers are fed into a pure acetic acid solvent through rollers for pure plasticization stretching. The stretching ratio is increased to 1.3 times. After drying, highly oriented and highly densified graphene oxide coarse fibers are obtained.

[0071] 6. The fiber obtained in step 5 is further fed into a sodium ascorbate solution through a roller, and is pulled out and dried to obtain chemically reduced graphene fiber. The graphene fiber stretching ratio is as high as 10%, and the carbon-oxygen ratio of the reduced fiber is 12.

[0072] 7. The chemically reduced graphene fibers were fed into a microwave-assisted thermal reduction drum at a reduction temperature of 350°C and a microwave power of 400 W, where they were thermally reduced under tension. The resulting fibers were uniform, coarse graphene fibers with a carbon-oxygen ratio of 27, a diameter of 56 μm, and a density of 1.9 g cm. -3 The orientation degree is 9.1. In the test length range of 0.5 cm-10 cm, the strength standard deviation is ≤0.072 and is maintained above 2.6 GPa. The elongation at break is 1%, and the electrical conductivity is 3.96×10 4 S m -1 , with a bending stiffness of 0.06 N mm².

[0073] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the scope of protection of the present invention.

[0074] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preparing uniform high-rigidity graphene fibers, characterized in that: The following steps are involved: (1) extruding a graphene oxide dispersion into a coagulation bath through a porous spinning head to obtain a primary graphene oxide filament bundle; the porous spinning head has 10 or more holes and a hole diameter of 60 μm to 240 μm; (2) feeding the primary graphene oxide tow into a first swelling bath for swelling, pulling out and drying, and obtaining primary wet-melt graphene oxide fibers; (3) continuing to perform two or more swelling baths, performing swelling rearrangement, pulling out and drying, and obtaining uniform and dense graphene oxide fibers with sufficient lamellar orientation; the polarity of the swelling bath solvent is gradually weakened; (4) The graphene oxide fibers with sufficient lamellae orientation are continuously fed into a chemical reduction bath and a microwave-assisted thermal reduction drum through rollers to obtain uniform high-rigidity graphene fibers.

2. The preparation method according to claim 1, characterized in that The swelling bath includes one or more of ethanol, acetone, isopropanol, ethyl acetate, methanol, water, glycerol, propylene glycol, ethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, oxalic acid, malonic acid, succinic acid, and acrylic acid.

3. The preparation method according to claim 1, characterized in that The chemical reduction bath in step 4 includes one or more of acetic acid, trifluoroacetic acid, vitamin C, hydroiodic acid, and hydrazine hydrate.

4. The preparation method according to claim 1, characterized in that The microwave-assisted thermal reduction cylinder in step 4 has a temperature of 100°C-350°C and a microwave power of 100W-800W.

5. A uniform high-rigidity graphene fiber prepared by the method according to any one of claims 1 to 4.

6. The uniform high-rigidity graphene fiber according to claim 5, characterized in that: Fiber diameter ≥20 μm.

7. The uniform high-rigidity graphene fiber according to claim 5, characterized in that: The graphene fiber density is greater than 1.8 g cm -3 .

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