Uniform and high-rigidity graphene fibers, and preparation method therefor

Abstract

Disclosed in the present invention are uniform and high-rigidity graphene fibers, and a continuous preparation method therefor. The preparation method comprises: extruding a graphene oxide dispersion into a coagulating bath by using a porous spinning head, drawing out and drying same to obtain primary graphene oxide tows, and then sequentially feeding the tows into three or more swelling baths by means of a roller to obtain uniform and high-rigidity graphene fibers exhibiting a tensile strength standard deviation of less than or equal to 0.095 across fibers having different diameters and test lengths, and a bending rigidity as high as 1.02 N / mm². During the continuous preparation process, the uniformity and compactness of axial and radial structures are optimized by means of repeated wet melting and splitting of the fibers, the rigidity of the fibers is improved, and the formation of a sheath-core structure and the reduction in the rigidity caused by direct wet spinning of the large-diameter fibers are avoided.

Description

Uniform high-rigidity graphene fiber and preparation method thereof TECHNICAL FIELD

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

[0002] Graphene is a new material with sp2 hybridization of carbon atoms tightly packed into a single layer of two-dimensional honeycomb lattice structure, which has excellent mechanical, electrical, thermal and optical properties. The graphene sheets are arranged in a one-dimensional direction, and a macroscopic high-performance graphene fiber can be prepared, which has important application prospects in the fields of aerospace, biosensing and intelligent fabric. Although the mechanical strength of small-diameter (diameter ≤ 10 μm) graphene fiber can reach 3.2 GPa, the small diameter leads to a bending stiffness of the fiber ≤ 2×10 -5 N mm², which is not resistant to bending and compression, and is difficult to apply in complex practical stress environment. One of the effective methods to improve the bending stiffness of graphene fiber is to increase the fiber diameter while ensuring the density and high orientation of the internal sheets. At present, the diameter of the fiber is mainly increased by increasing the diameter of the spinning head. However, this method has many problems. For example, the double diffusion process of gel fiber in the coagulation bath and the subsequent carbonization treatment will form a serious skin-core structure, and the internal sheets are relatively loose and have small density; due to the weak shear force on the graphene oxide sheets in the core, the orientation of the core sheets is poor, and the bending stiffness is less than 6×10 -4 N mm²; in addition, the radial and axial structures of the fiber are not uniform, and there is a serious size effect, that is, the performance of the fiber decreases sharply with the increase of the axial and radial size of the fiber. Although there are currently thick fibers integrated by bundle stretching, there are still problems such as non-uniform cross-section and insufficient density of the fiber, which seriously affect the performance of the large-diameter fiber. SUMMARY

[0003] The present application provides a preparation method of graphene fiber to solve the problems of non-uniform cross-section and insufficient density of the fiber in the prior art thick fiber integrated by bundle stretching.

[0004] The present application firstly proposes swelling for the nascent fiber which has not been completely dried, solves the problem that the tight stacking between the layers of the finished fiber in the swelling bath causes the layers to be unable to swell and separate sufficiently, the plasticity of the layer rearrangement is poor, and there are still many wrinkles on the surface of the fiber, which causes the fibers to be unable to be completely self-adaptive. After the nascent fiber is immersed in the swelling bath, the layers are in a state of not being completely stacked, the solvent can be better immersed between the layers of graphene sheets, and the sheet rearrangement can be induced to the maximum extent. And the sufficient immersion of the solvent causes the fiber to swell sufficiently to a state of no wrinkles on the surface, the surface of the fiber and the fiber can be fully attached, and the π-π stacking under the action of the van der Waals force is re-generated in the drying process, and the overall dense and highly oriented large-diameter graphene oxide fiber is obtained.

[0005] Secondly, by adjusting the polarity of the swelling bath solution, a multi-stage swelling bath with gradually weakened polarity is set, in the process of repeated wet melting and splitting, the uniformity and density of the axial and radial structure of the fiber bundle are optimized, and the decrease of the skin-core structure and rigidity caused by direct wet spinning is avoided. By stretching the chemical reduction bath and the specially designed microwave-assisted thermal reduction method, a high reduction with a carbon oxygen ratio of ≥25 is realized. The graphene fiber prepared by the method has a diameter of greater than 20 μm, a regular circular cross-section, high uniformity and density, high orientation, high rigidity, and a standard deviation of tensile strength of different diameters and test lengths of ≤0.095, and a bending stiffness of 1.02 N mm². And the preparation process is continuous, the silk collection efficiency is high, the prepared graphene fiber has the characteristics of large diameter, axial and radial uniformity, density, bending stiffness, etc., and has extremely important application value in spacecraft framework, biological electrodes, building materials, etc.

[0006] One of the technical solutions of the present application is to provide a preparation method of uniform high rigidity graphene fiber, comprising the following steps:

[0007] (1) The graphene oxide dispersion liquid is extruded into the coagulation bath through the porous spinning head to obtain the nascent graphene oxide fiber bundle;

[0008] (2) The nascent graphene oxide fiber bundle is sent into the first swelling bath for swelling, and is drawn out and dried to obtain the nascent wet-melted graphene oxide fiber;

[0009] (3) The swelling and rearrangement are continued for two times or more, the swelling bath is drawn out and dried to obtain the uniform and dense graphene oxide fiber with fully oriented layers; the polarity of the swelling bath solvent is gradually weakened to adjust the swelling degree of the fiber;

[0010] (4) The graphene oxide fiber with fully oriented layers is continuously sent into the chemical reduction bath and the microwave-assisted thermal reduction cylinder through the roller to obtain the uniform high rigidity graphene fiber.

[0011] Further, the number of holes of the multi-hole spinning head in step 1 is greater than or equal to 10, and the hole diameter is 60-240 μm.

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

[0013] Further, the swelling bath comprises one or more of ethanol, acetone, isopropyl alcohol, 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] Further, the chemical reduction bath in step 4 comprises one or more of acetic acid, trifluoroacetic acid, vitamin C, hydriodic acid, and hydrazine hydrate.

[0015] Further, the chemical reduction bath in step 4 is performed in a chemical reduction tank equipped with side-by-side multi-stage rollers, which sufficiently increase the draw ratio and reduction time of the fiber, the draw ratio being up to 10 %, and the carbon-oxygen ratio of the fiber after reduction being greater than or equal to 12, thereby ensuring high bending stiffness of the reduced fiber.

[0016] Further, the microwave-assisted thermal reduction cylinder in step 4 has a temperature of 100-350 ℃ and a microwave power of 100-800 W, and the dual reduction effect of high temperature and microwaves further increases the reduction degree of the fiber, the carbon-oxygen ratio of the fiber after reduction being greater than or equal to 25, thereby further improving the bending stiffness.

[0017] Further, the repeated wet-melting splitting process in step 3 can gradually increase the draft speed of the rollers, so that the fiber bundle is simultaneously densified and stretched to a certain extent during the densification process, thereby improving the orientation degree.

[0018] The second technical solution of the present application provides a uniform high-stiffness graphene fiber prepared by the above preparation method.

[0019] The graphene fiber prepared by the present application has a diameter greater than or equal to 20 μm, a standard deviation of tensile strength of different diameters and test lengths of less than or equal to 0.095, 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 different diameters of the graphene fiber greater than 1.8 g cm -3 , and an orientation degree greater than 8.5.

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

[0021] 1) The swelling process is gradually weakened, and repeated wet-melting splitting is performed.

[0022] 2) The newly born fiber which is not dried enough is immediately swollen in the continuous spinning line. After the newly born fiber is immersed in the swelling bath, the graphene sheets are better infiltrated by the solvent due to the incomplete stacking of the sheets, which can induce the rearrangement of the sheets to the greatest extent. The sufficient infiltration of the solvent causes the fiber to be fully swollen into a wrinkle-free state, and the surface energy between the fibers is fully adhered. In the drying process, the π-π stacking under the action of the van der Waals force is re-generated, and the whole dense and highly oriented large-diameter graphene oxide fiber is obtained.

[0023] 3) The continuous and highly reduced fiber with a carbon-oxygen ratio of greater than or equal to 25 is realized by using a chemical reduction bath equipped with multiple side-by-side rollers and a specially designed microwave-assisted heat reduction cylinder. The continuous integration of the reduction process facilitates the large-scale production.

[0024] 4) The prepared fiber can ensure high orientation and density of the internal sheets under the condition of any increase in diameter, and the fiber cross-section is regular and circular, and uniform in the axial and radial directions. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic diagram of the continuous preparation process.

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

[0027] Figure 3 is a graph showing the change of fiber strength with test length for the fiber prepared in Example 1.

[0028] Figure 4 is a graph showing the change of fiber strength with fiber diameter for the fiber prepared in Example 1. DETAILED DESCRIPTION

[0029] The following examples are used to further illustrate the present application, and the purpose is to illustrate the present application, and should not be interpreted as limiting the scope of the present application. The following uses weight parts and weight percentages unless otherwise specified.

[0030] The raw materials used in the present application are conventional commercially available products unless otherwise specified; the methods used in the present application are conventional methods in the art unless otherwise specified.

[0031] The following examples are used to further illustrate the present application, and the purpose is to illustrate the present application, and should not be interpreted as limiting the scope of the present application. The following uses weight parts and weight percentages unless otherwise specified.

[0032] It should be clear that the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0033] The wet fusion described in the present application refers to wet spinning fusion.

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

[0035] The terminology used in the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the content clearly dictates otherwise. Throughout this application the word "comprise" or variations such as "comprises" or "comprising," will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The use of the term "about" in relation to a particular value means that the value is within a range of 10% above and below the particular value. Embodiments

[0036] 1. 8 mg g-1 of DMF based graphene oxide spinning solution was loaded into a 100 ml syringe and pushed at a rate of 1 ml min-1 through a 100 hole porous spinneret with a pore size of 100 μm into an ethyl acetate coagulation bath with a coagulation time of 30 s and drawn in situ to dryness; -1 -1

[0037] 2. The graphene oxide fiber was sent through a roller into a first strong swelling bath which was a mixture of ethanol and water in a ratio of 2:1 with a swelling degree of 250 % and drawn out of the swelling bath to dryness to obtain a primary wet fused graphene oxide fiber;

[0038] 3. The primary wet fused graphene oxide fiber was sent through a roller into a second weak swelling bath which was a mixture of ethanol and water in a ratio of 3:1 with a swelling degree of 190 % and the draw speed was increased to 1.05 times, the fiber was split to some extent in this swelling bath and the orientation and uniformity were optimized and drawn out to dryness to achieve a secondary wet fusion;

[0039] 4. The fiber obtained in step 3 was sent through a roller into a third weak swelling bath, the ratio of ethanol and water was increased to 4:1 with a swelling degree of 130 % and the draw speed was increased to 1.1 times to further improve the orientation and density of the fiber.

[0040] 5. The fiber obtained in step 4 was sent through a roller into a fourth weak swelling bath, the ratio of ethanol and water was increased to 5:1 with a swelling degree of 90 % and the draw speed was increased to 1.2 times to obtain a high orientation and high density wet fused graphene oxide fiber.

[0041] 6. The wet fused graphene oxide fiber obtained in step 5 was sent through a roller into a mixed chemical reduction bath of acetic acid and trifluoroacetic acid in a ratio of 3:1 for continuous room temperature chemical reduction to obtain a reduced graphene oxide fiber with a draw ratio of up to 10 % and a carbon to oxygen ratio of 12 after reduction.

[0042] ​​7. The reduced graphene oxide fiber is continuously sent through the roller into the microwave-assisted thermal reduction cylinder for thermal reduction under tension, with the thermal reduction cylinder temperature being 100 °C and the microwave power being 100 W. Finally, the graphene fiber with a uniform and dense diameter of 124 μm is collected on a roller with a diameter of 15 cm, with the carbon-oxygen ratio of the fiber being 25 and the density being 1.87 g cm -3 . As shown in FIG. 3, the mechanical strength of the obtained fiber can be maintained at 2.5 GPa or more as the test length increases from 0.5 cm to 10 cm, and there is no obvious downward trend. The elongation at break is 2.5 %, the electrical conductivity is 6.28 x 10 4 S m -1 , and the bending stiffness is 1.02 N mm².

[0043] 8. The number of holes in the porous spinning head in step 1 is changed to 20, 40, 60, and 80, and other operation steps remain unchanged, so that 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 have an obvious downward trend as the diameter increases, and is maintained at 2.5 GPa or more, as shown in FIG. 4, and the density is basically consistent; the electrical conductivity is maintained at about 6 x 10 4 S m -1 ; and the bending stiffness increases as the diameter increases. As the diameter increases, the orientation degree is maintained at 8.5 or more.

[0044] The comparative example is the same as example 1, except that a large-pore single-hole spinning head with a hole diameter of 610 μm, 840 μm, 1000 μm, 1100 μm, and 1250 μm is directly used for spinning.

[0045] 1. 8 mg g -1 of DMF phase graphene oxide dispersion liquid is extruded from a large-diameter single-hole spinning head into an ethyl acetate coagulation bath, and a nascent graphene oxide coarse fiber is drawn out and dried.

[0046] 2. The graphene oxide coarse fiber obtained in step 1 is sent through a roller into an ethanol and water 3:1 swelling bath, with a draw ratio of 1.05, which is consistent with step 3 of example 1.

[0047] 3. The fiber obtained in step 2 is continuously sent through the roller into an ethanol and water 4:1 swelling bath, with a draw ratio of 1.1, which is consistent with step 2 of example 1.

[0048] 4. The chemical reduction process is the same as step 5 of example 1.

[0049] 5. Similarly, the chemically reduced fiber was put into a microwave-assisted thermal reduction cylinder with a temperature of 300 °C and a microwave power of 500 W. The final fiber had an irregular cross-section with an equivalent diameter of 23 μm, 49 μm, 82 μm, and 106 μm. The density was only 1.56 g cm -3 , the orientation degree was only 7.2, the maximum strength was only 560 MPa, the elongation at break was 3% to 6%, the conductivity was only 2.2 x 10 3 S m -1 , and the bending stiffness was ≤ 3.9 x 10 -3 N mm². The performance indicators decreased sharply with the increase of the diameter, and were significantly lower than those of Example 1.

[0050] The comparative example was the same as Example 1, except that there was no repeated wet splitting process.

[0051] 1. The same as step 1 of Example 1.

[0052] 2. The obtained graphene oxide fiber was sent through a roller into a swelling bath composed of ethanol and water in a ratio of 2:1, with a draw ratio of 1.1 times. After drying and wet splitting, a graphene oxide coarse fiber was obtained.

[0053] 3. The chemical reduction and thermal reduction processes were the same as step 6 of Example 1. The final fiber had an irregular cross-section with many voids and poor compactness, with a density of 1.71 g cm -3 , an orientation degree of 7.9, a strength of only 832 MPa, an elongation at break of 3%, an electrical conductivity of 0.97 x 10 4 S m -1 , and a bending stiffness of 0.11 N mm². Example

[0054] 1. 5 mg g -1 of DMSO phase graphene oxide spinning solution was loaded into a 50 ml syringe, which was pushed at a speed of 0.8 ml min -1 through a multi-hole spinning head with a 50-hole aperture size of 120 μm into a acetone coagulation bath, with a time of 25 s through the coagulation bath, and a nascent graphene oxide fiber was obtained by pulling out and drying in situ.

[0055] 2. The obtained graphene oxide fiber was sent through a roller into a swelling bath composed of a mixture of acetic acid and ethylene glycol, with a ratio of 3:1 and a swelling degree of 210%. The fiber was pulled out and dried.

[0056] 3. The fiber was continuously sent through a roller into a second swelling bath composed of acetic acid and water in a ratio of 4:1 and a swelling degree of 175%. The process had a draw ratio of 1.15 times. The fiber was pulled out and dried from the second swelling bath to achieve a second wet splitting.

[0057] 4. Continue through the third swelling bath, the ratio of acetic acid and water is increased to 5:1, the swelling degree is 110 %, continue to increase the draw ratio to 1.25 times, dry from the third swelling bath, achieve the third wet fusion. The orientation and density of the fiber are further increased.

[0058] 5. Finally, the resulting wet fusion fiber is sent into a pure acetic acid solvent through a roller, and a pure plasticization stretching is performed, the draw ratio is increased to 1.3 times, and after drying, a high-orientation and high-densification graphene oxide coarse fiber is obtained.

[0059] 6. The fiber obtained in step 5 is continuously sent into a hydrazine hydrate through a roller, and after drying, a chemically reduced graphene fiber is obtained, the stretching ratio of the graphene fiber is as high as 10 %, and the carbon-oxygen ratio of the fiber after reduction is 12.

[0060] 7. The obtained chemically reduced graphene fiber is sent into a microwave-assisted thermal reduction cylinder, the reduction temperature is 280 ℃, the microwave power is 800 W, and the thermal reduction is performed under tension. The final yarn collection obtains a uniform graphene coarse fiber, the carbon-oxygen ratio of the fiber is 31, the diameter is 82 μm, the density is 1.89 g cm -3 , the orientation is 8.8, the strength standard deviation is ≤0.082 in the test length range of 0.5 cm-10 cm, and all are above 2.5 GPa, the elongation at break is 2.1 %, the electrical conductivity is 9.73×10 4 S m -1 , and the bending stiffness is 0.2 N mm². Example

[0061] 1. 15 mg g -1 of NMP phase of graphene oxide spinning solution is loaded into a 100 ml syringe, which is pushed at a speed of 0.5 ml min -1 , and is extruded into a n-hexane coagulation bath through a 20-hole porous spinning head with a pore size of 200 μm, the time through the coagulation bath is 20 s, and the nascent graphene oxide filament is obtained by pulling out from the coagulation bath and drying in situ.

[0062] 2. The obtained graphene oxide filament is sent into a swelling bath composed of a mixture of ethanol and ethylene glycol through a roller, the ratio is 4:1, the swelling degree is 180 %, and the filament is pulled out and dried from the swelling bath.

[0063] 3. Continue to send into the second swelling bath through the roller, the ratio of ethanol and ethylene glycol is 5:1, the swelling degree is 160 %, the draw ratio in this process is 1.15 times, dry from the second swelling bath, achieve the second wet fusion.

[0064] 4. Continue to pass through the third swelling bath, the ratio of ethanol and ethylene glycol is increased to 6:1, the swelling degree is 130%, continue to increase the stretching ratio to 1.25 times, dry after drawing out from the third swelling bath, realize the third wet fusion. The orientation and density of the fiber are further increased.

[0065] 5. Finally, the obtained wet fusion fiber is sent into pure acetic acid solvent through a roller, and a pure plasticization stretching is performed, the stretching ratio is increased to 1.3 times, and after drying, a high-orientation and high-densification graphene oxide coarse fiber is obtained.

[0066] 6. The fiber obtained in step 5 is continuously sent into a sodium ascorbate solution through a roller, and after drying after drawing out, a chemical reduction graphene fiber is obtained, the stretching ratio of the graphene fiber is as high as 10%, and the carbon-oxygen ratio of the fiber after reduction is 12.

[0067] 7. The obtained chemical reduction graphene fiber is sent into a microwave-assisted thermal reduction cylinder, the reduction temperature is 350 DEG C, the microwave power is 400 W, and the thermal reduction is performed under tension. The uniform graphene coarse fiber is finally obtained by silk collection, the carbon-oxygen ratio of the fiber is 27, the diameter is 56 μm, the density is 1.9 g / cm -3 , the orientation is 9.1, the strength standard deviation is ≤0.072 in the test length range of 0.5 cm-10 cm, and is maintained above 2.6 GPa, the elongation at break is 1%, the conductivity is 3.96×10 4 S m -1 , and the bending stiffness is 0.06 N mm².

[0068] The above examples illustrate the structure, features and effects of the present application, and the above description is only the preferred embodiment of the present application, any changes or modifications made according to the idea of the present application, or equivalent embodiments with equivalent changes, still within the scope of the present application.

[0069] Although the embodiments of the present application are disclosed for the purpose of illustration, those skilled in the art can understand that various alternatives, changes and modifications are possible without departing from the spirit and scope of the present application and the appended claims, therefore, the scope of the present application is not limited to the disclosed content of the embodiments.

Claims

1. A method of producing a uniform high stiffness graphene fiber, characterized by, The method comprises the following steps: (1) extruding the graphene oxide dispersion through a porous spinneret into a coagulation bath to obtain nascent graphene oxide filaments; (2) sending the nascent graphene oxide filaments into a first swelling bath for swelling, drying and drawing to obtain nascent wet-fused graphene oxide fibers; (3) continuing to perform two or more swelling baths for swelling and rearrangement, drying and drawing to obtain graphene oxide fibers that are uniform, dense and fully oriented in layers; the solvent polarity of the swelling baths is gradually weakened; (4) continuously sending the graphene oxide fibers fully oriented in layers through a roller into a chemical reduction bath and a microwave-assisted heat reduction cylinder to obtain uniform high-stiffness graphene fibers.

2. The production method according to claim 1, characterized by, The number of holes of the porous spinneret in step 1 is ≥10, and the hole diameter is 60 μm-240 μm.

3. The preparation method according to claim 1, characterized in that, The swelling bath comprises one or more of ethanol, acetone, isopropyl alcohol, 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.

4. The method of claim 1, wherein, The chemical reduction bath in step 4 comprises one or more of acetic acid, trifluoroacetic acid, vitamin C, hydriodic acid and hydrazine hydrate.

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

6. A uniform high-stiffness graphene fiber prepared by the method of any one of claims 1-5.

7. The uniform high stiffness graphene fiber of claim 6, wherein, The fiber diameter is ≥20 μm.

8. The uniform high stiffness graphene fiber of claim 6, wherein, The graphene fiber has a density greater than 1.8 g cm -3 .

Images