High-performance graphene / carbon nanotube composite fiber and preparation method thereof

Abstract

The present invention discloses a graphene / carbon nanotube composite fiber with high tensile strength and electrical conductivity. The composite fiber is mainly composed of a graphene-like material and a carbon nanotube fiber. The graphene-like material is filled into the interior of the carbon nanotube fiber by the action of a strong acid. The graphene-like material includes one or more of graphene and reduced graphene oxide, preferably graphene. A specific preparation method of the composite fiber is also disclosed. The graphene / carbon nanotube composite fiber provided by the present invention has excellent mechanical and electrical properties. Compared with pure carbon nanotube fibers, the composite fiber structure is denser and has a higher degree of orientation. At the same time, the graphene / carbon nanotube composite fiber can be prepared continuously, has low equipment requirements, and has the advantages of simple operation and easy batch preparation.

Description

Technical Field

[0001] The present invention belongs to the field of new material preparation, and specifically relates to a high-performance graphene / carbon nanotube composite fiber and a preparation method thereof. Background Art

[0002] Carbon nanotubes have excellent mechanical and electrical properties. Their tensile strength and tensile modulus are as high as 100 GPa and 1 TPa respectively. The electrical conductivity of metallic carbon nanotubes is as high as 10 8 S / m. Carbon nanotube fibers are one-dimensional macroscopic assemblies of carbon nanotubes, promising to inherit the excellent mechanical and electrical properties of carbon nanotubes at the microscopic scale. However, the current mechanical and electrical properties of carbon nanotube fibers fall far short of their intrinsic properties, primarily due to problems such as numerous voids, poor orientation, and weak intertube interactions.

[0003] Introducing other components into the fibers or subjecting the fibers to solution densification treatment is considered an effective method to improve the performance of carbon nanotube fibers. The literature (Adv.Mater.2015,27,3259) reported a method for obtaining dense fibers by high-temperature treatment of carbon nanotube / polydopamine (PDA) composite fibers, which enhances the mechanical and electrical properties of the fibers. However, the pyrolysis treatment of PDA produces amorphous carbon, and the enhancement effect on fiber performance still needs to be further improved. The literature (Compos.Sci.Technol.2012,72,1402) reported two reinforcement methods: densification treatment of carbon nanotube fibers with different solvent solutions and introduction of bismaleimide polymers, thereby preparing carbon nanotube fibers with enhanced mechanical properties. However, these two treatment methods have limited effects on the improvement of the mechanical properties of the fibers, and the presence of the polymer will have a significant impact on the electrical properties of the fibers. Patent CN107473203B prepares carbon nanotube aggregates through floating catalytic chemical vapor deposition, continuously sprays a graphene oxide dispersion onto them, and then passes them through a liquid-sealed tank filled with water to produce carbon nanotube / graphene composite fibers. However, the resulting graphene / carbon nanotube composite fibers exhibit relatively low mechanical properties. Current methods for improving the performance of carbon nanotube fibers are relatively limited, and there is still room for further improvement in the structure and performance of carbon nanotube fibers. Summary of the Invention

[0004] To overcome the above-mentioned defects, the present invention provides a graphene / carbon nanotube composite fiber with high tensile strength and electrical conductivity and a preparation method thereof.

[0005] On the one hand, the present invention provides a graphene / carbon nanotube composite fiber with high tensile strength and electrical conductivity. The composite fiber is mainly composed of a graphene-like material and a carbon nanotube fiber, and the graphene-like material is filled in the interior of the carbon nanotube fiber; the size of the graphene-like material is 50nm~1μm, preferably 50nm~500nm; the fiber diameter of the carbon nanotube fiber is 10~100μm.

[0006] According to one embodiment of the present invention, the number of layers of the graphene-based material is 3-10 layers, preferably 3-5 layers.

[0007] According to one embodiment of the present invention, the carbon nanotube fibers are prepared by one of floating catalytic chemical vapor deposition, array spinning, and wet spinning.

[0008] According to one embodiment of the present invention, the graphene material includes one or more of graphene and reduced graphene oxide, preferably graphene.

[0009] Another aspect of the present invention provides a method for preparing the composite fiber, which specifically comprises the following steps:

[0010] S1, immersing the carbon nanotube fiber in the graphene-like material / strong acid dispersion, causing the carbon nanotube fiber to expand in volume, thereby promoting the graphene-like material to enter the interior of the carbon nanotube fiber;

[0011] S2, placing the carbon nanotube fiber in a graphene / strong acid dispersion for a period of time and applying a stretching with a certain stretching ratio;

[0012] S3, transferring the product obtained in S2 into a coagulation bath solution;

[0013] S4, transferring the product obtained in S3 to a cleaning bath solution for washing;

[0014] S5, drying to obtain graphene / carbon nanotube composite fibers.

[0015] According to one embodiment of the present invention, the strong acid is one or more of sulfuric acid, fuming sulfuric acid, nitric acid, chlorosulfonic acid, polyphosphoric acid, methanesulfonic acid, trifluoroacetic acid, and trifluoromethanesulfonic acid.

[0016] According to one embodiment of the present invention, in step S1, the concentration of the graphene-based material in the dispersion is 0.001 wt% to 1 wt%, preferably 0.01 wt% to 0.5 wt%.

[0017] According to one embodiment of the present invention, in step S1, the pKa (acidity coefficient) value of the strong acid in the dispersion is -15 to 0.3.

[0018] According to one embodiment of the present invention, in step S2, the carbon nanotube fibers are treated in the graphene / strong acid dispersion for a time period of 0.5 min to 60 min, preferably 1 min to 30 min.

[0019] According to one embodiment of the present invention, in step S2, the draft ratio is 5%-30%, and preferably the draft ratio is 15%-30%.

[0020] According to one embodiment of the present invention, in step S3, the components in the coagulation bath solution are one or more of acetone, ether, dichloromethane, ethyl acetate, and water.

[0021] According to one embodiment of the present invention, in step S4, the cleaning bath solution comprises a component selected from the group consisting of water, ethanol, isopropyl alcohol, and acetone.

[0022] According to one embodiment of the present invention, in step S5, the drying temperature is 20°C-1100°C.

[0023] Beneficial effects:

[0024] The graphene / carbon nanotube composite fibers provided by the present invention exhibit excellent mechanical and electrical properties. Compared with pure carbon nanotube fibers, the composite fibers are denser and more highly oriented. At a draw ratio of 18%, the tensile strength of the graphene / carbon nanotube composite fibers is 282% higher than that of pure carbon nanotube fibers and 23% higher than that of carbon nanotube fibers treated only with strong acid. The electrical conductivity of the graphene / carbon nanotube composite fibers is 500% higher than that of pure carbon nanotube fibers and 35% higher than that of carbon nanotube fibers treated only with strong acid. Furthermore, the graphene / carbon nanotube composite fibers can be produced continuously, requiring minimal equipment, and are simple to operate and readily available for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the experimental flow chart of Examples 1-10 and Comparative Examples 1-5.

[0026] Figure 2 These are scanning electron microscope (SEM) photos of the graphene / carbon nanotube composite fibers in Examples 1, 2, 7, 8, 9 and Comparative Example 1.

[0027] Figure 3 1-10 and comparative examples 1-5 are graphs comparing the tensile strength of the graphene / carbon nanotube composite fibers.

[0028] Figure 4 1-10 and comparative examples 1-5 are graphs comparing the electrical properties of the graphene / carbon nanotube composite fibers.

[0029] Figure 5 Raman characterization of untreated carbon nanotube fibers, carbon nanotube fibers treated with chlorosulfonic acid, and fibers treated with graphene / chlorosulfonic acid dispersion. Detailed Description of the Invention

[0031] The draft ratio refers to the ratio of the increase in fiber length during the stretching process to the original fiber length.

[0032] Tensile strength is the breaking strength of the fiber, which refers to the ratio of the tensile force when the fiber breaks to the cross-sectional area of ​​the fiber at break. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below with reference to specific examples. The methods described are conventional methods unless otherwise specified. The following examples are used to illustrate the present invention but should not be considered to limit the scope of the present invention.

[0034] The present invention aims to provide a high-performance graphene / carbon nanotube composite fiber and a method for preparing the same. In this composite fiber, graphene enters the carbon nanotube fiber due to the volume expansion caused by the protonation of the carbon nanotube fiber by a strong acid, thereby filling the fiber interstices, connecting the carbon nanotube endpoints, and enhancing the inter-tube interaction. The fiber is then subjected to a certain ratio of drafting to ultimately produce a high-density, highly oriented graphene / carbon nanotube composite fiber exhibiting excellent mechanical and electrical properties. This preparation method requires minimal equipment, is simple to operate, and is easily mass-produced, enabling the continuous production of graphene / carbon nanotube composite fibers.

[0035] The graphene / carbon nanotube composite fiber of the present invention, which has high tensile strength and electrical conductivity, is primarily composed of a graphene-like material and carbon nanotube fibers; the graphene-like material fills the interior of the carbon nanotube fibers; the graphene-like material has a size of 50 nm to 1 μm, preferably 50 nm to 500 nm; the carbon nanotube fibers have a fiber diameter of 10 to 100 μm; and the number of graphene-like material layers is 3 to 10, preferably 3 to 5. Smaller graphene is chosen because the voids within the fibers are on the order of hundreds of nanometers, making it easier for graphene to fill the carbon nanotube fibers. Larger graphene, on the other hand, fails to enhance the fiber's strength because larger graphene sheets tend to wrinkle, resulting in more voids in the fibers and reducing fiber performance. Graphene with fewer layers is chosen because the fewer layers of graphene, the better its intrinsic properties (such as conductivity) can be reflected; at the same time, as the number of graphene layers increases, it is also easy to introduce gaps in the fiber, resulting in stress concentration and reducing the tensile strength of the fiber.

[0036] In an optional embodiment, the graphene-based material includes one or more of graphene and reduced graphene oxide, preferably graphene. Graphene and reduced graphene oxide are selected as reinforcing materials for reinforcing carbon nanotube fibers because: they have a six-membered ring structure similar to that of carbon nanotubes, can form π-π interactions with carbon nanotubes, and at the same time, the sheet-like graphene material can play the role of overlapping between carbon nanotubes and between carbon nanotube bundles, further enhancing the force inside the fiber; graphene can connect adjacent carbon nanotubes, thereby forming more conductive paths and improving the conductivity of the fiber. Graphene is preferably selected because: compared to reduced graphene oxide, graphene has a more complete structure and better mechanical and conductive properties; and reduced graphene oxide still contains oxygen-containing groups due to the incomplete reduction process, and the oxygen-containing groups will exist as defects, resulting in a decrease in its own performance. In summary, we prefer graphene as a better reinforcing material.

[0037] The composite fiber can be prepared by the following method: S1, immersing the carbon nanotube fiber in the graphene material / strong acid dispersion, causing the carbon nanotube fiber to expand in volume, prompting the graphene material to enter the interior of the carbon nanotube fiber; S2, placing the carbon nanotube fiber in the graphene / strong acid dispersion for a period of time and applying a certain draft ratio; S3, transferring the product obtained in S2 to a coagulation bath solution; S4, transferring the product obtained in S3 to a cleaning bath solution for washing; S5, drying to obtain a graphene / carbon nanotube composite fiber. In this composite fiber, the volume expansion phenomenon caused by the protonation of the carbon nanotube fiber by the strong acid allows the graphene to enter the interior of the carbon nanotube fiber, thereby filling the fiber gaps, connecting the carbon nanotube endpoints, and enhancing the inter-tube interaction force. The reason for choosing a strong acid is mainly because the protonation of the graphene by the strong acid causes it to form a uniform and stable dispersion. In addition, as the degree of protonation increases, the fiber can undergo varying degrees of volume expansion. Optical microscopy tests show that the fiber can expand to nearly 10 times its original volume in chlorosulfonic acid. However, solutions such as H2O2 have no significant effect on the fiber's volume expansion.

[0038] In an optional embodiment, the strong acid is one or more of sulfuric acid, oleum, nitric acid, chlorosulfonic acid, polyphosphoric acid, methanesulfonic acid, trifluoroacetic acid, and trifluoromethanesulfonic acid. The acid needs to be a relatively strong protonic acid.

[0039] In an optional embodiment, in step S1, the concentration of the graphene-based material in the dispersion is 0.001 wt% to 1 wt%, preferably 0.01 wt% to 0.5 wt%. Higher concentrations present two major issues: first, the increased graphene concentration significantly reduces the dispersion effect; and second, at the same treatment time, more graphene enters the fiber, resulting in visible graphene aggregates. These larger aggregates create more voids in the fiber, leading to decreased fiber performance.

[0040] In an optional embodiment, in step S2, the treatment time of the carbon nanotube fiber in the graphene / strong acid dispersion is 0.5 min to 60 min, preferably 1 min to 30 min. The treatment time has a significant impact on fiber performance. When the treatment time of the fiber in the graphene dispersion is less than 1 min, the amount of graphene entering the fiber interior is very small, which does not improve the performance of the fiber. However, when the time is greater than 30 min, the amount of graphene filling the fiber increases, and sheets will stack and form wrinkles between the graphene, causing the fiber performance to decline.

[0041] In an optional embodiment, in step S2, the draft ratio is 5%-30%, preferably 15%-30%. Drafting the fiber at different ratios has different effects on the mechanical properties of the fiber. When the draft ratio is relatively low, a large number of tangled carbon nanotube bundles remain in the fiber, and the fiber orientation is not optimal, thus not maximizing the performance improvement. When the draft ratio is greater than 30%, slippage occurs between the bundles in the fiber. The reduced contact area leads to a decrease in the inter-bundle force, resulting in a decrease in fiber performance.

[0042] In an optional embodiment, in step S3, the coagulation bath comprises one or more of acetone, ether, dichloromethane, ethyl acetate, and water. The function of the coagulation bath is to cause double diffusion between the dispersion and the coagulation bath solution when the fiber enters the coagulation bath from the graphene / strong acid dispersion due to differences in concentration and temperature. This double diffusion process causes the fiber to change from an expanded state to a dense state, thereby achieving final fiber shaping.

[0043] The following examples illustrate the inventive concept of the present invention. Unless otherwise specified, the raw materials used in the examples can be obtained from public commercial sources.

[0044] The tensile strength test method is as follows: Cut the fiber into small segments approximately 3 cm for tensile strength testing. These segments are then fixed to a mechanical testing paper. The fiber testing distance is fixed at 1 cm and the tensile speed is 1 mm / min. At least 10 samples are tested per fiber group. The test instrument used is a Shimadzu EZ-LX 5N electronic universal testing machine.

[0045] The conductivity test method is as follows: a long fiber section is fixed to cardboard at both ends, and a test lead is clamped to the fiber. By adjusting the distance between the two clamps, the resistance value of the fiber at different spacings is measured, and the fiber conductivity is calculated using a formula. The instrument used for the test is a Keithley 2450 digital source meter.

[0046] Example 1

[0047] The carbon nanotube fibers were immersed in 0.05 wt% graphene / chlorosulfonic acid, where the graphene used had a size of 200-400 nm and a number of 3-5 layers, the treatment time was 1 min, and a draft ratio of 18% was applied;

[0048] The drawn graphene / carbon nanotube composite fibers were transferred to a coagulation bath for 5 min and then to a cleaning bath for 5 min;

[0049] After drying at 100℃, the film is rolled up.

[0050] The basic morphology of graphene / carbon nanotube composite fibers is shown in Figure 2 The tensile strength of the composite fiber is 4.3GPa and the electrical conductivity is 2.29MS / m. For a detailed comparison of the mechanical properties, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0051] Example 2

[0052] The specific process steps are basically the same as those in Example 1 of the present invention. The difference from Example 1 is that the carbon nanotube fibers are treated in the graphene / chlorosulfonic acid dispersion for 5 minutes to obtain graphene / carbon nanotube composite fibers. The basic morphology of the graphene / carbon nanotube composite fibers is shown in FIG. Figure 2 The tensile strength of the composite fiber is 4.1GPa and the electrical conductivity is 2.55MS / m. For a detailed comparison of the mechanical properties, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0053] Example 3

[0054] The specific process steps were essentially the same as those in Example 1 of the present invention, except that the carbon nanotube fibers were treated in the graphene / chlorosulfonic acid dispersion for 10 minutes to produce graphene / carbon nanotube composite fibers. The carbon nanotube composite fibers had a tensile strength of 4.0 GPa and an electrical conductivity of 2.70 MS / m.

[0055] For a detailed comparison of mechanical properties, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0056] Example 4

[0057] The specific process steps were essentially the same as those in Example 1 of the present invention, except that the carbon nanotube fibers were treated in the graphene / chlorosulfonic acid dispersion for 15 minutes to obtain graphene / carbon nanotube composite fibers. The carbon nanotube composite fibers had a tensile strength of 3.5 GPa and an electrical conductivity of 2.64 MS / m.

[0058] For a detailed comparison of mechanical properties, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0059] Example 5

[0060] The specific process steps are basically the same as those in Example 1 of the present invention. The difference from Example 1 is that the draft ratio of the graphene / carbon nanotube composite fiber is 10%. The tensile strength of the carbon nanotube composite fiber is 2.3 GPa and the electrical conductivity is 1.65 MS / m. For detailed mechanical property comparison, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0061] Example 6

[0062] The specific process steps are basically the same as those in Example 1 of the present invention. The difference from Example 1 is that the draft ratio of the graphene / carbon nanotube composite fiber is 12%. The tensile strength of the carbon nanotube composite fiber is 2.6 GPa and the electrical conductivity is 1.71 MS / m. For detailed mechanical property comparison, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0063] Example 7

[0064] The specific process steps are basically the same as those in Example 1 of the present invention, except that the draft ratio of the graphene / carbon nanotube composite fiber is 14%. The basic morphology of the graphene / carbon nanotube composite fiber is shown in FIG. Figure 1 The tensile strength of the composite fiber is 2.8GPa and the electrical conductivity is 1.97MS / m. For a detailed comparison of the mechanical properties, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0065] Example 8

[0066] The specific process steps are basically the same as those in Example 1 of the present invention. The difference from Example 1 is that the carbon nanotube fibers are dispersed in a graphene / concentrated sulfuric acid dispersion to obtain graphene / carbon nanotube composite fibers. The basic morphology of the graphene / carbon nanotube composite fibers is shown in FIG. Figure 2 The tensile strength of the composite fiber is 3.5GPa and the electrical conductivity is 2.05MS / m. For a detailed comparison of the mechanical properties, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0067] Example 9

[0068] The specific process steps are basically the same as those of Example 1 of the present invention. The difference from Example 1 is that the carbon nanotube fibers are dispersed in a graphene / nitric acid dispersion to obtain graphene / carbon nanotube composite fibers. The basic morphology of the graphene / carbon nanotube composite fibers is shown in FIG. Figure 2 The tensile strength of the composite fiber is 3.4GPa and the electrical conductivity is 2.11MS / m. For a detailed comparison of the mechanical properties, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0069] Example 10

[0070] The specific process steps are basically the same as those in Example 1 of the present invention. The difference from Example 1 is that the carbon nanotube fibers are placed in a reduced graphene oxide / chlorosulfonic acid dispersion to obtain reduced graphene oxide / carbon nanotube composite fibers. The tensile strength of the carbon nanotube composite fibers is 3.7 GPa and the electrical conductivity is 2.01 MS / m. For detailed mechanical property comparison, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0071] Comparative Example 1

[0072] The specific process steps are basically the same as those in Example 1 of the present invention, but without adding graphene-like substances, the carbon nanotube fibers are only immersed in chlorosulfonic acid to obtain the treated carbon nanotube fibers. The basic morphology of the carbon nanotube fibers is shown in FIG. Figure 2 The tensile strength of the fiber is 3.3GPa and the electrical conductivity is 1.50MS / m. For a detailed comparison of the mechanical properties, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0073] Comparative Example 2

[0074] The carbon nanotube fibers are not treated in any way and have a tensile strength of 1.1 GPa and an electrical conductivity of 0.45 MS / m. For a detailed comparison of mechanical properties, see Figure 3, for comparison of electrical properties see Figure 4 .

[0075] Comparative Example 3

[0076] The carbon nanotube fibers were immersed in 0.05 wt% graphene / H2O2, the graphene used had a size of 200-400 nm, the number of layers was 3-5, the treatment time was 1 min, and a draft ratio of 18% was applied;

[0077] The drawn graphene / carbon nanotube composite fibers were transferred to a coagulation bath for 5 min and then to a cleaning bath for 5 min;

[0078] After drying at 100℃, the film is rolled up.

[0079] The tensile strength of the composite fiber is 2.8GPa and the electrical conductivity is 0.73MS / m. For a detailed comparison of the mechanical properties, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0080] Comparative Example 4

[0081] The specific process steps are basically the same as those in Example 1 of the present invention. The difference from Example 1 is that the size of the selected graphene is 2-3 μm, and a larger size graphene / carbon nanotube composite fiber is obtained. The tensile strength of the carbon nanotube composite fiber is 3.4 GPa and the electrical conductivity is 1.99 MS / m. For detailed mechanical property comparison, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0082] Comparative Example 5

[0083] The specific process steps are basically the same as those in Example 1 of the present invention. The difference from Example 1 is that the number of graphene layers selected is 10-15 layers, and the graphene / carbon nanotube composite fiber is obtained. The tensile strength of the carbon nanotube composite fiber is 3.0 GPa and the electrical conductivity is 1.87 MS / m. For detailed mechanical properties comparison, see Figure 3 , for comparison of electrical properties see Figure 4 .

[0084] Table 1 and Figure 3 、 Figure 4 The performance comparison of the fibers in Examples 1-10 and Comparative Examples 1-5 is shown.

[0085] Table 1 Performance comparison of graphene / carbon nanotube composite fibers

[0086]

[0087] The above are only some embodiments of the present invention. It should be pointed out that for those skilled in the art, other variations and improvements can be made without departing from the creative concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite fiber, characterized in that: The specific steps include: S1, immersing the carbon nanotube fiber in a strong acid dispersion of a graphene-like material, causing the carbon nanotube fiber to expand in volume, thereby promoting the graphene-like material to enter the interior of the carbon nanotube fiber; S2, placing the carbon nanotube fiber in a strong acid dispersion of a graphene material for a period of time, and applying a drafting at a certain draft ratio; S3, transferring the product obtained in S2 into a coagulation bath solution; S4, transferring the product obtained in S3 to a cleaning bath solution for washing; S5, drying to obtain graphene / carbon nanotube composite fibers; In the step S1, the concentration of the graphene material in the dispersion is 0.001 wt% to 1 wt%, the size of the graphene material is 50 nm to 500 nm, and the number of layers is 3 to 5; In the step S2, the carbon nanotube fibers are placed in the strong acid dispersion of the graphene material for a time period of 1 min to 30 min, and the draft ratio is 15% to 30%.

2. The preparation method according to claim 1, characterized in that The strong acid is one or more of sulfuric acid, nitric acid, chlorosulfonic acid, methanesulfonic acid, trifluoroacetic acid, and trifluoromethanesulfonic acid.

3. The preparation method according to claim 1, characterized in that In the step S1, the concentration of the graphene-based material in the dispersion is 0.01 wt% to 0.5 wt%.

4. The preparation method according to claim 1, characterized in that In step S3, the components in the coagulation bath solution are one or more of acetone, ether, dichloromethane, ethyl acetate, and water.

5. The preparation method according to claim 1, characterized in that In step S4, the cleaning bath solution comprises one of water, ethanol, isopropanol, and acetone.

6. A graphene / carbon nanotube composite fiber, characterized in that: The method is prepared according to any one of claims 1 to 5.

7. The composite fiber according to claim 6, characterized in that The graphene-based material includes graphene.

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