A method for preparing high-strength and high-thermal-conductivity carbon nanotube fibers

Abstract

This invention relates to the field of carbon nanotube fiber technology and provides a method for preparing high-strength, high-thermal-conductivity carbon nanotube fibers. The invention uses chlorosulfonic acid to prepare the spinning solution and dichloromethane as the first coagulation bath. Taking advantage of the slow diffusion rate of chlorosulfonic acid in dichloromethane solvent, the nascent fiber achieves uniform shrinkage and coagulation during double diffusion. The nascent fiber is then passed through a secondary coagulation bath to remove residual chlorosulfonic acid and further improve fiber orientation and density. Subsequently, heating and stretching remove residual solvent from the secondary coagulation bath, ultimately obtaining carbon nanotube fibers with a rounded macrostructure and a dense microstructure. These carbon nanotube fibers exhibit high strength, high toughness, and high thermal conductivity.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube fiber technology, and in particular to a method for preparing high-strength, high-thermal-conductivity carbon nanotube fibers. Background Technology

[0002] High thermal conductivity carbon fiber reinforced carbon-carbon composites are key hot-end components for hypersonic aircraft in the aerospace field. Simultaneously improving the thermal conductivity and mechanical properties of carbon fibers and composites is a crucial step in advancing aircraft research and development. It is worth noting that there is an irreconcilable contradiction between the strength and thermal conductivity of commercially available high thermal conductivity pitch-based carbon fibers. Existing pitch-based carbon fibers have a mechanical strength between 3.1 and 3.5 GPa and a thermal conductivity between 600 and 1000 W / m·K. However, these fibers have low elongation at break, generally below 0.6%, and even less than 0.3%. Therefore, these fibers are brittle, have low bonding strength, are not suitable for small-angle bending, and are prone to fraying and breakage during use, increasing the difficulty of weaving these fiber materials in composite preforms. From the perspective of the raw materials constituting the fibers, carbon nanotubes, due to their excellent mechanical, thermal, and chemical stability properties, have become an ideal raw material for preparing high-strength, high-thermal-conductivity fibers. By aligning carbon nanotubes with a high degree of orientation along the fiber axis, the excellent properties of carbon nanotubes can be largely preserved on a macroscopic scale. Furthermore, using carbon nanotube fibers as a reinforcing phase not only allows for high addition amounts and highly oriented arrangements of carbon nanotubes in composite materials, but also enables fiber-reinforced composite materials to possess superior properties such as higher specific strength, specific modulus, and thermal characteristics.

[0003] Currently, there are three main methods for preparing carbon nanotube fibers: carbon nanotube array spinning, direct spinning via floating catalyst chemical vapor deposition, and wet spinning. Carbon nanotube fibers obtained by carbon nanotube array spinning can have nanotube lengths reaching the hundreds of micrometers, but the fibers have high porosity and low inter-tube performance transfer efficiency. From a technical perspective, this method is difficult to achieve large-scale and structurally controllable preparation of carbon nanotube fibers. Carbon nanotube fibers obtained by direct spinning via floating catalyst chemical vapor deposition can also have nanotube lengths reaching the hundreds of micrometers, but the structure of these fibers exhibits inhomogeneity and high porosity. Furthermore, residual metal catalysts in the fiber structure can affect the fiber's mechanical / electrical and thermal properties. Wet spinning technology utilizes the lyotropic liquid crystal properties of carbon nanotubes in acidic solvents. The resulting nematic liquid crystal phase structure is beneficial for obtaining fibers with high orientation and high density. Liquid crystal spinning technology facilitates the directional alignment of carbon nanotubes, reducing structural defects caused by bending and twisting of carbon nanotubes in the fiber, aiming to obtain fibers with higher breaking strength and modulus. It is worth noting that wet spinning technology, as a typical forming technology for chemical fibers, is more conducive to the large-scale production and preparation of fibers.

[0004] Currently, the strength and thermal conductivity of carbon nanotube fibers prepared by wet spinning are significantly lower than those of single carbon nanotubes. This is mainly due to two reasons: firstly, the inherent inhomogeneity of the carbon nanotube raw material's structure (such as wall count, diameter, chirality, length, and defects); secondly, during fiber preparation, the assembly of several carbon nanotube powders into macroscopic carbon nanotube fibers leads to inhomogeneity in fiber orientation and density, resulting in porosity and voids within the fiber, causing increased phonon scattering and lower thermal conductivity.

[0005] Therefore, the key issue in preparing high-strength and high-thermal-conductivity carbon nanotube fibers is how to improve the wet spinning technology of carbon nanotube fibers to prepare fiber materials with high orientation and high density, and obtain carbon nanotube fibers with high strength and high thermal conductivity. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing high-strength, high-thermal-conductivity carbon nanotube fibers. The preparation method provided by the present invention can obtain highly oriented, highly dense thermal carbon nanotube fibers, and the resulting carbon nanotube fibers have the advantages of high strength, high toughness, and high thermal conductivity.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A method for preparing high-strength, high-thermal-conductivity carbon nanotube fibers includes the following steps:

[0009] Carbon nanotubes and chlorosulfonic acid are mixed to obtain a spinning solution;

[0010] The spinning solution is extruded into a primary coagulation bath for solidification to obtain nascent filaments; the solvent in the primary coagulation bath is dichloromethane.

[0011] The nascent filaments are solidified in a secondary coagulation bath and then heated and stretched to obtain the high-strength, high-thermal-conductivity carbon nanotube fibers; the solvent in the secondary coagulation bath is ethanol.

[0012] Preferably, the carbon nanotubes are few-walled carbon nanotubes; the aspect ratio of the carbon nanotubes is greater than 5000, the residual catalyst content is less than 2 wt%, and the I in the Raman spectrum is... G / I D The value is not less than 40.

[0013] Preferably, the mass fraction of carbon nanotubes in the spinning solution is 0.75% to 2%.

[0014] Preferably, the extrusion rate of the spinning solution is 0.05 to 2 mL / min.

[0015] Preferably, the residence time of the filaments in the primary coagulation bath is 3-15 seconds, and the temperature of the primary coagulation bath is 22-30°C; the residence time of the filaments in the secondary coagulation bath is 5-10 seconds, and the temperature of the secondary coagulation bath is 22-30°C.

[0016] Preferably, the heating and stretching is performed by passing the filaments obtained after the secondary coagulation bath through a filament drying device under tension stretching conditions.

[0017] Preferably, the filament drying device is a hot tunnel; the residence time of the filaments obtained after the secondary coagulation bath in the hot tunnel is 5 to 10 seconds.

[0018] Preferably, the heating temperature for the heating and stretching is 100-400°C, and the stretching ratio is 1-2.

[0019] Preferably, the apparatus for preparing the high-strength, high-thermal-conductivity carbon nanotube fiber includes: an extrusion device, a primary coagulation bath, a first guide roller, a secondary coagulation bath, a second guide roller, a heating channel, a third guide roller, and a winding device; the primary coagulation bath is located at the outlet of the extrusion device; the primary coagulation bath, the first guide roller, the secondary coagulation bath, the second guide roller, the heating channel, the third guide roller, and the winding device are arranged sequentially in the drawing direction of the filament.

[0020] Preferably, the high-strength, high-thermal-conductivity carbon nanotube fiber has a diameter of 8–30 μm, a tensile breaking strength of 1–3.6 GPa, a breaking elongation of 2–2.6%, and a thermal conductivity of 212–521 W / mK.

[0021] This invention provides a method for preparing high-strength, high-thermal-conductivity carbon nanotube fibers, comprising the following steps: mixing carbon nanotubes and chlorosulfonic acid to obtain a spinning solution; extruding the spinning solution into a primary coagulation bath for solidification to obtain nascent fibers; the solvent used in the primary coagulation bath is dichloromethane; the nascent fibers are solidified in a secondary coagulation bath and then heated and stretched to obtain high-strength, high-thermal-conductivity carbon nanotube fibers; the solvent used in the secondary coagulation bath is ethanol. This invention uses chlorosulfonic acid to prepare the spinning solution and dichloromethane as the first coagulation bath. Taking advantage of the slow diffusion rate of chlorosulfonic acid in dichloromethane solvent, the nascent filaments are uniformly shrunken and coagulated during the double diffusion process. Under the stretching action, the nascent filaments are immersed in the second coagulation bath, where residual chlorosulfonic acid solvent diffuses into the second coagulation bath. Simultaneously, the stretching action of the first and second coagulation baths further improves the orientation and density of the fiber. Subsequently, through heating and stretching, the residual solvent in the second coagulation bath is removed, ultimately obtaining high-strength, high-thermal-conductivity carbon nanotube fibers with a rounded macrostructure and a dense microstructure.

[0022] The method provided by this invention can solve key technical problems in conventional carbon nanotube fiber wet spinning technology, such as low uniformity of fiber internal structure, difficulty in increasing draw ratio, and decreased fiber density due to insufficient double diffusion process caused by rapid coagulation of nascent fibers. The carbon nanotube fibers prepared using the method of this invention have an adjustable diameter in the range of 8–30 μm, a tensile breaking strength of 1.0–3.6 GPa, an elongation at break of 2–2.6%, and a thermal conductivity of 212–521 W / m·K. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the apparatus used to prepare high-strength and high-thermal-conductivity carbon nanotube fibers according to the present invention, wherein: 1-extrusion device, 2-first-stage coagulation bath, 3-first guide roller, 4-second-stage coagulation bath, 5-second guide roller, 6-heat channel, 7-third guide roller, 8-winding device;

[0024] Figure 2 The following are performance test images of the few-walled carbon nanotubes used in the embodiments of the present invention, wherein: (a) is a transmission electron microscope image; (b) is a magnified transmission electron microscope image; (c) is a Raman spectrum; and (d) is the thermogravimetric analysis result.

[0025] Figure 3 The images shown are performance test images of the carbon nanotube fibers prepared in Example 1, where: (a) is a SEM image, (b) is a cross-sectional image of the fiber obtained by focused ion beam cutting, (c) is a TEM image of the cross-section of the fiber obtained by focused ion beam radial cutting, and (d) is a TEM image of the cross-section of the fiber obtained by focused ion beam axial cutting.

[0026] Figure 4 The image on the right is an enlarged view of the part within the box on the left.

[0027] Figure 5 The image shown is a SEM image of the carbon nanotube fibers prepared in Example 3. The image on the right is an enlarged view of the part within the box on the left.

[0028] Figure 6 SEM image of the carbon nanotube fibers prepared in Example 4;

[0029] Figure 7 SEM image of the carbon nanotube fibers prepared in Example 5;

[0030] Figure 8 SEM image of the carbon nanotube fibers prepared in Comparative Example 1.

[0031] Figure 9 SEM image of the carbon nanotube fibers prepared in Comparative Example 2;

[0032] Figure 10SEM image of the carbon nanotube fibers prepared in Comparative Example 3.

[0033] Figure 11 SEM image of the carbon nanotube fibers prepared in Comparative Example 4.

[0034] Figure 12 Stress-strain curves of carbon nanotube fibers prepared in Examples 1, 4, 5 and Comparative Example 2; Detailed Implementation

[0035] This invention provides a method for preparing high-strength, high-thermal-conductivity carbon nanotube fibers, comprising the following steps:

[0036] Carbon nanotubes and chlorosulfonic acid are mixed to obtain a spinning solution;

[0037] The spinning solution is extruded into a primary coagulation bath for solidification to obtain nascent filaments; the solvent in the primary coagulation bath is dichloromethane.

[0038] The nascent filaments are solidified in a secondary coagulation bath and then heated and stretched to obtain high-strength, high-thermal-conductivity carbon nanotube fibers; the solvent in the secondary coagulation bath is ethanol.

[0039] This invention mixes carbon nanotubes and chlorosulfonic acid to obtain a spinning solution. In this invention, the carbon nanotubes are preferably few-walled carbon nanotubes; specifically, the few-walled carbon nanotubes are single-walled, double-walled, or triple-walled carbon nanotubes; the aspect ratio of the carbon nanotubes is preferably greater than 5000, more preferably 5000–6000, the residual catalyst content is preferably less than 2 wt%, and the Raman spectrum shows I0... G / I D The concentration of the carbon nanotubes is preferably not less than 40, more preferably 40-50; the concentration of the chlorosulfonic acid is preferably 99.5%; the mass fraction of carbon nanotubes in the spinning solution is preferably 0.75%-2%, more preferably 1-1.5%; the present invention does not have special requirements for the mixing method of the carbon nanotubes and chlorosulfonic acid, as long as the carbon nanotubes are fully dispersed in the chlorosulfonic acid. In a specific embodiment of the present invention, it is preferable to add the carbon nanotubes to the chlorosulfonic acid, and then stir the mixture in a dual-center disperser at a speed of 3000 r / min for 10 min to obtain a uniform and stable spinning solution.

[0040] After obtaining the spinning solution, the present invention extrudes the spinning solution into a primary coagulation bath for solidification to obtain nascent filaments; the solvent of the primary coagulation bath is dichloromethane. In the present invention, the residence time of the filaments in the primary coagulation bath is preferably 3-15s, more preferably 5-10s, and the temperature of the primary coagulation bath is preferably 22-30℃, more preferably 25℃; the present invention preferably uses an extrusion device to extrude the spinning solution into the primary coagulation bath; the extrusion device preferably includes a syringe and a spinneret; the inner diameter of the spinneret is preferably 60-80 micrometers, and the extrusion rate of the spinning solution is preferably 0.05-0.2mL / min; after the spinning solution is extruded into the primary coagulation bath, chlorosulfonic acid slowly diffuses in dichloromethane, and the extruded solution stream shrinks and solidifies uniformly in the double diffusion to form continuous gel-like nascent filaments.

[0041] After obtaining the nascent filament, the present invention solidifies the nascent filament in a secondary coagulation bath and then heats and stretches it to obtain the high-strength, high-thermal-conductivity carbon nanotube fiber; the solvent of the secondary coagulation bath is ethanol. In the present invention, the residence time of the filament in the secondary coagulation bath is preferably 5-10 s, more preferably 6-8 s, and the temperature of the secondary coagulation bath is preferably 22-30℃, more preferably 25℃; in a specific embodiment of the present invention, the nascent filament is preferably introduced into the secondary coagulation bath by a guide roller. In the secondary coagulation bath, the residual chlorosulfonic acid in the nascent filament diffuses into the solvent of the secondary coagulation bath, further solidifies it, and improves the orientation and density of the fiber.

[0042] In this invention, the heating and stretching is preferably performed by passing the filaments obtained after the secondary coagulation bath through a filament drying device under tension stretching conditions; the filament drying device is preferably a hot tunnel; the residence time of the filaments obtained after the secondary coagulation bath in the hot tunnel is preferably 5-10 s, more preferably 6-8 s; the heating temperature for heating and stretching is preferably 100-400℃, more preferably 200-300℃, and the stretching ratio is preferably 1-2, more preferably 1.6-2. This invention removes residual solvent from the filaments obtained after the secondary coagulation bath through heating and stretching, ultimately obtaining high-strength, high-thermal-conductivity carbon nanotube fibers with a rounded macrostructure and a dense microstructure; simultaneously, by controlling the stretching ratio during heating and stretching, this invention can change the fiber orientation, especially when the stretching ratio is 1.6-2, resulting in carbon nanotube fibers with high orientation, good thermal conductivity, and excellent mechanical properties.

[0043] In a specific embodiment of the present invention, the filaments solidified in the secondary coagulation bath are preferably introduced into the hot channel by the guide roller, and the carbon nanotube fibers after passing through the hot channel are preferably wound and collected by the take-up roller. The draw ratio can be adjusted by adjusting the tension generated by the guide roller and the take-up roller.

[0044] In this invention, the apparatus for preparing the high-strength, high-thermal-conductivity carbon nanotube fiber, according to the fiber drawing direction, preferably includes: an extrusion device, a primary coagulation bath, a first guide roller, a secondary coagulation bath, a second guide roller, a heating channel, a third guide roller, and a winding device; the primary coagulation bath is located at the outlet of the extrusion device; the primary coagulation bath, the first guide roller, the secondary coagulation bath, the second guide roller, the heating channel, the third guide roller, and the winding device are arranged sequentially in the fiber drawing direction; the extrusion device preferably includes an injector and a spinneret, the inner diameter of which will not be described further; the winding device is preferably a winding roller. Figure 1 This is a schematic diagram of the apparatus for preparing the high-strength, high-thermal-conductivity carbon nanotube fibers, wherein: 1-extrusion device, 2-primary coagulation bath, 3-first guide roller, 4-secondary coagulation bath, 5-second guide roller, 6-heat channel, 7-third guide roller, 8-winding device; The following is in conjunction with... Figure 1 The method of the present invention is described in detail as follows: the spinning solution is extruded from the extrusion device 1 into the primary coagulation bath 2, and the resulting nascent filament enters the secondary coagulation bath 4 under the traction of the first guide roller 3. The filament produced in the secondary coagulation bath 4 enters the hot channel 6 under the traction of the second guide roller 5. After passing through the hot channel 6, the filament enters the winding device 8 under the action of the third guide roller 7 for winding, and the finished product is obtained.

[0045] In this invention, the diameter of the high-strength, high-thermal-conductivity carbon nanotube fiber is preferably 8–30 μm, the elongation at break is 2–2.6%, the tensile breaking strength is preferably 1–3.6 GPa, more preferably 1.35–3.6 GPa, even more preferably 2.2–3.6 GPa, and the thermal conductivity is preferably 212–521 W / m·K, more preferably 322–521 W / m·K.

[0046] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0047] Example 1

[0048] (1) 90 mg of low-walled carbon nanotubes were dispersed in 6 mL of 99.5% chlorosulfonic acid and stirred at 3000 r / min for 10 min in a dual-center disperser to prepare a uniform and stable spinning solution with a mass fraction of 0.75 wt%.

[0049] (2) The spinning solution prepared in step (1) is transferred to the syringe of the extrusion device, and a spinneret with an inner diameter of 60 μm is selected. The extrusion rate is set to 0.05 mL / min. The carbon nanotube spinning solution in the syringe is injected into a primary coagulation bath containing dichloromethane to prepare nascent fibers. The nascent fibers are then introduced into a secondary coagulation bath containing ethanol for solidification via guide rollers. Subsequently, the fibers are tension-stretched in a hot tunnel at a drying temperature of 200 °C for further solidification. Finally, the carbon nanotube fibers are wound up by a collecting device. Under these conditions, the maximum draw ratio of the fibers is 2.

[0050] The few-walled carbon nanotubes used in this embodiment were characterized, and the results are as follows: Figure 2 As shown, Figure 2 In the image: (a) is a transmission electron microscope (TEM) image; (b) is a magnified TEM image; (c) is a Raman spectrum; (d) is the thermogravimetric analysis result; according to Figure 2 It is known that carbon nanotube raw materials used for spinning have structural characteristics such as high aspect ratio, low impurity content, and high crystallinity.

[0051] The carbon nanotube fibers prepared in this embodiment were structurally characterized, and the results are as follows: Figure 3 As shown, (a) is an SEM image, (b) is a cross-sectional image of the fiber obtained by focused ion beam cutting, (c) is a TEM image of the fiber cross-section obtained by focused ion beam radial cutting, and (d) is a TEM image of the fiber cross-section obtained by focused ion beam axial cutting. According to... Figure 3 As can be seen in (a), the prepared carbon nanotube fibers have uniform diameter and smooth surface. According to Figure 3 As can be seen from (b) in the figure, the fiber diameter is 10 ± 2 μm. According to... Figure 3 As can be seen in (c), carbon nanotubes exhibit a highly packed arrangement in the radial direction of the fiber. According to... Figure 3 As can be seen from (d) in the figure, the carbon nanotubes are arranged in a distinct orientation along the fiber axis.

[0052] The carbon nanotube fibers prepared in this embodiment were characterized for their properties. The results showed that the elongation at break was 2.2%, the tensile strength at break was 3.6 GPa, and the thermal conductivity of the fibers, determined using the 3ω steady-state method, was 521 W / m·K. The stress-strain curves of the carbon nanotube fibers are shown below. Figure 12 As shown.

[0053] Example 2

[0054] The other conditions are the same as in Example 1, except that the maximum draw ratio of the fiber in step 2 is changed to 1.6.

[0055] The carbon nanotube fibers prepared in this embodiment were structurally characterized. Figure 4 This is a SEM image of the carbon nanotube fibers prepared in this embodiment. Figure 4The image on the right is an enlarged view of the boxed area in the image on the left. Figure 4 The results show that the carbon nanotube fibers prepared in this embodiment have a uniform diameter but a rough surface structure, with a fiber diameter of 13±2μm.

[0056] The carbon nanotube fibers prepared in this embodiment were characterized for their properties. The results showed that the elongation at break of the carbon nanotube fibers was 2.35%, the tensile strength at break was 2.89 GPa, and the thermal conductivity of the carbon nanotube fibers was 322 W / m·K as determined by the 3ω steady-state method.

[0057] Example 3

[0058] The other conditions are the same as in Example 1, except that the maximum draw ratio of the fiber in step 2 is changed to 1.2.

[0059] The carbon nanotube fibers prepared in this embodiment were structurally characterized. Figure 5 This is a SEM image of the carbon nanotube fibers prepared in this embodiment. Figure 5 The image on the right is an enlarged view of the boxed area in the image on the left. Figure 5 The results show that the carbon nanotube fibers prepared in this embodiment have a uniform diameter but a rough surface structure, with a fiber diameter of 15±2μm.

[0060] The carbon nanotube fibers prepared in this embodiment were characterized for their properties. The results showed that the elongation at break of the carbon nanotube fibers was 2.45%, the tensile strength at break was 1.35 GPa, and the thermal conductivity of the carbon nanotube fibers was 212 W / m·K as determined by the 3ω steady-state method.

[0061] Example 4

[0062] Other conditions were the same as in Example 1, except that the content of low-walled carbon nanotubes in the spinning solution was adjusted to 1.25 wt%.

[0063] The carbon nanotube fibers prepared in this embodiment were structurally characterized. Figure 6 SEM images of the carbon nanotube fibers prepared in this embodiment show that the surface structure of the carbon nanotube fibers prepared in this embodiment is relatively dense. The elongation at break of the carbon nanotube fibers was tested to be 2.55%, the tensile strength at break was 2.23 GPa, and the thermal conductivity of the fibers, determined using the 3ω steady-state method, was 415 W / m·K. The stress-strain curve of the carbon nanotube fibers is shown below. Figure 12 As shown.

[0064] Example 5

[0065] The other conditions are the same as in Example 1, except that the drying temperature of the hot tunnel is adjusted to 400°C.

[0066] The carbon nanotube fibers prepared in this embodiment were structurally characterized. Figure 7 SEM images of the carbon nanotube fibers prepared in this embodiment show that the surface structure of the carbon nanotube fibers prepared in this embodiment is relatively dense. The elongation at break of the carbon nanotube fibers was tested to be 2%, the tensile strength at break was 2.83 GPa, and the thermal conductivity of the fibers, determined using the 3ω steady-state method, was 468 W / m·K. The stress-strain curves of the carbon nanotube fibers are shown below. Figure 12 As shown.

[0067] Comparative Example 1

[0068] The other conditions are the same as in Example 1, except that the primary coagulation bath is replaced with dimethyl sulfoxide.

[0069] The structure of the carbon nanotube fibers prepared in this comparative example was characterized. Figure 8 The image shows a SEM image of the carbon nanotube fibers prepared in this comparative example. The results indicate that the prepared carbon nanotube fibers exhibit poor shrinkage, a loose fiber surface, and the bundles fail to solidify sufficiently during the coagulation bath, shrinking into filaments and thus unable to pass through the guide roller into the secondary coagulation bath. Furthermore, due to the small sample size, it is impossible to obtain fiber performance data through mechanical and thermal tests.

[0070] Comparative Example 2

[0071] The other conditions were the same as in Example 1, except that the secondary coagulation bath process was removed, and the fibers were obtained directly.

[0072] The structure of the carbon nanotube fibers prepared in this comparative example was characterized. Figure 9 SEM images of the carbon nanotube fibers prepared in this comparative example show that the microstructure of the prepared carbon nanotube fibers is relatively dense. The absence of a secondary coagulation bath resulted in insufficient fiber coagulation and an irregular macroscopic morphology. The elongation at break of the carbon nanotube fibers was tested to be 2.6%, the tensile strength at break was 1.98 GPa, and the thermal conductivity, determined using the 3ω steady-state method, was 489 W / m K. The stress-strain curves of the carbon nanotube fibers are shown below. Figure 12 As shown. By comparing with the carbon nanotube fibers obtained in Example 1, it can be seen that the tensile breaking strength of the fibers obtained in Comparative Example 2 is significantly lower, and the thermal conductivity is also reduced. The above results indicate that omitting the secondary coagulation bath results in a lower degree of fiber orientation, leading to poorer mechanical properties of the fibers.

[0073] Comparative Example 3

[0074] The other conditions are the same as in Example 1, except that the secondary coagulation bath is replaced with water.

[0075] The structure of the carbon nanotube fibers prepared in this comparative example was characterized. Figure 10SEM images of the carbon nanotube fibers prepared in this comparative example show that the fiber skin structure exhibits a groove-like defect structure. The elongation at break of the carbon nanotube fiber was tested to be 2.8%, the tensile strength at break was 1.62 GPa, and the thermal conductivity, determined using the 3ω steady-state method, was 235 W / m K. The results in Comparative Example 3 indicate that the groove-like structure in the fiber surface skin results in poor mechanical properties of the fiber.

[0076] Comparative Example 4

[0077] The other conditions are the same as in Example 1, except that the secondary coagulation bath is replaced with an acetone-water mixed solvent.

[0078] The structure of the carbon nanotube fibers prepared in this comparative example was characterized. Figure 11 SEM images of the carbon nanotube fibers prepared in this comparative example show that the fibers were not fully solidified, the cortex structure was not dense enough, and unsolidified dendritic bundles were distributed on the surface. The elongation at break of the carbon nanotube fibers was tested to be 2.9%, the tensile strength at break was 1.45 GPa, and the thermal conductivity, determined using the 3ω steady-state method, was 192 W / m K. The results in Comparative Example 4 indicate that replacing the secondary coagulation bath with an acetone-water mixed solvent resulted in a less dense cortex structure, leading to poorer mechanical properties.

[0079] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength, high-thermal-conductivity carbon nanotube fibers, characterized in that, Includes the following steps: Carbon nanotubes and chlorosulfonic acid are mixed to obtain a spinning solution; The spinning solution is extruded into a primary coagulation bath for solidification to obtain nascent filaments; the solvent in the primary coagulation bath is dichloromethane. The nascent filaments are solidified in a secondary coagulation bath and then heated and stretched to obtain the high-strength, high-thermal-conductivity carbon nanotube fibers. The solvent in the secondary coagulation bath is ethanol. The heating temperature for the heating and stretching is 100–400°C, and the stretching ratio is 1.6–2. The tensile strength of the high-strength, high-thermal-conductivity carbon nanotube fibers is 2.2–3.6 GPa, and the thermal conductivity is 322–521 W / m·K.

2. The preparation method according to claim 1, characterized in that, The carbon nanotubes are few-walled carbon nanotubes; the aspect ratio of the carbon nanotubes is greater than 5000, the residual catalyst content is less than 2 wt%, and the I in the Raman spectrum is [missing information]. G / I D The value is not less than 40.

3. The preparation method according to claim 1, characterized in that, The mass fraction of carbon nanotubes in the spinning solution is 0.75% to 2%.

4. The preparation method according to claim 1, characterized in that, The extrusion rate of the spinning solution is 0.05–2 mL / min.

5. The preparation method according to claim 1, characterized in that, The residence time of the filaments in the primary coagulation bath is 3–15 s, and the temperature of the primary coagulation bath is 22–30 ℃; the residence time of the filaments in the secondary coagulation bath is 5–10 s, and the temperature of the secondary coagulation bath is 22–30 ℃.

6. The preparation method according to claim 1, characterized in that The heating and stretching process involves passing the filaments obtained after the secondary coagulation bath through a filament drying device under tension stretching conditions.

7. The preparation method according to claim 6, characterized in that, The filament drying device is a hot tunnel; the residence time of the filaments obtained after the secondary coagulation bath in the hot tunnel is 5-10 seconds.

8. The preparation method according to claim 1, characterized in that, The apparatus for preparing the high-strength, high-thermal-conductivity carbon nanotube fibers includes: an extrusion device, a primary coagulation bath, a first guide roller, a secondary coagulation bath, a second guide roller, a heating channel, a third guide roller, and a winding device; the primary coagulation bath is located at the outlet of the extrusion device; the primary coagulation bath, the first guide roller, the secondary coagulation bath, the second guide roller, the heating channel, the third guide roller, and the winding device are arranged sequentially in the drawing direction of the filament.

9. The preparation method according to claim 1, characterized in that, The high-strength, high-thermal-conductivity carbon nanotube fibers have a diameter of 8–30 μm and a breaking elongation of 2–2.6%.

Images