CN115418748B - A method for preparing circular cross-section highly conductive carbon nanotube fibers - Google Patents

Abstract

The invention relates to the field of preparing high-performance carbon nanotube fibers, specifically a method for preparing circular cross-section highly conductive carbon nanotube fibers. N-methylpyrrolidone, which can slow down the fiber coagulation rate, is used as a first-level coagulation bath. The carbon nanotube liquid crystal spinning solution dispersed in chlorosulfonic acid is injected into the first-level coagulation bath containing N-methylpyrrolidone to obtain a semi-solid Carbon nanotube fiber; then the semi-solid nanotube fiber is introduced into a secondary coagulation bath filled with ethanol through a smooth guide rail for complete solidification, and the fiber is pulled, rolled and collected, and finally dried and formed in a natural state. The invention utilizes the low diffusion rate of chlorosulfonic acid in N-methylpyrrolidone to solidify the fibers into fibers evenly and slowly in N-methylpyrrolidone, while ensuring the full stretching and refinement of the fibers and improving the The alignment and density of carbon nanotubes ultimately resulted in highly conductive carbon nanotube fibers with circular cross-sections.

Description

A method for preparing circular cross-section highly conductive carbon nanotube fibers

Technical field

The invention relates to the field of preparing high-performance carbon nanotube fibers, specifically a method for preparing circular cross-section highly conductive carbon nanotube fibers.

Background technique

Carbon nanotube fiber is a macro-scale fiber material assembled from single carbon nanotubes. It has excellent mechanical, electrical and thermal properties, and has the advantages of low density, large specific surface area and high aspect ratio. It is expected to become the next generation Lightweight, high-strength and high-conductivity material. Carbon nanotube fibers with excellent performance can be widely used in aerospace, wearable electronic devices, solar cells, supercapacitors, artificial muscles and other fields.

There are three main methods for preparing carbon nanotube fibers: array spinning, chemical vapor deposition direct spinning and wet spinning. The array spinning method is a method of pulling vertical arrays of carbon nanotubes prepared by chemical vapor deposition so that the carbon nanotubes are connected end to end to form fibers. The density of the fibers obtained by this method is low, so The electrical properties are poor (Document 1: Jiang K, Li Q, Fan S. Nature. 2002, 419 (6909), 801.). The chemical vapor deposition spinning method is a one-step method for preparing carbon nanotube fibers: by using an ethanol/ferrocene/thiophene solution as a liquid carbon source, it is introduced into a high-temperature reaction furnace at a certain injection rate under the action of a carrier gas. The liquid carbon source is vaporized in a high-temperature reactor to obtain a stocking-like carbon nanotube fiber precursor structure, which is then collected outside the reactor to obtain carbon nanotube fibers (Document 2: Koziol K, Vilatela J, Windle A, et al .Science 2007,318(5858),1892-1895.). Wet spinning is a spinning method that first prepares carbon nanotubes into a uniform and stable carbon nanotube dispersion, and then injects it into a coagulation bath for solidification and shaping (Document 3: Vigolo B, Penicaud A, Coulon C, et al .Science.2000,290(5495),1331-1334.). Since fibers produced by wet spinning have higher orientation and density, their electrical properties are better than those produced by dry spinning. In addition, wet spinning is easier to industrialize, thereby achieving large-scale production of carbon nanotube fibers.

The strength and electrical conductivity of carbon nanotube fibers currently prepared by wet spinning are far lower than those of a single carbon nanotube. On the one hand, it is due to the uneven structure of the carbon nanotubes themselves (such as wall number, diameter, chirality, length, defects, etc.); on the other hand, it is due to the process of assembling nano-sized single carbon nanotubes into macro-sized carbon nanotube fibers. In the fiber spinning process, the contact resistance between the inner tubes of the fiber is relatively large due to poor orientation and density. In addition, due to the high solidification rate of the fiber during the wet spinning process, it shrinks rapidly in the coagulation bath. At this time, the fiber's cortex and The shrinkage of the core layer is not synchronized, resulting in uneven shrinkage. Therefore, the cross-section of the fiber is generally irregular in shape, and there are many grooves and wrinkles on the surface, which limits the accurate calculation and practical application of fiber conductivity (Document 4: Bucossi A R, Cress C D, Schauerman C M, et al. ACS Appl Mater Interfaces, 2015, 7(49): 27299-27305.).

Therefore, a major issue in preparing high-performance carbon nanotube fibers is: how to develop or improve carbon nanotube fiber spinning technology, prepare carbon nanotube fibers with high alignment, high density, and smooth surface, and break through the fiber assembly process. to overcome the technical bottlenecks in the industry, obtain highly conductive carbon nanotube fibers, and promote their large-scale application.

Contents of the invention

In view of the problems that the carbon nanotube spinning liquid shrinks rapidly in the coagulation bath during the conventional liquid phase spinning process, resulting in multiple wrinkles and irregular shapes on the fiber surface, the purpose of the present invention is to provide a fiber with a smooth surface, high alignment, and The preparation method of high-density, circular cross-section and highly conductive carbon nanotube fibers solves the technical problems of conventional liquid-phase spinning methods that result in uneven fiber shrinkage and insufficient stretching and refinement due to rapid solidification of carbon nanotubes. The length of the carbon nanotube fiber produced is unlimited, the diameter is adjustable in the range of 5 to 30 μm, the electrical conductivity reaches 0.5 to 1.5×10 ⁷ S/m, and the tensile strength is 0.5 to 2 GPa.

The technical solution of the present invention is:

A method for preparing circular cross-section highly conductive carbon nanotube fibers, using N-methylpyrrolidone as the primary coagulation bath, ethanol, acetone, water or dimethyl sulfoxide as the secondary coagulation bath; using chlorosulfonic acid in the The low diffusion rate in N-methylpyrrolidone causes the carbon nanotube spinning liquid to uniformly shrink into fibers in N-methylpyrrolidone, and enters the secondary coagulation bath under the action of traction force for stretching and thinning to improve The alignment and density of carbon nanotubes ultimately lead to highly conductive carbon nanotube fibers with circular cross-sections.

The preparation method of the circular cross-section highly conductive carbon nanotube fiber, the carbon nanotube is one, two or three types of single-walled, double-walled, few-walled carbon nanotubes, carbon nanotube spinning The liquid is a liquid crystal solution of carbon nanotubes dispersed in chlorosulfonic acid, and the concentration of carbon nanotubes is 1 to 2 wt%.

In the preparation method of the circular cross-section highly conductive carbon nanotube fiber, the N-methylpyrrolidone solution is used as a first-level coagulation bath for the carbon nanotube fiber, the temperature of the first-level coagulation bath is -10~80°C, and the curing time is 3~30s.

According to the preparation method of circular cross-section highly conductive carbon nanotube fibers, the carbon nanotube fibers in the first-level coagulation bath are semi-solid and their diameter is 20 to 50 μm.

In the preparation method of the circular cross-section highly conductive carbon nanotube fiber, the secondary coagulation bath uses ethanol, acetone, water or dimethyl sulfoxide as the coagulant, and the temperature of the secondary coagulation bath is -10~30°C. The curing time is 3~30s.

According to the preparation method of circular cross-section highly conductive carbon nanotube fibers, the drawing ratio of the carbon nanotube fibers is controlled within the range of 120 to 260%.

According to the preparation method of the circular cross-section highly conductive carbon nanotube fiber, the prepared carbon nanotube fiber has a circular cross-section, few pores and cracks inside the fiber, and the fiber surface is smooth and uniform.

According to the preparation method of circular cross-section highly conductive carbon nanotube fibers, the length of the spun carbon nanotube fibers is not limited, the diameter is adjustable between 5 and 30 μm, and the electrical conductivity is 0.5 to 1.5×10 ⁷ S/m. , the tensile strength is 0.5~2GPa.

The design idea of the present invention is:

The present invention uses N-methylpyrrolidone as a first-level coagulation bath, and utilizes the characteristics of slow diffusion and low diffusion rate of chlorosulfonic acid in N-methylpyrrolidone, so that the carbon nanotube fibers shrink uniformly and slowly solidify in the first-level coagulation bath. , to obtain semi-solid single-wall, double-wall, and few-wall carbon nanotube fibers with smooth surfaces and circular cross-sections; at the same time, a secondary solidification process and drawing technology are added to allow the semi-solid fibers to fully shrink, stretch, and refine , improves the orientation, alignment and density of the fiber, thereby improving the conductivity and strength of the fiber.

The advantages and beneficial effects of the present invention are:

1. The present invention solves the problem that in the conventional liquid phase spinning process, the carbon nanotube spinning solution rapidly solidifies in the coagulation bath, resulting in uneven fiber shrinkage, resulting in uneven radial structure, uneven stretching and refinement of the carbon nanotubes. Sufficient problems were solved, and carbon nanotube fibers with a circular fiber cross-section and a smooth and uniform surface were prepared.

2. The present invention solves the problem that the fiber is not fully stretched and refined due to the rapid solidification of carbon nanotubes during the conventional spinning process, so that the fiber can be fully stretched and refined, and the orientation and consistency of the fiber are improved. Density, thereby improving the conductivity and strength of the fiber.

3. The fiber length prepared by the present invention is not limited, the diameter is adjustable in the range of 5-30 μm, the electrical conductivity is 0.5-1.5×10 ⁷ S/m, and the tensile strength is 0.5-2GPa.

4. The method of the present invention can continuously prepare high-performance carbon nanotube fibers, which are expected to find important applications in the fields of high-performance cables, flexible sensors, aerospace, military industry, and national defense.

5. The present invention uses non-volatile N-methylpyrrolidone to replace the volatile acetone solution in the traditional wet spinning process as the first-level coagulation bath, reducing the volatilization of toxic substances and the loss of the coagulation bath during the spinning process. , not only optimizes the operating environment, but also reduces spinning costs.

Description of the drawings

Figure 1. Schematic diagram of the device for preparing carbon nanotube fibers with circular cross-section, smooth surface, and high conductivity. In the figure, 1. Spinning solution extrusion device; 2. Primary coagulation bath; 3. Guide rail; 4. Secondary coagulation bath; 5. Fiber collection device.

Figure 2. Structural characterization diagram of carbon nanotubes. (a) TEM photo of single-walled carbon nanotubes; (b) TEM photo of double-walled carbon nanotubes; (c) TEM photo of few-walled carbon nanotubes.

Figure 3. Structural characterization diagram of carbon nanotube fibers. (a) and (b) are low-magnification and high-magnification SEM photos of carbon nanotube fibers prepared using N-methylpyrrolidone as the first-level coagulation bath; (c) and (d) are the carbon nanotube fibers prepared using acetone as the first-level coagulation bath. Low-magnification and high-magnification SEM photos of carbon nanotube fibers; (e) and (f) are low-magnification and high-magnification SEM photos of carbon nanotube fibers prepared using N-methylpyrrolidone as the first-level coagulation bath without pulling.

Figure 4. Cross-sectional characterization of carbon nanotube fibers. (a) and (b) are low-magnification and high-magnification focused ion beam cutting cross-sections of carbon nanotube fibers prepared using N-methylpyrrolidone as the first-stage coagulation bath; (c) and (d) are using acetone as the coagulation bath. Low-magnification and high-magnification focused ion beam cutting cross-sections of the prepared carbon nanotube fibers.

Figure 5. Comparison of tensile strength of carbon nanotube fibers. In the figure, the abscissa Strain represents strain (%), and the ordinate Tensile Stress represents tensile strength (MPa).

Figure 6. Comparison of conductive properties of carbon nanotube fibers. In the abscissa, SWCNT Fiber represents single-walled carbon nanotube fiber, DWCNT Fiber represents double-walled carbon nanotube fiber, FWCNT Fiber represents few-walled carbon nanotube fiber, and the ordinate Conductivity represents conductivity (MS/m).

Figure 7. Optical photos of short carbon nanotube fibers prepared using dichlorobenzene as the coagulation bath.

Detailed ways

During the specific implementation process, the invention proposes a method for preparing carbon nanotube fibers with circular cross-section, smooth surface, and high conductivity. N-methylpyrrolidone, which can slow down the coagulation rate of the fiber, is used as a first-level coagulation bath. The acid-dispersed carbon nanotube liquid crystal spinning liquid is injected into a first-level coagulation bath filled with N-methylpyrrolidone to obtain semi-solid carbon nanotube fibers; the semi-solid nanotube fibers are then introduced into the ethanol-filled chamber through a smooth guide rail. It is completely solidified in a secondary coagulation bath, and the fibers are pulled, rolled and collected, and finally dried and formed in a natural state.

As shown in Figure 1, the circular cross-section, smooth surface, and highly conductive carbon nanotube fiber preparation device of the present invention mainly includes: spinning solution extrusion device 1, primary coagulation bath 2, guide rail 3, and secondary coagulation bath 4 , Fiber collection device 5, its specific structure and preparation process are as follows: a guide rail 3 for carbon nanotube fibers is arranged above one side of the corresponding primary coagulation bath 2 and secondary coagulation bath 4, and the other side of the primary coagulation bath 2 A spinning liquid extrusion device 1 is provided above, and a fiber collection device 5 is provided above the secondary coagulation bath 4; the spinning liquid extrusion device 1 is composed of a vertically placed syringe pump and a syringe, and the spinning liquid output end of the syringe pump Connected to the syringe, the syringe pump can precisely control the extrusion rate of the spinning solution.

A needle tip is installed at the lower part of the syringe and extends into the first-level coagulation bath 2. The inner diameter of the needle tip is 0.11~0.21mm, the length is 14~50mm, and the extrusion rate is 0.03~0.1mL/min. The carbon nanotube spinning liquid passes through the needle tip and enters the first-level coagulation bath 2 to form stable and continuous semi-solid carbon nanotube fibers. The semi-solid carbon nanotube fibers are then introduced into the secondary coagulation bath 4 through the smooth guide rail 3 for further solidification. Finally, it is wound and collected on the fiber collection device 5, and then naturally dried and formed. The speed of the collecting device is adjustable, which controls the drawing ratio during fiber preparation. The present invention uses N-methylpyrrolidone as a primary coagulation bath to prepare semi-solid carbon nanotube fibers, and simultaneously uses a secondary coagulation bath to finally prepare highly conductive carbon nanotube fibers with circular cross-sections and smooth surfaces.

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is described in detail below through examples and drawings, but this is not intended to limit the scope of protection of the present application.

Example 1

In this embodiment, the preparation method of single-walled carbon nanotube fibers with circular cross-section and smooth surface includes the following steps:

(1) Disperse 80 mg of single-walled carbon nanotubes (Figure 2a) in 3 mL of chlorosulfonic acid with a concentration of 99.5%, stir in a high-speed mixer at a speed of 3000 r/min for 5 min, and prepare a mass fraction of 1.6 wt%. Uniform and stable single-walled carbon nanotube spinning solution.

(2) Transfer the single-walled carbon nanotube spinning solution prepared in step (1) to the syringe of the extrusion device, select a needle tip with an inner diameter of 0.18mm and a length of 50mm, and set the extrusion rate to 0.07mL/min. The carbon nanotube spinning liquid in the syringe is injected into the primary coagulation bath containing N-methylpyrrolidone to prepare semi-solid single-walled carbon nanotube fibers, and then introduced into the secondary coagulation bath containing ethanol through a smooth guide rail. Cure in bath. Finally, the single-walled carbon nanotube fibers are pulled and continuously collected by a collection device. Under this condition, the maximum fiber drawing ratio is 240%.

Conduct structural characterization of the single-walled carbon nanotube fibers prepared in step (2). Figure 3(a) and Figure 3(b) are low- and high-magnification SEM photos of the spun fibers. It can be seen that the single-walled carbon nanotube fibers have uniform diameters, smooth surfaces, and obvious single-walled carbon nanotubes inside the fibers along the fiber axis. Orientation arrangement, fiber diameter is 15±3μm. Figure 4(a) and Figure 4(b) are cross-sectional views of fibers cut by focused ion beam. It can be seen that the cross-section of the fiber is circular with very few internal voids and cracks.

Characterize the properties of the single-walled carbon nanotube fibers prepared in step (2). As shown in Figure 6, the electrical conductivity of the single-walled carbon nanotube fiber was determined to be 1×10 ⁷ S/m using the four-wire method, and the tensile strength of the fiber was 1.1GPa (Figure 5).

Example 2

In this embodiment, step (1) is exactly the same as step (1) in Embodiment 1, except that double-walled carbon nanotubes are used (Fig. 2b).

Step (2) is exactly the same as step (2) in Example 1. The inner diameter of the selected needle tip capillary is 0.16 mm, the extrusion rate is 0.05 mL/min, and the maximum fiber draw ratio under these conditions is 220%.

The structure and properties of the prepared double-walled carbon nanotube fibers were characterized. The SEM photos showed that the double-walled carbon nanotube fibers had a uniform diameter and a smooth surface. The double-walled carbon nanotubes inside the fiber were arranged at a high density along the fiber axis. The spun double-walled carbon nanotubes were The nanotube fiber diameter is 5±2μm. Focused ion beam cutting was used to observe the cross-section of the fiber, and it was found that the cross-section of the fiber was round and dense inside. As shown in Figure 6, the conductivity of the double-walled carbon nanotube fiber was measured to be 1.5×10 ⁷ S/m and the tensile strength was 1.2GPa using the four-wire method.

Example 3

In this embodiment, step (1) is exactly the same as step (1) in Embodiment 1, except that few-wall carbon nanotubes are used (Fig. 2c).

Step (2) is exactly the same as step (2) in Example 1. The inner diameter of the selected needle tip capillary is 0.16 mm, the extrusion rate is 0.05 mL/min, and the maximum fiber draw ratio under these conditions is 260%.

The structure and properties of the prepared few-wall carbon nanotube fibers were characterized. The SEM photos showed that the few-wall carbon nanotube fibers had a uniform diameter and a smooth surface. The few-wall carbon nanotubes inside the fiber were arranged at a high density along the fiber axis. The spun few-wall carbon nanotubes were The nanotube fiber diameter is 10±3μm. Focused ion beam cutting was used to observe the cross-section of the fiber, and it was found that the cross-section of the fiber was round and dense inside. As shown in Figure 6, the conductivity of the few-wall carbon nanotube fiber was measured to be 1.2×10 ⁷ S/m and the tensile strength was 1 GPa using the four-wire method.

Comparative example 1

In this comparative example, step (1) is exactly the same as step (1) of Example 1.

Step (2) is exactly the same as step (2) of embodiment (1). Just replace N-methylpyrrolidone in the first-level coagulation bath with acetone as the coagulation bath. Under this condition, the maximum fiber draw ratio is 110%.

The structure and properties of the prepared single-walled carbon nanotube fibers were characterized. Figure 3(c) and Figure 3(d) are low-magnification and high-magnification SEM photos of the spun fibers. It can be seen that the diameter of the single-walled carbon nanotube fibers is relatively uniform, as 25±5μm, with wrinkles on the surface, and single-walled carbon nanotubes inside the fiber are oriented along the fiber axis. Figure 4(c) and Figure 4(d) are cross-sectional views of fibers cut by focused ion beam. It is found that the cross-section of the fiber is irregular in shape, and there are large gaps and cracks inside the fiber. The conductivity of the single-walled carbon nanotube fiber was measured to be 2×10 ⁶ S/m and the tensile strength was 0.35GPa using the four-wire method.

Comparative example 2

In this comparative example, step (1) is exactly the same as step (1) of Example 1.

Step (2) is exactly the same as step (2) in Example 1. Just replace N-methylpyrrolidone in the first-level coagulation bath with o-dichlorobenzene as the coagulation bath, and the fiber cannot be stretched during the entire spinning process.

As shown in Figure 7, during the spinning process, it was found that continuous single-walled carbon nanotube fibers could not be formed, and only short fibers with a length of 1 to 3 cm could be prepared. The conductivity of the single-walled carbon nanotube fiber was measured using the four-wire method to be 8×10 ⁵ S/m, and the tensile strength was 0.3GPa.

Comparative example 3

In this comparative example, step (1) is exactly the same as step (1) of Example 1.

The secondary coagulation step is not performed in step (2), and the rest is the same as step (2) in Example 1. Under this condition, the maximum fiber drawing ratio is 150%.

Only semi-solid single-walled carbon nanotube fibers can be obtained. The fibers cannot shrink and form in their natural state and remain in a semi-solid state. The conductivity of the single-walled carbon nanotube fiber was measured by the four-wire method to be 7×10 ⁵ S/m, and the tensile strength was 0.2GPa.

Comparative example 4

In this comparative example, step (1) is exactly the same as step (1) of Example 1.

In step (2), the fiber collection device only plays a simple winding role and does not stretch the fibers. The remaining steps are the same as step (2) in Example 1.

The structure and performance of the fiber were characterized. Figure 3(e) and Figure 3(f) are low-magnification and high-magnification SEM photos of the spun fiber. It can be seen that the diameter of the prepared single-walled carbon nanotube fiber is larger, 30 to 40 μm. Moreover, the carbon nanotubes inside the fiber are arranged disorderly and have no obvious orientation. The conductivity of the single-walled carbon nanotube fiber was measured by the four-wire method to be 5×10 ⁵ S/m, and the tensile strength was 0.4GPa.

The results of the examples and comparative examples show that the present invention uses N-methylpyrrolidone as the first-level coagulation bath to slow down the shrinkage rate of the fiber and obtain semi-solid carbon nanotube fibers with smooth surfaces and ideally circular cross-sections; combined with the second-level coagulation bath The solidification effect and the stretching effect of the collection device on the fibers can fully stretch and refine the fibers, improving the orientation and density of the fibers; ultimately, circular cross-sections, smooth surfaces, and high alignment can be prepared High-density, high-conductivity carbon nanotube fibers. The circular cross-section, highly conductive carbon nanotube fiber prepared for the first time by this invention is expected to be applied in aerospace, wearable electronic devices, solar cells, supercapacitors, artificial muscles and other fields.

Although the present invention has been described in detail with general descriptions and specific embodiments above, it is obvious to those skilled in the art that some modifications or improvements can be made based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims (8)

1. A method for preparing circular cross-section highly conductive carbon nanotube fibers, characterized in that N-methylpyrrolidone is selected as the primary coagulation bath, and ethanol, acetone, water or dimethyl sulfoxide is used as the secondary coagulation bath. ; Inject the carbon nanotube spinning solution dispersed in chlorosulfonic acid into a first-level coagulation bath filled with N-methylpyrrolidone. The carbon nanotube spinning solution is a carbon nanotube liquid crystal solution dispersed in chlorosulfonic acid, using The low diffusion rate of chlorosulfonic acid in N-methylpyrrolidone allows the carbon nanotube spinning solution to uniformly shrink into fibers in N-methylpyrrolidone, and enter the secondary coagulation bath under the action of traction force for stretching and Refinement to improve the alignment and density of carbon nanotubes, and finally obtain highly conductive carbon nanotube fibers with circular cross-sections. 2. The method for preparing circular cross-section highly conductive carbon nanotube fibers according to claim 1, wherein the carbon nanotubes are one, two or more of single-wall, double-wall, and few-wall carbon nanotubes. For the three combinations, the concentration of carbon nanotubes is 1~2wt%. 3. The method for preparing circular cross-section highly conductive carbon nanotube fibers according to claim 1, wherein the N-methylpyrrolidone solution is used as a first-level coagulation bath for the carbon nanotube fibers, and the temperature of the first-level coagulation bath is The temperature is -10~80 ℃, and the curing time is 3~30 s. 4. According to the preparation method of circular cross-section highly conductive carbon nanotube fibers according to claim 1 or 3, it is characterized in that the carbon nanotube fibers in the first-level coagulation bath are semi-solid and their diameter is 20~50 μm. 5. The method for preparing circular cross-section highly conductive carbon nanotube fibers according to claim 1, characterized in that the secondary coagulation bath uses ethanol, acetone, water or dimethyl sulfoxide as the coagulant, and the secondary coagulation bath The temperature of the bath is -10~30 ℃, and the curing time is 3~30 s. 6. The method for preparing circular cross-section highly conductive carbon nanotube fibers according to claim 1, characterized in that the drawing ratio of the carbon nanotube fibers is controlled within the range of 120 to 260%. 7. The method for preparing circular cross-section highly conductive carbon nanotube fibers according to claim 1, characterized in that the prepared carbon nanotube fibers have a circular cross-section, few pores and cracks inside the fiber, and a smooth fiber surface. And uniform. 8. The method for preparing circular cross-section highly conductive carbon nanotube fibers according to claim 1, characterized in that the length of the spun carbon nanotube fibers is unlimited, the diameter is adjustable between 5 and 30 μm, and the conductivity is The rate is 0.5×10 ⁷ S/m ~1.5×10 ⁷ S/m, and the tensile strength is 0.5~2 GPa.