CN114477147A - Post-treatment method for improving densification degree of carbon nanotube fiber - Google Patents
Post-treatment method for improving densification degree of carbon nanotube fiber Download PDFInfo
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- CN114477147A CN114477147A CN202210197265.XA CN202210197265A CN114477147A CN 114477147 A CN114477147 A CN 114477147A CN 202210197265 A CN202210197265 A CN 202210197265A CN 114477147 A CN114477147 A CN 114477147A
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Abstract
The invention discloses a post-treatment method for improving the densification degree of carbon nano tube fibers. The post-processing method comprises the following steps: fully soaking original carbon nanotube fibers in chlorosulfonic acid, taking out the carbon nanotube fibers, and standing the carbon nanotube fibers in the air to enable the chlorosulfonic acid to fully react with moisture in the air; soaking the carbon nano tube fiber in chlorosulfonic acid again at a high speed to rapidly expand the carbon nano tube fiber, and continuously standing the carbon nano tube fiber in the chlorosulfonic acid until the volume of the carbon nano tube fiber is reduced; slowly taking the mixture out of the chlorosulfonic acid, and standing the mixture in the air to ensure that the chlorosulfonic acid and the moisture in the air are fully reacted; and finally, carrying out high-temperature annealing treatment under the vacuum condition to obtain the high-densification carbon nanotube fiber. The post-treatment method provided by the invention has the advantages that the operation process is simple, the existence of micro-gaps in the fiber is reduced, the densification degree of the carbon nanotube fiber is improved, the actual cross-sectional area of the carbon nanotube fiber is greatly reduced, and the electrical property of the carbon nanotube fiber is improved.
Description
Technical Field
The invention relates to a post-treatment method capable of effectively improving the densification degree of carbon nanotube fibers, and belongs to the technical field of post-treatment of carbon nanotubes.
Background
The carbon atom P orbital electron composing the carbon nano tube can form delocalized pi bond in a large range, the special conjugated effect of the electronic structure endows the carbon nano tube with unique electrical property, and the unique length-diameter ratio of the carbon nano tube monomer ensures that the carbon nano tube has a great electron mean free path. Research shows that the average electron free path of the carbon nano tube can exceed 30 mu m (copper is 40nm), the maximum electron average free path has important significance for improving the conductivity of the carbon nano tube, and the theoretical conductivity of the carbon nano tube can be one order of magnitude higher than that of copper. Meanwhile, carbon nanotubes also have the excellent characteristics of low density, good chemical stability, high thermal conductivity, high mechanical strength and the like, so the carbon nanotubes are one of candidates of a new generation of high-conductivity materials.
However, the macroscopic bodies of carbon nanotubes in various forms are difficult to overcome the influence of a series of factors such as structural defects (such as more gaps existing inside the macroscopic bodies, less contact areas among the carbon nanotubes and poor orientation of the carbon nanotubes) in the preparation process, and finally the actual electrical properties of the macroscopic bodies of the carbon nanotubes are far from the theoretical properties. The electrical conductivity of the carbon nanotube fiber prepared by the existing floating catalysis method is usually two orders of magnitude lower than that of copper, and the electrical conductivity level is lower. In order to solve the problem of low electrical conductivity of the carbon nanotube fibers, one method adopted is to perform drawing in chlorosulfonic acid on the carbon nanotube fibers. However, this method can only raise the conductivity of carbon nanotube fiber to 2 × 106About S/m, the diameter (densification degree) of the carbon nanotube fiber obtained by the method is not obviously changed, and more micro-gaps still exist in the treated fiber, which are not beneficial to the interconnection of carbon nanotube monomers, and finally, the electrical property of the carbon nanotube fiber is poor.
The prior chlorosulfonic acid treatment process has the following defects:
(1) the existing chlorosulfonic acid treatment process cannot effectively remove tiny voids inside the carbon nanotube fibers and cannot effectively improve the densification degree of the fibers, thereby achieving the purpose of reducing the cross-sectional area of the fibers;
(2) the existing chlorosulfonic acid treatment process relates to the pyrolysis of sulfuric acid, the sulfuric acid can generate gas in the pyrolysis process, the decomposition of sulfuric acid molecules in the fiber and the generation of gas can further cause the increase of micro-voids in the fiber, and the cross-sectional area of the carbon nanotube fiber is increased, so that the final electrical property of the carbon nanotube fiber is not favorably improved;
(3) the apparent appearance of the carbon nanotube fiber is basically not changed by the existing chlorosulfonic acid treatment process, more fluffy microstructure similar to sponge still exists on the surface of the treated carbon nanotube fiber, and the phenomenon shows that the connection between the carbon nanotube and the carbon nanotube in the fiber is weaker, and the weak connection between the carbon nanotube monomers inevitably reduces the transmission capability of electrons between the carbon nanotube and the carbon nanotube, so that the macroscopic electrical property of the carbon nanotube fiber is reduced finally.
Disclosure of Invention
The invention mainly aims to provide a post-treatment method for improving the densification degree of carbon nanotube fibers so as to overcome the defects in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the embodiment of the invention provides a post-treatment method for improving the densification degree of carbon nanotube fibers, which comprises the following steps:
(1) fully soaking original carbon nanotube fibers in chlorosulfonic acid, taking out the carbon nanotube fibers, and standing the carbon nanotube fibers in the air to enable chlorosulfonic acid to fully react with moisture in the air to generate concentrated sulfuric acid;
(2) soaking the carbon nanotube fiber obtained in the step (1) in chlorosulfonic acid again at a first speed to rapidly expand the carbon nanotube fiber, and continuously standing in the chlorosulfonic acid until the diameter and the volume of the carbon nanotube fiber are reduced;
(3) taking the carbon nano tube fiber obtained in the step (2) out of chlorosulfonic acid at a second speed, standing in air, and enabling the chlorosulfonic acid to fully react with moisture in the air to generate concentrated sulfuric acid, wherein the first speed is higher than the second speed;
(4) and (4) carrying out high-temperature annealing treatment on the carbon nanotube fiber obtained in the step (3) under a vacuum condition, and volatilizing and removing concentrated sulfuric acid to obtain the high-densification carbon nanotube fiber.
In some embodiments, step (1) comprises: fully soaking the original carbon nanotube fibers in chlorosulfonic acid for 1-2 h, taking out the original carbon nanotube fibers, and standing the original carbon nanotube fibers in the air for 30-60 min to enable chlorosulfonic acid to fully react with water in the air to generate concentrated sulfuric acid.
In some embodiments, step (2) comprises: so as to: and (2) soaking the carbon nanotube fiber obtained in the step (1) in chlorosulfonic acid again within 3-5 seconds at a first speed, so that the volume of the carbon nanotube fiber is rapidly expanded to 10-30 times within 1 second, and the carbon nanotube fiber is cylindrical in appearance.
In some embodiments, step (2) comprises: and standing the expanded carbon nanotube fiber in chlorosulfonic acid for 3-6 h until the diameter and the volume of the carbon nanotube fiber are reduced.
In some embodiments, step (3) comprises: and (3) slowly taking the carbon nano tube fiber obtained in the step (2) out of chlorosulfonic acid at a second speed, keeping the taking-out process for more than 15 minutes, and standing in the air for 30-60 minutes to enable chlorosulfonic acid to fully react with moisture in the air to generate concentrated sulfuric acid.
The embodiment of the invention also provides the high-densification carbon nanotube fiber prepared by the method.
Furthermore, the line resistance of the high-densification carbon nanotube fiber is 20-30% of that of the original carbon nanotube fiber, and the electric conductivity of the high-densification carbon nanotube fiber is 500-600% of that of the original carbon nanotube fiber.
Further, the cross-sectional area of the high-densification carbon nanotube fiber is 25% -45% of that of the original carbon nanotube fiber.
Compared with the prior art, the invention has the advantages that:
1) the post-treatment method for improving the densification degree of the carbon nanotube fiber reduces the existence of micro gaps in the fiber, improves the densification degree of the carbon nanotube fiber, greatly reduces the actual cross-sectional area of the carbon nanotube fiber and further improves the electrical property of the carbon nanotube fiber;
2) the operation process is simple, and the effect is obvious; the fiber densification can improve the contact degree between the carbon nano tube monomers and the electron transmission efficiency between the carbon nano tube monomers, thereby achieving the purposes of reducing the resistance of the carbon nano tube fiber and improving the electrical property of the carbon nano tube fiber.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart of a post-treatment process for increasing the degree of densification of carbon nanotube fibers in accordance with an exemplary embodiment of the present invention;
FIG. 2 is a graph comparing the change in electrical properties of carbon nanotube fibers before and after densification in example 1 of the present invention;
FIGS. 3a and 3b are graphs comparing the change in the surface morphology of carbon nanotube fibers before and after densification in example 1 of the present invention, respectively;
FIGS. 4a and 4b are graphs comparing the change in the cross-sectional morphology of carbon nanotube fibers before and after densification in example 1 of the present invention, respectively;
FIG. 5 is a graph comparing the change in the cross-sectional area of carbon nanotube fibers before and after densification in example 1 of the present invention;
fig. 6a and 6b are comparative graphs of the surface topography of the carbon nanotube fiber after the conventional process in comparative example 1 and the treatment in example 1, respectively.
Detailed Description
In view of the defects in the prior art, the inventor of the present invention has made long-term research and great practice to provide the technical scheme of the present invention, which mainly starts with the protonation mechanism of chlorosulfonic acid, avoids the generation of gas in the sulfuric acid removal process through high-temperature annealing treatment under a vacuum condition, prevents the expansion action of the gas on carbon nanotube fibers, reduces the internal porosity of the fibers, effectively reduces the sectional area of the carbon nanotube fibers, improves the fiber densification degree, and effectively optimizes the microstructure of the carbon nanotube fibers. The technical solution, its implementation and principles, etc. will be further explained as follows.
It is to be noted that the definitions of the terms mentioned in the description of the present invention are known to those skilled in the art. For example, some of the terms are defined as follows:
carbon nanotube fibers: the macroscopic one-dimensional fiber material is formed by mutually connecting macroscopic one-dimensional carbon nano tubes which are oriented along a single direction.
One aspect of the embodiments of the present invention provides a post-treatment method for increasing the densification degree of carbon nanotube fibers, including:
(1) fully soaking original carbon nanotube fibers in chlorosulfonic acid, taking out the carbon nanotube fibers, and standing the carbon nanotube fibers in the air to enable chlorosulfonic acid to fully react with moisture in the air to generate concentrated sulfuric acid;
(2) soaking the carbon nanotube fiber obtained in the step (1) in chlorosulfonic acid again at a first speed to rapidly expand the carbon nanotube fiber, and continuously standing in the chlorosulfonic acid until the diameter and the volume of the carbon nanotube fiber are reduced;
(3) taking the carbon nano tube fiber obtained in the step (2) out of chlorosulfonic acid at a second speed, standing in air, and enabling the chlorosulfonic acid to fully react with moisture in the air to generate concentrated sulfuric acid, wherein the first speed is higher than the second speed;
(4) and (4) carrying out high-temperature annealing treatment on the carbon nanotube fiber obtained in the step (3) under a vacuum condition, and volatilizing and removing concentrated sulfuric acid to obtain the high-densification carbon nanotube fiber.
In some embodiments, the pristine carbon nanotube fibers comprise carbon nanotube ribbons, carbon nanotube fibers, and the like.
In some embodiments, step (1) comprises: fully soaking the original carbon nanotube fibers in chlorosulfonic acid for 1-2 h, taking out the original carbon nanotube fibers, and standing the original carbon nanotube fibers in the air for 30-60 min to enable chlorosulfonic acid to fully react with water in the air to generate concentrated sulfuric acid. The method skillfully utilizes the inherent characteristics of chlorosulfonic acid: chlorosulfonic acid easily infiltrates the carbon nanotube fiber, but electrostatic repulsion force brought by chlorosulfonic acid molecules is not enough to cause the fiber to generate violent expansion; when the fiber is taken out of chlorosulfonic acid, chlorosulfonic acid reacts with moisture in the air to form concentrated sulfuric acid, the concentrated sulfuric acid has strong water absorption, so that a large amount of moisture is absorbed in the fiber, when the fiber with a large amount of moisture is placed in chlorosulfonic acid again, the moisture in the fiber can react with chlorosulfonic acid molecules violently to form hydrogen chloride gas, the strong air pressure causes the fiber to expand instantly, and the expanded carbon nanotube fiber can contract slowly under the electrostatic repulsion action of the chlorosulfonic acid molecules to achieve the purpose of plastic deformation and roundness, but the contraction amount is small, and further densification needs vacuum annealing treatment.
In some embodiments, step (2) comprises: and (2) soaking the carbon nanotube fiber obtained in the step (1) in chlorosulfonic acid again at a first speed within 3-5 seconds (namely, at a faster speed), so that the volume of the carbon nanotube fiber is rapidly expanded to 10-30 times within 1 second, and the carbon nanotube fiber is cylindrical in appearance. The densification of the carbon nanotube fiber is based on the electrostatic interaction between the carbon nanotube monomers, the cylindrical shape of the fiber can promote more carbon nanotube monomers or the mutual attraction of more carbon nanotube bundles in a three-dimensional space, so that the tight connection between the carbon nanotubes is realized, and finally the densification of the carbon nanotube fiber is realized through electrostatic acting force. The rapid speed is adopted in the step, so that the violent reaction of water molecules and chlorosulfonic acid is needed, and if the putting speed is slow, the pressure of hydrogen chloride generated by the reaction of the water molecules and the chlorosulfonic acid is not enough to cause the violent expansion of the fibers, so that the purpose of fiber expansion cannot be achieved, and the putting speed must be fast enough.
In some embodiments, step (2) comprises: and standing the expanded carbon nanotube fiber in chlorosulfonic acid for 3-6 h until the diameter and the volume of the carbon nanotube fiber are reduced to 20-30% of the expanded volume, wherein the volume reduction is derived from the inherent van der Waals force of the carbon nanotube, and macromolecules tend to attract each other.
In some embodiments, step (3) comprises: and (3) slowly taking out the carbon nano tube fiber obtained in the step (2) from chlorosulfonic acid at a second speed (namely a slower speed), keeping the taking-out process for more than 15 minutes, and standing in the air for 30-60 min to enable chlorosulfonic acid to fully react with moisture in the air to generate concentrated sulfuric acid. At this time, the carbon nanotube fibers are quite fluffy, the mechanical properties of the fluffy fibers are extremely reduced, and if the carbon nanotube fibers are taken out at an excessively high speed, the carbon nanotube fibers are broken.
In some embodiments, step (4) comprises: keeping the carbon nano tube fiber obtained in the step (3) in a tensioned state, and then carrying out high-temperature annealing treatment in a vacuum tube furnace, wherein the temperature of the high-temperature annealing treatment is 150-350 ℃, and the vacuum degree is 1-4 multiplied by 10-4Pa, and the time of high-temperature annealing treatment is 15-25 h.
Specifically, the invention applies the slow volatilization process of chlorosulfonic acid and sulfuric acid under the vacuum condition, and the vacuum degree is 1-4 multiplied by 10-4Pa, and the evaporation temperature is between 150 and 350 ℃.
The invention starts from the action mechanism of chlorosulfonic acid on the carbon nano tube, and leads the carbon nano tube fiber to be sequentially soaked, expanded and stood in the chlorosulfonic acid through the development of a new process, thereby finally realizing the change of the appearance of the carbon nano tube fiber and greatly improving the densification degree of the carbon nano tube fiber.
Conductivity formula of fiber:
wherein R is the resistance, S is the cross-sectional area, and L is the length of the fiber.
According to the formula, when the number of the micro-voids in the carbon nanotube fiber is reduced, the cross-sectional area of the carbon nanotube fiber is also reduced, and the reduction of the cross-sectional area S is helpful for improving the electrical conductivity of the fiber; meanwhile, densification can also increase interconnection among carbon nanotube monomers in the fiber, so that the electron transmission efficiency among the carbon nanotube monomers is improved, and the aim of reducing the resistance R of the fiber is fulfilled; finally, the purpose of improving the electrical property of the carbon nano tube fiber is achieved by reducing R and S.
Another aspect of an embodiment of the present invention also provides a highly densified carbon nanotube fiber produced by the foregoing method.
Further, compared with the original carbon nanotube fiber, the line resistance of the high-densification carbon nanotube fiber is reduced to 20-30% of the original resistance, and the conductivity is improved to 500-600% of the original conductivity.
Further, compared with the original carbon nanotube fiber, the cross-sectional area of the high-densification carbon nanotube fiber is reduced to 25% -45% of the original cross-sectional area.
In conclusion, the invention applies the long-time protonation and short-time expansion treatment of the carbon nano tube fiber in chlorosulfonic acid; through the reaction of chlorosulfonic acid and carbon nano tube fiber, the reaction of chlorosulfonic acid and water in the air and the rapid expansion and slow contraction behavior of carbon nano tube fiber in chlorosulfonic acid, the appearance change and densification of the carbon nano tube fiber are realized.
The densified carbon nanotube fiber structure can promote the connection between the carbon nanotubes in the fiber, reduce the transmission barrier of electrons between the carbon nanotubes, improve the transmission capacity of the electrons between the carbon nanotubes and achieve the aim of reducing the fiber resistance of the carbon nanotubes. Finally, the electrical performance of the carbon nanotube fiber is greatly improved by reducing the cross-sectional area of the carbon nanotube fiber and reducing the fiber resistance.
The technical solutions of the present invention will be described in further detail below with reference to several preferred embodiments and accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out under conventional conditions or conditions recommended by the manufacturers.
Example 1
Referring to fig. 1, a post-treatment method for increasing the densification degree of carbon nanotube fibers according to the present embodiment includes the following specific steps:
(1) pretreatment of carbon nanotube fibers
Slowly putting carbon nanotube fibers with the length of 35-45 cm into a measuring cylinder filled with chlorosulfonic acid, and standing for about 1-2 hours to enable the chlorosulfonic acid to fully infiltrate the carbon nanotube fibers; then taking out the carbon nano tube fiber from chlorosulfonic acid, and standing in the air for about 30-60 min to enable chlorosulfonic acid and water in the air to react sufficiently to generate concentrated sulfuric acid; then, the carbon nano tube fiber is put into chlorosulfonic acid again at a fast speed (the fiber is completely put into chlorosulfonic acid solution within 3-5 seconds as far as possible to ensure that enough hydrogen chloride gas pressure is generated by reaction) within 3-5 seconds, so that the fiber is obviously expanded (the volume is expanded to 10-30 times of the original volume) in a short time, and the appearance of the fiber is changed into an obvious cylindrical shape; keeping the carbon nano tube fiber standing in chlorosulfonic acid for about 3-6 hours until the volume of the fiber is obviously reduced, as shown in figure 1; and slowly taking out the carbon nano tube fiber from chlorosulfonic acid, standing in the air for 30-60 min until the carbon nano tube fiber reacts with moisture in the air, wherein the duration of the whole taking-out process is not less than 15 minutes.
(2) Vacuum annealing treatment of carbon nanotube fiber
Fixing the carbon nanotube fiber treated in the step (1) on a quartz frame, keeping the carbon nanotube fiber in a tightened state in the process, and then placing the quartz frame in a vacuum tube furnace for high-temperature vacuum treatment; the treatment temperature is 150-350 ℃, and the vacuum degree is 1-4 multiplied by 10-4Pa, and the treatment time is about 15-25 h.
The effect of the invention on the carbon nano tube fiber is embodied as follows:
(1) effect on the Electrical Properties of carbon nanotube fibers
By the above steps of this example, it can be observed that the diameter of the carbon nanotube fiber is significantly reduced, and the resistance of the carbon nanotube fiberThe significant reduction occurs, and the pair of electrical properties of the carbon nanotube fiber before and after densification is as shown in fig. 2; the wire resistance of the carbon nanotube fiber is reduced to about 35 percent of the original wire resistance, meanwhile, the sectional area of the carbon nanotube fiber is reduced to one fourth to two thirds of the original sectional area, and after densification, the conductivity of the carbon nanotube fiber is increased to 3 multiplied by 106S/m。
(2) Influence on the surface appearance of carbon nanotube fibers
Fig. 3a and 3b show the comparison of the surface topography of carbon nanotube fibers before and after densification. The results show that there are more fluffy textures on the surface of the original carbon nanotube fiber, and some carbon nanotube bundles are in a certain suspended state, and meanwhile, it can be observed that there are more burrs of the carbon nanotubes on the surface of the carbon nanotube fiber, as shown in fig. 3 a. In contrast, after the carbon nanotube fiber is densified by the method of the embodiment of the present invention, the surface characteristics of the carbon nanotube fiber are significantly changed, no burr phenomenon is observed on the surface of the carbon nanotube fiber, no significant suspended state of the carbon nanotube bundle is observed, and it is found that a part of the carbon nanotube bundles are significantly merged, as shown by a circle in fig. 3b, which is not present in the raw carbon nanotube fiber.
(3) Influence on the cross-sectional shape and cross-sectional area of carbon nanotube fiber
FIGS. 4a and 4b are cross-sectional topographical views of carbon nanotube fibers before and after densification, as shown in FIG. 4a, the original carbon nanotube fibers have more voids in their cross-section, larger void sizes, and a distinct sponge-like structure; in contrast, no significant voids were observed in the cross-section of the carbon nanotube fiber after densification of the carbon nanotube fiber, as shown in fig. 4b, indicating that the degree of tissue densification inside the carbon nanotube fiber was significantly increased compared to the original carbon nanotube fiber.
FIG. 5 shows a comparison of the cross-sectional area of the original carbon nanotube fiber with the cross-sectional area of the densified carbon nanotube fiber, showing that the cross-sectional area of the original carbon nanotube fiber is larger, about 740 μm2Left and right, after densification, carbon nanotube fiber is cutThe area becomes 200 μm2About, the sectional area of the carbon nanotube fiber is changed into about one fourth of the original sectional area, and the equivalent diameter of the carbon nanotube fiber is also changed from the original 30.68 mu m to the densified 15.96 mu m, which can show that the densification greatly reduces the diameter of the carbon nanotube fiber.
Comparative example 1
In this comparative example, the carbon nanotube fiber was treated by a conventional densification process, i.e., the carbon nanotube fiber was drawn in chlorosulfonic acid.
Referring to fig. 6a, which shows the surface morphology of the carbon nanotube fiber treated by the conventional densification process in comparative example 1, and fig. 6b, which shows the surface morphology of the carbon nanotube fiber treated by the embodiment 1 of the present invention, it can be known that, by comparing the two morphologies, the method of embodiment 1 of the present invention reduces the existence of the micro voids inside the carbon nanotube fiber, the densification degree of the treated carbon nanotube fiber is significantly improved, the actual cross-sectional area of the carbon nanotube fiber is significantly reduced, and thus the electrical properties of the carbon nanotube fiber are improved.
In addition, the inventors of the present invention have also made experiments with other materials, process operations, and process conditions described in the present specification with reference to the above examples, and have obtained preferable results.
The aspects, embodiments, features and examples of the present invention should be considered as illustrative in all respects and not intended to be limiting of the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.
While the invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions and/or additions may be made and substantial equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (10)
1. A post-treatment method for improving the densification degree of carbon nanotube fibers is characterized by comprising the following steps:
(1) fully soaking original carbon nanotube fibers in chlorosulfonic acid, taking out the carbon nanotube fibers, and standing the carbon nanotube fibers in the air to enable chlorosulfonic acid to fully react with moisture in the air to generate concentrated sulfuric acid;
(2) soaking the carbon nanotube fiber obtained in the step (1) in chlorosulfonic acid again at a first speed to rapidly expand the carbon nanotube fiber, and continuously standing in the chlorosulfonic acid until the diameter and the volume of the carbon nanotube fiber are reduced;
(3) taking the carbon nano tube fiber obtained in the step (2) out of chlorosulfonic acid at a second speed, standing in air, and enabling the chlorosulfonic acid to fully react with moisture in the air to generate concentrated sulfuric acid, wherein the first speed is higher than the second speed;
(4) and (4) carrying out high-temperature annealing treatment on the carbon nanotube fiber obtained in the step (3) under a vacuum condition, and volatilizing and removing concentrated sulfuric acid to obtain the high-densification carbon nanotube fiber.
2. The post-processing method according to claim 1, characterized in that: the pristine carbon nanotube fibers comprise narrow bands of carbon nanotubes or carbon nanotube fibers.
3. The post-processing method according to claim 1, wherein the step (1) comprises: fully soaking the original carbon nanotube fibers in chlorosulfonic acid for 1-2 h, taking out the original carbon nanotube fibers, and standing the original carbon nanotube fibers in the air for 30-60 min to enable chlorosulfonic acid to fully react with water in the air to generate concentrated sulfuric acid.
4. The post-processing method according to claim 1, wherein the step (2) comprises: and (2) soaking the carbon nanotube fiber obtained in the step (1) in chlorosulfonic acid again within 3-5 seconds at a first speed, so that the volume of the carbon nanotube fiber is rapidly expanded to 10-30 times within 1 second, and the carbon nanotube fiber is cylindrical in appearance.
5. The post-processing method according to claim 4, wherein the step (2) comprises: and standing the expanded carbon nanotube fiber in chlorosulfonic acid for 3-6 h until the diameter and the volume of the carbon nanotube fiber are reduced.
6. The post-processing method according to claim 1, wherein the step (3) comprises: and (3) slowly taking the carbon nano tube fiber obtained in the step (2) out of chlorosulfonic acid at a second speed, keeping the taking-out process for more than 15 minutes, and standing in the air for 30-60 minutes to enable chlorosulfonic acid to fully react with moisture in the air to generate concentrated sulfuric acid.
7. The post-processing method according to claim 1, wherein the step (4) comprises: keeping the carbon nano tube fiber obtained in the step (3) in a tensioned state, and then carrying out high-temperature annealing treatment in a vacuum tube furnace, wherein the temperature of the high-temperature annealing treatment is 150-350 ℃, and the vacuum degree is 1-4 multiplied by 10-4Pa, and the time of high-temperature annealing treatment is 15-25 h.
8. Highly densified carbon nanotube fiber produced by the method of any one of claims 1-7.
9. The highly densified carbon nanotube fiber of claim 8, wherein: the line resistance of the high-densification carbon nanotube fiber is 20-30% of that of the original carbon nanotube fiber, and the conductivity of the high-densification carbon nanotube fiber is 500-600% of that of the original carbon nanotube fiber.
10. The highly densified carbon nanotube fiber of claim 8, wherein: the cross-sectional area of the high-densification carbon nanotube fiber is 25-45% of that of the original carbon nanotube fiber.
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