Method for optimizing carbon nanotube fiber structure through post-treatment

Abstract

The invention discloses a method for optimizing a carbon nanotube fiber structure through post-treatment, which comprises the following steps: S1, immersing a carbon nanotube fiber into a protonic acid solution, and carrying out drafting treatment on the carbon nanotube fiber in the protonic acid solution, the drafting treatment being cyclic drafting; and S2, transferring the carbon nanotube fibers treated in the step S1 into a coagulating bath solution for densification treatment. According to the post-treatment method of the carbon nanotube fiber, the carbon nanotube fiber is fully swelled in the solution by virtue of the protonation effect of protonic acid on the carbon nanotube, and a large number of entanglement sites of the fiber are opened in the process; at the moment, the fibers are circularly drafted in a liquid-phase environment, so that the fibers are fully expanded and better orientation is realized at the same time; the density of the drafted fiber is improved through coagulating bath, and finally the carbon nanotube fiber with high density and high orientation degree is obtained and shows excellent mechanical properties.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of carbon materials, and particularly relates to a method for optimizing the structure of carbon nanotube fibers through post-treatment. BACKGROUND

[0002] Carbon nanotubes have excellent mechanical properties, and their tensile strength and Young's modulus are as high as 100 GPa and 1 TPa, respectively. Carbon nanotube fibers are one-dimensional macroscopic assemblies of carbon nanotubes, and are expected to inherit the excellent mechanical properties of carbon nanotubes at the microscale. However, the mechanical properties of carbon nanotube fibers are far from the intrinsic properties of single carbon nanotubes, which is mainly due to the problems of low density, disordered orientation, single and weak inter-tube interaction in carbon nanotube fibers.

[0003] Improving the mechanical properties of carbon nanotube fibers is a problem to be solved in the field. SUMMARY

[0004] In order to solve the above problems, the present application provides a method for optimizing the structure of carbon nanotube fibers through post-treatment and carbon nanotube fibers prepared by the method.

[0005] The present application provides a method for optimizing the structure of carbon nanotube fibers through post-treatment, which comprises: S1, immersing carbon nanotube fibers into a protonic acid solution, and performing a drawing treatment on the carbon nanotube fibers in the solution environment, wherein the drawing treatment is a cyclic drawing; and S2, transferring the carbon nanotube fibers treated in the step S1 into a coagulation bath solution for densification treatment.

[0006] According to an embodiment of the present application, the protonic acid is chlorosulfonic acid, oleum or methanesulfonic acid or an aqueous solution thereof, and the mass percentage of the protonic acid in the protonic acid solution is 95%-100%.

[0007] According to another embodiment of the present application, in the step S1, the carbon nanotube fibers are immersed in the protonic acid solution for 1-30 min, preferably 3-10 min, and then drawn.

[0008] According to another embodiment of the present application, the cyclic drawing treatment has a drawing number of 2-50 times, a drawing ratio of 5%-100%, a single cycle drawing ratio of 3%-5%, a single cycle backtracking ratio of 0.5%-2%, and a drawing rate of 1% / min-10% / min; preferably, the cyclic drawing has a drawing number of 4-10 times, a drawing ratio of 10%-30%, and a single cycle drawing rate of 3% / min-5% / min.

[0009] According to another embodiment of the present application, the single cycle drawing includes a drawing stage and a back-drawing stage, the drawing stage adopts multi-stage drawing, the number of times of the multi-stage drawing is 2-5, the single-stage drawing ratio is 1%-1.25%, and the drawing rate is 1% / min-5% / min; preferably, the number of times of the multi-stage drawing is 3-4.

[0010] According to another embodiment of the present application, the multi-stage drawing and / or the cycle drawing adopts mechanical force.

[0011] According to another embodiment of the present application, the coagulation bath solution is a combination of one or more of acetone, dichloromethane, N-methyl pyrrolidone, etc.; preferably, the coagulation bath solution is acetone.

[0012] According to another embodiment of the present application, the carbon nanotube fiber is prepared by a floating catalyst vapor deposition method.

[0013] The present application also provides a carbon nanotube fiber prepared by the post-treatment method.

[0014] According to an embodiment of the present application, the fiber diameter of the carbon nanotube fiber is 10-100 μm, and the tensile strength is 4.0 GPa or higher; preferably, 5.4 GPa or higher; more preferably, 6 GPa or higher.

[0015] The post-treatment method of the carbon nanotube fiber of the present application uses the protonation of the carbon nanotube fiber by a protonic acid to make the carbon nanotube fiber fully swell in a solution, during which a large number of entanglement sites of the fiber are opened, and at this time, the fiber is subjected to a certain proportion of cycle drawing in a liquid phase environment to realize better orientation while fully swelling; the fiber after drawing is subjected to a coagulation bath to improve the density of the fiber, and finally, a carbon nanotube fiber with high density and high orientation is obtained, which exhibits excellent mechanical properties. The cycle drawing adopted by the present application can avoid the risk of fiber breakage during the drawing process compared to one-time drawing; at the same time, the drawing process is carried out in a liquid phase, which can avoid the decrease of mechanical properties caused by oxidation of the fiber due to contact with air. The post-treatment method of the present application has low requirements for equipment, is simple to operate, and is easy to mass-produce, and can realize continuous production of high-strength carbon nanotube fibers. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a schematic diagram explaining the cycle drawing process.

[0017] Figure 2 is a schematic diagram explaining the multi-stage cycle drawing process.

[0018] Figure 3 is a schematic diagram of multi-stage and / or cycle drawing using mechanical force.

[0019] Figure 4 is a schematic diagram illustrating the uniformity test method.

[0020] Figure 5 is a SEM photo of the carbon nanotube fiber prepared in Example 1. DETAILED DESCRIPTION

[0021] The application will be described in detail below with specific embodiments.

[0022] The post-treatment method of the carbon nanotube fiber comprises: S1, immersing the carbon nanotube fiber into a protonic acid solution, and performing a drawing treatment on the carbon nanotube fiber in the solution environment, wherein the drawing treatment is a cyclic drawing; and S2, transferring the carbon nanotube fiber treated in the step S1 into a coagulation bath solution to perform a densification treatment.

[0023] In the step S1, the carbon nanotube fiber is immersed into the protonic acid solution, and the volume expansion caused by the protonation of the carbon nanotube fiber by the protonic acid is used to fully open the entanglement sites. In addition, the strength of the protonation can cause the fiber to expand in volume to different degrees, and selecting a protonic acid that can cause the carbon nanotube fiber to expand in volume to a large degree can better use the volume expansion to open the entanglement sites and improve the orientation degree of the carbon nanotube. The protonic acid can be chlorosulfonic acid, oleum, methanesulfonic acid, etc. Preferably, it is chlorosulfonic acid. Through in-situ observation under an optical microscope, the volume of the fiber can expand to nearly 10 times of its original volume in the chlorosulfonic acid, so that the entanglement sites can be more easily opened.

[0024] The dispersant of the protonic acid solution is water, and the mass percentage of the protonic acid in the protonic acid solution is 95%-100%. When the mass percentage of the protonic acid in the protonic acid solution is 100%, the solution is the protonic acid without water.

[0025] In the optional embodiment, the carbon nanotube fiber is immersed in the protonic acid solution for 1-30 min before being drawn. Immersing for a certain period of time can make the fiber fully expand, so that the subsequent drawing process can more easily open the entanglement. The specific immersion time can be selected according to the type and concentration of the protonic acid, and preferably, it is 3-10 min. The treatment time will affect the performance of the fiber. If the treatment time is short, the degree of opening of the fiber entanglement is small, and the improvement of the performance of the fiber is not large. If the treatment time is too long, a large number of groups will be introduced to the surface of the fiber, which will cause the performance of the fiber to decrease. Preferably, the treatment time is within 3-10 min, the protonation degree of the fiber is good, and the influence on the structure of the fiber itself is small, and the performance of the fiber is better.

[0026] The drawing treatment of the application adopts a cyclic drawing, such as Figure 1As shown, cyclic drafting refers to the process where the fiber is stretched to a certain draft ratio in a protic acid solution, the drafting force is removed, and the fiber contracts and rolls back a certain distance, repeating this process multiple times. During cyclic drafting, in the isothermal time period between two adjacent drafts (the time period when the drafting rate is 0, the isothermal time is 5-15s), the fiber rolls back a certain distance. Cyclic drafting means that the fiber has both elongation and contraction in the length direction. The number of cyclic drafting cycles in the protic acid solution is 2-50 times, with a draft ratio of 5%-100% (relative to the original fiber length), preferably 4-10 cycles with a draft ratio of 10%-30%. The draft ratio per cycle is 3%-5%, and the rollback ratio per cycle is 0.5%-2%. The drafting rate is 1% / min-10% / min, preferably 3% / min-5% / min.

[0027] A single cycle of drafting includes a drafting stage and a backtracking stage, where the drafting stage can be implemented using multi-stage drafting. For example... Figure 2 As shown, multi-stage drafting refers to repeatedly stretching to achieve a predetermined draft ratio, maintaining the tensile force to keep the draft ratio constant during the isothermal time period between adjacent drafts (the time period when the drafting rate is 0, and the isothermal time is 5-15s). During multiple drafting processes, there is no shrinkage in the fiber length direction; it can be understood as progressive drafting and elongation. The number of multi-stage drafting cycles in a single drafting cycle is 2-5 times, preferably 3-4 times. The single-stage draft ratio is 1%-1.25%, and the drafting rate is 1% / min-5% / min.

[0028] In an optional implementation, when the drawing stage of the cyclic drawing adopts multi-stage drawing, the single-stage drawing ratio is the single-cycle drawing ratio / the number of multi-stage drawing times. For example, the drawing ratio of the single-cycle drawing stage is 10% of the original length. If the drawing stage adopts five-stage drawing, the single-stage drawing ratio is 2.

[0029] The effect of different drawing ratios on the mechanical properties of fibers varies. When the drawing ratio is small, the carbon nanotube bundles in the fiber still have a lot of entanglement, the fiber orientation is not optimal, and the stress transmission during drawing is affected, thus failing to maximize performance improvement. When the fiber drawing ratio is greater than 30%, slippage occurs between the bundles in the fiber, the reduced contact area leads to a decrease in the inter-bundle force, and thus the fiber performance deteriorates. The drawability and maneuverability of fibers vary when drawn at different rates. When the fiber drawing rate is low, prolonged treatment in strong acid solutions can affect the fiber structure. When the fiber drawing rate is too high, the fiber itself becomes unstable, and the probability of breakage and unevenness increases. Those skilled in the art can select appropriate drawing ratios and drawing rates according to specific circumstances.

[0030] Cyclic drawing is performed using mechanical force. As Figure 3 Schematic diagram of cyclic drawing using mechanical force.

[0031] In step S2, the coagulation bath solution is a combination of one or more of acetone, dichloromethane, N-methyl pyrrolidone, etc. Preferably, the coagulation bath solution is acetone. The purpose of this step is that when the fiber enters the coagulation bath from the protonic acid solution, due to the difference in concentration, temperature, etc., double diffusion occurs between the solution and the solution in the coagulation bath, and during the double diffusion process, the fiber changes from a volume expansion state to a dense state, realizing the final shaping of the fiber.

[0032] In addition to the above necessary steps, the method of the present application can also include other auxiliary steps, such as but not limited to, transferring the fiber through the coagulation bath to water for washing, drying steps; and a purification step of the carbon nanotube fiber before the carbon nanotube is immersed in the protonic acid solution to remove impurities in the fiber.

[0033] The method of the present application is suitable for any carbon nanotube fiber containing entanglement sites, such as but not limited to carbon nanotube fibers prepared by floating catalyst vapor deposition method.

[0034] The carbon nanotube fiber obtained by the post-processing method of the present application has high orientation and high density, and therefore has good mechanical properties. The fiber diameter of the carbon nanotube fiber of the present application is 10-100 μm, and the tensile strength can reach 4.0 GPa or more. Preferably, it is 5.4 GPa or more. More preferably, it is 6 GPa or more.

[0035] The present application is further described below by specific examples. However, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present application. In the following examples and comparative examples, the reagents, materials and instruments used are commercially available unless otherwise specified.

[0036] Example 1

[0037] Take a carbon nanotube fiber with a diameter of 30 microns prepared by floating catalyst vapor deposition method.

[0038] Prepare a solution of chlorosulfonic acid. The mass percentage of chlorosulfonic acid is 99%, and the solvent is water.

[0039] After immersing the carbon nanotube fiber in the chlorosulfonic acid solution for 3 min, cyclic drawing is performed. The drawing times are 4 times, the final drawing ratio is 10%, the single drawing ratio is 3% of the original length, the fiber backtracking ratio after single drawing is 0.5% of the original length, and the pause time between two adjacent cyclic drawings is 10 s.

[0040] The fiber after the drawing treatment is transferred to a coagulation bath. The coagulation bath is acetone. The fiber is coagulated in the coagulation bath for 5 min.

[0041] The fiber after the coagulation bath is transferred to water for washing and drying to obtain the carbon nanotube fiber after the treatment of this example.

[0042] The carbon nanotube fiber before and after the treatment is tested for performance.

[0043] The test of the orientation degree uses a wide-angle X-ray diffractometer (WAXS). The test process is the scattering of X-ray diffraction experiment with θ greater than 5° and the use of a two-dimensional detector at the same time. The data of the two-dimensional image and the two-dimensional diffraction pattern recorded by the two-dimensional detector are processed, analyzed and interpreted. The test instrument of the tensile strength is a tensile testing machine. The test instrument of the uniformity is a scanning electron microscope (SEM). The uniformity test refers to selecting the SEM overall morphology magnification of the fiber, as shown in the SEM photo, selecting five positions of the fiber from left to right, and statistically testing the diameter and calculating the variance. If the ratio of the variance to the average value is less than 10%, the uniformity is evaluated as “good”; if the ratio of the variance to the average value is between 10% and 20%, the uniformity is evaluated as “better”; and if the ratio of the variance to the average value is greater than 20%, the uniformity is evaluated as “poor”. Figure 4

[0044] The test results are shown in Table 1.

[0045] Example 2

[0046] Except that the multi-stage and cyclic drawing is used, other parameters are the same as those in Example 1.

[0047] The process of the multi-stage and cyclic drawing is that each single drawing in the cyclic drawing process is replaced by multi-stage drawing.

[0048] The number of cyclic drawing is 4 times. The single drawing in the cyclic drawing is replaced by multi-stage drawing, and the number of multi-stage drawing is 4 times. The final drawing ratio is 10%. The single cyclic drawing ratio is 3% of the original length. The single cyclic drawing uses 4-stage multi-stage drawing. The single multi-stage drawing is 0.75% of the original length. The pause time between two adjacent multi-stage drawings is 10 s. The fiber backtracking ratio after the single cyclic drawing is 0.5% of the original length. The pause time between two adjacent cyclic drawings is 10 s.

[0049] The performance parameters of the fiber after the treatment of this example are shown in Table 1.

[0050] Comparative Example 1

[0051] Except that the drawing is performed once, other parameters are the same as those in Example 1. The parameters of the fiber after the treatment of this example are shown in Table 1.

[0052] ​Table 1 Comparison of properties of carbon nanotube fibers prepared in each example and comparative example

[0053]

[0054] From the table data, it can be seen that the orientation of the carbon nanotube fiber is improved after the cyclic drawing, thus improving the strength and uniformity of the fiber. Figure 5 The SEM photo of the carbon nanotube fiber prepared in Example 1 is shown, which also proves that the carbon nanotube fiber prepared in the present application has good uniformity.

[0055] The above disclosed preferred embodiments of the present application are only used to help explain the present application. The preferred embodiments do not describe all the details and limit the present application to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the present application. The present application selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and utilize the present application. The present application is limited only by the claims and their full scope and equivalents.

Claims

1. A method for post-processing optimization of carbon nanotube fiber structure, characterized in that, include: S1, immerse the carbon nanotube fiber in a protic acid solution, and perform a stretching treatment on the carbon nanotube fiber in the solution environment, wherein the stretching treatment is cyclic stretching; as well as S2, the carbon nanotube fibers treated in step S1 are transferred to a coagulation bath solution for densification.

2. The method according to claim 1, characterized in that, The protic acid solution is chlorosulfonic acid, fuming sulfuric acid, or methanesulfonic acid or an aqueous solution thereof, and the mass percentage of protic acid in the protic acid solution is 95%-100%.

3. The method according to claim 1, characterized in that, In step S1, the carbon nanotube fibers are immersed in the protic acid solution for 1-30 minutes and then stretched.

4. The method according to claim 1, characterized in that, The cyclic drawing process involves 2-50 draws, a draw ratio of 5%-100%, a single-cycle draw ratio of 3%-5%, a single-cycle backtracking ratio of 0.5%-2%, and a draw rate of 1% / min-10% / min. Preferably, the cyclic drawing process involves 4-10 draws, a draw ratio of 10%-30%, and a single-cycle draw rate of 3% / min-5% / min.

5. The method according to claim 4, characterized in that, The single cycle of drawing includes a drawing stage and a backtracking stage. The drawing stage employs multi-stage drawing, with the number of multi-stage drawing cycles being 2-5 times, the single-stage drawing ratio being 1%-1.25%, and the drawing rate being 1% / min-5% / min. Preferably, the number of multi-stage drawing cycles is 3-4 times.

6. The method according to claim 1, characterized in that, The cyclic stretching is performed using mechanical force.

7. The method according to claim 1, characterized in that, The coagulation bath solution is one or more of acetone, dichloromethane, N-methylpyrrolidone, etc.; preferably, the coagulation bath solution is acetone.

8. The method according to claim 1, characterized in that, The carbon nanotube fibers were prepared by floating catalyst vapor deposition.

9. A carbon nanotube fiber, characterized in that, Obtained by the method of any one of claims 1-8.

10. The carbon nanotube fiber according to claim 9, characterized in that, The carbon nanotube fibers have a diameter of 10–100 μm and a tensile strength of 4.0 GPa or higher; preferably, 5.4 GPa or higher. More preferably, it is above 6 GPa.

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