High-performance flexible carbon nanotube conductive composite fiber and its preparation method

Abstract

This application relates to a high-performance flexible carbon nanotube conductive composite fiber and its preparation method, belonging to the field of conductive fibers. Based on the wet spinning process of the dynamic bonding synergistic strengthening strategy, this application makes full use of the advantage that carbon nanotubes or their derivatives are easy to functionalize, introduces the reaction groups of carbon nanotubes or their derivatives and the end groups of TPU into the molecular necklace structure of dopamine or its derivatives at the same time, and further constructs a molecular necklace cross-linked multi-dimensional conductive network structure through chemical cross-linking of carbon nanotubes or their derivatives and physical cross-linking of TPU end groups respectively. The organic tight combination of zero-dimensional silver nanoparticles, one-dimensional carbon nanotubes or their derivatives and two-dimensional graphene or their derivatives is realized. It solves some problems existing in the existing carbon nanotube conductive composite fibers, such as the difficult uniform dispersion of conductive materials, small strain range, poor sensitivity and other technical problems.

Description

Technical Field

[0001] This application relates to the technical field of conductive fibers, and particularly relates to a high-performance flexible carbon nanotube conductive composite fiber and a preparation method thereof. Background Art

[0002] Conductive fibers with high flexibility and sensitive characteristics will promote their huge application prospects in various fields due to their characteristics such as being thin, light, portable, excellent electrical properties, and high integration, such as wearable displays, electronic skin, and human motion monitoring, etc.; while conductive fibers based on metals have defects such as a small strain range, low sensitivity, high hardness, and poor toughness, which often cause their functions to degenerate or be completely lost; therefore, it is inevitable to develop a new type of conductive fiber sensor with wide strain, sensitivity, and stability.

[0003] The rapid development of some conductive materials (such as carbon black, metal nanowires, carbon nanotubes, polyaniline, graphene, etc.) has opened up new ideas for the transformation and development of conductive fibers. In particular, carbon nanotubes, as one-dimensional nanomaterials, are lightweight and have a perfect hexagonal structure connection, with many extraordinary mechanical, electrical, and chemical properties. Currently, many studies have used the wet spinning method to prepare carbon nanotube fibers. For example, the Poulin research group at the University of Bordeaux 1 in France dispersed carbon nanotubes in an aqueous solution containing 1.0% sodium dodecyl sulfate (SDS), and then prepared carbon nanotube fibers by the wet spinning method in a PVA coagulation bath. The presence of PVA can improve the fiber-forming ability of the fibers and improve their mechanical properties. However, PVA is a non-conductive polymer, and a high proportion of PVA in carbon nanotube fibers will reduce the conductivity of the fibers (Vigolo, B.; Pénicaud, A.; Coulon, C.; Sauder, C.; Pailler, R.; Journet, C.; Bernier, P.; Poulin, P. Science 2000, 290(5495), 1331.). Therefore, in order to prepare carbon nanotube fibers without polymers, Kozlov et al. at Rice University dispersed carbon nanotubes in fuming sulfuric acid and then prepared carbon nanotube fibers by the wet spinning method. Since there is no polymer, the conductivity of the fibers can reach 500 S·cm-1. However, due to the protonation effect of concentrated sulfuric acid, it causes certain defects and pores on the surface of the fibers, and at the same time reduces the mechanical properties of the fibers. In addition, due to the presence of concentrated sulfuric acid, the requirements for production equipment are extremely harsh (Kozlov, M.E.; Capps, R.C.; Sampson, W.M.; Ebron, V.H.; Ferraris, J.P.; Baughman, R.H. Adv. Mater. 2005, 17(5), 614.). By introducing surfactants or strong acids to disperse carbon nanotubes, the intrinsic structure and properties of carbon nanotubes are affected, thereby reducing the conductivity of the fibers and affecting their tensile properties. Currently, its tensile properties are still lower than those of commercial carbon fibers, and the overall performance needs to be further improved.

[0004] In order to solve this problem, many researchers have introduced a large number of flexible polymer materials to change the conductive structure and improve the overall flexibility. For example, Wang et al. used thermoplastic polyurethane (TPU) as the matrix and carbon nanotubes as the conductive component to prepare carbon nanotube conductive composite fibers by wet spinning. In the uniaxial tensile test, the fiber showed a certain working strain range (320%), but the sensitivity was low (Wang, X.; Sun, H.; Yue, X.; Yu, Y.; Zheng, G.; Dai, K.; Liu, C.; Shen, C. A Highly Stretchable Carbon Nanotubes / Thermoplastic Polyurethane Fiber-Shaped Strain Sensor with Porous Structure for Human Motion Monitoring. Compos. Sci. Technol. 2018, 168, 126-132.). In order to ensure normal operation under low voltage, many researchers usually add a large amount of conductive fillers to the conductive fiber to obtain sufficient conductivity. This high content of conductive material is very easy to physically agglomerate due to its strong interaction, which affects the overlap efficiency of the conductive network. The above methods not only increase the economic cost of conductive materials, but also affect the flexibility of flexible conductive materials, thereby affecting the performance of conductive fibers. In addition, although carbon nanotubes have excellent conductivity and mechanical properties, they also have some problems that need to be solved, such as the brittleness of carbon nanotubes, the complex preparation process of carbon nanotube materials and the high price. Moreover, carbon nanotubes themselves cannot be directly applied. They must be assembled or effectively compounded with other conductive materials to form macroscopic materials to achieve practical applications. Organically matching and integrating carbon nanotube materials with other materials to exert synergistic effects can improve the comprehensive performance of conductive fibers, reduce the complexity and production cost of conductive fiber preparation, and meet the requirements of wide strain and high sensitivity sensing. Summary of the invention

[0005] The purpose of the present application is to provide a high-performance flexible carbon nanotube conductive composite fiber and a preparation method thereof, so as to solve the problems that a large amount of flexible polymer materials are introduced into the wet-spun carbon nanotube conductive composite fiber prepared by the existing method, resulting in the difficulty in uniform dispersion of conductive materials, small strain range, poor sensitivity and the like.

[0006] To achieve the above purpose, the technical solution adopted in this application is:

[0007] On the one hand, the present application provides a method for preparing a high-performance flexible carbon nanotube conductive composite fiber, comprising the following steps:

[0008] S1. Add TPU to the DMF solution and stir with a thermostatic magnetic stirrer to obtain a TPU spinning dope solution.

[0009] S2. Add dopamine or its derivative and Tris buffer solution to the DMF solution and stir with a thermostatic magnetic stirrer to obtain a dopamine or its derivative solution.

[0010] S3. Add TPU to the dopamine or its derivative solution and stir with a thermostatic magnetic stirrer to obtain a dopamine or its derivative mixed solution.

[0011] S4. Add carbon nanotubes or their derivatives, graphene or their derivatives, and silver powder to the dopamine or its derivative mixed solution in sequence and stir with a thermostatic magnetic stirrer to obtain a carbon nanotubes or their derivatives mixed conductive solution.

[0012] S5. Slowly pour the carbon nanotubes or their derivatives mixed conductive solution into the TPU spinning dope solution and stir with a thermostatic magnetic stirrer to obtain a carbon nanotubes or their derivatives mixed conductive spinning solution.

[0013] S6. Inject the carbon nanotubes or their derivatives mixed conductive spinning solution into a syringe, perform wet spinning at room temperature, use an injection pump to extrude the carbon nanotubes or their derivatives mixed conductive spinning solution into a DMF aqueous coagulation bath, perform three-fold mechanical drawing on the as-spun fibers solidified in the coagulation bath, then perform heat setting treatment, and finally wind the fibers after heat setting treatment onto a uniformly rotating hot roller for collection and drying to obtain high-performance flexible carbon nanotube conductive composite fibers.

[0014] In a possible implementation, in step S1:

[0015] The content of the TPU is 0.2 - 18.2 g / L.

[0016] The mass-volume concentration of the DMF is 20 - 600 mg / mL.

[0017] The constant temperature of the thermostatic magnetic stirrer is 40 - 60 °C, the stirring speed is 200 - 950 rpm, and the stirring time is 4 - 16 h.

[0018] In a possible implementation, in step S2:

[0019] The mass-volume concentration of the DMF is 20 - 600 mg / mL.

[0020] The pH of the solution after adding dopamine or its derivative and Tris buffer solution to the DMF solution is 8 - 10.

[0021] The constant temperature of the constant temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 150 - 850 rpm, and the stirring time is 15 - 45 min.

[0022] In a possible implementation, in step S2:

[0023] The dopamine or its derivative includes one of dopamine hydrochloride, polydopamine-like, N-3,4-dihydroxyphenethyl acrylamide, and 3,4-dihydroxyphenylalanine.

[0024] In a possible implementation, in step S3:

[0025] The constant temperature of the constant temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 250 - 850 rpm, and the stirring time is 6 - 18 h;

[0026] In the dopamine or its derivative mixed solution, the concentration of the dopamine or its derivative is 0.5 - 16.5 mol / L, the mass-volume concentration of the DMF is 5 - 60 mg / mL, and the content of the TPU is 0.5 - 4.5 g / L.

[0027] In a possible implementation, in step S4:

[0028] The concentrations of the carbon nanotube or its derivative, graphene or its derivative, and silver powder are 0.2 - 24.2 mol / L, 0.5 - 8.5 mol / L, and 1.5 - 4.5 mol / L respectively;

[0029] The constant temperature of the constant temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 250 - 650 rpm, and the stirring time is 2 - 8 h.

[0030] In a possible implementation, in step S4:

[0031] The carbon nanotube or its derivative includes one of amino-functionalized carbon nanotubes, carboxyl-functionalized carbon nanotubes, hydroxyl-functionalized carbon nanotubes, and CNTs-DMPA;

[0032] The graphene or its derivative includes one of graphene oxide, carboxyl-functionalized graphene, and amino-functionalized graphene.

[0033] In a possible implementation, in step S5:

[0034] The constant temperature of the constant temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 100 - 600 rpm, and the stirring time is 6 - 12 h.

[0035] In a possible implementation, in step S6:

[0036] The volume capacity of the syringe is 5 - 40 mL, and the inner diameter of the needle is 0.2 - 0.8 mm;

[0037] The spinning rate of the wet spinning is 0.5 - 10.5 mL / h;

[0038] The length of the coagulation bath is 90 cm;

[0039] The temperature of the heat setting treatment is 60 °C;

[0040] The drying temperature in the process of winding the fibers after heat setting treatment onto a uniformly rotating hot roller for collection and drying is 25 - 45 °C, and the drying time is 3 - 6 h.

[0041] On the other hand, the present application also provides a high-performance flexible carbon nanotube conductive composite fiber, and the high-performance flexible carbon nanotube conductive composite fiber is prepared by the preparation method of the above-mentioned high-performance flexible carbon nanotube conductive composite fiber.

[0042] The beneficial effects brought by the technical solution provided by the present application at least include:

[0043] (1) Based on the wet spinning process of the dynamic bonding synergistic strengthening strategy, the present application makes full use of the advantage that carbon nanotubes or their derivatives are easy to functionalize, introduces the reaction groups of carbon nanotubes or their derivatives and the end groups of TPU into the molecular necklace structure of dopamine or its derivatives at the same time, and further constructs a molecular necklace cross-linked multi-dimensional conductive network structure through chemical cross-linking of carbon nanotubes or their derivatives and physical cross-linking of TPU end groups respectively, realizing the organic and tight combination of zero-dimensional silver nanoparticles, one-dimensional carbon nanotubes or their derivatives, and two-dimensional graphene or their derivatives. The dynamic bonding synergistic strengthening strategy means that on the one hand, amine groups, imine groups, phenolic hydroxyl groups, etc. in dopamine or its derivatives are mechanically interlocked with the oxygen-containing groups of TPU through hydrogen bonds, π-π stacking, electrostatic interactions, etc.; on the other hand, carbon nanotubes or their derivatives form a stable molecular necklace cross-linked multi-conductive network structure with graphene or its derivatives and silver nanoparticles through metal chelation, covalent reaction, π-π stacking, hydrophobic interaction, etc. The molecular necklace cross-linked multi-conductive network structure means that on the one hand, it is a two-dimensional conductive network structure between carbon nanotubes or their derivatives with a mechanically interlocked cross-linked molecular chain structure and silver nanoparticles; on the other hand, it is a three-dimensional conductive network structure between carbon nanotubes or their derivatives with a mechanically interlocked cross-linked molecular chain structure and graphene or their derivatives and silver nanoparticles.

[0044] (2) Compared with the prior art, the high-performance flexible carbon nanotube conductive composite fiber prepared by the wet spinning method in this application provides a simple method for preparing fibers. The spinning process is simple, the production cost is low, large-scale production is easy to achieve, and the produced fibers not only have good conductivity but also high strength, meeting the requirements of subsequent processes such as textile. The conductive fibers obtained by this preparation method can be used in many fields such as flexible sensor devices, anti-static fabrics, and infrared rays.

[0045] (3) The tensile strength of the high-performance flexible carbon nanotube conductive composite fiber prepared by the preparation method of this application is 643.86 MPa, the strain is 1142.36%, and after 650 times of friction, the conductivity is within 1849 - 1879 S / cm; after 240 times of water washing, the conductivity is within 1845 - 1879 S / cm. In addition, the sensitivity coefficients GF of the carbon nanotube conductive composite fiber under 0 - 50%, 50 - 200%, 200 - 600%, and 600 - 1200% strain are 420.35, 638.24, 823.47, and 1293.48 respectively, indicating the controllability of the sensitivity of the carbon nanotube conductive composite fiber under different strains. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The drawings are used to provide a further understanding of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation to this application. In the drawings:

[0047] Figure 1 The flowchart of the preparation method of the high-performance flexible carbon nanotube conductive composite fiber provided by an exemplary embodiment of this application is shown;

[0048] Figure 2 The electron microscope image of the high-performance flexible carbon nanotube conductive composite fiber provided by an exemplary embodiment of this application is shown;

[0049] Figure 3 The synthesis mechanism and chemical structure schematic diagram of the CNTs-DMPA1 conductive composite material and the TPU 3 with a molecular necklace structure of end-group cross-linked polydopamine 2 are shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] The technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of this application.

[0051] Among them, the same component parts are denoted by the same reference numerals. It should be noted that the terms "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to the directions in the attached drawings of the present application specification, and the terms "bottom surface" and "top surface", "inner" and "outer" respectively refer to the directions towards or away from specific components. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application specification, "a plurality of" means two or more.

[0052] The present application will be further described below in conjunction with the attached drawings and embodiments.

[0053] First, a brief introduction to the nouns involved in the embodiments of the present application:

[0054] TPU, short for Thermoplastic Urethane, is called thermoplastic polyurethane elastomer in Chinese. TPU is a polymer material formed by the co-reaction polymerization of diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), macromolecular polyol, and chain extender.

[0055] DMF, dimethylformamide (DMF or N,N-dimethylformamide) is a transparent liquid that can be miscible with water and most organic solvents. It is a commonly used solvent for chemical reactions.

[0056] Tris buffer solution refers to Tris-HCl (tris(hydroxymethyl)aminomethane hydrochloride buffer solution), which is specifically obtained by mixing tris(hydroxymethyl)aminomethane (Tris) solution with hydrochloric acid and then diluting with water.

[0057] CNTs-DMPA refers to CNTs-DMPA obtained by surface modification of carboxylated CNTs with thionyl chloride (SOCl2) and triethylamine (TEA) and then crosslinking 2,2-dimethylolpropionic acid (DMPA).

[0058] Carboxylated CNTs are obtained by etching and ultrasonic treatment of carbon nanotubes in a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid, and then stirring at 70-80°C.

[0059] Figure 1 The flowchart of the preparation method of the high-performance flexible carbon nanotube conductive composite fiber provided by an exemplary embodiment of the present application is shown. The method includes the following steps:

[0060] Step S1: Add TPU into the DMF solution and stir it with a thermostatic magnetic stirrer to obtain a TPU spinning dope solution.

[0061] In step S1 of this embodiment, the content of TPU is 0.2 - 18.2 g / L; the mass - volume concentration of DMF is 20 - 600 mg / mL; the constant temperature of the thermostatic magnetic stirrer is 40 - 60 °C, the stirring speed is 200 - 950 rpm, and the stirring time is 4 - 16 h.

[0062] Step S2: Add dopamine or its derivative and Tris buffer solution into the DMF solution and stir it with a thermostatic magnetic stirrer to obtain a dopamine or its derivative solution.

[0063] In step S2 of this embodiment, the mass - volume concentration of DMF is 20 - 600 mg / mL; the pH of the solution after adding dopamine or its derivative and Tris buffer solution is 8 - 10; the constant temperature of the thermostatic magnetic stirrer is 40 - 60 °C, the stirring speed is 150 - 850 rpm, and the stirring time is 15 - 45 min. Optionally, the above - mentioned dopamine or its derivative includes but is not limited to one of dopamine hydrochloride (DA·HCl), polydopamine - like (DATA), N - 3,4 - dihydroxyphenethyl acrylamide (DAA), and 3,4 - dihydroxyphenylalanine (DOPA).

[0064] Step S3: Add TPU into the dopamine or its derivative solution and stir it with a thermostatic magnetic stirrer to obtain a dopamine or its derivative mixed solution.

[0065] In step S3 of this embodiment, the constant temperature of the thermostatic magnetic stirrer is 40 - 60 °C, the stirring speed is 250 - 850 rpm, and the stirring time is 6 - 18 h; the concentration of dopamine or its derivative in the dopamine or its derivative mixed solution is 0.5 - 16.5 mol / L, the mass - volume concentration of DMF is 5 - 60 mg / mL, and the content of TPU is 0.5 - 4.5 g / L.

[0066] Step S4: Add carbon nanotubes or their derivatives, graphene or their derivatives, and silver powder into the dopamine or its derivative mixed solution in sequence and stir it with a thermostatic magnetic stirrer to obtain a carbon nanotubes or their derivatives mixed conductive solution.

[0067] In step S4 of this embodiment, the concentrations of carbon nanotubes or their derivatives, graphene or their derivatives, and silver powder are 0.2 - 24.2 mol / L, 0.5 - 8.5 mol / L, and 1.5 - 4.5 mol / L respectively; the constant temperature of the constant temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 250 - 650 rpm, and the stirring time is 2 - 8 h. Optionally, the carbon nanotubes or their derivatives include but are not limited to one of aminated carbon nanotubes, carboxylated carbon nanotubes, hydroxylated carbon nanotubes, and CNTs-DMPA; the graphene or their derivatives include but are not limited to one of graphene oxide, carboxylated graphene, and aminated graphene.

[0068] Step S5: Slowly pour the carbon nanotube or its derivative mixed conductive solution into the TPU spinning dope. After stirring with a constant temperature magnetic stirrer, a carbon nanotube or its derivative mixed conductive spinning solution is obtained.

[0069] In step S5 of this embodiment, the constant temperature of the constant temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 100 - 600 rpm, and the stirring time is 6 - 12 h.

[0070] Step S6: Inject the carbon nanotube or its derivative mixed conductive spinning solution into a syringe, perform wet spinning at room temperature, use an injection pump to extrude the carbon nanotube or its derivative mixed conductive spinning solution into a DMF aqueous coagulation bath. After the nascent fiber solidified and formed in the coagulation bath is subjected to three-fold mechanical drawing, then heat setting treatment is carried out. Finally, the fiber after heat setting treatment is wound onto a uniformly rotating hot roller for collection and drying to obtain a high-performance flexible carbon nanotube conductive composite fiber.

[0071] In step S6 of this embodiment, the volume capacity of the syringe is 5 - 40 mL, the inner diameter of the needle is 0.2 - 0.8 mm; the spinning rate of wet spinning is 0.5 - 10.5 mL / h; the length of the coagulation bath is 90 cm; the temperature of heat setting treatment is 60 °C; the drying temperature for collecting and drying the fiber after heat setting treatment wound onto a uniformly rotating hot roller is 25 - 45 °C, and the drying time is 3 - 6 h.

[0072] Figure 2 The electron micrograph of the high-performance flexible carbon nanotube conductive composite fiber provided by an exemplary embodiment of the present application is shown. The high-performance flexible carbon nanotube conductive composite fiber is prepared by the preparation method of the above high-performance flexible carbon nanotube conductive composite fiber.

[0073] In summary, the wet spinning process of the present application based on the dynamic bonding synergistic strengthening strategy makes full use of the advantage that carbon nanotubes or their derivatives are easy to functionalize, introduces the reaction groups of carbon nanotubes or their derivatives and the end groups of TPU into the molecular necklace structure of dopamine or its derivatives at the same time, and further constructs a molecular necklace cross-linked multi-dimensional conductive network structure through chemical cross-linking of carbon nanotubes or their derivatives and physical cross-linking of TPU end groups respectively, realizing the organic and tight combination of zero-dimensional silver nanoparticles, one-dimensional carbon nanotubes or their derivatives, and two-dimensional graphene or their derivatives. The dynamic bonding synergistic strengthening strategy means that on the one hand, amino groups, imino groups, phenolic hydroxyl groups, etc. in dopamine or its derivatives carry out molecular chain mechanical interlocking with the oxygen-containing groups of TPU through hydrogen bonds, π-π stacking, electrostatic interactions, etc.; on the other hand, carbon nanotubes or their derivatives form a stable molecular necklace cross-linked multi-conductive network structure with graphene or its derivatives and silver nanoparticles through metal chelation, covalent reaction, π-π stacking, hydrophobic interaction, etc. The carbon nanotubes or their derivatives include but are not limited to one of aminated carbon nanotubes, carboxylated carbon nanotubes, hydroxylated carbon nanotubes, and CNTs-DMPA. The graphene or its derivatives include but are not limited to one of graphene oxide, carboxylated graphene, and aminated graphene. The molecular necklace cross-linked multi-conductive network structure means that on the one hand, it is a two-dimensional conductive network structure between carbon nanotubes or their derivatives with a cross-linked molecular chain mechanical interlocking structure and silver nanoparticles; on the other hand, it is a three-dimensional conductive network structure between carbon nanotubes or their derivatives with a cross-linked molecular chain mechanical interlocking structure and graphene or its derivatives and silver nanoparticles.

[0074] To better understand the present application, a specific embodiment is used to further illustrate the present application below. It should be noted that the embodiments described in this specific embodiment are only part of the embodiments of the present application and do not limit the scope of protection of the present application.

[0075] A method for preparing a high-performance flexible carbon nanotube conductive composite fiber includes the following steps:

[0076] Step S1: Add TPU to a DMF solution, and after stirring with a constant temperature magnetic stirrer, obtain a TPU spinning dope.

[0077] In step S1 of this embodiment, the content of TPU is 6 g / L; the mass-volume concentration of DMF is 60 mg / mL; the constant temperature of the constant temperature magnetic stirrer is 45 °C, the stirring speed is 350 rpm, and the stirring time is 5 h.

[0078] Step S2: Add dopamine and Tris buffer solution to a DMF solution, and after stirring with a constant temperature magnetic stirrer, obtain a dopamine solution.

[0079] In step S2 of this embodiment, the mass-volume concentration of DMF is 20 mg / mL; the pH of the solution after adding dopamine and Tris buffer solution to the DMF solution is 8.5; the constant temperature of the constant temperature magnetic stirrer is 45 °C, the stirring speed is 300 rpm, and the stirring time is 30 min.

[0080] Step S3: Add TPU to the dopamine solution, and after stirring with a constant temperature magnetic stirrer, a dopamine mixed solution is obtained.

[0081] In step S3 of this embodiment, the constant temperature of the constant temperature magnetic stirrer is 45 °C, the stirring speed is 550 rpm, and the stirring time is 8 h; the concentration of dopamine in the dopamine mixed solution is 2.5 mol / L.

[0082] Step S4: Add CNTs-DMPA, graphene (RGO), and silver powder to the dopamine mixed solution in sequence, and after stirring with a constant temperature magnetic stirrer, a CNTs-DMPA mixed conductive solution is obtained.

[0083] In step S4 of this embodiment, the concentrations of CNTs-DMPA, graphene (RGO), and silver powder are 15 mol / L, 3.5 mol / L, and 2 mol / L respectively; the constant temperature of the constant temperature magnetic stirrer is 45 °C, the stirring speed is 450 rpm, and the stirring time is 6 h.

[0084] Step S5: Slowly pour the CNTs-DMPA mixed conductive solution into the TPU spinning dope, and after stirring with a constant temperature magnetic stirrer, a CNTs-DMPA mixed conductive spinning solution is obtained.

[0085] In step S5 of this embodiment, the constant temperature of the constant temperature magnetic stirrer is 45 °C, the stirring speed is 450 rpm, and the stirring time is 8 h.

[0086] Step S6: Inject the CNTs-DMPA mixed conductive spinning solution into a syringe, perform wet spinning at room temperature, use the injection pump of the syringe to extrude the CNTs-DMPA mixed conductive spinning solution into the DMF aqueous coagulation bath, perform triple mechanical drawing on the as-spun fibers solidified by the coagulation bath, then perform heat setting treatment, and finally wind the fibers after heat setting treatment onto a uniformly rotating hot roller for collection and drying to obtain the Figure 2 high-performance flexible carbon nanotube conductive composite fiber as shown.

[0087] In step S6 of this embodiment, the volume capacity of the syringe is 20 mL, the inner diameter of the needle is 0.3 mm; the spinning rate of wet spinning is 2.5 mL / h; the length of the coagulation bath is 90 cm; the temperature of the heat setting treatment is 60 °C; the drying temperature during the collection and drying of the fibers wound on a uniformly rotating hot roller after the heat setting treatment is 45 °C, and the drying time is 5 h.

[0088] It should be noted that the 2,2-dimethylolpropionic acid (DMPA) used in this embodiment is purchased from Nanjing Runbang Chemical Co., Ltd., N,N-dimethylformamide (DMF) is purchased from Tianjin Damao Chemical Reagent Factory, thionyl chloride (SOCl2) is purchased from Tianjin Tianli Chemical Reagent Co., Ltd., carboxylated carbon nanotubes (CNTs-COOH), nano silver powder and graphene oxide are purchased from Nanjing Xianfeng Nano Materials Technology Co., Ltd., dopamine hydrochloride is purchased from Guorui Pharmaceutical Co., Ltd. of China National Pharmaceutical Group, and triethylamine (TEA) is purchased from Chemical Reagent Co., Ltd. of China National Pharmaceutical Group. Other solutions not specifically described use water as the solvent.

[0089] Furthermore, the preparation method of CNTs-DMPA powder in the example includes:

[0090] Place 3.0 g of carboxylated CNTs in a 500 mL four-necked flask, add 30 mL of DMF, ultrasonically disperse for 30 min, start stirring, and then slowly add 100 mL of SOCl2, heat to 70 °C and stir for reaction for 16 h. After cooling, filter by suction, and wash with DMF three times to remove the unreacted SOCl2 on its surface. Transfer the filter cake to a 500 mL conical flask, add 80 g of DMPA (using DMF as the solvent) and 20 mL of TEA respectively, heat to 50 °C, and stir magnetically for reaction for 24 h. After cooling, filter by suction, wash the filter cake with deionized water five times, and dry in an oven at 60 °C to constant weight to obtain chemically modified CNTs, denoted as CNTs-DMPA.

[0091] Furthermore, the preparation method of reduced graphene oxide (RGO) powder in the example includes:

[0092] Prepare an LAA solution with a concentration of 30 mg / mL, slowly pour it into the graphene oxide solution with a concentration of 30 mg / mL for reduction, the reduction temperature is 95 °C, the reduction time is 60 min, and finally wash with water and dry to obtain reduced graphene oxide nanosheets.

[0093] Next, perform performance tests on the above-obtained high-performance flexible carbon nanotube conductive composite fibers:

[0094] 1. Mechanical property test

[0095] At room temperature, the fiber was subjected to a tensile break test using a UTM2203 servo-controlled universal testing machine from Shenzhen Sansi Zongheng Technology Co., Ltd. The tensile rate was 10 mm / min, and at least 5 samples of each content were tested and their average values were calculated.

[0096] 1.1. The tensile strength of the specimen was calculated using the following formula (1):

[0097]

[0098] In the formula, σ is the tensile strength (Pa); P is the maximum load (N); S is the cross-sectional area of the specimen (m 2 ²).

[0099] 1.2. The elongation at break of the specimen was calculated using the following formula (2):

[0100]

[0101] In the formula: ε is the elongation at break; L0 is the initial length of the specimen (mm); L is the length of the specimen after stretching (mm).

[0102] 1.3. The Young's tensile modulus of the specimen was calculated using the following formula (3):

[0103]

[0104] In the formula, E is the Young's tensile modulus of the specimen (MPa); ε is a certain strain in the elastic region of the specimen; σ is the tensile strength corresponding to the strain ε in the elastic region of the specimen (MPa).

[0105] 2. Sensitivity test

[0106] Sensitivity is the most important parameter determining the strain sensing performance. Especially for various applications requiring weak displacement detection (such as ultra-sensitive skin), the change in the sensing response relative to the applied strain determines the sensitivity of the sensor. The sensitivity of the strain sensor is measured using the gauge factor (GF), and the corresponding GF formula is shown as the following formula (4):

[0107]

[0108] In the formula, R and R0 represent the measured resistance value of the sensor under the action of the external field and the initial resistance, respectively.

[0109] 3. Friction resistance test

[0110] The test was carried out with reference to the national standard GB / T21196.

[0111] 4. Water resistance test

[0112] The test was carried out with reference to the literature (Dca B, Xue B, Jpa B, et al. In situ hydrothermal growth of CuNPs on knitted fabrics through polydopamine templates for heating and sensing[J]. Chemical Engineering Journal, 382.).

[0113] The test results are as follows:

[0114] Figure 3 The synthesis mechanism and chemical structure schematic diagram of the CNTs-DMPA1 conductive composite material and the TPU 3 with a molecular necklace structure of end-group crosslinked polydopamine 2 are shown. From Figure 3 It can be seen that by taking advantage of the easy functionalization of CNTs-DMPA, the reaction groups of CNTs-DMPA and the end groups of TPU are simultaneously introduced into the molecular necklace structure of polydopamine. Further, a molecular necklace crosslinked multi-dimensional conductive network structure is constructed through chemical crosslinking 4, 5 of CNTs-DMPA and physical crosslinking 6, 7 of TPU end groups respectively. The zero-dimensional silver nanoparticles 8, one-dimensional CNTs-DMPA, and two-dimensional RGO 9 are organically and tightly combined. The dynamic bonding synergistic strengthening strategy means that on the one hand, the amino groups, imino groups, phenolic hydroxyl groups, etc. in polydopamine are mechanically interlocked with the oxygen-containing groups of TPU through hydrogen bonds, π-π stacking, electrostatic interactions, etc.; on the other hand, CNTs-DMPA constructs a stable molecular necklace crosslinked multi-conductive network structure with RGO and silver nanoparticles through metal chelation, covalent reaction, π-π stacking, hydrophobic interaction, etc. The molecular necklace crosslinked multi-conductive network structure means that on the one hand, it is a two-dimensional conductive network structure between CNTs-DMPA with a mechanically interlocked crosslinked molecular chain structure and silver nanoparticles; on the other hand, it is a three-dimensional conductive network structure between CNTs-DMPA and RGO with a mechanically interlocked crosslinked molecular chain structure and silver nanoparticles.

[0115] The tensile strength of the high-performance flexible carbon nanotube conductive composite fiber prepared by the preparation method of this application is 643.86 MPa, and the strain is 1142.36%. The sensitivity coefficients GF of the carbon nanotube conductive composite fiber at 0-50%, 50-200%, 200-600%, and 600-1200% strain are 420.35, 638.24, 823.47, and 1293.48 respectively, indicating the controllability of the sensitivity of the carbon nanotube conductive composite fiber at different strains, as shown in Table 1 below:

[0116] Table 1. Sensitivity-strain test results

[0117]

[0118] The test results of friction resistance and washing resistance of this embodiment are shown in Table 2 and Table 3 below. It can be seen from Table 2 and Table 3 that after 650 times of friction, the conductivity is within 1849 - 1879 S / cm; after 240 times of washing, the conductivity is within 1845 - 1879 S / cm.

[0119] Table 2. Test Results of Friction Resistance

[0120]

[0121]

[0122] Table 3. Test Results of Washing Resistance

[0123] Ultrasonic washing / minute Conductivity / S / cm 0 1879 20 1874 40 1867 80 1862 120 1859 160 1854 200 1849 240 1845

[0124] The above are only the preferred embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A preparation method of a high-performance flexible carbon nanotube conductive composite fiber, characterized in that It includes the following steps: S1. Add TPU into the DMF solution, and after stirring with a constant-temperature magnetic stirrer, obtain the TPU spinning dope. S2. Add dopamine or its derivative and Tris buffer solution into the DMF solution, and after stirring with a constant-temperature magnetic stirrer, obtain the dopamine or its derivative solution. S3. Add TPU into the dopamine or its derivative solution, and after stirring with a constant-temperature magnetic stirrer, obtain the dopamine or its derivative mixed solution. S4. Add carbon nanotubes or their derivatives, graphene or their derivatives, and silver powder into the dopamine or its derivative mixed solution in sequence, and after stirring with a constant-temperature magnetic stirrer, obtain the carbon nanotubes or their derivatives mixed conductive solution. S5. Slowly pour the carbon nanotubes or their derivatives mixed conductive solution into the TPU spinning dope, and after stirring with a constant-temperature magnetic stirrer, obtain the carbon nanotubes or their derivatives mixed conductive spinning solution. S6. Inject the carbon nanotubes or their derivatives mixed conductive spinning solution into a syringe, conduct wet spinning at room temperature, extrude the carbon nanotubes or their derivatives mixed conductive spinning solution into the DMF aqueous coagulation bath with an injection pump, conduct three-fold mechanical drawing on the as-spun fiber solidified by the coagulation bath, then conduct heat setting treatment, and finally wind the fiber after heat setting treatment onto a uniformly rotating hot roller for collection and drying to obtain the high-performance flexible carbon nanotube conductive composite fiber. In step S2: The dopamine or its derivative includes one of dopamine hydrochloride and polydopamine-like. In step S4: The carbon nanotubes or their derivatives include one of amino-functionalized carbon nanotubes, carboxyl-functionalized carbon nanotubes, hydroxyl-functionalized carbon nanotubes, and CNTs-DMPA; the graphene or its derivatives include one of graphene oxide, carboxyl-functionalized graphene, and amino-functionalized graphene.

2. The preparation method of the high-performance flexible carbon nanotube conductive composite fiber according to claim 1, wherein In step S1: The content of the TPU is 0.2 - 18.2 g / L. The mass-volume concentration of the DMF is 20 - 600 mg / mL. The constant temperature of the constant-temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 200 - 950 rpm, and the stirring time is 4 - 16 h.

3. The preparation method of the high-performance flexible carbon nanotube conductive composite fiber according to claim 1, wherein In step S2: The mass-volume concentration of the DMF is 20 - 600 mg / mL. The pH of the solution after adding dopamine or its derivative and Tris buffer solution into the DMF solution is 8 - 10. The constant temperature of the constant-temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 150 - 850 rpm, and the stirring time is 15 - 45 min.

4. The preparation method of the high-performance flexible carbon nanotube conductive composite fiber according to claim 1, characterized in that, In step S3: The constant temperature of the constant-temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 250 - 850 rpm, and the stirring time is 6 - 18 h. In the dopamine or its derivative mixed solution, the concentration of the dopamine or its derivative is 0.5 - 16.5 mol / L, the mass-volume concentration of the DMF is 5 - 60 mg / mL, and the content of the TPU is 0.5 - 4.5 g / L.

5. The preparation method of the high-performance flexible carbon nanotube conductive composite fiber according to claim 1, wherein, In step S4: The concentrations of the carbon nanotubes or their derivatives, graphene or its derivatives, and silver powder are 0.2 - 24.2 mol / L, 0.5 - 8.5 mol / L, and 1.5 - 4.5 mol / L respectively; The constant temperature of the constant temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 250 - 650 rpm, and the stirring time is 2 - 8 h.

6. The preparation method of the high-performance flexible carbon nanotube conductive composite fiber according to claim 1, wherein, In the step S5: The constant temperature of the constant temperature magnetic stirrer is 40 - 60 °C, the stirring speed is 100 - 600 rpm, and the stirring time is 6 - 12 h.

7. The preparation method of the high-performance flexible carbon nanotube conductive composite fiber according to claim 1, wherein In the step S6: The volume capacity of the syringe is 5 - 40 mL, and the inner diameter of the needle is 0.2 - 0.8 mm; The spinning rate of the wet spinning is 0.5 - 10.5 mL / h; The length of the coagulation bath is 90 cm; The temperature of the heat setting treatment is 60 °C; In the step of winding the fiber after the heat setting treatment onto a uniformly rotating hot roller for collection and drying, the drying temperature is 25 - 45 °C and the drying time is 3 - 6 h.

8. A high-performance flexible carbon nanotube conductive composite fiber, which is prepared by the preparation method of the high-performance flexible carbon nanotube conductive composite fiber according to any one of claims 1 to 7.

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