Carbon nanotube / polymer composite fiber preparation method and continuous production system

Abstract

The invention provides a preparation method of a carbon nanotube / polymer composite fiber. The preparation method comprises the following steps: preparing a polymer-protonated strong acid solution; putting carbon nanotube fibers into the high-molecular polymer-protonated strong acid solution for compounding treatment to obtain a protonated compound; carrying out densification treatment on the protonated compound to obtain a precursor fiber; cleaning the precursor fiber to obtain a carbon nanotube / polymer composite fiber; the invention also provides a continuous production system suitable for the preparation method of the carbon nanotube / polymer composite fiber. The preparation method provided by the invention overcomes the problem that continuous and uniform compounding between polyimide and carbon nanotubes cannot be realized in the prior art, and is simpler, more convenient and quicker to operate, regulate and control compared with the prior art, and the high-performance composite fiber can be prepared through more simple and convenient multi-step treatment.

Description

Technical Field

[0001] The invention relates to the technical field of carbon nano composite materials, and in particular to a method for preparing carbon nano tube / polymer composite fibers and a continuous production system. Background Art

[0002] Carbon nanotubes (CNTs) have a unique one-dimensional hollow linear structure, which gives them excellent mechanical, electrical and thermal properties. Macroscopic bodies assembled from them (such as films, narrow strips, and fibers) have broad application prospects in equipment manufacturing, functional composites and other fields. However, due to the existence of many nanopores and weak inter-tube forces, the performance of carbon nanotube macroscopic bodies is weaker than that of single carbon nanotubes. Taking carbon nanotube fibers as an example, the tensile strength of the fibers currently reported is far less than the strength of the carbon nanotubes themselves, and there is huge room for improvement.

[0003] To solve the above problems, researchers introduced polymers into carbon nanotube macrobodies to prepare polymer / carbon nanotube composites. At present, the preparation methods of polymer / carbon nanotube composites mainly include spraying, immersion, in-situ composite, electrolytic expansion composite, etc. Among them: the spraying method prepares composite materials by spraying polymers on carbon nanotubes; the immersion method prepares composite materials by immersing carbon nanotube aggregates in polymer solution and then treating them; the in-situ composite method mainly drips polymer solution during the production process of carbon nanotube macrobodies to make it infiltrate the inside of carbon nanotubes to obtain composite materials; the electrolytic expansion composite method mainly prepares composite materials by electrolytically decomposing hydrogen to expand carbon nanotube fibers, so that the polymer penetrates into the pores of carbon nanotubes.

[0004] However, the existing manufacturing technology of polymer / carbon nanotube composites has certain shortcomings:

[0005] When prepared by spraying or soaking, it is often difficult for the polymer to enter the nanoscale pores inside the carbon nanotubes, resulting in uneven composite and difficult continuous preparation. For example, CN110713615A discloses a method for preparing a carbon nanotube-polyimide composite film, in which molten polyimide is sprayed on a continuous carbon nanotube film at a certain flow rate, and then pressurized to prepare the carbon nanotube-polyimide composite film. However, this method cannot allow the polymer to penetrate into the nanopores inside the carbon nanotubes, resulting in uneven composite. CN107828164A discloses a method for preparing a carbon nanotube composite material, in which a carbon nanotube film is placed in a polymer solution containing a leavening agent, and then fully soaked and cured to form. However, this method has the problems of limited application range of the polymer and inability to prepare continuously.

[0006] The blending method has the problem that the amount of carbon nanotubes used is low and the continuous batch preparation of composite materials cannot be achieved. For example, CN 112898739A discloses a method for preparing a composite film using a conductive polymer and carbon nanotubes as raw materials, wherein the carbon nanotubes and polymer are blended in a strong acid, filtered, coated, and dried to prepare a composite film. However, this method requires multiple steps and cannot achieve continuous batch preparation of composite materials.

[0007] There are production limitations in the preparation of polymer / carbon nanotube composite materials by in-situ composite method. For example, CN 101967699A discloses a method for preparing high-performance carbon nanotube composite fibers: the method drips polyamic acid into a carbon nanotube film drawn from a spinnable carbon nanotube array, twists it, and solidifies it to prepare a carbon nanotube-polyimide composite fiber. This method needs to be carried out simultaneously with the fiber production process, which has production limitations. In addition, it is difficult for the polymer to evenly penetrate the internal pores of the carbon nanotubes during the impregnation process, resulting in uneven fiber composite.

[0008] Composite material preparation methods such as electrolytic expansion composite method have the problem of limited selection of polymers. For example, CN112301462B discloses a method for preparing carbon nanotube composite fibers. This method uses electrolyte hydrogen evolution expansion to expand carbon nanotubes significantly, and then uniformly infiltrates water-soluble polymers into the carbon nanotubes to prepare carbon nanotube-polymer composite fibers through continuous drawing and composite method; however, this method is mainly carried out in an acidic electrolyte solution containing polymers, and the polymers that can be selected are mainly water-soluble thermoplastic polymers, so the application range is limited. Summary of the invention

[0009] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a carbon nanotube / polymer composite fiber preparation method and a continuous production system to solve the problems in the prior art that polymers and carbon nanotubes cannot be uniformly and continuously composited and the application range of polymers is narrow.

[0010] To achieve the above-mentioned and other related purposes, the present invention provides a method for preparing a carbon nanotube / polymer composite fiber, comprising the following steps:

[0011] 1) preparing a high molecular polymer-protonated strong acid solution;

[0012] 2) placing the carbon nanotube fiber in the high molecular polymer-protonated strong acid solution for composite treatment to obtain a protonated composite;

[0013] 3) subjecting the protonated composite to a densification treatment to obtain a precursor fiber;

[0014] 4) Washing the precursor fiber to obtain carbon nanotube / polymer composite fiber.

[0015] The present invention also provides a continuous production system suitable for the above-mentioned carbon nanotube / polymer composite fiber preparation method, wherein the system includes: an unwinding device, a composite processing device, a densification processing device, a cleaning device and a winding device connected along a continuous production route;

[0016] The unwinding device is at least used to introduce the carbon nanotube fibers into the composite processing device and to regulate the speed at which the carbon nanotube fibers pass through the composite processing device;

[0017] The composite treatment device is at least used to contain a high molecular polymer-protonated strong acid solution, so that the carbon nanotube fibers are in contact with the high molecular polymer-protonated strong acid solution;

[0018] The coagulation bath device is at least used to contain a solution used for densification treatment, so that the fibers of the protonated composite shrink and densify in the solution used for densification treatment;

[0019] The cleaning bath device is used at least to accommodate the solution used for the cleaning treatment to remove the protonated strong acid and / or the solution used for the densification treatment;

[0020] The winding device is at least used for continuously collecting the composite carbon nanotube / polymer composite fibers.

[0021] The present invention also provides a carbon nanotube / polymer composite fiber prepared by the above-mentioned carbon nanotube / polymer composite fiber preparation method or the above-mentioned continuous production system.

[0022] As described above, the carbon nanotube / polymer composite fiber preparation method and continuous production system of the present invention have the following beneficial effects:

[0023] 1. In the method for preparing carbon nanotube / polymer composite fibers of the present invention, during the composite process of carbon nanotube fibers and polymers, the carbon nanotube fibers are protonated by a protonated strong acid. The carbon nanotube fibers swell due to the protonation, so that the polymer enters into a large number of nanopores inside the expanded carbon nanotube fibers, thereby achieving a completely uniform composite between the polymer and the carbon nanotube fibers. The structure of the expanded composite fibers is then densified again through a densification treatment, and finally, the carbon nanotube / polymer composite fibers with excellent mechanical properties are obtained through washing and high-temperature treatment.

[0024] 2. In the carbon nanotube / polymer composite fiber preparation method of the present invention, since the expansion process of the carbon nanotube fiber and the composite speed of the polymer and the carbon nanotube are extremely fast, the process does not require additional treatment and helps to achieve continuous batch preparation of polymer / carbon nanotube composite materials, bringing very significant preparation efficiency advantages and performance improvement advantages.

[0025] 3. The method for preparing the carbon nanotube / polymer composite fiber of the present invention is simple, fast, energy-saving and highly efficient.

[0026] 4. The continuous production system of carbon nanotube / polymer composite fibers of the present invention realizes continuous batch composite of carbon nanotube fibers and polymer solutions through continuous unwinding and winding devices by combining an unwinding device with a composite treatment device, a coagulation bath device, a cleaning bath device and a winding device, and allows composite and protonation processes to proceed simultaneously through a composite treatment device, and then densifies again through a coagulation bath device and a cleaning bath device to prepare carbon nanotube / polymer composite fiber materials with excellent mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Shown is a schematic diagram of the process of preparing the carbon nanotube / polymer composite fiber of the present invention.

[0028] Figure 2 It is a schematic diagram showing the composition of the carbon nanotube / polymer composite fiber continuous production system of the present invention.

[0029] Figure 3 Shown is an electron microscope photograph of the fracture morphology of the polyimide / carbon nanotube composite fiber provided in Example 1 of the present invention.

[0030] Figure 4 Shown is an electron microscope photograph of the surface morphology of the polyimide / carbon nanotube composite fiber provided in Example 1 of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 1 Unwinding device

[0033] 2. Composite treatment device

[0034] 3 Coagulation bath device

[0035] 4 Cleaning bath device

[0036] 5. Winding device

[0037] 6 High temperature treatment device DETAILED DESCRIPTION

[0038] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0039] In the present invention, relational terms such as “first” and “second” are merely used to distinguish one component or method step from another with the same name, but do not necessarily require or imply any actual relationship or order between these components or method steps.

[0040] Please refer to the attached drawings. It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show the components related to the present invention rather than the number, shape and size of the components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0041] The first aspect of the present invention provides a method for preparing a carbon nanotube / polymer composite fiber, comprising the following steps:

[0042] 1) preparing a high molecular polymer-protonated strong acid solution;

[0043] 2) placing the carbon nanotube fiber in the high molecular polymer-protonated strong acid solution for composite treatment to obtain a protonated composite;

[0044] 3) subjecting the protonated composite to a densification treatment to obtain a precursor fiber;

[0045] 4) Washing the precursor fiber to obtain carbon nanotube / polymer composite fiber. Figure 1 shown.

[0046] The original carbon nanotube fibers described in the present invention can be prepared by oneself or purchased from the market.

[0047] In some embodiments of the present invention, the preparation of the high molecular polymer-protonated strong acid solution includes: adding the polymer to the protonated strong acid, mixing uniformly at 60°C to 100°C, to obtain the high molecular polymer-protonated strong acid solution. For example, the temperature may be 60°C to 70°C, 70°C to 80°C, 80°C to 90°C, or 90°C to 100°C. The appropriate temperature also helps the polymer to dissolve in the protonated strong acid.

[0048] Wherein, the polymer is selected from any one or more of polyimide and polyamic acid. In the preferred embodiment of the present invention, the polymer is polyimide. Polyimide is a high molecular polymer with a five-membered imide ring as the core, which is usually condensed and polymerized into polyamic acid by dianhydride and diamine under certain conditions. It can be used as a precursor of polyimide and is applied to the preparation of composite materials; it can also be dehydrated and cyclized to form polyimide in a certain way. These polymer chains can be highly oriented and only dissolved in protonated strong acids. Strong acids can protonate aromatic groups and promote the dissolution of polymers containing the above groups. In addition, for polymers with polar functional groups (such as carboxylic acids and amines), strong acids as polar solvents can be dissolved in the form of protonated dissolution. The above effects make the preparation of polyimide / protonated strong acid solutions more convenient.

[0049] The protonated strong acid is selected from any one or more of methanesulfonic acid (95-98%, such as 95-96%, 96-97% or 97-98%), concentrated sulfuric acid (95-98%, such as 95-96%, 96-97% or 97-98%), and concentrated nitric acid (37%). The solvent with appropriate protonation ability in the present invention is more important. When the protonation ability of the solvent is too strong (such as chlorosulfonic acid), it is easy to cause damage to the polymer or the destruction of the ordered structure of the carbon nanotubes, or the destruction of the carbon nanotube / polymer composite structure. When the protonation ability is insufficient, it is impossible to obtain sufficient pore expansion and solvent introduction effects. Therefore, it is necessary to select a solvent with appropriate protonation ability. The protonated strong acid in the present invention can dissolve high-performance polymer materials and monomers with ultra-high molecular weight, including polyimide, so that the high-performance polymer materials and carbon nanotubes can be uniformly composited.

[0050] There are many nanometer-scale pores inside the carbon nanotube fiber, but it is difficult for high molecular weight polymers such as polyimide to enter such tiny pores, resulting in difficulty in uniform and effective compounding of the carbon nanotube fiber and the high molecular polymer. In the compounding process, the present invention uses a strong acid solution as a protonating agent, which can expand the carbon nanotubes through protonation in the compounding bath, expand the distance between the tubes, and make the structure loose, so that the polymer molecules can effectively enter the pores inside the carbon nanotubes, thereby achieving uniform compounding between the polymer and the carbon nanotubes.

[0051] The concentration of the polymer in the high molecular polymer-protonated strong acid solution is 0.05-25 g / L. For example, 0.05-0.1 g / L, 0.01-0.5 g / L, 0.5-1.0 g / L, 1.0-1.5 g / L, 1.5-2.0 g / L, 2.0-2.5 g / L, 2.5-3.0 g / L, 3.0-3.5 g / L, 3.5-4.0 g / L, 4.0-4.5 g / L, 4.5-5.0 g / L, 5.0-6.0 g / L, 6.0-7. 0g / L, 7.0-8.0g / L, 8.0-9.0g / L, 9.0-10.0g / L, 10.0-12.0g / L, 12.0-14.0g / L, 14.0-16.0g / L, 16.0-18.0g / L, 18.0-20.0g / L, 20.0-22.0g / L, 22.0-24.0g / L or 24.0-25.0g / L. In a preferred embodiment of the present invention, the concentration of the polymer in the high molecular polymer-protonated strong acid solution is 2.5-10g / L. Since the high molecular polymer-protonated strong acid solution is mainly obtained by polymer dissolution, not by polymerization reaction, and the dissolution of the polymer is by the protonation of the strong acid, its dissolution concentration has an upper limit. When the concentration is too high, the strong acid cannot completely protonate the carbon chains in the fiber, resulting in the polymer being unable to fully penetrate into the carbon nanotube fiber. In addition, the dissolution concentration cannot be too low. When the concentration is too low, the polymer content is too low, and the composite reinforcement effect on the carbon nanotube fiber is limited.

[0052] The uniform mixing is achieved by stirring.

[0053] In some embodiments of the present invention, the composite treatment specifically includes: continuously immersing the carbon nanotube fibers in and passing through the high molecular polymer-protonated strong acid solution.

[0054] In some embodiments of the present invention, the temperature of the composite treatment in step 2) is 15-35°C, for example, 15-20°C, 20-25°C, 25-30 or 30-35°C.

[0055] In some embodiments of the present invention, the duration of the composite treatment in step 2) is 1 to 7 minutes. For example, 1 to 2 minutes, 2 to 3 minutes, 3 to 4 minutes, 4 to 5 minutes, 5 to 6 minutes or 6 to 7 minutes. In a preferred embodiment of the present invention, the duration of the composite treatment is 3 to 5 minutes.

[0056] In some embodiments of the present invention, the densification treatment specifically comprises: continuously immersing the protonated composite into and passing through a solution for the densification treatment.

[0057] In some embodiments of the present invention, the densification treatment in step 3) is carried out in a coagulation bath solution, and the coagulation bath solution is selected from any one or more of water, alcohol, and acetone. In the coagulation bath solution, due to the effect of solubility difference, the protonated strong acid in the carbon nanotubes is precipitated, and the composite material structure is densified again, thereby realizing the preparation of carbon nanotube / polymer composite fibers. When water is used as a coagulation bath in step 3), it should be properly isolated from the composite solution. For example, the coagulation bath tank containing the coagulation bath is placed in a box that can isolate water vapor or the coagulation bath tank containing the coagulation bath is placed in a device containing a large amount of desiccant (such as silica gel).

[0058] In some embodiments of the present invention, the temperature of the densification treatment in step 3) is 15-35°C, for example, 15-20°C, 20-25°C, 25-30 or 30-35°C.

[0059] In some embodiments of the present invention, the densification treatment time in step 3) is 1 to 7 minutes. For example, 1 to 2 minutes, 2 to 3 minutes, 3 to 4 minutes, 4 to 5 minutes, 5 to 6 minutes or 6 to 7 minutes. In a preferred embodiment of the present invention, the densification treatment time is 3 to 5 minutes.

[0060] In some embodiments of the present invention, the cleaning specifically comprises: continuously immersing the precursor fiber in and passing through a cleaning solution.

[0061] In some embodiments of the present invention, the cleaning in step 4) is performed in a cleaning bath solution, and the cleaning bath solution is selected from any one or more of water, alcohol, and acetone.

[0062] When water is used as a cleaning bath in step 4), it should be properly isolated from the composite solution, such as placing the coagulation bath tank containing the coagulation bath in a box that can isolate water vapor or placing the coagulation bath tank containing the coagulation bath in a device containing a large amount of desiccant (such as silica gel).

[0063] In some embodiments of the present invention, the cleaning temperature in step 4) is 15-35°C, for example, 15-20°C, 20-25°C, 25-30 or 30-35°C.

[0064] In some embodiments of the present invention, the cleaning time in step 4) is 1 to 7 minutes. For example, 1 to 2 minutes, 2 to 3 minutes, 3 to 4 minutes, 4 to 5 minutes, 5 to 6 minutes or 6 to 7 minutes. In a preferred embodiment of the present invention, the cleaning time is 3 to 5 minutes.

[0065] In some embodiments of the present invention, the step 4) further includes a high temperature treatment step after the cleaning. When the carbon nanotube / polymer composite fiber is prepared, in some cases, there is still a certain amount of protonated strong acid residue. In order to completely remove the protonated strong acid and completely imidize the polymer (such as polyamic acid) of the composite fiber, a high temperature heat treatment process is required to achieve the above purpose.

[0066] By setting up a coagulation bath and a cleaning bath: First, the protonated strong acid inside the carbon nanotubes can be washed away, the charge distribution of the carbon nanotubes can be changed, and the carbon nanotube fibers can be re-densified. Second, the coagulation bath solution and the cleaning bath solution cannot dissolve polyimide. Therefore, the solubility difference can be used to precipitate the polyimide and deposit it on the carbon nanotube fibers, making the composite effect more obvious. In addition to thoroughly washing away the protonated strong acid, the cleaning bath can also take away the polyimide deposited on the fiber surface.

[0067] The temperature of the high temperature treatment is 200-400° C. For example, 200-220° C., 220-240° C., 240-260° C., 260-280° C., 280-300° C., 300-320° C., 320-340° C., 340-360° C., 360-380° C. or 380-400° C. The high temperature treatment can realize the crosslinking and curing of the polymer in the precursor fiber to improve the strength of the carbon nanotube / polymer composite fiber.

[0068] The high temperature treatment time is 1 to 6 hours, for example, 1 to 2 hours, 2 to 3 hours, 3 to 4 hours, 4 to 5 hours or 5 to 6 hours.

[0069] In the preparation method of the present invention, steps 1) to 4) are all required to be carried out in a dry atmosphere. The dry atmosphere is an air humidity of less than 40%. Since protonated strong acids: methanesulfonic acid, concentrated sulfuric acid and concentrated nitric acid are all highly hygroscopic, and polymers such as polyimide will cause high molecular crystallization when they come into contact with water, it is necessary to avoid water entering the solution system during the operation, and the operation must be carried out under dry conditions to avoid the acid absorbing a large amount of water in the air. If water is used as a component of the cleaning bath and the coagulation bath, it needs to be isolated from the composite bath solution.

[0070] The second aspect of the present invention provides a continuous production system suitable for the above-mentioned carbon nanotube / polymer composite fiber preparation method, and the system includes: an unwinding device 1, a composite processing device 2, a coagulation bath device 3, a cleaning bath device 4 and a winding device 5 connected along a continuous production route.

[0071] The unwinding device 1 is at least used to introduce the carbon nanotube fibers into the composite processing device 2 and to control the speed at which the carbon nanotube fibers pass through the composite processing device 2;

[0072] The composite treatment device 2 is at least used to contain a high molecular polymer-protonated strong acid solution, so that the carbon nanotube fibers are in contact with the high molecular polymer-protonated strong acid solution;

[0073] The coagulation bath device 3 is at least used to contain the solution used for the densification treatment, so that the fibers of the protonated composite shrink and densify in the solution used for the densification treatment;

[0074] The cleaning bath device 4 is used at least to accommodate the solution used for the cleaning treatment to remove the protonated strong acid and / or the solution used for the densification treatment;

[0075] The winding device 5 is at least used to continuously collect the composite carbon nanotube / polymer composite fibers. Figure 2 shown.

[0076] The solution used for densification treatment contained in the coagulation bath device 3, namely the coagulation bath solution, can remove the protonated strong acid in the precursor fiber through the effect of solubility difference.

[0077] In the present invention, the order and quantity of the composite treatment device 2, the coagulation bath device 3, and the cleaning bath device 4 can be adjusted and replaced according to actual conditions to achieve the preparation of composite fibers. For example, the system includes the following connected in sequence along the continuous production route: the unwinding device 1, the composite treatment device 2, the coagulation bath device 3, the cleaning bath device 4, and the winding device 5, or the system includes the following connected in sequence along the continuous production route: the unwinding device 1, the cleaning bath device 4, the composite treatment device 2, the coagulation bath device 3, and the winding device 5, or the system includes the following connected in sequence along the continuous production route: the unwinding device 1, the coagulation bath device 3, the composite treatment device 2, the cleaning bath device 4, and the winding device 5, and so on.

[0078] The present invention can adjust the unwinding rate of the unwinding device 1 and the winding rate of the winding device 5 to create an unwinding and winding speed difference, and the carbon nanotubes in the expanded state can be stretched by changing the speed difference, which can effectively improve the orientation of the carbon nanotubes and increase the densification degree, thereby further improving the mechanical properties of the composite material.

[0079] The unwinding device 1 and the winding device 5 of the present invention can control the carbon nanotube fibers to continuously immerse in and pass through the polymer-protonated strong acid solution, and can also control the protonated composite to continuously immerse in and pass through the solution used for densification treatment; and can also control the precursor fibers to continuously immerse in and pass through the solution used for cleaning.

[0080] In some embodiments of the present invention, as shown in the attached Figure 2 As shown, the system further comprises a high temperature treatment device 6, which is connected to the winding device 5, and is used for cross-linking and curing the polymer in the precursor fiber.

[0081] The high temperature treatment device 6 is a tubular furnace or a muffle furnace.

[0082] In some embodiments of the present invention, the composite treatment device (2) comprises a first container for containing a high molecular polymer-protonated strong acid solution.

[0083] In some embodiments of the present invention, the coagulation bath device (3) comprises a second container for containing a solution used for densification treatment.

[0084] In some embodiments of the present invention, the cleaning bath device (4) includes a third container for containing a solution used for cleaning treatment.

[0085] The third aspect of the present invention provides a method for preparing the carbon nanotube / polymer composite fiber as described above or a carbon nanotube / polymer composite fiber prepared by the continuous production system as described above.

[0086] The carbon nanotube / polymer composite fiber comprises a carbon nanotube body and a polymer composite phase composited in the carbon nanotube body.

[0087] The tensile strength of the nanotube / polymer composite fiber is greater than 1.8 GPa.

[0088] The breaking elongation of the nanotube / polymer composite fiber is 1-8%, for example, 1-2%, 2-3%, 3-4%, 4-5%, 5-6%, 6-7% or 7-8%.

[0089] The preparation method provided by the present invention can be applied to existing, spun, oriented and dense carbon nanotube fibers, rather than short carbon nanotubes or powders.

[0090] Example 1

[0091] Preparation of carbon nanotube / polymer composite fibers:

[0092] 1) Acquisition of carbon nanotube fibers: The carbon nanotube fibers are prepared by floating chemical catalytic vapor deposition method, and the prepared fibers are not subjected to any treatment;

[0093] 2) preparing a high molecular polymer-protonated strong acid solution in the composite treatment device 2: adding polyimide powder (constituents are 3,3',4,4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine, the molar ratio of the two being 1:1) to 98% methanesulfonic acid, stirring at 80° C. for 3 h, and preparing a 5 g / L polyimide / methanesulfonic acid solution;

[0094] 3) introducing the carbon nanotube fiber obtained in step 1) into the composite treatment device 2 containing the polyimide / methanesulfonic acid solution prepared in step 2) through the unwinding device 1, immersing the carbon nanotube fiber in the solution, and continuously moving the carbon nanotube fiber at a rate of 0.5 revolutions per minute, so that the carbon nanotube fiber stays in the solution for 3 minutes, and obtaining a protonated composite;

[0095] 4) introducing the protonated complex treated in step 3) into a coagulation bath device 3 filled with alcohol for densification treatment to obtain precursor fibers;

[0096] 5) introducing the precursor fiber treated in step 4) into a cleaning bath device 4 filled with alcohol for cleaning;

[0097] 6) collecting the composite fiber treated in the above steps in a winding device 5 to obtain polyimide / carbon nanotube fibers;

[0098] 7) The above steps 3) to 6) are carried out in a room with an air humidity below 30%, and a desiccant is placed near each device to maintain a dry atmosphere.

[0099] The obtained polyimide / carbon nanotube fiber was tested by a mechanical testing machine. The tensile strength of the polyimide / carbon nanotube composite fiber obtained in this embodiment was 2.45 GPa, and the elongation at break was 4.6%. The obtained polyimide / carbon nanotube fiber fracture scanning electron microscope image is as follows: Figure 3 The surface scanning electron microscope image is shown in Figure 4 As shown. Figure 3 It can be seen that polyimide and carbon nanotube fibers have been uniformly composited; Figure 4 It can be seen that the excess polyimide on the surface of the composite fiber has been washed away.

[0100] Example 2

[0101] 1) Acquisition of carbon nanotube fibers: The carbon nanotube fibers are prepared by floating chemical catalytic vapor deposition method, and the prepared fibers are not subjected to any treatment;

[0102] 2) preparing a high molecular polymer-protonated strong acid solution in the composite treatment device 2: adding polyimide powder (composed of pyromellitic anhydride and 4,4'-diaminodiphenyl ether, the molar ratio of the two being 1:1) to 98% methanesulfonic acid, stirring at 80° C. for 3 h, and preparing a 2.5 g / L polyimide / methanesulfonic acid solution;

[0103] 3) introducing the carbon nanotube fiber obtained in step 1) into the composite treatment device 2 containing the polyimide / methanesulfonic acid solution prepared in step 2) through the unwinding device 1, immersing the carbon nanotube fiber in the solution, and continuously moving the carbon nanotube fiber at a rate of 0.5 revolutions per minute, so that the carbon nanotube fiber stays in the solution for 3 minutes, and obtaining a protonated composite;

[0104] 4) introducing the protonated complex treated in step 3) into a coagulation bath device 3 filled with alcohol for densification treatment to obtain precursor fibers;

[0105] 5) introducing the precursor fiber treated in step 4) into a cleaning bath device 4 filled with water for cleaning;

[0106] 6) collecting the composite fiber treated in the above steps in a winding device 5 to obtain polyimide / carbon nanotube fibers;

[0107] 7) The above steps 3) to 6) are carried out in a room with an air humidity below 40%, and a desiccant is placed near each device to maintain a dry atmosphere.

[0108] The obtained polyimide / carbon nanotube fiber was tested by a mechanical testing machine. The tensile strength of the polyimide / carbon nanotube composite fiber obtained in this embodiment was 2.25 GPa, and the elongation at break was 4.5%.

[0109] Example 3

[0110] 1) Acquisition of carbon nanotube fibers: The carbon nanotube fibers are prepared by floating chemical catalytic vapor deposition method, and the prepared fibers are not subjected to any treatment;

[0111] 2) preparing a high molecular polymer-protonated strong acid solution in the composite treatment device 2: adding polyamic acid powder (composed of pyromellitic anhydride and 4,4'-diaminodiphenyl ether, the molar ratio of the two being 1:1) to 98% methanesulfonic acid, stirring at 80° C. for 3 h, and preparing a 5 g / L polyamic acid / methanesulfonic acid solution;

[0112] 3) introducing the carbon nanotube fiber obtained in step 1) into the composite treatment device 2 containing the polyimide / methanesulfonic acid solution prepared in step 2) through the unwinding device 1, immersing the carbon nanotube fiber in the solution and continuously moving at a rate of 0.4 rpm so that the carbon nanotube fiber stays in the solution for 5 min, thereby obtaining a protonated composite;

[0113] 4) introducing the protonated complex treated in step 3) into a coagulation bath device 3 filled with water for densification treatment to obtain a precursor fiber;

[0114] 5) introducing the precursor fiber treated in step 4) into a cleaning bath device 4 filled with water for cleaning;

[0115] 6) collecting the composite fiber after the treatment in the above steps in a winding device 5, and then heat-treating it at 300° C. for 3 h in a high-temperature device 6 to obtain polyimide / carbon nanotube fibers;

[0116] 7) The above steps 3) to 5) are carried out in a room with an air humidity below 40%, and a desiccant is placed near each device to maintain a dry atmosphere, and the ratio of the winding speed to the unwinding speed is 1.125.

[0117] The obtained polyimide / carbon nanotube fiber was tested by a mechanical testing machine. The tensile strength of the polyimide / carbon nanotube composite fiber obtained in this embodiment was 3.19 GPa, and the elongation at break was 3.42%.

[0118] Example 4

[0119] The preparation process of polyimide / carbon nanotube fibers in this embodiment is different from that in Embodiment 1 in that the methanesulfonic acid in step 2) is replaced by 95% concentrated sulfuric acid, and the remaining steps and treatment methods are the same as those in Embodiment 1.

[0120] The polyimide / carbon nanotube fiber obtained in this embodiment was tested by a mechanical testing machine. The tensile strength of the polyimide / carbon nanotube composite fiber obtained in this embodiment was 1.98 GPa, and the elongation at break was 8.29%.

[0121] Example 5

[0122] The preparation process of the polyimide / carbon nanotube fiber in this embodiment is different from that in Embodiment 3 in that:

[0123] The rate of continuous movement in step 3) is 1 revolution / min; the residence time of the carbon nanotubes in the solution is adjusted to 2 minutes;

[0124] In step 6), the heat treatment is adjusted to 200° C. for 3 h.

[0125] The remaining steps and processing methods are the same as those in Example 3.

[0126] The polyimide / carbon nanotube fiber obtained in this embodiment was tested by a mechanical testing machine. The tensile strength of the polyimide / carbon nanotube composite fiber obtained in this embodiment was 3.0 GPa, and the elongation at break was 2.2%.

[0127] Example 6

[0128] In this comparative example, steps 3) to 5) are as follows:

[0129] 3) introducing the carbon nanotube fibers obtained in step 1) into a cleaning bath device 4 filled with water for cleaning through an unwinding device 1, and continuously moving the fibers at a rate of 0.5 rpm so that the fibers stay in the solution for 5 min, thereby obtaining treated fibers;

[0130] 4) introducing the carbon nanotube fibers treated in step 3) into a composite treatment device 2 containing the polyimide / methanesulfonic acid solution prepared in step 2) and immersing the carbon nanotube fibers in the solution to obtain precursor fibers;

[0131] 5) introducing the precursor fiber treated in step 4) into a coagulation bath device 3 filled with alcohol for densification treatment to obtain a polyimide / carbon nanotube composite fiber;

[0132] The remaining steps and processing methods are the same as those in Example 1.

[0133] The carbon nanotube composite fiber obtained in this comparative example was tested by a mechanical testing machine, and the tensile strength was 2.05 GPa and the elongation at break was 4.4%, indicating that changing the position sequence of the composite treatment device 2, the coagulation bath device 3 and the cleaning bath device 4 has little effect on the mechanical properties of the obtained carbon nanotube composite fiber.

[0134] Example 7

[0135] In this comparative example, step 4) is eliminated, and the remaining steps and processing methods are the same as those in Example 1.

[0136] The carbon nanotube fiber obtained in this comparative example was tested by a mechanical testing machine, and the tensile strength was 2.18 GPa and the elongation at break was 6.45%, which shows that eliminating the cleaning bath device has little effect on the mechanical properties of the obtained carbon nanotube composite fiber.

[0137] Comparative Example 1

[0138] The preparation process of the polyimide / carbon nanotube fiber in this comparative example is different from that in Example 1 in that:

[0139] The polyimide / methanesulfonic acid solution prepared in step 2) is replaced by methanesulfonic acid, and the remaining steps and treatment methods are the same as those in Example 1.

[0140] The carbon nanotube fibers obtained in this comparative example were tested by a mechanical testing machine, and the tensile strength was only 0.86 GPa, indicating that the carbon nanotube fibers treated with methanesulfonic acid alone had loose carbon nanotube fiber structures, increased internal defects, and poor fiber orientation due to lack of physical stretching, thus poor mechanical properties.

[0141] Comparative Example 2

[0142] The preparation process of the polyimide / carbon nanotube fiber in this comparative example is different from that in Example 1 in that:

[0143] The protonated strong acid solvent of the polyimide / methanesulfonic acid solution prepared in step 2) is replaced with chlorosulfonic acid, and the remaining steps and treatment methods are the same as those in Example 1.

[0144] The carbon nanotube composite fiber obtained in this comparative example was tested by a mechanical testing machine, and the tensile strength was only 1.68 GPa. This was because the chlorosulfonic acid with too strong protonation could cause the carbon nanotube fiber structure to become loose, and the densification degree decreased during the coagulation bath and cleaning bath process.

[0145] Comparative Example 3

[0146] In this comparative example, steps 2) to 5) are as follows:

[0147] 2) preparing a high molecular polymer-organic solvent solution in the second composite treatment device 2: adding polyamic acid powder (constituents are pyromellitic anhydride and 4,4'-diaminodiphenyl ether, the molar ratio of the two is 1:1) to N'-methylpyrrolidone, stirring at a temperature of 25° C. for 3 hours to prepare a 5 g / L polyamic acid / N'-methylpyrrolidone solution;

[0148] 3) introducing the carbon nanotube fibers obtained in step 1) into the first composite treatment device 2 containing methanesulfonic acid through the unwinding device 1 for treatment, and continuously moving at a rate of 0.5 rpm, so that the residence time of the fibers in the solution is 5 min, to obtain treated fibers;

[0149] 4) introducing the carbon nanotube fibers treated in step 3) into a second composite treatment device 2 containing the polyimide / methanesulfonic acid solution prepared in step 2) and immersing the carbon nanotube fibers in the solution to obtain precursor fibers;

[0150] 5) introducing the precursor fiber treated in step 4) into a coagulation bath device 3 filled with alcohol for densification treatment to obtain a polyimide / carbon nanotube composite fiber;

[0151] The remaining steps and processing methods are the same as those in Example 1.

[0152] The carbon nanotube fiber obtained in this comparative example was tested by a mechanical testing machine, and the tensile strength was 1.45GPa and the elongation at break was 4.45%. This shows that the asynchronous protonation treatment and polymer compounding will cause the polyimide molecules to be unable to effectively enter the interior of the carbon nanotube fiber, making it impossible for the two to be evenly compounded, resulting in uneven force on the composite fiber, affecting the mechanical properties of the composite fiber.

[0153] Comparative Example 4

[0154] The preparation process of polyimide / carbon nanotube fibers in this comparative example is different from that in implementation 1 in that: when preparing the high molecular polymer-protonated strong acid solution in step 2), the concentration of the prepared polyimide / methanesulfonic acid solution is 30 g / L;

[0155] The remaining steps and processing methods are the same as those in Example 1.

[0156] The carbon nanotube fiber obtained in this comparative example was tested by a mechanical testing machine, and the tensile strength was 1.35GPa and the elongation at break was 5.1%. This shows that an excessively high concentration of polymer-protonated strong acid solution will lead to an excessively high content of polyimide in the fiber prepared after composite, causing the carbon nanotubes to be dispersed inside the polyimide, thereby weakening the force of the carbon nanotubes in the composite fiber and affecting the strength of the composite fiber.

[0157] In summary, the method for preparing carbon nanotube / polymer composite fibers of the present invention realizes continuous and uniform compounding between carbon nanotube fibers and polyimide by directly compounding carbon nanotube fibers with polyimide solution, and the process from compounding to treatment is completed in one step. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0158] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing carbon nanotube / polymer composite fibers, characterized in that: The following steps are involved: 1) preparing a high molecular polymer-protonated strong acid solution; 2) placing the carbon nanotube fiber in the high molecular polymer-protonated strong acid solution for composite treatment to obtain a protonated composite; 3) subjecting the protonated composite to a densification treatment to obtain a precursor fiber; 4) Washing the precursor fiber to obtain carbon nanotube / polymer composite fiber.

2. The method for preparing carbon nanotube / polymer composite fibers according to claim 1, characterized in that: The preparation of the high molecular polymer-protonated strong acid solution comprises: adding the polymer into the protonated strong acid, and mixing evenly at 60° C. to 100° C. to obtain the polymer-protonated strong acid solution; And / or, the composite treatment specifically includes: continuously immersing the carbon nanotube fibers into and passing through the high molecular polymer-protonated strong acid solution; And / or, the densification treatment specifically comprises: continuously immersing the protonated composite into and through a solution used for the densification treatment; And / or, the washing specifically comprises: continuously immersing the precursor fiber in and passing through a washing solution.

3. The method for preparing carbon nanotube / polymer composite fibers according to claim 2, characterized in that: The polymer is selected from any one or more of polyimide and polyamic acid; And / or, the protonated strong acid is selected from any one or more of methanesulfonic acid, concentrated sulfuric acid, and concentrated nitric acid; And / or, the concentration of the polymer in the high molecular polymer-protonated strong acid solution is 0.05-25 g / L.

4. The method for preparing carbon nanotube / polymer composite fibers according to claim 1, characterized in that: The temperature of the composite treatment in step 2) is 15-35°C; And / or, the time of the composite treatment in step 2) is 1 to 7 minutes; And / or, the densification treatment in step 3) is carried out in a coagulation bath solution, wherein the coagulation bath solution is selected from any one or more of water, alcohol, and acetone; And / or, the temperature of the densification treatment in step 3) is 15-35°C; And / or, the densification treatment time in step 3) is 1 to 7 minutes; And / or, the cleaning in step 4) is carried out in a cleaning bath solution, wherein the cleaning bath solution is selected from any one or more of water, alcohol, and acetone; And / or, the cleaning temperature in step 4) is 15-35°C; And / or, the cleaning time in step 4) is 1 to 7 minutes; And / or, steps 1) to 4) are all carried out in a dry atmosphere.

5. The method for preparing carbon nanotube / polymer composite fibers according to claim 1, characterized in that: The step 4) further includes a high temperature treatment step after the cleaning.

6. The method for preparing carbon nanotube / polymer composite fibers according to claim 5, characterized in that: The temperature of the high temperature treatment is 200-400°C; And / or, the high temperature treatment time is 1 to 6 hours.

7. A continuous production system suitable for the method for preparing carbon nanotube / polymer composite fibers according to any one of claims 1 to 6, characterized in that: The system comprises connected along a continuous production route: an unwinding device (1), a compound processing device (2), a coagulation bath device (3), a cleaning bath device (4) and a winding device (5); The unwinding device (1) is at least used to introduce the carbon nanotube fibers into the composite processing device (2) and to regulate the speed at which the carbon nanotube fibers pass through the composite processing device (2); The composite treatment device (2) is at least used to contain a high molecular polymer-protonated strong acid solution, so that the carbon nanotube fibers are in contact with the high molecular polymer-protonated strong acid solution; The coagulation bath device (3) is at least used to contain a solution used for densification treatment, so that the fibers of the protonated composite shrink and densify in the solution used for densification treatment; The cleaning bath device (4) is used at least to accommodate the solution used for the cleaning treatment to remove the protonated strong acid and / or the solution used for the densification treatment; The winding device (5) is at least used to continuously collect the composited carbon nanotube / polymer composite fibers.

8. The continuous production system according to claim 7, characterized in that: The system further comprises a high temperature treatment device (6), wherein the high temperature treatment device (6) is connected to the winding device (5), and the high temperature treatment device (6) is used to crosslink and solidify the polymer in the precursor fiber; And / or, the composite treatment device (2) comprises a first container for containing a high molecular polymer-protonated strong acid solution; And / or, the coagulation bath device (3) comprises a second container for containing a solution used for densification treatment; And / or, the cleaning bath device (4) comprises a third container for containing a solution used for cleaning treatment.

9. A carbon nanotube / polymer composite fiber prepared by the carbon nanotube / polymer composite fiber preparation method according to any one of claims 1 to 6 or by the continuous production system according to any one of claims 7 to 8.

10. The carbon nanotube / polymer composite fiber according to claim 9, characterized in that: The carbon nanotube / polymer composite fiber comprises a carbon nanotube body and a polymer composite phase composited in the carbon nanotube body; and / or, the tensile strength of the nanotube / polymer composite fiber is greater than 1.8 GPa; And / or, the elongation at break of the nanotube / polymer composite fiber is 1-8%.

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