Two-dimensional aromatic polyamide fiber and preparation method thereof

Abstract

The invention discloses a two-dimensional aromatic polyamide fiber and a preparation method thereof, and solves the problems that most of two-dimensional macromolecules obtained through organic synthesis are crystalline powder, are poor in dispersity and cannot be prepared into high-concentration dispersion liquid. The preparation method comprises the following steps: synthesizing two-dimensional polyamide powder through ammonolysis reaction of acyl chloride, mixing two-dimensional polyamide and polyethylene oxide (PEO) by using a specific solvent to prepare a spinning solution, and carrying out dry spinning to obtain the two-dimensional polyamide fiber. The preparation of the organically synthesized two-dimensional macromolecular fiber is realized, the prepared two-dimensional polyamide fiber has high strength, and the tensile strength can reach 2.7 GPa.

Description

Technical Field

[0001] The invention belongs to the technical field of polyamide fibers, and in particular relates to a two-dimensional aromatic polyamide fiber and a preparation method thereof. Background Art

[0002] Two-dimensional macromolecules have attracted much attention in the field of materials due to their high specific surface area, unique layered nanostructure and excellent performance. For example, graphene, a two-dimensional macromolecule composed of a single layer of carbon atoms arranged in a hexagonal honeycomb lattice, has great application potential in the fields of high-strength structural materials, flexible electronics and thermal management materials due to its high strength, high flexibility, high carrier mobility and high thermal conductivity. In addition to single-layer or few-layer two-dimensional macromolecules obtained by peeling off natural layered materials such as graphene, Mxene and molybdenum disulfide, two-dimensional macromolecules obtained by organic synthesis such as two-dimensional COF and MOF are also widely used in separation, catalysis and energy storage due to their high specific surface area. However, most of the two-dimensional macromolecules obtained by organic synthesis are crystalline powders with poor processing performance and are difficult to be used in the preparation of macroscopic assembly materials such as films and fibers. This is partly because the dispersibility of crystalline powders is poor, and the extremely strong interlayer forces in the ordered crystalline structure make the two-dimensional sheets tightly stacked to form agglomerates, which are difficult to disperse in solvents as single-layer or few-layer two-dimensional macromolecules. On the other hand, because sheet-like two-dimensional macromolecules cannot form entangled structures in solution like chain-like one-dimensional macromolecules, the dispersion of two-dimensional macromolecules lacks viscoelasticity and is no longer suitable for various processing methods that have been widely used in one-dimensional macromolecules, such as dry spinning. In summary, the molding and processing of organically synthesized two-dimensional macromolecules faces huge challenges. The existing materials are mainly nanometer-thick films obtained by spin coating, while the preparation of macroscopic assembly materials, especially fibers, is still rare.

[0003] In the prior art, two types of sulfonic acid group-containing COFs with liquid crystal behavior are used [DABA-TFP-COF and DASD-TFP-COF dispersions are respectively formed by the reaction of 1,3,5-triformylphloroglucinol (TFP) with diaminobenzenesulfonic acid (DABA) or 4,4'-diamino-2,2'-stilbene disulfonic acid (DASD)]. After these two types of COFs are configured into a relatively high concentration dispersion (up to 25 mg / ml), they can be processed into fibers on a large scale by wet spinning using a calcium ion solution as a coagulation bath. The two-dimensional COF molecules used in this method have poor dispersibility and cannot obtain a high concentration dispersion, so they are not suitable for processing by dry spinning technology. Summary of the invention

[0004] In view of the problem that most of the two-dimensional macromolecules obtained by organic synthesis are crystalline powders with poor dispersibility and cannot be prepared into high-concentration dispersions, the present invention discloses a two-dimensional aromatic polyamide fiber and a preparation method. First, the two-dimensional polyamide powder is synthesized by aminolysis of acyl chloride, and then the two-dimensional polyamide and polyethylene oxide (PEO) are mixed with a specific solvent to prepare a spinning solution, and then dry spinning is performed to obtain the two-dimensional polyamide fiber.

[0005] Unlike other organically synthesized two-dimensional macromolecules, the two-dimensional aromatic polyamide powder synthesized in the present invention is stacked by many small-sized two-dimensional sheets, and there is no large-area ordered crystalline structure inside the two-dimensional sheet, but it is composed of many small crystal areas arranged in disorder, so the interaction between the sheets is weak, so that the stacked sheets can be quickly dispersed in a specific solvent (or mechanical force accelerates the dispersion) to form a single layer or several layers of extremely thin layered molecules, and a stable high-concentration dispersion is obtained, and the concentration can be as high as 45 wt.%. At the same time, the present invention adds ultra-high molecular weight polyethylene oxide to the dispersion to introduce entanglement so that the dispersion has stretchability. Combined with the dry spinning process, highly oriented fibers are directly formed by natural stretching, and the fiber tensile strength reaches 2.7GPa, realizing the preparation of organically synthesized two-dimensional macromolecular macro fibers for the first time.

[0006] One of the technical solutions of the present invention is to provide a method for preparing a two-dimensional aromatic polyamide fiber, which specifically comprises the following steps: (1) Add melamine and an acyl chloride compound to N-methylpyrrolidone and stir to mix evenly, add a catalyst, and stir to react at 25-40° C. for 24 hours; the acyl chloride compound is 1,3,5-benzenetricarboxylic acid chloride or terephthaloyl chloride.

[0007] (2) The reaction product obtained in step 1 is added with a washing liquid at a volume ratio of 1:8, and then centrifuged to obtain a powder after washing. The washing liquid is water, ethanol or acetone.

[0008] (3) The powder was dried at 60 °C for 12 h and then transferred to a vacuum oven and dried at 60 °C for another 6 h to obtain a two-dimensional polyamide powder.

[0009] The two-dimensional aromatic polyamide powder synthesized by the present invention is composed of a large number of small-sized two-dimensional sheets stacked together, and there is no large-area ordered crystalline structure inside the two-dimensional sheet, but it is composed of many small crystal regions arranged in a disordered manner. Therefore, the interaction between the sheets is weak, so that the stacked sheets can be quickly dispersed into a single layer or several layers of extremely thin layered molecules under mechanical stirring or ultrasonic action, forming a stable high-concentration dispersion.

[0010] (4) preparing a spinning solution, heating 30-45 wt.% of a high-concentration two-dimensional polyamide dispersion and 1-2 wt.% of a polyethylene oxide solution at 60°C and mixing them uniformly to obtain a spinning solution; in the spinning solution, the mass ratio of polyethylene oxide to the two-dimensional polyamide is 1:(50-200); the solvents of the two-dimensional polyamide dispersion and the polyethylene oxide solution are one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0011] Pure two-dimensional polyamide is composed of stacked layers, so the introduction of ultra-high molecular weight polyethylene oxide and the entanglement structure of the molecular chains makes the spinning solution stretchable.

[0012] (5) Dry spinning: Under the irradiation of infrared light, the spinning solution is extruded from the spinning head, stretched onto the collection shaft, and solidified into a two-dimensional polyamide fiber. In the dry spinning process, when the dispersion is stretched to an extremely fine size, the solvent evaporates rapidly under the action of the hot air flow. At the same time, due to the high concentration of the dispersion, the two-dimensional polyamide nanosheets can be quickly assembled into solid fibers. The two-dimensional polyamide nanosheet layer is highly oriented along the axial direction during the stretching process. The orderly arrangement of the two-dimensional molecules gives the fiber excellent mechanical properties.

[0013] Furthermore, in step 1, the concentration of melamine in the mixture of the catalyst and N-methylpyrrolidone is 0.1 mol / L, the concentration of the acyl chloride compound in the mixture is 0.1 mol / L when it is 1,3,5-benzenetricarboxylic acid chloride, and the concentration of the acyl chloride compound in the mixture is 0.15 mol / L when it is terephthaloyl chloride.

[0014] Furthermore, the catalyst in step 1 is pyridine, and its concentration is generally 10 vol%.

[0015] Furthermore, in step 4, when mixing the two-dimensional polyamide solution and the polyethylene oxide solution, stirring is performed at a rate of 100-700 rpm at 60° C. for 20-30 min.

[0016] Furthermore, the diameter of the spinning head in step 5 is 200-500 μm.

[0017] The second technical solution of the present invention is to provide a two-dimensional aromatic polyamide fiber prepared by the above method.

[0018] The diameter of the prepared two-dimensional aromatic polyamide fiber is 2-20 μm, and the tensile strength of the fiber can reach 2.7 GPa.

[0019] Beneficial effects of the present invention: 1. The two-dimensional aromatic polyamide powder synthesized by the present invention can form a stable high-concentration dispersion in a specific solvent, solving the problem of dispersibility of two-dimensional molecules in organic synthesis.

[0020] 2. The present invention adds a small amount of ultra-high molecular weight polyethylene oxide to the dispersion to make the solution stretchable, thereby solving the problem that the two-dimensional molecular layered structure has no entanglement and therefore the dispersion has no viscoelasticity.

[0021] 3. On this basis, the present invention further combines the dry spinning process to realize the preparation of organic synthetic two-dimensional macromolecular fibers for the first time, filling the gap in this field and opening up the path of macroscopic materials assembled from two-dimensional macromolecules. The prepared fibers have the basic characteristics of high strength and high modulus. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Actual pictures of two types of two-dimensional polyamide powders prepared in Example 1 and Example 2.

[0023] Figure 2 Dispersions of different concentrations prepared in Example 1.

[0024] Figure 3 It is a schematic diagram of dry spinning of the present invention.

[0025] Figure 4 This is a physical picture of the two-dimensional polyamide (MA-2DPA-1) fiber of Example 1.

[0026] Figure 5 This is a polarizing fiber microscope photograph of the fiber of Example 1, with a scale of 50 μm.

[0027] Figure 6 This is a SEM photograph of the fiber of Example 1, with a scale of 5 μm.

[0028] Figure 7 The mechanical properties of the two-dimensional polyamide fibers of Example 1 and Example 2. DETAILED DESCRIPTION

[0029] The following examples are used to further illustrate the present invention, and their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all parts by weight and weight percentages are used below.

[0030] The raw materials used in the present invention, unless otherwise specified, are conventional commercially available products; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0031] As a conventional option for dispersing and removing impurities, when preparing the two-dimensional polyamide solution, the present invention first dissolves the two-dimensional polyamide powder in a solvent, stirs or ultrasonically dissolves it fully to prepare a two-dimensional polyamide concentrated solution, and then filters the clarified solution after dissolution with a filter to remove impurities to obtain a high-concentration two-dimensional polyamide solution.

[0032] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0033] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0034] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0035] In the following examples, the mechanical properties of two-dimensional polyamide fibers are tested using Keysight's nano-tensile tester, which has high precision and can accurately test the mechanical properties of nano-scale fibers. The tensile rate is 2 mm / min and the sample gauge length is 5 mm. First, a 5×5 mm paper frame is cut, and then the fiber is fixed to the paper frame with epoxy resin. After the epoxy resin is cured, the paper frame is fixed to the Keysight nano-tensile tester fixture, and the two sides of the paper frame are carefully cut with scissors. At this time, the software is started for mechanical testing. The cross-sectional area of ​​the fiber is obtained by photographing the morphology of the fiber fracture with a scanning electron microscope, and the cross-sectional area of ​​the fiber is calculated using software.

[0036] Example 1 (1) 1.26 g of melamine and 2.65 g of 1,3,5-benzenetricarboxylic acid chloride were added to 90 ml of N-methylpyrrolidone (NMP) and stirred to mix well. Then, 10 ml of pyridine was added as a catalyst and stirred at 200 rpm at 25 °C for 24 h. Then, 800 ml of ethanol, water and acetone were added to wash three times. After each washing, the solid was centrifuged at 12000 rpm for 2 min at room temperature. The solid was first dried in a conventional oven at 60 °C for 12 h and then transferred to a vacuum oven and dried at 60 °C for another 6 h to obtain 2.91 g of two-dimensional polyamide (MA-2DPA-1) powder with a yield of 74.4%.

[0037] (2) Weigh 0.4 g of two-dimensional polyamide (MA-2DPA-1) powder and add it into 0.6 g of N,N-dimethylformamide (DMF) solvent to obtain a 40 wt.% two-dimensional polyamide (MA-2DPA-1) dispersion.

[0038] (3) Weigh 0.2 g of polyethylene oxide and add 9.8 g of N,N-dimethylformamide (DMF) at 80°C with magnetic stirring at 300 rpm to prepare a 2 wt.% polyethylene oxide solution. The solvent is N,N-dimethylformamide (DMF).

[0039] (4) Preparing a composite spinning solution: filtering the two-dimensional polyamide (MA-2DPA-1) dispersion of step 2 with a 1500 mesh filter to obtain a clarified two-dimensional polyamide (MA-2DPA-1) solution, stirring the two-dimensional polyamide (MA-2DPA-1) solution with the polyethylene oxide solution obtained in step 3 at 60° C. for 20 min at a stirring rate of 700 rpm to obtain a spinning solution; in the spinning solution, the mass ratio of polyethylene oxide (PEO) to two-dimensional polyamide (MA-2DPA-1) was 1:50.

[0040] (5) Using dry spinning, the spinning solution prepared in step 4 is extruded from a spinning head with a diameter of 500 μm and stretched onto a receiving shaft. Under the irradiation of an infrared lamp, the high concentration of the spinning solution solvent evaporates and solidifies into fibers.

[0041] (6) The fiber was dried in a vacuum oven at 60 °C to completely remove the solvent, thereby obtaining high-strength two-dimensional polyamide (MA-2DPA-1) fibers with a fiber diameter of 20 μm and a measured tensile strength of 2.7 GPa.

[0042] Example 2 (1) 1.26 g of melamine and 3.04 g of terephthaloyl chloride were added to 90 ml of N-methylpyrrolidone (NMP), stirred and mixed, and then 10 ml of pyridine was added as a catalyst. The mixture was stirred and reacted at 200 rpm at 40 °C for 16 h. Then 800 ml of ethanol, water, and acetone were added to wash three times. After each washing, the mixture was centrifuged at 12000 rpm at room temperature for 2 min. The obtained solid was first dried in a conventional oven at 60 °C for 12 h, and then transferred to a vacuum oven and dried at 60 °C for another 6 h to obtain 2.17 g of two-dimensional polyamide (MA-2DPA-2) powder with a yield of 50.5%.

[0043] (2) Weigh 0.45g of two-dimensional polyamide (MA-2DPA-2) powder and add 0.55g of N,N-dimethyl Acetamide (DM AC ) solvent to obtain a 45wt.% two-dimensional polyamide (MA-2DPA-2) solution.

[0044] (3) Weigh 0.1 g of polyethylene oxide and add 9.9 g of N,N-dimethylacetamide (DMAC) at 60°C and 300 rpm magnetic stirring to prepare a 1 wt.% polyethylene oxide solution. The solvent is N,N-dimethylacetamide (DMAC).

[0045] (4) Preparing a composite spinning solution, filtering the two-dimensional polyamide (MA-2DPA-2) solution of step 2 to obtain a clarified two-dimensional polyamide (MA-2DPA-2) solution, heating and stirring the clarified two-dimensional polyamide (MA-2DPA-2) solution with the polyethylene oxide solution obtained in step 3 at a rate of 100 rpm at 60° C. for 30 min to obtain a spinning solution; in the spinning solution, the mass ratio of polyethylene oxide (PEO) to two-dimensional polyamide (MA-2DPA-2) is 1:100.

[0046] (5) Using dry spinning, the spinning solution prepared in step 4 is extruded from a 200 μm spinning head and stretched onto a receiving shaft. Under the irradiation of an infrared lamp, the high concentration of the spinning solution solvent evaporates and solidifies into fibers.

[0047] (6) The two-dimensional polyamide (MA-2DPA-2) fiber obtained in (5) was placed in an oven at 60°C and dried to obtain high-strength two-dimensional polyamide (MA-2DPA-2) fibers with a fiber diameter of 2 μm and a tensile strength of 2.2 GPa. The yield of MA-2DPA-2 powder was slightly lower than that of MA-2DPA-1 powder, and the fiber tensile strength was also lower than that of MA-2DPA-1 fiber.

[0048] Example 3 The difference from Example 1 is that a 30 wt.% dimethyl sulfoxide dispersion of two-dimensional polyamide and a 2 wt.% dimethyl sulfoxide solution of polyethylene oxide are used, and the mass ratio of polyethylene oxide to two-dimensional polyamide is 1: 200. The obtained fiber has a tensile strength of 2.4 GPa.

[0049] Comparative Example 1 Compared with Example 1, the method for preparing MA-2DPA-1 is the same, except that the solvent used is changed. 0.4 g of two-dimensional polyamide (MA-2DPA-1) powder is added to 0.6 g of ethanol solvent to obtain a 40 wt.% two-dimensional polyamide (MA-2DPA-1) dispersion. The dispersion is orange-yellow and opaque, and small particles are suspended and not completely dissolved. Therefore, a uniform dispersion cannot be obtained and filaments cannot be prepared.

[0050] Comparative Example 2 The only difference from Example 1 is that no polyethylene oxide solution is added ， By dry spinning, the prepared MA-2DPA-1 dispersion is directly extruded from the spinning head. The liquid has low viscosity and no stretchability, and cannot be prepared into silk.

[0051] Comparative Example 3 Compared with Example 1, the only difference is that the reaction temperature of melamine and 1,3,5-benzenetricarboxylic acid chloride is increased to 60°C, and the obtained powder is in the form of large particles, which is difficult to disperse in N,N-dimethylformamide (DMF), and a uniform dispersion cannot be obtained, and filaments cannot be prepared.

[0052] Comparative Example 4 Compared with Example 1, the only difference is that melamine is replaced by tris(4-aminophenyl)amine. When tris(4-aminophenyl)amine and 1,3,5-benzenetricarboxylic acid chloride are mixed, the product quickly becomes gel-like, and the reaction speed is fast and violent. The treated sample cannot be dispersed in N,N-dimethylformamide (DMF), a uniform dispersion cannot be obtained, and filaments cannot be prepared.

[0053] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the protection scope of the present invention.

Claims

1. A method for preparing a two-dimensional aromatic polyamide fiber, characterized in that: The following steps are involved: (1) adding melamine and an acyl chloride compound to N-methylpyrrolidone and stirring to mix evenly, adding a catalyst, and stirring to react at 25-40° C. for 24 hours; the acyl chloride compound is 1,3,5-benzenetricarboxylic acid chloride or terephthaloyl chloride; (2) adding a washing liquid to the reaction product obtained in step 1 at a volume ratio of 1:8, washing and centrifuging to obtain a powder, wherein the washing liquid is water, ethanol or acetone; (3) drying the powder at 60 °C for 12 h, and then transferring it to a vacuum oven and further drying it at 60 °C for 6 h to obtain a two-dimensional polyamide powder; (4) preparing a spinning solution, heating 30-45 wt.% of a high-concentration two-dimensional polyamide dispersion and 1-2 wt.% of a polyethylene oxide solution at 60° C. and mixing them uniformly to obtain a spinning solution; in the spinning solution, the mass ratio of polyethylene oxide to polyamide is 1:(50-200); the solvents of the two-dimensional polyamide dispersion and the polyethylene oxide solution are one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; (5) Dry spinning: Under the irradiation of infrared light, the spinning liquid is extruded from the spinning head, stretched onto the collection shaft, and solidified into two-dimensional polyamide fiber.

2. The method according to claim 1, characterized in that In step 1, the concentration of melamine in the mixture of the catalyst and N-methylpyrrolidone is 0.1 mol / L, the concentration of the acyl chloride compound in the mixture is 0.1 mol / L when it is 1,3,5-benzenetricarboxylic acid chloride, and the concentration of the acyl chloride compound in the mixture is 0.15 mol / L when it is terephthaloyl chloride.

3. The method according to claim 1, characterized in that The catalyst in step 1 is pyridine.

4. The method according to claim 1, characterized in that The diameter of the spinning head in step 5 is 200-500 μm.

5. The method according to claim 1, characterized in that Step 4: When mixing the two-dimensional polyamide solution and the polyethylene oxide solution, stir at 60° C. at a rate of 100-700 rpm for 20-30 min.

6. A two-dimensional aromatic polyamide fiber prepared by the method of claim 1.

7. The two-dimensional aromatic polyamide fiber according to claim 6, characterized in that: The diameter of the two-dimensional aromatic polyamide fibers is 2-20 μm.

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