A two-dimensional aramid fiber and a method of making

Abstract

The application discloses a two-dimensional aromatic polyamide fiber and a preparation method, and solves the problem that two-dimensional macromolecules obtained through organic synthesis are mostly crystalline powders, have poor dispersibility, and cannot be prepared into high-concentration dispersion liquids. Two-dimensional polyamide powder is synthesized through an ammonolysis reaction of acyl chloride, then two-dimensional polyamide and polyethylene oxide (PEO) are mixed to prepare a spinning liquid by using specific solvents, and then dry spinning is performed to obtain two-dimensional polyamide fiber. The preparation of two-dimensional macromolecule fiber through organic synthesis is realized, and the prepared two-dimensional polyamide fiber has high strength, and the tensile strength can reach 2.7 GPa.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyamide fibers, and particularly relates to a two-dimensional aromatic polyamide fiber and a preparation method. BACKGROUND

[0002] Two-dimensional macromolecules are widely concerned in the field of materials due to their high specific surface area, unique layered nanostructure and excellent performance. For example, graphene, as a two-dimensional macromolecule composed of single-layer carbon atoms arranged in a hexagonal honeycomb lattice, has great application potential in 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 graphene, Mxene, molybdenum disulfide and other single-layer or few-layer two-dimensional macromolecules obtained by exfoliating natural layered materials, 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, which have poor processability and are difficult to be used in the preparation of macroscopic assembly materials such as films and fibers. On the one hand, the dispersion of crystalline powders is poor, and the strong interlayer interaction in the ordered crystalline structure makes the two-dimensional sheets tightly stacked into agglomerates, which are difficult to disperse into single-layer or few-layer two-dimensional macromolecules in solvents. On the other hand, the sheet-like two-dimensional macromolecules cannot form a tangled structure in the solution like the chain-like one-dimensional macromolecules, so the dispersion of the two-dimensional macromolecules lacks viscoelasticity and is no longer suitable for various processing methods such as dry spinning process which have been widely used in one-dimensional macromolecules. In summary, the forming and processing of two-dimensional macromolecules obtained by organic synthesis face great challenges. At present, the existing materials are mainly nanoscale films obtained by spin coating, and the preparation of macroscopic assembly materials, especially fibers, is still rare.

[0003] Two types of COF containing sulfonic acid groups with liquid crystal behavior [DABA-TFP-COF and DASD-TFP-COF dispersions are respectively obtained by reacting 1,3,5-triformylphloroglucinol (TFP) with diaminobenzenesulfonic acid (DABA) or 4,4'-diamino-2,2'-stilbenedisulfonic acid (DASD)] are used in the prior art. After the two types of COF are configured into a dispersion liquid with a relatively high concentration (up to 25 mg / ml), the wet spinning method can be used to process the fibers on a large scale with a calcium ion solution as a coagulation bath. In this method, the two-dimensional COF molecules selected have poor dispersibility, and high-concentration dispersions cannot be obtained, so the method cannot be applied to the processing of dry spinning process. SUMMARY

[0004] The two-dimensional macromolecule obtained by organic synthesis is mostly in a crystalline state powder form, has poor dispersibility, and cannot be prepared into a high-concentration dispersion liquid, and the application discloses a two-dimensional aromatic polyamide fiber and a preparation method. Two-dimensional polyamide powder is synthesized through an ammoniaysis reaction of an acyl chloride, then the two-dimensional polyamide and polyethylene oxide (PEO) are mixed into a spinning solution using a specific solvent, and then dry spinning is performed to obtain two-dimensional polyamide fiber.

[0005] Unlike other two-dimensional macromolecules obtained by organic synthesis, the two-dimensional aromatic polyamide powder synthesized by the application is stacked by numerous small-size two-dimensional sheets, and the two-dimensional sheets have no large-area ordered crystalline structure inside but are arranged in disorder by many small crystal regions, so the interaction between the sheet layers is weak, and the stacked sheet layers can be quickly dispersed in a specific solvent (or accelerated by mechanical action) to form single-layer or several-layer extremely thin layered molecules, a stable high-concentration dispersion liquid is obtained, and the concentration can be as high as 45 wt.%. Meanwhile, the application adds ultra-high molecular weight polyethylene oxide into the dispersion liquid to introduce entanglement so that the dispersion liquid has tensile property. Combined with the dry spinning spinning process, a highly oriented fiber is directly formed by natural stretching, the fiber tensile strength reaches 2.7 GPa, and the preparation of the macroscopic fiber of the two-dimensional macromolecule obtained by organic synthesis is realized for the first time.

[0006] One of the technical solutions of the application is to provide a preparation method of two-dimensional aromatic polyamide fiber, which specifically comprises the following steps:

[0007] (1) melamine and an acyl chloride compound are added into N-methyl pyrrolidone and stirred and uniformly mixed, a catalyst is added, and stirring reaction is carried out at 25-40 DEG C for 24 hours; the acyl chloride compound is 1,3,5-benzene tricarbonyl chloride or p-phenylenediamine dichloride.

[0008] (2) the reaction product obtained in step 1 is added into a washing liquid at a volume ratio of 1:8, powder is obtained after centrifugation after washing, and the washing liquid is water, ethanol or acetone.

[0009] (3) the powder is dried at 60 DEG C for 12 h, and then transferred to a vacuum oven and dried at 60 DEG C for 6 h, to obtain two-dimensional polyamide powder.

[0010] The two-dimensional aromatic polyamide powder synthesized by the application is stacked by numerous small-size two-dimensional sheets, and the two-dimensional sheets have no large-area ordered crystalline structure inside but are arranged in disorder by many small crystal regions, so the interaction between the sheet layers is weak, and the stacked sheet layers can be quickly dispersed into single-layer or several-layer extremely thin layered molecules under mechanical stirring or ultrasonic action to form a stable high-concentration dispersion liquid.

[0011] (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.

[0012] Pure two-dimensional polyamide is composed of stacked layers, so the introduction of ultra-high molecular weight polyethylene oxide and the entangled structure of the molecular chains make the spinning solution stretchable.

[0013] (5) Dry spinning: Under infrared light, the spinning solution is extruded from the spinning head, stretched onto the take-up reel, 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. During the stretching process, the two-dimensional polyamide nanosheets are highly oriented along the axial direction. The orderly arrangement of the two-dimensional molecules gives the fiber excellent mechanical properties.

[0014] Furthermore, the concentration of melamine in the mixture of the catalyst and N-methylpyrrolidone in step 1 is 0.1 mol / L, the concentration of the acyl chloride compound in the above 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 above mixture is 0.15 mol / L when it is terephthaloyl chloride.

[0015] Furthermore, the catalyst in step 1 is pyridine, and its concentration is generally 10 vol%.

[0016] 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.

[0017] Furthermore, the diameter of the spinning head in step 5 is 200-500 μm.

[0018] The second technical solution of the present invention is to provide a two-dimensional aromatic polyamide fiber prepared by the above method.

[0019] 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.

[0020] Beneficial effects of the present invention:

[0021] 1. The two-dimensional aromatic polyamide powder synthesized in 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.

[0022] 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.

[0023] 3. Building on this foundation, the present invention further utilizes a dry spinning process to achieve the first production of organically synthesized two-dimensional macromolecular fibers, filling a gap in this field and paving the way for macroscopic materials assembled from two-dimensional macromolecules. The resulting fibers possess the fundamental characteristics of high strength and high modulus. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Actual photos of the two two-dimensional polyamide powders prepared in Example 1 and Example 2.

[0025] Figure 2 These are dispersions of different concentrations prepared in Example 1.

[0026] Figure 3 Schematic diagram of dry spinning of the present invention.

[0027] Figure 4 This is a physical picture of the two-dimensional polyamide (MA-2DPA-1) fiber of Example 1.

[0028] Figure 5 This is a polarizing fiberscope photograph of the fiber of Example 1, with a scale of 50 μm.

[0029] Figure 6 This is a SEM photograph of the fiber of Example 1, with a scale of 5 μm.

[0030] Figure 7 The mechanical properties of the two-dimensional polyamide fibers of Example 1 and Example 2. DETAILED DESCRIPTION

[0031] The following examples are used to further illustrate the present invention. 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 references are by weight and weight percentage.

[0032] Unless otherwise specified, the raw materials used in the present invention are conventional commercial products; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0033] 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, and prepares a concentrated two-dimensional polyamide solution. The clarified solution after dissolution is then filtered through a filter to remove impurities and obtain a high-concentration two-dimensional polyamide solution.

[0034] The embodiments of the present invention are further described below with reference to a number of embodiments.

[0035] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0036] 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", "an", "the" 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 otherwise.

[0037] In the following examples, the mechanical properties of two-dimensional polyamide fibers were tested using a Keysight nanotensile tester. This highly precise tester can accurately test the mechanical properties of nanoscale fibers at a tensile rate of 2 mm / min and a sample gauge length of 5 mm. A 5×5 mm paper frame was first cut, and the fibers were then fixed to the frame using epoxy resin. After the epoxy resin solidified, the frame was fixed to the Keysight nanotensile tester fixture. Scissors were used to carefully cut the two sides of the frame, and the software was then launched to perform mechanical testing. The cross-sectional area of ​​the fiber was determined by scanning electron microscopy to capture the morphology of the fiber fracture and calculating the fiber cross-sectional area using software.

[0038] Example 1

[0039] (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 evenly. 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 12,000 rpm at room temperature for 2 min. The solid was first dried in a conventional oven at 60 °C for 12 h, and then transferred to a vacuum oven at 60 °C for further drying for 6 h to obtain 2.91 g of two-dimensional polyamide (MA-2DPA-1) powder with a yield of 74.4%.

[0040] (2) Weigh 0.4 g of two-dimensional polyamide (MA-2DPA-1) powder and add it to 0.6 g of N,N-dimethylformamide (DMF) solvent to obtain a 40 wt.% two-dimensional polyamide (MA-2DPA-1) dispersion.

[0041] (3) 0.2 g of polyethylene oxide was weighed and added to 9.8 g of N,N-dimethylformamide (DMF) under the condition of 80°C and 300 rpm magnetic stirring to prepare a 2 wt.% polyethylene oxide solution, with N,N-dimethylformamide (DMF) as the solvent.

[0042] (4) A composite spinning solution was prepared. The two-dimensional polyamide (MA-2DPA-1) dispersion solution of step 2 was filtered through a 1500-mesh filter screen to obtain a clear two-dimensional polyamide (MA-2DPA-1) solution, which was stirred 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.

[0043] (5) The spinning solution prepared in step 4 was extruded from a spinning head with a diameter of 500 μm and drawn onto a take-up shaft under the irradiation of an infrared lamp, and the high-concentration spinning solution solvent was volatilized to form a fiber under the irradiation of an infrared lamp.

[0044] (6) The fiber was dried in a vacuum oven at 60°C to completely remove the solvent to obtain a high-strength two-dimensional polyamide (MA-2DPA-1) fiber. The fiber diameter was 20 μm, and the tensile strength of the fiber was measured to be 2.7 GPa.

[0045] Example 2

[0046] (1) 1.26 g of melamine and 3.04 g of terephthaloyl chloride were added to 90 ml of N-methylpyrrolidone (NMP) and stirred and mixed uniformly, 10 ml of pyridine was then added as a catalyst, and the mixture was stirred at 40°C and 200 rpm for 16 h. Then, 800 ml of ethanol, water, and acetone were added for washing three times, and after each washing, the obtained solid was centrifuged at room temperature and 12000 rpm for 2 min. The obtained solid was first dried in a general oven at 60°C for 12 h, and then transferred to a vacuum oven for further drying at 60°C for 6 h to obtain 2.17 g of two-dimensional polyamide (MA-2DPA-2) powder, with a yield of 50.5%.

[0047] (2) 0.45 g of two-dimensional polyamide (MA-2DPA-2) powder was weighed and added to 0.55 g of N,N-dimethyl acetamide (DM AC ) solvent to obtain a 45 wt.% two-dimensional polyamide (MA-2DPA-2) solution.

[0048] (3) Weigh 0.1 g of polyethylene oxide and add 9.9 g of N,N-dimethylacetamide (DMAC) at 60°C with magnetic stirring at 300 rpm to prepare a 1 wt.% polyethylene oxide solution. The solvent is N,N-dimethylacetamide (DMAC).

[0049] (4) Preparing a composite spinning solution: filtering the two-dimensional polyamide (MA-2DPA-2) solution obtained in 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.

[0050] (5) Using dry spinning, the spinning solution prepared in step 4 is extruded from a 200 μm spinning head and stretched onto a take-up shaft. Under the irradiation of an infrared lamp, the high concentration of the spinning solution solvent evaporates and solidifies into fibers.

[0051] (6) The two-dimensional polyamide (MA-2DPA-2) fibers obtained in (5) were dried in an oven at 60°C 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 fibers.

[0052] Example 3

[0053] The difference from Example 1 is that a 30 wt.% dimethyl sulfoxide dispersion of the two-dimensional polyamide and a 2 wt.% dimethyl sulfoxide solution of polyethylene oxide are used, and the mass ratio of polyethylene oxide to the two-dimensional polyamide is 1:200. The resulting fiber has a tensile strength of 2.4 GPa.

[0054] Comparative Example 1

[0055] The method for preparing MA-2DPA-1 was identical to that used in Example 1, differing only in the solvent used. 0.4 g of two-dimensional polyamide (MA-2DPA-1) powder was added to 0.6 g of ethanol to produce a 40 wt.% dispersion of the two-dimensional polyamide (MA-2DPA-1). The dispersion was opaque orange-yellow, with small particles suspended and not fully dissolved. Therefore, a uniform dispersion could not be obtained, and filaments could not be produced.

[0056] Comparative Example 2

[0057] The only difference from Example 1 is that no polyethylene oxide solution is added ，By using 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.

[0058] Comparative Example 3

[0059] 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. The resulting powder is in the form of large particles and is difficult to disperse in N,N-dimethylformamide (DMF). A uniform dispersion cannot be obtained, and silk cannot be prepared.

[0060] Comparative Example 4

[0061] Compared to Example 1, the only difference was that melamine was replaced with tris(4-aminophenyl)amine. When tris(4-aminophenyl)amine and 1,3,5-benzenetricarboxylic acid chloride were mixed, the product quickly gelled, and the reaction was rapid and intense. The treated sample could not be dispersed in N,N-dimethylformamide (DMF), resulting in a uniform dispersion and the inability to produce filaments.

[0062] 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 scope of protection 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) Add the reaction product obtained in step 1 to a washing solution at a volume ratio of 1:8, wash, and centrifuge to obtain a powder. The washing solution is water, ethanol, or acetone; (3) Dry the powder at 60 °C for 12 h, then transfer it to a vacuum oven and continue drying 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 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; (5) Dry spinning: Under the irradiation of infrared lamps, the spinning solution is extruded from the spinning head, stretched onto the winding shaft, and solidified into a two-dimensional aromatic polyamide fiber.

2. The method according to claim 1, characterized in that The concentration of melamine in the mixture of the catalyst and N-methylpyrrolidone in step 1 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, wherein The diameter of the spinning head in step 5 is 200-500 μm.

5. The method according to claim 1, wherein In step 4, the two-dimensional polyamide dispersion and the polyethylene oxide solution are mixed while stirring at a rate of 100-700 rpm at 60° C. 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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