Modified heterocyclic aramid fiber and method for producing the same

Abstract

The application provides a preparation method of modified heterocyclic aramid fiber and the fiber prepared by the method. The preparation method comprises the following steps: S1, dispersing graphene oxide in N,N-dimethylacetamide solvent to form a dispersion liquid; and S2, adding the dispersion liquid into a polymerization reaction system before aramid III monomers are polymerized to form a composite spinning liquid; wherein, the C-O / C=O of the graphene oxide is 2-5. The graphene oxide with high C-O content is used, and the dispersion liquid is formed by taking N,N-dimethylacetamide as a solvent. The graphene oxide is not easy to agglomerate in the composite solvent and is easy to store. The C-O in the graphene oxide is more prone to partial reduction in the fiber forming process to obtain reduced graphene oxide, which is more stable than the graphene oxide, thereby ensuring the stable storage of the subsequent fiber. Meanwhile, the addition of the graphene oxide can also prevent the fiber from fibrillating, thereby greatly improving the compression performance, tensile strength and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of heterocyclic aramid technology, and more specifically to graphene oxide-modified heterocyclic aramid fibers and their preparation methods. Background Technology

[0002] Heterocyclic aramid fiber is a high-performance organic fiber possessing excellent properties such as lightweight, high strength, high modulus, and impact resistance. It has important applications in aerospace and defense industries, including engine casings for weapon systems, bulletproof helmets, and aircraft skin. However, domestically produced heterocyclic aramid fibers still face significant gaps in mechanical properties compared to foreign products in engineering applications, limiting their application areas. Therefore, developing a series of fiber products that address the structural weaknesses of heterocyclic aramid fibers and meet the needs of practical applications is crucial for realizing the application of heterocyclic aramid fibers. Graphene is composed of... sp 2 Two-dimensional carbon nanomaterials composed of hybrid carbon atoms arranged in a honeycomb-like structure have high strength, high modulus and high specific surface area, making them ideal structural reinforcement materials.

[0003] Currently, some studies have introduced graphene into heterocyclic aramid fibers. For example, Chinese invention patent CN113718364A adds graphene material to aramid polymerization liquid as a graphene aramid spinning solution. However, direct mixing easily causes graphene agglomeration, resulting in uneven aramid composite fibers with poor stability and mechanical properties, making them difficult to use in actual production.

[0004] Compared to the method of directly adding graphene powder, pre-preparing a graphene dispersion can improve the dispersibility of graphene in spinning solutions to a certain extent. For example, Chinese invention patent CN115216857A describes dissolving graphene (carboxyl-containing graphene oxide or amino-based graphene) in an N,N-dimethylacetamide / lithium chloride composite solvent to obtain a graphene dispersion. Then, aramid monomers p-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzimidazole, and terephthaloyl chloride are added to the graphene dispersion to obtain a graphene-aramid spinning solution. However, due to the salt ion effect, lithium chloride in the composite solvent easily leads to graphene agglomeration. Therefore, this graphene dispersion cannot be stored for a long time and is only suitable for immediate use in the preparation of spinning solutions after preparation, which brings many inconveniences to actual production. In addition, dissolving p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole in the graphene oxide dispersion also has an adverse effect on the dispersibility of graphene.

[0005] To ensure better application of aramid fibers, their stability has become an important evaluation standard. Currently, many studies aim to achieve reinforcing effects by introducing graphene oxide into aramid systems. For example, Chinese invention patent CN115216857A adds carboxyl-containing graphene oxide to the aramid system. However, the addition of graphene oxide causes the mechanical properties of the composite fiber to slowly decline during later storage and use, posing a significant risk to the fiber's application. Summary of the Invention

[0006] To improve the long-term stability of fiber mechanical properties, this invention provides a method for preparing modified heterocyclic aramid fibers and the modified heterocyclic aramid fibers prepared by this method.

[0007] This invention discloses a method for preparing modified heterocyclic aramid fibers, comprising: S1, dispersing graphene oxide in N,N-dimethylacetamide solvent to form a dispersion; S2, adding the dispersion to the polymerization reaction system before the polymerization of aramid III monomers to form a composite spinning solution; and S3, using wet spinning to form the modified heterocyclic aramid fibers from the composite spinning solution, wherein the temperature of the hot stretching step is 400-420℃; wherein the CO / C=O ratio in the graphene oxide is 2-5.

[0008] According to one embodiment of the present invention, the graphene oxide has a carbon-to-oxygen ratio of 2-5, a number of layers of 1-10, and a sheet diameter of 0.01-3 μm; preferably, the number of layers is 1-3.

[0009] According to another embodiment of the present invention, the mass percentage of graphene oxide in the dispersion is 0.05-0.5%.

[0010] According to another embodiment of the present invention, step S2 includes: dissolving lithium chloride cosolvent, p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole in N,N-dimethylacetamide solvent to form a solution, cooling the solution to -10 to 10°C and then adding the dispersion, stirring for 5 to 20 minutes, and then adding terephthaloyl chloride to react and obtain the composite spinning solution.

[0011] According to another embodiment of the present invention, the viscosity of the composite spinning solution is 30,000 to 100,000 centipoise.

[0012] According to another embodiment of the present invention, the graphene oxide accounts for 0.02 to 0.8% of the mass percentage of the modified heterocyclic aramid fiber.

[0013] The present invention also provides a modified heterocyclic aramid fiber prepared by the above method.

[0014] This invention utilizes graphene oxide with a high CO content, forming a dispersion using N,N-dimethylacetamide as a solvent. Because graphene oxide is less prone to agglomeration in the composite solvent and is easy to store, and because CO in graphene oxide is more readily partially reduced during fiber forming, resulting in reduced graphene oxide, which is more stable than graphene oxide, this ensures stable fiber storage. Furthermore, the addition of graphene oxide in this invention can prevent fiber fibrillation, significantly improving compression performance, tensile strength, and corrosion resistance. Attached Figure Description

[0015] Figure 1 These are XPS spectra and thermogravimetric maps of graphene oxide before and after heat treatment.

[0016] Figure 2 This is a schematic diagram and a physical image of the graphene oxide-modified heterocyclic aramid fibers being reduced during the fiber forming process according to an embodiment of the present invention.

[0017] Figure 3 These are photographs of the storage process of the dispersions of Example 1 and Comparative Example 1.

[0018] Figure 4 These are photographs of the modified heterocyclic aramid fibers prepared in Example 1 and Comparative Example 1 in the organic solvent DMAc. Detailed Implementation

[0019] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the descriptions and drawings therein are for illustrative purposes only and not intended to limit the present invention.

[0020] The method for preparing modified heterocyclic aramid fibers of the present invention includes: S1, dispersing graphene oxide in N,N-dimethylacetamide solvent to form a dispersion; S2, adding the dispersion to the polymerization reaction system before the polymerization of aramid III monomer to form a composite spinning solution; and S3, using wet spinning to form modified heterocyclic aramid fibers from the composite spinning solution, wherein the temperature of the hot stretching step is 400-420℃; wherein the CO / C=O ratio in the graphene oxide is 2-5.

[0021] In this invention, "CO" refers to the CO bond; "C=O" refers to the C=O bond. The CO bond can be C-OH and / or COC. "CO / C=O" refers to the molar ratio or mass ratio of the CO bonds and the C=O bonds.

[0022] This invention utilizes graphene oxide in a dispersion formed with N,N-dimethylacetamide as the solvent. Because graphene oxide is less prone to agglomeration in composite solvents and is easy to store, it does not require any dispersants (such as lithium chloride or calcium chloride) to form a well-dispersed dispersion. Furthermore, the absence of other additives in the dispersion system prevents the introduction of impurities, ensuring the stability of subsequent reactions. This invention selects graphene oxide with a high CO content (CO / C=O ratio of 2-5). Compared to the C=O bond, the CO bond energy is lower, making it easier to undergo partial reduction during fiber forming, resulting in reduced graphene oxide, which is more stable than graphene oxide and ensures stable fiber storage.

[0023] Figure 1 The XPS spectra and thermogravimetric (TGA) plots of graphene oxide before and after heat treatment are shown. Figure a shows the XPS spectrum of graphene oxide, revealing the presence of numerous functional groups. Figure b shows the XPS spectrum of graphene oxide treated at 400℃, indicating the reduction of some functional groups. Functional groups containing CO bonds are reduced to a greater extent than those containing C=O bonds, demonstrating that CO bonds are more easily reduced than C=O bonds. Figure c shows the thermogravimetric curve, showing that around 200℃, most functional groups of graphene oxide disappear, resulting in a sharp decrease in weight, after which it almost reaches equilibrium. Figure 1 The information shown demonstrates that the presence of more CO bonds makes graphene oxide easier to reduce.

[0024] Figure 2 This is a schematic diagram and a physical image (far right) of graphene oxide-modified heterocyclic aramid fibers being reduced during fiber forming according to an embodiment of the present invention. The modified heterocyclic fibers obtained by the method of the present invention are green in color, while ordinary graphene oxide composite fibers are brown. Combined with... Figure 1 It can be inferred that the preparation method of the present invention uses graphene oxide with high CO content, so graphene oxide is more easily reduced during the stretching process, which leads to a change in the color of the resulting fiber.

[0025] Furthermore, the addition of graphene oxide in this invention can also prevent fiber fibrillation and greatly improve compression performance.

[0026] Therefore, the method of the present invention takes into account the dispersibility of graphene oxide while improving the mechanical properties and long-term stability of the composite fiber.

[0027] In optional embodiments, the graphene oxide has a carbon-to-oxygen ratio of 2-5, 1-10 layers, and a sheet diameter of 0.01-3 μm. Preferably, it has 1-3 layers. A carbon-to-oxygen ratio of 2-5 ensures uniform dispersion of graphene oxide in DMAc and facilitates reduction during heat treatment. If the carbon-to-oxygen ratio is too low (below 2), the graphene oxide has a high oxygen content and many defects, which is detrimental to improving mechanical properties; if the carbon-to-oxygen ratio is too high (above 5), it is detrimental to the dispersion of graphene oxide. The sheet diameter of graphene oxide between 0.01-3 μm is selected based on its dispersibility and fiber diameter. Generally, the fiber diameter is 10 μm. A sheet diameter that is too large (greater than 3 μm) will cause pore blockage during spinning and reduce mechanical properties. With a sheet diameter within this range, graphene oxide has good dispersibility in the dispersion solution and high spinnability.

[0028] In an optional embodiment, the mass percentage of graphene oxide in the dispersion is 0.05-0.5%.

[0029] In an optional embodiment, step S2 includes: dissolving lithium chloride co-solvent, p-phenylenediamine, and 2-(4-aminophenyl)-5-aminobenzimidazole in N,N-dimethylacetamide solvent to form a solution; cooling the solution temperature to -10 to 10°C and then adding the dispersion; stirring for 5 to 20 minutes; and then adding terephthaloyl chloride to react and obtain the composite spinning solution. The lithium chloride co-solvent, p-phenylenediamine, and 2-(4-aminophenyl)-5-aminobenzimidazole are added to the N,N-dimethylacetamide solvent and stirred under nitrogen protection until completely dissolved; the stirring time can be 5 to 20 minutes. After the solution temperature is lowered, terephthaloyl chloride can be added in batches, stirred thoroughly, to allow the polymerization reaction to occur and obtain the composite spinning solution.

[0030] In this invention, during the polymerization process (S2 step), a graphene oxide dispersion is added to a solution in which 2-(4-aminophenyl)-5-aminobenzimidazole and p-phenylenediamine are completely dissolved beforehand. After stirring for 5-20 minutes, terephthaloyl chloride is added in batches. The advantages are as follows: First, mixing 2-(4-aminophenyl)-5-aminobenzimidazole and p-phenylenediamine with the graphene oxide dispersion using a mixed solvent can effectively avoid graphene oxide agglomeration caused by the solid, highly viscous 2-(4-aminophenyl)-5-aminobenzimidazole and p-phenylenediamine. Simultaneously, adding the graphene oxide dispersion to a pre-dissolved solution of 2-(4-aminophenyl)-5-aminobenzimidazole and p-phenylenediamine / N,N-dimethylacetamide reduces the stirring time of graphene oxide in the reactor, allowing for good dispersion of graphene oxide in the composite solvent without agglomeration. Second, the addition of graphene oxide before terephthaloyl chloride allows it to participate in the polymerization process of the aramid monomer, resulting in good dispersion of graphene oxide in the polymer without agglomeration, thereby improving the mechanical properties of the fiber.

[0031] In an optional embodiment, the viscosity of the composite spinning solution is 30,000 to 100,000 centipoise.

[0032] In an optional embodiment, the preparation method further includes: S3, forming modified heterocyclic aramid fibers from the composite spinning solution by wet spinning. The wet spinning process may be, but is not limited to, vacuum degassing of the composite spinning solution, followed by uniform spraying from a spinneret, and then passing through a primary coagulation bath for double diffusion and a certain stretching action to form nascent fibers. These fibers are then passed through a secondary coagulation bath, washed with water, dried, and then subjected to hot stretching treatment at a temperature of 400-420℃ under a nitrogen atmosphere. During this process, the graphene oxide inside the aramid can be partially reduced, and finally wound into partially reduced graphene oxide / heterocyclic aramid composite fibers.

[0033] In an optional embodiment, the graphene oxide content of the modified heterocyclic aramid fiber is 0.02-0.8% by mass. Exceeding a certain limit in the addition of graphene oxide will reduce its dispersibility in the composite polymerization solution, leading to uneven mechanical properties of the composite fiber. This invention controls the graphene oxide content of the modified heterocyclic aramid fiber matrix to 0.02-0.8% by mass. The advantage of this addition amount is that it facilitates the uniform dispersion of graphene oxide in the polymer.

[0034] This invention also provides a modified heterocyclic aramid fiber prepared by the above method. The tensile properties, compressive strength, and interfacial properties of the fiber of this invention are all improved. After a certain period of storage, the mechanical properties of the fiber of this invention remain stable, while ordinary heterocyclic aramid fibers show a decrease of -1 cN / dtex. Furthermore, the mechanical property stability of the fiber of this invention in organic solvents such as DMSO, DMF, and DMAc is also improved.

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

[0036] Example 1

[0037] Take 0.02% (by mass) of graphene oxide powder (CO / C=O = 3, carbon-oxygen ratio = 2.8, 3 layers, 300 nm diameter) and dry it in an oven at 100 °C for 8 hours. Then, take out the graphene oxide powder and add it to N,N-dimethylacetamide organic solvent for ultrasonic dispersion for 30-60 minutes to obtain a uniform and stable graphene oxide dispersion.

[0038] The co-solvent LiCl, p-phenylenediamine, and 2-(4-aminophenyl)-5-aminobenzimidazole monomer were added to a reactor containing N,N-dimethylacetamide and stirred under nitrogen until completely dissolved. The temperature of the solution was lowered to 10 °C, and the prepared graphene oxide dispersion was added to the solution and stirred. After stirring for 20 minutes, terephthaloyl chloride was added in batches, and the mixture was stirred thoroughly for 5 hours to obtain the composite spinning solution.

[0039] The composite spinning solution was vacuum degassed, then uniformly spun from a spinneret. It then passed through a primary coagulation bath for double diffusion and stretching to form nascent fibers. These fibers were then subjected to a secondary coagulation bath, washing, and drying, followed by hot stretching at 400°C under a nitrogen atmosphere. This process partially reduced the graphene oxide within the aramid fibers. Finally, the fibers were wound into partially reduced graphene oxide / heterocyclic aramid composite fibers, which were green in color. The tensile strength of the composite fiber was measured at 35.74 cN / dtex. After three months, the tensile strength of the composite fiber was measured at 36.38 cN / dtex, showing stable and unchanged performance.

[0040] Figure 3 The figures show photographs illustrating the storage conditions of the graphene oxide dispersion prepared in this embodiment and the dispersion containing lithium chloride (Comparative Example 1). The figures show that graphene oxide dispersed in N,N-dimethylacetamide can remain non-agglomerated for up to 30 days. In contrast, graphene oxide dispersed in the N,N-dimethylacetamide / lithium chloride composite solvent exhibits significant precipitation after one day.

[0041] Figure 4 The images show heterocyclic aramid fibers and the modified heterocyclic aramid fibers prepared in this example after 20 minutes in the organic solvent DMAc. The heterocyclic aramid fibers completely swelled after 20 minutes in DMAc, while the modified aramid fibers prepared in this example did not swell after 20 minutes in DMAc and swelled completely after one month. This demonstrates that the modified heterocyclic aramid fibers prepared by the method of this invention exhibit good mechanical property stability in organic solvents.

[0042] Example 2

[0043] Except that the mass content of graphene oxide in the modified aramid fiber is 0.1%, all other conditions are the same as in Example 1.

[0044] The tensile strength of the modified heterocyclic aramid fiber prepared in this embodiment was measured to be 36.34 cN / dtex. After three months, the tensile strength of the composite fiber was measured to be 36.68 cN / dtex, and the performance remained stable.

[0045] Example 3

[0046] Except that the mass content of graphene oxide in the modified aramid fiber is 0.2%, all other conditions are the same as in Example 1.

[0047] The tensile strength of the modified heterocyclic aramid fiber prepared in this embodiment was measured to be 37.22 cN / dtex. After three months, the tensile strength of the composite fiber was measured to be 37.96 cN / dtex, and the performance remained stable.

[0048] Example 4

[0049] Except that the mass content of graphene oxide in the modified aramid fiber is 0.3%, all other conditions are the same as in Example 1.

[0050] The tensile strength of the modified heterocyclic aramid fiber prepared in this embodiment was measured to be 38.28 cN / dtex, and the tensile strength of the composite fiber was measured to be 38.68 cN / dtex after three months, showing stable performance.

[0051] Example 5

[0052] Except that the mass content of graphene oxide in the modified aramid fiber is 0.5%, all other conditions are the same as in Example 1.

[0053] The tensile strength of the modified heterocyclic aramid fiber prepared in this embodiment was measured to be 36.67 cN / dtex. After three months, the tensile strength of the composite fiber was measured to be 37.34 cN / dtex, and the performance remained stable.

[0054] Example 6

[0055] Except that the mass content of graphene oxide in the modified aramid fiber is 0.8%, all other conditions are the same as in Example 1.

[0056] The tensile strength of the modified heterocyclic aramid fiber prepared in this embodiment was measured to be 35.38 cN / dtex. After three months, the tensile strength of the composite fiber was measured to be 36.01 cN / dtex, and the performance remained stable.

[0057] Example 7

[0058] Except for the graphene oxide powder (CO / C=O = 2), all other conditions were the same as in Example 4.

[0059] The tensile strength of the modified heterocyclic aramid fiber prepared in this embodiment was measured to be 37.98 cN / dtex. After three months, the tensile strength of the composite fiber was measured to be 38.52 cN / dtex, and the performance remained stable.

[0060] Example 8

[0061] Except for the graphene oxide powder (CO / C=O = 4), all other conditions were the same as in Example 4.

[0062] The tensile strength of the modified heterocyclic aramid fiber prepared in this embodiment was measured to be 38.78 cN / dtex. After three months, the tensile strength of the composite fiber was measured to be 39.05 cN / dtex, and the performance remained stable.

[0063] Example 9

[0064] Except for the graphene oxide powder (CO / C=O = 5), all other conditions were the same as in Example 4.

[0065] The tensile strength of the modified heterocyclic aramid fiber prepared in this embodiment was measured to be 38.29 cN / dtex. After three months, the tensile strength of the composite fiber was measured to be 38.94 cN / dtex, and the performance remained stable.

[0066] Comparative Example 1

[0067] Except for the N,N'-dimethylacetamide / lithium chloride composite solvent used for the dispersion of graphene oxide powder, all other conditions were the same as in Example 4.

[0068] The tensile strength of the prepared composite fiber was measured to be 32.33 cN / dtex. From... Figure 1 As can be seen, the dispersion in the comparative example clearly showed graphene agglomeration, which is the reason why the fiber mechanical properties are not as good as those in the above examples.

[0069] Comparative Example 2

[0070] The graphene oxide dispersion was added to the solution of dissolved terephthaloyl chloride, and then other diamine monomers were added. Other reaction conditions were the same as in Example 4.

[0071] During the reaction process, significant graphene agglomeration was observed in the polymerization solution. The tensile strength of the modified fiber prepared in this comparative example was measured to be 29.83 cN / dtex.

[0072] Comparative Example 3

[0073] Without pre-dissolving p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole, the above-mentioned polymeric monomers were directly added to the graphene oxide dispersion, followed by the addition of terephthaloyl chloride. Other conditions were the same as in Example 4.

[0074] During the reaction process, graphene agglomeration was observed in the polymerization solution. The tensile strength of the obtained modified fiber was measured to be 32.83 cN / dtex.

[0075] Comparative Example 4

[0076] Except for the CO / C=O ratio of graphene oxide being 0.9, the other conditions were the same as in Example 4.

[0077] The comparison shows that the carboxylated graphene oxide heterocyclic aramid composite fiber is brown in color. The tensile strength of the composite fiber was measured to be 35.11 cN / dtex, and after three months the tensile strength was measured to be 33.21 cN / dtex, indicating that the mechanical properties are unstable.

[0078] Comparative Example 5

[0079] Except for the fact that the mass content of graphene oxide in the modified aramid fiber is 2%, all other conditions are the same as in Example 4.

[0080] During the reaction process, large-area agglomeration of graphene was observed in the polymerization solution. The tensile strength of the prepared modified fiber was measured to be 28.97 cN / dtex.

[0081] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing modified heterocyclic aramid fibers, characterized in that, include: S1, dispersing graphene oxide in N,N-dimethylacetamide solvent to form a dispersion; S2, the dispersion is added to the polymerization reaction system before the polymerization of aramid III monomer to form a composite spinning solution; S3, the modified heterocyclic aramid fiber is formed by wet spinning of the composite spinning solution, wherein the temperature of the hot stretching step is 400-420℃; Wherein, the CO / C=O ratio in the graphene oxide is 2-5, and the CO / C=O ratio refers to the molar ratio or mass ratio of CO bonds and C=O bonds; The graphene oxide has a carbon-to-oxygen ratio of 2-5, and the graphene oxide accounts for 0.02-0.8% of the mass of the modified heterocyclic aramid fiber. Step S2 includes: A solution is formed by dissolving lithium chloride co-solvent, p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole in N,N-dimethylacetamide solvent. The solution temperature is lowered to -10 to 10°C and then the dispersion is added. After stirring for 5 to 20 minutes, terephthaloyl chloride is added to react and the composite spinning solution is obtained.

2. The preparation method according to claim 1, characterized in that, The graphene oxide has 1-10 layers and a sheet diameter of 0.01-3 μm.

3. The preparation method according to claim 2, characterized in that, The graphene oxide has 1-3 layers.

4. The preparation method according to claim 1, characterized in that, The mass percentage of graphene oxide in the dispersion is 0.05-0.5%.

5. The preparation method according to claim 1, characterized in that, The viscosity of the composite spinning solution is 30,000 to 100,000 centipoise.

6. A modified heterocyclic aramid fiber, characterized in that, Prepared by the preparation method according to any one of claims 1-5.

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