Copolymer modified p-aramid and method of making and high compression strength fiber made therefrom

Abstract

The present application relates to a kind of copolymer modified para-aramid and preparation method and high compression strength fiber prepared therefrom, belong to the technical field of polymer compound synthesis.The method includes: under the protection of inert atmosphere, p-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzimidazole and modified monomer are dissolved in amide aprotic solvent containing Li2CO3;Polycondensation reaction is carried out by adding terephthaloyl chloride at low temperature;Finally, the product is obtained by precipitation, filtration, drying.The modified monomer used in the present application is a kind of monomer which can be heat crosslinked and has rigid conjugated structure, and the compression strength of the fiber can be improved by crosslinking reaction.The modified monomer does not destroy the regularity of original aramid molecular chain, so that the high tensile strength of original aramid fiber is retained.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, specifically to a copolymerized modified para-aramid fiber, its preparation method, and the high compressive strength fiber obtained therefrom. Background Technology

[0002] Para-aramid fibers possess ideal properties such as good heat resistance and excellent mechanical properties, and have been widely used in aerospace, bulletproof protection, and other fields. Although para-aramids (such as the well-known Kevlar and Twaron) are renowned for their extremely high tensile strength, their compressive strength is relatively low (typically only 1 / 5 to 1 / 4 of their tensile strength), thus limiting their application in fiber-reinforced composites. Macroscopic para-aramid fibers are composed of numerous nanofibers, and the low interaction force between these nanofibers is the main reason for their low compressive strength. Furthermore, the low interaction force between the nanofibers also leads to the aramid fibers easily peeling off from the matrix in fiber-reinforced composites, i.e., poor adhesion to the matrix, affecting the final strength of the fiber-reinforced composite.

[0003] In existing technologies, common methods to improve the compressive strength of para-aramid fibers include introducing monomers and introducing chemical crosslinks. Para-aramid PBIA is prepared by copolymerizing the heterocyclic monomer 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) with p-phenylenediamine. The benzimidazole groups on its molecular chain can form additional hydrogen bonds, increasing the compressive strength by 40%, reaching 390 MPa (Leal AA, et al, Compos Sci Technol 2007; 67:2786–94.). While introducing thermally reactive groups into the aramid side chains and generating free radicals through heat treatment to achieve crosslinking can increase the compressive strength of aramid fibers to some extent, the introduction of side chains disrupts the regularity of the para-aramid molecular chain, significantly reducing the tensile strength of the aramid fibers (Dai Y., et al, Composites Part A 2007;113: 233–241). Therefore, how to improve the compressive strength of aramid fibers without sacrificing tensile strength is an urgent problem to be solved. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a copolymer-modified para-aramid, a preparation method thereof, and a high compressive strength fiber obtained therefrom. The copolymer-modified para-aramid is obtained by introducing a thermally crosslinkable monomer with a rigid conjugated structure into the molecular chain of a hybrid aramid. The copolymer-modified para-aramid can undergo crosslinking under heating conditions without destroying the regularity of the aramid molecular chain, thereby achieving both high tensile strength and high compressive strength.

[0005] This invention is achieved through the following technical solution: A method for preparing copolymerized modified para-aramid fiber includes the following steps: (1) Under an inert atmosphere, lithium salt is dissolved in an organic solvent, and then p-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzimidazole and modified monomer are added and stirred until completely dissolved to obtain a mixed monomer solution. The modified monomer has the following structural formula: (2) Cool the mixed monomer solution obtained in step (1) to -5~0℃, add terephthaloyl chloride, react at low temperature first, and then raise to room temperature to continue the reaction to obtain polymer solution; After the reaction is complete, the polymer liquid is poured into water to precipitate solids. After filtration and drying, the copolymerized modified para-aramid polymer is obtained.

[0006] Further specified, the lithium salt mentioned in step (1) is Li2CO3, and its mass is 0.5% to 5% of the mass of the organic solvent.

[0007] Further specifying, the organic solvent mentioned in step (1) is N,N'-dimethylacetamide or N-methylpyrrolidone.

[0008] Further specifying, the molar ratio of p-phenylenediamine to 2-(4-aminophenyl)-5-aminobenzimidazole in step (1) is 0.1:1 to 10:1.

[0009] Further specifying, the molar fraction of the modified monomer in step (1) in all diamine monomers is 5% to 20%, and the diamine monomers include the modified monomer, p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole.

[0010] Further specified, the mass ratio of diamine monomer to organic solvent in step (1) is 0.1% to 5%.

[0011] Further specified, the molar ratio of the total amount of diamine monomer to terephthaloyl chloride in step (2) is 0.9:1 to 1.1:1.

[0012] Further specifying, in step (2), the low-temperature reaction time is 0.5~1 h, and the reaction time after raising to room temperature is 2~4 h.

[0013] A copolymer-modified para-aramid polymer prepared by the above method.

[0014] A method for preparing high compressive strength fiber involves dissolving the above-mentioned copolymerized modified para-aramid polymer in a polar solvent, wet spinning to obtain nascent fiber, and then heat-treating it at 350°C for 3 hours to obtain cross-linked copolymerized modified para-aramid fiber.

[0015] The beneficial effects of this invention are as follows: 1. The copolymerized modified para-aramid provided by this invention is readily soluble in common polar solvents such as N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone, making it easy to perform solution spinning in the later stages and exhibiting good processability.

[0016] 2. The copolymer-modified para-aramid prepared by the present invention can be cross-linked copolymer-modified hybrid fiber by solution wet spinning and heat treatment at 350 ℃ for 3 h. This fiber has both high compressive strength and high tensile strength.

[0017] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art based on the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0018] Figure 1 This is a comparison of the tensile properties of crosslinked copolymer modified para-aramid fiber products 1, 2, and 3 obtained by the present invention with para-aramid fiber (Kevlar 29); Figure 2 This is a comparison of the compression resistance of crosslinked copolymerized modified para-aramid fiber products 1, 2, and 3 prepared in this invention with that of para-aramid fiber (Kevlar 29). Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the above description of the present invention, it should be noted that the terms "one side," "the other side," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is conventionally placed during use. These terms are used only for the convenience of describing the present invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] Furthermore, terms such as "identical" do not imply that components must be absolutely identical; minor differences are permissible. The term "perpendicular" simply means that the positional relationship between components is more perpendicular than "parallel," not that the structure must be perfectly perpendicular; a slight tilt is acceptable.

[0024] A method for preparing copolymerized modified para-aramid fiber includes the following steps: (1) Under an inert atmosphere, lithium salt is dissolved in an organic solvent, and then p-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzimidazole and modified monomer are added and stirred until completely dissolved to obtain a mixed monomer solution. The modified monomer has the following structural formula: (2) Cool the mixed monomer solution obtained in step (1) to -5~0℃, add terephthaloyl chloride, react at low temperature first, and then raise to room temperature to continue the reaction to obtain polymer solution; After the reaction is complete, the polymer liquid is poured into water to precipitate solids. After filtration and drying, the copolymerized modified para-aramid polymer is obtained.

[0025] In step (1), the lithium salt is Li2CO3, and its mass is 0.5% to 5% of the mass of the organic solvent.

[0026] The organic solvent mentioned in step (1) is N,N'-dimethylacetamide or N-methylpyrrolidone.

[0027] In step (1), the molar ratio of p-phenylenediamine to 2-(4-aminophenyl)-5-aminobenzimidazole is 0.1:1 to 10:1.

[0028] In step (1), the molar fraction of the modified monomer in all diamine monomers is 5% to 20%, and the diamine monomers include the modified monomer, p-phenylenediamine, and 2-(4-aminophenyl)-5-aminobenzimidazole.

[0029] In step (1), the mass ratio of diamine monomer to organic solvent is 0.1% to 5%.

[0030] In step (2), the molar ratio of the total amount of diamine monomer to terephthaloyl chloride is 0.9:1 to 1.1:1.

[0031] In step (2), the low-temperature reaction time is 0.5~1 h, and the reaction time after raising to room temperature is 2~4 h.

[0032] Example 1 Under a nitrogen atmosphere, 300 mL of N,N'-dimethylacetamide and 8 g of Li₂CO₃ were added to a 500 mL flask and stirred until completely dissolved. Then, 1.5 g of p-phenylenediamine, 2.6 g of 2-(4-aminophenyl)-5-aminobenzimidazole, and 0.5 g of the modified monomer were added and stirred until completely dissolved. The temperature was lowered to -5 °C, and 5.6 g of terephthaloyl chloride was added. The temperature was maintained at -5 °C and the reaction was stirred for 0.5 h, followed by a 3 h reaction at room temperature. After the reaction was completed, the reaction solution was poured into a large amount of water, the precipitate precipitated, filtered, and dried to obtain the copolymerized modified para-aramid (product 1).

[0033] Example 2 Under a nitrogen atmosphere, 300 mL of N,N'-dimethylacetamide and 8 g of Li₂CO₃ were added to a 500 mL flask and stirred until completely dissolved. Then, 2 g of p-phenylenediamine, 2 g of 2-(4-aminophenyl)-5-aminobenzimidazole, and 0.3 g of the modified monomer were added and stirred until completely dissolved. The temperature was lowered to -5 °C, and 4.3 g of terephthaloyl chloride was added. The temperature was maintained at -5 °C and the reaction was stirred for 1 h, followed by a 2 h reaction at room temperature. After the reaction was completed, the reaction solution was poured into a large amount of water, the precipitate was precipitated, filtered, and dried to obtain the copolymerized modified para-aramid (product 2).

[0034] Example 3 Under a nitrogen atmosphere, 300 mL of N,N'-dimethylacetamide and 8 g of Li₂CO₃ were added to a 500 mL flask and stirred until completely dissolved. Then, 4 g of p-phenylenediamine, 2 g of 2-(4-aminophenyl)-5-aminobenzimidazole, and 1 g of the modified monomer were added and stirred until completely dissolved. The temperature was lowered to -5 °C, and 6.7 g of terephthaloyl chloride was added. The temperature was maintained at -5 °C and the reaction was stirred for 0.5 h, followed by a 3 h reaction at room temperature. After the reaction was completed, the reaction solution was poured into a large amount of water, the precipitate was precipitated, filtered, and dried to obtain the copolymerized modified para-aramid (product 3).

[0035] Products 1, 2, and 3 were all prepared into copolymerized para-aramid fibers using the following method, which correspond to products 1, 2, and 3, respectively.

[0036] The copolymerized modified para-aramid fibers (products 1, 2, and 3) obtained in the above examples are soluble in N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone. In contrast, poly(p-phenylene terephthalamide) (Kevlar 29 fiber) is insoluble in N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone.

[0037] To test the tensile strength of the crosslinked para-aramid fibers provided by this invention, products 1, 2, and 3 from the above examples were dissolved in N,N'-dimethylacetamide to obtain a 5% (w / w) spinning solution. Copolymer-modified para-aramid fibers were obtained by wet spinning, and then the copolymer-modified para-aramid fibers were heat-treated at 350°C for 3 hours to obtain crosslinked copolymer-modified para-aramid fiber products 1, 2, and 3. Kevlar 29 fiber, used for comparison, was a commercially available product.

[0038] The tensile test results for products 1, 2, and 3 are as follows: Figure 1 As shown, the tensile strengths of products 1, 2, and 3 are 3.1 GPa, 2.8 GPa, and 2.9 GPa, respectively, while the tensile strength of Kevlar 29 fiber is 3.0 GPa. It can be seen that the tensile strength of cross-linked copolymerized para-aramid fiber is comparable to that of Kevlar 29 fiber.

[0039] The compressive strength results for products 1, 2, and 3 are as follows: Figure 2 As shown, the compressive strengths of products 1, 2, and 3 are 750 MPa, 671 MPa, and 723 MPa, respectively, while the tensile strength of Kevlar 29 fiber is 360 MPa. Compared to Kevlar 29 fiber, the compressive strengths of products 1, 2, and 3 are increased by 110%, 86%, and 100%, respectively. It is evident that the compressive strength of cross-linked copolymerized para-aramid fiber is significantly higher than that of poly(p-phenylene terephthalamide) (Kevlar 29 fiber).

[0040] The method for testing fiber compressive strength is referenced in (Dai Y., et al, Composites Part A 2007;113: 233–241). Specifically, a certain tensile stress is first applied to the fiber, and then the fiber is cut in the middle. If the fiber becomes kinked after cutting, it indicates that the fiber has undergone compressive failure under this stress. The maximum tensile stress at which the fiber does not undergo compressive failure is the compressive strength of the fiber.

[0041] Experimental results can be attached in a separate table. As shown in the table above, this invention provides a copolymer-modified para-aramid fiber, a preparation method thereof, and a high compressive strength fiber obtained therefrom. The copolymer-modified para-aramid fiber is obtained by introducing a thermally crosslinkable monomer with a rigid conjugated structure into the molecular chain of a hybrid aramid fiber. Compared to commercially available Kevlar 29 aramid fiber, the modified para-aramid fiber exhibits comparable tensile strength, but its compressive strength is approximately twice that of Kevlar 29 aramid fiber, demonstrating a significant improvement.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing copolymerized modified para-aramid, characterized in that, Includes the following steps: (1) Under an inert atmosphere, lithium salt is dissolved in an organic solvent, and then p-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzimidazole and modified monomer are added and stirred until completely dissolved to obtain a mixed monomer solution. The modified monomer has the following structural formula: (2) Cool the mixed monomer solution obtained in step (1) to -5~0℃, add terephthaloyl chloride, react at low temperature first, and then raise to room temperature to continue the reaction to obtain polymer solution; After the reaction is complete, the polymer liquid is poured into water to precipitate solids. After filtration and drying, the copolymerized modified para-aramid polymer is obtained.

2. The method for preparing copolymerized modified para-aramid according to claim 1, characterized in that, The lithium salt mentioned in step (1) is Li2CO3, and its mass is 0.5% to 5% of the mass of the organic solvent.

3. The method for preparing copolymerized modified para-aramid according to claim 1, characterized in that, The organic solvent mentioned in step (1) is N,N'-dimethylacetamide or N-methylpyrrolidone.

4. The method for preparing copolymerized modified para-aramid according to claim 1, characterized in that, In step (1), the molar ratio of p-phenylenediamine to 2-(4-aminophenyl)-5-aminobenzimidazole is 0.1:1 to 10:

1.

5. The method for preparing copolymerized modified para-aramid according to claim 1, characterized in that, The modified monomer in step (1) accounts for 5% to 20% of the molar fraction of all diamine monomers, and the diamine monomers include the modified monomer, p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole.

6. The method for preparing copolymerized modified para-aramid according to claim 1, characterized in that, In step (1), the mass ratio of diamine monomer to organic solvent is 0.1% to 5%.

7. The method for preparing copolymerized modified para-aramid according to claim 1, characterized in that, In step (2), the molar ratio of the total amount of diamine monomer to terephthaloyl chloride is 0.9:1 to 1.1:

1.

8. The method for preparing copolymerized modified para-aramid according to claim 1, characterized in that, In step (2), the low-temperature reaction time is 0.5~1 h, and the reaction time after raising to room temperature is 2~4 h.

9. A copolymer-modified para-aramid polymer prepared by the method for preparing copolymer-modified para-aramid according to any one of claims 1 to 8.

10. A method for preparing high compressive strength fiber, characterized in that, The copolymer-modified para-aramid polymer of claim 9 is dissolved in a polar solvent, and the nascent fiber is obtained by wet spinning. Then, it is heat-treated at 350°C for 3 hours to obtain cross-linked copolymer-modified para-aramid fiber.

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