A kind of polyamic acid and its polyimide fiber and preparation method thereof

Abstract

The present invention relates to a polyamic acid and a polyimide fiber thereof and a preparation method thereof. The polyamic acid has a structure as shown in the following formula 1, wherein Ar is an aromatic residue containing a bridging structure; m is the molar ratio of a repeating unit having a structure of formula 2 in the polyamic acid, and 0.6≤m≤0.9. The polyimide fiber of the present invention has a breaking strength greater than 3.0 GPa, a modulus greater than 100 GPa, and an elongation at break greater than 4%, which solves the problem in the prior art that high-strength and high-model polyimide fibers are relatively brittle during imidization, have a generally low elongation at break, and are not conducive to continuous production and further processing.

Description

Technical Field

[0001] The invention relates to the field of polyimide, in particular to polyamic acid and polyimide fiber thereof and a preparation method thereof. Background Art

[0002] Polyimide (PI) fiber is a high-performance organic fiber with excellent properties such as high strength, high modulus, high and low temperature resistance, and radiation resistance. It is suitable for use under extreme conditions such as high temperature and high heat. It has extremely important applications in aerospace, marine engineering, advanced rail transportation, and high-temperature filtration.

[0003] With the development of science and technology, the application scope of PI fiber is constantly expanding, and it is increasingly penetrating into various fields from civil, industrial to national defense. Higher strength and modulus have become an important and challenging goal to pursue. However, the global PI fiber technology is mainly concentrated abroad, and exports to China are limited. Domestic fibers lack high-performance products, and their applications are mainly concentrated in the fields of heat resistance and radiation resistance. The quality is unstable, the mechanical properties are generally poor, and there are many broken fibers, which restricts its market promotion.

[0004] At present, high-strength and high-model polyimide fibers are mainly produced by copolymerization or introduction of heterocyclic diamines to bring higher rigidity or hydrogen bonds to the polymer to provide molecular chain interactions, thereby affecting the arrangement and crystallinity of the molecular chains in the polymer and giving the polyimide fibers higher mechanical properties. However, the heterocyclic and benzene rings in this type of molecular structure have high density and high rigidity. There are problems such as high fiber brittleness during the imidization process, generally low elongation at break, and easy breakage, which is not conducive to continuous production and further processing. Summary of the invention

[0005] One of the main problems solved by the present invention is that in the prior art, high-strength and high-model polyimide fibers are brittle during imidization, have generally low elongation at break, are prone to breakage, and are not conducive to continuous production and further processing.

[0006] The high-strength and high-modulus fiber involved in the present invention introduces heterocyclic monomers and aromatic diamine monomers containing bridging structures on the main chain, introduces hydrogen bonds, enhances the interaction between molecular chains, and introduces bridging structures at the same time, wherein flexible groups such as ether bonds, carbonyl groups, and sulfone groups can reduce the rotation energy barrier within the molecular chain, increase the free volume, and increase the flexibility of the polymer molecular main chain, which is beneficial to improving the drafting multiple of the fiber during the imidization process, so that the PI fiber has a greater orientation degree and mechanical properties, overcomes the above-mentioned shortcomings, further improves the mechanical properties of the fiber, has good production continuity, and is beneficial to subsequent processing.

[0007] One of the purposes of the present invention is to provide a polyamic acid having a structure shown in the following formula (1):

[0008]

[0009] Wherein, Ar is an aromatic residue containing a bridging structure;

[0010] m is the molar ratio of the repeating unit having the structure of formula (2) in the polyamic acid polymer structure of formula (1), 0.6≤m≤0.9, preferably, 0.7≤m≤0.8.

[0011]

[0012] In the polyamic acid of the present invention, Ar is preferably one of the aromatic residues shown in the following structural formula:

[0013]

[0014] Among them, R1 is preferably H-, CH3-, Cl-, Br-, F-, or CH3O-.

[0015] The second object of the present invention is to provide a method for preparing the polyamic acid, comprising the following steps:

[0016] The polyamic acid is obtained by polycondensing a diamine monomer and 3,3'4,4'-biphenyltetracarboxylic acid dianhydride, wherein the diamine monomer comprises 2-(4-aminophenyl)-5-aminobenzimidazole and an aromatic diamine monomer containing a bridging structure.

[0017] Preferably, the preparation method comprises mixing 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), an aromatic diamine monomer containing a bridging structure and 3,3'4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) in an organic solvent, and performing a polycondensation reaction to obtain a polyamic acid solution. Preferably, the polycondensation reaction temperature is -10°C to 50°C, and the reaction time is 1 to 10 hours.

[0018] The organic solvent is preferably at least one selected from strongly polar aprotic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide and sulfolane.

[0019] In the above technical solution, in the preparation method of the polyamic acid, the molar amount of 3,3'4,4'-biphenyltetracarboxylic dianhydride and the total molar amount of diamine monomers are mixed in a ratio of (0.95-1.05):1, preferably (0.98-1.02):1.

[0020] The ratio of the molar amount of 2-(4-aminophenyl)-5-aminobenzimidazole to the total molar amount of the diamine monomer is (0.6-0.9):1, preferably (0.7-0.8):1.

[0021] The aromatic diamine monomer containing a bridging structure has a structure shown in the following formula (3):

[0022] H2N-Ar-NH2 (3),

[0023] Wherein, Ar is selected from one of the aromatic residues shown in the following structural formula,

[0024]

[0025] R1 is H-, CH3-, Cl-, Br-, F-, CH3O-.

[0026] The aromatic diamine monomer containing a bridge structure is preferably at least one selected from 2,2-bis[4-(4-aminophenoxy)phenyl]propane, all-meta-triphenyl diether diamine, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenyl sulfide.

[0027] The third object of the present invention is to provide a polyimide having a structure shown in the following formula (4):

[0028]

[0029] Wherein, n is the molar ratio of the repeating unit having the structure of formula (5) in the polyimide, 0.6≤n≤0.9, preferably 0.7≤n≤0.8,

[0030]

[0031] The Ar is preferably one of the aromatic residues shown in the following structural formula:

[0032]

[0033] Among them, R1 is preferably H-, CH3-, Cl-, Br-, F-, or CH3O-.

[0034] In the above technical solution, the polyimide is obtained by imidizing the above polyamic acid or the polyamic acid obtained by the preparation method.

[0035] A fourth object of the present invention is to provide a polyimide fiber comprising the polyimide.

[0036] The polyimide has a structure shown in the following formula (4):

[0037]

[0038] wherein Ar is an aromatic residue; n is the molar ratio of the repeating unit having the structure of formula (5) in the polyimide, 0.6≤n≤0.9, preferably 0.7≤n≤0.8,

[0039]

[0040] Furthermore, the polyimide fiber is prepared by imidization of the polyamic acid or the polyamic acid obtained by the preparation method.

[0041] In the above technical solution, the breaking strength of the polyimide fiber is greater than 3.0 GPa, the modulus is greater than 100 GPa, and the breaking elongation is greater than 4%.

[0042] A fifth object of the present invention is to provide a method for preparing the polyimide fiber, comprising the following steps: spinning, imidizing, and heat-setting a spinning solution containing the polyamic acid to obtain the polyimide fiber.

[0043] According to a preferred embodiment of the present invention, the preparation method comprises the following steps:

[0044] The polyamic acid solution is degassed and filtered to obtain a spinning solution, which is spun using a wet spinning process or a dry-wet spinning process. After coagulation, water washing, oiling, drying and densification, imidization, and heat setting, uniform polyimide fibers are obtained.

[0045] In the above technical solution, there is no special limitation on the spinning, imidization and heat setting processes of the spinning solution, which are all common processes for preparing polyimide fibers in the art.

[0046] In the above technical solution, the solid content of the spinning solution is 5 to 30%, preferably 12 to 18%.

[0047] In the above technical solution, the degassing is preferably carried out by vacuum standing or degassing tower casting.

[0048] In the above technical solution, the filtering method is preferably multi-pass filtering, and the filtering accuracy is preferably 2 to 10 μm, with the filtering accuracy increasing step by step.

[0049] In the above technical solution, the coagulation bath medium can be a common coagulation bath medium in the art, preferably a dimethylacetamide aqueous solution, the concentration of the coagulation bath adopts step concentration coagulation, the concentration is preferably 3-35%, and the temperature of the coagulation bath is preferably 0-40°C.

[0050] In the above technical solution, the water washing is preferably multi-pass water washing, and the water washing temperature is preferably 40-65°C.

[0051] In the above technical solution, the oiling is preferably carried out by roller type oiling.

[0052] In the above technical solution, the drying and densification temperature is preferably 60-150°C.

[0053] In the above technical solution, the imidization treatment is preferably carried out by gradually increasing the temperature in multiple temperature zones, and the imidization temperature is preferably 100-550° C., more preferably 150-480° C.; the imidization process is preferably protected by nitrogen, and the oxygen content is preferably not more than 1%.

[0054] In the above technical solution, the temperature of the heat setting is preferably 200-300°C, more preferably 200-280°C.

[0055] The present invention introduces heterocyclic monomers and aromatic diamine monomers containing bridging structures into the main chain of high-strength and high-modulus fibers, introduces hydrogen bonds, enhances the interaction between molecular chains, and introduces bridging structures. Flexible groups such as ether bonds, carbonyl groups, and sulfone groups can reduce the rotation energy barrier within the molecular chain and increase the free volume, which is beneficial to increasing the drafting multiple of the fiber during the imidization process, so that the PI fiber has a greater orientation degree and mechanical properties, overcomes the above-mentioned shortcomings, further improves the mechanical properties of the fiber, has good production continuity, and is beneficial to subsequent processing.

[0056] The polyimide fiber obtained by adopting the scheme of the present invention has good production continuity and is conducive to further processing. The polyimide fiber has a breaking strength greater than 3.0GPa, a modulus greater than 100GPa, and an elongation at break greater than 4%, achieving good technical effects.

[0057] The present invention will be further described below by way of examples. DETAILED DESCRIPTION

[0058] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0059] The raw materials used in the specific implementation manner of the present invention are commercially available.

[0060] The test equipment and test conditions used in the present invention are:

[0061] Mechanical properties of fibers: Single-filament strength tests were performed on the fully automatic single-fiber universal tester FAVIMAT+. Single-filaments with a separation length of more than 20 mm were tested at an initial stress of 0.3 cN and a tensile speed of 10 mm / min.

[0062] [Example 1] BIA molar ratio 0.7

[0063] 1. Preparation of stock solution: (1) 4.10 kg (18.28 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 3.21 kg (7.83 mol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) were dissolved in 85 kg of N,N-dimethylacetamide (DMAc), and stirred at 25°C under N2 protection. After complete dissolution, 7.68 kg (26.12 mol) of 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. After the addition was completed, stirring was continued for 1 hour to obtain a polyamic acid (PAA) spinning stock solution with a solid content of 15%.

[0064] 2. Coagulation molding: After vacuum degassing, the spinning solution is filtered through 3μm and then extruded through a spinneret into the first coagulation bath. The coagulation bath temperature is 0°C, the concentration is 35%, and the draft ratio is -50%. The second coagulation bath is 30°C, the concentration is 20%, and the draft ratio is 110%. The third coagulation bath is 40°C, the concentration is 10%, and the draft ratio is 105% to obtain primary fibers.

[0065] 3. Washing: The raw fiber is washed 10 times at a temperature of 45°C and stretched 1.1 times during the washing stage.

[0066] 4. Oiling and drying and densification: The fiber obtained in step 3 is oiled once and then dried and densified at a temperature of 85°C, and then oiled again. After oiling, it is dried and densified for the second time at a temperature of 130°C.

[0067] 5. Imidization: The raw silk obtained in step 4 is imidized. The imidization process passes through 10 temperature zones in total. The temperature is gradually increased. The first temperature zone is 100°C, the second temperature zone is 150°C, the third temperature zone is 200°C, the fourth temperature zone is 260°C, the fifth temperature zone is 280°C, the sixth temperature zone is 300°C, the seventh temperature zone is 310°C, the eighth temperature zone is 320°C, the ninth temperature zone is 330°C, and the tenth temperature zone is 350°C. Nitrogen protection is used during the imidization process, and the oxygen content is less than 100ppm.

[0068] 6. Hot stretching, heat setting and collection: The fiber obtained in step 5 is hot stretched and then heat set and collected at 200° C. to obtain polyimide fiber. The hot stretching temperature is 480° C. and the drawing ratio is 1.6.

[0069] The obtained polyimide fiber monofilament strength is 3.7 GPa, the modulus is 130 GPa, and the elongation at break is 8.5%.

[0070] [Example 2] BIA molar ratio 0.6

[0071] 1. Preparation of stock solution: (1) 3.70 kg (16.49 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 3.21 kg (10.99 mol) of all-meta-triphenyl diether diamine (1,3,3-APB) were dissolved in 85 kg of N,N-dimethylacetamide (DMAc), and stirred at 25 °C under N2 protection. After complete dissolution, 8.08 kg (27.49 mol) of 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. After the addition was completed, stirring was continued for 1 hour to obtain a polyamic acid (PAA) spinning stock solution with a solid content of 15%.

[0072] The remaining steps were carried out in accordance with Example 1. The obtained polyimide fiber had a monofilament strength of 3.3 GPa, a modulus of 125 GPa, and an elongation at break of 6.3%.

[0073] [Example 3] BIA molar ratio 0.9

[0074] 1. Preparation of stock solution: (1) Dissolve 5.81 kg (25.91 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 0.71 kg (2.88 mol) of 4,4'-diaminodiphenyl sulfone (DDS) in 85 kg of N,N-dimethylacetamide (DMAc), stir under N2 protection at 25°C, and after complete dissolution, add 8.47 kg (28.79 mol) of 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA). After the addition is completed, continue stirring for 1 hour to obtain a polyamic acid (PAA) spinning stock solution with a solid content of 15%.

[0075] The remaining steps were carried out in accordance with Example 1. The obtained polyimide fiber had a monofilament strength of 3.2 GPa, a modulus of 105 GPa, and an elongation at break of 5.8%.

[0076] [Example 4] BIA molar ratio 0.7

[0077] 1. Preparation of stock solution: (1) Dissolve 4.61 kg (20.56 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 1.75 kg (8.81 mol) of 4,4'-diaminodiphenylmethane (DDM) in 85 kg of N,N-dimethylacetamide (DMAc), stir under N2 protection at 25°C, and after complete dissolution, add 8.64 kg (29.37 mol) of 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA). After the addition is completed, continue stirring for 1 hour to obtain a polyamic acid (PAA) spinning stock solution with a solid content of 15%.

[0078] The remaining steps were carried out in accordance with Example 1. The obtained polyimide fiber had a monofilament strength of 3.4 GPa, a modulus of 118 GPa, and an elongation at break of 7.7%.

[0079] [Example 5] BIA molar ratio 0.7

[0080] 1. Preparation of stock solution: (1) Dissolve 4.56 kg (20.34 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 1.88 kg (8.72 mol) of 4,4'-diaminodiphenyl sulfide (4,4-SDA) in 85 kg of N,N-dimethylacetamide (DMAc), stir under N2 protection at 25°C, and after complete dissolution, add 8.55 kg (29.06 mol) of 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA). After the addition is completed, continue stirring for 1 hour to obtain a polyamic acid (PAA) spinning stock solution with a solid content of 15%.

[0081] The remaining steps were carried out in accordance with Example 1. The obtained polyimide fiber monofilament had a strength of 3.6 GPa, a modulus of 133 GPa, and an elongation at break of 6.5%.

[0082] [Example 6] BIA molar ratio 0.6

[0083] 1. Preparation of stock solution: (1) 3.40 kg (15.18 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 4.15 kg (10.12 mol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) were dissolved in 85 kg of N,N-dimethylacetamide (DMAc), and stirred at 25°C under N2 protection. After complete dissolution, 7.44 kg (25.30 mol) of 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. After the addition was completed, stirring was continued for 1 hour to obtain a polyamic acid (PAA) spinning stock solution with a solid content of 15%.

[0084] The remaining steps were carried out in accordance with Example 1. The obtained polyimide fiber monofilament had a strength of 3.3 GPa, a modulus of 105 GPa, and an elongation at break of 9.6%.

[0085] [Comparative Example 1] BIA molar ratio 0.5

[0086] 1. Preparation of stock solution: (1) Dissolve 2.75 kg (12.26 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 5.03 kg (12.26 mol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) in 85 kg of N,N-dimethylacetamide (DMAc), stir under N2 protection at 25°C, and after complete dissolution, add 7.21 kg (24.52 mol) of 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA). After the addition is completed, continue stirring for 1 hour to obtain a polyamic acid (PAA) spinning stock solution with a solid content of 15%.

[0087] The remaining steps were carried out in accordance with Example 1. The obtained polyimide fiber monofilament had a strength of 2.7 GPa, a modulus of 85 GPa, and an elongation at break of 12.0%.

[0088] [Comparative Example 2] BIA molar ratio 1

[0089] 1. Preparation of stock solution: (1) Dissolve 6.48 kg (28.92 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) in 85 kg of N,N-dimethylacetamide (DMAc), stir at 25°C under N2 protection, and after complete dissolution, add 8.51 kg (28.92 mol) of 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA). After the addition is completed, continue stirring for 1 hour to obtain a polyamic acid (PAA) spinning stock solution with a solid content of 15%.

[0090] The remaining steps were carried out in accordance with Example 1. The obtained polyimide fiber monofilament had a strength of 2.6 GPa, a modulus of 95 GPa, and an elongation at break of 4.2%.

[0091] [Comparative Example 3] BIA molar ratio 0.7, without bridging structure rigid diamine monomer PDA

[0092] 1. Preparation of stock solution: (1) Dissolve 4.87 kg (21.71 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 1.00 kg (9.30 mol) of p-phenylenediamine (PDA) in 85 kg of N,N-dimethylacetamide (DMAc), stir under N2 protection at 25°C, and after complete dissolution, add 9.12 kg (31.01 mol) of 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA). After the addition is completed, continue stirring for 1 hour to obtain a polyamic acid (PAA) spinning stock solution with a solid content of 15%.

[0093] The remaining steps were carried out in accordance with Example 1, and the obtained polyimide fiber monofilament had a strength of 3.2 GPa, a modulus of 103 GPa, and an elongation at break of 2%.

Claims

1. A polyimide fiber, wherein the polyimide has a structure shown in the following formula (4): in, Ar is an aromatic residue containing a bridging structure; n is the molar ratio of the repeating unit having the structure of formula (5) in the polyamide imide, 0.6<n<0.8, Ar is selected from one of the aromatic residues shown in the following structural formulas, Wherein, R1 is H-, CH3-, Cl-, Br-, F-, CH3O-; The polyimide fiber is obtained by thermal imidization of the polyamic acid represented by formula (1).

2. The polyimide fiber according to claim 1, characterized in that: 0.7≤n＜0.8。 3. The polyimide fiber according to claim 1 or 2, characterized in that The breaking strength of the polyimide fiber is greater than 3.0 GPa, the modulus is greater than 100 GPa, and the breaking elongation is greater than 4%.

4. A method for preparing the polyimide fiber according to any one of claims 1 to 3, comprising the following steps: The polyimide fiber is obtained by spinning a spinning solution containing the polyamic acid, imidizing, and heat-setting, wherein the polyamic acid is prepared by the following steps: polycondensing a diamine monomer and 3,3'4,4'-biphenyltetracarboxylic dianhydride to obtain the polyamic acid, wherein the diamine monomer includes 2-(4-aminophenyl)-5-aminobenzimidazole and an aromatic diamine monomer containing a bridging structure, The aromatic diamine monomer containing a bridging structure has a structure shown in the following formula (3): H2N-Ar-NH2 (3), Wherein, Ar is selected from one of the aromatic residues shown in the following structural formula, R1 is H-, CH3-, Cl-, Br-, F-, CH3O-; The ratio of the molar amount of 2-(4-aminophenyl)-5-aminobenzimidazole to the total molar amount of the diamine monomers is greater than 0.6:1 and less than 0.8:

1.

5. The method for preparing the polyimide fiber according to claim 4, characterized in that: The solid content of the spinning solution is 5 to 30%; and / or, The imidization treatment adopts a multi-temperature zone gradual heating method, and the imidization temperature is 100-550° C.; the imidization process is protected by nitrogen, and the oxygen content is not more than 1%; and / or, The temperature of the heat setting is 200-300°C.

6. The method for preparing the polyimide fiber according to claim 5, characterized in that: The solid content of the spinning solution is 12-18%; and / or, The imidization temperature is 150-480° C.; and / or, The temperature of the heat setting is 200-280°C.

7. The method for preparing the polyimide fiber according to any one of claims 4 to 6, characterized in that The following steps are involved: The polyamic acid solution is degassed and filtered to obtain a spinning stock solution, which is spun using a wet spinning process or a dry-wet spinning process, and the polyimide fiber is obtained after coagulation, water washing, oiling, drying and densification, imidization, and heat setting.

8. The method for preparing the polyimide fiber according to claim 7, characterized in that: The degassing is carried out by vacuum standing or degassing tower casting; and / or, The filtering method is multi-pass filtering, the filtering accuracy is 2 to 10 μm, and the filtering accuracy is increased step by step; and / or, The coagulation bath medium is a dimethylacetamide aqueous solution, the concentration of the coagulation bath adopts step concentration coagulation, the concentration is 3-35%, and the temperature of the coagulation bath is 0-40°C; and / or, The water washing is a multi-pass water washing, and the water washing temperature is 40-65°C; and / or, The oiling is carried out by roller oiling; and / or, The drying and densification temperature is 60-150°C.

9. The method for preparing the polyimide fiber according to claim 4, characterized in that: The ratio of the molar amount of 3,3'4,4'-biphenyltetracarboxylic acid dianhydride to the total molar amount of the diamine monomer is (0.95-1.05):1; and / or, The ratio of the molar amount of 2-(4-aminophenyl)-5-aminobenzimidazole to the total molar amount of the diamine monomers is greater than or equal to 0.7:1 and less than 0.8:

1.

10. The method for preparing polyimide fiber according to claim 9, characterized in that: The ratio of the molar amount of 3,3'4,4'-biphenyltetracarboxylic dianhydride to the total molar amount of the diamine monomer is (0.98-1.02):

1.

11. The method for preparing polyimide fiber according to claim 4, characterized in that: The aromatic diamine monomer containing a bridging structure is selected from at least one of 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane and 4,4'-diaminodiphenyl sulfide.

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