High-strength high-modulus polyimide fiber and method for producing the same

Abstract

The application relates to the technical field of polyimide materials, and discloses a high-strength and high-modulus polyimide fiber and a preparation method thereof, which comprises the following steps: mixing aromatic dianhydride and nitrogen-containing organic base unit diamine monomers, and carrying out kettle polymerization to obtain rigid polymerization liquid 1; mixing aromatic dianhydride and flexible diamine monomers, and carrying out kettle polymerization to obtain flexible oligomer polymerization liquid 2; conveying the rigid polymerization liquid 1 and the flexible oligomer polymerization liquid 2 into a screw reactor to carry out secondary reaction, and obtaining polyamide acid spinning liquid; filtering and defoaming the polyamide acid spinning liquid, and obtaining polyamide acid fiber through dry spinning; and carrying out thermal imidization and thermal drawing on the polyamide acid fiber to obtain the high-strength and high-modulus polyimide fiber. The application adopts kettle pre-polymerization + screw final polymerization segmented polymerization, avoids gel explosion polymerization, and considers both high-strength and high-modulus and spinnability of the fiber, and cooperates with a channel in-situ catalytic cyclization to synergistically improve fiber orientation and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of polyimide materials technology, and more specifically, to a high-strength, high-modulus polyimide fiber and its preparation method. Background Technology

[0002] With the rapid development of aerospace, new energy and other fields, the requirements for materials have increased significantly, necessitating key basic materials with multiple properties and functions. Polyimide fiber, with its excellent mechanical properties, resistance to high and low temperatures, chemical corrosion resistance and radiation stability, is widely used in aerospace, special protection, new energy, semiconductor and composite material fields.

[0003] The preparation of high-strength, high-modulus polyimide fibers requires addressing two major issues: molecular structure design and spinning solution quality. Regarding molecular structure design, a combination of rigid and flexible chains is necessary to achieve a balance. This addresses the problems of poor spinnability, brittleness, and defect sensitivity associated with entirely rigid structures, while resolving the issues of low strength, high creep, and poor thermal stability associated with entirely flexible structures. As for spinning solution quality, high molecular weight, highly uniform spinning solutions can effectively improve the core-sheath structure and reduce defects during fiber formation, thereby enhancing fiber quality and production stability.

[0004] Therefore, providing a high-strength, high-modulus polyimide fiber and its preparation method has significant practical implications. Summary of the Invention

[0005] In view of this, the present invention proposes a high-strength, high-modulus polyimide fiber and its preparation method, aiming to solve at least one of the problems in the current background art.

[0006] This invention proposes a method for preparing high-strength, high-modulus polyimide fibers, comprising the following steps: S1: Aromatic dianhydride is mixed with nitrogen-containing organic base diamine monomer and polymerized in a batch reactor to obtain a rigid polymer solution 1 with precisely controllable molecular weight and containing nitrogen-containing organic base. S2: Mix aromatic dianhydride with flexible diamine monomer and polymerize by batch polymerization to obtain flexible oligomer polymer solution 2; S3: The rigid polymerization liquid 1 and the flexible oligomer polymerization liquid 2 are fed into a screw reactor for a secondary reaction to obtain polyamic acid spinning solution; S4: The polyamic acid spinning solution is filtered and defoamed, and polyamic acid fibers are obtained by dry spinning. S5: The polyamic acid fiber is subjected to thermal imidization and thermal stretching to finally obtain the high-strength, high-modulus polyimide fiber.

[0007] Preferably, the solvents used in steps S1 and S2 are the same, and each solvent is at least one of N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide.

[0008] Preferably, the aromatic dianhydride is one or more of the following: pyromellitic dianhydride, biphenyl dianhydride, diphenyl sulfone dianhydride, bisphenol A diether dianhydride, 4,4'-oxobisphthalic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, diphenyl ether dianhydride, benzophenone dianhydride, and benzyl phenone dianhydride.

[0009] Preferably, the nitrogen-containing organic base diamine monomer is one of 2-(4-aminophenyl)-5-aminobenzimidazole, bis(2-(4-aminophenyl))dibenzimidazole, 4,4'-(pyrimidin-2,5-diyl)diphenylamine, and 2,4-bis(4-aminoanilino)-6-anilino-1,3,5-triazine.

[0010] Preferably, the flexible diamine monomer is one of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenyl ether, and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane.

[0011] Preferably, the solid content of the rigid polymerization liquid 1 is 10wt%~40wt%, and the solid content of the flexible oligomer polymerization liquid 2 is 15wt%~30wt%. Preferably, in step S1, the molar ratio of the aromatic dianhydride to the nitrogen-containing organic basic diamine monomer is 0.6~1.05:1; in step S2, the degree of polymerization Xn of the flexible oligomer polymer liquid 2 is 5~20.

[0012] Preferably, in steps S1 and S2, the parameters for the batch polymerization are: temperature 0℃~50℃, time 1~8h; In step S3, the conveying speed of the rigid polymerization liquid 1 is 3 kg / h to 30 kg / h, and the conveying speed of the flexible oligomer polymerization liquid 2 is 1 kg / h to 30 kg / h; the mixing temperature is 10 to 80°C, and the rotation speed is 10 to 200 rpm; the number average molecular weight of the polyamic acid spinning solution is ≥200,000 g / mol, and the molecular weight distribution is ≤2.0.

[0013] Preferably, in step S4, the spinneret orifice diameter in the dry spinning process is 0.06~0.45mm, the tunnel temperature is 180℃~260℃, and the spinning speed is 300m / min~350m / min. In step S5, the thermal imidization specifically adopts a multi-gradient thermal imidization method with a temperature of 200℃~380℃ and a total draw ratio of 1.2~4.0; the thermal drawing specifically adopts a multi-stage thermal drawing method with a temperature of 350℃~500℃ and a total draw ratio of 2.0~6.8.

[0014] The present invention also provides a high-strength, high-modulus polyimide fiber, which is prepared by the preparation method described in the above technical solution.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention pioneered a segmented polymerization route of "pot prepolymerization + screw final polymerization", which completely solved the problem of gel block generation or even explosive polymerization caused by local overheating and uneven mixing in traditional one-time reaction polymerization, and achieved a high degree of controllability and safety and stability of the polymerization process.

[0016] (2) Based on the above process, the present invention successfully prepared a high molecular weight polyamic acid spinning solution with extremely narrow molecular weight distribution, which laid a key material foundation for the subsequent preparation of high performance polyimide fibers.

[0017] (3) The present invention precisely controls the rigid segment structure of the polymerization liquid 1, introduces nitrogen-containing organic base units to achieve in-situ catalytic cyclization, and introduces flexible units in the secondary reaction in the screw, which not only optimizes the spinning rheological properties and improves the high-temperature draw ratio, but also retains the regularity of the rigid segments. With its highly uniform, high molecular weight block structure, the polyimide fiber prepared by the present invention maximizes the advantages of the close packing of the rigid segments and exhibits excellent mechanical properties. Attached Figure Description

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a scanning electron microscope image of the surface of polyimide fiber in Example 2.

[0019] Figure 2 This is a scanning electron microscope image of a cross-section of polyimide fiber in Example 2. Detailed Implementation

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0021] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0022] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0023] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0024] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0025] This invention provides a method for preparing high-strength, high-modulus polyimide fibers, comprising the following steps: S1: Aromatic dianhydride is mixed with nitrogen-containing organic base diamine monomer and polymerized in a batch reactor to obtain a rigid polymer solution 1 with precisely controllable molecular weight and containing nitrogen-containing organic base. Specifically, the nitrogen-containing organic base diamine monomer is first mixed with a solvent, and then the aromatic dianhydride is added and mixed. After being mixed evenly, it is placed in a reactor for batch polymerization to obtain a rigid polymer liquid 1 with a precisely controllable molecular weight and containing nitrogen-containing organic bases. The solvent used is preferably at least one of N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide; the aromatic dianhydride is preferably one or more of pyromellitic dianhydride, biphenyl dianhydride, diphenyl sulfone dianhydride, bisphenol A diether dianhydride, 4,4'-oxobisphthalic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, diphenyl ether dianhydride, benzophenone dianhydride, and biphenyl phenone dianhydride; the nitrogen-containing organic base diamine monomer is preferably one of 2-(4-aminophenyl)-5-aminobenzimidazole, bis(2-(4-aminophenyl))dibenzimidazole, 4,4'-(pyrimidin-2,5-diyl)diphenylamine, and 2,4-bis(4-aminoanilino)-6-anilino-1,3,5-triazine; In this invention, the solid content of the obtained rigid polymer liquid 1 is 10wt%~40wt%; The molar ratio of aromatic dianhydride to nitrogen-containing organic base diamine monomer is 0.6~1.05:1; The preferred parameters for batch polymerization are: temperature 0℃~50℃, time 1~8h; more preferably, temperature 20℃~30℃, time 3~4h.

[0026] S2: Mix aromatic dianhydride with flexible diamine monomer and polymerize by batch polymerization to obtain flexible oligomer polymer solution 2; Specifically, the flexible diamine monomer is first mixed with a solvent, then mixed with an aromatic dianhydride. After being mixed evenly, the mixture is placed in a reactor for batch polymerization to obtain flexible oligomer polymerization liquid 2. The solvent used is preferably at least one of N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide; the flexible diamine monomer is preferably one of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenyl ether, and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane; the aromatic dianhydride is preferably one or more of pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, diphenyl sulfone tetracarboxylic dianhydride, bisphenol A diether dianhydride, 4,4'-oxobisphthalic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, diphenyl ether tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, and biphenylone tetracarboxylic dianhydride.

[0027] The degree of polymerization Xn of the flexible oligomer polymer liquid 2 obtained in this step is 5~20.

[0028] The preferred parameters for batch polymerization are: temperature 0℃~50℃, time 1~8h.

[0029] S3: The rigid polymerization liquid 1 and the flexible oligomer polymerization liquid 2 are fed into a screw reactor for a secondary reaction to obtain polyamic acid spinning solution; Specifically, polymerization solution 1 and polymerization solution 2 are transferred to a screw reactor by metering pump. By precisely matching the addition flow rates of the two, controllable chain extension of molecular chains under equivalent functional group reaction is achieved, resulting in high molecular weight and high uniformity polyamic acid spinning solution. The conveying speed of rigid polymer liquid 1 is 3 kg / h to 30 kg / h, and the conveying speed of flexible oligomer polymer liquid 2 is 1 kg / h to 30 kg / h; the mixing temperature is 10 to 80℃, and the rotation speed is 10 to 200 rpm. The obtained polyamic acid spinning solution has a number average molecular weight ≥200000 g / mol and a molecular weight distribution ≤2.0.

[0030] This invention successfully prepared a high-molecular-weight polyamic acid spinning solution with an extremely narrow molecular weight distribution, laying a crucial material foundation for the subsequent preparation of high-performance polyimide fibers.

[0031] S4: The polyamic acid spinning solution is filtered and defoamed, and polyamic acid fibers are obtained by dry spinning. Specifically, in dry spinning, the spinneret orifice diameter is preferably 0.06~0.45mm, the tunnel temperature is preferably 180℃~260℃, and the spinning speed is preferably 300m / min~350m / min; S5: The polyamic acid fiber is subjected to thermal imidization and thermal stretching to finally obtain the high-strength, high-modulus polyimide fiber.

[0032] Specifically, thermal imidization is carried out using a multi-gradient thermal imidization method with a temperature of 200℃~380℃ and a total draw ratio of 1.2~4.0; thermal drawing is carried out using a multi-stage thermal drawing method with a temperature of 350℃~500℃ and a total draw ratio of 2.0~6.8.

[0033] The present invention also provides a high-strength, high-modulus polyimide fiber, which is prepared by the preparation method described in the above technical solution.

[0034] Example 1 Step 1: In a 50L polymerization reactor, 13 kg of N,N-dimethylacetamide was added as the initial solvent. 4459.27 g of 4,4'-(pyrimidin-2,5-diyl)diphenylamine was added and stirred for 2 hours to ensure uniform dispersion. Then, 4501.6 g of biphenyltetracarboxylic dianhydride was dissolved in 7 kg of N,N-dimethylacetamide and poured into the reactor. The remaining 4.9 kg of N,N-dimethylacetamide was then added to flush the reactor walls and remove residual monomer from the stir bar. The reaction was carried out at 25°C for 3 hours, ultimately yielding a polymerization solution 1 with a solid content of 26.5 wt%.

[0035] Step 2: In a 100L polymerization reactor, 20 kg of N,N-dimethylacetamide was added as the initial solvent. 4004.8 g of 4,4'-diaminodiphenyl ether was added and stirred for 1 hour to ensure uniform dispersion. Then, 6820 g of diphenyl ether tetracarboxylic dianhydride was dissolved in 9 kg of N,N-dimethylacetamide and poured into the reactor. The remaining 3.2 kg of N,N-dimethylacetamide was then poured in to flush the reactor walls and remove residual monomer from the stir bar. The reaction was stirred at room temperature for 2 hours, ultimately yielding polymer solution 2 with a solid content of 25.1 wt% and a degree of polymerization of 10.

[0036] Step 3: Polymer solution 1 is transferred to a screw reactor at a rate of 10 kg / h and polymer solution 2 at a rate of 10.8 kg / h for secondary reaction. The screw reactor speed is set to 80 rpm and the temperature is set to 25℃. Finally, a polyamic acid A spinning solution with a number average molecular weight of 239000 g / mol and a molecular weight distribution of 1.17 is obtained.

[0037] Step 4: After the polyamic acid A spinning solution is extruded through a spinneret with a diameter of 0.12 mm, the nascent yarn A is obtained by dry spinning at a spinning temperature of 200℃ and a spinning speed of 320 m / min.

[0038] Step 5: The nascent yarn A is subjected to gradient thermal imidization at 200℃, 240℃ and 280℃ in a hot furnace, with a total draw ratio of 1.5. Then, the cyclized nascent yarn A is subjected to primary drawing at 350℃, secondary drawing at 380℃ and tertiary drawing at 450℃, with a total draw ratio of 3.6, and finally polyimide fiber is obtained.

[0039] Example 2 Step 1: In a 50L polymerization reactor, 10 kg of N,N-dimethylacetamide was added as the initial solvent. 4459.3 g of 4,4'-(pyrimidin-2,5-diyl)diphenylamine was added and stirred for 2 hours to ensure uniform dispersion. Then, 4951.7 g of biphenyltetracarboxylic dianhydride was dissolved in 8 kg of N,N-dimethylacetamide and poured into the reactor. The remaining 3.9 kg of N,N-dimethylacetamide was then added to flush the reactor walls and remove residual monomer from the stir bar. The reaction was carried out at 25°C for 4 hours, ultimately yielding a polymerization solution with a solid content of 30 wt%.

[0040] Step 2: In a 100L polymerization reactor, 30 kg of N,N-dimethylacetamide was added as the initial solvent. 2973.96 g of 4,4'-diaminodiphenylmethane was added and stirred for 1.5 h to ensure uniform dispersion. Then, 4960 g of diphenyl ether tetracarboxylic dianhydride was dissolved in 10 kg of N,N-dimethylacetamide and poured into the reactor. The remaining 4 kg of N,N-dimethylacetamide was then poured in to flush the reactor walls and remove residual monomers from the stir bar. The reaction was stirred at room temperature for 2.5 h, ultimately yielding polymer solution 2 with a solid content of 15.3 wt% and a degree of polymerization of 15.

[0041] Step 3: Polymer solution 1 is transferred to a screw reactor at a rate of 12 kg / h and polymer solution 2 at a rate of 3.4 kg / h for secondary reaction. The screw reactor speed is set to 150 rpm and the temperature is set to 10℃. Finally, a polyamic acid B spinning solution with a number average molecular weight of 255,000 g / mol and a molecular weight distribution of 1.08 is obtained.

[0042] Step 4: After the polyamic acid B spinning solution is extruded through a spinneret with a diameter of 0.30 mm, the nascent yarn B is obtained by dry spinning at a spinning temperature of 240℃ and a spinning speed of 330 m / min.

[0043] Step 5: The nascent filament B is subjected to gradient thermal imidization at 240℃, 280℃ and 320℃ in a hot furnace, with a total draw ratio of 2.0. Then, the cyclized nascent filament B is subjected to primary drawing at 360℃, secondary drawing at 420℃ and tertiary drawing at 450℃, with a total draw ratio of 4.8, finally producing polyimide fiber.

[0044] Example 3 Step 1: In a 50L polymerization reactor, 20 kg of N,N-dimethylacetamide was added as the initial solvent. Then, 3363.9 g of 2-(4-aminophenyl)-5-aminobenzimidazole was added and stirred for 2 hours to ensure uniform dispersion. Subsequently, 2846.5 g of pyromellitic dianhydride was dissolved in 8 kg of N,N-dimethylacetamide and poured into the reactor. The remaining 4.6 kg of N,N-dimethylacetamide was then added to flush the reactor walls and remove residual monomers from the stir bar. The reaction was carried out at 25°C for 4 hours, ultimately yielding a polymerization solution 1 with a solid content of 16 wt%.

[0045] Step 2: Same as Example 1.

[0046] Step 3: Polymer solution 1 is transferred to a screw reactor at a rate of 20 kg / h and polymer solution 2 at a rate of 21.6 kg / h for secondary reaction. The screw reactor speed is set to 100 rpm and the temperature is set to 35℃. Finally, a polyamic acid C spinning solution with a number average molecular weight of 228000 g / mol and a molecular weight distribution of 1.35 is obtained.

[0047] Step 4: After the polyamic acid C spinning solution is extruded through a spinneret with a diameter of 0.18 mm, the nascent yarn C is obtained by dry spinning at a spinning temperature of 210℃ and a spinning speed of 310 m / min.

[0048] Step 5: The nascent filament C is subjected to gradient thermal imidization at 240℃, 280℃ and 320℃ in a hot furnace, with a total draw ratio of 2.3. Then, the cyclized nascent filament C is subjected to primary drawing at 350℃, secondary drawing at 430℃ and tertiary drawing at 460℃, with a total draw ratio of 5.6, finally producing polyimide fiber.

[0049] Example 4 Step 1: In a 50L polymerization reactor, 12Kg of N,N-dimethylacetamide was added as the initial solvent. 3812.42g of 2-(4-aminophenyl)-5-aminobenzimidazole was added and stirred for 2 hours to ensure uniform dispersion. Then, 3633.9g of pyromellitic dianhydride was dissolved in 6Kg of N,N-dimethylacetamide and poured into the reactor. The remaining 4.3kg of N,N-dimethylacetamide was then added to flush the reactor walls and remove residual monomers from the stir bar. The reaction was carried out at 30℃ for 4 hours, ultimately yielding a polymerization solution 1 with a solid content of 25wt%.

[0050] Step 2: Same as Example 2.

[0051] Step 3: Polymer solution 1 is transferred to a screw reactor at a rate of 15 kg / h and polymer solution 2 at a rate of 8.9 kg / h for secondary reaction. The screw reactor speed is set to 80 rpm and the temperature is set to 30℃. Finally, a polyamic acid D spinning solution with a number average molecular weight of 235000 g / mol and a molecular weight distribution of 1.22 is obtained.

[0052] Step 4: After the polyamic acid D spinning solution is extruded through a spinneret with a diameter of 0.22 mm, the nascent yarn D is obtained by dry spinning at a spinning temperature of 200℃ and a spinning speed of 310 m / min.

[0053] Step 5: The nascent filament D is subjected to gradient thermal imidization at 220℃, 240℃ and 280℃ in a hot furnace, with a total draw ratio of 2.5. Then, the cyclized nascent filament D is subjected to primary drawing at 350℃, secondary drawing at 380℃ and tertiary drawing at 430℃, with a total draw ratio of 4.5, finally producing polyimide fiber.

[0054] Example 5 Step 1: Same as Example 2.

[0055] Step 2: Same as Example 2.

[0056] Step 3: Polymer solution 1 is transferred to a screw reactor at a rate of 12 kg / h and polymer solution 2 at a rate of 3.4 kg / h for secondary reaction. The screw reactor speed is set to 100 rpm and the temperature is set to 10℃. Finally, a polyamic acid H spinning solution with a number average molecular weight of 242000 g / mol and a molecular weight distribution of 1.16 is obtained.

[0057] Step 4: After the polyamic acid H spinning solution is extruded through a spinneret with a diameter of 0.30 mm, the nascent yarn H is obtained by dry spinning at a spinning temperature of 240℃ and a spinning speed of 330 m / min.

[0058] Step 5: The nascent filament H is subjected to gradient thermal imidization at 240℃, 280℃ and 320℃ in a hot furnace, with a total draw ratio of 2.0. Then, the cyclized nascent filament H is subjected to primary drawing at 360℃, secondary drawing at 420℃ and tertiary drawing at 450℃, with a total draw ratio of 4.8, finally producing polyimide fiber.

[0059] Example 6 Step 1: Same as Example 2.

[0060] Step 2: Same as Example 2.

[0061] Step 3: The polymerization solution 1 is transferred to the screw reactor at a rate of 12 kg / h and 3.4 kg / h for secondary reaction. The screw reactor speed is set to 190 rpm and the temperature is set to 10℃. Finally, a polyamic acid M spinning solution with a number average molecular weight of 228000 g / mol and a molecular weight distribution of 1.38 is obtained.

[0062] Step 4: After the polyamic acid M spinning solution is extruded through a spinneret with a diameter of 0.30 mm, the nascent yarn M is obtained by dry spinning at a spinning temperature of 240℃ and a spinning speed of 330 m / min.

[0063] Step 5: The nascent filament M is subjected to gradient thermal imidization at 240℃, 280℃ and 320℃ in a hot furnace, with a total draw ratio of 2.0. Then, the cyclized nascent filament M is subjected to primary drawing at 360℃, secondary drawing at 420℃ and tertiary drawing at 450℃, with a total draw ratio of 4.8, finally producing polyimide fiber.

[0064] Comparative Example 1 Step 1: In a 50L polymerization reactor, 10Kg of N,N-dimethylacetamide was added as the initial solvent. 4459.3g of 4,4'-(pyrimidin-2,5-diyl)diphenylamine was added and stirred for 2 hours to ensure uniform dispersion. Then, 5001.7g of biphenyltetracarboxylic dianhydride was dissolved in 7Kg of N,N-dimethylacetamide and poured into the reactor. The remaining 3.1kg of N,N-dimethylacetamide was then added to flush the reactor walls and remove residual monomers from the agitator. The reaction was carried out at room temperature for 7 hours, ultimately yielding a polyamic acid E spinning solution with a solid content of 20wt%, a number-average molecular weight of 153000g / mol, and a molecular weight distribution of 2.36.

[0065] Step 2: After the polyamic acid E spinning solution is extruded through a spinneret with a diameter of 0.30 mm, the nascent yarn E is obtained by dry spinning at a spinning temperature of 240℃ and a spinning speed of 330 m / min.

[0066] Step 3: The nascent filament E is subjected to gradient thermal imidization at 240℃, 280℃, and 320℃ in a hot furnace, with a total draw ratio of 2.0. Then, the cyclized nascent filament E is subjected to primary drawing at 360℃, secondary drawing at 420℃, and tertiary drawing at 450℃, with a total draw ratio of 4.8, finally producing polyimide fiber.

[0067] Comparative Example 2 Step 1: Same as Example 2.

[0068] Step 2: Same as Example 2.

[0069] Step 3: Pour polymerization solution 2 into the reactor of polymerization solution 1 at a rate of 50 kg / h, control the reaction temperature at 10℃, and continue the reaction for 6 hours to finally obtain polyamic acid F spinning solution with a number average molecular weight of 173000 g / mol and a molecular weight distribution of 1.82.

[0070] Step 4: After the polyamic acid F spinning solution is extruded through a spinneret with a diameter of 0.30 mm, the nascent yarn F is obtained by dry spinning at a spinning temperature of 240℃ and a spinning speed of 330 m / min.

[0071] Step 5: The nascent filament F is subjected to gradient thermal imidization at 240℃, 280℃ and 320℃ in a hot furnace, with a total draw ratio of 2.0. Then, the cyclized nascent filament F is subjected to primary drawing at 360℃, secondary drawing at 420℃ and tertiary drawing at 450℃, with a total draw ratio of 4.8, finally producing polyimide fiber.

[0072] Comparative Example 3 Step 1: Same as Example 2.

[0073] Step 2: Same as Example 2.

[0074] Step 3: Pour polymerization solution 2 into the reactor of polymerization solution 1 at a rate of 20 kg / h, control the reaction temperature at 10℃, and continue the reaction for 8 hours to finally obtain polyamic acid G spinning solution with a number average molecular weight of 193000 g / mol and a molecular weight distribution of 1.68.

[0075] Step 4: After the polyamic acid G spinning solution is extruded through a spinneret with a diameter of 0.30 mm, the nascent yarn G is obtained by dry spinning at a spinning temperature of 240℃ and a spinning speed of 330 m / min.

[0076] Step 5: The nascent yarn G is subjected to gradient thermal imidization at 240℃, 280℃ and 320℃ in a hot furnace, with a total draw ratio of 2.0. Then, the cyclized nascent yarn G is subjected to primary drawing at 360℃, secondary drawing at 420℃ and tertiary drawing at 450℃, with a total draw ratio of 4.8, and finally polyimide fiber is obtained.

[0077] Performance testing (1) The strength and modulus of the products obtained in Examples 1-6 and Comparative Examples 1-3 were tested according to GB / T 19975-2005 "Test Method for Tensile Properties of High-Strength Fiber Filaments". The test results are as follows: The polyimide fiber prepared in Example 1 has a strength of 28.5 cN / dtex and a modulus of 1180 cN / dtex. The polyimide fiber prepared in Example 2 has a strength of 31.5 cN / dtex and a modulus of 1280 cN / dtex. The polyimide fiber prepared in Example 3 has a strength of 26.7 cN / dtex and a modulus of 995 cN / dtex. The polyimide fiber prepared in Example 4 has a strength of 28.9 cN / dtex and a modulus of 1025 cN / dtex. The polyimide fiber prepared in Example 5 has a strength of 29.5 cN / dtex and a modulus of 1195 cN / dtex. The polyimide fiber prepared in Example 6 has a strength of 27.3 cN / dtex and a modulus of 1021 cN / dtex. The polyimide fiber prepared in Comparative Example 1 has a strength of 22.8 cN / dtex and a modulus of 852 cN / dtex. The polyimide fiber prepared in Comparative Example 2 has a strength of 23.6 cN / dtex and a modulus of 920 cN / dtex. The polyimide fiber prepared in Comparative Example 3 has a strength of 24.4 cN / dtex and a modulus of 965 cN / dtex.

[0078] Based on the above tests, a comparison of the strength and modulus of the polyimide fibers in Examples 1-4 and Comparative Examples 1-3 shows that the high molecular weight and high uniformity spinning solution with a rigid-flexible block structure can significantly improve the mechanical properties of polyimide fibers.

[0079] Furthermore, comparing the number-average molecular weights of the polyamic acid spinning solutions in Examples 1-4 and Comparative Examples 1-3, it can be seen that the process route of the present invention, "boiler prepolymerization + screw final polymerization," is significantly superior to simple batch polymerization. Comparing the molecular weight distribution, it can be seen that the spinning solution polymerized by the "boiler prepolymerization + screw final polymerization" process is more uniform and has a narrower molecular weight distribution, indicating that the screw reactor can effectively solve the problems of local overheating and mixing dead zones in the polymerization reaction process, and avoid the occurrence of explosive polymerization.

[0080] (2) The polyimide fibers obtained in Example 2 were subjected to electron microscopy to obtain... Figure 1 and Figure 2 ,in, Figure 1 This is a scanning electron microscope image of the polyimide fiber surface from Example 2. Figure 2 This is a scanning electron microscope image of a cross-section of polyimide fiber from Example 2, for observation. Figure 1 , Figure 2 Scanning electron microscopy images of the fibers revealed that the fiber surface was smooth and without defects, and the cross-section was dense and without pores, indicating that the fiber forming process was stable, which is attributed to the highly uniform spinning solution.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high-strength, high-modulus polyimide fibers, characterized in that, Includes the following steps: S1: Aromatic dianhydride is mixed with nitrogen-containing organic base diamine monomer and polymerized in a batch reactor to obtain a rigid polymer solution 1 with precisely controllable molecular weight and containing nitrogen-containing organic base. S2: Mix aromatic dianhydride with flexible diamine monomer and polymerize by batch polymerization to obtain flexible oligomer polymer solution 2; S3: The rigid polymerization liquid 1 and the flexible oligomer polymerization liquid 2 are fed into a screw reactor for a secondary reaction to obtain polyamic acid spinning solution; S4: The polyamic acid spinning solution is filtered and defoamed, and polyamic acid fibers are obtained by dry spinning. S5: The polyamic acid fiber is subjected to thermal imidization and thermal stretching to finally obtain the high-strength, high-modulus polyimide fiber.

2. The method for preparing high-strength, high-modulus polyimide fibers according to claim 1, characterized in that, The solvents used in steps S1 and S2 are the same, and each solvent is at least one of N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide.

3. The method for preparing high-strength, high-modulus polyimide fibers according to claim 1, characterized in that, The aromatic dianhydride is one or more of the following: pyromellitic dianhydride, biphenyl dianhydride, diphenyl sulfone dianhydride, bisphenol A diether dianhydride, 4,4'-oxobisphthalic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, diphenyl ether dianhydride, benzophenone dianhydride, and benzyl phenone dianhydride.

4. The method for preparing high-strength, high-modulus polyimide fibers according to claim 1, characterized in that, The nitrogen-containing organic base diamine monomer is one of 2-(4-aminophenyl)-5-aminobenzimidazole, bis(2-(4-aminophenyl))dibenzimidazole, 4,4'-(pyrimidin-2,5-diyl)diphenylamine, and 2,4-bis(4-aminoanilino)-6-anilino-1,3,5-triazine.

5. The method for preparing high-strength, high-modulus polyimide fibers according to claim 1, characterized in that, The flexible diamine monomer is one of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenyl ether, and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane.

6. The method for preparing high-strength, high-modulus polyimide fibers according to claim 1, characterized in that, The solid content of the rigid polymerization liquid 1 is 10wt%~40wt%, and the solid content of the flexible oligomer polymerization liquid 2 is 15wt%~30wt%.

7. The method for preparing high-strength, high-modulus polyimide fibers according to claim 1, characterized in that, In step S1, the molar ratio of the aromatic dianhydride and the nitrogen-containing organic basic diamine monomer is 0.6~1.05:1; in step S2, the degree of polymerization Xn of the flexible oligomer polymerization liquid 2 is 5~20.

8. The method for preparing high-strength, high-modulus polyimide fibers according to claim 1, characterized in that, In steps S1 and S2, the parameters for the batch polymerization are: temperature 0℃~50℃, time 1~8h; In step S3, the conveying speed of the rigid polymerization liquid 1 is 3 kg / h to 30 kg / h, and the conveying speed of the flexible oligomer polymerization liquid 2 is 1 kg / h to 30 kg / h; the mixing temperature is 10 to 80°C, and the rotation speed is 10 to 200 rpm; the number average molecular weight of the polyamic acid spinning solution is ≥200,000 g / mol, and the molecular weight distribution is ≤2.

0.

9. The method for preparing high-strength, high-modulus polyimide fibers according to claim 1, characterized in that, In step S4, the spinneret orifice diameter in the dry spinning process is 0.06~0.45mm, the tunnel temperature is 180℃~260℃, and the spinning speed is 300m / min~350m / min. In step S5, the thermal imidization specifically adopts a multi-gradient thermal imidization method with a temperature of 200℃~380℃ and a total draw ratio of 1.2~4.0; the thermal drawing specifically adopts a multi-stage thermal drawing method with a temperature of 350℃~500℃ and a total draw ratio of 2.0~6.

8.

10. A high-strength, high-modulus polyimide fiber, characterized in that, The high-strength, high-modulus polyimide fiber is prepared by the preparation method described in any one of claims 1-9.

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