A kind of polyimide fiber with ultra-high modulus and preparation method thereof

Abstract

The present invention provides a polyimide fiber with ultra-high modulus and a preparation method thereof, and relates to the technical field of high-performance organic fibers. Two diamine monomers, 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) and p-phenylenediamine (PPDA), are used to carry out polycondensation reaction with biphenyltetracarboxylic dianhydride (BPDA) in a solvent, N-methylpyrrolidone (NMP). The end-capping agent is used to control the dynamic viscosity of the polymerized slurry, and the plasticizing and stretching process of wet spinning and the multi-stage high-temperature stretching process are used to increase the molecular orientation degree inside the fiber while having ultra-high breaking strength, so that the polyimide fiber has an ultra-high elastic modulus. The diversity of polyimide fiber products is increased, and the downstream application market field is broadened. High-strength polyimide fibers can be continuously and stably produced, and the fibers have an ultra-high elastic modulus that the products on the market currently fail to achieve, and the force orientation degree inside the fiber molecules is greatly improved, so that the mechanical properties of the fibers are fully reflected.

Description

Technical Field

[0001] The invention belongs to the technical field of high-performance organic fibers, and more specifically, particularly relates to a polyimide fiber with ultra-high modulus and a preparation method thereof. Background Art

[0002] Polyimide fiber is composed of a series of repeating units containing imide rings ( CO—N—CO—) is a general term for PI fibers with different chemical structures. It has flexible chemical molecular structure design and can design different chemical structures according to the requirements of application scenarios to make the fiber products meet the ideal performance requirements. It is one of the polymer fiber materials with the highest temperature used in industry at present. It can maintain its main physical properties for a short time at 550℃ and can be used for a long time at around 350℃.

[0003] Generally, ordinary high-performance polyimide fibers are synthesized by the dicondensation of 4,4'-diaminodiphenyl ether and pyromellitic anhydride, and their breaking strength is only 5-8cN / dtex, and their elastic modulus is only 70-85cN / dtex. Although they have high thermal stability, their low mechanical properties make it difficult to use them as reinforcements to prepare resin-based composites for high-performance composites and military protection applications.

[0004] In order to obtain higher breaking strength and elastic modulus of polyimide fibers, it is necessary to prepare a polymer spinning slurry with higher molecular weight and rigid chain structure, control its spinnability, and then produce high-strength and high-modulus polyimide fibers through a series of special spinning processes. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a polyimide fiber with ultra-high modulus and a preparation method thereof to solve the above problems.

[0006] A method for preparing a polyimide fiber with ultra-high modulus comprises the following steps:

[0007] S1: Add N-methylpyrrolidone (NMP) solvent into a 1000L polymerization reactor;

[0008] S2: Add 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) and p-phenylenediamine (PPDA) into a polymerization reactor;

[0009] S3: Start stirring and dissolving, control the temperature of the polymerization kettle at 24-25°C, cool the diamine solution in the polymerization kettle through the polymerization kettle jacket, calculate the total amount of biphenyltetracarboxylic dianhydride (BPDA) by the reaction equation, and add 99.5% of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA) that has been previously dried at 235°C into the polymerization kettle for prepolymerization, stir and react for 3 hours, and then add the remaining part of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA) into the polymerization reactor for telomerization reaction in 3 times according to the dynamic viscosity of the polymer reactant, and then take samples for detection;

[0010] S4: Calculate the mass of benzoic anhydride to be added as the end-capping agent according to 0.01-0.1% of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA), add benzoic anhydride accordingly, continue stirring the reaction, and take samples to detect the dynamic viscosity;

[0011] S5: filtering and degassing the obtained polymer spinning slurry before entering the spinning main machine;

[0012] S6: After the polymerized spinning slurry is extruded through spinning metering, it is plasticized and stretched by a traction roller while the polyamic acid fiber is initially formed through a coagulation bath, the stretching ratio is 50-55%, and the coagulation liquid is an aqueous solution with a NMP content of 18-20%;

[0013] S7: The polyamic acid fiber is subjected to a washing and drying process, wherein the washing water is deionized water and the drying temperature is 150°C;

[0014] S8: The dried polyamic acid fiber is continuously fed into a high-temperature drying tunnel through a traction roller for imidization treatment. The traction rollers before and after the high-temperature drying tunnel control the tension of the fiber to be ≤0.1 cN / dtex. The length of the high-temperature drying tunnel is 5 meters, and the temperature is 100-200°C.

[0015] S9: The nascent polyimide fiber is stretched at high temperature and high magnification by using the speed difference of the traction rollers before and after the high-temperature drying oven. Nitrogen is used for protection inside the high-temperature drying oven. The temperature of the first-stage drying oven is controlled at 200-400°C; the draft ratio of the traction rollers before and after the drying oven is 50-80%, and the temperature of the second-stage drying oven is controlled at 400-450°C; the draft ratio of the traction rollers before and after the drying oven is 20-50%, and the temperature of the third-stage drying oven is controlled at 450-530°C; the draft ratio of the traction rollers before and after the drying oven is 10-30%;

[0016] S10: After the stretching and molding, the finished fiber is obtained and tested.

[0017] Preferably, the solid content of the polymer spinning slurry system is controlled at 9-13%.

[0018] Preferably, in S2, according to the requirement of 13% solid content of the polymer material, the molar ratio of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) to p-phenylenediamine (PPDA) is ≥1, the dissolved monomer is rapidly stirred and dissolved in the solvent NMP at room temperature, and the dissolution time is ≥3 hours. In S3, the diamine solution in the polymerization reactor is cooled to 3.5-3.9°C by the polymerization reactor jacket.

[0019] Preferably, in S8 imidization treatment, nitrogen is used for protection inside the high-temperature drying oven, the drying oven temperature is controlled at 100-150°C, the stretching tension of the front and rear traction rollers is 0.05-0.08 cN / dtex, in S9, the temperature of the first-level drying oven is controlled at 250-350°C; the drafting ratio of the front and rear traction rollers of the drying oven is 60%-80%, and the temperature of the second-level drying oven is controlled at 400-420°C; the drafting ratio of the front and rear traction rollers of the drying oven is 30%-50%, and the temperature of the third-level drying oven is controlled at 520-530°C; the drafting ratio of the front and rear traction rollers of the drying oven is 10%-25%, in S4, benzoic anhydride is added, and the stirring reaction time is continued for 1 hour, and in S6, the polymerization spinning slurry is extruded by spinning metering according to the linear density specification of 1500 dtex and the spinning speed of 20 m / min.

[0020] Another technical problem to be solved by the present invention is to provide a polyimide fiber with ultra-high modulus, which is prepared by the above-mentioned method for preparing a polyimide fiber with ultra-high modulus.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] In the present invention, high-strength polyimide fibers can be continuously and stably produced while having an ultra-high elastic modulus that cannot be achieved by products currently on the market. 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) and p-phenylenediamine (PPDA) are used to replace 4,4'-diaminodiphenyl ether (4,4-ODA) and biphenyltetracarboxylic dianhydride (BPDA) to carry out nucleophilic substitution reaction to generate new rigid chain structural units. The prepared polymer spinning slurry has a higher molecular weight, which not only adjusts the sequence structure in the macromolecular chain, but also achieves the purpose of changing the molecular conjugated macro-л bond, and increases the proportion of the rigid chain structure.

[0023] In the present invention, when the polymer spinning slurry reaches a dynamic viscosity range with good spinnability, a capping agent is used to control the dynamic viscosity to stop increasing, thereby increasing the plasticizing elongation of the primary polyamic acid fiber and utilizing a continuous multi-stage high-temperature and high-multiple stretching spinning process, thereby greatly improving the force orientation degree inside the fiber molecules, allowing the mechanical properties of the fiber to be thoroughly realized, thereby expanding its application field in the downstream market, and having important significance for the development of the entire high-performance organic fiber manufacturing industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall process of the present invention. DETAILED DESCRIPTION

[0025] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0026] Example 1

[0027] This embodiment discloses a method for preparing a polyimide fiber with ultra-high modulus, comprising the following steps:

[0028] S1. Add 800 L of N-methylpyrrolidone (NMP) solvent having a water content of 196 ppm into a 1000 L polymerization kettle.

[0029] S2. According to the requirement of 13% solid content of polymer material, the molar ratio of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) to p-phenylenediamine (PPDA) is 3:1. The material addition amount is calculated by the reaction equation, and 44.866 kg of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) and 7.211 kg of p-phenylenediamine (PPDA) are added to the polymerization kettle.

[0030] S3, start stirring and dissolving for 3 hours, control the temperature of the polymerization kettle at 25°C, cool the diamine solution in the polymerization kettle through the polymerization kettle jacket to 3.5°C, calculate the total amount of biphenyltetracarboxylic acid dianhydride (BPDA) added by the reaction equation, and add 99.5% of the theoretical total mass of biphenyltetracarboxylic acid dianhydride (BPDA) that has been previously dried at 235°C, i.e. 78.122 kg, into the polymerization kettle for prepolymerization. After stirring and reacting for 3 hours, according to the dynamic viscosity of the polymer reactant, the remaining part of the theoretical total mass of biphenyltetracarboxylic acid dianhydride (BPDA), i.e. 0.393 kg, is added into the polymerization reaction kettle in 3 times for telomerization reaction, and sampling is carried out for detection, and the dynamic viscosity is 95,000 centiber.

[0031] S4. The mass of benzoic anhydride as the end-capping agent to be added is calculated according to 0.05% of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA), and 0.039 kg of benzoic anhydride is added accordingly. The reaction is continued with stirring for 1 hour, and the dynamic viscosity is detected by sampling and is 98,230 centibarrels.

[0032] S5, filtering and degassing the obtained polymer spinning slurry and then entering the spinning main machine.

[0033] S6. The polymer spinning slurry is extruded through spinning metering at a spinning speed of 20 m / min according to the linear density specification of 1500 dtex. The polyamic acid fiber is initially formed and plasticized and stretched by a traction roller in a coagulation bath. The stretching ratio is 50%. The coagulation liquid is an aqueous solution with a 20% NMP content.

[0034] S7. The polyamic acid fiber is subjected to a washing and drying process, wherein the washing water is deionized water and the drying temperature is 150°C.

[0035] S8. The dried polyamic acid fiber is continuously fed into a high-temperature drying tunnel through traction rollers for imidization treatment. The traction rollers before and after the high-temperature drying tunnel control the tension of the fiber to be 0.08 cN / dtex. The length of the high-temperature drying tunnel is 5 meters, and the temperature is 100-150°C.

[0036] S9. The nascent polyimide fiber is stretched at high temperature and at high multiples by utilizing the speed difference of the traction rollers before and after the high-temperature drying oven. Nitrogen is used for protection inside the high-temperature drying oven. The temperature of the first-stage drying oven is controlled at 300°C. The drafting ratio of the traction rollers before and after the drying oven is 70%, and the temperature of the second-stage drying oven is controlled at 400°C. The drafting ratio of the traction rollers before and after the drying oven is 40%, and the temperature of the third-stage drying oven is controlled at 520°C. The drafting ratio of the traction rollers before and after the drying oven is 10%.

[0037] S10. After the stretching molding is completed, a finished fiber with a linear density of 1489 dtex is obtained. The test results are shown in Table 1.

[0038]

[0039] Table 1

[0040] Example 2

[0041] This embodiment discloses a method for preparing a polyimide fiber with ultra-high modulus, comprising the following steps:

[0042] S1. Add 800 L of N-methylpyrrolidone (NMP) solvent having a water content of 249 ppm into a 1000 L polymerization kettle.

[0043] S2. According to the requirement of 13% solid content of polymer material, the molar ratio of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) to p-phenylenediamine (PPDA) is 2:1. The material addition amount is calculated by the reaction equation, and 40.761 kg of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) and 9.826 kg of p-phenylenediamine (PPDA) are added to the polymerization kettle.

[0044] S3, start stirring and dissolving for 3 hours, control the temperature of the polymerization kettle at 24°C, cool the diamine solution in the polymerization kettle through the polymerization kettle jacket to 3.9°C, calculate the total amount of biphenyltetracarboxylic dianhydride (BPDA) added by the reaction equation, and add 99.5% of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA) that has been previously dried at 235°C, i.e. 79.847 kg, into the polymerization kettle for prepolymerization. After stirring and reacting for 3 hours, according to the dynamic viscosity of the polymer reactant, the remaining part of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA), i.e. 0.401 kg, is added into the polymerization reaction kettle in 3 times for telomerization reaction, and sampling is carried out for detection, and the dynamic viscosity is 72,000 centiber.

[0045] S4. The mass of benzoic anhydride as the end-capping agent to be added is calculated according to 0.1% of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA), and 0.080 kg of benzoic anhydride is added accordingly. The reaction is continued with stirring for 1 hour, and the dynamic viscosity is detected by sampling and is 79,750 centibarrels.

[0046] S5, filtering and degassing the obtained polymer spinning slurry and then entering the spinning main machine.

[0047] S6. The polymer spinning slurry is extruded through spinning metering at a spinning speed of 20 m / min according to the linear density specification of 1500 dtex. The polyamic acid fiber is initially formed and plasticized and stretched by a traction roller in a coagulation bath. The stretching ratio is 55%. The coagulation liquid is an aqueous solution with an NMP content of 18%.

[0048] S7. The polyamic acid fiber is subjected to a washing and drying process, wherein the washing water is deionized water and the drying temperature is 150°C.

[0049] S8. The dried polyamic acid fiber is continuously fed into a high-temperature drying tunnel through traction rollers for imidization treatment. The traction rollers before and after the high-temperature drying tunnel control the tension of the fiber to be 0.06 cN / dtex. The length of the high-temperature drying tunnel is 5 meters and the temperature is 120°C.

[0050] S9. The speed difference of the traction rollers before and after the high-temperature drying oven is used to perform high-temperature and high-multiple stretching on the nascent polyimide fiber. Nitrogen is used to protect the interior of the high-temperature drying oven. The temperature of the first-stage drying oven is controlled at 250°C; the drafting ratio of the traction rollers before and after the drying oven is 60%, and the temperature of the second-stage drying oven is controlled at 400°C; the drafting ratio of the traction rollers before and after the drying oven is 50%, and the temperature of the third-stage drying oven is controlled at 520°C; the drafting ratio of the traction rollers before and after the drying oven is 15%.

[0051] S10. After the stretching molding is completed, a finished fiber with a linear density of 1511 dtex is obtained. The test results are shown in Table 2.

[0052]

[0053] Table 2

[0054] Example 3

[0055] This embodiment discloses a method for preparing a polyimide fiber with ultra-high modulus, comprising the following steps:

[0056] S1. Add 800 L of N-methylpyrrolidone (NMP) solvent having a water content of 287 ppm into a 1000 L polymerization kettle.

[0057] S2. According to the requirement of 13% solid content of polymer material, the molar ratio of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) to p-phenylenediamine (PPDA) is 1:1. The material addition amount is calculated by the reaction equation, and 31.982 kg of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) and 15.420 kg of p-phenylenediamine (PPDA) are added to the polymerization kettle.

[0058] S3, start stirring and dissolving for 3 hours, control the temperature of the polymerization kettle at 24.5°C, cool the diamine solution in the polymerization kettle through the polymerization kettle jacket to 3.7°C, calculate the total amount of biphenyltetracarboxylic acid dianhydride (BPDA) added by the reaction equation, and add 99.5% of the theoretical total mass of biphenyltetracarboxylic acid dianhydride (BPDA) that has been previously dried at 235°C, i.e. 83.954 kg, into the polymerization kettle for prepolymerization. After stirring and reacting for 3 hours, according to the dynamic viscosity of the polymer reactant, the remaining part of the theoretical total mass of biphenyltetracarboxylic acid dianhydride (BPDA), i.e. 0.420 kg, is added into the polymerization reaction kettle in 3 times for telomerization reaction, and sampling is carried out for detection, and the dynamic viscosity is 65,410 centibarrels.

[0059] S4. The mass of benzoic anhydride as the end-capping agent to be added is calculated according to 0.01% of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA), and 0.008 kg of benzoic anhydride is added accordingly. The reaction is continued with stirring for 1 hour, and the dynamic viscosity is detected by sampling and is 82,630 centibarrels.

[0060] S5, filtering and degassing the obtained polymer spinning slurry and then entering the spinning main machine.

[0061] S6. The polymer spinning slurry is extruded through spinning metering at a spinning speed of 20 m / min according to the linear density specification of 1500 dtex. The polyamic acid fiber is initially formed and plasticized and stretched by a traction roller in a coagulation bath. The stretching ratio is 55%. The coagulation liquid is an aqueous solution with an NMP content of 18%.

[0062] S7. The polyamic acid fiber is subjected to a washing and drying process, wherein the washing water is deionized water and the drying temperature is 150°C.

[0063] S8. The dried polyamic acid fiber is continuously fed into a high-temperature drying tunnel through traction rollers for imidization treatment. The traction rollers before and after the high-temperature drying tunnel control the tension of the fiber to be 0.05 cN / dtex. The length of the high-temperature drying tunnel is 5 meters and the temperature is 130°C.

[0064] S9. The speed difference of the traction rollers before and after the high-temperature drying oven is used to perform high-temperature and high-multiple stretching on the nascent polyimide fiber. Nitrogen is used for protection inside the high-temperature drying oven. The temperature of the first-stage drying oven is controlled at 350°C; the drafting ratio of the traction rollers before and after the drying oven is 80%, and the temperature of the second-stage drying oven is controlled at 420°C; the drafting ratio of the traction rollers before and after the drying oven is 30%, and the temperature of the third-stage drying oven is controlled at 530°C; the drafting ratio of the traction rollers before and after the drying oven is 25%.

[0065] S10. After the stretching molding is completed, a finished fiber with a linear density of 1507 dtex is obtained. The test results are shown in Table 3.

[0066]

[0067] Table 3

[0068] Comparative Example 1

[0069] In this embodiment, as a comparative example of the present invention, a method for preparing high-strength polyimide fiber is disclosed, comprising the following steps:

[0070] S1. Add 800 L of N-methylpyrrolidone (NMP) solvent having a water content of 266 ppm into a 1000 L polymerization kettle.

[0071] S2. According to the requirement of 13% solid content of polymer material, the molar ratio of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) to p-phenylenediamine (PPDA) is 1:1. The material addition amount is calculated by the reaction equation, and 31.982 kg of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) and 15.420 kg of p-phenylenediamine (PPDA) are added to the polymerization kettle.

[0072] S3, start stirring and dissolving for 3 hours, control the temperature of the polymerization kettle at 24.5°C, cool the diamine solution in the polymerization kettle through the polymerization kettle jacket to 3.7°C, calculate the total amount of biphenyltetracarboxylic acid dianhydride (BPDA) added by the reaction equation, and add 99.5% of the theoretical total mass of biphenyltetracarboxylic acid dianhydride (BPDA) that has been previously dried at 235°C, i.e. 83.954 kg, into the polymerization kettle for prepolymerization. After stirring and reacting for 3 hours, according to the dynamic viscosity of the polymer reactant, the remaining part of the theoretical total mass of biphenyltetracarboxylic acid dianhydride (BPDA), i.e. 0.420 kg, is added into the polymerization reaction kettle in 3 times for telomerization reaction, and sampling is carried out for detection, and the dynamic viscosity is 65,410 centibarrels.

[0073] S4. The obtained polymer spinning slurry is filtered and degassed, and then fed into the spinning main machine. The dynamic viscosity is sampled and tested to be 295,420 centibars.

[0074] S5. The polymerized spinning slurry is extruded through spinning metering at a spinning speed of 20 m / min according to the linear density specification of 1500 dtex. The polyamic acid fiber is initially formed and plasticized and stretched by a traction roller in a coagulation bath. The stretching ratio is 30%. The coagulation liquid is an aqueous solution with a 19% NMP content.

[0075] S6. The polyamic acid fiber is subjected to a washing and drying process, wherein the washing water is deionized water and the drying temperature is 150°C.

[0076] S7. The dried polyamic acid fiber is continuously fed into a high-temperature drying tunnel through traction rollers for imidization treatment and heat stretching. The traction rollers before and after the high-temperature drying tunnel control the tension of the fiber to be 0.05 cN / dtex. The length of the high-temperature drying tunnel is 15 meters, and the temperature is gradually increased from 100 to 400°C.

[0077] S8. After the stretching molding is completed, the finished fiber with a linear density of 1525 dtex is obtained. The test results are shown in Table 4.

[0078]

[0079] Table 4

[0080] Comparative Example 2

[0081] In this embodiment, as a comparative example of the present invention, a method for preparing a high-performance polyimide fiber is disclosed, comprising the following steps:

[0082] S1. Add 800 L of N-methylpyrrolidone (NMP) solvent having a water content of 244 ppm into a 1000 L polymerization kettle.

[0083] S2. According to the requirement of 10% solid content of polymer material, the molar ratio of 4,4'-diaminodiphenyl ether (4,4-ODA) to pyromellitic dianhydride (PMDA) is 1:1. The material addition amount is calculated by the reaction equation, and 47.031 kg of 4,4'-diaminodiphenyl ether (4,4-ODA) is added to the polymerization kettle.

[0084] S3, start stirring and dissolving for 3 hours, control the temperature of the polymerization kettle at 24.5°C, cool the diamine solution in the polymerization kettle through the polymerization kettle jacket to 2.7°C, calculate the total feeding amount of the material PMDA through the reaction equation, and add 99.5% of the theoretical total mass of PMDA (preliminary high-temperature drying at 235°C), i.e. 51.008 kg, into the polymerization kettle for prepolymerization. After stirring and reacting for 3 hours, according to the dynamic viscosity of the polymer reactant, the remaining part of the theoretical total mass of PMDA (i.e. 0.256 kg) is added into the polymerization reaction kettle in 3 times for telomerization reaction, and sampling is carried out for detection. The dynamic viscosity is 92,610 centibars.

[0085] S4. The obtained polymer spinning slurry is filtered and degassed, and then fed into the spinning main machine. The dynamic viscosity is sampled and tested to be 86,941 centibars.

[0086] S5. The polymer spinning slurry is extruded through spinning metering at a spinning speed of 20 m / min according to the linear density specification of 1500 dtex. The polyamic acid fiber is initially formed and plasticized and stretched by a traction roller. The stretching ratio is 40%. The coagulation liquid is an aqueous solution with a 19% NMP content.

[0087] S6. The polyamic acid fiber is subjected to a washing and drying process, wherein the washing water is deionized water and the drying temperature is 150°C.

[0088] S7. The dried polyamic acid fiber is continuously fed into a high-temperature drying tunnel through traction rollers for imidization treatment and heat stretching. The traction rollers before and after the high-temperature drying tunnel control the tension of the fiber to be 0.05 cN / dtex. The length of the high-temperature drying tunnel is 15 meters, and the temperature is gradually increased from 100 to 450°C.

[0089] S8. After the stretching molding is completed, the finished fiber with a linear density of 1518 dtex is obtained. The test results are shown in Table 5.

[0090]

[0091] Table 5

[0092] The data of the embodiments and comparative examples are summarized in Table 6.

[0093]

[0094] Table 6

[0095] It can be seen from the above data that the elastic modulus of the ultra-high modulus polyimide fiber of the present invention is ≥920cN / dtex, which is more than 13% higher than that of general high-strength polyimide fiber and more than 1100% higher than that of ordinary high-performance polyimide fiber, and the breaking strength is always ≥27cN / dtex.

[0096] In Comparative Example 1, since no end-capping agent was added after polymerization to control the dynamic viscosity of the polymerization spinning slurry, the dynamic viscosity during spinning was greater than 200,000 centiber, the fiber spinnability was reduced, the plasticization elongation was low, the internal molecular pre-orientation degree of the polyamic acid fiber was reduced, and at the same time, without undergoing multiple stages of high-temperature drying and high-multiple stretching, the internal force orientation degree of the primary polyimide fiber molecules was low, resulting in low breaking strength of the product, high breaking elongation and low elastic modulus.

[0097] In Comparative Example 2, 4,4'-diaminodiphenyl ether (4,4-ODA) and pyromellitic dianhydride (PMDA) were used as raw materials for nucleophilic polycondensation. The molecular weight of the polymer spinning slurry was not high, and the molecular chain lacked rigid chain structural units, so the breaking strength and elastic modulus could not meet good quality requirements.

[0098] In the present invention, by introducing rigid chain structure materials, controlling the viscosity of the end-capping agent, and high-multiple stretching in the spinning multi-stage high-temperature drying tunnel, the product has a tensile strength of not less than 27 cN / dtex, and the elastic modulus is greatly improved. The product has a good appearance, continuous production and high stability, and is at the leading level at home and abroad. Only by introducing a small amount of low-cost end-capping agent and optimizing some spinning production process equipment, the stable production of ultra-high modulus polyimide fiber can be achieved, which has important value and significance for the development of the entire polyimide fiber manufacturing industry.

[0099] The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

Claims

1. A method for preparing a polyimide fiber with ultra-high modulus, characterized in that: The following steps are involved: S1: Add N-methylpyrrolidone (NMP) solvent into a 1000L polymerization reactor; S2: Add 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) and p-phenylenediamine (PPDA) into a polymerization reactor; S3: Start stirring and dissolving, control the temperature of the polymerization kettle at 24-25°C, cool the diamine solution in the polymerization kettle through the polymerization kettle jacket, calculate the total amount of biphenyltetracarboxylic dianhydride (BPDA) by the reaction equation, and add 99.5% of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA) that has been previously dried at 235°C into the polymerization kettle for prepolymerization. After stirring for 3 hours, according to the dynamic viscosity of the polymer reactant, add the remaining part of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA) into the polymerization reactor for telomerization reaction in 3 times, and then take samples for detection; S4: Calculate the mass of benzoic anhydride to be added as the end-capping agent according to 0.01-0.1% of the theoretical total mass of biphenyltetracarboxylic dianhydride (BPDA), add benzoic anhydride to the end-capping agent, continue stirring the reaction, and take samples to test the dynamic viscosity; S5: filtering and degassing the obtained polymer spinning slurry before entering the spinning main machine; S6: After the polymerized spinning slurry is extruded through spinning metering, it is plasticized and stretched by a traction roller while the polyamic acid fiber is initially formed through a coagulation bath, the stretching ratio is 50-55%, and the coagulation liquid is an aqueous solution with a NMP content of 18-20%; S7: The polyamic acid fiber is subjected to a washing and drying process, wherein the washing water is deionized water and the drying temperature is 150°C; S8: The dried polyamic acid fiber is continuously fed into a high-temperature drying tunnel through a traction roller for imidization treatment. The traction rollers before and after the high-temperature drying tunnel control the tension of the fiber to be ≤0.1 cN / dtex. The length of the high-temperature drying tunnel is 5 meters, and the temperature is 100-200°C. S9: The primary polyimide fiber is stretched at high temperature and high magnification by using the speed difference of the traction rollers before and after the high-temperature drying oven. Nitrogen is used for protection inside the high-temperature drying oven. The temperature of the first-stage drying oven is controlled at 200-400℃; the incremental draft ratio of the traction rollers before and after the drying oven is 50-80%, and the temperature of the second-stage drying oven is controlled at 400-450℃; the incremental draft ratio of the traction rollers before and after the drying oven is 20-50%, and the temperature of the third-stage drying oven is controlled at 450-530℃; the incremental draft ratio of the traction rollers before and after the drying oven is 10-30%; S10: After the stretching and molding, the finished fiber is obtained and tested.

2. The method for preparing a polyimide fiber with ultra-high modulus according to claim 1, characterized in that: The solid content of the polymer spinning slurry system is controlled at 9-13%.

3. A method for preparing a polyimide fiber with ultra-high modulus as claimed in claim 2, characterized in that: In S2, according to the requirement of 13% solid content of the polymer material, the molar ratio of 5(6)-amino-2-(4'-aminophenyl)benzimidazole (R3) to p-phenylenediamine (PPDA) is ≥1.

4. The method for preparing a polyimide fiber with ultra-high modulus according to claim 1, characterized in that: The stirring dissolution in S3 is to quickly stir and dissolve the monomers in S2 in the solvent NMP at room temperature, and the dissolution time is ≥3 hours.

5. The method for preparing a polyimide fiber with ultra-high modulus according to claim 1, characterized in that: In the S8 imidization treatment, nitrogen is used to protect the inside of the high-temperature drying oven, the oven temperature is controlled at 100-150°C, and the tensile tension of the front and rear traction rollers is 0.05-0.08 cN / dtex.

6. The method for preparing a polyimide fiber with ultra-high modulus according to claim 1, characterized in that: In S9, the temperature of the first-stage drying tunnel is controlled at 250-350℃; the incremental draft ratio of the traction rollers before and after the drying tunnel is 60%-80%, the temperature of the second-stage drying tunnel is controlled at 400-420℃; the incremental draft ratio of the traction rollers before and after the drying tunnel is 30%-50%, the temperature of the third-stage drying tunnel is controlled at 520-530℃; the incremental draft ratio of the traction rollers before and after the drying tunnel is 10%-25%.

7. The method for preparing a polyimide fiber with ultra-high modulus according to claim 1, characterized in that: In S3, the diamine solution in the polymerization kettle is cooled to 3.5-3.9°C through the jacket of the polymerization kettle.

8. The method for preparing a polyimide fiber with ultra-high modulus according to claim 1, characterized in that: In S4, benzoic anhydride was added and the stirring reaction was continued for 1 hour.

9. The method for preparing a polyimide fiber with ultra-high modulus according to claim 1, characterized in that: In S6, the polymer spinning slurry is extruded by spinning metering according to the linear density specification of 1500 dtex and the spinning speed of 20 m / min.

10. A polyimide fiber with ultra-high modulus, characterized in that: The polyimide fiber is prepared by the method for preparing a polyimide fiber with ultra-high modulus as described in any one of claims 1 to 9.

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