A heterocyclic arlan / polyimide block copolymer fiber and a method for preparing the same

Abstract

The application discloses a preparation method of a heterocyclic aramid / polyimide block copolymer fiber and belongs to the technical field of high-performance organic fibers. The method comprises the following steps: completely dissolving a diamine monomer in a solvent system composed of LiCl and an aprotic polar solvent; sequentially adding aromatic diacyl chloride to perform a low-temperature polycondensation reaction, and then adding aromatic dianhydride to perform a polycondensation reaction; and performing spinning forming and multi-stage heat treatment on a spinning dope obtained in the method to obtain the heterocyclic aramid / polyimide block copolymer fiber. Through the synergistic effect of multi-copolymerization and multi-stage gradient heat treatment, the obtained fiber has stable online density and basically unchanged breaking strength, the 5% thermal weight loss temperature (air) can reach above 530 DEG C, the strength retention rate after 1 h of 400 DEG C hot air aging can reach above 90%, and the performance requirements of high-temperature medium and long-term use are met. Meanwhile, the application also discloses a heterocyclic aramid / polyimide block copolymer fiber prepared by the above method.

Description

Technical Field

[0001] This invention belongs to the field of high-performance organic fiber technology, specifically relating to a heterocyclic aramid / polyimide block copolymer fiber and its preparation method. Background Technology

[0002] Heterocyclic aromatic polyamide fibers (hereinafter referred to as heterocyclic aramids) are a type of high-performance fiber in which nitrogen-containing heterocyclic structures are introduced into the main chain of aromatic polyamide macromolecules. Compared with p-phenylene terephthalamide fibers, they have superior heat resistance and mechanical properties, and therefore have broad application prospects in aerospace, military, protective equipment, and high-performance composite materials. Generally, heterocyclic aramids can reach 500℃ when they lose 5% of their weight in air, and their normal operating temperature can reach 300℃. However, when used for a long time above 380℃, their strength retention rate is only 60%, and their high-temperature long-term stability is still insufficient.

[0003] In recent years, with the continuous improvement of temperature resistance requirements for materials in fields such as aerospace, defense, and high-end protective equipment, the high-temperature resistance of existing heterocyclic aramid fibers above 400℃ has become insufficient. Polyimide fibers, on the other hand, possess excellent high-temperature resistance; their temperature at which they lose 5% of their weight in air is typically above 530℃, and they can maintain a strength retention rate of up to 90% during long-term use in high-temperature environments above 400℃. However, achieving the same mechanical strength for high-strength products usually requires a significant increase in the molar proportion of expensive heterocyclic diamine monomers to reach the strength level of heterocyclic aramid fibers. The molar proportion of these diamine monomers often exceeds 75%, leading to a significant increase in production costs and hindering their large-scale application in high-end manufacturing.

[0004] To address the aforementioned issues, existing technologies have reported on blended fibers of aromatic polyamides and aromatic polyimides. For example, Chinese Patent (Publication No.: CN102677225) discloses an aromatic polyamide / aromatic polyimide blended fiber and its preparation method, which is obtained by polymerizing the two polymers separately and then blending and spinning them. However, this technology mainly focuses on improving the fiber's UV resistance, and is insufficiently targeted at further improving its high-temperature resistance. More importantly, this technology uses a physical blending method after the two polymers are polymerized separately. The two components are only physically mixed at the molecular chain level, making it difficult to form chemical bonds and fully utilize the synergistic effect between the two, thus limiting the potential for performance improvement. Summary of the Invention

[0005] To address the above-mentioned problems, this invention provides a heterocyclic aramid / polyimide block copolymer fiber and its preparation method, the specific solution of which is as follows: First, this invention provides a method for preparing heterocyclic aramid / polyimide block copolymer fibers, comprising the following steps: The diamine monomer was completely dissolved in a solvent system consisting of lithium chloride (LiCl) and an aprotic polar solvent. Aromatic diacyl chloride was added, and the mixture underwent a low-temperature polycondensation reaction to obtain an amino-terminated heterocyclic aramid prepolymer liquid. The diamine monomer was a mixture of aromatic diamine and heterocyclic diamine. Aromatic dianhydride was added to the polymerization solution of amino-terminated heterocyclic aramid prepolymer, and a polycondensation reaction was carried out to obtain a spinning solution of heterocyclic aramid / polyamic acid block copolymer. Heterocyclic aramid / polyamic acid block copolymer spinning solution was spun and subjected to multi-stage heat treatment to obtain heterocyclic aramid / polyimide block copolymer fibers.

[0006] This invention provides a method for preparing heterocyclic aramid / polyimide block copolymer fibers. The method employs a sequential one-pot feeding process. First, under conditions of excess diamine monomer, aromatic diacyl chloride is completely reacted to generate an amino-terminated heterocyclic aramid prepolymer polymer solution. Then, aromatic dianhydride is added to react with the remaining diamine monomer to generate polyamic acid segments, thereby forming a heterocyclic aramid / polyamic acid block copolymer spinning solution in situ. Finally, the fibers undergo spinning, multi-stage heat treatment (imidization, dehydration, cyclization, dehydrochlorination, and high-temperature stretching) to obtain heterocyclic aramid / polyimide block copolymer fibers. This invention, through the synergistic effect of multi-component copolymerization combined with multi-stage gradient heat treatment, achieves fibers with stable linear density and essentially unchanged breaking strength. The 5% thermogravimetric temperature (in air) can reach over 530°C, and the strength retention rate after aging in 400°C hot air for 1 hour can reach over 90%, meeting the performance requirements for long-term use at high temperatures.

[0007] Preferably, the aromatic diamine includes at least one of p-phenylenediamine (PPDA) or m-phenylenediamine (MPDA).

[0008] Preferably, the heterocyclic diamine includes at least one of 2-(4-aminophenyl)-5-aminobenzimidazol [2-(4-Aminophenyl)-1H-benzimidazol-5-amine, APBIA] or 5-amino-2-(4-aminophenyl)benzoxazole.

[0009] Preferably, the aromatic dichloride includes at least one of terephthaloyl chloride (TPC) or isophthaloyl dichloride (IPC).

[0010] Preferably, the aromatic dianhydride includes at least one of pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA).

[0011] Preferably, the molar ratio of aromatic diacyl chloride to diamine monomer is (0.4~0.6):1.

[0012] More preferably, the molar ratio of aromatic diacyl chloride to diamine monomer is (0.45~0.49):1.

[0013] Preferably, the molar ratio of aromatic diamine to heterocyclic diamine is (3~5):(5~7).

[0014] Preferably, the molar ratio of aromatic dianhydride to diamine monomer is (0.4~0.6):1.

[0015] Preferably, the aprotic polar solvent includes at least one of N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), or N,N-dimethylformamide (DMF).

[0016] Preferably, the molar ratio of the diamine monomer to the solvent system composed of LiCl and an aprotic polar solvent is (1~3):100.

[0017] Preferably, the mass of lithium chloride (LiCl) is 4% to 8% of the mass of the aprotic polar solvent.

[0018] Preferably, the low-temperature polycondensation reaction includes: controlling the reaction temperature at -10~30℃ and the reaction time at 2~8h under an inert gas protective atmosphere.

[0019] Preferably, the intrinsic viscosity of the amino-terminated heterocyclic aramid prepolymer polymer solution is 2.5~4.5 dL / g.

[0020] Preferably, the polycondensation reaction includes: a reaction temperature of -5 to 30°C; and a reaction time of 4 to 12 hours.

[0021] Preferably, the solid content of the heterocyclic aramid / polyamic acid block copolymer spinning solution is 2-6%; the dynamic viscosity is 30,000-300,000 cP; and the intrinsic viscosity is 3.5-5.5 dL / g.

[0022] Preferably, the spinning process includes: The heterocyclic aramid / polyamic acid block copolymer spinning solution is extruded through a spinneret with a stretch rate of -50% to 100%; then it is coagulated in a coagulation bath at a temperature of 10 to 60°C to obtain nascent fibers. The coagulation bath is a DMAC aqueous solution with a mass fraction of 30% to 70%.

[0023] More preferably, before spinning, the heterocyclic aramid / polyamic acid block copolymer spinning solution is sequentially filtered and vacuum degassed.

[0024] More preferably, the filtration includes: using a screw pump or gear pump to pressurize and feed the heterocyclic aramid / polyamic acid block copolymer spinning solution into a plate and frame filter press or a cartridge filter for filtration, wherein the filter screen has a precision of 500~1000 mesh and the filter screen material is polypropylene (PP) or 316L stainless steel.

[0025] More preferably, vacuum degassing includes: pumping the filtered filtrate into a vacuum degassing tower or vacuum storage tank with an umbrella plate for static vacuum degassing, wherein the vacuum degree inside the vacuum degassing tower or vacuum storage tank is -0.09 to -0.07 MPa.

[0026] Preferably, the multi-stage heat treatment includes: subjecting the spun fibers to a three-stage heat treatment under an inert gas atmosphere to obtain heterocyclic aramid / polyimide block copolymer fibers, wherein the three-stage heat treatment includes: First-stage heat treatment: temperature 80~200℃, residence time 1~2min; Second-stage heat treatment: temperature is 350~430℃, fiber tension is controlled to be constant at 0.2~0.5cN / dtex, and residence time is 0.5~2min; Third-stage heat treatment: temperature 435℃~550℃, stretching ratio 1.02~1.5 times, residence time 0.5~2 min.

[0027] More preferably, the first stage of heat treatment includes: holding at 80~120℃ for 20~40s, then holding at 120~150℃ for 20~40s, and finally holding at 200℃ for 20~40s.

[0028] More preferably, the temperature of the third heat treatment is 480~520℃.

[0029] More preferably, before the multi-stage heat treatment, the spun fibers are sequentially washed and dried to remove residual solvents and unreacted small molecule impurities from the fibers.

[0030] A further preferred embodiment of the washing process includes: continuously introducing the nascent fibers into a deionized water spray washing tank using a stainless steel traction roller assembly, wherein the temperature of the deionized water is 85~95℃ and the conductivity of the deionized water is 10~20μS / cm.

[0031] More preferably, the drying process includes: continuously introducing the washed nascent fibers into the surface of the drying rollers in the drying chamber using a stainless steel traction roller assembly, wherein the drying rollers are heated by electric heating or steam heating, and the surface temperature is controlled at 110~150℃.

[0032] More preferably, the obtained heterocyclic aramid / polyimide block copolymer fibers are collected.

[0033] Secondly, the present invention provides a heterocyclic aramid / polyimide block copolymer fiber prepared by the above preparation method.

[0034] Preferably, in the heterocyclic aramid / polyimide block copolymer fiber, the molar ratio of heterocyclic aramid segments to polyimide segments is (2~3):(2~3), and both are independently taken from this range.

[0035] The beneficial effects of this invention are: (1) Pioneering sequential feeding one-pot synthesis of block copolymers: This invention involves the complete reaction of aromatic diacyl chloride under excess diamine monomer conditions to generate an amino-terminated heterocyclic aramid prepolymer polymer solution. Aromatic dianhydride is then added to react with the remaining diamine monomer to generate polyamic acid segments, thus forming a heterocyclic aramid / polyamic acid block copolymer spinning solution in situ within a single reaction system. Compared to the existing method of polymerizing the two polymers separately and then physically blending them, this invention achieves chemical bonding of the two components at the molecular chain level, resulting in a more significant synergistic effect.

[0036] (2) Simplified process and high efficiency: The present invention completes the synthesis of two polymers in one pot, avoiding the cumbersome process of separate polymerization, separate purification and re-blending, greatly shortening the production process and reducing energy consumption and equipment investment costs.

[0037] (3) Significantly improved high temperature resistance: Polyimide segments are chemically bonded to heterocyclic aramid molecular chains in a block form. Combined with multi-stage heat treatment process, the polyimide segments are fully imidized, resulting in a high degree of cyclization, which effectively improves the overall heat resistance of heterocyclic aramid.

[0038] (4) Good mechanical properties: High-temperature stretching in multi-stage heat treatment further optimizes the aggregated structure of the fiber, so that the mechanical properties of the fiber remain stable.

[0039] (5) Controllable side reactions: By precisely controlling the amount of aromatic diacyl chloride added [the molar ratio of aromatic diacyl chloride to diamine monomer is (0.4~0.6):1], aromatic dianhydride is added after the aromatic diacyl chloride has reacted completely, which effectively avoids the cross-side reaction between aromatic dianhydride and aromatic diacyl chloride as well as the acylation side reaction between aromatic dianhydride and the amide bond that has been formed, thus ensuring the regularity of the block copolymer structure.

[0040] (6) Low raw material cost: Under the premise that the mechanical properties are provided by the heterocyclic aramid block, high overall mechanical properties can be obtained without the need to use a large amount of heterocyclic diamine monomers, thus reducing the raw material cost. Attached Figure Description

[0041] Figure 1 This is a process flow diagram for the preparation of a heterocyclic aramid / polyimide block copolymer fiber. Detailed Implementation

[0042] The specific embodiments listed in this invention are merely examples, and the invention is not limited to the specific embodiments described below. For those skilled in the art, any equivalent modifications and substitutions to the embodiments described below are also within the scope of this invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of this invention should be covered within its scope. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are commercially available conventional products. To better illustrate this invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this invention can be practiced even without certain specific details. In other embodiments, methods, means, equipment, and steps well known to those skilled in the art are not described in detail in order to highlight the main points of this invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Unless otherwise specified, all units used in this specification are International Standard Units (SI), and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors unavoidable in industrial production.

[0044] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0045] I. Examples and Comparative Examples Example 1 This embodiment provides a heterocyclic aramid / polyimide block copolymer fiber, the preparation process flow diagram of which is shown below. Figure 1 As shown, the specific preparation steps are as follows: S1. Synthesis of amino-terminated heterocyclic aramid prepolymer polymer solution: In a polymerization reactor equipped with a stirrer, thermometer, and nitrogen inlet, 10000g of DMAC and 420g of dry LiCl were added and stirred until completely dissolved; then 1.5mol of diamine monomer was added and stirred until completely dissolved under nitrogen protection, with the system temperature controlled at 5℃; then 0.74mol of TPC was added in 4 batches, and the reaction continued for 6h. At this time, the system temperature did not increase and the dynamic viscosity tended to stabilize (5280cP). The intrinsic viscosity was measured to be 3.8dL / g, indicating that the reaction was basically completed, and an amino-terminated heterocyclic aramid prepolymer polymer solution was obtained, wherein the 1.5mol of diamine monomer included: 0.5mol of PPDA and 1mol of APBIA.

[0046] S2. Synthesis of spinning solution of heterocyclic aramid / polyamic acid block copolymer: The amino-terminated heterocyclic aramid prepolymer polymer solution obtained in S1 was cooled to 5°C, and 0.76 mol BPDA was added in 4 batches. The reaction was continued for 8 hours to obtain the spinning solution of heterocyclic aramid / polyamic acid block copolymer. The solid content was 5.6%, the dynamic viscosity was 98960 cP, the intrinsic viscosity was 4.8 dL / g, and the molar ratio of heterocyclic aramid segments to polyimide segments was 2:3.

[0047] S3. Filtration and vacuum degassing: The heterocyclic aramid / polyamic acid block copolymer spinning dope obtained in S2 is fed into a plate and frame filter press (the filter screen is 500 mesh and the filter screen material is PP) using a screw pump; the filtrate is then fed into a vacuum degassing tower with umbrella plates for static vacuum degassing, wherein the vacuum pressure of the vacuum degassing tower is -0.08MPa.

[0048] S4. Spinning: The filtered and vacuum degassed heterocyclic aramid / polyamic acid block copolymer spinning dope obtained in S3 is extruded through a 500-hole spinneret (0.08 mm orifice) with an elongation of 80%; then it enters a 30°C coagulation bath to coagulate and form nascent fibers, wherein the coagulation bath is a 50% DMAC aqueous solution by mass.

[0049] S5. Washing and drying: The nascent fibers obtained in S4 are continuously introduced into a deionized water spray washing tank through a stainless steel traction roller group for washing. The temperature of the deionized water is 110℃ and the conductivity of the deionized water is 12μS / cm. After washing, the fibers are continuously fed into a drying box by the traction roller group and dried by an electrically heated drying roller (surface temperature 110℃) to obtain blended nascent fibers.

[0050] S6. Multi-stage heat treatment: Under nitrogen protection, the blended nascent fibers obtained in S5 are fed into a hot drying tunnel at a speed of 10 m / min for three-stage heat treatment to obtain heterocyclic aramid / polyimide block copolymer fibers, wherein... First-stage heat treatment: The fiber enters a multi-stage heat treatment oven: First, it is held at 80℃ for 20 seconds to allow the residual solvent in the fiber to fully evaporate; then, it is held at 150℃ for 20 seconds to carry out the imidization reaction and dehydration cyclization of the polyamic acid segments; finally, it is held at 200℃ for 20 seconds to allow the imidization reaction to proceed fully, while simultaneously completing the further cyclization of the heterocyclic structure in the heterocyclic aramid prepolymer and the condensation of unreacted end groups, without stretching throughout the process; Second-stage heat treatment: After the first-stage heat treatment, the fiber enters a 10m long hot drying tunnel (temperature 400℃) and stays for 1 minute. The fiber tension is kept constant at 0.3cN / dtex by controlling the speed difference between the front and rear rollers, so that the fiber is fully softened and pre-oriented. Third-stage heat treatment: After the second-stage heat treatment, the fiber enters a 5m long hot drying tunnel (temperature 500℃) and stays for 30s to achieve 1.4 times stretching, so that the molecular chains are highly oriented along the axial direction.

[0051] S7. Fiber collection: The blended fibers obtained in S6 are oiled and wound up to obtain packaged heterocyclic aramid / polyimide block copolymer fibers.

[0052] Example 2 This embodiment provides a heterocyclic aramid / polyimide block copolymer fiber, and the specific preparation steps are as follows: S1. Synthesis of amino-terminated heterocyclic aramid prepolymer polymer solution: In a polymerization reactor equipped with a stirrer, thermometer, and nitrogen inlet, 10000g NMP and 600g LiCl were added and stirred until completely dissolved; then 1.5mol of diamine monomer was added and stirred until completely dissolved under nitrogen protection, with the system temperature controlled at 5℃; then 0.74mol of TPC was added in 4 batches, and the reaction continued for 6h. At this time, the system temperature did not increase and the dynamic viscosity tended to stabilize (3280cP). The intrinsic viscosity was measured to be 2.9dL / g, indicating that the reaction was basically completed, and an amino-terminated heterocyclic aramid prepolymer polymer solution was obtained, wherein the 1.5mol of diamine monomer included: 0.75mol of PPDA and 0.75mol of APBIA.

[0053] S2. Synthesis of spinning solution for heterocyclic aramid / polyamic acid block copolymer: The amino-terminated heterocyclic aramid prepolymer polymer solution obtained in S1 was cooled to 5°C, and 0.76 mol BPDA was added in 4 batches. The reaction was continued for 8 hours to obtain the spinning solution for heterocyclic aramid / polyamic acid block copolymer. The solid content was 5.3%, the dynamic viscosity was 85470 cP, the intrinsic viscosity was 5.4 dL / g, and the molar ratio of heterocyclic aramid segments to polyimide segments was 2:3.

[0054] S3. Filtration and vacuum degassing: Same as in Example 1, omitted here.

[0055] S4. Spinning and forming: Same as in Example 1, omitted here, to obtain nascent fibers.

[0056] S5. Washing and drying: Same as in Example 1, omitted here, to obtain blended nascent fibers.

[0057] S6. Multi-stage heat treatment: Under nitrogen protection, the blended nascent fibers obtained in S5 are fed into a hot drying tunnel at a speed of 10 m / min for three-stage heat treatment to obtain heterocyclic aramid / polyimide block copolymer fibers, wherein... First-stage heat treatment: The fiber enters a multi-stage heat treatment oven: First, it is held at 110℃ for 35 seconds to allow the residual solvent in the fiber to fully evaporate; then, it is held at 140℃ for 20 seconds to carry out the imidization reaction and dehydration cyclization of the polyamic acid segments; finally, it is held at 200℃ for 20 seconds to allow the imidization reaction to proceed fully, while simultaneously completing the further cyclization of the heterocyclic structure in the heterocyclic aramid prepolymer and the condensation of unreacted end groups, without stretching throughout the process; Second-stage heat treatment: After the first-stage heat treatment, the fiber enters a 10m long hot drying tunnel (temperature 430℃) and stays for 1.5min. The fiber tension is kept constant at 0.3cN / dtex by controlling the speed difference between the front and rear rollers, so that the fiber is fully softened and pre-oriented. Third-stage heat treatment: After the second-stage heat treatment, the fiber enters a 5m long hot drying tunnel (temperature 520℃) and stays for 30s to achieve 1.4 times stretching, so that the molecular chains are highly oriented along the axial direction.

[0058] S7. Fiber collection: Same as in Example 1, omitted here, to obtain rolled heterocyclic aramid / polyimide block copolymer fibers.

[0059] Example 3 This embodiment provides a heterocyclic aramid / polyimide block copolymer fiber, and the specific preparation steps are as follows: S1. Synthesis of amino-terminated heterocyclic aramid prepolymer polymer solution: In a polymerization reactor equipped with a stirrer, thermometer, and nitrogen inlet, 10000g DMF and 800g LiCl were added and stirred until completely dissolved; then 1.5mol of diamine monomer was added and stirred until completely dissolved under nitrogen protection, with the system temperature controlled at 5℃; then 0.74mol of TPC was added in 4 batches, and the reaction continued for 6h. At this time, the system temperature did not increase and the dynamic viscosity tended to stabilize (2540cP). The intrinsic viscosity was measured to be 2.3dL / g, indicating that the reaction was basically completed, and an amino-terminated heterocyclic aramid prepolymer polymer solution was obtained, wherein the 1.5mol of diamine monomer included: 0.5mol MPDA and 1mol 5-amino-2-(4-aminophenyl)benzoxazole.

[0060] S2. Synthesis of spinning solution of heterocyclic aramid / polyamic acid block copolymer: The amino-terminated heterocyclic aramid prepolymer polymer solution obtained in S1 was cooled to 5°C, and 0.76 mol BPDA was added in 4 batches. The reaction was continued for 8 hours to obtain the spinning solution of heterocyclic aramid / polyamic acid block copolymer. The solid content was 5.6%, the dynamic viscosity was 65470 cP, the intrinsic viscosity was 5.1 dL / g, and the molar ratio of heterocyclic aramid segments to polyimide segments was 2:3.

[0061] S3. Filtration and vacuum degassing: Same as in Example 1, omitted here.

[0062] S4. Spinning and forming: Same as in Example 1, omitted here, to obtain blended nascent fibers.

[0063] S5. Washing and drying: Same as in Example 1, omitted here, to obtain blended nascent fibers.

[0064] S6. Multi-stage heat treatment: Under nitrogen protection, the blended nascent fibers obtained in S5 are fed into a hot drying tunnel at a speed of 10 m / min for three-stage heat treatment to obtain heterocyclic aramid / polyimide block copolymer fibers, wherein... First-stage heat treatment: The fiber enters a multi-stage heat treatment oven: First, it is held at 80℃ for 20 seconds to allow the residual solvent in the fiber to fully evaporate; then, it is held at 150℃ for 20 seconds to carry out the imidization reaction and dehydration cyclization of the polyamic acid segments; finally, it is held at 200℃ for 20 seconds to allow the imidization reaction to proceed fully, while simultaneously completing the further cyclization of the heterocyclic structure in the heterocyclic aramid prepolymer and the condensation of unreacted end groups, without stretching throughout the process; Second-stage heat treatment: After the first-stage heat treatment, the fiber enters a 10m long hot drying tunnel (temperature 400℃) and stays for 1 minute. The fiber tension is kept constant at 0.3cN / dtex by controlling the speed difference between the front and rear rollers, so that the fiber is fully softened and pre-oriented. Third-stage heat treatment: After the second-stage heat treatment, the fiber enters a 5m long hot drying tunnel (temperature 490℃) and stays for 30s to achieve 1.1 times stretching, so that the molecular chains are highly oriented along the axial direction.

[0065] S7. Fiber collection: Same as in Example 1, omitted here, to obtain rolled heterocyclic aramid / polyimide block copolymer fibers.

[0066] Comparative Example 1 This comparative example provides a heterocyclic aramid / polyimide blend fiber, and the specific preparation steps are as follows: The heterocyclic aramid polymerization solution and the polyamic acid spinning solution were physically blended at a molar ratio of 4:2, and then subjected to the same spinning and multi-stage heat treatment process as in Example 1 to obtain heterocyclic aramid / polyimide blend fibers.

[0067] Comparative Example 2 To verify the effect of multi-stage heat treatment on the properties of the copolymer fiber of the present invention, this comparative example was designed. The only difference from Example 1 is that the second and third stages of heat treatment are not performed. Instead, the temperature is directly raised to 500°C, heat-treated for 1 minute, and stretched at this temperature with a stretching ratio of 1.5 times.

[0068] Comparative Example 3 To verify the effect of the polyimide component on the properties of the copolymer fibers of the present invention, this comparative example was designed. The difference from Example 1 is that no polyimide component was added; instead, only heterocyclic aramid polymerization solution was used for spinning, multi-stage heat treatment, and fiber collection.

[0069] II. Performance Testing and Characterization Table 1 shows a comparison of the properties of the fibers obtained in Examples 1-3 and Comparative Examples 1-3.

[0070] Table 1. Performance comparison of fibers obtained in Examples 1-3 and Comparative Examples 1-3

[0071] As shown in Table 1, the heterocyclic aramid / polyimide block copolymer fibers prepared in Examples 1-3, while maintaining stable linear density and essentially unchanged breaking strength, all achieved a 5% thermogravimetric temperature (in air) of over 530°C. After aging in hot air at 400°C for 1 hour, their strength retention rate reached over 90%, meeting the performance requirements for long-term use at high temperatures. In contrast, Comparative Example 1 (physical blend), Comparative Example 2 (without multi-stage heat treatment), and Comparative Example 3 (without polyimide component) all had 5% thermogravimetric temperatures below 530°C, and their strength retention rate after aging in hot air at 400°C for 1 hour was only a maximum of 75%, indicating significant performance degradation. This fully demonstrates that the present invention, through the synergistic effect of multi-component copolymerization combined with multi-stage gradient heat treatment, significantly improves the heat resistance stability and high-temperature service performance of the fiber while maintaining its strength.

[0072] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A method for preparing heterocyclic aramid / polyimide block copolymer fibers, characterized in that, Includes the following steps: The diamine monomer is completely dissolved in a solvent system consisting of LiCl and an aprotic polar solvent, aromatic diacyl chloride is added, and the mixture undergoes a low-temperature polycondensation reaction to obtain an amino-terminated heterocyclic aramid prepolymer polymer solution. The diamine monomer is a mixture of aromatic diamine and heterocyclic diamine. Aromatic dianhydride is added to the polymerization solution of the amino-terminated heterocyclic aramid prepolymer, and a polycondensation reaction is carried out to obtain a spinning solution of heterocyclic aramid / polyamic acid block copolymer. The heterocyclic aramid / polyamic acid block copolymer spinning solution is spun and subjected to multi-stage heat treatment to obtain heterocyclic aramid / polyimide block copolymer fibers.

2. The method for preparing heterocyclic aramid / polyimide block copolymer fibers according to claim 1, characterized in that, The aromatic diamine includes at least one of PPDA or MPDA; the heterocyclic diamine includes at least one of APBIA or 5-amino-2-(4-aminophenyl)benzoxazole.

3. The method for preparing heterocyclic aramid / polyimide block copolymer fibers according to claim 1, characterized in that, The aromatic diacyl chloride includes at least one of TPC or IPC.

4. The method for preparing heterocyclic aramid / polyimide block copolymer fibers according to claim 1, characterized in that, The aromatic dianhydride includes at least one of pyromellitic dianhydride or BPDA.

5. The method for preparing heterocyclic aramid / polyimide block copolymer fibers according to claim 1, characterized in that, The molar ratio of the aromatic diacyl chloride to the diamine monomer is (0.4~0.6):

1.

6. The method for preparing heterocyclic aramid / polyimide block copolymer fibers according to claim 1, characterized in that, The molar ratio of the aromatic dianhydride to the diamine monomer is (0.4~0.6):

1.

7. The method for preparing heterocyclic aramid / polyimide block copolymer fibers according to claim 1, characterized in that, The aprotic polar solvent includes at least one of DMAC, NMP, or DMF.

8. The method for preparing heterocyclic aramid / polyimide block copolymer fibers according to claim 1, characterized in that, The spinning process includes: The heterocyclic aramid / polyamic acid block copolymer spinning solution is extruded through a spinneret with a stretching ratio of -50% to 100%; then it is coagulated in a coagulation bath at a temperature of 10 to 60°C to obtain nascent fibers. The coagulation bath is a DMAC aqueous solution with a mass fraction of 30% to 70%.

9. The method for preparing heterocyclic aramid / polyimide block copolymer fibers according to claim 1, characterized in that, The multi-stage heat treatment includes: subjecting the spun fibers to a three-stage heat treatment under inert gas protection to obtain heterocyclic aramid / polyimide block copolymer fibers, wherein the three-stage heat treatment includes: First-stage heat treatment: temperature 80~200℃, residence time 1~2min; Second-stage heat treatment: temperature is 350~430℃, fiber tension is controlled to be constant at 0.2~0.5cN / dtex, and residence time is 0.5~2min; Third-stage heat treatment: temperature 435℃~550℃, stretching ratio 1.02~1.5 times, residence time 0.5~2 min.

10. A heterocyclic aramid / polyimide block copolymer fiber prepared by any one of the preparation methods described in claims 1-9.

Images