Integrated preparation method and application of high-strength high-modulus carbon fiber

Abstract

The application belongs to the field of polymer materials and advanced fiber manufacturing, and particularly relates to a high-strength and high-modulus carbon fiber integrated preparation method and application. The application significantly improves the uniformity of the internal structure of the fiber through a seed-induced gelation process, and effectively avoids the skin-core structure. The specific preparation method comprises the following steps: (1) introducing a supramolecular seed precursor monomer by using a "flat push type" water phase precipitation polymerization technology to synthesize PAN powder; (2) preparing a uniform spinning stock solution of the PAN copolymer powder, and using "dry spraying-gelation-wet spinning" to prepare a precursor fiber, in the process, the precursor monomer of the supramolecular seed in the stock solution forms uniformly dispersed supramolecular seeds through in-situ self-assembly, and cooperates with the auxiliary agent in the coagulation bath to trigger the rapid gelation of the spinning stock solution; (3) performing heat treatment on the obtained precursor fiber, using the template effect of the supramolecular seed to promote graphitization and promote the fiber to form a perfect graphite lattice structure, and finally obtaining a high-strength and high-modulus carbon fiber.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and advanced fiber manufacturing, specifically relating to an integrated preparation method and application of high-strength, high-modulus carbon fibers. Background Technology

[0002] Carbon fiber, especially polyacrylonitrile (PAN)-based carbon fiber, has become an irreplaceable material in aerospace, defense, and other fields due to its low density, high strength, and high modulus. However, in the current industrial production of high-performance carbon fiber, there are still a series of technical bottlenecks that urgently need to be overcome in the three core stages of polymerization, spinning, and heat treatment, such as: In the polymerization process, the temperature and concentration fields in the reactor of the mainstream batch solution polymerization process fluctuate with the reaction time, resulting in a wide distribution of polymer molecular weight, large batch differences, and uneven distribution of comonomer sequences. Although aqueous precipitation polymerization has improved heat dissipation and polymer purity to some extent, traditional batch reactors still have difficulty in achieving uniformity of material residence time.

[0003] Spinning process: In traditional dry-jet wet spinning, the solvent diffusion rate on the surface of the spinning stream is much higher than that in the core layer, resulting in a "dense on the outside and sparse on the inside" core-skin structure. This structure can induce or amplify defects such as microcracks and pores during subsequent heat treatment. Furthermore, the core-skin structure makes the core layer weak and limits the draw ratio, making it difficult to achieve high orientation.

[0004] Heat treatment: In order to obtain high modulus, graphitization is required at temperatures exceeding 2000℃, which faces the dilemma of extremely high energy consumption, demanding equipment requirements, and difficulty in synergistically improving strength and modulus.

[0005] Therefore, the industry urgently needs an integrated solution that starts from molecular design and extends through polymerization, spinning and heat treatment to ensure the uniformity of polymer structure from the source, completely eliminate the core-sheath structure and obtain precursors with ultra-high orientation, and construct efficient and uniformly dispersed graphitized templates in situ to achieve the preparation of high-strength and high-modulus carbon fibers. Summary of the Invention

[0006] In view of the needs of existing technologies, the purpose of this invention is to provide an integrated preparation method and application of high-strength, high-modulus carbon fibers. This invention discloses an integrated preparation method for the entire process from precursor polymer synthesis to carbon fiber molding. The core of this method includes: (1) using a "flat-push" aqueous precipitation polymerization technology to continuously synthesize polyacrylonitrile powder with uniform structure, while introducing supramolecular seed precursor monomers into the PAN molecular structure during the polymerization stage; (2) using a "two-step" process to prepare PAN precursor fibers, i.e., dissolving the PAN powder obtained from polymerization in dimethyl sulfoxide (DMSO) to prepare a uniform spinning solution, and then spinning the spinning solution into precursor fibers (precursor fibers); (3) using a "dry spray-gel-wet spinning" technology to prepare precursor fibers from the spinning solution. During the spinning process, the precursor monomers of supramolecular seed in the solution form uniformly dispersed supramolecular seed through in-situ self-assembly, which, together with the multifunctional gel induction agent in the coagulation bath, triggers the rapid gelation of the spinning solution; (4) heat-treating the obtained precursor fibers, and using the template effect of the supramolecular seed to promote carbonization and / or graphitization to obtain high-performance carbon fibers.

[0007] Specifically, the present invention provides the following technical solution: In a first aspect, the present invention provides an integrated method for preparing high-strength, high-modulus carbon fibers, comprising the following steps: Aqueous solutions of acrylonitrile monomer and supramolecular seed precursor monomer are mixed, and an initiator is added to carry out a polymerization reaction to obtain a polyacrylonitrile-based polymer slurry containing supramolecular seed precursor structural units. After drying, polymer powder is obtained. The polymer powder is dissolved in an organic solvent to obtain a spinning solution. The spinning solution is processed through a dry-jet-gel-wet spinning process, and then immersed in a coagulation bath to obtain nascent fibers. The nascent fibers are then processed into precursor fibers through a post-treatment process, and finally carbon fibers are produced through a pre-oxidation and carbonization process.

[0008] Preferably, the supramolecular seed precursor monomer accounts for 0.1 to 50 wt% of the mass of the acrylonitrile monomer; and the initiator accounts for 0.1 to 10 wt% of the mass of the acrylonitrile monomer.

[0009] Preferably, the supramolecular seed precursor monomer comprises a first monomer and a second monomer, wherein the first monomer is selected from one or more of 2,4,6-triaminopyrimidine, 2,6-diaminopyridine, melamine and its derivatives; the second monomer is selected from one or more of barbituric acid, cyanuric acid and its derivatives; and the molar ratio of the first monomer to the second monomer is 1:2 to 2:1.

[0010] Preferably, the polymerization reaction occurs in a plug flow reactor at a reaction temperature of 50-80°C and a reaction time of 1.5-2.5 h. In the polymerization reaction, the total conversion rate of acrylonitrile monomer to polyacrylonitrile is maintained at 70%-95%.

[0011] More preferably, the plug flow reactor is a tubular reactor or a multi-reactor reactor connected in series, and the material flows in a plug flow pattern within the reactor.

[0012] Preferably, the organic solvent is selected from one or more of dimethyl sulfoxide (DMSO), dimethylformamide, and dimethylacetamide; the solid content of the polymer powder in the spinning solution is 10% to 30%.

[0013] Preferably, the coagulation bath is a DMSO / water solution containing an additive, wherein the concentration of DMSO in the coagulation bath is 20% to 80%, the concentration of the additive is 0.1% to 20%, and the temperature of the coagulation bath is 2 to 80°C. The additive is a compound containing at least two functional groups in its molecule that can form polar interactions, ionic interactions, or coordination interactions with cyano (-CN) groups or supramolecular seeds on the polyacrylonitrile molecular chain.

[0014] More preferably, the auxiliaries are selected from one or more of polyols, polyamines, polyvalent metal salts, and polybasic organic acids and / or their salts; wherein the polyols are selected from at least one of ethylene glycol, glycerol, pentaerythritol, polyvinyl alcohol, and hexahydroxycyclohexanol; the polyamines are selected from at least one of ethylenediamine, p-phenylenediamine, m-phenylenediamine, and dicyandiamide; the polyvalent metal salts are selected from at least one of calcium chloride, zinc chloride, aluminum sulfate, and ferric nitrate; and the polybasic organic acids and / or their salts are selected from at least one of citric acid, sodium citrate, tartaric acid, potassium sodium tartrate, ethylenediaminetetraacetic acid, and disodium ethylenediaminetetraacetic acid.

[0015] Preferably, the dry-jet-gel-wet spinning process involves the spinning solution being extruded from the spinneret, passing through an air layer to allow the fine stream to undergo surface pre-curing, initial molecular chain orientation, seed crystal pre-assembly, and initial gelation of the spinning solution in the air before entering the coagulation bath; wherein the length of the air layer is 3~20 mm.

[0016] Preferably, the post-processing steps include washing, stretching, oiling, drying and densifying, and steam stretching of the nascent fibers.

[0017] Preferably, the total draw ratio in the process of making the nascent fiber into a raw filament is 20 to 40 times.

[0018] Preferably, the pre-oxidation treatment is carried out in an air atmosphere at a temperature of 200~300℃; the carbonization treatment is carried out in an inert atmosphere or under vacuum at a temperature of 300℃~1600℃.

[0019] In a second aspect, the present invention provides a high-strength, high-modulus carbon fiber, which is prepared by the preparation method described in the first aspect.

[0020] Preferably, the carbon fiber has a tensile strength ≥4.7 GPa, a tensile modulus ≥290 GPa, and a uniform fiber cross-sectional structure with no significant core-sheath structure.

[0021] A third aspect of the present invention provides an application of the high-strength, high-modulus carbon fiber described in the first aspect in the fields of aerospace or transportation.

[0022] The beneficial effects achieved by one or more of the above technical solutions of the present invention are as follows: (1) In this invention, supramolecular seed precursor monomers are introduced in the polymerization stage. During the spinning process, they are formed by in-situ self-assembly to form uniformly dispersed supramolecular seed. Combined with multifunctional auxiliary agents in the coagulation bath, the spinning solution is synergistically induced to rapidly and uniformly gel, avoiding the "dense outside and sparse inside" core structure caused by uneven solvent diffusion in traditional dry-jet wet spinning. The resulting precursor fiber cross-sectional structure is uniform and has few defects, providing uniform and stable carbon fibers for subsequent heat treatment (i.e., continuous polymerization can ensure the stability of polymer source quality, while in-situ self-assembly eliminates filler agglomeration).

[0023] (2) The present invention imparts good stretchability to the nascent fiber during the gelation process, significantly improves the tolerance of the stretching process, and the total stretch ratio can reach 20 to 40 times, which is much higher than the traditional process. This is conducive to the high orientation of molecular chains along the fiber axis and improves the mechanical properties of the fiber.

[0024] (3) In this invention, supramolecular seed crystals can be used as physical crosslinking points to induce gelation during the spinning stage, and can also be used as templates to induce graphitization during the heat treatment stage, thus achieving "one agent, two effects". By utilizing the template effect to promote the regular arrangement of carbon layers, a high degree of graphitization can be obtained under relatively mild heat treatment conditions, avoiding the high energy consumption and demanding equipment requirements caused by high-temperature graphitization exceeding 2000℃ in traditional processes.

[0025] (4) The present invention adopts the "flat push" aqueous precipitation polymerization technology, in which the material flows in a flat push flow, and the reaction temperature and time are uniform, avoiding the problem of temperature field and concentration field fluctuation in traditional batch polymerization. At the same time, from polymerization to spinning, the entire technical process is seamlessly connected, making it easy to realize automated and continuous industrial production.

[0026] (5) The carbon fiber obtained by the present invention has a tensile strength ≥4.7 GPa and a tensile modulus ≥290 GPa. In some embodiments, the modulus can reach 400 GPa after graphitization. The fiber cross section is uniform, there is no significant core-sheath structure, and the performance is stable. It is suitable for high-requirement fields such as aerospace and transportation. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0028] Figure 1 This is a complete flow diagram of the integrated preparation process of the present invention, wherein: 1. Polymerization device; 2. Drying device; 3. Dissolving device; 4. Coagulation bath device; 5. Water washing-stretching device; 6. Densification device; 7. Steam stretching device; 8. Pre-oxidation device; 9. Carbonization device; Figure 2 This is a SEM image of the polyacrylonitrile polymer powder obtained in Example 1 of the present invention; Figure 3 This is a schematic diagram of the self-assembled structure of 2,4,6-triaminopyrimidine and barbituric acid in Example 1 of the present invention; Figure 4 This is a schematic diagram of the self-assembled structure of 2,6-diaminopyridine and cyanuric acid in Example 2 of the present invention; Figure 5 This is a SEM image of the polyacrylonitrile precursor obtained in Example 1 of the present invention. Figure 6 The image shows the XRD pattern of the polyacrylonitrile precursor fiber obtained in Example 2 of this invention. Figure 7 This is a SEM image of the polyacrylonitrile precursor obtained in Example 2 of the present invention. Figure 8 This is a SEM image of the carbon fiber obtained in Example 1 of the present invention; Figure 9 This is a SEM image of the carbon fiber obtained in Example 2 of the present invention. Detailed Implementation

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] As mentioned above, the current development of carbon fiber technology faces a systemic problem: the uniformity of polymerization, the structural uniformity of spinning, and the efficiency of graphitization are being studied in isolation. Therefore, this invention proposes an integrated solution that starts from molecular design and extends through precursor synthesis, spinning, and structural transformation.

[0031] Specifically, this invention provides an integrated preparation method for high-strength, high-modulus carbon fibers, comprising the following steps: (a) Continuous aqueous precipitation polymerization: In a plug flow reactor, a mixed aqueous material containing acrylonitrile monomer and supramolecular seed precursor monomer is continuously fed and precipitation polymerization is initiated by an initiator to obtain a PAN-based polymer slurry containing supramolecular seed precursor structural units. (b) Polymer treatment and solution preparation: The slurry obtained in step (a) is dried to obtain polymer powder; the polymer powder is dissolved in an organic solvent to prepare a uniform spinning solution; (c) Supramolecular seed-induced dry-jet-gel-wet spinning: The spinning solution obtained in step (b) is extruded through a spinneret to form a fine stream. The fine stream first passes through an air layer and then is immersed in a coagulation bath to obtain nascent fibers. The nascent fibers are then subjected to subsequent processes such as water washing, stretching, drying and densification, and steam stretching to obtain precursor PAN yarn. (d) Heat treatment: The precursor filaments obtained in step (c) are subjected to pre-oxidation and carbonization treatments in sequence to obtain carbon fibers.

[0032] In one or more embodiments of this implementation, in step (a), the supramolecular seed precursor monomer accounts for 0.1 to 50 wt% of the mass of the acrylonitrile monomer; and the initiator accounts for 0.1 to 10 wt% of the mass of the acrylonitrile monomer.

[0033] In one or more embodiments of this implementation, in step (a), the supramolecular seed precursor monomer comprises a first monomer and a second monomer, wherein the first monomer is selected from one or more of 2,4,6-triaminopyrimidine, 2,6-diaminopyridine, melamine and its derivatives; the second monomer is selected from one or more of barbituric acid, cyanuric acid and its derivatives; and the molar ratio of the first monomer to the second monomer is 1:2 to 2:1.

[0034] In one or more embodiments of this implementation, in step (a), the plug flow reactor is a tubular reactor or a series of multi-reactor reactors, the material flows in a plug flow within the reactor, the polymerization temperature is controlled at 50~80℃, and the total conversion rate of acrylonitrile monomer is maintained at 70%~95%.

[0035] In one or more embodiments of this implementation, in step (b), the organic solvent is selected from one or more of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide; the solid content of the polymer powder in the spinning solution is 10% to 30%.

[0036] In one or more embodiments of this implementation, in step (c), the coagulation bath is a DMSO / water solution containing an additive, wherein the concentration of the DMSO is 20% to 80%, the additive accounts for 0.1% to 20% of the coagulation bath, and the temperature is 2 to 80°C. In one or more embodiments of this implementation, the additive is a compound containing at least two functional groups in its molecule that can form polar interactions, ionic interactions or coordination interactions with cyano groups or supramolecular seed crystals on the polyacrylonitrile molecular chain. In one or more embodiments of this implementation, the auxiliary agent is selected from one or more of polyols, polyamines, polyvalent metal salts, and polybasic organic acids and / or their salts; wherein the polyol is selected from at least one of ethylene glycol, glycerol, pentaerythritol, polyvinyl alcohol, and hexahydroxycyclohexanol; the polyamine is selected from at least one of ethylenediamine, p-phenylenediamine, m-phenylenediamine, and dicyandiamide; the polyvalent metal salt is selected from at least one of calcium chloride, zinc chloride, aluminum sulfate, and ferric nitrate; and the polybasic organic acid and / or its salt is selected from at least one of citric acid, sodium citrate, tartaric acid, potassium sodium tartrate, ethylenediaminetetraacetic acid, and disodium ethylenediaminetetraacetic acid.

[0037] The nascent fibers are processed into raw yarn through washing, stretching, oiling, drying and densification, and steam stretching processes.

[0038] In one or more embodiments of this implementation, the total draw ratio of the process of making the nascent fiber into raw yarn is 20 to 40 times.

[0039] In one or more embodiments of this implementation, in step (d), the pre-oxidation treatment is carried out in an air atmosphere at a temperature of 200~300°C; the carbonization treatment is carried out in an inert atmosphere or under vacuum at a temperature of 300°C~1600°C.

[0040] In one or more embodiments of this implementation, in step (d), graphitization can be performed after carbonization. The graphitization is carried out under an inert atmosphere or vacuum at a temperature of 2000℃~3000℃.

[0041] In this invention, the application of additives can work in conjunction with the supramolecular seeds formed by self-assembly within the spinning solution to induce gelation of the spinning solution during the solidification and molding process, effectively mitigating the violent phase transition process and weakening the core-sheath structure. If too little additive is added, the gelation-promoting effect will be weakened, while if too much is added, it will have an adverse effect on the solidification and molding process of the spinning solution and the regularity of the final fiber structure.

[0042] In this invention, the supramolecular seed precursor structural units in the spinning solution undergo in-situ self-assembly to form uniformly dispersed supramolecular seeds, while the coagulation bath contains a multifunctional gel inducing agent. Under the synergistic effect of the supramolecular seeds and the agent, the spinning stream undergoes rapid gelation and finally solidifies to form nascent fibers. The gelation process is synergistically initiated by the supramolecular seed crystals formed by in-situ self-assembly and the multifunctional gel-inducing agent in the coagulation bath. The gelation transformation effectively promotes uniform phase separation of the spinning stream in the coagulation bath, increases the drawability of the spinning stream, and enables the nascent fiber to withstand a draw ratio of not less than 4 times in the coagulation bath, and the total draw ratio can reach more than 30 times.

[0043] In this invention, the supramolecular seed crystals formed by in-situ self-assembly can serve as graphitization templates during heat treatment to promote the graphitization transformation of PAN precursors.

[0044] In this invention, self-assembling monomer units are introduced during the polymerization stage, laying a chemical foundation for the subsequent creation of uniformly dispersed "seeds" through in-situ self-assembly. At the spinning process level, a unique "dry spray-gel-wet spinning" technology is developed, which utilizes the synergistic effect of endogenous (supramolecular seed crystals) and exogenous (coagulation bath additives) to trigger rapid and controllable gelation, thereby achieving homogenized fiber structure formation and high-ratio oriented stretching. At the same time, the same supramolecular seed crystal is used as a physical crosslinking point to induce gelation during the spinning stage and as a chemical template to induce graphitization during the heat treatment stage, achieving a dual effect with a single agent.

[0045] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0046] Example 1: This example provides a high-strength, high-modulus carbon fiber and its preparation method. In this embodiment, 2,4,6-triaminopyrimidine and barbituric acid, uniformly mixed in a molar ratio of 1:1, are used as the supramolecular seed precursor monomer system (2,4,6-triaminopyrimidine / barbituric acid), and m-phenylenediamine is used as a multifunctional gel induction agent.

[0047] like Figure 1 The diagram shown is a complete flow chart of the integrated manufacturing process of this invention. The specific manufacturing method includes the following steps: (1) Continuous polymerization 1) Preparation of monomer aqueous solution: Acrylonitrile and 2,4,6-triaminopyrimidine / barbituric acid are dispersed and dissolved in deionized water to a total concentration of 20 wt% (wherein, the total mass of 2,4,6-triaminopyrimidine and barbituric acid is 3 wt% of acrylonitrile); ammonium persulfate and ammonium sulfite, the initiators, are dissolved in the above aqueous solution at a molar ratio of 1:1 to a total concentration of 2 wt% of acrylonitrile. 2) The monomer aqueous solution prepared in step 1 is continuously injected into a plug flow reactor with multi-stage internal stirring via a precision metering pump. The reaction temperature is set at 55℃, and the average residence time of the material is controlled at 2 hours. The monomer conversion rate is stabilized at 85%. After the reaction is completed, the outlet slurry is centrifuged and dried to obtain white polyacrylonitrile (PAN) polymer powder, such as... Figure 2 The SEM image is shown.

[0048] (2) Preparation of spinning solution The above powder was dissolved in DMSO at a mass concentration of 20 wt%, stirred at 60°C for 24 h, and then filtered and degassed to obtain a uniform and transparent spinning solution.

[0049] (3) Dry spray-gel-wet spinning After being metered and filtered, the spinning solution is extruded through a spinneret (containing 3,000 spinnerets with a diameter of 0.1 mm).

[0050] In this embodiment, the air layer distance of the dry spray section is set to 5 mm; the coagulation bath composition is: 35 wt% DMSO / water solution containing 2 wt% m-phenylenediamine, and the temperature is 10°C.

[0051] 1) During the spinning process, in the air layer, the 2,4,6-triaminopyrimidine / barbituric acid supramolecular seed precursor monomer units in the spinning solution begin to recognize each other and self-assemble through hydrogen bonds to form initial supramolecular aggregates (such as... Figure 3 (As shown in the schematic diagram). After entering the coagulation bath, the self-assembly reaction proceeds further, forming uniformly dispersed supramolecular seed crystals. The supramolecular seed crystals, together with the m-phenylenediamine in the coagulation bath, establish a non-covalent interaction network with the PAN molecular chains through polar interactions such as hydrogen bonds, which in turn rapidly leads to the overall gelation of the spinning stream, thus obtaining gelled nascent fibers with excellent drawability.

[0052] 2) The gelled nascent fibers obtained in step 1) are sequentially subjected to multi-stage washing and stretching treatments at 40, 50, 60, 70, 80, and 90°C, followed by oiling, drying and densification, and steam stretching processes to obtain highly oriented polyacrylonitrile precursor fibers. The total stretching ratio of the entire spinning process reaches 35 times.

[0053] (4) Heat treatment Polyacrylonitrile precursor fibers were pre-oxidized in air at six temperature zones: 210, 220, 230, 240, 250, and 260°C, with each zone lasting 10 minutes. Then, under nitrogen protection, they were carbonized in five temperature zones: 300, 500, 700, 1000, and 1400°C, with each zone lasting 20 seconds, to obtain carbon fibers.

[0054] Example 2: The difference between this embodiment and Embodiment 1 is that: Using 2,6-diaminopyridine / cyanuric acid as a supramolecular seed precursor monomer system (added at 5 wt% of acrylonitrile), the self-assembly process is as follows: Figure 3 As shown in the schematic diagram, sodium citrate is used as a multifunctional gel inducing agent; The coagulation bath composition is: 35 wt% DMSO / water solution, containing 5 wt% sodium citrate; The total draw ratio of the gelled nascent fibers after multi-stage draw was 33 times.

[0055] Example 3: The difference between this embodiment and Embodiment 1 is that: The monomer system using 2,4,6-triaminopyrimidine / barbituric acid as supramolecular seed precursor monomers, with a molar ratio of 2:1 and a total addition amount of 10 wt% of acrylonitrile, was used with ethylene glycol as a multifunctional gel induction agent. The coagulation bath consists of 28 wt% DMSO aqueous solution containing 3 wt% ethylene glycol.

[0056] Example 4: The difference between this embodiment and embodiment 1 is that in step (4), graphitization is performed after carbonization, that is, the carbonized fiber is heat-treated at 2500°C for 60 s in an argon atmosphere.

[0057] Comparative Example 1: The difference between this comparative example and Example 1 is as follows: The monomer system without supramolecular seed precursors is a traditional dry-jet wet spinning process. Specifically, in step (1), no supramolecular seed precursor monomer system is added during polymerization to obtain ordinary PAN.

[0058] In step (3), a DMSO / water solution with a mass concentration of 35% without any additives is used as a coagulation bath during spinning.

[0059] Other process parameters and preparation methods are the same as in Example 1.

[0060] The total draw ratio can only reach 28 times (a higher ratio will easily cause the yarn to break).

[0061] Comparative Example 2: The difference between this comparative example and Example 1 is that, in step (1), no supramolecular seed precursor monomer system is added during polymerization, resulting in ordinary PAN. Other process parameters and preparation methods are the same as in Example 1.

[0062] Comparative Example 3: The difference between this comparative example and Example 1 is that in step (3), a DMSO / water solution with a mass concentration of 35% without any additives is used as the coagulation bath during spinning.

[0063] Other process parameters and preparation methods are the same as in Example 1.

[0064] Comparative Example 4: The difference between this comparative example and Example 1 is as follows: In step (1), only 2,4,6-triaminopyrimidine was used as the supramolecular seed precursor monomer system during polymerization (the amount added was 3 wt% of acrylonitrile), and the content of other components and the preparation method were the same as in Example 1.

[0065] Comparative Example 5: The difference between this comparative example and Example 1 is as follows: In step (1), only barbituric acid was used as the supramolecular seed precursor monomer system during polymerization (the amount added was 3 wt% of acrylonitrile), and the content of other components and the preparation method were the same as in Example 1.

[0066] Comparative Example 6: The difference between this comparative example and Example 1 is as follows: In step (1), the molar ratio of 2,4,6-triaminopyrimidine to barbituric acid in the supramolecular seed precursor monomer system is 3:1, and other process parameters and preparation methods are the same as in Example 1.

[0067] Comparative Example 7: The difference between this comparative example and Example 1 is as follows: In step (1), the molar ratio of 2,4,6-triaminopyrimidine to barbituric acid in the supramolecular seed precursor monomer system is 1:3, and other process parameters and preparation methods are the same as in Example 1.

[0068] Experimental Example 1: This experimental example analyzes the morphology of the polyacrylonitrile precursor and carbon fibers obtained in Examples 1 and 2. like Figure 5 and Figure 7 As shown, the polyacrylonitrile precursor fibers obtained in Examples 1 and 2 have a uniform and smooth surface with no obvious defects, proving that the spinning process parameters set in the examples and comparative examples are reasonable and can obtain homogeneous polyacrylonitrile precursor fibers.

[0069] like Figure 6 As shown in the XRD pattern, the small peaks around 9° and 12° represent the synthesis of supramolecular seeds, while the peaks at 17° and 29° originate from the crystalline structure of PAN.

[0070] like Figures 8-9 As shown, the carbon fiber samples obtained in Examples 1 and 2 are uniform and straight, with smooth and regular surfaces and no defects such as broken fibers. This proves that the heat treatment process parameters set in the examples and comparative examples are reasonable and can produce homogeneous carbon fiber samples.

[0071] Experimental Example 1: This experimental example analyzes the performance of the carbon fibers prepared in the examples and comparative examples. The specific test data is shown in Table 1: Table 1

[0072] As shown in Table 1, the strength and modulus of Examples 1-3 are significantly better than those of the comparative examples, indicating that the integrated carbon fiber preparation scheme based on the self-assembled supramolecular seed system of this invention effectively improves the mechanical properties of carbon fibers. Among them, Example 1 (strength 5.8 GPa, modulus 298 GPa) has the best performance. Its supramolecular seed system (2,4,6-triaminopyrimidine / barbituric acid, molar ratio 1:1) and the auxiliary agent (m-phenylenediamine) have the best matching, and the total draw ratio reaches 35 times, laying the structural foundation for high orientation and uniform graphitization. Example 2 (5.6 GPa, 292 GPa) uses the 2,6-diaminopyridine / cyanuric acid system and sodium citrate auxiliary agent, with a total draw ratio of 33 times, and its performance is slightly lower than that of Example 1. Example 3 (5.5 GPa, 290 GPa) uses ethylene glycol as an auxiliary agent, with a slightly lower total draw ratio and slightly inferior performance to the previous two, but it is still significantly better than the comparative examples. Further observation of Example 4 shows that after graphitization treatment at 2500℃, the fiber modulus jumped to 400 GPa, which strongly proves the core role of supramolecular seeds as "graphitization templates" in inducing the orderly arrangement of carbon layers at high temperatures.

[0073] In contrast, Comparative Example 1, lacking supramolecular seeds and with no additives in the coagulation bath, lacked a synergistic gelation mechanism, resulting in poor drawability (total draw ratio of 28 times) and a significant decrease in strength and modulus (4.6 GPa and 280 GPa, respectively). Comparative Examples 2 (with only additives and no seeds) and 3 (with only seeds and no additives) showed performance inferior to Example 1, demonstrating the necessity of a synergistic mechanism between seeds and additives. Comparative Examples 4 and 5, using only single seed precursor monomers, failed to form complementary hydrogen bonds, resulting in weak gel induction. The final carbon fiber strength and modulus were 4.5 GPa and 270 GPa, respectively, confirming that the synergistic complementarity between the first and second monomers is crucial for constructing effective supramolecular seeds. Comparative Examples 6 and 7 investigated the monomer ratio variable. The molar ratio of the two monomers was adjusted to 3:1 and 1:3, respectively. The resulting fiber properties (4.7 GPa / 282 GPa and 4.6 GPa / 280 GPa) were significantly lower than those of Example 1. This strongly demonstrates that only under an ideal stoichiometric ratio close to 1:1 can the first and second monomers construct the highest density supramolecular self-assembly network through complementary hydrogen bonds. Any imbalance in the ratio will weaken the seed crystal's ability to induce the gelation process because the monomers cannot be completely paired, thus limiting the final performance of the fiber's strength and tensile properties.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An integrated preparation method for high-strength, high-modulus carbon fibers, characterized in that, Includes the following steps: An aqueous solution of acrylonitrile monomer and supramolecular seed precursor monomer is mixed, and an initiator is added to carry out a polymerization reaction to obtain a polyacrylonitrile-based polymer slurry containing supramolecular seed precursor structural units. After the slurry is dried, a polymer powder is obtained. The polymer powder is dissolved in an organic solvent to obtain a spinning solution. The polymerization reaction takes place in a plug flow reactor. The spinning solution is processed through a dry-jet-gel-wet spinning process, and then immersed in a coagulation bath to obtain nascent fibers. The nascent fibers are then processed into precursor fibers through a post-treatment process, and then carbon fibers are produced through a pre-oxidation and carbonization process. The coagulation bath is a DMSO / water solution containing an auxiliary agent; the auxiliary agent is a compound containing at least two functional groups in its molecule that can form polar interactions, ionic interactions or coordination interactions with cyano groups or supramolecular seed crystals on the polyacrylonitrile molecular chain. The supramolecular seed precursor monomer accounts for 0.1~10 wt% of the mass of the acrylonitrile monomer; the initiator accounts for 0.1~10 wt% of the mass of the acrylonitrile monomer. The supramolecular seed precursor monomer comprises a first monomer and a second monomer. The first monomer is selected from one or more of 2,4,6-triaminopyrimidine, 2,6-diaminopyridine, melamine and its derivatives. The second monomer is selected from one or more of barbituric acid, cyanuric acid and its derivatives. The molar ratio of the first monomer to the second monomer is 1:2 to 2:

1. The carbon fiber has a tensile strength ≥4.7 GPa, a tensile modulus ≥290 GPa, and a uniform fiber cross-sectional structure with no significant core-sheath structure.

2. The integrated preparation method as described in claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 50-80°C for 1.5-2.5 h, and the total conversion rate of the supramolecular seed precursor monomer is maintained at 70%-95%. The plug flow reactor is a tubular reactor or a multi-reactor reactor in series, and the material flows in a plug flow pattern within the reactor. The organic solvent is selected from one or more of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide; the solid content of the polymer powder in the spinning solution is 10% to 30%.

3. The integrated preparation method as described in claim 1, characterized in that, The concentration of DMSO in the coagulation bath is 20% to 80%, the concentration of the additive is 0.1% to 20%, and the temperature of the coagulation bath is 2 to 80°C.

4. The integrated preparation method as described in claim 1, characterized in that, The additive is selected from one or more of polyols, polyamines, polyvalent metal salts, and polybasic organic acids and / or their salts; wherein the polyols are selected from at least one of ethylene glycol, glycerol, pentaerythritol, polyvinyl alcohol, and hexahydroxycyclohexanol; the polyamines are selected from at least one of ethylenediamine, p-phenylenediamine, m-phenylenediamine, and dicyandiamide; the polyvalent metal salts are selected from at least one of calcium chloride, zinc chloride, aluminum sulfate, and ferric nitrate; and the polybasic organic acids and / or their salts are selected from at least one of citric acid, sodium citrate, tartaric acid, potassium sodium tartrate, ethylenediaminetetraacetic acid, and disodium ethylenediaminetetraacetic acid.

5. The integrated preparation method as described in claim 1, characterized in that, The dry-jet-gel-wet spinning process involves the spinning solution being extruded from the spinneret, passing through an air layer to allow the fine stream to undergo surface pre-curing, initial molecular chain orientation, seed crystal pre-assembly, and initial gelation of the spinning solution in the air before entering the coagulation bath; wherein the length of the air layer is 3~20 mm. The post-processing steps include washing, stretching, oiling, drying and densification, and steam stretching of the nascent fibers. The total draw ratio in the process of turning the nascent fibers into raw yarn is 20 to 40 times.

6. The integrated preparation method as described in claim 1, characterized in that, The pre-oxidation treatment is carried out in an air atmosphere at a temperature of 200~300℃; the carbonization treatment is carried out in an inert atmosphere or under vacuum at a temperature of 300℃~1600℃.

7. A high-strength, high-modulus carbon fiber, prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the high-strength, high-modulus carbon fiber as described in claim 7 in the aerospace or transportation fields.

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