High-temperature-resistant water-based sizing agent as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of advanced composite materials, and particularly relates to a high-temperature-resistant water-based sizing agent, a preparation method thereof and application of the high-temperature-resistant water-based sizing agent in a carbon fiber reinforced polyimide composite material. The water-based sizing agent is prepared by taking an aromatic triamine monomer, aromatic anhydride and an ionized functional agent as raw materials through a controllable condensation polymerization reaction. The high-temperature-resistant and high-temperature-resistant liquid crystal composition has excellent solubility, high-temperature stability and long-term storage stability, and 5% thermal weight loss temperature is higher than 550 DEG C. The sizing agent can significantly improve the interface bonding strength of carbon fibers and a resin matrix. The water-based sizing agent provided by the invention has the characteristics of high temperature resistance and interface enhancement function, can meet the strict requirements of the aerospace field on the mechanical properties of composite materials such as carbon fiber / polyimide in an extreme thermal environment, and has important application value.

Description

Technical Field

[0001] This invention belongs to the field of advanced composite materials technology, specifically relating to a high-temperature resistant water-based sizing agent, its preparation method, and its uses. Background Technology

[0002] Carbon fiber reinforced polymer matrix composites (CFRPs), with their high specific strength, high specific modulus, corrosion resistance, fatigue resistance, and excellent designability, have become indispensable strategic structural materials in aerospace, defense, transportation, and high-end civilian fields. As modern industrial technology advances towards high speed, high pressure, and extreme environments, traditional general-purpose thermosetting resins (such as epoxy resins and vinyl ester resins) are no longer sufficient to meet the long-term service requirements of CFRPs in high-temperature environments due to their limited heat resistance. To meet the demands for high-temperature resistance and high strength, special engineering plastics such as polyimide (PI), polyetheretherketone (PEEK), and polyphenylene sulfide (PPS) have gradually become the preferred matrix for composite materials. Among them, polyimide resin, due to its excellent heat stability (long-term service temperature can reach above 300℃) and superior mechanical properties, has become one of the main matrix resins for manufacturing high-temperature resistant carbon fiber composites.

[0003] However, carbon fibers undergo high-temperature graphitization during preparation, resulting in high surface chemical inertness, low surface energy, and few polar functional groups. This leads to poor wettability between the carbon fiber and the resin matrix, making it difficult to form strong interfacial chemical bonds. The low interfacial bonding strength makes the composite material prone to interfacial debonding under stress, severely limiting its overall performance. Surface modification of carbon fibers is one of the most effective ways to improve the interfacial bonding strength of composite materials.

[0004] Among numerous surface modification technologies (such as vapor-phase oxidation, electrochemical oxidation, and plasma treatment), water-based sizing technology is currently the mainstream modification method widely used in industry due to its simple process, continuous production capability, and ability to protect fibers from abrasion. Sizing agents form an extremely thin polymer transition layer on the fiber surface, which not only protects the fiber but also connects to the matrix through physical or chemical interactions, effectively improving the interfacial bonding between carbon fibers and the resin matrix. Currently, the most commonly used sizing agents in the industry include epoxy resin emulsions, polyurethane (PU), polyvinyl alcohol (PVA), and vinyl esters. These sizing agents perform excellently for low- and medium-temperature curing systems such as epoxy and polyester resins, but face significant challenges when applied to high-temperature resistant resin matrices such as polyimide. Because composite materials made with polyimide and other resin matrices typically require extremely high molding and processing temperatures (often reaching 300℃ or even above 380℃), while the thermal decomposition temperatures of the aforementioned sizing agents are generally low, usually undergoing significant thermal degradation around 200℃ to 250℃, the sizing agent layer decomposes before the matrix resin cures or melts. The resulting small-molecule volatiles easily form pores and defects at the interface, affecting the interfacial properties of the composite material. Furthermore, conventional epoxy or polyurethane sizing agents differ significantly from polyimide in molecular structure, exhibiting not only mismatched solubility parameters but also a lack of effective chemically reactive sites, making it difficult to achieve molecular-level fusion and strong chemical bonding. This is a key reason why the performance of high-performance, high-temperature resistant composite materials is difficult to achieve and why the molding pass rate is low.

[0005] To address the aforementioned bottlenecks, the development of polyimide sizing agents suitable for high-temperature resins has become an urgent need. However, existing technologies mainly suffer from two approaches and their inherent drawbacks: First, solvent-based polyimide sizing agents utilize high-boiling-point, highly polar solvents (such as DMAc and NMP) for dissolution. While offering good wetting properties, these solvents are highly toxic, prone to residue, and difficult to recycle, causing environmental pollution and leading to porosity in the composite material. Second, traditional water-based polyimide sizing agents inherently present a contradiction between water solubility and heat resistance in their molecular structure design. To impart water solubility or water dispersibility to polyimide resins, existing modification strategies typically require introducing a large number of flexible aliphatic chains, polyether segments, or polar hydrophilic groups (such as carboxyl groups and sulfonic acid groups) into the molecular backbone. Chen et al. designed a series of novel carboxylated waterborne polyimide sizing agents with different fat ratios and applied them to the interfacial modification of carbon fiber reinforced polyether ether ketone composites (Composites Part B: Engineering 2025;298:112388); Yuan et al. used soluble semi-aliphatic polyimide (S-SA-PI) suspension to sizing carbon fibers and applied it to the interfacial property enhancement of polyether imide composites (Composites Communications 2021;28:100982).

[0006] However, these flexible or hydrophilic structures introduced to achieve "water-based" properties become weak points with poor thermal stability. This disrupts the integrity of the original rigid aromatic heterocyclic structure of polyimide, significantly reducing the thermal decomposition temperature and glass transition temperature of the sizing agent. This makes it difficult for existing water-based polyimide sizing agents to maintain the stability of the water-based dispersion system while simultaneously ensuring thermal stability at extreme high temperatures, thus failing to truly meet the molding process requirements of high-performance polyimide composites.

[0007] Therefore, developing a novel polyimide sizing agent that combines excellent heat resistance, environmental friendliness, and good interfacial compatibility is of great application value and practical significance for improving the overall performance of high-temperature resistant carbon fiber composites. Summary of the Invention

[0008] Based on the aforementioned technical bottlenecks, this invention focuses on developing a novel high-temperature resistant waterborne polyimide sizing system. The waterborne sizing agent of this invention is based on the unique aromatic heterocyclic rigid structure of polyimide material, with a thermal decomposition temperature exceeding 550℃. After high-temperature thermo-oxidative aging, it still maintains excellent compatibility with the polyimide resin matrix, achieving excellent interfacial bonding strength and high-temperature stability in the composite material. This system is expected to overcome the high-temperature molding temperature limitations of high-temperature resistant composite materials, enabling the processing and molding of high-quality carbon fiber composite materials and the long-term maintenance of interfacial properties under extreme environments, thus promoting the upgrading of my country's high-performance composite materials industry.

[0009] This invention provides a high-temperature resistant aqueous sizing agent, wherein the sizing agent is a compound of formula I, or a salt thereof, or a stereoisomer thereof, or a solvate thereof: Formula I in, Ring A is selected from C6-C 20 The aryl group; R1 is selected from hydroxyl, amino, and mercapto groups; The structure of R2 is selected from L1 is selected from amide bonds, C2-C 10 Alkylenes containing amide bonds, where L2 is selected from alkynes, C3-C 10 Alkylene containing an alkene bond, R3 is selected from C1-C 10 Carboxyl group, C1-C 10 amide group, C1-C 10 The ester group, n, is selected from any one of 1-10; m is selected from any one of 1-10.

[0010] Preferably, ring A is selected from C6 aryl groups; and / or, R1 is selected from hydroxyl groups; And / or, L1 is selected from amide bond, L2 is selected from alkyne bond, R3 is selected from C1 carboxyl group, and n is selected from 1; And / or, m is selected from 1.

[0011] Preferably, the salt is selected from triethylamine salt, pyridine salt, and N,N-dimethylethanolamine salt.

[0012] Preferably, the structural formula shown in Formula I includes the following structure: .

[0013] This invention provides a method for preparing the aqueous sizing agent described in any one of the above claims, comprising the following steps: The product is obtained by reacting reactant 1 with reactant 2.

[0014] Preferably, the reaction conditions include: a reaction time of 1-24 h, a reaction temperature of 25-100°C, and the reaction being carried out under anhydrous conditions; And / or, the solvent for the reaction is selected from any one or a combination of several of N,N'-dimethylacetamide, N-methylpyrrolidone, N,N'-dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran; And / or, when the sizing agent is a salt of the compound shown in Formula I, the preparation method further includes: mixing the compound shown in Formula I with an ionizing reagent; the mixing time is 30-180 min.

[0015] The present invention provides a high-temperature resistant aqueous sizing agent solution, comprising 0.25-5 wt% of any one of the above-mentioned aqueous sizing agents.

[0016] Preferably, the mass concentration of the aqueous sizing agent solution is 1 wt%.

[0017] Preferably, the solvent of the aqueous sizing agent solution is selected from at least one or two of dimethylacetamide, water, ethanol, and acetone.

[0018] The present invention provides the use of the aqueous sizing agent described in any one of the above claims and the aqueous sizing agent solution described in any one of the above claims in the preparation of carbon fiber composite materials.

[0019] This invention provides a high-temperature resistant carbon fiber composite material, which is prepared by sizing carbon fiber using any one of the above-mentioned aqueous sizing agents or aqueous sizing agent solutions.

[0020] Preferably, the sizing process includes: immersing the carbon fiber in the aqueous sizing agent solution for heat treatment, thereby obtaining the final product.

[0021] Preferably, the soaking time is 30-180 min; and / or, the heat treatment step includes: treating at 80-250℃ for 1-8 h, then raising the temperature to 260-320℃ and treating for 30-240 min.

[0022] The compounds and derivatives provided in this invention can be named according to the IUPAC (International Union of Pure and Applied Chemistry) or CAS (Chemical Abstracts Service, Columbus, OH) nomenclature systems.

[0023] Regarding the definition of terms used in this invention: Unless otherwise stated, the initial definitions provided for groups or terms herein apply to the groups or terms used throughout this specification; for terms not specifically defined herein, the meanings that a person skilled in the art would give them should be given based on the disclosure and context.

[0024] "Substitution" refers to the replacement of hydrogen atoms in a molecule by other different atoms or molecules.

[0025] The minimum and maximum carbon atom content in hydrocarbon groups are indicated by a prefix, for example, the prefix C. a～b Alkyl indicates any alkyl group containing "a" to "b" carbon atoms. Therefore, for example, "C 1～4 "Alkyl" refers to an alkyl group containing 1 to 4 carbon atoms.

[0026] "Aryl" refers to an aromatic ring containing a specified number of member atoms and having a single ring, such as the benzene ring, which is a C6 aryl ring.

[0027] "Ester group" refers to a group containing at least one ester group. And a saturated alkane chain having a specified number of carbon atoms, for example It is a C2 ester group.

[0028] "Carboxyl group" refers to a saturated alkane chain containing at least one carboxyl group and having a specified number of carbon atoms, such as -CH2COOH, which is a C2 carboxyl group.

[0029] "Amide group" refers to a group containing at least one And a saturated alkane chain having a specified number of carbon atoms, for example It is a C2 amide group.

[0030] "Amide bond" refers to ; "Alkylenes containing amide bonds" refers to alkylenes consisting of a saturated alkane chain having a specified number of carbon atoms, wherein amide bonds are inserted, for example... or It is an alkylene group containing an amide bond at C2.

[0031] "Alkyne bond" refers to ; "Alkylenes containing alkynes" refers to alkylenes consisting of a saturated alkane chain having a specified number of carbon atoms, wherein alkynes are inserted, for example... It is a C3 acetylene bond.

[0032] "Hydroxy group" refers to -OH.

[0033] "Amino" refers to -NH2.

[0034] "Thiol group" refers to -SH.

[0035] This invention provides a high-temperature resistant aqueous sizing agent through raw material selection and preparation process. The sizing agent is prepared via a controlled polycondensation reaction using aromatic triamine monomers, aromatic anhydrides, and ionized functional agents as reactants. It exhibits good solvent universality and long-term storage stability, with a 5% thermogravimetric temperature >500℃. When used in solution impregnation processes to treat carbon fiber surfaces, this sizing agent significantly improves the interfacial bonding strength between carbon fiber and the resin matrix, maintaining excellent interfacial strength even after high-temperature treatment at 400℃. The aqueous sizing agent provided by this invention combines high-temperature resistance with interfacial reinforcement, effectively meeting the stringent requirements of the aerospace industry for the mechanical properties of carbon fiber / polyimide composites under extreme thermal environments. It has significant application value and promising application prospects.

[0036] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0037] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the synthesis and chemical structure of the aqueous sizing agent of the present invention; Figure 2 The figures show the solubility results of the aqueous sizing agent in Experiment 1 under different solvents. (a) shows the solubility characterization results in water, ethanol and acetone, and (b) shows the solubility results in water at different concentrations. Figure 3 The following are the storage stability results of the water-based sizing agent in Experiment Example 2: (a) is the room temperature stability result, (b) is the high temperature stability result, (c) is the dilution stability result, (d) is the centrifugation stability result, and (e) is the potential stability result. Figure 4 The graph shows the thermal degradation stability results of the water-based sizing agent in Experiment Example 3, where (a) is the thermogravimetric analysis (TGA) test result graph and (b) is the derivative thermogravimetric analysis (DTG) curve graph. Figure 5 The figures show the interlaminar shear strength results of carbon fiber composites after sizing with sizing agent. (a) shows the interlaminar shear strength results of carbon fiber-polyimide composites after annealing at room temperature with sizing agents of different concentrations and without sizing agent. (b) shows the interlaminar shear strength results of carbon fiber-polyimide composites after annealing at 200°C, 300°C, and 400°C with sizing agents of different concentrations and without sizing agent.

[0039] Figure 6 The figure shows the interlaminar shear strength results of the commercial T700 grade carbon fiber material after annealing at different temperatures, which is Comparative Example 1.

[0040] Figure 7 Figure 1 shows the interfacial bonding strength of carbon fiber-polyimide composites after sizing with no sizing agent and with different concentrations of sizing agent. Detailed Implementation

[0041] Unless otherwise specified, all reagents and materials used in the following examples and experimental cases are commercially available.

[0042] Example 1: A high-temperature resistant water-based sizing agent and its preparation method The synthesis process of the water-based sizing agent in this embodiment is as follows: Figure 1 As shown, the specific steps are as follows: Step 1: Pararosaniline base (hereinafter referred to as PA) was added to a three-necked flask containing N,N'-dimethylacetamide (DMAc). After complete dissolution at 25 °C, 4-Phenylethynylphthalic anhydride (hereinafter referred to as 4-PEPA) was added. Under the protection of a drying tube containing anhydrous calcium chloride, the reaction was carried out at room temperature for 3 h to obtain an amide acid with trifunctional phenylethynyl groups, wherein the molar ratio of PA to 4-PEPA was 1:3. Step 2: At room temperature, add triethylamine in an amount equal to the carboxyl group to the reaction system of Step 1. After reacting at room temperature for 30 min, the amic acid is ionized into amic acid salt, which is a 20 wt% aqueous sizing agent dissolved in DMAc. This sizing agent is named PA-3PEPA.

[0043] Example 2: A carbon fiber-polyimide composite material The sizing agent PA-3PEPA prepared in Example 1 was used to sizing carbon fibers. The sizing method is as follows: (1) Dilute 20wt% of the aqueous sizing agent dissolved in DMAc with deionized water to a concentration of 1wt% to obtain a sizing agent solution; (2) Immerse the sizing agent solution in the sizing agent solution for 30 minutes, then take it out and treat it in an 80°C forced-air oven for 8 hours to remove surface water residue. Then heat it to 280°C for 120 minutes to complete the thermal imidization.

[0044] In other embodiments, the concentration of the sizing agent solution may also be 0.5 wt% or 1.5 wt%.

[0045] Comparative Example 1 Commercial T700 grade carbon fiber was selected for comparison. Commercial T700 carbon fiber is T700 grade carbon fiber produced by Toray Industries, Inc. of Japan. The tow specification is 12k and it comes with epoxy sizing agent.

[0046] The technical solution of the present invention will be further explained through experiments below.

[0047] Experiment Example 1: Solubility in Multiple Solvents I. Experimental Methods (1) The 20wt% PA-3PEPA prepared in Example 1 was diluted 10 times with deionized water, ethanol and acetone, which are poor solvents for polyimide, and the dispersion was observed.

[0048] (2) Deionized water was selected as the solvent to further dilute the 20wt% PA-3PEPA sizing agent prepared in Example 1 to concentrations of 0.5wt%, 1wt% and 1.5wt%, observe the dispersion, and characterize the Tyndall effect using a laser pointer.

[0049] II. Experimental Results Dispersion results in poor solvents, such as Figure 2 As shown in (a), after PA-3PEPA is diluted in these unsuitable solvents, the solution remains clear and transparent without precipitation, indicating that PA-3PEPA has excellent solubility in unsuitable solvents of polyimide after ionization. This is closely related to the selection of raw materials and preparation method of the polyimide sizing agent of the present invention.

[0050] Dispersion in water as follows Figure 2 As shown in (b), with water as the solvent, the PA-3PEPA solutions at different concentrations are all clear and transparent; when the Tyndall effect is characterized using a laser pointer, a bright "path" can be observed, indicating that the solution is well dispersed and distributed at the nanoscale.

[0051] The above results indicate that the aqueous sizing agent prepared by this invention can be stably dissolved in a variety of solvents.

[0052] Experiment Example 2 Storage Stability The stability of sizing agents directly affects their production, storage, and use. To ensure the performance reliability and process adaptability of the water-based sizing agent of this invention in practical applications, stability tests were conducted on the water-based sizing agent of this invention in multiple dimensions. The sample tested in this experimental example is a 20wt% PA-3PEPA sizing agent prepared in Example 1.

[0053] I. Experimental Methods 1. Stability at room temperature PA-3PEPA was dissolved in deionized water at a concentration of 1.5 wt%, and the solution was left at room temperature for 30 days and 60 days, respectively, and the dispersion of the solution was observed.

[0054] 2. High temperature stability PA-3PEPA was dissolved in deionized water at a concentration of 1.5 wt%, and treated at 60 °C for 24 h. The dispersion of the solution was then observed.

[0055] 3. Dilution stability PA-3PEPA was dissolved in deionized water and diluted to concentrations of 1.5wt%, 1wt%, and 0.5wt%, respectively. The dispersion of the solutions was then observed.

[0056] 4. Centrifugal stability PA-3PEPA was dissolved in deionized water at a concentration of 1 wt‰, and centrifuged at 12000 rpm for 30 min. The dispersion of the solution was then observed.

[0057] 5. Potential stability PA-3PEPA was dissolved in deionized water, and the zeta potential was measured using a dynamic light scattering (DLS) instrument.

[0058] II. Experimental Results 1. Stability at room temperature The results of room temperature stability are as follows Figure 3 As shown in (a), the PA-3PEPA solution remained clear and transparent after 30 and 60 days of storage, demonstrating excellent stability.

[0059] 2. High temperature stability High temperature stability results are as follows Figure 3 As shown in (b), after treatment at 60°C for 24 hours, the PA-3PEPA solution remained clear, indicating that PA-3PEPA has good high-temperature stability.

[0060] 3. Dilution stability Dilution stability results are as follows Figure 3As shown in (c), the PA-3PEPA solution did not exhibit sedimentation or aggregation under different concentration gradients, indicating that PA-3PEPA has good dilution stability.

[0061] 4. Centrifugal stability Centrifugation stability results are as follows Figure 3 As shown in (d), the comparison results before and after centrifugation show that after high-speed and long-term centrifugation, the PA-3PEPA solution remains clear and transparent, without sedimentation or aggregation, indicating that PA-3PEPA has good centrifugal stability.

[0062] 5. Potential stability The potential stability results are as follows Figure 3 As shown in (e), the average value of the PA-3 PEPAZeta potential is -56.1mV, demonstrating excellent stability.

[0063] The above multi-dimensional stability characterization of PA-3PEPA demonstrates its excellent stability, ensuring its practical application.

[0064] Experimental Example 3 Thermal Degradation Stability The thermal degradation stability of sizing agents is crucial for ensuring the structural stability of composite materials during high-temperature processes and for constructing high-strength, heat-resistant composite material interfaces. The sample tested in this experiment was a 20 wt% PA-3PEPA sizing agent prepared in Example 1.

[0065] I. Experimental Methods To gain a comprehensive understanding of the stability of PA-3PEPA under high-temperature conditions, this experimental example involved performing thermogravimetric analysis (TGA) on PA-3PEPA after curing at 300°C for 150 minutes. Data on its thermal degradation behavior were obtained in both air and nitrogen atmospheres. 5wt% This refers to the temperature at which the sample mass decreases by 5% of its original mass, and is typically used to assess the thermal stability of materials.

[0066] II. Experimental Results The results of the thermal degradation experiment are as follows Figure 4 As shown, PA-3PEPA under a nitrogen (N2) atmosphere at T 5wt% The temperature was 572.74℃, while the temperature in an air atmosphere was... 5wt% The result is 550.34℃. This indicates that PA-3PEPA exhibits very high thermal degradation stability under both different atmospheres, especially in a nitrogen atmosphere, where it demonstrates excellent heat resistance, remaining stable at higher temperatures and slowing down the degradation process.

[0067] Patent CN 118146113 A discloses an ammonate acid aqueous sizing agent with a thermal weight loss temperature in air between 399 and 404°C. Compared with this patent, the ammonate acid aqueous sizing agent of the present invention has better thermal degradation stability.

[0068] The above results demonstrate that PA-3PEPA possesses excellent high-temperature resistance to degradation, maintaining its chemical structure unchanged during high-temperature curing and use. This superior thermal stability not only facilitates the smooth application of PA-3PEPA in high-temperature curing processes but also provides a solid foundation for constructing the interfacial structure of high-strength, heat-resistant composite materials. A high-temperature stable sizing agent can form a robust bonding layer at the interface of the composite material, preventing interface degradation or failure under high-temperature conditions, thereby ensuring the mechanical properties and reliability of the composite material under high-temperature operating conditions.

[0069] Experiment 4: Determination of interfacial properties after composite with carbon fiber The interlaminar shear strength and interfacial strength of carbon fiber-polyimide composites are the core properties for evaluating the effect of sizing agents on interfacial modification.

[0070] I. Experimental Methods 1. Test Object (1) Carbon fiber composite material prepared by Toray Industries T700 carbon fiber in Comparative Example 1; (2) Carbon fiber-polyimide composite material was prepared according to the method of Example 2, wherein the concentrations of PA-3PEPA sizing agent solution were 0, 0.5wt%, 1wt%, and 1.5wt%.

[0071] 2. Determination of interlaminar shear strength The carbon fiber composites prepared from commercially available T700 carbon fiber with self-sizing agent (Comparative Example 1) and carbon fiber-polyimide composites with different sizing agent concentrations were annealed at different temperatures (200℃, 24h; 300℃, 24h; 400℃, 12h), and their interlaminar shear strengths were measured using the following methods: The interlaminar shear strength of the composite material was determined using a universal testing machine (Instron 5567, USA) according to standard ASTM D 2344. The ILSS was calculated using the following formula: Where Pmax (N) represents the maximum load at which the composite specimen undergoes effective shear failure, and b (mm) and h (mm) represent the width and thickness of the specimen. At least 5 valid data points are tested for each group of specimens and the average value is taken.

[0072] 3. Determination of interfacial shear strength The interfacial shear strength of the composite material was evaluated using a polyimide droplet micro-debonding method. The instrument used was an improved composite material interfacial performance evaluation device (Fuyouma Technology, China). First, a single filament was separated from the carbon fiber bundle, stretched taut, and its ends were glued to a specially designed square mold. A small amount of prepared polyimide resin was applied to the carbon fiber filament using extremely fine tweezers. Under surface tension, the polyimide resin on the fiber surface formed microspheres. The sample was then cured under the following conditions: 200 ℃ / 1 h + 240 ℃ / 2 h + 300 ℃ / 1.5 h + 380 ℃ / 3 h, yielding the test sample. During testing, a suitable-sized polyimide droplet microsphere was selected using a built-in optical microscope. A scraper was moved below the microsphere, and the distance between the two scrapers was adjusted to be slightly larger than the diameter of the carbon fiber, thus securing the epoxy microsphere. During the test, the scraper moving at a speed of 0.1 mm / min resulted in interfacial debonding between the polyimide microspheres and carbon fibers under shearing action. The IFSS data can be calculated using the formula: Where F max (N) is the maximum load force that causes the epoxy microspheres to debond, d (m) is the diameter of the carbon fiber, and L (m) is the length of the fiber embedded in the epoxy microsphere.

[0073] II. Experimental Results 1. Interlaminar shear strength The interlaminar shear strength results of carbon fiber-polyimide composites with different sizing agent concentrations are as follows: Figure 5 As shown in Table 1, compared with sizing-free carbon fiber, the interlaminar shear strength of the carbon fiber-polyimide composite material is significantly improved. In particular, the improvement effect is best when the concentration of PA-3PEPA sizing agent is 1-1.5wt%, with an increase of 19.39 MPa in interlaminar shear strength at room temperature, 20 MPa after annealing at 200℃ (24h), 28 MPa after annealing at 300℃ (24h), and 14 MPa after annealing at 400℃ (12h). This indicates that the water-based sizing agent of the present invention significantly improves the interlaminar shear strength of carbon fiber, especially the interlaminar shear strength after high-temperature annealing.

[0074] Compared to the commercially available carbon fiber composite material in Comparative Example 1, its interlaminar shear strength performance under high-temperature conditions is relatively limited. Figure 6 When annealed at 300℃ for 24 hours, the interlaminar shear strength decreased by 16.1% compared to room temperature. However, the interlaminar shear strength of the carbon fiber-polyimide composite material of the present invention, after annealing at 300℃ for 24 hours, only decreased by 2.21-5.97% compared to room temperature. This indicates that the water-based sizing agent of the present invention significantly improves the performance of carbon fiber at high temperatures, and its effect is superior to that of epoxy resin-based sizing agents.

[0075] Table 1 Interlaminar shear strength performance data Patent CN 118727449 A discloses a high-temperature resistant polyimide water-based carbon fiber sizing agent. The carbon fiber-polyimide composite material prepared by sizing carbon fibers with this sizing agent exhibits an interlaminar shear strength between 150-156 MPa at room temperature and between 78-85 MPa at 300°C. Compared to this patent, the carbon fiber-polyimide composite material of this invention demonstrates significantly stronger high-temperature resistance.

[0076] Therefore, the aqueous sizing agent of the present invention significantly improves the interlaminar shear strength of carbon fibers, especially the interlaminar shear strength after high-temperature annealing.

[0077] 2. Interface bonding strength The results of the interface bonding strength are as follows Figure 7 As shown, the interfacial bonding strength of carbon fiber-polyimide composites prepared with different concentrations exhibits significant differences. In particular, the PA-3PEPA sizing agent solution with a concentration of 1wt% shows the best improvement effect, increasing the interfacial bonding strength by 17.26 MPa, which is 30.5% higher than that of unsizing carbon fiber. The results indicate that the modification of the aqueous sizing agent provides the composite material with excellent interfacial properties.

[0078] Based on the combined results of interlaminar shear strength and interfacial bonding strength, this experimental example demonstrates that the aqueous sizing agent of the present invention significantly improves the interfacial properties of carbon fibers. In particular, the improvement effect is best when the concentration of the sizing agent solution is 1 wt%.

[0079] The above experimental results show that the aqueous sizing agent prepared in this invention can be stably dissolved in a variety of solvents; it has excellent storage stability and excellent thermal degradation stability; carbon fiber-polyimide composite material was prepared by sizing carbon fiber with this aqueous sizing agent, and the interlaminar shear strength and interfacial bonding strength of the composite material were significantly improved, especially the properties at high temperature were significantly improved; compared with carbon fiber composite material prepared by epoxy resin-based sizing agent, carbon fiber-polyimide composite material has better performance at high temperature.

[0080] As can be seen from the above embodiments and experimental examples, this invention provides a high-temperature resistant aqueous sizing agent through optimized raw materials and preparation process. This sizing agent is prepared via a controlled polycondensation reaction using aromatic triamine monomers, aromatic anhydrides, and ionized functional agents as reactants. It exhibits good solvent universality and long-term storage stability, with a 5% thermogravimetric temperature >500℃. When used in solution impregnation processes to treat the surface of carbon fibers, this sizing agent significantly improves the interfacial bonding strength between carbon fibers and the resin matrix, especially maintaining excellent interfacial strength even after high-temperature treatment at 400℃. The aqueous sizing agent provided by this invention combines high-temperature resistance with interfacial reinforcement, effectively meeting the stringent requirements of the aerospace field for the mechanical properties of carbon fiber / polyimide composites under extreme thermal environments. It has significant application value and promising application prospects.

Claims

1. A high-temperature resistant water-based sizing agent, characterized in that, The sizing agent is a compound of formula I, or a salt thereof, or a stereoisomer thereof, or a solvate thereof: Formula I in, Ring A is selected from C6-C 20 The aryl group; R1 is selected from hydroxyl, amino, and mercapto groups; The structure of R2 is selected from L1 is selected from amide bonds, C2-C 10 Alkylenes containing amide bonds, where L2 is selected from alkynes, C3-C 10 Alkylene containing an alkene bond, R3 is selected from C1-C 10 Carboxyl group, C1-C 10 amide group, C1-C 10 The ester group, n, is selected from any one of 1-10; m is selected from any one of 1-10.

2. The aqueous sizing agent according to claim 1, characterized in that: Ring A is selected from a C6 aryl group; and / or, R1 is selected from a hydroxyl group; And / or, L1 is selected from amide bond, L2 is selected from alkyne bond, R3 is selected from C1 carboxyl group, and n is selected from 1; And / or, m is selected from 1.

3. The aqueous sizing agent according to claim 1, characterized in that: The salt is selected from triethylamine salt, pyridine salt, and N,N-dimethylethanolamine salt.

4. The aqueous sizing agent according to claim 1, characterized in that, The structural formula shown in Equation I includes the following structures: 。 5. A method for preparing the aqueous sizing agent according to any one of claims 1-4, characterized in that, Includes the following steps: The product is obtained by reacting reactant 1 with reactant 2.

6. A high-temperature resistant aqueous sizing agent solution, characterized in that, It contains an aqueous sizing agent according to any one of claims 1-4 at a mass concentration of 0.25-5 wt%.

7. The high-temperature resistant aqueous sizing agent solution according to claim 6, characterized in that: The mass concentration of the aqueous sizing agent solution is 1 wt%.

8. The high-temperature resistant aqueous sizing agent solution according to claim 6, characterized in that: The solvent of the aqueous sizing agent solution is selected from at least one or two of dimethylacetamide, water, ethanol, and acetone.

9. Use of the aqueous sizing agent according to any one of claims 1-4 and the aqueous sizing agent solution according to any one of claims 6-8 in the preparation of carbon fiber composite materials.

10. A high-temperature resistant carbon fiber composite material, characterized in that: It is prepared by sizing carbon fiber using an aqueous sizing agent comprising any one of claims 1-4 and any one of claims 6-8.

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