A synergistic repairing sizing agent for polyimide fiber and a preparation method and application thereof

Abstract

The present application relates to a kind of synergistic repair sizing polyimide fiber sizing agent and its preparation method and application, the raw material of the polyimide fiber sizing agent is composed of solute A and solvent B, the solute A is multifunctional epoxy resin, the solvent B is low-boiling solvent, the low-boiling solvent is acetone or ethanol, the proportion of the solute A and the solvent B is as follows: A 0.1%~10%;B 90%~99.9% by weight percentage.The polyimide fiber sizing agent of the present application can be used to repair the internal structure defect of high-performance polyimide fiber and improve the chemical activity of fiber surface, can improve the roughness of fiber surface in a short time, ensure the surface chemical reactivity, repair the internal defect of fiber by the formation of internal crosslinking point, the tensile strength and compression strength of fiber are improved, and waste liquid is easy to recover, low in cost.

Description

Technical Field

[0001] This invention relates to the field of high-performance organic fiber technology, and in particular to a polyimide fiber sizing agent, its preparation method, and its application. Background Technology

[0002] High-performance organic fibers, due to their superior properties such as high strength, high modulus, lightweight, high temperature resistance, and chemical resistance, are widely used in aerospace, electronics, power, and safety protection fields. However, during fiber preparation, the characteristics of the spinning process inevitably lead to structural defects within the fiber, affecting further improvements in mechanical properties such as tensile strength and compressive strength. Simultaneously, the smooth fiber surface, low chemical reactivity, poor adhesion to matrix materials, and chemical inertness limit their application in composite materials.

[0003] To address the problem of internal structural defects in fibers, many scholars have adopted structural design methods to enhance intermolecular radial interactions and reduce the generation of internal defects. However, this method is costly and time-consuming due to trial and error. In terms of improving fiber surface properties, sizing is widely used due to its simple process and ease of industrial production. It can form a coating layer on the fiber surface, improving the surface activity of the fiber through the active functional groups in the sizing agent. The mainstream sizing agent uses water as the solvent and water-based monomers as the solute, such as water-based epoxy, water-based polyurethane, and silane coupling agents. Current literature reports that water-based sizing agents can effectively improve fiber surface inertness, but their repair effect on internal microporous defects has not yet been found. Liu Xiangyang et al. used high-boiling-point DMAc as a solvent and methyl methacrylate / benzoyl peroxide / divinylbenzene crosslinking components as solutes to treat aramid fibers, achieving internal repair and improved surface roughness, thereby enhancing interfacial shear strength and single-fiber compression properties (Lv, J.; Yin, J.; Qin, Y.; Dai, Y.; Cheng, Z.; Luo, L.; Liu, X., Post-construction of weaving structure in aramid fiber towards improvements of its transverse properties. Composites Science and Technology 2021, 208.). This method involves a complex crosslinking system and uses a high-boiling-point solvent, making waste liquid difficult to recover. Furthermore, the improvement in fiber-resin interfacial bonding strength mainly relies on mechanical interlocking, without chemical reaction, resulting in relatively weak bonding. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a simple polyimide fiber sizing agent that can synergistically repair sizing, namely, synergistically repair internal structural defects of high-performance polyimide fibers and improve the chemical activity of fiber surfaces, and the waste liquid is easy to recycle and has low cost.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned polyimide fiber sizing agent.

[0006] Another object of the present invention is to provide a sizing method using the above-described polyimide fiber sizing agent.

[0007] Another object of the present invention is to provide the application of the above-mentioned polyimide fiber sizing agent or the above-mentioned sizing method.

[0008] According to the purpose of this invention, a polyimide fiber sizing agent is provided, the raw material of which is composed of solute A and solvent B, wherein solute A is a multifunctional epoxy resin, and solvent B is a low-boiling-point solvent, namely acetone or ethanol, and the ratio of solute A to solvent B by weight percentage is:

[0009] A 0.1% to 10%

[0010] B 90%~99.9%.

[0011] The polyimide fiber sizing agent of the present invention can be used to synergistically repair internal structural defects of high-performance polyimide fibers and improve the chemical activity of fiber surface. It can improve fiber surface roughness and surface chemical reactivity in a short time. At the same time, it repairs internal defects of the fiber by forming internal cross-linking points. The tensile strength and compressive strength of the fiber are improved. Moreover, the system is simple, the waste liquid is easy to recycle, and the cost is low.

[0012] Solute A is a multifunctional epoxy resin, preferably with a functionality of 3 to 4. For example, a multifunctional epoxy resin with a functionality of 3 is triglycidyl-p-aminophenol, and a multifunctional epoxy resin with a functionality of 4 is tetraglycidyl-4,4'-diaminodiphenylmethane, with the following structural formulas (1) and (2):

[0013]

[0014] For example, in a preferred embodiment, solute A is AG-80 epoxy resin, which is an industrially produced tetraglycidyl-4,4'-diaminodiphenylmethane, and solvent B is acetone.

[0015] Preferably, the ratio of solute A to solvent B is:

[0016] A 1%–7%

[0017] B 93%~99%.

[0018] In the above proportions, solute A can be, for example, 1%, 2%, 3%, 4%, 5%, 6%, or 7%, and solvent B can be, for example, 93%, 94%, 95%, 96%, 97%, 98%, or 99%. The percentages of solute A and solvent B should be chosen to satisfy the condition that the sum of the two is 100%.

[0019] According to another objective of the present invention, the present invention provides a method for preparing a polyimide fiber sizing agent, which includes the following steps: dissolving the epoxy resin in the low-boiling-point solvent, mixing them evenly, and obtaining the polyimide fiber sizing agent.

[0020] According to another objective of the present invention, a sizing method is provided, which uses the aforementioned polyimide fiber sizing agent to sizing organic fibers. The sizing method of the present invention is applicable to a variety of organic fibers, including polyimide fibers, aramid fibers, and poly(p-phenylenebenzodioxazole) (PBO) fibers.

[0021] Preferably, the organic fiber is one or more selected from polyimide fiber, aramid fiber, and poly(p-phenylenebenzodioxazole) fiber.

[0022] Preferably, when the organic fiber is a polyimide fiber, the sizing method includes the following steps:

[0023] 1) Immersion repair sizing: Immerse the polyimide fiber in the polyimide fiber sizing agent at a temperature of 10℃~45℃ for 1min-24h, and then take out the polyimide fiber;

[0024] 2) Removal of residual solution: The removed polyimide fibers are dried at 50℃~110℃ for 2min~60min to obtain sized polyimide fibers.

[0025] The soaking time in step 1) above is preferably 2 min to 10 min.

[0026] To achieve the above objectives, the present invention also provides a sized polyimide fiber, which is a sized polyimide fiber prepared by the sizing method described in claim 6. The sized polyimide fiber exhibits a monofilament tensile strength that is at least 4% higher than that of unsized fiber, a multifilament compressive strength that is at least 37% higher than that of unsized fiber, and an interfacial shear strength that is at least 40% higher than that of unsized fiber. Further, compared with unsized polyimide fiber, the monofilament tensile strength is increased by 4% to 20%, the multifilament compressive strength is increased by 37% to 60%, and the interfacial shear strength is increased by 40% to 80%.

[0027] According to another object of the present invention, the present invention provides the application of the above-mentioned polyimide sizing agent, sizing method or sizing polyimide fiber in the preparation of composite materials.

[0028] In the application of this invention, the composite material can be a polyimide fiber reinforced composite material used in aerospace, safety protection, electronics and power, automobiles, sports equipment, sporting goods and other fields.

[0029] High-performance organic fibers rely on weak interactions to bind their molecular chains radially. Combined with the double diffusion effect during actual spinning and solidification, micropores and core-sheath structures inevitably form between fibrils (within the fiber). Furthermore, the fiber surface is inert, hindering interfacial bonding between the fiber and resin. Currently, the mainstream approach to improving internal fiber defects involves molecular structure design or adjustments to the spinning process, which is costly to implement and has a long industrialization cycle. Regarding fiber surface activation, sizing is a commonly used industrial method for fiber surface modification, often using water-based sizing agents, but the contact angle between water and fiber is relatively large. This invention uses a polar, low-viscosity organic solvent as the main component, significantly reducing the contact angle between the fiber and the solution, improving the solution's wettability, and facilitating the penetration of epoxy monomers. This allows multifunctional epoxy to become cross-linking points within the fiber, repairing the porosity between fibrils. The residual epoxy monomers on the surface further improve surface roughness and chemical reactivity, effectively enhancing the fiber's interfacial properties while simultaneously addressing internal structural defects and surface inertness.

[0030] Therefore, this invention simultaneously addresses both the internal and surface issues of the fiber, significantly reducing the cost of fiber structure and process design through impregnation and sizing treatment. This invention not only enhances fiber surface activity, incorporating all the advantages of sizing treatment, but also repairs the fiber interior, improving fiber tensile strength and multifilament compressive strength.

[0031] Furthermore, this invention uses acetone or ethanol as a low-boiling-point solvent, which has high polarity and ultra-low viscosity. The solvent has excellent contact and wetting properties with the fiber, thus helping small molecules to penetrate into the fiber interior while also achieving surface sizing modification. While increasing surface roughness, the epoxy monomers also ensure surface chemical reactivity. In addition, after sizing modification, due to the low boiling point of the solvent, the solution composition is not complex; therefore, recycling can solve the waste liquid problem and allow for reuse, reducing costs.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The sizing agent of the present invention can simultaneously repair internal defects of fibers and improve surface activity. By means of impregnation sizing treatment, the cost of fiber structure and process design is greatly reduced.

[0034] (2) The sizing agent uses a low-boiling-point solvent, the solution composition is simple, and the waste liquid is easy to recycle and reuse, thus reducing costs. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope image of the repaired torn surface of polyimide fiber after sizing, as shown in Example 1.

[0036] Figure 2 This is a scanning electron microscope image of the torn surface of the unsized polyimide fiber in Comparative Example 1.

[0037] Figure 3 This is a scanning electron microscope image of the adhesion between polyimide fiber monofilaments in Comparative Example 4. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified in the embodiments, conditions are performed according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available products. The polyimide fiber filaments used in the experiments were provided by Jiangsu Xiannuo; the aramid fiber was aramid 1414 fiber purchased from Yantai Taihe New Material Co., Ltd., and the PBO fiber was purchased from Zhonglan Chenguang Chemical Research and Design Institute Co., Ltd. The multifunctional epoxy resin AG-80 used is an industrially produced tetraglycidyl-4,4'-diaminodiphenylmethane, and the multifunctional epoxy resin AFG-90 is an industrially produced triglycidyl-p-aminophenol.

[0039] Parameter measurement method:

[0040] Monofilament tensile strength: The tensile breaking strength of the fiber monofilament was tested according to GB / T 31290-2022 "Determination of tensile properties of carbon fiber monofilament".

[0041] Multifilament compressive strength: The multifilament compressive strength was tested according to Q / 110000BH005-2018 "Test Method for Compression Strain and Compression Strength of Carbon Fiber Multifilament".

[0042] Interfacial shear strength: Tested using a composite material interfacial performance evaluation instrument (HM410). The microspheres were cured from epoxy resins E51 and D400, and the diameter of the microspheres was 50-80 μm.

[0043] Fiber microstructure: Characterized using a scanning electron microscope (JSM-7800F).

[0044] Example 1

[0045] Solute A component: Multifunctional epoxy resin AG-80

[0046] Solvent component B: Acetone

[0047] Ratio of solute A to solvent B (by weight percentage):

[0048] A 4%

[0049] B 96%

[0050] Preparation method: Dissolve epoxy monomer A in acetone and mix thoroughly to obtain a synergistic repair sizing solution.

[0051] Sizing modification method:

[0052] (1) The polyimide fiber was immersed in the synergistic repair sizing solution and soaked at 25°C for 2 minutes before the fiber was removed.

[0053] (2) The removed fibers are dried at 70°C for 30 minutes to obtain repaired sizing polyimide fibers;

[0054] Tests showed that the tensile strength of polyimide fiber monofilament was 4232 MPa, 10% higher than that of unrepaired sized fiber. The compressive strength of multifilament was 278.1 MPa, 53% higher than that of unrepaired sized fiber. The interfacial shear strength was 38.07 MPa, 73% higher than that of unrepaired sized fiber.

[0055] In addition, the microstructure of the repaired sized polyimide fiber tear surface in Example 1 was characterized using a scanning electron microscope (JSM-7800F). See the SEM images below. Figure 1 .Depend on Figure 1 As shown, after repair sizing, the internal defects of the fiber are repaired.

[0056] Example 2

[0057] Solute A component: Multifunctional epoxy resin AG-80

[0058] Solvent component B: Acetone

[0059] Ratio of solute A to solvent B (by weight percentage):

[0060] A 0.1%

[0061] B 99.9%

[0062] Preparation method: Dissolve epoxy monomer A in acetone and mix thoroughly to obtain a synergistic repair sizing solution.

[0063] Sizing modification method:

[0064] (1) The polyimide fiber was immersed in the synergistic repair sizing solution and soaked at 25°C for 24 hours before the fiber was removed.

[0065] (2) The removed fibers are dried at 70°C for 30 minutes to obtain repaired and sized aramid fibers.

[0066] Tests showed that the monofilament tensile strength was 4198 MPa, a 9% increase compared to the unrepaired sized fiber. The multifilament compressive strength was 256.8 MPa, a 42% increase compared to the unrepaired sized fiber. The interfacial shear strength was 35.80 MPa, a 63% increase compared to the unrepaired sized fiber. Furthermore, scanning electron micrographs of the fiber tear surface... Figure 1 Similarly, it shows that the internal defects of the fiber were repaired after repair sizing.

[0067] Example 3

[0068] Solute A component: Multifunctional epoxy resin AFG-90

[0069] Solvent component B: Acetone

[0070] Ratio of solute A to solvent B (by weight percentage):

[0071] A 10%

[0072] B 90%

[0073] Preparation method: Dissolve epoxy monomer A in acetone and mix thoroughly to obtain a synergistic repair sizing solution.

[0074] Sizing modification method:

[0075] (1) The polyimide fiber was immersed in the synergistic repair sizing solution and removed after soaking at 25°C for 1 min.

[0076] (2) The removed fibers are dried at 70°C for 30 minutes to obtain repaired sizing polyimide fibers;

[0077] Tests showed that the monofilament tensile strength was 3987 MPa, a 4% increase compared to the unrepaired sized fiber. The multifilament compressive strength was 253.3 MPa, a 40% increase compared to the unrepaired sized fiber. The interfacial shear strength was 31.20 MPa, a 42% increase compared to the unrepaired sized fiber. Furthermore, scanning electron micrographs of the fiber tear surface... Figure 1 Similarly, it shows that the internal defects of the fiber were repaired after repair sizing.

[0078] Example 4

[0079] Solute A component: Multifunctional epoxy resin AG-80

[0080] Solvent component B: ethanol

[0081] Ratio of solute A to solvent B (by weight percentage):

[0082] A 2%

[0083] B 98%

[0084] Preparation method: Dissolve epoxy monomer A in ethanol and mix well to obtain a synergistic repair sizing solution.

[0085] Sizing modification method:

[0086] (1) The polyimide fiber was immersed in the synergistic repair sizing solution and soaked at 25°C for 10 hours before the fiber was removed.

[0087] (2) The removed fibers are dried at 50°C for 30 minutes to obtain repaired sizing polyimide fibers;

[0088] Tests showed that the monofilament tensile strength was 4058 MPa, a 6% increase compared to the unrepaired sized fiber. The multifilament compressive strength was 248.9 MPa, a 37% increase compared to the unrepaired sized fiber. The interfacial shear strength was 30.82 MPa, a 40% increase compared to the unrepaired sized fiber. Furthermore, scanning electron micrographs of the fiber tear surface... Figure 1 Similarly, it shows that the internal defects of the fiber were repaired after repair sizing.

[0089] Example 5

[0090] Solute A component: Multifunctional epoxy resin AG-80

[0091] Solvent component B: Acetone

[0092] Ratio of solute A to solvent B (by weight percentage):

[0093] A 4%

[0094] B 96%

[0095] Preparation method: Dissolve epoxy monomer A in acetone and mix thoroughly to obtain a synergistic repair sizing solution.

[0096] Sizing modification method:

[0097] (1) Immerse the aramid fiber in the synergistic repair sizing solution, soak it at 25°C for 2 minutes, and then remove the fiber;

[0098] (2) The removed fibers are dried at 70°C for 30 minutes to obtain repaired and sized aramid fibers.

[0099] Tests showed that the monofilament tensile strength was 3608 MPa, a 14% increase compared to the unrepaired sized fiber. The multifilament compressive strength was 235.8 MPa, a 44% increase compared to the unrepaired sized fiber. The interfacial shear strength was 36.94 MPa, a 63% increase compared to the unrepaired sized fiber. Furthermore, scanning electron microscope images of the torn surface of the unsized aramid fiber showed... Figure 2 Similarly, scanning electron microscope images of the repaired torn surface of aramid fibers and... Figure 1 Similarly, it was shown that the unsized aramid fibers had internal defects, which were repaired after repair sizing.

[0100] Example 6

[0101] Solute A component: Multifunctional epoxy resin AG-80

[0102] Solvent component B: Acetone

[0103] Ratio of solute A to solvent B (by weight percentage):

[0104] A 4%

[0105] B 96%

[0106] Preparation method: Dissolve epoxy monomer A in acetone and mix thoroughly to obtain a synergistic repair sizing solution.

[0107] Sizing modification method:

[0108] (1) PBO fibers were immersed in a synergistic repair sizing solution and soaked at 25°C for 2 minutes before being removed.

[0109] (2) The removed fibers were dried at 70°C for 30 minutes to obtain repaired and sized PBO fibers.

[0110] Tests showed that the monofilament tensile strength was 6076 MPa, a 6% increase compared to unrepaired sized fibers. The multifilament compressive strength was 229.8 MPa, a 39% increase compared to unrepaired sized fibers. The interfacial shear strength was 30.76 MPa, a 48% increase compared to unrepaired sized fibers. Furthermore, scanning electron micrographs of the torn surface of unsized PBO fibers were compared with... Figure 2 Similarly, scanning electron microscope images of the repaired torn surface of PBO fibers and... Figure 1 Similarly, it was shown that the unsized PBO fibers had internal defects, which were repaired after repair sizing.

[0111] Comparative Example 1

[0112] For unsized polyimide fibers, the following measurements were taken: the tensile strength of the polyimide fiber primary fiber was 3852 MPa, the compressive strength of the multifilament was 181.2 MPa, and the interfacial shear strength was 22.01 MPa.

[0113] In addition, the microstructure of the torn surface of the unsized polyimide fiber in Comparative Example 1 was characterized using a scanning electron microscope (JSM-7800F). The scanning electron microscope images are shown below. Figure 2 .Depend on Figure 2 As shown, the unsized fibers have internal defects.

[0114] Comparative Example 2

[0115] Unsized aramid fibers, after testing, showed a monofilament tensile strength of 3165 MPa, a multifilament compressive strength of 163.2 MPa, and an interfacial shear strength of 22.67 MPa. Furthermore, the microstructure of the torn surface of the unsized aramid fibers in Comparative Example 2 was characterized using a scanning electron microscope (JSM-7800F). The SEM images and... Figure 2 Similarly, it shows that the unsized fibers have internal defects.

[0116] Comparative Example 3

[0117] Unsized PBO fibers, after testing, showed a monofilament tensile strength of 5730 MPa, a multifilament compressive strength of 165.90 MPa, and an interfacial shear strength of 20.78 MPa. Furthermore, the microstructure of the torn surface of the unsized PBO fibers in Comparative Example 3 was characterized using scanning electron microscopy (JSM-7800F). The SEM images and... Figure 2 Similarly, it shows that the unsized fibers have internal defects.

[0118] Comparative Example 4

[0119] Solute A component: Multifunctional epoxy resin AG-80

[0120] Solvent component B: Acetone

[0121] Ratio of solute A to solvent B (by weight percentage):

[0122] A 0.05%

[0123] B 99.95%

[0124] Preparation method: Dissolve epoxy monomer A in acetone and mix thoroughly to obtain a synergistic repair sizing solution.

[0125] Sizing modification method:

[0126] (1) The polyimide fiber was immersed in the synergistic repair sizing solution and soaked at 25°C for 24 hours before the fiber was removed.

[0127] (2) The removed fibers are dried at 70°C for 30 minutes to obtain repaired sizing polyimide fibers;

[0128] Tests showed that the tensile strength of the single filament was 3690 MPa, a 4% decrease compared to the unrepaired sized fiber. The compressive strength of the multifilament was 176.7 MPa, a 2% decrease compared to the unrepaired sized fiber. The interfacial shear strength was 20.50 MPa, a 7% decrease compared to the unrepaired sized fiber.

[0129] Comparative Example 5

[0130] Solute A component: Multifunctional epoxy resin AG-80

[0131] Solvent component B: Acetone

[0132] Ratio of solute A to solvent B (by weight percentage):

[0133] A 15%

[0134] B 85%

[0135] Preparation method: Dissolve epoxy monomer A in acetone and mix thoroughly to obtain a synergistic repair sizing solution.

[0136] Sizing modification method:

[0137] (1) The polyimide fiber was immersed in the synergistic repair sizing solution and removed after soaking at 25°C for 1 min.

[0138] (2) The removed fibers are dried at 70°C for 30 minutes to obtain repaired sizing polyimide fibers;

[0139] Tests showed that the fiber filaments were stuck together. Figure 3 This is a scanning electron microscope image of the adhesion between polyimide fiber monofilaments in Comparative Example 4.

[0140] Comparative Example 6

[0141] Solute A component: Multifunctional epoxy resin AG-80

[0142] Solvent component B: Acetone

[0143] Ratio of solute A to solvent B (by weight percentage):

[0144] A 10%

[0145] B 90%

[0146] Preparation method: Dissolve epoxy monomer A in acetone and mix thoroughly to obtain a synergistic repair sizing solution.

[0147] Sizing modification method:

[0148] (1) The polyimide fiber was immersed in the synergistic repair sizing solution and removed after soaking at 25°C for 30 seconds.

[0149] (2) The removed fibers are dried at 70°C for 30 minutes to obtain repaired sizing polyimide fibers;

[0150] Tests showed that the tensile strength of the single filament was 3896 MPa, only 1% higher than that of the unrepaired sized fiber. The compressive strength of the multifilament was 185.8 MPa, only 3% higher than that of the unrepaired sized fiber. The interfacial shear strength was 23.87 MPa, only 8% higher than that of the unrepaired sized fiber.

[0151] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A polyimide fiber sizing agent, characterized in that, The raw material of the polyimide fiber sizing agent consists of solute A and solvent B. Solute A is a multifunctional epoxy resin, and solvent B is a low-boiling-point solvent, such as acetone or ethanol. The ratio of solute A to solvent B by weight percentage is: A 0.1％～10％ B 90％～99.9％。 2. The polyimide fiber sizing agent according to claim 1, characterized in that, The functionality of the multifunctional epoxy resin is 3 to 4.

3. The polyimide fiber sizing agent according to claim 1 or 2, characterized in that, The ratio of solute A to solvent B is: A 1％～7％ B 93％～99％。 4. The polyimide fiber sizing agent according to claim 2, characterized in that, The multifunctional epoxy resin is triglycidyl-p-aminophenol or tetraglycidyl-4,4'-diaminodiphenylmethane.

5. The method for preparing the polyimide fiber sizing agent according to any one of claims 1 to 4, characterized in that, Includes the following steps: The multifunctional epoxy resin is dissolved in the low-boiling-point solvent and mixed evenly to obtain a polyimide fiber sizing agent.

6. A sizing method, characterized in that, Organic fibers are sized using the polyimide fiber sizing agent according to any one of claims 1 to 4.

7. The sizing method according to claim 6, characterized in that, The organic fiber is selected from one or more of polyimide fiber, aramid fiber, and poly(p-phenylenebenzodioxazole) fiber; and / or When the organic fiber is a polyimide fiber, the sizing method includes the following steps: 1) Immersion repair sizing: Immerse the polyimide fiber in the polyimide fiber sizing agent at a temperature of 10℃~45℃ for 1min-24h, and then take out the polyimide fiber; 2) Removal of residual solution: The removed polyimide fibers are dried at 50℃~110℃ for 2min~60min to obtain sized polyimide fibers.

8. The sizing method according to claim 6, characterized in that, In step 1), soak for 2 to 10 minutes.

9. A sized polyimide fiber, characterized in that, The sized polyimide fiber prepared by the sizing method described in claim 7 or 8 has, compared with the unsized polyimide fiber, a 4% to 20% increase in monofilament tensile strength, a 37% to 60% increase in multifilament compressive strength, and a 40% to 80% increase in interfacial shear strength.

10. The application of the polyimide fiber sizing agent according to any one of claims 1 to 4, the sizing method according to any one of claims 6 to 8, or the sized polyimide fiber according to claim 9 in the preparation of composite materials. The composite material is a polyimide fiber reinforced composite material used in aerospace, safety protection, electronics and power, automobiles, sports equipment, or sporting goods.

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