Sizing agent for reinforced fibers as well as preparation method and application of sizing agent

Abstract

The invention discloses a sizing agent for reinforced fibers as well as a preparation method and application of the sizing agent, and relates to the technical field of fiber materials. The surface of the amino-modified nano silicon dioxide is provided with a certain amount of positive charges and hydrophilic groups, and the amino-modified nano silicon dioxide can be used as a nano emulsion stabilizer in the emulsion and has a synergistic effect with a sizing agent emulsion and a surfactant, so that the infiltration capacity and the wetting rate of the amino-modified nano silicon dioxide to carbon fiber monofilament gaps are improved. Meanwhile, the rheological property of the emulsion can be regulated and controlled by introducing the nano particles, so that the emulsion has good leveling property and film-forming property in the sizing process, and a sizing layer with a surface micro-nano structure is formed. The sizing agent provided by the invention can significantly improve the interlaminar shear strength (ILSS) and interface toughness of the composite material, so that the composite material still maintains excellent mechanical properties in a load environment.

Description

Technical Field

[0001] This invention relates to the field of fiber materials technology, and more specifically, to a sizing agent for reinforcing fibers, its preparation method, and its application. Background Technology

[0002] Carbon fiber reinforced resin matrix composites are widely used in aerospace, automotive, and sporting goods industries due to their superior properties such as high specific strength, high specific modulus, and fatigue resistance. Their mechanical properties are primarily dependent on the interfacial bonding strength between the reinforcing fiber and the resin matrix. Carbon fiber, with its high specific strength, is the preferred reinforcement for high-end composites; however, its inert surface structure requires modification with sizing agents to improve interfacial compatibility. Traditional sizing agents, such as epoxy resins, use these as film-forming matrices. While they can achieve fiber bundling, they suffer from limitations such as a single interfacial bonding mechanism and insufficient high-temperature stability. Nano-silica (SiO2) has been used for sizing agent modification due to its high specific surface area and thermal stability. However, unmodified nano-silica exhibits drawbacks such as poor dispersibility due to surface hydroxyl agglomeration, weak interfacial interaction due to lack of chemical bonding with carbon fibers and resins, and insufficient compatibility due to mismatch between its high surface energy and organic resins. Existing modification strategies either fail to improve interfacial bonding or easily induce secondary agglomeration. Therefore, developing modified sizing agents that combine stable dispersion, interfacial chemical bonding, and high-temperature stability with nano-silica has become a key technological requirement for achieving high-performance carbon fiber composites.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing and applying a novel sizing agent for carbon fiber, which aims to significantly improve the interfacial bonding performance between carbon fiber and resin and ensure the high-temperature stability of the sizing agent.

[0005] In a first aspect, the present invention provides a sizing agent for reinforcing fibers, the raw materials of which, by mass parts, include: 1-5 parts of amino-modified nano-silica, 10-40 parts of sizing agent emulsion, 1-10 parts of surfactant and 5-15 parts of water.

[0006] In an optional embodiment, the amino-modified nano-silica is obtained by reacting a silane coupling agent with nano-silica particles; Silane coupling agents contain hydrolyzable methoxy or ethoxy groups.

[0007] In an optional embodiment, the silane coupling agent is selected from at least one of 3-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane; And / or, the diameter of the nano-silica particles is 50nm-200nm.

[0008] In an optional embodiment, the sizing agent emulsion is selected from at least one of bisphenol A type epoxy resin and polyimide resin.

[0009] In an optional embodiment, the surfactant is selected from at least one of fatty alcohol polyoxyethylene ether, sodium dodecylbenzenesulfonate, and octylphenol polyoxyethylene ether.

[0010] Secondly, the present invention provides a method for preparing a modified sizing agent for carbon fiber according to any of the foregoing embodiments, comprising: Preparation of amino-modified nano-silica: Disperse nano-silica particles in a solvent, adjust the pH to 4-5, mix and react with a silane coupling agent, and separate the precipitate after the reaction; Preparation of sizing agent: Mix the sizing agent emulsion, surfactant and water in proportion, and carry out emulsification and phase inversion at 20℃-40℃. Then add the amino-modified nano silica and stir at 1000r / min-1500r / min for 30-60min.

[0011] In an optional embodiment, during the preparation of amino-modified nano-silica, the reaction temperature is controlled at 70℃-85℃ and the reaction time is 4-6 hours. And / or, the mass ratio of nano-silica particles to the silane coupling agent is 1:(0.5-2); And / or, the solvent is a mixture of ethanol and water, wherein the mass ratio of ethanol to water is 1:(0.5-1.5); And / or, the amount of solvent used for 1g of nano silica particles is 50mL-80mL; And / or, the stirring rate is controlled at 300 r / min-400 r / min during the reaction; And / or, after the reaction is completed, centrifuge the mixture, wash the precipitate 2-3 times with ethanol, and then vacuum dry it at 60℃-80℃ for 4-6 hours.

[0012] Thirdly, the present invention provides a reinforcing fiber, which is obtained by treating a fiber matrix with a reinforcing fiber sizing agent prepared by any of the reinforcing fiber sizing agents in the foregoing embodiments or by any of the preparation methods in the foregoing embodiments. Preferably, the fiber matrix is ​​carbon fiber; Preferably, the carbon fiber is immersed in a sizing tank for 20-30 seconds, the running speed is 50-200 m / h, the sizing amount is 1%-2%, and then dried.

[0013] Fourthly, the present invention provides a composite material comprising a resin matrix and the above-mentioned optimized carbon fiber, the preparation steps of which are as follows: (1) Prepreg preparation: The above-mentioned optimized carbon fiber is laid into a unidirectional fiber cloth with a surface density of 150-200g / m². It is then immersed in a polyimide resin or bisphenol A type epoxy resin matrix of the same type as the sizing agent by hot melt impregnation method, and the impregnation time is controlled at 20-30s and the pressure is 8-10MPa. (2) Molding process: The prepreg is orthogonally laid in [0° / 90°] and placed in a hot press molding mold for hot pressing and curing. After cooling to room temperature, it is demolded to obtain carbon fiber composite material sheet.

[0014] Performance test specimen preparation: Cut ILSS test strips (size: 25mm×10mm×2mm) according to GB / T 30969-2014 and GB / T 3357-2020, and prepare IFSS test specimens according to GB / T 39033-2020.

[0015] This invention offers the following advantages: The amino-modified nano-silica surface possesses a certain amount of positive charge and hydrophilic groups, allowing it to function as a "nano-emulsion stabilizer" in emulsions. It synergistically works with sizing agents and surfactants to enhance its penetration into the gaps between carbon fiber monofilaments and improve wetting rate. Simultaneously, the introduction of nanoparticles can regulate the rheological properties of the emulsion, enabling it to exhibit good leveling and film-forming properties during sizing, forming a sizing layer with a micro / nano-structured surface. The sizing agent provided by this invention can significantly improve the interlaminar shear strength (ILSS) and interfacial toughness of composite materials, ensuring that the composite material maintains excellent mechanical properties under load. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0017] This invention constructs a stable and efficient interfacial bonding system through surface modification of silica fillers, optimization of sizing agent formulation, and process control. It provides a modified sizing agent that is simple to process, environmentally friendly, and suitable for industrial production, meeting the requirements of high-end composite materials.

[0018] This invention provides a sizing agent for reinforcing fibers, comprising, by weight, 1-5 parts of amino-modified nano-silica, 10-40 parts of sizing agent emulsion, 1-10 parts of surfactant, and 5-15 parts of deionized water. The amino-modified nano-silica, with its positively charged surface and hydrophilic groups, acts as a "nano-emulsion stabilizer," working synergistically with the sizing agent emulsion and surfactant to achieve three effects: ① increasing the penetration and wetting rate between carbon fiber monofilaments; ② regulating the rheological properties of the emulsion to ensure leveling and film formation during the sizing process, forming a micro-nano structured sizing layer; ③ achieving a synergistic effect of "micro-nano rough structure - physical interlocking enhancement - compatibility optimization," improving the interfacial bonding performance between carbon fibers and the resin matrix while ensuring the high-temperature stability of the sizing agent.

[0019] Specifically, in the modified sizing agent, the amount of amino-modified nano-silica can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts, etc., by mass; the amount of sizing agent emulsion can be 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, etc.; and the amount of surfactant can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc.

[0020] In some embodiments, amino-modified nano-silica is obtained by reacting a silane coupling agent with nano-silica particles. The silane coupling agent contains hydrolyzable methoxy or ethoxy groups (preferably at least one of 3-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane), and the nano-silica particles have a diameter of 50 nm to 200 nm (e.g., 50 nm, 100 nm, 150 nm, 200 nm).

[0021] In some embodiments, the sizing agent emulsion is selected from at least one of bisphenol A type epoxy resin and polyimide resin. The amino functional groups of the amino-modified nano silica can undergo ring-opening reactions with the epoxy groups of the epoxy resin, or form hydrogen bonds / chemical bonds with the acyl anhydride / imide structure of the polyimide resin, thereby strengthening the "sizing agent-matrix" interfacial bonding.

[0022] In some embodiments, the surfactant is selected from at least one of fatty alcohol polyoxyethylene ether (AEO-9), sodium dodecylbenzenesulfonate (SDBS), and octylphenol polyoxyethylene ether (OP-10). Introducing the surfactant can significantly reduce the surface tension of the system and improve its penetration and spreading ability into the interior of carbon fiber monofilaments and bundles.

[0023] Furthermore, the raw materials for the modified sizing agent also include 5-15 parts of water. After mixing the sizing agent emulsion and surfactant, water is added for emulsification and phase inversion. When the average particle size of the emulsion is ≤500nm, the phase inversion is successful.

[0024] Furthermore, nano-silica is added to the sizing agent after the phase inversion is completed, and stirred at 1000r / min-1500r / min for 30-60min to obtain a uniform sizing agent.

[0025] This invention also provides a method for preparing a modified sizing agent, the steps of which are as follows: S1. Preparation of amino-modified nano-silica Nano-sized silica particles were dispersed in a solvent, the pH was adjusted to 4-5, and then mixed with a silane coupling agent to react. The precipitate was then separated after the reaction. The aforementioned silane coupling agents all contain hydrolyzable methoxy or ethoxy groups, which can undergo a condensation reaction with the hydroxyl groups on the surface of nano-SiO2 in an aqueous system to form stable Si-O-Si covalent bonds, effectively inhibiting the aggregation tendency of nano-SiO2 in the emulsion.

[0026] Specifically, the pH value of the reaction can be 4.0, 4.3, 4.5, 4.8, 5.0, etc.

[0027] In some embodiments, the solvent used is a mixture of ethanol and water, with a mass ratio of ethanol to water of 1:(0.5-1.5), such as 1:0.5, 1:1.0, 1:1.5, etc.; the amount of mixed solvent corresponding to 1g of nano silica particles is 50mL-80mL, such as 50mL, 55mL, 60mL, 65mL, 70mL, 75mL, 80mL, etc.

[0028] In some embodiments, the mass ratio of nano-silica particles to silane coupling agent is 1:(0.5-2), such as 1:0.5, 1:1, 1:1.5, 1:2, etc. The amount of silane coupling agent used is preferably within the above range so that the amount of surface amino groups introduced is more appropriate and the interface enhancement effect is improved.

[0029] In some embodiments, during the preparation of amino-modified nano-silica, the reaction temperature is controlled at 70℃-85℃, such as 70℃, 75℃, 80℃, 85℃, etc.; the reflux reaction is carried out for 4h-6h, such as 4h, 5h, 6h, etc. During the reaction, the stirring rate is controlled at 300r / min-400r / min, such as 300r / min, 330r / min, 350r / min, 380r / min, 400r / min, etc. After the reaction, the mixture is centrifuged (8000r / min-10000r / min), and the resulting precipitate is washed and dried to obtain amino-modified nano-silica. The washing method is not limited; for example, anhydrous ethanol can be used for washing, and the number of washings can be multiple times, such as 2-3 times. The drying temperature is not limited; for example, vacuum drying can be carried out at 60℃-80℃ for 4-6h.

[0030] S2. Preparation of sizing agent The sizing agent emulsion, surfactant, and water are mixed in proportion and emulsified and phase-inverted at 20℃-40℃ for 20-30 minutes. Then, amino-modified nano-silica is added and stirred at 1000r / min-1500r / min for 30-60 minutes to obtain the sizing agent product.

[0031] This invention also provides a carbon fiber, which is obtained by sizing with the sizing agent provided in this invention, but is not limited thereto. By improving the sizing agent for reinforcing fibers, the interfacial bonding performance between carbon fiber and polyimide resin is significantly enhanced.

[0032] The sizing agent provided in this invention can be used for the surface treatment of carbon fibers. The amino functional groups on the fiber surface form chemical bonds with the resin matrix, while the nano-SiO2 particles exert a pinning effect. This dual effect significantly improves the interfacial properties of the composite material. The sizing agent is stable in dispersion, environmentally friendly, and has good process compatibility.

[0033] The process of treating the fiber matrix with a sizing agent for reinforcing fibers can adopt existing processes. The specific steps are as follows: immerse the carbon fibers in a sizing tank for 20-30 seconds, run at a speed of 50-200 m / h, apply 1%-2% of the sizing amount, and then dry them.

[0034] Specifically, the impregnation time can be 20s, 23s, 25s, 28s, 30s, etc.; the running speed can be 50m / h, 100m / h, 150m / h, 200m / h. The sizing amount refers to the mass fraction of the sizing agent on the surface relative to the total weight of the carbon fiber, which can be 1%, 1.25%, 1.5%, 1.74%, 2%, etc.

[0035] This invention also provides a composite material comprising a resin matrix and the aforementioned optimized fibers. This composite material is formed by bonding and curing carbon fibers with an amino-modified nano-SiO2 coating on their surface to a resin matrix. Because the amount of fuzz on the carbon fiber surface is significantly reduced, and the nanoscale rough structure constructed by the amino-modified nano-SiO2 on the fiber surface can improve the mechanical anchoring effect between the fiber and the resin, the interlaminar shear strength (ILSS) and interfacial toughness of the composite material are significantly enhanced, allowing the composite material to maintain excellent mechanical properties even under load.

[0036] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0037] Example 1 This embodiment provides a method for preparing a modified sizing agent for carbon fibers, the steps of which are as follows: (1) Preparation of amino-modified nano silica: 3g of nano SiO2 with a diameter of 200nm was dispersed in 200mL of mixed solvent (ethanol and water in a mass ratio of 1:1.5), ultrasonically dispersed for 20min, pH was adjusted to 4.5 with 0.1mol / L dilute hydrochloric acid solution, 1.5g of γ-aminopropyltriethoxysilane was added, and the mixture was refluxed at 70℃ for 5h. The stirring rate was controlled at 350r / min during the reaction. After the reaction, the mixture was centrifuged and the precipitate was washed three times with anhydrous ethanol and vacuum dried at 80℃ for 5h to obtain amino-modified nano silica.

[0038] (2) Preparation of sizing agent: By mass, 25 parts of polyimide-based sizing agent, 5 parts of surfactant (fatty alcohol polyoxyethylene ether, purchased from Aladdin, model A304365) and 10 parts of deionized water were mixed and emulsified at 30℃ for 30 min; then 2.5 parts of amino-modified nano silica were gradually added and treated at a stirring speed of 1000 rpm for 2 h to obtain a uniform modified sizing agent.

[0039] This embodiment also provides a carbon fiber, which uses the sizing agent provided in this embodiment to modify the surface of the carbon fiber. During the preparation process, the sizing time is controlled at 25s, the running speed is 100m / h, the sizing amount is 1.5%, and after drying, the optimized carbon fiber is obtained.

[0040] This embodiment also provides a composite material, comprising a resin matrix and the above-mentioned optimized carbon fiber, and the preparation steps are as follows: S1. Prepreg preparation: The above-optimized carbon fibers are prepared according to an areal density of 200 g / m². 2 The fiber was laid as a unidirectional fiber cloth and immersed in a polyimide resin matrix of the same type as the sizing agent using a hot melt impregnation method. The impregnation time was controlled at 30s and the pressure at 10MPa to obtain an optimized carbon fiber prepreg. S2. Molding process: The prepreg is laid up at [0° / 90°] and placed in a hot press mold for hot pressing and curing. After cooling to room temperature, it is demolded to obtain an optimized carbon fiber composite material sheet. S3. Performance test specimen preparation: Cut ILSS test strips (size: 25mm×10mm×2mm) according to GB / T 30969-2014, and prepare IFSS test specimens according to GB / T 39033-2020.

[0041] Example 2 The only difference from Example 1 is that the silane coupling agent in step (1) is changed to an equal amount of 3-aminopropyltrimethoxysilane.

[0042] Example 3 The only difference from Example 1 is that the type of sizing agent emulsion in step (2) is changed to bisphenol A type epoxy resin base.

[0043] Example 4 The only difference from Example 2 is that the amount of 3-aminopropyltrimethoxysilane used is 3g, that is, the mass ratio of nano-silica particles to silane coupling agent is 1:1.

[0044] Example 5 The only difference from Example 2 is that the amount of 3-aminopropyltrimethoxysilane used is 4.5g, that is, the mass ratio of nano-silica particles to silane coupling agent is 1:1.5.

[0045] Example 6 The only difference from Example 2 is that the amount of 3-aminopropyltrimethoxysilane used is 6g, that is, the mass ratio of nano-silica particles to silane coupling agent is 1:2.

[0046] Example 7 The only difference from Example 2 is that the reaction temperature in step (1) is 80°C.

[0047] Example 8 The only difference from Example 2 is that the reaction temperature in step (1) is 85°C.

[0048] Example 9 The only difference from Example 2 is that the raw material ratio of the sizing agent is different. By mass, 10 parts of polyimide-based sizing agent, 1 part of surfactant and 5 parts of deionized water are mixed and emulsified at 30°C for 30 min for phase inversion. Then, 1 part of amino-modified nano silica is gradually added and treated at a stirring speed of 1000 rpm for 2 h to obtain a uniform modified sizing agent.

[0049] Example 10 The only difference from Example 2 is that the raw material ratio of the sizing agent is different. By mass, 40 parts of polyimide-based sizing agent, 10 parts of surfactant and 15 parts of deionized water are mixed and emulsified at 30°C for 30 min for phase inversion. Then, 5 parts of amino-modified nano silica are gradually added and treated at a stirring speed of 1000 rpm for 2 h to obtain a uniform modified sizing agent.

[0050] Example 11 The only difference from Example 2 is that the diameter of the nano-silica is 100 nm.

[0051] Comparative Example 1 This comparative example provides a method for preparing a modified sizing agent for carbon fibers, differing from Example 1 only in that the diameter of the nano-silica in step (1) is changed to 500 nm. The steps are as follows: (1) Preparation of amino-modified nano silica: 3g of nano SiO2 with a diameter of 500nm was dispersed in 200mL of mixed solvent (ethanol and water in a mass ratio of 1:1.5), ultrasonically dispersed for 20min, pH was adjusted to 4.5 with 0.1mol / L dilute hydrochloric acid solution, 1.5g of γ-aminopropyltriethoxysilane was added, and the mixture was refluxed at 70℃ for 5h. The stirring rate was controlled at 350r / min during the reaction. After the reaction, the mixture was centrifuged and the precipitate was washed three times with anhydrous ethanol and vacuum dried at 80℃ for 5h to obtain amino-modified nano silica.

[0052] (2) Preparation of sizing agent: By mass, 25 parts of polyimide-based sizing agent, 5 parts of surfactant (fatty alcohol polyoxyethylene ether, purchased from Aladdin, model A304365) and 10 parts of deionized water were mixed and emulsified at 30℃ for 30 min; then 2.5 parts of amino-modified nano silica were gradually added and treated at a stirring speed of 1000 rpm for 2 h to obtain a uniform modified sizing agent.

[0053] Comparative Example 2 The only difference from Example 1 is the raw material ratio of the sizing agent. By mass, 25 parts of bisphenol A type epoxy resin-based sizing agent, 5 parts of surfactant (fatty alcohol polyoxyethylene ether, purchased from Aladdin, model A304365) and 10 parts of deionized water are mixed and emulsified at 30°C for 30 min for phase inversion. Then, 10 parts of amino-modified nano silica are gradually added and the mixture is treated at a stirring speed of 1000 rpm for 2 h to obtain a uniform modified sizing agent.

[0054] Comparative Example 3 The only difference from Example 1 is the raw material ratio of the sizing agent. By mass, 25 parts of bisphenol A type epoxy resin-based sizing agent, 5 parts of surfactant (fatty alcohol polyoxyethylene ether, purchased from Aladdin, model A304365) and 10 parts of deionized water are mixed and emulsified at 30°C for 30 min for phase inversion. Then, 0.5 parts of amino-modified nano silica are gradually added and the mixture is treated at a stirring speed of 1000 rpm for 2 h to obtain a uniform modified sizing agent.

[0055] Comparative Example 4 The only difference from Example 1 is that step (1) is omitted, and step (2) directly replaces the amino-modified nano-silica with an equal amount of nano-silica particles.

[0056] Comparative Example 5 The only difference from Example 2 is that step (1) is omitted, and an equal amount of silane coupling agent is added in step (2).

[0057] Test case The modified sizing agents and optimized carbon fiber composites obtained in the above embodiments and comparative examples were subjected to comprehensive performance tests. The test results are shown in Table 1. The specific test methods are as follows: 1. Modified sizing agent (1) Average particle size: According to GB / T 29024.1-2012 "Dynamic Light Scattering Method for Particle Size Analysis", the dynamic light scattering (DLS) method was used for testing.

[0058] 2. Optimize carbon fiber composite materials (1) Interfacial shear strength (IFSS): According to ASTM D7234-19, the microbead debonding method combined with a self-made microdroplet debonding device was used for testing.

[0059] (2) Interlaminar shear strength: Cut ILSS test strips (size: 25mm×10mm×2mm) according to GB / T30969-2014, and prepare IFSS test specimens according to GB / T 39033-2020.

[0060] Table 1. Test results of interfacial shear performance in the examples and comparative examples.

[0061] Table 2. Interlaminar shear performance test results of the examples and comparative examples.

[0062] As shown in Table 1, the reaction temperature of amino-modified nano-silica has a very limited effect on the interfacial strength of carbon fiber and resin and the mechanical strength of the composite material. For Example 11, when the diameter of amino-modified nano-silica is 100 nm, the ILSS value of the composite material is increased by 6.6 MPa compared with Example 1, indicating that the smaller the diameter of amino-modified nano-silica, the more effective it is in improving the interfacial strength of carbon fiber and resin.

[0063] As can be seen from Tables 1 and 2, compared with Comparative Examples 1-5, the carbon fiber composite materials prepared in Examples 1-11 of this application have higher interfacial shear strength and interlaminar shear strength. This indicates that the introduction of silanized nano-SiO2 is the core step in improving the IFSS / ILSS of the composite material. The silane-modified nano-SiO2 sizing agent takes into account both the high crosslinking density and high toughness of the interface, meeting the interfacial performance requirements of high-end carbon fiber composite materials.

[0064] 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. A sizing agent for reinforcing fibers, characterized in that, By mass fraction, its raw materials include: 1-5 parts amino-modified nano silica, 10-40 parts sizing agent emulsion, 1-10 parts surfactant and 5-15 parts water.

2. The sizing agent for reinforcing fibers according to claim 1, characterized in that, The amino-modified nano-silica is obtained by reacting a silane coupling agent with nano-silica particles. The silane coupling agent contains hydrolyzable methoxy or ethoxy groups.

3. The sizing agent for reinforcing fibers according to claim 2, characterized in that, The silane coupling agent is selected from at least one of 3-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane; And / or, the diameter of the nano-silica particles is 50nm-200nm.

4. The sizing agent for reinforcing fibers according to claim 1, characterized in that, The sizing agent emulsion is selected from at least one of bisphenol A type epoxy resin and polyimide resin.

5. The sizing agent for reinforcing fibers according to claim 1, characterized in that, The surfactant is selected from at least one of fatty alcohol polyoxyethylene ether, sodium dodecylbenzenesulfonate, and octylphenol polyoxyethylene ether.

6. A method for preparing a sizing agent for reinforcing fibers according to any one of claims 1-5, characterized in that, include: Preparation of amino-modified nano-silica: Disperse nano-silica particles in a solvent, adjust the pH to 4-5, mix and react with a silane coupling agent, and separate the precipitate after the reaction; Preparation of sizing agent: Mix the sizing agent emulsion, surfactant and water in proportion, and carry out emulsification and phase inversion at 20℃-40℃. Then add the amino-modified nano silica and stir at 1000r / min-1500r / min for 30-60min.

7. The preparation method according to claim 6, characterized in that, In the preparation of the amino-modified nano-silica, the reaction temperature is controlled at 70℃-85℃, and the reaction time is 4h-6h. And / or, the mass ratio of the nano-silica particles to the silane coupling agent is 1:(0.5-2). And / or, the solvent is a mixture of ethanol and water, wherein the mass ratio of ethanol to water is 1:(0.5-1.5). And / or, 1g of the nano-silica particles corresponds to 50mL-80mL of the solvent; And / or, the stirring rate is controlled at 300 r / min-400 r / min during the reaction; And / or, after the reaction is completed, centrifuge the mixture, wash the precipitate 2-3 times with ethanol, and then vacuum dry it at 60℃-80℃ for 4-6 hours.

8. A reinforcing fiber, characterized in that, The fiber is obtained by using the sizing agent for reinforcing fibers according to any one of claims 1-5 or the preparation method according to any one of claims 6-7; Preferably, the fiber is carbon fiber; Preferably, the carbon fiber is immersed in a sizing tank for 20-30 seconds, the operating speed is 50-200 m / h, the sizing amount is 1%-2%, and then dried.

9. A composite material, characterized in that, It includes a resin matrix and the reinforcing fibers as described in claim 8.

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