A carbon fiber sizing agent and a preparation method thereof, a sized carbon fiber and a preparation method thereof

Abstract

This application relates to a carbon fiber sizing agent and its preparation method, as well as sized carbon fibers and their preparation method, belonging to the technical field of carbon fiber sizing agents. A carbon fiber sizing agent includes benzoxazine resin, amino-modified resin, emulsifier, and solvent. This application uses benzoxazine resin as the main raw material and introduces amino-modified resin, enabling the benzoxazine resin to undergo a graft crosslinking reaction with the amino-modified resin at high temperature during carbon fiber sizing, and also allowing the benzoxazine resin itself to undergo epoxy ring-opening polymerization, forming a self-crosslinking reaction. These crosslinking reactions improve the heat resistance and interfacial properties of the sizing agent, thereby effectively enhancing the interfacial properties of the composite material formed between the carbon fiber and the resin matrix.

Description

Technical Field

[0001] This application relates to the field of carbon fiber sizing agents, and particularly to a carbon fiber sizing agent and its preparation method, as well as sized carbon fibers and their preparation method. Background Technology

[0002] After low-temperature and high-temperature carbonization, carbon fibers exhibit surface inertness, resulting in fewer groups that interact with the resin matrix and weak interfacial bonding. Under no-tension conditions, they exist in a loose and disordered state, necessitating further sizing treatment. The sizing process provides bundle protection for the carbon fibers, reducing single-filament breakage caused by friction. Simultaneously, the sizing agent acts as an interfacial layer connecting the carbon fibers and the matrix resin, increasing the polar groups on the carbon fiber surface and improving the wettability and penetration of the resin, thereby enhancing the interfacial adhesion strength between the resin and the fiber.

[0003] Currently, emulsion-type sizing is widely used both domestically and internationally. Emulsion-type sizing uses resin as the main component, combined with certain emulsifiers to prepare an aqueous emulsion. The concentration of aqueous emulsions is easy to control and has excellent safety. However, most existing emulsion-type sizing agents have poor heat resistance, resulting in weak interfacial bonding strength between the carbon fibers and the resin matrix after sizing. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the objectives of this application include providing a carbon fiber sizing agent and its preparation method, as well as sized carbon fibers and their preparation method, to improve the heat resistance and interfacial properties of the sizing agent.

[0005] The embodiments of this application are implemented as follows:

[0006] In a first aspect, embodiments of this application provide a carbon fiber sizing agent, comprising benzoxazine resin, amino-modified resin, emulsifier, and solvent.

[0007] This application uses benzoxazine resin as the main raw material and introduces amino-modified resin. When the sizing agent is used to sizing carbon fibers, the benzoxazine resin undergoes a graft crosslinking reaction with the amino-modified resin at high temperatures, and the benzoxazine resin itself undergoes epoxy ring-opening polymerization, forming a self-crosslinking reaction. The network structure formed by self-crosslinking effectively improves the heat resistance of the resin because this structure can disperse heat energy and reduce heat conduction, making the resin less prone to degradation at high temperatures. The formation of this crosslinking network increases the rigidity and toughness of the resin, allowing the sizing agent to maintain good mechanical properties at high temperatures, thereby improving the strength of the composite material formed by the bonding of carbon fibers and the resin matrix. The graft crosslinking reaction forms new chemical bonds between the benzoxazine resin and the amino resin, enhancing the bonding force between the carbon fibers and the resin matrix. This enhanced interfacial bonding force effectively reduces the risk of interfacial delamination and improves the overall performance of the composite material. Moreover, the chemical bonds generated by the graft crosslinking reaction remain stable at high temperatures, further improving the heat resistance of the material. This robust interfacial characteristic allows the composite material to maintain good mechanical properties and stability even at high temperatures.

[0008] In some embodiments of this application, the components, by weight, include: 100 parts of benzoxazine resin, 20-50 parts of amino-modified resin, 20-40 parts of solvent, and 30-50 parts of emulsifier.

[0009] In this sizing agent, benzoxazine resin, as the main component, provides excellent heat resistance and thermal stability, enabling the sizing agent to maintain its physical and chemical properties even in high-temperature environments. It undergoes a self-crosslinking reaction at high temperatures, forming a three-dimensional crosslinked network, significantly enhancing the mechanical strength and rigidity of the material, thereby improving the overall performance of the composite material. Furthermore, the addition of amino-modified resin not only allows it to undergo a graft crosslinking reaction with benzoxazine resin to form a more complex polymer network, but also effectively improves the interfacial bonding force between carbon fibers and the resin matrix, reducing the risk of delamination and peeling, and improving interfacial properties. Further, the introduction of solvent plays a crucial role in adjusting the viscosity of the sizing agent, making it easier to coat and ensuring uniformity, thus improving the sizing effect. Simultaneously, the solvent also promotes the emulsification process of the sizing agent, allowing the active ingredients to be evenly dispersed, further enhancing the stability of the sizing agent. The use of emulsifiers plays a key role in stabilizing the emulsion, preventing delamination and sedimentation, and improving the consistency and reliability of the sizing agent during storage and use.

[0010] In some embodiments of this application, the particle size of the carbon fiber sizing agent is 200-500 nm.

[0011] The particle size of the carbon fiber sizing agent is in the range of 200-500nm, which can effectively improve dispersibility, enhance interfacial bonding, improve reactivity, improve flowability, and has good adaptability.

[0012] In some embodiments of this application, the benzoxazine resin includes one or more of bisphenol A type benzoxazine, bisphenol F type benzoxazine, and phenol type benzoxazine.

[0013] These types of benzoxazine resins not only offer excellent thermal stability and mechanical properties, but also good chemical resistance and tunability.

[0014] In some embodiments of this application, the amino-modified resin includes one or more of urea-formaldehyde resin, melamine-formaldehyde resin, and benzo-melamine-formaldehyde resin.

[0015] These amino-modified resins possess excellent adhesive properties, enhancing the bonding force between carbon fibers and the resin matrix. Furthermore, they exhibit good thermal stability at high temperatures and can undergo graft crosslinking reactions with other resins (such as benzoxazine resins) at high temperatures to form stable crosslinked networks. This crosslinking reaction not only improves the material's heat resistance but also enhances its mechanical properties and toughness.

[0016] In some embodiments of this application, the solvent includes one or more of toluene, acetone, and tetrahydrofuran.

[0017] The choice of solvents such as toluene, acetone, and tetrahydrofuran provides good solubility, appropriate volatility and flowability, while effectively adjusting viscosity and improving the overall performance of the sizing agent.

[0018] In some embodiments of this application, the emulsifier includes one or more of alkylphenol polyoxyethylene ether, polyethylene glycol, and polyoxyethylene sorbitan fatty acid ester.

[0019] These emulsifiers provide excellent emulsifying properties, improve the stability of sizing emulsions, and enhance the dispersibility of components in sizing agents, enabling the active ingredients to be evenly distributed.

[0020] Secondly, embodiments of this application provide a method for preparing the above-mentioned carbon fiber sizing agent, comprising: stirring and mixing benzoxazine resin, amino-modified resin, emulsifier and solvent, adding water for emulsification and phase inversion, to obtain carbon fiber sizing agent.

[0021] This method involves mixing benzoxazine resin, amino-modified resin, emulsifier, and solvent, followed by the addition of water for emulsification and phase inversion. The process is relatively simple and easy to operate. This simplified process helps improve production efficiency and reduce production time and costs.

[0022] Thirdly, embodiments of this application provide a sized carbon fiber, including carbon fiber and a sizing agent coating attached to the surface of the carbon fiber, wherein the sizing agent coating is formed from any of the aforementioned carbon fiber sizing agents.

[0023] In this sized carbon fiber, the sizing agent coating can effectively enhance the bonding force between the carbon fiber and the resin matrix. The sizing agent used (containing benzoxazine resin and amino-modified resin) has excellent heat resistance, which enables the sized carbon fiber to maintain good performance in high-temperature environments.

[0024] In some embodiments of this application, the sizing agent coating accounts for 0.5-1.0% of the mass fraction of the carbon fiber.

[0025] Controlling the sizing amount (the mass fraction of the sizing agent coating on the carbon fiber) to 0.5-1.0% makes it easier to achieve a uniform coating effect, effectively enhances interfacial bonding and heat resistance, and maintains the excellent mechanical properties of the carbon fiber.

[0026] Fourthly, this application provides a method for preparing the above-mentioned sized carbon fiber, comprising: preparing a sizing agent into a sizing agent solution, immersing carbon fiber in the sizing agent solution, and then subjecting the treated carbon fiber to drying and heating curing treatments in sequence to obtain sized carbon fiber.

[0027] This method involves preparing a sizing agent solution and then immersing the carbon fibers in it. This process is simple and easy to implement. Immersing the carbon fibers in the sizing agent solution improves the uniformity of the coating. The immersion process allows the sizing agent to fully penetrate each filament of the carbon fibers, thereby increasing the surface functionalization and enhancing interfacial adhesion. During drying and heat curing, the components in the sizing agent effectively cross-link, forming a stable coating. This cross-linking process not only improves the mechanical strength and heat resistance of the coating but also enhances the bonding force between the carbon fibers and the resin matrix, improving the overall performance of the composite material.

[0028] In some embodiments of this application, the drying conditions include a drying temperature of 130-160°C and a drying time of 30-60 seconds.

[0029] The drying conditions are set at a temperature of 130-160℃ and a time of 30-60 seconds, which can effectively remove solvents, prevent carbon fiber damage, promote cross-linking reaction, enhance coating adhesion, optimize the subsequent curing process, and improve production efficiency.

[0030] In some embodiments of this application, the conditions for heat curing include: a heating temperature of 180-220°C and a heating time of 30-60 seconds.

[0031] The heating and curing conditions are set at 180-220℃ and 30-60s, which can effectively promote cross-linking, improve coating uniformity, enhance heat resistance and chemical stability, strengthen adhesion, optimize processing performance, and improve production efficiency. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application 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.

[0033] The following is a detailed description of a carbon fiber sizing agent and its preparation method, as well as sized carbon fibers and their preparation method, according to embodiments of this application.

[0034] This application provides a carbon fiber sizing agent, comprising benzoxazine resin, amino-modified resin, emulsifier, and solvent.

[0035] Benzoxazines are a class of heterocyclic compounds synthesized from phenols, aldehydes, and primary amines. This application uses benzoxazine resin as the main component and introduces an amino-modified resin, enabling the sizing agent to undergo a series of crosslinking reactions with the amino-modified resin at high temperatures during carbon fiber sizing, including self-crosslinking and graft crosslinking reactions. After sizing the carbon fiber, it is dried. At high temperatures, the benzoxazine resin itself undergoes epoxy ring-opening polymerization, forming a self-crosslinking reaction. This process involves the formation of chemical bonds between the molecular chains of benzoxazine resin, creating a three-dimensional network structure. This network structure effectively improves the resin's heat resistance, increases its rigidity and toughness, and allows the sizing agent to maintain good mechanical properties at high temperatures, thereby enhancing the strength of the composite material formed by the bonding of carbon fibers and the matrix. On the other hand, the O-hexaazine ring in the benzoxazine resin undergoes a grafting crosslinking reaction with the amino group in the amino resin. This grafting crosslinking reaction not only improves the thermal stability of the sizing agent but also significantly enhances the bonding force between the carbon fibers and the resin matrix. Through the grafting crosslinking reaction, a more complex polymer network is formed, further improving interfacial properties and reducing the risk of delamination and debonding.

[0036] The composition, by weight, includes: 100 parts of benzoxazine resin, 20-50 parts of amino-modified resin, 20-40 parts of solvent, and 30-50 parts of emulsifier.

[0037] In this sizing agent, benzoxazine resin, as the main component, provides excellent thermal stability and high-temperature resistance, allowing the sizing agent to maintain its physical and chemical properties even at high temperatures. Benzoxazine resin can spontaneously undergo epoxy ring-opening polymerization at high temperatures, forming a cross-linked network that enhances the mechanical strength and rigidity of the resin, improving the overall performance of the composite material. Amino-modified resin can undergo graft cross-linking reactions with benzoxazine resin, forming a more complex polymer network. This reaction not only improves heat resistance but also enhances the toughness of the material. Amino-modified resin can strengthen the bonding force between carbon fibers and the resin matrix, improving interfacial properties and reducing the risk of delamination and peeling. Solvents can adjust the viscosity of the sizing agent, enabling it to be uniformly coated on the carbon fiber surface, improving the sizing effect. Furthermore, solvents facilitate the emulsification process of the sizing agent, allowing the active ingredients to be uniformly dispersed in the emulsion, thus improving the stability of the sizing agent. Emulsifiers play a role in stabilizing the emulsion in the formulation, preventing delamination and sedimentation, and also improving the dispersibility of the components in the sizing agent, allowing the active ingredients to fully contact the carbon fibers, improving the sizing effect.

[0038] In this embodiment, the particle size of the carbon fiber sizing agent is 200-500 nm.

[0039] Sizing agents with a particle size of 200-500 nm maintain good dispersibility and flowability in water or organic solvents, allowing for uniform coating of the carbon fiber surface and reducing the generation of bubbles and defects. Furthermore, sizing agents in this particle size range can better penetrate the microstructure of the carbon fiber, thereby increasing the contact area between the carbon fiber and the resin matrix. This improves interfacial adhesion, reduces the risk of delamination and peeling, and enhances the overall performance of the composite material. In addition, sizing agents in this particle size range have a large specific surface area, which can increase the reactivity between the carbon fiber and the resin matrix, thus promoting cross-linking reactions and further enhancing the material's heat resistance and mechanical properties.

[0040] As an example, benzoxazine resins include, but are not limited to, one or more of bisphenol A type benzoxazine, bisphenol F type benzoxazine, and phenol type benzoxazine.

[0041] Among them, bisphenol A, bisphenol F, and phenolic benzoxazine resins all exhibit high thermal stability, good resistance to various chemicals (such as acids, alkalis, and solvents), and good mechanical strength and toughness. Bisphenol A resin demonstrates excellent tensile strength and impact resistance, while bisphenol F resin excels in abrasion resistance. These benzoxazine resins can undergo self-crosslinking or crosslinking reactions with other components at high temperatures, forming complex polymer networks. This crosslinking ability not only improves the material's heat resistance and mechanical properties but also enhances the interfacial bonding between carbon fibers and the resin matrix.

[0042] As an example, amino-modified resins include, but are not limited to, one or more of urea-formaldehyde resin, melamine-formaldehyde resin, and benzo-melamine-formaldehyde resin.

[0043] Urea-formaldehyde resin and melamine-formaldehyde resin exhibit excellent adhesive properties, effectively enhancing the bonding force between carbon fibers and the resin matrix. This strong adhesive property helps improve the overall structural strength of the composite material and reduces the risk of delamination and peeling. Melamine-formaldehyde resin and benzo-melamine-formaldehyde resin demonstrate good thermal stability at high temperatures, maintaining their physical and chemical properties in high-temperature environments. These amino-modified resins exhibit good resistance to various chemicals (such as acids, alkalis, and solvents), allowing the composite material to maintain excellent performance even in harsh environments. Moreover, these amino-modified resins can undergo cross-linking reactions with other resins (such as benzoxazine resin) at high temperatures, forming a stable cross-linked network. This cross-linking reaction not only improves the material's heat resistance but also enhances its mechanical properties and toughness.

[0044] As an example, the solvent includes, but is not limited to, one or more of toluene, acetone, and tetrahydrofuran.

[0045] Toluene, acetone, and tetrahydrofuran are all excellent solvents, effectively dissolving benzoxazine resins and amino-modified resins. This excellent solubility allows for uniform dispersion of the active ingredients in the sizing agent, improving its performance. These solvents have moderate volatility, evaporating rapidly during coating and curing, reducing material drying time. This rapid volatility contributes to increased production efficiency, enabling the sizing agent to cure quickly and form a stable coating. Toluene, acetone, and tetrahydrofuran improve the flowability of the sizing agent, making it easier to flow and distribute during application, reducing the formation of bubbles and defects, thereby improving the quality of the final product.

[0046] As an example, the emulsifier includes, but is not limited to, one or more of alkylphenol polyoxyethylene ethers, polyethylene glycol, and polyoxyethylene sorbitan fatty acid esters.

[0047] These emulsifiers possess excellent emulsifying capabilities, effectively dispersing benzoxazine resins and amino-modified resins in aqueous phases or organic solvents to form stable emulsions. This improves the uniformity of the sizing agent and contributes to enhanced coating results. Alkylphenol polyoxyethylene ethers and polyethylene glycol, in particular, significantly improve emulsion stability, preventing delamination and sedimentation. These emulsifiers improve the dispersibility of components in the sizing agent, ensuring uniform distribution of active ingredients; they also improve the interfacial compatibility between the resin and carbon fiber, enhancing their bonding strength. By forming good interfacial contact, they improve the overall performance of the composite material and reduce the risk of delamination and peeling.

[0048] The preparation method of the above-mentioned carbon fiber sizing agent is described below.

[0049] A method for preparing the above-mentioned carbon fiber sizing agent includes: stirring and mixing benzoxazine resin, amino-modified resin, emulsifier and solvent, adding water to emulsify and invert the phase, and obtaining the carbon fiber sizing agent.

[0050] In this preparation method, stirring and mixing effectively transforms the organic phase into a stable emulsion, allowing the effective components of the resin to be well dispersed in the aqueous phase, thus improving the uniformity and stability of the sizing agent. Using an aqueous phase for emulsification reduces dependence on organic solvents, and the emulsification process significantly improves the stability of the sizing agent, preventing stratification and sedimentation. In summary, this preparation method simplifies the process flow, achieving uniform mixing of components, effective emulsification, and improved stability.

[0051] This application also provides a sized carbon fiber, including carbon fiber and a sizing agent coating attached to the surface of the carbon fiber, wherein the sizing agent coating is formed by any of the above-mentioned carbon fiber sizing agents.

[0052] By coating the carbon fiber with the sizing agent of this application, the surface of the carbon fiber is functionalized, improving its compatibility with the resin, thereby reducing the risk of delamination and peeling and improving the overall strength of the composite material; the sizing agent has excellent heat resistance, enabling the sized carbon fiber to maintain good performance in high-temperature environments.

[0053] The sizing agent coating accounts for 0.5-1.0% of the carbon fiber by mass. For example, the sizing agent coating accounts for, but is not limited to, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, and 1.0% of the carbon fiber by mass.

[0054] Within this sizing amount range, the coating can be more uniform, and the resulting sizing agent coating has a moderate thickness. While enhancing interfacial bonding and heat resistance, it can also maintain the excellent mechanical properties of carbon fibers.

[0055] The preparation method of the above-mentioned sized carbon fiber is described below.

[0056] A method for preparing the above-mentioned sized carbon fiber includes: preparing a sizing agent into a sizing agent solution, immersing carbon fiber in the sizing agent solution, and then subjecting the treated carbon fiber to drying and heating curing treatments in sequence to obtain sized carbon fiber.

[0057] The drying conditions include a drying temperature of 130-160℃ and a drying time of 30-60 seconds.

[0058] Within this temperature range, the solvent in the sizing agent solution can be removed quickly and effectively, improving the uniformity and stability of the coating. At the aforementioned drying temperature range, partial cross-linking of the resin components in the sizing agent can be promoted, contributing to improved mechanical strength and heat resistance of the coating.

[0059] The conditions for heat curing include: a heating temperature of 180-220℃ and a heating time of 30-60 seconds.

[0060] Within a temperature range of 180-220℃, the cross-linking reaction of the resin in the sizing agent can be effectively promoted. This process helps to form a stable three-dimensional network structure, significantly improving the mechanical strength and heat resistance of the coating, thereby enhancing the overall performance of the composite material. A heating time of 30-60 seconds allows the coating to be heated uniformly during the curing process. Through heat curing, the heat resistance and chemical stability of the coating can be significantly improved, as well as the adhesion between the sizing agent coating and the carbon fiber.

[0061] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0062] Example 1

[0063] This embodiment provides a carbon fiber sizing agent, the preparation method of which includes the following steps:

[0064] 100g of bisphenol A type benzoxazine resin, 20g of urea-formaldehyde resin, 30g of alkylphenol polyoxyethylene ether and 20g of acetone were stirred and mixed, and water was added for emulsification and phase inversion to obtain carbon fiber sizing agent.

[0065] Example 2

[0066] This embodiment provides a carbon fiber sizing agent, the preparation method of which includes the following steps:

[0067] 100g of bisphenol F type benzoxazine resin, 35g of melamine formaldehyde resin, 40g of polyethylene glycol and 30g of toluene were stirred and mixed, and water was added for emulsification and phase inversion to obtain carbon fiber sizing agent.

[0068] Example 3

[0069] This embodiment provides a carbon fiber sizing agent, the preparation method of which includes the following steps:

[0070] 100g of phenolic benzoxazine resin, 40g of melamine-formaldehyde resin, 50g of polyoxyethylene sorbitan fatty acid ester and 40g of tetrahydrofuran were stirred and mixed, and water was added for emulsification and phase inversion to obtain carbon fiber sizing agent.

[0071] Example 4

[0072] This embodiment provides a carbon fiber sizing agent, the preparation method of which includes the following steps:

[0073] 100g of bisphenol A type benzoxazine resin, 20g of urea-formaldehyde resin, 20g of alkylphenol polyoxyethylene ether and 10g of acetone were stirred and mixed, and water was added for emulsification and phase inversion to obtain carbon fiber sizing agent.

[0074] Example 5

[0075] This embodiment provides a carbon fiber sizing agent, the preparation method of which includes the following steps:

[0076] 100g of bisphenol A type benzoxazine resin, 60g of urea-formaldehyde resin, 30g of alkylphenol polyoxyethylene ether and 20g of acetone were stirred and mixed, and water was added for emulsification and phase inversion to obtain carbon fiber sizing agent.

[0077] Example 6

[0078] This embodiment provides a carbon fiber sizing agent, the preparation method of which includes the following steps:

[0079] 100g of bisphenol A type benzoxazine resin, 15g of urea-formaldehyde resin, 30g of alkylphenol polyoxyethylene ether and 20g of acetone were stirred and mixed, and water was added for emulsification and phase inversion to obtain carbon fiber sizing agent.

[0080] Comparative Example 1

[0081] This comparative example is basically the same as Example 1, except that urea-formaldehyde resin is not added.

[0082] Comparative Example 2

[0083] This comparative example is basically the same as Example 1, except that bisphenol A type benzoxazine resin is not added.

[0084] For some parameters of Examples 1-6 and Comparative Examples 1 and 2 above, please refer to Table 1.

[0085] Table 1

[0086]

[0087] Experimental Example 1

[0088] The sizing agents prepared in Examples 1-6 and Comparative Examples 1 and 2 were respectively formulated into sizing agent solutions. Seven groups of identical carbon fibers were divided and immersed in the sizing agent solutions. These treated carbon fibers were then dried at 140°C for 50 seconds and then cured at 210°C for 50 seconds to obtain sized carbon fibers (sizing amount 0.5–1.0%). Epoxy resin E51 and curing agent DDS were mixed to form an epoxy resin matrix mixture. The sized carbon fibers in each group were impregnated with the epoxy resin matrix mixture and cured to obtain carbon fiber composite materials. In this experimental example, the thermal decomposition initiation temperature of these sizing agents and the interlaminar shear strength of the composite materials were measured.

[0089] Among them, the determination of the thermal decomposition initiation temperature is the temperature at which the effective solid components of the sizing agent volatilize to 5% in an air environment.

[0090] Interlaminar shear strength determination: The test was conducted in accordance with the national standard GB / T30969-2014.

[0091] Please refer to Table 2 for the measurement results of the above items.

[0092] Table 2

[0093]

[0094] As shown in Table 2, the particle size of the sizing agent increased significantly after the solvent and emulsifier content was reduced in Example 4. This resulted in poorer uniformity of the sizing agent's wetting of the carbon fibers, which in turn led to a decrease in the interlaminar shear strength of the carbon fiber composite material and consequently reduced the interfacial bonding ability of the sizing agent. By comparing Examples 1, 5, and 6, it can be found that a mass ratio of amino-modified resin to benzoxazine resin in the range of (2-5):1 is more beneficial for improving the heat resistance and interfacial bonding ability of the sizing agent.

[0095] In Example 4, the emulsification effect was reduced due to insufficient emulsifier content. Secondly, the resin mixing and dissolution were insufficient due to insufficient solvent content, which increased the difficulty of resin emulsification and consequently led to larger particle size of the sizing agent emulsion.

[0096] In Comparative Example 1, without the addition of amino-modified resin, the thermal decomposition temperature was found to be significantly lower, indicating a decrease in the heat resistance of the sizing agent. At the same time, the interlaminar shear strength of the carbon fiber composite material also decreased, and the interfacial bonding reaction ability weakened.

[0097] In Comparative Example 2, without the addition of bisphenol A type benzoxazine resin, it was found that the thermal decomposition temperature and interlaminar shear strength both decreased significantly, indicating that the sizing agent had low heat resistance and weak interfacial properties.

[0098] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A carbon fiber sizing agent, characterized in that, By weight, it includes: The mixture comprises 100 parts of benzoxazine resin, 20-50 parts of amino-modified resin, 20-40 parts of solvent, and 30-50 parts of emulsifier; wherein the amino-modified resin includes one or more of urea-formaldehyde resin, melamine-formaldehyde resin, and benzo-melamine-formaldehyde resin.

2. The carbon fiber sizing agent according to claim 1, characterized in that, The particle size of the carbon fiber sizing agent is 200-500 nm.

3. The carbon fiber sizing agent according to claim 1 or 2, characterized in that, The benzoxazine resin includes one or more of bisphenol A benzoxazine, bisphenol F benzoxazine, and phenolic benzoxazine.

4. The carbon fiber sizing agent according to claim 1 or 2, characterized in that, The solvent includes one or more of toluene, acetone, and tetrahydrofuran.

5. The carbon fiber sizing agent according to claim 1 or 2, characterized in that, The emulsifier includes one or more of alkylphenol polyoxyethylene ether, polyethylene glycol, and polyoxyethylene sorbitan fatty acid ester.

6. A method for preparing a carbon fiber sizing agent as described in any one of claims 1-5, characterized in that, include: The benzoxazine resin, the amino-modified resin, the emulsifier, and the solvent are stirred and mixed, and water is added for emulsification and phase inversion to obtain the carbon fiber sizing agent.

7. A type of sized carbon fiber, characterized in that, Includes carbon fibers and a sizing agent coating attached to the surface of the carbon fibers, the sizing agent coating being as described in claim 1. The carbon fiber sizing agent as described in any one of the 5 is formed.

8. The sized carbon fiber according to claim 7, characterized in that, The sizing agent coating accounts for 0.5-1.0% of the mass fraction of the carbon fiber.

9. A method for preparing sized carbon fiber as described in claim 7 or 8, characterized in that, include: The sizing agent is prepared into a sizing agent impregnation solution, and the carbon fiber is immersed in the sizing agent impregnation solution. Subsequently, the treated carbon fiber is subjected to drying and heat curing treatment in sequence to obtain the sizing carbon fiber.

10. The preparation method according to claim 9, characterized in that, The drying conditions include: a drying temperature of 130-160℃ and a drying time of 30-60s.

11. The preparation method according to claim 9, characterized in that, The conditions for heat curing include: a heating temperature of 180-220℃ and a heating time of 30-60s.

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