Sizing agent, carbon fiber, composite material, preparation method and application

Abstract

The embodiment of the invention provides a sizing agent, a carbon fiber, a composite material, a preparation method and application, and relates to the technical field of carbon fiber application. The sizing agent is prepared from the following components in parts by weight: 90 to 100 parts of bismaleimide resin; 10 to 20 parts of an emulsifier; 5-10 parts of a diluent; wherein the emulsifier comprises a modified branched polyether nonionic emulsifier containing an epoxy group. According to the sizing agent, the carbon fiber, the composite material, the preparation method and the application, the sizing agent and the bismaleimide resin are good in adaptability, and the composite material formed by compounding the sized carbon fiber and the bismaleimide resin not only has higher interface bonding strength, but also has better impact resistance.

Description

[0001] This application claims priority to Chinese Patent Application No. 202511163070.3, filed on August 19, 2025, entitled "A Sizing Agent, Carbon Fiber, Composite Material and Preparation Method and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of carbon fiber application technology, and more specifically, to a sizing agent, carbon fiber, composite material, preparation method and application. Background Technology

[0003] Carbon fiber possesses advantages such as high specific strength, high specific modulus, light weight, high temperature resistance, and corrosion resistance, and is widely used in aerospace, transportation, construction, sporting goods, and other fields. Typically, carbon fiber undergoes surface treatment with a sizing agent and is then composited with a resin matrix to form composite materials to meet practical application requirements. Bismaleimide resin exhibits excellent heat resistance, good mechanical properties and dimensional stability, and a stable molding process, playing an irreplaceable role in the preparation of aerospace composite materials and is currently one of the most widely researched and applied important resin matrices.

[0004] Currently, epoxy sizing agents are used, with epoxy resin as their main component. Carbon fibers coated with this sizing agent exhibit good compatibility with epoxy resins, resulting in carbon fiber-epoxy resin composites with excellent interfacial properties. However, epoxy sizing agents have poor compatibility with bismaleimide resins, leading to poor interfacial properties in the resulting carbon fiber-bismaleimide resin composites, thus affecting the overall performance of the composite material. Summary of the Invention

[0005] The purpose of this application is to provide a sizing agent, carbon fiber, composite material, preparation method and application. The sizing agent has good compatibility with bismaleimide resin. The composite material formed by the sizing carbon fiber and bismaleimide resin not only has high interfacial bonding strength, but also has better impact resistance.

[0006] In a first aspect, embodiments of this application provide a sizing agent, comprising the following components by weight: 90-100 parts of bismaleimide resin; 10-20 parts emulsifier; 5-10 parts diluent; The emulsifier includes a modified branched polyether nonionic emulsifier containing epoxy groups.

[0007] In the above technical solution, the sizing agent uses bismaleimide resin as the main raw material and is mixed with a modified branched polyether nonionic emulsifier in an appropriate weight ratio to achieve good stability and adhesion. Specifically, the modified branched polyether nonionic emulsifier can uniformly disperse the bismaleimide resin, thereby improving the dispersibility and stability of the sizing agent. During the stage of applying the sizing agent to the carbon fiber and bismaleimide resin to form a composite material, the bismaleimide resin component in the sizing agent can form chemical bonds with the bismaleimide resin matrix during the curing process, thereby improving the interfacial bonding strength. Furthermore, the modified branched polyether nonionic emulsifier contains epoxy active groups in its structure, which can participate in the curing and crosslinking reaction, increasing the crosslinking density of the composite material and giving it better impact resistance. In addition, the bismaleimide resin can improve the heat resistance of the carbon fiber and even the composite material.

[0008] In one possible implementation, the bismaleimide resin includes at least one of diphenylmethane-type bismaleimide and aliphatic bismaleimide.

[0009] In one possible implementation, the diluent includes at least one of ethylene glycol butyl ether and ethanol.

[0010] In the above technical solution, the use of at least one of the diluents can be combined with the emulsifier to make the bismaleimide resin uniformly dispersed during the emulsification process, thereby improving the dispersibility and stability of the sizing agent.

[0011] In one possible implementation, the particle size of the sizing agent is 500~900 nm.

[0012] In the above technical solution, controlling the particle size of the sizing agent within the range of 500~900nm can make the sizing agent uniformly dispersed, with good stability and adhesion, improving the sizing effect on carbon fiber and enhancing the interfacial properties between carbon fiber and bismaleimide resin.

[0013] Secondly, embodiments of this application provide a method for preparing the sizing agent provided in the first aspect, which includes the following steps: The bismaleimide resin, the emulsifier, and the diluent are mixed in the above-mentioned weight proportions, and heated and stirred until uniformly mixed to obtain a mixture. Water is added to the mixture to perform reverse emulsification, thereby obtaining the sizing agent.

[0014] In the above technical solution, the sizing agent prepared by the above preparation method has good stability and adhesion, can be used to improve the interfacial properties between carbon fiber and bismaleimide resin, and has better impact resistance.

[0015] In one possible implementation, the heating and stirring conditions include: a stirring speed of 3500~5000 r / min and a heating temperature of 70~90℃.

[0016] Thirdly, embodiments of this application provide an application of the sizing agent provided in the first aspect, wherein the sizing agent is used as a sizing agent for carbon fiber surface modification.

[0017] Fourthly, embodiments of this application provide a carbon fiber, including a carbon fiber body and a coating layer located on the surface of the carbon fiber body, the coating layer being formed by curing the sizing agent provided in the first aspect.

[0018] Fifthly, embodiments of this application provide a composite material comprising a bismaleimide resin matrix and the carbon fiber provided in the fourth aspect.

[0019] Sixthly, embodiments of this application provide a method for preparing the composite material provided in the fifth aspect, which includes the following steps: Bismaleimide resin is mixed with a curing agent to form a resin mixture, and the carbon fiber is impregnated in the resin mixture and cured to form a shape.

[0020] In the above technical solution, the carbon fiber obtained by applying the sizing agent according to the above application method can be effectively adapted to the bismaleimide resin matrix and has a high interfacial bonding strength. Detailed Implementation

[0021] 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.

[0022] It should be noted that the terms "and / or" in this application, such as "feature 1 and / or feature 2", all refer to the three cases of "feature 1" alone, "feature 2" alone, and "feature 1" plus "feature 2".

[0023] In addition, in the description of this application, unless otherwise stated, "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two endpoints "a" and "b"; and "unit of measurement" in "numerical value a to numerical value b + unit of measurement" represents the "unit of measurement" of both "numerical value a" and "numerical value b".

[0024] The following provides a detailed description of the sizing agent, carbon fiber, composite material, preparation method, and application of the embodiments of this application.

[0025] This application provides a sizing agent, comprising the following components by weight: 90-100 parts of bismaleimide resin; 10-20 parts of emulsifier; and 5-10 parts of diluent. Exemplarily, the sizing agent comprises the following components by weight: 90, 92, 95, 98, or 100 parts of bismaleimide resin, or any value between any two of the above; 10, 12, 15, 17, or 20 parts of emulsifier, or any value between any two of the above; and 5, 7, 8, or 10 parts of diluent, or any value between any two of the above.

[0026] Among them, the emulsifiers include modified branched polyether nonionic emulsifiers containing epoxy groups.

[0027] For example, the modified branched polyether nonionic emulsifier includes at least one of XY-WL90 emulsifier and XY-WL80 emulsifier, which are purchased from Nanjing Xinyi Synthetic Co., Ltd.

[0028] XY-WL80 and XY-WL90 emulsifiers are epoxy-grafted modified polyether-type nonionic emulsifiers. Their structure contains epoxy active groups, which can participate in the curing and crosslinking reaction during the application stage, increasing the crosslinking density of the composite material.

[0029] The structural formula of bismaleimide is as follows: .

[0030] In this embodiment, the sizing agent uses bismaleimide resin as the main raw material and is mixed with a modified branched polyether nonionic emulsifier in an appropriate weight ratio to obtain a product with good stability and adhesion. Specifically, the modified branched polyether nonionic emulsifier can uniformly disperse the bismaleimide resin, thereby improving the dispersibility and stability of the sizing agent. During the stage of applying the sizing to the carbon fiber and bismaleimide resin to form a composite material, the bismaleimide resin component in the sizing agent can form chemical bonds with the bismaleimide resin matrix during curing, thereby improving the interfacial bonding strength. Furthermore, the modified branched polyether nonionic emulsifier contains epoxy active groups in its structure, which can participate in the curing and crosslinking reaction, increasing the crosslinking density of the composite material and giving it better impact resistance. Additionally, the bismaleimide resin can improve the heat resistance of the carbon fiber and even the composite material.

[0031] In some embodiments of this application, the bismaleimide resin includes at least one of diphenylmethane-type bismaleimide and aliphatic bismaleimide.

[0032] The structural formula of diphenylmethane bismaleimide is: .

[0033] Diphenylmethane-type bismaleimide, also known as N,N'-4,4'-diphenylmethane bismaleimide, has excellent heat resistance. The two maleimide groups are respectively attached to the two benzene rings at the 4,4' (para) positions. The methylene bridge provides a certain degree of rotational freedom, allowing the two benzene rings to rotate around the methylene group, giving the molecule a certain degree of flexibility.

[0034] For example, the diphenylmethane-type bismaleimide resin includes at least one of the grades SEM-A and SEM-B, and is purchased from Shaanxi Shuobo Electronic Materials Co., Ltd.

[0035] Among them, aliphatic bismaleimides are bifunctional maleimide compounds with an aliphatic chain as the main backbone. As one embodiment, the structural formula of aliphatic bismaleimides is two maleimide rings connected by a carbon chain, and the carbon chain structure is as follows: The carbon chain is connected to two maleimide nitrogen atoms at each end.

[0036] Aliphatic bismaleimide has low viscosity and not only possesses the heat resistance of aromatic bismaleimide resin systems, but can also improve the wettability of the resin matrix and carbon fiber during the application stage.

[0037] For example, the aliphatic bismaleimide resin includes grade SEM-23, which is purchased from Shaanxi Shuobo Electronic Materials Co., Ltd.

[0038] In some embodiments of this application, the diluent includes at least one of ethylene glycol butyl ether and ethanol.

[0039] In this embodiment, the use of at least one of the above-mentioned diluents can be combined with the emulsifier to ensure that the bismaleimide resin is uniformly dispersed during the emulsification process, thereby improving the dispersibility and stability of the sizing agent.

[0040] In some embodiments of this application, the particle size of the sizing agent is 500~900nm.

[0041] In this embodiment, controlling the particle size of the sizing agent within the range of 500~900nm can ensure uniform dispersion of the sizing agent, resulting in good stability and adhesion, improving the sizing effect on carbon fibers, and enhancing the interfacial properties between carbon fibers and bismaleimide resin.

[0042] Based on subsequent performance results, the sizing agent of this application embodiment uses bismaleimide resin as the main raw material and is mixed with modified branched polyether nonionic emulsifier in an appropriate weight ratio to obtain a sizing agent with good stability and adhesion. Furthermore, bismaleimide resin has good heat resistance, giving the sizing agent excellent heat resistance performance, with a 5% thermal weight loss > 300°C, making it suitable for the processing conditions of bismaleimide resin.

[0043] This application also provides a method for preparing the sizing agent described in the foregoing embodiments, which includes the following steps: S1. Mix the bismaleimide resin, emulsifier, and diluent according to the above weight proportions, and heat and stir until the mixture is uniform to obtain a mixture. In some embodiments of this application, the heating and stirring conditions include: a stirring speed of 3500~5000 r / min and a heating temperature of 70~90℃. Exemplarily, the stirring speed is 3500 r / min, 3700 r / min, 4000 r / min, 4200 r / min, 4500 r / min, 4800 r / min, 5000 r / min, or any intermediate value between any two of the above values; the heating temperature is 70℃, 75℃, 80℃, 85℃, 90℃, or any intermediate value between any two of the above values.

[0044] S2. Add water to the mixture to perform reverse emulsification and obtain a sizing agent.

[0045] This application also provides an application of the sizing agent described in the foregoing embodiments, wherein the sizing agent is used as a sizing agent for surface modification of carbon fibers.

[0046] This application also provides a carbon fiber, including a carbon fiber body and a coating layer located on the surface of the carbon fiber body, the coating layer being formed by curing the sizing agent of the aforementioned embodiments.

[0047] In this application embodiment, T700 grade carbon fiber was selected for evaluation and verification of the sizing agent performance. The verification showed that the sized carbon fiber had excellent abrasion resistance and fiber fuzzing amount ≤4mg / 50m.

[0048] This application also provides a method for preparing the carbon fiber described in the foregoing embodiments, comprising the following steps: The carbon fiber body is impregnated in the sizing agent of the aforementioned embodiment, and then dried after sizing.

[0049] This application also provides a composite material comprising a bismaleimide resin matrix and the carbon fiber described in the foregoing embodiments, namely, bismaleimide resin-based carbon fiber.

[0050] In the embodiments of this application, the bismaleimide matrix is ​​a bifunctional compound with maleimide (MI) as the active end group. It has similar flowability and moldability to epoxy resin, and can be processed and molded using general methods similar to epoxy resin matrix. It can also overcome the disadvantage of relatively low heat resistance of epoxy resin.

[0051] This application also provides a method for preparing the composite material of the foregoing embodiments, which includes the following steps: Carbon fiber is combined with bismaleimide resin film to make a prepreg; The prepreg is cut, laid up, and molded sequentially to obtain the composite material.

[0052] The carbon fiber after sizing in this embodiment has excellent wear resistance. In the application stage, it can be used with the processing conditions of bismaleimide resin. It has good compatibility with bismaleimide resin, high interfacial bonding strength and impact resistance, interlaminar shear strength > 90 MPa, and impact strength > 80 MPa.

[0053] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0054] Example 1 This embodiment provides a sizing agent, the preparation method of which is as follows: (1) Mix 100 parts of bismaleimide resin (specifically SEM-A), 20 parts of modified branched polyether nonionic emulsifier (specifically XY-WL90), and 10 parts of diluent (specifically ethylene glycol butyl ether), heat at 80°C, stir at 500 rpm for 30 min until the mixture is uniform, and form a mixture.

[0055] (2) Slowly add 100 parts of water to the mixture to perform reverse emulsification and form a sizing agent.

[0056] Examples 2-6 Each embodiment provides a sizing agent, the preparation method of which differs from that of Example 1 in that the composition of the sizing agent is different. The specific composition of each sizing agent is shown in Table 1.

[0057] Comparative Example 1 This comparative example provides a sizing agent selected from the commercially available sizing agent TH-831 from Tianhe Resin Co., Ltd., which is an epoxy sizing agent with modified epoxy resin as its main component.

[0058] Comparative Example 2 This comparative example provides a sizing agent selected from the commercially available sizing agent BME-21 from Shanghai Runtan New Material Technology Co., Ltd. It is a bismaleimide sizing agent, and its main component is modified bismaleimide.

[0059] Comparative Example 3 This comparative example provides a sizing agent, the preparation method of which differs from that of Example 1 in that: Tween 80 is used as an emulsifier in this comparative example, replacing the modified branched polyether nonionic emulsifier in Example 1.

[0060] Table 1 Composition of sizing agent

[0061] Experimental Example 1 I. The stability of the sizing agents provided in Examples 1-6 and Comparative Examples 1-3 was tested. The specific method was as follows: an appropriate amount of deionized water was slowly added to each of the above sizing agents and stirred continuously to prepare a sizing agent emulsion with a solid content of 10%. The emulsion was left to stand at room temperature for 24 hours and observed whether the sizing agent emulsion produced phenomena such as layering, precipitation, or demulsification.

[0062] II. The heat resistance of the sizing agents provided in Examples 1-6 and Comparative Examples 1-3 was analyzed and tested using a thermogravimetric analyzer. The specific method is as follows: Each of the above sizing agents was dripped onto a glass slide using a dropper (in a dotted pattern); the glass slide was dried in an oven at 120°C for 30 minutes; an appropriate amount (6-8 mg) of the dried sample was taken from the glass slide and added to a tare crucible, and the sample was ready for testing. Set the thermogravimetric analysis instrument test conditions, i.e., in an air atmosphere, set the temperature range to 30~800℃, the heating rate to 10℃ / min, and add the dried sample (6~8mg) to be tested to the crucible for testing.

[0063] 3. The carbon fiber body (T700 grade carbon fiber) was impregnated in the sizing agents provided in Examples 1-6 and Comparative Examples 1-3, respectively. After sizing, it was dried. During this process, the carbon fiber running speed was 600m / min, the carbon fiber impregnation time was 5s, the drying temperature was 200℃, and the drying time was 10s. The sized carbon fiber was obtained, and the content of the coating layer formed by the sizing agent on the surface of the carbon fiber was tested.

[0064] The test results are shown in Table 2.

[0065] Table 2 Performance of sizing agents

[0066] Note: " / " in the table indicates that the data cannot be tested.

[0067] As shown in Table 2, compared to the commercially available sizing agent in Comparative Example 1, the sizing agents provided in Examples 1-5 have higher 5% thermogravimetric temperatures, and the carbon fibers treated with the sizing agents provided in Examples 1-5 all have higher coating layer (sizing agent) content. Therefore, it can be concluded that the embodiments of this application, using bismaleimide resin as the main raw material and a modified branched polyether nonionic emulsifier in an appropriate weight ratio, can obtain a stable, uniform sizing agent with strong adhesion. Furthermore, based on the good heat resistance of bismaleimide resin, a sizing agent with high heat resistance is obtained. The sizing agent in Comparative Example 3 experienced emulsion stratification and could not be used for fiber sizing.

[0068] Experimental Example 2 I. Preparation of composite materials: (1) The carbon fibers after sizing were prepared using the above method and process; (2) The bismaleimide resin film (SC4-B, Zhongfu Shenying (Shanghai) Technology Co., Ltd.) was impregnated and cured with each sized carbon fiber. The specific process is as follows: each sized carbon fiber is combined with the bismaleimide resin film to make a prepreg; the prepreg is cut, laid up and molded in sequence to obtain bismaleimide resin-based carbon fiber composite material.

[0069] II. In accordance with GB / T 1043.2 The 2018 and ASTM D 2344 standards were used to conduct interlaminar shear tests and impact strength tests on various composite materials. The test results are shown in Table 3.

[0070] Table 3 Properties of Composite Materials

[0071] As shown in Table 3, compared with the composite material formed by carbon fiber and bismaleimide resin after sizing with the sizing agent provided in Comparative Example 1, the composite material formed by carbon fiber and bismaleimide resin after sizing with the sizing agents provided in Examples 1-5 has a significantly higher lamellar shear strength. Therefore, it can be seen that the use of bismaleimide resin as the main raw material in the embodiments of this application can improve the interfacial properties between the sizing carbon fiber and bismaleimide resin.

[0072] Compared to the composite materials formed by carbon fibers and bismaleimide resin after sizing with the sizing agents provided in Comparative Examples 1-2, the composite materials formed by carbon fibers and bismaleimide resin after sizing with the sizing agents provided in Examples 1-5 exhibit higher impact strength. This is because the modified branched polyether nonionic emulsifier in the sizing agent contains epoxy active groups, which can participate in the curing and crosslinking reaction, increasing the crosslinking density of the composite material. In contrast, the sizing agent provided in Comparative Example 2 uses traditional emulsifiers such as Span 80 and Tween 80, which only provide emulsification and dispersion in the system. During the curing process, because they do not participate in the curing reaction and have low temperature resistance, they may decompose or accumulate as impurities within the composite material due to heat, leading to performance defects.

[0073] Based on the results in Tables 2 and 3, it can be seen that the heat resistance of the sizing agents in Examples 1 to 5 is improved to varying degrees compared with Comparative Example 1. The interlaminar shear properties and impact resistance of the carbon fibers and bismaleimide resin after sizing with the sizing agents in Examples 1 to 5 are significantly improved compared with Comparative Example 1.

[0074] The heat resistance of the sizing agents in Examples 1-5 is improved or comparable to that of Comparative Example 2. The interlaminar shear properties of the carbon fibers and bismaleimide resin after sizing with the sizing agents in Examples 1-5 are similar to those in Comparative Example 2, but the impact resistance is improved compared to Comparative Example 2.

[0075] Therefore, it can be seen that the carbon fiber coated with the sizing agent in this application embodiment is suitable for the processing conditions of bismaleimide resin in the application stage; at the same time, the main component of the sizing agent, bismaleimide resin, can form chemical bonds with the bismaleimide resin matrix during the curing process, thereby effectively adapting to the bismaleimide resin and having high interfacial bonding strength.

[0076] The sizing agent provided in Example 6 is N,N'-m-phenylenebismaleimide. As the main component, bismaleimide resin has a rigid benzene ring and the two connection points are in the meta position, which makes the entire molecule almost inflexible. When subjected to impact, the molecule has poor buffering ability and low impact resistance. Furthermore, due to its high rigidity, this sizing agent can easily lead to high fiber hardness and poor fuzziness after sizing carbon fibers.

[0077] In summary, the sizing agent, carbon fiber, composite material, preparation method, and application of the embodiments of this application show that the sizing agent has good compatibility with bismaleimide resin. The composite material formed by the sizing carbon fiber and bismaleimide resin not only has high interfacial bonding strength but also good impact resistance.

[0078] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A sizing agent, characterized in that, By weight, it comprises the following components: 90-100 parts of bismaleimide resin; 10-20 parts emulsifier; 5-10 parts diluent; The emulsifier includes a modified branched polyether nonionic emulsifier containing epoxy groups.

2. The sizing agent according to claim 1, characterized in that, The bismaleimide resin includes at least one of diphenylmethane-type bismaleimide and aliphatic bismaleimide.

3. The sizing agent according to claim 1, characterized in that, The diluent includes at least one of ethylene glycol butyl ether and ethanol.

4. The sizing agent according to claim 1, characterized in that, The particle size of the sizing agent is 500~900nm.

5. A method for preparing a sizing agent as described in any one of claims 1 to 4, characterized in that, It includes the following steps: The bismaleimide resin, the emulsifier, and the diluent are mixed in the above-mentioned weight proportions, and heated and stirred until uniformly mixed to obtain a mixture. Water is added to the mixture to perform reverse emulsification, thereby obtaining the sizing agent.

6. The method for preparing the sizing agent according to claim 5, characterized in that, The heating and stirring conditions include: a stirring speed of 3500~5000 r / min and a heating temperature of 70~90℃.

7. The application of a sizing agent as described in any one of claims 1 to 4, characterized in that, The sizing agent is used as a sizing agent for carbon fiber surface modification.

8. A carbon fiber, characterized in that, It includes a carbon fiber body and a coating layer located on the surface of the carbon fiber body, the coating layer being formed by curing a sizing agent as described in any one of claims 1 to 4.

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

10. A method for preparing the composite material as described in claim 9, characterized in that, It includes the following steps: The carbon fiber is combined with a bismaleimide resin film to prepare a prepreg. The prepreg is sequentially cut, laid up, and molded to obtain the composite material.

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