Sizing agent with high humidity and heat resistance, carbon fiber, composite material and preparation method

Abstract

The embodiment of the invention provides a sizing agent with high humidity and heat resistance, a carbon fiber, a composite material and a preparation method, and relates to the technical field of preparation of high-performance carbon fibers. The sizing agent with high humidity and heat resistance comprises the following components in parts by weight: 20-30 parts of phenol novolac epoxy resin; 10 to 20 parts of dicyclopentadiene phenol epoxy resin; 10 to 30 parts of MDI modified epoxy resin; 10 to 15 parts of a nonionic surfactant; and 50-60 parts of water. According to the sizing agent with high humidity and heat resistance, the carbon fiber, the composite material and the preparation method, the interface bonding strength is high, and the humidity and heat resistance stability is good.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high-performance carbon fiber preparation, in particular to a sizing agent with high moisture and heat resistance, carbon fiber and composite material and a preparation method. BACKGROUND

[0002] During the preparation of carbon fiber, low-temperature and high-temperature carbonization treatment will cause surface inertness, and the carbon fiber is in a loose state under no tension and has few groups interacting with a resin matrix and weak interfacial bonding capacity, so that the surface of the carbon fiber needs to be sized. Through the sizing treatment process, the carbon fiber is protected and bundled, and the single fiber breakage caused by friction is reduced; meanwhile, the surface of the carbon fiber is increased in polar groups, which are used as an interfacial layer connecting the carbon fiber and the resin matrix, so that the wettability and permeability of the surface of the carbon fiber and the resin matrix are improved, and the interfacial adhesion strength of the resin matrix and the carbon fiber is enhanced.

[0003] At present, the sizing agent used for sizing treatment is mainly glycidyl ether type epoxy resin such as E51 and E44, the carbon fiber treated by the sizing agent has high interfacial bonding strength with the epoxy resin matrix; however, the corresponding carbon fiber reinforced resin matrix composite material has poor moisture and heat resistance, which affects the popularization and application of the sizing agent. SUMMARY

[0004] The purpose of the embodiment of the application is to provide a sizing agent with high moisture and heat resistance, carbon fiber and composite material and a preparation method, which have high interfacial bonding strength and good moisture and heat resistance.

[0005] In the first aspect, the embodiment of the application provides a sizing agent with high moisture and heat resistance, which comprises the following components in parts by weight: phenol novolac epoxy resin 20-30 parts; dicyclopentadiene phenol epoxy resin 10-20 parts; MDI modified epoxy resin 10-30 parts; non-ionic surfactant 10-15 parts; water 50-60 parts.

[0006] In the above technical solution, phenolic epoxy resin, dicyclopentadiene (DCPD) phenolic epoxy resin, and MDI-modified epoxy resin are used as the resin formulation, and mixed and emulsified with nonionic surfactants to form a sizing agent with high resistance to damp heat. Specifically, phenolic epoxy resin and dicyclopentadiene phenolic epoxy resin with high curing crosslinking density are used as the main resins. The cured products of phenolic epoxy resin and dicyclopentadiene phenolic epoxy resin have high crosslinking density and excellent resistance to damp heat, heat resistance, and chemical stability. MDI-modified epoxy resin is added to adjust flexibility. With the synergistic effect of the components and their proportions, a carbon fiber sizing agent with excellent resistance to damp heat is prepared.

[0007] In one possible implementation, the phenolic epoxy resin is formed by epoxyrating a phenolic resin, wherein the epoxy equivalent of the phenolic epoxy resin is 170~180 g / eq.

[0008] In the above technical solution, the molecular structure of phenolic epoxy resin has more than two epoxy groups and low epoxy equivalent, so the curing crosslinking density is high, and it has excellent bonding strength, heat resistance and chemical resistance, which can improve the stiffness and wear resistance of sized fibers.

[0009] In one possible implementation, the dicyclopentadiene phenol epoxy resin is obtained by modifying phenol epoxy resin with dicyclopentadiene (DCPD), wherein the epoxy equivalent of the dicyclopentadiene phenol epoxy resin is 230~275 g / eq.

[0010] In the above technical solution, the dicyclopentadiene phenol epoxy resin molecule structure contains not only benzene rings but also the alicyclic structure of dicyclopentadiene. It combines the rigid alicyclic structure of dicyclopentadiene with the reactivity of epoxy resin, thus giving the sizing fiber excellent heat resistance and low moisture absorption. The cured resin exhibits good heat resistance and chemical stability. Moreover, the epoxy equivalent is low, so the curing crosslinking density is high, giving the sizing fiber high stiffness and wear resistance.

[0011] In one possible implementation, the MDI-modified epoxy resin is obtained by reacting diphenylmethane diisocyanate (MDI) with an epoxy resin, wherein the epoxy equivalent of the MDI-modified epoxy resin is 280~320 g / eq.

[0012] In the above technical solution, MDI-modified epoxy resin incorporates a soft cyanate ester structure into the epoxy resin structure, which greatly improves the flexibility of the epoxy resin and overcomes the disadvantage of the epoxy resin being relatively brittle after curing. Therefore, MDI-modified epoxy resin improves the toughness of the epoxy resin system, thereby enabling the adjustment of the flexibility of the sizing fiber.

[0013] In one possible implementation, the nonionic surfactant includes at least one of fatty alcohol polyoxyethylene ether, fatty amine polyoxyethylene ether, and alkylphenol polyoxyethylene ether.

[0014] In one possible implementation, the emulsion particle size of the sizing agent is 300~500nm.

[0015] In the above technical solution, the sizing agent has the characteristics of small emulsion particle size and good wetting properties.

[0016] Secondly, embodiments of this application provide a method for preparing the sizing agent with high resistance to damp heat provided in the first aspect, which includes the following steps: The phenolic epoxy resin, the dicyclopentadiene phenolic epoxy resin, the MDI-modified epoxy resin, and the nonionic surfactant are mixed evenly according to the weight ratio, and then water is added to obtain the sizing agent by phase inversion emulsification.

[0017] In the above technical solution, the preparation method is simple, efficient, and has a high success rate, making it suitable for industrial production.

[0018] In one possible implementation, the stirring and mixing method includes: the stirring and mixing temperature is 67~73℃, the stirring and mixing rate is 800~1200 rpm, and the stirring and mixing time is 20~40 min; And / or, the method of phase inversion emulsification includes: a temperature of 75~85℃, a stirring rate of 4000~6000 rpm, and a stirring time of 60~90 min.

[0019] Thirdly, embodiments of this application provide a carbon fiber, which includes a carbon fiber body and a coating layer attached to the surface of the carbon fiber body. The coating layer is formed by curing the sizing agent provided in the first aspect, and the mass percentage of the coating layer is 0.5% to 1.5%.

[0020] In the above technical solution, the coating layer on the carbon fiber surface is formed by curing the sizing agent of the present application embodiment. The carbon fiber has good stiffness and wear resistance, and can effectively improve the damp heat resistance of carbon fiber and composite materials.

[0021] Fourthly, embodiments of this application provide a carbon fiber reinforced resin matrix composite material, including an epoxy resin matrix and the carbon fiber provided in the third aspect, wherein the carbon fiber is combined with the epoxy resin matrix, and the interlaminar shear strength of the composite material is >100MPa and the wet heat retention rate is >65%.

[0022] In the above technical solution, the sizing agent uses three specific epoxy resins as the resin matrix. The composite material after the carbon fiber and the resin matrix are sizing treated has high interfacial bonding strength and also has excellent resistance to humid heat. Detailed Implementation

[0023] 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.

[0024] The following is a detailed description of the sizing agent, carbon fiber and composite material with high resistance to damp heat and the preparation method of the present application embodiment, which have high interfacial bonding strength and good resistance to damp heat and stability.

[0025] This application provides a sizing agent with high resistance to damp heat, which, by weight, comprises the following components: 20-30 parts of phenolic epoxy resin; 10-20 parts of dicyclopentadiene phenol epoxy resin; 10-30 parts of MDI-modified epoxy resin (optionally 10-20 parts); 10-15 parts of nonionic surfactant; 50-60 parts of water.

[0026] By way of example, the sizing agent of this application embodiment comprises the following components by weight: 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, 30 parts of phenolic epoxy resin or any intermediate value between the above two values; 10 parts, 13 parts, 15 parts, 17 parts, 20 parts of dicyclopentadiene phenol epoxy resin or any intermediate value between the above two values; 10 parts, 13 parts, 15 parts, 17 parts, 20 parts, 25 parts, 30 parts of MDI modified epoxy resin or any intermediate value between the above two values; 10 parts, 11 parts, 12 parts, 13 parts, 15 parts of nonionic surfactant or any intermediate value between the above two values; and 50 parts, 55 parts, 60 parts of water or any intermediate value between the above two values.

[0027] In this embodiment, phenolic epoxy resin and dicyclopentadiene phenolic epoxy resin with high curing crosslinking density are used as the main resins. The cured products of phenolic epoxy resin and dicyclopentadiene phenolic epoxy resin have high crosslinking density and excellent resistance to damp heat, heat resistance and chemical stability. MDI modified epoxy resin is used to adjust the flexibility. With the synergistic effect of each component and its ratio, a carbon fiber sizing agent with excellent resistance to damp heat is prepared.

[0028] In some embodiments of this application, phenol novolac epoxy resin (PN or PEN) is a high-performance, multifunctional epoxy resin. It is formed by the condensation polymerization of phenol and formaldehyde under an acidic catalyst, followed by epoxy oxidation with epichlorohydrin. The epoxy equivalent of the phenol novolac epoxy resin is 170-180 g / eq, and this resin can be directly purchased from relevant products of Shandong Aimont New Materials Co., Ltd. Exemplarily, the epoxy equivalent of the phenol novolac epoxy resin is 170 g / eq, 172 g / eq, 174 g / eq, 176 g / eq, 178 g / eq, 180 g / eq, or any intermediate value between the above two values.

[0029] In this embodiment, epoxy equivalent is a core indicator characterizing the chemical activity of epoxy resin, defined as the mass of epoxy resin containing 1 equivalent of epoxy groups, expressed in grams per equivalent. This parameter, along with epoxy value (Ev=100 / En) and epoxy group content (Ec=43×100 / En), forms a conversion system that determines the molar ratio of the resin curing reaction.

[0030] In this embodiment, phenolic epoxy resin has the following characteristics: 1. Multifunctionality (the most significant characteristic): Unlike ordinary bisphenol A type epoxy resins (such as E-51 and E-44, which typically have only two epoxy groups), the molecular structure of phenolic epoxy resin contains an average of more than two epoxy groups (typically with an average functionality of around 3.5 to 4.0, or even higher), thus forming a highly cross-linked and extremely dense three-dimensional network structure during curing. 2. Excellent heat resistance: The high cross-linking density gives it an extremely high glass transition temperature; its heat distortion temperature is much higher than that of bisphenol A type epoxy resin, typically above 170°C; it has good long-term heat resistance, maintaining good mechanical properties and dimensional stability at high temperatures; and it has a high thermal decomposition temperature, exhibiting excellent heat aging resistance. 3. Excellent chemical resistance: The highly cross-linked structure gives it excellent resistance to acids, alkalis, solvents (including polar solvents), and various chemicals, especially at high temperatures.

[0031] In some embodiments of this application, the dicyclopentadiene phenol epoxy resin (DCPD type epoxy resin) is obtained by modifying phenol epoxy resin with dicyclopentadiene (DCPD); the epoxy equivalent of the dicyclopentadiene phenol epoxy resin is 230~275 g / eq, and this resin can be directly purchased from related products of Jinan Shengquan Group Co., Ltd. Exemplarily, the epoxy equivalent of the dicyclopentadiene phenol epoxy resin is 230 g / eq, 240 g / eq, 250 g / eq, 260 g / eq, 275 g / eq, or any intermediate value between the above two values.

[0032] In this embodiment, the dicyclopentadiene phenol epoxy resin has the following characteristics: 1. Excellent heat resistance: The rigid alicyclic structure restricts the movement of molecular chain segments, resulting in a high glass transition temperature (Tg) of its cured product, which is much higher than that of ordinary bisphenol A type epoxy resin. It also has a high thermal decomposition temperature and good thermal stability; 2. Excellent low hygroscopicity and resistance to damp heat: The alicyclic hydrocarbon structure of DCPD is hydrophobic, which significantly reduces the polarity of the resin itself, resulting in extremely low hygroscopicity; 3. Good chemical resistance: It has a certain resistance to acids, alkalis, solvents, etc.; 4. High reactivity: The reactivity of its epoxy groups is generally higher than that of bisphenol A type epoxy resin.

[0033] In some embodiments of this application, the MDI-modified epoxy resin is obtained by reacting diphenylmethane diisocyanate (MDI) with epoxy resin, for example, by chemically modifying bisphenol A type epoxy resin by introducing diphenylmethane diisocyanate (MDI). The epoxy equivalent of the MDI-modified epoxy resin is 280~320 g / eq, and this resin can be directly purchased from relevant products of Shandong Aimont New Materials. Exemplarily, the epoxy equivalent of the MDI-modified epoxy resin is 280 g / eq, 290 g / eq, 300 g / eq, 310 g / eq, 320 g / eq, or any intermediate value between the above two values.

[0034] In this embodiment, the MDI-modified epoxy resin has the following characteristics: 1. Excellent heat resistance: The rigid benzene ring structure of MDI enhances the rigidity of the molecular chain, increasing the heat distortion temperature (HDT) of the cured product (usually >100℃), and its heat aging resistance is superior to that of ordinary epoxy resin; 2. Balance between wear resistance and flexibility: It has high surface hardness and wear resistance while maintaining elasticity. The introduced urethane flexible segments can effectively absorb impact energy, overcoming the brittleness defects of traditional epoxy resin; 3. Chemical resistance: It has good resistance to oil, weak acid, alkali, salt solution, etc.

[0035] In some embodiments of this application, the nonionic surfactant includes at least one of fatty alcohol polyoxyethylene ether, fatty amine polyoxyethylene ether, and alkylphenol polyoxyethylene ether.

[0036] In some embodiments of this application, the emulsion particle size of the sizing agent is 300~500nm. Exemplarily, the emulsion particle size of the sizing agent is 300nm, 350nm, 400nm, 450nm, 500nm, or any intermediate value in nanometers between two of the above values.

[0037] This application also provides a method for preparing the sizing agent with high resistance to damp heat described in the foregoing embodiments, which includes the following steps: According to the weight ratio, phenolic epoxy resin, dicyclopentadiene phenolic epoxy resin, MDI modified epoxy resin and nonionic surfactant are stirred and mixed evenly, and then water is added to obtain a sizing agent by phase inversion emulsification.

[0038] In some embodiments of this application, the mixing method includes: a mixing temperature of 67~73°C, a mixing speed of 800~1200 rpm, and a mixing time of 20~40 min. Exemplarily, the mixing temperature is 67°C, 70°C, 73°C, or any intermediate value between the above two values; the mixing speed is 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, or any intermediate value between the above two values; and the mixing time is 20 min, 30 min, 40 min, or any intermediate value between the above two values.

[0039] Phase inversion emulsification is an important technique for preparing emulsions (especially fine emulsions or nanoemulsions). Its core principle lies in inducing a phase transition in the system by changing emulsification conditions (such as temperature and composition), thereby forming a stable emulsion of the desired type. In some embodiments of this application, the phase inversion emulsification method includes: a temperature of 75-85°C, a stirring rate of 4000-6000 rpm, and a stirring time of 60-90 min. Exemplarily, the temperature is 75°C, 80°C, 85°C, or any intermediate value between two of the above values; the stirring rate is 4000 rpm, 5000 rpm, 6000 rpm, or any intermediate value between two of the above values; and the stirring time is 60 min, 70 min, 80 min, 90 min, or any intermediate value between two of the above values.

[0040] This application also provides a carbon fiber, which includes a carbon fiber body and a coating layer attached to the surface of the carbon fiber body. The coating layer is formed by curing the sizing agent of the aforementioned embodiment, and the mass percentage of the coating layer is 0.5% to 1.5%. For example, the mass percentage of the coating layer in the carbon fiber is 0.5%, 0.8%, 1%, 1.2%, 1.5%, or any intermediate value between the above two values.

[0041] In some embodiments of this application, the method for preparing carbon fiber includes: impregnating the carbon fiber body in a sizing agent, and drying it after sizing. The impregnation process conditions include: a carbon fiber running speed of 500~700 m / min and an impregnation time of 3~9 s; the drying process conditions include: a drying temperature of 180~230℃ and a drying time of 5~15 s.

[0042] This application also provides a carbon fiber reinforced resin matrix composite material, including an epoxy resin matrix and the carbon fiber of the aforementioned embodiment. The carbon fiber is combined with the epoxy resin matrix, and the interlaminar shear strength of the composite material is >100MPa and the wet heat retention rate is >65%.

[0043] In this embodiment, the sizing agent uses three specific epoxy resins as the resin matrix. The composite material formed by the sizing treatment of carbon fiber and the resin matrix has high interfacial bonding strength and also has excellent resistance to humid heat.

[0044] In some embodiments of this application, the method for preparing the composite material includes: mixing resin and curing agent to form a resin mixture, impregnating carbon fiber with the resin mixture, and curing to obtain the composite material; wherein the resin includes epoxy resin.

[0045] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0046] Example 1 This embodiment provides a sizing agent, the preparation process of which is as follows: (1) Prepare the following raw material components by weight: 20 parts by weight of phenolic epoxy resin, 15 parts by weight of DCPD phenolic epoxy resin, 10 parts by weight of MDI modified epoxy resin, and 10 parts by weight of nonionic surfactant fatty alcohol polyoxyethylene ether.

[0047] The phenolic epoxy resin was purchased from Shandong Aimont New Material Co., Ltd., and the structural formula of the phenolic epoxy resin is as follows: , The product information indicates that its epoxy equivalent is 170~180g / eq.

[0048] The DCPD phenolic epoxy resin was purchased from Jinan Shengquan Group Co., Ltd., and the structural formula of the DCPD phenolic epoxy resin is as follows: , The product information indicates that its epoxy equivalent is 230~275g / eq.

[0049] The MDI-modified epoxy resin was purchased from Shandong Aimont New Material Co., Ltd., and its structural formula is as follows: , The product information indicates that its epoxy equivalent is 280~320g / eq.

[0050] The nonionic surfactant selected is fatty alcohol polyoxyethylene ether.

[0051] (2) Mix the above raw material components at a temperature of 70°C, a mixing rate of 1000 rpm, and a mixing time of 30 min. After thorough mixing, add 60 parts by weight of water and obtain the sizing agent by phase inversion emulsification. The temperature of phase inversion emulsification is 80°C, the mixing rate is 5000 rpm, and the mixing time is 90 min.

[0052] Stability testing (24 hours at room temperature) showed that the sizing agent remained a stable sizing emulsion with a particle size of 356 nm.

[0053] Example 2 This embodiment provides a sizing agent, which differs from Example 1 in that: (1) by weight, each raw material component is prepared as follows: 20 parts by weight of phenolic epoxy resin, 20 parts by weight of DCPD phenolic epoxy resin, 15 parts by weight of MDI modified epoxy resin, and 15 parts by weight of nonionic surfactant.

[0054] Finally, the sizing agent is obtained.

[0055] Stability testing showed that the sizing agent remained a stable sizing emulsion with a particle size of 332 nm.

[0056] Example 3 This embodiment provides a sizing agent, which differs from Example 1 in that: (1) by weight, each raw material component is prepared as follows: 15 parts by weight of phenolic epoxy resin, 10 parts by weight of DCPD phenolic epoxy resin, 20 parts by weight of MDI modified epoxy resin, and 13 parts by weight of nonionic surfactant.

[0057] Finally, the sizing agent is obtained.

[0058] Stability testing showed that the sizing agent remained a stable sizing emulsion with a particle size of 366 nm.

[0059] Example 4 This embodiment provides a sizing agent, which differs from Example 1 in that: (1) by weight, each raw material component is prepared as follows: 20 parts by weight of phenolic epoxy resin, 15 parts by weight of DCPD phenolic epoxy resin, 25 parts by weight of MDI modified epoxy resin, and 10 parts by weight of nonionic surfactant.

[0060] Finally, the sizing agent is obtained.

[0061] Stability testing showed that the sizing agent remained a stable sizing emulsion with a particle size of 466 nm.

[0062] Comparative Example 1 This comparative example provides a sizing agent, which differs from Example 1 in that: (1) by weight, each raw material component is prepared as follows: 20 parts by weight of phenolic epoxy resin, 5 parts by weight of DCPD phenolic epoxy resin, 10 parts by weight of MDI modified epoxy resin, and 10 parts by weight of nonionic surfactant.

[0063] Finally, the sizing agent is obtained.

[0064] Stability testing showed that the sizing agent remained a stable sizing emulsion with a particle size of 323 nm.

[0065] Comparative Example 2 This comparative example provides a sizing agent, which differs from Example 1 in that: (1) by weight, each raw material component is prepared as follows: 20 parts by weight of phenolic epoxy resin, 15 parts by weight of DCPD phenolic epoxy resin, 5 parts by weight of MDI modified epoxy resin, and 10 parts by weight of nonionic surfactant.

[0066] Finally, the sizing agent is obtained.

[0067] Stability testing showed that the sizing agent remained a stable sizing emulsion with a particle size of 323 nm.

[0068] Comparative Example 3 This comparative example provides a sizing agent, which differs from Example 1 in that: (1) each raw material component is prepared by weight: 10 parts by weight of phenolic epoxy resin, 15 parts by weight of DCPD phenolic epoxy resin, 10 parts by weight of MDI modified epoxy resin, and 10 parts by weight of nonionic surfactant.

[0069] Finally, the sizing agent is obtained.

[0070] Stability testing showed that the sizing agent remained a stable sizing emulsion with a particle size of 371 nm.

[0071] Comparative Example 4 This comparative example provides a sizing agent, which differs from Example 1 in that: (1) by weight, each raw material component is prepared as follows: 20 parts by weight of phenolic epoxy resin, 30 parts by weight of DCPD phenolic epoxy resin, 10 parts by weight of MDI modified epoxy resin, and 10 parts by weight of nonionic surfactant.

[0072] Finally, the sizing agent is obtained.

[0073] Stability testing revealed that the sizing agent exhibited stratification issues, resulting in an inability to obtain a stable sizing agent emulsion.

[0074] Comparative Example 5 This comparative example provides a sizing agent, which differs from Example 1 in that: (1) by weight, each raw material component is prepared as follows: 35 parts by weight of phenolic epoxy resin, 15 parts by weight of DCPD phenolic epoxy resin, 10 parts by weight of MDI modified epoxy resin, and 10 parts by weight of nonionic surfactant.

[0075] Finally, the sizing agent is obtained.

[0076] Stability testing revealed that the sizing agent exhibited stratification issues, resulting in an inability to obtain a stable sizing agent emulsion.

[0077] Test case I. The composition and emulsion stability of the sizing agents in the above examples and comparative examples were statistically analyzed, and the results are shown in Table 1.

[0078] Table 1. Composition and stability results of the sizing agents in each example and comparative example.

[0079] II. The performance of the sizing agents in the above embodiments and comparative examples was tested. The test method is as follows: (1) T700 carbon fiber (carbon fiber body) was immersed in each sizing agent for 2 minutes, and then the immersed T700 carbon fiber was subjected to high temperature vacuum drying. The drying temperature was 200℃ and the drying time was 10s, and the corresponding T700 carbon fiber after sizing was obtained, i.e. carbon fiber.

[0080] The sizing agent content, hardness, and hairiness of each sized T700 carbon fiber were tested using the following methods: Sizing agent content test method: Weigh the T700 carbon fiber and the sized T700 carbon fiber, and calculate the weight gain relative to the mass ratio of the sized T700 carbon fiber, i.e., the sizing agent content.

[0081] Fiber hardness test method: Take three valid carbon fiber samples after sizing with the sizing agent provided in each embodiment and comparative example, and cut 80cm of carbon fiber to be tested. Handle the carbon fiber gently during the cutting process to avoid changing the shape of the sample. Fix a 100g weight to one end of the sample and fix the other end to the crossbeam. When fixing it to the crossbeam, ensure that the weight does not generate torque due to swinging during the suspension process and twist the carbon fiber into a thin rope. Keep the carbon fiber as flat as possible throughout the operation. After suspending for 30 minutes, remove the carbon fiber from the crossbeam and keep it in the state during the suspension process. Cut 40cm of the carbon fiber with better shape in the middle. Do not touch the measurement area with your hands during the cutting process. Lay the cut carbon fiber flat on the platform, with one end extending 25cm beyond the edge of the platform and 15cm remaining on the platform. After checking that there are no abnormalities in the carbon fiber, press down the contact point between the carbon fiber and the edge of the platform, measure and record the straight-line distance from the end of the carbon fiber extending beyond the platform to the edge of the platform. This is the hardness of the carbon fiber.

[0082] Fiber hairiness test method: After the carbon fiber bundle passes through 3 rods, it is held by two sponges (32mm*64mm*10mm). A certain pressure is applied so that the sponge spacing is 5mm, the fiber traction speed is 15m / min, the running time is 20min, and the amount of hairiness attached to the sponge is measured (mg).

[0083] (2) Each T700 carbon fiber after sizing is combined with an epoxy resin film to make a prepreg; the prepreg is cut, laid up and molded in sequence to obtain a carbon fiber reinforced epoxy resin matrix composite material.

[0084] The obtained composite materials were subjected to interlaminar shear tests according to ASTM D 2344. Specifically, the interlaminar shear strength of each composite material sample in a dry state at room temperature was first tested according to ASTM D 2344. Then, the composite material samples were placed in water at 75°C for 14 days, and the interlaminar shear strength of each composite material sample after hygrothermal treatment was tested according to ASTM D 2344. The rate of change, i.e., the hygrothermal retention rate, was calculated based on the interlaminar shear strength of the composite material samples in a dry state at room temperature and the interlaminar shear strength after hygrothermal treatment.

[0085] The results are shown in Table 2.

[0086] Table 2 Performance results of the sizing agents in each example and comparative example

[0087] Combining the results in Tables 1 and 2, we can see that: After being treated with the sizing agent of Example 1, the T700 carbon fiber has a sizing agent content of 1.05%, a hardness of 10.5 cm, and a hairiness of 3.2 mg / 50 m. The carbon fiber reinforced epoxy resin matrix composite material formed using this carbon fiber has an interlaminar shear strength of 113 MPa and a wet heat retention rate of 70.7%, exhibiting excellent wet heat resistance.

[0088] After being treated with the sizing agent in Example 2, the T700 carbon fiber has a sizing agent content of 0.99%, a hardness of 11.3 cm, and a hairiness of 3.3 mg / 50 m. The carbon fiber reinforced epoxy resin matrix composite material formed using this carbon fiber has an interlaminar shear strength of 110 MPa and a wet heat retention rate of 69.1%, indicating good wet heat resistance.

[0089] After being treated with the sizing agent described in Example 3, the T700 carbon fiber has a sizing agent content of 0.95%, a fiber hardness of 10.8 cm, and a hairiness of 3.1 mg / 50 m. The interlaminar shear strength of the carbon fiber reinforced epoxy resin matrix composite material formed using this carbon fiber is 109 MPa, and the wet heat retention rate of the interlaminar shear strength is 66.9%, indicating good wet heat resistance.

[0090] After treatment with the sizing agent of Example 4, the T700 carbon fiber had a sizing agent content of 1.05%, a fiber hardness of 11 cm, and an abrasion resistance of 3.8 mg / 50 m. The interlaminar shear strength of the carbon fiber reinforced epoxy resin matrix composite formed using this carbon fiber was 111 MPa, and the wet heat retention rate was 69.3%, indicating good wet heat resistance. Compared with the sizing agent of Example 1, increasing the amount of MDI-modified epoxy resin in Example 4 did not significantly change the abrasion resistance, hardness, or wet heat resistance of the carbon fiber after sizing treatment. Therefore, further increasing the amount of MDI-modified epoxy resin has no substantial effect and may result in a waste of raw materials.

[0091] After treatment with the sizing agent of Comparative Example 1, the T700 carbon fiber had a sizing agent content of 1.02%, a fiber hardness of 11.3 cm, and an abrasion resistance of 4.3 mg / 50 m. The interlaminar shear strength of the carbon fiber reinforced epoxy resin matrix composite formed using this carbon fiber was 106 MPa, and the wet heat retention rate of the interlaminar shear strength was 59.4%, which was significantly lower than the wet heat retention rates of Examples 1-3. The reason for this is that, compared with the sizing agent of Example 1, the sizing agent of Comparative Example 1 reduced the amount of DCPD phenol epoxy resin, resulting in a tendency for increased carbon fiber hairiness after sizing treatment, decreased abrasion resistance, and reduced wet heat resistance of the composite material.

[0092] After treatment with the sizing agent of Comparative Example 2, the T700 carbon fiber had a sizing agent content of 0.96%, a fiber hardness of 16.8 cm, and an abrasion resistance of 9.3 mg / 50 m. The interlaminar shear strength of the carbon fiber reinforced epoxy resin matrix composite formed using this carbon fiber was 109 MPa, and the wet heat retention rate was 63.3%, which was lower than that of Examples 1-3. The reason for this is that, compared with the sizing agent of Example 1, the sizing agent of Comparative Example 2 reduced the amount of MDI-modified epoxy resin, resulting in increased stiffness, decreased flexibility, decreased fiber abrasion resistance, increased hairiness, and a certain degree of reduction in the wet heat resistance of the composite material.

[0093] After treatment with the sizing agent of Comparative Example 3, the T700 carbon fiber had a sizing agent content of 0.97%, a fiber hardness of 12.3 cm, and an abrasion resistance of 5.5 mg / 50 m. The interlaminar shear strength of the carbon fiber reinforced epoxy resin matrix composite formed using this carbon fiber was 101 MPa, and the wet heat retention rate was 49.5%, significantly lower than that of Examples 1-3. The reason for this is that, compared with the sizing agent of Example 1, the sizing agent of Comparative Example 3 reduced the amount of phenolic epoxy resin, resulting in poorer abrasion resistance and increased hairiness of the sizing-treated carbon fiber, a significant reduction in interlaminar shear strength of the composite material, and a deterioration in the wet heat resistance of the composite material.

[0094] The sizing agent in Comparative Example 4 exhibited stratification after standing, failing to yield a stable sizing agent emulsion and thus preventing the performance testing in Experiment 2. The reason for this is that, compared to the sizing agent in Example 1, the sizing agent in Comparative Example 4 contained a higher amount of DCPD phenol epoxy resin, leading to decreased stability in the emulsified sizing agent.

[0095] The sizing agent in Comparative Example 5 exhibited stratification after standing, failing to yield a stable sizing agent emulsion and thus preventing the performance testing in Experiment 2. The reason for this is that, compared to the sizing agent in Example 1, the sizing agent in Comparative Example 5 contained a higher amount of phenol-formaldehyde epoxy resin, leading to decreased stability in the emulsified sizing agent.

[0096] The test results of Examples 1-4 and Comparative Examples 1-3 show that only when phenolic epoxy resin, DCPD phenolic epoxy resin and MDI modified epoxy resin work together synergistically can the sizing treated carbon fiber have good fiber properties and the composite material have excellent resistance to damp heat.

[0097] Meanwhile, the test results of Example 1 and Comparative Examples 1-5 show that both insufficient and excessive relative amounts of phenolic epoxy resin, DCPD phenolic epoxy resin, and MDI-modified epoxy resin will adversely affect the performance of the sizing agent and the overall performance of the carbon fiber and composite material. It is evident that the relative amounts of phenolic epoxy resin, DCPD phenolic epoxy resin, and MDI-modified epoxy resin need to be controlled within a suitable ratio range in order to effectively work synergistically and enable the composite material to have excellent resistance to damp heat and better fiber characteristics.

[0098] In summary, the sizing agent, carbon fiber, and composite material and preparation method with high resistance to damp heat in the embodiments of this application have high interfacial bonding strength and good resistance to damp heat.

[0099] 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 with high resistance to damp heat, characterized in that, By weight, it comprises the following components: 20-30 parts of phenolic epoxy resin; 10-20 parts of dicyclopentadiene phenol epoxy resin; 10-30 parts of MDI-modified epoxy resin; 10-15 parts of nonionic surfactant; 50-60 parts water.

2. The sizing agent with high resistance to damp heat according to claim 1, characterized in that, The phenolic epoxy resin is formed by epoxyrating phenolic resin, and the epoxy equivalent of the phenolic epoxy resin is 170~180 g / eq.

3. The sizing agent with high resistance to damp heat according to claim 1, characterized in that, The dicyclopentadiene phenol epoxy resin is obtained by modifying phenol epoxy resin with dicyclopentadiene, and the epoxy equivalent of the dicyclopentadiene phenol epoxy resin is 230~275 g / eq.

4. The sizing agent with high resistance to damp heat according to claim 1, characterized in that, The MDI-modified epoxy resin is obtained by reacting diphenylmethane diisocyanate with epoxy resin, and the epoxy equivalent of the MDI-modified epoxy resin is 280~320 g / eq.

5. The sizing agent with high resistance to damp heat according to claim 1, characterized in that, The nonionic surfactant includes at least one of fatty alcohol polyoxyethylene ether, fatty amine polyoxyethylene ether, and alkylphenol polyoxyethylene ether.

6. The sizing agent with high resistance to damp heat according to claim 1, characterized in that, The emulsion particle size of the sizing agent is 300~500nm.

7. A method for preparing a sizing agent with high resistance to damp heat as described in any one of claims 1 to 6, characterized in that, It includes the following steps: The phenolic epoxy resin, the dicyclopentadiene phenolic epoxy resin, the MDI-modified epoxy resin, and the nonionic surfactant are mixed evenly according to the weight ratio, and then water is added to obtain the sizing agent by phase inversion emulsification.

8. The method for preparing a sizing agent with high resistance to damp heat according to claim 7, characterized in that, The mixing method includes: a mixing temperature of 67~73℃, a mixing speed of 800~1200 rpm, and a mixing time of 20~40 min; And / or, the method of phase inversion emulsification includes: a temperature of 75~85℃, a stirring rate of 4000~6000 rpm, and a stirring time of 60~90 min.

9. A type of carbon fiber, characterized in that, It includes a carbon fiber body and a coating layer attached to the surface of the carbon fiber body, wherein the coating layer is formed by curing the sizing agent as described in any one of claims 1 to 7, and the mass percentage of the coating layer is 0.5% to 1.5%.

10. A carbon fiber reinforced resin matrix composite material, characterized in that, The composite material includes an epoxy resin matrix and carbon fibers as described in claim 8, wherein the carbon fibers are bonded to the epoxy resin matrix, and the interlaminar shear strength of the composite material is >100 MPa and the wet heat retention rate is >65%.

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