Sizing carbon fiber as well as preparation method and application thereof

Abstract

The invention provides a sizing carbon fiber as well as a preparation method and application thereof. The sizing carbon fiber comprises a carbon fiber tow and a polyimide sizing agent loaded on the surface of the carbon fiber tow, the polyimide sizing agent has a structural unit shown as a formula I. Polyimide with the same ether ketone structure as the polyaryletherketone resin is adopted as a sizing agent, so that the carbon fibers and the polyaryletherketone resin form firm interface bonding more easily, and sufficient infiltration of the polyaryletherketone resin on the carbon fibers in the automatic laying process is facilitated; the internal defects of the composite material obtained through automatic laying forming are reduced, and the mechanical property of the composite material is improved; and the polyimide sizing agent has good temperature resistance and is suitable for preparing a carbon fiber reinforced high-performance thermoplastic composite material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon fiber surface modification, and particularly relates to a sizing carbon fiber and a preparation method and application thereof. BACKGROUND

[0002] Carbon fiber reinforced resin matrix composite (CFRP) has been widely used in aerospace, automotive lightweight and military fields due to its light weight, excellent mechanical properties, corrosion resistance, strong chemical stability and strong designability. CFRP is divided into carbon fiber reinforced thermosetting resin matrix composite and carbon fiber reinforced thermoplastic resin matrix composite (CFRTP) according to the different resin matrix. CFRTP has been widely used in aviation, aerospace, transportation and new energy fields due to its short molding cycle, high toughness and recyclability, and is also a key strategic material for the future development of China's high-end manufacturing industry.

[0003] Among the thermoplastic resins, high-performance thermoplastic resins such as polyaryletherketone ketone resins have excellent high-temperature resistance and mechanical properties due to the alternating arrangement of ketone groups and ether groups in the molecular backbone. They also have good hydrolysis resistance, ultraviolet resistance, corrosion resistance, easy melt processability and recyclability, and are the highest heat-resistant and best comprehensive performance resin among special engineering plastics. Due to the long molecular chain and stable chemical properties of high-performance thermoplastic resins, the highly graphitized structure of carbon fibers, the smooth surface and chemical inertness of carbon fibers, the adhesion between carbon fibers and thermoplastic resin matrix is poor, which significantly affects the mechanical properties of CFRTP. In order to solve this problem, carbon fiber sizing agent is usually used to improve the adhesion between carbon fibers and resin, thereby improving the mechanical properties of CFRTP. Most commercial carbon fiber products currently use thermosetting sizing agents, which have low heat resistance, generally below 250℃, while the processing temperature of high-performance polyaryletherketone resins is generally 320-420℃, and there is a compatibility problem between the two.

[0004] In the actual production of thermoplastic prepreg, carbon fibers are prone to fuzzing, loosening or splitting due to low elongation and brittleness, repeated friction, stretching and impact in the processing motion; secondly, the surface energy of the carbon fibers after surface treatment increases, and it is easy to adsorb moisture and impurities in the air. The longer the carbon fibers are exposed to the air, the worse the surface treatment effect of the fibers. Therefore, the carbon fibers must be sized and coated before the preparation of the prepreg to form an excessive bonding layer between the fibers and the matrix. On the one hand, this can improve the process application of carbon fibers by isolating impurities, compensating for defects and protecting the active surface after treatment; on the other hand, it can play a coupling role to improve the interfacial bonding by similar compatibility, surface bonding and van der Waals force, thereby improving the interfacial properties of the prepreg; at the same time, the interfacial bonding of carbon fiber reinforced thermoplastic prepreg is strong, which is beneficial to the full impregnation of polyaryletherketone resin on carbon fibers during automatic placement, reduces the internal defects of the composite material obtained by automatic placement molding, and improves the mechanical properties of the composite material.

[0005] CN111423694A discloses a dichloromethane organic solvent sizing agent for polyether ketone ketone oligomers, which is used for preparing carbon fiber reinforced polyether ether ketone (CF / PEEK) composite materials with high interlaminar shear strength; CN111410758B discloses an N,N-dimethylacetamide organic solvent sizing agent for polyaryl sulfone, which is used for preparing CF / PEEK composite materials with high impact resistance; CN111440342A discloses a dimethylformamide organic solvent sizing agent for aminated polyether ether ketone and carbon nanotubes, which is used for preparing CF / PEEK composite materials; CN111423695B discloses a dimethyl sulfoxide organic solvent sizing agent for sulfonated polyether ether ketone and carbon nanotubes, which is used for preparing CF / PEEK composite materials with high interlaminar shear strength and bending strength; CN111410759B discloses an N-methyl-2-pyrrolidone organic solvent sizing agent for polyamide acid and carbon nanotubes, which is used for preparing CF / PEEK composite materials with high fatigue strength. The advantages of these patents are that high-performance thermoplastic resins are used as sizing agents to improve the interfacial adhesion between carbon fibers and polyaryletherketone resins, and the disadvantages are that the sizing agents are all organic solvent type sizing agents, which are toxic to operators, need to be removed by heating, which can cause environmental pollution and equipment damage, and there are problems such as difficulty in completely removing the organic solvent.

[0006] At present, although there are a large number of studies on the sizing agent treatment modification on the surface of carbon fibers, most of these methods focus on improving the performance of the composite materials, and do not consider further widening the application, such as applying it to the preparation of composite materials in the automatic laying process. One is the material problem, the automatic laying process uses the prepreg of the composite material as the material, and the performance of the prepreg has a significant influence on the laying effect, and the inert interface between the carbon fiber and the resin will affect the performance of the prepreg, and ultimately affect the effect of automatic laying. Therefore, it is necessary to develop a sized carbon fiber suitable for the automatic laying process. SUMMARY

[0007] In view of the shortcomings of the prior art, the purpose of the present application is to provide a sized carbon fiber and its preparation method and application. By using a specific sizing agent, the carbon fiber is more easily formed into a firm interface with the polyaryletherketone resin, which is beneficial to the full impregnation of the polyaryletherketone resin to the carbon fiber in the automatic laying process, reduces the internal defects of the composite material obtained by automatic laying molding, and improves the mechanical properties of the composite material.

[0008] To achieve this purpose, the present application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a sized carbon fiber, which comprises a carbon fiber tows and a polyimide sizing agent loaded on the surface of the carbon fiber tows; the polyimide sizing agent has a structural unit as shown in formula I:

[0010]

[0011] L is selected from at least one of the following groups:

[0012] The connecting site of the group is represented.

[0013] n is selected from an integer greater than 1, for example, can be 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, etc.

[0014] Preferably, the number average molecular weight of the polyimide sizing agent is 10000-50000, for example, can be 12000, 15000, 18000, 20000, 22000, 25000, 28000, 30000, 32000, 35000, 38000, 40000, 42000, 45000, 48000, etc.

[0015] The present application provides a sizing carbon fiber, which uses polyimide with the same ether ketone structure as poly (aryl ether ketone) resin as a sizing agent. The polyimide sizing agent has high toughness and high heat resistance, and effectively improves the interfacial bonding between the carbon fiber and the poly (aryl ether ketone) resin through similar compatibility, thereby improving the comprehensive performance of the carbon fiber reinforced poly (aryl ether ketone) resin prepreg and meeting the requirements of automatic laying process.

[0016] The following is a preferred technical solution of the present application, but not as a limitation on the technical solutions provided by the present application. Through the following preferred technical solution, the purpose and beneficial effects of the present application can be better achieved and realized.

[0017] As a preferred technical solution, the K number of the carbon fiber tow is 3k-24k, for example, it can be 4k, 5k, 6k, 7k, 8k, 9k, 10k, 11k, 12k, 13k, 14k, 15k, 16k, 17k, 18k, 19k, 20k, 21k, 22k, 23k, etc.

[0018] Preferably, the mass ratio of the carbon fiber tow to the polyimide sizing agent in the sizing carbon fiber is 100:(0.5-2), for example, it can be 100:0.6, 100:0.7, 100:0.8, 100:0.9, 100:1, 100:1.1, 100:1.2, 100:1.3, 100:1.4, 100:1.5, 100:1.6, 100:1.7, 100:1.8, 100:1.9, etc., and further preferably 100:(0.5-1).

[0019] In a second aspect, the present application provides a preparation method of the sizing carbon fiber according to the first aspect, which comprises:

[0020] After the first impregnation of the carbon fiber tow in the polyamide acid, heat treatment is performed to obtain the sizing carbon fiber; the raw materials for preparing the polyamide acid include a combination of 4,4'-bis(3-aminophenoxy) benzophenone and dianhydride; the dianhydride includes any one or a combination of at least two of 1,2,4,5-cyclohexane tetracarboxylic dianhydride, pyromellitic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride or 1,2,3,4-cyclobutane tetracarboxylic dianhydride.

[0021] The preparation method of the sizing carbon fiber provided by the present application first uses polyamide acid (PAA) to size the carbon fiber tow, and then performs heat treatment to convert PAA into polyimide through thermal imidization, thereby generating polyimide in situ on the surface of the carbon fiber tow.

[0022] Preferably, the preparation method of the polyamide acid comprises:

[0023] The 4,4'-bis(3-aminophenoxy)benzophenone is reacted with the dianhydride to obtain the polyamic acid.

[0024] Preferably, the temperature of the reaction is 18-35℃, for example, it can be 20℃, 22℃, 24℃, 26℃, 28℃, 30℃, 32℃, 34℃, etc.

[0025] Preferably, the time of the reaction is 12-24h, for example, it can be 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, etc.

[0026] Preferably, the molar ratio of the 4,4'-bis(3-aminophenoxy)benzophenone to the dianhydride is 1:1.

[0027] Preferably, the 4,4'-bis(3-aminophenoxy)benzophenone and the dianhydride are first dried before the reaction.

[0028] Preferably, the temperature of the first drying is 50-80℃, for example, it can be 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃, etc.

[0029] Preferably, the time of the first drying is 8-12h, for example, it can be 8.2h, 8.4h, 8.6h, 8.8h, 9h, 9.2h, 9.4h, 9.6h, 9.8h, 10h, 10.2h, 10.4h, 10.6h, 10.8h, 11h, 11.2h, 11.4h, 11.6h, 11.8h, etc.

[0030] Preferably, the reaction is carried out in an organic solvent to obtain a polyamic acid solution.

[0031] Preferably, the organic solvent comprises any one or a combination of at least two of N,N-dimethylacetamide, N-methylpyrrolidone, N,N dimethylformamide or dimethyl sulfoxide.

[0032] Preferably, the solid content of the polyamic acid solution is 5-20%, for example, it can be 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, etc.

[0033] Preferably, after the polyamic acid solution is diluted with a solvent, the carbon fiber tows are first impregnated in the diluted polyamic acid solution.

[0034] Preferably, the solid content of the diluted polyamide acid solution is 0.1-5% (for example, it can be 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, etc.), further preferably 0.1-0.5%.

[0035] Preferably, the solvent comprises any one or a combination of at least two of water, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide.

[0036] Preferably, the first impregnation is performed for 1-3h, for example, it can be 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h, etc.

[0037] Preferably, the first impregnation is further followed by a second drying step.

[0038] Preferably, the temperature of the second drying is 70-90℃, for example, it can be 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃, etc.

[0039] Preferably, the time of the second drying is 8-12h, for example, it can be 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, etc.

[0040] Preferably, the temperature of the heat treatment is 100-200℃, for example, it can be 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, etc.

[0041] Preferably, the time of the heat treatment is 1-2h, for example, it can be 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, etc.

[0042] Preferably, the first impregnation is further followed by a second drying step.

[0043] Preferably, the method of desizing comprises: placing the carbon fiber tows in acetone at 60-80℃, and after refluxing the acetone for 12-24h, obtaining the desized carbon fiber tows.

[0044] Preferably, the method for activating the carbon fiber tows comprises: after the second impregnation of the carbon fiber tows in the mixed solution of the methanesulfonic acid and the ethanol, obtaining the activated carbon fiber tows.

[0045] Preferably, the time for the second impregnation is 2-3h, for example, can be 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, etc.

[0046] Preferably, the method for preparing the sized carbon fiber comprises the following steps:

[0047] (1) mixing 4,4'-bis(3-aminophenoxy)benzophenone, dianhydride and organic solvent, and reacting at 18-35℃ for 12-24h to obtain a polyamic acid solution; the dianhydride comprises any one or a combination of at least two of 1,2,4,5-cyclohexane tetracarboxylic dianhydride, pyromellitic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride or 1,2,3,4-cyclobutane tetracarboxylic dianhydride; the molar ratio of 4,4'-bis(3-aminophenoxy)benzophenone to dianhydride is 1:1; the solid content of the polyamic acid solution is 5-20%;

[0048] (2) sequentially performing desizing and activation on the carbon fiber tows to obtain the activated carbon fiber tows; diluting the polyamic acid solution to a solid content of 0.1-5% using a solvent, performing first impregnation of the activated carbon fiber tows in the diluted polyamic acid solution, then performing second drying, and then performing heat preservation at 100-200℃ for 1-2h to obtain the sized carbon fiber; the time for the first impregnation is 1-3h.

[0049] In a third aspect, the present application provides a prepreg comprising the sized carbon fiber according to the first aspect, and a polyaryletherketone resin attached to the sized carbon fiber.

[0050] Preferably, the polyaryletherketone resin comprises any one or a combination of at least two of polyether ether ketone resin, polyether ketone ketone or polyether ketone ether ketone ketone.

[0051] In a fourth aspect, the present application provides a composite material prepared from the prepreg according to the third aspect.

[0052] The numerical ranges disclosed in the present application include not only the point values listed, but also any intervening point values between the point values listed, which are not listed for the sake of brevity and clarity.

[0053] Compared with the prior art, the present application has the following beneficial effects:

[0054] (1) The polyimide with the same ether ketone structure as the polyaryletherketone resin is used as the sizing agent, and according to the similar compatibility principle, the polyimide is more easily combined with the high-performance polyaryletherketone resin to form a firm interface; the polyimide sizing agent has good temperature resistance, and the decomposition temperature is greater than 400℃, which is suitable for preparing carbon fiber reinforced high-performance thermoplastic composite materials;

[0055] (2) The polyimide sizing agent can form effective interface combination with the carbon fiber through hydrogen bond interaction, π-π interaction, mechanical interlocking, van der Waals force and other ways, and can also have melting entanglement, mechanical interlocking, hydrogen bond interaction and other ways with the thermoplastic resin matrix, so as to effectively improve the interface combination ability of the carbon fiber and the high-performance polyaryletherketone resin matrix;

[0056] (3) The oxygen-carbon ratio of the sized carbon fiber is 23.3-30.8%, which has high surface activity; the interlaminar shear strength of the composite material prepared by using the sized carbon fiber is 63-75MPa, the bending strength is 561-830MPa, and the bending modulus is 46-54GPa. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 is a comparison chart of the thermogravimetric curves of the polyimide sizing agent and the polyamide acid in Example 1;

[0058] Figure 2 is an infrared spectrum of the polyimide sizing agent and the polyamide acid in Example 1;

[0059] Figure 3 is a microstructure diagram of the composite material provided in Comparative Application Example 2;

[0060] Figure 4 is a microstructure diagram of the composite material provided in Application Example 2. DETAILED DESCRIPTION

[0061] The technical solutions of the present application will be further described below in combination with the drawings and through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application, and should not be regarded as a specific limitation on the present application.

[0062] Some components in the following examples and comparative examples are as follows:

[0063] (1) Carbon fiber tows: purchased from Zhongfu Haohua Carbon Co., Ltd., K number is 12k, and the width of the tows is 6.0-7.0mm;

[0064] (2) Pyromellitic dianhydride (PMDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, m-phenylenediamine, 4,4'-bis(3-aminophenoxy)benzophenone (APBP), N,N-dimethylacetamide (DMAc), ethanol and Michler's acid: all purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0065] Example 1

[0066] A sized carbon fiber, comprising a carbon fiber towpiece and a polyimide sizing agent loaded on the surface of the carbon fiber towpiece; the polyimide sizing agent has the following structural unit:

[0067]

[0068] A preparation method of the sized carbon fiber, comprising the following steps:

[0069] (1) 0.05 mol of 4,4'-bis(3-aminophenoxy)benzophenone (APBP) and 0.05 mol of pyromellitic dianhydride (PMDA) were respectively dried in a vacuum oven at 80°C for 12 h;

[0070] APBP was dissolved in a round-bottom flask containing an appropriate amount of N,N-dimethylacetamide (DMAc) at room temperature under nitrogen protection, and stirred uniformly; PMDA was added in batches to the APBP solution, and a 10wt% transparent viscous polyimide acid (PAA) solution was obtained after mechanical stirring at room temperature for 24 h;

[0071] (2) The carbon fiber towpiece was placed in acetone at 70°C, and the acetone was refluxed for 24 h to remove the commercial sizing agent and impurities on the surface of the carbon fiber towpiece; after winding was completed, drying was performed in an oven at 80°C to obtain a desized carbon fiber towpiece;

[0072] The desized carbon fiber towpiece was immersed in a mixed solution of Michler's acid / ethanol (1.5 g / 100 mL) for 3 h, then wound, and then dried in an oven at 80°C to obtain an activated carbon fiber towpiece;

[0073] The 10wt% PAA solution was diluted with water to obtain a 0.1wt% PAA solution, the activated carbon fiber towpiece was immersed in the 0.1wt% PAA solution for 2 h, then wound, and then baked in an oven at 80°C for 12 h, and then heat imidized at 200°C for 1 h to obtain PI, to obtain the sized carbon fiber, wherein the mass ratio of the carbon fiber towpiece to the polyimide sizing agent in the sized carbon fiber is 100:0.56;

[0074] The polyimide sizing agent and PAA were respectively subjected to thermal gravimetric test, and the test method was as follows: using a thermal gravimetric analyzer (TGA, NETZSCH TG209F1 Libra, Germany) to analyze the thermal gravimetric characteristics of PAA and PI under N2 atmosphere with the temperature rising to 800℃ at 10℃ per minute. The test results are shown in Figure 1 Figure 2, the temperature of the polyimide sizing agent at 5wt% thermal gravimetric loss is 433℃, indicating that the sizing agent has good thermal stability and can be applied to the interface modification of carbon fiber reinforced high-performance thermoplastic resin composite materials;

[0075] The polyimide sizing agent and PAA were tested by using a Fourier infrared spectrometer (FTIR, Nicolet is50, Thermo Fisher Scientific Corporation, USA), and the test results are shown in Figure 2 Figure 3. The infrared absorption band of PAA is at 3273cm -1 There is a weak absorption peak, which proves the existence of secondary amine (-NH-) in PAA; at the same time, the infrared absorption band of PI is at 1780cm -1 and 1720cm -1 which are respectively the asymmetric stretching vibration peak and the symmetric stretching vibration peak of C=O, and the stretching vibration absorption peak of C-N appears at 1360cm -1 which proves the existence of imide ring structure.

[0076] Example 2

[0077] A sizing carbon fiber and a preparation method thereof, which are different from example 1 only in that the obtained 10wt% PAA solution is diluted into 0.25wt% PAA solution with water in step (2), and the rest of raw materials, process parameters and steps are the same as those of example 1. The mass ratio of carbon fiber tows to polyimide sizing agent in the sizing carbon fiber is 100:0.8.

[0078] Example 3

[0079] A sizing carbon fiber and a preparation method thereof, which are different from example 1 only in that the obtained 10wt% PAA solution is diluted into 0.50wt% PAA solution with water in step (2), and the rest of raw materials, process parameters and steps are the same as those of example 1. The mass ratio of carbon fiber tows to polyimide sizing agent in the sizing carbon fiber is 100:1.0.

[0080] Example 4

[0081] A sizing carbon fiber and a preparation method thereof, which are different from example 1 only in that the obtained 10wt% PAA solution is diluted into 1.0wt% PAA solution with water in step (2), and the rest of raw materials, process parameters and steps are the same as those of example 1. The mass ratio of carbon fiber tows to polyimide sizing agent in the sizing carbon fiber is 100:1.2.

[0082] Example 5

[0083] A sized carbon fiber and a preparation method thereof, which differs from Example 1 only in that in step (1), an equimolar amount of pyromellitic dianhydride (PMDA) is replaced by 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and the remaining raw materials, process parameters and steps are the same as those in Example 1. The mass ratio of carbon fiber tow to polyimide sizing agent in the sized carbon fiber is 100:0.8.

[0084] Example 6

[0085] A sized carbon fiber and a preparation method thereof, which differs from Example 1 only in that an equimolar amount of pyromellitic dianhydride (PMDA) in step (1) is replaced by bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and the remaining raw materials, process parameters and steps are the same as those in Example 1. The mass ratio of the carbon fiber tow to the polyimide sizing agent in the sized carbon fiber is 100:1.0.

[0086] Comparative Example 1

[0087] A sized carbon fiber and a preparation method thereof, which differs from Example 1 only in that an equal molar amount of 4,4'-bis(3-aminophenoxy)benzophenone is replaced by m-phenylenediamine, and the remaining raw materials, process parameters and steps are the same as those in Example 1.

[0088] Application Example 1

[0089] A prepreg comprising the sized carbon fiber provided in Example 1 and a polyetheretherketone resin (purchased from Jilin Zhongyan Polymer Materials Co., Ltd., ZYPEEK330UPF) attached to the sized carbon fiber;

[0090] The prepreg preparation method comprises: using upper and lower guide rollers to straighten the sized carbon fibers provided in Example 1, passing the fibers through a suspension containing polyetheretherketone resin (composed of 300 parts by weight of polyetheretherketone resin, 9 parts by weight of polyethylene glycol dispersant, and 2700 parts by weight of deionized water) at a speed of 2 m / s; then, drying the water therein and press-molding the prepreg under a pressure of 2 bar to obtain the prepreg;

[0091] A composite material and a preparation method thereof, the preparation method comprising:

[0092] The prepreg was cut into a standard width of 6.35 mm and automatically laid and formed under the conditions of a laying pressure of 250 N, a laying speed of 5 mm / s, a heat source heating temperature of 500° C., and 25 laying layers to obtain the composite material of about 4 mm thickness.

[0093] Application Example 2-6, Comparative Application Example 1

[0094] A prepreg and a preparation method thereof, which are only different from application example 1 in that the sizing carbon fibers provided in example 1 are replaced by the sizing carbon fibers provided in examples 2-6 and comparative example 1, respectively, and the remaining raw materials, process parameters and steps are the same as those of application example 1.

[0095] After the obtained prepreg is subjected to the same automatic placement molding as application example 1, a composite material is obtained.

[0096] Comparative Application Example 2

[0097] A prepreg and a preparation method thereof, which are only different from application example 1 in that the sizing carbon fibers provided in example 1 are replaced by carbon fiber tows which are not sized using polyimide sizing agent, and the remaining raw materials, process parameters and steps are the same as those of application example 1.

[0098] After the obtained prepreg is subjected to the same automatic placement molding as application example 1, a composite material is obtained.

[0099] Performance test

[0100] (1) Element content test of sizing carbon fibers: X-ray photoelectron spectroscopy (XPS, ESCALAB250, Thermo Fisher Scientific) was used to determine the C, O and N element contents of the sizing carbon fibers, and Thermo advantage software was used to perform peak fitting processing on the C1s peak, and the obtained structure is shown in Table 1:

[0101] Table 1

[0102] C％ O％ N％ O / C % Example 1 78.67 18.33 3.00 23.30 Example 2 77.02 19.8 3.18 25.71 Example 3 74.41 20.48 5.11 27.52 Example 4 71.26 21.95 6.79 30.80 Example 5 77.8 18.52 3.68 23.80 Example 6 77.92 18.51 3.57 23.76 Comparative Example 1 78.43 17.81 3.76 22.71

[0103] As can be seen from the test data in Table 1, as the solid content of the polyamic acid solution increases, the proportion of polyimide sizing agent in the sizing carbon fibers increases, which can effectively increase the oxygen-carbon ratio of the carbon fiber tows, thereby improving the surface activity of the sizing carbon fibers.

[0104] (2) Interlaminar shear strength: tested according to ASTM D2344;

[0105] (3) Flexural strength: tested according to ASTM D7264;

[0106] (4) Flexural modulus: tested according to ASTM D7264;

[0107] The composite materials provided in application examples 1-6 and comparative application examples 1-2 were tested according to the above method, and the test results are shown in Table 2:

[0108] Table 2

[0109]

[0110]

[0111] It can be seen from the test data in Table 2 that the proportion of polyimide sizing agent in the sizing carbon fiber affects the interlaminar shear strength and bending performance of the carbon fiber reinforced polyether ether ketone composite material, and a suitable proportion can effectively improve the interfacial bonding between the carbon fiber and the polyether ether ketone.

[0112] (5) The composite materials provided by Comparative Application Example 2 and Application Example 2 were tested using a field emission scanning electron microscope (SEM, JSM-7500F, JEOL Ltd.), and the test results are shown in FIG. 2; it can be seen from FIG. 2 that the carbon fiber tows were not sized, and the adhesion of the carbon fiber tows to the polyether ether ketone resin was poor; Figures 3-4 Figure 3 It can be seen from FIG. 2 that the carbon fiber tows were not sized, and the adhesion of the carbon fiber tows to the polyether ether ketone resin was poor; Figure 4 It can be seen from FIG. 2 that the carbon fiber tows were not sized, and the adhesion of the carbon fiber tows to the polyether ether ketone resin was poor;

[0113] The applicant declares that the sizing carbon fiber, the preparation method and the application thereof of the present application are illustrated by the above examples, but the present application is not limited to the above examples, that is, it does not mean that the present application must rely on the above examples to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.​

Claims

1. A sized carbon fiber, characterized in that: The sized carbon fiber includes a carbon fiber tow and a polyimide sizing agent loaded on the surface of the carbon fiber tow; The polyimide sizing agent has a structural unit as shown in Formula I: Wherein, L is selected from at least one of the following groups: The attachment site of the representative group; n is selected from integers greater than 1.

2. The sized carbon fiber according to claim 1, characterized in that The K number of the carbon fiber tow is 3-24k; Preferably, the mass ratio of the carbon fiber tow to the polyimide sizing agent in the sized carbon fiber is 100:(0.5-2), and more preferably 100:(0.5-1).

3. A method for preparing sized carbon fiber according to claim 1 or 2, characterized in that: The preparation method comprises: After the carbon fiber tow is first impregnated in polyamic acid, heat treatment is performed to obtain the sized carbon fiber; The raw materials for preparing the polyamic acid include a combination of 4,4'-bis(3-aminophenoxy)benzophenone and dianhydride; The dianhydride includes any one of 1,2,4,5-cyclohexanetetracarboxylic dianhydride, pyromellitic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride or 1,2,3,4-cyclobutanetetracarboxylic dianhydride, or a combination of at least two thereof.

4. The preparation method according to claim 3, characterized in that The preparation method of the polyamic acid comprises: The 4,4'-bis(3-aminophenoxy)benzophenone reacts with the dianhydride to obtain the polyamic acid.

5. The preparation method according to claim 4, characterized in that The reaction temperature is 18-35°C; Preferably, the reaction time is 12-24 hours.

6. The preparation method according to claim 5, characterized in that The reaction is carried out in an organic solvent to obtain a polyamic acid solution; Preferably, the organic solvent comprises any one or a combination of at least two of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide or dimethyl sulfoxide; Preferably, the solid content of the polyamic acid solution is 5-20%.

7. The preparation method according to claim 6, characterized in that After diluting the polyamic acid solution with a solvent, the carbon fiber tow is first immersed in the diluted polyamic acid solution; Preferably, the solid content of the diluted polyamic acid solution is 0.1-5%, more preferably 0.1-0.5%; Preferably, the solvent includes any one of water, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide, or a combination of at least two thereof.

8. The preparation method according to any one of claims 3 to 7, characterized in that The first dipping time is 1-3 hours; Preferably, the temperature of the heat treatment is 100-200°C; Preferably, the heat treatment time is 1-2h; Preferably, before the first impregnation is performed, the method further comprises the steps of desizing and activating the carbon fiber tows in sequence.

9. A prepreg, characterized in that The prepreg comprises the sized carbon fiber according to claim 1 or 2, and a polyaryletherketone resin attached to the sized carbon fiber; Preferably, the polyaryletherketone resin includes any one of polyetheretherketone resin, polyetherketoneketone or polyetherketoneetherketoneketone, or a combination of at least two thereof.

10. A composite material, characterized in that The composite material is prepared from the prepreg according to claim 9.

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