Fiber composite material and preparation method thereof

Abstract

The invention provides a fiber composite material and a preparation method thereof, and belongs to the technical field of composite materials. The preparation method of the fiber composite material comprises the following steps: arranging a mixed solution on aramid fibers to obtain a prepreg, and carrying out hot press molding on the prepreg to obtain the fiber composite material, the mixed solution comprises hyperbranched epoxy resin modified carbon nanotubes, a bismaleimide-epoxy resin prepolymer and a solvent. According to the preparation method, the hyperbranched epoxy resin modified carbon nanotubes and the bismaleimide-epoxy resin prepolymer are compounded with the aramid fibers, on one hand, the dispersity of the carbon nanotubes can be improved through flexible hyperbranched epoxy long chains, agglomeration of the carbon nanotubes is reduced, and meanwhile the carbon nanotubes are adsorbed on the surface of the aramid fiber composite material; on the other hand, epoxy groups on the carbon nanotubes can be subjected to curing reaction with amino groups in a copolymer matrix formed by the bismaleimide-epoxy resin prepolymer, and the interface performance of the fiber composite material can be remarkably improved through the action of the epoxy groups on the carbon nanotubes and the amino groups in a copolymer matrix formed by the bismaleimide-epoxy resin prepolymer.

Description

Technical Field

[0001] The present application relates to the technical field of composite materials, and in particular to a fiber composite material and a preparation method thereof. Background Art

[0002] The performance of fiber-reinforced resin-based composites is primarily determined by the resin, fiber, and the interface between the two; the interface is a unique and extremely important component of composites. The interface refers to the three-dimensional region between two phases (resin and fiber), where the physical properties gradually change from one phase to another. The interface plays a vital role in the performance of composites, especially the mechanical properties. Aramid fiber (AF) has a relatively smooth surface and low surface energy. In addition, it and the resin contain different chemical components, resulting in poor interfacial compatibility and low interfacial strength. Therefore, the interface becomes the weak link in the composite. Under the action of external loads, stress concentration and microcrack propagation often occur at the interface, which damages the composite material. This phenomenon seriously affects the interfacial toughness and strength of AF composites and affects the large-scale application of composites. Based on this, improving the toughness and strength of the interface to enhance the impact resistance and mechanical properties of the composite is a key scientific issue in the construction of advanced AF / epoxy resin composites. Summary of the Invention

[0003] The present application provides a fiber composite material and a preparation method thereof, which has high thermal stability and mechanical properties.

[0004] The embodiment of the present application is implemented as follows:

[0005] In the first aspect, the present application example provides a method for preparing a fiber composite material, which includes: setting a mixed solution on aramid fiber, obtaining a prepreg after the solvent in the mixed solution evaporates, and then hot-pressing the prepreg to obtain a fiber composite material; wherein the mixed solution includes hyperbranched epoxy resin modified carbon nanotubes, bismaleimide-epoxy resin prepolymer and solvent.

[0006] In the above technical solution, the preparation method of the fiber composite material of the present application uses hyperbranched epoxy resin-modified carbon nanotubes and bismaleimide-epoxy resin prepolymer for composite with aramid fiber. On the one hand, the flexible hyperbranched epoxy long chain can improve the dispersibility of the carbon nanotubes, reduce the agglomeration of the carbon nanotubes, and at the same time adsorb them on the surface of the aramid fiber composite material; on the other hand, the epoxy groups on the carbon nanotubes can undergo a curing reaction with the amino groups in the copolymer matrix formed by the bismaleimide-epoxy resin prepolymer. The interaction of the two can significantly improve the interfacial properties of the fiber composite material. The preparation method of the fiber composite material of the present application is simple, and the obtained fiber composite material has good thermal stability, room temperature mechanical properties, and aging mechanical properties.

[0007] In some possible embodiments, the mass ratio of the hyperbranched epoxy resin modified carbon nanotubes to the bismaleimide-epoxy resin prepolymer in the mixed solution is 1-5:90-99.

[0008] In the above technical scheme, the present application makes the mass ratio of hyperbranched epoxy resin modified carbon nanotubes and bismaleimide-epoxy resin prepolymer in the mixed solution within the above range, which is conducive to the curing reaction of the amino groups in the copolymer matrix formed by hyperbranched epoxy resin modified carbon nanotubes and bismaleimide-epoxy resin prepolymer, thereby improving the interface performance of the fiber composite material.

[0009] In some possible embodiments, the fiber composite material includes bismaleimide-epoxy resin and aramid fiber, and the mass ratio of the bismaleimide-epoxy resin to the aramid fiber is 30-39:60-69.

[0010] In some possible embodiments, the pressure during hot pressing is 15 MPa to 25 MPa, and the curing procedure is sequentially curing at a temperature of 155°C to 165°C for 0.8 h to 1.2 h, curing at a temperature of 175°C to 185°C for 0.8 h to 1.2 h, and curing at a temperature of 195°C to 205°C for 0.8 h to 1.2 h.

[0011] In some possible embodiments, the hyperbranched epoxy resin modified carbon nanotubes are prepared by the following method: maintaining stirring, reacting carboxyl carbon nanotubes, hyperbranched epoxy resin and tert-butylammonium bromide at 80° C. to 120° C. for 20 h to 28 h.

[0012] In the above technical scheme, the present application utilizes hyperbranched epoxy groups to react with carbon nanotubes with carboxyl groups to graft carbon nanotubes to obtain a soft-rigid core-shell nanostructured particle, that is, the carbon nanotubes are the rigid core and the hyperbranched epoxy resin is the flexible shell. On the one hand, the flexible hyperbranched epoxy long chain can improve the dispersibility of the carbon nanotubes, reduce the agglomeration of the carbon nanotubes, and at the same time make it adsorbed on the surface of the aramid fiber composite material; on the other hand, the epoxy groups on the carbon nanotubes can undergo a curing reaction with the amino groups in the copolymer matrix formed by the bismaleimide-epoxy resin prepolymer. The action of the two can significantly improve the interfacial performance of the fiber composite material.

[0013] In some possible embodiments, the mass ratio of carboxyl carbon nanotubes, hyperbranched epoxy resin and tert-butylammonium bromide is 90-99:1-10:1-10.

[0014] In some possible embodiments, the bismaleimide-epoxy resin prepolymer is prepared by the following method: maintaining stirring, first melt-prepolymerizing the bismaleimide monomer and the epoxy resin monomer at 130°C to 140°C for 15min to 25min to prepare a first mixture, and then adding a curing agent to the first mixture and continuing the reaction for 5min to 15min.

[0015] In some possible embodiments, the mass ratio of bismaleimide monomer, epoxy resin monomer and curing agent is 10-19:60-69:20-29, and / or; the epoxy resin monomer includes bisphenol A epoxy resin monomer, and / or; the bismaleimide monomer includes 4,4'-bismaleimide diphenylmethane monomer.

[0016] In a second aspect, the present application provides an example of a fiber composite material, which is prepared according to the method for preparing the fiber composite material in the above embodiment.

[0017] In the above technical solution, the fiber composite material of the present application has good thermal stability, room temperature mechanical properties and aging mechanical properties.

[0018] In some possible embodiments, the maximum decomposition temperature of the fiber composite material is 550°C to 600°C, and / or; the residual carbon rate of the fiber composite material is 35% to 40%, and / or; after aging at 200°C and 220°C for 24 hours, the mass loss of the fiber composite material is less than 1%, and / or; the flexural strength of the fiber composite material is 400MPa to 600MPa, and / or; the interfacial shear strength of the fiber composite material is 20MPa to 30MPa, and / or; after aging at 200°C for 24 hours, the flexural strength and interfacial shear strength retention rates of the fiber composite material are both 90% to 100% of those before aging, and / or; after aging at 220°C for 24 hours, the flexural strength and interfacial shear strength retention rates of the fiber composite material are both 80% to 95% of those before aging, and / or; after aging at 240°C for 24 hours, the flexural strength and interfacial shear strength retention rates of the fiber composite material are both 50% to 75% of those before aging. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 Detailed photos of the fiber composite materials of Examples 1 to 3 and Comparative Examples 5 to 7 of the present application;

[0021] Figure 2 The bending stress-strain curves of the fiber composite materials of Examples 1 to 3 and Comparative Examples 5 to 7 of the present application are shown;

[0022] Figure 3 The force-displacement curves of the short beam interlaminar shear test of the fiber composite materials of Examples 1 to 3 and Comparative Examples 5 to 7 of the present application;

[0023] Figure 4 These are scanning electron micrographs of the fracture surfaces of the fiber composite materials of Example 2 and Comparative Example 5 of the present application. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0025] Currently, the interface modification of AF / epoxy resin composites mainly adopts two schemes: fiber surface treatment and resin matrix modification. Fiber surface modification is to modify active groups on the fiber surface or increase the roughness through different treatment methods, thereby achieving good chemical bonding and mechanical interlocking between the fiber and the matrix. However, from the perspective of practical application and large-scale production, fiber surface modification has many problems. For example, surface etching, plasma treatment and high-energy radiation treatment are based on the modification of fiber damage; the solvents involved in surface etching, chemical grafting and coating will inevitably have an impact on the environment; plasma treatment and high-energy radiation treatment have high energy consumption and strict requirements on treatment equipment; coupling agent treatment has limited capacity expansion effect; surface nanostructure construction method is limited by the easy agglomeration characteristics of nanoparticles, and the number of nanoparticles that can be loaded on the fiber is limited, that is, the capacity expansion effect is also limited, and many design methods are not suitable for the preparation of continuous fiber laminates; the above-mentioned fiber surface modification methods are highly designed and have many steps, which means that the operation is difficult and not conducive to large-scale production.

[0026] Resin matrix modification involves the direct introduction of a modifier into the matrix, where it chemically reacts with the fiber surface or physically fills the matrix. Furthermore, the modified resin matrix enhances its fundamental strength, thereby improving the overall mechanical properties of the composite material from both the interface and matrix dimensions. Polymer monomers and nanomaterials are commonly used to modify the resin matrix. Among polymers, bismaleimide is an ideal polymer for epoxy modification due to its excellent thermal stability, flame retardancy, and similar processing characteristics to epoxy resins, allowing it to dissolve in epoxy resin without phase separation. However, the performance of fiber composites is influenced not only by the matrix but also by the interface between the fiber and the resin. Therefore, nanomaterial modification is also necessary. Nanoparticles, as matrix modifiers, can act as a second phase to enhance overall mechanical properties. Furthermore, the nanoparticles achieve mechanical interlocking through physical adsorption, improving interfacial properties. Among numerous nanomaterials, carbon nanotubes (CNTs) have attracted considerable attention due to their exceptional strength, toughness, thermal conductivity, and high specific surface area. However, it is well known that nanoparticles easily agglomerate, resulting in uneven dispersion within the composite material, which compromises its overall performance.

[0027] Based on this, the present application provides a method for preparing a fiber composite material, which comprises the following steps:

[0028] S1. Preparation of hyperbranched epoxy resin modified carbon nanotubes

[0029] Carboxyl carbon nanotubes are uniformly dispersed in a first organic solvent by ultrasonic stirring to obtain a carbon nanotube dispersion. The carbon nanotube dispersion is added with hyperbranched epoxy resin and tert-butylammonium bromide while maintaining the stirring state. The mixture is reacted at 80° C. to 120° C. for 20 h to 28 h to obtain a first product. The first product is washed, collected by centrifugation, and dried to obtain hyperbranched epoxy resin-modified carbon nanotubes.

[0030] Carboxyl carbon nanotubes are a type of functionalized material in which carboxyl functional groups are introduced onto the surface of carbon nanotubes through chemical modification.

[0031] Optionally, the first organic solvent includes N,N-dimethylformamide, N-methylpyrrolidone or dimethyl sulfoxide.

[0032] Optionally, the power of ultrasonic stirring is 150W to 250W, and the stirring rate is 150r / min to 300r / min.

[0033] As an example, the reaction temperature may be 80° C., 90° C., 100° C., 110° C., or 120° C., and the reaction time may be 20 h, 22 h, 24 h, 26 h, or 28 h.

[0034] Optionally, the mass ratio of the carboxyl carbon nanotubes, the hyperbranched epoxy resin and the tert-butylammonium bromide is 90-99:1-10:1-10.

[0035] As an example, the mass ratio of the carboxyl carbon nanotube, the hyperbranched epoxy resin, and the t-butyl ammonium bromide can be 90:10:10, 92:8:8, 94:6:6, 95:5:5, 96:4:4, 98:2:2, or 99:1:1.

[0036] The present application grafts carbon nanotubes by reacting hyperbranched epoxy groups with carboxyl-containing carbon nanotubes, to obtain a soft-rigid shell core nanostructure particle, i.e., carbon nanotubes as a rigid core and hyperbranched epoxy resin as a flexible shell. On the one hand, the long flexible hyperbranched epoxy chains can improve the dispersibility of the carbon nanotubes, reduce the agglomeration of the carbon nanotubes, and simultaneously enable the carbon nanotubes to be adsorbed on the surface of aramid fiber composites. On the other hand, the epoxy groups on the carbon nanotubes can undergo a curing reaction with the amino groups in the copolymer matrix formed by the bismaleimide-epoxy resin prepolymer, and the two effects can significantly improve the interfacial properties of the fiber composite.

[0037] S2, preparing a bismaleimide-epoxy resin prepolymer

[0038] While stirring, first melt the bismaleimide monomer and the epoxy resin monomer at 130-140°C for 15-25 min to obtain a first mixture, and then add a curing agent to the first mixture and continue to react for 5-15 min.

[0039] Optionally, the stirring rate is 150-300 r / min.

[0040] As an example, the temperature of the melt prepolymerization can be 130°C, 132°C, 134°C, 136°C, 138°C, or 140°C, and the time of the melt prepolymerization can be 15 min, 17 min, 20 min, 22 min, or 25 min.

[0041] Optionally, the curing agent includes 4,4'-diamino diphenyl sulfone.

[0042] As an example, the reaction time after adding the curing agent can be 5 min, 8 min, 10 min, 12 min, or 15 min.

[0043] Optionally, the mass ratio of the bismaleimide monomer, the epoxy resin monomer, and the curing agent is 10-19:60-69:20-29.

[0044] As an example, the mass ratio of the bismaleimide monomer, the epoxy resin monomer, and the curing agent can be 10:60:29, 10:69:29, 10:60:20, 10:69:20, 19:60:29, 19:69:29, 19:60:29, or 19:69:20.

[0045] Optionally, the epoxy monomer comprises a bisphenol A type epoxy monomer.

[0046] Optionally, the bismaleimide monomer comprises a 4,4'-bismaleimide diphenyl methane monomer.

[0047] S3, preparing a mixed solution

[0048] The second organic solvent is added to the prepared bismaleimide-epoxy resin prepolymer, and after being fully dissolved, a pre-mixed solution is obtained. The prepared hyperbranched epoxy resin modified carbon nanotubes are added to the pre-mixed solution, and after ultrasonic stirring for 0.5h-3h, a mixed solution is prepared.

[0049] Optionally, the power of ultrasonic stirring is 150W-250W, and the stirring rate is 150r / min-300r / min.

[0050] For example, the time of ultrasonic stirring can be 0.5h, 1h, 1.5h, 2h, 2.5h or 3h.

[0051] Optionally, the mass ratio of the hyperbranched epoxy resin modified carbon nanotubes to the bismaleimide-epoxy resin prepolymer in the mixed solution is 1-5:90-99.

[0052] For example, the mass ratio of the hyperbranched epoxy resin modified carbon nanotubes to the bismaleimide-epoxy resin prepolymer in the mixed solution can be 1:99, 2:97, 3:95, 4:92 or 5:90.

[0053] The present application is advantageous for the curing reaction of the amino groups in the copolymer matrix formed by the hyperbranched epoxy resin modified carbon nanotubes and the bismaleimide-epoxy resin prepolymer, thereby improving the interfacial properties of the fiber composite material.

[0054] S4, preparing a prepreg

[0055] The prepared mixed solution is uniformly coated on the surface of aramid fiber (AF), and after the solvent in the mixed solution is volatilized, a prepreg is obtained.

[0056] S5, preparing a fiber composite material

[0057] The prepreg is stacked in a mold, and then placed in a hot press molding machine. The pressure is 15MPa-25MPa, and the curing program is to sequentially cure at a temperature of 155℃-165℃ for 0.8h-1.2h, at a temperature of 175℃-185℃ for 0.8h-1.2h, and at a temperature of 195℃-205℃ for 0.8h-1.2h. After the hot pressing is completed, the composite material is obtained.

[0058] As an example, the pressure of the thermoforming machine may be 15 MPa, 18 MPa, 20 MPa, 22 MPa or 25 MPa.

[0059] Optionally, the fiber composite material includes bismaleimide-epoxy resin and aramid fiber, and the mass ratio of the bismaleimide-epoxy resin to the aramid fiber is 30-39:60-69.

[0060] As an example, the mass ratio of the bismaleimide-epoxy resin to the aramid fiber may be 30:69, 35:65, or 39:60.

[0061] The preparation method of the fiber composite material of the present application adopts hyperbranched epoxy resin modified carbon nanotubes and bismaleimide-epoxy resin prepolymer for composite with aramid fiber. On the one hand, the flexible hyperbranched epoxy long chain can improve the dispersibility of carbon nanotubes, reduce the agglomeration of carbon nanotubes, and make them adsorbed on the surface of aramid fiber composite material; on the other hand, the epoxy groups on the carbon nanotubes can undergo a curing reaction with the amino groups in the copolymer matrix formed by bismaleimide-epoxy resin prepolymer. The action of the two can significantly improve the interface performance of the fiber composite material, improve the interface debonding and uneven dispersion of carbon nanotubes in the preparation process of aramid fiber reinforced carbon nanotube / epoxy resin composite material, as well as the processing problems and fiber structure destruction caused by fiber modification. The preparation method of the fiber composite material of the present application is simple, and the prepared fiber composite material has good thermal stability, room temperature mechanical properties and aging mechanical properties.

[0062] The present application also provides a fiber composite material, which is prepared according to the preparation method of the fiber composite material in the above embodiment.

[0063] The fiber composite material of the present application has good thermal stability, with a maximum decomposition temperature of 550°C to 600°C, a residual carbon rate of 35% to 40%, and a mass loss of less than 1% after aging at 200°C and 220°C for 24 hours.

[0064] The fiber composite material of the present application has good mechanical properties at room temperature, with a bending strength of 400MPa to 600MPa and an interface shear strength of 20MPa to 30MPa.

[0065] The fiber composite material of the present application has good aging mechanical properties. After aging at 200°C for 24 hours, the retention rates of the flexural strength and interfacial shear strength of the fiber composite material are both 90% to 100% of those before aging; after aging at 220°C for 24 hours, the retention rates of the flexural strength and interfacial shear strength of the fiber composite material are both 80% to 95% of those before aging; after aging at 240°C for 24 hours, the retention rates of the flexural strength and interfacial shear strength of the fiber composite material are both 50% to 75% of those before aging.

[0066] The fiber composite material of the present application has good thermal stability, room temperature mechanical properties and aging mechanical properties.

[0067] The fiber composite material and the preparation method thereof of the present application are further described in detail below with reference to the embodiments.

[0068] Example 1

[0069] The present invention provides a fiber composite material and a method for preparing the same, which comprises the following steps:

[0070] S1. Preparation of hyperbranched epoxy resin modified carbon nanotubes

[0071] Carboxyl carbon nanotubes were uniformly dispersed in N,N-dimethylformamide by ultrasonic stirring to obtain a carbon nanotube dispersion. The ultrasonic stirring power was 200 W and the stirring rate was 210 r / min. The stirring state was maintained. Hyperbranched epoxy resin and tert-butyl ammonium bromide were added to the carbon nanotube dispersion, and the mixture was reacted at 100° C. for 24 hours to obtain a first product. The first product was washed, centrifuged, collected, and dried to obtain hyperbranched epoxy resin-modified carbon nanotubes. The mass ratio of carboxyl carbon nanotubes, hyperbranched epoxy resin, and tert-butyl ammonium bromide was 95:5:5.

[0072] S2. Preparation of bismaleimide-epoxy resin prepolymer

[0073] Maintaining the stirring state at a stirring rate of 240 r / min, 4,4′-bismaleimide diphenylmethane monomer and bisphenol A epoxy resin monomer were first melt-prepolymerized at 135° C. for 20 minutes to obtain a first mixture, and then 4,4′-diaminodiphenyl sulfone was added to the first mixture and the reaction was continued for 10 minutes. The mass ratio of 4,4′-bismaleimide diphenylmethane monomer, bisphenol A epoxy resin monomer and 4,4′-diaminodiphenyl sulfone was 15:65:25.

[0074] S3. Preparation of mixed solution

[0075] A certain amount of acetone was added to the prepared bismaleimide-epoxy resin prepolymer and fully dissolved to obtain a premixed solution. The prepared hyperbranched epoxy resin-modified carbon nanotubes were then added to the premixed solution and ultrasonically stirred for 1 hour to obtain a mixed solution. The ultrasonic stirring power was 200 W and the stirring rate was 240 r / min. The mass ratio of the hyperbranched epoxy resin-modified carbon nanotubes to the bismaleimide-epoxy resin prepolymer in the mixed solution was 1:99.

[0076] S4. Preparation of prepreg

[0077] The prepared mixed solution is evenly coated on the surface of the aramid fiber, and a prepreg is obtained after the solvent in the mixed solution is volatilized.

[0078] S5. Preparation of fiber composite materials

[0079] The prepreg stack is stacked in a mold and then placed in a hot pressing molding machine at a pressure of 20 MPa. The curing procedure is sequentially curing at a temperature of 160°C for 1 hour, curing at a temperature of 180°C for 1 hour, and curing at a temperature of 200°C for 1 hour. After the hot pressing is completed, the composite material is obtained. The fiber composite material includes bismaleimide-epoxy resin and aramid fiber, and the mass ratio of bismaleimide-epoxy resin to aramid fiber is 35:65.

[0080] Example 2

[0081] The embodiment of the present application provides a fiber composite material and a preparation method thereof. Based on Example 1, the mass ratio of hyperbranched epoxy resin-modified carbon nanotubes and bismaleimide-epoxy resin prepolymer in the mixed solution in step S3 is changed to 2:98, while other parameters remain unchanged.

[0082] Example 3

[0083] The embodiment of the present application provides a fiber composite material and a preparation method thereof. Based on Example 1, the mass ratio of hyperbranched epoxy resin-modified carbon nanotubes and bismaleimide-epoxy resin prepolymer in the mixed solution in step S3 is changed to 3:97, while other parameters remain unchanged.

[0084] Example 4

[0085] The embodiment of the present application provides a fiber composite material and a preparation method thereof. Based on Example 1, the mass ratio of hyperbranched epoxy resin-modified carbon nanotubes and bismaleimide-epoxy resin prepolymer in the mixed solution in step S3 is changed to 5:90, while other parameters remain unchanged.

[0086] Example 5

[0087] The embodiment of the present application provides a fiber composite material and a preparation method thereof. The mass ratio of bismaleimide-epoxy resin to aramid fiber in the fiber composite material is 30:69, and other processes are the same as in Example 1.

[0088] Example 6

[0089] The embodiment of the present application provides a fiber composite material and a preparation method thereof. The mass ratio of bismaleimide-epoxy resin to aramid fiber in the fiber composite material is 39:60, and other processes are the same as in Example 1.

[0090] Comparative Example 1

[0091] The literature Patterson, Brendan A., et al. "Aramid nanofibers for multiscale fiber reinforcement of polymer composites." Composites Science and Technology 161 (2018): 92-99 reports that aramid nanofibers were prepared by a dissolution process in an alkaline solution. To modify the epoxy resin matrix, aramid nanofibers were dispersed in a curing agent at a weight ratio of 2.0% by weight using ultrasonic treatment. Subsequently, the mixture was added to the resin at a ratio of 35:100 (resin accounting for the larger proportion) and stirred using a high-speed shear mixer for 5 minutes. After a simple degassing treatment, the epoxy resin mixture modified with aramid nanofibers was ready for composite material preparation. Aramid nanofiber-reinforced composites were prepared using a vacuum-assisted resin transfer molding process. However, when the aramid nanofiber content in the matrix material is high, the increased resin viscosity hinders its rapid penetration into the sample, so the process needs to be improved. The improved process impregnates the fiber layer with the modified matrix material during the laying process and compacts it step by step at a pressure of 100 psi under a vacuum environment. The curing procedure is 80℃ / 2h; 125℃ / 3h.

[0092] Comparative Example 2

[0093] The literature Demircan, Gokhan, et al. "Surface-modified alumina nanoparticles-filled aramid fiber-reinforced epoxy nanocomposites: preparation and mechanical properties." Iranian Polymer Journal 29(2020): 253-264 reported that alumina nanoparticles were first modified with a silane coupling agent, and then epoxy resin was added with a mass fraction of 1%. The mixture was stirred with a magnetic stirrer at 500 r / min at 60°C for 1 hour, and then the speed was increased to 1000 r / min and continued to stir at 60 degrees Celsius for 1 hour. Thereafter, the mixture was immediately transferred to an ultrasonic stirrer and placed in an ice bath. After the modified alumina nanoparticles were evenly dispersed in the epoxy resin, a curing agent was added and manually stirred for 5 minutes. To eliminate bubbles, the mixture was placed in a vacuum degassing chamber for degassing for 6 minutes. After the modified epoxy resin was uniformly prepared, the nanocomposite plate was prepared by vacuum-assisted resin infusion. First, eight layers of aramid fiber, serving as reinforcement, were cut to size and laid flat on a release film. A release ply was then applied to the fiber layer, and a flow-guiding mesh was placed above the release ply to promote even distribution of the epoxy resin. Finally, the entire system was vacuum-bagged and connected to the necessary components. Modified epoxy resin was then injected into the system and cured at 80°C for 15 hours to produce the composite material.

[0094] Comparative Example 3

[0095] The literature Sharma, Sushant, et al. "Excellent mechanical properties of long multiwalled carbon nanotube bridged Kevlar fabric." Carbon 137 (2018): 104-117 reported that carbon nanotubes were dispersed in ethanol and ultrasonically treated with an ultrasonic frequency of 50 kHz and an ultrasonic time of 2 h. Different mass fractions of carbon nanotubes were used to prepare different samples. After the ultrasonic treatment, the carbon nanotubes were added to the epoxy resin and stirred with a homogenizer while the ethanol was volatilized. After that, the hardener was added to the epoxy resin and the mixture was stirred for another 30 min. The mixture was then coated on an AF sheet, and the coated fabric was then placed in a dryer and kept under a vacuum of 30 mm Hg for 3 h to allow the epoxy resin to evenly enter the AF. Finally, the impregnated fabric was placed between two release papers and mechanical rolling was provided to remove excess resin. The impregnated fabric was placed between square flat molds. A hydraulic press was used at 100 kg / cm 2The sample was pressed under pressure and cured simultaneously, and the curing procedure was 120℃ / 2h; 160℃ / 4h.

[0096] Comparative Example 4

[0097] The literature Suresha, B., et al. "Effect of carbon nanotubes reinforcement on mechanical properties of aramid / epoxy hybrid composites." Materials Today: Proceedings 43(2021): 1478-1484 reported that after preheating the epoxy resin to 60°C, a predetermined mass of carbon nanotubes was added and mechanically stirred for 20 minutes. In order to reduce the viscosity of the epoxy resin / carbon nanotube composite system, the temperature was maintained at 60°C with the help of a heating plate during the mixing process, and a uniform mixed solution was finally obtained. Degassing was then carried out to release bubbles in the mixture. To promote nanoscale dispersion of carbon nanotubes in the epoxy resin medium, the system was ultrasonically treated for 40 minutes. The curing agent was added to the resin / filler mixture in a mass ratio of 100:25 and stirred gently to avoid introducing bubbles. AF was stacked layer by layer, and each layer was carefully coated with a uniform mixture. The resin was squeezed using a roller press to eliminate bubble formation. The stacked laminate was cured under a constant pressure of 1 MPa to ensure uniform resin impregnation and squeeze out excess resin. The laminate was cured at room temperature for 24 h and then post-cured at 85 °C for 6 h.

[0098] Comparative Example 5

[0099] The comparative example of the present application provides a fiber composite material and a preparation method thereof, which comprises the following steps:

[0100] S1. Preparation of bismaleimide-epoxy resin prepolymer

[0101] Maintaining the stirring state at a stirring rate of 240 r / min, 4,4′-bismaleimide diphenylmethane monomer and bisphenol A epoxy resin monomer were first melt-prepolymerized at 135° C. for 20 minutes to obtain a first mixture, and then 4,4′-diaminodiphenyl sulfone was added to the first mixture and the reaction was continued for 10 minutes. The mass ratio of 4,4′-bismaleimide diphenylmethane monomer, bisphenol A epoxy resin monomer and 4,4′-diaminodiphenyl sulfone was 15:65:25.

[0102] S2. Preparation of mixed solution

[0103] A certain amount of acetone is added to the prepared bismaleimide-epoxy resin prepolymer and fully dissolved to obtain a mixed solution.

[0104] S3. Preparation of prepreg

[0105] The prepared mixed solution is evenly coated on the surface of the aramid fiber, and a prepreg is obtained after the solvent in the mixed solution is volatilized.

[0106] S4. Preparation of fiber composite materials

[0107] The prepreg stack is stacked in a mold and then placed in a hot pressing molding machine at a pressure of 20 MPa. The curing procedure is sequentially curing at a temperature of 160°C for 1 hour, curing at a temperature of 180°C for 1 hour, and curing at a temperature of 200°C for 1 hour. After the hot pressing is completed, the composite material is obtained. The fiber composite material includes bismaleimide-epoxy resin and aramid fiber, and the mass ratio of bismaleimide-epoxy resin to aramid fiber is 35:65.

[0108] Comparative Example 6

[0109] The comparative example of the present application provides a fiber composite material and a preparation method thereof, which comprises the following steps:

[0110] S1. Preparation of bismaleimide-epoxy resin prepolymer

[0111] Maintaining the stirring state at a stirring rate of 240 r / min, 4,4′-bismaleimide diphenylmethane monomer and bisphenol A epoxy resin monomer were first melt-prepolymerized at 135° C. for 20 minutes to obtain a first mixture, and then 4,4′-diaminodiphenyl sulfone was added to the first mixture and the reaction was continued for 10 minutes. The mass ratio of 4,4′-bismaleimide diphenylmethane monomer, bisphenol A epoxy resin monomer and 4,4′-diaminodiphenyl sulfone was 15:65:25.

[0112] S2. Preparation of mixed solution

[0113] A certain amount of acetone was added to the prepared bismaleimide-epoxy resin prepolymer and fully dissolved to obtain a premixed solution. Carboxyl carbon nanotubes were then added to the premixed solution and ultrasonically stirred for 1 hour to obtain a mixed solution. The ultrasonic stirring power was 200 W and the stirring rate was 240 r / min. The mass ratio of carboxyl carbon nanotubes to bismaleimide-epoxy resin prepolymer in the mixed solution was 2:98.

[0114] S4. Preparation of prepreg

[0115] The prepared mixed solution is evenly coated on the surface of the aramid fiber, and a prepreg is obtained after the solvent in the mixed solution is volatilized.

[0116] S5. Preparation of fiber composite materials

[0117] The prepreg stack is stacked in a mold and then placed in a hot pressing molding machine at a pressure of 20 MPa. The curing procedure is sequentially curing at a temperature of 160°C for 1 hour, curing at a temperature of 180°C for 1 hour, and curing at a temperature of 200°C for 1 hour. After the hot pressing is completed, the composite material is obtained. The fiber composite material includes bismaleimide-epoxy resin and aramid fiber, and the mass ratio of bismaleimide-epoxy resin to aramid fiber is 35:65.

[0118] Comparative Example 7

[0119] The comparative example of the present application provides a fiber composite material and a preparation method thereof, which comprises the following steps:

[0120] S1. Preparation of hyperbranched epoxy resin modified carbon nanotubes

[0121] Carboxyl carbon nanotubes were uniformly dispersed in N,N-dimethylformamide by ultrasonic stirring to obtain a carbon nanotube dispersion. The ultrasonic stirring power was 200 W and the stirring rate was 210 r / min. The stirring state was maintained. Hyperbranched epoxy resin and tert-butyl ammonium bromide were added to the carbon nanotube dispersion, and the mixture was reacted at 100° C. for 24 hours to obtain a first product. The first product was washed, centrifuged, collected, and dried to obtain hyperbranched epoxy resin-modified carbon nanotubes. The mass ratio of carboxyl carbon nanotubes, hyperbranched epoxy resin, and tert-butyl ammonium bromide was 95:5:5.

[0122] S2. Preparation of epoxy resin prepolymer

[0123] Maintaining the stirring state at a stirring rate of 240 r / min, a certain amount of bisphenol A epoxy resin monomer was first melt-prepolymerized at 135° C. for 20 minutes to obtain a first mixture, and then 4,4′-diaminodiphenyl sulfone was added to the first mixture and the reaction was continued for 10 minutes. The mass ratio of bisphenol A epoxy resin monomer to 4,4′-diaminodiphenyl sulfone was 80:25.

[0124] S3. Preparation of mixed solution

[0125] A certain amount of acetone was added to the prepared epoxy resin prepolymer and fully dissolved to obtain a premixed solution. The prepared hyperbranched epoxy resin-modified carbon nanotubes were then added to the premixed solution and ultrasonically stirred for 1 hour to obtain a mixed solution. The ultrasonic stirring power was 200 W and the stirring rate was 240 r / min. The mass ratio of the hyperbranched epoxy resin-modified carbon nanotubes to the epoxy resin prepolymer in the mixed solution was 1:99.

[0126] S4. Preparation of prepreg

[0127] The prepared mixed solution is evenly coated on the surface of the aramid fiber, and a prepreg is obtained after the solvent in the mixed solution is volatilized.

[0128] S5. Preparation of fiber composite materials

[0129] The prepreg stack is stacked in a mold and then placed in a hot pressing molding machine at a pressure of 20 MPa. The curing procedure is sequentially curing at a temperature of 160° C. for 1 hour, curing at a temperature of 180° C. for 1 hour, and curing at a temperature of 200° C. for 1 hour. After the hot pressing is completed, the composite material is obtained. The fiber composite material includes epoxy resin and aramid fiber, and the mass ratio of epoxy resin to aramid fiber is 35:65.

[0130] The raw materials and processes of Examples 1 to 6 and Comparative Examples 1 to 7 are shown in Table 1.

[0131] Table 1 Raw materials and process of Examples 1 to 6 and Comparative Examples 1 to 7

[0132]

[0133]

[0134] Test Example 1

[0135] Figure 1 These are actual pictures of the fiber composite materials of Examples 1 to 3 and Comparative Examples 5 to 7.

[0136] Depend on Figure 1 It can be seen that all samples have almost no difference in appearance under the same preparation process. They are all dense plates with no obvious defects and delamination. Only the color becomes darker with the increase of carbon nanotube content.

[0137] Test Example 2

[0138] Figure 2 The bending stress-strain curves of the fiber composite materials of Examples 1 to 3 and Comparative Examples 5 to 7 are shown.

[0139] Depend on Figure 2 It can be seen that Example 2 has the highest bending strength, and Comparative Example 5 and Examples 1 to 3 show a phenomenon in which the strength first increases and then decreases. This is because the modified carbon nanotubes with a higher content are prone to agglomeration, which easily leads to stress concentration problems. Comparative Example 7 does not use bismaleimide-modified epoxy resin on the basis of Example 2, so the mechanical properties and toughness of the matrix are reduced, which is reflected in the decrease in the mechanical properties of the composite material. Comparative Example 6 does not use hyperbranched epoxy resin to modify carbon nanotubes on the basis of Example 2. On the one hand, the dispersibility of the carbon nanotubes decreases, and the physical adsorption effect with the fibers is weakened. On the other hand, it cannot undergo a curing reaction with the matrix, and lacks chemical bonding to establish a stress transfer channel between the matrix and the fibers. Compared with Comparative Example 7, Comparative Example 6 highlights that the modification of hyperbranched epoxy resin is superior to that of bismaleimide-modified epoxy resin.

[0140] Test Example 3

[0141] Figure 3 The force-displacement curves of the short beam interlaminar shear test of the fiber composite materials of Examples 1 to 3 and Comparative Examples 5 to 7 are shown.

[0142] Depend on Figure 3 It can be seen that Example 2 can withstand the highest load and therefore has the best shear strength. In addition, the law shown is consistent with that of bending, which also illustrates the advantage of hyperbranched epoxy resin in enhancing the interfacial effect.

[0143] Test Example 4

[0144] Figure 4 These are scanning electron micrographs of the fracture surfaces of the fiber composite materials of Example 2 and Comparative Example 5.

[0145] Depend on Figure 4 As can be seen, the AF surface of the composite material in Comparative Example 5 is smooth, with only small, physically adsorbed resin fragments present in localized areas. These resin fragments are also smooth, indicating a weak interfacial bond between the fiber and matrix. In Example 2, the microfiber surface of the composite material is completely covered by a continuous, dense resin matrix, with virtually no exposed fibers. However, filamentous carbon nanotubes can be observed on the AF surface of the damaged areas. More notably, the resin surface is rougher, a phenomenon confirmed by higher magnification. This suggests a strong interaction between the resin matrix and the fibers, via the modified carbon nanotubes.

[0146] Test Example 5

[0147] The properties of the fiber composite materials of Examples 1 to 6 and Comparative Examples 1 to 7 were measured and are shown in Table 2.

[0148] The test method is as follows:

[0149] 1. Bending strength

[0150] Tested according to GB / T 1449-2005 standard.

[0151] 2. Interface shear strength

[0152] Tested according to ASTM D2344.

[0153] 3. Bending strength after aging at 200℃ for 24h

[0154] The samples were heat treated at 200°C for 24 h and then tested according to GB / T 1449-2005.

[0155] 4. Interface shear strength after aging at 200℃ for 24h

[0156] The samples were heat treated at 200 °C for 24 h and then tested according to ASTM D2344.

[0157] Table 2 Properties of fiber composite materials of Examples 1 to 6 and Comparative Examples 1 to 7

[0158]

[0159] As can be seen from Table 2, the bending strength of Examples 1 to 6 of the present application is 404.1 MPa to 505.6 MPa, the interface shear strength is 23.4 MPa to 26.8 MPa, the bending strength after aging at 200°C for 24 hours is 378.4 MPa to 497.3 MPa, and the interface shear strength after aging at 200°C for 24 hours is 22.9 MPa to 27.5 MPa.

[0160] By comparing Comparative Example 5 and Example 2, it can be seen that there are no hyperbranched epoxy resin-modified carbon nanotubes in the fiber composite material of Comparative Example 5, the bending strength of Comparative Example 5 is only 357.8 MPa, and the interfacial shear strength is only 20.4 MPa. The bending strength and interfacial shear strength of the fiber composite material of Comparative Example 5 are both lower than the bending strength and interfacial shear strength of the fiber composite material of Example 2.

[0161] From the comparison between Comparative Example 6 and Example 2, it can be seen that the filler in the fiber composite material of Comparative Example 6 is carboxyl carbon nanotubes, the bending strength of Comparative Example 6 is only 404.5 MPa, and the interfacial shear strength is only 24.4 MPa. The bending strength and interfacial shear strength of the fiber composite material of Comparative Example 6 are lower than those of the fiber composite material of Example 2.

[0162] From the comparison between Comparative Example 7 and Example 2, it can be seen that the resin matrix in the fiber composite material of Comparative Example 7 is epoxy resin, the flexural strength of Comparative Example 7 is only 443.8 MPa, and the interfacial shear strength is only 25.7 MPa. The flexural strength and interfacial shear strength of the fiber composite material of Comparative Example 7 are both lower than those of the fiber composite material of Example 2.

[0163] The foregoing description is merely a specific embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for preparing a fiber composite material, characterized in that: The preparation method of the fiber composite material comprises: placing a mixed solution on aramid fiber, volatilizing the solvent in the mixed solution to obtain a prepreg, and then hot-pressing the prepreg to obtain the fiber composite material; The mixed solution comprises hyperbranched epoxy resin modified carbon nanotubes, bismaleimide-epoxy resin prepolymer and solvent.

2. The method for preparing a fiber composite material according to claim 1, characterized in that: The mass ratio of the hyperbranched epoxy resin modified carbon nanotubes to the bismaleimide-epoxy resin prepolymer in the mixed solution is 1-5:90-99.

3. The method for preparing a fiber composite material according to claim 1, characterized in that: The fiber composite material includes bismaleimide-epoxy resin and the aramid fiber, and the mass ratio of the bismaleimide-epoxy resin to the aramid fiber is 30-39:60-69.

4. The method for preparing a fiber composite material according to claim 1, characterized in that: The pressure during hot pressing is 15MPa to 25MPa, and the curing procedures are curing at a temperature of 155°C to 165°C for 0.8h to 1.2h, curing at a temperature of 175°C to 185°C for 0.8h to 1.2h, and curing at a temperature of 195°C to 205°C for 0.8h to 1.2h.

5. The method for preparing a fiber composite material according to claim 1, characterized in that: The hyperbranched epoxy resin modified carbon nanotubes are prepared by the following method: Keep stirring and react the carboxyl carbon nanotubes, hyperbranched epoxy resin and tert-butylammonium bromide at 80° C. to 120° C. for 20 h to 28 h.

6. The method for preparing a fiber composite material according to claim 5, characterized in that: The mass ratio of the carboxyl carbon nanotubes, the hyperbranched epoxy resin and the tert-butylammonium bromide is 90-99:1-10:1-10.

7. The method for preparing a fiber composite material according to claim 1, characterized in that: The bismaleimide-epoxy resin prepolymer is prepared by the following method: Maintaining the stirring state, the bismaleimide monomer and the epoxy resin monomer are first melt-prepolymerized at 130° C. to 140° C. for 15 to 25 minutes to prepare a first mixture, and then a curing agent is added to the first mixture to continue the reaction for 5 to 15 minutes.

8. The method for preparing a fiber composite material according to claim 7, characterized in that: The mass ratio of the bismaleimide monomer, the epoxy resin monomer and the curing agent is 10-19:60-69:20-29, and / or; The epoxy resin monomer includes bisphenol A epoxy resin monomer, and / or; The bismaleimide monomer includes 4,4'-bismaleimide diphenylmethane monomer.

9. A fiber composite material, characterized in that The fiber composite material is prepared according to the method for preparing a fiber composite material according to any one of claims 1 to 8.

10. The fiber composite material according to claim 9, characterized in that The maximum decomposition temperature of the fiber composite material is 550° C. to 600° C., and / or; The carbon residue rate of the fiber composite material is 35% to 40%, and / or; After aging at 200° C. and 220° C. for 24 hours, the mass loss of the fiber composite material is less than 1%, and / or; The fiber composite material has a flexural strength of 400 MPa to 600 MPa, and / or; The interfacial shear strength of the fiber composite material is 20 MPa to 30 MPa, and / or; After aging at 200° C. for 24 hours, the retention rates of the flexural strength and interfacial shear strength of the fiber composite material are both 90% to 100% of those before aging, and / or; After aging at 220° C. for 24 hours, the retention rates of the flexural strength and interfacial shear strength of the fiber composite material are both 80% to 95% of those before aging, and / or; After aging at 240° C. for 24 hours, the retention rates of the flexural strength and interfacial shear strength of the fiber composite material are both 50% to 75% of those before aging.

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