A fiber composite material and a method for producing the same

Abstract

This application provides a fiber composite material and its preparation method, belonging to the field of composite material technology. The preparation method of the fiber composite material includes disposing a mixed solution on aramid fibers to obtain a prepreg, and hot-pressing the prepreg to obtain the fiber composite material. The mixed solution includes hyperbranched epoxy resin-modified carbon nanotubes, bismaleimide-epoxy resin prepolymer, and a solvent. The preparation method of this application uses hyperbranched epoxy resin-modified carbon nanotubes and bismaleimide-epoxy resin prepolymer to composite with aramid fibers. On the one hand, the flexible hyperbranched epoxy long chains can improve the dispersibility of carbon nanotubes, reduce their aggregation, and simultaneously adsorb them onto 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 combined effect of these two factors significantly improves the interfacial properties of the fiber composite material.

Description

Technical Field

[0001] This application relates to the field of composite materials technology, and more specifically, to a fiber composite material and a method for preparing the same. Background Technology

[0002] The properties of fiber-reinforced resin matrix composites are primarily determined by the resin, fibers, and the interfaces between them; among these, the interface is a unique and extremely important component of composite materials. The interface refers to the three-dimensional region between two phases (resin and fiber), representing a gradual transition of properties from one phase to another. The interface plays a crucial role in the properties of composite materials, especially their mechanical properties. Aramid fibers (AF) have a relatively smooth surface and low surface energy. Furthermore, their chemical composition differs from that of the resin, resulting in poor interfacial compatibility and low interfacial strength. Therefore, the interface becomes a weak link in the composite material. Under external loads, stress concentration and microcrack propagation often occur at the interface, damaging the composite material and severely affecting its interfacial toughness and strength, thus hindering its large-scale application. Therefore, improving the toughness and strength of AF composites from the interfacial perspective to enhance their impact resistance and mechanical properties is a key scientific issue in constructing advanced AF / epoxy resin composites. Summary of the Invention

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

[0004] The embodiments of this application are implemented as follows:

[0005] In a first aspect, this application provides a method for preparing a fiber composite material, comprising: placing a mixed solution on aramid fibers, obtaining a prepreg after the solvent in the mixed solution evaporates, and then hot-pressing the prepreg to obtain the fiber composite material; wherein the mixed solution comprises 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 this application uses hyperbranched epoxy resin modified carbon nanotubes and bismaleimide-epoxy resin prepolymer for composite with aramid fibers. On the one hand, the flexible hyperbranched epoxy long chains can improve the dispersibility of carbon nanotubes, reduce the aggregation of carbon nanotubes, and at the same time allow them to be 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 interaction of these two factors can significantly improve the interfacial properties of the fiber composite material. The preparation method of the fiber composite material of this 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 implementations, the mass ratio of hyperbranched epoxy resin-modified carbon nanotubes to bismaleimide-epoxy resin prepolymer in the mixed solution is 1–5:90–99.

[0008] In the above technical solution, this application improves the interfacial properties of fiber composite materials by keeping the mass ratio of hyperbranched epoxy resin modified carbon nanotubes and bismaleimide-epoxy resin prepolymer in the mixed solution within the above range. This is beneficial for the amino groups in the copolymer matrix formed by the hyperbranched epoxy resin modified carbon nanotubes and bismaleimide-epoxy resin prepolymer to undergo a curing reaction.

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

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

[0011] In some possible implementations, hyperbranched epoxy resin modified carbon nanotubes are prepared by reacting carboxyl carbon nanotubes, hyperbranched epoxy resin and tert-butylammonium bromide at 80°C to 120°C for 20 to 28 hours while maintaining a stirring state.

[0012] In the above technical solution, this application utilizes hyperbranched epoxy groups to react with carboxyl-containing carbon nanotubes to graft carbon nanotubes, thereby obtaining a flexible-rigid core-shell nanostructured particle. That is, the carbon nanotube is 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 carbon nanotubes and reduce their aggregation, while also allowing them to adsorb onto 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 bismaleimide-epoxy resin prepolymer. The interaction of these two factors can significantly improve the interfacial properties of the fiber composite material.

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

[0014] In some possible implementations, the bismaleimide-epoxy resin prepolymer is prepared by the following method: while keeping the mixture stirred, the bismaleimide monomer and the epoxy resin monomer are melt-prepolymerized at 130°C to 140°C for 15 min to 25 min to obtain a first mixture, and then a curing agent is added to the first mixture to continue the reaction for 5 min to 15 min.

[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 type epoxy resin monomer, and / or; the bismaleimide monomer includes 4,4′-bismaleimide diphenylmethane monomer.

[0016] In a second aspect, this application provides a fiber composite material prepared according to the fiber composite material preparation method described in the above embodiments.

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

[0018] In some possible implementations, the maximum decomposition temperature of the fiber composite material is 550℃~600℃, and / or; the char residue of the fiber composite material is 35%~40%, and / or; after aging at 200℃ and 220℃ for 24h, the mass loss of the fiber composite material is less than 1%, and / or; the flexural strength of the fiber composite material is 400MPa~600MPa, and / or; the interfacial shear strength of the fiber composite material is 20MPa~30MPa, and / or; after aging at 200℃ for 24h, the retention rate of both flexural strength and interfacial shear strength of the fiber composite material is 90%~100% of that before aging, and / or; after aging at 220℃ for 24h, the retention rate of both flexural strength and interfacial shear strength of the fiber composite material is 80%~95% of that before aging, and / or; after aging at 240℃ for 24h, the retention rate of both flexural strength and interfacial shear strength of the fiber composite material is 50%~75% of that before aging. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 These are physical images of the fiber composite materials of Examples 1-3 and Comparative Examples 5-7 of this application;

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

[0022] Figure 3 Force-displacement curves of interlaminar shear tests of fiber composite short beams of Examples 1-3 and Comparative Examples 5-7 of this application;

[0023] Figure 4 The images show scanning electron microscope (SEM) images of the fracture surfaces of the fiber composite materials of Example 2 and Comparative Example 5 of this application. Detailed Implementation

[0024] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0025] Currently, interface modification of AF / epoxy resin composites mainly employs two approaches: fiber surface treatment and resin matrix modification. Fiber surface modification involves modifying the fiber surface with active groups or increasing its roughness through various treatment methods, thereby achieving good chemical bonds and mechanical interlocking between the fiber and the matrix. However, from the perspective of practical application and large-scale production, fiber surface modification presents many challenges. For example, surface etching, plasma treatment, and high-energy ray treatment all rely on damaging the fiber for modification; the solvents involved in surface etching, chemical grafting, and coating methods inevitably have environmental impacts; plasma treatment and high-energy ray treatment are energy-intensive and require stringent equipment; coupling agent treatment has limited compatibilization effects; surface nanostructure construction methods are limited by the easy aggregation of nanoparticles, limiting the number of nanoparticles that can be loaded onto the fiber, thus limiting the compatibilization effect, and many design methods are not suitable for preparing continuous fiber laminates; the aforementioned fiber surface modification methods are highly design-intensive and involve numerous operational steps, meaning they are difficult to operate and unfavorable for large-scale production.

[0026] Resin matrix modification involves directly introducing modifiers into the matrix, where they react chemically or physically with the fiber surface. On the other hand, modifying the resin matrix improves its basic strength, thus enhancing the overall mechanical properties of the composite material from both interfacial and matrix perspectives. Generally, polymer monomers and nanomaterials are used to modify the resin matrix. Among polymers, bismaleimide is an ideal polymer for epoxy resin modification due to its excellent thermal stability, flame retardancy, and similar processing technology to epoxy resin, being soluble in epoxy resin without phase separation. However, the performance of fiber composites is affected not only by the matrix but also by the interface between the fiber and resin. Therefore, nanomaterial modification is also necessary, using nanoparticles as matrix modifiers. These nanoparticles can exist as a second phase to improve overall mechanical properties, while simultaneously achieving mechanical interlocking through physical adsorption to improve interfacial properties. Among numerous nanomaterials, carbon nanotubes are favored by researchers due to their extremely high strength, toughness, thermal conductivity, and high specific surface area. However, it is well known that nanoparticles are prone to agglomeration, leading to uneven dispersion in composite materials and affecting their overall performance.

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

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

[0029] Carboxylated carbon nanotubes were uniformly dispersed in a first organic solvent by ultrasonic stirring to obtain a carbon nanotube dispersion. While maintaining the stirring state, hyperbranched epoxy resin and tert-butylammonium bromide were added to the carbon nanotube dispersion, and the mixture was reacted at 80℃~120℃ for 20h~28h to obtain the first product. The first product was washed, collected by centrifugation, and dried to obtain hyperbranched epoxy resin modified carbon nanotubes.

[0030] Carboxyl-based carbon nanotubes are functionalized materials 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 ultrasonic stirring power is 150W to 250W, and the stirring speed is 150r / min to 300r / min.

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

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

[0035] As an example, the mass ratio of carboxylated carbon nanotubes, hyperbranched epoxy resin, and tert-butylammonium 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] This application utilizes the reaction of hyperbranched epoxy groups with carboxyl-containing carbon nanotubes to graft carbon nanotubes, obtaining a flexible-rigid core-shell nanostructured particle, where the carbon nanotubes form the rigid core and the hyperbranched epoxy resin forms the flexible shell. On the one hand, the flexible hyperbranched epoxy long chains can improve the dispersibility of carbon nanotubes, reduce their aggregation, and allow them to adsorb onto the surface of aramid fiber composite materials. 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 interaction of these two factors can significantly improve the interfacial properties of the fiber composite material.

[0037] S2. Preparation of bismaleimide-epoxy resin prepolymer

[0038] While maintaining stirring, first melt prepolymerize the bismaleimide monomer and epoxy resin monomer at 130℃~140℃ for 15min~25min to obtain the first mixture, then add the curing agent to the first mixture and continue the reaction for 5min~15min.

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

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

[0041] Optionally, the curing agent includes 4,4′-diaminodiphenyl 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 bismaleimide monomer, epoxy resin monomer and curing agent is 10-19:60-69:20-29.

[0044] As an example, the mass ratio of bismaleimide monomer, epoxy resin monomer and 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 resin monomer includes bisphenol A type epoxy resin monomer.

[0046] Optionally, the bismaleimide monomer includes 4,4′-bismaleimide diphenylmethane monomer.

[0047] S3. Preparation of mixed solution

[0048] The second organic solvent was added to the prepared bismaleimide-epoxy resin prepolymer and dissolved completely to obtain a premixed solution. Then, the prepared hyperbranched epoxy resin modified carbon nanotubes were added to the premixed solution and ultrasonically stirred for 0.5 h to 3 h to obtain a mixed solution.

[0049] Optionally, the ultrasonic stirring power is 150W to 250W, and the stirring speed is 150r / min to 300r / min.

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

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

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

[0053] This application improves the interfacial properties of fiber composites by ensuring that the mass ratio of hyperbranched epoxy resin-modified carbon nanotubes to bismaleimide-epoxy resin prepolymer in the mixed solution is within the above-mentioned range. This facilitates the curing reaction of amino groups in the copolymer matrix formed by the hyperbranched epoxy resin-modified carbon nanotubes and bismaleimide-epoxy resin prepolymer.

[0054] S4. Preparation of prepreg

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

[0056] S5. Preparation of fiber composite materials

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

[0058] As an example, the pressure of the hot press molding machine can be 15MPa, 18MPa, 20MPa, 22MPa or 25MPa.

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

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

[0061] The method for preparing the fiber composite material of this application involves using hyperbranched epoxy resin to modify carbon nanotubes and bismaleimide-epoxy resin prepolymers for composite with aramid fibers. On the one hand, the flexible hyperbranched epoxy long chains can improve the dispersibility of carbon nanotubes, reduce their agglomeration, and simultaneously adsorb them onto 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. This interaction significantly improves the interfacial properties of the fiber composite material, mitigating interfacial debonding, uneven carbon nanotube dispersion, processing problems caused by fiber modification, and fiber structure damage during the preparation of aramid fiber-reinforced carbon nanotube / epoxy resin composites. The method for preparing the fiber composite material of this application is simple, and the resulting fiber composite material exhibits good thermal stability, room temperature mechanical properties, and aging mechanical properties.

[0062] This application also provides a fiber composite material, which is prepared according to the fiber composite material preparation method in the above embodiments.

[0063] The fiber composite material of this application has good thermal stability, with a maximum decomposition temperature of 550℃~600℃, a char residue rate of 35%~40%, and a mass loss of less than 1% after aging at 200℃ and 220℃ for 24 hours.

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

[0065] The fiber composite material of this application has good aging mechanical properties. After aging at 200℃ for 24 hours, the flexural strength and interfacial shear strength of the fiber composite material are 90% to 100% of the original values. After aging at 220℃ for 24 hours, the flexural strength and interfacial shear strength of the fiber composite material are 80% to 95% of the original values. After aging at 240℃ for 24 hours, the flexural strength and interfacial shear strength of the fiber composite material are 50% to 75% of the original values.

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

[0067] The following detailed description of a fiber composite material and its preparation method, in conjunction with embodiments, further illustrates this application.

[0068] Example 1

[0069] This application provides a fiber composite material and a method for preparing the same, which includes the following steps:

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

[0071] Carboxylated carbon nanotubes were uniformly dispersed in N,N-dimethylformamide by ultrasonic stirring to obtain a carbon nanotube dispersion. The ultrasonic stirring power was 200W and the stirring speed was 210r / min. After stirring, hyperbranched epoxy resin and tert-butylammonium bromide were added to the carbon nanotube dispersion, and the mixture was reacted at 100℃ for 24h to obtain the first product. The first product was washed, collected by centrifugation, and dried to obtain hyperbranched epoxy resin modified carbon nanotubes. The mass ratio of carboxylated carbon nanotubes, hyperbranched epoxy resin, and tert-butylammonium bromide was 95:5:5.

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

[0073] While maintaining a stirring state at a stirring rate of 240 r / min, the 4,4′-bismaleimide diphenylmethane monomer and bisphenol A epoxy resin monomer were first melt-prepolymerized at 135℃ for 20 min to obtain a first mixture. Then, 4,4′-diaminodiphenyl sulfone was added to the first mixture and the reaction was continued for 10 min. 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 dissolved completely to obtain a premixed solution. Then, the prepared hyperbranched epoxy resin modified carbon nanotubes were added to the premixed solution and ultrasonically stirred for 1 hour to obtain a mixed solution. The ultrasonic stirring power was 200W and the stirring speed was 240r / min. The mass ratio of hyperbranched epoxy resin modified carbon nanotubes to bismaleimide-epoxy resin prepolymer in the mixed solution was 1:99.

[0076] S4. Preparation of prepreg

[0077] The prepared mixed solution is uniformly coated on the surface of aramid fibers, and the prepreg is obtained after the solvent in the mixed solution evaporates.

[0078] S5. Preparation of fiber composite materials

[0079] The prepreg is stacked in a mold and then placed in a hot press molding machine at a pressure of 20 MPa. The curing process is as follows: curing at 160°C for 1 hour, curing at 180°C for 1 hour, and curing at 200°C for 1 hour in sequence. After hot pressing, 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] This application provides a fiber composite material and its preparation method, which is based on Example 1, but with the mass ratio of hyperbranched epoxy resin modified carbon nanotubes and bismaleimide-epoxy resin prepolymer in the mixed solution in step S3 changed to 2:98, while other aspects remain unchanged.

[0082] Example 3

[0083] This application provides a fiber composite material and its preparation method, which is based on Example 1, but changes the mass ratio of hyperbranched epoxy resin modified carbon nanotubes and bismaleimide-epoxy resin prepolymer in the mixed solution in step S3 to 3:97, while keeping other aspects unchanged.

[0084] Example 4

[0085] This application provides a fiber composite material and its preparation method, which is based on Example 1, but changes the mass ratio of hyperbranched epoxy resin modified carbon nanotubes and bismaleimide-epoxy resin prepolymer in the mixed solution in step S3 to 5:90, while keeping other aspects unchanged.

[0086] Example 5

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

[0088] Example 6

[0089] This application provides a fiber composite material and its preparation method. The mass ratio of bismaleimide-epoxy resin to aramid fiber in the fiber composite material is 39:60, and other processes are as described 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 the preparation of aramid nanofibers via 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 ultrasonic treatment. Subsequently, this mixture was added to the resin at a ratio of 35:100 (resin comprising a larger proportion) and stirred for 5 minutes using a high-speed shear mixer. After simple degassing, 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, thus requiring process improvement. The improved process involves impregnating the fiber layer with the modified matrix material during the layup process and compacting it stepwise under a vacuum with a pressure of 100 psi. 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, reports the modification of alumina nanoparticles with a silane coupling agent, followed by the addition of 1% epoxy resin by mass. The mixture was stirred at 500 rpm for 1 h at 60 °C using a magnetic stirrer, then the speed was increased to 1000 rpm, and stirring continued at 60 °C for another 1 h. Immediately afterwards, the mixture was transferred to an ultrasonic stirrer and placed in an ice bath. After the modified alumina nanoparticles were uniformly dispersed in the epoxy resin, a curing agent was added and the mixture was manually stirred for 5 min. To eliminate air bubbles, the mixture was degassed in a vacuum degassing chamber for 6 min. After the modified epoxy resin was uniformly prepared, nanocomposite plates were prepared using a vacuum-assisted resin injection method. First, eight layers of aramid fibers, serving as reinforcement, are cut as needed and laid flat on a release film. Then, a release layer is applied to the fiber layers, and a flow guide mesh is laid above the release layer to promote uniform distribution of the epoxy resin. Finally, the entire system is sealed in a vacuum bag and the necessary devices are connected. After injecting the modified epoxy resin into the system, it is cured at 80°C for 15 hours to obtain 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, reports the dispersion of carbon nanotubes in ethanol followed by ultrasonic treatment at a frequency of 50 kHz for 2 hours. Different mass fractions of carbon nanotubes were used to prepare different samples. After ultrasonication, the carbon nanotubes were added to epoxy resin, and the mixture was stirred using a homogenizer while the ethanol evaporated. A hardener was then added to the epoxy resin, and the mixture was stirred for another 30 minutes. The mixture was then coated onto an AF sheet, and the coated fabric was placed in a desiccator and kept under a vacuum of 30 mm Hg for 3 hours to allow the epoxy resin to uniformly penetrate the AF. Finally, the impregnated fabric was placed between two release papers and subjected to mechanical rolling to remove excess resin. The impregnated fabric was then placed between square flat molds. A hydraulic press was used at 100 kg / cm². 2The sample is pressed and cured under pressure, with the curing procedure being 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, reports that after preheating epoxy resin to 60°C, a predetermined mass of carbon nanotubes was added, followed by mechanical stirring for 20 min. To reduce the viscosity of the epoxy resin / carbon nanotube composite system, the temperature was maintained at 60°C using a heating plate during mixing, ultimately obtaining a homogeneous mixture. Degassing was then performed to release air bubbles from the mixture. To promote nanoscale dispersion of carbon nanotubes in the epoxy resin medium, the system was sonicated for 40 min. A curing agent was added to the resin / filler mixture at a mass ratio of 100:25, with gentle stirring to avoid introducing air bubbles. AF layers were stacked one by one, each layer carefully coated with a uniform mixture, and the resin was extruded using a roller press to eliminate air bubble formation. The stacked laminate was cured under a constant pressure of 1 MPa, ensuring uniform resin impregnation and extruding excess resin. After the laminate is cured at room temperature for 24 hours, it is then post-cured at 85°C for 6 hours.

[0098] Comparative Example 5

[0099] This application provides a fiber composite material and a method for preparing the same, which includes the following steps:

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

[0101] While maintaining a stirring state at a stirring rate of 240 r / min, the 4,4′-bismaleimide diphenylmethane monomer and bisphenol A epoxy resin monomer were first melt-prepolymerized at 135℃ for 20 min to obtain a first mixture. Then, 4,4′-diaminodiphenyl sulfone was added to the first mixture and the reaction was continued for 10 min. 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 was added to the prepared bismaleimide-epoxy resin prepolymer, and after it was fully dissolved, a mixed solution was obtained.

[0104] S3. Preparation of prepreg

[0105] The prepared mixed solution is uniformly coated on the surface of aramid fibers, and the prepreg is obtained after the solvent in the mixed solution evaporates.

[0106] S4. Preparation of fiber composite materials

[0107] The prepreg is stacked in a mold and then placed in a hot press molding machine at a pressure of 20 MPa. The curing process is as follows: curing at 160°C for 1 hour, curing at 180°C for 1 hour, and curing at 200°C for 1 hour in sequence. After hot pressing, 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] This application provides a fiber composite material and a method for preparing the same, which includes the following steps:

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

[0111] While maintaining a stirring state at a stirring rate of 240 r / min, the 4,4′-bismaleimide diphenylmethane monomer and bisphenol A epoxy resin monomer were first melt-prepolymerized at 135℃ for 20 min to obtain a first mixture. Then, 4,4′-diaminodiphenyl sulfone was added to the first mixture and the reaction was continued for 10 min. 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 dissolved completely to obtain a premixed solution. Then, carboxylated carbon nanotubes were added to the premixed solution and ultrasonically stirred for 1 hour to obtain a mixed solution. The ultrasonic stirring power was 200W and the stirring speed was 240r / min. The mass ratio of carboxylated 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 uniformly coated on the surface of aramid fibers, and the prepreg is obtained after the solvent in the mixed solution evaporates.

[0116] S5. Preparation of fiber composite materials

[0117] The prepreg is stacked in a mold and then placed in a hot press molding machine at a pressure of 20 MPa. The curing process is as follows: curing at 160°C for 1 hour, curing at 180°C for 1 hour, and curing at 200°C for 1 hour in sequence. After hot pressing, 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] This application provides a fiber composite material and a method for preparing the same, which includes the following steps:

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

[0121] Carboxylated carbon nanotubes were uniformly dispersed in N,N-dimethylformamide by ultrasonic stirring to obtain a carbon nanotube dispersion. The ultrasonic stirring power was 200W and the stirring speed was 210r / min. After stirring, hyperbranched epoxy resin and tert-butylammonium bromide were added to the carbon nanotube dispersion, and the mixture was reacted at 100℃ for 24h to obtain the first product. The first product was washed, collected by centrifugation, and dried to obtain hyperbranched epoxy resin modified carbon nanotubes. The mass ratio of carboxylated carbon nanotubes, hyperbranched epoxy resin, and tert-butylammonium bromide was 95:5:5.

[0122] S2. Preparation of epoxy resin prepolymer

[0123] While maintaining the stirring state at a stirring rate of 240 r / min, a certain amount of bisphenol A type epoxy resin monomer was first melt-prepolymerized at 135℃ for 20 min to obtain the first mixture. Then, 4,4′-diaminodiphenyl sulfone was added to the first mixture and the reaction was continued for 10 min. The mass ratio of bisphenol A type 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 dissolved completely to obtain a premixed solution. Then, the prepared hyperbranched epoxy resin modified carbon nanotubes were added to the premixed solution and ultrasonically stirred for 1 hour to obtain a mixed solution. The ultrasonic stirring power was 200W and the stirring speed was 240r / min. The mass ratio of hyperbranched epoxy resin modified carbon nanotubes to epoxy resin prepolymer in the mixed solution was 1:99.

[0126] S4. Preparation of prepreg

[0127] The prepared mixed solution is uniformly coated on the surface of aramid fibers, and the prepreg is obtained after the solvent in the mixed solution evaporates.

[0128] S5. Preparation of fiber composite materials

[0129] The prepreg is stacked in a mold and then placed in a hot press molding machine at a pressure of 20 MPa. The curing process is as follows: curing at 160°C for 1 hour, curing at 180°C for 1 hour, and curing at 200°C for 1 hour in sequence. After hot pressing, 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 for Examples 1-6 and Comparative Examples 1-7 are shown in Table 1.

[0131] Table 1. Raw materials and processes for Examples 1-6 and Comparative Examples 1-7

[0132]

[0133]

[0134] Experimental Example 1

[0135] Figure 1 The images show actual photos of the fiber composite materials of Examples 1-3 and Comparative Examples 5-7.

[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 boards without obvious defects or delamination. Only the color becomes darker as the carbon nanotube content increases.

[0137] Experimental Example 2

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

[0139] Depend on Figure 2 It can be seen that Example 2 has the highest flexural strength, while Comparative Example 5 and Examples 1-3 show a phenomenon of strength first increasing and then decreasing. This is because the modified carbon nanotubes with a higher content are prone to agglomeration, which easily leads to stress concentration. Comparative Example 7, based on Example 2, did not use bismaleimide-modified epoxy resin, thus reducing the mechanical properties and toughness of the matrix, resulting in a decrease in the mechanical properties of the composite material. Comparative Example 6, based on Example 2, did not use hyperbranched epoxy resin to modify carbon nanotubes. On the one hand, the dispersion of carbon nanotubes decreased, and the physical adsorption with fibers weakened. On the other hand, it could not undergo a curing reaction with the matrix, lacking chemical bonding to establish a stress transfer channel between the matrix and fibers. Compared with Comparative Example 7, Comparative Example 6 highlights that modification with hyperbranched epoxy resin is superior to modification with bismaleimide-modified epoxy resin.

[0140] Experimental Example 3

[0141] Figure 3 Force-displacement curves for interlaminar shear tests of short beams of fiber composite materials in Examples 1-3 and Comparative Examples 5-7.

[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 pattern it exhibits 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 The images show scanning electron microscope (SEM) images 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 resin fragments physically adsorbed in local areas, and these resin surfaces are also smooth, indicating that the interfacial bonding between the fibers and the matrix is ​​weak. In Example 2, the microfiber surface of the composite material is completely covered by a continuous and dense resin matrix, with almost no exposed fibers. However, filamentous carbon nanotubes can be observed on the AF surface of the damaged area. More significantly, the resin surface is rougher, and the higher magnification also confirms the above phenomenon. This indicates that the resin matrix forms a strong interaction with the fibers through the modified carbon nanotubes.

[0146] Experimental Example 5

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

[0148] The testing method is as follows:

[0149] 1. Bending strength

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

[0151] 2. Interfacial shear strength

[0152] Tested according to ASTM D2344 standard.

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

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

[0155] 4. Interfacial shear strength after aging at 200℃ for 24 hours

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

[0157] Table 2 shows the properties of the fiber composite materials from Examples 1-6 and Comparative Examples 1-7.

[0158]

[0159] As shown in Table 2, the bending strength of Examples 1 to 6 of this application is 404.1 MPa to 505.6 MPa, the interfacial shear strength is 23.4 MPa to 26.8 MPa, the bending strength after aging at 200℃ for 24 hours is 378.4 MPa to 497.3 MPa, and the interfacial shear strength after aging at 200℃ for 24 hours is 22.9 MPa to 27.5 MPa.

[0160] As can be seen from the comparison between Comparative Example 5 and Example 2, the fiber composite material of Comparative Example 5 does not contain hyperbranched epoxy resin modified carbon nanotubes. The flexural strength of Comparative Example 5 is only 357.8 MPa and the interfacial shear strength is only 20.4 MPa. The flexural strength and interfacial shear strength of the fiber composite material of Comparative Example 5 are lower than those of the fiber composite material of Example 2.

[0161] As can be seen from the comparison between Comparative Example 6 and Example 2, the filler in the fiber composite material of Comparative Example 6 is carboxylated carbon nanotubes. The flexural strength of Comparative Example 6 is only 404.5 MPa and the interfacial shear strength is only 24.4 MPa. The flexural 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] As can be seen from the comparison between Comparative Example 7 and Example 2, 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 lower than those of the fiber composite material of Example 2.

[0163] The above description is merely a specific embodiment of this application and is not intended to limit 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 protection scope of this application.

Claims

1. A method for preparing a fiber composite material, characterized in that, The method for preparing the fiber composite material includes: placing a mixed solution on aramid fibers, obtaining a prepreg after the solvent in the mixed solution evaporates, and then hot-pressing the prepreg to obtain the fiber composite material. The mixed solution includes hyperbranched epoxy resin modified carbon nanotubes, bismaleimide-epoxy resin prepolymer and solvent. The mass ratio of the hyperbranched epoxy resin modified carbon nanotubes and the bismaleimide-epoxy resin prepolymer in the mixed solution is 1~5:90~99. The fiber composite material includes bismaleimide-epoxy resin and aramid fiber, and the mass ratio of bismaleimide-epoxy resin to aramid fiber is 30~39:60~69; The hyperbranched epoxy resin modified carbon nanotubes are prepared by the following method: while maintaining a stirring state, carboxyl carbon nanotubes, hyperbranched epoxy resin and tert-butylammonium bromide are reacted at 80℃~120℃ for 20h~28h. The bismaleimide-epoxy resin prepolymer was prepared by the following method: While maintaining stirring, first melt prepolymerize the bismaleimide monomer and epoxy resin monomer at 130℃~140℃ for 15min~25min to obtain a first mixture, then add a curing agent to the first mixture and continue the reaction for 5min~15min; wherein, the mass ratio of the bismaleimide monomer, the epoxy resin monomer and the curing agent is (10~19):(60~69):(20~29); the epoxy resin monomer includes bisphenol A type epoxy resin monomer; the bismaleimide monomer includes 4,4′-bismaleimide diphenylmethane monomer; the curing agent is 4,4′-diaminodiphenyl sulfone.

2. The method for preparing the fiber composite material according to claim 1, characterized in that, The hot pressing pressure is 15MPa~25MPa, and the curing procedure is to cure at 155℃~165℃ for 0.8h~1.2h, at 175℃~185℃ for 0.8h~1.2h, and at 195℃~205℃ for 0.8h~1.2h.

3. The method for preparing the fiber composite material according to claim 1, 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.

4. A fiber composite material, characterized in that, The fiber composite material is prepared by the method of any one of claims 1 to 3.

5. The fiber composite material according to claim 4, characterized in that, The maximum decomposition temperature of the fiber composite material is 550℃~600℃, and / or; The residual char rate of the fiber composite material is 35%~40%, and / or; After aging at 200℃ and 220℃ 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~600MPa, and / or; The interfacial shear strength of the fiber composite material is 20MPa~30MPa, and / or; After aging at 200℃ for 24 hours, the flexural strength and interfacial shear strength of the fiber composite material are both 90%~100% of those before aging, and / or; After aging at 220℃ for 24 hours, the flexural strength and interfacial shear strength retention rates of the fiber composite material are both 80%~95% of those before aging, and / or; After aging at 240℃ for 24 hours, the flexural strength and interfacial shear strength of the fiber composite material retained 50% to 75% of their original values.

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