Aramid fiber / phenolic resin composite material resistant to ablation and a preparation method thereof

Abstract

The application discloses an ablation-resistant aramid fiber / phenolic resin composite material and a preparation method thereof, and belongs to the technical field of polymer compound compositions. The preparation method comprises the following steps: preparing modified phenolic resin glue and modified aramid fiber, coating the modified phenolic resin glue on the modified aramid fiber, and performing heat treatment to prepare a prepreg; stacking and laying a plurality of layers of the prepreg, performing hot-pressing curing forming, cooling to room temperature, and demolding to obtain the ablation-resistant aramid fiber / phenolic resin composite material. The ablation-resistant aramid fiber / phenolic resin composite material prepared by the application has the characteristics of ablation resistance and mechanical strength, and can meet the safety protection requirements of special scenes such as high temperature and explosion prevention.

Description

Technical Field

[0001] This invention belongs to the field of polymer compound composition technology. Specifically, this invention relates to an ablation-resistant aramid fiber / phenolic resin composite material and its preparation method. Background Technology

[0002] As a key material in fields such as safety protection and special equipment, fiber composite materials' ablation resistance is crucial for ensuring reliable equipment operation and personnel safety in extreme environments. In harsh scenarios such as safety protection, fire rescue, and special operations, excellent ablation resistance effectively blocks high-temperature conduction and flame erosion, extending the stable operating time of equipment, buying time for personnel to evacuate and handle situations, and minimizing casualties and property losses.

[0003] Aramid fiber is a high-performance fiber with outstanding mechanical properties and good flexibility, and it has important applications in the field of safety protection. However, inherent defects of aramid fiber make it difficult to directly or alone meet the requirements of various applications: First, the surface of aramid fiber is chemically inert, and the molecular chain lacks active functional groups, resulting in weak interfacial bonding with the resin matrix. This leads to problems such as interlayer delamination and resin-fiber debonding in composite materials, which seriously affects the impact resistance. Second, although aramid fiber has some flame-retardant properties, its ablation resistance is poor. When exposed to combustion, the mechanical properties of the fiber will decrease sharply, or even completely lose its protective function, and it cannot guarantee the performance stability under high-temperature environments. Phenolic resin has good high-temperature resistance and flame resistance, but its molecular chain structure is highly active. It is prone to oxidative cross-linking or degradation reactions in high-temperature or oxidizing environments, making it difficult to withstand high-temperature conditions for a long time. Moreover, its high brittleness makes it unable to withstand large impact damage. It must be compounded with high-performance fibers to achieve better protective functions.

[0004] Therefore, by modifying phenolic resin to improve its ablation resistance and optimizing the composite process of aramid fiber and modified phenolic resin, ablation-resistant composite materials suitable for special scenarios such as high temperature and explosion protection can be prepared. This can significantly improve the comprehensive protection capabilities of existing materials and equipment, meet the special use needs of fields such as fire emergency response and military and police protection, and has important technical value and application prospects. Summary of the Invention

[0005] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0006] To achieve these objectives and other advantages of the present invention, a method for preparing an ablation-resistant aramid fiber / phenolic resin composite material is provided, comprising the following steps: Step 1: Preparation of modified phenolic resin solution: Dissolve phenolic resin in a solvent, add toughening agent, release agent and additives, and disperse by stirring and ultrasonication to obtain modified phenolic resin solution; Step 2: Preparation of modified aramid fibers, including the following steps: S21. Immerse the aramid fiber in potassium hypochlorite solution, take it out and rinse it with deionized water, then rinse it with ethanol solution, then immerse it in aniline methyltriethoxysilane solution and dry it to obtain pretreated aramid fiber. S22. The pretreated aramid fiber is immersed in a polyamic acid solution, taken out and pre-dried, and then vacuum dried to obtain modified aramid fiber. Step 3: Processing and molding: The modified phenolic resin adhesive is coated onto the modified aramid fiber and heat-treated to make a prepreg; multiple layers of prepreg are stacked and laid out, and then hot-pressed and cured to form a prepreg. After cooling to room temperature, the prepreg is demolded to obtain an ablation-resistant aramid fiber / phenolic resin composite material. Preferably, in step one, the phenolic resin is boron phenolic resin; the solvent is one of anhydrous ethanol, acetone, or ethylene glycol ethyl ether; and the toughening agent is a combination of polyvinyl methyl aldehyde and hydrogenated nitrile rubber in a mass ratio of 1:0.5~2.

[0007] Preferably, in step one, the release agent is palmitic acid; the auxiliary agent is one or more of nano-silica, graphene, graphene oxide and palygorskite; and the mass ratio of phenolic resin, solvent, toughening agent, release agent and auxiliary agent is 40~60:5~15:20~40:1:2~10.

[0008] Preferably, in step one, modified palygorskite is used to replace palygorskite; the method for preparing the modified palygorskite includes the following steps: A. Crush palygorskite, soak it in 5wt% dilute nitric acid for 20-40 minutes, wash it with deionized water 2-3 times, and dry it at 60-80℃ for 4-12 hours to obtain pretreated palygorskite. B. Add the pretreated palygorskite to ethylene glycol and disperse it ultrasonically. Then add hypophosphite and stir evenly. Slowly add zirconium oxychloride solution. After adding, adjust the pH to 2.5-4.0 with dilute ammonia. Heat to 60-95℃ and stir for 2-5 hours. Let stand for 4-10 hours. Wash with deionized water 2-3 times and dry at 60-80℃ for 4-12 hours to obtain zirconium hypophosphite modified palygorskite. C. Add zirconium hypophosphite-modified palygorskite to a 2wt% acetic acid solution, add octadecyltrimethoxysilane, stir evenly, heat to 60~80℃ and stir for 1~3h, wash 1~2 times with anhydrous ethanol, and vacuum dry at 60~80℃ for 6~10h to obtain modified palygorskite.

[0009] Preferably, in A, palygorskite is pulverized to 100-300 mesh, and the mass-to-volume ratio of palygorskite to dilute nitric acid is 1g: 20-50mL.

[0010] Preferably, in step B, the ultrasonic dispersion power is 200-400 W, the ultrasonic time is 20-40 min, the concentration of the zirconium oxychloride solution is 0.2-0.8 mol / L, the rate of adding the zirconium oxychloride solution is 1-3 mL / min, and the mass-volume ratio of the pretreated palygorskite, ethylene glycol solution, hypophosphite, and zirconium oxychloride solution is 1 g: 20-30 mL: 1-2 g: 5-15 mL.

[0011] Preferably, in C, the mass-to-volume ratio of zirconium hypophosphite modified palygorskite, acetic acid solution, and octadecyltrimethoxysilane is 1 g: 30~50 mL: 0.02~0.04 g; and the stirring speed is 400~700 rpm / min.

[0012] Preferably, in step one, the stirring temperature is 25~40℃, the stirring speed is 400~800rpm / min, and the stirring time is 30~60min; the ultrasonic dispersion power is 150~300W, and the dispersion time is 15~30min.

[0013] Preferably, in step S21, the aramid fiber is a para-aramid fiber plain weave fabric with an areal density of 100-300 g / m²; the potassium hypochlorite solution has a mass fraction of 1-3 wt%, the ethanol solution has a mass fraction of 50-70 wt%, and the aniline methyltriethoxysilane solution has a mass fraction of 1-2 wt%; the mass-volume ratio of the aramid fiber, potassium hypochlorite solution, and aniline methyltriethoxysilane solution is 1 g: 20-50 mL: 20-50 mL.

[0014] Preferably, in step S21, the soaking time in potassium hypochlorite solution is 10-40 min, the rinsing time in deionized water is 10-15 min, the rinsing time in ethanol solution is 5-20 min, and the soaking time in aniline methyltriethoxysilane solution is 30-60 min; the drying temperature is 60-80℃, and the drying time is 4-10 h.

[0015] Preferably, in step S22, the mass-to-volume ratio of pretreated aramid fiber to polyamic acid solution is 1g:30~60mL; the mass fraction of polyamic acid solution is 8~15wt%, the soaking time is 30~60min; the pre-drying temperature is 80~120℃, the pre-drying time is 2~8h; and the vacuum drying temperature is 260~280℃, the time is 5~15min.

[0016] Preferably, in step three, the coating method is blade coating or roller coating, the coating thickness is controlled to be 0.1~0.3mm, the heat treatment temperature is 80~100℃, and the heat treatment time is 1~2h.

[0017] Preferably, in step three, the number of prepreg layers is 8 to 15; the hot-press curing conditions are: maintaining a pressure of 5 to 8 MPa, holding at a temperature of 140 to 150°C for 1 to 2 hours, and then raising the temperature to 170 to 180°C and holding for 1 to 2 hours.

[0018] The present invention also provides an application of the ablation-resistant aramid fiber / phenolic resin composite material prepared by the above preparation method in high-temperature and explosion-proof scenarios.

[0019] The present invention has at least the following beneficial effects: This invention dissolves phenolic resin in a polar solvent and adds a toughening compound of polyvinyl acetal and hydrogenated nitrile rubber. This significantly improves toughness and crack resistance while retaining the inherent advantages of phenolic resin, such as high carbon residue, high temperature resistance, and ablation resistance. Furthermore, the introduction of additives such as nano-silica, graphene, and palygorskite significantly enhances the high-temperature stability, thermal insulation, and ablation resistance of the composite material. Under stirring and ultrasonic treatment, a uniform and stable modified phenolic resin solution is formed. In addition, this invention modifies the palygorskite by loading zirconium hypophosphite onto its surface and subjecting it to silane hydrophobic modification. This enhances the dispersibility and compatibility of palygorskite in the modified phenolic resin solution, improves the mechanical properties of the composite material, and allows it to form a dense ceramic layer at high temperatures, further improving ablation resistance. This modified phenolic resin solution exhibits excellent wettability, high toughness, excellent moldability, and outstanding high-temperature and ablation resistance. It also demonstrates excellent interfacial compatibility with surface-modified aramid fibers, comprehensively improving the mechanical properties and ablation resistance of the composite material.

[0020] This invention modifies aramid fibers by first using a potassium hypochlorite solution for gentle oxidation, introducing polar groups such as hydroxyl and carboxyl groups onto the surface to improve surface activity, wettability, and roughness. Then, washing with water and ethanol solutions stops the oxidation reaction and removes residual oxidants and impurities, preventing residues from affecting interfacial bonding. Subsequently, aromatic amino and siloxane groups are introduced under the action of an aniline methyltriethoxysilane solution, which enhances compatibility with resins. Finally, the fibers are thoroughly impregnated in a polyamic acid solution to ensure uniform adhesion of the precursor to the fiber surface. After pre-drying to remove the solvent, the polyamic acid undergoes a thermal imidization reaction at high temperature, generating a rigid polyimide layer similar in structure to aramid fibers, significantly improving the interfacial bonding performance of the aramid fibers.

[0021] The ablation-resistant aramid fiber / phenolic resin composite material prepared by this invention has the advantages of ablation resistance and strong flame retardancy, and can be adapted to special scenarios such as high temperature and explosion protection, taking into account protection, practicality and environmental protection.

[0022] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0023] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0024] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0025] Example 1 A method for preparing an ablation-resistant aramid fiber / phenolic resin composite material includes the following steps: Step 1: Preparation of modified phenolic resin solution: Dissolve phenolic resin (boron phenolic resin) in solvent (anhydrous ethanol), add toughening agent (polyvinyl methyl aldehyde and hydrogenated nitrile rubber, mass ratio 1:1), release agent (palmitic acid) and additive (nano silica), stir at 30℃ at 600 rpm / min for 45 min, and then ultrasonically disperse at 200W power for 20 min to obtain modified phenolic resin solution; wherein, the mass ratio of phenolic resin, solvent, toughening agent, release agent and additive is 50:10:35:1:4; Step 2: Preparation of modified aramid fibers, including the following steps: S21. Immerse a plain weave fabric of para-aramid fiber with an areal density of 200 g / m² in a 2 wt% potassium hypochlorite solution for 20 min, remove it, rinse it with deionized water for 10 min, then rinse it with a 70 wt% ethanol solution for 10 min, and then immerse it in a 1 wt% aniline methyltriethoxysilane solution for 30 min. Dry it at 80℃ for 6 h to obtain pretreated aramid fiber; wherein, the mass-volume ratio of the para-aramid fiber plain weave fabric, potassium hypochlorite solution, and aniline methyltriethoxysilane solution is 1 g:30 mL:30 mL. S22. The pretreated aramid fiber is immersed in a 12wt% polyamic acid solution for 45 min, then removed and pre-dried at 100℃ for 5 h, and then vacuum dried at 270℃ for 10 min to obtain the modified aramid fiber; wherein, the mass-volume ratio of the pretreated aramid fiber to the polyamic acid solution is 1 g: 40 mL. Step 3: Processing and Molding: The modified phenolic resin is coated onto the modified aramid fiber using a scraper coating method, with the coating thickness controlled at 0.2 mm. The prepreg is then heat-treated at 90℃ for 1.5 h to prepare the prepreg. Ten layers of prepreg are stacked and hot-pressed for curing, maintaining a pressure of 6.5 MPa. The temperature is then maintained at 145℃ for 1.5 h, followed by a further increase to 175℃ and maintenance for another 1.5 h. After cooling to room temperature, the material is demolded to obtain an ablation-resistant aramid fiber / phenolic resin composite material.

[0026] Example 2 A method for preparing an ablation-resistant aramid fiber / phenolic resin composite material includes the following steps: Step 1: Preparation of modified phenolic resin solution: Dissolve phenolic resin (boron phenolic resin) in solvent (anhydrous ethanol), add toughening agent (polyvinyl methyl aldehyde and hydrogenated nitrile rubber, mass ratio 1:1), release agent (palmitic acid) and additive (nano silica), stir at 30℃ at 600 rpm / min for 45 min, and then ultrasonically disperse at 200W power for 20 min to obtain modified phenolic resin solution; wherein, the mass ratio of phenolic resin, solvent, toughening agent, release agent and additive is 60:10:25:1:4; Step 2: Preparation of modified aramid fibers, including the following steps: S21. Immerse a plain weave fabric of para-aramid fiber with an areal density of 200 g / m² in a 2 wt% potassium hypochlorite solution for 20 min, remove it, rinse it with deionized water for 10 min, then rinse it with a 70 wt% ethanol solution for 10 min, and then immerse it in a 1 wt% aniline methyltriethoxysilane solution for 30 min. Dry it at 80℃ for 6 h to obtain pretreated aramid fiber; wherein, the mass-volume ratio of the para-aramid fiber plain weave fabric, potassium hypochlorite solution, and aniline methyltriethoxysilane solution is 1 g:30 mL:30 mL. S22. The pretreated aramid fiber is immersed in a 12wt% polyamic acid solution for 45 min, then removed and pre-dried at 100℃ for 5 h, and then vacuum dried at 270℃ for 10 min to obtain the modified aramid fiber; wherein, the mass-volume ratio of the pretreated aramid fiber to the polyamic acid solution is 1 g: 40 mL. Step 3: Processing and Molding: The modified phenolic resin is coated onto the modified aramid fiber using a scraper coating method, with the coating thickness controlled at 0.2 mm. The prepreg is then heat-treated at 90℃ for 1.5 h to prepare the prepreg. Ten layers of prepreg are stacked and hot-pressed for curing, maintaining a pressure of 6.5 MPa. The temperature is then maintained at 145℃ for 1.5 h, followed by a further increase to 175℃ and maintenance for another 1.5 h. After cooling to room temperature, the material is demolded to obtain an ablation-resistant aramid fiber / phenolic resin composite material.

[0027] Example 3 A method for preparing an ablation-resistant aramid fiber / phenolic resin composite material includes the following steps: Step 1: Preparation of modified phenolic resin solution: Dissolve phenolic resin (boron phenolic resin) in solvent (anhydrous ethanol), add toughening agent (polyvinyl acetal and hydrogenated nitrile rubber, mass ratio 1:1), release agent (palmitic acid) and additive (palmitite), stir at 30℃ at 600 rpm / min for 45 min, and then ultrasonically disperse at 200W power for 20 min to obtain modified phenolic resin solution; wherein, the mass ratio of phenolic resin, solvent, toughening agent, release agent and additive is 50:10:35:1:4; Step 2: Preparation of modified aramid fibers, including the following steps: S21. Immerse a plain weave fabric of para-aramid fiber with an areal density of 200 g / m² in a 2 wt% potassium hypochlorite solution for 20 min, remove it, rinse it with deionized water for 10 min, then rinse it with a 70 wt% ethanol solution for 10 min, and then immerse it in a 1 wt% aniline methyltriethoxysilane solution for 30 min. Dry it at 80℃ for 6 h to obtain pretreated aramid fiber; wherein, the mass-volume ratio of the para-aramid fiber plain weave fabric, potassium hypochlorite solution, and aniline methyltriethoxysilane solution is 1 g:30 mL:30 mL. S22. The pretreated aramid fiber is immersed in a 12wt% polyamic acid solution for 45 min, then removed and pre-dried at 100℃ for 5 h, and then vacuum dried at 270℃ for 10 min to obtain the modified aramid fiber; wherein, the mass-volume ratio of the pretreated aramid fiber to the polyamic acid solution is 1 g: 40 mL. Step 3: Processing and Molding: The modified phenolic resin is coated onto the modified aramid fiber using a scraper coating method, with the coating thickness controlled at 0.2 mm. The prepreg is then heat-treated at 90℃ for 1.5 h to prepare the prepreg. Ten layers of prepreg are stacked and hot-pressed for curing, maintaining a pressure of 6.5 MPa. The temperature is then maintained at 145℃ for 1.5 h, followed by a further increase to 175℃ and maintenance for another 1.5 h. After cooling to room temperature, the material is demolded to obtain an ablation-resistant aramid fiber / phenolic resin composite material.

[0028] Example 4 A method for preparing an ablation-resistant aramid fiber / phenolic resin composite material includes the following steps: Step 1: Preparation of modified phenolic resin solution: Dissolve phenolic resin (boron phenolic resin) in solvent (anhydrous ethanol), add toughening agent (polyvinyl methyl aldehyde and hydrogenated nitrile rubber, mass ratio 1:1), release agent (palmitic acid) and additive (nano silica), stir at 30℃ at 600 rpm / min for 45 min, and then ultrasonically disperse at 200W power for 20 min to obtain modified phenolic resin solution; wherein, the mass ratio of phenolic resin, solvent, toughening agent, release agent and additive is 50:10:35:1:4; Step 2: Preparation of modified aramid fibers, including the following steps: S21. Immerse a plain weave fabric of para-aramid fiber with an areal density of 200 g / m² in a 2 wt% potassium hypochlorite solution for 20 min, remove it, rinse it with deionized water for 10 min, then rinse it with a 70 wt% ethanol solution for 10 min, and then immerse it in a 1 wt% aniline methyltriethoxysilane solution for 30 min. Dry it at 80℃ for 6 h to obtain pretreated aramid fiber; wherein, the mass-volume ratio of the para-aramid fiber plain weave fabric, potassium hypochlorite solution, and aniline methyltriethoxysilane solution is 1 g:30 mL:30 mL. S22. The pretreated aramid fiber is immersed in a 12wt% polyamic acid solution for 45 min, then removed and pre-dried at 100℃ for 5 h, and then vacuum dried at 270℃ for 10 min to obtain the modified aramid fiber; wherein, the mass-volume ratio of the pretreated aramid fiber to the polyamic acid solution is 1 g: 40 mL. Step 3, Processing and Molding: The modified phenolic resin is coated onto the modified aramid fiber using a scraper coating method, with the coating thickness controlled at 0.2 mm. The prepreg is then heat-treated at 90℃ for 1.5 h to prepare the prepreg. Ten layers of prepreg are stacked and hot-pressed for curing, maintaining a pressure of 6.5 MPa. The temperature is maintained at 145℃ for 1 h, then raised to 175℃ and maintained for 1 h. After cooling to room temperature, the material is demolded to obtain an ablation-resistant aramid fiber / phenolic resin composite material.

[0029] Example 5 The preparation method in this embodiment is basically the same as that in Example 3, except that modified palygorskite is used instead of palygorskite in the modified phenolic resin solution; the preparation method of the modified palygorskite includes the following steps: A. Pulverized palygorskite to 200 mesh, soaked in 5wt% dilute nitric acid for 30 min, washed twice with deionized water, and dried at 60℃ for 8 h to obtain pretreated palygorskite; wherein, the mass-volume ratio of palygorskite to dilute nitric acid is 1 g: 30 mL. B. Pretreated palygorskite was added to ethylene glycol and ultrasonically dispersed at 400W for 20 min. Then, hypophosphite was added and stirred until homogeneous. A 0.5 mol / L zirconium oxychloride solution was then slowly added dropwise at a rate of 2 mL / min. After the addition, the pH was adjusted to 3.0 with 2wt% dilute ammonia, the temperature was raised to 80℃, stirred for 2 h, allowed to stand for 8 h, washed twice with deionized water, and dried at 80℃ for 6 h to obtain zirconium hypophosphite-modified palygorskite. The mass-to-volume ratio of pretreated palygorskite, ethylene glycol solution, hypophosphite, and zirconium oxychloride solution was 1 g: 30 mL: 1.5 g: 10 mL. C. Add zirconium hypophosphite-modified palygorskite to a 2 wt% acetic acid solution, add octadecyltrimethoxysilane, stir until homogeneous, heat to 70℃, stir at 500 rpm / min for 3 h, wash twice with anhydrous ethanol, and vacuum dry at 80℃ for 6 h to obtain modified palygorskite; wherein, the mass-volume ratio of zirconium hypophosphite-modified palygorskite, acetic acid solution, and octadecyltrimethoxysilane is 1 g: 40 mL: 0.03 g.

[0030] Example 6 The preparation method in this embodiment is basically the same as that in Example 3, except that modified palygorskite is used instead of palygorskite in the modified phenolic resin solution; the preparation method of the modified palygorskite includes the following steps: A. Pulverized palygorskite to 200 mesh, soaked in 5wt% dilute nitric acid for 30 min, washed twice with deionized water, and dried at 60℃ for 8 h to obtain pretreated palygorskite; wherein, the mass-volume ratio of palygorskite to dilute nitric acid is 1 g: 30 mL. B. Add the pretreated palygorskite to ethylene glycol and ultrasonically disperse it for 20 min at a power of 400 W. Then add hypophosphite and stir until homogeneous. Slowly add 0.5 mol / L zirconium oxychloride solution at a dropping rate of 2 mL / min. After the addition, adjust the pH to 3.0 with 2 wt% dilute ammonia water, heat to 80℃, stir for 2 h, let stand for 8 h, wash twice with deionized water, and dry at 80℃ for 6 h to obtain modified palygorskite. The mass-volume ratio of pretreated palygorskite, ethylene glycol solution, hypophosphite, and zirconium oxychloride solution is 1 g: 30 mL: 1.5 g: 10 mL.

[0031] Example 7 The preparation method in this embodiment is basically the same as that in Example 3, except that modified palygorskite is used instead of palygorskite in the modified phenolic resin solution; the preparation method of the modified palygorskite includes the following steps: A. Pulverized palygorskite to 200 mesh, soaked in 5wt% dilute nitric acid for 30 min, washed twice with deionized water, and dried at 60℃ for 8 h to obtain pretreated palygorskite; wherein, the mass-volume ratio of palygorskite to dilute nitric acid is 1 g: 30 mL. B. Add the pretreated palygorskite to a 2wt% acetic acid solution, add octadecyltrimethoxysilane, stir evenly, heat to 70℃, stir at 500 rpm / min for 3h, wash twice with anhydrous ethanol, and vacuum dry at 80℃ for 6h to obtain modified palygorskite; wherein, the mass-volume ratio of pretreated palygorskite, acetic acid solution, and octadecyltrimethoxysilane is 1g:40mL:0.03g.

[0032] Comparative Example 1 The preparation method of this comparative example is basically the same as that of Example 1, except that in step one, the modified phenolic resin solution is replaced with boron phenolic resin.

[0033] Comparative Example 2 The preparation method of this comparative example is basically the same as that of Example 1, except that the para-aramid fiber plain weave fabric is not modified in step two.

[0034] Comparative Example 3 The preparation method of this comparative example is basically the same as that of Example 1, except that no additives are added when preparing the modified phenolic resin solution.

[0035] Comparative Example 4 The preparation method of this comparative example is basically the same as that of Example 1, except that the polyamic acid solution is replaced with deionized water when preparing the modified aramid fiber.

[0036] The linear ablation rate, char residue, shear strength, and flexural strength of the aramid fiber / phenolic resin composites prepared in Examples 1-7 and Comparative Examples 1-4 were tested. The linear ablation rate was tested according to GJB 323A-96; the char residue at 800℃ was tested according to GB / T33047.1-2016; the interlaminar shear strength was tested according to ASTM D2344, and the interlaminar shear strength of the composite samples was obtained using a universal testing machine; the flexural strength was tested according to ASTM D7264, and the flexural strength of the composite samples was obtained using a universal testing machine. The test results are shown in Table 1.

[0037] Table 1. Ablation resistance and mechanical properties of the examples and comparative examples As can be seen from the table, the ablation-resistant aramid fiber / phenolic resin composite materials prepared in Examples 1-7 of this invention have significantly lower linear ablation rates and higher char rates compared to Comparative Examples 1-4, with a char rate of ≥65% at 800℃, exhibiting good ablation resistance and high flame retardancy. Furthermore, the ablation-resistant aramid fiber / phenolic resin composite materials prepared in Examples 1-7 have higher shear strength and flexural strength than Comparative Examples 1-4, possessing good toughness and impact deformation resistance, and can meet the protection requirements of special scenarios such as high temperature and explosion protection. In Example 5, palygorskite was modified by loading zirconium hypophosphite onto its surface and then hydrophobically modifying it with silane. This enhanced the dispersibility and compatibility of palygorskite in the modified phenolic resin solution, improving the mechanical properties of the composite material compared to Example 3. It could form a dense ceramic layer at high temperatures, reducing the linear ablation rate and increasing the char residue, shear strength, and flexural strength. However, in Examples 6 and 7, the modified palygorskite was not prepared with hydrophobically modified silane and zirconium hypophosphite, respectively. As a result, the ablation resistance and mechanical properties of the composite material were reduced compared to Example 5, but slightly improved compared to Example 3.

[0038] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A method for preparing an ablation-resistant aramid fiber / phenolic resin composite material, characterized in that, Includes the following steps: Step 1: Preparation of modified phenolic resin solution: Dissolve phenolic resin in a solvent, add toughening agent, release agent and additives, and disperse by stirring and ultrasonication to obtain modified phenolic resin solution; Step 2: Preparation of modified aramid fibers, including the following steps: S21. Immerse the aramid fiber in potassium hypochlorite solution, take it out and rinse it with deionized water, then rinse it with ethanol solution, then immerse it in aniline methyltriethoxysilane solution and dry it to obtain pretreated aramid fiber. S22. The pretreated aramid fiber is immersed in a polyamic acid solution, taken out and pre-dried, and then vacuum dried to obtain modified aramid fiber. Step 3, Processing and Molding: The modified phenolic resin adhesive is coated onto the modified aramid fiber and heat-treated to make a prepreg; multiple layers of prepreg are stacked and laid out, and then hot-pressed and cured to form a prepreg. After cooling to room temperature, the prepreg is demolded to obtain an ablation-resistant aramid fiber / phenolic resin composite material. In step one, the phenolic resin is boron phenolic resin; the solvent is one of anhydrous ethanol, acetone or ethylene glycol ethyl ether; the toughening agent is a combination of polyvinyl alcohol methyl acetal and hydrogenated nitrile rubber in a mass ratio of 1:0.5~2. In step one, the release agent is palmitic acid; the additives are one or more of nano-silica, graphene, graphene oxide and palygorskite. The mass ratio of phenolic resin, solvent, toughening agent, release agent and additives is 40~60:5~15:20~40:1:2~10.

2. The method for preparing the ablation-resistant aramid fiber / phenolic resin composite material as described in claim 1, characterized in that, In step one, the stirring temperature is 25~40℃, the stirring speed is 400~800rpm / min, and the stirring time is 30~60min; the ultrasonic dispersion power is 150~300W, and the dispersion time is 15~30min.

3. The method for preparing the ablation-resistant aramid fiber / phenolic resin composite material as described in claim 1, characterized in that, In step S21, the aramid fiber is a plain weave fabric of para-aramid fiber, and the areal density of the aramid fiber fabric is 100~300g / m²; the mass fraction of potassium hypochlorite solution is 1~3wt%, the mass fraction of ethanol solution is 50~70wt%, and the mass fraction of aniline methyltriethoxysilane solution is 1~2wt%; the mass-volume ratio of aramid fiber, potassium hypochlorite solution, and aniline methyltriethoxysilane solution is 1g:20~50mL:20~50mL.

4. The method for preparing the ablation-resistant aramid fiber / phenolic resin composite material as described in claim 1, characterized in that, In step S21, the soaking time in potassium hypochlorite solution is 10-40 min, the rinsing time in deionized water is 10-15 min, the rinsing time in ethanol solution is 5-20 min, and the soaking time in aniline methyltriethoxysilane solution is 30-60 min; the drying temperature is 60-80℃, and the drying time is 4-10 h.

5. The method for preparing the ablation-resistant aramid fiber / phenolic resin composite material as described in claim 1, characterized in that, In step S22, the mass-to-volume ratio of pretreated aramid fiber to polyamic acid solution is 1g:30~60mL; the mass fraction of polyamic acid solution is 8~15wt%, the soaking time is 30~60min; the pre-drying temperature is 80~120℃, the pre-drying time is 2~8h; and the vacuum drying temperature is 260~280℃, the time is 5~15min.

6. The method for preparing the ablation-resistant aramid fiber / phenolic resin composite material as described in claim 1, characterized in that, In step three, the coating method is blade coating or roller coating, and the coating thickness is controlled to be 0.1~0.3mm; the heat treatment temperature is 80~100℃, and the heat treatment time is 1~2h.

7. The method for preparing the ablation-resistant aramid fiber / phenolic resin composite material as described in claim 1, characterized in that, In step three, the number of prepreg layers is 8 to 15; the hot-press curing conditions are: maintain a pressure of 5 to 8 MPa, keep at a temperature of 140 to 150°C for 1 to 2 hours, and then raise the temperature to 170 to 180°C and keep at that temperature for 1 to 2 hours.

8. The application of an ablation-resistant aramid fiber / phenolic resin composite material prepared by the preparation method according to any one of claims 1-7 in high-temperature and explosion-proof scenarios.

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