Fiber-reinforced thermosetting composite material and preparation method thereof

Abstract

The invention discloses a fiber-reinforced thermosetting composite material and a preparation method thereof, and belongs to the technical field of thermosetting material processing.The preparation method comprises the steps that firstly, melamine and hexamethylenediamine are subjected to deamination polycondensation under the catalysis of ammonium chloride to synthesize thermosetting amino resin, then carbon fiber cloth is subjected to carboxylation, and carboxylated carbon fiber cloth is obtained; then aminated POSS and aminated boron nitride nanosheets are prepared respectively and grafted to carboxylated carbon fiber cloth through an amide reaction to obtain composite carbon fiber cloth, finally thermosetting amino resin is dissolved in an ethanol aqueous solution, the composite carbon fiber cloth is impregnated, and the composite carbon fiber cloth is prepared through pre-curing, vacuum treatment and a multi-stage hot-pressing curing method. The fiber-reinforced thermosetting composite material is obtained; and excellent interface bonding and mechanical properties are realized.

Description

Technical Field

[0001] This invention belongs to the field of thermosetting materials processing technology, specifically relating to a fiber-reinforced thermosetting composite material and its preparation method. Background Technology

[0002] Thermosetting composites are materials that use thermosetting resins as a matrix and add reinforcing materials, fillers, and other components to form a three-dimensional cross-linked network structure through irreversible chemical reactions. Once cured, they cannot be reshaped and possess core advantages such as heat resistance, corrosion resistance, and dimensional stability. With their high specific strength and high modulus, they have become key materials in aerospace, automotive lightweighting, wind turbine blades, and water supply pipes.

[0003] In recent years, with the rise of smart material systems such as shape memory polymers and self-healing materials, and the expanding application of non-metallic additive materials in the molding of complex components, the matrix design and interface control methods of thermosetting composite materials have been continuously developing towards functionalization, refinement, and high reliability. Meanwhile, although high-performance thermoplastic materials, represented by metallocene polyolefins and ethylene-vinyl alcohol copolymers, have replaced thermosetting resins in some fields, they still cannot completely replace thermosetting systems with three-dimensional cross-linked network structures in terms of heat resistance and dimensional stability.

[0004] In thermosetting composites, fibers serve as the core reinforcement. Pure resin is brittle and has low strength, while fibers can bear the main load and transfer stress through the interface, significantly improving the tensile, flexural, and impact resistance of the material, while also enhancing the durability and stability of the structure. However, fiber-reinforced thermosetting composites also face many challenges, such as poor interfacial bonding between fibers and resin, leading to debonding and reduced overall material performance; complex molding processes; and difficulty in controlling fiber layup and curing parameters, which can easily result in defects such as porosity and delamination in the finished product.

[0005] Chinese invention patent application CN112778549A discloses a carbon fiber reinforced thermosetting resin matrix composite material and its preparation method. The method involves compounding a matrix resin with various functional additives to form a resin paste, then combining it with a specific form of carbon fiber nonwoven fabric, and using a sheet molding compound process to prepare a multi-layer carbon fiber prepreg. Finally, the prepregs are stacked and vacuum hot-pressed to obtain a carbon fiber reinforced thermosetting resin matrix composite material with designable strength and modulus, isotropic properties, and easy large-area molding.

[0006] The above scheme uses a physical mixture of carbon fiber nonwoven fabric and resin paste without surface modification of the carbon fiber, which may result in weak interfacial bonding between the fiber and the resin matrix, affecting the mechanical properties and durability of the composite material. Summary of the Invention

[0007] The purpose of this invention is to provide a fiber-reinforced thermosetting composite material and its preparation method, so as to solve the problems of low interfacial bonding strength and uncontrollable functional distribution caused by the physical blending of carbon fiber and resin matrix in the prior art.

[0008] The objective of this invention can be achieved through the following technical solutions: A method for preparing a fiber-reinforced thermosetting composite material includes the following steps: Step 1: Melamine and hexamethylenediamine are deaminated and polymerized into a thermosetting amino resin under the catalysis of ammonium chloride.

[0009] Step 2: Carboxylate the carbon fiber cloth to obtain carboxylated carbon fiber cloth. Then, prepare amino-modified POSS and amino-modified boron nitride nanosheets respectively, and graft them onto the carboxylated carbon fiber cloth through an amide reaction to obtain a composite carbon fiber cloth.

[0010] Step 3: After dissolving the thermosetting amino resin in an aqueous ethanol solution, impregnate the composite carbon fiber cloth, and then obtain the fiber-reinforced thermosetting composite material through pre-curing, vacuum treatment and multi-stage hot pressing curing.

[0011] Furthermore, the specific preparation method of thermosetting amino resin is as follows: Melamine, hexamethylenediamine, and ammonium chloride are added to a three-necked flask, heated to 200-220°C in an oil bath, and stirred for 30-40 minutes. When the mixture becomes colorless and transparent, the reaction continues for 2-3 hours. After cooling to room temperature, a thermosetting amino resin is obtained.

[0012] Furthermore, the mass ratio of melamine, hexamethylenediamine, and ammonium chloride is 63-78:116-156:3.8-5.2.

[0013] Furthermore, the specific preparation method of carboxylated carbon fiber cloth is as follows: Carbon fiber cloth was added to acetone solution and water bathed at 60-70℃ for 24-26 hours. After removal, it was vacuum dried to constant weight to obtain desized carbon fiber cloth. The desized carbon fiber cloth was added to 68wt% concentrated nitric acid and reacted at 80-90℃ for 2-4 hours. After filtration, the filter cake was repeatedly washed with deionized water until the filtrate was neutral. It was then vacuum dried to constant weight to obtain carboxylated carbon fiber cloth.

[0014] Furthermore, the ratio of carbon fiber cloth to acetone solution is 30-40g: 600-800mL.

[0015] Furthermore, the ratio of desized carbon fiber cloth to 68wt% concentrated nitric acid is 24-28g: 2400-2600mL.

[0016] Furthermore, the specific preparation method of amination-modified POSS is as follows: Add 3-aminopropyltrimethoxysilane to methanol and stir for 20-30 min. Slowly add 36 wt% hydrochloric acid and reflux at 90-95 °C for 18-20 h. Remove the methanol solvent by rotary evaporation at 50-60 °C. Add tetrahydrofuran, allow to settle, filter under vacuum, collect the product, and wash the product repeatedly with tetrahydrofuran 3-5 times to obtain amination-modified POSS.

[0017] Furthermore, the volume ratio of 3-aminopropyltrimethoxysilane, methanol, 36 wt% hydrochloric acid, and tetrahydrofuran is 30-50:300-400:20-30:90-100.

[0018] Furthermore, the specific preparation method of aminated boron nitride nanosheets is as follows: Hexagonal boron nitride nanosheets were added to a 20 vol% aqueous ethanol solution, and silane coupling agent KH550 was slowly added dropwise. The mixture was stirred at 800-900 rpm for 20-24 h, vacuum filtered, and the product was collected. The product was washed with deionized water 3-5 times and vacuum dried to constant weight to obtain aminated boron nitride nanosheets.

[0019] Furthermore, the ratio of hexagonal boron nitride nanosheets, 20 vol% ethanol aqueous solution, and silane coupling agent KH550 is 3-5 g: 1500-2000 mL: 20-25 mL.

[0020] Furthermore, the specific preparation method of the composite carbon fiber cloth is as follows: Aminated POSS and aminated boron nitride nanosheets were added to N,N-dimethylformamide and sonicated for 1-2 hours. Carboxylated carbon fiber cloth and phosphate ester were added and magnetically stirred for 20-24 hours. The product was then removed and washed repeatedly with N,N-dimethylformamide and deionized water 3-5 times. The product was then vacuum dried at 80-90℃ to constant weight to obtain composite carbon fiber cloth.

[0021] Furthermore, the ratio of amino-modified POSS, amino-modified boron nitride nanosheets, N,N-dimethylformamide, carboxylated carbon fiber cloth, and phosphate ester is 1-3g: 1-3g: 800-1000mL: 20-30g: 2-2.6g.

[0022] Furthermore, the specific preparation method of fiber-reinforced thermosetting composite materials is as follows: Thermosetting amino resin was dissolved in a 28 vol% aqueous ethanol solution to obtain a resin solution. Composite carbon fiber cloth was added and fully impregnated. The solution was then removed and pre-cured at 120-130℃ for 30-40 minutes. The solution was then transferred to a vacuum drying oven and treated at 190-200℃ and -0.06 to -0.04 MPa for 2-3 hours. The prepreg layers were then placed in a mold and placed in a hot press. Through a multi-stage hot pressing curing method, fiber-reinforced thermosetting composite material was obtained.

[0023] Furthermore, the ratio of thermosetting amino resin, 28 vol% aqueous ethanol solution, and composite carbon fiber cloth is 80-100 g: 130-150 mL: 10-14 g.

[0024] Furthermore, the multi-stage hot-press curing method is as follows: after preheating at 220-230℃ for 40-50 minutes, cure sequentially at 240-250℃ and 2-3 MPa, 250-260℃ and 3-4 MPa, and 260-270℃ and 4.5-4.8 MPa for 30-40 minutes each. During this period, pressure needs to be released multiple times to expel the small molecule gases generated during curing. Finally, cure at 270-280℃ and 4.5-4.9 MPa for 2-3 hours, maintain pressure, and allow to cool naturally to room temperature before demolding.

[0025] The beneficial effects of this invention are: 1. This invention uses thermosetting amino resin as the matrix and carboxylated carbon fiber cloth as the reinforcing skeleton. Under the action of phosphate ester condensing agent, aminated POSS and aminated boron nitride nanosheets are simultaneously chemically grafted onto the carbon fiber surface to construct a multi-scale transition layer that combines rigidity and flexibility: the cage structure of POSS provides nanoscale reinforcement and heat resistance, while the boron nitride nanosheets impart excellent thermal conductivity and lubrication. The two are firmly anchored by amide bonds, which helps to solve the problems of easy agglomeration of nanofillers and weak bonding with the fiber interface.

[0026] 2. The carboxylated carbon fiber cloth of this invention removes industrial slurry from the fiber surface through acetone desizing, and then introduces carboxyl active sites through concentrated nitric acid oxidation treatment, which removes the impurity layer on the fiber surface and provides high-density reaction anchors for subsequent chemical grafting. This allows aminated POSS and aminated boron nitride nanosheets to be grafted onto the fiber surface through amide bonds to form chemical bonds. This chemical anchoring structure helps to improve the interfacial bonding force, and the grafted nanoparticles play a certain physical protection role on the fiber surface.

[0027] 3. The aminated POSS in this invention is prepared by hydrolysis and condensation of 3-aminopropyltrimethoxysilane under hydrochloric acid catalysis. The inherent cage-like silsesquioxane skeleton structure of POSS has a rigid nanoscale skeleton, which can form anti-deformation fulcrums in the interface region. The nanocavities inside the skeleton can accommodate resin molecular chain segments, inhibiting curing shrinkage by occupying free volume. At the same time, its cage-like structure has excellent thermal stability and can maintain structural integrity during high-temperature curing. The external amino groups provide active sites for subsequent amidation reactions.

[0028] 3. The aminated boron nitride nanosheets of this invention utilize a silane coupling agent KH550 to modify the surface of hexagonal boron nitride. While maintaining the intrinsic two-dimensional layered structure, high specific surface area, high mechanical modulus, and physical barrier properties of boron nitride, active amino groups are introduced onto its surface. The modified boron nitride nanosheets exert a physical barrier effect on the movement of resin molecular chains, effectively limiting the thermal motion and shrinkage of chain segments; the amino groups at the edge of the sheets provide reaction sites for chemical grafting.

[0029] The amino groups on the surface of both fibers and the carboxyl groups on the surface of carbon fibers undergo dehydration condensation under the action of phosphate ester condensing agent to form amide bonds, which chemically bond the organic fibers and inorganic nanoparticles into a whole. The resulting interface layer has both the nano-reinforcing effect of POSS and the thermal conductivity and lubrication properties of boron nitride.

[0030] The process employs stepped heating, segmented pressure changes, and multiple pressure releases to suit the characteristics of amino resin polycondensation curing. This effectively eliminates small molecule gases generated during the reaction, avoiding internal defects. Furthermore, high-temperature post-curing further improves the cross-linking network. The resulting composite material exhibits a dense internal structure, strong interfacial bonding, and excellent mechanical strength. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments in the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1: A method for preparing a fiber-reinforced thermosetting composite material, comprising the following steps: S1: Add 63g of melamine, 116g of hexamethylenediamine and 3.8g of ammonium chloride to a three-necked flask, heat to 200℃ in an oil bath and stir for 30min. At the same time, install a water bath absorption device at the upper end of the condenser to absorb the released ammonia gas. When the mixture becomes colorless and transparent, continue the reaction for 2h and cool to room temperature to obtain a thermosetting amino resin.

[0033] Melamine and hexamethylenediamine undergo binary deammoniation polycondensation under the catalysis of ammonium chloride to obtain a thermosetting amino resin.

[0034] S2: Add 30g of carbon fiber cloth to 600mL of acetone solution, bathe in a water bath at 60℃ for 24h, remove and vacuum dry at 60℃ to constant weight to obtain desized carbon fiber cloth; add 24g of desized carbon fiber cloth to 2400mL of 68wt% concentrated nitric acid, react at 80℃ for 2h, filter, wash the filter cake repeatedly with deionized water until the filtrate is neutral, vacuum dry at 60℃ to constant weight to obtain carboxylated carbon fiber cloth.

[0035] S3: Add 30 mL of 3-aminopropyltrimethoxysilane to 300 mL of methanol, stir for 20 min, slowly add 20 mL of 36 wt% hydrochloric acid, reflux at 90 °C for 18 h, remove methanol solvent by rotary evaporation at 50 °C, add 90 mL of tetrahydrofuran, allow to settle, vacuum filter, collect the product, wash the product repeatedly with tetrahydrofuran 3 times to obtain amination-modified POSS.

[0036] S4: Add 3g of hexagonal boron nitride nanosheets to 1500mL of 20vol% ethanol aqueous solution, slowly add 20mL of silane coupling agent KH550, stir at 800rpm for 20h, vacuum filter, collect the product, wash the product three times with deionized water, and vacuum dry at 50℃ to constant weight to obtain aminated boron nitride nanosheets.

[0037] S5: Add 1g of aminated POSS and 1g of aminated boron nitride nanosheets to 800mL of N,N-dimethylformamide, sonicate for 1h, add 20g of carboxylated carbon fiber cloth and 2g of phosphate ester, stir magnetically for 20h, take out the product, wash the product repeatedly with N,N-dimethylformamide and deionized water 3 times, and vacuum dry at 80℃ to constant weight to obtain composite carbon fiber cloth.

[0038] The carboxyl groups on the surface of carboxylated carbon fiber cloth and the amino groups on the surface of aminated POSS and aminated boron nitride nanosheets undergo dehydration condensation under the action of phosphate ester condensing agent to form amide bonds, thus achieving chemical grafting.

[0039] S6: Dissolve 80g of thermosetting amino resin in 130mL of 28vol% ethanol aqueous solution to obtain a resin solution. Add 10g of composite carbon fiber cloth, fully impregnate, and remove. Pre-cur at 120℃ for 30min, transfer to a vacuum drying oven, and treat at 190℃ and -0.06MPa for 2h. Place the prepreg layers into a mold, place it in a hot press, preheat at 220℃ for 40min, and then cure at 240℃ and 2MPa, 250℃ and 3MPa, and 260℃ and 4.5MPa for 30min each. During this period, pressure needs to be released multiple times to remove small molecule gases generated during curing. Finally, cure at 270℃ and 4.5MPa for 2h, maintain pressure and cool naturally to room temperature, demold, and obtain fiber-reinforced thermosetting composite material.

[0040] Example 2: A method for preparing a fiber-reinforced thermosetting composite material, comprising the following steps: S1: Add 70.5g of melamine, 136g of hexamethylenediamine and 4.5g of ammonium chloride to a three-necked flask, heat to 210℃ in an oil bath and stir for 35min. At the same time, install a water bath absorption device at the upper end of the condenser to absorb the released ammonia gas. When the mixture becomes colorless and transparent, continue the reaction for 2.5h, cool to room temperature, and obtain thermosetting amino resin.

[0041] S2: Add 35g of carbon fiber cloth to 700mL of acetone solution, bathe in a water bath at 65℃ for 25h, remove and vacuum dry at 65℃ to constant weight to obtain desized carbon fiber cloth; add 26g of desized carbon fiber cloth to 2500mL of 68wt% concentrated nitric acid, react at 85℃ for 3h, filter, wash the filter cake repeatedly with deionized water until the filtrate is neutral, vacuum dry at 65℃ to constant weight to obtain carboxylated carbon fiber cloth.

[0042] S3: Add 40 mL of 3-aminopropyltrimethoxysilane to 350 mL of methanol, stir for 25 min, slowly add 25 mL of 36 wt% hydrochloric acid, reflux at 92.5 °C for 19 h, remove methanol solvent by rotary evaporation at 55 °C, add 95 mL of tetrahydrofuran, allow to settle, vacuum filter, collect the product, wash the product repeatedly with tetrahydrofuran 4 times to obtain amination POSS.

[0043] S4: Add 4g of hexagonal boron nitride nanosheets to 1750mL of 20vol% ethanol aqueous solution, slowly add 22.5mL of silane coupling agent KH550, stir at 850rpm for 22h, vacuum filter, collect the product, wash the product with deionized water 4 times, and vacuum dry at 55℃ to constant weight to obtain aminated boron nitride nanosheets.

[0044] S5: Add 2g of aminated POSS and 2g of aminated boron nitride nanosheets to 900mL of N,N-dimethylformamide, sonicate for 1.5h, add 25g of carboxylated carbon fiber cloth and 2.3g of phosphate ester, stir magnetically for 22h, take out the product, wash the product repeatedly with N,N-dimethylformamide and deionized water 4 times, and vacuum dry at 85℃ to constant weight to obtain composite carbon fiber cloth.

[0045] S6: Dissolve 90g of thermosetting amino resin in 140mL of 28vol% ethanol aqueous solution to obtain a resin solution. Add 12g of composite carbon fiber cloth, fully impregnate the solution, and remove it. Pre-cure at 125℃ for 35min, transfer it to a vacuum drying oven, and treat it at 195℃ and -0.05MPa for 2.5h. Place the prepreg layers into a mold, place it in a hot press, preheat at 225℃ for 45min, and then cure it sequentially at 245℃, 2.5MPa, 255℃, 3.5MPa, 265℃, and 4.65MPa for 35min each. During this period, the pressure needs to be released multiple times to remove the small molecule gas generated during curing. Finally, cure it at 275℃ and 4.7MPa for 2.5h, maintain the pressure, and allow it to cool naturally to room temperature. Demold to obtain a fiber-reinforced thermosetting composite material.

[0046] Example 3: A method for preparing a fiber-reinforced thermosetting composite material, comprising the following steps: S1: Add 78g of melamine, 156g of hexamethylenediamine and 5.2g of ammonium chloride to a three-necked flask, heat to 220℃ in an oil bath and stir for 40min. At the same time, install a water bath absorption device at the upper end of the condenser to absorb the released ammonia gas. When the mixture becomes colorless and transparent, continue the reaction for 3h and cool to room temperature to obtain a thermosetting amino resin.

[0047] S2: Add 40g of carbon fiber cloth to 800mL of acetone solution, bathe in a water bath at 70℃ for 26h, remove and vacuum dry at 70℃ to constant weight to obtain desized carbon fiber cloth; add 28g of desized carbon fiber cloth to 2600mL of 68wt% concentrated nitric acid, react at 90℃ for 4h, filter, wash the filter cake repeatedly with deionized water until the filtrate is neutral, vacuum dry at 70℃ to constant weight to obtain carboxylated carbon fiber cloth.

[0048] S3: Add 50 mL of 3-aminopropyltrimethoxysilane to 400 mL of methanol, stir for 30 min, slowly add 30 mL of 36 wt% hydrochloric acid, reflux at 95 °C for 20 h, remove methanol solvent by rotary evaporation at 60 °C, add 100 mL of tetrahydrofuran, allow to settle, vacuum filter, collect the product, wash the product repeatedly with tetrahydrofuran 5 times to obtain amination-modified POSS.

[0049] S4: Add 5g of hexagonal boron nitride nanosheets to 2000mL of 20vol% ethanol aqueous solution, slowly add 25mL of silane coupling agent KH550, stir at 900rpm for 24h, vacuum filter, collect the product, wash the product 5 times with deionized water, and vacuum dry at 60℃ to constant weight to obtain aminated boron nitride nanosheets.

[0050] S5: Add 3g of aminated POSS and 3g of aminated boron nitride nanosheets to 1000mL of N,N-dimethylformamide, sonicate for 2h, add 30g of carboxylated carbon fiber cloth and 2.6g of phosphate ester, stir magnetically for 24h, take out the product, wash the product repeatedly with N,N-dimethylformamide and deionized water 5 times, and vacuum dry at 90℃ to constant weight to obtain composite carbon fiber cloth.

[0051] S6: Dissolve 100g of thermosetting amino resin in 150mL of 28vol% ethanol aqueous solution to obtain a resin solution. Add 14g of composite carbon fiber cloth, fully impregnate, and remove. Pre-cur at 130℃ for 40min, transfer to a vacuum drying oven, and treat at 200℃ and -0.04MPa for 3h. Place the prepreg layers into a mold, place it in a hot press, preheat at 230℃ for 50min, and then cure at 250℃ and 3MPa, 260℃ and 4MPa, and 270℃ and 4.8MPa for 40min each. During this period, pressure needs to be released multiple times to remove small molecule gases generated during curing. Finally, cure at 280℃ and 4.9MPa for 3h, maintain pressure and cool naturally to room temperature, demold, and obtain fiber-reinforced thermosetting composite material.

[0052] In Examples 1-3, the melamine was selected from Jinan Huijinchuan Trading Co., Ltd., CAS No. 108-78-1; hexamethylenediamine was selected from Jinan Shijitongda Chemical Co., Ltd., CAS No. 124-09-4; ammonium chloride was selected from Shandong Jubang Chemical Co., Ltd., CAS No. 12125-02-9; and the carbon fiber cloth was polyacrylonitrile-based carbon fiber plain weave cloth selected from Toray Industries, Inc. of Japan, model T300, bidirectional weave, with an areal density of 198 g / m². 2 The fiber density is 1.76 g / cm³. 3The raw materials were cut to 100mm x 100mm dimensions. The acetone solution was selected from Maoming Chuizi New Materials Co., Ltd., CAS No. 67-64-1; 3-aminopropyltrimethoxysilane was selected from Hubei Watson Chemical Technology Co., Ltd., CAS No. 13822-56-5; methanol was selected from Jinan Zesheng Chemical Co., Ltd., CAS No. 67-56-1; tetrahydrofuran was selected from Jinan Xinke Chemical Co., Ltd., CAS No. 109-99-9; hexagonal boron nitride nanosheets were selected from Ningbo Luofei Nanotechnology Co., Ltd., CAS No. 10043-11-5; silane coupling agent KH550 was selected from Shandong Qiyun Chemical Technology Co., Ltd., CAS No. 2530-85-0; N,N-dimethylformamide was selected from Shandong Hengshuo Chemical Co., Ltd., CAS No. 68-12-2; phosphate ester was selected from Sanda Chemical (Nantong) Co., Ltd.; the remaining raw materials were all commercially available products.

[0053] Comparative Example 1: The difference from Example 1 is that the step of carboxylating the desizing carbon fiber cloth in step S2 is omitted, and the carboxylated carbon fiber cloth in step S5 is replaced with desizing carbon fiber cloth. The remaining steps remain unchanged, and a fiber-reinforced thermosetting composite material is prepared.

[0054] Comparative Example 2: The difference from Example 1 is that step S3 is omitted, and only aminated boron nitride nanosheets are added in step S5, without the addition of aminated POSS. The remaining steps remain unchanged, and a fiber-reinforced thermosetting composite material is prepared.

[0055] Comparative Example 3: The difference from Example 1 is that step S4 is omitted, and only aminated POSS is added in step S5 without aminated boron nitride nanosheets, thus preparing a fiber-reinforced thermosetting composite material.

[0056] The following performance tests were performed on the fiber-reinforced thermosetting composites obtained in Examples 1-3 and Comparative Examples 1-3: Shrinkage: The test was conducted according to ASTM D2566, "Standard Test Method for Linear Shrinkage of Cured Thermosetting Cast Resins". The volumetric shrinkage rate of the sample was determined using the density method. First, the initial density P0 of the uncured resin mixture was measured. After the composite material was fully cured, a sample was cut and the density P1 of the cured resin matrix was measured. The volumetric shrinkage rate was calculated using the following formula: (P1 - P...) 0） / P1×100%; The lower the shrinkage rate, the better the dimensional stability of the material during the curing process and the smaller the residual stress at the interface.

[0057] Interlaminar shear strength: Tested according to ASTM D2344, "Standard Test Method for Short Beam Strength of Polymer-Based Composites and Laminates". The short beam method (three-point short beam shear) was used to determine the specimen. The loading head was applied to the specimen at a speed of 1 mm / min, the maximum failure load was recorded, and the interlaminar shear strength was calculated. The higher the interlaminar shear strength, the stronger the interfacial bonding between the fiber and the resin matrix.

[0058] Bending properties: Tested according to ASTM D7264, "Standard Test Method for Bending Properties of Polymer-Based Composite Materials". A three-point bending loading mode was used to determine the bending strength and bending modulus of the specimens; higher bending strength and greater modulus indicate a stronger resistance to bending deformation.

[0059] Tensile properties: Tested according to ASTM D3039, "Standard Test Method for Tensile Properties of Polymer-Based Composites". The specimen was clamped at both ends in the fixture of a universal testing machine, and a tensile load was applied at a speed of 5 mm / min. The maximum breaking load was recorded and the tensile strength was calculated. The higher the tensile strength, the more fully the strength of the reinforcing fiber was utilized.

[0060] The results are shown in Table 1: Table 1 Performance test results of fiber-reinforced thermosetting composites As can be seen from Table 1, the fiber-reinforced thermosetting composite materials prepared in Examples 1-3 of the present invention are significantly better than those in Comparative Examples 1-3 in terms of shrinkage rate, interlaminar shear strength, bending performance and tensile performance.

[0061] Comparative Example 1 showed the highest shrinkage rate, with comprehensive deterioration in interlaminar shear strength, flexural strength, flexural modulus, and tensile strength. This is likely due to the lack of carboxylation on the desizing carbon fiber cloth. The uncarboxylated desizing carbon fiber cloth lacks carboxyl active sites on its surface, preventing the amidation reaction with aminated POSS and aminated boron nitride nanosheets in step S5. The nanoparticles can only be physically adsorbed and loaded onto the fiber surface, resulting in low grafting quantity and easy detachment. This leads to a lack of chemical bonding between the fiber and the resin matrix, hindering effective load transfer. Simultaneously, the absence of a chemically anchored interfacial layer fails to effectively inhibit resin curing shrinkage, leading to increased shrinkage and interfacial residual stress. Physically adsorbed nanoparticles are prone to migration or aggregation during composite material molding, failing to fully utilize the rigidity enhancement of POSS and the two-dimensional sheet barrier effect of boron nitride, resulting in overall deterioration of the material's mechanical properties.

[0062] In Comparative Example 2, the interlaminar shear strength, flexural properties, and tensile properties were significantly lower than those in the Example. This may be because step S3 was omitted, and in step S5, only aminated boron nitride nanosheets were added without aminated POSS. Due to the lack of the cage-like rigid structure of POSS, although the functional layer grafted onto the fiber surface can provide some mechanical interlocking and physical barrier effects through the two-dimensional boron nitride sheets, the interface region lacks rigid nanoscale skeletal support, resulting in decreased load transfer efficiency and resistance to deformation. Simultaneously, the single boron nitride graft layer has limited effect on inhibiting resin curing shrinkage, with a higher shrinkage rate than in the Example. The absence of POSS prevents the interface layer from achieving rigidity reinforcement and volume filling, thus significantly deteriorating mechanical properties such as flexural modulus and tensile strength.

[0063] In Comparative Example 3, the interlaminar shear strength, flexural properties, and tensile properties were slightly lower than those of the Examples, while the shrinkage rate was slightly higher. This may be because step S4 was omitted, and in step S5, only aminated POSS was added without aminated boron nitride nanosheets. Although the successful grafting of POSS provided a rigid cage structure and chemical anchoring points, which enhanced interfacial bonding and suppressed curing shrinkage to some extent, the lack of a two-dimensional layered structure of boron nitride resulted in a lack of physical barrier effect and further mechanical interlocking in the interfacial region. The absence of boron nitride prevented the interfacial layer from obtaining the dual confinement effect of its layered structure on the movement of resin molecular chains, and also lost the synergistic reinforcing effect of boron nitride nanosheets and the POSS cage structure. Therefore, although the performance was better than Comparative Example 1, it was still significantly lower than that of Examples 1-3.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A fiber-reinforced thermosetting composite material, characterized in that, Raw materials comprising the following parts by weight: Melamine 63-78 parts, hexamethylenediamine 116-156 parts, ammonium chloride 3.8-5.2 parts, carbon fiber cloth 30-40 parts, 3-aminopropyltrimethoxysilane 30-50 parts, hexagonal boron nitride nanosheets 3-5 parts, silane coupling agent KH550 20-25 parts, aminated POSS 1-3 parts, aminated boron nitride nanosheets 1-3 parts, phosphate ester 2-2.6 parts, thermosetting amino resin 80-100 parts, composite carbon fiber cloth 10-14 parts.

2. The fiber-reinforced thermosetting composite material according to claim 1, characterized in that, The specific preparation method of the thermosetting amino resin is as follows: Melamine, hexamethylenediamine and ammonium chloride are added to a three-necked flask, heated to 200-220°C in an oil bath and stirred for 30-40 minutes. When the mixture becomes colorless and transparent, the reaction continues for 2-3 hours. After cooling to room temperature, a thermosetting amino resin is obtained. The mass ratio of melamine, hexamethylenediamine, and ammonium chloride is 63-78:116-156:3.8-5.

2.

3. The fiber-reinforced thermosetting composite material according to claim 1, characterized in that, The specific preparation method of the composite carbon fiber cloth is as follows: Aminated POSS and aminated boron nitride nanosheets were added to N,N-dimethylformamide and sonicated for 1-2 hours. Carboxylated carbon fiber cloth and phosphate ester were added and magnetically stirred for 20-24 hours. The product was then removed and washed repeatedly with N,N-dimethylformamide and deionized water 3-5 times. The product was then vacuum dried at 80-90℃ to constant weight to obtain composite carbon fiber cloth.

4. The fiber-reinforced thermosetting composite material according to claim 3, characterized in that, The ratio of the amount of aminated POSS, aminated boron nitride nanosheets, N,N-dimethylformamide, carboxylated carbon fiber cloth and phosphate ester is 1-3g: 1-3g: 800-1000mL: 20-30g: 2-2.6g.

5. The fiber-reinforced thermosetting composite material according to claim 1, characterized in that, The specific preparation method of the amination-modified POSS is as follows: Add 3-aminopropyltrimethoxysilane to methanol, stir for 20-30 min, slowly add 36 wt% hydrochloric acid, reflux at 90-95 °C for 18-20 h, remove methanol solvent by rotary evaporation at 50-60 °C, add tetrahydrofuran, allow to settle, vacuum filter, collect the product, wash the product repeatedly with tetrahydrofuran 3-5 times to obtain amination POSS; The volume ratio of 3-aminopropyltrimethoxysilane, methanol, 36 wt% hydrochloric acid, and tetrahydrofuran is 30-50:300-400:20-30:90-100.

6. The fiber-reinforced thermosetting composite material according to claim 1, characterized in that, The specific preparation method of the aminated boron nitride nanosheets is as follows: Hexagonal boron nitride nanosheets were added to a 20 vol% aqueous ethanol solution, and silane coupling agent KH550 was slowly added dropwise. The mixture was stirred at 800-900 rpm for 20-24 h, vacuum filtered, and the product was collected. The product was washed with deionized water 3-5 times and vacuum dried to constant weight to obtain aminated boron nitride nanosheets. The ratio of the hexagonal boron nitride nanosheets, 20 vol% ethanol aqueous solution, and silane coupling agent KH550 is 3-5 g: 1500-2000 mL: 20-25 mL.

7. The fiber-reinforced thermosetting composite material according to claim 3, characterized in that, The specific preparation method of the carboxylated carbon fiber cloth is as follows: Carbon fiber cloth is added to acetone solution and water bathed at 60-70℃ for 24-26 hours. It is then removed and vacuum dried to constant weight to obtain desized carbon fiber cloth. The desized carbon fiber cloth is added to 68wt% concentrated nitric acid and reacted at 80-90℃ for 2-4 hours. After filtration, the filter cake is repeatedly washed with deionized water until the filtrate is neutral. It is then vacuum dried to constant weight to obtain carboxylated carbon fiber cloth. The ratio of carbon fiber cloth to acetone solution is 30-40g: 600-800mL; The ratio of the desized carbon fiber cloth to 68wt% concentrated nitric acid is 24-28g: 2400-2600mL.

8. A method for preparing a fiber-reinforced thermosetting composite material, characterized in that, Includes the following steps: Thermosetting amino resin was dissolved in a 28 vol% aqueous ethanol solution to obtain a resin solution. Composite carbon fiber cloth was added and fully impregnated. The solution was then removed and pre-cured at 120-130℃ for 30-40 minutes. The solution was then transferred to a vacuum drying oven and treated at 190-200℃ and -0.06 to -0.04 MPa for 2-3 hours. The prepreg layers were then placed in a mold and placed in a hot press. Through a multi-stage hot pressing curing method, fiber-reinforced thermosetting composite material was obtained.

9. The method for preparing a fiber-reinforced thermosetting composite material as described in claim 8, characterized in that, The ratio of the thermosetting amino resin, 28 vol% aqueous ethanol solution, and composite carbon fiber cloth is 80-100 g: 130-150 mL: 10-14 g.

10. The method for preparing a fiber-reinforced thermosetting composite material as described in claim 8, characterized in that, The multi-stage hot-press curing method is as follows: after preheating at 220-230℃ for 40-50 minutes, it is cured sequentially at 240-250℃ and 2-3 MPa, 250-260℃ and 3-4 MPa, and 260-270℃ and 4.5-4.8 MPa for 30-40 minutes each. During this period, the pressure needs to be released multiple times to remove the small molecule gases generated during curing. Finally, it is cured at 270-280℃ and 4.5-4.9 MPa for 2-3 hours. The pressure is maintained and the material is allowed to cool naturally to room temperature before demolding.

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