Broadband wave-absorbing resin-based composite material and preparation method thereof

Abstract

The invention relates to the technical field of wave-absorbing materials, in particular to a broadband wave-absorbing resin-based composite material and a preparation method thereof. The composite material is prepared by compounding epoxy resin, triglycidyl isocyanurate, a tri (2-aminoethyl) amine curing agent partially coordinated with Fe < 3 + >, poly (perylenetetracarboxylic dianhydride-thiourea), surface-modified Fe3O4 (at) SiC core-shell nanoparticles and the like through a specific process. During preparation, the functional components are uniformly dispersed in the resin matrix, and then the resin matrix is subjected to cross-linking molding through a segmented heating curing process. The material realizes efficient electromagnetic wave absorption in a broadband range through a multi-polarization mechanism and a magnetic-dielectric synergistic effect, has good mechanical strength and stability, and is suitable for the field of advanced composite materials with strict requirements on wave absorbing performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wave-absorbing materials, and particularly relates to a wideband wave-absorbing resin-based composite material and a preparation method thereof. BACKGROUND

[0002] The demand for wave-absorbing materials in the fields of aerospace, military equipment and electromagnetic protection is increasingly urgent, and the core performance requirements thereof are focused on the coordination and unity of wideband absorption, high-efficiency loss and structural mechanical stability. Epoxy resin has become the mainstream choice of the matrix of wave-absorbing resin-based composite materials due to its good formability, strong adhesion and controllable crosslinking. However, the dielectric loss ability of pure epoxy resin is weak, and it is necessary to modify or composite wave-absorbing fillers to improve the wave-absorbing performance, which puts strict requirements on the loss efficiency of the modified components and the compatibility of the fillers and the matrix. How to realize the synergistic matching of dielectric loss and magnetic loss while avoiding performance fragmentation is the core difficulty in current research and development.

[0003] In the prior art, researchers often modify epoxy resin by introducing conjugated structures and polar groups to strengthen polarization loss. For example, patent CN117164819A discloses a poly(perylenetetracarboxylic dianhydride-urea) / isocyanuric acid triglycidyl ester epoxy matrix, which improves dielectric loss by combining the conjugated system of the perylene ring and the urea bond. However, this technology is limited by the structural characteristics of the urea bond, and the small dipole moment leads to insufficient polarization relaxation strength, making it difficult to achieve high-efficiency loss in a wide frequency band, and the wave-absorbing performance is insufficient. In addition, the existing technology also generally lacks the synergy of multiple loss mechanisms: single dielectric fillers (such as SiC) lack magnetic loss contribution, and the wave-absorbing frequency band is limited to high frequencies; single magnetic fillers (such as Fe3O4) have insufficient dielectric loss, impedance matching is unbalanced, and electromagnetic wave reflectivity is high. At the same time, poor interface compatibility between wave-absorbing fillers and resin matrix is another major bottleneck. Unmodified fillers and matrix are mostly physically combined, and under high filler content, stress concentration points are easily formed, which not only seriously affects the mechanical properties of the composite material, but also increases electromagnetic wave reflection and reduces wave-absorbing efficiency.

[0004] More importantly, the existing curing agent system has a single function and can only provide crosslinking activity, but cannot participate in wave-absorbing loss, failing to fully exploit the functional synergy potential of the components. The modification scheme based on traditional polar groups has inherent limitations, making it difficult to break through the performance ceiling of dielectric loss, resulting in the problems of narrow wave-absorbing frequency band, insufficient loss depth, and difficulty in balancing mechanical properties and wave-absorbing performance in existing wave-absorbing materials. These technical shortcomings seriously limit the application of wave-absorbing resin-based composite materials in high-end fields. Therefore, developing a resin-based composite material that has high-efficiency multiple loss synergy, excellent interface compatibility, wideband wave-absorbing and balanced mechanical properties has become a technical problem to be solved in the field of wave-absorbing materials. SUMMARY

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and to propose a broadband absorbing resin-based composite material and its preparation method.

[0006] To achieve the above objectives, the present invention provides a broadband absorbing resin-based composite material comprising the following raw materials in parts by weight: epoxy resin: 100 parts, triglycidyl isocyanate: 20-30 parts, curing agent: 30-40 parts, poly(perylenetetracarboxylic dianhydride-thiourea): 10-20 parts, Fe3O4@SiC core-shell nanoparticles: 120-180 parts, antioxidant 1010: 0.5-1.5 parts, and polyether-modified silicone oil: 1-2 parts; The curing agent refers to Fe 3+ Partially coordinated tris(2-aminoethyl)amine; The poly(perylenetetracarboxylic dianhydride-thiourea) is prepared by reacting 3,4,9,10-perylenetetracarboxylic dianhydride and thiourea. The Fe3O4@SiC core-shell nanoparticles were prepared by hydrothermal method to obtain Fe3O4 nanoparticles, which were then coated with tetraethyl orthosilicate sol-gel and carbonized with sucrose to form a SiC shell, and then modified with silane coupling agent KH-550.

[0007] Preferably, the epoxy resin is any one of E-51, E-44, and E-42; the epoxy value of triglycidyl isocyanate is 0.9 eq / 100g.

[0008] More preferably, the epoxy resin is E-51.

[0009] Preferably, the viscosity of the polyether-modified silicone oil is 2000 cst (25°C).

[0010] Preferably, the method for preparing the curing agent includes the following steps: Tris(2-aminoethyl)amine was added to deionized water and stirred at room temperature for 10-20 min. FeCl3·6H2O was added, and stirring was continued for 30-60 min. The mixture was then extracted three times with dichloromethane. The organic phases were combined, dried with anhydrous sodium sulfate, and the solvent was removed by rotary evaporation. The dried product was the curing agent.

[0011] More preferably, the method for preparing the curing agent includes the following steps: Tris(2-aminoethyl)amine was added to deionized water and stirred at room temperature for 15 min. FeCl3·6H2O was added, and stirring was continued for 45 min. The mixture was then extracted three times with dichloromethane. The organic phases were combined, dried with anhydrous sodium sulfate, and the solvent was removed by rotary evaporation. The dried product was the curing agent.

[0012] Preferably, in the preparation method of the curing agent, the molar ratio of tris(2-aminoethyl)amine and FeCl3·6H2O is 1:0.25-0.35.

[0013] More preferably, in the method for preparing the curing agent, the molar ratio of tris(2-aminoethyl)amine and FeCl3·6H2O is 1:0.3.

[0014] Preferably, in the preparation method of the curing agent, tris(2-aminoethyl)amine, deionized water and dichloromethane are in a weight ratio of 1:5-10:10-20.

[0015] More preferably, in the method for preparing the curing agent, tris(2-aminoethyl)amine, deionized water and dichloromethane are in a weight ratio of 1:8:15.

[0016] Preferably, the preparation method of the poly(perylenetetracarboxylic dianhydride-thiourea) includes the following steps: Under nitrogen protection, imidazole, 3,4,9,10-perylenetetracarboxylic dianhydride, thiourea, and anhydrous zinc acetate were added to a reaction vessel, and the mixture was heated to 140-150℃ with stirring and reacted for 5-6 hours. Then, it was cooled to room temperature, filtered, and the filter cake was washed and dried in a vacuum oven to obtain poly(perylenetetracarboxylic dianhydride-thiourea).

[0017] More preferably, the preparation method of the poly(perylenetetracarboxylic dianhydride-thiourea) includes the following steps: Under nitrogen protection, imidazole, 3,4,9,10-perylenetetracarboxylic dianhydride, thiourea, and anhydrous zinc acetate were added to a reaction vessel. The mixture was heated to 145°C with stirring and reacted for 5.5 h. The mixture was then cooled to room temperature, filtered, and the filter cake was washed and dried in a vacuum oven to obtain poly(perylenetetracarboxylic dianhydride-thiourea). The chemical reaction equation is as follows: ; Preferably, in the preparation method of poly(perylenetetracarboxylic dianhydride-thiourea), imidazole, 3,4,9,10-perylenetetracarboxylic dianhydride, thiourea and anhydrous zinc acetate are in a weight ratio of 8-12:1:0.12-0.18:0.3-0.4.

[0018] More preferably, in the preparation method of poly(perylenetetracarboxylic dianhydride-thiourea), imidazole, 3,4,9,10-perylenetetracarboxylic dianhydride, thiourea and anhydrous zinc acetate are in a weight ratio of 10:1:0.16:0.35.

[0019] Preferably, the preparation method of the Fe3O4@SiC core-shell nanoparticles includes the following steps: (1) Add deionized water to the lining of the high-pressure reactor, and add FeCl3·6H2O, FeSO4·7H2O and PEG-6000 in sequence under magnetic stirring at room temperature. Stir for 10-30 min, add NaOH solid, stir for 10-30 min, seal the reactor, keep it at 160-200℃ for 8-12 h, cool naturally to room temperature, collect the precipitate by centrifugation, wash, and dry to obtain Fe3O4 nanoparticles; (2) Disperse Fe3O4 nanoparticles in anhydrous ethanol and ultrasonically disperse for 10-30 min. Add ammonia to adjust the pH to 9-10, add tetraethyl orthosilicate dropwise for 30-60 min, stir at room temperature for 4-8 h, centrifuge to collect the precipitate, wash, dry, add to deionized water, then add sucrose, stir for 1-2 h, filter, dry, transfer to a tube furnace, heat to 1450-1650℃ at 3-7℃ / min under argon atmosphere, carbonize for 2-4 h, cool with the furnace, then add ethanol / water mixed solution, add silane coupling agent KH550, adjust the pH to 3-4 with dilute hydrochloric acid with a concentration of 0.1-1 mol / L, heat to 60-70℃ and stir for 2-4 h, cool to room temperature, centrifuge to collect the precipitate, wash, dry, and obtain Fe3O4@SiC core-shell nanoparticles.

[0020] More preferably, the preparation method of the Fe3O4@SiC core-shell nanoparticles includes the following steps: (1) Add deionized water to the lining of the high-pressure reactor, and add FeCl3·6H2O, FeSO4·7H2O and PEG-6000 in sequence under magnetic stirring at room temperature. Stir for 20 min, add NaOH solid, stir for 20 min, seal the reactor, keep it at 180℃ for 10 h, cool naturally to room temperature, collect the precipitate by centrifugation, wash, and dry to obtain Fe3O4 nanoparticles.

[0021] (2) Fe3O4 nanoparticles were dispersed in anhydrous ethanol and ultrasonically dispersed for 20 min. Ammonia was added to adjust the pH to 9-10. Tetraethyl orthosilicate was added dropwise over 50 min. The mixture was stirred at room temperature for 6 h. The precipitate was collected by centrifugation, washed, dried, and then added to deionized water. Sucrose was added and stirred for 1.5 h. The mixture was filtered, dried, and then transferred to a tube furnace. The temperature was increased to 1550℃ at 5℃ / min under an argon atmosphere and carbonized for 3 h. The furnace was then cooled. An ethanol / water mixture was added, along with silane coupling agent KH550. The pH was adjusted to 3-4 with 0.3 mol / L dilute hydrochloric acid. The temperature was increased to 65℃ and stirred for 3 h. After cooling to room temperature, the precipitate was collected by centrifugation, washed, and dried to obtain Fe3O4@SiC core-shell nanoparticles.

[0022] Preferably, in (1), the weight ratio of deionized water, FeCl3·6H2O, FeSO4·7H2O, PEG-6000 and NaOH solid is 280-320:18-22:10-15:1-2:12-18.

[0023] More preferably, in (1), the deionized water, FeCl3·6H2O, FeSO4·7H2O, PEG-6000 and NaOH solid are in a weight ratio of 300:20:13:1.5:15.

[0024] Preferably, in (2), the Fe3O4 nanoparticles, anhydrous ethanol, tetraethyl orthosilicate, deionized water, sucrose, ethanol / water mixed solution and silane coupling agent KH550 are in a weight ratio of 1:8-12:0.6-1:8-12:1-1.4:8-12:0.1-0.2.

[0025] More preferably, in (2), the Fe3O4 nanoparticles, anhydrous ethanol, tetraethyl orthosilicate, deionized water, sucrose, ethanol / water mixed solution and silane coupling agent KH550 are in a weight ratio of 1:10:0.8:10:1.2:10:0.15.

[0026] Preferably, the volume ratio of ethanol to water in the ethanol / water mixed solution in (2) is 9:1.

[0027] Furthermore, the present invention also provides a method for preparing a broadband absorbing resin-based composite material, comprising the following steps: S1. Add epoxy resin and triglycidyl isocyanate to a reaction vessel, heat to 40-60℃, and stir at 300-400r / min for 30-40min to obtain a uniform prepolymer matrix resin. S2. Add Fe3O4@SiC core-shell nanoparticles to the prepolymer matrix resin, first ultrasonically disperse at 200-300W for 20-30min, then mechanically stir at 400-500r / min for 1-2h, then add antioxidant 1010 and polyether modified silicone oil, stir for 20-30min, adjust the system temperature to 50-60℃, add poly(perylenetetracarboxylic dianhydride-thiourea) and curing agent, stir at 300-400r / min for 30-40min to obtain a uniform composite slurry; S3. Inject the composite slurry into a mold preheated to 50-60℃ and use a segmented heating and curing process: first, keep it at 60-70℃ for 1-2 hours, then raise the temperature to 90-100℃ and keep it for 2-3 hours, then raise the temperature to 120-130℃ and keep it for 2-3 hours, and finally raise the temperature to 150-160℃ and keep it for 1-2 hours. After curing, let it cool naturally to room temperature with the mold. After demolding, you will get a broadband microwave absorbing resin-based composite material.

[0028] Preferably, the working mechanism of the broadband absorbing resin-based composite material in this invention is explained as follows: The mechanism of action of a broadband microwave absorbing resin-based composite material in this invention will be explained from three aspects: component preparation mechanism, curing mechanism, and microwave absorption mechanism.

[0029] 1. Component preparation mechanism The preparation process of the key components of this invention directly endows them with subsequent functional properties, laying the foundation for the curing and microwave absorption properties of the composite material: The curing agent achieves a large excess of TAEA and Fe by strictly controlling the molar ratio of tris(2-aminoethyl)amine (TAEA) to FeCl3·6H2O. 3+ Partial coordination, this ratio is not a conventional equimolar or metal ion excess system, but rather a special reaction environment constructed through the excess design of TAEA, fundamentally altering the structure and solubility of the complex product: In the reaction system, excess TAEA makes the solution alkaline, promoting the reaction of Fe. 3+ Partial hydrolysis occurs to generate hydroxyl-coordinating species; Fe 3+ It does not completely chelate with all amino groups of TAEA, but only forms stable coordinate bonds with the lone pair electrons of some primary amine nitrogen atoms, constructing "Fe-N" magnetic loss sites. At this time, each Fe 3+ It will coordinate with a small amount of TAEA and multiple hydroxyl groups to form [Fe(TAEA)(OH)2]. + Equal low-charge (+1 valence or neutral) mixed complexes, with a large number of remaining primary amine nitrogen atoms (including primary amines in uncoordinated TAEA molecules and unbound Fe atoms in coordinated TAEA molecules). 3+ The primary amine remains in a free state, and these free primary amine nitrogen atoms provide sufficient active sites for subsequent crosslinking reactions with epoxy resin, ensuring that the crosslinking function of the curing agent is not affected; After the reaction was completed, the mixture was extracted three times with dichloromethane. The separation principle was not based on the solubility rules of conventional metal complexes, but on a synergistic extraction effect under special conditions: on the one hand, the low-charge mixed complexes react with Cl in the system. -The combination of TAEA molecules to form neutral ion pairs (such as [Fe(TAEA)(OH)2]Cl) significantly reduces hydrophilicity. On the other hand, a large number of uncoordinated free TAEA molecules in the solution form weak interactions (hydrogen bonds, coordination) with the ion pairs through their amino groups. Simultaneously, the ethylidene segments in the TAEA molecules generate hydrophobic interactions, creating a "wrapping or accompanying" effect on the neutral ion pairs, significantly enhancing their hydrophobicity and lowering the desolvation energy barrier for transfer from the aqueous phase to the organic phase. Ultimately, both the target coordination complex (in the form of neutral ion pairs) and the uncoordinated TAEA molecules are effectively soluble in the dichloromethane organic phase, while water-soluble impurities in the system (unreacted Fe) are dissolved. 3+ Hydrolysis products, excess inorganic salts, etc. remain in the aqueous phase. The target product and impurities are efficiently separated through three extractions, and finally a curing agent with both "Fe-N" magnetic loss sites and sufficient cross-linking activity is obtained. This extraction step is not a conventional purification operation, but a special chemical design based on "TAEA excess - low charge complex formation - synergistic extraction". It is a key technology for separating and enriching the target active curing component, and directly determines the structural integrity and functional effectiveness of the curing agent. Poly(perylenetetracarboxylic dianhydride-thiourea) was prepared under nitrogen protection using imidazole as solvent and anhydrous zinc acetate as catalyst. During the reaction, the large π-conjugated skeleton of perylenetetracarboxylic dianhydride covalently bonded to the strongly polar groups of thiourea to form a polymer with both electronic polarization and dipole polarization capabilities. The conjugated system provides a channel for electron migration, and the high dipole moment of the thiourea bond (-NH-CS-NH-) can initiate orientation polarization and relaxation. At the same time, the active sites of the end groups provide anchoring sites for subsequent crosslinking. Fe3O4@SiC core-shell nanoparticles were prepared in two steps: First, FeCl3·6H2O and FeSO4·7H2O were used as iron sources. Deionized water, FeCl3·6H2O, FeSO4·7H2O, PEG-6000, and NaOH were mixed and reacted hydrothermally to generate Fe3O4 nanocores with high magnetic saturation strength, providing a core for magnetic loss. Second, SiO2 precursors were coated onto the Fe3O4 surface using a tetraethyl orthosilicate sol-gel method. A SiC dielectric shell was then formed by carbonizing sucrose. The nanoparticles were then modified with a silane coupling agent, KH550, at pH 3-4 and 60-70℃ for 2-4 hours, introducing amino active groups onto the particle surface. This significantly improved the compatibility with the resin matrix, preventing performance degradation caused by uneven dispersion, and ultimately forming a synergistic structure of "magnetic core-dielectric shell."

[0030] 2. Curing Mechanism The curing process of the composite material involves multi-component synergistic crosslinking, forming a three-dimensional network structure that combines high strength with uniform functional dispersion. First, epoxy resin and triglycidyl isocyanurate (TGIC) are directly mixed and stirred at 40-60℃ until homogeneous. The rigid isocyanuric acid ring structure of TGIC will be uniformly dispersed in the epoxy resin matrix. Its own epoxy groups and the epoxy groups of epoxy resin together constitute a multi-active site system, which provides a basis for subsequent crosslinking. Subsequently, Fe3O4@SiC core-shell nanoparticles were added to the aforementioned prepolymer matrix resin, and the mixture was ultrasonically dispersed and stirred to ensure uniform dispersion of the microwave absorber. Next, antioxidant 1010 and polyether-modified silicone oil were added, and the system temperature was adjusted to 50-60℃ before adding the curing agent and poly(perylenetetracarboxylic acid dianhydride-thiourea). The uncoordinated free primary amine in the curing agent acts as a strong nucleophile, simultaneously attacking the electron-deficient carbon of the three-membered ring of the epoxy resin and TGIC, initiating epoxy ring opening and generating secondary amines and hydroxyl groups. The secondary amine further reacts with the remaining epoxy groups to generate tertiary amines and hydroxyl groups. The radicals undergo etherification with the epoxy groups to form multiple cross-linking nodes. The rigid ring structure of TGIC is fixed in the cross-linking network during this process, which not only improves the heat resistance of the matrix but also increases the cross-linking density. At the same time, the terminal amine active sites of poly(perylenetetracarboxylic dianhydride-thiourea) participate in cross-linking, anchoring its conjugated structure and thiourea bond polar groups in the network. Meanwhile, Fe3O4@SiC core-shell nanoparticles are connected to the resin matrix through the active amino groups of the silane coupling agent KH-550 on the surface medium, and are uniformly embedded in the cross-linking network without destroying the structural integrity. Finally, through a segmented heating and curing process, the cross-linking reaction is gradually deepened, ultimately forming a three-dimensional cross-linked network that combines high heat resistance, mechanical strength, and uniform dispersion of functional components.

[0031] 3. Mechanism of action The broadband absorption performance of composite materials stems from the synergistic effect of magnetic and dielectric losses, while also relying on the functional complementarity and uniform dispersion characteristics of each component: Magnetic loss is contributed synergistically by two systems: first, the hysteresis and eddy current losses of the Fe3O4 core in the Fe3O4@SiC core-shell nanoparticles. Under the action of an applied alternating electromagnetic field, the magnetic domains of Fe3O4 undergo orientation and domain wall resonance, simultaneously generating an eddy current effect that converts electromagnetic energy into heat energy; second, the magnetic moment resonance relaxation of the "Fe-N" coordination structure in the curing agent, Fe... 3+ The coordination with TAEA causes the magnetic moment to undergo directional vibration and relaxation in the external field, further replenishing magnetic loss and widening the frequency band of magnetic loss. Dielectric loss is achieved through the synergistic effect of multiple structures: the SiC shell of Fe3O4@SiC core-shell nanoparticles acts as a high dielectric material, dissipating electromagnetic energy through electronic polarization and charge accumulation at the core-shell interface; the large π-conjugated system of poly(perylenetetracarboxylic dianhydride-thiourea) allows π electrons to migrate freely under an external field, generating electronic polarization loss, while the high dipole moment of its thiourea bonds undergoes orientation polarization and relaxation loss in an alternating electric field, effectively compensating for insufficient dielectric loss in the low-frequency range; in addition, the difference in dielectric constant between the curing agent, poly(perylenetetracarboxylic dianhydride-thiourea), and the matrix resin forms a multi-component interface, and the charge accumulation at the interface further enhances the broadband characteristics of dielectric loss. Meanwhile, the Fe3O4@SiC core-shell nanoparticles, after being modified with KH550, exhibit excellent compatibility with the resin matrix, ensuring uniform dispersion even at high addition levels. This optimizes the impedance matching characteristics of the composite material and reduces electromagnetic wave reflection. Antioxidant 1010 enhances the material's thermo-oxidative stability, preventing performance degradation under high-temperature conditions. Polyether-modified silicone oil improves processing fluidity, ensuring uniform distribution of each component during molding. Ultimately, this achieves high-efficiency microwave absorption across a wide frequency band, while also considering the material's mechanical properties and operational stability.

[0032] The beneficial effects of this invention are: 1. This invention imparts excellent microwave absorption properties to materials through a synergistic effect of multiple loss mechanisms. The large π-conjugated system and high dipole moment thiourea bonds in poly(perylenetetracarboxylic dianhydride-thiourea) can efficiently generate electronic polarization and orientation polarization relaxation losses, compensating for insufficient dielectric loss in the low-frequency band. The Fe3O4@SiC core-shell structure achieves synergy between hysteresis loss, eddy current loss, and dielectric loss. Combined with the magnetic moment resonance relaxation of the Fe-N coordination structure in the curing agent, the magnetic loss bandwidth is further broadened. At the same time, the core-shell particles, after modification with KH550, exhibit excellent compatibility with the matrix, optimize impedance matching, reduce electromagnetic wave reflection, and ultimately achieve high-efficiency absorption over a wide frequency band, meeting the requirements for use in complex electromagnetic environments.

[0033] 2. The three-dimensional cross-linked network structure of the material in this invention endows it with excellent mechanical properties. The rigid isocyanuric acid ring of triglycidyl isocyanurate is embedded in the cross-linked network, improving the cross-linking density and structural rigidity of the matrix. The active sites of the end groups of poly(perylenetetracarboxylic dianhydride-thiourea) participate in cross-linking, enhancing the overall integrity of the network. The core-shell particles form a chemical bond with the resin through surface amino groups, avoiding agglomeration and stress concentration under high filling amounts. In addition, antioxidant 1010 effectively inhibits thermo-oxidative aging, and polyether-modified silicone oil improves processing fluidity, enabling the material to possess both high strength and toughness, as well as good moldability and service stability, and is not easily subject to performance degradation due to environmental factors.

[0034] 3. This invention achieves highly efficient integration of component functions, with each key component possessing multiple roles: the curing agent provides sufficient crosslinking activity and supplements magnetic loss through the Fe-N coordination structure; poly(perylenetetracarboxylic dianhydride-thiourea) enhances dielectric loss and acts as a "micro-reinforcing phase" to improve the mechanical properties of the matrix; Fe3O4@SiC core-shell particles serve as microwave absorbing functional components and can also enhance the matrix structure through interfacial bonding. This multifunctional integrated design avoids redundant addition of single functional components, simplifies the material system, and simultaneously optimizes microwave absorption performance and mechanical properties through the synergistic effect between components.

[0035] 4. The preparation process of this invention has good operability and scalability potential. The mixing and dispersion of each component does not require special equipment; uniform mixing can be achieved by combining ultrasonic dispersion and mechanical stirring. The segmented heating and curing process is mild and controllable, effectively avoiding structural defects caused by violent reactions, and is adaptable to molds of different sizes and shapes. The overall material preparation process is simple and cost-controllable, and the finished product has moderate density and strong environmental stability, making it widely applicable in aerospace, military equipment, electromagnetic protection, and other fields, with significant practical application value. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0037] Preparation Example 1: The specific preparation method of the curing agent includes the following steps: 100g of tris(2-aminoethyl)amine was added to 800g of deionized water and stirred at room temperature for 15min. Then, 55.45g of FeCl3·6H2O was added and stirred for another 45min. The mixture was then extracted three times with 1.5kg of dichloromethane. The organic phases were combined, dried with anhydrous sodium sulfate, and the solvent was removed by rotary evaporation. The dried product was the curing agent.

[0038] Preparation Example 2: A specific preparation method for poly(perylenetetracarboxylic dianhydride-thiourea) includes the following steps: Under nitrogen protection, 100g imidazole, 10g 3,4,9,10-perylenetetracarboxylic dianhydride, 1.6g thiourea and 3.5g anhydrous zinc acetate were added to a reaction vessel, heated to 145℃ with stirring, and reacted for 5.5h. Then the mixture was cooled to room temperature, filtered, and the filter cake was washed and dried in a vacuum oven to obtain poly(perylenetetracarboxylic dianhydride-thiourea).

[0039] Preparation Example 3: A method for preparing Fe3O4@SiC core-shell nanoparticles, comprising the following steps: (1) Add 300g of deionized water to the lining of a high-pressure reactor. Under magnetic stirring at room temperature, add 20g of FeCl3·6H2O, 13g of FeSO4·7H2O and 1.5g of PEG-6000 in sequence. Stir for 20min, add 15g of NaOH solid, stir for 20min and then seal the reactor. Keep the reactor at 180℃ for 10h. Cool naturally to room temperature, collect the precipitate by centrifugation, wash and dry to obtain Fe3O4 nanoparticles.

[0040] (2) 5g of Fe3O4 nanoparticles were dispersed in 50g of anhydrous ethanol and ultrasonically dispersed for 20min. Ammonia was added to adjust the pH to 9-10. 4g of tetraethyl orthosilicate was added dropwise over 50min. The mixture was stirred at room temperature for 6h. The precipitate was collected by centrifugation, washed, dried, and then added to 50g of deionized water. 6g of sucrose was added and stirred for 1.5h. The mixture was filtered, dried, and then transferred to a tube furnace. The temperature was raised to 1550℃ at 5℃ / min under an argon atmosphere and carbonized for 3h. The furnace was then cooled. 50g of ethanol / water mixed solution (ethanol to water volume ratio of 9:1) was added, along with 0.75g of silane coupling agent KH550. The pH was adjusted to 3-4 with 0.3mol / L dilute hydrochloric acid. The temperature was raised to 65℃ and stirred for 3h. After cooling to room temperature, the precipitate was collected by centrifugation, washed, and dried to obtain Fe3O4@SiC core-shell nanoparticles.

[0041] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 1 is that tris(2-aminoethyl)amine was used directly as the curing agent.

[0042] Comparative Preparation Example 2: The difference between Comparative Preparation Example 2 and Preparation Example 1 is that tri(2-aminoethyl)amine is replaced with triethylenetetramine.

[0043] Comparative Preparation Example 3: The difference between Comparative Preparation Example 3 and Preparation Example 2 is that thiourea is replaced with urea.

[0044] Example 1: A specific preparation method of a broadband absorbing resin-based composite material, comprising the following steps: S1. Add 1 kg of epoxy resin and 200 g of triglycidyl isocyanate to a reaction vessel, heat to 40°C, and stir at 300 r / min for 30 min to obtain a uniform prepolymer matrix resin. S2. Add 1.2 kg of Fe3O4@SiC core-shell nanoparticles prepared according to Preparation Example 3 to the prepolymer matrix resin. First, ultrasonically disperse the nanoparticles at a power of 200 W for 20 min, then mechanically stir at a speed of 400 r / min for 1 h. Then, add 5 g of antioxidant 1010 and 10 g of polyether modified silicone oil, stir for 20 min, adjust the system temperature to 50 °C, add 100 g of poly(perylenetetracarboxylic acid dianhydride-thiourea) prepared according to Preparation Example 2 and 300 g of curing agent prepared according to Preparation Example 1, and stir at a speed of 300 r / min for 30 min to obtain a homogeneous composite slurry. S3. Inject the composite slurry into a mold preheated to 50°C and use a segmented heating and curing process: first, keep it at 60°C for 1 hour, then raise the temperature to 90°C and keep it for 2 hours, then raise the temperature to 120°C and keep it for 2 hours, and finally raise the temperature to 150°C and keep it for 1 hour. After curing, let it cool naturally to room temperature with the mold. After demolding, you will get a broadband microwave absorbing resin-based composite material.

[0045] Example 2: A specific preparation method of a broadband absorbing resin-based composite material, comprising the following steps: S1. Add 1 kg of epoxy resin and 250 g of triglycidyl isocyanate to a reaction vessel, heat to 50 °C, and stir at 350 r / min for 35 min to obtain a uniform prepolymer matrix resin. S2. Add 1.5 kg of Fe3O4@SiC core-shell nanoparticles prepared according to Preparation Example 3 to the prepolymer matrix resin. First, ultrasonically disperse the nanoparticles at a power of 250 W for 25 min, then mechanically stir at a speed of 450 r / min for 1.5 h. Then add 10 g of antioxidant 1010 and 15 g of polyether modified silicone oil, stir for 25 min, adjust the system temperature to 55 °C, add 150 g of poly(perylenetetracarboxylic acid dianhydride-thiourea) prepared according to Preparation Example 2 and 350 g of curing agent prepared according to Preparation Example 1, stir at a speed of 350 r / min for 35 min to obtain a homogeneous composite slurry. S3. Inject the composite slurry into a mold preheated to 55°C and use a segmented heating and curing process: first, keep it at 65°C for 1.5 hours, then raise the temperature to 95°C and keep it at 2.5 hours, then raise the temperature to 125°C and keep it at 2.5 hours, and finally raise the temperature to 155°C and keep it at 1.5 hours. After curing, let it cool naturally to room temperature with the mold. After demolding, a broadband microwave absorbing resin-based composite material is obtained.

[0046] Example 3: A specific preparation method of a broadband absorbing resin-based composite material, comprising the following steps: S1. Add 1 kg of epoxy resin and 300 g of triglycidyl isocyanate to a reaction vessel, heat to 60°C, and stir at 400 r / min for 40 min to obtain a uniform prepolymer matrix resin. S2. Add 1.8 kg of Fe3O4@SiC core-shell nanoparticles prepared according to Preparation Example 3 to the prepolymer matrix resin. First, ultrasonically disperse the nanoparticles at a power of 300 W for 30 min, then mechanically stir at a speed of 500 r / min for 2 h. Then, add 15 g of antioxidant 1010 and 20 g of polyether modified silicone oil, stir for 30 min, adjust the system temperature to 60 °C, add 200 g of poly(perylenetetracarboxylic acid dianhydride-thiourea) prepared according to Preparation Example 2 and 400 g of curing agent prepared according to Preparation Example 1, and stir at a speed of 400 r / min for 40 min to obtain a homogeneous composite slurry. S3. Inject the composite slurry into a mold preheated to 60°C and use a segmented heating and curing process: first, keep it at 70°C for 2 hours, then raise the temperature to 100°C and keep it for 3 hours, then raise the temperature to 130°C and keep it for 3 hours, and finally raise the temperature to 160°C and keep it for 2 hours. After curing, let it cool naturally to room temperature with the mold. After demolding, you will get a broadband microwave absorbing resin-based composite material.

[0047] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the curing agent prepared according to Preparation Example 1 is replaced with the curing agent prepared according to Comparative Preparation Example 1.

[0048] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the curing agent prepared according to Preparation Example 1 is replaced with the curing agent prepared according to Comparative Preparation Example 2.

[0049] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the poly(perylenetetracarboxylic dianhydride-thiourea) prepared according to Preparation Example 2 is replaced with the poly(perylenetetracarboxylic dianhydride-urea) prepared according to Comparative Preparation Example 3.

[0050] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that poly(perylenetetracarboxylic acid dianhydride-thiourea) is not added.

[0051] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that the Fe3O4@SiC core-shell nanoparticles prepared according to Preparation Example 3 are replaced with nano Fe3O4.

[0052] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that the Fe3O4@SiC core-shell nanoparticles prepared according to Preparation Example 3 are replaced with nano-SiC.

[0053] Performance testing: 1. Correlation Test of Dielectric Parameters with Wideband Absorption Frequency: Referring to GB / T 5594.6-1996 "Test Methods for Dielectric Properties of Structural Ceramic Materials for Electronic Components" and GB / T 20046-2006 "Test Methods for Reflectivity of Radar Absorbing Materials," the composite materials of Examples 1-3 and Comparative Examples 1-6 were tested in the 2-18 GHz frequency band using the coaxial transmission line method combined with a vector network analyzer. Each sample was processed into a Φ22.8mm×2mm circular standard specimen. After removing surface impurities, it was tightly fitted into a coaxial test fixture, ensuring no gap between the specimen and the inner wall of the fixture. After calibration with a vector network analyzer, the scattering parameters (S11, S21) of the specimen were measured. Based on transmission line theory and the performance calculation model of the absorbing material, the real part (ε') and imaginary part (ε'') of the relative permittivity across the entire frequency band were calculated, and the numerical range of their variation with frequency was recorded. The polarization loss tangent was calculated using the formula (tanδ). e =ε'' / ε'), calculate the numerical range of polarization loss across the entire frequency band; combined with the relative permeability parameter of the material, further calculate the reflection loss (RL) of the sample, determine the effective absorption frequency range with reflection loss ≤ -10dB, and record the minimum reflection loss value (RL) across the entire frequency band. min The experimental results are shown in Table 1.

[0054] Table 1. Test results relating dielectric parameters to broadband absorption bands

[0055] 2. Mechanical property testing: Tensile strength testing was conducted according to GB / T 1447-2005 "Test Method for Tensile Properties of Fiber Reinforced Plastics". Samples from Examples 1-3 and Comparative Examples 1-6 were processed into dumbbell-shaped specimens of 150mm × 10mm × 2mm. A universal testing machine was used for testing at a tensile rate of 2mm / min. Five parallel samples were prepared for each group, and the average value was taken as the final tensile strength. The elongation at break was also recorded. Impact strength testing was conducted according to GB / T 1451-2005 "Impact Test Method for Simply Supported Beams of Fiber Reinforced Plastics". Unnotched specimens (80mm × 10mm × 2mm) were used, and the test was conducted using a pendulum impact testing machine. Five parallel samples were tested for each group, and the average value was taken. The experimental results are shown in Table 2.

[0056] Table 2 Mechanical Performance Test Results

[0057] Performance Analysis: As can be seen from the experimental data in Tables 1-2, the broadband absorbing resin-based composite materials provided in Examples 1-3 of this invention exhibit excellent comprehensive performance. This may be due to the introduction of Fe into the tris(2-aminoethyl)amine curing agent.3+ By employing coordination centers, preparing highly polar conjugated polymers using thiourea, and constructing Fe3O4@SiC core-shell nanoparticles as microwave absorbing fillers, this invention achieves an organic combination of dielectric loss, magnetic loss, and impedance matching. Among these, Example 2 exhibits the best overall performance in both broadband absorption and mechanical properties.

[0058] From the perspective of dielectric and absorption performance, Example 2 performs best because it constructs the most effective multipolarization and loss mechanism. First, the perylene ring large π-conjugated system in its poly(perylenetetracarboxylic dianhydride-thiourea) component provides a channel for electron migration, enhancing electronic polarization. Simultaneously, the C=S bond in the thiourea unit has a higher bond dipole moment than the C=O bond in urea in Comparative Example 3, resulting in stronger dipole orientation polarization and relaxation loss under an alternating electric field. Second, the Fe used in Example 2... 3+ In some coordination curing agents, the "Fe-N" coordination bond is not only a strongly polar relaxation center itself, but also... 3+ The d-orbital electrons can also undergo local resonance in high-frequency fields, contributing additional dielectric loss. Furthermore, the high content and uniform dispersion of Fe3O4@SiC core-shell particles form a large heterogeneous interface with significant interfacial polarization effects between the core and shell. Among them, the Fe3O4 core provides hysteresis and eddy current losses, while the SiC shell provides dielectric losses. This magnetic-dielectric synergy optimizes the overall impedance matching, allowing electromagnetic waves to enter the material interior more efficiently and be dissipated, thereby achieving a wider effective absorption frequency band and lower reflection loss.

[0059] From a mechanical performance perspective, Example 2 exhibits the highest overall mechanical properties due to the formation of a more uniform and robust three-dimensional cross-linked network. The terminal amine groups of poly(perylenetetracarboxylic dianhydride-thiourea) and the uncoordinated primary amine groups in the curing agent participate in the cross-linking reaction between the epoxy resin and TGIC. Its rigid conjugated perylene ring structure acts as a "micro-reinforcing phase" uniformly dispersed within the cross-linked network, enhancing the rigidity (tensile strength) of the matrix. Simultaneously, this conjugated polymer is chemically bonded to the resin matrix, improving interfacial compatibility and facilitating stress transfer. The Fe3O4@SiC core-shell particles are modified with KH-550 silane coupling agent to introduce amino groups, enabling them to form chemical bonds with the resin matrix rather than simple physical filling. This significantly reduces stress concentration points caused by weak interfacial bonding between the filler and the matrix, thus maintaining high impact toughness and elongation at break even with a large amount of filler added.

[0060] Comparative Example 1 and Example 2 were analyzed to identify the reasons for their performance deficiencies, which stemmed from the absence or alteration of key components or structures. Comparative Example 1 directly used uncoordinated tris(2-aminoethyl)amine, completely lacking the polarization relaxation and magnetic moment coupling contribution from the "Fe-N" coordination structure, resulting in reduced dielectric and magnetic losses and a comprehensive decline in absorption performance. Comparative Example 2 replaced tris(2-aminoethyl)amine with triethylenetetramine, a change that fundamentally affected the topology of the crosslinked network. Tris(2-aminoethyl)amine molecules exhibit a three-dimensional branched structure, with a central tertiary amine nitrogen linked to three terminal primary amines, forming a highly crosslinked and uniform three-dimensional network when used as a curing agent. Triethylenetetramine, however, is a straight-chain molecule with linearly arranged crosslinking points, making it more prone to forming locally ordered but less uniform networks. When carrying high-content, high-surface-energy nanofillers, such networks constructed with straight-chain curing agents may exhibit lower network toughness and stability in filler dispersion, leading to a decline in overall performance. Comparative Example 3 replaced thiourea with urea. The C=O bond is less polar than the C=S bond, which weakens the dipole moment and polarization relaxation strength of the conjugated polymer, reducing dielectric loss, especially low-frequency loss, and narrowing the absorption bandwidth. Comparative Example 4 completely omitted the poly(perylenetetracarboxylic dianhydride-thiourea) component, losing both the important conjugated electronic polarization and strong dipole relaxation source, as well as the polymer's reinforcing and toughening effect on the matrix, resulting in significant deterioration of both dielectric and mechanical properties. Comparative Example 5 used pure Fe3O4 nanoparticles. Although the magnetic loss was strong, the lack of the dielectric loss contribution of the SiC shell and the crucial core-shell interface polarization led to poor impedance matching and a narrowing absorption bandwidth. At the same time, pure magnetic particles were more prone to agglomeration, resulting in poor interfacial bonding and reduced mechanical properties. Comparative Example 6 uses pure SiC nanoparticles, which completely lose the magnetic loss mechanism, and the single dielectric filler is difficult to achieve good impedance matching, resulting in severely insufficient wave absorption performance; its interfacial bonding with resin is also not as good as that of particles with core-shell structure and surface modification, and its mechanical properties are the worst.

[0061] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A broadband wave-absorbing resin-based composite material, characterized by comprising: The composition comprises the following raw materials by weight: epoxy resin: 100 parts, triisocyanuric acid triglycidyl ester: 20-30 parts, curing agent: 30-40 parts, poly (perylene tetracarboxylic dianhydride-thiourea): 10-20 parts, Fe3O4@SiC core-shell nanoparticles: 120-180 parts, antioxidant 1010: 0.5-1.5 parts, polyether modified silicone oil: 1-2 parts; The curing agent refers to Fe 3+ Partially coordinating tris(2-aminoethyl)amine; The poly (perylene tetracarboxylic dianhydride-thiourea) is prepared by reacting 3,4,9,10-perylene tetracarboxylic dianhydride and thiourea; The Fe3O4@SiC core-shell nanoparticles are prepared by hydrothermal method to obtain Fe3O4 nanoparticles, then coated with tetraethyl orthosilicate sol-gel, carbonized with sucrose to form a SiC shell layer, and then modified with silane coupling agent KH-550.

2. The wideband wave-absorbing resin-based composite material according to claim 1, characterized in that, The epoxy resin is any one of E-51, E-44, and E-42; the epoxy value of triisocyanuric acid triglycidyl ester is 0.9 eq / 100g.

3. The wideband wave-absorbing resin-based composite material according to claim 1, characterized in that, The preparation method of the curing agent comprises the following steps: Tris (2-aminoethyl) amine is added to deionized water, stirred at room temperature for 10-20 min, FeCl3·6H2O is added, then stirring is continued for 30-60 min, then dichloromethane is extracted three times, the organic phase is combined, dried with anhydrous sodium sulfate, then the solvent is removed by rotary evaporation, and the curing agent is obtained after drying.

4. The wideband wave-absorbing resin-based composite material according to claim 3, characterized in that, In the preparation method of the curing agent, the molar ratio of tris (2-aminoethyl) amine to FeCl3·6H2O is 1:0.25-0.35; the weight ratio of tris (2-aminoethyl) amine, deionized water and dichloromethane is 1:5-10:10-20.

5. The wideband wave-absorbing resin-based composite material according to claim 1, characterized in that, The preparation method of the poly (perylene tetracarboxylic dianhydride-thiourea) comprises the following steps: Under nitrogen protection, imidazole, 3,4,9,10-perylene tetracarboxylic dianhydride, thiourea and anhydrous zinc acetate are added to a reaction container, stirred and heated to 140-150℃, reacted for 5-6h, then cooled to room temperature, filtered, the filter cake is washed and dried in a vacuum oven to obtain poly (perylene tetracarboxylic dianhydride-thiourea).

6. The wideband wave-absorbing resin-based composite material according to claim 5, characterized in that, In the preparation method of the poly (perylene tetracarboxylic dianhydride-thiourea), the weight ratio of imidazole, 3,4,9,10-perylene tetracarboxylic dianhydride, thiourea and anhydrous zinc acetate is 8-12:1:0.12-0.18:0.3-0.

4.

7. The wideband wave-absorbing resin matrix composite of claim 1, wherein, The preparation method of the Fe3O4@SiC core-shell nanoparticles comprises the following steps: (1) Deionized water is added to the inner liner of a high-pressure reaction kettle, FeCl3·6H2O, FeSO4·7H2O and PEG-6000 are sequentially added under magnetic stirring at room temperature, stirred for 10-30 min, NaOH solid is added, stirred for 10-30 min, then the reaction kettle is sealed, heated at 160-200℃ for 8-12h, naturally cooled to room temperature, the precipitate is collected by centrifugation, washed and dried to obtain Fe3O4 nanoparticles; (2) Fe3O4 nanoparticles are dispersed in anhydrous ethanol, ultrasonic dispersion for 10-30 min, add ammonia water to adjust pH to 9-10, dropwise add tetraethyl orthosilicate, dropwise time is 30-60 min, room temperature stirring for 4-8 h, centrifugal separation to collect the precipitate, washing, drying, then add deionized water, then add sucrose, stirring for 1-2 h, filter, dry, then transfer to a tube furnace, under argon atmosphere, heat to 1450-1650℃ at 3-7℃ / min, keep temperature for 2-4 h, furnace cooling, then add ethanol / water mixed solution, add silane coupling agent KH550, adjust pH to 3-4 with 0.1-1 mol / L dilute hydrochloric acid, heat to 60-70℃, stirring for 2-4 h, after cooling to room temperature, centrifugal collection of precipitate, washing, drying, to obtain Fe3O4@SiC core-shell nanoparticles.

8. The wideband wave-absorbing resin-based composite material according to claim 7, characterized in that, In the (1), the deionized water, FeCl3·6H2O, FeSO4·7H2O, PEG-6000 and NaOH solid are in a weight ratio of 280-320:18-22:10-15:1-2:12-18.

9. The wideband wave-absorbing resin-based composite material according to claim 7, characterized in that, In the (2), the Fe3O4 nanoparticles, anhydrous ethanol, tetraethyl orthosilicate, deionized water, sucrose, ethanol / water mixed solution and silane coupling agent KH550 are in a weight ratio of 1:8-12:0.6-1:8-12:1-1.4:8-12:0.1-0.2; the volume ratio of ethanol and water in the ethanol / water mixed solution is 9:

1.

10. The method of claim 1-9, wherein the broadband wave-absorbing resin-based composite material is prepared by the steps of: mixing the resin matrix, the absorbing material, the reinforcing material, and the coupling agent to obtain a mixture; and curing the mixture to obtain the broadband wave-absorbing resin-based composite material. Comprise the following steps: S1. Add epoxy resin and isocyanuric acid triglycidyl ester into a reaction container, heat to 40-60℃, stirring at a speed of 300-400 r / min for 30-40 min to obtain a uniform prepolymer matrix resin; S2. Add Fe3O4@SiC core-shell nanoparticles into the prepolymer matrix resin, first ultrasonic dispersion at a power of 200-300 W for 20-30 min, then mechanical stirring at a speed of 400-500 r / min for 1-2 h, then add antioxidant 1010 and polyether modified silicone oil, stirring for 20-30 min, adjust the system temperature to 50-60℃, add poly(perylenetetracarboxylic dianhydride-thiourea) and curing agent, stirring at a speed of 300-400 r / min for 30-40 min to obtain a uniform composite slurry; S3. Pour the composite slurry into a mold preheated to 50-60℃, adopt a staged temperature rising curing process: first heat at 60-70℃ for 1-2 h, then heat to 90-100℃ for 2-3 h, then heat to 120-130℃ for 2-3 h, finally heat to 150-160℃ for 1-2 h, after curing, naturally cool to room temperature with the mold, demold to obtain a broadband wave absorbing resin-based composite material.

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