A graphene-modified gypsum-based microwave absorbing material and its preparation method

Abstract

This invention discloses a graphene-modified gypsum-based microwave absorbing material and its preparation method, belonging to the field of microwave absorbing material technology. The material is composed of gypsum cementitious material, modified graphene, water-reducing agent, retarder, magnetic microwave absorbing filler, and water. The modified graphene is prepared as a dual-anchored block copolymer via RAFT polymerization, followed by mechanochemical modification and DA click chemistry grafting. It achieves stable dispersion of graphene in the gypsum system through the dual-anchored block copolymer, and achieves high-efficiency microwave absorption by relying on the synergistic effect of dielectric and magnetic losses, while breaking the antagonistic relationship between microwave absorption performance and mechanical properties. This material possesses excellent microwave absorption efficiency, mechanical strength, and water resistance, making it suitable for applications such as indoor electromagnetic protection in buildings and shielding in industrial plants, with promising industrialization prospects.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, and in particular to a graphene-modified gypsum-based microwave absorbing material and its preparation method. Background Technology

[0002] With the rapid development of modern electronic information technology, the widespread application of various electronic devices and communication base stations has led to increasingly prominent electromagnetic radiation pollution problems. This not only interferes with the normal operation of precision electronic instruments but may also pose potential health hazards. Therefore, in scenarios such as building interior protection, industrial plant shielding, and environmental remediation, the demand for materials that combine wave-absorbing functionality with building service performance is becoming increasingly urgent. Gypsum-based materials, as a traditional building material, have significant advantages such as wide availability of raw materials, environmental friendliness, rapid setting and hardening, and good workability. Furthermore, their stable dielectric properties and moderate density make them an ideal matrix for preparing wave-absorbing materials for buildings. Combining gypsum with high-dielectric-loss graphene and high-magnetic-loss magnetic fillers can endow the material with electromagnetic wave-absorbing capabilities, meeting the specific needs of building applications. Therefore, graphene-modified gypsum-based wave-absorbing materials have become a research hotspot in recent years.

[0003] To address the issues of graphene's tendency to agglomerate and poor dispersion stability in gypsum-based systems, existing technologies often employ methods such as mixed acid oxidation modification, silane coupling agent surface modification, or copolymer grafting to modify graphene. Simultaneously, magnetic absorbing fillers are often added to enhance microwave absorption performance through the synergistic effect of dielectric and magnetic losses. Mixed acid oxidation modification, by introducing oxygen-containing functional groups such as carboxyl and hydroxyl groups onto the graphene surface, improves its hydrophilicity and dispersibility. However, this method severely disrupts the integrity of the graphene basal planes. 2 The conjugated structure leads to a significant decrease in intrinsic dielectric loss, and the random distribution of functional groups makes directional grafting impossible, resulting in unsatisfactory long-term dispersion stability. Although silane coupling agent modification can improve the interfacial compatibility between graphene and gypsum matrix, the steric hindrance effect of a single silane molecule is limited, making it difficult to effectively suppress π-π stacking between graphene sheets, and the aggregation problem has not been fundamentally solved. Copolymer grafting modification is prone to mutual shielding of reaction sites due to the disordered distribution of functional groups, resulting in low grafting efficiency and an inability to precisely control the synergistic effect between graphene and gypsum hydration crystals and magnetic fillers.

[0004] Meanwhile, existing technologies also have several key drawbacks: First, the synergistic matching between graphene and magnetic microwave absorbing fillers is poor, and the imbalance between dielectric constant and magnetic permeability leads to poor electromagnetic wave impedance matching, weak absorption capacity, and narrow effective absorption bandwidth. Second, the grafting selectivity during graphene modification is poor, with indiscriminate grafting on the basal surface and edges, which not only destroys the intrinsic properties of graphene but also fails to form a continuous electromagnetic loss network, resulting in poor uniformity of microwave absorption performance. Third, the graphene agglomeration phenomenon leads to a large number of interface defects inside the gypsum matrix, significantly reducing mechanical properties and exhibiting an antagonistic effect of "improved microwave absorption performance and decreased mechanical properties." Fourth, the gypsum matrix itself has poor water resistance, and existing modification schemes mostly focus on dispersibility and microwave absorption performance optimization, with limited effect on improving water resistance, thus restricting the service stability of the material in humid environments. The existence of these problems makes it difficult for existing graphene-modified gypsum-based microwave absorbing materials to simultaneously meet the needs of practical applications, thus limiting their large-scale promotion in the construction field. Therefore, developing a graphene-modified gypsum-based microwave absorbing material with synergistic performance optimization and its preparation method has important practical significance and application value. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a graphene-modified gypsum-based microwave absorbing material and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a graphene-modified gypsum-based microwave absorbing material, comprising the following components by weight: gypsum gel material: 100 parts, modified graphene: 0.2-1 parts, water-reducing agent: 0.1-0.3 parts, retarder: 0.1-0.3 parts, magnetic microwave absorbing filler: 10-20 parts, and water: 50-80 parts;

[0007] The modified graphene is prepared as follows:

[0008] (1) Under nitrogen protection, furfuryl methacrylate, benzyl dithiobenzoate and azobisisobutyronitrile were added to anhydrous DMF, heated to 70-80℃, and stirred for 5-8 hours. Then, the mixture was placed in an ice-water bath to cool to room temperature. The reaction solution was then added to methanol at 0℃ to precipitate the precipitate. The precipitate was washed with deionized water and dried to obtain polyfurfuryl methacrylate. The chemical reaction equation is as follows:

[0009] This step is based on the mechanism of RAFT (Reactive Radical Polymerization), using benzyl dithiobenzoate as the RAFT chain transfer agent and azobisisobutyronitrile as the thermal initiator. During the reaction, the primary free radicals generated by the thermal decomposition of azobisisobutyronitrile first initiate the formation of growing chain free radicals from the furfuryl methacrylate monomer. These free radicals undergo a reversible addition-break reaction with the RAFT agent, causing the active growing chain to enter a dynamic equilibrium state of "dormant-re-growth". This fundamentally inhibits the irreversible chain termination and chain transfer side reactions in conventional free radical polymerization, and finally obtains polyfurfuryl methacrylate products with controllable molecular weight and narrow molecular weight distribution.

[0010] (2) Under nitrogen protection, polyfurfuryl methacrylate, 2-acrylamido-2-methylpropionic acid and azobisisobutyronitrile were added to anhydrous DMF, heated to 80-90℃, and stirred for 6-10 h. Then, the mixture was placed in an ice-water bath to cool to room temperature. The reaction solution was then added to methanol at 0℃ to precipitate the product. The precipitate was washed with deionized water and dried to obtain the bi-anchored block copolymer. The chemical reaction equation is as follows:

[0011] This step is based on the sequential feeding block copolymerization mechanism of RAFT polymerization. Relying on the intact RAFT active end groups of the poly(furfuryl methacrylate) prepared in the first step, under the activation of primary free radicals generated by azobisisobutyronitrile (AIB), the RAFT active end groups of the poly(furfuryl methacrylate) regenerate active growth free radicals. These free radicals can directionally initiate a continuous chain growth reaction of the 2-acrylamido-2-methylpropionophosphonic acid monomer in the system, forming a structurally continuous and functionally concentrated poly(2-acrylamido-2-methylpropionophosphonic acid) chain at the end of the original poly(furfuryl methacrylate) segments. The acid segments ultimately yielded a well-defined AB-type double-anchored block copolymer. This block structure achieves complete separation and concentrated distribution of the two functional groups. The polyfurfuryl methacrylate segment concentrates all furan ring reaction sites, enabling exclusive grafting with graphene. The poly-2-acrylamido-2-methylpropionic acid segment concentrates all phosphonic acid groups, which can form a strong chelation with calcium ions in gypsum hydration crystals, providing strong steric hindrance and dispersion stability for graphene in the gypsum system. This avoids the problems of reaction site shielding and insufficient dispersion effect caused by random copolymerization at the molecular structure level.

[0012] (3) Place the few-layer graphene powder in a vacuum drying oven at 70-80℃ for 8-12h to obtain dried few-layer graphene powder. Then, under nitrogen protection, add the dried few-layer graphene powder, pre-hydrolyzed N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and N-maleimide glycine to a planetary ball mill and ball mill at room temperature for 2-4h. After ball milling, prepare a 5mg / ml suspension with anhydrous ethanol, centrifuge for 5-10min, discard the supernatant, and wash and centrifuge the obtained precipitate three times with anhydrous ethanol. Then freeze-dry to obtain modified graphene with edge-oriented maleimide grafting. The chemical reaction diagram is as follows:

[0013] This step utilizes a low-energy mechanochemical-induced edge-selective covalent bonding mechanism in graphene. It leverages the intrinsic structural bond energy differences in graphene to achieve directional edge grafting of functional groups while preserving the sp24-p-column bond energy of the basal surface. 2 Zero structural damage. The pure shear force generated by low-energy ball milling can only cause homogeneous cleavage of the C-C bonds with low edge bond energy in graphene, generating highly active edge carbon free radicals and activated hydroxyl and carboxyl sites, while the aromatic sp groups on the intact graphene basal surface remain intact. 2 The six-membered ring has extremely high bond energy, preventing bond breakage and defects, thus structurally locking the reaction to occur only at the edge. The pre-hydrolyzed N-(2-aminoethyl)-3-aminopropyltrimethoxysilane produces highly reactive silanol groups, which undergo dehydration condensation with activated hydroxyl groups at the graphene edge to form stable Si-OC covalent bonds. This enables the silane coupling agent to be directionally anchored at the graphene edge. The exposed primary amino group at the end further undergoes a mechano-induced amidation reaction with the carboxyl group of N-maleimide glycine to form a stable amide bond. Ultimately, this introduces the electron-deficient dienophile maleimide group required for the Diels-Alder reaction into the graphene edge, providing a unique reaction site for subsequent edge-selective grafting, without any functional group introduction or structural damage on the basal surface.

[0014] (4) Under nitrogen protection, the modified graphene with edge-oriented maleimide grafts was added to anhydrous tetrahydrofuran and stirred for 5-10 min. Then, the double-anchored block copolymer and hydroquinone monomethyl ether were added, the temperature was raised to 60-70℃, and the reaction was stirred for 12-18 h. After cooling to room temperature, the mixture was centrifuged for 5-10 min, the supernatant was discarded, and the resulting precipitate was washed and centrifuged three times with anhydrous ethanol. Then, it was freeze-dried to obtain the modified graphene. The chemical reaction diagram is as follows:

[0015] This step utilizes the intrinsic edge-selective [4+2] cycloaddition reaction mechanism of Diels-Alder (DA) click chemistry, ensuring from a thermodynamic perspective that grafting only occurs at the edges of graphene, thus preventing basal grafting and structural damage. The DA click chemistry reaction can only occur between electron-rich conjugated dienes (furan rings in the side chains of the double-anchored block copolymer) and electron-deficient dienophiles (maleimide groups at the graphene edge). Thermodynamically, if the intact aromatic six-membered rings on the graphene basal surface undergo the DA reaction, they will lose their aromatic stabilization energy, resulting in a strongly endothermic reaction that is thermodynamically infeasible. However, the DA reaction between the maleimide groups at the graphene edge and the furan ring is exothermic and can proceed spontaneously. This inherent reaction dictates that grafting can only occur at the graphene edge. The hydroquinone monomethyl ether added to the system acts as a polymerization inhibitor, suppressing only the radical self-polymerization side reaction of the maleimide double bond without interfering with the main DA cycloaddition reaction. Ultimately, through stable six-membered ring covalent bonds, the double-anchored block copolymer is precisely grafted onto the graphene edge, thus completely preserving the sp(s) of the graphene basal surface. 2 The conjugated structure and intrinsic dielectric loss properties, along with the phosphonic acid groups in the side chains of the block copolymer, enable long-term dispersion stability of graphene in the gypsum hydration system, overcoming the shortcomings of existing technologies such as poor graphene grafting selectivity, basal structure destruction, and easy agglomeration in the gypsum system.

[0016] Preferably, the gypsum gel material refers to at least one of β-hemihydrate building gypsum, α-hemihydrate gypsum, desulfurized building gypsum, or phosphorus building gypsum.

[0017] More preferably, the gypsum gel material is β-hemihydrate building gypsum.

[0018] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent for gypsum, with a solid content of 35%-40% and a water reduction rate of ≥30%.

[0019] Preferably, the retarder refers to at least one of SGR-1801 protein retarder, citric acid, or sodium polyphosphate.

[0020] More preferably, the retarder refers to SGR-1801 protein retarder.

[0021] Preferably, the magnetic microwave absorbing filler refers to at least one of hydroxyl iron powder, ferrite, or ultrafine steel slag powder.

[0022] More preferably, the magnetic microwave absorbing filler refers to hydroxyl iron powder, which has an iron purity of ≥99.5%, a hydroxyl content of ≥0.3%, a regular spherical morphology, and a sphericity of ≥95%.

[0023] Preferably, in (1), the weight ratio of furfuryl methacrylate, benzyl dithiobenzoate, azobisisobutyronitrile, anhydrous DMF and methanol is 1:0.03-0.05:0.008-0.012:7-9:8-12.

[0024] Preferably, in (2), polymethyl methacrylate, 2-acrylamido-2-methylpropionic acid, azobisisobutyronitrile, anhydrous DMF and methanol are in a weight ratio of 1:2.8-3.2:0.03-0.04:10-15:15-25.

[0025] Preferably, the few-layer graphene powder in (3) has 1-5 layers, a sheet diameter of 1-5 μm, and a specific surface area of ​​300-500 m². 2 / g, carbon purity ≥99%.

[0026] Preferably, in step (3), the dry few-layer graphene powder, the pre-hydrolyzed N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and N-maleimide glycine are in a weight ratio of 1:0.01-0.03:0.02-0.04.

[0027] Preferably, the ball milling conditions in (3) are as follows: using zirconia grinding balls with a diameter of 3 mm, a ball-to-material ratio of 5:1, and a rotation speed of 200-260 rpm.

[0028] Preferably, the centrifugal speed in (3) is 8000-10000 rpm.

[0029] Preferably, in (4), the modified graphene with edge-oriented grafted maleimide, anhydrous tetrahydrofuran, dual-anchored block copolymer and hydroquinone monomethyl ether are in a weight ratio of 1:180-220:0.2-0.5:0.001-0.005.

[0030] Preferably, the centrifugation speed in (4) is 8000-12000 rpm.

[0031] Furthermore, the present invention also provides a method for preparing a graphene-modified gypsum-based microwave absorbing material, comprising the following steps:

[0032] S1. Add the modified graphene to water and stir at 60-120 rpm for 10-30 min to obtain a graphene dispersion;

[0033] S2. Add gypsum cementitious material, water-reducing agent, retarder, and magnetic microwave absorbing filler to a dry powder mixer and dry mix at 150-300 rpm for 1-2 minutes to obtain dry powder.

[0034] S3. Add the dry-mixed powder to the graphene dispersion and mechanically stir for 1-3 minutes at a rotation speed of 60-130 rpm and a revolution speed of 120-260 rpm to obtain the graphene-modified gypsum-based microwave absorbing material.

[0035] Preferably, the mechanism of action of the graphene-modified gypsum-based microwave absorbing material of the present invention is explained as follows:

[0036] This invention addresses the core challenges of graphene's tendency to aggregate and poor dispersion stability in highly alkaline gypsum systems with high calcium ion concentrations through edge-specific Diels-Alder click chemistry grafting and a dual-anchored block copolymer molecular design. By employing low-energy mechanochemistry and silane coupling agent-directed modification, maleimide active sites are introduced only at the graphene edges, thus fully preserving the sp0 of the graphene basal surface. 2 A conjugated structure, followed by a [4+2] cycloaddition click reaction, allows for precise and covalent grafting of the bi-anchored block copolymer onto the edge of graphene, avoiding the etching and structural damage to the graphene substrate caused by existing oxidation modification techniques. In the grafted bi-block copolymer, the poly-2-acrylamido-2-methylpropionic acid segments are densely distributed with phosphonic acid groups. These groups can react with the Ca2+ continuously released during gypsum hydration. 2+ Stable coordination chelate bonds are formed, achieving molecular-level bridging between graphene sheets and gypsum hydration crystals, structurally preventing the sedimentation and aggregation of graphene sheets. On the other hand, ionization can occur in the aqueous phase of gypsum slurry, forming a continuous hydration layer and generating strong steric hindrance and electrostatic repulsion. Thermodynamically, this suppresses the π-π stacking effect between two-dimensional graphene sheets, ensuring a uniform and stable dispersion of graphene throughout the gypsum hydration process, laying the core structural foundation for the continuous construction of a three-dimensional electromagnetic loss network.

[0037] This invention leverages the synergistic effect of dielectric and magnetic loss in modified graphene and magnetic absorber fillers to achieve efficient absorption of electromagnetic waves across the entire 2-18 GHz frequency band. The modified graphene, uniformly dispersed in a gypsum matrix, exhibits high absorption efficiency due to its intact spline surface. 2 The conjugated structure fully retains the intrinsic high electron mobility and dielectric loss capability. Under the action of an alternating electromagnetic field, the continuous three-dimensional conductive network formed by the overlapping of graphene sheets can induce strong conductivity loss. At the same time, structural defects at the edges of graphene and grafted polar block copolymers generate a large amount of interfacial polarization and dipole reversal polarization, which convert electromagnetic energy into heat energy dissipation through polarization relaxation effect, constituting the core source of dielectric loss in the material. The composite magnetic absorbing filler provides magnetic loss capability that is highly matched with dielectric loss through hysteresis loss, natural resonance and eddy current loss effects, forming a full-band loss synergy with modified graphene, especially compensating for the absorption shortcomings of the pure graphene system in the low-frequency range.

[0038] In this invention, the phosphonic acid groups in the side chains of the dual-anchored block copolymer react with Ca...2+ The dynamic chelation effect can regulate the nucleation and growth rate of gypsum dihydrate crystals, avoiding the problems of disordered gypsum hydration process, abnormal setting time, and insufficient early strength caused by increased graphene content. Simultaneously, it can form a synergistic effect with the gypsum-specific retarder compounded in the system, regulating the construction window of gypsum slurry and adapting to different engineering application scenarios. Uniformly dispersed two-dimensional graphene sheets, through edge-grafted block copolymers, form an interpenetrating and interlocking three-dimensional network structure with the needle-like gypsum dihydrate crystals generated by gypsum hydration. The graphene sheets can effectively fill the pores and microcracks of the gypsum matrix. Simultaneously, through classic toughening mechanisms such as crack bridging, crack deflection, and sheet pull-out, it dissipates the energy under external forces, significantly improving the flexural, compressive strength, and crack resistance of the gypsum matrix. Furthermore, the edge-grafted double-anchored block copolymer significantly improved the interfacial compatibility between graphene and the gypsum hydration matrix, eliminated interfacial defects between graphene and the matrix, further enhanced the density and long-term service stability of the gypsum matrix, and ultimately achieved synergistic optimization of material function and structural performance.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. This invention addresses the core problem of graphene's tendency to aggregate in gypsum systems by employing edge-selective grafting modification and the molecular design of dual-anchored block copolymers. The dual-anchored block copolymers are precisely grafted onto the edges of graphene via DA click chemistry, thus fully preserving the basal surface sp... 2 The conjugated structure and intrinsic dielectric loss properties, combined with the chelation effect of phosphonic acid groups with calcium ions in gypsum hydration crystals, and the steric hindrance and electrostatic repulsion effect, enable graphene to be uniformly and stably dispersed throughout the gypsum hydration process, avoiding sheet aggregation and sedimentation. This provides a structural basis for constructing a continuous three-dimensional electromagnetic loss network and significantly improves the uniformity and stability of the material's wave absorption performance.

[0041] 2. This invention achieves efficient absorption of electromagnetic waves by relying on the synergistic effect of dielectric and magnetic losses of modified graphene and magnetic absorbing filler. Uniformly dispersed graphene constructs a continuous conductive network, dissipating electromagnetic energy through conductivity loss and polarization relaxation loss. The magnetic absorbing filler provides hysteresis loss and natural resonance loss. The precise matching of the two achieves impedance balance, meeting the electromagnetic protection requirements of different scenarios.

[0042] 3. This invention achieves synergistic optimization of microwave absorption performance and mechanical properties, breaking the antagonistic effect of "functional improvement and structural strength reduction". Edge-grafted graphene and needle-like dihydrate gypsum crystals form an interpenetrating interlocking network, dissipating external forces through mechanisms such as crack bridging and sheet pull-out. The magnetic microwave absorbing filler plays a compacting role, filling the gaps between crystals and reducing structural defects. At the same time, the block copolymer improves the interfacial compatibility between graphene and gypsum matrix, eliminating interfacial defects. This allows the material to have excellent microwave absorption performance while significantly improving flexural strength, compressive strength, and crack resistance, meeting the service structural requirements of building materials.

[0043] 4. This invention significantly improves the water resistance and long-term service stability of gypsum-based microwave absorbing materials. The phosphonic acid groups on the side chains of the dual-anchored block copolymer form stable coordination chelates with calcium ions, optimizing the crystal growth morphology of dihydrate gypsum and reducing capillary pores and hydrophilic interfaces between crystals. At the same time, uniformly dispersed graphene sheets fill the interconnected pores of the matrix, blocking water penetration channels and effectively improving the inherent defect of poor water resistance in the gypsum matrix. This allows the material to maintain stable microwave absorption and mechanical properties in humid environments, expanding its application range.

[0044] 5. This invention possesses excellent prospects for industrialization and promotion, with a simple, controllable process and manageable costs. The raw materials used, such as β-hemihydrate building gypsum and hydroxyl iron powder, are commonly used in the construction industry, widely available and easily procured. The modified graphene preparation and microwave absorbing slurry molding processes are compatible with existing gypsum building material industrial production lines, requiring no additional specialized equipment. The production process is green and environmentally friendly, generating no harmful byproducts. Furthermore, the functional filler dosage is reasonable, and the cost increase is controllable, enabling large-scale mass production and providing a feasible solution for the engineering application of building electromagnetic protection materials. Detailed Implementation

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0046] Preparation Example 1: The specific preparation method of modified graphene includes the following steps:

[0047] (1) Under nitrogen protection, 10g of furfuryl methacrylate, 0.3g of benzyl dithiobenzoate and 0.08g of azobisisobutyronitrile were added to 70g of anhydrous DMF, heated to 70℃, stirred for 5h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to 80g of 0℃ methanol to precipitate. The precipitate was washed with deionized water and dried to obtain polyfurfuryl methacrylate.

[0048] (2) Under nitrogen protection, 10g of polymethyl methacrylate, 28g of 2-acrylamido-2-methylpropionic acid and 0.3g of azobisisobutyronitrile were added to 100g of anhydrous DMF, heated to 80℃, stirred for 6h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to 150g of 0℃ methanol to precipitate. The precipitate was washed with deionized water and dried to obtain a bi-anchored block copolymer.

[0049] (3) Few-layer graphene powder (1-5 layers, sheet diameter 1-5μm, specific surface area 300-500m²) 2 The graphene powder (with a carbon purity ≥ 99%) was placed in a vacuum drying oven at 70℃ for 8 hours to obtain dried few-layer graphene powder. Then, under nitrogen protection, 10g of dried few-layer graphene powder, 0.1g of pre-hydrolyzed N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 0.2g of N-maleimide glycine were added to a planetary ball mill. Zirconia grinding balls with a diameter of 3mm were used, the ball-to-material ratio was 5:1, the rotation speed was 200rpm, and the milling was carried out at room temperature for 2 hours. After the milling was completed, the product was prepared into a 5mg / ml suspension with anhydrous ethanol and centrifuged at 8000rpm for 5min. The supernatant was discarded, and the precipitate was washed and centrifuged three times with anhydrous ethanol. Then, it was freeze-dried to obtain modified graphene with edge-oriented grafting of maleimide.

[0050] (4) Under nitrogen protection, 10g of modified graphene with edge-oriented maleimide grafted onto the surface was added to 1.8kg of anhydrous tetrahydrofuran and stirred for 5min. Then, 2g of double-anchored block copolymer and 0.1g of hydroquinone monomethyl ether were added. The temperature was raised to 60℃ and stirred for 12h. After cooling to room temperature, the mixture was centrifuged at 8000rpm for 5min. The supernatant was discarded. The precipitate was washed and centrifuged three times with anhydrous ethanol and then freeze-dried to obtain modified graphene.

[0051] Preparation Example 2: The specific preparation method of modified graphene includes the following steps:

[0052] (1) Under nitrogen protection, 10g of furfuryl methacrylate, 0.4g of benzyl dithiobenzoate and 0.1g of azobisisobutyronitrile were added to 80g of anhydrous DMF, heated to 75℃, stirred for 6h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to 100g of 0℃ methanol to precipitate. The precipitate was washed with deionized water and dried to obtain polyfurfuryl methacrylate.

[0053] (2) Under nitrogen protection, 10g of polymethyl methacrylate, 30g of 2-acrylamido-2-methylpropionic acid and 0.35g of azobisisobutyronitrile were added to 120g of anhydrous DMF, heated to 85℃, stirred for 8h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to 200g of 0℃ methanol to precipitate. The precipitate was washed with deionized water and dried to obtain a bi-anchored block copolymer.

[0054] (3) Few-layer graphene powder (1-5 layers, sheet diameter 1-5μm, specific surface area 300-500m²) 2 The graphene powder (with a carbon purity ≥ 99%) was placed in a vacuum drying oven at 75℃ for 10 hours to obtain dried few-layer graphene powder. Then, under nitrogen protection, 10 g of dried few-layer graphene powder, 0.2 g of pre-hydrolyzed N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 0.3 g of N-maleimide glycine were added to a planetary ball mill. Zirconia grinding balls with a diameter of 3 mm were used, the ball-to-material ratio was 5:1, the rotation speed was 230 rpm, and the milling was carried out at room temperature for 3 hours. After the milling was completed, the product was prepared into a 5 mg / ml suspension with anhydrous ethanol and centrifuged at 9000 rpm for 8 minutes. The supernatant was discarded, and the precipitate was washed and centrifuged three times with anhydrous ethanol. Then, it was freeze-dried to obtain modified graphene with edge-oriented grafting of maleimide.

[0055] (4) Under nitrogen protection, 10g of modified graphene with edge-oriented maleimide grafted onto the surface was added to 2kg of anhydrous tetrahydrofuran and stirred for 8min. Then, 3g of double-anchored block copolymer and 0.03g of hydroquinone monomethyl ether were added. The temperature was raised to 65℃ and stirred for 15h. After cooling to room temperature, the mixture was centrifuged at 10000rpm for 8min. The supernatant was discarded. The precipitate was washed and centrifuged three times with anhydrous ethanol and then freeze-dried to obtain modified graphene.

[0056] Preparation Example 3: The specific preparation method of modified graphene includes the following steps:

[0057] (1) Under nitrogen protection, 10g of furfuryl methacrylate, 0.5g of benzyl dithiobenzoate and 0.12g of azobisisobutyronitrile were added to 90g of anhydrous DMF, heated to 80℃, stirred for 8h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to 120g of 0℃ methanol to precipitate. The precipitate was washed with deionized water and dried to obtain polyfurfuryl methacrylate.

[0058] (2) Under nitrogen protection, 10g of polymethyl methacrylate, 32g of 2-acrylamido-2-methylpropionic acid and 0.4g of azobisisobutyronitrile were added to 150g of anhydrous DMF, heated to 90℃, stirred for 10h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to 250g of 0℃ methanol to precipitate. The precipitate was washed with deionized water and dried to obtain a bi-anchored block copolymer.

[0059] (3) Few-layer graphene powder (1-5 layers, sheet diameter 1-5μm, specific surface area 300-500m²) 2 The graphene powder (with a carbon purity ≥ 99%) was placed in a vacuum drying oven at 80℃ for 12 hours to obtain dried few-layer graphene powder. Then, under nitrogen protection, 10 g of dried few-layer graphene powder, 0.3 g of pre-hydrolyzed N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 0.4 g of N-maleimide glycine were added to a planetary ball mill. Zirconia grinding balls with a diameter of 3 mm were used, the ball-to-material ratio was 5:1, the rotation speed was 260 rpm, and the milling was carried out at room temperature for 4 hours. After the milling was completed, the product was prepared into a 5 mg / ml suspension with anhydrous ethanol and centrifuged at 10000 rpm for 10 min. The supernatant was discarded, and the precipitate was washed and centrifuged three times with anhydrous ethanol. Then, it was freeze-dried to obtain modified graphene with edge-oriented grafting of maleimide.

[0060] (4) Under nitrogen protection, 10g of modified graphene with edge-oriented maleimide grafted onto the surface was added to 2.2kg of anhydrous tetrahydrofuran and stirred for 10min. Then, 5g of double-anchored block copolymer and 0.05g of hydroquinone monomethyl ether were added. The temperature was raised to 70℃ and stirred for 18h. After cooling to room temperature, the mixture was centrifuged at 12000rpm for 10min. The supernatant was discarded. The precipitate was washed and centrifuged three times with anhydrous ethanol and then freeze-dried to obtain modified graphene.

[0061] Comparative Preparation Example 1: The specific preparation method of modified graphene includes the following steps:

[0062] (1) Under nitrogen protection, 10g of furfuryl methacrylate, 0.5g of benzyl dithiobenzoate and 0.12g of azobisisobutyronitrile were added to 90g of anhydrous DMF, heated to 80℃, stirred for 8h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to 120g of 0℃ methanol to precipitate. The precipitate was washed with deionized water and dried to obtain polyfurfuryl methacrylate.

[0063] (2) Under nitrogen protection, 10g of polymethyl methacrylate, 32g of 2-acrylamido-2-methylpropionic acid and 0.4g of azobisisobutyronitrile were added to 150g of anhydrous DMF, heated to 90℃, stirred for 10h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to 250g of 0℃ methanol to precipitate. The precipitate was washed with deionized water and dried to obtain a bi-anchored block copolymer.

[0064] (3) Take 10g of few-layer graphene powder (1-5 layers, sheet diameter 1-5μm, specific surface area 300-500m²) 2 / g (carbon purity ≥99%) was added to 500ml of mixed acid solution (concentrated sulfuric acid: concentrated nitric acid volume ratio 3:1), stirred at 300rpm for 30min to disperse evenly, and heated to 80℃ and refluxed for 4h; after the reaction was completed, the mixture was slowly added dropwise to deionized water for dilution, and repeatedly centrifuged and washed with deionized water until the pH of the filtrate was neutral, and then freeze-dried to obtain mixed acid modified graphene;

[0065] (4) 10g of mixed acid modified graphene, 0.4g of N-maleimide glycine, 0.3g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.1g of N-hydroxysuccinimide were added to 2kg of anhydrous DMF. The mixture was stirred at 300rpm for 30min under nitrogen protection to disperse it evenly. Then the temperature was raised to 60℃ and stirred for 15h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 10000rpm for 8min. The supernatant was discarded, and the precipitate was washed with anhydrous ethanol and centrifuged 3 times. After freeze-drying, maleimide grafted modified graphene was obtained.

[0066] (5) Under nitrogen protection, 10g of maleimide-grafted modified graphene was added to 2.2kg of anhydrous tetrahydrofuran and stirred for 10min. Then, 5g of double-anchored block copolymer and 0.05g of hydroquinone monomethyl ether were added. The temperature was raised to 70℃ and stirred for 18h. After cooling to room temperature, the mixture was centrifuged at 12000rpm for 10min. The supernatant was discarded. The precipitate was washed and centrifuged three times with anhydrous ethanol and then freeze-dried to obtain modified graphene.

[0067] Comparative Preparation Example 2: The specific preparation method of modified graphene includes the following steps:

[0068] (1) Under nitrogen protection, 10g of furfury methacrylate, 30g of 2-acrylamido-2-methylpropionic acid and 0.35g of azobisisobutyronitrile were added to 120g of anhydrous DMF, heated to 85℃, stirred for 8h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to 200g of 0℃ methanol to precipitate. The precipitate was washed with deionized water and dried to obtain a random copolymer.

[0069] (3) Few-layer graphene powder (1-5 layers, sheet diameter 1-5μm, specific surface area 300-500m²) 2 The graphene powder (with a carbon purity ≥ 99%) was placed in a vacuum drying oven at 75℃ for 10 hours to obtain dried few-layer graphene powder. Then, under nitrogen protection, 10 g of dried few-layer graphene powder, 0.2 g of pre-hydrolyzed N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and 0.3 g of N-maleimide glycine were added to a planetary ball mill. Zirconia grinding balls with a diameter of 3 mm were used, the ball-to-material ratio was 5:1, the rotation speed was 230 rpm, and the milling was carried out at room temperature for 3 hours. After the milling was completed, the product was prepared into a 5 mg / ml suspension with anhydrous ethanol and centrifuged at 9000 rpm for 8 minutes. The supernatant was discarded, and the precipitate was washed and centrifuged three times with anhydrous ethanol. Then, it was freeze-dried to obtain modified graphene with edge-oriented grafting of maleimide.

[0070] (4) Under nitrogen protection, 10g of modified graphene with edge-oriented maleimide grafted onto the surface was added to 2kg of anhydrous tetrahydrofuran and stirred for 8min. Then, 3g of random copolymer and 0.03g of hydroquinone monomethyl ether were added. The temperature was raised to 65℃ and stirred for 15h. After cooling to room temperature, the mixture was centrifuged at 10000rpm for 8min. The supernatant was discarded. The precipitate was washed and centrifuged three times with anhydrous ethanol and then freeze-dried to obtain modified graphene.

[0071] Comparative preparation example 3: The difference between comparative preparation example 3 and preparation example 2 is that steps (1)-(2) and (4) are omitted, and the modified graphene is only subjected to maleimide grafting treatment.

[0072] Example 1: A specific preparation method of a graphene-modified gypsum-based microwave absorbing material, comprising the following steps:

[0073] S1. Add 2g of the modified graphene prepared according to Preparation Example 1 to 500g of water and stir at 60rpm for 10min to obtain a graphene dispersion;

[0074] S2. Add 1 kg of β-hemihydrate building gypsum, 1 g of gypsum polycarboxylate superplasticizer (solid content 35%-40%, water reduction rate ≥30%), 1 g of SGR-1801 protein retarder, and 100 g of hydroxyl iron powder (iron purity ≥99.5%, hydroxyl content ≥0.3%, microstructure is regular spherical, sphericity ≥95%) to a dry powder mixer and dry mix at 150 rpm for 1 min to obtain dry mixed powder.

[0075] S3. Add the dry-mixed powder to the graphene dispersion and mechanically stir for 1 minute at a rotation speed of 60 rpm and a revolution speed of 120 rpm to obtain the graphene-modified gypsum-based microwave absorbing material.

[0076] Example 2: A specific preparation method of a graphene-modified gypsum-based microwave absorbing material, comprising the following steps:

[0077] S1. Add 6g of the modified graphene prepared according to Preparation Example 2 to 650g of water and stir at 90rpm for 20min to obtain a graphene dispersion;

[0078] S2. Add 1 kg of β-hemihydrate building gypsum, 2 g of gypsum polycarboxylate superplasticizer (solid content 35%-40%, water reduction rate ≥30%), 2 g of SGR-1801 protein retarder, and 150 g of hydroxyl iron powder (iron purity ≥99.5%, hydroxyl content ≥0.3%, microstructure is regular spherical, sphericity ≥95%) to a dry powder mixer and dry mix at 200 rpm for 1.5 min to obtain dry mixed powder.

[0079] S3. Add the dry-mixed powder to the graphene dispersion and mechanically stir for 2 minutes at a rotation speed of 100 rpm and a revolution speed of 190 rpm to obtain the graphene-modified gypsum-based microwave absorbing material.

[0080] Example 3: A specific preparation method of a graphene-modified gypsum-based microwave absorbing material, comprising the following steps:

[0081] S1. Add 10g of the modified graphene prepared according to Preparation Example 3 to water and stir at 120rpm for 30min to obtain a graphene dispersion;

[0082] S2. Add 1 kg of β-hemihydrate building gypsum, 3 g of gypsum polycarboxylate superplasticizer (solid content 35%-40%, water reduction rate ≥30%), 3 g of SGR-1801 protein retarder, and 200 g of hydroxyl iron powder (iron purity ≥99.5%, hydroxyl content ≥0.3%, microstructure is regular spherical, sphericity ≥95%) to a dry powder mixer and dry mix at 300 rpm for 2 min to obtain dry mixed powder.

[0083] S3. Add the dry-mixed powder to the graphene dispersion and mechanically stir for 3 minutes at a rotation speed of 130 rpm and a revolution speed of 260 rpm to obtain the graphene-modified gypsum-based microwave absorbing material.

[0084] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the modified graphene prepared according to Preparation Example 2 is replaced with the modified graphene prepared according to Comparative Preparation Example 1.

[0085] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the modified graphene prepared according to Preparation Example 2 is replaced with the modified graphene prepared according to Comparative Preparation Example 2.

[0086] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the modified graphene prepared according to Preparation Example 2 is replaced with the modified graphene prepared according to Comparative Preparation Example 3.

[0087] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that the modified graphene prepared according to Preparation Example 2 was replaced with unmodified few-layer graphene.

[0088] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that no modified graphene is added.

[0089] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that hydroxyl iron powder is not added.

[0090] Performance testing:

[0091] The performance of the gypsum composite materials obtained in the above embodiments and comparative examples was tested, and the main performance test results are shown in Table 1.

[0092] Table 1 Performance Test Results

[0093]

[0094] Data Analysis:

[0095] As can be seen from the performance test data in Table 1, the graphene-modified gypsum-based microwave absorbing materials prepared by the technical solution of the present invention in each embodiment are significantly better than the comparative examples in terms of core performance dimensions such as mechanical strength, electromagnetic shielding effectiveness, and water resistance, thanks to the edge-selective grafting of modified graphene, the dispersion and strengthening effect of the double-anchored block copolymer, and the dielectric-magnetic loss synergistic effect of modified graphene and hydroxyl iron powder. Moreover, the performance is balanced without obvious shortcomings; among them, the comprehensive performance of Example 2 is the best.

[0096] Example 2 exhibits a reasonable bulk density and optimal pore structure, likely due to the uniform dispersion of the modified graphene and the micro-aggregate compaction effect of the hydroxyl iron powder: the edge-grafted double-anchored block copolymer ensures uniform dispersion of graphene throughout the gypsum hydration process, avoiding additional pores introduced by agglomeration. Meanwhile, the spherical hydroxyl iron powder precisely fills the interstices of the gypsum crystals, further optimizing the matrix density and keeping the porosity within a reasonable range, achieving a balance between bulk density and structural stability. Comparing the comparative examples, Comparative Example 1 uses mixed acid oxidatively modified graphene, and its basal surface sp... 2The structure was disrupted, and the random distribution of grafting sites led to graphene agglomeration, introducing a large number of interfacial pores into the matrix, resulting in a significant increase in porosity. In Comparative Example 2, the random copolymer had a chaotic distribution of functional groups, which shielded the furan ring reaction sites, reduced DA grafting efficiency, and insufficient graphene dispersion, resulting in a higher porosity than in Example 2. In Comparative Example 3, only maleimide grafting was performed on graphene, lacking the dispersion modification of the dual-anchored block copolymer, resulting in severe graphene agglomeration and the formation of a large number of interconnected pores, with the highest porosity among all groups. In Comparative Example 4, the unmodified graphene showed significant agglomeration due to the interlayer π-π stacking effect, which could not uniformly fill the pores, resulting in a high porosity. In Comparative Example 5, no modified graphene was added, so there was neither dense filling by functional fillers nor optimization of crystal growth by the dispersion system, resulting in high porosity and the lowest bulk density. In Comparative Example 6, lacking the micro-aggregate compaction effect of hydroxyl iron powder, it relied solely on the filling effect of graphene, resulting in a higher porosity than in Example 2 and a relatively low bulk density.

[0097] Example 2 exhibits the best mechanical properties, primarily because the edge-grafted modified graphene forms a continuous two-dimensional sheet network in the gypsum matrix, interpenetrating and locking with needle-like dihydrate gypsum crystals. It dissipates external force energy through mechanisms such as crack bridging and sheet pull-out. Meanwhile, the micro-aggregate effect of hydroxyl iron powder further fills the crystal gaps and reduces structural defects. The two work together to achieve a significant improvement in mechanical properties. The mechanical properties of all comparative examples were significantly lower than those of Example 2. The specific reasons are as follows: The mixed acid graphene oxide in Comparative Example 1 had a damaged basal structure and severe agglomeration, which prevented it from forming a continuous reinforcing network. It could only play a limited filling role, resulting in a slight increase in strength. The random copolymer in Comparative Example 2 caused mutual interference of functional groups, and the graphene grafting rate and dispersibility were insufficient, which greatly weakened the reinforcing effect. Comparative Example 3 had the most severe graphene agglomeration due to the lack of modification with the double-anchored block copolymer. It not only failed to reinforce but also introduced a large number of stress concentration points in the matrix, resulting in the lowest mechanical properties. The unmodified graphene in Comparative Example 4 had large particles formed by agglomeration, which had poor compatibility with the gypsum matrix interface and was difficult to form an effective bond. The reinforcing effect was far inferior to that of Example 2. Comparative Example 5 did not add modified graphene and relied solely on the crystal strength of the gypsum itself. Without an additional reinforcing mechanism, the strength was low. Comparative Example 6 lacked the micro-aggregate compaction effect of hydroxyl iron powder, and the matrix porosity was relatively high, resulting in mechanical properties lower than those of Example 2.

[0098] Example 2 exhibits the best electromagnetic shielding performance, which may be because the uniformly dispersed modified graphene overlaps with each other in the gypsum matrix to form a defect-free continuous three-dimensional conductive network. This network reflects electromagnetic waves through strong conductivity loss, while the grafted polar block copolymer induces interfacial polarization and dipole reversal polarization, further dissipating electromagnetic energy. Meanwhile, hydroxyl iron powder provides strong magnetic loss through hysteresis loss and natural resonance loss, which, together with dielectric loss, forms a full-band synergy, significantly improving the shielding effect. The electromagnetic shielding effectiveness of each comparative example was significantly insufficient: In Comparative Example 1, the mixed acid graphene oxide agglomeration led to the breakage of the conductive network, and the destruction of the basal structure reduced the dielectric loss capacity, weakening the synergistic effect with hydroxyl iron powder, resulting in a significant decrease in shielding effectiveness; In Comparative Example 2, the random copolymer resulted in insufficient graphene grafting, poor dispersion, poor continuity of the conductive network, and insufficient synergy between dielectric and magnetic losses, leading to low shielding effectiveness; In Comparative Example 3, due to severe graphene agglomeration, the conductive network was completely broken, and only a small amount of dispersed graphene sheets could play a weak role, resulting in the lowest shielding effectiveness; In Comparative Example 4, the unmodified graphene agglomerated to form isolated particles, making it impossible to construct a continuous conductive network, and the shielding effectiveness was only about half that of Example 2; In Comparative Example 5, no modified graphene was added, and the gypsum matrix itself had no conductivity, so it could only rely on the weak dielectric properties of gypsum to achieve a very low shielding effect; In Comparative Example 6, lacking the magnetic loss contribution of hydroxyl iron powder, it relied solely on the dielectric loss of graphene, failing to achieve synergistic loss across the entire frequency band, resulting in a significant decrease in shielding effectiveness.

[0099] The thermal conductivity of Example 2 is within a good range, which is the result of the synergistic effect of matrix density and high thermal conductivity filler: the uniformly dispersed modified graphene and hydroxyl iron powder form continuous thermal conduction pathways in the matrix, while the optimized pore structure reduces the obstruction of heat transfer by pores, making the thermal conductivity meet the service requirements of microwave absorbing materials. The thermal conductivity of each comparative example is lower than that of Example 2, but this is not the result of performance optimization, but rather due to structural defects: Comparative examples 1-4 have a large number of discrete pores and interfacial gaps in the matrix due to graphene agglomeration, forming significant interfacial thermal resistance and hindering heat transfer; Comparative example 5 does not add graphene and lacks the main thermally conductive reinforcing phase, resulting in the lowest thermal conductivity; Comparative example 6 lacks the thermal conduction pathway construction of hydroxyl iron powder and relies solely on the thermal conductivity of the gypsum matrix itself, resulting in a low thermal conductivity. These low thermal conductivity characteristics are all due to material structural defects and have no practical application value.

[0100] Example 2 exhibited the highest softening coefficient, which is attributed to the interfacial modification and structural optimization of the gypsum matrix by the dual-anchored block copolymer: the phosphonic acid groups on the side chains of the block copolymer react with the Ca released during gypsum hydration. 2+Stable coordination chelate bonds were formed, optimizing the growth morphology of gypsum dihydrate crystals and reducing capillary pores and hydrophilic interfaces between crystals. Simultaneously, uniformly dispersed graphene sheets filled the interconnected pores in the matrix, blocking water penetration channels and significantly improving water resistance. The softening coefficients of each comparative example were significantly lower than those of Example 2: Comparative Examples 1-4, due to insufficient graphene dispersion or agglomeration, formed numerous interconnected pores in the matrix, allowing water to easily penetrate the interior along these pores, leading to water erosion of the gypsum crystals and a reduced softening coefficient; Comparative Example 3, which only underwent maleimide grafting and lacked the interface modification of block copolymers, resulted in large-sized pores formed by agglomeration, making water penetration easier and resulting in an extremely low softening coefficient; Comparative Example 5, without modified graphene, lacked interface optimization and pore-filling effects, making the gypsum crystals easily damaged by water and resulting in a low softening coefficient; Comparative Example 6, lacking the dense filling of hydroxyl iron powder, had more interconnected pores, resulting in low water penetration resistance and a softening coefficient lower than that of Example 2.

[0101] 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 graphene-modified gypsum-based microwave absorbing material, characterized in that, It comprises the following components by weight: gypsum gel material: 100 parts, modified graphene: 0.2-1 parts, water-reducing agent: 0.1-0.3 parts, retarder: 0.1-0.3 parts, magnetic microwave absorbing filler: 10-20 parts, and water: 50-80 parts; The modified graphene is prepared as follows: (1) Under nitrogen protection, furfuryl methacrylate, benzyl dithiobenzoate and azobisisobutyronitrile were added to anhydrous DMF, heated to 70-80℃, stirred for 5-8h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to methanol at 0℃ to precipitate. The precipitate was washed with deionized water and dried to obtain polyfurfuryl methacrylate. (2) Under nitrogen protection, polyfurfury methacrylate, 2-acrylamido-2-methylpropionic acid and azobisisobutyronitrile were added to anhydrous DMF, heated to 80-90℃, stirred for 6-10h, and then placed in an ice-water bath to cool to room temperature. The reaction solution was then added to methanol at 0℃ to precipitate. The precipitate was washed with deionized water and dried to obtain a bi-anchored block copolymer. (3) Place the few-layer graphene powder in a vacuum drying oven at 70-80℃ for 8-12h to obtain dry few-layer graphene powder. Then, under nitrogen protection, add the dry few-layer graphene powder, pre-hydrolyzed N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and N-maleimide glycine into a planetary ball mill and ball mill at room temperature for 2-4h. After ball milling, prepare a 5mg / ml suspension with anhydrous ethanol, centrifuge for 5-10min, discard the supernatant, and wash and centrifuge the precipitate three times with anhydrous ethanol. Then freeze-dry to obtain modified graphene with edge-oriented grafted maleimide. (4) Under nitrogen protection, the modified graphene with maleimide grafted at the edge was added to anhydrous tetrahydrofuran and stirred for 5-10 min. Then, the double-anchored block copolymer and hydroquinone monomethyl ether were added, the temperature was raised to 60-70℃, and the reaction was stirred for 12-18 h. After cooling to room temperature, the mixture was centrifuged for 5-10 min, the supernatant was discarded, and the precipitate was washed and centrifuged 3 times with anhydrous ethanol. Then, it was freeze-dried to obtain the modified graphene.

2. The graphene-modified gypsum-based microwave absorbing material according to claim 1, characterized in that, The gypsum gel material refers to at least one of β-hemihydrate building gypsum or α-hemihydrate gypsum.

3. The graphene-modified gypsum-based microwave absorbing material according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent for gypsum, with a solid content of 35%-40% and a water reduction rate of ≥30%.

4. The graphene-modified gypsum-based microwave absorbing material according to claim 1, characterized in that, The retarder refers to at least one of SGR-1801 protein retarder, citric acid, or sodium polyphosphate.

5. The graphene-modified gypsum-based microwave absorbing material according to claim 1, characterized in that, The magnetic microwave absorbing filler refers to at least one of hydroxyl iron powder, ferrite, or ultrafine steel slag powder.

6. The graphene-modified gypsum-based microwave absorbing material according to claim 1, characterized in that, In (1), the weight ratio of furfuryl methacrylate, benzyl dithiobenzoate, azobisisobutyronitrile, anhydrous DMF and methanol is 1:0.03-0.05:0.008-0.012:7-9:8-12.

7. The graphene-modified gypsum-based microwave absorbing material according to claim 1, characterized in that, In (2), polymethyl methacrylate, 2-acrylamido-2-methylpropionic acid, azobisisobutyronitrile, anhydrous DMF and methanol are in a weight ratio of 1:2.8-3.2:0.03-0.04:10-15:15-25.

8. The graphene-modified gypsum-based microwave absorbing material according to claim 1, characterized in that, The few-layer graphene in (3) consists of 1-5 layers, with a sheet diameter of 1-5 μm and a specific surface area of ​​300-500 m². 2 / g, carbon purity ≥99%; dried few-layer graphene powder, pre-hydrolyzed N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and N-maleimide glycine in a weight ratio of 1:0.01-0.03:0.02-0.04; ball milling conditions: using zirconia grinding balls with a diameter of 3mm, ball-to-material ratio of 5:1, rotation speed of 200-260rpm; centrifugation speed of 8000-10000rpm.

9. The graphene-modified gypsum-based microwave absorbing material according to claim 1, characterized in that, In step (4), the modified graphene with edge-oriented maleimide grafting, anhydrous tetrahydrofuran, dual-anchored block copolymer and hydroquinone monomethyl ether are in a weight ratio of 1:180-220:0.2-0.5:0.001-0.005; the centrifugation speed is 8000-12000 rpm.

10. The method for preparing the graphene-modified gypsum-based microwave absorbing material according to any one of claims 1-9, characterized in that, Includes the following steps: S1. Add the modified graphene to water and stir at 60-120 rpm for 10-30 min to obtain a graphene dispersion; S2. Add the gypsum gel material, water-reducing agent, retarder, and magnetic microwave absorbing filler to a dry powder mixer and dry mix at 150-300 rpm for 1-2 minutes to obtain a dry powder mixture. S3. Add the dry-mixed powder to the graphene dispersion and mechanically stir for 1-3 minutes at a rotation speed of 60-130 rpm and a revolution speed of 120-260 rpm to obtain the graphene-modified gypsum-based microwave absorbing material.

Images