Homogeneous polymethacrylimide composite wave-absorbing material as well as preparation method and application thereof

Abstract

According to the homogeneous polymethacrylimide composite wave-absorbing material and the preparation method thereof provided by the invention, on one hand, the homogeneous polymethacrylimide composite wave-absorbing foam material adopts a copolymerizable foaming monomer to participate in copolymerization, so that the synthesized polymethacrylimide foam has a uniform polyhedral closed-cell structure; on the other hand, the wave absorbing agent is added, the wave absorbing agents with different structures and morphologies are selected to construct a gradient distribution structure to generate a synergistic effect, and the wave absorbing performance of the obtained homogeneous polymethacrylimide composite wave absorbing material is further improved in combination with the foam structure of the polymethacrylimide foam.

Description

Technical Field

[0001] The invention belongs to the technical field of wave absorbing materials, and in particular relates to a homogeneous polymethacrylimide composite wave absorbing material and a preparation method thereof. Background Art

[0002] With the rapid development of information technology, aerospace, and communication equipment, the problem of electromagnetic radiation interference is becoming increasingly serious. Therefore, it is necessary to study new absorbing materials. Polymethacrylimide foam is a cross-linked hard closed-cell material containing a hexavalent imide ring. It has the advantages of low density, high strength, heat resistance and chemical stability. It is an ideal core material for foam sandwich structure composite materials. At the same time, polymethacrylimide foam composite materials with absorbing function have the advantages of light weight, broadband, high efficiency, and compatibility. It has broad application prospects as radar absorbing materials in the fields of aerospace and communication equipment.

[0003] At present, polymethacrylimide foam, which can be used as high-temperature resistant structural materials and wave-transmitting materials, is mainly imported from abroad and is expensive. In order to meet the demand for polymethacrylimide foam in aviation, drones and radar detection, although a lot of research on wave-absorbing polymethacrylimide foam materials has been carried out in China, the wave-absorbing performance is far behind that of imported foams and is still in the exploratory stage; at the same time, the mechanical properties of polymethacrylimide foam obtained by existing technology decrease significantly after adding absorbents and other additives, making it difficult to meet the mechanical properties requirements of materials in aerospace, rail transit, ships, etc. For example, CN118027282A discloses a homogeneous absorbing polymethacrylimide foam, in which a composite foam with good absorbing and mechanical properties is obtained by adding two additives for synergistic effect. The two additives can improve the dispersibility of the absorber to a certain extent and cross-link with the polymer matrix to avoid the problem of mechanical property degradation caused by sedimentation. However, due to the influence of the additives, the mechanical properties of the obtained foam are not significantly reduced, but the improvement is not obvious. One of the reasons is that the traditional polymethacrylimide foaming process usually adopts an external foaming agent. When a large amount of absorbers and additives are added to the system, a considerable amount of foaming agent is also added to the system, which has a significant effect on the polymerization of polymethacrylimide. The prepared polymethacrylimide absorbing foam generally has the problems of poor uniformity, high density, weak mechanical properties and absorbing properties.

[0004] In addition, conductive carbon black has the advantages of light weight and high conductivity, and can be used as an absorber to improve the wave absorption performance of the foam. However, when doped alone, due to the high specific surface area, the polymerization of polymethacrylimide is affected after the conductive carbon black content reaches a certain level. At the same time, the limited doping amount causes the conductive carbon black to be distributed only in the bubble walls and bubble edges of the foam. The increase in the conductivity of the composite foam is limited, resulting in poor performance in the wave absorption and mechanical properties of the foam.

[0005] Therefore, developing a homogeneous polymethacrylimide composite absorbing material that can further improve its absorbing performance without affecting the mechanical and heat resistance of the polymethacrylimide foam material itself is still a technical problem that needs to be urgently solved in this field. Summary of the invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide a homogeneous polymethacrylimide composite absorbing material and a preparation method thereof. The homogeneous polymethacrylimide composite absorbing material has a uniform polyhedral closed-cell structure and has excellent mechanical properties, absorbing properties and heat resistance. It can be used as a functional absorbing foam interlayer material and also has the characteristics of simple process and green environmental protection.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a homogeneous polymethacrylimide composite absorbing material, wherein the raw materials of the homogeneous polymethacrylimide composite absorbing material include the following components in parts by weight:

[0009]

[0010]

[0011] The wave absorbing agent comprises a combination of carbon fiber and other carbon materials except carbon fiber.

[0012] The raw materials of the homogeneous polymethacrylimide composite absorbing material provided by the present invention include acrylonitrile monomer, methacrylic acid monomer, copolymerizable foaming monomer, absorbent, thickener, initiator and crosslinking agent. On the one hand, an "endogenous" self-foaming strategy is adopted, and the copolymerizable foaming monomer is introduced to copolymerize with acrylonitrile monomer and methacrylic acid monomer, and foaming is achieved by high-temperature thermal decomposition of thermally unstable groups contained or grafted in the polymer precursor molecular chain to release small molecular gases, and the foaming groups are uniformly distributed in the system, and no external foaming agent is required to affect the same, so that the obtained self-foaming polymethacrylimide has a uniform polyhedral closed-cell structure. On the other hand, the obtained self-foaming polymethacrylimide is used as a matrix, and absorbing materials with different structural morphologies are selected to construct a gradient distribution structure to produce a synergistic effect, and combined with the foam pore structure of the foam itself, the absorbing performance of the foam material is further improved without affecting the mechanics and heat resistance of the polymethacrylimide foam material, and finally a homogeneous polymethacrylimide composite absorbing material with light weight, high strength, high temperature resistance and excellent absorbing performance is obtained.

[0013] Wherein, the amount of the acrylonitrile monomer can be 40 parts by weight, 42 parts by weight, 44 parts by weight, 46 parts by weight, 48 parts by weight, 50 parts by weight, 52 parts by weight, 54 parts by weight, 56 parts by weight, 58 parts by weight or 60 parts by weight, etc.

[0014] The methacrylic acid monomer may be used in an amount of 20 parts by weight, 25 parts by weight, 30 parts by weight, 35 parts by weight, 40 parts by weight, 45 parts by weight, or 50 parts by weight.

[0015] The amount of the copolymerizable foaming monomer may be 5 parts by weight, 10 parts by weight, 15 parts by weight, 20 parts by weight, 25 parts by weight or 30 parts by weight.

[0016] The amount of the wave absorbing agent can be 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight or 10 parts by weight.

[0017] The thickener may be used in an amount of 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight or 5 parts by weight, etc.

[0018] The amount of the initiator used can be 0.1 parts by weight, 0.12 parts by weight, 0.14 parts by weight, 0.16 parts by weight, 0.18 parts by weight, 0.2 parts by weight, 0.22 parts by weight, 0.24 parts by weight, 0.26 parts by weight, 0.28 parts by weight or 0.3 parts by weight, etc.

[0019] The amount of the cross-linking agent can be 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight or 5 parts by weight.

[0020] The schematic diagram of the gradient distribution structure of the wave absorbing agent in the homogeneous polymethacrylimide composite wave absorbing material provided by the present invention is as follows Figure 1 As shown, it utilizes the density and structural differences of the absorber to form a concentration gradient by gravity sedimentation.

[0021] Specifically, from Figure 1 It can be seen that the surface layer of the homogeneous polymethacrylimide composite absorbing material has a small amount of absorber content and a low dielectric constant close to the air impedance, which promotes the incident wave to enter the interior of the material. The high-concentration absorber in the bottom layer realizes efficient absorption of electromagnetic waves through conductivity loss and polarization relaxation. The middle layer serves as a transition zone, which extends the electromagnetic wave transmission path through the gradient change of the dielectric constant to achieve the purpose of optimizing impedance matching. At the same time, the characteristics of various absorbers are combined to enhance multiple internal reflections and energy dissipation, and broadband absorption is achieved layer by layer through conductive loss, hysteresis loss and structural scattering, thereby optimizing impedance matching and electromagnetic wave absorption performance to meet the application requirements of different frequency bands.

[0022] Preferably, the copolymerizable foaming monomer includes any one of tert-butyl methacrylamide, tert-butyl acrylamide, tert-butyl methacrylate, tert-butyl acrylate, tert-butoxystyrene or tert-butyl carbonate-based styrene monomers, or a combination of at least two thereof.

[0023] Preferably, the other carbon materials except carbon fiber include any one of carbon nanotubes, carbon black, graphite, graphene or carbon powder, or a combination of at least two or more thereof.

[0024] Preferably, the thickener comprises any one of fumed silica, polyacrylate or hydroxyethyl cellulose, or a combination of at least two thereof.

[0025] Preferably, the initiator includes any one of azobisisobutyronitrile, azobisisoheptanenitrile or benzoyl peroxide, or a combination of at least two thereof.

[0026] Preferably, the cross-linking agent includes any one of methyl methacrylate, ethyl methacrylate, allyl methacrylate, butyl methacrylate, acrylamide or methacrylamide, or a combination of at least two thereof.

[0027] In a second aspect, the present invention provides a method for preparing the homogeneous polymethacrylimide composite absorbing material as described in the first aspect, the preparation method comprising the following steps:

[0028] (1) mixing acrylonitrile monomer, methacrylic acid monomer, copolymerizable foaming monomer, wave absorber, thickener, initiator and cross-linking agent to obtain a reaction solution;

[0029] (2) injecting the reaction solution obtained in step (1) into an assembled glass mold for copolymerization reaction to obtain an expandable polymethacrylimide copolymer plate;

[0030] (3) Dehydrating, foaming and post-treating the expandable polymethacrylimide copolymer plate obtained in step (2) to obtain the homogeneous polymethacrylimide composite absorbing material.

[0031] Preferably, the mixing in step (1) includes first stirring at 50-80°C (e.g., 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc.) for 1-2h (e.g., 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2h, etc.), and then continuing ultrasonication at 50-80°C (e.g., 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc.) for 10-60min (e.g., 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min or 60min, etc.).

[0032] Preferably, the copolymerization reaction in step (2) is carried out at a temperature of 50 to 80°C (e.g., 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc.), and the reaction time is 24 to 96h (e.g., 24h, 28h, 32h, 34h, 38h, 42h, 46h, 50h, 54h, 58h, 64h, 68h, 72h, 78h, 82h, 86h, 92h or 96h, etc.).

[0033] Preferably, the temperature of the dehydration treatment in step (3) is 80-110°C (for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C or 110°C, etc.), and the time is 30-120min (for example, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min or 120min, etc.).

[0034] Preferably, the temperature of the preheat treatment in step (3) is 160-200°C (for example, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or 200°C, etc.), and the time is 30-90min (for example, 30min, 40min, 50min, 60min, 70min, 80min or 90min, etc.).

[0035] Preferably, the temperature of the foaming treatment in step (3) is 170-230°C (for example, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C or 230°C, etc.), and the time is 20-120min (for example, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min or 120min, etc.).

[0036] Preferably, the post-treatment temperature in step (3) is 160-200°C (e.g., 160°C, 170°C, 180°C, 190°C or 200°C, etc.), and the time is 2-8h (e.g., 2h, 3h, 4h, 5h, 6h, 7h or 8h, etc.).

[0037] In a third aspect, the present invention provides a use of the homogeneous polymethacrylimide composite absorbing material as described in the first aspect in aerospace or communication equipment.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The raw materials of the homogeneous polymethacrylimide composite absorbing material provided by the present invention include acrylonitrile monomer, methacrylic acid monomer, copolymerizable foaming monomer, absorbent, thickener, initiator and crosslinking agent; an "endogenous" self-foaming strategy is adopted to introduce the copolymerizable foaming monomer and acrylonitrile monomer and methacrylic acid monomer for copolymerization without adding an external foaming agent, so that the obtained self-foaming polymethacrylimide has a uniform polyhedral closed-cell structure, and the self-foaming polymethacrylimide is used as a matrix, combined with an absorbent, and absorbents with different structural morphologies are selected to construct a gradient distribution structure to produce a synergistic effect, thereby obtaining a broadband absorbing homogeneous polymethacrylimide foam material;

[0040] (2) Specifically, the homogeneous polymethacrylimide composite absorbing material prepared by the present invention has the advantages of light weight, high strength and high temperature resistance, and the density is 85kg / m 3 The foam compression strength can reach 2.0MPa, and at low absorber content, the reflectivity in the range of 12 to 18GHz (Ku band) can reach a minimum of -16.7dB. It has good absorbing performance and can be used as an absorbing sandwich structure for electromagnetic wave absorption in the field of electronic information. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the gradient distribution structure of the absorber in the homogeneous polymethacrylimide composite absorber provided by the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0043] Unless otherwise specified, the raw materials involved in the following specific embodiments are all conventional materials in the art and can be purchased from commercial products.

[0044] Example 1

[0045] A homogeneous polymethacrylimide composite absorbing material, the raw materials of which include the following components in parts by weight:

[0046]

[0047]

[0048] The preparation method of the homogeneous polymethacrylimide composite absorbing material provided in this embodiment comprises the following steps:

[0049] (1) Adding acrylonitrile monomer, methacrylic acid monomer, tert-butyl acrylamide, carbon fiber, graphite, fumed silica, azobisisobutyronitrile and methyl methacrylate into a 100 mL reaction bottle, mechanically stirring for 2 h at 50° C., and then ultrasonically dispersing for 20 min to obtain a reaction solution;

[0050] (2) injecting the reaction solution obtained in step (1) into the assembled glass mold, and then reacting the mold in a constant temperature water bath at 50° C. for 48 hours to obtain a black expandable polymethacrylimide copolymer plate;

[0051] (3) placing the expandable polymethacrylimide copolymer plate obtained in step (2) in a high-temperature oven and maintaining a constant temperature of 100° C. for dehydration treatment for 1 hour, then heating to 190° C. for preheating for 1 hour, continuing to heat to 210° C. for foaming treatment for 1 hour, and finally post-treating at 180° C. for 4 hours to obtain the homogeneous polymethacrylimide composite absorbing material.

[0052] Example 2

[0053] A homogeneous polymethacrylimide composite absorbing material, the raw materials of which include the following components in parts by weight:

[0054]

[0055]

[0056] The preparation method of the homogeneous polymethacrylimide composite absorbing material provided in this embodiment comprises the following steps:

[0057] (1) Add acrylonitrile monomer, methacrylic acid monomer, tert-butoxystyrene, carbon fiber, conductive carbon black, hydroxyethyl cellulose, azobisisoheptanenitrile and ethyl methacrylate into a 100 mL reaction bottle, stir mechanically for 1 h at 50 °C, and then disperse ultrasonically for 20 min to obtain a reaction solution;

[0058] (2) injecting the reaction solution obtained in step (1) into the assembled glass mold, and then reacting the mold in a constant temperature water bath at 50° C. for 48 h to obtain a black expandable polymethacrylimide copolymer plate;

[0059] (3) placing the expandable polymethacrylimide copolymer plate obtained in step (2) in a high-temperature oven and maintaining a constant temperature of 80° C. for dehydration treatment for 2 h, then heating the oven to 180° C. for preheating for 1 h, continuing to heat the oven to 200° C. for foaming treatment for 1 h, and finally post-treating the oven at 180° C. for 4 h to obtain the homogeneous polymethacrylimide composite absorbing material.

[0060] Example 3

[0061] A homogeneous polymethacrylimide composite absorbing material, the raw materials of which include the following components in parts by weight:

[0062]

[0063]

[0064] The preparation method of the homogeneous polymethacrylimide composite absorbing material provided in this embodiment comprises the following steps:

[0065] (1) Adding acrylonitrile monomer, methacrylic acid monomer, tert-butyl acrylate, carbon fiber, carbon nanotube, conductive carbon black, hydroxyethyl cellulose, azobisisoheptanenitrile and allyl methacrylate into a 100 mL reaction bottle, mechanically stirring for 2 h at 50° C., and then ultrasonically dispersing for 20 min to obtain a reaction solution;

[0066] (2) injecting the reaction solution obtained in step (1) into the assembled glass mold, and then reacting the mold in a constant temperature water bath at 50° C. for 24 h, and then reacting in a constant temperature water bath at 55° C. for 12 h, to obtain a black expandable polymethacrylimide copolymer plate;

[0067] (3) placing the expandable polymethacrylimide copolymer plate obtained in step (2) in a high-temperature oven and maintaining a constant temperature of 100° C. for dehydration treatment for 1 hour, then heating the temperature to 170° C. for preheating for 1 hour, continuing to heat the temperature to 190° C. for foaming treatment for 1 hour, and finally post-treating the temperature at 180° C. for 4 hours to obtain the homogeneous polymethacrylimide composite absorbing material.

[0068] Example 4

[0069] A homogeneous polymethacrylimide composite absorbing material, the raw materials of which include the following components in parts by weight:

[0070]

[0071]

[0072] The preparation method of the homogeneous polymethacrylimide composite absorbing material provided in this embodiment comprises the following steps:

[0073] (1) Adding acrylonitrile monomer, methacrylic acid monomer, tert-butyl methacrylate, carbon fiber, graphite, conductive carbon black, hydroxyethyl cellulose, benzoyl peroxide and allyl methacrylate into a 100 mL reaction bottle, mechanically stirring for 1 h at 55° C., and then ultrasonically dispersing for 20 min to obtain a reaction solution;

[0074] (2) injecting the reaction solution obtained in step (1) into the assembled glass mold, and then reacting the mold in a constant temperature water bath at 55° C. for 24 hours, and then reacting in a constant temperature water bath at 60° C. for 12 hours to obtain a black expandable polymethacrylimide copolymer plate;

[0075] (3) placing the expandable polymethacrylimide copolymer plate obtained in step (2) in a high-temperature oven and maintaining a constant temperature of 100° C. for dehydration treatment for 1 hour, then heating the temperature to 170° C. for preheating for 1 hour, continuing to heat the temperature to 190° C. for foaming treatment for 1 hour, and finally post-treating the temperature at 180° C. for 4 hours to obtain the homogeneous polymethacrylimide composite absorbing material.

[0076] Example 5

[0077] A homogeneous polymethacrylimide composite absorbing material, the raw materials of which include the following components in parts by weight:

[0078]

[0079]

[0080] The preparation method of the homogeneous polymethacrylimide composite absorbing material provided in this embodiment comprises the following steps:

[0081] (1) Adding acrylonitrile monomer, methacrylic acid monomer, tert-butyl carbonate styrene, carbon fiber, graphite, conductive carbon black, hydroxyethyl cellulose, benzoyl peroxide and allyl methacrylate into a 100 mL reaction bottle, mechanically stirring for 1 h at 55° C., and then ultrasonically dispersing for 20 min to obtain a reaction solution;

[0082] (2) injecting the reaction solution obtained in step (1) into the assembled glass mold, and then reacting the mold in a constant temperature water bath at 55° C. for 12 h, and then in a constant temperature water bath at 60° C. for 24 h, to obtain a black expandable polymethacrylimide copolymer plate;

[0083] (3) placing the expandable polymethacrylimide copolymer plate obtained in step (2) in a high-temperature oven and maintaining a constant temperature of 100° C. for dehydration treatment for 1 hour, then heating the temperature to 160° C. for preheating for 1 hour, and continuing to heat the temperature to 180° C. for foaming treatment for 1 hour, and finally post-treating the temperature at 180° C. for 4 hours to obtain the homogeneous polymethacrylimide composite absorbing material.

[0084] Comparative Example 1

[0085] A homogeneous polymethacrylimide composite absorbing material, the raw materials of which include the following components in parts by weight:

[0086]

[0087]

[0088] The preparation method of the homogeneous polymethacrylimide composite absorbing material provided in this embodiment comprises the following steps:

[0089] (1) Adding acrylonitrile monomer, methacrylic acid monomer, tert-butyl methacrylate, carbon fiber, fumed silica, benzoyl peroxide and allyl methacrylate into a 100 mL reaction bottle, mechanically stirring for 2 h at 50 °C, and then ultrasonically dispersing for 20 min to obtain a reaction solution;

[0090] (2) injecting the reaction solution obtained in step (1) into the assembled glass mold, and then reacting the mold in a constant temperature water bath at 50° C. for 48 hours to obtain a black expandable polymethacrylimide copolymer plate;

[0091] (3) placing the expandable polymethacrylimide copolymer plate obtained in step (2) in a high-temperature oven and maintaining a constant temperature of 100° C. for dehydration treatment for 1 hour, then heating to 190° C. for preheating for 1 hour, continuing to heat to 210° C. for foaming treatment for 1 hour, and finally post-treating at 180° C. for 4 hours to obtain the homogeneous polymethacrylimide composite absorbing material.

[0092] Performance Test:

[0093] The homogeneous polymethacrylimide composite absorbing materials provided in Examples 1 to 5 and Comparative Example 1 were tested, and the test results are shown in Table 1:

[0094] Table 1

[0095]

[0096]

[0097] From the data in Table 1, we can see that:

[0098] (1) According to the data of Examples 1 to 5, it can be seen that the homogeneous polymethacrylimide composite absorbing materials prepared with different contents of the foaming agent have excellent absorbing properties while maintaining good mechanical properties.

[0099] (2) By comparing the data of Example 4 with that of Comparative Example 1, it can be seen that, at the same content of absorbent, adding multiple absorbents can construct a gradient distribution structure inside the polymethacrylimide matrix, thereby helping to improve the mechanical properties and absorbent properties of the foam material.

[0100] The applicant declares that the present invention illustrates a homogeneous polymethacrylimide composite absorbing material and a preparation method thereof through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A homogeneous polymethacrylimide composite absorbing material, characterized in that: The raw materials of the homogeneous polymethacrylimide composite absorbing material include the following components in parts by weight: The wave absorbing agent comprises a combination of carbon fiber and other carbon materials except carbon fiber.

2. The homogeneous polymethacrylimide composite absorbing material according to claim 1, characterized in that: The copolymerizable foaming monomer includes any one of tert-butyl methacrylamide, tert-butyl acrylamide, tert-butyl methacrylate, tert-butyl acrylate, tert-butoxy styrene or tert-butyl carbonate-based styrene monomers or a combination of at least two thereof.

3. The homogeneous polymethacrylimide composite absorbing material according to claim 1 or 2, characterized in that: The other carbon materials except carbon fiber include any one of carbon nanotubes, carbon black, graphite, graphene or carbon powder, or a combination of at least two or more thereof.

4. The homogeneous polymethacrylimide composite absorbing material according to any one of claims 1 to 3, characterized in that: The thickener includes any one or a combination of at least two of fumed silica, polyacrylate or hydroxyethyl cellulose; Preferably, the initiator includes any one of azobisisobutyronitrile, azobisisoheptanenitrile or benzoyl peroxide, or a combination of at least two thereof.

5. The homogeneous polymethacrylimide composite absorbing material according to any one of claims 1 to 4, characterized in that: The crosslinking agent includes any one of methyl methacrylate, ethyl methacrylate, allyl methacrylate, butyl methacrylate, acrylamide or methacrylamide, or a combination of at least two thereof.

6. A method for preparing the homogeneous polymethacrylimide composite absorbing material according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: (1) mixing acrylonitrile monomer, methacrylic acid monomer, copolymerizable foaming monomer, wave absorber, thickener, initiator and cross-linking agent to obtain a reaction solution; (2) injecting the reaction solution obtained in step (1) into an assembled glass mold for copolymerization reaction to obtain an expandable polymethacrylimide copolymer plate; (3) The expandable polymethacrylimide copolymer plate obtained in step (2) is subjected to dehydration treatment, preheating treatment, foaming treatment and post-treatment in sequence to obtain the homogeneous polymethacrylimide composite absorbing material.

7. The preparation method according to claim 6, characterized in that: The mixing in step (1) comprises first stirring at 50-80° C. for 1-2 hours, and then continuing ultrasonication at 50-80° C. for 10-60 minutes.

8. The preparation method according to claim 6 or 7, characterized in that: The copolymerization reaction temperature in step (2) is 50 to 80° C. and the reaction time is 24 to 96 hours.

9. The preparation method according to any one of claims 5 to 8, characterized in that: The temperature of the dehydration treatment in step (3) is 80-110° C. and the time is 30-120 min; Preferably, the preheating treatment in step (3) is carried out at a temperature of 160 to 200° C. and for a time of 30 to 90 minutes.

10. The preparation method according to any one of claims 5 to 9, characterized in that: The temperature of the foaming treatment in step (3) is 170-230° C. and the time is 20-120 min; Preferably, the post-treatment in step (3) is carried out at a temperature of 160 to 200° C. and for a time of 2 to 8 hours.

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