Rare earth PMI composite wave-absorbing foam and preparation method thereof

Abstract

The invention provides a preparation method of rare earth PMI composite wave-absorbing foam, which comprises the following steps: mixing methacrylonitrile and methacrylic acid, adding a foaming agent, an initiator and a cross-linking agent, uniformly stirring and mixing, pouring into a polymerization mold, sealing the polymerization mold, keeping the temperature in a constant-temperature water bath environment, demolding to obtain a PMI prepolymer, and drying to obtain the rare earth PMI composite wave-absorbing foam. Then, the PMI prepolymer is smashed, and PMI prepolymer particles are obtained; the method comprises the following steps: pretreating a composite wave-absorbing agent by adopting a surfactant, wherein the composite wave-absorbing agent comprises yttrium-doped cobalt powder and a carbon nanotube; adding the pretreated composite wave-absorbing agent into epoxy resin, uniformly mixing to obtain a dipping material, uniformly mixing PMI prepolymer particles and the dipping material, injecting into a mold, heating the mold in a foaming furnace, cooling to room temperature, and demolding to obtain the composite wave-absorbing foam. The foam provided by the invention can give full play to the advantages of the rare earth wave-absorbing agent and the carbon-series wave-absorbing agent, has good and stable mechanical properties and wave-absorbing properties, and has good military application value.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave absorbing materials, and in particular to a rare-earth-based PMI composite microwave absorbing foam and a preparation method thereof. Background Art

[0002] Polymethacrylimide (PMI) foam has the characteristics of low density, excellent mechanical properties and high temperature resistance, and is an ideal sandwich for structural microwave absorbing materials. However, the dielectric constant of PMI foam itself is small and it cannot provide the function of electromagnetic loss. Researchers have tried to introduce low-cost metal-based microwave absorbing agents (such as ferrite, carbonyl iron, etc.) and lightweight carbon-based microwave absorbing agents (such as carbon black, carbon nanotubes, graphene, short carbon fiber, etc.) into PMI foam. However, the metal-based microwave absorbing agents have a large density and the carbon-based microwave absorbing agents are prone to agglomeration. Therefore, sedimentation and poor dispersion occur during the preparation process, resulting in unstable microwave absorbing performance.

[0003] In view of this, the present invention is specifically proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a rare-earth-based PMI composite microwave absorbing foam and a preparation method thereof. The foam can give full play to the advantages of rare-earth-based microwave absorbing agents and carbon-based microwave absorbing agents, and has good and stable mechanical properties and microwave absorbing properties.

[0005] In the first aspect of the present invention, a preparation method of a rare-earth-based PMI composite microwave absorbing foam is provided, including the following steps:

[0006] S1. Mix methacrylonitrile and methacrylic acid, add a foaming agent, an initiator and a crosslinking agent, stir and mix evenly, then pour the mixture into a polymerization mold. Seal the polymerization mold and place it in a constant temperature water bath environment for heat preservation. After demolding, obtain a PMI prepolymer, and then crush the PMI prepolymer to obtain PMI prepolymer particles;

[0007] S2. Pretreat the composite microwave absorbing agent with a surfactant. The composite microwave absorbing agent includes yttrium-doped cobalt powder and carbon nanotubes;

[0008] S3. Add the pretreated composite microwave absorbing agent into epoxy resin, mix evenly to obtain an impregnating material. Uniformly mix the PMI prepolymer particles and the impregnating material and inject them into a mold. Place the mold in a foaming furnace for heating, demold after cooling to room temperature to obtain a composite microwave absorbing foam.

[0009] Preferably, in step S1, the mass ratio of methacrylonitrile to methacrylic acid is (4-6):(4-6).

[0010] Preferably, in step S1, the addition amount of the foaming agent is 4-8% wt, the addition amount of the initiator is 0.2-0.4% wt, and the addition amount of the crosslinking agent is 0.01-0.1% wt.

[0011] Preferably, in step S1, the foaming agent is formamide, the initiator is azodiisobutyronitrile, and the crosslinking agent is bismaleimide.

[0012] Preferably, in step S1, after sealing the polymerization mold, it is placed in a constant temperature water bath environment at 60-80 °C for heat preservation for 12-24 h.

[0013] Preferably, in step S2, the mass ratio of the yttrium-doped cobalt powder and the carbon nanotubes is (50-70):(1-3).

[0014] Preferably, in step S2, the yttrium-doped cobalt is easy-plane yttrium-doped cobalt, for example: Y 2 Co 17 .

[0015] Easy-plane yttrium-doped cobalt (Y 2 Co 17 ) is a rare-earth soft magnetic material (REM) with strong in-plane magnetocrystalline anisotropy. Compared with ferrite, Y 2 Co 17 has the characteristics of low density, high magnetic permeability, and excellent heat resistance, and is suitable for being introduced into PMI foam as a magnetic loss absorbing agent. In addition, carbon nanotubes (CNT) as an electrical loss type absorbing agent can assist in improving impedance matching.

[0016] In the present invention, there is no strict limitation on the sizes of the yttrium-doped cobalt powder and the carbon nanotubes used. Preferably, the average particle size of the yttrium-doped cobalt powder is 2-10 μm, and the average length of the carbon nanotubes is 10-50 μm.

[0017] Preferably, in step S2, the addition amount of the surfactant is 0.4-1.6% wt.

[0018] Preferably, in step S2, the surfactant includes one or more of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone (PVP), and polyethylene glycol octylphenyl ether (Triton).

[0019] Preferably, step S2 includes: adding the surfactant to deionized water, adding the yttrium-doped cobalt powder and the carbon nanotubes, stirring at a constant temperature of 40-80 °C for 1-2 h and then filtering, rinsing with absolute ethanol to remove the excess surfactant, drying at 60-80 °C for 6-18 h, and grinding to obtain the composite absorbing agent powder.

[0020] Preferably, in step S3, the mass ratio of the PMI prepolymer particles, epoxy resin, and composite wave-absorbing agent is (55 - 85):(5 - 30):(10 - 40).

[0021] Preferably, in step S3, the particle size of the PMI prepolymer particles is above 3 mm.

[0022] In the second aspect of the present invention, a rare-earth-based PMI composite wave-absorbing foam is provided, which is prepared by using the preparation method of the rare-earth-based PMI composite wave-absorbing foam as described in the above claims.

[0023] The present invention has at least the following beneficial effects:

[0024] By introducing yttrium-doped cobalt powder with low density, high magnetic permeability, and excellent heat resistance as a magnetic loss wave-absorbing agent in the PMI foam, and then introducing carbon nanotubes as an electric loss type wave-absorbing agent to assist in improving impedance matching, the magnetic loss and electric loss mechanisms are jointly exerted, giving full play to the advantages of low density of rare-earth-based wave-absorbing agents and carbon-based wave-absorbing agents. Moreover, by pretreating the composite wave-absorbing agent, the dispersibility and stability of the composite wave-absorbing agent during the preparation process are improved, making the prepared PMI wave-absorbing foam have excellent mechanical properties and stable wave-absorbing properties, and can be used as the core of a structural wave-absorbing material, having good military application value; in addition, using the mechanical mixing co-foaming technology, the preparation process is simple, can be mass-produced, and has broad industrial production and application prospects. Description of the Drawings

[0025] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 It is a schematic diagram of the preparation process of the PMI composite wave-absorbing foam provided by the present invention;

[0027] Figure 2 It is the microscopic morphology diagram of REM-CNT prepared in Example 1 of the present invention; among them, (a) is 10 μm, and (b) is 2 μm;

[0028] Figure 3 It is the XRD spectrum diagram of REM and REM-CNT prepared in Example 1 of the present invention;

[0029] Figure 4 It is the appearance diagram of the PMI wave-absorbing foam prepared in Examples 1 - 3 and Comparative Examples 1 - 3 of the present invention;

[0030] Figure 5 Scanning electron microscope images of the PMI microwave absorbing foams prepared in Comparative Examples 1-3 of the present invention; wherein, (a) is Comparative Example 1, (b) is Comparative Example 2, (c) is Comparative Example 3, (d) is a partial enlarged view of Comparative Example 1, and (d1) and (d2) are EDS spectra;

[0031] Figure 6 Mechanical property diagrams of the PMI microwave absorbing foams prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention; wherein, (a) is the compressive strength and compressive modulus, (b) is the tensile strength and tensile modulus, and (c) is the shear strength and shear modulus;

[0032] Figure 7 Reflection loss diagrams of the PMI microwave absorbing foams prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention; wherein, (a)-(f) correspond to Comparative Examples 1-3 and Examples 1-3 respectively. Detailed Description of the Invention

[0033] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs.

[0034] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms also include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of the described features, steps, operations, devices, components, and / or combinations thereof.

[0035] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] Example 1

[0037] As Figure 1 shown, this example provides a preparation method of a rare earth-based PMI composite microwave absorbing foam, and the raw materials used are as follows:

[0038] Yttrium-doped cobalt powder: with an average particle size of 3.7 μm, purchased from Ningbo Magnetic Materials Technology Research Institute;

[0039] Carbon nanotubes: with an average length of 10-50 μm, purchased from the JD.com self-operated store of Corecai Industrial Products;

[0040] Epoxy resin: E44 type resin liquid, and the curing agent is polyamide, purchased from Liang'en Industrial Products Franchise Store;

[0041] Methacrylonitrile, methacrylic acid, azodiisooctanenitrile (initiator), formamide (foaming agent), bismaleimide (crosslinking agent), polyethyleneglycol octyl phenyl ether (surfactant, Triton), were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. and Sinopharm Chemical Reagent Co., Ltd., and all were of analytical grade.

[0042] Specifically, it includes the following steps:

[0043] S1. Set the feeding ratio of methacrylonitrile (MAN) and methacrylic acid (MAA) to 1:1, add 6%wt formamide, 0.3%wt azodiisooctanenitrile, and 0.05%wt bismaleimide, mix evenly, stir for 2 h, and then pour into a polymerization mold.

[0044] Seal the mold and place it in a constant temperature water bath at 65 °C for 12 h. After demolding, obtain PMI prepolymer A. Use a crusher to crush PMI prepolymer A into particles at a speed of 600 r / min, and use a sieve to separate particles with a particle size of more than 3 mm for subsequent foaming process.

[0045] S2. Add 16 g of polyethyleneglycol octyl phenyl ether (Triton) to 1000 ml of deionized water, then add 300 g of yttrium-doped cobalt powder (REM) and 10 g of carbon nanotubes (CNT), stir at a constant temperature of 60 °C for 2 h, and then filter. Then rinse once with absolute ethanol to remove the excess surfactant, dry at 70 °C for 12 h, and grind to obtain REM-CNT composite microwave absorbing agent.

[0046] Figure 2 is the micrograph of REM-CNT after compounding. It can be intuitively seen from (a) and (b) that well-dispersed CNTs adhere and adsorb on the surface of REM particles. This work can effectively avoid the entanglement and agglomeration of CNTs during the mixing process with PMI prepolymer particles, thereby improving the stability of the microwave absorbing performance of PMI foam.

[0047] Figure 3 is the XRD pattern of REM and REM-CNT. The diffraction characteristic peaks and diffraction intensities of the REM sample are consistent with the Y 2 Co 17 standard spectrum (PDF#18-0434), and no obvious impurity peaks are generated, indicating that the REM sample has a high purity. After compounding with CNTs, the (002) and (100) characteristic peaks of carbon nanotubes appear in the XRD pattern, indicating that although the addition amount of CNTs is relatively small, they have been well dispersed on the surface of REM particles.

[0048] S3. Add 310 g of the pretreated REM-CNT composite wave-absorbing agent powder to 216 g of E44 type resin liquid. After mixing evenly, obtain epoxy resin impregnating material B. Stir 850 g of PMI prepolymer particles and epoxy resin impregnating material B at a speed of 1200 r / min for 0.5 h for uniform mixing. Inject the mixed slurry into a cube mold of 300×300×50 mm 3 . Place the mold in a foaming furnace, heat it at 120 °C for 1 h, adjust the temperature to 225 °C, keep it warm for 3 h, demold after cooling to room temperature, and then obtain REM-CNT / PMI foam, denoted as C1R30.

[0049] Example 2

[0050] This example provides a preparation method of rare earth-based PMI composite wave-absorbing foam, which is basically the same as the steps in Example 1. The difference lies in: in step S3, the following ratio is adopted: 282 g of E44 type resin liquid, 850 g of PMI prepolymer particles, 320 g of REM-CNT composite wave-absorbing agent powder (including 300 g of REM and 20 g of CNT), denoted as C2R30.

[0051] Example 3

[0052] This example provides a preparation method of rare earth-based PMI composite wave-absorbing foam, which is basically the same as the steps in Example 1. The difference lies in: in step S3, the following ratio is adopted: 348 g of E44 type resin liquid, 850 g of PMI prepolymer particles, 330 g of REM-CNT composite wave-absorbing agent powder (including 300 g of REM and 20 g of CNT), denoted as C3R30.

[0053] Comparative Example 1

[0054] This example provides a preparation method of rare earth-based PMI composite wave-absorbing foam, including the following steps:

[0055] S1. Set the feeding ratio of methylacrylonitrile (MAN) and methacrylic acid (MAA) to 1:1, add 4-8% wt of formamide, 0.2-0.4% wt of azobisisoheptonitrile, 0.01-0.1% wt of bismaleimide and mix evenly. After stirring for 2 h, pour it into a polymerization mold.

[0056] Seal the mold and place it in a constant temperature water bath at 65 °C for heat preservation for 12 h. After demolding, obtain PMI prepolymer. Use a crusher to crush the PMI prepolymer into particles at a speed of 600 r / min, and use a sieve to separate particles with a particle size of more than 3 mm for subsequent foaming process.

[0057] S2. Add 16 g of polyethylene glycol octyl phenyl ether (Triton) to 1000 ml of deionized water, and then add 300 g of yttrium-doped cobalt powder (REM). Stir for 2 h at a constant temperature of 60 °C and then filter. Then rinse once with absolute ethanol to remove the excess surfactant, dry at 70 °C for 12 h, and grind to obtain the REM wave-absorbing agent.

[0058] S3. Add 200 g of the pretreated REM wave-absorbing agent powder to 100 g of E44 type resin liquid, and mix evenly to obtain epoxy resin impregnating material B. Stir 850 g of PMI prepolymer particles and epoxy resin impregnating material B at a speed of 1200 r / min for 0.5 h for uniform mixing, and inject the mixed slurry into a 300×300×50 mm 3 cubic mold. Place the mold in a foaming furnace, heat at 120 °C for 1 h, adjust the temperature to 225 °C, keep warm for 3 h, demold after cooling to room temperature, and then the PMI composite wave-absorbing foam can be obtained, denoted as R20.

[0059] Comparative Example 2

[0060] This comparative example provides a preparation method of rare earth-based PMI composite wave-absorbing foam, which is basically the same as the steps in Comparative Example 1. The difference lies in that in step S3, the following ratio is adopted: 150 g of E44 type resin liquid, 850 g of PMI prepolymer particles, 300 g of REM wave-absorbing agent powder, denoted as R30.

[0061] Comparative Example 3

[0062] This comparative example provides a preparation method of rare earth-based PMI composite wave-absorbing foam, which is basically the same as the steps in Comparative Example 1. The difference lies in that in step S3, the following ratio is adopted: 200 g of E44 type resin liquid, 850 g of PMI prepolymer particles, 400 g of REM wave-absorbing agent powder, denoted as R40.

[0063] Test Example 1 Optical Photo and Microscopic Morphology Analysis

[0064] The PMI foams in Examples 1-3 and Comparative Examples 1-3 have the appearance as Figure 4 shown. It can be seen from the figure that the black wave-absorbing agent is evenly distributed inside the white PMI foam, forming an interconnected network pattern. The REM wave-absorbing agent is not enriched on the upper or lower surface of the PMI foam, and the sedimentation effect of the surface REM during the co-foaming process is not obvious, which benefits from the relatively small relative density of REM. By comparing different PMI foams, it can be seen that as the addition amount of REM increases, the aggregation phenomenon of black REM particles at the pattern is more obvious, which is obviously not conducive to the uniform dispersion of the wave-absorbing agent. The microscopic morphology of the cut PMI foams in Comparative Examples 1-3 was observed by SEM (see Figure 5 ). From Figure 5As can be seen from (a) in [reference], the pore sizes of the cells in the C20-PMI foam in Comparative Example 1 are relatively uniform. Around the REM enrichment region, the pore sizes of the cells are relatively small. From the EDS energy spectrum scanning diagrams of the enlarged regions ([ Figure 5 (d1) and (d2) in [reference]), it can be seen that cobalt and yttrium elements are mainly concentrated inside the epoxy resin and are evenly distributed internally. This reflects that the REM has good dispersibility and no obvious aggregation occurs, which will be beneficial to the exertion of electromagnetic loss. When the addition amount of REM continues to increase, it can be seen from Figure 5 (b) and (c) in [reference] that the pore sizes of the cells in the C30-PMI and C40-PMI foams in Comparative Examples 2 and 3 decrease sharply. This may be due to the excessive REM particles inhibiting the foaming behavior of the PMI prepolymer or the addition of excessive epoxy resin binder.

[0065] Test Example 2 Mechanical Property Test

[0066] The mechanical properties of the PMI foam were tested using an American Instron 5982 type electronic universal testing machine. The loading speed of the testing machine was uniformly set to 5 mm / min, and all samples were subjected to five repeated tests. The comparison sample was the PMI foam without filled wave-absorbing agent, denoted as C0R0. The compression test was carried out according to the GBT8813-2008 standard. The sample was a cube with a side length of 30 mm. The tensile test was carried out according to the GB 9641-1988 standard. The sample was dumbbell-shaped, with a total length of 150 mm, a width of 25 mm at the clamping section, and a thickness of 10 mm. The shear test was carried out according to the GBT1455-2005 standard. The length of the shear fixture was 200 mm, and the width was 60 mm. The sample was a cuboid with a length of 150 mm, a width of 60 mm, and a thickness of 14 mm. The DP460 epoxy adhesive (3M Company, USA) was used to tightly bond the sample and the fixture.

[0067] The mechanical properties of the PMI wave-absorbing foam are as Figure 6 shown. As shown in Figure 6 (a) in [reference], the compression strength of the PMI foam filled with wave-absorbing agent is slightly lower than that of the unfilled PMI foam. This may be because the air in the closed pores of the unfilled PMI foam provides additional supporting force. With the increase of the REM content, the compression strength first increases and then remains relatively stable; with the increase of the CNT content, the compression strength shows a slight downward trend. In addition, with the increase of the filling amount of the wave-absorbing agent, the error fluctuation of the compression strength of the sample increases, which has a direct relationship with the dispersion degree of the filler. The C1R30 sample in Example 1 shows the maximum compression strength of 2.35 ± 0.15 MPa, which is 11.9% higher than that of the unfilled PMI foam. Figure 6Among them, (b) is the histogram of the tensile strength and tensile modulus of different PMI foams. It can be seen that the overall tensile strength of the PMI foam is lower than that of the unfilled PMI foam. This may be related to the fact that the addition of a large amount of wave-absorbing agent and binder inhibits the foaming process of the PMI prepolymer. The decrease in the integrity of the cell wall structure leads to the reduction of the tensile strength. As the filling amount of the wave-absorbing agent increases, the tensile strength of the PMI foam shows an upward trend. In addition, the tensile modulus is generally higher than that of the unfilled PMI foam, indicating that the introduction of the wave-absorbing agent plays a certain strengthening role. In Example 3, the C3R30 sample shows the maximum tensile strength of 1.19 ± 0.22 MPa, which is close to the tensile strength of the unfilled PMI foam (2.10 ± 0.22 MPa) at this time. Figure 6 Among them, (c) is the histogram of the shear strength and shear modulus of different PMI foams. It can be seen from the figure that the shear strength of the PMI foam filled with the wave-absorbing agent is greater than that of the unfilled one, and it increases with the increase of the filler content. Its maximum shear strength is 1.54 ± 0.10 MPa, and the maximum shear modulus is 96.26 ± 13.02 MPa, with an increase of 22.2% and 32.8% respectively.

[0068] Test Example 3 Wave Absorbing Performance Test

[0069] The electromagnetic parameters of the PMI wave-absorbing foams in Examples 1-3 and Comparative Examples 1-3 were measured by the free space method. The sample size was a cuboid of 100 mm × 100 mm × 30 mm, and the test frequency band was 2-18 GHz.

[0070] Figure 7 It is the curve of the reflection loss of the PMI foam to electromagnetic waves at different matching thicknesses. As can be seen from Figure 7 Figure (a) among them, only when the matching thickness is 50 mm, the reflection loss of the R20-PMI foam in Comparative Example 1 is lower than -10 dB in the Ku band. Comparing Figure 7 Figures (a)-(c) among them, when the addition amount of REM increases, the matching thickness for the PMI foam to achieve the same wave-absorbing effect in the Ku band can be reduced to 30 mm. When the matching thickness is 50 mm, the maximum reflection loss of the R30-PMI foam in Comparative Example 2 is -24.1 dB, and the effective absorption bandwidth is 10.3 GHz (7.7-18 GHz); the maximum reflection loss of the R40-PMI foam in Comparative Example 3 is -19.9 dB, and the effective absorption bandwidth is 11.3 GHz (6.7-18 GHz). The electromagnetic reflection loss curve after adding CNT is as shown in Figure 7As shown in (d)-(f) therein. Comparing with the R30-PMI foam in Comparative Example 2, it can be seen that the maximum electromagnetic reflection loss has basically not increased significantly, but the effective absorption bandwidth has increased greatly. Especially when the matching thickness is 50 mm, the C3R30-PMI foam in Example 3 can achieve full coverage of effective absorption in the frequency band of 2-18 GHz. In addition, when the matching thickness is 30 mm, the C2R30-PMI foam in Example 2 shows the best performance, with a maximum reflection loss of -13.1 dB and an effective absorption bandwidth of 11.0 GHz (6.5-15.3 GHz and 15.8-18 GHz).

[0071] In summary, the present invention introduces yttrium-doped cobalt powder with low density, high magnetic permeability and excellent temperature resistance as a magnetic loss absorbing agent in PMI foam, and then introduces carbon nanotubes as an electric loss type absorbing agent to assist in improving impedance matching, jointly exerting the magnetic loss and electric loss mechanisms, and giving full play to the advantages of low density of rare earth absorbing agents and carbon-based absorbing agents. Moreover, by pre-treating the composite absorbing agent, the dispersibility and stability of the composite absorbing agent during the preparation process are improved, so that the prepared PMI absorbing foam has excellent mechanical properties and stable absorbing properties, and can be used as the core of a structural absorbing material, having good military application value; in addition, the mechanical mixing co-foaming technology is adopted, the preparation process is simple, and it can be mass-produced, having broad industrial production and application prospects.

[0072] The present invention gives full play to the advantages of low density of rare earth absorbing agents and carbon-based absorbing agents, and focuses on optimizing the dispersibility problem in the preparation process, which has important practical application value and significance for developing a PMI foam with "light, thin, wide, and strong" and stable absorbing properties.

[0073] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a rare earth PMI composite wave-absorbing foam, characterized in that: The steps include: S1, mixing methacrylonitrile and methacrylic acid, adding a blowing agent, an initiator and a cross-linking agent, stirring and mixing, and pouring into a polymerization mold, sealing the polymerization mold and placing it in a constant temperature water bath environment for heat preservation, demolding to obtain a PMI prepolymer, and then crushing the PMI prepolymer to obtain PMI prepolymer particles; S2, pretreating the composite absorber with a surfactant, wherein the composite absorber comprises yttrium-doped cobalt powder and carbon nanotubes; S3, adding the pretreated composite absorber to the epoxy resin, mixing to obtain an impregnation material, uniformly mixing the PMI prepolymer particles and the impregnation material and injecting them into a mold, placing the mold in a foaming furnace for heating, and demolding after cooling to room temperature to obtain a composite absorbing foam.

2. The method for preparing the rare earth PMI composite wave-absorbing foam according to claim 1, characterized in that: In step S1, the mass ratio of methacrylonitrile to methacrylic acid is (4-6):(4-6).

3. The method for preparing the rare earth PMI composite wave-absorbing foam according to claim 1, characterized in that: In step S1, the foaming agent is formamide, the initiator is azobisisoheptanenitrile, and the cross-linking agent is bismaleimide.

4. The method for preparing the rare earth PMI composite wave-absorbing foam according to claim 1, characterized in that: In step S2, the mass ratio of the yttrium-doped cobalt powder to the carbon nanotubes is (50-70):(1-3).

5. The method for preparing the rare earth PMI composite wave absorbing foam according to claim 1, characterized in that: In step S2, the yttrium-doped cobalt is an easy-face type yttrium-doped cobalt.

6. The method for preparing the rare earth PMI composite wave absorbing foam according to claim 1, characterized in that: In step S2, the average particle size of the yttrium-doped cobalt powder is 2-10 μm, and the average length of the carbon nanotubes is 10-50 μm.

7. The method for preparing the rare earth PMI composite wave absorbing foam according to claim 1, characterized in that: In step S2, the surfactant includes: one or more of sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, polyvinyl pyrrolidone, and polyethylene glycol octylphenyl ether.

8. The method for preparing the rare earth PMI composite wave absorbing foam according to claim 1, characterized in that: In step S3, the mass ratio of the PMI prepolymer particles, the epoxy resin and the composite absorber is (55-85):(5-30):(10-40).

9. The method for preparing the rare earth PMI composite wave-absorbing foam according to claim 1, characterized in that: In step S3, the particle size of the PMI prepolymer particles is greater than 3 mm.

10. A rare earth PMI composite wave absorbing foam, characterized in that: The composite wave-absorbing foam is prepared by the method for preparing the rare earth PMI composite wave-absorbing foam described in any one of claims 1 to 9.

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