Lightweight wave-absorbing polymethacrylimide composite material and preparation method thereof

Abstract

The invention discloses a lightweight wave-absorbing polymethacrylimide composite material and a preparation method thereof, and belongs to the technical field of functional foam materials.Mesoscopic MOF / MXene nanosheets are added to serve as a wave-absorbing material, and by means of the characteristic that the surfaces of the MXene nanosheets are negatively charged, the light wave-absorbing polymethacrylimide composite material is prepared. On the other hand, the methoxyl intercalator is used as a surface active agent, agglomeration of the MXene nanosheets can be avoided through a hydrophobic effect, and therefore the wave absorbing performance is stable, and on the other hand, the methoxyl intercalator is promoted to be embedded between the MXene nanosheets through the electrostatic attraction effect of a cationic quaternary ammonium salt group, so that the interlayer spacing of the MXene nanosheets is increased, and the MXene nanosheets are prevented from being agglomerated through the hydrophobic effect; the mesoscopic MOF / MXene nanosheet disclosed by the invention is used as a filler of the light wave-absorbing polymethacrylimide composite material, and in a foaming stage, a methoxyl intercalator for surface intercalation is used as a surfactant and has a foaming emulsification effect, so that foaming can be assisted, and the foaming uniformity can be improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of functional foam materials, and particularly relates to a lightweight wave-absorbing polymethacrylimide composite material and a preparation method thereof. BACKGROUND

[0002] Polymethacrylimide (PMI) foam is a kind of thermosetting rigid foam material, which has a 100% closed-cell structure. The uniform cross-linked cell wall structure endows it with outstanding structural stability and excellent mechanical properties. It is an ideal core material for manufacturing lightweight high-strength sandwich structures and has been widely used in large passenger aircraft and transport aircraft, fighter aircraft, helicopters, high-speed trains, wind turbine blades, satellites and launch vehicles, etc. In the prior art, the strength of polymethacrylimide foam itself is poor, and it is easy to break and fracture during use. The general practice is to add nano fillers such as silicon dioxide and carbon fibers to enhance the mechanical strength of the polymethyl methacrylate-based composite material. Due to the agglomeration characteristics of nano fillers, they usually need to be organically modified before use, which makes the preparation process of polymethacrylimide foam material more complex and the preparation process more lengthy. Meanwhile, the addition of modifiers may also affect the performance of polymethacrylimide foam material.

[0003] A polymethacrylimide wave-absorbing foam and a preparation method thereof are disclosed in Chinese Patent No. CN120158022A. The foam is prepared by stirring and mixing 55-60 parts of methacrylic acid, 45-55 parts of methacrylonitrile, 5-8 parts of 1-amino octadecane, 0.3-0.6 parts of N-acrylamide, 0.4-0.7 parts of N-hydroxysuccinimide ester, 0.5-1.2 parts of carbodiimide, 4-7 parts of methyl acrylate, 2-8 parts of functional filler, 0.35-0.40 parts of initiator, 0.6-0.8 parts of foaming agent, 12-15 parts of cross-linking agent, 8-12 parts of absorbent, 21-35 parts of modified cellulose, 12-25 parts of biomass-based additive and 5-18 parts of dispersant. In this scheme, the polymethacrylimide foam is endowed with wave-absorbing performance by adding exogenous absorbent. However, uniform dispersion of multiple materials cannot be achieved by only using a dispersant, which leads to uneven dispersion of the absorbent and unstable wave-absorbing performance. SUMMARY

[0004] The present application aims to provide a lightweight wave-absorbing polymethacrylimide composite material and a preparation method thereof. By adding mesoscopic MOF / MXene nanosheets as a wave-absorbing material, the MXene nanosheets are negatively charged on the surface, which promotes the methoxy intercalation agent to be embedded in the MXene nanosheet interlayer through the electrostatic attraction of the cationic quaternary ammonium salt group, increases the interlayer spacing of the MXene nanosheet, and improves the specific surface area. On the other hand, as a surfactant, the MXene nanosheet can be prevented from agglomerating through hydrophobic interaction, thereby stabilizing the wave-absorbing performance.

[0005] The object of the present application can be achieved by the following technical solutions: A preparation method of a lightweight wave-absorbing polymethacrylimide composite material, comprising the following steps: Step one: through the terminal alkenyl group of dodecyl dimethyl allyl ammonium chloride and methyl dichlorosilane, a silicon-hydrogen addition reaction is carried out under the catalysis of chloroplatinic acid to obtain an intercalation agent precursor, then a nucleophilic substitution reaction occurs between the intercalation agent precursor and methanol, the chlorine atom is replaced by a methoxy group, and a methoxy intercalation agent is obtained.

[0006] Step two: through the reaction of lithium fluoride and hydrochloric acid to generate hydrofluoric acid, and then through the etching of the Al atom layer in titanium aluminum carbide by hydrofluoric acid to form a suspension of MXene nanosheets; through the electrostatic attraction of the cation at one end of the methoxy intercalation agent and the negative charge between the MXene nanosheet layers, the methoxy intercalation agent is embedded between the MXene nanosheet layers to obtain intercalated MXene nanosheets.

[0007] Step three: taking the intercalated MXene nanosheet as a carrier, a stable and ordered heterojunction interface of iron-based MOF is generated on the surface of the MXene nanosheet to obtain mesoscopic MOF / MXene nanosheets.

[0008] Step four: uniformly mix methacrylic acid, methacrylonitrile, 1-amino octadecane, N-acrylamide, N-hydroxy succinimide ester, carbodiimide, tridecyl methacrylate, mesoscopic MOF / MXene nanosheets, azobisisobutyronitrile, tert-butyl methacrylate, and acrylamide for 22-24 hours, transfer to a mold, and then perform sealing, polymerization, foaming, and annealing to obtain a lightweight wave-absorbing polymethacrylimide composite material.

[0009] Further, the amount ratio of methacrylic acid, methacrylonitrile, 1-amino octadecane, N-acrylamide, N-hydroxy succinimide ester, carbodiimide, tridecyl methacrylate, mesoscopic MOF / MXene nanosheets, azobisisobutyronitrile, tert-butyl methacrylate, and acrylamide is 50-60g: 50-52g: 7-8g: 0.5-0.6g: 0.6-0.7g: 0.8-1g: 5-6g: 12-14g: 0.3-0.4g: 0.7-0.8g: 10-11g.

[0010] Further, the specific preparation steps of the intercalation agent precursor are as follows: Twelve alkyl dimethyl allyl ammonium chloride, methyl dichlorosilane and toluene are added to the reaction kettle, stirred at 20-25°C and 500-600r / min for 20-30min, then 1-2% mass fraction of chloroplatinic acid isopropanol solution is added, heated to 65-70°C under nitrogen protection for 2-3h, and distilled under reduced pressure to obtain the intercalation agent precursor.

[0011] Further, the amount ratio of twelve alkyl dimethyl allyl ammonium chloride, methyl dichlorosilane, toluene and chloroplatinic acid isopropanol solution is 20-30g:12-14g:20-30g:0.4-0.5g.

[0012] Further, the specific preparation steps of the methoxy intercalation agent are as follows: The pretreated precursor and methanol are mixed, stirred and dissolved at 20-25°C and 500-600r / min for 40-60min, transferred to a constant pressure dropping funnel, added dropwise to a reaction kettle containing methanol, heated to 70-80°C under nitrogen protection for 4-5h, and distilled under reduced pressure to obtain the methoxy intercalation agent.

[0013] Further, the amount ratio of the pretreated precursor and methanol is 40-50g:40-60g.

[0014] Further, the specific preparation steps of the MXene nanosheet suspension are as follows: Lithium fluoride and 25-35% mass fraction hydrochloric acid solution are added to the reaction kettle, stirred at 20-25°C and 400-500r / min for 20-30min, then titanium aluminum carbide is added, and stirring is continued for 48-50h, centrifuged at 5000-6000r / min for 3-4min, filtered, the filter cake is washed with deionized water and ethanol until the last washing liquid is neutral, ultrasonic stripping under argon flow of 20-30mL / min, centrifuged at 5000-6000r / min for 1-2min to obtain the MXene nanosheet suspension.

[0015] Further, the amount ratio of lithium fluoride, hydrochloric acid solution and titanium aluminum carbide is 25-30g:500-600mL:13-14g.

[0016] Further, the specific preparation steps of the intercalated MXene nanosheet are as follows: The methoxy intercalation agent and dimethyl sulfoxide are added into a reaction kettle, stirred at 20-25 DEG C and 500-600 r / min for 20-30 min, then the suspension of MXene nanosheet is added, continue to stir for 24-26 h, centrifuged at 5000-6000 r / min for 1-2 min, remove the residual methoxy intercalation agent, filter, vacuum dried at 60-70 DEG C for 1-2 h, to obtain intercalated MXene nanosheet.

[0017] Further, the use amount ratio of methoxy intercalation agent, dimethyl sulfoxide and the suspension of MXene nanosheet is 30-40 g: 120-140 mL: 30-40 g.

[0018] Further, the specific preparation steps of the mesoscopic MOF / MXene nanosheet are as follows: The intercalated MXene nanosheet, 2, 5-dihydroxyterephthalic acid and N, N-dimethylformamide are added into a polytetrafluoroethylene liner autoclave, stirred at 20-25 DEG C and 500-600 r / min for 30-40 min, then 60-70 wt% ethanol solution is added, heated to 50-60 DEG C, continue to stir for 1-2 h, then iron chloride is added, heated to 120-130 DEG C, continue to react for 20-22 h, naturally cooled to room temperature, filter, the filter cake is washed with methanol solution and deionized water for 2-4 times respectively, vacuum dried at 60-70 DEG C for 1-2 h, to obtain mesoscopic MOF / MXene nanosheet.

[0019] Further, the use amount ratio of intercalated MXene nanosheet, 2, 5-dihydroxyterephthalic acid, N, N-dimethylformamide, ethanol solution and iron chloride is 20-30 g: 15-20 g: 120-140 mL: 50-60 mL: 12-14 g.

[0020] The beneficial effects of the application are: 1. The lightweight wave-absorbing polymethacrylimide composite material prepared by the application has the characteristics of uniform foaming, stable density, good mechanical properties and excellent wave-absorbing performance by adding mesoscopic MOF / MXene nanosheet as a wave-absorbing material.

[0021] 2. The mesoscopic MOF / MXene nanosheet of the present application, the MXene nanosheet is inserted by the methoxy intercalation agent through the surface negative charge characteristics, on the one hand, the methoxy intercalation agent is inserted into the interlayer of the MXene nanosheet through the electrostatic attraction of the cationic quaternary ammonium salt group, increasing the interlayer spacing of the MXene nanosheet, improving the specific surface area, on the other hand, as a surfactant, the MXene nanosheet can be prevented from agglomerating by hydrophobic interaction, and the iron-based MOF is hydrothermally grown on the surface of the MXene nanosheet, the methoxy of the methoxy intercalation agent inserted between the layers of the MXene nanosheet is hydrolyzed into silanol groups in an ethanol solution, and assembled into micelles, on the one hand, the micelles can act as a soft template to induce the formation of an ordered mesoscopic iron-based MOF structure, and the silanol groups can bind to the hydroxyl groups of the monomer 2,5-dihydroxyterephthalic acid of the iron-based MOF, promoting the stable and ordered heterojunction interface of the MOF on the surface of the MXene nanosheet.

[0022] 3. The mesoscopic MOF / MXene nanosheet of the present application has super-high conductivity, free electrons migrate in an alternating electromagnetic field to generate Joule heat, directly dissipating electromagnetic energy, the enlarged interlayer spacing and layered stacking structure prolong the electromagnetic wave propagation path, and the energy attenuation is enhanced through multiple reflections / scattering, the MOF grows on the surface to form a core-shell structure, providing more heterojunction interfaces and constructing a three-dimensional conductive network.

[0023] 4. The mesoscopic MOF / MXene nanosheet of the present application is used as a filler for a lightweight wave-absorbing polymethacrylimide composite material, and during the foaming stage, the surface-intercalated methoxy intercalation agent acts as a surfactant with a foaming and emulsifying effect, which can assist foaming and improve the uniformity of foaming. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Scanning electron microscope images of the mesoscopic MOF / MXene nanosheets prepared for Examples 1-3 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0026] Example 1: A method for preparing a lightweight wave-absorbing polymethacrylimide composite material, comprising the following steps: S1: 20 g of dodecyl dimethyl allyl ammonium chloride, 12 g of methyldichlorosilane and 20 g of toluene were added to a reaction kettle, stirred at 20 °C and 500 r / min for 20 min, then 0.4 g of 1% mass fraction isopropanol solution of chloroplatinic acid was added, heated to 65 °C under nitrogen protection for 2 h, and distilled under reduced pressure to obtain an intercalation agent precursor; 40 g of pretreated precursor and 20 g of methanol were mixed and dissolved at 20 °C and 500 r / min for 40 min, then transferred to a constant pressure dropping funnel, added dropwise into a reaction kettle containing 20 g of methanol, heated to 70 °C under nitrogen protection for 4 h, and distilled under reduced pressure to obtain a methoxy intercalation agent.

[0027] S2: 25 g of lithium fluoride and 500 mL of 25% mass fraction hydrochloric acid solution were added to a reaction kettle, stirred at 20 °C and 400 r / min for 20 min, then 13 g of titanium aluminum carbide was added, and stirring was continued for 48 h, centrifuged at 5000 r / min for 3 min, filtered, and the filter cake was washed with deionized water and ethanol until the last washing liquid was neutral, ultrasonically stripped under an argon flow of 20 mL / min, and centrifuged at 5000 r / min for 1 min to obtain a suspension of MXene nanosheets.

[0028] S3: 30 g of methoxy intercalation agent and 120 mL of dimethyl sulfoxide were added to a reaction kettle, stirred at 20 °C and 500 r / min for 20 min, then 30 g of MXene nanosheet suspension was added, and stirring was continued for 24 h, centrifuged at 5000 r / min for 1 min to remove residual methoxy intercalation agent, filtered, and vacuum dried at 60 °C for 1 h to obtain intercalated MXene nanosheets.

[0029] S4: 20 g of intercalated MXene nanosheets, 15 g of 2,5-dihydroxyterephthalic acid and 120 mL of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave, stirred at 20 °C and 500 r / min for 30 min, then 50 mL of 60 wt% ethanol solution was added, heated to 50 °C, and stirring was continued for 1 h, then 12 g of iron chloride was added, heated to 120 °C, and reaction was continued for 20 h, then naturally cooled to room temperature, filtered, and the filter cake was washed with methanol solution and deionized water for 2 times respectively, and vacuum dried at 60 °C for 1 h to obtain mesoscopic MOF / MXene nanosheets.

[0030] S5: 50 g of methacrylic acid, 50 g of methacrylonitrile, 7 g of 1-aminooctadecane, 0.5 g of N-acrylamide, 0.6 g of N-hydroxysuccinimide ester, 0.8 g of carbodiimide, 5 g of tridecyl methacrylate, 12 g of mesoporous MOF / MXene nanosheets, 0.3 g of initiator azobisisobutyronitrile, 0.7 g of foaming agent tert-butyl methacrylate, and 10 g of crosslinking agent acrylamide are uniformly mixed for 22 h, transferred into a mold, subjected to air extraction treatment at a pressure of -0.04 MPa, sealed, polymerized at 55°C for 36 h, then foamed at 180°C for 2 h, and annealed at 150°C for 14 h to obtain a lightweight wave-absorbing polymethacrylimide composite material.

[0031] Example 2: A preparation method of a lightweight wave-absorbing polymethacrylimide composite material, comprising the following steps: S1: 25 g of dodecyl dimethyl allyl ammonium chloride, 13 g of methyldichlorosilane, and 25 g of toluene are added to a reaction kettle, stirred at 22.5°C and 550 r / min for 25 min, then 0.45 g of 1.5% mass fraction chloroplatinic acid isopropanol solution is added, heated to 67.5°C under nitrogen protection for 2.5 h, and distilled under reduced pressure to obtain an intercalation agent precursor; 45 g of the pretreated precursor and 25 g of methanol are mixed and stirred at 22.5°C and 550 r / min for 50 min to dissolve, then transferred to a constant-pressure dropping funnel and added dropwise into a reaction kettle containing 25 g of methanol, heated to 75°C under nitrogen protection for 4.5 h, and distilled under reduced pressure to obtain a methoxy intercalation agent.

[0032] S2: 27.5 g of lithium fluoride and 550 mL of 30% mass fraction hydrochloric acid solution are added to a reaction kettle, stirred at 22.5°C and 450 r / min for 25 min, then 13.5 g of titanium aluminum carbide is added, and stirring is continued for 49 h, centrifuged at 5500 r / min for 3.5 min, filtered, and the filter cake is washed with deionized water and ethanol until the last washing liquid is neutral, ultrasonically peeled under an argon flow of 25 mL / min, and centrifuged at 5500 r / min for 1.5 min to obtain a suspension of MXene nanosheets.

[0033] S3: 35 g of methoxy intercalation agent and 130 mL of dimethyl sulfoxide are added to a reaction kettle, stirred at 22.5°C and 550 r / min for 25 min, then 35 g of the suspension of MXene nanosheets is added, and stirring is continued for 25 h, centrifuged at 5500 r / min for 1.5 min to remove residual methoxy intercalation agent, filtered, and vacuum dried at 65°C for 1.5 h to obtain intercalated MXene nanosheets.

[0034] S4: 25 g of intercalated MXene nanosheets, 17.5 g of 2,5-dihydroxyterephthalic acid, and 130 mL of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave, stirred at 22.5°C and 550 r / min for 35 min, then 55 mL of a 65 wt% ethanol solution was added, heated to 55°C, and stirred for 1.5 h, then 13 g of iron chloride was added, heated to 125°C, and reacted for 21 h, then naturally cooled to room temperature, filtered, and the filter cake was washed with a methanol solution and deionized water three times each, vacuum dried at 65°C for 1.5 h, and mesoscopic MOF / MXene nanosheets were obtained.

[0035] S5: 55 g of methacrylic acid, 51 g of methacrylonitrile, 7.5 g of 1-aminooctadecane, 0.55 g of N-acrylamide, 0.65 g of N-hydroxysuccinimide ester, 0.9 g of carbodiimide, 5.5 g of tridecyl methacrylate, 13 g of mesoscopic MOF / MXene nanosheets, 0.35 g of initiator azobisisobutyronitrile, 0.75 g of foaming agent tert-butyl methacrylate, and 10.5 g of crosslinking agent acrylamide were uniformly mixed for 23 h, transferred to a mold, subjected to air extraction treatment at a pressure of -0.04 MPa, sealed, polymerized at 57.5°C for 37 h, then foamed at 190°C for 2.5 h, and annealed at 155°C for 15 h to obtain a lightweight wave-absorbing polymethacrylimide composite material.

[0036] Example 3: A method for preparing a lightweight wave-absorbing polymethacrylimide composite material, comprising the following steps: S1: 30 g of dodecyl dimethyl allyl ammonium chloride, 14 g of methyldichlorosilane, and 30 g of toluene were added to a reaction kettle, stirred at 25°C and 600 r / min for 30 min, then 0.5 g of a 2% mass fraction isopropyl alcohol solution of chloroplatinic acid was added, heated to 70°C under nitrogen protection for 3 h, and distilled under reduced pressure to obtain an intercalation agent precursor; 50 g of the pretreated precursor and 30 g of methanol were mixed, stirred and dissolved at 25°C and 600 r / min for 60 min, transferred to a constant-pressure dropping funnel, and added dropwise to a reaction kettle containing 30 g of methanol, heated to 80°C under nitrogen protection for 5 h, and distilled under reduced pressure to obtain a methoxy intercalation agent.

[0037] S2: 30 g of lithium fluoride and 600 mL of a 35% mass fraction hydrochloric acid solution were added to a reaction kettle, stirred at 25°C and 500 r / min for 30 min, then 14 g of titanium aluminum carbide was added, and stirring was continued for 50 h, centrifuged at 6000 r / min for 4 min, filtered, the filter cake was washed with deionized water and ethanol until the last washing liquid was neutral, ultrasonically peeled under an argon flow of 30 mL / min, and centrifuged at 6000 r / min for 2 min to obtain a suspension of MXene nanosheets.

[0038] S3: 40 g of methoxy intercalation agent and 140 mL of dimethyl sulfoxide were added to a reaction kettle, stirred at 25 °C and 600 r / min for 30 min, then 40 g of MXene nanosheet suspension was added, and stirring was continued for 26 h, centrifuged at 6000 r / min for 2 min, the residual methoxy intercalation agent was removed, filtered, and vacuum dried at 70 °C for 2 h to obtain intercalated MXene nanosheets.

[0039] S4: 30 g of intercalated MXene nanosheets, 20 g of 2,5-dihydroxyterephthalic acid and 140 mL of N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave, stirred at 25 °C and 600 r / min for 40 min, then 60 mL of 70 wt% ethanol solution was added, heated to 60 °C, and stirring was continued for 2 h, then 14 g of iron chloride was added, heated to 130 °C, and reaction was continued for 22 h, then naturally cooled to room temperature, filtered, and the filter cake was washed with methanol solution and deionized water for 4 times respectively, and vacuum dried at 70 °C for 2 h to obtain mesoporous MOF / MXene nanosheets.

[0040] S5: 60 g of methacrylic acid, 52 g of methacrylonitrile, 8 g of 1-aminooctadecane, 0.6 g of N-acrylamide, 0.7 g of N-hydroxysuccinimide ester, 1 g of carbodiimide, 6 g of tridecyl methacrylate, 14 g of mesoporous MOF / MXene nanosheets, 0.4 g of initiator azobisisobutyronitrile, 0.8 g of foaming agent tert-butyl methacrylate and 11 g of crosslinking agent acrylamide were mixed uniformly for 24 h, transferred to a mold, subjected to air extraction treatment at a pressure of -0.04 MPa, sealed, polymerized at 60 °C for 38 h, then foamed at 200 °C for 3 h, and annealed at 160 °C for 16 h to obtain a lightweight wave-absorbing polymethacrylimide composite material.

[0041] Comparative Example 1: On the basis of Example 3, the intercalated MXene nanosheets in step S4 were replaced by the MXene nanosheet suspension prepared in step S2.

[0042] Comparative Example 2: On the basis of Example 3, the intercalated MXene nanosheets in step S4 were replaced by a mixture of the MXene nanosheet suspension prepared in step S2 and the methoxy intercalation agent prepared in step S1.

[0043] Comparative Example 3: On the basis of Example 3, the mesoporous MOF / MXene nanosheets in step S5 were replaced by the intercalated MXene nanosheets prepared in step S3.

[0044] The light-weight wave-absorbing polymethacrylimide composite materials prepared in Example 1-Example 3 and Comparative Example 1-Comparative Example 3 were subjected to performance testing according to the QB / T5491-2020 "Polymethacrylimide Foam Board" standard test: 1. Tensile property test: The standard tensile mechanical test sample prepared was subjected to tensile test using a universal mechanical testing machine, and the tensile rate was 2 mm / min. 2. The test conditions were as follows: the tensile strength and elongation at break were tested according to GB / T9641; 2. Wave-absorbing performance test: The reflectivity test method for radar wave-absorbing materials was used, and the test was performed according to the GJB2038A-2011 arc test method, the test frequency band was (2-18) GHz, and the sample test sample size was (300±0.5) mm×(300±0.5) mm×(30±0.2) mm; 3. Density test: The national standard GB / T 6343-2009 "Determination of apparent density of foamed plastics and rubbers" was followed, and the results are shown in Table 1: Table 1

[0045] As can be seen from Table 1, the tensile strength and elongation at break of Example 1-Example 3 are significantly better than those of the comparative examples, and the reflectivity and density are significantly lower than those of the comparative examples, indicating that the light-weight wave-absorbing polymethacrylimide composite material prepared in the present application is uniformly foamed, has stable and smaller density than the comparative examples, has the characteristics of light weight, good mechanical properties, and excellent wave-absorbing performance.

[0046] In Comparative Example 1, the intercalated MXene nanosheets in step S4 were replaced by the suspension of MXene nanosheets prepared in step S2. The surface of the MXene nanosheets has a negative charge, and the intercalation is not electrostatically attracted by the intercalation agent. The interlayer spacing is small, the specific surface area is low, and the agglomeration is easy to occur due to the surface charge effect, resulting in uneven dispersion in the composite material. Due to the lack of the hydrophobic effect and soft template function of the intercalation agent, the iron-based MOF cannot stably and orderly grow on the surface of the MXene, and it is difficult to form a mesostructure and a core-shell heterojunction interface, and the wave-absorbing performance is greatly reduced. The agglomeration of MXene leads to stress concentration in the composite material, and the mechanical properties are reduced. The unintercalated MXene has poor dispersibility, and there is no intercalation agent to assist foaming, resulting in a decrease in foaming uniformity and an increase in density.

[0047] Comparative Example 2 replaces the intercalated MXene nanosheets in Step S4 with a mixture of the MXene nanosheets suspension prepared in Step S2 and the methoxy intercalation agent prepared in Step S1, and physical mixing cannot achieve the electrostatic attraction intercalation of the intercalation agent and MXene, the interlayer spacing increase effect is limited, the specific surface area is insufficiently improved, and the MXene still has partial agglomeration, the intercalation agent is not stably embedded between the layers, and its methoxy group is difficult to be orderly hydrolyzed into a silanol group and assembled into micelles, which cannot be used as a soft template to induce the formation of mesoscopic MOF structures, the interface bonding force between the MOF and the MXene is weak, the hetero-interface is reduced, the wave absorption performance is better than that of Comparative Example 1 but still lower than that of the embodiment, the insufficient dispersibility and interface bonding force result in limited improvement in mechanical properties, and the foaming uniformity is still poorer than that of the embodiment, and the density is relatively high.

[0048] Comparative Example 3 replaces the mesoscopic MOF / MXene nanosheets in Step S5 with the intercalated MXene nanosheets prepared in Step S3, and the porous structure and core-shell hetero-interface of the iron-free MOF cannot build a three-dimensional conductive network, electromagnetic wave reflection, the scattering path is shortened, the joule heat generated by the free electron migration is reduced, the wave absorption performance is reduced, the absence of the MOF leads to a reduction in the internal reinforcing phase of the composite material and a weakening of the interface interaction, the mechanical properties are better than those of Comparative Examples 1 and 2, but still lower than those of the embodiment, the lack of the porous characteristics of the MOF hinders lightweight, and the single structure of the intercalated MXene has limited improvement in foaming uniformity, and the density is slightly higher than that of the embodiment.

[0049] Although the embodiments of the present application have been shown and described, it can be understood by those of ordinary skill in the art that various changes, modifications, replacements and modifications can be made to these embodiments without departing from the principles and spirits of the present application.

Claims

1. A method for preparing a lightweight wave-absorbing polymethacrylimide composite material, characterized in that: The steps include: Step 1: The terminal alkenyl group of dodecyldimethylallylammonium chloride reacts with methyldichlorosilane under the catalysis of chloroplatinic acid to produce an intercalant precursor, which is then subjected to a nucleophilic substitution reaction with methanol to replace the chlorine atom with a methoxy group to produce a methoxy intercalant; Step 2: Lithium fluoride reacts with hydrochloric acid to generate hydrofluoric acid, which then etches the Al atomic layer in titanium aluminum carbide to form a suspension of MXene nanosheets. The cations at one end of the methoxy intercalant are electrostatically attracted to the negative charges between the MXene nanosheets to form intercalated MXene nanosheets. Step 3: Using intercalated MXene nanosheets as carriers, a stable and ordered heterogeneous interface of iron-based MOF is generated on the surface of the MXene nanosheets to obtain mesoscopic MOF / MXene nanosheets; Step 4: Mix methacrylic acid, methacrylonitrile, 1-aminooctadecane, N-acrylamide, N-hydroxysuccinimide ester, carbodiimide, tridecyl methacrylate, mesoscopic MOF / MXene nanosheets, azobisisobutyronitrile, tert-butyl methacrylate and acrylamide for 22-24 hours, transfer them to a mold, and obtain a lightweight absorbing polymethacrylimide composite material through sealing, polymerization, foaming and annealing.

2. The method for preparing a lightweight wave-absorbing polymethacrylimide composite material according to claim 1, characterized in that: The usage ratio of the methacrylic acid, methacrylonitrile, 1-aminooctadecane, N-acrylamide, N-hydroxysuccinimide ester, carbodiimide, tridecyl methacrylate, mesoscopic MOF / MXene nanosheets, azobisisobutyronitrile, tert-butyl methacrylate and acrylamide is 50-60g: 50-52g: 7-8g: 0.5-0.6g: 0.6-0.7g: 0.8-1g: 5-6g: 12-14g: 0.3-0.4g: 0.7-0.8g: 10-11g.

3. The method for preparing a lightweight wave-absorbing polymethacrylimide composite material according to claim 1, characterized in that: The specific preparation steps of the intercalant precursor are as follows: Add dodecyldimethylallylammonium chloride, methyldichlorosilane and toluene into a reactor, stir at 20-25°C and 500-600 r / min for 20-30 minutes, then add 1-2% by mass chloroplatinic acid isopropanol solution, heat to 65-70°C under nitrogen protection, react for 2-3 hours, and distill under reduced pressure to obtain an intercalant precursor; The usage ratio of the dodecyldimethylallylammonium chloride, methyldichlorosilane, toluene and chloroplatinic acid isopropanol solution is 20-30 g: 12-14 g: 20-30 g: 0.4-0.5 g.

4. The method for preparing a lightweight wave-absorbing polymethacrylimide composite material according to claim 1, characterized in that: The specific preparation steps of the methoxy intercalant are as follows: The pretreated precursor and methanol were mixed, stirred and dissolved at 20-25°C and 500-600 r / min for 40-60 minutes, transferred to a constant pressure dropping funnel, and added dropwise to a reactor containing methanol. Under nitrogen protection, the mixture was heated to 70-80°C for reaction for 4-5 hours, and distilled under reduced pressure to obtain a methoxy intercalant; The usage ratio of the pretreatment precursor and methanol is 40-50 g:40-60 g.

5. The method for preparing a lightweight wave-absorbing polymethacrylimide composite material according to claim 1, characterized in that: The specific preparation steps of the MXene nanosheet suspension are as follows: Lithium fluoride and a hydrochloric acid solution with a mass fraction of 25-35% are added to a reactor, stirred at 20-25°C and 400-500 r / min for 20-30 min, then titanium aluminum carbide is added, stirring is continued for 48-50 h, centrifuged at 5000-6000 r / min for 3-4 min, filtered, and the filter cake is washed with deionized water and ethanol until the last washing liquid is neutral, ultrasonically peeled at an argon flow rate of 20-30 mL / min, and centrifuged at 5000-6000 r / min for 1-2 min to obtain a suspension of MXene nanosheets; The usage ratio of the lithium fluoride, the hydrochloric acid solution and the titanium aluminum carbide is 25-30 g: 500-600 mL: 13-14 g.

6. The method for preparing a lightweight wave-absorbing polymethacrylimide composite material according to claim 1, characterized in that: The specific preparation steps of the intercalated MXene nanosheets are as follows: Add the methoxy intercalant and dimethyl sulfoxide into the reactor, stir at 20-25°C and 500-600 r / min for 20-30 min, then add the suspension of MXene nanosheets, continue stirring for 24-26 h, centrifuge at 5000-6000 r / min for 1-2 min to remove the residual methoxy intercalant, filter, and vacuum dry at 60-70°C for 1-2 h to obtain intercalated MXene nanosheets.

7. The method for preparing a lightweight wave-absorbing polymethacrylimide composite material according to claim 6, characterized in that: The usage ratio of the methoxy intercalant, dimethyl sulfoxide and MXene nanosheet suspension is 30-40 g: 120-140 mL: 30-40 g.

8. The method for preparing a lightweight wave-absorbing polymethacrylimide composite material according to claim 1, characterized in that: The specific preparation steps of the mesoscopic MOF / MXene nanosheets are as follows: The intercalated MXene nanosheets, 2,5-dihydroxyterephthalic acid and N,N-dimethylformamide were added to a polytetrafluoroethylene-lined autoclave and stirred at 20-25°C and 500-600r / min for 30-40min. Then, a 60-70wt% ethanol solution was added, heated to 50-60°C, and stirred for 1-2h. Then, ferric chloride was added, heated to 120-130°C, and the reaction was continued for 20-22h. The mixture was naturally cooled to room temperature and filtered. The filter cake was washed 2-4 times with methanol solution and deionized water respectively, and dried in vacuo at 60-70°C for 1-2h to obtain mesoscopic MOF / MXene nanosheets.

9. The method for preparing a lightweight wave-absorbing polymethacrylimide composite material according to claim 8, characterized in that: The amount ratio of the intercalated MXene nanosheets, 2,5-dihydroxyterephthalic acid, N,N-dimethylformamide, ethanol solution and ferric chloride is 20-30 g: 15-20 g: 120-140 mL: 50-60 mL: 12-14 g.

10. A lightweight wave-absorbing polymethacrylimide composite material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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