Broadband wave-absorbing polymethacrylimide composite material and preparation method thereof

Abstract

The invention belongs to the technical field of wave-absorbing composite materials, and particularly relates to a broadband wave-absorbing polymethacrylimide composite material and a preparation method thereof. The invention provides a broadband wave-absorbing polymethacrylimide composite material. The broadband wave-absorbing polymethacrylimide composite material comprises a wave-absorbing layer and a surface layer covering the surface of the wave-absorbing layer, the wave-absorbing layer is prepared from the following raw materials in parts by mass: 30 to 60 parts of methacrylic acid monomer, 20 to 40 parts of acrylonitrile monomer, 10 to 20 parts of anthracene-naphthene monomer, 5 to 10 parts of wave-absorbing agent, 2 to 10 parts of foaming agent, 1 to 5 parts of nucleating agent, 1 to 5 parts of initiator and 0 to 2 parts of cross-linking agent. By optimizing the components and the structure of the polymethacrylimide composite material, the prepared polymethacrylimide composite material has wide wave absorbing frequency.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave absorbing composite materials, and particularly relates to a broadband microwave absorbing polymethacrylimide composite material and a preparation method thereof. Background Art

[0002] Polymethacrylimide (PMI) has good mechanical properties, excellent heat resistance and processing properties. PMI itself does not have microwave absorbing properties. At present, PMI is mostly used as a matrix material and is well combined with other microwave absorbing fillers, fibers and other substances to form composite materials. In the microwave absorbing composite materials, PMI can be uniformly dispersed and carry these microwave absorbing components, so that the microwave absorbing materials have stable and good microwave absorbing properties.

[0003] With the rapid development of electronic information technology, the problems of electromagnetic interference and electromagnetic radiation are becoming increasingly serious, and the demand for microwave absorbing materials is also getting higher and higher. Broadband microwave absorbing materials can absorb electromagnetic waves in a relatively wide frequency range and have important application values. However, at present, there are few existing polymethacrylimide microwave absorbing materials and it is difficult to meet the requirements of broadband microwave absorption. Summary of the Invention

[0004] The present invention provides a broadband microwave absorbing polymethacrylimide composite material and a preparation method thereof, and solves the problem that the existing microwave absorbing polymethacrylimide composite materials are difficult to meet the requirements of broadband microwave absorption by optimizing the composition and structure of the polymethacrylimide composite materials.

[0005] In the first aspect, a broadband microwave absorbing polymethacrylimide composite material is provided, which includes a microwave absorbing layer and a surface layer covering the surface of the microwave absorbing layer; The microwave absorbing layer comprises raw materials in the following parts by mass: 30-60 parts of methacrylic acid monomer; 20-40 parts of acrylonitrile monomer; 10-20 parts of anthracene-naphthalene monomer; 5-10 parts of microwave absorber; 2-10 parts of foaming agent; 1-5 parts of nucleating agent; 1-5 parts of initiator; 0-2 parts of crosslinking agent; The anthracene-naphthalene monomer is at least one of 9,10-bis(1-naphthyl)-2-vinylanthracene, 9-(2-naphthyl)-10-(3-butenyl)anthracene, 9,10-bis(N-(2-naphthyl)-N-(4-pentenyl)anilino)anthracene, 9-vinyl-10-(2-naphthyl)anthracene and 9,10-bis(3-naphthyl-2-propenyl)anthracene.

[0006] Preferably, the surface layer is obtained by coating the surface of the wave-absorbing layer with a surface layer coating material, and the surface layer coating material comprises raw materials with the following mass parts: 40-60 parts of silicone resin, 10-20 parts of nano titanium dioxide, 2-5 parts of silane coupling agent, and 20-40 parts of organic solvent.

[0007] Preferably, the wave-absorbing agent is a carbon material, and the carbon material comprises carbon fiber.

[0008] Preferably, the wave-absorbing agent is an organic-inorganic hybrid hollow carbon short fiber.

[0009] Preferably, the preparation method of the organic-inorganic hybrid hollow carbon short fiber comprises: Step 1, dissolve polyacrylonitrile in an organic solvent, add ferrite and an antioxidant, and mix evenly to obtain a shell spinning solution stock solution; Step 2, dissolve polyvinylpyrrolidone in an organic solvent, add ferrite and an antioxidant, and mix evenly to obtain a core spinning solution stock solution; Step 3, perform coaxial electrospinning on the shell spinning solution stock solution and the core spinning solution stock solution to obtain a carbon fiber precursor, and then soak the carbon fiber precursor in water to obtain an organic-inorganic hybrid hollow carbon fiber precursor; Step 4, sequentially dry, pre-oxidize, and perform high-temperature carbonization on the organic-inorganic hybrid hollow carbon fiber precursor to obtain an organic-inorganic hybrid hollow carbon fiber, and perform acid leaching roughening and mechanical cutting on the organic-inorganic hybrid hollow carbon fiber to obtain the organic-inorganic hybrid hollow carbon short fiber. The obtained organic-inorganic hybrid hollow carbon short fiber has a rough surface, and the hollow and rough structures can improve the wave-absorbing ability of the wave-absorbing agent.

[0010] Preferably, the proportion of ferrite in the shell spinning solution stock solution is 10 wt%-20 wt% and the proportion of the antioxidant is 1 wt%-4 wt%; The proportion of ferrite in the core spinning solution is 8 wt%-15 wt% and the proportion of the antioxidant is 0.5 wt%-3 wt%.

[0011] Preferably, the acrylonitrile monomer contains at least one of a fluoroalkyl group, a phenyl group, a sulfonic acid group, and a carboxyl group.

[0012] Preferably, the acrylonitrile monomer is at least one of 4-(trifluoromethylsulfonyl)benzonitrile, 4-(phenylsulfonyl)benzonitrile, 4-(trifluoromethyl)benzonitrile-2-carboxylic acid, and 2-fluoro-5-(2-carboxyethyl)benzyl cyanide.

[0013] In a second aspect, the present invention provides a preparation method of a broadband wave-absorbing poly(methacrylimide) composite material, comprising the following steps: Step 1: Mix methacrylic acid monomer, acrylonitrile monomer, anthracene-naphthalene monomer, wave absorber, foaming agent, nucleating agent, initiator and crosslinking agent evenly to obtain a mixture; Step 2: Under closed conditions, carry out the prepolymerization reaction and copolymerization reaction on the obtained mixture in sequence to obtain a polymethacrylimide plate; Step 3: Carry out thermal foaming treatment on the obtained polymethacrylimide plate, and then cool it to room temperature to obtain polymethacrylimide foam; Step 4: Coat a surface layer coating on the surface of the polymethacrylimide foam to obtain a polymethacrylimide composite material.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: In the present invention, anthracene-naphthalene monomer is added for copolymerization to realize in-situ modification of polymethacrylimide. The obtained polymethacrylimide has a large conjugated system and a special molecular structure due to the anthracene-naphthalene monomer, and can interact with electromagnetic waves in a relatively wide frequency range. Adding it to prepare a wave-absorbing composite material can cooperate with the wave absorber to broaden the frequency range of the obtained wave-absorbing composite material. Even after being treated in a high-humidity environment, the wave-absorbing frequency range can reach 1.93 - 26.06 GHz, and the maximum absorption peak can reach -34.57 dB, having good application prospects. Specific Embodiments

[0015] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0016] The present invention provides a broadband wave-absorbing polymethacrylimide composite material, including a wave-absorbing layer and a surface layer covering the surface of the wave-absorbing layer; The wave-absorbing layer is made of raw materials including the following components by mass: 30 - 60 parts of methacrylic acid monomer; 20 - 40 parts of acrylonitrile monomer; 10 - 20 parts of anthracene-naphthalene monomer; 5 - 10 parts of wave absorber; 2 - 10 parts of foaming agent; 1 - 5 parts of nucleating agent; 1 - 5 parts of initiator; 0 - 2 parts of crosslinking agent.

[0017] The present invention adds anthracene naphthalene monomers for copolymerization in the preparation of the polymethacrylimide composite material. The obtained polymethacrylimide has a large conjugated system and a special molecular structure, and can interact with electromagnetic waves in a wider frequency range, which helps to broaden the absorbing frequency range of the obtained absorbing material.

[0018] The anthracene-naphthylene monomer is selected from at least one of 9,10-bis(1-naphthyl)-2-vinylanthracene, 9-(2-naphthyl)-10-(3-butenyl)anthracene, 9,10-bis(N-(2-naphthyl)-N-(4-pentenyl)anilino)anthracene, 9-vinyl-10-(2-naphthyl)anthracene and 9,10-bis(3-naphthyl-2-propenyl)anthracene.

[0019] In addition, the acrylonitrile monomer contains at least one of fluoroalkyl, phenyl, sulfonic acid, and carboxyl groups. Although the introduction of anthracene naphthylene monomers can improve the wave absorption performance and obtain a wider wave absorption frequency, the waterproof and anti-oxidation properties of the obtained polymethacrylimide wave absorbing composite material will deteriorate. The addition of acrylonitrile monomers containing at least one of fluoroalkyl, phenyl, sulfonic acid, and carboxyl groups helps to improve the moisture resistance and easy oxidation problems during copolymerization, and is conducive to improving the wave absorption stability.

[0020] In addition, the acrylonitrile monomer is at least one of 4-(trifluoromethylsulfonyl)benzonitrile, 4-(phenylsulfonyl)benzonitrile, 4-(trifluoromethyl)benzonitrile-2-carboxylic acid and 2-fluoro-5-(2-carboxyethyl)benzylacetonitrile.

[0021] In addition, the absorbent is a carbon material, and the carbon material includes carbon fiber; the carbon material has high electrical conductivity and dielectric properties, can produce strong dielectric loss, and realize the absorption of electromagnetic waves. Carbon materials have good chemical stability and corrosion resistance under general environmental conditions, and can maintain the stability of their absorbing performance in different use environments. Whether in corrosive environments such as humidity, acid and alkali, or in extreme conditions such as high temperature and low temperature, carbon materials can play a good absorbing role and are not prone to performance degradation due to environmental factors. Carbon fiber has excellent mechanical properties, and its strength and modulus are much higher than ordinary absorbing carbon materials. This makes carbon fiber, when added to composite materials as an absorbent, not only give the material good absorbing performance, but also significantly improve the mechanical strength and rigidity of the material, enhance the overall performance of the material, and enable it to maintain a stable absorbing effect when subjected to large external forces or complex stresses.

[0022] Preferably, the wave absorber is an organic-inorganic hybrid hollow carbon short fiber; the hollow structure further reduces the density of the wave absorber, making it lighter in weight and achieving efficient wave absorption; among them, the hollow structure increases the propagation path of electromagnetic waves inside the material, causing the electromagnetic waves to be reflected and scattered multiple times in the hollow cavity, prolonging the interaction time between the electromagnetic waves and the wave-absorbing material, thereby enhancing the absorption effect of the electromagnetic waves and improving the wave absorption efficiency. And the hollow structure helps to improve the thermal stability of the material. In a high-temperature environment, the hollow carbon fiber material can better maintain the stability of its structure and performance, preventing the wave absorption performance from decreasing due to temperature changes, and is suitable for some high-temperature working environments.

[0023] In addition, the blowing agent is not limited here, and conventional blowing agents can be selected. As an example, ethanol, propanol, isopropanol, water, butanol, tert-butanol, pentanol or isopentanol can be listed.

[0024] Here, the nucleating agent can be selected from at least one of carbonamide, formamide, methacrylamide, N-methylformamide and N-dimethylformamide.

[0025] In addition, the initiator can be selected from at least one of lauroyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, 4-(1,1-dimethylethyl) cyclohexanedicarboxylic acid peroxide, tert-butyl perpivalate, di-tert-butyl peroxide, tert-butyl 2-ethylhexanoate, tert-butyl benzoate and (4-tert-butylcyclohexyl) peroxydicarbonate.

[0026] In addition, the crosslinking agent can be selected from at least one of allyl acrylate, allyl methacrylate, magnesium methacrylate and zinc methacrylate.

[0027] In addition, the surface layer needs to have good bonding strength with the wave-absorbing layer, and also needs to have certain waterproof performance and antioxidant ability, and does not affect the wave absorption performance of the overall material; the surface layer is obtained by coating the surface layer coating on the surface of the wave-absorbing layer, and the surface layer coating includes raw materials with the following mass parts: 40-60 parts of silicone resin, 10-20 parts of nano-titanium dioxide, 2-5 parts of silane coupling agent and 20-40 parts of organic solvent.

[0028] Among them, the organic solvent in the surface layer coating is preferably one that has good dispersibility for the raw materials of the surface layer coating. As an example, toluene or xylene can be listed.

[0029] In addition, the silicone resin is at least one of methyl silicone resin and phenyl silicone resin.

[0030] In addition, the silane coupling agent is used to improve the bonding strength between the surface layer and the wave-absorbing layer. The specific type of the silane coupling agent is not limited here and can be selected according to requirements. As an example, KH560 and KH570 can be listed.

[0031] On the other hand, the present invention provides a method for preparing a broadband wave-absorbing polymethacrylimide composite material, comprising the following steps: Step 1: Mix methacrylic acid monomers, acrylonitrile monomers, anthracene-naphthalene monomers, wave-absorbing agents, foaming agents, nucleating agents, initiators and crosslinking agents evenly to obtain a mixture. Step 2: Under closed conditions, carry out a prepolymerization reaction and a copolymerization reaction on the obtained mixture in sequence to obtain a polymethacrylimide plate. Step 3: Carry out thermal foaming treatment on the obtained polymethacrylimide plate, and then cool it to room temperature to obtain a polymethacrylimide foam. Step 4: Coat a surface layer coating on the surface of the polymethacrylimide foam to obtain a polymethacrylimide composite material.

[0032] When the wave-absorbing agent is an organic-inorganic hybrid hollow carbon short fiber, the preparation method of the organic-inorganic hybrid hollow carbon short fiber comprises: Step 1: Dissolve polyacrylonitrile in an organic solvent, add ferrite and an antioxidant and mix evenly to obtain a shell spinning solution stock solution. Step 2: Dissolve polyvinylpyrrolidone in an organic solvent, add ferrite and an antioxidant and mix evenly to obtain a core spinning solution stock solution. Step 3: Carry out coaxial electrospinning on the shell spinning solution stock solution and the core spinning solution stock solution to obtain a carbon fiber precursor, and then soak the carbon fiber precursor in water to obtain an organic-inorganic hybrid hollow carbon fiber precursor. Step 4: Subject the organic-inorganic hybrid hollow carbon fiber precursor to drying, pre-oxidation and high-temperature carbonization in sequence to obtain an organic-inorganic hybrid hollow carbon fiber, and carry out acid leaching roughening and mechanical cutting on the organic-inorganic hybrid hollow carbon fiber to obtain the organic-inorganic hybrid hollow carbon short fiber.

[0033] Among them, in the shell spinning solution stock solution, the proportion of polyacrylonitrile is 10-20 wt%, the proportion of ferrite is 10 wt%-20 wt% and the proportion of antioxidant is 1 wt%-4 wt%; in the core spinning solution, the proportion of polyvinylpyrrolidone is 10-20 wt%, the proportion of ferrite is 8 wt%-15 wt% and the proportion of antioxidant is 0.5 wt%-3 wt%.

[0034] The function of preparing the organic-inorganic hybrid hollow carbon short fibers added with ferrite here is to interact with the modified poly (methyl methacrylimide) matrix to improve the wave absorption performance; the specific type of ferrite is not limited and can be selected according to actual needs. As an example, manganese-zinc ferrite, nickel-zinc ferrite, etc. can be listed.

[0035] In addition, the antioxidant is selected as a high-temperature resistant metal antioxidant, etc., including but not limited to at least one of titanium oxide and zinc oxide.

[0036] In addition, during the preparation process of the organic-inorganic hybrid hollow carbon short fibers, the organic solvents are all selected as solvents with good solubility in the system; as an example, N, N-dimethylformamide and dimethyl sulfoxide can be listed.

[0037] In addition, the applied voltage of the coaxial electrospinning is 12 kV to 26 kV, the distance between the needle and the receiving cylinder is 15 cm to 20 cm, the rate ratio of the flow rate of the outer shell spinning solution stock solution to the flow rate of the inner core spinning solution is 1.2 to 3:1, and the total liquid supply rate is 4.8 mL / h to 12.0 mL / h.

[0038] In addition, the soaking is carried out by soaking in water at a temperature of 25 °C to 80 °C for 6 h to 36 h.

[0039] In addition, the drying is carried out by drying at a temperature of 60 °C to 100 °C for 5 h to 20 h.

[0040] In addition, the pre-oxidation is carried out by oxidizing at a temperature of 220 °C to 260 °C for 1 h to 4 h.

[0041] In addition, the high-temperature carbonization is carried out by heating to 600 °C to 800 °C at a heating rate of 2 °C / min to 6 °C / min in an inert atmosphere and holding for 1 h to 3 h.

[0042] The hollow diameter of the obtained organic-inorganic hybrid hollow carbon short fibers here is 350 nm to 1000 nm, and the wall thickness is 60 nm to 120 nm. The hollow diameter and wall thickness here can be adjusted according to actual needs, and other hollow diameters and wall thicknesses can also be obtained by adjusting the electrospinning process parameters according to needs, and should not be construed as a limitation of the present invention.

[0043] In addition, the preparation method of the surface layer coating includes: Take 40 to 60 parts of silicone resin, 10 to 20 parts of nano-titanium dioxide, 2 to 5 parts of silane coupling agent and 20 to 40 parts of organic solvent, and mix them evenly to obtain.

[0044] Specific embodiments are provided below to further describe the present invention.

[0045] It should be noted that the microwave absorbing agent added in the following Examples 1 to 3 is an organic-inorganic hybrid hollow carbon short fiber material; preparation examples of the organic-inorganic hybrid hollow carbon short fibers described in Examples 1 to 3 are as follows: Step 1. Dissolve polyacrylonitrile in N,N-dimethylformamide, add BaFe 12 O 19 and titanium oxide and mix them evenly to obtain the original shell spinning solution; in the original shell spinning solution, the proportion of polyacrylonitrile is 15 wt%, the proportion of BaFe 12 O 19 is 15 wt% and the proportion of titanium oxide is 2 wt%; Step 2. Dissolve polyvinylpyrrolidone in N,N-dimethylformamide, add BaFe 12 O 19 and titanium oxide and mix them evenly to obtain the original core spinning solution; in the original core spinning solution, the proportion of polyvinylpyrrolidone is 15 wt%, the proportion of BaFe 12 O 19 is 10 wt% and the proportion of titanium oxide is 1 wt%; Step 3. Carry out coaxial electrospinning on the original shell spinning solution and the original core spinning solution at a rate ratio of the flow rates of the original shell spinning solution to the original core spinning solution of 2:1 and a total feeding rate of 8.0 mL / h to obtain a carbon fiber precursor, and then immerse the carbon fiber precursor in water at 50 °C for 24 h to obtain an organic-inorganic hybrid hollow carbon fiber precursor; the applied voltage for the coaxial electrospinning is 18 kV, and the distance between the needle and the receiving cylinder is 16 cm; Step 4. Dry the organic-inorganic hybrid hollow carbon fiber precursor at 60 °C for 12 h, oxidize it at 220 °C for 3 h, heat it to 800 °C at a heating rate of 4 °C / min in a nitrogen atmosphere and hold for 2 h to obtain an organic-inorganic hybrid hollow carbon fiber. Immerse the organic-inorganic hybrid hollow carbon fiber in a 10 wt% hydrochloric acid solution at 40 °C for 3 h for roughening, and then carry out mechanical cutting to obtain the organic-inorganic hybrid hollow carbon short fiber material; the hollow diameter of the obtained organic-inorganic hybrid hollow carbon short fiber material is 800 nm, and the wall thickness is 80 nm.

[0046] Example 1: Preparation of broadband microwave absorbing poly(methacrylimide) composite material: Step 1. Mix 31 parts of methacrylic acid monomer, 40 parts of 4-(phenylsulfonyl)benzonitrile, 10 parts of 9-(2-naphthyl)-10-(3-butenyl)anthracene, 8 parts of organic-inorganic hybrid hollow carbon short fibers, 6 parts of isoamyl alcohol, 2 parts of formamide and 3 parts of azobisisobutyronitrile evenly to obtain a mixture; Step 2: Under airtight conditions, react the obtained mixture at 100°C for 36 h first, and then react at 120°C for 36 h to obtain a polymethacrylimide plate; Step 3: Preheat the obtained polymethacrylimide plate at 100°C for 5 h, then perform thermal foaming treatment at 180°C for 3 h, and cool to room temperature to obtain polymethacrylimide foam; Step 4: Coat a surface layer coating on the surface of the polymethacrylimide foam to obtain a polymethacrylimide composite material; wherein, the preparation method of the surface layer coating includes: Take 20 parts of methyl silicone resin, 30 parts of phenyl silicone resin, 10 parts of nano-titanium dioxide, 3 parts of KH560 and 37 parts of toluene, and mix them evenly to obtain the product.

[0047] The effective frequency band of the polymethacrylimide composite material prepared in Example 1 for absorbing waves covers 2.02 - 18.96 GHz, and the maximum absorption peak can reach -30.57 dB.

[0048] Example 2: Preparation of a broadband wave-absorbing polymethacrylimide composite material: Step 1: Mix 52 parts of methacrylic acid monomer, 20 parts of 4-(trifluoromethyl)benzonitrile-2-carboxylic acid, 17 parts of 9,10-bis(N-(2-naphthyl)-N-(4-pentenyl)anilino)anthracene, 5 parts of an organic-inorganic hybrid hollow carbon short fiber material, 2 parts of isopropyl alcohol, 1 part of N-dimethylformamide, 2 parts of lauroyl peroxide and 1 part of allyl methacrylate evenly to obtain a mixture; Step 2: Under airtight conditions, react the obtained mixture at 100°C for 36 h first, and then react at 120°C for 36 h to obtain a polymethacrylimide plate; Step 3: Preheat the obtained polymethacrylimide plate at 100°C for 5 h, then perform thermal foaming treatment at 180°C for 3 h, and cool to room temperature to obtain polymethacrylimide foam; Step 4: Coat a surface layer coating on the surface of the polymethacrylimide foam to obtain a polymethacrylimide composite material; wherein, the preparation method of the surface layer coating includes: Take 40 parts of methyl silicone resin, 20 parts of nano-titanium dioxide, 5 parts of KH560 and 35 parts of toluene, and mix them evenly to obtain the product.

[0049] The effective frequency band of the polymethacrylimide composite material prepared in Example 2 for absorbing waves covers 2.00 - 21.35 GHz, and the maximum absorption peak can reach -25.57 dB.

[0050] Example 3: Preparation of a broadband wave-absorbing polymethacrylimide composite material: Step 1: Mix 40 parts of methacrylic acid monomer, 25 parts of 2-fluoro-5-(2-carboxyethyl)benzonitrile, 20 parts of 9,10-bis(3-naphthalen-2-ylprop-2-enyl)anthracene, 10 parts of organic-inorganic hybrid hollow carbon short fiber material, 2 parts of isopropanol, 1 part of N,N-dimethylformamide, and 2 parts of lauroyl peroxide evenly to obtain a mixture; Step 2: Under airtight conditions, react the obtained mixture at 100 °C for 36 h first, and then react at 120 °C for 36 h to obtain a polymethacrylimide plate; Step 3: Preheat the obtained polymethacrylimide plate at 100 °C for 5 h, then perform thermal foaming treatment at 180 °C for 3 h, and cool to room temperature to obtain polymethacrylimide foam; Step 4: Coat a surface layer coating on the surface of the polymethacrylimide foam to obtain a polymethacrylimide composite material; wherein, the preparation method of the surface layer coating includes: Take 40 parts of methyl silicone resin, 20 parts of nano-titanium dioxide, 5 parts of KH560, and 35 parts of toluene, and mix them evenly to obtain it.

[0051] The effective frequency band of the polymethacrylimide composite material prepared in Example 3 for wave absorption covers 1.93 - 26.06 GHz, and the maximum absorption peak can reach -34.57 dB.

[0052] Example 4: Preparation of broadband wave-absorbing polymethacrylimide composite material: The difference from Example 1 is that the organic-inorganic hybrid hollow carbon short fiber is replaced with commercially available carbon fiber (manufactured by Dongyiyang (Jinan) New Materials Co., Ltd.).

[0053] The effective frequency band of the polymethacrylimide composite material prepared in Example 4 for wave absorption covers 2.62 - 16.06 GHz, and the maximum absorption peak can reach -16.51 dB.

[0054] Example 5: Preparation of broadband wave-absorbing polymethacrylimide composite material: The difference from Example 1 is that the organic-inorganic hybrid hollow carbon short fiber in Example 5 is replaced with the organic-inorganic hybrid hollow carbon short fiber prepared by the following method: Step 1: Dissolve polyacrylonitrile in N,N-dimethylformamide, add BaFe 12 O 19 and titanium oxide and mix them evenly to obtain the original solution of the shell spinning solution; in the original solution of the shell spinning solution, the proportion of polyacrylonitrile is 15 wt%, the proportion of BaFe 12 O 19 is 15 wt%, and the proportion of titanium oxide is 2 wt%; Step 2: Dissolve polyvinylpyrrolidone in N,N-dimethylformamide, add BaFe 12 O 19 and titanium oxide and mix them evenly to obtain the original core spinning solution; in the core spinning solution, the proportion of polyvinylpyrrolidone is 15 wt%, the proportion of BaFe 12 O 19 is 10 wt% and the proportion of titanium oxide is 1 wt%; Step 3: Carry out coaxial electrospinning on the original shell spinning solution and the original core spinning solution at a rate ratio of the flow rate of the shell spinning solution to that of the core spinning solution of 2:1 and a total feeding rate of 8.0 mL / h to obtain a carbon fiber precursor, and then soak the carbon fiber precursor in water at 50 °C for 24 h to obtain an organic-inorganic hybrid hollow carbon fiber precursor; the applied voltage for the coaxial electrospinning is 18 kV, and the distance between the needle and the receiving cylinder is 16 cm; Step 4: Dry the organic-inorganic hybrid hollow carbon fiber precursor at 60 °C for 12 h, oxidize it at 220 °C for 3 h, heat it to 800 °C at a heating rate of 4 °C / min under a nitrogen atmosphere and hold for 2 h to obtain an organic-inorganic hybrid hollow carbon fiber, and then carry out mechanical cutting to obtain the organic-inorganic hybrid hollow carbon short fiber material; the hollow diameter of the obtained organic-inorganic hybrid hollow carbon short fiber material is 800 nm, and the wall thickness is 80 nm.

[0055] The effective frequency band of the poly(methacrylimide) composite material prepared in Example 5 for wave absorption covers 3.42 - 17.09 GHz, and the maximum absorption peak can reach -24.47 dB.

[0056] Comparative Example 1: The difference from Example 1 is that 4-(phenylsulfonyl)benzonitrile is replaced by methacrylonitrile.

[0057] The effective frequency band of the poly(methacrylimide) composite material prepared in Comparative Example 1 for wave absorption covers 4.14 - 12.96 GHz, and the maximum absorption peak can reach -12.57 dB.

[0058] Comparative Example 2: Preparation of a broadband wave-absorbing poly(methacrylimide) composite material: Step 1: Mix 41 parts of methacrylic acid monomer, 40 parts of 4-(phenylsulfonyl)benzonitrile, 8 parts of organic-inorganic hybrid hollow carbon short fibers, 6 parts of isopentyl alcohol, 2 parts of formamide and 3 parts of azobisisobutyronitrile evenly to obtain a mixture; Step 2: Under closed conditions, react the obtained mixture at 100 °C for 36 h first, and then react at 120 °C for 36 h to obtain a poly(methacrylimide) plate; Step 3: Preheat the obtained polymethacrylimide plate at 100 °C for 5 h, then perform thermal foaming treatment at 180 °C for 3 h, and cool to room temperature to obtain polymethacrylimide foam; Step 4: Coat a surface layer coating on the surface of the polymethacrylimide foam to obtain a polymethacrylimide composite material; wherein, the preparation method of the surface layer coating includes: Take 20 parts of methyl silicone resin, 30 parts of phenyl silicone resin, 10 parts of nano-titanium dioxide, 3 parts of KH560 and 37 parts of toluene, and mix them evenly to obtain.

[0059] The effective frequency band of the polymethacrylimide composite material prepared in Comparative Example 2 for wave absorption covers 2.04 - 14.89 GHz, and the maximum absorption peak can reach -25.57 dB.

[0060] The wave absorption performance test method of the polymethacrylimide composite materials prepared in the above examples and comparative examples is: place the polymethacrylimide composite material in an environment with a humidity of 85% for 24 h, then take it out, and refer to the standard SJ-20512-1995 to test the wave absorption performance.

[0061] It can be seen from the test results of the examples and comparative examples that the polymethacrylimide composite material prepared in the examples of the present invention still has a wide wave absorption frequency even after being treated in a high-humidity environment, and has good application prospects in a high-humidity environment; in addition, in Example 4, a conventional carbon fiber material is used. Since the conventional carbon fiber material has no hollow structure and the electromagnetic parameters are relatively fixed, its absorption efficiency is relatively low and the wave absorption frequency band is relatively narrow; in Example 5, the surface of the wave absorber is not treated by acid leaching roughening, and the surface is relatively smooth, and the mechanical biting effect and chemical bonding effect with the matrix material are weak. Although the hollow modified carbon fiber itself can adjust the wave absorption performance by adjusting the hollow structure parameters, the acid leaching roughening treatment may not only change the surface morphology of the fiber, but also change its surface chemical composition and electronic structure, further broadening the wave absorption frequency band or enhancing the absorption of electromagnetic waves at specific frequencies, ultimately resulting in a relatively narrow wave absorption frequency of the polymethacrylimide composite material prepared in Example 5 compared with Example 1. In Comparative Example 1, 4-(phenylsulfonyl)benzonitrile is replaced with methylacrylonitrile, which cannot improve the problem of the decrease in moisture-proof performance caused by adding anthracene-naphthalene monomers, resulting in the polymethacrylimide composite material prepared being affected by moisture in a humid environment, the structure changing, the wave absorption performance decreasing, and the wave absorption frequency becoming narrow. The polymethacrylimide composite material prepared in Comparative Example 2 does not add anthracene-naphthalene monomers and does not have a conjugated structure, and cannot interact with the wave absorber to better improve the wave absorption performance, resulting in a relatively narrow wave absorption frequency.

Claims

1. A broadband absorbing polymethacrylimide composite material, characterized in that, It includes an electromagnetic wave absorbing layer and a surface layer covering the surface of the electromagnetic wave absorbing layer; The electromagnetic wave absorbing layer comprises raw materials with the following parts by mass: 30 - 60 parts of methacrylic acid monomer; 20 - 40 parts of acrylonitrile monomer; 10 - 20 parts of anthracene naphthalene monomer; 5 - 10 parts of electromagnetic wave absorber; 2 - 10 parts of foaming agent; 1 - 5 parts of nucleating agent; 1 - 5 parts of initiator; 0 - 2 parts of crosslinking agent; The anthracene naphthalene monomer is at least one of 9,10 - bis(1 - naphthyl)-2 - vinyl anthracene, 9-(2 - naphthyl)-10-(3 - butenyl) anthracene, 9,10 - bis(N-(2 - naphthyl)-N-(4 - pentenyl) anilino) anthracene, 9 - vinyl - 10-(2 - naphthyl) anthracene and 9,10 - bis(3 - naphthyl - 2 - propenyl) anthracene.

2. The broadband absorbing polymethacrylimide composite material according to claim 1, wherein The surface layer is obtained by coating the surface of the electromagnetic wave absorbing layer with a surface layer coating, and the surface layer coating comprises raw materials with the following parts by mass: 40 - 60 parts of silicone resin, 10 - 20 parts of nano - titanium dioxide, 2 - 5 parts of silane coupling agent and 20 - 40 parts of organic solvent.

3. The broadband absorbing polymethacrylimide composite material according to claim 1, characterized in that The electromagnetic wave absorber is a carbon material, and the carbon material includes carbon fiber.

4. The broadband absorbing polymethacrylimide composite material according to claim 1 or 3, characterized in that, The electromagnetic wave absorber is an organic - inorganic hybrid hollow carbon short fiber.

5. The broadband absorbing polymethacrylimide composite material according to claim 4, wherein The preparation method of the organic - inorganic hybrid hollow carbon short fiber includes: Step 1: Dissolve polyacrylonitrile in an organic solvent, add ferrite and antioxidant and mix evenly to obtain a shell spinning solution stock solution; Step 2: Dissolve polyvinylpyrrolidone in an organic solvent, add ferrite and antioxidant and mix evenly to obtain a core spinning solution stock solution; Step 3: Perform coaxial electrospinning on the shell spinning solution stock solution and the core spinning solution stock solution to obtain a carbon fiber precursor, and then soak the carbon fiber precursor in water to obtain an organic - inorganic hybrid hollow carbon fiber precursor; Step 4: Dry, pre - oxidize and perform high - temperature carbonization on the organic - inorganic hybrid hollow carbon fiber precursor in sequence to obtain an organic - inorganic hybrid hollow carbon fiber, and perform acid leaching roughening and mechanical cutting on the organic - inorganic hybrid hollow carbon fiber to obtain the organic - inorganic hybrid hollow carbon short fiber.

6. The broadband absorbing polymethacrylimide composite material according to claim 5, characterized in that The proportion of ferrite in the shell spinning solution stock solution is 10wt% - 20wt% and the proportion of antioxidant is 1wt% - 4wt%; The proportion of ferrite in the core spinning solution is 8wt% - 15wt% and the proportion of antioxidant is 0.5wt% - 3wt%.

7. The broadband absorbing polymethacrylimide composite material according to claim 1, wherein The acrylonitrile monomer contains at least one of fluoroalkyl, phenyl, sulfonic acid group and carboxyl group.

8. The broadband absorbing polymethacrylimide composite material according to claim 7, wherein The acrylonitrile monomer is at least one of 4-(trifluoromethylsulfonyl) benzonitrile, 4-(phenylsulfonyl) benzonitrile, 4-(trifluoromethyl) benzonitrile - 2 - carboxylic acid and 2 - fluoro - 5-(2 - carboxyethyl) phenylacetonitrile.

9. A preparation method of the broadband absorbing polymethacrylimide composite material according to any one of claims 1 to 8, characterized in that, It includes the following steps: Step 1: Mix methacrylic acid monomer, acrylonitrile monomer, anthracene naphthalene monomer, electromagnetic wave absorber, foaming agent, nucleating agent, initiator and crosslinking agent evenly to obtain a mixture; Step 2: Under closed conditions, perform pre - polymerization reaction and copolymerization reaction on the obtained mixture in sequence to obtain a polymethacrylimide plate; Step 3: Thermally foam the obtained polymethacrylimide plate and then cool it to room temperature to obtain polymethacrylimide foam; Step 4: Coat a surface layer coating on the surface of the polymethacrylimide foam to obtain a polymethacrylimide composite material.