A poly(p-phenylene benzobisoxazole) wave-absorbing aerogel and its preparation method and application

Abstract

The present invention provides a poly(p-phenylene benzobisoxazole) absorbing aerogel, its preparation method, and its application, belonging to the technical field of absorbing materials. The poly(p-phenylene benzobisoxazole) absorbing aerogel provided by the present invention has a closed-cell foam structure, comprising an aerogel matrix formed of poly(p-phenylene benzobisoxazole), carbon nanotubes dispersed within the aerogel matrix, a silane coupling agent grafted onto the aerogel matrix, and a nanoscale metal-based material supported on the aerogel matrix. The nanoscale metal-based material is a metal oxide, metal hydroxide, or alloy. The poly(p-phenylene benzobisoxazole) absorbing aerogel provided by the present invention has the advantages of being lightweight, broadband, and having high absorption.

Description

Technical Field

[0001] The present invention relates to the technical field of wave-absorbing materials, and in particular to a poly(p-phenylene benzobisoxazole) wave-absorbing aerogel, a preparation method thereof, and applications thereof. Background Art

[0002] Poly(p-phenylene benzobisoxazole) (PBO) fiber is one of the most promising members of the heterocyclic aromatic polyamide family. It has a high modulus, does not burn or shrink in flames, and currently exhibits higher heat and flame resistance than other chemical fibers. Currently, PBO nanofibers are mostly used as reinforcements for other materials, with limited application in aerogels.

[0003] Absorbing materials are materials that absorb or significantly attenuate electromagnetic wave energy received by their surfaces, thereby reducing electromagnetic interference. Existing absorbing composite materials are primarily made from polymer matrices filled with carbon, iron, or ceramic materials. However, these materials struggle to achieve a balance between lightweight, broadband, and high absorption. Summary of the Invention

[0004] The object of the present invention is to provide a poly(p-phenylene benzobisoxazole) absorbing aerogel, a preparation method thereof, and an application thereof. The poly(p-phenylene benzobisoxazole) absorbing aerogel provided by the present invention has the advantages of being light, broadband, and highly absorbing.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a poly(p-phenylene benzobisoxazole) wave-absorbing aerogel having a closed-cell foam structure, comprising an aerogel matrix formed of poly(p-phenylene benzobisoxazole), carbon nanotubes dispersed in the aerogel matrix, a silane coupling agent grafted onto the aerogel matrix, and a nanoscale metal-based material supported on the aerogel matrix, wherein the nanoscale metal-based material is a metal oxide, a metal hydroxide or an alloy.

[0007] Preferably, the carbon nanotubes are multi-walled carbon nanotubes; the silane coupling agent is KH560; the metal oxide is Fe3O4, the metal hydroxide is Co(OH)2 and / or Ni(OH)2, and the alloy is iron-nickel alloy and / or cobalt-nickel alloy.

[0008] Preferably, the particle size of the nano-scale metal-based material is 0.5-4 μm.

[0009] Preferably, the raw materials for preparing the poly(p-phenylene benzobisoxazole) absorbing aerogel include poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, a silane coupling agent and a soluble metal salt corresponding to the nanoscale metal-based material, and the mass ratio of the poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, a silane coupling agent and a soluble metal salt is 1-1.5:0.5-1.5:20-30:25-35.

[0010] The present invention provides a method for preparing the poly(p-phenylene benzobisoxazole) absorbing aerogel described in the above technical solution, comprising the following steps:

[0011] The poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, an iron salt coordination agent and an acid reagent are mixed, and coordination reaction and gelation treatment are carried out in sequence to obtain an acid gel;

[0012] mixing the acid gel with an acid replacement reagent and performing an acid replacement treatment to obtain a replacement acid gel;

[0013] The displacement acid gel, the silane coupling agent and water are mixed to carry out a grafting reaction, the obtained grafted acid gel is mixed with water to carry out a water displacement treatment, and the obtained grafted hydrogel is freeze-dried to obtain a grafted aerogel;

[0014] The grafted aerogel, a soluble metal salt corresponding to the nanoscale metal-based material, a precipitant, water and an alcohol solvent are mixed and subjected to a hydrothermal reaction to obtain a poly(p-phenylene benzobisoxazole) absorbing aerogel in which the nanoscale metal-based material is a metal hydroxide;

[0015] The poly(p-phenylene benzobisoxazole) absorbing aerogel whose nano-scale metal-based material is a metal hydroxide is subjected to annealing treatment to obtain the poly(p-phenylene benzobisoxazole) absorbing aerogel whose nano-scale metal-based material is a metal oxide or alloy.

[0016] Preferably, the iron salt ligand is Fe2(SO4)3; the coordination reaction is carried out under stirring conditions, and the coordination reaction time is 20 to 28 hours; the gelation treatment is carried out under static conditions, and the gelation treatment time is 6 to 10 hours.

[0017] Preferably, the acid replacement reagent includes N,N-dimethylacetamide or N,N-dimethylformamide; and the acid replacement treatment time is 20 to 28 hours.

[0018] Preferably, the grafting reaction temperature is 55-65° C., and the time is 1-2 hours.

[0019] Preferably, the precipitant is hexamethylenetetramine; the temperature of the hydrothermal reaction is 105-115° C., and the time is 6-10 hours; the temperature of the annealing treatment is 350-450° C., and the holding time is 1.5-2.5 hours.

[0020] The present invention provides the use of the poly(p-phenylene benzobisoxazole) absorbing aerogel described in the above technical solution or the poly(p-phenylene benzobisoxazole) absorbing aerogel prepared by the preparation method described in the above technical solution in stealth absorbing materials or flame retardant and heat-insulating absorbing materials.

[0021] The present invention provides a poly (p-phenylene benzobisoxazole) absorbing aerogel having a closed-cell foam structure, comprising an aerogel matrix formed by poly (p-phenylene benzobisoxazole), carbon nanotubes dispersed in the aerogel matrix, a silane coupling agent grafted onto the aerogel matrix, and a nanoscale metal-based material loaded on the aerogel matrix, wherein the nanoscale metal-based material is a metal oxide, a metal hydroxide, or an alloy. The poly (p-phenylene benzobisoxazole) absorbing aerogel provided by the present invention has the advantages of light weight, broadband, and high absorption. Specifically, the present invention uses phenylene benzobisoxazole as an aerogel matrix and disperses carbon nanotubes therein, which is conducive to forming a conductive path, while loading the nanoscale metal-based material, which is conducive to improving the electromagnetic wave absorption performance of the aerogel; and the aerogel in the present invention has a closed-cell foam structure (i.e., a dense surface and holes inside), so that the electromagnetic wave undergoes a process of multiple absorption-reflection-reabsorption in the aerogel, thereby obtaining very excellent electromagnetic wave absorption performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Surface SEM image of the microwave-absorbing aerogel prepared in Example 1 (scale is 2 μm);

[0023] Figure 2 Surface SEM image of the microwave-absorbing aerogel prepared in Example 5 (scale: 2 μm);

[0024] Figure 3 Surface SEM image of the microwave-absorbing aerogel prepared in Example 5 (scale: 1 μm);

[0025] Figure 4 This is a cross-sectional SEM image of the microwave-absorbing aerogel prepared in Example 2 (scale: 50 μm);

[0026] Figure 5 This is a SEM image of the internal structure of the microwave-absorbing aerogel prepared in Example 1 (scale is 3 μm);

[0027] Figure 6 This is a SEM image of the internal structure of the microwave-absorbing aerogel prepared in Example 1 (scale is 1 μm). DETAILED DESCRIPTION

[0028] The present invention provides a poly(p-phenylene benzobisoxazole) wave-absorbing aerogel having a closed-cell foam structure, comprising an aerogel matrix formed of poly(p-phenylene benzobisoxazole), carbon nanotubes dispersed in the aerogel matrix, a silane coupling agent grafted onto the aerogel matrix, and a nanoscale metal-based material supported on the aerogel matrix, wherein the nanoscale metal-based material is a metal oxide, a metal hydroxide or an alloy.

[0029] The poly(p-phenylene benzobisoxazole) (PBO) wave-absorbing aerogel of the present invention has a closed-cell foam structure, so that the PBO wave-absorbing aerogel has good wave-absorbing performance.

[0030] The PBO absorbing aerogel of the present invention includes an aerogel matrix formed of PBO. The aerogel matrix prepared by using PBO has good flame retardancy and heat resistance, is easy to load with nano-scale metal oxides and nano-scale alloys (ensuring smooth annealing treatment during the preparation process), and the obtained absorbing aerogel has a low density.

[0031] The PBO absorbing aerogel described herein comprises carbon nanotubes (CNTs) dispersed within the aerogel matrix. The CNTs are preferably multi-walled CNTs (MWCNTs), more preferably carboxylated MWCNTs. In the present invention, CNTs are a one-dimensional quantum material with a unique structure. Their excellent mechanical and electrical properties have attracted widespread attention from researchers, and they currently possess the highest specific strength and highest melting point. CNTs have a hardness comparable to diamond but excellent toughness, and their extremely high aspect ratio makes them an ideal high-strength fiber material. The excellent electrical conductivity of CNTs significantly reduces electromagnetic wave loss, while their fiber-like structure allows them to form a three-dimensional network within the aerogel, significantly enhancing the modulus of the PBO absorbing aerogel. This also facilitates the overlapping of CNTs, forming conductive pathways, significantly enhancing the conductivity of the PBO absorbing aerogel. Multi-walled carbon nanotubes (MWCNTs) have high chemical activity. During the preparation of PBO absorbing aerogels, such as during hydrothermal reactions, defects or functional groups on their surfaces provide active sites, allowing the grafted aerogel to be evenly loaded with nanoscale metal hydroxides, greatly enhancing the polarization effect.

[0032] The PBO absorbing aerogel of the present invention includes a silane coupling agent, preferably KH560, grafted onto the aerogel matrix. In the present invention, the silane coupling agent can be grafted onto PBO, which helps enhance the mechanical properties of the PBO hydrogel and prevents collapse during the freeze-drying step, ultimately successfully producing a PBO absorbing aerogel with excellent overall performance.

[0033] The PBO absorbing aerogel of the present invention comprises a nanoscale metal-based material supported on the aerogel matrix. The particle size of the nanoscale metal-based material is preferably 0.5 to 4 μm, more preferably 0.6 to 1 μm, and even more preferably 0.8 μm. In the present invention, the nanoscale metal-based material is a metal oxide, metal hydroxide, or alloy. The metal oxide is preferably Fe3O4; the metal hydroxide is preferably Co(OH)2 and / or Ni(OH)2, more preferably Co(OH)2 and Ni(OH)2, with the molar ratio of Co(OH)2 to Ni(OH)2 preferably being 1:0.5 to 1.5, more preferably 1:1; the alloy is preferably an iron-nickel alloy and / or a cobalt-nickel alloy, more preferably a cobalt-nickel alloy, with the molar ratio of cobalt to nickel in the cobalt-nickel alloy preferably being 1:0.5 to 1.5, more preferably 1:1.

[0034] In the present invention, the raw materials for preparing the poly(p-phenylene benzobisoxazole) absorbing aerogel include poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, silane coupling agents, and soluble metal salts corresponding to nanoscale metal-based materials. The mass ratio of the poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, silane coupling agents, and soluble metal salts is preferably 1-1.5:0.5-1.5:20-30:25-35, more preferably 1-1.5:1-1.5:25:30. In the present invention, the density of the poly(p-phenylene benzobisoxazole) nanofibers is preferably 1.56 g / cm 3 , purchased from Toyo Co., Ltd., Osaka, Japan; the soluble metal salt is preferably a nitrate, more preferably a hydrated nitrate.

[0035] The present invention provides a method for preparing the poly(p-phenylene benzobisoxazole) absorbing aerogel described in the above technical solution, comprising the following steps:

[0036] The poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, an iron salt coordination agent and an acid reagent are mixed, and coordination reaction and gelation treatment are carried out in sequence to obtain an acid gel;

[0037] mixing the acid gel with an acid replacement reagent and performing an acid replacement treatment to obtain a replacement acid gel;

[0038] The displacement acid gel, the silane coupling agent and water are mixed to carry out a grafting reaction, the obtained grafted acid gel is mixed with water to carry out a water displacement treatment, and the obtained grafted hydrogel is freeze-dried to obtain a grafted aerogel;

[0039] The grafted aerogel, a soluble metal salt corresponding to the nanoscale metal-based material, a precipitant, water and an alcohol solvent are mixed and subjected to a hydrothermal reaction to obtain a poly(p-phenylene benzobisoxazole) absorbing aerogel in which the nanoscale metal-based material is a metal hydroxide;

[0040] The poly(p-phenylene benzobisoxazole) absorbing aerogel whose nano-scale metal-based material is a metal hydroxide is subjected to annealing treatment to obtain the poly(p-phenylene benzobisoxazole) absorbing aerogel whose nano-scale metal-based material is a metal oxide or alloy.

[0041] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known to those skilled in the art.

[0042] The present invention mixes poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, an iron salt ligand, and an acid reagent, and sequentially performs a coordination reaction and a gelation treatment to obtain an acid gel. In the present invention, the iron salt ligand is preferably Fe2(SO4)3, and the mass ratio of the iron salt ligand to the PBO nanofiber is preferably 4-6:1-1.5, more preferably 5:1-1.5. In the present invention, the acid reagent can be an inorganic acid or an organic acid, preferably an organic acid; the inorganic acid is preferably concentrated sulfuric acid, and the concentration of the concentrated sulfuric acid is preferably 96-98 wt%; the organic acid is preferably methanesulfonic acid and trifluoroacetic acid, and the volume ratio of methanesulfonic acid to trifluoroacetic acid is preferably 1:0.8-1.2, more preferably 1:1. In the present invention, the poly(p-phenylene benzobisoxazole) nanofibers are preferably dissolved in the acid reagent, and then the carbon nanotubes and the iron salt ligand are added to the resulting mixture for a coordination reaction. In the present invention, the temperature of the coordination reaction is preferably 15 to 35°C, more preferably room temperature. In the embodiment of the present invention, the room temperature is specifically 25°C; the time of the coordination reaction is preferably 20 to 28 hours, more preferably 24 hours; the coordination reaction is preferably carried out under stirring conditions. In the present invention, during the coordination reaction, the system becomes transparent and the viscosity increases. PBO is 3+ Coordination cross-linking (Fe 3+ Coordinates with nitrogen in PBO). After the coordination reaction, the present invention gelates the resulting solution to produce an acid gel. In the present invention, the gelation temperature is preferably 15-35°C, more preferably room temperature; the gelation time is preferably 6-10 hours, more preferably 8 hours; and the gelation is preferably performed under static conditions. In the present invention, during the gelation process, the system changes from transparent to opaque and the volume shrinks slightly because the solubility of PBO nanofibers in different solvents varies.

[0043] After obtaining the acid gel, the present invention mixes the acid gel with an acid displacement reagent and performs an acid displacement treatment to obtain a displacement acid gel. In the present invention, the acid displacement reagent preferably comprises N,N-dimethylacetamide or N,N-dimethylformamide. When N,N-dimethylacetamide is used, the resulting aerogel has a lower density; when N,N-dimethylformamide is used, the resulting aerogel has a higher density. In the present invention, the mass ratio of the acid displacement reagent to the PBO nanofibers is preferably 240-260:1-1.5, more preferably 250:1-1.5. In the present invention, the acid displacement reagent is preferably added to the acid gel for the acid displacement treatment. The acid displacement reagent is preferably added in batches to avoid the adverse effects of a large amount of heat released by a single addition on the system. The number of additions and the amount added each time are not particularly limited. In the present invention, the temperature for the acid displacement treatment is preferably 15-35°C, more preferably room temperature, and the duration of the acid displacement treatment is preferably 20-28 hours, more preferably 24 hours. In the present invention, during the acid replacement process, the acid replacement reagent will gradually replace the acid in the gel, and then the subsequent water replacement process will be carried out, which is conducive to ensuring uniform shrinkage of the gel and avoiding the problem of uneven shrinkage caused by direct water replacement. In addition, part of the Fe 3+ , to avoid its residue in the final PBO absorbing aerogel.

[0044] After obtaining the replacement acid gel, the present invention mixes the replacement acid gel, silane coupling agent and water to carry out a grafting reaction, mixes the obtained grafted acid gel with water, carries out a water replacement treatment, and freeze-dries the obtained grafted hydrogel to obtain a grafted aerogel. In the present invention, the water is preferably deionized water, and the mass ratio of the water to the silane coupling agent is preferably 8 to 11:1, more preferably 9:1. The present invention preferably mixes the silane coupling agent with water, and then adds the obtained mixture to the replacement acid gel to carry out a grafting reaction. In the present invention, the temperature of the grafting reaction is preferably 55 to 65°C, more preferably 60°C; the time is preferably 1 to 2h, more preferably 1.5h. In the present invention, during the grafting reaction, the silane coupling agent is grafted onto the PBO, which is beneficial to enhancing the mechanical properties of the PBO hydrogel so that it will not collapse in the subsequent freeze-drying step; moreover, the Fe in the system will be further removed during the grafting reaction. 3+, to avoid its residue in the final PBO absorbing aerogel. After the grafting reaction, the present invention mixes the obtained grafted acid gel with water and performs a water replacement treatment. In the present invention, the temperature of the water replacement treatment is preferably 15 to 35°C, more preferably room temperature; the water replacement treatment is based on the pH value of the replaced water = 7. After the water replacement treatment, the present invention freeze-dries the obtained grafted hydrogel to obtain a grafted aerogel. In the present invention, the freeze-drying time is preferably 40 to 55 hours, more preferably 48 hours. The present invention does not specifically limit the freeze-drying temperature, and a temperature familiar to those skilled in the art can be used.

[0045] After obtaining the grafted aerogel, the present invention mixes the grafted aerogel, a soluble metal salt corresponding to the nanoscale metal-based material, a precipitant, water, and an alcohol solvent, and conducts a hydrothermal reaction to obtain a poly(p-phenylene benzobisoxazole) absorbing aerogel in which the nanoscale metal-based material is a metal hydroxide. In the present invention, the precipitant is preferably hexamethylenetetramine, and the mass ratio of the precipitant to the soluble metal salt is preferably 20-28:25-35, more preferably 24:30. The present invention preferably uses hexamethylenetetramine as the precipitant, which can attach to the PBO surface through coordinate covalent bonds or hydrogen bonds, forming steric hindrance, thereby affecting the growth density and morphology of the metal hydroxide. The present invention preferably uses the above-mentioned amount of precipitant, which facilitates the formation of a uniform nanosheet structure in the resulting metal hydroxide.

[0046] In the present invention, the alcohol solvent is preferably ethanol, and the mass ratio of water, alcohol solvent, and soluble metal salt is preferably 800-1200:400-600:25-35, more preferably 1000:500:30. In the present invention, the soluble metal salt, precipitant, water, and alcohol solvent are preferably mixed, and the resulting mixture and the grafted aerogel are then placed in a reactor for a hydrothermal reaction. Prior to the hydrothermal reaction, the reactor is preferably evacuated to completely immerse the grafted aerogel in the mixture, ensuring that the hydrothermal reaction produces a PBO aerogel with excellent microwave absorption properties. In the present invention, the hydrothermal reaction temperature is preferably 105-115°C, more preferably 110°C, and the reaction time is preferably 6-10 hours, more preferably 8 hours. During the hydrothermal reaction, the soluble metal salt gradually grows on the aerogel, forming a nanosheet structure. After the hydrothermal reaction, the present invention preferably sequentially washes and dries the resulting aerogel to obtain a poly(p-phenylene benzobisoxazole) microwave-absorbing aerogel in which the nanoscale metal-based material is a metal hydroxide. In the present invention, the washing is preferably performed with water, preferably deionized water; the drying temperature is preferably 45-55°C, more preferably 50°C. The present invention does not specify the drying time; sufficient drying is sufficient.

[0047] After obtaining the poly(p-phenylene benzobisoxazole) microwave-absorbing aerogel whose nanoscale metal-based material is a metal hydroxide, the present invention anneals the poly(p-phenylene benzobisoxazole) microwave-absorbing aerogel whose nanoscale metal-based material is a metal hydroxide to obtain the poly(p-phenylene benzobisoxazole) microwave-absorbing aerogel whose nanoscale metal-based material is a metal oxide or alloy. This is described in detail below.

[0048] The present invention preferably subjects the poly(p-phenylene benzobisoxazole) absorbing aerogel, wherein the nanoscale metal-based material is a metal hydroxide, to a first annealing treatment to obtain a poly(p-phenylene benzobisoxazole) absorbing aerogel, wherein the nanoscale metal-based material is an alloy. In the present invention, the temperature of the first annealing treatment is preferably 350-450°C, more preferably 400°C; the heating rate to the desired temperature for the first annealing treatment is preferably 8-12°C / min, more preferably 10°C / min; the first annealing treatment duration is preferably 1.5-2.5 hours, more preferably 2 hours; the first annealing treatment is preferably performed in a protective atmosphere, preferably provided by argon; and the first annealing treatment preferably includes cooling to room temperature, at a cooling rate of preferably 8-12°C / min, more preferably 10°C / min. For example, if the alloy is a cobalt-nickel alloy, the cobalt-nickel alloy prepared using the above-described method of the present invention preferably has a flower ball shape.

[0049] The present invention preferably subjects the poly(p-phenylene benzobisoxazole) absorbing aerogel in which the nanoscale metal-based material is a metal hydroxide to a second annealing treatment to obtain a poly(p-phenylene benzobisoxazole) absorbing aerogel in which the nanoscale metal-based material is a metal oxide. In the present invention, the temperature of the second annealing treatment is preferably 350-450°C, more preferably 400°C; the heating rate to the temperature required for the second annealing treatment is preferably 8-12°C / min, more preferably 10°C / min; the time of the second annealing treatment is preferably 1.5-2.5 hours, more preferably 2 hours; the second annealing treatment is preferably performed in air; and after the second annealing treatment, the temperature is preferably cooled to room temperature, and the cooling rate is preferably 8-12°C / min, more preferably 10°C / min.

[0050] The present invention uses a sol-gel method to prepare a grafted aerogel with a closed-cell foam structure by means of trivalent iron ion coordination. The sol-gel method can improve the dispersibility of carbon nanotubes in the aerogel matrix, such as achieving nanometer-level uniformity in a short period of time, so that the carbon nanotubes and PBO nanofibers are interwoven to form a closed-cell foam-type three-dimensional porous network structure, which is more conducive to multiple absorption, reflection, and reabsorption of electromagnetic waves in the aerogel, thereby achieving very excellent wave absorption performance. Then, under the action of a precipitant, the grafted aerogel and a soluble metal salt undergo a hydrothermal reaction in the presence of water and an alcohol solvent, uniformly growing nano-sheet-shaped metal hydroxides on the grafted aerogel, thereby increasing the polarization effect of the aerogel on electromagnetic waves. Furthermore, the aerogel is annealed to convert the metal hydroxides into metal oxides or alloys, thereby increasing the magnetic properties of the PBO absorbing aerogel and thereby enhancing the electromagnetic loss capacity of the PBO absorbing aerogel. The method provided by the present invention is simple to operate and easy to implement on a large scale, and the prepared PBO absorbing aerogel has excellent wave absorption performance.

[0051] The present invention provides the use of the poly(p-phenylene benzobisoxazole) absorbing aerogel described in the above technical solution or the poly(p-phenylene benzobisoxazole) absorbing aerogel prepared by the preparation method described in the above technical solution in stealth absorbing materials or flame retardant and heat-insulating absorbing materials.

[0052] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0053] In the following examples of the present invention, unless otherwise specified, the amounts of each raw material are expressed in parts by mass.

[0054] Among them, the density of PBO nanofiber is 1.56g / cm 3 , purchased from Toyo Co., Ltd., Osaka, Japan;

[0055] Carboxylated multi-walled carbon nanotubes were purchased from MacLean with a CAS number of 308068-56-6.

[0056] Example 1

[0057] Methanesulfonic acid and trifluoroacetic acid were mixed in a volume ratio of 1:1 to obtain a mixed acid; 1.5 parts of PBO nanofibers were dissolved in 500 parts of the mixed acid, and then 1.5 parts of carboxylated multi-walled carbon nanotubes and 5 parts of Fe2(SO4)3 were added, and a coordination reaction was carried out at room temperature (25°C) for 24 hours under magnetic stirring conditions; after the reaction, the magnetic stirrer was removed, and the resulting solution was allowed to stand at room temperature for 8 hours for gelation treatment to obtain MWCNTs / PBO acid gel;

[0058] 250 parts of N,N-dimethylacetamide (DMAc) were added to the MWCNTs / PBO acid gel in batches, and the gel was allowed to stand at room temperature for 24 hours to perform an acid replacement treatment, thereby obtaining a replaced MWCNTs / PBO acid gel.

[0059] 25 parts of silane coupling agent KH560 and 225 parts of deionized water were mixed, and the resulting mixture was added to the replaced MWCNTs / PBO acid gel, and a grafting reaction was carried out at 60° C. for 1.5 hours to obtain a grafted MWCNTs / PBO acid gel; the grafted MWCNTs / PBO acid gel was placed in deionized water and subjected to water displacement treatment at room temperature until the pH value of the deionized water after displacement was 7 to obtain a grafted MWCNTs / PBO hydrogel, which was freeze-dried for 48 hours to obtain a grafted MWCNTs / PBO aerogel;

[0060] 15 parts of nickel nitrate hexahydrate, 15 parts of cobalt nitrate hexahydrate, 24 parts of hexamethylenetetramine, 1000 parts of deionized water and 500 parts of ethanol were mixed, and the obtained mixed solution and the grafted MWCNTs / PBO aerogel were placed in a reactor. After vacuum treatment, a hydrothermal reaction was carried out at 110°C for 8 hours. After the reaction, the obtained aerogel was washed with deionized water and then dried at 50°C to obtain MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel, which is an absorbing aerogel with a closed-cell foam structure, recorded as aerogel S-1.

[0061] After testing, the minimum reflection loss (RL) of the aerogel S-1 in the 2-18 GHz frequency band is min ) is -56dB, and the effective absorption bandwidth (RL<-10dB) is 4.16GHz.

[0062] Example 2

[0063] MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel was prepared according to the method of Example 1, except that the amount of PBO nanofibers and carboxylated multi-walled carbon nanotubes used in this example was 1 part. The MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel finally prepared was recorded as aerogel S-2.

[0064] After testing, the aerogel S-2 has a RL of 2 to 18 GHz. min It is -58dB and the effective absorption bandwidth is 5.76GHz.

[0065] Example 3

[0066] MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel was prepared according to the method of Example 1, except that the amount of carboxylated multi-walled carbon nanotubes used in this example was 0.5 parts. The MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel finally prepared was recorded as aerogel S-3.

[0067] After testing, the aerogel S-3 has a RL of 2 to 18 GHz. min It is -33dB and the effective absorption bandwidth is 10.88GHz.

[0068] Example 4

[0069] MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel was prepared according to the method of Example 1, except that the amount of carboxylated multi-walled carbon nanotubes used in this example was 1 part. The MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel finally prepared was recorded as aerogel S-4.

[0070] After testing, the aerogel S-4 has a RL of 2 to 18 GHz. min It is -53dB and the effective absorption bandwidth is 10.40GHz.

[0071] Example 5

[0072] MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel was prepared according to the method of Example 1;

[0073] The MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel was placed in a tubular furnace, argon gas was introduced, and the temperature was increased from room temperature to 400°C at a heating rate of 10°C / min, and the temperature was kept for annealing for 2 hours. Then, the temperature was cooled to room temperature at a cooling rate of 10°C / min to obtain a MWCNTs / CoNi / PBO aerogel containing a flower-shaped cobalt-nickel alloy, which was recorded as aerogel S-5.

[0074] After testing, the aerogel S-5 has a RL of 2 to 18 GHz. min It is -64dB and the effective absorption bandwidth is 8.96GHz.

[0075] Example 6

[0076] MWCNTs / CoNi / PBO aerogel was prepared according to the method of Example 5, except that DMAc was replaced with N,N-dimethylformamide (DMF) when preparing MWCNTs / Co(OH)2 / Ni(OH)2 / PBO aerogel in this example. The MWCNTs / CoNi / PBO aerogel finally prepared was recorded as aerogel S-6.

[0077] After testing, the aerogel S-6 has a RL of 2 to 18 GHz. min It is -45dB and the effective absorption bandwidth is 12.4GHz.

[0078] Figure 1 The surface SEM image of the absorbing aerogel prepared in Example 1 is at a scale of 2 μm. The results show that the absorbing aerogel is uniformly loaded with nano-scale sheets formed by Co(OH)2 and Ni(OH)2, and the size is uniform. The morphology of the nano-scale metal hydroxides in the absorbing aerogels prepared in Examples 2 to 4 is similar to that of the nano-scale metal hydroxides in the absorbing aerogels prepared in Examples 2 to 4. Figure 1 similar.

[0079] Figure 2 This is a surface SEM image of the microwave-absorbing aerogel prepared in Example 5, with a scale of 2 μm. The results show that a large number of nano-scale flower-shaped CoNi alloys exist in the microwave-absorbing aerogel. Figure 3 The surface SEM image of the microwave-absorbing aerogel prepared in Example 5 is 1 μm in scale. The results show that the flower-shaped CoNi alloy is formed by stacking of sheets. The morphology of the nano-scale alloy in the microwave-absorbing aerogel prepared in Example 6 is similar to that of the nano-scale alloy. Figure 2 and Figure 3 similar.

[0080] Figure 4 The cross-sectional SEM image of the absorbing aerogel prepared in Example 2 is at a scale of 50 μm. The results show that the surface of the absorbing aerogel is a closed-pore structure and the interior is a porous structure. Figure 4 similar.

[0081] Figure 5 This is a SEM image of the internal structure of the microwave-absorbing aerogel prepared in Example 1, with a scale of 3 μm; Figure 6 This is a SEM image of the internal structure of the microwave-absorbing aerogel prepared in Example 1, with a scale of 1 μm. The results show that the PBO nanofibers and carbon nanotubes are interwoven and arranged at the microscopic level to form a macroscopic lamellar structure.

[0082] The absorbing aerogel structure prepared in Examples 2 to 6 is Figure 5 and Figure 6 similar.

[0083] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A poly(p-phenylene benzobisoxazole) microwave-absorbing aerogel having a closed-cell foam structure, comprising an aerogel matrix formed of poly(p-phenylene benzobisoxazole), carbon nanotubes dispersed in the aerogel matrix, a silane coupling agent grafted onto the aerogel matrix, and a nanoscale metal-based material supported on the aerogel matrix, wherein the nanoscale metal-based material is a metal oxide, metal hydroxide, or alloy; The carbon nanotubes are multi-walled carbon nanotubes; the silane coupling agent is KH560; the metal oxide is Fe3O4, the metal hydroxide is Co(OH)2 and / or Ni(OH)2, and the alloy is an iron-nickel alloy and / or a cobalt-nickel alloy; The particle size of the nano-scale metal-based material is 0.5 to 4 μm; The raw materials for preparing the poly(p-phenylene benzobisoxazole) absorbing aerogel include poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, a silane coupling agent, and a soluble metal salt corresponding to a nanoscale metal-based material. The mass ratio of the poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, the silane coupling agent, and the soluble metal salt is 1-1.5:0.5-1.5:20-30:25-35.

2. The method for preparing the poly(p-phenylene benzobisoxazole) absorbing aerogel according to claim 1, comprising the following steps: The poly(p-phenylene benzobisoxazole) nanofibers, carbon nanotubes, an iron salt coordination agent and an acid reagent are mixed, and coordination reaction and gelation treatment are carried out in sequence to obtain an acid gel; mixing the acid gel with an acid replacement reagent and performing an acid replacement treatment to obtain a replacement acid gel; The displacement acid gel, the silane coupling agent and water are mixed to carry out a grafting reaction, the obtained grafted acid gel is mixed with water to carry out a water displacement treatment, and the obtained grafted hydrogel is freeze-dried to obtain a grafted aerogel; The grafted aerogel, a soluble metal salt corresponding to the nanoscale metal-based material, a precipitant, water and an alcohol solvent are mixed and subjected to a hydrothermal reaction to obtain a poly(p-phenylene benzobisoxazole) absorbing aerogel in which the nanoscale metal-based material is a metal hydroxide; The poly(p-phenylene benzobisoxazole) absorbing aerogel whose nano-scale metal-based material is a metal hydroxide is subjected to annealing treatment to obtain the poly(p-phenylene benzobisoxazole) absorbing aerogel whose nano-scale metal-based material is a metal oxide or alloy.

3. The preparation method according to claim 2, characterized in that The iron salt coordination agent is Fe2(SO4)3; the coordination reaction is carried out under stirring conditions, and the coordination reaction time is 20 to 28 hours; the gelation treatment is carried out under static conditions, and the gelation treatment time is 6 to 10 hours.

4. The preparation method according to claim 2, characterized in that The acid replacement reagent includes N,N-dimethylacetamide or N,N-dimethylformamide; the time of the acid replacement treatment is 20 to 28 hours.

5. The preparation method according to claim 2, characterized in that The grafting reaction temperature is 55-65° C. and the time is 1-2 hours.

6. The preparation method according to claim 2, characterized in that The precipitant is hexamethylenetetramine; the temperature of the hydrothermal reaction is 105-115° C., and the time is 6-10 hours; the temperature of the annealing treatment is 350-450° C., and the holding time is 1.5-2.5 hours.

7. Use of the poly(p-phenylene benzobisoxazole) absorbing aerogel according to claim 1 or the poly(p-phenylene benzobisoxazole) absorbing aerogel prepared by the preparation method according to any one of claims 2 to 6 in stealth absorbing materials or flame retardant and heat insulating absorbing materials.

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