Self-repairing broadband wave-absorbing composite material as well as preparation method and application thereof

Abstract

The invention discloses a self-repairing broadband wave-absorbing composite material as well as a preparation method and application thereof. The self-repairing broadband wave-absorbing composite material comprises a high impedance matching layer and a low impedance matching layer which are laminated and compounded, the high impedance matching layer comprises polysiloxane modified polyurethane and composite wave-absorbing powder, and the composite wave-absorbing powder is prepared by performing plasma ball milling on iron-based soft magnetic powder and an insulating inorganic compound. And the low impedance matching layer comprises polysiloxane modified polyurethane and soft magnetic powder. The self-repairing broadband wave-absorbing composite material has the advantages of being excellent in wave-absorbing performance, large in effective absorption bandwidth, small in thickness, good in mechanical performance, good in self-repairing performance and the like, can be used in the fields of 5G communication, new energy automobiles, consumer electronics, national defense and military industry and the like, and is simple in preparation method, low in production cost and suitable for large-scale industrial production and application.

Description

Technical Field

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

[0002] With the rapid development of wireless communication technology, human society has gradually entered the information age of "Internet of Everything". However, the electromagnetic radiation problem caused by the innovation of communication technology has become increasingly serious. Statistical data shows that the global environmental electromagnetic field radiation intensity has increased by nearly 3 times in the past decade, and the proportion of electromagnetic wave radiation in the frequency band of 2 GHz to 18 GHz exceeds 65%. Electromagnetic radiation pollution may not only cause serious electromagnetic interference, leading to the failure of electronic devices, but also pose health risks such as disorders of the human nervous system and endocrine disorders. In recent years, certain progress has been made in the research and application of electromagnetic wave absorbing materials. However, according to the Snoek limit in classical electromagnetic theory, there is a mutual restriction relationship between the magnetic permeability and the working frequency of traditional magnetic wave absorbing materials, resulting in a significant decrease in the wave absorbing performance when the material thickness becomes thinner. This "thickness-bandwidth" mutual exclusion result of existing magnetic wave absorbing materials makes it difficult to simultaneously meet the technical requirements of "broadband, strong absorption, light weight, and thin thickness", restricting their application in cutting-edge fields such as electronic communication and national defense. In addition, the commonly used substrates of traditional wave absorbing composite materials (such as rubber and plastic) are easily damaged by external forces or cracked due to material fatigue, seriously affecting their mechanical properties, wave absorbing performance, and service life, and it is difficult to meet the growing actual application requirements.

[0003] Therefore, it is crucial to develop a high-performance wave absorbing composite material with ultra-thin, light-weight, broadband, strong loss, and rapid self-healing capabilities to solve the problem of electromagnetic radiation pollution. Summary of the Invention

[0004] The purpose of the present invention is to provide a self-healing broadband microwave absorbing composite material, a preparation method thereof, and an application thereof.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A self-healing broadband microwave absorbing composite material, which comprises a stacked and composite high impedance matching layer and a low impedance matching layer;

[0007] The high impedance matching layer comprises the following components in mass percentage:

[0008] Polysiloxane-modified polyurethane: 20% - 50%;

[0009] Composite wave absorbing powder: 50% - 80%;

[0010] The composite wave-absorbing powder is prepared by subjecting iron-based soft magnetic powder and insulating inorganic compound to plasma ball milling;

[0011] The iron-based soft magnetic powder is at least one of carbonyl iron powder and iron-cobalt powder;

[0012] The low impedance matching layer comprises components in the following mass percentages:

[0013] Polysiloxane-modified polyurethane: 30% - 80%;

[0014] Soft magnetic powder: 20% - 70%;

[0015] The soft magnetic powder is at least one of iron-silicon-aluminum powder, zinc-manganese ferrite powder, magnetite powder, and iron-silicon-boron nanocrystals.

[0016] Preferably, the thickness of the self-healing broadband wave-absorbing composite material is 1 mm - 10 mm.

[0017] More preferably, the thickness of the self-healing broadband wave-absorbing composite material is 2 mm - 4 mm.

[0018] Preferably, the thickness of the high impedance matching layer is 0.8 mm - 9.8 mm.

[0019] More preferably, the thickness of the high impedance matching layer is 1 mm - 2 mm.

[0020] Preferably, the thickness of the low impedance matching layer is 0.2 mm - 9.2 mm.

[0021] More preferably, the thickness of the low impedance matching layer is 1 mm - 2 mm.

[0022] Preferably, the mass ratio of the iron-based soft magnetic powder to the insulating inorganic compound is 5 - 50:1.

[0023] Preferably, the insulating inorganic compound is at least one of hexagonal boron nitride, aluminum oxide, silicon dioxide, and silicon nitride.

[0024] Preferably, the process parameters of the plasma ball milling include: the atmosphere is one of argon atmosphere, nitrogen atmosphere, oxygen atmosphere, and air atmosphere, the atmosphere pressure is 0.01 MPa - 0.20 MPa, the plasma discharge frequency is 5 kHz - 12 kHz, the ball mill rotation speed is 100 rpm - 3000 rpm, and the ball milling time is 0.5 h - 48 h.

[0025] A preparation method of the self-healing broadband wave-absorbing composite material as described above comprises the following steps:

[0026] 1) Disperse polytetrahydrofuran diol, isocyanate, pyridine diol and catalyst in an organic solvent for prepolymerization reaction, then add amino propyl terminated polydimethylsiloxane for grafting reaction, then add carbohydrazide for chain extension reaction, and then add diboric acid for crosslinking reaction to obtain a polysiloxane modified polyurethane solution;

[0027] 2) Disperse the composite wave absorbing powder and soft magnetic powder in the polysiloxane modified polyurethane solution respectively, and then inject them into a mold for molding to obtain a high impedance matching layer material and a low impedance matching layer material;

[0028] 3) Coat one side of the high impedance matching layer material and the low impedance matching layer material with ethanol and then stack them together for lamination to obtain a self-healing broadband wave absorbing composite material.

[0029] Preferably, the molar ratio of the polytetrahydrofuran diol, isocyanate, pyridine diol, amino propyl terminated polydimethylsiloxane, carbohydrazide, and diboric acid in step 1) is 1:1.6 - 3.6:0.2 - 0.8:0.2 - 1.5:0.2 - 0.8:0.2 - 0.8.

[0030] Preferably, the number average molecular weight of the polytetrahydrofuran diol in step 1) is 500 g / mol - 5000 g / mol.

[0031] Preferably, the polytetrahydrofuran diol in step 1) has been subjected to drying treatment.

[0032] Preferably, the drying temperature of the drying treatment is 80°C - 130°C, and the drying time is 0.5 h - 6 h.

[0033] Preferably, the isocyanate in step 1) is at least one of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate.

[0034] Preferably, the pyridine diol in step 1) is at least one of 2,6-pyridine dimethanol, 2,6-pyridine diethanol, 3,5-pyridine dimethanol, 3,5-pyridine diethanol.

[0035] Preferably, the catalyst in step 1) is at least one of bis(dimethylaminoethyl) ether, pentamethyldiethylenetriamine, dibutyltin dilaurate.

[0036] Preferably, the dosage of the catalyst in step 1) is 1% - 2% of the weight of the polytetrahydrofuran diol.

[0037] Preferably, the organic solvent in step 1) is at least one of dimethylacetamide, dimethylformamide, tetrahydrofuran.

[0038] Preferably, the number-average molecular weight of the aminopropyl-terminated polydimethylsiloxane described in step 1) is 500 g / mol to 5000 g / mol.

[0039] Preferably, the diboric acid described in step 1) is at least one of 2,6-naphthalenediboronic acid and 1,4-benzenediboronic acid.

[0040] Preferably, the temperature of the prepolymerization reaction described in step 1) is 50 °C to 80 °C, and the reaction time is 2 h to 8 h.

[0041] Preferably, the prepolymerization reaction described in step 1) is carried out in a nitrogen atmosphere or an argon atmosphere.

[0042] Preferably, the temperature of the grafting reaction described in step 1) is 20 °C to 40 °C, and the reaction time is 6 h to 24 h.

[0043] Preferably, the grafting reaction described in step 1) is carried out in a nitrogen atmosphere or an argon atmosphere.

[0044] Preferably, the temperature of the chain extension reaction described in step 1) is 40 °C to 60 °C, and the reaction time is 6 h to 24 h.

[0045] Preferably, the chain extension reaction described in step 1) is carried out in a nitrogen atmosphere or an argon atmosphere.

[0046] Preferably, the temperature of the crosslinking reaction described in step 1) is 20 °C to 60 °C, and the reaction time is 3 h to 12 h.

[0047] Preferably, the crosslinking reaction described in step 1) is carried out in a nitrogen atmosphere or an argon atmosphere.

[0048] Preferably, the dispersion method described in step 2) is mechanical stirring.

[0049] Preferably, the time of the mechanical stirring is 1 h to 6 h.

[0050] Preferably, the molding described in step 2) is carried out under the condition that the temperature is 20 °C to 60 °C, and the molding time is 24 h to 72 h.

[0051] Preferably, the lamination described in step 3) is carried out under the conditions that the temperature is 20 °C to 80 °C and the pressure is 0 MPa to 0.3 MPa, and the lamination time is 1 h to 48 h.

[0052] An application of the self-healing broadband microwave absorbing composite material as described above in the fields of 5G communication, new energy vehicles, consumer electronics, or national defense and military industries.

[0053] Principle of the present invention: Based on the synergistic mechanism of permeability frequency band matching and impedance regulation, through the optimization of the material system and the innovation of the structure design, the present invention realizes broadband and efficient electromagnetic wave absorption in the range of 2 GHz to 18 GHz.

[0054] The core principle lies in:

[0055] First of all, by analyzing the frequency response characteristics of magnetic materials, a segmented enhanced magnetic loss system is constructed. Using FeSiAl, ferrite, etc. as the core wave-absorbing fillers, magnetic / dielectric synergistic loss is achieved for the medium and low frequency bands (S / C band, 2 GHz to 8 GHz).

[0056] Secondly, carbonyl iron powder (CIP) or / and iron cobalt (FeCo) powder is compounded with insulating inorganic materials to absorb electromagnetic waves in the high frequency band (X / Ku band, 8 GHz to 18 GHz) through domain wall resonance loss and natural resonance loss.

[0057] Thirdly, by constructing a "high impedance - low impedance" double-layer structure, the high impedance matching of the high impedance matching layer is used to achieve efficient transmission and absorption of high frequency electromagnetic waves in the high impedance matching layer. Combining the low impedance matching of the low impedance matching layer, the electromagnetic waves are reflected as much as possible. By means of "transmission - reflection - retransmission", the propagation path of the electromagnetic waves inside the composite material is extended, so as to achieve efficient electromagnetic absorption.

[0058] In addition, polysiloxane-modified polyurethane is used as the matrix of the composite material, which has excellent self-healing performance and mechanical properties, and can realize seamless bonding between the double-layer materials through a simple hot pressing process.

[0059] To sum up, through methods such as magnetic loss frequency band matching, impedance regulation and self-healing matrix design, the present invention has successfully realized "wide frequency band coverage - matrix self-healing - recycling" of the wave-absorbing composite material, providing an innovative solution for the electromagnetic protection and electromagnetic compatibility of a new generation of national defense weaponry and 5G communication equipment.

[0060] The beneficial effects of the present invention are as follows: The self-healing broadband wave-absorbing composite material of the present invention has the advantages of excellent wave-absorbing performance, large effective absorption bandwidth, thin thickness, good mechanical properties, good self-healing performance, etc. It can be used in the fields of 5G communication, new energy vehicles, consumer electronics, national defense and military industry, etc. Moreover, its preparation method is simple and the production cost is relatively low, which is suitable for large-scale industrial production and application.

[0061] Specifically:

[0062] 1) The present invention adopts a "high impedance - low impedance" double - layer structure design, which improves the electromagnetic wave energy coupling efficiency and realizes efficient wave absorption. First, optimization of high - frequency transmission: The high - impedance matching layer adopts a composite system of iron - based soft magnetic powder and inorganic materials with a low dielectric constant, so that the impedance matching value (Z) exceeds 0.4, enabling most of the incident electromagnetic waves to enter the material interior. Second, regulation of mid - and low - frequency reflection: The low - impedance matching layer adopts soft magnetic powder to maintain a high dielectric constant, and induces electromagnetic wave reflection through the impedance mismatch value (Z = 0.1 - 0.3), forming a standing - wave interference effect with the high - impedance matching layer structure. Third, achieving multi - level attenuation: Making the electromagnetic waves experience the process of "transmission - reflection - re - transmission" inside the composite material, extending the absorption path of the electromagnetic waves, enhancing the electromagnetic loss, and realizing efficient wave absorption.

[0063] 2) The present invention adopts the design concept of a layered structure and complementary magnetic permeability frequency bands to achieve thickness reduction and wide - band efficient absorption of the composite material. Ferrosilicon aluminum (FeSiAl) and ferrite are respectively selected to cover the mid - and low - frequency (2 GHz - 8 GHz) wave - absorbing frequency bands, and carbonyl iron powder (CIP) and iron - cobalt powder (FeCo) are used to cover the high - frequency (8 GHz - 18 GHz) wave - absorbing frequency bands. The layered structure is conducive to enhancing the electromagnetic absorption in specific frequency bands, realizing a reasonable match of the magnetic loss peak positions, enhancing the electromagnetic absorption in specific frequency bands, effectively reducing the overall thickness of the composite material (<4 mm), and broadening the wave - absorbing frequency band (>12 GHz).

[0064] 3) The present invention uses polysiloxane - modified polyurethane as the matrix of the composite material, which can realize self - repair of the wave - absorbing material. Utilizing the self - repair performance of polysiloxane - modified polyurethane, ethanol - assisted self - repair is carried out during the material preparation process to achieve inter - layer bonding without applying additional adhesives, and the bonding efficiency is high. In addition, when the composite material is damaged and cracked, it can also be repaired or even recycled. The repair efficiency of the wave - absorbing performance can reach up to 100%, and the repair efficiency of the mechanical properties can reach up to 94%, extending the service life of the composite material. Description of the Drawings

[0065] Figure 1 SEM image of the composite wave - absorbing powder in Example 1.

[0066] Figure 2 Reflection loss - frequency relationship curves of the self - reparable wide - band wave - absorbing composite materials in Examples 1 - 5 and the wave - absorbing composite materials in Comparative Examples 1 - 2.

[0067] Figure 3 Stress - strain relationship curves of the self - reparable wide - band wave - absorbing composite material in Example 1 and the wave - absorbing composite material in Comparative Example 1 before and after fracture self - repair.

[0068] Figure 4Reflection loss - frequency relationship curves of the self - healable broadband microwave absorbing composite material in Example 1 and the microwave absorbing composite material in Comparative Example 1 before and after fracture self - healing. Detailed implementation manners

[0069] The present invention will be further explained and described below in conjunction with specific embodiments.

[0070] Example 1:

[0071] A self - healable broadband microwave absorbing composite material is composed of a laminated high - impedance matching layer and a low - impedance matching layer.

[0072] The high - impedance matching layer is composed of the following components by mass percentage:

[0073] Polysiloxane - modified polyurethane: 40%;

[0074] Composite microwave absorbing powder (mass ratio of carbonyl iron powder to hexagonal boron nitride is 20:1): 60%;

[0075] The low - impedance matching layer is composed of the following components by mass percentage:

[0076] Polysiloxane - modified polyurethane: 50%;

[0077] Flaky iron - silicon - aluminum powder: 50%;

[0078] The preparation method of the composite microwave absorbing powder is as follows: Mix carbonyl iron powder (median particle size is 3μm) and hexagonal boron nitride (median particle size is 2μm) according to the mass ratio of 20:1. Then, load the obtained mixed powder and cemented carbide balls into a ball - milling tank at a mass ratio of 1:40. Seal the tank body and install it on a plasma ball - mill. Vacuumize and fill argon until the pressure in the tank reaches 0.05 MPa. Then, start the vibration control power supply and the plasma discharge control power supply for plasma ball - milling. The ball - milling parameters are as follows: The rotation speed of the ball - mill is 2000 rpm, the discharge frequency is 10 kHz, and the intermittent ball - milling mode is adopted, that is, run for 20 min and then stop for 20 min, cycle 12 times, and the total ball - milling time is 4 h. Then, open the ball - milling tank and collect the material to obtain the composite microwave absorbing powder.

[0079] The preparation method of the above - mentioned self - healable broadband microwave absorbing composite material is as follows:

[0080] 1) Poly(tetramethylene ether) glycol with a number-average molecular weight of 1000 g / mol was dried and dehydrated at 120 °C for 0.5 h. Then, poly(tetramethylene ether) glycol, isophorone diisocyanate, 2,6-pyridinedimethanol, and dibutyltin dilaurate were dispersed in tetrahydrofuran. The amount of dibutyltin dilaurate used was 1.5% of the weight of poly(tetramethylene ether) glycol. Then, it was stirred at a constant temperature of 60 °C for 3 h under nitrogen protection and cooled to room temperature (25 °C ± 5 °C). Then, aminopropyl-terminated polydimethylsiloxane with a number-average molecular weight of 1000 g / mol was added and stirring was continued for 12 h. Then, it was heated to 40 °C and carbohydrazide was added, and stirring was continued for 12 h. After cooling to room temperature, 1,4-benzenediboronic acid was added and stirring was continued for 4 h. The molar ratio of poly(tetramethylene ether) glycol, isophorone diisocyanate, 2,6-pyridinedimethanol, aminopropyl-terminated polydimethylsiloxane, carbohydrazide, and 1,4-benzenediboronic acid was 1:3:0.5:1:0.5:0.5, and a polysiloxane-modified polyurethane solution was obtained;

[0081] 2) The composite microwave-absorbing powder and flaky FeSiAl powder were respectively stirred and dispersed in the polysiloxane-modified polyurethane solution. The mass ratio of the composite microwave-absorbing powder to the polysiloxane-modified polyurethane solution was 3:20, and the mass ratio of the flaky FeSiAl powder to the polysiloxane-modified polyurethane solution was 1:10. The stirring time was 4 h, and then defoaming was carried out. Then, they were respectively injected into a polytetrafluoroethylene mold and left standing at room temperature for 48 h to obtain a high-impedance matching layer material and a low-impedance matching layer material;

[0082] 3) The single sides of the high-impedance matching layer material and the low-impedance matching layer material were sprayed with absolute ethanol and then superposed on each other, and then a pressure of 0.1 MPa was applied and left at 25 °C for 24 h to obtain a self-healing broadband microwave-absorbing composite material (the overall thickness was 3.58 mm, the thickness of the high-impedance matching layer was 1.79 mm, and the thickness of the low-impedance matching layer was 1.79 mm).

[0083] The scanning electron microscope (SEM) image of the composite microwave-absorbing powder in this example is as Figure 1 shown.

[0084] It can be seen from Figure 1 that: the surface of the composite microwave-absorbing powder is rough, hexagonal boron nitride is exfoliated into fine nanosheets and evenly distributed on the surface of carbonyl iron powder.

[0085] Example 2:

[0086] A self-healing broadband microwave-absorbing composite material, which is composed of a laminated and composite high-impedance matching layer and a low-impedance matching layer;

[0087] The high-impedance matching layer is composed of the following components by mass percentage:

[0088] Polysiloxane-modified polyurethane: 45%;

[0089] Composite wave-absorbing powder (mass ratio of carbonyl iron powder to hexagonal boron nitride is 30:1): 55%;

[0090] The low-impedance matching layer is composed of the following components by mass percentage:

[0091] Polysiloxane-modified polyurethane: 70%;

[0092] Flaky iron-silicon-aluminum powder: 30%;

[0093] The preparation method of the composite wave-absorbing powder is as follows: Mix carbonyl iron powder (median particle size is 10 μm) and hexagonal boron nitride (median particle size is 20 μm) according to a mass ratio of 30:1. Then, load the obtained mixed powder and cemented carbide balls into a ball mill tank at a mass ratio of 1:30. Seal the tank body and install it on a plasma ball mill. Evacuate and fill with argon until the pressure in the tank reaches 0.05 MPa. Then, start the vibration control power supply and the plasma discharge control power supply for plasma ball milling. The ball milling parameters are as follows: The rotation speed of the ball mill is 1500 rpm, the discharge frequency is 11 kHz. Adopt an intermittent ball milling mode, that is, run for 20 min and then stop for 20 min, cycle 24 times, and the total ball milling time is 8 h. Then, open the ball mill tank and collect the material to obtain the composite wave-absorbing powder.

[0094] The preparation method of the above self-healing broadband wave-absorbing composite material is as follows:

[0095] 1) Place polytetrahydrofuran diol with a number average molecular weight of 1000 g / mol at 120 °C for 0.5 h of drying and dehydration treatment. Then, disperse polytetrahydrofuran diol, isophorone diisocyanate, 2,6-pyridinedimethanol, and dibutyltin dilaurate in tetrahydrofuran. The dosage of dibutyltin dilaurate is 1.5% of the weight of polytetrahydrofuran diol. Then, stir at a constant temperature of 60 °C for 4 h under nitrogen protection, cool to room temperature, add aminopropyl-terminated polydimethylsiloxane with a number average molecular weight of 1000 g / mol and continue stirring for 8 h. Then, raise the temperature to 40 °C and add carbohydrazide, continue stirring for 12 h, cool to room temperature, and then add 1,4-benzenediboronic acid and continue stirring for 6 h. The molar ratio of polytetrahydrofuran diol, isophorone diisocyanate, 2,6-pyridinedimethanol, aminopropyl-terminated polydimethylsiloxane, carbohydrazide, and 1,4-benzenediboronic acid is 1:3:0.5:1:0.5:0.5 to obtain a polysiloxane-modified polyurethane solution;

[0096] 2) Stir and disperse the composite wave-absorbing powder and the flaky iron-silicon-aluminum powder in the polysiloxane-modified polyurethane solution respectively. The mass ratio of the composite wave-absorbing powder to the polysiloxane-modified polyurethane solution is 11:90, and the mass ratio of the flaky iron-silicon-aluminum powder to the polysiloxane-modified polyurethane solution is 3:70. The stirring time is 4 h, defoam, and then inject them into a polytetrafluoroethylene mold respectively and let it stand at room temperature for 48 h to obtain a high-impedance matching layer material and a low-impedance matching layer material;

[0097] 3) After spraying anhydrous ethanol on one side of the high-impedance matching layer material and the low-impedance matching layer material, stack them on top of each other, and then apply a pressure of 0.1 MPa and place them at 25 °C for 24 h to obtain a self-healing broadband microwave absorbing composite material (the overall thickness is 3.22 mm, the thickness of the high-impedance matching layer is 1.61 mm, and the thickness of the low-impedance matching layer is 1.61 mm).

[0098] Example 3:

[0099] A self-healing broadband microwave absorbing composite material, which is composed of a laminated high-impedance matching layer and a low-impedance matching layer;

[0100] The high-impedance matching layer is composed of the following components by mass percentage:

[0101] Polysiloxane-modified polyurethane: 30%;

[0102] Composite microwave absorbing powder (the mass ratio of iron-cobalt powder to silicon dioxide is 8:1): 70%;

[0103] The low-impedance matching layer is composed of the following components by mass percentage:

[0104] Polysiloxane-modified polyurethane: 50%;

[0105] Magnetite powder: 50%;

[0106] The preparation method of the composite microwave absorbing powder is as follows: Mix iron-cobalt powder (median particle size is 5 μm) and silicon dioxide (median particle size is 1 μm) according to a mass ratio of 8:1, and then load the obtained mixed powder and cemented carbide balls into a ball mill tank at a mass ratio of 1:30. Seal the tank body and install it on a plasma ball mill. Evacuate and fill with nitrogen until the pressure in the tank reaches 0.1 MPa, and then start the vibration control power supply and the plasma discharge control power supply for plasma ball milling. The ball milling parameters are as follows: the rotation speed of the ball mill is 1000 rpm, the discharge frequency is 10 kHz, and the intermittent ball milling mode is adopted, that is, run for 30 min and then stop for 30 min, and cycle 3 times. The total ball milling time is 1.5 h, and then open the ball mill tank and collect the material to obtain the composite microwave absorbing powder.

[0107] The preparation method of the above self-healing broadband microwave absorbing composite material is as follows:

[0108] 1) Poly(tetramethylene ether) glycol with a number-average molecular weight of 2000 g / mol was dried and dehydrated at 120 °C for 0.5 h. Then, poly(tetramethylene ether) glycol, toluene diisocyanate, 3,5-pyridinedimethanol, and dibutyltin dilaurate were dispersed in tetrahydrofuran. The amount of dibutyltin dilaurate was 1.0% of the weight of poly(tetramethylene ether) glycol. Then, it was stirred at a constant temperature of 60 °C for 4 h under nitrogen protection, cooled to room temperature, and then aminopropyl-terminated polydimethylsiloxane with a number-average molecular weight of 2000 g / mol was added and stirred continuously for 12 h. Then, it was heated to 40 °C and carbohydrazide was added, and stirring was continued for 24 h. After cooling to room temperature, 1,4-benzenediboronic acid was added and stirring was continued for 6 h. The molar ratio of poly(tetramethylene ether) glycol, toluene diisocyanate, 3,5-pyridinedimethanol, aminopropyl-terminated polydimethylsiloxane, carbohydrazide, and 1,4-benzenediboronic acid was 1:2.5:0.5:0.5:0.5:0.5, and a polysiloxane-modified polyurethane solution was obtained.

[0109] 2) The composite wave-absorbing powder and iron oxide powder were respectively stirred and dispersed in the polysiloxane-modified polyurethane solution. The mass ratio of the composite wave-absorbing powder to the polysiloxane-modified polyurethane solution was 7:30, and the mass ratio of the iron oxide powder to the polysiloxane-modified polyurethane solution was 1:10. The stirring time was 4 h, and then defoamed. Then, they were respectively injected into a polytetrafluoroethylene mold and left to stand at room temperature for 48 h to obtain a high-impedance matching layer material and a low-impedance matching layer material.

[0110] 3) The single sides of the high-impedance matching layer material and the low-impedance matching layer material were sprayed with absolute ethanol and then superimposed on each other, and then a pressure of 0.05 MPa was applied and left at 25 °C for 24 h to obtain a self-healing broadband wave-absorbing composite material (the overall thickness was 3.50 mm, the thickness of the high-impedance matching layer was 2.00 mm, and the thickness of the low-impedance matching layer was 1.50 mm).

[0111] Example 4:

[0112] A self-healing broadband wave-absorbing composite material, which consists of a laminated and composite high-impedance matching layer and a low-impedance matching layer;

[0113] The high-impedance matching layer is composed of the following components by mass percentage:

[0114] Polysiloxane-modified polyurethane: 50%;

[0115] Composite wave-absorbing powder (the mass ratio of iron cobalt powder to aluminum oxide is 9:1): 50%;

[0116] The low-impedance matching layer is composed of the following components by mass percentage:

[0117] Polysiloxane-modified polyurethane: 50%;

[0118] Zinc manganese ferrite powder: 50%;

[0119] The preparation method of the composite wave-absorbing powder is as follows: Mix iron-cobalt powder (median particle size of 10 μm) and aluminum oxide (median particle size of 500 nm) according to a mass ratio of 9:1. Then, load the obtained mixed powder and cemented carbide balls into a ball mill tank at a mass ratio of 1:10. After sealing the tank body, install and fix it on a plasma ball mill. Evacuate and fill with argon until the pressure in the tank reaches 0.02 MPa. Then, start the vibration control power supply and the plasma discharge control power supply for plasma ball milling. The ball milling parameters are as follows: the rotation speed of the ball mill is 2000 rpm, the discharge frequency is 11 kHz, and the intermittent ball milling mode is adopted, that is, run for 20 min and then stop for 20 min, and cycle 6 times. The total ball milling time is 2 h. Then, open the ball mill tank and collect the material to obtain the composite wave-absorbing powder.

[0120] The preparation method of the above self-healing broadband wave-absorbing composite material is as follows:

[0121] 1) Place polytetrahydrofuran diol with a number average molecular weight of 5000 g / mol at 120 °C for 1 h for drying and dehydration treatment. Then, disperse polytetrahydrofuran diol, diphenylmethane diisocyanate, 3,5-pyridinediol, and bis(dimethylaminoethyl) ether in tetrahydrofuran. The dosage of bis(dimethylaminoethyl) ether is 2.0% of the weight of polytetrahydrofuran diol. Then, stir at a constant temperature of 60 °C for 6 h under nitrogen protection, cool to room temperature, add aminopropyl-terminated polydimethylsiloxane with a number average molecular weight of 1000 g / mol and continue stirring for 12 h. Then, raise the temperature to 50 °C, add carbohydrazide, and continue stirring for 8 h. Cool to room temperature, add 2,6-naphthalenediboronic acid, and continue stirring for 4 h. The molar ratio of polytetrahydrofuran diol, diphenylmethane diisocyanate, 3,5-pyridinediol, aminopropyl-terminated polydimethylsiloxane, carbohydrazide, and 2,6-naphthalenediboronic acid is 1:2.5:0.2:0.8:0.5:0.5 to obtain a polysiloxane-modified polyurethane solution;

[0122] 2) Stir and disperse the composite wave-absorbing powder and zinc manganese ferrite powder in the polysiloxane-modified polyurethane solution respectively. The mass ratio of the composite wave-absorbing powder to the polysiloxane-modified polyurethane solution is 1:10, and the mass ratio of the zinc manganese ferrite powder to the polysiloxane-modified polyurethane solution is 1:10. Stir for 5 h, defoam, and then inject them into polytetrafluoroethylene molds respectively and let stand at room temperature for 24 h to obtain a high-impedance matching layer material and a low-impedance matching layer material;

[0123] 3) Spray anhydrous ethanol on one side of the high-impedance matching layer material and the low-impedance matching layer material and stack them on top of each other. Then, apply a pressure of 0.1 MPa and place at 40 °C for 12 h to obtain the self-healing broadband wave-absorbing composite material (the overall thickness is 3.34 mm, the thickness of the high-impedance matching layer is 1.60 mm, and the thickness of the low-impedance matching layer is 1.74 mm).

[0124] Example 5:

[0125] A self-healing broadband absorbing composite material is composed of a laminated high-impedance matching layer and a low-impedance matching layer.

[0126] The high-impedance matching layer is composed of the following components by mass percentage:

[0127] Polysiloxane-modified polyurethane: 30%;

[0128] Composite absorbing powder (mass ratio of carbonyl iron powder to silicon nitride is 5:1): 70%;

[0129] The low-impedance matching layer is composed of the following components by mass percentage:

[0130] Polysiloxane-modified polyurethane: 40%;

[0131] FeSiB nanocrystals: 60%;

[0132] The preparation method of the composite absorbing powder is as follows: Mix carbonyl iron powder (median particle size is 5 μm) and silicon nitride (median particle size is 1 μm) according to the mass ratio of 5:1. Then, load the obtained mixed powder and cemented carbide balls into a ball mill tank at a mass ratio of 1:50. After sealing the tank body, install and fix it on a plasma ball mill. Vacuumize and fill argon until the gas pressure in the tank reaches 0.1 MPa. Then, start the vibration control power supply and the plasma discharge control power supply for plasma ball milling. The ball milling parameters are as follows: The rotation speed of the ball mill is 1500 rpm, the discharge frequency is 9 kHz, and the intermittent ball milling mode is adopted, that is, run for 30 min and then stop for 30 min, and cycle 2 times. The total ball milling time is 1 h. Then, open the ball mill tank and collect the material to obtain the composite absorbing powder.

[0133] The preparation method of the above self-healing broadband absorbing composite material is as follows:

[0134] 1) Poly(tetramethylene ether) glycol with a number-average molecular weight of 2000 g / mol was dried and dehydrated at 120 °C for 1 h. Then, poly(tetramethylene ether) glycol, isophorone diisocyanate, 3,5-pyridinediethanol, and pentamethyldiethylenetriamine were dispersed in tetrahydrofuran. The amount of pentamethyldiethylenetriamine was 1.5% of the weight of poly(tetramethylene ether) glycol. Then, it was stirred at a constant temperature of 50 °C for 12 h under nitrogen protection, cooled to 30 °C, and then aminopropyl-terminated polydimethylsiloxane with a number-average molecular weight of 3000 g / mol was added and stirred continuously for 12 h. Then, it was heated to 50 °C and carbohydrazide was added, and stirring was continued for 8 h. After cooling to room temperature, 2,6-naphthalenediboronic acid was added and stirring was continued for 4 h. The molar ratio of poly(tetramethylene ether) glycol, isophorone diisocyanate, 3,5-pyridinediethanol, aminopropyl-terminated polydimethylsiloxane, carbohydrazide, and 2,6-naphthalenediboronic acid was 1:3.5:0.5:1.5:0.5:0.5, and a polysiloxane-modified polyurethane solution was obtained.

[0135] 2) The composite wave-absorbing powder and FeSiB nanocrystals were respectively stirred and dispersed in the polysiloxane-modified polyurethane solution. The mass ratio of the composite wave-absorbing powder to the polysiloxane-modified polyurethane solution was 7:30, and the mass ratio of FeSiB nanocrystals to the polysiloxane-modified polyurethane solution was 3:20. The stirring time was 5 h, and then degassing was carried out. Then, they were respectively injected into a polytetrafluoroethylene mold and left standing at room temperature for 48 h to obtain a high-impedance matching layer material and a low-impedance matching layer material.

[0136] 3) The single sides of the high-impedance matching layer material and the low-impedance matching layer material were sprayed with absolute ethanol and then superimposed on each other, and then a pressure of 0.2 MPa was applied and left at 20 °C for 48 h to obtain a self-healing broadband wave-absorbing composite material (the overall thickness was 3.92 mm, the thickness of the high-impedance matching layer was 1.92 mm, and the thickness of the low-impedance matching layer was 2.00 mm).

[0137] Comparative Example 1:

[0138] A wave-absorbing composite material is composed of the following components in mass percentage:

[0139] Polyurethane: 30%;

[0140] Carbonyl iron powder: 70%.

[0141] The preparation method of the above wave-absorbing composite material is as follows:

[0142] 1) Poly(tetramethylene ether) glycol with a number-average molecular weight of 1000 g / mol was dried and dehydrated at 120 °C for 0.5 h. Then, poly(tetramethylene ether) glycol, isophorone diisocyanate, and dibutyltin dilaurate were dispersed in dimethylacetamide. The amount of dibutyltin dilaurate was 1.5% of the weight of poly(tetramethylene ether) glycol. Then, under nitrogen protection, it was stirred at a constant temperature of 80 °C for 6 h. The molar ratio of poly(tetramethylene ether) glycol to isophorone diisocyanate was 1:1, and a polyurethane solution was obtained.

[0143] 2) Carbonyl iron powder was stirred and dispersed in the polyurethane solution. The mass ratio of carbonyl iron powder to the polyurethane solution was 7:30, and the stirring time was 4 h. After defoaming, it was poured into a polytetrafluoroethylene mold and left to stand at room temperature for 48 h, obtaining the microwave absorbing composite material (with a thickness of 1.46 mm). Comparative Example 2:

[0144] A microwave absorbing composite material is composed of a laminated high-impedance matching layer and a low-impedance matching layer.

[0145] The high-impedance matching layer is composed of the following components by mass percentage:

[0146] Polysiloxane-modified polyurethane: 40%;

[0147] Composite microwave absorbing powder (the mass ratio of flaky FeSiAl powder to hexagonal boron nitride is 20:1): 60%;

[0148] The low-impedance matching layer is composed of the following components by mass percentage:

[0149] Polysiloxane-modified polyurethane: 50%;

[0150] Flaky FeSiAl powder: 50%;

[0151] The preparation method of the composite microwave absorbing powder is as follows: Flaky FeSiAl powder (median chip diameter is 10 μm) and hexagonal boron nitride (median particle diameter is 2 μm) were mixed according to a mass ratio of 20:1. Then, the obtained mixed powder and cemented carbide balls were loaded into a ball mill tank at a mass ratio of 1:40. After sealing the tank body, it was installed and fixed on a plasma ball mill. The vacuum was pumped and argon was filled until the pressure in the tank reached 0.05 MPa. Then, the vibration control power supply and the plasma discharge control power supply were started for plasma ball milling. The ball milling parameters are as follows: the rotation speed of the ball mill is 2000 rpm, the discharge frequency is 10 kHz, and the intermittent ball milling mode is adopted, that is, it runs for 20 min and then stops for 20 min, and the cycle is 3 times. The total ball milling time is 1 h. Then, the ball mill tank was opened and the material was collected, obtaining the composite microwave absorbing powder.

[0152] The preparation method of the above microwave absorbing composite material is as follows:

[0153] 1) Poly(tetramethylene ether) glycol with a number average molecular weight of 1000 g / mol was dried and dehydrated at 120 °C for 0.5 h. Then, poly(tetramethylene ether) glycol, isophorone diisocyanate, 2,6-pyridinedimethanol, and dibutyltin dilaurate were dispersed in tetrahydrofuran. The amount of dibutyltin dilaurate was 1.5% of the weight of poly(tetramethylene ether) glycol. Then, it was stirred at a constant temperature of 60 °C for 3 h under nitrogen protection, cooled to room temperature, and then aminopropyl-terminated polydimethylsiloxane with a number average molecular weight of 1000 g / mol was added and stirred continuously for 12 h. Then, it was heated to 40 °C and carbohydrazide was added, and it was stirred continuously for 12 h. After cooling to room temperature, 1,4-benzenediboronic acid was added and stirred continuously for 4 h. The molar ratio of poly(tetramethylene ether) glycol, isophorone diisocyanate, 2,6-pyridinedimethanol, aminopropyl-terminated polydimethylsiloxane, carbohydrazide, and 1,4-benzenediboronic acid was 1:3:0.5:1:0.5:0.5 to obtain a polysiloxane-modified polyurethane solution;

[0154] 2) The composite microwave absorbing powder and flaky FeSiAl powder were respectively stirred and dispersed in the polysiloxane-modified polyurethane solution. The mass ratio of the composite microwave absorbing powder to the polysiloxane-modified polyurethane solution was 3:20, and the mass ratio of the flaky FeSiAl powder to the polysiloxane-modified polyurethane solution was 1:10. The stirring time was 4 h, and then degassed. Then, they were respectively injected into a polytetrafluoroethylene mold and left standing at room temperature for 48 h to obtain a high-impedance matching layer material and a low-impedance matching layer material;

[0155] 3) The single sides of the high-impedance matching layer material and the low-impedance matching layer material were sprayed with absolute ethanol and then superimposed on each other. Then, a pressure of 0.1 MPa was applied and placed at 25 °C for 24 h to obtain a microwave absorbing composite material (the overall thickness was 3.20 mm, the thickness of the high-impedance matching layer was 1.60 mm, and the thickness of the low-impedance matching layer was 1.60 mm).

[0156] Performance test:

[0157] 1) The reflection loss - frequency relationship curves of the self-healing broadband microwave absorbing composite materials in Examples 1 - 5 and the microwave absorbing composite materials in Comparative Examples 1 - 2 are as Figure 2 shown.

[0158] It can be Figure 2 seen that: compared with the microwave absorbing composite materials in Comparative Examples 1 - 2, the microwave absorbing performance of the self-healing broadband microwave absorbing composite materials in Examples 1 - 5 has been greatly improved, the effective absorption bandwidth (reflection loss RL < -10 dB) has increased significantly, and the thickness of the material is relatively thin, not exceeding 4 mm.

[0159] 2) The stress - strain relationship curves of the self-healing broadband microwave absorbing composite material in Example 1 and the microwave absorbing composite material in Comparative Example 1 before and after fracture self-healing are as Figure 3 shown.

[0160] It can be seen from Figure 3 that: Compared with the microwave absorbing composite material in Comparative Example 1, the tensile strength and self-healing performance of the self-healing broadband microwave absorbing composite material in Example 1 are both greatly improved.

[0161] 3) The reflection loss - frequency relationship curves of the self-healing broadband microwave absorbing composite material in Example 1 and the microwave absorbing composite material in Comparative Example 1 before and after fracture self-healing are as Figure 4 shown.

[0162] It can be seen from Figure 4 that: The self-healing broadband microwave absorbing composite material in Example 1 can achieve complete restoration of microwave absorbing performance after fracture self-healing, while the microwave absorbing performance of the microwave absorbing composite material in Comparative Example 1 cannot be restored.

[0163] 4) The test results of the microwave absorbing performance and self-healing performance of the self-healing broadband microwave absorbing composite materials in Examples 1 to 5 and the microwave absorbing composite materials in Comparative Examples 1 to 2 are shown in the following table:

[0164] Table 1 Test results of microwave absorbing performance and self-healing performance of composite materials

[0165]

[0166] Note:

[0167] Microwave absorbing performance: Tested by a vector network analyzer. Concentric ring samples with an inner diameter of 3.04 mm and an outer diameter of 7.00 mm are punched out. The complex permittivity and complex permeability of the single-layer material are tested by the coaxial method. The test frequency range is 2 GHz to 18 GHz. Based on the multi-layer material theory, the formula (1) is used for iterative calculation to determine the impedance between the nth layer (Z n ) and the (n + 1)th layer (Z n+1 ):

[0168] Formula (1): In the formula, η n , γ n and d n respectively represent the characteristic impedance, complex propagation constant and thickness of the nth layer. The calculation formulas of η n and γ n are as shown in formula (2) and formula (3):

[0169] Formula (2):

[0170] Formula (3): In the formula, η0 represents the characteristic impedance of air (η0 = 1), μ rn and ε rnrespectively represent the relative complex permeability and permittivity of the nth layer. The upper layer, lower layer and metal backplane of the composite absorbing material are denoted as Z1, Z2 and Z3 (Z3 = 0) respectively. By iterating equation (1), Z1 is determined. Finally, the reflection loss (RL) of the absorbing composite material is calculated according to formula (4):

[0171] Formula (4):

[0172] Self-healing performance: After splicing the fracture position of the tensile sample, spray ethanol on the splicing section, and then heat and repair at 80 °C for 30 min to volatilize the ethanol. Test the mechanical properties and absorbing properties of the repaired sample.

[0173] Mechanical property repair efficiency: The ratio (percentage) of the maximum tensile strength after repair to the strength of the undamaged composite material.

[0174] Absorbing property repair efficiency: The ratio (percentage) of the overlapping part of the absorption bandwidth of the repaired composite material to the absorption bandwidth of the undamaged composite material at the same thickness to the absorption bandwidth of the undamaged composite material.

[0175] As can be seen from Table 1:

[0176] a) Combining the absorbing property test results of the self-healing broadband absorbing composite materials in Examples 1-5 and the absorbing composite materials in Comparative Examples 1-2, the advantages of the high-low impedance design and the co-design strategy of the magnetic loss frequency band can be accurately demonstrated. Combining Figure 2 it can be known that the self-healing broadband absorbing composite materials in Examples 1-5 successfully constructed a high-low impedance matching system by adjusting the content of the inorganic insulating material, the composition of the soft magnetic metal phase, the process parameters of the plasma ball milling, and the ratio of the absorbing fillers in the double-layer material. Combining the complementary design of the magnetic loss frequency band, the effective absorption bandwidth (RL < -10 dB) of the self-healing broadband absorbing composite materials in Examples 1-5 reached 10.30 GHz - 12.98 GHz in the thickness range of 3.2 mm - 4.0 mm. Compared with the absorbing composite material (single layer) in Comparative Example 1, the effective absorption bandwidth was broadened by 123% - 182%;

[0177] b) The wave-absorbing composite material in Comparative Example 1 suffered from impedance mismatch due to the lack of impedance regulation, and its effective absorption bandwidth was only 4.61 GHz. Although the wave-absorbing composite material in Comparative Example 2 constructed a high-low impedance matching structure, since the wave-absorbing filler used in the high-impedance matching layer was made by plasma ball milling of flaky FeSiAl powder and hexagonal boron nitride, its magnetic loss factor μ" at high frequencies was relatively low, resulting in no electromagnetic wave absorption in the high-frequency band (>8 GHz) and failure to achieve magnetic loss matching. Therefore, the effective absorption bandwidth was reduced to 4.00 GHz. The self-healing broadband wave-absorbing composite materials in Examples 1 to 5 adopted a synergistic wave-absorbing mechanism to achieve double-loss peak coupling - in the medium-low frequency band (2 GHz to 8 GHz), it was jointly affected by the high dielectric loss and eddy current loss of the low-impedance matching layer, and in the high-frequency band (8 GHz to 18 GHz), it was affected by the magnetic domain resonance and multiple reflection interference effects of the high-impedance matching layer. Finally, the maximum limited absorption bandwidth of the composite material reached 12.98 GHz, and the sample thickness did not exceed 4 mm;

[0178] c) Combining Figure 3 It can be seen that the tensile strength of the self-healing broadband wave-absorbing composite material in Example 1 (with the substrate of polysiloxane-modified polyurethane) was significantly improved compared with that of the wave-absorbing composite material in Comparative Example 1 (with the substrate of ordinary polyurethane), indicating that multiple hydrogen bonds and coordination bonds enhanced the molecular chain crosslinking. Moreover, the polysiloxane chain segments promoted the microphase separation inside the material and improved the mechanical properties of the composite material. In addition, the combination of coordination bonds and multiple hydrogen bonds of the polysiloxane-modified polyurethane in Example 1 endows the composite material with excellent self-healing performance. After 30 minutes of heating repair after tensile fracture, the repair efficiency of the mechanical properties of the composite material can reach 94%, and the repair efficiency of the wave-absorbing performance can reach 98%.

[0179] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A self-repairable broadband wave-absorbing composite material, characterized in that: The composition includes a laminated high impedance matching layer and a low impedance matching layer; The high impedance matching layer includes the following components in mass percentage: Polysiloxane modified polyurethane: 20% to 50%; Composite absorbing powder: 50% to 80%; The composite wave-absorbing powder is made by plasma ball milling iron-based soft magnetic powder and insulating inorganic compound; The iron-based soft magnetic powder is at least one of carbonyl iron powder and iron-cobalt powder; The low impedance matching layer includes the following components in mass percentage: Polysiloxane modified polyurethane: 30% to 80%; Soft magnetic powder: 20% to 70%; The soft magnetic powder is at least one of iron-silicon-aluminum powder, zinc-manganese ferrite powder, ferroferric oxide powder, and iron-silicon-boron nanocrystals.

2. The self-repairable broadband wave-absorbing composite material according to claim 1, characterized in that: The thickness of the self-repairable broadband wave-absorbing composite material is 1 mm to 10 mm; the thickness of the high impedance matching layer is 0.8 mm to 9.8 mm; and the thickness of the low impedance matching layer is 0.2 mm to 9.2 mm.

3. The self-repairable broadband wave-absorbing composite material according to claim 1 or 2, characterized in that: The mass ratio of the iron-based soft magnetic powder to the insulating inorganic compound is 5 to 50:

1.

4. The self-repairable broadband wave-absorbing composite material according to claim 1 or 2, characterized in that: The insulating inorganic compound is at least one of hexagonal boron nitride, aluminum oxide, silicon dioxide and silicon nitride.

5. The self-repairable broadband wave-absorbing composite material according to claim 1 or 2, characterized in that: The process parameters of the plasma ball milling include: the atmosphere is one of argon atmosphere, nitrogen atmosphere, oxygen atmosphere and air atmosphere, the atmosphere pressure is 0.01MPa to 0.20MPa, the plasma discharge frequency is 5kHz to 12kHz, the ball mill speed is 100rpm to 3000rpm, and the ball milling time is 0.5h to 48h.

6. A method for preparing a self-repairable broadband wave-absorbing composite material as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: 1) dispersing polytetrahydrofuran diol, isocyanate, pyridine diol and a catalyst in an organic solvent for prepolymerization, then adding aminopropyl-terminated polydimethylsiloxane for grafting reaction, then adding carbohydrazide for chain extension reaction, then adding diboric acid for cross-linking reaction to obtain a polysiloxane-modified polyurethane solution; 2) dispersing the composite absorbing powder and the soft magnetic powder in a polysiloxane-modified polyurethane solution respectively, and then injecting them into molds for molding respectively to obtain a high impedance matching layer material and a low impedance matching layer material; 3) The high impedance matching layer material and the low impedance matching layer material are coated with ethanol on one side and then overlapped and bonded to each other to obtain a self-repairable broadband absorbing composite material.

7. The preparation method according to claim 6, characterized in that: Step 1): the molar ratio of the polytetrahydrofuran diol, isocyanate, pyridine diol, aminopropyl-terminated polydimethylsiloxane, carbohydrazide and diboric acid is 1:1.6-3.6:0.2-0.8:0.2-1.5:0.2-0.8:0.2-0.

8.

8. The preparation method according to claim 6 or 7, characterized in that: The number average molecular weight of the polytetrahydrofuran diol in step 1) is 500 g / mol to 5000 g / mol; the isocyanate in step 1) is at least one of toluene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate; the pyridine diol in step 1) is at least one of 2,6-pyridine dimethanol, 2,6-pyridine diethanol, 3,5-pyridine dimethanol, and 3,5-pyridine diethanol; the number average molecular weight of the aminopropyl-terminated polydimethylsiloxane in step 1) is 500 g / mol to 5000 g / mol; the diboric acid in step 1) is at least one of 2,6-naphthalene diboric acid and 1,4-phenyl diboric acid.

9. The preparation method according to claim 6 or 7, characterized in that: The temperature of the prepolymerization reaction in step 1) is 50°C to 80°C, and the reaction time is 2h to 8h; the temperature of the grafting reaction in step 1) is 20°C to 40°C, and the reaction time is 6h to 24h; the temperature of the chain extension reaction in step 1) is 40°C to 60°C, and the reaction time is 6h to 24h; the temperature of the cross-linking reaction in step 1) is 20°C to 60°C, and the reaction time is 3h to 12h; the molding in step 2) is carried out at a temperature of 20°C to 60°C, and the molding time is 24h to 72h; the lamination in step 3) is carried out at a temperature of 20°C to 80°C and a pressure of 0MPa to 0.3MPa, and the lamination time is 1h to 48h.

10. An application of the self-repairable broadband wave-absorbing composite material as claimed in any one of claims 1 to 5 in the fields of 5G communications, new energy vehicles, consumer electronics or national defense and military industries.

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