Preparation method, product and application of flexible wave-absorbing composite material

Abstract

The invention relates to the technical field of flexible wave-absorbing materials, in particular to a preparation method, a product and application of a flexible wave-absorbing composite material. Acrylamide and hydroxyethyl cellulose are used as raw materials, free radical copolymerization is adopted, and silica sol and GO are added to synthesize composite gel. And adding ferric chloride in different proportions to prepare the aerogel. The preparation method comprises the following steps: carrying out carbonization treatment at different temperatures to improve the wave-absorbing performance of aerogel, mixing a TPU (polyurethane) / DMF (dimethyl formamide) mixed solution into the aerogel, and carrying out structural design to finally prepare the flexible wave-absorbing composite material. The preparation method is simple, and large-scale industrial production is easy to realize. The prepared flexible wave-absorbing composite material is good in wave-absorbing performance and has a wide application prospect in electronic components.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible microwave absorbing materials, and particularly to a preparation method, product and application of a flexible microwave absorbing composite material. Background Art

[0002] Flexible microwave absorbing materials are products derived from microwave absorbing materials and emerged with the rise of power electric and telecommunications technologies. Their application scope is extremely wide. Flexible microwave absorbing materials are applied in the electrical field, the information field, the automotive field and other supporting fields. Most importantly, flexible microwave absorbing materials, as the main raw material for the production of electronic components, bring continuous demand. In electronic devices, high-frequency noise generated by flat circuits will have an unstable impact on the system. The limited circuit board area is wide and flat, and it is impossible to install a filter. At this time, flexible microwave absorbing materials are needed to cover the entire interference surface to form absorption and heat conversion. However, the microwave absorption performance of current flexible microwave absorbing materials still needs to be further improved. Summary of the Invention

[0003] Based on the above, the present invention provides a preparation method, product and application of a flexible microwave absorbing composite material.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention is a preparation method of a flexible microwave absorbing composite material, comprising the following steps:

[0006] Dissolve tetraethyl orthosilicate in water to prepare silica sol;

[0007] Mix hydroxyethyl cellulose and graphene oxide with water, perform water bath heating, then add an initiator and mix well, then add acrylamide and water and mix well, and then add N,N-methylenebisacrylamide and mix well to obtain a hydrogel;

[0008] Add the silica sol to the hydrogel and stir at a constant temperature, then raise the temperature and add FeCl3 and stir, let it stand and cool, and then freeze-dry to obtain GO / SiO2 / PAAM / HEC aerogel;

[0009] Perform pre-oxidation and high-temperature carbonization treatment on the GO / SiO2 / PAAM / HEC aerogel to obtain a carbonized aerogel;

[0010] Immerse the carbonized aerogel in a TPU solution, then cure and dry to obtain the flexible microwave absorbing composite material.

[0011] Another technical solution of the present invention is a flexible microwave absorbing composite material prepared according to the above preparation method.

[0012] The third technical solution of the present invention is the application of the flexible microwave-absorbing composite material in electronic components.

[0013] The present invention discloses the following technical effects:

[0014] The present invention uses acrylamide and hydroxyethyl cellulose as raw materials, adopts free radical copolymerization, adds silica sol and GO to synthesize hydrogel. Then aerogel is prepared by adding different proportions of ferric chloride. At the same time, carbonization treatment is carried out at different temperatures to improve the microwave absorption performance of the aerogel, and then a TPU / DMF mixed solution is mixed in it for structural design, and finally a flexible microwave-absorbing composite material is prepared. The preparation method of the present invention is simple and easy to realize large-scale industrial production.

[0015] The flexible microwave-absorbing composite material prepared by the present invention has good microwave absorption performance and has broad application prospects in electronic components. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 It is the SEM image of the uncarbonized GO / SiO2 / PAAM / HEC-1% aerogel of the present invention.

[0018] Figure 2 It is the SEM image of the GO / SiO2 / PAAM / HEC-0% + 700°C carbonized aerogel of the present invention.

[0019] Figure 3 It is the SEM image of the GO / SiO2 / PAAM / HEC-1% + 700°C carbonized aerogel of the present invention at different magnifications.

[0020] Figure 4 It is the microwave absorption performance curve of the GO / SiO2 / PAAM / HEC-0% + 600°C carbonized aerogel of the present invention.

[0021] Figure 5 It is the microwave absorption performance curve of the GO / SiO2 / PAAM / HEC-0% + 700°C carbonized aerogel of the present invention.

[0022] Figure 6 It is the microwave absorption performance curve of the GO / SiO2 / PAAM / HEC-0% + 800°C carbonized aerogel of the present invention.

[0023] Figure 7This is the wave absorption performance curve of the GO / SiO2 / PAAM / HEC-1% + 700 °C carbonized aerogel of the present invention.

[0024] Figure 8 This is the wave absorption performance curve of the GO / SiO2 / PAAM / HEC-3% + 700 °C carbonized aerogel of the present invention.

[0025] Figure 9 This is a physical diagram of the flexible wave-absorbing composite material formed by soaking the GO / SiO2 / PAAM / HEC-1% + 700 °C carbonized aerogel of the present invention in TPU.

[0026] Figure 10 This is the stress-strain curve of the flexible wave-absorbing composite material formed by soaking the GO / SiO2 / PAAM / HEC-1% + 700 °C carbonized aerogel of the present invention in TPU. Detailed implementation manners

[0027] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0028] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0029] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0030] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0031] As used herein, terms such as "comprising", "including", "having", "containing", etc. are all open-ended terms, meaning including but not limited to.

[0032] In the present invention, acrylamide (AM) and hydroxyethyl cellulose (HEC) are used to carry out a free radical copolymerization reaction to prepare a PAAM / HEC water-absorbing resin. Then, a stirred silica sol with weak acidity and GO are added to synthesize a GO / SiO2 / PAAM / HEC organic-inorganic hybrid hydrogel. Finally, a certain amount of ferric chloride is mixed in to enhance the electrical conductivity of the aerogel. Then, a vacuum freeze dryer is used for freeze drying to obtain a GO / SiO2 / PAAM / HEC aerogel. Then, it is subjected to high-temperature carbonization to obtain a GO / SiC aerogel (carbonized aerogel), which is then compounded with a TPU / DMF mixed solution to finally prepare a TPU / GO / SiO 2 / C flexible microwave absorbing composite material. In the present invention, by appropriately adjusting different carbonization temperatures, the influence of different carbonization temperatures on the microwave absorption performance of the aerogel is explored. Finally, the flexible microwave absorbing composite material is subjected to structural characterization and the structural design of the composite material is carried out.

[0033] The first aspect of the present invention provides a method for preparing a flexible microwave absorbing composite material, comprising the following steps:

[0034] Dissolve tetraethyl orthosilicate in water to prepare silica sol;

[0035] Mix hydroxyethyl cellulose and graphene oxide with water and carry out water bath heating. Then, add an initiator and mix well, then add acrylamide and water and mix well, and then add N,N-methylenebisacrylamide and mix well to obtain a hydrogel;

[0036] Add the silica sol to the hydrogel and stir at a constant temperature. Then, raise the temperature and add FeCl3 and stir. After standing and cooling, carry out freeze drying to obtain a GO / SiO2 / PAAM / HEC aerogel;

[0037] Carry out pre-oxidation and high-temperature carbonization treatment on the GO / SiO2 / PAAM / HEC aerogel to obtain a carbonized aerogel;

[0038] Immerse the carbonized aerogel in a TPU solution, and then cure and dry to obtain the flexible microwave absorbing composite material.

[0039] In a preferred embodiment of the present invention, the mass fraction of tetraethyl orthosilicate in the silica sol is 1% - 1.8%; the pH value of the silica sol is 3 - 5.

[0040] In a preferred embodiment of the present invention, the mass fraction of hydroxyethyl cellulose in the hydrogel is 1% - 2%; tetraethyl orthosilicate accounts for 29.58% - 53.52% of hydroxyethyl cellulose; the mass ratio of acrylamide to hydroxyethyl cellulose is 6:1 (acrylamide is used as a monomer in the present invention); the addition amount of N,N'-methylenebisacrylamide is 0.01% - 0.09% of the mass of acrylamide (N,N'-methylenebisacrylamide is used as a crosslinking agent in the present invention); the initiator is a 1:1 mixture of potassium sulfate and sodium bisulfite; the addition amount of the initiator is 0.1% - 0.9% of the mass of acrylamide (potassium persulfate and sodium bisulfite are used as initiators in the present invention. In some specific embodiments of the present invention, the initiator is added in the form of a solution). Through repeated experimental verification in the present invention, the above parameter ratios must be controlled within the above ranges to prepare a uniform and shaped hydrogel. For example, when grafting acrylamide onto hydroxyethyl cellulose, if the addition amount of the crosslinking agent is too low or the crosslinking time is insufficient, the viscosity of the product will decrease, the forming effect of the prepared aerogel will be poor, and graphene oxide will deposit at the bottom of the hydrogel, thereby affecting the wave absorption performance of the prepared wave-absorbing material. When the addition amount of the crosslinking agent is too high, the mechanical properties of the formed aerogel are poor, hard and brittle, and the carbon skeleton is fragile after carbonization. In addition, when the addition amount of hydroxyethyl cellulose is too small, the mechanical properties of the formed aerogel become poor, and the volume shrinkage rate of the carbonized aerogel formed after high-temperature carbonization is relatively large; when the addition amount of tetraethyl orthosilicate is relatively high, it will affect the electron transfer efficiency of the carbonized aerogel, thereby affecting the wave absorption effect.

[0041] In a preferred embodiment of the present invention, the concentration of graphene oxide in the hydrogel is 0.2 mg / ml - 5 mg / ml. In the present invention, if the concentration of graphene oxide is too low, the wave absorption performance will be reduced; if the concentration of graphene oxide is too high, the dielectric matching performance of the material will be reduced, and electromagnetic waves will be reflected on the surface of the material, resulting in a reduction in the wave absorption effect; therefore, the present invention preferably limits the concentration of graphene oxide in the hydrogel to the above parameter range.

[0042] In a preferred embodiment of the present invention, the temperature of the water bath heating is 55 - 100 °C.

[0043] In a preferred embodiment of the present invention, the addition amount of FeCl3 is 0.5 - 1.5% of the mass of the composite gel (hydrogel and silica sol).

[0044] In a further preferred embodiment of the present invention, the addition amount of FeCl3 is 1% of the mass of the composite gel. At this FeCl3 ratio, the wave-absorbing performance of the aerogel prepared is the best, the wave-absorbing width is 8.7 - 17.8 GHz, and the absorption bandwidth is 9.1 GHz; the improvement of the wave-absorbing performance of the aerogel by FeCl3 is particularly significant. As the FeCl3 ratio increases (from 0 to 2%), the wave-absorbing bandwidth of the aerogel increases from the original 6.7 GHz to 9.1 GHz.

[0045] In a preferred embodiment of the present invention, the temperature of the pre-oxidation is 200 °C and the time is 60 min; the temperature of the high-temperature carbonization treatment is 600 - 800 °C and the time is 60 min.

[0046] In a further preferred embodiment of the present invention, the temperature of the carbonization is 700 °C. At this carbonization temperature, the structure of the aerogel is the best, and a uniform willow-leaf-shaped structure is generated on its surface; at the carbonization temperature of 700 °C, the growth of the wave-absorbing performance is also the most obvious, and the absorption bandwidth increases from 1.32 GHz (15.52 GHz - 16.84 GHz) at 600 °C to 8.8 GHz at 700 °C, and then drops to 8.1 GHz at 800 °C.

[0047] In a preferred embodiment of the present invention, the TPU solution is a DMF solution of TPU with a concentration of 5% - 15%. The present invention does not make a special limitation on the impregnation time of the carbonized aerogel in the TPU solution. The purpose of impregnation is to form an organic network skeleton inside the carbonized aerogel to improve the mechanical properties of the aerogel, and the level of TPU content has no influence on its wave-absorbing performance. In some specific embodiments of the present invention, the impregnation time is 3 h - 24 h.

[0048] In a preferred embodiment of the present invention, the curing specifically is to place the carbonized aerogel saturated with the adsorbed TPU solution in water for curing.

[0049] The drying method is natural drying in a well-ventilated and dry place.

[0050] The second aspect of the present invention provides a flexible wave-absorbing composite material prepared according to the described preparation method.

[0051] The third aspect of the present invention provides the application of the described flexible wave-absorbing composite material in electronic components.

[0052] The technical solutions of the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels or are publicly available.

[0053] The following combines examples to elaborate in detail on the technical solutions provided by the present invention, but they cannot be understood as limiting the protection scope of the present invention.

[0054] Example 1

[0055] Preparation of Flexible Absorbing Composite Material

[0056] 1.1 Preparation of Silica Sol

[0057] First, weigh 0.3 g of tetraethyl orthosilicate with an electronic balance into a beaker, then add 20 mL of distilled water to make it mix evenly, and then add hydrochloric acid to make its pH reach 3 - 5. Put a magnetic rotor and stir it on a magnetic stirrer for 2 h to obtain silica sol.

[0058] 1.2 Preparation of Hydrogel

[0059] Turn on the constant temperature water bath and set the temperature to 55 °C. Weigh 0.71 g of hydroxyethyl cellulose (HEC) and 0.05 g of graphene oxide, then add 30 mL of distilled water and emulsify it with a dispersing homogenizer for 3 min, and then pour it into a three - necked flask and stir it in a water bath for 20 min; then weigh 0.001 mol of potassium persulfate and sodium bisulfite into two beakers respectively, add 10 ml of distilled water to make 0.1 mol / L potassium persulfate solution and 0.1 mol / L sodium bisulfite solution, and then pour the potassium persulfate solution and sodium bisulfite solution into the three - necked flask and stir for 30 min. Then weigh 4.3 g of acrylamide and 10 mL of distilled water and pour them into the three - necked flask and stir for 30 min; then add 0.0038 g of N,N - methylenebisacrylamide and stir for 30 min to obtain hydrogel.

[0060] 1.3 Preparation of Aerogel

[0061] Add the well - stirred silica sol into the above - mentioned three - necked flask and stir it at a constant temperature of 55 °C for 2 h; then raise the stirring temperature to 80 °C, and then weigh 0.76 g of FeCl3 and add it into the three - necked flask (i.e., the FeCl3 addition amount accounts for 1% of the total mass of the hydrogel and silica sol), and continue to stir for 30 min. Finally, pour the product into a beaker, let it stand and cool; then put it into a vacuum freeze - dryer and freeze - dry it for 48 h to obtain GO / SiO2 / PAAM / HEC - 1% aerogel (1% represents the mass percentage of FeCl3).

[0062] 1.4 Carbonization Treatment of Aerogel

[0063] The GO / SiO2 / PAAM / HEC aerogel was subjected to high-temperature carbonization at 700 °C. The sample was placed in a horizontal vacuum crucible furnace, and the temperature control program was set. It was heated from room temperature (20 °C) to 200 °C at a heating rate of 5 °C / min and maintained at this temperature for 60 min. Then, nitrogen was introduced, and it was heated to 700 °C at a heating rate of 5 °C / min and maintained at this temperature for 60 min to fully carbonize the sample. Then, it was cooled at a rate of 5 °C / min until it cooled to room temperature (20 °C) to obtain the carbonized aerogel, that is, the flexible wave-absorbing composite material, labeled as GO / SiO2 / PAAM / HEC-1% + 700 °C (700 °C represents the carbonization temperature).

[0064] Repeat the above experimental steps, adjusting the addition amount of FeCl3 and the high-temperature carbonization temperature (that is, different from 1.1 - 1.4 only in that the addition amount of FeCl3 is adjusted to 0%, 3% of the total mass of the hydrogel and silica sol, and / or the high-temperature carbonization temperature is adjusted to 600 °C, 800 °C, and the rest of the steps and parameters are the same as 1.1 - 1.4).

[0065] The corresponding carbonized aerogels prepared were labeled as GO / SiO2 / PAAM / HEC-0% + 600 °C, GO / SiO2 / PAAM / HEC-0% + 700 °C, GO / SiO2 / PAAM / HEC-0% + 800 °C, GO / SiO2 / PAAM / HEC-3% + 700 °C.

[0066] 1.5 Preparation of flexible wave-absorbing composite material

[0067] Take a certain mass of TPU and N,N'-methylenebisacrylamide (DMF), with a mass ratio of 1:10. Pour them into a beaker at the same time, place it in a water bath, and stir at 80 °C for 40 min to fully dissolve TPU in DMF to obtain a mixed solution. Then, completely immerse the above carbonized aerogel in the mixed solution and soak for 3 h to allow the mixed solution to fully enter the interior of the aerogel; then transfer it to distilled water to completely solidify the liquid, take out the sample and place it in a well-ventilated and dry place to completely dry it, and finally obtain the TPU / GO / SiO2 / C flexible wave-absorbing composite material.

[0068] 2 Structural characterization and performance testing of flexible wave-absorbing composite material

[0069] 2.1 Wave-absorbing performance testing

[0070] Preparation of dielectric ring: Melt paraffin on a heating platform, completely immerse the carbonized aerogel in the melted paraffin so that the interior of the aerogel is filled with paraffin, take it out and wait for cooling, and then use a special dielectric ring mold to remove the ring and drill holes in the paraffin-filled aerogel to obtain a complete dielectric ring.

[0071] Dielectric constant test: Measure the thickness of the prepared dielectric ring, conduct dielectric constant tests at a professional testing institution, and finally process and calculate the test data to obtain the final wave absorption performance of the sample.

[0072] 3 Results and Discussion

[0073] 3.1 Scanning Electron Microscopy (SEM) Test Analysis

[0074] Figure 1 It is the SEM image of the uncarbonized GO / SiO2 / PAAM / HEC-1% aerogel prepared in 1.3. It can be seen from Figure 1 that the GO / SiO2 / PAAM / HEC aerogel has a uniform three-dimensional network structure with an average pore size of 45 μm.

[0075] Figure 2 It is the SEM image of the GO / SiO2 / PAAM / HEC-0% + 700 °C carbonized aerogel. It can be seen from Figure 2 that after carbonization at 700 °C, the three-dimensional network structure is complete and uniform, with a sense of hierarchy, and its average pore size is 62 μm.

[0076] Figure 3 It is the SEM image of the GO / SiO2 / PAAM / HEC-1% + 700 °C carbonized aerogel; among them, a is the 200-fold magnification image, b is the 400-fold magnification image, and c is the 10000-fold magnification image. It can be seen from Figure 3 that a layer of willow-leaf-shaped substance is formed on the surface of the aerogel under high-temperature carbonization.

[0077] 3.2 Wave Absorption Performance Test Analysis

[0078] Figure 4 It is the wave absorption performance curve of the GO / SiO2 / PAAM / HEC-0% + 600 °C carbonized aerogel. It can be seen from Figure 4 that for this sample with a thickness of 4 mm, the effective absorption bandwidth (RL ≤ -10 dB) is 1.37 GHz, indicating that the electromagnetic wave absorption rate of this material reaches over 90% in the ranges of 15.49 GHz - 16.06 GHz and 17.2 GHz - 18 GHz, and the maximum absorption intensity of this sample is -29 dB.

[0079] Figure 5 It is the wave absorption performance curve of the GO / SiO2 / PAAM / HEC-0% + 700 °C carbonized aerogel. It can be seen from Figure 5 that for this sample with a thickness of 3 mm, the effective absorption bandwidth is 9.14 GHz, indicating that the electromagnetic wave absorption rate of this material reaches over 90% in the range of 9.07 GHz - 17.9 GHz, and the maximum absorption intensity of this sample is -29.5 dB.

[0080] Figure 6 This is the microwave absorption performance curve of GO / SiO2 / PAAM / HEC-0% + carbonized aerogel at 800 °C. As can be Figure 6 seen, the entire reflectivity curve is above -10 dB, indicating poor microwave absorption performance. In summary, the aerogel has the best microwave absorption performance at a carbonization temperature of 700 °C.

[0081] Figure 7 This is the microwave absorption performance curve of GO / SiO2 / PAAM / HEC-1% + carbonized aerogel at 700 °C. As can be Figure 7 seen, for this sample with a thickness of 3.5 mm, the effective absorption bandwidth is 9.14 GHz, indicating that in the range of 8.69 GHz to 17.83 GHz, the absorption rate of this material for electromagnetic waves reaches over 90%, and the maximum absorption intensity of this sample is -55.2 dB.

[0082] Figure 8 This is the microwave absorption performance curve of GO / SiO2 / PAAM / HEC-3% + carbonized aerogel at 700 °C. As can be Figure 8 seen, for this sample with a thickness of 3.5 mm, the effective absorption bandwidth is 8.28 GHz, indicating that in the range of 8.64 GHz to 16.92 GHz, the absorption rate of this material for electromagnetic waves reaches over 90%, and the maximum absorption intensity of this sample is -39.94 dB.

[0083] When the RL value is less than -10 dB, it indicates that the material can absorb 90% of the electromagnetic wave energy, and its effective absorption bandwidth is the corresponding frequency width less than -10 dB. Through the comparison of the above data, the aerogel with a ferric chloride addition ratio of 1% has the strongest microwave absorption ability among these four samples, and the maximum absorption bandwidth is 9.1 GHz. Therefore, at a carbonization temperature of 700 °C, the carbonized aerogel with a ferric chloride content of 1% is the most ideal microwave absorption material, possibly because the presence of Fe 3+ makes the pores on the network structure of the aerogel more uniform and dense, enhancing the internal structure of the aerogel and enabling better absorption of electromagnetic waves.

[0084] 3.3 Mechanical Property Test and Analysis

[0085] Figure 10 This is the stress-strain curve of the flexible microwave absorption composite material formed by soaking GO / SiO2 / PAAM / HEC-1% + carbonized aerogel in TPU under different compression ratios. Figure 9It is a physical photo. It can be seen that as the compressive strain increases, the stress rises linearly. For the first compression, when the strain reaches 50%, the stress reaches the maximum value of 13.92 kPa. When the second compression is carried out after rebounding and the strain reaches 50%, the stress is 12.32 kPa. When the third compression is carried out after rebounding and the strain reaches 50%, the stress is 11.83 kPa. When the fourth compression is carried out after rebounding and the strain reaches 50%, the stress is 11.73 kPa. When the fifth compression is carried out after rebounding and the strain reaches 50%, the stress is 11.69 kPa. After five cycles, the remaining compressive stress is 83.98% of the initial stress, showing good mechanical retention. After one cycle of the compressive strain, the plastic deformation is 5.2%. After five compression cycles, the plastic deformation is 8.4%, and the resilience is good.

[0086] The embodiments described above are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of a flexible wave-absorbing composite material, characterized in that, It includes the following steps: Dissolve tetraethyl orthosilicate in water to prepare silica sol; Mix hydroxyethyl cellulose and graphene oxide with water, carry out water bath heating, then add an initiator and mix well, then add acrylamide and water and mix well, and then add N,N'-methylenebisacrylamide and mix well to obtain a hydrogel; Add the silica sol to the hydrogel and stir at a constant temperature, then raise the temperature and add FeCl3 and stir, stand and cool, and then freeze-dry to obtain GO / SiO2 / PAAM / HEC aerogel; Carry out pre-oxidation and high-temperature carbonization treatment on the GO / SiO2 / PAAM / HEC aerogel to obtain a carbonized aerogel; Immerse the carbonized aerogel in a TPU solution, then cure and dry to obtain the flexible microwave absorbing composite material.

2. The preparation method of the flexible microwave absorbing composite material according to claim 1, characterized in that, The mass fraction of tetraethyl orthosilicate in the silica sol is 1% - 1.8%; the pH value of the silica sol is 3 - 5.

3. The preparation method of the flexible wave-absorbing composite material according to claim 1, characterized in that, The mass fraction of hydroxyethyl cellulose in the hydrogel is 1% - 2%; The tetraethyl orthosilicate accounts for 29.58% - 53.52% of the mass of the hydroxyethyl cellulose; The mass ratio of acrylamide to hydroxyethyl cellulose is 6 - 6.1:1; The addition amount of N,N'-methylenebisacrylamide is 0.01% - 0.09% of the mass of acrylamide; The initiator is a mixture of potassium sulfate and sodium bisulfite with a mass ratio of 1:1; the addition amount of the initiator is 0.1% - 0.9% of the mass of acrylamide; The concentration of graphene oxide in the hydrogel is 0.2mg / ml - 5mg / ml.

4. The preparation method of the flexible wave-absorbing composite material according to claim 1, wherein, The temperature of the water bath heating is 55 - 100°C.

5. The preparation method of the flexible wave-absorbing composite material according to claim 1, characterized in that The addition amount of FeCl3 is 0.5 - 1.5% of the total mass of the hydrogel and silica sol.

6. The preparation method of the flexible wave-absorbing composite material according to claim 1, wherein The temperature of the pre-oxidation is 200°C and the time is 60min; the temperature of the high-temperature carbonization treatment is 600 - 800°C and the time is 60min.

7. The preparation method of the flexible wave-absorbing composite material according to claim 1, wherein, The TPU solution is a DMF solution of TPU with a concentration of 5% - 15%.

8. The preparation method of the flexible wave-absorbing composite material according to claim 1, characterized in that, The curing specifically means placing the carbonized aerogel saturated with the adsorbed TPU solution in water for curing.

9. A flexible microwave absorbing composite material prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the flexible microwave absorbing composite material according to claim 9 in electronic components.

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