A reed-derived porous biochar / epoxy wave-absorbing material, a preparation method and application thereof

Abstract

This invention provides a reed-derived porous biochar / epoxy microwave absorbing material, its preparation method, and its application, belonging to the field of electromagnetic wave absorbing composite materials technology. The invention involves heating reed stalks to a carbonization temperature to obtain reed-derived porous biochar; the heating rate is 15℃ / min, and the carbonization temperature is 800℃. The reed-derived porous biochar, epoxy resin, and curing agent are mixed and then pre-cured and cured sequentially to obtain the reed-derived porous biochar / epoxy microwave absorbing material. This invention achieves ultra-thin matching thickness with low filler content by controlling the heating rate to 15℃ / min, while ensuring that the electromagnetic wave absorption performance meets daily civilian needs. Data from the embodiments show that this invention achieves significant thickness control with a low filler content of 10%: flexible switching from "strong absorption type" to "ultra-thin type," meeting the needs of aerospace and portable electronic devices.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing composite materials, and in particular to a reed-derived porous biochar / epoxy wave absorbing material, its preparation method, and its application. Background Technology

[0002] With the rapid development and widespread application of fifth-generation (5G) communication technology, the Internet of Things, artificial intelligence, and high-power electronic devices, electromagnetic radiation pollution has become an increasingly serious problem. Electromagnetic interference not only affects the normal operation of precision electronic equipment and information security, but may also pose a potential threat to human health. Therefore, developing materials with efficient electromagnetic wave absorption capabilities, especially lightweight, broadband, and strongly absorbing microwave absorbing materials (MAMs), has become a research hotspot in the fields of materials science and electronic engineering.

[0003] Carbon-based electromagnetic wave absorbing materials (such as carbon nanofibers, carbon nanotubes, graphene, and biochar) are considered the best candidates to replace traditional metal absorbing materials due to their advantages such as lightweight, good chemical stability, tunable conductivity, and excellent processing performance. Among them, biomass-derived porous char has attracted widespread attention from researchers in recent years due to its unique advantages such as wide availability of raw materials, renewability, low cost, and natural porous structure. In particular, reed stalks, as a widely distributed aquatic plant resource, have the natural characteristics of hollow, straight stems and a three-dimensional pore structure within the stalk wall. This three-dimensional pore structure creates ideal conditions for multiple reflections and scattering of electromagnetic waves within the material, making it a high-quality precursor for constructing high-performance absorbing fillers. Related technologies have disclosed the absorbing performance of reed char / epoxy composite materials carbonized at 800℃, finding that it can achieve high reflection loss and a wide effective absorption bandwidth with a low filling amount of 10wt% reed char. However, the material has the problem of large thickness, making it unsuitable for applications with strict limitations on coating thickness (such as aerospace and portable electronic devices). Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a reed-derived porous biochar / epoxy microwave absorbing material, its preparation method, and its application. The reed-derived porous biochar / epoxy microwave absorbing material prepared by this invention has a small thickness and its electromagnetic wave absorption performance can meet the needs of daily civilian use.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a reed-derived porous biochar / epoxy microwave absorbing material (RC / EP composite material), comprising the following steps: Reed stalks are heated to a carbonization temperature to obtain reed-derived porous biochar (RC); the heating rate is 15℃ / min and the carbonization temperature is 800℃. The reed-derived porous biochar, epoxy resin (EP), and curing agent are mixed and then pre-cured and cured sequentially to obtain the reed-derived porous biochar / epoxy microwave absorbing material.

[0006] Preferably, the mass of the reed-derived porous biochar is 5-20% of the mass of the epoxy resin.

[0007] Preferably, the mass of the reed-derived porous biochar is 10-15% of the mass of the epoxy resin.

[0008] Preferably, the epoxy resin comprises bisphenol A type epoxy resin.

[0009] Preferably, the mass ratio of the epoxy resin to the curing agent is 10:3~6.

[0010] Preferably, the mass ratio of the epoxy resin to the curing agent is 10:5.

[0011] Preferably, the carbonization holding time is 30 minutes.

[0012] Preferably, the curing temperature is 50~80℃ and the time is 12~48h.

[0013] The present invention also provides a reed-derived porous biochar / epoxy microwave absorbing material prepared by the preparation method described above, wherein the thickness of the reed-derived porous biochar / epoxy microwave absorbing material is 1.3 mm.

[0014] This invention also provides the application of the reed-derived porous biochar / epoxy microwave absorbing material described above in the fields of aerospace and portable electronic devices.

[0015] This invention provides a method for preparing reed-derived porous biochar / epoxy microwave absorbing material, comprising the following steps: heating reed stalks to a carbonization temperature for carbonization to obtain reed-derived porous biochar; the heating rate is 15℃ / min, and the carbonization temperature is 800℃; mixing the reed-derived porous biochar, epoxy resin, and curing agent, and then performing pre-curing and curing sequentially to obtain the reed-derived porous biochar / epoxy microwave absorbing material.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves optimal microstructure and dielectric properties in RC fillers by controlling the heating rate to 15℃ / min, thereby realizing ultra-thin matching thickness with low RC filler content while ensuring electromagnetic wave absorption performance meets daily civilian needs. Specifically, the heating rate is one of the core parameters in the carbonization process, determining the release rate of volatile substances, the rearrangement kinetics of the carbon skeleton, the formation and evolution of defects, and the shrinkage and collapse behavior of the pore structure during biomass pyrolysis. The heating rate affects the degree of graphitization: a slower heating rate (e.g., 5℃ / min) allows sufficient time for ordered rearrangement of biomass, which is beneficial for forming a more regular graphite microcrystalline structure, but may lead to slow release of volatile substances and tar blockage of some pores; a faster heating rate (e.g., 20℃ / min) will produce a thermal shock effect, resulting in the preservation of the carbon layer. Retaining more defects and irregular structures can enhance dipole polarization loss as polarization centers, but it may also lead to excessive shrinkage or even collapse of the carbon skeleton. The heating rate affects the pore structure: slow heating (e.g., 5℃ / min) favors the formation of numerous but small micropores, while rapid heating (e.g., 20℃ / min) may generate mesopores and macropores, affecting the material's specific surface area and electromagnetic wave scattering ability. The heating rate affects conductivity: the heating rate modulates the conductivity of the carbon material by influencing the degree of graphitization and the continuity of the conductive network, thus affecting the dielectric loss and impedance matching of the composite material. Furthermore, the preparation process of this invention is simple and low-cost, requiring no magnetic components or complex structural design, and is easy to industrialize.

[0017] Data from the embodiments show that the present invention can achieve significant thickness control at a low filler content of 10% by adjusting a single parameter (heating rate): flexible switching from "strong absorption type" (10℃ / min, 2.6mm) to "ultra-thin type" (15℃ / min, thickness 1.3mm), meeting the needs of aerospace and portable electronic devices, and is suitable for application scenarios with strict limitations on coating thickness. Detailed Implementation

[0018] This invention provides a method for preparing reed-derived porous biochar / epoxy microwave absorbing material, comprising the following steps: Reed stalks are heated to the carbonization temperature to obtain reed-derived porous biochar; the heating rate is 15℃ / min and the carbonization temperature is 800℃. The reed-derived porous biochar, epoxy resin, and curing agent are mixed and then pre-cured and cured sequentially to obtain the reed-derived porous biochar / epoxy microwave absorbing material.

[0019] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0020] This invention involves heating reed stalks to a carbonization temperature to obtain reed-derived porous biochar. The heating rate is 15℃ / min, and the carbonization temperature is 800℃. By controlling the heating rate to 15℃ / min, this invention obtains RC filler with optimal microstructure and dielectric properties, thereby achieving ultra-thin matching thickness with low filler content, while ensuring that electromagnetic wave absorption performance meets daily civilian needs.

[0021] In this invention, the carbonization is preferably carried out in an atmosphere furnace under the protection of a protective gas, which preferably includes nitrogen.

[0022] In this invention, the carbonization holding time is preferably 30 minutes.

[0023] The present invention preferably involves washing, drying, crushing, and sieving the reed straw waste to 40-60 mesh, drying it to absolute dryness, and then carbonizing it.

[0024] The present invention does not impose any special limitations on the specific parameters of washing, drying, crushing, sieving to 40-60 mesh and drying, and any method known to those skilled in the art can be used.

[0025] After carbonization is completed, it is preferable to allow it to cool naturally to room temperature to obtain the reed-derived porous biochar.

[0026] After obtaining the reed-derived porous biochar, the present invention mixes the reed-derived porous biochar, epoxy resin and curing agent and then performs pre-curing and curing in sequence to obtain the reed-derived porous biochar / epoxy microwave absorbing material.

[0027] In this invention, the mass of the reed-derived porous biochar is preferably 5-20% of the mass of the epoxy resin, specifically 5%, 10%, 15% or 20%.

[0028] In this invention, the epoxy resin preferably comprises bisphenol A type epoxy resin.

[0029] In this invention, the mass ratio of epoxy resin to curing agent is preferably 10:3 to 6, and more specifically, it can be 10:5.

[0030] The present invention does not specifically limit the type of curing agent for the epoxy resin; any type well known to those skilled in the art can be used.

[0031] In this invention, the pre-curing temperature is preferably room temperature, i.e. no additional heating or cooling is required, and the time is preferably 24~72h, specifically 24, 36, 48, 60 or 72h.

[0032] In this invention, the curing temperature is preferably 50~80℃, specifically 50, 60, 70 or 80℃, and the curing time is preferably 12~48h, specifically 12, 24, 36 or 48h.

[0033] In this invention, the epoxy resin is preferably mixed with reed-derived porous biochar, ultrasonically dispersed, and then the curing agent is added. After vacuum degassing, the mixture is cast, and then the pre-curing and curing are carried out in sequence.

[0034] The present invention does not impose any special limitations on the specific parameters of the mixing, ultrasonic dispersion, vacuum degassing and casting. Parameters known to those skilled in the art can be used, such as vacuum degassing for 30 minutes at a pressure of -1.5 MPa.

[0035] This invention is the first to systematically study the influence of carbonization heating rate in the range of 5~20℃ / min on the microwave absorption properties of reed biochar / epoxy composites, filling the gap in the existing technology for the structure-property relationship of "heating rate-microstructure-microwave absorption properties". The heating rate has a significant non-monotonic effect on the microwave absorption properties and thickness of RC / EP composites: when the heating rate is too low (5℃ / min), the pyrolysis process is slow, the release of volatile substances is insufficient, and the degree of RC graphitization is insufficient, leading to RL min With a low impedance of only -47.42dB and an effective absorption bandwidth of only 2.64GHz, coupled with a large matching thickness (6.4mm), the RC exhibits optimal graphitization and defect density at a heating rate of 10℃ / min, achieving synergy between conductivity and polarization losses. The RL... min The voltage reached -54.3dB, the EAB reached 5.59GHz, and the matching thickness was 2.6mm. However, at heating rates of 15℃ / min and 20℃ / min, the pyrolysis was too intense, resulting in numerous macroscopic defects and even structural collapse within the RC structure. min The absorption voltage drops to -34.5dB and -38.14dB respectively, but the matching thickness can be reduced to 1.3mm and 2.0mm respectively, making it suitable for scenarios with strict thickness requirements. This invention can achieve significant control over the microwave absorption performance at a low filling amount of 10% by adjusting a single parameter (heating rate): flexible switching from "strong absorption type" (10℃ / min) to "ultra-thin type" (15℃ / min, thickness 1.3mm) to meet the needs of different application scenarios. The preparation process of this invention is simple and low-cost, does not require the introduction of magnetic components or complex structural design, and is easy to industrialize.

[0036] The present invention also provides a reed-derived porous biochar / epoxy microwave absorbing material prepared by the preparation method described above, wherein the thickness of the reed-derived porous biochar / epoxy microwave absorbing material is 1.3 mm.

[0037] This invention also provides the application of the reed-derived porous biochar / epoxy microwave absorbing material described above in the fields of aerospace and portable electronic devices.

[0038] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0039] Example 1 (Heating rate 5°C / min) (1) Processing of reed raw materials: Wash the reed straw waste in water multiple times to remove impurities; after washing, dry it in the sun for 48 hours; crush it with a high-power crusher and sieve it to 40 mesh with an electric vibrating screen; put the powder into an electric heating drying oven and dry it until it is completely dry.

[0040] (2) Preparation of RC: Take a crucible containing reed powder and place it in a box-type atmosphere furnace. The carrier gas is N2, the gas flow rate is 500 mL / min, the heating rate is 5℃ / min, the temperature is raised to the target temperature of 800℃, the temperature is held for 30 min, and then naturally cooled to obtain RC-5.

[0041] (3) Preparation of RC / EP composite material: Take 10g of epoxy resin A (GCC135), add 1g of RC-5 (10wt%), stir until a homogeneous slurry is formed, sonicate for 20min, add 5g of curing agent D230 (mass ratio of epoxy resin to curing agent = 10:5), and continue stirring until completely mixed. Place the mixed colloid in a vacuum chamber for degassing treatment (pressure -1.5MPa, time 30min). Then pour the bubble-free mixture into a rubber mold for casting, pre-cur at room temperature (20℃) for 48h, and then cure at 60℃ for 24h to obtain RC-5 / EP composite material.

[0042] Example 2 (heating rate 10℃ / min) Same as Example 1, except that the heating rate was 10℃ / min, resulting in the RC-10 / EP composite material.

[0043] Example 3 (Heating rate 15℃ / min) Same as Example 1, except that the heating rate was 15°C / min, resulting in the RC-15 / EP composite material.

[0044] Example 4 (heating rate 20℃ / min) Same as Example 1, except that the heating rate was 20°C / min, resulting in the RC-20 / EP composite material.

[0045] The performance test results of the RC / EP composite materials in Examples 1-4 are shown in Table 1. As can be seen from Table 1, with the increase of the heating rate, the electromagnetic wave absorption performance of the RC / EP composite material shows a trend of first optimization and then attenuation, while the matching thickness decreases significantly. When the heating rate is 5℃ / min (Example 1), the pyrolysis process is slow, and the degree of RC graphitization is insufficient, resulting in limited electromagnetic wave absorption capacity (RL). min -47.42dB), and with a large matching thickness (6.4mm), the effective absorption bandwidth is narrow (only 2.64GHz), failing to meet the requirements for thinness; when the heating rate is 10℃ / min (Example 2), the RC achieves the best graphitization degree and defect density, realizing the best synergy between conductivity loss and polarization loss, RL min The voltage drop reached -54.3dB, and the effective absorption bandwidth (EAB) widened to 5.59GHz, with a suitable thickness (2.6mm). However, when the heating rate was increased to 15℃ / min (Example 3) and 20℃ / min (Example 4), the pyrolysis became too intense, resulting in excessive macroscopic defects and even local structural collapse within the RC, leading to RL... min The levels increased to -34.5 dB and -38.14 dB. However, the matching thickness was significantly reduced to 1.3 mm and 2.0 mm, with the 15 °C / min sample having a thickness of only 1.3 mm, the thinnest of all samples, making it suitable for applications with strict limitations on coating thickness (such as aerospace and portable electronic devices).

[0046] Table 1. Microwave absorption properties of RC / EP composites at different heating rates (RC content 10wt%)

[0047] Example 5 (different RC contents, fixed heating rate of 10℃ / min) Same as Example 2, except that 0.5g (5wt%) of RC-10 was added.

[0048] Example 6 (different RC contents, fixed heating rate of 10℃ / min) Same as Example 2, except that 1.5g (15wt%) of RC-10 was added.

[0049] Example 7 (different RC contents, fixed heating rate of 10℃ / min) Same as Example 2, except that 2g (20wt%) of RC-10 was added.

[0050] The performance test results of the RC / EP composite materials in Examples 2, 5-7 are shown in Table 2. Table 2 shows that the RC content affects the microwave absorption performance and the matching thickness.

[0051] Table 2. Microwave absorption properties of RC / EP composites with different RC contents (heating rate 10℃ / min)

[0052] Example 8 (different RC contents, fixed heating rate of 15℃ / min) Same as Example 3, except that 0.5g (5wt%) of RC-15 was added.

[0053] Example 9 (different RC contents, fixed heating rate of 15℃ / min) Same as Example 3, except that 1.5g (15wt%) of RC-15 was added.

[0054] Example 10 (different RC contents, fixed heating rate of 15℃ / min) Same as Example 3, except that 2g (20wt%) of RC-15 was added.

[0055] The performance test results of the RC / EP composite materials in Examples 3, 8-10 are shown in Table 3. As can be seen from Table 3, when the RC content is 10wt% and the heating rate is 15℃ / min, the prepared reed-derived porous biochar / epoxy microwave absorbing material has a small thickness and the electromagnetic wave absorption performance can meet the daily civilian needs.

[0056] Table 3. Microwave absorption properties of RC / EP composites with different RC contents (heating rate 15℃ / min)

[0057] Comparative Example 1 (pure epoxy, no RC filler) Without adding RC, the remaining steps are the same as in Example 1. Test results show that pure epoxy has almost no electromagnetic wave absorption capability (RL). min (-0.5dB).

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a reed-derived porous biochar / epoxy microwave absorbing material, characterized in that, Includes the following steps: Reed stalks are heated to the carbonization temperature to obtain reed-derived porous biochar; the heating rate is 15℃ / min and the carbonization temperature is 800℃. The reed-derived porous biochar, epoxy resin, and curing agent are mixed and then pre-cured and cured sequentially to obtain the reed-derived porous biochar / epoxy microwave absorbing material.

2. The preparation method according to claim 1, characterized in that, The mass of the reed-derived porous biochar is 5-20% of the mass of the epoxy resin.

3. The preparation method according to claim 2, characterized in that, The mass of the reed-derived porous biochar is 10-15% of the mass of the epoxy resin.

4. The preparation method according to claim 1 or 2, characterized in that, The epoxy resin includes bisphenol A type epoxy resin.

5. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of epoxy resin to curing agent is 10:3~6.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the epoxy resin to the curing agent is 10:

5.

7. The preparation method according to claim 1, characterized in that, The carbonization holding time is 30 minutes.

8. The preparation method according to claim 1, characterized in that, The curing temperature is 50~80℃ and the time is 12~48h.

9. The reed-derived porous biochar / epoxy microwave absorbing material prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The thickness of the reed-derived porous biochar / epoxy microwave absorbing material is 1.3 mm.

10. The application of the reed-derived porous biochar / epoxy microwave absorbing material according to claim 9 in the fields of aerospace and portable electronic devices.

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