An electromagnetic wave absorbing composite material, its preparation method and application

Abstract

This invention discloses an electromagnetic wave-absorbing composite material, its preparation method, and its applications, belonging to the technical field of electromagnetic functional materials and polymer composite materials. The composite material consists of a matrix material and a wave-absorbing agent. The matrix is ​​a biodegradable polyester, and the absorber is a transition metal nitride. The preparation method involves: weighing the matrix and absorber and mixing them uniformly; loading the mixed powder into a molding die and heating it to completely melt it; applying pressure in the molten state to densify the material and form a composite; and cooling and demolding to obtain the finished product. By adjusting the mass ratio of the matrix to the absorber, the electromagnetic parameters can be controlled and the wave-absorbing performance optimized. This invention features a simple preparation process, no solvent pollution throughout, and good repeatability. The resulting material possesses advantages such as lightweight, green biodegradability, and ease of processing into complex structures, showing broad application prospects in electromagnetic shielding, radar stealth, and electromagnetic compatibility of electronic equipment.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic functional materials and polymer composite materials technology. Specifically, it relates to a lightweight composite electromagnetic absorbing material based on polylactic acid (PLA) and iron-nitrogen (Fe-N) compounds, its preparation method and application. Background Technology

[0002] In recent years, with the rapid development of 5G mobile communication technology, the Internet of Things, radar detection technology, and high-frequency electronic equipment, electromagnetic waves, while bringing convenience to mankind, have also caused increasingly serious electromagnetic interference (EMI) and electromagnetic radiation pollution problems. Excessive electromagnetic radiation can not only interfere with the normal operation of precision electronic equipment, but may even pose potential hazards to human health. Furthermore, in the military field, stealth technology to counter radar detection urgently requires high-performance electromagnetic absorbing materials. Therefore, developing novel electromagnetic absorbing materials that meet the requirements of "thin, light, wide, and strong" (thin thickness, low density, wide bandwidth, and strong absorption) has become a research hotspot in the field of materials science.

[0003] Traditional electromagnetic absorbing materials are mostly magnetic materials such as ferrite and metal powder. Although these materials have good magnetic loss characteristics, they generally have defects such as high density, easy oxidation and corrosion, and difficulty in processing and forming, which make it difficult to meet the stringent requirements of modern aerospace and portable electronic devices for "lightweight" and "complex structure".

[0004] To address weight and processing issues, researchers often combine microwave absorbers with polymer matrices (such as epoxy resins, polyurethanes, and silicone rubbers). However, traditional polymer matrices are mostly derived from non-renewable petroleum resources, which are difficult to degrade naturally after disposal, easily causing "white pollution." Furthermore, traditional preparation processes often require the use of large amounts of organic solvents, posing potential environmental pollution risks.

[0005] Polylactic acid (PLA), as a bio-based biodegradable polymer, not only possesses excellent environmental characteristics and good mechanical properties, but is also the most commonly used matrix material in fused deposition modeling (FDM) 3D printing technology. Iron-nitrogen (Fe-N) compounds, on the other hand, are considered highly promising microwave absorbers due to their high saturation magnetization, excellent high-frequency permeability, and good environmental stability.

[0006] However, there are currently few reports on the preparation of high-performance microwave absorbing materials by combining PLA with Fe-N compounds. How to efficiently combine the two through a simple, green, and solvent-free process, and achieve tunable microwave absorption performance, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide an electromagnetic absorbing material based on a PLA / Fe-N compound composite system and its preparation method. This invention achieves uniform dispersion and dense molding of Fe-N compounds in a PLA matrix through a simple solvent-free hot-melt pressing process, endowing the material with excellent microwave absorption properties, as well as lightweight, environmentally friendly, and easy-to-process characteristics.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The present invention provides an electromagnetic wave absorbing composite material, which includes a matrix material and a wave absorbing agent, wherein the matrix is ​​a biodegradable polyester and the absorber is a transition metal nitride.

[0010] The biodegradable polyester includes PLA, polyglycolic acid, polycaprolactone, and polyhydroxyalkanoate.

[0011] The transition metal nitrides include Fe-N, Co-N, Ni-N, and Mn-N compounds.

[0012] Furthermore, the matrix of the composite material is PLA, and the absorbent is an Fe-N compound.

[0013] The method for preparing the electromagnetic absorbing composite material of the present invention includes the following steps:

[0014] Weigh the matrix and absorbent and mix them evenly; put the mixed powder into a molding mold and heat it to melt it completely; apply pressure in the molten state to densify the material and form a composite; cool and demold to obtain the finished product.

[0015] The mass ratio of the matrix to the absorbent is (0.5~5):1.

[0016] The heating temperature is 190℃~230℃, and the heating time is 10min~30min.

[0017] The applied pressure is 5MPa~30MPa.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. Lightweight and environmentally friendly biodegradable: Using PLA and other natural plant extracts as the matrix, the overall density of the material is significantly reduced, and it has excellent biodegradability, which is in line with the development trend of green environmental protection.

[0020] 2. Simple and green preparation process: The powder mixing and hot melt pressing process is adopted, and no organic solvents are used in the whole process, avoiding the solvent volatilization pollution in traditional wet process. The process flow is short, the repeatability is good, and it is easy to industrial mass production.

[0021] 3. Excellent and dynamically adjustable absorption performance: Fe-N compound powder provides excellent magnetic loss capability. By adjusting the mass ratio of PLA to Fe-N compound and the thickness of the molded sample, the electromagnetic parameters of the material can be effectively adjusted, and the position and intensity of the absorption peak can be controlled as needed in a wide frequency band of 0~18GHz.

[0022] 4. Excellent processability: The composite material retains the excellent thermoplasticity of the matrix material. It can be directly hot-pressed into various sheets and coatings, and can also be made into 3D printing filaments through hot melt extrusion. This enables the use of 3D printing technology to manufacture macroscopic metamaterials or customized wave-absorbing devices with complex geometries. Attached Figure Description

[0023] Figure 1 This is a cloud map showing the reflection loss (RL) distribution of the PLA:Fe-N compound = 1:1 sample under different thickness conditions in Example 1 of the present invention.

[0024] Figure 2 This is an RL curve of the PLA:Fe-N compound = 1:1 sample in Example 1 of the present invention under different thickness conditions.

[0025] Figure 3 This is a cloud map showing the RL distribution of the PLA:FN compound = 1:2 sample under different thickness conditions in Example 2 of the present invention.

[0026] Figure 4 This is an RL curve of the PLA:Fe-N compound = 1:2 sample in Example 2 of the present invention under different thickness conditions.

[0027] Figure 5 The XRD pattern is shown for the PLA:Fe-N compound = 1:2 sample in Example 2 of this invention.

[0028] Figure 6 This is a cloud map showing the RL distribution of the PLA:FN compound = 3:1 sample in Example 3 of the present invention under different thickness conditions.

[0029] Figure 7 This is an RL curve of the PLA:Fe-N compound = 3:1 sample in Example 3 of the present invention under different thickness conditions.

[0030] Figure 8 This is a cloud map showing the RL distribution of the PLA:FN compound = 1:3 sample in Example 3 of the present invention under different thickness conditions.

[0031] Figure 9 This is an RL curve of the PLA:Fe-N compound = 1:3 sample in Example 3 of the present invention under different thickness conditions. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Example 1

[0034] A method for preparing an electromagnetic wave absorbing composite material, the specific operation steps of which are as follows:

[0035] Step 1: Raw material preparation and pretreatment. Weigh commercially available PLA powder (average particle size approximately 50 μm) and Fe-N compound powder (average particle size approximately 10 μm). To prevent moisture from causing PLA degradation or bubble formation at high temperatures, place the PLA powder in a vacuum drying oven and dry it at 80°C for 4 hours.

[0036] Step 2: Proportioning and Mixing. Weigh the two powders according to a mass ratio of PLA:Fe-N compound = 1:1. Place the weighed powders into a ball mill jar or mechanical mixer and mix for 60 minutes to ensure that the Fe-N compound particles are uniformly dispersed in the PLA powder.

[0037] Step 3: Mold loading. The uniformly mixed composite powder is loaded into a specially made coaxial ring mold (the inner diameter of the mold is 3.04 mm and the outer diameter is 7.00 mm).

[0038] Step 4: Melting. Place the mold containing the powder in a constant temperature heating furnace or hot press, set the temperature to 210℃, and heat for 30 minutes to fully melt the PLA powder.

[0039] Step 5: Pressure molding. With the material in a molten state at 210℃, apply a pressure of about 15MPa to the mold for extrusion molding, which removes internal air, densifies the material, and forms a coaxial ring sample.

[0040] Step 6: Cooling and Demolding. Maintain pressure and allow the mold to cool naturally or with water to room temperature before demolding. Remove the finished PLA / Fe-N compound composite microwave absorbing material.

[0041] Step 7: Electromagnetic performance testing. The electromagnetic parameters of the prepared coaxial ring sample were tested using a vector network analyzer (VNA), and the reflection loss (RL) curve was calculated based on transmission line theory.

[0042] Performance characterization and data analysis:

[0043] To investigate the influence of thickness on microwave absorption performance, the reflection loss of the PLA:Fe-N compound 1:1 sample prepared in the above examples was calculated and characterized under different matching thicknesses. The results are as follows: Figure 1 and Figure 2 As shown.

[0044] Figure 1 The image shows the reflection loss distribution contour plots of a 1:1 PLA:Fe-N compound sample under different thicknesses and frequencies. Darker colors represent lower reflection loss values, indicating better absorption performance. Figure 1 As the sample thickness increases, the position of the effective absorption peak shows a clear trend towards lower frequencies (consistent with the quarter-wavelength matching model). Within the thickness range of 2.0 mm to 4.0 mm and the frequency range of 5 GHz to 7 GHz, a region of extremely dark absorption enhancement appears, indicating that the absorption performance of this composite material is highly sensitive and tunable to thickness.

[0045] Figure 2 The reflection loss curves of the PLA:Fe-N compound 1:1 sample in the 0GHz–18GHz frequency band show significant changes in the position and peak intensity of the absorption peak as the sample thickness gradually increases from 0.5mm to 3.0mm. Particularly at thicknesses of 2.5mm and 3.0mm, the thicker samples exhibit exceptionally superior absorption capabilities in the approximately 5GHz–7GHz frequency band, with the lowest reflection loss reaching a very deep valley. This further demonstrates that the absorption performance of the composite material in specific frequency bands can be effectively optimized and customized by simply adjusting the macroscopic thickness of the composite material.

[0046] Example 2

[0047] A method for preparing an electromagnetic wave absorbing composite material, the specific operation steps of which are as follows:

[0048] Step 1: Raw material preparation and pretreatment. Weigh commercially available PLA powder (average particle size approximately 50 μm) and Fe-N compound powder (average particle size approximately 10 μm). Place the PLA powder in a vacuum drying oven and dry at 80°C for 4 hours to remove moisture.

[0049] Step 2: Proportioning and Mixing. Weigh the two powders according to the mass ratio PLA:Fe-N compound = 1:2. Place the weighed powders into a mechanical mixer and mix for 60 minutes to ensure that the Fe-N compound particles are uniformly dispersed in the PLA matrix.

[0050] Step 3: Mold loading. Load the uniformly mixed composite powder into a coaxial ring mold (inner diameter 3.04 mm, outer diameter 7.00 mm).

[0051] Step 4: Heating and melting. Place the mold containing the powder in a hot press, set the temperature to 210℃, and heat at a constant temperature for 30 minutes to fully melt the PLA and coat it with a high content of Fe-N compound particles.

[0052] Step 5: Pressure molding. In the molten state at 210℃, a pressure of approximately 15MPa is applied to the mold for extrusion molding, which causes the internal pores of the high-density material to be discharged, thus achieving densification.

[0053] Step 6: Cooling and Demolding. Maintain pressure and wait for the mold to cool to room temperature before demolding and removing the finished PLA / Fe-N compound composite microwave absorbing material.

[0054] Step 7: Electromagnetic performance testing. The sample prepared in this embodiment was tested using a vector network analyzer, and the reflection loss in the thickness range of 0 mm to 10 mm was calculated.

[0055] Step 8: Characterization of crystal phase structure. The prepared sample is ground into powder, and the crystal phase structure of the sample is tested using an X-ray diffractometer to obtain the XRD diffraction pattern.

[0056] Performance characterization and data analysis:

[0057] To investigate the influence of thickness on microwave absorption performance, the absorption resistance (RL) of the PLA:Fe-N compound (1:2) samples prepared in the above examples under different matching thicknesses was calculated and characterized. The results are as follows: Figure 3 and Figure 4 As shown. Figure 3 The image shows the RL distribution contour plots of a PLA:Fe-N compound = 1:2 sample under different thickness and frequency conditions, as shown below. Figure 3 As shown, with the increase of Fe-N compound content, the effective electromagnetic loss region of the material shifts significantly, mainly concentrated in the low-frequency region. Over a very wide thickness range (especially beyond 2 mm), the material exhibits a distinct absorption band in the 0 GHz to 2 GHz (L-band), indicating that the sample has good absorption potential in the low-frequency range.

[0058] Figure 4 The RL curves for a PLA:Fe-N compound = 1:2 sample in the 0GHz~18GHz frequency band are shown below. Figure 4 As shown, when the thickness is relatively thin (0.5mm~3.0mm), the absorption peaks of each thickness curve are concentrated in the low-frequency range of 0.5GHz~2GHz. In particular, when the thickness is 1.5mm and 3.0mm, the reflection loss reaches a minimum value (close to -10dB) at about 0.5GHz~1GHz, achieving effective attenuation of low-frequency electromagnetic waves with a relatively thin thickness, which has important value in practical engineering applications.

[0059] Structural characterization and analysis:

[0060] Figure 5 The XRD pattern of the PLA:Fe-N compound = 1:2 sample is shown below. Figure 5 As shown, when the nitrogen content in the sample is 8.98%, the XRD pattern exhibits distinct diffraction peaks at approximately 38°, 41°, 43°, 57°, and 68° of 2θ. These characteristic peaks can be attributed to Fe3N. 1.3 The (110), (002), (111), (112), and (300) crystal planes of the phase were observed, with the (111) crystal plane near 43° exhibiting the highest diffraction peak intensity, indicating the formation of a relatively obvious Fe3N phase in the sample. 1.3 Iron nitride phase. Combined with XRD calibration results, it can be seen that under these nitrogen content conditions, the main phase of the sample is a nitrogen-rich iron nitride phase.

[0061] Example 3

[0062] A method for preparing an electromagnetic wave absorbing composite material, the specific operation steps of which are as follows:

[0063] Step 1: Raw material preparation and pretreatment. Weigh commercially available PLA powder (average particle size approximately 50 μm) and Fe-N compound powder (average particle size approximately 10 μm). Place the PLA powder in a vacuum drying oven and dry at 80°C for 4 hours to remove moisture.

[0064] Step 2: Proportioning and Mixing. Weigh the two powders according to a mass ratio of PLA:Fe-N compound = 3:1. Place the weighed powders into a mechanical mixer and mix for 60 minutes to ensure that the Fe-N compound particles are uniformly dispersed in the PLA matrix.

[0065] Step 3: Mold loading. Load the uniformly mixed composite powder into a coaxial ring mold (inner diameter 3.04 mm, outer diameter 7.00 mm).

[0066] Step 4: Heating and melting. Place the mold containing the powder in a hot press, set the temperature to 210℃, and heat at a constant temperature for 30 minutes to fully melt the PLA and coat it with a high content of Fe-N compound particles.

[0067] Step 5: Pressure molding. In the molten state at 210℃, a pressure of approximately 15MPa is applied to the mold for extrusion molding, which causes the internal pores of the high-density material to be discharged, thus achieving densification.

[0068] Step 6: Cooling and Demolding. Maintain pressure and wait for the mold to cool to room temperature before demolding and removing the finished PLA / Fe-N compound composite microwave absorbing material.

[0069] Step 7: Electromagnetic performance testing. The sample prepared in this embodiment was tested using a vector network analyzer, and the reflection loss in the thickness range of 0 mm to 10 mm was calculated.

[0070] Performance characterization and data analysis:

[0071] To investigate the influence of thickness on microwave absorption performance, the absorption resistance (RL) of the PLA:Fe-N compound (3:1) sample prepared in the above examples was calculated and characterized under different matching thicknesses. The results are as follows: Figure 6 and Figure 7 As shown. Figure 6 The figure shows the absorption frequency (RL) distribution of a PLA:Fe-N compound sample with a mass ratio of 3:1 under different thicknesses and frequencies. As can be seen, the absorption region of this sample is mainly concentrated in the high-frequency range and the low-frequency region corresponding to a larger thickness. In the high-frequency range of 14 GHz to 18 GHz, the sample exhibits multiple local absorption peaks; as the sample thickness further increases, the absorption peaks gradually shift towards lower frequencies, forming a more pronounced absorption region around 3 GHz to 4 GHz at a larger thickness. This indicates that the microwave absorption performance of the PLA:Fe-N=3:1 composite material is thickness-dependent, and the absorption frequency band can be shifted by adjusting the thickness.

[0072] Figure 7 The graphs show the absorption loss (RL) curves of PLA:Fe-N compound samples with a mass ratio of 3:1 at different thicknesses within the 0 GHz to 18 GHz frequency band. As can be seen from the graphs, the overall reflection loss of the samples is shallow and the absorption performance is not significant when the thickness is 0.5 mm and 1.0 mm. When the thickness increases to 1.5 mm and 2.0 mm, the samples show obvious absorption peaks in the high-frequency band. Specifically, the 2.0 mm thick sample has a minimum reflection loss close to -11 dB near approximately 15.5 GHz to 16 GHz, and the 1.5 mm thick sample also has a reflection loss close to -10 dB near approximately 17 GHz to 18 GHz, indicating that this ratio of sample can achieve effective attenuation of high-frequency electromagnetic waves under suitable thickness conditions. Further increasing the thickness to 2.5 mm and 3.0 mm, the absorption peak intensity weakens, indicating that this material has an optimal matching thickness range.

[0073] Comparative Example 1

[0074] A method for preparing an electromagnetic wave absorbing composite material, the specific operation steps of which are as follows:

[0075] Step 1: Raw material preparation and pretreatment. Weigh commercially available PLA powder (average particle size approximately 50 μm) and Fe-N compound powder (average particle size approximately 10 μm). Place the PLA powder in a vacuum drying oven and dry at 80°C for 4 hours to remove moisture.

[0076] Step 2: Proportioning and Mixing. Weigh the two powders according to the mass ratio PLA:Fe-N compound = 1:3. Place the weighed powders into a mechanical mixer and mix for 60 minutes to ensure that the Fe-N compound particles are uniformly dispersed in the PLA matrix.

[0077] Step 3: Mold loading. Load the uniformly mixed composite powder into a coaxial ring mold (inner diameter 3.04 mm, outer diameter 7.00 mm).

[0078] Step 4: Heating and melting. Place the mold containing the powder in a hot press, set the temperature to 210℃, and heat at a constant temperature for 30 minutes to fully melt the PLA and coat it with a high content of Fe-N compound particles.

[0079] Step 5: Pressure molding. In the molten state at 210℃, a pressure of approximately 15MPa is applied to the mold for extrusion molding, which causes the internal pores of the high-density material to be discharged, thus achieving densification.

[0080] Step 6: Cooling and Demolding. Maintain pressure and wait for the mold to cool to room temperature before demolding and removing the finished PLA / Fe-N compound composite microwave absorbing material.

[0081] Step 7: Electromagnetic performance testing. The sample prepared in this embodiment was tested using a vector network analyzer, and the reflection loss in the thickness range of 0 mm to 10 mm was calculated.

[0082] Performance characterization and data analysis:

[0083] To investigate the influence of thickness on microwave absorption performance, the absorption resistance (RL) of the PLA:Fe-N compound (1:3) sample prepared in the above examples was calculated and characterized under different matching thicknesses. The results are as follows: Figure 8 and Figure 9 As shown. Figure 8 This is a graph showing the RL curves of a PLA:Fe-N compound sample with a mass ratio of 1:3 at different thicknesses within the 0 GHz to 18 GHz frequency band. Figure 8 As can be seen, the RL values ​​of samples of all thicknesses are generally shallow, with the lowest reflection loss ranging from approximately -4dB to -5dB, failing to reach the effective absorption standard of -10dB. As the thickness increases from 0.5mm to 3.0mm, the reflection loss of the samples in the mid-to-high frequency range decreases, but the increase in absorption peak intensity is limited. This indicates that while this ratio can produce some attenuation of electromagnetic waves, the overall absorption performance is weak, and no significant strong absorption peak is formed.

[0084] Figure 9The graph shows the impedance matching (RL) distribution of a PLA:Fe-N compound mass ratio of 1:3 under different thicknesses and frequencies. As can be seen from the graph, the sample exhibits predominantly red, orange, and yellow colors in the 0 GHz to 18 GHz range, without any obvious deep blue or dark green strong absorption regions, indicating a relatively shallow overall reflection loss. With increasing thickness, a weak absorption band appears in the approximately 2.5 GHz to 4.5 GHz range, but the intensity of this absorption region is limited and does not reach a significant effective absorption level. This result suggests that when the Fe-N content is further increased to PLA:Fe-N = 1:3, the impedance matching of the material may be affected, and the overall absorption performance is not further enhanced. Example Comparison Conclusion:

[0085] A comparison of the test results from Example 1 (PLA:Fe-N compound = 1:1, main absorption frequency band of 5GHz~7GHz), Example 2 (PLA:Fe-N compound = 1:2, main absorption frequency band of 0.5GHz~2GHz), and Example 3 (PLA:Fe-N compound = 3:1, main absorption frequency band of 15.5GHz~18GHz) shows that the present invention can achieve dynamic modulation of the absorption frequency band from the C-band to lower frequency bands such as the L-band simply by changing the mass ratio of PLA to Fe-N compound. This allows the composite material to be customized for radar detection or electronic jamming scenarios of different frequencies, providing extremely high application flexibility.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electromagnetic wave absorbing composite material, characterized in that, The electromagnetic wave absorbing composite material includes a matrix material and a wave absorbing agent; wherein the matrix is ​​a biodegradable polyester and the absorber is a transition metal nitride.

2. The electromagnetic wave absorbing composite material according to claim 1, characterized in that, The biodegradable polyesters include polylactic acid, polyglycolic acid, polycaprolactone, and polyhydroxyalkanoates; the transition metal nitrides include Fe-N, Co-N, Ni-N, and Mn-N compounds.

3. The method for preparing the electromagnetic absorbing composite material according to any one of claims 1-2, characterized in that, The process includes the following steps: weighing the matrix and absorbent and mixing them evenly; loading the mixed powder into a molding mold and heating it to completely melt it; applying pressure in the molten state to densify the material and form a composite; cooling and demolding to obtain the finished product.

4. The method for preparing the electromagnetic absorbing composite material according to claim 3, characterized in that, The mass ratio of the matrix to the absorbent is (0.5~5):

1.

5. The method for preparing the electromagnetic absorbing composite material according to claim 3, characterized in that, The heating temperature is 190℃~230℃, and the heating time is 10min~30min.

6. The method for preparing the electromagnetic absorbing composite material according to claim 3, characterized in that, The applied pressure is 5MPa~30MPa.

7. The application of the electromagnetic absorbing composite material according to claim 1 in additive manufacturing of complex structure absorbing devices.

8. The application of the electromagnetic absorbing composite material according to claim 1 in the preparation of electromagnetic absorbing coatings.

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