CN108048034B - Preparation method of electromagnetic shielding material - Google Patents
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- CN108048034B CN108048034B CN201711283849.4A CN201711283849A CN108048034B CN 108048034 B CN108048034 B CN 108048034B CN 201711283849 A CN201711283849 A CN 201711283849A CN 108048034 B CN108048034 B CN 108048034B
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Abstract
The invention relates to a preparation method of an electromagnetic shielding material, which comprises the steps of processing wood into uniform wood chips; placing the mixture in a mixed solution of water and ethanol, performing ultrasonic oscillation, taking out and drying; preparing an iron acetylacetonate impregnation solution; placing the pretreated wood chips into an iron acetylacetonate impregnation solution, and incubating for 0.5-2 hours in a vacuum state; then under the protection of nitrogen, pressurizing and dipping; taking out the impregnated wood chips, slightly washing the surfaces of the wood chips with ethanol, standing the wood chips for 1 to 2 hours in a room temperature environment, and then drying the wood chips in vacuum; and finally, putting the mixture into a nitrogen-protected tube furnace for high-temperature pyrolysis step by step, taking out a product, crushing and sieving to obtain the catalyst. The method takes biomass raw materials as a carbon source to prepare magnetic carbon powder, and magnetic materials are uniformly dispersed in the carbon powder; meanwhile, the magnetic carbon powder has electromagnetic wave shielding property, and the electromagnetic wave shielding property of the product is controllable to a certain extent; and the cost is low, and the method is suitable for industrial production.
Description
Technical Field
The invention relates to the technical field of manufacturing of electromagnetic shielding materials, in particular to a novel biomass source magnetic carbon material with controllable electromagnetic wave absorption performance and a manufacturing method thereof.
Background
With the rapid increase of the application of wireless electronic devices such as mobile phones, local area networks, household robots and the like, the daily life and production of people are increasingly affected by electromagnetic waves generated by electromagnetic systems, and society urgently needs a wave-absorbing material with the characteristics of wide absorption frequency range, strong absorption capacity, controllability and the like. The magnetic carbon material has good magnetism and conductivity, so the magnetic carbon material can be used as a magnetic dielectric material with dielectric loss and magnetic loss at the same time, and has potential application as an excellent electromagnetic wave absorption material.
At present, a common method for preparing a magnetic carbon material is to compound a prepared magnetic material (such as iron, nickel, cobalt, molybdenum and other alloys, oxides or sulfides) and a carbon material (graphite, graphene, carbon nanotubes and the like) through a physical or chemical method. The method can obtain the product with uniform components and better electromagnetic wave shielding performance. However, due to the limitation of the preparation method of the magnetic material and the cost of the carbon material, the method is not suitable for industrial mass production and has high cost, so that the current social utilization rate is low. Meanwhile, the method cannot ensure the uniform dispersion of the magnetic material and the carbon material, and the electromagnetic wave absorption performance of different batches of products may be different.
In 2016, the nickel/Carbon Magnetic foam composite material is prepared by a method of pyrolyzing polymer microspheres containing divalent nickel at high temperature, and researches show that the material has good Electromagnetic wave shielding performance (Hai-Bo ZHao et al, Excellent Electromagnetic Absorption Capability of Ni/Carbon Based Conductive and Magnetic foam Synthesized via Green One Point Route, ACS Applied Materials & Interfaces,2016,8, 1468-1477).
Therefore, a method for preparing an electromagnetic shielding material with a good electromagnetic shielding performance needs to be found, which not only ensures that the prepared magnetic carbon material has electromagnetic wave absorption and magnetism, but also ensures that the electromagnetic wave absorption performance is controllable to a certain extent so as to meet application requirements in different aspects, and is low in cost and suitable for industrial production.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a preparation method of an electromagnetic shielding material, wherein biomass raw materials are used as carbon sources to prepare magnetic carbon powder, and the magnetic material is uniformly dispersed in the carbon powder; meanwhile, the magnetic carbon powder has electromagnetic wave shielding property, and the electromagnetic wave shielding property of the product is controllable to a certain extent; and the cost is low, and the method is suitable for industrial production.
Technical scheme
Biomass raw materials (such as wood, forest felling and processing residues or wood waste) are used as clean carbon sources, have been widely used for manufacturing carbon materials such as charcoal, carbon fiber and graphite, have the characteristics of low cost, wide distribution and the like, and are beneficial to improving the added value of forest products and reducing environmental pollution. The invention takes biomass material as a carbon source, and prepares the magnetic carbon material with better electromagnetic shielding performance by one step by using a high-temperature pyrolysis method, thereby simplifying the manufacturing process and reducing the production cost. The inventor firstly impregnates an organic solvent containing ferric acetylacetonate with a certain concentration into a pretreated biomass raw material body by a vacuum/pressure impregnation method, performs step-by-step high-temperature pyrolysis on the biomass raw material containing ferric acetylacetonate after drying treatment, and finally obtains magnetic carbon powder with different particle sizes after crushing and screening the obtained product.
The specific scheme is as follows:
a preparation method of an electromagnetic shielding material comprises the following steps:
step one, processing wood into wood chips with uniform thickness, length and width;
placing the wood chips into a mixed solution of water and ethanol, performing ultrasonic oscillation washing, taking out, and heating and drying to obtain pretreated wood chips;
dissolving ferric acetylacetonate in an organic solvent to prepare 0.02-0.06 g/mL ferric acetylacetonate impregnation solution;
step four, placing the wood chips pretreated in the step two into an iron acetylacetonate impregnation solution, and incubating for 0.5-2 hours in a vacuum state; then under the protection of nitrogen, pressurizing and dipping for 2-5 hours;
taking out the impregnated wood chips, slightly washing the surfaces of the wood chips with ethanol, standing the wood chips for 1 to 2 hours in a room temperature environment, and drying the wood chips in a vacuum drying oven;
and step six, taking out the completely dried wood chips, putting the wood chips into a nitrogen-protected tube furnace for high-temperature pyrolysis step by step, finally taking out the product, crushing and sieving to obtain the wood chip.
In the first step, the specific technical scheme takes wood as an example, but is not limited to wood, and the method is also suitable for forest felling and processing residues and wood product waste.
Further, in the first step, the wood is processed into wood chips by rotary cutting or shearing, wherein the wood chips are 3-6 cm in length, 3-6 cm in width and 1-3 mm in thickness. The wood fiber can also be processed into wood fiber by a pulverizer, and the fiber length is 1-2 mm.
Further, in the second step, the volume ratio of the ethanol to the water is 1-3: 1, and the ultrasonic vibration washing time is 1-5 hours.
Further, in the second step, the heating and drying temperature is 60-80 ℃, and the drying is carried out until the water content of the wood chips reaches 3-5%.
Further, in the third step, the organic solvent is selected from any one of benzene, toluene, chloroform, acetone, diethyl ether or N, N-Dimethylformamide (DMF).
Further, in the fourth step, the vacuum degree is 0.06-0.08 MPa.
Further, in the fourth step, in the process of pressure impregnation, the pressure of nitrogen is 0.60-1.00 MPa.
Further, in the fifth step, in the vacuum drying process, the temperature of the vacuum drying oven is 60-80 ℃.
Further, in the sixth step, the step-by-step high-temperature pyrolysis process is as follows: under the protection of nitrogen, firstly heating to 210-240 ℃ from room temperature at a heating rate of 5-10 ℃/min, and then keeping for 1-2 hours; further heating to 310-340 ℃ at a heating rate of 5-10 ℃/min, and then keeping for 1-2 hours; finally, further heating to 650-750 ℃ at a heating rate of 5-20 ℃/min, and keeping for 4-6 hours.
And in the sixth step, the sieving is to pass through a 100-mesh sieve, and the carbon powder which does not pass through the filter screen is further crushed until the carbon powder can pass through the filter screen.
The invention has the beneficial effects that:
firstly, the preparation method does not directly compound the prepared magnetic material and the carbon material together by a physical or chemical method, but impregnates a biomass raw material by a precursor of the magnetic material and synthesizes the magnetic material in situ in the biomass material by a high-temperature pyrolysis method; meanwhile, the biomass material is pyrolyzed at high temperature to generate a carbon material, and then the magnetic carbon material with the electromagnetic shielding effect is prepared. By doing so, the process flow is simplified, the use of organic solvents, surfactants and cross-linking agents is reduced, and the uniform dispersion of magnetic particles in carbon powder is ensured, so that the product has excellent magnetic and dielectric properties at the same time, and further has good electromagnetic shielding performance.
Secondly, the problems of low added value of wood and recycling of wood waste are solved, and biomass materials are used for replacing expensive carbon materials such as graphene and carbon nano tubes as carbon sources, so that the industrial cost is reduced, and the method is clean and environment-friendly; meanwhile, bio-oil, hydrogen, light hydrocarbon compounds and the like obtained by pyrolyzing the biomass material at high temperature can be further used as clean energy.
Finally, the magnetic carbon powder prepared by the method can adjust the magnetic property and the dielectric property of the product by controlling the concentration and the dipping time of the ferric acetylacetonate organic solution, the layer number of the wood composite magnetic plate and the thickness of the magnetic carbon powder after die pressing, thereby adjusting the electromagnetic wave shielding property of the product.
Drawings
FIG. 1 is a magnetization curve of an electromagnetic shielding material prepared in example 1;
FIG. 2 is a graph showing the electrical conductivity of the electromagnetic shielding material prepared in example 1;
FIG. 3 is a graph showing permeability of the electromagnetic shielding material prepared in example 1;
fig. 4 is an electromagnetic wave shielding performance of the electromagnetic shielding material prepared in example 1 after being doped with 20% paraffin;
FIG. 5 is a graph showing the electromagnetic wave-shielding properties of the electromagnetic shielding materials prepared in examples 2 to 6 after being doped with 20% paraffin, respectively;
fig. 6 shows the electromagnetic wave shielding performance of the electromagnetic shielding materials prepared in examples 1 and 7 to 9 after being doped with 20% paraffin, respectively.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following examples are all made of wood, but not limited to wood, and the method of the present invention is also applicable to forest harvesting and processing residues and wood waste.
Example 1
A preparation method of an electromagnetic shielding material comprises the following steps:
processing wood into wood chips with uniform thickness, length and width, wherein the length of the wood chips is 3-6 cm, the width of the wood chips is 3-6 cm, and the thickness of the wood chips is 1-3 mm;
placing the wood chips into a mixed solution of water and ethanol (the volume ratio of ethanol to water is 2:1) to be ultrasonically vibrated and washed for 3 hours, taking out the wood chips to be heated and dried at the temperature of 70 ℃ until the water content of the wood chips reaches 3-5%, and obtaining pretreated wood chips;
dissolving ferric acetylacetonate in organic solvent acetone to prepare 0.025g/mL ferric acetylacetonate impregnation solution;
step four, placing the wood chips pretreated in the step two into an iron acetylacetonate impregnation solution, and incubating for 1 hour in a vacuum state (the vacuum degree is 0.08 MPa); then under the protection of nitrogen, pressurizing (the pressure of nitrogen is 0.08MPa) and soaking for 3 hours;
taking out the impregnated wood chips, slightly washing the surfaces of the wood chips with ethanol, standing the wood chips for 1 hour in a room temperature environment, and drying the wood chips in a vacuum drying oven at the drying temperature of 70 ℃;
and sixthly, taking out the completely dried wood chips, putting the wood chips into a nitrogen-protected tube furnace for step-by-step high-temperature pyrolysis (the step-by-step high-temperature pyrolysis process comprises the steps of heating the wood chips from room temperature to 220 ℃ at the heating rate of 8 ℃/min under the protection of nitrogen, then keeping the temperature for 1 hour, further heating the wood chips to 320 ℃ at the heating rate of 8 ℃/min, then keeping the temperature for 1 hour, finally further heating the wood chips to 700 ℃ at the heating rate of 15 ℃/min, keeping the temperature for 4 hours), finally taking out products, crushing the wood chips and sieving the crushed wood chips with a 100-.
FIG. 1 is a magnetization curve of an electromagnetic shielding material prepared in example 1; it can be seen that the saturation magnetization of the obtained electromagnetic shielding material was 7.08emu/g and the magnetic coercive force was 704.12Oe, indicating that the obtained material was a hard magnetic material. Fig. 2 is a conductive curve of the electromagnetic shielding material prepared in example 1, and it can be seen from fig. 2 that the real part of the conductivity of the obtained electromagnetic shielding material is within a range of 9.38 to 25.99 and the imaginary part is within a range of 8.68 to 12.78 in an electromagnetic wave frequency range of 2 to 18GHz, which indicates that the obtained material has a certain conductivity; fig. 3 is a magnetic permeability curve of the electromagnetic shielding material prepared in example 1, and it can be seen from fig. 3 that the real part of the magnetic permeability of the obtained electromagnetic shielding material fluctuates between 1.00 and 1.20 and the imaginary part fluctuates between-0.10 and 0.10 in the electromagnetic wave frequency range of 2 to 18GHz, which shows that the obtained material has good electromagnetic matching in combination with fig. 2.
Example 2
The concentration of the iron acetylacetonate immersion liquid is 0.02g/mL, and the rest of the technological process is the same as that of example 1.
Example 3
The concentration of the iron acetylacetonate immersion liquid is 0.03g/mL, and the rest of the process is the same as that of example 1.
Example 4
The concentration of the iron acetylacetonate impregnation solution is 0.04g/mL, and the rest of the process is the same as that of example 1.
Example 5
The concentration of the iron acetylacetonate immersion liquid is 0.05g/mL, and the rest of the process is the same as that of example 1.
Example 6
The concentration of the iron acetylacetonate immersion liquid is 0.06g/mL, and the rest of the technological process is the same as that of example 1.
Example 7
In the fourth step, the pressure impregnation time was 2 hours, and the rest of the process was the same as in example 1.
Example 8
In the fourth step, the pressure impregnation time was 4 hours, and the rest of the process was the same as in example 1.
Example 9
In the fourth step, the pressure impregnation time was 5 hours, and the rest of the process was the same as in example 1.
1. Test of electromagnetic wave shielding property
Melting a paraffin block at 90 ℃, then uniformly dispersing the electromagnetic shielding material prepared in the embodiment 1 into a paraffin matrix, wherein the weight ratio of the electromagnetic shielding material to the paraffin is 5:1, respectively pressing the electromagnetic shielding material and the paraffin into paraffin pieces with the thicknesses of 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm and 5mm through a die, and then measuring the change condition of the electromagnetic wave shielding performance along with the thickness of the paraffin pieces. The test results are shown in FIG. 4.
Fig. 4 shows the electromagnetic wave shielding performance of the electromagnetic shielding material prepared in example 1 after being doped with 20% of paraffin, and as shown in fig. 4, the present invention realizes the adjustment of the electromagnetic wave shielding performance of the novel magnetic material by adjusting the thickness of the electromagnetic shielding material/paraffin composite sheet doped with 20% of the mass under the condition that other process parameters are not changed. In the figure, the electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the electromagnetic shielding material/paraffin wax sheet with the thickness of 1mm is 18.00GHz, the maximum shielding strength is 17.70dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 15.12 GHz-18.00 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the electromagnetic shielding material/paraffin thin sheet with the thickness of 1.5mm is 14.12GHz, the maximum shielding strength is 27.35dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 9.28 GHz-18.00 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the electromagnetic shielding material/paraffin thin sheet with the thickness of 2.0mm is 9.48GHz, the maximum shielding strength is 25.54dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 6.40 GHz-18.00 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the electromagnetic shielding material/paraffin thin sheet with the thickness of 2.5mm is 7.04GHz, the maximum shielding strength is 25.95dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 4.88 GHz-18.00 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the electromagnetic shielding material/paraffin thin sheet with the thickness of 3.0mm is 5.64GHz, the maximum shielding strength is 25.94dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 3.92 GHz-18.00 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the electromagnetic shielding material/paraffin thin sheet with the thickness of 3.5mm is 4.72GHz, the maximum shielding strength is 26.24dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 3.28 GHz-8.44 GHz and 12.16 GHz-18.00 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the electromagnetic shielding material/paraffin wax sheet with the thickness of 4.0mm is 3.88GHz, the maximum shielding strength is 27.61dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 2.84 GHz-7.04 GHz and 11.04 GHz-18.00 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the electromagnetic shielding material/paraffin wax sheet with the thickness of 4.5mm is 3.36GHz, the maximum shielding strength is 27.40dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 2.52 GHz-5.92 GHz and 9.84 GHz-18.00 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the electromagnetic shielding material/paraffin thin sheet with the thickness of 5.0mm is 2.88GHz, the maximum shielding strength is 28.75dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 2.24 GHz-5.04 GHz and 8.84 GHz-18.00 GHz. These results show that by adjusting the thickness of the prepared composite material sheet, the novel electromagnetic shielding material has no great obvious change on the maximum value of electromagnetic wave shielding, but the effective shielding ranges of the electromagnetic wave frequencies are different, and the electromagnetic wave frequencies corresponding to the maximum electromagnetic shielding effect are different, so that the effect of adjusting the electromagnetic wave shielding performance is achieved.
2. Test of influence of concentration of impregnation liquid on electromagnetic wave shielding performance
The electromagnetic shielding materials prepared in examples 2 to 6 were doped with 20% paraffin, respectively, and then pressure-equalized into a sheet having a thickness of 2mm, and the electromagnetic wave shielding performance was tested, and the results are shown in fig. 5.
FIG. 5 shows the electromagnetic wave shielding performance of the electromagnetic shielding materials prepared in examples 2-6 after being doped with 20% paraffin respectively, and it can be seen from FIG. 5 that the maximum shielding strength of the sample electromagnetic wave obtained with the concentration of ferric acetylacetonate of 0.02g/mL corresponds to an electromagnetic wave frequency of 12.48GHz, a maximum shielding strength of 22.08dB, and an effective electromagnetic wave shielding frequency range (shielding strength greater than 10dB) of 9.36 GHz-18 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the sample with the ferric acetylacetonate concentration of 0.03g/mL is 9.00GHz, the maximum shielding strength is 25.47dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 5.88 GHz-18 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the sample with the ferric acetylacetonate concentration of 0.04g/mL is 8.08GHz, the maximum shielding strength is 31.08dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 5.06 GHz-18 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the sample with the ferric acetylacetonate concentration of 0.05g/mL is 6.64GHz, the maximum shielding strength is 35.46dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 4.12 GHz-18 GHz. The electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of the sample with the ferric acetylacetonate concentration of 0.06g/mL is 5.20GHz, the maximum shielding strength is 43.51dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 3.04 GHz-18 GHz. These results show that as the concentration of the pressurized impregnation liquid is increased, the electromagnetic wave shielding strength of the product is gradually increased, the frequency corresponding to the maximum electromagnetic shielding strength is gradually decreased, but the effective shielding frequency range is gradually increased, and the purpose of adjusting the electromagnetic wave shielding performance of the product can be achieved by adjusting the concentration of the ferric acetylacetonate in the pressurized impregnation liquid.
3. Test of influence of pressurization time on electromagnetic wave shielding performance
The electromagnetic shielding materials prepared in examples 1, 7 to 9 were doped with 20% paraffin, respectively, and then pressure-equalized into a sheet having a thickness of 2mm, and the electromagnetic wave shielding performance was tested, and the results are shown in fig. 6.
Fig. 6 shows the electromagnetic wave shielding performance of the electromagnetic shielding materials prepared in examples 1 and 7 to 9 after being doped with 20% paraffin, and it can be seen from fig. 6 that the electromagnetic wave shielding performance of the products obtained at different pressure dipping times is obtained under the condition of the same thickness (2mm) of the electromagnetic shielding material/paraffin and the same concentration (0.025g/mL) of the pressure dipping solution. As can be seen from the figure, under the condition that other conditions are not changed, the frequency of the electromagnetic wave corresponding to the maximum shielding strength of the electromagnetic wave of the sample obtained by the pressurization and immersion time of 2 hours is 12.12GHz, the maximum shielding strength is 22.12dB, and the effective electromagnetic wave shielding frequency range (shielding strength is more than 10dB) is 9.12 GHz-18.00 GHz; the frequency of the electromagnetic wave corresponding to the maximum shielding strength of the electromagnetic wave of the sample obtained by the pressurization and immersion time of 3 hours is 9.64GHz, the maximum shielding strength is 25.57dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 6.4 GHz-18.00 GHz; the frequency of the electromagnetic wave corresponding to the maximum shielding strength of the electromagnetic wave of the sample obtained by the pressurizing and dipping time of 4 hours is 7.92GHz, the maximum shielding strength is 32.15dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 4.96 GHz-18.00 GHz; the frequency of the electromagnetic wave corresponding to the maximum shielding strength of the electromagnetic wave of the sample obtained by pressurizing and dipping for 2 hours is 12.12GHz, the maximum shielding strength is 22.12dB, and the effective electromagnetic wave shielding frequency range (the shielding strength is more than 10dB) is 9.12 GHz-18.00 GHz; the sample obtained by the pressurization and immersion time of 5 hours has an electromagnetic wave frequency corresponding to the maximum electromagnetic wave shielding strength of 5.00GHz, a maximum shielding strength of 47.21dB, and an effective electromagnetic wave shielding frequency range (shielding strength greater than 10dB) of 2.92 GHz-18.00 GHz. These results show that the maximum value, effective shielding range and characteristic frequency of the electromagnetic wave shielding material are different by adjusting the pressure impregnation time, and the effect of adjusting the electromagnetic wave shielding performance is achieved.
Claims (9)
1. The preparation method of the electromagnetic shielding material is characterized by comprising the following steps of:
step one, processing wood into wood chips with uniform thickness, length and width;
placing the wood chips into a mixed solution of water and ethanol, performing ultrasonic oscillation washing, taking out, and heating and drying to obtain pretreated wood chips;
dissolving ferric acetylacetonate in an organic solvent to prepare 0.02-0.06 g/mL ferric acetylacetonate impregnation solution;
step four, placing the wood chips pretreated in the step two into an iron acetylacetonate impregnation solution, and incubating for 0.5-2 hours in a vacuum state; then under the protection of nitrogen, pressurizing and dipping for 2-5 hours;
taking out the impregnated wood chips, slightly washing the surfaces of the wood chips with ethanol, standing the wood chips for 1 to 2 hours in a room temperature environment, and drying the wood chips in a vacuum drying oven;
taking out the completely dried wood chips, putting the wood chips into a nitrogen-protected tube furnace for high-temperature pyrolysis step by step, finally taking out the product, crushing and sieving to obtain the wood chips;
in the sixth step, the step-by-step high-temperature pyrolysis process comprises the following steps: under the protection of nitrogen, firstly heating to 210-240 ℃ from room temperature at a heating rate of 5-10 ℃/min, and then keeping for 1-2 hours; further heating to 310-340 ℃ at a heating rate of 5-10 ℃/min, and then keeping for 1-2 hours; finally, further heating to 650-750 ℃ at a heating rate of 5-20 ℃/min, and keeping for 4-6 hours.
2. The method for preparing an electromagnetic shielding material according to claim 1, wherein in the first step, the wood is processed into wood chips by rotary cutting or shearing, the wood chips have a length of 3 to 6 cm, a width of 3 to 6 cm and a thickness of 1 to 3 mm.
3. The method for preparing the electromagnetic shielding material of claim 1, wherein in the second step, the volume ratio of the ethanol to the water is 1-3: 1, and the ultrasonic vibration washing time is 1-5 hours.
4. The method for preparing the electromagnetic shielding material according to claim 1, wherein in the second step, the temperature for heating and drying is 60-80 ℃, and the drying is carried out until the moisture content of the wood chips reaches 3-5%.
5. The method for preparing an electromagnetic shielding material of claim 1, wherein in step three, the organic solvent is selected from any one of benzene, toluene, chloroform, acetone, diethyl ether or N, N-dimethylformamide.
6. The method for preparing an electromagnetic shielding material of claim 1, wherein in the fourth step, the vacuum degree is 0.06 to 0.08 MPa.
7. The method for preparing an electromagnetic shielding material of claim 1, wherein in the fourth step, the pressure of nitrogen is 0.60 to 1.00MPa during the pressure impregnation process.
8. The method of claim 1, wherein in the fifth step, the temperature of the vacuum drying oven is 60-80 ℃ during the vacuum drying process.
9. The method for preparing an electromagnetic shielding material according to any one of claims 1 to 8, wherein the sieving is a 100 mesh sieving.
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