Preparation method and application of wood-derived magnetic composite material

Abstract

The invention relates to the technical field of wood-derived materials, and particularly discloses a preparation method and application of a wood-derived magnetic composite material, and the method comprises the following steps: pretreatment of natural wood, preparation of a W / Fe composite material, preparation of a W / EP / Fe wood composite material, and preparation of a C / EP / Fe carbonized wood composite material. The composite material prepared by the invention has excellent electromagnetic shielding performance, magnetic performance and Joule heating performance, and is widely applicable to the related fields of electromagnetic shielding, electronic equipment protection, intelligent heating and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of wood-derived materials, and specifically relates to a preparation method and application of a wood-derived magnetic composite material. Background Art

[0002] With the widespread application of electronic and electrical devices, the problem of electromagnetic (EM) pollution has become increasingly prominent. Electromagnetic radiation not only interferes with the normal operation of electronic devices but may also pose potential hazards to human health. Electromagnetic interference (EMI) shielding materials can effectively attenuate electromagnetic waves through reflection, absorption, and multiple internal reflection mechanisms. However, the current mainstream materials have significant defects: metal-based materials (such as copper and aluminum) have high density, are prone to corrosion, and are difficult to process; carbon-based materials (such as graphene and carbon nanotubes) are lightweight but have complex preparation processes and high costs; porous conductive polymers are difficult to meet the requirements of sustainable development due to poor thermal stability and non-renewability.

[0003] In the prior art, although microporous conductive polymers or polymer foams can reflect and absorb electromagnetic waves through their porous structures, they have low mechanical strength, poor environmental tolerance, and are prone to performance degradation in high-temperature or humid environments. In addition, the functional singularity of traditional materials limits their application in complex scenarios, such as aerospace and portable electronic devices that require both lightweight and high performance.

[0004] Therefore, the development of a lightweight, renewable material with excellent EMI shielding performance has become an urgent need in the current material field.

[0005] Using natural wood as the matrix and constructing a three-dimensional conductive-magnetic composite structure through nanoparticle modification and gradient carbonization processes provides a new idea for solving the above problems. The inherent multi-level pore structure and oriented fiber arrangement of wood can effectively optimize the multiple scattering paths of electromagnetic waves, while the introduction of magnetic components (such as Fe nanoparticles) helps to improve the magnetic loss performance and synergistically enhance the electromagnetic shielding efficiency. This method not only retains the lightweight and renewable characteristics of wood but also enables the directional optimization of material properties through process control, meeting the core objectives of green manufacturing and sustainable development. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method and application of a wood-derived magnetic composite material to solve the problems raised in the above background art.

[0007] To achieve the above purpose, the present invention provides the following technical solutions:

[0008] A preparation method of a wood-derived magnetic composite material, comprising the following steps:

[0009] S1. Wood pretreatment:

[0010] The basswood was cut into wood chips with a size of 40 mm × 50 mm to 50 mm × 50 mm and a thickness of 2 mm. The wood chips were then immersed in a FeCl3 solution prepared by mixing 0.024 g to 0.973 g of ferric chloride with 300 ml of deionized water and placed in a vacuum environment for 10 hours.

[0011] Preparation of S2, W / Fe composite materials:

[0012] The impregnated wood chips were air-dried for 48 h and oven-dried at 60 °C for 2 h to obtain the W / Fe composite material.

[0013] Preparation of S3, W / EP / Fe wood composites:

[0014] 8-10 g of epoxy resin emulsion and 8-8.5 g of curing agent were mixed, and 500 mL of deionized water was added to make a uniform solution. The W / Fe composite material was immersed in the solution and vacuum impregnated for 10 hours, followed by hot pressing at 60°C and 15 MPa for 8 hours to obtain a W / EP / Fe composite material;

[0015] Preparation of S4, C / EP / Fe carbonized wood composite materials:

[0016] The W / EP / Fe composite material was sandwiched between graphite plates and placed in a tube furnace at 3-4 °C·min -1 The carbonized wood was heated to 600-650°C at a heating rate of 4-5°C·min-1 and maintained for 1 hour, then heated to 1000°C at a heating rate of 4-5°C·min-1 and maintained for 1 hour, and cooled to room temperature to obtain a C / EP / Fe carbonized wood composite material.

[0017] Preferably, the method for preparing the wood-derived magnetic composite material of the present invention is:

[0018] The natural wood pretreatment is to cut natural basswood into wood chips with a size of 40 mm×50 mm and a thickness of 2 mm; then soak the wood in a FeCl3 solution prepared by 0.487 g of ferric chloride and 300 mL of deionized water, and vacuum impregnate for 10 hours.

[0019] In the preparation step of the W / Fe composite material, the impregnated wood chips are air-dried for 48 hours and then dried at 60° C. for 2 hours to obtain the composite material.

[0020] In the preparation steps of the W / EP / Fe wood composite material, the epoxy resin solution soaking and hot pressing treatment processes are to ensure that the wood composite material has good mechanical properties.

[0021] In the preparation steps of the C / EP / Fe carbonized wood composite material, a tube furnace is used for carbonization treatment. By raising the temperature to 1000 °C and maintaining it for 1 hour, the carbon skeleton in the composite material is stabilized and its electrical conductivity is enhanced.

[0022] Application of the wood-derived magnetic composite material of the present invention:

[0023] The wood-derived magnetic composite material of the present invention, especially the C / EP / Fe carbonized wood composite material, has excellent electromagnetic shielding, can provide reliable safety protection in different environments, prevent information leakage, and ensure the safety of equipment.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] The microstructure of the material of the present invention is dense, and the graphite carbon matrix effectively disperses metal nanoparticles. XRD, FTIR and XPS analyses show that the material has completed the graphitization transformation and generated a stable sp 2 conjugated carbon skeleton, and Fe 3+ is reduced to Fe. The composite material after hot pressing treatment forms a uniform dense structure, significantly improving its mechanical properties and environmental adaptability.

[0026] At the same time, by introducing iron nanoparticles, the composite material has excellent electromagnetic shielding performance and can be widely used in fields such as protective equipment and communication systems. In the range of 8.2 - 12.4 GHz, the shielding effectiveness of C / EP / Fe-4 reaches 95.3 dB, and efficient shielding is achieved through reflection, absorption, magnetic loss of magnetic nanoparticles, and multiple reflection and scattering of electromagnetic waves by the hierarchical pore structure.

[0027] Moreover, the porous structure of the material of the present invention effectively blocks heat, the material has good thermal conversion stability and fast response to voltage changes. Under different voltages, the Joule heating performance is stable, and it has great application potential in fields such as intelligent heating. At the same time, in the alcohol lamp flame, the material has excellent flame retardant performance. Description of the drawings

[0028] Figure 1 It is a process flow chart for the preparation of the C / EP / Fe composite material.

[0029] Figure 2 It is a scanning electron microscope (SEM) image.

[0030] Figure 3 It is a transmission electron microscope (TEM) image.

[0031] Figure 4 It is a material characterization.

[0032] Figure 5 It is an EMI shielding value.

[0033] Figure 6 Schematic diagram of the dissipation mechanism of electromagnetic waves in C / EP / Fe composite materials.

[0034] Figure 7 Thermal insulation performance test chart.

[0035] Figure 8 Electromagnetic shielding performance test chart.

[0036] Figure 9 Flame retardancy performance test chart.

[0037] Figure 10 Thermal stability performance test chart.

[0038] Figure 11 Joule heating performance test chart. Specific implementation mode

[0039] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0040] Example 1:

[0041] Materials and chemicals:

[0042] Linden wood with an initial water content of 8-12% was cut along the growth direction into thin wood slices with dimensions of 40 mm × 50 mm × 2 mm. Ferric chloride (FeCl3, 98%) solution was prepared by dissolving 0.487 g of ferric chloride in 300 mL of deionized water, with a concentration of 10 mmol / L. The waterborne epoxy resin emulsion (DY-128-50) and the waterborne epoxy curing agent (DY-175) were purchased from Shenyang Dongyan Coating Decoration Co., Ltd. All solutions were prepared using deionized water, and the deionized water used in the experiment was obtained from the water purification system collection system.

[0043] Preparation method:

[0044] Preparation of W / Fe composite material:

[0045] The linden wood slices were treated with FeCl3 solution, soaked for 10 hours, and dried in vacuum and then dried at 60 °C for 2 hours to obtain the W / Fe composite material.

[0046] Preparation of W / EP / Fe composite material:

[0047] The W / Fe composite material was immersed in an aqueous epoxy resin (EP) solution and subjected to vacuum immersion for 10 hours. Then, it was hot-pressed at 60 °C under a pressure of 15 MPa for 8 hours to obtain the W / EP / Fe composite material.

[0048] Preparation of C / EP / Fe carbonized wood composite material:

[0049] The W / EP / Fe composite material was placed in a tubular furnace for carbonization treatment. It was heated to 600 °C at a heating rate of 3 °C·min -1 and held for 1 hour. Then, it was heated to 1000 °C at a heating rate of 5 °C·min -1 and held for 1 hour. Finally, it was cooled to room temperature to obtain the C / EP / Fe composite material.

[0050] Preparation of C / EP material:

[0051] 10 g of epoxy resin emulsion was mixed with 8.5 g of epoxy resin curing agent, 500 mL of deionized water was added and stirred evenly. Basswood slices were immersed in this solution and subjected to vacuum immersion for 10 hours. Subsequently, it was hot-pressed at 60 °C under a pressure of 15 MPa for 8 hours. The obtained material was placed in a tubular furnace for carbonization treatment. It was heated to 600 °C at a heating rate of 3 °C·min -1 and held for 1 hour. Then, it was heated to 1000 °C at a heating rate of 5 °C·min -1 and held for 1 hour. Finally, it was cooled to room temperature to obtain the C / EP material.

[0052] Functional principle:

[0053] Through the above method, iron nanoparticles in basswood grow on the surface of the wood conduit wall to form the C / EP / Fe composite material; through epoxy resin immersion and hot-pressing treatment, the structural stability and mechanical properties of the composite material are enhanced; the final carbonization treatment further enhances the conductivity of the composite material, forming a self-supporting three-dimensional conductive network structure, endowing the material with excellent electromagnetic interference shielding performance.

[0054] Figure 1 is the preparation flow chart of the C / EP / Fe carbonized wood composite material.

[0055] Research example:

[0056] Preparation of C / EP / Fe-1 composite material:

[0057] Prepare a 0.5 mmol / L iron chloride (FeCl3) solution by using 0.024 g of iron chloride and 300 mL of deionized water. Place natural linden wood chips in the 0.5 mmol / L FeCl3 solution and impregnate them under vacuum for 10 hours. After taking them out, air-dry for 48 hours and then dry at 60 °C for 2 hours. Mix 10 g of epoxy resin emulsion with 8.5 g of curing agent, add 500 mL of deionized water to prepare an EP solution. Immerse the above-treated wood chips in the EP solution and carry out vacuum immersion for 10 hours. After taking them out, immediately hot-press at 60 °C and 15 MPa for 8 hours. Finally, put the hot-pressed material into a tube furnace, heat it to 600 °C at a heating rate of 3 °C·min -1 and hold for 1 hour; then heat it to 1000 °C at a heating rate of 5 °C·min -1 and hold for 1 hour, and finally cool to room temperature to obtain the C / EP / Fe-1 composite material.

[0058] Preparation of C / EP / Fe-2 composite material:

[0059] Prepare a 1 mmol / L iron chloride (FeCl3) solution by using 0.049 g of iron chloride and 300 mL of deionized water. Place natural linden wood in the 1 mmol / L FeCl3 solution and impregnate it under vacuum for 10 hours. After taking it out, air-dry for 48 hours and then dry at 60 °C for 2 hours. Mix 10 g of epoxy resin emulsion with 8.5 g of curing agent, add 500 mL of deionized water to prepare an EP solution. Immerse the above-treated wood chips in the EP solution and carry out vacuum immersion for 10 hours. After taking them out, immediately hot-press at 60 °C and 15 MPa for 8 hours. Finally, put the hot-pressed material into a tube furnace, heat it to 600 °C at a heating rate of 3 °C·min -1 and hold for 1 hour; then heat it to 1000 °C at a heating rate of 5 °C·min -1 and hold for 1 hour, and finally cool to room temperature to obtain the C / EP / Fe-2 composite material.

[0060] Preparation of C / EP / Fe-3 composite material:

[0061] Prepare a 5 mmol / L iron chloride (FeCl3) solution using 0.243 g of iron chloride and 300 mL of deionized water. Place natural linden wood chips in the 5 mmol / L FeCl3 solution and impregnate them under vacuum for 10 hours. After taking them out, air dry for 48 hours and then dry at 60 °C for 2 hours. Mix 10 g of epoxy resin emulsion with 8.5 g of curing agent, add 500 mL of deionized water, and prepare an EP solution. Immerse the above-treated wood chips in the EP solution and conduct vacuum immersion for 10 hours. After taking them out, immediately hot press at 60 °C and 15 MPa for 8 hours. Finally, place the hot-pressed material in a tube furnace and heat it to 600 °C at a heating rate of 3 °C·min -1 and hold for 1 hour; then heat it to 1000 °C at a heating rate of 5 °C·min -1 and hold for 1 hour, and finally cool to room temperature to obtain the C / EP / Fe-2 composite material.

[0062] Manufacture of C / EP / Fe-5 composite material:

[0063] Prepare a 20 mmol / L iron chloride (FeCl3) solution using 0.973 g of iron chloride and 300 mL of deionized water. Place natural linden wood chips in the 20 mmol / L FeCl3 solution and impregnate them under vacuum for 10 hours. After taking them out, air dry for 48 hours and then dry at 60 °C for 2 hours. Mix 10 g of epoxy resin emulsion with 8.5 g of curing agent, add 500 mL of deionized water, and prepare an EP solution. Immerse the above-treated wood chips in the EP solution and conduct vacuum immersion for 10 hours. After taking them out, immediately hot press at 60 °C and 15 MPa for 8 hours. Finally, place the hot-pressed material in a tube furnace and heat it to 600 °C at a heating rate of 3 °C·min -1 and hold for 1 hour; then heat it to 1000 °C at a heating rate of 5 °C·min -1 and hold for 1 hour, and finally cool to room temperature to obtain the C / EP / Fe-5 composite material.

[0064] Denote the C / EP / Fe prepared in Example 1 as C / EP / Fe-4, and use the C / EP / Fe prepared in Example 1 in subsequent examples unless otherwise specified.

[0065] Example Two:

[0066] Material Characterization:

[0067] Immerse natural wood chips in the FeCl3 solution, and make Fe through a vacuum-assisted process 3+Ions penetrate into the inner wall and surface of wood conduits, thereby preparing a stable W / Fe composite material. To further enhance the structural stability, the W / Fe composite material is impregnated in an epoxy resin (EP) solution. Through vacuum soaking and hot pressing treatments, the resin uniformly fills the wood pores to obtain a W / EP / Fe composite material. After high-temperature carbonization of the W / EP / Fe composite material, a C / EP / Fe carbonized wood composite material is formed. The carbonized material retains the three-dimensional overall structure and natural porous characteristics of the wood. During this process, significant compressive changes occur in the pore structure of the C / EP / Fe composite material. Observation by scanning electron microscopy (SEM) reveals that the walls of the conduits are tightly bonded, forming a denser structure ( Figure 2 a-b). This dense structure realizes the multi-stage scattering and absorption of electromagnetic waves through the synergistic effects of interface reflection, internal micro-spaces, and channels. The surface of the material after hot pressing and carbonization treatments exhibits significant flattening characteristics ( Figure 2 d). Further observation of the high-magnification SEM images shows that tiny particles are attached to the cross-section and surface of the material ( Figure 2 c, f). In the energy-dispersive spectroscopy (EDS) elemental mapping of the material cross-section, elements including carbon (C), chlorine (Cl), oxygen (O), and iron (Fe) are present ( Figure 2 g). This indicates that through this treatment process, iron nanoparticles are successfully doped into the wood matrix, forming a nano-scale composite structure.

[0068] Figure 2 : (a, b, c) Cross-section SEM images of the C / EP / Fe composite material (perpendicular to the wood growth axis direction). (d, e, f) Surface SEM images of the C / EP / Fe composite material. (g) EDS elemental mapping image of the C / EP / Fe composite material on the cross-section.

[0069] The microstructure of the C / EP / Fe-5 composite material was characterized using transmission electron microscopy (TEM). Low-magnification TEM images ( Figure 3 a-b) show that a large number of approximately circular dark-field characteristic structures are uniformly distributed in the material. This indicates that the graphite carbon matrix has a significant dispersing effect on metal nanoparticles, effectively suppressing particle agglomeration. In the high-magnification TEM image ( Figure 3 c), lattice fringes can be clearly seen. The lattice spacings of 0.205 nm and 0.353 nm can be attributed to the (110) plane of iron nanoparticles and the (002) plane of graphite carbon. This large number of distributed Fe@C spheres, with a unique core-shell structure and abundant hetero-interfaces, can improve its electromagnetic shielding performance. From the selected area electron diffraction (SAED) Figure 3 d, the existence of different lattice planes of iron and graphite carbon is further demonstrated.

[0070] Figure 3 : TEM images of (a, b, c) C / EP / Fe-5 composite and (d) selected area electron diffraction image of crystal plane.

[0071] The phase types and crystal structures of the composites were analyzed by XRD. The XRD patterns of natural wood, W / EP / Fe-3 and C / EP / Fe-3 are as Figure 4 shown in a. The strong diffraction peaks of wood at 2θ of 15.9° and 22.4° can be attributed to the (101) and (002) crystal planes of the cellulose crystalline region in wood. It can be found that the intensities of these two diffraction peaks increase in the XRD pattern of W / EP / Fe-3. In the C / EP / Fe-3 spectrum, a diffraction peak appears at 2θ of 26°, corresponding to the (002) crystal plane of graphite carbon (PDF#41-1487), indicating that the prepared C / EP / Fe-3 composite has been graphitized. The clear lattice fringes (d = 0.35 nm) observed in TEM and the appearance of D peak and G peak in Raman spectrum also confirm the transformation of wood composite to graphitized structure during the carbonization process. In addition, the diffraction peak appearing at 2θ = 43.9° can be indexed to the (110) plane of α-Fe with a body-centered cubic structure (PDF#06-0696). It shows that after carbonization, ferric ions have been successfully reduced to metal particles.

[0072] The chemical compositions of natural wood, W / EP / Fe-5 and C / EP / Fe composites were analyzed by Fourier transform infrared spectroscopy (FTIR) ( Figure 4 b). In the spectrum of natural wood, the C-H stretching vibration at 2900 cm -1 , the C=O stretching vibration at 1738 cm -1 , and the C-O-C stretching vibration at 1030 cm -1 correspond to the characteristic functional groups of cellulose, hemicellulose and lignin respectively. In the EP spectrum, the characteristic absorption peak observed at 930 cm -1 corresponds to the symmetric stretching vibration of epoxy group (C-O-C). The disappearance of the characteristic absorption peak at 930 cm -1 is found in the spectrum of W / EP / Fe-5, proving that the curing reaction of EP occurs inside the wood. After high-temperature carbonization treatment, the FTIR spectrum of C / EP / Fe composite changes significantly, and the characteristic absorption peaks of most oxygen-containing functional groups disappear. This change indicates that during the carbonization process, the organic components in wood and epoxy resin have undergone pyrolysis reactions and transformed into highly graphitized carbon structures. This result corroborates with the graphitization characteristic peaks observed in XRD analysis, further verifying that the material has successfully achieved graphitization transformation during high-temperature carbonization treatment.

[0073] At Figure 4The Raman spectra of C / EP / Fe-5 are shown in c. In the spectrum of the C / EP / Fe-5 sample, the D-band peak at 1346 cm -1 originates from phonon scattering at the boundaries of sp 2 carbon domains, reflecting the presence of amorphous carbon and structural defects in the material. The G-band peak at 1587 cm -1 corresponds to the E2g vibration mode of sp 2 hybridized carbon, characterizing the ordered structure of graphitic carbon in the material. In the figure, the intensity ratio I D / I G = 1.26 of the D-band and G-band. The higher D-band intensity and lower G-band intensity indicate a higher proportion of amorphous carbon in the material.

[0074] The chemical composition and elemental valence state changes of the C / EP / Fe composite were analyzed by XPS method. As Figure 4 shown in d-f, in the C1s spectrum, the main components of carbon can be decomposed into C-C / C═C (284.8 eV), C-O-C (286.19 eV), and O-C═O (289.18 eV). It can be found from the figure that after the material is carbonized, the proportion of the C-C / C═C structure is the largest. This indicates that during the carbonization process of wood, a large number of oxygen functional groups are removed, forming a more stable sp 2 conjugated carbon skeleton, which is consistent with the analysis results of Raman spectroscopy. In the high-resolution O1s XPS spectrum, the characteristic peak with a binding energy of 532.51 eV can be attributed to the C-OH / C-O-C functional group. Three sets of characteristic peaks are shown in the Fe 2p XPS spectrum. Among them, the peak with a binding energy of 706.88 eV is attributed to the Fe 0 valence state, while the peaks at 710.86 eV and 715.03 eV correspond to Fe 3+ / Fe 2+ and satellite peaks, respectively. The Fe 0 peak confirms that the FeCl3 precursor is reduced to metallic Fe during the carbonization process, which is mainly attributed to the strong reducibility of the carbon matrix at high temperatures.

[0075] By measuring the N2 adsorption-desorption isotherm curve, specific surface area and pore size distribution information of the composite material are obtained ( Figure 4 g). The isotherm of the C / EP / Fe-5 material is a typical type IV, indicating that the material has a mesoporous structure. The significant increase in N2 adsorption at a relative pressure (P / P0) below 0.01 indicates the presence of micropores. The obvious hysteresis loop in the region of higher relative pressure further illustrates the presence of mesoporous structure in the material. The pore distribution peak of the material is in the range of 0 to 100 nm, indicating that the material has a hierarchical pore structure with micropores (<2 nm), mesopores (2 - 50 nm), and macropores (>50 nm) simultaneously ( Figure 4h). The incident electromagnetic wave can be reflected, scattered, and lost multiple times in such a porous structure, thereby enhancing the EMI shielding performance, especially its electromagnetic wave absorption ability. The hysteresis loop of the C / EP / Fe-5 composite material is as shown in Figure 4 Figure i, and the saturation magnetic induction intensity of this material is 1.55 emu·g -1 . It is proved that after carbonization treatment, the material exhibits obvious ferromagnetism.

[0076] Figure 4 . (a) XRD patterns of natural basswood, W / EP / Fe-3, and C / EP / Fe-3. (b) FTIR spectra of natural basswood, W / EP / Fe-5, and C / EP / Fe-4. (c) Raman spectrum of C / EP / Fe-5. (d-f) XPS spectra of C1s, O 1s, and Fe 2p in C / EP / Fe. (g) N2 adsorption-desorption isotherm curve of C / EP / Fe-5, (h) pore size distribution, and (i) hysteresis loop.

[0077] Conductivity is widely regarded as one of the key factors affecting electromagnetic shielding performance. Natural wood usually behaves as an insulator due to its layered porous structure and abundant cellulose chains. However, during the carbonization process, a continuous carbon skeleton structure is formed inside the wood, providing a conduction path for the transmission of electrons, thereby significantly improving the conductivity of the material. The conductivities of the C / EP / Fe-1, C / EP / Fe-2, C / EP / Fe-3, C / EP / Fe-4, and C / EP / Fe-5 materials are shown in Table 1. The results show that C / EP / Fe-4 has the highest conductivity of approximately 24.07 S·cm -1 . This indicates that an appropriate amount of iron helps to enhance the conductivity, while excessive iron may lead to the inhomogeneity of the conductive network, thus affecting the overall conductive performance.

[0078] Table 1 C / EP / Fe composite materials with different concentrations of FeCl3 and their conductivities

[0079]

[0080] Example 3:

[0081] Electromagnetic shielding performance:

[0082] The electromagnetic interference (EMI) shielding performance of the C / EP and C / EP / Fe(1-5) composite materials in the frequency range of 8.2–12.4 GHz (X-band) is as shown in Figure 5As shown in a). Before testing, all samples were cut to 22.9 mm × 10.2 mm × 1 mm to fit the waveguide size. The main component of carbonized wood (C / EP) is carbon, and its carbon skeleton structure endows the material with certain electrical conductivity. When electromagnetic waves act, the material will generate induced current to resist and weaken the propagation of electromagnetic waves, thus showing certain electromagnetic shielding performance. The appropriate embedding of magnetic nanoparticles can enhance the magnetism of the material, introduce magnetic loss mechanism, and improve the electromagnetic shielding performance. When the concentration of FeCl3 solution reaches 10 mmol / L, the shielding effectiveness of its corresponding C / EP / Fe-4 material is the highest, reaching 95.3 dB.

[0083] To more comprehensively evaluate the shielding performance, the absolute shielding effectiveness SSE / t (dB·cm 2 ·g -1 ) was calculated to comprehensively consider three key factors: EMI shielding efficiency, density, and thickness. Among them, the thickness and density of the materials are shown in Table 2. As found in Figure 5 b, under the synergistic modification of EP, carbonized wood achieved an absolute shielding effectiveness of up to 1631.42 dB cm 2 ·g -1 . EP not only filled the natural pore structure of wood as a reinforcing phase but also transformed into a continuous graphitized carbon network during the carbonization process, optimizing the electrical conductivity and electromagnetic shielding performance of the material. The absolute electromagnetic shielding effectiveness of C / EP / Fe(1-5) composites first increased and then decreased, and the best value was obtained in C / EP / Fe-4 material, about 2302 dB cm 2 ·g -1 .

[0084] Table 2 C / EP and C / EP / Fe composites with different densities and thicknesses

[0085]

[0086] The power coefficients of reflectivity (R), absorptivity (A), and transmittivity (T) are mainly used to evaluate the power balance when the material interacts with electromagnetic waves, and respectively reflect the reflection, absorption, and transmission capabilities of the material to electromagnetic waves ( Figure 5 c). These coefficients usually satisfy the energy conservation relationship: R + A + T = 1. The T value of C / EP / Fe composites is close to zero, indicating that the incident electromagnetic waves can be effectively shielded. It should be noted that at the same thickness, the R value of all materials is always higher than the A value, indicating that reflection is still the main shielding mechanism, but absorption also plays an important role in the shielding process. In the field of electromagnetic shielding materials, absorption efficiency (SE A ), reflection efficiency (SE R ), and total shielding effectiveness (SE T) is also a key indicator for measuring the electromagnetic shielding performance of materials. The SE of C / EP and C / EP / Fe(1-5) materials A , SE R and SE T values are shown in Figure 5 d. For the C / EP / Fe material with the best shielding effectiveness, the SE A , SE R and SE T values are 10.8 dB, 84.5 dB and 95.3 dB respectively.

[0087] Figure 5 : (a) EMI SE and (b) SSE / t of C / EP, C / EP / Fe-1, C / EP / Fe-2, C / EP / Fe-3, C / EP / Fe-4 and C / EP / Fe-5 at 8.2–12.4 GHz. (c) Corresponding average R, A and T values of C / EP and C / EP / Fe(1-5) materials. (d) Comparison of SE T , SE A and SE R of C / EP and C / EP / Fe(1-5) materials.

[0088] Figure 6 shows the electromagnetic shielding mechanism of the C / EP / Fe carbonized wood composite after loading iron nanoparticles. Through the EP impregnation and hot-press carbonization treatment of wood, the natural porous structure of this composite evolves into a conductive network that penetrates the whole, thus providing a favorable channel for the transmission and energy loss of electromagnetic waves. On this basis, the loaded iron nanoparticles improve the overall conductivity of the material and introduce rich loss active sites. When electromagnetic waves irradiate the material surface, the magnetic nanoparticles can generate magnetic loss through natural resonance or exchange resonance, thus promoting the effective dissipation of electromagnetic energy. In addition, the multi-level pore structure of the C / EP / Fe carbonized wood composite causes the electromagnetic waves to reflect and scatter multiple times inside it, extending the propagation path and further enhancing the attenuation effect of electromagnetic waves. The synergistic effect of this multiple loss mechanism enables this composite to possess excellent electromagnetic wave absorption and shielding performance.

[0089] Figure 6 : Schematic diagram of the dissipation mechanism of electromagnetic waves in the C / EP / Fe composite.

[0090] Example 4:

[0091] Thermal insulation performance test: As shown in Figure 7As shown, the heat insulation performance of the C / EP / Fe carbonized wood composite material was tested through heating experiments. When the temperature of the heating stage rose to 120.7 °C, the surface temperature of the material stabilized at around 88.2 °C, and the temperature difference from the environment reached 40 °C; when the ambient temperature dropped to 140.9 °C, the internal temperature of the material could still be maintained near 117.7 °C. This remarkable heat insulation effect benefits from the porous structure inside the material, which can effectively block heat transfer.

[0092] Electromagnetic shielding demonstration: Using a Tesla coil as a high-frequency electromagnetic interference source, the electromagnetic interference shielding performance of the C / EP / Fe material was tested ( Figure 8 ). By observing the on / off state of an incandescent lamp (5W), the EMI shielding effect was visually evaluated. After power-on, the strong electromagnetic field generated by the Tesla coil kept the incandescent lamp lit. When a C / EP / Fe material was added as a shielding layer between the lamp and the Tesla coil, the incandescent lamp immediately went out. An electromagnetic radiation detector was used to detect the electric and magnetic field signals before and after shielding. Before shielding, the magnetic field strength measured by the detector was 3.38 μT, and the electric field strength was 521 V / m. After shielding with the C / EP / Fe material, both the electric and magnetic fields were effectively shielded. It was proved that this material could effectively block electromagnetic wave signals and reduce the electromagnetic field strength.

[0093] Flame retardancy test: After the C / EP / Fe composite material was continuously heated in an alcohol lamp flame for 120 seconds, it still maintained its original shape, and there were no obvious combustion marks on the surface ( Figure 9 ). As the combustion time was extended to 240 s, red marks appeared at the four corners of the material surface. When the material was continuously burned in an open flame for 600 s, only the edges were carbonized, and there was no open flame spread or self-ignition phenomenon. After the heat source was removed, the self-extinguishing time of the material was less than 4 s, showing good flame retardancy.

[0094] Figure 7 : Heat insulation performance test of the C / EP / Fe carbonized wood composite material.

[0095] Figure 8 : Electromagnetic shielding performance test of the C / EP / Fe material.

[0096] Figure 9 : Flame retardancy test of the C / EP / Fe material.

[0097] Thermal stability test: The thermal stability of the material is an important performance index in its practical applications. Through thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses, the thermal decomposition behaviors of natural wood and the C / EP / Fe material in air and nitrogen atmospheres were compared and analyzed. In the air atmosphere ( Figure 10(a-b), the initial thermal decomposition temperature of the C / EP / Fe material is approximately 500 °C, while natural wood has poor thermal stability and begins to decompose at around 200 °C. On the DTG curve, natural wood exhibits two distinct weight loss peaks, indicating that its thermal decomposition process can be mainly divided into two stages. After carbonization, only one weight loss peak is shown, indicating a relatively single thermal decomposition process. Under a nitrogen atmosphere ( Figure 10 (c-d), natural wood shows earlier initial thermal decomposition behavior at 200 °C, which is mainly attributed to the poor thermal stability of its cellulose component. The final char yield of the C / EP / Fe material is as high as 96%, and the weight loss process shows a gentle trend, fully demonstrating the excellent thermal stability of this material.

[0098] Joule heating performance test: The temperature of the C / EP / Fe material increases with the increase of the applied voltage, showing good Joule heating performance, as Figure 11 shown in Fig. a. When a voltage of 2 V is applied, the surface temperature of the C / EP / Fe material reaches 26 °C, and when the voltage is increased to 5 V, its surface temperature rises to 134.5 °C. This phenomenon is mainly attributed to the Joule heat effect, that is, when an electric current passes through the material, due to the resistance of the material, electrical energy will be converted into heat energy, causing the material temperature to rise. Figure 11 The infrared thermal images in Fig. b intuitively show the surface temperature of the C / EP / Fe material at different voltages. The C / EP / Fe material shows stable Joule heating characteristics at different voltages, indicating its good application potential in the fields of electromagnetic shielding, intelligent heating, and temperature control systems. To evaluate the thermal conversion stability of the C / EP / Fe material, a cyclic thermal cycle experiment was carried out on its Joule heat performance ( Figure 11 (c). The experimental results show that after 10 cycles, the surface temperature of the material remains stable at approximately 70 °C; after 30 cycles, the surface temperature decreases slightly. It shows that the C / EP / Fe material can maintain good thermal conversion characteristics during long-term cyclic use. And this material shows a high sensitivity to the change of input voltage and has a fast thermal response characteristic ( Figure 11 (b). After the voltage is applied, the material can rapidly heat up from room temperature to the target temperature in a short time. After the voltage is cut off, the material temperature can also rapidly drop and return to room temperature.

[0099] Figure 10 : Thermal stability test of C / EP / Fe material: (a) TG and (b) DTG spectra of natural wood and C / EP / Fe material in air atmosphere. (c) TG and (d) DTG spectra of natural wood and C / EP / Fe material in nitrogen atmosphere. Figure 11:Research on the Joule heat characteristics of C / EP / Fe materials: (a) Variation of the surface temperature of C / EP / Fe with time under different input voltages. (b) Surface temperatures of the C / EP / Fe material under different input voltages. (c) Variation of the surface temperature of C / EP / Fe with the gradient voltage. (d) Cyclic heating performance of C / EP / Fe at the 1st, 10th, and 30th cycles under a voltage of 3V.

[0100] It should be understood that in the development process of any actual implementation, such as in any engineering or design project, a large number of specific implementation decisions can be made. Such development efforts may be complex and time-consuming, but for those of ordinary skill in the art who benefit from this disclosure, without excessive experimentation, the development efforts will be a routine task of design, manufacturing, and production.

[0101] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A preparation method of a wood-derived magnetic composite material, characterized in that, The following steps are involved: S1. Wood pretreatment: The basswood was cut into wood chips with a size of 40 mm × 50 mm to 50 mm × 50 mm and a thickness of 2 mm. The wood chips were then immersed in a FeCl3 solution prepared by mixing 0.024 g to 0.973 g of ferric chloride with 300 ml of deionized water and placed in a vacuum environment for 10 hours. Preparation of S2, W / Fe composite materials: The impregnated wood chips were air-dried for 48 h and oven-dried at 60 °C for 2 h to obtain the W / Fe composite material. Preparation of S3, W / EP / Fe wood composites: 8-10 g of epoxy resin emulsion and 8-8.5 g of curing agent were mixed, and 500 mL of deionized water was added to make a uniform solution. The W / Fe composite material was immersed in the solution and vacuum impregnated for 10 hours, followed by hot pressing at 60°C and 15 MPa for 8 hours to obtain a W / EP / Fe composite material; Preparation of S4, C / EP / Fe carbonized wood composite materials: The W / EP / Fe composite material was sandwiched between graphite plates, placed in a tubular furnace, heated to 600-650°C at a heating rate of 3-4°C·min-1 and maintained for 1 hour, then heated to 1000°C at a heating rate of 4-5°C·min-1 and maintained for 1 hour, and cooled to room temperature to obtain a C / EP / Fe carbonized wood composite material.

2. The preparation method and application of a wood-derived magnetic composite material according to claim 1, characterized in that: The size of the basswood chips in S1 is 40 mm×50 mm, and the thickness is 2 mm.

3. A preparation method and application of a wood-derived magnetic composite material according to claim 1, characterized in that: The FeCl3 solution in S1 is prepared by mixing 0.487 g of ferric chloride and 300 ml of deionized water.

4. The preparation method and application of a wood-derived magnetic composite material according to claim 1, characterized in that: In the S3, 10 g of epoxy resin emulsion and 8.5 g of curing agent are mixed, and 500 mL of deionized water is added to prepare a uniform solution. The models of the epoxy resin emulsion and curing agent are DY-128-50 and DY-175 respectively.

5. The preparation method and application of a wood-derived magnetic composite material according to claim 1, characterized in that: The S4 carbonization process is carried out in a tubular furnace filled with nitrogen.

6. The preparation method and application of a wood-derived magnetic composite material according to claim 1, characterized in that: The temperature was raised to 600°C at a rate of 3°C·min-1 and maintained at that temperature for 1 hour. The temperature was then raised to 1000°C at a rate of 5°C·min-1 and maintained at that temperature for 1 hour before cooling to room temperature.

7. Use of the wood-derived magnetic composite material obtained by the method for preparing a wood-derived magnetic composite material according to claim 1 in preparing electromagnetic shielding equipment.

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