A method for preparing a lignin microspheres cellulose composite paper for electromagnetic shielding

Abstract

The application discloses a preparation method of a lignin microsphere cellulose composite paper for electromagnetic shielding, and relates to the technical field of electromagnetic shielding materials; the method comprises the following steps: step 1, preparing a 2-5 mg / ml MXene nanosheet water dispersion; step 2, preparing lignin-based microspheres, denoted as LMs; step 3, carbonizing the LMs under nitrogen protection, and obtaining carbonized lignin-based microsphere powder CLMs after cooling to room temperature; step 4, preparing a 0.5-1 wt% TOCNF water dispersion; step 5, mixing the MXene nanosheet water dispersion and the TOCNF water dispersion, stirring continuously for a certain time, adding the CLMs and stirring, and obtaining a mixed dispersion system; the addition amount of the MXene nanosheet water dispersion is calculated according to 20%-60% of the absolute dry mass of the composite paper based on the addition amount of the MXene, the addition amount of the TOCNF water dispersion is calculated according to 35%-75% of the absolute dry mass of the composite paper based on the addition amount of the TOCNF, and the addition amount of the CLMs is calculated according to 5%-25% of the absolute dry mass of the composite paper; and the mixed dispersion system is subjected to vacuum-assisted suction filtration drying to obtain a MXene-CLMs-TOCNF composite paper.

Description

Technical Field

[0001] This invention discloses a method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding, which relates to the field of electromagnetic shielding materials technology. Background Technology

[0002] Ordinary paper is an insulator, requiring material composites or structural design to achieve electromagnetic shielding performance. Currently, surface coating methods are commonly used, such as applying silver nanowires (AgNW) or graphene to the paper surface. While simple to implement, this method suffers from poor abrasion resistance and the conductive pathways are easily broken when bent, leading to a significant drop in shielding performance. In-situ polymerization can also be used to add conductive polymers such as polyaniline (PANI) to the paper. Although this method offers good flexibility, it presents problems such as secondary pollution. Summary of the Invention

[0003] This invention addresses the problems of existing technologies by providing a method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding. The method uses cellulose nanofibers (TOCNF) as a flexible biomass matrix, MXene as a conductive phase, and carbonized lignin microspheres (CLMs) as a dielectric phase. Through structural regulation, MXene-CLMs-TOCNF composite paper is prepared.

[0004] The specific solution proposed in this invention is as follows: This invention provides a method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding, comprising: Step 1: Prepare an aqueous dispersion of 2-5 mg / ml MXene nanosheets. Step 2: Prepare lignin-based microspheres, denoted as LMs. Step 3: Under nitrogen protection, LMs are heated and carbonized, and then cooled to room temperature to obtain carbonized lignin-based microsphere powder CLMs. Step 4: Prepare a 0.5-1 wt% TOCNF aqueous dispersion. Step 5: Mix the MXene nanosheet aqueous dispersion and the TOCNF aqueous dispersion, stir continuously for a certain period of time, then add CLMs and stir to obtain a mixed dispersion system. Calculate the amount of MXene nanosheet aqueous dispersion to be added based on an MXene addition amount of 20%-60% of the oven-dry weight of the composite paper, calculate the amount of TOCNF aqueous dispersion to be added based on an TOCNF addition amount of 35%-75% of the oven-dry weight of the composite paper, and calculate the amount of CLMs to be added based on an oven-dry weight of 5%-25% of the composite paper. The mixed dispersion system was subjected to vacuum-assisted filtration and drying to obtain MXene-CLMs-TOCNF composite paper.

[0005] Preferably, step 1 of the method for preparing a lignin microsphere cellulose composite paper for electromagnetic shielding includes: The MAX phase ceramic powder was treated using a hydrochloric acid / lithium fluoride etching method. LiF was slowly dissolved in HCl, and the MAX ceramic powder was slowly added to the etchant. The reaction was carried out at 55°C to completely etch the Al layer of the MAX phase. The suspension obtained by repeated washing with deionized water was ultrasonically treated in an ice bath under argon protection, and the aqueous dispersion of MXene nanosheets was collected by centrifugation. The MXene is preferably titanium carbide (Ti3C2T). x T x Representative surface functional groups include -OH, -F, -O, etc.

[0006] Preferably, step 2 of the method for preparing a lignin microsphere cellulose composite paper for electromagnetic shielding includes: Lignin was dissolved in GVL-H2O solvent and titrated into four volumes of ultrapure water to promote lignin self-assembly. The suspension was then transferred to a dialysis bag and dialyzed in ultrapure water for 24-48 hours or more to remove organic solvents. The resulting solution was then freeze-dried to obtain lignin-based microspheres, denoted as LMs. Carbonized lignin microspheres were prepared from alkali lignin through high-temperature pyrolysis carbonization, with a particle size of 0.2-5 μm.

[0007] Preferably, step 4 of the method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding includes: adding TEMPO and NaBr to the paper dispersion, dissolving them, adding NaClO, stirring at room temperature, adjusting the pH value to maintain at around 10, stopping the reaction when all the coarse fibers of the paper sample disappear, washing the sample and removing impurities, diluting with water, dispersing by ultrasound to obtain a cellulose nanofiber suspension, centrifuging to take the supernatant, and obtaining a TOCNF aqueous dispersion.

[0008] Preferably, in step 5 of the method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding, the mixed dispersion system is ultrasonically treated in an ultrasonic cleaner for 0.5-1 h, and then mechanically stirred for 0.5-2 h to ensure that the components are uniformly dispersed without agglomeration or stratification; the uniform mixture is filtered through a cellulose filter membrane using a vacuum-assisted filtration method, with the filtration vacuum controlled below 0.08 MPa, until a uniform wet film is formed; the wet film and the filter membrane are dried together at room temperature and normal pressure for 24 h, and then transferred to a vacuum drying oven at 55-65℃ for 5-10 h; after drying, the filter membrane is peeled off to obtain MXene-CLMs-TOCNF composite paper.

[0009] The present invention also provides a lignin microsphere cellulose composite paper for electromagnetic shielding, the composite paper comprising: Cellulose nanofibers (TOCNF) form an interwoven nanofiber network framework, accounting for 35%-75% of the total oven-dry mass of the composite paper; MXene nanosheets are interspersed in the TOCNF network framework, accounting for 20%-60% of the total oven-dry mass of the composite paper; Carbonized lignin microspheres are embedded in the pores of TOCNF and MXene to form continuous conductive pathways, accounting for 5%-25% of the total oven-dry mass of the composite paper.

[0010] The present invention also provides a use of lignin microsphere cellulose composite paper for electromagnetic shielding, wherein the lignin microsphere cellulose composite paper for electromagnetic shielding is used to manufacture electromagnetic shielding materials.

[0011] Preferably, the electromagnetic shielding material made from the lignin microsphere cellulose composite paper used for electromagnetic shielding is applied to the manufacture of flexible wearable electronic devices, serving as an electromagnetic shielding layer for smart clothing and electronic skin to prevent external electromagnetic waves from interfering with the operation of the device, while protecting the human body from electromagnetic radiation.

[0012] The advantages of this invention are: The method and equipment of this invention are simple, easy to operate, environmentally friendly, and low in cost, making it suitable for continuous industrial production. The prepared composite paper can block more than 99.99% of electromagnetic radiation in the X-band (8.2-12.4GHz), and the tensile strength of the composite paper reaches 2.039MPa, the elongation at break reaches 5%, and it has good foldability, being able to be bent into any angle without damage. At the same time, the biomass-derived components TOCNF and carbonized lignin microspheres in the composite paper have biocompatibility and biodegradability, which is more environmentally friendly and suitable for various environmental applications. The thickness of the composite paper can be controlled within the range of 20μm-200μm, and the areal density is low, meeting the lightweight requirements of electronic devices. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, some simple figures will be drawn below to describe the sample data characterization process in the implementation of the present invention.

[0014] Figure 1 XRD patterns of lignin microspheres, carbonized lignin microspheres, MXene, and cellulose composite paper are shown. After carbonization, the lignin microspheres (CLMS) exhibit a significant (002) broad peak at 26°, indicating successful conversion into a carbon material containing graphite microcrystals. In the MXene-CLMS-TOCNF ternary composite system, the characteristic peak of MXene is significantly broadened and its intensity decreases at approximately 7°, while the characteristic peak of CLMS at 26° is retained. This indicates that the introduction of CLMS effectively inhibits the stacking of MXene sheets and promotes their uniform dispersion in the cellulose network.

[0015] Figure 2Infrared spectra of lignin microspheres, carbonized lignin microspheres, MXene, and cellulose composite paper are shown. The carbonization process fundamentally transforms the surface chemistry of the lignin microspheres. Compared to ALMs, the hydroxyl peak (~3400 cm⁻¹) of CLMs is significantly weakened, while a sharp new peak appears at ~1000 cm⁻¹, indicating successful transformation into a carbon material rich in ordered aromatic structures. The addition of CLMS significantly alters the interfacial chemical state of the composite paper. The hydroxyl peak of pure TOCNF at ~3400 cm⁻¹ is relatively sharp, while in the MXene-CLMS-TOCNF ternary composite system, this absorption peak is significantly broadened and shifted towards lower wavenumbers. This change directly demonstrates the stronger hydrogen bonding interactions between the oxygen-containing functional groups on the MXene surface, the residual polar groups in CLMS, and the cellulose hydroxyl groups.

[0016] Figure 3 SEM images of lignin microspheres and carbonized lignin microsphere-MXene-cellulose composite paper are shown. a) shows the lignin microspheres; b) shows the cross-sectional SEM image of the carbonized lignin microsphere-MXene-cellulose composite paper; and c) shows the planar SEM image of the carbonized lignin microsphere-MXene-cellulose composite paper. It can be seen that in the MXene-CLMs-TOCNF composite paper, spherical CLMs are uniformly dispersed in a three-dimensional network formed by interwoven sheet-like MXene and fibrous TOCNF.

[0017] Figure 4 Mechanical property analysis of the composite paper. The tensile strength of the composite paper is 2.039 MPa.

[0018] Figure 5 This is a graph showing the electromagnetic shielding performance analysis of the composite paper. It can be seen that most of the incident electromagnetic waves were reflected back during the power balance test, indicating that the carbonized lignin microspheres enhance multiple reflection losses. In the electromagnetic interference (EMI) shielding effectiveness test, it is shown that the composite paper's shielding effect against EMI through its absorption mechanism is relatively stable, fluctuating around 20 dB. It can effectively reflect most electromagnetic waves back, with values ​​fluctuating between 30-35 dB, and the total shielding effectiveness value fluctuates between 50-55 dB. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention. Example

[0020] This invention provides a method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding, comprising: Step 1: Prepare an aqueous dispersion of MXene nanosheets. The Ti3AlC2MAX phase ceramic powder is treated using a hydrochloric acid / lithium fluoride etching method. LiF is slowly dissolved in HCl, and the MAX ceramic powder is slowly added to the etchant. The reaction is carried out at 55°C to completely etch the Al layer of the MAX phase. The suspension was repeatedly washed with deionized water, and the resulting dispersion was ultrasonically treated in an ice bath under argon protection. The Ti3AlC2MAX nanosheets were then collected by centrifugation to prepare a 2 mg / ml Ti3AlC2MAX nanosheet aqueous dispersion.

[0021] Step 2: Prepare lignin-based microspheres, denoted as LMs. In this step, lignin is dissolved in GVL-H2O solvent and titrated into four times the volume of ultrapure water to promote lignin self-assembly. The suspension is then transferred to a dialysis bag and dialyzed in ultrapure water for 24-48 hours or more to remove organic solvents. Finally, the microspheres are freeze-dried to obtain lignin-based microspheres, denoted as LMs.

[0022] Step 3: Under nitrogen protection, LMs are heated and carbonized, and then cooled to room temperature to obtain carbonized lignin-based microsphere powder CLMs. An aqueous dispersion of carbonized lignin microspheres (CLMs) is prepared with a solid content of 0.5 wt%.

[0023] Step 4: Prepare a 1 wt% TOCNF aqueous dispersion. Soak white cardboard fragments in deionized water to make a paper dispersion. According to the requirements of the 1 wt% TOCNF aqueous dispersion, add TEMPO and NaBr to the paper dispersion. After dissolving, add NaClO, stir at room temperature, and adjust the pH value to maintain at around 10. When all the coarse fibers of the paper sample disappear, stop the reaction, wash the sample and remove impurities, dilute with water, and disperse by ultrasonication to obtain a cellulose nanofiber suspension. Centrifuge and take the supernatant to obtain the TOCNF aqueous dispersion.

[0024] Step 5: According to the mass ratio of TOCNF:MXene:CLMs=75:20:5 in the oven-dry composite paper, measure the dispersion of each component separately, add deionized water to dilute to a total solid content of 0.3wt%, and obtain a mixed dispersion system; place the mixed dispersion system in an ultrasonic cleaner for ultrasonic treatment for 30 min, and then mechanically stir for 60 min to ensure that each component is uniformly dispersed and there is no agglomeration or stratification; use vacuum-assisted filtration to filter the uniform mixture through a cellulose filter membrane, with the filtration vacuum degree controlled at 0.08 MPa, until a uniform wet film is formed; place the wet film and the filter membrane together at room temperature and normal pressure to dry for 24 h, and then transfer to a 60℃ vacuum drying oven to dry for 6 h. After complete drying, peel off the filter membrane to obtain the MXene-CLMs-TOCNF composite paper. Example

[0025] This invention provides a method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding, comprising: Step 1: Prepare an aqueous dispersion of MXene nanosheets. The Ti3AlC2MAX phase ceramic powder is treated using a hydrochloric acid / lithium fluoride etching method. LiF is slowly dissolved in HCl, and the MAX ceramic powder is slowly added to the etchant. The reaction is carried out at 55°C to completely etch the Al layer of the MAX phase. The suspension was repeatedly washed with deionized water, and the resulting dispersion was ultrasonically treated in an ice bath under argon protection. The Ti3AlC2MAX nanosheets were then collected by centrifugation to prepare a 3 mg / ml Ti3AlC2MAX nanosheet aqueous dispersion.

[0026] Step 2: Prepare lignin-based microspheres, denoted as LMs. In this step, lignin is dissolved in GVL-H2O solvent and titrated into four times the volume of ultrapure water to promote lignin self-assembly. The suspension is then transferred to a dialysis bag and dialyzed in ultrapure water for 24-48 hours or more to remove organic solvents. Finally, the microspheres are freeze-dried to obtain lignin-based microspheres, denoted as LMs.

[0027] Step 3: Under nitrogen protection, LMs were heated and carbonized, and then cooled to room temperature to obtain carbonized lignin-based microsphere powder CLMs. An aqueous dispersion of carbonized lignin microspheres (CLMs) was prepared with a solid content of 0.6 wt%.

[0028] Step 4: Prepare a 0.8 wt% TOCNF aqueous dispersion. Soak white cardboard fragments in deionized water to make a paper dispersion. According to the requirements of a 1 wt% TOCNF aqueous dispersion, add TEMPO and NaBr to the paper dispersion. After dissolving, add NaClO, stir at room temperature, and adjust the pH value to maintain at around 10. When all the coarse fibers of the paper sample disappear, stop the reaction, wash the sample and remove impurities, dilute with water, and disperse by ultrasonication to obtain a cellulose nanofiber suspension. Centrifuge and collect the supernatant to obtain the TOCNF aqueous dispersion.

[0029] Step 5: According to the mass ratio of TOCNF:MXene:CLMs=70:20:15 in the oven-dry composite paper, measure the dispersion of each component separately, add deionized water to dilute to a total solid content of 0.3wt%, and obtain a mixed dispersion system; place the mixed dispersion system in an ultrasonic cleaner for ultrasonic treatment for 30 min, and then mechanically stir for 60 min to ensure that each component is uniformly dispersed and there is no agglomeration or stratification; use vacuum-assisted filtration to filter the uniform mixture through a cellulose filter membrane, with the filtration vacuum degree controlled at 0.08 MPa, until a uniform wet film is formed; place the wet film and the filter membrane together at room temperature and normal pressure to dry for 20 h, and then transfer to a 60℃ vacuum drying oven to dry for 8 h. After complete drying, peel off the filter membrane to obtain the MXene-CLMs-TOCNF composite paper. Example

[0030] This invention provides a method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding, comprising: Step 1: Prepare an aqueous dispersion of MXene nanosheets. The Ti3AlC2MAX phase ceramic powder is treated using a hydrochloric acid / lithium fluoride etching method. LiF is slowly dissolved in HCl, and the MAX ceramic powder is slowly added to the etchant. The reaction is carried out at 55°C to completely etch the Al layer of the MAX phase. The suspension was repeatedly washed with deionized water, and the resulting dispersion was ultrasonically treated in an ice bath under argon protection. The Ti3AlC2MAX nanosheets were then collected by centrifugation to prepare a 5 mg / ml Ti3AlC2MAX nanosheet aqueous dispersion.

[0031] Step 2: Prepare lignin-based microspheres, denoted as LMs. In this step, lignin is dissolved in GVL-H2O solvent and titrated into four times the volume of ultrapure water to promote lignin self-assembly. The suspension is then transferred to a dialysis bag and dialyzed in ultrapure water for 24-48 hours or more to remove organic solvents. Finally, the microspheres are freeze-dried to obtain lignin-based microspheres, denoted as LMs.

[0032] Step 3: Under nitrogen protection, LMs were heated and carbonized, and then cooled to room temperature to obtain carbonized lignin-based microsphere powder CLMs. Aqueous dispersion of carbonized lignin microspheres (CLMs) was prepared with a solid content of 0.8 wt%.

[0033] Step 4: Prepare a 1 wt% TOCNF aqueous dispersion. Soak white cardboard fragments in deionized water to make a paper dispersion. According to the requirements of the 1 wt% TOCNF aqueous dispersion, add TEMPO and NaBr to the paper dispersion. After dissolving, add NaClO, stir at room temperature, and adjust the pH value to maintain at around 10. When all the coarse fibers of the paper sample disappear, stop the reaction, wash the sample and remove impurities, dilute with water, and disperse by ultrasonication to obtain a cellulose nanofiber suspension. Centrifuge and take the supernatant to obtain the TOCNF aqueous dispersion.

[0034] Step 5: According to the mass ratio of TOCNF:MXene:CLMs=55:20:25 in the oven-dry composite paper, measure the dispersion of each component separately, add deionized water to dilute to a total solid content of 0.3wt%, and obtain a mixed dispersion system; place the mixed dispersion system in an ultrasonic cleaner for ultrasonic treatment for 30 min, and then mechanically stir for 60 min to ensure that each component is uniformly dispersed and there is no agglomeration or stratification; use vacuum-assisted filtration to filter the uniform mixture through a cellulose filter membrane, with the filtration vacuum degree controlled at 0.08 MPa, until a uniform wet film is formed; place the wet film and the filter membrane together at room temperature and normal pressure to dry for 24 h, and then transfer to a 60℃ vacuum drying oven to dry for 10 h. After complete drying, peel off the filter membrane to obtain the MXene-CLMs-TOCNF composite paper. Example

[0035] This invention provides a method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding, comprising: Step 1: Prepare an aqueous dispersion of MXene nanosheets. The Ti3AlC2MAX phase ceramic powder is treated using a hydrochloric acid / lithium fluoride etching method. LiF is slowly dissolved in HCl, and the MAX ceramic powder is slowly added to the etchant. The reaction is carried out at 55°C to completely etch the Al layer of the MAX phase. The suspension was repeatedly washed with deionized water, and the resulting dispersion was ultrasonically treated in an ice bath under argon protection. The Ti3AlC2MAX nanosheets were then collected by centrifugation to prepare a 2 mg / ml Ti3AlC2MAX nanosheet aqueous dispersion.

[0036] Step 2: Prepare lignin-based microspheres, denoted as LMs. In this step, lignin is dissolved in GVL-H2O solvent and titrated into four times the volume of ultrapure water to promote lignin self-assembly. The suspension is then transferred to a dialysis bag and dialyzed in ultrapure water for 24-48 hours or more to remove organic solvents. Finally, the microspheres are freeze-dried to obtain lignin-based microspheres, denoted as LMs.

[0037] Step 3: Under nitrogen protection, LMs are heated and carbonized, and then cooled to room temperature to obtain carbonized lignin-based microsphere powder CLMs. An aqueous dispersion of carbonized lignin microspheres (CLMs) is prepared with a solid content of 0.5 wt%.

[0038] Step 4: Prepare a 1 wt% TOCNF aqueous dispersion. Soak white cardboard fragments in deionized water to make a paper dispersion. According to the requirements of the 1 wt% TOCNF aqueous dispersion, add TEMPO and NaBr to the paper dispersion. After dissolving, add NaClO, stir at room temperature, and adjust the pH value to maintain at around 10. When all the coarse fibers of the paper sample disappear, stop the reaction, wash the sample and remove impurities, dilute with water, and disperse by ultrasonication to obtain a cellulose nanofiber suspension. Centrifuge and take the supernatant to obtain the TOCNF aqueous dispersion.

[0039] Step 5: According to the mass ratio of TOCNF:MXene:CLMs=25:50:25 in the oven-dry composite paper, measure the dispersion of each component separately, add deionized water to dilute to a total solid content of 0.3wt%, and obtain a mixed dispersion system; place the mixed dispersion system in an ultrasonic cleaner for ultrasonic treatment for 30 min, and then mechanically stir for 60 min to ensure that each component is uniformly dispersed and there is no agglomeration or stratification; use vacuum-assisted filtration to filter the uniform mixture through a cellulose filter membrane, with the filtration vacuum degree controlled at 0.08 MPa, until a uniform wet film is formed; place the wet film and the filter membrane together at room temperature and normal pressure to dry for 24 h, and then transfer to a 60℃ vacuum drying oven to dry for 6 h. After complete drying, peel off the filter membrane to obtain the MXene-CLMs-TOCNF composite paper.

[0040] The carbonized lignin microspheres in this invention are spherical carbon-based materials prepared from lignin as a precursor through microspherization molding and high-temperature carbonization. Lignin is an abundant natural aromatic polymer, mainly derived from byproducts of the papermaking industry or residues in biomass refining processes. Carbonized lignin microspheres possess a porous structure, high specific surface area, controllable surface chemical properties, and certain electrical conductivity, making them an environmentally friendly and low-cost functional material.

[0041] In electromagnetic shielding applications, carbonized lignin microspheres play multiple roles: their spherical structure can serve as electromagnetic wave scattering centers, disrupting the straight-line propagation of electromagnetic waves, extending the propagation path, and enhancing multiple reflection losses; their surface defect structure and oxygen-containing functional groups can serve as dipole polarization centers, enhancing dielectric loss; the heterogeneous interface formed with MXene and cellulose can strengthen the interface polarization effect; at the same time, their own conductivity complements the MXene conductive network, optimizing the overall conductivity.

[0042] The above are preferred embodiments of the present invention. Within the scope of the technical solution of the present invention, the degradation of polybenzoxazine resin can be obtained by adjusting the type and amount of reagents according to the actual situation.

[0043] Unless otherwise specified, all reagents used in the method of this invention were purchased or obtained through legitimate channels.

[0044] The lignin microsphere cellulose composite paper of the present invention can be used to manufacture electromagnetic shielding materials. Electromagnetic shielding materials made from the aforementioned lignin microsphere cellulose composite paper can be used in the manufacture of flexible wearable electronic devices, serving as an electromagnetic shielding layer for smart clothing and electronic skin, preventing external electromagnetic waves from interfering with device operation, while simultaneously protecting the human body from electromagnetic radiation.

[0045] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding, characterized in that: include: Step 1: Prepare an aqueous dispersion of 2-5 mg / ml MXene nanosheets. Step 2: Prepare lignin-based microspheres, denoted as LMs. Step 3: Under nitrogen protection, LMs are heated and carbonized, and then cooled to room temperature to obtain carbonized lignin-based microsphere powder CLMs. Step 4: Prepare a 0.5-1 wt% TOCNF aqueous dispersion. Step 5: Mix the MXene nanosheet aqueous dispersion and the TOCNF aqueous dispersion, stir continuously for a certain period of time, then add CLMs and stir to obtain a mixed dispersion system. Calculate the amount of MXene nanosheet aqueous dispersion to be added based on an MXene addition amount of 20%-60% of the oven-dry weight of the composite paper, calculate the amount of TOCNF aqueous dispersion to be added based on an TOCNF addition amount of 35%-75% of the oven-dry weight of the composite paper, and calculate the amount of CLMs to be added based on an oven-dry weight of 5%-25% of the composite paper. The mixed dispersion system was subjected to vacuum-assisted filtration and drying to obtain MXene-CLMs-TOCNF composite paper.

2. The method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding according to claim 1, characterized in that step 1 includes: The MAX phase ceramic powder was treated using a hydrochloric acid / lithium fluoride etching method. LiF was slowly dissolved in HCl, and the MAX ceramic powder was slowly added to the etchant. The reaction was carried out at 55°C to completely etch the Al layer of the MAX phase. The suspension obtained by repeated washing with deionized water was ultrasonically treated in an ice bath under argon protection, and the aqueous dispersion of MXene nanosheets was collected by centrifugation.

3. The method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding according to claim 1, characterized in that: Step 2 includes: Lignin was dissolved in GVL-H2O solvent and titrated into four times the volume of ultrapure water to promote lignin self-assembly. The suspension was then transferred to a dialysis bag and dialyzed in ultrapure water for 24-48 hours or more to remove organic solvents. The lignin-based microspheres, denoted as LMs, were then freeze-dried.

4. The method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding according to claim 1, characterized in that: Step 4 includes: adding TEMPO and NaBr to the paper dispersion, dissolving them, adding NaClO, stirring at room temperature, adjusting the pH to around 10, stopping the reaction when all the coarse fibers in the paper sample disappear, washing the sample and removing impurities, diluting with water, and dispersing by ultrasound to obtain a cellulose nanofiber suspension, centrifuging to collect the supernatant, and obtaining a TOCNF aqueous dispersion.

5. The method for preparing lignin microsphere cellulose composite paper for electromagnetic shielding according to claim 1, characterized in that: In step 5, the mixed dispersion system is ultrasonically treated in an ultrasonic cleaner for 0.5-1 h, and then mechanically stirred for 0.5-2 h to ensure that the components are uniformly dispersed without agglomeration or stratification. The uniform mixture is filtered through a cellulose filter membrane using a vacuum-assisted filtration method, with the vacuum degree controlled below 0.08 MPa, until a uniform wet membrane is formed. The wet membrane and the filter membrane are dried together at room temperature and normal pressure for 24 h, and then transferred to a vacuum drying oven at 55-65℃ for 5-10 h. After drying, the filter membrane is peeled off to obtain MXene-CLMs-TOCNF composite paper.

6. A lignin microsphere cellulose composite paper for electromagnetic shielding, characterized in that... The composite paper comprises: Cellulose nanofibers (TOCNF) form an interwoven nanofiber network framework, accounting for 35%-75% of the total oven-dry mass of the composite paper; MXene nanosheets are interspersed in the TOCNF network framework, accounting for 20%-60% of the total oven-dry mass of the composite paper; Carbonized lignin microspheres are embedded in the pores of TOCNF and MXene to form continuous conductive pathways, accounting for 5%-25% of the total oven-dry mass of the composite paper.

7. The use of a lignin microsphere cellulose composite paper for electromagnetic shielding, characterized in that... The lignin microsphere cellulose composite paper for electromagnetic shielding described in claim 6 is used to manufacture electromagnetic shielding materials.

8. The use of the lignin microsphere cellulose composite paper for electromagnetic shielding according to claim 7, characterized in that: Electromagnetic shielding materials are used in the manufacture of flexible wearable electronic devices, serving as electromagnetic shielding layers for smart clothing and electronic skin to prevent external electromagnetic waves from interfering with the operation of the devices, while also protecting the human body from electromagnetic radiation.

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