Cellulose nanofiber-based electromagnetic shielding composite film and preparation method and application thereof

Abstract

The application provides a cellulose nanofiber-based electromagnetic shielding composite film and a preparation method and application thereof, and relates to the technical field of electromagnetic shielding materials.The application provides a cellulose nanofiber-based electromagnetic shielding composite film, which comprises MXene / CNF layers and BNNS-OH / CNF layers arranged in a stack.The application uses MXene as a conductive and heat-conductive filler, uses BNNS-OH as a heat-conductive filler, and uses cellulose nanofiber as a reinforced matrix;the content of MXene in the MXene / CNF layer is controlled to be 5-90wt%, and the content of BNNS-OH in the BNNS-OH / CNF layer is controlled to be 5-90wt%, so that the cellulose nanofiber-based electromagnetic shielding composite film has both heat-conductive performance and electromagnetic shielding performance, has the characteristic of being light in weight, and realizes the adjustment of the single performance of the heat-conductive performance and the electromagnetic shielding performance of the cellulose nanofiber-based electromagnetic shielding composite film.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding materials technology, specifically relating to a cellulose nanofiber-based electromagnetic shielding composite film, its preparation method, and its application. Background Technology

[0002] Cellulose nanofibers (CNFs) possess advantages such as being environmentally friendly, having abundant natural sources, and exhibiting excellent processing and mechanical properties, leading to their widespread application in electronics, construction, sporting goods, and aerospace. However, cellulose nanofibers exhibit low thermal conductivity and shielding effectiveness, failing to meet the electromagnetic shielding and heat dissipation requirements of electronic devices. To meet the ever-increasing electromagnetic shielding demands of electronic devices, simultaneously improving the electromagnetic shielding and thermal conductivity properties of cellulose nanofibers has become an important research topic. Traditional methods for improving the thermal conductivity and electromagnetic shielding properties of cellulose nanofibers involve filling with a single filler, making it difficult to achieve controllable adjustment of these individual properties. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a cellulose nanofiber-based electromagnetic shielding composite film, its preparation method, and its application. The cellulose nanofiber-based electromagnetic shielding composite film provided by this invention possesses both thermal conductivity and electromagnetic shielding properties, and achieves adjustable performance for both thermal conductivity and electromagnetic shielding properties.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solutions.

[0005] This invention provides a cellulose nanofiber-based electromagnetic shielding composite film, comprising an MXene / CNF layer and a BNNS-OH / CNF layer located on the surface of the MXene / CNF layer; the MXene / CNF layer comprises a first cellulose nanofiber matrix and MXene doped in the first cellulose nanofiber matrix, wherein the mass fraction of MXene in the MXene / CNF layer is 5-90%; the BNNS-OH / CNF layer comprises a second cellulose nanofiber matrix and hydroxyl-functionalized boron nitride (BNNS-OH) doped in the second cellulose nanofiber matrix; wherein the mass fraction of hydroxyl-functionalized boron nitride in the BNNS-OH / CNF layer is 5-90%.

[0006] Preferably, the thickness of the MXene / CNF layer is 10–200 μm.

[0007] Preferably, the thickness of the MXene is 1 to 8 nm.

[0008] Preferably, the thickness of the BNNS-OH / CNF layer is 10–200 μm.

[0009] This invention provides a method for preparing the cellulose nanofiber-based electromagnetic shielding composite film described in the above technical solution, comprising the following steps:

[0010] (1) Mix MXene, first cellulose nanofibers and water to obtain an MXene / CNF mixture; the mass of MXene is 5-90% of the total mass of the first cellulose nanofibers and MXene;

[0011] (2) Hydroxyfunctionalized boron nitride, second cellulose nanofibers and water are mixed to obtain BNNS-OH / CNF mixture; the mass of the hydroxyfunctionalized boron nitride is 5 to 90% of the total mass of the second cellulose nanofibers and hydroxyfunctionalized boron nitride.

[0012] (3) The MXene / CNF mixture is used to form a film to obtain an MXene / CNF layer;

[0013] (4) The BNNS-OH / CNF mixture is formed on the surface of the MXene / CNF layer to obtain a cellulose nanofiber-based electromagnetic shielding composite film.

[0014] Steps (1) and (2) are not in any particular order.

[0015] Preferably, the first mixing is a first mixing of MXene and a first aqueous solution of cellulose nanofibers; the concentration of the first aqueous solution of cellulose nanofibers is 0.01 to 2 wt%.

[0016] Preferably, the second mixing is a second mixing of hydroxyl-functionalized boron nitride with a second aqueous solution of cellulose nanofibers; the concentration of the second aqueous solution of cellulose nanofibers is 0.01-2 wt%.

[0017] Preferably, the preparation method of the hydroxyl-functionalized boron nitride includes the following steps: dispersing boron nitride nanosheets in concentrated sulfuric acid, adding hydrogen peroxide dropwise to perform hydroxyl modification, and obtaining hydroxyl-functionalized boron nitride.

[0018] Preferably, the solid-liquid ratio of BNNS-OH to concentrated sulfuric acid is 0.5–8 g: 10–120 mL; and the mass concentration of the concentrated sulfuric acid is ≥70%.

[0019] The solid-liquid ratio of BNNS-OH to hydrogen peroxide is 0.5–8 g: 5–80 mL;

[0020] The hydroxyl modification time is 1 to 12 hours.

[0021] This invention provides the application of the cellulose nanofiber-based electromagnetic shielding composite film described in the above technical solution or the cellulose nanofiber-based electromagnetic shielding composite film prepared by the above technical solution in electronic packaging, automotive or aerospace.

[0022] This invention provides a cellulose nanofiber-based electromagnetic shielding composite film (denoted as MXene / BNNS-OH / CNF composite film), comprising an MXene / CNF layer and a BNNS-OH / CNF layer located on the surface of the MXene / CNF layer; the MXene / CNF layer comprises a first cellulose nanofiber matrix and MXene doped in the first cellulose nanofiber matrix, wherein the mass fraction of MXene in the MXene / CNF layer is 5-90%; the BNNS-OH / CNF layer comprises a second cellulose nanofiber matrix and hydroxyl-functionalized boron nitride doped in the second cellulose nanofiber matrix; wherein the mass fraction of hydroxyl-functionalized boron nitride in the BNNS-OH / CNF layer is 5-90%. This invention uses MXene as a conductive and thermally conductive filler, BNNS-OH as a thermally conductive filler, and cellulose nanofibers (CNF) as a reinforcing matrix. By controlling the content of MXene and BNNS-OH, the cellulose nanofiber-based electromagnetic shielding composite film possesses both thermal conductivity and electromagnetic shielding properties, while also being lightweight. Furthermore, the thermal conductivity and electromagnetic shielding performance of the cellulose nanofiber-based electromagnetic shielding composite film are individually adjustable. The thermal conductivity of the cellulose nanofiber-based electromagnetic shielding composite film provided by this invention is increased from 1.2 W / (m·K) in the prior art to 8.6 W / (m·K), and the shielding effectiveness is increased from 1 dB to 68 dB, exhibiting excellent thermal conductivity and electromagnetic shielding performance.

[0023] The method for preparing cellulose nanofiber-based electromagnetic shielding composite film provided by this invention is simple to operate, has low production cost, is green and pollution-free, and is suitable for industrial production. Detailed Implementation

[0024] This invention provides a cellulose nanofiber-based electromagnetic shielding composite film, comprising an MXene / CNF layer and a BNNS-OH / CNF layer located on the surface of the MXene / CNF layer; the MXene / CNF layer comprises a first cellulose nanofiber matrix and MXene doped in the first cellulose nanofiber matrix, wherein the mass fraction of MXene in the MXene / CNF layer is 5-90%; the BNNS-OH / CNF layer comprises a second cellulose nanofiber matrix and hydroxyl-functionalized boron nitride doped in the second cellulose nanofiber matrix; wherein the mass fraction of hydroxyl-functionalized boron nitride in the BNNS-OH / CNF layer is 5-90%.

[0025] In this invention, the thickness of the MXene / CNF layer is preferably 10–200 μm, more preferably 50–150 μm, and even more preferably 100 μm. In this invention, the mass fraction of MXene in the MXene / CNF layer is preferably 10–70%, more preferably 35–60%; the thickness of the MXene is preferably 1–8 nm, more preferably 2–7 nm, and even more preferably 3–6 nm; the MXene is preferably few-layer MXene.

[0026] In this invention, the thickness of the BNNS-OH / CNF layer is preferably 10–200 μm, more preferably 50–150 μm, and even more preferably 100 μm. In this invention, the mass fraction of BNNS-OH in the BNNS-OH / CNF layer is preferably 10–60%, more preferably 15–50%.

[0027] This invention provides a method for preparing the cellulose nanofiber-based electromagnetic shielding composite film described in the above technical solution, comprising the following steps:

[0028] (1) Mix MXene, first cellulose nanofibers and water to obtain an MXene / CNF mixture; the mass of MXene is 5-90% of the total mass of the first cellulose nanofibers and MXene;

[0029] (2) Hydroxyfunctionalized boron nitride, second cellulose nanofibers and water are mixed to obtain BNNS-OH / CNF mixture; the mass of the hydroxyfunctionalized boron nitride is 5 to 90% of the total mass of the second cellulose nanofibers and hydroxyfunctionalized boron nitride.

[0030] (3) The MXene / CNF mixture is used to form a film to obtain an MXene / CNF layer;

[0031] (4) The BNNS-OH / CNF mixture is formed on the surface of the MXene / CNF layer to obtain a cellulose nanofiber-based electromagnetic shielding composite film.

[0032] Steps (1) and (2) are not in any particular order.

[0033] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0034] In this invention, MXene, first cellulose nanofibers, and water are first mixed to obtain an MXene / CNF mixture; the mass of MXene is 5-90% of the total mass of the first cellulose nanofibers and MXene.

[0035] In this invention, the concentration of the first cellulose nanofiber in the MXene / CNF mixture is preferably 0.1–2 wt%, more preferably 0.5–1.5 wt%, and even more preferably 0.6–1 wt%. In this invention, the mass of the MXene is preferably 5–80% of the total mass of the first cellulose nanofiber and MXene, more preferably 10–70%, and even more preferably 35–60%.

[0036] In this invention, the first mixing is preferably performed by dissolving the first cellulose nanofibers in water to obtain an aqueous solution of the first cellulose nanofibers; and then mixing MXene with the aqueous solution of the first cellulose nanofibers. In this invention, the concentration of the aqueous solution of the first cellulose nanofibers is preferably 0.01–2 wt%, more preferably 0.05–1.5 wt%, and even more preferably 0.1–1 wt%. In this invention, the temperature of the first mixing is preferably room temperature, and the time of the first mixing is preferably 0.1–12 h, more preferably 2–10 h.

[0037] In this invention, the preferred method for preparing MXene includes the following steps: mixing LiF, hydrochloric acid solution and Ti3AlC2, performing an etching reaction to obtain multilayer MXene; dispersing the multilayer MXene in water and centrifuging, and ultrasonically treating the resulting supernatant to obtain few-layer MXene.

[0038] This invention involves mixing LiF, hydrochloric acid solution, and Ti3AlC2, followed by an etching reaction to obtain multilayer MXene. In this invention, the mass ratio of LiF to Ti3AlC2 is preferably 1:0.05–8, more preferably 1:0.1–5, and even more preferably 1:0.5–2. In this invention, the concentration of the hydrochloric acid solution is preferably 1–12 mol / L, more preferably 2–10 mol / L, and even more preferably 3–8 mol / L. In this invention, the mass ratio of LiF to the amount of HCl dissolved in the hydrochloric acid is preferably 1 g:0.8–720 mmol, more preferably 1 g:10–500 mmol, and even more preferably 1 g:20–100 mmol. In this invention, the mixing is preferably performed by ultrasonically mixing LiF and hydrochloric acid solution, followed by adding Ti3AlC2 to the resulting mixture under ice bath conditions. In this invention, the ultrasonic mixing power is preferably 50-500W, more preferably 150-300W; the ultrasonic mixing temperature is preferably room temperature; and the ultrasonic mixing time is preferably 1-60 min, more preferably 10-20 min. In this invention, the addition rate of Ti3AlC2 is preferably 0.3-3 g / min, more preferably 0.5-2 g / min. In this invention, the etching reaction temperature is preferably 15-60℃, more preferably 20-50℃, and further preferably 30-40℃; and the etching reaction time is preferably 12-96 h, more preferably 15-80 h, and further preferably 20-50 h. After the etching reaction, this invention preferably further includes washing the obtained etching product with water until neutral to obtain multilayer MXene.

[0039] After obtaining multilayer MXene, the present invention disperses the multilayer MXene in water and centrifuges it. The resulting supernatant is then ultrasonically treated to obtain a few-layer MXene. In the present invention, the solid-liquid ratio of the multilayer MXene (based on Ti3AlC2) to water is preferably 1g:8-300mL, more preferably 1g:12.5-100mL. In the present invention, the centrifugation speed is preferably 1000-10000rpm, more preferably 3500-5500rpm, and the centrifugation time is preferably 1-60min, more preferably 2-10min; the purpose of centrifugation is to remove unetched Ti3AlC2. In this invention, the power of the ultrasonic treatment is preferably 10-900W, more preferably 200-400W; the ultrasonic treatment is preferably performed under ice bath conditions; the ultrasonic treatment time is preferably 1-120min, more preferably 5-30min; the ultrasonic treatment is preferably performed under inert gas protection, the inert gas being preferably helium or argon; the ultrasonic treatment is preferably performed using a cell disruptor; the purpose of the ultrasonic treatment is to peel off multilayer MXene to obtain few-layer MXene. In this invention, after the ultrasonic treatment, the invention preferably further includes centrifuging the obtained ultrasonic treatment system, filtering the obtained supernatant, and freeze-drying the obtained liquid component to obtain a few-layer MXene; the centrifugation speed is preferably 1000-10000 rpm, more preferably 3500-5500 rpm, the centrifugation time is preferably 5-240 min, more preferably 30-120 min; the freeze-drying temperature is preferably -60--20℃, more preferably -50--30℃; the freeze-drying pressure is preferably 0.1-100 Pa, more preferably 1-50 Pa; the freeze-drying time is preferably 24-72 h, more preferably 30-50 h.

[0040] This invention involves mixing hydroxyl-functionalized boron nitride, second cellulose nanofibers, and water to obtain a BNNS-OH / CNF mixture; the mass of the hydroxyl-functionalized boron nitride is 5-90% of the total mass of the second cellulose nanofibers and hydroxyl-functionalized boron nitride.

[0041] In this invention, the concentration of the second cellulose nanofiber in the BNNS-OH / CNF mixture is preferably 0.1–2 wt%, more preferably 0.5–1.5 wt%, and even more preferably 0.6–1 wt%. In this invention, the mass of the BNNS-OH is preferably 5–80% of the total mass of the second cellulose nanofiber and BNNS-OH, more preferably 10–60%, and even more preferably 15–50%.

[0042] In this invention, the second mixing is preferably performed by dissolving the second cellulose nanofibers in water to obtain an aqueous solution of the second cellulose nanofibers; and then mixing BNNS-OH with the aqueous solution of the second cellulose nanofibers. In this invention, the concentration of the aqueous solution of the second cellulose nanofibers is preferably 0.01–2 wt%, more preferably 0.05–1.5 wt%, and even more preferably 0.1–1 wt%. In this invention, the temperature of the second mixing is preferably room temperature, and the time of the second mixing is preferably 0.1–12 h, more preferably 2–10 h.

[0043] In this invention, the preparation method of BNNS-OH preferably includes the following steps: dispersing boron nitride nanosheets in concentrated sulfuric acid, and adding hydrogen peroxide dropwise for hydroxyl modification to obtain BNNS-OH. In this invention, the solid-liquid ratio of BNNS-OH to concentrated sulfuric acid is preferably 0.5–8 g: 10–120 mL, more preferably 1–7 g: 20–100 mL, and even more preferably 2–6 g: 30–80 mL; the mass concentration of the concentrated sulfuric acid is preferably ≥70%, more preferably 70–98%, and even more preferably 90–98%. In this invention, the dropping rate of the hydrogen peroxide is preferably 1–3 drops / second, more preferably 2 drops / second. In this invention, the solid-liquid ratio of BNNS-OH to hydrogen peroxide is preferably 0.5–8 g: 5–80 mL, more preferably 1–7 g: 10–70 mL, and even more preferably 2–6 g: 10–60 mL. In this invention, the temperature for hydroxyl modification is preferably room temperature, and the time for hydroxyl modification is preferably 1–12 h, more preferably 2–10 h, and even more preferably 3–5 h. After hydroxyl modification, this invention preferably further includes: filtering the obtained hydroxyl-modified reaction solution, washing the obtained solid component with water until neutral, and then drying it to obtain BNNS-OH. In this invention, the drying temperature is preferably 40–90 °C, more preferably 50–80 °C, and the drying time is preferably 8–36 h, more preferably 10–20 h.

[0044] After obtaining the MXene / CNF mixture, the present invention forms a film from the MXene / CNF mixture to obtain an MXene / CNF layer. In the present invention, the film formation method is preferably vacuum filtration, and the vacuum filtration is preferably vacuum-assisted filtration; the vacuum degree of the vacuum filtration is preferably 0.2-2 kPa, more preferably 0.5-1.5 kPa, and even more preferably 0.5-1 kPa; the filtration time is preferably 1-36 h, more preferably 2-30 h, and even more preferably 5-20 h.

[0045] After obtaining the NNS-OH / CNF mixture and the MXene / CNF layer, the present invention forms a film of the NNS-OH / CNF mixture on the surface of the MXene / CNF layer to obtain a cellulose nanofiber-based electromagnetic shielding composite membrane. In this invention, the preferred method for film formation is vacuum filtration, and the preferred method is vacuum-assisted filtration; the vacuum degree of the filtration is preferably 0.2–2 kPa, more preferably 0.5–1.5 kPa, and even more preferably 0.5–1 kPa; the preferred filtration time is 1–36 h, more preferably 2–30 h, and even more preferably 5–20 h.

[0046] This invention provides the application of the cellulose nanofiber-based electromagnetic shielding composite film described in the above technical solution or the cellulose nanofiber-based electromagnetic shielding composite film prepared by the above technical solution in electronic packaging, automotive or aerospace.

[0047] To further illustrate the present invention, the cellulose nanofiber-based electromagnetic shielding composite film, its preparation method, and its application are described in detail below with reference to embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0048] Example 1

[0049] Preparation of 80wt% MXene / 10wt% BNNS-OH / CNF composite membrane

[0050] (a) Add 2 mol / L HCl solution to a tetrafluoroethylene beaker, then add LiF, sonicate at room temperature and 200W for 20 min, then slowly add Ti3AlC2 at 1 g / min under ice bath, react at 35℃ for 72 h, centrifuge at 3000 rpm for 5 min, wash with deionized water until the pH of the solution is neutral, then disperse the obtained multilayer MXene in deionized water, centrifuge the obtained multilayer MXene aqueous dispersion at 3500 rpm for 5 min, take the supernatant and sonicate with a cell disruptor at room temperature and 300W for 30 min under inert gas and ice bath conditions to peel off the multilayer MXene, centrifuge at 5500 rpm for 60 min, take the supernatant, filter and freeze dry at -60℃ and 1 Pa for 72 h to obtain a few-layer MXene with a thickness of 2 nm. The ratio of LiF, HCl and Ti3AlC2 is 3g:60mmol:4g, and the ratio of multilayer MXene (calculated as Ti3AlC2) to deionized water in the multilayer MXene aqueous dispersion is 4g:50mL.

[0051] (b) Boron nitride nanosheets were dispersed in 80 wt% concentrated sulfuric acid, and hydrogen peroxide was slowly added at a rate of 2 drops / second. The mixture was stirred at room temperature for 4 h, filtered, and the resulting solid component was washed with water until neutral. The solid was then dried at 50 °C for 26 h to obtain BNNS-OH. The ratio of boron nitride nanosheets, concentrated sulfuric acid, and hydrogen peroxide was 1 g: 30 mL: 10 mL.

[0052] (c) A few-layer MXene was mixed with a 0.1 wt% aqueous solution of cellulose nanofibers and stirred for 2 h. The mixture was then vacuum-assisted filtered for 6 h at 200 Pa to obtain an 80 wt% MXene / CNF layer. The mass ratio of few-layer MXene to cellulose nanofibers was 8:2.

[0053] (d) BNNS-OH was mixed with a 0.1 wt% aqueous solution of cellulose nanofibers and stirred for 2 h. The resulting BNNS-OH / CNF mixture was placed on the surface of the MXene / CNF layer and vacuum-assisted filtration was performed at 300 Pa for 8 h to form a 30 wt% BNNS-OH / CNF layer, thus obtaining a cellulose nanofiber-based electromagnetic shielding composite membrane (denoted as 80 wt% MXene / 10 wt% BNNS-OH / CNF composite membrane). The mass ratio of BNNS-OH to cellulose nanofibers was 1:9; the mass ratio of the few-layer MXene in step (c) to BNNS-OH in step (d) was 8:1.

[0054] The prepared 80wt% MXene / 10wt% BNNS-OH / CNF composite film has a conductivity of 6.7 W / (m·k) and a shielding effectiveness of 68 dB.

[0055] Example 2

[0056] Preparation of 10wt% MXene / 80wt% BNNS-OH / CNF composite membrane

[0057] (a) Add 4 mol / L HCl solution to a tetrafluoroethylene beaker, then add LiF, sonicate at room temperature and 200 W for 20 min, then slowly add Ti3AlC2 at 3 g / min under ice bath, react at 55 °C for 36 h, centrifuge at 2000 rpm for 8 min, then wash with deionized water until the pH of the solution is neutral, then disperse the obtained multilayer MXene in deionized water, centrifuge the obtained multilayer MXene aqueous dispersion at 5000 rpm for 2 min, take the supernatant and sonicate it for 20 min at room temperature and 400 W under inert gas and ice bath conditions using a cell disruptor to peel off the multilayer MXene, centrifuge at 4000 rpm for 120 min, take the supernatant, filter and freeze dry at -50 °C and 0.8 Pa for 48 h to obtain a few-layer MXene with a thickness of 4 nm. The ratio of LiF, HCl and Ti3AlC2 is 2g:160mmol:2g. The ratio of multilayer MXene (calculated as Ti3AlC2) to deionized water in the multilayer MXene aqueous dispersion is 2g:200mL.

[0058] (b) Boron nitride nanosheets were dispersed in 90 wt% concentrated sulfuric acid, and hydrogen peroxide was slowly added at a rate of 3 drops / second. The mixture was stirred at room temperature for 6 h, filtered, and the resulting solid component was washed with water until neutral. The solid was then dried at 60 °C for 26 h to obtain BNNS-OH. The ratio of boron nitride nanosheets, concentrated sulfuric acid, and hydrogen peroxide was 2 g: 50 mL: 10 mL.

[0059] (c) A few-layer MXene was mixed with a 0.5 wt% cellulose nanofiber aqueous solution and stirred for 4 h. The mixture was then vacuum-assisted filtered for 12 h at 500 Pa to obtain a 50 wt% MXene / CNF layer. The volume ratio of few-layer MXene:deionized water:4 wt% cellulose nanofiber aqueous solution was 20 mg:10 mL:40 mL. The mass ratio of few-layer MXene to cellulose nanofibers was 1:1.

[0060] (d) BNNS-OH was mixed with a 0.5 wt% aqueous solution of cellulose nanofibers and stirred for 4 h. The resulting BNNS-OH / CNF mixture was placed on the surface of the MXene / CNF layer and vacuum-assisted filtration was performed at 100 Pa for 16 h to form a 50 wt% BNNS-OH / CNF layer, thus obtaining a cellulose nanofiber-based electromagnetic shielding composite membrane (denoted as 10 wt% MXene / 80 wt% BNNS-OH / CNF composite membrane). The mass ratio of BNNS-OH to cellulose nanofibers was 1:8. The mass ratio of the few-layer MXene in step (c) to BNNS-OH in step (d) was 1:8.

[0061] The prepared 10wt% MXene / 80wt% BNNS-OH / CNF composite film has a conductivity of 8.6 W / (m·k) and a shielding effectiveness of 17 dB.

[0062] Example 3

[0063] Preparation of 10wt% MXene / 20wt% BNNS-OH / CNF composite membrane

[0064] (a) 9 mol / L HCl solution was added to a tetrafluoroethylene beaker, followed by LiF. After sonication at 300 W for 20 min at room temperature, Ti3AlC2 was slowly added at 1 g / min under ice bath conditions. The reaction was carried out at 35 °C for 24 h, centrifuged at 3000 rpm for 5 min, and then washed with deionized water until the pH of the solution was neutral. The resulting multilayer MXene was then dispersed in deionized water. The resulting multilayer MXene aqueous dispersion was centrifuged at 3500 rpm for 10 min. The supernatant was taken and sonicated at 300 W for 10 min under inert gas and ice bath conditions using a cell disruptor at room temperature to peel off the multilayer MXene. The dispersion was centrifuged at 4500 rpm for 30 min, the supernatant was filtered, and then freeze-dried at -60 °C and 0.8 Pa for 24 h to obtain a few-layer MXene with a thickness of 4 nm. The ratio of LiF, HCl and Ti3AlC2 is 3.6g:360mmol:2g, and the ratio of multilayer MXene (calculated as Ti3AlC2) to deionized water in the multilayer MXene aqueous dispersion is 2g:100mL.

[0065] (b) Boron nitride nanosheets were dispersed in 70 wt% concentrated sulfuric acid, and hydrogen peroxide was slowly added at a rate of 1 drop / second. The mixture was stirred at room temperature for 4 h, filtered, and the resulting solid component was washed with water until neutral. The solid component was then dried at 70 °C for 8–15 h to obtain BNNS-OH. The ratio of boron nitride nanosheets, concentrated sulfuric acid, and hydrogen peroxide was 4 g: 60 mL: 30 mL.

[0066] (c) A few-layer MXene was mixed with a 1 wt% aqueous solution of cellulose nanofibers and stirred for 4 h. The mixture was then vacuum-assisted filtered at 100 Pa for 30 h to obtain a 10 wt% MXene / CNF layer. The mass ratio of few-layer MXene to cellulose nanofibers was 1:9.

[0067] (d) BNNS-OH was mixed with a 1 wt% aqueous solution of cellulose nanofibers and stirred for 4 h. The resulting BNNS-OH / CNF mixture was placed on the surface of the MXene / CNF layer and vacuum-assisted filtration was performed at 100 Pa for 16 h to form a 20 wt% BNNS-OH / CNF layer, thus obtaining a cellulose nanofiber-based electromagnetic shielding composite membrane (denoted as 10 wt% MXene / 20 wt% BNNS-OH / CNF composite membrane). The mass ratio of BNNS-OH to cellulose nanofibers was 2:8; the mass ratio of the few-layer MXene in step (c) to BNNS-OH in step (d) was 1:2.

[0068] The prepared 10wt% MXene / 20wt% BNNS-OH / CNF composite film has a conductivity of 5.6 W / (m·k) and a shielding effectiveness of 24 dB.

[0069] Example 4

[0070] Preparation of 35wt% MXene / 15wt% BNNS-OH / CNF composite membrane

[0071] (a) Add 9 mol / L HCl solution to a tetrafluoroethylene beaker, then add LiF, sonicate at room temperature and 200W for 20 min, then slowly add Ti3AlC2 at 2 g / min under ice bath, react at 35℃ for 48 h, centrifuge at 3000 rpm for 5 min, wash with deionized water until the pH of the solution is neutral, then disperse the obtained multilayer MXene in deionized water, centrifuge the obtained multilayer MXene aqueous dispersion at 5500 rpm for 5 min, take the supernatant and sonicate it for 5 min at room temperature and 200W using a cell disruptor under inert gas and ice bath conditions to peel off the multilayer MXene, centrifuge at 3500 rpm for 60 min, take the supernatant, filter and freeze dry at -50℃ and 10 Pa for 8 h to obtain a few-layer MXene with a thickness of 6 nm. The ratio of LiF, HCl and Ti3AlC2 is 4g:360mmol:2g, and the ratio of multilayer MXene (calculated as Ti3AlC2) to deionized water in the multilayer MXene aqueous dispersion is 2g:200mL.

[0072] (b) Boron nitride nanosheets were dispersed in 60 wt% concentrated sulfuric acid, and hydrogen peroxide was slowly added at a rate of 2 drops / second. The mixture was stirred at room temperature for 4 h, filtered, and the resulting solid component was washed with water until neutral. It was then dried at 40 °C for 24 h to obtain BNNS-OH. The ratio of boron nitride nanosheets, concentrated sulfuric acid, and hydrogen peroxide was 5 g: 50 mL: 40 mL.

[0073] (c) MXene was mixed with a 0.1 wt% aqueous solution of cellulose nanofibers and stirred for 10 h, then vacuum-assisted filtered for 10 h at 100 Pa to obtain a 35 wt% MXene / CNF layer. The mass ratio of MXene to cellulose nanofibers in the few-layer layer was 35:65.

[0074] (d) BNNS-OH was mixed with a 0.1 wt% aqueous solution of cellulose nanofibers and stirred for 10 h. The resulting BNNS-OH / CNF mixture was placed on the surface of the MXene / CNF layer and vacuum-assisted filtration was performed at 300 Pa for 10 h to form a 15 wt% BNNS-OH / CNF layer, thus obtaining a cellulose nanofiber-based electromagnetic shielding composite membrane (denoted as 35 wt% MXene / 15 wt% BNNS-OH / CNF composite membrane). The mass ratio of BNNS-OH to cellulose nanofibers was 15:85; the mass ratio of the few-layer MXene in step (c) to BNNS-OH in step (d) was 7:3.

[0075] The obtained 35wt% MXene / 15wt% BNNS-OH / CNF composite film has a conductivity of 6.1 W / (m·k) and a shielding effectiveness of 43 dB.

[0076] Comparative Example 1

[0077] Preparation of 2.5wt% MXene / 2.5wt% BNNS-OH / CNF composite membrane

[0078] (a) Add 4 mol / L HCl solution to a tetrafluoroethylene beaker, then add LiF, sonicate for 20 min at room temperature and 200 W, then slowly add Ti3AlC2 at 3 g / min under ice bath, react at 35 °C for 36 h, centrifuge at 4000 rpm for 6 min, wash with deionized water until the pH of the solution is neutral, then disperse the obtained multilayer MXene in deionized water, centrifuge the obtained multilayer MXene aqueous dispersion at 5000 rpm for 5 min, take the supernatant and sonicate for 20 min at room temperature and 300 W using a cell disruptor under inert gas and ice bath conditions to peel off the multilayer MXene, centrifuge at 4000 rpm for 120 min, take the supernatant, filter and freeze dry at -50 °C and 0.7 Pa for 40 h to obtain a few-layer MXene with a thickness of 4 nm. The ratio of LiF, HCl and Ti3AlC2 is 3g:120mmol:2g, and the ratio of multilayer MXene (calculated as Ti3AlC2) to deionized water in the multilayer MXene aqueous dispersion is 2g:200mL.

[0079] (b) Boron nitride nanosheets were dispersed in 70 wt% concentrated sulfuric acid, and hydrogen peroxide was slowly added at a rate of 2 drops / second. The mixture was stirred at room temperature for 9 h, filtered, and the resulting solid component was washed with water until neutral. It was then dried at 50 °C for 27 h to obtain BNNS-OH. The ratio of boron nitride nanosheets, concentrated sulfuric acid, and hydrogen peroxide was 3 g: 50 mL: 15 mL.

[0080] (c) A few-layer MXene was mixed with a 0.5 wt% aqueous solution of cellulose nanofibers and stirred for 4 h. The mixture was then vacuum-assisted filtered for 26 h at 200 Pa to obtain a 2.5 wt% MXene / CNF layer. The mass ratio of few-layer MXene to cellulose nanofibers was 2.5:97.5.

[0081] (d) BNNS-OH was mixed with a 0.5 wt% aqueous solution of cellulose nanofibers and stirred for 4 h. The resulting BNNS-OH / CNF mixture was placed on the surface of the MXene / CNF layer and vacuum-assisted filtration was performed at 300 Pa for 25 h to form a 2.5 wt% BNNS-OH / CNF layer, thus obtaining a cellulose nanofiber-based electromagnetic shielding composite membrane (denoted as 2.5 wt% MXene / 2.5 wt% BNNS-OH / CNF composite membrane). The mass ratio of BNNS-OH to cellulose nanofibers was 2.5:97.5; the mass ratio of the few-layer MXene in step (c) to BNNS-OH in step (d) was 1:1.

[0082] The prepared 2.5wt% MXene / 2.5wt% BNNS-OH / CNF composite film has a conductivity of 2.1 W / (m·k) and a shielding effectiveness of 8 dB.

[0083] Comparative Example 2

[0084] Preparation of 1.5wt% MXene / 3.5wt% BNNS-OH / CNF composite membrane

[0085] (a) Add 4 mol / L HCl solution to a tetrafluoroethylene beaker, then add LiF, sonicate at room temperature and 400W for 20 min, then slowly add Ti3AlC2 at 2 g / min under ice bath conditions, react at 45℃ for 36 h, centrifuge at ... rpm for 8 min, wash with deionized water until the pH of the solution is neutral, then disperse the obtained multilayer MXene in deionized water, centrifuge the obtained multilayer MXene aqueous dispersion at 4000 rpm for 5 min, take the supernatant and sonicate it for 20 min at room temperature and 300W under inert gas and ice bath conditions using a cell disruptor to peel off the multilayer MXene, centrifuge at 3000 rpm for 60 min, take the supernatant, filter and freeze dry at -60℃ and 5Pa for 40 h to obtain a few-layer MXene with a thickness of 3 nm. The ratio of LiF, HCl and Ti3AlC2 is 5g:120mmol:3g. The ratio of multilayer MXene (calculated as Ti3AlC2) to deionized water in the multilayer MXene aqueous dispersion is 3g:200mL.

[0086] (b) Boron nitride nanosheets were dispersed in 90 wt% concentrated sulfuric acid, and hydrogen peroxide was slowly added at a rate of 3 drops / second. The mixture was stirred at room temperature for 4 h, filtered, and the resulting solid component was washed with water until neutral. It was then dried at 50 °C for 30 h to obtain BNNS-OH. The ratio of boron nitride nanosheets, concentrated sulfuric acid, and hydrogen peroxide was 2 g: 50 mL: 35 mL.

[0087] (c) A few-layer MXene was mixed with a 0.5 wt% aqueous solution of cellulose nanofibers and stirred for 4 h. The mixture was then vacuum-assisted filtered at 400 Pa for 9 h to obtain a 1.5 wt% MXene / CNF layer. The mass ratio of few-layer MXene to cellulose nanofibers was 1.5:98.5.

[0088] (d) BNNS-OH was mixed with a 0.5 wt% aqueous solution of cellulose nanofibers and stirred for 4 h. The resulting BNNS-OH / CNF mixture was placed on the surface of the MXene / CNF layer and vacuum-assisted filtration was performed at 300 Pa for 24 h to form a 3.5 wt% BNNS-OH / CNF layer, thus obtaining a cellulose nanofiber-based electromagnetic shielding composite membrane (denoted as 1.5 wt% MXene / 3.5 wt% BNNS-OH / CNF composite membrane). The mass ratio of BNNS-OH to cellulose nanofibers was 3.5:96.5; the mass ratio of the few-layer MXene in step (c) to BNNS-OH in step (d) was 3:7.

[0089] The prepared 1.5wt% MXene / 3.5wt% BNNS-OH / CNF composite film has a conductivity of 2.4 W / (m·k) and a shielding effectiveness of 5 dB.

[0090] Comparative Example 3

[0091] Preparation of 4wt% MXene / 2wt% BNNS-OH / CNF composite membrane

[0092] (a) Add 9 mol / L HCl solution to a tetrafluoroethylene beaker, then add LiF, sonicate at room temperature and 300W for 20 min, then slowly add Ti3AlC2 at 4 g / min under ice bath, react at 45℃ for 36 h, centrifuge at 4000 rpm for 7 min, wash with deionized water until the pH of the solution is neutral, then disperse the obtained multilayer MXene in deionized water, centrifuge the obtained multilayer MXene aqueous dispersion at 3000 rpm for 5 min, take the supernatant and sonicate it for 10 min at room temperature and 300W using a cell disruptor under inert gas and ice bath conditions to peel off the multilayer MXene, centrifuge at 3000 rpm for 60 min, take the supernatant, filter and freeze dry at -50℃ and 10 Pa for 27 h to obtain a few-layer MXene with a thickness of 4 nm. The ratio of LiF, HCl and Ti3AlC2 is 5g:360mmol:5g. The ratio of multilayer MXene (calculated as Ti3AlC2) to deionized water in the multilayer MXene aqueous dispersion is 5g:200mL.

[0093] (b) Boron nitride nanosheets were dispersed in 80 wt% concentrated sulfuric acid, and hydrogen peroxide was slowly added at a rate of 2 drops / second. The mixture was stirred at room temperature for 5 h, filtered, and the resulting solid component was washed with water until neutral. The solid component was then dried at 50 °C for 24 h to obtain BNNS-OH. The ratio of boron nitride nanosheets, concentrated sulfuric acid, and hydrogen peroxide was 4 g: 50 mL: 35 mL.

[0094] (c) A few-layer MXene was mixed with a 0.1 wt% aqueous solution of cellulose nanofibers and stirred for 4 h. The mixture was then vacuum-assisted filtered at 300 Pa for 20 h to obtain a 4 wt% MXene / CNF layer. The mass ratio of few-layer MXene to cellulose nanofibers was 4:96.

[0095] (d) BNNS-OH was mixed with a 0.1 wt% aqueous solution of cellulose nanofibers and stirred for 4 h. The resulting BNNS-OH / CNF mixture was placed on the surface of the MXene / CNF layer and vacuum-assisted filtration was performed at 300 Pa for 27 h to form a 2 wt% BNNS-OH / CNF layer, thus obtaining a cellulose nanofiber-based electromagnetic shielding composite membrane (denoted as 4 wt% MXene / 2 wt% BNNS-OH / CNF composite membrane). The mass ratio of BNNS-OH to cellulose nanofibers was 2:98; the mass ratio of the few-layer MXene in step (c) to BNNS-OH in step (d) was 1:0.5.

[0096] The prepared 4wt% MXene / 2wt% BNNS-OH / CNF composite film has a conductivity of 2.7 W / (m·k) and a shielding effectiveness of 9 dB.

[0097] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A cellulose nanofiber-based electromagnetic shielding composite membrane, characterized in that, The MXene / CNF layer comprises an MXene / CNF layer and a BNNS-OH / CNF layer located on the surface of the MXene / CNF layer. The MXene / CNF layer comprises a first cellulose nanofiber matrix and MXene doped in the first cellulose nanofiber matrix, wherein the mass fraction of MXene in the MXene / CNF layer is 5-90%. The BNNS-OH / CNF layer comprises a second cellulose nanofiber matrix and hydroxyl-functionalized boron nitride doped in the second cellulose nanofiber matrix, wherein the mass fraction of hydroxyl-functionalized boron nitride in the BNNS-OH / CNF layer is 5-90%.

2. The cellulose nanofiber-based electromagnetic shielding composite membrane according to claim 1, characterized in that, The thickness of the MXene / CNF layer is 10~200μm.

3. The cellulose nanofiber-based electromagnetic shielding composite membrane according to claim 1 or 2, characterized in that, The thickness of the MXene is 1~8nm.

4. The cellulose nanofiber-based electromagnetic shielding composite membrane according to claim 1, characterized in that, The thickness of the BNNS-OH / CNF layer is 10~200μm.

5. The method for preparing the cellulose nanofiber-based electromagnetic shielding composite film according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Mix MXene, first cellulose nanofibers and water to obtain an MXene / CNF mixture; the mass of MXene is 5-90% of the total mass of the first cellulose nanofibers and MXene; (2) Hydroxyfunctionalized boron nitride, second cellulose nanofibers and water are mixed to obtain BNNS-OH / CNF mixture; the mass of the hydroxyfunctionalized boron nitride is 5-90% of the total mass of the second cellulose nanofibers and hydroxyfunctionalized boron nitride. (3) The MXene / CNF mixture is used to form a film to obtain an MXene / CNF layer; (4) The BNNS-OH / CNF mixture is formed on the surface of the MXene / CNF layer to obtain a cellulose nanofiber-based electromagnetic shielding composite film; Steps (1) and (2) are not in any particular order.

6. The preparation method according to claim 5, characterized in that, The first mixing involves mixing MXene with a first aqueous solution of cellulose nanofibers; the concentration of the first aqueous solution of cellulose nanofibers is 0.01~2wt%.

7. The preparation method according to claim 5, characterized in that, The second mixing involves mixing hydroxyl-functionalized boron nitride with a second aqueous solution of cellulose nanofibers; the concentration of the second aqueous solution of cellulose nanofibers is 0.01~2wt%.

8. The preparation method according to claim 5 or 7, characterized in that, The preparation method of the hydroxyl-functionalized boron nitride includes the following steps: dispersing boron nitride nanosheets in concentrated sulfuric acid, adding hydrogen peroxide dropwise to modify the hydroxyl groups, and obtaining hydroxyl-functionalized boron nitride.

9. The preparation method according to claim 8, characterized in that, The solid-liquid ratio of BNNS-OH to concentrated sulfuric acid is 0.5~8g:10~120mL; the mass concentration of the concentrated sulfuric acid is ≥70%. The solid-liquid ratio of BNNS-OH to hydrogen peroxide is 0.5~8g:5~80mL; The hydroxyl modification time is 1~12h.

10. The application of the cellulose nanofiber-based electromagnetic shielding composite film according to any one of claims 1 to 4 or the cellulose nanofiber-based electromagnetic shielding composite film prepared by the preparation method according to any one of claims 5 to 9 in electronic packaging, automotive or aerospace.