A self-reinforced lignin-containing nanocellulose film and preparation method thereof

Abstract

The present invention relates to a self-reinforced nanocellulose film containing lignin and a preparation method thereof. The film formula includes 60-95% cellulose, 10-30% lignin, and 0%-10% hemicellulose in weight percentage. The method includes pre-treating plant fiber raw materials with mild alkali and mechanical grinding, washing the treated raw materials with water to neutrality to obtain a nanocellulose suspension raw material containing lignin, at which time the lignin is unevenly distributed, the structure is inconsistent, and the reinforcing effect of the nanocellulose film is poor; reconstructing the structure and distribution of lignin by a lignin dissolution-regeneration method, the particle structure is stable after lignin regeneration, washing to neutrality to obtain a well-dispersed nanocellulose suspension containing reconstructed lignin, and vacuum filtering and drying after diluting the suspension to prepare a self-reinforced nanocellulose film material containing lignin. The present invention effectively enhances the strength and toughness of the nanocellulose film containing lignin.

Description

Technical Field

[0001] The invention belongs to the field of biomass-based materials and nano-composite materials, and specifically relates to a self-reinforced lignin-containing nano-cellulose film and a preparation method thereof. Background Art

[0002] Nanocellulose is regarded as a potential substitute for traditional petroleum-based materials due to its abundant sources, biodegradability, low environmental impact and excellent mechanical properties. Nanocellulose membranes have good mechanical strength, light weight, porous structure and good biocompatibility, which makes them show great application prospects in packaging, filtration, biomedicine, electronic devices and other fields.

[0003] As an abundant biomass resource in nature, lignin has shown significant advantages in the application of nanocellulose materials. Lignin can not only enhance the mechanical properties of nanocellulose materials, but also give the materials certain antioxidant and UV shielding properties. Due to the hydrophobicity and high thermal stability of lignin, compounding it with nanocellulose can help improve the strength, heat resistance and stability of the material in a humid environment. However, there are some disadvantages of lignin in the process of enhancing nanocellulose materials that cannot be ignored. First, there is a significant difference between the hydrophobicity of lignin and the hydrophilicity of nanocellulose. This interfacial incompatibility will lead to a decrease in the performance of the composite material, such as the material structure may become uneven, which in turn affects the mechanical properties and stability. Secondly, the molecular structure of lignin is complex and changeable. The chemical composition and physical properties of lignin extracted from different plants or different processes are quite different, resulting in the instability of the performance of the composite material and increasing the difficulty of process control. In addition, lignin is often difficult to disperse evenly in the material, especially when the lignin content is high, it is easy to agglomerate, which will further reduce the overall performance of the material.

[0004] At present, in the research of lignin-enhanced nanocellulose materials, the enhancement method is mostly a blending composite method, that is, by directly mixing lignin with nanocellulose, the mechanical strength and thermal stability of the material can be significantly improved. For example, patent CN112876744A discloses a method for enhancing the mechanical properties of nanocellulose membranes using lignin sulfonate, which is to hydrothermally react a mixed dispersion of nanocellulose and lignin sulfonate, and the hydrothermal reaction product is washed and filtered to obtain a sodium lignin sulfonate-modified nanocellulose composite membrane. The principle is to modify the nanocellulose membrane using lignin sulfonate to improve its mechanical properties. However, this type of method has complicated steps and high costs, and the lignin contained in the wood fiber raw material itself is not utilized, resulting in a waste of resources of the original component. The present invention utilizes the lignin contained in the wood fiber raw material itself, reconstructs its structure and distribution, and can prepare a self-enhanced nanocellulose membrane containing lignin, which fully and efficiently utilizes the original components of the wood fiber raw material, and saves energy consumption costs and time costs to a great extent. The mechanical properties of the self-reinforced lignin-containing nanocellulose membrane prepared by the present invention are significantly improved, which not only fully exerts the ultraviolet shielding, anti-oxidation and other functions of lignin, but also can give the material hydrophobic, heavy metal adsorption and other properties according to different lignin reconstruction methods. Summary of the invention

[0005] In order to solve the challenges of low component utilization and complex preparation methods in the prior art, the purpose of the present invention is to provide a method for preparing a self-reinforced lignin-containing nanocellulose film to enhance the mechanical properties of the nanocellulose film and improve its application potential in packaging, construction, biomedicine, etc.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, a method for preparing a self-reinforced lignin-containing nanocellulose film comprises the following steps:

[0008] (1) treating the plant fiber raw material with alkali-assisted mechanical grinding, washing with water until neutral, and obtaining a nanocellulose suspension containing lignin;

[0009] (2) dissolving and regenerating lignin in the suspension obtained in step (1), reconstructing the distribution and structure of lignin, and washing with water until neutrality, thereby obtaining a nanocellulose suspension containing reconstructed lignin;

[0010] (3) The suspension in step (2) is prepared into a certain proportion, and vacuum filtered and dried to obtain a self-reinforced lignin-containing nanocellulose film.

[0011] Furthermore, the alkali is one or a mixture of two or more of sodium hydroxide, potassium hydroxide and calcium hydroxide, and the mass concentration of the alkali solution is 0.05%-2% (preferably 0.1%-1%, more preferably 0.3%-0.5%);

[0012] When the plant fiber raw material is 5 g, the usage amount is 60-200 g, preferably 80-120 g, and more preferably 90-110 g.

[0013] Furthermore, the grinding equipment used in the mechanical method includes: one or more of a planetary ball mill, a hybrid ball mill, a vibrating ball mill, a self-mortar grinder or a horizontal rolling ball mill; the mechanical grinding time is 1-10 hours (preferably 2-6 hours, more preferably 2-4 hours), and the grinding speed is 100-1000rpm (preferably 300-700rpm, more preferably 500-600rpm).

[0014] Furthermore, the plant fiber raw material is a mixture of roots, stems, leaves of one or more plants selected from trees, shrubs, vines, grasses, ferns, etc., and one or more industrial biomass wastes such as furfural residue, xylose residue (the residue obtained by producing xylose from one or more plants selected from corn cobs, plant straws, etc.), and sugarcane bagasse.

[0015] Furthermore, the method of washing to neutrality is one or a combination of two or more methods such as filtration, centrifugation, and decantation;

[0016] The suspension in step (1) is an aqueous solution with a mass fraction of 0.1%wt-5%wt (preferably 0.5%wt-5wt%, more preferably 1%wt-3%wt).

[0017] Furthermore, the lignin dissolution-regeneration method is an acid precipitation method, an organic solvent method, a sulfate method, or a combination of two or more thereof;

[0018] The acid used in the acid precipitation method includes one or a combination of two or more of hydrochloric acid, sulfuric acid, lactic acid, etc., the acid concentration is 1mmol / L-10 mol / L (preferably 1mmol / L-1 mol / L, more preferably 10mmol / L-50mmol / L), the acid precipitation titration time is 3-20 min (preferably 5-15 min, more preferably 8-12 min), and the system pH after acid titration is 1-7 (preferably pH=2-6, more preferably pH=3-5);

[0019] The solvent used in the organic solvent method is one or a combination of two or more of acetone, ethyl acetate, methanol, etc. When the plant fiber raw material is 2 g, the amount thereof is 5-20 g (preferably 8-15 g, more preferably 10-12 g), and the treatment time is 1-6 h (preferably 2-5 h, more preferably 3-4 h);

[0020] The reagents used in the sulfate method are sodium sulfite, sodium bisulfite, calcium bisulfite or a combination of two or more thereof. When the plant fiber raw material is 1 g, the dosage is 0.05-0.5 g (preferably 0.05-0.25 g, more preferably 0.1-0.2 g), and the treatment time is 0.5-5 h (preferably 1-4 h, more preferably 2-3 h).

[0021] Furthermore, the dilution solvent in step (3) is water, ethanol, tert-butanol, or a mixture of two or more thereof, and the mass fraction of the diluted suspension is 0.1‰wt-5‰wt (preferably 0.5‰wt-5‰wt, more preferably 1‰wt-3‰wt).

[0022] Furthermore, the method for preparing the suspension into a lignin-containing nanocellulose membrane comprises vacuum filtration followed by drying, the filtration vacuum degree is 0.05-0.1 MPa, and the drying temperature is 30°C-60°C (preferably 35°C-55°C, more preferably 40°C-50°C).

[0023] In a second aspect, the method for preparing the self-reinforced lignin-containing nanocellulose membrane is used to prepare the self-reinforced lignin-containing nanocellulose membrane.

[0024] The nanofibers in the lignin-containing nanocellulose have a length of 1-3 μm and a diameter of 3-50 nm; the average particle size of the reconstructed lignin particles is 0.1-1 μm;

[0025] The film comprises 60-90% by weight of cellulose, 10-30% by weight of lignin, and 0%-10% by weight of hemicellulose; and the film thickness is 10-70 μm (preferably 20-50 μm, more preferably 25-35 μm).

[0026] Compared with the prior art, the gain effect of the present invention is mainly reflected in:

[0027] (1) The self-reinforced lignin-containing nanocellulose composite membrane of the present invention utilizes the original components of the raw materials without the need for exogenous additions, designs a self-reinforcement strategy, and realizes the acid-restructured lignin self-reinforced nanocellulose membrane. Compared with the nanocellulose membrane without acid-restructured lignin structure, the mechanical properties of the membrane after self-reinforcement are significantly improved.

[0028] (2) The self-reinforced lignin-containing nanocellulose composite membrane of the present invention is prepared using various plants, biomass waste, etc. as raw materials, with a wide range of options, no pollution to the environment, and a simple process. The reagents used are mild, and the conditions can be controlled to prepare nanocellulose membranes with different lignin loading amounts, which has the basis for large-scale preparation.

[0029] (3) The lignin-containing nanocellulose membrane prepared by the present invention has excellent mechanical properties. Due to the adhesion of lignin particles to nanofibers and the reconstruction of the lignin structure, the surface hydroxyl groups of cellulose are greatly reduced, so that the water resistance and stability of the membrane are improved to a certain extent, and the membrane is endowed with anti-ultraviolet and anti-oxidation properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 : Mechanical properties of the lignin-containing nanocellulose films of Example 1 and Example 2.

[0031] Figure 2 : Effect of different acids in the acid precipitation method of Example 2 and Comparative Example 1 on the mechanical properties of the film.

[0032] Figure 3 : The influence of different raw materials on the mechanical properties of the film in Example 3 and Comparative Example 2.

[0033] Figure 4 : Effects of different organic solvents in Example 4 and Comparative Example 3 on the mechanical properties of the film.

[0034] Figure 5 : Effects of different lignin dissolution-regeneration methods on the mechanical properties of the film in Example 5 and Comparative Example 4.

[0035] Figure 6 : SEM images of lignin micro-nanoparticles on the lower surface of the film of Example 1 and Example 2, (a) before reconstruction, (b) after reconstruction.

[0036] Figure 7 : UV shielding properties of self-reinforced lignin-containing nanocellulose films of Examples 1-3. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail with reference to the following embodiments, but the implementation method of the present invention is not limited thereto.

[0038] Tensile property test: The prepared self-reinforced lignin-containing nanocellulose membrane was dried and cut into tensile test specimens with a width of 5 mm and a length of 30 mm for mechanical property testing. The tensile strength and elongation at break of the membrane were tested using a universal mechanical testing machine. Each group was measured 5 times and the average value was taken. The tensile rate was 2 mm / min (Carbohydrate Polymers 223 (2019)115057).

[0039] Surface morphology SEM test: The surface morphology characteristics of the self-reinforced lignin-containing nanocellulose membrane were observed by scanning electron microscopy with a magnification of 5000 times.

[0040] Table 1 Tensile strength and elongation at break of nanocellulose membranes

[0041] sample Tensile strength (MPa) Elongation at break (%) Example 1 34.72 1.35 Example 2 68.27 1.59 Example 3 59.67 2.79 Example 4 75.68 1.72 Example 5 83.02 2.36 Comparative Example 1 55.26 2.71 Comparative Example 2 73.45 2.00 Comparative Example 3 73.63 1.93 Comparative Example 4 78.92 1.87

[0042] Example 1

[0043] Preparation of lignin-containing nanocellulose membranes without lignin structural reconstruction: a case study of corncob xylose residue;

[0044] 5 g of xylose residue was added to 100 g of 0.3% NaOH solution and ball-milled at 500 rpm for 3 hours. After completion, it was washed with water until neutral and prepared into a suspension with a mass concentration of 1% with water. Without using any lignin dissolution-regeneration method to reconstruct its structure, it was directly prepared into a suspension with a mass concentration of 1‰ with water and vacuum filtration was used to prepare a self-reinforced lignin-containing nanocellulose film with a thickness of about 30 μm. At this time, the film composition was 85.50% cellulose, 12.30% lignin and 2.20% hemicellulose; the length of the nanofibers was 1-3 μm and the diameter was 3-50 nm. The lignin particles (particle size range 200 nm-2 μm) were irregular spherical, and the size and distribution were uneven, and they could not form adhesion to the fibers, so the mechanical properties of the prepared film were poor (see Table 1).

[0045] Example 2

[0046] Preparation of self-reinforced lignin-containing nanocellulose membranes: Taking corncob xylose residue and sulfuric acid heavy structure as examples;

[0047] 5 g of xylose residue was added to 100 g of 0.3% NaOH solution and ball-milled at 500 rpm for 3 hours. After completion, it was washed with water until neutral and prepared into a suspension with a mass concentration of 1% with water. The suspension was titrated to pH = 2 with a molar concentration of 0.1 mol / L sulfuric acid solution under constant temperature magnetic stirring at 36°C for grafting of lignin micro-nano particles with cellulose fibers. The titration time was controlled at 5 min. After completion, it was washed with water until neutral. Finally, it was prepared into a suspension with a mass fraction of 1‰ with water. A self-reinforced lignin-containing nanocellulose film with a thickness of about 30 μm was prepared by vacuum filtration. At this time, the film composition was 85.50% cellulose, 12.30% lignin and 2.20% hemicellulose; the length of the nanofibers was 1-3 μm and the diameter was 3-50 nm. The particle size of lignin particles was uniformly gathered at about 0.8μm, evenly distributed (particle size range 0.5μm -1μm), regular spherical, and adhered to the fiber surface;

[0048] The mechanical properties of the lignin-containing nanocellulose membrane after self-reinforcement with reconstructed lignin are significantly improved compared to the membrane without lignin reconstruction, with the tensile strength increased by about 96.63% and the elongation at break increased by about 17.78% (see Table 1). The reason is that the micro-nanoparticles of lignin after reconstruction are grafted (or adhered) to the cellulose nanofibers. When the fibers are stretched, the lignin particles not only act as an adhesive, but also increase the stress transfer efficiency between the fibers, so that the stress on the local fibers is dispersed to the outside, thus increasing the mechanical properties of the membrane. Figure 6 The particle size of lignin particles on the surface of the film without lignin reconstruction (a) is between 200 nm and 2 μm, which is uneven and sparse. However, after reconstruction (b), the particle size of lignin particles is uniformly aggregated at about 1 μm, evenly distributed, and effectively bonded with nanocellulose fibers, confirming that the reconstructed lignin improves the mechanical properties of the film.

[0049] Example 3

[0050] Preparation of self-reinforced nanocellulose membranes containing lignin: An example of reconstruction using bamboo powder and hydrochloric acid precipitation;

[0051] 5 g of bamboo powder (passed through a 60-40 mesh sieve) was added to 100 g of 0.5% NaOH solution and ball-milled at 500 rpm for 6 hours. After completion, it was washed with water to neutrality and prepared into a 1% suspension with water. The suspension was titrated to pH = 4 with 10 mmol / L hydrochloric acid solution under constant temperature magnetic stirring at 45 ° C to graft lignin micro-nano particles with cellulose fibers. The titration time was controlled at 15 min. After completion, it was washed with water to neutrality and finally prepared into a 1‰ suspension with water. A self-reinforced lignin-containing nanocellulose film with a thickness of about 30 μm was prepared by vacuum filtration. At this time, the film composition was 80.75% cellulose, 15.60% lignin and 3.65% hemicellulose; the length of the nanofibers was 1-2 μm and the diameter was 3-50 nm; the particle size of the lignin particles was uniformly gathered at about 0.8 μm, evenly distributed (particle size range 0.5 μm -1 μm) in a regular spherical shape, and adhered to the fiber surface;

[0052] The tensile strength of the lignin nanocellulose film after self-reinforcement with reconstructed lignin was 59.67 MPa, and the elongation at break was 2.79%, which were increased by 71.86% and 107.4% compared with those before reconstruction (see Table 1). The reason for the enhancement was consistent with that in Example 2.

[0053] Example 4

[0054] Preparation of self-reinforced lignin-containing nanocellulose membranes: Taking bagasse and organic solvent reconstruction as an example;

[0055] 5 g of bagasse was added to 100 g of 0.5% NaOH solution and ball-milled at 500 rpm for 4 hours. After completion, it was washed with water until neutral, centrifuged and freeze-dried. 2 g of the dried lignin-containing nanocellulose powder was weighed and added to 10 g of ethyl acetate, and 0.1 g of anhydrous sodium acetate was added as a catalyst to promote the acetylation reaction. The entire reaction was reacted at 45 °C under magnetic stirring for 3 hours. After the reaction was completed, it was centrifuged and washed with water to remove excess solvent and catalyst residues. Finally, it was prepared with water into a suspension with a mass fraction of 1‰ and a self-reinforced lignin-containing nanocellulose film with a thickness of about 30 μm was prepared by vacuum filtration. At this time, the film composition was 90.25% cellulose, 9.50% lignin and 0.25% hemicellulose. The length of the nanofibers was 1-3 μm and the diameter was 3-50 nm. The particle size of the lignin particles was uniformly aggregated at about 0.8 μm, evenly distributed (particle size range 0.5 μm -1 μm), regular spherical, and adhered to the fiber surface.

[0056] Since the adhesion to the nanofibers increases the stress transfer between the fibers, the tensile strength of the lignin-containing nanocellulose film is increased by about 117.98%, and the elongation at break is increased by about 27.40% (see Table 1).

[0057] Example 5

[0058] Preparation of self-reinforced lignin-containing nanocellulose membranes: Taking xylose residue and sulfite method reconstruction as an example;

[0059] 5 g of xylose residue was added to 100 g of 0.3% NaOH solution and ball milled at 500 rpm for 3 hours. After completion, it was washed with water until neutral and prepared into a 1% suspension with water. 0.1 g of sodium bisulfite was added to 200 ml of the suspension and reacted in a reactor at 130 °C for 2 h. After the reaction was completed, the pH of the solution was adjusted to 2 for grafting of sulfonic acid lignin and nanocellulose, then washed to neutral, and finally prepared into a suspension with a mass fraction of 1‰. Self-reinforced nanocellulose membrane containing lignin was prepared by vacuum filtration. At this time, the film composition was 85.50% cellulose, 12.30% lignin and 2.20% hemicellulose; the length of the nanofibers was 1-3μm and the diameter was 3-50 nm; the tensile strength increased by about 96.63%, and the elongation at break increased by about 17.78%;

[0060] Since a large number of sulfonic acid groups are introduced into the molecular structure of lignin, it is suitable as a plasticizer and adhesive for the material. Therefore, the mechanical properties of the prepared self-reinforced lignin-containing nanocellulose membrane are greatly improved, and the tensile strength reaches 83.02 MPa (see Table 1).

[0061] Comparative Example 1

[0062] Example 2 was repeated (with the same process and conditions), except that the acid precipitation reagent was replaced with hydrochloric acid, and the other conditions remained unchanged.

[0063] like Figure 2 As shown, by comparing with Example 1, it can be seen that the tensile strength of the membrane is reduced by about 19.06%, but the elongation at break is increased by nearly 70.44%. It can be inferred that the type of inorganic acid will affect the morphology, size and structure of lignin micro-nano particles, and even affect the interaction between micro-nano particles and cellulose nanofibers, thereby having a greater impact on the mechanical properties of the membrane.

[0064] Comparative Example 2

[0065] Example 3 was repeated (with the same process and conditions), except that the experimental material was replaced with hardwood pulp board, and the other conditions remained unchanged.

[0066] like Figure 3As shown, by comparing with Example 1, it can be seen that, affected by the fiber strength of the raw material itself, the overall mechanical properties of the film are improved, the tensile strength is increased by 7.59%, and the elongation at break is increased by 25.79%. According to the above results, it can be inferred that this method is suitable for lignin reconstruction and enhancement of lignin-containing nanocellulose prepared from different raw materials.

[0067] Comparative Example 3

[0068] like Figure 4 As shown, Example 4 was repeated (with the same process and conditions), except that the organic solvent during lignin reconstruction was replaced with acetone, and the other conditions remained unchanged.

[0069] By comparison, it can be seen that after replacing the organic solvent, the tensile strength increased by about 33.24% and the elongation at break decreased by about 28.78%. However, the reconstruction of lignin particles by organic solvent can enhance the mechanical properties of the film.

[0070] Comparative Example 4

[0071] like Figure 5 As shown, Example 5 was repeated (with the same process and conditions), except that the reaction reagent during lignin reconstruction was replaced with magnesium bisulfite, and the other conditions remained unchanged.

[0072] By comparison, it can be seen that after changing the reaction solvent, the tensile strength and elongation at break of the film have slightly decreased to varying degrees, but are still greatly improved compared to the film without lignin reconstruction. It can be seen from the previous examples and comparative examples that changing different lignin dissolution-regeneration methods has a good strengthening effect on the nanocellulose film containing lignin.

[0073] Application Examples

[0074] like Figure 7 As shown in the figure, the UV shielding performance of the self-reinforced lignin-containing nanocellulose film of Examples 1-3 is shown respectively. It can be seen from the figure that within the wavelength range of 200-400 nm, the UV shielding rate of the prepared film can reach more than 95%, and after lignin reconstruction, the UV shielding rate of the film can reach 99%. In addition, the film has good mechanical properties, which proves that it can be used as a UV shielding material.

Claims

1. A method for preparing a self-reinforced lignin-containing nanocellulose film, characterized in that: The method comprises the following steps: (1) The plant fiber raw material was treated with a 0.3% mass concentration NaOH solution in combination with mechanical grinding, and then washed with water until neutral to obtain a lignin-containing nanocellulose suspension; (2) dissolving and regenerating lignin in the suspension obtained in step (1), reconstructing the distribution and structure of lignin, and washing with water until neutrality, thereby obtaining a nanocellulose suspension containing reconstructed lignin; (3) The suspension in step (2) is prepared with a diluent solvent in a certain proportion, and vacuum filtered and dried to obtain a self-reinforced lignin-containing nanocellulose film; The lignin dissolution-regeneration method is one of an acid precipitation method, an organic solvent method, and a sulfite method; The suspension in step (1) is an aqueous solution with a mass fraction of 1%wt; The mechanical grinding treatment time is 3 hours, and the grinding speed is 500 rpm; The acid used in the acid precipitation method is one or both of sulfuric acid and lactic acid, the acid concentration is 1 mmol / L-10 mol / L, the acid precipitation titration time is 3-20 min, and the system pH is 2 after the acid is added for titration; The reagent used in the sulfite method is one or a combination of two or more of sodium sulfite, sodium bisulfite, and calcium bisulfite. When the plant fiber raw material is 1 g, the dosage is 0.05-0.5 g, and the processing time is 0.5-5 h.

2. The method for preparing the self-reinforced lignin-containing nanocellulose film according to claim 1, characterized in that: When the plant fiber raw material is 5 g, the amount of NaOH solution used is 60-200 g.

3. The method for preparing the self-reinforced lignin-containing nanocellulose film according to claim 1, characterized in that: The grinding equipment used in the mechanical grinding process includes: one or more of a planetary ball mill, a hybrid ball mill, a vibration ball mill, a self-mortar grinder or a horizontal rolling ball mill.

4. The method for preparing the self-reinforced lignin-containing nanocellulose film according to claim 1, characterized in that: The plant fiber raw material is roots, stems, leaves of one or more plants among trees, rattans, grasses, ferns, and a mixture of one or more industrial biomass wastes such as furfural residue, xylose residue, and sugarcane residue.

5. The method for preparing the self-reinforced lignin-containing nanocellulose film according to claim 1, characterized in that: The method of washing with water to neutrality is one or a combination of two or more of filtration, centrifugation and decantation.

6. The method for preparing the self-reinforced lignin-containing nanocellulose film according to claim 1, characterized in that: The solvent used in the organic solvent method is one or a combination of two or more of acetone, ethyl acetate and methanol. When the plant fiber raw material is 2 g, the dosage is 5-20 g and the processing time is 1-6 h.

7. The method for preparing the self-reinforced lignin-containing nanocellulose film according to claim 1, characterized in that: The dilution solvent in step (3) is one of water, ethanol, tert-butanol or a mixture of two or more thereof, and the mass fraction of the diluted suspension is 0.1‰wt-5‰wt.

8. The method for preparing the self-reinforced lignin-containing nanocellulose film according to claim 1, characterized in that: The method for preparing the suspension into a nanocellulose film containing lignin comprises vacuum filtration followed by drying, wherein the vacuum degree of the filtration is 0.05-0.1 MPa and the drying temperature is 30°C-60°C. 9 . A self-reinforced lignin-containing nanocellulose membrane prepared by the method for preparing a self-reinforced lignin-containing nanocellulose membrane according to any one of claims 1 to 8 .

10. The self-reinforced lignin-containing nanocellulose film according to claim 9, characterized in that: The nanofibers in the lignin-containing nanocellulose membrane have a length of 1-3 μm and a diameter of 3-50 nm; the average particle size of the reconstructed lignin particles is 0.1-1 μm; The film comprises 60-90% by weight of cellulose, 10-30% by weight of lignin, and 0%-10% by weight of hemicellulose; and the film thickness is 10-70 μm.

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