Method for preparing nano cellulose composite membrane

Abstract

The invention discloses a method for preparing a nanocellulose composite film, and belongs to the technical field of biomass high-value utilization and nanocellulose resource utilization. The polyethylene glycol-assisted pretreatment method provided by the invention is simple and convenient to operate, does not need an additional complex process, and can realize effective modification of lignin only by adding polyethylene glycol in a biomass pretreatment stage. The introduction of polyethylene glycol not only improves the compatibility of lignin and nanocellulose, but also significantly improves the color, dispersibility and thermal stability of fibrils, and endows the composite membrane with excellent tensile strength and good toughness.

Description

Technical Field

[0001] The invention relates to a method for preparing a nano-cellulose composite film, and belongs to the technical field of high-value utilization of biomass and resource utilization of nano-cellulose. Background Art

[0002] Lignocellulose is a widely occurring renewable organic resource in nature. Due to its abundant source and multifunctional properties, it is widely used in textiles, papermaking, energy, and materials. In recent years, the preparation of biomass nanomaterials using lignocellulose as a raw material through processes such as dissolution, separation, regeneration, and dispersion has become a research hotspot. Among them, nanocellulose fibrils, as an emerging bio-based nanomaterial, have attracted widespread attention due to their abundant source, renewable nature, high strength, and excellent biocompatibility. However, nanocellulose itself has inherent defects, such as weak hydrophobicity and limited interfacial bonding properties with other polymers, which to some extent restrict its further application in composite materials. Furthermore, since natural wood, bamboo, and grasses only contain approximately 35% to 50% cellulose, the manual isolation of pure cellulose is not only complex and costly, but also difficult to achieve high-value-added industrial applications.

[0003] Lignin, a key component of wood and plant cell walls, is a natural aromatic polymer with excellent antioxidant properties, hydrophobicity, and a natural affinity for cellulose. Introducing lignin into nanocellulose fibrils not only helps reduce the fibrils' hydrophilicity and polarity, but also improves their thermal stability and UV-blocking properties. Therefore, preparing lignin-containing nanocellulose fibrils not only effectively expands the range of raw material sources for cellulose nanofibrils, but also avoids the high cost associated with removing lignin from wood fibers. It also offers the advantages of low cost, environmental friendliness, and environmental friendliness. This makes lignin-containing nanocellulose fibrils a highly promising nanocellulose material.

[0004] Although the introduction of lignin has improved the thermal stability of nanocellulose fibrils to a certain extent, its overall thermal stability is still insufficient and it is difficult to meet the use requirements of certain high-performance materials. In addition, due to the strong structural rigidity and high hydrophobicity of lignin molecules, they are prone to agglomeration in nanocellulose fibrils. At the same time, the lignin chromophores exposed during the pretreatment process may also cause the fibrils to darken in color, affecting the uniformity and appearance quality of the material. Therefore, how to further optimize the lignin modification process to prepare lignin-containing nanocellulose fibrils with higher thermal stability, lighter color and more uniform dispersion remains a major challenge in current research.

[0005] Patent CN112709090 A discloses the use of NaOH solution as a pretreatment in combination with enzyme and mechanical grinding treatment to prepare cellulose nanofibrils with different lignin contents; this solution uses NaOH in the pretreatment process, and consumes a large amount of chemical reagents, which not only increases costs but is also not conducive to subsequent environmental protection treatment. In addition, the process relies on the action of biological enzymes, and excessive enzyme dosage also affects the technical cost, further limiting the industrial application of the technology. Although the mechanical grinding treatment step helps to improve the refinement of the fibrils, the entire process is relatively cumbersome, resulting in low production efficiency. More importantly, although this method can prepare cellulose nanofibrils containing lignin, the thermal stability of the resulting fibrils is still limited, which cannot meet the use requirements of composite membrane materials under certain high temperature conditions.

[0006] Patent CN110130136 A reports the preparation of cellulose nanofibers containing lignin using a low eutectic solvent and mechanical grinding. However, the cellulose nanofibers prepared in this scheme have a large diameter (20 to 100 nm), which significantly affects the dispersion and uniformity of the fibers. The larger fiber diameter easily leads to agglomeration of the fibers in the composite membrane, thereby destroying the microstructural uniformity of the membrane. This agglomeration phenomenon not only reduces the strength of the composite membrane, but also limits the improvement of its modulus. In addition, although the use of low eutectic solvents has certain environmental advantages, the selection and ratio of the solvents need to be strictly controlled, which increases the complexity of the process and also places higher requirements on production costs.

[0007] Patent CN116426585 A discloses a method for pretreating agricultural and forestry biomass with the assistance of surfactants and organic solvents. The main purpose is to construct a pretreatment method to efficiently remove lignin while improving the enzymatic hydrolysis efficiency of the pretreated matrix. The core of this method is to utilize the synergistic effect of surfactants and organic solvents to improve the enzymatic hydrolysis efficiency of cellulose. However, this technology focuses more on improving the glucose yield after enzymatic hydrolysis rather than being directly applied to the preparation of cellulose nanofibers. In addition, this method requires a high pretreatment intensity, which may cause certain damage to the structural integrity of cellulose. Experiments have found that the embodiments of the patent that achieve better enzymatic hydrolysis effects have a significant reduction in the lignin content in the cellulose film due to the high lignin removal rate, resulting in low thermal stability of the prepared nanocomposite membrane. This lack of thermal stability makes it difficult to directly apply this method to the preparation of high-performance membrane materials, limiting its application potential in certain specific fields.

[0008] Furthermore, the performance of lignin-containing nanocellulose composite membranes is also significantly influenced by the properties of lignin. Lignin, a natural aromatic polymer, contains numerous benzene rings and ether bonds in its molecular structure, imparting excellent hydrophobicity and antioxidant properties. These properties manifest in nanocellulose composite membranes by enhancing the membrane's hydrophobicity, improving its water resistance, and providing a certain degree of reinforcement. However, lignin's rigid molecular structure also presents some negative effects. First, due to the low flexibility of lignin molecular chains, its distribution within the composite membrane often reduces the overall toughness of the material. Second, lignin's high hydrophobicity weakens its interfacial bonding with the hydrophilic nanocellulose fibrils, potentially leading to interfacial defects in the composite membrane, significantly impacting the membrane's mechanical properties. Furthermore, lignin's chemical structure contains chromophoric groups, such as phenolic hydroxyl groups and quinone structures. These groups are easily oxidized or exposed during pretreatment, resulting in a darker color in the composite membrane. This not only negatively impacts the material's appearance but also potentially limits its application in applications requiring high optical transparency. In addition, lignin has a complex molecular structure and poor uniform dispersion in composite materials, which further increases the difficulty of optimizing material properties.

[0009] Therefore, in the process of preparing lignin-containing nanocellulose composite membranes, how to effectively address the negative effects of lignin introduction has become a key research issue. This requires optimizing the dispersibility of lignin in the pretreatment process, while improving the interfacial bonding performance between lignin and nanocellulose fibrils through chemical modification or surface functionalization to achieve comprehensive improvements in the mechanical properties, thermal stability, and appearance quality of the composite membrane. The preparation of high-quality lignin nanocellulose fibrils and high-performance lignin-containing nanocomposite membranes has extremely high practical and economic value. This not only promotes the high-value-added applications of lignin and nanocellulose, but also provides important technical support for the efficient utilization of renewable resources. Summary of the Invention

[0010] To address the current challenges of insufficient thermal stability, darker color, poor dispersibility, and high brittleness in the preparation of lignin nanocellulose fibrils and composite films, this paper proposes a novel method for introducing polyethylene glycol (PEG) into the pretreatment of agricultural and forestry biomass. By chemically modifying lignin molecules with PEG to manipulate lignin's molecular structure and properties, the paper successfully produces lignin-containing nanocellulose fibrils with high thermal stability, lighter color, and superior dispersibility, as well as nanocomposite films with significantly improved performance.

[0011] The first object of the present invention is to provide a method for preparing a nanocellulose composite film, comprising the steps of:

[0012] (1) Bagasse is mixed with a solvent, sulfuric acid and polyethylene glycol are added for reaction, and after the reaction, the solid matrix is obtained by cooling, washing, and drying; the solvent is any one of water, glycerol aqueous solution, and 1,4-butanediol aqueous solution; the mass ratio of bagasse, solvent, sulfuric acid, and PEG 4000 is 1:5-15:0.0025-0.3:0.005-0.25;

[0013] (2) resuspending, grinding, and filtering the solid matrix to obtain a solid, and dispersing the solid in water to obtain a nanocellulose fibril dispersion;

[0014] (3) The nanocellulose fibril dispersion was filtered and combined with the PVDF membrane to prepare a nanocellulose composite membrane.

[0015] Optionally, in step (1), the mass ratio of bagasse, solvent, sulfuric acid and PEG 4000 is 1:10-15:0.01-0.2:0.01-0.1.

[0016] In one embodiment, the reaction in step (1) is carried out at 100-500 rpm and 120-200° C. for 15-90 min.

[0017] In one embodiment, the mass concentration of the glycerol aqueous solution and the 1,4-butanediol aqueous solution in step (1) is 20 to 90% w / w.

[0018] Preferably, the mass concentration of the glycerol aqueous solution and the 1,4-butanediol aqueous solution is 50 to 80% w / w;

[0019] More preferably, the mass concentration of the 1,4-butanediol aqueous solution is 60 to 80% w / w.

[0020] In one embodiment, the cooling in step (1) is to reduce the temperature to 80±5°C.

[0021] In one embodiment, the washing in step (1) refers to washing the solid matrix 1-3 times with tap water having a volume of 1 to 5 times that of the solvent.

[0022] In one embodiment, the grinding in step (2) is 50 μm, 1500 rpm grinding 5 times, 2000 rpm, 100 μm grinding 10 times, and 2000 rpm, 150 μm grinding 5 times.

[0023] In one embodiment, the concentration of the suspension obtained by resuspension in step (2) is 0.5% to 10% w / vg / mL;

[0024] Optionally, the concentration of the suspension is 1% to 5% w / vg / mL.

[0025] In one embodiment, in step (3), the nanocellulose fibril dispersion is passed through a PVDF membrane to retain solids, and another PVDF membrane is used to cover the solids, followed by drying to obtain a nanocellulose composite membrane.

[0026] In one embodiment, in step (3), the nanocellulose fibril dispersion is passed through a PVDF membrane to retain solids, and another PVDF membrane is used to cover the solids, and dried at 0.05-0.5 MPa and 30-105° C. for 0.5-8 h to obtain a nanocellulose composite membrane.

[0027] The second object of the present invention is to provide a nanocellulose composite membrane prepared by any of the above methods.

[0028] The third object of the present invention is to provide applications of any of the above methods or the above nanocellulose composite membranes in the fields of water treatment, biomedical materials, and food packaging.

[0029] In one embodiment, the application includes preparing water purification membranes, biomedical dressings, and food preservation packaging films.

[0030] The third object of the present invention is to provide a packaging material comprising the above-mentioned nanocellulose composite film.

[0031] A fourth object of the present invention is to provide a method for simultaneously improving the mechanical properties and appearance of a nanocellulose composite film, comprising the steps of:

[0032] (1) Bagasse is mixed with a solvent, sulfuric acid and polyethylene glycol are added for reaction, and after the reaction, the solid matrix is obtained by cooling, washing, and drying; the solvent is any one of water, glycerol aqueous solution, and 1,4-butanediol aqueous solution; the mass ratio of bagasse, solvent, sulfuric acid, and PEG 4000 is 1:5-15:0.0025-0.3:0.005-0.25;

[0033] (2) resuspending, grinding, and filtering the solid matrix to obtain a solid, and dispersing the solid in water to obtain a nanocellulose fibril dispersion;

[0034] (3) The nanocellulose fibril dispersion was filtered and combined with the PVDF membrane to prepare a nanocellulose composite membrane.

[0035] Optionally, in step (1), the mass ratio of bagasse, solvent, sulfuric acid and PEG 4000 is 1:10-15:0.01-0.2:0.01-0.1.

[0036] In one embodiment, the reaction in step (1) is carried out at 100-500 rpm and 120-200° C. for 15-90 min.

[0037] In one embodiment, the mass concentration of the glycerol aqueous solution and the 1,4-butanediol aqueous solution in step (1) is 20 to 90% w / w.

[0038] Preferably, the mass concentration of the glycerol aqueous solution and the 1,4-butanediol aqueous solution is 50-80% w / w.

[0039] In one embodiment, the cooling in step (1) is to reduce the temperature to 80±5°C.

[0040] In one embodiment, the washing in step (1) refers to washing the solid matrix 1-3 times with tap water having a volume of 1 to 5 times that of the solvent.

[0041] In one embodiment, the grinding in step (2) is 50 μm, 1500 rpm grinding 5 times, 2000 rpm, 100 μm grinding 10 times, and 2000 rpm, 150 μm grinding 5 times.

[0042] In one embodiment, the concentration of the suspension obtained by resuspension in step (2) is 0.5% to 10% w / vg / mL;

[0043] Optionally, the concentration of the suspension is 1% to 5% w / vg / mL.

[0044] In one embodiment, in step (3), the nanocellulose fibril dispersion is passed through a PVDF membrane to retain solids, and another PVDF membrane is used to cover the solids, followed by drying to obtain a nanocellulose composite membrane.

[0045] In one embodiment, in step (3), the nanocellulose fibril dispersion is passed through a PVDF membrane to retain solids, and another PVDF membrane is used to cover the solids, and dried at 0.05-0.5 MPa and 30-105° C. for 0.5-8 h to obtain a nanocellulose composite membrane.

[0046] Beneficial effects of the present invention:

[0047] (1) The present invention utilizes polyethylene glycol to assist in the pretreatment of lignocellulose and combines it with mechanical grinding to successfully prepare cellulose nanofibers containing polyethylene glycol-lignin. The addition of polyethylene glycol to the lignin structure improves the dispersibility of the nanofibers and enhances their thermal stability. Furthermore, the resulting cellulose nanocomposite film containing polyethylene glycol-lignin exhibits excellent mechanical properties, significantly increasing its tensile strength and toughness. This opens the possibility for the efficient nano-scaling of high-quality lignin-containing wood fibers.

[0048] (2) Polyethylene glycol is widely available and inexpensive, and is environmentally friendly, green, renewable, and biodegradable. The polyethylene glycol-assisted pretreatment method proposed in the present invention is universally applicable to different treatment methods and is widely used in agricultural and forestry biomass raw materials from various sources. The operating conditions are controllable and no redundant steps are required to modify lignin, thereby reducing production costs. It is green, environmentally friendly, energy-saving, efficient, simple to operate, and easy to industrialize.

[0049] (3) The lignin content of the nanocellulose fibrils prepared by this method can be controlled to be between 1% and 30%, making it suitable for the development and preparation of cellulose nanomaterials containing different lignin mass fractions. The diameter of the lignin-containing nanocellulose fibrils prepared by the present invention ranges from 2 to 30 nm, with a relatively small distribution range. Scanning electron microscopy reveals a fibril-like network structure and a light-colored appearance. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The morphology (a) and appearance (b) of lignin-containing nanocellulose fibrils;

[0051] Figure 2 To evaluate the tensile properties of nanocomposite films containing lignin;

[0052] Figure 3 This is the appearance of the nanocellulose composite membrane. DETAILED DESCRIPTION

[0053] The following describes preferred embodiments of the present invention. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0054] The raw materials of the present invention are various agricultural and forestry biomasses, such as sugarcane bagasse, straw, wheat straw, rice straw, hardwood, softwood fibrous waste and herbaceous plants, which can be applied to the present invention. The following uses sugarcane bagasse as a preferred embodiment to introduce the implementation steps of the present invention.

[0055] The raw materials used in the embodiment are:

[0056] Bagasse was obtained from a sugar factory in Guangxi, and its composition was 39.1% cellulose, 22.0% hemicellulose, and 25.2% lignin.

[0057] PEG 4000, PEG 6000, and Tween 80 were purchased from Sinopharm Chemical Reagent Co., Ltd.;

[0058] PVDF membrane was purchased from Beyotime Reagent, with specifications of 6.6×8.5 cm and 0.22 μm.

[0059] Test method:

[0060] 1. Thermal stability

[0061] The thermal stability was determined using a thermogravimetric analyzer (TGA Q50, USA). The test sample was heated from 30°C to 800°C at a heating rate of 10°C / min under a high-purity nitrogen flow (flow rate of 20 mL / min).

[0062] 2. Tensile strength

[0063] Mechanical properties were measured using a universal tester (CMT6103, Meters Industrial Systems, China) using a 500 N load cell at room temperature and 50% relative humidity. The span length was set to 25 mm and the tensile rate was 2.5 mm / min.

[0064] 3. Fiber structure observation

[0065] Transmission electron microscopy (TEM) analysis was performed using a Hitachi TEM instrument (HT7700, Japan) to reveal the fiber morphology. Prior to TEM analysis, a drop of approximately 10 μL of a 0.01 wt% nanocellulose suspension was placed on a copper grid, stained with 3% phosphotungstic acid, and then dried at room temperature before direct TEM observation. TEM measurements were performed at an accelerating voltage of 100 kV.

[0066] Example 1

[0067] A method for preparing a nanocellulose composite film containing polyethylene glycolized lignin comprises the steps of:

[0068] (1) crushing the bagasse, passing it through a 20-mesh sieve, and drying it in an oven at 60° C. to a constant weight to obtain dried bagasse;

[0069] (2) 20 g of dried bagasse was mixed with 200 g of water, and then 0.4 g of H2SO4 and 0.8 g of PEG 4000 were added. The mixture was heated to 170 °C at 180 rpm in a 500 mL autoclave for 60 min.

[0070] The mixture was cooled to 80±5°C, stirred for 10 min, and then filtered using a G1 sand core funnel to separate the solid matrix and the pretreatment solution; the solid matrix was washed twice with 200 mL of tap water, filtered, and dried at 60°C to obtain a dried solid matrix;

[0071] (3) The dried solid matrix was directly prepared into a suspension (1.5% w / v, g / mL) with water and subjected to grinding treatment, in the following order: grinding at 50 μm (grinding gap size, i.e., the distance between the grinding discs) and 1500 rpm (grinding disc rotation speed) for 5 times, grinding at 2000 rpm and 100 μm for 10 times, and grinding at 2000 rpm and 150 μm for 5 times; after grinding, the suspension was filtered through a microporous filter membrane (0.22 μm) to remove soluble organic matter, and the solid was repeatedly washed with deionized water for 3 times and re-dispersed in an aqueous solution by ultrasonication to obtain a nanocellulose fibril dispersion containing polyethylene glycolized lignin;

[0072] (4) The nanocellulose fibril dispersion was filtered through a PVDF membrane to retain the solids, and another PVDF membrane was placed on the solids; the double-layer PVDF membrane containing the retained solids was placed between two 3 mm thick smooth absorbent fiber boards and maintained at 0.2 MPa and 80°C for 2 h to obtain a nanocellulose composite membrane containing polyethylene glycol lignin.

[0073] Example 2

[0074] On the basis of Example 1, the following steps are modified:

[0075] 20 g of oven-dried bagasse was mixed with 200 g of 70% w / w aqueous glycerol solution, and then 0.4 g of H2SO4 and 0.8 g of PEG 4000 were added. The mixture was heated to 170°C in an autoclave at 180 rpm for 60 min.

[0076] The remaining steps were the same as those in Example 1, and a nanocellulose fibril dispersion containing polyethylene glycolized lignin and a nanocellulose composite film containing polyethylene glycolized lignin were prepared.

[0077] Example 3

[0078] On the basis of Example 1, the following steps are changed in step (2):

[0079] 20 g of oven-dried bagasse was mixed with 200 g of 1,4-butanediol aqueous solution (70%, w / w), and then 0.4 g of H2SO4 and 0.8 g of PEG 4000 were added. The mixture was heated to 150°C in an autoclave at 180 rpm for 60 min.

[0080] The remaining steps were the same as those in Example 1, and a nanocellulose fibril dispersion containing polyethylene glycolized lignin and a nanocellulose composite film containing polyethylene glycolized lignin were prepared.

[0081] Comparative Example 1

[0082] On the basis of Example 1, PEG 4000 was not added in step (2), and the remaining steps were the same as in Example 1 to prepare a nanocellulose fibril dispersion containing PEGylated lignin and a nanocellulose composite film containing PEGylated lignin.

[0083] Comparative Example 2

[0084] On the basis of Example 2, PEG 4000 was not added in step (2), and the remaining steps were consistent with Example 2 to prepare a nanocellulose fibril dispersion containing PEGylated lignin and a nanocellulose composite film containing PEGylated lignin.

[0085] Comparative Example 3

[0086] On the basis of Example 3, PEG 4000 was not added in step (2), and the remaining steps were consistent with Example 3 to prepare a nanocellulose fibril dispersion containing PEGylated lignin and a nanocellulose composite film containing PEGylated lignin.

[0087] Comparative Example 4

[0088] Based on Example 2, step (2) is changed to:

[0089] 10 g of oven-dried bagasse was mixed with 100 g of glycerol (100%) in a 500 mL three-necked flask. 0.49 g of NaOH and 0.48 g of PEG 6000 were added. The flask was then placed on a heating mantle and heated to 202°C with stirring at 180 rpm for 43 minutes. After the heating mantle was removed, the mixture was cooled to 100 ± 5°C with continuous stirring. 150 mL of boiling water was added, and the mixture was stirred for 10 minutes before filtration to separate the solid matrix from the pretreatment solution. The solid matrix was then washed twice with 150 mL of tap water and dried.

[0090] The remaining steps were the same as those in Example 2, and a nanocellulose fibril dispersion containing polyethylene glycolized lignin and a nanocellulose composite film containing polyethylene glycolized lignin were prepared.

[0091] Comparative Example 5

[0092] On the basis of Example 3, the following steps are changed in step (2):

[0093] 10 g of oven-dried bagasse and 100 g of 1,4-butanediol (100%) were mixed in a 500 mL three-necked flask. 0.6 g of NaOH and 0.6 g of Tween 80 were added, and the mixture was heated to 180°C with stirring at 180 rpm and maintained for 45 minutes. After the temperature was lowered with continued stirring to dissipate heat, 150 mL of boiling water was added, and the mixture was stirred for 10 minutes before filtration to separate the solid matrix from the pretreatment solution. The solid matrix was then washed twice with 150 mL of tap water and dried.

[0094] The remaining steps were the same as those in Example 3, and a nanocellulose fibril dispersion containing polyethylene glycolized lignin and a nanocellulose composite film containing polyethylene glycolized lignin were prepared.

[0095] Example 6

[0096] The nanocellulose fibril dispersions containing polyethylene glycolized lignin and the nanocellulose composite films containing polyethylene glycolized lignin prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were tested for appearance and performance.

[0097] The appearance, structure and thermal stability of the nanocellulose fibril dispersion containing polyethylene glycol lignin are as follows Figure 1 , as shown in Table 1; the mechanical properties of the nanocomposite film containing polyethylene glycol lignin are shown in Figure 2 Compared with Table 1, the appearance is as follows Figure 3 shown.

[0098] Table 1 Thermogravimetric analysis and mechanical properties of lignin-containing nanocellulose fibrils

[0099] Residual mass (%) Maximum decomposition temperature (℃) Tensile strength (MPa) Elongation at break (%) Example 1 16.4 368.1 21.5 1.0 Example 2 12.7 366.8 58.5 1.7 Example 3 10.4 362.4 71.6 4.6 Comparative Example 1 18.4 367.5 8.7 0.9 Comparative Example 2 14.5 363.2 30.2 1.2 Comparative Example 3 12.1 358.0 54.0 2.2 Comparative Example 4 20.2 346.2 11.5 0.9 Comparative Example 5 21.1 348.6 22.0 1.4

[0100] The results showed that the color, dispersibility, thermal stability of nanocellulose fibrils containing polyethylene glycol-lignin and the mechanical strength (tensile strength and elongation at break) of the composite films were closely related to the addition of polyethylene glycol during the pretreatment process.

[0101] The example of achieving better enzymatic hydrolysis effect reported in patent CN116426585A was used to prepare nanocellulose fibrils and nanocomposite membranes, and a comparative study was conducted with the samples prepared in this patent. The results showed that the nanocellulose fibrils prepared by the patent method had a larger diameter and a dark black appearance (see Figure 1 The main reason is that the cellulose structure is destroyed during the high temperature treatment and the chromophores in the lignin are exposed.

[0102] At the same time, the sample showed insufficient performance in terms of thermal stability and tensile properties (see Table 1 and Figure 2The performance of the samples prepared using our proposed polyethylene glycol modification strategy was significantly lower than that of the samples prepared using Comparative Examples 4 and 5). This result further demonstrates that chemical modification of lignin by adding polyethylene glycol significantly improves its molecular structure and properties, thereby successfully preparing high-quality nanocellulose fibrils containing polyethylene glycol-modified lignin and their composite films.

[0103] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a nanocellulose composite film, characterized in that: Including steps: (1) Bagasse is mixed with a solvent, sulfuric acid and polyethylene glycol are added for reaction, and after the reaction, the solid matrix is obtained by cooling, washing, and drying; the solvent is any one of water, glycerol aqueous solution, and 1,4-butanediol aqueous solution; the mass ratio of bagasse, solvent, sulfuric acid, and PEG4000 is 1:5-15:0.0025-0.3:0.005-0.25; (2) resuspending, grinding, and filtering the solid matrix to obtain a solid, and dispersing the solid in water to obtain a nanocellulose fibril dispersion; (3) The nanocellulose fibril dispersion was filtered and combined with the PVDF membrane to prepare a nanocellulose composite membrane.

2. The method according to claim 1, characterized in that In step (1), the reaction is carried out at 100-500 rpm and 120-200° C. for 15-90 min.

3. The method according to claim 1, characterized in that The mass concentration of the glycerol aqueous solution and the 1,4-butanediol aqueous solution in step (1) is 20 to 90% w / w.

4. The method according to claim 1, wherein The grinding in step (2) is 50 μm, 1500 rpm grinding 5 times, 2000 rpm, 100 μm grinding 10 times, 2000 rpm, 150 μm grinding 5 times.

5. The method according to claim 1, wherein In step (3), the nanocellulose fibril dispersion is passed through a PVDF membrane to retain solid matter, and another PVDF membrane is used to cover the solid matter, followed by drying to obtain a nanocellulose composite membrane.

6. The nanocellulose composite film prepared by the method according to any one of claims 1 to 5.

7. Use of the method according to any one of claims 1 to 5 or the nanocellulose composite membrane according to claim 6 in the fields of water treatment, biomedical materials, and food packaging.

8. The use according to claim 7, characterized in that The applications include the preparation of water purification membranes, biomedical dressings, and food preservation packaging films.

9. A packaging material, characterized in that: Contains the nanocellulose composite film according to claim 6.

10. A method for simultaneously improving the mechanical properties and appearance of a nanocellulose composite film, characterized in that: Including steps: (1) Bagasse is mixed with a solvent, sulfuric acid and polyethylene glycol are added for reaction, and after the reaction, the solid matrix is obtained by cooling, washing, and drying; the solvent is any one of water, glycerol aqueous solution, and 1,4-butanediol aqueous solution; the mass ratio of bagasse, solvent, sulfuric acid, and PEG4000 is 1:5-15:0.0025-0.3:0.005-0.25; (2) resuspending, grinding, and filtering the solid matrix to obtain a solid, and dispersing the solid in water to obtain a nanocellulose fibril dispersion; (3) The nanocellulose fibril dispersion was filtered and combined with the PVDF membrane to prepare a nanocellulose composite membrane.

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