A method for preparing a nanocellulose composite film

Abstract

The application discloses a method for preparing nanocellulose composite membranes, and belongs to the technical field of biomass high-value utilization and nanocellulose resource utilization. The application provides a pretreatment method assisted by polyethylene glycol. The method is simple to operate, does not need additional complex processes, and can realize effective modification of lignin by only adding polyethylene glycol in the 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 the nanofilament, and endows the composite membrane with excellent tensile strength and good toughness.

Description

Technical Field

[0001] This invention relates to a method for preparing nanocellulose composite membranes, belonging to the technical field of high-value utilization of biomass and resource utilization of nanocellulose. Background Technology

[0002] Lignocellulose is a widely available renewable organic resource in nature, and due to its abundant sources and multifunctional properties, it is widely used in textiles, papermaking, energy, and materials. In recent years, the preparation of biomass nanomaterials from lignocellulose through processes such as dissolution, separation, regeneration, and dispersion has become a research hotspot. Among them, cellulose nanofibers, as an emerging bio-based nanomaterial, have attracted widespread attention due to their abundant sources, renewability, high strength, and excellent biocompatibility. However, cellulose nanofibers themselves have inherent defects, such as weak hydrophobicity and limited interfacial bonding performance with other polymer materials, which to some extent limits their further application in composite materials. In addition, since natural wood, bamboo, and grasses contain only about 35% to 50% cellulose, the artificial separation of pure cellulose is not only complex and costly, but also difficult to achieve high-value-added industrial applications.

[0003] Lignin, an important 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 cellulose nanofibers not only helps reduce the hydrophilicity and polarity of the fibers but also improves their thermal stability and UV blocking properties. Therefore, the preparation of lignin-containing cellulose nanofibers effectively expands the range of raw material sources for cellulose nanofibers and avoids the high costs associated with removing lignin from wood fibers, while also offering advantages such as low cost, environmental friendliness, and green environmental protection. This makes lignin-containing cellulose nanofibers a highly promising nanofiber material.

[0004] Although the introduction of lignin improves the thermal stability of cellulose nanofibers to some extent, their overall thermal stability remains insufficient, making it difficult to meet the requirements of certain high-performance materials. Furthermore, due to the strong structural rigidity and high hydrophobicity of lignin molecules, they are prone to agglomeration within cellulose nanofibers. Additionally, the lignin chromophores exposed during pretreatment can lead to a darker color in the fibers, affecting the uniformity and appearance of the material. Therefore, further optimizing the lignin modification process to prepare lignin-containing cellulose nanofibers with higher thermal stability, lighter color, and more uniform dispersion remains a major challenge in current research.

[0005] Patent CN112709090 A discloses a method for preparing cellulose nanofibers with varying lignin contents using NaOH solution as a pretreatment combined with bio-enzyme and mechanical grinding. This method utilizes NaOH in the pretreatment process, consuming large amounts of chemical reagents, which not only increases costs but also hinders subsequent environmentally friendly treatment. Furthermore, the process relies on bio-enzyme activity, and excessive enzyme usage also impacts the technology's cost, further limiting its industrial application. While the mechanical grinding step helps improve the fineness of the nanofibers, the entire process is cumbersome, resulting in low production efficiency. More importantly, although this method can prepare lignin-containing cellulose nanofibers, the thermal stability of the resulting nanofibers remains limited, failing to meet the requirements for composite membrane materials under certain high-temperature conditions.

[0006] Patent CN110130136 A reports the preparation of lignin-containing cellulose nanofibers using a eutectic solvent and mechanical milling. However, the cellulose nanofibers prepared in this method have a relatively large diameter (20–100 nm), which significantly affects the fiber dispersibility and uniformity. The large fiber diameter easily leads to fiber aggregation in the composite membrane, thereby disrupting the microstructure uniformity of the membrane. This aggregation not only reduces the strength of the composite membrane but also limits its modulus improvement. Furthermore, while the use of a eutectic solvent has certain environmental advantages, the selection and ratio of the solvent need strict control, which increases the complexity of the process and also places higher demands on production costs.

[0007] Patent CN116426585 A discloses a method for pretreating agricultural and forestry biomass using surfactant-assisted organic solvents. The main purpose is to construct a pretreatment method to efficiently remove lignin while improving the enzymatic hydrolysis of the pretreated matrix. The core of this method lies in utilizing the synergistic effect of surfactants and organic solvents to enhance the enzymatic hydrolysis efficiency of cellulose. However, this technology focuses more on increasing glucose yield after enzymatic hydrolysis than on its direct application in the preparation of cellulose nanofibers. Furthermore, this method requires a high pretreatment intensity, which may damage the structural integrity of cellulose. Experiments have shown that the embodiment in this patent that achieves good enzymatic hydrolysis results in a significant reduction in lignin content in the cellulose membrane due to the high lignin removal rate, leading to lower thermal stability of the prepared nanocomposite membrane. This insufficient 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. As a natural aromatic polymer, lignin contains numerous benzene rings and ether bonds in its molecular structure, endowing it with excellent hydrophobicity and antioxidant properties. These properties manifest in nanocellulose composite membranes as enhanced hydrophobicity, improved water resistance, and a certain reinforcing effect. However, the rigid molecular structure of lignin also brings some negative impacts. First, due to the low flexibility of lignin molecular chains, its distribution in the composite membrane often leads to a decrease in the overall toughness of the material. Second, the high hydrophobicity of lignin results in weak interfacial bonding between it and hydrophilic nanocellulose filaments, which may lead to interfacial defects in the composite membrane, thus significantly affecting its mechanical properties. On the other hand, the chemical structure of lignin contains chromophores, such as phenolic hydroxyl groups and quinone structures. These groups are easily oxidized or exposed during pretreatment, leading to a darker color in the composite membrane. This not only negatively impacts the appearance quality of the material but may also limit its application in fields requiring high optical transparency. In addition, the complex molecular structure of lignin results in poor uniform dispersion in composite materials, which further increases the difficulty of optimizing material properties.

[0009] Therefore, effectively addressing the negative impacts of lignin introduction during the preparation of lignin-containing nanocellulose composite membranes has become a key research issue. This requires optimizing lignin dispersion in the pretreatment process and improving the interfacial bonding between lignin and nanocellulose fibers through chemical modification or surface functionalization to achieve a comprehensive improvement in the composite membrane's mechanical properties, thermal stability, and appearance quality. The preparation of high-quality lignin-containing nanocellulose fibers and high-performance lignin-containing nanocomposite membranes has extremely high practical and economic value. This not only enhances 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 problems of insufficient thermal stability, darkening color, poor dispersibility, and high brittleness in the current preparation of lignin-based cellulose nanofibers and composite films, this invention proposes a novel method that introduces polyethylene glycol (PEG) into the pretreatment process of agricultural and forestry biomass. By chemically modifying lignin molecules with PEG to regulate the molecular structure and properties of lignin, lignin-containing cellulose nanofibers with high thermal stability, lighter color, and better dispersibility, as well as nanocomposite films with significantly improved performance, were successfully prepared.

[0011] The first objective of this invention is to provide a method for preparing a nanocellulose composite membrane, comprising the steps of:

[0012] (1) Sugarcane bagasse is mixed with a solvent, sulfuric acid and polyethylene glycol are added to react, and after the reaction, the mixture is cooled, washed and dried to obtain a solid matrix; the solvent is any one of water, glycerol aqueous solution and 1,4-butanediol aqueous solution; the mass ratio of sugarcane bagasse, solvent, sulfuric acid and PEG 4000 is 1:5~15:0.0025~0.3:0.005~0.25;

[0013] (2) The solid matrix is ​​resuspended, ground and filtered to obtain a solid, which is then dispersed in water to obtain a nanocellulose fiber dispersion;

[0014] (3) The nanocellulose fiber dispersion was filtered and then mixed with a 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 20-90% w / w.

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

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

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

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

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

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

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

[0025] In one embodiment, in step (3), the nanocellulose fiber dispersion is passed through a PVDF membrane to trap solids, and another PVDF membrane is used to cover the solids and then dried to obtain a nanocellulose composite membrane.

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

[0027] A second objective of this invention is to provide a nanocellulose composite membrane prepared by any of the methods described above.

[0028] A third objective of this invention is to provide the application of any of the above-described methods or the above-described nanocellulose composite membranes in the fields of water treatment, biomedical materials, and food packaging.

[0029] In one embodiment, the applications include the preparation of water purification membranes, biomedical dressings, and food preservation packaging films.

[0030] A third objective of this invention is to provide a packaging material comprising the aforementioned nanocellulose composite film.

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

[0032] (1) Sugarcane bagasse is mixed with a solvent, sulfuric acid and polyethylene glycol are added to react, and after the reaction, the mixture is cooled, washed and dried to obtain a solid matrix; the solvent is any one of water, glycerol aqueous solution and 1,4-butanediol aqueous solution; the mass ratio of sugarcane bagasse, solvent, sulfuric acid and PEG 4000 is 1:5~15:0.0025~0.3:0.005~0.25;

[0033] (2) The solid matrix is ​​resuspended, ground and filtered to obtain a solid, which is then dispersed in water to obtain a nanocellulose fiber dispersion;

[0034] (3) The nanocellulose fiber dispersion was filtered and then mixed with a 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 20-90% 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, cooling in step (1) is to reduce the temperature to 80±5°C.

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

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

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

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

[0044] In one embodiment, in step (3), the nanocellulose fiber dispersion is passed through a PVDF membrane to trap solids, and another PVDF membrane is used to cover the solids and then dried to obtain a nanocellulose composite membrane.

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

[0046] The beneficial effects of this invention are:

[0047] (1) This invention utilizes polyethylene glycol-assisted pretreatment of lignocellulose combined with mechanical grinding to successfully prepare cellulose nanofibers containing polyethylene glycol-modified lignin. The addition of polyethylene glycol grafted onto the lignin structure improves the dispersibility and thermal stability of the nanofibers; furthermore, the resulting cellulose nanocomposite film containing polyethylene glycol-modified lignin exhibits excellent mechanical properties, significantly increasing its tensile strength and toughness. This provides a possibility for the efficient nano-sizing of high-quality lignin-containing lignocellulose.

[0048] (2) Polyethylene glycol is widely available and inexpensive, and has the characteristics of being environmentally friendly, green, renewable, and biodegradable. The polyethylene glycol-assisted pretreatment proposed in this invention has universality, is 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 extra steps are required to modify lignin, reducing production costs. It is green, environmentally friendly, energy-efficient, simple to operate, and easy to industrialize.

[0049] (3) The lignin content of the nanocellulose filaments prepared by this method can be controlled between 1% and 30%, which is suitable for the development and preparation of cellulose nanomaterials with different lignin mass fractions. The lignin-containing nanocellulose filaments prepared by this invention have a diameter between 2 and 30 nm, a small distribution range, and exhibit a filamentous network structure when observed by scanning electron microscopy, and have a light color. Attached Figure Description

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

[0051] Figure 2 Evaluation of the tensile properties of lignin-containing nanocomposite films;

[0052] Figure 3 This is an image of the appearance of the nanocellulose composite membrane. Detailed Implementation

[0053] The preferred embodiments of the present invention are described below. 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 for this invention are various agricultural and forestry biomass, such as sugarcane bagasse, straw, wheat straw, rice straw, hardwood, softwood fibrous waste, and herbaceous plants, all of which can be used in this invention. Sugarcane bagasse is used below as a preferred embodiment to describe the implementation steps of this invention.

[0055] Raw materials used in the examples:

[0056] The bagasse was taken from a sugar factory in Guangxi and consisted of 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] The PVDF membrane was purchased from Beyotime Reagents, with dimensions of 6.6 × 8.5 cm and a thickness of 0.22 μm.

[0059] Test method:

[0060] 1. Thermal stability

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

[0062] 2. Tensile strength

[0063] Mechanical properties were measured using a universal testing instrument (China Meters Industrial Systems, CMT6103), with a 500N load sensor, 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. Observation of fiber structure

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

[0066] Example 1

[0067] A method for preparing a nanocellulose composite membrane containing polyethylene glycol-modified lignin includes the following steps:

[0068] (1) Sugarcane bagasse is crushed, passed through a 20-mesh sieve, and dried in an oven at 60°C until constant weight is obtained to obtain dried sugarcane bagasse;

[0069] (2) Mix 20g of dried sugarcane bagasse with 200g of water, then add 0.4g of H2SO4 and 0.8g of PEG 4000, and heat to 170℃ at 180rpm in a 500mL high-pressure reactor for 60min.

[0070] After cooling to 80±5℃ and stirring for 10 min, the mixture was 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℃ to obtain the dried solid matrix.

[0071] (3) The dried solid matrix was directly mixed with water to form a suspension (1.5% w / v, g / mL), and then ground. The grinding process was carried out in sequence at 50 μm (grinding gap size, i.e., the distance between grinding discs) and 1500 rpm (grinding disc rotation speed) for 5 times, at 2000 rpm and 100 μm for 10 times, and at 2000 rpm and 150 μm for 5 times. After grinding, the suspension was filtered through a microporous membrane (0.22 μm) to remove dissolved organic matter. The solids were washed three times with deionized water and then ultrasonically redispersed in an aqueous solution to obtain a dispersion of cellulose nanofibers containing polyethylene glycol lignin.

[0072] (4) The nanocellulose fiber 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 3mm thick smooth absorbent fiber boards and kept at 0.2MPa and 80℃ for 2h to obtain a nanocellulose composite membrane containing polyethylene glycol lignin.

[0073] Example 2

[0074] Based on Example 1, step (2) is modified as follows:

[0075] 20g of dried sugarcane bagasse was mixed with 200g of glycerol aqueous solution (70%, w / w), and then 0.4g of H2SO4 and 0.8g of PEG 4000 were added. The mixture was heated to 170℃ at 180rpm in a high-pressure reactor and maintained for 60min.

[0076] The remaining steps are the same as in Example 1, and a nanocellulose fiber dispersion containing polyethylene glycol lignin and a nanocellulose composite film containing polyethylene glycol lignin are prepared.

[0077] Example 3

[0078] Based on Example 1, step (2) is modified as follows:

[0079] 20g of dried sugarcane bagasse was mixed with 200g of 1,4-butanediol aqueous solution (70%, w / w), and then 0.4g of H2SO4 and 0.8g of PEG 4000 were added. The mixture was heated to 150℃ at 180rpm in a high-pressure reactor and maintained for 60min.

[0080] The remaining steps are the same as in Example 1, and a nanocellulose fiber dispersion containing polyethylene glycol lignin and a nanocellulose composite film containing polyethylene glycol lignin are prepared.

[0081] Comparative Example 1

[0082] Based on Example 1, PEG 4000 is not added in step (2), and the remaining steps are the same as in Example 1, to prepare a nanocellulose fiber dispersion containing polyethylene glycol lignin and a nanocellulose composite film containing polyethylene glycol lignin.

[0083] Comparative Example 2

[0084] Based on Example 2, PEG 4000 is not added in step (2), and the remaining steps are the same as in Example 2, to prepare a nanocellulose fiber dispersion containing polyethylene glycol lignin and a nanocellulose composite film containing polyethylene glycol lignin.

[0085] Comparative Example 3

[0086] Based on Example 3, PEG 4000 is not added in step (2), and the remaining steps are the same as in Example 3, to prepare a nanocellulose fiber dispersion containing polyethylene glycol lignin and a nanocellulose composite film containing polyethylene glycol lignin.

[0087] Comparative Example 4

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

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

[0090] The remaining steps are the same as in Example 2, and a nanocellulose fiber dispersion containing polyethylene glycol lignin and a nanocellulose composite film containing polyethylene glycol lignin are prepared.

[0091] Comparative Example 5

[0092] Based on Example 3, step (2) is modified as follows:

[0093] 10g of dried sugarcane bagasse was mixed with 100g of 1,4-butanediol (100%) in a 500mL three-necked flask. 0.6g of NaOH and 0.6g of Tween 80 were added. The mixture was heated to 180℃ with stirring at 180rpm and maintained for 45min. After the time was up, stirring was continued to cool the mixture. 150mL of boiling water was added, and the mixture was stirred for 10min. Filtering was then performed to separate the solid matrix from the pretreated liquid. The solid matrix was washed twice with 150mL of tap water and then dried.

[0094] The remaining steps are the same as in Example 3, to prepare a nanocellulose fiber dispersion containing polyethylene glycol lignin and a nanocellulose composite film containing polyethylene glycol lignin.

[0095] Example 6

[0096] The appearance and properties of the cellulose nanofiber dispersions containing polyethylene glycol-modified lignin prepared in Examples 1-3 and Comparative Examples 1-5 were tested.

[0097] The appearance, structure, and thermal stability of the cellulose nanofiber dispersion containing polyethylene glycol-modified lignin are as follows: Figure 1 Table 1 shows the mechanical properties of the lignin-containing nanocomposite membrane; see Table 1 for details. Figure 2 Compared with Table 1, the appearance is as follows Figure 3 As shown.

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

[0099] 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, and mechanical strength (tensile strength and elongation at break) of the cellulose nanofibers containing polyethylene glycol-modified lignin were closely related to the addition of polyethylene glycol during the pretreatment process.

[0101] Using the embodiment reported in patent CN116426585A that achieved better enzymatic hydrolysis, nanocellulose filaments and nanocomposite membranes were prepared, and compared with the samples prepared in this patent. The results showed that the nanocellulose filaments prepared by the patented method had a larger diameter and a dark black appearance (see...). Figure 1 The main reason for the damage to the cellulose structure during high-temperature treatment (comparative examples 4 and 5) is that the chromophores in the lignin are exposed at the same time.

[0102] Meanwhile, the sample showed deficiencies in thermal stability and tensile properties (see Table 1 and ). Figure 2The performance of the samples prepared by the comparative examples 4 and 5 was significantly lower than that of the samples prepared by our proposed polyethylene glycol modification strategy. This result further illustrates that chemical modification of lignin by adding polyethylene glycol significantly improves the molecular structure and properties of lignin, thereby successfully preparing high-quality cellulose nanofibers and their composite films containing polyethylene glycol-modified lignin.

[0103] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a nanocellulose composite membrane, characterized in that, Including the following steps: (1) Sugarcane bagasse is mixed with a solvent, sulfuric acid and polyethylene glycol are added to react, and after the reaction, the mixture is cooled, washed and dried to obtain a solid matrix; the solvent is any one of water, glycerol aqueous solution and 1,4-butanediol aqueous solution; the mass ratio of sugarcane bagasse, solvent, sulfuric acid and PEG4000 is 1:5~15:0.0025~0.3:0.005~0.25; (2) The solid matrix is ​​resuspended, ground and filtered to obtain a solid, which is then dispersed in water to obtain a nanocellulose fiber dispersion; (3) The nanocellulose fiber dispersion was filtered and then mixed with a PVDF membrane to prepare a nanocellulose composite membrane.

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

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

4. The method according to claim 1, characterized in that, In step (2), the grinding is performed at 50μm and 1500rpm for 5 times, at 2000rpm and 100μm for 10 times, and at 2000rpm and 150μm for 5 times.

5. The method according to claim 1, characterized in that, In step (3), the nanocellulose fiber dispersion is passed through a PVDF membrane to retain solids, and another PVDF membrane is used to cover the solids and then dried to obtain a nanocellulose composite membrane.

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

7. The application 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 application 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, The nanocellulose composite membrane as described in claim 6 is contained in the membrane.

10. A method for simultaneously improving the mechanical properties and appearance of nanocellulose composite membranes, characterized in that, Including the following steps: (1) Sugarcane bagasse is mixed with a solvent, sulfuric acid and polyethylene glycol are added to react, and after the reaction, the mixture is cooled, washed and dried to obtain a solid matrix; the solvent is any one of water, glycerol aqueous solution and 1,4-butanediol aqueous solution; the mass ratio of sugarcane bagasse, solvent, sulfuric acid and PEG4000 is 1:5~15:0.0025~0.3:0.005~0.25; (2) The solid matrix is ​​resuspended, ground and filtered to obtain a solid, which is then dispersed in water to obtain a nanocellulose fiber dispersion; (3) The nanocellulose fiber dispersion was filtered and then mixed with a PVDF membrane to prepare a nanocellulose composite membrane.

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