A ZIF-8 nanoparticle-loaded cellulose barrier film and a method for preparing the same

Abstract

The application discloses a kind of ZIF-8 nanoparticle loaded cellulose barrier membrane and preparation method thereof, comprising the following steps: (1) TOCNF suspension gel is diluted into TOCNF suspension by deionized water, to obtain nanocellulose suspension solution A;(2) zinc nitrate hexahydrate is added in solution A to obtain solution B;(3) polyvinylpyrrolidone is added in solution B to obtain solution C;(4) 2-methylimidazole is added in solution C to obtain solution D;(5) solution D is placed in mold by vacuum filtration device to form a wet film, the wet film is removed, and the wet film is clamped between two pieces of acrylic plate, dried in vacuum drying oven, to obtain ZIF-8 nanoparticle loaded cellulose barrier membrane.The application selects TOCNF as the template for ZIF-8 growth, TOCNF as the template for ZIF-8 in-situ growth, which can effectively prevent them from forming aggregates, and load ZIF-8 nanoparticles through in-situ + non-in-situ method to improve the hydrophobicity, thermal stability and ultraviolet shielding property of TOCNF membrane.

Description

Technical Field

[0001] This invention belongs to the field of modified cellulose barrier membrane technology, and particularly relates to a cellulose barrier membrane loaded with ZIF-8 nanoparticles and its preparation method. Background Technology

[0002] In recent years, with the development of packaging materials, many non-degradable materials have been applied to barrier packaging, such as glass, aluminum, and petroleum-based derivative polymers. These materials have disadvantages including high weight, non-renewability, increased transportation costs and energy consumption, and environmental pollution. To reduce energy consumption and environmental pollution, there is growing interest in cellulose materials. Cellulose is the most common and abundant renewable organic polymer on Earth. Natural cellulose is a polymer composed of D-glucopyranose ring units linked by β-1,4-glycosidic bonds. As an important natural polymer, it also possesses excellent renewability, biocompatibility, environmental degradability, and biological functions, making it widely used in packaging industry production.

[0003] TEMPO (2,2,6,6-tetramethylpiperidine-1-oxygen radical) oxidized cellulose nanofibers (TOCNFs) are promising nanomaterials widely used in the preparation of bio-based thin films. The resulting films have attracted considerable attention due to their large specific surface area, rigidity, transparency, and biodegradability. However, conventional paper made from lignocellulose fibers has some inherent drawbacks. These drawbacks include low barrier properties against water, water vapor, oxygen, or oil, and these shortcomings need to be addressed to produce high-quality packaging products that meet various specifications. The main challenge in modifying TOCNFs is to increase the hydrophobicity and flexibility of the films while maintaining the required mechanical and optical properties.

[0004] Metal-organic frameworks (MOFs) are novel porous materials formed by the self-assembly of metal ions or clusters with organic ligands through coordination bonds. MOFs possess characteristics such as high porosity, large specific surface area, customizable topologies, and functional diversity, exhibiting enormous application potential and promising development prospects in various fields. Furthermore, MOFs can be designed and regulated by selecting different metal ions, organic ligands, functional groups, and activation methods to control the pore size and function of the resulting materials. Currently, MOFs are widely used in gas storage and separation, air purification, energy storage and conversion, drug delivery, catalysis, dye adsorption, and antibacterial applications. Zeolite imidazole salt frameworks (ZIFs) belong to a subclass of hydrophobic porous MOFs and exhibit stability in water due to the presence of anionic nitrogen-containing ligands within the MOF framework. Among the many ZIFs, ZIF-8 exhibits excellent hydrophobicity. Its pore size (0.34 nm) is too small to allow water clusters to form, while the lack of polar groups further facilitates the removal of liquid water. Therefore, ZIF-8 is a potential material for use in humid conditions.

[0005] Since MOFs are typically present in nanoscale powder form, they are prone to aggregation, which poses a significant challenge to achieving uniform dispersion. To improve the flexibility, processability, and recyclability of MOFs, they are often deposited on a two-dimensional support matrix. The presence of structural materials can provide synergistic effects and additional functionalities for MOFs.

[0006] To address the aforementioned problems in existing technologies, we propose a cellulose barrier membrane loaded with ZIF-8 nanoparticles and its preparation method. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a cellulose barrier membrane with ZIF-8 nanoparticles loaded in situ.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles, comprising the following steps:

[0009] (1) Dilute the TOCNF suspension gel with deionized water to a TOCNF suspension of 0.4-0.6 mg / mL, sonicate the suspension for 15-30 min, and then stir at 500-800 rpm for 12-18 h to make the TOCNF suspension gel uniformly dispersed, thus obtaining nanocellulose suspension solution A.

[0010] (2) Add zinc nitrate hexahydrate to solution A obtained in step (1), stir at 500-800 rpm for 3-5 hours, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF suspension gel after metal ion exchange in deionized water to obtain solution B with 0.4-0.6 mg / mL.

[0011] (3) Add polyvinylpyrrolidone to solution B obtained in step (2) and stir at 500-800 rpm for 4-6 hours to obtain solution C;

[0012] (4) Add 2-methylimidazole to the solution C obtained in step (3) and stir at 500-800 rpm for 1-2 hours to obtain solution D;

[0013] (5) The solution D obtained in step (4) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 40-70℃ for 12-18 hours to obtain a cellulose barrier membrane with ZIF-8 nanoparticles loaded in situ.

[0014] Preferably, in step (1), the solid content of the TOCNF suspension gel is 1.0-1.2 wt%, and the carboxyl content is 1.3-2.5 mmol / g.

[0015] Preferably, the amount of zinc nitrate hexahydrate added to solution A in step (2) is 0.4-0.8 mg / mL.

[0016] Preferably, the mass ratio of polyvinylpyrrolidone added to solution B in step (3) to the mass ratio of TOCNF added in step (1) is 2:1-5:1. Here, the amount of TOCNF added refers to the oven-dry mass of TOCNF.

[0017] Preferably, the molar ratio of the amount of 2-methylimidazole added to solution C in step (4) to the amount of zinc nitrate hexahydrate in step (2) is 1:6-1:9.

[0018] Another objective of this invention is to provide a method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles in both in-situ and non-in-situ conditions.

[0019] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles, comprising the following steps:

[0020] (1) Dilute the TOCNF suspension gel with deionized water to a TOCNF suspension of 0.4-0.6 mg / mL, sonicate the suspension for 15-30 min, and then stir at 500-800 rpm for 12-18 h to make the TOCNF suspension gel uniformly dispersed, thus obtaining nanocellulose suspension solution A.

[0021] (2) Add zinc nitrate hexahydrate to solution A obtained in step (1), stir at 500-800 rpm for 3-5 hours, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF suspension gel after metal ion exchange in deionized water to obtain solution B with 0.4-0.6 mg / mL.

[0022] (3) Add polyvinylpyrrolidone to solution B obtained in step (2) and stir at 500-800 rpm for 4-6 hours to obtain solution C;

[0023] (4) Add zinc nitrate hexahydrate to solution C obtained in step (3) again, and stir at 500-800 rpm for 3-5 hours to obtain solution C+;

[0024] (5) Add 2-methylimidazole to the solution C+ obtained in step (4) and stir at 500-800 rpm for 1-2 hours to obtain solution D+.

[0025] (6) The solution D+ obtained in step (5) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 40-70℃ for 12-18 hours to obtain a cellulose barrier membrane with in-situ and non-in-situ loaded ZIF-8 nanoparticles.

[0026] Preferably, in step (1), the solid content of the TOCNF suspension gel is 1.0-1.2 wt%, and the carboxyl content is 1.3-2.5 mmol / g.

[0027] Preferably, the amount of zinc nitrate hexahydrate added to solution A in step (2) is 0.4-0.8 mg / mL.

[0028] Preferably, the mass ratio of polyvinylpyrrolidone added to solution B in step (3) to the mass ratio of TOCNF added in step (1) is 2:1-5:1. Here, the amount of TOCNF added refers to the oven-dry mass of TOCNF.

[0029] Preferably, the molar ratio of the amount of 2-methylimidazole added in solution C in step (4) to the total amount of zinc nitrate hexahydrate added in steps (2) and (4) is 1:6-1:9.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] (1) In this invention, TOCNF is selected as a template for ZIF-8 growth to prepare a highly transparent barrier film. TOCNF can be used as a template for in-situ growth of ZIF-8, effectively preventing them from forming aggregates. ZIF-8 nanoparticles are loaded in an "in-situ + non-in-situ" manner to improve the hydrophobicity, thermal stability and mechanical strength of the TOCNF film. Furthermore, since ZIF-8 has certain hydrophobic properties and UV shielding capabilities, it can improve the water vapor barrier performance and UV shielding performance of TOCNF on the one hand, and solve the disadvantage of ZIF-8 being difficult to process and shape on the other hand.

[0032] (2) This invention overcomes the problems of poor bonding between non-in-situ blended ZIF-8 nanoparticles and nanocellulose and low loading of single in-situ grown ZIF-8 nanoparticles by growing ZIF-8 nanoparticles in TOCNF in "in-situ + non-in-situ". Furthermore, the gaps between fibers in the "in-situ + non-in-situ" ZIF-8@CNF hybrid membrane can be filled by ZIF-8 nanoparticles, increasing the steric hindrance for water vapor molecule permeation.

[0033] (3) The hybrid membrane of the present invention uses TEMPO oxidized nanocellulose, zinc nitrate hexahydrate, 2-methylimidazolium and polyvinylpyrrolidone as the main raw materials. The solvent used in the entire preparation process is deionized water and no organic solvents are used. Therefore, it will not cause pollution to the environment and is economically feasible.

[0034] (4) The present invention is simple to operate. Compared with the TOCNF membrane, the prepared ZIF-8@CNF hybrid membrane has improved water vapor barrier performance and low wettability, and has certain UV shielding ability and thermal stability. Attached Figure Description

[0035] Figure 1 SEM images of the TOCNF membrane in Comparative Example 1;

[0036] Figure 2 SEM images of the in-situ ZIF-8@CNF hybrid film in Example 1;

[0037] Figure 3 SEM images of the in-situ and non-in-situ ZIF-8@CNF hybrid film in Example 5;

[0038] Figure 4 TGA images of Examples 1-6 and Comparative Examples 1-2;

[0039] Figure 5 UV-Vis spectra of Examples 1 and 5 and Comparative Example 1. Detailed Implementation

[0040] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, preparation methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0041] The present invention prepares a cellulose barrier membrane with "in-situ" loaded ZIF-8 nanoparticles by the following steps:

[0042] (1) Dilute the TOCNF suspension gel with deionized water to a TOCNF suspension of 0.4-0.6 mg / mL, sonicate the suspension for 15-30 min, and then stir at 500-800 rpm for 12-18 h to make the TOCNF suspension gel uniformly dispersed, thus obtaining nanocellulose suspension solution A.

[0043] (2) Add zinc nitrate hexahydrate to solution A obtained in step (1), stir at 500-800 rpm for 3-5 hours, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF suspension gel after metal ion exchange in deionized water to obtain solution B with 0.4-0.6 mg / mL.

[0044] (3) Add polyvinylpyrrolidone to solution B obtained in step (2) and stir at 500-800 rpm for 4-6 hours to obtain solution C;

[0045] (4) Add 2-methylimidazole to the solution C obtained in step (3) and stir at 500-800 rpm for 1-2 hours to obtain solution D;

[0046] (5) The solution D obtained in step (4) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 40-70℃ for 12-18 hours to obtain a cellulose barrier membrane with ZIF-8 nanoparticles loaded in situ.

[0047] In step (2), the carboxyl group in TOCNF reacts with the metal ion Zn. 2+ Chelation forms nucleation sites for in situ growth of ZIF-8.

[0048] In step (3), polyvinylpyrrolidone (PVP) acts as both a dispersant and a structure-directing agent. As a dispersant, its hydrophobic carbon chains extend into the solvent and interact to generate repulsive forces, preventing the aggregation of ZIF-8 nanoparticles generated in the next reaction. This ensures that the ZIF-8 nanoparticles are uniformly distributed on TOCNF, while aggregated ZIF-8 would cause the film to appear milky white. Therefore, the addition of PVP ensures good transparency of the barrier film. As a structure-directing agent, the presence of carbonyl groups on the mutually repulsive PVP molecules allows for hydrogen bonding with solvent molecules, forming hydrogen bonds between them. This allows the PVP to combine with and encapsulate the ZIF-8 crystals, enabling the ZIF-8 crystals to grow with a specific morphology, thus playing a role in growth modification (structure guidance).

[0049] In step (4), the organic ligand 2-methylimidazole reacts with the metal ions Zn in the solution. 2+ ZIF-8 nanoparticles were synthesized in situ with an excess of 2-methylimidazole to ensure the loading rate of ZIF-8.

[0050] The present invention prepares a cellulose barrier membrane loaded with ZIF-8 nanoparticles in both in-situ and ex-situ conditions, comprising the following steps:

[0051] (1) Dilute the TOCNF suspension gel with deionized water to a TOCNF suspension of 0.4-0.6 mg / mL, sonicate the suspension for 15-30 min, and then stir at 500-800 rpm for 12-18 h to make the TOCNF suspension gel uniformly dispersed, thus obtaining nanocellulose suspension solution A.

[0052] (2) Add zinc nitrate hexahydrate to solution A obtained in step (1), stir at 500-800 rpm for 3-5 hours, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF suspension gel after metal ion exchange in deionized water to obtain solution B with 0.4-0.6 mg / mL.

[0053] (3) Add polyvinylpyrrolidone to solution B obtained in step (2) and stir at 500-800 rpm for 4-6 hours to obtain solution C;

[0054] (4) Add zinc nitrate hexahydrate to solution C obtained in step (3) again, and stir at 500-800 rpm for 3-5 hours to obtain solution C+;

[0055] (5) Add 2-methylimidazole to the solution C+ obtained in step (4) and stir at 500-800 rpm for 1-2 hours to obtain solution D+.

[0056] (6) The solution D+ obtained in step (5) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 40-70℃ for 12-18 hours to obtain a cellulose barrier membrane with in-situ and non-in-situ loaded ZIF-8 nanoparticles.

[0057] Compared to cellulose barrier membranes that only "in situ" load ZIF-8 nanoparticles, the addition of excess Zn in step (4) above... 2+ This process creates free, non-in-situ growth nucleation sites for ZIF-8 in the suspension. It overcomes the problem of weak bonding between ZIF-8 nanoparticles and nanocellulose in non-in-situ blended hybrid membranes. Furthermore, compared to hybrid membranes with only in-situ grown ZIF-8 nanoparticles, the "in-situ + non-in-situ" ZIF-8@CNF hybrid membrane fills the gaps between fibers with ZIF-8 nanoparticles, further increasing the ZIF-8 nanoparticle loading and enhancing the steric hindrance for water vapor molecule permeation.

[0058] Example 1:

[0059] The experimental steps are as follows:

[0060] (1) Add 23.16g of TOCNF suspension gel (solid content = 1.0wt%, carboxyl content = 2.5mmol / g) to 500mL of deionized water to dilute it into a TOCNF suspension of 0.5mg / mL. Sonicate the suspension for 20min and then stir it at 500rpm for 12h to disperse it evenly to obtain solution A.

[0061] (2) Add 0.411 g of zinc nitrate hexahydrate to the solution A obtained in step (1), stir at 500 rpm for 4 h, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF after metal ion exchange in 500 g of deionized water to obtain solution B.

[0062] (3) Add 1.01g of polyvinylpyrrolidone to the solution B obtained in step (2) and stir at 500rpm for 5h to obtain solution C.

[0063] (4) Add 1.0125 g of 2-methylimidazole to the solution C obtained in step (3) and stir at 500 rpm for 4 h to obtain solution D.

[0064] (5) The solution D obtained in step (4) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 60°C for 12 hours to obtain an in-situ ZIF-8@CNF hybrid membrane.

[0065] Example 2:

[0066] The experimental steps are as follows:

[0067] (1) Add 23.16g of TOCNF suspension gel (solid content = 1.0wt%, carboxyl content = 2.5mmol / g) to 500mL of deionized water to dilute it into a TOCNF suspension of 0.5mg / mL. Sonicate the suspension for 20min and then stir it at 500rpm for 12h to disperse it evenly to obtain solution A.

[0068] (2) Add 0.411 g of zinc nitrate hexahydrate to the solution A obtained in step (1), stir at 800 rpm for 4 h, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF after metal ion exchange in 500 g of deionized water to obtain solution B.

[0069] (3) Add 0.58g of polyvinylpyrrolidone to the solution B obtained in step (2) and stir at 500rpm for 5h to obtain solution C.

[0070] (4) Add 0.054 g of zinc nitrate hexahydrate to the solution C obtained in step (3) and stir at 500 rpm for 4 h to obtain solution C+.

[0071] (5) Add 1.0125 g of 2-methylimidazole to the solution C+ obtained in step (4) and stir at 500 rpm for 1 h to obtain solution D.

[0072] (6) The solution D obtained in step (5) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 60°C for 12 hours to obtain an in-situ + non-in-situ ZIF-8@CNF hybrid membrane.

[0073] Example 3

[0074] The experimental steps are as follows:

[0075] (1) Add 23.16g of TOCNF suspension gel (solid content = 1.0wt%, carboxyl content = 2.5mmol / g) to 500mL of deionized water to dilute it into a TOCNF suspension of 0.5mg / mL. Sonicate the suspension for 20min and then stir it at 500rpm for 12h to disperse it evenly to obtain solution A.

[0076] (2) Add 0.411 g of zinc nitrate hexahydrate to the solution A obtained in step (1), stir at 500 rpm for 4 h, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF after metal ion exchange in 500 g of deionized water to obtain solution B.

[0077] (3) Add 0.726g of polyvinylpyrrolidone to the solution B obtained in step (2) and stir at 500rpm for 5h to obtain solution C.

[0078] (4) Add 0.054 g of zinc nitrate hexahydrate to the solution C obtained in step (3) and stir at 500 rpm for 4 h to obtain solution C+.

[0079] (5) Add 1.0125 g of 2-methylimidazole to the solution C+ obtained in step (4) and stir at 500 rpm for 1 h to obtain solution D.

[0080] (6) The solution D obtained in step (5) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 60°C for 12 hours to obtain an in-situ + non-in-situ ZIF-8@CNF hybrid membrane.

[0081] Example 4:

[0082] The experimental steps are as follows:

[0083] (1) Add 23.16g of TOCNF suspension gel (solid content = 1.0wt%, carboxyl content = 2.5mmol / g) to 500mL of deionized water to dilute it into a TOCNF suspension of 0.5mg / mL. Sonicate the suspension for 20min and then stir it at 500rpm for 12h to disperse it evenly to obtain solution A.

[0084] (2) Add 0.411 g of zinc nitrate hexahydrate to the solution A obtained in step (1), stir at 500 rpm for 4 h, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF after metal ion exchange in 500 g of deionized water to obtain solution B.

[0085] (3) Add 0.87g of polyvinylpyrrolidone to the solution B obtained in step (2) and stir at 500rpm for 5h to obtain solution C.

[0086] (4) Add 0.054 g of zinc nitrate hexahydrate to the solution C obtained in step (3) and stir at 500 rpm for 4 h to obtain solution C+.

[0087] (5) Add 1.0125 g of 2-methylimidazole to the solution C+ obtained in step (4) and stir at 500 rpm for 1 h to obtain solution D.

[0088] (6) The solution D obtained in step (5) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 60°C for 12 hours to obtain an in-situ + non-in-situ ZIF-8@CNF hybrid membrane.

[0089] Example 5:

[0090] The experimental steps are as follows:

[0091] (1) Add 23.16g of TOCNF suspension gel (solid content = 1.0wt%, carboxyl content = 2.5mmol / g) to 500mL of deionized water to dilute it into a TOCNF suspension of 0.5mg / mL. Sonicate the suspension for 20min and then stir it at 500rpm for 12h to disperse it evenly to obtain solution A.

[0092] (2) Add 0.411 g of zinc nitrate hexahydrate to the solution A obtained in step (1), stir at 500 rpm for 4 h, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF after metal ion exchange in 500 g of deionized water to obtain solution B.

[0093] (3) Add 1.01g of polyvinylpyrrolidone to the solution B obtained in step (2) and stir at 500rpm for 5h to obtain solution C.

[0094] (4) Add 0.054 g of zinc nitrate hexahydrate to the solution C obtained in step (3) and stir at 500 rpm for 4 h to obtain solution C+.

[0095] (5) Add 1.0125 g of 2-methylimidazole to the solution C+ obtained in step (4) and stir at 500 rpm for 1 h to obtain solution D.

[0096] (6) The solution D obtained in step (5) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 60°C for 12 hours to obtain an in-situ + non-in-situ ZIF-8@CNF hybrid membrane.

[0097] Example 6:

[0098] The experimental steps are as follows:

[0099] (1) Add 23.16g of TOCNF suspension gel (solid content = 1.0wt%, carboxyl content = 2.5mmol / g) to 500mL of deionized water to dilute it into a TOCNF suspension of 0.5mg / mL. Sonicate the suspension for 20min and then stir it at 500rpm for 12h to disperse it evenly to obtain solution A.

[0100] (2) Add 0.4110g of zinc nitrate hexahydrate to the solution A obtained in step (1), stir at 500rpm for 4h, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF after metal ion exchange in 500g of deionized water to obtain solution B.

[0101] (3) Add 1.162g of polyvinylpyrrolidone to the solution B obtained in step (2) and stir at 500rpm for 5h to obtain solution C.

[0102] (4) Add 0.054 g of zinc nitrate hexahydrate to the solution C obtained in step (3) and stir at 500 rpm for 4 h to obtain solution C+.

[0103] (5) Add 1.0125 g of 2-methylimidazole to the solution C+ obtained in step (4) and stir at 500 rpm for 1 h to obtain solution D.

[0104] (6) The solution D obtained in step (5) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 60°C for 12 hours to obtain an in-situ + non-in-situ ZIF-8@CNF hybrid membrane.

[0105] Comparative Example 1:

[0106] The experimental steps are as follows:

[0107] (1) Add 23.16g of TOCNF suspension gel (solid content = 1.0wt%, carboxyl content = 2.5mmol / g) to 500mL of deionized water to dilute it into a TOCNF suspension of 0.5mg / mL. Sonicate the suspension for 20min and then stir it at 500rpm for 12h to disperse it evenly to obtain solution A.

[0108] (2) The solution A in step (1) is filtered by a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 60°C for 12 hours to obtain a pure TOCNF film.

[0109] Comparative Example 2:

[0110] The experimental steps are as follows: 1.17 g of zinc nitrate hexahydrate was dissolved in 8 mL of deionized water to obtain solution A. Then, 22.70 g of 2-methylimidazole was dissolved in 80 mL of deionized water to obtain solution B. The two solutions A and B were then mixed and stirred for 5 min to synthesize a milky white solution. The product was collected by centrifugation and washed 2-3 times with deionized water. The washed product was dried overnight in a forced-air drying oven at 65℃ to obtain ZIF-8 nanoparticles.

[0111] Table 1 Comparison of component addition amounts in different embodiments and comparative examples

[0112]

[0113] Figures 1-3 SEM images of Comparative Example 1, Example 1, and Example 5 are shown below. Figure 1 It can be seen that the surface of TOCNF without ZIF-8 nanoparticles is smooth; Figure 2 It can be seen that the TOCNF surface loaded with ZIF-8 in situ was not uniformly covered with ZIF-8 nanoparticles; by Figure 3 It is known that the TOCNF surface loaded with ZIF-8 in both in-situ and non-in-situ conditions contains continuous and uniform ZIF-8 nanoparticles, which tightly encapsulate the TOCNF surface, forming a "core-shell structure". The encapsulation of ZIF-8 on TOCNF increases the roughness of the TOCNF surface, and ZIF-8 itself has hydrophobic properties, further enhancing the hydrophobic properties of TOCNF. Therefore, the hybrid membrane of this invention has a significantly improved waterproof performance compared to the pure TOCNF membrane.

[0114] Figure 4 These are the thermogravimetric analyses of Examples 1-6 and Comparative Examples 1-2, from... Figure 4 It can be seen that the thermal stability of the hybrid film is significantly improved with the addition of ZIF-8. We also calculated the ZIF-8 loading rate of each hybrid film by thermogravimetric analysis. The ZIF-8 loading rate of Example 1 is 26.29%. Among Examples 2 to 6, the loading rate of Example 5 is the highest, reaching 37.35%. This shows that the addition of non-in-situ ZIF-8 improves the thermal stability of the hybrid film.

[0115] like Figure 5 As shown, the light transmittance of the thin film materials in Examples 1 and 5 and Comparative Example 1 in the 200-800 nm range and the ultraviolet transmittance in the 280-400 nm range are obtained. The transmittance of the pure TOCNF film in Comparative Example 1 in the 280-400 nm range is relatively higher than that of the ZIF-8@CNF hybrid films in Examples 1 and 5, indicating that the ZIF-8@CNF hybrid film has a certain ultraviolet shielding capability. Since the ZIF-8@CNF hybrid film in Example 5 has a higher ZIF-8 loading rate, its ultraviolet shielding effect is also better than that in Example 1, because ZIF-8 itself has an ultraviolet shielding effect. Therefore, introducing ZIF-8 into TOCNF can significantly improve the ultraviolet protection performance of the film, and the resulting transparent hybrid film has good prospects for ultraviolet protection applications.

[0116] Table 2 Comparison of water vapor permeation data for different embodiments and comparative examples

[0117]

[0118]

[0119] This invention uses polyvinylpyrrolidone (PVP) as a structure directing agent for ZIF-8, which improves the loading capacity and UV shielding performance of ZIF-8 while maintaining the good transparency of the hybrid film. As shown in Table 2, when the amount of PPVP added is 1.01 g (i.e., the oven-dry mass ratio of PPVP to TOCNF is 1:5), it is beneficial for the hybrid film to achieve optimal performance. The water vapor transmission rate and water vapor transmission coefficient of the "in-situ" grown ZIF-8@CNF hybrid film are reduced by 47% and 27% respectively compared with the TOCNF film, while the water vapor transmission rate and water vapor transmission coefficient of the "non-in-situ + in-situ" grown ZIF-8@CNF hybrid film are reduced by 54% and 28% respectively compared with the TOCNF film. Table 2 also shows that the ZIF-8@CNF hybrid membrane grown in both in-situ and non-in-situ conditions has a greater thickness. This is because the presence of more ZIF-8 particles increases the distance between fibers, as well as the path and steric hindrance for water vapor permeation. This, to some extent, contributes to the better water vapor barrier performance of Example 5 compared to Example 1. The improved water vapor barrier performance broadens the application of nanocellulose in food packaging, while also reducing the use of non-renewable resources, environmental pollution, and energy consumption.

[0120] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles, characterized in that: Includes the following steps, (1) Dilute the TOCNF suspension gel with deionized water to a TOCNF suspension of 0.4-0.6 mg / mL, sonicate the suspension for 15-30 min, and then stir at 500-800 rpm for 12-18 h to make the TOCNF suspension gel uniformly dispersed, thus obtaining nanocellulose suspension solution A. (2) Add zinc nitrate hexahydrate to solution A obtained in step (1), stir at 500-800 rpm for 3-5 h, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF suspension gel after metal ion exchange in deionized water to obtain solution B with 0.4-0.6 mg / mL. (3) Add polyvinylpyrrolidone to the solution B obtained in step (2) and stir at 500-800 rpm for 4-6 h to obtain solution C; (4) Add 2-methylimidazole to the solution C obtained in step (3) and stir at 500-800 rpm for 1-2 h to obtain solution D; (5) The solution D obtained in step (4) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 40-70℃ for 12-18 h to obtain a cellulose barrier membrane with ZIF-8 nanoparticles loaded in situ.

2. The method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles according to claim 1, characterized in that: In step (1), the solid content of the TOCNF suspension gel is 1.0-1.2 wt%, and the carboxyl content is 1.3-2.5 mmol / g.

3. The method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles according to claim 2, characterized in that: In step (2), the amount of zinc nitrate hexahydrate added to solution A is 0.4-0.8 mg / mL.

4. The method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles according to claim 3, characterized in that: The mass ratio of the amount of polyvinylpyrrolidone added in solution B in step (3) to the amount of TOCNF added in step (1) is 2:1-5:

1.

5. The method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles according to claim 4, characterized in that: The molar ratio of the amount of 2-methylimidazole added in solution C in step (4) to the amount of zinc nitrate hexahydrate added in step (2) is 1:6-1:

9.

6. A method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles as described in any one of claims 1-5, characterized in that: Includes the following steps, (1) Dilute the TOCNF suspension gel with deionized water to a TOCNF suspension of 0.4-0.6 mg / mL, sonicate the suspension for 15-30 min, and then stir at 500-800 rpm for 12-18 h to make the TOCNF suspension gel uniformly dispersed, thus obtaining nanocellulose suspension solution A. (2) Add zinc nitrate hexahydrate to solution A obtained in step (1), stir at 500-800 rpm for 3-5 h, then centrifuge and wash to remove the supernatant, and redisperse the TOCNF suspension gel after metal ion exchange in deionized water to obtain solution B with 0.4-0.6 mg / mL. (3) Add polyvinylpyrrolidone to the solution B obtained in step (2) and stir at 500-800 rpm for 4-6 h to obtain solution C; (4) Add zinc nitrate hexahydrate to the solution C obtained in step (3) again, and stir at 500-800 rpm for 3-5 hours to obtain solution C+; (5) Add 2-methylimidazole to the solution C+ obtained in step (4) and stir at 500-800 rpm for 1-2 h to obtain solution D+; (6) The solution D+ obtained in step (5) is filtered through a vacuum filtration device to form a wet film. The wet film is peeled off and sandwiched between two acrylic plates and placed in a vacuum drying oven at 40-70℃ for 12-18 h to obtain a cellulose barrier membrane with in-situ and non-in-situ loaded ZIF-8 nanoparticles.

7. The method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles according to claim 6, characterized in that: In step (1), the solid content of the TOCNF suspension gel is 1.0-1.2 wt%, and the carboxyl content is 1.3-2.5 mmol / g.

8. The method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles according to claim 7, characterized in that: In step (2), the amount of zinc nitrate hexahydrate added to solution A is 0.4-0.8 mg / mL.

9. The method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles according to claim 8, characterized in that: The mass ratio of the amount of polyvinylpyrrolidone added in solution B in step (3) to the amount of TOCNF added in step (1) is 2:1-5:

1.

10. The method for preparing a cellulose barrier membrane loaded with ZIF-8 nanoparticles according to claim 9, characterized in that: The molar ratio of the amount of 2-methylimidazole added in solution C in step (4) to the total amount of zinc nitrate hexahydrate added in steps (2) and (4) is 1:6-1:9.

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