Montmorillonite / cellulose nanocrystalline composite film as well as preparation method and application thereof

Abstract

The invention discloses a montmorillonite / cellulose nanocrystalline composite film as well as a preparation method and application thereof. The method disclosed by the invention comprises the following steps: firstly, preparing polyether amine D230 modified montmorillonite aqueous dispersion by taking polyether amine D230 as a modifier; and mixing the polyether amine D230 modified montmorillonite aqueous dispersion liquid with the carboxylated cellulose nanocrystal aqueous dispersion liquid, and carrying out solvent exchange to prepare the montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion liquid. Finally, a cross-linking agent is introduced to enhance the interface interaction between the montmorillonite and the carboxylated cellulose nanocrystals. According to the preparation method provided by the invention, stable dispersion of montmorillonite is realized by utilizing a dispersion effect of carboxylated cellulose, and lyotropic liquid crystal characteristics of carboxylated cellulose nanocrystals are combined; a montmorillonite filler network with an ordered structure is constructed through a solvent evaporation self-assembly method, so that the high-barrier-property composite film with a brick-mud structure is prepared. The composite film provided by the invention has a wide application prospect in the field of packaging materials.

Description

Technical Field

[0001] The present invention relates to the field of packaging barrier materials, and particularly to a montmorillonite / cellulose nanocrystal composite film, a preparation method thereof, and an application thereof. Background Art

[0002] The "white pollution" caused by the extensive application of plastic packaging products is becoming increasingly serious. Natural biodegradable bio-based packaging materials have become a new trend in the development of the packaging industry. As the most widely sourced natural polymer material in nature, cellulose has the advantages of good flexibility, high transparency, and low gas permeability, and is a potential substitute for traditional packaging materials. However, insufficient mechanical strength and poor water resistance are the biggest problems faced by cellulose films when applied in the field of packaging barrier materials. Research has found that adding montmorillonite (MMT) is an effective method to endow cellulose films with excellent flame retardancy, barrier properties, etc.

[0003] A shell is a high-performance natural composite material composed of calcium carbonate - biopolymers. Its unique "brick - mud" microstructure endows the shell with high strength, high toughness, and other characteristics. Inspired by the "brick - mud" microstructure in the shell, to retain or enhance the original properties of cellulose films, it is necessary to finely regulate the internal structure of the films and construct a highly ordered film structure. The ordered structure is conducive to transferring the unique properties of cellulose and MMT to the macroscopic film material respectively, so that the composite film obtains properties that single components do not have. Therefore, the formation of an ordered structure in the composite film is the key to preparing a high-performance montmorillonite / cellulose composite film. To construct an ordered structure inside the composite film, a common strategy is to start from layered silicate materials, prepare a stable and fully exfoliated lamellar silicate dispersion, and then prepare a composite film with excellent properties through self-assembly.

[0004] Nanocellulose is a semi-crystalline material composed of crystalline regions and amorphous regions. The disordered regions and semi-crystalline regions of cellulose are more easily hydrolyzed, while the crystalline regions with stronger resistance to acid remain intact. Therefore, by acid hydrolyzing cellulose, the microfibrils at the defect sites are removed, and rod-shaped cellulose nanocrystals (CNC) with anisotropy are obtained. The CNC and its derivatives prepared by hydrolysis with sulfuric acid and phosphoric acid have a high surface charge density and are uniformly dispersed in water or organic solvents such as formamide, DMSO, and N,N-dimethylformamide. When the CNC reaches the critical phase transition concentration as the solvent volatilizes, in order to minimize the electrostatic repulsion between the CNC, the CNC forms a chiral nematic liquid crystal.

[0005] Therefore, by utilizing the lyotropic liquid crystal property of CNC, through the solvent evaporation self-assembly technique, montmorillonite nanomaterials can be induced to form a layered ordered arrangement in the CNC matrix, and a high-performance bionic structure montmorillonite / cellulose nanocrystal composite film can be prepared. Summary of the Invention

[0006] To achieve the above object, the present invention provides the following technical solutions: In a first aspect of the present invention, a method for preparing a montmorillonite / cellulose nanocrystal composite film is provided. The preparation method includes the following steps: S1: Preparation of a carboxylated cellulose nanocrystal aqueous dispersion; S2: Preparation of a polyetheramine D230-modified montmorillonite aqueous dispersion; S3: Adding the polyetheramine D230-modified montmorillonite aqueous dispersion prepared in step S2 to the carboxylated cellulose nanocrystal aqueous dispersion prepared in step S1. After mixing, ultrasonic dispersion is carried out to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then, the water in the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion is replaced with an organic solvent to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion; S4: Adding a crosslinking agent to the montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion in step S3, and stirring and mixing evenly to obtain a composite solution; S5: Pouring the composite solution in step S4 into a mold, and vacuum drying at 40 - 60 °C, followed by heat treatment to obtain the montmorillonite / cellulose nanocrystal composite film.

[0007] Further, in step S1, the concentration of the carboxylated cellulose nanocrystal aqueous dispersion is 3 - 8 wt%, preferably 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% or 8 wt%.

[0008] Further, in step S1, the preparation of the carboxylated cellulose nanocrystal aqueous dispersion includes the following steps: adding carboxylated cellulose nanocrystals to deionized water, stirring at room temperature and then performing ultrasonic dispersion to obtain a carboxylated cellulose nanocrystal aqueous dispersion.

[0009] In a specific embodiment of the present invention, in step S1, the carboxylated cellulose nanocrystals are purchased from Angxing New Carbon Materials Changzhou Co., Ltd. In some other specific embodiments of the present invention, in step S1, the room temperature stirring is carried out for 30 - 60 min, preferably 30 min. In still some other specific embodiments of the present invention, in step S1, the ultrasonic dispersion is carried out for 1 - 2 h, preferably 1 h.

[0010] Further, in step S2, the concentration of the polyetheramine D230-modified montmorillonite aqueous dispersion is 0.5 - 3 wt%, preferably, the concentration of the polyetheramine D230-modified montmorillonite aqueous dispersion is 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt% or 3 wt%.

[0011] Further, in step S2, the preparation of the polyetheramine D230 modified montmorillonite aqueous dispersion comprises the following steps: S2-1: Disperse montmorillonite (MMT) in deionized water by mechanical stirring to obtain an MMT aqueous dispersion; S2-2: Slowly add dilute hydrochloric acid dropwise to an aqueous solution of polyetheramine D230 to prepare protonated polyetheramine D230; S2-3: Under stirring conditions, add the protonated polyetheramine D230 obtained in step S2-2 to the MMT aqueous dispersion obtained in step S2-1 for an ion exchange reaction. After the reaction is completed, wash with water and filter by suction to obtain wet polyetheramine D230 modified montmorillonite containing water; S2-4: Add the wet polyetheramine D230 modified montmorillonite containing water prepared in step S2-3 to deionized water, ultrasonicate, centrifuge, and take the supernatant to obtain the polyetheramine D230 modified montmorillonite aqueous dispersion, and calibrate the concentration.

[0012] In some specific embodiments of the present invention, the concentration of the dilute hydrochloric acid used in step S2-2 is 0.2N, and the amount used is the amount capable of protonating one amine group, preferably 435 ml.

[0013] In some specific embodiments of the present invention, in step S2-3, the molar amount of polyetheramine D230 is 1.2 times the molar amount of exchangeable sodium ions between the MMT layers.

[0014] In some specific embodiments of the present invention, the ion exchange reaction in step S2-3 is carried out at 60-100°C, preferably 80°C; further preferably, the ion exchange reaction is carried out for 6-10 h, preferably 8 h.

[0015] In some specific embodiments of the present invention, the ultrasonication in step S2-4 is carried out using an ultrasonic cell disruptor. More specifically, the ultrasonication is carried out with the following parameters: power: 500 W; 60%; 4 s on and 2 s off.

[0016] In some specific embodiments of the present invention, the centrifugation in step S2-4 is carried out at 5000 rpm for 30 min.

[0017] Further, in the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion and / or organic solvent dispersion in step S3, the mass ratio of polyetheramine D230-modified montmorillonite to carboxylated cellulose nanocrystals is 1:1 - 20, preferably 1:1 - 15, more preferably 1:1 - 10, still more preferably 1:1 - 6, and even more preferably 1:1 - 3. In some specific embodiments of the present invention, in the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion and / or organic solvent dispersion in step S3, the mass ratio of polyetheramine D230-modified montmorillonite to carboxylated cellulose nanocrystals is 1:1, 1:3, 1:6, 1:10, 1:15, or 1:20.

[0018] Further, in step S3, the ultrasonic dispersion is carried out using a well-known ultrasonic cell disruptor in the art. In a specific embodiment, the ultrasonic dispersion in step S3 is carried out as follows: The mixed polyetheramine D230-modified montmorillonite aqueous dispersion and carboxylated cellulose nanocrystal aqueous dispersion are placed into an ultrasonic cell disruptor and ultrasonically dispersed for 30 min (power: 500 W; 60%; 4 s on and 2 s off) to obtain a mixed dispersion.

[0019] Further, in step S3, the replacement of water in the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion with an organic solvent is carried out as follows: An organic solvent with the same volume as the water contained therein is added to the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion, and deionized water is evaporated and collected by rotary evaporation to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0020] Further, in step S3, the organic solvent is selected from one or more of N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0021] Further, in step S4, the crosslinking agent is a mixture of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol with a mass ratio of 9:1.

[0022] Further, in step S4, the dosage of the crosslinking agent is in a ratio of 3:7 to the sum of the masses of polyetheramine D230-modified montmorillonite and carboxylated cellulose nanocrystals.

[0023] Further, in step S5, the mold can be a polytetrafluoroethylene mold. Preferably, the depth of the polytetrafluoroethylene mold is ≤4 mm.

[0024] Further, in step S5, the heat treatment includes: heat treatment at 100 - 120 °C for 2 - 3 h, and then heat treatment at 150 - 170 °C for 1 - 3 h.

[0025] In the second aspect of the present invention, a montmorillonite / cellulose nanocrystal composite film is provided, which is prepared by the method provided by the present invention.

[0026] In the third aspect of the present invention, there is provided the use of the montmorillonite / cellulose nanocrystal composite film described in the present invention or the montmorillonite / cellulose nanocrystal composite film prepared by the preparation method described in the present invention as a barrier material.

[0027] The present invention first uses water-soluble polyetheramine D230 as a modifier to prepare polyetheramine D230-modified montmorillonite, and uses ultrasonic dispersion method to achieve the exfoliation and dispersion of polyetheramine D230-modified montmorillonite in water, obtaining a stable monolayer polyetheramine D230-modified montmorillonite aqueous dispersion. This stable monolayer dispersion of polyetheramine D230-modified montmorillonite is the basis for obtaining the "brick-clay" structure through solvent evaporation self-assembly. Cellulose nanocrystals are rod-shaped fibers with high crystallinity obtained by acid hydrolysis of the amorphous region of cellulose, which can be uniformly dispersed in water or polar organic solvents. During the solvent evaporation process, when cellulose nanocrystals reach the critical phase transition concentration, in order to minimize the electrostatic repulsion between cellulose nanocrystals, cellulose nanocrystals form a cholesteric liquid crystal. In the liquid crystal structure, cellulose nanocrystals are arranged parallel within the layer and are twisted and stacked between layers. The distance between two layers with a twist angle of 360° is the single pitch, and the formed cholesteric liquid crystal can directly observe the bright and dark fingerprint texture under cross-polarized light. The layered ordered structure formed by cellulose nanocrystals during the solvent evaporation process can be used as a template to assist the oriented arrangement of polyetheramine D230-modified montmorillonite layers.

[0028] The present invention utilizes the dispersion effect and lyotropic liquid crystal characteristics of carboxylated cellulose nanocrystals, and through solvent evaporation self-assembly, constructs an ordered and oriented polyetheramine D230-modified montmorillonite layer network, and further adds a cross-linking agent to enhance the interfacial interaction, thereby preparing a composite film with a shell-like structure.

[0029] The composite film prepared by the present invention has good flexibility, thermal stability, tensile strength and water and oxygen barrier properties, and has broad application prospects as a barrier material. Description of the Drawings

[0030] Figure 1 It is the Zeta potential diagram of the hybrid aqueous dispersion in Examples 1-12; Figure 2 It is the transmission electron microscope diagram of the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion prepared in Example 1; Figure 3 It is the Tyndall effect test diagram of the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion prepared in Example 12; Figure 4Tyndall effect test diagram of the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion prepared in Example 3 and Example 4; Figure 5 Cross-sectional scanning electron microscope image of the composite film prepared in Example 2; Figure 6 Transmission electron microscope image of the composite film prepared in Example 3; Figure 7 Transmission electron microscope image of the ultrathin section of the composite film prepared in Example 8; Figure 8 Barrier property test diagram of the composite films prepared in Examples 1 - 12; Figure 9 Mechanical property test diagram of the composite films prepared in Examples 1 - 9; Figure 10 Physical image of the composite film prepared in Example 13. Specific embodiments To make the technical problems, technical solutions, and advantages to be solved by the present invention clearer, the following will be described in detail with reference to specific embodiments. All materials selected in the present invention are commercially available materials without special requirements.

[0032] Among them, the montmorillonite is PGW sodium-based montmorillonite from NANOCOR (the molar amount of exchangeable sodium ions between layers CEC = 145 mmol / 100 g), the carboxylated cellulose nanofibers (5 wt%, liquid) are reagents from Macklin, and the remaining raw materials such as polypropylene glycol diglycidyl ether, 2, 4, 6-tris(dimethylaminomethyl)phenol, polyetheramine D230, and D400 are all commercially available products without special restrictions. The experimental methods without specific conditions are conventional methods and conventional conditions well-known in the art, or conditions recommended by the instrument manufacturer.

[0033] Example 1 (1) Weigh 10 g of carboxylated cellulose nanocrystals and add them to 190 g of deionized water. Stir and disperse at room temperature for 30 min with a magnetic stirrer and then ultrasonically disperse for 1 h to prepare a 5 wt% carboxylated cellulose nanocrystal aqueous dispersion for later use.

[0034] (2) Weigh 20.01 g of polyetheramine D230 and add 150 ml of deionized water to dilute it. Slowly add 435 ml of 0.2 N hydrochloric acid dropwise under stirring to ensure the protonation of one amine group to prepare protonated polyetheramine D230 for later use.

[0035] (3) Add 50 g of MMT to 5000 ml of deionized water and mechanically stir at room temperature for 3 h to obtain an MMT aqueous dispersion. Under stirring conditions, add the protonated polyetheramine D230 prepared in step (2) dropwise to the MMT aqueous dispersion. After the addition is complete, raise the temperature to 80 °C, stop stirring after reacting for 8 h, cool, filter to collect the solid, and wash the solid product with deionized water until no precipitate is detected in the deionized water with silver nitrate. The obtained product is hydrated wet polyetheramine D230-modified montmorillonite.

[0036] (4) Weigh 30 g of the product from step (3) and add it to deionized water. After stirring and dispersing, place the mixed dispersion into an ultrasonic cell disruptor and ultrasonicate for 30 min (power: 500 W; 60%; 4 s on and 2 s off). Then centrifuge the dispersion at 5000 rpm for 30 min, collect the upper-layer dispersion, and calibrate the concentration of the dispersion by the weighing method to obtain a 2 wt% polyetheramine D230-modified montmorillonite aqueous dispersion.

[0037] (5) Add 16.5 g of the polyetheramine D230-modified montmorillonite aqueous dispersion prepared in step (4) (the mass of polyetheramine D230-modified montmorillonite is 0.33 g) to 133.4 g of a 5 wt% carboxylated cellulose nanocrystal dispersion (the mass of carboxylated cellulose nanocrystals is 6.67 g). After mixing, ultrasonicate (power: 500 W; 60%; 4 s on and 2 s off) for 30 min to disperse and obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then add an equal volume of N-methylpyrrolidone to the hybrid aqueous dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0038] (6) Add 3 g of a 9:1 mass ratio of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol to the hybrid organic solvent dispersion prepared in step (5), stir and mix evenly to obtain a composite solution. Pour the obtained composite solution into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, vacuum dry at 40 °C, heat-treat at 120 °C for 2 h after drying, and heat-treat at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film.

[0039] Example 2 Steps (1) to (4) are the same as in Example 1.

[0040] (5) Add 22 g of the polyetheramine D230 modified montmorillonite aqueous dispersion prepared in step (4) (the mass of the polyetheramine D230 modified montmorillonite is 0.44 g) to 131.2 g of a 5 wt% carboxylated cellulose nanocrystal dispersion (the mass of the carboxylated cellulose nanocrystals is 6.56 g). After mixing, ultrasonicate (power: 500 W; 60%; 4 s on, 2 s off) for 30 min to disperse and obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then, add an equal volume of dimethyl sulfoxide to the hybrid aqueous dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0041] (6) Add 3 g of a 9:1 mass ratio of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol to the hybrid organic solvent dispersion prepared in step (5). After stirring and mixing evenly, a composite solution is obtained. Pour the obtained composite solution into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, vacuum dry at 40 °C, heat treat at 120 °C for 2 h after drying, and heat treat at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film.

[0042] Example 3 Steps (1) to (4) are the same as those in Example 1.

[0043] (5) Add 32 g of the polyetheramine D230 modified montmorillonite aqueous dispersion prepared in step (4) (the mass of the polyetheramine D230 modified montmorillonite is 0.64 g) to 127.2 g of a 5 wt% carboxylated cellulose nanocrystal dispersion (the mass of the carboxylated cellulose nanocrystals is 6.36 g). After mixing, ultrasonicate (power: 500 W; 60%; 4 s on, 2 s off) for 30 min to disperse and obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then, add an equal volume of dimethyl sulfoxide to the hybrid aqueous dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0044] (6) Add 3 g of a 9:1 mass ratio of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol to the hybrid organic solvent dispersion prepared in step (5). After stirring and mixing evenly, a composite solution is obtained. Pour the obtained composite solution into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, vacuum dry at 40 °C, heat treat at 120 °C for 3 h after drying, and heat treat at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film.

[0045] Example 4 Steps (1) to (4) are the same as those in Example 1.

[0046] (5) Add 50 g of the polyetheramine D230 modified montmorillonite aqueous dispersion prepared in step (4) (the mass of the polyetheramine D230 modified montmorillonite is 1.00 g) to 120.0 g of a 5 wt% carboxylated cellulose nanocrystal dispersion (the mass of the carboxylated cellulose nanocrystals is 6.00 g). After mixing, sonicate (power: 500 W; 60%; 4 s on, 2 s off) for 30 min to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then, add an equal volume of dimethyl sulfoxide to the hybrid aqueous dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0047] (6) Add 3 g of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol with a mass ratio of 9:1 to the hybrid organic solvent dispersion prepared in step (5). After stirring and mixing evenly, a composite solution is obtained. Pour the obtained composite solution into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, and vacuum dry at 40 °C. After drying, heat-treat at 120 °C for 3 h and then at 150 °C for 2 h to obtain a montmorillonite / cellulose nanocrystal composite film.

[0048] Example 5 Steps (1)-(4) are the same as in Example 1.

[0049] (5) Add 116.5 g of the polyetheramine D230 modified montmorillonite aqueous dispersion prepared in step (4) (the mass of the polyetheramine D230 modified montmorillonite is 2.33 g) to 93.4 g of a 5 wt% carboxylated cellulose nanocrystal dispersion (the mass of the carboxylated cellulose nanocrystals is 4.67 g). After mixing, sonicate (power: 500 W; 60%; 4 s on, 2 s off) for 30 min to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then, add an equal volume of dimethyl sulfoxide to the hybrid aqueous dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0050] (6) Add 3 g of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol with a mass ratio of 9:1 to the hybrid organic solvent dispersion prepared in step (5). After stirring and mixing evenly, a composite solution is obtained. Pour the obtained composite solution into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, and vacuum dry at 40 °C. After drying, heat-treat at 120 °C for 3 h and then at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film.

[0051] Example 6 Steps (1) to (4) are the same as those in Example 1.

[0052] (5) Add 175.0 g of the polyetheramine D230 modified montmorillonite aqueous dispersion prepared in step (4) (the mass of the polyetheramine D230 modified montmorillonite is 3.50 g) to 70.0 g of a 5 wt% carboxylated cellulose nanocrystal dispersion (the mass of the carboxylated cellulose nanocrystals is 3.50 g). After mixing, ultrasonicate (power: 500 W; 60%; 4 s on and 2 s off) for 30 min to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then add an equal volume of dimethyl sulfoxide to the hybrid aqueous dispersion and mix well. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0053] (6) Add 3 g of a 9:1 mass ratio of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol to the hybrid organic solvent dispersion prepared in step (5). After stirring and mixing evenly, obtain a composite solution. Pour the obtained composite solution into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, and vacuum dry at 40 °C. After drying, heat treat at 120 °C for 3 h and then at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film.

[0054] Example 7 (1) Weigh 10 g of carboxylated cellulose nanocrystals and add them to 190 g of deionized water. Stir and disperse at room temperature for 30 min using a magnetic stirrer and then ultrasonically disperse for 1 h to prepare a 5 wt% carboxylated cellulose nanocrystal aqueous dispersion for later use.

[0055] (2) Weigh 140.0 g of a 5 wt% carboxylated cellulose nanocrystal dispersion (the mass of the carboxylated cellulose nanocrystals is 7.0 g). Then add 3 g of a 9:1 mass ratio of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol. After stirring and mixing evenly, pour it into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, and vacuum dry at 40 °C. After drying, heat treat at 120 °C for 3 h and then at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film.

[0056] Example 8 (1) Weigh 20.01 g of polyetheramine D230 and add 150 ml of deionized water to dilute it. Slowly add 435 ml of 0.2 N hydrochloric acid dropwise under stirring to ensure the protonation of one amine group to prepare protonated polyetheramine D230 for later use.

[0057] (2) Add 50 g of MMT to 5000 ml of deionized water, and mechanically stir at room temperature for 3 h to obtain an MMT aqueous dispersion. While stirring, dropwise add the protonated polyetheramine D230 solution prepared in step (1) thereto. After the addition is complete, raise the temperature to 80 °C, stop stirring after reacting for 8 h, cool, filter to collect the solid, and wash the solid product with deionized water until no precipitate is detected in the deionized water with silver nitrate. The obtained product is hydrated polyetheramine D230-modified montmorillonite.

[0058] (3) Weigh 30 g of the product from step (3) and add it to deionized water. After stirring and dispersing, place the mixed dispersion into an ultrasonic cell disruptor and ultrasonicate for 30 min (power: 500 W; 60%; 4 s on and 2 s off). Then centrifuge the dispersion at 5000 rpm for 30 min, collect the upper-layer dispersion, and calibrate the concentration of the dispersion by the weighing method to obtain a 2 wt% polyetheramine D230-modified montmorillonite aqueous dispersion.

[0059] (4) Add 116.5 g of the polyetheramine-modified montmorillonite aqueous dispersion prepared in step (3) (the mass of D230-modified montmorillonite is 2.33 g) to 93.4 g of 5 wt% carboxylated cellulose nanofibers (liquid) (the mass of carboxylated cellulose nanofibers is 4.67 g). After mixing, ultrasonicate (power: 500 W; 60%; 4 s on and 2 s off) for 30 min to disperse and obtain a montmorillonite / carboxylated cellulose nanofiber hybrid aqueous dispersion. Then add an equal volume of dimethyl sulfoxide to the mixed dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanofiber hybrid organic solvent dispersion.

[0060] (5) Add 3 g of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol with a mass ratio of 9:1 to the hybrid dispersion prepared in step (4). After stirring and mixing evenly, pour it into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, vacuum dry at 40 °C, heat-treat at 120 °C for 2 h after drying, and heat-treat at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film. Example 9

[0061] (1) Weigh 5 g of carboxylated cellulose nanocrystals and add them to 95 g of deionized water. Stir and disperse at room temperature for 30 min with a magnetic stirrer and then ultrasonically disperse for 1 h to prepare a 5 wt% carboxylated cellulose nanocrystal aqueous dispersion for use.

[0062] (2) Preparation of montmorillonite aqueous dispersion: Weigh 5 g of MMT and add it to 245 g of deionized water. Mechanically stir and disperse it at a rotation speed of 2000 r / min for 24 h, then place it in an ultrasonic cell disruptor, insert the probe, and perform ultrasonic treatment for 20 minutes at a power of 500 W (the ultrasonic process alternates between working for 2 seconds and pausing for 2 seconds) to obtain a montmorillonite aqueous dispersion with a mass fraction of 2 wt%.

[0063] (3) Add the montmorillonite aqueous dispersion prepared in step (2) (the mass of montmorillonite is 2.33 g) to 93.4 g of a 5 wt% carboxylated cellulose nanocrystal dispersion (the mass of carboxylated cellulose nanocrystals is 4.67 g). After mixing, perform ultrasonic treatment (power: 500 W; 60%; 4 s on and 2 s off) for 30 min to disperse and obtain a mixed dispersion. Then add an equal volume of dimethyl sulfoxide to the mixed dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a carboxylated cellulose nanocrystal / montmorillonite hybrid dispersion.

[0064] (4) Add 3 g of polypropylene glycol diglycidyl ether and 2, 4, 6-tris(dimethylaminomethyl)phenol with a mass ratio of 9:1 to the hybrid dispersion prepared in step (3). After stirring and mixing evenly, pour it into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, perform vacuum drying at 40 °C, and then perform heat treatment at 120 °C for 3 h and at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film. Example 10

[0065] (1) Weigh 6 g of carboxylated cellulose nanocrystals and add them to 194 g of deionized water. Stir and disperse them with a magnetic stirrer at room temperature for 30 min and then perform ultrasonic dispersion for 1 h to prepare a carboxylated cellulose nanocrystal aqueous dispersion with a mass fraction of 3 wt% for later use.

[0066] (2) Weigh 20.01 g of polyetheramine D230 and add 150 ml of deionized water to dilute it. Slowly add 435 ml of 0.2 N hydrochloric acid dropwise under stirring conditions to ensure the protonation of one amine group to prepare protonated polyetheramine D230 for later use.

[0067] (3) Add 50 g of MMT to 5000 ml of deionized water and mechanically stir at room temperature for 3 h to obtain an MMT aqueous dispersion. Under stirring conditions, slowly add the protonated polyetheramine D230 solution prepared in step (2) to the MMT aqueous dispersion. After the addition is complete, raise the temperature to 80 °C, stop stirring after reacting for 8 h, cool, filter and collect the solid, and wash the solid product with deionized water until no precipitation is detected in the deionized water with silver nitrate. The obtained product is a wet polyetheramine D230-modified montmorillonite containing water.

[0068] (4) Weigh 30 g of the product from step (3) and add it to deionized water. After stirring and dispersing, place the mixed dispersion into an ultrasonic cell disruptor and sonicate for 30 min (power: 500 W; 60%; 4 s on and 2 s off). Then centrifuge the dispersion at 5000 rpm for 30 min, collect the upper-layer dispersion, and calibrate the concentration of the dispersion by the weighing method to obtain a 0.5 wt% polyetheramine D230 modified montmorillonite aqueous dispersion.

[0069] (5) Add 66 g of the polyetheramine D230 modified montmorillonite aqueous dispersion prepared in step (4) (the mass of D230 modified montmorillonite is 0.33 g) to 222.3 g of a 3 wt% carboxylated cellulose nanocrystal dispersion (the mass of carboxylated cellulose nanocrystals is 6.67 g). After mixing, sonicate (power: 500 W; 60%; 4 s on and 2 s off) for 30 min to disperse and obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then add an equal volume of N-methylpyrrolidone to the hybrid aqueous dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0070] (6) Add 3 g of a 9:1 mass ratio of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol to the hybrid organic solvent dispersion prepared in step (5). After stirring and mixing evenly, pour it into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, vacuum dry at 40 °C, heat-treat at 120 °C for 3 h after drying, and heat-treat at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film. Example 11

[0071] (1) Weigh 16 g of carboxylated cellulose nanocrystals and add them to 184 g of deionized water. Stir and disperse at room temperature for 30 min with a magnetic stirrer and then sonicate for 1 h to prepare an 8 wt% carboxylated cellulose nanocrystal aqueous dispersion for use.

[0072] (2) Weigh 20.01 g of polyetheramine D230 and add 150 ml of deionized water to dilute it. Slowly add 435 ml of 0.2 N hydrochloric acid dropwise under stirring conditions to ensure the protonation of one amine group to prepare protonated polyetheramine D230 for use.

[0073] (3) Add 50 g of MMT to 5000 ml of deionized water, and mechanically stir at room temperature for 3 h to obtain an MMT aqueous dispersion. Under stirring conditions, dropwise add the protonated polyetheramine D230 solution prepared in step (2) to the MMT aqueous dispersion. After the addition is complete, raise the temperature to 80 °C, stop stirring after reacting for 8 h, cool, filter to collect the solid, and wash the solid product with deionized water until no precipitate is detected in the deionized water with silver nitrate. The obtained product is wet polyetheramine D230-modified montmorillonite containing water.

[0074] (4) Weigh 30 g of the product from step (3) and add it to deionized water. After stirring and dispersing, place the mixed dispersion into an ultrasonic cell disruptor and ultrasonicate for 30 min (power: 500 W; 60%; 4 s on and 2 s off). Then centrifuge the dispersion at 5000 rpm for 30 min, collect the upper-layer dispersion, and calibrate the concentration of the dispersion by the weighing method to obtain a 3 wt% polyetheramine D230-modified montmorillonite aqueous dispersion.

[0075] (5) Add 11 g of the polyetheramine D230-modified montmorillonite aqueous dispersion prepared in step (4) (the mass of polyetheramine D230-modified montmorillonite is 0.33 g) to 83.4 g of an 8 wt% carboxylated cellulose nanocrystal dispersion (the mass of carboxylated cellulose nanocrystals is 6.67 g). After mixing, ultrasonically disperse to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then add an equal volume of N-methylpyrrolidone to the hybrid aqueous dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0076] (6) Add 3 g of a 9:1 mass ratio of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol to the hybrid organic solvent dispersion prepared in step (5), stir and mix evenly to obtain a composite solution. Pour the obtained composite solution into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, vacuum dry at 40 °C, and heat-treat at 120 °C for 3 h and at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film. Example 12

[0077] (1) Weigh 10 g of carboxylated cellulose nanocrystals and add them to 190 g of deionized water. Stir and disperse at room temperature for 30 min with a magnetic stirrer and then ultrasonically disperse for 1 h to prepare a 5 wt% carboxylated cellulose nanocrystal aqueous dispersion for use.

[0078] (2) Weigh 34.8 g of polyetheramine D400 and add 1000 ml of deionized water to dilute it. Slowly add 435 ml of 0.2 N hydrochloric acid under stirring conditions to ensure the protonation of one amine group, and prepare protonated polyetheramine D400 for later use.

[0079] (3) Add 50 g of MMT to 5000 ml of deionized water and mechanically stir at room temperature for 3 h to obtain an MMT aqueous dispersion. Under stirring conditions, add the protonated polyetheramine D400 solution prepared in step (2) dropwise to the MMT aqueous dispersion. After the addition is complete, raise the temperature to 80 °C, stop stirring after reacting for 8 h, cool, filter to collect the solid, and wash the solid product with deionized water until no precipitate is detected in the deionized water with silver nitrate. The obtained product is wet polyetheramine D400-modified montmorillonite containing water.

[0080] (4) Weigh 30 g of the product from step (3) and add it to deionized water. After stirring and dispersing, place the mixed dispersion into an ultrasonic cell disruptor and ultrasonicate for 30 min (power: 500 W; 60%; 4 s on and 2 s off). Then centrifuge the dispersion at 5000 rpm for 30 min, collect the upper-layer dispersion, and calibrate the concentration of the dispersion by the weighing method to obtain a 2 wt% polyetheramine D400-modified montmorillonite aqueous dispersion.

[0081] (5) Add 16.5 g of the polyetheramine D400-modified montmorillonite aqueous dispersion prepared in step (4) (the mass of polyetheramine D400-modified montmorillonite is 0.33 g) to 133.4 g of a 5 wt% carboxylated cellulose nanocrystal dispersion (the mass of carboxylated cellulose nanocrystals is 6.67 g). After mixing, ultrasonicate (power: 500 W; 60%; 4 s on and 2 s off) for 30 min to disperse and obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then add an equal volume of dimethyl sulfoxide to the hybrid aqueous dispersion and mix evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0082] (6) Add 3 g of a 9:1 mass ratio of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol to the hybrid organic solvent dispersion prepared in step (5), stir and mix evenly to obtain a composite solution. Pour the obtained composite solution into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, vacuum dry at 40 °C, and then heat-treat at 120 °C for 3 h and at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film. Example 13

[0083] (1) Weigh 16 g of carboxylated cellulose nanocrystals and add them to 184 g of deionized water. Stir and disperse them at room temperature for 30 min using a magnetic stirrer, and then ultrasonically disperse them for 1 h to prepare an 8 wt% aqueous dispersion of carboxylated cellulose nanocrystals for later use.

[0084] (2) Weigh 20.01 g of polyetheramine D230 and add 150 ml of deionized water to dilute it. Slowly add 435 ml of 0.2 N hydrochloric acid dropwise under stirring conditions to ensure the protonation of one amine group, and prepare protonated polyetheramine D230 for later use.

[0085] (3) Add 50 g of MMT to 5000 ml of deionized water and mechanically stir it at room temperature for 3 h to obtain an MMT aqueous dispersion. Then, under stirring conditions, slowly add the protonated polyetheramine D230 solution prepared in step (2). After the addition is complete, raise the temperature to 80 °C, stop stirring after reacting for 8 h, cool it, filter and collect the solid, and wash the solid product with deionized water until no precipitate is detected in the deionized water with silver nitrate. The obtained product is hydrated wet polyetheramine D230-modified montmorillonite.

[0086] (4) Weigh 30 g of the product from step (3) and add it to deionized water. After stirring and dispersing, place the mixed dispersion in an ultrasonic cell disruptor and ultrasonicate it for 30 min (power: 500 W; 60%; 4 s on and 2 s off). Then, centrifuge the dispersion at 5000 rpm for 30 min, collect the upper-layer dispersion, and calibrate the concentration of the dispersion by the weighing method to obtain a 3 wt% aqueous dispersion of polyetheramine D230-modified montmorillonite.

[0087] (5) Add 11 g of the polyetheramine D230-modified montmorillonite aqueous dispersion prepared in step (4) (the mass of polyetheramine D230-modified montmorillonite is 0.33 g) to 83.4 g of an 8 wt% carboxylated cellulose nanocrystal dispersion (the mass of carboxylated cellulose nanocrystals is 6.67 g). After mixing, ultrasonicate it (power: 500 W; 60%; 4 s on and 2 s off) for 30 min to disperse and obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion. Then, add an equal volume of N-methylpyrrolidone to the hybrid aqueous dispersion and mix it evenly. Use a rotary evaporator to perform solvent exchange at 80 °C to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion.

[0088] (6) Add 3 g of bisphenol A epoxy resin and 2,4,6-tris(dimethylaminomethyl)phenol with a mass ratio of 9:1 to the organic solvent dispersion of the hybrid prepared in step (5), stir and mix evenly to obtain a composite solution. Pour the obtained composite solution into a rectangular polytetrafluoroethylene mold with a depth of 4 mm, vacuum dry at 40 °C, and after drying, heat-treat at 120 °C for 3 h and at 150 °C for 3 h to obtain a montmorillonite / cellulose nanocrystal composite film.

[0089] The composite film prepared in this example has no specific size and shape. Figure 10 It is a physical picture of the composite film prepared according to the method steps described in Example 13. The composite film breaks after heat treatment. The reason may be that the crosslinking agent is not properly selected, resulting in poor flexibility of the composite film.

[0090] Example 14: Performance Test

[0091] (1) Measurement of surface potential: Use a Nano-ZS90 particle size analyzer from Malvern, UK, and the test solvent is deionized water.

[0092] Generally, when the Zeta potential is higher than +30 mV or lower than -30 mV, the nanomaterials are stably dispersed in water. Figure 1 It is the Zeta potential test result of the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion or the montmorillonite / carboxylated cellulose nanofiber hybrid aqueous dispersion (Example 8) in Examples 1-12. As can be seen from Figure 1 it that in Example 6, when the ratio of carboxylated cellulose nanocrystals to polyetheramine D230-modified montmorillonite is 1:1, the Zeta potential of the hybrid aqueous dispersion is as low as -34.8 mV. With the further increase in the content of carboxylated cellulose nanocrystals, the Zeta potential of the hybrid aqueous dispersion further decreases. In contrast, in Example 12, polyetheramine D400 was used to prepare D400-modified montmorillonite, and then the Zeta potential of the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion prepared was -22.4 mV, and no Tyndall effect was observed (as shown in Figure 3 ), and the hybrid aqueous dispersion flocculated after standing for 12 h, indicating that the D400-modified montmorillonite did not form a stable monolayer dispersion environment before solvent evaporation and it was difficult to form an ordered "brick-clay" structure.

[0093] (2) Transmission electron microscopy: Observe the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion prepared in Example 1 using a Tecnai G2 20 transmission electron microscope from FEI, Netherlands. The results are as shown in Figure 2 As shown in. As can be seen from Figure 2It can be seen that the montmorillonite sheets are dispersed as single sheets, establishing a prerequisite for the preparation of a "brick - mud" structure composite film. After standing for 12 h, the hybrid aqueous dispersion prepared in Example 1 remained stable, no sedimentation of montmorillonite sheets was observed, and it still had the Tyndall effect.

[0094] (3)Tyndall effect: In Example 12, polyetheramine D400 was used to prepare D400 - modified montmorillonite, and then no Tyndall effect was observed in the aqueous dispersion of montmorillonite / carboxylated cellulose nanocrystal hybrid prepared (as Figure 3 shown). The aqueous dispersions of montmorillonite / carboxylated cellulose nanocrystal hybrids prepared in Example 3 and Example 4 had the Tyndall effect (as Figure 4 shown).

[0095] (4)Morphology test: First, the composite film prepared in the example was cryo - fractured in liquid nitrogen, and then the sample was fixed on a copper stage and sputter - coated with platinum.

[0096] The morphology of the thin - film sample was observed using a Nova Nano SEM 450 field - emission scanning electron microscope of FEI Company in the Netherlands, and the acceleration voltage for testing was 10 kV. The inventor also used a Tecnai G220 transmission electron microscope of FEI Company in the Netherlands to observe the sample morphology. Through the scanning electron microscope test, it can be observed that the montmorillonite in the composite films prepared in Examples 1 - 6 was oriented and arranged between the layers of carboxylated cellulose nanocrystals, forming a dense layered structure. However, after using carboxylated cellulose nanofibers in Example 8, the montmorillonite sheets showed a random distribution. Figure 5 The cross - sectional scanning electron micrograph of the composite film prepared in Example 2 is shown. Figure 6 The transmission electron micrograph of the composite film prepared in Example 3 is shown. Figure 7 The transmission electron micrograph of the ultrathin section of the composite film prepared in Example 8 is shown.

[0097] (5)Barrier property test: The oxygen barrier property test was carried out using an oxygen barrier property tester of Jinan Labthink Instruments Co., Ltd. The test environmental temperature was 23℃ and the relative humidity was 50%. Each group of thin - film samples was tested three times.

[0098] The water barrier property test was carried out using a water vapor tester of Jinan Mile Instruments Co., Ltd. The water vapor transmission rate test was carried out according to GB1037 - 1958. First, 3 g of anhydrous CaCl2 was added to the moisture - permeable cup, and then the composite film to be tested was sealed at the mouth of the moisture - permeable cup. The temperature in the dryer was set at 23℃ and the relative humidity was set at 85%. The mass of the moisture - permeable cup was weighed once every 24 h for 7 consecutive days. Each group of samples was measured 3 times.

[0099] The test results are as Figure 8As shown. From the test results, it can be seen that in Examples 1-6 and Examples 11-12, due to the ordered arrangement of montmorillonite layers, a composite film with a brick-mortar structure was formed, and the oxygen barrier performance and water barrier performance were significantly improved, that is, the oxygen permeability coefficient and water vapor permeability coefficient were significantly decreased, far lower than the film prepared in Example 7 without adding montmorillonite. By comparing Example 8, it can be found that after using carboxylated cellulose nanofibers as the matrix of the composite film, the montmorillonite layers did not align, resulting in a barrier performance lower than that of Example 5 with the same amount of montmorillonite added. This once again proves that the lyotropic liquid crystal effect of carboxylated cellulose nanocrystals can effectively orient montmorillonite layers and improve the barrier performance of the composite film. By comparing Example 9, it can be found that the barrier performance is also lower than that of Example 5 with the same amount of montmorillonite added, indicating that the interfacial force between unmodified montmorillonite and the carboxylated cellulose nanocrystal matrix is weak, increasing the gas passage path and reducing the barrier performance. In addition, the barrier performance of Example 8 and Example 9 is better than that of some examples with a lower montmorillonite content, indicating that the inorganic nanomaterial montmorillonite with excellent barrier performance plays a more important role in the water and oxygen barrier coefficients of the composite film.

[0100] (6)Mechanical property test: Cut the composite film into specimens with dimensions of 40 mm × 5 mm × 100 μm, and fix both ends of the sample film on two customized steel sheets with 502 super glue. Use an electronic universal testing machine (E44.104) from MTS Corporation. According to the ASTM D-638 standard, the tensile rate is 3 mm / min, and the original gauge length is 20 mm to test the mechanical properties of the composite film.

[0101] In Examples 1-6, carboxylated cellulose nanocrystals and montmorillonite self-assembled to form a layered "brick-mortar" structure. After introducing a cross-linking agent, cross-linking occurred with carboxylated cellulose nanocrystals and montmorillonite, effectively enhancing the interfacial interaction between the filler and the matrix, which is beneficial to the stress transfer in the composite film. By comparing Example 5 and Example 8 with the same montmorillonite fraction, carboxylated cellulose nanofibers without the lyotropic liquid crystal effect could not induce the orientation arrangement of montmorillonite nanosheets during the solvent self-evaporation process, showing a random distribution and not forming a "brick-mortar" structure, resulting in a significant decrease in its mechanical properties. Similarly, in Example 9, there was a poor interfacial interaction between unmodified montmorillonite and carboxylated cellulose nanocrystals, resulting in the inability of stress to transfer at the interface, affecting its mechanical properties. The test results are as Figure 9 shown.

Claims

1. A preparation method of a montmorillonite / cellulose nanocrystal composite film, characterized in that, The preparation method includes the following steps: S1: Preparation of carboxylated cellulose nanocrystal aqueous dispersion; S2: Preparation of polyetheramine D230 modified montmorillonite aqueous dispersion; S3: Add the polyetheramine D230 modified montmorillonite aqueous dispersion prepared in step S2 to the carboxylated cellulose nanocrystal aqueous dispersion prepared in step S1. After mixing, ultrasonically disperse to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion, and then replace the water in the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion with an organic solvent to obtain a montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion; S4: Add a crosslinking agent to the montmorillonite / carboxylated cellulose nanocrystal hybrid organic solvent dispersion in step S3, stir and mix evenly to obtain a composite solution; S5: Pour the composite solution in step S4 into a mold, and vacuum dry at 40 - 60 °C, and heat-treat to obtain the montmorillonite / cellulose nanocrystal composite film.

2. The preparation method according to claim 1, characterized in that, In step S1, the concentration of the carboxylated cellulose nanocrystal aqueous dispersion is 3 - 8 wt%, preferably 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt% or 8 wt%; Preferably, in step S2, the concentration of the polyetheramine D230 modified montmorillonite aqueous dispersion is 0.5 - 3 wt%, and more preferably, the concentration of the polyetheramine D230 modified montmorillonite aqueous dispersion is 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt% or 3 wt%.

3. The preparation method according to claim 1, characterized in that, In step S2, the preparation of the polyetheramine D230 modified montmorillonite aqueous dispersion includes the following steps: S2-1: Disperse montmorillonite (MMT) in deionized water by mechanical stirring to obtain an MMT aqueous dispersion; S2-2: Slowly drop dilute hydrochloric acid into an aqueous solution of polyetheramine D230 to prepare protonated polyetheramine D230; S2-3: Under stirring conditions, add the protonated polyetheramine D230 in step S2-2 to the MMT aqueous dispersion in step S2-1 for an ion exchange reaction. After the reaction, wash with water and filter by suction to obtain wet polyetheramine D230 modified montmorillonite containing water; S2-4: Add the wet polyetheramine D230 modified montmorillonite containing water prepared in step S2-3 to deionized water, ultrasonicate, centrifuge, and take the supernatant to obtain a polyetheramine D230 modified montmorillonite aqueous dispersion, and calibrate the concentration; Among them, preferably, the concentration of the dilute hydrochloric acid used in step S2-2 is 0.2N.

4. The preparation method according to claim 1, wherein, In the montmorillonite / carboxylated cellulose nanocrystal hybrid aqueous dispersion and / or organic solvent dispersion in step S3, the mass ratio of polyetheramine D230 modified montmorillonite to carboxylated cellulose nanocrystal is 1:1 - 20, preferably 1:1 - 15, further preferably 1:1 - 10, still further preferably 1:1 - 6, and even more preferably 1:1 - 3.

5. The preparation method according to claim 1, characterized in that, In step S3, the organic solvent is selected from one or more of N,N-dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone.

6. The preparation method according to claim 1, characterized in that, In step S4, the crosslinking agent is a mixture of polypropylene glycol diglycidyl ether and 2,4,6-tris(dimethylaminomethyl)phenol with a mass ratio of 9:

1.

7. The preparation method according to claim 1, characterized in that, In step S4, the dosage of the crosslinking agent is in a ratio of 3:7 to the sum of the masses of polyetheramine D230-modified montmorillonite and carboxylated cellulose nanocrystals.

8. The preparation method according to claim 1, wherein, In step S5, the mold can be a polytetrafluoroethylene mold. Preferably, the depth of the polytetrafluoroethylene mold is ≤4 mm; Preferably, in step S5, the heat treatment includes: heat treatment at 100 - 120 °C for 2 - 3 h, and then heat treatment at 150 - 170 °C for 1 - 3 h.

9. A montmorillonite / cellulose nanocrystal composite film, characterized in that, The montmorillonite / cellulose nanocrystal composite film is made by the preparation method described in any one of claims 1 - 8.

10. Use of the montmorillonite / cellulose nanocrystal composite film prepared by the preparation method described in any one of claims 1 - 8 as a barrier material.

Images