A highly transparent chitin nanocrystal-based coating and its application in food paper

Abstract

The invention discloses a high-transparency chitin nanocrystal-based coating and its application in food paper, relating to the field of food packaging technology. In the present invention, the high-transparency chitin nanocrystal-based coating is made by the following method: 70-90 parts by mass of chitin nanocrystal suspension, 5-15 parts by mass of polyvinyl alcohol, 5-15 parts by mass of silver / chitosan composite antibacterial agent, 3-15 parts by mass of modified nano titanium dioxide, 1-5 parts by mass of nano silicon dioxide, 2-5 parts by mass of thickener, 2-10 parts by mass of plasticizer and 0.1-2 parts by mass of antioxidant are uniformly mixed to obtain a high-transparency chitin nanocrystal-based coating. The high-transparency chitin nanocrystal-based coating prepared by the present application can improve the transparency, waterproofness and antibacterial properties of food paper.

Description

Technical Field

[0001] The present invention relates to the technical field of food packaging, and in particular to a highly transparent chitin nanocrystal-based coating and application thereof in food paper. Background Art

[0002] Chitin, the second largest natural high-molecular-weight polysaccharide after cellulose, is a linear polymer polysaccharide composed of 2-acetylglucosamine linked by β-1,4-glycosidic bonds. It is widely found in the skeletons of crustaceans such as shrimp and crabs, as well as mollusks such as squid and shellfish. With the advancement of nanotechnology, its application in the food industry has attracted considerable attention. Nanochitin (NCh) is a nanoscale chitin material formed by physically or chemically breaking down the long chitin chain structure. NCh not only possesses the properties of chitin but also forms a uniform dispersion in aqueous solution. It also possesses the characteristics of nanomaterials, including small size, low density, high surface area, excellent biocompatibility and mechanical properties, and reproducibility. It has been investigated for applications in composite materials, pharmaceuticals, and food. In the food industry, NCh, due to its superior mechanical properties, barrier properties, amphiphilicity, and polyhydroxyl functional groups, has attracted widespread attention for its applications in novel food active packaging, emulsion stabilizers, functional factor carriers, and quality improvers.

[0003] As a biodegradable material, paper is widely used in the packaging of various foods or the preparation of disposable containers. Since the fibers in paper have hydrophilic and lipophilic properties, untreated paper is difficult to effectively block water penetration and grease leakage in food, which is not conducive to the packaging and storage of food. The common treatment method for paper used in existing food packaging or food containers is to form a coating by applying a coating on paper to isolate the paper and food and improve its waterproof and oil-proof properties. Currently, in order to prevent oil and moisture, commercially available food packaging paper is waxed and coated. Not only is the oil and moisture-proof effect limited, but long-term storage or exposure to high temperatures will cause the wax and coating to gradually penetrate into the paper, causing contamination to the food, affecting the nutrition, flavor and hygiene of the food, and the low transparency without antibacterial properties, making it difficult to observe the condition of the food. Therefore, there is an urgent need to develop a coating containing nano-chitin to overcome the shortcomings of current food paper, such as low transparency, poor waterproof performance and non-antibacterial properties. Summary of the Invention

[0004] The purpose of the present invention is to provide a highly transparent chitosan nanocrystal-based coating and its application in food paper to solve the following technical problems:

[0005] Existing waterproof and moisture-proof coatings applied on the surface of food paper have problems such as low transparency, poor waterproof performance and no antibacterial effect.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A highly transparent chitin nanocrystal-based coating, wherein the highly transparent chitin nanocrystal-based coating is prepared by the following method:

[0008] 70-90 parts by mass of chitin nanocrystal suspension, 5-15 parts by mass of polyvinyl alcohol, 5-15 parts by mass of silver / chitosan composite antibacterial agent, 3-15 parts by mass of modified nano-titanium dioxide, 1-5 parts by mass of nano-silicon dioxide, 2-5 parts by mass of thickener, 2-10 parts by mass of plasticizer and 0.1-2 parts by mass of antioxidant are uniformly mixed to obtain a highly transparent chitin nanocrystal-based coating.

[0009] As a further solution of the present invention: the preparation method of the modified nano titanium dioxide comprises the following steps:

[0010] Ammonia water and nano-titanium dioxide are dispersed in an ethanol aqueous solution, and then an ethanol solution of methacryloxypropyltrimethoxysilane is added, and the modified nano-titanium dioxide is obtained after reaction, centrifugation, washing and drying.

[0011] As a further solution of the present invention: the ammonia water is a 25-30 wt % ammonia water solution, and the mass ratio of the methacryloxypropyltrimethoxysilane to the nano-titanium dioxide is 1:6-10.

[0012] As a further embodiment of the present invention, the preparation method of the silver / chitosan composite antibacterial agent comprises the following steps:

[0013] The carboxymethyl chitosan is dissolved in deionized water, the pH is adjusted to 10, and the temperature is raised to 70-80° C., a silver ammonia solution is added, the solution is dialyzed for purification, dried and ground to obtain a silver / chitosan composite antibacterial agent.

[0014] As a further embodiment of the present invention: the carboxymethyl chitosan and the silver ammonia solution [Ag (NH3) 2] + The addition ratio is 100 mg: 0.4-0.5 mmol.

[0015] As a further embodiment of the present invention, the method for preparing the chitosan nanocrystal suspension comprises at least the following steps:

[0016] The shrimp and crab shells are sequentially subjected to decalcification, deproteinization and bleaching treatments to obtain purified chitin;

[0017] The purified chitosan is suspended in dilute hydrochloric acid for hydrolysis, and then centrifuged, washed and dispersed to obtain a chitosan nanocrystal suspension.

[0018] As a further embodiment of the present invention, the chitin nanocrystal content in the chitin nanocrystal suspension is 1-2%, the chitin nanocrystal length is 150-600 nm, the aspect ratio is 20-120, the concentration of the dilute hydrochloric acid is 3-5 mol / L, the hydrolysis temperature is 60-80° C., and the hydrolysis time is 2-6 h.

[0019] As a further embodiment of the present invention, the thickener includes one or a mixture of xanthan gum, sodium alginate or hydroxyethyl cellulose, the plasticizer includes one or a mixture of glycerol, sorbitol or polyethylene glycol, and the antioxidant includes one or a mixture of tea polyphenols, vitamin E or synthetic antioxidants.

[0020] An application of any of the above-mentioned highly transparent chitin nanocrystal-based coatings in food paper, wherein the highly transparent chitin nanocrystal-based coating can be coated on translucent paper and applied to food paper after drying, curing and calendering.

[0021] As a further embodiment of the present invention: the coating thickness is 3-20 μm, the coating method is one of blade coating, roller coating or spray coating, and the drying temperature is 50-80°C

[0022] Beneficial effects of the present invention:

[0023] The present invention adopts chitin nanocrystal as base material, adds polyvinyl alcohol, silver / chitosan composite antimicrobial agent, modified nano titanium dioxide, nano silicon dioxide, thickener, plasticizer and antioxidant to prepare coating, and is coated on translucent food paper, thereby improving the transparency of translucent paper and making translucent paper obtain waterproof, antibacterial and oleophobic performance. Among them, chitin nanocrystal dispersion can form a film on the surface of base paper, block grease penetration, and improve oil-proof performance, polyvinyl alcohol improves the bonding strength of coating and paper base as a binder, silver / chitosan composite antimicrobial agent has antimicrobial effect, and can produce synergistic effect with chitin nanocrystal and polyvinyl alcohol, improve the tensile strength of food paper, make coating not easy to fall off, nano silicon dioxide ensures the transparency of coating as optical enhancer, modified nano titanium dioxide namely improves the hydrophobic property of coating as hydrophobic agent, and can produce synergistic effect with nano silicon dioxide, improve transparency, thickener improves the uniformity of coating application, plasticizer improves the flexibility of coating, and antioxidant improves the service life of coating. The highly transparent chitosan nanocrystal-based coating prepared in the present invention can be used to prepare functional papers such as transparent packaging paper, antibacterial paper and oil-proof paper, and has broad application scenarios in the fields of food, medicine and high-end printing.

[0024] The present invention adopts natural shrimp shells and crab shells as raw materials to prepare chitosan nanocrystals. This biomass raw material is abundant in source and has advantages such as reproducibility and degradability, which not only reduces environmental pollution but also has great significance for the high-value utilization of wastes such as abundant crab shells. Calcium carbonate, protein and pigment in the shrimp and crab shells are removed in sequence by dilute acid, dilute alkali and bleaching agent, and then unnecessary parts in the chitosan fibers are removed by acid hydrolysis to form rod-shaped or needle-shaped nanocrystals with high crystallinity. The length and aspect ratio of the nanocrystals are controlled so that the surface of the obtained chitosan nanocrystals is rich in hydroxyl groups and acetylamino groups, and a small amount of amino groups are also present. The presence of amino groups can make the chitosan surface positively charged, thereby improving the bonding strength of the coating and the paper base. The present invention selects polyvinyl alcohol as a binding agent. The chitosan nanocrystals and polyvinyl alcohol are mixed in water to generate hydrogen bond interactions. The chitosan nanocrystals and the polyvinyl alcohol are subjected to hot air drying and heat treatment to provide more physical crosslinking points between the chitosan nanocrystals and the polyvinyl alcohol, thereby improving the thermal stability, water resistance and tensile strength of the coating.

[0025] The present invention prepares a silver / chitosan antibacterial composite antimicrobial agent, in which nanosilver is uniformly loaded within a chitosan network structure. The nanosilver has high purity, a good crystal structure, and a small, uniform particle size, preventing nanosilver aggregation that would affect antimicrobial properties and coating transparency. Compared to single nanosilver or chitosan antimicrobial agents, the composite antimicrobial agent offers significant advantages in antimicrobial properties, safety, and durability. The amino groups of chitosan in the composite antimicrobial agent bond with the hydroxyl groups of polyvinyl alcohol through hydrogen bonds or ion-dipole interactions, further enhancing the coating's flexibility and tear resistance and improving the folding resistance of food paper. Chitosan has cationic properties, and chitin nanocrystals are also positively charged, reducing aggregation through electrostatic repulsion. Polyvinyl alcohol acts as a "bridge" to promote uniform dispersion of the two, forming a uniform and stable composite matrix, thereby improving the mechanical properties of the coating. Furthermore, the cations electrostatically adsorb onto paper fibers (anions), further enhancing the bonding strength between the coating and the paper substrate. This invention uses methacryloxypropyltrimethoxysilane as a hydrophobic modifier for nano-titanium dioxide. Methacryloxypropyltrimethoxysilane has a long hydrophobic chain and moderate reactivity, readily reacting with hydroxyl groups on the surface of nano-titanium dioxide to form stable covalent bonds, eliminating the risk of perfluorinated compounds. Nano-silica is also used as an optical enhancer. The synergistic effect between nano-silica and nano-titanium dioxide further improves the transparency of the coating. The nano-size of the material, combined with the chitin nanocrystals, enhances the mechanical interlocking effect, improving the mechanical properties of the coating. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0027] Example 1 The preparation method of modified nano-titanium dioxide comprises the following steps:

[0028] 20 ml of anhydrous ethanol and 20 ml of water were mixed to obtain an ethanol aqueous solution, the pH was adjusted to 9 with 25 wt % ammonia water, 4 g of nano-titanium dioxide was added, and ultrasonic dispersion was performed for 20 minutes. Then, 0.5 g of methacryloyloxypropyltrimethoxysilane was dissolved in 10 ml of anhydrous ethanol and added to the above ethanol aqueous solution. The mixture was magnetically stirred for 2 hours. After the reaction was completed, the reaction solution was evenly divided into centrifuge tubes and centrifuged at 8000 r / min for 20 minutes. The lower precipitate was washed with anhydrous ethanol and then dried to obtain modified nano-titanium dioxide.

[0029] Example 2 The preparation method of modified nano-titanium dioxide comprises the following steps:

[0030] 20 ml of anhydrous ethanol and 20 ml of water were mixed to obtain an ethanol aqueous solution, the pH was adjusted to 9 with 25 wt % ammonia water, 4 g of nano-titanium dioxide was added, and ultrasonic dispersion was performed for 20 minutes. Then, 0.75 g of methacryloyloxypropyltrimethoxysilane was dissolved in 10 ml of anhydrous ethanol and added to the above ethanol aqueous solution. The mixture was magnetically stirred for 2 hours. After the reaction was completed, the reaction solution was evenly divided into centrifuge tubes and centrifuged at 8000 r / min for 20 minutes. The lower precipitate was washed with anhydrous ethanol and then dried to obtain modified nano-titanium dioxide.

[0031] Example 3 The preparation method of the silver / chitosan composite antibacterial agent comprises the following steps:

[0032] 0.136 g of silver nitrate was weighed and dissolved in 10 mL of deionized water. 1 mol / L sodium hydroxide solution was added dropwise with constant stirring until the precipitate no longer increased. Subsequently, 2 wt % ammonia solution was added dropwise until the precipitate was completely dissolved. The solution was filtered through a 0.45 μm filter membrane to obtain a silver ammonia solution.

[0033] 0.2 g of carboxymethyl chitosan was dissolved in 100 mL of deionized water, and the pH of the solution was adjusted to 10 with 1 mol / L sodium hydroxide solution. The solution was placed in a microwave synthesis reactor (power 600 W), the system temperature was raised to 70 ° C, and then the above-mentioned silver ammonia solution was quickly injected. Stirring was started to mix evenly, and the reaction was carried out for 40 minutes. The solution was taken out and cooled to room temperature, and then placed in a dialysis bag for dialyzed purification for 3 days and freeze-dried for 48 hours to obtain a silver / chitosan antibacterial agent.

[0034] Example 4 The preparation method of chitosan nanocrystal suspension comprises the following steps:

[0035] The shrimp and crab shells are treated with dilute hydrochloric acid to remove inorganic matter, followed by dilute alkali to remove protein, and then bleached with hydrogen peroxide to increase purity. The decalcification, deproteinization and bleaching processes are completed in sequence to obtain purified chitin.

[0036] The purified chitin was suspended in 4 mol / L dilute hydrochloric acid, hydrolyzed at 70 °C for 4 h, and centrifuged to obtain chitin nanocrystals. The chitin nanocrystals were then washed repeatedly with deionized water until the pH was close to neutral, and dispersed in deionized water to obtain a chitin nanocrystal suspension with a solid content of 2%.

[0037] Example 5 The preparation method of highly transparent chitin nanocrystal-based coating comprises the following steps:

[0038] 80 parts by mass of the chitin nanocrystal suspension prepared in Example 4, 10 parts by mass of polyvinyl alcohol, 10 parts by mass of the silver / chitosan composite antibacterial agent prepared in Example 3, 6 parts by mass of the modified nano-titanium dioxide prepared in Example 1, 2 parts by mass of nano-silicon dioxide, 4 parts by mass of thickener sodium alginate, 5 parts by mass of plasticizer polyethylene glycol and 0.5 parts by mass of antioxidant tea polyphenol were added to a high-speed stirrer and mixed evenly to obtain a highly transparent chitin nanocrystal-based coating.

[0039] Example 6 The preparation method of highly transparent chitin nanocrystal-based coating comprises the following steps:

[0040] 80 parts by mass of the chitin nanocrystal suspension prepared in Example 4, 10 parts by mass of polyvinyl alcohol, 10 parts by mass of the silver / chitosan composite antibacterial agent prepared in Example 3, 6 parts by mass of the modified nano-titanium dioxide prepared in Example 2, 2 parts by mass of nano-silicon dioxide, 4 parts by mass of thickener sodium alginate, 5 parts by mass of plasticizer polyethylene glycol and 0.5 parts by mass of antioxidant tea polyphenol were added to a high-speed stirrer and mixed evenly to obtain a highly transparent chitin nanocrystal-based coating.

[0041] Example 7 The preparation method of highly transparent chitin nanocrystal-based coating comprises the following steps:

[0042] 80 parts by mass of the chitin nanocrystal suspension prepared in Example 4, 12 parts by mass of polyvinyl alcohol, 8 parts by mass of the silver / chitosan composite antibacterial agent prepared in Example 3, 5 parts by mass of the modified nano-titanium dioxide prepared in Example 1, 1.5 parts by mass of nano-silicon dioxide, 4 parts by mass of sodium alginate as a thickener, 5 parts by mass of polyethylene glycol as a plasticizer, and 0.5 parts by mass of tea polyphenols as an antioxidant were added to a high-speed stirrer and mixed uniformly to obtain a highly transparent chitin nanocrystal-based coating.

[0043] Example 8 The preparation method of highly transparent chitin nanocrystal-based coating comprises the following steps:

[0044] 80 parts by mass of the chitin nanocrystal suspension prepared in Example 4, 12 parts by mass of polyvinyl alcohol, 8 parts by mass of the silver / chitosan composite antibacterial agent prepared in Example 3, 5 parts by mass of the modified nano-titanium dioxide prepared in Example 2, 1.5 parts by mass of nano-silicon dioxide, 4 parts by mass of thickener sodium alginate, 5 parts by mass of plasticizer polyethylene glycol and 0.5 parts by mass of antioxidant tea polyphenol were added to a high-speed stirrer and mixed evenly to obtain a highly transparent chitin nanocrystal-based coating.

[0045] Comparative Example 1 Compared with Example 5, in Comparative Example 1, the modified nano-titanium dioxide prepared in Example 1 added in Example 5 is replaced by the unmodified nano-titanium dioxide in Example 1. The remaining components and preparation method are completely consistent with those in Example 5.

[0046] Comparative Example 2 Compared with Example 5, in Comparative Example 2, no nano-silicon dioxide is added, and the remaining components and preparation method are completely consistent with those of Example 5.

[0047] Comparative Example 3 Compared with Example 5, the content of polyvinyl alcohol added in Comparative Example 3 was reduced from 10 parts by mass to 4 parts by mass, and the remaining components and preparation method were completely the same as those in Example 5.

[0048] Comparative Example 4 Compared with Example 5, in Comparative Example 3, the silver / chitosan composite antibacterial agent prepared in Example 3 added in Example 4 was replaced by nanosilver particles. The remaining components and preparation method were exactly the same as those in Example 5.

[0049] Comparative Example 5 Compared with Example 5, in Comparative Example 5, the modified nano-titanium dioxide prepared in Example 1 and the silver / chitosan composite antibacterial agent prepared in Example 3 were not added. The remaining components and preparation methods were completely consistent with those in Example 5.

[0050] Performance testing

[0051] Preparation of food paper coated with highly transparent chitosan nanocrystal-based coating:

[0052] The highly transparent chitin nanocrystal-based coatings obtained in Examples 5-8 and Comparative Examples 1-5 were applied by roller coating on both sides of food translucent paper and dried with hot air at 50-80° C.;

[0053] The dried food paper was calendered by a calender to form a highly transparent chitosan nanocrystal-based coating with a thickness of 5 μm, thereby obtaining food paper coated with a highly transparent chitosan nanocrystal-based coating.

[0054] Tensile Strength: The tensile strength of the food paper coated with the highly transparent chitin nanocrystal-based coatings obtained in Examples 4-8 and Comparative Examples 1-5 was tested according to TAPPI standards (T494om-96) and expressed as a tensile index. The test results are shown in Table 1.

[0055] Folding resistance: Food paper coated with the highly transparent chitin nanocrystal-based coatings obtained in Examples 4-8 and Comparative Examples 1-5 was cut into 200 mm × 500 mm strips and repeatedly folded in half at an extension of 250 mm until the coating cracked. The number of folds was recorded. The test results are shown in Table 1.

[0056] Transparency: The light transmittance (T%) of the food paper coated with the highly transparent chitin nanocrystal-based coatings obtained in Examples 4-8 and Comparative Examples 1-5 was measured using an ultraviolet-visible spectrophotometer (UV-240, Shimadzu, Japan) in the wavelength range of 200-800 nm. The test results are shown in Table 1.

[0057] Hydrophobicity: According to GB / T 30693-2014, the water contact angles of the food paper coated with the highly transparent chitin nanocrystal-based coatings obtained in Examples 4-8 and Comparative Examples 1-5 were tested; the test results are shown in Table 1;

[0058] Antibacterial performance test: Weigh 0.1g of food paper coated with highly transparent chitosan nanocrystal-based coating and cut it into small pieces. Dilute the bacterial solution with physiological saline to 10 5 cfu / mL, add paper to the test tube and place it in a constant temperature shaker (set the temperature to 37°C and shake for 2 hours). After the shaking is completed, dilute the shaken bacterial solution again to 10 3 Then, the plates were coated. The plates were placed in an incubator with the temperature and humidity controlled at 72% RH. After 24 hours of incubation, the plates were observed. The bacteria used were E. coli and S. aureus. The test results are shown in Table 1.

[0059] Table 1: Statistical table of performance test data of food paper coated in Examples 5-8 and Comparative Examples 1-5

[0060]

[0061] As can be seen from Table 1, the highly transparent chitin nanocrystal-based coating material prepared in the present application is coated on the surface of translucent food paper, giving the food paper excellent hydrophobicity, mechanical properties, transparency and antibacterial properties. In Comparative Example 1, the modified nano-titanium dioxide is replaced with unmodified nano-titanium dioxide, and the hydrophobicity of the obtained coating is greatly reduced. In Comparative Example 2, nano-silicon dioxide is not added, and the transparency of the obtained coating is reduced, and the tensile strength is also reduced. In Comparative Example 3, polyvinyl alcohol is not added, and the tensile strength of the obtained coating is reduced, and the coating is easy to fall off. In Comparative Example 4, the silver / chitosan composite antibacterial agent is replaced with nano-silver particles, and the tensile strength, bonding strength, antibacterial properties and transparency of the obtained coating are all reduced. In Comparative Example 5, modified nano-titanium dioxide and silver / chitosan composite antibacterial agent are not added, and the performance of the obtained coating is poor in all aspects.

[0062] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A highly transparent chitin nanocrystal-based coating, characterized in that: The highly transparent chitosan nanocrystal-based coating is prepared by the following method: 70-90 parts by mass of chitin nanocrystal suspension, 5-15 parts by mass of polyvinyl alcohol, 5-15 parts by mass of silver / chitosan composite antibacterial agent, 3-15 parts by mass of modified nano-titanium dioxide, 1-5 parts by mass of nano-silicon dioxide, 2-5 parts by mass of thickener, 2-10 parts by mass of plasticizer and 0.1-2 parts by mass of antioxidant are uniformly mixed to obtain a highly transparent chitin nanocrystal-based coating; The preparation method of the modified nano titanium dioxide comprises the following steps: Dispersing ammonia water and nano-titanium dioxide in an aqueous solution of ethanol, adding an ethanol solution of methacryloxypropyltrimethoxysilane, reacting, centrifuging, washing and drying to obtain modified nano-titanium dioxide, wherein the mass ratio of the methacryloxypropyltrimethoxysilane to the nano-titanium dioxide is 1:6-10; The preparation method of the silver / chitosan composite antibacterial agent comprises the following steps: The carboxymethyl chitosan is dissolved in deionized water, the pH is adjusted to 10, and the temperature is raised to 70-80° C., a silver ammonia solution is added, the solution is dialyzed for purification, dried and ground to obtain a silver / chitosan composite antibacterial agent.

2. A highly transparent chitosan nanocrystal-based coating according to claim 1, characterized in that: The ammonia water is a 25-30wt% ammonia water solution.

3. A highly transparent chitosan nanocrystal-based coating according to claim 1, characterized in that: [Ag(NH3)2] in the carboxymethyl chitosan and the silver ammonia solution + The addition ratio is 100 mg: 0.4-0.5 mmol.

4. The highly transparent chitosan nanocrystal-based coating according to claim 1, characterized in that: The preparation method of the chitosan nanocrystal suspension comprises at least the following steps: The shrimp and crab shells are sequentially subjected to decalcification, deproteinization and bleaching treatments to obtain purified chitin; The purified chitosan is suspended in dilute hydrochloric acid for hydrolysis, and then centrifuged, washed and dispersed to obtain a chitosan nanocrystal suspension.

5. A highly transparent chitosan nanocrystal-based coating according to claim 4, characterized in that: The chitin nanocrystal content in the chitin nanocrystal suspension is 1-2%, the chitin nanocrystal length is 150-600 nm, the aspect ratio is 20-120, the concentration of the dilute hydrochloric acid is 3-5 mol / L, the hydrolysis temperature is 60-80° C., and the time is 2-6 h.

6. The highly transparent chitosan nanocrystal-based coating according to claim 1, characterized in that: The thickener includes one or a mixture of xanthan gum, sodium alginate or hydroxyethyl cellulose, the plasticizer includes one or a mixture of glycerol, sorbitol or polyethylene glycol, and the antioxidant includes one or a mixture of tea polyphenols, vitamin E or synthetic antioxidants.

7. Use of the highly transparent chitosan nanocrystal-based coating according to any one of claims 1 to 6 in food paper, characterized in that: The highly transparent chitosan nanocrystal-based coating is coated on translucent paper, dried, cured and calendered, and then applied to food paper.

8. The use of a highly transparent chitosan nanocrystal-based coating in food paper according to claim 7, characterized in that: The coating thickness is 3-20 μm, the coating method is one of blade coating, roller coating or spray coating, and the drying temperature is 50-80° C.

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