Preparation method and application of environment-friendly easily-degradable hydrogel coating

Abstract

The invention discloses a preparation method and application of an environment-friendly easily-degradable hydrogel coating, and relates to the technical field of hydrogel coatings. The coating is a coating comprising chitosan, acrylic acid, sericin, silk fibroin, silk peptide, tea polyphenol, a photoinitiator, a plasticizer and a leveling agent. The preparation method comprises the following steps: (1) preparing the coating containing the components; (2) coating the surface of food packaging paper with the coating liquid in a slit coating manner; and (3) performing ultraviolet light initiation to obtain the coating. The hydrogel coating has a synergistic effect with the sericin, the silk fibroin, the silk peptide and the tea polyphenol to form a compact and uniform network structure, so that the water-retaining property, the mechanical strength, the flexibility and the antibacterial property are enhanced; the preservative not only has the advantages of environmental protection and degradability, but also has the functions of moisturizing, antibiosis and preservation, and can significantly prolong the shelf life of food and improve the quality. The environment-friendly packaging paper is applied to food packaging paper, not only conforms to the green packaging trend, but also expands the use scenes of environment-friendly materials in the fields of fresh food, baking and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogel coatings, and in particular relates to a preparation method of an environmentally friendly and easily degradable hydrogel coating and an application thereof. Background Art

[0002] Food packaging materials play a critical role in ensuring food safety, maintaining product quality, and extending shelf life. They are also crucial in reducing global food waste. However, current mainstream food packaging materials face significant technical and environmental challenges. Petroleum-based plastics, such as polyethylene and polypropylene, are non-biodegradable, resulting in approximately 300 million tons of plastic waste generated globally annually, 40% of which comes from single-use packaging. The resulting environmental pollution and microplastics problem pose a serious threat to ecosystems.

[0003] Although existing environmentally friendly alternative materials such as paper or biodegradable plastics have alleviated environmental pressure to a certain extent, they still have obvious limitations in practical applications. The mechanical strength and barrier properties of these materials often cannot meet the packaging requirements of high-demand foods such as fresh and baked goods. Their typical performance indicators are oxygen transmission rate ≥ 20cm 3 / (m 2 ·day·atm), water vapor transmission rate ≥5g / (m 2 In addition, chemical antimicrobial agents such as silver nanoparticles are widely used in traditional antimicrobial packaging, but they have problems such as easy migration, high cost, and potential food safety risks.

[0004] In order to solve the above problems, the existing technical improvement schemes also have many shortcomings: (1) Although PVDC (polyvinylidene chloride) coating has excellent barrier properties, its processing process produces carcinogens and is non-degradable, and has been restricted by the European Union; (2) Bio-based polymers such as PLA and PBAT are biodegradable, but their barrier properties are poor, and they often require complex blending and modification processes, resulting in a significant increase in costs; (3) Conventional chitosan-based hydrogels have natural degradability and antibacterial properties, but due to insufficient cross-linking density, their mechanical properties are poor, their elongation at break is <100%, and their functional scalability is limited. Therefore, in response to the above technical bottlenecks, the development of new food packaging materials that have both degradability, excellent barrier properties, high efficiency antibacterial properties and good flexibility has become an urgent need for the development of the industry. To this end, the present invention innovatively proposes a preparation method for an environmentally friendly and easily degradable hydrogel coating and its application scheme in food packaging paper, which has important practical significance. Summary of the Invention

[0005] The present invention provides a preparation method of an environmentally friendly and easily degradable hydrogel coating and its application, which solves the above problems.

[0006] To solve the above technical problems, the present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for preparing an environmentally friendly and easily degradable hydrogel coating, wherein the hydrogel coating is a coating comprising chitosan, acrylic acid, sericin, silk fibroin, silk peptide, tea polyphenols, a photoinitiator, a plasticizer, and a leveling agent;

[0008] The preparation method of the hydrogel coating comprises the following steps:

[0009] S1. Preparation of a coating comprising the above ingredients, specifically comprising the following steps:

[0010] S11, preparing a chitosan-acrylic acid-based precursor solution: slowly dissolving chitosan in an acidic aqueous solution, adjusting the solution pH to 5.5-6.0, then adding acrylic acid dropwise in batches with continuous stirring, then adding a crosslinking agent N-hydroxymethyl acrylamide, continuously stirring until a homogeneous transparent solution is formed, and finally performing a vacuum degassing treatment;

[0011] S12, distribution and addition of functional ingredients:

[0012] Adding sericin: slowly add the prepared sericin pre-solution to the chitosan-acrylic acid precursor solution, stirring while adding, so that the sericin is fully dispersed in the solution;

[0013] Adding silk fibroin: adding the silk fibroin solution to the above mixed solution and ultrasonically treating;

[0014] Silk peptide addition: add silk peptide to the solution and continue stirring;

[0015] Add tea polyphenols: dissolve tea polyphenols in the solution and stir evenly;

[0016] S13, adding additives:

[0017] Adding a photoinitiator, a plasticizer, and a leveling agent to the mixed solution obtained in step S12, and stirring evenly to obtain a coating;

[0018] S2, coating on the surface of food packaging paper using a slit coating method;

[0019] S3. After UV light initiation, an environmentally friendly and easily degradable hydrogel coating is obtained.

[0020] Furthermore, the parameters of the slit coating method in step S2 are set as follows:

[0021] Slot die gap setting value: 8-12μm;

[0022] Coating speed: 8-15m / min;

[0023] Coating temperature: 20-30℃, substrate temperature: 25-35℃.

[0024] Furthermore, the UV curing method is used for the UV initiation in S3, and the parameters are set as follows: light intensity: 80-200mW / cm 2 ; Irradiation distance: 5-15cm; Curing time: 5-30 seconds.

[0025] Furthermore, the coating forms a transparent film with a thickness of 8-12 μm after curing, and the oxygen transmission rate of the coating is ≤5 cm 3 / (m 2 ·day·atm), water vapor transmission rate ≤1.2g / (m 2 ·day), the inhibition rate against Escherichia coli and Staphylococcus aureus is ≥99%, and the degradation rate under composting conditions is ≥80% within 180 days.

[0026] Furthermore, the components of the coating include, by weight percentage, 80-90% chitosan-acrylic acid-based precursor solution, 2-4% sericin, 3-6% silk fibroin, 1-3% silk peptide, 0.5-1% tea polyphenols, 1-2% photoinitiator, 1-3% plasticizer and 0.5-1% leveling agent.

[0027] Furthermore, the preparation method of the sericin pre-solution is as follows:

[0028] Prepare sericin with a purity of ≥90% and a molecular weight of 10-50 kDa. Add deionized water at a ratio of 1:20-1:30 to silk:silicin. Stir at 300-500 rpm in a 40-50°C water bath for 1-2 hours to completely dissolve the sericin. Adjust the pH of the solution to 5.5-6.0 with citric acid or sodium hydrogen phosphate buffer. Filter through a 0.45μm microporous membrane and refrigerate at 4°C until ready to use. Return to room temperature and shake well before use.

[0029] An environmentally friendly and easily degradable hydrogel coating is prepared according to the above preparation method.

[0030] The invention discloses an application of an environmentally friendly and easily degradable hydrogel coating, wherein the hydrogel coating is applied to food packaging paper.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) Process innovation: Chitosan-acrylic acid is selected as the main matrix, and it works synergistically with natural ingredients such as sericin, silk fibroin, silk peptide and tea polyphenols. Sericin is used for water retention, silk fibroin is used for reinforcement, silk peptide is used for dense filling, and tea polyphenols are used for antibacterial properties, forming a dense network structure to achieve performance optimization. High-precision slit coating combined with UV curing technology is used, with an accuracy of ±0.1μm, which solves the problem of perfectly balancing the flexibility and high barrier properties of traditional hydrogel coatings.

[0033] (2) Performance breakthrough: oxygen transmission rate ≤5cm 3 / (m 2 ·day·atm), water vapor transmission rate ≤1.2g / (m 2 ·day), antibacterial rate against Escherichia coli and Staphylococcus aureus ≥99%, flexibility (elongation at break) ≥300%, mechanical strength (tensile strength) ≥5.5MPa;

[0034] (3) Environmental advantages: The degradation rate is ≥80% within 180 days under composting conditions, which complies with the EU EN 13432 standard. The degradation products are safe small molecule organic acids with a heavy metal content of <10ppm, and there is no risk of secondary pollution.

[0035] (4) Significant preservation: After experiments, fresh-cut apples were stored for 12 days: the weight loss rate was only 2.5%, while the control group was 5.8%, and browning was reduced by 57%;

[0036] (5) Wide application: The coating process parameters are precise, which is suitable for large-scale application of degradable hydrogels. It is also applicable to a wide range of occasions, such as fresh food, baked goods, dry goods and other food packaging.

[0037] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. DETAILED DESCRIPTION

[0038] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0039] The present invention provides a method for preparing an environmentally friendly and easily degradable hydrogel coating, wherein the hydrogel coating is composed of chitosan, acrylic acid, sericin, silk fibroin, silk peptide, tea polyphenols, a photoinitiator, a plasticizer, and a leveling agent. The preparation method comprises the following steps:

[0040] (1) preparing a coating comprising the above ingredients;

[0041] (2) Applying on the surface of food packaging paper by slit coating;

[0042] (3) The coating is obtained after being initiated by ultraviolet light.

[0043] Among them, the hydrogel coating forms a dense and uniform network structure through the synergistic action of various components. It is not only biodegradable and environmentally friendly, but also has water retention, high mechanical strength, flexibility and antibacterial properties.

[0044] As a further description of this technical solution: Step 1 is subdivided into:

[0045] 1-a. Preparation of chitosan-acrylic acid-based precursor solution:

[0046] Chitosan is slowly dissolved in an acidic aqueous solution, and the pH of the solution is adjusted to 5.5-6.0. Acrylic acid is then added dropwise in batches with continuous stirring. Then, crosslinking agent N-hydroxymethyl acrylamide (NMA) is added and continuously stirred until a uniform transparent solution is formed. Finally, vacuum degassing is performed.

[0047] 1-b. Then add the functional ingredients step by step:

[0048] Addition of sericin: Slowly add the prepared sericin pre-solution into the chitosan-acrylic acid-based precursor solution while stirring to fully disperse the sericin in the solution. The sericin forms hydrogen bonds with water to increase the water retention of the hydrogel, and its soft molecular chains give the coating good flexibility.

[0049] Addition of silk fibroin: adding the silk fibroin solution to the above mixed solution and ultrasonically treating it to promote the dispersion and cross-linking reaction of the β-pleated structure silk fibroin in the hydrogel network and enhance the mechanical properties of the coating.

[0050] Addition of silk peptide: Add silk peptide to the solution and continue stirring to allow the silk peptide molecules to fill the gaps in the hydrogel network, enhancing the density and uniformity of the coating.

[0051] Addition of tea polyphenols: Dissolve tea polyphenols in the solution and stir evenly, which can synergistically enhance the antibacterial and antioxidant effects with sericin.

[0052] 1-c. Finally add the additives:

[0053] Irgacure 2959 (photoinitiator), glycerin (plasticizer) and ethyl acetate (leveling agent) were added to the mixed solution prepared in step b and stirred evenly to obtain an environmentally friendly and easily degradable hydrogel coating.

[0054] The coating process adopted is the slot coating method, and its parameters are set as follows: slot die gap setting value: 8-12 μm; coating speed: 8-15 m / min; coating temperature: 20-30°C, substrate temperature: 25-35°C.

[0055] UV curing method is used, and its parameters are set as follows: Light intensity: 80-200mW / cm 2 , irradiation distance: 5-15cm, curing time: 5-30 seconds.

[0056] 80-90% chitosan-acrylic acid-based precursor solution, 2-4% sericin, 3-6% silk fibroin, 1-3% silk peptide, 0.5-1% tea polyphenols, 1-2% photoinitiator, 1-3% plasticizer, 0.5-1% leveling agent.

[0057] The sericin pre-solution is prepared as follows: Dissolve sericin with a purity of ≥90% and a molecular weight of 10-50 kDa in deionized water at a ratio of 1:20-1:30. Stir at 300-500 rpm in a 40-50°C water bath for 1-2 hours to completely dissolve the sericin. Adjust the pH of the solution to 5.5-6.0 with a citric acid / sodium hydrogen phosphate buffer solution and filter through a 0.45 μm microporous filter. Refrigerate at 4°C until ready for use. Return to room temperature and shake well before use.

[0058] The coating forms a transparent film with a thickness of 8–12 μm after UV curing, and the oxygen transmission rate is ≤5 cm 3 / (m 2 ·day·atm), water vapor transmission rate ≤1.2g / (m 2 ·day), the inhibition rate against Escherichia coli and Staphylococcus aureus is ≥99%, the degradation rate is ≥80% within 180 days under composting conditions, the weight loss rate of fresh-cut apples stored for 12 days is only 2.5% (5.8% for the control group), and browning is reduced by 57%. It is suitable for fresh-keeping packaging of fresh food, baked food and dry food.

[0059] (1) Preparation process:

[0060] 1. Chitosan-acrylic acid precursor solution: Chitosan was slowly dissolved in an acidic aqueous solution, and the pH of the solution was adjusted to 5.5. Acrylic acid was added dropwise in batches and stirred continuously for 2 hours. After adding NMA, stirring was continued for 1 hour until a uniform transparent solution was formed. Finally, vacuum degassing was performed.

[0061] 2. Prepare a sericin pre-solution as follows: Dissolve sericin with a purity of ≥90% and a molecular weight of 35 kDa in deionized water at a ratio of 1:25. Stir at 300-500 rpm in a 40°C water bath for 2 hours to completely dissolve the sericin. Adjust the pH of the solution to 5.5-6.0 with citric acid / sodium hydrogen phosphate buffer, filter through a 0.45 μm microporous filter, and refrigerate at 4°C until ready for use. Return to room temperature and shake well before use.

[0062] 3. Adding functional ingredients: Add sericin pre-solution, silk fibroin solution, silk peptide and tea polyphenols in order. Add the sericin pre-solution dropwise while stirring. After adding the silk fibroin solution, ultrasonicate (40kHz, 15 minutes). After adding the silk peptide, stir continuously for 30 minutes. After adding the tea polyphenols, stir evenly.

[0063] 4. Coating preparation: Add Irgacure 2959, glycerol and ethyl acetate and stir until the viscosity reaches about 8000-8500 mPa·s (measured by Brookfield RVDV-II).

[0064] 5. Coating and curing: Slit coating method (die gap 8μm, coating speed 8m / min), coating temperature 20℃, substrate temperature 25℃, UV curing (light intensity 80mW / cm 2 , irradiation distance 5 cm, curing time 5 seconds).

[0065] (2) Comparative Examples and Examples

[0066] Control group 1: chitosan-acrylic acid-based precursor solution (weight percentage): 94% (chitosan 8wt%, acrylic acid 86wt%), additives: 1% Irgacure 2959, 3% glycerol, 2% ethyl acetate were used to prepare a degradable hydrogel coating according to the above preparation process.

[0067] Example 1: A biodegradable hydrogel coating was prepared by using a chitosan-acrylic acid precursor solution (85% chitosan, 77% acrylic acid, 5% N-hydroxymethylacrylamide (NMA)), functional ingredients (2% sericin, 3% silk fibroin, 1% silk peptide, and 0.5% tea polyphenols), as well as additives (1% Irgacure 2959, 1% glycerol, and 0.5% ethyl acetate) according to the above preparation process.

[0068] Example 2: A degradable hydrogel coating was prepared according to the above preparation process by using a chitosan-acrylic acid-based precursor solution: 84% (chitosan 8wt%, acrylic acid 76wt%, NMA 6wt%), functional ingredients: sericin 4%, silk fibroin 6%, silk peptide 2%, tea polyphenols 1%, additives: Irgacure 29592%, glycerol 2%, ethyl acetate 1%.

[0069] Example 3: A degradable hydrogel coating was prepared according to the above preparation process by using a chitosan-acrylic acid-based precursor solution: 83% (chitosan 8wt%, acrylic acid 75wt%, NMA 7wt%), functional ingredients: sericin 3%, silk fibroin 4%, silk peptide 3%, tea polyphenols 1.5%, additives: Irgacure 2959 1.5%, glycerol 2.5%, and ethyl acetate 0.8%.

[0070] Example 4: A degradable hydrogel coating was prepared according to the above preparation process by using a chitosan-acrylic acid-based precursor solution: 84% (chitosan 8wt%, acrylic acid 76wt%, NMA 6wt%), functional ingredients: sericin 3%, silk fibroin 5%, silk peptide 2%, tea polyphenols 1%, additives: Irgacure 29592%, glycerol 3%, ethyl acetate 1%.

[0071] Experimental methods for preserving data:

[0072] 1. Sample preparation: Control group: fresh-cut apples wrapped in ordinary wrapping paper without hydrogel coating;

[0073] 2. Experimental group: fresh-cut apples wrapped in wrapping paper coated with hydrogels of different formulations (Examples 1-5);

[0074] 3. Sample size for each group: at least 3 parallel samples (to reduce random errors);

[0075] 3. Storage conditions: Temperature: 4±0.5°C (simulating commercial refrigeration environment), relative humidity: 90±5% (controlled by saturated salt solution, such as KNO3 solution), storage time: 12 days (environmental parameters are recorded daily)

[0076] 4. Experimental procedures: Select apples of uniform maturity and without damage, soak them in 0.1% NaClO solution for 2 minutes for disinfection, rinse three times with deionized water, peel them, and cut them into 10 × 10 × 5 mm cubes (precisely control the exposed area of ​​the cut surface). Spread the cut pieces in a single layer on a hydrogel-coated wrapping paper (contact area ≥ 80%) and seal them in a PET / PE tray (leaving a 5% porosity at the top to simulate modified atmosphere packaging).

[0077]

[0078]

[0079] Table 1: Insurance data table;

[0080] By adjusting the chitosan-acrylic acid-based hydrogel coating formula and preparation process, the inventor successfully developed a hydrogel coating with excellent mechanical properties, high barrier properties, strong antibacterial properties and environmental friendliness. Experimental data showed that the coating achieved significant breakthroughs in key performance indicators: oxygen transmission rate as low as 4.2-6.5cm 3 / (m 2 ·day·atm), water vapor transmission rate is controlled at 1.0-2.0g / (m 2·day), and the antibacterial rates against Escherichia coli and Staphylococcus aureus were both over 99%. It is worth noting that through the synergistic effect of silk fibroin (3-6%) and silk peptide (1-3%), the coating exhibited excellent mechanical properties and flexibility (tensile strength 5.5-6.2MPa, elongation at break 300-320%) and good adhesion to the substrate (peel strength 1.6-1.8N / cm), while also having good degradability (compost degradation rate of more than 80% within 180 days). In the fresh-cut apple preservation test, the weight loss rate of apples after 12 days of refrigeration was reduced to 2.5-3.2% (5.8% for the control group), the browning index was controlled at 1.8-2.1 (4.2 for the control group), and the total number of microorganisms was maintained at 10 3 -10 4 CFU / g level (control group 8.5×10 4 CFU / g). In terms of comprehensive performance, its barrier properties are superior to PVDC, PLA, and PBAT coatings, and it has outstanding antibacterial and fresh-keeping effects. It also has good degradability and meets environmental protection requirements, providing an innovative solution to the difficult problem of balancing environmental protection and functionality faced by the food packaging industry.

[0081] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing an environmentally friendly and easily degradable hydrogel coating, characterized in that: The hydrogel coating is a coating comprising chitosan, acrylic acid, sericin, silk fibroin, silk peptide, tea polyphenols, a photoinitiator, a plasticizer and a leveling agent; The preparation method of the hydrogel coating comprises the following steps: S1. Preparation of a coating comprising the above ingredients, specifically comprising the following steps: S11, preparing a chitosan-acrylic acid-based precursor solution: slowly dissolving chitosan in an acidic aqueous solution, adjusting the solution pH to 5.5-6.0, then adding acrylic acid dropwise in batches with continuous stirring, then adding a crosslinking agent N-hydroxymethyl acrylamide, continuously stirring until a homogeneous transparent solution is formed, and finally performing a vacuum degassing treatment; S12, distribution and addition of functional ingredients: Adding sericin: slowly add the prepared sericin pre-solution to the chitosan-acrylic acid precursor solution, stirring while adding, so that the sericin is fully dispersed in the solution; Adding silk fibroin: adding the silk fibroin solution to the above mixed solution and ultrasonically treating; Silk peptide addition: add silk peptide to the solution and continue stirring; Add tea polyphenols: dissolve tea polyphenols in the solution and stir evenly; S13, adding additives: Adding a photoinitiator, a plasticizer, and a leveling agent to the mixed solution obtained in step S12, and stirring evenly to obtain a coating; S2, coating on the surface of food packaging paper using a slit coating method; S3. After UV light initiation, an environmentally friendly and easily degradable hydrogel coating is obtained.

2. The method for preparing an environmentally friendly and degradable hydrogel coating according to claim 1, characterized in that: The parameters for the slit coating method in step S2 are set as follows: Slot die gap setting value: 8-12μm; Coating speed: 8-15m / min; Coating temperature: 20-30℃, substrate temperature: 25-35℃.

3. The method for preparing an environmentally friendly and degradable hydrogel coating according to claim 1, characterized in that: The UV curing method is used for UV initiation in S3, and the parameters are set as follows: light intensity: 80-200mW / cm 2 ; Irradiation distance: 5-15cm; Curing time: 5-30 seconds.

4. The method for preparing an environmentally friendly and easily degradable hydrogel coating according to claim 3, characterized in that: The coating forms a transparent film with a thickness of 8-12 μm after curing, and the oxygen transmission rate of the coating is ≤5 cm 3 / (m 2 ·day·atm), water vapor transmission rate ≤1.2g / (m 2 ·day), the inhibition rate against Escherichia coli and Staphylococcus aureus is ≥99%, and the degradation rate under composting conditions is ≥80% within 180 days.

5. The method for preparing an environmentally friendly and easily degradable hydrogel coating according to claim 1, characterized in that: The components of the coating include, by weight percentage, 80-90% of a chitosan-acrylic acid-based precursor solution, 2-4% of sericin, 3-6% of silk fibroin, 1-3% of silk peptide, 0.5-1% of tea polyphenols, 1-2% of a photoinitiator, 1-3% of a plasticizer, and 0.5-1% of a leveling agent.

6. The method for preparing an environmentally friendly and easily degradable hydrogel coating according to claim 1, characterized in that: The preparation method of the sericin pre-solution is as follows: Prepare sericin with a purity of ≥90% and a molecular weight of 10-50 kDa. Add deionized water at a ratio of 1:20-1:30 to silk:silicin. Stir at 300-500 rpm in a 40-50°C water bath for 1-2 hours to completely dissolve the sericin. Adjust the pH of the solution to 5.5-6.0 with citric acid or sodium hydrogen phosphate buffer. Filter through a 0.45μm microporous membrane and refrigerate at 4°C until ready to use. Return to room temperature and shake well before use.

7. An environmentally friendly and easily degradable hydrogel coating, characterized in that: The preparation is carried out according to the preparation method according to any one of claims 1 to 5.

8. The use of the environmentally friendly and easily degradable hydrogel coating according to claim 7, characterized in that: The hydrogel coating is applied on food wrappers.

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