Food oxygen uptake packaging double-layer film and preparation method thereof

Abstract

The invention discloses a food oxygen-uptake packaging double-layer film and a preparation method thereof. The preparation method comprises the following steps: S1, dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol solution, adding glycerol, stirring, acidifying, adding citric acid, and stirring and reacting at 50-98 DEG C for 5-10 hours; adding gallic acid, stirring and reacting at 50-98 DEG C for 1-2 hours, and obtaining a membrane casting solution A after the reaction is finished; casting the membrane casting solution A into a mold, and drying to form a modified polyvinyl alcohol membrane layer; s2, dissolving chitosan in an acetic acid aqueous solution with the mass concentration of 1-2% to obtain a chitosan solution, adding glycerol, stirring, then adding sodium carbonate, and stirring at 55-70 DEG C for 0.5-2 hours to obtain a membrane casting solution B; casting the membrane casting solution B on the modified polyvinyl alcohol membrane layer in the mold, and drying to form a modified chitosan membrane layer; and demolding to prepare the food oxygen uptake packaging double-layer film. The food oxygen-absorbing packaging double-layer film prepared by the method disclosed by the invention has the advantages of efficient oxygen-absorbing performance, excellent mechanical property and degradability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of food packaging materials, in particular to a food oxygen-absorbing packaging double-layer film and a preparation method thereof. BACKGROUND

[0002] During storage, oxygen can cause oxidation of components such as fatty acids, proteins, and vitamins, leading to food spoilage, nutrient loss, darkening of color, and deterioration of odor. At the same time, oxygen conditions are suitable for the growth and reproduction of various microorganisms (such as molds and yeasts), which can easily accelerate food spoilage. In order to extend the shelf life of food, oxygen-absorbing packaging technology is widely used, such as oxygen absorber sachets and modified atmosphere packaging. However, oxygen absorber sachets have the risks of increasing production line processes, being unable to be heated by microwaves, being mistaken for food, and leaking; and modified atmosphere packaging has a relatively short shelf life due to the influence of the barrier properties of the packaging material.

[0003] Active packaging is an emerging technology that integrates oxygen absorbers into packaging materials, enabling the materials themselves to have oxygen-absorbing functions, and has good application prospects in the field of food packaging. For example, Chinese Patent Application CN114196048A discloses a preparation method for an oxygen-absorbing bottle cap gasket, in which an oxygen absorber is added to a plastic matrix through melt blending, extrusion granulation, film casting of the granules, and tabletting to obtain an oxygen-absorbing bottle cap gasket. However, food packaging generally uses natural organic oxygen absorbers that are safer, and the high-temperature conditions of melt processing can easily cause the inactivation of natural organic oxygen absorbers, resulting in poor oxygen-absorbing performance of the product.

[0004] Chinese Patent Application CN103407259A discloses an oxygen-absorbing functional soft packaging material based on natural gallic acid, which includes four functional structure layers: an outer oxygen barrier layer, an oxygen-absorbing layer that is also an adhesive layer, an activation layer that is also a catalytic layer, and a food contact layer; the food contact layer is the innermost layer and is also an oxygen permeation layer; the packaging material is obtained by using a dry composite process, in which an EVA water-based emulsion containing sodium carbonate is first coated on the surface of the food contact layer to prepare a pre-coated film, then a polyurethane or polyacrylate adhesive containing gallic acid is coated on the oxygen barrier layer film, and the pre-coated film is then compounded; the prepared packaging material has good oxygen-absorbing and carbon dioxide-releasing performance. This scheme disperses gallic acid in a polyurethane or polyacrylate adhesive as an adhesive layer and is compounded with other film layers, but the use of adhesives has the potential risk of residual migration of organic additives; and its complex four-layer structure also increases the complexity and cost of the production process; in addition, it uses traditional petroleum-based polymers (such as polyethylene and polypropylene) as the base material, which cannot be reused and is difficult to degrade, causing environmental problems such as "white pollution" after use, which is not consistent with the current trend of green and environmentally friendly packaging Chitosan materials have been widely studied in the field of food packaging due to their biocompatibility, biodegradability, antibacterial properties, and film-forming properties. However, the current chitosan materials generally have poor mechanical properties, which limits their application as food packaging materials.

[0005] Therefore, there is an urgent need for a new type of food packaging material that combines high oxygen absorption performance, excellent mechanical properties, and degradability to meet the comprehensive needs of food safety, environmental protection, and preservation effect. SUMMARY

[0006] To overcome the shortcomings of the prior art, the present application aims to provide a food oxygen absorption packaging double-layer film with high oxygen absorption performance, excellent mechanical properties, and degradability, as well as a preparation method thereof.

[0007] The present application is achieved by the following technical solutions: The present application provides a preparation method of a food oxygen absorption packaging double-layer film, comprising the following steps: S1. Dissolve polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol solution, add glycerol, stir, and after acidification, add citric acid, stir at 50-98℃ for 5-10h; then add gallic acid, stir at 50-98℃ for 1-2h, and obtain casting solution A after the reaction is completed; cast the casting solution A in a mold, dry, and form a modified polyvinyl alcohol film layer; S2. Dissolve chitosan in a 1-2% mass concentration acetic acid aqueous solution to obtain a chitosan solution, add glycerol, stir, then add sodium carbonate, and stir at 55-70℃ for 0.5-2h to obtain casting solution B; cast the casting solution B on the modified polyvinyl alcohol film layer in the mold, dry, and form a modified chitosan film layer; demold to obtain the food oxygen absorption packaging double-layer film.

[0008] Further, the alcoholysis degree of the polyvinyl alcohol is 78.5%-100%, and the molecular weight is 30000-50000.

[0009] Further, in step S1, the mass concentration of the polyvinyl alcohol solution is 1-5%.

[0010] Further, in step S1, the mass ratio of glycerol to polyvinyl alcohol is (0.25-1.5):1.

[0011] Further, in step S1, the amount of citric acid is 5%-20% of the mass of polyvinyl alcohol.

[0012] Further, in step S1, the amount of gallic acid is 20%-60% of the mass of polyvinyl alcohol.

[0013] Further, in step S1, the stirring temperature after adding glycerol is 90-98℃, and the stirring time is 1-3h.

[0014] Further, in step S1, the acidification is adding acid liquid to make the pH value of the solution reach 2-6, and the acid liquid is at least one of acetic acid, oxalic acid and citric acid. The acidification is stirring at 55-70℃ for 0.5-2h after adding the acid liquid.

[0015] Further, the deacetylation degree of the chitosan is ≥90%, and the molecular weight is 100000-150000.

[0016] Further, in step S2, the mass concentration of the chitosan solution is 1-2%.

[0017] Further, in step S2, the amount of glycerol is 5-75% of the mass of chitosan.

[0018] Further, in step S2, the amount of sodium carbonate is 5%-60% of the mass of chitosan.

[0019] Further, in step S2, the stirring temperature after adding glycerol is 20-30℃, and the stirring time is 1-2h.

[0020] Further, in the preparation method of the food oxygen-absorbing packaging double-layer film, the drying is drying to remove the solvent under the conditions of temperature 20-60℃ and humidity 10-60%.

[0021] Further, in the preparation method of the food oxygen-absorbing packaging double-layer film, the mass ratio of gallic acid to sodium carbonate is (2-3):1.

[0022] The application also provides a food oxygen-absorbing packaging double-layer film prepared by the preparation method of the food oxygen-absorbing packaging double-layer film.

[0023] Further, the thickness of the food oxygen-absorbing packaging double-layer film is 20-400μm, and the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer is (0.4-1.8):1.

[0024] The application has the following beneficial effects: The food oxygen absorption packaging double-layer film is prepared by compounding the modified polyvinyl alcohol film layer and the modified chitosan film layer through a layered casting method.

[0025] The food oxygen absorption packaging double-layer film of the present application is a degradable film material with excellent mechanical properties, is green and environmentally friendly, and has the advantages of controllable activation of oxygen absorption activity, and has excellent oxygen absorption performance after activation, and has high application advantages in the field of food packaging. DETAILED DESCRIPTION

[0026] The following examples are provided to better further understand the present application, and are not limited to the best mode, and do not limit the content and protection scope of the present application. Any person under the inspiration of the present application or the combination of the present application with other prior art features can obtain any product same or similar to the present application, which falls within the protection scope of the present application.

[0027] If the specific experimental steps or conditions are not specified in the examples, the operation or conditions can be carried out according to the conventional experimental steps described in the literature in the art. If the reagents or instruments are not specified by the manufacturer, they are conventional reagent products that can be obtained by market purchase.

[0028] Unless otherwise specified, the room temperature or normal temperature in the examples of the present application refers to 25±1℃.

[0029] The materials used in the examples and comparative examples are as follows, but are not limited to these materials: Polyvinyl alcohol: Tianjin Damao Chemical Reagent Factory, molecular weight 31000-50000, alcoholysis degree: 87.0-89.0mol%, Chitosan: Macklin, molecular weight 100000, degree of deacetylation ≥90%, Gallic acid: Macklin, analytical pure; Citric acid: Tianjin Damao Chemical Reagent Factory, analytical pure; Sodium carbonate: Huiquan Biotechnology Co., Ltd., food grade, Glycerol: Tianjin Fuyu Fine Chemical Co., Ltd., analytical pure; Acetic acid: Tianjin Fuyu Fine Chemical Co., Ltd., analytical pure; Ethyl cellulose: Comie reagent, analytical pure, viscosity 20-30 mPa-S. Example 1

[0030] The present embodiment provides a food oxygen absorbing packaging double-layer film, and the preparation method is as follows: S1. 2g of polyvinyl alcohol was dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass concentration of 2%, 3g of glycerol was added, and stirring was performed at 90°C for 2h until complete dissolution, 12.5mL of acetic acid was added, and stirring was performed at 65°C for 30min for acidification, the solution had a pH value of 2.8, 0.17g of citric acid was added, and stirring was performed at 65°C for 8h for reaction, then 0.4g of gallic acid was added, and stirring was performed at 65°C for 1h for reaction, and after the reaction was completed, casting solution A was obtained; 20mL of casting solution A was cast in a 10cm*10cm polytetrafluoroethylene mold, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40%RH to form a modified polyvinyl alcohol film layer; S2. 2g of chitosan was dissolved in an aqueous acetic acid solution with a mass concentration of 2% to obtain a chitosan solution with a mass concentration of 2%, 1.3g of glycerol was added, and stirring was performed at room temperature for 30min until complete dissolution, then 0.2g of sodium carbonate was added, and stirring was performed at 65°C for 1h, and casting solution B was obtained; 20mL of casting solution B was cast on the modified polyvinyl alcohol film layer in the mold in step S1, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40%RH to form a modified chitosan film layer; demolding was performed to obtain the food oxygen absorbing packaging double-layer film, which had a thickness of 123μm, and the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer was 11:10. Example 2

[0031] The present embodiment provides a food oxygen absorbing packaging double-layer film, and the preparation method is as follows: S1. 2g of polyvinyl alcohol was dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass concentration of 2%, 3g of glycerol was added, and stirring was performed at 90°C for 2h until complete dissolution, 12.5mL of acetic acid was added, and stirring was performed at 65°C for 30min for acidification, the solution had a pH value of 2.8, 0.17g of citric acid was added, and stirring was performed at 65°C for 8h for reaction, then 0.6g of gallic acid was added, and stirring was performed at 65°C for 1h for reaction, and after the reaction was completed, casting solution A was obtained; 20mL of casting solution A was cast in a 10cm*10cm polytetrafluoroethylene mold, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40%RH to form a modified polyvinyl alcohol film layer; S2. 2 g of chitosan was dissolved in 2% acetic acid aqueous solution to obtain a chitosan solution with a mass concentration of 2%, 1.3 g of glycerol was added, and stirring was performed at room temperature for 30 min until complete dissolution, then 0.3 g of sodium carbonate was added, and stirring was performed at 65°C for 1 h to obtain casting solution B; 20 mL of casting solution B was cast on the modified polyvinyl alcohol film layer in the mold in step S1, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40% RH to form a modified chitosan film layer; demolding was performed to obtain the food oxygen absorption packaging double-layer film, the thickness of which was 131 μm, and the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer was 9:11. Example 3

[0032] The present embodiment provides a food oxygen absorption packaging double-layer film, and the preparation method thereof is as follows: S1. 2 g of polyvinyl alcohol was dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass concentration of 2%, 3 g of glycerol was added, and stirring was performed at 90°C for 2 h until complete dissolution, 12.5 mL of acetic acid was added, and stirring was performed at 65°C for 30 min for acidification, the pH value of the solution was 2.8, 0.17 g of citric acid was added, and stirring was performed at 65°C for 8 h for reaction, then 0.8 g of gallic acid was added, and stirring was performed at 65°C for 1 h for reaction, and casting solution A was obtained after the reaction; 20 mL of casting solution A was cast in a 10 cm x 10 cm polytetrafluoroethylene mold, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40% RH to form a modified polyvinyl alcohol film layer; S2. 2 g of chitosan was dissolved in 2% acetic acid aqueous solution to obtain a chitosan solution with a mass concentration of 2%, 1.3 g of glycerol was added, and stirring was performed at room temperature for 30 min until complete dissolution, then 0.3 g of sodium carbonate was added, and stirring was performed at 65°C for 1 h to obtain casting solution B; 20 mL of casting solution B was cast on the modified polyvinyl alcohol film layer in the mold in step S1, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40% RH to form a modified chitosan film layer; demolding was performed to obtain the food oxygen absorption packaging double-layer film, the thickness of which was 131 μm, and the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer was 9:11. Example 4

[0033] The present embodiment provides a food oxygen absorption packaging double-layer film, and the preparation method thereof is as follows: S1. 2 g of polyvinyl alcohol was dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass concentration of 2%, 3 g of glycerol was added, and stirring was performed at 90°C for 2 h until complete dissolution, 12.5 mL of acetic acid was added, and stirring was performed at 65°C for 30 min for acidification, the solution had a pH value of 2.8, 0.17 g of citric acid was added, and stirring was performed at 65°C for 8 h for reaction, then 1 g of gallic acid was added, and stirring was performed at 65°C for 1 h for reaction, and after the reaction was completed, casting solution A was obtained; 20 mL of casting solution A was cast in a 10 cm x 10 cm polytetrafluoroethylene mold, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40% RH to form a modified polyvinyl alcohol film layer; S2. 2 g of chitosan was dissolved in an aqueous acetic acid solution with a mass concentration of 2% to obtain a chitosan solution with a mass concentration of 2%, 1.3 g of glycerol was added, and stirring was performed at room temperature for 30 min until complete dissolution, then 0.5 g of sodium carbonate was added, and stirring was performed at 65°C for 1 h to obtain casting solution B; 20 mL of casting solution B was cast on the modified polyvinyl alcohol film layer in the mold in step S1, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40% RH to form a modified chitosan film layer; demolding was performed to obtain the food oxygen-absorbing packaging double-layer film, which had a thickness of 151 μm, and the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer was 43:50.

[0034] Comparative Example 1 This comparative example provides a food packaging film, which differs from Example 1 in that the amounts of gallic acid and sodium carbonate are different, and the preparation method is as follows: S1. 2 g of polyvinyl alcohol was dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass concentration of 2%, 3 g of glycerol was added, and stirring was performed at 90°C for 2 h until complete dissolution, 12.5 mL of acetic acid was added, and stirring was performed at 65°C for 30 min for acidification, the solution had a pH value of 2.8, 0.17 g of citric acid was added, and stirring was performed at 65°C for 8 h for reaction, then 1 g of gallic acid was added, and stirring was performed at 65°C for 1 h for reaction, and after the reaction was completed, casting solution A was obtained; 20 mL of casting solution A was cast in a 10 cm x 10 cm polytetrafluoroethylene mold, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40% RH to form a modified polyvinyl alcohol film layer; S2. 2 g of chitosan was dissolved in 2% acetic acid aqueous solution to obtain a chitosan solution with a mass concentration of 2%, 1.3 g of glycerol was added, and stirring was performed at room temperature for 30 min until complete dissolution, then 0.15 g of sodium carbonate was added, and stirring was performed at 65°C for 1 h to obtain casting solution B; 20 mL of casting solution B was cast on the modified polyvinyl alcohol film layer in the mold in step S1, and the modified chitosan film layer was formed by fully drying and removing the solvent in a constant temperature and humidity box at 40°C and 40% RH; demolding to obtain the food oxygen-absorbing packaging double-layer film, the thickness of which was 113 μm, and the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer was 3:5.

[0035] Comparative Example 2 This comparative example provides a food packaging film, which is different from Example 1 in that polyvinyl alcohol is used to carry sodium carbonate, and chitosan is used to carry gallic acid, and the preparation method is as follows: S1. 2 g of polyvinyl alcohol was dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass concentration of 2%, 3 g of glycerol was added, and stirring was performed at 90°C for 2 h until complete dissolution, 12.5 mL of acetic acid was added, and stirring was performed at 65°C for 30 min to acidify the solution to a pH value of 2.8, 0.17 g of citric acid was added, and stirring was performed at 65°C for 8 h for reaction; then 0.2 g of sodium carbonate was added, and stirring was performed at 65°C for 1 h, and the casting solution A was obtained after the reaction; 20 mL of casting solution A was cast in a 10 cm x 10 cm polytetrafluoroethylene mold, and the modified polyvinyl alcohol film layer was formed by fully drying and removing the solvent in a constant temperature and humidity box at 40°C and 40% RH; S2. 2 g of chitosan was dissolved in 2% acetic acid aqueous solution to obtain a chitosan solution with a mass concentration of 2%, 1.3 g of glycerol was added, and stirring was performed at room temperature for 30 min until complete dissolution, then 0.15 g of sodium carbonate was added, and stirring was performed at 65°C for 1 h to obtain casting solution B; 20 mL of casting solution B was cast on the modified polyvinyl alcohol film layer in the mold in step S1, and the modified chitosan film layer was formed by fully drying and removing the solvent in a constant temperature and humidity box at 40°C and 40% RH; demolding to obtain the food oxygen-absorbing packaging double-layer film, the thickness of which was 113 μm, and the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer was 3:5.

[0036] Comparative Example 3 This comparative example provides a food packaging film, and the preparation method is as follows: S1. 2 g of polyvinyl alcohol was dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass concentration of 2%, 3 g of glycerol was added, and stirring was performed at 90°C for 2 h until complete dissolution, 12.5 mL of acetic acid was added, and stirring was performed at 65°C for 30 min for acidification, the solution had a pH value of 2.8, 0.17 g of citric acid was added, and stirring was performed at 65°C for 8 h for reaction, and then 0.4 g of gallic acid and 0.2 g of sodium carbonate were added, and stirring was performed at 65°C for 1 h to obtain casting solution A; 20 mL of the casting solution A was cast in a 10 cm x 10 cm polytetrafluoroethylene mold, and the solvent was completely removed by drying in a constant-temperature and constant-humidity box at 40°C and 40% RH to form a modified polyvinyl alcohol film layer; S2. 2 g of chitosan was dissolved in an aqueous acetic acid solution with a mass concentration of 2% to obtain a chitosan solution with a mass concentration of 2%, 1.3 g of glycerol was added, and stirring was performed at room temperature for 30 min until complete dissolution to obtain casting solution B; 20 mL of the casting solution B was cast on the modified polyvinyl alcohol film layer in the mold in step S1, and the solvent was completely removed by drying in a constant-temperature and constant-humidity box at 40°C and 40% RH to form a modified chitosan film layer; demolding was performed to obtain the food oxygen-absorbing packaging double-layer film, which had a thickness of 123 μm, and the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer was 31:50.

[0037] Comparative Example 4 This comparative example provides a food packaging film, which is prepared according to the following method: S1. 2 g of polyvinyl alcohol was dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass concentration of 2%, 3 g of glycerol was added, and stirring was performed at 90°C for 2 h until complete dissolution, 12.5 mL of acetic acid was added, and stirring was performed at 65°C for 30 min for acidification, the solution had a pH value of 2.8, 0.17 g of citric acid was added, and stirring was performed at 65°C for 8 h for reaction, and then 0.4 g of gallic acid and 0.2 g of sodium carbonate were added, and stirring was performed at 65°C for 1 h to obtain casting solution A; 20 mL of the casting solution A was cast in a 10 cm x 10 cm polytetrafluoroethylene mold, and the solvent was completely removed by drying in a constant-temperature and constant-humidity box at 40°C and 40% RH to form a modified polyvinyl alcohol film layer; S2. 2 g of chitosan was dissolved in an aqueous acetic acid solution with a mass concentration of 2% to obtain a chitosan solution with a mass concentration of 2%, 1.3 g of glycerol was added, and stirring was performed at room temperature for 30 min until complete dissolution, and then 0.4 g of gallic acid and 0.2 g of sodium carbonate were added, and stirring was performed at 65°C for 1 h to obtain casting solution B; 20 mL of the casting solution B was cast on the modified polyvinyl alcohol film layer in the mold in step S1, and the solvent was completely removed by drying in a constant-temperature and constant-humidity box at 40°C and 40% RH to form a modified chitosan film layer; demolding was performed to obtain the food oxygen-absorbing packaging double-layer film, which had a thickness of 165 μm, and the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer was 4:5.

[0038] Comparative Example 5 The comparative example provides a food packaging film, which is different from example 1 in that ethyl cellulose is used to carry gallic acid, and the preparation method is as follows: S1. 2g of ethyl cellulose was dissolved in 100mL of anhydrous ethanol to obtain an ethyl cellulose solution, 3g of glycerol was added, and stirring was carried out at 60°C for 1h until complete dissolution, 0.4g of gallic acid was added, and stirring was carried out at room temperature for 1h to obtain casting solution A; 20mL of casting solution A was cast into a 10cm×10cm polytetrafluoroethylene mold, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40%RH to form a modified ethyl cellulose film layer; S2. 2g of chitosan was dissolved in a 2% mass concentration of acetic acid aqueous solution to obtain a 2% mass concentration of chitosan solution, 1.3g of glycerol was added, and stirring was carried out at room temperature for 30min until complete dissolution, then 0.2g of sodium carbonate was added, and stirring was carried out at 65°C for 1h to obtain casting solution B; 20mL of casting solution B was cast onto the modified ethyl cellulose film layer in the mold of step S1, and the solvent was completely dried in a constant temperature and humidity box at 40°C and 40%RH to form a modified chitosan film layer; demolding was carried out to obtain the food oxygen-absorbing packaging double-layer film, the thickness was 131μm, and the thickness ratio of the modified ethyl cellulose film layer to the modified chitosan film layer was 4:5.

[0039] Comparative example 6 The comparative example provides an oxygen-absorbing homogeneous film prepared by extrusion blow molding, the substrate uses polyethylene (PE), and the oxygen absorber gallic acid and sodium carbonate are blended with PE to prepare a film by extrusion blow molding. The specific preparation method comprises the following steps: S1. 240g of polyethylene was weighed and vacuum dried at 80°C for 12h; 40g of gallic acid and 20g of sodium carbonate were weighed and vacuum dried at 105°C for 12h; S2. 8mL of tributyl citrate was added to the dried polyethylene in step S1, and the mixture was thoroughly mixed in a mixer; then the dried gallic acid and sodium carbonate in step S1 were added and thoroughly mixed in the mixer to obtain a premix; S3. The premix obtained in step S2 was prepared into a blow molding master batch by a twin-screw extruder, wherein the heating temperatures of zones 1-6 of the extruder were 130°C, 150°C, 170°C, 180°C, 180°C and 180°C; S4. The blow molding master batch was blown into a film by a film blowing machine, wherein the heating temperatures of zones 1-6 of the film blowing machine were 100°C, 120°C, 140°C, 160°C, 180°C and 180°C; and an oxygen-absorbing homogeneous film was prepared, with a thickness of 135μm.

[0040] Related performance tests: 1. Oxygen-absorbing performance test: Accurately cut several samples of 10 cm x 5 cm size, and measure the mass using an electronic balance (accuracy 0.1 mg). Use a digital thickness gauge (accuracy 1 μm) to record the thickness at five evenly selected points on the surface of the sample according to the GB / T 6672-2001 standard, and take the arithmetic mean as the sample thickness. Place the sample in a 130 mL standard test bottle, inject 2.0 mL of deionized water to provide a humidity environment, immediately seal with a butyl rubber plug, and tighten with sealing film. Place the sealed sample bottle in a constant temperature oven at room temperature, 40°C, and 60°C, respectively, and stand for 2 days and 5 days, then take out and measure the residual oxygen concentration in the bottle using a CY-12C oxygen analyzer (measurement range 0-100%, accuracy ±0.5% FS). Test using the 50% notch, use a syringe to extract 50 mL of gas from the sample bottle, inject into the analyzer gas inlet, and read the data. The oxygen absorption performance is calculated according to the following formula: ; In the formula, R represents the oxygen absorption rate, with units of mL / (g·m 2 ) V represents the system volume, with units of mL; ∅O2 represents the residual oxygen concentration, dimensionless, ranging from 0 to 1; m m represents the mass of the film, with units of g; A m represents the area of the film, with units of m 2 ; Each group of samples is tested in triplicate, and the results are expressed as the mean.

[0041] 2. Tensile strength test: Use a 100N microcomputer-controlled electronic universal testing machine according to GB / T1040.3-2006 as the experimental specification, cut the film into dumbbell-shaped samples with a total length of 75 mm, a gauge length of 30 mm, and a width of 4 mm, and set the sample length between the two clamps to 50-70 mm. Measure the thickness at three different positions with a screw micrometer, and select the film with uniform thickness and no obvious defects for mechanical property testing. Set the tensile speed to 30 mm / min, and record the relevant data when the film is pulled apart.

[0042] (1) Tensile strength During the tensile process, the material enters the strengthening stage after the yield stage, and the maximum force (F b ) borne by the sample when it is pulled apart, divided by the original cross-sectional area (S0) of the sample, is called the tensile strength or strength limit (R m ), with units of N / mm 2 or MPa. The tensile strength calculation formula is derived as follows: ; In the formula R m Tensile strength is expressed in MPa. F b This indicates the maximum tensile force required when the film breaks or fails, and is measured in N. b represents the film width, in mm; d represents the film thickness, in mm.

[0043] (2) Elongation at break In any material, stress and deformation always coexist and develop simultaneously. Under tensile force, a material generally elongates. The elongation at which a fiber breaks is called the elongation at break, denoted by e, and expressed as a percentage (%). The elongation at break represents the elongation deformation capacity of a film under maximum load. Therefore, the formula for the elongation at break of a film is: ; In the formula, e represents the elongation at break of the film; L represents the maximum length of the film before it breaks, in mm; L0 represents the length of the film between the clamps before stretching, in mm.

[0044] Table 1: Performance test results of the examples and comparative examples

[0045] ; As can be seen from the above results, the double-layer oxygen-absorbing packaging film of the present invention exhibits strong oxygen absorption performance in the packaging, while also maintaining excellent mechanical properties (tensile strength ≥9MPa, elongation at break ≥110%).

[0046] The food packaging film prepared by the method in Comparative Example 1 showed poor oxygen absorption performance. The main reason for this was that the amount of gallic acid added was too low, resulting in a severe deficiency in the overall oxygen absorption capacity of the material, which fell far short of the standards required for practical applications.

[0047] The food packaging film prepared by the method in Comparative Example 2 showed poor oxygen absorption performance. The main reason for this is that gallic acid reacts with the chitosan substrate, causing the active components to be consumed prematurely, resulting in a significant deficiency in the effective oxygen absorption capacity after film formation.

[0048] The food packaging film prepared by the method of Comparative Example 3 and Comparative Example 4 has an initial oxygen absorption performance better than that of Example 1, but the oxygen absorption amount changes little after being placed for 2 days and 5 days due to the direct contact between the oxygen absorption main agent and the auxiliary agent, indicating that the active component is released in a short time and cannot achieve slow release. The main reason is that the active component (gallic acid and sodium carbonate) is directly contacted in water during preparation, and the interlayer diffusion regulation step is lacking, which causes the reaction to be triggered too early before film formation, which may lead to a shortened material shelf life.

[0049] The food packaging film prepared by the method of Comparative Example 5 has poor mechanical properties and cannot measure the tensile strength and elongation at break, and has little oxygen absorption performance. Analysis shows that the adhesion and wettability between the ethyl cellulose film layer and the modified chitosan film layer are weak, resulting in a serious lack of interlayer bonding strength, which easily causes interlayer separation, and the overall mechanical properties of the film product are significantly deteriorated; in addition, gallic acid is prone to agglomeration during processing due to poor compatibility with the ethyl cellulose matrix, which limits the amount of addition, resulting in uneven distribution and insufficient concentration of the active component in the film layer, which ultimately leads to the difficulty of the oxygen absorption performance of the film to meet the actual application standard.

[0050] The food packaging film prepared by the method of Comparative Example 6 has poor oxygen absorption performance and mechanical properties. The main reason is that gallic acid and sodium carbonate are directly blended and contacted during processing, and the reaction occurs too early in the high-temperature environment of extrusion and film blowing, consuming the active component and resulting in a significant lack of effective oxygen absorption capacity after film formation; in addition, the oxygen absorption system is unevenly dispersed in the film, forming obvious particles that destroy the continuity and uniformity of the film structure and form mechanical weak points, thereby weakening the overall mechanical properties of the film.

[0051] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements within the technical range disclosed by the present application can be easily thought of by those skilled in the art, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a double-layer film for oxygen-absorbing packaging of food, characterized in that, Includes the following steps: S1. Dissolve polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol solution, add glycerol, stir, acidify, add citric acid, and stir and react at 50-98℃ for 5-10 hours. Gallic acid is then added, and the mixture is stirred at 50-98℃ for 1-2 hours. After the reaction is complete, casting solution A is obtained. Casting solution A is poured into a mold and dried to form a modified polyvinyl alcohol film. S2. Dissolve chitosan in an aqueous solution of acetic acid with a mass concentration of 1-2% to obtain a chitosan solution. Add glycerol and stir. Then add sodium carbonate and stir at 55-70℃ for 0.5-2 hours to obtain casting solution B. Cast casting solution B onto a modified polyvinyl alcohol film layer in a mold and dry to form a modified chitosan film layer. Demolding yields the oxygen-absorbing packaging double-layer film for the food.

2. The method for preparing the double-layer film for oxygen-absorbing packaging of food according to claim 1, characterized in that, In step S1, the mass concentration of the polyvinyl alcohol solution is 1-5%; the mass ratio of glycerol to polyvinyl alcohol is (0.25-1.5):1; the amount of citric acid used is 5%-20% of the mass of polyvinyl alcohol; and the amount of gallic acid used is 20%-60% of the mass of polyvinyl alcohol.

3. The method for preparing the double-layer film for oxygen-absorbing packaging of food according to claim 1, characterized in that, In step S1, the stirring temperature after adding glycerol is 90-98℃, and the stirring time is 1-3h.

4. The method for preparing the double-layer film for oxygen-absorbing packaging of food according to claim 1, characterized in that, In step S1, the acidification involves adding an acid solution to bring the pH value of the solution to 2-6. The acid solution is at least one of acetic acid, oxalic acid, and citric acid.

5. The method for preparing the double-layer film for oxygen-absorbing packaging of food according to claim 1, characterized in that, In step S2, the mass concentration of the chitosan solution is 1-2%, the amount of glycerol used is 5-75% of the mass of chitosan, and the amount of sodium carbonate used is 5%-60% of the mass of chitosan.

6. The method for preparing the double-layer film for oxygen-absorbing packaging of food according to claim 1, characterized in that, In step S2, the stirring temperature after adding glycerol is 20-30℃, and the stirring time is 0.5-2h.

7. The method for preparing the double-layer film for oxygen-absorbing packaging of food according to claim 1, characterized in that, The drying process involves removing the solvent at a temperature of 20-60℃ and a humidity of 10-60%.

8. The method for preparing the double-layer film for oxygen-absorbing packaging of food according to claim 1, characterized in that, The mass ratio of gallic acid to sodium carbonate is (2-3):

1.

9. A double-layer film for oxygen-absorbing packaging of food, characterized in that, It is prepared by the method of any one of claims 1-8 for preparing a double-layer film for oxygen-absorbing packaging of food.

10. The double-layer film for oxygen-absorbing packaging of food according to claim 9, characterized in that, The thickness of the double-layer oxygen-absorbing packaging film for food is 20-400 μm; the thickness ratio of the modified polyvinyl alcohol film layer to the modified chitosan film layer is (0.4-1.8):1.

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