Preparation and application of a hydrophobic modified polyvinyl alcohol antibacterial packaging film

Abstract

This invention belongs to the field of packaging material technology. More specifically, this invention provides a composition, by weight, comprising the following components: 3-7 parts polyvinyl alcohol, 0.1-0.3 parts polyacrylic acid, 1.25-2.5 parts glutaraldehyde, 0.5-1.5 parts citric acid, 4-10 parts glycerol, and 2-4 parts magnesium chloride. The packaging film prepared using this composition exhibits excellent thermal stability and low water vapor permeability, preventing moisture loss from meat products and better maintaining the texture and flavor of the meat. Furthermore, the CO2 permeability of the packaging film is significantly higher than the O2 permeability, which can inhibit aerobic microorganisms and reduce fat oxidation. The packaging film of this invention has excellent antibacterial and antioxidant properties, showing excellent performance in meat preservation, maintaining meat color, elasticity, and chewiness, and has great application prospects and value in the field of meat product packaging and preservation.

Description

Technical Field

[0001] This invention belongs to the field of packaging materials technology. More specifically, it relates to the preparation and application of a hydrophobic modified polyvinyl alcohol antibacterial packaging film. Background Technology

[0002] In the food industry, packaging films, as crucial food contact materials, play a vital role in ensuring food safety and extending shelf life. Traditional plastic packaging materials such as polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) have long dominated the food packaging market due to their excellent barrier properties, mechanical strength, and cost advantages. However, these materials are difficult to degrade in the natural environment, leading to the continuous accumulation of "white pollution." Studies show that a single-layer PE film takes more than 200 years to completely degrade in soil, placing enormous pressure on the ecological environment. Furthermore, the microplastic particles formed from plastic breakdown can accumulate in the human bloodstream through the food chain, inducing inflammatory responses and cytotoxicity, threatening human health. This has prompted the industry to seek environmentally friendly and sustainable packaging solutions.

[0003] Current research is developing novel bio-based biodegradable materials, such as polyvinyl alcohol (PVA), polylactic acid (PLA), and chitosan, to prepare packaging films. Among these, PVA has attracted significant attention due to its excellent biocompatibility and biodegradability. PVA can be completely decomposed into carbon dioxide and water by microorganisms in the natural environment, avoiding threats to the ecosystem and health. However, existing PVA packaging films suffer from problems such as easy water absorption and swelling, lack of antibacterial activity, poor oil resistance, and poor thermal stability, which limit its application in the food packaging field. Improving the performance of PVA films to make them suitable for food packaging has become a current research hotspot. Summary of the Invention

[0004] The present invention aims to overcome the defects and shortcomings of the existing PVA film and provide a modified PVA film with strong oil resistance, low water vapor permeability and low O2 permeability, and excellent antibacterial and antioxidant properties. It is particularly effective in meat preservation, maintaining the color, elasticity and chewiness of meat, and is especially suitable as a packaging film for meat products.

[0005] The first object of the present invention is to provide a composition and its application.

[0006] A second objective of this invention is to provide a packaging film and a method for preparing the same.

[0007] A third objective of this invention is to provide applications of the aforementioned packaging film.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] The present invention provides a composition comprising, by weight, the following components: 3-7 parts polyvinyl alcohol, 0.1-0.3 parts polyacrylic acid, 1.25-2.5 parts glutaraldehyde, 0.5-1.5 parts citric acid, 4-10 parts glycerol, and 2-4 parts magnesium chloride.

[0010] Preferably, the composition comprises, by weight, the following components: 3-7 parts polyvinyl alcohol, 0.2-0.3 parts polyacrylic acid, 1.25-2.5 parts glutaraldehyde, 0.5-1.5 parts citric acid, 4-8 parts glycerol, and 3-4 parts magnesium chloride.

[0011] More preferably, the composition comprises, by weight, the following components: 5 parts polyvinyl alcohol, 0.2 parts polyacrylic acid, 1.25 parts glutaraldehyde, 1 part citric acid, 5 parts glycerol, and 4 parts magnesium chloride.

[0012] The packaging film prepared using this composition exhibits excellent thermal stability, low water vapor permeability, and significantly higher CO2 permeability than O2 permeability, thus inhibiting aerobic microorganisms and reducing lipid oxidation. Furthermore, the packaging film of this invention possesses excellent antibacterial and antioxidant properties, resulting in superior food preservation. Therefore, the following technical solutions are also claimed:

[0013] This invention provides the application of the above composition in the preparation of thin films.

[0014] This invention provides the application of the above composition in the preparation of food packaging films.

[0015] The present invention also provides a method for preparing a packaging film, wherein the packaging film is prepared using the above composition.

[0016] Preferably, the preparation method is as follows: the above composition is added to water to obtain a mixture, the mixture is reacted at 80-100℃ for 90-150 min, and the packaging film is obtained after drying.

[0017] As an alternative implementation, in the preparation method, the mixture is reacted at 90°C for 120 min.

[0018] Preferably, in the mixture, the concentration of polyvinyl alcohol is 30-70 mg / mL, the concentration of polyacrylic acid is 1-3 mg / mL, the concentration of glutaraldehyde is 0.125-0.25 mmol / mL, the concentration of citric acid is 5-15 mg / mL, the concentration of glycerol is 0.4-0.9 mmol / mL, and the concentration of magnesium chloride is 20-40 mg / mL.

[0019] More preferably, in the mixture, the concentration of polyvinyl alcohol is 50 mg / mL, the concentration of polyacrylic acid is 2 mg / mL, the concentration of glutaraldehyde is 0.125 mmol / mL, the concentration of citric acid is 10 mg / mL, the concentration of glycerol is 0.54 mmol / mL, and the concentration of magnesium chloride is 40 mg / mL.

[0020] Preferably, the pH value of the mixture is 2-4.

[0021] More preferably, the pH value of the mixture is 2.

[0022] As an alternative implementation, the packaging film is prepared as follows: 5g of polyvinyl alcohol is dissolved in 100mL of distilled water at 90℃ to obtain a film solution. 0.2g of polyacrylic acid, 1.25mL of glutaraldehyde, 1g of citric acid, 4mL of glycerol, and 4g of magnesium chloride are added to the film solution, and the mixture is stirred thoroughly. The pH of the film solution is then adjusted to 2, and the mixture is reacted at 90℃ for 120min. After the reaction, the film solution is dried to obtain the packaging film.

[0023] As an alternative implementation, the drying is performed at 30-40°C for 3-7 hours.

[0024] As an alternative implementation, the drying is performed at 35°C for 5 hours.

[0025] As an alternative implementation, the dried packaging film is equilibrated for 8-16 hours at 20-25°C and 40-60% relative humidity.

[0026] As an alternative implementation, the dried packaging film is equilibrated for 12 hours at 23°C and 53% relative humidity.

[0027] As an alternative implementation, the mixture is degassed before the drying process.

[0028] As an alternative implementation, the degassing process takes 20-40 minutes.

[0029] As an alternative implementation, the degassing process can be carried out in a vacuum drying oven.

[0030] This invention provides a packaging film prepared by the above-described preparation method.

[0031] The application of the aforementioned packaging film in food preservation, or in packaged food, should also be within the scope of protection of this invention.

[0032] The present invention has the following beneficial effects:

[0033] (1) The packaging film of the present invention is prepared from polyvinyl alcohol, polyacrylic acid, glutaraldehyde, citric acid, glycerol and magnesium chloride in a specific ratio. Compared with the existing polyvinyl alcohol packaging film, the packaging film of the present invention greatly enhances the thermal stability of the film and reduces the melting temperature, which is beneficial to the thermoplastic processing of the packaging film.

[0034] (2) The packaging film of the present invention has strong oil resistance and can prevent additives (such as plasticizers) in the packaging from dissolving into the oil, thereby reducing food safety risks.

[0035] (3) The packaging film of the present invention has a low water vapor permeability, which can reduce the exchange of moisture inside and outside the packaging, avoid moisture loss of meat products, and better maintain the taste and flavor of meat.

[0036] (4) The CO2 permeability of the packaging film of the present invention is significantly higher than that of O2 permeability, which can easily form a "high CO2, low O2" environment, inhibit aerobic microorganisms, reduce fat oxidation, maintain the color of meat, and is very suitable for food packaging.

[0037] (5) The packaging film of the present invention has excellent antibacterial and antioxidant properties, excellent preservation effect on meat, can maintain the color of meat, reduce the juice loss rate, and maintain the elasticity and chewiness of meat. Attached Figure Description

[0038] Figure 1 The results show the effect of polyacrylic acid solid content on membrane properties (Figure A shows the results of tensile strength and elongation at break; Figure B shows the results of water absorption and solubility).

[0039] Figure 2 The results show the effect of glutaraldehyde solid content on membrane performance (Figure A shows the results of tensile strength and elongation at break; Figure B shows the results of water absorption and solubility).

[0040] Figure 3 The results show the effect of citric acid solid content on membrane properties (Figure A shows the results of tensile strength and elongation at break; Figure B shows the results of water absorption and solubility).

[0041] Figure 4 The results show the effect of glycerol solid content on membrane performance (Figure A shows the results of tensile strength and elongation at break; Figure B shows the results of water absorption and solubility).

[0042] Figure 5 The results show the effect of magnesium chloride solid content on membrane performance (Figure A shows the results of tensile strength and elongation at break; Figure B shows the results of water absorption and solubility).

[0043] Figure 6The results show the effect of pH changes on membrane performance (Figure A shows the results of tensile strength and elongation at break; Figure B shows the results of water absorption and solubility measurements).

[0044] Figure 7 The results are infrared spectral measurements of different PVA-modified films.

[0045] Figure 8 Thermogravimetric analysis results of different PVA modified films (Figure A shows the thermogravimetric analysis of PVA 0-6 films);

[0046] Figure B shows the thermogravimetric analysis (TGA) curve of the PVA 0-6 film; Figure C shows the TGA curve of the PVA 0-3 film; Figure D shows...

[0047] Thermogravimetric analysis diagrams of PVA-0 and PVA 3-6 films).

[0048] Figure 9 The X-ray diffraction test results are for different PVA modified films.

[0049] Figure 10 The results show the tensile strength and elongation at break of different PVA-modified films.

[0050] Figure 11 The results of water absorption and solubility tests for different PVA modified films are shown in Figure A (water absorption test results); Figure B (solubility test results).

[0051] Figure 12 The results show the oil resistance of different PVA-modified films.

[0052] Figure 13 The results show the water vapor transmission rate of different PVA-modified membranes.

[0053] Figure 14 The results show the contact angle test results for different PVA-modified films.

[0054] Figure 15 The results of gas permeability measurements for different PVA-modified membranes are shown in Figure A (oxygen permeability measurement results; carbon dioxide permeability measurement results).

[0055] Figure 16 The results are from antibacterial kinetic tests of different PVA-modified films.

[0056] Figure 17 The results of antibacterial plate tests on different PVA-modified films are shown.

[0057] Figure 18 The results of antioxidant performance determination of different PVA modified films (Figure A shows the DPPH free radical scavenging rate; Figure B shows the ABTS free radical scavenging rate).

[0058] Figure 19 Radar chart showing the overall performance of different PVA-modified films.

[0059] Figure 20 Sensory evaluation results for meat samples with different treatments.

[0060] Figure 21 The results of meat color measurement for meat samples with different treatments are shown in Figure A (blindness L* measurement results), Figure B (red-green hue a* measurement results), and Figure C (yellow-blue hue b* measurement results).

[0061] Figure 22 Results of juice loss determination for meat samples with different treatments.

[0062] Figure 23 Results of volatile basic nitrogen determination in meat samples with different treatments.

[0063] Figure 24 The results of thiobarbituric acid determination in meat samples with different treatments.

[0064] Figure 25 The pH values ​​of meat samples with different treatments were measured.

[0065] Figure 26 Results of metmyoglobin determination in meat samples with different treatments.

[0066] Figure 27 The results show the total bacterial count of meat samples treated with different methods.

[0067] Figure 28 The results of texture analysis of meat samples with different treatments are shown in Figure A (hardness test results); Figure B (cohesiveness test results); Figure C (elasticity test results); and Figure D (chewability test results). Detailed Implementation

[0068] The present invention will be further described below with reference to the accompanying drawings and specific examples, but the examples do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0069] Unless otherwise specified, the reagents and materials used in the following examples were commercially available.

[0070] Polyvinyl alcohol, polyacrylic acid, and glycerol were purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with product numbers P875275, P815683, and G810575, respectively.

[0071] Glutaraldehyde and citric acid were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0072] In the embodiments, the solid content is calculated based on the mass or volume ratio of each component, specifically using the formula: solid content (%) = (mass of solid components and / or total mass of the mixture) × 100, or (volume of solid components and / or total volume of the mixture) × 100.

[0073] The methods for determining tensile strength and elongation at break are based on ISO 1924-2.

[0074] The methods for determining water absorption, solubility, and water vapor transmission rate are referenced in the literature "Yang Yujing. Preparation of Eugenol-Carboxymethyl Chitosan / Pullulan Polysaccharide Composite Membrane and Its Application in Preservation of Chilled Pork [D]. Sichuan Agricultural University, 2023."

[0075] The method for determining oil resistance is referenced in the literature "Luo Shuwen. Preparation and performance study of EC / PAN@SPA cellulose-based composite film [D]. Guangxi University, 2024."

[0076] The method for determining gas permeability is referenced in the literature "Han Xiao. Study on the preservation of chilled pork by antibacterial polyvinyl alcohol film [D]. Guangxi University, 2021."

[0077] The methods for determining antibacterial properties and antioxidant capacity are referenced in the literature "Yan Lijuan. Preparation and performance study of antibacterial polyvinyl alcohol composite film [D]. Jiangnan University, 2023."

[0078] In Example 11, the sensory evaluation method, meat color determination method, juice loss rate determination method, volatile basic nitrogen determination method, thiobarbituric acid determination method, meat pH value determination method, metmyoglobin determination method, total bacterial count determination method, and texture analysis method are referenced in "Zhong Yang. Preparation of Sugarcane Bagasse Extract Combined with Starch-Based Antioxidant Preservative Film and Its Preservation Effect on Beef [D]. Chengdu University, 2024."

[0079] Example 1: Single-factor experimental design of modified PVA film

[0080] I. Preparation method of modified PVA film

[0081] Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water to dissolve it. Then, add polyacrylic acid, glutaraldehyde, citric acid, glycerol, and magnesium chloride in sequence, stirring to dissolve. Adjust the membrane solution environment with 0.01mol / L HCl or NaOH. Stir the membrane solution at 90℃ for 120min to achieve complete homogenization, and then place it in a vacuum drying oven for 30min to degas. After that, transfer the membrane solution to a petri dish and dry it in a 35℃ oven for 5h. Finally, cool it and peel off the membrane, placing it in a 23℃ constant temperature and humidity oven for 12h to equilibrate, thus obtaining the modified PVA membrane. Then, place the membrane in a sealed bag for subsequent performance determination.

[0082] Modified PVA membranes were prepared according to the above method, with the following experimental settings: polyacrylic acid solid content 0.3%, glutaraldehyde solid content 2.5%, citric acid solid content 1.5%, glycerol solid content 6%, magnesium chloride solid content 3%, and pH=4. Tensile strength (TS), elongation at break (EB), water absorption, and solubility of the membrane were used as single-factor experimental indicators.

[0083] II. The Influence of Polyacrylic Acid Solid Content on Membrane Performance

[0084] 1. Preparation of polyacrylic acid modified PVA film

[0085] Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve it at 90℃ to prepare a 5% PVA solution. Keep other variables fixed (glutaraldehyde solid content 2.5%, citric acid solid content 1.5%, glycerol solid content 6%, magnesium chloride solid content 3%, pH=4). Under a 90℃ water bath, add 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% polyacrylic acid to the PVA solution respectively. After stirring thoroughly, react at a constant temperature for about 120min. Cool to room temperature to obtain polyacrylic acid modified PVA film.

[0086] 2. Test index measurement results

[0087] The measurement results are as follows Figure 1 As shown, the results indicate that the tensile strength of the membrane gradually increases when the polyacrylic acid content is between 0 and 0.2%; however, the tensile strength gradually decreases after exceeding 0.2%. Furthermore, the water absorption and solubility of the membrane gradually decrease with increasing polyacrylic acid solid content.

[0088] III. Effect of glutaraldehyde solid content on membrane performance

[0089] 1. Preparation of glutaraldehyde-modified PVA film

[0090] Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve at 90℃ to prepare a 5% PVA solution. Keep other variables fixed (polyacrylic acid solid content 0.3%, citric acid solid content 1.5%, glycerol solid content 6%, magnesium chloride solid content 3%, pH=4). Under a 90℃ water bath, add 0.625%, 1.25%, 1.875%, 2.5%, and 3.125% glutaraldehyde to the PVA solution respectively. After stirring thoroughly, react at a constant temperature for about 120min. Cool to room temperature to obtain the modified PVA film.

[0091] 2. Test index measurement results

[0092] The measurement results are as follows Figure 2 As shown, the results indicate that when the glutaraldehyde content is between 0-1.25%, the tensile strength of the film gradually increases; further increasing the glutaraldehyde content leads to a gradual decrease in the tensile strength of the film. The elongation at break of the film increases rapidly with increasing glutaraldehyde content, then decreases rapidly. Water absorption and solubility are relatively high at 0% glutaraldehyde content, and both gradually decrease with increasing glutaraldehyde content. This suggests that the cross-linking effect of glutaraldehyde restricts the penetration of water molecules and the dissolution of the material, thereby reducing water absorption and solubility. Therefore, the glutaraldehyde content should be between 0-1.25%.

[0093] IV. Effect of Citric Acid Solid Content on Membrane Performance

[0094] 1. Preparation of Citric Acid Modified PVA Film

[0095] Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve it at 90℃ to prepare a 5% PVA solution. Keep other variables fixed (polyacrylic acid solid content 0.3%, glutaraldehyde solid content 2.5%, glycerol solid content 6%, magnesium chloride solid content 3%, pH=4). Under a 90℃ water bath, add 0.5%, 1%, 1.5%, 2%, and 2.5% citric acid to the PVA solution respectively. After stirring thoroughly, react at a constant temperature for about 120min. Cool to room temperature to obtain citric acid modified PVA film.

[0096] 2. Test index measurement results

[0097] The measurement results are as follows Figure 3 As shown, the results indicate that after adding citric acid, the elongation at break and tensile strength are low at 0%, gradually increasing with increasing citric acid content, peaking at 1.0%, and then decreasing. This suggests that the material exhibits optimal ductility and strength at a citric acid content of 1.0%. Water absorption and solubility are high at 0%, gradually decreasing with increasing citric acid content. This indicates that the addition of citric acid limits the penetration of water molecules and the dissolution of the material.

[0098] V. Effect of Glycerol Solid Content on Membrane Performance

[0099] Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve it at 90℃ to prepare a 5% PVA solution. Keep other variables fixed (polyacrylic acid solid content 0.3%, glutaraldehyde solid content 2.5%, citric acid solid content 1.5%, magnesium chloride solid content 3%, pH=4). Under a 90℃ water bath, add 2%, 4%, 6%, 8%, and 10% glycerol to the PVA solution respectively. After stirring thoroughly, react at a constant temperature for about 30 minutes. Cool to room temperature to obtain the modified PVA film.

[0100] 2. Test index measurement results

[0101] The measurement results are as follows Figure 4 As shown, the results indicate that with increasing glycerol solid content, the elongation at break of the material first increases and then decreases, reaching a maximum at 6%, indicating that the material's ductility is optimal at this level. Tensile strength peaks at 8%, indicating the highest strength of the material at this level. The water absorption and solubility of the material first decrease and then increase, reaching a minimum at 6%. Therefore, it can be seen that a dosage of 4%-8% is more suitable.

[0102] VI. Effect of magnesium chloride solid content on membrane performance

[0103] Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve at 90℃ to prepare a 5% PVA solution. Keep other variables fixed (polyacrylic acid solid content 0.3%, glutaraldehyde solid content 2.5%, citric acid solid content 1.5%, glycerol solid content 6%, pH=4). Under a 90℃ water bath, add 1%, 2%, 3%, 4%, and 5% MgCl2 to the PVA solution respectively. After stirring thoroughly, react at a constant temperature for about 120min. Cool to room temperature to obtain the modified PVA film.

[0104] 2. Test index measurement results

[0105] The measurement results are as follows Figure 5 As shown, the results indicate that the elongation at break and tensile strength are low at 0% MgCl2. Both gradually increase with increasing MgCl2 content, peaking at 3% and then decreasing. This suggests that the material exhibits optimal ductility and strength at 3% MgCl2. Water absorption and solubility are high at 0% MgCl2, gradually decreasing with increasing MgCl2 content, reaching their lowest values ​​at 3%.

[0106] VII. Effects of pH Changes on Membrane Performance

[0107] Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve at 90℃ to prepare a 5% PVA solution. Keep other variables fixed (polyacrylic acid solid content 0.3%, glutaraldehyde solid content 2.5%, citric acid solid content 1.5%, glycerol solid content 6%, magnesium chloride solid content 3%). In a 90℃ water bath, add HCl or NaOH to the PVA solution to adjust the pH of the membrane solution to 2, 3, 4, 5, and 6 respectively. After stirring thoroughly, react at a constant temperature for 120min and cool to room temperature to obtain the modified PVA membrane.

[0108] 2. Test index measurement results

[0109] The measurement results are as follows Figure 6 As shown, the results indicate that the elongation at break and tensile strength reach their peak values ​​at pH 3, indicating optimal ductility and strength of the material. Water absorption and solubility are lowest at pH 3, gradually increasing with increasing pH. Changes in pH affect the structure and properties of the material.

[0110] Example 2

[0111] I. Calculation Method for Comprehensive Scoring of Various Indicators of Polyvinyl Alcohol Film

[0112] TS, EB, water absorption, and solubility were used as evaluation indicators, and a comprehensive scoring method was employed to score membrane performance. This method weights or scores each indicator based on its importance, transforming multiple indicators into a single comprehensive indicator. The specific method involves: first, calculating the weights of the membrane performance indicators using principal component analysis; then, calculating the membership degree of each indicator using a membership degree calculation formula; and finally, calculating the comprehensive score of the membrane.

[0113] II. Orthogonal Experiment

[0114] Based on the single-factor experiments, a six-factor, three-level orthogonal experiment was selected. The factor levels of the orthogonal experiment are shown in Table 1. They are: solid content of polyacrylic acid (factor A) 0.1%, 0.2%, 0.3%; solid content of glutaraldehyde (factor B) 0.625%, 1.25%, 1.875%; solid content of citric acid (factor C) 0.5%, 1%, 1.5%; solid content of glycerol (factor D) 4%, 6%, 8%; solid content of MgCl2 (factor E) 2%, 3%, 4%; and pH (factor F) adjusted to 2, 3, 4. Based on the content of each component in the orthogonal experiment table in Table 2, PVA modified films for experiments 1-18 were prepared.

[0115] Table 1. Factor Levels in Orthogonal Experiments

[0116]

[0117] Table 2 Orthogonal Experiment Table

[0118]

[0119]

[0120] III. Comprehensive Evaluation of Membrane Performance

[0121] Using the mechanical and barrier properties of polyvinyl alcohol (PVA) films as the analytical objects, principal component analysis was performed on 12 randomly selected single-factor experimental data sets. The eigenvalues ​​and contribution rates of the relevant components were analyzed. The results showed that, taking the mechanical and barrier properties of PVA films as the analytical objects, the eigenvalues ​​of both the first and second principal components were greater than 1, with variance contribution rates of 57.065% and 27.481%, respectively, and a cumulative variance contribution rate of 84.546%. Since the cumulative variance contribution rates of the first and second principal components exceeded 80%, they essentially covered most of the information in the samples and could be used to replace the original TS, EB, water absorption, and solubility of PVA films.

[0122] (1) Overall membrane performance score

[0123] Based on the principal component analysis results, normalization calculations were performed, and the weights of the four indicators—TS, EB, water absorption, and solubility—of the polyvinyl alcohol (PVA) film were found to be 0.25, 0.24, 0.24, and 0.27, respectively. Therefore, the mathematical model for the comprehensive score of the PVA-modified film is: Y = 0.25P1 + 0.24P2 + 0.24P3 + 0.27P4.

[0124] (2) Orthogonal experiment for the preparation of polyvinyl alcohol film

[0125] The orthogonal experimental results are shown in Table 3. The range R indicates that the order of influence of various factors on the polyvinyl alcohol (PVA) film is E > B > D > A > C > F, which corresponds to magnesium chloride > glutaraldehyde > glycerol > polyacrylic acid > citric acid > pH. By comparing the K values, the optimal combination was determined: polyacrylic acid solid content 0.20%, glutaraldehyde solid content 1.25%, citric acid solid content 1.00%, glycerol solid content 4.00%, magnesium chloride solid content 4.00%, and pH 2. The PVA-modified film prepared using the optimal combination was tested, and the actual average comprehensive score of the PVA-modified film with the optimal combination was 99.330%.

[0126] Table 3 Results of the orthogonal experiment

[0127]

[0128]

[0129] Example 3: Preparation of PVA-modified film

[0130] The solid content of polyacrylic acid (PAA) is 0.20%, the solid content of glutaraldehyde (GA) is 1.25%, the solid content of citric acid (CA) is 1.00%, the solid content of glycerol (GLY) is 4.00%, the solid content of magnesium chloride (MgCl2) is 4.00%, and the pH is pH2.

[0131] (1) Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve it at 90℃ to prepare a 5% PVA solution. Cool to room temperature to obtain a modified PVA-0 film.

[0132] (2) Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve it at 90℃ to prepare a 5% PVA solution for later use. Add polyacrylic acid (PAA) to the membrane solution with a solid content ratio of 0.2% (V / V0), stir thoroughly, and react in a water bath at 90℃ for about 120min. Cool to room temperature to obtain the modified PVA-1 membrane.

[0133] (3) Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve it at 90℃ to prepare a 5% PVA solution for later use. Add polyacrylic acid (PAA) and glutaraldehyde (GA) to the membrane solution in sequence, with solid contents of 0.2% and 1.25% respectively. Stir thoroughly and react in a water bath at 90℃ for about 120min. Cool to room temperature to obtain the modified PVA-2 membrane.

[0134] (4) Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve it at 90℃ to prepare a 5% PVA solution for later use. Add polyacrylic acid (PAA), glutaraldehyde (GA), and citric acid (CA) to the membrane solution in sequence, with solid contents of 0.2%, 1.25%, and 1%, respectively. Stir thoroughly and react in a water bath at 90℃ for about 120min. Cool to room temperature to obtain the modified PVA-3 membrane.

[0135] (5) Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve it at 90℃ to prepare a 5% PVA solution for later use. Add polyacrylic acid (PAA), glutaraldehyde (GA), citric acid (CA), and glycerol (GLY) to the membrane solution in sequence, with solid contents of 0.2%, 1.25%, 1%, and 4%, respectively. Stir thoroughly and react in a water bath at 90℃ for about 120min. Cool to room temperature to obtain the modified PVA-4 membrane.

[0136] (6) Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve it at 90℃ to prepare a 5% PVA solution for later use. Add polyacrylic acid (PAA), glutaraldehyde (GA), citric acid (CA), glycerol (GLY), and magnesium chloride (MgCl2) to the membrane solution in sequence, with solid contents of 0.2%, 1.25%, 1%, 4%, and 4%, respectively. Stir thoroughly and react in a water bath at 90℃ for about 120min. Cool to room temperature to obtain the modified PVA-5 membrane.

[0137] (7) Take 5g of polyvinyl alcohol and place it in a 500mL beaker. Add 100mL of distilled water and dissolve at 90℃ to prepare a 5% PVA solution for later use. Add polyacrylic acid (PAA), glutaraldehyde (GA), citric acid (CA), glycerol (GLY), and magnesium chloride (MgCl2) to the membrane solution in sequence, with solid contents of 0.2%, 1.25%, 1%, 4%, and 4%, respectively. Stir thoroughly and adjust the pH of the PVA solution to 2 with 0.01mol / L HCl or NaOH. Then react in a water bath at 90℃ for about 120min and cool to room temperature to obtain the modified PVA-6 membrane.

[0138] PVA-0, PVA-1, PVA-2, PVA-3, PVA-4, PVA-5, and PVA-6 membranes were placed in a vacuum drying oven for 30 minutes to degas. The membrane solution was then transferred to a petri dish and dried in an oven at 35°C for 5 hours. After cooling, the membranes were peeled off and equilibrated in a constant temperature and humidity chamber at 23°C for 12 hours to obtain hydrophobic modified polyvinyl alcohol antibacterial membranes. These membranes were then placed in sealed bags for subsequent performance testing.

[0139] Example 4: Structural Characterization of PVA-Modified Membrane

[0140] The structures of PVA-0, PVA-1, PVA-2, PVA-3, PVA-4, PVA-5, and PVA-6 membranes were determined and characterized.

[0141] I. Fourier Transmission Infrared Spectroscopy (FTIR) Test

[0142] The FTIR spectra of PVA-0, PVA-1, PVA-2, PVA-3, PVA-4, PVA-5, and PVA-6 films are as follows: Figure 7 As shown in the figure, the PVA film located at 3279 cm⁻¹... 1 The characteristic broad peak is related to the stretching vibration of OH, 2910 cm⁻¹ -1 The characteristic peak originates from the contractile vibration of -CH2. 1658 cm⁻¹ -1The absorption peak at this point is attributed to the stretching vibration of -COOR. PVA exhibits this absorption peak due to incomplete hydrolysis. With increasing glutaraldehyde and citric acid content, the absorption peak of -OH decreases; with increasing glycerol content, the absorption peak of -OH increases. Furthermore, PVA-6 has an absorption peak at 1658 cm⁻¹. -1 The absorption peak area of ​​the polyvinyl alcohol film increased, indicating that the polymer underwent esterification. Furthermore, PVA-4, PVA-5, and PVA-6 showed an increased absorption peak area at 1047 cm⁻¹. -1 A new characteristic peak appears at a certain point, which corresponds to the stretching vibration peak of COC, indicating the esterification and acetal reactions between PVA and PAA.

[0143] II. Thermogravimetric Analysis (TGA)

[0144] Test results are as follows Figure 8 As shown in Table 4, the thermal weight loss of PVA polyvinyl alcohol films can be divided into three stages: the first stage, due to the removal of bound water, is from 50 to 250°C, with a maximum loss rate at 210°C; the second stage is from 250 to 340°C, during which the film weight decreases rapidly, with a maximum loss rate at 285°C; and the third stage is above 340°C. The thermal weight loss behavior of polyvinyl alcohol films with different components is basically similar. However, compared with uncrosslinked films, the thermal decomposition temperature of crosslinked films increases by 20°C, and the thermal stability of polyvinyl alcohol films is significantly improved. After crosslinking, the maximum loss rate temperatures in the second and third stages shift significantly, indicating enhanced thermal stability and quantitatively confirming the positive impact on thermal stability.

[0145] Furthermore, the effects of PAA content on the thermal stability of the film were analyzed using the temperatures at which weight loss reached 10% (T10%), 50% (T50%), the temperature of the first decomposition (Tdec), and the residual amount (%) at 600℃. The T10% of pure PVA was 240.937℃. With the addition of PAA, CA, GA, GLY, and MgCl2, T10% increased to 267.885℃, an increase of approximately 30%. Correspondingly, the T50% of pure PVA was 301.937℃, and with the addition of PAA, T50% increased to 331.385℃, an increase of approximately 20℃. Simultaneously, the maximum weight loss rate of the film shifted towards higher temperatures with the addition of PAA, CA, GA, GLY, and MgCl2. The results show that the incorporation of PAA, CA, GA, GLY, and MgCl2 significantly enhanced the thermal stability of the film matrix while reducing the melting temperature, which is beneficial for the thermoplastic processing of the film.

[0146] Table 4. T values ​​for different membrane samples 10％ , T 50％ , T dec and the residual amount at 600℃

[0147]

[0148] III. X-ray Diffraction (XRD) Test

[0149] XRD patterns reflect the changes and transfer of crystal structure in the modified film, which helps in analyzing the compatibility between various matrices. Polyvinyl alcohol (PVA) is a semi-crystalline polymer, and its crystallization behavior is crucial to the performance of the modified film. To investigate the effect of polymer crosslinking on PVA crystallinity, the crystallization behavior of the modified film was characterized. The test results are as follows: Figure 9 As shown, the results indicate a strong diffraction absorption peak at 19.48° and a weaker diffraction absorption peak at 44.89°. After the addition of PAA, the position and intensity of the diffraction peak at 19.48° remained unchanged. With the addition of glutaraldehyde, the diffraction peak shifted from 19.48° to 19.68°. This characteristic peak can be observed in modified films with different components, indicating that chain entanglement and chemical cross-linking between polymer chains promote increased crystallinity.

[0150] Example 8: Performance Characterization of PVA-Modified Membranes

[0151] I. Determination of Tensile Strength and Elongation at Break (TS / EB) of Thin Films

[0152] Excellent mechanical properties ensure the film remains intact when subjected to external forces, making it an indispensable property of packaging materials. Mechanical property tests were conducted on different PVA-modified films, and the results are as follows: Figure 10 As shown, the results indicate that the elongation at break of the PVA-modified film is improved compared to the pure PVA film phase. Specifically, the tensile strength of PVA-6 decreased from 37.73 MPa to 12.99 MPa, while the tensile breaking rate increased from 50.35 MPa to 114.49 MPa.

[0153] II. Determination of Water Absorption and Solubility Properties of Thin Films

[0154] A key characteristic of food packaging films is their ability to prevent water transfer between the two sides of the film. Water permeability is primarily due to the hydrophilic groups providing binding sites for water molecules. The results of water absorption and solubility tests are as follows: Figure 11 As shown, the results indicate that as the PVA sample number increases, both the water absorption rate and solubility generally show a decreasing trend.

[0155] III. Oil Resistance

[0156] Oil resistance is an extremely important indicator in food preservation. The results of oil resistance testing are as follows: Figure 12As shown, the results indicate that the oil absorption rate (OAR value) from largest to smallest is PVA-0 > PVA-1 / PVA-2 > PVA-3 > PVA-4 > PVA-6, with the PVA-0 group having an OAR value of 69.75 ± 0.62%. Due to the dissolution of the PVA membrane, certain pores exist within the membrane, and there are pores on the surface, allowing oil to penetrate into the pores, thus increasing the OAR. However, with the addition of PAA, GA, and CA, whose main components are carboxyl and aldehyde groups, aldehyde condensation and esterification reactions occur with continuous addition, forming a dense structure, which leads to a decrease in OAR.

[0157] IV. Measurement of Water Vapor Transmission Rate (WVP) of Thin Films

[0158] Water vapor transmission rate measurement results are as follows Figure 13 As shown, the PVA-0 group had the highest water vapor transmission rate. After adding PAA, GA, and CA, the water vapor transmission rate was lower than that of the polyvinyl alcohol membrane. However, with the increase of glycerol, the hydroxyl groups increased, which increased the hydrophilicity of the membrane.

[0159] V. Contact Angle Test

[0160] The water contact angle (WCA) of the thin film was measured to characterize its surface wettability, which depends on the surface microstructure and chemical composition. The contact angle test results are as follows: Figure 14 As shown, the results indicate that PVA is a hydrophilic polymer. The contact angle of a pure PVA film is 57.78°. When PAA, GLY, and CA crosslinking polymers are added, the contact angle of the crosslinked films is larger than that of the pure PVA film, since the added materials are all typical hydrophilic materials. This is because the esterification and aldol condensation reactions reduce the number of hydroxyl groups.

[0161] VI. Gas Transmission Rate Analysis

[0162] Establishing a high-CO2, low-O2 gas environment in food packaging systems is beneficial for extending shelf life because CO2 and O2 molecules have similar diameters. The gas permeability measurement results are as follows: Figure 15 As shown, the results indicate that the O2 permeability of pure PVA membrane is significantly higher than that of other modified membranes. With the addition of PAA, CA, GA, MgCl2, and GLY, CO2 permeability initially decreases, then increases, and then decreases again. For PVA-6, this decrease is observed from 4.94 g / (m²·h) to 2.89 g / (m²·h). This demonstrates that the CO2 permeability of the PVA-6 modified membrane is significantly higher than its O2 permeability. Furthermore, PVA, CA, GA, MgCl2, and GLY are all hydrophilic materials, while water is a polar substance and CO2 is a polar gas, easily creating a "high CO2, low O2" environment, making it highly suitable for food packaging.

[0163] Example 9: Antibacterial properties of PVA-modified membrane

[0164] I. Antimicrobial kinetic test

[0165] To determine the bactericidal activity of polyvinyl alcohol (PVA) films against Staphylococcus aureus and Escherichia coli, a co-culture model was established in LB broth. The OD values ​​of the culture medium were measured. 600 The increase or decrease in bacterial count was assessed to determine the antibacterial effect of the polyvinyl alcohol film. Experimental results are as follows: Figure 16 As shown, the results indicate that the proliferation rates of *Escherichia coli* and *Staphylococcus aureus* were significantly inhibited after the addition of PBS compared to the control group. The PVA-6 membrane exhibited the best antibacterial activity against both *Staphylococcus aureus* and *Escherichia coli*.

[0166] II. Antibacterial susceptibility test

[0167] The plate counting method was used for the determination, and the results are as follows: Figure 17 As shown, the results indicate that the PVA-6 membrane has the best antibacterial effect, with an antibacterial effect of up to 99% against Escherichia coli and Staphylococcus aureus.

[0168] Example 10: Antioxidant properties of PVA-modified films

[0169] DPPH and ABTS free radical scavenging rates are important indicators for evaluating the antioxidant capacity of food preservation film materials. The antioxidant performance test results of PVA-modified films are as follows: Figure 18 As shown, compared with PVA-0 membrane, PVA-6 showed an increase of approximately 10% in DPPH radical scavenging and approximately 5% in ABTS radical scavenging.

[0170] Example 11: Preservation effect of PVA modified film

[0171] Different performance data of PVA modified films are presented as indicators in a radar chart, as shown in the radar chart below. Figure 19 As shown in the results, among all the films tested, the PVA-6 film outperforms other modified films in various properties, indicating that the film has excellent overall performance.

[0172] Under aseptic conditions, pork was skinned and defatted, then cut into rectangles to obtain experimental meat samples of equal weight. Three treatment groups were set up: the control group (CK) had its meat samples unpackaged; the PE group had its meat samples packaged with PE film; and the PVA-6 group had its meat samples packaged with PVA-6 film. The PE and PVA-6 groups were sealed with sealant and then stored at 4°C. The preservation index of the meat samples was measured at 0, 3, 6, 9, 12, and 15 days.

[0173] (1) Sensory evaluation of chilled pork

[0174] The effects of different treatments (CK, PE, PVA-6) on the color, odor, elasticity, and viscosity of meat samples at 0, 3, 6, 9, 12, and 15 days were demonstrated. Sensory evaluation results are as follows: Figure 20 As shown in the figure, the scores for color, odor, elasticity, and viscosity of the meat samples in the CK group gradually decreased over time, reaching their lowest point at 15 days. The score decrease in the PE group was smaller, but still lower than that of the PVA-6 group. The PVA-6 group maintained higher scores at all time points, demonstrating better preservation. This indicates that the PVA-6 treatment is superior to the CK and PE treatments in maintaining color, odor, elasticity, and viscosity.

[0175] (2) The influence of meat color on chilled pork

[0176] The color change of pork is mainly due to microbial spoilage and lipid oxidation. The color of pork is essentially determined by myoglobin (Mb) and hemoglobin (Hb). Myoglobin (Mb) itself is purplish-red; when Mb combines with oxygen, it forms oxymyoglobin (MbO2), which is bright red; when left for too long or under low O2 partial pressure, Mb and MbO2 are oxidized to methemoglobin (MIMb), which appears brown. The results of meat color determination for meat samples from different treatment groups are as follows: Figure 21 As shown, the results indicate that:

[0177] Compared to the CK and PE treatments, the L* value of the PVA-6 treatment remained at a higher level during storage, indicating that PVA-6 treatment effectively maintains the brightness of the pork and slows down the darkening process. The a* value rose rapidly in the early stages of storage (0-3 days) and then gradually decreased. The a* value of the CK treatment fluctuated more significantly, while the a* value of the PVA-6 treatment changed more gradually. This indicates that PVA-6 treatment better maintains the red and green hues of the product and reduces color fluctuations. The b* value gradually increased during storage, but the increase was smaller in the PVA-6 treatment, especially compared to the CK and PE treatments. This indicates that PVA-6 treatment effectively inhibits the increase of yellowness and maintains the product's color.

[0178] (3) Juice loss rate

[0179] The spoilage of chilled meat is mainly due to the proliferation of microorganisms, and the moisture content of chilled meat plays a significant role in the reproduction of these microorganisms. The juice loss rate of meat samples from different treatment groups was measured, and the results are as follows: Figure 22 As shown, the results indicate that the juice loss rate in the CK group was low in the early stages of storage (0-2 days), but increased rapidly from day 4. The juice loss rate in the PVA-6 group increased the slowest throughout the storage period, reaching approximately 10% by day 16. This suggests that the PVA-6 treatment was the most effective in reducing juice loss, followed by the PE treatment, with the CK group experiencing the fastest juice loss.

[0180] (4) Determination of volatile basic nitrogen

[0181] During storage, the presence of enzymes and bacteria causes the proteins in meat to decompose, producing volatile nitrogenous substances such as ammonia and amines. Therefore, volatile basic nitrogen (TVB-N) is also an important indicator for assessing the freshness of chilled meat. According to national standards, Grade 1 freshness is ≤15mg / 100g, Grade 2 freshness is ≤25mg / 100g, and spoiled meat is >25mg / 100g. The TVB-N of meat samples from different treatment groups was measured, and the results are as follows: Figure 23 As shown, the black dashed line represents the critical point of Grade 1 freshness, 15 mg / 100g. The results show that the CK group and the PE group reached the critical value of Grade 1 freshness on the 3rd and 6th days, respectively, while the PVA-6 group exceeded the national standard for Grade 1 freshness around the 9th day, indicating that the PVA-6 film has better preservation performance.

[0182] (5) Thiobarbituric acid determination

[0183] The TBARS value is used to represent the degree of lipid oxidation. Lipid oxidation in pork is a significant cause of meat spoilage, and 0.5 mg / kg is generally considered the critical TBARS value. The dashed line in the figure represents the TBARS threshold (0.5 mg / kg). When the TBARS value exceeds this threshold, the degree of oxidation in the food is generally considered high. Thiobarbituric acid was determined in meat samples from different treatment groups, and the results are shown below. Figure 24 As shown, the results indicate that the CK group exceeded the TBARS value on day 3, the PE group exceeded the threshold on day 6, and the PVA-6 group exceeded the threshold on day 9. This demonstrates that PVA-6 treatment has significant advantages in food preservation.

[0184] (6) pH measurement

[0185] Over time, the acids produced by proteins are broken down into amino acids by bacteria, leading to an increase in the pH value within the muscle tissue. When the pH value rises to a certain level, it affects the quality and texture of pork, causing it to become dry, hard, or even rotten. Generally, when pH 5.7 < pH < 6.2, it is considered fresh meat; when pH 6.3 < pH < 6.6, it is considered slightly undercooked meat; and when pH > 6.7, it is considered spoiled meat. The initial pH value of the fresh pork used in this experiment was 5.82, which is considered acceptable for fresh meat.

[0186] pH values ​​were measured in meat samples from different treatment groups, and the results are as follows: Figure 25As shown, the results indicate that the pH value of the PVA-6 group increased the slowest compared to the CK and PE groups, reaching approximately 7.5 by day 15, and remained lower than the other two groups throughout the storage period. This demonstrates that the PVA-6 treatment is highly effective in maintaining pH stability.

[0187] (7) Methemoglobin assay

[0188] As storage time increases, myoglobin is gradually oxidized to metmyoglobin (MetMb). MetMb is brown in color, causing the meat to darken. Metmyoglobin levels were measured in meat samples from different treatment groups, and the results are as follows: Figure 26 As shown, the results indicate that the percentage increase of MetMb in the PVA-6 group was the slowest compared to the CK and PE groups, reaching approximately 20% by day 15. The PVA-6 treatment demonstrated the best performance in inhibiting MetMb formation and delaying food oxidation.

[0189] (8) Total bacterial count determination

[0190] According to the national standard GB / T 9959.2-2008 "Separated Fresh and Frozen Lean Pork", the total bacterial count of separated fresh and frozen lean pork should be less than or equal to 1×10⁻⁶. 6 CFU / g is equivalent to 6.0 l g CFU / g. The total bacterial count was determined in meat samples from different treatment groups, and the results are as follows: Figure 27 As shown, the results indicate that the total bacterial count in the PVA-6 group increased the slowest throughout the storage period, reaching approximately 10 on day 16. 5 The CFU / g concentration was measured, and the data for the PVA-6 group showed relatively small fluctuations, indicating a stable antibacterial effect.

[0191] (9) Texture analysis

[0192] Texture is an important quality characteristic of meat, influenced by various factors such as meat type and size, fat and protein content, the effects of different microorganisms, and storage temperature and time. Relevant texture parameters include: adhesiveness, chewiness, cohesiveness, francurability, gumminess, hardness, resilience, and springiness. Hardness describes the force required for an object to deform; elasticity indicates the object's ability to return to its original shape after an external force is applied and removed; cohesiveness is the amount of binding force required to maintain the integrity of food; and chewiness is the energy required to chew solid food for swallowing. The relationship between these four parameters is: Chewiness = Hardness × Elasticity × Cohesiveness. Hardness, the maximum force exerted by the probe during the first press, reflects the chewiness of the meat sample to a certain extent; higher hardness indicates greater difficulty in chewing. Elasticity is an important parameter for evaluating the tissue structure of chilled meat. Meat samples with better elasticity have a more stable tissue structure and a better taste when eaten. Chewability is the result of the combined effect of hardness and elasticity.

[0193] Texture analysis was performed on meat samples from different treatment groups, and the results are as follows: Figure 28 As shown, the results indicate that the firmness of the meat in all three treatment groups changed with increasing storage days. The firmness of the pork in the CK and PE groups increased rapidly in the initial stage, peaking around day 6, and then began to decline. The firmness of PVA-6 changed relatively slowly; although it also showed an upward trend, there was no obvious peak. Furthermore, compared to the CK and PE groups, the cohesiveness of PVA-6 was relatively stable, with little change, generally remaining between 0.5% and 0.7%. The elasticity of the CK group increased rapidly in the initial stage, peaking around day 4, and then gradually declined. In terms of elasticity, the change in elasticity of PVA-6 was relatively slow, with smaller fluctuations. In terms of chewiness, compared to the CK and PE groups, the chewiness of PVA-6 changed slowly, without any obvious peak.

[0194] Overall, the pork treated in the CK and PE groups showed significant fluctuations in meat quality during storage, especially in terms of firmness and chewiness, while the pork treated in the PVA-6 group exhibited very stable meat quality.

[0195] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A composition, characterized in that, By weight, it includes the following components: 3-7 parts polyvinyl alcohol, 0.1-0.3 parts polyacrylic acid, 1.25-2.5 parts glutaraldehyde, 0.5-1.5 parts citric acid, 4-10 parts glycerol, and 2-4 parts magnesium chloride.

2. The composition according to claim 1, characterized in that, By weight, it includes the following components: 3-7 parts polyvinyl alcohol, 0.2-0.3 parts polyacrylic acid, 1.25-2.5 parts glutaraldehyde, 0.5-1.5 parts citric acid, 4-8 parts glycerol, and 3-4 parts magnesium chloride.

3. The composition according to claim 1 or 2, characterized in that, By weight, it includes the following components: 5 parts polyvinyl alcohol, 0.2 parts polyacrylic acid, 1.25 parts glutaraldehyde, 1 part citric acid, 5 parts glycerol, and 4 parts magnesium chloride.

4. Use of the composition according to any one of claims 1-3 in the preparation of thin films.

5. The use of the composition according to any one of claims 1-3 in the preparation of food packaging films.

6. A method for preparing a packaging film, characterized in that, A packaging film is prepared using the composition according to any one of claims 1-3.

7. The preparation method according to claim 6, characterized in that, Add the composition of any one of claims 1-3 to water to obtain a mixture, react the mixture at 80-100°C for 90-150 min, and then dry to obtain a packaging film.

8. The preparation method according to claim 7, characterized in that, The pH value of the mixture is 2-4.

9. A packaging film, characterized in that, It is prepared by any one of the preparation methods described in claims 6-8.

10. The application of the packaging film of claim 9 in food preservation, or in packaged food.

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