Preparation and application of hydrophobic modified polyvinyl alcohol antibacterial packaging film

Abstract

The invention belongs to the technical field of packaging materials. More specifically, the invention provides a composition which is prepared from the following components in parts by weight: 3 to 7 parts of polyvinyl alcohol, 0.1 to 0.3 part of polyacrylic acid, 1.25 to 2.5 parts of glutaraldehyde, 0.5 to 1.5 parts of citric acid, 4 to 10 parts of glycerol and 2 to 4 parts of magnesium chloride. The packaging film prepared from the composition has excellent thermal stability and low water vapor transmission rate, can avoid moisture loss of meat products, and is more beneficial to maintaining the taste and flavor of meat. In addition, the CO2 transmittance of the packaging film is obviously higher than the O2 transmittance, aerobic microorganisms can be inhibited, and fat oxidation is reduced. The packaging film disclosed by the invention has excellent antibacterial and antioxidant properties, has an excellent effect in meat preservation, can maintain the color and luster of meat and maintain the elasticity and chewiness of the meat, and has a good application prospect and value in the fields of meat product packaging and preservation.

Description

Technical Field

[0001] The present invention belongs to the technical field of packaging materials, and more specifically, relates to the preparation and application of a hydrophobically modified polyvinyl alcohol antibacterial packaging film. Background Art

[0002] In the food industry, packaging film, as an important food contact material, plays a key 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, resulting in the continuous accumulation of "white pollution". Studies have shown that it takes more than 200 years for a single-layer PE film to completely degrade in the soil, which has put tremendous pressure on the ecological environment. In addition, plastics split to form microplastic particles, which can enter the human blood circulation through the food chain, induce inflammatory reactions and cytotoxicity, and threaten human health. This has prompted the industry to seek environmentally friendly and sustainable packaging solutions.

[0003] At present, research is developing new bio-based degradable materials, such as polyvinyl alcohol (PVA), polylactic acid (PLA), chitosan, etc., and using degradable materials to prepare packaging films. Among them, PVA has attracted much attention due to its good biocompatibility and degradability. PVA can be completely decomposed into carbon dioxide and water by microorganisms in the natural environment, avoiding threats to ecology and health. However, the existing PVA packaging film has 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 field of food packaging. How to improve the performance of PVA film to make it suitable for application in the field of food packaging has become a hot topic of current research. Summary of the invention

[0004] The present invention aims to overcome the defects and shortcomings of the above-mentioned existing PVA films and provide a modified PVA film, which has strong oil resistance, low water vapor permeability, low O2 permeability, excellent antibacterial and antioxidant properties, excellent effect in meat preservation, can maintain the color of meat, maintain the elasticity and chewiness of meat, and is particularly 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] The second object of the present invention is to provide a packaging film and a method for preparing the same.

[0007] The third object of the present invention is to provide application of the above packaging film.

[0008] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

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

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

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

[0012] The packaging film prepared by using the composition of the present invention has excellent thermal stability, low water vapor permeability, and CO2 permeability is significantly higher than O2 permeability, which can inhibit aerobic microorganisms and reduce fat oxidation. In addition, the packaging film of the present invention has excellent antibacterial and antioxidant properties and has excellent food preservation effects, so the following technical solutions are also required to be protected:

[0013] The present invention provides the use of the above composition in preparing a film

[0014] The invention provides application of the composition in preparing food packaging film.

[0015] The invention also provides a method for preparing a packaging film, and the packaging film is prepared by adopting the composition.

[0016] Preferably, the preparation method is: adding the above composition into water to obtain a mixed solution, reacting the mixed solution at 80-100° C. for 90-150 min, and obtaining a packaging film after drying.

[0017] As an optional embodiment, in the preparation method, the mixed solution is reacted at 90° C. for 120 min.

[0018] Preferably, in the mixed solution, 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 mixed solution, 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 mixed solution is 2-4.

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

[0022] As an optional implementation scheme, the preparation method of the packaging film is: take 5g of polyvinyl alcohol and dissolve it in 100mL of distilled water at 90°C to obtain a film liquid, add 0.2g of polyacrylic acid, 1.25mL of glutaraldehyde, 1g of citric acid, 4mL of propylene glycol, and 4g of magnesium chloride to the film liquid respectively, stir it thoroughly, adjust the pH value of the film liquid to 2, and then react at 90°C for 120min. The reacted film liquid is dried to obtain a packaging film.

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

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

[0025] As an optional embodiment, the packaging film obtained after drying is equilibrated at 20-25° C. and 40-60% relative humidity for 8-16 hours.

[0026] As an alternative embodiment, the packaging film obtained after drying is equilibrated at 23° C. and 53% relative humidity for 12 h.

[0027] As an optional embodiment, the mixed liquid is degassed before the drying process.

[0028] As an optional embodiment, the degassing treatment time is 20-40 minutes.

[0029] As an optional embodiment, the degassing treatment can be performed in a vacuum drying oven.

[0030] The invention provides a packaging film, which is prepared by the above preparation method.

[0031] The application of the above packaging film in food preservation or in packaging food should also be within the protection scope of the present 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, which can prevent additives (such as plasticizers) in the packaging from dissolving into oils and fats, thereby reducing food safety risks.

[0035] (3) The packaging film of the present invention has a low water vapor permeability, which can reduce the moisture exchange inside and outside the package, avoid moisture loss of meat products, and is more conducive to maintaining 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, and it is easy to form a "high CO2, low O2" environment, which can inhibit aerobic microorganisms, reduce fat oxidation, and 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, has excellent preservation effect on meat, can maintain the color of meat, reduce the juice loss rate, and maintain the elasticity and chewiness of meat. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

[0043] Figure 6The results of the effect of pH change 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).

[0044] Figure 7 The infrared spectra of different PVA modified films are shown in Figure 2.

[0045] Figure 8 Thermogravimetric test results of different PVA modified films (Figure A is the thermogravimetric analysis diagram of PVA 0-6 film;

[0046] Figure B is the thermogravimetric analysis of the PVA 0-6 film; Figure C is the thermogravimetric analysis of the PVA 0-3 film; Figure D is

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

[0048] Fig. 9 X-ray diffraction test results of different PVA modified films.

[0049] Fig.10 The tensile strength and elongation at break of different PVA modified films are measured.

[0050] Fig.11 The water absorption and solubility test results of different PVA modified films (Figure A shows the water absorption test results; Figure B shows the solubility test results).

[0051] Fig.12 The oil resistance test results of different PVA modified films are shown in Figure 2.

[0052] Fig.13 The water vapor transmission rate of different PVA modified films is measured.

[0053] Fig.14 Contact angle test results of different PVA modified films.

[0054] Fig.15 The gas permeability test results of different PVA modified films (Figure A is the oxygen permeability test result; Figure B is the carbon dioxide permeability test result).

[0055] Fig.16 The antibacterial kinetic test results of different PVA modified films.

[0056] Fig.17 The antibacterial plate test results of different PVA modified films.

[0057] Fig.18 The results of antioxidant performance test of different PVA modified membranes (Figure A is DPPH free radical scavenging rate; Figure B is ABTS free radical scavenging rate).

[0058] Fig.19 This is a radar chart of the comprehensive performance of different PVA modified films.

[0059] Fig. 20 These are the sensory evaluation results of meat samples with different treatments.

[0060] Fig.21 The meat color measurement results of meat samples with different treatments (Figure A is the measurement result of brightness L*; Figure B is the measurement result of redness and greenness a*; Figure C is the measurement result of yellowness and blueness b*).

[0061] Fig. 22 The results of juice loss rate determination of meat samples with different treatments.

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

[0063] Fig.24 Results of thiobarbituric acid assay in different processed meat samples.

[0064] Fig.25 The pH values ​​of meat samples treated with different methods were measured.

[0065] Fig.26 These are the results of metmyoglobin determination in meat samples with different treatments.

[0066] Fig. 27 The results of total colony count of meat samples treated differently.

[0067] Fig.28 The texture analysis results of meat samples with different processing (Figure A is the hardness measurement result; Figure B is the cohesion measurement result; Figure C is the elasticity measurement result; Figure D is the chewiness measurement result). DETAILED DESCRIPTION

[0068] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. 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 are commercially available.

[0070] Polyvinyl alcohol, polyacrylic acid, and propylene glycol were purchased from Shanghai MacLean Biochemical Technology Co., Ltd. with catalog numbers P875275, P815683, and G810575.

[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, with reference to the formula: solid content (%) = (mass of solid component and / or total mass of the mixture) × 100, or (volume of solid component and / or total volume of the mixture) × 100.

[0073] The tensile strength and elongation at break were determined according to ISO 1924-2.

[0074] The determination methods of water absorption, solubility and water vapor permeability refer to the methods in the literature "Yang Yujing. Preparation of eugenol-carboxymethyl chitosan / pululan composite film and its application in preservation of fresh pork [D]. Sichuan Agricultural University, 2023."

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

[0076] The gas permeability measurement method refers to the method in the literature "Han Xiao. Research on the preservation of fresh pork with antibacterial polyvinyl alcohol film [D]. Guangxi University, 2021."

[0077] The determination methods of antibacterial properties and antioxidant capacity refer to the methods 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 colony count determination method, and texture analysis method refer to "Zhong Yang. Preparation of sugarcane bagasse extract combined with starch-based antioxidant cling film and study on its preservation effect on beef [D]. Chengdu University, 2024.".

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

[0080] 1. Preparation method of modified PVA film

[0081] Take 5g of polyvinyl alcohol and place it in a 500mL beaker. After adding 100mL of distilled water to dissolve, add polyacrylic acid, glutaraldehyde, citric acid, glycerol and magnesium chloride in turn, stir to dissolve, and then adjust the membrane liquid environment with 0.01mol / L HCl or NaOH. Stir and dissolve the membrane liquid at 90℃ for 120min to completely homogenize, and then place it in a vacuum drying oven for 30min to degas. After that, transfer the membrane liquid to a culture dish, and then place it in a 35℃ oven to dry for 5h, finally cool and remove the film, and place it in a 23℃ constant temperature and humidity chamber for 12h to balance, you can get a modified PVA film, and then place the film in a sealed bag for subsequent performance measurements.

[0082] The modified PVA film was prepared according to the above method by selecting 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%, pH = 4 as the central experimental point. The tensile strength (TS), elongation at break (EB), water absorption and solubility of the film were used as single factor test indicators.

[0083] 2. Effect of polyacrylic acid solid content on membrane performance

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

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

[0086] 2. Test index measurement results

[0087] The results of the test are as follows Figure 1 As shown in the figure, the results show that when the polyacrylic acid content is 0-0.2%, the tensile strength of the film gradually increases; after exceeding 0.2%, the tensile strength gradually decreases. In addition, with the increase of the polyacrylic acid solid content, the water absorption and solubility of the film gradually decrease.

[0088] 3. Effect of glutaraldehyde solid content on membrane performance

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

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

[0091] 2. Test index measurement results

[0092] The results of the test are as follows Figure 2 As shown, the results show that when the amount of glutaraldehyde is 0-1.25%, the tensile strength of the film gradually increases; as the amount of glutaraldehyde continues to increase, the tensile strength of the film gradually decreases. The elongation at break of the film increases rapidly with the increase of glutaraldehyde, and then decreases rapidly. The water absorption and solubility are high at 0%, and both gradually decrease as the glutaraldehyde content increases. This shows that the cross-linking effect of glutaraldehyde limits the penetration of water molecules and the dissolution of the material, thereby reducing the water absorption and solubility. Therefore, the amount of glutaraldehyde should be 0-1.25%.

[0093] 4. 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 put it in a 500mL beaker, add 100mL of distilled water to dissolve it at 90℃ to prepare a PVA solution with a mass fraction of 5%, fix other variables (polyacrylic acid solid content 0.3%, glutaraldehyde solid content 2.5%, glycerol solid content 6%, magnesium chloride solid content 3%, pH = 4), and add 0.5%, 1%, 1.5%, 2%, and 2.5% of citric acid to the PVA solution in a 90℃ water bath, respectively. After fully stirring, react at a constant temperature for about 120min, and cool to room temperature to obtain a citric acid-modified PVA film.

[0096] 2. Test index measurement results

[0097] The results of the test are as follows Figure 3 As shown, the results show that after adding citric acid, the elongation at break and tensile strength are low at 0%, and both gradually increase with the increase of citric acid content, reaching a peak at 1.0%, and then decrease. This shows that the ductility and strength of the material are optimal at a citric acid content of 1.0%. Water absorption and solubility are high at 0%, and both gradually decrease with the increase of citric acid content. This shows that the addition of citric acid limits the penetration of water molecules and the dissolution of the material.

[0098] 5. Effect of glycerol solid content on membrane performance

[0099] Take 5g of polyvinyl alcohol and put it in a 500mL beaker, add 100mL of distilled water to dissolve it at 90℃ to prepare a PVA solution with a mass fraction of 5%, fix other variables (polyacrylic acid solid content 0.3%, glutaraldehyde solid content 2.5%, citric acid solid content 1.5%, magnesium chloride solid content 3%, pH = 4), and add 2%, 4%, 6%, 8%, and 10% of propylene glycol to the PVA solution in a 90℃ water bath, respectively. After fully stirring, react at a constant temperature for about 30min, and cool to room temperature to obtain a modified PVA film.

[0100] 2. Test index measurement results

[0101] The results of the test are as follows Figure 4 As shown, the results show that with the increase of glycerol solid content, the elongation at break of the material first increases and then decreases, reaching the maximum value at 6%, indicating that the ductility of the material is the best at this time. The tensile strength reaches a peak at 8%, indicating that the strength of the material is the highest at this time. The water absorption and solubility of the material first decrease and then increase, reaching the lowest value at 6%. Therefore, it can be seen that the dosage is more appropriate at 4%-8%.

[0102] 6. Effect of magnesium chloride solid content on membrane performance

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

[0104] 2. Test index measurement results

[0105] The results of the test are as follows Figure 5 As shown in the figure, the elongation at break and tensile strength are low at 0% MgCl2. As the MgCl2 content increases, both gradually increase, reach a peak at 3%, and then decrease. This shows that the ductility and strength of the material are optimal at 3% MgCl2. Water absorption and solubility are high at 0% MgCl2, and gradually decrease with the increase of MgCl2 content, reaching the lowest value at 3%.

[0106] 7. Effect of pH Change on Membrane Performance

[0107] Take 5g of polyvinyl alcohol and put it in a 500mL beaker, add 100mL of distilled water to dissolve it at 90℃ to prepare a PVA solution with a mass fraction of 5%, fix other variables (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%), add HCl or NaOH to the PVA solution in a 90℃ water bath, adjust the pH of the membrane liquid to 2, 3, 4, 5, and 6, respectively, stir well, react at a constant temperature for 120min, and cool to room temperature to obtain a modified PVA film.

[0108] 2. Test index measurement results

[0109] The results of the test are as follows Figure 6 As shown, the results show that at a pH value of 3, the elongation at break and tensile strength reach peak values, and the ductility and strength of the material are optimal. Water absorption and solubility are lowest at a pH value of 3 and gradually increase with increasing pH. Changes in pH value can affect the structure and properties of the material.

[0110] Example 2

[0111] 1. Calculation method for comprehensive scoring of various indicators of polyvinyl alcohol film

[0112] TS, EB, water absorption and solubility are used as evaluation indicators, and the comprehensive scoring method is used to score the membrane performance. The comprehensive scoring method is to weight or score each indicator according to its importance, and convert multiple indicators into a single comprehensive indicator. Specific method: First, the indicator weights of membrane performance are calculated through principal component analysis; then, the membership calculation formula is used to calculate the membership of the indicator; finally, the comprehensive score of the membrane is calculated.

[0113] 2. Orthogonal test

[0114] Six factors and three levels of orthogonal test were selected according to the single factor experiment. The orthogonal test factor levels are shown in Table 1, which are respectively the solid content of polyacrylic acid (factor A) 0.1%, 0.2%, 0.3%, the solid content of glutaraldehyde (factor B) 0.625%, 1.25%, 1.875%, the solid content of citric acid (factor C) 0.5%, 1%, 1.5%, the solid content of glycerol (factor D) 4%, 6%, 8%, the solid content of MgCl2 (factor E) 2%, 3%, 4%, and pH (factor F) was adjusted to 2, 3, 4. According to the content of each component in the orthogonal test table of Table 2, PVA modified membranes of test numbers 1-18 were prepared.

[0115] Table 1 Orthogonal test factor levels

[0116]

[0117] Table 2 Orthogonal experiment table

[0118]

[0119]

[0120] 3. Comprehensive evaluation of membrane performance

[0121] Taking the mechanical properties and barrier properties of polyvinyl alcohol film as the analysis objects, 12 groups of single-factor test data were randomly selected for principal component analysis, and the eigenvalues ​​and contribution rates of the relevant components were analyzed. The results show that the first component takes the mechanical properties and barrier properties of polyvinyl alcohol film as the analysis objects, the eigenvalues ​​of the first principal component and the second principal component are both greater than 1, the variance contribution rates are 57.065% and 27.481% respectively, and the cumulative variance contribution rate of the two is 84.546%. Since the cumulative variance contribution rate of the first principal component and the second principal component exceeds 80%, it basically covers most of the information in the sample and can be used to replace the original TS, EB, water absorption and solubility of polyvinyl alcohol film.

[0122] (1) Comprehensive evaluation of membrane performance

[0123] According to the results of principal component analysis, normalized calculation was performed, and the weights of the four indicators of TS, EB, water absorption and solubility of the polyvinyl alcohol film were 0.25, 0.24, 0.24 and 0.27 respectively. Therefore, the mathematical model of the comprehensive score of the polyvinyl alcohol modified film is: Y = 0.25P1 + 0.24P2 + 0.24P3 + 0.27P4.

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

[0125] The results of the orthogonal test are shown in Table 3. It can be seen from the range R that the order of the factors affecting the polyvinyl alcohol film is E>B>D>A>C>F, that is, magnesium chloride>glutaraldehyde>glycerol>polyacrylic acid>citric acid>pH. By comparing the K values, the best combination is determined, that is, 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 value 2. The PVA modified film prepared by the dosage ratio of the best combination was tested, and the actual average comprehensive score of the PVA modified film with the best combination was measured to be 99.330%.

[0126] Table 3 Orthogonal test results

[0127]

[0128]

[0129] Example 3 Preparation of PVA modified membrane

[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) 5 g of polyvinyl alcohol was placed in a 500 mL beaker, 100 mL of distilled water was added and dissolved at 90° C. to prepare a 5% by mass PVA solution, which was then cooled to room temperature to obtain a modified PVA-0 film.

[0132] (2) 5 g of polyvinyl alcohol was placed in a 500 mL beaker, and 100 mL of distilled water was added to dissolve at 90°C to prepare a 5% PVA solution for later use. Polyacrylic acid (PAA) was added to the membrane solution with a solid content ratio of 0.2% (V / V0), stirred thoroughly, reacted in a water bath at 90°C for about 120 min, and cooled to room temperature to obtain a 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 standby 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 well, react in a water bath at 90℃ for about 120min, and cool to room temperature to obtain a 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 standby 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 well, react in a water bath at 90℃ for about 120min, and cool to room temperature to obtain a 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 standby 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 well, react in a water bath at 90℃ for about 120min, and cool to room temperature to obtain a 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 standby 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 well, react in a water bath at 90℃ for about 120min, and cool to room temperature to obtain a 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 it at 90℃ to prepare a 5% PVA solution for standby 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 well, and then adjust the pH value 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 a modified PVA-6 membrane.

[0138] PVA-0 film, PVA-1 film, PVA-2 film, PVA-3 film, PVA-4 film, PVA-5 film, and PVA-6 film were placed in a vacuum drying oven for 30 minutes for degassing. Then the film solution was transferred to a culture dish, and then placed in a 35°C oven for drying for 5 hours, and finally cooled and the film was removed, and placed in a 23°C constant temperature and humidity chamber for 12 hours to obtain a hydrophobically modified polyvinyl alcohol antibacterial film, and then the film was placed in a sealed bag for subsequent performance determination.

[0139] Example 4 Structural Characterization of PVA Modified Film

[0140] The structural characterization of PVA-0 film, PVA-1 film, PVA-2 film, PVA-3 film, PVA-4 film, PVA-5 film and PVA-6 film was determined.

[0141] 1. Infrared spectroscopy (FTIR) test

[0142] FTIR spectra of PVA-0 film, PVA-1 film, PVA-2 film, PVA-3 film, PVA-4 film, PVA-5 film and PVA-6 film are as follows Figure 7 As shown in the figure, it can be seen that the PVA film is located at 3279cm- 1 The characteristic broad peak at 2910 cm-1 is related to the stretching vibration of OH. -1 The characteristic peak comes from the contraction vibration of -CH2. 1658cm -1The absorption peak at 1658cm belongs to the stretching vibration of -COOR. PVA has an absorption peak here due to incomplete hydrolysis. With the increase of glutaraldehyde and citric acid, the absorption peak of -OH decreases. With the increase of glycerol, the absorption peak of -OH increases. And PVA-6 has an absorption peak at 1658cm -1 The absorption peak area of ​​the polyvinyl alcohol film at 1047 cm-1 increased, indicating that the polymer had undergone esterification reaction. -1 A new characteristic peak appears at the α-aminobutyric acid ester, which corresponds to the stretching vibration peak of COC, indicating the esterification reaction and acetalization reaction between PVA and PAA.

[0143] 2. Thermogravimetric (TGA) test

[0144] Test results such as Figure 8 As shown in Table 4, the thermal weight loss of PVA polyvinyl alcohol film can be divided into three stages: the first stage is 50-250℃ due to the departure of bound water, and the maximum loss rate is at 210℃; the second stage is 250-340℃, in which the weight of the film decreases rapidly, and the maximum loss rate is at 285℃; the third stage is above 340℃. The thermal weight loss behaviors of polyvinyl alcohol films of different components are basically similar, but compared with the film without chemical crosslinking, the thermal decomposition temperature of the film after crosslinking is increased by 20℃, and the thermal stability of the polyvinyl alcohol film is significantly improved. After crosslinking, the maximum loss rate temperature in the second and third stages is highly shifted, indicating that the thermal stability is enhanced, and the positive effect on thermal stability is also quantitatively confirmed.

[0145] In addition, the effect of PAA content on the thermal stability of the film was analyzed by the 10% weight loss temperature (T10%), 50% weight loss temperature (T50%), the first decomposition temperature (Tdec) and the residual amount (%) at 600℃. The T10% of pure PVA is 240.937℃. After adding PAA, CA, GA, GLY and MgCl2, T10% rises to 267.885, an increase of about 30%. Correspondingly, the T50% of pure PVA is 301.937℃. After adding PAA, T50% rises to 331.385℃, an increase of about 20℃. At the same time, the maximum weight loss rate of the film also moves to the high temperature area with the addition of PAA, CA, GA, GLY and MgCl2. The results show that the mixing of PAA, CA, GA, GLY and MgCl2 greatly enhances the thermal stability of the film matrix and reduces the melting temperature, which is beneficial to the thermoplastic processing of the film.

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

[0147]

[0148] 3. X-ray diffraction (XRD) test

[0149] The XRD spectrum reflects the changes and transfer of the crystal structure in the modified film, which helps to analyze the compatibility between various matrices. Polyvinyl alcohol is a semi-crystalline polymer, and its crystallization behavior is crucial to the performance of the modified film. In order to study the effect of polymer cross-linking on the crystallinity of PVA, the crystallization behavior of the modified film was characterized. The test results are as follows Fig. 9 As shown in the figure, the results show that there is a relatively strong diffraction absorption peak at 19.48° and a relatively weak diffraction absorption peak at 44.89°. After adding PAA, the position of the diffraction peak at 19.48° did not change, and the intensity of the diffraction peak did not change. With the addition of glutaraldehyde, the diffraction peak moved from 19.48° to 19.68°, and this characteristic peak can be observed in modified films of different components, indicating that the chain entanglement and chemical cross-linking between polymer chains promote the improvement of crystallinity.

[0150] Example 8 Performance Characterization of PVA Modified Film

[0151] 1. Determination of tensile strength and elongation at break (TS / EB) of films

[0152] Excellent mechanical properties can ensure that the film remains intact when subjected to external forces, which is one of the indispensable properties of packaging materials. The mechanical properties of different PVA modified films were tested, and the test results are as follows: Fig.10 As shown, the results show that compared with the pure PVA film phase, the elongation at break of the PVA modified film is improved, among which the tensile strength of PVA-6 is reduced from 37.73 to 12.99MPA, and the tensile break rate is increased from 50.35 to 114.49.

[0153] 2. Determination of water absorption and solubility of films

[0154] An important property of food packaging film is to prevent water transfer on both sides of the film. Water permeability is mainly due to the hydrophilic groups providing binding sites for water molecules. The results of water absorption and solubility test are as follows: Fig.11 As shown, the results indicate that as the PVA sample number increases, both the water absorption and solubility generally show a downward trend.

[0155] 3. Oil resistance

[0156] Oil resistance is an extremely important indicator in food preservation. The results of oil resistance test are as follows: Fig.12As shown in the figure, the results show that the oil absorption rate (OAR value) is PVA-0>PVA-1 / PVA-2>PVA-3>PVA-4>PVA-6 from large to small, and the PVA-0 group is 69.75±0.62%. Due to the dissolution of the PVA membrane, there are certain pores in the membrane and pores on the surface. Oil can penetrate into the pores and increase OAR. However, with the addition of PAA, GA, and CA, whose main components are carboxyl and aldehyde groups, condensation and esterification reactions occur with their continuous increase to form a dense structure, which leads to a decrease in OAR.

[0157] 4. Determination of water vapor transmission rate (WVP) of films

[0158] The water vapor transmission rate test results are as follows Fig.13 As shown, the water vapor permeability of the PVA-0 group is the highest. After adding PAA, GA, and CA, the water vapor permeability is lower than that of the polyvinyl alcohol film. However, with the increase of glycerol, the hydroxyl group increases, which increases the hydrophilicity of the membrane.

[0159] 5. Contact angle test

[0160] The water contact angle (WCA) of the film was tested to describe the surface wettability, which depends on the surface microstructure and its chemical composition. The contact angle test results are shown in Fig.14 As shown, the results show that PVA is a hydrophilic polymer. The contact angle of the pure PVA film is 57.78°. When PAA, GLY, and CA cross-linked polymers are added, the contact angle of the cross-linked film is greater than that of the pure PVA film because the added materials are typical hydrophilic materials. This is due to the esterification reaction and aldehyde condensation reaction, which leads to a reduction in hydroxyl groups.

[0161] 6. Gas Permeability Analysis

[0162] Establishing high CO2 and low O2 gas conditions in the food packaging system, since the molecular diameters of CO2 and O2 are similar, increasing the CO2 permeability of the membrane is beneficial to extending the shelf life of the food. Fig.15 As shown, the results show that the O2 permeability of pure PVA film is significantly higher than that of other modified films. With the addition of PAA, CA, GA, MgCl2, and GLY, CO2 permeability first decreases, then increases, and then decreases. From PVA-6, it can be seen that it decreases from 4.94g / (m2·h) to 2.89g / (m2·h). This shows that the CO2 permeability of PVA-6 modified film is significantly higher than the O2 permeability, and PVA, CA, GA, MgCl2, and GLY are all hydrophilic materials, while water is a polar substance and CO2 is a polar gas, which can easily form a "high CO2, low O2" environment, which is very suitable for food packaging.

[0163] Example 9 Antibacterial properties of PVA modified membranes

[0164] 1. Antimicrobial kinetics test

[0165] In order to test the bactericidal activity of polyvinyl alcohol film against Staphylococcus aureus and Escherichia coli, a co-culture model was established in LB broth. 600 The value is used to evaluate the increase or decrease in the number of bacteria, thereby determining the antibacterial effect of the polyvinyl alcohol film. Fig.16 As shown, the results showed that the proliferation rate of Escherichia coli and Staphylococcus aureus was significantly inhibited after the addition of PVA-6 membrane compared with the PBS control group. Among them, the antibacterial performance of PVA-6 membrane against Staphylococcus aureus and Escherichia coli was the best.

[0166] 2. Antimicrobial Sensitivity Test

[0167] The plate count method was used for determination, and the results were as follows Fig.17 As shown, the results showed that PVA-6 membrane had the best antibacterial effect, with an inhibition rate of up to 99% against Escherichia coli and Staphylococcus aureus.

[0168] Example 10 Antioxidant properties of PVA modified membrane

[0169] DPPH and ABTS free radical scavenging rate is an important indicator for evaluating the antioxidant capacity of cling film materials. The antioxidant performance test results of PVA modified film are shown in Figure 2. Fig.18 As shown, compared with PVA-0 membrane, the DPPH free radical scavenging rate of PVA-6 increased by about 10%, and the ABTS free radical scavenging rate increased by about 5%.

[0170] Example 11 Preservation effect of PVA modified film

[0171] The different performance data of PVA modified membrane are placed as indicators in the radar chart. Fig.19 As shown, the results show that among all the films tested, the various properties of PVA-6 film are better than those of other modified films, indicating that the film has excellent comprehensive performance.

[0172] Under sterile conditions, pork was peeled and defatted and cut into rectangles to obtain experimental meat samples of the same quality. Three treatment groups were set up. The meat samples in the CK group were not packaged, the meat samples in the PE group were packaged with PE film, and the meat samples in the PVA-6 group were packaged with PVA-6 film. The PE group and the PVA-6 group were sealed with sealant and then stored in a refrigerator at 4°C. The freshness index of the meat samples was measured at 0 days, 3 days, 6 days, 9 days, 12 days and 15 days.

[0173] (1) Sensory evaluation of fresh pork

[0174] The effects of different treatments (CK, PE, PVA-6) on the color, smell, elasticity and viscosity of meat samples at 0, 3, 6, 9, 12 and 15 days are shown. Fig. 20 As shown in the figure, it can be seen that the scores of meat samples in the CK group in terms of color, smell, elasticity and viscosity gradually decreased over time, with the lowest score at 15 days. The score of the PE group decreased less, but was still lower than that of the PVA-6 group. The PVA-6 group maintained a high score at all time points, showing a better preservation effect. This shows that the PVA-6 treatment is superior to the CK and PE treatments in maintaining color, smell, elasticity and viscosity.

[0175] (2) Effect of fresh pork color

[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 purple-red; Mb combines with oxygen to form oxymyoglobin (MbO2), which appears bright red; when left for too long or under low O2 partial pressure, Mb and MbO2 will be oxidized to metmyoglobin (MIMb) and appear brown. The results of meat color determination of meat samples from different treatment groups are shown below. Fig.21 As shown, the results show that:

[0177] Compared with the CK and PE treatments, the L* value of the PVA-6 treatment remained at a high level during storage, indicating that the PVA-6 treatment can effectively maintain the brightness of pork and delay the darkening process. The a* value rose rapidly in the early stage of storage (0-3 days) and then gradually decreased. The a* value of the CK treatment changed greatly, while the a* value of the PVA-6 treatment changed more slowly. This shows that the PVA-6 treatment can better maintain the red and green degree of the product and reduce color fluctuations. The b* value gradually increased during storage, but the increase in the PVA-6 treatment was smaller, especially compared with the CK and PE treatments. This shows that the PVA-6 treatment can effectively inhibit the increase in yellowness and maintain the color of the product.

[0178] (3) Juice loss rate

[0179] The spoilage of fresh meat is mainly due to the growth of microorganisms, and the water content in fresh meat plays an important role in the growth of microorganisms. The juice loss rate of meat samples in different treatment groups was measured, and the results were as follows: Fig. 22 As shown, the results showed that the juice loss rate of the CK group was low at the beginning of storage (0-2 days), but it increased rapidly from day 4. The juice loss rate of the PVA-6 group increased the slowest during the entire storage period, reaching about 10% on day 16. This indicates that the PVA-6 treatment was the most effective in reducing juice loss, followed by the PE treatment, and the CK group had the fastest juice loss.

[0180] (4) Determination of volatile basic nitrogen

[0181] During storage, due to the presence of enzymes and bacteria, the protein in the meat will be decomposed and produce volatile nitrogen-containing substances such as ammonia and amines. Therefore, volatile basic nitrogen (TVB-N) is also one of the important indicators for evaluating the freshness of chilled meat. According to national standards, the first-level freshness is ≤15mg / 100g, the second-level freshness is ≤25mg / 100g, and spoiled meat is >25mg / 100g. The volatile basic nitrogen content of meat samples from different treatment groups was determined, and the results are as follows: Fig.23 As shown, the black dotted line represents the critical point of first-grade freshness, 15 mg / 100 g. The results show that the CK group and PE group reached the critical value of first-grade freshness on the 3rd and 6th days, respectively, while the PVA-6 group exceeded the national standard of first-grade freshness around the 9th day, indicating that the PVA-6 film has better preservation performance.

[0182] (5) Thiobarbituric acid determination

[0183] TBARS values ​​are used to indicate the degree of lipid oxidation. Fat oxidation in pork is an important cause of meat spoilage. It is generally believed that 0.5 mg / kg is the critical value of TBARS. The dotted line in the figure represents the threshold value of TBARS value (0.5 mg / kg). When the TBARS value exceeds this threshold, the degree of oxidation of the food is generally considered to be high. Thiobarbituric acid was measured for meat samples from different treatment groups. The results are shown in Figure 1. Fig.24 As shown, the results showed that the TBARS value of the CK group exceeded the threshold on the 3rd day, the PE group exceeded the threshold on the 6th day, and the PVA-6 group exceeded the threshold on the 9th day. This shows that PVA-6 treatment has a significant advantage in food preservation.

[0184] (6) pH determination

[0185] As time goes by, the acid produced by protein is broken down into amino acids by bacteria, which in turn increases the pH value in muscle tissue. When the pH value rises to a certain level, it will affect the quality and taste of pork, making the pork dry, hard, and even corrupt. Normally, when 5.7 < pH < 6.2, it is fresh meat; when 6.3 < pH < 6.6, it is sub-fresh meat; and when pH > 6.7, it is spoiled meat. The initial pH value of the fresh pork used in this experiment was 5.82, which is qualified fresh meat.

[0186] The pH values ​​of meat samples from different treatment groups were measured. Fig.25The results showed that the pH value of the PVA-6 group increased most slowly compared with the CK group and the PE group, reaching a pH value of approximately 7.5 on the 15th day, and was lower than that of the other two groups during the entire storage period. This indicates that PVA-6 treatment is effective in maintaining pH stability.

[0187] (7) Determination of metmyoglobin

[0188] As the storage time increases, myoglobin will gradually be oxidized to metmyoglobin (MetMb), which will appear brown and cause the meat color to darken. Metmyoglobin was measured in meat samples from different treatment groups. The results are as follows: Fig.26 As shown, the results showed that the percentage of MetMb in the PVA-6 group increased most slowly compared with the CK and PE groups, reaching approximately 20% on day 15. PVA-6 treatment performed best in inhibiting MetMb formation and delaying food oxidation.

[0189] (8) Determination of total colony count

[0190] According to the national standard GB / T 9959.2-2008 "Divided Fresh and Frozen Pork Lean Meat", the total number of colonies in divided fresh and frozen pork lean meat should be less than or equal to 1×10 6 CFU / g is 6.0l gCFU / g. The total number of colonies in meat samples from different treatment groups was determined, and the results were as follows Fig. 27 The results showed that the total number of colonies in the PVA-6 group increased the slowest during the entire storage period, reaching approximately 10 on the 16th day. 5 CFU / g, and the data of the PVA-6 group fluctuated slightly, and the antibacterial effect was stable.

[0191] (9) Texture analysis

[0192] The texture of meat is an important quality feature, which is affected by many factors such as the type and size of meat, fat and protein content, the action of different microorganisms, and the temperature and time of storage. The relevant parameters of texture are: Adhesiveness, Chewiness, Cohesiveness, Fracturability, Gumminess, Hardness, Resilience, Springiness, etc. Hardness is used to describe the force required for an object to deform; elasticity is the ability of an object to return to its original shape when an external force is applied to the object and the force is withdrawn to deform it; cohesion is the size of the binding force required to keep the food intact; chewiness is the energy required to chew solid food so that it can be swallowed. The correlation between the above four parameters is: chewiness = hardness × elasticity × cohesion. Hardness is the maximum force value of the probe during the first downward pressure process, which reflects the chewiness of the meat sample to a certain extent. The greater the hardness, the more difficult it is to chew. Elasticity is an important parameter for evaluating the tissue structure of fresh meat. The better the elasticity, the more stable the meat tissue structure and the better the taste when eaten. Chewability is the result of the combined effect of hardness and elasticity.

[0193] The texture analysis of meat samples from different treatment groups was carried out, and the results were as follows: Fig.28 As shown, the results show that with the increase of storage days, the hardness of the meat treated in the three groups has changed. The hardness of pork treated with CK and PE groups increased rapidly in the early stage, reached a peak around the 6th day, and then began to decline. The hardness of PVA-6 changed relatively slowly. Although there was also an upward trend, there was no obvious peak. In addition, compared with the CK combined with PE group, the cohesion of PVA-6 was relatively stable and did not change much, and remained between 0.5% and 0.7% overall. The elasticity of CK increased rapidly in the early stage, reached a peak around the 4th day, and then gradually decreased. In terms of elasticity, the elasticity of PVA-6 changed relatively slowly, with a small fluctuation range. In terms of chewiness, compared with the CK combined with PE group, the chewiness of PVA-6 changed slowly, without an obvious peak.

[0194] In general, the meat quality of pork treated with CK and PE groups showed great fluctuations during storage, especially in terms of hardness and chewiness, while the meat quality of pork treated with PVA-6 group was very stable.

[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 equivalent replacement methods and are included in the protection scope of the present invention.

Claims

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

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

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

4. Use of the composition according to any one of claims 1 to 3 in the preparation of a film.

5. Use of the composition according to any one of claims 1 to 3 in preparing food packaging films.

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

7. The preparation method according to claim 6, characterized in that: The composition according to any one of claims 1 to 3 is added to water to obtain a mixed solution, the mixed solution is reacted at 80-100° C. for 90-150 minutes, and the packaging film is obtained after drying.

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

9. A packaging film, characterized in that: The invention is prepared by the preparation method according to any one of claims 6 to 8.

10. Use of the packaging film according to claim 9 in food preservation or in food packaging.

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