Slow-release long-acting food preservative film containing natural preservative and preparation method thereof

Abstract

The invention relates to the technical field of polymer composite materials, in particular to a slow-release long-acting food preservative film containing a natural preservative and a preparation method of the slow-release long-acting food preservative film. In order to improve the mildew-proof and antibacterial performance of the preservative film, eugenol with a natural antibacterial function is loaded on the preservative film to serve as an active raw material; in order to avoid volatilization of effective components caused by purely adding the eugenol, the eugenol-containing sustained-release microcapsule is prepared by carrying out sustained-release embedding treatment on the eugenol-containing sustained-release microcapsule; on the basis, the preservative film material is treated, bacteriostatic modified PBAT with imidazole groups is prepared, the imidazole groups can effectively influence vital activities of microorganisms and play a role in bacteriostasis and mildew prevention, and on the basis, the preservative film prepared by the preparation method disclosed by the invention has the advantages that the service life of the preservative film is prolonged, and the service life of the preservative film is prolonged. All the components can be naturally degraded, and compared with a common polyethylene material and the like, the environment-friendly polyethylene material has the obvious environment-friendly advantage.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a slow-release, long-lasting food preservation film containing natural preservatives and its preparation method. Background Technology

[0002] Food preservation bags, widely used in daily life, primarily function to reduce the risk of food contamination and extend shelf life by physically isolating food from the external environment. However, traditional food preservation bags only isolate the air inside and outside the bag, failing to address two key factors contributing to food spoilage: Firstly, fresh produce such as fruits and vegetables continuously produce ethanol during ripening inside the bag. If these metabolic byproducts cannot be promptly eliminated or decomposed, they accumulate in the sealed space, accelerating over-ripening and spoilage. Secondly, before being placed in food preservation bags, fresh and cooked foods are prone to harboring bacteria, mold, and other microorganisms. The sealed and suitable temperature and humidity environment provides ideal conditions for these microorganisms to multiply rapidly, ultimately shortening the food's shelf life. Summary of the Invention

[0003] The purpose of this invention is to provide a CPET composite material resistant to high and low temperatures and its preparation method, so as to solve the problems raised in the prior art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a slow-release, long-lasting food preservation film containing natural preservatives, comprising the following steps: S1. Preparation of natural preservative microspheres; S11. Dissolve chitosan in acetic acid solution, stir until uniformly mixed, add eugenol, and emulsify by high-speed stirring for 30-45 minutes to obtain a dispersion emulsion; S12. After adjusting the pH value to 6.0~6.5 by adding sodium alginate solution dropwise to the dispersion emulsion, glutaraldehyde is added, the temperature is raised to 45~50℃, the reaction is stirred for 1.5~2h, centrifuged, and dried at 60℃ for 4~8h to obtain natural preservative microspheres. S2. Preparation of antibacterial modified PBAT masterbatch; S21. Mix p-phenylenediamine with potassium carbonate, add it to acetonitrile, stir to disperse and form a suspension, then add ethyl bromoacetate dropwise. During the dropwise addition, control the temperature of the reaction system at 15~30℃. After the dropwise addition is completed, protect the system under a nitrogen atmosphere, raise the temperature to 80~82℃, reflux and stir for 8~10h, cool to room temperature, filter and collect the filtrate, and evaporate under vacuum to constant weight to obtain intermediate 1. S22. After heating DMF to 115~120℃ and holding it at that temperature for 1~2h to remove moisture, cool it to room temperature, add intermediate 1, imidazole, and potassium iodide, and under nitrogen atmosphere protection, heat the reaction system to 80~85℃, stir the reaction for 12~18h, stop heating, remove excess reaction solvent by vacuum evaporation, wash the dried product 2~3 times with low-temperature deionized water and ethanol respectively, and then vacuum dry to constant weight to obtain intermediate 2; S23. Disperse intermediate 2 in an ethanol-water solution, stir until evenly dispersed, add sodium hydroxide solution to adjust the pH to 12-12.5, control the reaction temperature at 25-40℃, stir for 6-8 hours, continuously monitor the pH and add sodium hydroxide solution dropwise during stirring to control the pH of the reaction system at 12-12.5. After the reaction is complete, add hydrochloric acid dropwise until the pH is 2-3, stir for 30-45 minutes, filter to collect the precipitate, wash with deionized water until the pH is 6-7, stop washing, vacuum dry, collect the precipitate, and obtain the carboxyl-terminated antibacterial intermediate; S24. Disperse the carboxyl-terminated antibacterial intermediate and p-toluenesulfonic acid in DMF, stir until evenly dispersed, then add it dropwise to 1,4-butanediol, heat to 70~85℃, stir and react for 2~4 hours to obtain the antibacterial diol intermediate; S25. Mix 1,4-butanediol, antibacterial diol intermediate, adipic acid and terephthalic acid, stir evenly, add diisopropyl di(triethanolamine)titanate, heat to 190~195℃ and esterify under normal pressure for 1.5~2h, then add polycarbodiimide, heat to 270~275℃ and reduce pressure to 80~85Pa, continue the polycondensation reaction for 2.5~3.5h to obtain antibacterial modified PBAT material; S3. Mix PBAT masterbatch with antibacterial modified PBAT masterbatch and PLA masterbatch, add maleic anhydride grafted polyethylene and natural preservative microspheres, melt-blend, and then extrude to obtain blended masterbatch. Then add the blended masterbatch to a blown film machine, extrude and blow film, and roll and cut to obtain a slow-release long-lasting food preservation film containing natural preservative.

[0005] Furthermore, in step S1, the concentration of the acetic acid solution is 0.5~1wt%; the mass of the chitosan is 5~8wt% of the acetic acid solution.

[0006] Furthermore, in step S1, the amount of eugenol added is 5-15 wt% of the mass of the acetic acid solution, and the amount of glutaraldehyde added is 0.1-0.15 wt% of the mass of the acetic acid solution.

[0007] Furthermore, in step S21, the amount of each component added, by weight, is 1 part of p-phenylenediamine, 2-2.5 parts of potassium carbonate, and 2.3-2.7 parts of ethyl bromoacetate.

[0008] Furthermore, in step S22, the amount of each component added, by weight, is 1 part of intermediate 1, 0.4~0.48 parts of imidazole, and 0.03~0.05 parts of potassium iodide.

[0009] Furthermore, in step S24, the amount of each component added, by weight, is 1 part of the carboxyl-terminated antibacterial intermediate, 0.08~0.11 parts of p-toluenesulfonic acid, and 0.4~0.45 parts of 1,4-butanediol.

[0010] Furthermore, in step S25, the amounts of each component added, by weight, are 1.2 to 1.5 parts of 1,4-butanediol, 0.3 to 0.7 parts of antibacterial diol intermediate, 0.9 to 1 part of adipic acid and 0.95 to 1.05 parts of terephthalic acid, 0.0005 to 0.0008 parts of diisopropyl di(triethanolamine)titanate and 0.0001 to 0.00015 parts of polycarbodiimide.

[0011] Furthermore, in step S3, by weight, the addition amounts of each component are 30-45 parts of PBAT masterbatch, 10-25 parts of antibacterial modified PBAT masterbatch, and 25-35 parts of PLA masterbatch, mixed together, and 1-1.5 parts of maleic anhydride grafted polyethylene and 1.5-3 parts of natural preservative microspheres are added.

[0012] Furthermore, a slow-release, long-lasting food preservation film containing natural preservatives is prepared by the above method.

[0013] Compared with the prior art, the beneficial effects of the present invention are: In order to improve the anti-mold and antibacterial properties of plastic wrap, this invention loads eugenol, which has natural antibacterial function, onto the plastic wrap as an active raw material. In order to avoid the volatilization of the effective ingredients caused by simply adding eugenol, this invention also performs a slow-release encapsulation treatment, using chitosan and sodium alginate polysaccharide as wall materials, and using glutaraldehyde as a crosslinking agent to further enhance the strength of the wall materials, thereby preparing a slow-release microcapsule containing eugenol. Furthermore, to further enhance the antibacterial and antifungal properties of the cling film, this invention also treats the cling film material itself. First, using p-phenylenediamine as a raw material, the nitrogen atom affinity is enhanced under the action of potassium carbonate. Then, it is mixed with ethyl bromoacetate. Because the bromine atom in ethyl bromoacetate has strong electronegativity, a large electron radius, and strong leaving ability, it leads to a decrease in the electron cloud density of the carbon atom of the bromine-attached methylene group, thus becoming an electrophilic nucleus that can be attacked by the amino group in p-phenylenediamine. This causes the amino nitrogen atom in p-phenylenediamine to attach... After adding a methylene group, an imidazole ring is added. The nitrogen atom in the imidazole ring acts as a nucleophilic center, attacking the electrophilic carbon atom of the methylene group in intermediate 1, thereby achieving N-substitution of the imidazole ring and forming intermediate 2 containing an imidazole ring structure. Then, under the action of sodium hydroxide, hydroxide ions attack the ester group in intermediate 2, and after acidification, a terminal carboxyl antibacterial intermediate containing a carboxyl group is obtained. Based on this, it is mixed with 1,4-butanediol, and the reaction between the carboxyl group and the hydroxyl group is utilized. By controlling the reaction conditions, an antibacterial diol intermediate with antibacterial and antifungal functions is obtained. Subsequently, an antibacterial diol intermediate was reacted with 1,4-butanediol, adipic acid, and terephthalic acid for polycondensation to prepare antibacterial modified PBAT with imidazole groups. The imidazole groups can effectively affect the life activities of microorganisms, playing an antibacterial and antifungal role. Furthermore, based on this, the present invention further uses the antibacterial modified PBAT masterbatch prepared in this invention to mix with PBAT and PLA, and extrude it into a film to jointly prepare a food preservation film. All components of the film can be naturally degraded, which has obvious environmental advantages compared with general polyethylene materials. Detailed Implementation

[0014] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] The PBAT masterbatch used in the embodiments and comparative examples of this invention is BASF PBAT Batch C Black; the PLA used is commercially available CCBM30-244 type polylactic acid. Example 1. A method for preparing a slow-release, long-lasting food preservation film containing natural preservatives, comprising the following steps: S1. Preparation of natural preservative microspheres; S11. Dissolve 5 wt% chitosan in acetic acid solution, stir until homogeneous, add 5 wt% eugenol to the mixture, and emulsify by high-speed stirring for 30 min to obtain a dispersion emulsion. S12. After adjusting the pH value to 6.0 by adding sodium alginate solution dropwise to the dispersion emulsion, 0.1 wt% glutaraldehyde of acetic acid solution was added, the temperature was raised to 50℃, the reaction was stirred for 2 hours, centrifuged, and dried at 60℃ for 4 hours to obtain natural preservative microspheres. S2. Preparation of antibacterial modified PBAT masterbatch; S21. By weight, 1 part of p-phenylenediamine and 2 parts of potassium carbonate were mixed and added to acetonitrile. After stirring and dispersing to form a suspension, 2.3 parts of ethyl bromoacetate were added dropwise. During the dropwise addition, the temperature of the reaction system was controlled at 25°C. After the dropwise addition was completed, the system was protected under a nitrogen atmosphere, heated to 80°C, refluxed and stirred for 8 hours, cooled to room temperature, and the filtrate was collected by filtration and vacuum evaporated to constant weight to obtain intermediate 1. S22. By weight, DMF was heated to 115°C and kept at that temperature for 1 hour to remove moisture. After cooling to room temperature, 1 part of intermediate 1, 0.4 parts of imidazole, and 0.05 parts of potassium iodide were added. Under nitrogen atmosphere protection, the reaction system was heated to 80°C and stirred for 18 hours. After heating was stopped, excess reaction solvent was removed by vacuum evaporation. The product was washed twice with low-temperature deionized water and ethanol at 0~2°C, and then vacuum dried to constant weight to obtain intermediate 2. S23. By weight, 1 part of intermediate 2 was dispersed in an ethanol-water solution. After stirring and dispersing evenly, sodium hydroxide solution was added to adjust the pH to 12-12.5. The reaction temperature was controlled at 25-30℃. The reaction was stirred for 8 hours. During the stirring process, the pH was continuously monitored and sodium hydroxide solution was added dropwise to control the pH of the reaction system to 12-12.5. After the reaction was completed, hydrochloric acid was added dropwise until the pH was 2. After stirring for 45 minutes, the precipitate was collected by filtration and washed with deionized water until the pH was 6. Washing was stopped and the precipitate was vacuum dried to obtain the carboxyl-terminated antibacterial intermediate. S24. By weight, 1 part of the carboxyl-terminated antibacterial intermediate and 0.11 parts of p-toluenesulfonic acid were dispersed in DMF and stirred until evenly dispersed. Then, the mixture was added dropwise to 0.4 parts of 1,4-butanediol, heated to 85°C, and stirred for 4 hours to obtain the antibacterial diol intermediate. S25. By weight, 1.5 parts of 1,4-butanediol, 0.3 parts of antibacterial diol intermediate, 0.9 parts of adipic acid and 0.95 parts of terephthalic acid are mixed and stirred evenly. Then, 0.0008 parts of diisopropyl di(triethanolamine)titanate are added, and the mixture is heated to 190°C and esterified under normal pressure for 2 hours. Then, 0.0001 parts of polycarbodiimide are added, the temperature is raised to 270°C, and the pressure is reduced to 80 Pa. The polycondensation reaction is continued for 2.5 hours to obtain the antibacterial modified PBAT material. S3. By weight, 45 parts of PBAT masterbatch, 10 parts of antibacterial modified PBAT masterbatch, and 25 parts of PLA masterbatch are mixed. 1 part of maleic anhydride-grafted polyethylene and 1.5 parts of natural preservative microspheres are added. After melt blending, the mixture is extruded to obtain a blended masterbatch. The blended masterbatch is then added to a blown film machine, extruded and blown into a film, and then wound and cut to obtain a slow-release long-lasting food preservation film containing natural preservatives.

[0016] Example 2. A method for preparing a slow-release, long-lasting food preservation film containing natural preservatives, comprising the following steps: Compared with Example 1, this example increases the amount of eugenol added in step S11, while the other steps remain unchanged; S1. Preparation of natural preservative microspheres; S11. Dissolve 5 wt% chitosan in acetic acid solution, stir until homogeneous, add 15 wt% eugenol to the mixture, and emulsify by high-speed stirring for 30 min to obtain a dispersion emulsion. S12. After adjusting the pH value to 6.0 by adding sodium alginate solution dropwise to the dispersion emulsion, 0.1 wt% glutaraldehyde of acetic acid solution was added, the temperature was raised to 50℃, the reaction was stirred for 2 hours, centrifuged, and dried at 60℃ for 4 hours to obtain natural preservative microspheres.

[0017] Example 3. A method for preparing a slow-release, long-lasting food preservation film containing natural preservatives, comprising the following steps: Compared with Example 2, this example increases the amount of 1,4-butanediol added in step S24; S2. Preparation of antibacterial modified PBAT masterbatch; S21. By weight, 1 part of p-phenylenediamine and 2 parts of potassium carbonate were mixed and added to acetonitrile. After stirring and dispersing to form a suspension, 2.3 parts of ethyl bromoacetate were added dropwise. During the dropwise addition, the temperature of the reaction system was controlled at 25°C. After the dropwise addition was completed, the system was protected under a nitrogen atmosphere, heated to 80°C, refluxed and stirred for 8 hours, cooled to room temperature, and the filtrate was collected by filtration and vacuum evaporated to constant weight to obtain intermediate 1. S22. By weight, DMF was heated to 115°C and kept at that temperature for 1 hour to remove moisture. After cooling to room temperature, 1 part of intermediate 1, 0.4 parts of imidazole, and 0.05 parts of potassium iodide were added. Under nitrogen atmosphere protection, the reaction system was heated to 80°C and stirred for 18 hours. After heating was stopped, excess reaction solvent was removed by vacuum evaporation. The product was washed twice with low-temperature deionized water and ethanol at 0~2°C, and then vacuum dried to constant weight to obtain intermediate 2. S23. By weight, 1 part of intermediate 2 was dispersed in an ethanol-water solution. After stirring and dispersing evenly, sodium hydroxide solution was added to adjust the pH to 12-12.5. The reaction temperature was controlled at 25-30℃. The reaction was stirred for 8 hours. During the stirring process, the pH was continuously monitored and sodium hydroxide solution was added dropwise to control the pH of the reaction system to 12-12.5. After the reaction was completed, hydrochloric acid was added dropwise until the pH was 2. After stirring for 45 minutes, the precipitate was collected by filtration and washed with deionized water until the pH was 6. Washing was stopped and the precipitate was vacuum dried to obtain the carboxyl-terminated antibacterial intermediate. S24. By weight, 1 part of the terminal carboxyl antibacterial intermediate and 0.11 parts of p-toluenesulfonic acid were dispersed in DMF and stirred until evenly dispersed. Then, the mixture was added dropwise to 0.45 parts of 1,4-butanediol, heated to 85°C, and stirred for 4 hours to obtain the antibacterial diol intermediate. S25. By weight, 1.5 parts of 1,4-butanediol, 0.3 parts of antibacterial diol intermediate, 0.9 parts of adipic acid and 0.95 parts of terephthalic acid are mixed and stirred evenly. Then, 0.0008 parts of diisopropyl di(triethanolamine)titanate are added, and the mixture is heated to 190°C and esterified under normal pressure for 2 hours. Then, 0.0001 parts of polycarbodiimide are added, the temperature is raised to 270°C, and the pressure is reduced to 80 Pa. The polycondensation reaction is continued for 2.5 hours to obtain the antibacterial modified PBAT material.

[0018] Example 4. A method for preparing a slow-release, long-lasting food preservation film containing a natural preservative, comprising the following steps: Compared with Example 3, this example increases the amount of antibacterial diol intermediate added in step S25; S2. Preparation of antibacterial modified PBAT masterbatch; S21. By weight, 1 part of p-phenylenediamine and 2 parts of potassium carbonate were mixed and added to acetonitrile. After stirring and dispersing to form a suspension, 2.3 parts of ethyl bromoacetate were added dropwise. During the dropwise addition, the temperature of the reaction system was controlled at 25°C. After the dropwise addition was completed, the system was protected under a nitrogen atmosphere, heated to 80°C, refluxed and stirred for 8 hours, cooled to room temperature, and the filtrate was collected by filtration and vacuum evaporated to constant weight to obtain intermediate 1. S22. By weight, DMF was heated to 115°C and kept at that temperature for 1 hour to remove moisture. After cooling to room temperature, 1 part of intermediate 1, 0.4 parts of imidazole, and 0.05 parts of potassium iodide were added. Under nitrogen atmosphere protection, the reaction system was heated to 80°C and stirred for 18 hours. After heating was stopped, excess reaction solvent was removed by vacuum evaporation. The product was washed twice with low-temperature deionized water and ethanol at 0~2°C, and then vacuum dried to constant weight to obtain intermediate 2. S23. By weight, 1 part of intermediate 2 was dispersed in an ethanol-water solution. After stirring and dispersing evenly, sodium hydroxide solution was added to adjust the pH to 12-12.5. The reaction temperature was controlled at 25-30℃. The reaction was stirred for 8 hours. During the stirring process, the pH was continuously monitored and sodium hydroxide solution was added dropwise to control the pH of the reaction system to 12-12.5. After the reaction was completed, hydrochloric acid was added dropwise until the pH was 2. After stirring for 45 minutes, the precipitate was collected by filtration and washed with deionized water until the pH was 6. Washing was stopped and the precipitate was vacuum dried to obtain the carboxyl-terminated antibacterial intermediate. S24. By weight, 1 part of the terminal carboxyl antibacterial intermediate and 0.11 parts of p-toluenesulfonic acid were dispersed in DMF and stirred until evenly dispersed. Then, the mixture was added dropwise to 0.45 parts of 1,4-butanediol, heated to 85°C, and stirred for 4 hours to obtain the antibacterial diol intermediate. S25. By weight, 1.5 parts of 1,4-butanediol, 0.7 parts of antibacterial diol intermediate, 0.9 parts of adipic acid and 0.95 parts of terephthalic acid are mixed and stirred evenly. Then, 0.0008 parts of diisopropyl di(triethanolamine)titanate are added, and the mixture is heated to 190°C and esterified under normal pressure for 2 hours. Then, 0.0001 parts of polycarbodiimide are added, the temperature is raised to 270°C, and the pressure is reduced to 80 Pa. The polycondensation reaction is continued for 2.5 hours to obtain the antibacterial modified PBAT material.

[0019] Example 5. A method for preparing a slow-release, long-lasting food preservation film containing natural preservatives, comprising the following steps: Compared with Example 4, this example increases the amount of antibacterial modified PBAT masterbatch added in step S3; S2. Preparation of antibacterial modified PBAT masterbatch; S21. By weight, 1 part of p-phenylenediamine and 2 parts of potassium carbonate were mixed and added to acetonitrile. After stirring and dispersing to form a suspension, 2.3 parts of ethyl bromoacetate were added dropwise. During the dropwise addition, the temperature of the reaction system was controlled at 25°C. After the dropwise addition was completed, the system was protected under a nitrogen atmosphere, heated to 80°C, refluxed and stirred for 8 hours, cooled to room temperature, and the filtrate was collected by filtration and vacuum evaporated to constant weight to obtain intermediate 1. S22. By weight, DMF was heated to 115°C and kept at that temperature for 1 hour to remove moisture. After cooling to room temperature, 1 part of intermediate 1, 0.4 parts of imidazole, and 0.05 parts of potassium iodide were added. Under nitrogen atmosphere protection, the reaction system was heated to 80°C and stirred for 18 hours. After heating was stopped, excess reaction solvent was removed by vacuum evaporation. The product was washed twice with low-temperature deionized water and ethanol at 0~2°C, and then vacuum dried to constant weight to obtain intermediate 2. S23. By weight, 1 part of intermediate 2 was dispersed in an ethanol-water solution. After stirring and dispersing evenly, sodium hydroxide solution was added to adjust the pH to 12-12.5. The reaction temperature was controlled at 25-30℃. The reaction was stirred for 8 hours. During the stirring process, the pH was continuously monitored and sodium hydroxide solution was added dropwise to control the pH of the reaction system to 12-12.5. After the reaction was completed, hydrochloric acid was added dropwise until the pH was 2. After stirring for 45 minutes, the precipitate was collected by filtration and washed with deionized water until the pH was 6. Washing was stopped and the precipitate was vacuum dried to obtain the carboxyl-terminated antibacterial intermediate. S24. By weight, 1 part of the carboxyl-terminated antibacterial intermediate and 0.11 parts of p-toluenesulfonic acid were dispersed in DMF and stirred until evenly dispersed. Then, the mixture was added dropwise to 0.4 parts of 1,4-butanediol, heated to 85°C, and stirred for 4 hours to obtain the antibacterial diol intermediate. S25. By weight, 1.5 parts of 1,4-butanediol, 0.3 parts of antibacterial diol intermediate, 0.9 parts of adipic acid and 0.95 parts of terephthalic acid are mixed and stirred evenly. Then, 0.0008 parts of diisopropyl di(triethanolamine)titanate are added, and the mixture is heated to 190°C and esterified under normal pressure for 2 hours. Then, 0.0001 parts of polycarbodiimide are added, the temperature is raised to 270°C, and the pressure is reduced to 80 Pa. The polycondensation reaction is continued for 2.5 hours to obtain the antibacterial modified PBAT material. S3. By weight, 45 parts of PBAT masterbatch, 25 parts of antibacterial modified PBAT masterbatch, and 25 parts of PLA masterbatch are mixed. 1 part of maleic anhydride-grafted polyethylene and 1.5 parts of natural preservative microspheres are added. After melt blending, the mixture is extruded to obtain a blended masterbatch. The blended masterbatch is then added to a blown film machine, extruded and blown into a film, and then wound and cut to obtain a slow-release long-lasting food preservation film containing natural preservatives.

[0020] Comparative Example 1. A method for preparing a slow-release, long-lasting food preservation film containing natural preservatives, comprising the following steps: Compared with Example 1, no antibacterial modified PBAT masterbatch was prepared in this comparative example; S1. Preparation of natural preservative microspheres; S11. Dissolve 5 wt% chitosan in acetic acid solution, stir until homogeneous, add 5 wt% eugenol to the mixture, and emulsify by high-speed stirring for 30 min to obtain a dispersion emulsion. S12. After adjusting the pH value to 6.0 by adding sodium alginate solution dropwise to the dispersion emulsion, 0.1 wt% glutaraldehyde of acetic acid solution was added, the temperature was raised to 50℃, the reaction was stirred for 2 hours, centrifuged, and dried at 60℃ for 4 hours to obtain natural preservative microspheres. S2. By weight, 70 parts of PBAT masterbatch and 25 parts of PLA masterbatch are mixed, 1 part of maleic anhydride-grafted polyethylene and 1.5 parts of natural preservative microspheres are added, melt-blended and extruded to obtain blended masterbatch, then the blended masterbatch is added to a blown film machine, extruded and blown film is formed, rolled and cut to obtain a slow-release long-lasting food preservation film containing natural preservative.

[0021] Comparative Example 2. A method for preparing a slow-release, long-lasting food preservation film containing natural preservatives, comprising the following steps: Compared with Example 1, this comparative example did not prepare antibacterial modified PBAT masterbatch and natural preservative microspheres; S1. By weight, 70 parts of PBAT masterbatch and 25 parts of PLA masterbatch are mixed, and 1 part of maleic anhydride-grafted polyethylene is added. After melt blending, the mixture is extruded to obtain a blended masterbatch. Then, the blended masterbatch is added to a blown film machine, extruded and blown into a film, and then wound and cut to obtain a slow-release long-lasting food preservation film containing natural preservatives.

[0022] Testing: The samples prepared in Examples 1-5 and Comparative Examples 1-2 were processed into test samples; the fracture strength of the samples was tested according to GB 1040.3-2006. The antibacterial properties of the samples against Staphylococcus aureus and Escherichia coli were tested according to QB / T 2591-2003A. The samples were tested for their resistance to Aspergillus niger according to ASTM G21-96, with the standards for each level as follows: Grade 0 - No signs of mold growth; Level 1 - Coverage area less than 10%; Level 2 - Coverage area greater than 10%; The test results are shown in Table 1 below;

[0023] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a slow-release, long-lasting food preservation film containing natural preservatives, characterized in that, Includes the following steps: S1. Preparation of natural preservative microspheres; S11. Dissolve chitosan in acetic acid solution, stir until uniformly mixed, add eugenol, and emulsify by high-speed stirring for 30-45 minutes to obtain a dispersion emulsion; S12. After adjusting the pH value to 6.0~6.5 by adding sodium alginate solution dropwise to the dispersion emulsion, glutaraldehyde is added, the temperature is raised to 45~50℃, the reaction is stirred for 1.5~2h, centrifuged, and dried at 60℃ for 4~8h to obtain natural preservative microspheres. S2. Preparation of antibacterial modified PBAT masterbatch; S21. Mix p-phenylenediamine with potassium carbonate, add it to acetonitrile, stir to disperse and form a suspension, then add ethyl bromoacetate dropwise. During the dropwise addition, control the temperature of the reaction system at 15~30℃. After the dropwise addition is completed, protect the system under a nitrogen atmosphere, raise the temperature to 80~82℃, reflux and stir for 8~10h, cool to room temperature, filter and collect the filtrate, and evaporate under vacuum to constant weight to obtain intermediate 1. S22. After heating DMF to 115~120℃ and holding it at that temperature for 1~2h to remove moisture, cool it to room temperature, add intermediate 1, imidazole, and potassium iodide, and under nitrogen atmosphere protection, heat the reaction system to 80~85℃, stir the reaction for 12~18h, stop heating, remove excess reaction solvent by vacuum evaporation, wash the dried product 2~3 times with low-temperature deionized water and ethanol respectively, and then vacuum dry to constant weight to obtain intermediate 2; S23. Disperse intermediate 2 in an ethanol-water solution, stir until evenly dispersed, add sodium hydroxide solution to adjust the pH to 12-12.5, control the reaction temperature at 25-40℃, stir for 6-8 hours, continuously monitor the pH and add sodium hydroxide solution dropwise during stirring to control the pH of the reaction system at 12-12.

5. After the reaction is complete, add hydrochloric acid dropwise until the pH is 2-3, stir for 30-45 minutes, filter to collect the precipitate, wash with deionized water until the pH is 6-7, stop washing, vacuum dry, collect the precipitate, and obtain the carboxyl-terminated antibacterial intermediate; S24. Disperse the carboxyl-terminated antibacterial intermediate and p-toluenesulfonic acid in DMF, stir until evenly dispersed, then add it dropwise to 1,4-butanediol, heat to 70~85℃, stir and react for 2~4 hours to obtain the antibacterial diol intermediate; S25. Mix 1,4-butanediol, antibacterial diol intermediate, adipic acid and terephthalic acid, stir evenly, add diisopropyl di(triethanolamine)titanate, heat to 190~195℃ and esterify under normal pressure for 1.5~2h, then add polycarbodiimide, heat to 270~275℃ and reduce pressure to 80~85Pa, continue the polycondensation reaction for 2.5~3.5h to obtain antibacterial modified PBAT material; S3. Mix PBAT masterbatch with antibacterial modified PBAT masterbatch and PLA masterbatch, add maleic anhydride grafted polyethylene and natural preservative microspheres, melt-blend, and then extrude to obtain blended masterbatch. Then add the blended masterbatch to a blown film machine, extrude and blow film, and roll and cut to obtain a slow-release long-lasting food preservation film containing natural preservative.

2. The method for preparing a slow-release, long-lasting food preservation film containing a natural preservative according to claim 1, characterized in that: In step S1, the concentration of the acetic acid solution is 0.5~1wt%; the mass of the chitosan is 5~8wt% of the acetic acid solution.

3. The method for preparing a slow-release, long-lasting food preservation film containing a natural preservative according to claim 1, characterized in that: In step S1, the amount of eugenol added is 5-15 wt% of the mass of the acetic acid solution, and the amount of glutaraldehyde added is 0.1-0.15 wt% of the mass of the acetic acid solution.

4. A method for preparing a slow-release, long-lasting food preservation film containing a natural preservative according to claim 1, characterized in that: In step S21, the amount of each component added, by weight, is 1 part of p-phenylenediamine, 2-2.5 parts of potassium carbonate, and 2.3-2.7 parts of ethyl bromoacetate.

5. A method for preparing a slow-release, long-lasting food preservation film containing a natural preservative according to claim 1, characterized in that: In step S22, the amount of each component added, by weight, is 1 part of intermediate 1, 0.4 to 0.48 parts of imidazole, and 0.03 to 0.05 parts of potassium iodide.

6. A method for preparing a slow-release, long-lasting food preservation film containing a natural preservative according to claim 1, characterized in that: In step S24, the amount of each component added, by weight, is 1 part of the carboxyl-terminated antibacterial intermediate, 0.08~0.11 parts of p-toluenesulfonic acid, and 0.4~0.45 parts of 1,4-butanediol.

7. A method for preparing a slow-release, long-lasting food preservation film containing a natural preservative according to claim 1, characterized in that: In step S25, the amounts of each component added, by weight, are 1.2 to 1.5 parts of 1,4-butanediol, 0.3 to 0.7 parts of antibacterial diol intermediate, 0.9 to 1 part of adipic acid and 0.95 to 1.05 parts of terephthalic acid, 0.0005 to 0.0008 parts of diisopropyl di(triethanolamine)titanate and 0.0001 to 0.00015 parts of polycarbodiimide.

8. A method for preparing a slow-release, long-lasting food preservation film containing a natural preservative according to claim 1, characterized in that: In step S3, by weight, the following components are added: 30-45 parts of PBAT masterbatch, 10-25 parts of antibacterial modified PBAT masterbatch, and 25-35 parts of PLA masterbatch are mixed together, and 1-1.5 parts of maleic anhydride grafted polyethylene and 1.5-3 parts of natural preservative microspheres are added.

9. A slow-release, long-lasting food preservation film containing a natural preservative, prepared by the preparation method according to any one of claims 1 to 8.

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