Bacteriostatic fresh-keeping composite film as well as preparation method and application thereof

Abstract

The invention discloses an antibacterial and fresh-keeping composite film as well as a preparation method and application thereof, and relates to the technical field of film materials. According to the antibacterial preservative film, modified ZIF-8 and silver heterojunction particles are introduced into a film forming matrix with chitosan and radix puerariae powder as main components, paeonol is loaded on the modified ZIF-8, the antibacterial preservative film has antibacterial and fresh-keeping functions, and the prepared antibacterial preservative film can effectively delay the rotting process of fruits. The membrane material adopts natural degradable components, so that the requirements of environmental protection and sustainable development are met, and the membrane material has a relatively strong market application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of membrane materials, and in particular to an antibacterial and fresh-keeping composite film and a preparation method and application thereof. Background Art

[0002] As people's living standards improve, higher requirements are placed on food preservation. Cling film is a fresh-keeping material used in daily life, which has a direct impact on the preservation effect. In order to achieve better antibacterial effect, antibacterial ingredients are often added to cling film to prepare antibacterial cling film. Antibacterial cling film can be used as a carrier of various food antioxidants and antibacterial agents, and has a preservation function for food.

[0003] Traditional antibacterial cling film is mainly made of petroleum-based raw materials, which are not easy to degrade and difficult to recycle. In addition, the preservation effect of antibacterial cling film needs to be improved, and it cannot meet the requirements of long-term preservation of perishable fruits such as strawberries.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide an antibacterial fresh-keeping composite film and a preparation method and application thereof, aiming to significantly improve the fresh-keeping effect of the antibacterial fresh-keeping composite film.

[0006] The present invention is achieved in that:

[0007] In a first aspect, the present invention provides an antibacterial and fresh-keeping composite film, comprising a film-forming matrix and effective ingredients dispersed in the film-forming matrix, wherein the film-forming matrix comprises chitosan and kudzu root powder, the effective ingredients comprise modified ZIF-8 and silver heterojunction particles, and the modified ZIF-8 comprises a ZIF-8 carrier and paeonol loaded on the ZIF-8 carrier.

[0008] In an optional embodiment, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 is (1000-10000): (1000-2000): (10-50): (50-300);

[0009] Preferably, when preparing the modified ZIF-8, the molar ratio of zinc salt, imidazole organic ligand and paeonol is controlled to be 1:(2-34):(2.3-2.4);

[0010] Preferably, the silver heterojunction particles include silver carbonate and silver oxide.

[0011] In a second aspect, the present invention provides a method for preparing the antibacterial and fresh-keeping composite film of the aforementioned embodiment, comprising:

[0012] In the process of preparing ZIF-8 material, paeonol is introduced, so that paeonol is loaded on the generated ZIF-8 material to obtain modified ZIF-8;

[0013] Silver heterojunction particles are prepared by using a precipitation reaction of silver ions in a solution;

[0014] The film-forming matrix, silver heterojunction particles and modified ZIF-8 are mixed to prepare a film-forming solution, and the film is formed using the film-forming solution.

[0015] In an optional embodiment, the process for preparing modified ZIF-8 comprises:

[0016] Dissolving zinc salt and imidazole organic ligand respectively to obtain zinc salt solution and ligand solution, and mixing paeonol and organic solvent to obtain paeonol solution;

[0017] The paeonol solution and the zinc salt solution are mixed, and then mixed with the ligand solution for reaction, and then the solid-liquid separation is carried out, and the obtained solid material is washed and dried;

[0018] Preferably, the paeonol solution and the zinc salt solution are first mixed and stirred for 0.5 h to 2 h, and then mixed and stirred with the ligand solution for 2 h to 5 h.

[0019] In an optional embodiment, the molar ratio of zinc salt, imidazole organic ligand and paeonol is 1:(2-34):(2.3-2.4);

[0020] Preferably, the zinc salt is Zn(NO3)2·6H2O, and the imidazole organic ligand is 2-methylimidazole;

[0021] Preferably, the solvent used to prepare the zinc salt solution and the ligand solution is water, and the solvent used to prepare the paeonol solution is an organic alcohol solvent. The concentration of the zinc salt solution is 0.05mmol / mL-0.20mmol / mL, the concentration of the ligand solution is 1.0mmol / mL-2.5mmol / mL, and the concentration of the paeonol solution is 0.05mmol / mL-0.20mmol / mL.

[0022] In an optional embodiment, the preparation process of the silver heterojunction particles includes: mixing silver nitrate, water and a surfactant to obtain a mixed solution, heating the mixed solution to 50° C.-70° C., mixing and reacting the mixed solution with a carbonate for 2 h-6 h, then separating the solid from the liquid, and washing and drying the obtained solid material;

[0023] Preferably, the surfactant is polyvinyl pyrrolidone with a molecular weight of 8000Mw-360000Mw;

[0024] Preferably, the carbonate is selected from at least one of sodium carbonate and potassium carbonate.

[0025] In an optional embodiment, the mass ratio of silver nitrate to the surfactant is 1:(8-10), and the molar ratio of silver nitrate to carbonate ions in the carbonate is 1:(1-3).

[0026] In an optional embodiment, the process of preparing the film-forming solution comprises:

[0027] Mixing and dissolving chitosan and acetic acid aqueous solution to obtain a chitosan solution;

[0028] Disperse the kudzu root powder in hot water at 93°C-98°C and stir for 30-90 minutes to obtain a paste;

[0029] The paste is mixed with the plasticizer, then cooled to 55°C-70°C and mixed with the chitosan solution for 10-60 minutes, then the silver heterojunction particles are added and stirred for 5-60 minutes, and when the temperature is reduced to 35°C-45°C, the modified ZIF-8 is mixed and stirred for 10-60 minutes, and then a defoaming treatment is performed;

[0030] Preferably, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 is (1000-10000): (1000-2000): (10-50): (50-300);

[0031] Preferably, the plasticizer is glycerol, and the mass ratio of glycerol to chitosan is (10-50):100;

[0032] Preferably, the volume fraction of acetic acid in the acetic acid aqueous solution is 0.05-0.2%, and the mass fraction of chitosan in the chitosan solution is 1%-2%;

[0033] Preferably, the mass ratio of kudzu root powder to hot water is (1-10): (95-105).

[0034] In an alternative embodiment, the film-forming solution is poured into a film-forming container and then dried to form a film.

[0035] In a third aspect, the present invention provides use of any antibacterial and fresh-keeping composite film according to the aforementioned embodiments or an antibacterial and fresh-keeping composite film prepared by any preparation method according to the aforementioned embodiments in preparing antibacterial and fresh-keeping packaging materials.

[0036] The invention has the following beneficial effects: the invention introduces modified ZIF-8 and silver heterojunction particles into a film-forming matrix with chitosan and kudzu root powder as main components, wherein the modified ZIF-8 is loaded with paeonol, which has antibacterial and fresh-keeping functions, and the prepared antibacterial fresh-keeping film can effectively delay the corruption process of fruits. Since the film material adopts natural degradable components, it meets the requirements of green environmental protection and sustainable development and has strong market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 SEM morphology images of ZIF-8, PAE@ZIF-8 and silver heterojunction; (A) represents ZIF-8, (B) represents PAE@ZIF-8, and (C) represents silver heterojunction;

[0039] Figure 2 Infrared spectra and X-ray diffraction patterns of three materials; (A) represents infrared spectra; (B) represents X-ray diffraction patterns;

[0040] Figure 3 is the X-ray diffraction pattern of the nanocomposite film;

[0041] Figure 4 This is a diagram showing the preservation effect of different nanocomposite films on raspberries;

[0042] Figure 5 This is the graph showing the weight loss rate of raspberries. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0044] The present invention provides a method for preparing an antibacterial and fresh-keeping composite film, which uses chitosan and kudzu root powder as film-forming matrices, and adds a ZIF-8 material (PAE@ZIF-8) loaded with paeonol and a silver heterojunction therein, and is a composite film with high-efficiency antibacterial and fresh-keeping functions, which can effectively delay the corruption process of fruits. The preparation steps are as follows:

[0045] S1. Preparation of modified ZIF-8

[0046] Paeonol is introduced into the process of preparing ZIF-8 material, so that paeonol is loaded on the generated ZIF-8 material to obtain modified ZIF-8. ZIF-8 material has become an ideal carrier due to its high specific surface area and porosity, and is widely used in the adsorption and release of active ingredients. By loading the active molecule paeonol, ZIF-8 can exert its excellent functions and stably release these active ingredients, thereby realizing a variety of functional applications. Paeonol was loaded into ZIF-8 using a one-pot synthesis method. The study found that the loading rate of ZIF-8 for paeonol can reach 36.33%, and a sustained release effect can be achieved.

[0047] It should be noted that paeonol (PAE) is a natural phenolic compound widely found in the root bark of peony. It has biological activities such as antioxidant, anti-inflammatory, antibacterial, and anti-tumor. Paeonol contains phenolic hydroxyl groups in its chemical structure, which can effectively remove free radicals, delay cell aging, and has strong antioxidant capacity. In addition, paeonol also has a certain antibacterial effect and can inhibit the growth of various pathogenic microorganisms. In the field of food, paeonol has gradually been concerned about the application in the research and development of fresh-keeping film due to its natural antibacterial and antioxidant properties. By adding paeonol to the fresh-keeping film material, the shelf life of food can be effectively extended, food oxidation and bacterial contamination can be prevented, and the taste and nutritional value of food can be maintained. Due to its natural source, the application of paeonol in fresh-keeping film not only conforms to the trend of green environmental protection, but also reduces the dependence on artificial synthetic chemicals, and has important market prospects. Therefore, the application of paeonol in fresh-keeping film can not only improve the preservation effect, but also enhance the biodegradability of the film material.

[0048] It should be noted that the zinc-based metal organic framework (ZIF-8) is composed of zinc ions and 2-methylimidazole as ligands and has a topological structure similar to zeolite. The advantages of ZIF-8 include good thermal stability and chemical stability, especially showing strong resistance to hydrolysis in a humid environment. In addition, ZIF-8 also has a high specific surface area and porosity, which is suitable for adsorption and release of active ingredients. Although ZIF-8 has many advantages, it also has some disadvantages, such as the need for organic solvents in its synthesis process, which may cause environmental pollution problems. In addition, the pore structure and chemical stability of ZIF-8 still need to be improved under certain specific conditions to ensure its stability in long-term applications.

[0049] In the embodiments of the present invention, ZIF-8 has a high specific surface area and an adjustable pore structure, which can effectively adsorb and slowly release active substances such as antioxidants, antimicrobial agents and preservatives, thereby extending the shelf life of food. In addition, they can effectively isolate external gases, reduce oxidation and water loss of food, and maintain the taste and nutrition of food.

[0050] In certain embodiments, the process of preparing modified ZIF-8 includes: dissolving zinc salt and imidazole organic ligand respectively to obtain zinc salt solution and ligand solution, mixing paeonol and organic solvent to obtain paeonol solution; mixing paeonol solution and zinc salt solution, and then reacting with ligand solution, and then solid-liquid separation, washing and drying the obtained solid material. Paeonol and zinc salt are first mixed evenly and then ligand is added to react, so that paeonol is loaded on the formed ZIF-8 material to prepare modified ZIF-8. Specifically, the method of solid-liquid separation is not limited, and can be a centrifugal filtration method, the centrifugal speed can be 7000r / min-9000r / min (such as 8000r / min), and the centrifugal time can be 10min-20min (such as 15min); washing solvent can be water, and the number of washing times is not limited; drying method is not limited, and vacuum freeze drying can be used, and the drying time can be 10h-15h.

[0051] In some embodiments, the paeonol solution and the zinc salt solution are first mixed and stirred for 0.5h-2h (such as 0.5h, 1.0h, 1.5h, 2.0h, etc.), and then the ligand solution is slowly added and mixed and stirred for 2h-5h (such as 2h, 3h, 4h, 5h, etc.), and the reaction is fully carried out by regulating the mixing time, and the paeonol is uniformly loaded. Before mixing the paeonol solution and the zinc salt solution, the paeonol solution, the zinc salt solution, and the ligand solution can be ultrasonically treated to ensure complete dissolution.

[0052] In some embodiments, the molar ratio of zinc salt, imidazole organic ligand and paeonol is 1:(2-34):(2.3-2.4), and the preservation effect can be further improved by regulating the dosage of zinc salt, imidazole organic ligand and paeonol. The zinc salt can be Zn(NO3)2·6H2O, but is not limited thereto; the imidazole organic ligand can be 2-methylimidazole, but is not limited thereto. The molar ratio of zinc salt, imidazole organic ligand and paeonol can be 1:2:2.30, 1:5:2.31, 1:8:2.32, 1:10:2.33, 1:13:2.34, 1:15:2.35, 1:20:2.36, 1:23:2.37, 1:25:2.38, 1:30:2.39, 1:34:2.40, etc.

[0053] In certain embodiments, the solvent for preparing zinc salt solution and ligand solution is water, and the solvent for preparing paeonol solution is an organic alcohol solvent (such as methanol, but not limited thereto), the concentration of zinc salt solution is 0.05mmol / mL-0.20mmol / mL, the concentration of ligand solution is 1.0mmol / mL-2.5mmol / mL, and the concentration of paeonol solution is 0.05mmol / mL-0.20mmol / mL. The concentration of solution can better dissolve the reaction raw materials within the above range, so that the reaction is fully carried out. The total amount of water refers to the total amount of water used to prepare zinc salt solution and ligand solution, and the total amount of water corresponding to each gram of imidazole organic ligand can be 6mL, 7mL, 8mL, etc., and the amount of corresponding organic alcohol solvent can be 15mL, 16mL, 17mL, 18mL, etc.

[0054] S2. Preparation of silver heterojunction particles

[0055] Silver heterojunction particles are prepared by precipitation reaction of silver ions in solution, and the antibacterial effect of silver is used to further increase the preservation effect of the composite film. Silver heterojunction is synthesized by hydrothermal method, and its ability to release silver ions and exert bactericidal effect is used to provide antibacterial function for membrane materials.

[0056] In some embodiments, the preparation process of silver heterojunction particles includes: mixing silver nitrate, water and a surfactant to obtain a mixed solution, heating the mixed solution to 50°C-70°C (such as 50°C, 60°C, 70°C, etc.), and then mixing with carbonate for 2h-6h (such as 2h, 3h, 4h, 5h, 6h, etc.), followed by solid-liquid separation, and washing and drying the obtained solid material. During the reaction, anions and carbonates are combined and deposited, and a small amount of anions are oxidized, and finally brown silver heterojunction particles (AgH) containing Ag2CO3 and Ag2O are obtained. By adding a surfactant, the particles can be effectively prevented from growing too large, which affects the dispersion effect in the composite film.

[0057] Specifically, there is no limit to the solid-liquid separation method, and centrifugal filtration can be used; there is no limit to the washing method, and water washing can be used; drying can be carried out in a vacuum drying oven, and the drying temperature can be controlled to be 50°C-70°C, and the drying time can be 10h-15h.

[0058] In some embodiments, the surfactant may be polyvinyl pyrrolidone (PVP) with a molecular weight of 8000Mw-360000Mw, such as 8000Mw, 10000Mw, 50000Mw, 100000Mw, 200000Mw, 300000Mw, 360000Mw, etc. The molecular weight within the above range can play a good role in regulating the size of silver heterojunction particles. The carbonate is selected from at least one of sodium carbonate and potassium carbonate, and the carbonate can be any one or more of the above.

[0059] In some embodiments, the mass ratio of silver nitrate to surfactant is 1:(8-10), such as 1:8, 1:9, 1:10, etc., and the molar ratio of silver nitrate to carbonate ions in carbonate is 1:(1-3), such as 1:1, 1:2, 1:3, etc. By adjusting the amount of each raw material, the silver ions are fully reacted, and the particle size of the obtained silver heterojunction particles is more appropriate.

[0060] It should be noted that silver heterojunction (AgH) has excellent optical, electrical and catalytic properties. Its main advantage is that it has strong antibacterial properties, which can effectively inhibit the growth of microorganisms in food, thereby extending the shelf life of food. In addition, the photocatalytic properties of silver heterojunction enable it to decompose harmful substances under ultraviolet light, further improving food safety. In the field of food packaging, the antibacterial properties and photocatalytic effects of silver heterojunction provide it with great potential. By applying silver heterojunction to packaging materials, food contamination and corruption can be effectively inhibited, and the quality and shelf life of food can be improved. It is especially suitable for packaging perishable foods and high humidity environments.

[0061] S3. Preparation of antibacterial fresh-keeping composite film

[0062] The film-forming matrix, silver heterojunction particles and modified ZIF-8 are mixed to prepare a film-forming solution, and the film-forming solution is used to form a film to prepare a composite film with antibacterial and fresh-keeping properties. In the field of food packaging, the adsorption properties of ZIF-8 can effectively capture and release ingredients that are beneficial to food preservation, such as antioxidants and antibacterial agents. On this basis, the antibacterial properties of the packaging film can be further enhanced by combining silver heterojunction materials. The silver heterojunction can not only release silver ions, but also effectively inhibit the growth and reproduction of common bacteria in food, reducing the risk of food corruption. By combining ZIF-8-loaded paeonol with the silver heterojunction, the prepared composite material has a strong antibacterial function, can significantly extend the shelf life of food, and is particularly suitable for the packaging of perishable foods.

[0063] In some embodiments, the process of preparing a film-forming solution includes: (1) mixing and dissolving chitosan and acetic acid aqueous solution to obtain a chitosan solution; (2) dispersing kudzu root powder in hot water at 93°C-98°C and stirring for 30min-90min to completely gelatinize the kudzu root powder to obtain a paste; (3) mixing the paste with a plasticizer, then cooling the temperature to 55°C-70°C and mixing with the chitosan solution and stirring for 10min-60min, then adding silver heterojunction particles and stirring for 5min-60min, and when the temperature is reduced to 35°C-45°C, mixing with modified ZIF-8 and stirring for 10min-60min, and then performing a defoaming treatment.

[0064] It should be noted that by adjusting the order and temperature of adding the raw materials, the raw materials can be more easily dispersed evenly. For example, if silver heterojunction particles are added at around 40° C., they tend to aggregate, which is not conducive to preparing a uniform film layer.

[0065] Specifically, the temperature of the hot water in the above step (2) can be 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, etc., and the stirring time can be 30min, 40min, 50min, 60min, 70min, 80min, 90min, etc. In the above step (3), the temperature of adding the chitosan solution can be 55°C, 60°C, 65°C, 70°C, etc., and the stirring time can be 10min, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, etc.; the stirring time after adding the silver heterojunction particles can be 5min, 10min, 20min, 30min, 40min, 50min, 60min, etc.; the temperature when adding the modified ZIF-8 can be 35°C, 40°C, 45°C, etc., and the stirring time can be 10min, 20min, 30min, 40min, 50min, 60min, etc. The method of debubbling treatment is not limited, and the bubbles may be removed by ultrasound, and the ultrasound time may be 1 min-5 min.

[0066] It should be noted that chitosan itself has natural antibacterial properties and is a biodegradable material with excellent biocompatibility. On this basis, combined with natural ingredients such as kudzu root powder, the prepared nanocomposite film not only has multiple functions such as anti-oxidation and antibacterial, but also can effectively delay the oxidation process of fruits and vegetables and other foods, reduce water loss, and maintain the freshness and nutrients of food. This membrane material can not only provide protection for food, but also naturally degrade after application, avoiding the pollution of traditional plastic packaging to the environment. Therefore, the composite material formed by combining ZIF-8 loaded paeonol with silver heterojunction has significant antibacterial and fresh-keeping effects. Coupled with the combination of natural materials such as chitosan and kudzu root powder, this composite film can not only extend the shelf life of food, maintain its taste and nutrition, but also meet the needs of environmental protection and sustainable development. Its biosafety and degradable properties make it an ideal choice for future development in the field of food packaging.

[0067] In some embodiments, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 is (1000-10000): (1000-2000): (10-50): (50-300). By regulating the mass of the above main raw materials, the effective ingredients in the prepared composite film are evenly dispersed, thereby achieving a better preservation and antibacterial effect. Specifically, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 can be 1000:1000:10:50, 2000:1100:15:80, 3000:1200:20:100, 4000:1300:25:130, 5000:1400:30:150, 6000:1500:35:180, 7000:1600:40:200, 8000:1700:43:250, 9000:1800:45:280, 10000:2000:50:300, etc.

[0068] Furthermore, the plasticizer can be glycerol, and the mass ratio of glycerol to chitosan is (10-50):100, such as 10:100, 20:100, 30:100, 40:100, 50:100, etc. The volume fraction of acetic acid in the acetic acid aqueous solution is 0.05-0.2%, such as 0.05%, 0.10%, 0.15%, 0.20%, etc.; by adjusting the amount of the acetic acid aqueous solution, the mass fraction of chitosan in the chitosan solution is 1%-2%, such as 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, etc.

[0069] The mass ratio of kudzu root powder to hot water is (1-10): (95-105), within which the effective ingredients can be better dispersed to prepare a uniform composite film. Specifically, the mass ratio of kudzu root powder to hot water can be 1:95, 3:98, 5:100, 8:102, 10:105, etc.

[0070] In some embodiments, the film forming method is not limited, for example, the film forming solution can be poured into a film forming container and then dried to form a film. The film forming container can be, for example, a culture dish with a diameter of 15 cm, the drying temperature can be 30° C.-40° C., and the drying time can be 30 h-40 h.

[0071] The embodiment of the present invention provides an antibacterial fresh-keeping composite film, including a film-forming matrix and an effective component dispersed in the film-forming matrix, the film-forming matrix including chitosan and kudzu root powder, the effective component including modified ZIF-8 and silver heterojunction particles, and the modified ZIF-8 including a ZIF-8 carrier and paeonol loaded on the ZIF-8 carrier. The antibacterial fresh-keeping film can effectively delay the corruption process of fruits. Fresh-keeping experiments were carried out with raspberries as model fruits, and the results showed that the film material showed excellent effects in extending the shelf life of fruits. Since the film material uses natural degradable components, it meets the requirements of green environmental protection and sustainable development and has strong market application prospects. In addition, the slow-release characteristics of ZIF-8 in the film and the antibacterial effect of the silver heterojunction further improve the overall performance of the film material. In general, the nano-preservative composite film shows great application potential in the field of food preservation, which can not only inhibit bacterial growth, but also extend the shelf life of food, while meeting environmental protection requirements and having broad application prospects.

[0072] In some embodiments, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 is (1000-10000): (1000-2000): (10-50): (50-300); when preparing modified ZIF-8, the molar ratio of zinc salt, imidazole organic ligand and paeonol is controlled to be 1: (2-34): (2.3-2.4). By adjusting the amount of key raw materials in the preparation process, the antibacterial and fresh-keeping effects of the product can be improved.

[0073] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0074] Example 1

[0075] This embodiment provides a method for preparing an antibacterial fresh-keeping composite film, the steps are as follows:

[0076] (1) Preparation of modified ZIF-8

[0077] 1 mmol Zn(NO3)2·6H2O and 10 mL deionized water were mixed and dissolved to obtain a zinc salt solution, and 16 mmol 2-methylimidazole and 10 mL deionized water were mixed and dissolved to obtain a ligand solution. 2.4 mmol paeonol was dissolved in 20 mL methanol to obtain a paeonol solution. The zinc salt solution, ligand solution and paeonol solution were ultrasonically treated at room temperature (about 25°C, the same below) to ensure complete dissolution.

[0078] The paeonol solution was mixed with the zinc salt solution and magnetically stirred for 1 hour. The ligand solution was slowly added and magnetically stirred for 3 hours. The mixture was centrifuged (centrifugal conditions: 8000 r / min, 15 min), washed with water, and vacuum freeze-dried for 12 hours to obtain the paeonol-loaded ZIF-8 material (PAE@ZIF-8).

[0079] Note: In this embodiment, the molar ratio of zinc salt, imidazole organic ligand and paeonol is 1:16:2.4.

[0080] (2) Preparation of silver heterojunction particles

[0081] 0.1mmol of AgNO3 and 1mL of deionized water were mixed and dissolved, and then added to 10mL of PVP aqueous solution (PVP concentration was 1.88mol / L, and the molecular weight of PVP used was 8000Mw). The obtained mixture was magnetically stirred at room temperature for 1 hour, and after the solution temperature was raised to 60°C, 1mL of 0.1mol / L sodium carbonate solution was added, stirred at this temperature for 4 hours, centrifuged and filtered, washed 3 times at room temperature, and placed in a vacuum drying oven at 60°C for 12 hours to obtain a brown Ag2CO3 / Ag2O silver heterojunction (AgH).

[0082] Note: In this embodiment, the mass ratio of silver nitrate to PVP is 1:8.8, and the molar ratio of silver nitrate to carbonate ions in carbonate is 1:1.

[0083] (3) Preparation of antibacterial fresh-keeping composite film

[0084] First, 2g of chitosan was dissolved in 100mL of 0.1% v / v acetic acid and stirred until completely dissolved. Then, 5g of kudzu root powder was dispersed in 100mL of 95℃ water and stirred for 60min to complete the complete gelatinization of kudzu root powder. Then, 0.6g of glycerol was added as a plasticizer and stirred until completely uniform. When the temperature of kudzu root powder dropped to 60℃, the chitosan solution was poured in and mixed and stirred for 30 minutes. Then, 40mg of AgH particles were added and stirred for 20 minutes. When the temperature of the solution dropped to 40℃, 100mg of PAE@ZIF-8 was added and stirred for 20 minutes. Finally, the bubbles were removed after ultrasonic treatment for 2 minutes. The film-forming solution was poured into a 15cm diameter culture dish and dried in an oven at a constant temperature of 35℃ for 36 hours to obtain a mixed film of chitosan, kudzu root powder, PAE@ZIF-8 and AgH (CS-KP-AgH). Prior to testing the properties of the films, the films were conditioned at 25°C and 50% relative humidity until a constant weight was achieved.

[0085] Note: In this embodiment, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 is 5000:2000:40:100; the mass ratio of glycerol to chitosan is 30:100; and the mass ratio of kudzu root powder to hot water is 5:100.

[0086] Example 2

[0087] The only difference from Example 1 is that in step (3), the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 is different. The mass ratio of this embodiment is 5000:2000:10:100, the mass of kudzu root powder remains unchanged, and the masses of chitosan, silver heterojunction particles and modified ZIF-8 are adjusted accordingly, and the amounts of other raw materials remain unchanged.

[0088] Example 3

[0089] The only difference from Example 1 is that in step (3), the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 is different. The mass ratio of this embodiment is 5000:2000:20:100, the mass of kudzu root powder remains unchanged, and the masses of chitosan, silver heterojunction particles and modified ZIF-8 are adjusted accordingly, and the amounts of other raw materials remain unchanged.

[0090] Example 4

[0091] The only difference from Example 1 is that the mass ratio of glycerol to chitosan in step (3) is different. The mass ratio of this example is 10:100. Only the amount of glycerol is changed, and the amounts of other raw materials remain unchanged.

[0092] Example 5

[0093] The only difference from Example 1 is that the mass ratio of glycerol to chitosan in step (3) is different. The mass ratio of this example is 20:100. Only the amount of glycerol is changed, and the amounts of other raw materials remain unchanged.

[0094] Comparative Example 1

[0095] This comparative example provides a pure chitosan film (CS), and the specific steps are as follows: first, 2g of chitosan is dissolved in 100mL, 0.1% v / v acetic acid and stirred until completely dissolved. Then 0.06g of glycerol is added as a plasticizer and stirred until completely uniform. When the temperature of the kudzu root powder drops to 60°C, the chitosan solution is poured in and mixed and stirred for 30 minutes. Finally, the bubbles are removed after ultrasonication for 2 minutes. The film-forming solution is poured into a culture dish with a diameter of 15cm and dried in an oven at a constant temperature of 35°C for 36 hours to obtain a pure chitosan film (CS).

[0096] Comparative Example 2

[0097] This comparative example provides a pure chitosan and kudzu root powder mixed film (CS-K), and the specific steps are as follows: First, 2g of chitosan is dissolved in 100mL, 0.1% v / v acetic acid and stirred until completely dissolved. Then 5g of kudzu root powder is dispersed in 100g, 95°C water and stirred for 60min to complete the complete gelatinization of the kudzu root powder. Then 0.06g of glycerol is added as a plasticizer and stirred until completely uniform. When the temperature of the kudzu root powder drops to 60°C, the chitosan solution is poured in and mixed and stirred for 30 minutes. Finally, the bubbles are removed after 2 minutes of ultrasound. The film-forming solution is poured into a culture dish with a diameter of 15cm and dried in an oven at a constant temperature of 35°C for 36 hours to obtain a chitosan and kudzu root powder mixed film (CS-K).

[0098] Comparative Example 3

[0099] This comparative example provides a chitosan, kudzu root powder and PAE@ZIF-8 mixed membrane (CS-KP), and the specific steps are as follows: First, 2g of chitosan is dissolved in 100mL, 0.1% v / v acetic acid and stirred until completely dissolved. Then 5g of kudzu root powder is dispersed in 100g, 95°C water and stirred for 60min to complete the complete gelatinization of the kudzu root powder. Then 0.06g of glycerol is added as a plasticizer and stirred until completely uniform. When the temperature of the kudzu root powder drops to 60°C, the chitosan solution is poured in and mixed and stirred for 30 minutes. When the temperature of the solution drops to 40°C, 100mg of PAE@ZIF-8 is added and stirred for 20 minutes. Finally, the bubbles are removed after 2 minutes of ultrasound. The film-forming solution is poured into a culture dish with a diameter of 15cm and dried at a constant temperature of 35°C in an oven for 36 hours to obtain a chitosan, kudzu root powder and PAE@ZIF-8 mixed membrane (CS-KP).

[0100] Comparative Example 4

[0101] This comparative example 4 provides a commercially available PVC film.

[0102] Test Example 1

[0103] The antibacterial fresh-keeping films prepared in Example 1 and Comparative Examples 1-4 were subjected to antibacterial fresh-keeping tests:

[0104] Raspberries of similar size, color and freshness were selected for actual preservation experiments. Specifically, the raspberries were washed and disinfected with deionized water. Then the raspberries were wrapped with pure chitosan film (CS), chitosan and kudzu root powder mixed film (CS-K), chitosan and kudzu root powder and PAE@ZIF-8 mixed film (CS-KP), chitosan and kudzu root powder and PAE@ZIF-8 and AgH mixed film (CS-KP-AgH) and commercially available PVC film. At the same time, untreated raspberries were used as the control group. The above-treated raspberries were placed at room temperature to study the changes in their appearance and quality.

[0105] from Figure 1 The SEM images in the figure show that ZIF-8 is a dodecahedral structure with an average diameter of 90.56±17.31nm. After PAE modification, the nanoparticles changed from a dodecahedral structure to a spherical structure with a more uniform size and an average diameter of 42.65±3.79nm. The bulk structure of AgH has a rough surface with many small spherical particles attached. It is possible that small particles of silver oxide are attached to the surface of silver carbonate.

[0106] Please refer to Figure 2 In the infrared spectrum of PAE@ZIF-8, it can be observed that the intensity of many absorption bands of ZIF-8 is significantly weakened or disappears, indicating that PAE is mainly wrapped in the material or partially adsorbed on the surface of ZIF-8. -1 The absorption band at is the C=O characteristic peak of PAE, which proves the successful loading of PAE on ZIF-8. It can be observed that ZIF-8 and PAE@ZIF-8 have many very similar absorption bands, indicating that PAE@ZIF-8 has formed a complete structure.

[0107] The crystal structure of the composite film was studied by XRD analysis. Figure 3 As shown in the figure. The appearance of the peak near 20.5 degrees indicates the non-crystalline structure of chitosan. The addition of kudzu root powder and nanomaterials did not change the position of the peak, but weakened the peak intensity. This shows that hydrogen bonds are formed between chitosan and starch in kudzu root powder, which restricts the movement of molecular bonds and inhibits the crystallization process. It also shows the complete structure and successful synthesis of the nanocomposite film.

[0108] from Figure 4It can be seen that the raspberries in the control group lost water very quickly, and after 5 days they shrank to almost half their original size. The volume of the raspberries wrapped in CS and CS-K shrank slightly, but it can be observed that the raspberries in the CS group had holes due to a large amount of water loss. The raspberries wrapped in CS-KP began to turn white on the 5th day. The raspberries wrapped in commercially available PVC had mold on the 3rd day. This shows that CS-KP-AgH successfully extended the shelf life of raspberries.

[0109] Figure 5 The changes in the weight loss rate of raspberries are shown. The raspberries in the control group lost the fastest mass. On the 5th day, the mass loss exceeded half, reaching 54.92%. The mass loss rates of CS, CS-K, and CS-KP coated raspberries were 48.06%, 45.92%, and 44.83%, respectively. The weight loss rate of CS-KP-AgH packaged raspberries was smaller, at 36.22%. Although the mass loss of PVC-treated raspberries was smaller, it may be due to the airtightness of the film that the raspberries rotted faster. Therefore, the prepared nanocomposite film has a certain preservation effect.

[0110] Test Example 2

[0111] The performance of the antibacterial cling film prepared in Examples 1-7 was tested, and the results are shown in Table 1.

[0112]

[0113] As can be seen from Table 1, the composite film prepared in the embodiment of the present invention has a more excellent antibacterial and fresh-keeping effect. Comparative Examples 1-5 show that a single factor change will affect the water vapor permeability, film thickness, ABTS free radical scavenging rate and other properties of the film. By comparison, it is found that the composite film prepared in the present invention can have better barrier properties and antioxidant properties, and has a moderate thickness, can play an antibacterial role, and effectively prolong the shelf life of raspberries.

[0114] Example 1 is the optimal example. The antibacterial cling film prepared in Example 1 has low water vapor permeability and can effectively block external moisture; the film has a moderate thickness and a darker color, which can effectively block ultraviolet rays; it has strong antioxidant properties and good antibacterial properties.

[0115] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An antibacterial fresh-keeping composite film, characterized in that: The invention comprises a film-forming matrix and effective ingredients dispersed in the film-forming matrix, wherein the film-forming matrix comprises chitosan and kudzu root powder, the effective ingredients comprise modified ZIF-8 and silver heterojunction particles, and the modified ZIF-8 comprises a ZIF-8 carrier and paeonol loaded on the ZIF-8 carrier.

2. The antibacterial fresh-keeping composite film according to claim 1, characterized in that: The mass ratio of kudzu root powder, chitosan, the silver heterojunction particles and the modified ZIF-8 is (1000-10000): (1000-2000): (10-50): (50-300); Preferably, when preparing the modified ZIF-8, the molar ratio of zinc salt, imidazole organic ligand and paeonol is controlled to be 1:(2-34):(2.3-2.4); Preferably, the silver heterojunction particles include silver carbonate and silver oxide.

3. A method for preparing the antibacterial fresh-keeping composite film according to claim 1 or 2, characterized in that: include: In the process of preparing ZIF-8 material, paeonol is introduced, so that paeonol is loaded on the generated ZIF-8 material to obtain modified ZIF-8; Silver heterojunction particles are prepared by using a precipitation reaction of silver ions in a solution; The film-forming matrix, the silver heterojunction particles and the modified ZIF-8 are mixed to prepare a film-forming solution, and the film is formed using the film-forming solution.

4. The preparation method according to claim 3, characterized in that: The process of preparing the modified ZIF-8 comprises: Dissolving zinc salt and imidazole organic ligand respectively to obtain zinc salt solution and ligand solution, and mixing paeonol and organic solvent to obtain paeonol solution; The paeonol solution and the zinc salt solution are mixed, and then mixed with the ligand solution for reaction, followed by solid-liquid separation, and the obtained solid material is washed and dried; Preferably, the paeonol solution and the zinc salt solution are first mixed and stirred for 0.5 h to 2 h, and then mixed and stirred with the ligand solution for 2 h to 5 h.

5. The preparation method according to claim 4, characterized in that: The molar ratio of the zinc salt, the imidazole organic ligand and the paeonol is 1:(2-34):(2.3-2.4); Preferably, the zinc salt is Zn(NO3)2·6H2O, and the imidazole organic ligand is 2-methylimidazole; Preferably, the solvent used to prepare the zinc salt solution and the ligand solution is water, the solvent used to prepare the paeonol solution is an organic alcohol solvent, the concentration of the zinc salt solution is 0.05mmol / mL-0.20mmol / mL, the concentration of the ligand solution is 1.0mmol / mL-2.5mmol / mL, and the concentration of the paeonol solution is 0.05mmol / mL-0.20mmol / mL.

6. The preparation method according to claim 3, characterized in that: The preparation process of the silver heterojunction particles comprises: mixing silver nitrate, water and a surfactant to obtain a mixed solution, heating the mixed solution to 50° C.-70° C., mixing with carbonate for reaction for 2 h-6 h, then separating the solid from the liquid, and washing and drying the obtained solid material; Preferably, the surfactant is polyvinyl pyrrolidone with a molecular weight of 8000Mw-360000Mw; Preferably, the carbonate is selected from at least one of sodium carbonate and potassium carbonate.

7. The preparation method according to claim 6, characterized in that: The mass ratio of silver nitrate to the surfactant is 1:(8-10), and the molar ratio of silver nitrate to carbonate ions in the carbonate is 1:(1-3).

8. The preparation method according to claim 3, characterized in that: The process of preparing the film-forming solution comprises: Mixing and dissolving chitosan and acetic acid aqueous solution to obtain a chitosan solution; Disperse the kudzu root powder in hot water at 93°C-98°C and stir for 30-90 minutes to obtain a paste; The paste is mixed with a plasticizer, then cooled to 55°C-70°C and mixed with a chitosan solution for 10-60 minutes, then the silver heterojunction particles are added and stirred for 5-60 minutes, and when the temperature is reduced to 35°C-45°C, the modified ZIF-8 is mixed and stirred for 10-60 minutes, and then a defoaming treatment is performed; Preferably, the mass ratio of kudzu root powder, chitosan, the silver heterojunction particles and the modified ZIF-8 is (1000-10000): (1000-2000): (10-50): (50-300); Preferably, the plasticizer is glycerol, and the mass ratio of glycerol to chitosan is (10-50):100; Preferably, the volume fraction of acetic acid in the acetic acid aqueous solution is 0.05-0.2%, and the mass fraction of chitosan in the chitosan solution is 1%-2%; Preferably, the mass ratio of kudzu root powder to hot water is (1-10): (95-105).

9. The preparation method according to claim 8, characterized in that: The film-forming solution is poured into a film-forming container and then dried to form a film.

10. Use of the antibacterial and fresh-keeping composite film according to any one of claims 1 to 2 or the antibacterial and fresh-keeping composite film prepared by the preparation method according to any one of claims 3 to 9 in preparing antibacterial and fresh-keeping packaging materials.

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