Copper-doped lasting antibacterial fresh-keeping material as well as preparation method and application thereof

Abstract

According to the technical scheme, the copper-doped lasting antibacterial fresh-keeping material comprises a base body, an antibacterial nanofiber and copper ion loaded antibacterial hydrogel layer and a surface coating, the antibacterial nanofiber and copper ion loaded antibacterial hydrogel layer comprises antibacterial nanofibers and copper ion loaded antibacterial hydrogel, and the surface coating is coated with the antibacterial nanofibers and the copper ion loaded antibacterial hydrogel. The surface coating comprises microcapsules for contactable food products; the preparation method comprises the following steps: preparation of the copper-tannic acid coordination compound, preparation of the antibacterial nanofiber layer, preparation of the copper ion loaded antibacterial hydrogel, preparation of the substrate, interlayer compounding process, preparation of the sustained-release microcapsule coating, crosslinking and post-treatment. The humidity-responsive on-demand release of copper ions of the fresh-keeping material is realized, the antibacterial and fresh-keeping effects are good, the safety is high, and the environment-friendly effect is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical materials, and in particular to a copper-doped long-lasting antibacterial and fresh-keeping material, a preparation method thereof, and an application thereof. Background Art

[0002] Currently, commercial antimicrobial cling films on the market primarily rely on silver ion coatings or organic antimicrobial blending technologies, but these technologies have significant drawbacks. For example, silver ions are prone to excessive migration in acidic food environments. For example, when in contact with lemon juice, the migration amount may exceed 3.2 mg / kg, exceeding the limit set by the US Food and Drug Administration (FDA) in 21 CFR 175.300. Furthermore, organic antimicrobial agents such as triclosan may interfere with the human endocrine system, posing a potential health risk. Furthermore, the limited functionality of existing commercial antimicrobial cling films is a drawback. For example, the copper-doped carbon nanoparticle fruit preservative solution used in patent CN108576211A, while effective in preserving fruit, suffers from a "burst release" of copper ions, potentially exceeding 80% within 24 hours, resulting in an antimicrobial efficacy period of less than seven days. Furthermore, the film fails to effectively inhibit lipid oxidation, and its environmental sustainability is also a significant concern. Among the commonly used substrates for cling film, petroleum-based films (such as LDPE) are non-degradable, while purely bio-based films (such as PLA) suffer from a tensile strength drop of over 40% (according to ASTM D882 testing) due to copper particle agglomeration, making them difficult to meet the mechanical performance requirements for cold chain transportation. To address these issues, there is an urgent need to develop a cling film that can intelligently release copper ions in response to achieve better preservation effects, a longer antibacterial shelf life, and maintain excellent mechanical properties while maintaining environmentally friendly cling film materials. Summary of the Invention

[0003] In order to solve the existing technical problems, the present invention provides a copper-doped long-lasting antibacterial and fresh-keeping material, a preparation method and application thereof. Through the structural design of the copper and tannic acid coordinated hydrogel network (micrometer level), the humidity-responsive on-demand release of copper ions is achieved, with good antibacterial and fresh-keeping effects, high safety, and environmental friendliness.

[0004] A copper-doped long-lasting antibacterial and fresh-keeping material comprises a substrate, antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel layer, and a surface coating. The antibacterial nanofibers and the copper ion-loaded antibacterial hydrogel layer comprise antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel, and the surface coating comprises food-contactable microcapsules.

[0005] Furthermore, the antibacterial nanofibers contain copper ions.

[0006] Furthermore, the food-contactable microcapsules include chitosan microcapsules, gelatin microcapsules and perillaldehyde microcapsules.

[0007] Furthermore, the fresh-keeping material includes fresh-keeping film and fresh-keeping box.

[0008] A method for preparing a copper-doped long-lasting antibacterial and fresh-keeping material comprises the following steps: S1. Preparation of copper-tannic acid complex: tannic acid and copper sulfate are mixed, dissolved in deionized water, the pH value of the mixed solution of tannic acid and copper sulfate is adjusted to 3-5, and stirred evenly to form a stable copper-tannic acid complex; Furthermore, in S1, tannic acid and copper sulfate are mixed in a molar ratio of 2:1, and the weight ratio of the mixture of tannic acid and copper sulfate to deionized water is 1:20.

[0009] Preferably, the mixed solution of tannic acid and copper sulfate in S1 is stirred at 25-30° C. and 500 rpm for 2-3 hours.

[0010] Preferably, the pH value of the mixed solution of tannic acid and copper sulfate in S1 is 4.

[0011] S2. Preparation of an antibacterial nanofiber layer: Copper-tannic acid complex and polycaprolactone (PCL) solution are blended and ultrasonically dispersed, and then nanofibers are prepared by electrospinning to obtain an antibacterial nanofiber layer; Furthermore, the concentration of the polycaprolactone (PCL) solution in S2 is 8 wt %, and the solvents are dichloromethane and tetrahydrofuran, wherein the volume ratio of dichloromethane to tetrahydrofuran is (3-4):1; the copper-tannic acid coordination compound and the polycaprolactone (PCL) solution are blended in a mass ratio of 1:5.

[0012] Preferably, the volume ratio of dichloromethane to tetrahydrofuran in S2 is 4: 1. The volume ratio of dichloromethane to tetrahydrofuran further improves spinning uniformity.

[0013] Preferably, the ultrasonic dispersion time in S2 is 1 hour, the power is 300W; the voltage of the electrospinning process is 15kV~18kV, the receiving distance is 10cm~15cm, the spinning speed is 1mL / h, and the ambient humidity is ≤40%.

[0014] S3. Preparation of copper ion-loaded antibacterial hydrogel: Polyvinyl alcohol and sodium alginate were mixed and cross-linked in a Ca²⁺ environment. PNIPAm (poly (N-isopropylacrylamide)) microgel was then added and irradiated with ultraviolet light to form a hydrogel with a three-dimensional network structure. The hydrogel was then immersed in a copper citrate solution to fully swell and freeze-dried to obtain the copper ion-loaded antibacterial hydrogel. PNIPAm microgels exhibit a reversible volume phase transition near their critical solution temperature (approximately 32–35°C), a property not possessed by many traditional gels (such as polyacrylic acid and sodium alginate gels). PNIPAm microgels form a three-dimensional hydrogel network structure through a UV-induced grafting reaction. The micron-scale pore structure provides channels for the permeation and diffusion of water molecules, simultaneously providing the structural foundation for humidity-responsiveness. Under low humidity conditions (e.g., RH <60%), the coordination network shrinks due to dehydration, closing the pores and inhibiting the release of the active ingredient, copper ions. When the humidity rises (e.g., RH >80%), water molecules enter the network through capillary action, triggering partial dissociation of coordination bonds and pore expansion, accelerating the diffusion and release of the active ingredient. The hydrogel structure is immersed in a copper citrate solution to fully swell, achieving effective copper ion loading. After swelling, the water is removed by freeze-drying to facilitate subsequent composite with a matrix.

[0015] Furthermore, the polyvinyl alcohol in S3 is a polyvinyl alcohol aqueous solution with a concentration of 10wt%, the sodium alginate is a sodium alginate aqueous solution with a concentration of 2wt%, the polyvinyl alcohol and sodium alginate are mixed in a volume ratio of 3:1 and cross-linked in a 0.1M Ca²⁺ environment; the PNIPAm microgel is 5% of the total mass of the polyvinyl alcohol and sodium alginate; and the concentration of the copper citrate solution is 0.1mol / L.

[0016] Preferably, the wavelength of the ultraviolet light in S3 is 200nm~300nm, the intensity is 10mW / cm²~20mW / cm², and the ultraviolet light irradiation time is 30min.

[0017] Preferably, the swelling time in S3 is 6 h to 72 h, the swelling temperature is 25° C., and the freeze-drying temperature is -50° C., and the time is 24 h.

[0018] Preferably, the freeze drying in S3 adopts a gradient cooling method, specifically pre-freezing at -20°C for 2 hours and then cooling to -50°C for complete freeze drying.

[0019] S4, matrix preparation: preparing a matrix from a blend of polylactic acid (PLA) and polycaprolactone (PCL); S5, interlayer composite process: composite the copper ion loaded antibacterial hydrogel and antibacterial nanofiber layer on the upper layer of the substrate to obtain a double-layer composite structure; S6. Preparation of sustained-release microcapsule coating: Using a high-pressure sprayer, spray the food-contact microcapsule coating on the upper layer of the double-layer composite structure and fully dry it to obtain a three-layer composite structure; Furthermore, the food-contact microcapsule coating in S6 includes chitosan microcapsules, gelatin microcapsules, and perillaldehyde microcapsules in a mass ratio of 2:1:0.5. The solvent is a 1% by volume aqueous acetic acid solution with a solid content of 10%. The particle size of the chitosan microcapsules, gelatin microcapsules, and perillaldehyde microcapsules is controlled to be between 1 and 5 μm. By controlling the microcapsule particle size, the sustained-release effect is further enhanced.

[0020] Preferably, the thickness of the food-contactable microcapsule coating in S6 is 10-30 μm.

[0021] Preferably, the spraying pressure of the S6 medium-pressure sprayer is 0.3 MPa, the nozzle diameter is 0.5 mm, the drying temperature is 40° C., and the drying time is 30 min.

[0022] S7. Cross-linking and post-processing: The three-layer composite structure is cross-linked by ultraviolet light irradiation, and then argon gas is introduced to eliminate residual free radicals to complete the preparation of the fresh-keeping material.

[0023] After UV irradiation cross-linking, argon gas is introduced for a certain period of time to improve the hydrophilicity of the material.

[0024] Preferably, the wavelength of the ultraviolet light irradiation in S7 is 300-400 nm, the intensity is 50 mW / cm², the time is 1-2 min, the flow rate of argon is 10 L / min, the time is 10 min, and the purity of argon is ≥99.99%.

[0025] A copper-doped long-lasting antibacterial fresh-keeping material prepared by the above-mentioned method for preparing the copper-doped long-lasting antibacterial fresh-keeping material is used in food preservation, seed storage, flower preservation and packaging of sterile medical consumables.

[0026] By adopting the above technical solution, the present invention achieves the following beneficial effects: (1) The present invention innovatively proposes a synergistic system of "copper doping-dynamic coordination-multilayer composite". Through the structural design of the copper-tannic acid coordinated hydrogel network (micrometer level), the humidity-responsive on-demand release of copper ions is achieved. Copper ions are released according to the humidity gradient. The copper ion release rate is increased by 300% under high humidity, which not only improves the antibacterial effect of the preservation material, but also extends the antibacterial validity period.

[0027] (2) The outer layer of the fresh-keeping material of the present invention is coated with chitosan, gelatin, and perillaldehyde microcapsules, which is an edible coating that complies with the GB 4806.6-2016 standard and effectively blocks copper from direct contact with food, ensuring food safety. The copper-tannic acid fiber in the middle layer not only has an antibacterial effect, but also can scavenge free radicals (ORAC value ≥ 800μmol TE / g), providing an antioxidant and fresh-keeping effect. The polycaprolactone (PCL) matrix in the inner layer ensures the mechanical properties of the material, with an elongation at break exceeding 250%, meeting the requirements of cold chain transportation. The fresh-keeping material of the present invention breaks through the limitations of traditional fresh-keeping materials in terms of "antibacterial-mechanical-safety", and provides an innovative solution that combines intelligent antibacterial, antioxidant preservation, and zero-pollution degradation for high-end fresh food supply chains, flower supply chains, and medical sterile consumables packaging, and has broad application prospects and market potential.

[0028] (3) The fresh-keeping material of the present invention has closed-loop degradation properties. The disintegration rate of the fresh-keeping film under composting conditions can reach more than 95% within 30 days, which complies with the ISO 20200 standard. The released copper ions can be fixed by natural chelating agents, and the cumulative concentration in the soil is lower than 0.15 mg / kg (lower than the GB 15618-2018 agricultural land standard), achieving environmentally friendly closed-loop degradation.

[0029] (4) Existing antibacterial cling films are mostly doped with Ag⁺, which is relatively expensive. The present invention uses multiple components of copper, which is relatively low in cost.

[0030] (5) The preparation method of the copper-doped long-lasting antibacterial and fresh-keeping material prepared by the present invention is simple and has low requirements for production equipment. Although there are a few steps, the technical requirements for each step are low, and it is very easy to roll out on a large scale to form a modular process. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a comparison chart of copper ion release curves of the cling film of Example 1 under different humidity conditions; Figure 2 This is a comparison chart of the antibacterial ability of the cling film of Example 1 and Comparative Example 1; Figure 3 This is a comparison chart of the antibacterial properties of the cling film of Example 1 and Comparative Example 1; Figure 4 This is a comparison chart of the effects of cling film on the storage quality of bean sprouts in Example 1 and Comparative Example 1; Figure 5 This is a comparison chart of the effects of the cling film on the storage quality of green vegetables between Example 1 and Comparative Example 1; Figure 6 This is a comparison chart of the effects of the plastic wrap of Example 1 and Comparative Example 1 on the storage quality of bananas; Figure 7 This is a comparison chart of the effects of the plastic wrap of Example 1 and Comparative Example 1 on the storage quality of blueberries; Figure 8 This is a comparison chart of the effects of the cling film on the storage quality of fresh flowers between Example 1 and Comparative Example 1; Figure 9 This is a comparison chart of copper migration in the cling film of Example 1; Figure 10 This is a compost degradation rate curve of the fresh-keeping box in Example 4. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to specific embodiments. Example 1

[0033] A copper-doped long-lasting antibacterial fresh-keeping film comprises a substrate, antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel layer, and a surface coating. The antibacterial nanofibers and the copper ion-loaded antibacterial hydrogel layer comprise antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel, wherein the antibacterial nanofibers contain copper ions. The surface coating comprises food-contact microcapsules, which are chitosan, gelatin, and perillaldehyde microcapsules.

[0034] The method for preparing the copper-doped long-lasting antibacterial cling film of Example 1 comprises the following steps: S1. Preparation of copper-tannic acid complex: tannic acid and copper sulfate were mixed, dissolved in deionized water, the pH value of the mixed solution of tannic acid and copper sulfate was adjusted to 4, and stirred evenly to form a stable copper-tannic acid complex; Furthermore, in S1, tannic acid and copper sulfate are mixed in a molar ratio of 2:1, and the weight ratio of the mixture of tannic acid and copper sulfate to deionized water is 1:20.

[0035] Preferably, the mixed solution of tannic acid and copper sulfate in S1 is stirred at 25° C. and 500 rpm for 3 hours.

[0036] S2. Preparation of an antibacterial nanofiber layer: Copper-tannic acid complex and polycaprolactone (PCL) solution are blended and ultrasonically dispersed, and then nanofibers are prepared by electrospinning to obtain an antibacterial nanofiber layer; Furthermore, the concentration of the polycaprolactone (PCL) solution in S2 is 8 wt %, and the solvents are dichloromethane and tetrahydrofuran, wherein the volume ratio of dichloromethane to tetrahydrofuran is 3:1; the copper-tannic acid coordination compound and the polycaprolactone (PCL) solution are blended in a mass ratio of 1:5.

[0037] Preferably, the volume ratio of dichloromethane to tetrahydrofuran in S2 is 4:1.

[0038] Preferably, the ultrasonic dispersion time in S2 is 1 hour, the power is 300 W; the voltage of the electrospinning process is 15 kV, the receiving distance is 15 cm, the spinning speed is 1 mL / h, and the ambient humidity is ≤40%.

[0039] S3. Preparation of copper ion-loaded antibacterial hydrogel: Polyvinyl alcohol and sodium alginate were mixed and cross-linked in a Ca²⁺ environment. PNIPAm microgel was then added and irradiated with ultraviolet light to form a three-dimensional hydrogel network. The hydrogel was then immersed in a copper citrate solution to fully swell and freeze-dried to obtain the copper ion-loaded antibacterial hydrogel. Furthermore, the polyvinyl alcohol in S3 is a polyvinyl alcohol aqueous solution with a concentration of 10wt%, the sodium alginate is a sodium alginate aqueous solution with a concentration of 2wt%, the polyvinyl alcohol and sodium alginate are mixed in a volume ratio of 3:1 and cross-linked in a 0.1M Ca²⁺ environment; the PNIPAm microgel is 5% of the total mass of the polyvinyl alcohol and sodium alginate; and the concentration of the copper citrate solution is 0.1mol / L.

[0040] Preferably, the wavelength of the ultraviolet light in S3 is 250 nm, the intensity is 15 mW / cm², and the ultraviolet light irradiation time is 30 min.

[0041] Preferably, the swelling time in S3 is 6 hours, the swelling temperature is 25° C., and the freeze-drying temperature is -50° C., and the time is 24 hours.

[0042] Preferably, the freeze drying in S3 adopts a gradient cooling method, specifically pre-freezing at -20°C for 2 hours and then cooling to -50°C for complete freeze drying.

[0043] S4, matrix preparation: using a twin-screw extruder to extrude a blend of polylactic acid (PLA) and polycaprolactone (PCL) to obtain a matrix; Furthermore, the mass ratio of polylactic acid (PLA) to polycaprolactone (PCL) in S4 is 7:3.

[0044] Preferably, when the twin-screw extruder in S4 extrudes the cast polylactic acid (PLA) and polycaprolactone (PCL) blend, the melt index is 4 g / 10 min, the extrusion temperature is 200° C., the screw speed is 50 rpm, and the casting roller temperature is 60° C.

[0045] Preferably, the thickness of the substrate in S4 is 50 μm.

[0046] S5. Interlayer composite process: hot pressing the copper ion-loaded antibacterial hydrogel into a film, and then performing plasma treatment to obtain a copper ion-loaded antibacterial hydrogel layer. The antibacterial nanofiber layer and the copper ion-loaded antibacterial hydrogel layer are composited with the substrate by hot pressing on the upper layer of the substrate to obtain a double-layer composite structure; Preferably, the hot pressing in S5 is performed at a temperature of 90° C., a pressure of 5 MPa, and a time of 10 to 15 minutes. The plasma treatment is performed in an argon atmosphere with a power of 100 W and a time of 5 minutes.

[0047] S6. Preparation of sustained-release microcapsule coating: Using a high-pressure sprayer, spray the food-contact microcapsule coating on the upper layer of the double-layer composite structure and fully dry it to obtain a three-layer composite structure; Furthermore, the food-contact microcapsule coating in S6 includes chitosan microcapsules, gelatin microcapsules and perillaldehyde microcapsules in a mass ratio of 2:1:0.5, the solvent is 1% by volume acetic acid aqueous solution, and the solid content is 10%; the particle size of the chitosan microcapsules, gelatin microcapsules and perillaldehyde microcapsules is controlled at 4 μm.

[0048] Preferably, the thickness of the food-contactable microcapsule coating in S6 is 15 μm.

[0049] Preferably, the spraying pressure of the S6 medium-pressure sprayer is 0.3 MPa, the nozzle diameter is 0.5 mm, the drying temperature is 40° C., and the drying time is 30 min.

[0050] S7. Cross-linking and post-processing: The three-layer composite structure is cross-linked by ultraviolet light irradiation, and then argon gas is introduced to eliminate residual free radicals to complete the preparation of the plastic wrap.

[0051] Preferably, the wavelength of the ultraviolet light irradiation in S7 is 365 nm, the intensity is 50 mW / cm², the time is 1.5 min, the flow rate of argon is 10 L / min, the time is 10 min, and the purity of argon is ≥99.99%. Example 2

[0052] A copper-doped long-lasting antibacterial fresh-keeping film comprises a substrate, antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel layer, and a surface coating. The antibacterial nanofibers and the copper ion-loaded antibacterial hydrogel layer comprise antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel, wherein the antibacterial nanofibers contain copper ions. The surface coating comprises food-contact microcapsules, which are chitosan, gelatin, and perillaldehyde microcapsules.

[0053] The preparation method of the copper-doped long-lasting antibacterial cling film of this embodiment 2 comprises the following steps: S1. Preparation of copper-tannic acid complex: tannic acid and copper sulfate were mixed, dissolved in deionized water, the pH value of the mixed solution of tannic acid and copper sulfate was adjusted to 3, and stirred evenly to form a stable copper-tannic acid complex; Furthermore, in S1, tannic acid and copper sulfate are mixed in a molar ratio of 2:1, and the weight ratio of the mixture of tannic acid and copper sulfate to deionized water is 1:20.

[0054] Preferably, the mixed solution of tannic acid and copper sulfate in S1 is stirred at 30° C. and 500 rpm for 2 hours.

[0055] S2. Preparation of an antibacterial nanofiber layer: Copper-tannic acid complex and polycaprolactone (PCL) solution are blended and ultrasonically dispersed, and then nanofibers are prepared by electrospinning to obtain an antibacterial nanofiber layer; Furthermore, the concentration of the polycaprolactone (PCL) solution in S2 is 8 wt %, and the solvents are dichloromethane and tetrahydrofuran, wherein the volume ratio of dichloromethane to tetrahydrofuran is 4:1; the copper-tannic acid coordination compound and the polycaprolactone (PCL) solution are blended in a mass ratio of 1:5.

[0056] Preferably, the volume ratio of dichloromethane to tetrahydrofuran in S2 is 4:1.

[0057] Preferably, the ultrasonic dispersion time in S2 is 1 hour, the power is 300 W; the voltage of the electrospinning process is 18 kV, the receiving distance is 10 cm, the spinning speed is 1 mL / h, and the ambient humidity is ≤40%.

[0058] S3. Preparation of copper ion-loaded antibacterial hydrogel: Polyvinyl alcohol and sodium alginate were mixed and cross-linked in a Ca²⁺ environment. PNIPAm microgel was then added and irradiated with ultraviolet light to form a three-dimensional hydrogel network. The hydrogel was then immersed in a copper citrate solution to fully swell and freeze-dried to obtain the copper ion-loaded antibacterial hydrogel. Furthermore, the polyvinyl alcohol in S3 is a polyvinyl alcohol aqueous solution with a concentration of 10wt%, the sodium alginate is a sodium alginate aqueous solution with a concentration of 2wt%, the polyvinyl alcohol and sodium alginate are mixed in a volume ratio of 3:1 and cross-linked in a 0.1M Ca²⁺ environment; the PNIPAm microgel is 5% of the total mass of the polyvinyl alcohol and sodium alginate; and the concentration of the copper citrate solution is 0.1mol / L.

[0059] Preferably, the wavelength of the ultraviolet light in S3 is 200 nm, the intensity is 10 mW / cm², and the ultraviolet light irradiation time is 30 min.

[0060] Preferably, the swelling time in S3 is 6 hours, the swelling temperature is 25° C., and the freeze-drying temperature is -50° C., and the time is 24 hours.

[0061] Preferably, the freeze drying in S3 adopts a gradient cooling method, specifically pre-freezing at -20°C for 2 hours and then cooling to -50°C for complete freeze drying.

[0062] S4, matrix preparation: using a twin-screw extruder to extrude a blend of polylactic acid (PLA) and polycaprolactone (PCL) to obtain a matrix; Furthermore, the mass ratio of polylactic acid (PLA) to polycaprolactone (PCL) in S4 is 7:3.

[0063] Preferably, when the twin-screw extruder in S4 extrudes the cast polylactic acid (PLA) and polycaprolactone (PCL) blend, the melt index is 4 g / 10 min, the extrusion temperature is 180° C., the screw speed is 50 rpm, and the casting roller temperature is 60° C.

[0064] Preferably, the thickness of the substrate in S4 is 50 μm.

[0065] S5. Interlayer composite process: hot pressing the copper ion-loaded antibacterial hydrogel into a film, and then performing plasma treatment to obtain a copper ion-loaded antibacterial hydrogel layer. The antibacterial nanofiber layer and the copper ion-loaded antibacterial hydrogel layer are composited with the substrate by hot pressing on the upper layer of the substrate to obtain a double-layer composite structure; Preferably, the hot pressing in S5 is performed at a temperature of 90° C., a pressure of 5 MPa, and a time of 15 min; and the plasma treatment is performed in an argon atmosphere, with a power of 50 W and a time of 2 min.

[0066] S6. Preparation of sustained-release microcapsule coating: using a high-pressure sprayer to spray chitosan microcapsules, gelatin microcapsules, and perillaldehyde microcapsules onto the upper layer of the double-layer composite structure, and then fully drying to obtain a three-layer composite structure; Furthermore, the mass ratio of chitosan, gelatin and perillaldehyde in the chitosan microcapsule, gelatin microcapsule and perillaldehyde microcapsule coating in S6 is 2:1:0.5, the solvent is 1% by volume acetic acid aqueous solution, and the solid content is 10%; the particle size of the chitosan microcapsule, gelatin microcapsule and perillaldehyde microcapsule is controlled at 1 μm.

[0067] Preferably, the coating thickness of the chitosan microcapsules, gelatin microcapsules and perillaldehyde microcapsules in S6 is 10 μm.

[0068] Preferably, the spraying pressure of the S6 medium-pressure sprayer is 0.3 MPa, the nozzle diameter is 0.5 mm, the drying temperature is 40° C., and the drying time is 30 min.

[0069] S7. Cross-linking and post-processing: The three-layer composite structure is cross-linked by ultraviolet light irradiation, and then argon gas is introduced to eliminate residual free radicals to complete the preparation of the plastic wrap.

[0070] Preferably, the wavelength of the ultraviolet light irradiation in S7 is 300 nm, the intensity is 50 mW / cm², the time is 1 min, the flow rate of argon is 10 L / min, the time is 10 min, and the purity of argon is ≥99.99%. Example 3

[0071] A copper-doped long-lasting antibacterial fresh-keeping film comprises a substrate, antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel layer, and a surface coating. The antibacterial nanofibers and the copper ion-loaded antibacterial hydrogel layer comprise antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel, wherein the antibacterial nanofibers contain copper ions. The surface coating comprises food-contact microcapsules, which are chitosan, gelatin, and perillaldehyde microcapsules.

[0072] The preparation method of the copper-doped long-lasting antibacterial fresh-keeping film of this embodiment 3 comprises the following steps: S1. Preparation of copper-tannic acid complex: tannic acid and copper sulfate were mixed, dissolved in deionized water, the pH value of the mixed solution of tannic acid and copper sulfate was adjusted to 5, and stirred evenly to form a stable copper-tannic acid complex; Furthermore, in S1, tannic acid and copper sulfate are mixed in a molar ratio of 2:1, and the weight ratio of the mixture of tannic acid and copper sulfate to deionized water is 1:20.

[0073] Preferably, the mixed solution of tannic acid and copper sulfate in S1 is stirred at 30° C. and 500 rpm for 2 hours.

[0074] S2. Preparation of an antibacterial nanofiber layer: Copper-tannic acid complex and polycaprolactone (PCL) solution are blended and ultrasonically dispersed, and then nanofibers are prepared by electrospinning to obtain an antibacterial nanofiber layer; Furthermore, the concentration of the polycaprolactone (PCL) solution in S2 is 8 wt %, and the solvents are dichloromethane and tetrahydrofuran, wherein the volume ratio of dichloromethane to tetrahydrofuran is 4:1; the copper-tannic acid coordination compound and the polycaprolactone (PCL) solution are blended in a mass ratio of 1:5.

[0075] Preferably, the volume ratio of dichloromethane to tetrahydrofuran in S2 is 4:1.

[0076] Preferably, the ultrasonic dispersion time in S2 is 1 hour, the power is 300 W; the voltage of the electrospinning process is 18 kV, the receiving distance is 10 cm, the spinning speed is 1 mL / h, and the ambient humidity is ≤40%.

[0077] S3. Preparation of copper ion-loaded antibacterial hydrogel: Polyvinyl alcohol and sodium alginate were mixed and cross-linked in a Ca²⁺ environment. PNIPAm microgel was then added and irradiated with ultraviolet light to form a three-dimensional hydrogel network. The hydrogel was then immersed in a copper citrate solution to fully swell and freeze-dried to obtain the copper ion-loaded antibacterial hydrogel. Furthermore, the polyvinyl alcohol in S3 is a polyvinyl alcohol aqueous solution with a concentration of 10wt%, the sodium alginate is a sodium alginate aqueous solution with a concentration of 2wt%, the polyvinyl alcohol and sodium alginate are mixed in a volume ratio of 3:1 and cross-linked in a 0.1M Ca²⁺ environment; the PNIPAm microgel is 5% of the total mass of the polyvinyl alcohol and sodium alginate; and the concentration of the copper citrate solution is 0.1mol / L.

[0078] Preferably, the wavelength of the ultraviolet light in S3 is 300 nm, the intensity is 20 mW / cm², and the ultraviolet light irradiation time is 30 min.

[0079] Preferably, the swelling time in S3 is 72 hours, the swelling temperature is 25° C., and the freeze-drying temperature is -50° C., and the time is 24 hours.

[0080] Preferably, the freeze drying in S3 adopts a gradient cooling method, specifically pre-freezing at -20°C for 2 hours and then cooling to -50°C for complete freeze drying.

[0081] S4, matrix preparation: using a twin-screw extruder to extrude a blend of polylactic acid (PLA) and polycaprolactone (PCL) to obtain a matrix; Furthermore, the mass ratio of polylactic acid (PLA) to polycaprolactone (PCL) in S4 is 7:3.

[0082] Preferably, when the twin-screw extruder in S4 extrudes the cast polylactic acid (PLA) and polycaprolactone (PCL) blend, the melt index is 4 g / 10 min, the extrusion temperature is 200° C., the screw speed is 50 rpm, and the casting roller temperature is 60° C.

[0083] Preferably, the thickness of the substrate in S4 is 50 μm.

[0084] S5. Interlayer composite process: hot pressing the copper ion-loaded antibacterial hydrogel into a film, and then performing plasma treatment to obtain a copper ion-loaded antibacterial hydrogel layer. The antibacterial nanofiber layer and the copper ion-loaded antibacterial hydrogel layer are composited with the substrate by hot pressing on the upper layer of the substrate to obtain a double-layer composite structure; Preferably, the hot pressing in S5 is performed at a temperature of 90° C., a pressure of 5 MPa, and a time of 10 min; and the plasma treatment is performed in an argon atmosphere, with a power of 100 W and a time of 5 min.

[0085] S6. Preparation of sustained-release microcapsule coating: using a high-pressure sprayer to spray chitosan microcapsules, gelatin microcapsules, and perillaldehyde microcapsules onto the upper layer of the double-layer composite film, and then fully drying to obtain a three-layer composite film; Furthermore, the mass ratio of chitosan, gelatin and perillaldehyde in the chitosan microcapsule, gelatin microcapsule and perillaldehyde microcapsule coating in S6 is 2:1:0.5, the solvent is 1% by volume acetic acid aqueous solution, and the solid content is 10%; the particle size of the chitosan microcapsule, gelatin microcapsule and perillaldehyde microcapsule is controlled at 5 μm.

[0086] Preferably, the coating thickness of the chitosan microcapsules, gelatin microcapsules and perillaldehyde microcapsules in S6 is 20 μm.

[0087] Preferably, the spraying pressure of the S6 medium-pressure sprayer is 0.3 MPa, the nozzle diameter is 0.5 mm, the drying temperature is 40° C., and the drying time is 30 min.

[0088] S7. Cross-linking and post-processing: The three-layer composite structure is cross-linked by ultraviolet light irradiation, and then argon gas is introduced to eliminate residual free radicals to complete the preparation of the plastic wrap.

[0089] Preferably, the wavelength of the ultraviolet light irradiation in S7 is 400 nm, the intensity is 50 mW / cm², the time is 2 min, the flow rate of argon is 10 L / min, the time is 10 min, and the purity of argon is ≥99.99%. Example 4

[0090] A copper-doped long-lasting antibacterial fresh-keeping box comprises a substrate, an antibacterial nanofiber and a copper ion-loaded antibacterial hydrogel layer, and a surface coating. The antibacterial nanofiber and the copper ion-loaded antibacterial hydrogel layer comprise antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel, wherein the antibacterial nanofibers contain copper ions. The surface coating comprises food-contact microcapsules, which are chitosan, gelatin, and perillaldehyde microcapsules.

[0091] A method for preparing a copper-doped long-lasting antibacterial fresh-keeping box comprises the following steps: S1. Preparation of copper-tannic acid complex: tannic acid and copper sulfate are mixed, dissolved in deionized water, the pH value of the mixed solution of tannic acid and copper sulfate is adjusted to 3-5, and stirred evenly to form a stable copper-tannic acid complex; Furthermore, in S1, tannic acid and copper sulfate are mixed in a molar ratio of 2:1, and the weight ratio of the mixture of tannic acid and copper sulfate to deionized water is 1:20.

[0092] Preferably, the mixed solution of tannic acid and copper sulfate in S1 is stirred at 25-30° C. and 500 rpm for 2-3 hours.

[0093] Preferably, the pH value of the mixed solution of tannic acid and copper sulfate in S1 is 4.

[0094] S2. Preparation of an antibacterial nanofiber layer: Copper-tannic acid complex and polycaprolactone (PCL) solution are blended and ultrasonically dispersed, and then nanofibers are prepared by electrospinning to obtain an antibacterial nanofiber layer; Furthermore, the concentration of the polycaprolactone (PCL) solution in S2 is 8 wt %, and the solvents are dichloromethane and tetrahydrofuran, wherein the volume ratio of dichloromethane to tetrahydrofuran is (3-4):1; the copper-tannic acid coordination compound and the polycaprolactone (PCL) solution are blended in a mass ratio of 1:5.

[0095] Preferably, the volume ratio of dichloromethane to tetrahydrofuran in S2 is 4:1.

[0096] Preferably, the ultrasonic dispersion time in S2 is 1 hour, the power is 300W; the voltage of the electrospinning process is 15kV~18kV, the receiving distance is 10cm~15cm, the spinning speed is 1mL / h, and the ambient humidity is ≤40%.

[0097] S3. Preparation of copper ion-loaded antibacterial hydrogel: Polyvinyl alcohol and sodium alginate were mixed and cross-linked in a Ca²⁺ environment. PNIPAm (poly (N-isopropylacrylamide)) microgel was then added and irradiated with ultraviolet light to form a hydrogel with a three-dimensional network structure. The hydrogel was then immersed in a copper citrate solution to fully swell and freeze-dried to obtain the copper ion-loaded antibacterial hydrogel. Furthermore, the polyvinyl alcohol in S3 is a polyvinyl alcohol aqueous solution with a concentration of 10wt%, the sodium alginate is a sodium alginate aqueous solution with a concentration of 2wt%, the polyvinyl alcohol and sodium alginate are mixed in a volume ratio of 3:1 and cross-linked in a 0.1M Ca²⁺ environment; the PNIPAm microgel is 5% of the total mass of the polyvinyl alcohol and sodium alginate; and the concentration of the copper citrate solution is 0.1mol / L.

[0098] Preferably, the wavelength of the ultraviolet light in S3 is 200nm~300nm, the intensity is 10mW / cm²~20mW / cm², and the ultraviolet light irradiation time is 30min.

[0099] Preferably, the swelling time in S3 is 6 h to 72 h, the swelling temperature is 25° C., the freeze-drying temperature is -50° C., and the time is 24 h.

[0100] Preferably, the freeze drying in S3 adopts a gradient cooling method, specifically pre-freezing at -20°C for 2 hours and then cooling to -50°C for complete freeze drying.

[0101] S4. Matrix preparation: After drying the blend of polylactic acid (PLA) and polycaprolactone (PCL), injection molding is performed using a twin-screw injection molding machine, and cooling is performed to obtain a matrix; the surface has a micron-scale pore structure to enhance interlayer bonding; Furthermore, the mass ratio of polylactic acid (PLA) to polycaprolactone (PCL) in S4 is 7:3.

[0102] Preferably, the injection molding temperature of the twin-screw injection molding machine in S4 is 180-200° C., the mold temperature is 60° C., and the holding pressure is 80 MPa.

[0103] Preferably, the thickness of the substrate in S4 is 1-2 mm.

[0104] S5, interlayer composite process: The copper ion-loaded antibacterial hydrogel is dispersed in deionized water to form a 5wt% slurry, which is evenly sprayed on the inner wall of the substrate using a high-pressure sprayer; the antibacterial nanofiber layer is cut and laid flat on the inner wall of the substrate, and then composited with the substrate through a hot pressing process (temperature 90°C, pressure 5MPa, time 10min) to obtain a double-layer composite structure; Preferably, the spraying pressure of the high-pressure sprayer in S5 is 0.4 MPa, the drying temperature is 40° C., and the time is 30 min; the temperature of the hot pressing is 90° C., the pressure is 5 MPa, and the time is 10 min.

[0105] S6. Preparation of sustained-release microcapsule coating: Using a high-pressure sprayer, spray the food-contact microcapsule coating on the upper layer of the double-layer composite structure and fully dry it to obtain a three-layer composite structure; Furthermore, the food-contact microcapsule coating in S6 includes chitosan microcapsules, gelatin microcapsules, and perillaldehyde microcapsules in a mass ratio of 2:1:0.5. The solvent is a 1% by volume aqueous acetic acid solution with a solid content of 10%. The particle size of the chitosan microcapsules, gelatin microcapsules, and perillaldehyde microcapsules is controlled to be between 1 and 5 μm. By controlling the microcapsule particle size, the sustained-release effect is further enhanced.

[0106] Preferably, the thickness of the food-contactable microcapsule coating in S6 is 10-30 μm.

[0107] Preferably, the spraying pressure of the S6 medium-pressure sprayer is 0.3 MPa, the nozzle diameter is 0.5 mm, the drying temperature is 40° C., and the drying time is 30 min.

[0108] S7. Cross-linking and post-processing: The three-layer composite structure is cross-linked by ultraviolet light irradiation, and then argon gas is introduced to eliminate residual free radicals to complete the preparation of the fresh-keeping box.

[0109] After UV irradiation cross-linking, argon gas is introduced for a certain period of time to improve the hydrophilicity of the material.

[0110] Preferably, the wavelength of the ultraviolet light irradiation in S7 is 300-400 nm, the intensity is 50 mW / cm², the time is 1-2 min, the flow rate of argon is 10 L / min, the time is 10 min, and the purity of argon is ≥99.99%.

[0111] Furthermore, the copper-doped durable antibacterial fresh-keeping box is provided with a sealing cover, which includes a substrate, antibacterial nanofibers and a copper ion-loaded antibacterial hydrogel layer and a surface coating. The preparation method of the sealing cover is as described in S1-S7, and the sealing cover has a built-in silicone sealing ring.

[0112] Preferably, the sealing cover includes a substrate, a copper ion-loaded antibacterial hydrogel layer and a surface coating. The preparation method of the sealing cover includes S3-S7, wherein S5 is an interlayer composite process: the copper ion-loaded antibacterial hydrogel is dispersed in deionized water to form a 5wt% slurry, which is evenly sprayed on the inner wall of the substrate by a high-pressure sprayer to obtain a double-layer composite structure; a silicone sealing ring is embedded in the sealing cover. Example 5

[0113] The fresh-keeping materials prepared in Examples 1 to 4 are used for packaging fresh foods such as fruits, vegetables, meat, and seafood, as well as for storing seeds. They can also be used for wrapping flowers to preserve them, and for packaging sterile consumables.

[0114] Comparative Example 1

[0115] Comparative Example 1 is a silver ion antibacterial cling film sold in supermarkets, the brand is *jie. Comparative Example 2

[0116] Comparative Example 2 is a silver ion antibacterial fresh-keeping box sold in supermarkets, the brand is Le** Buckle.

[0117] (1) Copper ion humidity responsive release test The experiment was carried out in a constant temperature and humidity chamber. A saturated solution of magnesium nitrate was used to simulate a 50% relative humidity environment, and a saturated solution of potassium sulfate was used to simulate a 90% relative humidity environment. 2 The cling film prepared in Example 1 was used as a single sample. Three parallel samples were set for each sample. The sampling frequencies were 0 h (initial), 2 h, 4 h, 6 h, 8 h, 12 h, and 24 h. A copper ion concentration standard curve was configured. The copper ion concentration in the sample was measured using an inductively coupled plasma mass spectrometer. The obtained data was processed and plotted into a dotted line graph, as shown in FIG. Figure 1 shown.

[0118] from Figure 1It can be clearly seen that under high relative humidity conditions, the copper ion release performance of the cling film of Example 1 is much higher than that under low relative humidity conditions. It can be seen that the cling film of Example 1 can release copper ions according to humidity responsiveness. As the storage time of fresh products increases, the released water vapor gradually accumulates, and the humidity in the storage environment gradually increases, which is more conducive to bacterial growth. The existing cling film produces an explosive release of copper ions at the beginning of storage. As the storage time of fresh products increases, it is unable to release sufficient copper ions to prevent bacterial growth. The cling film of Example 1 releases copper ions in a more intelligent response to the humidity of the fresh storage environment, more reasonably inhibiting bacterial proliferation. The cling film of Example 1 has a better antibacterial effect and achieves a longer shelf life.

[0119] (2) Antibacterial test The antibacterial experiment was carried out using a coating method, strictly following the national standard GB / T2591 and the Japanese JIS Z2801-2000 standard. The cling film of Example 1 and Comparative Example 1 was cut into 50mm×20mm film samples, and 300μL of bacterial solution with a concentration of 1.0×10^5 CFU / mL was dripped on the surface of the glass slide. Subsequently, sterilized tweezers were used to clamp the film samples of Example 1 and Comparative Example 1, gently cover the surface of the glass slide, and ensure that the surface was flat so that the bacteria evenly contacted the glass slide and the film sample. Then, the glass slide was placed in a constant temperature incubator with a humidity greater than 90% and a temperature of 37°C for 24 hours. After the incubation was completed, the glass slide covered with bacteria was removed, and 15mL of PBS eluent was used to repeatedly rinse the bacteria on the surface of the film sample and the glass slide. In order to ensure the complete collection of bacteria on the surface of the film sample and the glass slide, ultrasonic vibration was used to assist in cleaning. The washed bacteria were collected in a beaker together with the liquid and thoroughly mixed. Then, take 100 μL of bacterial liquid from the beaker and drop it into the culture dish containing nutrient agar medium. After spreading it evenly with a triangular spreading stick, place it in the incubator at 37°C and culture it for 24 hours. After the culture is completed, take out the culture dish, count the bacteria, and calculate the sterilization rate based on the number of bacteria. The results are as follows: Figure 2 shown.

[0120] Figure 2 The vertical axis is the sterilization rate, from Figure 2 The results show that the sterilization rate of the cling film of Example 1 is better than that of the cling film of Comparative Example 1.

[0121] The cling film of Example 1 and Comparative Example 1 were cut into 1 cm 2 The membrane sample was placed in a culture dish inoculated with the mixed bacterial solution and cultured in a 37°C incubator for 24 hours. Figure 3 shown.

[0122] from Figure 3It can be clearly seen from the results that there are no visible colonies in the area covered by the cling film of Example 1, while the surface of the area covered by the cling film of Comparative Example 1 is covered with a large number of colonies.

[0123] (3) Freshness preservation test Common varieties of apples on the market were selected and covered and packaged with the plastic wrap of Example 1 and the plastic wrap of Comparative Example 1, respectively. Apples without any packaging were used as a blank control group. The apples were stored at room temperature for 28 days and the freshness index test was performed. The weight loss rate and sensory evaluation of the apples were recorded. The results are shown in Tables 1 and 2. Table 1 Effects of different plastic wraps on apple weight loss rate As can be seen from the results in Table 1, at room temperature, the weight loss rate of apples preserved without any plastic wrap in the blank control group was 7.7% over 28 days, the weight loss rate of apples preserved with the plastic wrap of Comparative Example 1 was 5.1% over 28 days, and the weight loss rate of apples preserved with the plastic wrap of Example 1 was only 3.7% over 28 days, indicating that the plastic wrap of Example 1 has a good preservation effect and is significantly better than the plastic wrap of Comparative Example 1.

[0124] Table 2 Sensory evaluation of apples stored for 28 days using different plastic wraps Types of plastic wrap Appearance Flesh color and flavor Blank control group The skin is completely dry and wrinkled with a lot of black spots, and the flavor is significantly reduced Not recommended for consumption Comparative Example 1 Some parts of the apple surface are still shiny, but the overall skin is shriveled. The flesh is yellow-white and basically edible Example 1 The apples are plump and are basically in the best eating state. The flesh is crisp and can be stored for a period of time As can be seen from the results in Table 2, at room temperature, the appearance and flavor of the apples in the blank control group that were not preserved with any plastic wrap seriously deteriorated after 28 days and were no longer edible; the appearance and flavor of the apples preserved with the plastic wrap of Comparative Example 1 significantly deteriorated after 28 days, but were still barely edible; while the appearance and flavor of the apples preserved with the plastic wrap of Example 1 remained essentially unchanged after 28 days, maintaining the optimal edible state, indicating that the plastic wrap of Example 1 had a good preservation effect and was significantly superior to the plastic wrap of Comparative Example 1.

[0125] In order to comprehensively compare the effects of the cling film of Example 1 and Comparative Example 1 on the storage quality of various fruits and vegetables, four fruits and vegetables, bean sprouts, green vegetables, bananas and blueberries, were selected for a five-day fresh-keeping performance comparison test. The cling film of Example 1 and the cling film of Comparative Example 1 were used to cover and package the fruits and vegetables, respectively, and stored at room temperature for 5 days. The fresh-keeping performance of the four fruits and vegetables was recorded. The specific results are as follows: Figures 4 to 7 and shown in Table 3.

[0126] Table 3 Comparison of the effects of different plastic wraps on the storage quality of fruits and vegetables Sample Group Comparative Example 1 Example 1 bean sprouts Under light conditions, the bean sprouts sprouted on the third day and were inedible; they began to rot on the fifth day. Under light conditions, the bean sprouts remained fresh for 5 days, but the moisture at the bottom caused some of the bean sprouts to rot. Green vegetables On the third day, the leaves of the vegetables became dull and soft, and cuts and damage appeared on the leaves; on the fifth day, mold spots appeared on the leaves and the leaves turned brown. There was no obvious change in the green vegetables for 5 days, the leaves were shiny and green. banana On the third day, a small amount of brown spots appeared on the bananas, with no noticeable odor; on the fifth day, the brown spots expanded in size and had an alcohol smell. There are no obvious brown spots on the bananas until a small amount of brown spots appear on the 5th day, and the alcohol smell is lighter. blueberry On the third day, the blueberry skin will shrink, lose its luster, and become soft to the touch. The flesh will ooze juice; on the fifth day, white fuzz will appear on the surface. The blueberries remained intact for 5 days without any obvious changes in characteristics. from Figures 4 to 7 As can be seen from Table 3, the cling film of Example 1 performs excellently in the storage of bean sprouts, green vegetables, bananas and blueberries, far exceeding the fresh-keeping performance of the cling film of Comparative Example 1.

[0127] Select common flowers on the market, cover and package them with the cling film of Example 1 and the cling film of Comparative Example 1, respectively, store them at 5°C for 21 days, and record the freshness of the flowers. The specific results are as follows: Figure 8 shown.

[0128] from Figure 8 It can be seen that the cling film of Example 1 performs well in preserving flowers and still maintains the color and moisture of the flowers, while the flowers wrapped with the cling film of Comparative Example 1 have yellow petals and lack of water. The cling film of Example 1 far exceeds the cling film of Comparative Example 1 in preserving flowers.

[0129] Common mango varieties on the market were selected and wrapped with the fresh-keeping box of Example 4, the fresh-keeping box of Comparative Example 2, and the plastic wrap of Comparative Example 1, respectively, and then packed in the fresh-keeping box of Comparative Example 2. The mangoes were stored at 5° C. for 15 days, and the fresh-keeping index test was performed. The weight loss rate and sensory evaluation of the mangoes were recorded. The results are shown in Table 4.

[0130] Table 4 Comparison of fresh-keeping box test results Group Weight loss rate (%) Total colony count (CFU / g) Sensory score (1-5 points) Comparative Example 2 8.2 <![CDATA[1.2×10 6 ]]> 2.0 (severe mildew) Comparative Example 1+Comparative Example 2 5.5 <![CDATA[3.5×10 4 ]]> 3.5 (slight browning) Example 4 2.1 ＜10² 4.8 (fresh color) From the results in Table 4, it can be seen that compared with the comparative example, the fresh-keeping box of Example 4 significantly inhibits the proliferation of microorganisms, the weight loss rate is reduced by 75%, and the sensory quality is close to that of fresh mangoes. It can be seen that the fresh-keeping box of Example 4 has a good preservation effect.

[0131] (4) Copper ion migration test In order to verify the safety of the cling film, a copper ion migration experiment was conducted with reference to GB 31604.1-2015 "General Rules for Migration Tests of Food Contact Materials" and GB4806.7-2016 "Plastic Materials and Products for Food Contact". The specific method is as follows: the cling film of Example 1 was cut into 6 dm² squares and exposed to 1 kg of different food simulants. Three food simulants were selected, namely 10% volume fraction ethanol solution (representing non-acidic food), 4% volume fraction acetic acid solution (representing acidic food), and a certain brand of edible oil. The cling film was soaked at 37°C for 24 hours, and then filtered to measure the copper content in the food simulants. The copper content was determined by atomic absorption spectrometry. The test results are as follows: Figure 9 shown.

[0132] from Figure 9 The results show that the copper migration amount of the cling film of Example 1 is 0.2 mg / kg in ethanol solution, 0.5 mg / kg in edible oil, and 0.6 mg / kg in acetic acid, which are all far lower than the 5.0 mg / kg specified in the national standard, indicating that Example 1 has safe biological toxicity.

[0133] (5) Degradability test In response to environmentally friendly requirements, the cling film of Example 1 was subjected to a degradation test to verify its natural degradation performance and copper ion metal contamination. The 30-day disintegration rate and organic matter conversion rate were measured using a dynamic composting box method, the copper ion release and heavy metal bioavailability were measured using an acetate buffer method, and the soil copper accumulation rate was measured using an inductively coupled plasma method. Reference standards include ISO 20200, GB 15618-2018, HJ 557-2010, and ASTM D5511. The final test results are shown in Table 5.

[0134] Table 5 Degradability test results Test indicators Test results Standard requirements Conclusion 30-day disintegration rate ≥95% ISO 20200 ≥90% meet the standards Copper ion release ≤0.08 mg / kg·d ASTM D5511 Controllable chelation Cumulative concentration of soil copper 0.12±0.03 mg / kg GB 15618-2018 ≤0.2 mg / kg Meet agricultural land standards Organic matter conversion rate 89.7% ISO 20200 ≥85% High-quality compost products Heavy metal bioavailability Not detected HJ 557-2010 Environmental safety As can be seen from Table 5, the cling film of Example 1 can achieve a 30-day disintegration rate of over 95% under composting conditions (in compliance with ISO 20200 standards), and the released copper ions can be fixed by natural chelating agents. The cumulative concentration in the soil is lower than 0.15 mg / kg (lower than the GB 15618-2018 agricultural land standard), and no heavy metals are detected. This shows that the cling film of Example 1 achieves environmentally friendly closed-loop degradation.

[0135] The fresh-keeping box of Example 4 was subjected to a degradation test. The fresh-keeping box of Example 4 and commercially available PLA fresh-keeping boxes and PP fresh-keeping boxes (Comparative Example 2) were subjected to a 60-day degradation test using the dynamic composting box method (ISO 20200). The results are as follows: Figure 10 As shown. Figure 10 The results show that the mass residual rate of the fresh-keeping box of Example 4 is only 8.3%, the mass residual rate of the ordinary PLA fresh-keeping box is 81.6%, and the mass residual rate of the petroleum-based PP fresh-keeping box is 93.7%. It can be seen that the mass residual rate of the fresh-keeping box of Example 4 is significantly lower than that of the ordinary PLA fresh-keeping box and the petroleum-based PP fresh-keeping box, which fully proves that the fresh-keeping box of Example 4 has excellent compost degradation performance and can achieve a disintegration rate of more than 90% within 60 days, fully meeting the degradation requirements of environmentally friendly materials.

Claims

1. A copper-doped long-lasting antibacterial and fresh-keeping material, characterized by: The invention comprises a matrix, an antibacterial nanofiber and copper ion loaded antibacterial hydrogel layer and a surface coating. The antibacterial nanofiber and copper ion loaded antibacterial hydrogel layer comprises antibacterial nanofiber and copper ion loaded antibacterial hydrogel, and the surface coating comprises microcapsules that can contact food.

2. The copper-doped long-lasting antibacterial fresh-keeping material according to claim 1, characterized in that: The antibacterial nanofibers contain copper ions.

3. The copper-doped long-lasting antibacterial fresh-keeping material according to claim 1, characterized in that: The food-contact microcapsules include chitosan, gelatin and perillaldehyde microcapsules.

4. The copper-doped long-lasting antibacterial cling film according to claim 1, characterized in that: The fresh-keeping materials include fresh-keeping films and fresh-keeping boxes.

5. The copper-doped long-lasting antibacterial fresh-keeping film according to claim 4, characterized in that: The fresh-keeping box is provided with a sealing cover, which comprises a base, a copper ion-loaded antibacterial hydrogel layer and a surface coating, and a silicone sealing ring is embedded in the sealing cover.

6. The method for preparing a copper-doped long-lasting antibacterial fresh-keeping material according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Preparation of copper-tannic acid complex: tannic acid and copper sulfate are mixed, dissolved in deionized water, the pH value of the mixed solution of tannic acid and copper sulfate is adjusted to 3-5, and stirred evenly to form a stable copper-tannic acid complex; S2. Preparation of an antibacterial nanofiber layer: Copper-tannic acid complex and polycaprolactone solution are blended and ultrasonically dispersed, and then nanofibers are prepared by electrospinning to obtain an antibacterial nanofiber layer; S3. Preparation of copper ion-loaded antibacterial hydrogel: Polyvinyl alcohol and sodium alginate were mixed and cross-linked in a Ca²⁺ environment. PNIPAm microgel was then added and irradiated with ultraviolet light to form a three-dimensional hydrogel network. The hydrogel was then immersed in a copper citrate solution to fully swell and freeze-dried to obtain the copper ion-loaded antibacterial hydrogel. S4, matrix preparation: preparing a matrix from a blend of polylactic acid (PLA) and polycaprolactone (PCL); S5, interlayer composite process: composite the copper ion loaded antibacterial hydrogel and antibacterial nanofiber layer on the upper layer of the substrate to obtain a double-layer composite structure; S6. Preparation of sustained-release microcapsule coating: Using a high-pressure sprayer, spray the food-contact microcapsule coating on the upper layer of the double-layer composite structure and fully dry it to obtain a three-layer composite structure; S7. Cross-linking and post-processing: The three-layer composite structure is cross-linked by ultraviolet irradiation, and then argon gas is introduced to eliminate residual free radicals to complete the preparation of the fresh-keeping material.

7. The method for preparing a copper-doped long-lasting antibacterial fresh-keeping material according to claim 6, characterized in that: In the S1, tannic acid and copper sulfate are mixed in a molar ratio of 2:1, and the weight ratio of the mixture of tannic acid and copper sulfate to deionized water is 1:20; the concentration of the polycaprolactone solution in the S2 is 8wt%, and the solvents are dichloromethane and tetrahydrofuran, wherein the volume ratio of dichloromethane to tetrahydrofuran is (3-4):1; the copper-tannic acid complex and the polycaprolactone solution are blended in a mass ratio of 1:

5.

8. The method for preparing a copper-doped long-lasting antibacterial fresh-keeping material according to claim 6, characterized in that: The polyvinyl alcohol in S3 is a 10wt% polyvinyl alcohol aqueous solution, the sodium alginate is a 2wt% sodium alginate aqueous solution, the polyvinyl alcohol and sodium alginate are mixed in a volume ratio of 3:1 and cross-linked in a 0.1M Ca²⁺ environment; the PNIPAm microgel is 5% of the total mass of the polyvinyl alcohol and sodium alginate; and the concentration of the copper citrate solution is 0.1mol / L.

9. The method for preparing a copper-doped long-lasting antibacterial fresh-keeping material according to claim 6, characterized in that: The food-contact microcapsule coating in S6 includes chitosan microcapsules, gelatin microcapsules and perillaldehyde microcapsules in a mass ratio of 2:1:0.5, the solvent is 1% by volume acetic acid aqueous solution, and the solid content is 10%; the particle size of the chitosan microcapsules, gelatin microcapsules and perillaldehyde microcapsules is controlled at 1 to 5 μm.

10. Use of the copper-doped long-lasting antibacterial preservative material prepared by the method for preparing a copper-doped long-lasting antibacterial preservative material according to any one of claims 6 to 9 in food preservation, seed storage, flower preservation, and packaging of sterile medical consumables.

Images