Degradable preservative film and preparation method thereof

Abstract

The invention discloses a degradable preservative film and a preparation method thereof. The film takes nano chitosan / agarose in a ratio of 1: 1 as a matrix, contains 0.5-5wt% of PVA (Polyvinyl Alcohol), 1-4wt% of protein powder or starch, 0.2-3wt% of tea polyphenol / carvacrol, 5-20wt% of glycerol and optional 5-15wt% of polylactic acid, and is cross-linked with sodium alginate. And carrying out tape casting at 55-65 DEG C, and carrying out gradient drying at 40-50 DEG C, thereby obtaining the product. The film is compact and flexible, the breaking strength is larger than or equal to 69 MPa, the oxygen permeability is low, the inhibition zone on six germs is enlarged by 3-4 mm, 98% of natural soil is degraded 20 days later, and no toxic smoke is generated during incineration. The biodegradable film is solvent-free in preparation, can be produced by existing equipment, is lower than a traditional biodegradable film in cost, can be in direct contact with food, remarkably prolongs the fresh-keeping period of fruits and vegetables, replaces PE and PVC, and solves white pollution.

Description

Technical Field

[0001] This invention relates to the field of new food packaging materials, and in particular to a biodegradable preservation film and its preparation method. Background Technology

[0002] With the rapid development of the social economy and the continuous improvement of people's living standards, the demand for packaging of various commodities is increasing day by day. As an important part of the packaging industry, food packaging has seen its market size continue to expand. As one of the main forms of food packaging, food packaging film has shown a steady upward trend in consumption, output, and market size.

[0003] However, the mainstream food packaging materials currently on the market, such as polyethylene (PE) and polyvinyl chloride (PVC) films, while possessing good mechanical properties and a certain degree of preservation, cause serious environmental problems due to their non-degradability. These traditional plastic packaging materials are often carelessly discarded or landfilled after use, failing to degrade in the natural environment and remaining for hundreds of years. This not only occupies vast amounts of land resources but also affects soil structure, hinders crop growth, and can even lead to the death of animals if ingested, posing a serious threat to ecosystems. Furthermore, some plastic packaging materials contain plasticizers and other chemicals added during the production process, which may enter the human body through the food chain, posing potential health risks such as weakened immunity and increased cancer risk.

[0004] In response to pollution issues and to actively promote green and environmentally friendly policies, the development of environmentally friendly and biodegradable new food packaging materials has become an inevitable trend in the industry.

[0005] Currently, some biodegradable packaging materials have emerged on the market, such as photodegradable films and biodegradable films (e.g., polylactic acid films). However, these materials still have many limitations: photodegradable films rely on specific light conditions, the degradation process and products are uncontrollable, and there is a risk of secondary pollution; biodegradable films, although degradable, are usually expensive, have long degradation cycles, and are highly dependent on specific environments such as industrial composting, limiting their widespread application. Furthermore, existing biodegradable materials still have shortcomings in terms of antibacterial properties, antioxidant properties, and preservation effects, making it difficult to fully meet the high requirements of applications such as fresh food and cold chain transportation. Summary of the Invention

[0006] The present invention aims to provide a biodegradable food preservation film and its preparation method to solve the problems of existing plastic food preservation films having poor preservation effect, being non-degradable, and polluting the environment.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a biodegradable food preservation film, wherein the food preservation film uses nano-chitosan and agarose as a composite film-forming matrix, the mass ratio of nano-chitosan to agarose is 1:1, and contains: 0.5-5 wt% polyvinyl alcohol resin; 1-4 wt% protein powder or starch; 0.2-3 wt% polyphenol antibacterial component, wherein the polyphenol antibacterial component is tea polyphenol, carvacrol or a combination thereof; and 5-20 wt% plasticizer glycerin.

[0008] Specifically, the nano-chitosan has a particle size ≤100 nm and a degree of deacetylation ≥85%.

[0009] Specifically, the plastic wrap further comprises polylactic acid, which is added in an amount of 5 to 15% of the total mass of the film-forming solution.

[0010] A method for preparing a biodegradable food preservation film includes the following steps:

[0011] S1. Dissolve nano-chitosan in a 0.5–2 wt% aqueous acetic acid solution to prepare a chitosan solution with a concentration of 1–2 wt%.

[0012] S2. Dissolve agarose in hot water at 85-95 ℃ to prepare an agarose solution with a concentration of 1-2 wt%.

[0013] S3. Mix the nano-chitosan solution and agarose solution at a mass ratio of 1:1 and maintain the temperature at 55–65 °C.

[0014] S4. Add polyvinyl alcohol resin, protein powder or starch, polyphenol antibacterial component and glycerin in sequence, stir evenly and then degas using ultrasound.

[0015] S5. Pour the film-forming solution obtained in step S4 into a horizontal mold, 30 g / plate, and dry at 40-50 ℃ for 12-24 h. Remove the film to obtain a biodegradable antibacterial preservation film.

[0016] Specifically, when a high-strength plastic wrap is required, 5-15 wt% polylactic acid is added to the system after step S4, dissolved in a water bath at 55 ℃, and then poured into a mold to form a film. After film formation, the film is immersed in a 2-6 mg / mL sodium alginate aqueous solution for crosslinking for 6-18 h, and then vacuum dried at 40 ℃ for 24-48 h.

[0017] Specifically, the drying step employs a gradient temperature increase: maintaining 40 ℃ for 4 h and 50 ℃ for 2 h to prevent the film from shrinking and cracking.

[0018] Specifically, the entire preparation process is carried out under aseptic conditions, and the resulting cling film can be directly used for food contact packaging.

[0019] The principle and beneficial effects of this technical solution:

[0020] This technical solution uses nano-chitosan and agarose as a composite film-forming matrix, taking advantage of their natural biodegradability and good biocompatibility. Through hydrogen bonding and electrostatic interactions, a dense three-dimensional network is formed, giving the membrane both mechanical strength and selective gas permeability. Because the nano-chitosan has a particle size ≤100 nm and a degree of deacetylation ≥85%, it carries a high density of positive charge, which can insert into the cell membrane of microorganisms, chelate metal ions and block nutrient transport, achieving synergistic physical-chemical antibacterial action. The antibacterial components of polyphenols such as tea polyphenols and carvacrol are embedded in the network through hydrogen bonds, continuously releasing reactive oxygen species scavengers, inhibiting oxidase activity, and reducing oxygen permeability, thereby delaying the respiratory climacteric and water evaporation of fruits and vegetables. Polyvinyl alcohol resin and glycerin respectively enhance water solubility and plasticize the film, making it smooth and flexible after gradient drying at 40–50 ℃, allowing for heat sealing and printing. When 5–15% polylactic acid is introduced and cross-linked with sodium alginate, the crystalline and amorphous regions interpenetrate, achieving a tensile strength of up to 69.1 MPa while maintaining an elongation of over 300%, meeting the demands of high-end packaging such as wrapping and stretching. All components of the entire formula are food-grade or GRAS substances, capable of 98% degradation in natural soil within 20 days, producing CO2, water, and biomass, with no dioxins upon incineration. The preparation process involves aseptic casting, requiring no organic solvents, and is simple and energy-efficient. It can be directly integrated with existing food preservation film production lines, enabling cost-effective large-scale production. This fundamentally replaces traditional non-degradable films such as PE and PVC, solving the problem of "white pollution" and improving the preservation effect of fresh food in the cold chain, resulting in significant economic and environmental benefits. Attached Figure Description

[0021] Figure 1 This is a flowchart of a biodegradable food preservation film manufacturing process;

[0022] Figure 2 Infrared spectrum of biodegradable material;

[0023] Figure 3 Comparison of the preservation effects of biodegradable plastic wrap;

[0024] Figure 4 The diagram shows a comparison of the diameters of the inhibition zones, where (a) represents Escherichia coli, (b) represents saprophytic bacteria, (c) represents Staphylococcus aureus, (d) represents Lactobacillus, (e) represents Candida albicans, and (f) represents Salmonella.

[0025] Figure 5 Figures showing soil degradation at 8 and 16 days;

[0026] Figure 6 This is a comparison chart of fracture strength.

[0027] Figure 7 The graph shows the effect of the chitosan to agarose solid content ratio on the water solubility of the film. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments:

[0029] Example: Preparation of biodegradable food preservation film

[0030] This embodiment details a specific preparation process for the biodegradable food preservation film of the present invention. The raw materials used are widely available, aligning with the concept of sustainable development. For example, chitosan can be extracted from the crustaceans of marine arthropods, cell membranes of fungi and algae, and the shells and bones of mollusks, and then prepared into nano-chitosan through techniques such as ion cross-linking. Under current experimental conditions, we purchase readily available nano-chitosan for preparation, at a cost of approximately 80-100 yuan per kilogram. Based on our preparation process, each kilogram of nano-chitosan can produce approximately 15 rolls of food preservation film with a specification of 30cm × 400m, demonstrating cost feasibility for large-scale production.

[0031] The specific preparation process is as follows: Figure 1 As shown in the flowchart, the steps are as follows:

[0032] 1. Solution Preparation: First, dissolve the nano-chitosan in a 0.5–2 wt% aqueous acetic acid solution and stir magnetically until completely dissolved to obtain a homogeneous and clear nano-chitosan solution with a concentration of 1–2 wt%. Simultaneously, add agarose powder to hot water at 85–95 °C and stir continuously until fully dissolved to obtain an agarose solution with a concentration of 1–2 wt%.

[0033] 2. Matrix Mixing: Mix the prepared nano-chitosan solution and agarose solution at a 1:1 mass ratio. For example, weigh 50g of nano-chitosan solution and 50g of hot agarose solution, and stir thoroughly in a constant temperature water bath at 55-65℃ to form a homogeneous composite film-forming matrix. This temperature range effectively prevents premature gelation of agarose and ensures the fluidity of the mixed solution.

[0034] 3. Additives and Homogenization: To the matrix mixture under stirring, add the formulated amounts of polyvinyl alcohol (PVA) resin, protein powder (or starch), polyphenolic antibacterial components (tea polyphenols or carvacrol), and plasticizer glycerin sequentially. PVA resin further enhances the membrane's water solubility and film-forming properties; protein powder or starch acts as a reinforcing phase, improving the membrane's mechanical properties; the polyphenolic components provide core antibacterial and antioxidant functions; and glycerin acts as a plasticizer, effectively improving the membrane's flexibility and extensibility, preventing brittleness. After all components are added, the mixture is placed in an ultrasonic cleaner for ultrasonic treatment (a boiling water bath helps reduce solution viscosity) to remove air bubbles and achieve more uniform dispersion of the components.

[0035] 4. Casting and Drying: The homogenized film-forming solution, after ultrasonic degassing, is quantitatively poured into clean, horizontally placed petri dishes (30g per dish), and then transferred to a forced-air drying oven for drying and shaping. To effectively prevent shrinkage and cracking of the film due to rapid moisture evaporation during drying, this invention employs a gradient temperature drying process: first, the film is held at 40℃ for 4 hours to slowly set; then, the temperature is increased to 50℃ for another 2 hours to ensure thorough drying. This process effectively guarantees the integrity and flatness of the finished film.

[0036] 5. Film Removal and Storage: After drying, carefully peel off the formed plastic wrap completely, starting from the edge of the mold, using tweezers. Store it in a desiccator, away from light and moisture, for subsequent testing and use. The plastic wrap prepared using this standard procedure has the following Fourier Transform Infrared (FTIR) spectrum: Figure 2 As shown, it can be used to analyze the molecular interactions between components.

[0037] Preparation of highly ductile variants:

[0038] To obtain a food preservation film with better extensibility and higher mechanical strength to suit specific applications such as wrapping and high-tension covering, an enhancement treatment can be performed after step (3) above. Specifically, add 5-15% polylactic acid (PLA) to the system, and stir in a 55°C water bath until completely dissolved. Then pour it into a mold to form a film in the same way. After the initial film formation, immerse the film in a sodium alginate aqueous solution with a concentration of 2-6 mg / mL and perform crosslinking treatment for 6-18 hours. This crosslinking process can further improve the network structure strength and degradation controllability of the film. After crosslinking is completed, remove the film and dry it in a 40°C vacuum drying oven for 24-48 hours to obtain a highly extensible biodegradable food preservation film.

[0039] The entire preparation process is recommended to be carried out in a sterile operating table or clean environment to ensure that the resulting plastic wrap meets the hygiene standards for food contact materials and can be directly used for packaging various types of food.

[0040] Comparative example: Commercially available ordinary PE food wrap

[0041] To objectively and fairly evaluate the overall performance of the product of this invention, in all subsequent comparative experiments, we selected ordinary polyethylene (PE) food wrap, which is currently the most common and widely used on the market, as the comparative example. This comparative example represents the current technical level of mainstream non-degradable plastic food wrap.

[0042] Comparative experiments and performance analysis

[0043] I. Comparison Experiment on Preservation Effect

[0044] Preservation is one of the most essential functions of plastic wrap. To verify the preservation efficacy of the product in this embodiment of the invention, we designed a rigorous apple preservation experiment.

[0045] Experimental Method: Several fresh apples of similar size, weight, and freshness were selected, washed, and cut into uniform segments. Three segments were used as test samples: the first segment served as a blank control group, exposed directly to air without any packaging; the second segment was tightly wrapped with PE cling film (comparative); and the third segment was tightly wrapped with the biodegradable cling film prepared according to the present invention. The three groups of samples were placed under the same environmental conditions (same temperature, humidity, and light), and their appearance, color changes, mold growth, and odor were observed periodically.

[0046] Results and Analysis Figure 3 (and Table 1):

[0047] At 3 days: The apple segments in the blank control group showed obvious changes, with the surface becoming dry and wrinkled due to rapid moisture evaporation. The apples in the comparative example (PE plastic wrap) group and the group described in this invention showed little change, with acceptable moisture retention and no significant difference in appearance. This indicates that both types of plastic wrap can provide a certain degree of physical insulation in the short term.

[0048] At 6 days: The apple slices in the blank control group softened further, with obvious mold spots appearing on the surface, and began to emit a putrid, sour odor. In the comparative example (PE plastic wrap) group, a large amount of water droplets condensed inside the packaging, which was due to the poor moisture permeability of the PE film leading to internal moisture saturation. Simultaneously, the apple color began to darken, and mold spots appeared in some areas. In contrast, the apples in the embodiment of this invention maintained their normal color, remained dry, and no mold spots were observed.

[0049] At 9 days: The apple segments in the blank control group were completely rotten and spoiled, and inedible. The apples in the comparative example (PE plastic wrap) group had softened, with most areas covered in mold and a slight putrid odor. In contrast, the apples in the embodiment of this invention showed no significant color change in most areas, with only a slight decrease in firmness, demonstrating a significantly better preservation effect than the former two.

[0050] Table 1. Observation Record of Apple Preservation Effect

[0051]

[0052] To further quantify the preservation effect, we simultaneously measured the weight loss rate of apples, and the results are shown in Table 2. The data clearly show that throughout the entire experimental period, the apple weight loss rate in the embodiment group of this invention was consistently the lowest (1.10% at 3 days, 2.60% at 6 days, and 4.56% at 9 days), significantly lower than the comparative group (PE preservation film) (1.97% at 3 days, 4.74% at 6 days, and 8.90% at 9 days) and the blank control group. This quantitatively demonstrates the superior performance of the preservation film of this invention in inhibiting moisture evaporation and slowing down the weight loss of fruits and vegetables.

[0053] Table 2 Comparison of Apple Weight Loss Rate

[0054]

[0055] Results analysis:

[0056] Synergistic effects of nano-chitosan: Nano-sized chitosan increases its specific surface area, enhances its activity, and strengthens its permeability. On one hand, nano-chitosan can more effectively enter microorganisms, binding with negatively charged cellular components through electrostatic interactions, interfering with metabolism, and thus exerting a stronger antibacterial effect, delaying spoilage caused by microorganisms. On the other hand, nanoparticles help form a denser membrane structure, greatly improving the membrane's barrier properties against gases such as oxygen and carbon dioxide.

[0057] "Breathable" Microenvironment Regulation: Unlike PE films that completely isolate gases, the film formed by this invention has a certain degree of selective permeability. It effectively blocks excessive external oxygen from entering, inhibiting the intensity of aerobic respiration in fruits and vegetables and delaying the arrival of their respiration peak; at the same time, it allows a moderate amount of carbon dioxide produced by the respiration of fruits and vegetables to escape, avoiding fermentation and spoilage caused by anaerobic respiration. By dynamically adjusting the gas composition (O2 and CO2 concentrations) within the packaging, a microenvironment conducive to preservation is created, thereby significantly extending the shelf life of fruits and vegetables.

[0058] Physical barrier function: A complete edible film layer can form a physical barrier on the surface of fruits and vegetables, effectively blocking the direct contact between external pathogens and fruit and vegetable tissues, reducing the chance of infection, and delaying the occurrence of diseases and cell aging.

[0059] In contrast, the comparison (PE preservation film) can only provide simple physical isolation. Its poor air permeability can easily lead to excessive humidity and gas composition imbalance (high humidity, low oxygen, high carbon dioxide) inside the packaging, which may accelerate the growth of certain anaerobic microorganisms or cause physiological disorders in fruits and vegetables. This is also the reason why mold spots and water droplets appeared in the PE film group in the later stage of the experiment.

[0060] II. Comparative Experiment on Antibacterial Effect

[0061] Experimental Method: Agar plates containing specific bacterial species (Escherichia coli, saprophytic bacteria, Staphylococcus aureus, Lactobacillus, Candida albicans, and Salmonella) were prepared. Equal amounts of the sterilized liquid film-forming material and liquid PE material from this embodiment were dropped onto the center of the plate coated with the bacterial solution and incubated in a constant temperature incubator for 24 hours. The antibacterial ability was evaluated by measuring the diameter of the transparent inhibition zone formed around the material. A larger inhibition zone diameter indicates a stronger antibacterial effect.

[0062] Results and Analysis: The experimental results are as follows... Figure 4 As shown in Table 3, the inhibition zone diameters produced by the material of the present invention were significantly larger than those of the comparative example (PE plastic wrap) for all six bacterial species tested. For example, against *Escherichia coli*, the inhibition zone diameter of the embodiment was 32.5 mm, while that of the comparative example was only 29.6 mm; against *Staphylococcus aureus*, the diameter of the embodiment was 32.1 mm, while that of the comparative example was 28.8 mm. This fully demonstrates that the embodiments of the present invention possess broad-spectrum and highly efficient antibacterial capabilities.

[0063] Table 3 Comparison of inhibition zone diameters

[0064]

[0065] Results analysis:

[0066] Membrane barrier mechanism: Chitosan can adsorb onto the surface of microbial cells and form a dense polymer membrane, which effectively hinders the transport of nutrients into the cells, thereby limiting microbial growth or even causing death.

[0067] Electrochemical mechanism of action: Chitosan molecules are rich in amino groups, which protonate and carry a positive charge under acidic conditions. As a polyvalent cationic surfactant, it can strongly bind to negatively charged components such as lipopolysaccharides and phospholipids on the surface of bacterial cell membranes, thereby disrupting the integrity of the cell wall, interfering with the normal metabolic function of the membrane, altering membrane permeability, causing leakage of intracellular contents (such as proteins and nucleotides), and triggering cell death.

[0068] Chelation mechanism: The amino and hydroxyl groups in chitosan molecules can act as effective chelating groups, selectively complexing metal ions (such as Mg) that are crucial for microbial growth. 2+ Ca 2+ Fe 2+ (etc.), cutting off the nutrient source of microorganisms and inhibiting their enzyme activity, thereby inhibiting their growth and toxin production.

[0069] Nanoscale enhancement effect: The small size effect and huge specific surface area of ​​chitosan particles at the nanoscale make it easier to penetrate the cell wall and cell membrane of microorganisms, enter the cell interior, and destroy the cell structure from the inside and outside, thus achieving a dual enhancement of physical and chemical sterilization.

[0070] In contrast, the PE plastic wrap itself does not have any active antibacterial function. The formation of its antibacterial ring may only be due to the oxygen-deficient environment caused by physical covering. Its antibacterial effect is weak and not universal.

[0071] III. Environmental Degradability Comparison Experiment

[0072] Degradability is a key indicator of the environmental friendliness of packaging materials. We simulated the natural degradation environment through soil landfill experiments.

[0073] Experimental Method: Two pieces each of the plastic wrap from this invention (circular shape with a radius of 5cm) and a commercially available "biodegradable" packaging material (as a reference) of the same area were cut and buried in natural soil with the same composition and humidity, maintaining the same environmental conditions. The materials were periodically dug up to observe and record the changes in their physical morphology, and their degradation rate was calculated.

[0074] Results and Analysis:

[0075] Qualitative observations: as shown in Table 4 and Figure 5 As shown, after 8 days of landfilling, the commercially available biodegradable product showed no significant change in appearance, while the product of this embodiment showed obvious signs of degradation, such as thinning, breakage, and decreased strength. By day 16, the commercially available product still showed no significant change, while the product of this embodiment had degraded to only a portion of the membrane remaining. By day 20, the commercially available product remained unchanged, while the product of this embodiment had essentially degraded completely and integrated into the soil.

[0076] Table 4. Observation Record of Degradation in Soil

[0077]

[0078] Quantitative analysis: The degradation rate data in Table 5 further confirms the above observations. The degradation rates of the product in this embodiment reached 48%, 78%, and 98% at 8 days, 16 days, and 20 days, respectively, while the degradation rate of the commercially available biodegradable product used as a reference remained at 0% at the same time points.

[0079] Table 5 Comparison of Degradation Rates in Soil

[0080]

[0081] Comprehensive comparison and advantages analysis:

[0082] Compared to traditional degradable materials (Table 6): Photodegradable materials heavily rely on sufficient ultraviolet radiation and are almost impossible to degrade under conditions of no light or low light (such as inside landfills), and their degradation products may be unstable. Biodegradable materials (such as pure PLA) typically require industrial composting conditions above 50°C to achieve effective degradation, with a cycle lasting 3-6 months. They have stringent environmental requirements and are costly. This results in very low actual degradation efficiency in natural environments.

[0083] Table 6 Comparison of Biodegradable Materials

[0084]

[0085] Advantages of the product of this invention (Table 7): The product of this invention uses natural biodegradable nano-chitosan and agarose as the matrix, and the PVA resin it contains also has good water solubility and biodegradability. Therefore, under normal soil landfill conditions, it can quickly start and complete the degradation process without any external conditions (such as specific light, high temperature, or specific microbial inoculation). Its degradation rate is fast, the cycle is short, and the degradation products are water, carbon dioxide, and biomass, which are non-toxic and harmless and will not cause secondary pollution to the soil. Even under incineration treatment, since its components are carbohydrates and their derivatives, the combustion products are mainly CO2 and water, and no toxic gases such as dioxins and HCl are produced, resulting in an extremely low environmental impact. This truly achieves environmental friendliness throughout the entire life cycle from "cradle to grave".

[0086] Table 7. Explanation of the Implementation Methods and Results

[0087]

[0088] IV. Study on Mechanical Properties and Barrier Properties

[0089] 1. Tensile strength determination

[0090] Packaging materials need to possess sufficient mechanical strength to prevent damage during packaging, transportation, and use. Referring to the national standard GB / T 1040.3-2006, we tested the tensile strength of the cling film in our examples at different solid contents.

[0091] Experimental results are as follows Figure 6 As shown, the film exhibits the highest tensile strength, reaching 69.1 MPa, when the solid content of the film-forming matrix (chitosan and agarose) is 2.0%. The tensile strength decreases with decreasing solid content. This is because at excessively low concentrations, the intermolecular forces in the film-forming solution are weak, resulting in a loose and uneven film structure, leading to decreased mechanical properties. Simultaneously, a higher solid content also results in a higher elongation at break, indicating that the film maintains both strength and good toughness.

[0092] 2. Oxygen Transmission Rate Experiment

[0093] Oxygen is a major factor leading to food oxidative spoilage. We used a VAC-V2 differential pressure gas permeation analyzer, referring to GB / T 1038 standard, to test the oxygen barrier performance of the preservation films in our examples. The study found that when the added tea polyphenols concentration was 2%, the film exhibited the best overall performance, with a significantly reduced oxygen permeability and a 58.54% increase in antioxidant capacity compared to the unoptimized formulation. This is attributed to the strong intermolecular forces (such as hydrogen bonds) formed between tea polyphenol molecules and chitosan molecular chains, resulting in a denser film structure. Furthermore, tea polyphenols themselves are excellent antioxidants, actively consuming the permeated oxygen.

[0094] V. Analysis of water solubility and moisture permeability

[0095] Determination of water solubility:

[0096] We systematically studied the effect of different solid content ratios of chitosan and agarose (from 9:1 to 1:9) on the water solubility of the films. The determination method was as follows: the films dried to constant weight were soaked in distilled water at room temperature for 24 hours, dried again, and weighed. The water solubility value Q was calculated using a formula.

[0097] The results are as follows Figure 7 As shown, the water solubility of the film increases with the increase of starch (or agarose, both of which are hydrophilic polysaccharides) content in the formulation. Chitosan films typically swell and absorb moisture in water but do not dissolve, while starch and agarose films can gradually hydrolyze and dissolve in water. This controllable water solubility means that the product of this invention is more flexible in post-use treatment. Under specific conditions (such as high temperature and high humidity), it can be partially water-soluble, further accelerating its breakage and subsequent biodegradation process, and greatly shortening its residual time in the environment.

[0098] The above descriptions are merely embodiments of the present invention, and common technical solutions or characteristics known in the schemes are not described in detail here. For those skilled in the art, various modifications and improvements can be made without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A degradable cling film, characterized by: The preservative film uses nanochitosan and agarose as a composite film-forming matrix, the mass ratio of nanochitosan to agarose is 1:1, and contains: 0.5-5 wt % polyvinyl alcohol resin; 1-4 wt % protein powder or starch; 0.2-3 wt % polyphenol antibacterial component, the polyphenol antibacterial component is tea polyphenol, carvacol or a combination thereof; 5-20 wt % plasticizer glycerol.

2. The degradable cling film according to claim 1, wherein: The particle size of the nanochitosan is ≤100 nm, and the degree of deacetylation is ≥85 %.

3. The degradable cling film according to claim 1, wherein: The preservative film further comprises polylactic acid, and the addition amount is 5-15 % of the total mass of the film-forming solution.

4. A method of preparing the degradable cling film according to claim 1, characterized in that, The method comprises the following steps: S1, dissolve nanochitosan in 0.5-2 wt % acetic acid aqueous solution to prepare a chitosan solution with a concentration of 1-2 wt %; S2, dissolve agarose in hot water at 85-95 ℃ to prepare an agarose solution with a concentration of 1-2 wt %; S3, mix the nanochitosan solution and the agarose solution according to a mass ratio of 1:1, and keep the temperature at 55-65 ℃; S4, add polyvinyl alcohol resin, protein powder or starch, polyphenol antibacterial component and glycerol in sequence, stir uniformly, and then ultrasonic defoam; S5, pour the film-forming solution obtained in step S4 into a horizontal mold, 30 g / pan, dry at 40-50 ℃ for 12-24 h, and then remove the film to obtain a degradable antibacterial preservative film.

5. The method for preparing a biodegradable food preservation film according to claim 4, characterized in that: When a high-ductility preservative film is needed, 5-15 wt % polylactic acid is added to the system after step S4, dissolved in a 55 ℃ water bath, and then poured into a mold to form a film; after film formation, the film is immersed in a 2-6 mg / mL sodium alginate aqueous solution for crosslinking for 6-18 h, and then taken out and vacuum dried at 40 ℃ for 24-48 h.

6. A method of preparing a degradable cling film as claimed in claim 4, wherein: The drying step uses gradient heating: 40 ℃ for 4 h and 50 ℃ for 2 h to prevent film shrinkage and cracking.

7. The method for preparing a biodegradable food preservation film according to claim 4, characterized in that: The entire preparation process is carried out under sterile conditions, and the obtained preservative film can be directly used for food contact packaging.

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