Composite biodegradable packaging film as well as preparation method and application thereof

Abstract

The invention discloses a composite biodegradable packaging film as well as a preparation method and application thereof, and belongs to the field of bio-based materials. In order to solve the problems that an existing packaging film is single in function and high in cost, the composite biodegradable packaging film comprises an outer layer, a first middle layer, a second middle layer and an inner layer which are sequentially arranged; each of the outer layer, the first middle layer, the second middle layer and the inner layer comprises a main material and an auxiliary material, and the main material is a mixture of polylactic acid and polypropylene carbonate; an auxiliary material of the outer layer is a blocking agent; an auxiliary material of the first middle layer is an antioxidant; the auxiliary material of the second middle layer is a photo-thermal stimulation response isolation agent, and the auxiliary material of the inner layer is an antibacterial agent. On one hand, auxiliary materials with different functions are correspondingly added to each layer, so that the functions are diversified; the main material ensures the overall biodegradability of the packaging film and is purchased in batches, so that the cost is reduced; the same main material mixture ensures the performance consistency between the layers, and the overall stability and durability are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of bio-based intelligent materials, more specifically, relates to a composite biodegradable packaging film, a preparation method and applications thereof. BACKGROUND

[0002] Traditional petroleum-based plastic packaging materials are difficult to degrade, causing serious environmental pollution. Existing biodegradable materials (such as pure PLA) have problems such as high brittleness, poor barrier performance, and lack of real-time monitoring of food freshness. Existing intelligent packaging mostly uses solution casting method, which requires the use of harmful solvents such as chloroform, which does not meet the needs of industrial scale production. In addition, existing indicators (such as anthocyanin) have poor thermal stability (decompose at 60℃), limiting their application scenarios.

[0003] Existing biodegradable packaging materials generally have the following technical bottlenecks: 1. Single function: existing intelligent packaging mostly relies on a single response mechanism (such as pH or ammonia gas), which cannot adapt to complex environmental changes; 2. Insufficient thermal stability: natural active ingredients (such as curcumin) are easily degraded (deactivation temperature ≤180℃) during high-temperature processing, limiting industrial application; 3. Limited barrier performance: the oxygen permeability of PLA / PPC blended materials is still higher than the requirement for food preservation (>3.5 mL·mm / m² / day); 4. Material surface is prone to micro-cracks due to mechanical stress, leading to functional failure.

[0004] Corresponding improvements have been made for the above problems, such as Chinese patent application number CN202411261025.7, published on December 13, 2024, which discloses a multi-layer structure biodegradable modified atmosphere film, including a first surface layer, a middle layer and a second surface layer, the modified atmosphere film is composed of the first surface layer, the middle layer and the second surface layer by co-extrusion process, wherein the first surface layer and the second surface layer are mainly made of one or more biodegradable plastics polyesters such as polylactic acid (PLA), polycaprolactone (PCL), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), and polyhydroxyalkanoate (PHA), supplemented with functional masterbatch (addition amount ≥1%), and a small amount of additives (addition amount <1%); the middle layer is mainly made of polypropylene carbonate (PPC), supplemented with functional masterbatch (addition amount ≥1%), and a small amount of additives (addition amount <1%). The shortcomings of this patent are: the main materials of the first surface layer and the second surface layer are not the same as the main material of the middle layer, which may cause interface compatibility problems and insufficient interlayer adhesion strength; and multiple raw materials need to be purchased and stored, resulting in increased cost.

[0005] For example, Chinese Patent Application No. CN202510069431.1, published on April 25, 2025, discloses a degradable packaging film and its preparation method, belonging to the technical field of food packaging. The preparation method includes the following steps: (1) uniformly mixing PLA, PBAT and curcumin to obtain a mixture; (2) placing the mixture into the hopper of a twin-screw extruder, running the machine to obtain a molten material, and cutting the molten material after it cools to obtain modified masterbatch; (3) stirring the modified masterbatch in an organic solvent to obtain a film-forming solution, pouring the film-forming solution into a mold, drying until all the organic solvent is volatilized, and obtaining a degradable preservative antibacterial antioxidant packaging film. The shortcomings of this patent are: the single-layer film synthesized from PLA, PBAT and curcumin has single function and great limitations; and the barrier performance is insufficient. SUMMARY

[0006] 1. Problem to be solved In view of the problem of single function and high cost of existing packaging films, the present application provides a composite biodegradable packaging film, a preparation method and its application. The present application diversifies the functions by adding different functional additives to each layer, and uses a mixture of polylactic acid and polypropylene carbonate as the main material to ensure the overall biodegradability of the packaging film and environmental friendliness. It can be purchased in bulk to reduce costs, and the same main material mixture ensures the performance consistency between layers, improving overall stability and durability.

[0007] 2. Technical solution To solve the above problems, the present application adopts the following technical solution.

[0008] A composite biodegradable packaging film, comprising an outer layer, a first intermediate layer, a second intermediate layer and an inner layer arranged in sequence; the outer layer, the first intermediate layer, the second intermediate layer and the inner layer all comprise a main material and an additive, the main material is a mixture of polylactic acid and polypropylene carbonate; the additive of the outer layer is a barrier agent; the additive of the first intermediate layer is an antioxidant; the additive of the second intermediate layer is a light-heat stimulus response insulating agent, and the additive of the inner layer is an antibacterial agent.

[0009] By adopting the technical scheme, on one hand, by adding different auxiliary materials with different functions in each layer, the barrier agent in the outer layer improves the barrier property of the packaging film, effectively prevents the penetration of oxygen, water vapor and other penetrants, prolongs the shelf life of the packaged contents, and maintains the freshness and quality thereof; the antioxidant in the first intermediate layer inhibits the oxidation reaction of the packaging film during processing, storage and use, and maintains the stability and reliability thereof; the light-heat stimulus response insulator in the second intermediate layer enables the packaging film to respond to light or heat stimulation, realizes intelligent control of the packaging film, and meets the needs of specific application scenarios; and the antibacterial agent in the inner layer inhibits or kills microorganisms on the inner surface of the packaging film, prevents the contents from being contaminated or deteriorated, maintains the hygiene and safety thereof, and realizes multifunctional consideration. On the other hand, by using a mixture of polylactic acid and polypropylene carbonate as the main material in each layer, polylactic acid and polypropylene carbonate are both biodegradable polymers, the use of their mixture as the main material ensures the overall biodegradability of the packaging film, which is conducive to environmental protection; and polylactic acid provides rigidity and thermal stability, while polypropylene carbonate improves toughness and barrier property, so that the packaging film has sufficient strength, good flexibility and barrier property; more importantly, the same main material mixture ensures the performance consistency between the layers, which helps to enhance the bonding force between the layers, reduce the risk of delamination or peeling, and thus improve the overall stability and durability of the packaging film; and raw materials can be purchased in bulk, reducing costs.

[0010] In summary, the composite biodegradable packaging film not only realizes multifunctional consideration, but also meets the biodegradable and environmentally friendly requirements, avoids the risk of delamination or peeling between layers during preparation, has high stability and durability, reduces cost investment, and greatly increases the application range thereof.

[0011] Further, the content of polylactic acid in the outer layer main material < the content of polylactic acid in the first intermediate layer main material < the content of polylactic acid in the inner layer main material; The content of polylactic acid in the outer layer main material < the content of polylactic acid in the second intermediate layer main material < the content of polylactic acid in the inner layer main material; The content of polypropylene carbonate in the outer layer main material > the content of polypropylene carbonate in the first intermediate layer main material > the content of polypropylene carbonate in the inner layer main material; The content of polypropylene carbonate in the outer layer main material > the content of polypropylene carbonate in the second intermediate layer main material > the content of polypropylene carbonate in the inner layer main material.

[0012] According to the technical scheme, polylactic acid is a rigid material but has poor toughness, and polypropylene carbonate is a flexible material but has poor rigidity and thermal stability, therefore, for the mixture of the two, the content of the two in the four layers is designed according to the gradient design principle, in order to consider that the outer layer directly contacts the external environment and needs to have high rigidity and thermal stability to resist mechanical impact and thermal stress of the external environment, and the inner layer gradually transitions to a higher content of PLA to maintain a certain rigidity while reducing the influence of the flexibility of PPC on the performance of the inner layer, and the middle layer needs to simultaneously withstand stress from the outer layer and the inner layer, and the toughness is improved by increasing the content of PLC and reducing the content of PPC to prevent peeling between the outer layer and the inner layer due to micro deformation in the case of photothermal response, and the gradient design of the overall content of PLA and PPC helps to gradually transition the material performance and reduce stress concentration between layers, thereby ensuring the stability of the whole.

[0013] Furthermore, the ratio of the weight fraction of polylactic acid to the weight fraction of polypropylene carbonate in the main material of the outer layer is (75-80):(20-25). The ratio of the weight fraction of polylactic acid to the weight fraction of polypropylene carbonate in the main material of the first middle layer and the second middle layer is (80-85):(15-20). The ratio of the weight fraction of polylactic acid to the weight fraction of polypropylene carbonate in the main material of the inner layer is (85-90):(10-15).

[0014] According to the above technical scheme, PLA has certain rigidity and certain antibacterial effect, and PPC has certain flexibility and good barrier property, therefore, the content of PPC in the outer layer is the highest to play a role in blocking the external environment, and the content of PLA in the inner layer is the highest to play a role in inhibiting bacteria, and the gradient addition amount of the two in the outer layer and the inner layer achieves the synergistic effect of packaging performance.

[0015] Furthermore, the barrier agent includes a mixture of graphene oxide and titanium dioxide nanoparticles, the antioxidant includes a mixture of curcumin, rosemary extract, resveratrol and tea polyphenol, the photothermal stimulus response insulating agent includes a mixture of temperature-responsive polymer and photosensitive polymer, and the antibacterial agent includes nano-silver particles.

[0016] The barrier agent utilizes the two-dimensional sheet structure of graphene oxide to prolong the penetration path of small molecules such as oxygen and water vapor, and significantly improves the barrier property of the material; the titanium dioxide nanoparticles can reflect / absorb ultraviolet rays, reduce the oxidative degradation of the contents caused by light, enhance the barrier to oxygen and water vapor, and make the outer layer have excellent barrier performance; the antioxidant uses a variety of natural antioxidants to cover a wider range of free radical scavenging, reduces the oxidation and rancidity of the contents, and the natural ingredients are non-toxic and have greatly improved safety; the photo-thermal stimulus responsive barrier agent can realize multi-dimensional intelligent response; when the temperature is greater than 30 DEG C, the PNIPAM shrinks to reduce the air permeability, and the ultraviolet light triggers the azobenzene polymer to change the air permeability, thereby saving energy and reducing consumption; the innermost layer of nano-silver particles has strong killing effect on bacteria, fungi and viruses, which can significantly reduce the risk of microbial contamination of the packaging contents, and has a slow-release property, which can maintain the antibacterial effect for a long time, and reduce the amount and frequency of adding the antibacterial agent.

[0017] Further, the curcumin is nano-encapsulated curcumin prepared by supercritical carbon dioxide, and the specific preparation method is as follows: curcumin and chitosan solution are mixed, injected into a supercritical CO2 reactor to form a homogeneous emulsion, sodium alginate solution is injected into the homogeneous emulsion, and after pressure reduction to normal pressure, freeze-drying is performed to obtain nano-encapsulated curcumin.

[0018] By using the unique solubility, rapid phase change characteristics and green process advantages of the supercritical carbon dioxide process, the precise deposition of the wall material and the high efficiency of the core material are realized by regulating the phase behavior, the wall material (chitosan / sodium alginate) is precipitated and wrapped around the core material (curcumin) by the supercritical solution rapid expansion method (RESS): the high-pressure SC-CO2 solution is rapidly expanded by the nozzle, CO2 is instantaneously gasified, the wall material (chitosan / sodium alginate) is precipitated and wrapped around the core material (curcumin); this embedding method has the advantages of green environmental protection, no need for organic solvents, avoiding residual toxicity, mild conditions: low-temperature operation, protecting the activity of heat-sensitive substances, controllable particle size: by adjusting the pressure, temperature and nozzle parameters, the size of the microcapsules can be accurately controlled, high encapsulation rate: the high permeability of SC-CO2 helps the uniform dispersion and high efficiency of the core material.

[0019] Further, the weight fractions of the substances in the outer layer are as follows: 75-80 parts of polylactic acid; 20-25 parts of polypropylene carbonate; 0.1-0.3 parts of graphene oxide; 0.2-0.4 parts of titanium dioxide nanoparticles; The weight fractions of the substances in the first intermediate layer are as follows: 80-85 parts of polylactic acid; 15-20 parts of polypropylene carbonate; 1-2 parts of nano-encapsulated curcumin; 0.5-1 part of rosemary extract; 0.3-0.5 part of resveratrol; 0.2-0.4 part of tea polyphenol; The weight parts of each substance of the second intermediate layer are as follows: polylactic acid 80-85 parts; polypropylene carbonate 15-20 parts; poly N-isopropyl acrylamide 1-2 parts; azobenzene polymer 0.5-1 part; The weight parts of each substance of the inner layer are as follows: polylactic acid 85-90 parts; polypropylene carbonate 10-15 parts; silver nanoparticles 0.05-0.1 parts.

[0020] Further, the barrier agent further comprises a dynamic crosslinking agent, the weight parts of the dynamic crosslinking agent being 0.5-1 part; the dynamic crosslinking agent is a polyethylene glycol prepolymer containing a disulfide bond; the outer layer and the inner layer further comprise nanocellulose, the weight parts of the nanocellulose being 0.8-1.2 parts; and the diameter of the nanocellulose is 10-30 nm, and the length of the nanocellulose is 1-2 μm.

[0021] By using the above technical solution, the addition of the dynamic crosslinking agent together with graphene oxide in the outer layer plays a self-healing effect, so that the dynamic crosslinking agent realizes crack repair at 40℃ / 20min, and the tensile strength recovery rate is ≥95%; in combination with the conductivity of graphene oxide, the repair efficiency is improved by 10%; and meanwhile, the increase of nanocellulose in the inner and outer layers enhances the mechanical properties of the inner and outer layers.

[0022] Further, the thickness of the outer layer accounts for 20-25% of the thickness of the entire composite biodegradable packaging film; the thickness of the first intermediate layer accounts for 25-30% of the thickness of the entire composite biodegradable packaging film; the thickness of the second intermediate layer accounts for 25-30% of the thickness of the entire composite biodegradable packaging film; and the thickness of the inner layer accounts for 20-25% of the thickness of the entire composite biodegradable packaging film.

[0023] By using the above technical solution, A preparation method of the composite biodegradable packaging film as described in any one of the above, comprising the following steps: The outer layer mixture, the first intermediate layer mixture, the second intermediate layer mixture and the inner layer mixture are prepared according to the main materials and auxiliary materials respectively; The outer layer mixture, the first intermediate layer mixture, the second intermediate layer mixture and the inner layer mixture are blended to form a film; The surface of the formed film is subjected to plasma treatment, and finally the composite biodegradable packaging film is obtained.

[0024] By using the above technical solution, the preparation method is simple to operate, does not need to introduce a complex process, and reduces the preparation cost; and through the multi-layer co-extrusion process, the precise compounding of each layer of material is realized, so as to ensure the interlayer bonding strength; the blending forming can reduce the interlayer defects such as delamination and bubbles, and improve the mechanical stability and barrier consistency of the packaging film; and at the same time, the surface functionalization and performance improvement are realized through the plasma treatment, so as to improve the interlayer adhesion and surface hydrophilicity.

[0025] Use of the composite biodegradable packaging film according to any one of the preceding items in the fields of food, medicine and cosmetics.

[0026] The technical scheme has the functions of ultraviolet blocking, oxidation resistance, ammonia / temperature dual response and self-repairing, and is suitable for fields such as food, medicine and cosmetics that have high requirements for safety and barrier properties. DETAILED DESCRIPTION The application will be further described below in combination with specific examples.

[0027] The composite biodegradable packaging film comprises an outer layer, a first intermediate layer, a second intermediate layer and an inner layer arranged in sequence. The outer layer directly contacts the external environment, and the inner layer contacts the object contained in the packaging film. The outer layer, the first intermediate layer, the second intermediate layer and the inner layer all comprise a main material and an auxiliary material. The main material of the four layers is a mixture of polylactic acid and polypropylene carbonate. The auxiliary material of the outer layer is a barrier agent. The auxiliary material of the first intermediate layer is an antioxidant. The auxiliary material of the second intermediate layer is a light-heat stimulus response insulating agent. The auxiliary material of the inner layer is an antibacterial agent.

[0028] In the embodiment, there are two core improvements: one is to add corresponding functional auxiliary materials to each layer. Since the outermost layer directly contacts the external environment, the barrier performance requirement is high. A barrier agent is added to the outer layer to effectively prevent the penetration of oxygen, water vapor and other penetrants, thereby prolonging the shelf life of the packaged contents, maintaining their freshness and quality, and improving the barrier performance of the packaging film. The inner layer directly contacts the object inside the packaging film, so the antibacterial performance requirement is high. An antibacterial agent is added to the inner layer to inhibit or kill microorganisms on the inner surface of the packaging film, prevent the object inside the packaging film from being contaminated or deteriorated, improve safety and prolong the shelf life. The first intermediate layer and the second intermediate layer serve as intermediate transition layers, and an antioxidant and a light-heat stimulus response insulating agent are added. The antioxidant inhibits the oxidation reaction of the packaging film during processing, storage and use, thereby maintaining its stability and reliability. The light-heat stimulus response insulating agent enables the packaging film to respond to light or heat stimulation, thereby realizing intelligent control of the packaging film and meeting the needs of specific application scenarios. In this way, the multifunctional requirements are met while taking into account the compatibility, thereby solving the problem that the traditional packaging film only has a single function and is limited in use.

[0029] The second is to use a mixture of polylactic acid and polypropylene carbonate as the main material in each layer. Both polylactic acid and polypropylene carbonate are biodegradable polymers. Using their mixture as the main material ensures the overall biodegradability of the packaging film, which is beneficial to environmental protection. Moreover, polylactic acid provides rigidity and thermal stability, while polypropylene carbonate improves toughness and barrier properties, making the packaging film have sufficient strength, good flexibility, and barrier performance. More importantly, the same main material mixture ensures the consistency of performance between layers, which helps to enhance the bonding force between layers, reduce the risk of delamination or peeling, and thus improve the overall stability and durability of the packaging film. In addition, raw materials can be purchased in bulk, reducing costs.

[0030] The applicant would like to emphasize that the existing packaging film has composite layers, and the main materials of the composite layers are different. However, composite layers with different main materials have the following problems: 1. Insufficient interlayer bonding strength: the chemical structure and polarity difference of different base materials may lead to poor interlayer compatibility, and delamination or peeling may occur during co-extrusion. To avoid this phenomenon, additional additives are usually added to solve it, which increases the cost and complexity of the process; 2. Inconsistent degradation rate: the difference in degradation rate of different materials may lead to uneven performance of the film during degradation. If the degradation rate of the surface layer and the intermediate layer does not match, they may exhibit different degradation behaviors under different environmental conditions such as humidity and temperature, limiting the application of the film in complex environments. Therefore, based on this phenomenon, the inventors of the present application designed the main materials of the four layers to be the same, which has more advantages in process controllability, performance stability, and cost-effectiveness.

[0031] In summary, the composite biodegradable packaging film in this embodiment breaks through the limitations of single signal monitoring, can realize multiple functions at the same time, and meets the biodegradable and environmentally friendly requirements. At the same time, the risk of delamination or peeling between each layer during preparation is avoided, the stability and durability are high, the cost investment is reduced, and the application range is greatly increased.

[0032] In one specific embodiment, the content of polylactic acid in the outer layer main material < the content of polylactic acid in the first intermediate layer main material < the content of polylactic acid in the inner layer main material; The content of polylactic acid in the outer layer main material < the content of polylactic acid in the second intermediate layer main material < the content of polylactic acid in the inner layer main material; The content of polypropylene carbonate in the outer layer main material > the content of polypropylene carbonate in the first intermediate layer main material > the content of polypropylene carbonate in the inner layer main material; The content of polypropylene carbonate in the outer layer main material > the content of polypropylene carbonate in the second intermediate layer main material > the content of polypropylene carbonate in the inner layer main material.

[0033] In the present embodiment, since the main materials of the four layers are all mixtures of polylactic acid and polypropylene carbonate, polylactic acid (PLA) is a rigid material with good biodegradability and processability, but poor toughness, which is prone to brittle fracture when subjected to external force; polypropylene carbonate (PPC) is a flexible material also with good biodegradability, which can significantly improve the toughness of the material, but may reduce the rigidity and thermal stability of the material; therefore, the content of PLA and PPC in the four layers is adjusted in a stepwise manner to gradually transition the material properties, thereby balancing the processability, rigidity and toughness.

[0034] Since the outermost layer directly contacts the external environment, it requires relatively low PLA content and relatively high PCC content to make the outer layer of the packaging film have high rigidity and thermal stability to resist mechanical impact and thermal stress from the external environment; the inner layer directly contacts the object inside the packaging film, so relatively high PLA content and relatively low PCC content can reduce the negative impact of flexible materials on the rigidity and thermal stability of the inner layer, while maintaining good bonding force between the inner layer and the middle layer; and the two middle layers act as transition layers between the outer layer and the inner layer, needing to withstand stress from both the outer layer and the inner layer. By maintaining appropriate PLA content and PCC content, the middle layers have both certain rigidity and good toughness, thereby effectively transmitting and dispersing stress and reducing stress concentration.

[0035] In summary, the stepwise design of the content of PLA and PCC in the main material of each layer can avoid micro-deformation of the material layer under light and heat stimulation, such as thermal expansion, shrinkage or phase change, which leads to too large difference in material properties between layers. This micro-deformation causes stress concentration between layers, which in turn triggers peeling; it helps to gradually transition the material properties and reduce stress concentration between layers, thereby ensuring the overall stability.

[0036] In a specific embodiment, the ratio of the weight fraction of polylactic acid to the weight fraction of polypropylene carbonate in the main material of the outer layer is (75-80):(20-25); The ratio of the weight fraction of polylactic acid to the weight fraction of polypropylene carbonate in the main material of the first and second middle layers is both (80-85):(15-20); The ratio of the weight fraction of polylactic acid to the weight fraction of polypropylene carbonate in the main material of the inner layer is both (85-90):(10-15).

[0037] In one specific embodiment, the barrier agent comprises a mixture of graphene oxide and titanium dioxide nanoparticles; the antioxidant comprises a mixture of curcumin, rosemary extract, resveratrol and tea polyphenols; the photo-thermal stimulus response insulator comprises a mixture of temperature-responsive polymers and photosensitive polymers; the antibacterial agent comprises silver nanoparticles.

[0038] Specifically, in the present embodiment, the barrier agent utilizes the two-dimensional sheet structure of graphene oxide to prolong the penetration path of small molecules such as oxygen and water vapor, significantly improving the barrier property of the material; supplemented by titanium dioxide nanoparticles, which can reflect / absorb ultraviolet light, reducing the oxidative degradation of the contents caused by light, enhancing the barrier to oxygen and water vapor, and making the outer layer have excellent barrier performance; the antioxidant utilizes a variety of natural antioxidants to cover a wider range of free radical scavenging, reducing the oxidation and rancidity of the contents, and the natural ingredients are non-toxic and have greatly improved safety; the photo-thermal stimulus response insulator can achieve multi-dimensional intelligent response: 0.1 ppm NH3 triggers color change (ΔE≥2.8), PNIPAM shrinks to reduce air permeability when the temperature is >30℃, and ultraviolet light triggers azobenzene polymer to change air permeability, saving energy and reducing consumption; the innermost layer of silver nanoparticles has strong killing effect on bacteria, fungi and viruses, which can significantly reduce the risk of microbial contamination of the contents of the package, and has a slow-release property, which can maintain the antibacterial effect for a long time, reducing the amount and frequency of adding antibacterial agents.

[0039] In one specific embodiment, the curcumin is nano-encapsulated curcumin prepared by supercritical carbon dioxide, and the specific preparation method is as follows: curcumin is mixed with a chitosan solution with pH=4.5, injected into a supercritical CO2 reaction kettle, and after stirring, a homogeneous emulsion is formed, the reaction conditions are pressure of 15 MPa, temperature of 45℃, and reaction time of 2h; slowly inject sodium alginate solution into the homogeneous emulsion, the mass ratio of sodium alginate solution to homogeneous emulsion is 1:1; after pressure reduction to normal pressure, freeze-drying is performed to obtain nano-encapsulated curcumin.

[0040] In the present embodiment, the curcumin is prepared by supercritical carbon dioxide process, the core is to form nano-capsules of curcumin, chitosan and sodium alginate in supercritical CO2, the nano-encapsulated curcumin has a coating rate of ≥96.2%, which is 15% higher than that of traditional ultrasonic method, and the thermal stability breaks through the processing limit of 200℃. Chitosan solution is used to dissolve curcumin, instead of organic solvent, and sodium alginate solution is injected in the reaction, which is more environmentally friendly. The sample obtained by freeze-drying has better dispersibility and more uniform size.

[0041] In one specific embodiment, the weight parts of each substance of the outer layer are as follows: polylactic acid 75-80 parts; polypropylene carbonate 20-25 parts; graphene oxide 0.1-0.3 parts; titanium dioxide nanoparticles 0.2-0.4 parts; The weight parts of each substance of the first intermediate layer are as follows: polylactic acid 80-85 parts; polypropylene carbonate 15-20 parts; nanocapsulated curcumin 1-2 parts; rosemary extract 0.5-1 part; resveratrol 0.3-0.5 parts; tea polyphenol 0.2-0.4 parts; The weight parts of each substance of the second intermediate layer are as follows: polylactic acid 80-85 parts; polypropylene carbonate 15-20 parts; poly-N-isopropyl acrylamide 1-2 parts; azobenzene polymer 0.5-1 part; The weight parts of each substance of the inner layer are as follows: polylactic acid 85-90 parts; polypropylene carbonate 10-15 parts; silver nanoparticles 0.05-0.1 parts.

[0042] In one specific embodiment, the barrier agent further comprises a dynamic crosslinking agent, the weight parts of the dynamic crosslinking agent being 0.5-1 part; the dynamic crosslinking agent is a polyethylene glycol prepolymer containing a disulfide bond; the outer layer and the inner layer further comprise nanocellulose, the weight parts of the nanocellulose being 0.8-1.2 parts; and the diameter of the nanocellulose is 10-30 nm, and the length of the nanocellulose is 1-2 μm.

[0043] In one specific embodiment, the thickness of the outer layer accounts for 20-25% of the thickness of the entire composite biodegradable packaging film; the thickness of the first intermediate layer accounts for 25-30% of the thickness of the entire composite biodegradable packaging film; the thickness of the second intermediate layer accounts for 25-30% of the thickness of the entire composite biodegradable packaging film; and the thickness of the inner layer accounts for 20-25% of the thickness of the entire composite biodegradable packaging film.

[0044] In one specific embodiment, a method for preparing a composite biodegradable packaging film as described in any one of the above embodiments, comprising the following steps: S1: preparing an outer layer mixture, a first intermediate layer mixture, a second intermediate layer mixture, and an inner layer mixture according to the main ingredients and auxiliary ingredients respectively; S2: blending the outer layer mixture, the first intermediate layer mixture, the second intermediate layer mixture, and the inner layer mixture into a shaped film; S3: performing plasma treatment on the surface of the shaped film, the plasma treatment process parameters being power 50 W and time 30 s; and finally obtaining a composite biodegradable packaging film.

[0045] Specifically, in this embodiment, the preparation method of the composite biodegradable packaging film adopts a four-channel co-extruder to blend the formed film, i.e., the raw materials of four layers are respectively introduced into four different channels and then uniformly introduced into a customized die to form the packaging film, and the customized die is the shape of the formed packaging film.

[0046] The preparation method is simple to operate, does not need to introduce a complex process, and reduces the preparation cost; and through the multi-layer co-extrusion process, the precise compounding of each layer of material is realized, and the interlayer bonding strength is ensured; the blending forming can reduce interlayer defects such as delamination and bubbles, and improve the mechanical stability and barrier consistency of the packaging film; at the same time, the surface functionalization and performance improvement are carried out through the plasma treatment, so as to improve the interlayer adhesion and surface hydrophilicity.

[0047] The application of a composite biodegradable packaging film as described in any one of the above embodiments is used in the fields of food, medicine and cosmetics.

[0048] In order to further verify the effect of the present application, the following examples and comparative examples are used for illustration: Example 1: Outer layer: 75 parts of polylactic acid; 20 parts of polypropylene carbonate; 0.1 part of graphene oxide; 0.2 part of titanium dioxide nanoparticles; First intermediate layer: 80 parts of polylactic acid; 15 parts of polypropylene carbonate; 2 parts of nanocapsulated curcumin; 0.5 part of rosemary extract; 0.3 part of resveratrol; 0.2 part of tea polyphenol; Second intermediate layer: 80 parts of polylactic acid; 15 parts of polypropylene carbonate; 1 part of poly N-isopropyl acrylamide; 0.5 part of azobenzene polymer; Inner layer: 85 parts of polylactic acid; 10 parts of polypropylene carbonate; 0.05 part of nano-silver particles.

[0049] Example 2: Outer layer: 80 parts of polylactic acid; 25 parts of polypropylene carbonate; 0.3 part of graphene oxide; 0.4 part of titanium dioxide nanoparticles; First intermediate layer: 85 parts of polylactic acid; 15 parts of polypropylene carbonate; 2 parts of nanocapsulated curcumin; 1 part of rosemary extract; 0.5 part of resveratrol; 0.4 part of tea polyphenol; Second intermediate layer: 85 parts of polylactic acid; 20 parts of polypropylene carbonate; 2 parts of poly N-isopropyl acrylamide; 1 part of azobenzene polymer; Inner layer: 90 parts of polylactic acid; 15 parts of polypropylene carbonate; 0.1 part of nano-silver particles.

[0050] Example 3: Outer layer: 75 parts of polylactic acid; 25 parts of polypropylene carbonate; 0.2 part of graphene oxide; 0.3 part of titanium dioxide nanoparticles; First intermediate layer: polylactic acid 80 parts; polypropylene carbonate 20 parts; nanocapsulated curcumin 2 parts; rosemary extract 0.5 parts; resveratrol 0.3 parts; tea polyphenols 0.2 parts; Second intermediate layer: polylactic acid 80 parts; polypropylene carbonate 20 parts; poly N-isopropyl acrylamide 1.5 parts; azobenzene polymer 0.5 parts; Inner layer: polylactic acid 85 parts; polypropylene carbonate 15 parts; nanosilver particles 0.1 parts.

[0051] Example 4: Outer layer: polylactic acid 75 parts; polypropylene carbonate 25 parts; graphene oxide 0.2 parts; titanium dioxide nanoparticles 0.3 parts; 1 part nanocellulose; First intermediate layer: polylactic acid 80 parts; polypropylene carbonate 20 parts; nanocapsulated curcumin 2 parts; rosemary extract 0.5 parts; resveratrol 0.3 parts; tea polyphenols 0.2 parts; Second intermediate layer: polylactic acid 80 parts; polypropylene carbonate 20 parts; poly N-isopropyl acrylamide 1.5 parts; azobenzene polymer 0.5 parts; Inner layer: polylactic acid 85 parts; polypropylene carbonate 15 parts; nanosilver particles 0.1 parts, 0.8 parts nanocellulose.

[0052] Example 5: Outer layer: polylactic acid 75 parts; polypropylene carbonate 20 parts; graphene oxide 0.1 parts; titanium dioxide nanoparticles 0.2 parts; nanocellulose 0.8 parts; First intermediate layer: polylactic acid 80 parts; polypropylene carbonate 15 parts; nanocapsulated curcumin 2 parts; rosemary extract 0.5 parts; resveratrol 0.3 parts; tea polyphenols 0.2 parts; Second intermediate layer: polylactic acid 80 parts; polypropylene carbonate 15 parts; poly N-isopropyl acrylamide 1 part; azobenzene polymer 0.5 parts; Inner layer: polylactic acid 85 parts; polypropylene carbonate 10 parts; nanosilver particles 0.05 parts, nanocellulose 0.8 parts.

[0053] Example 6: Outer layer: polylactic acid 80 parts; polypropylene carbonate 25 parts; graphene oxide 0.3 parts; titanium dioxide nanoparticles 0.4 parts; nanocellulose 1.2 parts; First intermediate layer: polylactic acid 85 parts; polypropylene carbonate 15 parts; nanocapsulated curcumin 2 parts; rosemary extract 1 part; resveratrol 0.5 parts; tea polyphenols 0.4 parts; Second intermediate layer: polylactic acid 85 parts; polypropylene carbonate 20 parts; poly N-isopropyl acrylamide 2 parts; azobenzene polymer 1 part; Inner layer: polylactic acid 90 parts; polypropylene carbonate 15 parts; nano silver particles 0.1 part; nanocellulose 1.2 parts.

[0054] Example 7: Outer layer: polylactic acid 75 parts; polypropylene carbonate 25 parts; graphene oxide 0.2 parts; titanium dioxide nanoparticles 0.3 parts; 1 part nanocellulose; First intermediate layer: polylactic acid 80 parts; polypropylene carbonate 20 parts; nanoencapsulated curcumin 2 parts; rosemary extract 0.5 parts; resveratrol 0.3 parts; tea polyphenols 0.2 parts; Second intermediate layer: polylactic acid 80 parts; polypropylene carbonate 20 parts; poly N-isopropyl acrylamide 1.5 parts; azobenzene polymer 0.5 parts; polyethylene glycol prepolymer containing disulfide bond (PEG-SS) 0.5 parts; Inner layer: polylactic acid 85 parts; polypropylene carbonate 15 parts; nano silver particles 0.1 part, 0.8 parts nanocellulose.

[0055] Comparative Example 1: The same as Example 3, except that the main material of the four layers is polylactic acid 75 parts.

[0056] Comparative Example 2: The same as Example 3, except that the main material of the four layers is polylactic acid 75 parts.

[0057] Comparative Example 3: The same as Example 3, except that the main material of the four layers is polylactic acid 75 parts.

[0058] Comparative Example 4: The same as Example 3, except that the main material of the four layers is polylactic acid 75 parts.

[0059] Comparative Example 5: The same as Example 3, except that the main material of the four layers is polylactic acid 75 parts. The same as Example 3, except that the main material of the four layers is polylactic acid 75 parts.

[0060] Table 1 experimental data table

[0061] From Table 1, it can be seen that PPC can significantly enhance the toughness of the system, and cellulose can improve the mechanical properties of the system, so the elongation at break of Example 3 is the highest, and the elongation at break of Example 5 is the lowest. Graphene oxide and titanium dioxide can reduce the oxygen permeability, so the values of Examples 2 and 6 are the lowest, and the value of Example 1 is the highest. Antioxidants can improve the DPPH clearance rate, and the antioxidants contained in Examples 2 and 6 in the system are the highest, so the value of DPPH is also the highest. Nano-silver can effectively inhibit E. coli, so the inhibition rate of Example 4 is the highest, and the content of nano-silver in Examples 2, 3, 6 and 7 is equal, and the bacteriostatic rate is similar, followed by Examples 1 and 5, and the values are similar. However, the values of Examples 1-7 as a whole meet the use requirements. In contrast, the bacteriostatic rates of Comparative Examples 1-5 are significantly lower than those of Examples 1-7, and some indicators have dropped significantly, which cannot meet the existing use requirements.

[0062] The examples described in the present application are only used to describe the preferred embodiments of the present application, and do not limit the concept and scope of the present application. Without departing from the design idea of the present application, various modifications and improvements of the technical solutions of the present application made by the engineering and technical personnel in the field shall fall within the protection scope of the present application.

Claims

1. A composite biodegradable packaging film, characterized in that: It includes an outer layer, a first middle layer, a second middle layer and an inner layer arranged in sequence; the outer layer, the first middle layer, the second middle layer and the inner layer all include a main material and an auxiliary material, the main material is a mixture of polylactic acid and polypropylene carbonate; the auxiliary material of the outer layer is a barrier agent; the auxiliary material of the first middle layer is an antioxidant; the auxiliary material of the second middle layer is a photothermal stimulus responsive isolation agent, and the auxiliary material of the inner layer is an antibacterial agent.

2. The composite biodegradable packaging film according to claim 1, characterized in that: The content of polylactic acid in the main material of the outer layer is less than the content of polylactic acid in the main material of the first intermediate layer and less than the content of polylactic acid in the main material of the inner layer; The content of polylactic acid in the main material of the outer layer is less than the content of polylactic acid in the main material of the second intermediate layer and less than the content of polylactic acid in the main material of the inner layer; The content of polypropylene carbonate in the outer layer main material is greater than the content of polypropylene carbonate in the first intermediate layer main material and greater than the content of polypropylene carbonate in the inner layer main material; The content of polypropylene carbonate in the main material of the outer layer is greater than the content of polypropylene carbonate in the main material of the second intermediate layer and greater than the content of polypropylene carbonate in the main material of the inner layer.

3. The composite biodegradable packaging film according to claim 2, characterized in that: The weight ratio of polylactic acid to polypropylene carbonate in the main material of the outer layer is (75-80): (20-25); The weight ratio of polylactic acid to polypropylene carbonate in the main materials of the first intermediate layer and the second intermediate layer is (80-85): (15-20); The weight ratio of polylactic acid to polypropylene carbonate in the main material of the inner layer is (85-90): (10-15).

4. The composite biodegradable packaging film according to claim 1, characterized in that: The barrier comprises a mixture of graphene oxide and titanium dioxide nanoparticles; the antioxidant comprises a mixture of curcumin, rosemary extract, resveratrol and tea polyphenols; the photothermal stimulation responsive insulating agent comprises a mixture of temperature responsive polymer and photosensitive polymer; and the antibacterial agent comprises nanosilver particles.

5. The composite biodegradable packaging film according to claim 4, characterized in that: The curcumin is nano-encapsulated curcumin prepared by supercritical carbon dioxide. The specific preparation method is as follows: curcumin and chitosan solution are mixed, injected into a supercritical CO2 reactor for reaction to form a homogeneous emulsion, sodium alginate solution is injected into the homogeneous emulsion, and the pressure is reduced to normal pressure and then freeze-dried to obtain nano-encapsulated curcumin.

6. The composite biodegradable packaging film according to claim 4, characterized in that: The weight proportions of the materials in the outer layer are as follows: 75-80 parts of polylactic acid; 20-25 parts of polypropylene carbonate; 0.1-0.3 parts of graphene oxide; 0.2-0.4 parts of titanium dioxide nanoparticles; The weight proportions of the materials in the first intermediate layer are as follows: 80-85 parts of polylactic acid; 15-20 parts of polypropylene carbonate; 1-2 parts of nanoencapsulated curcumin; 0.5-1 part of rosemary extract; 0.3-0.5 parts of resveratrol; and 0.2-0.4 parts of tea polyphenols. The weight proportions of the materials in the second intermediate layer are as follows: 80-85 parts of polylactic acid; 15-20 parts of polypropylene carbonate; 1-2 parts of poly-N-isopropylacrylamide; and 0.5-1 part of azobenzene polymer. The weight proportions of the materials in the inner layer are as follows: 85-90 parts of polylactic acid; 10-15 parts of polypropylene carbonate; and 0.05-0.1 parts of nano silver particles.

7. The composite biodegradable packaging film according to claim 4 or 6, characterized in that: The barrier also includes a dynamic cross-linking agent, the weight portion of the dynamic cross-linking agent is 0.5~1 parts; the dynamic cross-linking agent is a polyethylene glycol prepolymer containing a disulfide bond; the outer layer and the inner layer also include nanocellulose, the weight portion of the nanocellulose is 0.8~1.2 parts; and the diameter of the nanocellulose is 10~30nm, and the length of the nanocellulose is 1~2μm.

8. The composite biodegradable packaging film according to claim 1, characterized in that: The thickness of the outer layer accounts for 20-25% of the thickness of the entire composite biodegradable packaging film; the thickness of the first intermediate layer accounts for 25-30% of the thickness of the entire composite biodegradable packaging film; the thickness of the second intermediate layer accounts for 25-30% of the thickness of the entire composite biodegradable packaging film; and the thickness of the inner layer accounts for 20-25% of the thickness of the entire composite biodegradable packaging film.

9. A method for preparing the composite biodegradable packaging film according to any one of claims 1 to 8, characterized in that: The following steps are involved: According to the main ingredients and auxiliary materials, an outer layer mixture, a first intermediate layer mixture, a second intermediate layer mixture and an inner layer mixture are prepared respectively; blending the outer layer mixture, the first middle layer mixture, the second middle layer mixture and the inner layer mixture to form a film; The surface of the formed film is subjected to plasma treatment to finally obtain a composite biodegradable packaging film.

10. Use of a composite biodegradable packaging film according to any one of claims 1 to 8, characterized in that: Used in food, medical and cosmetic fields.

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