High-barrier antibacterial polylactic acid packaging material and preparation method thereof

Abstract

The present invention relates to a high-barrier and antibacterial polylactic acid packaging material and a preparation method thereof, and belongs to the technical field of biodegradable packaging materials. The invention solves the technical problems that traditional polylactic acid materials have insufficient barrier properties, poor antibacterial performance and are difficult to meet the packaging needs of livestock and poultry meat, food and medicine. Graphene oxide sheet material is functionalized with copper ions and bridged with tannic acid molecules through copper ions to form a nanofiller, which is then blended with a plasticized polylactic acid solution to form a film. Graphene oxide and copper nitrate are used to prepare a copper ion functionalized dispersion, which is self-assembled with tannic acid at pH 8-10 to generate a nanofiller, which is then evenly dispersed and mixed with polylactic acid, polyethylene glycol and glycerol in a specific mass ratio. The high-performance packaging material is obtained by coating to form a film and controlling the solvent volatilization conditions. The method significantly improves the oxygen barrier and antibacterial activity of the material by evenly dispersing the nanofiller and strengthening the coordination network. The obtained material is suitable for packaging livestock and poultry meat and other foods.

Description

Technical Field

[0001] The invention belongs to the technical field of biodegradable packaging materials, and in particular relates to a method for preparing a high-barrier and antibacterial polylactic acid packaging material. Background Art

[0002] Polylactic acid (PLA), a biodegradable material, holds great potential in the packaging sector, but its practical application is still limited by performance deficiencies. Conventional PLA materials exhibit low barrier properties against gases such as oxygen and water vapor, making them inadequate for applications requiring high barrier performance, such as food and pharmaceutical packaging. This problem stems from the chemical properties of the PLA molecular chain, which results in limited crystallinity, a large internal free volume, and weak intermolecular forces, allowing gas molecules to diffuse and penetrate easily. While increasing the material's thickness can partially improve barrier properties, this reduces its flexibility, increases its cost, and conflicts with the demand for lightweight packaging. Existing attempts to enhance barrier properties include the introduction of inorganic nanofillers (such as montmorillonite and nanosilica). However, nanofillers tend to aggregate and disperse poorly within the matrix, leading to internal defects and limited improvements in barrier properties. Furthermore, surface coatings can enhance barrier properties, but the interfacial bonding between the coating and the PLA matrix is ​​weak, making it prone to flaking. Furthermore, the coating process is complex and may introduce non-degradable components, compromising the material's environmental friendliness.

[0003] In terms of antibacterial properties, polylactic acid itself lacks antibacterial activity and requires the addition of external antibacterial agents. Traditional methods often use physically mixed antibacterial agents such as silver ions and quaternary ammonium salts, but these methods have significant drawbacks: silver ions easily migrate to the packaging surface or contents, posing a potential biotoxicity risk and a short antibacterial effect. Organic antibacterial agents (such as triclosan) have poor thermal stability and are prone to decomposition and ineffectiveness under the high-temperature conditions of polylactic acid processing. Furthermore, antibacterial agents have poor compatibility with the polylactic acid matrix and tend to form aggregates within the material, which not only reduces antibacterial efficiency but also disrupts material uniformity and reduces mechanical strength. Existing studies have attempted to graft antibacterial groups onto the polylactic acid molecular chain through chemical modification, but the modification process is complex and may compromise the biodegradability of polylactic acid. Furthermore, the grafting rate is difficult to precisely control, affecting the stability of the antibacterial effect.

[0004] Furthermore, the synergistic improvement of barrier and antibacterial properties faces technical bottlenecks. For example, the introduction of high levels of antibacterial agents may exacerbate filler agglomeration, further weakening barrier properties; while excessive pursuit of barrier optimization may lead to increased material brittleness and deteriorate processing performance. The existing technology lacks effective methods that can simultaneously achieve high dispersion of nanofillers, long-lasting antibacterial activity, and a stable barrier structure within a polylactic acid matrix. Furthermore, the complexity of the material preparation process is a limiting factor: while multi-step modification or complex composite processes may improve performance, they significantly increase production costs and hinder large-scale production. For example, surface functionalization of nanofillers typically requires strictly controlled reaction conditions (such as specific pH, temperature, and ultrasonic power). Even the slightest deviation in these process parameters can lead to structural damage or functional failure of the filler, posing significant challenges to the stability and reproducibility of industrial production. Therefore, developing a simple, cost-effective method that can simultaneously enhance the barrier and antibacterial properties of polylactic acid materials remains a pressing technical challenge in this field. Summary of the Invention

[0005] One purpose of the present invention is to solve how to improve the preparation process of polylactic acid material while improving its oxygen barrier property, antibacterial activity and processing controllability, while avoiding nanofiller agglomeration and matrix performance degradation.

[0006] Solve how to optimize the formation of copper-tannic acid coordination network during ultrasonic treatment, ensure the stability of nanofiller structure, and avoid uneven dispersion caused by insufficient power or structural damage caused by excessive power.

[0007] The goal is to achieve a balance between film thickness uniformity and solvent evaporation rate through refined control of coating process parameters, thereby avoiding film defects or residual solvents affecting material properties.

[0008] The solution is to solve how to balance film continuity and complete solvent removal by controlling the humidity in stages during the solvent volatilization stage, to prevent excessive humidity from causing film dissolution or excessive humidity from causing surface cracking.

[0009] Solve how to establish a dynamic relationship between coating speed, gap width and substrate temperature to ensure the stability and repeatability of the coating process and avoid film thickness fluctuations or material waste caused by parameter mismatch.

[0010] The goal is to achieve uniform dispersion of fillers in a polylactic acid matrix by adding nanofillers in stages and controlling mixing conditions, thereby avoiding agglomeration or insufficient mixing caused by one-time addition.

[0011] Solve the problem of how to obtain size-controlled and uniformly distributed flaky materials through segmented ultrasonic treatment and static process during the dispersion of graphene oxide, avoiding excessive crushing or insufficient exfoliation.

[0012] Solve the problem of how to ensure the stability of the reaction system through precise stage-by-stage control and online feedback during the pH adjustment process, and avoid pH mutations that may cause structural destruction or functional failure of the nanofiller.

[0013] The goal is to solve the problem of how to maintain the uniformity of the reaction system through staged stirring control and dynamic pH monitoring, and avoid local concentration gradients or pH fluctuations affecting the integrity of the copper-tannic acid coordination network.

[0014] The goal is to solve the problem of how to compound nanofillers with polylactic acid matrix in a specific mass ratio to ensure that the material has high barrier properties, long-term antibacterial properties and biodegradability, thereby avoiding performance imbalance or environmental hazards.

[0015] The present invention provides a method for preparing a high-barrier and antibacterial polylactic acid packaging material, comprising the following steps:

[0016] S1: dissolving a graphene oxide sheet material in deionized water to form a dispersed solution, adding copper nitrate, wherein the mass ratio of copper nitrate to graphene oxide is 20:1 to 80:1, to obtain a copper ion functionalized graphene oxide sheet material;

[0017] S2: dissolving the copper ion functionalized graphene oxide sheet material obtained in S1 in an ethanol-water mixed solution, adding tannic acid molecules, wherein the mass ratio of the copper ion functionalized graphene oxide sheet material to tannic acid is 1:2 to 1:60, heating and stirring at 45° C. to 65° C., and adjusting the pH of the reaction system to 8 to 10, to obtain a copper ion bridged tannic acid-graphene oxide nanofiller;

[0018] S3: dissolving the copper ion-bridged tannic acid-graphene oxide nanofiller obtained in S2 in deionized water at a mass ratio of nanofiller to deionized water of 1:25 to 1:100, magnetically stirring at 300 to 500 r / min and ultrasonically treating to obtain a uniformly dispersed functionalized nanofiller suspension;

[0019] S4: dissolving polylactic acid in a dichloromethane solvent, wherein the mass ratio of polylactic acid to dichloromethane is 1:5 to 1:10, adding polyethylene glycol and glycerol, wherein the mass ratio of polylactic acid to polyethylene glycol is 1:0.05 to 1:0.1, and the mass ratio of polylactic acid to glycerol is 1:0.1 to 1:0.5, to form a plasticized polylactic acid solution;

[0020] S5: Blend the nanofiller suspension of S3 with the plasticized polylactic acid solution of S4, the mass ratio of the nanofiller suspension to the plasticized polylactic acid solution is 1:20 to 1:200, and the total mass ratio of the nanofiller to polylactic acid, dichloromethane, polyethylene glycol and glycerol is 0.005:1 to 0.02:1. After film formation, the solvent is evaporated at 25°C to 35°C to obtain a high barrier and antibacterial polylactic acid packaging material.

[0021] Preferably, the power of the ultrasonic treatment in step S3 of the present invention is not less than 100 W, wherein: during the self-assembly process of tannic acid molecules and copper ion functionalized graphene oxide sheet materials, an ultrasonic power of 100 W to 200 W is used for 10 to 30 minutes; the ultrasonic treatment is carried out in two stages: the first stage is treated with a power of 100 W to 150 W for 5 to 15 minutes to initially coordinate the tannic acid molecules with the copper ions; the second stage is treated with a power of 150 W to 200 W for 5 to 15 minutes to strengthen the copper-tannic acid coordination network structure; the interval time of the two-stage ultrasonic treatment is 1 to 3 minutes, and the total treatment time is controlled within the range of 10 to 30 minutes.

[0022] Preferably, the film formation in step S5 of the present invention is completed by an automatic coating machine, the coating speed of the automatic coating machine is 0.5 m / min to 2.0 m / min, the coating gap width is 0.1 mm to 0.5 mm, and the substrate temperature during the coating process is 25°C to 35°C; the scraper angle of the automatic coating machine is 30° to 60°, and after coating, the film layer is allowed to stand in an environment of 25°C to 35°C to volatilize the solvent for 10 minutes to 60 minutes, and the volatilization environment humidity is controlled within the range of 30% RH to 60% RH.

[0023] Preferably, the standing process of the present invention is divided into two stages: the first stage is standing for 10 minutes to 30 minutes, the ambient humidity is 50% RH to 60% RH, so that the solvent is initially evaporated to form a continuous film layer; the second stage is standing for the remaining time, the ambient humidity is adjusted to 30% RH to 50% RH, and the solvent is accelerated to completely evaporate; during the two-stage standing process, the ambient temperature is kept constant, and the temperature difference does not exceed ±2°C.

[0024] Preferably, the relationship between the coating speed and the coating gap width of the present invention satisfies the following conditions: when the coating speed is 0.5 m / min to 1.0 m / min, the coating gap width is 0.3 mm to 0.5 mm; when the coating speed is 1.0 m / min to 2.0 m / min, the coating gap width is 0.1 mm to 0.3 mm; the substrate temperature is linked to the coating speed and is controlled so that for every 0.5 m / min increase in the coating speed, the substrate temperature decreases by 2°C to 5°C, and the temperature fluctuation does not exceed ±1°C; the coating gap width is calibrated in real time by a laser rangefinder with a calibration accuracy of ±0.01 mm, and the gap deviation is automatically adjusted after each 10 m of coating is completed.

[0025] Preferably, the mass ratio of polylactic acid to dichloromethane of the present invention is 1:5 to 1:10; the mass ratio of polylactic acid to polyethylene glycol is 1:0.05 to 1:0.1; the mass ratio of polylactic acid to glycerol is 1:0.1 to 1:0.5; the addition of nanofillers is carried out in two stages: in the first stage, nanofillers with a total mass ratio of 0.002:1 to 0.01:1 are added and pre-mixed with the polylactic acid solution for 10 to 20 minutes at a mixing temperature of 25°C to 35°C; in the second stage, the remaining 0.003:1 to 0.01:1 of nanofillers are added and mixing is continued for 20 to 40 minutes, with the mixing speed increased to 500 r / min to 800 r / min.

[0026] Preferably, the step of dissolving the graphene oxide sheet material in deionized water to form a dispersed solution in the present invention comprises: dispersing the graphene oxide sheet material in deionized water at a concentration of 0.5 mg / mL to 2.0 mg / mL, ultrasonically treating the graphene oxide sheet material for 10 to 30 minutes at a power of 100 W to 200 W and an ultrasonic frequency of 20 kHz to 40 kHz; the ultrasonic treatment is performed twice, the first ultrasonic treatment lasts for 10 to 15 minutes, and the ultrasonic treatment is allowed to stand for 5 to 10 minutes, followed by a second ultrasonic treatment for 10 to 15 minutes; the lateral size of the graphene oxide sheet material in the dispersed solution is 0.5 μm to 5 μm, and the thickness is 1 nm to 10 nm; the dispersed solution is allowed to stand for 24 to 48 hours after ultrasonic treatment, and the upper uniform suspension is taken for subsequent reaction.

[0027] Preferably, the specific steps of adjusting the pH of the reaction system to 8 to 10 of the present invention include: adding an alkaline solution with a concentration of 0.1 mol / L to 1.0 mol / L dropwise to a mixed solution of copper ion functionalized graphene oxide sheet material and tannic acid in ethanol and water, and adjusting the pH at a rate of 0.5 to 2 pH units per minute; the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution; the pH adjustment is completed in two stages: in the first stage, the pH is quickly adjusted from the initial value to 8 to 9, and the adjustment time is controlled within 1 minute to 5 minutes; in the second stage, the pH is slowly adjusted from 8 to 9 to 9 to 10, and the adjustment time is controlled within 5 minutes to 15 minutes; after the adjustment is completed, stirring is continued for 10 minutes to 30 minutes so that the pH fluctuation range of the system does not exceed ±0.2, and real-time feedback control is performed by an online pH monitor.

[0028] Preferably, the specific step of continuously stirring for 10 to 30 minutes after the step adjustment of the present invention is completed includes: adopting two-stage stirring control, stirring at a speed of 200 r / min to 400 r / min for 5 to 15 minutes in the first stage, and stirring at a speed of 50 r / min to 150 r / min for the remaining time in the second stage; during the stirring process, the pH value of the system is detected in real time by an online pH monitor, and the detection frequency is once every 10 to 30 seconds. When the pH fluctuation exceeds ±0.2, alkaline solution or acidic solution is automatically added, and the single addition amount is 0.01% to 0.1% of the total mass of the system; the stirring temperature is linked to the temperature of the reaction system, the temperature fluctuation does not exceed ±1°C, and the diameter of the stirring blade is 1 / 3 to 1 / 2 of the inner diameter of the reaction vessel; the electrode response time of the online pH monitor is less than 5 seconds, the calibration error does not exceed ±0.05 pH unit, and it is dynamically matched with the stirring speed: when the stirring speed is higher than 300 r / min, the pH detection frequency is increased to once every 10 seconds; when the stirring speed is lower than 300 When the pH value is set at r / min, the pH detection frequency is adjusted to once every 30 seconds.

[0029] Preferably, the present invention also provides a high-barrier and antibacterial polylactic acid packaging material, which comprises copper ion-bridged tannic acid-graphene oxide nanofillers uniformly dispersed in a polylactic acid matrix, and the mass ratio of the nanofiller to the polylactic acid is 0.005:1 to 0.02:1; the thickness of the packaging material is 0.01 mm to 0.5 mm.

[0030] Beneficial effects:

[0031] The copper-bridged tannic acid-graphene oxide nanofiller, combined with plasticized polylactic acid, significantly improves the material's oxygen barrier properties (reducing permeability by 30%-50%) and antibacterial efficiency (>99% against Escherichia coli and Staphylococcus aureus). Uniform dispersion of the nanofiller prevents agglomeration defects, while the synergistic plasticizing effect of polyethylene glycol and glycerol improves the material's flexibility, ensuring a controllable processing process and increasing yield by over 20%.

[0032] A phased ultrasonic treatment optimizes the formation of the copper-tannic acid coordination network. Low power in the first phase promotes initial molecular coordination, while high power in the second phase enhances structural stability. Intervals prevent filler fragmentation caused by energy accumulation. This design results in a concentrated lateral size distribution of the nanofiller (CV <10%), a 15%-20% increase in antibacterial activity, and a narrowing of the barrier performance fluctuation range to ±5%.

[0033] Linked control of coating speed, gap width, and substrate temperature ensures film thickness deviations of less than ±0.01mm. Matching solvent evaporation rate with film formation speed prevents surface pinholes and cracks. Optimized blade angles reduce coating fluid residue, improve film uniformity, and reduce material tensile strength fluctuations from ±15% to ±5%.

[0034] Staged humidity control balances film continuity and solvent removal efficiency. High humidity (50%-60% RH) in the first stage prevents film shrinkage and cracking, while low humidity (30%-50% RH) in the second stage accelerates solvent evaporation to a residual level of <0.1%. Maintaining a constant temperature (±2°C) prevents sudden changes in solvent evaporation rate and improves film transparency (haze <5%).

[0035] Dynamic matching of coating parameters reduces process fluctuations. Laser ranging uses real-time calibration of gap width (accuracy ±0.01mm) to reduce material waste by 10%-15%. The substrate temperature is linked to the coating speed (reduced by 2°C-5°C per 0.5 m / min) to ensure uniform thermal stress in the film layer and avoid warping or curling defects.

[0036] Nanofillers were added in stages and the mixing speed was increased gradually. The first pre-mixing (25℃-35℃) promoted filler wetting, and the second high-speed mixing (500-800 r / min) broke up the agglomerates. Finally, the filler dispersion uniformity (D90 <5.0 μm) was improved by 40%, and the material elongation at break was increased to 120%-150%.

[0037] A segmented sonication and static process yields graphene oxide flakes with lateral dimensions of 0.5-5.0 μm and thicknesses of 1-10 nm, achieving a flake exfoliation rate >90%, preventing degradation of barrier properties due to excessive fragmentation. After static processing, the upper suspension layer (solids content deviation <2%) is collected to ensure precise control of filler concentration in subsequent reactions.

[0038] Phased pH adjustment and online feedback control avoid local over-alkalinity (pH>10) that triggers tannic acid oxidation or copper ion precipitation. pH fluctuation <±0.2 ensures the integrity of the coordination network, increases the functionalization efficiency of nanofillers to more than 95%, and significantly improves the stability of antibacterial performance (30-day attenuation <5%).

[0039] Dynamic stirring and pH monitoring match process parameters. High-speed stirring (200-400 r / min) eliminates concentration gradients, low-speed stirring (50-150 r / min) maintains system stability, and automatic rehydration (single 0.01%-0.1%) prevents pH shift. The filler-matrix interface bonding strength is increased by 20%-30%.

[0040] By limiting the mass ratio of nanofiller to polylactic acid (0.005:1-0.02:1) and the thickness range (0.01-0.5mm), and balancing barrier properties, mechanical properties and cost, the material oxygen permeability can be less than 20 cm³ / (m²·day·0.1 Mpa) and water vapor permeability can be less than 10 g / (m 2·24 h), the antibacterial activity can be maintained at >99% (60 days), and the complete biodegradation period is shortened to 6-12 months. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the preparation of copper ion-bridged tannic acid-graphene oxide nanofillers.

[0042] Figure 2 It is a copper ion bridged tannic acid-graphene oxide nanofiller.

[0043] Figure 3 X-ray diffraction pattern of tannic acid-graphene oxide nanofiller bridged by copper ions.

[0044] Figure 4 Schematic diagram of the structure of high barrier and antibacterial polylactic acid packaging material.

[0045] Figure 5 This is a physical picture of high-barrier and antibacterial polylactic acid packaging material. DETAILED DESCRIPTION

[0046] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0047] The embodiments of the present application provide a method for preparing a high-barrier antibacterial polylactic acid packaging material, comprising:

[0048] S1: Preparation of copper ion functionalized graphene oxide sheet materials by coordination modification.

[0049] The positively charged copper ions are combined with the oxygen-containing functional groups of the graphene oxide sheet material, such as carboxyl or hydroxyl groups, through coordination modification. With the copper ions as anchor points, they lay the material foundation for the subsequent loading of the antibacterial substance tannic acid. The copper ion-functionalized graphene oxide sheet material has both the coordination effect of copper ions and the barrier properties of the two-dimensional graphene oxide network.

[0050] S2: Utilizing the multidentate coordination between tannic acid molecules and copper ions, self-assembled tannic acid-graphene oxide nanofillers bridged by copper ions were constructed.

[0051] The antibacterial substance tannic acid molecules self-assemble with the anchor points of copper ion functionalized graphene oxide sheet materials to form tannic acid-graphene oxide nanofillers bridged by copper ions, which increases the bonding ability between the antibacterial substance tannic acid and graphene oxide, gives the nanofiller structural stability, and lays the foundation for industrial production.

[0052] S3: The nanofiller obtained in S2 is subjected to ultrasonic dispersion treatment to obtain a uniformly dispersed functionalized nanofiller suspension.

[0053] Copper ion-bridged tannic acid-graphene oxide nanofillers were dissolved in deionized water and ultrasonically treated to maintain the dispersion of the nanofillers, increase their surface area, and improve the interfacial stability of the nanofillers.

[0054] S4: dissolving polylactic acid in dichloromethane solvent and performing plasticization modification.

[0055] Polylactic acid particles are dissolved in dichloromethane solvent and magnetically stirred until completely dissolved. Polyethylene glycol and glycerol are added in sequence for plasticization. Polyethylene glycol acts as a long-chain plasticizer to improve the flexibility of the chain segments, and glycerol can reduce interchain entanglement. Continuous stirring forms a transparent and viscous plasticized polylactic acid solution.

[0056] S5: The nanofiller suspension of S3 is blended with the plasticized polylactic acid solution of S4 to form a film, thereby obtaining a high-barrier and antibacterial polylactic acid packaging material.

[0057] Copper ion-bridged tannic acid-graphene oxide nanofiller is blended with polylactic acid, polyethylene glycol, and glycerol for plasticization modification and film formation to obtain a high-barrier and antibacterial polylactic acid packaging material. In this embodiment, positively charged copper ions are coordinated to modify graphene oxide sheet materials to enhance the interaction between the antibacterial substance tannic acid and graphene oxide, increase the loading capacity of graphene oxide on tannic acid, construct copper ion-bridged tannic acid-graphene oxide nanofiller, and use a synergistic plasticization and blending process to prepare a high-barrier and antibacterial packaging material. This solves the problems of poor barrier properties and poor antibacterial effect of polylactic acid packaging materials, achieves improved water vapor barrier properties and antibacterial activity of polylactic acid packaging materials, and has great application potential in meat packaging, providing antibacterial active packaging materials for the research and development of food packaging preservation technology.

[0058] In another embodiment, in S1, the preparation method of the copper ion functionalized graphene oxide sheet material includes: dissolving graphene oxide in deionized water, adding copper nitrate, and preparing the copper ion functionalized graphene oxide sheet material by reacting copper ions with the surface active groups of graphene oxide; that is, utilizing the coordination effect of copper ions and oxygen-containing functional groups to anchor copper ions on the surface of graphene oxide, and the anchored copper ions enable graphene oxide to have the ability to bind more antibacterial substances such as tannic acid, thereby realizing the copper ion functionalization modification of graphene oxide; optionally, the mass ratio of copper nitrate to graphene oxide is (20~80):1.

[0059] In another embodiment, in S2, the method for constructing a copper ion-bridged tannic acid-graphene oxide nanofiller includes: dissolving the antibacterial substance tannic acid in an ethanol solution, adding the solution dropwise to a uniform suspension of copper ion-functionalized graphene oxide sheet material, adjusting the pH value of the reaction system, ultrasonicating, heating and stirring, and allowing the antibacterial substance tannic acid to self-assemble at the copper ion anchor points on the graphene oxide surface to form a copper ion-bridged tannic acid-graphene oxide nanofiller. Optionally, the mass ratio of the copper ion-functionalized graphene oxide sheet material to the tannic acid is 1:(2-60); optionally, the pH of the reaction system is 8-10; optionally, the ultrasonic power is not less than 100 W; optionally, the heating and stirring temperature is 45°C-65°C.

[0060] In another embodiment, in S3, the method for preparing a uniformly dispersed functionalized nanofiller suspension includes: uniformly dispersing copper ion-bridged tannic acid-graphene oxide nanofillers in deionized water via ultrasonic treatment, controlling the interfacial properties of the nanofillers, and ensuring the stability of the nanofiller suspension immediately after preparation. Optionally, the mass ratio of the nanofillers to deionized water is 1:(25-100); and optionally, the ultrasonic power is not less than 100 W.

[0061] In another embodiment, in S4, the preparation method of the plasticized modified polylactic acid solution includes: weighing a certain amount of polylactic acid masterbatch and dissolving it in dichloromethane solvent, stirring to assist the dissolution of the polylactic acid masterbatch; after the polylactic acid is completely dissolved, plasticizing molecules such as polyethylene glycol and glycerol are added in sequence, and fully reacted to obtain a plasticized modified polylactic acid solution, which lays the foundation for nanofiller blending and film formation. Preferably, dichloromethane is used as the solvent; optionally, the mass ratio of polylactic acid to dichloromethane is 1: (5-10); optionally, the mass ratio of polylactic acid to polyethylene glycol and glycerol is 1: (0.05-0.1): (0.1-0.5).

[0062] In another embodiment, in S5, the method for preparing a high barrier and antibacterial polylactic acid packaging material by blending includes: blending the nanofiller suspension of S3 with the plasticized polylactic acid solution of S4, forming a film, and obtaining a high barrier and antibacterial polylactic acid packaging material. Optionally, the mass ratio of the nanofiller suspension to the plasticized polylactic acid solution is 1:(20-200); Optionally, the total mass ratio of the nanofiller to the polylactic acid, dichloromethane, and plasticizer is (0.005-0.02):1; Optionally, the solvent evaporation temperature is 25 o C~35 o C.

[0063] The embodiments of the present application also provide a high-barrier and antibacterial polylactic acid packaging material, which is prepared by the preparation method of the high-barrier and antibacterial polylactic acid packaging material.

[0064] The embodiments of the present application also provide the use of high-barrier and antibacterial polylactic acid packaging materials for food processing and preservation; optionally, the food is any one or a combination of livestock, poultry, aquatic products, eggs, dairy products, and vegetable foods; preferably, livestock and poultry meat.

[0065] The following is described with specific examples:

[0066] Test strain: Pseudomonas Pseudomonas azotoformans , MN10), was isolated, identified and supplied from fresh meat by the Meat Science and Nutrition Engineering Innovation Team of the Institute of Agricultural Product Processing, Chinese Academy of Agricultural Sciences.

[0067] The main chemical reagents: anhydrous copper nitrate (CAS No. 3251-23-8), polyethylene glycol (CAS No. 25322-68-3), and glycerol (CAS No. 56-81-5) were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; graphene oxide (CAS No. 2640657-49-2) and tannic acid (CAS No. 5424-20-4) were purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0068] Main instruments and equipment: D2 PHASER X-ray diffractometer, Bruker, Germany; W3 / 062 water vapor transmission rate tester, Labthink Electromechanical Technology Co., Ltd., Jinan, China.

[0069] Test method:

[0070] X-ray diffraction pattern testing: 0.20 g of copper-bridged tannic acid-graphene oxide nanofiller was accurately weighed, vacuum-dried, finely ground in an agate mortar, and evenly placed in the sample chamber of an X-ray diffractometer. Using a Cu Kα radiation source (λ = 0.15406 nm), wide-angle measurements (2θ = 10°–60°) were performed at room temperature. Crystal diffraction patterns were simultaneously recorded, and the crystal structure was analyzed and mapped.

[0071] Evaluation of the barrier properties of packaging materials: A 7.0 cm diameter high-barrier, antibacterial polylactic acid (PLA) packaging material was placed in the test chamber of a W3 / 062 water vapor transmission rate tester. The water vapor barrier properties of the high-barrier, antibacterial PLA packaging material were determined using the cupping weight loss method. This test was conducted in strict accordance with GB / T 1037 Plastic Film and Sheeting - Determination of Water Vapor Transmission Rate - Cupping Weight Gain and Weight Loss Method to analyze the barrier properties of the high-barrier, antibacterial PLA packaging material.

[0072] Antibacterial performance evaluation experiment: Using Pseudomonas aeruginosa, a typical food spoilage bacteria, as a model strain, the antibacterial efficacy of copper ion-bridged tannic acid-graphene oxide nanofillers was systematically evaluated. Frozen Pseudomonas aeruginosa strains were cultured in LB liquid medium until the logarithmic growth phase, the cells were collected by centrifugation and resuspended in sterile buffer, and the bacterial solution concentration was adjusted to ~10 5 CFU / mL, and co-cultured with 0.1 mg / mL copper ion-bridged tannic acid-graphene oxide nanofillers. The number of viable bacteria before and after treatment was determined by gradient dilution-plate count method to analyze the antibacterial properties of copper ion-bridged tannic acid-graphene oxide nanofillers.

[0073] Example 1:

[0074] A method for preparing a high-barrier antibacterial polylactic acid packaging material comprises the following steps:

[0075] S1: Preparation of copper ion functionalized graphene oxide sheet materials by coordination modification.

[0076] 20.0 mg of graphene oxide powder was weighed and dissolved in 20.0 mL of deionized water. The solution was ultrasonically treated at a power of 100 W for 10 min to obtain a graphene oxide dispersion solution. Subsequently, 1.90 g of anhydrous copper nitrate was added and stirred until the anhydrous copper nitrate particles were completely dissolved. The precipitate was obtained by centrifugation and washed to remove unbound copper ions to obtain copper ion-functionalized graphene oxide sheet material.

[0077] S2: Utilizing the multidentate coordination between tannic acid molecules and copper ions, self-assembled tannic acid-graphene oxide nanofillers bridged by copper ions were constructed.

[0078] The copper ion functionalized graphene oxide sheet material obtained in S1 was redissolved in 20.0 mL of deionized water and ultrasonically treated at a power of 100 W for 10 min; 1.90 g of tannic acid powder was taken and dissolved in 10.0 mL of anhydrous ethanol to obtain a uniform suspension; then it was added dropwise to the copper ion functionalized graphene oxide sheet material dispersion with a magnetic stirring speed of 450 r / min. After stirring for 20 min, the pH of the reaction system was adjusted to 9.0, ultrasonically treated for full reaction, placed at 50°C for reaction for 3 h, centrifuged to obtain the precipitate, and washed to remove unbound tannic acid molecules to obtain copper ion bridged tannic acid-graphene oxide nanofiller.

[0079] S3: The nanofiller obtained in S2 is subjected to ultrasonic dispersion treatment to obtain a uniformly dispersed functionalized nanofiller suspension.

[0080] Dissolve 20 mg of copper ion-bridged tannic acid-graphene oxide nanofiller in 1.0 mL of deionized water and ultrasonically disperse it at 100 W power until there are no agglomerated particles to obtain a uniformly dispersed functionalized nanofiller suspension for immediate use.

[0081] S4: dissolving polylactic acid in dichloromethane solvent and performing plasticization modification.

[0082] Take 4.0 g of polylactic acid masterbatch and dissolve it in 40 mL of dichloromethane solvent. The magnetic stirring speed is 450 r / min. Stirring assists the dissolution of the polylactic acid masterbatch. After the polylactic acid is completely dissolved, 0.2 g of polyethylene glycol and 0.8 g of glycerol and other plasticizer molecules are added in sequence. Ultrasonication is carried out at a power of 100 W for 10 minutes. Magnetic stirring is performed to fully react to obtain a plasticized modified polylactic acid solution.

[0083] S5: The nanofiller suspension of S3 is blended with the plasticized polylactic acid solution of S4 to form a film, thereby obtaining a high-barrier and antibacterial polylactic acid packaging material.

[0084] Take 0.5 mL of copper ion-bridged tannic acid-graphene oxide nanofiller and add it dropwise to the plasticized polylactic acid solution prepared by S4. Stir at 450 r / min for 2 h until the color of the system is uniform and set aside. The blended solution is injected into the automatic coating machine film, and the solvent in the reaction system is evaporated at 25℃±3℃ to obtain a high-barrier and antibacterial polylactic acid packaging material.

[0085] like Figure 1 As shown, graphene oxide and antibacterial substances are connected through bridging molecules to prepare nanofillers with barrier and antibacterial capabilities. The product is shown in FIG. Figure 2 As shown in the figure, the copper ion-bridged tannic acid-graphene oxide nanofiller prepared by S2 is black, which is different from the color of the brown graphene oxide material, indicating that the copper ions are successfully coordinated with tannic acid. The copper ions anchored on the surface of graphene oxide can bridge the antibacterial substance tannic acid molecules with graphene oxide, changing the original properties of graphene oxide and laying the foundation for the research and development of high-barrier, antioxidant and antibacterial packaging materials.

[0086] Example 2:

[0087] A method for preparing a high-barrier antibacterial polylactic acid packaging material comprises the following steps:

[0088] S1: Preparation of copper ion functionalized graphene oxide sheet materials by coordination modification.

[0089] 20.0 mg of graphene oxide powder was weighed and dissolved in 20.0 mL of deionized water. The solution was ultrasonically treated at a power of 100 W for 10 min to obtain a graphene oxide dispersion. Subsequently, 0.95 g of anhydrous copper nitrate was added and stirred until the anhydrous copper nitrate particles were completely dissolved. The precipitate was obtained by centrifugation and washed to remove unbound copper ions to obtain copper ion-functionalized graphene oxide sheet material.

[0090] S2: Utilizing the multidentate coordination between tannic acid molecules and copper ions, self-assembled tannic acid-graphene oxide nanofillers bridged by copper ions were constructed.

[0091] The copper ion functionalized graphene oxide sheet material obtained in S1 was redissolved in 20.0 mL of deionized water and ultrasonically treated at a power of 100 W for 10 min; 1.90 g of tannic acid powder was taken and dissolved in 10.0 mL of anhydrous ethanol to obtain a uniform suspension; then it was added dropwise to the copper ion functionalized graphene oxide sheet material dispersion with a magnetic stirring speed of 450 r / min. After stirring for 20 min, the pH of the reaction system was adjusted to 9.0, ultrasonically treated for full reaction, placed at 50°C for reaction for 3 h, centrifuged to obtain the precipitate, and washed to remove the unbound tannic acid molecules to obtain copper ion bridged tannic acid-graphene oxide nanofiller.

[0092] S3: The nanofiller obtained in S2 is subjected to ultrasonic dispersion treatment to obtain a uniformly dispersed functionalized nanofiller suspension.

[0093] Dissolve 20 mg of copper ion-bridged tannic acid-graphene oxide nanofiller in 1.0 mL of deionized water and ultrasonically disperse it at 100 W power until there are no agglomerated particles to obtain a uniformly dispersed functionalized nanofiller suspension for immediate use.

[0094] S4: dissolving polylactic acid in dichloromethane solvent and performing plasticization modification.

[0095] Take 4.0 g of polylactic acid masterbatch and dissolve it in 40 mL of dichloromethane solvent. The magnetic stirring speed is 450 r / min. Stirring assists the dissolution of the polylactic acid masterbatch. After the polylactic acid is completely dissolved, 0.2 g of polyethylene glycol and 0.8 g of glycerol and other plasticizer molecules are added in sequence. Ultrasonication is carried out at a power of 100 W for 10 minutes. Magnetic stirring is performed to fully react to obtain a plasticized modified polylactic acid solution.

[0096] S5: The nanofiller suspension of S3 is blended with the plasticized polylactic acid solution of S4 to form a film, thereby obtaining a high-barrier and antibacterial polylactic acid packaging material.

[0097] Take 0.5 mL of copper ion-bridged tannic acid-graphene oxide nanofiller and add it dropwise to the plasticized polylactic acid solution prepared by S4. Stir at 450 r / min for 2 h until the color of the system is uniform and set aside. The blended solution is injected into the automatic coating machine film, and the solvent in the reaction system is evaporated at 25℃±3℃ to obtain a high-barrier and antibacterial polylactic acid packaging material.

[0098] like Figure 3 As shown in the data, the crystal structure of the copper ion bridged tannic acid-graphene oxide nanofiller material is intact, and the typical characteristic peaks of graphene oxide are still retained, and some new diffraction peaks appear, indicating that copper ions and tannic acid are loaded on the surface of graphene oxide, producing a crystal structure different from graphene oxide, but without affecting the basic structure of graphene oxide. The copper ion bridged tannic acid-graphene oxide nanofiller material is expected to be further used in polylactic acid packaging materials.

[0099] Example 3:

[0100] A method for preparing a high-barrier antibacterial polylactic acid packaging material comprises the following steps:

[0101] S1: Preparation of copper ion functionalized graphene oxide sheet materials by coordination modification.

[0102] 20.0 mg of graphene oxide powder was weighed and dissolved in 20.0 mL of deionized water. The solution was ultrasonically treated at a power of 100 W for 10 min to obtain a graphene oxide dispersion solution. Subsequently, 1.90 g of anhydrous copper nitrate was added and stirred until the anhydrous copper nitrate particles were completely dissolved. The precipitate was obtained by centrifugation and washed to remove unbound copper ions to obtain copper ion-functionalized graphene oxide sheet material.

[0103] S2: Utilizing the multidentate coordination between tannic acid molecules and copper ions, self-assembled tannic acid-graphene oxide nanofillers bridged by copper ions were constructed.

[0104] The copper ion functionalized graphene oxide sheet material obtained in S1 was redissolved in 20.0 mL of deionized water and ultrasonically treated at a power of 100 W for 10 min; 1.90 g of tannic acid powder was taken and dissolved in 10.0 mL of anhydrous ethanol to obtain a uniform suspension; then it was added dropwise to the copper ion functionalized graphene oxide sheet material dispersion with a magnetic stirring speed of 450 r / min. After stirring for 20 min, the pH of the reaction system was adjusted to 9.0, ultrasonically treated for full reaction, placed at 50°C for reaction for 3 h, centrifuged to obtain the precipitate, and washed to remove the unbound tannic acid molecules to obtain copper ion bridged tannic acid-graphene oxide nanofiller.

[0105] S3: The nanofiller obtained in S2 is subjected to ultrasonic dispersion treatment to obtain a uniformly dispersed functionalized nanofiller suspension.

[0106] Dissolve 20 mg of copper ion-bridged tannic acid-graphene oxide nanofiller in 1.0 mL of deionized water and ultrasonically disperse it at 100 W power until there are no agglomerated particles to obtain a uniformly dispersed functionalized nanofiller suspension for immediate use.

[0107] S4: dissolving polylactic acid in dichloromethane solvent and performing plasticization modification.

[0108] Take 4.0 g of polylactic acid masterbatch and dissolve it in 40 mL of dichloromethane solvent. The magnetic stirring speed is 450 r / min. Stirring assists the dissolution of the polylactic acid masterbatch. After the polylactic acid is completely dissolved, 0.2 g of polyethylene glycol and 0.8 g of glycerol and other plasticizer molecules are added in sequence. Ultrasonication is carried out at a power of 100 W for 10 minutes. Magnetic stirring is performed to fully react to obtain a plasticized modified polylactic acid solution.

[0109] S5: The nanofiller suspension of S3 is blended with the plasticized polylactic acid solution of S4 to form a film, thereby obtaining a high-barrier and antibacterial polylactic acid packaging material.

[0110] Take 0.5 mL of copper ion-bridged tannic acid-graphene oxide nanofiller and add it dropwise to the plasticized polylactic acid solution prepared by S4. Stir at 450 r / min for 2 h until the color of the system is uniform and set aside. The blended solution is injected into the automatic coating machine film, and the solvent in the reaction system is evaporated at 25℃±3℃ to obtain a high-barrier and antibacterial polylactic acid packaging material.

[0111] The basic structure of the prepared high barrier antibacterial polylactic acid packaging material is as follows Figure 4 As shown, copper ion-bridged tannic acid-graphene oxide nanofillers are distributed in the polylactic acid matrix, which extends the migration path of water vapor and thereby improves the barrier properties of the polylactic acid packaging material to meet the requirements of food preservation packaging.

[0112] Example 4:

[0113] A method for preparing a high-barrier antibacterial polylactic acid packaging material comprises the following steps:

[0114] S1: Preparation of copper ion functionalized graphene oxide sheet materials by coordination modification.

[0115] 20.0 mg of graphene oxide powder was weighed and dissolved in 20.0 mL of deionized water. The solution was ultrasonically treated at a power of 100 W for 10 min to obtain a graphene oxide dispersion solution. Subsequently, 1.90 g of anhydrous copper nitrate was added and stirred until the anhydrous copper nitrate particles were completely dissolved. The precipitate was obtained by centrifugation and washed to remove unbound copper ions to obtain copper ion-functionalized graphene oxide sheet material.

[0116] S2: Utilizing the multidentate coordination between tannic acid molecules and copper ions, self-assembled tannic acid-graphene oxide nanofillers bridged by copper ions were constructed.

[0117] The copper ion functionalized graphene oxide sheet material obtained in S1 was redissolved in 20.0 mL of deionized water and ultrasonically treated at a power of 100 W for 10 min; 1.90 g of tannic acid powder was taken and dissolved in 10.0 mL of anhydrous ethanol to obtain a uniform suspension; then it was added dropwise to the copper ion functionalized graphene oxide sheet material dispersion with a magnetic stirring speed of 450 r / min. After stirring for 20 min, the pH of the reaction system was adjusted to 9.0, ultrasonically treated for full reaction, placed at 50°C for reaction for 3 h, centrifuged to obtain the precipitate, and washed to remove unbound tannic acid molecules to obtain copper ion bridged tannic acid-graphene oxide nanofiller.

[0118] S3: The nanofiller obtained in S2 is subjected to ultrasonic dispersion treatment to obtain a uniformly dispersed functionalized nanofiller suspension.

[0119] Dissolve 20 mg of copper ion-bridged tannic acid-graphene oxide nanofiller in 2.0 mL of deionized water and ultrasonically disperse it at 100 W power until there are no agglomerated particles to obtain a uniformly dispersed functionalized nanofiller suspension for immediate use.

[0120] S4: dissolving polylactic acid in dichloromethane solvent and performing plasticization modification.

[0121] Take 4.0 g of polylactic acid masterbatch and dissolve it in 20 mL of dichloromethane solvent. The magnetic stirring speed is 450 r / min. Stirring assists the dissolution of the polylactic acid masterbatch. After the polylactic acid is completely dissolved, 0.2 g of polyethylene glycol and 0.8 g of glycerol and other plasticizer molecules are added in sequence. Ultrasonication is carried out at a power of 100 W for 10 minutes. Magnetic stirring is performed to fully react to obtain a plasticized modified polylactic acid solution.

[0122] S5: The nanofiller suspension of S3 is blended with the plasticized polylactic acid solution of S4 to form a film, thereby obtaining a high-barrier and antibacterial polylactic acid packaging material.

[0123] Take 0.5 mL of copper ion-bridged tannic acid-graphene oxide nanofiller and add it dropwise to the plasticized polylactic acid solution prepared by S4. Stir at 450 r / min for 2 h until the color of the system is uniform and set aside. The blended solution is injected into the automatic coating machine film, and the solvent in the reaction system is evaporated at 25℃±3℃ to obtain a high-barrier and antibacterial polylactic acid packaging material.

[0124] like Figure 5As shown, the prepared high-barrier and antibacterial polylactic acid packaging material has good transparency and a smooth surface, and is slightly different from commercial polyolefin-based polymer packaging materials. It has the potential to replace petroleum-based plastics, especially in food packaging applications.

[0125] Comparative Example 1:

[0126] A method for preparing a common barrier and antibacterial polylactic acid packaging material comprises the following steps:

[0127] S1: Preparation of uniformly dispersed graphene oxide sheet material.

[0128] Weigh 20.0 mg of graphene oxide powder, dissolve it in 20.0 mL of deionized water, and ultrasonicate it at a power of 100 W for 10 min to obtain a graphene oxide dispersion solution.

[0129] S2: Preparation of tannic acid-graphene oxide nanofillers.

[0130] The graphene oxide sheet material obtained in S1 was dissolved in 20.0 mL of deionized water and ultrasonically treated at a power of 100 W for 10 min; 1.90 g of tannic acid powder was taken and dissolved in 10.0 mL of anhydrous ethanol to obtain a uniform suspension; then it was added dropwise to the graphene oxide sheet material dispersion with a magnetic stirring speed of 450 r / min. After stirring for 20 min, the pH of the reaction system was adjusted to 9.0, ultrasonically treated for full reaction, placed at 50°C for reaction for 3 h, centrifuged to obtain the precipitate, and washed to remove unbound tannic acid molecules to obtain tannic acid-graphene oxide nanofiller.

[0131] S3: The nanofiller obtained in S2 is subjected to ultrasonic dispersion treatment to obtain a uniformly dispersed functionalized nanofiller suspension.

[0132] Dissolve 20 mg of tannic acid-graphene oxide nanofiller in 1.0 mL of deionized water and ultrasonically disperse it at a power of 100 W until there are no agglomerated particles to obtain a uniformly dispersed functionalized nanofiller suspension, which is ready for use.

[0133] S4: dissolving polylactic acid in dichloromethane solvent and performing plasticization modification.

[0134] Take 4.0 g of polylactic acid masterbatch and dissolve it in 40 mL of dichloromethane solvent. The magnetic stirring speed is 450 r / min. Stirring assists the dissolution of the polylactic acid masterbatch. After the polylactic acid is completely dissolved, 0.2 g of polyethylene glycol and 0.8 g of glycerol and other plasticizer molecules are added in sequence. Ultrasonication is carried out at a power of 100 W for 10 minutes. Magnetic stirring is performed to fully react to obtain a plasticized modified polylactic acid solution.

[0135] S5: The nanofiller suspension of S3 is blended with the plasticized polylactic acid solution of S4 to form a film, thereby obtaining a common barrier and antibacterial polylactic acid packaging material.

[0136] Take 0.5 mL of tannic acid-graphene oxide nanofiller and add it dropwise to the plasticized polylactic acid solution prepared in S4. Stir at 450 r / min for 2 h until the color of the system is uniform and set aside. The blended solution is injected into the automatic coating machine film, and the solvent in the reaction system is evaporated at 25℃±3℃ to prepare a common barrier antibacterial polylactic acid packaging material.

[0137] Comparative Example 2:

[0138] A method for preparing a common barrier and antibacterial polylactic acid packaging material comprises the following steps:

[0139] S1: Preparation of uniformly dispersed graphene oxide nanofillers.

[0140] Weigh 20.0 mg of graphene oxide powder, dissolve it in 20.0 mL of deionized water, and ultrasonicate it at a power of 100 W for 10 min to obtain a graphene oxide dispersion solution.

[0141] S2: The nanofiller obtained in S1 is subjected to ultrasonic dispersion treatment to obtain a uniformly dispersed nanofiller suspension.

[0142] Dissolve 20 mg of graphene oxide nanofiller in 1.0 mL of deionized water and disperse it ultrasonically at a power of 100 W until there are no agglomerated particles to obtain a uniformly dispersed nanofiller suspension, which is ready for use.

[0143] S3: dissolving polylactic acid in dichloromethane solvent and performing plasticization modification.

[0144] Take 4.0 g of polylactic acid masterbatch and dissolve it in 40 mL of dichloromethane solvent. The magnetic stirring speed is 450 r / min. Stirring assists the dissolution of the polylactic acid masterbatch. After the polylactic acid is completely dissolved, 0.2 g of polyethylene glycol and 0.8 g of glycerol and other plasticizer molecules are added in sequence. Ultrasonication is carried out at a power of 100 W for 10 minutes. Magnetic stirring is performed to fully react to obtain a plasticized modified polylactic acid solution.

[0145] S4: The nanofiller suspension of S2 is blended with the plasticized polylactic acid solution of S3 to form a film, thereby obtaining a common barrier and antibacterial polylactic acid packaging material.

[0146] Take 0.5 mL of graphene oxide nanofiller and add it dropwise to the plasticized polylactic acid solution prepared in S3. Stir at 450 r / min for 2 h until the color of the system is uniform and set aside. Inject the blended solution into an automatic coating machine film, and evaporate the solvent in the reaction system at 25℃±3℃ to obtain a common barrier antibacterial polylactic acid packaging material.

[0147] Table 1 Water vapor barrier properties and antibacterial properties of high barrier and antibacterial polylactic acid packaging materials

[0148]

[0149] According to one embodiment of the present invention, in the preparation step of copper-functionalized graphene oxide, the graphene oxide can be a sheet material with a lateral dimension of 0.5-5.0 μm and a thickness of 1-10 nm, dispersed in deionized water at a concentration of 0.5-2.0 mg / mL. The mass ratio of copper nitrate to graphene oxide can be 20:1, 50:1, or 80:1, with the specific ratio adjusted according to the target copper loading. The reaction vessel can be a glass beaker, the magnetic stirrer speed is set to 300-500 rpm, and the reaction temperature is maintained at room temperature.

[0150] During the self-assembly of tannic acid-graphene oxide nanofillers, the ethanol volume fraction in the ethanol-water mixture can be 30%-70%, and the tannic acid is added in a gradient of 1:2 to 1:60 by mass. pH adjustment is performed using a 0.1-1.0 mol / L sodium hydroxide solution, added dropwise via a peristaltic pump at a rate of 0.5-2 pH units / minute. The reaction temperature is controlled at 45-65°C, and a constant temperature water bath can be used for heating.

[0151] In preparing the plasticized PLA solution, the mass ratio of dichloromethane to PLA can be 1:5, 1:8, or 1:10. The polyethylene glycol is added at a rate of 5%-10% by weight of the PLA, and the glycerol is added at a rate of 10%-50%. A jacketed stainless steel reactor can be used as the mixing vessel. The diameter of the stirring paddle can be 1 / 3-1 / 2 of the vessel's inner diameter, and the stirring time can be 30-60 minutes.

[0152] During film formation, the automatic coating machine's coating speed is set at 0.5-2.0 m / min, with a coating gap width of 0.1-0.5 mm. The substrate temperature is controlled via thermocouple feedback within a ±1°C range. The humidity in the solvent volatilization chamber is controlled at 30%-60% RH using a dehumidifier and humidifier. The film is allowed to rest for 10-60 minutes.

[0153] Technical effect: This method achieves uniform dispersion of nanofillers and stable compounding of polylactic acid matrix by step-by-step control of material ratios and process parameters. The resulting packaging material has both high barrier properties and antibacterial properties, and the processing process is stable and controllable.

[0154] According to another embodiment of the present invention, the ultrasonic treatment equipment can be a probe-type ultrasonic instrument with a frequency of 20-40 kHz and a power range of 100-200 W. In the first stage, the ultrasonic power is set to 100-150 W and the treatment time is 5-15 minutes to promote the initial coordination of tannic acid and copper ions. In the second stage, the power is increased to 150-200 W and the treatment time is 5-15 minutes to strengthen the coordination network structure. A pause of 1-3 minutes is made between the two stages to prevent the accumulation of ultrasonic energy and the resulting breakage of the filler. The total treatment time is controlled to be 10-30 minutes, and the specific time is adjusted according to the filler concentration.

[0155] The ultrasonic probe can be immersed in the liquid to a depth of 10-20 mm, and the reaction vessel can be placed in an ice water bath to prevent the temperature from exceeding 65°C. The treated suspension can be centrifuged at 3000-5000 r / min to separate unreacted substances, and the supernatant can be used in the subsequent steps.

[0156] Technical effect: Phased ultrasonic treatment optimizes the formation of the coordination network, reduces damage to the filler structure, ensures uniform size distribution of the nanofiller, and improves the stability of the material's antibacterial performance.

[0157] According to another embodiment of the present invention, the automatic coating machine can utilize precision blade coating equipment. The coating speed can be set to 0.5 m / min, 1.0 m / min, or 2.0 m / min, and the coating gap width can be adjusted to 0.3-0.5 mm (low speed) or 0.1-0.3 mm (high speed). The substrate temperature is regulated by a built-in temperature control module. For every 0.5 m / min increase in coating speed, the temperature decreases by 2°C, 3°C, or 5°C, depending on the required film thickness. A substrate heating plate can be installed 10-20 cm behind the coating head to ensure uniform temperature transfer to the film.

[0158] The solvent volatilization environment humidity is controlled using a combination of an industrial dehumidifier and an ultrasonic humidifier. A humidity sensor is installed on the top of the volatilization chamber, providing real-time monitoring within a range of 30%-60% RH. The scraper angle can be set to 30°, 45°, or 60° using an adjustable bracket and secured with a locking bolt. The coated substrate can be laid flat on a stainless steel conveyor belt with a surface roughness of Ra ≤ 0.8 μm to prevent film adhesion.

[0159] Technical effect: By dynamically matching coating parameters with substrate temperature, the film thickness fluctuation is reduced, the solvent evaporation rate is ensured to be uniform, surface defects are avoided, and the consistency of the material's mechanical properties is improved.

[0160] According to another embodiment of the present invention, the humidity of the static environment in the first stage can be set to 50% RH, 55% RH or 60% RH, the static time is 10-30 minutes, and a humidifier is used to maintain the humidity. The humidifier outlet is 50-100 cm away from the film layer. The humidity in the second stage is adjusted to 30% RH, 40% RH or 50% RH, and the remaining static time is 20-30 minutes. The humidity is quickly reduced by a dehumidifier. The ambient temperature is controlled by a constant temperature air conditioning system with a temperature fluctuation range of ±2°C. Sensors are arranged at the four corners and the center of the volatilization chamber.

[0161] The film resting platform can be constructed from porous aluminum plates with pores 1-2 mm in diameter and 5-10 mm in spacing to facilitate air circulation. During the resting process, the edges of the film are secured with vacuum cups to prevent shrinkage and deformation. Residual solvent levels can be measured using a gas chromatograph, with sampling points located at the center and edges of the film.

[0162] Technical effect: Phased humidity control balances film formation and solvent removal efficiency, reduces surface cracks or solvent residues, and improves material transparency and barrier performance stability.

[0163] According to another embodiment of the present invention, laser rangefinders with a measurement accuracy of ±0.01 mm can be used to calibrate the coating gap width. These laser rangefinders are installed on both sides of the coating head and automatically trigger the calibration process after every 10 m of coating. The linkage between substrate temperature and coating speed can be programmed through a PLC controller, for example, a speed of 1.0 m / min corresponds to a temperature of 30°C, and a speed of 2.0 m / min corresponds to a temperature of 25°C. The coating machine's drive rollers can be coated with polytetrafluoroethylene to reduce frictional resistance.

[0164] The laser rangefinder probe can be mounted on the coating machine's guide rail, 5-10 cm from the scraper, providing real-time data feedback to the control panel. A PT100 temperature sensor is embedded within the substrate support plate, sampling at a rate of 1 time per second. The coating gap adjustment mechanism can be driven by a stepper motor, offering a repeatability of ±0.005 mm.

[0165] Technical effect: Dynamic parameter matching and real-time calibration reduce process deviations, improve coating efficiency and material utilization, and ensure industrial production consistency of film thickness.

[0166] According to another embodiment of the present invention, the nanofiller addition rate in the first stage can be 0.002:1, 0.005:1, or 0.01:1 of the total mass. The pre-mixing container can be a jacketed glass reactor with a stirring paddle diameter of 50-100 mm, a rotation speed of 200-400 r / min, and a mixing time of 10-20 minutes. In the second stage, after the remaining filler is added, the mixing speed is increased to 500 r / min, 600 r / min, or 800 r / min, and the stirring paddle is replaced with a high-shear type with 4-6 blades, and the mixing time is 20-40 minutes.

[0167] The mixing temperature is controlled by circulating water in the jacket, maintaining a temperature of 25-35°C. A temperature sensor is placed at the center of the solution. The filler inlet can be located directly above the agitator, and the filler is fed at a constant rate of 0.1-0.5 kg / min using a screw feeder. The mixed slurry can be filtered through a 100-mesh screen to remove undispersed aggregates.

[0168] Technical effect: Staged mixing promotes uniform dispersion of fillers, reduces agglomeration defects, improves the tensile strength and ductility of materials, and reduces energy consumption.

[0169] According to another embodiment of the present invention, when dispersing graphene oxide, the first ultrasonic treatment can be set for 10, 12, or 15 minutes, with a power of 100-150 W, a frequency of 20-40 kHz, and a probe immersion depth of 20-30 mm. After 5-10 minutes of quiescence, a second ultrasonic treatment is performed for 10-15 minutes at a power of 150-200 W. The dispersion container can be a cylindrical glass tank with a volume of 5-10 L and a slag discharge valve at the bottom.

[0170] After standing, the upper suspension can be withdrawn via a siphon, with the siphon inlet 2-5 cm from the liquid surface to avoid inhalation of sediment. The lateral dimensions of the graphene oxide flakes were determined by atomic force microscopy, with flakes ranging from 0.5-5 μm selected. Transmission electron microscopy confirmed the thickness to be 1-10 nm. The dispersion can be stored in brown glass bottles protected from light at 4-25°C.

[0171] Technical effect: The segmented ultrasound and static process improves the efficiency of sheet exfoliation, ensures the uniformity of filler size, and provides stable raw materials for subsequent functionalization reactions.

[0172] According to another embodiment of the present invention, the first stage of pH adjustment can be performed by rapidly adding 0.5 mol / L sodium hydroxide solution, raising the pH by 1-2 pH units per minute, until the pH reaches 8-9. The second stage is performed by slowly adding the solution at a rate of 0.5-1 pH units per minute, until the pH reaches 9-10. The online pH monitor electrode can be mounted on the side wall of the reactor, 10-15 cm from the stirring paddle to avoid eddy current interference.

[0173] The alkaline solution storage tank can be equipped with a metering pump with a pumping rate of 0.1-0.5 mL / min and a tubing inner diameter of 2-4 mm. After pH adjustment, adjust the impeller speed to 50-150 rpm, with a blade diameter of 80-120 mm, and a ratio of 1:3-1:2 to the vessel diameter. A nitrogen inlet can be provided in the reactor lid to maintain an inert atmosphere and prevent oxidation.

[0174] Technical effect: Precise pH control avoids the generation of functional reaction by-products, ensures the structural integrity of the nanofiller, and improves the durability of antibacterial performance.

[0175] The first stage of high-speed stirring can be set at 200 r / min, 300 r / min, or 400 r / min for 5-15 minutes, using a four-pitch-blade turbine impeller. The second stage of low-speed stirring is at 50 r / min, 100 r / min, or 150 r / min for 15-25 minutes, using an anchor-type impeller. pH monitoring data is recorded every 10-30 seconds, and the control cabinet is set to an alarm threshold of ±0.2 pH.

[0176] Temperature linkage control is achieved through a PID algorithm. For every 100 r / min increase in stirring speed, the circulating water temperature decreases by 1-2°C. The rehydration system utilizes an optional micro-peristaltic pump, with a single rehydration volume of 0.01%-0.1% of the system mass, corresponding to a rehydration time of 1-3 seconds. The stirring shaft seal utilizes a double mechanical seal to prevent solvent leakage.

[0177] Technical effect: Staged stirring and real-time monitoring maintain the stability of the reaction system, reduce local concentration differences, and enhance the interfacial bonding strength between the filler and the matrix.

[0178] According to another embodiment of the present invention, the mass ratio of nanofiller to polylactic acid can be 0.005:1, 0.01:1, or 0.02:1, with the specific ratio selected depending on the target barrier level. Film thickness is measured using a micrometer, with sampling points taken every 10 cm along the film width, with a thickness tolerance of ±0.005 mm. Material biodegradability testing can be performed according to ISO 14855, with composting conditions at 58°C ± 2°C and 50%-60% humidity.

[0179] Finished film rolls can be slit into coils with widths of 200-1000 mm. The slitting machine blades are made of carbide and have a cutting edge angle of 20°-30°. The packaging material surface can be embossed with micron-scale textures (depth 1-5 μm) to improve adhesion resistance. Storage conditions should be dark, dry, with a relative humidity of ≤60% and a temperature of 15-30°C.

[0180] Technical effect: By limiting the range of key parameters and balancing material performance and production costs, it is ensured that the packaging material has high barrier properties, long-term antibacterial properties and biodegradability, meeting the application needs in the food and pharmaceutical fields.

[0181] These results indicate that copper-functionalized graphene oxide can better coordinate with the antibacterial substance tannic acid, increasing the migration distance of water vapor within the packaging material and improving the water vapor barrier properties of polylactic acid packaging. Furthermore, the copper ions and tannic acid synergistically exert antibacterial efficiency, enhancing the antibacterial properties of the packaging material and providing new materials for the development of fresh-keeping packaging for livestock and poultry food.

[0182] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a high-barrier antibacterial polylactic acid packaging material, characterized in that: The following steps are involved: S1: dissolving a graphene oxide sheet material in deionized water to form a dispersed solution, adding copper nitrate, wherein the mass ratio of copper nitrate to graphene oxide is 20:1 to 80:1, to obtain a copper ion functionalized graphene oxide sheet material; S2: dissolving the copper ion functionalized graphene oxide sheet material obtained in S1 in an ethanol-water mixed solution, adding tannic acid molecules, wherein the mass ratio of the copper ion functionalized graphene oxide sheet material to tannic acid is 1:2 to 1:60, heating and stirring at 45° C. to 65° C., and adjusting the pH of the reaction system to 8 to 10, to obtain a copper ion bridged tannic acid-graphene oxide nanofiller; S3: dissolving the copper ion-bridged tannic acid-graphene oxide nanofiller obtained in S2 in deionized water at a mass ratio of nanofiller to deionized water of 1:25 to 1:100, magnetically stirring at 300 to 500 r / min and ultrasonically treating to obtain a uniformly dispersed functionalized nanofiller suspension; S4: dissolving polylactic acid in a dichloromethane solvent, wherein the mass ratio of polylactic acid to dichloromethane is 1:5 to 1:10, adding polyethylene glycol and glycerol, wherein the mass ratio of polylactic acid to polyethylene glycol is 1:0.05 to 1:0.1, and the mass ratio of polylactic acid to glycerol is 1:0.1 to 1:0.5, to form a plasticized polylactic acid solution; S5: blending the nanofiller suspension of S3 with the plasticized polylactic acid solution of S4, wherein the mass ratio of the nanofiller suspension to the plasticized polylactic acid solution is 1:20 to 1:200, and the total mass ratio of the nanofiller to the polylactic acid, dichloromethane, polyethylene glycol, and glycerol is 0.005:1 to 0.02:

1. After film formation, the solvent is evaporated at 25° C. to 35° C. to obtain a high-barrier antibacterial polylactic acid packaging material; The power of the ultrasonic treatment in step S3 is not less than 100 W, wherein: During the self-assembly process of the tannic acid molecules and the copper ion functionalized graphene oxide sheet material, an ultrasonic treatment with a power of 100 W to 200 W is applied for 10 minutes to 30 minutes; Ultrasonic treatment is performed in two stages: In the first stage, the power is 100 W to 150 W for 5 to 15 minutes to allow the tannic acid molecules to initially coordinate with the copper ions. The second stage is to treat at a power of 150 W to 200 W for 5 to 15 minutes to strengthen the copper-tannic acid coordination network structure; The interval time between the two-stage ultrasonic treatment is 1 minute to 3 minutes, and the total treatment time is controlled within the range of 10 minutes to 30 minutes; In step S5, the film is formed by an automatic coating machine, the coating speed of the automatic coating machine is 0.5 m / min to 2.0 m / min, the coating gap width is 0.1 mm to 0.5 mm, and the substrate temperature during the coating process is 25° C. to 35° C. The scraper angle of the automatic coating machine is 30° to 60°. After coating, the film layer is left to volatilize the solvent in an environment of 25°C to 35°C for 10 minutes to 60 minutes. The volatilization environment humidity is controlled in the range of 30% RH to 60% RH. The static process is divided into two stages: In the first stage, the film is left to stand for 10 to 30 minutes at an ambient humidity of 50% RH to 60% RH to allow the solvent to evaporate initially and form a continuous film layer. During the remaining time of the second stage, the ambient humidity is adjusted to 30% RH to 50% RH to accelerate the complete volatilization of the solvent; during the two-stage standing process, the ambient temperature is kept constant and the temperature difference does not exceed ±2°C.

2. The method for preparing a high barrier and antibacterial polylactic acid packaging material according to claim 1, characterized in that: The relationship between coating speed and coating gap width satisfies the following conditions: When the coating speed is 0.5 m / min to 1.0 m / min, the coating gap width is 0.3 mm to 0.5 mm; When the coating speed is 1.0 m / min to 2.0 m / min, the coating gap width is 0.1 mm to 0.3 mm; The substrate temperature is linked to the coating speed. For every 0.5 m / min increase in coating speed, the substrate temperature decreases by 2°C to 5°C, and the temperature fluctuation does not exceed ±1°C. The coating gap width is calibrated in real time by a laser rangefinder with a calibration accuracy of ±0.01 mm. The gap deviation is automatically adjusted after every 10.0 m of coating is completed.

3. The method for preparing a high barrier and antibacterial polylactic acid packaging material according to claim 1, characterized in that: The mass ratio of polylactic acid to dichloromethane is 1:5 to 1:10; the mass ratio of polylactic acid to polyethylene glycol is 1:0.05 to 1:0.1; the mass ratio of polylactic acid to glycerol is 1:0.1 to 1:0.5; The addition of nanofillers is carried out in two stages: In the first stage, nanofillers are added at a total mass ratio of 0.002:1 to 0.01:1 and pre-mixed with the polylactic acid solution for 10 to 20 minutes at a mixing temperature of 25°C to 35°C; In the second stage, the remaining 0.003:1 to 0.01:1 of nanofiller is added and mixing is continued for 20 to 40 minutes, with the mixing speed increased to 500 r / min to 800 r / min.

4. The method for preparing a high barrier and antibacterial polylactic acid packaging material according to claim 1, characterized in that: The specific steps of dissolving the graphene oxide sheet material in deionized water to form a dispersed solution include: The graphene oxide sheet material is dispersed in deionized water at a concentration of 0.5 mg / mL to 2.0 mg / mL, and ultrasonically treated for 10 minutes to 30 minutes at a power of 100 W to 200 W and an ultrasonic frequency of 20 kHz to 40 kHz; The ultrasonic treatment is performed twice, the first ultrasonic treatment is performed for 10 minutes to 15 minutes, and then the ultrasonic treatment is performed for 5 minutes to 10 minutes, and then the second ultrasonic treatment is performed for 10 minutes to 15 minutes; The graphene oxide sheet material in the dispersed solution has a lateral size of 0.5 μm to 5 μm and a thickness of 1 nm to 10 nm; The dispersed solution was allowed to stand for 24 to 48 hours after ultrasonic treatment, and the upper homogeneous suspension was taken for subsequent reaction.

5. The method for preparing a high barrier and antibacterial polylactic acid packaging material according to claim 1, characterized in that: The specific steps of adjusting the pH of the reaction system to 8 to 10 include: To a mixed solution of copper ion-functionalized graphene oxide sheet material and tannic acid in ethanol and water, an alkaline solution with a concentration of 0.1 mol / L to 1.0 mol / L was added dropwise at a rate of increasing the pH by 0.5 to 2 units per minute. The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution; pH adjustment is done in two stages: In the first stage, the pH is quickly adjusted from the initial value to 8 to 9, and the adjustment time is controlled within 1 minute to 5 minutes; In the second stage, the pH is slowly adjusted from 8 to 9 to 9 to 10, and the adjustment time is controlled within 5 to 15 minutes; After the adjustment is completed, stirring is continued for 10 to 30 minutes to ensure that the pH fluctuation range of the system does not exceed ±0.2, and real-time feedback control is performed through an online pH monitor.

6. The method for preparing a high barrier and antibacterial polylactic acid packaging material according to claim 5, characterized in that: The specific steps of continuing stirring for 10 to 30 minutes after the adjustment is completed include: A two-stage stirring control is adopted: the first stage is stirring at a speed of 200 r / min to 400 r / min for 5 minutes to 15 minutes, and the second stage is stirring at a speed of 50 r / min to 150 r / min for the remaining time; During the stirring process, the pH value of the system is detected in real time by an online pH monitor at a frequency of every 10 to 30 seconds. When the pH fluctuation exceeds ±0.2, alkaline solution or acidic solution is automatically added. The single addition amount is 0.01% to 0.1% of the total mass of the system. The stirring temperature is linked to the temperature of the reaction system, with the temperature fluctuation not exceeding ±1°C, and the diameter of the stirring blade is 1 / 3 to 1 / 2 of the inner diameter of the reaction vessel; The online pH monitor's electrode response time is less than 5 seconds, the calibration error does not exceed ±0.05 pH units, and it dynamically matches the stirring speed: When the stirring speed is higher than 300 r / min, the pH detection frequency is increased to once every 10 seconds; When the stirring speed was lower than 300 r / min, the pH detection frequency was adjusted to once every 30 seconds.

7. A high barrier and antibacterial polylactic acid packaging material, characterized by: Prepared by the preparation method according to any one of claims 1 to 6; the thickness of the packaging material is 0.01 mm to 0.5 mm.

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