CN120484304B

CN120484304B - High-barrier antibacterial polylactic acid packaging material and preparation method thereof

Info

Publication number: CN120484304B
Application number: CN202511002270.0A
Authority: CN
Inventors: 侯成立; 张德权; 杨庆锋; 王振宇; 李欣; 王德宝
Original assignee: Institute of Food Science and Technology of CAAS
Current assignee: Institute of Food Science and Technology of CAAS
Priority date: 2025-07-21
Filing date: 2025-07-21
Publication date: 2025-09-30
Anticipated expiration: 2045-07-21
Also published as: CN120484304A

Abstract

The invention relates to a high-barrier antibacterial polylactic acid packaging material and a preparation method thereof, belonging to the technical field of biodegradable packaging materials. Solves the technical problems that the traditional polylactic acid material has insufficient barrier property and poor antibacterial property and is difficult to meet the packaging requirements of livestock and poultry meat, food and medicine. And carrying out copper ion functionalization treatment on the graphene oxide lamellar material, bridging the graphene oxide lamellar material with tannic acid molecules through copper ions to form nano filler, and then blending the filler with the plasticized polylactic acid solution to prepare the film. Preparing copper ion functionalized dispersion liquid from graphene oxide and copper nitrate, self-assembling with tannic acid under the condition of pH 8-10 to generate nano filler, uniformly dispersing the nano filler, mixing the nano filler with polylactic acid, polyethylene glycol and glycerin according to a specific mass ratio, and obtaining the high-performance packaging material through coating to form a film and controlling solvent volatilization conditions. The method remarkably improves the oxygen barrier property and the antibacterial activity of the material through uniform dispersion of the nano filler and reinforcement of a coordination network. The obtained material is suitable for packaging foods such as livestock and poultry meat.

Description

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

Technical Field

The invention belongs to the technical field of biodegradable packaging materials, and particularly relates to a preparation method of a high-barrier antibacterial polylactic acid packaging material.

Background

Polylactic acid has application potential in the packaging field as a biodegradable material, but practical application is still limited by performance defects. The traditional polylactic acid material has lower barrier property to gases such as oxygen, water vapor and the like, and is difficult to meet the scene of higher requirements on packaging barrier property of foods, medicines and the like. The root of the problem is that the polylactic acid molecular chain has limited crystallinity due to chemical characteristics, the free volume inside the material is larger, the intermolecular acting force is weaker, and gas molecules are easy to permeate through diffusion. While the barrier properties may be partially improved by increasing the thickness of the material, this results in reduced flexibility of the material, increased cost, and is counter to the need for lightweight packaging. In the prior art, an inorganic nano filler (such as montmorillonite and nano silicon dioxide) is tried to be introduced to improve the barrier property, but the nano filler is easy to agglomerate in a matrix, and has poor dispersion uniformity, so that defects are formed in the material, the barrier property is improved only a limited extent, and meanwhile, the mechanical property is possibly deteriorated. In addition, although the surface coating technology can enhance the barrier property, the interface bonding force between the coating and the polylactic acid matrix is insufficient and is easy to peel off, and the coating technology is complex, non-degradable components can be introduced, and the environmental friendliness of the material is weakened.

In the aspect of bacteriostasis performance, polylactic acid lacks bacteriostasis activity and depends on an external bacteriostat. The traditional method mostly adopts physical mixed silver ions, quaternary ammonium salt and other bacteriostats, but has obvious defects that the silver ions are easy to migrate to the surface or the content of the package, have potential biotoxicity risks, have short antibacterial time effect, have poor thermal stability of organic bacteriostats (such as triclosan) and are easy to decompose and lose efficacy under the high-temperature condition of polylactic acid processing. In addition, the antibacterial agent has poor compatibility with the polylactic acid matrix, and an aggregation area is easily formed in the material, so that the antibacterial efficiency is reduced, the uniformity of the material is damaged, and the mechanical strength is reduced. The prior research attempts to graft the antibacterial group to the polylactic acid molecular chain through chemical modification, but the modification process is complex, the degradability of the polylactic acid can be damaged, the grafting rate is difficult to control accurately, and the stability of the antibacterial effect is affected.

Further, the cooperative improvement of barrier performance and antibacterial performance faces a technical bottleneck. For example, the introduction of high levels of bacteriostat may exacerbate filler agglomeration, further impairing barrier properties, while excessive pursuit of barrier property optimization may result in increased brittleness of the material and deteriorated processability. The prior art lacks an effective method for simultaneously realizing the high dispersion, long-acting antibacterial activity and stable barrier structure of the nano filler in the polylactic acid matrix. In addition, the complexity of the material preparation process is also a limiting factor, and if a multi-step modification or complex composite process is adopted, the performance can be improved, but the production cost can be remarkably increased, and the large-scale production is difficult to realize. For example, surface functionalization of nanofillers typically requires tightly controlled reaction conditions (e.g., specific pH, temperature, ultrasonic power) and slight deviations in process parameters lead to structural destruction or functional failure of the filler, which poses serious challenges for stability and reproducibility of commercial processes. Therefore, developing a method which has simple process and controllable cost and can simultaneously improve the barrier and antibacterial properties of the polylactic acid material is still a technical problem to be broken through in the field.

Disclosure of Invention

The invention aims to solve the problem of how to synchronously improve the oxygen barrier property, the antibacterial activity and the processing controllability of the polylactic acid material by improving the preparation process of the polylactic acid material, and simultaneously avoid the agglomeration of nano fillers and the degradation of matrix performance.

Solves the problem of optimizing the formation of copper-tannic acid coordination network in the ultrasonic treatment process, ensures the stability of the nano filler structure, and avoids uneven dispersion caused by insufficient power or structural damage caused by overhigh power.

The method solves the problem of realizing the balance of the uniformity of the thickness of the film and the volatilization rate of the solvent by the fine control of the coating process parameters, and avoids the influence of the defects of the film or the residual solvent on the material performance.

The method solves the problems of film continuity and complete solvent removal by staged humidity regulation and control in the solvent volatilization stage, and prevents the film from dissolving back due to excessive humidity or surface cracking caused by excessive low humidity.

The method solves the problem of how to establish dynamic correlation between the coating speed, the gap width and the substrate temperature, ensures the stability and repeatability of the coating process, and avoids film thickness fluctuation or material waste caused by parameter mismatch.

Solves the problem of how to realize the uniform dispersion of the filler in the polylactic acid matrix by adding the nano filler in stages and controlling the mixing condition, and avoids agglomeration or insufficient mixing caused by one-time addition.

The method solves the problem how to obtain the sheet material with controllable size and uniform distribution through sectional ultrasonic treatment and standing technology in the graphene oxide dispersion process, and avoids excessive crushing or insufficient stripping.

The method solves the problems of ensuring the stability of a reaction system and avoiding the structural damage or functional failure of the nano-filler caused by pH mutation by stage accurate control and online feedback in the pH adjustment process.

The method solves the problem of how to maintain the uniformity of a reaction system through staged stirring control and dynamic pH monitoring, and avoids the influence of local concentration gradient or pH fluctuation on the integrity of a copper-tannic acid coordination network.

Solves the problem of how to ensure the material to have high barrier property, long-acting bacteriostasis and biodegradability by compounding the nano filler with the polylactic acid matrix according to a specific mass ratio, and avoids the performance imbalance or the environmental hazard.

The invention provides a preparation method of a high-barrier antibacterial polylactic acid packaging material, which comprises the following steps:

s1, dissolving a graphene oxide sheet material in deionized water to form a dispersion solution, and adding copper nitrate, wherein the mass ratio of the copper nitrate to the graphene oxide is 20:1-80:1 to obtain a copper ion functionalized graphene oxide sheet material;

S2, dissolving the copper ion functionalized graphene oxide sheet material obtained in the S1 into an ethanol water mixed solution, adding tannic acid molecules, heating and stirring the copper ion functionalized graphene oxide sheet material and tannic acid at a temperature of 45-65 ℃ and regulating the pH value of a reaction system to 8-10 to obtain the copper ion bridged tannic acid-graphene oxide nano filler;

s3, dissolving the copper ion bridged tannic acid-graphene oxide nanofiller obtained in the S2 in deionized water, wherein the mass ratio of the nanofiller to the deionized water is 1:25-1:100, magnetically stirring and carrying out ultrasonic treatment at 300 r/min-500 r/min to obtain a uniformly dispersed functionalized nanofiller suspension;

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

And S5, blending the nano filler suspension of S3 with the plasticized polylactic acid solution of S4, wherein the mass ratio of the nano filler suspension to the plasticized polylactic acid solution is 1:20-1:200, the total mass ratio of the nano filler to the polylactic acid, methylene dichloride, polyethylene glycol and glycerin is 0.005:1-0.02:1, and volatilizing the solvent at 25-35 ℃ after film making to obtain the high-barrier antibacterial polylactic acid packaging material.

Preferably, the power of the ultrasonic treatment in the step S3 is not lower than 100W, wherein the ultrasonic power of 100W to 200W is adopted for 10 minutes to 30 minutes in the self-assembly process of tannic acid molecules and copper ion functionalized graphene oxide sheet materials, the ultrasonic treatment is carried out in two stages, wherein the first stage is carried out at the power of 100W to 150W for 5 minutes to 15 minutes to primarily coordinate tannic acid molecules and copper ions, the second stage is carried out at the power of 150W to 200W for 5 minutes to 15 minutes to strengthen the copper-tannic acid coordination network structure, the intermittent time of the ultrasonic treatment in the two stages is 1 minute to 3 minutes, and the total treatment time is controlled within the range of 10 minutes to 30 minutes.

Preferably, the film formation in the step S5 of the invention is completed by adopting an automatic coater, the coating speed of the automatic coater is 0.5 m/min to 2.0 m/min, the coating gap width is 0.1 mm to 0.5mm, the temperature of a base material in the coating process is 25 ℃ to 35 ℃, the scraper angle of the automatic coater is 30 ℃ to 60 ℃, the film layer is kept stand in an environment of 25 ℃ to 35 ℃ for volatilizing the solvent for 10 minutes to 60 minutes after the coating, and the volatilizing environment humidity is controlled in the range of 30%RH to 60%RH.

Preferably, the standing process of the invention comprises two stages, namely, the first stage is kept for 10 minutes to 30 minutes, the ambient humidity is 50% RH to 60% RH, the solvent is initially volatilized to form a continuous film layer, the second stage is kept for the rest time, the ambient humidity is adjusted to 30% RH to 50% RH, the solvent is accelerated to be completely volatilized, and the ambient temperature is kept constant and the temperature difference is not more than +/-2 ℃ in the two stages of standing process.

Preferably, the relation between the coating speed and the coating gap width of the invention meets the following conditions that the coating gap width is 0.3mm to 0.5 mm when the coating speed is 0.5 m/min to 1.0 m/min, the coating gap width is 0.1mm to 0.3mm when the coating speed is 1.0 m/min to 2.0 m/min, the coating speed and the substrate temperature are controlled in a linkage way, the substrate temperature is reduced by 2 ℃ to 5 ℃ every time the coating speed is increased by 0.5 m/min, the temperature fluctuation is not more than +/-1 ℃, the coating gap width is calibrated in real time by a laser range finder, the calibration precision is +/-0.01 mm, and the gap deviation is automatically adjusted after 10m coating is finished.

Preferably, the mass ratio of the polylactic acid to the methylene dichloride is 1:5-1:10, the mass ratio of the polylactic acid to the polyethylene glycol is 1:0.05-1:0.1, the mass ratio of the polylactic acid to the glycerol is 1:0.1-1:0.5, the nano filler is added in two stages, wherein the nano filler with the total mass ratio of 0.002:1-0.01:1 is added in the first stage, the nano filler is premixed with the polylactic acid solution for 10 minutes-20 minutes, the mixing temperature is 25-35 ℃, the rest nano filler with the mass ratio of 0.003:1-0.01:1 is added in the second stage, the mixing is continued for 20 minutes-40 minutes, and the mixing speed is improved to 500 r/min-800 r/min.

Preferably, the specific step of dissolving the graphene oxide platelet material in deionized water to form a dispersion solution comprises dispersing the graphene oxide platelet material in deionized water at a concentration of 0.5mg/mL to 2.0 mg/mL, conducting ultrasonic treatment for 10 minutes to 30 minutes under the condition of power of 100W to 200W and ultrasonic frequency of 20 kHz to 40 kHz, conducting ultrasonic treatment for 10 minutes to 15 minutes for the first time, conducting standing for 5 minutes to 10 minutes, conducting ultrasonic treatment for 10 minutes to 15 minutes for the second time, conducting ultrasonic treatment for the graphene oxide platelet material in the dispersion solution, wherein the transverse dimension of the graphene oxide platelet material is 0.5 mu m to 5 mu m, and the thickness is 1 nm to 10 nm, conducting ultrasonic treatment for the dispersion solution, and then conducting standing for 24 hours to 48 hours for the upper layer uniform suspension for subsequent reaction.

Preferably, the specific step of adjusting the pH of the reaction system to 8-10 comprises the steps of dropwise adding an alkaline solution with the concentration of 0.1 mol/L-1.0 mol/L into an ethanol water mixed solution of copper ion functionalized graphene oxide sheet material and tannic acid, wherein the adjusting speed is increased by 0.5-2 pH units per minute, the alkaline solution is sodium hydroxide solution or potassium hydroxide solution, the pH adjustment is completed in two stages, the pH is quickly adjusted to 8-9 from an initial value, the adjusting time is controlled to 1-5 minutes, the pH is slowly adjusted to 9-10 from 8-9, the adjusting time is controlled to 5-15 minutes, and the continuous stirring is carried out for 10-30 minutes after the adjustment is completed, so that the fluctuation range of the pH of the system is not more than +/-0.2, and the real-time feedback control is carried out through an online pH monitor.

Preferably, the method comprises the specific steps of adopting two-stage stirring control, wherein the first stage is stirring at the rotating speed of 200 r-400 r/min for 5-15 min, the second stage is stirring at the rotating speed of 50 r-150 r/min for the rest time, the pH value of the system is detected in real time through an online pH monitor during stirring, the detection frequency is once every 10 seconds to 30 seconds, the alkaline solution or the acid solution is automatically added when the pH fluctuation exceeds +/-0.2, the single addition amount is 0.01-0.1% of the total mass of the system, the stirring temperature and the temperature of the reaction system are controlled in a linkage way, the temperature fluctuation does not exceed +/-1 ℃, the diameter of stirring blades is 1/3-1/2 of the inner diameter of a reaction container, the electrode response time of the online pH monitor is less than 5 seconds, the calibration error does not exceed +/-0.05 pH units, the pH value is dynamically matched with the stirring speed, the pH detection frequency is increased to once every 10 seconds when the stirring speed is higher than 300 r/min, the pH detection frequency is adjusted to be once every 30 seconds when the stirring speed is lower than r/300 min.

Preferably, the invention also provides a high-barrier antibacterial polylactic acid packaging material, which comprises tannic acid-graphene oxide nano-filler bridged by copper ions uniformly dispersed in a polylactic acid matrix, wherein the mass ratio of the nano-filler to the polylactic acid is 0.005:1 to 0.02:1, and the thickness of the packaging material is 0.01 mm to 0.5 mm.

The beneficial effects are that:

The tannic acid-graphene oxide nano filler bridged by copper ions is compounded with the plasticized polylactic acid, so that the oxygen barrier property (the permeability is reduced by 30% -50%) and the antibacterial rate (the antibacterial rate on escherichia coli and staphylococcus aureus is more than 99%) of the material are obviously improved. The uniform dispersion of the nano filler avoids agglomeration defect, and meanwhile, the synergistic plasticization effect of polyethylene glycol and glycerol improves the flexibility of the material, so that the controllable processing process is ensured, and the yield is improved by more than 20%.

The formation of a copper-tannic acid coordination network is optimized by staged ultrasonic treatment, the primary coordination of molecules is promoted by low power in the first stage, the structural stability is enhanced by high power in the second stage, and the filler breakage caused by energy accumulation is avoided in the intermittent time. The design ensures that the transverse size distribution of the nano filler is concentrated (CV is less than 10%), the antibacterial activity is improved by 15% -20%, and the fluctuation range of the barrier property is reduced to +/-5%.

The linkage control of the coating speed, the gap width and the substrate temperature ensures that the deviation of the film thickness is < +/-0.01 mm, and the solvent volatilization rate is matched with the film forming speed, thereby avoiding surface pinholes or cracks. The doctor blade angle is optimized to reduce the residual coating liquid, the uniformity of the film layer is improved, and the fluctuation range of the tensile strength of the material is reduced from +/-15% to +/-5%.

The film continuity and the solvent removal efficiency are both considered in the staged humidity regulation, the film shrinkage cracking is prevented by the high humidity (50% -60% RH) in the first stage, and the solvent volatilization is accelerated to the residual quantity of <0.1% by the low humidity (30% -50% RH) in the second stage. The constant temperature (+ -2 ℃) avoids abrupt change of solvent volatilization rate, and the transparency of the film layer is improved (haze < 5%).

Coating parameters are dynamically matched, process fluctuation is reduced, gap width (precision +/-0.01 mm) is calibrated in real time by laser ranging, material waste is reduced by 10% -15%, and base material temperature and coating speed are controlled in a linkage mode (each 0.5 m/min is reduced by 2-5 ℃), so that film thermal stress uniformity is ensured, and warping or curling defects are avoided.

Nano-filler is added in stages, the mixing speed is increased in a gradient way, the first pre-mixing (25 ℃ to 35 ℃) promotes the wetting of the filler, the second high-speed mixing (500 to 800 r/min) breaks up the aggregate, the final filler dispersion uniformity (D90 <5.0 mu m) is increased by 40%, and the material breaking elongation is increased to 120 to 150%.

The graphene oxide sheet with the transverse dimension of 0.5-5.0 mu m and the thickness of 1-10 nm is obtained by the segmented ultrasonic and standing process, the sheet peeling rate is more than 90%, and the reduction of barrier property caused by excessive crushing is avoided. And standing, and taking an upper suspension (the solid content deviation is less than 2%), so as to ensure that the concentration of the filler in the subsequent reaction is accurately controllable.

The pH adjustment and the on-line feedback control are carried out in stages, tannic acid oxidation or copper ion precipitation caused by partial overbase (pH > 10) is avoided, the pH fluctuation < +/-0.2 ensures the integrity of a coordination network, the functionalization efficiency of the nano-filler is improved to more than 95%, and the stability of antibacterial performance (attenuation of 30 days < 5%) is obviously improved.

Dynamic stirring and pH monitoring are matched with technological parameters, high-speed stirring (200-400 r/min) eliminates concentration gradient, low-speed stirring (50-150 r/min) maintains system stability, automatic liquid supplementing (0.01% -0.1% for a single time) prevents pH deviation, and filler-matrix interface bonding strength is improved by 20% -30%.

By limiting the mass ratio (0.005:1-0.02:1) and the thickness range (0.01-0.5 mm) of the nano filler to the polylactic acid, the barrier property, the mechanical property and the cost are balanced, the oxygen permeability of the material can be less than 20 cm < 3 >/(m < 2 >. Day.0.1 > Mpa), the water vapor permeability can be less than 10 g/(m ².24 h), the antibacterial activity can be kept to be more than 99% (60 days), and the complete biodegradation period is shortened to 6-12 months.

Drawings

Fig. 1 is a schematic illustration of copper ion bridged tannic acid-graphene oxide nanofiller preparation.

Fig. 2 is a copper ion bridged tannic acid-graphene oxide nanofiller.

Fig. 3 is an X-ray diffraction pattern of a copper ion bridged tannic acid-graphene oxide nanofiller.

Fig. 4 is a schematic structural diagram of a high-barrier antibacterial polylactic acid packaging material.

Fig. 5 is a physical diagram of a high-barrier antibacterial polylactic acid packaging material.

Detailed Description

The present invention is described in further detail below with reference to the drawings to enable those skilled in the art to practice the invention by referring to the description.

The embodiment of the application provides a preparation method of a high-barrier antibacterial polylactic acid packaging material, which comprises the following steps:

s1, preparing a copper ion functionalized graphene oxide lamellar material through coordination modification.

The copper ions with positive charges are combined with oxygen-containing functional groups of carboxyl or hydroxyl of the graphene oxide lamellar material in a coordination modification mode, copper ions are used as anchor points, a material foundation is laid for loading tannic acid serving as a subsequent antibacterial material, and the copper ion functionalized graphene oxide lamellar material has both the coordination function of the copper ions and the barrier property of a graphene oxide two-dimensional network.

S2, constructing the tannic acid-graphene oxide nano filler bridged by the copper ions by self-assembly by utilizing the multidentate coordination effect of tannic acid molecules and the copper ions.

The tannic acid molecules of the antibacterial substance and anchor points of the copper ion functionalized graphene oxide lamellar material are self-assembled to form tannic acid-graphene oxide nanofiller bridged by copper ions, so that the bonding capability of the tannic acid of the antibacterial substance and the graphene oxide is improved, the structural stability of the nanofiller is endowed, and a foundation is laid for industrial production.

And S3, carrying out ultrasonic dispersion treatment on the nano filler obtained in the step S2 to obtain a uniformly dispersed functionalized nano filler suspension.

Copper ion bridged tannic acid-graphene oxide nanofiller is dissolved in deionized water, and the dispersibility of the nanofiller is maintained, the surface area of the nanofiller is increased, and the interface stability of the nanofiller is improved through ultrasonic treatment.

And S4, dissolving polylactic acid in a dichloromethane solvent, and plasticizing and modifying.

Polylactic acid particles are dissolved in a dichloromethane solvent, magnetic stirring is carried out until the polylactic acid particles are completely dissolved, polyethylene glycol and glycerin are sequentially added for plasticizing, wherein the polyethylene glycol is used as a long-chain plasticizer to improve the flexibility of chain segments, the glycerin can reduce the entanglement among chains, and the transparent viscous plasticizing polylactic acid solution is formed by continuous stirring.

And S5, blending the nano filler suspension of the S3 and the plasticized polylactic acid solution of the S4, and preparing films to obtain the high-barrier antibacterial polylactic acid packaging material.

Blending, plasticizing and modifying the tannic acid-graphene oxide nano filler bridged by copper ions with polylactic acid, polyethylene glycol and glycerol, and preparing a film to obtain the high-barrier antibacterial polylactic acid packaging material; according to the embodiment, through the coordination modification of the copper ions with the positive nuclei and the graphene oxide lamellar material, the interaction of the antibacterial substance tannic acid and the graphene oxide is improved, the loading capacity of the graphene oxide to the tannic acid is increased, the tannic acid-graphene oxide nanofiller bridged by copper ions is constructed, a synergistic plasticization blending process is adopted, the high-barrier antibacterial packaging material is prepared, the problems of poor barrier property and poor antibacterial effect of the polylactic acid packaging material are solved, the water vapor barrier property and antibacterial activity of the polylactic acid packaging material are improved, the application potential in meat packaging is huge, and the antibacterial activity packaging material is provided for research and development of food packaging and fresh-keeping technology.

In another embodiment, in S1, the preparation method of the copper ion functionalized graphene oxide sheet material comprises the steps of dissolving graphene oxide in deionized water, adding copper nitrate, and reacting the copper ions with active groups on the surface of the graphene oxide to obtain the copper ion functionalized graphene oxide sheet material, namely anchoring the copper ions on the surface of the graphene oxide by utilizing the coordination effect of the copper ions and oxygen-containing functional groups, wherein the anchored copper ions enable the graphene oxide to have the capability of combining more antibacterial substances tannic acid, so that the copper ion functionalized modification of the graphene oxide is realized, and optionally, the mass ratio of the copper nitrate to the graphene oxide is (20-80): 1.

In another embodiment, in S2, the construction method of the tannic acid-graphene oxide nano filler bridged by copper ions comprises the steps of dissolving tannic acid serving as a bacteriostatic substance in ethanol solution, dropwise adding the tannic acid into a uniform suspension of copper ion functionalized graphene oxide lamellar material, regulating the pH value of a reaction system, carrying out ultrasonic treatment, heating and stirring, and carrying out self-assembly on tannic acid serving as the bacteriostatic substance on copper ion anchor points on the surface of graphene oxide to form the tannic acid-graphene oxide nano filler bridged by copper ions. The mass ratio of the copper ion functionalized graphene oxide sheet material to the tannic acid is 1 (2-60), the pH of a reaction system is 8-10, the ultrasonic power is not lower than 100W, and the heating and stirring temperature is 45-65 ℃.

In another embodiment, in S3, the preparation method of the uniformly dispersed functionalized nano filler suspension comprises the steps of uniformly dispersing the copper ion-bridged tannic acid-graphene oxide nano filler in deionized water through ultrasonic treatment, regulating and controlling interface properties of the nano filler, and fully ensuring the stability of the properties of the nano filler suspension. Optionally, the mass ratio of the nano filler to the deionized water is 1 (25-100), and optionally, the ultrasonic power is not lower than 100W.

In another embodiment, in the step S4, the preparation method of the plasticizing modified polylactic acid solution comprises the steps of weighing a certain amount of polylactic acid master batch to dissolve in a dichloromethane solvent, stirring to assist the dissolution of the polylactic acid master batch, adding plasticizing molecules such as polyethylene glycol, glycerol and the like in sequence after the polylactic acid is completely dissolved, and fully reacting to obtain the plasticizing modified polylactic acid solution, so that conditions are laid for the blending and film making of the nano filler. Preferably, dichloromethane is used as a solvent, the mass ratio of polylactic acid to dichloromethane is (5-10), and the mass ratio of polylactic acid to polyethylene glycol to glycerin is (0.05-0.1), wherein the mass ratio of polylactic acid to polyethylene glycol to glycerin is (0.1-0.5).

In another embodiment, in S5, the method for preparing the high-barrier antibacterial polylactic acid packaging material by blending comprises the steps of blending the nano filler suspension of S3 with the plasticized polylactic acid solution of S4, and forming a film to obtain the high-barrier antibacterial polylactic acid packaging material. The mass ratio of the nanofiller suspension to the plasticized polylactic acid solution is 1 (20-200), the total mass ratio of the nanofiller to the polylactic acid, the methylene dichloride and the plasticizer is 0.005-0.02:1, and the solvent volatilization temperature is 25 ^oC~35^o ℃.

The embodiment of the application also provides a high-barrier antibacterial polylactic acid packaging material, which is prepared by the preparation method of the high-barrier antibacterial polylactic acid packaging material.

The embodiment of the application also provides application of the high-barrier antibacterial polylactic acid packaging material in food processing and fresh-keeping, wherein the food is optionally one or a combination of more of livestock, poultry, aquatic products, eggs, dairy products and vegetable foods, and preferably livestock and poultry meat.

The following is a description of specific embodiments:

the test strain Pseudomonas (Pseudomonas azotoformans, MN 10) is separated from fresh meat by meat science and nutrition engineering innovation team of agricultural product processing institute of China academy of agricultural science and supplied.

The main chemical reagents include anhydrous copper nitrate (CAS No. 3251-23-8), polyethylene glycol (CAS No. 25322-68-3), glycerol (CAS No. 56-81-5), graphene oxide (CAS No. 2640657-49-2), and tannic acid (CAS No. 5424-20-4), which are purchased from Shanghai Seilin Biotechnology Co.

The main instrument and equipment are a D2 PHASER X-ray diffractometer, bruce, germany, a W3/062 water vapor transmittance tester, and a light and electricity technology Co., ltd.

The testing method comprises the following steps:

And (3) testing an X-ray diffraction pattern, namely accurately weighing 0.20 g of copper ion bridged tannic acid-graphene oxide nanofiller, carrying out vacuum drying and fine grinding by an agate mortar, and uniformly placing in a sample groove of an X-ray diffractometer. The crystal diffraction pattern was recorded simultaneously, the crystal structure was analyzed and plotted using a Cu ka radiation source (λ= 0.15406 nm) at room temperature for wide angle testing (2θ=10° -60 °).

The barrier performance of the packaging material is evaluated by taking the high-barrier antibacterial polylactic acid packaging material with the diameter of 7.0 cm, placing the packaging material into a test cavity of a W3/062 water vapor transmission rate tester, measuring the water vapor barrier property of the high-barrier antibacterial polylactic acid packaging material by adopting a cup test weight reduction method, and analyzing the barrier performance of the high-barrier antibacterial polylactic acid packaging material by strictly performing the test method according to a cup test weight increase and weight reduction method for measuring the water vapor transmission rate of GB/T1037 plastic films and sheets.

And (3) a bacteriostasis performance evaluation experiment, namely systematically evaluating the bacteriostasis performance of the copper ion bridged tannic acid-graphene oxide nano filler by taking a typical food spoilage bacterium-pseudomonas as a model strain. Amplifying and culturing the frozen pseudomonas strain to a logarithmic growth phase by an LB liquid culture medium, centrifugally collecting thalli, re-suspending by using a sterile buffer solution, regulating the concentration of the bacterial solution to be 10 ⁵ CFU/mL, co-culturing with 0.1 mg/mL of copper ion bridged tannic acid-graphene oxide nanofiller, measuring the viable count before and after treatment by using a gradient dilution-plate counting method, and analyzing the antibacterial performance of the copper ion bridged tannic acid-graphene oxide nanofiller.

Example 1:

the preparation method of the high-barrier antibacterial polylactic acid packaging material comprises the following steps:

Weighing 20.0 mg graphene oxide powder, dissolving in 20.0 mL deionized water, performing ultrasonic treatment for 10 min under the condition of power of 100W to obtain graphene oxide dispersion solution, then adding 1.90 g anhydrous copper nitrate, stirring until the anhydrous copper nitrate particles are completely dissolved, centrifuging to obtain precipitate, washing to remove unbound copper ions, and obtaining the copper ion functionalized graphene oxide lamellar material.

The preparation method comprises the steps of re-dissolving the S1-obtained copper ion functionalized graphene oxide sheet material in 20.0mL deionized water, carrying out ultrasonic treatment for 10min under the condition of 100: 100W power, taking 1.90 g tannic acid powder, dissolving in 10.0mL absolute ethyl alcohol to obtain uniform suspension, then dropwise adding the suspension into the copper ion functionalized graphene oxide sheet material dispersion, carrying out magnetic stirring at the speed of 450r/min, stirring for 20: 20 min, regulating the pH value of a reaction system to 9.0, carrying out ultrasonic treatment for full reaction, placing the reaction product under the condition of 50 ℃, carrying out reaction for 3: 3 h, centrifuging to obtain precipitate, washing to remove unbound tannic acid molecules, and obtaining the copper ion bridged tannic acid-graphene oxide nano filler.

Dissolving 20 mg copper ion bridged tannic acid-graphene oxide nanofiller in 1.0 mL deionized water, and performing ultrasonic dispersion at 100W power until no agglomerated particles are obtained, so as to obtain a uniformly dispersed functionalized nanofiller suspension for use.

Dissolving 4.0 g polylactic acid master batch in 40 mL dichloromethane solvent, stirring at magnetic stirring speed of 450 r/min to assist the dissolution of polylactic acid master batch, sequentially adding plasticizing molecules such as 0.2 g polyethylene glycol and 0.8 g glycerin after polylactic acid is completely dissolved, performing ultrasonic treatment under 100W power for 10min, and performing magnetic stirring to fully react to obtain plasticized modified polylactic acid solution.

Adding 0.5 mL copper ion bridged tannic acid-graphene oxide nano filler into the plasticized polylactic acid solution prepared in the step S4 dropwise, stirring for 2 h under the condition of 450: 450 r/min until the system color is uniform for standby, injecting the blending solution into an automatic coating machine film, volatilizing the solvent in the reaction system under the condition of 25 ℃ plus or minus 3 ℃ to prepare the high-barrier antibacterial polylactic acid packaging material.

As shown in figure 1, graphene oxide and bacteriostatic substances are connected through bridging molecules to prepare nano-fillers with barrier property and bacteriostatic ability, the product is shown in figure 2, and the tannic acid-graphene oxide nano-fillers bridged by copper ions prepared in S2 are black and different in color from tan graphene oxide materials, so that copper ions and tannic acid are successfully coordinated, copper ions anchored on the surface of graphene oxide can bridge the tannic acid molecules of the bacteriostatic substances and graphene oxide, original properties of graphene oxide are changed, and a foundation is laid for research and development of high-barrier antioxidation bacteriostatic packaging materials.

Example 2:

Weighing 20.0 mg graphene oxide powder, dissolving in 20.0 mL deionized water, performing ultrasonic treatment for 10 min under the condition of power of 100W to obtain graphene oxide dispersion solution, then adding 0.95 g anhydrous copper nitrate, stirring until the anhydrous copper nitrate particles are completely dissolved, centrifuging to obtain precipitate, washing to remove unbound copper ions, and obtaining the copper ion functionalized graphene oxide lamellar material.

The preparation method comprises the steps of re-dissolving the S1-obtained copper ion functionalized graphene oxide sheet material in 20.0 mL deionized water, carrying out ultrasonic treatment on the solution under the condition of 100: 100W power for 10: 10 min, taking 1.90: 1.90 g tannic acid powder, dissolving the powder in 10.0: 10.0 mL absolute ethyl alcohol to obtain uniform suspension, then dropwise adding the suspension into the copper ion functionalized graphene oxide sheet material dispersion, regulating the pH value of a reaction system to 9.0 after stirring for 20: 20 min at the magnetic stirring speed of 450: 450 r/min, carrying out ultrasonic treatment for full reaction, placing the reaction product under the condition of 50 ℃, carrying out reaction for 3: 3 h, centrifuging to obtain precipitate, washing to remove unbound tannic acid molecules, and obtaining the copper ion bridged tannic acid-graphene oxide nano filler.

As shown in fig. 3, the crystal structure of the copper ion bridged tannic acid-graphene oxide nano filling material is complete, typical characteristic peaks of graphene oxide are still reserved, and a part of new diffraction peaks appear, which indicate that copper ions and tannic acid are loaded on the surface of graphene oxide to generate a crystal structure different from that of graphene oxide, but the basic structure of graphene oxide is not affected, and the copper ion bridged tannic acid-graphene oxide nano filling material is expected to be further applied to polylactic acid packaging materials.

Example 3:

The preparation method comprises the steps of re-dissolving the S1-obtained copper ion functionalized graphene oxide lamellar material in 20.0mL of deionized water, carrying out ultrasonic treatment on the mixture under the condition of 100W ℃ for 10min, taking 1.90 g tannic acid powder, dissolving the tannic acid powder in 10.0mL of absolute ethyl alcohol to obtain uniform suspension, then dropwise adding the suspension into the copper ion functionalized graphene oxide lamellar material dispersion, regulating the pH value of a reaction system to 9.0 after stirring the mixture for 20 min at the magnetic stirring speed of 450r/min, carrying out ultrasonic treatment for full reaction, placing the mixture under the condition of 50 ℃ for reaction for 3 h, centrifuging to obtain precipitate, washing to remove unbound tannic acid molecules, and obtaining the copper ion bridged tannic acid-graphene oxide nano filler.

The basic structure of the prepared high-barrier antibacterial polylactic acid packaging material is shown in figure 4, and the tannic acid-graphene oxide nano filler bridged by copper ions is distributed in the polylactic acid base material, so that the migration path of water vapor is prolonged, and the barrier property of the polylactic acid packaging material is improved, so that the food fresh-keeping packaging requirement is met.

Example 4:

Dissolving 20 mg copper ion bridged tannic acid-graphene oxide nanofiller in 2.0 mL deionized water, and performing ultrasonic dispersion at 100W power until no agglomerated particles are obtained, so as to obtain a uniformly dispersed functionalized nanofiller suspension for use.

Dissolving 4.0 g polylactic acid master batch in 20mL dichloromethane solvent, stirring at magnetic stirring speed of 450 r/min to assist the dissolution of polylactic acid master batch, sequentially adding plasticizing molecules such as 0.2 g polyethylene glycol and 0.8 g glycerin after polylactic acid is completely dissolved, performing ultrasonic treatment under 100W power for 10min, and performing magnetic stirring to fully react to obtain plasticized modified polylactic acid solution.

As shown in fig. 5, the prepared high-barrier antibacterial polylactic acid packaging material has good transparency, flat surface, small difference with a commercial polyolefin-based high polymer packaging material, has the potential of replacing petroleum-based plastics, and has good prospect in food packaging application in particular.

Comparative example 1:

A preparation method of a common barrier antibacterial polylactic acid packaging material comprises the following steps:

S1, preparing a uniformly dispersed graphene oxide lamellar material.

Weighing 20.0 mg graphene oxide powder, dissolving in 20.0 mL deionized water, and performing ultrasonic treatment on the solution under the condition of power of 100W for 10min to obtain a graphene oxide dispersion solution.

S2, preparing tannic acid-graphene oxide nano filler.

Dissolving the graphene oxide sheet material obtained in S1 in 20.0 mL deionized water, carrying out ultrasonic treatment on the mixture for 10 min under the condition of 100: 100W power, dissolving 1.90: 1.90 g tannic acid powder in 10.0: 10.0 mL absolute ethyl alcohol to obtain uniform suspension, then dropwise adding the uniform suspension into the graphene oxide sheet material dispersion, stirring the mixture for 20: 20 min at the magnetic stirring speed of 450: 450 r/min, regulating the pH value of a reaction system to 9.0, carrying out ultrasonic treatment for full reaction, placing the mixture under the condition of 50 ℃, carrying out reaction for 3: 3 h, centrifuging to obtain precipitate, washing to remove unbound tannic acid molecules, and obtaining the tannic acid-graphene oxide nano filler.

Dissolving 20 mg tannic acid-graphene oxide nanofiller in 1.0 mL deionized water, and performing ultrasonic dispersion at the power of 100W until no agglomerated particles are obtained, so as to obtain a uniformly dispersed functionalized nanofiller suspension for preparation.

And S5, blending the nano filler suspension of S3 with the plasticized polylactic acid solution of S4, and preparing films to obtain the common barrier antibacterial polylactic acid packaging material.

Adding 0.5 mL tannic acid-graphene oxide nano filler dropwise into the plasticized polylactic acid solution prepared in the step S4, stirring for 2h under the condition of 450 r/min until the system color is uniform for standby, injecting the blending solution into an automatic coating machine film, volatilizing the solvent in the reaction system under the condition of 25 ℃ plus or minus 3 ℃ to prepare the common barrier antibacterial polylactic acid packaging material.

Comparative example 2:

S1, preparing uniformly dispersed graphene oxide nanofiller.

S2, carrying out ultrasonic dispersion treatment on the nano filler obtained in the step S1 to obtain uniformly dispersed nano filler suspension.

Dissolving 20 mg graphene oxide nanofiller in 1.0 mL deionized water, and performing ultrasonic dispersion at the power of 100W until no agglomerated particles are obtained, so as to obtain uniformly dispersed nanofiller suspension for use.

And S3, dissolving polylactic acid in a dichloromethane solvent, and plasticizing and modifying.

And S4, blending the nano filler suspension of S2 with the plasticized polylactic acid solution of S3, and preparing films to obtain the common barrier antibacterial polylactic acid packaging material.

And (3) dropwise adding 0.5mL graphene oxide nano filler into the plasticized polylactic acid solution prepared in the step (S3), stirring for 2h under the condition of 450: 450 r/min until the system is uniform in color for standby, injecting the blending solution into an automatic coating machine film, and volatilizing the solvent in the reaction system under the condition of 25 ℃ plus or minus 3 ℃ to prepare the common barrier antibacterial polylactic acid packaging material.

Table 1 high barrier antibacterial polylactic acid packaging material water vapor barrier property and antibacterial property

According to one embodiment of the invention, in the preparation step of the copper ion functionalized graphene oxide, the graphene oxide can be selected from lamellar materials with the transverse dimension of 0.5-5.0 mu m and the thickness of 1-10nm, and the lamellar materials are dispersed in deionized water, and the concentration can be 0.5-2.0 mg/mL. The mass ratio of copper nitrate to graphene oxide can be 20:1, 50:1 or 80:1, and the specific ratio is adjusted according to the target copper load. The reaction vessel can be a glass beaker, the rotating speed of a magnetic stirrer is set to 300-500 r/min, and the reaction temperature is maintained at room temperature.

When the tannic acid-graphene oxide nano filler is self-assembled, the volume fraction of ethanol in the ethanol-water mixed solution can be 30% -70%, and the addition amount of tannic acid is added in a gradient manner according to the mass ratio of 1:2 to 1:60. The pH is regulated by using 0.1-1.0 mol/L sodium hydroxide solution, dropwise adding is carried out at the speed of 0.5-2 pH units/min by a peristaltic pump, the reaction temperature is controlled at 45-65 ℃, and a heating device can adopt a constant-temperature water bath.

In the preparation of the plasticized polylactic acid solution, the mass ratio of dichloromethane to polylactic acid can be 1:5, 1:8 or 1:10, the polyethylene glycol is added according to 5-10% of the mass of the polylactic acid, and the glycerol is added according to 10-50%. The mixing container can be a jacketed stainless steel reaction kettle, the diameter of the stirring paddle can be 1/3-1/2 of the inner diameter of the container, and the stirring time is 30-60 minutes.

When blending and film making are carried out, the coating speed of the automatic coating machine is set to be 0.5-2.0 m/min, the coating gap width is 0.1-0.5 mm, the substrate temperature is controlled by thermocouple feedback, and the fluctuation range is +/-1 ℃. The humidity of the solvent volatilizing chamber is controlled to be 30-60% RH, a dehumidifier and a humidifier are adopted for linkage adjustment, and the standing time of the film layer is 10-60 minutes.

The method has the technical effects that the method realizes the uniform dispersion of the nano filler and the stable compounding of the polylactic acid matrix by controlling the material proportion and the technological parameters step by step, and the obtained packaging material has high barrier property and antibacterial property and is stable and controllable in processing process.

According to yet another embodiment of the invention, the ultrasonic treatment device may be a probe type ultrasonic instrument with a frequency of 20-40 kHz and a power range of 100-200W. The ultrasonic power in the first stage is set to be 100-150W, the treatment time is 5-15 minutes, and the preliminary coordination of tannic acid and copper ions is promoted. The power of the second stage is raised to 150-200W, the treatment time is 5-15 minutes, and the coordination network structure is enhanced. And the time is stopped for 1-3 minutes between the two stages, so that the filler is prevented from being broken due to the accumulation of ultrasonic energy. The total treatment time is controlled between 10 and 30 minutes, and the specific time is adjusted according to the filler concentration.

The immersion depth of the ultrasonic probe into the liquid surface can be 10-20 mm, and the reaction vessel is placed in an ice-water bath to prevent the temperature from exceeding 65 ℃. The treated suspension may be passed through a centrifuge to separate unreacted materials at a rotational speed of 3000-5000 r/min, and the supernatant used in the subsequent steps.

The method has the technical effects that the formation of a coordination network is optimized by staged ultrasonic treatment, the damage of a filler structure is reduced, the uniform size distribution of the nano filler is ensured, and the stability of the antibacterial performance of the material is improved.

According to another embodiment of the invention, the automatic coater can be a precision doctor blade coater, 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 correspondingly adjusted to 0.3-0.5 mm (low speed) or 0.1-0.3 mm (high speed). The temperature of the base material is regulated by the built-in temperature control module, when the coating speed is increased by 0.5 m/min, the temperature can be reduced by 2 ℃,3 ℃ or 5 ℃, and the specific value is selected according to the thickness requirement of the film layer. The substrate heating plate can be installed at the position 10-20cm behind the coating head, so that the temperature is ensured to be uniformly transferred to the film layer.

The humidity control of the solvent volatilization environment can be realized by adopting the combination of an industrial dehumidifier and an ultrasonic humidifier, a humidity sensor is arranged at the top of the volatilization chamber, and the real-time monitoring range is 30% -60% RH. The angle of the scraper is set to be 30 degrees, 45 degrees or 60 degrees through an adjustable bracket, and the scraper is fixed through a locking bolt after the angle is adjusted. The coated substrate can be spread on a stainless steel conveyor belt, and the surface roughness Ra of the conveyor belt is less than or equal to 0.8 mu m, so that the adhesion of a film layer is avoided.

The method has the technical effects that through dynamically matching the coating parameters with the substrate temperature, the film thickness fluctuation is reduced, the solvent volatilization rate is ensured to be uniform, the surface defects are avoided, and the consistency of the mechanical properties of the material is improved.

According to another embodiment of the invention, the first stage resting ambient humidity can be set to 50% RH, 55% RH or 60% RH for 10-30 minutes with a humidifier to maintain humidity and with the humidifier outlet at a distance of 50-100 cm from the membrane layer. The humidity of the second stage is adjusted to be 30 percent RH, 40 percent RH or 50 percent RH, the rest time is 20-30 minutes, and the humidity is quickly reduced through a dehumidifier. The environmental temperature control adopts a constant temperature air conditioning system, the temperature fluctuation range is +/-2 ℃, and the sensors are arranged at four corners and the center of the volatilization chamber.

The membrane layer standing platform can be made of a porous aluminum plate, the aperture is 1-2 mm, the pitch is 5-10 mm, and air circulation is promoted. In the standing process, the edges of the film layers are fixed through the vacuum chuck, so that shrinkage deformation is prevented. The residual solvent can be detected by gas chromatograph, and sampling points are positioned in the center and edge areas of the film layer.

The method has the technical effects that the forming and solvent removal efficiency of the balance film layer is regulated and controlled by humidity in stages, surface cracks or solvent residues are reduced, and the transparency and barrier property stability of the material are improved.

According to another embodiment of the invention, the coating gap width calibration can be performed by using a laser range finder with measurement accuracy of + -0.01 mm, which is arranged on two sides of the coating head, and the calibration procedure is automatically triggered after 10: 10m coating is completed. The linkage relationship between the substrate temperature and the coating speed can be realized through programming of a PLC controller, for example, the speed of 1.0 m/min corresponds to the temperature of 30 ℃, and the speed of 2.0 m/min corresponds to the temperature of 25 ℃. The surface of the driving roller of the coating machine can be coated with a polytetrafluoroethylene coating, so that the friction resistance is reduced.

The laser range finder probe can be arranged on a guide rail of the coating machine, is 5-10 cm away from the scraper, and feeds real-time data back to the control panel. The temperature sensor adopts PT100 type, is embedded into the substrate supporting plate, and has sampling frequency of 1 time/second. The coating gap adjusting mechanism can be driven by a stepping motor, and the repeated positioning accuracy is +/-0.005 mm.

The method has the technical effects that the dynamic parameter matching and the real-time calibration reduce the process deviation, improve the coating efficiency and the material utilization rate, and ensure the consistency of the industrial production of the film thickness.

According to another embodiment of the invention, the addition amount of the nano-filler in the first stage can be 0.002:1, 0.005:1 or 0.01:1 of the total mass, a glass reaction kettle with a jacket can be selected as the premixing container, the diameter of a stirring paddle is 50-100 mm, the rotating speed is 200-400 r/min, and the mixing time is 10-20 minutes. After the residual filler in the second stage is added, the mixing speed is increased to 500r/min, 600 r/min or 800 r/min, the stirring paddles are replaced by high-shearing type, the number of blades is 4-6, and the mixing time is 20-40 minutes.

The mixing temperature is controlled by jacket circulating water, the water temperature is 25-35 ℃, and a temperature sensor is arranged at the center of the solution. The filler adding port can be arranged right above the stirring paddle, and is added at a constant speed by adopting a screw feeder, and the feeding speed is 0.1-0.5 kg/min. The slurry after mixing can be filtered through a 100 mesh screen to remove undispersed agglomerates.

The method has the technical effects that the filler is uniformly dispersed by staged mixing, the agglomeration defect is reduced, the tensile strength and the ductility of the material are improved, and the energy consumption is reduced.

According to yet another embodiment of the present invention, the first ultrasonic treatment may be set to 10 minutes, 12 minutes or 15 minutes, power of 100-150W, frequency of 20-40 kHz, and probe immersion depth of 20-30 mm when graphene oxide is dispersed. Standing for 5-10 min, performing ultrasonic treatment for 10-15 min for the second time, and performing power of 150-200W. The dispersing container can be a cylindrical glass tank with a volume of 5-10L, and a slag discharging valve is arranged at the bottom.

After standing, the upper suspension can be pumped by a siphon, and the inlet of the siphon is 2-5 cm away from the liquid level, so that suction and precipitation are avoided. The transverse dimension of the graphene oxide sheet is detected by an atomic force microscope, the sheet with the thickness of 0.5-5 mu m is screened, and the thickness is 1-10nm through a transmission electron microscope. The dispersion storage container can be brown glass bottle, and can be stored in 4-25deg.C in dark place.

The method has the technical effects that the sectional ultrasonic and standing process improves the sheet stripping efficiency, ensures the uniformity of the size of the filler, and provides stable raw materials for the subsequent functionalization reaction.

According to yet another embodiment of the invention, the first stage of pH adjustment may be followed by rapid dropwise addition of 0.5 mol/L sodium hydroxide solution, increasing 1-2 pH units per minute to a pH of 8-9. The second stage is changed into slow dripping, the speed is 0.5-1 pH units/min, and the final pH is 9-10. The electrode of the online pH monitor can be arranged on the side wall of the reaction kettle and is 10-15cm away from the stirring paddle, so that vortex interference is avoided.

The alkaline solution storage tank can be provided with a metering pump, the pumping speed is 0.1-0.5 mL/min, and the inner diameter of the pipeline is 2-4 mm. After the pH adjustment is completed, the rotating speed of the stirring paddle is adjusted to be 50-150 r/min, the diameter of the paddle is 80-120 mm, and the diameter ratio of the stirring paddle to the container is 1:3-1:2. The cover body of the reaction kettle can be provided with a nitrogen inlet, and an inert atmosphere is maintained to prevent oxidation.

The method has the technical effects that the accurate pH control avoids the generation of functional reaction byproducts, ensures the structural integrity of the nano-filler, and improves the durability of antibacterial performance.

The high-speed stirring in the first stage can be set to be 200 r/min, 300 r/min or 400 r/min for 5-15 min, and the stirring paddles are four-inclined She Guo wheels. In the second stage, stirring is carried out at a low speed of 50 r/min, 100r/min or 150 r/min for 15-25 min, and the stirring is replaced by an anchor stirring paddle. The pH monitoring data is recorded every 10-30 seconds, and the control cabinet sets the alarm threshold to be +/-0.2 pH.

The temperature linkage control is realized through a PID algorithm, and the temperature of the circulating water is reduced by 1-2 ℃ when the stirring speed is increased by 100 r/min. The liquid supplementing system can select a miniature peristaltic pump, and the single liquid supplementing amount is 0.01% -0.1% of the system mass, and the corresponding liquid supplementing time is 1-3 seconds. The stirring shaft is sealed by adopting a double mechanical sealing structure, so that the leakage of the solvent is prevented.

The method has the technical effects of maintaining the stability of the reaction system by stirring in stages and monitoring in real time, reducing local concentration difference and improving the interface bonding strength of the filler and the matrix.

According to yet another embodiment of the invention, the mass ratio of nanofiller to polylactic acid may be 0.005:1, 0.01:1 or 0.02:1, the specific ratio being selected according to the targeted barrier grade. The thickness of the film is measured by a micrometer, and the sampling point is taken every 10 cm points along the width direction of the film, and the thickness tolerance is +/-0.005 mm. The biodegradability test of the material can refer to ISO 14855 standard, the composting condition is 58 ℃ plus or minus 2 ℃ and the humidity is 50% -60%.

The finished film roll can be cut into coiled materials with the width of 200-1000 mm, the cutter blade is made of hard alloy, and the cutting edge angle is 20-30 degrees. The surface of the packaging material can be embossed with micron-sized textures (depth of 1-5 mu m) so as to improve the blocking resistance. The storage conditions are light-proof and dry environment, the relative humidity is less than or equal to 60 percent, and the temperature is 15-30 ℃.

The technical effect is that by limiting the key parameter range, the material performance and the production cost are balanced, the packaging material is ensured to have high barrier property, long-acting antibacterial property and degradability, and the application requirements of the food and medicine fields are met.

The result shows that the copper ion functionalized graphene oxide can better coordinate antibacterial substance tannic acid, increase the migration distance of water vapor in the packaging material, and improve the water vapor barrier property of the polylactic acid packaging material. Meanwhile, copper ions and tannic acid cooperatively play a role in inhibiting bacteria, so that the antibacterial performance of the packaging material is improved, and a new material is provided for fresh-keeping packaging research and development of livestock and poultry foods.

Although embodiments of the present invention have been disclosed above, it is not limited to the details and embodiments shown and described, it is well suited to various fields of use for which the invention would be readily apparent to those skilled in the art, and accordingly, the invention is not limited to the specific details and illustrations shown and described herein, without departing from the general concepts defined in the claims and their equivalents.

Claims

1. A method for preparing a high-barrier antibacterial polylactic acid packaging material, comprising the following steps:

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 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, wherein 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; and 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, wherein the 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, wherein the specific step of adjusting the pH of the reaction system to 8 to 10 comprises:

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, wherein the step of continuously stirring for 10 to 30 minutes after the adjustment is completed comprises:

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.